Modified nucleoside having guanidino structure in bridging part, and method for producing oligonucleotide using same

Abstract

The compound or the salt thereof has a structure represented by formula (I) and has excellent chemical stability. The present invention can be used, for example, as a starting material for a nucleic acid drug used in an antisense method, an antigene method, a method using an aptamer, a method using siRNA, or the like, which is expected as a novel therapeutic or prophylactic method for diseases. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a modified nucleoside having a guanidino structure in a bridging moiety and a method for producing an oligonucleotide using the same. Background Art

[0002] As therapeutic methods for diseases using nucleic acid drugs, there are antisense methods, antigene methods, methods using aptamers, methods using siRNA, and the like. Among them, the antisense method is a method of treating or preventing a disease by introducing an oligonucleotide (antisense strand) complementary to a disease-related mRNA from the outside to form a double strand, thereby blocking the translation process of pathogenic RNA. The method using siRNA is also similar to the antisense method, and inhibits the translation from mRNA to protein by administering double-stranded RNA to an organism. On the other hand, the antigene method is a method of inhibiting the transcription from DNA to RNA by introducing a triple-stranded forming oligonucleotide corresponding to a DNA site that transcribes pathogenic RNA from the outside. In addition, an aptamer is a short nucleic acid molecule (oligonucleotide), and thus functions by binding to a biological component such as a protein that causes a disease.

[0003] As raw materials for such nucleic acid drugs, various artificial nucleic acids have been developed. For example, as raw materials for nucleic acid drugs developed so far, there are phosphorothioate (S-PO3) type oligonucleotides (S-oligo), 2′,4′-bridged nucleic acid (BNA) / 2′,4′-locked nucleic acid (LNA) (Patent Documents 1 to 4 and Non-Patent Documents 1 to 4), and the like. Among them, S-oligo has high nuclease resistance, but has the drawback of low binding affinity to a target nucleic acid strand and needs to be improved. Both 2′,4′-BNA / 2′,4′-LNA have high binding affinity to a target nucleic acid strand and are the most promising molecules as raw materials for future nucleic acid drugs. However, the resistance to nucleases is insufficient, and there is room for improvement in terms of stability in vivo.

[0004] Therefore, there is a need for a nucleic acid molecule for oligonucleotides that has high binding affinity and specificity for a target nucleic acid and exhibits high nuclease resistance. In this regard, new nucleic acids having a guanidine structure introduced into the bridging portion of a nucleic acid and their improvements have been proposed in recent years (Patent Document 5 and Non-Patent Documents 6 to 8).

[0005] However, the nucleic acid molecules described in Patent Document 5 and Non-Patent Documents 6 to 8 do not necessarily have sufficient stability in maintaining industrial productivity, and further improvements are desired.

[0006] Prior Art Documents

[0007] Patent literature

[0008] Patent Document 1: WO 98 / 39352

[0009] Patent Document 2: WO 2005 / 021570

[0010] Patent Document 3: WO 2003 / 068795

[0011] Patent Document 4: WO 2011 / 052436

[0012] Patent Document 5: WO 2014 / 046212

[0013] Non - patent literature

[0014] Non - patent Document 1: C. Wahlestedt et al., Proc. Natl. Acad. Sci. USA, 2000, 97(10), pp. 5633 - 5638

[0015] Non - patent Document 2: Y. Hari et al., Bioorg. Med. Chem., 2006, 14, pp. 1029 - 1038

[0016] Non - patent Document 3: K. Miyashita et al., Chem. Commun., 2007, pp. 3765 - 3767

[0017] Non - patent Document 4: S. M. A. Rahman et al., J. Am. Chem. Soc., 2008, 130(14), pp. 4886 - 4896

[0018] Non - patent Document 5: M. Kuwahara et al., Nucleic Acids Res., 2008, 36(13), pp. 4257 - 4265

[0019] Non - patent Document 6: S. Obika et al., Bioorg. Med. Chem., 2001, 9, pp. 1001 - 1011

[0020] Non - patent Document 7: A. R. Shreshta et al., Chem. Commun., 2014, 50(5), pp. 575 - 577

[0021] Non - patent Document 8: S. Kumagai et al., Org. Biomol. Chem., 2020, 18(46), pp. 9461 - 9472 Summary of the invention

[0022] Problems to be Solved by the Invention

[0023] The present invention aims to solve the above problems, and an object thereof is to provide a modified nucleoside having a guanidino structure in a bridging moiety and excellent chemical stability, an intermediate thereof, and a modified nucleotide, and a method for producing the modified nucleoside, the intermediate, and the modified nucleotide. In addition, a method for producing an oligonucleotide using the modified nucleoside and / or the modified nucleotide is also provided.

[0024] Means for Solving the Problems

[0025] The present invention is a compound represented by the following formula (I) or a salt thereof:

[0026] [Chemical Formula 1]

[0027]

[0028] (In formula (I),

[0029] B 1 is:

[0030] (a) a purin-9-yl which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0031] (b) a 1,2-dihydropyrimidin-1-yl which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom,

[0032] R 2 and R 3 each independently are:

[0033] (a) a hydrogen atom;

[0034] (b) a protecting group for a hydroxyl group in nucleic acid synthesis;

[0035] (c) an alkyl group having 1 to 7 carbon atoms which may form a branch (side chain) or a ring;

[0036] (d) an alkenyl group having 2 to 7 carbon atoms which may form a branch or a ring;

[0037] (e) an aryl group having 6 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0038] (f) a heteroaryl group having 1 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0039] (g) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0040] (h) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0041] (i) an acyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0042] (j) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0043] (k) A phosphate group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0044] (l) A phosphate group protected by a protecting group for nucleic acid synthesis; or

[0045] (m) -P(R 4 )R 5

[0046] [In the formula,

[0047] R 4 and R 5 each independently is:

[0048] (a) A hydroxyl group;

[0049] (b) A hydroxyl group protected by a protecting group for nucleic acid synthesis;

[0050] (c) A mercapto group;

[0051] (d) A mercapto group protected by a protecting group for nucleic acid synthesis;

[0052] (e) An amino group;

[0053] (f) An alkoxy group having 1 to 5 carbon atoms;

[0054] (g) An alkylthio group having 1 to 5 carbon atoms;

[0055] (h) A cyanoalkoxy group having 1 to 6 carbon atoms;

[0056] (i) A dialkylamino group having alkyl groups with 1 to 6 carbon atoms that may be the same or different from each other; or

[0057] (j) A cyclic alkylamino group having 3 to 6 carbon atoms;

[0058] Or,

[0059] R 4 and R 5Together form the following formula:

[0060] [Chemical Formula 2]

[0061]

[0062] (In the formula, R 13a and R 13b each independently represents a hydrogen atom, a branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein R a is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2, and * is a bonding site); or

[0063] [Chemical Formula 3]

[0064]

[0065] (In the formula, R 14 and R 15 each independently is a hydrogen atom, a branched alkyl group having 1 to 3 carbon atoms, or a phenyl group, and * is a bonding bond),

[0066] R 6 is a group represented by the following formula:

[0067] [Chemical Formula 4]

[0068]

[0069] [In the formula,

[0070] R 8a and R 8b each independently are:

[0071] (a) An alkyl group having 1 to 9 carbon atoms that can form a branch or a ring;

[0072] (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0073] (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or

[0074] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0075] * is a bonding bond], and

[0076] R 7 is:

[0077] (a) An alkyl group having 1 to 8 carbon atoms that may be substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring and that may form a branch or a ring;

[0078] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0079] (c) An aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0080] (d) A heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0081] (e) A group represented by the following formula:

[0082] [Chemical formula 5]

[0083]

[0084] [In the formula,

[0085] R 8'a and R 8'b each independently are:

[0086] (a) An alkyl group having 1 to 9 carbon atoms that can be branched;

[0087] (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0088] (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or

[0089] (d) A silyl group that can have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0090] * is a bonding site],

[0091] Or

[0092] R 6 is:

[0093] (a) An alkyl group having 1 to 8 carbon atoms that can form a branch or a ring and can be substituted by an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0094] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0095] (c) An aralkyl group having an aryl moiety with 6 to 12 carbon atoms that can have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0096] (d) A heteroaralkyl group having a heteroaryl moiety with 3 to 12 carbon atoms that can have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that can form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that can form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0097] (e) A group represented by the following formula:

[0098] [Chemical formula 6]

[0099]

[0100] [In the formula,

[0101] R 8'a and R 8'b are each independently:

[0102] (a) an alkyl group having 1 to 9 carbon atoms which may be branched;

[0103] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0104] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0105] (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, a straight-chain alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis); and

[0106] * is a bonding site], and

[0107] R 7 is a group represented by the following:

[0108] [Chemical formula 7]

[0109]

[0110] [In the formula,

[0111] R 8a and R 8b are each independently:

[0112] (a) an alkyl group having 1 to 9 carbon atoms which may be branched;

[0113] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0114] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0115] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0116] * represents a bonding bond],

[0117] R 9 and R 10 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, or R 9 and R 10 together form -(CH2) m -(where m is an integer from 2 to 7),

[0118] R 11 and R 12 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring,

[0119] or R 11 and R 12 together form the oxygen atom part of a carbonyl group (=O),

[0120] or R 11 and R 12 together form -(CH2) n -(where n is an integer from 2 to 7)).

[0121] In one embodiment, in formula (I), R 6 is a group represented by the following formula:

[0122] [Chemical formula 8]

[0123]

[0124] [In the formula,

[0125] R 8a and R 8b are each independently:

[0126] (a) An alkyl group having 1 to 9 carbon atoms that may be branched;

[0127] (b) An alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring;

[0128] (c) An alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring; or

[0129] (d) A silyl group that may have at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0130] * represents a bonding bond], and

[0131] R 7 is:

[0132] (a) An alkyl group having 1 to 8 carbon atoms that may be substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring and that may form a branch or a ring;

[0133] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0134] (c) An aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0135] (d) A heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms that may have at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0136] (e) A group represented by the following formula:

[0137] [Chemical Formula 9]

[0138]

[0139] [In the formula,

[0140] R 8'a and R 8'b each independently are:

[0141] (a) An alkyl group having 1 to 9 carbon atoms that can be branched;

[0142] (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0143] (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or

[0144] (d) A silyl group that can have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0145] * represents a bonding site.

[0146] In a further embodiment, the above formula (I) is represented by the following formula (I').

[0147] [Chemical formula 10]

[0148]

[0149] In a further embodiment, R of the above formula (I) 7 is an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring.

[0150] In a further embodiment, R of the above formula (I) 8a and R 8b are both alkyl groups having 3 to 8 carbon atoms that can form a branch or a ring.

[0151] In addition, in a further embodiment, R of the above formula (I) 8a and R 8b are both tert-butyl groups.

[0152] The present invention also provides a method for producing an oligonucleotide or a pharmaceutically acceptable salt thereof, the method comprising a step of nucleic acid synthesis using the above compound or a salt thereof.

[0153] In one embodiment, the above oligonucleotide is an oligonucleotide containing at least one phosphorothioate bond.

[0154] The present invention also provides a compound represented by the following formula (II) or a salt thereof.

[0155] [Chemical formula 11]

[0156]

[0157] In formula (II),

[0158] R 7 is:

[0159] (a) an alkoxy group having 1 to 8 carbon atoms which may be branched or form a ring and an alkyl group having 1 to 8 carbon atoms which may be branched or form a ring;

[0160] (b) a cyanoalkoxy group having 1 to 8 carbon atoms;

[0161] (c) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may be branched or form a ring, an alkoxy group having 1 to 8 carbon atoms which may be branched or form a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may be branched or form a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms which may be branched or form a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0162] (d) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may be branched or form a ring, an alkoxy group having 1 to 6 carbon atoms which may be branched or form a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may be branched or form a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may be branched or form a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0163] (e) a group represented by the following formula:

[0164] [Chemical formula 12]

[0165]

[0166] wherein,

[0167] R 8'a and R 8'b are each independently:

[0168] (a) a branched alkyl group having 1 to 9 carbon atoms;

[0169] (b) an alkoxy group having 1 to 8 carbon atoms which may be branched or form a ring;

[0170] (c) an alkylamino group having 1 to 8 carbon atoms which may be branched or form a ring; or

[0171] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0172] * represents a bonding bond],

[0173] R 8a and R 8b are each independently:

[0174] (a) An alkyl group having 1 to 9 carbon atoms that may form a branch or a ring;

[0175] (b) An alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring;

[0176] (c) An alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring; or

[0177] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis,

[0178] R 16 is a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched alkenyl group having 2 to 6 carbon atoms].

[0179] The present invention also provides a method for producing a compound represented by formula (II) or a salt thereof,

[0180] [Chemical formula 13]

[0181]

[0182] The method includes a step of reacting a reaction product of a compound represented by the following formula (III) with a compound represented by the following formula (IV) and a compound represented by the following formula (V):

[0183] [Chemical formula 14]

[0184]

[0185] [Chemical formula 15]

[0186]

[0187] [Chemical formula 16]

[0188]

[0189] [In formula (III),

[0190] R 8a and R 8b each independently is:

[0191] (a) an alkyl group having 1 to 9 carbon atoms which may form a branch or a ring;

[0192] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0193] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0194] (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis,

[0195] In formula (IV),

[0196] p is independently an integer from 0 to 3,

[0197] In formula (V),

[0198] R 7 is:

[0199] (a) an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring and which may be substituted by an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0200] (b) a cyanoalkoxy group having 1 to 8 carbon atoms;

[0201] (c) an aralkyl group having an aryl moiety having 6 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0202] (d) a heteroalkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected with a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected with a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected with a protecting group for nucleic acid synthesis, and a halogen atom; or

[0203] (e) a group represented by the following formula:

[0204] [Chemical Formula 17]

[0205]

[0206] (wherein,

[0207] R 8'a and R 8'b are each independently:

[0208] (a) a branched alkyl group having 1 to 9 carbon atoms;

[0209] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0210] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0211] (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected with a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected with a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected with a protecting group for nucleic acid synthesis; and

[0212] * is a bonding bond),

[0213] R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms,

[0214] X - is a counter anion].

[0215] The present invention also provides a method for producing the compound represented by the above formula (I) or a salt thereof, the method comprising using a compound represented by the following formula (VI) or a salt thereof:

[0216] [Chemical Formula 18]

[0217]

[0218] Step of guanidinylating the compound represented by formula (II) or its salt:

[0219] [Chemical Formula 19]

[0220]

[0221] In formula (VI),

[0222] B 1 is:

[0223] (a) A purin-9-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0224] (b) A 1,2-dihydropyrimidin-1-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom,

[0225] R 2 and R 3 are:

[0226] (a) A hydrogen atom;

[0227] (b) A protecting group for the hydroxyl group in nucleic acid synthesis;

[0228] (c) An alkyl group having 1 to 7 carbon atoms which may form a branch or a ring;

[0229] (d) An alkenyl group having 2 to 7 carbon atoms which may form a branch or a ring;

[0230] (e) An aryl group having 6 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0231] (f) A heteroaryl group having 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0232] (g) An aralkyl group having an aryl moiety having 6 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0233] (h) A heteroaralkyl group having a heteroaryl moiety having 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0234] (i) An acyl group having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0235] (j) A silyl group having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0236] (k) A phosphate group having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0237] (l) A phosphate group protected by a protecting group for nucleic acid synthesis,

[0238] R 9 and R 10 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, or R 9 and R 10 together form -(CH2) m -(wherein m is an integer of 2 to 7),

[0239] R 11 and R 12 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring,

[0240] or R 11 and R 12 together form the oxygen atom moiety of a carbonyl group (=O),

[0241] or R 11 and R 12 together form -(CH2) n -(wherein n is an integer of 2 to 7),

[0242] In formula (II),

[0243] R 7 is:

[0244] (a) An alkyl group having 1 to 8 carbon atoms which may form a branch or a ring and is substituted by an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0245] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0246] (c) An aralkyl group having an aryl moiety having 6 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0247] (d) a heteroarylalkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0248] (e) a group represented by the following formula:

[0249] [Chemical formula 20]

[0250]

[0251] [In the formula,

[0252] R 8'a and R 8'b are each independently:

[0253] (a) an alkyl group having 1 to 9 carbon atoms which may be branched;

[0254] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0255] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0256] (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0257] * is a bonding site],

[0258] R 8a and R 8b are each independently:

[0259] (a) an alkyl group having 1 to 9 carbon atoms which may form a branch or a ring;

[0260] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0261] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0262] (d) a silyl group that may have at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis,

[0263] R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms.

[0264] In one embodiment, the guanidination step is carried out in the presence of a metal salt.

[0265] In a further embodiment, the metal salt is silver nitrate, silver chloride, silver bromide, silver iodide, silver trifluoromethanesulfonate, silver tetrafluoroborate or silver hexafluorophosphate.

[0266] In a further embodiment, the metal salt is copper(I) chloride, copper(I) bromide, copper(I) iodide, copper(I) trifluoromethanesulfonate, copper(I) tetrafluoroborate or copper(I) hexafluorophosphate.

[0267] In one embodiment, R in formula (VI) 2 is a hydrogen atom.

[0268] In one embodiment, R in formula (I) 2 is a compound of -P(R 4 )R 5 wherein,

[0269] [In the formula,

[0270] R 4 and R 5 are each independently:

[0271] (a) a hydroxyl group;

[0272] (b) a hydroxyl group protected by a protecting group for nucleic acid synthesis;

[0273] (c) a mercapto group;

[0274] (d) a mercapto group protected by a protecting group for nucleic acid synthesis;

[0275] (e) an amino group;

[0276] (f) an alkoxy group having 1 to 5 carbon atoms;

[0277] (g) an alkylthio group having 1 to 5 carbon atoms;

[0278] (h) Cyanoalkoxy having 1 to 6 carbon atoms;

[0279] (i) Dialkylamino having alkyl groups with 1 to 6 carbon atoms which may be the same or different from each other; or

[0280] (j) Cycloalkylamino having 3 to 6 carbon atoms,

[0281] Or,

[0282] R 4 Together with R 5 Form the following formula:

[0283] [Chemical formula 21]

[0284]

[0285] (In the formula, R 13a And R 13b Each independently represents a hydrogen atom, a branched or unbranched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein, R a Is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2, * is a bonding site); or

[0286] [Chemical formula 22]

[0287]

[0288] (In the formula, R 14 And R 15 Each independently is a hydrogen atom, a branched or unbranched alkyl group having 1 to 3 carbon atoms, or a phenyl group, * is a bonding site)],

[0289] The method includes, after the above-mentioned guanidination step, a step of further amiditing (phosphoramiditing) the obtained product.

[0290] In one embodiment, R 2 In formula (VI) is a protecting group for the hydroxyl group in nucleic acid synthesis, and the method further includes a step of deprotecting this protecting group.

[0291] In a further embodiment, R 2 In the above formula (I) is a compound of -P(R 4 )R 5 ,

[0292] [In the formula,

[0293] R 4 And R 5 Each independently is:

[0294] (a) Hydroxyl group;

[0295] (b) Hydroxyl group protected by a protecting group for nucleic acid synthesis;

[0296] (c) Mercapto group;

[0297] (d) Mercapto group protected by a protecting group for nucleic acid synthesis;

[0298] (e) Amino group;

[0299] (f) Alkoxy group having 1 to 5 carbon atoms;

[0300] (g) Alkylthio group having 1 to 5 carbon atoms;

[0301] (h) Cyanoalkoxy group having 1 to 6 carbon atoms;

[0302] (i) Dialkylamino group having alkyl groups of 1 to 6 carbon atoms which may be the same or different from each other; or

[0303] (j) Cycloalkylamino group having 3 to 6 carbon atoms,

[0304] Or,

[0305] R 4 together with R 5 forms the following formula:

[0306] [Chemical formula 23]

[0307]

[0308] (In the formula, R 13a and R 13b each independently represent a hydrogen atom, a branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein R a is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2, * is a bonding site); or

[0309] [Chemical formula 24]

[0310]

[0311] (In the formula, R 14 and R 15 each independently is a hydrogen atom, a branched alkyl group having 1 to 3 carbon atoms, or a phenyl group, * is a bonding site)],

[0312] The method includes a step of further amiditing the obtained product after the above-mentioned deprotection step.

[0313] Advantages of the Invention

[0314] According to the present invention, it is possible to improve the stability of the protecting group of the guanidino structure constituting the bridging moiety. The compound of the present invention can also provide a nucleic acid molecule for an oligonucleotide having good binding affinity for a target nucleic acid and showing good nuclease resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0315] Figure 1 is the 1 1H-NMR spectrum of the compound (compound a2) obtained in Example 1 (1-1(1)).

[0316] Figure 2 is the 1 1H-NMR spectrum of the compound (Amidite a3) obtained in Example 1 (1-2).

[0317] Figure 3 is the 1 1H-NMR spectrum of the compound (compound b2) obtained in Example 2 (2-1(1)).

[0318] Figure 4 is the 1 1H-NMR spectrum of the compound (Amidite b3) obtained in Example 2 (2-2).

[0319] Figure 5 is the 1 1H-NMR spectrum of the compound (compound c1) obtained in Example 3 (3-1).

[0320] Figure 6 is the 1 1H-NMR spectrum of the compound (compound c2) obtained in Example 3 (3-2).

[0321] Figure 7 is the 1 1H-NMR spectrum of the compound (compound c3) obtained in Example 3 (3-3).

[0322] Figure 8 is the 1 1H-NMR spectrum of the compound (compound c4) obtained in Example 3 (3-4).

[0323] Figure 9 is the 1 1H-NMR spectrum of the compound (Amidite c5) obtained in Example 3 (3-5).

[0324] Figure 10 is the 1 1H-NMR spectrum of the compound (compound d2)) obtained in Example 4 (4-1(1)).

[0325] Figure 11 is the 1 1H-NMR spectrum of the compound (Amidite form d3) obtained in Example 4 (4-2).

[0326] Figure 12 is the result of UPHLC-MS of compound a3 in the stability test conducted in Example 5.

[0327] Figure 13 is the result of UPHLC-MS of compound a3' in the stability test conducted in Example 5.

[0328] Figure 14 is the 1 1H-NMR spectrum of the compound (compound e4) obtained in Example 6 (6-2).

[0329] Figure 15 is the 1 1H-NMR spectrum of the compound (compound e5) obtained in Example 6 (6-3).

[0330] Figure 16 is the 1 1H-NMR spectrum of the compound (compound e6) obtained in Example 6 (6-4).

[0331] Figure 17 is the 1 1H-NMR spectrum of the compound (compound e7) obtained in Example 6 (6-5).

[0332] Figure 18 is the 1 1H-NMR spectrum of the compound (compound B2)) obtained in Example 8 (8-1).

[0333] Figure 19 is the 1 1H-NMR spectrum of the compound (compound B3)) obtained in Example 8 (8-2).

[0334] Figure 20 is the 1 1H-NMR spectrum of the compound (compound B5)) obtained in Example 8 (8-3).

[0335] Figure 21 is the 11H-NMR spectrum.

[0336] Figure 22 is the 1 1H-NMR spectrum of the compound (Compound B7)) obtained in Example 8 (8-5). Detailed implementation

[0337] Define the terms used in this specification.

[0338] In this specification, the term "linear alkyl group having 1 to 6 carbon atoms" refers to any linear alkyl group having 1 to 6 carbon atoms. Specifically, it refers to methyl, ethyl, n-propyl, n-butyl, n-pentyl or n-hexyl. On the other hand, in the case of the term "alkyl group having 1 to 6 carbon atoms", it refers to any linear, branched or cyclic alkyl group having 1 to 6 carbon atoms.

[0339] In this specification, the term "linear alkoxy group having 1 to 6 carbon atoms" includes alkoxy groups having any linear alkyl group having 1 to 6 carbon atoms. For example, methoxy, ethoxy, n-propoxy, etc. can be cited. On the other hand, in the case of the term "alkoxy group having 1 to 6 carbon atoms", it refers to any linear, branched or cyclic alkoxy group having 1 to 6 carbon atoms. In addition, in the case of the term "linear alkoxy group having 1 to 6 carbon atoms that can be substituted by a linear alkoxy group having 1 to 6 carbon atoms", it refers to the above-mentioned "linear alkoxy group having 1 to 6 carbon atoms", and one or more hydrogen atoms constituting the "linear alkoxy group having 1 to 6 carbon atoms" are substituted by other "linear alkoxy groups having 1 to 6 carbon atoms" that can be the same or different to obtain an alkyl group. As such a "linear alkoxy group having 1 to 6 carbon atoms that can be substituted by a linear alkoxy group having 1 to 6 carbon atoms", for example, methoxy, ethoxy, n-propoxy, methoxymethoxy, ethoxymethoxy, n-propoxymethoxy, methoxyethoxy (for example, 2-methoxyethoxy), ethoxyethoxy (for example, 2-ethoxyethoxy) and n-propoxyethoxy can be cited.

[0340] In this specification, the term "cyanoalkoxy group having 1 to 6 carbon atoms" refers to a group in which at least one hydrogen atom in any linear, branched or cyclic alkoxy group having 1 to 6 carbon atoms is substituted by a cyano group.

[0341] In this specification, the term "linear alkylthio group having 1 to 6 carbon atoms" includes alkylthio groups having any linear alkyl group having 1 to 6 carbon atoms. For example, methylthio, ethylthio, n-propylthio, etc. can be cited. On the other hand, in the case of the term "alkylthio group having 1 to 6 carbon atoms", it refers to any linear, branched or cyclic alkylthio group having 1 to 6 carbon atoms.

[0342] In this specification, the term "linear alkylamino having 1 to 6 carbon atoms" includes an alkylamino having an alkylamino group with one or two arbitrary linear alkyl groups having 1 to 6 carbon atoms. Examples thereof include methylamino, dimethylamino, ethylamino, methylethylamino, diethylamino, and the like.

[0343] In this specification, the term "alkyl having 1 to 7 carbon atoms which may form a branch or a ring" includes any linear alkyl group having 1 to 7 carbon atoms, any branched alkyl group having 3 to 7 carbon atoms, and any cyclic alkyl group having 3 to 7 carbon atoms. Sometimes it is also simply referred to as "lower alkyl". For example, as any linear alkyl group having 1 to 7 carbon atoms, methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, and n-heptyl can be cited; as any branched alkyl group having 3 to 7 carbon atoms, isopropyl, isobutyl, tert-butyl, isopentyl, and the like can be cited; and as any cyclic alkyl group having 3 to 7 carbon atoms, cyclopropylmethyl, cyclobutyl, cyclopentyl, cyclopentylmethyl, cyclohexyl, and the like can be cited.

[0344] In this specification, the term "alkenyl having 2 to 7 carbon atoms which may form a branch or a ring" includes any linear alkenyl group having 2 to 7 carbon atoms, any branched alkenyl group having 3 to 7 carbon atoms, and any cyclic alkenyl group having 3 to 7 carbon atoms. Sometimes it is also simply referred to as "lower alkenyl". For example, as any linear alkenyl group having 2 to 7 carbon atoms, vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, and the like can be cited; as any branched alkenyl group having 3 to 7 carbon atoms, isopropenyl, 1-methyl-1-propenyl, 1-methyl-2-propenyl, 2-methyl-1-propenyl, 2-methyl-2-propenyl, 1-methyl-2-butenyl, and the like can be cited; and as any cyclic alkenyl group having 3 to 7 carbon atoms, cyclobutenyl, cyclopentenyl, cyclohexenyl, and the like can be cited.

[0345] In this specification, the term "aryl having 6 to 12 carbon atoms" is any aryl group having 6 to 12 carbon atoms composed only of hydrocarbons, and examples thereof include phenyl, naphthyl, indenyl, azulyl, and the like.

[0346] In this specification, the term "heteroaryl having 1 to 12 carbon atoms" includes any heteroaryl group having 1 to 12 carbon atoms in which at least one carbon atom constituting the ring structure of any aryl group having 5 to 14 carbon atoms composed only of hydrocarbons is replaced by a heteroatom (such as a nitrogen atom, an oxygen atom, a sulfur atom, and combinations thereof). Examples of the heteroaryl group having 1 to 12 carbon atoms include pyridyl, pyrrolyl, quinolinyl, indolyl, imidazolyl, furyl, thienyl, and the like.

[0347] In the present specification, examples of the term "aralkyl having an aryl moiety with 6 to 12 carbon atoms" include benzyl, phenethyl, naphthylmethyl, 3-phenylpropyl, 2-phenylpropyl, 4-phenylbutyl, 2-phenylbutyl, and the like.

[0348] In the present specification, examples of the term "heteroaralkyl having a heteroaryl moiety with 1 to 12 carbon atoms" include pyridylmethyl, indolylmethyl, furylmethyl, thienylmethyl, pyrrolylmethyl, 2-pyridylethyl, 1-pyridylethyl, 3-thienylpropyl, and the like.

[0349] In the present specification, examples of the term "acyl group" include aliphatic acyl groups and aromatic acyl groups. Specifically, examples of aliphatic acyl groups include alkyl carbonyl groups such as formyl, acetyl, propionyl, butyryl, isobutyryl, pentanoyl group, pivaloyl group (neopentanoyl group), valeryl group, isovaleryl, octanoyl, nonanoyl, decanoyl, 3-methylnonanoyl, 8-methylnonanoyl, 3-ethyloctanoyl, 3,7-dimethyloctanoyl, undecanoyl, dodecanoyl, tridecanoyl, tetradecanoyl, pentadecanoyl, hexadecanoyl, 1-methylpentadecanoyl, 14-methylpentadecanoyl, 13,13-dimethyltetradecanoyl, heptadecanoyl, 15-methylhexadecanoyl, octadecanoyl, 1-methylheptadecanoyl, nonadecanoyl, eicosanoyl, and heneicosanoyl; carboxylated alkyl carbonyl groups such as succinyl, glutaroyl, and adipoyl; halogenated lower alkyl carbonyl groups such as chloroacetyl, dichloroacetyl, trichloroacetyl, and trifluoroacetyl; lower alkoxy lower alkyl carbonyl groups such as methoxyacetyl; and unsaturated alkyl carbonyl groups such as (E)-2-methyl-2-butenoyl. In addition, examples of aromatic acyl groups include aryl carbonyl groups such as benzoyl, α-naphthoyl, and β-naphthoyl; halogenated aryl carbonyl groups such as 2-bromobenzoyl and 4-chlorobenzoyl; lower alkylated aryl carbonyl groups such as 2,4,6-trimethylbenzoyl and 4-toluoyl; lower alkoxylated aryl carbonyl groups such as 4-anisoyl group; carboxylated aryl carbonyl groups such as 2-carboxybenzoyl, 3-carboxybenzoyl, and 4-carboxybenzoyl; nitrated aryl carbonyl groups such as 4-nitrobenzoyl and 2-nitrobenzoyl; lower alkoxycarbonylated aryl carbonyl groups such as 2-(methoxycarbonyl)benzoyl; and arylated aryl carbonyl groups such as 4-phenylbenzoyl, and the like.

[0350] In the present specification, examples of the term "silyl group" include tri-lower alkylsilyls such as trimethylsilyl, triethylsilyl, isopropyldimethylsilyl, tert-butyldimethylsilyl, methyldiisopropylsilyl, methyldi-tert-butylsilyl, and triisopropylsilyl; silyls substituted with 1 to 2 aryl groups such as diphenylmethylsilyl (SiMePh2 group), butyldiphenylbutylsilyl, diphenylisopropylsilyl, and phenyldiisopropylsilyl; and triarylsilyls substituted with 3 aryl groups such as triphenylsilyl. Examples of the term "sulfonyl group" include arylsulfonyls such as phenylsulfonyl (SO2Ph group) and 4-methylphenylsulfonyl; and lower alkylsulfonyls such as methylsulfonyl and trifluoromethanesulfonyl.

[0351] In the present specification, examples of the term "halogen atom" include a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom.

[0352] In the present specification, the "protecting group" of the terms "protecting group for amino group in nucleic acid synthesis", "protecting group for hydroxyl group in nucleic acid synthesis", "hydroxyl group protected by protecting group for nucleic acid synthesis", "phosphate group protected by protecting group for nucleic acid synthesis", and "sulfhydryl group protected by protecting group for nucleic acid synthesis" is not particularly limited as long as it can stably protect an amino group, a hydroxyl group, a phosphate group, or a sulfhydryl group during nucleic acid synthesis. Specifically, it refers to a protecting group that is stable during the synthesis of oligonucleotides and can be cleaved by chemical methods such as hydrogenolysis, hydrolysis, electrolysis, and photolysis. Examples of such a protecting group include lower alkyl, lower alkenyl, acyl, tetrahydropyranyl or tetrahydrothiopyranyl, tetrahydrofuranyl or tetrahydrothiofuranyl, silyl, lower alkoxymethyl, lower alkoxylated lower alkoxymethyl, halogenated lower alkoxymethyl, lower alkoxylated ethyl, halogenated ethyl, methyl substituted with 1 to 3 aryl groups, "methyl substituted with 1 to 3 aryl groups in which the aryl ring is substituted with a lower alkyl, a lower alkoxy, a halogen atom, or a cyano group", lower alkoxycarbonyl, "aryl substituted with a halogen atom, a lower alkoxy, or a nitro group", "lower alkoxycarbonyl substituted with a halogen atom or a tri-lower alkylsilyl", alkenyloxycarbonyl, "aralkyloxycarbonyl in which the aryl ring may be substituted with a lower alkoxy or a nitro group", dimethylformamidyl group, diphenylcarbamoyl, and the like.

[0353] More specifically, examples of the tetrahydropyranyl or tetrahydrothiopyranyl group include tetrahydropyran-2-yl, 3-bromotetrahydropyran-2-yl, 4-methoxytetrahydropyran-4-yl, tetrahydrothiopyran-4-yl, 4-methoxytetrahydrothiopyran-4-yl, etc. Examples of the tetrahydrofuranyl or tetrahydrothiofuranyl group include tetrahydrofuran-2-yl, tetrahydrothiofuran-2-yl. Examples of the lower alkoxymethyl group include methoxymethyl, 1,1-dimethyl-1-methoxymethyl, ethoxymethyl, propoxymethyl, isopropoxymethyl, butoxymethyl, tert-butoxymethyl, etc. Examples of the lower alkoxylated lower alkoxymethyl group include 2-methoxyethoxymethyl, etc. Examples of the halogenated lower alkoxymethyl group include 2,2,2-trichloroethoxymethyl, bis(2-chloroethoxy)methyl, etc. Examples of the lower alkoxylated ethyl group include 1-ethoxyethyl, 1-(isopropoxy)ethyl, etc. Examples of the halogenated ethyl group include 2,2,2-trichloroethyl, etc. Examples of the methyl group substituted with 1 to 3 aryl groups include benzyl, α-naphthylmethyl, β-naphthylmethyl, diphenylmethyl, triphenylmethyl, α-naphthyldiphenylmethyl, 9-anthrylmethyl, etc. Examples of the "methyl group substituted with 1 to 3 aryl groups in which the aryl ring is substituted with a lower alkyl group, a lower alkoxy group, a halogen atom or a cyano group" include 4-methylbenzyl, 2,4,6-trimethylbenzyl, 3,4,5-trimethylbenzyl, 4-methoxybenzyl, 4-methoxyphenyldiphenylmethyl, 4,4'-dimethoxytriphenylmethyl, 2-nitrobenzyl, 4-nitrobenzyl, 4-chlorobenzyl, 4-bromobenzyl, 4-cyanobenzyl, etc. Examples of the lower alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl, tert-butoxycarbonyl. Examples of the "aryl group substituted with a nitro group" include 4-chlorophenyl, 2-fluorophenyl, 4-methoxyphenyl, 4-nitrophenyl, 2,4-dinitrophenyl, etc. Examples of the "lower alkoxycarbonyl group substituted with a halogen atom or a tri-lower alkylsilyl group" include 2,2,2-trichloroethoxycarbonyl, 2-trimethylsilylethoxycarbonyl, etc. Examples of the alkenyloxycarbonyl group include vinyloxycarbonyl, aryloxycarbonyl, etc. Examples of the "aralkyloxycarbonyl group in which the aryl ring may be substituted with a lower alkoxy group or a nitro group" include benzyloxycarbonyl, 4-methoxybenzyloxycarbonyl, 3,4-dimethoxybenzyloxycarbonyl, 2-nitrobenzyloxycarbonyl, 4-nitrobenzyloxycarbonyl, etc.

[0354] In one embodiment, examples of the "protecting group for a hydroxyl group in nucleic acid synthesis" include, for example, an aliphatic acyl group, an aromatic acyl group, a methyl group substituted with 1 to 3 aryl groups, "a methyl group substituted with 1 to 3 aryl groups in which the aryl ring is substituted with a lower alkyl group, a lower alkoxy group, a halogen atom, or a cyano group", and a silyl group. Alternatively, in one embodiment, examples of the "protecting group for a hydroxyl group in nucleic acid synthesis" include, for example, an acetyl group, a benzoyl group, a benzyl group, a p-methoxybenzoyl group, a p-methoxybenzyl group, a trityl group, a 4,4'-dimethoxytrityl (DMTr) group, a 4-monomethoxytrityl group, a tert-butyldiphenylsilyl group, a trimethylsilyl group, a triethylsilyl group, an isopropyldimethylsilyl group, a methyldiisopropylsilyl group, a methyldi-tert-butylsilyl group, a triisopropylsilyl group, a tert-butyldimethylsilyl (TBDMS) group, a [(triisopropylsilyl)oxy]methyl (TOM) group, a [(2-nitrobenzyl)oxy]methyl (NBOM) group, a bis(acetoxyethoxy)methyl ether (ACE) group, a tetrahydro-4-methoxy-2H-pyran-2-yl (Mthp) group, a 1-(2-cyanoethoxy)ethyl (CEE) group, a 2-cyanoethoxymethyl (CEM) group, a tert-butyldithio methyl (DTM) group, a 2-(4-toluenesulfonyl)ethoxymethyl (TEM) group, and a 4-(N-dichloroacetyl-N-methylamino)benzyloxymethyl (4-MABOM) group.

[0355] In one embodiment, examples of the "protecting group for a hydroxyl group protected by a protecting group in nucleic acid synthesis" include, for example, an aliphatic acyl group, an aromatic acyl group, "a methyl group substituted with 1 to 3 aryl groups", "an aryl group substituted with a halogen atom, a lower alkoxy group, or a nitro group", a lower alkyl group, and a lower alkenyl group. Alternatively, in one embodiment, examples of the "protecting group for a hydroxyl group protected by a protecting group in nucleic acid synthesis" include, for example, a benzoyl group, a benzyl group, a 2-chlorophenyl group, a 4-chlorophenyl group, and an allyl group.

[0356] In one embodiment, examples of the "protecting group for an amino group in nucleic acid synthesis" include, for example, an acyl group (preferably a benzoyl group), a dimethylformamidine group, and a diphenylcarbamoyl group.

[0357] In one embodiment, examples of the "amino group protected by a protecting group in nucleic acid synthesis" include, for example, an amino group protected by an acyl group, preferably an amino group protected by a benzoyl group.

[0358] In one embodiment, examples of the "protecting group" for the "phosphate group protected by a protecting group for nucleic acid synthesis" include lower alkyl, lower alkyl substituted by a cyano group, aralkyl, "aralkyl in which the aryl ring is substituted by a nitro group or a halogen atom", and "aryl substituted by a lower alkyl group, a halogen atom or a nitro group". Alternatively, in one embodiment, examples of the "protecting group" for the "phosphate group protected by a protecting group for nucleic acid synthesis" include 2-cyanoethyl, 2,2,2-trichloroethyl, benzyl, 2-chlorophenyl, and 4-chlorophenyl.

[0359] In one embodiment, examples of the "protecting group" for the "mercapto group protected by a protecting group for nucleic acid synthesis" include aliphatic acyl groups and aromatic acyl groups, preferably benzoyl group.

[0360] In this specification, -P(R 4 )R 5 [wherein, R 4 and R 5 each independently represent a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an amino group, an alkoxy group having 1 to 6 carbon atoms, an alkylthio group having 1 to 6 carbon atoms, a cyanoalkoxy group having 1 to 6 carbon atoms, or a dialkylamino group having an alkyl group having 1 to 6 carbon atoms], in the group represented by, R 4 is OR 4a and R 5 is NR 5a The group is called a "phosphoramidite group" (here, R 4a is, for example, a cyanoalkoxy group having 1 to 6 carbon atoms, and R 5a is, for example, an alkyl group having 1 to 6 carbon atoms). As the phosphoramidite group, the group represented by the formula -P(OC2H4CN)(N(iPr)2) or the group represented by the formula -P(OCH3)(N(iPr)2) can be preferably cited. Here, iPr represents isopropyl.

[0361] In this specification, the terms "nucleoside" and "nucleoside analog" refer to non-natural substances in the "nucleoside" formed by bonding a purine or pyrimidine base to a sugar, and substances formed by bonding a part of a purine or pyrimidine base that can be replaced by an aromatic heterocyclic ring and an aromatic hydrocarbon ring other than purine and pyrimidine to a sugar.

[0362] In the present specification, the terms "artificial oligonucleotide" and "oligonucleotide analog" refer to unnatural derivatives of "oligonucleotides" formed by binding, for example, 2 to 50 identical or different "nucleosides" or "nucleoside analogs" via phosphodiester bonds. As such analogs, sugar derivatives with modified sugar moieties; thioester derivatives with phosphorothioated phosphodiester moieties; esters with esterified terminal phosphate moieties; amides with amidated amino groups on purine bases can be preferably cited, and sugar derivatives with modified sugar moieties can be more preferably cited.

[0363] In the present specification, the term "its salt" refers to salts of the compounds represented by formula (I) of the present invention. As such salts, for example, alkali metal salts such as sodium salt, potassium salt, lithium salt; alkaline earth metal salts such as calcium salt, magnesium salt; metal salts such as aluminum salt, iron salt, zinc salt, copper salt, nickel salt, cobalt salt; inorganic salts such as ammonium salt; amine salts such as tert-octylamine salt, dibenzylamine salt, morpholine salt, glucosamine salt, phenylglycine alkyl ester salt, ethylenediamine salt, N-methylglucosamine salt, guanidine salt, diethylamine salt, triethylamine salt, dicyclohexylamine salt, N,N'-dibenzylethylenediamine salt, chloroprocaine salt, procaine salt, diethanolamine salt, N-benzyl-phenethylamine salt, piperazine salt, tetramethylammonium salt, tris(hydroxymethyl)aminomethane salt; inorganic acid salts such as hydrofluoride salt, hydrochloride salt, hydrobromide salt, hydroiodide salt, nitrate salt, perchlorate salt, sulfate salt, phosphate salt; lower alkane sulfonates such as methanesulfonate salt, trifluoromethanesulfonate salt, ethanesulfonate salt, aryl sulfonates such as benzenesulfonate salt, p-toluenesulfonate salt, organic acid salts such as acetate salt, malate salt, fumarate salt, succinate salt, citrate salt, tartrate salt, oxalate salt, maleate salt; and amino acid salts such as glycine salt, lysine salt, arginine salt, ornithine salt, glutamate salt, aspartate salt.

[0364] In the present specification, the term "its pharmaceutically acceptable salt" refers to a salt of an oligonucleotide analogue containing at least one nucleoside structure of the compound represented by formula (I) of the present invention. Examples of such salts include alkali metal salts such as sodium salt, potassium salt, and lithium salt; alkaline earth metal salts such as calcium salt and magnesium salt; metal salts such as aluminum salt, iron salt, zinc salt, copper salt, nickel salt, and cobalt salt; inorganic salts such as ammonium salt; amine salts such as tert-octylamine salt, dibenzylamine salt, morpholine salt, glucosamine salt, phenylglycine alkyl ester salt, ethylenediamine salt, N-methylglucosamine salt, guanidine salt, diethylamine salt, triethylamine salt, dicyclohexylamine salt, N,N'-dibenzylethylenediamine salt, chloroprocaine salt, procaine salt, diethanolamine salt, N-benzyl-phenethylamine salt, piperazine salt, tetramethylammonium salt, and tris(hydroxymethyl)aminomethane salt; inorganic acid salts such as hydrofluoride salt, hydrochloride salt, hydrobromide salt, hydroiodide salt, nitrate salt, perchlorate salt, sulfate salt, and phosphate salt; lower alkane sulfonate salts such as methanesulfonate salt, trifluoromethanesulfonate salt, and ethanesulfonate salt; aryl sulfonate salts such as benzenesulfonate salt and p-toluenesulfonate salt; organic acid salts such as acetate salt, malate salt, fumarate salt, succinate salt, citrate salt, tartrate salt, oxalate salt, and maleate salt; and amino acid salts such as glycine salt, lysine salt, arginine salt, ornithine salt, glutamate salt, and aspartate salt.

[0365] Hereinafter, the present invention will be described in detail.

[0366] (Nucleoside and its salt)

[0367] The compound (nucleoside) of the present invention is a compound represented by the following formula (I) or its salt.

[0368] [Chemical formula 25]

[0369]

[0370] In formula (I), B 1 is:

[0371] (a) a purin-9-yl which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0372] (b) A 1,2-dihydropyrimidin-1-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected with a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected with a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected with a protecting group for nucleic acid synthesis, and a halogen atom.

[0373] In the above formula (I), as the above B 1 Specific examples include an adenine group, a guanine group, a cytosine group, a uracil group, a thymine group, and a 6-aminopurin-9-yl group, a 2,6-diaminopurin-9-yl group, a 2-amino-6-chloropurin-9-yl group, a 2-amino-6-fluoropurin-9-yl group, a 2-amino-6-bromopurin-9-yl group, a 2-amino-6-hydroxypurin-9-yl group, a 6-amino-2-methoxypurin-9-yl group, a 6-amino-2-chloropurin-9-yl group, a 6-amino-2-fluoropurin-9-yl group, a 2,6-dimethoxypurin-9-yl group, a 2,6-dichloropurin-9-yl group, a 6-mercaptopurin-9-yl group, a 2-oxo-4-amino-1,2-dihydropyrimidin-1-yl group, a 4-amino-2-oxo-5-fluoro-1,2-dihydropyrimidin-1-yl group, a 4-amino-2-oxo-5-chloro-1,2-dihydropyrimidin-1-yl group, a 2-oxo-4-methoxy-1,2-dihydropyrimidin-1-yl group, a 2-oxo-4-mercapto-1,2-dihydropyrimidin-1-yl group, a 2-oxo-4-hydroxy-1,2-dihydropyrimidin-1-yl group, a 2-oxo-4-hydroxy-5-methyl-1,2-dihydropyrimidin-1-yl group, and a 4-amino-5-methyl-2-oxo-1,2-dihydropyrimidin-1-yl group.

[0374] Alternatively, for the reason that the compound of the present invention can be effectively introduced as a nucleic acid medicine, B 1 is preferably the following structural formula:

[0375] [Chemical formula 26]

[0376]

[0377] (Here, * is a bonding site) The groups represented respectively, and a 2-oxo-4-hydroxy-5-methyl-1,2-dihydropyrimidin-1-yl group, a 2-oxo-4-amino-1,2-dihydropyrimidin-1-yl group, a 6-aminopurin-9-yl group, a 2-amino-6-hydroxypurin-9-yl group, a 4-amino-5-methyl-2-oxo-1,2-dihydropyrimidin-1-yl group, and a 2-oxo-4-hydroxy-1,2-dihydropyrimidin-1-yl group. In addition, for B 1 , it is preferred that during the synthesis of the oligonucleotide, the hydroxyl groups and amino groups constituting the above groups are protected with protecting groups.

[0378] In addition, in formula (I), R 2 and R 3 are each independently:

[0379] (a) a hydrogen atom;

[0380] (b) a protecting group for a hydroxyl group in nucleic acid synthesis;

[0381] (c) an alkyl group having 1 to 7 carbon atoms that can form a branch or a ring;

[0382] (d) an alkenyl group having 2 to 7 carbon atoms that can form a branch or a ring;

[0383] (e) an aryl group having 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0384] (f) a heteroaryl group having 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0385] (g) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0386] (h) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0387] (i) an acyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0388] (j) a silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0389] (k) a phosphate group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0390] (l) a phosphate group protected by a protecting group for nucleic acid synthesis; or

[0391] (m) -P(R 4 )R 5

[0392] [wherein,

[0393] R 4 and R 5 are each independently:

[0394] (a) a hydroxyl group;

[0395] (b) a hydroxyl group protected by a protecting group for nucleic acid synthesis;

[0396] (c) a mercapto group;

[0397] (d) a mercapto group protected by a protecting group for nucleic acid synthesis;

[0398] (e) an amino group;

[0399] (f) an alkoxy group having 1 to 5 carbon atoms;

[0400] (g) an alkylthio group having 1 to 5 carbon atoms;

[0401] (h) a cyanoalkoxy group having 1 to 6 carbon atoms;

[0402] (i) a dialkylamino group having an alkyl group with 1 to 6 carbon atoms which may be the same or different from each other; or

[0403] (j) a cycloalkylamino group having 3 to 6 carbon atoms,

[0404] alternatively,

[0405] R 4 and R 5 together form the following formula:

[0406] [Chemical Formula 27]

[0407]

[0408] (wherein, R 13a and R 13b are each independently a hydrogen atom, a branched or unbranched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein, R a is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2 [here, Ph represents a phenyl group], * represents a bonding site); or

[0409] [Chemical Formula 28]

[0410]

[0411] (wherein, R 14 and R 15 are each independently a hydrogen atom, a branched or unbranched alkyl group having 1 to 3 carbon atoms, or a phenyl group, * represents a bonding site)].

[0412] In one embodiment, in formula (I), preferably either R 2 or R 3 is

[0413] (m)-P(R 4 )R 5

[0414] [wherein,

[0415] R 4 and R 5 are each independently:

[0416] (a) a hydroxyl group;

[0417] (b) a hydroxyl group protected by a protecting group for nucleic acid synthesis;

[0418] (c) a mercapto group;

[0419] (d) a mercapto group protected by a protecting group for nucleic acid synthesis;

[0420] (e) amino;

[0421] (f) an alkoxy group having 1 to 5 carbon atoms;

[0422] (g) an alkylthio group having 1 to 5 carbon atoms;

[0423] (h) a cyanoalkoxy group having 1 to 6 carbon atoms;

[0424] (i) a dialkylamino group having alkyl groups with 1 to 6 carbon atoms which may be the same or different from each other; or

[0425] (j) a cycloalkylamino group having 3 to 6 carbon atoms.

[0426] As a specific example of the above “-P(R 4 )R 5 ”, phosphoramidite groups can be cited, and as more specific examples, the following groups can be cited:

[0427] [Chemical Formula 29]

[0428]

[0429] (wherein, * is a bonding site).

[0430] In addition, in formula (I), R 6 and R 7 are each composed of any one of the following “Combination A” or “Combination B”.

[0431] First, as “Combination A”, in one embodiment, in formula (I), R 6 is a group represented by the following formula:

[0432] [Chemical Formula 30]

[0433]

[0434] [In the formula,

[0435] R 8a and R 8b are each independently:

[0436] (a) an alkyl group having 1 to 9 carbon atoms which may form a branch or a ring;

[0437] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0438] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0439] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0440] * is a bonding bond], and

[0441] R 7 is:

[0442] (a) An alkyl group having 1 to 8 carbon atoms that may form a branch or a ring and may be substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring;

[0443] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0444] (c) An aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0445] (d) A heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0446] (e) A group represented by the following formula:

[0447] [Chemical formula 31]

[0448]

[0449] [In the formula,

[0450] R 8'a and R 8'b each independently are:

[0451] (a) An alkyl group having 1 to 9 carbon atoms that can be branched;

[0452] (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0453] (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or

[0454] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0455] * is a bonding site.

[0456] In the above “Combination A”, R 7 is preferably an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring. Additionally, in the above “Combination A”, R 8a and R 8b are both preferably alkyl groups having 3 to 8 carbon atoms that can form a branch or a ring, more preferably tert-butyl groups.

[0457] Alternatively, as “Combination B”, in one embodiment, R 6 is:

[0458] (a) An alkyl group having 1 to 8 carbon atoms that can form a branch or a ring and is substituted by an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0459] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0460] (c) An aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0461] (d) a heteroarylalkyl having a heteroaryl moiety with 3 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0462] (e) a group represented by the following formula:

[0463] [Chemical Formula 32]

[0464]

[0465] [In the formula,

[0466] R 8'a and R 8'b are each independently:

[0467] (a) a branched alkyl group having 1 to 9 carbon atoms;

[0468] (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0469] (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0470] (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, a linear alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0471] * is a bonding site], and

[0472] R 7 is a group represented by the following:

[0473] [Chemical Formula 33]

[0474]

[0475] [In the formula,

[0476] R 8a and R 8b are each independently:

[0477] (a) An alkyl group having 1 to 9 carbon atoms that can be branched;

[0478] (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0479] (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or

[0480] (d) A silyl group that can have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0481] * represents a bonding bond.

[0482] In the present invention, for the reason of having a more stable chemical structure, R 6 and R 7 preferably have a group composed of the above "Combination A".

[0483] In addition, in formula (I), R 9 and R 10 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that can form a branch or a ring, or R 9 and R 10 together form -(CH2) m -(where m is an integer from 2 to 7).

[0484] Furthermore, in formula (I), R 11 and R 12 can each independently be a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that can form a branch or a ring. Or, R 11 and R 12 can together form the oxygen atom part (=O) of a carbonyl group (-(CO)-). Or R 11 and R 12 can together form -(CH2) n -(where n is an integer from 2 to 7).

[0485] Here, in one embodiment, for the reason of being able to more stably maintain the guanidine structure of the bridging part, the compound represented by formula (I) of the present invention or a salt thereof is preferably a compound represented by the following formula (I') or a salt thereof:

[0486] [Chemical formula 34]

[0487]

[0488] (In formula (I'), B 1 , R 2 , R 3 , R 7 , R 8a , R 8b , R 9 , R 10 , R 11 , R 12 are each independently defined as above).

[0489] Among the compounds or salts thereof of the present invention, one of the structural features is that a guanidino structure is introduced into the bridging moiety of 2′,4′-BNA / LNA. Since guanidine has a positive charge, the compounds and salts thereof of the present invention can be expected to improve the double-strand forming ability of the target nucleic acid and the enzyme resistance ability, for example, by suppressing anion repulsion (electrostatic interaction) of the phosphodiester moiety and enhancing the hydration effect.

[0490] In addition, the compound or salt thereof of the present invention contains a protecting group (9-fluorenylmethyloxycarbonyl; Fmoc group) having a specified substituent in R 6 or R 7 of formula (I). By containing such a protecting group having a specified substituent, the resulting compounds and salts can maintain a stable state for a long time compared to, for example, compounds or salts having an unsubstituted Fmoc group (9-fluorenylmethyloxycarbonyl itself). The protecting group (Fmoc group) having such a specified substituent is not particularly limited, and examples thereof include an Fmoc group (di-tBu-Fmoc) substituted with two tert-butyl groups.

[0491] It should be noted that by using the compound or salt thereof of formula (I) of the present invention, a 2′,4′-bridged artificial nucleotide can be easily synthesized. For example, the phosphorylation of the 2′,4′-bridged artificial nucleotide can be easily carried out by those skilled in the art according to the method described in Non-Patent Document 5.

[0492] (Guanidinating reagent)

[0493] The compound or salt thereof of formula (I) above can be produced, for example, by reacting a guanidinating reagent with a compound having a specified nucleoside structure as exemplified in the following examples.

[0494] Examples of the guanidinating reagent that can be used in such a reaction include, for example, the compound or salt thereof represented by the following formula (II):

[0495] [Chemical formula 35]

[0496]

[0497] [In formula (II),

[0498] R 7 is:

[0499] (a) an alkoxy group having 1 to 8 carbon atoms that can be branched or form a ring and an alkyl group having 1 to 8 carbon atoms that can be branched or form a ring;

[0500] (b) a cyanoalkoxy group having 1 to 8 carbon atoms;

[0501] (c) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can be branched or form a ring, an alkoxy group having 1 to 8 carbon atoms that can be branched or form a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can be branched or form a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that can be branched or form a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0502] (d) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that can be branched or form a ring, an alkoxy group having 1 to 6 carbon atoms that can be branched or form a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that can be branched or form a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that can be branched or form a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0503] (e) a group represented by the following formula:

[0504] [Chemical formula 36]

[0505]

[0506] [wherein,

[0507] R 8'a and R 8'b are each independently:

[0508] (a) a branched alkyl group having 1 to 9 carbon atoms;

[0509] (b) an alkoxy group having 1 to 8 carbon atoms that can be branched or form a ring;

[0510] (c) an alkylamino group having 1 to 8 carbon atoms that can be branched or form a ring; or

[0511] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0512] * represents a bonding bond],

[0513] R 8a and R 8b are each independently:

[0514] (a) An alkyl group having 1 to 9 carbon atoms that may form a branch or a ring;

[0515] (b) An alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring;

[0516] (c) An alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring; or

[0517] (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis;

[0518] R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms].

[0519] It should be noted that in the present invention, the compounds represented by the above formula (II) include any of their tautomers and geometric isomers.

[0520] As a specific example of the compound represented by formula (II), the following compound represented by formula (II') can be cited:

[0521] [Chemical formula 37]

[0522]

[0523] [In formula (II'), R 7 , R 8a , R 8b and R 16 are the same as those defined in the above formula (II).

[0524] In formulas (I), (I'), (II) and (II'), R 8a and R 8b are preferably alkyl groups having 1 to 9 carbon atoms which can form a branch or a ring, more preferably branched alkyl groups having 1 to 6 carbon atoms, still more preferably tertiary alkyl groups having 4 to 6 carbon atoms, and particularly preferably tert-butyl groups.

[0525] In formulas (I), (I'), (II) and (II'), R 7 is an alkyl group having 1 to 8 carbon atoms which can be substituted by an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring and which can form a branch or a ring, more preferably an alkyl group having 1 to 8 carbon atoms which can form a branch or a ring, still more preferably a branched alkyl group having 1 to 8 carbon atoms, and particularly preferably tert-butyl group.

[0526] R 16 is preferably a straight-chain or branched alkyl group having 1 to 6 carbon atoms, still more preferably methyl, ethyl, n-propyl or n-butyl, and particularly preferably methyl.

[0527] In the present invention, the compound of formula (II) which can be used as a guanidinating agent can be produced by reacting a compound represented by the following formula (III) with a compound represented by the following formula (IV), and then reacting the reaction product with a compound represented by the following formula (V).

[0528] [Chemical formula 38]

[0529]

[0530] [In formula (III), R 8a and R 8b are each independently the same as defined in formula (II) above.

[0531] [Chemical formula 39]

[0532]

[0533] [In formula (IV), p is independently an integer from 0 to 3.

[0534] [Chemical formula 40]

[0535]

[0536] [In formula (V), R 7 and R 16 are respectively the same as defined in formula (II) above, and X - is a counter anion.

[0537] In formula (IV), p is preferably independently 1 or 2, particularly preferably 1. Specific examples of X include a halogen atom, p-toluenesulfonyloxy, methanesulfonyloxy, trifluoromethanesulfonyloxy, etc. X is preferably a halogen atom, particularly preferably an iodine atom.

[0538] Here, the reaction product of the compound represented by formula (III) and the compound represented by formula (IV) is represented by the following formula. For example, it can be obtained by reacting the compound of formula (III) and the compound of formula (IV) in a suitable solvent in the presence of a base.

[0539] [Chemical formula 41]

[0540]

[0541] The solvent is not particularly limited as long as the reaction proceeds well. Specific examples include halogenated hydrocarbon solvents (dichloromethane (DCM), chloroform, etc.), lower aliphatic acid ester solvents (ethyl acetate, etc.), nitrile solvents (acetonitrile, etc.), and combinations thereof. The solvent is preferably an organic solvent, more preferably a halogenated hydrocarbon solvent, particularly preferably dichloromethane. Examples of the base include pyridine, N-methylmorpholine, and combinations thereof, preferably pyridine. The equivalent amount of the base is, for example, 1 to 5 equivalents, preferably 1 to 2 equivalents, relative to 1 mole of the compound of formula (III).

[0542] The amount of the compound represented by formula (IV) used is, for example, 1 to 5 equivalents, preferably 1 to 2 equivalents, relative to 1 mole of the compound represented by formula (III).

[0543] The reaction temperature is, for example, -78°C to the reflux temperature of the solvent, preferably 0 to 50°C, particularly preferably 10 to 40°C.

[0544] The reaction time is preferably 10 minutes to 48 hours, more preferably 20 minutes to 10 hours, and further preferably 30 minutes to 5 hours.

[0545] As the reaction conditions for the reaction product and the compound represented by formula (V), the solvent is not particularly limited as long as the reaction proceeds well. Specific examples include water in addition to the same solvents as those in the step of reacting the compound of formula (III) and the compound of formula (IV). A mixed solvent of a halogenated hydrocarbon solvent and water is preferred, and a mixed solvent of dichloromethane and water is particularly preferred. The mixed solvent of the halogenated hydrocarbon solvent and water forms a two-layer solvent system.

[0546] Examples of the base include alkali metal carbonates (such as sodium carbonate and potassium carbonate) and alkali metal hydrogen carbonates (such as sodium hydrogen carbonate and potassium hydrogen carbonate), preferably alkali metal carbonates, and particularly preferably potassium carbonate. The equivalent amount of the base, for example, relative to 1 mole of the compound of formula (III), is 1 to 5 equivalents (preferably 1 to 2 equivalents) in the case of alkali metal carbonates and 2 to 10 equivalents (preferably 2 to 4 equivalents) in the case of alkali metal hydrogen carbonates.

[0547] The reaction temperature is, for example, 0 °C to the reflux temperature of the solvent, preferably 0 to 50 °C, and particularly preferably 10 to 40 °C.

[0548] The reaction time is preferably 10 minutes to 48 hours, more preferably 20 minutes to 10 hours, and further preferably 30 minutes to 5 hours.

[0549] The compound of formula (II) can be purified by adding an aliphatic hydrocarbon solvent such as heptane, heating, then cooling, and then filtering. As the heating temperature, for example, 40 to the reflux temperature of the solvent can be cited, preferably 40 to 60 °C. As the cooling temperature, for example, it is -20 to 30 °C, preferably -10 to 20 °C.

[0550] It should be noted that the compounds represented by the above (III) and the compound of formula (V) can be synthesized as follows, for example.

[0551] The synthesis procedure of the compound represented by formula (III) will be described. First, a fluorene compound represented by formula (A-5) is reacted with a formate (such as ethyl formate and methyl formate) in a solvent in the presence of a base, whereby a compound represented by formula (A-6) can be obtained. Then, by reacting the compound represented by formula (A-6) with a reducing agent such as sodium borohydride and sodium triacetoxyborohydride, the compound represented by the above formula (III) can be obtained:

[0552] [Chemical formula 42]

[0553]

[0554] (In formulas (A-5) and (A-6), R 8a and R 8b are each independently the same as defined in the above formula (II).).

[0555] As the reaction conditions for the reaction from the compound of formula (A-5) to the compound of formula (A-6), there is no particular limitation on the solvent as long as the reaction proceeds well. An organic solvent is preferred. For example, ether solvents (such as tetrahydrofuran and diethyl ether) can be cited, and tetrahydrofuran is particularly preferred.

[0556] As the base, there is no particular limitation as long as the reaction proceeds. For example, metal alkoxides (potassium tert-butoxide, sodium tert-butoxide, sodium ethoxide, sodium methoxide, etc.) can be cited, and potassium tert-butoxide is particularly preferred. The equivalent amount of the base is, for example, 1 to 5 equivalents, preferably 1 to 3 equivalents, relative to 1 mole of the compound of formula (A-5).

[0557] The reaction temperature is, for example, -78 °C to the reflux temperature of the solvent, preferably -20 to 50 °C, more preferably -10 to 30 °C, and particularly preferably -10 to 10 °C.

[0558] The reaction time is preferably 10 minutes to 48 hours, more preferably 10 minutes to 10 hours, and further preferably 20 minutes to 2 hours.

[0559] As the reaction conditions for the reaction from the compound of formula (A-6) to the compound of formula (III), there is no particular limitation on the solvent as long as the reaction proceeds well. For example, water, alcohols (methanol, ethanol, isopropanol, etc.), ether solvents (tetrahydrofuran, diethyl ether, etc.), or combinations thereof can be cited, and water or isopropanol or a combination thereof is particularly preferred.

[0560] It is preferred to use a base. For the base, there is no particular limitation as long as the reaction proceeds. For example, metal hydroxides (potassium hydroxide, sodium hydroxide, etc.) can be cited, and sodium hydroxide is particularly preferred. The equivalent amount of the base is, for example, 1 to 5 equivalents, preferably 1 to 3 equivalents, relative to 1 mole of the compound of formula (A-6).

[0561] The reaction temperature is, for example, -78 °C to the reflux temperature of the solvent, preferably 0 to 50 °C, and particularly preferably 20 to 40 °C.

[0562] The reaction time is preferably 10 minutes to 48 hours, more preferably 20 minutes to 10 hours, and further preferably 30 minutes to 5 hours.

[0563] After the reaction, a treatment of adding camphorsulfonic acid and stirring in an aromatic hydrocarbon solvent such as toluene can be carried out.

[0564] The compound of formula (III) can be purified by adding an aliphatic hydrocarbon solvent such as heptane, heating, then cooling, and then filtering. The heating temperature can be, for example, 40 °C to the reflux temperature of the solvent, preferably 40 to 70 °C, more preferably 50 to 70 °C. The cooling temperature is, for example, -20 to 30 °C, preferably -10 to 20 °C.

[0565] On the other hand, the synthesis procedure of the compound represented by formula (V) will be described. First, the amine represented by formula (A-1) is reacted with benzoyl isothiocyanate in a suitable solvent (such as acetonitrile) to produce the following compound represented by formula (A-2).

[0566] [Chemical formula 43]

[0567]

[0568] (In formulas (A-1) and (A-2), R 7 is the same as defined in formula (II) above).

[0569] For the solvent, as long as the reaction proceeds well, there is no particular limitation, and an organic solvent is preferred. For example, nitrile solvents (such as acetonitrile) can be mentioned, and acetonitrile is particularly preferred.

[0570] The equivalent amount of benzoyl isothiocyanate is, for example, 1 to 5 equivalents, preferably 1 to 3 equivalents, relative to 1 mole of the compound of formula (A-1).

[0571] The reaction temperature is, for example, -78°C to the reflux temperature of the solvent, preferably -20 to 50°C, more preferably -10 to 30°C, and particularly preferably -10 to 10°C.

[0572] The reaction time is preferably 10 minutes to 48 hours, more preferably 10 minutes to 10 hours, and further preferably 30 minutes to 2 hours.

[0573] The compound of formula (A-2) can be purified by washing with a nitrile solvent such as acetonitrile. Here, acetonitrile is preferably used after cooling. The cooling temperature is, for example, -20 to 10°C, preferably -10 to 10°C.

[0574] Next, the compound of formula (A-2) is reacted with a nucleophile in a solvent, and after removing the benzoyl group, it is reacted with an alkyl-introducing reagent, whereby the compound represented by formula (V) above can be obtained via the compound of formula (A-3).

[0575] [Chemical formula 44]

[0576]

[0577] (In formulas (A-2), (A-3) and (V), R 7 is the same as defined in formula (II) above, and in formula (V), R 16 is the same as defined in formula (II) above).

[0578] As the reaction conditions for the reaction from the compound of formula (A-2) to the compound of formula (A-3), for the solvent, as long as the reaction proceeds well, there is no particular limitation, and an organic solvent is preferred. For example, alcohol solvents (such as methanol, ethanol, n-propanol, etc.) can be mentioned, and methanol is particularly preferred.

[0579] As the nucleophile, there is no particular limitation as long as the reaction proceeds. For example, metal alkoxides (sodium ethoxide, sodium methoxide, etc.) can be cited, and sodium methoxide is particularly preferred. The equivalent amount of the base is, for example, 0.001 to 1 equivalent relative to 1 mole of the A-2 compound, and preferably 0.01 to 0.1 equivalent. The reaction temperature is, for example, -78°C to the reflux temperature of the solvent, preferably 0°C to the reflux temperature of the solvent, and more preferably 40 to 70°C.

[0580] The reaction time is preferably 10 minutes to 48 hours, more preferably 10 minutes to 10 hours, and further preferably 20 minutes to 3 hours.

[0581] As the reaction conditions for the reaction from the compound of formula (A-3) to the compound of formula (V), there is no particular limitation for the solvent as long as the reaction proceeds well. An organic solvent is preferred. For example, alcohol solvents (methanol, ethanol, n-propanol, etc.) can be cited, and more preferably the same solvent as that in the step of producing the compound of formula (A-3) from the compound of formula (A-2).

[0582] As the alkyl-introducing reagent, alkyl halides (methyl iodide, methyl bromide, methyl chloride, ethyl iodide, ethyl bromide, ethyl chloride, etc.), sulfonic acid esters (methyl methanesulfonate, methyl p-toluenesulfonate, methyl trifluoromethanesulfonate, etc.), and sulfuric acid diesters (dimethyl sulfate, diethyl sulfate, etc.) can be cited, and methyl iodide is particularly preferred. The equivalent amount of the alkyl-introducing reagent is 1 to 5 equivalents, preferably 1 to 3 equivalents, relative to, for example, 1 mole of the compound of formula (A-3).

[0583] The reaction temperature is, for example, -78°C to the reflux temperature of the solvent, preferably 0°C to the reflux temperature of the solvent, and more preferably 20 to 40°C.

[0584] The reaction time is preferably 10 minutes to 48 hours, more preferably 10 minutes to 10 hours, and further preferably 20 minutes to 3 hours.

[0585] The compounds represented by the formulas (III), (V), (A-2), and (A-6) can all be used in the next step without column purification. In addition, it is possible to avoid using reagents that require attention in the operation (p-nitrophenyl chloroformate, n-butyllithium, ammonia-methanol solution, etc.) to produce the compound represented by the above formula (II). The manufacturing method of the aforementioned compound represented by the formula (II) can be applied to industrial production methods.

[0586] (Guanidination step using a guanidinating reagent)

[0587] By using the compound represented by formula (II) or a salt thereof prepared as described above as a guanidinylating agent and reacting it with the compound represented by the following formula (VI), the compound represented by formula (I) or a salt thereof can be produced through, for example, the following reaction step (guanidinylation step). It should be noted that the term "guanidinylation" used in this specification may also be expressed as "guanidylation" or "guanidination", and they have the same meaning.

[0588] Specifically, the compound represented by the following formula (VI) or a salt thereof:

[0589] [Chemical formula 45]

[0590]

[0591] Guanidinylation using the compound represented by formula (II) or a salt thereof:

[0592] [Chemical formula 46]

[0593]

[0594] (In formula (VI),

[0595] B 1 is:

[0596] (a) A purin-9-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0597] (b) A 1,2-dihydropyrimidin-1-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom,

[0598] R 2 and R 3 are:

[0599] (a) A hydrogen atom;

[0600] (b) A protecting group for a hydroxyl group in nucleic acid synthesis;

[0601] (c) an alkyl group having 1 to 7 carbon atoms that can form a branch or a ring;

[0602] (d) an alkenyl group having 2 to 7 carbon atoms that can form a branch or a ring;

[0603] (e) an aryl group having 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0604] (f) a heteroaryl group having 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0605] (g) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0606] (h) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0607] (i) an acyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0608] (j) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0609] (k) A phosphate group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0610] (l) A phosphate group protected by a protecting group for nucleic acid synthesis,

[0611] R 9 and R 10 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, or R 9 and R 10 together form -(CH2) m -(where m is an integer from 2 to 7),

[0612] R 11 and R 12 are each independently a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring,

[0613] or R 11 and R 12 together form the oxygen atom part of a carbonyl group (=O),

[0614] or R 11 and R 12 together form -(CH2) n -(where n is an integer from 2 to 7),

[0615] In formula (II),

[0616] R 7 is:

[0617] (a) An alkyl group having 1 to 8 carbon atoms that may form a branch or a ring and is substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring;

[0618] (b) A cyanoalkoxy group having 1 to 8 carbon atoms;

[0619] (c) An aralkyl having an aryl moiety with 6 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom;

[0620] (d) A heteroaralkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or

[0621] (e) A group represented by the following formula:

[0622] [Chemical formula 47]

[0623]

[0624] [In the formula,

[0625] R 8'a and R 8'b are each independently:

[0626] (a) An alkyl group having 1 to 9 carbon atoms which may be branched;

[0627] (b) An alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring;

[0628] (c) An alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or

[0629] (d) A silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and

[0630] * is a bonding site],

[0631] R 8aand R 8b Each independently is:

[0632] (a) an alkyl group having 1 to 9 carbon atoms that can form a branch or a ring;

[0633] (b) an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring;

[0634] (c) an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or

[0635] (d) a silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis,

[0636] R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms).

[0637] For the solvent that can be used in the above guanidination step, as long as the reaction proceeds well, there is no particular limitation, and an organic solvent is preferred. For example, an ether solvent (diethyl ether, diisopropyl ether, tetrahydrofuran, 4-methyltetrahydropyran, etc.) can be mentioned, and tetrahydrofuran is particularly preferred.

[0638] The reaction is preferably carried out using a metal salt. As the metal salt, as long as the reaction proceeds well, there is no particular limitation, and a thiophilic metal salt is preferred. Silver salts (silver chloride, silver bromide, silver nitrate, silver iodide, silver trifluoromethanesulfonate, silver tetrafluoroborate, silver hexafluorophosphate, etc.), copper(I) salts (copper(I) chloride, copper(I) bromide, copper(I) iodide, copper(I) trifluoromethanesulfonate, copper(I) tetrafluoroborate, copper(I) hexafluorophosphate, etc.), and mercury(II) salts (mercury(II) chloride, etc.) can be mentioned. A silver salt or a copper(I) salt is preferred, a copper(I) salt is more preferred, and copper(I) chloride is particularly preferred. The copper(I) salt is inexpensive and safe. The equivalent amount of the metal salt, for example, is 1 to 5 equivalents relative to 1 mole of the compound of formula (II), and preferably 1 to 2 equivalents.

[0639] Here, the term "thiophilic metal" used in this specification refers to a soft metal to which a soft sulfide binds. The term "thiophilic" is based on the HSAB rule. The HSAB rule is an acronym related to hard and soft (Lewis) acids and bases. According to the HSAB rule, for soft metal ions, a soft sulfide is preferably used as a counterion.

[0640] The reaction is preferably carried out under a nitrogen atmosphere. Further, in the case of using a copper(I) salt, the reaction is preferably started under a nitrogen atmosphere, and an oxygen-containing gas (such as air) is added midway and stirred. By oxygen, the copper ion is oxidized from the +1 valence to the +2 valence, and the reaction rate is increased.

[0641] The reaction is preferably carried out in the presence of a base. The base is not particularly limited as long as the reaction proceeds well, and examples include trialkylamines (such as triethylamine), pyridine, etc. Pyridine is particularly preferred. The equivalent of the metal salt is, for example, 1 to 20 equivalents, preferably 2 to 10 equivalents, relative to 1 mole of the compound of formula (II).

[0642] The reaction temperature is, for example, -78 °C to the reflux temperature of the solvent, preferably 0 to 70 °C, more preferably 30 to 70 °C, and particularly preferably 50 to 70 °C.

[0643] The reaction time is preferably 5 minutes to 48 hours, more preferably 10 minutes to 10 hours, further preferably 30 minutes to 5 hours, and particularly preferably 1 to 2 hours.

[0644] R can also be 2 The guanidination step is carried out on the compound of formula (I) in which R is a protecting group for the hydroxyl group in nucleic acid synthesis (such as trimethylsilyl, triethylsilyl (TMS group), tert-butyldimethylsilyl, etc. silyl groups), and this protecting group is removed using a fluorine reagent (such as tetrabutylammonium fluoride), etc., thereby producing a compound of formula (I) in which R 2 is a hydrogen atom.

[0645] As a post-treatment of the guanidination step, the solution containing the compound of formula (I) as the product can be treated with a solution containing an aqueous solution of ethylenediaminetetraacetic acid (EDTA) and a metal hydroxide (such as sodium hydroxide, potassium hydroxide, etc.). This post-treatment is effective for removing the metal salt. The equivalent of ethylenediaminetetraacetic acid is 1 to 5 equivalents, preferably 1 to 2 equivalents, relative to 1 mole of the metal salt used. The aqueous solution of the metal hydroxide is 1 to 4 equivalents, preferably 2 equivalents, relative to 1 mole of the ethylenediaminetetraacetic acid used.

[0646] In addition, it goes without saying that the above steps of obtaining the compound of formula (A-6) from the compound of formula (A-5), obtaining the compound of formula (III) from the compound of formula (A-6), obtaining the compound of formula (II) from the compound of formula (III), and obtaining the compound of formula (I) from the compound of formula (II) can also be respectively applied to the case where R 8a and / or R 8b is a hydrogen atom, and can be carried out in the same manner as described above.

[0647] It should be noted that between the guanidination step and the next amidite step, a protection reaction and / or deprotection reaction of the nucleic acid base group, and / or a protection reaction and / or deprotection reaction of the hydroxyl group at the 3'-position and / or 5'-position can be carried out as needed. For example, a compound in which R in formula (VI) in the above guanidination step 2 is a protecting group for the hydroxyl group in nucleic acid synthesis can be used as a raw material for the guanidination step, and then the protecting group is deprotected to obtain a compound of formula (I) in which R 2 is a hydrogen atom. Furthermore, the compound of formula (I) in which R 2 is a hydrogen atom can be provided to the next amidite step.

[0648] (Amidite step)

[0649] Next, by subjecting the compound of formula (I) after the above guanidination in which R 2 and / or R 3 is a hydrogen atom or a salt thereof to amidite as described below, the desired amidite can be produced.

[0650] That is, the amidite (a compound in which R 2 and / or R 3 in formula (I) is -P(R 4 )R 5 as represented) (here, R 4 and R 5 are as defined above) can be produced by converting the hydroxyl group of the compound in which R 2 and / or R 3 in formula (I) is a hydroxyl group to -P(R 4 )R 5 using an amidite reagent.

[0651] This step can be carried out, for example, under the conditions described in Org. Process Res. Dev. 2005, 9, 6, 730 - 737.

[0652] Specifically, for example, an activator (such as 4,5-dicyanoimidazole, 5-phenyltetrazole, or 1H-tetrazole) and an amidite reagent corresponding to -P(R 4 )R 5 (such as 2-cyanoethoxy N,N,N',N'-tetraisopropylphosphorodiamidite or 2-cyanoethoxy N,N-diisopropylchlorophosphoramidite, etc.) can be used to carry out the reaction.

[0653] As the solvent that can be used in the above amidite step, as long as it does not affect the reaction. Preferred are halogenated hydrocarbon solvents such as dichloromethane, or nitrile solvents such as acetonitrile.

[0654] As the reaction temperature, it is preferably 0 to 50 °C, more preferably 20 to 30 °C.

[0655] As the reaction time, for example, it is 0.5 to 48 hours, preferably 1 to 36 hours, and more preferably 1 to 8 hours.

[0656] Thus, an Amidite body (the compound represented by R in formula (I)) can be produced from the compound of formula (I) after the above guanidination. 2 is -P(R 4 )R 5 )

[0657] (oligonucleotide or a pharmaceutically acceptable salt thereof)

[0658] In the present invention, an oligonucleotide or a pharmaceutically acceptable salt thereof can be produced by nucleic acid synthesis using the compound or a salt thereof represented by the above formula (I) (hereinafter sometimes referred to as "the compound of formula (I)", etc.).

[0659] Such an oligonucleotide has at least one nucleoside structure derived from the compound of formula (I), etc. at an arbitrary position. The number and position of the above nucleoside structures contained in one oligonucleotide are not particularly limited and can be appropriately designed according to the purpose. The larger the number, the higher the binding affinity and specificity of the oligonucleotide to the target nucleic acid, the faster the formation rate of double strands and triple strands, and the higher the nuclease resistance. In the present specification, the 2′,4′-bridged artificial nucleoside of the present invention and the above nucleoside structure contained in the oligonucleotide of the present invention are also collectively referred to as "guanidine-bridged artificial nucleic acid" or "guanidine-bridged nucleic acid".

[0660] An oligonucleotide and an analogue thereof containing such a nucleoside structure have a structure fixed by bridging of the sugar moiety as described above, and thus are hardly degraded by various nucleases. After administration to an organism, they can exist in the organism for a long time. Furthermore, due to the electrostatic action of the cationic guanidine present on the bridge of the sugar moiety, for example, a stable double strand is formed with mRNA to hinder the biosynthesis of the causative protein, or a triple strand is formed between the double-stranded DNA in the genome to hinder transcription into mRNA. In addition, the proliferation of the infected virus can also be inhibited.

[0661] Therefore, an oligonucleotide and an analogue thereof synthesized using the compound of formula (I) of the present invention, etc. are useful as pharmaceuticals (antisense molecules, etc.) that treat diseases by hindering the action of a specific gene, such as an antitumor agent and an antiviral agent.

[0662] In particular, in the antisense method, it is necessary to have both binding affinity for complementary sense-strand RNA and resistance to DNA-degrading enzymes in vivo. It is known that generally in the single-stranded state of nucleic acids, the structure of the sugar moiety continuously oscillates between forms similar to double-stranded DNA, double-stranded DNA-RNA, or double-stranded RNA. When a single-stranded nucleic acid forms a double-strand with a complementary RNA strand, the structure of its sugar moiety is fixed. Therefore, in the compounds of formula (I) of the present invention, etc., since the sugar moiety is pre-fixed in the state when forming a double-strand, it can easily form a double-strand with the target RNA strand and can exist stably. In addition, it is also known that nucleic acid double-strands can be stabilized by hydration water connected in a chain-like manner called a water molecule network. In the compounds of formula (I) of the present invention, etc., since the bridging moiety has a guanidino structure, it is expected, for example, to improve the double-strand forming ability and the enzyme resistance ability through electrostatic interaction and hydration effect. Furthermore, by introducing a guanidino structure into the bridging moiety, the position of the cation can be fixed, and thus it is also expected to enhance the electrostatic interaction and hydration effect. In the compounds of formula (I) of the present invention, etc., having a positive charge derived from a guanidinium group in the molecule, compared with natural nucleic acids or artificial nucleic acids known so far, it can improve the uptake efficiency into cells, and it is also expected to further increase the hybridization formation rate with the target nucleic acid. From this, it can be expected to enhance the antisense effect and extend the residence time in vivo, and thus side effects can be reduced and costs can be cut by reducing the dosage.

[0663] In addition, the oligonucleotides of the present invention may also contain at least one phosphorothioate bond within their structure.

[0664] The oligonucleotides or their pharmaceutically acceptable salts obtained using the compounds of formula (I) of the present invention, etc. can be admixed with excipients, binders, preservatives, oxidation stabilizers, disintegrants, lubricants, flavoring agents, etc., which are commonly used in the pharmaceutical technology field of drugs, to prepare parenteral administration preparations or liposomal preparations. In addition, for example, drug carriers commonly used in this technical field can be admixed to prepare topical preparations such as liquid preparations, creams, and ointments.

[0665] Examples

[0666] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to these examples.

[0667] In the examples, "LC-MS" refers to liquid chromatography mass spectrometry, "NMR" refers to nuclear magnetic resonance, "CDCl3" refers to deuterated chloroform, and "DMSO-d6" refers to deuterated dimethyl sulfoxide. "(v / v)" refers to (volume / volume). "qCV" (where q represents a number) in silica gel column chromatography purification refers to the volume amount of the developing solvent that is q times the volume of silica gel used.

[0668] In the following Examples 1 to 6 (except for Example 1 (1-1(2)), Example 2 (2-1(2)), Example 2 (2-1(3)), and Example 4 (4-1(2))), the measuring devices and measuring conditions used are as follows.

[0669] (1) NMR

[0670] Equipment used: JEOL ECX-400P and ECS-400 manufactured by JEOL Ltd.

[0671] Measuring conditions: 1 H-NMR (DMSO-d6, CDCl3)

[0672] 31 P-NMR (CDCl3)

[0673] (2) UHPLC

[0674] Equipment used: ACQUITY Arc UHPLC system manufactured by Waters

[0675] Column: Xbridge BEH C18, 2.5μm, 3.0X 100mm, Column XP manufactured by Waters

[0676] Mobile phase: gradient

[0677] [Table 1]

[0678]

[0679]

[0680] Flow rate: 0.85 mL / minute

[0681] Detection: PDA (200 - 400 nm)

[0682] Column temperature: 30°C

[0683] Analysis time: 10.00 minutes

[0684] The measuring devices and measuring conditions used in Example 1 (1-1(2)), Example 2 (2-1(2)), Example 2 (2-1(3)), Example 4 (4-1(2)), and Example 7 are as follows.

[0685] (1) NMR

[0686] Equipment used: JNM-ECP300, JNM-ECX300, or JNM-ECZ400S manufactured by JEOL Ltd.

[0687] Measuring conditions: 1 1H-NMR (DMSO-d6 or CDCl3)

[0688] Tetramethylsilane (0.0 ppm) was used as the internal standard. The J value is expressed in Hz, and the chemical shift is expressed in ppm. "s" means singlet, "d" means doublet, "t" means triplet, "q" means quartet, "quint" means quintet, "dd" means double doublet, "m" means multiplet, "brs" means broad singlet, and "brm" means broad multiplet.

[0689] (2) LC-MS

[0690] Regarding the data, unless otherwise specified, it was measured using the ESI (electrospray ionization) method under the following conditions. "ESI + " means the ESI positive ion mode, and "ESI - " means the ESI negative ion mode.

[0691] In addition, regarding the LC purity, unless otherwise specified, it was measured under either of the following conditions A or B and calculated by the area percentage method.

[0692] LC-MS analysis condition A:

[0693] High-performance liquid chromatography: HPLC manufactured by Waters

[0694] Column: ACQUITY UPLC BEH C18 1.7 μM 2.1×50 mm manufactured by Waters

[0695] Chromatography temperature: 40 °C

[0696] Eluent: Solution A: 0.1% formic acid aqueous solution

[0697] Solution B: 0.1% formic acid acetonitrile solution

[0698] Gradient conditions:

[0699] After starting the measurement by mixing Solution A and Solution B at a mixing ratio of 80 / 20 at a flow rate of 0.6 mL / minute, the mixing ratio of Solution A and Solution B was linearly changed to 0 / 100 in 3 minutes. Then, the mixing ratio of Solution A and Solution B was fixed at 0 / 100 within 0.7 minutes. Within the subsequent 0.1 minute, the mixing ratio of Solution A and Solution B was linearly changed to 90 / 10 at a flow rate of 0.8 mL / minute. Then, the mixing ratio of Solution A and Solution B was fixed at 90 / 10 within the subsequent 1 minute.

[0700] Detection wavelength: 254 nm

[0701] LC-MS analysis condition B:

[0702] High-performance liquid chromatography: HPLC manufactured by Waters Corporation

[0703] Column: ACQUITY UPLC BEH C18 1.7 μM 2.1×50 mm manufactured by Waters Corporation

[0704] Chromatography temperature: 40 °C

[0705] Eluent: Solution A: 10 mM aqueous ammonium bicarbonate solution

[0706] Solution B: 10 mM aqueous ammonium bicarbonate solution / acetonitrile = 1:9

[0707] Gradient condition:

[0708] After starting the measurement at a flow rate of 0.6 mL / minute and a mixing ratio of 80 / 20 of Solution A and Solution B, the mixing ratio of Solution A and Solution B was linearly changed to 0 / 100 in 3 minutes. Within the subsequent 3.7 minutes, the mixing ratio of Solution A and Solution B was fixed at 0 / 100. Within the subsequent 0.1 minute, the mixing ratio of Solution A and Solution B was linearly changed to 90 / 10 at a flow rate of 0.8 mL / minute. Then, the mixing ratio of Solution A and Solution B was fixed at 90 / 10 within the subsequent 1 minute.

[0709] Detection wavelength: 254 nm

[0710] The measuring device and measuring conditions used in Example 8 below are as follows.

[0711] (1) NMR

[0712] Equipment used: JEOL ECX-400P and ECS-400 manufactured by JEOL Ltd., Japan

[0713] Measuring conditions: 1 H-NMR (DMSO-d6, CDCl3)

[0714] (2) UHPLC

[0715] Equipment used: ACQUITY Arc UHPLC system manufactured by Waters

[0716] Column: Xbridge BEH C18, 2.5 μm, 3.0 X 100 mm, Column XP manufactured by Waters

[0717] Mobile phase: Gradient

[0718] [Table 2]

[0719] Time / Solvent <![CDATA[H2O(%)]]> <![CDATA[CH3CN (%)]]> 0 minutes 95 0 0.60 minutes 95 0 4.50 minutes 0 95 7.50 minutes 0 95 9.50 minutes 0 100 10.00 minutes 0 100

[0720] Flow rate: 0.85 mL / minute

[0721] Detection: PDA (200 - 400 nm)

[0722] Column temperature: 40 °C

[0723] Analysis time: 10.00 minutes

[0724] (Reference Example 1: Preparation of Triethylamine-Treated Silica Gel)

[0725] Prepare the triethylamine-treated silica gel used in Examples 2 (2-1(2)), 2 (2-1(3)), and 4 (4-1(2)) described below in the following manner.

[0726] Add n-hexane (600 mL) to 200 g of silica gel (FL100D manufactured by Fuji Silysia Chemical Ltd.), and stir with a mechanical stirrer (170 rpm). Add triethylamine (40 g) to it all at once, stir until the heat generation ends (usually about 1 hour), and filter through a glass filter. Transfer the filtered material to a round-bottomed flask and dry it under reduced pressure using an evaporator to obtain 212 g of triethylamine-treated silica gel.

[0727] (Example 1: Synthesis of Amidite (a3))

[0728] Synthesize the following Amidite (di-tBu-Fmoc-GuNA[t-Bu]-T Amidite) (a3) as follows:

[0729] [Chemical Formula 48]

[0730]

[0731] (1-1(1): Synthesis of Compound a2 (1))

[0732] [Chemical Formula 49]

[0733]

[0734] Under an argon stream, compound a1 (39.6 g, 69.3 mmol) obtained by the methods described by A. S. Madsen et al. in J. Org. Chem. 2012, 77, 10718 - 10728 and H. Sawamoto et al. in Org. Lett. 2018, 20, 1928 - 1931 and the guanidinylation reagent (di - tBu - Fmoc protected form) (40 g, 83.0 mmol) obtained in the following examples were suspended in tetrahydrofuran (THF) (400 mL) and cooled to an internal temperature of 5 °C or lower in an ice bath. N,N - Diisopropylethylamine (DIPEA) (18.2 mL, 104 mmol) and silver trifluoromethanesulfonate (AgOTf) (26.7 g, 104 mmol) were added, and the mixture was stirred at room temperature for 2 hours and 35 minutes. Since starting materials remained, DIPEA (6.06 mL, 34.7 mmol) and AgOTf (8.91 g, 34.7 mmol) were added, and stirring was continued for 1 hour and 5 minutes.

[0735] After confirming the disappearance of the starting materials, ethyl acetate (250 mL) and saturated NaCl aqueous solution (250 mL) were added to the reaction mixture. After stirring for a while, the mixture was filtered through Celite. The residue was washed successively with ethyl acetate (300 mL) and water (250 mL), and then the filtrate was separated. The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (neutral silica 1.0 kg, developing solvent: n - heptane / acetone (1% triethylamine) = 80 / 20 → 70 / 30 → 60 / 40 → 50 / 50), and azeotroped with acetonitrile to obtain the title compound a2 (68.8 g (containing 3.87 wt% acetonitrile), 65.9 mmol, 95% yield) as a white amorphous solid. The 1H - NMR spectrum of compound a2 obtained in this Example 1 (1 - 1(1)) 1 is shown in Figure 1 below.

[0736] (1 - 1(2): Synthesis of compound a2 (2))

[0737] [Chemical formula 50]

[0738]

[0739] To a suspension of compound a1 (1.00 g) obtained by the method described in J. Org. Chem. 2012, 77, 10718 - 10728 by A.S. Madsen et al. and Org. Lett. 2018, 20, 1928 - 1931 by H. Sawamoto et al. in THF (15 mL), pyridine (705 μL) was added under a nitrogen atmosphere. After stirring at room temperature for 7 minutes, copper(I) chloride (208 mg) was added and stirred for 1 hour. After adding a solution of the guanidylation reagent (di - tBu - Fmoc protected form) (925 mg) in THF (2.0 mL), it was stirred at 60 °C for 30 minutes, then switched to an air atmosphere and stirred at 60 °C for another 2 hours.

[0740] After cooling the reaction mixture to room temperature in a water bath, the insoluble matter was removed by filtration (washing: ethyl acetate 5 mL × 2). The filtrate was concentrated, and the residue was dissolved in ethyl acetate (15 mL). A solution prepared from EDTA [ethylenediaminetetraacetic acid] (511 mg), 1 M aqueous sodium hydroxide solution (3.5 mL), and water (10 mL) was added thereto, shaken well, and allowed to stand.

[0741] The aqueous layer was removed, water (10 ml) was added to the organic layer and shaken well, and after standing, the aqueous layer was removed. The organic layer was concentrated under reduced pressure. The concentrated residue was purified by silica gel column chromatography (DIOLMB100 - 40 / 75 manufactured by Fuji Silysia Chemical Ltd., 30 g, developing solvent: n - heptane / ethyl acetate = 90 / 10 (0.1 CV) → 70 / 30 (5 CV) → 30 / 70 (5 CV) → 0 / 100 (2 CV)) to obtain the title compound a2 (1.74 g, yield 99%) as a cream - colored amorphous solid. The physical property data of compound a2 obtained in Example 1 (1 - 1(2)) are shown in Table 3.

[0742] [Table 3]

[0743]

[0744] (1 - 2: Synthesis of Amidite form (a3))

[0745] [Chemical formula 51]

[0746]

[0747] Under an argon stream, the compound a2 (65.0 g (containing 3.87 wt% acetonitrile), 62.2 mmol) obtained in the above Example 1 (1-1(1)) was charged into dry dichloromethane (DCM) (600 mL) and cooled to an internal temperature of 10 °C or lower in an ice bath. 2-Cyanoethyl N,N,N',N'-tetraisopropylphosphorodiamidite (37.5 g, 124 mmol) was added and washed with dry DCM (30 mL). While maintaining the internal temperature at 6 °C or lower, diisopropylammonium salt tetrazolide (DIPA-tetrazolide) (32.0 g, 187 mmol) was added and washed with dry DCM (20 mL), and the mixture was stirred for 15 minutes. The reaction solution was warmed to room temperature and stirred for 3 hours and 25 minutes.

[0748] After confirming the disappearance of the starting materials, the reaction solution was poured into ice-containing saturated aqueous NaHCO3 solution (600 mL) for quenching and liquid separation. The aqueous layer was extracted with chloroform (500 ml). After combining the organic layers, they were washed with saturated aqueous NaCl solution (600 mL), dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (neutral silica gel 1.0 kg, developing solvent: n-heptane / ethyl acetate (1% triethylamine) = 80 / 20 → 70 / 30 → 60 / 40 → 50 / 50), whereby a crude product containing impurities derived from the Amidite reagent was obtained.

[0749] The obtained crude product was dissolved in n-heptane / ethyl acetate c = 1 / 1 (800 mL) and washed with water / N,N-dimethylformamide (DMF) = 1 / 1 (400 mL) twice, water (400 mL) twice, and saturated aqueous NaCl solution (400 mL). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated, whereby the title Amidite a3 as a white amorphous solid (61.1 g (containing 8.42 wt% ethyl acetate), 46.5 mmol, yield 74%) was obtained. The 1 1H-NMR spectrum of the obtained Amidite a3 is shown in Figure 2 . In addition, the physical property data of the obtained Amidite a3 are as follows: 31 31P-NMR (CDCl3): δ 148.7, 150.6 ppm.

[0750] (Example 2: Synthesis of Amidite (b3))

[0751] The following Amidite (di-tBu-Fmoc-GuNA[t-Bu]-AAmidite) (b3) was synthesized as follows:

[0752] [Chemical formula 52]

[0753]

[0754] (2-1(1): Synthesis of Compound b2 (1))

[0755] [Chemical Formula 53]

[0756]

[0757] Under an argon stream, compound b1 (45.0 g, 65.7 mmol) obtained by the method described in S. Kumagai et al., Org. Biomol. Chem., 2020, 18, 9461 - 9471, Org. Lett. 2018, 20, 1928 - 1931, and the guanidinating reagent (di-tBu-Fmoc protected form) (37.9 g, 79.0 mmol) obtained in the following examples were suspended in THF (450 mL) and cooled to an internal temperature of 5 °C or lower with an ice bath. Subsequently, DIPEA (17.2 mL, 99.0 mmol) and AgOTf (25.3 g, 99.0 mmol) were added, and the mixture was stirred at room temperature for 2 hours and 50 minutes. Since starting materials remained, DIPEA (5.74 mL, 33.0 mmol) and AgOTf (8.44 g, 33.0 mmol) were added, and stirring was continued for another 2 hours.

[0758] After confirming the disappearance of the starting materials, ethyl acetate (450 mL) and saturated aqueous NaCl solution (900 mL) were added to the reaction mixture. After stirring briefly after the addition, the mixture was filtered through diatomaceous earth. The residue was washed successively with ethyl acetate (450 mL) and water (900 mL), and then the filtrate was separated. The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (400 g of neutral silica gel, developing solvent: n-heptane / acetone (1% triethylamine) = 80 / 20 → 70 / 30 → 60 / 40 → 50 / 50), and azeotroped with acetonitrile and DCM to obtain a crude product as a white amorphous solid (60.7 g (containing 2.6 wt% acetonitrile, 7.4 wt% DCM), 34.9 mmol, 74% yield). The 1H-NMR spectrum of compound b2 obtained in this Example 2 (2-1(1)) 1 1H-NMR spectrum is shown in Figure 3 the following.

[0759] (2-1(2): Synthesis of Compound b2 (2))

[0760] [Chemical Formula 54]

[0761]

[0762] A suspension of compound b1 (1.00 g) obtained by the method described in Org. Biomol. Chem., 2020, 18, 9461 - 9472 by S. Kumagai et al. in THF (15 mL) was stirred at room temperature for 20 minutes under a nitrogen atmosphere, then pyridine (590 μL) and copper(I) chloride (361 mg) were added, and the mixture was stirred for 2 hours. After adding a solution of the guanidylation reagent (di - tBu - Fmoc protected form) (722 mg) in THF (2.0 mL), the mixture was stirred at 60 °C for 6 minutes, then switched to an air atmosphere and further stirred at 60 °C for 4 hours.

[0763] After the reaction mixture was cooled to room temperature in a water bath, the insoluble matter was removed by filtration (washing: toluene 10 mL × 1). The filtrate was concentrated under a weak vacuum, and most of the THF was distilled off. Then, a solution prepared from EDTA (860 mg), 1 M aqueous sodium hydroxide solution (5.8 mL), and water (10 mL) was added to the residue, and the mixture was vigorously stirred for 10 minutes and allowed to stand. The aqueous layer was removed, and a solution prepared from EDTA (860 mg), 1 M aqueous sodium hydroxide solution (5.8 mL), and water (10 mL) was added to the organic layer, and the mixture was vigorously stirred for 10 minutes and allowed to stand. The aqueous layer was removed, water (10 mL) was added to the organic layer, and the mixture was vigorously stirred for 10 minutes. After standing, the aqueous layer was removed, and the organic layer was concentrated under reduced pressure.

[0764] The concentrated residue was purified by silica gel column chromatography (22 g of silica gel treated with triethylamine, developing solvent: n - hexane / ethyl acetate = 50 / 50 (4 CV) → 0 / 100 (3.5 CV)) to obtain the title compound b2 (949 mg, yield 58%) as a white amorphous solid. The physical property data of compound b2 obtained in Example 2 (2 - 1(2)) are shown in Table 4.

[0765] [Table 4]

[0766]

[0767] (2 - 1(3): Synthesis of compound b2 (3))

[0768] [Chemical formula 55]

[0769]

[0770] To a solution of compound bb1 (111 mg) obtained by the method described in Org. Lett. 2018, 20, 1928 - 1931 by H. Sawamoto et al. in THF (1.5 mL), pyridine (59 μL) and copper(I) chloride (36 mg) were added under a nitrogen atmosphere, and the mixture was stirred for 1 hour. After adding a solution of the guanidylation reagent (di - tBu - Fmoc protected form) (77 mg) in THF (0.20 mL), the mixture was stirred at 60 °C for 6 minutes, then switched to an air atmosphere and further stirred at 60 °C for 2 hours.

[0771] After the reaction mixture was cooled to room temperature by air cooling, the reaction mixture was centrifuged and the supernatant was taken out. Toluene (1.5 mL) was added to the precipitate and shaken well, then centrifuged again and the supernatant was taken out. Toluene (1.5 mL) was added to the combined two supernatants, and the mixture was concentrated under a weak vacuum to distill off most of the THF. A solution prepared from EDTA (86 mg), 1 M aqueous sodium hydroxide solution (0.58 mL) and water (2.0 mL) was added to the residue, and the mixture was shaken well for 10 minutes. After standing, the aqueous layer was removed, and the organic layer was concentrated under reduced pressure.

[0772] Acetic acid (8 μL) and tetrabutylammonium fluoride (about 1 mol / L in 146 μL of THF) were added to a solution of the concentrated residue in THF (1.5 mL), and the mixture was stirred at room temperature for 15 hours. Toluene (2.0 mL) and water (2.0 mL) were added to the reaction solution, and the mixture was shaken well and then allowed to stand. The aqueous layer was removed, water (2.0 mL) was added to the organic layer, and the mixture was shaken well and allowed to stand. The aqueous layer was removed, and the organic layer was concentrated under reduced pressure. The concentrated residue was purified by silica gel column chromatography (5.0 g of silica gel treated with triethylamine, developing solvent: n - hexane / ethyl acetate = 50 / 50 (4 CV) → 0 / 100 (4 CV)) to obtain the title compound b2 (128 mg, yield 79%) as a white amorphous solid. The physical property data of compound b2 obtained in Example 2 (2 - 1(3)) are shown in Table 5.

[0773] [Table 5]

[0774]

[0775] (2 - 2: Synthesis of Amidite form (b3))

[0776] [Chemical formula 56]

[0777]

[0778] Under an argon stream, the compound b2 (55.9 g (containing 6.0 wt% acetonitrile, 7.3 wt% DCM), 43.4 mmol) obtained in the above Example 2 (2-1(1)) was charged into dry DCM (485 mL) and cooled to an internal temperature of 3 °C or lower using an ice bath. DIPA-tetrazolide (22.3 g, 130 mmol) was added, and 2-cyanoethyl N,N,N',N'-tetraisopropylphosphorodiamidite (26.5 g, 87.0 mmol) dissolved in dry DCM (145 mL) was added while maintaining the internal temperature at 5 °C or lower. The reaction solution was warmed to room temperature and stirred for 3 hours and 15 minutes.

[0779] After confirming the disappearance of the starting materials, the reaction solution was quenched by injecting it into a saturated NaHCO3 aqueous solution (600 mL) containing ice and separated by liquid-liquid extraction. The aqueous layer was extracted with DCM (550 mL). After combining the organic layers, they were washed with a saturated NaCl aqueous solution (550 mL), dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (600 g of neutral silica gel, developing solvent: n-heptane / ethyl acetate (1% triethylamine) = 80 / 20 → 70 / 30 → 60 / 40 → 50 / 50), whereby a crude product containing impurities derived from the Amidite reagent was obtained.

[0780] The obtained crude product was dissolved in n-heptane / ethyl acetate = 1 / 1 (600 mL), washed twice with water / DMF = 1 / 1 (600 mL), washed twice with water (600 mL), and washed with a saturated NaCl aqueous solution (600 mL). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated, whereby a white amorphous solid di-tBu-Fmoc-GuNA[t-Bu]-AAmidite b3 (40.4 g (containing 5.6 wt% ethyl acetate), 28.9 mmol, yield 67%) was obtained. The 1 1H-NMR spectrum of the obtained Amidite b3 is shown in Figure 4 the following. In addition, the physical property data of the obtained Amidite b3 are as follows: 31 31P-NMR (CDCl3): δ 149.3, 150.8 ppm.

[0781] (Example 3: Synthesis of Amidite (c5))

[0782] The following Amidite (di-tBu-Fmoc-GuNA[t-Bu]-mC Amidite) (c5) was synthesized as follows:

[0783] [Chemical formula 57]

[0784]

[0785] (3-1: Synthesis of Compound c1)

[0786] [Chemical Formula 58]

[0787]

[0788] Under an argon stream, 5-methylcytosine (100 g, 799 mmol) was suspended in DMF (1.00 L), and DIPEA (140 mL, 799 mmol, 1.0 equivalent), N,N-dimethylformamide-dimethylacetal (DMF-DMA) (531 mL, 4.00 mol, 5.0 equivalents) were added, and the mixture was stirred at room temperature for 20 hours and 20 minutes. After confirming the completion of the reaction, methyl tert-butyl ether (MTBE) (1.00 L) was added to the reaction solution, and after stirring for 1 hour and 20 minutes, filtration was carried out, and the filter cake was washed with MTBE (1.40 L). The obtained residue was dried under reduced pressure at room temperature to obtain the title compound c1 as a white solid (109 g, 607 mmol, yield 76%). The 1 1H-NMR spectrum is shown in Figure 5 .

[0789] (3-2: Synthesis of Compound c2)

[0790] [Chemical Formula 59]

[0791]

[0792] Under an argon stream, DMTr-amino LNA-T (130 g, 227 mmol) obtained by the methods described in A.S. Madsen et al. J. Org. Chem. 2012, 77, 10718 - 10728 and H. Sawamoto et al. Org. Lett. 2018, 20, 1928 - 1931 and the compound c1 obtained above (123 g, 682 mmol, 3.0 equivalents) were charged into 1,2-dichloroethane (DCE) (1.30 L), and the mixture was immersed in an ice bath and cooled to an internal temperature of 5 °C or lower. While maintaining the internal temperature at 10 °C or lower, N,O-bis(trimethylsilyl)acetamide (BSA) (416 g, 2.05 mol, 9.0 equivalents) was added over 1 hour and 5 minutes, then the mixture was taken out of the ice bath and stirred for 1 hour while warming to room temperature. The reaction solution was immersed in an ice bath and cooled to an internal temperature of 5 °C or lower, and trimethylsilyl trifluoromethanesulfonate (TMSOTf) (7.58 g, 34.1 mmol, 0.15 equivalent) was added dropwise over 5 minutes. Then, the mixture was stirred for 15 hours and 30 minutes while heating with a 45 °C water bath.

[0793] After confirming the completion of the reaction, the reaction solution was cooled to an internal temperature of 5 °C. Ethyl acetate (1.30 L) was added, and the solution was quenched by injecting it into a saturated aqueous NaHCO3 solution (1.30 L) containing ice, and filtered through diatomaceous earth. The filter cake was washed with ethyl acetate (500 mL). After separating the filtrate, the aqueous layer was extracted once with ethyl acetate (700 mL). The organic layers were combined and concentrated under reduced pressure. MTBE (2.00 L) was added to the resulting concentrated residue for dissolution, washed once with water (2.00 L), and washed once with a saturated aqueous NaCl solution (2.00 L). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated to obtain the title compound c2 (198 g (crude product)), which was a brown amorphous solid, containing impurities. The 1 1H-NMR spectrum is shown in Figure 6 the following.

[0794] (3-3: Synthesis of compound c3)

[0795] [Chemical formula 60]

[0796]

[0797] Under an argon stream, the compound c2 (198 g (crude product), 227 mmol (converted based on the feeding amount of compound c2 (DMTr-ALNA-T) itself since it is a crude product)) obtained above, the guanidinylation reagent (di-tBu-Fmoc protected form) (120 g, 250 mmol, 1.1 equivalents) obtained in the following examples, and DIPEA (59.5 mL, 341 mmol, 1.5 equivalents) were suspended in THF (1.50 L), and cooled to an internal temperature of 25 °C or lower using a water bath. AgOTf (87.5 g, 341 mmol) was added in portions over 5 minutes, washed with THF (100 mL), and stirred at room temperature for 1 hour and 50 minutes.

[0798] After confirming the disappearance of the starting materials, ethyl acetate (1.30 L) and a saturated aqueous NaCl solution (1.30 L) were added to the reaction solution. After adding and stirring for a while, it was filtered through diatomaceous earth. After washing the residue with ethyl acetate (500 mL), the filtrate was separated. After washing the organic layer with water (1.30 L), it was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated to obtain the title compound c3 (241 g (crude product)), which was an orange-brown amorphous solid. The 1 1H-NMR spectrum is shown in Figure 7 the following.

[0799] (3-4: Synthesis of compound c4)

[0800] [Chemical formula 61]

[0801]

[0802] Under an argon stream, the compound c3 obtained above (241 g (crude product), 227 mmol (converted based on the feeding amount of the compound c3 (DMTr-ALNA-T) itself since it is a crude product)) was charged into THF (2.50 L), and cooled to an internal temperature of 20 °C or lower with a water bath. DIPEA (119 mL, 681 mmol, 3.0 equivalents) and triethylamine trihydrofluoride (3HF-TEA) (54.9 g, 341 mmol, 1.5 equivalents) were added, and it was washed with THF (100 mL), and stirred at an internal temperature of 20 °C or lower for 2 hours in this state.

[0803] After confirming the disappearance of the raw materials, the reaction solution was poured into a saturated NaHCO3 aqueous solution (2.00 L) containing ice. Ethyl acetate (1.30 L) was added and separated by liquid separation, and the organic layer was washed with a saturated NaCl aqueous solution (2.00 L). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (3.00 kg of neutral silica gel manufactured by Kanto Chemical Co., Ltd., developing solvent: MTBE / ethyl acetate (0.5% pyridine) = 70 / 30 → 50 / 50 → 30 / 70 → 10 / 90) to obtain a crude product (146 g).

[0804] A part (19 g) of the obtained crude product was purified again by silica gel column chromatography (285 g of neutral silica gel manufactured by Kanto Chemical Co., Ltd., developing solvent: MTBE / THF (1.0% pyridine) = 90 / 10 → 70 / 30 → 50 / 50 → 30 / 70). The obtained pyridine-containing compound c4 was dissolved in ethyl acetate (200 mL), washed twice with water (200 mL), and washed once with a saturated NaCl aqueous solution (200 mL). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated to obtain the title compound c4 as a white amorphous solid (15.6 g (containing 9.29 wt% ethyl acetate and 1.49 wt% dibutylhydroxytoluene (BHT))).

[0805] A portion (127 g) of the obtained crude product was purified again by silica gel column chromatography (2.00 kg of neutral silica gel manufactured by Kanto Chemical Co., Inc., developing solvent: MTBE / THF (1.0% pyridine) = 90 / 10 → 70 / 30 → 60 / 40 → 50 / 50 → 30 / 70). The obtained pyridine-containing compound c4 was dissolved in ethyl acetate (1.50 L), washed twice with water (1.50 L), and washed once with saturated NaCl aqueous solution (1.50 L). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. Since pyridine remained in the obtained residue, it was dissolved again in ethyl acetate (1.50 L), washed twice with water (1.50 L), and washed once with saturated NaCl aqueous solution (1.50 L). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated, whereby compound c4 as a white amorphous solid was obtained (95.8 g (containing 6.70 wt% ethyl acetate, 1.79 wt% BHT)). The total amount of compound c4 obtained was 101 g (96.0 mmol, 3 steps, yield 42%) in terms of pure component. The 1 1H-NMR spectrum is shown in Figure 8 the following.

[0806] (3 - 5: Synthesis of amidite c5)

[0807] [Chemical formula 62]

[0808]

[0809] Under an argon stream, the compound c4 obtained above (60.0 g (containing 6.70 wt% ethyl acetate, 1.79 wt% BHT), 51.9 mmol) was charged into dry DCM (500 mL) and cooled to an internal temperature of 10°C or lower with an ice bath. 2-Cyanoethyl N,N,N',N'-tetraisopropylphosphorodiamidite (31.3 g, 104 mmol) was added and washed with dry DCM (50 mL). While maintaining the internal temperature at 6°C or lower, DIPA-tetrazolide (26.6 g, 156 mmol) was added and washed with dry DCM (50 mL), and then directly stirred for 10 minutes. The reaction solution was warmed to room temperature and stirred for 2 hours and 20 minutes.

[0810] After confirming the disappearance of the raw materials, the reaction solution was poured into a saturated aqueous solution of NaHCO3 (600 mL) containing ice for quenching and liquid separation. The aqueous layer was extracted with CHCl3 (500 mL). After combining the organic layers, they were washed with a saturated aqueous solution of NaCl (600 mL), dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (Diol Silica 600 g manufactured by Fuji Silysia Chemical Ltd., developing solvent: n-heptane / ethyl acetate (1% pyridine) = 70 / 30 → 60 / 40 → 50 / 50 → 40 / 60), and thus the title Amidite c5 (di-tBu-Fmoc-GuNA[t-Bu]-mC Amidite) containing impurities was obtained.

[0811] The obtained Amidite c5 was dissolved in n-heptane / ethyl acetate = 1 / 1 (2.00 L), washed twice with water / DMF = 1 / 1 (1.50 L), washed twice with water (1.50 L), and washed once with a saturated aqueous solution of NaCl (1.50 L). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified again by silica gel column chromatography (neutral silica gel 600 g manufactured by Kanto Chemical Co., Inc., developing solvent: n-heptane / ethyl acetate (1% pyridine) = 50 / 50 → 40 / 60 → 30 / 70 → 20 / 80), and thus the pyridine-containing Amidite c5 (di-tBu-Fmoc-GuNA[t-Bu]-mC Amidite) was obtained.

[0812] The obtained Amidite c5 was dissolved in n-heptane / ethyl acetate = 1 / 1 (2.00 L), washed twice with water / DMF = 1 / 1 (1.50 L), washed twice with water (1.50 L), and washed once with a saturated aqueous solution of NaCl (1.50 L). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated, and thus Amidite c5 as a white amorphous solid (62.7 g (containing 9.56 wt% ethyl acetate), 45.0 mmol, yield 89%) was obtained. The 1 1H-NMR spectrum is shown in Figure 9 the following. In addition, the physical property data of the obtained Amidite c5 are as follows: 31 31P-NMR (CDCl3): δ 148.3, 150.7 ppm.

[0813] (Example 4: Synthesis of Amidite d3)

[0814] Synthesize the following Amidite (di-tBu-Fmoc-GuNA[t-Bu]-G Amidite) (d3) as follows:

[0815] [Chemical Formula 63]

[0816]

[0817] (4-1(1): Synthesis of Compound d2 (1))

[0818] [Chemical Formula 64]

[0819]

[0820] Under an argon atmosphere, dissolve the compound d1 (9.00 g, 13.5 mmol) obtained in the following examples and the guanidinylation reagent (7.79 g, 16.2 mmol) obtained in the following examples in dry THF (90 mL). Add DIPEA (3.54 mL, 20.3 mmol) and AgOTf (5.20 g, 20.3 mmol), and stir at room temperature for 1 hour and 40 minutes. Confirm the residue of the starting materials, add DIPEA (3.54 mL, 20.3 mmol) and AgOTf (5.20 g, 20.3 mmol), and stir at room temperature for another 1 hour and 40 minutes.

[0821] After confirming the disappearance of the starting materials, quench the reaction solution into ethyl acetate / saturated NaCl aqueous solution = 1 / 1 (600 mL). Stir briefly after injection and then filter through diatomaceous earth. Wash the residue with ethyl acetate (100 mL), separate the filtrate. Extract the aqueous layer with ethyl acetate (200 mL), dry the combined organic layers with Na2SO4, filter off the desiccant, and concentrate the filtrate. Purify the concentrated residue by silica gel column chromatography (First time: SI50 manufactured by Fuji Silysia Chemical Ltd., SIZE200+SIZE200, developing solvent: CHCl3 / methanol = 100 / 0 → 97 / 3 → 96 / 4 → 95 / 5, Second time: SI50 manufactured by Fuji Silysia Chemical Ltd., SIZE200+SIZE200, developing solvent: CHCl3 / methanol = 100 / 0 → 97 / 3 → 96 / 4 → 95 / 5). Concentrate the fraction containing the target compound to obtain the title compound d2 (11.63 g, 10.2 mmol (in terms of pure component), yield 75%) as a light brown amorphous solid. The 1 1H-NMR spectrum of the compound d2 obtained in this Example 4 (4-1(1)) is shown in Figure 10 the following.

[0822] (4-1(2): Synthesis of Compound d2 (2))

[0823] [Chemical Formula 65]

[0824]

[0825] A solution of compound d1 (100 mg) obtained from the following examples in THF (1.5 mL) was stirred under a nitrogen atmosphere at room temperature for 30 minutes, then pyridine (61 μL) and copper(I) chloride (18 mg) were added and stirred for 40 minutes. After adding a solution of the guanidylation reagent (di-tBu-Fmoc protected form) (79 mg) in THF (0.2 mL), it was stirred at 60 °C for 4 minutes, then switched to an air atmosphere and further stirred at 60 °C for 4 hours.

[0826] The reaction mixture was air-cooled to room temperature, toluene (1.0 mL) was added and shaken well, then the reaction mixture was centrifuged and the supernatant was taken out. Toluene (2.0 mL) was added to the precipitate and shaken well, then centrifuged again and the supernatant was taken out. The combined two supernatants were concentrated under a weak vacuum to distill off most of the THF. A solution prepared from EDTA (88 mg), 1 M aqueous sodium hydroxide solution (0.60 mL) and water (2.0 mL) was added to the residue, shaken well for 4 minutes, allowed to stand, and the aqueous layer was removed. Water (2.0 mL) was added to the organic layer and shaken well, allowed to stand, and the aqueous layer was removed. Water (2.0 mL) was added to the organic layer again and shaken well, allowed to stand, and the aqueous layer was removed, and the organic layer was concentrated under reduced pressure.

[0827] The concentrated residue was purified once by silica gel column chromatography (DIOL MB100-40 / 75, 7.0 g, manufactured by Fuji Silysia Chemical Ltd., developing solvent: n-heptane / ethyl acetate = 50 / 50 (4 CV) → 0 / 100 (4 CV)), and then purified by silica gel column chromatography (5.0 g of silica gel treated with triethylamine, developing solvent: n-hexane / ethyl acetate = 50 / 50 (7 CV) → 0 / 100 (5 CV)) to obtain the title compound d2 (112 mg, yield 68%) as a white amorphous solid. The physical property data of compound d2 obtained in this Example 4 (4-1(2)) are shown in Table 6.

[0828] [Table 6]

[0829]

[0830] (4-2: Synthesis of Amidite d3)

[0831] [Chemical Formula 66]

[0832]

[0833] Under an argon atmosphere, the compound d2 (13.6 g, 11.5 mmol in terms of pure component) obtained in the above Example 4 (4-1(1)) was charged into dry DCM (136 mL) and cooled to 4 °C in an ice bath. 2-Cyanoethyl N,N,N',N'-tetraisopropylphosphorodiamidite (6.96 g, 23.1 mmol) and DIPA-tetrazolide (5.93 g, 34.6 mmol) were added, and after stirring for 10 minutes in the cold state, the reaction solution was stirred for 2 hours and 45 minutes while warming up to room temperature.

[0834] After confirming the disappearance of the raw materials, the reaction solution was quenched by adding it to a mixed solution of ice and saturated NaHCO3 aqueous solution (300 mL), CHCl3 (300 mL) was added, and liquid separation was carried out. The aqueous layer was extracted with CHCl3 (200 mL). After combining the organic layers, they were washed with saturated NaCl aqueous solution (300 mL). The organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (SI50 manufactured by Fuji Silysia Chemical Ltd., SIZE200 + 180 g of neutral silica gel, developing solvent: n-heptane / ethyl acetate (containing 1% pyridine) = 70 / 30 → 50 / 50 → 40 / 60 → 30 / 70). The crude product obtained by concentrating the fraction containing the target compound was dissolved in n-heptane / ethyl acetate = 1 / 1 (400 mL), washed twice with water / DMF = 1 / 1 (300 mL), washed twice with water (300 mL), the organic layer was dried over Na2SO4, the desiccant was filtered off, and the filtrate was concentrated. The obtained concentrated residue was purified again by silica gel column chromatography (DIOL MB100-40 / 75, 200 g manufactured by Fuji Silysia Chemical Ltd., developing solvent: n-heptane / ethyl acetate (containing 1% pyridine) = 70 / 30 → 60 / 40 → 50 / 50 → 40 / 60). The fraction containing the target compound was concentrated and azeotroped with toluene and acetonitrile, whereby the title Amidite d3 (di-tBu-Fmoc-GuNA[t-Bu]-G Amidite) as a white amorphous solid was obtained (12.62 g, 9.14 mmol in terms of pure component, containing 5.9 wt% acetonitrile, yield 79%). The 1 1H-NMR spectrum of the obtained Amidite d3 is shown in Figure 11 the following. In addition, the physical property data of the obtained Amidite d3 are as follows: 31 31P-NMR (CDCl3): δ 149.4, 149.9 ppm.

[0835] (Example 5: Stability test of Amidite)

[0836] The Amidite a3 (purity 96.3%) obtained in Example 1 and the Amidite a3' (purity 90.9%) synthesized according to the method described in Patent Document 5 were separately dissolved in acetonitrile to prepare 0.1 M solutions.

[0837] [Chemical formula 67]

[0838]

[0839] Among the two obtained 0.1 M solutions, the solution containing the Amidite a3 of Example 1 was stored in the dark at room temperature for 7 days. On the other hand, the solution containing the Amidite a3' of Patent Document 5 was stored in the dark at room temperature for 17 hours.

[0840] The UHPLC results of the Amidite a3 and a3' contained in each solution after storage are shown in Tables 7 and 8, and the UHPLC-MS results of the Amidite a3 and a3' contained in each solution after storage are shown in Figure 12 and Figure 13 .

[0841] [Table 7]

[0842]

[0843] [Table 8]

[0844]

[0845]

[0846] As can be seen from Tables 7, 8, Figure 12 and Figure 13 the Amidite a3 obtained in Example 1, which was stored for 7 days, had fewer split peaks caused by UHPLC and better stability compared to the Amidite a3' of Patent Document 5, which was stored for 17 hours, despite the longer storage period.

[0847] (Example 6: Synthesis of Compound d1)

[0848] The above-mentioned compound d1 used was synthesized as follows:

[0849] (6-1: Synthesis of Compound e4)

[0850] [Chemical formula 68]

[0851]

[0852] (1) Fmoc protection

[0853] Under an argon atmosphere, dissolve the compound e3 (1.00 g, 1.07 mmol) described in WO 2020 / 100826 in dry DCM (10 mL), add DIPEA (374 μL, 2.14 mmol), N-[(9H-fluoren-9-ylmethoxy)carbonyloxy]succinimide (Fmoc-OSu) (542 mg, 1.61 mmol), and stir at room temperature for 1 hour and 40 minutes. Confirm the disappearance of the starting material, and quench the reaction solution by adding it to ethyl acetate / water = 1 / 1 (100 mL) and separate the layers. Wash the organic layer with water (50 mL) and dry it over Na2SO4. After filtering off the desiccant, concentrate the filtrate to obtain the crude product (1.51 g) of the Fmoc-protected product. Use this crude product of the Fmoc-protected product directly in the next step.

[0854] (2) TMS deprotection

[0855] Under an argon atmosphere, dissolve the crude product (1.51 g, 1.07 mmol (in terms of pure component)) of the Fmoc-protected product obtained above in dry THF (10 mL), add DIPEA (561 μL, 3.21 mmol), triethylamine trihydrofluoride (3HF-TEA) (174 μL, 1.07 mmol), and stir at room temperature for 35 minutes. Confirm the disappearance of the starting material, and quench the reaction solution by adding it to saturated NaCl water / water = 1 / 1 (50 mL) and separate the layers. Re-extract the aqueous layer with ethyl acetate (50 mL), combine the organic layers, wash with saturated NaCl water (50 mL), and dry over Na2SO4. After filtering off the desiccant, concentrate the filtrate. Purify the concentrated residue by silica gel column chromatography (FujiSilysia, SI50, SIZE60, developing solvent: n-heptane / ethyl acetate = 90 / 10 → 50 / 50 → 10 / 90). Concentrate the fraction containing the title target compound to obtain compound e4 (0.89 g, 0.821 mmol, two-step yield 77%) as a pale yellow amorphous solid. The 1 1H-NMR spectrum of the obtained compound e4 is shown in Figure 14 .

[0856] (6-2: Synthesis of compound e5)

[0857] [Chemical formula 69]

[0858]

[0859] Under an argon atmosphere, the compound e4 (0.89 g, 0.821 mmol) obtained above was dissolved in dry DCM (9.0 mL) and cooled to 5 °C in an ice bath. TFA (949 μL, 12.3 mmol) was added, and the mixture was stirred for 1 hour and 5 minutes under ice cooling. The formation of the target compound was confirmed, and the reaction solution was concentrated. CHCl3 (50 mL) and saturated aqueous NaHCO3 solution (50 mL) were added to the residue and separated by liquid-liquid extraction. The organic layer was washed with saturated NaCl aqueous solution (50 mL) and dried over Na2SO4. After filtering off the desiccant, the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (Fuji Silysia, SI50, SIZE60, developing solvent: CHCl3 / MeOH = 100 / 0 → 90 / 10). The fraction containing the title target compound was concentrated to obtain the crude product (453 mg) of compound e5 as a white amorphous solid. Compound e5 was used directly in the next step without further purification. The 1 1H-NMR spectrum is shown in Figure 15 the following.

[0860] (6-3: Synthesis of compound e6)

[0861] [Chemical formula 70]

[0862]

[0863] Under an argon atmosphere, the compound e5 (450 mg, 0.767 mmol (calculated as pure component)) obtained above was dissolved in dry DCM (10 mL), DIPEA (670 μL, 3.84 mmol) was added, and the mixture was cooled to 5 °C in an ice bath. DMTrCl (389 mg, 1.15 mmol) was added, and the mixture was stirred for 1 hour and 15 minutes while warming to room temperature naturally. The residual raw material was confirmed, DMTrCl (194 mg, 0.575 mmol) was added, and the mixture was stirred for another 1 hour and 40 minutes at room temperature. After confirming the disappearance of the raw material, the reaction solution was quenched by adding it to a mixed solution of ice and saturated aqueous NaHCO3 solution (50 mL), and CHCl3 (50 mL) was added and separated by liquid-liquid extraction. The aqueous layer was extracted with CHCl3 (50 mL), and the combined organic layers were dried over Na2SO4. After filtering off the desiccant, the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (Fuji Silysia, SI50, SIZE60, developing solvent: CHCl3 / MeOH = 100 / 0 → 90 / 10). The fraction containing the title target compound was concentrated to obtain compound e6 (556 mg, 0.625 mmol, two-step yield 76%) as a pale yellow amorphous solid. The 1 1H-NMR spectrum is shown in Figure 16 the following.

[0864] (6-4: Synthesis of Compound d1)

[0865] [Chemical Formula 71]

[0866]

[0867] Under an argon atmosphere, the compound e6 (550 mg, 0.619 mmol) obtained above was dissolved in dry DCM (10 mL), piperidine (1.23 mL, 12.4 mmol) was added, and the mixture was stirred at room temperature for 1 hour. After confirming the disappearance of the starting material, the reaction solution was concentrated. The concentrated residue was washed twice by suspension with IPE and then purified by silica gel column chromatography (Fuji Silysia, SI50, SIZE60, developing solvent: CHCl3 / MeOH (containing 1% TEA) = 100 / 0 → 90 / 10). The fraction containing the title target compound was concentrated to obtain compound d1 (340 mg, 0.493 mmol, yield 80%) as a white amorphous solid. The 1 1H-NMR spectrum of the obtained compound d1 is shown in Figure 17 .

[0868] (Example 7: Synthesis of Guanidylation Reagent (di-tBu-Fmoc Protecting Group)) (A))

[0869] (7-1) Synthesis of Compound A2 (N-(tert-Butylthiocarbamoyl)benzamide)

[0870] [Chemical Formula 72]

[0871]

[0872] tert-Butylamine (A1) (9.37 mL) was added to dehydrated acetonitrile (26.0 mL), and the mixture was stirred in an ice bath. While maintaining the internal temperature below 35 °C, benzoyl isothiocyanate (13.23 g) was added dropwise over 8 minutes. After stirring in the ice bath for 75 minutes, the resulting solid was filtered off and the solid was washed with cold acetonitrile (6 mL × 2). The obtained solid was dried under reduced pressure to obtain the title compound A2 (N-(tert-Butylthiocarbamoyl)benzamide) as a white solid (11.6 g, yield 61%). The physical property data of the obtained compound A2 are shown in Table 9.

[0873] [Table 9]

[0874]

[0875] (7-2) Synthesis of Compound A4 (1-(tert-Butyl)-2-methylisothiouronium Iodide)

[0876] [Chemical Formula 73]

[0877]

[0878] After suspending the obtained compound A2 (N-(tert-butylthiocarbamoyl)benzamide) (1.00 g) in methanol (5.0 mL), the temperature was raised to 60 °C. At the same temperature, a 28 wt% sodium methoxide-methanol solution (21 μL) was added, and the mixture was stirred for 40 minutes and cooled to room temperature over 1 hour and 50 minutes. Subsequently, methyl iodide (395 μL) was added, and the mixture was stirred at room temperature for 3 hours. After concentrating the reaction mixture to a mass of 1.76 g, ethyl acetate (5.0 mL) was added and stirred. The resulting solid was collected by filtration and washed with ethyl acetate. The obtained solid was dried under reduced pressure to obtain the title compound A4 (1-(tert-butyl)-2-methylisothiouronium iodide) as a white solid (1.04 g, yield 89%). The physical property data of the obtained compound A4 are shown in Table 10.

[0879] [Table 10]

[0880]

[0881] (7-3) Synthesis of compound A7 ((2,7-di-tert-butyl-9H-fluoren-9-yl)methanol)

[0882] [Chemical formula 74]

[0883]

[0884] Potassium tert-butoxide (10.9 g) was placed in a reaction vessel and purged with nitrogen. After adding dehydrated THF (81 mL) thereto and stirring for 5 minutes, it was cooled to an internal temperature of 1 °C under ice-cooling. A solution obtained by dissolving 2,7-di-tert-butyl-9H-fluorene (A5) (13.5 g) in dehydrated THF (34 mL) was added dropwise over 11 minutes while maintaining the internal temperature below 3 °C (washed with 7.0 mL of dehydrated THF), and stirred under ice-cooling for 22 minutes. Ethyl formate (7.81 ml) was added dropwise over 21 minutes while maintaining the internal temperature below 5 °C. Then, it was stirred under ice-cooling for 23 minutes, and then changed from an ice bath to a water bath and stirred for 28 minutes. 2M hydrochloric acid (49 mL) was added over 3 minutes, and after vigorously stirring for 9 minutes, stirring was stopped, and then cleanly separated into two layers within 2 minutes. After removing the lower layer (42 mL), an aqueous solution of sodium chloride (8.1 g) in water (80 mL) was added, and vigorously stirred for 36 minutes. After stopping the stirring, it was cleanly separated into two layers within 1 minute. After removing the lower layer (110 mL), the upper layer was concentrated under reduced pressure, most of the THF was distilled off, and isopropanol (81 mL) and water (27 mL) were added to obtain an orange transparent solution containing compound A6.

[0885] Dilute 1 M aqueous sodium hydroxide solution (4.85 mL) with water (4.85 ml), and dissolve sodium borohydride (1.83 g) therein. While maintaining the internal temperature below 28 °C in an ice bath, add this solution dropwise to the orange solution containing compound A6 obtained above over 10 minutes. Then stir in a water bath for 2 hours, add acetone (12.8 mL) in 3 minutes in an ice bath, and stir in a water bath for 14 minutes. Add 2 M hydrochloric acid (29 mL), stir vigorously for 30 minutes, concentrate the reaction mixture under reduced pressure, and distill off most of the isopropanol. Add toluene (135 mL) thereto, stir vigorously for 16 minutes, then stop stirring, and it will cleanly separate into two layers within 2 minutes. Then, leave it to stand overnight at room temperature in this two-layer state.

[0886] After removing the lower layer (60 mL), concentrate the upper layer under reduced pressure and distill off most of the toluene. Then, add toluene (100 mL), and the reaction mixture becomes an orange solution. Add (+)-10-camphorsulfonic acid (2.25 g) to this solution, stir at an internal temperature of 90 - 105 °C for 2 hours, then remove the warm bath and stir for another 30 minutes. Add an aqueous solution of potassium bicarbonate (1.46 g) in water (40 mL), stir vigorously for 20 minutes and then stop stirring, and it will cleanly separate into two layers within 3 minutes. Remove the lower layer, add water (40 ml) to the upper layer, stir vigorously for 10 minutes and then stop stirring, and it will cleanly separate into two layers within 4 minutes. Remove the lower layer, concentrate the upper layer under reduced pressure to a mass of 26.0 g, add n-heptane (135 ml) to the residue and stir, thereby obtaining an amber transparent liquid. Leave this solution to stand overnight at room temperature.

[0887] The next morning, concentrate this solution under reduced pressure to a mass of 16.7 g, add n-heptane (68 ml) to the residue and heat to 65 °C, thereby obtaining a homogeneous solution. Stir this solution under natural cooling for 18 minutes, then stir in an ice bath for 2 hours, filter off the resulting solid, and wash this solid with cold n-heptane (14 mL and 7 mL each once). Dry the obtained solid under reduced pressure to obtain the title compound A7 ((2,7-di-tert-butyl-9H-fluoren-9-yl)methanol) as a white solid (13.6 g, yield 90%). The physical property data of the obtained compound A7 are shown in Table 11.

[0888] [Table 11]

[0889]

[0890] (7-4) Synthesis of compound A9 ((tert-butylamino)(methylthio)methylene)carbamic acid (2,7-di-tert-butyl-9H-fluoren-9-yl)methyl ester)

[0891] [Chemical formula 75]

[0892]

[0893] Put the obtained compound A7 ((2,7 - di - tert - butyl - 9H - fluoren - 9 - yl) methanol) (1.36 g) and bis(N - succinimidyl) carbonate (1.36 g) into a reaction vessel, add dichloromethane (6.8 mL), and while stirring at room temperature, add pyridine (534 μL) all at once. After stirring at room temperature for 3 hours, add water (6.8 mL) all at once and stir vigorously for 10 minutes.

[0894] To the obtained two - layer reaction mixture, while stirring at room temperature, add all at once a dichloromethane (2.7 mL) solution of the above - obtained compound A4 (1 - (tert - butyl) - 2 - methylisothiouronium iodide) (1.21 g). Then, add a water (2.7 mL) solution of potassium carbonate (1.04 g) and stir for 2 hours. Here, let it stand in a two - layer state for three nights.

[0895] Take out the lower layer and concentrate it under reduced pressure until the mass of the reaction mixture is 3.48 g. Add n - heptane (14 mL) to the residue and concentrate it under reduced pressure until the mass of the reaction mixture is 3.06 g. Add n - heptane (7.0 mL) to the residue and stir at 45 °C to obtain a slightly turbid solution. Stir this solution under natural cooling for 40 minutes, then stir in an ice bath for 60 minutes, filter the resulting solid, and wash the solid with n - heptane (2 mL × 2) at about 0 °C. Dry the obtained solid under reduced pressure to obtain the title compound A9 ((tert - butylamino)(methylthio)methylene)carbamic acid (2,7 - di - tert - butyl - 9H - fluoren - 9 - yl) methyl ester) (guanidylation reagent (di - tBu - Fmoc protecting group) (1.85 g, yield 87%) as a white solid. The physical property data of the obtained compound A9 are shown in Table 12.

[0896] [Table 12]

[0897]

[0898] (Example 8: Synthesis of guanidylation reagent (di - tBu - Fmoc protecting group))(B))

[0899] (8 - 1) Synthesis of compound B2

[0900] [Chemical formula 76]

[0901]

[0902] Compound B1 (tert-butyl isothiocyanate) (305 g, 2.65 mol) was charged, and 7 M ammonia / MeOH (1.51 L, 10.6 mol, 4.0 eq) was added while cooling with an ice bath. The reaction solution was removed from the ice bath and allowed to warm to room temperature naturally, and stirred for 4 days.

[0903] Via 1 1H-NMR confirmed the disappearance of the starting material, and the reaction solution was concentrated using a rotary evaporator. Methyl tert-butyl ether (MTBE) (600 mL) was added to the concentrated residue, and stirred at room temperature. The suspension was filtered, and the residue was washed with MTBE (400 mL) and then dried under reduced pressure at 40 °C to obtain the title compound B2 as a white solid (268 g, 2.03 mol, 77% yield). The 1H-NMR spectrum of the obtained compound B2 is shown in 1 1H-NMR spectrum is shown in Figure 18 in.

[0904] (8-2) Synthesis of Compound B3

[0905] [Chemical formula 77]

[0906]

[0907] Compound B2 (267 g, 2.02 mol) obtained above was charged into MeOH (1.6 L) and cooled in an ice bath. MeI (430 g, 3.03 mol, 1.5 eq) was added, and the reaction solution was removed from the ice bath and allowed to warm to room temperature naturally, and stirred for 24 hours and 15 minutes. Via 1 1H-NMR confirmed the disappearance of the starting material, and the reaction solution was concentrated using a rotary evaporator. The concentrated residue was dried under reduced pressure to obtain compound B3 as a yellow solid (554 g, 2.02 mol, quantitative). The 1H-NMR spectrum of the obtained compound B3 is shown in 1 1H-NMR spectrum is shown in Figure 19 in.

[0908] (8-3) Synthesis of Compound B5

[0909] [Chemical formula 78]

[0910]

[0911] Under an argon stream, compound B4 (250 g, 898 mmol) was dissolved in dry THF (2.50 L), and the internal temperature was cooled to -2 °C using an ice-salt bath. n-BuLi (1.6 M in n-hexane, 673 mL, 1.08 mol) was added dropwise over 62 minutes, and stirred for 40 minutes. (CH2O) n(40.4 g, 1.35 mol) was stirred in an ice-salt bath for 30 minutes. The progress of the reaction was confirmed by TLC, and a saturated aqueous NaHCO₃ solution (1.00 L) was added dropwise over 20 minutes while remaining in the ice-salt bath. The reaction solution was extracted with ethyl acetate (1.00 L), and the aqueous layer was extracted again with ethyl acetate (1.00 L). After combining the organic layers, they were washed with a saturated aqueous NaCl solution (1.00 L) and dried over Na₂SO₄. After filtering off the solid, the filtrate was concentrated.

[0912] Compound B4 (250 g, 898 mmol) was used again and the same operation as above was carried out to obtain a concentrated residue.

[0913] After combining these concentrated residues, they were purified by silica gel column chromatography (neutral silica gel 5.5 kg, developing solvent: n-heptane / ethyl acetate = 100 / 0 → 95 / 5 → 90 / 10 → 50 / 50), and thus the title compound B5 (383 g, 1.24 mol, yield 69%) as a yellowish-white solid was obtained. The 1 ¹H-NMR spectrum of the obtained compound B5 is shown in Figure 20 .

[0914] (8 - 4) Synthesis of Compound B6

[0915] [Chemical formula 79]

[0916]

[0917] Under an argon stream, the compound B5 (380 g, 1.23 mol) obtained above was dissolved in dry DCM (3.80 L) and cooled to 4 °C in an ice bath. Pyridine (200 mL, 2.47 mol) was added and stirred for 8 minutes, and 4-nitrophenyl chloroformate (372 g, 1.85 mol) dissolved in dry DCM (1.52 L) was added dropwise over 1 hour, and then stirred at room temperature for 2 hours and 15 minutes. The disappearance of the starting material was confirmed by UHPLC, and the reaction solution was added to water (3.00 L) and extracted twice with DCM (3.00 L). After combining the organic layers, they were washed with a saturated aqueous NaCl solution (3.00 L) and dried over Na₂SO₄. After filtering off the solid, the filtrate was concentrated. The concentrated residue was dissolved in DCM (1.20 L), and n-heptane (3.80 L) was added dropwise. After filtering off the resulting solid, the filtrate was concentrated. Here, the filtered solid is referred to as solid (1), and the concentrated residue of the filtrate is referred to as residue (1).

[0918] Solid (1) was dissolved in DCM (2.00 L), and n-heptane (2.50 L) was added dropwise. After filtering off the resulting solid, the filtrate was concentrated. Here, the concentrated residue of this filtrate is referred to as residue (2).

[0919] The residues (1) and (2) obtained above were combined, suspended and washed with n-heptane (2.00 L), and the resulting solid was filtered to obtain the title compound B6 (592 g, 1.18 mol, yield 96%) as a yellow solid. The 1 1H-NMR spectrum of the obtained compound B6 is shown in Figure 21 .

[0920] (8-5) Synthesis of Compound B7 (Guanidination Reagent (di-tBu-Fmoc Protected Form))

[0921] [Chemical Formula 80]

[0922]

[0923] The compound B6 (590 g, 1.28 mol) obtained above was dissolved in THF (4.00 L). The compound B3 (484 g, 1.77 mol) obtained above was added thereto and washed with THF (2.30 L). After dropwise adding N,N-diisopropylethylamine (DIPEA) (1.03 L, 5.89 mol) over 25 minutes, the mixture was stirred at room temperature for 17 hours and 15 minutes. After confirming the disappearance of the starting materials by UHPLC, the reaction solution was added to a saturated aqueous NaHCO3 solution (6.00 L) and separated. The aqueous layer was extracted again with ethyl acetate (6.00 L), the organic layers were combined, washed with a saturated aqueous NaCl solution (3.00 L), dried over Na2SO4, the solid was filtered off, and the filtrate was concentrated. The concentrated residue was purified by silica gel column chromatography (amino silica gel NH-DM1020 10 kg manufactured by Fuji Silysia Chemical Ltd., developing solvent: n-heptane / ethyl acetate = 100 / 0 → 90 / 10 → 80 / 20). Thus, the title compound B7 (479.85 g, 1.03 mol, yield 80%) as a guanidination reagent (di-tBu-Fmoc protected form) was obtained. The 1 1H-NMR spectrum of the obtained compound B7 is shown in Figure 22 .

[0924] Industrial Applicability

[0925] The present invention can be used as a raw material for nucleic acid drugs used, for example, in antisense methods, antigene methods, aptamer-based methods, siRNA-based methods, etc., which are expected to be new therapeutic or prophylactic methods for diseases. In addition, the guanidination reagent of the present invention can be applied not only to the production of the modified nucleosides of the present invention having a guanidino structure in the bridging moiety, but also to the production of various compounds having a guanidinyl structure (-N-C(=N)-N-).

Claims

1. A compound represented by the following formula (I) or a salt thereof: [Chemical formula 1] (In formula (I), B 1 is: (a) A purin-9-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (b) A 1,2-dihydropyrimidin-1-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom, R 2 and R 3 each independently is: (a) A hydrogen atom; (b) A protecting group for a hydroxyl group in nucleic acid synthesis; (c) An alkyl group having 1 to 7 carbon atoms which may form a branch or a ring; (d) An alkenyl group having 2 to 7 carbon atoms which may form a branch or a ring; (e) An aryl group having 6 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (f) A heteroaryl group having 1 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (g) An aralkyl having an aryl moiety with 6 to 12 carbon atoms and having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (h) A heteroaralkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (i) An acyl group having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (j) A silyl group having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (k) A phosphate group having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (l) A phosphate group protected by a protecting group for nucleic acid synthesis; or (m) -P(R 4 )R 5 [wherein, R 4 and R 5 are each independently: (a) A hydroxyl group; (b) A hydroxyl group protected by a protecting group for nucleic acid synthesis; (c) A mercapto group; (d) A mercapto group protected by a protecting group for nucleic acid synthesis; (e) An amino group; (f) An alkoxy group having 1 to 5 carbon atoms; (g) An alkylthio group having 1 to 5 carbon atoms; (h) A cyanoalkoxy group having 1 to 6 carbon atoms; (i) A dialkylamino group having alkyl groups which may be the same or different and have 1 to 6 carbon atoms; or (j) A cycloalkylamino group having 3 to 6 carbon atoms; Or, R 4 Together with R 5 Forms the following formula: [Chemical formula 2] (In the formula, R 13a And R 13b Each independently represents a hydrogen atom, a branched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein R a Is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2, and * is a bonding site); or [Chemical formula 3] (In the formula, R 14 And R 15 Each independently is a hydrogen atom, a branched alkyl group having 1 to 3 carbon atoms, or a phenyl group, and * is a bonding site)], R 6 Is a group represented by the following formula: [Chemical formula 4] [In the formula, R 8a And R 8b Each independently is: (a) An alkyl group having 1 to 9 carbon atoms which may form a branch or a ring; (b) An alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * represents a bonding bond], and R 7 is: (a) An alkyl group having 1 to 8 carbon atoms that may form a branch or a ring and may be substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring; (b) A cyanoalkoxy group having 1 to 8 carbon atoms; (c) An aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (d) a heteroarylalkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (e) a group represented by the following formula: [Chemical Formula 5] [In the formula, R 8'a and R 8'b Each independently is: (a) an alkyl group having 1 to 9 carbon atoms which may be branched; (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring; (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * is a bonding site], or R 6 is: (a) an alkyl group having 1 to 8 carbon atoms which may be substituted by an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring and which may form a branch or a ring; (b) a cyanoalkoxy group having 1 to 8 carbon atoms; (c) an arylalkyl having an aryl moiety with 6 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (d) a heteroarylalkyl having a heteroaryl moiety with 3 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (e) a group represented by the following formula: [Chemical Formula 6] [In the formula, R 8'a and R 8'b each independently is: (a) an alkyl group having 1 to 9 carbon atoms which may be branched; (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring; (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, a straight-chain alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * represents a bonding bond], and R 7 is the group represented by the following: [Chemical formula 7] [In the formula, R 8a and R 8b each independently is: (a) An alkyl group having 1 to 9 carbon atoms that may be branched; (b) An alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * represents a bonding bond], R 9 and R 10 each independently represents a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, or R 9 and R 10 together form -(CH2) m -(where m is an integer from 2 to 7), R 11 and R 12 each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, or R 11 and R 12 together form the oxygen atom part (=O) of the carbonyl group, or R 11 and R 12 together form -(CH2) n -(where n is an integer from 2 to 7).

2. The compound or its salt according to claim 1, wherein, In formula (I), R 6 is a group represented by the following formula: [Chemical formula 8] [In the formula, R 8a and R 8b each independently is: (a) An alkyl group having 1 to 9 carbon atoms that may be branched; (b) An alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * represents a bonding bond], and R 7 is: (a) An alkyl group having 1 to 8 carbon atoms that may form a branch or a ring and may be substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring; (b) A cyanoalkoxy group having 1 to 8 carbon atoms; (c) An aralkyl group having an aryl moiety having 6 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (d) a heteroarylalkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (e) a group represented by the following formula: [Chemical Formula 9] [In the formula, R 8'a and R 8'b each independently is: (a) an alkyl group having 1 to 9 carbon atoms which may be branched; (b) an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring; (c) an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or (d) a silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * represents a bonding site].

3. The compound or its salt according to claim 2, wherein, (I) is represented by the following formula (I'): [Chemical Formula 10] 4. The compound or its salt according to claim 2, wherein, The R of formula (I) 7 is an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring.

5. The compound or its salt according to claim 2, wherein, R of the formula (I) 8a and R 8b are each independently an alkyl group having 3 to 8 carbon atoms which may form a branch or a ring.

6. The compound or its salt according to claim 5, wherein, R of formula (I) as described above 8a and R 8b are both tert-butyl groups.

7. A method for producing an oligonucleotide or a pharmaceutically acceptable salt thereof, the method comprising a step of nucleic acid synthesis using the compound or its salt according to any one of claims 1 to 6.

8. The method according to claim 7, wherein, The oligonucleotide is an oligonucleotide containing at least one phosphorothioate bond.

9. A compound or its salt represented by the following formula (II): [Chemical formula 11] [In formula (II), R 7 is: (a) An alkyl group having 1 to 8 carbon atoms which may be substituted with an alkoxy group having 1 to 8 carbon atoms capable of forming a branch or a ring, and capable of forming a branch or a ring; (b) A cyanoalkoxy group having 1 to 8 carbon atoms; (c) An aralkyl having an aryl moiety with 6 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (d) A heteroaralkyl having a heteroaryl moiety with 1 to 12 carbon atoms and having at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms which may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (e) A group represented by the following formula: [Chemical Formula 12] [In the formula, R 8'a and R 8'b are each independently: (a) An alkyl group having 1 to 9 carbon atoms which may be branched; (b) An alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or (d) A silyl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms which may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * is a bonding site], R 8a and R 8b are each independently: (a) An alkyl group having 1 to 9 carbon atoms which may form a branch or a ring; (b) An alkoxy group having 1 to 8 carbon atoms which may form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms which may form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis, R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms].

10. A method for producing a compound represented by formula (II) or a salt thereof, [Chemical formula 13] The method includes a step of reacting a reaction product of a compound represented by the following formula (III) and a compound represented by the following formula (IV) with a compound represented by the following formula (V): [Chemical formula 14] [Chemical formula 15] [Chemical formula 16] [In formula (III), R 8a and R 8b are each independently: (a) An alkyl group having 1 to 9 carbon atoms that may form a branch or a ring; (b) An alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis, In formula (IV), p is independently an integer from 0 to 3, In formula (V), R 7 is: (a) an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring and an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring; (b) a cyanoalkoxy group having 1 to 8 carbon atoms; (c) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (d) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms, which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that can form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that can form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (e) a group represented by the following formula: [Chemical formula 17] (In the formula, R 8'a and R 8'b are each independently: (a) a branched alkyl group having 1 to 9 carbon atoms; (b) an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring; (c) an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or (d) a silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * is a bonding site), R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms, X -as a counter anion].

11. A method for producing a compound represented by formula (I) or a salt thereof according to claim 1, the method comprising guanidinating a compound represented by the following formula (VI) or a salt thereof: [Chemical formula 18] with a compound represented by formula (II) or a salt thereof: [Chemical formula 19] In formula (VI), B 1 is: (a) a purin-9-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (b) a 1,2-dihydropyrimidin-1-yl group which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom, R 2 and R 3 are: (a) a hydrogen atom; (b) a protecting group for a hydroxyl group in nucleic acid synthesis; (c) an alkyl group having 1 to 7 carbon atoms which may form a branch or a ring; (d) an alkenyl group having 2 to 7 carbon atoms which may form a branch or a ring; (e) an aryl group having 6 to 12 carbon atoms which may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 6 carbon atoms, a straight-chain alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a straight-chain alkylthio group having 1 to 6 carbon atoms, an amino group, a straight-chain alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (f) a heteroaryl group having 1 to 12 carbon atoms and having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (g) an aralkyl group having an aryl moiety having 6 to 12 carbon atoms and having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (h) a heteroaralkyl group having a heteroaryl moiety having 1 to 12 carbon atoms and having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (i) an acyl group having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (j) a silyl group having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (k) a phosphate group having at least one substituent selected from the group consisting of a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a linear alkyl group having 1 to 6 carbon atoms, a linear alkoxy group having 1 to 6 carbon atoms, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, a linear alkylthio group having 1 to 6 carbon atoms, an amino group, a linear alkylamino group having 1 to 6 carbon atoms, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (l) a phosphate group protected by a protecting group for nucleic acid synthesis, R 9 and R 10Each independently is a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, or R 9 and R 10 together form -(CH2) m -(where m is an integer from 2 to 7), R 11 and R 12 each independently is a hydrogen atom, or an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, or R 11 and R 12 together form the oxygen atom part of a carbonyl group (=O), or R 11 and R 12 together form -(CH2) n -(where n is an integer from 2 to 7), In formula (II), R 7 is: (a) an alkyl group having 1 to 8 carbon atoms that may be substituted by an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring and that may form a branch or a ring; (b) a cyanoalkoxy group having 1 to 8 carbon atoms; (c) an aralkyl group having an aryl moiety with 6 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 8 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; (d) a heteroaralkyl group having a heteroaryl moiety with 1 to 12 carbon atoms that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 6 carbon atoms that may form a branch or a ring, an alkoxy group having 1 to 6 carbon atoms that may form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group, an alkylamino group having 1 to 6 carbon atoms that may form a branch or a ring, an amino group protected by a protecting group for nucleic acid synthesis, and a halogen atom; or (e) a group represented by the following formula: [Chemical formula 20] [In the formula, R 8'a and R 8'b each independently are: (a) An alkyl group having 1 to 9 carbon atoms that can be branched; (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, a straight-chain alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis; and * is a bonding site, R 8a and R 8b are each independently: (a) An alkyl group having 1 to 9 carbon atoms that can form a branch or a ring; (b) An alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring; (c) An alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring; or (d) A silyl group that may have at least one substituent selected from a hydroxyl group, a hydroxyl group protected by a protecting group for nucleic acid synthesis, an alkyl group having 1 to 8 carbon atoms that can form a branch or a ring, an alkoxy group having 1 to 8 carbon atoms that can form a branch or a ring, a mercapto group, a mercapto group protected by a protecting group for nucleic acid synthesis, an alkylthio group having 1 to 8 carbon atoms that can form a branch or a ring, an alkylamino group having 1 to 8 carbon atoms that can form a branch or a ring, and an amino group protected by a protecting group for nucleic acid synthesis, R 16 is a straight-chain or branched alkyl group having 1 to 6 carbon atoms, or a straight-chain or branched alkenyl group having 2 to 6 carbon atoms.

12. The manufacturing method according to claim 11, wherein, The guanidination step is carried out in the presence of a metal salt.

13. The manufacturing method according to claim 12, wherein, The metal salt is silver nitrate, silver chloride, silver bromide, silver iodide, silver trifluoromethanesulfonate, silver tetrafluoroborate, or silver hexafluorophosphate.

14. The manufacturing method according to claim 12, wherein, The metal salt is copper(I) chloride, copper(I) bromide, copper(I) iodide, copper(I) trifluoromethanesulfonate, copper(I) tetrafluoroborate, or copper(I) hexafluorophosphate.

15. The manufacturing method according to claim 11, wherein, R in formula (VI) 2 is a hydrogen atom.

16. The manufacturing method according to any one of claims 11 to 15, wherein, R in the formula (I) 2 is a compound of -P(R 4 )R 5 and [In the formula, R 4 and R 5 each independently is: (a) a hydroxyl group; (b) a hydroxyl group protected by a protecting group for nucleic acid synthesis; (c) a mercapto group; (d) a mercapto group protected by a protecting group for nucleic acid synthesis; (e) an amino group; (f) an alkoxy group having 1 to 5 carbon atoms; (g) an alkylthio group having 1 to 5 carbon atoms; (h) a cyanoalkoxy group having 1 to 6 carbon atoms; (i) a dialkylamino group having alkyl groups with 1 to 6 carbon atoms which may be the same or different from each other; or (j) a cyclic alkylamino group having 3 to 6 carbon atoms, or, R 4 Together with R 5 forms the following formula: [Chemical Formula 21] (wherein, R 13a and R 13b each independently represents a hydrogen atom, a branched or unbranched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein, R a is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2, and * represents a bonding site); or [Chemical Formula 22] (wherein R 14 and R 15 are each independently a hydrogen atom, a branched or unbranched alkyl group having 1 to 3 carbon atoms, or a phenyl group, and * represents a bonding site), The method includes a step of further amiditing the obtained product after the guanidination step.

17. According to the manufacturing method described in claim 11, wherein, R in formula (VI) 2 is a protecting group for the hydroxyl group for nucleic acid synthesis, and the method further includes a step of deprotecting the protecting group.

18. According to the manufacturing method described in claim 17, wherein, R in the formula (I) described above 2 is a compound of -P(R 4 )R 5 as described [In the formula, R 4 and R 5 each independently is: (a) a hydroxyl group; (b) a hydroxyl group protected by a protecting group for nucleic acid synthesis; (c) a mercapto group; (d) a mercapto group protected by a protecting group for nucleic acid synthesis; (e) an amino group; (f) an alkoxy group having 1 to 5 carbon atoms; (g) an alkylthio group having 1 to 5 carbon atoms; (h) a cyanoalkoxy group having 1 to 6 carbon atoms; (i) a dialkylamino group having alkyl groups with 1 to 6 carbon atoms which may be the same or different from each other; or (j) a cyclic alkylamino group having 3 to 6 carbon atoms, or, R 4 Together with R 5 forms the following formula: [Chemical Formula 23] (wherein, R 13a and R 13b each independently represent a hydrogen atom, a branched or unbranched alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, a nitro group, a halogen atom, a cyano group, Si(R a )3 (wherein, R a is an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms), a sulfonyl group, SO2Ph or SiMePh2, and * represents a bonding site); or [Chemical Formula 24] (wherein, R 14 and R 15 are each independently a hydrogen atom, a branched or unbranched alkyl group having 1 to 3 carbon atoms, or a phenyl group, and * represents a bonding site), The method includes a step of further amiditing the obtained product after the deprotection step.

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