Method for producing azanucleoside precursors

Abstract

To provide a method for producing an azanucleoside precursor having a hydroxyl group introduced at the N-α position more easily.SOLUTION: There is provided a method for producing a compound represented by the following formula (A'), in which the N-α position of a compound represented by the formula (A) is hydroxylated by the electrolytic oxidation of the compound represented by the following formula (A) in the presence of a supporting electrolyte and water in at least one organic solvent selected from the group consisting of nitrile solvents, ether solvents, ketone solvents, ester solvents, sulfoxide solvents, amide solvents, and nitro solvents, [where, R1 represents a -CH2OPG4 group or an alkoxycarbonyl group, R2 represents a -OPG2 group or H, R3 represents a -OPG3 group or H, PG1 indicates a protective group for the amino group, and PG2, PG3, and PG4 each independently represent a hydroxyl-protecting group].SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an azanucleoside precursor or the like. [Background technology]

[0002] In recent years, drug discovery research has undergone a major shift from traditional small molecule drugs and antibody-based biopharmaceuticals to "medium molecule" drugs. Peptides and nucleic acids form the core of medium molecule drugs, and chemical synthesis has also seen a rapid increase in interest. In particular, nucleic acid drugs, which use nucleic acids and their analogs, are attracting considerable attention as next-generation drug candidates with the potential to cure diseases that have been difficult to treat with traditional small molecule drugs and antibody drugs. Natural oligonucleotides (nucleic acids) themselves can also be used as drugs, but they have the disadvantage of not being resistant to digestive enzymes and being quickly decomposed in the body.

[0003] To date, various nucleic acid analogs have been designed and synthesized by chemically modifying natural oligonucleotides and nucleosides. Substitution of one oxygen atom in the phosphodiester bond with sulfur and replacement of the ribose moiety with a morpholino backbone have been reported, and research and development is currently underway. Among these, azanucleosides, in which the oxygen atom in the ribose backbone is replaced with a nitrogen atom, are considered highly promising due to their low toxicity due to their chemical structure being very similar to natural nucleosides. However, they have also been reported to confer resistance to digestive enzymes (see the chemical formula below for the structure of azanucleosides, etc.). Additionally, azanucleosides such as forodesine, which is expected to be effective against T-cell leukemia / lymphoma despite being monomer units, and galidesivir, which is expected to be an anti-Ebola virus drug, have already been reported, and are attracting considerable attention as next-generation drug candidates.

[0004] [ka]

[0005] However, even the monomer units of these azanucleosides require 20 to 30 steps for their chemical synthesis, and the overall yield is often only about 1%, posing significant challenges in terms of manufacturing time and cost as pharmaceuticals. Even before that, it is extremely difficult to supply the amount required for activity testing at the laboratory level.

[0006] In response to this, the present inventors have proposed in Non-Patent Document 1 a method for producing an azanucleoside precursor by using a raw material that can be easily synthesized from commercially available prolinol, performing electrolytic oxidation in the presence of a carboxylic acid additive and a supporting electrolyte, and introducing a carboxylic acid-derived substituent at the N-α position. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] K. Okamoto et al. Chem. Eur. J. 2018, 24, 17902-17905. Summary of the Invention [Problem to be solved by the invention]

[0008] Considering the convenience of using them as pharmaceutical intermediates, the group introduced at the N-α position is preferably a hydroxyl group. Because the hydroxyl group can be chemically modified in various ways through subsequent reactions, azanucleoside precursors with a hydroxyl group introduced at the N-α position can be easily converted to various azanucleosides.

[0009] In this regard, Non-Patent Document 1 discloses a method for introducing a hydroxyl group at the N-α position by electrolytic oxidation of a prolinol-derived raw material in the presence of trifluoroacetic acid, introducing a trifluoroacetyl group derived from trifluoroacetic acid at the N-α position, and then stopping the electrolytic oxidation and performing workup with saturated saline. However, this method leaves room for improvement in that it takes a long time to work up and uses relatively expensive trifluoroacetic acid, and a simpler method is desired.

[0010] Therefore, an object of the present invention is to provide a method for more simply producing an azanucleoside precursor having a hydroxyl group introduced at the N-α position. [Means for solving the problem]

[0011] In view of the above circumstances, the present invention provides a method for producing a compound represented by the following formula (A'), which comprises electrolytically oxidizing a compound represented by the following formula (A) in the presence of a supporting electrolyte and water in at least one organic solvent selected from the group consisting of nitrile solvents, ether solvents, ketone solvents, ester solvents, sulfoxide solvents, amide solvents, and nitro solvents, thereby hydroxylating the N-α position of the compound represented by formula (A): [ka] [In the formula, R 1 is -CH2OPG 4 group or alkoxycarbonyl group, R 2 -OPG 2 R represents a group or a hydrogen atom. 3 -OPG 3 represents a group or a hydrogen atom, and PG 1 indicates a protecting group for the amino group, and PG 2 , P.G. 3 and PG 4 each independently represents a protecting group for a hydroxyl group.

[0012] According to this production method, inexpensive water can be used as a nucleophile, and an azanucleoside precursor having a hydroxyl group introduced at the N-α position can be easily produced in a one-step reaction, rather than the two-step reaction described in Non-Patent Document 1, thereby increasing the yield.

[0013] Conventionally, electrolytic oxidation reactions using water as a reactant have been considered extremely difficult. Specifically, because water itself is a substance that is easily oxidized, it was thought that electrolytic oxidation of compounds that are less oxidizable than water was impossible in the presence of water. For this reason, in the production method described in Non-Patent Document 1, electrolytic oxidation was performed in the absence of water, and then the electrolytic oxidation was stopped and saturated saline was added to carry out the reaction. Surprisingly, the present inventors have discovered that in this reaction system, even in the presence of water, electrolytic oxidation of a compound represented by formula (A) proceeds to produce an iminium cation, and water acts as a nucleophile to produce a compound represented by formula (A') in which the N-α position is hydroxylated.

[0014] From the viewpoint of improving reactivity, the organic solvent preferably contains a nitrile-based solvent.

[0015] From the viewpoint of improving yield, the supporting electrolyte preferably contains a lithium salt or an ammonium salt.

[0016] The present invention also provides a method for hydroxylating the N-α position of a compound having a pyrrolidine ring by electrolytically oxidizing the compound in the presence of a supporting electrolyte and water in at least one organic solvent selected from the group consisting of nitrile solvents, ether solvents, ketone solvents, ester solvents, sulfoxide solvents, amide solvents, and nitro solvents. The compound having a pyrrolidine ring hydroxylated at the N-α position may be useful as a pharmaceutical intermediate, etc.

[0017] Although several methods for hydroxylating the N-α position of compounds having a pyrrolidine ring have been reported, they have been limited to those requiring rare metals or harsh reaction conditions, or those using explosive reagents. Furthermore, the applicable substrates are limited, and scaling up the reaction is difficult. In contrast, the method of the present invention enables simple and large-scale production of compounds having a pyrrolidine ring hydroxylated at the N-α position. [Effects of the Invention]

[0018] According to the present invention, it is possible to more easily produce an azanucleoside precursor having a hydroxyl group introduced at the N-α position or a compound having a pyrrolidine ring hydroxylated at the N-α position, and since the reaction can be carried out continuously in a single step, it is possible to increase the yield. DETAILED DESCRIPTION OF THE INVENTION

[0019] In the method of the present embodiment, a compound having a pyrrolidine ring is electrolytically oxidized in an organic solvent in the presence of a supporting electrolyte and water, thereby hydroxylating the N-α position of the compound having a pyrrolidine ring.

[0020] The compound having a pyrrolidine ring may be any compound that generates an iminium cation by electrolytic oxidation, and when the compound has a substituent that inhibits the generation of an iminium cation, a compound protected with an appropriate protecting group can be used. For example, the nitrogen atom in the pyrrolidine ring can be protected with an amino-protecting group, and when the compound has other reactive groups such as a hydroxyl group or an amino group, each of these can be protected with a protecting group.

[0021] The compound having a pyrrolidine ring is preferably a compound represented by the following formula (A), which allows the production of a compound represented by the following formula (A'), which is an azanucleoside precursor having a hydroxyl group introduced at the N-α position. [ka] [In the formula, R 1 is -CH2OPG 4 group or alkoxycarbonyl group, R 2 -OPG 2 R represents a group or a hydrogen atom. 3 -OPG 3 represents a group or a hydrogen atom, and PG 1 indicates a protecting group for the amino group, and PG 2 , P.G. 3 and PG 4 each independently represents a protecting group for a hydroxyl group.

[0022] Examples of the alkoxycarbonyl group include a methoxycarbonyl group, an ethoxycarbonyl group, and a t-butoxycarbonyl group.

[0023] As the above-mentioned "amino-protecting group", a conventionally known amino-protecting group can be appropriately used. Specific examples thereof include an acetyl group (Ac group), a trifluoroacetyl group, a pivaloyl group, a tert-butoxycarbonyl group (Boc group), a 2,2,2-trichloroethoxycarbonyl group, a benzyloxycarbonyl group (Cbz group), a 9-fluorenylmethyloxycarbonyl group (Moc group (Fmoc group)), a benzhydryl group, a trityl group, a phthaloyl group, an allyloxycarbonyl group, a p-toluenesulfonyl group, an o-nitrobenzenesulfonyl group, and a trimethylsilylethoxycarbonyl group.

[0024] As the "hydroxyl-protecting group", a conventionally known hydroxyl-protecting group can be appropriately used. Specific examples thereof include alkyl groups (e.g., methyl, ethyl, t-butyl, etc.), arylalkyl groups (e.g., benzyl, etc.), p-alkoxyarylalkyl groups (e.g., p-methoxybenzyl, etc.), alkoxyalkyl groups (e.g., methoxymethyl, 2-tetrahydropyranyl, acyl groups (e.g., acetyl (Ac), pivaloyl, benzoyl, etc.), silyl-protecting groups (e.g., trimethylsilyl, triethylsilyl, t-butyldimethylsilyl, triisopropylsilyl, t-butyldiphenylsilyl, etc.), etc.

[0025] The compound represented by the formula (A) can be produced from commercially available prolinol by a conventionally known method, for example, the method described in the Supporting Information of Non-Patent Document 1.

[0026] The concentration of the compound having a pyrrolidine ring, preferably the compound represented by the above formula (A), relative to the organic solvent can be, for example, 0.001 to 0.05 mol / L or 0.005 to 0.02 mol / L.

[0027] Examples of the supporting electrolyte include lithium salts such as lithium chloride, lithium bromide, lithium iodide, lithium perchlorate (LiClO), lithium nitrate, lithium sulfate, lithium fluoroborate, lithium trifluoromethanesulfonate (LiOTf), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI), as well as lithium salts such as sodium chloride; sodium salts such as sodium bromide and sodium iodide; potassium salts such as potassium chloride, potassium bromide, and potassium iodide; and ammonium salts such as tetrabutylammonium bromide, tetrabutylammonium chloride, tetraethylammonium fluoroborate, tetrabutylammonium fluoroborate, tetrabutylammonium perchlorate (BuNClO), tetrabutylammonium hexafluorophosphate (BuNPF), and tetrabutylammonium tetrafluoroborate. These may be used alone or in combination of two or more.

[0028] The supporting electrolyte is preferably a lithium salt or an ammonium salt, more preferably a lithium salt, from the viewpoint of improving yield, etc. Also, from the same viewpoint, the supporting electrolyte is preferably a perchlorate, more preferably lithium perchlorate or tetrabutylammonium perchlorate.

[0029] The concentration of the supporting electrolyte relative to the organic solvent can be, for example, 0.01 to 0.5 mol / L or 0.05 to 0.2 mol / L.

[0030] The concentration of water relative to the organic solvent can be, for example, 0.01 to 5.0 mol / L, 0.05 to 2.5 mol / L, or 0.25 to 1.0 mol / L.

[0031] Examples of the organic solvent include nitrile solvents such as acetonitrile and benzonitrile; ether solvents such as diethyl ether and tetrahydrofuran; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as methyl acetate and ethyl acetate; sulfoxide solvents such as dimethyl sulfoxide; amide solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and nitro solvents such as nitromethane and nitroethane. These may be used alone or in combination of two or more. These organic solvents are desirable because they can dissolve water as a reactant and have low nucleophilicity.

[0032] From the viewpoint of improving reactivity, the organic solvent is preferably a nitrile solvent, and more preferably acetonitrile.

[0033] The electrolytic oxidation can be carried out by a conventional method in which an anode and a cathode are used to pass electricity through a reaction solution. When the electrolytic oxidation is carried out on a large scale, it is preferable to use a glassy carbon beaker as a reaction vessel.

[0034] Examples of the anode include glassy carbon, graphite, carbon felt, gold, and platinum anodes. Examples of the cathode include glassy carbon, graphite, carbon felt, gold, platinum, nickel, and aluminum cathodes.

[0035] The current intensity during the electrode oxidation can be, for example, 0.01 to 100 mA or 0.1 to 10 mA. The quantity of electricity during the electrode oxidation can be, for example, 0.5 to 10 F / mol or 1 to 5 F / mol. The temperature during the electrolytic oxidation can be, for example, 10 to 50°C or room temperature.

[0036] The compound represented by formula (A') obtained by the production method of the present invention can be used as an azanucleoside precursor, and various azanucleoside derivatives can be produced by reacting the carbon atom to which a hydroxyl group is linked with a nucleobase such as adenine, guanine, cytosine, thymine, or uracil as a nucleophilic reagent. Furthermore, various nucleophilic reagents, in addition to nucleobases, can also be introduced into the compound represented by formula (A').

[0037] The reaction of linking a nucleic acid base to the compound represented by formula (A') can be carried out, for example, using trimethylsilyl trifluoromethanesulfonate (TMSOTf) under Silyl-Hilbert-Johnson (SHJ) reaction conditions.

[0038] The azanucleoside derivatives thus obtained are useful compounds for the development and production of nucleic acid medicines containing non-natural nucleic acids. [Example]

[0039] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0040] <Study on supporting electrolyte> A glassy carbon anode (80 mm × 40 mm) and a platinum cathode (40 mm × 40 mm) were attached to a solution of the following compound 1 (0.10 mmol), water (0.5 mmol, 9.0 μL), and the supporting electrolyte (1.0 mmol) listed in Table 1 in acetonitrile (10 mL). After applying a constant current (1.0 mA) of 2.6 F / mol (25.1 C) at room temperature, the reaction mixture was diluted with saturated aqueous sodium bicarbonate and extracted with ethyl acetate (15 mL × 3). The combined organic layer was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. The following compound 2 was obtained by silica gel column chromatography (hexane / ethyl acetate). The yield of compound 2 was determined using benzaldehyde as an internal standard. 1 The results are shown in Table 1. [ka]

[0041] [Table 1]

[0042] <Substrate considerations> Under the conditions of entry 5 (supporting electrolyte: LiClO4), various substrates were used instead of compound 1. The results are shown below. Compounds 3 to 8 are products, and the corresponding compounds without a hydroxyl group at the N-α position were used as substrates. [ka]

[0043] <Large-scale experiment using glassy carbon beaker> A solution of the substrate corresponding to compound 3 (5.0 mmol), water (100 mmol, 1.8 mL), and lithium perchlorate (2.12 g, 20 mmol) in acetonitrile (200 mL) was prepared in a cylindrical glassy carbon beaker (D × H = 74 mm × 82 mm, thickness 3 mm). A platinum cathode (50 mm × 50 mm) was attached to the top. After applying a constant current (5.0 mA) of 2.6 F / mol (1255 C) at room temperature, the reaction mixture was transferred to a round-bottom flask. Most of the solvent was removed under reduced pressure, and the resulting residue was dissolved in ethyl acetate. The organic layer was washed with saturated aqueous sodium bicarbonate and saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure. Compound 3 was obtained by silica gel column chromatography (hexane / ethyl acetate). The results are shown below.

[0044] Similar large-scale experiments were carried out using a substrate corresponding to compound 4 (4.0 mmol) or a substrate corresponding to compound 5 (5.0 mmol) instead of the substrate corresponding to compound 3. The results are shown below. [ka]

Claims

1. A method for producing a compound represented by the following formula (A'), which comprises electrolytically oxidizing a compound represented by the following formula (A) in the presence of a supporting electrolyte and water in at least one organic solvent selected from the group consisting of nitrile solvents, ether solvents, ketone solvents, ester solvents, sulfoxide solvents, amide solvents and nitro solvents, thereby hydroxylating the N-α position of the compound represented by the formula (A). 【Chemistry 1】 [In the formula, R １ is -CH ２ OPG ４ represents a group, and R ２ is -OPG ２ group or a hydrogen atom, R ３ is -OPG ３ group or a hydrogen atom, PG １ represents a protecting group for an amino group, and PG ２ , P.G. ３ and P.G. ４ each independently represents a protecting group for a hydroxyl group.

2. The method according to claim 1 , wherein the organic solvent comprises a nitrile solvent.

3. The method according to claim 1 or 2, wherein the supporting electrolyte comprises a lithium salt or an ammonium salt.

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