Process for the synthesis of piclidenoson from adenosine

Abstract

The present invention relates to a process for the synthesis of Piclidenoson (I), starting from adenosine (II), (2R,3R,4S,5R)-2-(6-amino-9H-purin-9-yl)-5- (hydroxymethyl)oxolan-3,4-diol.

Description

[0001] “PROCESS FOR THE SYNTHESIS OF PICLIDENOSON FROM ADENOSINE”

[0002] DESCRIPTION

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a process for the synthesis of Piclidenoson (I), (2S,3S,4R,5R)-3,4-dihydroxy-5-(6-((3-iodobenzyl)amino)-9H-purin-9-yl)-N- methyltetrahydrofuran-2-carboxamide, starting from adenosine (II), (2R,3R,4S,5R)-

[0005] 2-(6-amino-9H-purin-9-yl)-5-(hydroxymethyl)oxolan-3,4-diol

[0006] Piclidenoson (ij Adenosine ii;;

[0007] STATE OF THE ART

[0008] Piclidenoson (I) is a molecule with anti-inflammatory activity capable of inhibiting the Wnt / [3-catenin transduction cascade and the production of pro-inflammatory cytokines thanks to its agonist activity towards A3AR. Thanks to its high oral bioavailability, when Piclidenoson is formulated in tablet form, it is used in the treatment of psoriasis, rheumatoid arthritis and other autoimmune diseases. Numerous processes for the synthesis of Piclidenoson (I) starting from three different starting ribonucleosides are described in the literature: adenosine (II), 6- chloropurine riboside (III), and inosine (IV).

[0009] Adenosine ('IQ 6-€hieropurine riboside {III) inosine (iV|

[0010] These approaches can be distinguished based on the strategy followed to introduce the 3-iodobenzyl fragment of the product: nucleophilic aromatic substitution starting from a 6-chloropurine derivative or reductive amination starting from a 6- aminopurine intermediate. The International Publication W02008 / 111082 describes the synthesis of Piclidenoson (I) by means of a linear sequence of four steps starting from the advanced intermediate 6-chloropurine riboside (III). The core of this approach, also pursued in other strategies reported in the literature (WO2015 / 009008, W09502604, Gallo-Rodriguez et al. J. Med. Chem. 1994), is the introduction of the 3-iodobenzyl moiety by nucleophilic aromatic substitution. This transformation involves the use of 3-iodobenzylamine hydrochloride (V), a very expensive reagent that sometimes requires recrystallization before its use. The operating sequence is reported below:

[0011] The same approach was described by Gallo-Rodriguez et al. (Gallo-Rodriguez et al. J. Med. Chem. 1994, 37, 636) starting from the advanced derivative of inosine (IV), / .e. (3aS,4S,6R,6aR)-2,2-dimethyl-6-(6-oxo-1 ,6-dihydro-9H-purin-9- yl)tetrahydrofuro[3,4-d][1 ,3]dioxol-4-carboxylic acid (X). This derivative is subjected to extensive chlorination of both the carboxylic and purinone moieties by thionyl chloride and N,N-dimethyl formamide, and subsequently to amidation. At this point, the same final steps described above are pursued, i.e. nucleophilic aromatic substitution and deprotection of the vicinal diol.

[0012]

[0013] Piclidenoson fl|

[0014] In the application IN201911019318, the synthesis of Piclidenoson (I) starting from different adenine derivatives (II, XI-XI 11) and 3-iodobenzaldehyde (XIV) by reductive amination is suggested. In particular, the adenine derivative is first condensed with 3-iodobenzaldehyde (XIV) obtaining the corresponding imine product (C=N connected with a double bond; XV’- XVIII’) and then treated and reduced with sodium borohydride (XV- XVIII), and subsequently converted into Piclidenoson (I). In the examples reported in the application IN201911019318, the reaction yields are not reported and cannot even be inferred from the text.

[0015] Furthermore, the exact reproduction of the described reaction conditions did not provide any conversion of the starting adenine derivatives and there are no examples published in the literature where the above sequence is found to be productive. Afify et al. (J. Heterocyclic Chem. 2000, 37, 339) reported the synthesis of Piclidenoson (I) starting from an advanced adenosine intermediate, namely the compound (2S,3S,4R,5R)-5-(6-amino-9H-purin-9-yl)-3,4-dihydroxy-N- methyltetrahydrofuran-2-carboxamide (XIX), by reduction with sodium borohydride of a benzotriazole N,N-aminal adduct (XX), as reported below.

[0016] As is clear from the analysis of the literature commented above, the synthesis of Piclidenoson (I) from adenosine (II) uses very expensive reagents making it not cost-effective from an industrial point of view.

[0017] Therefore, it is still felt the need for a new process for the synthesis of Piclidenoson that is cost-effective, potentially scalable and high yielding.

[0018] SUMMARY OF THE INVENTION

[0019] The inventors have surprisingly identified a process for the synthesis of Piclidenoson (I) from adenosine (II) comprising five steps: and comprising the synthesis of a diastereoisomeric mixture of N,O-aminals of formula (XXIV) and (XXV) through the use of 3-iodobenzaldehyde (XIV) and subsequent reduction to a benzylic amine thanks to the combination of a hydride source (H-donor) and a Lewis acid (LA), wherein Ri, R2 e R3, each independently from the other, are an alkyl group.

[0020] The inventors have thus surprisingly succeeded in identifying a new synthetic approach for the production of Piclidenoson by means of a new and inventive step of reduction through a diastereoisomeric mixture of N,O-aminals, i.e. an intermediate different from the imines and N,N-aminals of the prior art.

[0021] Therefore, in a first aspect the invention concerns a process for the synthesis of Piclidenoson (I) comprising the following steps: 1 ) protecting the compound adenosine (II) in the presence of a ketone of formula (XXVH) or a ketal of formula (XXVIII) wherein R1.R2.R4 ed R5. each independently from the other, are (Ci-Cs)alkyl, thus obtaining the compound (XXI)

[0022] 2) oxidizing the primary alcohol of compound (XXI) with an oxidizing agent to give the carboxylic acid (XXII)

[0023] 3) amidating the carboxylic acid (XXII) with methylamine after activation by a chlorinating agent to give (XXIII) 4) reacting the compound (XXIII) with 3-iodobenzaldehyde (XIV), a linear or branched alkyl chain alcohol with structure R3OH, and a trialkyl orthoformate with linear or branched alkyl chains to obtain the diastereoisomeric mixture (XXIV) + (XXV), which is subjected to a reduction reaction with a reducing mixture comprising an H-donor compound and a Lewis acid (LA) to give the where R3 is (Ci-C3)alkyl

[0024] 5) deprotecting the compound (XXVI) in an acidic medium to give Piclidenoson (I)

[0025] In an advantageous and preferred embodiment, R1 and R2 are methyl.

[0026] In another aspect, the invention concerns the diastereoisomeric mixture of the compounds of formula (XXIV) and (XXV) where R1, R2 and R3, each independently from the other, are an alkyl group.

[0027] The inventors of the present invention, therefore, through a new operating sequence and, in particular, through the formation of the diastereoisomeric mixture of N,O- aminals, have succeeded in obtaining a new process for the synthesis of Piclidenoson that is cost-effective, potentially scalable and high yielding, as will be apparent from the experimental part.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention therefore concerns a process for the synthesis of Piclidenoson (I) comprising the following steps: 1 ) protecting the compound adenosine (II) in the presence of a ketone of formula (XXVII) or a ketal of formula (XXVIII) wherein Ri, R2, R4, Rs, each independently from the other, are an alkyl, thus obtaining the compound (XXI)

[0030] 2) oxidizing the primary alcohol of compound (XXI) with an oxidizing agent to give the carboxylic acid (XXII)

[0031] 3) amidating the carboxylic acid (XXII) with methylamine after activation by a chlorinating agent to give (XXIII)

[0032] 4) reacting the compound (XXIII) with 3-iodobenzaldehyde (XIV), a linear or branched alkyl chain alcohol with R3OH structure, and a trialkyl orthoformate with linear or branched alkyl chains to obtain the diastereoisomeric mixture (XXIV) + (XXV), which is subjected to a reduction reaction with a reducing mixture comprising an H-donor compound and a Lewis acid (LA) to give the compound (XXVI) where R3 is an alkyl

[0033] 5) deprotecting compound (XXVI) in an acidic medium to give Piclidenoson (I)

[0034] In the present invention when using the term:

[0035] - “H-donor” is intended to mean a compound containing a X-H bond, wherein X is a B, Al or Si atom. When X is B or Al, the H-donor is a metal borohydride or aluminum hydride. When X is Si, the H-donor is a silane; and

[0036] - “LA” is intended to mean any Lewis acid, preferably a boron halide Lewis acid, e.g. BF3, or a Lewis acid with structure XY, wherein Y is a metal, semimetal or metalloid, and Z is selected from a halogen, preferably chlorine and iodine, tosylate, mesylate and triflate.

[0037] In the process of invention, step 1 ) consists in protecting the compound adenosine (II) in the presence of a ketone of formula (XXVII) or a ketal of formula (XXVIII) wherein R1, R2, R4, Rs, each independently from the other, are alkyl, thus obtaining the compound (XXI)

[0038] Adenosine (II) XXI

[0039] Step 1 ) of protection therefore occurs on the vicinal diol of adenosine.

[0040] It is carried out in the presence of a ketone of formula (XXVII) or a ketal of formula (XXVIII) wherein Ri, R2, R4 e R5, each independently from the other, are alkyl, preferably they are selected from methyl or ethyl.

[0041] In said ketal, R1, R2, R4, Rs, each independently from the other, are alkyl, preferably they are methyl.

[0042] In a preferred embodiment, therefore, said ketal is 2,2-dimethoxypropane.

[0043] Step 1 ) of protection involves a substep 1 a) of protection reaction.

[0044] Substep 1 a) of protection reaction occurs preferably at ambient pressure (1 atm), more preferably in an open reactor, or at a pressure higher than ambient, more preferably in an autoclave.

[0045] Substep 1 a) of protection reaction occurs optionally in the presence of an organic solvent. Preferably said organic solvent is selected from the group consisting of acetone, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1 ,4-dioxane, diisopropyl ether, diethyl ether, methyl-t-butyl ether (MTBE), cyclopentyl-methyl- ether (CPME), methyl isobutyl ketone (MIBK), acetonitrile and toluene. Preferably said organic solvent, if present, is used in an amount in the range from 5 to 200 volumes.

[0046] In an advantageous embodiment, step 1 a) occurs without the use of a solvent.

[0047] In a preferred and advantageous embodiment of the invention, step 1a) of protection reaction is carried out as follows. 1 mole of adenosine (II) is reacted with an amount in the range from 1 to 200 moles of ketone (XXVII) or ketal (XXVIII), preferably 2,2-dimethoxypropane, in the presence of a Brdnsted acid, in an amount in the range from 0.01 to 50 moles, preferably from 0.20 to 20 moles. Said Brdnsted acid is preferably selected from the group consisting of mineral and (organo)sulfonic acids, more preferably it is selected from the group consisting of hydrochloric acid, hydrobromic acid, p-toluenesulfonic acid and methanesulfonic acid, still more preferably it is p-toluenesulfonic acid.

[0048] In the preferred and advantageous embodiment of step 1a) of the invention, the order of addition of the reagents may also be different from that indicated above.

[0049] In a further advantageous embodiment of the invention, step 1 ) of protection provides for further substeps, subsequent to the protection reaction ( / .e. substep 1 a)), as reported below, before the execution of step 2).

[0050] The process of the invention therefore comprises a substep 1 b) of treatment at a temperature in the range from O to 40 °C, preferably 15-25 °C, of the reaction mixture containing the protected adenosine, followed by the addition of an inorganic base aqueous solution.

[0051] Specifically, and preferably, in said substep 1 b) the reaction mixture containing the protected vicinal diol (XXI) is brought to a temperature in the range from 15 to 25°C and is added with an amount in the range from 10 to 200 volumes of an inorganic base aqueous solution, preferably NaHCOs or NaOH, more preferably with a concentration in the range from 0.1 to 10%.

[0052] The mixture resulting from the treatment with the organic base solution is then preferably concentrated in substep 1 b), more preferably under vacuum at a temperature in the range from 25 to 80 °C, even more preferably from 40 to 60 °C, thus obtaining a suspension.

[0053] In substep 1 c) of filtration subsequent to substep 1 b), the resulting suspension of substep 1 b) is filtered under vacuum and the filtrate washed 1 -5 times with an amount of water in the range from 1 to 100 volumes, more preferably at a temperature in the range from 0 to 50 °C. The filtrate is then dried, preferably under vacuum, at a temperature in the range from 20 to 100 °C, more preferably from 30 to 60 °C, to obtain the protected vicinal diol (XXI). The protected vicinal diol (XXI) according to the invention is obtained in step 1 ) with a yield equal to or greater than 90%, and a purity equal to or greater than 80%.

[0054] In the preferred and advantageous embodiment, wherein Ri and R2 are methyl, step 1 ) allows to obtain the compound (3aR,4R,6R,6aR)-6-(6-amino-9H-purin-9-yl)-2,2- dimethyltetrahydrofuro[3,4-d][1 ,3]dioxol-4-yl)methanol.

[0055] Step 2) consists in oxidizing the primary alcohol of the compound (XXI) with an oxidizing agent to give the acid (XXII)

[0056] Step 2) of oxidation involves substep 2a) of oxidation reaction.

[0057] Substep 2a) occurs in the presence of an oxidizing mixture, preferably comprising a stoichiometric oxidizing agent, more preferably selected from the group consisting of (diacetoxyiodo)benzene (PIDA), sodium periodate, N-methylmorpholine-N-oxide (NMO), (bis(trifluoroacetoxy)iodo)benzene (PIFA), 2-iodoxybenzoic acid (IBX) and mixtures thereof, in the presence of a catalyst, preferably selected from 2, 2,6,6- tetramethylpiperidine 1 -oxyl radical (TEMPO), 9-azabicyclo[3.3.1 ]nonan-N-oxyl (ABNO), ruthenium trichloride, 2-azaadamantane-N-oxyl (AZADO), more preferably the catalyst is 2,2,6,6-tetramethylpiperidine 1 -oxyl radical (TEMPO). Substep 2a) of oxidation reaction preferably occurs at ambient pressure (1 atm), more preferably in an open reactor, or at a pressure higher than ambient, more preferably in an autoclave.

[0058] Substep 2a) optionally occurs in the presence of a solvent selected from organic solvent, water and a mixture of the two.

[0059] Preferably said solvent is a binary mixture of solvents selected from tetrahydrofuran / water, 1 ,4-dioxane / water, propionitrile / water, aceton itrile / water. Among these, the aceton itrile / water mixture is preferred. Preferably said solvent, if present, is used in an amount in the range from 5 to 200 volumes. In a preferred and advantageous embodiment of the invention, step 2a) of oxidation reaction is performed as follows.

[0060] 1 mole of compound (XXI), i.e. protected adenosine, is reacted with an oxidizing mixture, i.e. an amount in the range from 0.001 to 2 moles of catalytic oxidant and an amount from 1 to 200 moles of stoichiometric oxidant. Preferably such catalytic oxidant comprises from 0.01 to 0.8 moles of 2,2,6,6-tetramethylpiperidine 1 -oxyl radical (TEMPO) while such stoichiometric oxidant comprises from 2 to 20 moles of stoichiometric (diacetoxyiodo)benzene (PIDA).

[0061] In the preferred and advantageous embodiment of step 2a) of the invention, the order of addition of the reagents may also be different from that indicated above.

[0062] In an advantageous embodiment of the invention, step 2) of oxidation provides for further substeps, as reported below, before execution of step 3).

[0063] At the end of substep 2a), the process of the invention comprises a substep 2b) of cooling and filtration, wherein the reaction mixture containing the carboxylic acid (XXII) obtained from step 2a) is cooled and the resulting suspension is filtered under vacuum.

[0064] At the end of substep 2b), the process provides for substep 2c) wherein the filtrate obtained from substep 2b) is triturated 1 -5 times with an amount in the range from 1 to 100 volumes of an organic solvent, preferably selected from the group consisting of a protic organic solvent, an aprotic solvent or mixtures thereof, more preferably it is selected from the group consisting of an alcohol, an ether, an ester, a carboxylic acid, an aliphatic hydrocarbon and an aromatic hydrocarbon, and binary or ternary mixtures of solvents or solvents / water, even more preferably it is diisopropyl ether.

[0065] In a further step 2c) the filtrate obtained from step 2b) is then dried, preferably under vacuum, more preferably at a temperature in the range from 30 to 60 °C, to obtain the carboxylic acid (XXII) with a yield equal to or greater than 90%, and a purity equal to or greater than 90%.

[0066] In the preferred and advantageous embodiment, wherein Ri and R2 are methyl, step 2) allows to obtain the compound (3aS,4S,6R,6aR)-6-(6-amino-9H-purin-9-yl)-2,2- dimethyltetrahydrofuro[3,4-d][1 ,3]dioxolan-4-carboxylic acid. Step 3) consists in amidating the carboxylic acid (XXII) with methylamine after activation by a chlorinating agent to give (XXIII)

[0067] Step 3) comprises 2 substeps:

[0068] 3a) chlorinating the carboxylic acid by activating it with a chlorinating agent;

[0069] 3b) carrying out a nucleophilic acyl reaction with methylamine on the chlorinated carboxylic acid.

[0070] Substep 3a) consists of a chlorination reaction of the carboxylic acid by using a chlorinating agent, preferably selected from the group consisting of oxalyl chloride, thionyl chloride and phosphoryl chloride. In a preferred embodiment, the chlorinating agent is in a mixture with N,N-dimethylformamide (DMF), in a catalytic amount. In this preferred embodiment, the chlorinating agent is in a stoichiometric or (supra)stoichiometric amount with respect to the carboxylic acid.

[0071] Step 3a) of chlorination occurs more preferably in the presence of a chlorinating mixture comprising a catalytic amount of DMF in the range of 0.001 -2 eq and a (supra)stoichiometric amount of chlorinating reagent selected from the group consisting of oxalyl chloride, thionyl chloride and phosphoryl chloride in the range of 1 -50 eq., more preferably in the range of 1 -10 eq.

[0072] Substep 3a) occurs preferably at ambient pressure (1 atm), more preferably in an open reactor, or at a pressure higher than ambient, more preferably in an autoclave, and may optionally be carried out in an inert environment, preferably in a nitrogen or argon atmosphere.

[0073] Said substep 3a) optionally occurs in the presence of an organic solvent. Preferably, said organic solvent is selected from the group consisting of toluene, acetonitrile, THF and mixtures thereof, more preferably it is toluene. Preferably said organic solvent, if present, is used in an amount in the range from 5 to 200 volumes. In a preferred and advantageous embodiment of the invention, step 3a) of chlorination reaction is carried out as follows.

[0074] 1 mole of carboxylic acid (XXII) is reacted with a chlorinating agent corresponding to a chlorinating mixture comprising a catalytic amount of N,N-dimethylformamide (DMF) in the range from 0.01 to 0.8 moles, and an amount of chlorinating reagent, preferably thionyl chloride in an amount in the range from 1 to 10 moles.

[0075] In the preferred and advantageous embodiment of step 3a) of the invention, the order of addition of the reagents may also be different from that indicated above. When the activation of the carboxylic acid is not carried out telescopically to the nucleophilic acyl substitution, the reaction mixture containing the chlorinated carboxylic acid obtained in substep 3a) is dried under vacuum at a temperature in the range from 20 to 80 °C and the residue is taken up in the solvent of the subsequent nucleophilic acyl substitution reaction. Said solvent is preferably toluene.

[0076] Substep 3b) consists of the amidation reaction, i.e. the nucleophilic acyl substitution reaction with methylamine.

[0077] In a preferred embodiment, substep 3b) occurs in the presence of a mixture comprising anhydrous methylamine or dissolved in an organic solvent in a concentration in the range of 0.01 -20 M, and optionally an organic base, preferably a tertiary or secondary amine, more preferably a tertiary amine, in a catalytic or supra-stoichiometric amount.

[0078] Substep 3b) optionally occurs in the presence of an organic solvent. Preferably said organic solvent is selected from the group consisting of toluene, acetonitrile, THF and mixtures thereof, preferably acetonitrile. Preferably said organic solvent, if present, is used in an amount in the range from 5 to 200 volumes.

[0079] Step 3b) preferably occurs at ambient pressure (1 atm), more preferably in an open reactor, or at a pressure higher than ambient pressure, more preferably in an autoclave, and can optionally be carried out in an inert environment, preferably in a nitrogen or argon atmosphere.

[0080] In a preferred and advantageous embodiment of the invention, step 3b) of protection reaction is performed as follows. 1 mole of carboxylic acid activated as acyl chloride obtained in step 3a) is reacted with methylamine, preferably in the range of 1-100 moles, in the form of a solution in THF at a concentration of 0.01 -5 M, in the presence of an organic base, preferably triethylamine in amounts in the range of 0.1 -20 moles.

[0081] As soon as the nucleophilic acyl substitution reaction is completed, the process of the invention comprises a further substep 3c) wherein the solution obtained in substep 3b) is washed with an inorganic base aqueous solution, preferably NaHCOs, in an amount in the range from 10 to 200 volumes, and then optionally with a NaCI aqueous solution in an amount in the range from 10 to 200 volumes.

[0082] In a preferred embodiment, 1 to 5 back-extractions of the intermediate aqueous phases are carried out with an organic solvent, preferably dichloromethane.

[0083] Said organic solvent is removed, preferably under vacuum, at a temperature in the range from 20 to 100 °C, more preferably from 30 to 60 °C, to obtain the crude amide (XXIII).

[0084] In a subsequent substep 3d), the obtained crude amide (XXIII) is triturated 1 -5 times at a temperature in the range from -20 to 150 °C with a solvent selected from the group consisting of acetonitrile, acetone, methanol, ethanol, diisopropyl ether, preferably it is acetonitrile.

[0085] Once trituration is completed, the reaction mixture containing the amide (XXIII) is filtered, preferably under vacuum.

[0086] In a further substep 3e), the reaction mixture containing the crushed amide (XXIII) obtained in substep 3d), is dried, preferably under vacuum, at a temperature in the range from 20 to 100 °C, more preferably from 30 to 60 °C, to obtain the amide (XXIII) with a yield greater than or equal to 90%, and a purity greater than or equal to 90%.

[0087] In the preferred and advantageous embodiment, wherein Ri and R2 are methyl, step 3) allows to obtain (3aS,4S,6R,6aR)-6-(6-amino-9H-purin-9-yl)-N,2,2- trimethyltetrahydrofuro[3,4-d][1 ,3]dioxolan-4-carboxamide (XXIII).

[0088] Step 4) consists in the conversion of the amide (XXIII) into the protected benzylamine, compound (XXVI), and comprises 2 substeps: a) synthesizing diastereoisomeric N,O-aminals (XXIV) + (XXV); b) reducing the O-C bond.

[0089] Substep 4a) consists of the synthesis of the diastereoisomeric N,O-aminals (XXIV) + (XXV) using 3-iodobenzaldehyde (XIV), preferably in an amount of 1-5 eq, a linear or branched alkyl chain alcohol with R3OH structure, wherein R3 is an alkyl, preferably it is ethanol, a trialkyl orthoformate with linear or branched alkyl chains, and a Brdnsted acid, preferably selected from mineral, (organo)sulfonic and carboxylic acids, such as acetic acid.

[0090] In step 4b) of reduction of the O-C bond, a combination of a hydride source (H- donor) and a Lewis acid (LA) is used.

[0091] The hydride donor is a compound containing a X-H bond, wherein X is B, Al or Si. When X is B or Al, the hydride donor is a metal borohydride or aluminum hydride. When X is Si, the H-donor is a silane.

[0092] LA is any Lewis acid, (in the preferred and advantageous procedure a Lewis acid boron halide, e.g., BF3) with structure XY, wherein Y is a metal, semimetal or metalloid, and Z is selected from a halogen, preferably chlorine and iodine, tosylate, triflate and mesylate. In some examples, the Lewis acid (LA) may be a Lewis adduct with an organic solvent selected from the group consisting of diethyl ether, diisopropyl ether, THF, MTBE, 2-MeTHF, EtOH, MeOH, IPA, ethylene glycol.

[0093] Both steps 4a) and 4b) can be carried out at ambient pressure, for example in an open reactor, or at a pressure higher than ambient, for example in an autoclave.

[0094] In the step of synthesis of diastereoisomeric N,O-aminals (XXIV) + (XXV), 3- iodobenzaldehyde (XIV) is used in an amount of 1 -5 eq, also used are a linear or branched alkyl chain alcohol with structure R3OH, wherein R3 is an alkyl, preferably it is ethanol, a trialkyl orthoformate with linear or branched alkyl chains, and a Brdnsted acid, preferably selected from mineral, (organo)sulfonic and carboxylic acids, such as acetic acid. According to a preferred and advantageous version, the process for the synthesis of N,O-aminals is carried out as follows. The order of addition of the raw materials may also be different from that reported below.

[0095] 1 mole of amide (XXIII) is reacted with 1 -5 eq of 3-iodobenzaldehyde (XIV), preferably 1-3 moles, and an alcohol, in the presence of a Brdnsted acid, preferably 0.01 -1 moles of acetic acid, and a trialkyl orthoformate, preferably 1 -50 moles of triethyl orthoformate.

[0096] When the reaction is carried out in the presence of solvent, 5-200 volumes of the latter are used.

[0097] In a further substep 4c), subsequent to substep 4b), when the reduction reaction is completed, the volatile components are removed from the reaction mixture containing the amide (XXIII), under vacuum, at a temperature in the range of 20- 100 °C, preferably 30-60 °C, to obtain the mixture of crude N,O-aminals (XXIV) + (XXV).

[0098] Optionally, the mixture of N,O-aminals (XXIV) + (XXV) can be purified by reversed phase chromatography (C18) using a mixture of water and acetonitrile as the eluent phase.

[0099] According to a preferred and advantageous version, the process of reduction of the N,O-aminals is performed as follows. The order of addition of the raw materials may also be different from that reported below.

[0100] 1 mole of N,O-aminals (XXIV) + (XXV) is reacted with an H-donor, preferably 1 -10 moles of triethylsilane, and a Lewis acid, preferably 0.1 -10 moles of boron trifluoride THF complex. Once the reaction is completed, in substep 4d), the reaction mixture containing the protected benzylamine (XXVI) is diluted with an organic solvent selected from the group consisting of dichloromethane, toluene, ethyl acetate, 2- MeTHF, isopropyl acetate, diisopropyl ether, and MTBE, preferably dichloromethane. Subsequently, according to the invention, the resulting solution was then preferably washed with an inorganic base aqueous solution, preferably NaHCOs in substep 4e), and optionally with a NaCI aqueous solution. Typically, it is necessary to perform 1 -5 back-extractions of the intermediate aqueous phases with one of the organic solvents listed above. After washing, the solvent was removed preferably under vacuum at 20-100 °C, preferably 30-60 °C, to obtain the crude benzylamine (XXVI).

[0101] The crude compound (XXVI) thus obtained was treated by substep 4e) of 1-5 times crystallization from an organic solvent, or a binary or ternary mixture of different organic solvents, with or without water (in the preferred and advantageous procedure the preferable solvent for crystallization is MeOH).

[0102] According to the invention, a drying step is then preferably carried out, preferably under vacuum, to obtain the protected benzylamine (XXVI) with a yield equal to or greater than 90%, and a purity equal to or greater than 95%.

[0103] Step 5) consists in the deprotection of the vicinal diol of compound (XXVI) in an acidic medium to give Piclidenoson (I)

[0104] Step 5) of deprotection comprises a substep 5a) of deprotection reaction preferably with a Brdnsted acid selected from the group consisting of hydrochloric acid, hydrobromic acid, p-toluenesulfonic acid and methanesulfonic acid, more preferably hydrochloric acid and further substeps to obtain Piclidenoson (I).

[0105] Substep 5a) of deprotection reaction preferably occurs at ambient pressure (1 atm), more preferably in an open reactor, or at a pressure higher than ambient, more preferably in an autoclave.

[0106] Substep 5a) optionally occurs in the presence of an organic solvent. Preferably said organic solvent is selected from the group consisting of water, acetonitrile, tetrahydrofuran, 1 ,4-dioxane, N,N-dimethylformamide, acetic acid, ethanol and methanol, more preferably it is acetonitrile. Preferably said organic solvent, if present, is used in an amount in the range from 5 to 200 volumes.

[0107] In a preferred and advantageous embodiment of the invention, step 5a) of deprotection reaction is carried out as follows. 1 mole of protected benzylamine (XXVI) is reacted with a mixture of aceton itrile / water in the presence of a Brdnsted acid selected from the group consisting of hydrochloric acid, hydrobromic acid, p-toluenesulfonic acid and methanesulfonic acid, preferably hydrochloric acid in an amount in the range from 0.1 to 10 moles.

[0108] In the preferred and advantageous embodiment of step 5a) of the invention, the order of addition of the reagents may also be different from that indicated above.

[0109] In an advantageous embodiment of the invention, step 5) of deprotection provides for further substeps, as reported below, before obtaining Piclidenoson (I).

[0110] In an advantageous embodiment of the invention, the process of the invention comprises a step 5b) further to step 5a) wherein the volatile components are preferably removed under vacuum, and the crude Piclidenoson is obtained as a residue. Optionally, dilution in an organic solvent and aqueous washing can be carried out before this step.

[0111] The last step provides for the crude Piclidenoson be crystallized 1-5 times from an organic solvent or a binary or ternary mixture, preferably selected from the group consisting of water, methanol, ethanol, tetrahydrofuran, acetonitrile, water / MeOH, THF / ACN / water, water / EtOH and mixtures thereof, more preferably a water / EtOH mixture.

[0112] The crystallized crude Piclidenoson is then dried, preferably under vacuum, at a temperature in the range from 20 to 100 °C, preferably from 30 to 60 °C, to obtain Piclidenoson (I) with a yield equal to or greater than 90%, and a purity equal to or greater than 99%.

[0113] In another aspect, the invention concerns the diastereoisomeric mixture of the compounds of formula (XXIV) and (XXV) where Ri , R2 e R3, each independently from the other, are an alkyl.

[0114] The inventors of the present invention, therefore, through a new operating sequence and, in particular, through the formation of the diastereoisomeric mixture of N,O- aminals, succeeded in obtaining a new process for the synthesis of Piclidenoson that is cost-effective, potentially scalable and high yielding as will be apparent from the experimental part.

[0115] The invention will now be exemplified with reference to examples of preparation of Piclidenoson (I) of the invention by way of example and not limitation.

[0116] EXPERIMENTAL PART

[0117] Example 1 : Synthesis of Piclidenoson (I)

[0118] Example 1.1: Synthesis of ((3aR,4R,6R,6aR)-6-(6-amino-9H-purin-9-yl)-2,2- dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-il)methanol

[0119] A 5 L glass reactor equipped with a mechanical stirrer was charged with acetone (2 L), adenosine (100.00 g, 274.00 mmol, 1 eq), p-toluenesulfonic acid (77.60 g, 452.00 mmol, 1.21 eq), and 2,2-dimethoxypropane (180.0 mL, 1469.00 mmol, 5.36 eq) under a nitrogen atmosphere. The resulting suspension was stirred at 250 rpm for 48 h at room temperature. After this period, a 10% NaOH solution (200 mL) was added to achieve a pH of about 8. The resulting mixture was concentrated under vacuum to about 10 volumes and filtered under vacuum. The filtered solid was washed with ice-cold water (100 mL). Finally, the solid was dried under vacuum at 40 °C. The product was obtained with a molar yield of 90%, and a purity of 85% (qNMR).

[0120] Example 1.2: Synthesis of (3aS,4S,6R,6aR)-6-(6-amino-9H-purin-9-yl)-2,2- dimethyltetrahydrofuro[3,4-d][1,3]dioxolan-4-carboxylic

[0121] A 1 L glass reactor equipped with a mechanical stirrer was charged with acetonitrile (150 mL), water (150 mL), ((3aR,4R,6R,6aR)-6-(6-amino-9H-purin-9-yl)-2,2- dimethyltetrahydrofuro[3,4-d][1 ,3]dioxol-4-yl)methanol (46.10 g, 150.00 mmol, 1 eq), PIDA (106.30 g, 330.00 mmol, 2.2 eq), and TEMPO (9.37 g, 60.00 mmol, 0.4 eq). The resulting mixture was stirred at 400 rpm for 24 h at room temperature. After this period, the suspension was filtered under vacuum, and the solid was triturated twice with diisopropyl ether (2 x 450 mL). Finally, the solid was dried under vacuum at 40 °C. The product was obtained with a molar yield of 95%, and a purity of 99%

[0122] (qNMR).

[0123] Example 1.3: Synthesis of (3aS,4S,6R,6aR)-6-(6-amino-9H-purin-9-yl)-N,2,2- trimethyltetrahydrofuro[3,4-d][1,3]dioxolan-4-carboxamide

[0124] A 250 mL glass reactor equipped with a magnetic stirrer was charged with toluene (85 mL), (3aS,4S,6R,6aR)-6-(6-amino-9H-purin-9-yl)-2,2- dimethyltetrahydrofuro[3,4-d][1 ,3]dioxolan-4-carboxylic acid (2.00 g, 6.20 mmol, 1 eq), DMF (22.5 mg, 0.31 mmol, 0.05 eq) and thionyl chloride (1.98 g, 16.50 mmol, 2.66 eq) under an inert nitrogen atmosphere. The resulting mixture was heated to 70 °C (external temperature) and stirred at 500 rpm for 4 h. After this period, the mixture was dried under vacuum at 45 °C. The crude was taken up in acetonitrile (21 mL) and cooled to 0 °C. Triethylamine (1.16 g, 11.46 mmol, 1.85 eq) and a 3.3 M solution of methylamine in THF (6.0 mL, 20.00 mmol, 3.2 eq) were added to the resulting suspension. The resulting mixture was stirred at 500 rpm for 15 min. After this period, a 5% NaHCOs solution (25 mL) was added, and the resulting mixture was extracted four times with dichloromethane (4 x 20 mL). After removal of the volatile components under vacuum at 40 °C, the crude product was triturated once with acetonitrile (5 mL). The product was obtained with a molar yield of 92%, and a purity of 98% (qNMR).

[0125] Example 1.4: Synthesis of (3aS,4S,6R,6aR)-6-(6-((3-iodobenzol)amino)-9H- purin-9-yl)-N,2,2-trimethyltetrahydrofuro[3,4-d][1,3]dioxolan-4-carboxamide A 250 mL glass reactor equipped with a magnetic stir bar was charged with ethanol (28 mL), (3aS,4S,6R,6aR)-6-(6-amino-9H-purin-9-yl)-N,2,2- trimethyltetrahydrofuro[3,4-d][1 ,3]dioxolan-4-carboxamide (2.82 g, 8.43 mmol, 1 eq), triethyl orthoformate (4.21 g, 28.08 mmol, 3.33 eq), acetic acid (126 mg, 2.10 mmol, 0.25 eq), and 3-iodobenzaldehyde (2.01 g, 8.42 mmol, 1 eq). The resulting mixture was brought to reflux and stirred at 600 rpm for 72 h. After this period, it was dried under vacuum at 45 °C. The crude was taken up with dichloromethane (100 mL) and cooled to -10 °C. Triethylsilane (1.80 g, 16.86 mmol, 2.00 eq) and boron trifluoride THF complex (2.38 g, 16.86 mmol, 2.00 eq) were added to the resulting mixture. The resulting solution was stirred at 600 rpm for 1 h. After this period, a 5% NaHCOs solution (25 mL) was added, and the resulting mixture was extracted twice with dichloromethane (2 x 20 mL). After removal of the volatile components under vacuum at 40 °C, the crude product was crystallized from 10 volumes of MeOH. The product was obtained with a molar yield of 91 %, and a purity of 99% (qNMR).

[0126] Example 1.5: Synthesis of (2S,3S,4R,5R)-3,4-dihydroxy-5-(6-((3- iodobenzyl)amino)-9H-purin-9-yl)-N-methyltetrahydrofuran-2-carboxamide

[0127] A 100 mL glass reactor equipped with a magnetic stir bar was charged with acetonitrile (10 mL), (3aS,4S,6R,6aR)-6-(6-((3-iodobenzol)amino)-9H-purin-9-yl)- N,2,2-trimethyltetrahydrofuro[3,4-d][1 ,3]dioxolan-4-carboxamide (1.00 g, 1.82 mmol, 1 eq), and 1 N HCI aqueous solution (13 mL). The resulting mixture was stirred at 600 rpm for 4 h at 50 °C. After removal of the volatile components under vacuum at 40 °C, the crude product was crystallized from 5 volumes of water and 5 volumes of EtOH. The product was obtained with a molar yield of 98% and a purity of 99.95% (qNMR).

Claims

CLAIMS1 . A process for the synthesis of Piclidenoson (I) comprising the following steps:1 ) protecting the compound adenosine (II) in the presence of a ketone of formula (XXVII) or a ketal of formula (XXVIII)wherein R1, R2, R4, Rs, each independently from the other, are an alkyl, thus obtaining the compound (XXI)2) oxidizing the primary alcohol of compound (XXI) with an oxidizing agent to give the carboxylic acid (XXII)3) amidating the carboxylic acid (XXII) with methylamine, after activation by a chlorinating agent, to give (XXIII) / . chlorinating agentA methylaminexxit4) reacting the compound (XXIII) with 3-iodobenzaldehyde (XIV), a linear or branched alkyl chain alcohol with structure R3OH, and a trialkyl orthoformate with linear or branched alkyl chains to obtain the diastereoisomeric mixture (XXIV) +(XXV), which is subjected to a reduction reaction with a reducing mixture comprising an H-donor compound and a Lewis acid (LA) to give the compound (XXVI)where R3 is an alkyl5) deprotecting the compound (XXVI) in an acidic medium to give Piclidenoson (I)2. The process according to claim 1 , wherein Ri, R2, R3, R4, Rs, each independently from the other, are selected from methyl and ethyl.

3. The process according to any one of claims 1 and 2, wherein step 1 comprises a substep 1 a) of protection and a substep 1 b) of treatment, subsequent to substep 1 a), at a temperature in the range from 0 to 40 °C, preferably 15-25°C, followed by the addition of an inorganic base aqueous solution.4 The process according to any one of claims 1 and 3, wherein in step 2) an oxidizing mixture is employed, comprising a stoichiometric oxidizing agent preferably selected from the group consisting of (diacetoxyiodo)benzene (PIDA), sodium periodate, N- methylmorpholine-N-oxide (NMO), (bis(trifluoroacetoxy)iodo)benzene (PIFA), 2- iodoxybenzoic acid (IBX) and mixtures thereof, more preferably in the presence of a catalyst selected from 2,2,6,6-tetramethylpiperidine 1 -oxyl radical (TEMPO), 9- azabicyclo[3.3.1]nonan-N-oxyl (ABNO), ruthenium trichloride, 2-azaadamantane-N- oxyl (AZADO), more preferably the catalyst is 2,2,6,6-tetramethylpiperidine 1 -oxyl radical (TEMPO).

5. The process according to any one of claims 1 and 4, wherein step 3) comprises the following substeps:3a) chlorinating the carboxylic acid through activation of the same with a chlorinating agent selected from the group consisting of oxalyl chloride, thionyl chloride and phosphoryl chloride, preferably in a mixture with N,N-dimethylformamide (DMF), in a catalytic amount;3b) carrying out a nucleophilic acyl reaction with methylamine on the chlorinated carboxylic acid, said nucleophilic acyl substitution preferably occurs in the presence of a base, more preferably a tertiary amine.

6. The process according to any one of claims 1 to 5, wherein step 4) comprises- a substep 4a) of synthesis of the diastereoisomeric N,O-aminals (XXIV) and (XXV) by using 3-iodobenzaldehyde (XIV), preferably in an amount of 1 -5 eq, with a linear or branched alkyl chain alcohol with structure R3OH, wherein R3 is an alkyl, preferably it is ethanol, a trialkyl orthoformate with linear or branched alkyl chains, and a Brdnsted acid, preferably selected from mineral, (organo)sulfonic and carboxylic acids such as acetic acid;- a substep 4b) of reduction with a combination of a hydride source (H-donor) containing a X-H bond, wherein X is B, Al or Si, and a Lewis acid (LA) with structure XY, wherein Y is a metal, semimetal or metalloid and Z is selected from a halogen, preferably chlorine and iodine, tosylate, triflate and mesylate.

7. The process according to any one of claims 1 to 6, wherein step 5) of deprotection occurs by means of a Brdnsted acid selected from the group consisting of hydrochloric acid, hydrobromic acid, p-toluenesulfonic acid and methanesulfonic acid, more preferably hydrochloric acid.

8. A diastereoisomeric mixture of the compounds of formula (XXIV) and (XXV)where R1, R2 and R3, each independently from the other, are an alkyl.

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