合成路线1

A new synthesis of clevudine has been described: Peracetylation of L-arabinose (I) with acetic anhydride and pyridine provides acetylated arabinose (II), which is then brominated by means of HBr in AcOH/Ac2O to furnish the bromo-sugar (III). Treatment of the sugar (III) with Zn dust, CuSO4 and NaOAc in AcOH/H2O, followed by chromatographic separation, gives L-arabinal (IV), which is then converted to the fluoro derivative (V) by reaction with Selectfluor?(F-TEDA-BF4) in refluxing nitromethane/H2O. Deacetylation of compound (V) with NaOMe in MeOH yields compound (VI), which is then converted into the methyl furanoside (VII) by treatment with H2SO4 in MeOH. Benzoylation of the furanoside (VII) with benzoyl chloride in pyridine affords a mixture of isomers, from which (VIII) is separated by chromatography and then brominated with HBr/AcOH in CH2Cl2 to provide the bromo-sugar (IX). Condensation of the sugar (IX) with the silylated pyrimidine derivative (X) in refluxing chloroform affords 3,5-di-O-benzoylclevudine (XI), which is finally deprotected by treatment with n-butylamine in refluxing methanol. Compound (X) is obtained by treatment of thymine (XII) with HMDS (1,1,1,3,3,3-hexamethyldisilazane) and ammonium sulfate in refluxing chloroform.

合成路线2

The reaction of L-arabinose (I) with acetic anhydride and HBr gives tri-O-acetyl-b-L-arabinopyranosyl bromide (II), which is treated with Zn and Cu-Zn couple in aqueous AcOH to yield 3,4-di-O-acetyl-L-arabinal (III) (1). Reaction of compound (III) with HCl followed by treatment with refluxing methanol affords methyl 3,4-di-O-acetyl-2-deoxy-L-riboside (IV), which is deacetylated by means of NaOMe in methanol to provide methyl 2-deoxy-L-riboside (V). Reaction of riboside (V) with benzoic acid gives 2-deoxy-L-ribofuranose (VI), which, alternatively, can be obtained directly from diacetate (III) by treatment with aqueous HClO4 in AcOH/Ac2O. Reaction of ribofuranose (VI) with p-toluoyl chloride and methanol gives methyl 3,4-di-O-toluoyl-2-deoxy-L-riboside (VII), which is demethylated with HCl to yield 3,4-di-O-toluoyl-2-deoxy-L-ribose (VIII). Acylation of the ribose (VIII) with Ac2O and pyridine affords 1-O-acetyl-3,4-di-O-toluoyl-2-deoxy-L-ribose (IX), which is treated with HCl to provide the chloro-ribose (X). Condensation of compound (X) with thymine (XI) by means of HgCl2 and CdCO3 gives the acylated thymidine (XII), which is finally deacylated by treatment with NaOMe in methanol.

合成路线3