Preparation of alkyl-substituted 2-deoxy-2-fluoro-D-ribofuranosyl pyrimidines and purines and their derivatives

A method for the preparation of a 2′-deoxy-2′-fluoro-2′-C-methyl-β-D-ribofuranosyl nucleoside of the following formula:

• wherein the base is:
• wherein R2 and R4 are independently H, OH, NH2, or OR′;
• R′ is an optionally substituted straight, branched, or cyclic alkyl of C1-C12;
• Y is N or CH;
• the method comprising the following steps:
• (a) reacting a nucleoside intermediate of the following formula:
• wherein the protected base is the base protected by a protecting group, wherein the protecting group is benzoyl;
• wherein R3 and R5 are each independently tetrahydropyranyl, methyl, ethyl, benzyl, p-methoxybenzyl, benzyloxymethyl, phenoxymethyl, methoxymethyl, ethoxymethyl, mesyl, tosyl, trifluoroacetyl, or trichloroacetyl,
• with diethylaminosulfur trifluoride or bis(2-methoxyethyl)aminosulfur trifluoride to yield a fluorinated intermediate of the following formula:
• (b) deprotecting the R3 and R5 groups of the product of step (a) by treatment with a boron trihalide to yield an intermediate of the following formula:
• (c) saponifying the product of step (b) to yield the desired nucleoside.