A short-step chemo-enzymatic synthesis of a precursor for l-nucleosides from d-lyxose

A new chemo-enzymatic route to tetra-O-acetyl-l-ribofuranose from d-lyxose is described. Lipase-catalyzed regioselective transesterification of acetate proceeded on C-4 of the d-lyxopyranoside. Subsequently, stereochemistry of liberated secondary alcohol was inverted by way of oxidation and reduction by IBX and NaBH(OAc)3 to give l-ribopyranoside. After deprotection, the furanose–pyranose isomeric mixture was converged to the target molecule, taking advantage of lipase-catalyzed preferential acetylation of primary alcohol on C-5.