The present invention provides processes for preparing intermediates
useful in the preparation of gemcitabine and other nucleosides, and
processes for preparing gemcitabine therewith. Exemplary intermediates
include mixtures of D-erythro and D-threo isomers of
3-(hydroxy)-2,2-difluoro-3-(2,2-dimethyldioxolan-4-yl)-propionic acid
salts. Also provided is a process for selectively isolating the D-erythro
and D-threo isomers of D-erythro and D-threo isomers of
3-(hydroxy)-2,2-difluoro-3-(2,2-dimethyldioxolan-4-yl)-propionic acid
salts, and processes for using such isomers in the preparation of
nucleoside analogs such as, e.g., gemcitabine, intermediates thereof, and
analogs thereof.