Patent ID: 8350030

Claim:
An improved process for producing 5-Fluoro-1-(2R,5S)-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine of Formula I and its pharmaceutically acceptable salts, the process comprising the steps of: a. reducing the compound (2R,5S)-5-(4-Amino-5-fluoro-2-oxo-2H pyrimidin-1-yl)-[1,3]-oxathiolane-2-carboxylic acid, 2S-isopropyl-5R-methyl-1R-cyclohexyl Ester) of Formula II employing a reducing agent; to obtain the compound (2R-Cis)-2-hydroxymethyl-5-(5 fluoro cytosine-yl)-1,3-oxathiolane of Formula III; b. followed by in_situ salification of compound (2R-Cis)-2-hydroxymethyl-5-(5′fluoro cytosine-1′-yl)-1,3-oxathiolane of Formula III employing a mineral acid or sulfonic acid in presence of an organic solvent to give compound (2R-Cis)-2-hydroxymethyl-5-(5′fluoro cytosine-1′-yl)-1,3-oxathiolane salt of Formula IV, wherein X is mineral acid or sulfonic acid; and c. neutralizing the compound of Formula IV employing an organic solvent in presence of an organic amine base to obtain 5-Fluoro-1-(2R,5S)-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine of Formula I.