Velpatasvir intermediate -II-RS isomer

Velpatasvir intermediate -II-RS isomer is a stereoisomeric byproduct arising during the synthesis of the antiviral agent velpatasvir. It features a pyridine-linked tetrahydrothiophene core with a (R,S)-configured chiral center at the thiomorpholine moiety, differing from the parent drug's (S,R) configuration. The compound retains key functional groups, including a 4-aminopyridine and a thiomorpholine-1,1-dioxide, but exhibits altered stereochemistry that reduces its pharmacological activity. This isomer serves as a critical HPLC reference standard for quantifying enantiomeric impurities in velpatasvir active pharmaceutical ingredients.