Velpatasvir Intermediate-2 (RSS) isomer

Velpatasvir Intermediate-2 (RSS) isomer is a stereoisomeric precursor in the synthesis of the NS5A inhibitor velpatasvir, characterized by a (2R,3S,4S) configuration at its pyrrolidin-2-ylmethyl moiety. It retains the core 1,2,4-triazole-1-ylmethyl scaffold and a substituted phenyl ring, but features an inverted stereochemistry at the piperidine-4-ylmethyl side chain relative to the parent drug. This structural deviation arises from a kinetic resolution step during chiral auxillary-mediated synthesis, yielding a diastereomeric impurity. The compound serves as a critical HPLC reference standard for quantifying stereoisomeric impurities in velpatasvir active pharmaceutical ingredient batches.