rilpivirine Z-isomer

Rilpivirine Z-isomer is a geometric isomer of the antiretroviral agent rilpivirine, characterized by a cis-configuration around the central pyrimidine-phenyl double bond. Its structure features a substituted pyridine ring linked to a pyrimidine core via a piperazine bridge, with the Z-configuration inducing distinct steric and electronic properties compared to the E-isomer. This isomer arises as a synthetic byproduct during rilpivirine production due to partial isomerization during double bond formation. The compound exhibits reduced pharmacological activity owing to altered conformational stability. This Z-isomer serves as an HPLC reference standard for quantifying isomer-specific impurities in rilpivirine drug substance analysis.