Liquid chromatographic analysis, stability and protein binding studies of the anti-HIV agent benzoic acid, 2-chloro-5[[(1-methylethoxy)thioxomethyl]amino]-,1-methylethyl ester

A method was developed for the assay of benzoic acid, 2-chloro-5-[[(1-methylethoxyl)thioxomethyl]amino]-, 1-methylethyl ester (NSC 629243) in hamster, mouse, human and, to a limited extent, dog plasma. Protein in 0.5 ml of plasma was precipitated with four volumes of methanol and the supernatant was analysed for NSC 629243 by LC. Liquid chromatography was carried out on a reversed-phase Nova-Pak C 18 column, with a mobile phase of 60% acetonitrile in water at 1 ml min −1, and the compound was quantified with a UV detector set at 283 nm. Two standard curves of NSC 629243 were needed to cover a concentration range of 0.05–100 μg ml −1. All standard curves had correlation coefficients >x0.999. In practice, the minimum quantifiable concentration was approximately 0.05 μg ml −1 in 0.5 ml of plasma. NSC 629243 appeared to have good stability at 37°C in hamster, human and dog plasma at concentrations of 1 and 50 μg ml −1 (at least 80% remained in plasma after a 4 h incubation). Breakdown occurred in mouse plasma after 1 h at 37°C, with extensive breakdown occurring after 24 h. NSC 629243 was extensively bound to plasma proteins of Syrian hamsters and humans. The extent of binding ranged from a minimum of 88.6% to a maximum of 99.9% over a concentration range of ca 1–100 μg ml −1.