Authors: Tao Zhuang Guohai Wang Xiaohong Cui Yin Chen Liang Chen Guisen Zhang
Publish Date: 2016/05/28
Volume: 79, Issue: 15-16, Pages: 1041-1047
Abstract
Flupirtine is well accepted as a centrally acting nonopioid analgesic with a favorable tolerability During the stability study of flupirtine maleate drug product an unknown degradation product referred to as DPI exceeding the identification threshold was detected by gradient reverse phase HPLC method To obtain this unknown impurity the drug product was subjected to stress to enhance the level of DPI Furthermore DPI and three other thermal degradants referred to as DPII DPIII and DPIV respectively were isolated by preparative HPLC An isocratic preparative HPLC method was developed with a Welch Xtimate C18 column 250 mm × 30 mm 5 µm and the mobile phase composed of acetonitrile and 025 ammonium hydroxide in water 7030 v/v The flow rate was 200 mL min−1 and the chromatographic experiments were conducted at room temperature UV detection was carried out at 252 nm Based on 1DNMR 2DNMR and LC–MS spectral data the structures of two novel degradation products were confirmed as diethyl 54fluorobenzylamino2oxo1Himidazo45bpyridine132Hdicarboxylate for DPI and ethyl 234dimethyl25dioxo25dihydro1Hpyrrol1yl64fluorobenzylaminopyridin3ylcarbamate for DPII Moreover the degradation mechanism from flupirtine maleate to DPI and DPII was also proposed
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