Identification of novel ondansetron metabolites using LC/MSn and NMR

Ondansetron, a potent and highly sensitive 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist, has been used for the treatment of chemotherapy- and radiotherapy-induced nausea and vomiting. The isolation and identification of ondansetron metabolites were investigated in our research. The feces and bile samples collected after oral administration of ondansetron were extracted and then isolated by semi-preparative HPLC. Then the pretreated samples were characterized by LC/MSn and NMR. In rats feces, a total of four metabolites were isolated and elucidated including 7-hydroxyl-ondansetron (M1), 8-hydroxyl-ondansetron (M2), 7-hydroxyl-N-desmethyl-ondansetron (M3), and 8-hydroxyl-N-desmethyl-ondansetron (M4). In addition, a kind of metabolite of phase II isolated in rats bile was characterized as N-desmethyl-ondansetron-7-O-β-D-glucuronide (M5). To our knowledge, three metabolites were reported for the first time. LC/MSn and NMR-based approach was proved to be useful for full structure elucidation of unknown metabolites. The systematic metabolites isolation and elucidation provided metabolite reference standards for metabolites detection of ondansetron.