Identification of in‐vivo and in‐vitro metabolites of palmatine by liquid chromatography–tandem mass spectrometry

Objectives Despite its important therapeutic value, the metabolism of palmatine is not yet clear. Our objective was to investigate its in‐vivo and in‐vitro metabolism. Methods Liquid chromatography–tandem electrospray ionization mass spectrometry (LC‐ESI/MSⁿ) was employed in this work. In‐vivo samples, including faeces, urine and plasma of rats, were collected after oral administration of palmatine (20 mg/kg) to rats. In‐vitro samples were prepared by incubating palmatine with intestinal flora and liver microsome of rats, respectively. All the samples were purified via a C₁₈ solid‐phase extraction procedure, then chromatographically separated by a reverse‐phase C₁₈ column with methanol–formic acid aqueous solution (pH 3.5, 70: 30 v/v) as mobile phase, and detected by an on‐line MSⁿ detector. The structure of each metabolite was elucidated by comparing its molecular weight, retention time and full‐scan MSⁿ spectra with those of the parent drug. Key findings The results revealed that 12 metabolites were present in rat faeces, 13 metabolites in rat urine, 7 metabolites in rat plasma, 10 metabolites in rat intestinal flora and 9 metabolites in rat liver microsomes. Except for six of the metabolites in rat urine, the other in‐vivo and in‐vitro metabolites were reported for the first time. Conclusions Seven new metabolites of palmatine (tri‐hydroxyl palmatine, di‐demethoxyl palmatine, tri‐demethyl palmatine, mono‐demethoxyl dehydrogen palmatine, di‐demethoxyl dehydrogen palmatine, mono‐demethyl dehydrogen palmatine, tri‐demethyl dehydrogen palmatine) were reported in this work.