Metabolite identification of arbidol in human urine by the study of CID fragmentation pathways using HPLC coupled with ion trap mass spectrometry.

The metabolism of arbidol in humans was studied using liquid chromatography-electrospray ionization (ESI) ion trap mass spectrometry (ITMS) after an oral dose of 300-mg arbidol. A total of 17 metabolites were identified including the glucuronide arbidol and the glucuronide sulfinylarbidol as the major metabolites. Arbidol and its metabolites have some common fragmentation patterns as a result of a homolytic bond cleavage. This cleavage will form odd-electron ions with the loss of a radical. The arbidol fragmentation sequence is first to lose dimethylamine (45 Da), followed by the loss of acetaldehyde (44 Da), and then the phenylthio radical (109 Da). This fragmentation sequence is also observed from N-demethylarbidol, sulfonylarbidol, and N-demethylsulfonylarbidol. However, for sulfinylarbidol and N-demethylsulfinylarbidol, the fragmentation sequence is reversed so that the phenylsulfiny radical (125 Da) was lost first, followed by the loss of dimethylamine (45 Da), and then acetaldehyde (44 Da). The exact masses for arbidol and sulfinylarbidol fragment ions were determined by a quadrupole/time-of-flight mass spectrometer (Q-TOF MS). The phase II metabolites, such as sulfate and glucuronide conjugates of arbidol, N-demethylarbidol, sulfonylarbidol, and N-demethylsulfonylarbidol were identified by observing the neutral loss of 80 Da (SO(3)) or 176 Da (glucuronic acid) from the MS(2) spectra. The sulfate and glucuronide conjugates such as sulfinylarbidol and N-demethylsulfinylarbidol had an unusual fragmentation pattern, in which the phenylsulfinyl radical (125 Da) was lost before the loss of SO(3) group (80 Da) or glucuronic acid (176 Da) occurred.