Elucidation of a Novel Bioactivation Pathway of 3,4-Unsubstituted Isoxazole by Mass Spectrometry

摘要

Scheme 1 shows the proposed bioactivation pathway for compound A. The 3-unsubstituted isoxazole moiety underwent a concerted beta-elimination involving enzymecatalyzed deprotonation followed by N-O bond cleavage, which resulted in a 3-hydroxyacrylonitrile product (M1). When the 4-position of the isoxazole ring was also unsubstituted, the corresponding hydroxyacrylonitrile intermediate condensed with formaldehyde to generate an electrophilic intermediate (I), which further reacted with nucleophilic GSH to yield the final GSH conjugate (M2). ~(13)C labeled methanol was used to confirm the incorporation of a CH_(2) moiety from formaldehyde (which was generated through enzyme catalyzed oxidation of methanol) in the metabolite.