NEGATIVE-ION ELECTROSPRAY TANDEM MASS-SPECTROMETRIC STRUCTURAL CHARACTERIZATION OF LEUKOTRIENE B-4 (LTB(4)) AND LTB(4)-DERIVED METABOLITES

The low energy collision induced dissociation (CTD) of the carboxylate anions generated by electrospray ionization of leukotriene B-4 (LTB(4 )) and 16 of its metabolites was studied in a tandem quadrupole mass s pectrometer. LTB(4) is a biologically active lipid mediator whose acti vity is terminated by metabolism into a wide variety of structural var iants. The collision-induced dissociation spectra of the carboxylate a nions revealed structurally informative ions whose formation was deter mined by the position of hydroxyl substituents and double bonds presen t in the LTB, metabolite. Major ions resulted from charge remote alpha -hydroxy fragmentation or charge directed alpha-hydroxy fragmentation. The conjugated triene moiety present in some metabolites was proposed to undergo cyclization to a 1,3-cyclohexadiene structure prior to cha rge remote or charge driven alpha-hydroxy fragmentation. The mechanism s responsible for all major ions observed in the CID spectra were stud ied using stable isotope labeled analogs of the LTB(4) metabolites. In general, the collision-induced decomposition of carboxylate anions pr oduced unique spectra for all LTB(4) derived metabolites. The observed decomposition product ions from the carboxylate anion could be useful in developing assays for these molecules in biological fluids.