Application of fast atom bombardment combined with tandem mass spectrometry to the structural elucidation of O-demethylabierixin and related polyether antibiotics.

O-Demethylabierixin, a new polyether antibiotic, was isolated from a Streptomyces spp. Its structure elucidation was carried out with fast atom bombardment mass spectrometry (FAB-MS) and fast atom bombardment mass spectrometry-mass spectrometry (FAB-MS/MS) by comparing spectral patterns with those of structurally similar polyether compounds, nigericin and abierixin. The collision-induced dissociation (CID) of sodium-adduct and deprotonated molecular ions produced many cyclic ether rings-opened product ions via a series of the dissociative processes. Because of the negative charge of the carboxylate group at the end of the molecule, the charge-remote fragmentation pattern in the negative CID spectra of deprotonated molecular ions was very helpful for complete identification of product ions which are characteristic for cyclic ether structures. From this study, the new polyether antibiotic was identified to be O-demethylabierixin in which the methoxy group of six-membered ether ring in abierixin was replaced by the hydroxy group.