Negative ion multiple-stage mass spectrometric analysis of complex oligosaccharides (everninomicins) in a quadruple ion trap: implications for charge-remote fragmentation

Negative ion electrospray ionization (ESI) tandem mass spectrometry (MS/MS) by a quadrupole ion-trap has been utilized to characterize a class of complex oligosaccharide antibiotics (everninomicins), that includes everninomicin-D, SCH 27899, amino everninomicin (SCH 27900), and SCH 49088 containing a hydroxylamino-ether sugar. The deprotonated molecules are dominant ions in the negative ion ESI mass spectra of these compounds. The multiple-stage mass spectrometric analysis (MS n ) of these deprotonated species indicates that the negative charge resides in the deprotonated dichlorophenoxyl group in the substituted aromatic ester ring (ring 1) and the fragmentation occurs remote to this charge site in generating simple sugar sequence-specific fragment ions. One exception to this process is SCH 49088 in which the side chain of the hydroxylamino-ether sugar dominates fragmentation pathway in a charge-driven mechanism and results in less structural information.