Electrospray ionization multiple-stage tandem mass spectrometric analysis of diglycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus

Electrospray ionization (ESI) combined with multiple-stage tandem mass spec trometry (MSn) was used to directly analyze the glycolipid mixture from bac teria Bacillus pumilus without preliminary separation. Full scan ESI-MS rev ealed the composition of picomole quantities of glycerolglycolipid species containing C-14-C-19 fatty acids, some of which were monounsaturated, Two m ain components were identified from their molecular masses and fragmentatio n pathways. The fragmentation pathway of the known compound compared with t he investigated compound verified the proposed structure as 1(3)-acyl-2-pen tadecanoyl-3(1)-O-[beta-D-glucopyranosyl-(1-->6)-O-beta-D-glucopyranosyl]-s n-glycerols. A comparison of the multiple tandem mass spectra of the differ ent alkali-metal cation adducts indicates that the intensity of fragments a nd the dissociation pathways are dependent on the alkali-metal type, The ba sic structures of glycerolglycolipids were reflected clearly from the fragm entation patterns of the sodium cations, The intense fragments of the sugar residue from the precursor ions were obtained from the lithiated adduct io ns. ESI-MSn spectra of [M + K](+) ions did not provide as much fragmentatio n as [M + Na](+) and [M + Li](+) adducts, but their spectra allow the posit ion of glycerol acylation to be determined. On the basis of MS2 spectra of[ M + K](+) ions, it was established that all components have a C-15:0 fatty acid at the sn-2 position of the glycerol backbone and C-14-C-19 acids at t he sn-1 position of the glycerol backbone. Copyright (C) 1999 John Wiley & Sons, Ltd.