Structural validation of saccharomicins by high resolution and high mass accuracy Fourier transform-ion cyclotron resonance-mass spectrometry and infrared multiphoton dissociation tandem mass spectrometry

Exceptionally high mass resolving power and mass accuracy combined with tan dem mass spectrometry (MSn) capability make Fourier transform ion cyclotron resonance mass spectrometry a powerful tool for structure verification and determination of biological macromolecules. By means of local internal cal ibration and electron mass correction, mass accuracy better than +/-0.5 ppm was achieved for two oligosaccharide antibiotics, Saccharomicins A and B, consistent with the proposed elemental compositions based upon NMR data. Hi gh resolution and high mass accuracy MS/MS data were obtained for both olig osaccharides by use of infrared multiphoton dissociation (IRMPD) with a 40 W continuous-wave CO2 laser. The spectra were charge-state deconvolved by t he "Z-score" algorithm to yield much simpler mass-only spectra. Sequences o f 15 sugar residues could be confirmed from the charge state deconvolved ac curate mass MS/MS spectra for Saccharomicins A and B, even without use of t raditional prior permethylation. A fragment corresponding to an internal su gar loss rearrangement was observed by IRMPD and studied by collision activ ated dissociation MS4. (C) 1999 American Society for Mass Spectrometry.