Field Desorption Mass Spectrometry of Physiologically Active Steroid- and Dammarane-Saponins *

Natural Products, Physiologically Active Saponins, Sequencing of Underivatized Oligoglycosides, Field Desorption Mass Spectrometry The use of field desorption mass spectrometry is demonstrated not only for molecular weight determination but also for detailed structural analysis of large, underivatized natural products. Owing to cationization by small alkali salt impurities, saponins carrying one to four sugar units gave abundant quasimolecular ions. In addition, the observed sequence-specific fragment ions reflected the complete sequence of the sugar units in the oligoglycosides. This fragmentation of the oligosaccharidic moiety of the natural products was interpreted by analogy with acidic solvolysis, a mechanism well established in solution chemistry. O f particular interest was a first com­ parison of the field desorption mass spectra obtained from two different commercially available instruments operated by different groups in order to give an estimate of interlaboratory repro­ ducibility in field desorption mass spectrometry.