Application of Tandem Mass Spectral Approaches to Structural Determinations of Saponins
Structural determinations of saponins present challenges to the analyst because of the variety of potential modification sites, the incorporation of both carbohydrate and non-carbohydrate moieties, and the occurrence of mixtures that may include isomeric species and highly-active minor components. These quite daunting features of the research problem represent an excellent opportunity for effective application of new analytical methodologies. Tandem mass spectrometry is a particularly logical choice: advances in sample preparation, ionization methods and analyzer techniques can now lessen the sample requirements, shorten the analysis time and provide detailed structural information for individual mixture components. We are utilizing liquid secondary ionization, matrix-assisted laser desorption/ ionization and electrospray ionization in conjunction with high- and low-energy collision-induced decomposition and post-source decay tandem mass analysis to probe the structures of saponins with established biological activities. Methods developed with known compounds are then used for the structural elucidation of unknowns. In the work described here, structures of saponins from a cardivascular active Chinese medicine were determined first and the fragmentation information was used as a guide in the interpretation of the spectra from more complex saponins found in extracts of the bark of Quillaja saponaria Molina that may have use as adjuvants in vaccines.
KeywordsOleanolic Acid Fast Atom Bombardment Fast Atom Bombardment Mass Spectrometry Mass Spectrometry Liquid Secondary Ionization Liquid Secondary Ionization
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