Structural analysis of ginsenosides and sugars: An electrospray and tandem mass spectrometry study

Carbohydrates are an abundant class of biological molecules. This thesis presents methodologies for structure characterization of a class of triterpene glycosides, the ginsenosides, sugars and polyols. The sugars included simple monosaccharides, as well as complex saccharides such as the carrageenans, a family of sulfated polysaccharides. The methodologies employed positive and negative ion electrospray ionization (ESI) mass spectrometry and tandem mass spectrometry (MS/MS).; Positive ion electrospray mass spectrometry (ESMS) of solutions containing a ginsenoside and any alkali metal ion produced the [M+metal]+ ion. By contrast, when the transition metal ions, Ni++, Co ++ and Zn++, are used, the [M+metal-H]+ ion was observed. Collision-induced dissociation (CID) of the metal attachment ions accommodated their structure characterization. The relative intensity ratio of the product ions provided information on the point of attachment of the sugars to the core, as well as whether they are monosaccharides or disaccharides.; Negative ion ESMS of basic solutions of ginsenosides showed a peak corresponding to the [M-H]− ion whose CID spectrum provided the identity of the core, the sugars comprised in the ginsenoside and their order of attachment to the ginsenoside. Both positive and negative ion CID experiments provided information that can be used to propose a structure for ginsenosides. In line with this, these methodologies were used to develop a liquid chromatography mass spectrometry (LC/MS) and LC/MS/MS method for separation and structural characterization of new ginsenosides from root extracts. The structure proposals for ten new ginsenosides are provided.; The carrageenans are a family of partially sulfated polysaccharides of which there are three major types, kappa (k), iota (i) and lamda (l). These types are different because each has a disaccharide subunit containing a specific number of sulfate groups with Na+ counterions. Both matrix-assisted laser/desorption ionization time-of-flight mass spectrometry and negative ion ESMS proved to be useful structure probes for these compounds. Dilute solutions of carrageenans undergo H+ exchange and subsequent expulsion of SO₃ thus generating a carrageenan with lower sulfate content. (Abstract shortened by UMI.)...