Intra-molecular inter-chain reactions in bidesmosidic glycosides, a new insight into carbohydrate rearrangements induced by electrospray ionization

Glycoconjugates are a class of complex mols. that are widely distributed in the plant kingdom and in some marine organisms. This class of compds. has a wide range of biol. activities such as anti-inflammatory, antimicrobial, antifungal, anticancer, antiulcer, and immunoenhancing actions. Some of them also show various toxic activities such as cytotoxic, hemolytic, cardiotoxic, and teratogenic. Among these compds., steroidal and triterpenoid saponins have long been known as components of widely used herbal drugs and pharmaceutical prepns.; ginseng, Tribulus terrestris, Quillaja saponaria, and Digitalis ssp. are just a few examples. Thus, identification of saponins in herbal drugs used worldwide is of significance in phytochem. and toxicol. quality control studies, and for the prodn. of safe health products. Therefore, there is continuing demand for methods to rapidly identify and characterize these natural products. An interchain rearrangement on steroidal and triterpenoid bidesmosidic saponins involving an intramol. reaction between the two glycosidic moieties leading to the formation of a single saccharide chain composed of all the monosaccharide residues was described. Eleven different compds. were analyzed to study the influence of structural characteristics of the mols. on the interchain reaction. Electrospray-ionization mass spectrometry (ESI-MS) and MS/MS analyses of deuterium-exchanged and per-O-methylated compds. were also performed. The results indicated that these rearrangements occurred independently of the nature of the sugar residues or the length of the saccharide chains. The rearranged compds. showed the same mol. wt. as the original ones and could be revealed only by using tandem mass spectrometric approaches. An approach combining tandem mass spectrometry of [M+H]+ and [M+Na] + ions is strongly recommended to obtain the best mass spectrometric structural anal.