Rapid differentiation of isobaric and positional isomers of structurally related glycosides from Phytolacca bogotensis

摘要

Through the action of glycosyltransferases, a plant can biosynthetically assemble small differentaglycons or 'templates' to various polysaccharides to produce numerous glycoconjugates differing inthe type of the attached aglycon, the anomeric configuration of C-1 of the glycosylating sugar, the typeof sugar and the different position of attachments of the sugar unit present in the polysaccharidechain. The position of attachments and the anomeric configuration of the different sugar present inthe polysaccharide create the opportunity to generate molecules with either the same or very closemolecular weights, which have relative structural similarity - forming isobaric and positionalisomers. Although isomeric differentiation was once considered outside of the domain of massspectrometry, this task can now be resolved using tandem mass spectrometry. In a standardizedpurified glycoconjugate fraction (SPT01) from Phytolacca bogotensis, we report conventional elec-trospray ionization mass spectrometry and collision-induced dissociation (CID) MS/MS parameterswhich favored the formation of characteristic product ions. This allowed us to suggest the type ofsugar linkages present in a specific glycoconjugate. Ten new glycoconjugate are described from thisplant and another twelve known saponins were structurally characterized using the automatic MS~nacquisition mode. The differentiation of two pairs of positional isomers and four isobaric glycosidesand the production of a library of 30 glycosides present in P. bogotensis were accomplished.