科研之友
微信
新浪微博
Facebook
分享链接
摘要
The saponins in Caulophyllum robustum have not yet been fully characterized. Furthermore these saponins are often present in trace amounts and are structurally complex. Here, a simple direct infusion electro-spray ion trap multiple-stage tandem mass spectrometry (DI-ESI-IT-MSn) method was described for the characterization of trace C robustum saponins. Eight reference saponins from the C. robustum hairy root were investigated by DI-ESI-IT-MSn in positive ion mode. Some fragmentation approaches were proposed through analysis of the [M+Na](+) ions: (1) preferential cleavage of the C-28 ester glycosidic bond to provide complementary [Y-0 alpha,+Na](+) and [B-alpha+Na](+) ions for bidesmosidic saponins; (2) diagnostically neutral loss of CO2 from free carboxyl groups at C-28 for monodesmosidic saponins; and (3) the ion intensity ratio between [C-2 beta+Na](+) and [B-2 beta+Na](+), which is sensitive to the structural differences between the two isomeric beta-sugar chains (Glc ->(2)Ara and Glc ->(3)Ara). The DI-ESI-IT-MSn method was successfully used for the analysis of trace C. robustum saponins with [M+Na](+) ions at m/z 1745.6, 1729.5, 1583.7, 1567.7, 1421.7 and 1405.7. This article highlights the discovery and identification of complex alpha- and beta-oligosaccharide moieties in Caulophyllum saponins by glycosidic product ions along with cross ring cleavage product ions. Five oligosaccharide moieties were unambiguously or tentatively identified as Rha ->(4)Glc ->(6)Glc ->(4)Rha ->(4)Glc ->(6)Glc, Glc ->(4)Glc ->(6)Glc ->(4)Rha-(4)Glc ->(6)Glc, Rha -> Glc -> Glc (Glc)->(2,3)Ara, Glc -> Glc (Glc) -> (2,3)Ara and Glc (Glc)->(2,3)Ara. Accuracy of the analytical procedure was demonstrated by structural identification of two saponins isolated using 1D and 2D-NMR spectroscopy. The DI-ESI-IT-MSn method facilitates rapid discovery and analysis of trace Caulophyllum saponins and is a powerful and practical tool for structural characterization of complex oligosaccharide moieties in triterpene saponins.
