Iridoid glycoside permethylation enhances chromatographic separation and chemical ionization

Abstract

RATIONALE While natural products isolated from medicinal plants can serve as a rich source of biologically active metabolites, mixtures of structurally related compounds of a polar nature are often difficult to chemically resolve by traditional separation techniques. Chemical derivatization to reduce metabolite polarity combined with liquid chromatography is the strategy presented here to resolve a mixture of structurally related natural product glycosides solvent extracted from the medicinal herb Teucrium polium for mass spectroscopy characterization. METHODS The partially-purified plant extract was chemical derivatization and electrospray ionization mass spectrometry (ESI-MS) fragmentation-pattern analysis allowed for structural characterization of iridoid and secoiridoid glycosides. Select ions were subjected to tandem MS analysis with a relatively higher-energy collision dissociation to assist in structural elucidation. RESULTS Permethylation replaced all protons from free hydroxyl and amino groups with methyls and resulted in increases in both hydrophobicity, for facilitated chromatographic separation, and proton affinity, for enhanced chemical ionization. Protonated and/or sodiated adducts were observed for the six compounds detected in positive ion mode ESI-MS with a mass accuracy of less than 2 ppm. CONCLUSIONS Permethylation combined with LC-MS analysis is shown here to be an effective chemical practice for separating and characterizing iridoid glucosinolates and is expected to be well suited for the chemical characterization of other polar natural-product mixtures of closely related compounds.

Euphosantianane A–D: Antiproliferative Premyrsinane Diterpenoids from the Endemic Egyptian Plant Euphorbia Sanctae-Catharinae

“…Some Euphorbia species are indigenous to the Sinai Peninsula [ 16 , 17 ] with E. sanctae-catharinae (also known as St. Katherine spurge) endemic to the Gebel Wadi, a system of deep/dry river valleys separated by the high elevation Katherine Mountains. As part of our research to investigate and biologically evaluate the wild Egyptian plants [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ], herein, it is the first phytochemical investigation of E. sanctae-catharinae that specifically targets secondary metabolites that may exhibit anti-tumor activity.…”