Qualitative characterization of Desmodium adscendens constituents by high-performance liquid chromatography-diode array ultraviolet-electrospray ionization multistage mass spectrometry

The many effects of the African medicinal herb Desmodium adscendens were studied in the 1980s and 90s. In spite of this, no comprehensive analytical protocol for the quality control of its constituents (soyasaponins, alkaloids and flavonoids) was still formulated and reported. This study deals about optimization of extraction conditions from the plant and qualitative identification of the constituents by HPLC - diode array UV and multistage mass spectrometry: Plant constituents were extracted from leaves by liquid-liquid and solid matrix dispersion extraction. Separation was achieved via RP-C18 liquid chromatography with UV and MSn detection, and mass spectrometry analysis was conducted by electro-spray ionization ion trap or orbitrap mass spectrometry. High resolution mass spectrometry was used for structural identification of active molecules bearing to soyasaponins and alkaloids. The flavonoid fragmentations were preliminary studied by HRMS in order to accurately characterize the more common neutral losses. Anyway the high number of isomeric species induced us to make recourse to a more extended chromatographic separation in order to allow MS/MS and UV spectra interpretation useful to propose a reasonable chemical classification of these polyphenols. 35 compounds of this class were identified herein respect to the five reported in literature. In this way we made up a comprehensive protocol for the qualitative analysis of the high complexity content of this plant. This result pave the road both to reliable quality control of potential phytochemical medicaments and to possible future systematic clinical studies.