Bioactive compounds from Boerhavia erecta L. : an African medicinal plant

A protocol was developed for the extraction of the traditional African medicinal plant Boerhavia erecta L. and this resulted in eight compounds being isolated. From the less polar fraction, four constituents were isolated using thin layer chromatography techniques but only one was fully characterised and was elucidated as β-sitosterol. This sterol was previously reported from the same species. The remaining three constituents were only partially identified due to insufficient material but are likely to also be sterols. From the polar fraction four glycosides were isolated using reverse phase high performance liquid chromatography. Only two of the four isolates were fully characterised and were shown to be 3′,4′,5,7-tetrahydroxyflavone-3-O-α-D-rhamnopyranosyl-(1→6)-O-β-D-glucopyranoside and 4′,5,7-tetrahydroxy-3′-methoxy flavone-3-O-α-D-rhamnopyranosyl-(1→6)-O-β-D-glucopyranoside. The remaining two constituents were partially elucidated due to limited yield but are likely to also be flavonoids. The one and two dimensional nuclear magnetic resonance spectral analysis were successful in assisting the molecular structure elucidation of these glycosides. The absolute configuration of the sugar was assigned using anomeric proton-carbon coupling constant analysis in which we found α-D-rhamnopyranoside and β-D-glucopyranoside. While the α-L-rhamnopyranoside derivative has been reported previously, the D-form isolated here is new and further, it is the first time these compounds (regardless of stereochemistry) have been found in this genus, Boerhavia. The bioassay of the isolates against microbes (S. aureus, S. epidermidis, MRSA, Mu50, E. faecium WT) did not possess significant activities. The anti-viral activity against HIV-infected cells, revealed 3′,4′,5,7-tetrahydroxyflavone-3-O-α-D-rhamnopyranosyl-(1→6)-O-β-D-glucopyranoside as the most active isolate.