BIOASSAY-GUIDED STUDIES ON Bombax ceiba LEAF EXTRACT: ISOLATION OF SHAMIMOSIDE, A NEW ANTIOXIDANT XANTHONE C-GLUCOSIDE

摘要

Bioassay-guided isolation studies on the methanolic extract of the leaves of Bombax ceiba employing DPPH antioxidant assay led to the isolation of a new xanthone C-glucoside, shamimoside (2), along with three known constituents, mangiferin (1), stigma-5-en-3-O-β-glucoside, and β-amyrin. The structure of shamimoside has been elucidated through extensive spectroscopic methods, including 1D and 2D NMR experiments, as 4-C-β-D-glucopyranosyl-1,3,6,8-tetrahydroxy-7-O-(p-hydroxybenzoyl)-9H-xanthen-9-one (2). It is the first naturally occurring xanthone containing a benzoate moiety directly attached to an aromatic ring. Polar extracts and fractions demonstrated better antioxidant activity, and 1 was found to be more potent than 2 in this assay.