Decorosides A and B, cytotoxic flavonoid glycosides from the leaves of Rhododendron decorum

Bioassay and NMR-guided fractionation of the methanolic extract of Rhododendron decorum leaves resulted in the isolation of two new flavonoid glycosides, 5,7-dihydroxy-6,8-dimethyldihydroflavanone-7-O-α-L- arabinopyranosyl(1→6)-β-D-glucopyranoside (decoroside A, 1 ) and its 3-hydroxy congener (decoroside B, 2), along with five known compounds myricitrin (3), afzelin (4), (-)-epicatechin (5 ), (+)-catechin (6), and ampeloptin (7 ). The structures of the isolated compounds were elucidated by extensive interpretation of their spectral data. Biological evaluation using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed promising cytotoxic activities of these compounds against different cancer cell lines.