Ericoside, a new antibacterial biflavonoid from Erica mannii (Ericaceae)

A new dihydroflavonol-flavonol biflavonoid derivative, named ericoside was isolated from the ethanol extract of the whole plant of Erica mannii along with the known flavonoid, taxifolin 3-O-α-L-rhamnopyranoside; and two readily available sterols (sitosterol, sitosterol 3-O-β-D-glucopyranoside). The isolation was performed using chromatographic methods and the structure of purified molecules were elucidated using spectroscopic techniques (e.g. MS, NMR) and by comparison with literature data. The crude ethanol extract, ericoside, and taxifolin 3-O-α-L-rhamnopyranoside were tested against ten Gram-negative bacteria including multidrug resistant clinical isolates using a broth microdilution method. The crude ethanol extract showed no noteworthy activity. Of the purified compounds, ericoside displayed moderate activity against the resistant Escherichia coli AG100 with a MIC of 64 μg/mL.