Antioxidant norbergenin derivatives from the leaves of Diospyros gilletii De Wild (Ebenaceae)

Abstract

Two new norbergenin derivatives, 4-O-p-hydroxybenzoylnorbergenin (1) and 11-O-(E)-cinnamoylnorbergenin (2), were isolated from the leaves of Diospyros gilletii De Wild along with nine known compounds, including norbergenin (3), 4-O-galloylnorbergenin (4), betulin (5), betulinic acid (6), lupeol (7), ursolic acid (8), corosolic acid (9), β-sitosterol (10) and quercitol (11). Their structures were elucidated from the analysis of their 1D and 2D 1H and 13C NMR spectral data in conjunction with mass spectrometry. Single-crystal X-ray diffraction technique unambiguously established the structure of compound (1). The antimicrobial properties of the eleven compounds isolated were investigated as well as the antioxidant activity of the norbergenin derivatives (1–4). The results obtained showed that none of those compounds displayed antimicrobial activity at 0.5 μg/ml whereas norbergenin derivatives exhibited noteworthy antioxidant property with IC50 values ranging from 8.2 μg/ml to 41.6 μg/ml.