A new triglycosyl flavonoid isolated from leaf juice of kalanchoe gastonis-bonnieri (crassulaceae)

Abstract

Kalanchoe gastonis-bonnieri R. Hamet &H. Perrier (Crassulaceae) is a succulent species empirically used as a vaginal contraceptive as well as to heal genitourinary infections. A phytochemical study of leaf juice prepared from specimens collected in the flowering season resulted in the isolation of the new flavonoid quercetin 3-O-α-rhamnopyranoside-7-O-β-D-glucopyranosyl-(1→3)-α-L-rhamnopyranoside, as well as the already known 6-C-β-D-glucopyranosyl-8-C-β-D-glucopyranosylapigenin (vicenin-2). The NMR spectra of this flavonoid at room temperature exhibited broad and duplicated signals, suggesting the existence of rotameric conformers, which was confirmed by coalescence of the signals at 40oC. The structural elucidation was based on 1H and 13C NMR (HMQC and HMBC) analyses and MS data. This is the first report of a C-glycosyl flavonoid (vicenin-2) in the Crassulaceae family. Additionally, this is the first study in which atropoisomerism has been shown for vicenin-2.