Isolation, structural elucidation of flavonoid constituents from Leptadenia pyrotechnica and evaluation of their toxicity and antitumor activity

An investigation of Leptadenia pyrotechnica (Forsk.) Decne (Asclepiadaceace) chemical constituents led to the isolation of six flavonoids, kaempferol-3-O-α-l-rhamnopyranosyl (1′″→6″)-O-β-d-glucopyranoside (E-I.1), kaempferol-3-O-β-d-rhamnopyranosyl (1′″→6″)-O-β-d-glucopyranoside (E-I.2), texasin-7-O-β-d-glucopyranoside E-II.2, kaempferol-3-O-β-d-glucopyranoside (E-III.1), kaempferol (E-IV.1) and kaempferide-3-O-α-l-rhamnopyranosyl (1′″→6″)-O-β-d-glucopyranoside (E-I.1a). The isolation of these compounds was carried out using Sephadex LH-20 low pressure liquid chromatography (LPLC), preparative paper chromatography (PC), and high performance liquid chromatography (HPLC). The chemical structures of the isolated compounds were established by mass spectrometry (FAB- and EI- techniques), nuclear magnetic resonance NMR (1H-, 13C- and COSY) spectral data and ultraviolet (UV) spectroscopic techniques. The acute toxicity of total alcoholic and total flavonoid extracts were examined by brine shrimp. The LC50 values were 11.89 and 84.14 ppm for the total alcoholic and total flavonoid extracts, respectively. The mortality rates of the isolated flavonoid fractions of E-I, E-I.1, E-I.2 represent the higher percentages of mortality compared with the rest of the flavonoid fractions. The plant exhibited activity as an antitumor agent in the initial potato disc screen.