Antioxidant and cytotoxic activity of polyphenolic compounds isolated from the leaves of Leucenia leucocephala

Context: Cancer is a serious clinical problem to the health care system. Anticancer drugs have been extracted from plants containing phenolic compounds. Leucenia species (Fabaceae) contain a variety of bioactive components of numerous biological and pharmacological properties. Objective: This study explored the constitutive polyphenols of Leucenia leucocephala Lam. growing in Egypt and evaluated the antioxidant and cytotoxic activity. Materials and methods: Chemical structures of the isolated compounds from the leaves of L. leucocephala were established by spectral techniques (UV, H-1, and C-13 NMR, MS). Results: Chromatographic separation of 80% MeOH extract of the leaves of L. leucocephala have resulted in a novel flavonoid-galloyl glycoside [myricetin 3-O-(2',3'4'-tri-O-galloyl)-alpha-L-rhamnopyranoside] with three known polyphenolic compounds isolated for the first time from this species (apigenin 7-O-beta-D-glucuronopyranoside methyl ester, luteolin 7-O-beta-D-glucuronopyranoside methyl ester, and 1,3,6-tri-O-galloyl-beta-D-glucopyranose) and seven known previously isolated compounds. Also, 80% methanol extract exhibited high antioxidant activity (SC50 = 3.94 mu g/ml), which is correlated with its phenolic content. The extract also showed cytotoxic activity against Hep G2 (IC50 value 1.41 mu g/ml) confirming its anticancer activity against hepatocellular carcinoma. Among the tested compounds (4-8) for antioxidant property, compound 7 was the most active compound (SC50 = 2.49 mu g/ml). Also compounds 7 and 8 exhibited high cytotoxic activity (IC50 = 2.41 and 2.81 mu g/ml, respectively). Discussion and conclusion: These findings demonstrate that the leaves of L. leucocephala contain a considerable amount of polyphenolic compounds with high antioxidant properties, thus it has great potential as a source for natural health products.