Title: Antioxidant and cytotoxic flavonoids from the flowers of Melastoma malabathricum L

Phytochemical and bioactivity studies of the flowers of Melastoma malabathricum L. (Melastomataceae) have been carried out. The ethyl acetate extract yielded three compounds, identified as naringenin, kaempferol and kaempferol-3-O-d-glucoside, and methanol extract gave kaempferol-3-O-(2′′,6′′-di-O-p-trans-coumaroyl)glucoside and kaempferol-3-O-d-glucoside. The crude extracts and isolated compounds were screened for their antioxidant and cytotoxic activities. The antioxidant assay was carried out by the DPPH radical-scavenging electron spin resonance (ESR) spectroscopic method. The cytotoxicity was measured by the MTT assay against a MCF7 cell line. Naringenin, kaempferol, kaempferol-3-O-d-glucoside, kaempferol-3O-(2′′,6′′-di-O-p-trans-coumaroyl) glucoside, ethyl acetate and methanol extracts were found to be active as radical-scavengers with IC50 values of 0.52 mM, 81.5 μM, 1.07 mM, 35.8 μM, 7.21 μg/ml and 6.59 μg/ml, respectively. Naringenin and kaempferol-3-O-(2′′,6′′-di-O-p-trans-coumaroyl)glucoside were also found to be active in inhibiting cell proliferation of MCF7 with IC50 values of 0.28 μM and 1.3 μM, respectively.