Chemical constituents and evaluation of the toxic and antioxidant activities of Averrhoa carambola leaves

The liquid-liquid partitioning of a crude hydroalcoholic extract of Averrhoa carambola L., Oxalidaceae, leaves led to the isolation of a sterol and three flavone C-glycosides. From the n-hexane fraction beta-sitosterol was isolated and from the ethyl acetate fraction apigenin-6-C-beta-L-fucopyranoside (1) and apigenin-6-C-(2-O-alpha-L-rhamnopyranosyl)-beta-L-fucopyranoside (2) were obtained. Apigenin-6-C-(2-O-alpha-L-rhamnopyranosyl)-beta-D-glucopyranoside (3) was isolated from the n-butanol fraction. Compound 3 is new, while 1 and 2 have been previously isolated from A. carambola. The antioxidant activity was measured using the DPPH radical scavenging assay and reducing power of iron (III) to iron (II) ions. The ethyl acetate and n-butanol fractions showed the most antioxidant activity. As evaluated by ability of the sample to scavenge DPPH the IC50 values were 90.92 and 124.48 mu g/mL, respectively. In the assay of reducing power these fractions presented 135.64 and 125.12 of ascorbic acid equivalents, respectively. The antioxidant activity exhibited a significant relationship with the phenolic content (r(2) = 0.997), but a poor relationship with the flavonoids content (r(2) = 0.424). The n-hexane fraction was the only fraction to present good toxicity using A. salina with LC50 800.2 mu g/mL.