Antioxidant and α-glucosidase inhibitory phenolic constituents of Lactuca indica L.

Lactuca indica L. (Compositae) has been used as a folk medicine for the treatment of intestinal disorders. Phytochemical constituents of L. indica were investigated, and their antioxidant and α-glucosidase inhibitory activities thoroughly studied. A phytochemical investigation of the aerial parts of L. indica resulted in the isolation and identification of eight phenolic compounds. The structures of the compounds were elucidated on the basis of spectroscopic evidence as apigenin, luteolin, isoquercitrin, chlorogenic acid, protocatechuic acid, p-hydroxymethyl benzoic acid, trans-cinnamic acid, and p-coumaric acid. Luteolin, isoquercitrin, chlorogenic acid, and p-hydroxymethyl benzoic acid showed antioxidant activities with IC₅₀ values in the range of 35.5–52.5 μM. In addition, apigenin and luteolin showed α-glucosidase inhibition activities with IC₅₀ values of 96.4 and 100.7 μM, respectively. These findings strongly suggest that L. indica is a potential source of natural antioxidants and/or anti-diabetic agents in pharmaceutical and health functional foods.