Potent lipid peroxidation inhibitors from Withania somnifera fruits

A bioassay-guided purification of the methanolic extract of Withania somnifera fruits yielded novel withanamides A–I () and withanolides (). Among the withanolides, compound is novel. The structures of these compounds were determined by using FABMS, HRFABMS, 1D and 2D NMR spectral and chemical methods. The withanamides possess novel chemical structures and consisted of serotonin, glucose and long-chain hydroxyl fatty acid moieties. The stereochemistry of the hydroxyl group in the long-chain fatty acid moiety in compound was determined by the modified Mosherʹs ester method. Compounds were tested for their ability to inhibit lipid peroxidation in a model system using large unilamellar vesicles. Withanamides and inhibited lipid peroxidation by 98, 93, 79, 94, 81 and 86%, respectively, at 1 μg/mL. However, compounds inhibited the lipid peroxidation by 85, 82 and 90%, respectively, at 0.5 μg/mL. Withanolides were also tested and only compound inhibited the lipid peroxidation by 82% at 10 μg/mL. To evaluate the structure activity relationships of withanamides A–I, compounds were purchased and their lipid peroxidation activity determined as in the case of compounds . Commercial antioxidants, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ), were also tested in this assay at 1 μg/mL and showed 80, 81 and 85% of inhibition, respectively. Our results suggest that the potent antioxidant activity exhibited by novel withanamides is probably due to the hydroxylated long-chain acyl group. This is the first report of withanamides, unique serotonin conjugates, from W. somnifera fruits.