Flavan-3-ol-cysteine and acetylcysteine conjugates from edible reagents and the stems of Cynomorium songaricum as potent antioxidants

Flavan-3-ol derivatives, including 3 cysteine conjugates and 3 acetylcysteine conjugates, were prepared using Cynomorium songaricum and edible reagents. The structures were determined, based on NMR and MS spectra. All compounds had stronger radical-scavenging activity than catechin and epicatechin. Moreover, the cysteine conjugates were active against α-glucosidase, whereas catechin and epicatechin were not. Two acetylcysteine flavan-3-ol conjugates, 4β-(l-acetylcysteinyl)-epicatechin 3-O-gallate and 4β-(l-acetylcysteinyl)-epiafzelechin, are novel compounds with better log P values than their cysteine counterparts. These conjugates can be prepared from purified flavan-3-ol polymers or directly from herbal material.