Antioxidant activity of O-protected derivatives of (-)-epigallocatechin-3-gallate: inhibition of soybean and rabbit 15-lipoxygenases

-)-Epigallocatechin-3-gallate (EGCG) was protected at all eight phenolic groups as the methyl ether or acetate, propionate or butyrate esters. The synthetic derivatives were examined for antioxidant activities. The compounds were tested as potential diphenylpicrylhydrazyl (DPPH) radical scavengers and as inhibitors of 15-lipoxygenase (15-LO) enzymes from soybeans and rabbit reticulocytes. The O-protected EGCG derivatives were essentially inactive as DPPH scavengers but showed profound inhibiting effects on both types of 15-LO, and the inhibitory effects towards the two enzymes were significantly correlated. The O-protected EGCG derivatives inhibited 15-LO more strongly that EGCG itself. EGCG and its O-protected derivatives were also screened for antibacterial activity against M. tuberculosis.