FIG. 7.

Structural comparisons of inhibitory and noninhibitory polyphenols. Epicatechin and epigallocatechin were not inhibitors until the addition of a gallate, which was not an inhibitor on its own. Compared to epicatechin, the inhibitor 2,3,5,7,3′,4′-pentahydroxyflavan has one additional conjugated double bond and an additional hydroxyl group. The double-ring system in the flavan should be more planar than the corresponding rings in epicatechin.