QUERCETIN GLUCOSIDES AND GALACTOSIDES - SUBSTRATES AND INHIBITORS OF APPLE BETA-GALACTOSIDASE

Quercetin 3-O-β-D-glucoside and -galactoside, 7-O-β-D-glucoside and -galactoside, and 3,7-di-O-β-D-glucoside and -galactoside were synthesized in improved yields by established methods. The last named compound, not previously described, was characterized by1H and13C NMR. The major β-galactosidase of apple fruit hydrolyzed the 7-galactosyl group but not the 3-galactosyl or any glucosyl group from the quercetin glycosides. The apple β-galactosidase was inhibited to a similar extent by quercetin and its 7-glycosides. Quercetin 3-glycosides were somewhat more effective inhibitors, and the 3,7-digalactoside was 25 times more effective [K1= 10-5M). The strong inhibition of the (β-galactosidase was not accounted for by the substrate properties of quercetin 3,7-digalactoside. © 1990, American Chemical Society. All rights reserved.