Enzymic and nonenzymic reduction of (+)-dihydroquercetin to its 3,4,-diol.

A NADPH-dependent reductase activity, capable of converting (+)-dihydroquercetin (2,3-trans) to its 3,4-diol (a leucocyanidin), has been demonstrated in crude, soluble protein extracts derived from cell suspension cultures of Douglas fir (Pseudotsuga menziessi). Neither NADH nor ascorbate substituted as the H-donor. Quantitative analyses were based on the production of cyanidin, the formation of an adduct with vanillin, and on absorbance at 280 nanometers. Nonenzymic reduction of (+)-dihydroquercetin with NaBH(4) produced two presumably isomeric flavan-3,4,-diols. One of these was similar to the enzymically produced diol, based on products isolated by chromatography on paper, on thin-layer cellulose and on C(18) reversed-phase columns (high performance liquid chromatography), and on the conversion of the diol to the all-trans dimer of (+)-catechin upon the addition of (+)-catechin.