Biotransformation of quercetin by Gliocladium deliquescens NRRL 1086.

With an attempt to synthesize high-value isoquercitrin (quercetin-3-O-β-D-glucopyranoside), we carried out the biotransformation of quercetin (1) by Gliocladium deliquescens NRRL 1086. Along with the aimed product quercetin 3-O-β-D-glycoside (2), three additional metabolites, 2-protocatechuoyl-phlorogucinol carboxylic acid (3), 2,4,6-trihydroxybenzoic acid (4), and protocatechuic acid (5), were also isolated. The time-course experiments revealed that there were two metabolic routes, regio-selectivity glycosylation and quercetin 2,3-dioxygenation, co-existing in the culture. Both glycosylation and oxidative cleavage rapidly took place after quercetin feeding; about 98% quercetin were consumed within the initial 8 h and the oxdized product (2-protocatechuoyl-phlorogucinol carboxylic acid) was hydrolyzed into two phenolic compounds (2,4,6-trihydroxybenzoic acid and protocatechuic acid). We also investigated the impact of glucose content and metal ions on the two reactions and found that high concentrations of glucose significantly inhibited the oxidative cleavage and improved the yield of isoquercitrin and that Ca