Synthesis and characterization of novel quercetin-α-d-glucopyranosides using glucansucrase from Leuconostoc mesenteroides

In this study, two quercetin-α-d-glucopyranosides were synthesized via the acceptor reaction of a glucansucrase obtained from Leuconostoc mesenteroides B-1299CB, with quercetin and sucrose. The two transfer products were purified via HPLC, and the structures of the products were identified as quercetin-4′-O-α-d-glucopyranoside (Q-G1) and quercetin-3′-O-α-d-glucopyranoside (Q-G1′), in accordance with the results of 1H, 13C, HSQC, H-H COSY, HMBC analyses. The primary product (Q-G1) evidenced slower effects on DPPH radical-scavenging activity (SC50 = 25.2 μM) than was seen with quercetin (SC50 = 6.5 μM). The water solubility of Q-G1 was 12.7 mM, whereas the quercetin was barely soluble in water. The Ki value of Q-G1 (674.5 μM) was almost identical to that of quercetin (673.3 μM) with regard to tyrosinase inhibition effects.