Cyclodextrin Glycosyltransferase-Catalyzed Synthesis of Pinoresinol-α-D-glucoside Having Antioxidant and Anti-Inflammatory Activities

Enzymatic synthesis of pinoresinol-alpha-glucosides (PG(s)) was performed through the transglycosylation reaction catalyzed by the recombinant cyclodextrin glycosyltransferase (CGTase) from Bacillus circulans A11 using beta-cyclodextrin as the glycosyl donor and pinoresinol as the acceptor molecule. Incubation of 0.5% (wt/vol) beta-cyclodextrin with 1.5% (wt/vol) pinoresinol (P) and 80.0 U/mL of CGTase in 20 mM of Tris-HCl buffer (pH 9.0) at 50(o)C for 60 h was optimal for PG(s) synthesis. Under these conditions, two PG transfer products with molecular weights of 544 and 682 Da corresponding to pinoresinol monoglucoside (PG(1)-I and PG(1)-II) and pinoresinol diglucoside (PG(2)), respectively, were detected by TLC and MS. The structures of PG(1) and PG(2) were confirmed as pinoresinol-alpha-D-glucopyranoside and pinoresinol-alpha-D-diglucopyranoside, respectively, by H-1-NMR analysis. The free-radical scavenging and anti-inflammatory activities of PG(1) and PG(2) were reduced as compared with the original P using alpha,alpha-diphenyl-beta-picrylhydrazyl radical scavenging reactions and the beta-glucuronidase inhibition assay. The loss of antioxidant and anti-inflammatory activities might result from the addition of glucose in the position 4-OH of P that may have disturbed its electron rotation. In vivo, PG(s) are converted to P-s before they are absorbed and so loss of activity may be minimal. Interestingly, the alpha-glycosylated compounds which showed the change of physicochemical properties such as increase of solubility and sweetness could promote a positive effect on the bioavailability of original P.