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

Abstract

Enzymatic synthesis of pinoresinol-α-glucosides (PG_s) was performed through the transglycosylation reaction catalyzed by the recombinant cyclodextrin glycosyltransferase (CGTase) from Bacillus circulans A11 using β-cyclodextrin as the glycosyl donor and pinoresinol as the acceptor molecule. Incubation of 0.5% (wt/vol) β-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^oC 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 (PG₁-I and PG₁-II) and pinoresinol diglucoside (PG₂), respectively, were detected by TLC and MS. The structures of PG₁ and PG₂ were confirmed as pinoresinol-α-D-glucopyranoside and pinoresinol-α-D-diglucopyranoside, respectively, by ¹H-NMR analysis. The free-radical scavenging and anti-inflammatory activities of PG₁ and PG₂ were reduced as compared with the original P using α,α-diphenyl-β-picrylhydrazyl radical scavenging reactions and the β-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 α-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.