The stilbene compound resveratrol was glycosylated to give its 4'-O-β-D-glucoside as the major product in addition to its 3-O-β-D-glucoside by a plant glucosyltransferase from Phytolacca americana expressed in recombinant Escherichia coli. This enzyme transformed pterostilbene to its 4'-O-β-D-glucoside, and converted pinostilbene to its 4'-O-β-D-glucoside as a major product and its 3-O-β-D-glucoside as a minor product. An analysis of antioxidant capacity showed that the above stilbene glycosides had lower oxygen radical absorbance capacity (ORAC) values than those of the corresponding stilbene aglycones. The 3-O-β-D-glucoside of resveratrol showed the highest ORAC value among the stilbene glycosides tested, and pinostilbene had the highest value among the stilbene compounds. The tyrosinase inhibitory activities of the stilbene aglycones were improved by glycosylation; the stilbene glycosides had higher activities than the stilbene aglycones. Resveratrol 3-O-β-D-glucoside had the highest tyrosinase inhibitory activity among the stilbene compounds tested.
Biotransformation of artepillin C was investigated using cultured plant cells as biocatalysts. Artepillin C was converted into its 4- and 9-β-D-glucosides, and 4,9-β-D-diglucoside by cultured cells of Phytolacca americana. In contrast, cultured Ipomoea batatas cells glucosylated artepillin C to only its 4- and 9-β-D-glucosides.
To enhance their water solubility and pharmacological activities, the stilbenes resveratrol, pterostilbene, and piceatannol were glycosylated to their monoglucosides (β-glucosides) and diglycosides (β-maltosides) by cultured cells and cyclodextrin glucanotransferase (CGTase). Cultured cells of Phytolacca americana and glucosyltransferase (PaGT) were capable of glucosylation of resveratrol to its 3- and 4'-β-glucosides. Pterostilbene was slightly transformed into its 4'-β-glucoside by P. americana cells. Piceatannol was readily converted into piceatannol 4'-β-glucoside, with the highest yield among the three substrates. The 3- and 4'-β-glucosides of resveratrol were subjected to further glycosylation by CGTase to give 3- and 4'-β-maltoside derivatives. The inhibitory action of resveratrol and pterostilbene toward histamine release induced with compound 48/80 from rat peritoneal mast cells was improved by β-glucosylation and/or β-maltosylation (i.e., the inhibitory activity for histamine release of the 3- and 4'-β-glucosides of resveratrol, the 3- and 4'-β-maltosides of resveratrol, and the 4'-β-glucoside of pterostilbene was higher than that of the corresponding aglycones, resveratrol and pterostilbene, respectively). In addition, the phosphodiesterase (PDE) inhibitory activity of resveratrol and pterostilbene was enhanced by β-glucosylation and/or β-maltosylation (i.e., the PDE inhibitory activities of the 3- and 4'-β-glucosides of resveratrol, the 4'-β-maltoside of resveratrol, and the 4'-β-glucoside of pterostilbene were higher than those of the corresponding aglycones, resveratrol and pterostilbene, respectively).
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