Enzymatic Synthesis of α-Glucosides of Resveratrol with Surfactant Activity

We report the synthesis of a series of alpha-glucosyl derivatives of resveratrol (3,5,4'-trihydroxy-stilbene) by a transglycosylation reaction catalyzed by the enzyme cyclodextrin glucanotransferase (CGTase) using starch as glucosyl donor. Several reaction parameters (temperature, solvent composition, enzyme concentration and starch/resveratrol ratio) were optimized. The yield of alpha-glucosylated products reached 50% in 24 h. The structures of the derivatives were determined by a combination of amyloglucosidase-hydrolysis tests, MS and 2D-NMR. Three families of products were obtained: glucosylated at 3-OH, at 4'-OH and at both 3-OH and 4'-OH. The bonds between glucoses were basically alpha(1 -> 4). Interestingly, the water solubilities of the alpha-glucosylated derivatives were at least 65- and 5-fold higher than those of resveratrol and the natural beta-glucosylated derivative (piceid), respectively. In contrast with piceid, the synthesized alpha-glucosylated compounds exhibited surfactant activity, with critical micelle concentration (CMC) values in the range 0.5-3.6 mM. Although the incorporation of a glucosyl moiety caused a loss of antioxidant activity (more pronounced in the position 3-OH compared with 4'-OH), the fact that the glycosides need to be converted into the aglycones before they are absorbed minimizes such an effect. In contrast, the modification of physicochemical properties such as solubility and partition coefficient by glycosylation could exert a positive influence on the bioavailability of resveratrol.