Enzymatic glycosylation of hydrophobic scaffolds can be catalyzed by glycosidases and glycosyltransferases. Glycosylation dramatically changes the physico-chemical properties of bioactive molecules, modulates their pharmacokinetic properties and influences their membrane transport. Polyphenols are, in general, hydrophobic compounds exhibiting poor absorption, which renders a very low bioavailability. The main objective of this work was to develop strategies for the enzymatic glycosylation of polyphenols, namely epigallocatechin gallate (EGCG, present in green tea), hesperetin (citrus fruits), resveratrol (grapes) and hydroquinone. The yield of glycoderivatives is usually low because the active-site architecture of glycosidic enzymes is not designed to accommodate non-natural acceptors −in contrast with the natural ones, i.e. carbohydrates−. In addition, the reactivity of phenolic groups is notably lower than the corresponding to typical hydroxyls. However, the synergistic combination of enzyme screening, medium engineering and structural analysis was employed to develop strategies for the glycosylation of different polyphenols. We have achieved the enzymatic synthesis of various α-glucosyl derivatives of resveratrol, EGCG or hesperetin by a transglycosylation reaction catalyzed by cyclodextrin glucanotransferase (EC 2.4.1.19, CGTase), a transglycosidase that employs easily available carbohydrates (e.g. starch or maltodextrins) as glucose donors. A common strategy to increase the yield of glycoderivatives was the use of cosolvents that favoured the solubilization of the phenolic acceptors. The antioxidant and surfactant properties of several of the synthesized compounds were evaluated. For the introduction of fructosyl groups, we found that the β-fructofuranosidase (EC 3.2.1.26) from the yeast Xanthophyllomyces dendrorhous was able to fructosylate hydroquinone. Interestingly, other polyphenols such as EGCG acted as strong inhibitors of β-fructofuranosidases from X. dendrorhous and Schwanniomyces occidentalis. The experimental results were validated by soaking the enzyme with the polyphenols followed by structural characterization of the complexes.

Trabajo presentado en el evento conjunto de la 12ª ed. del simposio internacional "Jornada de Carbohidratos" y la 3ª ed. de la reunión nacional "Grupo Especializado de Química Biológica" organizado por la Real Sociedad Española de Química en el Centro de Investigaciones Biológicas (CIB, CSIC) en Madrid (España) del 14 al 16 de marzo del año 2016.

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