Enzymatic acylation as an efficient tool for an easy access to specific acyl derivatives of the natural antioxidants verbascoside, teupolioside and echinacoside

The natural antioxidants phenylpropanoids glycosides echinacoside (1), verbascoside (2) and teupolioside (3) were efficiently and regiospecifically monoacylated by means of the enzyme lipase PS. While acylation of teupolioside (3) and of echinacoside (1) occurred at a sugar primary OH in the “lower” or in the “upper” part of the molecule, respectively, verbascoside (2) was acetylated at one of its sugars secondary OHs. At variance to enantioselectivity, which can be rationalized in terms of steric effects due to substituents bulkiness, our new results confirm that enzyme regioselectivity is mainly dictated by the electrostatic interactions of the different OHs of the substrates with the amino acids of the enzyme.