Enzymatic acylation of flavonoids

Flavonoids (aglycon, glycosylated) are widely used in pharmaceutic, cosmetic and food preparation. They have several physico-chemical properties and biological activities but they are characterized by a low solubility and stability. In order to take advantage of these properties, the enzymatic acylation of these molecules with fatty and aromatic acids by protease and lipase under different operating conditions has been suggested as a promising route by several authors. However, it is very important to make a compromise between improving the stability and the solubility without affecting the biological activities. In fact, the position of acylation (regioselectivity) can drastically modify these properties. This article reviews the main work done on the influence of the type, origin and concentration of the enzyme, the nature of the reaction, the operating conditions, the composition of the reactional media and the nature of substrates on regioselectivity, initial rates and conversions yields of the acylation. The published data showed that with glycosylated flavonoids, acylation occurred with all lipases and subtilisin tested, whereas with aglycon flavonoids, acylation was possible only with Pseudomons cepacia lipase and carboxyl-esterase. When acylation occurred, several products were obtained (mono-, diesters). The regioselectivity of acylation depends on the type of the enzyme. For a given enzyme, regioselectivity is affected by the structure of the flavonoid and the acyl donor. The position of acylation on the flavonoid and the nature of the acyl donor could improve the properties of these molecules. The nature of the flavonoid also plays a major role on the conversion yields and initial rates. When optimal conditions (temperature, enzyme, substrates and solvent) were applied, the conversion yield was often more than 95% and the properties are increased.