Direct acylation of flavonoid glycosides with phenolic acids catalysed by Candida antarctica lipase B (Novozym 435®)

Immobilised Candida antarctica lipase B (Novozym 435®) was used to acylate flavonoid glycosides, both purified and in fruit extracts, using carboxylic acids as acyl donors, in the presence of 4 Å molecular sieves, using 2-methyl-2-propanol as solvent. Conversions ranged from ∼25% to ∼95% using palmitic, cinnamic and phenylpropionic (PPA) acids and hydroxylated derivatives of PPA as acyl donors. Both naringin (naringenin-7-rhamnoglucoside) and isoquercetin (quercetin-3-O-glucopyranoside) were readily acylated. Both compounds gave a major mono-acylated product, along with minor mono-acylated products, which were presumably positional isomers and also di-acylated products. When apple or blueberry extracts were the source of flavonoids, the enzyme showed strong selectivity for acylation of glycosides with a primary aliphatic hydroxyl group on the sugar moiety, such as phloridzin (phloretin-2-glucoside) and anthocyanidin glucosides and galactosides. No acylation of compounds lacking a primary aliphatic hydroxyl group, such as flavonoid aglycones, chlorogenic acid (caffeoyl quinate) or anthocyanidin arabinosides was observed. Acylation, particularly with palmitic acid, greatly increased lipophilicity and solubility in the reaction solvent.