Lipase‐catalyzed synthesis of ferulate esters

Four commercially available esterases were screened for their ability to esterify ferulic acid (4‐hydroxy‐3‐methoxy cinnamate). Novozym® 435 was found to be the only one of those screened to convert ferulic acid to ethyl and octyl ferulate at 20 and 14% yields, respectively. The highest percentage conversion was obtained using a 1∶1 mole ratio of alcohol to ferulic acid in stirred batch reactions in anhydrous 2‐methyl‐2‐propanol at 60°C using one equivalent (wt/wt based on ferulic acid) of Novozym 435. Increased water content and a higher alcohol/ethyl ferulate ratio had adverse effects on the lipase‐catalyzed esterification. The Novozym 435 activity was tested in less polar solvents (anhydrous toluene and hexane) by monitoring the alcoholysis of ethyl ferulate with 1‐octanol, which resulted in a 50% yield of octyl ferulate. The alcoholysis was improved to 83% by applying a 16 mm Hg vacuum for 5 min every 24 h to remove the ethanol co‐product. The optimal alcoholysis parameters were applied to the alcoholysis of ethyl ferulate with monoolein and the transesterification with triolein. The transesterification of ethyl ferulate with triolein in anhydrous toluene produced a combined 44% yield of ferulyl monoolein and ferulyl diolein, a 20% greater yield than that obtained for alcoholysis using monoolein. The highest yield, 77%, of ferulyl monoolein and ferulyl diolein was achieved using a threefold excess of neat triolein. The lipase‐catalyzed transesterification of ethyl ferulate with triolein appears to be a technically feasible route to ferulyl‐substituted acylglycerols, which are potentially useful sunscreen ingredients.