Straightforward Enzyme-Catalyzed Asymmetric Synthesis of Caffeic Acid Esters in Enantioenriched Form

Enantiopure caffeic acid esters were successfully synthesized from caffeic acid and corresponding (R,S)-alcohol catalyzed by an immobilized lipase (Novozym 435) from Candida antarctica. Effects of the alcohol carbon chain length and the type of organic solvents were first investigated, and anhydrous isooctane was finally selected as the most suitable reaction medium. The optimal synthesis parameters for caffeic acid ester synthesis were evaluated using response surface methodology. The actual experimental conversions of 33.8 +/- 1.8% and an E value of >100 for (R)-1-methylbutyl caffeate, achieved under optimized reaction conditions, indicated a good fit to the predictive model. Kinetic and thermodynamic analyses were conducted to determine the main factors affecting enantiomeric discrimination. Results from the batch reuse stability study show that the immobilized enzyme could be effectively reused. The present study is the first to use lipase as the chiral catalyst to prepare optically pure caffeic acid ester compounds.