Asymmetric reduction of (4S)-(+)-carvone catalyzed by baker's yeast: A green method for monitoring the conversion based on liquid-liquid-liquid microextraction with polypropylene hollow fiber membranes

The α,β-unsaturated carbonyl compound (4S)-(+)-carvone was selectively reduced to (1R,2R,4S)-iso-dihydrocarveol using baker's yeasts. The conversion of the bioreduction reaction was monitored using a green hollow-fiber liquid-liquid-liquid microextraction (HF-LLLME) technique. Several parameters which may affect the bioreduction of (4S)-(+)-carvone, such as temperature, time, substrate/enzyme ratio, pH and buffer concentration, were evaluated. The effect of some additives, such as trehalose, DMSO and the ionic liquid [BMIm][PF6], was also studied. The (1R,2R,4S)-iso-dihydrocarveol was recovered with 52.7% conversion and diastereoisomeric excess >99% after 48 h of reaction at 40 °C in an aqueous monophasic system, with 0.1 mol L−1 buffer concentration (pH 7.5) and a substrate/yeast cell mass ratio of 8.0 mg g−1. The HF-LLLME microextraction technique allowed the optimization of the reaction with a reduction of over 99.5% in relation to the use of organic solvents.