A Study On Baker's Yeast Mediated Bioreduction Of α-alkyl-β-arylacrolein

Chiral primary alcohols are important fine chemicals and pharmaceutical intermediates, but few synthetic methods were reported. Recently, our group obtained (S)-2-ethylhexan-1-ol in good yield (91%) with high e.e.(99%) via bioreduction of 2-ethylhex-2-enal, which aroused our interest to further our research on the baker's yeast mediated transformation of enals to prepare chiral primary alcohols.At first, a series ofα-alkyl-β-arylacroleins were prepared to systematically investigate the substituent effects on the bioreduction mediated by baker's yeast. Theαgroup change from small H atom to larger alkyl groups like CH3, C2H5, C3H7, C4H9, and C5H11. The conversions decreased from 99% to 21% at 30 min, while the ratios of saturated alcohol to allyl alcohol were 0.79, 0.54, 1.11, 0.85, 0.43 and 0.49, indicating the formation of saturated alcohol is mostly favored for ethyl. The final conversions come to 99% for 24 h, and the ratios were 98%, 64%, 71%, 65%, 37%, 54%, respectively.When theβgroup changes from phenyl group to furyl group, the conversion increased (85% to 94% for CH3, 67% to 75% for C2H5) at 30 min. Furylacrolein was firstly converted to allyl alcohol (up to 90%), but the latter was easily oxidized to the corresponding acrolein and subsequently transformed to the saturated alcohol. After 24h, the yield of saturated alcohol is higher up to 99% for methyl group.These results indicated thatαandβsubstituents have significant effect on the bioreduction. The e.e. values of 2-ethyl-3-(2-furyl)-propyl alcohol converted fromα- ethyl -β- furylacrolein and 2- ethyl -3- (2-furyl)-allylic alcohol are both above 99% This work provides some useful hints for the baker's yeast mediated bioreduction of substituentedα,β- unsaturated aldehydes.