Caffeine affects the stereoselectivity of microbial high cell density reductions with commercial grade Saccharomyces cerevisiae (Baker's yeast). Cyclic β-keto esters ethyl 2-oxocyclopentanoate (1) and ethyl 2-oxocyclohexanoate (3) were shown to be reduced with increased diastereoselectivity (1: 90.1 → 92.1% de, 3: 75.0 → 90.0% de) after addition of caffeine. Effects on enantioselectivity were less pronounced (1: 97.3 → 98.5% ee, 3: 90.1 → 92.1% ee). The observations are ascribed to the action of caffeine on cellular calcium homeostasis. These effects are accompanied by caffeine-induced cell-death, which preferably takes effect on pre-stressed cells which were found to decrease diastereoselectivity.
Organic & Biomolecular Chemistry
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