Effects of cell stress protectant glutathione on the whole-cell biotransformation of ethyl 2-chloro-acetoacetate with Saccharomyces cerevisiae

The whole-cell biotransformation of the β-keto ester ethyl 2-chloro-acetoacetate to ethyl (2R,3S)-2-chloro-3-hydroxybutyrate with Saccharomyces cerevisiae was investigated. Due to the xenobiotic stress exerted by the alkylating substrate, several competing reactions (up to 54%) were encountered at the activated positions of the substrate molecule which are mediated by cytosolic glutathione (GSH): reductive dehalogenation, ester hydrolysis and cleavage of the C4-backbone (retro-Claisen condensation). The catalytic effect of a glutathione S-transferase accelerates these processes, but is not necessarily required for the reactions to occur. The ester hydrolysis product chloro-acetone and retro-Claisen product ethyl chloro-acetate significantly affect the stereoselectivity of the whole-cell reduction. However, for the dehalogenation product ethyl (S)-3-hydroxybutyrate no effects on the biotransformation were observed.