Facile Synthesis of Enantiopure 4-Substituted 2-Hydroxy-4-butyrolactones using a Robust Fusarium Lactonase

A facile chemo-enzymatic process has been developed for producing stereoisomers of 4-substituted 2-hydroxy-4-butyrolactones with good to excellent enantioselectivity. This process involves an easy separation of the diastereoisomers by column chromatography and efficient enzymatic resolution by whole cells of Escherichia coli JM109 expressing Fusarium proliferatum lactonase gene. This biocatalyst shows strong tolerance towards different substrate structures and at least three out four possible isomers could be obtained in excellent enantiomeric purity. Different substrate concentrations (10 mM-200 mM) were examined, giving a substrate to catalyst ratio of up to 26:1. This general and efficient enzymatic process provides access to stereoisomers of 4-substituted 2-hydroxy-4-butyrolactones readily and cost-effectively. The stereochemical assignments were conducted systematically based on NMR, X-ray diffraction and circular dichroism, leading to further understanding of the enzyme's stereoselectivity.