Microbiological transformations: 49. Asymmetric biocatalysed Baeyer–Villiger oxidation: improvement using a recombinant Escherichia coli whole cell biocatalyst in the presence of an adsorbent resin

The biocatalyst used in this work was whole cells of Escherichia coli TOP10 [pQR239] into which had been cloned the cyclohexanone mono-oxygenase from Acinetobacter calcoaceticus NCIMB 9871. Here we describe how, using whole resting cells of this recombinant strain, the biotransformation of bicyclo[3.2.0]hept-2-en-6-one (1) to its corresponding regioisomeric lactones (−)-(1S,5R)-2-oxabicyclo[3.3.0]oct-6-en-3-one (2) and (−)-(1R,5S)-3-oxabicyclo[3.3.0]oct-6-en-2-one (3) could be improved from levels of 1 g l−1 (9.3 mM) to 20 g l−1 (185 mM). The rate and yield of the biotransformation were improved by (i) increasing the cell concentration, (ii) using a specially designed vessel with high aeration rates, and (iii) adding an adsorbent resin directly to the biotransformation medium. We tested a series of resins and selected Amberlite XAD-4 and Optipore L-493 for further studies. In the presence of 100 g l−1 Optipore L-493 resin, 20 g l−1 bicycloheptanone (1) was successfully converted to a mixture of the two expected lactones at an overall yield of 83% (70% preparative yield after purification). Both these products were obtained in nearly enantiopure form (e.e.>98%).