Biotechnological Production, Isolation and Characterisation of (2R,3S)-2,3-Dihydroxy-2,3-Dihydrobenzoate.

Bacterial Rieske non-heme iron oxygenases catalyse the transformation of a wide range of aromatic compounds to vicinal cis-dihydrodiols. Such compounds have been successfully applied in chemoenzymatic synthetic routes for, for example, pharmaceuticals, natural products and polymers. In the case of benzoate, only (1S,2R)-cis-1,2-dihydroxy-2-hydrobenzoate is readily accessible via enzymatic transformation, but not the regioisomeric cis-2,3-dihydroxy-2,3-dihydrobenzoate (2,3-DD) or cis-3,4-dihydroxy-3,4-dihydrobenzoate. While trace amounts of putative cis-2,3-DD have been obtained before by using p-cumate 2,3-dioxygenase (PCDO) or a combination of chlorobenzene dioxygenase and nitrilase, none of these approaches enabled its production and isolation at a greater scale for potential use as a chiral building block in organic synthesis. We here provide a protocol for biotransformation of benzoate yielding (2R,3S)-2,3-dihydroxy-2,3-dihydrobenzoate using the PCDO of Pseudomonas citronellolis strain EB200 with negligible formation of side products. An isolation procedure suitable for production of the 2,3-DD sodium salt monohydrate at high purity (> 95%) at a gram scale, and a comprehensive characterisation of this novel metabolite is given.