Stereoselective benzylic hydroxylation of 2-substituted indanes using toluene dioxygenase as biocatalyst

Indane, 1A, and a series of 2-substituted indane substrates, 1B-1D, 1G, 1I- 1L, were found to undergo benzylic monohydroxylation catalysed by toluene d ioxygenase, present in the intact cells of Pseudomonas putida UV 4, to yiel d enantiopure cis-indan-1-ols, 2A-2D, 2G, 2I-2L of the same absolute config uration at C-1 as major bioproducts. Enantiopure trans-indan-1-ols 6B, 6C, and 6G were also obtained as minor metabolites. Evidence of further sequent ial benzylic hydroxylation (bis-hydroxylation) was found only with substrat es 2A, 1C, 1D and 1L to yield the corresponding enantiopure trans-1,3-diols , 3A, 3C, 3D and 3L. Minor enzyme-catalysed processes also observed include benzylic alcohol oxidation to ketones (4A, 5A, 4B, 4L, 5L), ketone reducti on to benzylic alcohol 6A, ester hydrolysis to indan-2-ol 1B, and cis-dihyd roxylation of indan-1-ol 6A to triol 7. The enantiopurities and absolute co nfigurations of bioproducts have been determined using MTPA ester formation , circular dichroism spectroscopy and stereochemical correlation methods. The contribution of asymmetric oxidation and kinetic resolution to the prod uction of bioproducts of high ee (>98%), and the metabolic sequence involve d in their biotransformation by P. putida UV4 is discussed. Enantiocompleme ntarity was found during the benzylic hydroxylation of indan-2-ol 1B, using toluene dioxygenase and naphthalene dioxygenase, when both single enantiom ers of the metabolites 2B, 4B and 6B of opposite configurations were obtain ed.