Organic & Biomolecular Chemistry Dynamic Article Links Cite this: DOI: 10.1039/c1ob06678a www.rsc.org/obc PAPER Bacterial dioxygenase- and monooxygenase-catalysed sulfoxidation of benzo[b]thiophenes† Derek R. Boyd,* a Narain D. Sharma, a Brian McMurray, a Simon A. Haughey, a Christopher C. R. Allen, b John T. G. Hamilton, b,c W. Colin McRoberts, c Rory A. More O’Ferrall, d Jasmina Nikodinovic-Runic, e Lydie A. Coulombel e and Kevin E. O’Connor* e Received 3rd October 2011, Accepted 26th October 2011 DOI: 10.1039/c1ob06678a Asymmetric heteroatom oxidation of benzo[b]thiophenes to yield the corresponding sulfoxides was catalysed by toluene dioxygenase (TDO), naphthalene dioxygenase (NDO) and styrene monooxygenase (SMO) enzymes present in P. putida mutant and E. coli recombinant whole cells. TDO-catalysed oxidation yielded the relatively unstable benzo[b]thiophene sulfoxide; its dimerization, followed by dehydrogenation, resulted in the isolation of stable tetracyclic sulfoxides as minor products with cis-dihydrodiols being the dominant metabolites. SMO mainly catalysed the formation of enantioenriched benzo[b]thiophene sulfoxide and 2-methyl benzo[b]thiophene sulfoxides which racemized at ambient temperature. The barriers to pyramidal sulfur inversion of 2- and 3-methyl benzo[b]thiophene sulfoxide metabolites, obtained using TDO and NDO as biocatalysts, were found to be ca.: 25–27 kcal mol -1 . The absolute configurations of the benzo[b]thiophene sulfoxides were determined by ECD spectroscopy, X-ray crystallography and stereochemical correlation. A site-directed mutant E. coli strain containing an engineered form of NDO, was found to change the regioselectivity toward preferential oxidation of the thiophene ring rather than the benzene ring. Introduction Monooxygenase- and dioxygenase-catalysed oxidations of the isosteric substrates indene 1, 1a–c,2a–f benzo[b]thiophene (B[b]T) 2, 3a–l and substituted derivatives, have previously been studied in these and other laboratories. The stereoselective oxidation product from indene 1, was the (1S,2R)-epoxide 3 (up to 97% ee, Scheme 1) when using SMO from a Pseudomonas putida strain (CA-3) and derived E. coli recombinant strains. 1a–c Earlier studies 2a–f have also shown that biocatalytic asymmetric cis-dihydroxylation of the alkene bond in substrate 1, using different P. putida strains, can give the corresponding (1S,2R)- dihydrodiol 4 cis with variable degrees of stereoselectivity (20– >98% ee) depending on the type of dioxygenase used. Rhodococ- a School of Chemistry and Chemical Engineering, Queen’s University Belfast, Belfast, UK, BT9 5AG. E-mail: dr.boyd@qub.ac.uk; Tel: +44 (0) 28 90975419 b School of Biological Sciences, Queen’s University Belfast, Belfast, UK, BT9 5AG c Agri-food and Biosiences Institute for Northern Ireland, Belfast, UK, BT95PX d School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin, 4, Ireland e School of Biomolecular and Biomedical Sciences and Centre for Synthesis and Chemical Biology, University College Dublin, Belfield, Dublin, 4, Ireland. E-mail: kevin.oconnor@ucd.ie † Electronic supplementary information (ESI) available. See DOI: 10.1039/c1ob06678a Scheme 1 Isolated and potential products resulting from enzyme– catalysed oxidation of the five-membered rings in indene 1 and benzo[b]thiophene 2. cus strains have also been reported to yield epoxide 3, trans- indandiol 4 trans and cis-indandiol 4 cis among bioproducts obtained via oxygenase-catalysed oxidation of indene 1. 2e,2f In addition, asymmetric benzylic hydroxylation of indene 1 to yield (1R)- indenol 5 of variable enantiopurity (up to >98% ee) was also observed using different P. putida dioxygenases (Scheme 1). 2a–d Thus epoxide 3, cis-diol 4 cis , and benzylic alcohol 5, can each be formed by oxygenase-catalysed asymmetric oxidation of indene 1 with high ee values (≥97%) according to the type of oxygenase enzyme selected. This journal is © The Royal Society of Chemistry 2012 Org. Biomol. Chem. Downloaded by UNSW Library on 08 December 2011 Published on 01 December 2011 on http://pubs.rsc.org | doi:10.1039/C1OB06678A View Online / Journal Homepage