Dioxygenase-catalysed oxidation of monosubstituted thiophenes: sulfoxidation versus dihydrodiol formation

Abstract

Toluene dioxygenase (TDO)-catalysed sulfoxidation, using Pseudomonas putida UV4, was observed for the thiophene substrates 1A-1N. The unstable thiophene oxide metabolites, 6A-6G, 6K-6N, spontaneously dimerised yielding the corresponding racemic disulfoxide cycloadducts 7A-7G, 7K-7N. Dimeric or crossed [4 + 2] cycloaddition products, derived from the thiophene oxide intermediates 6A and 6D or 6B and 6D, were found when mixtures of thiophene substrates 1A and 1D or 1B and 1D were biotransformed. The thiophene sulfoxide metabolite 6B was also trapped as cycloadducts 17 or 18 using stable dienophiles. Preferential dioxygenase-catalysed oxidation of the substituent on the thiophene ring, including exocyclic sulfoxidation (1H-1J) and cis-dihydroxylation of a phenyl substituent (1G and 1N), was also observed. An enzyme-catalysed deoxygenation of a sulfoxide in P. putida UV4 was noticed when racemic disulfoxide cyclo-adducts 7A, 7B and 7K were converted to the corresponding enantioenriched monosulfoxides 8A, 8B and 8K via a kinetic resolution process. The parent thiophene 1A and the 3-substituted thiophenes 1K-1N were also found to undergo ring dihydroxylation yielding the cis/trans-dihydrodiol metabolites 9A and 9K-9N. Evidence is provided for a dehydrogenase-catalysed desaturation of a heterocyclic dihydrodiol (9Kcis/9Ktrans) to yield the corresponding 2,3-dihydroxythiophene (24) as its preferred thiolactone tautomer (23). A simple model to allow prediction of the structure of metabolites, formed from TDO-catalysed bacterial oxidation of thiophene substrates 1, is presented.

Microbial transformation of benzothiophenes, with carbazole as the auxiliary substrate, by Sphingomonas sp. strain XLDN2-5

“…Bioremediation is a potential treatment alternative for eliminating these contaminants in the environment. Fundamental research has been conducted to examine the biodegradation of these hazardous compounds (Fedorak & Grbić-Galić, 1991;Boyd et al, 1993;Kropp et al, 1994a;Boyd et al, 2003;Yu et al, 2006;Safinowski et al, 2006;Gai et al, 2007;Wang et al, 2007). However, it remains unclear whether benzothiophenes have an inhibitory effect on N-heterocyclic compounds such as CA, although other studies have shown that S-, N-and O-heterocyclic aromatic compounds can have a significant inhibitory effect on the biodegradation of polycyclic aromatic hydrocarbons (Dyreborg et al, 1996a(Dyreborg et al, , b, 1997Meyer & Steinhart, 2000).…”

Enantiopurity and absolute configuration determination of arene cis‐dihydrodiol metabolites and derivatives using chiral boronic acids

“…The enantiomeric mixtures of diols ( 68a cis ‐d cis and 71a cis ‐c cis ), on reaction with (−)‐( S )‐MEPBA 4a S , formed the major boronate diastereomers ( 70a–d and 73a–c ). 1 H–NMR analyses of the boronates showed the upfield OMe signals between ( δ OMe 3.06–3.27) and provided a range of Δ δ OMe values (15–120); the ee values were found in the range 43–63% (Table ) . As recorded earlier for boronates of carbocyclic cis ‐dihydrodiols, from polycyclic arenes, larger Δ δ OMe values were again observed for metabolites ( 71a cis ‐c cis , Δ δ OMe 90–120 Diagram 4) compared with the much smaller Δ δ OMe values from the monocyclic cis diols ( 68a cis ‐d cis , Δ δ OMe 15–25).…”

“…Stereochemical characterization of cis ‐diol metabolites, initially formed by TDO‐catalyzed dihydroxylation of thiophene ( 68a cis ‐d cis , 71a cis , and 71b cis ) and furan ( 71c cis ) rings (Scheme ), proved to be difficult, due to their equilibration (epimerization) with the corresponding trans isomers ( 68a trans ‐d trans and 71a trans ‐c trans ) at ambient temperature …”

“…The epimerization involved a spontaneous ring opening process via acyclic aldehyde intermediates ( 69a–d and 72a–c ), with the equilibrium favoring trans isomers in hydroxylic solvents (80–100% trans in CD 3 OD or D 2 O) and cis isomers in less polar solvents (60–80% cis in CDCl 3 ) . Reaction with (−)‐( S )‐MEPBA 4a S simplified the problem of stereochemical analysis, presented by cis / trans isomerization of the heterocyclic diols, as the corresponding boronates ( 70a–d and 73a–c ) were only formed from cis isomers.…”

Tandem enzyme‐catalysed reduction/ cis‐dihydroxylation of 2,2,2‐trifluoroace‐ tophenone: chemoenzymatic routes to new enantiopure phenol and benzylic alcohol reagents

“…The regio‐ and stereo‐selective dioxygenase‐catalysed cis ‐dihydroxylation of substituted benzene substrates, to yield the corresponding cis ‐dihydrodiols, has been extensively studied 1–11. These dioxygenase enzymes have also been found to catalyse stereoselective mono‐oxygenations (benzylic hydroxylation,12–18 sulfoxidation19–29) and alkene dihydroxylations 30. Due to the remarkable range, marked stereoselectivity and complexity of dioxygenase‐catalysed oxidation reactions observed earlier, recent studies have focused on identifying the factors that can determine the preference for different types of dioxygenase‐catalysed oxidation including arene or alkene cis ‐dihydroxylation,30 sulfoxidation or arene cis ‐dihydroxylation,29 benzylic hydroxylation or arene cis ‐dihydroxylation 18.…”