Enzyme‐Catalysed Synthesis of Cyclohex‐2‐en‐1‐one cis‐Diols from Substituted Phenols, Anilines and Derived 4‐Hydroxycyclohex‐2‐en‐1‐ones

Abstract

Toluene dioxygenase‐catalysed cis‐dihydroxylations of substituted aniline and phenol substrates, with a Pseudomonas putida UV4 mutant strain and an Escherichia coli pCL‐4t recombinant strain, yielded identical arene cis‐dihydrodiols, which were isolated as the preferred cyclohex‐2‐en‐1‐one cis‐diol tautomers. These cis‐diol metabolites were predicted by preliminary molecular docking studies, of anilines and phenols, at the active site of toluene dioxygenase. Further biotransformations of cyclohex‐2‐en‐1‐one cis‐diol and hydroquinone metabolites, using Pseudomonas putida UV4 whole cells, were found to yield 4‐hydroxycyclohex‐2‐en‐1‐ones as a new type of phenol bioproduct. Multistep pathways, involving ene reductase‐ and carbonyl reductase‐catalysed reactions, were proposed to account for the production of 4‐hydroxycyclohex‐2‐en‐1‐one metabolites. Evidence for the phenol hydrate tautomers of 4‐hydroxycyclohex‐2‐en‐1‐one metabolites was shown by formation of the corresponding trimethylsilyl ether derivatives.magnified image

Toluene Dioxygenase-Catalyzed cis-Dihydroxylation of Quinolines: A Molecular Docking Study and Chemoenzymatic Synthesis of Quinoline Arene Oxides

“…Molecular docking studies of TDO-catalyzed cisdihydroxylations of mono-and di-substituted benzene substrates were conducted in other laboratories, using the GOLD program (Vila et al, 2016a(Vila et al, ,b, 2017. AutoDock and AutoDock Vina programs have similarly been used in our laboratories, to study TDO-catalyzed cis-dihydroxylation of other types of monocyclic arenes, e.g., substituted phenols and anilines and tricyclic heteroarenes, e.g., dibenzofuran and dibenzothiophene (Hoering et al, 2016;Boyd et al, 2017Boyd et al, , 2019. Relative free binding energies (kcal/mol −1 ) and relative proximity of arene bonds to dioxygen, within the TDO active site (Å), were determined by applying the AutoDock Vina program to monocyclic arenes (toluene, chlorobenzene) and mono-and bicyclic-azarenes in the current study.…”

Cis‐Dihydroxylation of Tricyclic Arenes and Heteroarenes Catalyzed by Toluene Dioxygenase: A Molecular Docking Study and Experimental Validation

“…Thus, AutoDock 4.2 molecular docking studies, of substituted phenol and aniline substrates with TDO, led to predictions about: (a) their preferred orientations during ci s‐dihydroxylation and (b) the resulting regioselectivity and stereoselectivity. These expectations were later confirmed by experimental results . This approach was applied to the TDO docking results obtained using 3‐hydroxybiphenyl 1 a as substrate, where the corresponding metabolites 2 a and 3 a were predicted to be the major and minor products respectively, resulting from lateral cis ‐dihydroxylation .…”

“…The TDO‐catalysed formation of cis ‐dihydrodiols from monocyclic phenols, e. g . compounds 2 a and 3 a from substrate 1 a was established earlier …”

“…Several molecular docking studies of TDO with monocyclic aromatic substrates, have recently been used to successfully match the resulting in silico predictions with reported benzylic monohydroxylation and arene cis ‐dihydroxylation results –. Thus, AutoDock 4.2 molecular docking studies, of substituted phenol and aniline substrates with TDO, led to predictions about: (a) their preferred orientations during ci s‐dihydroxylation and (b) the resulting regioselectivity and stereoselectivity.…”

Chemoenzymatic Synthesis of (−)-Ribisins A and B from Dibenzo[b,d]furan

“…In our laboratories, anilines, phenols, phenolic ethers, dibenzothi-ophene and dibenzofuran are among the more unexpected substrates recently found to undergo TDO-catalyzed cis-dihydroxylations. [24][25][26][27] One possible chemoenzymatic approach to the synthesis of ribisins, was to start with dibenzofuran as substrate, and then to add the required four oxygen atoms to the metabolite in a stereocontrolled manner. This method had the advantage that no carbon-carbon bond-forming reactions occurred in the entire synthetic sequence and the number of steps in the synthesis could in principle, be reduced.…”