Gary N. Sheldrake

Enantioselective bacterial biotransformation routes to cis-diol metabolites of monosubstituted benzenes, naphthalene and benzocycloalkenes of either absolute configuration

Enzyme-catalysed kinetic resolution and asymmetric dihydroxylation routes to enantiopure cis-diol metabolites of arenes and benzocycloalkenes of either absolute configuration have been developed using appropriate strains of the bacterium Pseudomonas putida.

Enantiocomplementary preparation of (S)- and (R)-1-pyridylalkanols via ketone reduction and alkane hydroxylation using whole cells of Pseudomonas putida UV4

Abstract A previously unreported alcohol dehydrogenase enzyme in the mutant soil bacterium Pseudomonas putida UV4 catalyses the reduction of 2-, 3- and 4-acylpyridines to afford the corresponding ( S )-1-pyridyl alkanols, with moderate to high e.e., whilst under the same conditions 2,6-diacetylpyridine is readily converted to the corresponding enantiopure C 2 -symmetric ( S , S )-diol in one step. In contrast, the toluene dioxygenase enzyme in the same organism catalyses the hydroxylation of 2- and 3-alkylpyridines to ( R )-1-(2-pyridyl) and ( R )-1-(3-pyridyl)alkanols. This combination of oxidative and reductive biotransformations thus provides a method for preparing both enantiomers of chiral 1-pyridyl alkanols using one biocatalyst.

Toluene and naphthalene dioxygenase-catalysed sulfoxidation of alkyl aryl sulfides

A series of alkyl aryl sulfides were metabolised, using selected strains of the soil bacterium Pseudomonas putida containing either toluene dioxygenase (TDO) or naphthalene dioxygenase (NDO), to give chiral sulfoxides. Alkyl aryl sulfoxides 2a–2k, 4a–4j and 4l, having enantiomeric excess (ee) values of >90%, were obtained by use of the appropriate strain of P. putida (UV4 or NCIMB 8859). Enantiocomplementarity was observed for the formation of sulfoxides 2a, 2b, 2d, 2j, 4a, 4b and 4d, with TDO-catalysed (UV4) oxidation favouring the (R) enantiomer and NDO-catalysed oxidation (NCIMB 8859) the (S) enantiomer. Evidence of involvement of the TDO enzyme was obtained using a recombinant strain of Escherichia coli (pKST 11). The marked degree of stereoselectivity appears to be mainly due to enzyme-catalysed asymmetric sulfoxidation, however the possibility of a minor contribution from kinetic resolution, in some cases, cannot be excluded.

Structure and stereochemistry of cis-dihydro diol and phenol metabolites of bicyclic azaarenes from Pseudomonas putida UV4

Biotransformation of quinoline, isoquinoline, quinoxaline and quinazoline using growing cultures of Pseudomonas putida UV4 yielded cis-dihydro diols from the oxidation of the carbocyclic aromatic ring. Aromatic hydroxylation was observed in both carbocyclic and heterocyclic rings. Ring cleavage of the quinoline skeleton to yield anthranilic acid, and cis-diol formation (with alkene bond reduction) to yield cis-5, 6, 7, 8-tetrahydroquinazoline-5, 6-diol from quinazoline were observed. The cis-dihydro diol metabolites of quinoline (5, 6- and 7, 8-) and quinoxaline (5, 6-) were found to be optically pure, while metabolism of isoquinoline gave one homochiral (5, 6-) and one racemic (7, 8-)cis-dihydro diol product. The absolute configurations of the cis-dihydro diol metabolites have been determined using 1H NMR analyses, stereochemical correlations and X-ray crystallography methods.

Stereoselective cis-dihydroxylation of azulene and related non-aromatic polyenes

Abstract Dioxygenase-catalysed dihydroxylation of azulene and related non-aromatic polyenes has been found to yield enantiopure chiral cis -diols of synthetic potential.

Biotransformation of unsaturated heterocyclic rings by Pseudomonas putida to yield cis-diols

New cis-diol metabolites of both aromatic and non-aromatic heterocyclic rings have been isolated from growing cultures of a mutant strain of the soil bacterium Pseudomonas putida(UV4) and stereochemically assigned; a novel heterocyclic cis-diol of benzothiophene, 2,3-dihydroxy-2,3-dihydrobenzothiophene is found to exist exclusively in the cis-configuration in water but equilibrates readily with the trans-isomer.

Sulfoxides of high enantiopurity from bacterial dioxygenase-catalysed oxidation

Selected strains of the bacterium Pseudomonas putida(previously shown to effect dioxygenase-catalysed asymmetric cis-dihydroxylation of alkenes) have been found to yield chiral sulfoxides from the corresponding sulfides with a strong preference for the (R)- or (S)-configurations but without evidence of sulfone formation; similar results obtained using an Escherichia coli clone (pKST11, containing the Tod C1 C2 B and A genes encoding toluene dioxygenase from P. putida NCIMB 11767) are again consistent with a stereoselective dioxygenase-catalysed sulfoxidation.

Stereodirecting substituent effects during enzyme-catalysed synthesis of cis-dihydrodiol metabolites of 1,4-disubstituted benzene substrates

The cis-dihydrodiol enantiomer preferentially formed, by dioxygenase-catalysed oxidation of 1,4-disubstituted benzene substrates in growing cultures of Pseudomonas putida UV4, is found to be largely controlled by the relative size of the substituents.

An efficient and flexible synthesis of model lignin oligomers

The use of model compounds in the development of selective lignin depolymerisation processes has been limited by the lack of complexity of these models compared with lignin itself. In this paper we report a convergent and efficient synthetic method for the flexible, multi-gram preparation of model lignin hexamers and octamers containing three of the most common connectivity motifs found within native lignin, namely β-O-4′, 5-5′ and β-5′, which will be used to further the mechanistic understanding of lignin depolymerisation processes.

Enzymatic and chemoenzymatic synthesis and stereochemical assignment of cis-dihydrodiol derivatives of monosubstituted benzenes

Toluene dioxygenase-catalysed oxidation of mono-substituted benzene substrates (Rxa0=xa0F, Cl, Br, I, Me, Et, CH2OAc, CHCH2, CCH, CF3, CN, OMe, OEt, SMe) in growing cultures of Pseudomonas putida UV4 yielded the corresponding cis-dihydrodiol metabolites. Palladium-catalysed cross-coupling of cis-(1S,2S)-1,2-dihydroxy-3-iodocyclohexa-3,5-diene with a range of tributyltin compounds provided a chemoenzymatic route to a further series of cis-dihydrodiol derivatives of monosubstituted benzenes (Rxa0=xa0D, CH2CHCH2, Bun, SEt, SPri, SBut, SPh, SC6H4Me-4). The enantiopurities and absolute configurations of the cis-dihydrodiols, obtained by both enzymatic and chemoenzymatic routes, were determined by several new methods including 1H NMR spectroscopic analysis of the bis-MTPA esters of the 4-phenyl-1,2,4-triazoline-3,5-dione cycloadducts, X-ray crystallography, circular dichroism spectroscopy and stereochemical correlation.