Dioxygenase-catalysed oxidation of disubstituted benzene substrates: benzylic monohydroxylation versus aryl cis-dihydroxylation and the meta effect.
Biotransformations of a series of ortho-, meta- and para-substituted ethylbenzene and propylbenzene substrates have been carried out, using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). The ortho- and para-substituted alkylbenzene substrates yielded, exclusively, the corresponding enantiopure cis-dihydrodiols of the same absolute configuration. However, the meta isomers, generally, gave benzylic alcohol bioproducts, in addition to the cis-dihydrodiols (the meta effect). The benzylic alcohols were of identical (R) absolute configuration but enantiomeric excess values were variable. The similar (2R) absolute configurations of the cis-dihydrodiols are consistent with both the ethyl and propyl groups having dominant stereodirecting effects over the other substituents. The model used earlier, to predict the regio- and stereo-chemistry of cis-dihydrodiol bioproducts derived from substituted benzene substrates has been refined, to take account of non-symmetric substituents like ethyl or propyl groups. The formation of benzylic hydroxylation products, from meta-substituted benzene substrates, without further cis-dihydroxylation to yield triols provides a further example of the meta effect during toluene dioxygenase-catalysed oxidations.
Boyd
Derek R
DR
School of Chemistry and Chemical Engineering, Queen's University of Belfast, Belfast, UKBT9 5AG. dr.boyd@qub.ac.uk
Sharma
Narain D
ND
Bowers
Nigel I
NI
Dalton
Howard
H
Garrett
Mark D
MD
Harrison
John S
JS
Sheldrake
Gary N
GN
D001426:Bacterial Proteins / Q000378:metabolism; D001555:Benzene Derivatives / Q000737:chemistry* / Q000378:metabolism; D001711:Biotransformation; D049308:Dioxygenases / Q000378:metabolism*; D006900:Hydroxylation; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D016958:Pseudomonas putida / Q000201:enzymology
D001426:Bacterial Proteins; D001555:Benzene Derivatives; D049308:Dioxygenases