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Lookup NU author(s): Emeritus Professor Bernard Golding
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Coenzyme B12-dependent diol dehydratase converts 1,2-diols (e.g. propane-1,2-diol) into the corresponding aldehyde and water. The similar enzyme ethanolamine ammonia lyase transforms vicinal aminoalcohols (e.g. 2-aminoethanol) into the corresponding aldehyde and ammonia. Model systems have been developed that replicate key features of the putative enzymatic mechanism, i.e. removal of a hydrogen atom from the CH2OH group of a 1,2-diol or vicinal aminoalcohol by a methylene radical derived from an alkylcobalt compound, and conversion of a 1,2-diol or vicinal aminoalcohol into a carbonyl compound and water or ammonia triggered by such a methylene radical. The models are based on alkyl(pyridine)bis(dimethylglyoximato)cobalt complexes [alkyl(pyridine)cobaloximes, Cbx], which were synthesised from appropriate organic precursors using standard methodology. The complexes contain a 1,2-diol [as in 4,5-dihydroxy-2,2-dimethylpentyl(pyridine)cobaloxime] or vicinal aminoalcohol [as in 6-amino-5-hydroxy-2,2-dimethylhexyl(pyridine)cobaloxime] tethered to the cobalt by a carbon chain. Photolysis or thermolysis of 4,5-dihydroxy-2,2-dimethylpentyl(pyridine)cobaloxime at pH 3 or 9 gave 4,4-dimethylpentanal. It is proposed that homolysis of the Co-C bond of 4,5-dihydroxy-2,2-dimethylpentyl(pyridine)cobaloxime induced by photolysis or thermolysis affords the 1,2-dihydroxy-4,4-dimethyl-l-pentyl radical via a 1,5-H shift, which is converted into the 4,4-dimethyl-1-oxo-2-pentyl radical, and hence 4,4-dimethylpentanal. The pathway for formation of the aldehyde was diagnosed using the specifically deuteriated analogue [5,5-2H 2]-4,5-dihydroxy-2,2-dimethylpentyl(pyridine)-cobaloxime, which gave [1,5-2H2]-4,4-dimethylpentanal accompanied by 3,3-dimethylbutanal on thermolysis or photolysis at pH 3. The protected model compound 2a was hydrolysed to 6-amino-5-hydroxy-2,2-dimethylhexyl(pyridine)cobaloxime, which was heated at pH 3 or 9 to give 5,5-dimethylhexan-2-one and ammonia. © The Royal Society of Chemistry 2000.
Author(s): Andersen RJ, Ashwell S, Garnett I, Golding BT
Publication type: Article
Publication status: Published
Journal: Journal of the Chemical Society, Perkin Transactions 1
ISSN (print): 1472-7781
ISSN (electronic): 1364-5463
Publisher: Royal Society of Chemistry
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