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| - Electronic Substituent Effects on the Cleavage Specificity of a Non-HemeFe2+-Dependent β-Diketone Dioxygenase and Their Mechanistic Implications
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| - Acinetobacter johnsonii acetylacetone dioxygenase (Dke1) is a non-heme Fe(II)-dependent dioxygenase that cleaves C−C bonds in various β-dicarbonyl compounds capable of undergoing enolization to a cis-β-keto enol structure. Results from 18O labeling experiments and quantitative structure−reactivity relationship analysis of electronic substituent effects on the substrate cleavage specificity of Dke1 are used to distinguish between two principle chemical mechanisms of reaction: one involving a 1,2-dioxetane intermediate and another proceeding via Criegee rearrangement. Oxygenative cleavage of asymmetrically substituted β-dicarbonyl substrates occurs at the bond adjacent to the most electron-deficient carbonyl carbon. Replacement of the acetyl group in 1-phenyl-1,3-butanedione by a trifluoro-acetyl group leads to a complete reversal of cleavage frequency from 83% to only 8% fission of the bond next to the benzoyl moiety. The structure−activity correlation for Dke1 strongly suggests that enzymatic bond cleavage takes place via nucleophilic attack to generate a dioxetane, which then decomposes into the carboxylate and α-keto-aldehyde products.
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