α-Hydroxy-β-keto acid rearrangement-decarboxylation: impact on thiamine diphosphate-dependent enzymatic transformations.

Maryam Beigi, Sabrina Loschonsky, Patrizia Lehwald, Volker Brecht, Susana L A Andrade, Finian J Leeper, Werner Hummel, Michael Müller

Index: Org. Biomol. Chem. 11(2) , 252-6, (2013)

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Abstract

The thiamine diphosphate (ThDP) dependent MenD catalyzes the reaction of α-ketoglutarate with pyruvate to selectively form 4-hydroxy-5-oxohexanoic acid 2, which seems to be inconsistent with the assumed acyl donor role of the physiological substrate α-KG. In contrast the reaction of α-ketoglutarate with acetaldehyde gives exclusively the expected 5-hydroxy-4-oxo regioisomer 1. These reactions were studied by NMR and CD spectroscopy, which revealed that with pyruvate the observed regioselectivity is due to the rearrangement-decarboxylation of the initially formed α-hydroxy-β-keto acid rather than a donor-acceptor substrate role variation. Further experiments with other ThDP-dependent enzymes, YerE, SucA, and CDH, verified that this degenerate decarboxylation can be linked to the reduced enantioselectivity of acyloins often observed in ThDP-dependent enzymatic transformations.