α-Hydroxy-β-keto acid rearrangement–decarboxylation: impact on thiamine diphosphate-dependent enzymatic transformations
作者:Maryam Beigi、Sabrina Loschonsky、Patrizia Lehwald、Volker Brecht、Susana L. A. Andrade、Finian J. Leeper、Werner Hummel、Michael Müller
DOI:10.1039/c2ob26981c
日期:——
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 rearrangementâdecarboxylation of the initially formed α-hydroxy-β-keto acid rather than a donorâacceptor 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.
依赖硫胺二磷酸(ThDP)的MenD催化α-酮戊二酸与丙酮酸的反应,选择性地形成4-羟基-5-氧代己酸2,这似乎与生理底物α-酮戊二酸的酰基供体角色不一致。相比之下,α-酮戊二酸与乙醛的反应仅生成预期的5-羟基-4-氧代区位异构体1。这些反应通过核磁共振(NMR)和圆二色谱(CD)进行了研究,结果表明,与丙酮酸的反应中,观察到的区位选择性是由于最初形成的α-羟基-β-酮酸的重排-脱羧反应,而不是供体-受体底物角色的变化。进一步针对其他依赖ThDP的酶进行的实验,如YerE、SucA和CDH,验证了这种退化性脱羧反应可以与ThDP依赖的酶促转化中常见的酰醇的较低对映选择性相关。