Institut für Chemie, Carl von Ossietzky Universität Oldenburg, 26111, Oldenburg, Germany.
Institut für Chemie und Biologie des Meeres (ICBM), Carl von Ossietzky Universität Oldenburg, 26111, Oldenburg, Germany.
Chemistry. 2019 Mar 27;25(18):4722-4731. doi: 10.1002/chem.201805837. Epub 2019 Mar 1.
The constitutions and absolute configurations of two previously unknown intermediates, (1S,2S,4S)-2-hydroxy-4-isopropylcyclohexane-1-carboxylate and (S)-3-isopropylpimelate, of anaerobic degradation of p-cymene in the bacterium Aromatoleum aromaticum pCyN1 are reported. These intermediates (as CoA esters) are involved in the further degradation of 4-isopropylbenzoyl-CoA formed by methyl group hydroxylation and subsequent oxidation of p-cymene. Proteogenomics indicated 4-isopropylbenzoyl-CoA degradation involves (i) a novel member of class I benzoyl-CoA reductase (BCR) as known from Thauera aromatica K172 and (ii) a modified β-oxidation pathway yielding 3-isopropylpimeloyl-CoA analogously to benzoyl-CoA degradation in Rhodopseudomonas palustris. Reference standards of all four diastereoisomers of 2-hydroxy-4-isopropylcyclohexane-1-carboxylate as well as both enantiomers of 3-isopropylpimelate were obtained by stereoselective syntheses via methyl 4-isopropyl-2-oxocyclohexane-1-carboxylate. The stereogenic center carrying the isopropyl group was established using a rhodium-catalyzed asymmetric conjugate addition. X-ray crystallography revealed that the thermodynamically most stable stereoisomer of 2-hydroxy-4-isopropylcyclohexane-1-carboxylate is formed during p-cymene degradation. Our findings imply that the reductive dearomatization of 4-isopropylbenzoyl-CoA by the BCR of A. aromaticum pCyN1 stereospecifically forms (S)-4-isopropyl-1,5-cyclohexadiene-1-carbonyl-CoA.
报告了先前未知的两种中间产物（1S，2S，4S）-2-羟基-4-异丙基环己烷-1-羧酸酯和（S）-3-异丙基戊二酸单酯在细菌 Aromatoleum aromaticum pCyN1 中对 p-枯烯厌氧降解的结构和绝对构型。这些中间产物（作为 CoA 酯）参与了由甲基羟基化和随后氧化 p-枯烯形成的 4-异丙基苯甲酰-CoA 的进一步降解。蛋白基因组学表明，4-异丙基苯甲酰-CoA 的降解涉及（i）一种新型的 I 类苯甲酰-CoA 还原酶（BCR），如 Thauera aromatica K172 中所熟知，以及（ii）一种经过修饰的β-氧化途径，类似于 Rhodopseudomonas palustris 中苯甲酰-CoA 的降解生成 3-异丙基戊二酸单酯。通过立体选择性合成，通过甲基 4-异丙基-2-氧环己烷-1-羧酸酯获得了所有四个立体异构体的 2-羟基-4-异丙基环己烷-1-羧酸酯以及两种对映体的 3-异丙基戊二酸单酯的参考标准。手性中心携带异丙基使用铑催化的不对称共轭加成来建立。X 射线晶体学表明，在 p-枯烯降解过程中形成了热力学上最稳定的 2-羟基-4-异丙基环己烷-1-羧酸酯立体异构体。我们的发现表明，A. aromaticum pCyN1 的 BCR 对 4-异丙基苯甲酰-CoA 的还原去芳构化特异性地形成（S）-4-异丙基-1,5-环己二烯-1-羰基-CoA。
