Speare Damian M, Fleming Sarah M, Beckett Martin N, Li Jian-Jun, Bugg Timothy D H
Department of Chemistry, University of Warwick, Coventry, UK.
Org Biomol Chem. 2004 Oct 21;2(20):2942-50. doi: 10.1039/B410322J. Epub 2004 Sep 16.
A chemical synthesis of the 2-hydroxy-6-ketohexa-2,4-dienoic acid intermediates on bacterial meta-cleavage pathways has been established, using a Heck coupling strategy. Coupling of ethyl 3-bromo-2-acetoxyacrylate with 1-aryl vinyl ketals or 1-aryl allylic alcohols proceeded in 70-90% yield. Heck coupling with an alkyl vinyl ketal was also successful, allowing the synthesis of an alkyl-substituted ring fission intermediate. The synthetic ring fission intermediates were used to investigate the enzymatic reaction catalysed by C-C hydrolase BphD from Pseudomonas LB400. A reduced substrate analogue 2,6-dihydroxy-6-phenylhexa-2,4-dienoic acid was processed enzymatically to benzaldehyde by C-C hydrolase BphD, consistent with a catalytic mechanism involving general base-catalysed attack of water to give a gem-diol intermediate, and not consistent with a nucleophilic mechanism. A series of para-substituted 2-hydroxy-6-keto-6-phenylhexa-2,4-dienoic acid substrates were assayed against BphD, and the derived Hammett plot (rho=-0.71) is consistent with a departing carbanion in the transition state for C-C cleavage.
利用Heck偶联策略，已建立了细菌间位裂解途径中2-羟基-6-氧代己-2,4-二烯酸中间体的化学合成方法。3-溴-2-乙酰氧基丙烯酸乙酯与1-芳基乙烯基缩酮或1-芳基烯丙醇的偶联反应产率为70-90%。与烷基乙烯基缩酮的Heck偶联也取得成功，从而能够合成烷基取代的环裂变中间体。合成的环裂变中间体用于研究来自假单胞菌LB400的C-C水解酶BphD催化的酶促反应。还原的底物类似物2,6-二羟基-6-苯基己-2,4-二烯酸被C-C水解酶BphD酶促加工为苯甲醛，这与涉及水的一般碱催化攻击以生成偕二醇中间体的催化机制一致，而与亲核机制不一致。针对BphD测定了一系列对取代的2-羟基-6-氧代-6-苯基己-2,4-二烯酸底物，得到的哈米特图（ρ = -0.71）与C-C裂解过渡态中离去的碳负离子一致。
