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Synthetic 6-aryl-2-hydroxy-6-ketohexa-2,4-dienoic Acid Substrates for C-C Hydrolase BphD: Investigation of a General Base Catalytic Mechanism

Synthetic 6-aryl-2-hydroxy-6-ketohexa-2,4-dienoic Acid Substrates for C-C Hydrolase BphD: Investigation of a General Base Catalytic Mechanism

Damian M Speare, Sarah M Fleming, Martin N Beckett, Jian-Jun Li, Timothy D H Bugg

Org Biomol Chem. 2004 Oct 21;2(20):2942-50.

PMID: 15480459

Abstract:

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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP352535843	3-Bromo-2,6-difluorophenylboronic acid		352535-84-3	Price

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