- Chemistry of Extradiol Aromatic Ring Cleavage: Isolation of a Stable Dienol Ring Fission Intermediate and Stereochemistry of Its Enzymatic Hydrolytic Cleavage
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The meta-ring fission intermediate on the phenylpropionate catabolic pathway exists as a stable trans-dienol; its breakdown by hydrolase enzyme MhpC proceeds with overall replacement of the succinyl group by a proton from water with retention of stereochemistry.
- Lam, Winnie W. Y.,Bugg, Timothy D. H.
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- Stereochemistry of the reaction catalysed by 2-hydroxy-6-keto-6-phenyl-hexa-2,4-dienoic acid 5,6-hydrolase (BphD).
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The stereochemical course of the reaction catalysed by C-C hydrolase BphD from Burkholderia xenovorans LB400 occurs with replacement of a benzoyl group by hydrogen with overall retention of stereochemistry.
- Li, Jian-Jun,Bugg, Timothy D H
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p. 130 - 132
(2007/10/03)
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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
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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 (ρ = -0.71) is consistent with a departing carbanion in the transition state for C-C cleavage.
- Speare, Damian M.,Fleming, Sarah M.,Beckett, Martin N.,Li, Jian-Jun,Bugg, Timothy D. H.
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p. 2942 - 2950
(2007/10/03)
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