A solvolytic C-C cleavage reaction of 6-acetoxycyclohexa-2,4-dienones: mechanistic implications for the intradiol catechol dioxygenases.
6-Acetoxycyclohexa-2,4-dienones are found to undergo a rapid reaction in methanol/water under mildly basic conditions to give an acyclic ketoester as the major product for 6-phenyl and 6-methyl substrates. Reaction monitoring by UV spectroscopy indicates the formation of an unsaturated ketone reaction intermediate (lambda(max) 275 nm, R = Ph) and the transient appearance of a highly conjugated species. Reaction of the 6-phenyl substrate (4.95 x 10(-6) s(-1)) is 2-fold faster than the 6-methyl substrate (2.47 x 10(-6) s(-1)). The reaction rate is first order with respect to substrate concentration, and the final step in the reaction is pH-dependent. No cleavage was observed for a substrate lacking an acetyl substituent. A reaction mechanism for C-C cleavage is proposed involving a benzene oxide-oxepin interconversion. The possible relevance to the catalytic mechanism of the intradiol catechol dioxygenases is discussed.
Eley
K L
KL
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
Crowley
P J
PJ
Bugg
T D
TD
D050548:Catechol 1,2-Dioxygenase; D003510:Cyclohexanes / Q000737:chemistry*; D053138:Cyclohexenes; D049308:Dioxygenases; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D010105:Oxygenases / Q000737:chemistry*; D012997:Solvents; D013057:Spectrum Analysis
D003510:Cyclohexanes; D053138:Cyclohexenes; D012997:Solvents; C048401:1,4-cyclohexadiene; D010105:Oxygenases; D049308:Dioxygenases; D050548:Catechol 1,2-Dioxygenase