Evidence for the formation of an enamine species during aldol and Michael-type addition reactions promiscuously catalyzed by 4-oxalocrotonate tautomerase.
The enzyme 4-oxalocrotonate tautomerase (4-OT), which has a catalytic N-terminal proline residue (Pro1), can promiscuously catalyze various carbon-carbon bond-forming reactions, including aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde, and Michael-type addition of acetaldehyde to a wide variety of nitroalkenes to yield valuable γ-nitroaldehydes. To gain insight into how 4-OT catalyzes these unnatural reactions, we carried out exchange studies in D2 O, and X-ray crystallography studies. The former established that H-D exchange within acetaldehyde is catalyzed by 4-OT and that the Pro1 residue is crucial for this activity. The latter showed that Pro1 of 4-OT had reacted with acetaldehyde to give an enamine species. These results provide evidence of the mechanism of the 4-OT-catalyzed aldol and Michael-type addition reactions in which acetaldehyde is activated for nucleophilic addition by Pro1-dependent formation of an enamine intermediate.
Department of Pharmaceutical Biology, Groningen Research Institute of Pharmacy, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen (The Netherlands).
Harshwardhan
H
Poddar
Mehran
M
Rahimi
Edzard M
EM
Geertsema
Andy-Mark W H
AM
Thunnissen
Gerrit J
GJ
Poelarends
D000447:Aldehydes / Q000737:chemistry / Q000378:metabolism*; D000588:Amines / Q000737:chemistry / Q000378:metabolism*; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D007535:Isomerases / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D015394:Molecular Structure
D000447:Aldehydes; D000588:Amines; C021918:4-oxalocrotonate tautomerase; D007535:Isomerases
4-oxalocrotonate tautomerase; H-D exchange; Michael addition; aldol reaction; enamine formation