Nornicotine aqueous aldol reactions: synthetic and theoretical investigations into the origins of catalysis.
The recent discovery that nornicotine 1, a minor nicotine metabolite, can catalyze the aldol reaction under physiologically relevant conditions has initiated research efforts into the potential chemical roles of nicotine metabolites. Herein, we disclose studies aimed at determining the origin and thus mechanism of the nornicotine-catalyzed aqueous aldol reaction. Conformationally constrained compounds designed to mimic the low-energy conformations of nornicotine were synthesized and tested for aldol catalysis; however, none showed rate enhancements on par with nornicotine. To further explore the mechanism of this process, a density functional theory (DFT) study was performed by using a variety of compounds previously tested for catalysis. These in silico studies have uncovered an unprecedented mechanistic subtlety of aqueous aldol reactions. Unlike the single transition state model observed for aldol reactions in organic solvent, the nornicotine-catalyzed reaction in water proceeds via a two-step mechanism in which a water molecule is utilized in both steps and a stable intermediate is generated. In total, these studies validate the proposed enamine-based mechanism of nornicotine-catalyzed aqueous aldol reactions and also provide the basis for future studies into the stereoelectronic nature of individual catalyst structures.
Dickerson
Tobin J
TJ
Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA.
Lovell
Timothy
T
Meijler
Michael M
MM
Noodleman
Louis
L
Janda
Kim D
KD
D002384:Catalysis; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009538:Nicotine / Q000031:analogs & derivatives* / Q000737:chemistry*
D009538:Nicotine; C005311:nornicotine