title: Reexamination of the 1H NMR assignments and solution conformations of L-carnitine and O-acetyl-L-carnitine using C-2 stereospecifically labeled monodeuterated isomers.
abstract: The two C-2 monodeuterated isomers of L-carnitine were synthesized by enzymatic hydration of crotonobetaine in D2O and by enzymatic proton exchange of L-[2-2H2]carnitine in H2O. These reactions, catalyzed by an induced Escherichia coli carnitine hydrolyase proceed stereospecifically. The two isomers of L-[2-2H]carnitine were examined by 1H NMR at 500 MHz, which allowed us to independently monitor the pD dependence and coupling constants of the H-2 protons. The results obtained indicate that there is little effect of the carboxyl charge on the conformational state(s) of L-carnitine about the C-2/C-3 bond. The NMR data obtained in this study do not support previous solution studies of the pH-dependent conformational changes for DL-carnitine nor the proposed conformation of O-acetyl-DL-carnitine in the crystalline state.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: F
authors.initials: F
authors.lastname: Brewer
authors.forename: H
authors.initials: H
authors.lastname: Seim
authors.forename: S
authors.initials: S
authors.lastname: Englard
mesh_terms: D000108:Acetylcarnitine; D002331:Carnitine / Q000031:analogs & derivatives; D003903:Deuterium; D006859:Hydrogen; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D000108:Acetylcarnitine; D006859:Hydrogen; D003903:Deuterium; D002331:Carnitine