Reexamination of the 1H NMR assignments and solution conformations of L-carnitine and O-acetyl-L-carnitine using C-2 stereospecifically labeled monodeuterated isomers.
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.
Brewer
F
F
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
Seim
H
H
Englard
S
S
D000108:Acetylcarnitine; D002331:Carnitine / Q000031:analogs & derivatives; D003903:Deuterium; D006859:Hydrogen; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008968:Molecular Conformation; D013237:Stereoisomerism
D000108:Acetylcarnitine; D006859:Hydrogen; D003903:Deuterium; D002331:Carnitine