NMR-STUDIES OF DRUGS - H-1 AND C-13 NMR CHEMICAL-SHIFT ASSIGNMENTS IN ETIDOCAINE AND ETIDOCAINE HYDROCHLORIDE DETERMINED BY 2-DIMENSIONAL NMR-SPECTROSCOPY

H-1 and C-13 NMR chemical shift assignments were obtained for the local anesthetics etidocaine (1) and etidocaine hydrochloride (2) in CDCl3 solution, as well as for 2 in D2O solution. The COSY experiment was employed for proton-proton correlation, while one-bond and long-range 2D heteronuclear techniques allowed the assignments of all C-13 chemical shifts in each molecule. Etidocaine has a chiral carbon; etidocaine hydrochloride has, in addition to the natural chiral center, an acid-induced chirality at the protonated amine nitrogen, resulting in solvent-dependent diastereomers. Ten of the fourteen magnetically nonequivalent C-13 nuclei of 2 exhibit doubled C-13 resonance peaks (50.3 MHz, 20-degrees-C, CDCl3 solution) due to the presence of the two diastereomers.