Optical purity determination and 1H NMR spectral simplification with lanthanide shift reagents — V. Mephenytoin, 5-ethyl-3-methyl-5-phenyl-2,4-imidazolidinedione

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The 60-MHz 1H NMR spectra of racemic mephenytoin, I, have been studied with the achiral shift reagent, tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octane-dionato) europium (III), II, and the chiral reagent, tris[3-(trifluoromethylhydroxy-methylene)-d-camphorato] europium (III), III. Moderate values of the enantiomeric shift differences, Delta, were clearly observed for the NCH3, NH, aryl and CCH3 resonances in CDCl3 solution at 28 degrees C with added III. The NCH3 and NH absorptions could be useful for direct assays of optical purity. Thus, for a 0.34 molal solution of I in CDCl3 with a molar ratio III:I of 0.138, the value of Delta for the NCH3 resonance was 3.1 Hz (0.052 ppm) with 32% valley resolution.