NMR regulatory analysis: enantiomeric purity determination for (R)-(-)-desoxyephedrine and antipode methamphetamine

Regulatory enantiomeric purity direct determination for (S)-(+)-methamphetamine, the widely abused DEA schedule II controlled substance, and (R)-(-)-desoxyephedrine, over-the-counter nasal inhaler decongestant were developed using 400 MHz 1H NMR spectroscopy. The efficient enantiomeric differentiation was obtained using a diamagnetic chiral solvating agent to dissimilarly perturb the NMR spectra of the enantiomeric solutes. Nonequivalence behavior was studied in terms of all variables that affect population and intrinsic spectra of the fast diastereomeric solvates. Assignment of enantiomer configuration was based on the relative field position of the resolved enantiomeric signals. Optimization of experimental conditions provided significant resolved enantiomeric signals suitable for quantification. Utilizing the relative intensities of the corresponding enantiomeric signals of the N-CH3 assigned to (S)-(+)-methamphetamine and (R)-(-)-desoxyephedrine, the analysis of synthetic enantiomeric mixtures by the proposed methods demonstrated excellent agreements with the known values of the enantiomers present. The mean +/- SD recovery values for the (R)-(-)-enantiomer was 99.9 +/- 0.4% of added antipode (n = 7). The optically pure enantiomer was used to establish the minimum amount detected by the proposed NMR spectroscopic method.