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Direct enantiomeric purity determination of the chiral anesthetic drug bupivacaine by 1H NMR spectroscopy.

The direct determination of the enantiomeric purity of the chiral anaesthetic drug bupivacaine has been developed using 1H NMR (400 MHz) spectroscopy with a chiral solvating agent. Optimization of experimental conditions in terms of temperature, substrate concentration and solvating agent to substrate molar ratio provided two significant signal splittings for chiral recognition resulting from diastereomeric solvation. Based on the relative intensities of the aliphatic methyl resonances assigned to (S)-(-)- and ($)-(+)-bupivacaine, the analysis of synthetic mixtures of the enantiomers by the proposed NMR method resulted in assay values which agreed closely with the known quantities of each enantiomer in the mixtures tested. The mean +/- SD recovery values for the (R)-(+)-enantiomer was 100.0 +/- 0.6% of added antipode (n = 7). The optically pure enantiomers were used to establish the minimum sensitivity of the NMR spectroscopic method of chiral analysis.