Quantitative NMR analysis of L-Dopa in seeds from two varieties of Mucuna pruriens.

Abstract

L-Dopa, a key neurotransmitter used to treat neural disorders such as Parkinson's disease, is found in the seeds of the genus Mucuna at a sufficient concentration for possible commercial use. To develop a simple and reliable method to extract L-Dopa from M. pruriens seeds in an aqueous medium and then quantitate this compound using a 1 H qNMR method (internal standard); and also to evaluate the accuracy and reproducibility of this method with an NMR calibration curve. The extraction method of L-Dopa from M. pruriens was optimized. The quantitation with single point quantitative NMR (qNMR) and NMR calibration curve was based on the resonance properties of the main functional groups of the L-Dopa molecule, in particular the signals of the three aromatic protons, which were compared with the signal of an internal standard such as syringic acid. The accuracy (precision and trueness) and reproducibility of both NMR techniques were evaluated. The methods of single point qNMR and NMR calibration curve, applied to the seeds of two M. pruriens varieties, gave very similar L-Dopa contents: 3.0-3.2% and 3.0-3.1%, respectively. The statistical analysis confirmed the accuracy and reproducibility of this single point qNMR method (internal standard) for determining L-Dopa, as well as other commercial preparations of this species, without performing an NMR calibration curve.