Studies on the neuroexcitotoxin beta-N-oxalo-L-alpha,beta-diaminopropionic acid and its isomer alpha-N-oxalo-L-alpha,beta-diaminopropionic acid from the root of Panax species.

The neuroexcitotoxic nonprotein amino acid, beta-N-oxalo-L-alpha,beta-diaminopropionic acid (beta-N-ODAP) was found in Panax species such as Panax ginseng 'C.A. Meyer' (cultivated in Northeastern China), Panax quinquefolius (L), Panax notoginseng 'F.H. Chen' (cultivated in Southwestern China), Korean red ginseng and Jilin (China) red ginseng. beta-N-ODAP was verified to be a natural substance, and its isomer alpha-N-oxalo-L-alpha,beta-diaminopropionic acid (alpha-N-ODAP) is very likely an artifact generated during the separation process. The interconversion between beta-N-ODAP and alpha-N-ODAP was observed. Results showed that both beta-N-ODAP and alpha-N-ODAP can easily be converted into their isomers at higher temperature or in acidic and basic solution. Their interconversion equilibrium constant and rate constants were obtained. Upon extensive study and a good understanding of the interconversion, accurate physical constants and spectroscopic data such as MS, 1H NMR, 13C NMR and UV were obtained.