Studies on the neuroexcitotoxin β‐N‐oxalo‐L‐α, β‐diaminopropionic acid and its isomer α‐N‐oxalo‐L‐α, βdiaminopropionic acid from the root of Panax species

The neuroexcitotoxic nonprotein amino acid, β‐ N ‐oxalo‐L‐α, β‐diaminopropionic acid (β‐ 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. β‐ N ‐ODAP was verified to be a natural substance, and its isomer α‐ N ‐oxalo‐L‐α, β‐diaminopropionic acid (α‐ N ‐ODAP) is very likely an artifact generated during the separation process. The interconversion between β‐ N ‐ODAP and α‐ N ‐ODAP was observed. Results showed that both β‐ N ‐ODAP and α‐ 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, 1 H NMR, 13 C NMR and UV Mere obtained. ©Munksgaard 1996.