The neurotoxic constituent of the legume Lathyrus sativus, beta-N-oxal
yl-alpha,beta-diaminopropionic acid, was thermally isomerized to an eq
uilibrium mixture (60/40) containing the non-toxic alpha-N-oxalyl-alph
a,beta-diaminopropionic acid. The same equilibrium mixture was establi
shed by starting with the alpha-isomer but required longer time. alpha
- and gamma-N-Oxalyl-alpha,gamma-diaminobutyric acids also underwent t
hermally induced isomerization with alpha-gamma, or gamma-alpha migrat
ion of the oxalyl group. Delta-N-Oxalylomithine and epsilon-N-oxalylly
sine did not isomerize under these conditions. The observation that th
e higher homologues do not undergo isomerization suggests the intramol
ecular nature of the reaction.