Glutamate and Aspartate Agonists Structurally Related to Ibotenic Acid

This mini-review describes a noval class of excitatory heterocyclic amino acid. The selective interactions of these synthetic amino acids with the central glutamic acid (GLU) and aspartic acid (ASP) receptors have been established on the basis of microelectrophoretic techniques using glutamic acid diethyl ester (GDEE) and alpha-aminoadipic acid (alpha-AA) as selective antagonists for GLU and ASP, respectively. The parent compound, ibotenic acid (IBO) preferentially activates ASP receptors, but elongation of the side chain of IBO afforded homoibotenic acid (homo-IBO), a GLU agonist. The introduction of bulky substituents into the heterocyclic ring of homo-IBO resulted in a dramatic increase in potency. Alteration of the position of the side chain in IBO to give alpha-amino-5-methyl-3-hydroxy-4-isoxazoleacetic acid (AMAA), preserved the ASP agonism. However, elongation of the side chain of AMAA gave alpha-amino-5-methyl-3-hydroxy-4-isoxazolepropionic acid (AMPA), which is a very powerful neuronal excitant with selective interaction with the GLU receptors. None of the new compounds are inhibitors of the binding of 3H-kainic acid (3H-KAIN) to rat brain membranes, indicating that the mechanism of action of these compounds is different from that of the neurotoxic compound KAIN. The described compounds may be important tools in future investigations of the physiological role and the mechanism of action of ASP and GLU in the central nervous system.