Isomers of 2-amino-7-phosphonoheptanoic acid as antagonists of neuronal excitants.

The D(-)-isomer of 2-amino-7-phosphonoheptanoic acid ( (-)APH) was active as an antagonist of N-methyl-D-aspartate (NMDA) excitation of central neurones. The L(+)-isomer was inactive. The antagonism was also selective, kainate and glutamate responses being relatively unaffected. Excitatory responses to ibotenic acid, a neurotoxic amino acid analogue, were less susceptible to blockade by (-)APH than NMDA, but more so than kainic acid. Ibotenate may therefore act partly on NMDA receptors.