The solitary digger wasp Philanthus triangulum preys on honeybees with paralyzing venom, and then feeds the victims to their larvae. T. Piek and his colleagues have shown that the venom contains low molecular weight, polyamine-like components, philanthotoxins (PTX), which exhibit a variety of pharmacological properties on insect skeletal muscle. We isolated a potent glutamate receptor antagonist in this wasp venom, and determined the structure as being philanthotoxin (PhTX)〜433 (1) by spectral analyses and synthesis. L-Glutamate is a putative excitatory neurotransmitter at many synapses in vertebrates and invertebrates. Glutamate receptors are presumably involved in higher neural functions such as memory and learning, and in neurological disorders, e. g., epilepsy and Huntington's disease. With the aim of the isolation of the glutamate receptor, we next explored the structure-activity relationships of PhTX analogs, which resulted in higher active analogs such as 10 and 11. We then synthesized the radioactive analogs labeled with ^<125>I. Furthermore, syntheses of the ligands for affinity chromatography and the photoaffinity labeling reagents were investigated.