Polyamines and the NMDA receptor: Modifying intrinsic activities with aromatic substituents

Thirty-four spermidine (SPD) and spermine (SPM) derivatives with aromatic substituents were synthesized and tested as inhibitors of specific binding of the NMDA channel blocker [3H]MK-801 to membranes prepared from rat hippocampus and cerebral cortex. SPD and SPM derivatives with aromatic substituents at the primary amino groups were the most potent inhibitors (IC50 3.9–4.7 μM). These compounds most likely act directly at the NMDA ion channel, since 30 μM SPM had no pronounced influence on their inhibiting activities. SPD derivatives with aromatic substituents at the secondary amino group were either inactive or highly SPM-sensitive inhibitors (IC50 10–82 μM), depending on the size of the substituent. Our results support the hypothesis that an aromatic interaction site near the center of polyamine derivatives contributes to polyamine inverse agonism.