Assessment of structurally diverse philanthotoxin analogues for inhibitory activity on ionotropic glutamate receptor subtypes: discovery of nanomolar, nonselective, and use-dependent antagonists.

An array of analogues of the wasp toxin philanthotoxin-433, in which the asymmetric polyamine moiety was exchanged for spermine and the headgroup replaced with a variety of structurally diverse moieties, was prepared using parallel solid-phase synthesis approaches. In three analogues, the spermine moiety was extended with an amino acid tail, six compounds contained an N-acylated cyclohexylalanine, and four analogues were based on a novel diamino acid design with systematically changed spacer length between N-cyclohexylcarbonyl and N-phenylacetyl substituents. The analogues were studied using two-electrode voltage-clamp electrophysiology employing Xenopus laevis oocytes expressing GluA1(i) AMPA or GluN1/2A NMDA receptors. Several of the analogues showed significantly increased inhibition of the GluN1/2A NMDA receptor. Thus, an analogue containing N-(1-naphtyl)acetyl group showed an IC(50) value of 47 nM. For the diamino acid-based analogues, the optimal spacer length between two N-acyl groups was determined, resulting in an analogue with an IC(50) value of 106 nM.