Inverse agonists at the polyamine-sensitive modulatory site of the NMDA receptor:: 50-fold increase in potency by insertion of an aromatic ring into an alkanediamine chain

Polyamines like spermine and spermidine increase the opening frequency of the NMDA receptor associated ion channel and, as a consequence, specific binding of non-saturating concentrations of the channel radioligand [H-3]MK-801. Compounds exhibiting the contrary effect have been described as polyamine inverse agonists, with 1,12-dodecanediamine (N-12-N) being one of the most specific ones (IC50 16.5 mu M). Here we describe the synthesis of a series of long-chain alkanediamines, with a thiophene nucleus inserted at various positions, and report the discovery of 5-(4-aminobutyl)-2-thiopheneoctanamine (N-4-T-8-N), which inhibited specific binding of [H-3]MK-801 by 50 % at 0.33 mu M. In the presence of 100 mu M of spermine, 4.0 mu M N-4-T-8-N was necessary to achieve the same degree of inhibition. N-4-T-8-N is the most potent polyamine inverse agonist presently known and should be a useful tool to elucidate the physiological significance of the polyamine regulatory site of the NMDA receptor complex. (C) Elsevier, Paris.