Structure-activity relationships for allosteric NMDA receptor inhibitors based on 2-naphthoic acid.

Over-activation of N-methyl-d-aspartate (NMDA) receptors is critically involved in many neurological conditions, thus there has been considerable interest in developing NMDA receptor antagonists. We have recently identified a series of naphthoic and phenanthroic acid compounds that allosterically modulate NMDA receptors through a novel mechanism of action. In the present study, we have determined the structure-activity relationships of 18 naphthoic acid derivatives for the ability to inhibit the four GluN1/GluN2(A-D) NMDA receptor subtypes. 2-Naphthoic acid has low activity at GluN2A-containing receptors and yet lower activity at other NMDA receptors. 3-Amino addition, and especially 3-hydroxy addition, to 2-naphthoic acid increased inhibitory activity at GluN1/GluN2C and GluN1/GluN2D receptors. Further halogen and phenyl substitutions to 2-hydroxy-3-naphthoic acid leads to several relatively potent inhibitors, the most potent of which is UBP618 (1-bromo-2-hydroxy-6-phenylnaphthalene-3-carboxylic acid) with an IC(50) âˆ¼ 2 µM at each of the NMDA receptor subtypes. While UBP618 is non-selective, elimination of the hydroxyl group in UBP618, as in UBP628 and UBP608, leads to an increase in GluN1/GluN2A selectivity. Of the compounds evaluated, specifically those with a 6-phenyl substitution were less able to fully inhibit GluN1/GluN2A, GluN1/GluN2B and GluN1/GluN2C responses (maximal % inhibition of 60-90%). Such antagonists may potentially have reduced adverse effects by not excessively blocking NMDA receptor signaling. Together, these studies reveal discrete structure-activity relationships for the allosteric antagonism of NMDA receptors that may facilitate the development of NMDA receptor modulator agents for a variety of neuropsychiatric and neurological conditions.

Ca2+-calmodulin increases RyR2 open probability yet reduces ryanoid association with RyR2.

We have shown that physiological levels of Ca(2+)-calmodulin (Ca(2+)CaM; 50-100 nM) activate cardiac ryanodine receptors (RyR2) incorporated into bilayers and increase the frequency of Ca(2+) sparks and waves in cardiac cells. In contrast, it is well known that Ca(2+)CaM inhibits [(3)H]ryanodine binding to cardiac sarcoplasmic reticulum. Since the [(3)H]ryanodine binding technique does not reflect the effects of Ca(2+)CaM on RyR2 open probability (Po), we have investigated, using the reversible ryanoid, ryanodol, whether Ca(2+)CaM can directly influence the binding of ryanoids to single RyR2 channels independently of Po. We demonstrate that Ca(2+)CaM reduces the rate of ryanodol association to RyR2 without affecting the rate of dissociation. We also find that ryanodol-bound channels fluctuate between at least two distinct subconductance states, M(1) and M(2), in a voltage-dependent manner. Ca(2+)CaM significantly alters the equilibrium between these two states. The results suggest that Ca(2+)CaM binding to RyR2 causes a conformation change to regions of the channel that include the ryanoid binding site, thereby leading to a decrease in ryanoid association rate and modulation of gating within the ryanoid/RyR2 bound state. Our data provide a possible explanation for why the effects of Ca(2+)CaM at the single-channel level are not mirrored by [(3)H]ryanodine binding studies.

Aspartyl phosphonates and phosphoramidates: the first synthetic inhibitors of bacterial aspartate-semialdehyde dehydrogenase.

The synthesis of methylene phosphonate, difluoromethylene phosphonate and phosphoramidate analogues of aspartyl phosphate, together with reduced analogues, is described. These compounds were shown to be effective inhibitors of aspartate-semialdehyde dehydrogenase (ASA-DH) from Escherichia coli. However, despite the structural similarity of the compounds, different patterns of inhibition were observed, indicative of two phases of recognition and binding. Correlation between measured inhibition constants with pK(a) values supports the theory that binding at the phosphate binding site is optimised for singly ionised phosphate analogues.