Subtype‐selective inhibition of [methyl‐ 3 H] ‐N‐methylscopolamine binding to muscarinic receptors by α‐truxillic acid esters

Seven esters of α‐truxillic acid have been synthesized: bis‐3‐piperidylpropyl ester and its quaternary bis‐N‐ethyl derivative, bis‐N‐diethylaminopropyl ester and its quaternary bis‐N‐methyl derivative, and bis‐4‐piperidylbutyl ester and its quaternary bis‐N‐methyl and bis‐N‐ethyl derivatives. All esters inhibited the specific binding of muscarinic receptor antagonist [methyl‐ 3 H] ‐N‐methylscopolamine ([ 3 H]‐NMS) to muscarinic receptors in membranes of CHO cell lines stably expressing the human gene for the M 1 , M 2 , M 3 or M 4 subtype of muscarinic receptors. All esters displayed the highest potency at the M 2 and the lowest potency at the M 3 receptor subtype. In experiments performed on the M 2 muscarinic receptor subtype, the affinity between the receptors and the esters was greatly increased when the concentration of ions was diminished. The highest affinities were found for the tertiary bis‐3‐piperidylpropyl and bis‐4‐piperidylbutyl aminoesters (equilibrium dissociation constants of 52 and 179 pM, respectively, in the low ionic strength medium). All investigated esters slowed down the dissociation of [ 3 H]‐NMS from the M 2 muscarinic receptor subtype. [ 3 H]‐NMS dissociation from the M 1 , M 3 and M 4 muscarinic receptor subtypes was investigated in experiments with the bis‐4‐piperidylbutyl aminoester and also found to be decelerated. It is concluded that the esters of α‐truxillic acid act as M 2 ‐selective allosteric modulators of muscarinic receptors and that, by their potency, the tertiary bis‐3‐piperidylpropyl and bis‐4‐piperidylbutyl aminoesters surpass the other known allosteric modulators of these receptors.British Journal of Pharmacology (1999) 127 , 1240–1246; doi: 10.1038/sj.bjp.0702646