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

Seven esters of alpha-truxillic acid have been synthesized: bis-3-piperidyl propyl ester and its quaternary bis-N-ethyl derivative, bis-N-diethylaminop ropyl ester and its quaternary bis-N-methyl derivative, and bis-4-piperidyl butyl ester and its quaternary bis-N-methyl and bis-N-ethyl derivatives. 2 All esters inhibited the specific binding of muscarinic receptor antagoni st [methyl-H-3]-N-methylscopolamine ([H-3]-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 hi ghest potency at the M-2 and the lowest potency at the M-3 receptor subtype . 3 In experiments performed on the M-2 muscarinic receptor subtype, the affi nity between the receptors and the esters was greatly increased when the co ncentration of ions was diminished. The highest affinities were found for t he tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters (equ ilibrium dissociation constants of 52 and 179 pM, respectively, in the low ionic strength medium). 4 All investigated esters slowed down the dissociation of [H-3]-NMS from th e M-2 muscarinic receptor subtype. [H-3]-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. 5 It is concluded that the esters of alpha-truxillic acid act as M-2-select ive allosteric modulators of muscarinic receptors and that, by their potenc y, the tertiary bis-3-piperidylpropyl and bis-4-piperidylbutyl aminoesters surpass the other known allosteric modulators of these receptors.