Synthesis, radioligand binding, and pharmacologic activities of a series of muscarinic receptor ligands including and related to azaprophen (6-methyl-6-azabicyclo[3.2.1]octan-3 alpha-ol 2,2-diphenylpropionate, 1) have been measured to determine activity and selectivity for muscarinic receptor subtypes. Pharmacologic affinities of antagonists were determined as pA2 values for antagonism of methacholine-induced tension responses in guinea pig ileum. Binding affinities were measured by competition against [3H]QNB binding in guinea pig ileum, rat heart and brain, and m1- or m3-transfected Chinese hamster ovary (CHO) cells. The efficacies of muscarinic agonists in brain were determined by the ratio of binding affinities against [3H]QNB or [3H]NMS and [3H]oxotremorine-M ([3H]Oxo-M). Nine muscarinic antagonists, including azaprophen, did not discriminate significantly between the subtypes of muscarinic receptors. KI values for receptor binding for azaprophen (1) were between 8.81 x 10(-11) and 4.72 x 10(-10) M in ileum, heart, brain, and m1- or m3-transfected CHO cells. The alpha- and beta-benzilate esters 5 and 6 are as potent as azaprophen, and diphenylacetate esters 3 and 4 and N-(6)-benzyl alpha-isomer 7 are less potent than azaprophen. Significant stereoselectivity was exhibited with (+)-azaprophen being approximately 200 times more potent than the (-)-enantiomers and the 3 beta-ol isomer 2 being ca. 50 times less potent than azaprophen in all systems. A molecular modeling-molecular mechanics study was conducted to account for the difference. Putative muscarinic agonists (analogues and isomers of 6-methyl-6-azabicyclo[3.2.1]octan-3-ol acetate) did not discriminate muscarinic receptor subtypes with KI values between 2.77 x 10(-6) and 4.33 x 10(-5) M without significant stereoselectivity in the systems examined. The most active analogue was (1R,3R,5S)-6-[1(R)-phenylethyl]-6-azabicyclo[3.2.1]octan-3 alpha-ol acetate. However, efficacies of these putative agonists were in general very low
Synthesis, molecular modeling studies, and muscarinic receptor activity of azaprophen analogues
Triggle, DJ., Kwon, YW., Abraham, P., Pitner, J., Mascarella, S., & Carroll, F. (1991). Synthesis, molecular modeling studies, and muscarinic receptor activity of azaprophen analogues. Journal of Medicinal Chemistry, 34(11), 3164-3171.