6β-Acetoxynortropane: A Potent Muscarinic Agonist with Apparent Selectivity toward M<sub>2</sub>-Receptors
作者:Xue-Feng Pei、Tara H. Gupta、Barbara Badio、W. L. Padgett、John W. Daly
DOI:10.1021/jm9705115
日期:1998.6.1
A series of tropane derivatives, related in structure to baogongteng A (1), an alkaloid from a Chinese herb, were synthesized. 6 beta-Acetoxynortropane (5) had weak affinity (K-i 22 mu M) for central (M-1) muscarinic receptors in a [H-3]quinuclidinyl benzilate binding assay but had extremely high affinity (K-i 2.6 nM) and selectivity for M-2-muscarinic receptors expressed in CHO cells. It had 13-fold lower affinity for M-4-receptors, 260-fold lower affinity for M-3-receptors, and 8200-fold lower affinity for M-1-receptors expressed in CHO cells. The 6 beta-carbomethoxy analogue (14) of baogongteng A had only weak affinity for M-2-muscarinic receptors, as did 6 beta-carbomethoxynortropane (13) and 6 beta-acetoxytropane (4). In transfected CHO cells, 6 beta-acetoxynortropane (5) was an agonist at M-2-receptors, based on a GTP-elicited decrease in affinity, and a full agonist with an IC50 of 11 nM at M-4-receptors, based on inhibition of cyclic AMP accumulation, while being a full agonist at M-1-receptors with an EC50 Of 23 nM and a partial agonist at M-3-receptors with an EC50 Of 3.6 nM, based in both cases on stimulation of phosphoinositide breakdown. All of the 16 tropane derivatives had weak affinities for central alpha(4) beta(2)-nicotinic receptors with 6 beta-carbomethoxynortropane (13) having the highest affinity, which was still 150-fold less than that of nicotine. 6 beta-carbomethoxynortropane (5) represents a potent muscarinic agonist with apparent selectivity toward M-2-receptors.