6beta-Acyloxy(nor)tropanes: affinities for antagonist/agonist binding sites on transfected and native muscarinic receptors.
A series of esters of 6beta-hydroxynortropane and the N-methyl analogue 6beta-tropanol were synthesized and screened versus binding of an antagonist (quinuclidinyl benzilate) and an agonist (oxotremorine-M) at sites on human m(1)-, m(2)-, m(3)-, and m(4)-muscarinic receptors in transfected cell membranes and on native M(1)-muscarinic receptors in rat brain membranes and native M(2)-muscarinic receptors in rat heart membranes. Most 6beta-acyloxy(nor)tropanes had higher affinity versus oxotremorine-M binding compared to quinuclidinyl benzilate binding at transfected m(1)- and native M(1)-receptors, indicative of agonist activity. 6beta-Acetoxynortropane had K(i) values versus oxotremorine-M binding at m(1)-, m(2)-, and m(4)-receptors ranging from 4 to 7 nM. N-Methylation reduced affinity greatly as did increasing the size of the acyl moiety. The affinity of 6beta-benzoyloxynortropane and other analogues with larger acyl moieties was little affected by N-methylation or in some cases was increased. 6beta-Acyloxy(nor)tropanes and classical muscarinic agonists, such as muscarine and oxotremorine, had higher affinity versus oxotremorine-M binding compared to quinuclidinyl benzilate binding at native M(2)-muscarinic receptors of heart, but not at transfected m(2)-muscarinic receptors. Antagonist/agonist binding ratios were not obtained for transfected m(3)-receptors, since significant oxotremorine-M binding could not be detected. 6beta-Acyloxy(nor)tropane, two other (nor)tropanes, and the classical muscarinic agonists had higher affinity versus agonist binding compared to antagonist binding for transfected m(4)-receptors. The antagonist/agonist binding ratio method is clearly not always reliable for predicting agonist activity at muscarinic receptors.
Daly
J W
JW
National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA. johnd@intra.niddk.nih.gov
Gupta
T H
TH
Padgett
W L
WL
Pei
X F
XF
D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002540:Cerebral Cortex / Q000378:metabolism; D006224:Cricetinae; D006801:Humans; D066298:In Vitro Techniques; D018721:Muscarinic Agonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000378:metabolism; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D051381:Rats; D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D043588:Receptor, Muscarinic M4; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D014162:Transfection; D014326:Tropanes / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D018721:Muscarinic Agonists; D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D043588:Receptor, Muscarinic M4; D011976:Receptors, Muscarinic; D014326:Tropanes; D010095:Oxotremorine; C042743:oxotremorine M; D011813:Quinuclidinyl Benzilate