Structure-activity relationships of dimethindene derivatives as new M2-selective muscarinic receptor antagonists.
A series of 2,3-disubstituted indenes, which are analogues of the widely used histamine H(1) receptor antagonist dimethindene, have been synthesized and studied as muscarinic and histamine receptor antagonists. The affinities of these compounds for the five human muscarinic receptor subtypes (M(1)-M(5)) and for human histamine H(1) receptors were determined in radioligand binding studies using membranes from transfected Chinese hamster ovary (CHO) cells and [(3)H]N-methylscopolamine ([(3)H]NMS). The results demonstrate that the diisopropyl analogue 19 has a similar high affinity as (S)-dimethindene at M(2) receptors ((S)-dimethindene: pK(i) = 7.52; (-)-19: pK(i) = 7.37) with an improved selectivity pattern ((S)-dimethindene: M(2)/M(1) = 6-fold, M(2)/M(3) = 5-fold, M(2)/M(4) = 10-fold, M(2)/M(5) = 25-fold; (-)-19: M(2)/M(1) = 36-fold, M(2)/M(3) = 96-fold, M(2)/M(4) = 42-fold, M(2)/M(5) = 275-fold). In addition, compound (-)-19 showed 35-fold lower affinity at histamine H(1) receptors (pK(i) = 5.61) than (S)-dimethindene (pK(i) = 7.16). Another interesting compound is the fluoroethyl derivative 20 (pK(i)/M(2) = 7.49), which also exhibits a higher M(2) selectivity (M(2)/M(1) = 19-fold; M(2)/M(3) = 22-fold; M(2)/M(4) = 13-fold; M(2)/M(5) = 62-fold) than (S)-dimethindene. Unfortunately, compound 20 also shows a high affinity for histamine H(1) receptors (pK(i) = 8.14). The compound with the highest affinity for M(2) receptors (pK(i) = 7.91), the dimethylaminomethylene analogue 31, displayed only a small preference for M(2) receptors. In conclusion, compound (-)-19 might be useful to test the hypothesis that blockade of muscarinic M(2) receptors in the brain is a viable mechanism by which to produce improved cognition. This second-generation dimethindene analogue might also be the starting point for the development of M(2)-selective muscarinic antagonists useful for quantifying M(2) receptors in the central nervous system with positron emission tomography imaging.
Böhme
Thomas M
TM
Institute of Pharmacy, Johannes Gutenberg-University of Mainz, Staudinger Weg 5, D-55099 Mainz, Germany.
Keim
Christine
C
Kreutzmann
Kai
K
Linder
Matthias
M
Dingermann
Theo
T
Dannhardt
Gerd
G
Mutschler
Ernst
E
Lambrecht
Günter
G
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004115:Dimethindene / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D007192:Indenes / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D011869:Radioligand Assay; D043585:Receptor, Muscarinic M2; D011969:Receptors, Histamine H1 / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D007192:Indenes; D018727:Muscarinic Antagonists; D043585:Receptor, Muscarinic M2; D011969:Receptors, Histamine H1; D011976:Receptors, Muscarinic; C472571:diisopropyl(2-(3-(1-pyridin-2-ylethyl)-1H-inden-2-yl)ethyl)amine; D004115:Dimethindene