Novel functional M1 selective muscarinic agonists. 2. Synthesis and structure-activity relationships of 3-pyrazinyl-1,2,5,6-tetrahydro-1- methylpyridines. Construction of a molecular model for the M1 pharmacophore

Article abstract of DOI:10.1021/jm00100a005

A series of 3-(3-substituted-pyrazinyl)-1,2,5,6-tetrahydro-1- methylpyridines were synthesized and found to have high affinity for central muscarinic receptors. The ability of some of these compounds to inhibit the electrically stimulated twitch of the guinea pig vas deferens indicated that the compounds were M₁ agonists. M₁ agonist activity was related to the length of the side chain attached to the pyrazine ring, with maximal activity being obtained with the hexyloxy side chain. The (hexyloxy)pyrazine 3f lacked M₂ agonist activity as it failed to affect the guinea pig atria and was also relatively devoid of M₃ agonist activity as determined by its lack of tremorogenic and sialogogic effects in mice. A comparison of the M₁ agonist efficacy of these pyrazines and related 1,2,5-thiadiazoles and 1,2,5- oxadiazoles suggested that M₁ efficacy was related to the magnitude of electrostatic potential located over the nitrogens of the respective heterocycles. The heteroatom directly attached to the 3 position of the pyrazine or 1,2,5-thiadiazole heterocycle markedly influenced the M₁ efficacy of the compounds by determining the energetically favorably conformers for rotation about the bond connecting the tetrahydropyridyl ring and the heterocycle. A three-dimensional model for the M₁-activating pharmacophore was proposed based on computational studies and the model of the muscarinic pharmacophore proposed by Schulman.