Synthesis and antagonistic activity at muscarinic receptor subtypes of some 2-carbonyl derivatives of diphenidol.

A series of 2-carbonyl analogues of the muscarinic antagonist diphenidol bearing 1-substituents of different lipophilic, electronic, and steric properties was synthesized and their affinity for the M2 and M3 muscarinic receptor subtypes was evaluated by functional tests. Two derivatives (2g and 2d) showed an M2-selective profile which was confirmed by functional tests on the M1 and M4 receptors. A possible relationship between M2 selectivity and lipophilicity of the 1-substituent was suggested by structure-activity analysis. This work showed that appropriate structural modification of diphenidol can lead to M2-selective muscarinic antagonists of possible interest in the field of Alzheimer's disease.