Novel long-acting antagonists of muscarinic ACh receptors

The aim of this study was to develop potent and long-acting antagonists of muscarinic ACh receptors. The 4-hexyloxy and 4-butyloxy derivatives of 1-[2-(4-oxidobenzoyloxy)ethyl]-1,2,3,6-tetrahydropyridin-1-ium were synthesized and tested for biological activity. Antagonists with long-residence time at receptors are therapeutic targets for the treatment of several neurological and psychiatric human diseases. Their long-acting effects allow for reduced daily doses and adverse effects.

The binding and antagonism of functional responses to the agonist carbachol mediated by 4-hexyloxy compounds were investigated in CHO cells expressing individual subtypes of muscarinic receptors and compared with 4-butyloxy analogues.

The 4-hexyloxy derivatives were found to bind muscarinic receptors with micromolar affinity and antagonized the functional response to carbachol with a potency ranging from 30 nM at M₁ to 4 μM at M₃ receptors. Under washing conditions to reverse antagonism, the half-life of their antagonistic action ranged from 1.7 h at M₂ to 5 h at M₅ receptors.

The 4-hexyloxy derivatives were found to be potent long-acting M₁ -preferring antagonists. In view of current literature, M₁ -selective antagonists may have therapeutic potential for striatal cholinergic dystonia, delaying epileptic seizure after organophosphate intoxication or relieving depression. These compounds may also serve as a tool for research into cognitive deficits.