Muscarinic thioligands with cyclopentane nucleus

Synthesis and pharmacological characterization of new chiral derivatives of muscarine and allo-muscarine

Novel derivatives of natural muscarine and allo-muscarine, i.e. the benzyl ethers (-)-10 and (-)-12 and the benzoate (-)-13, were synthesized in very high enantiomeric excess. Target compounds were tested in vitro on guinea pig tissues, and their muscarinic potency was evaluated at M2 (heart force and rate) and M3 (ileum and bladder) receptor subtypes. The derivatives under study were also assayed in vivo on pithed rat. In addition, muscarinic receptor heterogeneity was investigated by determining the affinity and the relative efficacy of compounds (-)-10, (-)-12 and (-)-13 at M2 (heart force and rate) and M3 (ileum and bladder) receptor subtypes.

Evaluation of an agonist index: affinity ratio for compounds active on muscarinic cholinergic M2 receptors

A protocol for predicting full agonist, partial agonist, and antagonist profiles of compounds with M2 muscarinic cholinergic receptor activity was developed using radioligand binding assay techniques with [3H]-N-methyl scopolamine (NMS) and [3H]-Oxotremorine-M (Oxo-M) as radioligands. Full muscarinic cholinergic receptor agonists such as muscarine and oxotremorine-M expressed a high agonist index (> 3000 for M1 muscarinic cholinergic receptors and > 900 for M2 muscarinic cholinergic receptor), whereas muscarinic receptor antagonists (selective or non-selective) for different receptor subtypes gave a low (0.5-10) agonist index. Functional studies performed on preparations of guinea-pig ileum and heart were consistent with radioligand binding assay experiments. The above results suggest that similarly as already established for the M1 muscarinic cholinergic receptor subtype, evaluation of the [3H]-NMS/[3H]-Oxo-M ratio may provide useful information on the profile of compounds acting at the M2 muscarinic cholinergic receptor subtype. The availability of simple and predictive techniques for the characterization of muscarinic M2 cholinergic receptor agonists, may help the identification of new compounds in therapeutic areas in which stimulation or inhibition of this receptor is desirable.