3-HETEROARYL-SUBSTITUTED QUINUCLIDIN-3-OL AND QUINUCLIDIN-2-ENE DERIVATIVES AS MUSCARINIC ANTAGONISTS - SYNTHESIS AND STRUCTURE-ACTIVITY-RELATIONSHIPS

A number of 3-heteroaryl-substituted quinuclidin-3-ol and quinuclidin- 2-ene derivatives have been prepared and evaluated for muscarinic and antimuscarinic properties. The affinities of the new compounds (13, 14 , 16-32, and 36-52a,b) were tested in homogenates of cerebral cortex, heart, parotid gland, and urinary bladder from guinea pigs using (-)-[ H-3]-3-quinuclidinyl benzilate [(-)-[H-3]QNB] as the radioligand and i n a functional assay using isolated guinea pig urinary bladder. The pr esent compounds behaved as competitive muscarinic antagonists in the u rinary bladder. The highest receptor binding affinity, K-i (cortex) = 9.6 nM, was observed for 3-(2-benzofuranyl)quinuclidin-2-ene (31). The corresponding 3-benzofuranyl (36) and 3-benzothienyl (37) homologues had about 3.5-fold lower affinity for cortical muscarinic receptors. A ll quinuclidin-3-ol derivatives (14 and 16-25) had lower binding affin ities for the different muscarinic receptor subtypes than the correspo nding quinuclidin-2-ene analogues when examined in the various tissue homogenates. In general, the new compounds showed low subtype selectiv ity. The structure-affinity relationships are discussed in terms of di fferences in proton basicity of the azabicyclic nitrogen and differenc es in geometric, conformational, and/or electronic properties of the c ompounds. The cortical antimuscarinic potency is also related to the c omplementarity of the compounds to the putative binding site of the mu scarinic mi receptor.