Unlocking Nicotinic Selectivity via Direct C-H Functionalization of (-)-Cytisine

Differentiating nicotinic acetylcholine receptors (nAChR) to target the highaffinity nicotine alpha 4 beta 2 subtype is amajor challenge in developing effective addiction therapies. Although cytisine 1 and varenicline 2 (current smoking-cessation agents) are partial agonists of alpha 4 beta 2, these drugs display full agonism at the alpha 7 nAChR subtype. Site-specific modification of (-)-cytisine via Ir-catalyzed C. H activation provides access to C(10) variants 6-10, 13, 14, 17, 20, and 22, and docking studies reveal that C(10) substitution targets the complementary region of the receptor binding site, mediating subtype differentiation. C(10)modified cytisine ligands retain affinity for alpha 4 beta 2 nAChR and are partial agonists, show enhanced selectivity for alpha 4 beta 2 versus both alpha 4 beta 2 and alpha 7 subtypes, and critically, display negligible activity at alpha 7. Molecular dynamics simulations link the C(10) moiety to receptor subtype differentiation; key residues beyond the immediate binding site are identified, and molecular-level conformational behavior responsible for these crucial differences is characterized.