Conjugation of Short Peptides to Dibenzodiazepinone-Type Muscarinic Acetylcholine Receptor Ligands Determines M2R Selectivity

Muscarinic acetylcholine receptors (MRs), comprising five subtypes (M1R-M5R) in humans, exhibit a high degree of structural similarity. Therefore, subtype selective MR agonists and antagonists are lacking. We present an approach to highly M2R-selective MR antagonists based on the conjugation of di- or tripeptides to M2R-preferring dibenzodiazepinone-type MR antagonists. M2R selectivity was dependent on the peptide sequence and on the type of linker. The introduction of basic amino acids resulted in improved M2R selectivity (e.g., UR-AP148 (48): pK(i) (hM(2)R) of 8.97, ratio of K-i M1R/M2R/M3R/M4R/M5R of 49:1:6500:60:400) compared to reported pyridobenzo- and dibenzodiazepinone-type MR ligands. A supposed dualsteric binding mode of the DIBA-peptide conjugates, such as 48, at MRs was supported by molecular dynamics simulations.