The Design, Synthesis and Pharmacological Characterization of Potent Xanomeline-Based M1 and M4 mAChR Bitopic Ligands

The M4R has emerged as a promising therapeutic target for schizophrenia, highlighted by the recent FDA approval of Cobenfy (xanomeline coformulated with trospium chloride). However, xanomeline itself exhibits limited subtype selectivity and moderate efficacy. To address this, we applied a bitopic ligand strategy by combining xanomeline with the M4 muscarinic acetylcholine receptor (M4R) positive allosteric modulator MK cpd-97. Herein, we report on the design, synthesis, and pharmacological evaluation of a series of bitopic ligands featuring various aliphatic linkers. Derivatives with different linker lengths and types were tested across muscarinic receptor subtypes. Polymethylene-linked compounds showed minimal signaling bias and poor subtype selectivity, whereas PEG and polyamide linkers improved both properties. Notably, bitopic ligands incorporating diglycyl polyamide linkers exhibited the highest subtype preference with pronounced signaling bias. These findings provide insights into muscarinic ligand-receptor interactions and offer guidance for future bitopic ligand development.