Synthesis and Evaluation of Fluorinated Peptidomimetics Enabling the Development of ¹⁸ F‐Labeled Radioligands Targeting Muscarinic Acetylcholine Receptor Subtype M3

The muscarinic acetylcholine receptor subtype M3 is validated as a promising target for imaging and therapy in breast cancer. Transcriptomic and proteomic profiling reveal its overexpression, particularly in triple-negative breast cancer. To overcome challenges in developing selective M3 inhibitors, fluorinated peptidomimetic compounds are designed featuring a β-alanine-glycine scaffold that mimics key M3 pharmacophore elements. These constructs show strong potential as lead structures for ¹⁸F-labeled positron emission tomography (PET) radioligands, as demonstrated with lead compound 24, exhibiting M3-selective binding (M1/M3, M2/M3, M4/M3, and M5/M3 > 45) with an IC₅₀ value of 0.3 μM. Compound [¹⁸F]24 is prepared as the first M3-selective PET radioligand using reductive amination with 4-[¹⁸F]fluorobenzaldehyde, in a 35% decay-corrected radiochemical yield. Radioligand [¹⁸F]24 is tested for PET imaging of M3 receptors in preclinical breast cancer models.