Muscarinic M3 receptor antagonists with (2R)-2-[(1R)-3,3-Difluorocyclopentyl]-2-hydroxyphenylacetamide Structures. Part 2

Optimization of the amine part of our original muscarinic M3 receptor antagonist 1 was performed to identify M3 receptor antagonists that are superior to 1. Compounds carrying a variety of diamine moieties without hydrophobic substituent on the nitrogen atom were screened against the binding affinity for the M3 receptor and the selectivity for M3 over the M1 and M2 receptors. This process led to a 4-aminopiperidinamide (2l) with a Ki value of 5.1 nM and with a selectivity of the M3 receptor that was 46-fold greater than that of the M2 receptor. Further derivatization of 2l by inserting a spacer group or by incorporating alkyl group(s) into the amine part resulted in the identification of an 4-(aminoethyl)piperidinamide 2l–b with a Ki value of 3.7 nM for the M3 receptor and a selectivity for the M3 receptor that was 170-fold greater than that of the M2 receptor.