Identification of novel muscarinic M(3) selective antagonists with a conformationally restricted Hyp-Pro spacer

The identification of potent and selective muscarinic M(3) antagonists that are based on the recently discovered triphenylpropioamide derivative, 1, and have a unique amino acid spacer group is described. The introduction of a hydroxyproline-proline group to the spacer site and the use of a propyl or cyclopropylmethyl group as the piperidine N-substituent led to the discovery of the novel M(3) selective antagonists [8c, 8g; K(i)700-fold, M(2)/M(3)>180-fold], which have a more rigid structure than 1.