N-Methylation of backbone amide bonds was conducted on a tetrapeptide that had been identified previously (Shiosaki, K.; et al. J. Med. Chem. 1991, 34, 2387-2842) as a potent and selective CCK-A agonist. No-Methylation at the position corresponding to A~ p 3~(CCK- 33 numbering) was consistent with high affinity, efficacy, and selectivity for the CCK-A receptor. Combination of this (N-Me) Asp with the (N-Me) Phe modification also provided a ...
