CCK-A receptor selective antagonists derived from the CCK-A receptor selective tetrapeptide agonist Boc-Trp-Lys(Tac)-Asp-MePhe-NH2 (A-71623).

Analogs of the CCK-A receptor selective agonist Boc-Trp-Lys(Tac)-Asp-MePhe-NH2 (A-71623) were prepared in which the lysine residue was replaced with L-4-aminophenylalanine and D-or L-3-aminophenylalanine. These new analogs were moderately potent antagonists of CCK-8 in the isolated guinea pig gallbladder with exceptional CCK-A receptor selectivity as evaluated in membrane preparations from CHO K1 cells stably transfected with human CCK-A and CCK-B receptors.