Synthesis and biological activities of pseudopeptide analogs of the C-terminal heptapeptide of cholecystokinin. On the importance of the peptide bonds

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Abstract
A series of pseudopeptide analogues of the C-terminal heptapeptide of cholecystokinin in which each peptide bond, one at a time, has been replaced by a CH2NH bond were synthesized: Z-Tyr(SP3-)-Nle-Gly-Trp-Nle-A.psi.-(CH2NH)Phe-NH2 (1), Z-Tyr(SO3-)-Nle-Gly-Trp-Nle.psi.(CH2NH)Asp-Phe-NH2 (2), Z-Tyr(SO3-)-Nle-Gly-Trp.psi.-(CH2NH)Nle-Asp-Phe-NH2 (3), Z-Tyr(SO3-)-Nle-Gly.psi.(CH2NH)Trp-Nle-Asp-Phe-NH2 (4), Z-Tyr(SO3-)-Nle.psi.-(CH2NH)Gly-Trp-Nle-Asp-Phe-NH2 (5), Z-Tyr(SO3-)-Met-Gly-Trp-Nle-Asp.psi.(CH2NH)Phe-NH2 (6), Z-Tyr-(SO3-)-Met-Gly-Trp-Nle.psi.(CH2NH)-Asp-Phe-NH2 (7), Z-Tyr(SO3-)-Met-Gly-Trp.psi.(CH2NH)Nle-Asp-Phe-NH2 (8). These derivatives were studied for their ability to stimulate amylase release from rat pancreatic acini and to inhibit the binding of labeled CCK-9 to rat pancreatic acini and to guinea pig brain membrane CCK receptors. They were compared to the potent CCK-8 analogue Boc-Asp-Tyr(SO3-)-Nle-Gly-Trp-Nle-Asp-Phe-NH2. All of these pseudopeptides were able to stimulate amylase secretion with the same efficacy as CCK-8 but with varying potencies. These compounds were also potent in inhibiting the binding of labeled CCK-9 to CCK receptors from rat pancreatic acini and from guinea pig brain membranes.