SYNTHESIS AND BIOLOGICAL EVALUATION OF CHOLECYSTOKININ ANALOGS IN WHICH THE ASP-PHE-NH2 MOIETY HAS BEEN REPLACED BY A 3-AMINO-7-PHENYLHEPTANOIC ACID OR A 3-AMINO-6-(PHENYLOXY)HEXANOIC ACID

Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester (JMV180), an ana log of the C-terminal octapeptide of cholecystokinin (CCK-8), shows in teresting biological activities behaving as an agonist at the high-aff inity CCK binding sites and as an antagonist at the low-affinity CCK b inding sites in rat pancreatic acini. Although we did not observe any major hydrolysis of the ester bond of Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-As p-2-phenylethyl ester in our in vitro studies, we were aware of a poss ible and rapid cleavage of this ester bond during in vivo studies. To improve the stability of Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-2-phenyleth yl ester, we decided to synthesize analogs in which the ester bond wou ld be replaced by a carba (CH2-CH2) linkage. We synthesized the 3-amin o-7-phenylheptanoic acid (beta-homo-Aph) with the R configuration in o rder to mimic the Asp-2-phenylethyl ester moiety and the 3-amino-6-(ph enyloxy)hexanoic acid (H-beta-homo-App-OH), an analog of H-beta-homo-A ph-OH in which a methylene group has been replaced by an oxygen. (R)-b eta-Homo-Aph and (R)-H-beta-homo-App-OH were introduced in the CCK-8 s equence to produce Boc-Tyr(SO3H)-Nle-Gly-Trp-Nle-(R)-beta-homo-Aph-OH and oc-Tyr(SO3H)-Nle-Gly-Trp-Nle-(R)-beta-homo-App-OH. Both compounds were able to recognize the CCK receptor on rat pancreatic acini (IC50 = 12 +/- 8 nM and 13 +/- 5 nM, respectively), on brain membranes (IC50 = 32 +/- 2 nM and 57 +/- 5 nM, respectively), and on Jurkat T cells ( IC50 = 75 +/- 15 nM and 65 +/- 21 nM, respectively). Like Boc-Tyr(SO3H )-Nle-Gly-Trp-Nle-Asp-2-phenylethyl ester, both compounds produced max imal stimulation of amylase secretion (EC50 = 6 +/- 2 nM and 4 +/- 2 n M, respectively) with no decrease of the secretion at high concentrati on indicating that these compounds probably act as agonists at the hig h-affinity peripheral CCK-receptor and as antagonists at the low-affin ity CCK-receptor. Replacing the tryptophan by a D-tryptophan in such a nalogs produced full CCK-receptor antagonists. All these analogs might be more suitable for in vivo studies than Boc-Tyr(SO3H)-Nle-Gly-Trp-N le-Asp-2-phenylethyl ester.