Synthesis and biological activity of CCK26-33-related analogs modified in position 31

Abstract

The role of the amino acid in position 31 of cholecystokinin CCK26-33 in the recognition of central and peripheral receptors was investigated by replacement of methionine-31 by amino acids with side chains of various chemical nature. Thus, phenylalanine, alanine, glutamic acid, and ornithine and its analogue with the epsilon-amino group protected by a benzyloxycarbonyl group were introduced as X residues in Boc(Nle28,X31)-CCK27-33 since the related analogue Boc(Nle28,Nle31)-CCK27-33 was shown to be equipotent to CCK26-33. The binding properties to both mouse brain membranes and guinea pig pancreatic acini and the peripheral activities (amylase secretion and contractile potency on guinea pig ileum) were determined. Whereas the introduction of phenylalanine, alanine, or ornithine residues in position 31 led to compounds that still displayed peripheral agonist properties, the presence of a negative charge in the side chain of the amino acid in position 31 prevented the binding of the peptide to both pancreatic and brain binding sites. Introduction of Phe31 and Ala31 residues increased the specificity of the peptides for the central receptors. Interestingly, when the amine function in the side chain of the ornithine-31 was protected by a benzyloxycarbonyl group, an unusual high affinity for pancreatic binding sites was observed and the related analogue proved to be a new peripheral CCK antagonist.

Structure-Based Design of New Constrained Cyclic Agonists of the Cholecystokinin CCK-B Receptor

“…59 On the other hand, introduction of a Phe 31 residue in CCK 8 analogs was found to favor recognition of the CCK-B receptor site. 60 As listed in Table 1, some of the compounds show slight differences in binding affinities using either the CCK-B receptor from guinea pig brain or CHO cells stably transfected with the rat CCK-B receptor, in accordance with variations observed in various species. 61 In vivo binding experiments on mice, performed using [ 3 H]pBC 264, gave an ID 50 value of (29 ( 6.5 nmol/kg) for 8b, while in the same conditions an ID 50 value of 8.5 ( 0.4 nmol was obtained for CCK 8 .…”

Structural studies on radiopharmaceutical DOTA-minigastrin analogue (CP04) complexes and their interaction with CCK2 receptor

“…Short Ala side chain in this position brings about a notable decrease in affinity 4. The drop is dramatic upon introduction of charged ornithine or glutamic acid side chains (similar to Met regarding the length) The side chain lies in a rather non-polar area with some free space around it allowing for example accommodation of a phenyl ring but not of the charged side chains [ 50 , 52 ] Trp −4 1. A change in stereochemistry results in a binding decrease 2.…”

Molecular Models for Cholecystokinin‐A Receptor

“…Negatively charged amino acid substitutions at CCK 7 position 31 are not tolerated and eliminate detectable binding at central and peripheral CCK‐receptors. However, agonists with hydrophobic substitutions at this position retain agonist activity (Marseigne et al 1988; Maletinska et al 1992).…”