Development of potent and selective CCK-A receptor agonists from Boc-CCK-4: tetrapeptides containing Lys(N epsilon)-amide residues

Hydrocarbon activation. Synthesis of beta-cycloalkyl (di)nitriles through photosensitized conjugate radical addition

Photoinduced hydrogen abstraction from aliphatic cyclic hydrocarbons (C(5) to C(7), C(12), as well as adamantane) by triplet aromatic ketones in the presence of alpha,beta-unsaturated (di)nitriles offers a straightforward entry to the corresponding alkylated (di)nitriles via the alkyl radicals. Yields are moderate to good depending on the olefins structure (substitution in beta slows down the addition to mononitriles, but with alpha,alpha-dinitriles electronic activation allows efficient alkylation also of beta,beta-disubstituted substrates). A tandem alkylation-cyclization process has been obtained with (1-methylpent-4-enylidene)malononitrile.

CCK peptides with combined features of hexa- and tetrapeptide CCK-A agonists

Selective CCK-A agonist activity has been reported to induce satiety in a variety of animals, including man, and thereby suggests a therapeutic role for CCK in the management of obesity. To date, three general classes of CCK-A agonists have been reported, the full-length, sulfated hepta- and hexapeptides, a series of tetrapeptides, and most recently a series of benzodiazepines. The SAR of the hexa- and tetrapeptide classes suggests that the Hpa(SO(3)H) and Tac groups may not interact at the CCK-A receptor in the same location. However, the C-terminal dipeptide part of the hexapeptides and tetrapeptides appear to interact at the CCK-A receptor in a similar manner. Compound 7 (Hpa-Nle-Gly-Trp-Lys(Tac)-Asp-MePhe-NH(2)) derived from combining the features of the hexapeptides and the tetrapeptides has subnanomolar affinity and 3500-fold selectivity for CCK-A receptors. Compound 7 administered intraperitoneally produces potent, long-lasting reduction in food intake in rats and a corresponding weight loss when administered over nine consecutive days.

Structure-based design of new constrained cyclic agonists of the cholecystokinin CCK-B receptor

New constrained cyclic pseudopeptide cholecystokinin-B (CCK-B) agonists have been designed on the basis of conformational characteristics of the potent and selective CCK-B agonist Boc-Trp-(NMe)Nle-Asp-Phe-NH2 (Ki = 0.8 nM, selectivity ratio CCK-A/CCK-B > 6000) (Goudreau et al. Biopolymers, 1994, 34, 155-169). These compounds are among the first successful examples of macrocyclic constrained CCK4 analogs endowed with agonist properties and as such may be of value for the development of nonpeptide CCK-B agonists. The affinities and selectivities of these compounds for CCK-B and CCK-A receptors have been determined in vitro by measuring the displacement of [3H]pCCK8 binding to guinea pig cortex and pancreas membranes, respectively. The most potent compound, 8b, N-(cycloamido)-alpha-Me(R)Trp-[(2S)-2-amino-9- ((cycloamido)carbonyl)nonanoyl]-Asp-Phe-NH2, has a Ki value of 15 +/- 1 nM for guinea pig cortex membranes with a good CCK-B selectivity ratio (CCK-A/CCK-B = 147). Furthermore, 8b behaved as a potent and full agonist in a functional assay which measures the stimulation of inositol phosphate accumulation in CHO cells transfected with the rat CCK-B receptor (EC50 = 7 nM). The in vivo affinity of 8b for mouse brain CCK-B receptors was determined following intracerebroventricular injection (ID50 approximately 29 nmol/kg). 8b was also shown to cross the blood-brain barrier (0.16%), after intravenous administration in mice. 8b also increased gastric acid secretion measured in anesthetized rats after intravenous injection. Therefore, 8b appears to be an interesting pharmacological tool and is currently under investigation as a lead for further development of nonpeptide CCK-B agonists.