Cholecystokinin (CCK) is a 33-amino acid peptide with multiple functions in both the central nervous system (via CCK-B receptors) and the periphery (via CCK-A receptors). CCK mediation of satiety via the A-receptor subtype suggest a role for CCK in the management of obesity. The carboxy terminal octapeptide (CCK-8) is fully active in this regard, but is lacking in receptor selectivity, metabolic stability, and oral bioavailability. Inversion of the chirality of Asp7 in conjunction with N-methylation of Phe8 produces compound 5 which exhibits high affinity and 2100-fold selectivity for CCK-A receptors. Compound 6 (Hpa(SO3H)-Nle-Gly-Trp-Nle-MeAsp-Phe-NH2), derived from moving the N-methyl group from Phe to Asp, decreased CCK-B affinity substantially without affecting CCK-A affinity, giving a compound with 6600-fold selectivity for CCK-A receptors. These compounds inhibit food intake with nanomolar potency following intraperitoneal administration in fasted rats. In addition to greater potency, compound 6 produces weight loss in rats when administered over nine consecutive days. Intranasal administration of 6 potently inhibits feeding in beagle dogs. Compound 6 produces potent anorectic activity via the CCK-A receptor system.

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.