5-(Tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-Based Potent and Selective CCK1 Receptor Antagonists: Structure−Activity Relationship Studies on the Central 1,3-Dioxoperhydropyrido[1,2-c]pyrimidine Scaffold

To further define the pharmacophore of the potent and selective 5-(tryptophyl)amino-1,3-dioxoperhydropyrido[1,2-c]pyrimidine-based CCK1 receptor antagonists the electronic and topographic properties of the central 1,3-dioxoperhydro-pyrido[1,2-c]pyrimidine scaffold have been modified. With this aim, the 1- and 3-oxo groups have been replaced by the thioxo- and deoxi-analogues, and the fused piperidine ring has been contracted to the corresponding pyrrolidine moiety. The results of the evaluation of the new analogues as CCK receptor ligands, in rat pancreas and cerebral cortex preparations, showed that, whereas replacement of oxygen with sulfur is allowed, reduction of the 1- or 3-oxo groups or the contraction of the fused piperidine ring lead to the complete loss of binding affinity at CCK1 receptors. The thioxo-analogues 5a, 8a, 12a, and 12b showed functional CCK1 antagonist activity, inhibiting the CCK-8-stimulated amylase release from pancreatic acinar cells. The 1-thioxo analogue 5a, with subnanomolar ...