Highly constrained dipeptoid analogues containing a type II' beta-turn mimic as novel and selective CCK-A receptor ligands.

Conformationally constrained dipeptoid analogues containing the type II' beta-turn mimic (2S,5s,11bR)-2-amino-3-oxohexahydroindolizino[8,7-b]indole-5 -carboxylate framework in place of the alpha-MeTrp residue, show high binding affinity and selectivity for CCK-A receptors, suggesting that a turn-like conformation could contribute to the bioactive conformation at this CCK receptor subtype.