A novel beta-turn mimic useful for mapping the unknown topology of peptide receptors.

Ethers of cis or trans D-4-hydroxyproline (Hype), adjacent to octahydroindole-carboxylic acid (Oic), introduce a beta-turn into the backbone of peptides when positioned respectively at the i+1 and i+2 position of the turn. This is confirmed by NMR experiments performed on a model tetrapeptide in water. Synthetic alteration of the ether group allows simple probing of the steric limits and electrostatic potential of a receptor binding site, a technique applied successfully to the bradykinin receptor.