Synthesis of 2-substituted -tryptophan-containing peptide derivatives with endothelin receptor antagonist activity

Peptide derivatives with 2-substituted -tryptophan analogues were synthesized. All prepared peptide derivatives showed potent affinity for ETB receptors, while their ETA affinity depended on the substituents of the -tryptophanyl residue. A 2-bromo- -tryptophan derivative 16b (BQ-928) was a combined ETA/ETB receptor antagonist and a 2-cyano- -tryptophan derivative 17c (BQ-017) was a selective ETB receptor antagonist.