Conformational constraints in angiotensin IV to probe the role of Tyr², Pro⁵ and Phe⁶

The aromatic amino acids Tyr and Phe in angiotensin IV (Ang IV) were conformationally constrained by the use of β-Me substituted analogs, or cyclic constrained analogs. None of these modifications was allowed for Tyr¹, while only e-β-MePhe⁶ substitution resulted in an AngIV analog with high IRAP potency and selectivity versus AP-N or the AT₁ receptor. This indicates an important role of the orientation of the Phe⁶ for inducing selectivity. Pro⁵ replacement with 2-aminocyclopentanecarboxylic acid maintained IRAP potency and abolished AT₁ affinity. These results confirm the importance of conformational constrained amino acids to generate selectivity in bioactive peptides.