Small potent ligands to the insulin-regulated aminopeptidase (IRAP)/AT(4) receptor.

Angiotensin IV analogs encompassing aromatic scaffolds replacing parts of the backbone of angiotensin IV have been synthesized and evaluated in biological assays. Several of the ligands displayed high affinities to the insulin-regulated aminopeptidase (IRAP)/AT(4) receptor. Displacement of the C-terminal of angiotensin IV with an o-substituted aryl acetic acid derivative delivered the ligand 4, which exhibited the highest binding affinity (K(i) = 1.9 nM). The high affinity of this ligand provides support to the hypothesis that angiotensin IV adopts a gamma-turn in the C-terminal of its bioactive conformation. Ligand (4) inhibits both human IRAP and aminopeptidase N-activity and induces proliferation of adult neural stem cells at low concentrations. Furthermore, ligand 4 is degraded considerably more slowly in membrane preparations than angiotensin IV. Hence, it might constitute a suitable research tool for biological studies of the (IRAP)/AT(4) receptor.