Manipulating Y receptor subtype activation of short neuropeptide Y analogs by introducing carbaboranes

Abstract Short selective neuropeptide Y (NPY) analogs are highly attractive because of their facile synthesis. Based on the reduced-size NPY analog [Pro30 , Nle31 , Bpa32 , Leu34 ]NPY 28–36 position 32 was identified as a key position to alter the preferential activation pattern of the human neuropeptide Y receptors (hYRs). By replacing benzoylphenylalanine (Bpa) by a biphenylalanine (Bip) the photostability was first improved while the biological activity was maintained. SAR-studies showed that both aromatic rings have a high influence on the preferential hYR subtype activation. Interestingly, replacement of Bpa32 by a strongly hydrophobic moiety changed the hYR subtype preference of the analog. Whereas the parent compound is able to activate the human neuropeptide Y1 receptor (hY1 R) subtype, the introduction of an Nε - ortho -carbaboranyl propionic acid modified lysine resulted in a loss of activity at the hY1 R but in an increased activity at both the hY2 R and the hY4 R. However, subsequent receptor internalization studies with this novel analog revealed that receptor internalization can neither be triggered at the hY2 R nor at the hY4 R suggesting a biased ligand. Surprisingly, investigations by1 H NMR spectroscopy revealed structural changes in the side chains of residues Pro30 and Leu34 which nicely correlates with the shift from hY1 R/hY4 R to hY2 R/hY4 R activation preference. Thus, position 32 has been identified to switch the bioactive conformation and subsequently influences receptor subtype activation behavior.