STRUCTURE-ACTIVITY STUDIES OF PEPTIDE YY(22-36) - N-ALPHA-AC-[PHE(27)]PYY(22-36), A POTENT ANTISECRETORY PEPTIDE IN RAT JEJUNUM

Peptide YY (PYY) and its homologous peptide, neuropeptide Y (NPY), are known to exhibit potent antisecretory effects in the intestine. To determine the structural requirements to elicit antisecretory effects, we have synthesized several analogs of the PYY active site, PYY(22-36), and compared their binding affinities and antisecretory potencies in rat jejunum. These investigations revealed that the hydroxyl groups of Ser23 and Thr32, as well as the imidazole group of His26, are important for activity in the intestine. N-alpha-acetylation of PYY(22-36) increased both the binding affinity and antisecretory potency. Structure-activity studies with N-alpha-Ac-PYY(22-36) showed that substitution of His26 with parachlorophenylalanine (pCl-Phe) or Tyr36 with N-Me-Tyr reduced receptor affinity, while replacement of Tyr27 with Phe increased the activity substantially. Furthermore, acylation of the alpha-NH2 group with hydrophobic groups, myristic and naphthaleneacetic acids, substantially reduced the antisecretory potencies but not the binding affinities. Further modification of N-alpha-Ac-[Phe27]PYY(22-36) may lead to the development of more potent agonist compounds, which may provide a framework for the design of a new class of antidiarrheal drugs.