Structure-activity relationship study of opiorphin, a human dual ectopeptidase inhibitor with antinociceptive properties

J Med Chem. 2012 Feb 9;55(3):1181-8. doi: 10.1021/jm2012112. Epub 2012 Jan 25.


Toward developing new potential analgesics, this first structure-activity relationship study of opiorphin (H-Gln-Arg-Phe-Ser-Arg-OH), a human peptide inhibiting enkephalin degradation, was performed. A systematic Ala scanning proved that Phe(3) is a key residue for neprilysin and aminopeptidase N (AP-N) ectoenkephalinase inhibition. A series of Phe(3)-halogenated analogues revealed that halogen bonding based optimization strategies are not applicable to this residue. Additional substituted Phe(3) derivatives showed that replacing l-Phe(3) for d-Phe(3) increased the AP-N inhibition potency by 1 order of magnitude. NMR studies and molecular mechanics calculations indicated that the improved potency may be due to CH-π stacking interactions between the aromatic ring of d-Phe(3) and the Hγ protons of Arg(2). This structural motif is not possible for the native opiorphin and may be useful for the design of further potent and metabolically stable analogues.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Analgesics / chemical synthesis*
  • Analgesics / chemistry
  • CD13 Antigens / antagonists & inhibitors*
  • CD13 Antigens / chemistry
  • Enzyme Assays
  • Humans
  • Magnetic Resonance Spectroscopy
  • Models, Molecular
  • Neprilysin / antagonists & inhibitors*
  • Neprilysin / chemistry
  • Oligopeptides / chemical synthesis*
  • Oligopeptides / chemistry
  • Protease Inhibitors / chemical synthesis*
  • Protease Inhibitors / chemistry
  • Quantum Theory
  • Salivary Proteins and Peptides / chemical synthesis*
  • Salivary Proteins and Peptides / chemistry
  • Solid-Phase Synthesis Techniques
  • Solutions
  • Structure-Activity Relationship


  • Analgesics
  • Oligopeptides
  • Protease Inhibitors
  • Salivary Proteins and Peptides
  • Solutions
  • glutaminyl-arginyl-phenylalanyl-seryl-arginine
  • CD13 Antigens
  • Neprilysin