Solid phase synthesis and evaluation of Tyr-Tic-Phe-Phe(p-NHCOCH(2)Br) ([Phe(p-bromoacetamide)(4)]TIPP), a potent affinity label for delta opioid receptors.

Derivatives of the delta opioid receptor selective peptide Tyr-Tic-Phe-Phe-OH (TIPP) containing a p-bromoacetamide moiety on the phenyl ring of Phe(3) or Phe(4) were prepared by solid phase synthesis. [Phe(p-NHCOCH(2)Br)(4)]TIPP exhibited high affinity for cloned delta receptors (IC(50) = 5.4 nM), and incubation with only 2.5 nM resulted in 85% wash resistant inhibition of radioligand binding to delta receptors. Therefore, this peptide is a potent affinity label for further study of delta opioid receptors.