TAPP analogs containing β3 -homo-amino acids: synthesis and receptor binding

β-Amino acids containing α,β-hybrid peptides show great potential as peptidomimetics. In this paper, we describe the synthesis and affinity to μ-opioid and δ-opioid receptors of α,β-hybrids, analogs of the tetrapeptide Tyr- d-Ala-Phe-Phe-NH(2) (TAPP). Each amino acid was replaced with an l- or d-β(3) -h-amino acid. All α,β-hybrids of TAPP analogs were synthesized in solution and tested for affinity to μ-opioid and δ-opioid receptors. The analog Tyr-β(3) h- d-Ala-Phe-PheNH(2) was found to be as active as the native tetrapeptide.