Synthesis and action of opiate receptor binding of endomorphin-1 and their analogs

Endomorphin-1 (EM-1) and its six analogs which were designed by rationally replacing the 2-/3-amino acid (Aa) of EM-1 were synthesized by using liquid phase peptides synthesis method to study their action of opiate receptor binding(AORB). The order of their affinity intensity for p-opiate receptor (MOR) was EM-1 > [D-Ala(2)]EM-1 > [D-Pro(2)]EM-1 > [Gly(2)]EM-1 > [L-Tyr(3)]EM > [L-Pro(3)]EM > [Gly(3)]EM The sequence of their selectivity for MOR is EM-1 > [D-Pro(2)]EM-1 = [L-Tyr(3)]EM > [D-Ala(2)]EM-1 = [L-Pro(3)]EM > [Gly(3)]EM The results showed that, comparatively speaking, the 2-Aa was more closely related to the selectivity of EM-1 while the 3-Aa to their affinity, though the different replacement changed the AORB of EM-1 dissimilarly.