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 μ opiate receptor(MOR) was EM 1 >[ D Ala 2]EM 1 >[ D Pro 2]EM 1 > EM 1 >[ L Tyr 3]EM >[ L Pro 3]EM >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 >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.
