Synthesis of mixed MOR/KOR efficacy cyclic opioid peptide analogs with antinociceptive activity after systemic administration

open10siSupported by the grant from the Medical University of Lodz No 503/1-156-02/503-01, a grant from the Medical University of Lodz for young researchers No 502-03/1-156-02/502-14-121 (RP). The authors wish to thank Jozef Cieslak for his excellent technical assistance and the Polish Ministry of Science and Higher Education for a Scholarship for Young Outstanding Scientists (RP).Cyclic pentapeptide Tyr-c[D-Lys-Phe-Phe-Asp]NH2, based on the structure of endomorphin-2 (EM-2), which shows high affinity to the μ-opioid receptor (MOR) and a very strong antinociceptive activity in mice was used as a parent compound for the structure-activity relationship studies. In this report we synthesized analogs of a general sequence Dmt-c[D-Lys-Xaa-Yaa-Asp]NH2, with D-1- or D-2-naphthyl-3-alanine (D-1-Nal or D-2-Nal) in positions 3 or 4. In our earlier papers we have indicated that replacing a phenylalanine residue by the more extended aromatic system of naphthylalanines may result in increased bioactivities of linear analogs. The data obtained here showed that only cyclopeptides modified in position 4 retained the sub-nanomolar MOR and nanomolar κ-opioid receptor (KOR) affinity, similar but not better than that of a parent cyclopeptide. In the in vivo mouse hot-plate test, the most potent analog, Dmt-c[D-Lys-Phe-D-1-Nal-Asp]NH2, exhibited higher than EM-2 but slightly lower than the cyclic parent peptide antinociceptive activity after peripheral (ip) and also central administration (icv). Conformational analyses in a biomimetic environment and molecular docking studies disclosed the structural determinants responsible for the different pharmacological profiles of position 3- versus position 4-modified analogs.partially_openembargoed_20180116Perlikowska, Renata; Piekielna, Justyna; Gentilucci, Luca; De Marco, Rossella; Cerlesi, Maria Camilla; Calo, Girolamo; Artali, Roberto; Tömböly, Csaba; Kluczyk, Alicja; Janecka, AnnaPerlikowska, Renata; Piekielna, Justyna; Gentilucci, Luca; De Marco, Rossella; Cerlesi, Maria Camilla; Calo, Girolamo; Artali, Roberto; Tömböly, Csaba; Kluczyk, Alicja; Janecka, Ann