ABSTRACT
Six hybrid N-ureidoethylamides of octapeptides in which an N-terminal cyclic structure related to enkephalin was elongated by a C-terminal fragment of deltorphin were synthesized on MBHA resin. The synthetic procedure involved deprotection of Boc groups with HCl/dioxane and cleavage of the peptide resin with 45 % TFA in DCM. d-Lys and d-Orn were incorporated in position 2, and Lys, Orn, Dab, or Dap in position 5. The side chains of the dibasic amino function were protected with the Fmoc group. This protection was removed by treatment with 55 % piperidine in DMF, and cyclization was achieved by treatment with bis-(4-nitrophenyl)carbonate. Using various combinations of dibasic amino acids, peptides containing a 17-, 18-, 19- or 20-membered ring structure were obtained. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. Diverse opioid activities were observed, depending on the size of the ring. Extension of the enkephalin sequence at the C-terminus by a deltorphin fragment resulted in a change of receptor selectivity in favor of the δ receptor. The conformational propensities of selected peptides were determined using the EDMC method in conjunction with data derived from NMR experiments carried out in water. This approach allowed proper examination of the dynamical behavior of these small peptides. The results were compared with those obtained earlier with corresponding N-(ureidoethyl)pentapeptide amides.
Subject(s)
Enkephalins/chemical synthesis , Oligopeptides/chemical synthesis , Peptides, Cyclic/chemical synthesis , Animals , Enkephalins/chemistry , Enkephalins/pharmacology , Guinea Pigs , Ileum/drug effects , In Vitro Techniques , Male , Mice , Models, Molecular , Nuclear Magnetic Resonance, Biomolecular , Oligopeptides/chemistry , Oligopeptides/pharmacology , Peptides, Cyclic/chemistry , Peptides, Cyclic/pharmacology , Protein Conformation , Vas Deferens/drug effectsABSTRACT
Novel N-(ureidoethyl)amides of cyclic enkephalin analogs have been synthesized. The p-nitrophenyl carbamate of 1-Boc-1,2-diaminoethane was coupled with 4-methylbenzhydrylamine (MBHA) resin. The Boc group was removed by treatment with HCl/dioxane, and the peptide chain was assembled using Boc strategy. For deprotection of amino function, HCl/dioxane was used. D-Lys or D-Orn were incorporated in position 2, and the side chains of Lys, Orn, Dab, or Dap in position 5 were protected with Fmoc group. Side chain protection was removed by treatment with 55% piperidine in DMF, and cyclization was achieved by treatment with bis-(4-nitrophenyl)carbonate to form a urea bridge. The peptide was cleaved from the resin by treatment with 45% TFA in DCM. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. Divers opioid activities were observed, depending on the size of the ring. In comparison with [Leu(5)]enkephalin, all peptides were more active in the GPI assay (between 125 and 12 times), and some of them were also more potent in the MVD assay. The conformational propensities of each peptide were determined using the EDMC method in conjunction with NMR experiments. This approach allows treating the dynamical behavior of small peptides properly. The results were compared with those obtained previously for corresponding nonsubstituted amides and are in agreement with the biologically active conformation proposed by us earlier.
Subject(s)
Enkephalins/chemical synthesis , Animals , Enkephalins/chemistry , Enkephalins/pharmacology , Guinea Pigs , Ileum/drug effects , In Vitro Techniques , Magnetic Resonance Spectroscopy , Male , Mice , Models, Molecular , Molecular Structure , Protein Conformation , Structure-Activity Relationship , Vas Deferens/drug effectsABSTRACT
Six cyclic peptides related to dermorphin(1-7) have been synthesized. The synthesis of linear peptides containing diamino acid residues in positions 2 and 4 was carried out on a 4-methylbenzhydrylamine resin, and cyclization was achieved by treatment with bis-(4-nitrophenyl)carbonate to form a urea unit. The peptides were tested in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays. Diverse opioid agonist activities were observed, depending on the size of the ring. The results were compared with those obtained earlier for 1-4 dermorphin analogues. The conformations of all six dermorphin analogues were studied. The conformational space of the peptides was examined using the electrostatically driven Monte Carlo method. On the basis of NMR data, an ensemble of conformations was obtained for each peptide. The opioid activity profiles of the compounds are discussed in the light of the structural data.
