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Structural comparison of endomorphin-2 and its conformationally restricted analog

100%
Borics A., Gach K., Fichna J., Sobolewski D., Toth G., Janecka A.
Open Chemistry
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2012
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vol. 10
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issue 1
172-179
EN
In the present study, the effect of a conformational constraint introduced into the endomorphin-2 (Tyr-Pro-Phe-Phe-NH2, EM-2) structure was studied using computational analysis and radioligand binding assay. EM-2 was modified by connecting nitrogen atoms of both phenylalanine residues by a methylene bridge. The obtained analog did not bind to the µ- or δ-opioid receptors in the in vitro studies. The computational analysis of this analog showed twisted, type IV turns and the absence of canonical β-turns typical for the EM-2 structure, which can be explained by the lack of hydrogen bonds involving Phe4. Our results show that the introduction of chemical constraint in the EM-2 structure has a significant effect on opioid receptor affinity and in vitro bioactivity.
2
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New bradykinin analogues acylated on the N-terminus: effect on rat uterus and blood pressure

84%
Labudda O., Wierzba T., Sobolewski D., Śleszyńska M., Gawiński Ł., Plackova M., Slaninová J., Prahl A.
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2007
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vol. 54
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issue 1
193-198
EN
Our previous studies suggested that acylation of the N-terminus of several known B2 antagonists with various kinds of bulky acyl groups consistently improved their antagonistic potency in rat blood pressure assay. On the other hand, our earlier observations also seemed to suggest that the effects of acylation on the contractility of isolated rat uterus depended substantially on the chemical character of the acyl group, as we observed that this modification might either change the range of antagonism or even transform it into agonism. Bearing all this in mind, we decided to synthesize seven new analogues of bradykinin by N-terminal acylation with various acyl groups of a moderately potent B2 antagonist, previously synthesized by Stewart's group, D-Arg-Arg-Pro-Hyp-Gly-Thr-Ser-D-Phe-Thi-Arg. The analogues were tested in vitro for their blood pressure-lowering and uterotonic activities. The modifications either preserved or increased the antagonistic potency in the rat blood pressure test. On the other hand, all seven substituents negatively influenced the interaction with the rat uterine receptors. Our results may be helpful for designing new B2 agonists and antagonists.
3
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New bradykinin B2 receptor antagonists - influence of C-terminal segment modifications on their pharmacological properties

84%
Śleszyńska M., Kwiatkowska A., Sobolewski D., Wierzba T., Katarzyńska J., Zabrocki J., Borovickova L., Slaninová J., Prahl A.
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EN
In the present study we describe the synthesis and some pharmacological properties of eight new analogues of bradykinin (BK). Two peptides were designed by substitution of position 7 or 8 of the known [d-Arg0,Hyp3,Thi5,8,d-Phe7]BK antagonist (Stewart's antagonist) with l-pipecolic acid (l-Pip). The next two analogues were obtained by replacement of the d-Phe residue in position 7 of the Stewart's peptide with l-β2-isoproline (l-β2-iPro) or l-β3-homoproline (l-β3-hPro). The four analogues mentioned above were also prepared in N-acylated form with 1-adamantaneacetic acid (Aaa). Biological activity of the compounds was assessed by isolated rat uterus and rat blood pressure tests. Our results showed that l-Pip in position 7 slightly increased antagonistic potency in the blood pressure test, but it turned the analogue into an agonist in the rat uterus test. Replacement of Thi by l-Pip in position 8 also enhanced antagonism in the rat pressure test but preserved the antagonism in the rat uterus test. l-β2-iPro or l-β3-hPro in position 7 decreased the potencies in both tests. We also demonstrated that acylation of the N-terminus did not increase, as was claimed previously, the antagonistic potencies of the resulting peptides. The results thus support the hypothesis about the existence of different types of BK receptors in the rat uterus and blood vessels. Our studies provide new information about the structure-activity relationship of BK antagonists which may help in designing more potent BK receptor blockers.
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