Introduction of a cis-prolyl mimic in position 7 of the peptide hormone oxytocin does not result in antagonistic activity
ABSTRACT New insights into the structure-activity relationship of the peptide hormone oxytocin are presented. Incorporation of the novel cis-prolyl mimic 2,2-dimethyl-1,3-thiazolidine-4-carboxylic acid (pseudoproline, PsiPro) at position 7 of the hormone yielded the analogue [Cys(Psi(Me,Me)pro)]7oxytocin (1) that showed a 92-95% induction of the cis peptide bond conformation between Cys6 and PsiPro7, as determined by one- and two-dimensional NMR spectra in water and in DMSO-d6. The impact of the dimethyl moiety regarding conformation and bioactivity was investigated by the synthesis of the corresponding dihydro compound, [Cys(Psi(H,H)pro)]7oxytocin (2). Biological tests of the uterotonic activity, the pressor activity, and the binding affinity to the rat and human oxytocin receptors were carried out. As a most significant result, no antagonistic activities were found for both the cis-constrained analogue 1 and analogue 2, suggesting that a cis conformation between residues 6 and 7 of the molecule does not result in antagonistic activity. However, the about 10-fold reduction in agonistic activity of 1 as compared to oxytocin is consistent with the reduction of the trans conformation from 90% for oxytocin to 5-8% for compound 1. Compound 1 retained a high binding affinity for the oxytocin receptor, with K(i) values of 8.0 and 1.9 nM for the rat and the human receptor, respectively. The correlation between the biological activities and the cis contents obtained from NMR analysis for compounds 1, 2, and oxytocin leads to the hypothesis that a cis/trans conformational change plays an important role in oxytocin receptor binding and activation.
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ABSTRACT: Eight synthetic histidine analogues of oxytocin and vasopressin are subject of investigations. The spectra of the peptides have been investigated in the terahertz band. The results are obtained in the terahertz time-domain spectroscopy arrangement.Optica Applicata 01/2014; 44(1). DOI:10.5277/oal40114 · 0.64 Impact Factor
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ABSTRACT: Incorporation of L- or D-Tic into position 7 of oxytocin (OT) and its deamino analogue ([Mpa(1)]OT) resulted in four analogues, [L-Tic(7)]OT (1), [D-Tic(7)]OT (2), [Mpa(1),L-Tic(7)]OT (3) and [Mpa(1),D-Tic(7)]OT (4). Their biological properties were described by Fragiadaki et al. (Eur J Med Chem 42:799-806, 2007). Their NMR study (NOESY, TOCSY, (1)H-(13)C HSQC spectra) is presented here. Analogues 1, 3 and 4 showed partial agonistic activity, analogue 2 was pure antagonist, suggesting that a cis conformation between residues 6 and 7 of the molecule does not result in antagonistic activity. However, the reduction in agonistic activity of analogues 1, 3 and 4 in comparison to oxytocin is consistent with the reduction of the trans conformation form. Binding affinity for the human oxytocin receptor with IC(50) value of 130, 730, 103, and 380 nM for peptides 1, 2, 3, and 4, respectively, showed lower affinity in the case of D analogues. Deamination slightly increased the affinity. The existence of both cis and trans configurations of the Cys(6)-D-Tic(7) bond is supported by observation of two sets of cross-peaks for (1)H and (13)C nuclei for most of the residues of the peptide not only in NOESY and TOCSY but also in (1)H-(13)C HSQC spectra. The MS and HPLC indicate the presence of a single molecule/peptide, and NMR data thus suggest that this second set of peaks is due to the cis conformation.Amino Acids 07/2010; 39(2):539-48. DOI:10.1007/s00726-009-0470-1 · 3.65 Impact Factor
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ABSTRACT: To answer the question of whether the conformation of the Leu-Pro bond is cis or trans in Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH2 when complexed with the SH2 domain of Stat3, we substituted 2,2-dimethyloxazolidines derived from serine (Ser(ΨMe,Mepro)) and threonine (Thr(ΨMe,Mepro)) for proline. The 2,2-dimethyloxazolidine and 2,2-dimethylthiazolidine pseudoproline (ΨPro) analogs induce predominantly cis Xxx-ΨPro peptide bonds. As these ΨPro analogs are acid-labile, the phosphopeptides were synthesized using Fmoc-based SPPS using unprotected phosphotyrosine and 4-hydroxybenzoate as the linker that allowed release from the support by alkaline ammonolysis, conditions that kept the oxazolidine rings intact. Incorporation of Ser(ΨMe,Mepro) resulted in 69% cis Leu-ΨPro bond content in aqueous solution whereas that for Thr(ΨMe,Mepro) analog was 63%. Affinities for Stat3 were 3–5 fold lower than the lead compound and were inversely correlated with cis content. Thus we conclude that the Leu-Pro peptide bond is trans when the peptide is bound to Stat3.International Journal of Peptide Research and Therapeutics 03/2007; 14(1):1-9. DOI:10.1007/s10989-007-9099-7 · 0.83 Impact Factor