Cyclic peptides with intramolecular S-S bonds are an important segment of the pharmaceutical market and are actively investigated as drug candidates for cancer, orphan, and autoimmune diseases. The disulfide bond-forming step often dictates the yield and purity of these peptides, yet its molecular mechanism in iodine-mediated oxidation remains poorly understood, and no predictive model is available. Herein, we employ hybrid density functional theory methods (PBE0-D3BJ/def2-TZVP/PCM(DMF)) to establish the intramolecular SN2-cyclization mechanism and demonstrate that it closely competes with a second cysteine oxidation. We present the first computational evidence for a diiodinated intermediate formed under excess iodine conditions, which reduces cyclic disulfide yield by favoring the linear SH-peptide. Based on this mechanistic insight, we develop a two-parameter kinetic model predicting the optimal iodine stoichiometry for S-S bond closure in peptides of varying ring size and structure. The model shows excellent agreement with experimental data for three desamino analogues of neurohypophyseal hormones: atosiban, desmopressin, and desaminooxytocin.

Exogenous N-terminal fragments of galanin, which are agonists of the GalR2 receptor, have therapeutic potential in experimental cardiac pathology. This implies the need to study their proteolytic stability in biological environments. The aim of this work was to evaluate the proteolytic degradation of galanin G1 (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2), its natural and modified fragments G2 and G3 (WTLNSAGYLLGPHA-OH and WTLNSAGYLLGPβAH-OH, respectively) in human plasma. The peptides were obtained by solid-phase synthesis using the Fmoc methodology, purified by HPLC; their structure was confirmed by MALDI-TOF mass spectrometry and 1H-NMR spectroscopy. The kinetics of galanins G1-G3 degradation in blood plasma was studied by 1H-NMR spectroscopy based on changes in the intensity of Trp2 signals at 310 K. The results indicate a higher proteolytic stability of the G3 peptide compared to the natural G2 fragment and full-length galanin G1. They indicate the potential of using modified peptide agonists of GalR2 receptors to protect vital organs in pathophysiological conditions.

Type 1 diabetes mellitus (T1DM) is the most severe form of diabetes, which is characterized by absolute insulin deficiency induced by the destruction of pancreatic beta cells. The aim of this study was to evaluate the effect of a structural analogue of apelin-12 ((NαMe)Arg-Pro-Arg-Leu-Ser-His-Lys-Gly-Pro-Nle-Pro-Phe-OH, metilin) on hyperglycemia, mitochondrial (MCh) respiration in permeabilized cardiac left ventricular (LV) fibers, the myocardial energy state, and cardiomyocyte membranes damage in a model of streptozotocin (STZ) diabetes in rats. Metilin was prepared by solid-phase synthesis using the Fmoc strategy and purified using HPLC. Four groups of animals were used: initial state (IS); control (C), diabetic control (D) and diabetic animals additionally treated with metilin (DM). The following parameters have been studied: blood glucose, MCh respiration in LV fibers, the content of cardiac ATP, ADP, AMP, phosphocreatine (PCr) and creatine (Cr), the activity of creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH) in blood plasma. Administration of metilin to STZ-treated rats decreased blood glucose, increased state 3 oxygen consumption, the respiratory control ratio in MCh of permeabilized LV fibers, and increased the functional coupling of mitochondrial CK (mt-CK) to oxidative phosphorylation compared with these parameters in group D. In STZ-treated animals metilin administration caused an increase in the PCr content and prevention of the loss of total creatine (ΣCr=PCr+Cr) in the diabetic hearts, as well as restoration of the PCr/ATP ratio in the myocardium and a decrease in the activity of CK-MB and LDH in plasma to initial values. Thus, metilin prevented energy disorders disturbances in cardiomyocytes of animals with experimental T1DM.

An industry-ready approach for the synthesis of terlipressin is developed: the entire peptide chain assembly and subsequent disulfide bond closure are carried out on a polymeric carrier with a specific precaution for the protection of the N-terminal α-amino group. The effect of various factors on the purity of crude disulfide was studied, and the solid-phase cyclization process was optimized. The designed approach has high fidelity and reproducibility and is applicable for a large-scale peptide synthesis (we show it up to 15 g of the pure product). Using molecular modeling, we have found that the state of the N-terminal amino group (free or protected) has a significant influence on the ability of two cysteine side chains to reach each other, paving the way to a rational choice of protecting groups in peptide synthesis.

Objectives: The aim of this work was to elucidate the role of GalR2 receptor activation in protecting the rat heart in vivo from ischemia/reperfusion (I/R) damage by a pharmacological peptide agonist WTLNSAGYLLGP beta AH-OH (G1) and full-length rat galanin GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2 (G2) using M871, a selective inhibitor of GalR2. Methods: The peptides were prepared by the automatic solid-phase synthesis using the Fmoc-strategy and purified by high-performance liquid chromatography (HPLC). A 40-min left anterior descending (LAD) coronary artery occlusion followed by a 60-min reperfusion was performed. The criteria for damage/protection of the heart were the infarct size (IS) and plasma activity of creatine kinase-MB (CK-MB) at the end of reperfusion. Results: Intravenous injection of G1 or G2 at an optimal dose of 1 mg/kg at the fifth minute of reperfusion significantly reduced the IS (by 35% and 32%, respectively) and activity of CK-MB at the end of reperfusion (by 43% and 38%, respectively) compared with the control. Administration of M871 (8 mg/kg) 5 min before the onset of reperfusion abolished the effects of G1 on IS and CK-MB activity, returning them to control values. Co-administration of M871 (8 mg/kg) with G2 attenuated protective effect of G2 on both IS and plasma CK-MB activity. However, differences in these parameters between the M871+G2 and G2 groups did not reach statistical significance (P = 0.139 and P = 0.121, respectively). Conclusion: Thus, GalR2 is the principal receptor subtype that transduces the protective effects of galanin and ligand G1 in myocardial I/R injury. This suggests that GalR2-specific peptide agonists could be used as drug candidates for treating ischemic heart disease.

The aim of this work was to design and characterize peptides based on the α-helices h1 and h2 of the ACE2 receptor, forming the interaction interface between the receptor-binding domain (RBD) of the SARS-CoV-2 S protein and the cellular ACE2 receptor. Monomeric and heterodimeric peptides connected by disulfide bonds at different positions were synthesized. Solubility, RBD-binding affinity, and peptide helicity were experimentally measured, and molecular dynamics simulation was performed in various solvents. It was established that the preservation of the helical conformation is a necessary condition for the binding of peptides to RBD. The peptides have a low degree of helicity and low affinity for RBD in water. Dimeric peptides have a higher degree of helicity than monomeric ones, probably due to the mutual influence of helices. The degree of helicity of the peptides in trifluoroethanol is the highest; however, for in vitro studies, the most suitable solvent is a water-ethanol mixture.

Antioxidant and anti-ischemic properties of the pharmacological agonist of galanin receptor GalR2 WTLNSAGYLLGPβAH (Gal) and its C-terminal fragment, dipeptide carnosine (βAH), were studied in the model of regional ischemia and reperfusion of the rat heart in vivo in the dose range of 0.5-5.0 mg/kg and Cu²⁺-induced free radical oxidation of low density lipoproteins (LDL) of human plasma in vitro for peptide concentrations of 0.01 mM and 0.1 mM. Gal was obtained by automatic solid phase synthesis using the Fmoc methodology; its structure was characterized by 1H-NMR spectroscopy and MALDI-TOF mass spectrometry. Intravenous administration of the optimal dose of Gal (1 mg/kg) to rats after ischemia was more effective than carnosine in reducing of the myocardial infarct size and the activity of creatine kinase-MB and lactate dehydrogenase in blood plasma at the end of reperfusion. It also improved the metabolic state of the reperfused myocardium and reduced the formation of peroxidation products during reperfusion. Gal reduced more effectively the formation of adducts of hydroxyl radicals in the interstitium of the area at risk (AAR) of the rat heart than carnosine. Carnosine at a dose of 1 mg/kg more effectively increased the activity of catalase and glutathione peroxidase in the AAR by the end of reperfusion compared to Gal. In a model of Cu²⁺-initiated oxidation of human plasma LDL 0.1 mM carnosine demonstrated a significantly more pronounced reduction in the formation of lipid radicals compared to Gal. The results show that Gal can be considered as a promising agent that reduces myocardial injury during reperfusion and oxidative stress.

Anew high-tech methodology for the synthesis of desamino-analogs of neurohypophyseal hormones has been developed. The procedure is a completely solid-phase variant including the disulfide bond closure step. All crude products are obtained with 92

The dose-dependent action of the M871 synthetic peptide antagonist of the GalR2 galanin receptor (H-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu-Leu-Gly-Pro-Glu-His-Pro-Pro-Pro-Ala-Leu-Ala-Leu-Ala-NH2) and the pharmacological agonist G (H-Trp-Thr-Leu-Asn-Ser-Ala-Gly-Tyr-Leu-Leu-Gly-Pro-βAla-His-OH) on sizes of the myocardial infarction (MI) and an activity of creatine kinase (CK-MB) in the blood plasma was studied on the in vivo model of regional ischemia and reperfusion of the rat heart. The peptides were prepared by the automatic solid phase synthesis using the Fmoc-strategy and purified by HPLC. The peptides had the appropriate molecular mass and the homogeneity of 97–98%. A blockage of the GalR2 receptors by the intravenous injection of M871 in doses of 3, 6, and 8 mg/kg before the beginning of the reperfusion had no influence on the MI sizes and the CK-MB activity in comparison with the control. The intravenous injection of the agonist G in a dose of 1 mg/kg at the beginning of the reperfusion significantly decreased the MI sizes and the CK-MB activity in the blood plasma in comparison with the control by 38 and 40%, respectively. Peptides M871 and G did not significantly affect the hemodynamic parameters of the heart. The preliminary intravenous injection of increasing doses of peptide M871 before an administration of agonist G resulted in a gradual increase in the MI sizes and the CK-MB activity. An application of compound M871 in doses of 6 or 8 mg/kg completely abrogated the cardioprotective effects of agonist G. These results suggested the participation of the GalR2 receptor in the protective action of the chimeric agonist G on the heart that was subjected to ischemia and reperfusion and pointed to the considerable promise of the molecular engineering of the peptide agonists of the GalR2 receptor for a design of therapeutic agents for a treatment of cardiovascular diseases.

Herewith, we report for the first time the crystal structure of tetrapeptide FwKT (Phe-D-Trp-Lys-Thr), which is considered to represent an epitope for biomedically relevant hormone somatostatin. The target molecule was successfully crystalized, solved and refined as a conjugate of the tetrapeptide moiety bearing a protective group DOTA at the N-terminus and methylated at the O-terminus. The combination of a hormone active site and a powerful chelator make the substance a highly prospective targeted drug delivery system, especially for peptide receptor radionuclide therapy (PRRT) applications.

This work is devoted to the large-scale solid-phase synthesis (SPS) of Atosiban, Mpa 1 -D-Tyr(OEt)-Ile-Thr-Asn-Cys 6 -Pro-Orn-Gly-NH 2 cyclic 1,6 disulfide, the only clinically used oxytocin receptor antagonist. The conditions have been selected for the closure of the disulfide bond (S–S) in the Atosiban molecule both in the solution and solid phase with the minimal formation of by-products. A comparative assessment of the formation of the S–S bond was carried out under various conditions. The formation of by-products during the closure of the disulfide bond has been studied both in solution and on the polymer support. The developed technique allows for the synthesis of Atosiban on an enlarged scale (10–20 mmol) involving the cyclization of a protected intermediate with the formation of the S–S bond during solid-phase synthesis with the minimal formation of by-products.

The full-length rat galanin (GWTLNSAGYLLGPHAIDNHRSFSDKHGLT-NH2, G29) was prepared by the solid phase peptide synthesis using the Fmoc-strategy. The peptide chain was elongated both by one amino acid and by a fragment condensation. Fragments with the C-terminal glycine residue were synthesized by the solid phase method on the 2-chlorotrityl chloride resin or by the method of conventional peptide synthesis in solution. After the reversed phase HPLC, galanin had the correct molecular weight and 98% purity. We studied the G29 cardioprotective properties on a model of acute myocardial infarction in rats. The G29 administration reduced the infarct size by 40% and decreased the activity of necrosis markers CK-MB (Creatine Kinase-MB) and LDH (Lactate Dehydrogenase) in the blood plasma. The peptide improved metabolic state of the infarcted heart, increased the ATP content, the total adenine nucleotide pool, phosphocreatine, and total creatine, and decreased the lactate level compared to a control. These results indicated the possibility of the G29 use as a drug for reducing the myocardial reperfusion injury. In addition, the mechanisms of the G29 action should be studied.

— The solid phase synthesis (SPS) of the ingramon peptide antagonist of the human monocyte chemoattractant protein-1 (H-Asp-His-Leu-Asp-Lys-Gln-Thr-Gln-Thr-Pro-Lys-Thr-OH), which exhibited the anti-inflammatory activity, was optimized. Side products of the Fmoc-SPS of this peptide were studied. Their structures were determined by the 1 H NMR spectroscopy and confirmed by the synthesis. Methodological ways to minimize of a formation of impurities in the course of the ingramon SPS were found. The reproducible SPS procedure of the ingramon preparation that resulted in the formation of the minimum amount of such side products as [Asi 4 ]-, [D-Asp 4 ]-, and [βAsp 4 ]-peptides was elaborated.

This study aims at analyzing complexation properties of two new short somatostatin analogues, their synthesis, radiolabeling with 44 Sc, 207 Bi, and 152 Eu and stability in vitro. Short tetrapeptide Phe-d-Trp-Lys-Thr and pentapeptide Thz-Phe-d-Trp-Lys-Thr were first conjugated with the DOTA macrocyclic chelator. These conjugates were radiolabeled with 44 Sc, 207 Bi, and 152 Eu and characterized by thin-layer chromatography (TLC) and HPLC. The radiochemical purity was measured using digital autoradiography and gamma spectrometry. Optimum conditions of DOTA-conjugate labeling were found: 0.1mM, pH 8.0 to 8.4 at 90°C for DOTA-tetrapeptide complexes with 207 Bi and 152 Eu; 0.05mM, pH 4.0 to 5.0 at 90°C for 44 Sc-DOTA-tetrapeptide; 0.2mM, pH 4.0 to 5.0 at 90°C for 44 Sc-DOTA-pentapeptide. Complexes of DOTA-pentapeptide with 207 Bi and 152 Eu of radiochemical purity more than 95% were probably unstable at temperature higher than 37°C and were obtained at 37°C, pH 8.0 to 8.4 within 4 days. Mass spectra of the Eu-DOTA-pentapeptide revealed the presence of small fragments of the pentapeptide conjugate in the complex solution. in vitro stability studies were performed in saline in the presence of serum proteins and biologically relevant metal cations. All complexes demonstrated no cation release in vitro within 1 to 4 hours.

New somatostatin analogs containing the fragments of adamantane, coumarin, tetrahydrocarbazole, and palmitic acid of the general formula R-Phe-D-Trp-Lys(Boc)-Thr-OMe have been synthesized. The structure of the conjugates combines a peptide fragment, which has affinity for somatostatin receptors (sstr), and a nonpeptide fragment, which potentially possesses antitumor activity. Presumably, the compounds synthesized are the agonists of sstr. The amide bond between the peptide and nonpeptide fragments has been formed using the carbodiimide method and the method of activated esters. The structures of the conjugates have been confirmed by mass spectrometry (ESI + ) and 1 H NMR spectroscopy. The antitumor activity of the conjugates has been examined by the MTT test on human lung adenocarcinoma (A549), human prostate adenocarcinoma (PC3), human colon cancer (HCT-116), human breast cancer (MCF7), and acute human T‑cell leukemia (Jurkat) cell lines. Compounds selectively inhibiting the growth of A549 cells have been identified.