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Many patients with different malignancies require analgesic therapy not only at advanced stages of the disease, but also during their diagnosis and treatment, as well as after treatment completion to ensure pain relief. New highly effective painkillers with a lower adverse event burden are critical to improve the quality of life of cancer patients with chronic pain syndrome. Tafalgin (tyrosyl-arginyl-phenylalanyl-glycinamide) is a highly specific μ1-opioid receptor agonist. It is an innovative Russian drug for subcutaneous administration, which has no analogues abroad. This article discusses the results of phase I–III clinical trials assessing tafalgin efficacy, safety, and potential to improve patients’ quality of life.

Peptide-based therapeutics are increasingly pushing to the forefront of biomedicine with their promise of high specificity and low toxicity. Although noncanonical residues can always be used, employing only the natural 20 residues restricts the chemical space to a finite dimension allowing for comprehensive in silico screening. Towards this goal, the dataset comprising all possible di-, tri-, and tetra-peptide combinations of the canonical residues has been previously reported. However, with increasing computational power, the comprehensive set of pentapeptides is now also feasible for screening as the comprehensive set of cyclic peptides comprising four or five residues. Here, we provide both the complete and prefiltered libraries of all di-, tri-, tetra-, and penta-peptide sequences from 20 canonical amino acids and their homodetic (N-to-C-terminal) cyclic homologues. The FASTA, simplified molecular-input line-entry system (SMILES), and structure-data file (SDF)-three dimension (3D) libraries can be readily used for screening against protein targets. We also provide a simple method and tool for conducting identity-based filtering. Access to this dataset will accelerate small peptide screening workflows and encourage their use in drug discovery campaigns. As a case study, the developed library was screened against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease to identify potential small peptide inhibitors.

Peptide-based therapeutics are increasingly pushing to the forefront of biomedicine with their promise of high specificity and low toxicity. Although noncanonical residues can always be used, employing only the natural 20 residues restricts the chemical space to a finite dimension allowing for comprehensive in silico screening. Towards this goal, the dataset comprising all possible di-, tri-, and tetra-peptide combinations of the canonical residues has been previously reported. However, with increasing computational power, the comprehensive set of pentapeptides is now also feasible for screening as the comprehensive set of cyclic peptides comprising four or five residues. Here, we provide both the complete and prefiltered libraries of all di-, tri-, tetra-, and penta-peptide sequences from 20 canonical amino acids and their homodetic (N-to-C-terminal) cyclic homologues. The FASTA, simplified molecular-input line-entry system (SMILES), and structure-data file (SDF)-three dimension (3D) libraries can be readily used for screening against protein targets. We also provide a simple method and tool for conducting identity-based filtering. Access to this dataset will accelerate small peptide screening workflows and encourage their use in drug discovery campaigns. As a case study, the developed library was screened against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease to identify potential small peptide inhibitors. [Display omitted] • All possible sequences of di, tri, tetra, and pentapeptides using canonical amino acids provided. • N-to-C-terminal cyclization of all peptides provided. • Methods for the filtration of peptides based on ease of synthesis, solubility, and stability provided. • Methods for the removal of duplicate cyclicpeptides implemented. • The toolkit is used to identify SARS-CoV-2 Mpro inhibitors. [ABSTRACT FROM AUTHOR]

In the Russian Federation, tetrapeptide tyrosyl-D-arginyl-phenylalanyl-glycine amide (Tafalgin), a novel analgesic, selective agonist of 1-opioid receptors, was developed and approved in 2022. The article presents the first experience of the successful use of Tafalgin in treating chronic pain in a cancer patient with poor tolerance to traditional opioids (tramadol, tapentadol, morphine). At baseline, pain severity, according to the Neurological Rating Scale (NRS), was 57 points at rest and up to 9 points in motion out of the maximum 10. The combination of 400 mg/day of tramadol with gabapentin and a non-steroidal anti-inflammatory drug was ineffective; 400 mg/day of tapentadol in combination with gabapentin and a non-steroidal anti-inflammatory drug also was ineffective. Morphine tablets 60 mg/day were effective (NRS score of 23), but unrelenting nausea and vomiting were unmanageable and significantly reduced quality of life. Reducing the dose of oral morphine to 20 mg/day mitigated adverse events but reduced the effectiveness of pain relief (resting NRS score of 4 points). Tafalgin 4 mg subcutaneously BID, then TID reduced the pain severity to an average daily NRS score of 1.22 over the first 3 days of treatment with no adverse events. Sleep, appetite, and physical activity improved. The patient received Tafalgin for 84 days, and she gained 5 kg due to improved nutrition during that time. The drug is comparable in efficacy to morphine and is associated with fewer adverse events. A limitation to widespread use is the availability of a formulation for subcutaneous injection only.

Chronic diseases, such as hypertension, cause great harm to human health. Conventional drugs have promising therapeutic effects, but also cause significant side effects. Food-sourced angiotensin-converting enzyme (ACE) inhibitory peptides are an excellent therapeutic alternative to pharmaceuticals, as they have fewer side effects. However, there is no systematic and effective screening method for ACE inhibitory peptides, and the lack of understanding of the sequence characteristics and molecular mechanism of these inhibitory peptides poses a major obstacle to the development of ACE inhibitory peptides. Through systematically calculating the binding effects of 160,000 tetrapeptides with ACE by molecular docking, we found that peptides with Tyr, Phe, His, Arg, and especially Trp were the characteristic amino acids of ACE inhibitory peptides. The tetrapeptides of WWNW, WRQF, WFRV, YYWK, WWDW, and WWTY rank in the top 10 peptides exhibiting significantly high ACE inhibiting behaviors, with IC50 values between 19.98 ± 8.19 μM and 36.76 ± 1.32 μM. Salt bridges, π–π stacking, π–cations, and hydrogen bonds contributed to the high binding characteristics of the inhibitors and ACE. Introducing eight Trp into rabbit skeletal muscle protein (no Trp in wide sequence) endowed the protein with a more than 90% ACE inhibition rate, further suggesting that meat with a high content of Trp could have potential utility in hypertension regulation. This study provides a clear direction for the development and screening of ACE inhibitory peptides. [ABSTRACT FROM AUTHOR]

Chemical investigation of the psychrophilic fungus Pseudogymnoascus sp. HDN17-933 derived from Antarctica led to the discovery of six new tetrapeptides psegymamides A–F (1–6), whose planar structures were elucidated by extensive NMR and MS spectrometric analyses. Structurally, psegymamides D–F (4–6) possess unique backbones bearing a tetrahydropyridoindoles unit, which make them the first examples discovered in naturally occurring peptides. The absolute configurations of structures were unambiguously determined using solid-phase total synthesis assisted by Marfey's method, and all compounds were evaluated for their inhibition of human (h) nicotinic acetylcholine receptor subtypes. Compound 2 showed significant inhibitory activity. A preliminary structure–activity relationship investigation revealed that the tryptophan residue and the C-terminal with methoxy group were important to the inhibitory activity. Further, the high binding affinity of compound 2 to hα4β2 was explained by molecular docking studies. [ABSTRACT FROM AUTHOR]

The incorporation of dehydroamino acid or fragments of oxazole into peptide chain is accompanied by a distorted three-dimensional structure and additionally enables the introduction of non-typical side-chain substituents. Thus, such compounds could be building blocks for obtaining novel foldamers and/or artificial enzymes (artzymes). In this paper, effective synthetic procedures leading to such building blocks—tetrapeptides containing glycyldehydroalanine, glycyldehydrophenylalanine, and glycyloxazole subunits—are described. Peptides containing serine were used as substrates for their conversion into peptides containing dehydroalanine and aminomethyloxazole-4-carboxylic acid while considering possible requirements for the introduction of these fragments into long-chain peptides at the last steps of synthesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Aβ 39-42 -based amidated C-terminal fragment (CTF) peptides attenuate Aβ-induced aggregation. • In the MTT cell viability assay, peptide 13 exhibited 90.2 % protection against Aβ-induced toxicity at a concentration of 10 μM. • CD analysis displayed the deterrence of β-sheet formation in the presence of peptide 13, with a concomitant increase in α-helical content due to the presence of α-helix-inducing "Aib" in its sequence. • In an electron microscopy study, the absence of a fibrillar network of Aβ on co-incubation with peptide 13 was observed. Amyloid plaque formation in the brain is mainly responsible for the onset of Alzheimer's disease (AD). Structure-based peptides have gained importance in recent years, and rational design of the peptide sequences for the prevention of Aβ-aggregation and related toxicity is imperative. In this study, we investigate the structural modification of tetrapeptides derived from the hydrophobic C-terminal region of Aβ 42 "VVIA-NH 2 " and its retro -sequence "AIVV-NH 2." A preliminary screening of synthesized peptides through an MTT cell viability assay followed by a ThT fluorescence assay revealed a peptide 13 (Ala-Ile-Aib-Val-NH 2) that showed protection against Aβ-aggregation and associated neurotoxicity. The presence of the α-helix inducer "Aib" in peptide 13 manifested the conformational transition from cross-β-sheets to α-helical content in Aβ 42. The absence of fibrils in electron microscopic analysis suggested the inhibitory potential of peptide 13. The HRMS, DLS, and ANS studies further confirmed the inhibitory activity of 13 , and no cytotoxicity was observed. The structure-based peptide described herein is a promising amyloid-β inhibitor and provides a new lead for the development of AD therapeutics. [ABSTRACT FROM AUTHOR]

Chronic diseases, such as hypertension, cause great harm to human health. Conventional drugs have promising therapeutic effects, but also cause significant side effects. Food-sourced angiotensin-converting enzyme (ACE) inhibitory peptides are an excellent therapeutic alternative to pharmaceuticals, as they have fewer side effects. However, there is no systematic and effective screening method for ACE inhibitory peptides, and the lack of understanding of the sequence characteristics and molecular mechanism of these inhibitory peptides poses a major obstacle to the development of ACE inhibitory peptides. Through systematically calculating the binding effects of 160,000 tetrapeptides with ACE by molecular docking, we found that peptides with Tyr, Phe, His, Arg, and especially Trp were the characteristic amino acids of ACE inhibitory peptides. The tetrapeptides of WWNW, WRQF, WFRV, YYWK, WWDW, and WWTY rank in the top 10 peptides exhibiting significantly high ACE inhibiting behaviors, with IC50 values between 19.98 ± 8.19 μM and 36.76 ± 1.32 μM. Salt bridges, π–π stacking, π–cations, and hydrogen bonds contributed to the high binding characteristics of the inhibitors and ACE. Introducing eight Trp into rabbit skeletal muscle protein (no Trp in wide sequence) endowed the protein with a more than 90% ACE inhibition rate, further suggesting that meat with a high content of Trp could have potential utility in hypertension regulation. This study provides a clear direction for the development and screening of ACE inhibitory peptides.

Chemical investigation of the psychrophilic fungus Pseudogymnoascus sp. HDN17-933 derived from Antarctica led to the discovery of six new tetrapeptides psegymamides A–F (1–6), whose planar structures were elucidated by extensive NMR and MS spectrometric analyses. Structurally, psegymamides D–F (4–6) possess unique backbones bearing a tetrahydropyridoindoles unit, which make them the first examples discovered in naturally occurring peptides. The absolute configurations of structures were unambiguously determined using solid-phase total synthesis assisted by Marfey’s method, and all compounds were evaluated for their inhibition of human (h) nicotinic acetylcholine receptor subtypes. Compound 2 showed significant inhibitory activity. A preliminary structure–activity relationship investigation revealed that the tryptophan residue and the C-terminal with methoxy group were important to the inhibitory activity. Further, the high binding affinity of compound 2 to hα4β2 was explained by molecular docking studies.

The incorporation of dehydroamino acid or fragments of oxazole into peptide chain is accompanied by a distorted three-dimensional structure and additionally enables the introduction of non-typical side-chain substituents. Thus, such compounds could be building blocks for obtaining novel foldamers and/or artificial enzymes (artzymes). In this paper, effective synthetic procedures leading to such building blocks—tetrapeptides containing glycyldehydroalanine, glycyldehydrophenylalanine, and glycyloxazole subunits—are described. Peptides containing serine were used as substrates for their conversion into peptides containing dehydroalanine and aminomethyloxazole-4-carboxylic acid while considering possible requirements for the introduction of these fragments into long-chain peptides at the last steps of synthesis.

Influenza is a highly contagious, acute respiratory illness, which represents one of the main health issues worldwide. Even though some antivirals are available, the alarming increase in virus strains resistant to them highlights the need to find new drugs. Previously, Superti et al. deeply investigated the mechanism of the anti-influenza virus effect of bovine lactoferrin (bLf) and the role of its tryptic fragments (the N- and C-lobes) in antiviral activity. Recently, through a truncation library, we identified the tetrapeptides, Ac-SKHS-NH2 (1) and Ac-SLDC-NH2 (2), derived from bLf C-lobe fragment 418–429, which were able to bind hemagglutinin (HA) and inhibit cell infection in a concentration range of femto- to picomolar. Starting from these results, in this work, we initiated a systematic SAR study on the peptides mentioned above, through an alanine scanning approach. We carried out binding affinity measurements by microscale thermophoresis (MST) and surface plasmon resonance (SPR), as well as hemagglutination inhibition (HI) and virus neutralization (NT) assays on synthesized peptides. Computational studies were performed to identify possible ligand–HA interactions. Results obtained led to the identification of an interesting peptide endowed with broad anti-influenza activity and able to inhibit viral infection to a greater extent of reference peptide.

A series of branched tetrapeptide Schiff bases 3−6 were designed and synthesized from corresponding tetrapeptide hydrazide 2 as a starting material.In vitroevaluation of the synthesized compounds 4−6 against breast MCF-7 carcinoma cells identified their excellent anticancer potency, with IC50 ranging from 8.12 ± 0.14 to 17.55 ± 0.27 μM in comparison with the references, cisplatin and milaplatin (IC50= 13.34 ± 0.11and 18.43 ± 0.13 μM, respectively). Furthermore, all derivatives demonstrated promising activity upon evaluation of theirin vitroandin vivosuppression of p53 ubiquitination and inhibition assessment for LDHA kinase. Finally, molecular docking studies were performed to predict the possible binding features of the potent derivatives within the ATP pocket of LDHA in an attempt to get a lead for developing a more potent LDHA inhibitor with anti-proliferative potency.

Herein we report the unique conformations adopted by linear and cyclic tetrapeptides (CTPs) containing 2-aminobenzoic acid (2-Abz) in solution and as single crystals. The crystal structure of the linear tetrapeptide H2N- d-Leu- d-Phe-2-Abz- d-Ala-COOH ( 1) reveals a novel planar peptidomimetic β-turn stabilized by three hydrogen bonds and is in agreement with its NMR structure in solution. While CTPs are often synthetically inaccessible or cyclize in poor yield, both 1 and its N-Me- d-Phe analogue ( 2) adopt pseudo-cyclic frameworks enabling near quantitative conversion to the corresponding CTPs 3 and 4. The crystal structure of the N-methylated peptide ( 4) is the first reported for a CTP containing 2-Abz and reveals a distinctly planar 13-membered ring, which is also evident in solution. The N-methylation of d-Phe results in a peptide bond inversion compared to the conformation of 3 in solution. [ABSTRACT FROM AUTHOR]

The five melanocortin receptors (MC1R–MC5R) are involved in numerous biological pathways, including steroidogenesis, pigmentation, and food intake. In particular, MC3R and MC4R knockout mice suggest that the MC3R and MC4R regulate energy homeostasis in a non-redundant manner. While MC4R-selective agonists have been utilized as appetite modulating agents, the lack of MC3R-selective agonists has impeded progress in modulating this receptor in vivo. In this study, the (pI)DPhe position of the tetrapeptide Ac-His-Arg-(pI)DPhe-Tic-NH2 (an MC3R agonist/MC4R antagonist ligand) was investigated with a library of 12 compounds. The compounds in this library were found to have higher agonist efficacy and potency at the mouse (m) MC3R compared to the MC4R, indicating that the Arg-DPhe motif preferentially activates the mMC3R over the mMC4R. This observation may be used in the design of new MC3R-selective ligands, leading to novel probe and therapeutic lead compounds that will be useful for treating metabolic disorders.

In this study semisolid formulations containing AcYPFF ( N-acetyl-Tyr-Pro-Phe-Phe-NH) tetrapeptide were obtained and characterized in terms of rheology, stability by multiple light scattering and particle size distribution by laser diffraction. Additionally, the release studies of tetrapeptide from formulations obtained were performed. The influence of different factors such as semisolid and membrane type on tetrapeptide release rate was examined. The release experiments of tetrapeptide modified with palmitoyl group (PalmYPFF) were also carried out. The results proved that formulation type and its rheological properties strongly determined the permeation process of the tetrapeptide. The fastest release of tetrapeptide was observed from hydrogel that had the lowest viscosity. The kinetic data of tetrapeptide released from oil-in-water (o/w) and water-in-oil (w/o) emulsions prepared at elevated temperature showed good fit to the Higuchi equation, whereas when AcYPFF was released from oil-in-water (o/w) emulsion prepared with the addition of auto-emulsifier high linearity with Korsmeyer-Peppas model was observed. While when tetrapeptide was released from Hydrogel the most suitable model was the first-order kinetics. It was suggested that mechanism that led to the release of tetrapeptide from all formulations was non-Fickian diffusion transport. The presence of palmitoyl group changed the solubility of tetrapeptide both in formulation and receptor fluid and thus the release rate of active compound was modified. [ABSTRACT FROM AUTHOR]

The cyclization of the linear tetrapeptides sequence H-NMePhe-Xaa¹-NMePhe-Xaa²-OH (for which Xaa¹ = Xaa² = Ile, Val, or Leu; Xaa¹ = Val; Xaa² = Ile or Leu) by using 1-propane-phosphonic acid anhydride was explored. An unanticipated finding is the cyclization towards cyclotetrapeptide conformers (kinetic products) that were highly prone to hydrolysis and that slowly interconvert into the more stable trans, cis, trans, cis (tctc) conformers (thermodynamic products). [ABSTRACT FROM AUTHOR]

The present study describes an approach to synthesize the smaller chain tripeptides and tetrapeptides and to test their antinociceptive potency in mice. Based on rational drug design using hydrophobic ratio and total net charge as descriptors, five leads were selected, viz., Met-Arg-Tyr (MRY), Met-Val-Tyr (MVY), Met-Ile-Cys-Tyr (MICY), Met-Trp-Lys-Tyr (MWKY) and Phe-Trp-Lys-Tyr (FWKY) from the subjected 65 templates and synthesized by dicyclohexyl carbodiimide coupling using polystyrene as solid support. All the synthesized compounds were purified by column chromatography and further confirmed by melting point, infrared, proton nuclear magnetic resonance and mass spectral datas. Acute toxicity studies were performed for dose selection in all the compounds using OECD guidelines 423 (Annexure 2b). Antinociceptive potency of peptides was tested in Swiss albino mice using acetic acid writhing and hot plate method. The LD cut-off mg/kg body weight for tripeptides (MRY, MVY) and tetrapeptides (Met-Ile-Cys-Tyr, Met-Trp-Lys-Tyr, Phe-Trp-Lys-Tyr) were found to be 500-2000 mg/kg and 200-300 mg/kg respectively. The tripeptide MVY have shown maximum antinociceptive action with an average number of writhing as 13 at 150 mg/kg body weight by writhing method, whereas the tripeptide Met-Arg-Tyr have shown maximum potency with the average reaction time of 5.75 min after 15 min at a dose of 150 mg/kg by hot plate method, which clearly indicated that the tripeptides are comparatively potent antinociceptive agents than the tetrapeptides for central neuropathic pain. [ABSTRACT FROM AUTHOR]

Ultra-short peptides 1-9 were designed and synthesized with phenylalanine, ornithine and proline amino acid residues and their effect on antimalarial activity was analyzed. On the basis of the IC50 data for these compounds, the effects of nature, polarity, and amino acid sequence on Plasmodium berghei schizont cultures were analyzed too. Tetrapeptides Phe-Orn-Phe-Orn (4) and Lys-Phe-Phe-Orn (5) showed a very important activity with IC50 values of 3.31 and 2.57 μM, respectively. These two tetrapeptides are candidates for subsequent in vivo assays and SARS investigations.

Cyclic tetrapeptides exhibit high cellular permeability and a wide range of biological properties and thus have gained great interest in the field of medicinal chemistry. We synthesized highly strained 12-membered head to tail cyclic peptides with varying reactive amino acids, without oligomerization using the exclusively intramolecular CyClick chemistry. This occurs by a two-step process involving the low-energy formation of a 15 atom-containing cyclic imine, followed by a chemoselective ring contraction of the peptide backbone generating a highly strained 12 atom-containing cyclic tetrapeptide. This reaction exhibited high substrate scope and generated head to tail cyclic tetrapeptides with varying amino acids at the N-terminus, showing chemoselectivity without the need for side group protection. [Display omitted] [ABSTRACT FROM AUTHOR]

The title achiral peptide N-benzyloxycarbonyl-α-aminoisobutyryl-α-aminoisobutyryl-α-aminoisobutyrylglycine tert-butyl ester or Z-Aib-Aib-Aib-Gly-OtBu (Aib is α-aminoisobutyric acid, Z is benzyloxycarbonyl, Gly is glycine and OtBu indicates the tert-butyl ester), C26H40N4O7, is partly hydrated (0.075H2O) and has two different conformations which together constitute the asymmetric unit. Both molecules form incipient 310-helices. They differ in the relative orientation of the N-terminal protection group and at the C-terminus. There are two 4→1 intramolecular hydrogen bonds. [ABSTRACT FROM AUTHOR]

Sound speeds have been measured for aqueous solutions of five tetrapeptides and five pentapeptides at T=298.15 K. The partial molar isentropic compressions at infinite dilution, $K_{S,2}^{\circ}$, were derived for the peptides using conventional methods. The results were compared with those calculated using group additivity methods, with the amino acid side-chain contributions derived using $K_{S,2}^{\circ}$ data reported previously for some tripeptides of sequence gly-X-gly, where X represents an amino acid, and also for some N-acetyl amino acid amides. The tripeptides are the preferred model compounds for the estimation of the side-chain contributions to $K_{S,2}^{\circ}$ of a polypeptide. Our study also confirms that simple group additivity schemes are not feasible for the estimation of $K_{S,2}^{\circ}$ values for polypeptides and unfolded proteins. [ABSTRACT FROM AUTHOR]

Abstract: A convenient synthetic pathway to novel functionalized tetrapeptides containing the 1,2,3-triazole moiety is described. The target molecules were obtained by the reaction of fluorinated α-amino acids or α-aminophosphonates with azidopeptides via Cu(I)-catalyzed Huisgen cycloaddition reaction (click chemistry). The synthesized tetrapeptides may find important applications in biomedical chemistry as potential drugs. [Copyright &y& Elsevier]

Ultra-short peptides 1-9 were designed and synthesized with phenylalanine, ornithine and proline amino acid residues and their effect on antimalarial activity was analyzed. On the basis of the IC50 data for these compounds, the effects of nature, polarity, and amino acid sequence on Plasmodium berghei schizont cultures were analyzed too. Tetrapeptides Phe-Orn-Phe-Orn (4) and Lys-Phe-Phe-Orn (5) showed a very important activity with IC50 values of 3.31 and 2.57 μM, respectively. These two tetrapeptides are candidates for subsequent in vivo assays and SARS investigations. [ABSTRACT FROM AUTHOR]

The equilibrium constants K1, Ka and β1 of 25 copper(II) complexes with di-(N= 15), tri-(N= 5), tetra- (N = 2), and pentapeptides (N = 3) were estimated by using linear models based on the valence con- nectivity index of the 3rd order (3χv). For the stability constant K1 two kinds of models were developed: bivariate models, which divide a molecule into N- and C-terminal segments, and multivariate models, which treat the connectivity index of each chelate ring as a separate variable. The models proved equally successful, yielding fair reproduction of experimental log K1 (S.E.cv = 0.16-0.19, max. error = 0.4). Overall deprotonation constant Ka was estimated from the 3χv, calculated for the whole molecule of the complex, with the addition of two indicator variables to distinguish various classes of ligands. In this way, the overall stability constant (log β1 = log K1 - pKa) was reproduced with the error < 0.81 (S.E. = 0.31). [ABSTRACT FROM AUTHOR]

Among the 160000 combinatorially possible tetrapeptides, 1500 tend to certain conformational states. Analysis of all high-resolution structures in PDB select reveals that most of the conformationally stanch tetrapeptides are in α-helical form. Their composition is analyzed. [ABSTRACT FROM AUTHOR]

Abstract: Quinoline-2,4-dicarboxylic acids (QDCs) bearing lipophilic substituents in the 6- or 7-position were shown to be inhibitors of the glutamate vesicular transporter (VGLUT). Using the arrangement of the QDC lipophilic substituents as a template, libraries of X1X2EF and X1X2EW tetrapeptides were synthesized and tested as VGLUT inhibitors. The peptides QIEW and WNEF were found to be the most potent. Further stereochemical deconvolution of these two peptides showed dQlIdElW to be the best inhibitor (K i =828±252μM). Modeling and overlay of the tetrapeptide inhibitors with the existing pharmacophore showed that H-bonding and lipophilic residues are important for VGLUT binding. [Copyright &y& Elsevier]

Abstract: Reversible tetrapeptide-based compounds have been shown to effectively inhibit the hepatitis C virus NS3·4A protease. Inhibition of viral replicon RNA production in Huh-7 cells has also been demonstrated. We show herein that the inclusion of hydrogen bond donors on the P4 capping group of tetrapeptide-based inhibitors result in increased binding potency to the NS3·4A protease. The capping groups also impart significant effects on the pharmacokinetic profile of these inhibitors. [Copyright &y& Elsevier]

A capillary electrophoresis (CE) method has been developed and validated for separating the tetrapeptide H-Tyr-(d)Arg-Phe-Phe-NH2 and nine related substances. The method was developed using experimental design in a four-step procedure, in which eight variables were investigated in a total of 47 experiments. The preferred background electrolyte (BGE) consisted of 0.1 M malonic acid at pH 2.5 with 7 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin (2,6-DM-β-CD). The separation of H-Tyr-(d)Arg-Phe-Phe-NH2 and the related substances was accomplished within 15 min, with a resolution greater than 1.5 between all peaks. The method was then investigated with respect to its selectivity, linearity, precision, detection limit (LOD) and quantitation limit (LOQ). In addition, a system suitability test was performed and response factors were determined, essentially following International Conference of Harmonization guidelines for the validation of analytical methods. LOD and LOQ for the related substance H-Arg-Phe-NH2 were found to be 0.3 and 0.8 μg/ml, respectively, at a target H-Tyr-(d)Arg-Phe-Phe-NH2 concentration of 1 mg/ml. The method performed well with respect to all of the validation parameters. [Copyright &y& Elsevier]

Src homology-2 (SH2) domains are noncatalytic motifs containing approximately 100 amino acid residues that are involved in intracellular signal transduction. The phosphotyrosine-containing tetrapeptide pTyr-Glu-Glu-Ile (pYEEI) binds to Src SH2 domain with high affinity (Kd=100 nM). The development of five classes of tetrapeptides as inhibitors for the Src SH2 domain is described. Peptides were prepared via solid-phase peptide synthesis and tested for affinity to Src SH2 domain using a fluorescence polarization based assay. All of the N-terminal substituted pYEEI derivatives (class II) presented binding affinity (IC50=of 2.7–8.6 μM) comparable to pYEEI (IC50=6.5 μM) in this assay. C-Terminal substituted pYEEI derivatives (class III) showed a lower binding affinity with IC50 values of 34–41 μM. Amino-substituted phenylalanine derivatives (class IV) showed weak binding affinities (IC50=16–153 μM). Other substitutions on phenyl ring (class I) or the replacement of the phenyl ring with other cyclic groups (class V) dramatically decreased the binding of tetrapeptides to Src SH2 (IC50>100 μM). The ability of pYEEI and several of the tetrapeptides to inhibit the growth of cancer cells were assessed in a cell-based proliferation assay in human embryonic kidney (HEK) 293 tumor cells. The binding affinity of several of tested compounds against Src SH2 domain correlates with antiproliferative activity in 293T cells. None of the compounds showed any significant antifungal activity against Candida albicans ATCC 14053 at the maximum tested concentration of 10 μM. Overall, these results provided the structure–activity relationships for some FEEI and YEEI derivatives designed as Src SH2 domain inhibitors. [Copyright &y& Elsevier]

The support vector machine approach was introduced to predict the β-turns in proteins. The overall self-consistency rate by the re-substitution test for the training or learning dataset reached 100%. Both the training dataset and independent testing dataset were taken from Chou [J. Pept. Res. 49 (1997) 120]. The success prediction rates by the jackknife test for the β-turn subset of 455 tetrapeptides and non-β-turn subset of 3807 tetrapeptides in the training dataset were 58.1 and 98.4%, respectively. The success rates with the independent dataset test for the β-turn subset of 110 tetrapeptides and non-β-turn subset of 30,231 tetrapeptides were 69.1 and 97.3%, respectively. The results obtained from this study support the conclusion that the residue-coupled effect along a tetrapeptide is important for the formation of a β-turn. [Copyright &y& Elsevier]

Stoichiometry, stability constants and solution structures of the copper(II) complexes of the N-acetylated tetrapeptide HisGlyHisGly were determined in aqueous solution in the pH range 2–11. The potentiometric and spectroscopic data (UV–Vis, CD, EPR and Raman scattering) show that acetylation of the amino terminal group induces drastic changes in the coordination properties of AcHGHG compared to HGHG. The N3 atoms of the histidine side chains are the first anchoring sites of the copper(II) ion. At pH 4.7 and 5.6 both the imidazole rings cooperate in the formation of a 2N equatorial set, while, at higher pH values, 3N and 4N complexes are formed through the coordination of peptide N− atoms. The log β values of the copper complexes of AcHGHG are by far lower than those of the corresponding species in the parent CuII–HGHG system. [ABSTRACT FROM AUTHOR]

Influenza is a highly contagious, acute respiratory illness, which represents one of the main health issues worldwide. Even though some antivirals are available, the alarming increase in virus strains resistant to them highlights the need to find new drugs. Previously, Superti et al. deeply investigated the mechanism of the anti-influenza virus effect of bovine lactoferrin (bLf) and the role of its tryptic fragments (the N- and C-lobes) in antiviral activity. Recently, through a truncation library, we identified the tetrapeptides, Ac-SKHS-NH2 (1) and Ac-SLDC-NH2 (2), derived from bLf C-lobe fragment 418–429, which were able to bind hemagglutinin (HA) and inhibit cell infection in a concentration range of femto- to picomolar. Starting from these results, in this work, we initiated a systematic SAR study on the peptides mentioned above, through an alanine scanning approach. We carried out binding affinity measurements by microscale thermophoresis (MST) and surface plasmon resonance (SPR), as well as hemagglutination inhibition (HI) and virus neutralization (NT) assays on synthesized peptides. Computational studies were performed to identify possible ligand–HA interactions. Results obtained led to the identification of an interesting peptide endowed with broad anti-influenza activity and able to inhibit viral infection to a greater extent of reference peptide. [ABSTRACT FROM AUTHOR]

A series of branched tetrapeptide Schiff bases 3–6 were designed and synthesized from corresponding tetrapeptide hydrazide 2 as a starting material.In vitroevaluation of the synthesized compounds 4–6 against breast MCF-7 carcinoma cells identified their excellent anticancer potency, with IC50 ranging from 8.12 ± 0.14 to 17.55 ± 0.27 μM in comparison with the references, cisplatin and milaplatin (IC50= 13.34 ± 0.11and 18.43 ± 0.13 μM, respectively). Furthermore, all derivatives demonstrated promising activity upon evaluation of theirin vitroandin vivosuppression of p53 ubiquitination and inhibition assessment for LDHA kinase. Finally, molecular docking studies were performed to predict the possible binding features of the potent derivatives within the ATP pocket of LDHA in an attempt to get a lead for developing a more potent LDHA inhibitor with anti-proliferative potency. [ABSTRACT FROM AUTHOR]

The five melanocortin receptors (MC1R–MC5R) are involved in numerous biological pathways, including steroidogenesis, pigmentation, and food intake. In particular, MC3R and MC4R knockout mice suggest that the MC3R and MC4R regulate energy homeostasis in a non-redundant manner. While MC4R-selective agonists have been utilized as appetite modulating agents, the lack of MC3R-selective agonists has impeded progress in modulating this receptor in vivo. In this study, the (pI)DPhe position of the tetrapeptide Ac-His-Arg-(pI)DPhe-Tic-NH2 (an MC3R agonist/MC4R antagonist ligand) was investigated with a library of 12 compounds. The compounds in this library were found to have higher agonist efficacy and potency at the mouse (m) MC3R compared to the MC4R, indicating that the Arg-DPhe motif preferentially activates the mMC3R over the mMC4R. This observation may be used in the design of new MC3R-selective ligands, leading to novel probe and therapeutic lead compounds that will be useful for treating metabolic disorders. [ABSTRACT FROM AUTHOR]