A new general solid-phase method for the synthesis of backbone-to-backbone cyclized peptides

A model peptide with the sequences Ala-Pro-Lys(2ClZ)-Tyr(2BrZ) was synthesized on a 4-methylbenzhydryl amine (MBHA) polystyrene resin using conventional Boc/benzyl protective group strategy. The amino acid aldehyde Boc-valinal was coupled by reductive alkylation with NaCNBH₃ in acidified DMF for 1 h. The secondary amine in the peptide-resin Boc-Valψ[CH₂NH]Ala-Pro-Lys(2CIZ)-Tyr(2BrZ)-MBHA was reductively alkylated by 3(4-methylbenzylthio)-propanal at 40 °C for 6 h, resulting the peptide-resin Boc-Valψ[CH₂N(CH₂CH²CH₂-S-pMeBzl)]Ala-Pro-Lys(2ClZ)-Tyr(2BrZ)-MBHA. After the removal of the Boc group the synthesis was continued employing the above-mentioned methods, which led to the resin-bound peptide Leuψ[CH₂N(CH₂CH₂CH₂S-pMeBzl)]Ser-Pro-Gly-Lys(2ClZ)-Valψ[CH₂N(CH₂CH₂CH₂-S-pMeBzl)]Ala-Pro-Lys(2ClZ)-Tyr(2BrZ)-MBHA. The peptide was cleaved from the resin with hydrogen fluoride. Reversed-phase HPLC and plasma desorbtion mass spectrometry analysis showed that the expected peptide Leuψ[CHIN(CH₂CH₂CH₂SH)ISer-Pro-Gly-Lys-Valψ[CH₂N(CH₂CH₂CH₂-SH)]Ala-Pro-Lys-Tyr-NH₂ was obtained as the major product with low levels of side products. Intramolecular oxidation of the thiols gave the backbone to backbone cyclized peptide Leuψ[CH₂N(CH₂CH₂CH₂S)]Ser-Pro-Gly-Lys-Valψ[CH₂N(CH₂CH₂CH₂-S)]A1a-Pro-Lys-Tyr-NH₂.     

Synthesis and biological evaluation of biotinyl hydrazone derivatives of muramyl peptides

Muramyl peptides derived from bacterial peptidoglycan have long been known for their ability to trigger host innate immune responses, including inflammation and antimicrobial defense. Muramyl peptides have also been widely studied for their role as immune adjuvants. In mammals, the nucleotide-binding oligomerization domain (Nod) proteins Nod1 and Nod2 detect distinct muramyl peptide structures and mediate their biological activity. Because of the poor immunogenicity of these small peptidoglycan derivatives, research in this field is currently limited by the lack of reagents to track or immobilize specific muramyl peptides. We present here the generation and initial biological characterization of synthetic muramyl peptides covalently coupled to dansyl or biotinyl derivatives and demonstrate that biotinyl coupling on the muramyl moiety results in derivatives that can be tracked by immunofluorescence and maintain full biological activity, as observed by their capacity to trigger Nod signaling. Moreover, using digitonin-mediated permeabilization techniques on live cells, we also demonstrate that biotinylated muramyl peptides efficiently reach the host cytosol, where they activate Nod signaling. Therefore, these derivatives represent useful probes to study the cell biology and the biochemistry of host responses to muramyl peptides.     

Synthesis of aldehydic peptides inhibiting renin

Reduction of peptidyl N,O-dimethyl hydroxamates with lithium aluminium hydride in diethyl ether at 0° allowed the preparation of peptidyl aldehydes in excellent yield and optical purity. These aldehydic peptides are able to inhibit renin activity. They are the shortest renin inhibitors known to date.     

Efficiency of cell-penetrating peptides on the nasal and intestinal absorption of therapeutic peptides and proteins

The purpose of our study was to investigate the potential of cell-penetrating peptides; penetratin as novel delivery vector, on the systemic absorption of therapeutic peptides and proteins across different mucosal administration sites. The absorption-enhancing feasibility of l- and d-penetratin (0.5 mM) was used for glucagon-like peptide-1 (GLP-1), and exendin-4 as novel antidiabetic therapy, in addition to interferon-β (IFN-β) as protein biotherapeutic model from nasal and intestinal route of administration was evaluated as first time in rats. Nasal route is the most feasible for the delivery of therapeutic peptides coadministered with penetratin whereas the intestinal route appears to be more restricted. The absolute bioavailability (BA (%)) values depend on the physichochemical characters of drugs, stereoisomer character of penetratin, and site of administration. Penetratin significantly increased the nasal more than intestinal absorption of GLP-1 and exendin-4, as the BA for nasal and intestinal administration of GLP-1 was 15.9% and 5%, and for exendin-4 were 7.7% and 1.8%, respectively. Moreover, the BA of IFN-β coadministered with penetratin was 11.1% and 0.17% for nasal and intestinal administration, respectively. From these findings, penetratin is a promising carrier for transmucosal delivery of therapeutic peptides and macromolecules as an alternative to conventional parenteral routes.     

Enhanced antitumor activity and selectivity of lactoferrin‐derived peptides

Abstract: A number of peptide analogs derived from the N‐terminal α‐helical region of bovine lactoferrin (LFB 14–31), were designed in order to investigate how deviating numbers and positions of positively charged residues and numbers of aromatic residues affected their activity against prokaryotic, normal and transformed eukaryotic cells. Most of the LFB derivatives were highly active against both Escherichia coli and Staphylococcus aureus. The peptides were more active against the tumor cell lines MethA, HT‐29 and MT‐1 than normal eukaryotic cells. The peptides that were most active against the tumor cell lines had all cationic residues concentrated in one sector of the helical structure. These peptides were less selective against the tumor cell lines than against normal fibroblasts. Quantitative structure?activity relationship studies showed that certain structural parameters affected toxicity against the tumor cell lines more than against fibroblasts. Peptides encompassing these parameters were slightly less active against tumor cells, but gained significant selectivity.     

Crystallographic characterization of geometry and conformation of TOAC,a nitroxide spin-labelled Cα,α-disubstituted glycine,in simple derivatives and model peptides *

The molecular and crystal structures of one derivative and two oligopeptides of TOAC, a nitroxide spin-labelled C^αα-disubstituted glycine, have been determined by X-ray diffraction. The derivative is the 5(4H)-oxazolone from Piv-TOAC-OH; the oligopeptides are Z-TOAC-(L-Ala)₂-NHtBu sesquihydrate and p BrBz-TOAC-(L-Ala)₂-TOAC-L-Ala-NHtBu hemihydrate. Incipient and fully developed right-handed 3₁₀-helical conformations are formed by both independent molecules in the asymmetric unit of the terminally blocked tripeptide amide and the terminally blocked pentapeptide amide, respectively. The average geometry and preferred conformation for the piperidine ring of the TOAC residues are also discussed in detail. © Munksgaard 1996.     

The potential of retro-inverso peptides as synthetic vaccines

Retro-inverso peptides, also known as all-D-retro or retro-enantio peptides, are composed of D-amino acids assembled in the reverse order from that of the parent L-sequence. Since the orientation of the side-chains in a retro-inverso analogue is very similar to that in the parent L-peptide, this leads to a high level of antigenic cross-reactivity between the two peptides. The potential of retro-inverso peptides as synthetic vaccines has been investigated in the case of foot-and-mouth disease. A single inoculation of retro-inverso peptide corresponding to residues 141 - 159 of the VP1 protein of foot-and-mouth disease virus induced longer-lasting and higher antibody titres in immunised animals than the corresponding L-peptides. The antibodies cross-reacted strongly with virus particles and with L-peptides and conferred substantial protection in guinea-pigs challenged with the cognate virus. Retro-inverso peptides have considerable potential as synthetic vaccines, since their increased resistance to proteases may overcome one of the major drawbacks of classical L-peptide vaccines.     

海洋生物活性肽研究进展

综述几种海洋天然生物活性肽的研究进展，阐明酶解生物活性肽的理论基础和海洋生物活性肽的吸收理论。对活性肽在养殖业中的作用、当前海洋生物活性肽研究的不足及研究前景作了评述。     

Antimicrobial peptides: premises and promises

Antimicrobial peptides (AMPs) are an important component of the natural defences of most living organisms against invading pathogens. These are relatively small (<10 kDa), cationic and amphipathic peptides of variable length, sequence and structure. During the past two decades several AMPs have been isolated from a wide variety of animals, both vertebrates and invertebrates, and plants as well as from bacteria and fungi. Most of these peptides are obtained from different sources like macrophages, neutrophils, epithelial cells, haemocytes, fat body, reproductive tract, etc. These peptides exhibit broad-spectrum activity against a wide range of microorganisms including Gram-positive and Gram-negative bacteria, protozoa, yeast, fungi and viruses. A few peptides have also been found to be cytotoxic to sperm and tumour cells. AMPs are classified based on the three dimensional structural studies carried out with the help of NMR. The peptides are broadly classified into five major groups namely (a) peptides that form -helical structures, (b) peptides rich in cysteine residues, (c) peptides that form β-sheet, (d) peptides rich in regular amino acids namely histatin, arginine and proline and (e) peptides composed of rare and modified amino acids. Most of these peptides are believed to act by disrupting the plasma membrane leading to the lysis of the cell. AMPs have been found to be excellent candidates for developing novel antimicrobial agents and a few of these peptides show antimicrobial activity against pathogens causing sexually transmitted infection (STI), including HIV/HSV. Peptides, namely magainin and nisin have been shown to demonstrate contraceptive properties in vitro and in vivo. A few peptides have already entered clinical trials for the treatment of impetigo, diabetic foot ulcers and gastric helicobacter infections. In this review, we discuss the source, structures and mode of action with special reference to therapeutic considerations of various AMPs.     

Recent updates of marine antimicrobial peptides

Antimicrobial peptides are group of proteins showing broad-spectrum antimicrobial activity that have been known to be powerful agents against a variety of pathogens. This class of compounds contributed to solving the microbial resistance dilemma that limited the use of many potent antimicrobial agents. The marine environment is known to be one of the richest sources for antimicrobial peptides, yet this environment is not fully explored. Hence, the scientific research attention should be directed toward the marine ecosystem as enormous amount of useful discoveries could be brought to the forefront. In the current article, the marine antimicrobial peptides reported from mid 2012 to 2017 have been reviewed.     

Local interactions in peptides

We report the results of a joint NMR and theoretical investigation devoted to the conformational properties of N-acetyl-N′-methylamides of aliphatic amino acids with side chains of increasing bulkiness: Gly, Ala, Leu, Ile, and tert. Leu. In this series, determination of the coupling constants ³J_HNCαH together with the coupling constants ³J_C′NCαH (thanks to specific carbon-13 labeling of the N-acetyl carbonyl group) led to the derivation of alternative A, B, and C parameters in a Karplus-type relation expressing the dependence of ³J_C′NCαH upon the φ dihedral angle. The value of the latter is found to increase regularly following the increase of the side-chain bulkiness. The theoretical conformational analysis is performed by applying the SIBFA procedure, which uses empirical formulas based on ab initio SCF computations. The conformational energy maps illustrate the progressive distortion of the backbone conformation incurred in the series Gly to tert.Leu. Theoretical values computed for ³J_HNCαH and ³J_C′NCαH are found to be in a good quantitative agreement with the experimental ones.     

Analgesic cross-tolerance between morphine and opioid peptides

The analgesic effect, of intracerebroventricular administration of morphine, ketocyclazocine, [D-ala²]-methionine enkephalinamide (DAM), [D-ala²-D-leu⁵]-enkephalin. (DADLE), leuenkephalin, metenkephalin, and -endorphin on acetic acid-induced abdominal writhing (AAW) was investigated in naive and morphine-tolerant mice. It was found that the relative potencies of a series of opioids are different in naive and morphine-tolerant groups. In naive animals, the order of potency (ED₅₀, nmol) was -endorphin > morphine=DAM > DADLE > ketocyclazocine=leuenkephalin=metenkephalin. The morphine-tolerant animals were cross-tolerant to ketocyclazocine and to all the peptides studied; DAM and -endorphin exhibited the highest degree of tolerance. In morphine-tolerant animals, the order of potency was morphine=DADLE=-endorphin > DAM=ketocyclazocine =metenkephalin > leuenkephalin. The results indicate that endogenous opioid systems may be affected by tolerance development to morphine.     

海洋抗肿瘤活性蛋白与多肽的研究进展

海洋是人类赖以生存的资源宝库，海洋生物的多样性和特殊性，为人类提供了许多结构新颖、功能独特的生理活性物质。本文就具有抗肿瘤作用的海洋生物活性蛋白与多肽的研究现状作一概述。     

Synthesis of α-thiophenylglycine peptides

The synthesis of peptides useful for the investigation of microbial peptide transport is reported. These peptides, L-alanyl-L-2-thiophenylglycine (Ala-α-TPG), L-alanyl-L-2-thiophenylglycyl-L-alanine (Ala-α-TPG-Ala) and L-alanyl-L-alanyl-L-2-thiophenylglycine (Ala-Ala-α-TPG), contain a phenylthio group attached to the α carbon of glycine.     

抗菌肽抗菌机制的研究进展

抗菌肽是广泛存在于生物体内的一类小分子多肽,是生物固有免疫系统的重要组成部分.抗菌肽不仅能够有效杀灭细菌,而且还对真菌、病毒、寄生虫甚至肿瘤细胞都具有一定的杀伤作用.抗菌肽因其作用迅速、广谱抗菌、不易产生耐药性等诸多特点,已成为医药卫生、畜牧养殖、水产动物等领域研究的热点.本文就当前抗菌肽抗菌机制的研究进展作一综述.     

天然抗生素—抗菌肽

目的概述抗菌肽的分类、结构特征、生物活性、作用机制,指出抗菌肽研究的存在问题及应用前景。方法查阅中、英文相关文献20篇,对蟾饲五谷虫抗菌肽进行详细的概括总结。结果通过对抗菌肽的了解,了解到抗菌肽的种类,理化性质,结构特点以及家蝇抗菌肽的作用特点。结论抗菌肽的性质明确,作用机制完善,适合未来抗生素的开发利用。     

New semi-synthetic cyclic peptides as potential antifungal and antiprotozoal agents

This patent deals with the synthesis, characterisation and biological activity of a large series of cyclic hexapeptides which display interesting activity against fungi (including Pneumocystis carinii) and protozoa. Novel semisynthetic methods are described and a broad spectrum antifungal activity is expected, as cyclic-hexapeptides are naturally occurring inhibitors of β-glucan synthesis. The antiprotozoal activity is surprising, since these organisms do not have cell walls, and suggests a novel mechanism of action. However, the information on antiprotozoal activity is scant and precludes the evaluation of the potential these new compounds have as antiparasitic drugs.     

一类潜在的新药--抗菌肽

抗菌肽是生物防御系统产生的一类对抗外源性病原体的肽类物质，具有抗细菌、真菌、霉菌、病毒、原虫、癌细胞等多种活性，且不易产生耐药性，具有广阔的应用前景。本文概述了抗菌肽的分类、结构特征、作用机制、药用前景及存在的问题等5个方面的内容。     

Heterochiral N-formyl methionyl peptides

Crystal and molecular structures for the heterochiral sequence N-formyl-l -methionine-d -phenylalanine, 1, and its tertiary butyl ester, 2, are reported. The solid-state peptide conformation is compared to that observed in solution by n.m.r. techniques. For N-f-Met-d -Phe, 1, the crystal was orthorhombic, space group P2₁ 2₁2₁ with a cell of dimensions a = 5.061(3), b = 16.575(5) and c = 19.656(6) Å at ambient temperature of 293K; V = 1649(2)ų, Z = 4, D_m= 1.31(2)gcm^?3, D_x= 1.307gcm^?3, μ(Mokx) = 2.047cm^?1. For N-f-Met-d -Phe-OtBu. 2, the crystal was monoclinic, space group P2₁ with a cell of dimensions a = 9.963(2), b = 11.147(2), c = 19.166(3)Å. β= 102.31(1) at 273K; V = 2080(2) ų Z = 4, D_m= 1.22(2)gcm^?3, D_x= 1.215gcm^?3μ(MoKx) = 1.714cm^?1. The structures were solved from diffractometer data and refined to conventional final R = 0.046, R_w= 0.053 for F-Met-d -Phe (1301 observations. I ≥ 3σ(I)) and to R = 0.056, R_w= 0.064 for the t-butylester (2411 observations. I ≥ 3σ(I)). The l-d acid, 1, crystallizes in an extended β-sheet conformation with trans-planar peptide bond; the principal torsion angle values are φ₁=– 141.2(4).Ψ₁= 149.6(4)³, φ₂= 157.4(4)°. The methionine side chain adopts a common coiled conformation with x¹₁= - 58.0(5).x²¹= 175.1(4), x³₁= 76.5(5). The Phe side chain adopts the statistically least favored g orientation in contrast to the most populated rotamer in solution. The crystal structure is composed of parallel β-sheets held together by four weak intermolecular contacts including two C-H O contacts from the alpha carbons to the formyl and peptide carbonyl oxygens. Sheet layers are joined in a head-to-tail fashion through a very short (2.569(4) Å) contact between the carboxyl OH and the formyl oxygen and may be further stabilized by a C-H—O interaction between the formyl proton and the carboxyl OH. Two crystallographically independent molecules are observed in the crystal structure of N-f-l -Met-d -Phe-OtBu, 2. These are distinct conformational isomers differing principally at both the N and C termini. Particularly noteworthy is the synplanar orientation of the ester C = O with respect to the peptide nitrogen in molecule A. which contrasts to the antiplanar orientation in molecule B. Additionally, the formyl group is coiled more towards the C-terminus in molecule B. Principal torsion angles are φ₁(A) = - 120.6(5), Ψ₁(A) = 102.0(6)°, φ₂(A) = 128.1(6), φ₁(B) = - 94.6(5), Ψ₁(B) = 91.9(6)°. 121.7(6)°. The peptide bond is trans-planar in both molecules. Side chain dispositions are essentially identical in both structures. The Met side chain adopts the zig-zag trans-planar conformation while the Phe residue adopts an orientation near + 60° in agreement with rotamer populations observed by solution n.m.r. Typical peptide intermolecular H-bonding is observed in the ester crystal structure; both the peptide and formyl groups participate in the proposed H-bonding scheme.