BackgroundZinc is essential for the activities of pancreatic β-cells, especially insulin storage and secretion. Insulin secretion leads to co-release of zinc which contributes to the paracrine communication in the pancreatic islets. Zinc-transporting proteins (zinc-regulated transporter, iron-regulated transporter-like proteins [ZIPs] and zinc transporters [ZnTs]) and metal-buffering proteins (metallothioneins, MTs) tightly regulate intracellular zinc homeostasis. The present study investigated how modulation of cellular zinc availability affects β-cell function using INS-1E cells.ResultsUsing INS-1E cells, we found that zinc supplementation and zinc chelation had significant effects on insulin content and insulin secretion. Supplemental zinc within the physiological concentration range induced insulin secretion. Insulin content was reduced by zinc chelation with N,N,N’,N-tektrakis(2-pyridylmethyl)-ethylenediamine. The changes in intracellular insulin content following exposure to various concentrations of zinc were reflected by changes in the expression patterns of MT-1A, ZnT-8, ZnT-5, and ZnT-3. Furthermore, high zinc concentrations induced cell necrosis while zinc chelation induced apoptosis. Finally, cell proliferation was sensitive to changes in zinc the concentration.ConclusionThese results indicate that the β-cell-like function and survival of INS-1E cells are dependent on the surrounding zinc concentrations. Our results suggest that regulation of zinc homeostasis could represent a pharmacological target.

The introduction of macrocyclic constraints in peptides (peptide stapling) is an important tool within peptide medicinal chemistry for stabilising and pre-organising peptides in a desired conformation. In recent years, the copper-catalysed azide-alkyne cycloaddition (CuAAC) has emerged as a powerful method for peptide stapling. However, to date CuAAC stapling has not provided a simple method for obtaining peptides that are easily diversified further. In the present study, we report a new diversity-oriented peptide stapling (DOPS) methodology based on CuAAC chemistry. Stapling of peptides incorporating two azide-modified amino acids with 1,3,5-triethynylbenzene efficiently provides (i, i+7)- and (i, i+9)-stapled peptides with a single free alkyne positioned on the staple, which can be further conjugated or dimerised. A unique feature of the present method is that it provides easy access to radiolabelled stapled peptides by catalytic tritiation of the alkyne positioned on the staple.

A conotoxin peptidomimetic was developed as a potential muscle relaxant that is highly potent and blood plasma stable.

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Constraining the conformation of flexible peptides is a proven strategy to increase potency, selectivity, and metabolic stability. The focus has mostly been on constraining the backbone dihedral angles; however, the correct orientation of the amino acid side chains (χ-space) that constitute the peptide pharmacophore is equally important. Control of χ-space utilizes conformationally constrained amino acids that favor, disfavor, or exclude the gauche (-), the gauche (+), or the trans conformation. In this review we focus on cyclic aromatic amino acids in which the side chain is connected to the peptide backbone to provide control of χ- and χ-space. The manifold applications for cyclized analogues of the aromatic amino acids Phe, Tyr, Trp, and His within peptide medicinal chemistry are showcased herein with examples of enzyme inhibitors and ligands for G protein-coupled receptors.

RESULTS AND DISCUSSIONThe first stage of the synthesis of the -pyridyl -amino acids involved the preparation of suitably protected enone-derived -amino acids (Scheme 1). Initially, N-trityl protected phosphonate ester 3 was prepared in three-steps (92% overall yield) from L-aspartic acid 1. 13 Following protection of the amino and carboxylic acid groups, the key step involved the highly regioselective reaction of the anion of dimethyl methylphosphonate with the sterically accessible -methyl ester of 2 to give phosphonate ester 3. Horner-Wadsworth-Emmons reaction of 3 with a wide range of aldehydes under mild conditions, gave enones 4a-j, exclusively as the E-isomers. 14,15 The focus of this project was to prepare aryl substituted pyridyl side-chains and therefore, benzaldehyde derivatives were mainly used to explore the scope of this reaction. As expected, the majority of these gave high yields of the E-enones (66-95%), although highly electron-rich aldehydes required longer reaction times (120 h) and gave more modest yields (e.g. 4e). Scheme 1. Synthesis of Enone-Derived -Amino Acids 4a-j a a Isolated yields are shown. peptide synthesizer using Rink Amide ChemMatrix® resin as the polymer support 22 and routine SPPS methodology (Scheme 3). On coupling Fmoc-L-Lys(Boc)-OH onto the polymer support using HCTU activation, successive rounds of piperidine-mediated N-deprotection and coupling using the next amino acid gave the pentapeptide. Following a subsequent N-terminal Fmoc-deprotection, the Fmoc-protected version of -pyridyl -amino acid 8d, compound 9 was coupled onto the polymer-supported pentapeptide. 23 After a final Fmoc-deprotection step, the N-terminus was acetyl capped and a TFA cleavage cocktail that included triisopropylsilane (TIPS) as a cation scavenger was used to remove the side-chain protecting groups and release the peptide from the polymer support. The resulting hexapeptide, 10 was purified by reverse phase-HPLC (>95% purity) and characterized by high-resolution electrospray ionization mass spectrometry (see Supporting Information for data). Scheme 3. SPPS of a -Pyridyl -Amino Acid Containing HexapeptideAs the -amino acids contained -deficient pyridine moieties, it was proposed that electron-rich conjugating groups may confer fluorescent properties through a charge-transfer (push-pull) mechanism. 24 Accordingly, the optical properties of -pyridyl -amino acids 8a-l were measured. As expected, pyridines with non-conjugating or electron-deficient substituents showed weak fluorescence, while compounds with electron-rich substituents showed strong fluorescence (Figure 2b and Table 1). In

Solid-phase peptide synthesis (SPPS) is used to create peptidomimetics in which one of the backbone amide C=O bonds is replaced by a four-membered oxetane ring. The oxetane containing dipeptide building blocks are made in three steps in solution, then integrated into peptide chains by conventional Fmoc SPPS. This methodology is used to make a range of peptides in high purity including backbone modified derivatives of the nonapeptide bradykinin and Met-and Leu-enkephalin.Despite resurgent interest in the use of peptides as drugs, 1 their development is often hampered by their poor oral bioavailability and short plasma half-lives. As a consequence, there is intense interest in the discovery of molecules that can mimic the structure and biological function of native peptides yet possess better drug-like properties.

Conformationally rigid unnatural α-amino acids bearing a pyrazoloquinazoline ring system that are amenable to both one- and two-photon excitation have been developed as new fluorescent probes.