Head-to-tail macrocyclization of cysteine-free peptides using an o-aminoanilide linker.

A head-to-tail macrocyclization protocol for the preparation of cysteine-free cyclic peptides was investigated. The o-aminoanilide linker constructed in the peptide sequence by a standard Fmoc-based peptide synthesis procedure was subjected to nitrite-mediated activation under acidic conditions toward N-acyl benzotriazole as the active ester species. The subsequent cyclization smoothly proceeded by neutralization in the presence of additives such as 1-hydroxybenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt) to afford the expected cyclic pentapeptide, a CXCR4 antagonist. The cyclization efficiencies were dependent on the precursor open-chain sequence. The application of this step-wise activation-cyclization protocol to microflow reaction systems is also described.

Total synthesis of odoamide, a novel cyclic depsipeptide, from an Okinawan marine cyanobacterium.

Odoamide is a novel cyclic depsipeptide with highly potent cytotoxic activity isolated from the Okinawan marine cyanobacterium Okeania sp. It contains a 26-membered macrocycle composed of a fatty acid moiety, a peptide segment and isoleucic acid. Four possible stereoisomers of the odoamide polyketide substructure were synthesised using a chiral pool approach. The first total synthesis of odoamide was also successfully achieved. The structure of synthetic odoamide was verified by comparing its NMR spectra with those of the natural product.

Polyamine modification by acrolein exclusively produces 1,5-diazacyclooctanes: a previously unrecognized mechanism for acrolein-mediated oxidative stress.

Acrolein, a toxic unsaturated aldehyde generated as a result of oxidative stress, readily reacts with a variety of nucleophilic biomolecules. Polyamines, which produced acrolein in the presence of amine oxidase, were then found to react with acrolein to produce 1,5-diazacyclooctane, a previously unrecognized but significant downstream product of oxidative stress. Although diazacyclooctane formation effectively neutralized acrolein toxicity, the diazacyclooctane hydrogel produced through a sequential diazacyclooctane polymerization reaction was highly cytotoxic. This study suggests that diazacyclooctane formation is involved in the mechanism underlying acrolein-mediated oxidative stress.

Design and synthesis of fluorescent probes for GPR54.

Kisspeptins are neuropeptides that induce the secretion of gonadotropin-releasing hormone via the activation of the cognate receptor, G-protein coupled receptor 54 (GPR54). The kisspeptin-GPR54 axis is associated with the onset of puberty and the maintenance of the reproductive system. In this study, several fluorescent probes have been designed and synthesized for rat GPR54 through the modification of the N-terminus of rat kisspeptins to allow for the visualization of the expression and localization of kisspeptin receptor(s) in living cells and native tissues. The tetramethylrhodamine (TMR) and rhodamine green (RG)-labeled kisspeptins exhibited good binding and agonistic activities towards GPR54, and the results of the application studies demonstrated that these fluorescent probes could be used effectively for the detection of GPR54 receptors in flow cytometry and confocal microscopy experiments.

Affinity-based screening of MDM2/MDMX-p53 interaction inhibitors by chemical array: identification of novel peptidic inhibitors.

MDM2 and MDMX are oncoproteins that negatively regulate the activity and stability of the tumor suppressor protein p53. The inhibitors of protein-protein interactions (PPIs) of MDM2-p53 and MDMX-p53 represent potential anticancer agents. In this study, a novel approach for identifying MDM2-p53 and MDMX-p53 PPI inhibitor candidates by affinity-based screening using a chemical array has been established. A number of compounds from an in-house compound library, which were immobilized onto a chemical array, were screened for interaction with fluorescence-labeled MDM2 and MDMX proteins. The subsequent fluorescent polarization assay identified several compounds that inhibited MDM2-p53 and MDMX-p53 interactions.

Characterization of the receptor binding residues of kisspeptins by positional scanning using peptide photoaffinity probes.

Kisspeptins, endogenous peptide ligands for GPR54, play an important role in GnRH secretion. Since in vivo administration of kisspeptins induces increased plasma LH levels, GPR54 agonists hold promise as therapeutic agents for the treatment of hormonal secretion diseases. To facilitate the design of novel potent GPR54 ligands, residues in kisspeptins that involve in the interaction with GPR54 were investigated by kisspeptin-based photoaffinity probes. Herein, we report the design and synthesis of novel kisspeptin-based photoaffinity probes, and the application to crosslinking experiments for GPR54-expressing cells.