Synthesis of Histidine-Containing Oligopeptides via Histidine-Promoted Peptide Ligation

Cesium Carbonate Promoted Direct Amidation of Unactivated Esters with Amino Alcohol Derivatives

Cesium carbonate promoted direct amidation of unactivated esters with amino alcohols was developed without the use of transition-metal catalysts and coupling reagents. This method enabled the synthesis of several serine-containing oligopeptides and benzamide derivatives with yields up to 90%. The methodology proceeds under mild reaction conditions and exhibits no racemization for most naturally occurring amino acid substrates. The reaction demonstrates good compatibility with primary alkyl and benzyl esters and broad tolerance for a range of amino acid substrates with nonpolar and protected side chains. The hydroxy group on the amine nucleophile was found to be critical for the reaction to be successful. A likely mechanism involving cesium coordination to the substrates enabling the subsequent proximity-driven acyl transfer was proposed. The practicality of this approach was demonstrated in the preparation of a biologically active nicotinamide derivative in a reasonable yield.

The First Dimeric Derivatives of the Glycopeptide Antibiotic Teicoplanin

Various dimeric derivatives of the glycopeptide antibiotic teicoplanin were prepared with the aim of increasing the activity of the parent compound against glycopeptide-resistant bacteria, primarily vancomycin-resistant enterococci. Starting from teicoplanin, four covalent dimers were prepared in two orientations, using an α,ω-bis-isothiocyanate linker. Formation of a dimeric cobalt coordination complex of an N-terminal L-histidyl derivative of teicoplanin pseudoaglycone has been detected and its antibacterial activity evaluated. The Co(III)-induced dimerization of the histidyl derivative was demonstrated by DOSY experiments. Both the covalent and the complex dimeric derivatives showed high activity against VanA teicoplanin-resistant enterococci, but their activity against other tested bacterial strains did not exceed that of the monomeric compounds.

Recent applications of N-acyl imidazole chemistry in chemical biology

N-Acyl imidazoles are unique electrophiles that exhibit moderate reactivity, relatively long-half life, and high solubility in water. Thanks to their tunable reactivity and chemical selectivity, the application of N-acyl imidazole derivatives has launched to a number of chemical biology researches, which include chemical synthesis of peptide/protein, chemical labeling of native proteins of interest (POIs), and structural analysis and functional manipulation of RNAs. Since proteins and RNAs play pivotal roles in numerous biological events in all living organisms, the methods that enable the chemical modification of endogenously existing POIs and RNAs in live cells may offer a variety of opportunities not only for fundamental scientific study but also for biotechnology and drug development. In this review, we discuss the recent progress of N-acyl imidazole chemistry that contributes to the chemical labeling and functional control of endogenous proteins and RNAs under multimolecularly crowded biological conditions of live cells.

Supercritical fluid assembly of albendazole liposomes targeting gastrin-releasing peptide receptor overexpressing tumors

Aim: To develop albendazole (ABZ)-loaded bombesin(6-14) (BBN(6-14)) functionalized liposomes for targeting GRPR to enhance delivery to cancer cells. Materials & methods: ABZ-loaded liposomes were formulated using supercritical CO2 technology; functionalized with a GRPR-targeted lipid-anchored BBN(6-14) peptide; and evaluated for effects on cell viability, particle size and targeted cell uptake. Results: BBN(6-14)-coated ABZ liposomes decreased cell viability compared with nonfunctionalized ABZ liposomes. The level of GRPR expression positively correlated with intracellular uptake and decreased cell viability. The reduced cell viability, higher cell uptake and GRPR expression were observed in the order PC-3 > Caco-2 > HepG2 cells. Conclusion: BBN(6-14)-functionalized ABZ liposomes showed enhanced reduction in cell viability compared with nonfunctionalized ABZ liposomes.