Synthesis of Biaryl‐Bridged Cyclic Peptides via Catalytic Oxidative Cross‐Coupling Reactions

Biaryl‐bridged cyclic peptides comprise an intriguing class of structurally diverse natural products with significant biological activity. Especially noteworthy are the antibiotics arylomycin and its synthetic analogue G0775, which exhibits potent activity against Gram‐negative bacteria. Herein, we present a simple, flexible, and reliable strategy based on activating‐group‐assisted catalytic oxidative coupling for assembling biaryl‐bridged cyclic peptides from natural amino acids. The synthetic approach was utilized for preparing a number of natural and unnatural biaryl‐bridged cyclic peptides, including arylomycin/G0775 and RP 66453 cyclic cores.     

A mechanistic and kinetic study of the formation of metal nanoparticles by using synthetic tyrosine-based oligopeptides

Synthetic oligopeptides containing redox-active tyrosine residues have been employed to prepare gold and silver nanoparticles. In this reduction process an electron from the tyrosinate ion of the peptide is transferred to the metal ion at basic pH through the formation of a tyrosyl radical, which is eventually converted to its dityrosine form during the reaction. This reaction mechanism was confirmed from UV-visible, fluorescence, and EPR spectroscopy and was found to be pH-dependent. Transmission electron microscopy measurement shows that the average size and the monodispersity of gold nanoparticles increase as the number of tyrosine residues in the peptide increases. The kinetic study, based on spectrophotometric measurements of the surface plasmon resonance optical property, shows that the rate of formation of gold nanoparticles was much faster at higher pH than at lower pH and was also dependent on the number of tyrosine residues present in the peptide. The dityrosine form of the peptide was found to retain reducing properties like those of tyrosine in basic medium.     

金属离子对过亚硝酸根损伤酪氨酸的影响

NO^· and ^·O₂^- combine each other to form peroxynitrite (ONOO^-) in vivo. Peroxynitrite is very cytotoxic, and it damages many biomolecules. 3-nitrotyrosine and dityrosine are two main products from the reaction of ONOO^- and tyrosine. Lots of metallic ions in vivo influence the modification of tyrosine by peroxynitrite. UV-Vis and Fluorescence spectrophotometer were used to study the catalysis and inhibition of metallic ions on the production of 3-nitrotyrosine and dityrosine in vitro. Present results showed that Co(Ⅱ), Cu(Ⅱ) and Mn(Ⅱ) enhance the production of 3-nitrotyrosine, and among them Co(Ⅱ) and Mn(Ⅱ) have been reported rarely before about it. In addition, Mn(Ⅱ) inhibits the production of dityrosine to a certain extent.