Chemo‐ and Regioselective Ethynylation of Tryptophan‐Containing Peptides and Proteins

Ethynylation of various tryptophan‐containing peptides and a single model protein was achieved using Waser's reagent, 1‐[(triisopropylsilyl)ethynyl]‐1,2‐benziodoxol‐3(1 H)‐one (TIPS‐EBX), under gold(I) catalysis. It was demonstrated by NMR that the ethynylation occured selectively at the C2‐position of the indole ring of tryptophan. Further, MS/MS showed that the tryptophan residues could be modified selectively with ethynyl functionalities even when the tryptophan was present as a part of the protein. Finally, the terminal alkyne was used to label a model peptide with a fluorophore by means of copper‐catalyzed click chemistry.     

Incorporation of β‐Silicon‐β3‐Amino Acids in the Antimicrobial Peptide Alamethicin Provides a 20‐Fold Increase in Membrane Permeabilization

Incorporation of silicon‐containing amino acids in peptides is known to endow the peptide with desirable properties such as improved proteolytic stability and increased lipophilicity. In the presented study, we demonstrate that incorporation of β‐silicon‐β3‐amino acids into the antimicrobial peptide alamethicin provides the peptide with improved membrane permeabilizing properties. A robust synthetic procedure for the construction of β‐silicon‐β3‐amino acids was developed and the amino acid analogues were incorporated into alamethicin at different positions of the hydrophobic face of the amphipathic helix by using SPPS. The incorporation was shown to provide up to 20‐fold increase in calcein release as compared with wild‐type alamethicin.     

Robust conductance of dumbbell molecular junctions with fullerene anchoring groups

The conductance of a molecular wire connected to metallic electrodes is known to be sensitive to the atomic structure of the molecule-metal contact. This contact is to a large extent determined by the anchoring group linking the molecular wire to the metal. It has been found experimentally that a dumbbell construction with C(60) molecules acting as anchors yields more well-defined conductances as compared to the widely used thiol anchoring groups. Here, we use density functional theory to investigate the electronic properties of this dumbbell construction. The conductance is found to be stable against variations in the detailed bonding geometry and in good agreement with the experimental value of G=3×10(-4) G(0). Electron tunneling across the molecular bridge occurs via the lowest unoccupied orbitals of C(60) which are pinned close to the Fermi energy due to partial charge transfer. Our findings support the original motivation to achieve conductance values more stable towards changes in the structure of the molecule-metal contact leading to larger reproducibility in experiments.     

Access to 1,2‐Dihydroisoquinolines through Gold‐Catalyzed Formal [4+2] Cycloaddition

A new synthetic route to the privileged 1,2‐dihydroisoquinolines is reported. This method, which relies on a gold‐catalyzed formal [4+2] cycloaddition between ynamides and imines, provides a new retrosynthetic disconnection of the 1,2‐dihydroisoquinoline core by installing the 1,8a C?C and 2,3 C?N bonds in one step. Both aldimines and ketimines can be used as substrates. In addition, one example of dihydrofuropyridine synthesis is also demonstrated.     

Pd‐Catalyzed C?N Bond Formation with Heteroaromatic Tosylates

A protocol for the palladium(0)‐catalyzed amidation of heteroaromatic tosylates was successfully developed. The methodology proved to be effective for a variety of heteroaryl tosylates including the pyridine, pyrimidine, quinoline and quinoxaline ring systems. Successful carbon? nitrogen bond formation with these heteroaryl tosylates could be performed with a wide range of primary amides, oxazolidinones, lactams, anilines and indoles, including one cyclic urea. Moreover, this C? N bond forming reaction provided products with high structural diversity. The coupling reaction was also amenable to scale up applications.     

Heteroaromatic Tosylates as Electrophiles in Regioselective Mizoroki–Heck‐Coupling Reactions with Electron‐Rich Olefins

Easy and direct : Regioselective Mizoroki–Heck‐coupling reactions using heteroaromatic tosylates as electrophiles were achieved, thus providing direct and easy access to highly functionalized α‐heteroarylvinyl amides and ethers.

     

Unique Identification of Supramolecular Structures in Amyloid Fibrils by Solid‐State NMR Spectroscopy

The fibril structure formed by the amyloidogenic fragment SNNFGAILSS of the human islet amyloid polypeptide (hIAPP) is determined with 0.52 Å resolution. Symmetry information contained in the easily obtainable resonance assignments from solid‐state NMR spectra (see picture), along with long‐range constraints, can be applied to uniquely identify the supramolecular organization of fibrils.