Cation-Transporting Peptides: Scaffolds for Functionalized Pores?

Expedient and divergent synthesis of unnatural peptides through cobalt-catalyzed diastereoselective umpolung hydrogenation

The development of a reliable method for asymmetric synthesis of unnatural peptides is highly desirable and particularly challenging. In this study, we present a versatile and efficient approach that uses cobalt-catalyzed diastereoselective umpolung hydrogenation to access noncanonical aryl alanine peptides. This protocol demonstrates good tolerance toward various functional groups, amino acid sequences, and peptide lengths. Moreover, the versatility of this reaction is illustrated by its successful application in the late-stage functionalization and formal synthesis of various representative chiral natural products and pharmaceutical scaffolds. This strategy eliminates the need for synthesizing chiral noncanonical aryl alanines before peptide formation, and the hydrogenation reaction does not result in racemization or epimerization. The underlying mechanism was extensively explored through deuterium labeling, control experiments, HRMS identification, and UV-Vis spectroscopy, which supported a reasonable CoI/CoIII catalytic cycle. Notably, acetic acid and methanol serve as safe and cost-effective hydrogen sources, while indium powder acts as the terminal electron source.

Ligand Induced CuII Transport Restricts Cancer and Mycobacterial Growth: Towards a Plug-and-Select Ion Channel Scaffold

Synthetic channels with high ion selectivity are attractive drug targets for diseases involving ion dysregulation. Achieving selective transport of divalent ions is highly challenging due their high hydration energies. A small tripeptide amphiphilic scaffold installed with a pybox ligand selectively transports Cu^II ions across membranes. The peptide forms stable dimeric pores in the membrane and transports ions by a Cu²⁺ /H⁺ antiport mechanism. The ligand-induced excellent Cu^II selectivity as well as high membrane permeability of the peptide is exploited to promote cancer cell death. The peptide's ability to restrict mycobacterial growth serves as seeds to evolve antibacterial strategies centred on selectively modulating ion homeostasis in pathogens. This simple peptide can potentially function as a universal, yet versatile, scaffold wherein the ion selectivity can be precisely controlled by modifying the ligand at the C terminus.

Structure-activity relationship (SAR) studies of N-(3-methylpyridin-2-yl)-4-(pyridin-2-yl)thiazol-2-amine (SRI-22819) as NF-ҡB activators for the treatment of ALS

ALS is a rare type of progressive neurological disease with unknown etiology. It results in the gradual degeneration and death of motor neurons responsible for controlling the voluntary muscles. Identification of mutations in the superoxide dismutase (SOD) 1 gene has been the most significant finding in ALS research. SOD1 abnormalities have been associated with both familial as well as sporadic ALS cases. SOD2 is a highly inducible SOD that performs in concurrence with SOD1 to detoxify ROS. Induction of SOD2 can be obtained through activation of NF-ҡBs. We previously reported that SRI-22819 increases NF-ҡB expression and activation in vitro, but it has poor ADME properties in general and has no oral bioavailability. Our initial studies were focused on direct modifications of SRI-22819. There were active compounds identified but no improvement in microsomal stability was observed. In this context, we focused on making more significant structural changes in the core of the molecule. Ataluren, an oxadiazole compound that promotes read-through and expression of dystrophin in patients with Duchenne muscular dystrophy, bears some structural similarity to SRI-22819. Thus, we synthesized a series of SRI-22819 and Ataluren (PTC124) hybrid compounds. Several compounds from this series exhibited improved activity, microsomal stability and lower calculated polar surface area (PSA). This manuscript describes the synthesis and biological evaluation of SRI-22819 analogs and its hybrid combination with Ataluren.

The Role of Terminal Functionality in the Membrane and Antibacterial Activity of Peptaibol-Mimetic Aib Foldamers

Peptaibols are peptide antibiotics that typically feature an N-terminal acetyl cap, a C-terminal aminoalcohol, and a high proportion of α-aminoisobutyric acid (Aib) residues. To establish how each feature might affect the membrane-activity of peptaibols, biomimetic Aib foldamers with different lengths and terminal groups were synthesised. Vesicle assays showed that long foldamers (eleven Aib residues) with hydrophobic termini had the highest ionophoric activity. C-terminal acids or primary amides inhibited activity, while replacement of an N-terminal acetyl with an azide group made little difference. Crystallography showed that N₃ Aib₁₁ CH₂ OTIPS folded into a 3₁₀ helix 2.91 nm long, which is close to the bilayer hydrophobic width. Planar bilayer conductance assays showed discrete ion channels only for N-acetylated foldamers. However long foldamers with hydrophobic termini had the highest antibacterial activity, indicating that ionophoric activity in vesicles was a better indicator of antibacterial activity than the observation of discrete ion channels.

Optimizing the Readout of Lanthanide-DOTA Complexes for the Detection of Ligand-Bound Copper(I)

The CuAAC ‘click’ reaction was used to couple alkyne-functionalized lanthanide-DOTA complexes to a range of fluorescent antennae. Screening of the antenna components was aided by comparison of the luminescent output of the resultant sensors using data normalized to account for reaction conversion as assessed by IR. A maximum 82-fold enhanced signal:background luminescence output was achieved using a Eu(III)-DOTA complex coupled to a coumarin-azide, in a reaction which is specific to the presence of copper(I). This optimized complex provides a new lead design for lanthanide-DOTA complexes which can act as irreversible ‘turn-on’ catalytic sensors for the detection of ligand-bound copper(I).

Triamide macrocyclic chloride receptors via a one-pot tandem reduction–condensation–cyclization reaction

A chloride binding triamide macrocycle has been developed in one pot from the corresponding monomer via tandem reduction–condensation–cyclization reactions.

Cation–halide transport through peptide pores containing aminopicolinic acid

Aminopicolinic acid incorporated peptides form pores that promote cation–halide co-transport across lipid bilayers and do not show a closed state.