An efficient methodology to introduce o-(aminomethyl)phenyl-boronic acids into peptides: alkylation of secondary amines

Capturing Sialyl-glycan on Live Cancer Cells by Tailored Boronopeptide

Boronic acid-containing molecules are substantially popularized in chemical biology and medicinal chemistry due to the broad spectrum of covalent conjugations as well as interaction modules offered by the versatile boron atom. Apparently, the WGA peptide (wheat germ agglutinin, 62-73), which shows a considerably low binding affinity to sialic acid, turned into a selective and >5 folds potent binder with the aid of a suitable boronic acid probe installed chemoselectively. In silico studies prompted us to install BA probes on the cysteine residue, supposedly located in close proximity to the bound sialic acid. In vitro studies revealed that the tailored boronopeptides show enhanced binding ability due to the synergistic recognition governed by selective non-covalent interactions and cis-diol boronic acid conjugation. The intense binding is observed even in 10 % serum, thus enabling profiling of sialyl-glycan on cancer cells, as compared with the widely used lectin, Sambucus nigra. The synergistic binding mode between the best boronopeptide (P3) binder and sialic acid was analyzed via 1 H and 11 B NMR.

Tunable Orthogonal Reversible Covalent (TORC) Bonds: Dynamic Chemical Control over Molecular Assembly

Dynamic assembly of macromolecules in biological systems is one of the fundamental processes that facilitates life. Although such assembly most commonly uses noncovalent interactions, a set of dynamic reactions involving reversible covalent bonding is actively being exploited for the design of functional materials, bottom-up assembly, and molecular machines. This Minireview highlights recent implementations and advancements in the area of tunable orthogonal reversible covalent (TORC) bonds for these purposes, and provides an outlook for their expansion, including the development of synthetically encoded polynucleotide mimics.

2,2'-Bipyridine and hydrazide containing peptides for cyclization and complex quaternary structural control

A synthetic peptide containing two N_ε-methyl lysines (Ac-K(N_ε-Me)GYTGYTGK(N_ε-Me)D-OH) was alkylated with bipyridine (bipy) ligands substituted at the fifth (MP-5) and sixth (MP-6) positions, thereby creating Ac-K(N_ε-Me, N_ε-Bipy)GYTGYTGK(N_ε-Me, N_ε-Bipy)D-OH. Peptides with 6-position bipyridine did not bind to Fe²⁺ and Zn²⁺. Peptides with 5-position bipyridine bound these metals, and in the presence of one equivalent of a free bipy derivative folded into a macrocycle. Further, the free bipy derivative could also contain a cyclized peptide derived from hydrazone formation, resulting in complex but controlled quaternary peptide structure.

The binding of boronated peptides to low affinity mammalian saccharides

A 54-member library of boronated octapeptides, with all but the boronated residue being proteinogenic, was tested for affinity to a set of saccharides commonly found on the terminus of mammalian glycans. After experimentation with a high-throughput dye-displacement assay, attention was focused on isothermal titration calorimetry as a tool to provide reliable affinity data, including enthalpy and entropy of binding. A small number of boronated peptides showed higher affinity and significant selectivity for N-acetylneuraminic acid over methyl-α-d-galactopyranoside, methyl-α/β-l-fucopyranoside and N-acetyl-d-glucosamine. Thermodynamic data showed that for most of the boronated peptides studied, saccharide binding was associated with a significant increase in entropy, presumably resulting from the displacement of semiordered water molecules from around the sugar and/or peptide.

RNA-based boronate internucleosidic linkages: an entry into reversible templated ligation and loop formation

The synthesis of a 5′-boronoribonucleotidic phosphoramidite building block has been achieved and incorporated at the 5′ extremities of RNA sequences for the templated assembly of RNA shortmers.