Catalyst free hydrazone ligation for protein labeling and modification using electron-deficient benzaldehyde reagents

Injectable isoniazid-loaded bone cement based on hydrazone bonds achieving long-term release and decent mechanical properties

A robust and easily manufactured high-strength and long-term release hydrazone-based isoniazid acrylic (HIA) bone cement is reported. The mechanical strength of HIA bone cement is similar to that of normal polymethyl methacrylate (PMMA) bone cement, far surpassing that of traditional isoniazid-containing antibiotic-loaded bone cement (INH bone cement). Isoniazid is connected to the bone cement through bioorthogonal hydrazone chemistry, and it possesses release properties superior to those of INH bone cement, allowing for the sustained release of isoniazid for up to 12 weeks. In vivo and in vitro studies also indicate that HIA cement exhibits better biocompatibility than INH bone cement. The results of this study not only signify progress in the realm of antimicrobial bone cement for addressing bone tuberculosis but also enhance our capacity to create and comprehend high-performing antimicrobial bone cement.

carba-Nucleopeptides (cNPs): A Biopharmaceutical Modality Formed through Aqueous Rhodamine B Photoredox Catalysis

Exchanging the ribose backbone of an oligonucleotide for a peptide can enhance its physiologic stability and nucleic acid binding affinity. Ordinarily, the eneamino nitrogen atom of a nucleobase is fused to the side chain of a polypeptide through a new C-N bond. The discovery of C-C linked nucleobases in the human transcriptome reveals new opportunities for engineering nucleopeptides that replace the traditional C-N bond with a non-classical C-C bond, liberating a captive nitrogen atom and promoting new hydrogen bonding and π-stacking interactions. We report the first late-stage synthesis of C-C linked carba-nucleopeptides (cNPs) using aqueous Rhodamine B photoredox catalysis. We prepare brand-new cNPs in batch, in parallel, and in flow using three long-wavelength photochemical setups. We detail the mechanism of our reaction by experimental and computational studies and highlight the essential role of diisopropylethylamine as a bifurcated two-electron reductant.

β-Hydroxy-Stabilized Boron-Nitrogen Heterocycles Enable Rapid and Efficient C-Terminal Protein Modification

Bioorthogonal chemistry has enabled the development of bioconjugates in physiological environments while averting interference from endogenous biomolecules. Reactions between carbonyl-containing molecules and alkoxyamines or hydrazines have experienced a resurgence in popularity in bioorthogonal chemistry owing to advances that allow the reactions to occur under physiological conditions. In particular, ortho-carbonyl-substituted phenylboronic acids (CO-PBAs) exhibit greatly accelerated rates of hydrazone and oxime formation via intramolecular Lewis acid catalysis. Unfortunately, the rate of the reverse reaction is also increased, yielding a kinetically less stable bioconjugate. When the substrate is a hydrazine derivative, an intramolecular reaction between the boronic acid and the hydrazone can lead to the formation of a heterocycle containing a boron-nitrogen bond. We have shown previously that α-amino hydrazides undergo rapid reaction with CO-PBAs to form highly stable, tricyclic products, and that this reaction is orthogonal to the popular azide-alkyne and tetrazine-alkene reactions. In this work, we explore a series of heteroatom-substituted hydrazides for their ability to form tricyclic products with two CO-PBAs, 2-formylphenylboronic acid (2fPBA), and 2-acetylphenylboronic acid (AcPBA). In particular, highly stable products were formed using β-hydroxy hydrazides and 2fPBA. C-Terminal β-hydroxy hydrazide proteins are available using conventional biochemical methods, which alleviates one of the difficulties with applications of bioorthogonal chemical reactions: site-specific incorporation of a reactive group into the biomolecular target. Using sortase-mediated ligation (SML), C-terminal threonine and serine hydrazides were appended to a model eGFP protein in high yield. Subsequent labeling with 2fPBA functionalized probes could be performed quickly and quantitatively at neutral pH using micromolar concentrations of reactants. The SML process was applied directly to an expressed protein in cellular extract, and the C-terminal modified target protein was selectively immobilized using 2fPBA-agarose. Elution from the agarose yielded a highly pure protein that retained the hydrazide functionality. This strategy should be generally applicable for rapid, efficient site-specific protein labeling, protein immobilization, and preparation of highly pure functionalized proteins.