Chemoselective Caging of Carboxyl Groups for On-Demand Protein Activation with Small Molecules

α-Silylated Diazoalkynes: New Tools for Bioconjugation of Proteins

α-Silylated diazoalkynes are stabilized diazo compounds that can selectively react with carboxylic residues in buffered aqueous media. In-situ fluoride induced desilylation increases this reactivity, leading to a very fast reaction. Application to the selective functionalization of RNase A, followed by post-functionalization using click chemistry, is described. These new reagents expand the toolbox for native protein modification at carboxylic residues.

Pinpointing Acidic Residues in Proteins

It is of great importance to pinpoint specific residues or sites of a protein in biological contexts to enable desired mechanism of action for small molecules or to precisely control protein function. In this regard, acidic residues including aspartic acid (Asp) and glutamic acid (Glu) hold great potential due to their great prevalence and unique function. To unlock the largely untapped potential, great efforts have been made recently by synthetic chemists, chemical biologists and pharmacologists. Herein, we would like to highlight the remarkable progress and particularly introduce the electrophiles that exhibit reactivity to carboxylic acids, the light-induced reactivities to carboxylic acids and the genetically encoded noncanonical amino acids that allow protein manipulations at acidic residues. We also comment on certain unresolved challenges, hoping to draw more attention to this rapidly developing area.

Covalent fragment approaches targeting non-cysteine residues

Covalent fragment approaches combine advantages of covalent binders and fragment-based drug discovery (FBDD) for target identification and validation. Although early applications focused mostly on cysteine labeling, the chemistries of available warheads that target other orthosteric and allosteric protein nucleophiles has recently been extended. The range of different warheads and labeling chemistries provide unique opportunities for screening and optimizing warheads necessary for targeting non-cysteine residues. In this review, we discuss these recently developed amino-acid-specific and promiscuous warheads, as well as emerging labeling chemistries, which includes novel transition metal catalyzed, photoactive, electroactive, and noncatalytic methodologies. We also highlight recent applications of covalent fragments for the development of molecular glues and proteolysis-targeting chimeras (PROTACs), and their utility in chemical proteomics-based target identification and validation.