Bioinspired Nitroalkylation for Selective Protein Modification and Peptide Stapling

Abstract

Nitroalkanes react specifically with aldehydes, providing rapid, stable, and chemoselective protein bioconjugation. These nitroalkylated proteins mimic key post‐translational modifications (PTMs) of proteins and can be used to understand the role of these PTMs in cellular processes. Demonstrated here is the substrate scope of this bioconjugation by attaching a variety of tags, such as NMR tags, fluorescent tags, affinity tags, and alkyne tags, to proteins. The structure and enzymatic activity of modified proteins remain conserved after labeling. Notably, the nitroalkane group leads to easy characterization of proteins by mass spectrometry because of its distinct fingerprint pattern. Importantly, the nitro‐alkylated peptides provide a new handle for site‐selective fluorination of peptides, thus installing a specific probe to study peptide–protein interactions by 19F NMR spectroscopy. Furthermore, nitroalkane reagents can be used for the late‐stage diversification of peptides and for the synthesis of peptide staples.

Recent Advances in Metal-Free Peptide Stapling Strategies

“…By stapling two glutamic acids rapidly through a reaction between nitroalkanes and aldehydes, Raj et al demonstrated the efficiency and selectivity of nitroalkanes in bioconjugation reactions. 31 These compounds can be easily incorporated into various proteins using chemical and biochemical methods (Scheme 4).…”

Drug design targeting active posttranslational modification protein isoforms

“…In addition to the above progress, manipulation and understanding the biological function of PTM protein isoform can be achieved through PTM site‐specific installation of covalent PTM modification on wild type proteins 184 . Currently, chemical methods 185,186 or genetic methods have been successfully developed to incorporate many different PTM modifications including phosphorylation, 187,188 glycosylation, 189,190 ubiquitination, lipidation, acetylation, 191 methylation, 192 ADP‐ribosylation, sulfation, 193,194 SUMOylation, 195 nitro alkylation, 196 and oxidation of cysteines 197 . There are three types of chemical biology methods allowing covalent modifications, especially for histone, namely chemical mutagenesis, protein semisynthesis, and genetic code expansion 198 .…”

A Tale of Two Bioconjugations: pH Controlled Divergent Reactivity of Protein α-oxo-Aldehydes in Competing α-oxo-Mannich and Catalyst-Free Aldol Ligations

“…In particular, α-oxo aldehydes, 32 which can now be routinely incorporated site-selectively at both N-terminal and internal positions within proteins, 33−35 offer great potential for the development of novel bioconjugations due to their uniquely electrophilic nature. Although recent studies have shown these α-oxo aldehydes are reactive in C−C ligations, 36,37 much of the work in this field has been focused on the synthesis of heteroatom linked thiazolidine, 38 oxime, and hydrazone bioconjugates from aldehyde precursors. 39−41 These transformations have principally employed anilines as organocatalysts, leading to large increases in reaction rates at neutral pH or below.…”