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.

Stapled Helical Peptides Bearing Different Anchoring Residues

“…Another Glu-Glu initialized peptide stapling was developed by Raj and co-workers, which took advantage of the rapid, stable, and chemo-selective protein bioconjugation between nitroalkanes and peptide aldehydes. 131 Although this study focused on the bioconjugation of various functional motifs, including NMR tags, fluorescent tags, affinity tags, and alkyne tags, a preliminary exploration of nitroalkane-triggered peptide stapling was conducted. The selectively exposed side chain carboxylic acids of Glu-Glu paired residues were amidated by aminoacetaldehyde dimethyl acetal on resin, which was followed by TFA cleavage to yield the linear peptide precursor containing two aldehyde groups.…”

“…Additionally, this stapling technique based on the Henry reaction, which involved a nucleophilic attack of the α-carbon of nitroalkane to the electrophilic aldehyde on a peptide, was sterically hindered by α-carbon substitution and showed chemo-selectivity for the N-terminal exposed SVF peptide sequence. 131…”

“…Another Glu-Glu initialized peptide stapling was developed by Raj and co-workers, which took advantage of the rapid, stable, and chemo-selective protein bioconjugation between nitroalkanes and peptide aldehydes . Although this study focused on the bioconjugation of various functional motifs, including NMR tags, fluorescent tags, affinity tags, and alkyne tags, a preliminary exploration of nitroalkane-triggered peptide stapling was conducted.…”

One‐Step Azolation Strategy for Site‐ and Chemo‐Selective Labeling of Proteins with Mass‐Sensitive Probes

“…Such as N‐terminal cysteines leading to the formation of thiazolidines with aldehydes [13] . Periodate oxidation of N‐terminal serine and threonine residues [14] for oxime, [15] hydrazone, [16] Wittig, [17] Aldol [18] and Henry bioconjugation [19] . N‐terminal tryptophans can be modified via Pictet‐Spengler reactions [20] .…”

Stereoselective Oxidative Bioconjugation of Amino Acids and Oligopeptides to Aldehydes

“…Amino acids and oligopeptides are inherently chiral, and despite examples of Pd-catalyzed diastereoselective function-alization of amino acids, [4] the majority of bioconjugation strategies that generate a new stereocenter do not normally proceed in a stereoselective manner. [5] Most bioconjugations are based on thiols and amines as nucleophilic partners, while the carboxylic acid moiety is underdeveloped.…”