Mass-spectrometry-based
chemoproteomics has enabled the rapid and
proteome-wide discovery of functional and potentially ’druggable’
hotspots in proteins. While numerous transformations are now available,
chemoproteomic studies still rely overwhelmingly on copper(I)-catalyzed
azide–alkyne cycloaddition (CuAAC) or ’click’
chemistry. The absence of bio-orthogonal chemistries that are functionally
equivalent and complementary to CuAAC for chemoproteomic applications
has hindered the development of multiplexed chemoproteomic platforms
capable of assaying multiple amino acid side chains in parallel. Here,
we identify and optimize Suzuki–Miyaura cross-coupling conditions
for activity-based protein profiling and mass-spectrometry-based chemoproteomics,
including for target deconvolution and labeling site identification.
Uniquely enabled by the observed orthogonality of palladium-catalyzed
cross-coupling and CuAAC, we combine both reactions to achieve dual
labeling. Multiplexed targeted deconvolution identified the protein
targets of bifunctional cysteine- and lysine-reactive probes.
Mass spectrometry-based chemoproteomics
has enabled functional
analysis and small molecule screening at thousands of cysteine residues
in parallel. Widely adopted chemoproteomic sample preparation workflows
rely on the use of pan cysteine-reactive probes such as iodoacetamide
alkyne combined with biotinylation via copper-catalyzed azide–alkyne
cycloaddition (CuAAC) or “click chemistry” for cysteine
capture. Despite considerable advances in both sample preparation
and analytical platforms, current techniques only sample a small fraction
of all cysteines encoded in the human proteome. Extending the recently
introduced labile mode of the MSFragger search engine, here we report
an in-depth analysis of cysteine biotinylation via click chemistry
(CBCC) reagent gas-phase fragmentation during MS/MS analysis. We find
that CBCC conjugates produce both known and novel diagnostic fragments
and peptide remainder ions. Among these species, we identified a candidate
signature ion for CBCC peptides, the cyclic oxonium-biotin fragment
ion that is generated upon fragmentation of the N(triazole)–C(alkyl)
bond. Guided by our empirical comparison of fragmentation patterns
of six CBCC reagent combinations, we achieved enhanced coverage of
cysteine-labeled peptides. Implementation of labile searches afforded
unique PSMs and provides a roadmap for the utility of such searches
in enhancing chemoproteomic peptide coverage.
We review the development of photoaffinity labeling (PAL) chemistries and the application of PAL to chemoproteomic target deconvolution for small molecules, lipids, and metabolites.
Reported herein is a one‐pot protocol for the oxodealkenylative introduction of carbonyl functionalities into terpenes and terpene‐derived compounds. This transformation proceeds by Criegee ozonolysis of an alkene, reductive cleavage of the resulting α‐alkoxy hydroperoxide, trapping of the generated alkyl radical with 2,2,6,6‐tetramethylpiperidin‐1‐yl (TEMPO), and subsequent oxidative fragmentation with MMPP. Using readily available starting materials from chiral pool, a variety of carbonyl‐containing products have been accessed rapidly in good yields.
Pericyclic
processes such as [3,3]-sigmatropic rearrangements leading
to the rapid generation of molecular complexity constitute highly
valuable tools in organic synthesis. Herein, we report the formation
of particularly hindered tertiary alcohols via rearrangement of Breslow
intermediates formed in situ from readily available N-allyl thiazolium salts and benzaldehyde derivatives. Experimental
mechanistic studies performed suggest that the reaction proceeds via
a close radical pair which recombine in a regio- and diastereoselective
manner, formally leading to [3,3]-rearranged products.
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