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https://www.selleckchem.com/products/azaindole-1.html We report here a photochemical process for the selective modification of tryptophan (Trp) residues in peptides and small proteins using electron-responsive N-carbamoylpyridinium salts and UV-B light. Preliminary mechanistic experiments suggest that the photoconjugation process proceeds through photoinduced electron transfer (PET) between Trp and the pyridinium salt, followed by fragmentation of the pyridinium N-N bond and concomitant transfer of this group to Trp. The reaction displays excellent site selectivity for Trp and is tolerant to other, redox-active amino-acid residues. Moreover, the reaction proceeds in pure aqueous conditions without the requirement of organic cosolvents or photocatalysts, is enhanced by glutathione, and operates efficiently over a wide range of peptide concentrations (10-700 μM). The scope of the process was explored through the labeling of 6-Trp-containing peptides and proteins ranging from 1 to 14 kDa. We demonstrate the versatility of the N-carbamoylpyridinium salt both by tuning the electrochemical and photochemical properties of the pyridinium scaffold to enable challenging photoconjugation reactions and by using the carbamoyl moiety to tether a plethora of productive functional groups, including reactive handles, purification tags, and removable protecting groups.While the number of characterized radical S-adenosyl-l-methionine (SAM) enzymes is increasing, the roles of these enzymes in radical catalysis remain largely ambiguous. In radical SAM enzymes, the slow radical initiation step kinetically masks the subsequent steps, making it impossible to study the kinetics of radical chemistry. Due to this kinetic masking, it is unknown whether the subsequent radical reactions require rate acceleration by the enzyme active site. Here, we report the first evidence that a radical SAM enzyme MoaA accelerates the radical-mediated C-C bond formation. MoaA catalyzes an unprecedented 3',8-cyc

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