University of Wyoming, Department of Chemistry, Laramie, Wyoming 82071, United States.
J Am Chem Soc. 2020 May 20;142(20):9112-9118. doi: 10.1021/jacs.0c03039. Epub 2020 May 5.
We report here a photochemical process for the selective modification of tryptophan (Trp) residues in peptides and small proteins using electron-responsive -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 -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.
我们在此报告了一种光化学方法，用于使用电子响应的 - 碳酰胺吡啶鎓盐和 UV-B 光选择性修饰肽和小蛋白中的色氨酸（Trp）残基。初步的机理实验表明，光共轭过程通过色氨酸和吡啶鎓盐之间的光诱导电子转移（PET）进行，随后吡啶鎓 N-N 键断裂，并伴随该基团转移到色氨酸。该反应对色氨酸具有优异的位点选择性，并且耐受其他氧化还原活性氨基酸残基。此外，该反应在纯水性条件下进行，无需有机溶剂或光催化剂，谷胱甘肽可增强反应，并且在广泛的肽浓度（10-700 μM）范围内有效进行。该过程的范围通过标记含有 6-Trp 的肽和蛋白质（分子量为 1 至 14 kDa）进行了探索。我们通过调整吡啶鎓支架的电化学和光化学性质来实现挑战性的光共轭反应，并通过使用氨基甲酰基部分连接大量有生产性的官能团，包括反应性接头、纯化标签和可去除的保护基团，展示了 - 碳酰胺吡啶鎓盐的多功能性。
