Utilizing Alkyne-Nitrone Cycloaddition for the Convenient Multi-Component Assembly of Protein Degraders and Biological Probes.

Proteolysis-targeting chimeras (PROTACs) have become a popular therapeutic strategy, and the development of multi-functional PROTACs has added complexity to their synthetic process. Although click reactions have been widely applied to prepare highly functionalized biomolecules, most of them are limited to two-component reactions, restricting the creation of more complex structures. Here, we developed a convenient multi-component assembly strategy via strain-promoted alkyne-nitrone cycloaddition (SPANC), which can be extended to a 3-component reaction when combined with nitrone formation. Using the 2-component assembly, we demonstrated the targeted protein degradation with both preassembled and in-cell assembled PROTACs. This strategy was also applied to facilitate the screening of E3 ligases in PROTACs and the preparation of various biological probes. Moreover, the 3-component assembly, via sequential nitrone formation and SPANC, enabled the synthesis of trifunctional 3-component PROTACs. The N-substituent, serving as an additional functional moiety, was designed as a photocage for sterically controlling PROTAC activity. The 3-component assembly can be further modified to provide additional control or enhance the cell-targeting ability of PROTACs. In short, our multi-component SPANC assembly strategy offers a modular and versatile synthetic platform for creating multi-functional PROTACs and biological probes.