Microwave-Assisted Facile Synthesis of Red-Shifted Azobenzene Glycoconjugates

Azobenzene glycoconjugates are important tools used to study the effect of sugar orientation in molecular recognition. This is possible through the reversible photoinduced trans/cis isomerization of the N=N double bond in the sugar-presenting azobenzene units. However, all the azobenzene glycoconjugates used so far need ultraviolet light for trans-to-cis switching, restricting their use in in vivo applications. Herein, we report the first synthesis of red-shifted azobenzene glycoconjugates. After tetra-ortho-chlorination of the azobenzene moiety, the respective glycoazobenzenes can be switched from the trans to the cis state with visible light. We report scope and limitations of microwave-assisted late-stage C-H chlorination to afford tetra-ortho-chloroazobenzene glycoconjugates. Furthermore, synthesis of a red-shifted azobenzene glycoconjugate carrying a thioacetate-terminated linker is reported to allow for fabrication of red-shifted photoswitchable glyco-SAMs on gold surface. The photochromic properties of all red-shifted azobenzene glycoconjugates are described.