Copper-Catalyzed Azide–Alkyne Cycloaddition-Oriented Multifunctional Bio-Orthogonal Linker BPPA: Design, Synthesis and Evaluation

Abstract

The multifunctional linker molecules are crucial for the bio-orthogonal reaction for proteomic target profiling. Herein, we wish to present a novel type of biotin-based tetra-functional bio-orthogonal linkers 3a–3h named BPPA which, possessing a unique photolabile phenacyl ester motif, were readily prepared in 85–90% yields by a simple and green one-step protocol from commercially available and inexpensive reagents of biotin acids and 4’-ethynyl/azido 2-bromoacetophenones. The typical click reaction of BPPA linkers 3a and 3e via copper-catalyzed azide–alkyne cycloaddition (CuAAC) took place easily, resulting in the corresponding BPPA-triazole adducts 4a and 4b in nearly quantitative yields. A further cleavability evaluation of 4a and 4b demonstrated that the expected C-O bond detachment could be accomplished efficiently and rapidly by UV irradiation or by ammonia hydrolysis, respectively, resulting in the residual (hydroxyl)acetylphenyl triazole fragment supposed to be attached to proteins during biological manipulations. The BPPA linkers, with dual clickable options of either the terminal azide or alkyne clickable group, exhibit high potentials for various CuAAC-oriented bio-orthogonal reactions.

Keywords

• bio-orthogonal linker
• phenacyl ester motif
• click-cleavage evaluation
• CuAAC reaction