Triazabutadienes and a Glycoprotein-Targeted Photocrosslinker as Protein-Labeling Agents

Abstract

Labeling proteins with chemical tools is important for examining natural systems, discovering therapeutic agents and developing protein constructs. These methods offer simple but reliable chemistry to the study of peptides and proteins and thus have gained popularity among chemists and biologists. Despite the fact that the number of successful examples has been largely increased over the past decade, there is still an ongoing need for new reagents with better accessibility and reactivity. Diazonium ions are known to selectively react with tyrosine residues for more than a century. But the harsh condition required for diazotization makes it difficult to use this strategy in biological applications. To address this, bench-stable triazabutadienes are made to release diazonium ions upon mild acidification or photoirradiation. Based on our previous study, imidazole N-alkyl substituted triazabutadienes were synthesized and tested for diazonium ion-releasing rates. Surprisingly, the imidazole N-tert-butyl substituted triazabutadiene showed the fastest rate in neutral and basic aqueous solutions. A subsequent NMR study revealed that this rapid release of diazonium ions might be ascribed to the lack of intramolecular π-interactions. In addition, triazabutadienes can be rendered more basic upon photo-isomerization. A water-soluble triazabutadiene was shown to adjust the pH of aqueous solutions. These findings open up new opportunities in protein labeling with unprecedented ease. Moreover, a boronic acid-based photocrosslinker was synthesized to detect protein-protein interactions of glycoproteins. By incorporating benzophenone with a boronic acid and a terminal alkyne, this photocrosslinker is designed to capture the glycoprotein-substrate complex using the combination of photochemistry and bioorthogonal reactions. In conclusion, this dissertation demonstrates progress in developing new probes for protein labeling and protein-protein interactions. These newly developed strategies offer convenient alternatives to those wishing to explore protein activities.