Thesis advisor: Jia Niu / O-Sulfation is an important chemical code existing widely in nature, participating in a variety of biological activities including immune response, hemostasis, hormone regulation, cell signaling, and viral invasion. The heterogeneous nature, high polarity with negative charge, and the chemical lability of the sulfate modification have created significant challenges in the synthesis and structure-function studies of O-sulfated biomolecules. It is therefore highly desirable to achieve caging and selective release of the O-sulfated biomolecules. Inspired by sulfur (VI) fluoride exchange reaction, our group developed a series of general approaches to caged O-sulfated biomolecules and their selective deprotection. First, an O-sulfation strategy is developed by coupling aromatic fluorosulfate with silylated target molecules. Scalable synthesis was demonstrated on monosaccharides, disaccharides, amino acid, and steroid. Selective hydrolytic and hydrogenolytic removal of the aryl masking groups yielded the corresponding O-sulfated products in excellent yields. Furthermore, a complete knowledge gap was noted in biocompatible caging of sulfate. With the rational design and systematic optimizations, we discovered that fluorosulfotyrosine in peptides and proteins was an ideal precursor for sulfotyrosine (sY), which can be efficiently converted into the anionic active form by hydroxamic acid activators under physiologically relevant conditions. Photocaging the hydroxamic acid activators further allowed for light-controlled activation of functional sulfopeptides. This system featuring fast kinetics, high selectivity, excellent robustness, and on-demand release provides a valuable tool for probing functional roles of sulfation in the peptides and proteins. / Thesis (PhD) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.