Construction of a library of fully protected oligosaccharide for preparing various subtypes of chondroitin sulfate

Chondroitin sulfate (CS) regulates a wide range of biological processes, including cell differentiation and division, cancer development, and viral infections. We herein explored and established the method to selectively remove the 4,6-benzyl protective group of galactosamine, selectively introduced different types of protecting groups at positions 4 and 6, and synthesized four different subtypes of CS oligosaccharide modules—CS-O, A, C, and E—and a small library of 16 fully protected tetrasaccharides with different subtypes of CS disaccharides, which could be converted into the final corresponding CS product according to the literature. This work will be helpful for the research of structure–activity relationship and pharmacological mechanism of CS in the future and unlocking the “sulfation code.”