Studies on the sialylation of galactoses with different C-5 modified sialyl donors

Synthetic sialylated glycans provide useful tools to study carbohydrate-mediated biological recognition; however chemical sialylation is the most challenging practice in preparative carbohydrate chemistry, which is often associated with low yields and poor stereoselectivity. Herein, we conducted extensive studies on sialylation with five types of 5-N-modified sialyl donors and four types of galactosyl acceptors. Our studies have shown that a good combination between the donor and the acceptor seems necessary to achieve high yield and stereoselectivity. None of the donors or acceptors showed 'universal' utility toward the sialylation reaction.