Transglycosylation in the Modification and Isotope Labeling of Pyrimidine Nucleosides

Transglycosylation of pyrimidine nucleosides is demonstrated in a one-pot synthesis of uridine derivatives under microwave irradiation. Inductive activation of 2',3',5'-tri-O-acetyl uridine with a 5-nitro group produces a more-reactive glycosyl donor. Under optimized Vorbrüggen conditions, the 5-nitrouridine facilitates a reversible nucleobase exchange with a series of 5-substituted uracils. The protocol is also exemplified in a gram-scale reaction under thermal heating. The strategy provides easy access to isotopically labeled uridine.