Efficient Synthesis of Exo-N-carbamoyl Nucleosides: Application to the Synthesis of Phosphoramidate Prodrugs

[摘要]：An efficient protection Protocol for the 6-exo-amino group of purine nucleosides with various chloroformates was developed utilizing N-methylimidazole (NMI). The reaction of an exo-N-6-group of adenosine analogue 1 with alkyl/and aryl chloroformates under optimized conditions provided the N-6-carbamoyl adenosines (2a-j) in good to excellent yields. The reaction of N-6-Cbz-protected nucleosides (5a-c) with phenyl phosphoryl chloride (7) using t-BuMgCl followed by catalytic hydrogenation afforded the corresponding phosphoramidate pronucleotides (13a-c) in excellent yield.

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