Improved synthesis of 9-(2,3-dideoxy-2-fluoro-β-d-threo-pentofuranosyl)adenine (FddA) using triethylamine trihydrofluoride

An improved synthesis of 9-(2,3-dideoxy-2-fluoro-β-d-threo-pentofuranosyl)adenine (1, FddA) via a fluorination of 3′-O-benzoyl-5′-O-tritylriboside (4a) using noncorrosive triethylamine trihydrofluoride (Et3N·3HF) is described. The method is suitable for large-scale synthesis. In particular, the synthesis of the pivotal intermediate 4a was much improved in avoidance of the use of toxic tin reagent. Radical deoxygenation with several silanes was also studied. The total yield of FddA from 6-chloropurine riboside (2) in this study was greater than that we reported previously.