Synthesis of 9-(2-Deoxy-2-fluoro-β-D-arabinofuranosyl)adenine Bearing a Slectively Removable Protecting Group

Abstract

A facile and practicam method to infroduce fluorine at the up-side of the 2'-carbon of nucleosides is described. 6-Chloropurine riboside 3 was converted to the 3'-O-benzoate 4a via a stannylene complex, then converted to the 3'-O-benzoyl-5'-O-tritylriboside 5a. In the presence of pyridine, migration of the 3'-benzoyl groups of 4a and 5a to 2'-OH was rather slow. Hence, 5a was reacted with diethylaminosulfur trifluoride (DAST) in CH₂Cl₂ in the presence of pyridine to give the 2'-deoxy-2'-fluoroarabinoside 6 in good yield. The 3'-O-benzoyl-5'-O-trityl protecting system was easy to deprotect selectively. Thus, treatment of 6 with ammonia in MeOH gave the 5'-O-trityl compound 7, which was subjected to esterificaiton with phenyl chlorothionoformate, radical deoxygenation with tris(trimethylsilyl)silane and acid treatment to afford 9-(2, 3-dideoxy-2-fluoro-β-D-threo-pento-furanosyl)adenine(FddA) 2. In addition, acid treatment of 7 gave 9-(2-deoxy-2-fluoro-β-D-arabinofuranosyl)adenine (FdaraA) 1.