Photochemical synthesis of adenosine-8-phosphonic acid derivatives

Photochemical reaction of 2',3',5'-tri-O-acetyl-8-bromoadenosine (2) with triethyl phosphite, followed by deacetylation, gave diethyl adenosine-8-phosphonate (1). Intramolecular cyclization of diethyl 8-bromo-2',3'-O-isopropylideneadenosine-5'-phosphite (6) was accomplished with photo-irradiation to yield ethyl 2',3'-O-isopropylidene-adenosine-8,5'-phosphonate (4).