2'-DEOXYISOGUANOSINE AND BASE-MODIFIED ANALOGS - CHEMICAL AND PHOTOCHEMICAL-SYNTHESIS

The synthesis of 2'-deoxyisoguanosine (2), and the pyrrolo[2,3-d]pyrimidine and pyrazolo[3,4-d]pyrimidine 2'-deoxyribonucleosides 3 and 4 is described. Condensation of the imidazole precursor 5 with benzoyl isocyanate followed by reaction with ammonia gave 2. Its N(7) regioisomer was obtained from 6. Compound 2 was also prepared by the photochemically induced conversion of 2-chloro- and 2-bromopurine 2'-deoxyribofuranosides 9a and 10, respectively, in aqueous solution. The photo reaction was further used for the synthesis of the compounds 3 and 4 starting with the amino-chloro-2'-deoxynucleosides 9b and 9c, respectively.