2′‐Deoxyisoguanosine and Base‐Modified Analogues: 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.