Synthesis of carbon-bridged 8,5'-cyclopurine nucleosides: Nucleosides and nucleotides—XXIV1

Treatment of 2',3'-O-isopropylidene-5'-deoxy-8,5'-cycloadenosine with selenium oxide afforded the 5'-oxo-compound. Reduction of the product with sodium borohydride proceeded stereoselectively to give the 8,5'(S)-cycloadenosine. The 5'-R-isomer was obtained by the inversion of the 5'-OH group of the S-epimer via the mesyloxy derivative. Hydrolytic deamination of 8,5'-cycloadenosines gave the inosine counterparts. Photo-irradiation of 2',3'-O-isopropylidene-5'-deoxy-5'-phenylthio-N²-benzoylguanosine afforded the 8,5'-cyclo-5'-deoxyguanosine, which was also converted to the 5'-oxo-derivative. Reduction of the product also afforded to give the 8,5'-(S)-cycloguanosine. The CD spectra of these cyclonucleosides reflect the chiralities at the 5'-position.