Nucleosides. Part LV. Efficient synthesis of arabinoguanosine building blocks

From guanosine (1) as starting molecule, protected arabinoguanosine derivatives such as phosphoramidite precursors and arabinoguanosine (18) itself were prepared in high yields. Inversion of the configuration at C(2′) was achieved by introduction of the (trifluoromethyl)sulfonyl residue and subsequent displacement by nucleophiles like acetate, bromide, and azide. The guanine moiety was protected at the amide function by the 2‐(4‐nitrophenyl)ethyl (npe) group on O6 and at the NH2 function by the 2‐(4‐nitrophenyl)ethoxycarbonyl (npeoc) group.