SYNTHESIS OF OLIGORIBONUCLEOTIDES CONTAINING ISOGUANOSINE

Oligoribonucleotides containing isoguanosine(= 1,2-dihydro-2-oxoadenos ine; isoG; 1) were prepared. The building block 2 was synthesized usin g the (dimethylamino)methylidene residue as NH2 protecting group. The monomethoxytrityl as well as dimethoxytrityl group were introduced at OH-C(5')(-->5 and 6). Silylation of 5 with triisopropylsilyl chloride formed the 2'-O-blocked derivative 7 almost exclusively. Reaction with PCl3/1,2,4-1H-triazole furnished the phosphonate 2 which was used in solid-phase synthesis of the oligoribonucleotides 10 and 11. RNAse T-1 hydrolyzed U-A-G-U-U-isoG-U-U-A-G (10) at the 3'-site of G but not of isoG. The self-complementary oligomer (A-U-isoc-U)(3) (11) formed a d uplex which was less stable than that of(A-U)(6).