5'-O-(Dimethoxytrityl)-N(sup 1)-(2-nitrobenzyl)-2-azainosine 7-[5-O-[bis(4-methoxyphenyl)phenylmethyl]-beta-D-ribofurano~ syl]-3,7-dihydro-3-[(2-nitrophenyl)methyl]-4H-imidazo[4,5-d]1,2,3-triazine-4-one NSC688542