1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-2-O-[(S)-[bis(1-methylethyl)amino](2-cyanoethoxy)phosphino]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-1,5-dihydro-4H-imidazo[4,5-d]pyridazin-4-one

1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-2-O-[(R)-[bis(1-methylethyl)amino](2-cyanoethoxy)phosphino]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-1,5-dihydro-4H-imidazo[4,5-d]pyridazin-4-one

1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-1,5-dihydro-4H-imidazo[4,5-d]pyridazin-4-one

1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-2-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-1,5-dihydro-4H-imidazo[4,5-d]pyridazin-4-one

1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-β-D-ribofuranosyl]-1,5-dihydro-4H-imidazo[4,5-d]pyridazin-4-one