1H-Imidazo[2,1-b]purine, 1-[2-O-[[[(1S,2R,3R)-3-(6-chloro-9H-purin-9-yl)-2-(hydroxymethyl)cyclobutyl]methoxy]mercaptophosphinyl]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-4-[2-(4-nitrophenyl)ethoxy]-

1H-Imidazo[2,1-b]purine, 1-[5-O-[bis(4-methoxyphenyl)phenylmethyl]-2-O-[[[(1S,2R,3R)-3-(6-chloro-9H-purin-9-yl)-2-[(triphenylmethoxy)methyl]cyclobutyl]methoxy]mercaptophosphinyl]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-4-[2-(4-nitrophenyl)ethoxy]-

1H-Imidazo[2,1-b]purine, 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]-4-[2-(4-nitrophenyl)ethoxy]-

1H-Imidazo[2,1-b]purine, 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]-4-[2-(4-nitrophenyl)ethoxy]-

1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-4-[2-(4-nitrophenyl)ethoxy]-1H-imidazo[2,1-b]purine

1-[5-O-[Bis(4-methoxyphenyl)phenylmethyl]-β-D-ribofuranosyl]-4-[2-(4-nitrophenyl)ethoxy]-1H-imidazo[2,1-b]purine

4-[2-(4-Nitrophenyl)ethoxy]-1-β-D-ribofuranosyl-1H-imidazo[2,1-b]purine

1H-Imidazo[2,1-b]purine, 1-[2-O-[[[(1S,2R,3R)-3-(6-chloro-9H-purin-9-yl)-2-(hydroxymethyl)cyclobutyl]methoxy](2-cyanoethoxy)phosphinothioyl]-3-O-[(1,1-dimethylethyl)dimethylsilyl]-β-D-ribofuranosyl]-4-[2-(4-nitrophenyl)ethoxy]-