2′-Guanylic acid, N-benzoyl-2′-O-[[[2-[[(1,1-dimethylethoxy)carbonyl]methylamino]ethyl]methylamino]carbonyl]adenylyl-(3′→5′)-3′-O-[(1,1-dimethylethyl)dimethylsilyl]-N-(2-methyl-1-oxopropyl)-, cyclic nucleotide