Guanosine, [P(S)]-3′-amino-N-benzoyl-3′-deoxy-2′,5′-bis-O-[(1,1-dimethylethyl)dimethylsilyl]-P-thioadenylyl-(3′→5′)-3′-amino-2′-O-[(1,1-dimethylethyl)dimethylsilyl]-N-(2-methyl-1-oxopropyl)-