[9-[(2R,4S,5R)-4-(tert-Butyl-dimethyl-silanyloxy)-5-(tert-butyl-dimethyl-silanyloxymethyl)-tetrahydro-furan-2-yl]-6-(3-nitro-[1,2,4]triazol-1-yl)-9H-purin-2-yl]-trityl-amine