Trifluoro-methanesulfonic acid (2R,3R,3aR,9aR)-2-(6-benzoylamino-purin-9-yl)-5,5,7,7-tetraisopropyl-tetrahydro-1,4,6,8-tetraoxa-5,7-disila-cyclopentacycloocten-3-yl ester