(5-Methyl-2-oxo-1,3-dioxol-4-yl)methyl 3-[[[[9-[3-O-[3-[2-(acetyloxy)-4,6-dimethylphenyl]-3-methyl-1-oxobutyl]-2-deoxy-4-C-ethynyl-β-D-erythro-pentofuranosyl]-2-fluoro-9H-purin-6-yl]amino]carbonyl]oxy]-3-methylbutanoate