5H-Pyrrolo3,2-dpyrimidine, 5-(1,1-dimethylethyl)dimethylsilyl-7-(3aS,4S,6R,6aR)-6-(1,1-dimethylethyl)dimethylsilyloxymethyltetrahydro-2,2-dimethyl-4H-1,3-dioxolo4,5-cpyrrol-4-yl-2-fluoro-4-(phenylmethoxy)-