5H-1,3-Dioxolo4,5-cpyrrole-5-carboxylic acid, 4-2-bis(4-methoxyphenyl)methylamino-4-(phenylmethoxy)-5-(phenylmethoxy)methyl-5H-pyrrolo3,2-dpyrimidin-7-yl-6-(1,1-dimethylethyl)dimethylsilyloxymethyltetrahydro-2,2-dimethyl-, 1,1-dimethylethyl ester, (3aS,4S