{3-[6-[5-[6-(1-benzyloxymethyl-propyl)-4-cyano-2,2-dimethyl-[1,3]dioxan-4-yl]-2-(tert-butyl-dimethyl-silanyloxy)-pentyl]-4-(tert-butyl-dimethyl-silanyloxy)-6-methoxy-3-vinyl-tetrahydro-pyran-2-yl]-2-hydroxy-propyl}-phosphonic acid diethyl ester