2,2-Dimethyl-propionic acid (E)-(2R,3S,6R)-7-(tert-butyl-diphenyl-silanyloxy)-2-[(1S,2R)-3-(tert-butyl-diphenyl-silanyloxy)-1-(3,4-dimethoxy-benzyloxy)-2-methyl-propyl]-3-hydroxy-4,6-dimethyl-hept-4-enyl ester