(2E,8E,10Z,14E)-(1R,5R,13R,17R)-13-(tert-Butyl-dimethyl-silanyloxy)-5-[(R)-2-(3,4-dimethoxy-benzyloxy)-1-(4-methoxy-benzyloxy)-ethyl]-3,11-dimethyl-19-methylene-6,21-dioxa-bicyclo[15.3.1]henicosa-2,8,10,14-tetraen-7-one