(2E,4E)-7-[(2R,3R)-3-(1-{(2R,3R)-3-[(E)-(6R,7S)-7-Hydroxy-8-(4-methoxy-benzyloxy)-6-methyl-4-methylene-oct-1-enyl]-1,4-dioxa-spiro[4.4]non-2-yl}-vinyl)-1,4-dioxa-spiro[4.4]non-2-yl]-3-methyl-octa-2,4,7-trienoic acid