Benzoic acid (2S,4S,6R)-6-[(2R,3R)-3-benzyloxy-2-(4-methoxy-benzyloxy)-butyl]-2-methoxy-2-[(E)-4-(4-methoxy-benzyloxy)-1,1-dimethyl-but-2-enyl]-3-oxo-tetrahydro-pyran-4-yl ester