Crystal structure of 5R,7S,9S,10-tetrahydroxy- 7,9-di-O-isopropylidene-8S-methyl-3-methoxy-dec- 2Z-enoic acid 1,5-lactone, (C4H3O2)(CH3)2(CH2OH)(CH3)(CH2)(C5H4O)OO(CH3)