(2R,3R,4R,5S)-2,3-(Isopropylidenedioxy)-5-<(1R)-1,2-(isopropylidenedioxy)ethyl>-4-<(Z)-2-(methoxycarbonyl)ethenyl>-4-<4-<(tert-butyldimethylsilyl)oxy>butyl>tetrahydrofuran