Ethyl-{(3S,4S,6R)-4-methoxy-6-[(3aS,4R,6R,7R,7aS)-4-methyl-6-(2-nitro-benzyloxy)-2-oxo-tetrahydro-[1,3]dioxolo[4,5-c]pyran-7-yloxy]-tetrahydro-pyran-3-yl}-carbamic acid 9H-fluoren-9-ylmethyl ester