4-benzyloxy-3,5-dichloro-2-methoxy-6-methyl-benzoic acid 6-(5-acetoxy-4-benzyloxy-2-methyl-6-phenylselanyl-tetrahydro-pyran-3-yloxy)-4-(5-methoxy-4,6-dimethyl-4-nitro-tetrahydro-pyran-2-yloxy)-2-methyl-tetrahydro-pyran-3-yl ester