4-Nitro-benzoic acid (2R,3R,4S,6S)-6-((1S,3S)-3-acetyl-3,5,12-trihydroxy-10-methoxy-6,11-dioxo-1,2,3,4,6,11-hexahydro-naphthacen-1-yloxy)-2-methyl-4-(2,2,2-trifluoro-acetylamino)-tetrahydro-pyran-3-yl ester