(2R)-3,4,5,6,9,11,12,13,14,16-Decahydro-4α-(dimethylamino)-3β,5β,8,10,13α-pentahydroxy-6,13-dimethyl-9,16-dioxo-2α,6α-epoxy-2H-naphthaceno[1,2-b]oxocin-14α-carboxylic acid methyl ester