Figure 1.  (A) The molecular structure of streptonigrin based on the crystallographic study [2].  (B) The molecular structure of a metal complex of streptonigrin based on our NMR studies.  The metal is put in the quinolinequinone-picolinate site according to the results from the NMR studies.  This structure requires ~180º rotation of the bipyridine C2—C2' bond in the crystal structure of the drug.  The numbering of SN follows the nomenclature: 3-amino-2-(7'-amino- 6'methoxyquinoline-5',8'-quinone-2'-yl)-4-(3",4"-dimethoxyl-2"-hydroxylphenyl)-6-carboxyl-5-methylpyridine.