Examination of the role of the duocarmycin SA methoxy substituents: Identification of the minimum, fully potent DNA binding subunit

The preparation and examination of 4–7 revealed that (+)-5 and (+)-duocarmycin SA were indistinguishable. In contrast, 6 and 7 exhibited properties more analogous to 4 illustrating that the C6 and C7 methoxy substituents of duocarmycin SA contribute little or nothing to its properties. Thus, the C5 methoxy substituent of the 5,6,7-trimethoxyindole subunit of duocarmycin SA is necessary and sufficient for observation of the full potency of the natural product.