Seven novelpotentantitumorantibiotics, duocarmycins A (1), C1 (2), C2 (3), D (4), B1 (5), B2 (6) and SA (7), were isolated from three independently collected Streptomyces sp. The complete structures, including absolute stereochemistry, were determined by spectral and chemical studies of those duocarmycins and several derivatives. Duocarmycins A (1) and SA (7) possess a 1,2,7,7a-tetrahydrocycloprop[1