Calicheamicins, a novel family of antitumor antibiotics. 3. Isolation, purification and characterization of calicheamicins beta 1Br, gamma 1Br, alpha 2I, alpha 3I, beta 1I, gamma 1I and delta 1I

Novel antitumor antibiotics, calicheamicins beta 1Br, gamma 1Br, alpha 2I, alpha 3I, beta 1I, gamma 1I and delta 1I were recovered from the fermentation broth of Micromonospora echinospora ssp. calichensis by solvent extraction, selective precipitation, normal phase, reversed phase and partition chromatography. The individual components were characterized by their UV, IR, 1H and 13C NMR spectral data.