BBM-928, a new antitumor antibiotic complex. III. Structure determination of BBM-928 A, B and C

Structures of antitumor antibiotics BBM-928 A, B and C have been determined. They are cyclic decadepsipeptides containing 3-hydroxy-6-methoxyquinaldic acid as a chromophore. Two amino acids, not found in nature, L-beta-hydroxyl-N-methylvaline and trans-(3S,4S)-4-hydroxy-2,3,4,5-tetrahydropyridazine-3-carboxylic acid, were identified as structural constituents of the antibiotic. In gross structure, BBM-928 resembles the echinomycin group of antibiotics which are cyclic octadepsipeptides having a quinoxaline chromophore, but BBM-928 differs from the latter group by virtue of the lack of a sulfur-containing cross linkage.