26 The Structures of Trioxacarcin A, a New Antitumor Antibiotic, and Its Related Compounds
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In the course of our screening for new anticancer antibiotics three compounds, trioxacarcins A, B, and C, were isolated from the culture broth of a new Streptomyces species, Streptomyces ochraceus, which was obtained from a soil sample collected in Sapporo. Trioxacarcins showed anticancer activity against mouse Sarcoma 180 and Leukemia P-388 and also showed antibacterial activity against both Gram-positive and Gram-negative bacteria. Methanolysis of trioxacarcin A(TOC-A)(1) gave a mixture of methylα-trioxacar-cinoside A(Fig. 2), its β anomer, methyl α-trioxacarcinoside B(Fig. 3), its β anomer, and trioxacarcinone A(3) together with compound (2). Deacetyl trioxacar-cinoside A was identified with axenoside, and trioxacarcinoside B was identified with the sugar component of quinocycline B. On the other hand oxidation of tetramethyl derivative(5) of the aglycone(3) gave a crystalline compound(6). X-ray analysis of 6 could revealed its novel structure as depicted in Fig. 5. Finally, the structure of TOC-A was determined on the basis of the findings obtained from detailed PMR and CMR experiments on compounds 1, 2, 3, 4, and 5. The structures of TOC-B and C were also elucidated as shown in Fig. 4.
