82 Structures and Chemical Properties of Quartromicins A1, A2, A3. Macrocyclic Antibiotics Containing Four Tetronic Acid Moieties
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Quartromicins A1 (1), A2 (2), and A3 (3) are the antibiotics isolated from Amycolatopsis orientalis. These compounds have been isolated by use of Diaion HP-20, SiO_2 and ODS column chromatographies as water-soluble amorphouses. The structure of quartromicin A3 (3) has been elucidated by combination of spectroscopic analyses and chemical reactions. These works have revealed its unique structural features with a symmetric dimeric structure that possesses a large ring composed of only C-C linkages and bears four tetronic acid moieties. To verify the structure, compounds 6-9 have been prepared and their spectroscopic properties compared with those of 3. Good agreement in the spectral data has been observed between them. The structures of quartromicins A1 (1) and A2 (2) have been determined by the analogous spectroscopic analyses and chemical correlations with 3. Quartromicin A3 exists as a salt. The results of the ICP analyses have shown the presence of Na^+, K^+, Ca^<2+>, the proportion of the cations varying lot to lot. The NMR properties of 3 in the presence of several metal cations have been studied. There have been found very few macrocyclic antibiotics, the carbon frameworks of which are composed of only C-C linkages thus far. Quartromicins A1-A3 are the largest members of this category.
