40 アフラトキシン生産阻害物質aflastatinに関する研究(口頭発表の部)

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A novel inhibitor of aflatoxin production of Aspergillus parasiticus was isolated from the mycelial extracts of Streptomyces sp. MRI142 and termed aflastatin A (1). The molecular formula of 1 was determined as C_<62>H_<115>NO_<24>, and its structure was elucidated by NMR and chemical degradation experiments. By analyzing a variety of 2D-NMR spectra of 1, a partial polyhydroxylated structure (A) was identified. Based on the structure of A, 1 was oxidized with NaIO_4, and three fragment molecules, 2, 3 and 4, were obtained. Since all carbon atoms contained in 1 were involved in the partial and fragment structures, its carbon chain was constructed with them. Finally, the stereochemistry of a tetrahydropyran ring was determined by J values and NOEs among the ring protons. Thus, the total structure of aflastatin A was characterized as 1, which is a unique tetramic acid derivative having a highly oxygenated long alkyl chain. To determine the absolute configuration of 4, 2,4-dimethyl-1,6-hexanediol dibenzoate (6) was prepared from 4. By comparison of its CD spectrum with those of opticaly active (2R, 4S)- and (2S, 4S)-6, which were derivatized from cycloheximide, the configurations of natural 6 were determined to (2S, 4R). On the other hand, N-methylalanine from 4 was determined to have a D configuration. The incorporation experiments using ^<13>C-labeled acetate and propionate suggested that most of the C_2 and C_3 units involved in the alkyl chain moiety of 1 were biosynthesized from acetic and propionic acid. Unexpectedly, no incorporation was observed in one of the C_2 units and two of the C_4 units in the alkyl chain. Aflastatin A inhibited aflatoxin production in A. parasiticus at the concentration of 0.5μg/mL completely, but didn't inhibit its growth at the same concentration.
天然有機化合物討論会の論文
1997-07-20

40 アフラトキシン生産阻害物質aflastatinに関する研究(口頭発表の部)

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