71 多重標識化合物の生合成研究への応用

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The dectction of <18>^O through its isotope shift in the ^<13>C-NMR spectra of microbial metabolites labelled with [1-^<13>C,^<18>O_2] acetate offers a new method to establish the integrity of C-O bonds during the course of biosynthesis. [2-^<13>C,2-^2H_3] and [1-^<13>C,^<18>O_2]Acetate were incorporated into citrinin(1), averufin(6), sterigmatocystin(9), and penicillic acid(12). The presence of ^2H on C-4 and C-9 in citrinin(1), on C-4, C-5, C-7, C-2', C-4' and C-6' in averufin(6), and on C-4, C-6, C-11, C-15, C-17 in sterigmatocystin(9) was confirmed by their ^<13>C-NMR spectra. On the other hand, shifted signals induced by the presence of ^<13>O were detected at C-3, C-6 and C-8 in citrinin(1), at C-1, C-3, C-8, and C-10 in sterigmatocystin(9), and at C-3 in penicllic acid(12). The loss of ^<18>O at C-1 in citrinin(1) and the integrity of C-O bond between C-3 and O-2 indicate that the quinone-methide structure of citrinin(1) is formed by the elimination of hemi-acetal hydroxyl at C-1 in a biosynthetic intermediate(3). The absence of ^<18>O at C-14 in sterigmatocystin(9) demonstrated that ^<18>O atom originally present at C-1' of averufin(6) was lost during the course of transformation of the side chain. Incorporation of [1-^<13>C,^<17>O] acetate was investigated in citrinin(1), sterigmatocystin(9) and islandin in(15). ^<17>O- Signals were directly observed in the ^<17>O-NMR spectrum of citrinin(1), however chemical shift values for C-6 and C-8 oxygen atoms were unusual. This suggested keto-enol tautomerism of citrinin(1), which caused large shifts of ^<17>O signals. The results of X-ray analysis support this view and the bond lengths of carbonyl(C-6) and hydroxy(C-8) are both unusual. This is the first case that ^<17>O-NMR was successfully applied in biosynthetic study. Incorporation of ^<17>O from [1-^<13>O,^<17>O] acetate was also confirmed in sterigmatocystin(9) and islandicin(15), while no incorporation was observed in rugulosin(14). Negative result in rugulosin(14) arose a question, why oxygen atoms were lost in the course of biosynthesis, in contrast to positive incorporation of H from acetate. Since ^<17>O chemical shift value is strongly affected by chemical nature of oxygen atom, new application of ^<17>O- NMR would be possible in various fields, not limited to biosynthetic study.
天然有機化合物討論会の論文
1981-09-10

71 多重標識化合物の生合成研究への応用

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