65 アミジグサ科褐藻の生産する新ジテルペン

概要

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Crenulacetals A (1), B (2), C (3), and D (4) have been isolated from the Dictyotaceae algae, Dictyota spinulosa, D. dichotoma, and an unidentified species of Dictyota. On the basis of spectral properties, their structures have been elucidated. A (1) and B (2) have one stable conformation at room temperature, while C (3) and D (4) consist of several conformations, which result in broadening of the NMR signals. When 3 and 4 are treated with hydrochloric acid in methanol, they change into the known diterpenes 5 and 6. Acetoxypachydiol (7), isolated from Pachydictyon coriaceum, exhibit ambiguous signals in the ^1H and ^<13>C-NMR spectra taken at 27℃. On the contrary, when the spectrum was recorded at -50℃, only one set of well-defined signals appear, indicating this compound takes one stable conformation at that low temperature. By analyzing the 1D-^1H-NMR spectrum and 2D-COSY, the structure including the relative configurations, have been determined to be 7. NOE experiments did not work when they were done at -50℃ using a 400 MHz NMR instrument. However, significant NOEs were observed when NOEDS experiments were performed using a 250 MHz instrument.
天然有機化合物討論会の論文
1985-09-07