35 褐藻サナダグサ中の新ジテルペンの構造

概要

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From the brown alga, Pachydictyon coriaceum, which was collected at the Izu-Shimoda beach, Japan, five new diterpenes, sanadaol (5), acetylsanadaol (6) acetyldictyolal (7), acetals (9a) and (9b), and acetyldictyol C (10), were isolated together with the known diterpenes, dictyolactone (1), dictyodial (2), dictyol E (3), and 18-hydroxy-2,7-dolabelladiene (4). The structures of the new diterpenes were elucidated by spectroscopic analyses and chemical conversions. Among the new diterpenes, 5 and 6 have the novel skeleton, which has not been found in natural products. Noteworthy is the fact that sanadaol (5) is formed in a considerable yield from dictyodial (2), when the latter was allowed to stand with silica gel in dichloromethane at room temperature. Possibly, an intramolecular ene reaction took place between the aldehyde (C-18) and the transannular olefin (C-6,7) groups. The detailed mechanism of this unusual cyclization is discussed. Acetyldictyolal (7) was converted into dictyolactone (1) by hydrolysis followed by oxidation (MnO_2/CH_2Cl_2). Also, acetyldictyol C(10) was transformed into known dictyol C (12) by hydrolysis at 65℃ (KOH/MeOH). When the acetals (9a,b) were hydrolyzed (SiO_2), dictyodial (2) was formed, besides 5. It is of interest that the present alga produces plenty of diterpenes composed of various kinds of skeletons.
天然有機化合物討論会の論文
1982-09-10