17 マキ属植物に含まれる生理活性ノルジテルペン,ナギラクトンFの合成

概要

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Nagilactone F (1), one of the simplest member of the biologically active nor-diterpenoid dilactones of Podocarpus nagi, was first synthesized from (+)-[4S]-podocarpic acid (2). Ozonolysis of a 14-isopropyl-enone 10, derived from (+)-podocarpic acid in several steps, gave a keto-acid 12. The acid 12 was transformed into epimeric (at C-14) enolides, 22 and 23, via reductive lactonization and subsequent dehydrogenation. The two enolides gave the same diene-acid 24 on treatment with KOtBu in DMSO. Stereospecific lactonization of 24 to 14α-isopropyl-8:9-enolide 25 was achieved photochemically under irradiation in ethanol solution. On dehydrogenation with DDQ/BF_3:ether in refluxing dioxane, 25 gave a dienolide 27, which equipped with suitable functional groups and stereochemistry on the ring C necessary for nagilactone F. The dienolide ester 27 was hydrolyzed with conc. H_2SO_4 to form a dienolide acid 28, which was successfully changed to nagilactone F by Pb(OAc)_4 oxidation. Reductive degradation of nagilactone F to the synthetic intermediates, 28, 25 and 24, was also done, starting from nagilactone E, a typical natural dilactone of P. nagi.
天然有機化合物討論会の論文
1979-09-20