1968 年 88 巻 5 号 p. 562-572
A reinvestigation of the structure of bilobanone, a sesquiterpene isolated from the heartwood extracts of Ginkgo biloba was undertaken in view of the discrepancy between its NMR spectrum and that expected for the structure (I) provisionally assigned to it. Mass spectrometry showed that bilobanone has the formula C15H20O2 rather than C15H22O2 previously assigned. Bilobanone contains an α, β'-disubstituted furan, an α, β-unsaturated α-methylketone, and an isobutyl side chain as inferred from its spectrometric data. Ozonolysis of dihydrobilobanone (VI) afforded isovaleric acid and 4-methyl-3-oxocyclohexanecarboxylic acid (XIII) and the Alder-Rickert reaction of dihydrobilobanone gave α-isobutyl-β, β'-furandicarboxylic acid (XIV) and 2-methyl-5-vinylcyclohexanone (XX), the latter of which was oxidized to XIII. The acid (XIV) and the racemic modification of XIII were prepared synthetically and were found to be identical with the respective compounds from natural sources. These results led to the revised structure (V) for bilobanone. Autoxidation of bilobanone gave an α, β-unsaturated γ-lactone (XXI) and peracid oxidation of dihydrobilobanol p-nitrobenzoate (XXIII) gave β, γ-unsaturated γ-lactone (XXIV) which was readily converted into the α, β-unsaturated γ-lactone (XXV). The spectral properties of these compounds confirmed the assignment of structure (V) to bilobanone. The absolute configuration (XXVI) of bilobanone was also established based on the ORD curve of the acid (XIII). Biogenesis of this terpene is discussed.