Long-chain aliphatic beta-diketones from epicuticular wax of Vanilla bean species. Synthesis of nervonoylacetone

Analysis of the neutral lipids from Vanilla fragrans and Vanilla tahitensis (Orchidaceae) without saponification resulted in the isolation and identif ication of a new product family in this plant: B-dicarbonyl compounds. The compound structures are composed of a long aliphatic chain with 2,4-dicarbo nyl carbons and a cis double bond at the n-9 position. They represent simil ar to 28% of the neutral lipids, that is, 1.5%, in immature beans, and simi lar to 10% of the neutral lipids, that is, 0.9%, in mature beans. Using ret ention indices, gas chromatography-mass spectrometry, derivatization reacti ons, and chemical degradation, five beta -dicarbonyl compounds have been id entified including 16-pentacosene-2,4-dione, 18-heptacosene-2,4-dione, 20-n onacosene-2,4- dione, 22-hentriacontene-2,4-dione, and 24-tritriacontene-2, 4-dione. Among them (Z)-18-heptacosene-2,4-dione, or nervonoylacetone, has been synthesized in two steps starting from nervonic acid. The major consti tuent, nervonoylacetone, represented 74.5% of the beta -dicarbonyl fraction . The range of these compounds has been studied in relation with bean matur ity for V. fragrans and Tr. tahitensis species. This compound family has no t been found in the leaves or stems of any of the three vanilla species stu died and is markedly absent in the beans of V. madagascariensis.