Essential Oils and Compounds Isolated from the Leaves and Rhizomes of Aframomum Atewae

Abstract

Aframomum species have been reported to be at an alarming rate of decline due to climate change and anthropogenic activities. This work investigated for the first time the chemical composition of Aframomum atewae, a less common species of the genus. Essential oils of the leaves and rhizomes were obtained either through hydrodistillation or solvent extraction followed by chromatographic separation. GC-MS analysis of the constituents revealed that the fresh leaf essential oil was rich in monoterpenes (22.4%) while sesquiterpenes dominated the fresh rhizome essential oil (24.4%). Steroids and long chain hydrocarbons were the major constituents of the dichloromethane-extracted rhizome essential oil. The results for the petroleum ether-extracted rhizome essential oil are pending (due to sample mix up when submitted for GC-MS analysis). The major constituents identified in the three essential oils were 1-methyl-1-(methylamino)isobenzofuran-3-one (17.27%), 2,5-ditertbutylhydroxybenzene (7.80%) and 14-pregnane (56.95 %) for the leaf, rhizome and DCM-extracted essential oils, respectively. To the best of my knowledge, this is the first time these compounds have been identified in the genus. The antifungal potential of the 4 essential oils was evaluated against Candida albicans and Saccharomyces cerevisiae in an Alamar Blue-based broth dilution assay. The fresh rhizome and the DCM-extracted rhizome essential oils exhibited fungicidal activity against C. albicans while fungistatic activity was observed for the fresh leaf and the PE-extracted rhizome essential oils. With the exception of the PE-extracted oil which was fungistatic against S. cerevisiae, the remaining essential oils did not exhibit any activity against S. cerevisiae. Crude PE, DCM and MeOH extracts of the air-dried pulverized rhizome were prepared by cold percolation. The PE and DCM crude extracts tested positive for terpenoids and steroids while the MeOH contained alkaloids, flavonoids, cardiac glycosides, saponins, and tannins. Through column chromatographic separations of the three extracts, 10 compounds were isolated, out of which 4 compounds were identified to be 1(E)-8-methylundec-8-en-1-yl-3-(cyclohexa-2,5-dien-1-yl)propanoate, 2-(6-oxotetrahydro-2H-pyran-2-yl)ethyl dodec-8-enoate, myristic acid and stigmasterol. Characterization of the compounds was achieved through IR, 1D- and 2D NMR, LC-MS and HR-MS techniques