Chemical Composition and Biological Activity of Haplophyllum tuberculatum Juss. Essential Oil
The essential oil of Haplophyllum tuberculatum Juss. (Rutaceae), collected from Saudi Arabia, was obtained by hydrodistillation. The oil was subsequently analyzed by GC and GC-MS and 37 compounds that were identified which accounted for 96.4% of the composition. The major components were trans-p-menth-2-en-1-ol (19.2%), cis-p-menth-2-en-1-ol (13.2%), myrcene (10.1%), δ-3-carene (8.8%), β-phellandrene (6.9%), limonene (6.6%) and cis-piperitol (6.4%). Antimicrobial activity of the essential oil was determined using the broth microdilution method against various human pathogens, where a relatively low inhibitory range was observed (MIC 1 mg/mL). Furthermore, the oil was evaluated for its antifungal activity against the strawberry anthracnose-causing fungal plant pathogens Colletotrichum acutatum, C. fragariae and C. gloeosporioides using the direct overlay bioautography assay . The essential oil showed no antifungal activity at 80 and 160 µg/spot concentrations compared to commercial antifungal standards. The oil was also investigated for its insecticidal and repellent activity against Aedes aegypti. The oil was repellent to the yellow fever mosquito Ae. aegypti using the “cloth patch assay” down to a concentration of 0.074 mg/cm2; however, the oil had low toxicity against first instar larvae and adults of Ae. aegypti in a high throughput larval bioassay and adult topical assay. Additionally, enzyme activity was measured using the spectrophotometric Ellman method . The oil showed weakly acetylcholinesterase (AChE) inhibitory activity at the tested concentration, compared to standard substances, whereas no inhibition on butyrylcholinesterase (BuChE) activity was observed. Acknowledgements: The authors thank Ms. J. Linda Robertson and Ms. Ramona Pace, Mr. Nathan Newton, Mr. Greg Allen, Ms. Natasha Elejalde and Ms. Katelyn Chalaire for their assistance with the antifungal and mosquito bioassays. This study was supported by a grant from the Deployed War-Fighter Protection (DWFP) Research Program and the U.S. Department of Defense through the Armed Forces Pest Management Board (AFPMB). This work was also partially supported by Global Research Netwrok for Medicinal Plants (GRNMP) and King Saud University. References:  Tabanca N, Wedge, DE, et al. (2008) Nat Prod Commun, 3: 1073 – 1078.  Ellman GI, Courtney KD, et al. (1961) Biochem Pharmacol, 7: 88 – 95.