ARS | Publication request: IDENTIFICATION OF COMPOUNDS IN THREE SPECIES OF FALSE ROSEMARY (CONRADINA SP.) NATIVE TO FLORIDA AS CANDIDATE MOSQUITO REPELLENTS

Submitted to: Meeting Abstract
Publication Type: Abstract
Publication Acceptance Date: May 28, 2006
Publication Date: N/A

Technical Abstract: Introduction: Bloodsucking flies and mosquitoes are responsible for the transmission of diseases such as Leishmaniasis, malaria, and West Nile fever. One method of reducing disease risk is through the use of topical or spatial repellents. Natural compounds from plants and animals that exhibit repellency against arthropods are currently being sought as alternatives to synthetic repellents. False rosemary plants are rare and seldom studied members of the mint family (Lamiaceae). Therefore, compounds extracted from these plants could be repellent to mosquitoes or other biting insects. [84/120] Method: Five grams of plant material from three species of Conradina that are native to Florida were collected, macerated and each was placed in a separate beaker. A solvent (either 100 mL hexane or ethanol) was added to each beaker and allowed to evaporate to ~0.5 mL in a fume hood, prior to injection of 1 µL of this solution. The instrument used was a ThermoQuest Trace GC/MS, equipped with a 30 m DB-WAXetr column, and operated in EI mode. The sample in the third beaker was transferred to a 1-L Tedlar bag, sealed, purged with nitrogen and sampled by headspace concentration with an Entech 7001A and analyzed on a ThermoQuest DSQ GC/MS equipped with a Restek 60 m DB-1 column. [116/120] Preliminary Data: The composition of solvent extracts for three of the species (Conradina canescens, Conradina etonia, and Conradina grandiflora) were remarkably similar qualitatively. However, quantitative differences in compound abundances were apparent. Many terpenes including '-pinene, cymene, and caryophyllene were detected in all three hexane extracts. Alcohols such as linalool, cadinol, borneol, eucalyptol, p-cymen-8-ol, and 2-pinen-10-ol were present in high abundance in all hexane extracts of the three species. The compound p-menth-1-en-8-ol was found in high concentrations in Conradina grandiflora. Identification of this compound in the sample was interesting because of its structural similarity to p-menthane-3,8-diol, the active ingredient in a commercial repellent derived from lemon eucalyptus oil. The major peak in all samples was identified as camphor, and the ethanol extracts contained a high level of linalool oxide and caryophyllene oxide. Dimethylformamide was also a major component in the hexane extracts of all species analyzed. Microscale purge and trap provided data revealed numerous terpenes that were not observed in the hexane extracts. Additionally, a number of carbonyl compounds, e.g. 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, ethyl acetate, and 2-methyl-2-propenal, were observed in the headspace samples but not in the extracts. These data indicate the importance of using complementary sampling and instrumental techniques to provide a more comprehensive profile of the volatile organic compounds. Novel Aspect: Identification of novel volatile compounds from false rosemary (Conradina sp.) that may function as insect spatial repellents and biting deterrents. [20/20]