Unusual Alkynes Found in the Essential Oil of Artemisia Dracunculus L. var. dracunculus from the Pacific Northwest
Robert S. Pappas*
Essential Oil University, 2676 Charlestown Rd. STE#3, New Albany, IN 47150
31787 Peoria Rd., Albany, OR 97321
The volatile oil of Artemisia dracunculus L. var. dracunculus grown in Oregon was obtained by steam distillation and analyzed by GC/MS. The chemical composition of the oil was very different than the typical oil of tarragon (Artemisia dracunculus L. var. sativa), with very little (0.1%) methyl chavicol detected. The main components found were terpinolene at 25.4% and (Z)-beta-ocimene at 22.2%. Perhaps the most interesting characteristic of the oil was the presence of two unusual and rarely occurring alkynes, 5-phenyl-1,3-pentadiyne (11.7%) and 6-phenyl-2,4-hexadiyne (also known as capillene) (4.8%).
Key Word Index
Artemisia dracunculus, tarragon, essential oil composition, terpinolene, and (Z)-beta-ocimene, 5- phenyl-1,3-pentadiyne, 6-phenyl-2,4-hexadiyne, capillene.
Artemisia dracunculus L.. var. dracunculus
The plant material used was collected from Artemisia dracunculus L.. var. dracunculus growing in Malheur County, Oregon. Plant identification was carried out by Oregon State University Herbarium and voucher number 191207 was deposited.
Approximately 4 kilograms of dried leaves and flowers were distilled with an oil yield of 0.9%
None known for this particular variety. Previous work on Artemisia dracunculus L. var. sativa (tarragon) is adequately represented in the literature with three example references supplied here (1-3).
The freshly distilled oil was analyzed by GC/MS carried out on a Perkin-Elmer Autosystem XL with Turbo Mass software version 4.1.1 and a DB-5 capillary column (20 m long x 0.18 mm ID x 0.18 micron film thickness). The GC/MS was operated under the following conditions: injector and detector temperatures at 250°C; injection size of 0.3 mL (10% soln.) split ratio 1:50; He carrier gas at 1.0 mL/min; oven temperature programmed from 50 - 250°C at 2°C/min. MS were taken at 70 eV with a mass range from m/z 20 to 450. Identification of components was done by library searches using the NIST spectral database as well as by comparison of MS of authentic samples and by retention indices. The compounds identified are listed in Table I.
Table I. Chemical composition of oil from Artemisia dracunculus L. var. dracunculus.
Results and Discussion
The oil obtained from this particular variety of A. dracunculus differed drastically from the typical, high methyl chavicol type. The oil was very high in terpenes with very little methyl chavicol detected. From a chemical standpoint, the most interesting aspect was the relatively high amounts of some unusual, phenyl substituted di-alkynes, namely 5-phenyl-1,3-pentadiyne (or 1-phenyl-2,4-pentadiyne) and 6-phenyl-2,4-hexadiyne (also known as capillene). The molecular structures of these di-alkynes are shown in Figures 1 and 2. In general, alkynes (also referred to as acetylenes by some in the field) are rarely occurring in significant amounts in essential oil chemistry and seem to be a class of molecules mainly occurring in certain species of Artemisia. Of particular interest in this study was the high level of 5-phenyl-1,3-pentadiyne which has previously been reported as a significant component in Artemisia capillaris Thunb. (4,5), but at lower levels than observed here. Phenyl acetylenes such as 5-phenyl-1,3-pentadiyne and capillene are of interest because of their effective antifeeding activity to certain insect larva (5).
Figure 1. Molecular structure of 5-phenyl-1,3-pentadiyne and capillene.
Figure 2. Mass spectra of 5-phenyl-1,3-pentadiyne (MW=140, RT=27.42 min) and capillene (MW=154, RT=40.56 min)