The Essential Oil Compositions of Ambrosia acanthicarpa Hook., Artemisia ludoviciana Nutt., and Gutierrezia sarothrae (Pursh) Britton & Rusby (Asteraceae) from the Owyhee Mountains of Idaho

As part of our interest in the volatile phytoconstituents of aromatic plants of the Great Basin, we have obtained essential oils of Ambrosia acanthicarpa (three samples), Artemisia ludoviciana (12 samples), and Gutierrezia sarothrae (six samples) from the Owyhee Mountains of southwestern Idaho. Gas chromatographic analyses (GC-MS, GC-FID, and chiral GC-MS) were carried out on each essential oil sample. The essential oils of A. acanthicarpa were dominated by monoterpene hydrocarbons, including α-pinene (36.7–45.1%), myrcene (21.6–25.5%), and β-phellandrene (4.9–7.0%). Monoterpene hydrocarbons also dominated the essential oils of G. sarothrae, with β-pinene (0.5–18.4%), α-phellandrene (2.2–11.8%), limonene (1.4–25.4%), and (Z)-β-ocimene (18.8–39.4%) as major components. The essential oils of A. ludoviciana showed wide variation in composition, but the relatively abundant compounds were camphor (0.1–61.9%, average 14.1%), 1,8-cineole (0.1–50.8%, average 11.1%), (E)-nerolidol (0.0–41.0%, average 6.8%), and artemisia ketone (0.0–46.1%, average 5.1%). This is the first report on the essential oil composition of A. acanthicarpa and the first report on the enantiomeric distribution in an Ambrosia species. The essential oil compositions of A. ludoviciana and G. sarothrae showed wide variation in composition in this study and compared with previous studies, likely due to subspecies variation.


Introduction
Ambrosia acanthicarpa Hook.(bur ragweed, burweed, bur-sage) is an annual member of the Asteraceae.The leaves are deltoid to narrowly lanceolate, to 8 cm long and 6 cm wide, pinnately to tripinnately lobed, and both leaf surfaces are green and have a dense covering of short, matted hairs [1].The stems are grayish-green, with stiff, bristly hairs (Figure 1).In the United States, the plant ranges from eastern Washington and Oregon, eastern and southern California, east to western North Dakota, South Dakota, Nebraska, and Kansas, and the panhandle of Texas [1].
The plant is used in traditional herbal medicine throughout its range.In Mexico, the people use an infusion of the aerial parts of A. ludoviciana to treat diarrhea, parasitic diseases, painful conditions, and diabetes [10,11].In the Great Basin of North America, the Paiute people used a decoction of A. ludoviciana as a bath for aching feet, as a poultice for rheumatism or other aches, to treat rashes and skin eruptions, and to relieve diarrhea, while the Shoshone took the plant for coughs, colds, and influenza, and to stop diarrhea [12].Artemisia ludoviciana Nutt.(white sage, silver wormwood, Asteraceae) is a perennial herb, 30-70 cm tall, with a sagebrush odor.The leaves are alternate, entire, or lobed, 3-11 cm long, and up to 1.5 cm wide, with a dense covering of short, matted hairs.The plant flowers from August through September, producing numerous nodding flower heads (Figure 2) [4,5].The plant is highly polymorphic and there are several subordinate taxa.World Flora Online currently lists seven subspecies, including Artemisia ludoviciana subsp.albula (Wooton) D.D. Keck, Artemisia ludoviciana subsp.candicans (Rydb.)D.D. Keck, Artemisia ludoviciana subsp.incompta (Nutt.)D.D. Keck, Artemisia ludoviciana subsp.lindleyana (Besser) Lesica, Artemisia ludoviciana subsp.ludoviciana, Artemisia ludoviciana subsp.mexicana (Spreng.)D.D. Keck, and Artemisia ludoviciana subsp.redolens (A.Gray) D.D. Keck.[6].Of these, A. ludoviciana subsp.ludoviciana [7], A. ludoviciana subsp.candicans [8], and A. ludoviciana subsp.incompta [9] are known to occur in Idaho.However, these subspecies are variable morphologically, intergrade between taxa, and recognition of the discreet taxa is therefore difficult and questionable.Artemisia ludoviciana is widespread throughout western North America, ranging from Ontario and Michigan, west to British Columbia, and south through Texas, Louisiana, California, and Mexico [4,5].
As part of our ongoing efforts to obtain and characterize essential oils from the Asteraceae of the Great Basin [38], the purpose of this study is to obtain and chemically characterize the essential oils of A. acanthicarpa, A. ludoviciana, and G. sarothrae from southwestern Idaho.Although there have been previous investigations on the essential oils of A. ludoviciana and G. sarothrae, this present study is focused on the species from southwestern Idaho and also includes enantioselective gas chromatographic analyses to determine the enantiomeric distributions of chiral terpenoid constituents in these essential oils.

Ambrosia acanthicarpa
Hydrodistillation of the aerial parts of A. acanthicarpa yielded salmon-colored essential oils with a fish-like odor in yields of 4.36-5.01%.Gas chromatographic analysis led to identification of 135 components representing 97.6-98.0% of the total compositions (Table 1).Monoterpene hydrocarbons dominated the essential oils with α-pinene (36.7-45.1%),myrcene (21.6-25.5%),and β-phellandrene (4.9-7.0%) as the major components.As part of our ongoing efforts to obtain and characterize essential oils from the Asteraceae of the Great Basin [38], the purpose of this study is to obtain and chemically characterize the essential oils of A. acanthicarpa, A. ludoviciana, and G. sarothrae from southwestern Idaho.Although there have been previous investigations on the essential oils of A. ludoviciana and G. sarothrae, this present study is focused on the species from southwestern Idaho and also includes enantioselective gas chromatographic analyses to determine the enantiomeric distributions of chiral terpenoid constituents in these essential oils.
Table 5. Enantiomeric distribution (percent) of chiral terpenoid components of the essential oil of Artemisia ludoviciana.

Plant Material, Hydrodistillation
Aerial parts of several individuals of A. acanthicarpa, A. ludoviciana, and G. sarothrae were collected from the Owyhee mountains of southwestern Idaho.The plants were identified by W.N. Setzer by comparison with samples from the New York Botanical Garden [52-54] and the Brigham Young University Herbarium via the Intermountain Region Herbarium Network [55].Voucher specimens (WNS-Aa-7768, WNS-Al-7669, WNS-Al-7782, WNS-Gs-7772) have been deposited with the University of Alabama in Huntsville herbarium.The plant materials were frozen fresh (−20 • C) and stored frozen until distilled.For each plant sample, the fresh-frozen aerial parts were hydrodistilled for 4 h using a Likens-Nickerson apparatus with continuous extraction of the distillate with dichloromethane.The collection and hydrodistillation details are summarized in Table 8.

Gas Chromatographic Analyses
The essential oils of the aerial parts of Ambrosia acanthicarpa, Artemisia ludoviciana, and Gutierrezia sarothrae were analyzed by gas chromatography coupled with flame ionization detection (GC-FID, gas chromatography-mass spectrometry (GC-MS), and chiral GC-MS as previously described [56].Instrumental details are provided as supplementary material (Supplementary Table S1).Retention indices (RI) were calculated based on a homologous series of n-alkanes using the linear equation of van den Dool and Kratz [57].The essential oil components were identified by comparing their RI values (within ten RI units) and their MS fragmentation patterns (>80% similarity) with those reported in the Adams [58], FFNSC3 [59], NIST20 [60], and Satyal [61] databases.The compound percentages were based on raw peak areas without standardization.The individual enantiomers were determined from the chiral GC-MS analysis by comparison of RI values with authentic samples (Sigma-Aldrich, Milwaukee, WI, USA), which have been compiled in our in-house database.Percentages of each enantiomer were calculated from raw peak integration.

Conclusions
This is the first report on the chemical characterization of A. acanthicarpa essential oil.This species is wide-ranging in western North America, but the plants in this investigation were obtained from only one location in southwestern Idaho.Clearly, additional collections are needed to characterize the essential oil of this species more fully.In addition, this work complements previous investigations of A. ludoviciana by extending the geographical
Retention index from our in-house database.RI calc = Calculated retention index based on a homologous series of n-alkanes on a Restek B-Dex 325 capillary column.A.l. = Artemisia lucoviciana.na = Reference compound not available.no = not observed.-= compound not detected.

Table 1 .
Chemical composition (percent of total) of the essential oil from the aerial parts of Ambrosia acanthicarpa from southwestern Idaho.

Table 1 .
Chemical composition (percent of total) of the essential oil from the aerial parts of Ambrosia acanthicarpa from southwestern Idaho.

Table 2 .
Major components of Ambrosia essential oils from the literature.

Table 3 .
Enantiomeric distribution of chiral terpenoids in the essential oil from the aerial parts of Ambrosia acanthicarpa.
RI db = Retention index from our in-house database.RI calc = Calculated retention index based on a homologous series of n-alkanes on a Restek B-Dex 325 capillary column.A.a. = Ambrosia acanthicarpa.no = not observed.-= compound not detected.

Table 4 .
Chemical composition (percent of total) of the essential oil from the aerial parts of Artemisia ludoviciana from the Owyhee Mountains of Idaho.
RI calc = Retention index determined with respect to a homologous series of n-alkanes on a ZB-5ms column.RI db = Reference retention index from the databases.A.l. = Artemisia ludoviciana.tr = trace (< 0.05%).

Table 6 .
Chemical composition (percent of total) of the essential oil from the aerial parts of Gutierrezia sarothrae from southwestern Idaho.

Table 6 .
Cont.RI calc = Retention index determined with respect to a homologous series of n-alkanes on a ZB-5ms column.RI db = Reference retention index from the databases.G.s. = Gutierrezia sarothrae.tr = trace (< 0.05%).

Table 7 .
Enantiomeric distribution of chiral terpenoids in the essential oil from the aerial parts of Gutierrezia sarothrae.
RI db = Retention index from our in-house database.RI calc = Calculated retention index based on a homologous series of n-alkanes on a Restek B-Dex 325 capillary column.G.s. = Gutierrezia sarothrae.-= compound not detected.