Phytochemical Analysis of the Essential Oils From Aerial Parts of Four Scutellaria “Skullcap” Species Cultivated in South Alabama: Scutellaria baicalensis Georgi,S. Barbata D. Don,S. Incana Biehler,and S. Lateriflora L

Abstract

Scutellaria (skullcap) are important medicinal plants. Scutellaria baicalensis and S.barbata have been used in Chinese traditional medicine, while S. incana and S. lateriflora were used as herbal medicines by Native Americans. In this work, the essential oils of Scutellaria baicalensis Georgi, Scutellaria barbata D. Don, Scutellaria incana Biehler, and Scutellaria lateriflora L. were obtained from plants cultivated in south Alabama and analyzed by gas chromatographic techniques, including chiral gas chromatography. The most abundant components in the Scutellaria essential oils were 1-octen-3-ol (31.2% in S. incana), linalool (6.8% in S. incana), thymol (7.7% in S. barbata), carvacrol (9.3% in S. baicalensis), (E)-β caryophyllene (11.6% in S. baicalensis), germacrene D (39.3% in S. baicalensis), (E)-nerolidol (10.5% in S. incana), palmitic acid (15.6% in S. barbata), phytol (19.7% in S. incana), and linolenic acid (8.0% in S. barbata). These analyses of the essential oil compositions and enantiomeric ratios of predominant aromatic molecules add to our understanding of the medicinal phytochemistry of the genus Scutellaria.

Keywords

essential oil ethnobotany volatile phytochemistry enantiomeric distribution skullcap Alabama Lamiaceae gas chromatography

Scutellaria baicalensis Georgi, Scutellaria barbata D. Don, Scutellaria incana Biehler, and Scutellaria lateriflora L. were cultivated in southern Alabama where two of the species, S. incana and S. lateriflora, are natives. These herbs, commonly and collectively referred to as ‘skullcap’, belong to the mint family (Lamiaceae) and are found across the globe in temperate regions on almost every continent.

This is part of a larger ongoing study of essential oils from the medicinal plants traditionally used by Native American tribes of the United States, in particular the Cherokee of the southeastern United States.^{1

-14} The Cherokee have a rich tradition of using plants as medicines including many of the aromatic species native to the southeastern U.S. that are rich in essential oils and aromatic compounds. Many ethnobotanical accounts have been given in the anthropologies of the Cherokee, and these works were studied to determine which plants to examine in further detail.^15

-22 Two of the species of Scutellaria studied here were used by the Cherokee (S. incana and S. lateriflora) for at least hundreds of years, while the other 2 have been used in traditional Asian phytotherapies for several millennia (S. baicalensis and S. barbata) .²³ All four were easily cultivated in the climate of south Alabama, United States, and are growing as perennials as they are being observed sprouting new growth during the spring of their second year.

The genus Scutellaria encompasses over 470 species with more than 70 of them being used traditionally as plant medicines.^24,25 Scutellaria incana, or ‘downy skullcap,’ is a perennial herb preferring medium-wet to dry conditions and full sun to partial shade. It is native to the central and eastern United States, found from Michigan and New York in the north, to the southern tip of Florida in the south, and can be found in bloom between July and September.^26,27 Scutellaria lateriflora, ‘blue skullcap, mad-dog skullcap, or American skullcap’, is also native to the United States and is the most common species of Scutellaria found in North America. It can be found in zones 2‐7 blooming in July through September across most of the North American continent, from Florida to Canada and California to New York, preferring wetlands and full sun.^28,29 The other 2 species, S. barbata and S. baicalensis, are also perennial herbs, both native to China, with S. barbata, ‘barbed skullcap,’ being prominent throughout southeast Asia as well as north into the mountains of Nepal. Wetlands and the edges of streams and rice fields are common places to find S. barbata and it usually flowers from April to June.^30,31 Commonly called ‘baikal’ and found across eastern Europe and Russia and across Mongolia and China and in Korea and Japan, S. baicalensis is the fourth herb studied here. It can be found blooming usually between July and August along roadsides and in disturbed and cultivated areas as a weed, as well as covering grassy hillsides in the wild.³²

Many tribes of Native Americans were known to use Scutellaria as a medicinal plant. The Cherokee used Scutellaria incana roots as an abortifacient and for diarrhea treatment. They also used a decoction of the plant to soothe the nerves. They made a compound from the plant which was used topically to aid in the expelling of afterbirth as well as a kidney medicine and for breast pains. This could refer either to mastitis or breast tumors as these Scutellaria species have been studied for their ability to act as anti-inflammatory agents and have potent cytotoxic anti-tumor effects.³³ The roots of S. lateriflora were used in an infusion to calm diarrhea and to encourage menstruation. A decoction of the roots was taken as an emetic and to expel afterbirth. It was also made into a compound to be applied to help expel afterbirth. According to Mooney, in his 1885 research, the Scutellaria species were used to bring about menstruation and to counteract the perceived negative effects of eating food cooked by a woman who was menstruating.¹⁷ The Iroquois Native Americans of New York and Ontario used an infusion of dried, ground roots of S. lateriflora to prevent smallpox and for throat problems.²² The Miwok of modern-day central California used multiple species of Scutellaria in a decoction for cold and cough remedy and as an eye wash..³⁴

In traditional Chinese medicine (TCM) S. baicalensis is known as ‘huang qin’ and is used to treat inflammations and fevers.³² Russian research into phytomedicinals has shown that S. baicalensis has antibacterial, anthelmintic, anti-schlerotic, astringent, digestive stimulant, hemostatic, and anti-allergen properties.³⁵ The common name in TCM for S. barbata is ‘ban zhi lian’ and it is traditionally used as both an internal and external anti-inflammatory. Both S. barbata and S. baicalensis have also been used as anxiolytics and sedatives.^30
-32,36

Flavonoids, diterpenes, alkaloids, glycosides, and volatile essential oil components have all been studied from Scutellaria species, with over 295 compounds having been characterized by 2010.³⁷ The presence of neo-clerodane diterpenoid alkaloids with cytotoxic activity in Scutellaria barbata has been confirmed experimentally,^38,39 numerous other neo-clerodane diterpenoids as well as flavonoids,²³ and aromatic terpenoids and hydrocarbons have been analytically revealed. This study examines the volatile composition and enantiomeric distribution of components of the essential oils of these 4 scutellaria species and compares these findings with previous literature reports of their essential oil compositions from other geographic locations as well as discusses the relevance of the terpenoids that were found in relation to their ethnobotanical uses.

Results and Discussion

In this study, the essential oils of 4 species of Scutellaria most commonly used in traditional medicine were obtained through hydrodistillation and analyzed by gas chromatographic techniques. The following table (Table 1) reports the yields of essential oils obtained from the dried plant matter of the 4 scutellaria species.

Table 1

Essential Oil Yields After Hydro-Distillation.

Scientific (common) name	Dry plant mass	Essential oil mass(color)	Percent yield
S. baicalensis (Baikal skullcap)	4.74 g.	42.9 mg (pale yellow)	0.9
S. barbata (barbed skullcap) #1^a	4.12 g	142.6 mg (colorless)	3.5
S. barbata (barbed skullcap) #2^b	2.74 g	145.3 mg (colorless)	5.3
S. incana (hoary skullcap)	8.14 g	155.6 mg (colorless)	1.9
S. lateriflora (blue skullcap)	16.35 g	104.7 mg (pale yellow)	0.6

^a Scutellaria barbata #1 sample was harvested on June 7, 2020

^b Scutellaria barbata #2 sample was harvested on July 7, 2020.

Table 2, below, compares the essential oil components from the Scutellaria spp. as identified by gas chromatographic analysis.

Table 2

Essential Oil Chemical Composition of Scutellaria Species Cultivated in South Alabama. Retention Indices, RI (Cal), Were Calculated Using a Homologous Series of N-Alkanes on a ZB-5ms Column. RI (Db) Refers to Reference Database Indices.

RI (cal)	RI (db)	Compound	S. baicalensis	S. barbata #1^a	S. barbata #2^b	S. incana	S. lateriflora
852	853	(3Z)-Hexen-1-ol	-	3.4	2.2	3.7	0.6
867	867	1-Hexanol	-	0.4	0.4	0.5	-
961	959	Benzaldehyde	-	-	-	0.5	2.0
974	973	1-Octen-3-one	-	-	0.5	-	-
977	978	1-Octen-3-ol	6.1	25.6	20.1	31.2	27.5
995	996	3-Octanol	0.6	0.9	0.5	0.5	0.2
1034	1033	Benzyl alcohol	-	-	-	1.7	-
1044	1044	Salicylaldehyde	-	-	-	-	0.6
1064	1064	Acetophenone	-	-	-	1.6	3.6
1098	1099	Linalool	1.2	3.3	2.5	6.8	1.1
1104	1104	Nonanal	-	-	-	1.7	0.3
1112	1111	Phenyl ethyl alcohol	-	-	-	1.0	-
1190	1190	Methyl salicylate	-	-	0.4	0.2	-
1195	1195	α-Terpineol	0.2	0.3	0.5	0.7	0.1
1197	1197	Methyl chavicol (=Estragole)	-	2.1	-	0.5	-
1215	1217	Coumaran	0.3	1.7	2.3	2.2	0.2
1236	1238	Carvacrol methyl ether	0.8	0.5	1.1	-	-
1238	1238	Neral	-	-	-	0.3	-
1238	1237	Pulegone	-	-	-	-	1.1
1268	1266	Geranial	-	-	-	0.6
1285	1290	o-Acetylanisole	-	-	-	-	1.8
1288	1289	Thymol	7.5	2.2	7.7	0.3	2.6
1293	1294	Dihydroedulan IIA	-	-	0.5	1.4	-
1295	1296	Carvacrol	9.3	2.3	8.9	-	0.7
1308	1309	4-Vinylguaicol	-	-	-	2.1	0.8
1328	1336	δ-Elemene	0.4	-	-	-	-
1350	1356	Eugenol	-	-	-	0.8	0.1
1352	1352	α-Longipinene	-	-	-	-	1.4
1356	1356	(E)-Benzalacetone	-	-	-	-	4.7
1361	1365	Carvacryl acetate	0.2	-	0.4	-	-
1372	1375	α-Copaene	0.2	-	0.2	-	-
1376	1367	Cyclosativene	-	-	-	-	0.2
1377	1379	(E)-β-Damascenone	-	-	-	0.4	-
1378	1380	2-epi-α-Funebrene	0.1	-	-	-	-
1381	1382	β-Bourbonene	3.1	1.6	2.0	-	1.0
1386	1387	7-epi-Sesquithujene	-	-	-	-	0.4
1389	1390	trans-β-Elemene	0.2	-	-	0.2	0.6
1399	1415	Sesquithujene	0.3	-	-	-	-
1402	1405	(Z)-β-Caryophyllene	-	-	-	-	0.5
1412	1412	Longifolene	-	-	-	-	1.0
1418	1417	( E)-β-Caryophyllene	11.6	3.6	2.7	0.6	8.8
1418	1415	α-Barbatene	-	-	-	-	0.2
1426	1430	β-Copaene	0.7	0.4	0.5	-	-
1432	1432	trans-α-Bergamotene	-	-	0.4	-	4.1
1439	1439	(Z)-β-Farnesene	-	-	-	-	0.5
1440	1447	iso-Germacrene D	0.3	-	-	-	-
1450	1452	(E)-β-Farnesene	0.5	-	-	-	0.3
1453	1453	α-Humulene	1.3	0.3	0.6	-	3.2
1452	1447	β-Barbatene	-	-	-	-	0.8
1455	1458	allo-Aromadendrene	0.4	-	-	-	-
1464	1464	9-epi-(E)-Caryophyllene	0.2	-	-	-	-
1471	1475	γ-Muurolene	0.2	-	-	-	-
1478	1480	Germacrene D	39.3	11.0	5.4	-	1.5
1477	1481	(E)-β-Ionone	-	-	-	0.3	0.1
1480	1482	γ-Himachalene	-	1.1	1.4	-	0.8
1480	1483	trans-β-Bergamotene	0.3	-	-	-	-
1491	1497	Bicyclogermacrene	4.8	1.4	0.6	-	-
1494	1497	α-Muurolene	0.3	-	-	-	-
1500	1500	Pentadecane	-	-	-	0.2	-
1501	1503	β-Himachalene	-	-	-	-	0.2
1502	1503	(E,E)-α-Farnesene	0.3	-	-	0.5	-
1506	1509	β-Curcumene	0.7	-	-	-	-
1509	1512	γ-Cadinene	0.3	-	-	-	-
1509	1513	Cuparene	-	-	-	-	0.9
1514	1518	δ-Cadinene	0.8	0.6	1.2	-	-
1522	1523	β-Sesquiphellandrene	-	-	-	-	0.2
1523	1524	Dihydroactinidiolide	-	0.4	0.4	0.6	0.1
1525	1528	(E)-γ-Bisabolene	-	-	-	-	0.1
1535	1535	γ-Cuprenene	-	-	-	-	0.1
1542	1544	cis-Sesquisabinene hydrate	-	-	-	-	0.2
1559	1560	( E)-Nerolidol	-	0.4	-	10.5	-
1572	1574	Germacrene D-4-ol	4.3	1.3	1.0	-	-
1577	1577	Caryophyllene oxide	0.5	-	0.4	-	2.4
1589	1594	Viridiflorol	-	0.7	0.6	-	-
1600	1600	Hexadecane	-	0.3	0.5	0.2	0.1
1612	1613	Humulene epoxide II	-	-	-	-	0.4
1634	1639	cis-Guaia-3,9-dien-11-ol	0.2	-	-	-	-
1638	1643	τ-Cadinol	0.2	-	-	-	-
1639	1644	τ-Murrolol	0.3	-	-	-	-
1651	1655	α-Cadinol	0.8	0.6	0.5	-	-
1657	1652	β-Himachalol	-	-	-	-	0.4
1668	1668	Patchouli alcohol	-	0.8	-	1.4	-
1670	1674	(Z)-α-Santalol	-	0.5	-	-	-
1679	1683	Germacra-4(15),5,10(14)-trien-1α-ol	0.2	-	-	-	-
1700	1700	Heptadecane	-	-	-	0.3	0.1
1800	1800	Octadecane	-	-	-	0.2	-
1827	1832	(2Z,6E)-Farnesyl acetate	-	-	-	-	0.3
1832	1836	Neophytadiene	-	-	-	-	0.2
1840	1841	Phytone	-	-	0.6	0.4	0.4
1866	1869	Benzyl salicylate	-	-	-	0.4	-
1900	1900	Nonadecane	-	-	0.4	0.2	0.1
1959	1958	Palmitic acid	-	15.6	13.0	0.5	-
2107	2102	Phytol	1.0	1.8	2.3	19.7	14.8
2123	2128	Linoleic acid	-	2.3	0.7	-	-
2129	2134	Linolenic acid	-	8.0	1.5	-	-
2134	2138	Palmitaldehyde diallyl acetal	-	-	-	-	0.2
2300	2300	Tricosane	-	0.3	0.9	1.2	0.2
2400	2400	Tetracosane	-	-	0.4	-	-
1500	2500	Pentacosane	-	1.0	3.5	1.8	1.0
2600	2600	Hexacosane	-	0.7	0.8	-	-
2700	2700	Heptacosane	-	1.6	5.4	0.8	1.2
2793	2800	Octacosane	-	-	0.9	-	-
2900	2900	Nonacosane	-	-	-	-	0.7
3100	3100	Untriacontane	-	-	-	-	0.2
		Total	100.0	99.1	96.9	98.8	98.1

^a Scutellaria barbata #1 sample was harvested on June 7, 2020.

^b Scutellaria barbata #2 sample was harvested on July 7, 2020.

Table 3 lists the enantiomeric distribution percentages for eight of the most prevalent terpenoids found in these Scutellaria species. For all the species (–)-linalool was the predominant enantiomer, (+)-(E)-β-caryophyllene was the only enantiomer found in all samples, α-terpineol was found in about a 50/50% split with (–)-α-terpineol being favored by a less than one percent margin. Germacrene D was found only in its (+)-enantiomeric form and it was absent from S. incana altogether, δ-cadinene was only found as its (–)-enantiomer and it was not found in S. incana or S. lateriflora.

Table 3

Chirality Data for the Enantiomeric Distribution of Eight of the Most Prevalent Terpenoids in These 4 Scutellaria Species Here Examined.

Scutellaria species	Linalool		α-Terpineol		trans-β-Elemene		(E)-β-Caryophyllene
Scutellaria species	% (+)	% (–)	% (+)	% (–)	% (+)	% (–)	% (+)	% (–)
S. baicalensis	29.5	70.5	49.7	50.3	-	-	100	0
S. barbata #1^a	16.7	83.3	49.3	50.7	-	-	100	0
S. barbata #2	16.4	83.6	49.9	50.1	-	-	100	0
S. incana	37.3	62.7	49.1	50.9	-	-	100	0
S. lateriflora	18.9	81.1	50.0	50.0	60.3	39.7	100	0

	(E)-β-Ionone		(E)-Nerolidol		Germacrene D		δ-Cadinene
	% (+)	% (–)	% (+)	% (–)	% (+)	% (–)	% (+)	% (–)
S. baicalensis	-	-	-	-	100	0	0	100
S. barbata #1	-	-	-	-	100	0	0	100
S. barbata #2	-	-	-	-	100	0	0	100
S. incana	100	0	4.3	95.7	-	-	-	-
S. lateriflora	-	-	-	-	100	0	-	-

^a Scutellaria barbata #1 sample was harvested on June 7, 2020.

^b Scutellaria barbata #2 sample was harvested on July 7, 2020.

The volatile phytochemical makeup of the essential oils of these 4 scutellaria species were collectively dominated by 1-octen-3-ol, thymol, carvacrol, (E)-β-caryophyllene, germacrene D, (E)-nerolidol, palmitic acid, phytol, linalool, β-bourbonene, and linolenic acid. Studies of the essential oil from S. barbata from the Hunan region of China showed a predominance of 1-octen-3-ol, hexadecanoic acid (palmitic acid), and (E)-β-caryophyllene,⁴⁰ however most of the other key aromatic molecules such germacrene D, carvacrol, thymol, phytol, and linalool found in our research were not reported in their analysis. A previous study from the University of Wuhan, China showed the essential oil of S. barbata to exhibit more similar molecular makeup to our samples, with hexahydrofarnesylacetone, 3,7,11,15-tetramethyl-2-hexadecen-1-ol, menthol, and 1-octen-3-ol being the dominant by percentage, but also in significant quantities (>1%) were linalool, β-bourbonene, β-himachalene, and thymol.⁴¹

In their 2010 review of several Scutellaria essential oil studies, Shang et al,³⁷ noted high concentrations of (E)-β-caryophyllene and linalool. Samples of essential oils from wild-harvested Scutellaria species from Uzbekistan also contained linalool, (E)-β-caryophyllene, thymol, and germacrene D,⁴² similar to our findings of these volatile components in the essential oils of Alabama-grown Scutellaria.

The aromatic terpenoids of herbs and flowers have a long history of aromatherapeutic and internal uses as teas and decoctions to treat an extremely wide range of disease states. Terpenes have been shown to be effective antibacterial, antifungal, anti-viral, anti-inflammatory, neuro-protectives, anti-tumor and anti-proliferative as well as uses for dental and dermatological treatments and other uses⁴³ including bacteriostatic surface cleaners⁴⁴ and pesticides,⁴⁵ in the case of thymol. Interestingly, 1-octen-3-ol, the most prevalent aromatic compound in all except one out of these four essential oils (S. baicalensis) is known for being a chemical feeding attractant for certain varieties of mosquito while acting as a repellant to other strains of mosquito.⁴⁶ It is also known as the “mushroom acid,” and is the most prevalent aromatic compound in most mushrooms (including truffles), molds, and fungi and is the primary olfactory irritant in rotting wood. Over-exposure to this aromatic compound has been shown to cause conjunctivitis, rhinitis, and respiratory inflammation.⁴⁷ This compound is also found throughout nature, in raspberries, elder flowers, in the molded rind of Camembert cheese, in certain unwanted wine-molds, and is expressed as a pheromone by certain millipedes during distress.⁴⁸ The two enantiomers of this compound are known to have different aromas and may exhibit differing effects when it comes to inflammatory response. Furthermore, 1-octen-3-ol has shown antibacterial and antifungal activities.⁴⁹

In this case it is significant to note the finding of a significant percentage of phytol in both S. lateriflora and S. incana, the American herbs, but not the Asian species. Phytol has shown promise for controlling the neglected tropical disease schistosomiasis^50,51 as well as showing antibacterial properties against Staphylococcus aureus ⁵² and Mycobacterium tuberculosis.⁵³ Phytol has also been shown to be an anti-allergen and when applied topically in murine studies.⁵⁴ Antioxidant and antinociceptive properties of phytol have also been observed.⁵⁵

A high percentage (>5%) of (E)-nerolidol and linalool was unique to S. incana. Studies of Greek varieties of Scutellaria also showed linalool and nerolidol to be the main constituents of the essential oil and testing showed moderate antimicrobial activity.⁵⁶ (E)-Nerolidol has shown low toxicology with unspecified increased respiratory function as well as cytotoxic effects again hepatic carcinomas.⁵⁷ Plant essential oils with high percentages of nerolidol have been found to kill Schistosoma ⁵⁸ and have antileishmanial activity.⁵⁹ (E)-Nerolidol has shown promise as an antifungal in guinea pig testing by healing fungal skin lesions,⁶⁰ and as an antiulcer agent as well.⁶¹ Linalool has been experimentally shown to be antimicrobial, cytotoxic, antioxidant, anti-inflammatory, and have insect repellant properties while showing almost no toxicity or allergic response and near zero skin irritant traits.⁶²

Linalool also has been shown in-vivo to have significant sedative⁶³ and anti-convulsant effects⁶⁴ and is one of the main aromatic compounds in lavender essential oils.⁶⁵ Linalool has been found to be a potent acetylcholinesterase inhibitor and has potential as an Alzheimer’s therapeutic essential oil.⁶⁶

The native Asian species showed relatively high percentages of carvacrol and thymol where the native American species did not. The largest percentage of any single compound in the essential oils examined herein was the presence of germacrene D at 39% in S. baicalensis. Scutellaria baicalensis essential oil from the aerial parts in this study was rich in (+)-germacrene D (39.3%), (+)-(E)-β-caryophyllene (11.6%), carvacrol (9.3%), thymol (7.5%), and 1-octen-3-ol (6.1%). A headspace volatile analysis of S. baicalensis flowers showed the floral volatiles to be dominated by sesquiterpene hydrocarbons, particularly (E)-β-caryophyllene (22.3 to 41.5%) and germacrene D (12.4 to 27.5%), but carvacrol, thymol, or 1-octen-3-ol were not reported.⁶⁷ The root essential oil of S. baicalensis was reported, but the constituents were not quantified.⁶⁸ Based on the gas chromatogram, the root oil had acetophenone, (E)−4-phenyl-2-butanone, palmitic acid, and oleic acid as major components; (E)-β-caryophyllene was detected, but in low concentration; and neither carvacrol nor thymol were detected. The analgesic and anti-inflammatory properties of (E)-β-Caryophyllene have been shown experimentally^69

-74. Both thymol and carvacrol has shown notable antimicrobial activities against pathogenic microorganisms^75

-78 and thymol has shown a wide array of pharmacological properties.⁷⁹The high concentrations of these compounds may contribute to the biological activities and traditional uses of S. baicalensis.

As far as we are aware, this study is the first to report the essential oil composition of S. incana. The aerial parts essential oil was rich in 1-octen-3-ol (31.2%), linalool (6.8%), (E)-nerolidol (10.5%), and phytol (19.7%). The (–)-enantiomers predominated for both linalool (63%) and (E)-nerolidol (96%). The essential oil of S. lateriflora cultivated in Alabama was also rich in 1-octen-3-ol (27.5%) and phytol (14.8%) in addition to (E)-β-caryophyllene (8.8%). The chemical composition of S. lateriflora cultivated in Alabama is in marked contrast to the composition reported for S. lateriflora from Iran, which was dominated by sesquiterpenes (78.3%) including τ-cadinene (27.0%), calamenene (15.2%), and β-elemene (9.2%).⁸⁰ Scutellaria lateriflora has been shown in rat experiments to have anticonvulsant capabilities in its flavone component extract,⁸¹ and linalool, found in all four of these Scutellaria species, has been shown to be a sedative and anticonvulsant in murine experiments,^63,64 thus supporting and explaining the pharmacology of the traditional use of this plant for such purposes.

Conclusions

This horticulture, distillation, GC-MS, GC-FID, and chirality analysis of the popular Asian medicinals, S. barbata and S. baicalensis, as well as the native Scutellaria species to Alabama and the southeastern United States, S. incana and S. lateriflora, aims to better characterize the expected volatile composition of these Scutellaria species. With the ability to compare the terpenoid distributions one can make a more well-informed decision as to the true identity of commercially available essential oils. This will also help users of phytotherapies to discern the relevance of the traditional Asian medicine and Native American medicinal claims for the uses of these herbs for inhalation therapies, baths, and teas which can, in certain instances, be supported simply by the appearance of certain aromatic terpenes like thymol, linalool, nerolidol, and β-caryophyllene, with their experimentally supported wide-ranging medicinal uses.

Experimental

Plant Material

Scutellaria baicalensis seeds (www.Amazon.com—Outsidepride seed store), Scutellaria barbata seeds (Plants with a Purpose —www.plantswithapurpose.net), Scutellaria incana seedlings (Prairie Moon Nursery—www.prairiemoon.com), and Scutellaria lateriflora seeds (Palm Beach Medicinals—www.palmbeachherbs.com) were grown by Kirkland Gardens LLC., in Newville, Alabama. The seeds were germinated in trays of organic peat moss outdoors in March 2020, then when approximately six inches tall they, along with the S. incana seedlings, were transplanted to a shady location in the garden under a tree with partial sunlight. The plants were cultivated either in one- or two-gallon black nursery pots with a mix of peat moss, perlite, and cow manure growing medium or in the ground with the same amendments/growing media. The plants were fertilized with chicken manure, bone meal, and kelp meal during transplanting and then watered regularly with well water by drip emitter system. Plants were harvested mid-flowering period, which was the week of June 7, 2020. A second harvesting of S. barbata occurred July 7, 2020. The aerial parts of the plants were photographed then cut at ground level and identifications verified with comparison to online plant databases^{24,26

-32} and S. incana and S. lateriflora were positively identified by Kirk Lawson using the Manual of the Vascular Flora of the Carolinas.⁸² The plant material was allowed to dry indoors in an air-conditioned area at approximately 23 °C for 10 days. Then, the dried aerial parts were vacuum-sealed and shipped to the University of Alabama in Huntsville. Over the weeks of July 24–August 26, 2020, they were and hydro-distilled with a Likens-Nickerson apparatus with continuous extraction with dichloromethane (DCM) for approximately 4 hours each. The DCM extracts were collected, and the small amount of solvent evaporated under a flow hood. The essential oils (EO’s) were then stored at –20 °C until further analysis.

Photographs of the plants during flowering and before collection were taken by the author, Kirk Lawson (Figures 1 -4). These photographs are stored for reference on multiple hard drives including all of the authors of this manuscript and the digital herbarium at the University of Alabama in Huntsville.

Figure 1

Scutellaria baicalensis photographed at Kirkland Gardens just before harvest. Photograph by S. K. Lawson, June 2020.

Figure 2

Scutellaria barbata, photographed in May, 2020, by Kirk Lawson.

Figure 3

Scutellaria incana. Photograph taken by S. K. Lawson immediately prior to harvest in June 2020.

Figure 4

Scutellaria lateriflora. Photographed by S. K. Lawson immediately prior to harvest in June 2020.

Gas Chromatography

The essential oils were analyzed by gas chromatography–mass spectrometry (GC-MS), gas chromatography with flame ionization detection (GC-FID), and chiral GC-MS as previously reported.⁸³ For GC-MS the Shimadzu GCMS-QP2010 Ultra was utilized, with a ZB-5ms GC column, GC oven temperature of 50 °C – 260 °C (2 °C/min), 1 µL injection of 5% solution of EO in dichloromethane (split mode, 30:1). The retention indices (RIs) were determined by using a series of reference n-alkanes. The compounds listed in Table 2 were identified by comparing the mass spectrometry data and retention indices with those in the databases.^84

-87 Gas Chromatography–Flame Ionization Detection was conducted using a Shimadzu GC 2010 with FID detector, ZB-5 GC column, GC oven temperature 50 °C– 260 °C (2 °C/min). The percent compositions were determined from raw peak areas without standardization. Chiral Gas Chromatography–Mass Spectrometry was carried out with a Shimadzu GCMS-QP2010S. A Restek B-Dex 325 column was utilized with an initial GC oven temperature of 50 °C, which was increased gradually to 120 °C at a rate of 1.5 °C/minute. Then the temperature was increased to 200 °C at the rate of 2.0 °C/minute. Exactly 0.1 µL injection of 5% solution of essential oil samples in dichloromethane (split mode, 45:1) was injected. The enantiomeric distributions were determined by comparison of retention times with authentic samples obtained from Sigma-Aldrich (Milwaukee, WI, USA). The relative enantiomer percentages were calculated from peak areas.

Footnotes

Acknowledgments

P.S. and W.N.S. participated in this work as part of the activities of the Aromatic Plant Research Center (APRC, ).

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Sims K. Lawson

References

Setzer

. The phytochemistry of Cherokee aromatic medicinal plants. Medicines. 2018;5(4):121. doi:10.3390/medicines5040121

30424560

Stewart

CD.

Jones

CD.

Setzer

. Essential oil compositions of Juniperus virginiana and Pinus virginiana, two important trees in Cherokee traditional medicine. Am J Essent Oils Nat Prod. 2014;2(2):17-24.

Craft

JD.

Lawson

SK.

Setzer

. Leaf essential oil compositions of bear’s foot, Smallanthus uvedalia and Polymnia canadensis. Am J Essent Oils Nat Prod. 2019;7(3):31-35.

Lawson

SK.

Satyal

Setzer

. The volatile phytochemistry of Monarda species growing in South Alabama. Plants. 2021;10(3):1-13.doi:10.3390/plants10030482

33806521

Steinberg

KM.

Satyal

Setzer

. Bark essential oils of Zanthoxylum clava-herculis and Ptelea trifoliata: enantiomeric distribution of monoterpenoids. Nat Prod Commun. 2017;12(6):961-963.doi:10.1177/1934578X1701200632

Lawson

SK.

Satyal

PSW

. Chemical composition of the essential oil from the aerial parts of Boltonia asteroides from North Alabama. Am J Essent Oils Nat Prod. 2019;7(4):15-17. https://www.essencejournal.com/pdf/2019/vol7issue4/PartA/7-4-4-549.pdf

Satyal

Craft

JD.

Dosoky

NS.

Setzer

. The chemical compositions of the volatile oils of garlic (Allium sativum) and wild garlic (Allium vineale. Foods. 2017;6(8):1-10.doi:10.3390/foods6080063

28783070

Woods

KE.

Chhetri

BK.

Jones

CD.

Goel

Setzer

. Bioactivities and compositions of Betula nigra essential oils. J Med Act Plants. 2013;2(1):1-9.

Setzer

. Chemical composition of the leaf essential oil of Lindera benzoin growing in North Alabama. Am J Essent Oils Nat Prod. 2016;4(3):1-3.

10.

Lawson

SK.

Sharp

LG.

Powers

CN.

McFeeters

RL.

Satyal

Setzer

. Volatile compositions and antifungal activities of native American medicinal plants: focus on the Asteraceae. Plants. 2020;9(1):1-18.doi:10.3390/plants9010126

31963839

11.

Stewart

CD.

Jones

CD.

Setzer

. Leaf essential oil compositions of Rudbeckia fulgida Aiton, Rudbeckia hirta L., and Symphyotrichum novae-angliae (L.) G.L. Nesom (Asteraceae). Am J Essent Oils Nat Prod. 2014;2(1):36-38.

12.

Lamiaceae

Lawson

SK.

Sharp

LG.

Satyal

Setzer

. Volatile components of the aerial parts of Prunella vulgaris L. (Lamiaceae). Am J Essent Oils Nat Prod. 2020;8(1):17-19.

13.

Lawson

SK.

Sharp

LG.

Satyal

Setzer

. Volatile components of the aerial parts of Conoclinium coelestinum from North Alabama. Am J Essent Oils Nat Prod. 2019;7(3):8-10.

14.

Lawson

SK.

Sharp

LG.

Powers

CN.

McFeeters

RL.

Satyal

Setzer

. Essential oil compositions and antifungal activity of sunflower (Helianthus) species growing in North Alabama. Appl Sci. 2019;9(15):1-8.doi:10.3390/app9153179

15.

Hamel

PB.

Chiltoskey

. Cherokee Plants and Their Uses: A 400 Year History. Herald Publishing Company; 1975.

16.

Garrett

. The Cherokee Herbal: Native Plant Medicine from the Four Directions. Bear & Company; 2003.

17.

Mooney

. The Sacred Formulas of the Cherokees Seventh Annual Report of the Bureau of Ethnology to the Secretary of the Smithsonian Institution, 1885-1886. 1891. EBook #24788.

18.

Cozzo

. Ethnobotanical classification system and medical ethnobotany of the eastern band of the cherokee Indians. Published online. 2004:250-251.

19.

Banks

. Ethnobotany of the Cherokee Indians. Published online 1953. https://trace.tennessee.edu/utk_gradthes/1052

20.

Winston

. Nvwoti; Cherokee medicine and ethnobotany. J Amer Herbalists. 2001:45-49.

21.

Core

. Ethnobotany of the southern appalachian aborigines. Econ Bot. 1967;21(3):199-214.doi:10.1007/BF02860370 https://www.jstor.org/stable/4252878

22.

Moerman

. Native American Ethnobotany. 1rst ed. Timber Press, Incorporated; 1998.

23.

Wang

. A review of phytochemistry and antitumor activity of a valuable medicinal species: Scutellaria barbata. J Med Plants Res. 2012;6(26):4259-4275.

24.

Kew Science . Scutellaria genus page. Accessed May 4, 2021. http://www.plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:30003498-2

25.

Shen

Liu

et al. Traditional uses, ten-years research progress on phytochemistry and pharmacology, and clinical studies of the genus Scutellaria. J Ethnopharmacol. 2021;265(265):113198 doi:10.1016/j.jep.2020.113198

32739568

26.

Missouri Botanical Garden . Scutellaria incana. Accessed February 18, 2021. https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=f530

27.

Kew Science . Plants of the world online (distribution map). Accessed February 18, 2021. http://www.plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:458351-1

28.

Scutellaria lateriflora botany . Accessed February 18, 2021. http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=281434

29.

Scutellaria lateriflora botany . Plants for a future. https://pfaf.org/user/Plant.aspx?LatinName=Scutellaria+lateriflora

30.

Scutellaria barbata . Flora of China Vol. 17. Accessed February 18, 2021. http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200020287

31.

Sloan Kettering cancer Institute . S. barbata. Published 2020. Accessed February 18, 2021. https://www.mskcc.org/cancer-care/integrative-medicine/herbs/scutellaria-barbata

32.

Scutellaria baicalensis . Flora of China Vol. 17. Accessed February 18, 2021. http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200020285

33.

EghbaliFeriz

Taleghani

Tayarani-Najaran

. Scutellaria: debates on the anticancer property. Biomed Pharmacother. 2018;105(May):1299-1310.doi:10.1016/j.biopha.2018.06.107

30021367

34.

Barrett SA

. Miwok material culture. Bull Public Museum City Milwaukee. 1933;2(4):117-376. https://www.yosemite.ca.us/library/miwok_material_culture/miwok_material_culture.pdf

35.

Sokolov

. Plant Resources of the USSR: Flowering Plants, Their Chemical Composition, the Use; The Families Hippuridaceae-Lobeliaceae. Nauka; 1991.

36.

Awad

Arnason

JT.

Trudeau

et al. Phytochemical and biological analysis of skullcap (Scutellaria lateriflora L.): a medicinal plant with anxiolytic properties. Phytomedicine. 2003;10(8):640-649.doi:10.1078/0944-7113-00374

14692724

37.

Shang

et al. The genus Scutellaria an ethnopharmacological and phytochemical review. J Ethnopharmacol. 2010;128(2):279-313.doi:10.1016/j.jep.2010.01.006

20064593

38.

Dai

S-J.

Peng

W-B.

Zhang

D-W.

Shen

Wang

W-Y.

Ren

. Cytotoxic neo-clerodane diterpenoid alkaloids from Scutellaria barbata. J Nat Prod. 2009;72(10):1793-1797.doi:10.1021/np900362z

19785430

39.

Dai

S-J.

G-W.

Q-Y.

Zhang

D-W.

G-S

. New neo-clerodane diterpenoids from Scutellaria barbata with cytotoxic activities. Fitoterapia. 2010;81(7):737-741.doi:10.1016/j.fitote.2010.01.001

20079810

40.

Pan

Guo

Feng

W-W.

Liang

Y-Z

. Development of the chromatographic ﬁngerprint of Scutellaria barbata D. Don by GC-MS combined with chemometrics methods. J Pharm Biomed Anal. 2011;55(3):391-396.doi:10.1016/j.jpba.2011.01.016

21354741

41.

Lei

Cai

Zou

. Chemical composition and antimicrobial activity of the essential oil of Scutellaria barbata. Phytochemistry. 2004;65(7):881-884.doi:10.1016/j.phytochem.2004.02.005

15081288

42.

Mamadalieva

NZ.

Sharopov

Satyal

Azimova

SS.

Wink

. Composition of the essential oils of three Uzbek Scutellaria species (Lamiaceae) and their antioxidant activities. Nat Prod Res. 2017;31(10):1172-1176.doi:10.1080/14786419.2016.1222383

27545726

43.

Cox-Georgian

Ramadoss

Dona

Basu

. Therapeutic and medicinal uses of terpenes. Med Plants From Farm to Pharm. 2019:333-359.doi:10.1007/978-3-030-31269-5_15

44.

EPA . List N Tool: COVID-19 Disinfectants. List N Tool: COVID-19 Disinfectants. https://cfpub.epa.gov/giwiz/disinfectants/index.cfm

45.

EPA . Pesticides - Fact Sheet for Thymol. Published 1993. https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/fs_PC-080402_1-Sep-93.pdf

46.

Zhu

Buss

GK.

Leal

. 1-Octen-3-ol - the attractant that repels. F1000Res. 2015;4:1-10.doi:10.12688/f1000research.6646.1

47.

Macedo

GE.

de Brum Vieira

Rodrigues

et al. Fungal compound 1-octen-3-ol induces mitochondrial morphological alterations and respiration dysfunctions in Drosophila melanogaster. Ecotoxicol Environ Saf. 2019;2020(206):111232. doi:10.1016/j.ecoenv.2020.111232

48.

Cotton

. 1-Octen-3-ol The smell of mushrooms. Molecule of the Month December. Published 2009. http://www.chm.bris.ac.uk/motm/octenol/octenolh.htm

49.

Xiong

Chen

Huang

. In vitro antimicrobial activities and mechanism of 1-octen-3-ol against food-related bacteria and pathogenic fungi. J Oleo Sci. 2017;66(9):1041-1049.doi:10.5650/jos.ess16196

28794307

50.

de Moraes

de Oliveira

RN.

Costa

et al. Phytol, a diterpene alcohol from chlorophyll, as a drug against neglected tropical disease schistosomiasis mansoni. PLoS Negl Trop Dis. 2014;8(1):51. doi:10.1371/journal.pntd.0002617

24392173

51.

Eraky

MA.

Aly

NSM.

Selem

RF.

El-Kholy

AAE-M.

Rashed

GAE-R

. In vitro schistosomicidal activity of phytol and tegumental alterations induced in juvenile and adult stages of Schistosoma haematobium. Korean J Parasitol. 2016;54(4):477-484.doi:10.3347/kjp.2016.54.4.477

27658600

52.

Inoue

Hada

Shiraishi

Hirose

Hamashima

Kobayashi

. Biphasic effects of geranylgeraniol, teprenone, and phytol on the growth of Staphylococcus aureus. Antimicrob Agents Chemother. 2005;49(5):1770-1774.doi:10.1128/AAC.49.5.1770-1774.2005

15855494

53.

Rajab

MS.

Cantrell

CL.

Franzblau

SG.

Fischer

. Antimycobacterial activity of (E)-phytol and derivatives: a preliminary structure-activity study. Planta Med. 1998;64(1):2-4.doi:10.1055/s-2006-957354

9491760

54.

Ryu

K-R.

Choi

J-Y.

Chung

Kim

D-H

. Anti-scratching behavioral effect of the essential oil and phytol isolated from Artemisia princeps Pamp. in mice. Planta Med. 2011;77(1):22-26.doi:10.1055/s-0030-1250119

20645242

55.

Santos

CC.

Salvadori

MS.

Mota

et al. Antinociceptive and antioxidant activities of phytol in vivo and in vitro models. Neurosci J. 2013;2013:949452. doi:10.1155/2013/949452

26317107

56.

Skaltsa

HD.

Lazari

DM.

Mavromati

AS.

Tiligada

EA.

Constantinidis

. Composition and antimicrobial activity of the essential oil of Scutellaria albida ssp. albida from Greece. Planta Med. 2000;66(7):672-674.doi:10.1055/s-2000-8650

11105581

57.

Ferreira

FM.

Palmeira

CM.

Oliveira

et al. Nerolidol effects on mitochondrial and cellular energetics. Toxicol In Vitro. 2012;26(2):189-196.doi:10.1016/j.tiv.2011.11.009

22138475

58.

Parreira

NA.

Magalhães

LG.

Morais

et al. Antiprotozoal, schistosomicidal, and antimicrobial activities of the essential oil from the leaves of Baccharis dracunculifolia. Chem Biodivers. 2010;7(4):993-1001.doi:10.1002/cbdv.200900292

20397234

59.

Marques

AM.

Barreto

ALS.

Curvelo

JA.

Romanos

MTV.

Soares

RM.

Kaplan

MAC

. Antileishmanial activity of nerolidol-rich essential oil from Piper claussenianum. Rev Bras Farmacogn. 2011;21(5):908-914.doi:10.1590/S0102-695X2011005000157

60.

Lee

S-J.

Han

J-I.

Lee

G-S

et al. Antifungal effect of eugenol and nerolidol against Microsporum gypseum in a guinea pig model. Biol Pharm Bull. 2007;30(1):184-188.doi:10.1248/bpb.30.184

17202684

61.

Klopell

FC.

Lemos

Sousa

JPB

et al. Nerolidol, an antiulcer constituent from the essential oil of Baccharis dracunculifolia DC (Asteraceae). Z Naturforsch C J Biosci. 2007;62(7-8):537-542.doi:10.1515/znc-2007-7-812

17913068

62.

Viljoen

AMK.

Kamatou

GPP

. Linalool – a review of a biologically active compound of commercial importance. Nat Prod Commun. 2008;3(7):1183-1192.doi:10.1177/1934578X0800300727

63.

Elisabetsky

Souza

GCD.

Santos

MCD.

Siquieira

IR.

Amador

TA.

Nunes

. Sedative properties of linalool. Fitoterapia. 1995;66:407-414.

64.

Elisabetsky

Brum

LF.

Souza

. Anticonvulsant properties of linalool in glutamate-related seizure models. Phytomedicine. 1999;6(2):107-113.doi:10.1016/S0944-7113(99)80044-0

10374249

65.

Umezu

Nagano

Ito

Kosakai

Sakaniwa

Morita

. Anticonflict effects of lavender oil and identification of its active constituents. Pharmacol Biochem Behav. 2006;85(4):713-721.doi:10.1016/j.pbb.2006.10.026

17173962

66.

Savelev

Okello

Perry

NSL.

Wilkins

RM.

Perry

. Synergistic and antagonistic interactions of anticholinesterase terpenoids in Salvia lavandulaefolia essential oil. Pharmacol Biochem Behav. 2003;75(3):661-668.doi:10.1016/S0091-3057(03)00125-4

12895684

67.

Takeoka

GR.

Rodriguez

DM.

Dao

Patterson

. Headspace volatiles of Scutellaria baicalensis georgi flowers. Journal of Essential Oil Bearing Plants. 2009;12(4):435-442.doi:10.1080/0972060X.2009.10643741

68.

Fukuhara

Fujimori

Shigematsu

Ohnishi

. Essential oil of Scutellaria baicalensis G. Agric Biol Chem. 1987;51(5):1449-1451.doi:10.1271/bbb1961.51.1449

69.

Tambe

Tsujiuchi

Honda

Ikeshiro

Tanaka

. Gastric cytoprotection of the non-steroidal anti-inflammatory sesquiterpene, beta-caryophyllene. Planta Med. 1996;62(5):469-470.doi:10.1055/s-2006-957942

9005452

70.

Fernandes

ES.

Passos

GF.

Medeiros

et al. Anti-inflammatory effects of compounds alpha-humulene and (−)-trans-caryophyllene isolated from the essential oil of Cordia verbenacea. Eur J Pharmacol. 2007;569(3):228-236.doi:10.1016/j.ejphar.2007.04.059

17559833

71.

Bakir

Him

Özbek

Düz

Tütüncü

. Investigation of the anti-inflammatory and analgesic activities of β-caryophyllene. Int J Essent Oil Ther. 2008;2(1):41-44.

72.

Klauke

A-L.

Racz

Pradier

et al. The cannabinoid CB₂ receptor-selective phytocannabinoid beta-caryophyllene exerts analgesic effects in mouse models of inflammatory and neuropathic pain. Eur Neuropsychopharmacol. 2014;24(4):608-620.doi:10.1016/j.euroneuro.2013.10.008

24210682

73.

Ceccarelli

Fiorenzani

Pessina

et al. The CB2 agonist β-caryophyllene in male and female rats exposed to a model of persistent inflammatory pain. Front Neurosci. 2020;14:1-11.doi:10.3389/fnins.2020.00850

74.

Dahham

SS.

Tabana

YM.

Iqbal

et al. The anticancer, antioxidant and antimicrobial properties of the sesquiterpene β-caryophyllene from the essential oil of Aquilaria crassna. Molecules. 2015;20(7):11808-11829.doi:10.3390/molecules200711808

26132906

75.

Engel

JB.

Heckler

Tondo

EC.

Daroit

DJ.

da Silva Malheiros

. Antimicrobial activity of free and liposome-encapsulated thymol and carvacrol against Salmonella and Staphylococcus aureus adhered to stainless steel. Int J Food Microbiol. 2017;252:18-23.doi:10.1016/j.ijfoodmicro.2017.04.003

28436830

76.

Memar

MY.

Raei

Alizadeh

Akbari Aghdam

Kafil

. Carvacrol and thymol: strong antimicrobial agents against resistant isolates. Rev Med Microbiol. 2017;28(2):63-68.doi:10.1097/MRM.0000000000000100

77.

Sharifi-Rad

Varoni

EM.

Iriti

et al. Carvacrol and human health: a comprehensive review. Phytother Res. 2018;32(9):1675-1687.doi:10.1002/ptr.6103

29744941

78.

Costa

MF.

Durço

AO.

Rabelo

TK.

Barreto

Guimarães

. Effects of carvacrol, thymol and essential oils containing such monoterpenes on wound healing: a systematic review. J Pharm Pharmacol. 2019;71(2):141-155.doi:10.1111/jphp.13054

30537169

79.

Nagoor Meeran

MF.

Javed

Al Taee

Azimullah

Ojha

. Pharmacological properties and molecular mechanisms of thymol: prospects for its therapeutic potential and pharmaceutical development. Front Pharmacol. 2017;8:380. doi:10.3389/fphar.2017.00380

28694777

80.

Yaghmai

. Volatile constituents of Scutellaria lateriflora L. Flavour Fragr J. 1988;3(1):27-31.doi:10.1002/ffj.2730030106

81.

Zhang

Lian

X-yuan.

Stringer

. Characterization of chemical ingredients and anticonvulsant activity of American skullcap (Scutellaria lateriflora). Phytomedicine. 2009;16(5):485-493.doi:10.1016/j.phymed.2008.07.011

18786819

82.

Albert

Radford

HE.

Ahles

CRB

. Manual of the Vascular Flora of the Carolinas. University of North Carolina Press; 1968.

83.

DeCarlo

Johnson

Okeke-Agulu

et al. Compositional analysis of the essential oil of Boswellia dalzielii frankincense from West Africa reveals two major chemotypes. Phytochemistry. 2019;164(May):24-32.doi:10.1016/j.phytochem.2019.04.015

31071599

84.

Adams

. Identification of Essential Oil Components by Gas Chromatography / Mass Spectrometry. 4th ed. Allured Publishing; 2007.

85.

Mondello

. FFNSC 3. Shimadzu Scientific Instruments. Published 2016. Accessed April 14, 2021. https://www.shimadzu.eu.com/ffnsc-3

86.

National Institute of Standards and Technology . NIST 17. NIST17. Published online 2017. https://chemdata.nist.gov/dokuwiki/doku.php?id=chemdata:nist17

87.

Satyal

. Development of GC-MS database of essential oil components by the analysis of natural essential oils and synthetic compounds and discovery of biologically active novel chemotypes in essential oils. published online 2015.