1.   Introduction

Purshia tridentata (Pursh) DC. (syn. Kunzia tridentata Spreng., bitterbrush), Rosaceae, is an evergreen or partially deciduous shrub around 1-5 m tall with three-lobed leaves 4-15 mm long ´ 3-7 mm wide (Fig. 1) [1]. Two varieties of P. tridentata are currently recognized, Purshia tridentata var. tridentata (antelope bitterbrush), and Purshia tridentata var. glandulosa (Curran) M.E. Jones (syn. Purshia glandulosa Curran, desert bitterbrush) [2]. Purshia tridentata var. tridentata normally ranges from southern British Columbia, south through eastern Washington, eastern Oregon, Idaho, Nevada, and Utah, and into northern Arizona (Fig. 2), while P. tridentata var. glandulosa is found in Nevada, Utah, south into northern Sonora, Mexico [3].

Figure 1. Purshia tridentata var. tridentata from southern Idaho.

Photograph by K. Swor.

Figure 2. Distribution of Purshia tridentata var. tridentata

(antelope bitterbrush) in western North America. Adapted

from McArther et al. [3].

The Paiute and Shoshoni people took an infusion of the aerial parts as a cathartic/emetic, while a poultice of the leaves was used to treat skin problems [4]. The Chumash people took a tea made from P. tridentata to ease menstrual cramps [5]. The triterpenoids cucurbitacin D and cucurbitacin I [6] as well as the cyanogenic glycosides purshianin and menisdaurin [7] have been isolated from P. tridentata. Several ungulates utilize P. tridentata for forage [8], in particular mule deer (Odocoileus hemionus) rely heavily on the plant in the winter [9–11]. Domestic sheep and cattle, but not horses, have also shown a preference for P. tridentata [12,13].  

The purpose of this present study was to collect P. tridentata var. tridentata from several locations in southern Idaho, obtain the essential oils by hydrodistillation and characterize the essential oils using gas chromatographic techniques. As far as we are aware, this is the first report on the essential oil composition of P. tridentata.

 

2. Materials and methods

2.1 Plant material

The aerial parts of P. tridentata var. tridentata were collected from several different plants (samples #1, #2, #3, #4, and #5) growing wild in southern Idaho (Table 1). The plants were identified by Daniel Murphy, Collections Curator, Idaho Botanical Garden, and verified by W.N. Setzer based on botanical descriptions [1] and by comparison with samples from the New York Botanical Garden virtual herbarium (https://sweetgum.nybg.org/science/vh/specimen-list/?SummaryData=Purshia%20 tridentata, accessed on June 29, 2022). A voucher specimen (WNS-Ptt-5682) has been deposited in the University of Alabama in Huntsville herbarium. The aerial parts were immediately frozen (–20 °C) until distilled. Each of the plant samples was hydrodistilled using a Likens-Nickerson apparatus with continuous extraction with dichloromethane for 3 h to give the essential oils (Table 1).

2.2 Gas chromatographic analysis

The essential oils were analyzed by gas chromatography with flame ionization detection (GC-FID), gas chromatography – mass spectrometry (GC- MS) and chiral GC-MS as previously described [14]. Retention index values were determined using a homologous series of n-alkanes on a ZB-5ms column using the linear formula of van den Dool and Kratz [15]. The essential oil components were identified by comparison of the mass spectral fragmentation patters and by comparison of retention index (RI) values available in the Adams [16], FFNSC 3 [17], NIST20 [18], and our own in-house database [19]. The identification of enantiomers was determined by comparison of retention times with authentic samples obtained from Sigma-Aldrich (Milwaukee, WI, USA).

2.3. Multivariate analyses

For the agglomerative hierarchical cluster (AHC) analyses, the essential oil compositions for the five samples were treated as operational taxonomic units (OTUs), and the percentages of the most abundant essential oil components (heptacosane, trans-calamenene, 2-coumaranone, (3Z)-hexen-1-ol, trans-cadina-1,4-diene, (2E)-hexenal, α-muurolol, α-cadinol, pentacosane, linalool, bornyl acetate, tetradecanal, (E)-nerolidol, dodecanal, (3Z)-hexenyl benzoate, germacrene D, cubenol, benzyl alcohol, nonanal, and δ-cadinene) were used to establish the chemical associations between the essential oil samples. Pearson correlation was used to measure similarity, and the unweighted pair group method with arithmetic average (UPGMA) was used for cluster definition. Principal component analysis (PCA) was  performed for the visual verification of the essential oil interrelationships of the different samples of P. tridentata var. tridentata using the major components as variables with a Pearson correlation matrix. The AHC and PCA analyses were performed using XLSTAT v. 2018.1.1.62926 (Addinsoft, Paris, France).

3. Results and discussion

3.1 Essential oil composition

Hydrodistillation of the aerial parts of P. tridentata var. tridentata gave colorless essential oils in yields ranging from 0.301% to 0.969%. The gas chromatographic analysis (GC-MS and GC-FID) results are summarized in Table 2.

Table 2. Essential oil compositions (percentages) of the aerial parts of Purshia tridentata var. tridentata collected in southern Idaho.

RIcalc	RIdb	Compound	#1		#2	#3	#4	#5
800	801	Hexanal	0.8		0.7	-	1.0	0.1
850	850	(2E)-Hexenal	5.1		4.0	-	3.4	-
852	853	(3Z)-Hexen-1-ol	5.5		5.5	0.3	3.0	8.0
863	863	(2E)-Hexen-1-ol	0.5		0.4	tr	0.3	0.4
867	867	1-Hexanol	0.5		0.4	tr	0.3	0.4
902	905	Heptanal	-		0.3	-	0.3	-
934	933	α-Pinene	0.9		1.9	tr	0.2	2.7
947	942	4,4-Dimethyl-2-butenolide	0.9		1.0	0.2	0.3	-
950	953	Camphene	-		-	-	-	0.2
963	964	Benzaldehyde	0.5		0.6	0.1	0.4	0.7
972	974	Hexanoic acid	-		-	0.2	-	-
972	972	Sabinene	-		-	-	-	0.1
978	978	β-Pinene	1.0		0.3	tr	0.4	1.4
989	989	Myrcene	-		-	-	-	0.2
1005	1006	Octanal	0.5		0.6	0.1	1.4	0.3
1024	1025	p-Cymene	0.3		0.3	tr	0.1	-
1029	1030	Limonene	0.8		0.3	tr	0.3	0.6
1031	1031	β-Phellandrene	0.7		0.4	tr	2.3	0.2
1032	1032	1,8-Cineole	-		-	tr	0.2	-
1033	1033	Benzyl alcohol	3.8		1.4	0.4	0.8	0.2
1035	1034	(Z)-β-Ocimene	0.8		0.5	tr	-	1.1
1043	1045	Phenylacetaldehyde	0.5		1.2	0.1	0.7	-
1044	1044	Salicylaldehyde	0.5		0.3	-	-	0.5
1046	1046	(E)-β-Ocimene	0.4		0.2	tr	0.2	0.1
1050	1049	cis-Arbusculone	0.4		0.4	tr	0.2	-
1055	1047	Methyl 2-hydroxyhexanoate	-		-	0.1	-	-
1069	1068	trans-Arbusculone	-		-	tr	-	-
1070	1073	Allyl hexanoate	-		-	0.1	-	-
1071	1069	cis-Linalool oxide (furanoid)	-		-	-	0.4	-
1086	1086	Terpinolene	0.6		0.3	0.1	-	-
1087	1086	trans-Linalool oxide (furanoid)	-		-	tr	0.4	-
1100	1101	Linalool	1.1		0.5	0.2	5.7	1.7
1103	1102	6-Methylhepta-3,5-diene	-		-	0.1	-	-
1105	1107	Nonanal	1.1		1.6	0.3	1.6	1.5
1107	1105	α-Thujone	2.0		0.4	0.3	0.3	-
1112	1113	Phenethyl alcohol	1.8		1.5	0.6	0.7	0.2
1113	1113	(E)-4,8-Dimethylnona-1,3,7-triene	-		-	0.1	0.3	-
1126	1126	α-Campholenal	-		0.3	0.1	-	-
1145	1145	trans-Verbenol	0.3		0.7	0.1	-	-
1148	1149	Camphor	0.8		0.5	0.1	0.5	0.3
1152	1153	(2E,6Z)-Nonadienal	0.6		0.3	0.1	0.4	-
1156	1156	Camphene hydrate	-		-	-	-	0.1
1162	1162	β-Artemisyl acetate	-		0.9	-	0.4	-
1168	1169	3-Thujanol	0.4		-	0.3	-	-
1171	1171	p-Mentha-1,5-dien-8-ol	-		-	0.1	-	-
1180	1180	Terpinen-4-ol	0.3		0.5	0.1	0.3	0.3
1192	1192	Methyl salicylate	0.4		0.2	0.1	-	-
1195	1195	α-Terpineol	0.4		0.1	0.1	1.1	1.4
1196	1195	Myrtenol	-	0.4		-	-	-
1206	1206	Decanal	1.0	1.1		0.3	1.9	0.6
1232	-	2-Coumaranone	5.3	3.8		0.5	2.9	11.3
1251	1249	Geraniol	-	-		-	0.4	-
1284	1285	Bornyl acetate	-	-		-	-	8.7
1285	1286	2,4-Pentadiynylbenzene	0.7	0.3		0.1	-	-
1292	1293	2-Undecanone	-	-		-	-	0.2
1300	1300	Tridecane	0.3	0.4		0.1	0.6	0.2
1309	1309	Undecanal	0.6	0.5		0.3	1.9	1.3
1310	1309	4-Vinylguaiacol	0.5	0.4		-	-	-
1349	1349	α-Cubebene	0.7	0.9		2.4	0.4	-
1350	1356	Eugenol	-	-		-	-	0.2
1376	1375	α-Copaene	0.4	0.3		0.5	0.2	-
1383	1382	β-Bourbonene	0.4	0.3		1.4	0.2	-
1385	1385	α-Bourbonene	-	-		0.1	-	-
1386	1387	β-Cubebene	-	-		0.3	-	-
1389	1390	trans-β-Elemene	-	-		-	1.6	-
1389	1387	(6E)-6-Methyl-5-(1-methylethylidene)-6,8-nonadien-2-one	2.1	1.3		0.4	1.1	0.5
1400	1403	Methyl eugenol	0.4	0.3		-	-	-
1405	1406	α-Gurjunene	-	-		0.4	-	-
1409	1409	Dodecanal	2.2	2.1		0.3	2.3	0.7
1419	1418	(E)-β-Caryophyllene	1.4	1.1		0.7	1.0	tr
1428	1430	β-Copaene	-	-		0.2	-	-
1433	1432	trans-α-Bergamotene	-	0.3		0.6	-	-
1443	1444	Guaia-6,9-diene	1.6	-		-	-	-
1451	1453	trans-Muurola-3,5-diene	0.6	0.5		1.5	-	-
1453	1454	α-Humulene	-	-		0.4	-	-
1463	1463	γ-Decalactone	-	-		-	-	0.6
1471	1472	trans-Cadina-1(6),4-diene	-	-		1.0	-	-
1478	1479	α-Amorphene	-	-		-	0.5	-
1480	1480	Germacrene D	2.6	1.6		2.0	1.1	-
1484	1483	Davana ether 1	0.3	0.5		-	0.2	-
1490	1490	γ-Amorphene	-	-		3.2	0.4	tr
1494	1496	trans-Muurola-4(14),5-diene	0.9	1.0		-	-	-
1496	1598	Viridiflorol	-	-		0.9	-	-
1497	1497	epi-Cubebol	0.5	0.6		0.5	-	1.9
1498	1497	Bicyclogermacrene	-	-		0.5	-	-
1499	1497	Capillene	0.9	0.7		-	-	-
1499	1500	α-Muurolene	-	-		0.5	-	0.6
1500	1500	Pentadecane	0.3	0.6		-	-	0.2
1502	1502	Davana ether 2	1.5	1.8		-	0.9	-
1503	1503	(Z)-α-Bisabolene	-	-		0.6	-	-
1504	1504	Davana ether 3	0.5	0.5		0.1	0.2	-
1510	1510	β-Bisabolene	-	-		0.4	-	0.4
1511	1510	Tridecanal	-	-		-	0.2	tr
1511	1511	(Z)-γ-Bisabolene	0.4	0.8		0.9	0.1	-
1513	1512	γ-Cadinene	-	-		-	-	0.3
1516	1515	Cubebol	0.6	0.5		1.2	0.2	0.8
1518	1518	δ-Cadinene	0.6	0.6		1.3	0.5	3.0
1523	1527	trans-Calamenene	5.3	7.9		17.1	4.2	0.5
1526	1526	Zonarene	-	-		1.3	-	-
1535	1533	trans-Cadina-1,4-diene	1.7	2.6		7.0	1.2	0.2
1543	1544	α-Calacorene	0.8	0.8		2.0	0.8	-
1546	1550	5-Ethyl-1-tetralone	0.8	1.0		2.1	0.7	-
1549	1549	α-Elemol	-	-		-	0.4	1.7
1562	1562	(E)-Nerolidol	2.5	2.6		-	3.0	0.2
1564	1564	β-Calacorene	-	-		1.3	-	-
1572	1571	(3Z)-Hexenyl benzoate	1.3	2.4		0.9	1.7	1.2
1573	1567	Palustrol	-	-		0.8	-	-
1578	1576	Spathulenol	0.3	-		0.4	-	tr
1579	1577	Davanone	-	1.0		-	0.6	-
1580	1578	Furopelargone B	1.6	-		-	-	-
1584	1587	Caryophyllene oxide	0.9	1.0		2.3	0.9	tr
1594	1593	Salvial-4(14)-en-1-one				0.5
1595	1594	Viridiflorol	0.6	0.6		-	-	0.8
1598	-	Unidentified	-	-		1.2	1.5	-
1600	1600	Hexadecane	-	-		-	-	0.1
1603	1607	β-Oplopenone	-	-		-	-	0.4
1606	1605	Ledol	-	-		0.5	-	-
1611	1611	Humulene epoxide II	-	-		1.3	-	-
1616	1614	Tetradecanal	1.9	2.2		0.5	2.6	1.3
1630	1631	1-epi-Cubenol	-	0.5		1.2	0.5	1.3
1631	1629	iso-Spathulenol	1.3	-		-	-	-
1632	1632	γ-Eudesmol	-	-		-	-	0.4
1644	1644	τ-Muurolol	-	-		-	-	2.6
1645	1646	Cubenol	0.9	1.6		2.6	0.8	1.1
1649	1651	α-Muurolol (= δ-Cadinol)	1.3	2.6		4.8	1.4	1.6
1655	1655	α-Cadinol	2.2	2.1		-	0.7	6.0
1656	1656	β-Eudesmol	-	-		-	1.9	-
1657	-	Unidentified	-	-		1.9	-	0.3
1660	1660	Selin-11-en-4α-ol	-	-		-	0.8	-
1665	1665	Intermedeol	-	-		-	-	3.4
1666	1670	trans-Calamenen-10-ol	-	-		0.4	-	-
1674	1674	β-Bisabolol	-	0.6		-	-	-
1676	1677	Cadalene	0.9	0.8		2.6	1.0	tr
1687	1688	α-Bisabolol	-	1.0		0.8	0.4	0.6
1692	1690	Germacra-4(15),5,10(14)-trien-1β-ol	-	-		0.4	-	-
1699	-	Unidentified	-	-		1.0	-	-
1700	1700	Heptadecane	-	-		-	-	0.2
1716	1715	5-Hydroxy-cis-calamenene				0.6
1728	-	Unidentified	-	0.5		1.3	0.5	-
1742	1742	(6S,7R)-Bisabolone	-	-		-	-	0.4
1766	1769	Benzyl benzoate	0.6	1.1		-	0.8	tr
1818	1817	Hexadecanal	1.0	1.1		0.4	1.2	0.7
1842	1841	Phytone	0.4	0.3		0.2	0.7	0.3
1876	-	Unidentified	1.3	0.3		0.2	-	-
1900	1900	Nonadecane	-	-		0.2	-	-
1937	-	Unidentified	-	-		-	1.0	-
1961	1958	Palmitic acid	-	-		0.4	-	-
1975	-	Unidentified	-	-		-	1.2	-
1998	-	Unidentified	-	-		-	1.3	-
2000	2000	Eicosane	-	-		0.1	-	-
2100	2100	Heneicosane	0.3	0.7		0.2	0.3	-
2111	2109	Phytol	1.6	0.6		0.2	2.0	-
2194	2193	Ethyl stearate	-	-		0.2	-	-
2200	2200	Docosane	-	-		0.1	-	-
2245	2243	9-Hexylheptadecane	-	-		-	3.5	-
2300	2300	Tricosane	1.4	1.9		1.1	1.1	0.3
2394	2394	Ethyl eicosanoate	-	-		0.5	-	-
2400	2400	Tetracosane	-	-		0.1	-	-
2500	2500	Pentacosane	2.2	2.4		1.0	2.7	1.5
2600	2600	Hexacosane	-	-		0.1	-	-
2700	2700	Heptacosane	5.2	7.0		3.1	12.0	18.7
		Essential oil compound classes
		Monoterpene hydrocarbons	5.5	4.1		0.1	3.5	6.7
		Oxygenated monoterpenoids	5.3	4.4		1.4	9.7	12.5
		Sesquiterpene hydrocarbons	18.2	19.7		50.2	13.1	4.7
		Oxygenated sesquiterpenoids	15.1	17.6		19.3	12.7	23.2
		Diterpenoids	1.6	0.6		0.2	2.0	0.0
		Benzenoid aromatics	17.2	14.1		2.7	8.0	14.3
		Fatty acid derivatives	30.8	33.6		10.1	42.0	37.5
		Others	4.6	4.0		3.1	3.2	0.8
		Total identified	98.2	98.0		87.1	94.2	99.7

RI_calc=Retention index determined using a homologous series of n-alkanes on a ZB-5ms column [15]. RI_db= Reference retention index from the databases [16–19]. tr = trace (< 0.5%). #1-#5 refer to sample numbers of the collected plants.

Monoterpenoids made up relatively small percentages in the essential oils. Sesquiterpenoids and fatty acid derivatives, however, were relatively abundant. The components in the essential oils with the highest concentrations were heptacosane (3.1-18.7%), trans-calamenene (0.5%-17.1%), 2-couma-ranone (0.5-11.3%), trans-cadina-1,4-diene (0.2-7.0%), (3Z)-hexen-1-ol (0.3-8.0%), and linalool (0.5-5.7%). Bornyl acetate was relatively abundant in sample #5 (8.7%), but not detected in the other samples, and (2E)-hexenal was relatively abundant in samples #1, #2 and #4 (5.1%, 4.0%, and 3.4%, respectively), but not observed in samples #3 or #5.

There are some notable differences in the essential oil compositions. In order to assess the differences, an agglomerative hierarchical cluster (AHC) analysis as well as a principal cluster analysis (PCA) were carried out (Fig. 3 and 4). The AHC analysis reveals samples #1 and #2 to have 83% similarity, while samples #4 and #5 have 59% similarity. Sample #3 shows only 22% similarity to the other samples. The PCA further explains the differences. Samples #1 and #2 correlate strongly with heptacosane, 2-coumaranone, (3Z)-hexen-1-ol, and (2E)-hexenal. Samples #4 and #5 correlate very strongly with heptacosane, while #5 also correlates with bornyl acetate. Sample #3, on the other hand, shows correlation with trans-calamenene as well as trans-cadina-1,4-diene and α-muurolol.

Figure 3. Dendrogram based on hierarchical cluster analysis of

Purshia tridentata var. tridentata essential oil compositions.

Figure 4. Biplot based on principal component analysis of

Purshia tridentata var. tridentata chemical compositions.

It is not obvious what factors may be attributable to the compositional differences. Essential oil differences are often attributed to geographical, edaphic, climatic, or genetic differences. Samples #1, #2, and #3 were collected from the same location on the same day; differences in composition are likely attributable to the variation within the species. Samples #4 and #5 were collected on different dates from different locations, so compositional differences may be attributed to seasonal (although all samples were collected in mid-summer), edaphic, geographical (although the locations are relatively close to one another), or elevation (sample #5 was collected at much lower elevation than the others).

 

Outside of floral essential oils, the Rosaceae is not considered to be an essential oil-bearing plant family [20]. Fatty acid derivatives and sesquiterpenoids generally dominate the essential oils of aerial parts of members of the Rosaceae.

For example, the aerial parts essential oils of Rosa spp. were dominated by long-chain n-alkanes [21,22]. Long-chain n-alkanes as well as other fatty acid derivatives were abundant in the essential oil of Filipendula hexapetala [23], while Sibiraea laevigata was a rich source of fatty acid esters [24]. Thus, the essential oil compositions of P. tridentata var. tridentate are consistent with those observed in other members of the Rosaceae.

3.2 Enantiomeric distributions

The P. tridentata var. tridentata essential oils were analyzed using chiral GC-MS. The enantiomeric distributions of chiral terpenoid components are listed in Table 3.

Table 3. Enantiomeric distribution, %(+), %(–), for Purshia tridentata var. tridentata aerial parts essential oils from southern Idaho.

Compounds	#1		#2		#3		#4		#5
	%(+)	%(–)	%(+)	%(–)	%(+)	%(–)	%(+)	%(–)	%(+)	%(–)
α-Pinene	0.0	100.0	0.0	100.0	0.0	100.0	nd		22.0	78.0
β-Pinene	0.0	100.0	0.0	100.0	0.0	100.0	0.0	100.0	0.0	100.0
Limonene	80.7	19.3	71.6	28.4	nd		nd		62.5	37.5
β-Phellandrene	26.9	73.1	20.7	79.3	nd		0.0	100.0	nd
α-Thujone	0.0	100.0	0.0	100.0	nd		0.0	100.0	nd
Linalool	54.3	45.7	nd		62.3	37.7	61.7	38.3	55.9	44.1
Camphor	100.0	0.0	100.0	0.0	100.0	0.0	100.0	0.0	nd
Bornyl acetate	nd		nd		nd		nd		0.0	100.0
α-Terpineol	nd		nd		nd		38.4	61.6	31.2	78.8
(E)-β-Caryophyllene	0.0	100.0	0.0	100.0	0.0	100.0	0.0	100.0	nd
Germacrene D	0.0	100.0	0.0	100.0	0.0	100.0	0.0	100.0	nd
β-Bisabolene	nd		nd		0.0	100.0	nd		nd
δ-Cadinene	100.0	0.0	100.0	0.0	100.0	0.0	100.0	0.0	100.0	0.0
(E)-Nerolidol	0.0	100.0	0.0	100.0	0.0	100.0	0.0	100.0	nd
nd = not detected.

The (–)-enantiomers predominated in the essential oils for α-pinene, β-pinene, β-phellandrene, α-thujone, α-terpineol, bornyl acetate, (E)-β-caryophyllene, germacrene D, β-bisabolene, and (E)-nerolidol, while the (+)-enantiomers for limonene, linalool, camphor,  and δ-cadinene were dominant. The floral essential oil of Rosa damascena Mill., in comparison, showed (+)-α-pinene, (+)-β-pinene, and (+)-α-terpineol to be the dominant enantiomers, while (–)-linalool predominated over (+)-linalool, and the enantiomeric distribution of limonene depended on the geographical location (Bulgaria or Türkiye) [25]. Thus, the enantiomeric distributions of chiral terpenoids in P. tridentata var. tridentata are consistent throughout the samples. However, the enantiomeric distributions of monoterpenoids are different between P. tridentata and R. damascena.

 

4. Conclusions

This is the first report on the essential oil composition and enantiomeric distribution of P. tridentata var. tridentata. As in other members of the Rosaceae, fatty acid derivatives and sesquiterpenoids dominated the aerial parts essential oils P. tridentata var. tridentata.

Additional research is needed to adequately describe the volatile phytochemistry of Purshia species, particularly P. tridentata var. glandulosa as well as Purshia plicata (D. Don) Henrickson, Purshia mexicana (D. Don) Henrickson, Purshia stansburiana (Torr.) Henrard, and Purshia ericifolia (Torr. ex A. Gray) Henrickson. The low yields and variable chemical compositions likely preclude any industrial exploitation of P. tridentata essential oil.

 

Authors’ contributions

Conceptualization, W.N.S.; Methodology, P.S. and

W.N.S.; Software, P.S.; Validation, W.N.S., Formal Analysis, A.P., P.S., and W.N.S.; Investigation, K.S., A.P., P.S., and W.N.S.; Resources, P.S. and W.N.S.; Data Curation, W.N.S.; Writing – Original Draft Preparation, W.N.S.; Writing – Review & Editing, K.S., P.S., and W.N.S.; Project Administration, W.N.S.

 

Acknowledgements

This work was carried out as part of the activities of the Aromatic Plant Research Center (APRC, https://aromaticplant.org/).

 

Funding

This research received no specific grant from any funding agency.

 

Conflicts of interest

The authors declare no conflict of interest.

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