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Research Article
Comparative Phytochemical Analyses of Resins of
Boswellia Species (B. papyrifera (Del.) Hochst., B. neglecta S.
Moore, and B. rivae Engl.) from Northwestern, Southern, and
Southeastern Ethiopia
Deribachew Bekana,1Tesfahun Kebede,1Mulugeta Assefa,1and Habtemariam Kassa2
1Department of Chemistry, College of Natural and Computational Sciences, Haramaya University, P.O. Box 138, Dire Dawa, Ethiopia
2Centre for International Forestry Research, Ethiopia Oce, P.O. Box 5689, Addis Ababa, Ethiopia
Correspondence should be addressed to Deribachew Bekana; gado@yahoo.com
Received September ; Accepted November ; Published February
Academic Editors: A. Bouklouze, A. Garcia Asuero, and R. N. Rao
Copyright © Deribachew Bekana et al. is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Oleogum resins of B. papyrifera,B. neglecta,andB. rivae were collected from northwestern, southern, and southeastern Ethiopia,
and their respective methanol extracts and essential oils were extracted and analyzed by gas chromatography (GC) and gas
chromatography-mass spectrometry (GC-MS). e investigation on essential oils led to the identication of , , and constituents
for B. papyrifera,B. neglecta,andB. rivae, respectively. e essential oil of B. papyrifera is mainly characterized by the presence of
octyl acetate (.–.%) and n-octanol (.–.%). B. neglecta is rich in 𝛼-pinene (.–.%) followed by terpinen--ol (.–
.%) and 𝛼-thujene (.–.%), whereas B. rivae was predominated by 𝛼-pinene (.–.%) followed by p-cymene (.–.%)
and limonene (.–.%). Methanol extracts of the three Boswellia species were found to consist of diterpines (incensole, incensyl
acetate and verticilla-(),,-triene), triterpenes (𝛽-amyrin, 𝛼-amyrin, 𝛽-amyrenone, and 𝛼-amyrenone), nortriterpenes (-
noroleana-,-diene and -norursa-,-diene), and 𝛼-boswellic acid. e investigation on the methanol extract showed that
only B. papyrifera contains diterpenes and nortriterpenes, whereas B. rivae and B. neglecta consist of only triterpenes. e results
indicate that the three Boswellia species were characterized by some terpenes and these terpenoic constituents could be recognized
as chemotaxonomical markers for each species.
1. Introduction
e family Burseraceae is represented by genera and –
species, widespread in tropical and subtropical regions.
e genus Boswellia has about species of small trees and
shrubs occurring in dry land regions from west Africa to
Arabia and from south to northeast Tanzania, in India, and
one species in Madagascar. e genus is centered in northeast
Africa where about % of the species are endemic to the area.
eyaretreesorshrubsoenwithlatex,resins,oroilswhich
are strongly aromatic [,].
Frankincense, gum olibanum, or olibanum are the
common names given to the oleogum resin which is
obtained through incisions made in the trunks of trees of
the genus Boswellia (family Burseraceae). It is plant product
and belongs to a group of aromatic gums and resins which
contain odiferous substances [–].
Frankincense consists of essential oils, gum, and ter-
penoids []. It is a complex of –% alcohol soluble
resins (diterpenes, triterpenes), –% essential oil, which
is soluble in organic solvents, and the rest is made up of
polysaccharides (gum), which are soluble in water []. Its
essential oil portion is composed of ester (.%), alco-
hol (.%), monoterpene hydrocarbons (.%), diterpenes
(.%) [], and sesquiterpenes. Gum fraction is composed
of pentose and hexose sugar and resin portion is mainly
composed of pentacyclic triterpene acid of which boswellic
acidistheactivemoiety[]. Mono- and sesquiterpenes are
highly volatile compounds, diterpenes exhibit low volatility,
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Volume 2014, Article ID 374678, 9 pages
http://dx.doi.org/10.1155/2014/374678
ISRN Analytical Chemistry
triterpenes exhibit very low volatility, and polysaccharides are
not volatile [].
Dierent commercial varieties of frankincense can be
distinguished by the chemical constituents of their essential
oil. e constituents of the essential oil of frankincense were
rst investigated by Stenhouse [] and he identied fourteen
monoterpenoic constituents. Chemical investigation by Basar
[]ontheessentialoilofB. neglecta and B. rivae led to
isolation and identication of monoterpenes. e major
compounds identied in B. neglecta were 𝛼-thujene (.%),
𝛼-pinene (.%), sabinene (.%), Δ--carene (.%), p-
cymene (.%), terpinen--ol (.%), and verbenone (.%).
B.rivae resin oil composition is quite similar to that
of B. neglecta which consists of cara-,-diene (.%), 𝛼-
thujene (.%), 𝛼-pinene (.%), o-cymene (.%), Δ--
carene (.%), p-cymene (.%), and limonene (.%). In
the study, triterpenoic constituents, namely, 𝛼-amyrin (.%),
𝛽-amyrin (.%), epi-𝛼-amyrin (.%), 𝛽-amyrenone (.%),
𝛼-and𝛽-amyrin (-,-dien-𝛼-amyrin (.%), and -,-
dien-𝛽-amyrin (.%), were also identied from pyrolysate
of B. neglecta. Similarly, -norursa-,-diene (.%), 𝛼-
amyrin (.%), 𝛽-amyrin (.%), 𝛼-amyrenone (.%), 𝛽-
amyrenone (.%), and epi-𝛽-amyrin (.%) were detected
in the pyrolysate of B. rivae. Dekebo et al. []reportedthe
essential oil constituents of the resin of B. papyrifera and
identied n-hexyl acetate (%), 𝛼-pinene (.%), limonene
(.%), n-octanol (.%), linalool (.%), octyl acetate (%),
caryophyllene oxide (%), and 𝛽-elemene (%).
Although Ethiopia is one of the few countries that are
endowed with large frankincense resources, little proper
exploitation of this resource has been made so far (i.e.,
the export market from Ethiopia has been weakened) due
to inconsistent supply and ambiguity of grades []. Of
the three Boswellia species found in Ethiopia, frankincense
resin obtained from B. papyrifera is the most widely traded
frankincense accounting for over % of the natural gum
exported. e frankincense obtained from B. rivae and
B. neglecta species is yet not of export standard []. As
reported by Assefa et al. [] basis for selection of export
item and the respective price quotations need to be revised
to reect contents of ingredients sought aer by buyers.
Ethiopia will be more beneted from the export of these
items provided eorts are made to develop these resources
more than the current situation. However, there is paucity
of information on chemical quality variations between the
export standard frankincense (B. papyrifera) and the other
two Boswellia species (B. rivae and B. neglecta)whichare
not of export standard. is study is, therefore, initiated
for comparative purpose, where essential oil and methanol
extract composition of one species were contrasted with the
other(s) to characterize the chemical classes of constituents
present and to nd chemotaxonomical markers, among these
constituents, for the three Boswellia species.
2. Materials and Methods
2.1. Description of Sampling Sites and Sample Collection. e
resin samples of frankincense (Boswellia species) used for this
study were collected in August from northwestern and
southeastern Ethiopia. From northwestern Ethiopia, three
sites were selected: Metema from Amhara region, Humera
from Tigray regional state, and Metekel from Benishangul
Gumuz regional state. From these sites, exudates were col-
lected from B. papyrifera. Samples from southeastern part
of the country were collected from three districts, namely,
Mega, Dubuluk, and Wachile from Borana zone of Oromiya
region. In these entire three sites, one dominant species
known as B. neglecta is widely grown. en samples were
also collected from Filtu, Chereti, and Dolo Odo districts of
Somalia regional state. In these sites, B. rivae was dominant.
e studied samples were an authentic sample which are
certied for their authenticity by Agricultural Department
of the Ethiopian Government Natural Gum Processing and
Marketing Enterprise. e geographical locations of the
districts are given in Table .
2.2. Chemicals and Reagents. All chemicals and reagents used
were of analytical grade. Chloroform (.%) and methanol
(.%) were purchased from Merck (Darmstadt, Germany).
Anhydrous sodium sulfate was purchased from Fluka (Buchs,
Switzerland).
2.3. Equipment and Instruments. Polyethylene plastic bags,
ceramic mortar and pestle (Haldenwanger, Germany),
a digital analytical balance (Mettler Toledo, Model AG
, Switzerland), round bottom ask (Mumbai, India),
Clevenger apparatus (Rac, India), rotary evaporator and
heating mantle (Buchi, Switzerland), Gas chromatography
(Monza, Italy), Gas chromatography-mass spectrometry
(PerkinElmer, USA), and syringes (Hamilton Bonaduz AG,
Switzerland) are among the equipment and instruments that
were used in the study.
2.4. Methanol Extraction and Isolation of Essential Oils. e
resins of the three Boswellia species were air-dried at room
temperature for weeks, grinded and homogenized to a
uniform powder by ceramic mortar and pestle, and sieved.
Two grams of grinded and homogenized resins powder was
extracted with mL of methanol at room temperature. e
extracts were concentrated using a rotary evaporator and
analyzed by GC-MS. For essential oils, the ground resins of
the three Boswellia species: B. papyrifera,B. neglecta,and
B. rivae were submitted for h to hydrodistillation using a
Clevenger-type apparatus. e obtained oils were allowed to
dry over anhydrous sodium sulphate. Aer ltration, the oils
were stored at +∘Cuntilanalyzed[].
2.5. Gas Chromatography. GC analyses were performed
on Dani model Gas chromatography (Monza, Italy)
equipped with ame ionization detector (FID). e analysis
was carried out on a fused silica capillary column coated with
HP- column length m, internal diameter . mm, lm
thickness . micron, and % phenyl % methyl polysilox-
ane as stationary phase. e oven was programmed at –
∘Catarateof
∘C/min using N2as carrier gas; injector
and detector (FID) temperatures were ∘Cand
∘C,
ISRN Analytical Chemistry
T : Geographical locations of the study areas.
Region Areas Latitude and longitude
Northwestern
Metema ∘. N
∘. E
Metekel . N
∘. E
Humera ∘. N
∘. E
Southeastern
Wachile ∘. N
∘. E
Dubuluk ∘. N
∘. E
Mega ∘. N
∘. E
Eastern
Filtu ∘. N
∘. E
Dolo Odo ∘. N
∘. E
Chereti ∘. N
∘. E
T : Chemical compositions (%) of essential oils of three
B.neglecta resins.
Retention time (min) Components Dubuluk Mega Wachile∗
%%%
. 𝛼-ujene . . .
. 𝛼-Pinene . . .
. 𝛽-Pinene . . .
. Sabinene . . .
. p-Cymene . . .
. Terpinen--ol . . .
. Verbenone . . .
∗Components identied from the essential oil of same sample reported in
our previous study [].
respectively. Calculation of peak area percentage was per-
formed on basis of the FID signal using the GC HP-
Chemstation soware (Agilent Technologies).
2.6. Gas Chromatography-Mass Spectrometry. GC-MS analy-
ses were performed using a series PerkinElmer Clarus GC
coupled with Perkin Elmer Clarus MS quadrupole analyzer
mass spectrometer at eV. Fused silica capillary column type
was DB- ( m ×. mm i.d.) and the oven temperature
was programmed at –∘Catarateof
∘C/min using
helium as carrier gas; injector and detector (FID) tempera-
tures were both maintained at ∘C. e constituents were
identied by matching their eV mass spectra with NIST
Wiley databases and user generated mass spectral libraries,
by comparing their corresponding retention time (𝑡𝑅)on
the chromatogram, by interpretation of the mass spectra
fragmentation data, and by comparison of the mass spectra
obtained with those of the published literature data [,,–
].
3. Results and Discussion
3.1. Chemical Compositions of the Essential Oils. e essential
oils of the resins of B. neglecta,B. rivae,andB. papyrifera were
obtained by hydrodistillation. e essential oils obtained as
such were analyzed by GC and their corresponding results
(chromatograms) are presented subsequently in Figures ,,
and and Tables ,,and.
56 7 8 9 10111213141516
0.0
0.2
0.4
0.6
Intensity (a.u.)
Retention time (min)
Wach i l e
Mega
Dubuluk
F : Comparison of chromatogram of essential oil of three B.
neglecta resins.
67 8 9 1011121314
0.0
0.1
0.2
0.3
0.4
Intensity (a.u.)
Retention time (min)
Dolo Odo
Filtu
Chereti
F : Comparison of chromatogram of essential oil of three B.
rivae resins.
3.2. Chemical Composition of the Methanol Extracts. Frank-
incense is a complex mixture of essential oils and alcohol
soluble resins, and the remaining are water-soluble gums
whicharepolysaccharides.Inthisstudy,chemicalcompo-
sitions of methanol extract of resins of the three Boswellia
species were investigated by GC-MS and their corresponding
chromatograms are presented in Figures –.
e chromatogram (Figure ) for the methanol extract of
resin of B. neglecta collected from Wachile area revealed one
monoterpene: 𝛼-pinene and three triterpenoic constituents:
𝛽-amyrenone, 𝛼-amyrenone, and 𝛼-amyrin. e rst peak
which appeared at .min was identied as 𝛼-pinene.
e components having retention time of ., ., and
. min were identied as 𝛽-amyrenone, 𝛼-amyrenone,
and 𝛼-amyrin, respectively. e chromatographic prole
(Figure ) of the methanol extract of B.rivae resin collected
ISRN Analytical Chemistry
67 8 9 10 11 12 13 14 15 16 17 18 19 20
0.00
0.05
0.10
0.15
0.20
0.25
Intensity (a.u.)
Retention time (min)
Metema
Metekel
Humera
F : Comparison of chromatogram of essential oil of three of
B.papyrifera resins.
T : Chemical compositions (%) of essential oils of three of
B.rivae resins.
Retention
time (min) Components Dolo Odo Filtu Chereti∗
%%%
. 𝛼-ujene . . .
. 𝛼-Pinene . . .
. o-Cymene . . .
. Δ--Carene . . .
. p-Cymene . . .
. Limonene . . .
. 𝛼-Campholene aldehyde . . .
. trans-Verbenol . . .
∗Components identied from the essential oil of same sample reported in
our previous study [].
T : Chemical compositions (%) of essential oils of three of
B.papyrifera resins.
Retention
time (min) Components Metekel Metema Humera∗
%%%
. 𝛼-Pinene . . .
. Limonene . . .
. n-Octanol . . .
. Linalool . . .
. Octyl acetate . . .
. Geraniol . . .
∗Components identied from the essential oil of same sample reported in
our previous study [].
from Chereti area evidenced the presence of one monoter-
pene: 𝛼-pinene and two triterpenoic constituents: 𝛽-amyrin
and 𝛼-amyrin. e components which had retention time
of ., . and . min were identied as 𝛼-pinene, 𝛽-
amyrin and 𝛼-amyrin, respectively.
100
0
(%)
6.00 11.00 16.00 21.00 26.00 31.00 36.00
Time
6.33
28.88 36.78
38.20
38.93
F : Chromatogram of methanol extract of B. neglecta resin
ofWachile origin.
6.38
27.99
37.47
38.13
38.88
100
0
(%)
6.00 11.00 16.00 21.00 26.00 31.00 36.00
Time
F : Chromatogram of methanol extract of B. rivae resin of
Chereti origin.
Another species studied was B. papyrifera,theresinof
which was collected from northern part of Ethiopia (Metema,
Metekel, and Humera areas). e methanol extract of B.
papyrifera resinwasfoundtobecomposingonediter-
pene and three triterpenes. e chromatogram (Figure )
of methanol extract of B. papyrifera resin collected from
Humera area revealed components with retention time
of ., ., ., and . min which were identi-
ed as incensyl acetate, 𝛽-amyrenone, 𝛽-amyrin, and 𝛼-
amyrin, respectively. For those, collected from Metekel area,
the chromatographic prole (Figure )revealedcompo-
nents with retention time of ., ., ., ., and
. min and were recognized as verticilla-(),,-triene,
incensole, incensyl acetate, -noroleana-,-diene, and -
norursa-,-diene, respectively, whereas the chromatogram
(Figure ) of methanol extract of B. papyrifera resin collected
from Metema area revealed components with retention time
of . and . min and these were identied as incensyl
acetate and 𝛼-boswellic acid, respectively.
3.3. Interpretation of Mass Spectra of the Identied Compo-
nents. In the present study, the identied components were
conrmed by interpretation of their mass spectra (MS).
ISRN Analytical Chemistry
100
(%)
20.87
24.83
24.95
26.25
27.03
3.00 7.00 11.00 15.00 19.00 23.00 27.00 31.00
Time
0
F : Chromatogram of methanol extract of B. papyrifera resin
of Humera origin.
100
0
(%)
6.00 11.00 16.00 21.00 26.00 31.00 36.00
Time
20.41
21.87
21.78
30.47
31.28
37.18
F : Chromatogram of methanol extract of B. papyrifera resin
of Metekel origin.
Some chemical compositions of methanol extract of frank-
incense samples examined were found to be very similar,
and the identied compounds have already been reported
fromsimilarandotherspeciesofBoswellia as well as in
other plants. Most of them are triterpenes which belong to
the oleanane or ursane series and are characterized by a
base peak at 𝑚/𝑧 = 218. Hence, to avoid confusion on
interpreting mass spectra of terpenes identied, analytical
review on the base peaks, main fragments, and fragmentation
patterns of the skeleton of terpenes identied was presented.
e fragmentation patterns of pentacyclic triterpenoid com-
pounds having a double bond at position (-oleanane
type and -ursane type) show similar fragment at 𝑚/𝑧 =
218 which is formed by Retro-Diels-Alder (RDA) fragment.
e MS of -ursane type triterpene resembles that of -
oleanene type. e compounds have been identied by their
retention time and mass spectral comparison. -Ursane and
-oleanene type pentacyclic triterpenes undergo primarily
RDA fragmentation. e RDA fragment including rings D
and E of both types of compounds altered only in the
position of a single methyl group at C-. In -ursane type
triterpenes C-, C-, and C- were occupied with methyl
groups whereas in -oleanene types C- was occupied
with two methyl groups. e retention time is inuenced
100
(%)
3.00 7.00 11.00 15.00 19.00 23.00 27.00 31.00
Time
0
19.54
20.90
26.44
29.53
F : Chromatogram of methanol extract of B. papyrifera resin
of Metema origin.
by the number and the type of functional groups present
and generally increases with increasing molecular weight of
triterpenes []. Depending on the absolute conguration,
𝛼-conguration (ursane type) was found to have longer
retention time than 𝛽-conguration (oleanane type) due to
shi of the CH3group from an axial conformation at C-
in oleanane structures to an equatorial conformation at C-
in ursane type compounds which caused an increase in the
planarity of the molecules that related to their retention time
[]. Comparison in their MS between peaks at 𝑚/𝑧 = 203 and
𝑚/𝑧 = 189 allows making the distinction between oleanane
andursanetypetriterpenes.Butalossofamethylgroup
produced the signal at 𝑚/𝑧 = 203 for both compounds.
However, the later fragment was more abundant in the mass
spectrum of oleanane type than ursane type. is happens
becauseofmorestabletertiarycarbeniumionformedin
oleanane type of triterpenes than the secondary carbenium
ionformedinursanetypeoftriterpenesasaresultofmethyl
cleavage []. As reported by Mathe et al. [], for oleanene
derivative, the fragment ion at 𝑚/𝑧 = 203 is more intense
than the peak at 𝑚/𝑧 = 189, while for identical ursane
derivatives both peaks have almost similar intensities in their
mass spectra.
Accordingly, the two components identied, in this study,
as 𝛽-amyrenone and 𝛼-amyrenone showed molecular ion
peaks (M+)at𝑚/𝑧 = 424 in their mass spectrum which is
consistent with molecular formula of C30H48O. However, the
abundant ions at 𝑚/𝑧, , , , and are typical for
the fragmentation of 𝛽-amyrenone and 𝛼-amyrenone. Both
compounds showed similar MS and their mass spectrum
shows a typical fragmentation pattern of ursane and oleanane
type triterpenes. Finally, identication was made by compar-
ing their retention time and intensity of signal at 𝑚/𝑧 = 189
and 𝑚/𝑧 = 203. erefore, the component which had shorter
retention time and more intense peak at 𝑚/𝑧 = 203 was
assigned as 𝛽-amyrenone and 𝛼-amyrenone was found to
be compound with longer retention time and similar peak
signal intensity at 𝑚/𝑧 = 189and . Possible fragmentation
pattern for 𝛽-amyrenone is presented in Figure .
Compounds identied as 𝛽-amyrin and 𝛼-amyrin pro-
duced molecular ion peak signal at 𝑚/𝑧 = 426 in their mass
ISRN Analytical Chemistry
H
H
OH
H
O
−CH3m/z = 409
m/z = 424
RDA
m/z = 218
−CH3
m/z = 203
−CH2CH3
m/z = 189
Om/z = 205
∙+
CH2
F : Possible fragmentation patterns for 𝛽-amyrenone.
m/z = 426
m/z = 411
m/z = 218
m/z = 203
m/z = 189
m/z = 393
m/z = 207
m/z = 409
H
H
H
H
−CH3
−CH3
−OH
−H2O
OH
OH
CH2
RDA
∙+
F : Possible fragmentation patterns for 𝛼-amyrin.
spectrum that corresponded to an elemental composition
of C30H50O. Similar to that of amyrenone derivative, they
produced similar MS. e dierence of two in the mass
unit indicates exchange of a keto group for a hydroxy group
which leads to an increase of molecular weight and polarity.
As a consequence, this compound had longer retention
time than derivative of amyrenone. 𝛼-and𝛽-Amyrin were
dierentiated by examination of the relative intensities of
the peaks at 𝑚/𝑧 = 189 and . 𝛽-Amyr in had hi gh
intensity peak at 𝑚/𝑧 = 203 which is around twice that
of 𝑚/𝑧 = 189 peak, while 𝛼-amyrin spectra show similar
intensity for both peaks which was consistent with the earlier
results []. Generally, the 𝛼-amyrin triterpene possesses a
basicskeletonoftheursanetypeandthe𝛽-amyrin triterpene
possesses a basic skeleton of the oleanane type, and the only
dierence between them is the methyl position in the E-ring.
Accordingly, the possible fragmentation pattern for 𝛼-amyrin
is shown in Figure .
Two nortriterpenes (-norursa-,-diene and -
noroleana-,-diene) identied from resin of B. papyrifera
produced molecular ion (M+)peaksignalat𝑚/𝑧 = 394
intheirmassspectrumthatcorrespondedtoanelemental
composition of C29H46.Bothcompoundsshowedsimilar
m/z = 394
m/z = 218
m/z = 203
m/z = 175
m/z = 161
−CH3
−CH3
H
H
H
+∙
+
F : Possible fragmentation patterns for -norursa-,-
diene [].
∙+
m/z = 306 m/z = 263
O
OH OH
O
−C3H7
+
F : Possible fragmentation patterns of incensole.
MS and their mass spectrum showed a similar fragmentation
pattern to ursane and oleanane type triterpenes having a
double bond at position . For both compounds, the RDA
reaction revealed a fragment ion signal at 𝑚/𝑧 = 218 and a
further methyl cleavage from this fragment formed signal at
𝑚/𝑧 = 203. But the intensity of the fragment ion signal at
𝑚/𝑧 = 203 produced by -norursa-,-diene was found
to be greater almost by % than that produced by -
noroleana-,-diene because the former is ursane derivative
of the latter. As such, the two nortriterpenes were identied.
Possible fragmentation pattern for -norursa-,-diene is
given in Figure .
e compound which produced molecular ion peak
signal at (M+)𝑚/𝑧 = 306 in its mass spectrum corresponded
to an elemental composition of C20H34O2.Cleavageofthe
isopropyl group from molecular ion at 𝑚/𝑧 = 306 produced
fragment with an elemental composition of C17H27O2which
gave rise to peak at 𝑚/𝑧 = 263. is diterpene is found to be
incensole. Possible fragmentation pattern for incensole was
given in Figure .
Another compound identied in this study produced
molecular ion peaks signal at (M+)𝑚/𝑧 = 348 in its mass
spectrum that corresponded to an elemental composition of
C22H36O3.erearepeaksthatappearedinthemassspectra
at , , and . Elimination of the isopropyl group from
molecular ion at 𝑚/𝑧 = 348 produced fragment with an
elemental composition of C19H29O3whichgaverisetopeak
at 𝑚/𝑧 = 305, whereas the fragment ion signal 𝑚/𝑧 = 288
is produced by cleavage of acetic acid group from molecular
ion (M+). Fragment ion peak signal at 𝑚/𝑧 = 245 could be
produced by loss of an isopropyl group from 𝑚/𝑧 = 288.
ISRN Analytical Chemistry
O
O
O
O
O
O
OO
−C3H7
−C3H7
+
+
+
+
m/z = 348 m/z = 305
m/z = 288
m/z = 245
−CH3COOH
−CH3COOH
F : Possible fragmentation patterns for incensyl acetate [].
is compound was identied as incensyl acetate. Possible
fragmentation pattern for incensyl acetate was presented in
Figure .
Another pentacyclic triterpene identied from resin of B.
papyrifera produced molecular ion peak signal at (M+)𝑚/𝑧 =
456 in its mass spectrum that corresponded to an elemental
composition of C30H48O3.Whenmethylgroupislostfrom
molecular ion peak signal (𝑚/𝑧 = 456)fragmentwithan
elemental composition of C29H45O3is produced which gave
rise to peak at 𝑚/𝑧 = 441.eRDAreactionproducedpeak
signal at 𝑚/𝑧 = 218which produces peak signal at 𝑚/𝑧 = 203
by loss of methyl group. ese fragmentations hold true for
both 𝛽-boswellic acid and 𝛼-boswellic acid. However, the
fragment at 𝑚/𝑧 = 203 was more abundant in the mass
spectrum of 𝛼-boswellic acid than 𝛽-boswellic acid due to the
more stable ion formed from 𝛼-boswellic acid []. Possible
fragmentation pattern for 𝛼-boswellic acid was presented in
Figure .
Another diterpene was also identied from methanol
extract of B. papyrifera by GC-MS. e compound produced
molecular ion (M+)𝑚/𝑧 = 272 initsmassspectrum
that corresponded to an elemental composition of C20H32.
e fragmentation mechanism shows initially cleavage of
allyl methyl group from the molecular ion which further
undergoes RDA reaction in the cyclohexene ring to produce
peak signal at 𝑚/𝑧 = 257 representing the base peak in its
mass spectra. Accordingly, possible fragmentation pattern for
verticilla-(),,-triene was presented in Figure .
3.4. Comparison of Chemical Compositions of the ree
Boswellia Species. As the concern of this study was com-
parative chemical investigation on resins of three dierent
Boswellia species, the essential oil and methanol extract of
B. papyrifera,B. neglecta,andB. rivae resin were analysed
by GC and GC-MS. is led to the identication of the
chemotaxonomical markers for each species. e GC investi-
gationsoftheessentialoilsofB. papyrifera,B. neglecta,and
B. rivae resin showed that these oils were composed of a
number of monoterpenoic constituents. But investigation on
the methanol extract of three Boswellia species showed that
they are composed of diterpenes and triterpenes. However,
B. papyrifera was identiable by its diterpenoic and nortriter-
penoic constituents.
e essential oil of B. papyrifera was found to be
dominated by octyl acetate (.–.%) followed by high
content of n-octanol (.–.%), linalool (.–.%), and
others monoterpenes. In our previous study, preliminary data
obtained by investigation on resin samples of three types of
Boswellia species collected from very limited area revealed
similar results with the current study []. In the present
study, except for their composition, similar constituents
were identied from the essential oils of the three Boswellia
species []. Surprisingly, similar components with identical
percent composition were obtained for samples collected
from the same areas with samples collected for preliminary
investigation in our previous study. e result obtained in
this study is also consistent with result obtained by other
authors: .% according to Hamm et al. [], .% by
Camarda et al. [], and % by Dekebo et al. []. Assefa
et al. []alsoreportedoctylacetateasmajorcomponent
of B. papyrifera. In addition, incensyl acetate was found
to be dominant component in methanol extract of resins
of B. papyrifera. B. papyrifera was the only species that
was found to contain octyl acetate, n-octanol, linalool, and
geraniol and they are chemotaxonomical markers for this
species. Octyl acetate and n-octanol were reported as they
areresponsibleforacridodouroftheresin[]. Oils from
both B. neglecta and B. rivae were predominantly composed
of 𝛼-pinene. B. neglecta was found to be rich in 𝛼-pinene
(.–.%) followed by terpinen--ol (.–.%) and 𝛼-
thujene (.–.%). Similarly, B. rivae was predominated by
𝛼-pinene(.–.%)followedbyp-cymene(.–.%)and
limonene (.–.%).
e methanol extract of the Boswellia species resin sam-
ples had considerable importance because the resin portion
(di-and tri-terpenes) of frankincense is alcohol soluble. e
boswellic acid was identied in frankincense samples as
pentacyclic triterpenoic acids which follow the ursane and
oleanane basic skeletons. e presence of diterpenoic (incen-
sole, incensyl acetate, and verticilla-(),,-triene), nor-
triterpenes (-noroleana-,-diene and -norursa-,-
diene), and pentacyclic triterpene acid (𝛼-boswellic acid)
constituents turned out to be a chemotaxonomical marker
for B. papyrifera. Methanol extract of B. rivae and B. neglecta
was also found to contain monoterpene (𝛼-pinene) and triter-
penes, namely, 𝛽-amyrin, 𝛼-amyrin, 𝛽-amyrenone, and 𝛼-
amyrenone. Most importantly, two monoterpenes (p-cymene
and 𝛼-thujene) were found to be characteristic for the B.
rivae and B. neglecta. Terpinen--ol and verbenone were
two constituents identied as chemotaxonomical markers
of essential oil of B. neglecta, whereas transverbenol and
𝛼-campholene aldehyde are two monoterpenes which were
identied only from essential oil of B. rivae and hence are
characteristic for this species.
4. Conclusion
In this study, essential oils and methanol extract
of B. papyrifera,B.neglecta,andB. rivae were investigated.
ISRN Analytical Chemistry
H
H
H
RDA
∙
−CH3
−CH3
m/z = 441
m/z = 203
m/z = 456
m/z = 218
HOOC
HO
+
F : Possible fragmentation patterns of 𝛼-boswellic acid.
HH
RDA
−CH3−CH3
m/z = 272 m/z = 257m/z = 257
+
∙+
F : Possible fragmentation mechanism for verticilla-(),
,-triene [].
e investigations which were carried out by GC and GC-MS
led to the identication of the chemotaxonomical markers for
each species. Some dierences in their chemical constituents
were observed and are chemotaxonomical markers for each
species.
e chemical investigationsperformed on three Boswellia
species show that they consist of high number of monoter-
penoic constituents and their methanol extract is composed
of diterpenes and triterpenes. e presence of octyl acetate, n-
octanol, and incensyl acetate provided an immediate recog-
nition of B. papyrifera from the other two species. But still it
is dicult to conclude that there is profound chemical quality
variation between B. papyrifera and the other two species
(B.neglecta and B.rivae) that makes them not of export
standard even though further study is required. However,
a further investigation is crucial especially to extract some
chemical information regarding the constituents which might
be reasonable for their dierence in color and physical
appearance.
Conflict of Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
Acknowledgments
e authors would like to thank Center for International
Forestry Research, Ethiopia Oce Addis Ababa; the Central
Laboratory of the Haramaya University; the Department of
Chemistry of Addis Ababa University; Department of Chem-
istry of Indian Institute of Technology; and the Ethiopian
Natural Gum and Marketing Enterprise for their collabora-
tions during the research work that led to the production
of this paper. Most of the expenses of this research work
were funded by the Austrian Development Agency through
CIFOR’s Community Forestry Project in Ethiopia (Project
no. /). e authors are thankful to the people and
Government of Austria.
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