Chemistry of khusinol: A sesquiterpenoid isolated from vetiver oil

Article abstract of DOI:10.14233/ajchem.2016.20017

Vetiver essential oil was obtained from roots of Vetiveria zizanioides by hydrodistillation method. The unique feature of oil is the presence of antipodal terpenoids of which khusinol may be mentioned as representative. Khusinol, a white crystalline solid (m.p. 87°C) isolated by column chromatography from vetiver oil was subjected to chemical transformations to afford khusinol oxides, cadina-4α,10β-diol and trans-calamenene derivatives. The structures of khusinol and its derivatives were elucidated using spectroscopic techniques.

Full text of DOI:10.14233/ajchem.2016.20017

Asian Journal of Chemistry; Vol. 28, No. 11 (2016), 2461-2463
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.20017
Chemistry of Khusinol: A Sesquiterpenoid Isolated from Vetiver Oil
*
URVASHI BHARDWAJ, K.K. CHAHAL and RAMANDEEP KAUR
Department of Chemistry, Punjab Agricultural University, Ludhiana-141 004, India
*Corresponding author: E-mail: drkkchahal@pau.edu
Received: 11 April 2016; Accepted: 30 June 2016;
Published online: 10 August 2016;
AJC-18018
Vetiver essential oil was obtained from roots of Vetiveria zizanioides by hydrodistillation method. The unique feature of oil is the presence
of antipodal terpenoids of which khusinol may be mentioned as representative. Khusinol, a white crystalline solid (m.p. 87 °C) isolated
by column chromatography from vetiver oil was subjected to chemical transformations to afford khusinol oxides, cadina-4α,10β-diol and
trans-calamenene derivatives. The structures of khusinol and its derivatives were elucidated using spectroscopic techniques.
Keywords: Vetiver oil, Sesquiterpenoid, Khusinol, Cadina-4α,10β-diol, trans-Calamenene.
solution of semicarbazide hydrochloride (20 g) in water (200
mL) and ethanol (40 mL). The mixture was kept at 0 °C for 24
h with regular shaking. The semicarbazone was obtained in
the form of yellow cake. The crude semicarbazone (30 g)
obtained was chromatographed as such over silica gel (1 kg).
Elution with petroleum ether afforded a complicated mixture
of hydrocarbons (5 g) as evidenced by thin layer chromato-
graphy. Elution with benzene afforded a fraction containing
mixture of compounds from which khusinol was isolated using
extensive column chromatography.
Isolation of khusinol: Khusinol rich fraction of the oil
(10 g) was subjected to column chromatography over silica
gel (600 g). The column was eluted using petroleum ether:
CH2Cl2 in order of increasing polarity. Khusinol (1, 2.5 g), a
white crystalline solid with m.p. 87 °C was isolated using
petroleum ether:CH2Cl2 (20 %) as eluting solvent.
Reaction of khusinol with perbenzoic acid: A solution
of khusinol (1.0 g) in CH3Cl (20 mL) was treated with 1 mol
of perbenzoic acid. The reaction was allowed to complete and
checked by TLC.After the completion of reaction, the reaction
mixture was diluted with water, washed with sodium thiosulfate,
NaHCO3 solution, finally with water and then dried over
anhydrous Na2SO4. Evaporation of solvent afforded a thick
yellow liquid (0.80 g). The crystalline compound (2, 0.5 g)
with m.p. 113 °C and (3, 0.2 g) with m.p. 82 °C were obtained
by chromatography over silica gel using petroleum ether and
CH2Cl2 as solvents of increasing polarity. However, khusinol
on treatment with excess of perbenzoic acid yielded a pure
crystalline compound (4) with m.p. 105 °C.
INTRODUCTION
Vetiveria zizanioides L. commonly known as khus grass
belonging to family poaceae is the major source of well known
essential oil obtained by hydrodistillation of the fragrant roots.
It is only grass cultivated worldwide for the root essential oil
used in perfumery and aromatherapy [1-3]. It grows abundantly
as a wild cultivated and semi wild plant in several tropical
countries of Asia, Africa and Australia. Khusimol, α-vetivone
and β-vetivone are the major constituents of vetiver oil extrac-
ted throughout the world [4-8]. The vetiver oil of commerce
coming from Jawa and Reunion islands is dextrorotatory in
nature while all the north Indian oil are laevorotatory. One of
the important points of difference between highly priced
variety of north Indian (Bharatpur variety) and the oil coming
from foreign countries is the absence of important terpenoid
vetivone in Indian oil [9,10]. The extensive chemical studies
of north Indian vetiver oil revealed the presence of several
sesquiterpenoids like khusinol, khusol, khusimol, khusilic acid
and khusilal. Isolation of khusinol from vetiver oil and its
transformation products are reported.
EXPERIMENTAL
Perkin Elmer, Model RX-1 FT-IR spectrophotometer.
1H NMR (400 MHz) and 13C NMR (100 MHz): Bruker AC
(400 MHz) or mentioned otherwise as solutions (in CDCl3)
using TMS as an internal reference.
Fractionation of vetiver oil:Vetiver oil (100 g) was frac-
tionated by chromatography over silica gel (1.5 kg) into three
fractions using viz. petroleum ether, benzene and acetone as
eluting solvents. Benzene fraction was further mixed with a
Reaction of khusinol with t-butyl hydroperoxide in
presence of vanadium oxyacetylacetonate: To a solution of

2462 Bhardwaj et al.
Asian J. Chem.
khusinol (1 g) in CH2Cl2 (20 mL) was added VO(acac)2 (5 mg)
and the green reaction mixture was stirred at room temperature.
A solution of t-butyl hydroperoxide (TBHP) (3 mL, 70 %)
was added drop-wise. The colour of reaction mixture changed
to brown. It was further stirred for 15 min at the same tempe-
rature. The reaction was allowed to stand for 24 h. After comp-
letion of reaction, mixture was diluted with water, extracted
with CH2Cl2 and dried over anhydrous Na2SO4. Evaporation
of the solvent under reduced pressure gave a thick liquid yellow
liquid (0.82 g) chromatographed over silica gel yielded the
product (2, 0.7 g) with m.p. 113 °C.
Reaction of khusinol with iodine: In a round bottom
flask, khusinol (1, 0.5 g) in benzene (20 mL) was refluxed
with catalytic amount of metallic iodine for 6 h. The progress
of reaction was monitored by TLC. After the completion of
reaction, the reaction mixture was diluted with water and
extracted with diethyl ether. The diethyl ether layer was washed
over sodium thiosulfate to remove iodine and dried over sodium
sulfate. Removal of solvent gave a single product b.p. 105 °C
(8, 0.4 g). Structure of khusinol (1) and its derivatives (2-8)
1
were identified on the basis of IR, H NMR and 13C NMR
spectral data (Table-1).
Reaction of khusinol with N-bromosuccinimide/NaOH:
To a solution of khusinol (1 g) in acetone (4 mL) and N-bromo-
succinimide (0.98 g) in water (1 mL), 0.04 g of silica was
added and the reaction mixture was stirred at room temperature.
To the bromodydrin of khusinol formed, aqueous NaOH was
added with constant stirring. At the end of reaction, mixture
was diluted with 50 mL of water and extracted with diethyl
ether, washed with water and dried over anhydrous Na2SO4.
Evaporation of the solvent under reduced pressure gave a
mixture of two products 5 and 6 separated by chromatography
over silica gel.
Reaction of khusinol with mercuric acetate: To a solution
of khusinol (0.5 g) in 1 mL of water and 2 mL of tetrahydro-
furan, mercuric acetate (300 mg) was added in a round bottom
flask. The reaction mixture was refluxed for 0.5 h and 10 mL
each of 20 % aqueous sodium hydroxide and 3 N NaBH4 were
added with constant stiring. The reaction mixture was cooled
down to room temperature and mercury was allowed to
coalesce. The upper tetrahydrofuran layer was extracted with
dichloromethane (3 × 25 mL) and dried over anhydrous
Na2SO4. The evaporation of solvent afforded a white crystalline
compound (7) with m.p. 210 °C.
RESULTS AND DISCUSSION
North Indian vetiver oil obtained from S.H. Kelkar &
Company, Mumbai. was yellowish-brown in colour having
strong smell. The pH, specific gravity and refractive index of
vetiver oil were 4.0, 1.004 and 1.494, respectively. The essential
oil was soluble in acetone, benzene, methanol, dichloromethane
and insoluble in water. Khusinol (m.p. 87 °C) was isolated by
column chromatography and chemical modifications of two
double bonds present in khusinol are reported. The derivatives
of khusinol (1) synthesized via reaction with perbenzoic
acid,vanadium oxyacetylacetonate/t-butyl hydroperoxide, N-
bromosuccinimide, mercuric acetate/NaBH4, hydrochloric gas
and iodine-benzene afforded khusinol mono epoxides (2, 3,
5), khusinol diepoxides (4, 6), cadina-4α,10β-diol (7) and
(-)-trans-calamenene (8) as products, respectively.
Khusinol on treatment with VO(acac)2/t-butyl hydro-
peroxide resulted in the formation of monoepoxide (2) similar
in all aspects with the monoepoxide formed with perbenzoic
acid. Vanadium oxyacetylacetonateis a stereoselective reagent
known for epoxidation of allylic or homoallylic alcohols. Thus
the epoxide formed will be of same stereochemistry as that of
the hydroxyl group present at homoallylic position. However,
indirect epoxidation of khusinol with 1 mol of N-bromo-
succinimide and sodium hydroxide system yielded a mono-
epoxide (2) and diepoxide (5) with stereochemistry opposite
to that formed with perbenzoic acid and VO(acac)2/t-butyl
hydroperoxide. Reaction with hydrochloric gas and iodine
resulted in aromatization of ring (8).
Reaction of khusinol with hydrochloric gas: A slow stream
of dry hydrochloric acid gas was bubbled through a solution of
khusinol (0.5 g) in diethyl ether (20 mL) at 0 °C till the solution
was saturated. The reaction mixture was diluted with water and
thoroughly extracted with diethyl ether (3 × 50 mL). The mixture
was finally dried over sodium sulfate. Evaporation of the solvent
yielded a thick brownish liquid with b.p. 105 °C (8, 0.46 g).
TABLE-1
SPECTROSCOPIC DATA OF KHUSINOL (1) AND ITS DERIVATIVES (2-8)
1H NMR
13C NMR
IR (νmax, cm-1)
Compounds
OH
H
52.37 (C1), 67.26 (C2), 38.46 (C3),
132.21 (C4), 121.54 (C5), 45.49
(C6), 47.28 (C7), 27.33 (C8), 37.29
(C9), 103.77 (C10), 26.69 (C11),
21.56 (C12), 15.08 (C13), 150.95
(C14) and 23.74 (C15)
0.67 (d, 3H, J = 6.96 Hz, C12), 0.85
(d, 3H, J = 6.96 Hz, C13), 1.63 (s,
3H, C15), 3.98-4.04 (m, 1H, C2),
4.80 and 4.71 (d each, 1H, J = 0.5
Hz, C14) and 5.47 (brs, 1H, C5s)
3389, 2964, 2872, 2850, 1650,
1675, 1446, 1074 and 908
H
(1)
OH
O
0.76 (3H, d, J = 6.92 Hz, C12),
0.93 (3H, d, J = 6.92 Hz, C13),
1.7 (3H, s, C15), 2.66 (1H, d,
J = 3.52 Hz, C14), 3.18 (1H, d,
46.82 (C1), 68.45 (C2), 38.83 (C3),
132.69 (C4), 120.24 (C5),
42.27(C6), 46.17 (C7), 26.52 (C8),
35.13 (C9), 64.85 (C10), 23.48
3460, 3064, 2958, 2930, 2870,
1446, 1069 and 1047
J = 3.2 Hz C14), 3.69-3.75 (1H, (C11), 21.44 (C12), 14.93 (C13),
m, C2) and 5.44 (1H, brs, C5) 49.94 (C14) and 23.70 (C15)
(2)

Vol. 28, No. 11 (2016)
Chemistry of Khusinol: A Sesquiterpenoid Isolated from Vetiver Oil 2463
1H NMR
13C NMR
IR (νmax, cm-1)
Compounds
OH
0.69 (3H, d, J = 5.28 Hz, C12),
0.55 (3H, d, J = 5.28 Hz, C13),
1.07 (3H, s, C15), 2.69 (1H, d,
J = 11.52 Hz, C5), 3.52-3.62
44.20 (C1), 60.00 (C2), 37.24 (C3),
46.85 (C4), 66.01 (C5), 37.00 (C6),
44.39 (C7), 26.73 (C8), 29.66 (C9),
150.54 (C10), 27.26 (C11), 21.36
3462, 2958, 2940, 2865, 1422,
1069 and 1047
(m, 1H, C2), 4.45 and 4.59 (1H, d, (C12), 15.26 (C13), 104.73 (C14)
O
J = 0.5 Hz, C14)
and 24.52 (C15)
(3)
OH
O
0.84 (3H, d, J = 6.8 Hz, C12),
0.99 (3H, d, J = 3.2 Hz, C13),
1.34 (3H, s, C15), 2.64 (1H, d,
J = 4Hz, C14), 2.98 (1H, s, C5),
3.13(1H, d, J = 4Hz) and 3.46-
3.52 (1H, m, C2)
43.54 (C1), 65.01 (C2), 41.26 (C3),
57.08 (C4), 59.42 (C5), 26.61 (C6),
41.53 (C7), 24.49 (C8), 37.51 (C9),
67.63 (C10), 34.95 (C11), 15.28
(C12), 21.37 (C13), 49.65 (C14) and
23.53 (C15)
3436, 2953, 2927, 2872, 1419,
1070 and 1043
O
(4)
OH
O
0.77 (3H, d, J = 6.96 Hz, C12),
0.95 (3H, d, J = 6.96 Hz, C13),
1.68 (3H, s, C15), 2.68 (1H, d, J
= 3.6 Hz, C14), 3.19 (1H, d, J =
3.2 Hz, C10), 3.69-3.76 (1H, m,
C2) and 5.45(1H, brs, C5)
46.82 (C1), 68.50 (C2), 38.84 (C3),
132.77 (C4), 120.27 (C5), 42.30
(C6), 46.17 (C7), 26.55 (C8), 35.15
(C9), 64.95 (C10), 23.52 (C11),
21.47 (C12), 14.95 (C13), 50.03
(C14) and 23.72 (C15)
3430, 2966, 2927, 2908, 2861,
1425, 1047 and 875
(5)
OH
O
0.85 (3H, dd, J = 6.92 Hz, 46.45 (C1), 64.71 (C2), 42.68
C12), 0.98 (3H, dd, J = 6.96 (C3), 59.21 (C4), 59.45 (C5),
Hz, C13), 1.32 (3H, s, C15), 2.63 26.60 (C6), 43.89 (C7), 23.81
(1H, d, J = 3.52 Hz, C14), 2.94 (C8), 38.41 (C9), 66.71 (C10),
(1H, s, C5), 3.09 (1H, d, J = 34.89 (C11), 15.23 (C12), 21.47
3.0 Hz, C14) and 3.50-3.53 (1H, (C13), 49.86 (C14) and 23.27
3431, 2957, 2926, 2870, 1427,
1046 and 835.
O
m, C2)
(C15)
(6)
OH
OH
54.17 (C1), 68.82 (C2), 48.02
(C3), 70.80 (C4), 39.67 (C5),
15.16 (C6), 45.50 (C7), 21.00
(C8), 42.72 (C9), 74.08 (C10),
29.72 (C11), 21.51 (C12),
26.25(C13), 33.66 (C14), and
31.99 (C15)
0.75 (3H, d, J = 6.88Hz, C12),
0.88 (3H, d, J = 7.20 Hz, C13),
1.22 (3H, s, C4) and 1.26 (3H,
s, C15)
3435, 2875, 1427, 1230 and 835
OH
(7)
140.04 (C1), 127.00 (C2),
126.43 (C3), 134.62 (C4),
128.94 (C5), 140.23 (C6),
44.05 (C7), 22.55 (C8), 31.11
(C9), 32.17 (C10), 32.76 (C11),
21.37 (C12), 17.57(C13), 21.52
(C14) and 21.76 (C15)
0.97 (3H, d, J = 6.96 Hz, C12),
1.26 (3H, d, J = 6.96 Hz, C13),
1.55 (3H, d, J = 6.88 Hz), 2.55
(3H, s, C15) and 7.18- 7.38 (3H, m)
2957, 2928, 2869, 1613,
1498, 1462 and 814
(8)
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Am.-Eur. J. Agric. Environ. Sci., 10, 458 (2011).
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