Chemical study of the essential oil of Cyperus rotundus

Article abstract of DOI:10.1016/S0031-9422(01)00301-6

Minor constituents of the essential oil of Cyperus rotundus have been investigated. The three new sesquiterpene hydrocarbons (-)-isorotundene, (-)-cypera-2,4(15)-diene, (-)-norrotundene and the ketone (+)-cyperadione were isolated and their structures elu

Full text of DOI:10.1016/S0031-9422(01)00301-6

Phytochemistry 58 (2001) 799–810
www.elsevier.com/locate/phytochem
Chemical study of the essential oil of Cyperus rotundus
Mesmin Mekem Sonwa, Wilfried A. Konig*
Institut fur Organische Chemie, Universitat Hamburg, D-20146 Hamburg Germany
¨
¨
Received 4April 2001; received in revised form 25 June 2001
Abstract
Minor constituents of the essential oil of Cyperus rotundus have been investigated. The three new sesquiterpene hydrocarbons
(ꢀ)-isorotundene, (ꢀ)-cypera-2,4(15)-diene, (ꢀ)-norrotundene and the ketone (+)-cyperadione were isolated and their structures
elucidated. The absolute configuration of (ꢀ)-rotundene was derived by chemical correlation and enantioselective gas chromato-
graphy. # 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Cyperus rotundus; Cyperaceae; Sesquiterpenes; Norsesquiterpene; (ꢀ)-Isorotundene; (ꢀ)-Cypera-2,4(15)-diene; (ꢀ)-Norrotundene; (+)-
Cyperadione
1. Introduction
(17) by comparison with a spectral library established
under identical experimental conditions (Joulain and
Konig, 1998), cyperotundone (18) (Hikino et al., 1966),
mustakone (19) (Nyasse et al., 1988), cyperol (20)
(Hikino et al., 1967), isocyperol (21) (Hikino et al.,
1967) and a-cyperone (22) (Howe and McQuillin, 1955;
Haaksma et al., 1992) (Fig. 1). However, several minor
compounds could not be identified by their mass spectra
and had to be isolated for further investigations. Con-
sequently, the essential oil was first separated by silica
chromatography into a hydrocarbon fraction and a
more polar oxygenated fraction. The hydrocarbon frac-
tion was further separated by column chromatography,
TLC over silver nitrate precoated silica and preparative
GC. This resulted in the isolation and characterization
of isorotundene (23), cypera-2,4(15)-diene (24) and nor-
rotundene (25). From the oxygenated fraction cyper-
adione (26), a patchoulane type sesquiterpene, was
isolated.
Cyperus rotundus is a cosmopolitan sedge belonging to
the family of the Cyperaceae. It is encountered in tropi-
cal, subtropical and temperate regions. C. rotundus is a
traditional medicinal plant appearing among Indian,
Chinese and Japanese natural drugs used against spasms
and stomach disorders (Dassanayake and Fosberg,
1985). The essential oil as well as solvent extracts of the
rhizomes of C. rotundus have been subject to numerous
studies (Ohira et al., 1998 and cited literature) resulting
in the isolation of many terpenoids. Here we describe
the isolation and structure elucidation of new patch-
oulane and rotundane sesquiterpenes from the essential
oil of this plant.
2. Results and discussion
The analysis of the essential oil of Cyperus rotundus by
GC and GC–MS allowed the identification of cyprotene
(1), cypera-2,4-diene (2), a-copaene (3), cyperene (4), a-
selinene (5), rotundene (6), valencene (7), ylanga-2,4-
diene (8), g-gurjunene (9), trans-calamenene (10), d-cadi-
nene (11), g-calacorene (12), epi-a-selinene (13), a-muur-
olene (14), g-muurolene (15), cadalene (16), nootkatene
2.1. (ꢀ)-Isorotundene (23)
The unknown compound 23 was assigned the mole-
cular formula C15H24 ([M]+at m/z=204). The 13C NMR
spectrum showed 15 carbon signals, two of which were
olefinic (ꢀ 107.9 and 151.08). Through the DEPT tech-
nique two methyl groups, seven methylene groups, four
methine and two quaternary carbon atoms were identi-
fied. The compound has four unsaturations and only
one double bond, therefore the presence of three rings
* Corresponding author. Tel.: +49-40-42838-2824; fax: +49-40-
42838-2893.
E-mail address: wkoenig@chemie.uni-hamburg.de (W.A. Konig).
0031-9422/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(01)00301-6

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Fig. 1. Sesquiterpenes from the essential oil of Cyperus rotundus.
was concluded. The 1H NMR and 13C NMR signal
assignments, achieved by 1H–1H-COSY and HMQC,
correlations, afforded three substructures. The methine
proton CH-5 (ꢀ 1.99) couples with the methine proton
CH-4( ꢀ 1.90) which is vicinal to methyl group CH3-15
(ꢀ 0.86). The latter methine proton also couples with the
methylene group CH2-3 (ꢀ 1.22 and 1.68) itself coupled
to another methylene group CH2-2 (ꢀ 1.46 and 1.52)
which further couples with the methine proton CH-1 (ꢀ
1.81) giving the partial structure–CH–CH(CH3)–CH2–
CH2–CH–. The methine proton ꢀ 1.99 also couples with
a methylene group CH2-6 (ꢀ 1.00 and 1.70) itself cou-
pled to the methine proton CH-7 (ꢀ 2.52). The proton
H-7 also couples with the methylene group CH2-8 (ꢀ
1.05 and 1.71) which again couples with CH2-9 (ꢀ 1.44
and 1.72) to give the second substructure–CH–CH2–
CH–CH2–CH2–. The methylene group CH2-11 (ꢀ 2.14
and ꢀ 2.27) and the olefinic proton at d 5.85 couple with
each other and give the third substructure–CH2–
C¼CH2. The proton-carbon long-range coupling corre-
lations derived from the HMBC spectrum allowed to
identify the skeleton of the compound. Long-range
coupling correlations were found between the protons
H-11, H-13 and carbon C-7 as well as between the
methine proton H-7 and the carbons C-11, C-12 and C-
13, indicating a bond connecting C-7 and C-12. The

M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
¨
801
proton H-11 also correlated with the carbons C-1, C-9,
C-10 and C-14while the methyl group H-14correlates
with the carbons C-1, C-9, C-10 and C-11. From these
observations it was deduced that C-10 is connected to
C-11, C-14to C-10, and C-10 to C-1. Long-range cor-
relations were observed between the protons H-6, H-5,
H-4and carbon C-1 as well as between H-1 and the
carbons C-2, C-4, C-5, C-6 and C-10 indicating a bond
between C-1 and C-5. The combination of all these
informations led to a rotundane skeleton with an exo-
cyclic double bond. The relative configuration at the
chiral centres C-1, C-4, C-5, C-7 and C-10 was con-
cluded from the NOESY diagram. The correlations
observed between protons H-1, H-4and H-5 indicate
that these protons are on the same side of the molecule.
Furthermore, the protons H-1 and H-5 show spatial
interactions with the proton H-11a, which is only pos-
sible if H-1 and H-5 are located at the same side as the
C-11-C-12 bridge. Therefore, compound 23, which was
named isorotundene, has the relative configuration as
shown in Fig. 2.
To verify the rotundane skeleton a partial synthesis of
23 by oxymercuration-demercuration (Brown and Geo-
ghegam, 1970) of rotundene (6) to isorotundenol (27)
and subsequent dehydration (Greenwood et al., 1968) to
isorotundene (23) and rotundene (6) was performed
(Fig. 3). The synthesized and the isolated compounds 23
have identical spectroscopic data. Although rotundene
(6) has been known for a long time its stereochemistry
was not known as yet. The relative configuration of
rotundene could not be derived from its NOESY dia-
gram because of the overlapping of all the important
signals. However, the fact that isorotundene (23) could
be obtained from rotundene as shown in Fig. 3, proves
that rotundene and isorotundene have the same relative
configuration.
order to correlate it with (+)-g-gurjunene (9). Rotun-
dene (6) was submitted to ozonolysis followed by
reduction with dimethyl sulfide under nitrogen
(McMurry and Bosch, 1987). The desired aldehyde was
not stable and was oxydised directly the to ketoacid 28
which could be isolated. The acid 28 was then dec-
arboxylated (Fristad et al., 1983) to give ketone 29.
Subsequently 29 was allowed to react with methylene-
triphenylphosphine in dimethyl sulfoxide (Greenwald et
al., 1963) to yield the hydrocarbon 30 which was
hydrogenated (Harmon et al., 1969) to give compound
31 (Fig. 4). Compound 31 was finally compared by
enantioselective gas chromatography with the fully
hydrogenated products of (+)-g-gurjunene (5) and
proved to have the same retention time with the major
hydrogenation product (Fig. 5). The co-injection was
made in a column which separates (+)- and (ꢀ)-g-gur-
junene (Fig. 6). Unfortunately, the small quantity of
(ꢀ)-g-gurjunene (which we isolated from the liverwort
Marchantia polymorpha) was insufficient for hydro-
genation and comparison with 31. However, it is very
probable that the used column also would have sepa-
rated the hydrogenation products of the two enantio-
mers. Therefore, it is very likely that rotundene has the
absolute configuration as shown for 23.
2.2. (ꢀ)-Cypera-2,4(15)-diene (24)
The isolation of cypera-2,4(15)-diene (24) was
achieved by a combination of column chromatography
and preparative GC. The compound was assigned the
molecular formula C15H22 ([M]+ at m/z=202). The 13
C
NMR spectrum combined with the DEPT technique
revealed three methyl groups, four methylene groups,
one being olefinic (ꢀ 102.84), five methine groups, two of
which are olefinic (ꢀ 133.26 and 139.17) and three
quaternary carbon atoms, one of which is olefinic
(d 148.94).
The identity of the relative configuration of rotundene
(6) and isorotundene (23) still leaves the question about
the absolute configuration open. In order to determine
the absolute configuration of the two compounds, a
chemical transformation of rotundene was performed in
The proton NMRspectrum displayed some signals
common to patchoulane sesquiterpenes, namely the two
Fig. 2. Relative configuration of isorotundene with relevant NOEs.
Fig. 3. Preparation of isorotundene (23) from rotundene (6).

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M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
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Fig. 4. Chemical conversion of the rotundane to a guaiane skeleton.
geminal methyl groups H-12 and H-13 (d 0.99 and 1.01)
which are coupled to each other (W-coupling), the
methyl group at ꢀ 0.77, appearing as a doublet and
coupling with the methine proton H-10 (ꢀ 2.12). The
vinylic proton H-2 (d 6.17) couples with another vinylic
proton H-3 (ꢀ 5.69), itself coupled to the olefinic meth-
ylene group H-15 (ꢀ 4.98) and also to the methine pro-
ton H-5 (ꢀ 3.03) giving the substructure –CH¼CH–
C(CH)¼CH2. Moreover, the coupling constant between
H-2 and H-3 (J=5.60 Hz) indicates that they belong to
a five-membered ring. The methine proton H-5 also
couples with the methylene group CH2-6 (ꢀ 1.68 and
2.10) which further couples with the methine proton H-
7 (d 1.85) itself coupled to the methylene group CH2-8
(d 1.51 and 1.86) which again couples with the methyl-
ene group CH2-9 (d 1.03 and 1.29) itself coupled to the
methine proton CH-10 (d 2.12). From these informa-
tions the substructure CH–CH2–CH–CH2–CH2–CH– is
derived.
All these informations from the 13C NMR and DEPT
1
as well as the H–1H-COSY led us to propose structure
24 for the compound. Its relative configuration resulted
from the NOESY diagram which shows NOE correla-
tions between H-5, H-9 and H-14at one side and
between H-13 and H-10 at the other. The observed cor-
relations indicate that the methine proton H-10 is on the
same side with the bridge C-1–C-7, while H-5, H-9 and
H-14are located at the opposite side of the molecule
(Fig. 7). 24 was before found as a minor product during
the reduction of cyperotundone (18) to the correspond-
ing alcohol and subsequent dehydration to 2 (Fig. 8)
(Mekem Sonwa et al., 1997).
2.3. (ꢀ)-Norrotundene (25)
The isolation of 25 was performed by the combina-
tion of many separation methods including CC at low
temperature (ꢀ20ꢁ C), CC over silver nitrate precoated

M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
¨
803
Fig. 5. Chemical transformation of rotundene and GC comparison with the hydrogenation product of (+)-g-gurjunene.
silica, preparative TLC and GC. The compound has the
molecular formula C14H22 in agreement with its mass
spectrum ([M]+ at m/z =190). The 13C NMR and
DEPT spectra revealed 14carbon atoms, two methyl
groups, five methylene groups, six methine groups from
which two are olefinic (ꢀ 129.15 and 139.10) and one
quaternary carbon atom. Therefore the compound
should consist of three rings since it has a total of four
unsaturations, one being a double bond. The constitu-
1
tion of 25 was derived from interpretation of the H
1
NMR spectrum and the phase-sensitive H–1H-COSY
spectrum together with the HMQC and the HMBC
diagrams.The methine proton CH-1 (ꢀ 2.20) couples
with the methylene group CH2-2 (ꢀ 1.61 and 1.54) which

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M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
¨
assumption is confirmed by the HMBC diagram which
shows long-range correlations between the protons H-
13 and C-1, C-10 and C-11. Proton H-1 shows long-
range connectivities to C-2, C-5, C-10 and C-11. The
protons of methylene group CH2-9 show connectivities
to C-1, C-8, C-10 and C-11, while the olefinic proton H-
11 is long-range coupled to C-1, C-7, C-9, C-10, C-12
and C-13. All these observations imply the two carbon-
carbon connections between C-10–C-1 and C-10–C-11,
leading to a rotundane skeleton for 25 (Fig. 9).
Fig. 6. Separation of (ꢀ)- and (+)-g-gurjunene by capillary gas chro-
matography on a 25 m capillary column with heptakis(6-O-t.butyldi-
methylsilyl-2,3-di-O-methyl)-b-cyclodextrin (50% in OV 1701, w/w) at
100 ꢁC.
The relative stereochemistry at the chiral centres of
the molecule could not be derived from the NOESY
spectrum. The signals of the two methine protons H-1
and H-4overlap and hence it is not possible to know
which one of them is responsible for the NOE with the
proton H-5. However, using the phase-sensitive COSY
technique as well as the gradient selected HMQC
method, it was possible to calculate the scalar coupling
constant between H-4and H-5 ( J=5.85 Hz). This value
of the coupling constant corresponds (Karplus curve) to
an angle of È=35ꢁ between the two protons, which
means that they are on the same side of the molecule.
Accordingly, both of them have spatial interactions
with H-1. It remains to investigate the stereochemistry
at C-7 and C-10. To solve this problem the NOESY
diagram was of no help because the protons H-1 and H-
5 are too far from the vinylic protons H-11 and H-12.
The solution came from the 1H–1H-COSY diagram
where a long-range coupling correlation is found
between proton H-1 and one of the H-9 protons. This is
a case of 4J coupling through a s-bond which requires a
particular geometry (W arrangement of the two pro-
tons) for the molecule, and this is only possible if the H-
1 proton and the C-11–C12 bridge are on the same side
of the molecule. Moreover, the axial–axial coupling
between H-5 and H-6a is only possible for this stereo-
chemistry of the molecule (Fig. 10). Norrotundene is
probably biogenetically related to rotundene and should
have the same absolute configuration.
Fig. 7. Stereostructure of cypera-2,4(15)-diene (24) and important
NOEs.
further couples with another methylene group CH2-3 (ꢀ
1.42 and 1.87) which couples again with the methine
proton H-4( ꢀ 2.10) itself coupled to the methyl group
CH3-14( ꢀ 0.90) and the methine proton CH-5 (ꢀ 1.80)
which further couples with the methine proton H-1 (ꢀ
2.20) and gives rise to a five-ring partial structure a:
C1H–CH2–CH2–CH(CH3)–CH–C1H–.
2.4. Cyperadione (26)
The methine proton H-5 also couples with methylene
group CH2-6 (ꢀ 0.95 and 1.66) which further couples
with the methine proton H-7 (ꢀ 2.56), itself coupled to
the methylene group H-8 (ꢀ 1.12 and 1.91) which cou-
ples again with the methylene group H-9 (ꢀ 1.52 and
1.83) to give the substructure b: CH–CH2–CH–CH2–
CH2–. Moreover, the vinylic protons H-11 and H-12 (ꢀ
6.02) are coupled to the methine proton H-7, indicating
a partial structure c: –CH¼CH–CH–. Observing that
the substructures a and b have C-5 in common and that
b and c have C-7 in common, the three partial structures
can be connected to give a new substructure A (Fig. 9).
It may be assumed that the only tertiary methyl group
of the molecule CH3-13 is linked to the only quaternary
carbon and thus yielding substructure B: CH3–C. This
Cyperadione (26) was isolated from the oxygenated
fraction of C. rotundus oil by preparative GC. The
compound has the molecular formula C15H24O2 ([M]+
at m/z=236). The 13C NMR- and the DEPTspectrum
indicate that it has four methyl groups, two methine
protons and four quaternary carbon atoms, two of
which being carbonyl carbons (ꢀ 208.50 and 220.25).
From the 1H NMR and the 1H 1H-COSY spectra, three
substructures were assigned which helped to derive the
full structure of the product. The methyl group CH3-14
(ꢀ 0.78) couples with the methine proton CH-10 (ꢀ 2.10)
which also couples with the methylene group CH2-9
(ꢀ 1.10 and 1.68) itself coupled to the methylene group
CH2-8 (ꢀ 1.45 and 2.01) which further couples with the

M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
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805
Fig. 8. Formation of cypera-2,4(15)-diene (24) form cyperotundone (18).
Fig. 9. Important proton-carbon long-range correlations in the HMBC spectrum of norrotundene (25).
group. This is confirmed by the HMBC diagram where
correlations are observed between the protons H-6 and
carbonyl carbon C-7. From all this information sub-
structure CH3–CH–CH2–CH2–CH–CH2–CO can be
derived. The two methyl groups at ꢀ 0.98 and 1.28
appearing as singlets are coupled to each other (W cou-
pling), what indicates that they are linked to the same
quaternary carbon atom giving the substructure CH3–
C–CH3. The deshielded methyl group CH3-15 at ꢀ 2.18
is probably adjacent to a carbonyl function (this is also
confirmed by the HMBC spectrum) and shows a long-
range coupling correlation to the methylene group CH2-
3 (ꢀ 2.35 and 2.44) which further couples with the meth-
ylene group CH2-2 (ꢀ 1.50 and 2.11) to give the partial
structure CH3–CO–CH2–CH2–. Additional structural
informations were drawn from the HMBC diagram. The
methylene protons H-2 are long-range correlated to
carbons C-1, C-3, C-4, C-5, C-10 and C-11 while the
methine proton H-10 shows connectivities to C-1, C-2,
C-5, C-9, C-11 and C-14. From these observations the
Fig. 10. Relative configuration of norrotundene (25). Note the W-
arrangement between H-1 and H-9e, and the axial-axial disposition
between H-5 and H-6a. These two geometrical patterns which are
supported by the observed coupling correlations are only possible for
the given stereostructure of the molecule.
methine proton CH-7 (ꢀ 1.90) itself coupled to the
methylene group CH2-6 (ꢀ 1.96 and 2.48). It should be
pointed out that the signals of this methylene group
appearing at lower field and showing no other coupling
correlation to a proton may be adjacent to a carbonyl

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¨
three carbon–carbon connections C-1–C-2, C-1–C-10
and C-1–C-5 were deduced. Moreover, the methyl pro-
tons H-12 and H-13 are long-range correlated to C-1, C-
7 and C-11, establishing the two connections C-11–C-1
and C-11–C-7. All these considerations led to structure
26 (Fig. 11), with a skeleton related to the patchoulane
skeleton of cyperene (4). To confirm structure 26 we
performed an ozonolysis of cyperene (4) (Fig. 12). The
reaction product displayed the same spectral data as the
isolated compound.
The biosynthesis of cyperene and rotundene may
involve two successive cyclisation steps of farnesyl di-
phosphate FDP leading via a cyclodecadienyl to a
cationic azulane type intermediate. At this stage two
pathways a and b may take place: Path a proceeds by a
1,2- proton shift followed by a deprotonation leading to
a-guaiene from which cyperene is formed by subsequent
protonation, cyclisation and deprotonation. Path b
proceeds by ring formation followed by a deprotonation
yielding rotundene or isorotundene (Fig. 13).
2.5. Biogenesis of patchoulane and rotundane type
sesquiterpenes
3. Experimental
Patchoulane and rotundane sesquiterpenes are char-
acteristic for the genus Cyperus. Cyperene (4) is always
the major hydrocarbon component in Cyperus species.
Rotundene (6) also is always present as a major sesqui-
terpene hydrocarbon component. These two compounds
appear to be of some chemotaxonomic importance. We
have previously reported the isolation of cyprotene (1),
a norsesquiterpene biogenetically related to cyperene
from the essential oil of Cyperus alopecuroides. Here, we
described a new norsesquiterpene, norrotundene (25),
which most likely has a biogenetic relationship to
rotundene. Besides 1 compound 25 was also identified in
C. papyrus. It, therefore, seems to be a peculiarity of
Cyperus species to produce norsesquiterpenes.
3.1. GC-MS
Electron impact (70 eV) GC–MS measurements were
carried out on a Hewlett-Packard HP 5890 gas chro-
matograph equipped with a 25 m polydimethylsiloxane
(Chrompack CP Sil 5 CB) capillary column and coupled
to a VG Analytical VG 70-250S mass spectrometer.
Helium was used as carrier gas.
3.2. NMR spectroscopy
NMR spectra were recorded using a Bruker DRX 500
(1H: 500 MHz, 13C: 125 MHz) and a Bruker DRX 400
(1H: 400 MHz, 13C: 100 MHz). Tetramethylsilane
(TMS) was used as reference signal (ꢀ=0.00).
3.3. Capillary GC
Orion Micromat 412 double column instrument with
25 m fused silica capillaries with CPSil 5 and CPSil 19
(Chrompack); Carlo Erba Fractovap 2150, 4160 instru-
ments with 25 m fused silica capillaries with hepta-
kis(2,6-di-O-methyl-3-O-pentyl)-b- (2,6-Me-3-Pe-b-CD)
and - g - cyclodextrin, respectively, and heptakis(6 - O -
t.butyldimethylsilyl-2,3-di-O-methyl)-b-cyclodextrin (6T-
2,3-Me-b-CD), all in polysiloxane OV1701 (50 wt%);
split injection, flame ionization detection; carrier gas 0.5
bar hydrogen.
Fig. 11. Long-range correlations from the HMBC spectrum of cyper-
adione (26).
Fig. 12. Preparation of cyperadione by ozonolysis of cyperene.

M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
¨
807
Fig. 13. Proposed biogenetic pathway for cyperene, rotundene and isorotundene.
3.4. Column chromatography at low temperature
an oven. An ethanolic solution of sulfuric acid (10%)
was used as a spray reagent.
Prefractionations of essential oils were performed on
a silica gel column equipped with a condenser and con-
nected to a Kryoflex KF 40 cooling system from Mess-
gerate-Werk Lauda atꢀ20 ꢁC. Ethanol was used as
cooling liquid.
3.6. Essential oil
The essential oil of C. rotundus was a gift of K.-D.
Protzen, Paul Kaders GmbH, Hamburg.
3.5. Thin layer chromatography
3.7. Isolation of compound 23
Thin layer chromatography was effected using glass
and aluminum plates of silica 60 F254 (Merck). Silver
nitrate coated plates were prepared by immersing the
plates into an ethanol–water (4:1) solution of silver
nitrate (5 mg AgNO3 in 50 ml of solvent). After 30 min
the plates were removed from the solution and dried in
A preliminary separation of the essential oil was per-
formed by column chromatography at low temperature
ꢁ
(ꢀ20 C). This resulted in a fractionation of the oil into
a hydrocarbon and an oygenated fraction. One gram of
the hydrocarbon fraction was then separated by TLC
using petroleum ether as eluting solvent. The aim of this

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¨
separation was to eliminate the major hydrocarbon
(cyperene) from the sample before any other operation.
Three bands were obtained, the first two containing
mainly cyperene and a-copaene. Only the third fraction
(Rf=0.45) was interesting because it contained the
unknown products. This fraction was further separated
by preparative GC (column 6T-2,3-ꢁMe-b-CD, tempera-
ture programme: from 110 to 180 C, heating rate 2ꢁ/
min). Fraction 5 of the chromatogram contained (+)-
ylanga-2,4(15)-diene (8). Fraction 8 was analysed by
GC–MS and three major products were present: a-seli-
nene (5), valencene (7), and an unknown product. This
sample was further separated by preparative TLC on
silver nitrate precoated plates, using petroleum ether as
eluting solvent. Two bands were obtained, the second of
which (Rf=0.35) was taken up in petroleum ether and
purified by preparative GC. Spectroscopic analysis
resulted in the structure of isorotundene 23.
3.9. Preparation of isorotudene (23) from rotundene
(6)
3.9.1. Hydration of rotundene by oxymercuration-
demercuration
In a 50 ml flask, fitted with a magnetic stirrer, 48 mg
of mercuric acetate were placed. To this, 3 ml of water
were added followed by 3 ml of THF. After addition
of 30 mg (0.148 mmol) of rotundene the reaction mix-
ture was stirred for 15 min at room temp. to complete
the oxymercuration. 3 ml of 3.0 M sodium hydroxyde
were added followed by 3 ml of a solution of 0.50 M
sodium borohydride in 3.0 M sodium hydroxide.
Reduction of the mercurial complex is almost instan-
taneous. The mercury is allowed to precipitate. Sodium
chloride was added to saturate the water layer. The
upper layer of THF was removed and purified by pre-
parative GC, yielding 26 mg (80%) of isorotundenol
(27).
3.8. (ꢀ)- Isorotundene (23)
3.9.2. Isorotundenol C15H25OH (27)
1H NMR (500 MHz, C6D6): see Table 1. 13C NMR
(100 MHz, C6D6): ꢀ 16.10 (q, C-15), 25.20 (t, C-2), 27.53
(t, C-8), 29.28 (t, C-9), 31.48 (t, C-3), 32.28 (q, C-14),
33.15 (t, C-6), 34.38 (s, C-10), 38.25 (d, C-4), 38.64 (d,
C-7), 41.52 (d, C-5), 44.36 (t, C-11), 56.19 (t, C-1),
107.98 (t, C-13), 151.08 (s, C-12). MS (EI, 70 eV), m/z
(rel. int.) : 204(33) [M] +, 189 (84), 175 (25), 161 (64),
144 (45), 133 (41), 119 (54 ), 108 (100), 93 (91), 79 (71),
67 (46), 55 (51), 41 (82).
1H NMR (500 MHz, C6D6): ꢀ 0.75 (3H, d, J=6.61
Hz), 0.76 (3H, s), 1.02 (3H, s), 1.08-1.54(12H, m), 1.57–
1.65 (2H, m), 1.75 (1H, m), 2.15 (1H, m). MS (EI, 70
eV), m/z (rel. int.) : 222 (5), 204(19), 189 (27), 175 (7),
161 (14), 147 (12), 133 (13), 121 (33), 108 (100), 93 (57),
81 (39), 67 (24), 55 27), 41 (35).
3.9.3. Dehydration of isorotundenol
Phosphoryl chloride (0.5 ml) was added to a pyridine
solution (1 ml) of isorotundenol (10 mg). The mixture
was stirred for 10 h and pyridine was then removed by
distillation at low pressure. The remaining residue was
taken up in hexane and separation by prep. GC yielded
3 mg of isorotundene and 3 mg of rotundene.
Table 1
1H NMR spectral data for compounds 23 and 25a
H
23
25
1
2
1.81 ddd (9.5, 9.5, 5.9)
1.46 dd (9.5, 3.2)
1.52 m
2.20 dddd (13.5, 6.6, 6.4, 7.0)
1.54 m
1.61 m
3.10. Ozonolysis of rotundene
A solution of rotundene (50 mg) in dichloromethane
(20 ml) was treated at ꢀ78ꢁ C with a stream of ozone
until a persistant blue colour was observed. The solu-
tion was then purged with nitrogen for 5 min. After
addition of dimethylsulfide (3 ml) the solution was
washed with ice-cold sodium bicarbonate solution (25
ml), water and brine. The organic layer was dried
(NaSO4) and the solvent was evaporated. Purification of
the residue by prep. GC gave the keto-acid 28 (45 mg).
1H NMR (400 MHz, CDCl3): ꢀ 1.10 (3H, d, J=6.61
Hz), 1.30 (1H, m), 1.35 (3H, s), 1.65–1.92 (9H, m), 2.11
(1H, m), 2.20 (1H, m), 2.29 (3H, s), 2.58–2.85 (2H,m).
13C NMR (100 MHz, CDCl3): 16.73, 25.10, 25.66,
27.47, 28.30, 30.07, 31.09, 31.60, 39.64, 41.70, 48.56,
48.64, 50.55, 184.59, 212.01. MS (EI, 70 eV) m/z (rel.
int): 252 (13) [M]+, 234(7), 206 (15), 191 (11), 163 (36),
149 (7), 133 (10), 121 (18), 107 (25), 95 (68), 81 (43), 67
(22), 55 (28), 43 (100).
3
1.22 dddd (13.6, 11.4, 11.4, 6.7) 1.42 dddd (13.5, 11.0, 11.0, 6.7)
1.68 m
dddd (13.6, 6.9, 6.6, 6.4)
1.99 dddd (13.2, 6.4, 6.4, 5.9)
1.87 m
2.10 m
41.90
5
6
1.80 dddd (13.2, 6.4, 6.4, 6.4)
0.95 dd (13.2, 13.2)
1.66 ddd (13.2, 9.1, 6.4)
2.56 m
1.00 t (13.2)
1.70 m
2.52 m
7
8
1.05 dd (12.9, 9.5)
1.71 m
1.44 m
1.12 ddd (13.8, 11.7, 5.1)
1.91 ddd (13.8, 9.4, 5.0)
1.52 ddd (11.7, 9.4, 6.1)
1.83 m
9
1.72 m
11 2.14 dt (17.0, 2.5, 2.5)
2.27 dd (17.0, 2.2)
6.02 m
12
13 5.85 m
5.85 m
6.02 m
1.13 s
140.80
15 0.86 d (6.6)
s
0.99 d (6.6)
a
All the measurements were done in C6D6. The assignments were
established by 13C–1H HMBC and HMQC

M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
¨
809
3.11. Decarboxylation of keto-acid 28
under normal pressure for 15 min. The solvent was
removed under reduced pressure and petroleum ether
was added, since most of the catalyst remains undis-
solved. Filtration through a column of alumina afforded
the pure alkane 31. MS (EI, 70 eV), [M]+ m/z=208.
b. The hydrogenation of (+)-g-gurjunene (9) followed
the same procedure as that of the alkene 30 except the
catalyst was replaced by nickel on charcoal.
The keto-acid (40 mg, 0.16 mol) and silver nitrate (1
mg) were dissolved in acetonitrile (6 ml) and water (2
ml) and heated to reflux. To this solution potassium
peroxosulfate (K2S2O8) (0.32 mg) in water (5 ml) was
slowly added. Refluxing was continued for another 5
min before the reaction mixture was cooled and extrac-
ted with a saturated sodium bicarbonate solution (10
ml, three times), dried (MgSO4) and purified by prep.
GC to give 14mg of ketone 28.
3.14. Isolation of cypera-2,4(15)-diene and
norrotundene
1H NMR (500 MHz, CDCl3): 0.96 (3H, dd, J=6.62
Hz), 1.06 (3H, s), 1.40 (1H, m), 1.60–1.84(7 H, m),
1.97–2.1 (2H, m), 2.13–2.24(3H, m), 2.27 (3H,s), 2.44 (1
H, m), 2.69 (1H, dd, J1=13.87 Hz, J2=6.94Hz). 13C
NMR (100 MHz, CDCl3): 15.10 (q), 21.52 (q), 26.09 (t),
26.80 (t), 27.85 (q), 30.26 (t), 33.25 (t), 37.46 (t), 37.99
(d), 38.04( d), 46.82 (d), 56.70 (d), 61.65 (d), 207.93 (s).
MS, (EI, 70 eV), m/z (rel. int): 208 (5) [M]+, 190 (7), 175
(6), 161 (5), 150(8), 135 (9), 123 (27), 109 (23), 95 (100),
81 (31), 67 (25), 55 (29), 43 (52).
For the above described chemical transformation, a
relatively large amount of rotundene had to be isolated
from the essential oil of C. rotundus. For the isolation 5 g
of the hydrocarbon fraction of the oil were separated by
column chromatography over silver nitrate precoated
silica using a petroleum ether–chloroform gradient for
elution. The eluent from the column was monitored by
capillary GC and 16 fractions were collected. Fractions
1–6 obtained by elution with petroleum ether contained
only known hydrocarbons. Fractions 7–10 were obtained
by elution with petroleum ether–chloroform (7/3) and
contained the rotundene. It could be proved by GC–MS
of fraction eighth that the sample also contained an
unknown minor component. The separation of this frac-
tion was performed by prep. GC (column: 2,6-Me-3Pe-b-
CD; temp. programme: 100–140 C, heating rate 2 C/
min). The chromatogram displayed five peaks the fifth
containing the pure unknown product which was char-
acterized as cypera-2,4(15)-diene (24). Fractions 11–15
were eluted with petroleum ether–chloroform (1/1).
GC–MS revealed the presence of an unknown product
of molecular weight 190 among many known sesqui-
terpene hydrocarbons. In order to isolate the unknown
compound, the joined fractions 14and 15 were first
separated by prep. TLC over silver nitrate precoated
plates, using petroleum ether–chloroform (7/3) as elut-
ing solvent. Three bands were obtained and the third
one, which contained the norsesquiterpene as major
product was separated by preparative GC (column: SE
30, temp. 125 ꢁC). Spectroscopic data permitted the
characterization of the compound as norrotundene (25).
3.12. Reduction of ketone 29
In a three-necked flask sodium hydride (0.45 mmol)
was washed with several portions of pentane to remove
the mineral oil. The flask was then equipped with rubber
stopper, a reflux condenser and a magnetic stirrer. The
system was alternately evacuated and filled with nitrogen;
3 ml of dimethyl sulfoxide was introduced via a syringe
and the mixture was heated at 75–80ꢁ C for 4 5 min. The
resulting solution of methylsulfinyl carbanion was cooled
in an ice-water bath, and 108 mg of methyltriphenylpho-
sphonium bromide in 100 ml of warm dimethyl sulfoxide
were added. The resulting dark red solution of the ylide
was stirred at room temperature for 10 min before 7 mg of
the ketone 29 in two ml of dimethyl sulfoxide were added.
The reaction mixture was then heated at 56ꢁC for 16 h
after which the solution was allowed to cool and 10 ml of
water were added. The two phases were extracted three
times with n-pentane (40 ml). The n-pentane fractions
were combined and washed with 10 ml of a (1/1) water/
dimethyl sulfoxide solution and then with 30 ml of 50%
saturated sodium chloride solution. The pentane layer
was then dried over anhydrous sodium sulfate and pur-
ification by preparative GC gave 2 mg of the alkene 30.
MS (EI, 70 eV), m/z (rel. int): 206 (12) [M]+, 191 (18),
177 (6), 163 (51), 149 (25), 122 (39), 107 (56), 95 (60), 81
(100), 67 (57), 55 (66), 41 (79).
ꢁ
ꢁ
3.14.1. (ꢀ)-Cypera-2,4(15)-diene (24)
1H NMR (400 MHz, C6D6): see Table 2. 13C NMR
(400 MHz, C6D6) : 17.32 (q), 19.61 (q), 26.36 (q), 26.64
(q), 27.70 (t), 28.48 (s), 30.16 (t), 32.58 (t), 44.96 (d), 47.66
(d), 61.93 (s), 102.84( t), 133.26 (d), 139.17 (d), 148.94 (s).
MS (EI, 70 eV) m/z (rel. int.): 202 (83) [M]+, 187 (24),
173 (6), 173 (6), 159 (46), 145 (24), 131 (37), 118 (85), 106
(100), 91 (78), 77 (33), 69 (17), 65 (18), 55 (26), 41 (61).
3.13. Hydrocarbon 31
a. 30 (1 mg) was dissolved in a mixture of ethanol (1
ml) and benzene (1 ml). The catalyst [(Ph)3P]3RhCl (1
mg) was added and the solution turned orange. A gentle
stream of hydrogen was then passed through the solution
3.14.2. (ꢀ)-Norrotundene (25)
1H NMR (500 MHz, C6D6):see Table 1. 13C NMR
(125 MHz, C6D6) : 14.73 (q), 22.95 (t), 28.00 (t), 28.67

810
M.M. Sonwa, W.A. Konig / Phytochemistry 58 (2001) 799–810
¨
Table 2
1H NMR spectral data for compounds 24 and 26a
vent evaporated. The residue was then purified by prep.
GC to give 3 mg of cyperadione (26).
H
2
24
26
6.17 d (5.6)
2.11 m
1.50 ddd (15.4, 11.7, 5.7)
Acknowledgements
3
5.69 dd (5.6, 1.0)
2.44 ddd (16.4, 12.3, 5.7)
2.35 ddd (16.4, 11.7, 4.4)
The financial support of DAAD (scholarship for M.
Mekem Sonwa) and of the Fonds der Chemischen
Industrie is gratefully acknowledged. We also thank Dr.
V. Sinnwell, University of Hamburg, for his support in
obtaining the NMR spectra and to A. Meiners and M.
Preusse for recording the mass spectra.
5
6
3.03 m
1.68 m
2.10 m
1.85 m
1.96 d (19.0)
2.48 dd (19.0, 7.3)
1.90 ddd (6.6, 3.3, 3.3)
1.45 dq (13.6, 3.2)
2.01 dddd (13.6, 12.9, 6.0, 2.7)
1.10 dddd (14.5, 12.9, 12.9, 6.6)
1.68 ddd 14.5, 6.0, 6.0)
7
8
1.51 dt (14.8, 6.1)
1.86 m
1.03 m
1.29 m
2.12 dddd (13.2, 6.1, 6.1, 6.1)
0.99 s
1.01 s
d (6.6)
4.98 m
4.98 m
9
10
12
13
140.77
15
1.22 s
0.98 s
0.78 d (6.6)
2.18 s
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