The role of germacrene D as a precursor in sesquiterpene biosynthesis: Investigations of acid catalyzed, photochemically and thermally induced rearrangements

Article abstract of DOI:10.1016/S0031-9422(00)00266-1

Germacrene D is considered as a precursor of many sesquiterpene hydrocarbons. We have investigated the acid catalyzed as well as the photochemically and thermally induced rearrangement processes of germacrene D isolated from several Solidago species, which contain both enantiomers of germacrene D. Enantiomeric mixtures of sesquiterpenes of the cadinane, eudesmane (selinane), oppositane, axane, isodaucane, and bourbonane group as well as isogermacrene D were identified as main products and made available as reference compounds for structure investigations and stereochemical assignments of plant constituents. δ-Amorphene, one of the rearrangement products, was identified as a natural product for the first time. The absolute configuration of γ-amorphene was revised by correlation with the absolute configuration of germacrene D. The mechanisms of the rearrangement reactions are discussed. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0031-9422(00)00266-1

Phytochemistry 55 (2000) 141±168
www.elsevier.com/locate/phytochem
The role of germacrene D as a precursor in sesquiterpene
biosynthesis: investigations of acid catalyzed, photochemically
and thermally induced rearrangements
Nils Bulow, Wilfried A. Konig *
Institut fur Organische Chemie, Universitat Hamburg, Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany
È
È
Received 5 May 2000; received in revised form 29 June 2000
Abstract
Germacrene D is considered as a precursor of many sesquiterpene hydrocarbons. We have investigated the acid catalyzed as well
as the photochemically and thermally induced rearrangement processes of germacrene D isolated from several Solidago species,
which contain both enantiomers of germacrene D. Enantiomeric mixtures of sesquiterpenes of the cadinane, eudesmane (selinane),
oppositane, axane, isodaucane, and bourbonane group as well as isogermacrene D were identi®ed as main products and made
available as reference compounds for structure investigations and stereochemical assignments of plant constituents. ꢀ-Amorphene,
one of the rearrangement products, was identi®ed as a natural product for the ®rst time. The absolute con®guration of ꢁ-amor-
phene was revised by correlation with the absolute con®guration of germacrene D. The mechanisms of the rearrangement reactions
are discussed. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Carbocations; Germacrene D; Isogermacrene D; Photochemistry; Rearrangement; Sesquiterpenes; Solidago spec.; Thermochemistry
1. Introduction
The importance of germacrene D (1) as a biogenetic
precursor of many other sesquiterpene structures was
already recognized at its ®rst description in the litera-
ture and some acid catalyzed and photochemically
induced rearrangements have been reported (Yoshihara
et al., 1969). In the past all rearrangement products
obtained from germacrene D were eventually also found
as natural products. The elucidation of yet unknown
rearrangement products should facilitate the discovery
of new natural products.
In this work we have attempted to identify the whole
band-width of rearrangement products of germacrene D
by utilizing modern two-dimensional NMR techniques
and enantioselective gas chromatography as an ecient
tool for stereochemical assignments.
To date more than 200 di€erent sesquiterpene skele-
tons are known, which are predominantly formed from
farnesyl diphosphate (FDP) as a common acyclic pre-
cursor by enzymatic cyclizations and further transfor-
mations (Cane, 1990). Using this concept, it was
attempted to derive a biogenetic relationship between
certain natural sesquiterpene structures on the basis of
skeletal rearrangements (Andersen and Syrdal, 1970;
Andersen et al., 1978). More recently, feeding experi-
ments with isotopically labeled FDP or mevalonate or
incubations of these labeled precursors with isolated
sesquiterpene cyclases have become a powerful tool in
biogenetic studies (Arigoni, 1975; Cane et al., 1993).
However, not all of the correlations discussed in the
earlier literature are experimentally proven, and many
structures were only tentatively assigned.
2. Results and discussion
2.1. Biogenesis of sesquiterpenes involving germacrenyl
cations
* Corresponding author. Tel.: +49-404-28382824; fax: +49-404-
28382893.
According to currently accepted hypotheses, in addi-
tion to FDP nerolidyl diphosphate (NDP) may be a
E-mail address: wkoenig@chemie.uni-hamburg.de (W.A. Konig),
nils.bulow@wsso.com (N. Bulow)
0031-9422/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0031-9422(00)00266-1

142
N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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precursor in the enzymatically catalyzed formation of
sesquiterpenes in order to allow adequate alignment of
p-orbitals for the formation of products with cis double
bonds (Cane, 1985). It can be assumed that in the cycli-
sation process after loss of the diphosphate residue the
germacrenyl cations A and B and, after hydride migra-
tion, the cations C and D are formed (Scheme 1). Cation
A is considered as precursor for the elemanes, guaianes
and germacranes. After conversion to cation E the
eudesmanes (selinanes) may be formed. This suggests
that germacrene type sesquiterpenes are biogenetic
intermediates for certain groups of sesquiterpenes. As
an example ( )-germacrene A (2) is assumed as an
intermediate in the biosynthesis of (+)-aristolochene (3)
(Cane, 1990) and in the biosynthesis of bitter sesqui-
terpene lactones in chicory (de Kraker et al., 1998) (Fig.
2).
For the biosynthesis of cadinane type sesquiterpenes
Arigoni suggested two alternatives (Arigoni, 1975). The
primarily formed cation A may be deprotonated to ger-
macrene D (1) after hydride migration to cation C. The
subsequent conformational change from cisoid structure
1a to transoid 1b is crucial for the formation of cadinane
type sesquiterpenes (with a Z double bond in the ring)
following protonation and rearrangement to cation D.
It should be mentioned that germacrene D very often
occurs in plants together with ꢀ-cadinene (4, Scheme 3)
(Yoshihara and Hirose, 1978). Investigations of the
(+)-ꢀ-cadinene synthase from cotton (Gossypium hirsu-
tum), however, did not reveal any germacrene D in the
products. This does not exclude 1 as a biosynthetic
intermediate, though, as it may be tightly bound to the
enzyme as a primary cyclization product and immedi-
ately be further rearranged (Davis and Essenberg, 1995;
Davis et al., 1996).
As alternative, NDP may serve as a substrate for
cadinane type sesquiterpene biosynthesis. In this case
the cyclization to the cadinanes would simply proceed
via cations B and D. In fact, for the biosynthesis of the
cadinane derivative (+)-1-epi-cubenol (5, Fig. 2) NDP
could be identi®ed as a precursor (Cane and Tandon,
1995).
A series of investigations related to acid catalyzed
rearrangements of germacrene D derivatives has led to
substituted cadinenes, selinenes, oppositenes and iso-
daucadienes (Niwa et al., 1976a,b, 1978, 1979; Yama-
mura et al., 1982; Itokawa et al., 1983; Shizuri et al.,
1986) but little is known about the rearrangement to
Scheme 1. Supposed biogenesis of germacrene related sesquiterpenes.

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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143
both plants. Both enantiomers are present in widely
varying proportions in dependence on the collection
site. In a few cases only one enantiomer was detected.
The enantiomeric composition of 1 also varies with the
part of the plant. A series of investigations of a plant
from the same location during the entire ¯owering sea-
son (July±September) showed that the enantiomeric
composition remained constant in di€erent parts of the
plant over the whole season and over three years. The
investigation of some other Solidago species from Eur-
ope and the United States gave similar results with
respect to the enantiomeric composition of 1 (Bulow
and Konig, 1996; Bulow, 1999). We, therefore, assume
that the occurrence of both enantiomers of 1 is common
to Solidago species.
The biosynthetic pathway of 1 was recently elucidated
by incubation of isolated enzymes (Schmidt et al., 1998)
with isotopically labeled FDP and mass spectrometric
analysis of the products (Schmidt et al., 1999) and
proceeds in di€erent steps for both enantiomers as
already suspected by Niwa et al. (1980) and as shown in
Scheme 1.
For the following rearrangement reactions germa-
crene D was isolated from the essential oil of Solidago
species either by preparative gas chromatography or by
silica gel chromatography at low temperature. In cases
with over 90% germacrene D in the original oil no fur-
ther puri®cation was carried out.
Fig. 1. 1H, 1H-NOESY interactions observed in germacrene D.
sesquiterpene hydrocarbons (Yoshihara et al., 1969;
Nishimura et al., 1979; Itokawa et al., 1988). It is likely
that new natural compounds will be discovered after
identi®cation of new rearrangement products of germa-
crene D. Moreover, with an enantiomeric mixture of 1 of
a de®ned composition stereochemical and mechanistic
aspects of rearrangement processes may be unravelled.
2.3. Acid catalyzed rearrangement reactions
Germacrene D completely rearranges to di€erent ses-
quiterpene hydrocarbons merely by contact with weakly
acidic media like silica gel over a period of several days
(Yoshihara et al., 1969). Under these conditions cadi-
nane type products are formed almost exclusively. A
similar spectrum of compounds was formed under the
in¯uence of carboxylic acids, but the yield is lower due
to ester formation (Nishimura et al., 1979). A greater
variety of products is formed with p-toluene sulphonic
acid or acidic ion exchange resin. Complete rearrange-
ment can be achieved in only minutes with strong Lewis
acids with predominant formation of thermodynamically
more stable products (Table 1). The product mixtures
obtained in these reactions were preseparated by silica gel
chromatography, isolated by preparative gas chromato-
graphy and identi®ed by comparison with authentic
samples (GC±MS) and/or with published data (NMR).
2.2. Occurrence and isolation of germacrene D
enantiomers
Although a synthesis of germacrene D was reported
(Schreiber and Hawley, 1985) it is more convenient to
obtain 1 from natural sources. In most higher plants 1 is
present as its ( )-enantiomer, while the (+)-enantiomer
is more likely to occur in lower organisms (Beecham
and Djerassi, 1978; Lorimer and Weavers, 1987; Konig
et al., 1996). For the higher plants Solidago altissima L.
(Niwa et al., 1980), Torilis japonica D. C. (Itokawa et
al., 1983) and Araucaria bidwillii (Pietsch and Konig,
2000) the occurrence of both enantiomers has been
described, although we found that 1 is only a minor
component in T. japonica. To obtain sucient amounts
of both enantiomers of 1 we analysed the ``goldenrod''
Solidago canadensis L. and S. gigantea Ait., both very
common in central Europe, by enantioselective gas
chromatography (Konig et al., 1996). It turned out that
1 is the main constituent of the sesquiterpene fraction in
2.3.1. Cadinane type sesquiterpenes
As main products of acid catalyzed rearrangements
cadinenes, muurolenes and amorphenes, which are com-
mon in nature, are formed with the cadinenes in pre-
dominance, which can be explained by reaction pathways
via the cations G, H and J (Scheme 2). According to
MM2 molecular mechanics calculations 99% of 1 are

144
N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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Scheme 2. Protonation of germacrene D resulting in cadinenyl (G), muurolenyl (H), and amorphenyl (J) cations.
present in two preferred conformations 1a and 1b in a
82:17 ratio (Shizuri et al., 1986). This result is qualita-
tively con®rmed by H-NOESY investigations (Fig. 1).
Kotake, 1969), ꢀ-cadinene (4) (Wenkert et al., 1992), ꢁ-
muurolene (8) (Beecham and Djerassi, 1978), ꢂ-muur-
olene (9) (Beecham and Djerassi, 1978), cadina-1,4-
diene (cubenene, 10) (Connolly et al., 1982), ꢂ-copaene
(11) (Wenkert et al., 1992), ꢁ-amorphene (12) (Motl et
al., 1966), ꢂ-amorphene (13) (Gregson and Mirrington,
1976) and ꢂ-ylangene (14) (Melching et al., 1997) could
be identi®ed (Scheme 3). ꢀ-Amorphene (15) could not be
isolated in a pure state from the product mixture. It was
identi®ed by comparison (GC±MS) with 15 prepared by
acid catalyzed rearrangement from ꢃ-ylangene (16,
Schemes 11 and 12) (Melching et al., 1997).
1
Thus, it can be assumed that in the rearrangement pro-
cesses at room temperature 1 is attacked by an electro-
phile in one of the two conformations. Cation D1
cyclizes to the cadinenyl cation G, a step, which could
proceed from 1b in a concerted fashion. In contrast, a
conformational change to D2 or D3 is necessary for the
formation of muurolenyl and amorphenyl cations H
and J (Scheme 2). As a consequence of this thermo-
dynamically unfavourable process to the cis-decalin
systems, the muurolenes and amorphenes are formed in
smaller quantities.
With increasing reaction time in the product mixture
secondary rearrangement products are formed, which
can not be directly related to germacrene D. By iso-
merization of isolated pure compounds it could be proven
The primary rearrangement products ꢁ-cadinene (6)
(Andersen and Syrdal, 1970), ꢂ-cadinene (7) (Naya and

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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145
Scheme 3. Sesquiterpenes with cadinane skeleton obtained from germacrene D.
that ꢂ-cadinene (7) rearranges mainly to ꢃ-cadinene (17)
(Fringuelli et al., 1985), while the latter is isomerized to
the thermodynamically more stable !-cadinene (18)
(Vlahov et al., 1967; Connell et al., 1968; Nagasampagi
et al., 1968). The latter is also formed from ꢀ-cadinene
(4) in a ratio of 1.4:1. Furthermore, !-amorphene (19) is
obtained from 13 and from 15. The structure assign-
ment of 19 was proven by identical hydrogenation pro-
ducts formed from 15 and 19 and further supported by
the ®nding that the mass spectra of 18 and 19 are iden-
tical as are the mass spectra of 4 and 15 (Melching et al.,
1997).
The preference of a 2,3-double bond versus a 1,2-
double bond in trans-decalins has been known before
and is associated with the ring strain, which increases
when another ring is attached at the ꢂ-position of a
cyclohexene (Taylor, 1954; Corey and Sneen, 1955;
Turner et al., 1957). In a cyclohexene system the sub-
stituents at the ꢂ-carbon atoms of the double bond are
in pseudo-axial and -equatorial orientation. By annela-
tion of another ring to the system, the former pseudo-
equatorial substituent is forced into a less favorable
position increasing the ring strain (Turner et al., 1957).
By the thermodynamically favoured isomerization of an
1,2- to a 2,3-double bond, the second ring is shifted to
the b-position resulting in a strain decrease (e.g. com-
pare 7!17).
Since germacrene D was always used in a de®ned
enantiomeric ratio, it was also possible to investigate the
products with respect to their enantiomeric composi-
tion. It turned out that in most cases the ratio of the
enantiomers is retained as long as the stereogenic cen-
tres are not involved in the reaction. Minor deviations
from the original enantiomeric composition can be
explained by the fact that the rearrangements take place
in a chiral environment, which may cause some dia-
stereoselective induction.
Assuming the rearrangement mechanism for the for-
mation of the cadinenes to proceed as described above,
ꢁ-amorphene (12) with the absolute con®guration as
shown in Scheme 3 is formed from ( )-1. This con®g-
uration was assigned to ( )-12 in the original descrip-
tion (Motl et al., 1966). However, by comparison with
( )-12, which we obtained from an enantiomeric mix-
ture by preparative GC using a chiral stationary phase
(cyclodextrin derivative) and after measuring the optical
rotation of the isolated material we could unambigu-
ously prove, that the structure of 12 as depicted in
Scheme 3 corresponds to the (+)-enantiomer.
If the rearrangement processes are catalyzed by strong
Lewis acids the thermodynamically most stable com-
pounds zonarene (20) (Melching et al., 1997) and epi-
zonarene (21) (Mehta and Singh, 1977) are
predominantly formed. They can either be formed

146
N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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Table 1
Yield (%) of rearrangement products in dependence on the reaction conditionsg
Acetic acidb
TsOHc or
Amberlyst115d
dto./longer BF3
reaction timee
BF3
AlCl
a
f
f
SiO2
ꢀ-Cadinene (4)
ꢁ-Cadinene (6)
ꢂ-Cadinene (7)
ꢁ-Muurolene (8)
ꢂ-Muurolene (9)
Cadina-1,4-diene (10)
ꢂ-Copaene (11)
g-Amorphene (12)
ꢂ-Amorphene (13)
ꢂ-Ylangene (14)
ꢀ-Amorphene (15)
ꢃ-Cadinene (17)
!-Cadinene (18)
!-Amorphene (19)
Zonarene (20)
30
14
28
7
13±19
9±17
4±6
8±12
3±5
0±1.5
0.5±2.5
2±6
2±6
0±1.5
2±4
0±0.5
Trace
±
16±23
0±10
0±4
26±30
9±13
7±10
9±13
4±7
1.5±2.5
±
0±3
±
3.5
2
±
15
9
6
0.5±2
7±8
±
7
±
3
2.5
1.5
1
0±1.5
Trace
0±4
±
±
Trace
Trace
2.5
8
1±7
5±6
±
±
0±4
±
1
5.5
0.5
5.5
±
Trace
1±3
3±8
±
3±4
0±0.5
±
±
Trace
Trace
±
±
5±12
1±3
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
±
0.5±2
0.5±8
Trace
±
1±7
0±1
3±8
Trace
Trace
Trace
±
5±25
45±80
3±15
1±5
Trace
1±4
0±2
Trace
0±2
0±1
0±1
Epizonarene (21)
Calamenene (22/23)
ꢂ-Calacorene (24)
g-Calacorene (25)
Cadalene (26)
±
8±19
2±6
±
±
0.5±2.5
Trace
Trace
±
±
±
±
±
cis-Muurola-4(15),5-diene (27)
Bicyclosesquiphellandrene (28)
Cadina-3,5-diene (29)
Cadina-1(6),4-diene (30)
4S,4aS-1,7-Dimethyl-4-(methylethyl)-
2,3,4,4a,5,6-hexahydronaphthalene (31)
Daucalene (32)
±
±
Trace
±
±
±
±
Trace
±
±
±
Trace
±
±
±
±
±
±
±
±
±
±
±
±
1±4
Selina-4(15),6-diene (43)
Selina-4(15),7-diene (44)
Selina-4(15),5-diene (45)
Selina-3,5-diene (46)
ꢀ-Selinene (49)
4(15)-Cyclooppositene (51)
Opposita-4(15),7-diene (52)
Opposita-4(15),11-diene (53)
4(15)-Cycloaxene (54)
4-Cyclooppositene (57)
3-Cycloaxene (58)
±
Trace
Trace
0.5
1.0
±
2±3
1±6
0±1.5
0±3
0±1
0.5±2
0.5±2
Trace
1.5±5
0.5±1
0±1.5
1.5±5
1±8
±
Trace
±
±
0.5±2.5
2±6
0±2
±
4.0
±
0±3
±
Trace
12±23
0±3
1±6
±
1.5
0.5
±
1±4
±
±
4±11
1.5±3
0±1
±
±
0±2
0±1
±
0.5
±
0.5
±
±
±
±
Trace
Trace
±
Trace
Trace
1±3
±
±
±
±
±
Isodauca-4,7(14)-diene (60)
Isodauca-4,6-diene (61)
Unidenti®ed
±
±
0±0.5
0.5±4
10±18
±
1.5
7.5
±
26.5
0.5±4
15±30
0.5±1
5±15
±
5±10
a
10 mg SiO2 in 0.5 ml n-hexane, c(1)=15 mmol/l, 2 days.
c(1) in glacial acetic acid=20 mmol/l, 24 h.
3±10 mg CH3PhSO3H in 5±15 ml CH2Cl2, c(1)=15- 70 mmol/l, 3 h±4 days.
b
c
d
e
f
2±20 mg Amberlyst115 in 0.5±1.5 ml n-hexane, c(1)=15±220 mmol/l, 1±10 days.
3±7 days and 3±30 days, respectively.
50 ml BF3 [60% in dimethyl ether] (24.2 g, 0.36 mol) in 180 ml diethyl ether, c(1)=9 mmol/l, 0 ꢀC, 12 min.
15 mg AlCl3 in 0.5 ml CH2Cl2, c(1)=15 mmol/l, 1 h (use of ZnCl2 will give comparable results).
g
directly from germacrene D (1) or from other inter-
mediate cadinenes (Schemes 4 and 5). For 20 and 21
varying enantiomeric proportions are found, which can
be explained by the proposed mechanism of formation.
Scheme 4 presents the identi®ed rearrangement pro-
ducts initiating from ( )-1, (+)-4, (+)-6, and ( )-8.
Thus, from (+)-6 enantiomerically pure ( )-21 was
formed as the main product (Osadchii et al., 1981),
whereas ( )-20 (Mehta and Singh, 1977; Polovinka et
al., 1981) and (+)-21 as well as the oxidation products
cis-/trans-calamenene 22/23 (Croft et al., 1978; Melch-
ing et al., 1997), ꢂ-calacorene (24, Fig. 2) (Hardt, 1994),
ꢁ-calacorene (25, Fig. 2) (Adachi and Mori, 1983) and
cadalene (26, Fig. 2) (Bohlmann and Zdero, 1976) are
formed from ( )-8. The assumed mechanism of forma-
tion is supported by the occurrence of trace components

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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147
Scheme 4. Mechanism of formation of products obtained from germacrene D, cadinenes and muurolenes, respectively, with strong Lewis acids.
et al., 1981) and by oxidation to daucalene (32), which is
also a known oxidation product of carotol (33, Fig. 2)
(Sykora et al., 1961; de Broissia et al., 1972). We got 32
as a reference compound by sulfur induced dehy-
drogenation from daucene (34), a dehydration product
of 33 (Hashidoko et al., 1992). 31 was formed by treat-
ment of g-muurolene (8) with super acids according to a
mechanism proposed by Polovinka et al. (1981)
(Scheme 5). In the reaction with AlCl3 31 is obtained as
a major product from muurolenes or as a minor pro-
duct from 1 while 32 is formed as a trace compound. An
Scheme 5. Acid catalyzed rearrangement via the muurolenyl cation
(H) to daucalene derivatives.
alcohol (35, Fig. 2) with this unusual skeleton was
already described (Bohlmann and Zdero, 1976).
According to Osadchii et al. (1981) a 1,2-hydride shift
is strongly favoured over a 1,3-hydride shift. Corre-
spondingly, (+)-21 is not formed via the germacrenyl
cation G (Scheme 4). Alternatively, the formation of
(+)-21 is only possible over a deprotonation/protona-
tion step starting from cation H. Andersen et al. (1973)
obtained (+)-21 with only 17% ee by acid treatment of
as cis-muurola-4(15),5-diene (27) (Kim et al. 1994),
bicyclosesquiphellandrene (28) (Melching et al., 1997),
cadina-3,5-diene (29) (Melching et al., 1997) and cadina-
1(6),4-diene (30) (Melching et al., 1997). Finally, the
rearrangement product 31 (Scheme 5) was identi®ed by
1
comparison with published H-NMR data (Polovinka

148
N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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Fig. 2. Sesquiterpenes mentioned in the text.
(+)-4. By repeating this experiment with ( )-4, we got
(+)-21 with 40% ee and (+)-20 and ( )-24 with similar
enantiomeric composition. Our results con®rm that
enantiomeric mixtures of 20, 21 and 24 may be formed
from enantiomerically pure 4 and that the less probable
process via deprotonation/protonation may lead to the
formation of the minor enantiomers. A similar scheme
can be established for the amorphenes and the germa-
crenyl cation J according to experimental evidence
(Scheme 6).
educt for the preparation of these isomerization pro-
ducts (see Table 1).
Nishimura et al. (1979) described ꢁ1-cadinene (36,
Fig. 2) as an additional rearrangement product. We did
not ®nd this component, although it can not be exclu-
ded that it is one of the not identi®ed minor products.
The formation of 36 appears rather unlikely since it
would imply in 1 a protonation of C-5, whereas the
highest electron density and nucleophilicity of a buta-
diene system should be located at the carbon atom in
the 1- or 4-position (Streitwieser et al., 1965).
Although 20 and 21 and their dehydrogenated deri-
vatives are obtained in an unpredictable enantiomeric
composition, germacrene D (1) is, nevertheless, a suitable
Interestingly, we obtained no sesquiterpenes with the
rare bulgarane skeleton (37, Fig. 2), of which only a few

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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149
Scheme 6. Mechanism of formation of products obtained from germacrene D and amorphenes with strong Lewis acids.
natural compounds were reported so far (Connolly and
Hill, 1991). The fact that bulgarenes can not be formed
from germacrene D may explain that they rarely, if at
all, occur in nature.
4(15),5-diene (45) and selina-3,5-diene (46) (Blay et al.,
1996) (Scheme 7). At least for the ®rst two products the
rearrangement proceeds via cation K. For the products
45 and 46 the intermediate cis-substituted cation L can
not be excluded. By acid treatment of 43, besides 44,
which is already formed under the in¯uence of CHCl3,
the intermediates selina-3,7-diene (47) and selina-4,7-
diene (48) (Fricke, 1999) could be identi®ed by GC±MS.
43 is also known as a rearrangement product of germa-
crene C (42, Fig. 2) (Morikawa and Hirose, 1969). The
structure of 43 was con®rmed by NMR and by com-
parison with the product mixture of an isomerization
experiment of 42 (GC±MS). All products resulted in
ꢀ-selinene (49) (Fricke, 1999) after prolonged acid
treatment.
Even more sensitive against acid is the diene 45, which
rearranges in CHCl3 solution even at 0ꢀC mainly to 46.
The structures of these products were con®rmed by
1H-1H-COSY-NMR. ( )-46 was recently synthesized
(Blay et al., 1996), while structure 45 had been ascribed
to ``sibirene'' (Pentegova et al., 1966; Ohta and Hirose,
1972), a sesquiterpene known for more than 30 years,
but with NMR data di€ering from those of the germa-
2.3.2. Eudesmane type sesquiterpenes
Protonation of the 1,10-double bond of 1 initiates the
rearrangement to sesquiterpenes with eudesmane (seli-
nane) skeleton accounting for approx. 10±20% of the
reaction mixture (Scheme 7). Eudesmane derivatives
were obtained as main products when epoxygermacrene
D (38) (Niwa et al., 1978; Shizuri et al., 1986), germa-
crone (39) (Niwa et al., 1976a) and epoxygermacrone
(40) (Niwa et al., 1976b) (Fig. 2), respectively, were
submitted to acid catalyzed rearrangement. Selinenes
are furthermore typical rearrangement products of E,E-
1,5-cyclodecadienes, e. g. germacrene B (41) (Brown et
al., 1967; De Pascual Teresa et al., 1978) and germa-
crene C (42) (Morikawa and Hirose, 1969) (Fig. 2),
suggesting the biosynthetic pathway as shown in
Scheme 1 (cation A!E). Rearrangement of germacrene
D furnished selina-4(15),6-diene (43), selina-4(15),7-diene
(vetiselinene, 44) (Garratt and Porter, 1986), selina-

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(path b) that may either immediately be converted to
opposita-4(15),7-diene (52) or may form opposita-
4(15),11-diene (53) (after hydride shift via cation O) by
deprotonation. Cyclization to the axanes with a cis-
fused indene skeleton is initiated by a conformational
change from M1 to M2. 4(15)-Cycloaxene (54) is
formed by cyclization of cation P. Open-chain analo-
gues of 52 and 53 were not observed. All structures were
veri®ed by careful NMR studies (HMBC, HMQC and
NOESY). The 1-hydroxy compound 55 (Fig. 2, analo-
gous to 51) was isolated from Torilis japonica D.C. 55 is
considered as a biogenetic precursor of oppositol type
compounds like 56 (Fig. 2), although the cyclopropane
ring system is inert against acid treatment (Yamamura
et al., 1982). The observed stability can be con®rmed:
compounds 51 and 54 are almost quantitatively con-
verted to the isomers 57 and 58 with endocyclic double
bonds under retention of the cyclopropane partial
structure. Although the 1-hydroxy derivative 55 was
described, none of the beforementioned oppositane and
axane type hydrocarbons could be detected in our sam-
ples of Torilis japonica D. C. essential oil.
2.3.4. Isodaucadienes
This compound class has been found in functionalized
form in several plants and marine organisms (Connolly
and Hill, 1991). Isodaucadienes contribute approx. 5%
to the reaction mixture of the germacrene D rearrange-
ment products. Interestingly, no isodaucadienes were
obtained when carboxylic acids or strong Lewis acids
like AlCl3 were used as catalysts (Table 1). Isodaucenol
59 (Fig. 2) was formed by treatment of germacrene D
(1) with NBS (Shizuri et al., 1986). Epoxygermacrene D
(38) was isomerized to corresponding isodaucadiene
derivatives (Niwa et al., 1979). According to these
authors it can be concluded that the acid induced rear-
rangement proceeds via the cis-substituted cation Q
(Scheme 9). Hydride shift furnishes isodauca-4,7(14)-
diene (60), which isomerizes under acidic conditions to
isodauca-4,6-diene (61). This compound is also known
to be formed by rearrangement of a-humulene (62, Fig.
2) (Naya and Hirose, 1973; Dauben et al., 1975).
Scheme 7. Sesquiterpenes with selinane skeleton obtained from ger-
macrene D.
crene D rearrangement product. With 46 as a rearran-
gement product of 45 it is obvious that the structure of
sibirene needs to be revised. These facts justify the
doubts of Andersen et al. (1977), who proposed struc-
ture 50 (Fig. 2) for sibirene.
2.3.3. Oppositane and axane type sesquiterpenes
2.3.5. Miscellaneous
Oppositane and axane type sesquiterpenes are rarely
found in nature. They are formed in similar amounts as
the eudesmanes by rearrangement of germacrene D.
Substituted oppositanes have been obtained before by
rearrangement of epoxygermacrene D (38) (Yamamura
et al., 1982; Shizuri et al., 1986). As in the case of the
structurally related selinanes, cation K is formed by
ring closure from cation M1 (Scheme 8), which by loss
of a proton from C-8 may lead to cyclization and for-
mation of 4(15)-cyclooppositene (51) (path a) (Yama-
mura et al., 1982). Alternatively, a Wagner±Meerwein
rearrangement results in a ring contraction to cation N
Although according to above considerations the acid
catalyzed rearrangement of germacrene D proceeds regio-
and, in general, stereospeci®cally to cadinane, eudesmane,
oppositane, axane and isodaucane sesquiterpene skele-
tons, one observes certain transitions between the groups.
In the GC±MS investigation of an acid catalyzed rear-
rangement process of selina-4(15),6-diene (43) to ꢀ-seli-
nene (49) a small amount of isodauca-4,6-diene (61) was
detected (Scheme 10). The rearrangement of 61 to 49
under the in¯uence of strong acid has already been
described (Mehta and Singh, 1977). When 49 was trea-
ted with ion exchange resin Amberlyst115 over several

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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151
days, we obtained cadalene (26) and daucalene (32),
while 61 only gave 26 among other products. In this
context a rearrangement of ꢁ-guaiene (63, Fig. 2) to
epizonarene (21) in concentrated sulfuric acid is
remarkable (Mehta and Singh, 1977).
2.4. Biogenesis of sesquiterpenes involving radical
intermediates
Since the ®rst description of germacrene D (Yoshi-
hara et al., 1969) it is known that it may be converted to
Scheme 8. Sesquiterpenes with the oppositane and axane skeleton obtained from germacrene D.

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were reported more than 25 years ago (Lawrence et al.,
1972), a reexamination seems reasonable.
2.4.1. Photochemical reactions
2.4.1.1. Irradiaton. Germacrene D (1) was irradiated in
n-hexane solution using a low pressure Hg lamp (254
nm). In addition to b-bourbonene (64), which according
to the ``rule of ®ve'' (Brown, 1968), was formed as the
major product (Table 2), traces of a compound with a
similar mass spectrum as for 64 were formed. By GC±MS
comparison this compound was found not to be identical
with a-bourbonene (67) (White and Gupta, 1968), which
can be easily obtained from 64 under acid catalysis
(Scheme 11). It was reported (Heathcock and Badger,
1972; Heathcock et al., 1972) that 1,6-cyclodecadienes
under irradiation formed not only cis,anti,cis-tricy-
clo[5.3.0.02,6]decanes (corresponding to the bourbonene
skeleton) but also cis, syn, cis-isomers. For comparison
we therefore prepared 1,5-di-epi-b-bourbonene (68)
from mint sulphide (69) according to a literature proto-
col (Uyehara et al., 1981, 1988). 69 can be obtained
from 1, if the irradiation proceeds in the presence of
sulphur (Scheme 11) (Yoshida et al., 1979; Takahashi et
al., 1981). A GC±MS comparison of 1,5-di-epi-b-bour-
bonene (68) and of 1,5-di-epi-a-bourbonene (70), which
is obtained from 69 by acid induced rearrangement,
showed no identity with our trace component. It can be
assumed that the unknown bourbonene isomer is iden-
tical with one of the alternate stereoisomers 71, 72 or 73
(Fig. 3). 71 has been described as a constituent of the
gorgonian Eunicea succinea (Gopichand et al., 1984;
Tursch et al., 1978). In the case of the cis,syn,cis-isomer 72
the isopropyl residue is very likely to cause considerable
tensions and repulsion forces in the molecule, while 73 or
other isomers with one of the substituents at the four-
membered ring in opposite direction compared to the
other substituents should be energetically unfavorable
because of ring tension. Nevertheless, compounds of this
type have been described as products of photochemically
induced intramolecular cycloadditions (Orahovats et al.,
1983). As additional products of a cross-addition of the
endocyclic double bonds b-copaene (65) and b-ylangene
(16) (Kulkarni et al., 1987) are formed (Scheme 11).
Their formation can formally be rationalized as shown in
Scheme 12 by a 180ꢀ turn of the 1,10- and 5,6-double
bonds, respectively, following addition of an inner-face
to an outer-face ole®nic double bond. One should, how-
ever, keep in mind, that this is a simpli®ed description
and the molecule is present in a photochemically excited
state (1*), with a geometry and electron distribution dif-
ferent from the ground state (Horspool and Arnesto,
1992).
Scheme 9. Sesquiterpenes with the isodaucane skeleton obtained from
germacrene D.
Scheme 10. Acid catalysed transitions between sesquiterpene groups.
b-bourbonene (64) (Tomioka et al., 1989) and b-
copaene (65) (Kulkarni et al., 1987) in photochemical
rearrangement reactions (Scheme 11). The biosynthesis
of 64 and 65 is still unknown. Due to its molecular
geometry (note the spatial proximity of the double
bonds, Fig. 1) germacrene D is most suited for intra-
molecular rearrangement reactions with radical type
intermediates. This fact suggests to include radical in
addition to cationic intermediates into biogenetic stu-
dies. It has been proposed that a pigment-sensitised
photocyclization of germacrene D (1) or of its endo-
cyclic double bond isomer (66) (Fig. 3) could result in
the formation of the bourbonene and copaene skeletons
(Brown, 1968). As an additional rearrangement
mechanism of terpenes lacking a diphosphate moiety
photochemically triggered cyclizations via single elec-
tron transfer have been suggested (Ho€mann et al.,
1993). Although the photochemical rearrangement of
germacrene D for the production of b-bourbonene has
been an established method for quite some time (Chem.
Abstr., 1978, 1981) and thermally induced reactions
The identi®ed photoisomerization products can be
considered as [2ps+2ps]-cycloaddition products accord-
ing to the Woodward±Ho€mann rules (Ho€mann and
Woodward, 1965, 1968), in case the reaction proceeds in

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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153
Scheme 11. Photochemical and thermal induced rearrangements of germacrene D and isogermacrene D.
it was reported that the reaction rate and the yield in the
formation of b-bourbonene (64) is increased when tri-
plet sensitizers were used (Chem. Abstr., 1978). When 1
was irradiated with a medium pressure Hg lamp (300 nm)
in acetone as a triplet sensitizer complete conversion was
observed after short reaction time. All products obtained
in the direct irradiation reaction were also obtained in
this reaction, but in a di€erent proportion (Table 2). To
make sure that no secondary reactions were induced by
the triplet sensitizer acetone in the ole®nic photoreaction
products, which could be responsible for the di€erences
in the product concentrations, the isolated compounds
and the product mixture were irradiated under identical
conditions. No conversions or changes in the propor-
tions were observed. Comparing the direct and sensibi-
lized irradiations, it can be assumed that germacrene
D reacts at least in part over the S1-state to its photo-
products. Otherwise we would have expected the same
product proportions in both cases. The parallel occur-
ence of triplet transitions in the direct irradiation pro-
cesses is documented by the formation of the di€erent
b-bourbonene isomers. A more detailed comparison
with the results obtained under the conditions of triplet
sensibilization is questionable since isogermacrene D
(74) and 1,5-di-epi-b-bourbonene (68) are formed. 74 is
a photo-educt of 68 and of the products also obtained
from 1 (Table 2). Therefore, a photochemical equili-
brium exists between 1 and 74 under triplet conditions
and the product mixture represents the result of the tri-
plet-sensitized rearrangement of 1 and 74.
Fig. 3. Sesquiterpenes mentioned in the text.
a concerted fashion (Scheme 12, path a). However, a
photo-educt promoted to the S1-state by direct irradia-
tion is rapidly converted into a T1-state by intersystem-
crossing. Thus, most photochemical reactions proceed
in several steps over bi-radical or bi-ionic intermediates
(Scheme 12, alternative path b) (Coxon and Halton,
1974; Horspool and Arnesto, 1992). For germacrene D

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Table 2
Results of the irradiation of 1 under several conditiones and of 74 with triplet sensibilization
Experiment/(%/ratio)
1, 254 nm
1+sulfur,
254 nm
1, 300 nm,
sensibilized (acetone)
74, 300 nm,
sensibilized (acetone)
b-Bourbonene (64)
78.9/18
0.9/0.2
10.0/18.3
0.3/0.6
±
77.0/12.6
0.9/0.2
6.6/1.1
7.0/1.2
6.1/1
50.2/22.5
1.8/0.8
8.2/3.7
24.0/10.8
2.2/1
Monoepi-b-Bourbonene (71, 72 or 73)
1,5-Diepi-b-Bourbonene (68)
b-Copaene (65)
b-Ylangene (16)
Mintsul®de (69)
Isogermacrene D (74)
±
14.9/3.4
4.4/1
1.8/3.3
0.6/1
±
±
86.2/157
±
±
Trace
±
±
Unidenti®ed
0.9/0.2
1.1/2
2.3/0.4
13.5/6.1
16 is produced in excess of 65, while 64 is not obtained
at all. No interconversion is observed in the thermal
treatment of single components (16, 65, 75, 76 or 64)
under the same conditions as used for 1. It should be
mentioned that Roth (1966) obtained products with the
tricyclo[5.3.0.02,6]decane skeleton (corresponding to 64)
in thermal rearrangements of trans,trans- and cic,cis-
1,6-cyclodecadienes, respectively, whereas no tricy-
clo[4.42,7.2.0]decanes (corresponding to 16 und 65) were
formed. While 16 and 65 are generated in photo-
chemically induced rearrangements of 1 from excited
states, 1 reacts in thermal excitations from the ground
state (Horspool and Arnesto, 1992). In a concerted,
thermally induced [2ps+2pa]-cycloaddition one of the
components would react in suprafacial and the other in
antarafacial mode. Considering the substituents at the
ole®nic double bonds, this appears to be highly unlikely
in germacrene D (1). A non-concerted process and a
biradical intermediate can be assumed. According to
Hammond (1955) and Streitwieser (1956) the transition
state is energetically the lower, the higher the stability of
the formed biradical. Accordingly, a reaction pathway
(Scheme 12, path b) is proposed, implying a C1±C6-
bond formation. In this reaction the more stable bi-
radical is formed (tertiary and allylic radical site versus
two secondary radical sites). Collapse of the biradical
(path b) results in 16 and 65, respectively. Correspond-
ingly, for the formation of b-bourbonene (64) a 1,5- or
6,10-biradical would be necessary. In contrast to the
formation of 16 and 65, a biradical with a less favoured
secondary radical site would always be involved, which
may explain that 64 is not formed.
Scheme 12. Mechanisms of formation of muurolane and amorphane
type sesquiterpenes obtained by irradiation and thermal treatment.
2.4.1.2. Thermal treatment. Germacrene D (1) is stable
up to approx. 180ꢀC. By heating up to 240ꢀC over sev-
eral hours in n-hexane solution in a sealed tube 1 is
rearranged to b-ylangene (16), b-copaene (65), E-muur-
olene (75) and E-amorphene (76) as major products
(Koster et al., 1986) (Scheme 12, Table 3). Identical
products were obtained when a solution of 1 was injec-
ted into the hot injector (400ꢀC) of a gas chromato-
graph. Lawrence et al. (1972) also found products
typical for acid induced rearrangements in the thermal
rearrangement of 1 in ethylene glycol at 190ꢀC. We also
detected such products in small amounts, of which the
formation probably has been induced by the presence of
impurities in the liner of the injector, reacting as cataly-
tically active sites.
E-Muurolene (75) and E-amorphene (76) can be ratio-
nalized as products of an intramolecular ene-reaction
according to Scheme 12 (Ho€mann, 1969). Probably the
reaction does not proceed in a concerted fashion as the
same biradical intermediates as in the formation of 16
and 65 can be assumed, however, with an abstraction of
the allylic hydrogen from CH3-14 and without bond
formation to a cyclobutane (path c).
From a mechanistic point of view it is interesting that,
compared to photochemical rearrangement processes,
Moreover, as a side product a compound was detec-
ted, which we identi®ed as a double bond isomer of

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155
Table 3
Results of the thermal induced rearrangement of 1
b-Ylangene (16)
b-Copaene (65)
13.4/1.7
Isogermacrene D (74)
E-Muurolene (75)
E-Amorphene (76)
%/ratio
39.1/5
7.8/1
20.0/2.6
18.0/2.3
germacrene D and which we named isogermacrene D
(74). The cis-con®guration of the 5,6-double bond can
be established from the vicinal coupling constant of
J=11.4 Hz, the con®guration of the 1,10-double bond
was derived from NOESY measurements (Fig. 4).
Accordingly, a chair conformation can be attributed to
74, as it was already con®rmed for similar cis,cis-1,6-
cyclodecadiene systems (Dale and Moussebois, 1966;
Allinger et al., 1972; Ermer and Lifson, 1973; Turner et
al., 1973; White and Bovill, 1975). A boat conformation
is unfavourable because of the repulsion of p-electrons.
Moreover, a bathochromic shift would be expected in
the UV spectrum of 74 for the absorption of the 1,10-
double bond in the case of a boat conformation. How-
ever, the absorption maximum is found slightly below
200 nm (E=7300) as expected for non-conjugated ole-
®ns. It is con®rmed by investigations of the photoelec-
tron spectra of 1,6-cyclodecadienes that almost no
interactions exist for the cis,cis-isomer but very strong
transannular interaction of the endocyclic double bonds
for the trans,trans-isomer (Bischof and Helbronner,
1970), as it is observed for germacrene D (1) (Yoshihara
et al., 1969). Because of the isolated double bond and
based on the equilibrium of the cisoid and transoid
conformations of the conjugated double bonds (1a and
1b, Fig. 1), UV maxima at 208 nm (E=13 400) and 258
nm (E=4500) are observed for 1. No additional maxima
are observed for isogermacrene D (74), which shows
only weak absorption at higher wave length. This
proves that the 4,15- and 5,6-double bonds are not
coplanar and conjugation is not possible. These results
are in agreement with the observation of diene 77 (Fig.
3), for which a dihedral angle between the double bonds
of 60ꢀ is assumed (Dauben et al., 1970). The rearrange-
ment of the trans,trans- to the thermodynamically more
stable cic,cis-isomer of the 1,6-cyclodecadiene system is
supported by experimental results (Dale and Mou-
sesbois, 1966; Roth, 1966).
2.5. Rearrangements of isogermacrene D
As germacrene D (1) proved to be a very useful source
for a multitude of sesquiterpenes, it was prompting to
submit isogermacrene D (74) to the same rearrangement
conditions to investigate, if it could be an educt for new
sesquiterpenes with unknown structures. Moreover, it
was interesting from a mechanistic point of view to ®nd
out, in which way the con®guration of the double bonds
in¯uences the reaction pathways. Isogermacrene D does
not rearrange under the conditions at its formation
from germacrene D (240ꢀC). No investigations were
performed at temperatures above 240ꢀC.
2.5.1. Acid catalyzed rearrangements
74 was submitted to rearrangement under the in¯u-
ence of acidic ion exchange resin Amberlyst115 in
microscale amounts and the products were investigated
by GC±MS and by comparison with a library of refer-
ence compounds. We obtained a-muurolene (9), d- (4)
and o-cadinene (18), 4,7-selinadiene (48), 3,5-selina-
diene (46) and d-selinene (49) in addition to traces of
4,6-isodaucadiene (61) (Scheme 13) in proportions as lis-
ted in Table 4. Although a major portion of the products
could not be identi®ed, it is obvious that the proportion
of selinenes is higher than in the case of germacrene D
(at least 18% selinenes formed from 74 compared to in
total 12% from 1). Consequently, the electrophilic
attack at the 1,10-double bond is more pronounced in
the case of 74 and the cyclization to selinenes is favoured.
A preference for the protonation at the isolated double
bond can be concluded from the considerations about
the conformation of 74. Normally a 1,3-diene, as a
conjugated system, exhibits enhanced reactivity towards
electrophiles. Since the conjugation between the 4,15-
and 5,6-bond in 74 is hindered, the nucleophilicity of the
double bonds is solely determined by their relative elec-
tron density. The cation S1, resulting from protonation
of C-1, has to turn around the 1,10-bond to approach
the 5,6-double bond to facilitate ring closure via S2 to
cations L or Q (Scheme 13). L is most likely represented
Fig. 4. 1H,1H-NOESY interactions observed in isogermacrene D.

156
N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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by a 5-epi-eudesmane skeleton. Thus, ( )-74 with a b-
orientated isopropyl substituent as depicted in Scheme
13, is rearranged to (+)-d-selinene (49) with a b-orientated
C-14 methyl group. The b-position of H-5 consequently
follows from the reaction sequence. It is therefore quite
conceivable that the majority of the unidenti®ed com-
pounds generated in the acid induced rearrangement of
isogermacrene D (74) consists of 5-epi-selinenes. Such
structures have only occasionally been described as
natural compounds (Ando et al, 1994a,b). As an exam-
ple compound 78, a termite defense substance, should
be mentioned (Fig. 3). The acid induced rearrangement
to the cadinenes may be described as shown in Scheme
13. As a major product a-muurolene (9) was obtained
from which the other cadinenes are formed by iso-
merization. As a consequence of the cis-decalin struc-
ture of 9 a rotation of the 1,10-double bond is necessary,
following the protonation of C-15 in 74, before cycliza-
tion to H can take place.
2.5.2. Irradiation
74 was directly irradiated under the same conditions
as 1. In the mixture of products (Table 5) d-elemene (79)
(Ganter and Keller-Wojkiewicz, 1971) and 1,5-di-epi-b-
bourbonene (68) were identi®ed by comparison of their
GC±MS data, while the tricyclic compound 80 and the
cyclobutene derivative 81 were identi®ed by NMR. The
irradiation of isogermacrene D (74), as in the case of 1,
was repeated with acetone as triplet sensitizer. In con-
trast to 1 the product spectrum of 74 is changed com-
pletely, thus proving a process originating from the
singlet state for the products of the direct irradiation.
The formation of 68 can be explained by a conforma-
tional change from chair-74 to boat-74 (Scheme 11)
prior to a concerted [2ps-2ps]-cycloaddition. Product 81
is formed by an electrocyclic reaction of the diene sys-
tem (Ho€mann and Woodward, 1968; Dauben et al.,
1970). From the conformation of 74 in its ground state
it can be concluded that 81 is formed as 6S,7S-isomer.
However, following a conformational turn of 74 around
C-3 and C-7 and subsequent cyclization the diastereo-
isomer 82 with 6R,7S-con®guration (Fig. 3) may be
obtained. Incidentally, inspection of the GC±MS data
of some minor constituents reveals a compound with
identical mass spectrum and very similar retention time
as 81 which could be identical with 82. The photo-
chemically induced rearrangements to 79 and 80 prob-
ably proceed simultaneously. Primarily a 1,5-sigmatropic
rearrangement has to take place, which proceeds in a
concerted way via an antarafacial arrangement and
which is favoured by the conformation of 74 as descri-
bed above. Formally the (not identi®ed) intermediate 83
is formed, which according to the rearrangement
mechanism possesses a 4,5-trans- and a 6,7-cis-double
bond (Ho€mann and Woodward, 1968). 83 may exist in
a photochemical equilibrium with the cis,cis-isomer 84
as it is assumed for the photochemical rearrangement of
Scheme 13. Sesquiterpenes obtained from isogermacrene D under acid
catalysis.
Table 4
Products (%) of the acid catalyzed rearrangement of 74
a-Muurolene (9)
d-Cadinene (4)
o-Cadinene (18)
Unidenti®ed
15.7
1.8
4,7-Selinadiene (48)
3,5-Selinadiene (46)
d-Selinene (49)
0.5
1.9
15.2
0.6
0.8
ꢁ63
4,6-Isodaucadiene (61)
Table 5
Results of the irradiation of 74
1,5-Diepi-b-bourbonene (68)
16.6/4.9
d-Elemene (79)
3.4/1
Tricyclic compound 80
Cyclobutene derivative 81
Unidenti®ed
23
%/ratio
29.8/8.8
26.2/7.7

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157
77 to 85 (Fig. 3) (Dauben et al., 1970). Compound 80
may be formed from 84 via a concerted [2ps-2ps]-
cycloaddition or from 83 via a biradical intermediate. An
alternate cross-addition would generate the tricyclic
tion of eudesmane and the related oppositane and axane
as well as isodaucane type compounds could be proved.
In photochemical conversions mainly bourbonane,
muurolane and amorphane type sesquiterpene hydro-
carbons were obtained. Furthermore, a new germacrene
D isomer, isogermacrene D (74), was discovered and its
reactivity was investigated and compared with that of
germacrene D. By speci®c choice of the rearrangement
conditions the use of 1 as a synthetic precursor for certain
cadinane type sesquiterpenes can be proposed. Starting
from a certain enantiomeric composition of 1, products of
equal or similar enantiomeric composition are obtained,
which proved to be very useful reference compounds for
the identi®cation and stereochemical investigation of ses-
quiterpene constituents of essential oils. Thus, it could be
proved that not E-bulgarene (Vlahov et al., 1967) but E-
amorphene is a constituent of Bulgarian peppermint oil
(Bulow, 1999). d-Amorphene (15) was for the ®rst time
detected as a natural compound in both enantiomeric
forms in various essential oils (Melching et al., 1997).
Furthermore, ( )-muurola-4,11-diene was identi®ed as a
minor constituent in the essential oil of Amyris balsami-
fera (Konig et al., 1999) and its (+)-enantiomer as a major
constituent of the moss Mnium hornum (Musci) (Konig,
2000) by a chemical correlation with an enantiomeric
mixture of g-muurolene obtained by rearrangement of a
corresponding mixture of germacrene D enantiomers. A
similar approach was successfully applied in the determi-
nation of the absolute con®guration of 11-bourbonene, a
new sesquiterpene hydrocarbon from the essential oil of
liverworts (Warmers et al., 1998).
1
compound 86 (Fig. 3). The H-NMR-spectrum of 80
shows a doublet for H-8 (J=8.1 Hz). In the tricyclic
compound 86 a triplet would be expected for H-8, since
the torsion angle between H-8 and the two H-9 protons
should be identical, which should give identical coupling
constants for both protons. The doublet in 80 results from
a 0ꢀ angle for proton H-9a, while the angle to proton H-
9b should be close to 90ꢀ (Jꢂ0 Hz, Fig. 3). It could fur-
ther be proved by NOESY measurements that 80, which
shows strong interaction of H-5 and both methyl sing-
lets, has a cis,syn,cis- and not a cis,anti,cis-con®guration.
Compounds of type 80 with both cis,syn,cis- and cic,an-
ti,cis-con®gurations were obtained by irradiation of ger-
macrene B (41) (Reijnenders et al., 1980; Peijnenburg et
al., 1988). d-Elemene (79) is a typical Cope rearrangement
product easily obtained by thermal treatment of germa-
crene C (42) (Konig et al., 1996). Here it could be formed
from 83 or 84 as an intermediate by a mechanism most
likely involving a biradical. 79 is also formed from 80 as a
minor constituent by thermal treatment. Therefore, it can
not be excluded that 80 is rearranged to 79 by the heat
developed during the reaction (ꢂ50ꢀC) over a biradical
intermediate.
The photo products obtained from the triplet state of
74 in a qualitative way correspond to those obtained
from the triplet-sensitized irradiation of germacrene D
(1) (Table 2). In comparing the generated product
amounts from both experiments it can be concluded
that the triplet states of 1 and 74 are not identical.
Otherwise identical product amounts should have been
obtained. This can be rationalized by the fact that the
photochemical excitation primarily e€ects the 1,3-diene
system but does not e€ect the non-conjugated double
bonds which have di€erent con®guration in 1 and 74.
From the quantitative comparison of di-epi-b-bourbo-
nene (68) and of b-copaene (65) it can be concluded that
74 as formed by isomerization of 1 is not the only
precursor of 68, but that 68 is also generated from the
triplet state of 1. While 74 could be identi®ed as an
intermediate in the photochemical rearrangement of 1,
there is no indication that 74 can isomerize to 1.
However, it should be realized that 1 reacts faster under
irradiation than 74 and may be not detected for this
reason.
From a biogenetic point of view a large variety of
products were identi®ed for which germacrene D or a
germacrenyl cation D could be a potential precursor in
the enzymatic sesquiterpene biosynthesis. The detection
of some new natural compounds, as mentioned above
and the correction of erroneous stereochemical assign-
ments, as described for ꢁ-amorphene (12), demonstrate
the value of systematic studies of sesquiterpene struc-
tural correlations.
4. Experimental section
4.1. Collection of plant material and isolation of
essential oils
Solidago canadensis L. and S. gigantea Ait. were col-
lected at several locations near Hamburg and at áro/
Denmark (summer 1995 and 1996), species of S. caesia,
S. missouriensis, S. nemoralis, S. oliensis, S. rigida, S.
squarossa and S. virgaurea ssp. praecox were provided
by the Botanical Garden of the University of Hamburg
(summer 1996), or collected at Zion National Park
(Utah/USA) and at Crabtree Falls (Virginia/USA)
(summer 1997). Samples of the collected Solidago
3. Conclusions
It was shown that germacrene D (1) is isomerized
under acidic conditions to a multitude of naturally
occuring cadinane, muurolane and amorphane type
sesquiterpene hydrocarbons. Furthermore, the forma-

158
N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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È
species are deposited in the Institut fur Allgemeine
Botanik, University of Hamburg. S. canadensis L.
essential oil from plants collected at several locations in
Poland was kindly provided by Dr. D. Kalemba, Tech-
nical University, Lodz/Poland. Torilis japonica D.C.
was collected at several locations in Germany (autumn
1996). Volatile constituents of the plants were obtained
by hydrodistillation (2 h) of aq. homogenates of plant
material using n-hexane as collection solvent.
position of known components was tested by compar-
ison with enantiomerically pure authentic reference
material. Only for new compounds with a purity 595%
(GC) the optical rotation was determined. Since we
obtained enantiomeric mixtures, the values for single
enantiomers were extrapolated.
4.8. Photolyses
Irradiations were performed with a Rayonet RPR-100
photoreactor equipped with 254 and 300-nm lamps,
respectively.
4.2. Isolation of germacrene D (1)
Solidago essential oil was either chromatographed on
silica gel at 25ꢀC with n-pentane as eluent or fractio-
nated by prep. GC to obtain 1 in 99% purity. Pre-
parative GC (Hardt and Konig, 1994). Isolation of all
pure compounds was performed by preparative GC on
a Varian 1400 instrument, equipped with stainless steel
columns (Silcosteel, Amchro). The substances were
fractionated using a column with 10% polysiloxane SE
30 on Chromosorb W-HP (1.85 mÂ4.3 mm). (+)-6 and
( )-12 were isolated and 18 and 33 were further puri®ed
on a column with 2.5% heptakis(2,6-di-O-methyl-3-O-
pentyl)-ꢃ-cyclodextrin in OV-1701 (w/w) on Chromo-
sorb G-HP (2.00 mÂ5.3 mm; 2,6-Me-3-Pe-ꢃ-CD (Konig
4.9. Acidic rearrangement of germacrene D (1)
(a) p-Toluene sulfonic acid: An enantiomeric mixture
of 1 [( ):(+)=1.3:1, 270 mg, 1.32 mmol] in a solution
of p-toluene sulfonic acid (10 mg) in CH2Cl2 (15 ml) was
stirred at room temp. (rt) until 1 had completely dis-
appeared. The reaction was controlled by GC. The
solution was shaken several times with a saturated aqu-
eous solution of NaHCO3 (2 ml). The solvent was eva-
porated and the residue was prefractionated by column
chromatography on silica gel at 25ꢀC with n-pentane
as eluent. The fractions were further fractionated by
prep. GC. (b) Amberlyst115 (Fluka): A solution of 1
[( ):(+)=1.3:1, 61 mg, 0.3 mmol] in n-hexane (1.5 ml)
was mixed with Amberlyst115 (8 mg) and left at rt until
1 had completely disappeared (GC control). The solu-
tion was ®ltered, the catalyst washed once with n-hexane
(0.5 ml) and the solvent evaporated. Isolation of single
compounds was performed as described. (c) BF3: To a
solution of 1 [(+):( )=1.2:1, 420 mg, 2.06 mmol] in
et al., 1992a). Helium was employed as carrier gas at a
1
¯ow rate of 240 ml min
.
4.3. Enantioselective capillary GC
Capillary columns with cyclodextrin derivatives were
prepared as described earlier (Konig et al., 1992b).
.
4.4. NMR spectroscopy
diethyl ether (180 ml) BF3 Me2O (50 ml, as 60% solu-
tion in dimethyl ether, 0.21 mol) was added at 0 ꢀC. The
solution was stirred for 12 min. Then ice cooled aqueous
0.5 N KOH (150 ml) was added. The organic layer was
washed several times with aqueous 0.5 N KOH, then
with satured aqueous NaCl and dried over MgSO4; the
solvent was evaporated. Puri®cation and isolation, as
described. (d) AlCl3 or ZnCl2: To a solution of 1
NMR measurements were performed with the instru-
ments WM 400 (400 MHz, Bruker) and WM 500 (500
MHz, Bruker) using TMS (d=0.00 ppm) as internal
standard.
4.5. UV spectroscopy
3
[( ):(+)=2:1, 1.5 mg, 7Â10 mmol] in CH2Cl2 (0.5
UV spectra were recorded on a Perkin Elmer 552
spectrometer.
ml) AlCl3 (15 mg, 0.03 mmol) was added and stirred for
1 h. The mixture was diluted with diethyl ether (0.5 ml)
and washed two times with aqueous 0.5 N KOH (0.5
ml), satured aqueous NaCl and dried over MgSO4. The
solution was used for GC analysis.
4.6. GC±MS
Electron impact (70 eV) GC±MS measurements
were carried out on a Hewlett Packard HP 5890 gas
chromatograph coupled to a VG Analytical VG 70-
250S mass spectrometer.
4.10. Germacrene D (1)
1H NMR (Kitamura et al., 1976; Mori et al., 1990),
13C NMR (Randriamiharisoa et al., 1968), 13C NMR
(125.8 MHz, C6D6): ꢀ=149.2 (s, C-4), 136.6 (d, C-5),
133.9 (s, C-10), 133.4 (d, C-6), 130.1 (d, C-1), 109.6 (t,
C-15), 53.8 (d, C-7), 41.2 (t, C-9), 35.1 (t, C-3), 33.2 (d,
C-11), 29.9 (t, C-2), 27.0 (t, C-8), 21.2, 19.7 (2 q, C-12,-
4.7. Polarimetry
Optical rotation measurements were performed with a
Perkin Elmer 241 polarimeter. The enantiomeric com-

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
È
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159
13), 16.2 (q, C-14); MS: m/z (%): 204 (16) [M+], 161
(100) [M+ C3H7], 133 (15), 120 (23), 119 (29), 105 (47),
91 (42), 81 (37).
4.15. ꢂ-Muurolene (9)
1H NMR (Beecham and Djerassi, 1978), H NMR
(400 MHz, CDCl3): ꢀ=5.48 (mc, 1H), 5.41 (br. s, 1H),
2.10±1.70 (m, 8H), 1.69 (br. s, 6H; H-14,-15), 1.48±1.36
(m, 2H), 0.89, 0.83 (2 d, J12/13-11=7 Hz, 6H; H-12,-13);
MS: m/z (%): 204 (23) [M+], 189 (9) [M+ CH3], 161
(50) [M+ C3H7], 105 (100), 94 (31), 93 (34).
1
4.11. ꢀ-Cadinene (4)
1H, 13C NMR (Wenkert et al., 1992; Randriamihar-
isoa et al., 1968); MS: m/z (%): 204 (42) [M+], 189 (17)
[M+ CH3], 161 (100) [M+ C3H7], 134 (67), 119 (58),
105 (53), 91 (35).
4.16. Cadina-1,4-diene (10)
4.12. ꢁ-Cadinene (6)
1H, 13C NMR (Connolly et al., 1982); MS: m/z (%):
204 (22) [M+], 161 (49) [M+ C3H7], 119 (100), 105
(77).
1H NMR (Andersen and Syrdal, 1970), 13C NMR
(100.6 MHz, CDCl3): ꢀ=122.5 (d, C-5), 103.2 (t, C-14),
46.9 (d, C-7), 45.2 (d, C-6), 44.2 (d, C-1), 36.3 (t, C-9),
30.5 (t, C-3), 26.6 (t, C-8), 26.2 (d, C-11), 25.8 (t, C-2),
23.9 (q, C-15), 21.6, 15.1 (2 q, C-12,-13); MS: m/z (%):
204 (15) [M+], 189 (6) [M+ CH3], 161 (100)
[M+ C3H7], 133 (22), 119 (32), 93 (36), 91 (38), 79 (30).
4.17. ꢂ-Copaene (11)
1H, 13C NMR (Wenkert et al., 1992); MS: m/z (%):
204 (15) [M+], 161 (95) [M+ C3H7], 161 (95), 119
(100), 105 (96), 93 (58).
4.13. ꢂ-Cadinene (7)
4.18. ꢁ-Amorphene (12)
1
1H NMR (Naya and Kotake, 1969), H NMR (400
1H NMR, 13C NMR (Weyerstahl et al., 1996); MS:
m/z (%): 204 (20) [M+], 189 (6) [M+ CH3], 161 (100)
[M+ C3H7], 133 (21), 119 (50), 105 (56), 93 (60).
MHz, CDCl3): ꢀ=5.61 (br. s, 1H), 5.40 (br. s, 1H), 2.21
(mc, 1H; H-11), 1.76±2.14 (m, 7H), 1.62 (br. s, 6H; H-
14,-15), 1.43 (mc, 1H), 1.25 (mc, 1H), 0.89, 0.79 (2 d, J12/
13-11=6.9 Hz, 6H; H-12,-13); 13C-NMR (100.6 MHz,
CDCl3): ꢀ=136.03 (s), 134.85 (s), 122.39 (d), 121.96 (d),
42.62 (d), 42.39 (d), 41.13 (d), 31.37 (t), 26.35 (d), 26.66
(t), 24.96 (t), 23.78 (q), 20.92 (q), 20.72 (q), 14.54
(q); MS: m/z (%): 204 (21) [M+], 189 (10) [M+ CH3],
161 (58) [M+ C3H7], 119 (20), 105 (100), 93 (29), 81
(30).
4.19. ꢂ-Amorphene (13)
1
1H NMR (Gregson and Mirrington, 1976), H NMR
(400 MHz, CDCl3): ꢀ=5.42 (m, 1H), 5.17 (s, 1H), 2.64
(br. s, 1H), 2.32 (br. s, 1H), 1.94-2.03 (m, 2H), 1.78±1.89
(m, 1H), 1.63 (mc, 6H), 1.50±1.71 (m, 4H), 1.09±1.18
(m, 1H), 0.94, 0.91 (2 d, J12/13-11=6.6 Hz, 6H; H-12,-
13); MS: m/z (%): 204 (28) [M+], 189 (10) [M+ CH3],
161 (54) [M+ C3H7], 119 (26), 105 (100), 94 (58), 93
(56).
4.14. ꢁ-Muurolene (8)
1H NMR (Beecham and Djerassi, 1978), 13C NMR
(Weyerstahl et al., 1996; Randmriamiharisoa et al., 1968),
1H-NMR (400 MHz, CDCl3): ꢀ=5.54 (br. d, J=3.6 Hz,
1H; H-5), 4.65 (br. s, 1H; H-14a), 4.59 (t, J=2.0 Hz, 1H;
H-14b), 2.37 (mc, 1H; H-1), 2.19 (dt, Jt=4 Hz, JAB=13.2
Hz, 1H; H-9 eq), 2.13 (dtt, J9ax-8eq= 4 Hz, J9ax-14=1.9 Hz,
J9ax-9eq,8ax=13.2 Hz, 1H; H-9ax), 1.87±2.10 (m, 5H), 1.67
(s, 3H; H-15), 1.66 (dq, J8eq-7,9ax/eq=4 Hz, JAB=12.2 Hz,
1H; H-8eq), 1.37±1.45 (m, 2 H), 0.91 (d, J12-11=6.8 Hz,
3H; H-12), 0.88±1.07 (m, 1H; H-8ax), 0.78 (d, J13-11=6.8
Hz, 3H; H-12); MS: m/z (%): 204 (21) [M+], 189 (5) [M+-
CH3], 161 (100) [M+- C3H7], 133 (19), 119 (40), 105 (48),
93 (40); 13C-NMR (100 MHz, CDCl3): ꢀ=154.32, 133.86
(2 s, C-4,-10), 124.57 (d, C-5), 106.51 (t, C-14), 44.80 (d, C-
7), 43.54 (s, C-1), 39.75, 26.71 (2 d, C-6,-11), 31.62 (t, C-9),
30.86 (t, C-3), 25.87 (t, C-8), 25.41 (t, C-2), 23.89 (q, C-15),
21.72, 15.49 (2 q, C-12,-13); MS: m/z (%): 204 (19) [M+],
189 (7) [M+ CH3], 161 (100) [M+ C3H7], 133 (23), 119
(45), 105 (52), 93 (50), 91 (42), 79 (38).
4.20. a-Ylangene (14)
1H NMR (Melching et al., 1997), 13C NMR (De
Buyck et al., 1989); MS: m/z (%): 204 (20) [M+], 189 (8)
[M+ CH3], 161 (70) [M+ C3H7], 120 (70), 119 (91),
105 (100), 93 (82).
4.21. ꢀ-Amorphene (15)
1H NMR, MS (Melching et al., 1997).
4.22. ꢃ-Cadinene (17)
1H NMR (Fringuelli et al., 1985), 1H NMR (400
MHz, CDCl3): ꢀ=5.43 (mc, 2H), 2.30 (mc, 1H), 2.08
(mc, 1H), 2.00 (dsept, J11-7=2.8 Hz, J11-12/13=6.8 Hz,
1H; H-11), 1.68, 1.62 (2 s, 6H, H-14,-15), 1.30±1.95 (m,
7 H), 0.91, 0.77 (2 d, J12/13-11=6.8 Hz, 6H; H-12,-13);

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N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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13C-NMR (100 MHz, CDCl3): ꢀ=121.44, 120.46, 42.83,
41.19, 38.37, 34.60, 30.56, 25.70, 23.41, 23.16, 20.88,
20.20, 14.27; MS: m/z (%): 204 (28) [M+], 161 (46)
[M+ C3H7], 119 (41), 105 (62), 93 (100).
4.30. Bicyclosesquiphellandrene (28)
MS (Melching et al., 1997): m/z (%): 204 (25) [M+],
189 (10) [M+ CH3], 161 (100) [M+ C3H7], 147 (17),
133 (15), 119 (36), 105 (61), 91 (49).
4.23. !-Cadinene (18)
4.31. cis-/trans-Calamenene (22/23)
1H NMR (Vlahov et al., 1967) [these data were origin-
ally assigned to 4 which was assumed to be 18 (Connell et
MS (Croft et al., 1978; Melching et al., 1997): m/z
(%): 202 (8) [M+], 159 (100) [M+ C3H7], 128 (16).
1
al., 1968; Nagasampagi et al., 1968)], H NMR (400
MHz, CDCl3): d=5.36 (br. s, 1H; H-3), 2.96 (br. d,
JAB=19.5 Hz, 1H; H-2a), 2.55 (br. d, JAB=19.5 Hz, 1H;
H-2b), 1.55-2.15 (m, 12H), 1.04±1.39 (m, 3H), 0.95, 0.82
(2 d, J12/13-11=6.6 Hz, 6H; H-12,-13); MS: m/z (%): 204
(37) [M+], 161 (63) [M+ C3H7], 119 (100), 105 (72).
4.32. ꢂ-Calacorene (24)
1H NMR (Hardt, 1994), 1H NMR (400 MHz, CDCl3):
ꢀ=7.12 (d, J2-3=7.6 Hz, 1H; H-2), 7.00 (mc, 1H; H-3),
6.92 (s, 1H; H-5), 5.66 (s, 1H; H-9), 2.29±2.37 (m, 6H; H-
7,-8a/b,-15), 2.01 (br. s, 3H; H-14), 1.88 (mc, 1H; H-11),
0.89, 0.80 (2 d, J12/13-11=6.6 Hz, 6H; H-12,-13); MS: m/z
(%): 200 (16) [M+], 157 (100) [M+ C3H7], 142 (36).
4.24. !-Amorphene (19)
[ꢂ]2D0= 43 (c=0.002, CHCl3); H NMR (400 MHz,
1
CDCl3): ꢀ=5.36 (br. s, 1H; H-3), 2.91 (mc, 1H; H-2a),
2.55 (mc, 1H; H-2b), 2.35 (mc, 2H), 1.66, 1.62 (2 br. s,
6H; H-14,-15), 1.15±2.10 (m, 7H), 0.93 (d, J12/13-11=6.6
Hz, 6H; H-12,-13); MS: m/z (%): 204 (38) [M+], 161
(98) [M+ C3H7], 119 (100), 105 (79).
4.33. ꢁ-Calacorene (25)
MS (Adachi and Mori, 1983): m/z (%): 200 (16)
[M+], 157 (100) [M+ C3H7], 142 (36).
4.25. Zonarene (20)
4.34. Cadalene (29)
1H, 13C NMR, MS (Melching et al., 1997).
4.26. Epizonarene (21)
1H NMR (Bohlmann and Zdero, 1976); MS: m/z (%):
198 (42) [M+], 183 (100) [M+ CH3], 168 (13).
4.35. 4S,4aS-1,7-Dimethyl-4-(methylethyl)-2,3,4,4a,5,6-
hexahydronaphthalene (31)
1H NMR (Andersen et al., 1973), 1H-NMR (400 MHz,
CDCl3): ꢀ=6.22 (s, 1H; H-5), 3.03 (sept, J11-12/13=7 Hz;
H-11), 2.19±1.90 (m, 6H), 1.77 (s, 3H, H-15), 1.75±1.55
(m, 2H), 1.21±1.09 (m, 2H), 0.99 (d, J14-10=6 Hz),
0.96, 0.95 (2 d, J12/13-11=7 Hz; H-12,-13); MS: m/z (%):
204 (57) [M+], 189 (43) [M+ CH3], 161 (100)
[M+ C3H7], 147 (18), 133 (23), 119 (39), 105 (58), 91
(36), 81 (67).
1H NMR (Polovinka et al., 1981), 1H NMR (400
MHz, CDCl3): d=6.17 (s, 1H; H-8), 1.80±2.20 (m, 5H),
1.78 (br. s, 3H; Me-7), 1.70 (br. s, 3H; Me-1), 1.65 (mc,
1H), 1.00±1.25 (m, 4H), 0.96, 0.74 (2 d, JMe(iPr)-
H(iPr)=7.1 Hz, 6H; Me(iPr)); MS: m/z (%): 204 (69)
[M+], 189 (15) [M+ CH3], 161 (100) [M+ C3H7], 145
(15), 133 (17), 122 (38), 119 (59), 105 (58), 91 (38).
4.27. cis-Muurola-4(15),5-diene (27)
4.36. Daucalene (32)
MS (Kim et al., 1994): m/z (%): 204 (16 ) [M+], 161
(100) [M+ C3H7], 119 (20), 105 (27), 91 (21).
MS (Hashidoko et al., 1992): m/z (%): 198 (51) [M+],
183 (100) [M+ CH3], 168 (31).
4.28. Cadina-1(6),4-diene (30)
4.37. Selina-4(15),6-diene (43)
MS (Melching et al., 1997): m/z (%): 204 (29) [M+],
189 (13) [M+ CH3], 161 (100) [M+ C3H7], 134 (15),
119 (24), 105 (36), 91 (18), 81 (29).
1H NMR (400 MHz, CDCl3): ꢀ=5.41 (s, 1H; H-6), 4.75,
4.56 (2 q, J=1.5 Hz, 2H; H-15), 2.53 (br. s, 1H; H-5), 2.32
(dm, JAB=12.7 Hz, 1H; H-3eq), 2.20 (br. sept, J11-12/
13=7.1 Hz, 1H; H-11), 1.89±2.14 (m, 3H), 1.62±1.73 (m,
2H, H-2a/b), 1.40±1.52 (m, 3H), 1.29 (dt, J1ax-2eq=5.1 Hz,
J1ax-1eq,2ax=12.7 Hz, 1H; H-1ax), 1.02 (d, J12/13-11=7.1 Hz,
6H; H-12,-13), 0.63 (s, 3H; H-14); 13C-NMR (100.6 MHz,
CDCl3): d=142.90, 149.86 (2 s, C-4,-7), 118.58 (d, C-6),
4.29. Cadina-3,5-diene (29)
MS (Melching et al., 1997): m/z (%): 204 (22) [M+],
161 (100) [M+ C3H7], 119 (41), 105 (64), 91 (16), 81
(22).

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
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161
104.74 (t, C-15), 49.09 (d, C-5), 40.13 (t, C-1), 37.63 (t, C-
9), 36.77 (t, C-3), 35.04 (d, C-11), 23.77 (t, C-2), 23.28 (t,
C-8), 21.84, 21.47 (2 q, C-12,-13), 15.50 (q, C-14); MS:
m/z (%): 204 (40) [M+], 189 (27) [M+ CH3], 161 (100)
[M+ C3H7], 133 (42), 119 (31), 105 (52), 91 (49).
4.44. 4(15)-Cyclooppositene (51)
[ꢂ]2D0=+18.7 (c=1.47, CHCl3); H NMR (500 MHz,
CDCl3): ꢀ=4.71, 4.75 (2 q, J15a-15b,3a/b=1.8 Hz, 2H; H-
15), 2.24 (dm, JAB=11.7 Hz, 1H; H-3a), 1.80±1.90 (m,
1H; H-3b), 1.75 (dd, J9a-8=7.0 Hz, JAB=12.2 Hz, 1H; H-
9a), 1.47±1.60 (m, 3H), 1.47 (br. d, J5-6=4.9 Hz, 1H; H-
5), 1.25 (ddd, J6-7=2.9 Hz, J6-5=4.9 Hz, J6-8=7.7 Hz,
1H; H-6), 1.20±1.29 (m, 1H, H-1a), 1.12 (ddt, J8-7,9b=3.6
Hz, J8-9a=7.0 Hz, J8-6=7.7 Hz, 1H; H-8), 0.94 (mc, 6H;
H-12,-13), 0.83±1.00 (m, 2H), 0.79 (s, 3H, H-14), 0.51
(ddd, J7-6=2.9 Hz, J7-8=3.6 Hz, J7-11=8.0 Hz, 1H; H-7);
13C-NMR (125.8 MHz, CDCl3): ꢀ=148.54 (s, C-4),
103.94 (t, C-15), 59.84 (d, C-5), 54.77 (s, C-10), 48.69 (d,
C-7), 44.95 (t, C-9), 36.96 (t, C-1), 35.49 (t, C-3), 32.48 (d,
C-11), 24.79 (d, C-6), 24.58 (d, C-8), 23.12 (t, C-2), 22.00,
21.84 (2 q, C-12,-13), 19.71 (q, C-14); MS: m/z (%): 204
(17) [M+], 189 (34) [M+ CH3], 161 (75) [M+ C3H7],
147 (42), 133 (100), 119 (51), 105 (86), 91 (84).
1
4.38. Selina-4(15),7-diene (vetiselinene, 44)
1
1H, 13C NMR (Garratt and Porter, 1986), H NMR
(400 MHz, CDCl3): ꢀ=5.29 (br. d, J=5.7 Hz, 1H; H-8),
4.58, 4.78 (2 br. s, 2H, H-15), 2.35 (dm, 1H), 2.20 (sep, J11-
12/13=6.9 Hz, 1H; H-11), 1.50±2.05 (m, 9H), 1.30 (dt,
Jd=3.5 Hz, Jt=13.5 Hz, 1H), 1.01, 1.02 (2 d, J12/13-11=6.9
Hz, 6H; H-12,-13), 0.67 (s, 3H; H-14); MS: m/z (%): 204
(63) [M+], 189 (37) [M+ CH3], 161 (85) [M+ C3H7], 147
(32), 133 (68), 119 (42), 105 (100), 93 (82), 91 (73).
4.39. Selina-4(15),5-diene (45)
1H NMR (500 MHz, CDCl3): ꢀ=5.44 (br.s, 1H; H-6),
4.58, 4.77 (2 dd, J15-3eq=2.0 Hz, JAB=3.0 Hz, 2H; H-15a/
b), 2.36 (ddt, J3eq-2eq=4 Hz, JAB=13.2 Hz, J3eq-
2ax,15a=2.0 Hz, 1H; H-3eq), 2.10 (ddt, JAB=13.2 Hz, J3ax-
2ax=6.1 Hz, J3ax-2eq,15a=2.2 Hz, 1H; H-3ax), 2.01±2.10
(m, 1H, H-7), 1.69 (dt, J=13.1 Hz, J=4 Hz, 1H; H-2b),
1.48±1.69 (m, 5H), 1.35±1.44 (m, 2H), 1.32 (dt, J1ax-
2eq=4.5 Hz, J1ax-1eq,2ax=13.2 Hz, 1H; H-1ax), 0.95 (s, 3H;
4.45. Opposita-4(15),7-diene (52)
1H NMR (400 MHz, CDCl3): ꢀ=4.99 (dsept, J7-12/
13=1.3 Hz, J7-6=9.5 Hz, 1H; H-7), 4.39, 4.73 (2 q, J15a-
15b,3eq,5=1.9 Hz, 2H; H-15), 2.75 (ddt, Jd=6.6 Hz, J6-
7=9.5 Hz, Jt=10.8 Hz, 1H; H-6), 2.25 (ddt, J1eq-
2ax,15a=1.6 Hz, J3eq-2eq=4.7 Hz, JAB=13.5 Hz, 1H; H-
3eq), 1.94±2.04 (m, 1H; H-8b), 1.91 (br. dt, J3ax-2eq 5.3
Hz, J3ax-3eq,2ax=13.5 Hz, 1H; H-3ax), 1.67 (2 d, J12/13-
7=1.5 Hz, 6H; H-12,-13); 1.48±1.73 (m, 5H), 1.24±1.40
(m, 3H), 0.68 (s, 3H; H-14); 13C NMR (125.8 MHz,
CDCl3): ꢀ=156.1, 111.6 (2 s, C-4,-11), 130.43 (d, C-7),
105.42 (t, C-15), 59.92 (d, C-5), 43.9 (s, C-10), 39.72 (t,
C-1), 39.08 (t, C-9), 36.29 (d, C-6), 35.99 (t, C-3), 29.05
(t, C-8), 25.84, 18.22 (2 q, C-12,-13), 23.76 (t, C-2), 18.52
(q, C-14); MS: m/z (%): 204 (9) [M+], 189 (75)
[M+ CH3], 161 (62) [M+ C3H7], 148 (20), 135 (43),
109 (46), 82 (100), 67 (48).
H-14), 0.88, 0.90 (2 d, J12/13-11=7.1 Hz, 6H; H-12,-13); 13
C
NMR (125.8 MHz, CDCl3): ꢀ=149.96 (s), 123.97 (s),
118.88 (d), 108.07 (t), 42.54 (d), 41.32 (t), 38.84 (t), 35.77 (t),
35.51 (s), 32.22 (d), 24.60 (q), 22.44 (t), 21.19 (t), 19.53 (q),
19.09 (q); MS: m/z (%): 204 (28) [M+], 189 (9) [M+ CH3],
161 (100) [M+ C3H7], 133 (38), 119 (25), 105 (50), 91 (46).
4.40. Selina-3,5-diene (46)
1H NMR, 13C-NMR (Blay et al., 1996); MS: m/z (%):
204 (13) [M+], 189 (3) [M+ CH3], 161 (100)
[M+ C3H7], 119 (17), 105 (25), 81 (30).
4.46. Opposita-4(15),11-diene (53)
4.41. Selina-3,7-diene (47)
1H NMR (500 MHz, CDCl3): ꢀ=4.70, 4.68 (2 mc, 2H;
H-12), 4.78, 4.48 (2 q, J=1.7 Hz, 2H; H-15), 2.39 (d,
JAB=14.6 Hz, 1H; H-7a), 2.27 (dm, JAB= 13.3 Hz, 1H;
H-3a), 2.14 (ddq, J6-7a=2.8 Hz, J6-8a=5.6 Hz, J6-
5,7b,8b=11.0 Hz, 1H; H-6), 1.85±1.95 (m, 2H), 1.74 (br.
s, 3H, H-13), 1.69 (dd, J7-6=10.7 Hz, JAB=14.6 Hz,
1H; H-7b), 1.65±1.73 (m, 1H; H-1a), 1.53±1.64 (m, 3H),
1.50 (dd, J=8.4 Hz, J=10.5 Hz, 1H; H-9a), 1.22±1.33
(m, 3H), 0.66 (s, 3H; H-14); 13C-NMR (125.8 MHz,
CDCl3): ꢀ=110.45 (t, C-12), 104.41 (t, C-15), 59.45 (d,
C-5), 43.91 (t, C-7), 39.52 (t, C-1), 39.08 (t, C-9), 36.20
(t, C-3), 34.48 (d, C-6), 27.76 (t, C-8), 23.93 (t, C-2),
22.77 (q, C-13), 18.04 (q, C-14); MS: m/z (%): 204 (2)
[M+], 189 (100) [M+ CH3], 148 (28), 133 (50), 121
(21), 107 (28), 91 (38).
(Fricke, 1999). MS: m/z (%): 204 (61) [M+], 189 (4)
[M+ CH3], 161 (85) [M+ C3H7], 147 (35), 133 (68),
119 (44), 105 (100), 93 (87), 91 (78).
4.42. Selina-4,7-diene (48)
(Fricke, 1999). MS: m/z (%): 204 (85) [M+], 189 (100)
[M+ CH3], 161 (75) [M+ C3H7], 147 (59), 133 (79),
119 (44), 105 (89), 91 (99).
4.43. ꢀ-Selinene (49)
1H, 13C NMR (Sun and Erickson, 1978); MS: m/z
(%): 204 (65) [M+], 189 (100) [M+ CH3], 161 (72)
[M+ C3H7], 133 (32), 119 (25), 105 (37), 91 (40).

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4.47. 4(15)-Cycloaxene (54)
(m, 6 H), 1.01 (s, 3H; H-15), 0.99, 0.95 (2 d, J12/13-
11=6.9 Hz, 6H; H-12,-13); 13C-NMR (125.8 MHz,
C6D6): ꢀ=150.14 (s, C-7), 141.97 (s, C-4), 138.01 (s, C-
5), 110.02 (t, C-14), 50.21 (s, C-1), 40.90 (t, C-10), 38.87
(t, C-8), 38.72 (t, C-2), 33.60 (t, C-6), 27.60 (t, C-3),
27.31 (d, C-11), 25.03 (t, C-9), 24.64 (q, C-15), 21.29,
21.00 (2 q, C-12,-13); MS: m/z (%): 204 (17) [M+], 189
(48) [M+ CH3], 161 (100) [M+ C3H7], 133 (21), 91
(24).
[ꢂ]2D0= 3.2 (c=12.9, CHCl3); H NMR (500 MHz,
CDCl3): d=4.68 (mc, 1H; H-15a), 4.64 (br. d, JAB=2.8
Hz, 1H; H-15b), 2.10±2.15 (m, 2H; H-3a/b), 1.80 (dd,
J5-15b=0.5 Hz, J5-6=3.3 Hz, 1H; H-5), 1.76 (dt, J1eq-
1ax,2ax=13.7 Hz, J1eq-2eq=3.6 Hz, 1H; H-1eq), 1.66 (dd,
J9b-8=6.8 Hz, JAB=12.9 Hz, 1H; H-9b), 1.63 (dquin,
J2eq-1,3=3.6 Hz, JAB=13.1 Hz, 1H; H-2eq), 1.29±1.42
(m, 1H; H-2ax), 1.22 (dm, JAB=13.7 Hz, 1H; H-1ax),
1.16 (ddt, J8-7,9a=3.3 Hz, J8-9b=6.8 Hz, J8-6=7.6 Hz,
1H; H-8), 1.08 (dt, J6-5,7=3.3 Hz, J6-8=7.6 Hz, 1H;
H-6), 1.04 (dd, J9a-8=3.3 Hz, JAB=12.9 Hz, 1H; H-9a),
0.92 (2 d, J12/13-11=5.1 Hz, 6H; H-12,-13), 0.88 (mc, 1H;
H-11), 0.80 (s, 3H; H-14), 0.45 (dt, J7-11=7.7 Hz,
J7-6,8=3.3 Hz, 1 H, H-7); 13C-NMR (125.8 MHz,
CDCl3): ꢀ=149.44 (s, C-4), 108.80 (t, C-15), 59.86
(d, C-5), 53.82 (s, C-10), 47.44 (d, C-7), 46.56 (t, C-9),
35.06 (t, C-1), 32.36 (d, C-11), 32.07 (d, C-6), 31.99
(t, C-3), 24.96 (d, C-8), 24.39 (t, C-2), 22.77 (q, C-14),
21.98, 21.79 (2 q, C-12,-13); MS: m/z (%): 204 (17)
[M+], 189 (22) [M+CH3], 161 (38) [M+ C3H7], 148
(42), 133 (88), 119 (45), 108 (100), 105 (60), 93 (72), 91
(70).
1
4.51. Isodauca-4,6-diene (61)
[ꢂ]2D0= 81 (c=0.28, CHCl3); H, 13C NMR (Naya
1
and Hirose, 1973; Dauben et al., 1975); MS: m/z (%):
204 (58) [M+], 189 (100) [M+ CH3], 161 (94)
[M+ C3H7], 133 (31), 119 (30), 105 (43).
4.52. Hydrogenation of 15 and 19
Pd/C (10%, 5 mg) was added to a solution of ꢀ-
amorphene (15) (0.5 mg) in n-hexane (1 ml) and a H2
¯ow was bubbled through the suspension for 1.5 min.
The mixture was stirred under a H2 atmosphere for 15
min and then ®ltered through Al2O3. The same proce-
dure was repeated for !-amorphene (19). The resulting
solutions were used for GC±MS analysis.
4.48. 4-Cyclooppositene (55)
1H NMR (500 MHz, CDCl3): ꢀ=1.68 (br. s, 3H; H-15),
1.54±1.93 (m, 10H), 1.20 (mc, 1H), 1.03 (s, 3H; H-14),
1.00, 0.97 (2 d, J12/13-11=6.1 Hz, 6H; H-12,-13), 0.18 (dt,
J7-11=8.1 Hz, J7-6,8=3.1 Hz, 1H; H-7); MS: m/z (%): 204
(59) [M+], 189 (60) [M+ CH3], 161 (100) [M+ C3H7],
147 (40), 133 (87), 119 (48), 105 (77), 91 (53).
4.53. Isomerization of single compounds
The following sesquiterpenes were used as enantio-
meric mixtures. (a) To a solution of ꢀ-cadinene (4)
(ꢂ0.5 mg) in n-hexane (0.5 ml) Amberlyst115 (3 mg)
was added and left at rt. The progress of the iso-
merization was controlled by GC. The same proce-
dure was repeated for ꢂ-cadinene (7) (2 mg), ꢃ-
cadinene (17) (0.5 mg), ꢁ-amorphene (12) (ꢂ0.25 mg),
ꢂ-amorphene (13) (ꢂ0.25 mg), ꢀ-amorphene (15) (1
mg), selina-4(15),6-diene-(43) (ꢂ0.25 mg), selina-
4(15),7-diene (44) (ꢂ0.25 mg), selina-3,5-diene (46)
(ꢂ0.25 mg), 4(15)-cyclooppositene (51) (3 mg), 4(15)-
cycloaxene (54) (3 mg) and isodauca-4,7(14)-diene
(60) (ꢂ0.25 mg). In the case of 7, 15, 51 and 54 the
resulting solution was directly used for injection into
the prep. GC and 17, 19, 57 and 58 were isolated.
(b) To a solution of ꢀ-cadinene (4) (1.5 mg) in
CH2Cl2 (0.5 ml) AlCl3 (15 mg) was added and stirred
for 1 h at rt. The reaction mixture was worked up as
described before. The resulting solution was fractio-
nated by prep. GC to isolate a-calacorene (24),
cadalene (26) and 4S,4aS-1,7-dimethyl-4-(methy-
lethyl)-2,3,4,4a,5,6-hexahydronaphthalene (31). The
same procedure was repeated for ( )-ꢀ-cadinene (4)
(Hardt et al., 1995), (+)-ꢁ-cadinene (6), ꢂ-cadinene
(7), ( )/(Æ)-ꢁ-muurolene (8) and ( )/(Æ)-ꢁ-amor-
phene (12) (each ꢂ0.25 mg). The resulting solutions
were used for GC-MS analysis.
4.49. 3-Cycloaxene (58)
[ꢂ]2D0=+10 (c=0.02, CHCl3); H NMR (500 MHz,
1
CDCl3): ꢀ=5.35 (br. s, 1H; H-3), 1.94 (mc, 2H; H-2a/b),
1.77 (br. d, J15-3=2.0 Hz, 3H; H-15), 1.68 (dd, J9b-8=7.1
Hz, JAB=13.2 Hz, 1H; H-9b), 1.66 (dt, J1b-2a=6.1 Hz,
J1b-1a,2b=12.2 Hz, 1H; H-1b), 1.44 (br. s, 1H; H-5), 1.19
(dd, J9-8=3.1 Hz, JAB=13.2 Hz, 1H; H-9a), 1.13 (mc,
1H; H-1a), 1.10 (ddt, J8-6=6.6 Hz, J8-9eq=7.1 Hz, J8-
7,9ax=3.1 Hz, 1H; H-8), 0.95, 0.93, (2 d, J12/13-11=6.1
Hz, 6H; H-12,-13), 0.97±0.79 (m, 2H), 0.79 (s, 3H; H-
14), 0.39 (dt, J7-11=8.6 Hz, J7-6,8=3.1 Hz, 1H; H-7);
MS: m/z (%): 204 (45) [M+], 189 (38) [M+ CH3], 175
(15), 161 (76), 147 (32), 133 (83), 121 (68), 108 (90), 105
(69), 93 (100).
4.50. Isodauca-4,7(14)-diene (60)
1H NMR (500 MHz, C6D6): ꢀ=4.76, 4.75 (2 br. s, 2H;
H-14), 3.17 (d, JAB=14.8 Hz, 1H; H-6a), 2.70 (sept, J11-
12/13=6.8 Hz, 1H; H-11), 2.58 (d, JAB=14.8 Hz, 1H; H-
6b), 2.19 (mc, 2H; H-3), 2.12 (mc, 2H; H-8), 1.32±1.64

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163
4.54. Isolation of (+)-carotol (33)
4.58. Irradiation of germacrene D (1)
Minced carrot seeds (200 g) were extracted in a soxhlet
apparatus with n-pentane/diethyl ether (1:1, 250 ml) for 2
days. The solvent was evaporated and the residue chro-
matographed on silica gel (400 g) with petrol ether/ethyl
acetate (40:1) as eluent. The crude 33 was further puri®ed
(a) An enantiomeric mixture of 1 [( ):(+)=1.3:1, 20
mg, 0.1 mmol] in n-hexane (3 ml) [c(1)=32.7 mmol/l] was
degased with argon and irradiated for 3 h at 254 nm. The
resulting solution was fractionated by prep. GC. (b) The
procedure was repeated in the presence of sulfur (0.8 g)
with stirring. The solvent was evaporated and the residue
was fractionated by column chromatography on silica
gel with petrol ether as eluent. (c) The same enantiomeric
mixture of 1 (4 mg, 0.02 mmol) in acetone (1 ml)
[c(1)=19.6 mmol/l] was degased and irradiated for 2 min
at 300 nm. The resulting solution was used for GC-MS
analysis.
1
by prep. GC yielding 30 mg (90% purity). H NMR
1
(Hashidoko et al., 1992), H NMR (400 MHz, CDCl3):
d=5.32 (mc, 1H; H-9), 2.26 (br. d, JAB16 Hz, 1H; H-
10a), 2.08 (mc, 2H; H-7a/b), 1.94 (mc, 1H; H-6a), 1.80
(mc, 2H; H-4,-11), 1.70 (mc, 1H; H-10b), 1.67 (br. s, 3H;
H-14), 1.67±1.43 (m, 4H), 1.30 (ddd, Jd=7.6 Hz, Jd=8.1
Hz, JAB=12.2 Hz, 1H; H-2a), 1.14 (br. s, 1H; OH), 1.00,
0.94 (2 d, J12/13-11=6.6 Hz, 6H; H-12,-13), 0.95 (s, 3H; H-
15); 13C-NMR (100.6 MHz, CDCl3): ꢀ=138.60 (s, C-8),
122.13 (d, C-9), 84.55 (s, C-5), 52.54 (d, C-4), 49.09 (s, C-
1), 39.45 (t, C-2), 38.62 (t, C-10), 34.45 (t, C-6), 29.45 (t,
C-7), 27.58 (d, C-11), 25.23 (q, C-14), 24.39 (t, C-3), 24.04
(q, C-12), 21.38, 21.47 (2 q, C-13,-15); MS: m/z (%): 222
(1) [M+], 204 (20) [M+ H2O], 189 (8) [M+ H2O, -
CH3], 179 (7), 161 (100) [M+ H2O, -C3H7], 151 (14),
137 (21), 123 (28), 119 (35), 107 (29), 105 (31), 97 (33), 84
(33), 81 (32), 69 (29).
4.59. ꢃ-Bourbonene (64)
1H NMR (Tomioka et al., 1989), 1H NMR (400 MHz,
CDCl3): ꢀ=4.69, 4.71 (2 s, 2H; H-15a/b), 2.54 (m, 1H; H-
3a), 2.40 (dd, J5-1=3.6 Hz, J5-6=7.1 Hz, 1H; H-5), 2.24±
2.33 (m, 2H; H-1,-3b), 1.89 (m, 1H; H-8a), 1.80 (dd, J=8.1
Hz, J=13.2 Hz, 1H; H-2a), 1.45±1.63 (m, 6H), 1.24 (dsept,
J11-12,13=6.6 Hz, J11-7=9.2 Hz, 1H; H-11), 0.99 (s, 3H; H-
14), 0.85, 0.87 (2 d, J12/13-11=6.6 Hz, 6H; H-12,-13); 13C
NMR (100 MHz, CDCl3): d=157.57 (s, C-4), 103.59 (t, C-
15), 56.76 (d, C-7), 54.96 (d, C-6), 47.87 (d, C-5), 45.68 (d,
C-1), 43.15 (s, C-10), 42.02 (t, C-9), 33.81 (t, C-3), 31.14 (d,
C-11), 29.98 (t, C-8), 27.30 (t, C-2), 21.56 (q, C-14), 21.51,
21.83 (2 q, C-12,-13); MS: m/z (%): 204 (1) [M+], 161 (25)
[M+ C3H7], 123 (50) [M+ C6H9], 81 (100)
[M+ C9H13], 80 (71) [M+ C9H14].
4.55. Preparation of (+)-daucene (34)
A solution of carotol (33) (16 mg, 0.072 mmol) in dry
pyridine (1 ml) was cooled down to 0ꢀC and SOCl2
(0.01 ml, 17 mg, 0.14 mmol) was added. The solution
was stirred for 15 min. Then water (5 ml) was added and
extracted 5 times with n-pentane. The organic layer was
dried over MgSO4 and the residue fractionated by prep.
GC. As main product 34 (4 mg) was isolated. 1H NMR,
MS (Andersen et al., 1973).
4.60. ꢃ-Copaene (65)
1H NMR, 13C NMR (Kulkarni et al., 1987); MS: m/z
(%): 204 (7) [M+], 189 (3) [M+ CH3], 161 (100)
[M+ C3H7], 120 (21), 119 (22), 105 (37), 91 (33), 81
(28).
4.56. Dehydrogenation of 31 and 34
4.61. ꢃ-Ylangene (16)
A solution of 4S,4aS-1,7-dimethyl-4-(methylethyl)-
2,3,4,4a,5,6-hexahydronaphthalene (31) (ꢂ0.25 mg) in
toluene (1 ml) and sulfur (5 mg) were heated at 280ꢀC
for 5 h. The cooled mixture was ®ltered through Al2O3
and carefully evaporated. To the residue was added n-
pentane (1 ml), the mixture was ®ltered through Al2O3
again and used for GC±MS analysis. The procedure was
repeated for daucene (34).
1H NMR, 13C NMR (Kulkarni et al., 1987); MS:
m/z (%): 204 (9) [M+], 189 (6) [M+ CH3], 161
(100) [M+ C3H7], 120 (88), 105 (53), 91 (47), 79
(31).
4.62. Monoepi-ꢃ-Bourbonene (71, 72 or 73)
MS: m/z (%): 204 (3) [M+], 189 (4) [M+ CH3], 161
(18) [M+ C3H7], 123 (87) [M+ C6H9], 81 (100)
[M+ C9H13], 80 (86) [M+ C9H14].
4.57. Isomerization of germacrene C (42)
Germacrene C (0.5 mg), isolated from Preissia quad-
rata (Konig et al., 1996), in n-hexane (0.5 ml) and silica
gel (3 mg) was left at rt for 24 h. The resulting solution
was used directly for GC±MS analysis.
4.63. Mintsul®de (69)
1H NMR (Yoshida et al., 1979), 1H NMR (400 MHz,
CDCl3): ꢀ=4.61, 4.67 (2 t, J15a-b,3a/b=2 Hz, 2H; H-15a/

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È
È
b), 3.69 (d, J5-6=6.1 Hz, 1H; H-5), 2.88 (t, J1-2a/b=3.3 Hz,
1H; H-1), 2.38±2.62 (m, 2H; H-3a/b), 2.14±2.25 (m, 3H;
H-2a/b,-6), 1.24±2.00 (m, 6H), 1.35 (s, 3H; H-14), 0.86,
0.90 (2 d, J12/13-11=6.6 Hz, 6H; H-12,-13); MS: m/z (%):
236 (17) [M+], 123 (100) [M+ C6H9S], 112 (78), 79 (69).
53.53, 51.24, 44.95 (s, C-10), 43.28, 31.07, 29.70/33.31/
41.39 (3 t, C-2,-8,-9), 22.50, 21.22, 21.04, 13.82; MS: m/z
(%): 204 (1) [M+], 123 (42) [M+ C6H9], 81 (84)
[M+ C9H15], 80 (100) [M+ C9H14].
4.69. 1,5-diepi-ꢂ-Bourbonene (70)
4.64. Synthesis of 1,5-diepi-ꢃ-bourbonene (68)
1H NMR (CDCl3, 500 MHz): ꢀ=5.39 (br. s, 1H; H-3),
3.08 (br. t, J5-1,6=8.4 Hz, 1H; H-5), 2.44 (t, J1-2a,5=8.4
Hz, 1H; H-1), 2.31 (m, 1H; H-2a), 2.18 (br. d, JAB ꢂ17
Hz, 1H; H-2b), 2.00 (dd, J6-7=5.6 Hz, J6-5=8.4 Hz, 1H;
H-6), 1.73 (m, 1H; H-8a), 1.68 (br. s, 3H; H-15), 1.50±
1.65 (m, 2H; H-7,-9a), 1.34 (dsept, J11-7=8.5 Hz, J11-
12,13=6.6 Hz, 1H; H-11), 1.09±1.26 (m, 2H; H-8b,-9b),
1.09 (s, 3H; H-14), 0.86, 0.89 (2 d, J12/13-11=6.6 Hz, 6H;
H-12,-13); MS: m/z (%): 204 (1) [M+], 189 (2)
[M+ CH3], 161 (8) [M+ C3H7], 123 (62) [M+ C6H9],
81 (83) [M+ C9H15], 80 (100) [M+ C9H14].
8 was prepared from 69 according to described proce-
dures (Uyehara et al., 1981, 1988). 68 and 87 were obtained
in a ratio of 2.7:1 and were separated by prep. GC.
4.65. 1,5-diepi-ꢃ-Bourbonene (68)
1
1H NMR (Uyehara et al., 1988), H NMR: (CDCl3,
400 MHz): ꢀ=4.71, 4.97 (2 br. s, 2H; H-15), 3.09 (dd,
J5-1=8.1 Hz, J5-6=9.4 Hz, 1H; H-5), 2.44 (t, J1-2,5=8.1
Hz, 1H; H-1), 2.42 (m, 1H; H-3a), 2.31 (dd, J3b-2=9.2
Hz, JAB=15.7 Hz, 1H; H-3b), 1.87 (dd, J6-7=6.9 Hz, J6-
5=9.4 Hz, 1H; H-6), 1.55±1.80 (m, 4H, H-2a/b,-8a,-9a),
1.51 (m, 1H; H-7), 1.27 (dsept, J11-7=9.1 Hz, J11-
12,13=6.6 Hz, 1H; H-11), 1.07±1.17 (m, 2H; H-8b,-9b),
1.11 (s, 3H; H-14), 0.81, 0.84 (2 d, J12/13-11=6.6 Hz; 6H;
H-12,-13); MS: m/z (%): 204 (1) [M+], 161 (26)
[M+ C3H7], 123 (40) [M+ C6H9], 81 (100)
[M+ C9H15], 80 (74) [M+ C9H14].
4.70. Thermal treatment of germacrene D (1)
(a) In a typical experiment an enantiomeric mixture of
1 [(+):( )=5.7:1, 13 mg, 0.06 mmol] in n-hexane (0.7
ml) [c(1)=0.91 mol/l] was heated in a sealed tube at
220±240ꢀC for 0.5±2 days. The resulting solution was
prefractionated by column chromatography on silica gel
at 25ꢀC with n-pentane as eluent. The fractions were
further separated by prep. GC. (b) 100 ml of the enan-
tiomer mixture of 1 in n-hexane was injected in the prep.
GC at an injector temperature of 400ꢀC and the rear-
rangement products were fractionated.
4.66. Isodauca-6,9-diene (87)
1
1H NMR (Uyehara et al., 1988), H NMR: (CDCl3,
400 MHz): ꢀ=5.42 (m, 2H), 5.31 (m, 1H), 2.83, 2.55 (2
m, 2H; H-8), 2.0±1.0 (m, 7H), 1.70 (s, 3H; H-14), 0.82,
0.88 (2 d, J12/13-11=7.1 Hz, H; H-12,-13); MS: m/z (%):
204 (13) [M+], 189 (13) [M+ CH3], 161 (84)
[M+ C3H7], 119 (88), 105 (100), 91 (41).
4.71. Isogermacrene D (74)
[ꢂ]2D0= 320 (c=0.042, CHCl3); H NMR (400 MHz,
1
C6D6): ꢀ=5.78 (d, J5-6=11.4 Hz, 1H; H-5), 5.11
(dd=dt, J6-5,7=11.4 Hz, 1H; H-6), 5.07 (dd, Jd=4.6 Hz,
Jd=11.7 Hz, 1H; H-1), 4.87, 4.88 (2 br. s, 2H; H-15),
2.29±2.52 (m, 3H; H-7,-2a,-9a), 2.18 (br. d, JAB=13.2
Hz, 1H; H-3a), 2.03 (dt, J3b-2a/b=3.6 Hz, J3b-2a/
b,3a=13.2 Hz, 1H; H-3b), 1.79 (m, 1H, H-2b), 1.67 (ddt,
Jd=3.1 Hz, Jd=4.1 Hz, Jt=13.2 Hz, 1H; H-8b), 1.61
(m, 1H; H-9b), 1.60 (br. s, 3H; H-14), 1.44 (okt, J11-
7,12,13=6.6 Hz, 1H; H-11), 1.00 (ddt, Jd=2.6 Hz,
Jd=4.1 Hz, Jt=13.2 Hz, 1H; H-8a), 0.92, 0.94 (2 d, J12/
13-11=6.6 Hz, 6H; H-12,-13); 13C NMR (100.6 MHz,
C6D6): ꢀ=146.44 (q), 135.57, 134.66 (q), 131.88, 125.92,
113.36 (s), 41.03, 36.98 (s), 32.65, 29.11 (s), 28.51 (s),
26.23 (s), 22.36, 20.94, 20.81; MS: m/z (%): 204 (23)
[M+], 189 (7), 161 (100) [M+ C3H7], 133 (25), 119 (34),
105 (58), 93 (48), 91 (60), 81 (51).
4.67. Isomerization of ꢃ-bourbonene (64) and 1,5-diepi-
ꢃ-bourbonene (68)
3
A solution of 64 [( ):(+)=1.3:1, 1.5 mg, 7.4Â10
mmol] in CDCl3 (0.6 ml) [c(64)=0.12 mol/l] was mixed
with Amberlyst115 (8 mg) and left at rt until 64 had
almost disappeared (GC control). The catalyst was ®l-
tered o€. The procedure was repeated with 68.
4.68. ꢂ-Bourbonene (67)
1
1H NMR (White and Gupta, 1968), H NMR (400
MHz, CDCl3): ꢀ=5.26 (s, 1H; H-3), 2.43±2.48 (m, 2H),
2.31±2.36 (m, 2H), 1.95 (ddt, Jt= 6.4 Hz, Jd=9.1 Hz,
Jd=12.7 Hz, 1H), 1.69 (br. s, 3H; H-15), 1.65 (br. s,
1H), 1.44±1.62 (m, 3H), 1.39 (ddd, J=6.1 Hz, J=9.2
Hz, J=12.3 Hz, 1H), 1.31 (ddt, Jd=6.6 Hz, Jd=8.7 Hz,
Jt=13.2 Hz, 1H), 1.02 (s, 3H; H-14), 0.86, 0.87 (2 d, J12/
13-11=6.6 Hz, 6H; H-12,-13); 13C NMR (100 MHz,
CDCl3): ꢀ=143.11 (s, C-4), 124.10 (d, C-3), 54.77,
4.72. E-Muurolene (75)
1
1H NMR, 13C NMR (Koster et al., 1986), H NMR
(400 MHz, CDCl3): ꢀ=4.64, 4.67 (2 br. s, 2H), 4.59 (m,

N. Bulow, W.A. Konig / Phytochemistry 55 (2000) 141±168
È
È
165
2H), 2.43±2.52 (m, 2H), 2.31 (dm, J=12.7 Hz, 1H),
1.95±2.19 (m, 5H), 1.89 (dq, Jd=4.7 Hz, Jq=12.6 Hz,
1H), 1.0±1.73 (m, 5H), 0.89, 0.70 (2 d, J12/13-11=7.1 Hz,
6H; H-12,-13); MS: m/z (%): 204 (14) [M+], 189 (5), 176
(3), 161 (100) [M+ C3H7], 148 (13), 133 (21), 119 (30),
105 (45), 93 (45), 91 (49), 81 (62).
36.1 [d, CH(CH3)2], 30.7 (q, C7-CH3), 29.0 (t, C-6), 27.4
(t, C-5), 26.1 (q, C1-CH3), 24.0, 19.6 (2 t, C-9,-10), 21.8,
21.3 [2 q, CH(CH3)2]; MS: m/z (%): 204 (5) [M+], 189
(13), 161 (58) [M+ C3H7], 136 (52), 121 (100), 105 (49),
93 (86), 91 (51).
4.78. cis-Bicyclo[7.1.1]-5-methyl-8-
(methylethyl)undeca-1(10),4-diene (81)
4.73. E-Amorphene (76)
1NMR, 13C NMR (Koster et al., 1986), 1H NMR
(400 MHz, CDCl3): d=4.75, 4.91 (2 q, J=2.2 Hz, 2H),
4.56 (br. s, 2 H), 2.33±2.44 (m, 2H), 2.28 (br. s, 1H), 2.20
(ddt, Jt=2.2 Hz, Jd=5.1 Hz, Jd=13.2 Hz, 1H), 1.10±
2.10 (m, 10H), 0.90, 0.91 (2 d, J12/13-11=6.6 Hz, 6H, H-
12,-13); MS: m/z (%): 204 (23) [M+], 189 (7), 161 (100)
[M+- C3H7], 137 (25), 120 (50), 105 (49), 93 (51), 91
(56), 81 (63).
1H NMR (400 MHz, C6D6): ꢀ=5.66 (s, 1H; H-10),
5.12 (dd, Jd=7.5 Hz, Jd=8.7 Hz, 1H; H-4), 3.04 (br. s,
1H; H-9), 2.34 (br. s, 2H; H-11a/b), 1.83±2.03 (m, 6H),
1.71 (s, 3H; C5-CH3), 1.64 [dsept, JCH(CH3)2-8=2.9 Hz,
JCH(CH3)2-CH(CH3)2=6.6 Hz, 1H; CH(CH3)2], 1.56±1.71
(m, 1H; H-6a), 1.21±1.33 (m, 2H; H-7a,-8), 0.89, 0.92 [2
d, JCH(CH3)2-CH(CH3)2=6.6 Hz, 6H; CH(CH3)2]; MS: m/z
(%): 204 (2) [M+], 189 (8), 161 (51) [M+ C3H7], 133
(27), 119 (42), 105 (61), 93 (66), 91 (69), 81 (78), 41 (100).
4.74. Acidic rearrangement of isogermacrene D (74)
4.79. Thermal treatment of tricyclus 80
3
A solution of 74 [(+):( )=5.7:1, 2 mg, 9.8Â10
3
mmol] in n-hexane (1 ml) [c(74)=9.8 mmol/l] was mixed
with Amberlyst115 (8 mg) and left at rt until 74 had
almost disappeared (GC control). The solution was ®l-
tered, the catalyst washed once with n-hexane (0.5 ml)
and the resulting solution was used for GC±MS analysis.
rac-80 (0.5 mg, 2.5Â10 mmol) in n-hexane (0.7 ml)
[c(80)=35.0 mmol/l] was heated in a sealed tube at 50±
60ꢀC for 8 h and 79 was identi®ed by GC and GC±MS
as a minor compound.
4.75. Irradiation of isogermacrene D (74)
Acknowledgements
(a) An enantiomeric mixture of 74 [(+):( )=5.7:1, 8
mg, 0.04 mmol] in n-hexane (2 ml) [c(74)=19.6 mmol/l]
was degassed with argon and irradiated for 3 h at 254
nm. The resulting solution was fractionated by prep.
GC. (b) The same enantiomeric mixture of 74 (2.5 mg,
0.01 mmol) in acetone (1 ml) [c(74)=12.2 mmol/l] was
degassed and irradiated for 2 min at 300 nm. The
resulting solution was used for GC±MS analysis.
We would like to thank Professor P. Margaretha,
Universitat Hamburg, for helpful discussions, M. Wrobel,
Universitat Hamburg, for performing numerous irra-
diation experiments and Dr. V. Sinnwell, Universitat
Hamburg, for his support in the discussion of NMR
spectra. We also thank Dr. D. Kalemba, University of
Lodz, Poland, for providing several samples of Solidago
canadensis L. essential oil. The ®nancial support of
Fonds der Chemischen Industrie is acknowledged.
4.76. rac-ꢀ-Elemene (79)
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