Correction of the structure of a new sesquiterpene from Cistus creticus ssp. creticus

Article abstract of DOI:10.1021/np0498556

In an attempt to identify the structure of a sesquiterpene from Cistus creticus ssp. creticus proposed in the literature as 1,1,4a,6-tetramethyl-5- methylene-1,2,3,4,4α,5,8,8α-octahydronaphthalene, the synthesis of its cis isomer 2 was carried out in 11 steps and 9.5% yield. Comparison of the spectra of 2 and those reported earlier for the synthetic irons isomer 1 with the spectral profile of the isolated natural product indicated that the latter was not compatible with either 1 or 2. The correct structure was assigned, by detailed spectroscopic analysis of the natural product, as 6-isopropenyl-4,4a- dimethyl-1,2,3,4,4a,5,6,7-octahydronaphthalene (3).

Full text of DOI:10.1021/np0498556

1996
J. Nat. Prod. 2004, 67, 1996-2001
Correction of the Structure of a New Sesquiterpene from
Cistus creticus ssp. creticus
Konstantinos Hatzellis,† Georgia Pagona,† Apostolos Spyros,† Costas Demetzos,*,‡ and
Haralambos E. Katerinopoulos*,†
Department of Chemistry, University of Crete, Heraklion 71409, Crete, Greece, and School of Pharmacy, Department of
Pharmaceutical Technology, University of Athens, Panepistimiopolis Zografou 15771, Athens, Greece
Received April 23, 2004
In an attempt to identify the structure of a sesquiterpene from Cistus creticus ssp. creticus proposed in
the literature as 1,1,4a,6-tetramethyl-5-methylene-1,2,3,4,4R,5,8,8R-octahydronaphthalene, the synthesis
of its cis isomer 2 was carried out in 11 steps and 9.5% yield. Comparison of the spectra of 2 and those
reported earlier for the synthetic trans isomer 1 with the spectral profile of the isolated natural product
indicated that the latter was not compatible with either 1 or 2. The correct structure was assigned, by
detailed spectroscopic analysis of the natural product, as 6-isopropenyl-4,4a-dimethyl-1,2,3,4,4a,5,6,7-
octahydronaphthalene (3).
Cistus creticus ssp. creticus (L.) Greuter et Burdet [syn.
Cistus incanus ssp. creticus (L.) Heywood; Cistus creticus
(L.)] (Cistaceae) is a perennial shrub that grows in the
Mediterranean area, especially in Crete.1-3 During hot
summer days its leaves secrete a thick, aromatic resin,
called by the locals “ladano”.2,3 The resin has been used in
folkloric medicine as an anticancer agent since ancient
times.4 This traditional use was supported by a recent
study5 indicating that its major labdane-type components
extracted from the plant exhibited strong cytotoxic activity.
Another major component was isolated from the essential
oil of the resin and assigned the structure of a new
drimane-type sesquiterpene,6 namely, 1,1,4a,6-tetramethyl-
5-methylene-1,2,3,4,4a,5,8,8a-octahydronaphthalene (drima-
7,9(11)-diene, following drimane carbon framework num-
bering).
considered necessary at that point given that the spectral
data of the racemic mixture were sufficient to indicate
structural differences of the synthetic and natural product.
Results and Discussion
The synthetic pathway, depicted in Scheme 1, involves
initial selective protection of the (() Wieland-Miescher
ketone (4) to monoketal 5. Although a number of conditions
have been, even recently, reported in the literature,10-14
we performed the reaction in benzene using 1 equiv of
PTSA, and 10 equiv of ethylene glycol at 60 °C for 4 h. The
use of a Dean-Stark trap was not necessary under these
conditions, which gave 5 in 84-88% yield. Subsequent C-1
dimethylation15 using t-BuOK/t-BuOH and MeI (0 °C, 75
min) produced 6 in 74% yield. Huang-Minlon reduction
of the ketone group14 (H2NNH2‚H2O, DEG, 120 °C, 2.5 h,
then KOH 170-245 °C, 4 h, 94%) followed by hydrolysis
of ketal 7 (PPTS, EtOH/H2O, 9:1, 99%) furnished 8,16 as
the common intermediate to both cis and trans decalin
systems. It was realized that the problem of the ring fusion
stereochemistry should be dealt with at this early stage of
the synthesis. Given that the decalin framework was
already present in the starting material, stereoselective
cyclization17-20 was not a feasible alternative, and therefore
the cis or trans disposition of the decalin system would be
arranged via face-selective reactions, possibly through the
The stereochemistry at the fusion of the decalin ring was
tentatively assigned as trans. However, subsequent pub-
lications reported the isolation of the trans isomer 1 as a
byproduct in the synthesis of structurally related natural
products.7-9 The spectral (1H and 13C NMR) characteristics
of synthetic 1 were clearly different than those of the
natural product.6 We therefore undertook the total syn-
thesis of the cis compound 2 with the purpose of comparing
its spectral profile with that of the natural product and
studying its cytotoxic activity. From the synthetic point of
view, the project also led to the development of a flexible
synthetic pathway toward the target molecule which, upon
simple synthetic modifications, would lead to both cis/trans
isomers. Asymmetric synthesis of the target was not
reduction of similar-structure substrates incorporating the
4,4a
∆
olefinic moiety.
On the basis of the rationale put forth above the olefinic
bond in 8 was catalytically reduced (H2, 10%Pd/C, EtOH,
3.5 h), yielding, as expected from literature precedents,21
cis decalone 9 as the major product (90%) together with
8% of the trans isomer 12. It was anticipated that exposure
of the hindered face of the ∆4,4a double bond in 8 would be
achieved through relief of the additional strain imposed
by the carbonyl moiety, i.e., by altering the sp2 hybridiza-
tion in C-1 to sp3. Indeed, carbonyl reduction in 8 (NaBH4)
furnished the corresponding alcohol 1022 in 88% yield.
Catalytic reduction of 10b under identical conditions as
mentioned above yielded compound 1122 (95%), which was
transformed by Jones oxidation to the desired trans deca-
lone 1222,23 (91%), containing only 1.5% of the inseparable
cis isomer 9. MS as well as NMR spectra confirmed the
difference in stereochemistry in structures 9 and 12. A clear
* To whom correspondence should be addressed. (H.E.K.) Tel: +30 2810
393 626. Fax: +30 2810 393 601. E-mail: kater@chemistry.uoc.gr, and
(C.D.) Fax: +301-210-7274596. E-mail: demetzos@pharm.uoa.gr.
† University of Crete.
‡ University of Athens.
10.1021/np0498556 CCC: $27.50
© 2004 American Chemical Society and American Society of Pharmacognosy
Published on Web 11/17/2004

New Sesquiterpene from Cistus creticus
Journal of Natural Products, 2004, Vol. 67, No. 12 1997
Scheme 1. Synthetic Pathway to cis, trans Isomers 9 and 12
Scheme 2. Synthetic Pathway to cis Drimane Sesquiterpene 2
indication of the cis fusion of the decalin rings in 9 came
from its NOESY spectrum, which shows an interaction
between the C-4a methine and the C-11 methyl protons;
such an interaction is absent in the corresponding spectrum
of 12.
The problem of the diastereoselective synthesis of the
ketone intermediates being solved, and given that the
spectral profile of the trans drimanediene 1 was known,7-9
we focused on the synthesis of the cis diastereomer (Scheme
2). Following a literature procedure,22b the methylation of
9 was carried out by initial silylation of the corresponding
enolate 13 (THF, LDA, Me3SiCl, 79%). It is worth noting
that at this point the diastereomeric trans impurity was
separable and the synthesis was continued with the pure
cis isomers in hand. Deprotection22b of the enolate by
anhydrous C6H5CH2N(CH3)3F in the presence of MeI in
THF furnished a diastereomeric mixture of the R-methy-
lated ketones 14 in 90% yield. Bromination (pyridinium
bromide perbromide (PBP), AcOH, rt, 2.5 h, 94%) and
subsequent dehydrohalogenation22b,24 (DBU, toluene, 110

1998 Journal of Natural Products, 2004, Vol. 67, No. 12
Table 1. NMR Data for Compound 3a
Hatzellis et al.
position
protonb
δ1H
COSY
NOESY
H-7, H-8
δ13
C
HBMC
1
2
H-1
H-2
H-2′
H-3
H-3′
H-4
H-4′
1.64 (m)
H-2, H-2′, H-12
H-1, H-2′, H-3′
H-1, H-2, H-3, H-3′
H-3′, H-4′
H-2, H-2′, H-3, H-4, H-4′
H-3′, H-4′
H-3, H-3′, H-4
38.71
31.40
H-2, H-2′, H-8′, H-13
1.49 (m)
1.39 (m)
1.76 (m)
1.28 (m)
1.90 (m)
2.17 (m)
H-12
H-13
3
29.26
32.30
H-2′, H-4′
4
H-5
H-13
H-3, H-5
4a
146.39
H-13, H-1, H-3, H-3′, H-4,
H-4′, H-6, H-6′, H-8′
H-4, H-4′, H-6, H-6′, H-8′
H-8, H-8′, H-5
5
6
H-5
H-6
H-6′
H-7
H-8
H-8′
5.33 (brd, 6.0)
1.98 (m)
1.84 (m)
2.12 (brd, 13.0)
1.90 (brd, 13.0)
1.11 (dd, 13.0,13.0
H-6, H-6′
H-4
117.90
31.50
H-5, H-6′, H-7
H-5, H-6, H-7
H-6, H-6′, H-8′
H-8
7
8
H-1
H-12
H-13
37.71
39.65
H-5, H-8′, H-10
H-7, H-13
H-7, H-8
8a
9
10
11
39.43
150.29
21.09
H-1, H-5, H-13
H-7, H-8, H-8′, H-10, H-11
H-7, H-11
H-10
H-11
H-11′
H-12
H-13
1.72 (s)
H-11
H-10
H-10
H-1
H-11
4.70 (bs)
4.71 (bs)
0.78 (d,7.0)
0.91 (s)
H-10
108.26
H-7, H-10
H-10
12
13
H-13, H-8
20.77
15.76
H-1, H-2, H-2′
H-12S, H-2′, H-4′, H-8
H-1, H-8
a All spectra were recorded on a Bruker AMX 500, in CDCl3. Chemical shifts are expressed in ppm, and J values in parentheses are
in Hz. b In proton numbering, protons at pseudoaxial positions are denoted with prime symbol (′).
°C, 3.5 h) of the resulting R-bromoketones 15 yielded R,â-
unsaturated ketone 16 in 93% yield.
Conversion of 16 to the desired diastereomer 2 was
troublesome25 since a number of attempts using Wittig-
type reaction26-30 conditions either failed or gave the
product in small yields together with a number of insepa-
rable byproducts (data not shown). A dimethyltitanocene
methylenation reaction31,32 was also fruitless. A two-step
Figure 1. Structure of eremophilene isomer 3 and its key NOE
sequence involving attack of the carbonyl function by
methyllithium (MeLi, THF/HPMA, 7:1, -78 °C f rt, 24 h)
and dehydration of tertiary alcohol 17 using the Burgess
reagent33,34 (MeO2CNSO2NEt3, THF, Et3N, 65 °C, 48 h)
gave 2 in 26% yield from 16. A small amount of an isomeric
impurity was detected by GC/MS analysis after workup of
the reaction mixture. Studies of the spectral profile of 2
correlations.
ture was suggested to contain two rings and two double
bonds. In total, the 13C NMR spectrum along with the
DEPT experiments indicated the presence of three qua-
ternary, three methine, six methylene, and three methyl
carbons. Using the above-mentioned information as well
as the data from the COSY, HMQC, 1H-1H NOESY, NOE
enhancement, and 1H-13C HMBC long-range coupling
NMR spectra presented in Table 1, we assigned the struc-
ture of the new natural product as an eremophilene isomer,
namely, 1,8a-dimethyl-7-(1-methylethenyl)-1,2,3,4,6,7,8,8a-
octahydronaphthalene (3) (Figure 1) in the following man-
ner. The third quaternary carbon (39.43 ppm) was assigned
as C-8a, a ring fusion carbon connected to the C-13 methyl.
The tertiary carbon, connected to the second (C-12) methyl
group, was assigned as C-1. This carbon also exhibited a
strong long-range coupling with the H-13 protons, indicat-
ing the proximity of the two methyl groups. Long-range
interaction of the third methyl carbon (C-10) with the
exocyclic methylene C-11 protons as well as the C-7
methine proton suggested the presence of an isopropenyl
substituent, with C-9 being one of the quaternary olefinic
carbons. The second quaternary olefinic carbon, with a
strong long-range coupling with the H-13 methyl protons,
was therefore assigned as C-4a, the second ring fusion
carbon. Results from the COSY experiment were in agree-
ment with this assignment, establishing the presence of
two isolated ring systems, namely, H-1-(2,2′)-(3,3′)-(4,4′)
and H-5-(6,6′)-7-(8,8′). The use of 1D NOE spectra was
instrumental in differentiating the overlapping H-4 and
H-8 protons.
1
indicated that mass spectra as well as H NMR and 13C
NMR data showed clear and distinct differences from those
of the natural product.6,35 We were therefore prompted to
reinvestigate the structure of the natural product in greater
detail by means of NMR and mass spectra analysis.
Following the published procedure6 we were able to
isolate from the methanol extract of the resin a 10 mg
sample of the natural product, whose mass spectrum was
identical to that reported in the literature.6,35 The molec-
ular ion at m/z 204 suggested a molecular formula of
C15H24. Analysis of the 1H NMR spectrum of the compound
revealed the presence of three methyl groups appearing
as two singlets at 1.72 and 0.91 ppm and a doublet at 0.78
ppm, indicating that the latter is connected to a tertiary
1
carbon atom. In earlier H NMR studies,6 overlap of the
doublet at 0.78 ppm with an aliphatic proton peak of an
unidentified impurity, still present as a trace in our
samples, gave the erroneous impression of the presence of
two methyl groups. In agreement with the initial report,
two olefinic-proton resonances were observed, with one an
exocyclic methylene occurring as two broad singlets at 4.71
and 4.70 ppm, and the second, apparently of an endocyclic
double bond, as a broad doublet at 5.33 ppm. These
assignments were verified by the 13C NMR spectrum
showing the corresponding carbons at 108.26 and 117.90
ppm, respectively. Analysis of the 13C DEPT subspectra
indicated that the former carbon was secondary, with the
latter being tertiary. Two more (quaternary) olefinic car-
bons appeared in the 13C NMR spectrum at 150.29 and
146.39 ppm. With an unsaturation degree of 4, the struc-
The relative configuration of the three substituents was
deduced by the following observations. The resonance of
axial proton H-8′ appears as a pseudotriplet (doublet of
doublets) due to J-coupling with protons H-8 and H-7 with
3
2J8,8′ ) J7,8′ ) 13 Hz. The latter value corresponds to a

New Sesquiterpene from Cistus creticus
Journal of Natural Products, 2004, Vol. 67, No. 12 1999
was removed in vacuo. Diethyl ether (50 mL) was added to
the system, the aqueous layer was separated and extracted
with diethyl ether (3 × 10 mL), and the combined organic
layers were washed with water (3 × 20 mL) and saturated
NaCl solution (2 × 10 mL). The organic phase was dried
(MgSO4), and the solvent was removed in vacuo to give 2.45 g
(98%) of the crude product, which was purified by flash
chromatography (ether/pet. ether, 20-60%). The yield of the
pure product was 2.1 g (84%): 1Η ΝΜR data of 5 (CDCl3) δ
1.36 (3H, s), 1.67-1.73 (3H, m), 1.78-1.80 (1H, m), 1.87-1.93
(1H, m), 2.26-2.36 (2H, m), 2.39-2.46 (3H, m), 3.94-4.00 (4H,
O-CH2CH2-O, m), 5.81 (1H, CdC-H, s); MS m/z 222 [M]+.
Preparation of 1,1-Ethylenedioxy-5,5,8a-trimethyl-
1,2,3,5,6,7,8,8a-octahydro-6-oxonaphthalene (6). In a two-
neck 250 mL round-bottomed flask were placed benzene (60
mL), t-BuOH (40 mL), and t-BuOK (5.04 g, 45 mmol), and the
system was cooled to 0 °C. To this mixture was added, under
vigorous stirring, compound 5 (2.0 g, 9.0 mmol) dissolved in a
minimum amount of BuOH. The system was stirred at 0 °C
for 0.5 h, and then MeI (5.6 mL, 90 mmol) was added dropwise.
After 70 min further stirring the reaction was quenched via
addition of water, the organic solvent was removed in vacuo,
and diethyl ether (50 mL) was added to the system. The
aqueous phase was separated and extracted with diethyl ether
(4 × 15 mL), and the combined organic layers were washed
with water (3 × 20 mL) and saturated NaCl solution (15 mL)
and dried over MgSO4. The solvent was removed in vacuo,
yielding 2.0 g (89%) of a yellow oil, which was purified by flash
chromatography (AcOEt/pet. ether, 5-20%) to give 1.66 g
(74%) of white solid product: 1Η ΝΜR data of 6 (CDCl3) δ 1.15
(3H, s), 1.29 (6H, s), 1.69-1.76 (2H, m), 1.90-1.96 (1H, m),
2.25-2.32 (3H, m), 2.49-2.55 (1H, m), 2.61 (1H, ddd, J1 ) 18.1
Hz, J2 ) 8.0 Hz, J3 ) 2.2 Ηz), 3.95-4.08 (4H, O-CH2CH2-O,
m), 5.61 (1H, dd, CdC-H, J1 ) J2 ) 3.4 Hz); MS m/z 250 [M]+.
Preparation of 1,1-Ethylenedioxy-1,2,3,5,6,7,8,8a-oc-
tahydro-5,5,8a-trimethylnaphthalene (7). In a two-neck 50
mL round-bottomed flask were placed compound 6 (0.62 g, 2.48
mmol) and diethylene glycol (12.5 mL), followed by hydrazine
hydrate, and the mixture was stirred at 120 °C for 2.5 h. To
this mixture was then added KOH pellets (0.93 g, 18.1 mmol),
and the system was gradually heated to 170 °C to distill off
water and hydrazine. The system was heated under reflux for
4 h, then cooled to room temperature, and diluted with pet.
ether (30 mL) and water (30 mL). The aqueous phase was
separated and extracted with ether (2 × 10 mL), and the
combined organic layers were washed with water (2 × 20 mL)
and saturated NaCl solution (2 × 10 mL) and dried over
MgSO4. The solvent was removed in vacuo, yielding 0.55 g
(94%) of pure 7, a yellowish oil, which was used in the next
step without further purification. 1Η ΝΜR data for 7 (CDCl3)
δ 1.13 (3H, s), 1.15 (3H, s), 1.32-1.37 (1H, m), 1.35 (3H, s),
1.43-1.49 (2H, m), 1.53-1.57 (1H, m), 1.62-1.69 (2H, m),
1.73-1.79 (1H, m), 1.91-1.97 (1H, m), 2.13-2.18 (1H, m),
2.25-2.31 (1H, m), 3.92-4.04 (4H, O-CH2CH2-O, m), 5.52
(1H, CdC-H, bs); MS m/z 236 [M]+.
trans-diaxial conformation for H-8′ and H-7 and suggests
a pseudoequatorial orientation for the isopropyl group,
positioning it on the same side with H-8′. The observation
is in agreement with dihedral angle values from theoretical
calculations.36 The strong NOE observed between methyl
protons H-12 and H-13 established the proximity of the
two methyl groups in space. Since H-8′ showed a strong
NOE effect with H-13, it was concluded that H-13 is
pseudoaxial, and all three substituents adopt a syn con-
figuration. The observation of a strong H-7/H-1 NOE
interaction verified that the proposed structure of 3 is
correct, since this is the only configuration that brings H-1
and H-7 in close proximity.
The relative configuration being established, we were
able to define absolute configuration of 3 using literature
data. The proposed structure has been mentioned in the
literature as synthetic intermediate in reactions involving
the known eremophilane carbon framework.37,38 Although
the 1H NMR data were incomplete, 13C NMR values
reported by Itokawa et al.38 were in perfect agreement with
our data. A value of [R]25D +12.5° (c 2.5, CHCl3) compared
to the reported [R]25D -11.1° (c 0.18, CHCl3)38 suggests that
3 is the enantiomer of the compound reported by Itokawa
et al.
Prompted by the fact that major, labdane-type compo-
nents extracted from Cistus creticus ssp. creticus exhibited
strong cytotoxic activity, we investigated the cytotoxic
activity of sesquiterpene 3 in three human cancer cell
linessMCF7 (breast cancer), H460 (non small cell lung
cancer), and SF268 (central nervous system)sand in rest-
ing or activated normal human peripheral blood mono-
nuclear cells (PBMCs) isolated from healthy human donors.
Compound 3 exhibited low activity, reducing the growth
rate of MCF7 and H460 to 93.6% and 80.8%, respectively,
compared to the untreated cells after a 48 h continuous
incubation and was found not toxic against SF268 and
PBMCs at concentrations as high as 100 µM.
In conclusion, in this report we presented the total
synthesis of cis-drima-7,9(11)-diene (2), proposed as a
component from Cistus creticus ssp. creticus. We also
developed a common synthetic pathway, using an “unfold-
ing of structure” approach that could eventually lead to
both cis (2) and trans (1) isomers of this drimane sesquit-
erpene, as well as numerous cis/trans analogues. Exclud-
ing, by both synthetic means and literature data, the
possibility that the natural product is either 1 or 2, we were
also able to assign its correct structure 3 via spectroscopic
analysis. Compound 3 exhibited limited cytotoxic activity
when tested against three human cancer cell lines.
Experimental Section
Preparation of 3,5,6,7,8,8a-Hexahydro-5,5,8a-trimeth-
ylnaphthalene-1(2H)-one (8). In a 10 mL round-bottomed
flask were placed compound 7 (0.1 g, 0.42 mmol), a 4 mL
solution of EtOH/H2O (9:1), and PPTS (0.013 g, 0.052 mmol).
The system was heated under reflux for 1.5 h, then cooled to
room temperature, and the organic solvent was removed in
vacuo. The remaining solution was extracted with 10 mL of
ether, and the organic layer was washed with water (3 × 10
mL) and saturated NaCl solution (10 mL) and dried over
MgSO4. The solvent was removed in vacuo to yield 0.081 g
(99%) of pure 8, which was used in the next step without
General Experimental Methods. Solvents were dried and
freshly distilled under argon before use. All reactions were
performed under argon atmosphere. Thin-layer chromatogra-
phy was performed on precoated TLC plates (silica gel). Flash
chromatography was carried out with silica gel 60 (particle
size 0.040-0.063 mm). Melting points are uncorrected. NMR
spectra were recorded at 500 ΜΗz on a ΑΜÌ 500 Bruker
1
instrument. Chemical shifts of H and 13C NMR spectra are
reported in parts per million downfield from TMS as an
internal standard. GC/MS spectra were recorded on a Schi-
madzu GC/MS-QP5050A instrument.
Preparation of 1,1-Ethylenedioxy-8a-methyl-6-oxo-
1,2,3,4,6,7,8,8a-octahydronaphthalene (5). In a two-neck
250 mL round-bottomed flask were placed compound 4 (2.0 g,
11.23 mmol), benzene (100 mL), and ethylene glycol (8.5 mL,
152.3 mmol) followed by PTSA‚H2O (2.13 g, 11.23 mmol). The
solution was heated at 60 °C for 3.5 h. A saturated solution of
NaHCO3 was added to the system, and the organic solvent
1
further purification. Η ΝΜR data for 8 (CDCl3) δ 1.13 (3H,
s), 1.19 (3H, s), 1.23-1.29 (1H, m), 1.37 (3H, s), 1.45-1.48 (2H,
m), 1.57-1.61 (1H, m), 1.75-1.79 (2H, m), 2.28-2.33 (1H, m),
2.39-2.42 (1H, m), 2.44-2.48 (1H, m), 2.69-2.75 (1H, m), 5.73
(1H, CdC-H, bs); 13C ΝΜR (CDCl3) δ 18.33 (CH2, C-7), 25.23
(CH3, C-9), 22.56 (CH2, C-3), 30.59 (CH3, C-11), 32.70 (CH3,
C-10), 34.21 (CH2, C-8), 35.61 (CH2, C-2), 36.52 (C, C-5), 41.06
(CH2, C-6), 48.18 (C, C-8a), 119.19 (CH, C-4), 149.67 (C, C-4a),
216.44 (CdO, C-1); MS m/z 192 [M]+.

2000 Journal of Natural Products, 2004, Vol. 67, No. 12
Hatzellis et al.
Preparation of cis-3,4,4a,5,6,7,8,8a-Octahydro-5,5,8a-
trimethylnaphthalene-1(2H)-one (9). In a two-neck 50 mL
round-bottomed flask were placed compound 8 (0.15 g, 0.78
mmol), ethanol (12 mL), and 10% Pd/C (0.039 g), and the
system was hydrogenated for 3.5 h. Addition of CH2Cl2 (1 mL)
was followed by filtration through Celite, and removal of
solvent gave 0.15 g (97%) of a mixture of the cis isomer 9 (91%
by GC/MS) and its trans isomer 12 (9% by GC/MS). The two
isomers were separated as their enolate trimethylsilyl ethers
as described below. 1Η ΝΜR data for 9 (CDCl3) δ 0.82 (3H, s),
0.78-0.84 (1H, m), 0.94 (3H, s), 1.12-1.17 (1H, m), 1.24 (3H,
s), 1.25-1.30 (1H, m), 1.31-1.36 (1H, m), 1.48-1.58 (2H, m),
1.81-1.90 (2H, m), 2.00-2.09 (2H, m), 2.17-2.25 (2H, m),
2.56-2.63 (1H, m); 13C ΝΜR (CDCl3) δ 19.09, 20.12, 23.53,
24.72, 29.69, 32.06, 34.68, 34.78, 36.37, 43.24, 48.17, 54.09,
216.76; ΜS m/z 194 [M]+.
(10 mmol) in THF (6 mL) was added dropwise. After 2 h
stirring at 0 °C, Me3SiCl (1.36 mL, 10.0 mmol) was added, and
the system was stirred at room temperature for 2 h. The
reaction was then quenched via addition of saturated Na2CO3
solution (10 mL), and the aqueous layer was separated and
washed with ether (3 × 15 mL). The combined organic
fractions were washed with saturated NaCl solution (2 × 10
mL) and dried over MgSO4, and the solvents were removed in
vacuo to give 2.6 g of a mixture of enol ethers. Flash
chromatography using petroleum ether as eluent gave pure
fractions of 13 (2.1 g, 79%) as a colorless oil, and its trans
isomer. Analytical samples of the two products were hydro-
lyzed to yield pure 9 and 12, respectively, which were
1
characterized by their H NMR, 13C NMR, and mass spectra.
All spectral data were identical to those taken from 9 or 12 as
mixtures with their respective minor components, mentioned
1
Preparation of trans-1,2,3,5,6,7,8,8a-Octahydro-5,5,8a-
trimethylnaphthalen-1-ol (10). Into a 25 mL round-bot-
tomed flask were placed compound 8 (0.11 g, 0.57 mmol) and
anhydrous ethanol (5 mL). The system was cooled to -30 °C,
and NaBH4 (0.02 g, 0.9 mmol) was added under vigorous
stirring. The system was then stirred at 0 °C for 2 h, when
acetone (5 mL) was added, and stirring was continued at room
temperature for 1 h. The solvents were removed in vacuo, and
the residue was diluted with ether (30 mL) and washed
consequently with 1 M NaOH solution (2 × 15 mL), water (2
× 10 mL), and saturated NaCl solution (10 mL). The ether
layer was dried over MgSO4 and the solvent was removed in
vacuo, yielding 0.11 g of an epimeric mixture of 10a and 10b
in a ratio of 1:9. The epimers were separated by flash
chromatography using AcOEt/pet. ether (2-5%) as eluent. The
yield of white crystalline 10b was 0.098 g (88%): 1Η ΝΜR data
for 10b (CDCl3) δ 1.02 (3H, s), 1.09 (3H, s), 1.10 (3H, s), 1.19-
1.25 (1H, m), 1.41-1.51 (3H, m), 1.62-1.77 (3H, m), 1.84-
1.87 (1H, m), 2.04-2.20 (2H, m), 3.41 (1H, dd, J1 ) 11.6 Hz,
J2 ) 4.4 Hz) 5.38 (1H, dd, J1 ) 3.9, J2 ) 3.45 Hz); 13C ΝΜR
(CDCl3) δ 18.13, 19.47, 24.61, 26.06, 30.33, 32.25, 35.24, 37.58,
39.14, 41.05, 78.27, 117.79, 148.69; MS m/z 194 [M]+.
Preparation of trans-1,2,3,4,4a,5,6,7,8,8a,-Decahydro-
5,5,8a-trimethylnaphthalen-1-ol (11). In a two-neck 25 mL
round-bottomed flask were placed compound 10b (0.045 g, 0.23
mmol), hexane (5.0 mL), and 10% Pd/C (0.025 g), and the
system was hydrogenated for 3.5 h. Addition of CH2Cl2 (1 mL)
was followed by filtration through Celite, and removal of
solvent gave 0.043 g (97%) of a mixture of 11 (98% by GC/MS)
and 2% of a diastereomeric side product. 1Η ΝΜR data for 11
(CDCl3) δ 0.77-0.80 (1H, m), 0.82 (3H, s), 0.84 (3H, s), 0.87
(3H, s), 0.93-0.99 (1H, m), 1.10-1.30 (4H, m), 1.34-1.63 (5H,
m), 1.72-1.79 (2H, m), 3.13 (1H, dd, J1 ) 11.4 Hz, J2 ) 4.27
Hz); 13C ΝΜR (CDCl3) δ 12.04, 18.29, 20.83, 21.70, 24.44, 30.09,
32.79, 33.23, 37.48, 39.41, 42.05, 52.28, 80.79; MS m/z196 [M]+.
Preparation of trans-3,4,4a,5,6,7,8,8a-Octahydro-5,5,-
8a-trimethylnaphthalene-1(2H)-one (12). Into a 25 mL
round-bottomed flask was placed a solution of compound 11
(0.042 g, 0.21 mmol, including the 2% isomer) in acetone (3
mL), and Jones reagent was added dropwise under vigorous
stirring until the red color of the reagent persisted. The excess
reagent was quenched by addition of isopropyl alcohol, the
solution was diluted with ether (15 mL), washed successively
with water (2 × 10 mL) and saturated NaHCO3 (2 × 15 mL),
and dried over MgSO4, and the solvent was removed in vacuo,
yielding 0.038 g (92%) of colorless liquid containing 12 and 9
in 98.5% and 1.5% yield, respectively, as indicated by GC/MS.
The two isomers were separated as their enolate trimethylsilyl
ethers as described below. 1Η ΝΜR data for 12 (CDCl3) δ 0.86
(3H, s), 0.90 (3H, s), 1.12 (3H, s), 1.08-1.14 (2H, m), 1.35-
1.38 (1H, m), 1.44-1.63 (6H, m), 1.70-1.73 (1H, m) 2.01-2.03
(1H, m), 2.14-2.17 (1H, m), 2.51-2.57 (1H, m); 13C ΝΜR
(CDCl3) δ 17.97, 18.47, 20.84, 21.95, 26.21, 32.93, 33.02, 34.04,
37.50, 41.49, 48.98, 53.38, 215.80; MS m/z 194 [M]+.
above. Η ΝΜR data for 13 (CDCl3) δ 0.17 (9H, s), 0.97 (3H,
s), 1.01 (3H, s), 1.17 (3H, s), 1.10-1.24 (3H, m), 1.28-1.41 (3H,
m), 1.57-1.63 (1H, m), 1.78-1.89 (2H, m), 1.94-2.01 (1H, m),
2.06-2.11 (1H, m), 4.62-4.61 (1H, m); 13C ΝΜR (CDCl3) δ 0.31,
19.52, 19.69, 23.43, 27.01, 29.13, 32.29, 34.14, 34.52, 38.64,
40.49, 50.44, 101.13, 156.35; MS m/z 266 [M]+.
1Η ΝΜR data for the minor trans isomer of 13 (CDCl3) δ
0.14 (9H, s), 0.82 (3H, s), 0.86 (3H, s), 1.02 (3H, s), 1.01-1.19
(3H, m), 1.30-1.46 (3H, m), 1.49-1.62 (2H, m), 1.76-1.78 (1H,
m), 1.94-2.02 (2H, m), 4.50-4.51 (1H, m); 13C ΝΜR (CDCl3)
δ 0.31, 18.43, 18.65, 19.52, 21.48, 24.28, 33.01, 33.07, 35.21,
39.14,. 41.80, 51.53, 99.73, 158.87; MS m/z 266 [M]+.
Preparation of cis-3,4,4a,5,6,7,8,8a-Octahydro-2,5,5,8a-
tetramethylnaphthalene-1(2H)-one (14). In a 20 mL round-
bottomed flask were placed BnMe3NF (0.6 g, 4.0 mmol),
predried in vacuo at 65 °C for 24 h, molecular sieves (2 g),
and THF (20 mL), and the system was stirred at room
temperature for 24 h. To this mixture was added MeI (1.2 mL,
10 mmol). After 15 min stirring, a solution of compound 13
(0.84 g, 4.0 mmol) in THF (6 mL) was added dropwise, and
the mixture was stirred for 1 h, then diluted with ether and
filtered through Celite. The solvent was removed in vacuo to
give 0.65 g of a yellow oil, which was purified by flash
chromatography using 1% ether/pet. ether as eluent. The yield
of 14 as a mixture of diastereomers was 0.59 g (90%). A small
1
amount (0.025 g) of starting material was also recovered. Η
ΝΜR data for 14 (CDCl3) δ 0.72 (3H, s), 0.84 (3H, s), 0.91 (3H,
s), 0.95 (3H, d, J ) 6.4 Hz), 1.00 (3H, d, J ) 6.6 Hz), 1.04 (3H,
s), 1.24 (3H, s), 1.25 (3H, s), 1.19-1.98 (20H, m), 2.16-2.27
(2H, m), 2.51-2.59 (1H, m), 2.72-2.74 (1H, m); 13C ΝΜR
(CDCl3) δ 15.37, 16.19, 18.79, 19.17, 20.35, 23.29 24.27, 24.53,
29.96, 30.62, 31.07, 32.23, 32.37, 32.72, 33.43, 33.64, 34.64,
35.45, 36.57, 38.61, 40.12, 43.75, 48.05, 49.72, 52.32, 54.81,
217.38. 218.10; MS m/z 208 [M]+.
Preparation of cis-2-Bromo-3,4,4a,5,6,7,8,8a-octahy-
dro-2,5,5,8a-tetramethylnaphthalene-1(2H)-one (15). In
a two-neck 100 mL round-bottomed flask were placed com-
pound 14 (0.4 g, 1.8 mmol), CH3COOH (25 mL), and pyri-
dinium bromide perbromide (0.75 g, 2.34 mmol), and the
mixture was stirred at room temperature for 2.5 h. Water (50
mL) was then added, and the resulting solution was extracted
with ether (4 × 75 mL). The combined organic fractions were
washed with saturated NaCO3 solution (4 × 50 mL) and dried
over MgSO4, and the solvent was removed in vacuo, yielding
0.55 g of a yellow oil, which was purified by flash chromatog-
raphy using 2% ether/pet. ether as eluent. The yield of the
diastereomeric bromides 15 was 0.52 g (94%): 1Η ΝΜR data
for 15 (CDCl3) δ 0.75 (3H, s), 0.92 (3H, s), 0.96 (3H, s), 1.14
(3H, s), 1.32 (3H, s), 1.63 (3H, s), 1.79 (6H, s), 1.15-2.06 (14H,
m), 2.24-2.46 (8H, m); 13C ΝΜR (CDCl3) δ 18.28, 18.65, 18.67,
21.13, 25.56, 26.53, 30.43, 30.93, 31.03, 31.48, 32.01, 33.21,
34.07, 35.68, 35.72, 36.23, 40.65, 41.87, 42.23, 48.22, 50.53,
51.69, 52.17, 59.33, 62.45, 209.62, 210.60; MS m/z 288 [M]+.
Preparation of cis-4,4a,5,6,7,8,-Hexahydro-2,5,5,8a-tet-
ramethylnaphthalene-1(8aH)-one (16). In a 200 mL round-
bottomed flask were placed a solution of compound 15 (0.84 g
2.92 mmol), in toluene (45 mL), and DBU (0.57 mL, 3.8 mmol).
The solution was heated under reflux for 3.5 h, then cooled to
room temperature, diluted with ether (120 mL), and washed
Preparation of cis-3,4,4a,5,6,7,8,8a-Octahydro-5,5,8a-
trimethyl-1-trimethylsiloxynaphthalene (13). To a 50 mL
round-bottomed flask was placed a solution of the mixture of
9 and 12 in a ratio of 91:9 (1.94 g, 10.0 mmol) in 10 mL of
THF, the system was cooled to 0 °C, and a solution of LDA

New Sesquiterpene from Cistus creticus
Journal of Natural Products, 2004, Vol. 67, No. 12 2001
(2) Demetzos, C.; Katerinopoulos, H.; Kouvarakis, A.; Stratigakis, N.;
Loukis, A.; Ekonomakis, C.; Spiliotis, V.; Tsaknis, J. Planta Med.
1997, 63, 477-479.
(3) Demetzos, C.; Loukis, A.; Spiliotis, V.; Zoakis, N.; Stratigakis, N.;
Katerinopoulos, H. E. J. Essent. Oil Res. 1995, 7, 407-410.
(4) Demetzos, C. Phytochemical Analysis of Cistus creticus. Isolation,
Synthesis, and Structure Elucidation of a New Flavonoid Glycoside
from Kalanhoe prolifera R. Hamet. Ph.D. Thesis, University of
Athens, Greece, 1990.
(5) Chinou, I.; Demetzos, C.; Harvala, C.; Roussakis, C.; Verbist, J. F.
Planta Med. 1994, 60, 34-6.
(6) Demetzos, C.; Stahl, B.; Anastassaki, T.; Gazouli, M.; Tzouvelekis,
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successively with water (2 × 30 mL), 3 N HCl solution (2 ×
30 mL), and saturated NaCl solution (2 × 40 mL). The organic
fraction was dried over MgSO4, and the solvents were removed
to give 0.59 g of product, which was purified by flash chroma-
tography (5% AcOEt/pet ether). The yield of 16 was 0.56 g
(93%) as a yellowish oil: 1Η ΝΜR data for 16 (CDCl3) δ 0.55
(3H, s), 0.77-0.83 (1H, m), 0.83 (3H, s), 1.08 (3H, s), 1.12-
1.17 (1H, m), 1.26-1.38 (3H, m), 1.69 (1H, d, J ) 6.8 Hz),
1.66-1.67 (3H, m, CH3), 2.23-2.35 (2H, m), 2.52-2.58 (1H,
m), 6.37-6.38 (1H, m); 13C ΝΜR (CDCl3) δ 16.06, 19.12, 23.32,
23.80, 28.56, 31.25, 34.13, 34.40, 42.22, 44.97, 51.86, 133.80,
141.11, 203.43; MS m/z 206 [M]+.
(7) Polovinka, M. P.; Korchagtna, D. V.; Gatilov, Y. V.; Bagrianskaya, I.
Y.; Barkhash, V. A.; Perutskii, V. B.; Ungur, N. D.; Vlad, P. V.;
Shcherbukhin, V. V.; Zefirov, N. S. J. Org. Chem. 1994, 59, 1509-
1517.
Preparation of cis-1,4,4a,5,6,7,8,8a-Octahydro-1,5,5,8a-
tetramethylnaphth-1-ol (17). In a two-neck 100 mL round-
bottomed flask was placed a solution of compound 16 (0.19 g,
0.92 mmol), in HMPA/THF, 1:7 (3.37 mL), the system was
cooled at -78 °C, and a 1.4 M solution of MeLi in hexane (0.92
mL, 1.29 mmol) was added dropwise. The system was then
stirred at room temperature for 24 h, and the reaction was
quenched via addition of a trace of water, with the solution
extracted with ether (3 × 10 mL). The organic fractions were
washed successively with water (3 × 10 mL), saturated NH4-
Cl solution (2 × 15 mL), and saturated NaCl solution (10 mL).
The organic fraction was dried over MgSO4, the solvents were
removed in vacuo, and the crude product was purified by flash
chromatography using 1-2% AcOEt/pet. ether as eluent to give
0.1 g (47%) of 17 as a yellowish oil: 1Η ΝΜR data for 17
(CDCl3) δ 0.82 (3H, s), 1.10 (3H, s), 1.09-1.13 (1H, m), 1.14
(3H, s), 1.16 (3H, s), 1.22-1.30 (2H, m), 1.38-1.44 (1H, m),
1.47-1.52 (2H, m), 1.60-1.65 (1H, m), 1.68-1.70 (3H, m, CH3),
(8) Barrero, A. F.; Alvarez-Manzaneda, E. J.; Chanboun, R. Tetrahedron
1998, 54, 5635-5650.
(9) Akita, H.; Nozawa, M.; Mitsuda, A.; Ohsawa, H. Tetrahedron Asymm.
2000, 11, 1375-1388.
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Lett. 2000, 2, 2073-2076.
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2207.
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1807.
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Kelly, R. B. J. Am. Chem. Soc. 1954, 76, 2852-2853.
(16) Experimental conditions used were similar to those reported by: King
J.; Quale, P.; Malone, J. F. Tetrahedron Lett. 1990, 31, 5221-5224.
(17) Gesson, J.-P.; Jacquesy, J.-C.; Renoux, B. Tetrahedron Lett. 1986, 27,
4461-4464.
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5853-5866.
1.88-1.93 (1H, m), 1.94-1.96 (1H, m), 5.26-5.28 (1H, m); 13
C
ΝΜR (CDCl3) δ 18.13, 18.83, 21.49, 23.42, 26.09, 26.64, 30.53,
31.21, 32.87, 34.28, 40.82, 45.38, 77.20, 121.25, 136.29; MS
m/z 222 [M]+, m/z 204 [M+ - 18].
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1987, 28, 6645-6648.
(20) Anderson, J. C.; Pearson, D. J. Chem. Soc., Perkin Trans. 1 1998,
2023-2029.
Preparation of cis-1,1,4a,6-Tetramethyl-5-methylene-
1,2,3,4,4a,5,8,8a-octahydronaphthalene (2). In a 25 mL
round-bottomed flask were placed compound 17 (0.1 g, 0.45
mmol), THF (2 mL), triethylamine (0.7 mL, 5.0 mmol), and
Burgess reagent (0.12 g, 0.5 mmol), and the solution was
heated under reflux for 48 h. The system was then cooled to
room temperature, water (3 mL) and ether (10 mL) were added
to the solution, and the organic phase was washed successively
with water (3 × 10 mL) and saturated NaCl solution (2 × 10
mL). The organic fraction was dried over MgSO4, and the
solvents were removed in vacuo to afford a crude product. GC/
MS analysis of this crude mixture indicated the presence of
the dehydration product 2, a small amount of a side product,
and unreacted starting material, which was removed by flash
chromatography using 1-3% AcOEt/pet. ether as eluent to give
0.036 g (36%) of 17 and 0.037 g of a yellowish oil (55% yield,
74% conversion). 1Η ΝΜR data for 2 (CDCl3) δ 0.70 (3H, s,
H-12), 0.83 (3H, s, H-11), 1.02 (3H, s, H-13), 1.10-1.17 (1H,
m), 1.21-1.37 (3H, m), 1.61-1.68 (2H, m), 1.77-1.78 (3H, m,
CH3), 2.12-2.17 (2H, m, H-8), 2.34-2.38 (1H, m, H-8a), 4.91
(1H, bs, H-9), 4.92 (1H, bs, H-9), 5.48-5.49 (1H, m); 13C ΝΜR
(CDCl3) δ 18.73 (CH2, C-3), 20.40 (CH3, C-10), 21.51 (CH3,
C-13), 23.68 (CH2, C-8), 32.26 (CH3, C-12), 33.02 (CH3, C-11),
34.23 (C, C-1), 37.57, (CH2, C-4), 37.82 (C, C-4a), 43.78 (CH2,
C-2), 49.81 (CH, C-8a), 104.91 (CH2, C-9), 125.26 (CH, C-7),
131.70 (C, C-6), 150.20(C, C-5); MS m/z 204 [M]+.
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Acknowledgment. This work was funded by an EPEAEK
educational grant from the EU. The authors would like to
thank Mr. E. Roussakis and Mr. G. Mpourmpakis for excellent
technical assistance, and Dr. K. Dimas for his assistance for
the in vitro experiments.
(36) Calculations were performed with the GAUSSIAN 94 program
package. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
Johnson, B. G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Petersson,
G. A.; Montgomery, J. A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J. V.; Foresman, J. B.; Cioslowski, J.;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.;
Ayala, P. Y.; Chen, W.; Wong, M. W.; Andres, J. L.; Replogle, E. S.;
Gomperts, R.; Martin, R. L.; Fox, D. J.; Binkley, J. S.; Defrees, D. J.;
Baker, J.; Stewart, J. P.; Head-Gordon, M.; Gonzalez, C.; Pople, J. A.
Gaussian 94, Revision D.4; Gaussian, Inc.: Pittsburgh, PA, 1995.
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1269.
Supporting Information Available: Copies of 1H and 13C 1D and
2D NMR spectra of compounds 9, 10b, 11, 12, 2, and 3, as well as
mass spectra of compounds 9, 12, 2, and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
(38) Itokawa, H.; Morita, H.; Watanabe, K.; Mihashi, S.; Itaka, Y. Chem.
Pharm. Bull. 1985, 33, 1148-1153.
References and Notes
(1) Demetzos, C.; Mitaku, S.; Loukis, A.; Harvala, C.; Gally, A. J. Essent.
Oil Res. 1994, 61, 37-41.
NP0498556