Tridemethylisovelleral, a potent cytotoxic agent

Article abstract of DOI:10.1016/j.bmc.2005.06.035

The synthesis and in vitro cytotoxicity toward various tumor cell lines of (±)-tridemethylisovelleral, an analogue of the bioactive fungal sesquiterpene (+)-isovelleral retaining the bicyclo[4,1,0]hept-2-en-1,2- dicarbaldehyde system but lacking the three methyl groups, is reported. The cytotoxicity of tridemethylisovelleral toward several tumor cell lines was found to be comparable with those of established antitumor drugs, and significantly higher than that of isovelleral.

Full text of DOI:10.1016/j.bmc.2005.06.035

Bioorganic & Medicinal Chemistry 13 (2005) 6145–6150
Tridemethylisovelleral, a potent cytotoxic agent
Isabelle Aujard,a Daniel Rome,a Erwan Arzel,a Martin Johansson,a
¨
Dick de Vosb and Olov Sternera,*
aDepartment of Organic Chemistry, Lund University, PO Box 124, S-221 00 Lund, Sweden
bMedical Department, Pharmachemie BV, NL-2003 RN Haarlem, The Netherlands
Received 19 May 2005; revised 10 June 2005; accepted 13 June 2005
Available online 1 August 2005
Abstract—The synthesis and in vitro cytotoxicity toward various tumor cell lines of ( )-tridemethylisovelleral, an analogue of the
bioactive fungal sesquiterpene (+)-isovelleral retaining the bicyclo[4,1,0]hept-2-en-1,2-dicarbaldehyde system but lacking the three
methyl groups, is reported. The cytotoxicity of tridemethylisovelleral toward several tumor cell lines was found to be comparable
with those of established antitumor drugs, and significantly higher than that of isovelleral.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
(+)-Isovelleral (2) (see Fig. 1) is an extremely pungent
marasmane sesquiterpene with potent cytotoxic and
antimicrobial activities1 that was originally isolated
from the fruit bodies of Lactarius vellereus. It is
formed enzymatically in seconds from an inactive
precursor (stearoylvelutinal) as a response to injury
to the fruit body (Scheme 1), and is the active princi-
ple in a binary chemical defense system developed by
evolution to protect the fruit bodies from parasites
and predators.2
Figure 1.
The biological activities of isovelleral (2) depend on the
on the cyclopropane ring is involved in the biological
effects,6 and there is less steric hindrance for such an
attack in 3.7 In addition, the cyclopentane ring of
isovelleral (2) seems to play a role, as 2 is considerably
more potent than 4.6 In order to confirm these sugges-
tions, and to prepare a more potent analogue of the
natural product, tridemethylisovelleral (1) was synthe-
sized and assayed.
electrophilic unsaturated 1,4-dialdehyde moiety, present
in numerous other terpenoids claimed to be part of the
natural defense systems,3 as the transformation of either
of the aldehyde functions to an alcohol or keto group or
the reduction of the carbon–carbon double bond is asso-
ciated with loss of activity.4 Also the cyclopropane ring
and its environment appears to be important for the bio-
logical activity of 2, as suggested by the difference in
antimicrobial activity and cytotoxicity toward mamma-
lian cells of the two bicyclic analogues 3 and 4;5 3 is at
least 10 times more potent than 4.6 The reason for this
difference is believed to be that a nucleophilic attack
2. Results and discussion
Although the original goal was to prepare the analogue
of 2 lacking only the methyl attached to the cyclopro-
pane ring, we decided to omit also the geminal methyls
of the cyclopentane ring as it is unlikely that they
will moderate the reactivity of the dialdehyde moiety.
However, it should be remembered that the geminal
Keywords: Tridemethylisovelleral; Isovelleral; Unsaturated dialdehy-
des; Cytotoxicity.
*
Corresponding author. Tel.: +4646 22 28 213; fax: +464 622 28
209; e-mail: olov.sterner@organic.lu.se
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.06.035

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I. Aujard et al. / Bioorg. Med. Chem. 13 (2005) 6145–6150
Commercially available 5-indanol was converted into its
methyl ether and was immediately reduced with lithium
in ammonia to the bicyclic ketone 6 (Scheme 2). The
introduction of the ester group of 7 was achieved by
the reaction of the enolate ion of 6 with ethylcyanofor-
mate,9 yielding the b-keto ester as a 3:1 diastereomeric
mixture of epimeric esters. No migration of the double
bond was observed. The cis bicyclic framework of tri-
demethylisovelleral (1) was obtained by hydrogenation
of the bicyclic enone, a reaction that, as expected,10
was stereoselective. Both epimers of 7 gave the same
product 8, and the reaction was run with the 3:1 dia-
stereomeric mixture obtained in the preceding step.
The introduction of the conjugated double bond in 9
was accomplished by treatment of the enol ester 8 with
phenylselenyl chloride in the presence of pyridine fol-
lowed by oxidation with hydrogen peroxide and subse-
quent pyrolysis.11 Using the Corey–Chaykovsky
reagent (methylsulfoxonium ylid),12 the cyclopropane
ring was introduced in a stereoselective manner giving
only one cyclopropane diastereomer. From this point,
HeathcockÕs route to racemic isovelleral (2)13 was essen-
tially followed. b-Keto ester (10) was deprotonated with
LDA and the enolate was trapped as the corresponding
enol triflate (11). Carbonylation with palladium acetate
under a carbon monoxide14 atmosphere gave the diester
12. Subsequently, the ester groups were reduced to diol
13 and then reoxidized using Swern conditions15 to give
the desired dialdehyde 1 in racemic form.
Scheme 1. Conversion of stearoylvelutinal to isovelleral (2) as a
response to injury.
methyl groups may provide for some increase in steric
hindrance for reagents that have to react with the cyclo-
propane ring and in that way cause even a decrease in
activity. The strategy selected was to start from commer-
cially available 5-indanol (5), and to introduce the two
aldehyde groups and the cyclopropane ring later. a,b-
Unsaturated ketones can easily be made from aromatic
methyl ethers through Birch reduction followed by
acidic hydrolysis.8
Scheme 2. Reagents and conditions: (a) i—MeI, K2CO3, DMF, 55 ꢁC; ii—Li, NH3, EtOH, THF, À78 ꢁC; iii—10% HCl, MeOH, 85% from 5-
indanol; (b) i—DIPA, n-BuLi, ethylcyanoformate, THF, À78 ꢁC 90%; (c) HCO2NH4, 10% Pd/C, MeOH, reflux, 76%; (d) i—DIPA, n-BuLi, PhSeCl,
THF, À78 ꢁC ii—35% H2O2, CH2Cl2, 86%; (e) NaH (oil free), Me3SOI, DMF, À15 ꢁC, 69%; (f) LDA, PhNTf2, THF, 85%; (g) Pd(OAc)2, PPh3, CO,
MeOH, Et3N, DMF, 20 ꢁC, 90%; (h) DIBAL-H, THF, 65%; (i) oxalyl chloride, DMSO, Et3N, CH2Cl2, À78 ꢁC, 80%.

I. Aujard et al. / Bioorg. Med. Chem. 13 (2005) 6145–6150
6147
The cytotoxic activity of tridemethylisovelleral (1) was
tested against a series of tumor cell lines,16 and the
IC50 values obtained are given in Table 1. For compar-
ison, the activities of isovelleral (2) as well as of several
established antitumor drugs are also given. The cells
were plated in 96-wells flat bottom microtiter plates
and preincubated in RPMI 1640 medium supplemented
with 10% FCS for 48 h at 37 ꢁC. The test compounds
were dissolved in DMSO and a dilution series in the
medium was prepared and added to the cells. After 5
days, the incubation was terminated by washing the
plate twice with PBS and fixing the cells with 10% tri-
chloroacetic acid in PBS, whereafter the cells were
stained and the result was recorded in an automated
microplate reader. A detailed description of the test
procedure is published elsewhere.16
higher in these assays. Assuming that the effect of the
geminal methyls of the cyclopentane ring of 2 is insig-
nificant, this would confirm that the cyclopentane ring
is important for the biological activities of the isovell-
eraloids. The cyclopentane ring increases the rigidity
of 1 and 2 compared to 3 and 4, thereby altering the
dihedral angle between the two aldehyde groups. In
addition, the methyl adjacent to the cyclopropane ring
in isovelleral (2) will also affect the conformation
slightly, by its steric interaction with the cyclopentane
ring. This can be observed in Figure 2, where the low-
est energy conformers of 1 and 2 are shown. The dihe-
dral angle between the two aldehyde groups is 52ꢁ in 1
and 36ꢁ in 2. As the aldehyde groups are anticipated to
take part in the events that lead to the biological activ-
ity, conformational effects on the dialdehyde moiety
may be important.18
It is noteworthy that 1 is very potent toward all cell
lines, also those that are considered less sensitive to
chemotherapy (e.g., the lung cancer cell line H226),
and the concentrations required for inhibition are
approximately 0.1 nmol/ml. Although the lack of selec-
tivity makes 1 useless as a drug by itself, but the pos-
sibility to disguise it as a prodrug that is activated
selectively by tumor cells is attractive. Such efforts
are currently in progress. Both enantiomers of isovell-
eral (2) have previously been shown to possess similar
antimicrobial and cytotoxic activities,17 and it is there-
fore relevant to compare with racemic tridemethyliso-
velleral (1). In comparison with the natural product
2, the cytotoxicity of 1 is between 4 and 11 times
3. Conclusions
The demethylated analogue 1 of the potent fungal unsat-
urated dialdehyde isovelleral (2) was shown to inhibit
the growth of different tumor cell lines at around
0.1 nmol/ml. Although the lack of selectivity of 2 ren-
ders it useless for direct pharmaceutical applications,
the unsaturated 1,4-dialdehyde functionality can be
disguised chemically in ways that are (a) chemically
relatively stable and (b) transformed back to the unsat-
urated dialdehyde in the presence of certain chemical or
enzymatic conditions. This makes tridemethylisovelleral
Table 1. Cytotoxicity of tridemethylisovelleral (1), isovelleral (2) and several antitumor drugs towards seven tumor cell linesa
Cell lineb
Compound
MCF7
EVSA-T
WiDr
IGROV
M19
A498
H226
1
0.17
0.56
0.02
2.21
5.77
0.04
4.41
0.07
0.28
0.01
1.34
3.65
0.01
0.54
0.18
1.08
0.06
0.66
0.11
0.54
2.28
0.02
0.99
0.17
0.66
0.03
1.77
3.40
0.05
0.86
0.21
1.87
0.17
7.13
1.10
0.08
2.23
0.23
1.78
0.37
10.35
2.61
5.03
6.68
2
DOXc
CPTc
5-FUc
MTXc
ETOc
0.02
3.06
1.73
<0.01
0.25
a IC50 values of test compounds (nmol/ml) in vitro using SRB as a cell viability test.16
b Tumor cell line: human breast adenocarcinoma (MCF-7), human breast carcinoma (EVSA-T), human colon colorectal adenocarcinoma (WiDr),
human ovary carcinoma (IGROV-1), human skin melanoma (M19-MEL, human kidney carcinoma (A498), and human lung mesothelioma.
c Established cytotoxic drugs: doxorubicin (DOX), cisplatin (CPT), 5-fluorouracil (5-FU), methotrexate (MTX), and etoposide (ETO).
Figure 2. The lowest energy conformations of tridemethylisovelleral (1) (left) and isovelleral (2) (right).

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I. Aujard et al. / Bioorg. Med. Chem. 13 (2005) 6145–6150
(1) a suitable base for a prodrug that for example is
liberated in a tumor tissue that overexpresses a certain
enzyme, or that is specifically activated in an insect or
another pest. Such work is currently in progress in our
laboratory.
of 10% aqueous HCl, and stirred for 3 h at room tem-
perature. The solution was concentrated and the residue
was diluted with water and extracted with CH2Cl2. The
combined organic layers were washed with brine and
dried. Evaporation of the solvent afforded an oil, which
was purified by distillation (88–90 ꢁC, 1 mmHg). Ketone
6 was obtained as 10.9 g (85% from 5-indanol (5)) of a
pale yellow oil: 1H NMR (CDCl3) d 1.23 (1H, dq,
J = 11.8 and 7.2 Hz), 1.59 (1H, m), 1.69 (1H, m), 1.89
(1H, m), 2.06 (1H, J = 13.2, 6.7 Hz), 2.22 (1H, m),
2.31 (1H, dd, J = 14.3 and 4.8 Hz), 2.40–2.55 (3H, m),
2.63 (1H, dd, J = 19.3 and 9.1 Hz), 5.86 (1H, s); 13C
NMR (CDCl3) d 24.3, 29.7, 32.3, 33.2, 37.9, 43.5,
122.7, 176.1, 200.5; HRMS (EI) [M]+ calcd for
C9H12O, 136.0888; found, 136.0889.
4. Experimental
Materials were obtained from commercial suppliers and
were used without further purification unless otherwise
noted. THF was dried by refluxing over sodium/benzo-
phenone ketyl immediately prior to use. CH2Cl2 and tri-
ethylamine were distilled from calcium hydride prior to
use. DMF and DMSO were distilled under reduced pres-
˚
sure and kept over 4A MS. MeOH was dried by distilling
from magnesium/iodine. All moisture and air-sensitive
reactions were carried out under an atmosphere of dry
nitrogen using oven-dried glassware. HRESIMS spectra
were recorded with a Micromass Q-TOF Micro spec-
trometer and HREIMS spectra (direct inlet, 70 eV) were
recorded with a JEOL SX102 spectrometer. NMR spec-
tra (in CDCl3) were recorded with a Bruker DRX 400
spectrometer at 400 MHz (1H) and at 100 MHz (13C)
and with a Bruker DRX 500 spectrometer at 500 MHz
(1H) and at 125 MHz (13C). Chemical shifts are given in
ppm relative to TMS using the residual CHCl3 peak in
CDCl3 solution as internal standard (7.26 and
77.0 ppm, respectively, relative to TMS). Organic extracts
were dried over MgSO4. All flash chromatography was
4.2. 6-Oxo-2,3,3a,5,7-hexahydroindene-5-carboxylic acid
ethyl ester (7)
A measure of 3.36 ml (2.5 M in hexanes) of n-BuLi was
added at À78 ꢁC to a solution of 1.23 ml (8.8 mmol) of
dry diisopropylamine in 20 ml of THF. The mixture
was stirred at À78 ꢁC for 30 min. A solution of 1.09 g
(8.0 mmol) of 6 in 4 ml of THF was added over 20 min
at À78 ꢁC. The resulting mixture was stirred at À78 ꢁC
for 1 h whereafter 800 lL (8.0 mmol) of ethylcyanofor-
mate was added in one aliquot. After 1 h at À78 ꢁC the
reaction was quenched with water. The mixture was al-
lowed to warm to room temperature and extracted with
Et2O. The combined organic layers were dried over
MgSO4, filtered and concentrated to afford an oil which
was purified by flash chromatography (petroleum ether/
ethyl acetate 8:2) to give 1.50 g of 7 (90%) as a 3:1 dia-
stereomeric mixture of epimeric esters (NMR data are
˚
performed on 60 A 35–70 lm Matrex silica gel (Grace
Amicon). TLC analyses were made on silica gel 60 F254
(Merck) plates and visualized with anisaldehyde/sulfuric
acid and heating. The cytotoxicity was assayed according
to Ref. 16. Calculations were performed using Macro-
Model v8.6 (Force field: MMFFs; solvent: water (using
the analytical gereralized born/surface area (GB/SA)
model); minimization method: TNCG; conformational
search: MonteCarlo (MCMM); steps: 2000).
1
given for the major isomer): H NMR (CDCl3) d 1.30
(3H, t, J = 7.1 Hz), 1.33 (1H, q, J = 7.3 Hz), 1.72 (1H,
m), 1.95 (1H, m), 2.03 (1H, ddd, J = 12.8 and 1.2,
1.1 Hz), 2.13 (1H, m), 2.41 (1H, dt, J = 12.8 and
4.4 Hz), 2.45–2.73 (3H, m), 3.35 (1H, dd, J = 14.1 and
4.6 Hz), 4.22 (2H, dq, J1 = 7.1 and 1.7 Hz), 5.95 (1H,
m); 13C NMR d 14.6, 24.0, 32.3, 32.8, 33.1, 42.6, 54.4,
61.5, 122.1, 171.3, 176.0, 194.7; HRMS (EI) [M]+ calcd
for C12H16O3, 208.1099; found, 208.1101.
4.1. 1,2,3,6,7,7a-Hexahydroinden-5-one (6)
To a solution of 12.6 g (0.09 mol) of 5-indanol (5) in
70 ml of DMF was added 9.0 ml (0.14 mol) of MeI
and 21.0 g (0.15 mol) of anhydrous K2CO3. The result-
ing solution was stirred at 55 ꢁC for 4 h under a nitrogen
atmosphere. The mixture was cooled to room tempera-
ture, diluted with 70 ml of ether and 110 ml of water
and extracted with ether. The organic layers were
washed with 5% aqueous NaOH, dried over K2CO3
and concentrated. The methyl ether was obtained as
an orange oil (13.9 g). To a stirred solution of 13.9 g
of the crude methyl ether in 80 ml of THF, 80 ml of
EtOH and 500 ml of liquid ammonia, 2.8 g (0.4 mol)
lithium in small pieces was carefully added at À78 ꢁC
under an inert atmosphere. The stirring was continued
at À78 ꢁC until the blue color had disappeared where-
after the ammonia was allowed to evaporate. Water
was added to dissolve lithium salts and the aqueous
layer was extracted three times with ether. The com-
bined extracts were washed with brine, dried, and con-
centrated. The residue, obtained as a yellow oil, was
dissolved in a mixture of 400 ml of MeOH and 120 ml
4.3. 6-Oxo-2,3,3a,5,7,7a,8-octahydroindane-5-carboxylic
acid ethyl ester (8)
A measure of 1.89 g (30.0 mmol) of ammonium formate
was added to a mixture of 1.26 g (6.0 mmol) of 7 and
63 mg of 10% Pd/C in 60 ml of dry MeOH at room tem-
perature under a nitrogen atmosphere. The resulting
solution was refluxed for 10 min. The reaction mixture
was filtered through celite and washed with MeOH.
The solvent was removed under reduced pressure and
the residue was dissolved in a mixture of water and
ether. The layers were separated and the aqueous layer
was extracted with ether. The combined organic layers
were dried and concentrated. Flash chromatography
(heptane/ethyl acetate 98:2) of the residue yielded
1
946 mg 8 (75%) as a colorless oil: H NMR (CDCl3) d
1.31 (3H, t, J = 7.1 Hz), 1.39 (2H, m), 1.54 (1H, m),
1.75 (3H, m), 2.05–2.17 (4H, m), 2.40 (2H, m), 4.21
(2H, dq, J = 7.1 and 0.9 Hz), 12.21 (1H, s); 13C NMR

I. Aujard et al. / Bioorg. Med. Chem. 13 (2005) 6145–6150
6149
d 14.7, 22.7, 25.0, 31.3, 31.8, 31.9, 36.8, 37.0, 60.6, 96.5,
172.4, 172.9; HRMS (EI) [MÀH]+ calcd for C12H17O3,
209.1178; found, 209.1174.
37.7, 40.4, 61.8, 170.7, 208.3; HRMS (EI) [M]+ calcd
for C13H18O3, 222.1256; found, 222.1254.
4.6. 2-Trifluoromethanesulfonyloxy-3a,4,5,6,6a,6b-hexa-
hydro-1H-cyclprop[e]indene-1a-carboxylic acid ethyl
ester (11)
4.4. 6-Oxo-2,3,7,7a,8-hexahydroindene-5-carboxylic acid
ethyl ester (9)
A measure of 2.20 ml (2.5 M in hexanes) of n-BuLi was
added at À78 ꢁC to a solution of 0.77 ml (5.5 mmol) of
dry diisopropylamine in 20 ml of THF. The mixture
was stirred at À78 ꢁC for 30 min. A solution of 1.01 g
(5.0 mmol) of 8 in 5 ml of dry THF was added over
5 min. The resulting mixture was stirred at À78 ꢁC for
40 min, then a solution of 920 mg (5.0 mmol) of phenyl-
selenyl chloride in 5 ml of THF was added in one ali-
quot. The ice bath was removed, and the solution was
washed with aqueous 1 M HCl, water, aqueous saturat-
ed NaHCO3 solution, and then dried on Na2SO4. After
filtration and evaporation of the solvent, the afforded oil
was diluted in CH2Cl2 (40 ml) and the solution was
cooled to 0 ꢁC, at which time 0.33 ml of 35% aqueous
H2O2 was slowly added. An additional 0.33 ml of 35%
aqueous H2O2 was added after 10 min, and again after
20 min. After an additional 10 min, H2O was added
and the organic layer was separated, washed with satu-
rated NaHCO3, dried over MgSO4, and evaporated. The
crude oil was purified by flash chromatography on silica
gel (petroleum ether/ethyl acetate 7:3) to give 854 mg
To an ice cold solution of 240 ll (1.69 mmol) of diiso-
propylamine in 1.25 ml of THF was added dropwise
800 ll (1.9 M in cyclohexane) of n-BuLi under a nitro-
gen atmosphere. After 10 min the solution was cooled
to À78 ꢁC and 311 mg (1.40 mmol) of 10 dissolved in
0.63 ml of THF was added dropwise. The reaction
mixture was stirred for 40 min at À78 ꢁC when 536 mg
(1.50 mmol) of N-phenyltrifluoromethanesulfonimide
in 1.5 ml of THF was added. The resulting solution
was allowed to reach room temperature and stirred for
1 h. The reaction mixture was then diluted with 10 ml
saturated aqueous NaHCO3 and extracted with 10 ml
of ether. The organic phase was washed with water,
brine, dried and concentrated. The crude product was
purified with flash chromatography (heptane/ethyl ace-
tate 4:1, 1% EtOH) to give 468 mg (94%) of 11: 1H
NMR (CDCl3) d 1.17 (1H, dd, J = 7.5 and 4.5 Hz),
1.29 (3H, t, J = 7.1 Hz), 1.45–1.65 (4H, m), 1.77 (1H,
m), 1.86 (1H, dt, J = 9.3 and 1.9 Hz), 1.93 (1H, m),
1.99 (1H, dd, J = 9.3 and 4.5 Hz), 2.43 (1H, dq,
J = 8.5 and 2.0 Hz), 2.57 (1H, m), 4.21 (1H, dq,
J = 10.8 and 7.1 Hz), 4.23 (1H, dq, J = 10.8 and
7.1 Hz), 5.42 (1H, d, J = 3.6); HRMS (EI) [M]+ calcd
for C14H17F3O5S, 354.0749; found, 354.0761.
1
of 6 (86%) as a pale yellow oil: H NMR (CDCl3) d
1.30 (3 H, dt, J = 7.1, 0.5 Hz), 1.40 (1H, m), 1.65–1.75
(3H, m), 1.85 (1H, m), 2.05 (1H, m), 2.48 (1H, t,
J = 8.6 Hz), 5.57 (1H, m), 2.61 (1H, t, J = 5.6 Hz),
2.92 (1H, m), 4.24 (2H, q, J = 7.1 Hz), 7.43 (1H, d,
J = 3.8 Hz); 13C NMR d 14.6, 24.7, 31.1, 31.5, 38.3,
40.6, 41.9, 61.5, 131.8, 158.5, 165.0, 195.4; HRMS (EI)
[M]+ calcd for C12H16O3, 208.1099; found, 208.1097.
4.7. 3a,4,5,6,6a,6b-Hexahydro-1H-cycloprop[e]indene-
1a,2-dicarboxylic acid 1a-ethyl ester 2-methyl ester (12)
A measure of 468 mg (1.32 mmol) of 11, 400 ll
(2.91 mmol) of triethylamine, 2.5 ml (55 mmol) of
MeOH, 15 mg (0.066 mmol) of palladium acetate, and
21 mg (0.079 mmol) of triphenylphosphine were dis-
solved in 6 ml of DMF. CO was bubbled through the
solution and the reaction mixture was stirred for 2 h un-
der a CO atmosphere at room temperature. The mixture
was diluted with 60 ml of ether, washed with 60 ml of
water and 60 ml brine, dried, and concentrated. Flash
chromatography (heptane/ethyl acetate 4:1, 1% EtOH)
gave 314 mg (1.19 mmol, 90 %) of 12: 1H NMR (CDCl3)
d 0.72 (1H, dd, J = 7.1 and 4.3 Hz), 1.21 (3H, t,
J = 7.1 Hz), 1.45 (1H, dt, J = 8.6 and 12.6 Hz), 1.43–
1.55 (3H, m), 1.65 (1H, m), 1.74 (1H, m), 1.83 (1H,
dd, J = 9.3 and 4.3 Hz), 1.87 (1H, m), 2.42 (2H, m),
3.75 (3H, s), 4.07 (1H, dq, J = 10.8 and 7.1 Hz), 4.18
(1H, dq, J1 = 10.8 and 7.1 Hz), 6.46 (1H, d,
J = 3.3 Hz); 13C NMR d 13.9, 22.9, 23.0, 23.9, 27.6,
32.0, 32.8, 36.2, 37.2, 51.3, 60.4, 129.8, 138.8, 167.2,
173.1; HRMS (ESI) [M]+ calcd for C15H20O4,
264.1362; found, 264.1369.
4.5. 7-Oxo-2,3,8,8a-octahydro-cyclopropindene-6-
carboxylic acid ethyl ester (10)
A flask containing 0.40 g (16.5 mmol, oil free) of fresh
NaH and 3.37 g (16.5 mmol) of trimethylsulfoxonium
iodide followed by 50 ml of dry DMF, which was added
slowly via a syringe and the hydrogen generated was
ventilated. The mixture was stirred at room temperature
until it became clear and all hydride was consumed. The
flask was cooled in an acetone-ice bath to À15 ꢁC and a
solution 3.26 g (15.7 mmol) of 9 in 5 ml of DMF was
added in one portion to the flask via a syringe and the
solution turned orange. After 7 min TLC indicated com-
plete consumption of starting material 9, and the reac-
tion was quenched by addition of 150 ml of H2O. The
mixture was extracted with 3 · 100 ml Et2O, and the
combined extracts were washed with large amounts of
water, dried, and concentrated. After purification by
flash chromatography (heptane/ethyl acetate), 10 was
1
obtained as 2.4 g (69%) of a pale yellow oil: H NMR
(CDCl3) d 1.20 (1H, d, J = 1.7 Hz), 1.27 (3H, t,
J = 7.1 Hz), 1.43 (1H, m), 1.60–1.80 (5H, m), 1.89
(1H, m), 1.99 (1H, m), 2.06 (1H, dd, J1 = 9.5 Hz,
J2 = 15.72 Hz), 2.17 (1H, m), 2.27 (1H, q, J = 15.6 and
5.0 Hz), 2.38 (1H, m), 4.18 (2H, q, J = 7.2 Hz); 13C
NMR d 14.5, 20.3, 22.5, 31.2, 31.4, 31.8, 35.4, 36.3,
4.8. (2-Hydroxymethyl-3a,4,5,6,6a,6b-hexahydro-1H-
cycloprop[e]inden-1a-yl)-methanol (13)
A measure of 1 ml (1 mmol) of DIBAL-H (1 M in
hexane) was added dropwise to a solution of 53 mg
(0.21 mmol) of 12 in 2 ml of THF at À78 ꢁC. The

6150
I. Aujard et al. / Bioorg. Med. Chem. 13 (2005) 6145–6150
reaction mixture was allowed to warm to room temper-
ature and stirred for 30 min. The solution was then
cooled with an ice-bath to 0 ꢁC and quenched with a
saturated aqueous potassium sodium tartrate solution.
The mixture was extracted with ether and the ether
extract was washed with brine, dried, and concentrated.
Flash chromatography (heptane/ethyl acetate 4:1) affor-
ded 25.2 mg (0.13 mmol, 65%) of the diol 13 as a color-
Acknowledgments
Financial support from the Swedish Natural Science
Council and the European Commission (Fair CT69-
1781) is gratefully acknowledged.
References and notes
1
less oil: H NMR (CDCl3) d 0.64 (1H, dd, J = 5.7 and
4.6 Hz), 0.89 (1H, dd, J = 8.7 and 4.3 Hz), 1.19 (1H,
m), 1.32 (2H, m), 1.45 (1H, m), 1.55 (1H, m), 1.64
(1H, m), 1.81 (1H, m), 2.35 (2H, m), 3.45 (1H, d,
J = 11.9 Hz), 3.50 (2H, br s), 3.72 (1H, dd, J = 11.9
and 2.7 Hz), 4.25 (2H, m), 5.17 (1H, m); 13C NMR
(CDCl3) d 19.9, 24.2, 24.9, 30.7, 32.3, 33.4, 36.6, 37.4,
67.2, 6.3, 128.7, 139.2; HRMS (ESI) [M+Na]+ calcd
for C12H18O2Na, 217.1191; found, 217.1204.
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1a,2-dicarbaldehyde (1)
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To a solution of 92 ll (6.33 mmol) of DMSO in 2 ml of
CH2Cl2 was added 218 ll (2.54 mmol) of oxalyl chloride
at À78 ꢁC. The solution was stirred for 15 min before a
solution of 123 mg (0.63 mmol) of 13 in 2 ml of CH2Cl2
was added dropwise during 5 min. After stirring for
45 min at À78 ꢁC, 2.12 ml (0.64 mmol) of triethylamine
was added. The solution was stirred for an additional
30 min at À78 ꢁC before equilibrating to room tempera-
ture. After 30 min stirring at room temperature the reac-
tion mixture was diluted with 20 ml of water and 20 ml
of ether. The phases were separated and the aqueous
phase was extracted with an additional 10 ml of ether.
The combined ether extracts were dried and concentrat-
ed. Flash chromatography (heptane/ethyl acetate 8:1)
gave 96 mg (0.50 mmol, 80%) of the dialdehyde 1 as a
11. Liotta, D.; Barnum, C.; Puleo, R.; Zima, G.; Bayer, C.;
Kezar, H. S. J. Org. Chem. 1981, 46, 2920.
12. (a) Corey, E. J.; Chaykovsky, M. J. Am. Chem. Soc. 1965,
´
87, 1353; (b) Cativiela, C.; Dıaz-de-Villegas, M. D.;
Jimenez, A. I. Tetrahedron 1994, 50, 9157.
´
13. Heathcock, C. H.; Thompson, S. K. J. Org. Chem. 1992,
57, 5979.
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26, 1109.
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1
colorless oil: H NMR (CDCl3) d 0.88 (1H, dd, J = 7.0
and 4.1 Hz), 1.28 (1H, m), 1.60–1.72 (4H, m), 1.92
(1H, m), 1.98 (1H, m), 2.08 (1H, dd, J = 9.2 and
4.1 Hz), 2.53 (1H, dq, J = 8.2 and 1.7 Hz), 2.63 (1H,
tt, J = 8.6 and 3.0 Hz), 6.50 (1H, d, J = 2.9 Hz), 9.51
(1H, s), 9.78 (1H, s); 13C NMR (CDCl3) d 24.6, 24.6,
29.5, 31.9, 32.6, 33.0, 36.8, 38.4, 139.7, 153.6, 193.0,
199.9. HRMS (CI) [M+H]+ calcd for C12H15O2,
191.1072; found, 191.1071.
18. DÕIschia, M.; Prota, G.; Sodano, G. Tetrahedron Lett.
1982, 23, 3295.