The high-intrinsic diels-alder reactivity of (-)-galiellalactone; generating four quaternary carbon centers under mild conditions

Article abstract of DOI:10.1002/ejoc.200400137

The Interleukin-6 (IL-6) responsive JAK/STAT pathway seems to be correlated with major diseases such as chronic inflammation, arteriosclerosis, liver fibrosis, Parkinson and Alzheimer disease. In order to take a look at (-)-galiellalactone as a potential

Full text of DOI:10.1002/ejoc.200400137

FULL PAPER
The High-Intrinsic Diels؊Alder Reactivity of (؊)-Galiellalactone; Generating
Four Quaternary Carbon Centers under Mild Conditions
Franz von Nussbaum,*[a] Roman Hanke,[a] Thomas Fahrig,[a] and Jordi Benet-Buchholz[b]
Dedicated to Prof. Wolfgang Steglich on the occasion of his 70th birthday
Keywords: Biological activity / Biosynthesis / Medicinal chemistry / Natural products / Polyketides / Signal transduction
The Interleukin-6 (IL-6) responsive JAK/STAT pathway se-
ems to be correlated with major diseases such as chronic in-
flammation, arteriosclerosis, liver fibrosis, Parkinson and Alz-
heimer disease. In order to take a look at (−)-galiellalactone
as a potential low-molecular-weight lead structure for non-
Diels−Alder product of complicated architecture. During this
extraordinary Diels−Alder-type conversion four quaternary
carbon centers were generated at room temperature under
mild conditions in a regio- and stereoselective fashion. The
novel Diels−Alder transformation was used for a stereoselec-
proteinogenic IL-6 antagonists we carried out a microderiva- tive hetero-derivatization of the natural product leading to an
tization program that was aiming at bioactive congeners of
the natural product and a preliminary structure-activity rela-
tionship. During this effort, galiellalactone showed reactivity
aza congener of altered IL-6 antagonistic activity in HepG2
hepatoma cells. The absolute (4S,5aR,7aR,7bS) configuration
of natural (−)-galiellalactone was confirmed by X-ray crystal-
generally governed by convex-concave face selectivity. O- lography with Cu-Kα radiation.
Acyl derivatives of galiellalactone turned out to be precur-
sors of bis(dehydratogaliellalactone), a novel oligocyclic
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
(Ϫ)-Galiellalactone (4) was first isolated from cultures of
the ascomycete Galiella rufa A75-86 by Anke and Haut-
zel,[1] and since then further wood-inhabiting fungi have
been found to produce 4.[2] The unusual tricyclic structure
of galiellalactone (4) did not, however, automatically impli-
cate a common biogenesis. Nonetheless, a biosynthesis that
involves a 1,2-rearrangement of a hexaketide precursor (1
Ǟ 2) and an intramolecular DielsϪAlder cyclization (2 Ǟ
3) as key steps has been proposed by Steglich (Scheme 1).[3]
Feeding experiments[3] and recent microbiological investi-
gations[4] support such an unusual pathway. The
DielsϪAlder step in particular is remarkable. To date, not
many natural products are known that are biosynthesized
by an enzyme-catalyzed [4ϩ2] cycloaddition.[5]
Scheme 1. Biosynthesis of (Ϫ)-galiellalactone (4)[3]
The relative stereochemistry of galiellalactone was orig-
inally deduced by NMR spectroscopic[6] and X-ray diffrac-
tion[1] measurements. However, the absolute configuration
of the natural product was only clarified recently by synth-
eses of (ϩ)-galiellalactone (ent-4)[7,8] and (Ϫ)-galiellalac-
tone (4).[7]
Recently, (Ϫ)-galiellalactone (4) was described as a selec-
tive, non-peptidic, low-molecular-weight inhibitor of the in-
terleukin 6 (IL-6) responsive JAK/STAT pathway (Janus ki-
nase/signal transducer and activator of transcription).[9]
The activity of 4 was determined with a reporter gene assay
to be submicromolar (IC50 ϭ 0.25 µ) in HepG2 cells.[9]
Systemic changes of the organism that are a consequence of
[a]
Medicinal Chemistry, Bayer HealthCare AG
42096 Wuppertal, Germany
E-mail: franz.nussbaum@bayerhealthcare.com
[b]
Bayer Industry Services, Analytics, X-ray Laboratory
51368 Leverkusen, Germany
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Eur. J. Org. Chem. 2004, 2783Ϫ2790
DOI: 10.1002/ejoc.200400137
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inflammation are termed ‘‘acute-phase response’’ (APR).[10]
Clearly, the chemistry of galiellalactone (4) is governed
The cytokine interleukin 6 (IL-6) acts as the major inducer by convex/concave face selectivity: catalytic hydrogenation
of acute-phase proteins in the liver by the JAK/STAT path- of 4 yields (2aS)-2a,3-dihydrogaliellalactone (6a) exclusively
way. Accordingly, IL-6 responsive genes (IL-6RE) play a (Scheme 2). Michael additions generally seem to take place
key role within the acute-phase response and seem to be at C3 from the Re face. Hence, the (3R) addition product
involved in many diseases such as liver fibrosis,[11] Alzhei- was obtained by stirring 4 with phenylmethanethiol under
mer’s disease,[12] Parkinson’s disease,[13] arteriosclerosis,[14] basic conditions (4 Ǟ 7a), or with sodium azide under
and chronic inflammation.[15] Controlled regulation of the mildly acidic conditions (4 Ǟ 7b). Subsequent reduction
IL-6 induced cell signaling with low-molecular-weight yielded the corresponding amine (7b Ǟ 7c) or the (tert-but-
drugs would therefore be a favorable starting point to de- oxycarbonyl)amine in the presence of di-tert-butyl dicar-
velop new treatments for these diseases.
bonate (7b Ǟ 7d). Epoxidation also took place from the
convex face, yielding 8 in good yield under anhydrous con-
ditions. When electrophiles like alkyl halides were allowed
to react with the dianionic enolate of 4 at lower tempera-
tures, C2a derivatives with a shifted double bond were ob-
tained, as is exemplified by the methyl product 5. Within
our IL-6 responsive assay system, compounds 5, 6, 7 and 8
turned out to be inactive.
Results and Discussion
In order to obtain IL-6 antagonistic analogues of 4 that
also inhibit JAK/STAT signaling we carried out a chemical
derivatization program. Concurrently, a preliminary struc-
ture-activity relationship (SAR) should be established. A
broad ‘‘decorating’’ derivatization approach, that uses the
natural product more as a template, was avoided as it would
most likely lead to inactive derivatives due to capping or
‘‘dilution’’ of the chemical functional groups which are
often also the pharmacophores. Instead, we decided to fo-
cus on singular modifications of only individual functional
groups within 4. A luciferase reporter gene assay in HepG2
hepatoma cells permanently transfected with a respective
reporter was used to monitor the bioactivity of the synthe-
sized compounds. Within our assay system 4 showed single-
digit micromolar activity (IC50 ϭ 2.7 µ).
First, a new X-ray structure of natural 4 was obtained
(Figure 1).[16] Although the natural product does not con-
tain heavy hetero atoms, we were able to confirm[7] the
absolute (4S,5aR,7aR,7bS) configuration of 4 by using Cu-
Kα radiation as the X-ray source. The folded geometry of 4
implicates a convex side, bearing the tertiary alcohol at C7b
at its very center, and a concave face that is fenced by the
carbonyl group at C2, the methyl group at C4 and various
hydrogen atoms (at C3, C5, C6 and C7). The central six-
membered ring (C2aϪC7b) is forced into the boat confor-
mation by the annulated cyclopenta[b]furan-2-one system
and the methyl substituent at C4.
Scheme 2. Face selectivity governs the chemistry of (Ϫ)-galiellalac-
tone (4)
A major synthetic aim of our derivatization efforts was
to obtain hetero-congeners of 4 that bear a nitrogen func-
tionality at C7b instead of the hydroxy group. One advan-
tage of such a substitution would be the possibility to intro-
duce further residues (N-alkyl, N-aryl), without abandon-
ment of a hydrogen donor at this position. SN2 reactions
did not appear to be a promising strategy as inversion of
stereochemistry is unfavorable at C7b. In order to evaluate
SN1 modifications at C7b that take place with retention of
configuration, the tertiary alcohol was first activated by
Figure 1. X-ray structure with the absolute configuration of natural
(Ϫ)-galiellalactone (4)[16]
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The High-Intrinsic DielsϪAlder Reactivity of (Ϫ)-Galiellalactone
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acylation. Conversion of 4 by addition of a large excess of unprecedented and complicated architecture of 11. Structure
acyl chloride (e.g. AcCl, BzCl, 4-PhC6H4COCl) in aprotic 11 presents a new heptacyclic oxa-carbon ring system.
solvents yielded products 9, which are stable enough to be Again, the absolute configuration was determined by an X-
stored at Ϫ18 °C for months (Scheme 3). However, in solu- ray structure (2aЈR,5aЈR,7aЈR,4R,7bЈS,5aR,7aR,7bS) using
tion, especially in the presence of strong bases (e.g. DBU), Cu-Kα radiation (Figure 2). The connectivity between the
the esters 9 decomposed. To our surprise the nucleophilic two galiellalactone units over the central unsaturated six-
base 4-(dimethylamino)pyridine (DMAP) triggered a high membered ring system (C2a,3,4,2aЈ,7bЈ,7b) specified 11 as
yielding conversion of 9 to a defined product which turned a DielsϪAlder-type dimerization product of dehydratogali-
out to be a formal dimer of dehydratogaliellalactone (10) ellalactone (10). This high-yielding DielsϪAlder reaction[17]
by LC-HR-MS. Extensive 2D NMR experiments revealed the is remarkable for several reasons: (a) four quaternary car-
bon centers are generated under mild conditions (room
temperature, atmospheric pressure). Very few examples
have been described[18] for DielsϪAlder cyclizations of
comparable steric demand, most of which were performed
under harsh reaction conditions (elevated temperature,[19]
high pressure[20]) or took advantage of highly electrophilic
dienophiles like tetracyanoethylene (TCNE);[21] (b) the reac-
tion proceeds with high regio- (Ͼ 95%) and diastereoselec-
tivity (Ͼ 95%), and only one DielsϪAlder product (11) was
detected by HPLC-UV-MS; (c) tricyclic inner dienes like
in situ intermediate 10 have not been described within the
multitude of DielsϪAlder-reactive cyclohexadienes.
Figure 2. X-ray structure of 11 (ORTEP; 50% probability
level)[16,19]
Strained diene 10 is postulated as an intermediate which
is formed in situ[17,22] (additional DielsϪAlder products of
10 are discussed below). However, ionic intermediates may
also play a role in the conversion of 9 or 10 to 11, as they
do in many DielsϪAlder-type reactions.[17,23] A possible
mechanism for the DMAP-catalyzed in situ formation of
10 is depicted in Scheme 4. The overall 1,4-elimination of
acetic acid (9a Ǟ 10) is initiated by a Michael addition step
(9a Ǟ 15), followed by extrusion of the carboxylate (15 Ǟ
16)[24] and is finally completed with a 1,2-elimination of the
dimethylpyridinium cation (16 Ǟ 10). Formation of 11
points at increased reactivity of 10 in comparison to open-
chain diene analogues (e.g. 1,3-butadiene-2-carboxylic es-
ters), that did not react under our reaction conditions. As
expected, aromatizing oxidation of tricyclo[5.5.6] systems
like 10 is unfavorable (10 Ǟ 17) due to increased ring
Scheme 3. DielsϪAlder dimerization and hetero-derivatization of 4 strain[25] of the corresponding tricyclic cyclophanes 17. Al-
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F. von Nussbaum, R. Hanke, T. Fahrig, J. Benet-Buchholz
FULL PAPER
Figure 3. X-ray structure of 13b[26]
may be replaced with anilines without loss of activity; (b)
introduction of additional oxygen substituents is allowed at
C4; (c) dihydro congeners like 6a, devoid of the central
Michael system and thereby conformationally distorted, do
not show IL-6 antagonistic activity.
Scheme 4. Possible mechanism for the DMAP-catalyzed formation
of diene 10 from 9a in situ
Conclusion
though conversion of 9 to 10 is accompanied by a flattening
of the tricyclo[5.5.6] system, face selectivity is still high with
regard to the diene and the dienophile. The convex/convex
DielsϪAlder product 11 is observed exclusively. Now, that
the ‘‘lower’’ diene moiety of 11 (O1ϪC7b) showed the com-
pletely retained ‘‘natural’’ (4S,7bS) stereochemistry, a
DielsϪAlder strategy appeared promising to synthesize
C7b-hetero-substituted congeners of 4, and thereby circum-
vent our ‘‘SN2 problem’’ at C7b.
Indeed, addition of DMAP to a stirred solution of 9 and
nitrosobenzene (12) in dichloromethane at room tempera-
ture and atmospheric pressure triggered the anticipated
DielsϪAlder reaction in good yield with high regio- and
diastereoselectivity (Scheme 3). Only the regioisomer 13a
with an oxygen atom at C4 and a nitrogen atom at C7b was
obtained. X-ray structure analyses of 13a and 13b indicated
that a selective cycloaddition of the nitroso dienophile had
taken place at the convex face of the diene 10, again yield-
ing systems with the ‘‘natural’’ (7bS) configuration (Fig-
ure 3). The boat conformation of the central six-membered
ring within 13a strongly resembled the situation known
from 4. Our efforts were rewarded with the altered potency
(Ϫ)-Galiellalactone
(4)
disclosed
an
intrinsic
DielsϪAlder principle that is as stimulating for further
chemical and biological investigations as it is surprising due
to the seemingly simple structure of this natural product,
and clearly corresponds with the biogenesis of 4. A new
aspect is appended to a ‘‘DielsϪAlder story’’ that originally
started with Steglich’s biosynthesis proposal[3] and very re-
cently concluded with Sterner’s[4] observation of a rate-en-
hanced cyclization of 2 within G. rufa cultures. It is the sub-
ject of ongoing experiments whether [4ϩ2] cycloadditions
of diene 10 also take place in a natural environment with
dienophiles, present in vivo. Biological activity, correlated
to the special DielsϪAlder reactivity of galiellalactone,
could be triggered in a targeted[27] fashion by activation at
C7b through in vivo acylation.
Experimental Section
General Remarks: Chemicals of analytical grade were obtained
from Merck KGaA (Germany) or Sigma Aldrich (Germany).
Chromatography was carried out on silica gel 60 230Ϫ400 mesh
of 13a (IC50 ϭ 1.7 µ) in comparison with natural 4 (Merck KGaA, Germany) or Sephadex LH-20 (Pharmacia). Ana-
lytical HPLC was carried out with a WATERS 2690 unit with auto-
mated sample injector and Waters 996 diode array detector, em-
ploying the following instrumental conditions: column Xterra RP8
5 µm (3.9 ϫ 150 mm); mobile phase A: 0.01% TFA in water; B:
0.01% TFA in acetonitrile; flow: 1.2 mL/min; gradient: start 95%
A; 12 min 5% A; 13 min 5% A; detection at 190Ϫ400 nm. HPLC-
ESI-MS was performed with an HP 1100 HPLC system (Hewlett
Packard GmbH, Germany) coupled to a Micromass-LCT mass
spectrometer (Micromass, UK) using a Waters Symmetry 3 µm
column as stationary phase (50 ϫ 2.1 mm); mobile phase A: 0.1%
(IC50 ϭ 2.7 µ).
Hydrogenation (13a Ǟ 14) not only opened the bicyclic
cage by cleavage of the NϪO bond (Scheme 3) but further-
more reduced the enone, thereby moving the system into
the inactive dihydro series (cf. compound 6a). Accordingly,
no IL-6 antagonistic activity was observed for 14.
Further synthetic work is underway in order to establish
a first SAR for (Ϫ)-galiellalactone (4). However, three
trends are already apparent for the IL-6 antagonistic ac-
tivity within this series: (a) the alcohol functionality at C7b formic acid in water; B: 0.1% formic acid in acetonitrile; gradient:
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The High-Intrinsic DielsϪAlder Reactivity of (Ϫ)-Galiellalactone
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start 100% A; 1 min 100% A; 5 min 10% A; 6 min 10% A; 7 min
100% B. The FT-ICR instrument (HR-FT-ICR-MS) was an APEX
II mass spectrometer (Bruker Daltonics, Billerica, MA, USA)
equipped with a 160-mm room-temperature 7 Tesla actively shi-
elded magnet, electrostatic ion transfer optics, octupole ion storage
Filtration through Celite, followed by evaporation of the solvent
under reduced pressure yielded the crude product, which was
further purified by flash chromatography (SiO2; EtOAc/cyclohex-
ane, 1:2). The title compound was obtained as a colorless solid
(11.6 mg, 88%). 1H NMR (400 MHz, CDCl3): δ ϭ 0.49 (m, 1 H,
device and external off-axis electrospray ion source. HPLC-FT- 5-H), 0.94 (d, J ϭ 6.6 Hz, 3 H, CH3), 1.25 (m, 1 H), 1.34 (s, 9 H,
ICR-MS was performed with an HP 1100 HPLC system synchron-
ized to the FT-ICR spectrometer by contact closure. The whole
tBu), 1.47 (br. s, 1 H, OH), 1.77 (m, 1 H), 1.85Ϫ2.00 (m, 2 H),
2.00Ϫ2.24 (m, 3 H), 3.04 (br. ‘‘s’’, 1 H, 2a-H), 3.15 (m, 1 H, 3-H),
effluent (250 µL/min) was directed to the external electrospray 4.54 (d, J ϭ 3.0 Hz, 1 H, 7a-H), 5.44 (br. d, J ϭ 6.7 Hz, 1 H, NH)
source. A heated nitrogen flow of 8 L/min with a temperature of
250 °C was used as both nebulizing and drying gas. TOF-HR-ESI-
ppm. HPLC-ESI-MS: m/z (%) ϭ 334 (100) [M ϩ Na]ϩ, 312 (20)
[M ϩ H]ϩ. FT-ICR-MS: m/z ϭ 334.16255 [M ϩ Na]ϩ (calcd. for
MS spectra were obtained with a Micromass-LCT mass spec- C16H25NNaO5: 334.16249).
trometer (capillary 3.2 kV, cone 42 V, source: 120 °C). Samples
3β-Amino-2aβ,3-dihydrogaliellalactone (7c). Method A: A solution
were injected with a syringe pump (Harvard Apparatus). Leucine-
enkephaline was used as standard. NMR spectra were recorded
with a Bruker Advance 400, a Bruker DRX 500 instrument with a
of freshly prepared azide 7b (10.4 mg, 0.04 mmol) in EtOAc
(1.5 mL) was stirred with 10% Pd/C (2 mg) under hydrogen at nor-
mal pressure for 3 h. After filtration through Celite, and evapor-
ation of the solvent under reduced pressure, the title compound
was obtained as the free base as a colorless oil (9.2 mg, quant., Ͼ
95% pure by HPLC). Method B: TFA (0.4 mL) was added dropwise
to solution of 7d (21 mg, 0.07 mmol) and the mixture stirred until
HPLC monitoring indicated total conversion (ca. 3 h). After evap-
oration of the solvent, supported by sequential trituration with
heptane (twice) and methanol, the crude product was purified by
1
TXI CryoProbe, or a Bruker DRX 700 spectrometer. H and 13C
chemical shifts are given with respect to TMS or the solvent as
internal standard ([D6]DMSO: δH ϭ 2.49, δC ϭ 39.5 ppm; CDCl3:
δH ϭ 7.25, δC ϭ 77.0 ppm).
3β-(Benzylthio)-2aβ,3-dihydrogaliellalactone (7a): A solution of
phenylmethanethiol (6 µL, 0.05 mmol) in EtOH (0.1 mL) was ad-
ded slowly to a solution of galiellalactone (5 mg, 0.03 mmol) in
ethanol (1 mL). The reaction mixture was stirred at room temp. for gel chromatography (Sephadex LH-20; MeOH/TFA, 1:0.001).
12 h and concentrated in vacuo. Purification of the crude product
was carried out by flash chromatography (SiO2; EtOAc/cyclohex-
After evaporation of the solvent, the title compound was obtained
1
as the trifluoroacetate as a colorless solid (16 mg, 73%). H NMR
ane, 1:3) yielding 7a as a colorless solid (9.5 mg, quant.). 1H NMR (400 MHz, CD3OH): δ ϭ 0.73 (m, 1 H, 5-H), 1.14 (d, J ϭ 6.6 Hz,
(500 MHz, CDCl3): δ ϭ 0.74 (m, 1 H, 5-H), 1.02 (d, J ϭ 6.8 Hz, 3
3 H, CH3), 1.31 (m, 1 H), 1.88 (m, 1 H, 4-H), 1.95Ϫ2.04 (m, 3 H),
H, CH3), 1.48 (m, 1 H, 6-H), 1.60 (m, 1 H, 4-H), 1.74 (ddd, J ϭ 2.20 (m, 2 H), 3.13 (d, J ϭ 1.6 Hz, 1 H, 2a-H), 3.37 (dd, J ϭ 9.5,
14.3, 6.1, 4.1 Hz, 1 H, 5-H), 1.99 (m, 1 H, 7-H), 2.06 (m, J ϭ 8.5, 2.5 Hz, 1 H, 3-H), 4.61 (br. t, 1 H, 7a-H) ppm. HPLC-ESI-MS:
4.8 Hz, 1 H, 7-H), 2.09 (m, 1 H, 5a-H), 2.21 (m, 1 H, 6-H), 2.37 m/z (%) ϭ 212 (100) [M ϩ H]ϩ. HR-FT-ICR-MS: m/z ϭ 212.12803
(s, 1 H, OH), 3.03 (dd, J ϭ 7.2, 3.0 Hz, 1 H, 3-H), 3.16 (s, 1 H,
2a-H), 3.81 (s, 2 H, CH2S), 4.54 (d, J ϭ 4.5 Hz, 1 H, 7a-H), 3.25
(m, 1 H, ArH), 7.32 (m, 4 H, ArH) ppm. 13C NMR (176 MHz,
CDCl3, TMS): δ ϭ 21.43 (CH3), 29.49 (C-7), 31.33 (C-6), 34.72 (C-
4), 35.43 (C-5), 36.54 (SCH2), 44.78 (C-3), 46.77 (C-5a), 51.72 (C-
2a), 85.07 (C-7b), 88.89 (C-7a), 127.29 (C-4Ј), 128.68, 128.93 (2 C
each, C-2Ј, C-3Ј, C-5Ј, C-6Ј), 137.56 (C-1Ј), 174.87 (C-2) ppm.
HPLC-ESI-MS: m/z (%) ϭ 319 (100) [M ϩ H]ϩ. HR FT-ICR-MS:
m/z ϭ 319.13620 [M ϩ H]ϩ (calcd. for C18H23O3S: 319.13624),
341.11812 [M ϩ Na]ϩ (calcd. for C18H22O3SNa: 341.11819).
[M ϩ H]ϩ (calcd. for C11H18NO3 212.12812).
2aβ,3-Dihydrogaliellalactone (6a): A solution of galiellalactone (4;
100 mg, 0.51 mmol) in methanol (2.0 mL) was stirred with 10% Pd/
C (200 mg) under hydrogen at normal pressure for 3 h. After fil-
tration through Celite and evaporation of the solvent under re-
duced pressure, the title compound was obtained as a colorless
solid (95 mg, 94%, Ͼ 95% pure by HPLC). 1H NMR (700 MHz,
CDCl3): δ ϭ 0.67 (m, 1 H, 5-H), 0.92 (d, J ϭ 6.7 Hz, 3 H, CH3),
1.37 (m, 1 H, 6-H), 1.52 (ddd, J ϭ 14.0, 10.5, 3.5 Hz, 1 H, 3-H),
1.66 (m, 1 H, 4-H), 1.79 (m, 1 H, 5-H), 1.89 (m, 1 H, 7-H),
1.92Ϫ1.97 (m, 2 H, 7-H, 5a-H), 2.02Ϫ2.09 (m, 2 H, 3-H, 6-H),
2.84 (dd, J ϭ 10.0, 3.8 Hz, 1 H, 2a-H), 4.49 (d, J ϭ 4.1 Hz, 1 H,
7a-H) ppm. 13C NMR (126 MHz, CDCl3, TMS): δ ϭ 22.12 (CH3),
3β-Azido-2aβ,3-dihydrogaliellalactone (7b): Sodium azide (200 mg,
3.1 mmol) was added to a stirred solution of galiellalactone (4;
50.0 mg, 0.26 mmol) in acetic acid (1.5 mL). When HPLC monitor-
ing indicated total conversion of the starting material (ca. 1 h), the 26.64 (C4), 28.29 (C-3), 29.77 (C-7), 32.05 (C-6), 36.00 (C-5), 45.29
reaction mixture was diluted with tert-butyl methyl ether (40 mL), (C-2a), 47.46 (C-5a), 84.24 (C-7b), 89.57 (C-7a), 177.68 (C-2) ppm.
then washed with saturated aqueous NaHCO3 (2 ϫ 10 mL), as well IR (KBr): ν˜ ϭ 3431 (m, br.), 2951 (m), 2927 (m), 1744 (s), 1459
as brine (10 mL), dried (Na2SO4), filtered through a silica cartridge
and concentrated under reduced pressure. The title compound was
obtained as a colorless liquid (61 mg, quant.). 1H NMR (400 MHz,
(m), 1184 (s), 1088 (s), 981 (s). HR-ESI-MS: m/z ϭ 238.1432 [M
ϩ CH3CN ϩ H]ϩ (calcd. for C13H20NO3: 238.1443). HR-FT-ICR-
MS: m/z ϭ 415.20886 [2 M ϩ Na]ϩ (calcd. for C22H32NaO6:
CDCl3): δ ϭ 0.70 (m, 1 H, 5-H), 1.08 (d, J ϭ 6.6 Hz, 3 H, CH3), 415.20911).
1.34 (m, 1 H), 1.52 (br. s, 1 H, OH), 1.70Ϫ1.86 (m, 2 H), 1.87Ϫ2.05
2aβ,3-Dihydrogaliellalacton-7b-yl Acetate (6b): A solution of acetic
(m, 3 H), 2.07Ϫ2.18 (m, 1 H), 3.03 (d, J ϭ 1.1 Hz, 1 H, 2a-H),
3.65 (dd, J ϭ 8.3, 2.1 Hz, 1 H, 3-H), 4.54 (d, J ϭ 3.0 Hz, 1 H, 7a-
H) ppm. HPLC-(neg.)ESI-MS: m/z (%) ϭ 236 (100) [M Ϫ H]Ϫ.
Due to low stability, as a result of HN3 elimination, azide 7b was
immediately hydrogenated (7b Ǟ 7c) or converted into the (tert-
butoxycarbonyl)amine (7b Ǟ 7d).
anhydride (10.4 mg, 0.1 mmol) in dichloromethane (200 µL) was
added at 0 °C to a solution of dihydrogaliellalactone (6a; 10 mg,
0.05 mmol), triethylamine (16 µL, 0.1 mmol), and DMAP (1.3 mg,
10 µmol) in dichloromethane (1 mL) and stirred at room tempera-
ture for 12 h. The reaction mixture was diluted with EtOAc
(50 mL) and washed with 2  aqueous citric acid (2 ϫ 10 mL),
saturated aqueous NaHCO3 (2 ϫ 10 mL), and brine (10 mL). It
was then dried (Na2SO4), filtered and concentrated under reduced
pressure. Flash chromatography (SiO2; EtOAc/cyclohexane, 1:2) of
the crude product afforded 6b (4.5 mg, 35%) as a colorless solid.
3β-[(tert-Butoxycarbonyl)amino]-2aβ,3-dihydrogaliellalactone (7d):
A solution of freshly prepared azide 7b (10.0 mg, 0.04 mmol) and
Boc2O (18.4 mg, 0.08 mmol) in EtOAc (1.5 mL) was stirred with
10% Pd/C (2 mg) under hydrogen at normal pressure for about 3 h.
Eur. J. Org. Chem. 2004, 2783Ϫ2790
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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F. von Nussbaum, R. Hanke, T. Fahrig, J. Benet-Buchholz
FULL PAPER
1H NMR (700 MHz, CDCl3): δ ϭ 0.81 (m, 1 H, 5-H), 0.96 (d, J ϭ
ing in vacuo yielded 9a as a colorless solid (236 mg, 97%, Ͼ 95%
1
6.7 Hz, 3 H, CH3), 1.34 (m, 1 H, 3-H), 1.45 (m, 1 H, 6-H), 1.77 pure by HPLC): H NMR (400 MHz, CDCl3, TMS): δ ϭ 0.99 (m,
(m, 1 H, 4-H), 1.88 (m, 2 H, 7-H, 5-H), 2.01 (m, 1 H, 6-H), 2.03 1 H, 5-H), 1.18 (m, 1 H, 6-H), 1.21 (d, J ϭ 7.9 Hz, 3 H, CH3),
(s, 3 H, CH3CO), 2.18 (m, 2 H, 7-H, 3-H), 2.49 (m, 1 H, 5a-H), 1.88Ϫ1.97 (m, 2 H, 7-H, 6-H), 2.05 (s, 3 H, COCH3), 2.10 (m, 1
3.19 (‘‘t’’, J ϭ 8.6 Hz, 1 H, 2a-H), 5.02 (dd, J ϭ 5.9, 2.8 Hz, 1 H, H, 7-H), 2.25 (m, 1 H, 5-H), 2.55 (m, 1 H, 4-H), 2.75 (m, 1 H, 5a-
7a-H) ppm. 13C NMR (176 MHz, CDCl3, TMS): δ ϭ 21.86 H), 5.08 (d, J ϭ 6.9 Hz, 1 H, 7a-H), 6.97 (d, J ϭ 3.3 Hz, 1 H, 3-
(CH3CO), 22.13 (CH3), 26.09 (C-4), 30.36 (C-3), 30.67 (C-7), 31.99 H) ppm. 13C NMR (125 MHz, CDCl3, TMS): δ ϭ 20.36 (CH3),
(C-6), 34.57 (C-5), 42.57 (C-5a), 43.76 (C-2a), 87.48 (C-7a), 90.68
21.08 (CH3CO), 28.97 (C-4), 31.34 (C-6), 31.84 (C-7), 32.87 (C-5),
(C-7b), 170.21 (CH3CO), 177.44 (C-2) ppm. HPLC-ESI-MS: m/z 41.68 (C-5a), 85.61 (C-7a), 87.13 (C-7b), 129.10 (C-2a), 148.24 (C-
(%) ϭ 239 (100) [M ϩ H]؉.
11), 169.00 (C-2), 170.45 (CH3CO) ppm. HPLC-ESI-MS: m/z
(%) ϭ 177 (100) [M Ϫ AcOH ϩ H]ϩ ϭ [10 ϩ H]ϩ, 237 (40) [M
ϩ H]ϩ. HR-FT-ICR MS: m/z ϭ 237.11224 [M ϩ H]ϩ (calcd. for
C13H17O4 237.11214).
2aβ,3β-Epoxy-2aβ,3-dihydrogaliellalactone (8): Solid vanadyl ace-
tylacetonate (4.1 mg, 0.02 mmol) was added at 0 °C to a solution
of galiellalactone (4; 30.0 mg, 0.15 mmol) in dry CH2Cl2 (1.0 mL),
followed 5 min later by a 3  solution of dry tert-butyl hydroper-
oxide (139.2 mg, 1.54 mmol) in dry toluene (0.515 mL), which was
added dropwise with vigorous stirring. Subsequently, the reaction
mixture was allowed to warm up to room temperature under argon.
When total consumption of the starting material was observed (ca.
16 h, HPLC monitoring), a stock aqueous solution of Na2SO3
(2 mL) was added and the mixture stirred for a further 30 min.
Afterwards, the reaction mixture was diluted with EtOAc (50 mL)
and washed with water (3 ϫ 10 mL) and brine (10 mL). It was then
dried (Na2SO4), filtered and concentrated under reduced pressure.
Flash chromatography (SiO2; EtOAc/cyclohexane, 1:1) of the crude
product afforded 8 (26.1 mg, 80%) as a colorless solid. 1H NMR
(700 MHz, CDCl3): δ ϭ 1.15 (d, J ϭ 7.8 Hz, 3 H, CH3), 1.28 (dt,
J ϭ 14.9, 4.2 Hz, 1 H, 5-H), 1.45 (m, 1 H, 6-H), 1.72 (ddd, J ϭ
14.9, 6.9, 4.8 Hz, 1 H, 5-H), 1.77 (m, 1 H, 6-H), 1.83 (m, 1 H, 7-
H), 1.98-2.05 (m, 2 H, 5a-H, 7-H), 2.09 (m, 1 H, 4-H), 2.55 (br. s,
1 H, OH), 3.47 (s, 1 H, 3-H), 4.92 (d, J ϭ 7.2 Hz, 1 H, 7a-H) ppm.
13C NMR (176 MHz, CDCl3): δ ϭ 20.40 (CH3), 25.87, 26.10,
28.34, 30.68, 42.13, 57.48, 64.73, 77.28 (C-7b), 89.84 (C-7a), 172.98
(C-2) ppm. HR-ESI-MS: m/z ϭ 443.1696 [2 M ϩ Na]ϩ (calcd. for
C22H28O8Na: 443.1682).
General Procedure for Diels؊Alder Reactions with Diene Precursors
9: DMAP (2 mg, 0.01Ϫ0.1 mmol) was added to a solution of 9
(0.1 mmol) and the dienophile (0.2Ϫ1.0 mmol) in dry acetonitrile
or dichloromethane (2Ϫ10 mL). The reaction mixture was stirred
at room temperature until HPLC showed no more starting material
(reaction time: several hours at 1 equiv. DMAP to several days at
0.1 equiv. DMAP). The reaction mixture was concentrated in vacuo
followed by dilution with EtOAc (20 mL). The organic layer was
washed with 5% aqueous citric acid (1 mL) and saturated aqueous
NaHCO3 (4 ϫ 100 mL), dried with anhydrous Na2SO4, and con-
centrated under reduced pressure. Purification of the crude product
was carried out by flash chromatography (SiO2; EtOAc/cyclohex-
ane, 1:2) or preparative HPLC (RP18; acetonitrile/water/0.1%
TFA).
Bis(dehydratogaliellalactone) (11): This compound was prepared
according to the General Procedure, from either 9a (25 mg,
0.1 mmol), 9b or 9c and DMAP (0.1 mmol). It was obtained as a
colorless solid after preparative HPLC purification (19.5 mg, qu-
ant.). [α]2D0 ϭ ϩ108 (c ϭ 0.075, CHCl3). NMR: see Table 2 (Sup-
porting Information). HR-FT-ICR-MS: m/z ϭ 353.17479 [M ϩ
H]ϩ (calcd. for C22H25O4: 353.17474), 727.32414 [2 M ϩ Na]ϩ
(calcd. for C44H48O8Na: 727.32414). X-ray: see Table 1. Compound
11 was also obtained in a one-pot procedure starting from 4. After
acylation with acetyl chloride (1.1 equiv.) DMAP (1 equiv.) was
added to the reaction mixture.
2aβ-Methyl-3,4-didehydro-2a,3-dihydrogaliellalactone (5):
A 1 
solution of LiHMDS in THF (645 µL) was added dropwise at Ϫ78
°C to a solution of galiellalactone (4; 50 mg, 0.26 mmol) in dry
THF (1 mL). After 20 min, iodomethane (160 µL, 2.57 mmol) was
added with vigorous stirring. The reaction mixture was allowed to
warm up to room temperature over about 16 h, then quenched at 0
°C with methanol (1 mL) and saturated aqueous NaHCO3 (1 mL),
stirred for another 5 min and diluted with EtOAc (50 mL). The
organic phase was then washed with saturated aqueous NaHCO3
(10 mL), 5% aqueous citric acid (10 mL), and brine (10 mL), dried
(Na2SO4), filtered and concentrated under reduced pressure. Flash
chromatography (SiO2; EtOAc/cyclohexane 1:1) of the crude prod-
uct and subsequent purification by preparative HPLC (RP18;
acetonitrile/water/0.1% TFA) afforded the title compound
(20.2 mg, 38%) as a colorless solid. 1H (400 MHz, CDCl3): δ ϭ
1.33 (s, 3 H, CH3), 1.51 (m, 1 H), 1.73Ϫ1.80 (m, 1 H), 1.76 (s, 3
H, CH3), 1.86 (d, J ϭ 17.3 Hz, 1 H), 1.93Ϫ2.05 (m, 2 H), 2.18 (s,
1 H, OH), 2.22 (m, 1 H), 2.34 (dd, J ϭ 17.4, 6.5 Hz, 1 H), 4.70 (d,
J ϭ 4.6 Hz, 1 H, 7a-H), 5.44 (s, 1 H, 3-H) ppm. 13C NMR
(101 MHz, CDCl3): δ ϭ 21.64, 23.67, 28.98, 29.33, 31.13, 46.51,
47.22, 83.63, 89.87, 121.48, 133.18, 179.88 ppm. HPLC-ESI-MS:
m/z (%) ϭ 209 (100) [M ϩ H]ϩ. HR-ESI-MS: m/z ϭ 439.2090
[2 M ϩ Na]ϩ (calcd. for C24H32O6Na: 439.2097).
Aza Derivative 13a: This compound was prepared according to the
General Procedure from 9a or 9b (0.1 mmol) and nitrosobenzene
(12; 1.0 mmol). Yield: 18.5 mg (66%). HPLC-UV (CH3CN/H2O ϩ
0.1% TFA, 6:4) λmax ϭ 219 (s), 239 (sh), 332 (m) nm. 1H NMR
(500 MHz, CDCl3): δ ϭ 1.04 (m, J ϭ 12.9, 6.4 Hz, 1 H, 6-H), 1.33
(dd, J ϭ 12.9, 5.3 Hz, 1 H, 5-H), 1.69 (s, 3 H, CH3), 1.92 (d‘‘t’’,
J ϭ 12.8, 6.4 Hz, 1 H, 6-H), 2.09 (dd, J ϭ 14.8, 6.4 Hz, 1 H, 7-H),
2.18 (m, 1 H, 7-H), 2.32 (dd, J ϭ 12.9, 8.9 Hz, 1 H, 5-H), 2.64 (m,
1 H, 5a-H), 5.24 (d, J ϭ 6.8 Hz, 1 H, 7a-H), 6.94 (m, 2 H, 2Ј-H,
6Ј-H), 7.07 (m, 1 H, 4Ј-H), 7.21 (m, 2 H, 3Ј-H, 5Ј-H), 7.33 (s, 1 H,
3-H) ppm. 13C NMR (176 MHz, CDCl3): δ ϭ 21.24 (CH3), 29.71
(C-6), 34.36 (C-7), 39.00 (C-5), 40.97 (C-5a), 75.99 (C-7b), 77.09
(C-4), 82.45 (C-7a), 121.02 (2 C, C-2Ј, C-6Ј), 125.63 (C-4Ј), 128.50
(2 C, C-3Ј, C-5Ј), 130.32 (C-2a), 140.00 (C-3), 148.00 (C-1Ј), 165.57
(C-2) ppm. HPLC-ESI-MS: m/z (%) ϭ 284 (100) [M ϩ H]ϩ. HR-
ESI-MS: m/z ϭ 284.1257 [M ϩ H]ϩ (calcd. for C17H18NO3:
284.1287). X-ray: see Table 1.
Bromo Aza Derivative 13b: Solid NBS (3.8 mg, 21 µmol) was added
to a solution of 13a (5 mg, 18 µmol) in dichloromethane (500 µL).
Galiellalacton-7b-yl Acetate (9a): Acetyl chloride (1.5 mL,
35.2 mmol) was added dropwise to a solution of 4 (200 mg, The reaction mixture was stirred at room temperature overnight,
1.03 mmol) in dry acetonitrile (5 mL) at room temperature (water
bath). The reaction mixture was stirred for an additional 2 h and
the solvent was then removed under reduced pressure. Careful dry-
concentrated under reduced pressure, diluted with acetonitrile
(2 mL) and purified by preparative HPLC (RP18; acetonitrile/
water/0.1% TFA). The title compound was obtained as a colorless
2788
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 2783Ϫ2790

The High-Intrinsic DielsϪAlder Reactivity of (Ϫ)-Galiellalactone
Table 1. Crystallographic data as well as details of the structure solution and refinement procedures for 4, 11, 13a and 13b
FULL PAPER
4
11
13a
13b
Empirical formula
Formula mass [g molϪ1
T [K]
C11H14O3
194.22
90
1.54178
P212121
7.2434(2)
9.2195(2)
14.2172(3)
949.43(4)
4
1.359
0.805
C22H24O4
352.41
90
1.54178
P212121
7.46630(10)
12.5508(2)
18.1910(2)
1704.64(4)
4
1.373
0.753
C17H17NO3
283.32
153
0.71073
P212121
8.9290(2)
9.0771(2)
17.1453(4)
1389.62(5)
4
C17H16Br1NO3
362.22
153
0.71073
P212121
9.4343(5)
9.4343(5)
9.4343(5)
1509.03(15)
4
1.594
2.736
]
˚
λ [A]
Space group
˚
a [A]
˚
b [A])
˚
c [A]
3
˚
V [A ]
Z
dcalcd. [Mg·mϪ3
]
1.354
0.093
600
µ [mmϪ1
F(000)
]
416
752
736
Crystal size [mm]
θ range [°]
Reflections collected
0.5 ϫ 0.5 ϫ 0.5
5.72Ϫ71.00
9554
0.60 ϫ 0.10 ϫ 0.04
4.28Ϫ72.40
17997
0.40 ϫ 0.40 ϫ 0.03
2.38Ϫ30.53
16139
1.50 ϫ 0.30 ϫ 0.02
2.42Ϫ28.50
17948
Independent reflections [R(int)]
Observed reflections [Fo Ͼ 4σ(Fo)]
Data/restraints/parameters
Absolute structure parameter[29]
Basf [with Twin (σ)]
1764 [0.0343]
1762
1764/0/184
0.01(19)
0.01(19)
0.055(3)
3251 [0.0482]
2977
3251/1/331
Ϫ0.04(13)
0.00(14)
Ϫ
1.067
0.0345, 0.0881
0.0348, 0.0885
0.195/Ϫ0.324
0.551/0.2430
1.000000/0.854653
4159 [0.0463]
3631
4159/1/258
Ϫ
Ϫ
Ϫ
3822 [0.0960]
2587
3822/1/216
Ϫ0.009(14)
0.000(14)
Ϫ
Extinction coefficient
Goodness-of-fit on F2
1.101
1.009
0.990
Final R1, wR2 [I Ͼ 2σ(I)][a,b]
Final R1, wR2 (all data)[a,b]
0.0345, 0.0844
0.0345, 0.0844
0.208/Ϫ0.326
0.582/0.1529
1.000000/0.852724
0.0359, 0.0881
0.0439, 0.0934
0.289/Ϫ0.206
0.551/0
0.0492, 0.0957
0.0909, 0.1097
0.650/Ϫ0.808
0.609/0
Ϫ3
˚
Max./min. diff. [e·A
]
a/b[b]
Absorption correction max./min.
1.000000/0.557525
1.000000/0.364383
[a]
[b]
2
2 2
2 2
2
2
2
R1 ϭ Σ(Fo Ϫ Fc)/ΣFo. wR2 ϭ [Σ{w(Fo Ϫ Fc ) }/Σ{w(Fo ) }]1/2, w ϭ 1/[σ2Fo ϩ (aP)2 ϩ bP], P ϭ (Fo ϩ 2Fc )/3.
solid (5.4 mg, 85%). HPLC-UV (CH3CN/H2O ϩ 0.1% TFA, 7:3)
by limiting dilution. The clone showing the best induction of lu-
λmax ϭ 217 (s), 252 (s), 333 (m) nm. HPLC-ESI-MS: m/z (%) ϭ ciferase activity in response to IL-6 was used for all subsequent
362 (100) [M (79Br) ϩ H]ϩ. HR-ESI-MS: m/z ϭ 362.0365 [M (79Br)
ϩ H]ϩ (calcd. for C17H17NO3Br: 362.0392). X-ray: see Table 1.
experiments.
Reporter-Gene Assay: Cells were maintained in RPMI 1640 sup-
plemented with 25 m HEPES, 10% FCS, penicillin/streptomycin,
and 0.5 mg/mL G418 (Life Technologies). After reaching conflu-
ency, cells were seeded in 384-well microlite F plates at a density
of 1 ϫ 10Ϫ4 cells/well in 25 µL of RPMI 1640 supplemented with
1 mg/mL BSA and cultured for 24 h. Stock solutions of test com-
pounds dissolved in DMSO were diluted in RPMI 1640, and 1 mg/
mL BSA (final DMSO concentration in the assay 0.1% DMSO)
and 5 µL of this test-compound solution was added to each well;
16 h after test-compound addition, the cells were stimulated with
1 ng/mL (final concentration) of human recombinant IL-6 (Sigma)
diluted in RPMI 1640 and 1 mg/mL BSA. Following cell lysis and
substrate addition, luciferase activity was determined 4 h after
stimulation by means of a luminometer (Hamamatsu).
4β-Hydroxy-7bβ-(phenylamino)-2aβ,3-dihydrogaliellalactone (14): A
solution of 13a (20 mg, 71 µmol) in methanol (2.0 mL) was stirred
with 10% Pd/C (10 mg) under hydrogen at normal pressure for 3 h.
After filtration, evaporation of the solvent under reduced pressure
and further purification by preparative HPLC (RP18; acetonitrile/
water/0.1% TFA), the title compound was obtained as a colorless
solid (14 mg, 69%). 1H NMR (700 MHz, CDCl3): δ ϭ 1.24 (dd,
J ϭ 14.4, 9.2 Hz, 1 H), 1.31 (s, 3 H, CH3), 1.46 (m, 1 H), 1.92Ϫ1.99
(m, 2 H), 2.01Ϫ2.13 (m, 4 H), 2.27 (m, 1 H), 3.39 (dd, J ϭ 9.6,
4.2 Hz, 1 H, 2a-H), 5.10 (d, J ϭ 4.1 Hz, 1 H, 7a-H), 6.75 (d, J ϭ
7.6 Hz, 2 H, ArH), 6.92 (‘‘t’’, J ϭ 6.9 Hz, 1 H, ArH), 7.23 (‘‘t’’,
J ϭ 8.4 Hz, 2 H) ppm. 13C NMR (176 MHz, CDCl3): δ ϭ 30.40,
30.86, 31.20, 34.80, 37.97, 40.35, 44.38, 68.37, 69.38, 85.50, 119.45
(2 C), 121.37, 129.55 (2 C), 144.36, 178.08 ppm. HR-FT-ICR-MS:
m/z ϭ 288.15938 [M ϩ H]ϩ (calcd. for C17H22NO3: 288.15942).
X-ray Crystallography: Measurements for 4 and 11 were carried
out with a Bruker-Nonius diffractometer equipped with a Proteum
CCD area detector, an FR591 rotating anode with Cu-Kα radi-
ation, Montel mirrors as monochromator and a Kryoflex low-tem-
perature device. Software: Data collection Proteum version 1.37
(Bruker-Nonius 2002), data reduction Saint Plus Version 6.22
(Bruker-Nonius 2002), absorption correction SADABS version
Assay
Plasmids and Transfections: Three copies of the SIF-RE (serum-
inducible factor-response element) from the published c-fos pro-
moter were cloned into a pcDNA1-CMV-promoter luciferase re-
porter vector (Promega). The identity of the promoter insert was
confirmed by sequencing. Transfection of the SIF-RE-luciferase 2.03 (2002) and structure solution and refinement SHELXTL ver-
construct in combination with pRSVneo gene was performed using
Lipofectamine (Life Technologies). Cells stably expressing the
transgene were selected by addition of G418 (Life Technologies) to
sion 6.12 (Sheldrick, 2000). Measurements for 13a and 13b were
performed with a Siemens P4 diffractometer equipped with a
SMART-CCD-1000 area detector, a MACScience Co. rotating an-
the growth medium and single IL-6 responsive clones were isolated ode with Mo-Kα radiation, a graphite monochromator and a Sie-
Eur. J. Org. Chem. 2004, 2783Ϫ2790
www.eurjoc.org  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2789

F. von Nussbaum, R. Hanke, T. Fahrig, J. Benet-Buchholz
FULL PAPER
[15]
[16]
C. Tetta, M. Gallieni, V. Panichi, D. Brancaccio, Int. J. Artif.
Organs 2002, 25, 18Ϫ26.
mens low-temperature device LT2. Software: Data collection Smart
version 5.060 (BrukerAXS 1999), data reduction Saintϩ version
6.02 (Bruker AXS 1999), absorption correction SADABS (Bruker
AXS 1999) and structure solution and refinement SHELXTL ver-
sion 6.12 (Sheldrick, 2000).[28] The crystallographic data as well as
details of the structure solution and refinement procedures for 4,
11, 13a and 13b are reported in Table 1. CCDC-206595 (4), -206596
(11), -206598 (13a) and -206597 (13b) contain the supplementary
crystallographic data for this paper. This data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.html [or from
the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; Fax: (internat.) ϩ 44-1223-336033;
E-mail: deposit@ccdc.cam.ac.uk].
The absolute configuration (4S,5aR,7aR,7bS) of 4 was also re-
confirmed by the X-ray structures of 11 and the bromo deriva-
tive 13b.
[17] [17a]
W. Oppolzer, ‘‘Intermolecular DielsϪAlder Reactions’’, in
Comprehensive Organic Synthesis (Eds.: B. M. Trost, I. Flem-
ing, L. A. Paquette), Pergamon Press, Oxford, 1991, vol. 5, p.
315Ϫ449. [17b]J. Jurczak, T. Bauer, C. Chapius, Methods Org.
[17c]
Chem. (Houben-Weyl) 1995, E21c, 2735Ϫ2952.
The
DielsϪAlder Reaction: Selected Practical Methods (Eds.: F.
Fringuelli, A. Taticchi), John Wiley & Sons, Chichester, 2002.
[17d]K. C. Nicolaou, S. A. Snyder, T. Montagnon, G. E. Vassili-
kogiannakis, Angew. Chem. 2002, 114, 1742Ϫ1773; Angew.
Chem. Int. Ed. 2002, 41, 1668Ϫ1698. [17e] L. F. Tietze, G. Ketts-
chau, Top. Curr. Chem. 1997, 189, 1Ϫ120.
[18] [18a]
S. Szilagyi, J. A. Ross, D. M. Lemal, J. Am. Chem. Soc.
[18b]
1975, 97 5586Ϫ5588.
I. Lamparth, C. Maichle-Mössmer,
Acknowledgments
A. Hirsch, Angew. Chem. Int. Ed. Engl. 1995, 34, 1607Ϫ1609.
G. Dyker, J. Koerning, P. Bubenitschek, P. G. Jones, Tetra-
hedron 1996, 47, 14777Ϫ14786.
We thank Prof. Heidrun Anke, Prof. Timm Anke and Dr. Gerhard
Erkel (IBWF, Kaiserslautern, Germany) for the delivery of several
grams of natural (Ϫ)-galiellalactone. The help of Dr. Joachim Wes-
ener, Heinz Musche (MS), Dr. Daniel Gondol (NMR) and Dr. Oli-
ver Gutbrod (molecular modeling) is also gratefully acknowledged.
Furthermore, we are grateful to Drs. Markus Weidler, Robert
Velten, and Martin Hendrix for helpful discussions, as well as to
Dr. Timo Flessner for proof reading of the manuscript.
[19]
[20] [20a] R. van Eldik, F.-G. Klarner, High Pressure Chemistry: Syn-
thetic, Mechanistic, and Supercritical Applications, Wiley-VCH,
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M. Shuntaro, K. Rauch, M. Noltemeyer, A. de Meijere, J.
[20c]
Chem. Soc., Perkin Trans. 1 2000, 2968Ϫ2976.
Several
works have been published by Winterfeldt on DielsϪAlder re-
actions under high pressure, for example the formation of three
quaternary carbon centers: E. Winterfeldt, V. Wray, Chem. Ber.
1992, 125, 2159Ϫ2161.
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R. Hautzel, H. Anke, Z. Naturforsch., Teil C 1990, 45,
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W. Steglich, Abstr. Int. Congr. Pestic. Chem., 7th 1990, 1, 213.
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[21b]
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Received March 1, 2004
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