Synthetic and biological studies on the spiro-mamakone system

Article abstract of DOI:10.1039/b812263f

An exploration of the chemistry of the spiro-mamakone system, exemplified by the cytotoxic, fungal metabolite spiro-mamakone A, is presented. The first reported synthesis of the spiro-mamakone carbon skeleton was achieved, as well as the synthesis of a variety of closely related analogues of the natural product. Biological testing of the synthetic analogues generated a structure-activity profile for the natural product, establishing the importance of the enedione moiety to biological activity. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b812263f

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthetic and biological studies on the spiro-mamakone system†
Annabel C. Murphy, Sean R. A. Devenish, Andrew C. Muscroft-Taylor, John W. Blunt and Murray H. G. Munro*
Received 17th July 2008, Accepted 5th August 2008
First published as an Advance Article on the web 3rd September 2008
DOI: 10.1039/b812263f
An exploration of the chemistry of the spiro-mamakone system, exemplified by the cytotoxic, fungal
metabolite spiro-mamakone A, is presented. The first reported synthesis of the spiro-mamakone carbon
skeleton was achieved, as well as the synthesis of a variety of closely related analogues of the natural
product. Biological testing of the synthetic analogues generated a structure–activity profile for the
natural product, establishing the importance of the enedione moiety to biological activity.
preparation of a series of spiro-mamakone analogues is presented
here, along with their observed biological activities.
Introduction
As part of on-going studies on biologically active fungal metabo-
lites from New Zealand sources, our group recently disclosed
the structure of spiro-mamakone A, 1, isolated from a non-
Results and discussion
sporulating, endophytic fungus of the New Zealand native tree
Knightia excelsa (rewarewa).1 This compound, and related natural
Synthetic studies
products,2 represent new members of the spirobisnaphthalene
family of natural products.3 The spirobisnaphthalenes are a
relatively new and diverse class of compounds in which two
naphthalene-derived C10 units are bridged by a spiro-acetal linkage
with, in some cases, further bridging bonds: an additional oxygen
bridge for the preussomerins and a C–C bond in the case of the
spiroxins.4,5 This class displays a variety of biological activities,
with many possessing antimicrobial, herbicidal and antitumour
properties.
The carbon skeleton of the spiro-mamakone system was assembled
via modification of the synthetic strategy reported by Taylor
and co-workers in their synthesis of palmarumycin CP1, CP2
and other spirobisnaphthalenes.7,8 Thus, the spiro-acetal linkage
between 1,8-dihydroxynaphthalene and an appropriate ketone
was to be generated. The known spiro[4.4]nonadione, 3,9 was
chosen as the precursor as it has the appropriate C9 skeleton and
contains orthogonal functionality in each ring. The synthesis of
3 was undertaken, with minor changes to the original literature
protocol (Scheme 1). Thus, diallylation of cyclopentanone was
accomplished via the recent procedure reported by Kayaki et al.10
and ring-closing metathesis was carried out using Grubbsꢀ 2nd,
rather than 1st, generation catalyst. It was found that the yield
of the spiro-annulated adduct 3 could be improved if crude 2
was subjected directly to ring-closing metathesis, such that near
quantitative yields could be obtained over two steps.
spiro-Mamakone A displays potent cytotoxicity (IC50 of
0.33 lM against the murine leukaemia cell line P388) and an-
timicrobial activity. It is particularly interesting from a structural
perspective, containing an unprecedented spiro-nonadiene motif
which features a high degree of oxidation and unsaturation. This
entity has been shown by our group to be derived biosynthetically
from one of the naphthalene units via oxidative rearrangement
of an epoxide followed by decarboxylation and ring-closure.6
Interestingly, spiro-mamakone A was isolated as a racemate, which
is accounted for by the proposed biosynthetic pathway. The
relationship between the chemical structure of this unusual motif
and the biological activity of 1 is of interest, and an exploration of
the chemistry of the spiro-mamakone system was undertaken. The
Scheme 1 Preparation of starting materials: (a) allyl alcohol, Pd2(dba)3,
P(OC6H5)3; (b) Grubbsꢀ 2nd generation catalyst; (c) KOH, D.
Department of Chemistry, University of Canterbury, Christchurch, New
Zealand. E-mail: murray.munro@canterbury.ac.nz; Fax: +64 3 364 2110;
Tel: +64 3 364 2434
1,8-Dihydroxynaphthalene, 4, was synthesised following the
protocol employed by Taylor and co-workers, and first described
by Erdmann (Scheme 1).11 Next, coupling of 3 and 4 to form
a spiro-acetal linkage was investigated. A variety of acids and
† Electronic supplementary information (ESI) available: 1H NMR data for
new compounds. See DOI: 10.1039/b812263f
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dehydration conditions were surveyed but without success. The
oxidative autopolymerisation of 1,8-dihydroxynaphthalene to give
a black tar competed with acetal formation under these conditions,
despite efforts to preclude oxygen.
An acetal exchange method was successfully employed
to form the crucial spiro-acetal linkage (Scheme 2). 1,8-
Dihydroxynaphthalene was converted to the acetonide, 5, and an
acetal exchange with 3 yielded 6 in the presence of triflic acid
under gentle heating, albeit in a modest 15% yield (60%, based on
recovered starting material).
Scheme 2 Preparation of spiro-mamakone skeleton: (d) dimethoxy-
propane, pTSA; (e) triflic acid.
With the spiro-mamakone carbon skeleton in hand, attention
was turned to exploring the oxidation level of the northern hemi-
sphere (Scheme 3). Manipulation of ring A was first examined.
Ketone 6 was reduced to racemic alcohol 7. Whilst treatment of 6
with DDQ (in refluxing benzene or dioxane) returned only starting
material, reaction with IBX, with N-methoxypyridine-N-oxide
hydrate as an additive, at elevated temperatures afforded enone 9
in moderate yield (42%).12 Enone 9 was selectively reduced to the
allylic alcohol 10 under Luche reduction conditions.13 Alcohols
7 and 10 were converted to acetates, 8 and 11 respectively, to
facilitate further chemical modifications.
Scheme 3 Manipulation of the degree of oxidation of ring A: (f) NaBH4;
(g) Ac2O, pyridine; (h) IBX, MPO; (i) NaBH4, CeCl3, MeOH.
Having prepared analogues with varying degrees of oxidation in
ring A, including allylic alcohol 10 which is directly analogous to
the natural product, manipulation of ring B was next examined.
Analogues featuring an enone in place of the enedione of the
parent natural product, such as 12, would be useful for comparison
in a structure–activity profile. A single allylic oxidation was
therefore investigated with analogues 6, 8, 9 and 11. The rhodium-
catalysed, allylic oxidant system developed by Catino et al.
successfully oxidized these substrates to yield enones.14 However,
1H and 2D NMR spectroscopy suggested that the enones formed
were not analogous to enone 12, and were instead enones formed
with olefin migration (Scheme 4). Specifically, it was observed
that the COSY coupling between the down-field enone protons
(for example 7.55 ppm in enone 13) and the methylene protons
(2.94 and 2.50 ppm) which would be anticipated, was absent.
To unambiguously distinguish between the regioisomeric enone
possibilities, 18 and its enantiomer were reduced under Luche
reduction conditions (Scheme 5). This yielded one major isomer,
whose 1H and COSY NMR data corresponded to 19, confirming
that allylic oxidation had occurred with olefin migration. Several
alternative allylic oxidant systems were also examined (Pd(OH)2–
tBuOOH,15 CrO3–DMP,16 PDC–tBuOOH17 and Bi(NO3)3·5H2O–
tBuOOH18), but these also yielded enones with olefin migration
and furthermore, were slower in achieving the oxidation than the
rhodium-catalysed oxidation. Allylic oxidation of olefins 8 and 11
yielded separable mixtures of enones 14 and 15 (ratio of 1 : 1.3, as
judged by 1H NMR of the crude mixture), and 17 and 18 (ratio of
1 : 2.4) respectively.
The generation of allylic alcohol 19 led to the consideration of a
cyclopentadiene analogue of spiro-mamakone A, via dehydration
(Scheme 6), as a target. Luche reduction of the mixture of
diastereoisomers17 and 18 gave a complex mixture of diastereoiso-
meric allylic alcohols, 20. Dehydration of this mixture using
Burgessꢀ reagent yielded the cyclopentadiene analogue, 21.19,20 The
unprotected analogue of 20, 22, was also obtained, via the selective
1,2 enone reduction of both enones of 16 (Scheme 7), and its fully
protected analogue, 23 was generated via acetylation of 22.
Finally, the introduction of halogens on ring B was briefly
examined, via allylic bromination of the olefin using enone 9 as a
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Scheme 6 Preparation of a cyclopentadiene analogue: (k) Burgessꢀ
reagent.
Scheme 4 Allylic oxidation of ring B of synthetic spiro-mamakone
analogues: (j) Rh2(cap)4, tBuOOH, NaHCO3.
Scheme 7 Synthesis of further analogues.
Scheme 5 Confirmation of enone regiochemistry.
model system. However, the activated naphthalene moiety proved
more reactive towards the bromine generated in situ, yielding
analogue 24 (Scheme 8). Interestingly, the product of an olefin
migration, analogue 25, was also obtained from the reaction
mixture.
Scheme 8 Reactivity under bromination conditions: (l) NBS, AIBN.
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Table 1 Summary of biological activity against murine leukaemia cell-
line P388 displayed by spiro-mamakone A and synthetic analogues
With a variety of compounds based on the spiro-mamakone
skeleton prepared, their biological activities were next explored.
IC50/lM
Biological testing
1
6
0.33
>42
>42
>37
The potent cytotoxicity displayed by spiro-mamakone A (IC50
of 0.33 lM in the murine leukaemia cell line P388 assay)
prompted the testing of all synthetic analogues described above
for equivalent biological activity, in order to develop a structure–
activity profile for the spiro-mamakone system. The results are
presented in Table 1. The most striking conclusion which can be
drawn from these results is that spiro-mamakone A represents a
highly refined entity with respect to its biological activity. The
synthetic analogues tested all share the carbon skeleton of spiro-
mamakone A, but vary widely in the degree and positions of
oxidation on the northern hemisphere. Most analogues displayed
at least 100-fold lower biological activity than the natural product,
including some which feature very similar substitution. The
lack of, or weak activity of analogues 10 and 22, which differ
from the natural product only in the substitution of the right-
hand ring, highlights the importance of the enedione moiety to
biological activity. Interestingly, two synthetic analogues, enones
9 and 16, display cytotoxicity of the same order of magnitude as
the natural product. Brominated enones 24 and 25 also display
significant biological activity. Since enones are known biological
pharmacophores, and are not present in the natural product, it
is possible that the biological activity of these analogues is due
to a different biological mechanism. However, the low activities
of enones 13 to 15, 17 and 18 indicate that an enone moiety
is not sufficient to induce potent cytotoxicity in this class of
compounds. It is interesting to note that the biologically active
analogues have an enone located in ring A, but when the enone
is located in ring B they are inactive. This suggests that the
biologically active form of spiro-mamakone A may possibly
require an enone or equivalent in ring A. Biosynthetic studies6
established that the most likely final step in the biosynthesis
of spiro-mamakone A was the aldol type formation of the
C4-C5 bond to form ring A from the likes of the a,b-unsaturated
aldehyde 26 (Scheme 9) and that this step was possibly freely
reversible (as the enedione motif is a stable leaving group). We
therefore speculate that an enone in ring A may mimic this ring-
opened isomer of spiro-mamakone A, and may also explain the
low activities of allylic alcohols 10 and 22, which do not contain
an enedione, and therefore cannot isomerise to an a,b-unsaturated
aldehyde.
7
8
9
0.9
10
11
13
14
15
16
17
18
20
21
22
23
24
25
43
>37
36
>36
30
0.7
>36
30
>36
>38
>41
25
10
9
Scheme 9 Biosynthetic precursor of spiro-mamakone A.
Experimental
General experimental
Anhydrous CHCl3 and DCM were distilled under nitrogen over
calcium hydride, while anhydrous benzene was distilled under ni-
trogen over sodium. Reagents obtained from commercial suppliers
were used without further purification. Column chromatography
was performed using silica gel (230–400 mesh, 60 A pore size)
and commercial grade solvents. IR measurements were taken on
a Shimadzu FTIR-8201PC spectrophotometer or a Perkin Elmer
˚
1
Spectrum One FTIR spectrophotometer. H NMR (500 MHz)
and 13C NMR (125 or 75 MHz) spectra were recorded on Varian
NMR instruments in CDCl3 (referenced using tetramethylsilane).
Samples were analysed on a Micromass LCT mass spectrometer
equipped with an electrospray ionisation (ESI) probe or on a high
resolution VG-70SE mass spectrometer equipped with electron
ionisation or chemical ionisation (using ammonia gas) probes.
Where noted, flash chromatography was carried out on silica
which was first deacidified by addition of triethylamine (∼1–2%)
to a suspension of silica in the initial eluent. Analytical high
pressure liquid chromatography (HPLC) was carried out on a
Dionex HPLC instrument. For the P388 cytotoxicity assays, two-
fold dilution series for each synthetic analogue were incubated for
72 h with fast-growing murine leukaemia cells (ATCC CCL 46
P388D1). The concentration of the sample required to inhibit cell
growth to 50% of the growth of a cell control (IC50) was determined
Conclusion
The carbon skeleton of spiro-mamakone A has been success-
fully assembled and manipulated, yielding a series of synthetic
analogues of the natural product. These analogues feature a
wide variety of oxidation patterns in the northern hemisphere.
Biological testing of the synthetic analogues allowed a structure–
activity relationship profile to be developed, and thereby allow
speculation on the active form of the natural product and its
chemical reactivity at its biological target. The significant bio-
logical activities of several synthetic analogues prepared suggests
that the natural product may prove to be a useful platform for lead
optimisation.
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by interpolation from the absorbances obtained upon staining
with MTT tetrazolium. The positive control was mitomycin C
(0.06 lg mL−1), which inhibited cell growth by 43–75%.
br d, 14.0 Hz, 6/9-H), 2.61 (2H, br d, 14.0 Hz, 6/9-H), 2.53 (2H,
dd, 8.2 Hz, 7.7 Hz, 2-H or 3-H), 2.17 (2H, dd, 8.2 Hz, 7.7 Hz, 2-H
or 3-H); dC (75 MHz, CDCl3) 214.3 (C, C-4), 147.5 (C, C-10/18),
134.2 (C, C-14), 128.1 (CH, C-7/8), 127.3 (CH, C-12/16), 120.6
(CH, C-13/15), 113.9 (C, C-19), 109.3 (CH, C-11/17), 108.1 (C,
C-1), 62.0 (C, C-5), 36.4 (CH2, C-6/9), 33.7 (CH2, C-2 or C-3),
28.1 (CH2, C-2 or C-3); HRESIMS m/z = 293.1187 [M + H]+
3.1 ppm (293.1178 calcd for C19H17O3).
spiro[4.4]Nona-7-ene-1,4-dione, 3. Crude 2,2-diallylcyclopen-
tane-1,3-dione (2, ∼1.8 g, ∼10 mmol)10 was dissolved in anhydrous
DCM (30 mL), Grubbsꢀ 2nd generation catalyst was added (350 mg,
0.41 mmol, 4 mol%) and the reaction was stirred under an inert
atmosphere for 18 h. Removal of solvents in vacuo and silica
chromatography using a gradient of 20 to 30% diethyl ether in
petroleum ether gave 3 as an off-white crystalline solid (1.48 g,
9.88 mmol, 97% over two steps). Rf 0.18 (silica, 4 : 1 petroleum
ether–EtOAc, PMA); mp 91–93 ◦C (diethyl ether, lit. 89–90 ◦C);9
IR (diffuse reflectance) mmax/cm−1 1751, 1713, 1443, 1273, 1227,
1111; dH (500 MHz, CDCl3, Me4Si) 5.62 (2H, br s), 2.83 (4H, s),
2.67 (4H, br s);9 dC (75 MHz, CDCl3) 214.4, 127.4, 61.3, 41.1,
34.9; HRCIMS m/z = 150.0684 [M]+• 2.0 ppm (150.0681 calcd for
C9H10O2).
4-Hydroxy-spiro[4.4]nona-7-ene-1-one-1,1-[1,8-dihydroxynaph-
thalene]-acetal, 7. spiro[4.4]Nona-7-ene-1,4-dione-1,1-[1,8-dihy-
droxynaphthalene]-acetal (6, 10 mg, 0.034 mmol) was dissolved
in MeOH (1 mL) and NaBH4 (7.5 mg, 0.20 mmol, 5.9 eq) was
added. The reaction was stirred at room temperature for 16 h,
then NaHCO3(aq) (1 M, 2 mL) was added and the reaction extracted
with EtOAc (3 × 2 mL). After drying over MgSO4, filtration and
removal of solvent in vacuo, the crude product was purified on
deacidified silica using a gradient of 0 to 10% diethyl ether in
petroleum ether, to give 7 as a colourless oil (4.8 mg, 0.016 mmol,
47%). Rf 0.26 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR (thin
film) mmax/cm−1 3406, 2926, 1609, 1411, 1381, 1275; dH (500 MHz,
CDCl3, Me4Si) 7.47 (1H, dd, 8.3 Hz, 0.9 Hz, 13-H or 15-H), 7.46
(1H, dd, 8.3 Hz, 0.9 Hz, 13-H or 15-H), 7.40 (1H, dd, 8.3 Hz, 7.4
Hz, 12-H or 16-H), 7.395 (1H, dd, 8.3 Hz, 7.4 Hz, 12-H or 16-H),
6.89 (1H, dd, 7.4 Hz, 0.9 Hz, 11-H or 17-H), 6.88 (1H, dd, 7.4
Hz, 0.9 Hz, 11-H or 17-H), 5.77 (1H, m, 7-H or 8-H), 5.69 (1H,
m, 7-H or 8-H), 4.08 (1H, m, 4-H), 3.05 (1H, m, 6-H or 9-H),
2.86 (1H, m, 6-H or 9-H), 2.76 (1H, m, 6-H or 9-H), 2.48 (1H, d,
9.3 Hz, OH), 2.31 (1H, m, 3-H), 2.15 (1H, m, 6-H or 9-H), 2.06
(1H, m, 2-H), 1.80 (2H, m, 2/3-H); dC (75 MHz, CDCl3) 148.4
(C, C-10 or C-18), 147.6 (C, C-10 or C-18), 134.4 (C, C-14), 129.9
(CH, C-7 or C-8), 127.8 (CH, C-7 or C-8), 127.3 (CH, C-12 or
C-16), 127.2 (CH, C-12 or C-16), 120.6 (CH, C-13 or C-15), 120.4
(CH, C-13 or C-15), 114.0 (C, C-19), 112.0 (C, C-1), 109.3 (CH,
C-11 or C-17), 109.2 (CH, C-11 or C-17), 77.8 (CH, C-4), 58.9 (C,
C-5), 39.2 (CH2, C-6 or C-9), 32.7 (CH2, C-6 or C-9), 30.7 (CH2,
C-2), 29.7 (CH2, C-3); HRESIMS m/z 295.1339 [M + H]+ 1.7 ppm
(295.1334 calcd for C19H19O3).
1,8-Dihydroxynaphthalene acetonide, 5. 1,8-Dihydroxynaph-
thalene (4, 640 mg, 4.0 mmol)8,11 was dissolved in
dimethoxypropane (10 mL) and pTSA (10 mg, 0.06 mmol)
added. The reaction was refluxed for 16 h, then cooled to room
temperature. Diethyl ether (10 mL) was added and the mixture was
washed with NaHCO3(aq) (1 M, 2 × 10 mL). The organic phase
was dried over MgSO4 and filtered. The crude residue was passed
through a short silica column eluting with petroleum ether and the
solvent removed in vacuo to give a yellow solid. The residue was
then passed through a C18 reverse phase pad with a solution of 60%
MeCN in H2O. Removal of MeCN in vacuo yielded an aqueous
suspension which was extracted exhaustively using diethyl ether.
The combined organic phases were dried over MgSO4, filtered and
the solvent removed in vacuo to yield 5 as a white crystalline solid
(590 mg, 2.95 mmol, 74%). Mp 61–64 ◦C (petroleum ether); Rf
0.75 (silica, 4 : 1 petroleum ether–EtOAc, UV/PMA); IR (thin
film) mmax/cm−1 1608, 1411, 1385, 1375, 1281, 1265; dH (500 MHz,
CDCl3, Me4Si) 7.44–7.36 (4H, m, 3/4/5/6-H), 6.86 (2H, dd, 6.8
Hz, 1.4 Hz, 2/8-H), 1.66 (6H, s, C(CH3)2); dC (75 MHz, CDCl3)
148.0 (C-1/8), 134.2 (C-4a), 127.3 (C-3/6), 120.0 (C-4/5), 113.5
(C-8a), 108.7 (C-2/7), 101.7 (C(CH3)2), 25.2 (C(CH3)2); HREIMS
O-Acetyl-4-hydroxy-spiro[4.4]nona-7-ene-1-one-1,1-[1,8-dihy-
droxynaphthalene]-acetal, 8. 4-Hydroxy-spiro[4.4]nona-7-ene-1-
one-1,1-[1,8-dihydroxynaphthalene]-acetal (7, 20 mg, 0.068 mmol)
was dissolved in pyridine (500 lL) and acetic anhydride was added
(200 lL, 2.1 mmol, 31 eq). The reaction was stirred at room
temperature for 16 h. Deionised H2O (3 mL) was added and the
mixture extracted with diethyl ether (4 × 3 mL). The combined
organic phases were dried over MgSO4, filtered and the solvents
removed in vacuo. No further purification was required. The
product (8, 19 mg, 0.056 mmol, 82%) was obtained as a colourless
oil. IR (thin film) mmax/cm−1 1738, 1609, 1412, 1381, 1243; dH
(500 MHz, CDCl3, Me4Si) 7.45–7.36 (4H, m, 12/13/15/16-H),
6.90 (1H, d, 7.5 Hz, 11-H or 17-H), 6.88 (1H, d, 7.5 Hz, 11-H or
17-H), 5.71–5.65 (2H, m, 7/8-H), 5.41 (1H, dd, 8.2 Hz, 6.7 Hz, 4-
H), 3.05 (1H, m, 6-H or 9-H), 2.85 (1H, m, 6-H or 9-H), 2.68 (1H,
m, 6-H or 9-H), 2.42 (1H, m, 6-H or 9-H), 2.28 (1H, m, 3-H), 2.09
(3H, s, 21-H), 1.93 (2H, m, 2-H), 1.72 (1H, m, 3-H); dC (75 MHz,
CDCl3) 171.3 (C, C-20), 148.5 (C, C-10 or C-18), 148.4 (C, C-10
or C-18), 134.5 (C, C-14), 129.01 (CH, C-7 or C-8), 128.97 (CH,
C-7 or C-8), 127.6 (CH, C-12 or C-16), 127.5 (CH, C-12 or C-16),
120.6 (CH, C-13 or C-15), 120.5 (CH, C-13 or C-15), 114.4 (C,
•
m/z = 200.0835 [M]+ 1.0 ppm (200.0837 calcd for C13H12O2).
spiro[4.4]Nona-7-ene-1,4-dione-1,1-[1,8-dihydroxynaphthalene]-
acetal, 6. 1,8-Dihydroxynaphthalene acetonide (5, 900 mg,
4.50 mmol, 1.7 eq) and spiro[4.4]nona-7-ene-1,4-dione (3, 400 mg,
2.66 mmol) were dissolved in anhydrous CHCl3 (6 mL) and triflic
acid (40 lL, 0.45 mmol, 0.17 eq) was added. The reaction mixture
became a dark brown colour upon addition of the acid and was
stirred at 45 ◦C for 48 h. The reaction mixture was then diluted with
diethyl ether (2 mL) and washed with NaHCO3(aq) (1 M, 2 × 1 mL).
The organic phase was dried over MgSO4, filtered and the solvent
R
removed in vacuo. The crude residue was purified on Florisilꢀ using
a gradient of 0 to 20% diethyl ether in petroleum ether. This gave 6
as an off-white solid (120 mg, 0.41 mmol, 15%). Starting material,
3, was also recovered (180 mg, 1.20 mmol, 45%). Mp 150–151
◦C (diethyl ether); Rf 0.46 (silica, 4 : 1 petroleum ether–EtOAc,
UV/PMA); IR (diffuse reflectance) mmax/cm−1 1744, 1611, 1414,
1275, 1248; dH (500 MHz, CDCl3, Me4Si) 7.49 (2H, dd, 8.4 Hz, 0.7
Hz, 13/15-H), 7.41 (2H, dd, 8.4 Hz, 7.5 Hz, 12/16-H), 6.91 (2H,
dd, 7.5 Hz, 0.7 Hz, 11/17-H), 5.70 (2H, br m, 7/8-H), 3.05 (2H,
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C-19), 110.0 (C, C-1), 109.7 (CH, C-11 or C-18), 109.4 (CH, C-11
or C-18), 79.3 (CH, C-4), 57.8 (C, C-5), 38.2 (CH2, C-6 or C-9),
34.4 (CH2, C-6 or C-9), 30.9 (CH2, C-2), 26.3 (CH2, C-3), 21.5
(C, C-1), 109.2 (CH, C-11 or C-17), 108.8 (CH, C-11 or C-17), 81.1
(CH, C-4), 59.9 (C, C-5), 40.3 (CH2, C-6/9); HRESIMS m/z =
293.1186 [M + H]+ 2.7 ppm (293.1178 calcd for C19H17O3).
•
(CH3, C-21); HREIMS m/z = 336.1366 [M]+ 1.2 ppm (336.1362
O-Acetyl-4-hydroxy-spiro[4.4]nona-2,7-diene-1-one-1,1-[1,8-
dihydroxynaphthalene]-acetal, 11. 4-Hydroxy-spiro[4.4]nona-2,
7-diene-1-one-1,1-[1,8-dihydroxynaphthalene]-acetal (10, 5 mg,
0.017 mmol) was dissolved in pyridine (500 lL) and acetic
anhydride was added (200 lL, 2 mmol, 120 eq). The reaction
was stirred at room temperature for 20 h, then diethyl ether was
added (2 mL) and the mixture extracted with NaHCO3(aq) (1 M,
3 × 2 mL). After drying over MgSO4, filtration and removal of
solvent in vacuo, the crude product was purified on deacidified
silica using a gradient of 0 to 12% diethyl ether in petroleum ether,
to give 1 as a colourless oil (5.5 mg, ∼0.017 mmol, ∼100%). Rf 0.69
(4 : 1 petroleum ether–EtOAc, UV/PMA); IR (thin film) mmax/cm−1
1738, 1607, 1412, 1381, 1279, 1219; dH (500 MHz, CDCl3, Me4Si)
7.46 (1H, dd, 8.4 Hz, 0.9 Hz, 13-H or 15-H), 7.45 (1H, dd, 8.4 Hz,
0.9 Hz, 13-H or 15-H), 7.40 (1H, dd, 8.4 Hz, 7.5 Hz, 12-H or 16-
H), 7.39 (1H, dd, 8.4 Hz, 7.5 Hz, 12-H or 16-H), 6.91 (1H, dd, 7.5
Hz, 0.9 Hz, 11-H or 17-H), 6.86 (1H, dd, 7.5 Hz, 0.9 Hz, 11-H or
17-H), 6.17 (1H, dd, 6.0 Hz, 2.2 Hz, 3-H), 6.05 (1H, dd, 6.0 Hz, 1.2
Hz, 2-H), 5.74 (1H, dd, 2.2 Hz, 1.2 Hz, 4-H), 5.68 (2H, m, 7/8-H),
3.18 (1H, m, 6-H or 9-H), 2.97 (1H, m, 6-H or 9-H), 2.60 (1H, m,
6-H or 9-H), 2.45 (1H, m, 6-H or 9-H), 2.11 (3H, s, 21-H); dC (75
MHz, CDCl3) 170.8 (C, C-20), 148.8 (C, C-10 or C-18), 148.5 (C,
C-10 or C-18), 136.8 (CH, C-3), 134.3 (C, C-14), 133.2 (CH, C-2),
128.7 (CH, C-7 or C-8), 128.4 (CH, C-7 or C-8), 127.32 (CH, C-12
or C-16), 127.28 (CH, C-12 or C-18), 120.4 (CH, C-13 or C-15),
120.3 (CH, C-13 or C-15), 114.1 (C, C-19), 109.9 (C, C-1), 108.9
(CH, C-11/17), 82.1 (CH, C-4), 60.5 (C, C-5), 38.9 (CH2, C-6 or
C-9), 34.3 (CH2, C-6 or C-9), 21.1 (CH3, C-21); HRESIMS m/z =
335.1293 [M + H]+ 3.0 ppm (335.1283 calcd for C21H19O4).
calcd for C21H20O4).
spiro[4.4]Nona-2,7-diene-1,4-dione-1,1-[1,8-dihydroxynaphtha-
lene]-acetal,
9. spiro[4.4]Nona-7-ene-1,4-dione-1,1-[1,8-dihy-
droxynaphthalene]-acetal, (6, 95 mg, 0.33 mmol), IBX (380 mg,
1.36 mmol, 4.1 eq) and N-methoxypyridine-N-oxide hydrate
(170 mg, 1.36 mmol, 4.1 eq) were dissolved in DMSO (1.4 mL)
at 70 ◦C (over 15 min) to form a clear reddish solution. The
reaction was then stirred at 70 ◦C for 20 h during which time
a white precipitate formed. NaHCO3(aq) was slowly added (1 M,
approximately 2 mL) and the resulting mixture was extracted with
diethyl ether (4 × 3 mL). The combined organic phases were dried
over MgSO4, filtered and the solvent removed in vacuo. The crude
product was purified by chromatography on deacidified silica
using a gradient of 0 to 2% diethyl ether in petroleum ether. The
product, 9, was obtained as a white solid (40 mg, 0.14 mmol, 42%)
◦
and remaining starting material, 6, eluted after. Mp 142–144 C
(diethyl ether); Rf 0.56 (4 : 1 petroleum ether–EtOAc, UV/PMA);
IR (diffuse reflectance) mmax/cm−1 1725, 1611, 1411, 1278, 1262,
1250; dH (500 MHz, CDCl3, Me4Si) 7.51 (2H, dd, 8.4 Hz, 0.7 Hz,
13/15-H), 7.43 (2H, dd, 8.4 Hz, 7.5 Hz, 12/16-H), 7.38 (1H, d, 6.1
Hz, 2-H or 3-H), 6.93 (2H, dd, 7.5 Hz, 0.7 Hz, 11/17-H), 6.39 (1H,
d, 6.1 Hz, 2-H or 3-H), 5.65 (2H, br s, 7/8-H), 3.22 (2H, br d, 16.0
Hz, 6/9-H), 2.64 (2H, br d, 16.0 Hz, 6/9-H); dC (75 MHz, CDCl3)
206.6 (C, C-4), 153.3 (CH, C-2), 147.6 (C, C-10/18), 135.2 (CH,
C-3), 134.2 (C, C-14), 128.0 (CH, C-7/8), 127.5 (CH, C-12/C16),
120.9 (CH, C-13/C15), 113.7 (C, C-19), 109.3 (CH, C-11/17),
105.8 (C, C-1), 61.2 (C, C-5), 38.0 (CH2, C-6/9); HRESIMS
m/z = 291.1030 [M + H]+ 3.1 ppm (291.1021 calcd for C19H15O3).
4-Hydroxy-spiro[4.4]nona-2,7-diene-1-one-1,1-[1,8-dihydroxy-
naphthalene]-acetal, 10. spiro[4.4]Nona-2,7-diene-1,4-dione-1,1-
[1,8-dihydroxynaphthalene]-acetal (9, 10 mg, 0.034 mmol) and
CeCl3 (anhydrous, 9 mg, 0.036 mmol, 1.1 eq) were dissolved in
MeOH (500 lL) and cooled to 0 ◦C. NaBH4 (1.3 mg, 0.034 mmol, 1
eq) was added and the reaction stirred at 0 ◦C for 1 h. NaHCO3(aq) (1
M, 1 mL) was added and the reaction extracted with diethyl ether
(4 × 1 mL). The combined organic phases were dried over MgSO4,
filtered and the solvent removed in vacuo. The crude product was
purified by chromatography on deacidified silica using a gradient
of 0 to 12% diethyl ether in petroleum ether, to give 10 as a
colourless oil (10 mg, 0.034 mmol, ∼100%). Rf 0.31 (4 : 1 petroleum
ether–EtOAc, UV/PMA); IR (thin film) mmax/cm−1 1607, 1413,
1382, 1277, 1100; dH (500 MHz, CDCl3, Me4Si) 7.47 (1H, dd, 8.3
Hz, 0.8 Hz, 13-H or 15-H), 7.45 (1H, dd, 8.3 Hz, 0.8 Hz, 13-H or
15-H), 7.40 (1H, dd, 8.3 Hz, 7.5 Hz, 12-H or 16-H), 7.38 (1H, dd,
8.3 Hz, 7.5 Hz, 12-H or 16-H), 6.91 (1H, dd, 7.5 Hz, 0.8 Hz, 11-H
or 17-H), 6.83 (1H, dd, 7.5 Hz, 0.8 Hz, 11-H or 17-H), 6.35 (1H,
dd, 6.0 Hz, 2.7 Hz, 3-H), 6.02 (1H, d, 6.0 Hz, 2-H), 5.76 (1H, m,
7-H or 8-H), 5.69 (1H, m, 7-H or 8-H), 4.39 (1H, d, 2.7 Hz, 4-H),
3.19 (1H, ddd, 16.9 Hz, 2.6 Hz, 2.4 Hz, 6-H or 9-H), 2.85 (2H,
m, 6/9-H), 2.09 (1H, 16.9 Hz, 1.9 Hz, 1.6 Hz, 6-H or 9-H); dC (75
MHz, CDCl3) 148.6 (C, C-10 or C-18), 148.3 (C, C-10 or C-18),
140.3 (CH, C-3), 134.3 (C, C-14), 132.9 (CH, C-2), 129.5 (CH, C-7
or C-8), 128.2 (CH, C-7 or C-8), 127.3 (CH, C-12/16), 120.5 (CH,
C-13 or C-15), 120.4 (CH, C-13 or C-15), 114.1 (C, C-19), 111.0
spiro[4.4]Nona-6-ene-1,4,8-trione-1,1-[1,8-dihydroxynaphtha-
lene]-acetal, 13. spiro[4.4]Nona-7-ene-1,4-dione-1,1-[1,8-dihy-
droxynaphthalene]-acetal (6, 12 mg, 0.041 mmol) was dissolved in
anhydrous DCM (1 mL) and dirhodium(II)tetrakis(caprolactam)
(0.3 mg, 0.45 lmol, 1 mol%) and NaHCO3 (1.5 mg, 0.018 mmol,
t
0.4 eq) were added. Butyl hydroperoxide (anhydrous, 5 M in
decanes, 40 lL, 0.20 mmol, 5 eq) was added and an immediate
colour change from light purple to deep pink was observed. The
reaction was stirred at room temperature for 16 h, then filtered
through a deacidified silica pad using DCM. The crude product
was purified on deacidified silica using a gradient of 0 to 24%
diethyl ether in petroleum ether to give 13 as a colourless oil
(5.5 mg, 0.018 mmol, 44%) and recovered starting material (6,
3 mg, 0.010 mmol, 24%). Rf 0.23 (4 : 1 petroleum ether–EtOAc,
UV/PMA); IR (thin film) mmax/cm−1 1750, 1718, 1609, 1270; dH
(500 MHz, CDCl3, Me4Si) 7.55 (1H, d, 5.7 Hz, 6-H), 7.523 (1H, dd,
8.3 Hz, 0.8 Hz, 13-H or 15-H), 7.518 (1H, dd, 8.3 Hz, 0.8 Hz, 13-H
or 15-H), 7.44 (1H, dd, 8.3 Hz, 7.6 Hz, 12-H or 16-H), 7.43 (1H,
dd, 8.3 Hz, 7.6 Hz, 12-H or 16-H), 6.93 (1H, dd, 7.6 Hz, 0.8 Hz,
11-H or 17-H), 6.92 (1H, dd, 7.6 Hz, 0.8 Hz, 11-H or 17-H), 6.36
(1H, d, 5.7 Hz, 7-H), 2.94 (1H, d, 18.3 Hz, 9-H), 2.69 (2H, m, 2-H
or 3-H), 2.50 (1H, d, 18.3 Hz, 9-H), 2.46 (1H, ddd, 14.0 Hz, 9.4 Hz,
6.0 Hz, 2-H or 3-H), 2.33 (1H, ddd, 14.0 Hz, 9.4 Hz, 7.4 Hz, 2-H
or 3-H); dC (75 MHz, CDCl3) 210.4 (C, C-4), 205.9 (C, C-8), 157.6
(CH, C-6), 146.8 (C, C-10 or C-18), 146.6 (C, C-10 or C-18), 136.6
(CH, C-7), 134.2 (C, C-14), 127.5 (CH, C-12 or C-16), 127.4 (CH,
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C-12 or C-16), 121.2 (CH, C-13/15), 113.5 (C, C-19), 109.6 (CH,
C-11 or C-17), 109.4 (CH, C-11 or C-17), 107.1 (C, C-1), 66.8 (C,
C-5), 38.3 (CH2, C-9), 35.1 (CH2, C-2 or C-3), 29.1 (CH2, C-2 or C-
3); HRESIMS m/z = 307.0979 [M + H]+ 2.9 ppm (307.0970 calcd
for C19H15O4).
was dissolved in anhydrous DCM (1 mL) and dirho-
dium(II)tetrakis(caprolactam) (0.2 mg, 0.3 lmol,
1 mol%)
t
and NaHCO3 (1.4 mg, 0.017 mmol, 0.5 eq) were added. Butyl
hydroperoxide (anhydrous, 5 M in decanes, 35 lL, 0.17 mmol,
5 eq) was added and an immediate colour change from light
purple to deep pink was observed. The reaction was stirred at
room temperature for 20 h, then filtered through a deacidified
silica pad using DCM. The crude product was further purified
on deacidified silica using a gradient of 0 to 16% diethyl ether in
petroleum ether, to give 16 as a colourless oil (3.4 mg, 0.011 mmol,
33%). Rf 0.20 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR
(thin film) mmax/cm−1 1732, 1725, 1609, 1581, 1411, 1378, 1270; dH
(500 MHz, CDCl3, Me4Si) 7.59 (1H, d, 6.0 Hz, 2-H), 7.56 (1H, d,
5.6 Hz, 6-H), 7.55 (2H, m, 13/15-H), 7.454 (1H, dd, 8.4 Hz, 7.6
Hz, 12-H or 16-H), 7.448 (1H, dd, 8.4 Hz, 7.6 Hz, 12-H or 16-H),
6.97 (1H, dd, 7.6 Hz, 0.8 Hz, 11-H or 17-H), 6.95 (1H, dd, 7.6 Hz,
0.8 Hz, 11-H or 17-H), 6.52 (1H, d, 6.0 Hz, 3-H), 6.33 (1 H, d, 5.6
Hz, 7-H), 3.09 (1H, d, 18.7 Hz, 9-H), 2.62 (1H, d, 18.7 Hz, 9-H);
dC (75 MHz, CDCl3) 206.5 (C, C-8), 201.5 (C, C-4), 159.1 (CH,
C-6), 154.3 (CH, C-2), 146.6 (C, C-10/18), 135.4 (CH, C-7), 135.1
(CH, C-3), 134.2 (C, C-14), 127.6 (CH, C-12 or C-16), 127.5 (CH,
C-12 or C-16), 121.52 (CH, C-13 or C-15), 121.49 (CH, C-13 or
C-15), 109.6 (CH, C-11/17), 105.3 (C, C-1), 65.0 (C, C-5), 39.0
(CH2, C-9), C-19 not observed; HRESIMS m/z = 305.0821 [M +
H]+ 2.3 ppm (305.0814 calcd for C19H13O4).
O-Acetyl-4-hydroxy-spiro-nona-6-ene-1,8-dione-1,1-[1,8-dihy-
droxynaphthalene]-acetal, 14 ([4R,5S] and [4S,5R]), and 15
([4R,5R] and [4S,5S]). O-Acetyl-4-hydroxy-spiro-nona-7-ene-1-
one-1,1-[1,8-dihydroxynaphthalene]-acetal
(8,
19
mg,
0.056 mmol) was dissolved in DCM (1 mL) and dirhodium-
(II)tetrakis(caprolactam) (0.4 mg, 0.56 lmol, 1 mol%) and
NaHCO3 (2.3 mg, 0.028 mmol, 0.5 eq) were added. tButyl
hydroperoxide (anhydrous, 5 M in decanes, 0.5 mL, 2.5 mmol,
45 eq) was added and an immediate colour change from light
purple to deep pink was observed. The reaction was stirred at
room temperature for 16 h then filtered through a deacidified
silica pad using DCM. The crude product was further purified
on deacidified silica using a gradient of 0 to 20% diethyl ether
in petroleum ether to give the isomeric products 14 (4.1 mg,
0.012 mmol, 21%) and 15 (8.7 mg, 0.025 mmol, 45%) as colourless
oils.
14. Rf 0.14 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR (thin
film) mmax/cm−1 1738, 1721, 1609, 1412, 1379, 1276, 1236, 1054; dH
(500 MHz, CDCl3, Me4Si) 7.65 (1H, d, 5.9 Hz, H9), 7.48 (2H, d,
8.1 Hz, H13 and H15), 7.41 (1H, t, 7.4 Hz, H12 or H16), 7.39 (1H,
t, 7.4 Hz, H12 or H16), 6.91 (1H, d, 7.5 Hz, H11 or H17), 6.87 (1H,
d, 7.5 Hz, H11 or H17), 6.31 (1H, d, 5.8 Hz, H8), 5.46 (1H, dd,
8.1 Hz, 6.3 Hz, H4), 3.06 (1H, d, 18.9 Hz, H6), 2.45 (1H, m, H3),
2.43 (1H, d, 18.8 Hz, H6), 2.21 (1H, m, H2), 2.10 (1H, m, H2),
2.09 (3H, s, H21), 1.95 (1H, m, H3); dC (75 MHz, CDCl3) 207.5
(C, C6), 170.7 (C, C20), 160.6 (CH, C9), 147.8 (C, C10 or C18),
147.5 (C, C10 or C18), 136.2 (C, C14), 134.5 (C, C8), 127.7 (CH,
C12 or C16), 127.6 (CH, C12 or C16), 121.2 (CH, C13 or C15),
121.1 (CH, C13 or C15), 114.0 (C, C19), 109.9 (CH, C11 or C17),
109.6 (CH, C11 or C17), 108.9 (C, C1), 78.8 (CH, C4), 61.7 (C,
C5), 40.7 (CH2, C9), 31.9 (CH2, C2), 27.3 (CH2, C3), 21.2 (CH3,
C21); HRESIMS m/z = 351.1242 [M + H]+ 2.8 ppm (351.1232
calcd for C21H19O5).
O-Acetyl-4-hydroxy-spiro[4.4]nona-2,6-diene-1,8-dione-1,1-[1,
8-dihydroxynaphthalene]-acetal, 17 ([4R,5R] and [4S,5S]) and
18 ([4R,5S] and [4S,5R]). O-Acetyl-4-hydroxy-spiro[4.4]nona-
2,7-diene-1-one-1,1-[1,8-dihydroxynaphthalene]-acetal (11, 5 mg,
0.015 mmol) was dissolved in anhydrous DCM (1 mL) and
dirhodium(II)tetrakis(caprolactam) (0.1 mg, 0.15 lmol, 1 mol%)
t
and NaHCO3 (0.7 mg, 0.008 mmol, 0.5 eq) were added. Butyl
hydroperoxide (anhydrous, 5 M in decanes, 20 lL, 0.08 mmol,
5 eq) was added and an immediate colour change from light
purple to deep pink was observed. The reaction was stirred at room
temperature for 16 h, then filtered through a deacidified silica pad
using DCM. The crude product was purified on deacidified silica
using a gradient of 8 to 16% diethyl ether in petroleum ether, to
give 17 (0.8 mg, 0.0023 mmol, 15%) and 18 (2.1 mg, 0.0060 mmol,
40%) as colourless oils.
15. Rf 0.19 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR (thin
film) mmax/cm−1 1741, 1721, 1610, 1411, 1380, 1276, 1236, 1053; dH
(500 MHz, CDCl3, Me4Si) 7.67 (1H, d, 5.8 Hz, H6), 7.49–7.36 (4H,
m, H12, H13, H15 and H16), 6.97 (1H, d, 7.4 Hz, H11 or H17),
6.86 (1H, d, 7.4 Hz, H11 or H17), 6.18 (1H, d, 5.8 Hz, H7), 5.72
(1H, t, 8.5 Hz, H4), 2.86 (1H, d, 18.1 Hz, H9), 2.66 (1H, d, 18.1
Hz, H9), 2.43 (1H, m, H3), 2.16 (1H, m, H2), 2.05 (1H, m, H2),
2.04 (3H, s, H21), 1.82 (1H, m, H3); dC (75 MHz, CDCl3) 207.4
(C, C8), 170.7 (C, C20), 162.6 (CH, C6), 147.6 (C, C10 or C18),
147.4 (C, C10 or C18), 136.5 (C, C14), 134.5 (CH, C7), 127.7 (CH,
C12 or C16), 127.6 (CH, C12 or C16), 121.2 (CH, C13 or C15),
121.1 (CH, C13 or C15), 114.0 (C, C19), 109.8 (CH, C11 or C17),
109.6 (CH, C11 or C17), 108.9 (C, C1), 74.9 (CH, C4), 61.7 (C,
C5), 36.8 (CH2, C9), 32.1 (CH2, C2), 26.8 (CH2, C3), 21.2 (CH3,
C21); HRESIMS m/z = 351.1235 [M + H]+ 0.9 ppm (351.1232
calcd for C21H19O5).
17. Rf 0.16 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR
(thin film) mmax/cm−1 1740, 1722, 1608, 1412, 1221; dH (500 MHz,
CDCl3, Me4Si) 7.58 (1H, d, 5.8 Hz, 6-H), 7.50 (1H, dd, 8.3 Hz, 0.8
Hz, 13-H or 15-H), 7.48 (1H, dd, 8.3 Hz, 0.8 Hz, 13-H or 15-H),
7.41 (1H, dd, 8.3 Hz, 7.6 Hz, 12-H or 16-H), 7.40 (1H, dd, 8.3
Hz, 7.6 Hz, 12-H or 16-H), 6.89 (1H, dd, 7.6 Hz, 0.8 Hz, 11-H or
17-H), 6.87 (1H, dd, 7.6 Hz, 0.8 Hz, 11-H or 17-H), 6.28 (1H, d,
5.8 Hz, 7-H), 6.24 (1H, dd, 6.1 Hz, 1.6 Hz, 2-H or 3-H), 6.13 (1H,
dd, 6.1 Hz, 1.6 Hz, 2-H or 3-H), 5.95 (1H, t, 1.6 Hz, 4-H), 3.2 (1H,
d, 19.0 Hz, 9-H), 2.74 (1H, d, 19.0 Hz, 9-H), 2.07 (3H, s, 21-H); dC
(125 MHz, observed by 2D NMR, CDCl3) 207.8 (C, C-8), 170.4
(C, C-20), 161.8 (CH, C-6), 147.8 (C, C-10/18), 136.6 (CH, C-2
or C-3), 135.1 (CH, C-7), 134.5 (C, C-14), 132.3 (CH, C-2 or C-3),
127.6 (CH, C-12/16), 121.0 (CH, C-13/15), 113.9 (C, C-19), 109.5
(CH, C-11/17), 109.3 (C, C-1), 81.6 (CH, C-4), 63.4 (C, C-5), 40.3
(CH2, C-9), 21.0 (CH3, C-21); HRESIMS m/z = 349.1082 [M +
H]+ 1.7 ppm (349.1076 calcd for C21H17O5).
spiro[4.4]Nona-2,6-diene-1,4,8-trione-1,1-[1,8-dihydroxynaph-
thalene]-acetal,
16. spiro[4.4]Nona-2,7-diene-1,4-dione-1,1-
[1,8-dihydroxynaphthalene]-acetal (9, 10 mg, 0.034 mmol)
3860 | Org. Biomol. Chem., 2008, 6, 3854–3862
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18. Rf 0.18 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR
(thin film) mmax/cm−1 1742, 1723, 1607, 1412, 1225; dH (500 MHz,
CDCl3, Me4Si) 7.80 (1H, d, 5.7 Hz, 6-H), 7.49 (1H, dd, 8.4 Hz, 0.9
Hz, 13-H or 15-H), 7.48 (1H, dd, 8.4 Hz, 0.9 Hz, 13-H or 15-H)
7.41 (2H, dd, 8.4 Hz, 7.5 Hz, 12/16-H), 6.93 (1H, dd, 7.5 Hz, 0.9
Hz, 11-H or 17-H), 6.89 (1H, dd, 7.5 Hz, 0.9 Hz, 11-H or 17-H),
6.24 (1H, dd, 6.1 Hz, 1.8 Hz, 3-H), 6.21 (1H, d, 5.7 Hz, 7-H), 6.11
(1H, dd, 6.1 Hz, 1.8 Hz, 2-H), 6.05 (1H, t, 1.8 Hz, 4-H), 3.06 (1H,
d, 18.8 Hz, 9-H), 2.63 (1H, d, 18.8 Hz, 9-H), 2.11 (3H, s, 21-H); dC
(125 MHz, observed by 2D NMR, CDCl3) 207.6 (C, C-6), 170.5
(C, C-20), 162.2 (CH, C-6), 148.3 (C, C-10 or C-18), 147.6 (C, C-10
or C-18), 137.1 (CH, C-3), 136.0 (CH, C-7), 134.4 (C, C-14), 132.5
(CH, C-2), 127.5 (CH, C-12/16), 121.1 (CH, C-13/15), 113.8 (C,
C-19), 109.5 (C/CH, C-11/17/1), 78.0 (CH, C-4), 63.5 (C, C-5),
37.3 (CH2, C-9), 20.9 (CH3, C-21); HRESIMS m/z = 349.1081
[M + H]+ 1.4 ppm (349.1076 calcd for C21H17O5).
filtered and the solvent removed in vacuo. The residue was purified
on deacidified silica using a gradient of 10 to 24% diethyl ether in
petroleum ether. 20 was obtained as a mixture of stereoisomers as a
colourless oil (11 mg, 0.031 mmol, 91%). IR (thin film) mmax/cm−1
3400–3100, 2916, 1729, 1719, 1607, 1412, 1379; dH (500 MHz,
CDCl3, Me4Si) 7.51–7.36 (4H, m, 12/13/15/16-H), 6.98–6.82 (2H,
m, 11/17-H), 6.22–5.75 (5H, m, 2/3/4/6/7-H), 4.84–4.79 (1H, m,
8-H), 3.52–1.77 (2H, m, 9-H), 2.14 (∼2H, s, 21-H), 2.10 (∼1H, s,
21-H); HRESIMS m/z = 333.1124 [M − OH]+ 0.9 ppm (333.1127
calcd for C21H17O4).
O-Acetyl-4-hydroxy-spiro[4.4]nona-2,6,8-triene-1,1-[1,8-dihy-
droxynaphthalene]-acetal, 21. Allyl alcohol 20 (mixture of iso-
mers, 11 mg, 0.031 mmol) was dissolved in anhydrous benzene
(2 mL) and Burgessꢀ reagent (15 mg◦, 0.063 mmol, 2 eq) was
added.21 The reaction was stirred at 50 C for 16 h, then cooled to
room temperature. Diethyl ether (3 mL) was added and the mixture
was extracted with NaHCO3(aq) (1 M, 2 × 3 mL). The organic phase
was dried over MgSO4, filtered and the solvent removed in vacuo.
The crude residue was purified by chromatography on deacidified
silica using a gradient of 0 to 6% diethyl ether in petroleum ether,
which gave 21 as a colourless oil (3 mg, 0.01 mmol, 29%). Rf
0.41 (4 : 1 petroleum ether–EtOAc, UV/PMA); IR (thin film)
mmax/cm−1 1739, 1607, 1412, 1380, 1274, 1233, 1222, 1025; dH
(500 MHz, CDCl3, Me4Si) 7.42 (1H, d, 8.4 Hz, 13-H or 15-H),
7.41 (1H, d, 8.4 Hz, 13-H or 15-H), 7.37–7.33 (2H, m, 12/16-H),
6.85 (1H, dd, 7.6 Hz, 0.9 Hz, 11-H or 17-H), 6.80 (1H, dd, 7.6
Hz, 0.9 Hz, 11-H or 17-H), 6.38 (1H, dd, 5.9 Hz, 2.2 Hz, 3-H),
6.31 (1H, ddd, 5.3 Hz, 2.2 Hz, 1.5 Hz, 6-H, 7-H, 8-H or 9-H),
6.29–6.26 (2H, m, 2-H and 6-H, 7-H, 8-H or 9-H), 6.18–6.14 (2H,
m, 6-H, 7-H, 8-H or 9-H), 6.00 (1H, dd, 2.2 Hz, 1.1 Hz, 4-H),
2.03 (3H, s, 21-H); dC (75 MHz, CDCl3) 170.3 (C, C-20), 148.3 (C,
C-10 or C-18), 148.1 (C, C-10 or C-18), 136.4 (CH, C-3), 135.9
(CH, C-6, C-7, C-8 or C-9), 134.4 (CH, C-2, C-6, C-7, C-8 or C-9),
134.3 (CH, C-2, C-6, C-7, C-8 or C-9), 132.6 (CH, C-6, C-7, C-8
or C-9), 132.2 (CH, C-6, C-7, C-8 or C-9), 127.1 (CH, C-12 and
C-16), 120.4 (CH, C-13 or C-15), 120.3 (CH, C-13 or C-15), 113.9
(C, C-19), 111.6 (C, C-1), 108.8 (CH, C-11 or C-17), 108.7 (CH,
C-11 or C-17), 78.3 (CH, C-4), 72.8 (C, C-5), 21.0 (CH3, C-21);
HRESIMS m/z = 333.1117 [M + H]+ 3.0 ppm (333.1127 calcd for
C21H17O4).
O4 -Acetyl-4,8-dihydroxy-spiro[4.4]nona-2,6-diene-1-one-1,1-
[1,8-dihydroxynaphthalene]-acetal,
19. O-Acetyl-4-hydroxy-
spiro[4.4]nona-2,6-diene-1,8-dione-1,1-[1,8-dihydroxynaphtha-
lene]acetal (18, 2 mg, 0.006 mmol) was dissolved in MeOH (1 mL)
with CeCl3 (anhydrous, 3 mg, 0.012 mmol, 2 eq). The mixture
was cooled in an ice-bath and NaBH4 (0.3 mg, 0.008 mmol, 1.3
eq) was added. The mixture was stirred at 0 ◦C for 1 h, then
NaHCO3(aq) (1 M, 2 mL) was added. The mixture was extracted
with diethyl ether (4 × 2 mL) and the combined organic phases
dried over MgSO4, filtered and the solvent removed in vacuo.
The residue was purified on deacidified silica using a gradient
of 10 to 24% diethyl ether in petroleum ether to obtain 19 as a
colourless oil (0.9 mg, 0.003 mmol, 42%). Rf 0.21 (2 : 1 petroleum
ether–EtOAc, UV/PMA); IR (thin film) mmax/cm−1 3400–3200,
1738, 1606, 1413, 1381, 1226; dH (500 MHz, CDCl3, Me4Si) 7.50
(1H, d, 8.3 Hz, 13-H or 15-H), 7.47 (1H, d, 8.3 Hz, 13-H or 15-H),
7.41 (1H, dd, 8.3 Hz, 7.6 Hz, 12-H or 16-H), 7.40 (1H, dd, 8.3 Hz,
7.6 Hz, 12-H or 16-H), 6.96 (1H, d, 7.6 Hz, 11-H or 17-H), 6.87
(1H, d, 7.6 Hz, 11-H or 17-H), 6.20 (1H, dd, 6.1 Hz, 1.8 Hz, 2-H
or 3-H), 6.12 (1H, d, 5.7 Hz, 6-H), 6.08 (1H, dd, 5.7 Hz, 2.3 Hz,
7-H), 6.05 (1H, dd, 6.1 Hz, 1.8 Hz, 2-H or 3-H), 5.92 (1H, t, 1.8
Hz, 4-H), 4.81 (1H, ddd, 7.1 Hz, 2.6 Hz, 2.3 Hz, 8-H), 2.50 (1H,
dd, 14.7 Hz, 7.1 Hz, 9-H), 2.25 (1H, dd, 14.6 Hz, 2.6 Hz, 9-H),
2.14 (3H, s, 21-H); dC (75 MHz, CDCl3) 170.4 (C-20), 148.3 (C,
C-10 or C-18), 147.8 (C, C-10 or C-18), 137.7 (CH, C-6 or C-7),
137.4 (CH, C-2 or C-3), 134.3 (CH, C-6 or C-7), 134.1 (C, C-14),
131.9 (CH, C-2 or C-3), 127.5 (CH, C-12 or C-16), 127.2 (CH,
C-12 or C-16), 121.0 (CH, C-13 or C-15), 120.6 (CH, C-13 or
C-15), 114.0 (C, C-19), 109.20 (CH, C-11 or C-17), 109.17 (CH,
C-11 or C-17), 109.0 (C, C-1), 78.9 (C, C-4), 75.9 (C, C-8), 67.0
(C, C-5), 35.5 (CH2, C-9), 21.1 (CH3, C-21); HRESIMS m/z =
333.1120 [M − OH]+ 2.1 ppm (333.1127 calcd for C21H17O4).
4,8-Dihydroxy-spiro[4.4]nona-2,6-diene-1-one-1,1-[1,8-dihydro-
xynaphthalene]-acetal, 22 (mixture of diastereoisomers). spiro-
[4.4]Nona-2,7-diene-1,4,6-trione-1,1-[1,8-dihydroxynaphtha-
lene]-acetal (16, 3.2 mg, 0.010 mmol) and CeCl3 (anhydrous, 5.4
mg, 0.022 mmol, 2.1 eq) were dissolved in MeOH (500 lL) and
cooled to 0 ◦C. NaBH4 (0.8 mg, 0.022 mmol, 2.1 eq) was added and
the reaction stirred at 0 ◦C for 1 h. NaHCO3(aq) (1 M, 1 mL) was
added and the reaction extracted with diethyl ether (4 × 1 mL).
The combined organic phases were dried over MgSO4, filtered
and the solvent removed in vacuo. The crude product, obtained
as a colourless oil (22, mixture of isomers, 3.2 mg, 0.010 mmol,
98%), was used directly in the next step. IR (thin film) mmax/cm−1
3400–3200, 1607, 1412, 1381, 1275; dH (500 MHz, CDCl3, Me4Si)
7.55–7.34 (4H, 12/13/15/16-H), 7.0–6.82 (2H, 11/17-H), 6.38–
5.94 (4H, 2/3/7/6-H), 4.98–4.62 (2H, 4/8-H), 2.91–2.63 (1H, 9-
H), 2.32–1.96 (1H, 9-H); HRESIMS m/z = 331.0961 [M + Na]+
4.5 ppm (331.0946 calcd for C19H16O4Na).
O4 -Acetyl-4,8-dihydroxy-spiro[4.4]nona-2,6-diene-1-one-1,1-
[1,8-dihydroxynaphthalene]-acetal, 20 (stereoisomeric mixture).
A mixture of O-acetyl-4-hydroxy-spiro[4.4]nona-2,6-diene-1,8-
dione-1,1-[1,8-dihydroxynaphthalene]-acetal stereoisomers (17
and 18, 12 mg, 0.034 mmol) were dissolved in MeOH (1 mL) with
CeCl3 (anhydrous, 10 mg, 0.041 mmol, 1.2 eq). The mixture was
cooled in an ice-bath and NaBH4 (1.3 mg, 0.034 mmol, 1 eq) was
added. The mixture was stirred at 0 ◦C for 1 h, then NaHCO3(aq) (1
M, 3 mL) was added. The mixture was extracted with diethyl ether
(4 × 3 mL) and the combined organic phases dried over MgSO4,
This journal is
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Org. Biomol. Chem., 2008, 6, 3854–3862 | 3861
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O,O-Diacetyl-4,8-dihydroxy-spiro[4.4]nona-2,6-diene-1-one-1,
1-[1,8-dihydroxynaphthalene]-acetal, 23. 4,8-Dihydroxy-spiro-
[4.4]nona-2,6-diene-1-one-1,1-[1,8-dihydroxynaphthalene]-acetal
(22, 3.2 mg, 0.010 mmol) was dissolved in pyridine (500 lL) and
acetic anhydride was added (200 lL). The reaction was stirred
at room temperature for 16 h, then diethyl ether was added
(2 mL) and the mixture extracted with NaHCO3(aq) (1 M, 3 ×
2 mL). After drying the organic phase over MgSO4, filtration
and removal of solvent in vacuo, the crude product was purified
on deacidified silica using a gradient of 0 to 12% diethyl ether in
petroleum ether, to give 23 as a colourless oil (mixture of isomers,
3.1 mg, 79%). Rf 0.35 (4 : 1 petroleum ether–EtOAc, UV/PMA);
IR (thin film) mmax/cm−1 1735, 1607, 1412, 1372, 1238; dH (500
MHz, CDCl3, Me4Si) 7.49–7.35 (4H, 12/13/15/16-H), 6.95–6.82
(2H, 11/17-H), 6.22–5.72 (6H, 2/3/4/6/7/8-H), 3.15–2.41 (2H,
9-H), 2.17–2.04 (6H, 21/23-H); HRESIMS m/z = 415.1167 [M +
Na]+ 2.2 ppm (415.1158 calcd for C23H20O6Na).
7.69 (1H, d, 8.1 Hz, H12), 7.56 (1H, dd, 8.6 Hz, 7.6 Hz, H16),
7.45 (1H, d, 6.1 Hz, H2), 7.01 (1H, dd, 7.6 Hz, 0.7 Hz, H17), 6.80
(1H, d, 8.1 Hz, H11), 6.47 (1H, d, 6.1 Hz, H3), 6.01 (1H, m, H7
or H8), 5.60 (1H, m, H7 or H8), 2.51 (2H, m, H6/9), 2.17 (2H,
m, H6ꢀ/9ꢀ); dC (125 MHz, observed by 2D NMR, CDCl3) 206.5
(C, C4), 153.7 (CH, C2), 147.8 (C, C18), 147.4 (C, C10), 137.0
(CH, C7 or C8), 136.2 (CH, C3), 133.0 (C, C14), 131.2 (CH, C12),
129.0 (CH, C16), 128.7 (CH, C7 or C8), 120.9 (CH, C15), 114.5
(C, C19), 110.6 (CH, C17), 110.5 (CH, C11), 69.9 (C, C5), 32.5
(CH2, C6 or C9), 29.4 (CH2, C6 or C9), C1/C13 not observed;
HRESIMS m/z = 369.0115 [M + H]+ 3.0 ppm (369.0126 calcd for
C19H1479BrO3).
Acknowledgements
This work was supported by University of Canterbury Com-
monwealth Doctoral Funding for A.C.M. We thank Dr Marie
Squire, Mr Rob Stainthorpe and Ms Raisa Imatdieva for mass
spectrometric analyses, Ms Gill Ellis for biological testing and
Professor Chris Willis for review of the manuscript.
spiro-Nona-2,7-diene-1,4-dione-1,1-[1,8-dihydroxy-4-bromona-
phthalene]-acetal, 24, and spiro-nona-2,6-diene-1,4-dione-1,1-[1,8-
dihydroxy-4-bromo-naphthalene]-acetal,
25. spiro-Nona-2,7-
diene-1,4-dione-1,1-[1,8-dihydroxynaphthalene]-acetal (9, 5 mg,
17 lmol) was dissolved in CCl4 (500 lL), NBS (3.3 mg,
0.019 mmol, 1.1 eq) and AIBN (trace) were added and the
reaction was stirred at room temperature for 20 h. Additional
NBS (1.1 eq) was then added and the reaction stirred for a further
24 hours. After removal of the solvent in vacuo, the crude mixture
was partially purified on deacidified silica using a gradient of 0
to 6% diethyl ether in petroleum ether, giving a crude mixture of
products. 25 (Rt 16.96 min, 0.6 mg, 1.6 lmol, 9%) was purified by
separation on an analytical C18 HPLC column using 70% MeCN
in H2O (isocratic), then 24 (Rt 17.29 min, 0.9 mg, 2.4 lmol,
14%) was separated from an impurity on an analytical C18 HPLC
column using 80% MeOH in H2O (isocratic).
Notes and references
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isolated and characterised.
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Mixture—Rf 0.54–0.63 (4
: 1 petroleum ether–EtOAc,
UV/PMA).
24. IR (thin film) mmax/cm−1 1732, 1609, 1413, 1365, 1268; dH
(500 MHz, CDCl3, Me4Si) 7.81 (1H, dd, 8.6 Hz, 0.7 Hz, H15),
7.70 (1H, d, 8.1 Hz, H12), 7.56 (1H, dd, 8.5 Hz, 7.7 Hz, H16),
7.35 (1H, d, 6.1 Hz, H2), 7.01 (1H, dd, 7.7 Hz, 0.7 Hz, H17),
6.83 (1H, d, 8.1 Hz, H11), 6.41 (1H, d, 6.1 Hz, H3), 5.65 (2H,
br s, H7/H8), 3.18 (2H, m, H6/H9), 2.63 (2H, m, H6ꢀ/H9ꢀ); dC
(125 MHz, observed by 2D NMR, CDCl3) 206.5 (C, C4), 152.9
(CH, C2), 147.6 (C, C18), 147.3 (C, C10), 135.9 (CH, C3), 132.8
(C, C14), 131.1 (CH, C12), 129.1 (CH, C16), 128.2 (CH, C7/C8),
121.0 (CH, C15), 114.3 (C, C19), 114.0 (C, C13), 110.8 (CH, C17),
110.5 (CH, C11), 106.4 (C, C1), 61.4 (C, C5), 38.3 (CH2, C6/C9);
HRESIMS m/z = 369.0131 [M + H]+ 1.4 ppm (369.0126 calcd for
C19H1479BrO3).
17 N. Chidambaram and S. Chandrasekaran, J. Org. Chem., 1987, 52,
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21 E. M. Burgess, H. R. Penton, Jr., E. A. Taylor and W. M. Williams,
Org. Synth., 1977, 56, 40–43.
25. IR (thin film) mmax/cm−1 1729, 1609, 1413, 1365, 1269; dH
(500 MHz, CDCl3, Me4Si) 7.80 (1H, dd, 8.6 Hz, 0.7 Hz, H15),
3862 | Org. Biomol. Chem., 2008, 6, 3854–3862
This journal is
The Royal Society of Chemistry 2008
©