Synthesis of 2,6-aceanthrylenedione, a cyclic vinylog of anthraquinone

Article abstract of DOI:10.1021/jo1003983

Figure presented The first synthesis of 2,6-aceanthrylenedione (6), a cyclic vinylog of anthraquinone and a useful starting material for the synthesis of 1-phenylaceanthrylene-2,6-diones such as 7, 8, and 9, is described. (10-Oxo-10H-anthracen-9-ylidene) acetyl chloride (5) cyclizes intramolecularly at room temperature in the presence of AlCl₃ to give 6. We found that 6 is a cytotoxic compound that inhibits tubulin polymerization.

Full text of DOI:10.1021/jo1003983

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aromatic compounds in a Friedel-Crafts acylation reaction
Synthesis of 2,6-Aceanthrylenedione, a Cyclic
Vinylog of Anthraquinone
in the presence of 1 equiv of AlCl3 at 0 °C.3
‡
†
Helge Prinz,*,† Konrad J. Bohm, and Klaus Muller
€
€
†Institute of Pharmaceutical and Medicinal Chemistry,
Westphalian Wilhelms-University, Hittorfstrasse 58-62,
D-48149 Mu€nster, Germany, and Leibniz Institute for Age
‡
Research-Fritz Lipmann Institute (FLI), Beutenbergstrasse
11, D-07745 Jena, Germany
prinzh@uni-muenster.de
Received March 3, 2010
FIGURE 1. Anthraquinone (1), 10-(2-oxo-2-phenylethylidene)-10H-
anthracen-9-ones 2a,b, and 1,2-aceanthrylenedione (3).
Now, we found that 5 can be readily cyclized at room
temperature and in the presence of 2 equiv of AlCl3 to afford
2,6-aceanthrylenedione 6 in working quantities (Scheme 1).
To our knowledge, this is the first synthesis of that parti-
cular cyclic vinylog of anthraquinone. Recently, Chunyan
et al.4 have reported the preparation of 1,2-aceanthrylene-
dione 3 through acylation of anthracene with oxalyl chlor-
ide catalyzed by anhydrous AlCl3. It has to be pointed out
that 6 was not formed during the synthesis of 10-(2-oxo-2-
phenylethylidene)-10H-anthracen-9-ones represented by
2a and 2b at 0 °C. Stimulated by the synthesis of 6, we
studied the acylation reaction of reactive arenes such as
anisole, veratrole, and 1,2,3-trimethoxybenzene by 5 at
room temperature. Interestingly, when using 5 as a starting
material in the presence of 3 equiv of AlCl3, we isolated 7, 8,
and 9 in each case as deep red products. Using veratrole as a
starting material, we clearly assigned the product to the
1-(3,4-dimethoxyphenyl)aceanthrylene-2,6-dione (8), being
deficient of one aromatic and one vinyl H atom in the
proton NMR, as compared with the 10-[2-(3,4-dimetho-
xyphenyl)-2-oxoethylidene]-10H-anthracen-9-one3 2b. In
the same way way, we obtained 7 and 9 from the reac-
tion of 6 with anisole and 1,2,3-trimethoxybenzene, res-
pectively. In the light of these findings, we hypothesized
that the formation of such phenylaceanthrylene-2,6-diones
could possibly proceed via 6 as an intermediate step.
Indeed, we found that 6 provides access to phenylacean-
thrylene-2,6-diones 7, 8, and 9 after prolonged reaction
times (24 h) in the presence of 3 equiv of AlCl3, as docu-
mented by comparison with the authentic samples prepared
by Friedel-Crafts acylation via 5. Confirmation of the
The first synthesis of 2,6-aceanthrylenedione (6), a cyclic
vinylog of anthraquinone and a useful starting material
for the synthesis of 1-phenylaceanthrylene-2,6-diones
such as 7, 8, and 9, is described. (10-Oxo-10H-anthracen-
9-ylidene) acetyl chloride (5) cyclizes intramolecularly at
room temperature in the presence of AlCl3 to give 6. We
found that 6 is a cytotoxic compound that inhibits tubulin
polymerization.
Anthracenediones constitute an important group of natu-
rally occurring pigments that are widely distributed in nat-
ure. Substituted anthraquinones and polycyclic quinones
have been reported for various uses, including cancer
treatment.1 Moreover, 9,10-anthraquinone (1, Figure 1) is
the parent compound for a large palette of anthraquinone
dyes and polycyclic quinones. Despite many attempts utiliz-
ing cyclodehydration of 1-substituted anthraquinones,2 the
2,6-aceanthrylenedione (6), a cyclic vinylog of the anthra-
quinone, has never been prepared. Recently, we described a
series of 10-(2-oxo-2-phenylethylidene)-10H-anthracen-9-ones
as potent inhibitors of tubulin polymerization, with 2a
(Figure 1) being the most active analogue.3 These compounds
are characterized as possessing an enone moiety between
the anthracenone and the terminal aromatic ring.3 To obtain
2a and related compounds the (10-oxo-10H-anthracen-9-
ylidene) acetyl chloride3 (5, Scheme 1) was synthesized from
commercially available 10H-anthracen-9-one 4 via the inter-
mediate carboxylic acid followed by reaction with suitable
1
substitution pattern was based on H NMR spectral ana-
lysis data. The crystal structure of 1-phenylaceanthrylene-
2,6-dione (10, Figure 1) has recently been published,5 with
the aceanthrylene-2,6-dione unit being essentially planar.
However, 1-phenylaceanthrylene-2,6-dione (10) cannot be
obtained easily, utilizing a photoinduced reaction between
anthraquinone and 1-trimethylsilyl-2-phenylacetylene.5 Our
(1) Thomson, R. H. Naturally Occurring Quinones, 2nd ed.; Academic
Press: New York, 1971.
(2) Klingsberg, E.; Lewis, C. E. J. Org. Chem. 1975, 40, 366.
(4) Chunyan, Z.; Min, C.; Yan, Z.; Xinhua, Y.; Hua, L. Mater. Sci. Forum
2007, 561-565, 683.
(5) Li, Z.; Fun, H.-K.; Chantrapromma, S.; Xu, J.-H. Acta Crystallogr.
2007, E63, o2499.
€
€
(3) Prinz, H.; Schmidt, P.; Bohm, K. J.; Baasner, S.; Muller, K.; Unger,
€
E.; Gerlach, M.; Gunther, E. G. J. Med. Chem. 2009, 52, 1284.
DOI: 10.1021/jo1003983 Published on Web 05/11/2010
r
J. Org. Chem. 2010, 75, 3867–3870 3867
2010 American Chemical Society

Prinz et al.
JOCNote
SCHEME 1. Preparation of 2,6-Aceanthrylenedione (6) and
Phenylaceanthrylene-2,6-diones 7, 8, and 9a
aReagents and conditions: (a) OHC-COOH H2O, ethanol/piperidine,
3
90 °C, N2; (b) SOCl2, CH2Cl2, reflux, 2 h; (c) 1,2-DCE, 2 equiv AlCl3, rt,
5 h; (d) methoxy-, 1,2-, or 1,2,3-trimethoxybenzene, 1,2-DCE, 3 equiv
AlCl3, rt, 4-5 h; (e) methoxy-, 1,2-dimethoxy-, or 1,2,3-trimethoxy-
benzene, 1,2-DCE, 3 equiv AlCl3, rt, 24 h; (f) methoxy- or 1,2-dimetho-
xybenzene 1,2-DCE, 1 equiv AlCl3, 0 °C, 4-5 h.
FIGURE 2. Inhibition of in vitro polymerization of tubulin (in
total 1.2 mg/mL protein; ∼80-90% tubulin plus ∼10-20% micro-
tubule-associated proteins) at 37 °C by various concentrations of 6.
The steady-state tubulin assembly level in the absence of inhibitor
was set 100%. (A) IC50 value (IC50=6.7 ( 1.4 μM), representing the
drug concentration for 50% inhibition, was determined by sigmoi-
dal fitting of the plot of the steady-state levels of tubulin polymer-
ization (taken at 45 min) in dependence on the drug concentration
and represents the concentration for 50% inhibition of the max-
imum tubulin polymerization level. (B) IC50 value (IC50 =5.3 (
1.2 μM), in the presence of BSA (1.2 mg/mL).
SCHEME 2. Proposed Reaction Mechanism of the Formation
of Compounds 6, 7, 8, and 9
the nucleophilic attack of the arene toward the acyl group,
catalyzed by the Lewis acid AlCl3. The formation of 7, 8, and
9 from 6 can possibly be explained through the alkylation of
the arene by an intermediate carbocation in the presence of
AlCl3.
Because of the structural similarity of 6 to the antimitotic
compounds recently described by us,3,8 we evaluated 6 for
antiproliferative activity against the human chronic myelo-
genous leukemia cell line K562, which is widely used for
testing of potential antitumor compounds.
Cell proliferation was determined directly by counting the
cells with a hemocytometer after 48 h of treatment. Com-
pound 6 displayed strong antiproliferative activity with an
IC50 value of 1.0 μM as compared to anthraquinone 1 (IC50
K562>100 μM). To investigate whether the antiproliferative
activity of 6 was related to an interaction with tubulin, the
compound was assayed for inhibition of tubulin polymeriz-
ation (ITP). If an inhibitor binds to or interferes with tubulin,
the assembly steady-state level is decreased, as demonstrated
for 6 (Figure 2A). Our results showed that 6 is a mode-
rate inhibitor of tubulin polymerization (ITP; IC50=6.7 (
1.4 μM, Figure 2A), being 5-fold less active than the reference
compound colchicine (ITP; IC50=1.4 μM). Specific binding
was confirmed by performing the tubulin polymerization
assay in the presence of bovine serum albumin (BSA)9
(Figure 2B), which gave slightly improved but comparable
findings suggest that 6 is obviously able to alkylate the arene
in the presence of AlCl3. In a mechanistic view, the formation
of 6, 7, 8, and 9 could be explained as depicted in Scheme 2.
The most plausible explanation for the formation of 6 is a
Friedel-Craftsintramolecularacylationreaction,6,7 including
(6) Holden, M. S.; Crouch, R. D.; Barker, K. A. J. Chem. Educ. 2005,
82, 934.
(7) Lan, K.; Fen, S.; Shan, Z. Aust. J. Chem. 2007, 60, 80.
(8) Prinz, H.; Ishii, Y.; Hirano, T.; Stoiber, T.; Camacho Gomez, J. A.;
€
Schmidt, P.; Dussmann, H.; Burger, A. M.; Prehn, J. H.; Gunther, E. G.;
Unger, E.; Umezawa, K. J. Med. Chem. 2003, 46, 3382.
€
3868 J. Org. Chem. Vol. 75, No. 11, 2010

Prinz et al.
JOCNote
data (ITP; IC50=5.3 ( 1.2 μM, Figure 1B). Therefore we
conclude that inhibition of tubulin polymerization is a plau-
sible explanation for the antiproliferative potency of 6.
Among the 1-phenylaceanthrylene-2,6-diones, only 9 also
inhibited tubulin polymerization (9, ITP; IC50 = 6.6 (
0.7 μM; 7, 8 ITP; IC50>10 μM) and had antiproliferative
potencies comparable to 6 (9, IC50 K562 1.7 μM; 7, 8, IC50
K562>80 μM).
In conclusion we have presented the first protocol for the
synthesis of 2,6-aceanthrylenedione, which was demon-
strated to be a biologically active compound revealing a re-
markably increased antiproliferative potency as compared
with simple anthraquinone. This property is related to the
inhibition of tubulin polymerization. In addition, we showed
that the synthesis of 1-phenylaceanthrylene-2,6-diones could
proceed via the 2,6-aceanthrylenedione. Given the impor-
tance of anthraquinones and related quinones for anticancer
chemotherapy, we hope that the novel 2,6-aceanthrylene-
dione, which can be regarded as a cyclic vinylog of anthra-
quinone, might be of interest for the development of novel
anticancer drugs. Further studies around this interesting
compound are in progress and will be reported in due course.
1-(3,4-Dimethoxyphenyl)aceanthrylene-2,6-dione (8). Method
A. Anhydrous AlCl3 (3.20 g, 24.00 mmol) was added in one
portion to a suspension of crude 5 (2.14 g, 8 mmol) in DCE
(30 mL). Then, a solution of 1,2-dimethoxybenzene (3.22 g,
24 mmol) in 5 mL of DCE was added dropwise. After the dark
red solution stirred for 4 h at rt (TLC control, CH2Cl2), the
reaction mixture was poured into water (300 mL)/6 N HCl
(50 mL), stirred for 10 min, and then extracted with CH2Cl2 (4 ꢀ
50 mL). The combined organic layers were washed with water,
dried (Na2SO4), and concentrated. Purification by silica gel
chromatography (CH2Cl2) afforded 8 as a red powder (0.45 g,
16%): mp 217 °C; FTIR 1711, 1657; 1H NMR (CDCl3, 400 MHz,
300 K) δ 8.54-8.52 (m, 1H), 8.21-8.19 (m, 1H), 8.18-8.16
(m, 1H), 7.84-7.82 (m, 1H), 7.69-7.65 (m, 1H), 7.58-7.52
(m, 2H), 7.19-7.16 (m, 1H), 7.07 (d, 1H, J=1.57 Hz), 7.05
(d, 1H, J = 8.21 Hz), 3.99 (s, 3H), 3.88 (s, 3H); 13C NMR
(CDCl3, 101 MHz) δ 195.4, 181.8, 150.4, 149.3, 147.8, 140.5,
136.0, 133.8, 131.4, 132.8, 131.8, 129.8, 129.6, 129.1, 129.0,
128.0, 126.6, 126.1, 123.6, 123.3, 112.9, 111.7, 56.3, 56.2; MS
m/z 368 (100). Anal. (C24H16O4, 368.1): calcd C, 78.25; H, 4.38;
found C, 78.25; H, 4.16. Purity (HPLC): 97.51%.
Method B. Anhydrous AlCl3 (0.40 g, 3 mmol) was added
in one portion to a suspension of 6 (0.23 g, 1 mmol) and
1,2-dimethoxybenzene (0.14 g, 1 mmol) in DCE (15 mL). After
the dark red solution stirred for 24 h at rt (TLC control,
CH2Cl2), the reaction mixture was poured into water (100 mL)/
6 N HCl (50 mL), stirred for 10 min, and then extracted with CH2Cl2
(4 ꢀ 50 mL). The combined organic layers were washed with water,
dried (Na2SO4,) and concentrated. Purification by silica gel chro-
matography (CH2Cl2) afforded 8 as a red powder (97 mg, 26%).
1-(2,3,4-Trimethoxyphenyl)aceanthrylene-2,6-dione (9). Method
A. The title compound was prepared from 5 (2.14 g, 8.00 mmol),
1,2,3-trimethoxybenzene (4.03 g, 24.00 mmol), and AlCl3 (3.20 g,
24.00 mmol) in a similar manner as described for the prepara-
tion of 8 (method A). Purification by silica gel chromatography
(CH2Cl2) afforded 9 as a red powder (0.44 g, 14%): mp 193 °C;
FTIR 1711, 1658; 1H NMR (CDCl3, 400 MHz, 300 K) δ 8.54
(dd, 1H, J=8.02 Hz, J=1.17 Hz), 8.21 (dd, 1H, J=8.01 Hz, J=
0.78 Hz), 7.86-7.83 (m, 2H), 7.70-7.66 (m, 1H), 7.60-7.53
(m, 2H), 7.05 (d, 1H, J=8.60 Hz, 6.84 (d, 1H, J=8.59 Hz), 3.99
(s, 3H), 3.97 (s, 3H), 3.79 (s, 3H); 13C NMR (CDCl3, 101 MHz)
δ 195.3, 182.0, 155.3, 152.7, 147.8, 142.8, 142.1, 133.5, 133.0,
132.9, 131.7, 131.5, 129.8, 129.4, 129.3, 128.8, 128.4, 126.6,
126.1, 125.6, 118.1, 107.9, 61.7, 61.3, 56.4; MS m/z 398 (100).
Anal. (C25H18O5, 398.12): calcd C, 75.37; H, 4.55; found C,
75.30; H, 4.47. Purity (HPLC): 97.8%.
Experimental Section
(10-Oxo-10H-anthracen-9-ylidene) Acetyl Chloride (5).3
2,6-Aceanthrylenedione (6). Anhydrous AlCl3 (2.15 g, 16 mmol)
was added in one portion to a suspension of crude 5 (2.14 g, 8
mmol) in DCE (30 mL), and the solution was stirred at rt for 5 h.
Then, the reaction mixture was poured into a mixture of water
(150 mL)/6N HCl (50 mL), stirred for 10 min, and then extracted
with CH2Cl2 (4 ꢀ 50 mL). The combined organic layers were
washed with water, dried (Na2SO4), and concentrated. There-
after, the residue was purified by silica gel chromatography
(CH2Cl2) to afford 5 as an orange powder (0.79 g, 43%, not
1
optimized): mp 225 °C; FTIR 1704, 1657; H NMR (CDCl3,
400 MHz, 300 K) δ 8.51-8.50 (m, 1H), 8.14 (dd, 1H, J=8.22 Hz,
J=0.78 Hz), 8.06-8.04 (m, 1H), 7.81-7.73 (m, 3H), 7.61 (t, 1H,
J=7.43 Hz), 6.59 (s, 1H); 13CNMR (CDCl3, 101 MHz) δ 195.9,
181.8, 149.6, 147.1, 133.4, 132.9, 132.7, 130.7, 130.3, 130.1,
129.1, 129.0, 127.6, 126.6, 126.1,121.2; MS m/z 232 (100). Anal.
(C16H8O2, 232.05): calcd C, 82.75; H, 3.47; found C, 82.42;
H, 3.31.
1-(4-Methoxyphenyl)aceanthrylene-2,6-dione (7). Method A.
The title compound was prepared from 5 (2.14 g, 8.00 mmol)
and methoxybenzene (2.59 g, 24.00 mmol) in a similar manner as
described for the preparation of 8. Purification by silica gel
chromatography (CH2Cl2) afforded 7 as a red-orange powder
(0.38 g, 11%): mp 209 °C; FTIR 1708, 1661; 1H NMR (CDCl3,
400 MHz, 300 K) δ 8.46 (dd, 1H, J=7.83 Hz, J=1.56 Hz), 8.13
(dd, 1H, J = 7.83 Hz, J = 0.78 Hz), 8.09-8.08 (m, 1H), 7.76
(dd, 1H, J=7.04 Hz, J=0.78 Hz), 7.61-7.57 (m, 1H), 7.50-7.43
(m, 4H), 7.00 (d, 2H, J=9.0 Hz), 3.85 (s, 3H); 13CNMR (CDCl3,
101 MHz) δ 195.5, 181.8, 160.8, 147.8, 140.2, 135.9, 133.0, 132.8,
131.7, 131.66 (2 ꢀ C), 131.4, 129.7, 129.5, 129.05, 129.0, 127.8,
126.6, 126.0, 123.3, 114.6 (2 ꢀ C), 55.6; MS m/z 338 (100); high
resolution ESIMS (C23H14O3 þ Na): calcd 361.08406, found
361.08368.
Method B. The title compound was prepared from 6 (0.23 g,
1 mmol), 1,2,3-trimethoxybenzene (0.17 g, 1 mmol), and anhy-
drous AlCl3 (0.40 g, 3 mmol) in DCE (15 mL) in a similar
manner as described for the preparation of 8. Purification by
silica gel chromatography (CH2Cl2) afforded 9 as a red powder
(0.06 g, 15%): mp 192 °C.
Assay of Cell Growth. K562 cells were plated at 2 ꢀ 105 cells/
mL in 24-well dishes (Costar, Cambridge, MA). Untreated
control wells were assigned a value of 100%. Drugs were made
soluble in DMSO/methanol 1:1, and control wells received
equal volumes (0.5%) of vehicle alone. Drugs were dissolved
in methanol/DMSO 1:1. To each well was added 5 μL of drug,
and the final volume in the well was 500 μL. Cell numbers were
counted with a Neubauer counting chamber (improved, double
grid) after treatment with chemicals for 48 h. Each assay condi-
tion was prepared in triplicate, and the experiments were carried
out three times. IC50 values were obtained by nonlinear regres-
sion (GraphPad Prism) and represent the concentration at which
cell growth was inhibited by 50%. The adjusted cell number
was calculated as a percentage of the control, which was the
number of cells in wells without the addition of compound.
Method B. The title compound was prepared from 6 (0.23 g,
1 mmol), methoxybenzene (0.11 g, 1 mmol), and anhydrous
AlCl3 (0.40 g, 3 mmol) in DCE (15 mL) according to the pre-
paration of 8. Purification by silica gel chromatography
(CH2Cl2) afforded 7 as a red-orange powder (74 mg, 22%).
ꢀ
(9) Morais, S.; OMalley, S.; Chen, W.; Mulchandani, A. Anal. Biochem.
2003, 321, 44.
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Prinz et al.
JOCNote
Isolation of MTP and in Vitro Microtubule Polymerization
Assay. Microtubule protein (MTP) consisting of 80-90% tu-
bulin and 10-20% microtubule associated proteins was isolated
from porcine brain by two cycles of temperature-dependent
disassembly (0 °C)/reassembly (37 °C) according to the method
described by Shelanski et al.,10 with modifications described by
Vater et al.11 Throughout the preparation, a buffer containing
20 mM PIPES (1,4-piperazine diethane sulfonic acid, pH 6.8),
80 mM NaCl, 0.5 mM MgCl2, 1 mM EGTA (ethylene bis
(oxyethylenenitrilo) tetraacetic acid), and 1 mM DTT was used.
The protein concentration was determined by the Lowry pro-
cedure using bovine serum albumin as a standard. Antitubulin
activity was assayed by recording the turbidity increase accom-
panying tubulin polymerization in glass cuvettes. To start tubulin
polymerization, the stock MTP solutions were diluted with ice-cold
preparation buffer to 1.2 mg/mL, GTP (guanosin-50-triphosphate)
was added to 0.6 mM (final concentration), and the samples
were transferred into a spectrophotometer (Cary 4E, Varian
Inc.) equipped with a temperature-controlled multichannel
cuvette holder. Tubulin polymerization was initiated by shift-
ing the temperature to 37 °C and turbidity was recorded over
45 min at 360 nm. The tubulin effectors were added from stock
solutions in DMSO. The final DMSO concentration was 1%.
Control measurements were made with DMSO only. To quan-
tify drug activity, the turbidity signal after 45 min (plateau
level, representing the assembly/disassembly steady state) was
compared with that of the control samples. The IC50 value is
defined as the drug concentration that causes a 50% inhibition
in relation to the assembly level without the drug.
€
Acknowledgment. We wish to thank Tim Schrader, Marcel
Overmann, Angelika Zinner, and Marina Wollmann for
excellent technical assistance.
Supporting Information Available: General experimental
methods, copies of spectra, and compensation of cpd 6-caused
inhibition of tubulin polymerization by paclitaxel. This material
is available free of charge via the Internet at http://pubs.acs.org.
(10) Shelanski, M. L.; Gaskin, F.; Cantor, C. R. Proc. Natl. Acad. Sci.
U.S.A. 1973, 70, 765.
€
(11) Vater, W.; Bohm, K. J.; Unger, E. Acta Histochem. Suppl. 1986,
33, 123.
3870 J. Org. Chem. Vol. 75, No. 11, 2010