Synthesis and antitumor activity of benzils related to combretastatin A-4

Article abstract of DOI:10.1016/j.bmcl.2008.04.053

A series of benzil derivatives related to combretastatin A-4 (CA-4) have been synthesized by oxidation of diarylalkynes promoted by PdI₂ in DMSO. Using this new protocol, 14 benzils were prepared in good to excellent yields and their biological

Full text of DOI:10.1016/j.bmcl.2008.04.053

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 3266–3271
Synthesis and antitumor activity of benzils related
to combretastatin A-4
a
a
a
a
b
´
´
Celine Mousset, Anne Giraud, Olivier Provot, Abdallah Hamze, Jeroˆme Bignon,
b
b
b
a
a,
*
ˆ
Jian-Miao Liu, Sylviane Thoret, Joe¨lle Dubois, Jean-Daniel Brion and Mouad Alami
aUniv Paris-Sud, CNRS, BioCIS-UMR 8076, Laboratoire de Chimie The´rapeutique, Faculte´ de Pharmacie,
ˆ
rue J.B. Cle´ment, F-92296 Chatenay-Malabry, France
bInstitut de Chimie des Substances Naturelles, UPR 2301, CNRS, avenue de la Terrasse, F-91198 Gif sur Yvette, France
Received 17 March 2008; revised 18 April 2008; accepted 19 April 2008
Available online 25 April 2008
Abstract—A series of benzil derivatives related to combretastatin A-4 (CA-4) have been synthesized by oxidation of diarylalkynes
promoted by PdI2 in DMSO. Using this new protocol, 14 benzils were prepared in good to excellent yields and their biological activ-
ity has been delineated. Several benzils exhibited excellent antiproliferative activity: for example, 4j and 4k bearing the greatest
resemblance to CA-4 and AVE-8062, respectively, were found to inhibit cell growth at the nanomolar level (20–50 nM) on four
human tumor cell lines. Flow cytometric analysis indicates that these compounds act as antimitotics and arrest the cell cycle in
G2/M phase. A cell-based assay indicated that compounds 4j and 4k displayed a similar inhibition of tubulin assembly with an
IC50 value similar to CA-4. These results clearly demonstrated that the Z-double bond of CA-4 can be replaced by a 1,2-diketone
unit without significant loss of cytotoxicity and inhibition of tubulin assembly potency.
ꢀ 2008 Elsevier Ltd. All rights reserved.
Microtubules are dynamic structures that play an essen-
tial role in cellular functions including motility, division,
shape maintenance, and intracellular transport.1 The
discovery of natural and synthetic substances able of
interfering with the assembly or disassembly of microtu-
bules has attracted much attention because microtubules
are recognized as an attractive pharmacological target
for anticancer drug discovery.2 Recently, it was demon-
strated that some tubulin-binding agents also target the
vascular system of tumors, inducing morphological
changes in the endothelial cells of the tumor blood ves-
sels so as to occlude flow.3
ble prodrug, as well as AC-7739 (1c) and its amino acid
derivative 1d (AVE-8062)7 have been demonstrated to
cause reversible vascular shutdown in established tu-
mors in vivo, consistent with an anti-vascular mecha-
nism of action.8 Currently, CA4-P (ZybrestatTM), either
as a single agent or in combination therapy, is world-
wide undergoing several advanced clinical trials for the
treatment of age-related macular degeneration
(AMD)9 or anaplastic thyroid cancer.10
The structural simplicity of CA-4 combined with its
excellent antitumoral and antivascular activities encour-
aged the scientific community to synthesize numerous
analogs.11 From these structure–activity relationship
(SAR) investigations, it has been established that the
cis-orientation of the two aryl rings is crucial for the
activity of 1 as well as the trimethoxyaryl unit, whereas,
the hydroxyl group on the 30-position is not essential.12
However, during the storage and administration cis-
combretastatin analogs tend to isomerize to trans-forms
which show dramatic reduction in both anti-tubulin and
cytotoxic activities. Therefore, many studies have fo-
cused on the design of analogs by altering the linking
group and the B-ring of 1 to provide better biological
activities. Among these, analogs phenstatin13 (2), and
chalcone14 3 (Fig. 1) where the olefinic bridge of CA-4
Combretastatin A-4 (CA-4, 1a), a natural Z-stilbene iso-
lated from the South African willow Combretum caff-
rum,4 has been found to strongly inhibit the tubulin
assembly by binding to the colchicine site5,6 and to be
a cytotoxic agent6 against a wide variety of cell lines,
including multidrug-resistant lines. Additionally, the
disodium phosphate of CA-4 (CA-4P, 1b), a water-solu-
Keywords: Benzils; Oxidation; Alkynes; Combretastatin; Antitumor;
Antiproliferative; Antimitotic; Inhibition of tubulin assembly;
Antiangiogenic.
*
Corresponding author. Tel.: +33 146845887; fax: +33 146845827;
e-mail: mouad.alami@u-psud.fr
0960-894X/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.04.053

C. Mousset et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3266–3271
3267
Table 1. Oxidation of diarylalkynes 5 to benzil derivatives 4 with the
PdI2-DMSO couple
O
3'
MeO
MeO
R
MeO
MeO
OH
A
B
MeO
MeO
MeO
Entry Compoundsa Ar
O
Ar
OMe
MeO
MeO
OMe
PdI2 (2 mol%)
OMe
Ar
OMe
O
DMSO, 140 °C
1a R = OH (CA-4)
2 (Phenstatin)
OMe
5
4
1b R = OP(O)(ONa)2 (CA-4P)
1c R = NH2 (AC-7739)
1d R = NH-Ser-H (AVE-8062)
Time (h) Yieldb (%)
1
2
3
4
5
4a
4b
4c
4d
4e
4
12
2
62
O
O
Ar
MeO
MeO
OH
OMe
Chalcone, 3
MeO
MeO
O
85
NC
OMe
OMe
Benzils, 4
100
93
CN
Figure 1. Representative tubulin binding agents and general structure
of the synthesized benzils 4.
6
OMe
was replaced by a carbonyl group or an enone function,
respectively, were identified as potent inhibitors of tubu-
lin assembly and also displayed cytotoxic activities at a
nanomolar level (IC50 = 0.2–30 nM). In an ongoing
medicinal chemistry program towards the synthesis of
CA-4 analogs,15 we also were interested in exploring
the alteration of the linker and the B-ring. In the present
study, introduction of two carbonyl functions between
the two aromatic rings leading to benzil derivatives 4
was expected to maintain on one hand the appropriate
two carbon-distance between the aromatic rings and
on the other hand, the crucial sp2 hybridization of the
two carbon linkers (Fig. 1). Furthermore, we envisioned
that variation of the substituents on the B-ring would
provide significant SAR informations about these CA-
4 analogs. The potencies of newly synthesized benzils 4
were evaluated for their capacity to inhibit cancer cellu-
lar growth and, to act as potential antimitotic agents as
well as for potential apoptosis induction.
OMe
OMe
14
67
OAc
OMe
6
4f
3
85
NHAc
7
8
4g
4h
4i
5
4
83
84
82
86
OMe
F
OMe
OH
OH
9
6
10
4j
16
OMe
NH2
OMe
The oxidation of substituted diarylalkynes, readily
accessible via Sonogashira–Linstrumelle (S–L) coupling,
constitutes one of the most versatile processes in organic
chemistry for the synthesis of benzils. We recently re-
ported the oxidation of functionalized diarylalkynes
with DMSO in the presence of a catalytic amount of
the environmentally friendly FeBr3 catalyst.16 However,
during this study, we observed that substrates contain-
ing a heteroaryl nucleus or having a free phenolic or ani-
line function as well as a nitrile group were resistant to
DMSO-oxidation. Herein, we described the use of
DMSO–PdI2 (2 mol %) couple as a more reliable and
chemoselective procedure17 to provide functionalized
benzils 4 from alkynes 5. The synthesis of the alkyne
precursors 5 was achieved by S–L18 cross-coupling and
Table 1 summarized the results of 5 oxidation with the
PdI2–DMSO couple. Accordingly, this procedure conve-
niently provided a small library of benzil compounds
possessing various substituted B-rings even those having
a free OH group (entries 9 and 10; 4i, 82%; 4j 86%).
However, with substrate 5k having a free amino group
the use of PdI2 was ineffective whereas, PdCl2 (10 mol
%) promotes smoothly the oxidation reaction providing
11
4k
5
31c
12
13
14
4l
8
7
68
70
93
4m
4n
N
N
94
a All compounds 419 were unambiguously characterized by spectro-
scopic (IR, 1H and 13C NMR) techniques.
b Isolated yield.
c PdCl2 (10 mol %) was used instead of PdI2.
4k but in low yield (31%, entry 11). This problem could
be easily circumvented by hydrolyzing the acetamido
derivative 4g in alkaline media leading to aniline 4k in
a satisfactory 78% yield. Finally, under these conditions,

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C. Mousset et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3266–3271
alkynes 4m and 4n bearing a nitrogen-containing hetero-
cycle, as B-rings, were successfully transformed into
their corresponding benzils (entries 13 and 14) with
good yields.
lated only for compounds inhibiting tubulin assembly
by more than 50% at 1.3 · 10ꢁ5 M. The tubulin assem-
bly assay was realized according to a slightly modified
´
compound.
Guenard’s protocol21 using CA-4 as reference
In vitro antiproliferative activity of the synthesized 1,2-
diketones 4 was first determined against the human co-
lon carcinoma cell line (HCT116) using CA-4 as refer-
ence15b compound, and the results of this study are
summarized in Table 2. The diketone 4j bearing the
greatest resemblance to combretastatin A-4 displays a
high activity at the nanomolar level (35 nM). This result
is very useful and clearly indicates that introduction of a
1,2-dicarbonyl unit between the two aromatic rings
maintains good to excellent antiproliferative properties.
Interestingly, the corresponding acetate 4f and com-
pound 4k related to AVE-8062 have been showed to
possess similar interesting antiproliferative activities,
indicating that the amino and hydroxyl groups are bio-
equivalent at the C-3 position of these analogs. By com-
parison, compounds 4d, 4e and 4g possessing only a
methoxy, a dimethoxy or an acetamido substituent re-
tained much of the bioactivity. These results indicate
that those 1,2 diketones shared similar SAR with com-
bretastatins reported previously.20
Compounds 4j and 4k, the most closely resembling CA-
4 and AVE-8062 in structure, respectively, displayed po-
tent antimitotic activities (entries 10 and 11; 1.5 and
5.0 lM, respectively). Compound 4d, lacking the 3-OH
residue, showed a slight loss of activity compared to 4j
and 4k as inhibitor of tubulin assembly. Similarly, one
can note that the substitution of the C-3 hydroxy group
with a methoxy group, to give 4e, had a modest effect on
activity as compared to CA-4 (1.0 lM). Unfortunately,
acetate 4f which exhibited a significant cytotoxicity
against the studied cells line (Tables 2 and 3) was not
effective as inhibitor of tubulin assembly. It can be as-
sumed that the acetoxy group is hydrolyzed by esterases
in cell which cannot happen in the tubulin assay. The
lack of activity displayed by the other benzils 4 suggests
that modifications of the B-ring disrupt the ligand–pro-
tein binding. These variations should prevent the two
vicinally related aryl units from adopting the necessary
conformation for binding at the colchicine site on
tubulin.
Compounds 4f, 4j and 4k that displayed the better cyto-
toxicity against HCT116 were next evaluated against
three different cancer cell lines of diverse origins. The
IC50 (nM) values obtained with selected cell lines are
summarized in Table 3. Results from the cytotoxicity
study provide evidence that benzil derivatives 4f, 4j
and 4k are good structural analogs of CA-4. It is note-
worthy that all of these compounds retained strong
cytotoxic activity (about 30 nM) against the tested cell
lines.
The effect of selected compounds 4j and 4k on the cell
cycle of HCT116 and H1299 cell lines was then investi-
gated by flow cytometry at various concentrations. As
shown in Table 5, after 24 h of treatment, a net progres-
sion in the number of HCT116 cells arrested at the G2/
M growth stage was observed with increasing concentra-
tion of 4j and 4k. A similar trend was observed in H1299
cells. Thus, treatment of H1299 cells with 50 nM of 4j
for 24 h led to 27.7% of cells arrested at the G2/M stage,
while, at 10 nM only 11.4% were in this stage.
All benzil derivatives 4 prepared above were next evalu-
ated for their ability to inhibit tubulin assembly (Table
4). All samples were dissolved in DMSO, incubated at
37 ꢁC for 10 min and at 0 ꢁC for 5 min before evaluation
of the tubulin assembly rate. Compounds 4 were tested
at ꢀ1.3 · 10ꢁ4 and 1.3 · 10ꢁ5 M. The IC50 was calcu-
It should be noted that in all cells treated with 4j or 4k
for 24 h, a sub-diploid DNA content was observed (data
not shown) indicating that cells are undergoing apopto-
sis probably as a result of the cell cycle being arrested in
the G2/M phase.
Table 2. Cytotoxicities of benzils4 against human colon carcinoma cell line (HCT116)
Compound
a
IC50 (nM)
4a
3000
4b
NAb
4c
NA
4d
300
4e
300
4f
40
4g
350
4h
700
Compound
a
IC50 (nM)
4i
2000
4j
35
4k
38
4l
3000
4m
NA
4n
NA
CA-4
1.8
a A sample’s concentration which produces a 50% reduction cell growth. Each drug concentration was tested in triplicate.
b Non-active.
Table 3. Cytotoxicities of 4f, 4j and 4k against different human cancer cell lines
a
Compound IC50 (nM)
Cell line
4f
4j
4k
CA-4
Human colon carcinoma (HCT116)
Chronic mylogenous leukemia (K562)
Non-small lung human carcinoma (H1299)
Human breast cancer (MDA-MB231)
40
25
30
40
30
25
30
40
38
20
50
30
1.8
3.6
5.0
3.0
a A sample’s concentration which produces a 50% reduction cell growth. Each drug concentration was tested in triplicate.

C. Mousset et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3266–3271
3269
Table 4. Effects on tubulin assembly of benzils 4
Entry Compounds % Inhibition % Inhibition
at 1.3 · 10ꢁ4 M at 1.3 · 10ꢁ5 M (lM)
pounds 4j and 4k, then caspases 3 and 7 activities were
evaluated using the standard caspase cleavage assays
(Fig. 2). It was observed after 24 h of treatment that 4j
and 4k induced apoptosis in the investigated cell lines.
These results show that treatment of cancer cells with
compounds 4j and 4k activates caspases leading to cellu-
lar apoptosis in the same manner as that of CA-4 (data
not shown, 466% at 10 nM in H1299 cells).
a,b
IC50
1
2
4a
4b
4c
79
0
34
12
—
58
52
—
45
47
42
65
82
23
—
35
77
—
—
—
21
63
—
—
—
—
3
28
89
85
14
45
73
69
73
88
80
23
58
88
4
4d
4e
5
6
4f
7
4g
4h
4i
In order to expand our studies, the effects of compounds
4j and 4k on the proliferation of human umbilical vein
endothelial cells (HUVEC) were determined. The results
revealed that, after 72 h of incubation, compounds 4j
and 4k exhibit good growth inhibition activity against
HUVEC proliferation with an IC50 of 35 and 40 nM,
respectively (IC50 2.5 nM for CA-4). Additionally, in or-
der to evaluate whether the compound 4k affects newly
formed blood vessels in vitro, the HUVEC tube forma-
tion assay was performed. As shown in Fig. 3, addition
of 4k (100 nM) to formed cords rapidly disrupted the
integrity of the network. This effect was visible after
3 h of treatment at doses which were not cytotoxic for
such incubation time (data not shown). Altogether,
our results suggest that these derivatives 4j and 4k might
be lead compounds for use as antiangiogenic inhibitors.
8
9
10
11
12
13
14
15
4j
1.5
5.0
4k
4l
—
4m
4n
CA-4
—
—
1.0
a Values are means of at least three experiments.
bConcentration inhibiting 50% of about 2.0 mg/mL microtubular
protein assembly.
Table 5. Flow cytometry analysis of compounds 4j and 4k in HCT116
and H1299 cancer cellsa
Compound
Concentration
(nM)
HCT116
(% G2/M)
H1299
(% G2/M)
In conclusion, we have demonstrated that using a low
loading of PdI2 (2 mol %) in DMSO proved to be a reli-
able procedure for the oxidation of various functional-
ized diarylalkynes. This new catalytic system has
proved to be high yielding, easy to handle, and gave rap-
idly a small library of the desired benzil analogs of CA-
4. Next, we have found that many of the synthesized
benzil derivatives show excellent antiproliferative activi-
ties at the nanomolar level. The most active compounds
4j and 4k were found to be almost as potent as CA-4. It
is clear from these results that the replacement of the Z
double bond by a 1,2-dicarbonyl unit maintained a pow-
erful anticancer activity. This study contributes to the
knowledge about the SAR in the CA-4 series that may
allow the design and synthesis of other derivatives hav-
ing a superior anticancer activity. To this end, a series of
nitrogen-containing heterocycles such as imidazoles or
DMSO
4j
—
10
20
50
11.5
11
8.4
11.4
15
18.5
22.8
27.7
4k
10
20
50
13
11.7
12.2
16.5
15.9
28
a Data represent percentage of cells in G2/M phase of the cell cycle
after 24 h of treatment with 4j and 4k. Data are representative of
three independent experiments.
The ability of compounds 4j and 4k to induce apoptosis
was further characterized by a specific apoptosis assay.
Cleavage of pro-caspases to active caspases is one of
the hallmarks of apoptosis. HT1299 and HCT116 cell
lines were thus treated with 10, 50 and 100 nM of com-
OMe
O
OMe
O
700
10 nM
10 nM
50 nM
100 nM
500
400
300
200
100
0
MeO
MeO
MeO
OH
NH2
50 nM
O
O
600
MeO
100 nM
4j
4k
OMe
OMe
500
400
300
200
100
0
H1299
HCT116
H1299
HCT116
Figure 2. Apoptotic effects of benzils 4j and 4k on HCT116 and H1299 cells. Percentage of apoptotic cells induced by different concentrations of 4j
and 4k (evaluation after 48 h of treatment).

3270
C. Mousset et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3266–3271
Figure 3. Effects of benzil 4k on newly formed vessels. In vitro, 4k or vehicle was added to cords formed by endothelial cells on Matrigel, 24 h after
HUVEC seeding; Images were taken 3 h after addition of the compound. (A) Control; (B) 4k (100 nM).
11. For a review, see: Tron, G. C.; Pirali, T.; Sorba, G.;
Pagliai, F.; Dusacca, S.; Genazzani, A. A. J. Med. Chem.
2006, 49, 3032.
quinoxalines easily available from benzil derivatives are
currently under investigation.
12. (a) Hadfield, J. A.; McGown, A. T. Synth. Commun. 1998,
28, 1421; (b) Lin, C. M.; Singh, S. B.; Chu, P. S.; Dempcy,
R. O.; Schmidt, J. M.; Pettit, G. R.; Hamel, E. Mol.
Pharmacol. 1998, 34, 200; (c) Nandy, P.; Banerjee, S.;
Gao, H.; Hui, M. B. V.; Lien, E. J. Pharm. Res. 1991, 8,
776.
13. (a) Pettit, G. R.; Toki, B.; Herald, D. L.; Verdier-Pinard,
P.; Boyd, E.; Hamel, M. R.; Pettit, R. K. J. Med. Chem.
1998, 41, 1688; (b) Liou, J.-P.; Chang, C.-W.; Song, J.-S.;
Yang, Y.-N.; Yeh, C.-F.; Tseng, H.-Y.; Lo, Y.-K.; Chang,
Y.-L.; Chang, C.-M.; Hsieh, H.-P. J. Med. Chem. 2002,
45, 2556; (c) Liou, J.-P.; Chang, J.-Y.; Chang, C.-W.;
Chang, C.-Y.; Mahindroo, N.; Kuo, F.-M.; Hsieh, H.-P.
J. Med. Chem. 2004, 47, 2897.
Acknowledgments
The authors gratefully acknowledge support of this pro-
ject by CNRS and the MNSER for doctoral fellowships
to C.M. and A.G.
References and notes
1. (a) Hadfield, J. A.; Ducki, S.; Hirst, N.; McGown, A. T.
Prog. Cell Cycle Res. 2003, 5, 309; (b) Attard, G.;
Greystoke, A.; Kaye, S.; De Bono, J. Pathol. Biol. 2006,
54, 72; (c) Bhattacharayya, B.; Panda, D.; Gupta, S.;
Banerjee, M. Med. Res. Rev. 2008, 28, 155.
14. Ducki, S.; Forrest, R.; Hadfield, J. A.; Kendall, A.;
Lawrence, N. J.; McGown, A. T.; Rennison, D. Bioorg.
Med. Chem. Lett. 1998, 8, 1051.
15. (a) Provot, O.; Giraud, A.; Peyrat, J.-F.; Alami, M.;
Brion, J.-D. Tetrahedron Lett. 2005, 46, 8547; (b) Giraud,
A.; Provot, O.; Hamze, A.; Brion, J.-D.; Alami, M.
Tetrahedron Lett. 2008, 49, 1107.
16. Giraud, A.; Provot, O.; Peyrat, J.-F.; Alami, M.; Brion,
J.-D. Tetrahedron 2006, 62, 7667.
2. (a) Hamel, E. Med. Chem. Rev. 1996, 16, 207; (b) Jordan,
A.; Hadfield, J. A.; Lawrence, N. J.; McGown, A. T. Med.
Res. Rev. 1998, 18, 259; (c) Li, Q.; Sham, H. L. Expert
Opin. Ther. Pat. 2002, 12, 1663; (d) Jordan, M. A. Curr.
Med. Chem. 2002, 2, 1.
3. (a) Jordan, M. A.; Wilson, L. Nat. Rev. Cancer 2004, 4,
253; (b) Siemann, D. W.; Bibby, M. C.; Dark, G. G.;
Dicker, A. P.; Eskens, F. A. L. M.; Horsman, M. R.;
Marme, D.; LoRusso, P. M. Clin. Cancer Res. 2005, 11,
416; (c) Siemann, D. W. Vascular-Targeted Therapies in
Oncology; John Wiley and Sons: New York, 2006.
4. (a) Pettit, G. R.; Singh, S. B.; Niven, M. L.; Hamel, E.;
Schmidt, J. M. J. Nat. Prod. 1987, 50, 119; (b) Pettit, G.
R.; Singh, S. B.; Hamel, E.; Lin, C. M.; Alberts, D. S.;
Garcia-Kendall, D. Experientia 1989, 45, 209.
17. Mousset, C.; Provot, O.; Hamze, A.; Bignon, J.; Brion,
J.-D.; Alami, M. Tetrahedron 2008, 64, 4287.
18. (a) Sonogashira, K.; Tokai, Y.; Hagihara, N. Tetrahe-
dron Lett. 1975, 4467; (b) Alami, M.; Ferri, F.;
Linstrumelle, G. Tetrahedron Lett. 1993, 34, 1433; (c)
Alami, M.; Ferri, F.; Gaslain, Y. Tetrahedron Lett.
1996, 37, 57.
19. Spectral data for representative compounds:
Compound 4j: IR (neat, cmꢁ1) 3378, 1654, 1605, 1578,
1501, 1471, 1418, 1341, 1311, 1290, 1241, 1154, 1120, 1004.
1H NMR (CDCl3, 200 MHz) d 3.87 (s, 6H), 3.93 (s, 3H),
3.97 (s, 3H), 5.76 (br s, 1H), 6.90 (d, 1H, J = 8.4 Hz), 7.20
(s, 2H), 7.49 (dd, 1H, J = 8.4 Hz, J = 2.1 Hz), 7.55 (d, 1H,
J = 2.1 Hz), 6.90 (d, 1H, J = 8.4 Hz). 13C NMR (CDCl3,
75 MH) d 56.0 (CH3), 56.3 (2CH3), 61.0 (CH3), 107.1
(2CH), 110.3 (CH), 115.4 (CH), 123.3 (CH), 126.6 (C),
128.3 (C), 144.0 (C), 148.6 (C), 153.3 (2C), 154.1 (C), 193.6
(C), 194.0 (C). Mp = 153–154 ꢁC. Anal. Calcd for
C18H18O7: C, 62.42; H 5.24. Found: C, 62.29; H 5.11.
Compound 4k: IR (neat, cmꢁ1) 3400, 1668, 1651, 1519,
1502, 1445, 1412, 1340, 1304, 1240, 1123, 1018. 1H
NMR (CDCl3, 200 MHz) d 3.87 (s, 6H), 3.93 (s, 3H),
6.82 (d, 1H, J = 8.2 Hz), 7.20 (s, 2H), 7.33 (dd, 1H,
J = 8.2 Hz), J = 2.2 Hz), 7.37 (d, 1H, J = 2.2 Hz). 13C
NMR (CDCl3, 75 MH) d 55.7 (CH3), 56.2 (2CH3), 61.0
5. (a) McGown, A. T.; Fox, B. W. Anti-Cancer Drug Des.
1989, 3, 249; (b) Aleksandrzak, K.; McGown, A. T.;
Hadfield, J. A. Anti-Cancer Drugs 1998, 9, 545.
6. Pettit, G. R.; Singh, S. G.; Boyd, M. R.; Hamel, E.; Pettit,
R. K.; Schmidt, J. M.; Hogan, F. J. Med. Chem. 1995, 38,
1666.
7. Oshumi, K.; Nakagawa, R.; Fukuda, Y.; Hatanaka, T.;
Tsuji, T. J. Med. Chem. 1998, 41, 3022.
8. (a) Tozer, G. M.; Kanthou, C.; Baguley, B. C. Nat. Rev.
Cancer 2005, 5, 423; (b) Tozer, G. M.; Kanthou, C.;
Parkins, C. S.; Hill, S. A. Int. J. Exp. Pathol. 2002, 83, 21.
9. Patterson, D. M.; Rustin, G. J. S. Drugs Future 2007, 32,
1025.
10. (a) Lippert, J. W. Bioorg. Med. Chem. 2007, 15, 605; (b)
Patterson, D. M.; Rustin, G. J. S. Clin. Oncol. 2007, 19,
443.

C. Mousset et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3266–3271
3271
(CH3), 107.0 (2CH), 109.5 (C), 114.8 (CH), 123.0 (CH),
126.3 (C), 128.2 (C), 136.7 (C), 143.8 (C), 153.2 (2C),
153.6 (CH), 193.5 (CO), 193.8 (CO). Mp = 146–147 ꢁC.
SM (ESI+, m/z, %): 368 (M+Na, 100). Anal. Calcd for
C18H19NO6: C, 62.60; H 5.55; N 4.06. Found: C, 62.39;
H 5.41; N 3.96.
20. (a) Cushman, M.; Nagarathnam, D.; Gopal, D.; He, H.
M.; Lin, C. M.; Hamel, E. J. Med. Chem. 1991, 34, 2579;
(b) Cushman, M.; Nagarathnam, D.; Gopal, D.; He, H .
M.; Lin, C. M.; Hamel, E. J. Med. Chem. 1992, 35, 2293.
´
21. Zavala, F.; Guenard, D.; Robin, J.-P.; Brown, E. J. Med.
Chem. 1980, 23, 546.