Discovery of 4-amino and 4-hydroxy-1-aroylindoles as potent tubulin polymerization inhibitors

Article abstract of DOI:10.1021/jm800150d

1-Aroylindoline, 1-aroyl-1,2,3,4-tetrahydroquinoline, and 1-aroylindole derivatives were synthesized and evaluated for anticancer activity. The 4-amino and 4-hydroxy-1-aroylindoles 26 and 27 with IC₅₀ of 0.9 and 0.6 μM, respectively, exhibited

Full text of DOI:10.1021/jm800150d

J. Med. Chem. 2008, 51, 4351–4355
4351
Discovery of 4-Amino and 4-Hydroxy-1-aroylindoles as Potent Tubulin Polymerization
Inhibitors
Jing-Ping Liou,† Zi-Yi Wu,† Ching-Chuan Kuo,‡ Chi-Yen Chang,‡ Pei-Yi Lu,† Chi-Ming Chen,† Hsing-Pang Hsieh,*,¶ and
Jang-Yang Chang*,‡,§
College of Pharmacy, Taipei Medical UniVersity, Taipei 110, Taiwan, Republic of China, National Institute of Cancer Research, National
Health Research Institutes, Tainan 704, Taiwan, Republic of China, DiVision of Biotechnology and Pharmaceutical Research, National Health
Research Institutes, Miaoli 350, Taiwan, Republic of China, and DiVision of Hematology/Oncology, Department of Internal Medicine, National
Cheng Kung UniVersity Hospital, Tainan 704, Taiwan, Republic of China
ReceiVed February 13, 2008
1-Aroylindoline, 1-aroyl-1,2,3,4-tetrahydroquinoline, and 1-aroylindole derivatives were synthesized
and evaluated for anticancer activity. The 4-amino and 4-hydroxy-1-aroylindoles 26 and 27 with IC50 of 0.9
and 0.6 µM, respectively, exhibited antitubulin activity superior or comparable to that of colchicine and
combretastatin A-4. They also showed antiproliferative activity with IC50 of 0.3-5.4 nM in a set of human
cancer cell lines.
Introduction
One of the currently useful chemotherapy drugs in oncology
is represented by antimitotic agents, for example, taxanes and
vinca alkaloids.1 However, the issues of high systemic toxicity,
complex syntheses, drug resistance, and isolation procedures
have encouraged scientists to develop new antimitotic agents.
Recent literature reported that the antitubulin agents targeting
the colchicine-binding domain rapidly depolymerize microtu-
bules of vasculatures changing morphology in the endothelial
cells of tumor’s vessels to block the blood supply to tumors
and can act as vascular-disrupting agents,2 for example, 2, 3,
and 5 (Figure 1).
The encouraging antivascular and antitumor prolife of 2 has
stimulated interest in design and synthesis of a variety of derivatives
Figure 1
or analogues.3 One of the modified sites in combretastatin structure
is the olefin functionality of Z-stilbene; for instance, it was replaced
4-amino- and 4-hydroxy-1-aroylindoles as novel, highly potent
with a 1,3-diaryl five-member ring (oxazoline and oxadiazoline),4
antimitotic agents.
1,2-diaryl five-member ring (triazole,5 pyrazole, tetrazole, thiazole,6
imidazole,7 furan,8 furazan9), carbonyl bridge,10 and 2- or 3-car-
bonylthiophene.11 Attempts to replace the double bond bridge in
1 with an amide bond resulted in dramatic loss of activity12 (6 vs
1). Despite this, the amide moiety was used for isosteric replace-
ment with an olefin group.13 In this paper, we use 6 as a base to
design a series of heterocyclic analogues of 1 to improve activity
by a restricted approach connecting the amide moiety and the
B-ring of 6 via a five- or six-member ring to introduce a series of
1-aroylindolines, 1-aroyl-1,2,3,4-tetrahydroquinoline, and 1-aroylin-
doles (Figures 2 and 3). Here, we describe the discovery of
Results and Discussion
Chemistry. Diphenylamide 612 was prepared as shown in
Scheme 1. To synthesize 7 and 9, 5-methoxyindole (28) and
2-methyl-5-methoxyindole (29) were treated with sodium cy-
anoborohydride in acetic acid to give indoline 30 and 31,
respectively (Scheme 2). The electrophilic substitution of 30
and 31 with the 3,4,5-trimethoxybenzoyl chloride in pyridine
gave the desired 1-aroylindoline 7 and 9 in 87% and 88% yield,
respectively. The 1-aroyl-1,2,3,4-tetrahydroquinoline 8 was
prepared in 89% yield by treatment of commercially available
1,2,3,4-tetrahydroquinoline (32) with 3,4,5-trimethoxybenzoyl
chloride in pyridine (Scheme 3). The general method for the
synthesis of 1-aroylindoles 1014-14, 17,14 20, and 24 is depicted
in Scheme 4. The direct electrophilic substitution of 3,4,5-
trimethoxybenzoyl chloride at the N1-position of various
commercially available indoles in the presence of KOtBua gave
the desired 1-aroylindoles in 25-95% yield. Compounds 15
* To whom correspondence should be addressed. For H.-P.H.: (phone)
886-37-586-456,ext35708;(fax)886-37-586-456;(e-mail)hphsieh@nhri.org.tw.
For J.-Y.C.: (address) 2F, No. 367, Sheng Li Road, Tainan 704, Taiwan,
Republic of China; (phone) 886-6-700-0123, ext 65100; (fax) 886-6-208-
3427; (e-mail) jychang@nhri.org.tw.
†
Taipei Medical University.
National Institute of Cancer Research, National Health Research
‡
a Abbreviations: KOtBu, potassium tert-butoxide; TBDMSCl, tert-
butyldimethylsilyl chloride; NaBH3CN, sodium cyanoborohydride; K2CO3,
potassium carbonate; DMF, N,N-dimethylformamide; THF, tetrahydrofuran;
MDR, multidrug-resistant; TBAF, tetra-n-butylammonium floride.
Institutes.
¶
Division of Biotechnology and Pharmaceutical Research, National
Health Research Institutes.
§
National Cheng Kung University Hospital.
10.1021/jm800150d CCC: $40.75
2008 American Chemical Society
Published on Web 06/28/2008

4352 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 14
Brief Articles
Figure 3
Scheme 4a
Figure 2
Scheme 1a
a Reagents and conditions: (a) 3,4,5-trimethoxybenzoyl chloride, pyridine,
room temp.
a Reagents and conditions: (a) 3,4,5-trimethoxybenzoic anhydride, KtO-
Bu, THF.
Scheme 2a
Scheme 5a
a Reagents and conditions: (a) (i) LiAlH4, THF; (ii) imidazole, TBDM-
SCl, DMF, 0 °C; (b) (i) KOtBu, 3,4,5-trimethoxybenzoic anhydride, THF;
(ii) TBAF, THF, 0 °C; (c) (CH3)2NH·HCl, Et3N, NaBH3CN, EtOH; (d)
KOtBu, 3,4,5-trimethoxybenzoic anhydride, THF.
a Reagents and conditions: (a) AcOH, NaBH3CN; (b) 3,4,5-trimethoxy-
benzoyl chloride, pyridine.
by TBDMSCl, indole N1-aroylation, and fluoride-mediated
desilylation. Compound 19, with a C5-dimethylamino substitu-
ent, was synthesized starting from the 2-methyl-5-nitroindole
(36), which on N1-aroylation with 3,4,5-trimethoxybenzoyl
chloride in the presence of NaH followed by Fe/NH4Cl-mediated
reduction afforded 18. The amine 18 was converted into the
desired C5-dimethylamino 19 in 30% yield by reaction with
iodomethane in the presence of K2CO3 and DMF (Scheme 6).
The modification at the C2-position of 10 by the hydroxy and
amino moieties, giving 21 and 22, were prepared as shown in
the Schemes 7 and 8, respectively. Starting from the ethyl
5-methoxyindole-2-carboxylate (38), the synthesis of 21 was
carried out in four steps through LiAlH4-mediated reduction,
protection with the tert-butyldimethylsilyl group, N1-aroylation
with 3,4,5-trimethoxybenzoic anhydride, and deprotection with
tetrabutylammonium fluoride in 21% yield (four steps, Scheme
7). Compound 22 was synthesized starting from the 5-meth-
oxyindole-2-carboxyaldehyde (41), which was subjected to the
Scheme 3a
a Reagents and conditions: (a) 3,4,5-trimethoxybenzoyl chloride, pyridine.
and 16, with a C5-hydroxymethyl and C5-dimethylaminomethyl
groups, respectively, were prepared by starting from the indole-
5-carboxyaldehyde (33) as shown in Scheme 5. Dimethylamine/
sodium cyanoborohydride mediated reductive amination of 33
followed by electrophilic substitution with 3,4,5-trimethoxy-
benzoic anhydride gave 16 in 37% yield (two steps). Compound
33 was converted into the desired the C5-hydroxymethyl 15 in
23% yield in four steps: LiAlH4-mediated reduction, protection

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 14 4353
Scheme 10a
Scheme 6a
a Reagents and conditions: (a) NaH, 3,4,5-trimethoxybenzoyl chloride,
toluene, DMF; (b) Fe, NH4Cl, isopropanol, H2O, reflux; (c) CH3I, K2CO3,
DMF.
a Reagents and conditions: (a) (i) TBDMSCl, Et3N, CH2Cl2; (ii) KOtBu,
3,4,5-trimethoxybenzoic anhydride, THF, room temp; (iii) TBAF, THF,
0 °C.
Scheme 7a
Table 1. IC50 Values of Compounds 6-27, 4, and 1
cell type (IC50 ( SD,a nM)
compd
KB
H460
MKN45
KB-vin10
6
7
8
9
>5000
>5000
>5000
>5000
89 ( 2.9
596 ( 123
370 ( 33
208 ( 58
371 ( 111
575 ( 55
>5000
98 ( 1
53 ( 1.4
395 ( 51
257 ( 30
198 ( 13
314 ( 35
521 ( 51
>5000
84 ( 11
586 ( 82
372 ( 18
197 ( 20
400 ( 80
587 ( 42
>5000
652 ( 32
413 ( 6
232 ( 21
353 ( 75
559 ( 81
>5000
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
4
a Reagents and conditions: (a) LiAlH4, THF, room temp; (b) imidazole,
TBDMSCl, DMF, 0 °C; (c) (CH3)2NH·HCl, Et3N, NaBH3CN, CH2Cl2; (d)
(i) KOtBu, 3,4,5-trimethoxybenzoic anhydride, THF, room temp; (ii) TBAF,
THF, 0 °C to room temp; (e) KOtBu, 3,4,5-trimethoxybenzoic anhydride,
THF.
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
18 ( 6
23 ( 7
17 ( 3
11 ( 4
Scheme 8a
345 ( 17
42 ( 21
230 ( 71
>5000
334 ( 84
52 ( 7
156 ( 54
41 ( 13
101 ( 19
>5000
312 ( 20
38 ( 14
185 ( 21
>5000
198 ( 1.4
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
a Reagents and conditions: (a) (i) imidazole, TBDMSCl, DMF, 0 °C;
(ii) KOtBu, 3,4,5-trimethoxybenzoic anhydride, THF; (iii) TBAF, THF, 0
°C; (b) CH3I, K2CO3, DMF.
>5000
>5000
>5000
>5000
>5000
>5000
>5000
>5000
1.2 ( 0.4
0.3 ( 0.3
11.4 ( 1
2.2 ( 0.3
5.4 ( 1.2
0.5 ( 0.4
20 ( 2
3.1 ( 2.3
0.6 ( 0.8
11 ( 1
2.4 ( 1.3
0.3 ( 0.2
125 ( 10
1.8 ( 0.4
Scheme 9a
1
2.8 ( 0.8
5.6 ( 0.2
a SD: standard deviation. All experiments were independently performed
at least three times.
material 47, which was prepared by the literature methodology.16
The 4-hydroxy-2-methyl-5-methoxyindole (47) was converted
into the 4-hydroxy-1-aroylindole 27 in three steps via the
protection with tert-butyldimethylsilyl group, N1-aroylation with
3,4,5-trimethoxybenzoic anhydride, and fluoride ion-mediated
deprotection to afford the desired 27 in 19% yield (Scheme 10).
a Reagents and conditions: (a) KOH, tetrabutylammonium bisulfate,
PhSO2Cl, CH2Cl2; (b) HNO3; (c) (i) NaOH, EtOH, reflux; (ii) KOtBu, 3,4,5-
trimethoxybenzoic anhydride, THF; (d) Fe, NH4Cl, isopropanol, H2O, reflux.
Biological Evaluation. (A) In Vitro Cell Growth Inhibi-
tory Activity. The synthesized 1-aroylindolines 7 and 9, 1-aroyl-
1,2,3,4-tetrahydroquinoline 8, and 1-aroylindoles 10-27 were
evaluated for antiproliferative activities against three types of
human cancer cell lines, oral epidermoid carcinoma KB cells,
non-small-cell lung carcinoma H460 cells, and stomach carci-
noma MKN45 cells, as well as one type of MDR-positive cell
line, KB-vin10 cells, overexpressed P-gp 170/MDR (Table 1).
reductive amination of C2-aldehyde in the presence of
(CH3)2NH and NaBH3CN to give unexpected 42 that followed
by indole N1-aroylation with 3,4,5-trimethoxybenzoic anhydride,
affording 22 (Scheme 7). Compound 23, the C3-ethyl carboxy-
late analogue of 17, was prepared starting from commercially
available 43 by treating with the TBDMSCl/imidazole, 3,4,5-
trimethoxybenzoic anhydride/KOtBu, and then tetrabutylam-
monium fluoride to give 44. The O-methyation of 44 in the
presence of CH3I and K2CO3 afforded the desired 23 in 52%
yield (Scheme 8). Compound 26, with an additional amino group
at the 4-position of indole in 10, was prepared by starting from
the 5-methoxyindole (28) in five steps, as shown in the Scheme
9. N1-Benzenesulfonyl protection of 28 followed by nitration15
gave the 5-methoxy-4-nitro-substituted indole 46. The N1-
benzenesulfonyl of 46 was deprotected with NaOH and then
treated with the 3,4,5-trimethoxybenzoic anhydride in the
presence of KOtBu and THF and then subjected to Fe-mediated
reduction to give the desired 26 in 16% overall yield (five steps).
Compound 27, with an additional hydroxyl group at the
4-position of 1-aroylindole 17, was synthesized from the key
We first evaluated the effect of adding a five- or six-member
ring upon the B-ring of 6, i.e., to cyclize the amide bond and
B-ring in 6, for cytotoxicity activity. Indoline 7, tetrahydro-
quinoline 8, and indole 10 were evaluated for antiproliferative
activity. Structure-activity relationships indicated that the five-
member ring based heterocycles, 1-aroylindoline (7) and
1-aroylindole (10), and the six-member ring based heterocycles,
1-aroyltetrahydroquinoline (8), all show stronger activity than
the parent (6), with mean IC50 values of 81, 208, 557 nM against
four lines, respectively. On the basis of these results of five-
member-ring-containing heterocyclic analogues showing good
cellular growth inhibitory activity, the substituted 1-aroylindoline

4354 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 14
Brief Articles
Table 2. Inhibition of Tubulin Polymerization and Colchicine Binding
by Compounds 7, 8, 10, 19, 26, 27, 4, and 1
derivative (9) and 1-aroylindole derivatives (11-27) were
further prepared and evaluated for activity.
colchicine bindingb ( SD (%)
tubulina
In the SAR study of 1, the p-methoxy substitution of the
B-ring of Z-stilbene plays a pivotal role for activity.10a,12 So
we prepared 11-16 with a methyl, methylenedioxy, methyl-
carboxylate, carboxyaldehyde, hydroxymethyl, and dimethy-
laminomethyl groups at the 5- or 5,6-postion of 1-aroylindoles.
Compounds 11 and 12, with electron-donating groups C5-methyl
and C5,6-methylenedioxy groups, respectively, slightly reduced
the activity compared to 10. But changing the C5-methoxy group
of 10 to electron-withdrawing CO2CH3 and CHO groups in 13
and 14, respectively, resulted in drastic loss of activity.
Compounds 15 and 16, with a CH2OH and CH2N(CH3)2 group
at C5-postion, respectively, displayed no activity, thus revealing
that the steric effect of substituents at C5-position may influence
cellular growth inhibitory activity. In order to investigate the
effect of substitution at C2-position of 1-aroylindoles, 17, 20,
21, and 22 with an alkyl, ester, alcohol, and amine functional-
ities, respectively, on the 2-indole were tested for their anti-
proliferative activity. Compound 17, with a C2-methyl substi-
tution on the 1-aroylindole 10, showed the most potent activity,
changing to the C2-ethyl carboxylate substitution (20), which
resulted in moderate activity with mean IC50 of 178 nM against
four lines comparable to the that of 10, while changing to the
alcohol or amino functionalities (21 and 22) decreased the
activity drastically. On the basis of these results (C2-modifica-
tion), the introduction of an alkyl or ester functional group at
the C2-position of 1-aroylindoles seems to be preferable in
activity. The introduction of a methyl group at the C2-position
of 1-aroylindoles exerted a potency increase that intrigued us
to explore whether 1-aroylindolines also exhibit this effect.
Contrary to expectation, 9 with an additional methyl group in
1-aroylindoline 7 showed a decreased growth inhibition by a
>3-fold magnitude in four cell lines (9 vs 7). As the C2-ethyl
carboxylate substitution in 1-aroylindoles (20) exhibited moder-
ate cytotoxicity, 23 and 24, with the CO2Et and CH2N(CH3)2
groups at the C3-position, respectively, were also prepared. But
no activity was observed in 23 and 24. A literature report12
showing that the 4-methoxy group in the B-ring of 1 skeleton
can be replaced with a 4-N,N-dimethylamino group inspired us
to synthesize 19, with the C2-methyl and C5-dimethylamino
groups on the indole ring. Indeed, 19 demonstrated strong
antiproliferative activity in four cell lines, with mean IC50 values
of 43 nM.
compd
IC50 ( SD (µM)
1 µM inhibitor
27 ( 2
5 µM inhibitor
55 ( 3
7
8
10
19
26
27
4
2.6 ( 0.3
>5
2.5 ( 0.6
1.5 ( 0.5
0.9 ( 0.2
0.6 ( 0.1
3.0 ( 0.4
1.1 ( 0.3
45 ( 3
72 ( 1
71 ( 2
94 ( 1
72 ( 2
89 ( 1
93 ( 1
97 ( 0.5
1
85 ( 0.2
93 ( 2
a Inhibition of tubulin polymerization.17 Tubulin was at 1 µM. b Inhibition
of [3H]colchicine binding. [3H]Colchicine was at 5 µM.
(B) Inhibition of Tubulin Polymerization and Colchicine
Binding Activity. To examine whether 1-aroylindoline, 1-aroyltet-
rahydroquinoline, and 1-aroylindoles were tubulin inhibitors
through the colchicine-binding site, the selected compounds 7,
8, 10, 19, 26, 27 and reference compounds (1 and 4) were
evaluated for antitubulin activity and the ability to compete for
the colchicine-binding site (Table 2). Results indicated that the
compounds’ antiproliferative activity positively correlated with
the inhibition of tubulin polymerization. Compounds 19, 26,
and 27 were efficacious in inhibiting microtubulin assembly,
with IC50 values of 1.5, 0.9, 0.6 µM, respectively. In the
[3H]colchicine binding assay, data indicated the 4-amino-1-
aroylindoles (26) and 4-hydroxy-1-aroylindoles (27) were
strongly bound to the colchicine-binding domain on microtu-
bulin. Compound 27 showed substantial activity. It inhibited
colchicine binding by 94% (27 was 1 µM with colchicine at 5
µM) and 97% (27 was 5 µM with colchicine at 5 µM).
Conclusion
Synthesis and structure-activity relationship of synthetic
anticancer agents 1-aroylindoline, 1-aroyltetrahydroquinoline,
and 1-aroylindoles skeleton were described. The synthesized
1-aroylindoline (7) and 1-aroylindoles (19, 26, and 27) are potent
cytotoxic agents and antitubulin agents acting through the
colchicine-binding site on tubulin. Compounds 19, 26, and 27
displayed antiproliferative activity with IC50 values of 38-52,
1.2-5.4, and 0.3-0.6 nM, respectively, in a variety of human
cancer cell lines from different organs. They also showed
substantial antitubulin activity with IC50 values of 1.5, 0.9, and
0.6 µM, respectively. SAR data revealed that the introduction
of amino or hydroxyl group at the C4-position of 1-aroylindole
series significantly increased activity than the parent (26 vs 10;
27 vs 17). Thus, the amino or hydroxyl substituents located at
position 4 of 1-aroylindole moieties apparently plays an
important role in the activity of this series of compounds.
Utilizing a restricted approach of drug design, we effectively
converted inactive diphenylamide 6 into active compounds, for
example, 1-aroylindoline (7 and 9), 1-aroyltetrahydroquinoline
(8), and 1-aroylindoles (10-12, 17-20, 26, and 27), with
substantial activity. This information maybe can be applied to
other corresponding tubulin inhibitors or combretastatin ana-
logues modification.
In an effort to increase the corresponding 1-aroylindoles
structure’s polarity, the 4-amino and 4-hydroxy-substituted
1-aroylindoles 26 and 27 were prepared to mimic the structure
of 3 and 2 with a amino and hydroxy group at the C3′-position
of B-ring of Z-stilbene, respectively. Compound 26, namely,
4-amino-5-methoxy-1-(3′,4′,5′-trimethoxybenzoyl)indole, dis-
played a mean IC50 of 3.0 nM against four cell lines comparable
to the reference compound 1 (IC50 ) 3.1 nM). Compound 27,
with a hydroxyl group at C-4 position of indole ring, namely,
4-hydroxyl-2-methyl-5-methoxy-1-(3′,4′,5′-trimethoxybenzoyl)in-
dole, showed mean a IC50 of 0.42 nM in all four lines, thus
exhibiting stronger cytotoxicity than 1. Interestingly, 26 and 27
with additional amino and hydroxyl groups showed approxi-
mately >10-fold improvement in IC50 values over analogues
10 and 17, respectively (26 vs 10; 27 vs 17). Hence, it may be
concluded that the introduction of an amino or hydroxyl group
at the C-4 position of 1-aroylindoles, in addition to a methoxy
group at C-5 position, is important for maximal cytotoxicity.
Experimental Section
4-Hydroxy-5-methoxy-2-methyl-1-(3′,4′,5′-trimethoxyben-
zoyl)indole (27). To a solution of 47 (1.46 g, 8.24 mmol) and
triethylamine (2.29 mL, 16.48 mmol) in CH2Cl2 (20 mL) was added
tert-butyldimethylsilyl chloride (1.86 g, 12.36 mmol) at room
temperature. After the mixture was stirred for 18 h, the reaction
was quenched with water and the layer was extracted with CH2Cl2
(30 mL × 3). The combined organic layer was dried over anhydrous

Brief Articles
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 14 4355
(4) Szczepankiewicz, B. G.; Liu, G.; Jae, H. S.; Tasker, A. S.; Gunawardana,
I. W.; von Geldern, T. W.; Gwaltney, S. L., II; Wu-Wong, J. R.; Gehrke,
L.; Chiou, W. J.; Credo, R. B.; Alder, J. D.; Nukkala, M. A.; Zielinski,
N. A.; Jarvis, K.; Mollison, K. W.; Frost, D. J.; Bauch, J. L.; Hui, Y. H.;
Claiborne, A. K.; Li, Q.; Rosenberg, S. H. New Antimitotic Agents with
Activity in Multi-Drug-Resistant Cell Lines and in Vivo Efficacy in
Murine Tumor Models. J. Med. Chem. 2001, 44, 4416–4430.
(5) Zhang, Q.; Peng, Y.; Wang, X. I.; Keenan, S. M.; Arora, S.; Welsh,
W. J. Highly Potent Triazole-Based Tubulin Polymerization Inhibitors.
J. Med. Chem. 2007, 50, 749–754.
(6) Ohsumi, K.; Hatanaka, T.; Fujita, K.; Nakagawa, R.; Fukuda, Y.; Nihei,
Y.; Suga, Y.; Morinaga, Y.; Akiyama, Y.; Tsuji, T. Syntheses and
Antitumor Activity of cis-Restricted Combretastatins: 5-Membered
Heterocyclic Analogues. Bioorg. Med. Chem. Lett. 1998, 8, 3153–3158.
(7) Wang, L.; Woods, K. W.; Li, Q.; Barr, K. J.; McCroskey, R. W.;
Hannick, S. M.; Gherke, L.; Credo, R. B.; Hui, Y. H.; Marsh, K.;
Warner, R.; Lee, J. Y.; Zielinski-Mozng, N.; Frost, D.; Rosenberg,
S. H.; Sham, H. L. Potent, Orally Active Heterocycle-Based Com-
bretastatin A-4 Analogues: Synthesis, Structure-Activity Relationship,
Pharmacokinetics, and in Vivo Antitumor Activity Evaluation. J. Med.
Chem. 2002, 45, 1697–1711.
(8) Pirali, T.; Busacca, S.; Beltrami, L.; Imovilli, D.; Pagliai, F.; Miglio,
G.; Massarotti, A.; Verotta, L.; Sorba, G.; Genazzani, A. A. Synthesis
and Cytotoxic Evaluation of Combretafurans, Potential Scaffolds for
Dual-Action Antitumoral Agents. J. Med. Chem. 2006, 49, 5372–5376.
(9) Tron, G. C.; Pagliai, F.; Del Grosso, E.; Genazzani, A. A.; Sorba, G.
Synthesis and Cytotoxic Evaluation of Combretafurazans. J. Med.
Chem. 2005, 48, 3260–3268.
(10) (a) Cushman, M.; Nagarathnam, D.; Gopal, D.; He, H. M.; Lin, C. M.;
Hamel, E. Synthesis and Evaluation of Analogues of (Z)-1-(4-
Methoxyphenyl)-2-(3,4,5-trimethoxyphenyl)ethane as Potential Cy-
totoxic and Antimitotic Agents. J. Med. Chem. 1992, 35, 2293–2306.
(b) Pettit, G. R.; Toki, B.; Herald, D. L.; Verdier-Pinard, P.; Boyd,
M. R.; Hamel, E.; Pettit, R. K. Antineoplastic Agents. 379. Synthesis
of Phenstatin Phosphate. J. Med. Chem. 1998, 41, 1688–1695. (c) 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. Synthesis
and Structure-Activity Relationship of 2-Aminobenzophenone De-
rivatives as Antimitotic Agents. J. Med. Chem. 2002, 45, 2556–2562.
(d) Liou, J. P.; Chang, J. Y.; Chang, C. W.; Chang, C. Y.; Mahindroo,
N.; Kuo, F. M.; Hsieh, H. P. Synthesis and Structure-Activity
Relationships of 3-Aminobenzophenones as Antimitotic Agents.
J. Med. Chem. 2004, 47, 2897–2905. (e) Liou, J. P.; Wu, C. Y.; Hsieh,
H. P.; Chang, C. Y.; Chen, C. M.; Kuo, C. C.; Chang, J. Y. 4- and
5-Aroylindoles as Novel Classes of Potent Antitubulin Agents. J. Med.
Chem. 2007, 50, 4548–4552.
MgSO4 and concentrated under reduced pressure to give a yellow
oil residue, which was treated with potassium tert-butoxide (1.39
g, 12.36 mmol) in the presence of THF (50 mL) and stirred for 15
min at room temperature. The 3,4,5-trimethoxybenzoyl chloride
(2.14 g, 9.27 mmol) was added to the reaction mixture. After 1 h,
the solvent was evaporated and the residue was neutralized with
NaHCO3(sat.) and then extracted with EtOAc (20 mL × 2) and
CH2Cl2 (20 mL × 2). The combined organic layers were dried over
MgSO4 and evaporated to give a residue, which was dissolved in
THF (20 mL) and then was subjected to 1.0 M tetra-n-butylam-
monium floride/THF (12.4 mL) with stirring at 0 °C for 1 h. The
reaction mixture was evaporated and purified by silica gel chro-
matography (EtOAc/n-hexane ) 1: 3; recrystallized by EtOAc/n-
hexane) to afford 27 as a yellow crystalline solid: yield 19%, mp
1
153-155 °C. H NMR (500 MHz, CDCl3): δ 2.39 (s, 3H), 3.82
(s, 6H), 3.88 (s, 3H), 3.95 (s, 3H), 5.76 (br, 1H), 6.53 (s, 1H), 6.63
(d, J ) 8.9 Hz, 1H), 6.69 (d, J ) 8.9 Hz, 1H), 6.95 (s, 2H). 13C
NMR (125 MHz, CDCl3): δ 15.8, 56.3, 57.1, 61.1, 105.1, 105.7,
107.0, 107.8, 118.5, 130.3, 133.5, 137.0, 137.6, 141.1, 141.8, 153.1,
169.3. MS (EI) m/z: 371 (M+, 44%), 195 (100%). HRMS (EI) for
C20H21NO6 (M+): calcd, 371.1371; found, 371.1370. Anal.
(C20H21NO6 ·0.5H2O) C, H, N.
Acknowledgment. This research was supported by the
National Science Council of the Republic of China (Grants NSC
96-2320-B-038-003, NSC 96-2752-B-400-001-PAE, and NSC-
95-2113-M-400-001-MY3) and by National Health Research
Institutes, Taiwan (Grant CA-097-PP-02).
Supporting Information Available: Spectral data of 6-26, 37,
42, 44, 46 and details for synthesis and biological evaluations. This
material is available free of charge via the Internet at http://
pubs.acs.org.
References
(1) (a) Jordan, A.; Hadfield, J. A.; Lawrence, N. J.; McGown, A. T.
Tubulin as a Target for Anticancer Drugs: Agents Which Interact with
the Mitotic Spindle. Med. Res. ReV. 1998, 18, 259–296. (b) Jordan,
M. A.; Wilson, L. Microtubules as a Target for Anticancer Drugs.
Nat. ReV. Cancer 2004, 4, 253–265.
(2) (a) Hinnen, P. Eskens, FALM Vascular Disrupting Agents in Clinical
Development. Br. J. Cancer 2007, 96, 1159–1165. (b) Lippert, J. W.,
III. Vascular Disrupting Agents. Bioorg. Med. Chem. 2007, 15, 605–
615. (c) Siemann,D. W., Ed. Vascular-Targeted Therapies in Oncol-
ogy; John Wiley & Sons: Chichester, U.K., 2006. (d) 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. Differentiation and
Definition of Vascular-Targeted Therapies. Clin. Cancer Res. 2005,
11, 416–420. (e) Gaya, A. M.; Rustin, G. J. Vascular Disrupting
Agents: A New Class of Drug in Cancer Therapy. Clin. Oncol. 2005,
17, 277–290. (f) Tozer, G. M.; Kanthou, C.; Baguley, B. C. Disrupting
Tumour Blood Vessels. Nat. ReV. Cancer 2005, 5, 423–435. (g)
Patterson, D. M.; Rustin, G. J. S. Vascular Damaging Agents. Clin.
Oncol. 2007, 19, 443–456.
(3) (a) Tron, G. C.; Pirali, T.; Sorba, G.; Pagliai, F.; Busacca, S.;
Genazzani, A. A. Medicinal Chemistry of Combretastatin A4: Present
and Future Directions. J. Med. Chem. 2006, 49, 3033–3044. (b) Hsieh,
H. P.; Liou, J. P.; Mahindroo, N. Pharmaceutical Design of Antimitotic
Agents Based on Combretastatins. Curr. Pharm. Des. 2005, 11, 1655–
1677. (c) Li, Q.; Sham, H. L. Discovery and Development of
Antimitotic Agents That Inhibit Tubulin Polymerisation for the
Treatment of Cancer. Expert Opin. Ther. Patents 2002, 12, 1663–
1702. (d) Nam, N. H. Combretastatin A-4 Analogues as Antimitotic
Antitumor Agents. Curr. Med. Chem. 2003, 10, 1697–1722. (e)
Mahindroo, N.; Liou, J. P.; Chang, J. Y.; Hsieh, H. P. Antitubulin
Agents for the Treatment of Cancer-a Medicinal Chemistry Update.
Expert. Opin. Ther. Pat. 2006, 16, 647–691. (f) Chaplin, D. J.;
Horsman, M. R.; Siemann, D. W. Current Development Status of
Small-Molecule Vascular Disrupting Agents. Curr. Opin. InVest. Drugs
2006, 7, 522–528. (g) Romagnoli, R.; Baraldi, P. G.; Carrion, M. D.;
Cara, C. L.; Preti, D.; Fruttarolo, F.; Pavani, M. G.; Tabrizi, M. A.;
Tolomeo, M.; Grimaudo, S.; Cristina, A. D.; Balzarini, J.; Hadfield,
J. A.; Brancale, A.; Hamel, E. Synthesis and Biological Evaluation of
2- and 3-Aminobenzo[b]thiophene Derivatives as Antimitotic Agents
and Inhibitors of Tubulin Polymerization. J. Med. Chem. 2007, 50,
2273–2277.
(11) (a) Romagnoli, R.; Baraldi, P. G.; Pavani, M. G.; Tabrizi, M. A.; Preti,
D.; Fruttarolo, F.; Piccagli, L.; Jung, M. K.; Hamel, E.; Borgatti, M.;
Gambari, R. Synthesis and Biological Evaluation of 2-Amino-3-
(3′,4′,5′-trimethoxybenzoyl)-5-aryl Thiophenes as a New Class of
Potent Antitubulin Agents. J. Med. Chem. 2006, 49, 3906–3915. (b)
Romagnoli, R.; Baraldi, P. G.; Remusat, V.; Carrion, M. D.; Lopez
Cara, C.; Preti, D.; Fruttarolo, F.; Pavani, M. G.; Tabrizi, M. A.;
Tolomeo, M.; Grimaudo, S.; Balzarini, J.; Jordan, M. A.; Hamel, E.
Synthesis and Biological Evaluation of 2-(3′,4′,5′-Trimethoxybenzoyl)-
3-amino 5-aryl thiophenes as a New Class of Tubulin Inhibitors.
J. Med. Chem. 2006, 49, 6425–6428.
(12) Cushman, M.; Nagarathnam, D.; Gopal, D.; Chakraborti, A. K.; Lin,
C. M.; Hamel, E. Synthesis and Evaluation of Stilbene and Dihydros-
tilbene Derivatives as Potential Anticancer Agents That Inhibit Tubulin
Polymerization. J. Med. Chem. 1991, 34, 2579–2588.
(13) (a) Silverman, R. B. The Organic Chemistry of Drug Design and Drug
Action, 2nd ed.; Elsevier Academic Press: Amsterdam, 2004; p 538.
(b) Patrick, G. L. An Introduction to Medicinal Chemistry, 3rd ed.;
Oxford University Press: Oxford, U.K., 2005; pp 191-192. (c) Borne,
R.; Levi, M.; Wilson, N. Nonsteroidal Anti-Inflammatory Drugs. In
Foye’s Principles of Medicinal Chemistry, 6th ed.; Lemke, T. L.,
Williams, D. A., Roche, V. F., Zito, S. W., Eds.; Lippincott Williams:
Philadelphia, PA, 2008.
(14) Liou, J. P.; Chang, Y. L.; Kuo, F. M.; Chang, C. W.; Tseng, H. Y.; Wang,
C. C.; Yang, Y. N.; Chang, J. Y.; Lee, S. J.; Hsieh, H. P. Concise Synthesis
and Structure-Activity Relationships of Combretastatin A-4 Analogues,
1-Aroylindoles and 3-Aroylindoles, as Novel Classes of Potent Antitubulin
Agents. J. Med. Chem. 2004, 47, 4247–4257.
(15) Roue, N.; Delahaigue, T.; Barret, R. Efficient Mononitration of Indolic
Compounds with Nitric Acid Impregnated on Silica Gel. Heterocycles
1996, 43, 263–266.
(16) Chilin, A.; Rodighiero, P.; Guiotto, A. Isomerization of 4-Aminoben-
zofurans to 4-Hydroxyindoles. Synthesis 1998, 3, 309–311.
JM800150D