Identification of benzofuro[2,3-b]quinoline derivatives as a new class of antituberculosis agents

Article abstract of DOI:10.1016/j.ejmech.2009.10.050

A series of 11-alkoxylated and 11-aminated benzofuro[2,3-b]quinoline derivatives were designed, synthesized, and evaluated for their anti-TB and cytotoxic activities. The known 11-chlorobenzofuro[2,3-b]quinoline (3) was synthesized in a single step from anthranilic acid and 2-coumaranone in phosphorus oxychloride in 51% yield for the first time. Treatment of 3 with alcohols and amines gave 11-alkoxylated and 11-aminated benzofuro[2,3-b]quinoline derivatives respectively, which were evaluated for their anti-TB and cytotoxic activities. Our results indicated that 11-arylaminated derivatives were more active than their respective 11-aryloxylated isosteric isomers against Mycobacterium tuberculosis. Among the tested compounds, 11-methoxybenzofuro[2,3-b]quinoline (4), 11-methylamino- benzofuro[2,3-b]quinoline (9), and 11-dimethylaminobenzofuro[2,3-b]quinoline (14) exhibited significant activities against the growth of M. tuberculosis (MIC values of <0.20 μg/mL) and low cytotoxicities against VERO cell with IC₅₀ values of 11.77, 5.55, and >30.00 μg/mL respectively. The selectivity index (SI = IC₅₀/MIC) for 4, 9, and 14 was greater than 58.85, 27.75, and 150 respectively.

Full text of DOI:10.1016/j.ejmech.2009.10.050

European Journal of Medicinal Chemistry 45 (2010) 602–607
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Identification of benzofuro[2,3-b]quinoline derivatives as a new class
of antituberculosis agents
,
,
Chiao-Li Yang a b, Chih-Hua Tseng a, Yeh-Long Chen a, Chih-Ming Lu a b, Chai-Lin Kao a,
Ming-Hsien Wu c, Cherng-Chyi Tzeng a
,
*
a Department of Medicinal and Applied Chemistry, College of Life Science, Kaohsiung Medical University, Kaohsiung City 807, Taiwan
b Graduate Institute of Pharmaceutical Sciences, College of Pharmacy, Kaohsiung Medical University, Kaohsiung City 807, Taiwan
c Division of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Miaoli County 350, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 11-alkoxylated and 11-aminated benzofuro[2,3-b]quinoline derivatives were designed,
synthesized, and evaluated for their anti-TB and cytotoxic activities. The known 11-chlorobenzofuro[2,3-
b]quinoline (3) was synthesized in a single step from anthranilic acid and 2-coumaranone in phosphorus
oxychloride in 51% yield for the first time. Treatment of 3 with alcohols and amines gave 11-alkoxylated
and 11-aminated benzofuro[2,3-b]quinoline derivatives respectively, which were evaluated for their anti-
TB and cytotoxic activities. Our results indicated that 11-arylaminated derivatives were more active than
their respective 11-aryloxylated isosteric isomers against Mycobacterium tuberculosis. Among the tested
compounds, 11-methoxybenzofuro[2,3-b]quinoline (4), 11-methylamino- benzofuro[2,3-b]quinoline (9),
and 11-dimethylaminobenzofuro[2,3-b]quinoline (14) exhibited significant activities against the growth
Received 3 June 2009
Received in revised form
23 October 2009
Accepted 29 October 2009
Available online 10 November 2009
Keywords:
Benzofuro[2,3-b]quinoline
Antimycobacterial activity
Cytotoxic activity
of M. tuberculosis (MIC values of <0.20
11.77, 5.55, and >30.00
g/mL respectively. The selectivity index (SI ¼ IC50/MIC) for 4, 9, and 14 was
greater than 58.85, 27.75, and 150 respectively.
mg/mL) and low cytotoxicities against VERO cell with IC50 values of
m
Ó 2009 Elsevier Masson SAS. All rights reserved.
1. Introduction
indoloquinoline derivatives, because of their potential biological
activities [19–27]. However, the isomeric benzofuroquinoline
derivatives have attracted only limited attention [28–32]. In
continuation of our efforts to identify potential anti-TB agents with
novel types of structures which are distinct from those of existing
drugs, we herein describe the synthesis of certain alkoxy, aryloxy,
alkylamino, or arylamino substituted benzofuro[2,3-b]quinoline
derivatives for anti-TB evaluations. Recently, three quinoline alka-
loids were isolated from the leaves of Lunasia amara Blanco (Ruta-
ceae) which exhibited good inhibitory activities against M.
tuberculosis H37Rv. One of the common structural features among
these alkaloids is the presence of a 4-methoxy group [33]. We have
also reported certain biologically active furo[2,3-b]quinoline and
indolo[2,3-b]quinoline derivatives which possess alkoxy, aryloxy,
alkylamino, or arylamino group [12,34].
Since the structures of these newly synthesized benzofuro[2,3-
b]quinoline derivatives in which the 2-phenyl group and the bicy-
clic quinoline are locked by an oxygen bridge to form a coplanar
tetracyclic structure [35], belong to potential DNA intercalators,
their cytotoxicities against a 3-cell line panel consisting of MCF7
(Breast), NCI-H460 (Lung), and SF-268 (CNS) were also evaluated.
The aim of our current study is to identify novel skeletons that
confer anti-TB activities with low cytotoxicities.
The first-line drugs currently used for the treatment of tubercu-
losis (TB) infection are streptomycin, isoniazid, ethambutol, pyr-
azinamide, and rifampicin [1]. However, the current TB treatment
regimens, although highly effective, are far from ideal. Recently, the
emergence of multi-drug resistant (MDR) strains and the global
human immunodeficiency virus (HIV) pandemic have amplified the
incidence of TB and have created an urgent need for alternative drug
treatments for M. tuberculosis infection [2–7]. Over the past few
years, we have been particularly interested in the synthesis of fluo-
roquinolones for anti-TB and anticancer evaluations [8–11]. We have
also synthesized certain polycyclic heterocycles such as indolo[2,3-
b]quinoline for anticancer evaluation on the premise that these
tetracyclic heterocycles can bind strongly to double helical DNA by
intercalation and cause inhibition of DNA replication and transcrip-
tion [12,13]. The indoloquinoline skeleton is present in a number of
natural alkaloids with broad biological effects including antibacte-
rial, antihyperglycemic, antiinflammatory, and antimalarial activities
[14–18]. Currently there is considerable interest in the synthesis of
* Corresponding author. Tel.: þ886 7 3121101x2123; fax: þ886 7 3125339.
E-mail address: tzengch@kmu.edu.tw (C.-C. Tzeng).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.10.050

C.-L. Yang et al. / European Journal of Medicinal Chemistry 45 (2010) 602–607
603
O
OH
O
OMe
OMe
O
N
H
OMe
N
O
NH2
Cl
O
H
2
1
(a)
O
Cl
(b)
OH
NH2
O
O
O
N
3
Scheme 1. Reactions and conditions (a) Procedures of Kawase, et. al. [29,30]; (b) POCl3, reflux, 24 h.
2. Chemistry
activities especially anticancer and anti-infectious evaluations of
these benzofuro[2,3-b]quinoline derivatives had not been explored.
The known 11-chlorobenzofuro[2,3-b]quinoline (3) was selected
as the starting material. According to the reported procedures of
Kawase, et. al. [29,30], 4-hydroxy-3-(2-methoxyphenyl)-1,2-dihy-
droquinolin- 2-one (1), prepared from methyl anthranilate and 2-
methoxyphenylacetyl chloride, was treated with pyridine
hydrochloride to furnish a mixture of the linear benzofuro[2,3-
b]quinolin-11-one (2) and its angular isomer. Purification of 2 fol-
lowed by the chlorination with phosphorus pentachloride afforded
desired 3 in an overall yield of 32%. Therefore, we decided to explore
an alternative synthetic pathway for the preparation of 3 with
a better overall yield. A survey of literature revealed that 10-chloro-
11H-indeno[1,2-b]quinoline had been prepared from anthranilic
acid and 1-indanone in phosphorous oxychloride in a single step
[36]. Under similar reaction conditions, we were able to obtain 3 in
a yield of 51% by refluxing anthranilic acid and 2-coumaranone in
phosphorus oxychloride as outlined in Scheme 1.
Conversion of 3 into 11-aminated benzofuro[2,3-b]quinoline
derivatives 8–14 was carried out and their structures have been
characterized by ESIMS, HRMSESI, elemental analysis, and NMR
spectra.
3. Results and discussion
The anti-TB activities of 11-substituted benzofuro[2,3-b]quino-
line derivatives are summarized in Table 1. For comparison
purposes, rifampin was used as the positive drug standard. 11-
Methoxybenzofuro[2,3-b]quinoline (4) was found to be very potent
in being able to inhibit 99% growth of M. tuberculosis at a concen-
tration of <0.20
the less bulky methoxy derivative 4 was more active than its ethoxy
counterpart 5 (MIC ¼ 1.44 g/mL) which in turn was more active
than the most bulky phenoxy congener 6 (MIC > 100 g/mL). The
same order was observed for the 11-aminated derivatives in which
the less bulky methylamino derivative 9 (MIC < 0.20 g/mL) was
a more potent anti-TB agent than its phenylamino counterpart 10
g/mL). Introduction of a 4-methoxy substituent on the
mg/mL. For the 11-alkoxy substituted derivatives,
m
m
By the treatment with various alcohols, compound 3 was con-
verted into 11-alkoxylated benzofuro[2,3-b]quinoline derivatives
4–7 as described in Scheme 2. Although the preparation of
11-methoxybenzofuro[2,3-b]quinoline (4) and 11-ethoxybenzofuro
[2,3-b]quinoline (5) had been previously described [30], biological
m
(MIC ¼ 5.35
m
11-phenylamino moiety was found to enhance anti-TB activity (10,
OR
4 R = Me
5 R = Et
6 R = Ph
(a), (b), or (c)
O
7 R = Ph-4-COMe
N
Cl
NHR
8 R = H
(d) or (e)
9 R = Me
O
10 R = Ph
N
O
N
11 R = Ph-4-COMe
12 R = Ph-4-OMe
13 R = Ph-3-OMe
3
Me
Me
N
(f)
O
N
14
Scheme 2. Reactions and conditions (a) RONa, ROH, reflux for 3 h (for 4 and 5); (b) PhOH, K2CO3, 100 ꢀC, 2 h (for 6); (c) 4-hydroxyacetophenone, K2CO3 in DMF, 100 ꢀC, 6 h (for 7);
(d) RNH2 (aq) in sealed vessel, 70 ꢀC, 24 h (for 8 and 9); (e) substituted aniline in ethoxyethanol, reflux, 24 h (for 10–13); (f) 40% Me2NH (aq) in sealed vessel, 70 ꢀC, 24 h.

604
C.-L. Yang et al. / European Journal of Medicinal Chemistry 45 (2010) 602–607
Table 1
activities against the growth of M. tuberculosis with MIC values of
<0.20 g/mL respectively and low cytotoxicities against VERO cell
with IC50 values of 11.77, 5.55, and >30.00 g/mL respectively. The
Anti-M. tuberculosis H37Rv (ATCC 27294) activities of 11-substituted benzofuro[2,3-
b]quinoline derivatives.
m
m
selectivity index (SI) values for 4, 9, and 14 were greater than 58.85,
27.75, and 150 respectively.
XR
All compounds were evaluated in vitro against a 3-cell line panel
consisting of MCF7 (Breast), NCI-H460 (Lung), and SF-268 (CNS). In
this protocol, each cell line was inoculated and preincubated on
a microtiter plate. Test agents were then added at concentrations of
20.0 and 4.0 mg/mL respectively and the culture incubated for 48 h.
End-point determinations were made with sulforhodamine B,
a protein-binding dye. Results for each test agent are reported as
the percent of growth of the treated cells against the untreated
control cells. Results from Table 2 indicated that all the compounds
are not cytotoxic at a concentration of 4.0 mg/mL.
O
N
Compd
X
R
MIC (
m
g/mL)
IC50
(
m
g/mL)
SI (IC50/MIC)
4
5
6
7
8
9
10
11
12
13
14
Rifampin
O
O
O
O
NH
NH
NH
NH
NH
NH
N
Me
Et
Ph
Ph-4-COMe
H
Me
<0.20
1.44
11.77
10.34
NDa
ND
>58.85
7.18
ND
ND
ND
>27.75
1.15
ND
1.38
ND
>100
>100
>100
<0.20
5.35
14.57
2.63
17.83
<0.20
ND
5.55
6.14
ND
3.63
ND
Ph
4. Conclusion
Ph-4-COMe
Ph-4-OMe
Ph-3-OMe
(Me)2
We have identified certain benzofuro[2,3-b]quinoline derivatives
as potential anti-TB agents with low cytotoxicies. Among them, 11-
dimethylaminobenzofuro[2,3-b]quinoline (14) exhibited the most
>30.00
100
>150
400
0.125–0.25
a
potent anti-TB activity with MIC value of < 0.20
mg/mL and very low
Not determined.
cytotoxicity against VERO cell with IC50 value of >30.00
mg/mL. The
selectivity index (SI) for 14 was greater than 150. Further evaluation
of 14 as an anti-TB drug candidate is on-going.
5.35 v.s. 12, 2.63) while introduction of a 4-methylcarbonyl or 3-
methoxy substituent (11, 14.57 and 13, 17.83 respectively) was found
to decrease anti-TB activity. 11-Aminobenzofuro[2,3-b]quinoline (8),
a primary amine derivative, was devoid of anti-TB activity while 11-
5. Experimental
dimethylaminobenzofuro[2,3-b]quinoline (14),
derivative, inhibited 99% growth of M. tuberculosis at a concentra-
tion of <0.20 g/mL. In general, 1-arylaminated derivatives were
a tertiary amine
5.1. General
m
Melting points were determined on a Electrothermal IA9100
melting point apparatus and are uncorrected. Nuclear magnetic
resonance (1H and 13C) spectra were recorded on a Varian Gemini
200 spectrometer or Varian-Unity-400 spectrometer. Chemical
more active than their respective 11-aryloxylated isosteric isomers
(6 v.s. 10; 7 v.s. 11) against M. tuberculosis. The anti-TB activities of
compounds 4, 9, and 14 were comparable to the positive rifampin.
The cytotoxicity (IC50) against mammalian VERO cells as well as
the selectivity index (SI), defined as IC50/MIC, for compounds 4, 5, 9,
10, 12, and 14 were also determined. Compounds with an SI of >10
are of interest for further development as potential anti-TB agents.
Results indicated that compounds 4, 9, and 14 exhibited significant
shifts were expressed in parts per million
(d
)
with
tetramethylsilane (TMS) as an internal standard. Thin-layer chro-
matography was performed on silica gel 60 F-254 plates purchased
from E. Merck and Co. The elemental analyses were performed in
the Instrument Center of National Science Council at National
Cheng-Kung University and National Chung-Hsing University using
Heraeus CHN-O Rapid EA, and all values are within ꢁ0.4% of the
theoretical compositions.
Table 2
Cytotoxicity of 11-substituted benzofuro[2,3-b]quinoline derivatives.
5.1.1. 11-Chlorobenzofuro[2,3-b]quinoline (3)
A mixture of anthranilic acid (1.37 g, 10.0 mmol) and 2-coumar-
anone (1.34 g, 10.0 mmol) in phosphorus oxychloride (60 mL) was
refluxed for 24 h (TLC monitoring). After cooling, the mixture was
poured into ice-water (50 mL) and neutralized with saturated
NaHCO3 until pH 7 resulted. The brown precipitate thus obtained
was collected, purified by column chromatography (CH2Cl2), and
crystallized from EtOH to give 3 (1.29 g, 51%). Mp: 208–210 (lit: 211–
212 ꢀC) [30]. 1H NMR (400 MHz, DMSO-d6): 7.53–7.57 (m, 1H, 9-H),
7.71–7.83 (m, 3H, 2-, 7-, 8-H), 7.90–7.94 (m, 1H, 3-H), 8.12 (d, 1H,
J ¼ 8.4 Hz, 10-H), 8.36–8.41 (m, 2H, 1-, 4-H). 13C NMR (100 MHz,
DMSO-d6): 93.87, 111.88, 115.18, 120.68, 123.48, 123.50, 124.16,
126.47, 128.29, 130.45, 130.81, 145.34, 154.90, 159.11, 161.06. ESIMS
(m/z): 254 [M þ H]þ. HRMS (ESI): m/z calcd for C15H9ClNO [M þ H]þ
254.0373, found 254.0372. Anal. calcd for C15H8ClNO: C 71.02, H 3.18,
N 5.52; found: C 71.03, H 3.24, N 5.41.
XR
O
N
Compd
X
R
MCF7
NCI-H460
SF-268
(CNS)
20
(Breast cancer) (Lung cancer)
20
g/mL
4
20
g/mL
4
m
4
m
m
g/mL
m
g/mL
m
g/mL
m
g/mL
4
5
6
7
8
9
10
11
12
13
14
O
O
O
O
Me
Et
Ph
Ph-4-COMe
H
92
77
64
88
113
99
44
49
35
84
48
102
99
94
68
84
91
62
107
99
53
20
17
46
76
90
92
99
98
90
108
100
72
86
76
63
87
98
86
108
104
84
100
114
100
118
106
109
107
87
104
110
102
104
64
NH
NH Me
NH Ph
NH Ph-4-COMe
NH Ph-4-OMe
NH Ph-3-OMe
98
5.1.2. 11-Methoxybenzofuro[2,3-b]quinoline (4)
118
109
111
97
A slurry of 3 (0.25 g, 1.0 mmol) in methanol (100 mL) was
added to the stirred solution of sodium methoxide in methanol
(prepared by dissolving 120 mg of freshly cut sodium in 12 mL of
methanol under argon). The reaction mixture was refluxed for 3 h
83
99
60
91
N
(Me)2
108
102

C.-L. Yang et al. / European Journal of Medicinal Chemistry 45 (2010) 602–607
605
(TLC monitoring). The solvent was removed in vacuo, and the
residue was poured into H2O (50 mL) and extracted with CH2Cl2
(50 mL ꢂ 3). The organic layer was washed with brine, dried over
MgSO4 and evaporated in vacuo. The resulting precipitate was
purified by column chromatography (MeOH:CH2Cl2 1/50) and
crystallized from EtOH to give 4 (0.15 g, 60%). Mp: 152–153 ꢀC (lit:
165–165.5 ꢀC) [30]. 1H NMR (400 MHz, CDCl3): 4.32 (s, 3H, OMe),
7.41–7.45 (m, 1H, 9-H), 7.53–7.64 (m, 3H, 2-, 7-, 8-H), 7.75–7.80
(m, 1H, 3-H), 8.10 (dd, 1H, J ¼ 1.6, 8.0 Hz, 10-H), 8.14 (d, 1H,
J ¼ 8.4 Hz, 4-H), 8.32 (dd, 1H, J ¼ 0.8, 8.4 Hz, 1-H). 13C NMR
(100 MHz, CDCl3): 61.96, 111.81, 113.87, 119.14, 120.95, 122.25,
123.57, 123.63, 124.66, 128.64, 129.20, 130.14, 147.34, 154.88,
159.54, 164.13. ESIMS (m/z): 250 [M þ H]þ. HRMS (ESI): m/z calcd
for C16H12NO2 [M þ H]þ 250.0868, found 250.0869. Anal. calcd for
C16H11NO2$0.5H2O: C 74.40, H 4.69, N 5.42; found: C 74.41, H 4.83,
N 5.06.
for C23H16NO3 [M þ H]þ 354.1130, found 354.1131. Anal. calcd for
C23H15NO3: C 78.17, H 4.28, N 3.96; found: C 78.05, H 4.46, N 3.81.
5.1.6. Benzofuro[2,3-b]quinolin-11-amine (8)
A mixture of 3 (0.25 g, 1.0 mmol) and ammonia water (20 mL) in
a sealed vessel was heated at 70 ꢀC for 24 h (TLC monitoring). The
solvent was removed in vacuo, and the residue was poured into H2O
(100 mL). The resulting precipitate that separated was collected
and crystallized from EtOH to give 8 (0.14 g, 60%). Mp: >300 ꢀC. 1H
NMR (400 MHz, DMSO-d6): 7.43–7.56 (m, 3H, 3-, 8-, 9-H), 7.70 (dd,
1H, J ¼ 0.8, 8.4 Hz, 7-H), 7.77–7.81 (m, 1H, 2-H), 7.88 (dd, 1H, J ¼ 0.8,
8.4 Hz, 10-H), 8.08 (br s, 2H, NH2), 8.54 (dd, 1H, J ¼ 0.8, 7.2 Hz, 4-H),
8.03 (d, 1H, J ¼ 8.0 Hz, 1-H). 13C NMR (100 MHz, DMSO-d6): 96.37,
110.91, 115.89, 121.67, 122.38, 123.35, 123.38, 123.69, 125.29, 126.37,
130.93, 143.18, 149.32, 152.39, 161.75. ESIMS (m/z): 235 [M þ H]þ.
HRMS (ESI): m/z calcd for C15H11N2O [M þ H]þ 235.0871, found
235.0873. Anal. calcd for C15H10N2O$1.0H2O$1.0HCl: C 62.38, H
4.55, N 9.70; found: C 62.77, H 4.92, N 9.87.
5.1.3. 11-Ethoxybenzofuro[2,3-b]quinoline (5)
Prepared from 3 and sodium ethoxide in ethanol by the same
procedure as described for the preparation of 4. Yield: 62%. Mp:
80–82 ꢀC (lit: 72–73 ꢀC) [30]. 1H NMR (400 MHz, CDCl3): 1.63 (t, 3H,
J ¼ 7.2 Hz, CH3), 4.54 (q, 2H, J ¼ 7.2 Hz, OCH2), 7.39–7.43 (m,1H, 9-H),
7.52–7.58 (m, 2H, 2-, 8-H), 7.61–7.63 (m, 1H, 7-H), 7.74–7.79 (m, 1H,
3-H), 8.06–8.08 (m, 1H, 10-H), 8.13 (d, 1H, J ¼ 8.4 Hz, 4-H), 8.30–8.33
(m, 1H, 1-H). 13C NMR (100 MHz, CDCl3): 16.02, 70.82, 108.39, 111.77,
121.19, 122.05, 122.56, 123.36, 123.54, 124.53, 128.40, 128.52, 130.07,
147.31, 154.83, 158.68, 164.14. ESIMS (m/z): 264 [M þ H]þ. HRMS
(ESI): m/z calcd for C17H14NO2 [M þ H]þ 264.1024, found 264.1026.
Anal. calcd for C17H13NO2$0.5H2O: C 74.97, H 5.19, N 5.14; found: C
74.87, H 4.86, N 5.30.
5.1.7. N-methylbenzofuro[2,3-b]quinolin-11-amine (9)
Compound 9 was prepared from 3 and 40% methylamine by the
same procedure as described for the preparation of 8. Yield: 64%.
Mp: 214–216 ꢀC. 1H NMR (400 MHz, DMSO-d6): 3.50 (d, 3H,
J ¼ 5.2 Hz, CH3), 7.35–7.48 (m, 4H, NH, 3-, 8-, 9-H), 7.62 (dd, 1H,
J ¼ 0.8, 8.0 Hz, 7-H), 7.67–7.72 (m, 1H, 2-H), 7.83 (dd, 1H, J ¼ 0.8,
8.4 Hz, 10-H), 8.16 (dd, 1H, J ¼ 0.8, 8.0 Hz, 4-H), 8.45 (dd, 1H, J ¼ 0.8,
8.4 Hz, 1-H). 13C NMR (100 MHz, DMSO-d6): 34.85, 97.34, 110.75,
117.83, 121.67, 122.71, 122.97, 123.02, 123.04, 126.11, 127.89, 129.57,
146.17, 150.34, 152.81, 163.89. ESIMS (m/z): 249 [M þ H]þ. HRMS
(ESI): m/z calcd for C16H13N2O [M þ H]þ 249.1028, found 249.1029.
Anal. calcd for C16H12N2O: C 77.40, H 4.87, N 11.28; found: C 77.49, H
5.10, N 11.24.
5.1.4. 11-Phenoxybenzofuro[2,3-b]quinoline (6)
A mixture of 3 (0.25 g, 1.0 mmol), K2CO3 (0.28 g, 2.0 mmol) and
phenol (15 mL) was stirred at 100 ꢀC for 2 h (TLC monitoring). After
cooling, the mixture was poured into 2 N NaOH solution (50 mL).
The solution was extracted with CH2Cl2 (50 mL ꢂ 3), washed with
brine, dried over MgSO4 and evaporated in vacuo. Purification by
column chromatography (MeOH:CH2Cl2 1/50) and crystallization
5.1.8. N-phenylbenzofuro[2,3-b]quinolin-11-amine (10)
A mixture of 3 (0.25 g, 1.0 mmol) and aniline (0.28 g, 3.0 mmol)
in ethoxyethanol (30 mL) was refluxed for 24 h (TLC monitoring).
The solvent was removed in vacuo, and the residue was poured into
H2O (100 mL). The resulting precipitate that separated was
collected and crystallized from EtOH to give 10 (0.12 g, 38%). Mp:
134–135 ꢀC.1H NMR (400 MHz, DMSO-d6): 6.47 (d,1H, J ¼ 7.6 Hz, 7-
H), 6.99–7.04 (m, 4H, 9-, Ar–H), 7.25–7.29 (m, 2H, Ar–H), 7.38–7.43
(m, 1H, 8-H), 7.57–7.61 (m, 1H, 3-H), 7.63 (d, 1H, J ¼ 8.0 Hz, 10-H),
7.78–7.83 (m, 1H, 2-H), 8.00 (d, 1H, J ¼ 8.4 Hz, 4-H), 8.54 (d, 1H,
J ¼ 8.4 Hz, 1-H), 9.62 (s, 1H, NH). 13C NMR (100 MHz, DMSO-d6):
104.76, 110.62, 118.34 (2C), 120.82, 121.60, 121.67, 122.60, 123.58,
123.94, 124.64, 127.50, 128.10, 129.32 (2C), 130.08, 142.29, 142.38,
146.41, 153.63, 163.43. ESIMS (m/z): 311 [M þ H]þ. HRMS (ESI): m/z
calcd for C21H15N2O [M þ H]þ 311.1184, found 311.1182. Anal. calcd
for C21H14N2O$0.25H2O: C 80.10, H 4.65, N 8.90; found: C 80.16, H
4.65, N 8.78.
from EtOH gave
6
(0.26 g, 84%). Mp: 120–122 ꢀC. 1H NMR
(400 MHz, DMSO-d6): 7.10–7.28 (m, 5H, 8-, 9-, Ar–H), 7.36–7.42 (m,
2H, Ar–H), 7.55–7.66 (m, 2H, 2-, 7-H), 7.75–7.77 (m, 1H, 10-H),
7.87–7.91 (m, 1H, 3-H), 8.13–8.18 (m, 2H, 1-, 4-H). 13C NMR
(100 MHz, DMSO-d6): 108.47, 111.66, 115.73 (2C), 119.90, 120.82,
122.16, 123.48, 123.63, 123.85, 125.51, 128.10, 129.48, 130.41 (2C),
130.74, 146.81, 152.43, 154.37, 156.87, 163.26. ESIMS (m/z): 312
[M þ H]þ. HRMS (ESI): m/z calcd for C21H14NO2 [M þ H]þ 312.1024,
found 312.1025. Anal. calcd for C21H13NO2: C 81.01, H 4.21, N 4.50;
found: C 81.05, H 4.43, N 4.47.
5.1.5. 1-[4-(Benzofuro[2,3-b]quinolin-11-yloxy)phenyl]ethanone (7)
A mixture of 3 (0.25 g, 1.0 mmol), 4-hydroxyacetophenone
(0.27 g, 2.0 mmol), and K2CO3 (0.28 g, 2.0 mmol) in DMF (50 mL)
was stirred at 100 ꢀC for 6 h (TLC monitoring). The solvent was
removed in vacuo, and the residue was poured into H2O (100 mL).
The resulting precipitate that separated was collected, purified by
column chromatography (MeOH:CH2Cl2 1/50), and crystallized
from EtOH to give 7 (0.28 g, 80%). Mp: 162–163 ꢀC. 1H NMR
(400 MHz, CDCl3): 2.17 (s, 3H, CH3), 7.03–7.07 (m, 2H, Ar–H), 7.17–
7.21 (m,1H, 9-H), 7.37 (dd,1H, J ¼ 0.8, 8.0 Hz, 7-H), 7.47–7.56 (m, 2H,
3-, 8-H), 7.60 (d, 1H, J ¼ 8.4 Hz, 10-H), 7.79–7.83 (m, 1H, 2-H), 7.94–
7.98 (m, 2H, Ar–H), 8.13 (dd, 1H, J ¼ 1.2, 8.4 Hz, 4-H), 8.21 (d, 1H,
J ¼ 8.4 Hz, 1-H). 13C NMR (100 MHz, CDCl3): 26.42, 109.26, 111.71,
115.43 (2C), 120.13, 120.90, 122.06, 123.71, 123.85, 125.39, 128.57,
129.32, 130.53, 131.08 (2C), 132.42, 147.34, 151.88, 155.11, 160.64,
163.66, 196.47. ESIMS (m/z): 354 [M þ H]þ. HRMS (ESI): m/z calcd
5.1.9. 1-[4-(Benzofuro[2,3-b]quinolin-11-ylamino)phenyl]
ethanone (11)
Compound 11 was prepared from 3 and 4-aminoacetophenone
by the same procedure as described for the preparation of 10. Yield:
46%. Mp: 198–200 ꢀC. 1H NMR (400 MHz, DMSO-d6): 2.49 (s, 3H,
CH3), 6.86 (d, 1H, J ¼ 7.6 Hz, 7-H), 6.95–7.98 (m, 2H, Ar–H), 7.17–7.21
(m, 1H, 9-H), 7.49–7.54 (m, 1H, 8-H), 7.64–7.68 (m, 1H, 3-H), 7.73 (d,
1H, J ¼ 8.0 Hz, 10-H), 7.85–7.89 (m, 3H, 2-, Ar–H), 8.08 (dd, 1H,
J ¼ 0.4, 8.4 Hz, 4-H), 8.44 (dd,1H, J ¼ 0.8, 8.4 Hz,1-H),10.05 (br s,1H,
NH). 13C NMR (100 MHz, DMSO-d6): 26.27, 108.40, 111.11, 115.52
(2C), 121.12, 121.81, 123.13, 123.66, 124.61 (2C), 128.24, 128.49,
129.17, 130.35 (2C), 131.024, 140.33, 146.41, 147.46, 154.18, 163.10,
195.97. ESIMS (m/z): 353 [M þ H]þ. HRMS (ESI): m/z calcd for
C23H17N2O2 [M þ H]þ 353.1290, found 353.1287. Anal. calcd for

606
C.-L. Yang et al. / European Journal of Medicinal Chemistry 45 (2010) 602–607
C23H16N2O2$1.0H2O: C 74.57, H 4.91, N 7.56; found: C 74.37, H 4.91, N
7.56.
in a 24-well plate. The cells were exposed to various concentrations
of the tested drugs for 72 h. The methylene blue dye assay was used
to evaluate the effect of the tested compounds on cell growth as
described previously [38].
5.1.10. N-(4-methoxyphenyl)benzofuro[2,3-b]quinolin-11-amine (12)
Compound 12 was prepared from 3 and p-anisidine by the same
procedure as described for the preparation of 10. Yield: 35%. Mp:
166–167 ꢀC. 1H NMR (400 MHz, CDCl3): 3.80 (s, 3H, OCH3), 6.60 (d,
1H, J ¼ 8.0 Hz, 7-H), 6.83–6.87 (m, 2H, Ar–H), 6.97–7.04 (m, 4H, NH,
9-, Ar–H), 7.33–7.38 (m,1H, 8-H), 7.44–7.48 (m, 1H, 3-H), 7.51 (d,1H,
J ¼ 8.0 Hz, 10-H), 7.70–7.74 (m, 1H, 2-H), 8.05–8.12 (m, 2H, 1-, 4-H).
13C NMR (100 MHz, CDCl3): 55.60,104.44,110.82,114.83 (2C),119.84,
121.28 (2C), 121.31, 121.98, 122.68, 123.98, 124.53, 127.21, 129.01,
129.76, 135.00, 142.38, 146.81, 154.32, 155.88, 164.01. ESIMS (m/z):
341 [M þ H]þ. HRMS (ESI): m/z calcd for C22H17N2O2 [M þ H]þ
341.1290, found 341.1292. Anal. calcd for C22H16N2O2$0.5H2O: C
75.62, H 4.91, N 8.02; found: C 75.95, H 5.03, N 7.83.
Acknowledgements
Financial support of this work by the National Science Council of
the Republic of China is gratefully acknowledged. We also thank
National Center for High-Performance Computing for providing
computer resources and chemical database services. Anti-
mycobacterial data were provided by Tuberculosis Antimicrobial
Acquisition& Coordinating Facility (TAACF) through a research and
development contract with the US National Institute of Allergy and
Infectious Diseases.
References
5.1.11. N-(3-methoxyphenyl)benzofuro[2,3-b]quinolin-11-amine (13)
Compound 13 was prepared from 3 and m-anisidine by the same
procedure as described for the preparation of 10. Yield: 32%. Mp:
134–135 ꢀC. 1H NMR (400 MHz, CDCl3): 3.65 (s, 3H, OCH3), 6.49–
6.55 (m, 2H, Ar–H), 6.60 (dd, 1H, J ¼ 2.0, 8.4 Hz, Ar–H), 6.82 (d, 1H,
J ¼ 7.6 Hz, 7-H), 6.97 (br s, 1H, NH), 7.07–7.11 (m, 1H, 9-H), 7.15–7.20
(m, 1H, Ar–H), 7.38–7.42 (m, 1H, 8-H), 7.48–7.55 (m, 2H, 3-, 10-H),
7.72–7.76 (m, 1H, 2-H), 8.11–8.15 (m, 2H, 1-, 4-H). 13C NMR
(100 MHz, CDCl3): 55.24, 104.04, 107.03, 108.08, 110.67, 110.95,
120.88, 121.62, 121.75, 122.82, 124.35, 124.85, 127.77, 129.00, 129.88,
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72.80, H 5.15, N 7.72; found: C 72.82, H 5.23, N 7.55.
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