Benzofuran-isatin hybrids tethered via different length alkyl linkers and their in vitro anti-mycobacterial activities

Article abstract of DOI:10.1016/j.bmc.2019.04.017

A series of novel benzofuran-isatin hybrids 6a–m tethered through different length alkyl linkers propylene, butylene, pentylene and hexylene were designed, synthesized and evaluated for their in vitro anti-mycobacterial activities against both drug-suscep

Full text of DOI:10.1016/j.bmc.2019.04.017

Accepted Manuscript
Benzofuran-isatin hybrids tethered via different length alkyl linkers and their in
vitro anti-mycobacterial activities
Feng Gao, Zijian Chen, Long Ma, Lin Qiu, Jianguo Lin, Guangming Lu
PII:
S0968-0896(19)30409-2
https://doi.org/10.1016/j.bmc.2019.04.017
BMC 14871
DOI:
Reference:
Bioorganic & Medicinal Chemistry
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Accepted Date:
12 March 2019
4 April 2019
9 April 2019
Please cite this article as: Gao, F., Chen, Z., Ma, L., Qiu, L., Lin, J., Lu, G., Benzofuran-isatin hybrids tethered
via different length alkyl linkers and their in vitro anti-mycobacterial activities, Bioorganic & Medicinal
Chemistry (2019), doi: https://doi.org/10.1016/j.bmc.2019.04.017
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Benzofuran-isatin hybrids tethered via different length alkyl
linkers and their in vitro anti-mycobacterial activities
Feng Gao1*, Zijian Chen1, Long Ma1, Lin Qiu2, Jianguo Lin2*, Guangming Lu1*
1 Department of Medical Imaging, Jinling Hospital, Medical School of Nanjing
University, Nanjing, PR China;
2 Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of
Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, PR
China
Abstract: A series of novel benzofuran-isatin hybrids 6a-m tethered through different
length alkyl linkers propylene, butylene, pentylene and hexylene were designed,
synthesized and evaluated for their in vitro anti-mycobacterial activities against both
drug-susceptible and multi-drug resistant (MDR) Mycobacterium tuberculosis (MTB)
and cytotoxicity towards VERO cells. All hybrids with acceptable cytotoxicity in
VERO cells (CC50: 64->1,024 μg/mL) also exhibited considerable anti-mycobacterial
activities against both drug-susceptible and MDR-MTB strains with MIC in a range of
0.125 to 4 μg/mL. The SAR indicated that the length of the linker played a pivotal role
on the activity, and the longer linker could enhance the activity. The most active
hybrid 6d (MIC: 0.125 and 0.125 μg/mL) was comparable to or better than rifampicin
(MIC: 0.5 μg/mL) and isoniazid (MIC: 0.06 μg/mL) against MTB H37Rv, and was
≥256 folds more potent than rifampicin (MIC: 64 μg/mL) and isoniazid (MIC: >128
μg/mL) against MDR-MTB strain, but was less active than TAM16 (MIC: <0.06
μg/mL against the tested two strains). The hybrid 6d also showed low cytotoxicity
towards VERO cell (CC50: 128 μg/mL), but it was inferior to TAM16 in metabolic
stability and in vivo pharmacokinetic profiles.
Keywords: benzofuran-isatin hybrids; anti-mycobacterial; anti-tubercular; multi-drug
resistant; structure-activity relationship
*Corresponding authors: rggaofeng@hotmail.com (F. Gao); linjianguo@jsinm.org (J.
Lin); cjr.luguangming@vip.163.com (G. Lu).
1

1. Introduction
Tuberculosis (TB), predominantly caused by Mycobacterium tuberculosis (MTB), is
an infectious disease which has been the ninth leading cause of death globally [1,2].
Specific targets set in the End TB Strategy include a 90% reduction in TB deaths and a
80% reduction in TB incidence (new cases per year) by 2030, compared with 2015 [1].
However, the widely spread of drug-resistant TB (DR-TB), especially multi-drug
resistant TB (MDR-TB), is one of the major obstacles for the treatment of the global
TB epidemic [3,4]. Therefore, it is imperative to develop new agents with great
potency against both susceptible and MDR MTB infections.
Figure 1 Chemical structures of TAM16, isatin and 1,2,3-triazole tethered
benzofuran-isatin hybrids 1
Benzofuran-based derivatives possess various biological properties including anti-TB
activity [5-13]. Benzofuran derivative TAM16 (Figure 1) demonstrated promising
activity against 38 MTB isolates including MDR-MTB in vitro, and exhibited
excellent in vivo pharmacological properties, indicating its potential for the treatment
of TB [13]. Isatin (indoline-2,3-dione) (Figure 1) also endowed with promising
anti-TB activities [14-17], and incorporation of the pharmacophores of TAM16 and
isatin into one molecular may provide more effective anti-TB candidates [18,19].
2

Figure 2 The design strategy for benzofuran-isatin hybrids
Our previous studies indicated the 1,2,3-triazole tethered benzofuran-isatin hybrids 1
possess great potency against both drug-susceptible and MDR MTB strains [20]. In
this paper, a series of novel benzofuran-isatin hybrids 6a-m tethered through different
length linkers propylene, butylene, pentylene and hexylene were designed, synthesized
and evaluated for their in vitro anti-mycobacterial activities against both
drug-susceptible and MDR MTB strains. We intend to investigate the influence of the
linkers between the benzofuran and isatin motifs on their anti-mycobacterial activities
in this study.
2
Results and discussion
All of the desired benzofuran-isatin hybrids 6a-m were prepared by the synthetic
route depicted in Scheme 1. Alkylation of 5-substituted isatins 1a-c with
1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane or 1,6-dibromohexane
provided
N-(3-bromopropyl/4-bromobutyl/5-bromopentyl/6-bromohexyl)isatin
derivatives 3a-j (yield: 63-87%) [15,16]. The benzofuran intermediates 5a-c was
obtained by cyclization of ethyl 3-(4-substituted phenyl)-3-oxopropanoates 4a-c and
benzoquinone with copper (II) triflate (Cu(OTf)2) as catalyst [12]. Treatment of isatin
derivatives 3a-j and benzofuran intermediates 5a-c with potassium carbonate as base
generated the desired benzofuran-isatin hybrids 6a-m (58-83%).
3

Scheme 1 Synthesis of benzofuran-isatin hybrids 6a-m
The minimum inhibitory concentration (MIC) of the desired benzofuran-isatin hybrids
6a-m along with the references TAM16, RIF and INH against MTB H37Rv and
MDR-MTB strains was listed in Table 1.
All hybrids 6a-m tethered via propylene, butylene, pentylene and hexylene displayed
considerable anti-mycobacterial activities against the tested MTB H37Rv and
MDR-MTB strains with MIC in a range of 0.125 to 4 μg/mL, but were less active than
TAM16 (MIC: <0.06 μg/mL). The SAR results suggested that the activity was
influenced greatly by the substituents at C-5 position of isatin moiety, and hybrids
with electron-withdrawing -F at this position showed higher activity, while
electron-donating -OMe reduced the activity when compared with unsubstituted
analogs. For R position, electron-donating -OMe was favorable to the activity, while
-F decreased the activity. The length of the linker played a pivotal role on the activity,
and the longer linker could enhance the activity, and the contribution order was
hexylene > pentylene > butylene > propylene.
Among the synthesized benzofuran-isatin hybrids, hybrid 6d (MIC: 0.125 and 0.125
μg/mL) was found to be the most active compound against MTB H37Rv and
MDR-MTB strains, which was comparable to or better than RIF (MIC: 0.5 μg/mL)
and INH (MIC: 0.06 μg/mL) against MTB H37Rv, and was ≥512 folds more potent
than RIF (MIC: 64 μg/mL) and INH (MIC: >128 μg/mL) against MDR-MTB strain,
4

but was less active than TAM16 (MIC: <0.06 μg/mL) against the tested two strains.
The resistance index values (RI, MIC(MDR-TB)/MIC(MTB H37Rv)) for a significant part of
the synthesized benzofuran-isatin hybrids 6a-m were around 1, indicating that these
hybrids may have novel action mechanism.
Table 1 Structure, anti-mycobacterial activity and cytotoxicity of benzofuran-isatin
hybrids 6a-m
MIC (μg/mL)
Compd.
R1
R2
n
CC50 (μΜ)
SIb
MTB H37Rv
MDR-MTBa
6a
6b
6c
6d
6e
6f
F
F
OMe
F
2
2
4
5
5
2
2
3
4
2
0.5
1
0.25
1
256
512
128
128
512
256
128
64
512
512
F
OMe
OMe
F
0.25
0.125
0.25
0.25
1
0.25
0.125
0.25
0.25
2
512
F
1,024
2,048
1,024
128
F
OMe
OMe
OMe
OMe
H
H
6g
6h
6i
F
OMe
F
2
4
32
0.5
2
1
128
256
256
6j
F
1
128
5

6k
6l
H
H
H
-
OMe
2
3
5
-
1
1
64
>1,024
256
64
OMe
0.5
1
>2,048
1,024
6m
OMe
0.25
<0.06
0.06
0.5
0.125
<0.06
>128
64
TAM16
INH
RIF
-
-
-
>1,024
256
>16,384
4,096
-
-
-
-
512
1,024
aMDR-MTB: resistant to ethambutol, INH and RIF
bSI: selectivity index, CC50/MICMTB H37Rv
All hybrids also showed low cytotoxicity with CC50 ranging from 64 to >1,024 μg/mL,
and possessed moderate to high selectivity index (SI: CC50/MICMTB H37Rv) values
(32->2,048). The structure-cytotoxicity relationship study indicated that introduction
of -F or -OMe at C-5 position of isatin motif could reduce the cytotoxicity when
compared with the unsubstituted analogs. The most active hybrid 6d (CC50: 128
μg/mL) also showed acceptable cytotoxicity against VERO cells. The SI value of the
most active hybrid 6d was over 1,024, and was comparable to that of RIF and INH (SI
values: 1,024 and 4,096, respectively), demonstrating that hybrid 6d possess an
excellent selectivity profile.
Table 2 The metabolic stability and in vivo pharmacokinetic values of hybrid 6d and
TAM16 in mice
Pharmacokinetics (p.o.)
Compd.
metabolic stability
(t1/2, min)
AUC0-inf
(ng•h/mL)
Cmax (ng/mL)
t1/2 (h)
Tmax (h)
31.6
>60
1,218
6,830
2.48
8.59
1.76
3.12
3,682
6d
31,756
TAM16
t1/2: half-life;
6

Cmax: the peak concentration;
Tmax: the time to reach peak concentration;
AUC: the area under the curve.
The most active hybrid 6d was selected for the further investigation on metabolic
stability and in vivo pharmacokinetics in mice (25 mg/kg, single oral administration),
and the results were listed in Table 2. Compared with the parent TAM16 (t1/2: >60
min), hybrid 6d showed much lower metabolic stability (t1/2: 31.6 min).
Pharmacokinetic parameters of hybrid 6d was also inferior to the parent TAM16 in
terms of Cmax (1,218 ng/mL vs 6,830 ng/mL), t1/2 (2.48 h vs 8.59 h), Tmax (1.76 h vs
3.12 h) and AUC0-inf (3,682 ng•h/mL vs 3,1756 ng•h/mL). Thus, hybrid 6d still needs
to be further modification.
3 Conclusions
In conclusion, thirteen novel benzofuran-isatin hybrids 6a-m tethered via different
length linkers propylene, butylene, pentylene and hexylene were designed, synthesized
and evaluated for their in vitro anti-mycobacterial activities against MTB H37Rv and
MDR-MTB strains as well as cytotoxicity in VERO cells. All hybrids exhibited
considerable in vitro anti-mycobacterial activities and low cytotoxicity. In spite of the
in vitro activity, metabolic stability and pharmacokinetic profiles for the most active
hybrid 6d were inferior to TAM16, the anti-mycobacterial activity of hybrid 6d was
comparable to or better than the first-line anti-TB agents RIF and INH against both
drug-sensitive MTB H37Rv and MDR-MTB strains. Therefore, hybrid 6d could act as
a starting point for further optimization to improve the activity, metabolic stability
and pharmacokinetic profiles.
4. Experimental section
N-(3-bromopropyl/4-bromobutyl/5-bromopentyl/6-bromohexyl)isatin derivatives 3a-j
(yield:
63-87%)
[15,16]
and
ethyl
2-(4-substituted
7

phenyl)-5-(prop-2-yn-1-yloxy)benzofuran-3-carboxylate 5a-c were prepared via
literature methods [12,13].
A mixture of N-(3-bromopropyl/4-bromobutyl/5-bromopentyl/6-bromohexyl)isatin
derivatives
3a-j
(1.0
mmol),
ethyl
2-(4-substituted
phenyl)-5-(prop-2-yn-1-yloxy)benzofuran-3-carboxylate 5a-c (1.0 mmol) and K2CO3
(3.0 mmol) in DMF (50 mL) was stirred at room temperature for 48 h. After filtration,
the filtrate was concentrated under reduced pressure. The residue was purified by
silica gel column chromatography with PE:EA=1:1 to give the desired
benzofuran-isatin hybrids 6a-m.
4.1.
ethyl
5-(3-(5-fluoro-2,3-dioxoindolin-1-yl)propoxy)-2-(4-methoxyphenyl)benzofuran-3-car
boxylate (6a)
1
Yellow solid, yield: 69%. H NMR (400 MHz, DMSO-d6) δ 1.33 (3H, t, J = 4.0 Hz,
CO2CH2CH3), 2.11 (2H, t, J = 4.0 Hz, -CH2-), 3.85 (3H, s, OCH3), 3.89 (2H, t, J = 4.0
Hz, -CH2-), 4.12 (2H, t, J = 4.0 Hz, -CH2-), 4.33 (2H, q, J = 4.0 Hz, CO2CH2CH3),
6.94 (1H, dd, J = 4.0, 8.0 Hz, Ar-H), 7.09 (2H, d, J = 4.0 Hz, Ar-H), 7.25-7.28 (1H, m,
Ar-H), 7.39 (1H, d, J = 4.0 Hz, Ar-H), 7.45-7.50 (2H, m, Ar-H), 7.57 (1H, d, J = 8.0
Hz, Ar-H), 7.94-7.97 (2H, m, Ar-H). 13C NMR (100 MHz, DMSO-d6) δ 183.32, 163.62,
161.44, 161.26, 158.77, 157.67, 156.02, 148.32, 147.45, 131.41, 127.93, 124.48,
124.24, 121.70, 119.04, 118.96, 114.50, 112.42, 112.31, 111.98, 111.74, 107.69,
105.75, 100.01, 66.23, 60.84, 55.87, 37.35, 27.05, 14.49. ESI-MS m/z: 540 [M+Na]+.
4.2.
ethyl
5-(3-(5-fluoro-2,3-dioxoindolin-1-yl)propoxy)-2-(4-fluorophenyl)benzofuran-3-carbo
xylate (6b)
1
Yellow solid, yield: 77%. H NMR (400 MHz, DMSO-d6) δ 1.31 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 2.12 (2H, t, J = 4.0 Hz, -CH2-), 3.89 (2H, t, J = 4.0 Hz, -CH2-), 4.12 (2H,
t, J = 4.0 Hz, -CH2-), 4.32 (2H, q, J = 8.0 Hz, CO2CH2CH3), 6.98 (1H, dd, J = 4.0, 8.0
Hz, Ar-H), 7.24-7.28 (1H, m, Ar-H), 7.36-7.41 (2H, m, Ar-H), 7.44-7.42 (2H, m,
Ar-H), 7.60 (1H, d, J = 12.0 Hz, Ar-H), 8.01-8.04 (2H, m, Ar-H). 13C NMR (100 MHz,
DMSO-d6) δ 183.33, 164.89, 163.37, 162.42, 160.04, 158.76, 157.67, 156.12, 148.58,
147.43, 132.36, 132.27, 127.60, 126.01, 125.98, 124.48, 124.24, 119.02, 118.95,
8

115.91, 115.69, 115.05, 112.53, 112.48, 112.41, 111.97, 111.73, 108.93, 105.73, 66.24,
60.99, 37.34, 27.04, 14.40. ESI-MS m/z: 528 [M+Na]+.
4.3.
ethyl
5-((5-(5-fluoro-2,3-dioxoindolin-1-yl)pentyl)oxy)-2-(4-methoxyphenyl)benzofuran-3-
carboxylate (6c)
1
Yellow solid, yield: 58%. H NMR (400 MHz, DMSO-d6) δ 1.32 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.51-1.54 (2H, m, -CH2-), 1.66-1.70 (2H, m, -CH2-), 1.78-1.82 (2H, m,
-CH2-), 3.68 (2H, t, J = 8.0 Hz, -CH2-), 3.85 (3H, s, OCH3), 4.01 (2H, t, J = 8.0 Hz,
-CH2-), 4.32 (2H, q, J = 4.0 Hz, CO2CH2CH3), 6.96 (1H, dd, J = 4.0, 8.0 Hz, Ar-H),
7.09 (2H, d, J = 8.0 Hz, Ar-H), 7.41-7.45 (2H, m, Ar-H), 7.49-7.57 (2H, m, Ar-H),
13
7.57 (1H, d, J = 8.0 Hz, Ar-H), 7.94-7.97 (2H, m, Ar-H). C NMR (100 MHz,
DMSO-d6) δ 183.40, 163.64, 161.43, 161.22, 158.61, 157.69, 156.25, 148.25, 147.42,
131.41, 127.97, 124.59, 124.35, 121.73, 118.89, 114.45, 114.16, 112.62, 112.55,
112.29, 112.03, 111.79, 107.69, 105.67, 68.36, 60.81, 55.87, 28.83, 26.89, 23.31, 14.47.
ESI-MS m/z: 568 [M+Na]+.
4.4.
ethyl
5-((6-(5-fluoro-2,3-dioxoindolin-1-yl)hexyl)oxy)-2-(4-methoxyphenyl)benzofuran-3-
carboxylate (6d)
1
Yellow solid, yield: 62%. H NMR (400 MHz, DMSO-d6) δ 1.32 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.35-1.49 (4H, m, 2×-CH2-), 1.59-1.66 (2H, m, -CH2-), 1.70-1.77 (2H,
m, -CH2-), 3.66 (2H, t, J = 8.0 Hz, -CH2-), 3.85 (3H, s, OCH3), 4.00 (2H, t, J = 8.0 Hz,
-CH2-), 4.32 (2H, q, J = 8.0 Hz, CO2CH2CH3), 6.94 (1H, dd, J = 4.0, 8.0 Hz, Ar-H),
7.07 (2H, d, J = 8.0 Hz, Ar-H), 7.19-7.22 (1H, m, Ar-H), 7.40-7.43 (2H, m, Ar-H),
7.49-7.54 (2H, m, Ar-H), 7.93-7.96 (2H, m, Ar-H). 13C NMR (100 MHz, DMSO-d6) δ
183.38, 163.62, 161.40, 161.17, 160.07, 158.53, 157.67, 156.23, 148.22, 147.42,
131.37, 127.97, 124.56, 124.32, 121.73, 118.85, 114.43, 114.11, 112.54, 112.47,
112.21, 111.99, 111.75, 107.66, 105.64, 68.40, 60.78, 55.83, 49.07, 29.08, 27.13, 26.45,
25.73, 14.44. ESI-MS m/z: 582 [M+Na]+.
4.5.
ethyl
ethyl
5-((6-(5-fluoro-2,3-dioxoindolin-1-yl)hexyl)oxy)-2-(4-fluorophenyl)benzofuran-3-car
boxylate (6e)
9

1
Yellow solid, yield: 62%. H NMR (400 MHz, DMSO-d6) δ 1.31 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.39-1.51 (4H, m, 2×-CH2-), 1.62-1.65 (2H, m, -CH2-), 1.73-1.77 (2H,
m, -CH2-), 3.68 (2H, t, J = 4.0 Hz, -CH2-), 4.03 (2H, t, J = 4.0 Hz, -CH2-), 4.32 (2H, q,
J = 8.0 Hz, CO2CH2CH3), 7.00 (1H, dd, J = 4.0, 8.0 Hz, Ar-H), 7.21-7.24 (2H, m,
Ar-H), 7.36-7.54 (5H, m, Ar-H), 7.58 (1H, d, J = 8.0 Hz, Ar-H), 8.01-8.05 (2H, m,
13
Ar-H). C NMR (100 MHz, DMSO-d6) δ 183.39, 163.39, 162.41, 160.00, 158.57,
157.68, 156.36, 148.51, 147.45, 132.36, 132.27, 127.65, 126.04, 124.58, 124.34,
115.90, 115.68, 115.06, 112.58, 112.51, 108.94, 105.63, 100.00, 68.45, 60.96, 29.05,
27.13, 26.44, 25.73, 14.39. ESI-MS m/z: 570 [M+Na]+.
4.6.
ethyl
5-(3-(5-methoxy-2,3-dioxoindolin-1-yl)propoxy)-2-phenylbenzofuran-3-carboxylate
(6f)
1
Yellow solid, yield: 59%. H NMR (400 MHz, DMSO-d6) δ 1.42 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 2.24-2.27 (2H, m, -CH2-), 3.85 (3H, s, OCH3), 4.00 (2H, t, J = 8.0 Hz,
-CH2-), 4.13 (2H, t, J = 8.0 Hz, -CH2-), 4.42 (2H, q, J = 8.0 Hz, CO2CH2CH3), 6.90
(1H, dd, J = 4.0, 8.0 Hz, Ar-H), 6.99-7.02 (3H, m, Ar-H), 7.07-7.11 (1H, m, Ar-H),
7.38 (1H, d, J = 12.0 Hz, Ar-H), 7.50-7.55 (2H, m, Ar-H), 7.59-7.61 (1H, m, Ar-H),
8.00-8.02 (2H, m, Ar-H). 13C NMR (100 MHz, DMSO-d6) δ 183.46, 164.16, 161.77,
161.21, 160.70, 158.39, 155.52, 151.08, 148.70, 138.46, 131.14, 128.22, 125.42,
123.91, 123.71, 122.10, 117.58, 113.89, 113.52, 111.57, 110.22, 109.86, 107.78,
105.94, 65.59, 60.55, 55.40, 37.49, 27.43, 14.35. ESI-MS m/z: 522 [M+Na]+.
4.7.
ethyl
5-((5-(5-fluoro-2,3-dioxoindolin-1-yl)pentyl)oxy)-2-(4-methoxyphenyl)benzofuran-3-
carboxylate (6g)
1
Yellow solid, yield: 76%. H NMR (400 MHz, DMSO-d6) δ 1.31 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 2.12 (2H, t, J = 4.0 Hz, -CH2-), 3.76 (3H, s, OCH3), 3.87 (2H, t, J = 4.0
Hz, -CH2-), 4.12 (2H, t, J = 4.0 Hz, -CH2-), 4.32 (2H, q, J = 8.0 Hz, CO2CH2CH3),
6.98 (1H, dd, J = 4.0, 8.0 Hz, Ar-H), 7.14-7.20 (3H, m, Ar-H), 7.37-7.42 (3H, m,
Ar-H), 7.60 (1H, d, J = 12.0 Hz, Ar-H), 8.01-8.05 (2H, m, Ar-H). 13C NMR (100 MHz,
DMSO-d6) δ 184.20, 163.37, 160.06, 158.73, 156.14, 156.10, 148.60, 145.02, 132.37,
10

132.28, 127.61, 124.26, 118.55, 115.92, 115.70, 115.06, 112.53, 112.14, 109.66,
105.78, 99.99, 66.30, 60.98, 56.34, 37.28, 27.12, 14.41. ESI-MS m/z: 540 [M+Na]+.
4.8.
ethyl
5-(4-(5-methoxy-2,3-dioxoindolin-1-yl)butoxy)-2-(4-methoxyphenyl)benzofuran-3-ca
rboxylate (6h)
1
Yellow solid, yield: 62%. H NMR (400 MHz, DMSO-d6) δ 1.32 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.80-1.84 (4H, m, 2×-CH2-), 3.71-3.76 (5H, m, -CH2- and OCH3), 3.85
(3H, s, OCH3), 4.06 (2H, t, J = 8.0 Hz, -CH2-), 4.33 (2H, q, J = 8.0 Hz, CO2CH2CH3),
6.96 (1H, dd, J = 4.0, 8.0 Hz, Ar-H), 7.08-7.16 (4H, m, Ar-H), 7.22-7.25 (1H, m,
Ar-H), 7.42 (1H, d, J = 4.0 Hz, Ar-H), 7.55 (1H, d, J = 8.0 Hz, Ar-H), 7.94-7.97 (2H,
m, Ar-H). 13C NMR (100 MHz, DMSO-d6) δ 184.19, 163.63, 161.43, 161.24, 158.62,
156.13, 148.27, 144.92, 131.40, 127.96, 124.28, 121.72, 118.45, 114.46, 114.16,
112.29, 112.23, 109.69, 107.68, 105.79, 68.03, 60.82, 56.33, 55.86, 26.47, 23.96, 14.46.
ESI-MS m/z: 566 [M+Na]+.
4.9.
ethyl
2-(4-fluorophenyl)-5-((5-(5-methoxy-2,3-dioxoindolin-1-yl)pentyl)oxy)benzofuran-3-
carboxylate (6i)
1
Yellow solid, yield: 66%. H NMR (400 MHz, DMSO-d6) δ 1.32 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.50-1.55 (2H, m, -CH2-), 1.65-1.71 (2H, m, -CH2-), 1.76-1.82 (2H, m,
-CH2-), 4.68 (2H, t, J = 8.0 Hz, -CH2-), 3.85 (3H, s, OCH3), 4.01 (2H, t, J = 8.0 Hz,
-CH2-), 4.32 (2H, q, J = 8.0 Hz, CO2CH2CH3), 6.96 (1H, dd, J = 4.0, 8.0 Hz, Ar-H),
7.08-7.11 (2H, m, Ar-H), 7.22-7.25 (1H, m, Ar-H), 7.41-7.45 (2H, m, Ar-H), 7.49-7.57
(2H, m, Ar-H), 7.94-7.97 (2H, m, Ar-H). ESI-MS m/z: 568 [M+Na]+.
4.10.
ethyl
5-(3-(2,3-dioxoindolin-1-yl)propoxy)-2-(4-fluorophenyl)benzofuran-3-carboxylate
(6j)
1
Yellow solid, yield: 83%. H NMR (400 MHz, DMSO-d6) δ 1.31 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 2.13 (2H, t, J = 8.0 Hz, -CH2-), 3.89 (2H, t, J = 4.0 Hz, -CH2-), 4.12 (2H,
t, J = 4.0 Hz, -CH2-), 4.33 (2H, q, J = 8.0 Hz, CO2CH2CH3), 6.98 (1H, dd, J = 4.0, 8.0
Hz, Ar-H), 7.11 (1H, t, J = 4.0 Hz, Ar-H), 7.24 (1H, d, J = 8.0 Hz, Ar-H), 7.37-7.42
11

(3H, m, Ar-H), 7.54-7.64 (3H, m, Ar-H), 8.01-8.05 (2H, m, Ar-H). ESI-MS m/z: 510
[M+Na]+.
4.11.
ethyl
5-(3-(2,3-dioxoindolin-1-yl)propoxy)-2-(4-methoxyphenyl)benzofuran-3-carboxylate
(6k)
1
Yellow solid, yield: 77%. H NMR (400 MHz, DMSO-d6) δ 1.33 (3H, t, J = 4.0 Hz,
CO2CH2CH3), 2.13 (2H, t, J = 4.0 Hz, -CH2-), 3.86 (3H, s, OCH3), 3.88 (2H, t, J = 4.0
Hz, -CH2-), 4.12 (2H, t, J = 4.0 Hz, -CH2-), 4.34 (2H, q, J = 4.0 Hz, CO2CH2CH3),
6.96 (1H, dd, J = 4.0, 8.0 Hz, Ar-H), 7.08-7.13 (3H, m, Ar-H), 7.24 (1H, d, J = 8.0 Hz,
Ar-H), 7.40 (1H, d, J = 8.0 Hz, Ar-H), 7.54-7.63 (3H, m, Ar-H), 7.96 (2H, d, J = 8.0
Hz, Ar-H). 13C NMR (100 MHz, DMSO-d6) δ 183.95, 163.63, 161.44, 161.26, 158.74,
156.03, 151.23, 148.32, 138.52, 131.41, 127.93, 124.87, 123.53, 121.71, 118.09,
114.51, 114.18, 112.31, 111.06, 107.70, 105.77, 66.24, 60.84, 55.87, 37.28, 27.14,
14.51. ESI-MS m/z: 522 [M+Na]+.
4.12.
ethyl
5-(4-(2,3-dioxoindolin-1-yl)butoxy)-2-(4-methoxyphenyl)benzofuran-3-carboxylate
(6l)
1
Yellow solid, yield: 68%. H NMR (400 MHz, CDCl3) δ 1.39 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.86-1.94 (4H, m, 2×-CH2-), 3.78 (2H, t, J = 8.0 Hz, -CH2-), 3.84 (3H,
s, OCH3), 4.04 (2H, t, J = 4.0 Hz, -CH2-), 4.38 (2H, q, J = 8.0 Hz, CO2CH2CH3),
6.85-6.91 (2H, m, Ar-H), 6.94-6.89 (2H, m, Ar-H), 7.06 (1H, t, J = 8.0 Hz, Ar-H), 7.34
(1H, d, J = 12.0 Hz, Ar-H), 7.48 (1H, d, J = 4.0 Hz, Ar-H), 7.50-7.53 (1H, m, Ar-H),
7.95-7.99 (2H, m, Ar-H). 13C NMR (100 MHz, DMSO-d6) δ 183.51, 164.17, 161.63,
161.17, 158.22, 155.86, 150.86, 148.54, 138.39, 131.11, 128.15, 125.40, 123.67,
122.11, 117.57, 113.94, 113.50, 111.47, 110.22, 107.75, 105.86, 67.72, 60.51, 55.39,
29.91, 26.63, 24.13, 14.35. ESI-MS m/z: 536 [M+Na]+.
4.13.
ethyl
5-((6-(2,3-dioxoindolin-1-yl)hexyl)oxy)-2-(4-methoxyphenyl)benzofuran-3-carboxyla
te (6m)
12

1
Yellow solid, yield: 59%. H NMR (400 MHz, CDCl3) δ 1.43 (3H, t, J = 8.0 Hz,
CO2CH2CH3), 1.48-1.56 (4H, m, 2×-CH2-), 1.76-1.87 (4H, m, 2×-CH2-), 3.76 (2H, t, J
= 8.0 Hz, -CH2-), 3.88 (3H, s, OCH3), 4.05 (2H, t, J = 8.0 Hz, -CH2-), 4.43 (2H, q, J =
8.0 Hz, CO2CH2CH3), 6.91-6.94 (2H, m, Ar-H), 7.02 (2H, d, J = 8.0 Hz, Ar-H), 7.12
(1H, t, J = 4.0 Hz, Ar-H), 7.40 (1H, d, J = 8.0 Hz, Ar-H), 7.53 (1H, d, J = 4.0 Hz,
Ar-H), 7.57-7.63 (2H, m, Ar-H), 7.99-8.02 (2H, m, Ar-H). ESI-MS m/z: 565 [M+Na]+.
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Graphical Abstract
Benzofuran-isatin hybrids tethered via different length alkyl
linkers and their in vitro anti-mycobacterial activities
Feng Gao1*, Zijian Chen1, Long Ma1, Lin Qiu2, Jianguo Lin2*, Guangming Lu1*
1 Department of Medical Imaging, Jinling Hospital, Medical School of Nanjing
University, Nanjing, PR China;
2 Key Laboratory of Nuclear Medicine, Ministry of Health, Jiangsu Key Laboratory of
Molecular Nuclear Medicine, Jiangsu Institute of Nuclear Medicine, Wuxi, PR
China
15