Y. Xu et al.
Fitoterapia xxx (xxxx) xxx–xxx
NNHCSNH
2
> O > NOMe > NOEt > NOH; 2) introduction of elec-
DMSO-d
4.41 (2H, q, NOCH
AreH), 7.53 (1H, d, AreH), 7.62 (1H, t, AreH), 7.86 (1H, d, AreH).
ESI-MS m/z: 364 [M + H]+
6
) δ 1.34 (3H, t, NOCH
2 3 2 2
CH ), 3.98–4.04 (4H, m, eCH CH e),
CH ), 7.08–7.15 (4H, m, AreH), 7.41 (1H, t,
tron-withdrawing group -F at C-5 position of isatin moiety was pre-
ferred. Interestingly, the heteronuclear bis-isatin derivative 4a was
more potent than the corresponding homonuclear analog 4e, while
heteronuclear bis-isatin 4g was less active than 4e.
2
3
.
It is worth to notice that the resistance index (RI) for almost all
homonuclear and heteronuclear bis-isatin derivatives was around 1,
and four of them was < 1, indicating they may bear novel action me-
chanism.
Among the synthesized homonuclear and heteronuclear bis-isatin
derivatives, the heteronuclear bis-isatin 4e (MIC: 25 and 16 μg/mL) was
most active against MTB H37Rv and MDR-TB strains. It was 4 and > 8
folds more potent than the first-line anti-TB agents RIF (MIC: 64 μg/
mL) and INH (MIC: > 128 μg/mL) against MDR-TB, and has the po-
tential for further investigations.
3.1.3. 1-(2-(5-fluoro-3-(methoxyimino)-2-oxoindolin-1-yl)ethyl)indoline-
2,3-dione (4c)
Yellow solid, yield: 67%. Mp: 177–179 °C. 1H NMR (400 MHz,
DMSO-d
6
) δ 3.97–4.18 (4H, m, eCH
2 2
CH e), 4.21, 4.22 (3H, s, NOMe),
7.12–7.16 (3H, m, AreH), 7.26–7.31 (1H, m, AreH), 7.63 (1H, d,
AreH), 7.64–7.66 (2H, m, AreH). ESI-MS m/z: 368 [M + H]
+
.
3.1.4. 1-(2-(3-(ethoxyimino)-5-fluoro-2-oxoindolin-1-yl)ethyl)indoline-
2,3-dione (4d)
Yellow solid, yield: 44%. Mp: 136–138 °C. 1H NMR (400 MHz,
In conclusion, a new class of novel homonuclear and heteronuclear
bis-isatin derivatives tethered through ethylene and propylene was
designed, synthesized and evaluated for their in vitro anti-mycobacterial
activities against MTB H37Rv and MDR-TB in this paper. The most
active heteronuclear bis-isatin 4e exhibited considerable activity
against MDR-TB, and could act as a starting point for further optimi-
DMSO-d
4.48 (2H, q, NOCH
AreH). ESI-MS m/z: 382 [M + H]
6
) δ 1.35 (3H, t, NOCH
2 3 2 2
CH ), 3.93–4.02 (4H, m, eCH CH e),
2
CH ), 7.07–7.37 (4H, m, AreH), 7.41–7.65 (3H, m,
3
+
.
3.1.5. 1,1′-(ethane-1,2-diyl)bis(3-(methoxyimino)indolin-2-one) (4e)
Yellow solid, yield: 71%. Mp: 169–171 °C. 1H NMR (400 MHz,
zation. The SAR was discussed, and NNHCSNH
2
at C-3 position as well
DMSO-d
2 × NOMe), 6.97–7.09 (4H, m, AreH), 7.40–7.46 (3H, m, AreH), 7.84
(1H, d, AreH). ESI-MS m/z: 379 [M + H]+
6
) δ 3.96–4.00 (4H, m, eCH
2 2
CH e), 4.09, 4.17 (6H, s,
as -F at C-5 position favored the activity. The enriched SAR may pave
the way for further development of this kind of bis-isatin derivatives
especially heteronuclear bis-isatin derivatives.
.
3
.1.6. 3-(hydroxyimino)-1-(2-(3-(methoxyimino)-2-oxoindolin-1-yl)ethyl)
indolin-2-one (4f)
Yellow solid, yield: 79%. Mp: 193–195 °C. 1H NMR (400 MHz,
DMSO-d ) δ 3.98–4.00 (4H, m, eCH CH e), 4.09, 4.17 (3H, s, NOMe),
.02–7.08 (4H, m, AreH), 7.37–7.39 (2H, m, AreH), 7.84 (1H, d,
AreH), 7.94 (1H, d, AreH), 13.36 (1H, s, NOH). ESI-MS m/z: 365
[M + H]+
3
. Experimental section
3.1. The general procedure for preparing targets 4a–i
6
2
2
7
To a mixture of C-5 substituted isatins (10 mmol) and potassium
carbonate (30 mmol), in water (10 mL) and THF (50 mL), methox-
yamine or ethoxyamine hydrochloride (15 mmol) was added. The
mixture was stirred at 50 °C for 12 h. After cooling to room tempera-
ture, the mixture was extracted with EA (100 mL*2). The combined
organic layers were washed with H
in sequence, and dried over Na SO
.
3.1.7. 3-(ethoxyimino)-1-(2-(3-(methoxyimino)-2-oxoindolin-1-yl)ethyl)
indolin-2-one (4g)
2
O (100 mL*2) and brine (100 mL)
. After filtration, the filtrate was
Yellow solid, yield: 45%. Mp: 133–135 °C. 1H NMR (400 MHz,
2
4
DMSO-d
4.09, 4.17 (3H, s, NOMe), 4.42 (2H, q, NOCH
AreH), 7.40–7.46 (3H, m, AreH), 7.85 (1H, t, AreH). ESI-MS m/z: 393
[M + H]+
6
) δ 1.35 (3H, t, NOCH
2
CH
3
), 3.96–4.00 (4H, m, eCH
2 2
CH e),
concentrated under reduced pressure to give crude intermediates 3a-d
which were used directly without further purification.
2
CH ), 7.03–7.08 (4H, m,
3
To a mixture of intermediates 3a-d (5 mmol) and potassium car-
bonate (20 mmol) in DMF (50 mL), intermediate 2 was added. The
mixture was stirred at room temperature overnight. TLC (PE:EA = 1:1)
indicated the reaction completed. After filtration, the filtrate was con-
centrated under reduced pressure, and the residue was purified by silica
gel chromatography eluted with PE:EA = 3:1 to give the desired pro-
ducts 4a-d.
.
3.1.8. 3-(ethoxyimino)-1-(2-(3-(hydroxyimino)-2-oxoindolin-1-yl)ethyl)
indolin-2-one (4h)
Yellow solid, yield: 57%. Mp: 159–160 °C. 1H NMR (400 MHz,
DMSO-d
4.46 (2H, q, NOCH
AreH), 7.81 (1H, d, AreH), 7.92 (1H, d, AreH), 13.42 (1H, s, NOH).
ESI-MS m/z: 379 [M + H]+
6
) δ 1.35 (3H, t, NOCH
2 3 2 2
CH ), 3.98–4.02 (4H, m, eCH CH e),
CH ), 7.02–7.12 (4H, m, AreH), 7.40–7.43 (2H, m,
2
3
The mixture of 4a–c (1 mmol), potassium carbonate (3 mmol), and
methoxyamine or ethoxyamine hydrochloride (1.4 mmol) in water
.
(
10 mL) and THF (50 mL) was stirred at 50 °C for 12 h. After cooling to
room temperature, the mixture was extracted with EA (100 mL*2). The
combined organic layers were washed with H O (100 mL*2) and brine
100 mL) in sequence, and dried over Na SO . After filtration, the fil-
3.1.9. 2-(1-(2-(5-fluoro-3-(methoxyimino)-2-oxoindolin-1-yl)ethyl)-2-
oxoindolin-3-ylidene)hydrazinecarbothioamide (4i)
2
(
2
4
Yellow solid, yield: 23%. Mp: 206–208 °C. 1H NMR (400 MHz,
trate was concentrated under reduced pressure to give a residue which
was purified by silica gel chromatography eluted with PE:EA = 2:1 to
give the desired products 4e-i.
DMSO-d
(1H, d, AreH), 7.12–7.16 (2H, m, AreH), 7.28–7.34 (2H, m, AreH),
7.64–7.68 (2H, m, AreH), 8.75, 9.09 (1H, s, NNHCSNH ), 12.18 (1H, s,
NNHCSNH
). ESI-MS m/z: 441 [M + H]+
6
) δ 3.99–4.03 (4H, m, eCH
2 2
CH e), 4.18 (3H, s, NOMe), 7.03
2
2
.
3
.1.1. 1-(2-(3-(methoxyimino)-2-oxoindolin-1-yl)ethyl)indoline-2,3-dione
4a)
Yellow solid, yield: 51%. Mp: 173–175 °C. 1H NMR (400 MHz,
DMSO-d ) δ 3.95–4.09 (4H, m, eCH CH e), 4.17, 4.20 (3H, s, NOMe),
.05–7.16 (4H, m, AreH), 7.42 (1H, t, AreH), 7.53 (1H, d, AreH), 7.63
1H, t, AreH), 7.84 (1H, d, AreH). ESI-MS m/z: 350 [M + H]+
(
3.2. MIC determination
6
2
2
The bis-isatin derivatives 4a–i along with the references RIF and
INH were evaluated for their in vitro activities against MTB H37Rv and
MDR-TB via rapid direct susceptibility test technique [11,12]. The wells
of a sterile 48-well plate were filled with 100 mL two-fold diluted tested
compounds and 100 mL MTB H37Rv or MDR-TB suspension containing
7
(
.
3
.1.2. 1-(2-(3-(ethoxyimino)-2-oxoindolin-1-yl)ethyl)indoline-2,3-dione
4b)
Yellow solid, yield: 56%. Mp: 128–130 °C. 1H NMR (400 MHz,
−3
(
4 × 10 mg cells. Pure medium replaced the diluted compounds in
two wells as the positive control of growth, and deionized water instead
3