Design, Synthesis, and Cytotoxicity of Indolizinoquinoxaline-5,12-dione Derivatives
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Sodium bisulfite (8.0 g) was dissolved in water (12 mL) at
55◦C and glyoxal (40%, 3.6 mL) was then added to give a white
suspension. To this mixture was added more water (24 mL)
and the mixture was heated to 75◦C. The mixture of 3a and
3b (3.2 g, 25.6 mmol) was added and the reaction mixture was
stirred and heated at 75◦C for 3 h. After filtration, the filtrate
was basified to pH 8∼9 with aqueous NaOH and extracted with
dichloromethane (3 × 200 mL). The combined organic phase
was dried with MgSO4, and the solvent was removed under
vacuum. The residue was purified through silica gel column
chromatography using a mixture of ethyl acetate and petroleum
ether (2:3) as the eluent, to give a yellowish solid (4, 2.5 g), yield
89% based on substrate 2b, mp 146–147◦C (lit.[13] 147–148◦C).
δH (300 MHz, CDCl3) 8.87 (2H, s), 7.02 (2H, s), 4.06 (6H, s).
m/z (ESI) 191.0 [M + 1]+.
d, J 6.9), 8.99 (1H, d, J 2.1), 8.97 (1H, d, J 2.1), 8.43 (1H, d, J 9.0),
7.55 (1H, dd, J 9.0, 6.9), 7.29 (1H, t, J 6.9), 4.51 (2H, q, J 7.2),
1.52 (3H, t, J 7.2). 13C NMR (100 MHz, CDCl3) δ: 176.1, 170.7,
162.0, 147.1, 146.7, 144.72, 144.67, 139.5, 128.3, 127.6, 127.2,
121.6, 120.2, 117.6, 106.2, 60.4, 13.2. UV/vis λmax (EtOH, ε):
227 (9600), 255 (11800), 332 (5100), 475 (3200) nm. ESI-MS
m/z: 322.1 [M + 1]+. Anal. Calc. for C17H11N3O4: C 63.55,
H 3.45, N 13.08, O 19.92. Found: C 63.53, H 3.46, N 13.10%.
Methyl 5,12-Dioxo-5,12-dihydroindolizino[2,3-g]
quinoxaline-11-carboxylate 7b
Compound 6, pyridine (0.6 mL, 6.8 mmol), and methyl aceto-
acetate (0.3 mL, 2.6 mmol) were used as reagents, and a mixture
of dichloromethane and methanol (50:1) was used as the elu-
ent. A red solid 7b (258.0 mg) was obtained, yield 38%, mp
288–299◦C. 1H NMR (300 MHz, CDCl3) δ: 9.91 (1H, d, J 6.9),
8.99 (1H, d, J 2.1), 8.97 (1H, d, J 2.1), 8.42 (1H, d, J 9.0),
7.55 (1H, ddd, J 9.0, 6.9, 0.9), 7.30 (1H, td, J 6.9, 0.9), 4.04
(3H, s). 13C NMR (100 MHz, CDCl3) δ: 176.2, 170.7, 162.4,
147.1, 146.7, 144.7, 139.6, 128.4, 127.7, 127.4, 121.6, 120.3,
117.6, 105.7, 51.2. UV/vis λmax (EtOH, ε): 205 (25000), 226
(22600), 254 (23400), 335 (9500), 477 (5800) nm. ESI-MS m/z:
308.1 [M + 1]+, 330.0 [M + Na]+. Anal. Calc. for C16H9N3O4:
C 62.54, H 2.95, N 13.68, O 20.83. Found: C 62.53, H 2.97,
N 13.66%.
Synthesis of Quinoxaline-5,8-dione 5
A solution of 5,8-dimethoxyquinoxaline (4, 3.8 g, 20.0 mmol) in
MeCN (57 mL) was stirred at room temperature while a solution
of CAN (31.8 g, 60.0 mmol) in water (57 mL) was added in por-
tions over a period of 7 min. The reaction mixture was diluted
with water (100 mL) after further stirring for 8 min, and was
extracted with chloroform (3 × 200 mL). The combined organic
layer was dried with MgSO4, and concentrated under vacuum.
The yellow residue was purified through silica gel column chro-
matography using a mixture of ethyl acetate and petroleum ether
(1:1) as the eluent, to give a yellowish solid (5, 2.2 g), yield 69%,
mp 126–128◦C (from CHCl3) (lit.[17] 172–173◦C, from ethyl
acetate). δH (300 MHz, DMSO-d6) 9.07 (2H, s), 7.22 (2H, s).
m/z (ESI) 161.1 [M + 1]+.
11-Acetylindolizino[2,3-g]quinoxaline-5,12-dione 7c
Compound 6, pyridine (0.6 mL, 6.8 mmol), and acetylacetone
(0.3 mL, 2.6 mmol) were used as reagents, and a mixture of
dichloromethane and methanol (40:1) was used as the elu-
ent. A dark red solid 7c (176.1 mg) was obtained, yield 28%,
mp >300◦C. 1H NMR (300 MHz, DMSO-d6) δ: 9.77 (1H, d, J
6.9), 9.07 (1H, d, J 2.4), 9.05 (1H, d, J 2.4), 8.29 (1H, d, J 9.0),
7.70 (1H, dd, J 9.0, 6.9), 7.49 (1H, t, J 6.9), 2.76 (3H, s). 13C
NMR (100 MHz, CDCl3) δ: 195.6, 178.1, 171.8, 147.4, 146.7,
144.9, 139.3, 129.2, 127.5, 126.1, 121.1, 118.2, 114.7, 106.6.
UV/vis λmax (EtOH, ε): 205 (7000), 264 (4100), 340 (1800),
490 (1000) nm. ESI-MS m/z: 292.1 [M + 1]+. Anal. Calc. for
C16H9N3O3: C 65.98, H 3.11, N 14.43, O 16.48. Found: C 65.96,
H 3.15, N 14.40%.
Synthesis of 6,7-Dichloroquinoxaline-5,8-dione 6
A solution of 5 (0.5 g, 3.1 mmol) and thionyl chloride (3.0 mL,
42.0 mmol) in chloroform (50 mL) was heated under reflux and
pyridine (3.0 mL, 37.5 mmol) was added dropwise over a period
of 1 h. The reaction was quenched after the completion by the
addition of pyridine and chloroform was added.The mixture was
washed with ice/water (2 × 20 mL), and the solvent was removed
under vacuum to give a light yellowish solid (6, 0.6 g), yield
84%, mp 192–194◦C (from CHCl3) (lit.[13] 171–175◦C, from
diethyl ether). δH (300 MHz, CDCl3) 9.08 (s, 2H). m/z (ESI)
228.9 (100%), 230.9 (64%), 232.9 (10%) [M + 1]+.
5,12-Dioxo-5,12-dihydroindolizino[2,3-g]quino-xaline-
11-carbonitrile 7d
General Synthesis of Indolizinoquinoxaline-5,12-dione
Derivatives 7a–7h
Compound 6, pyridine (0.6 mL, 6.8 mmol), and ethyl cyano-
acetate (0.3 mL, 2.6 mmol) were used as reagents, and a mixture
of dichloromethane and methanol (50:1) was used as the elu-
ent. A dark red solid 7d (68.0 mg) was obtained, yield 11%,
mp >300◦C. 1H NMR (400 MHz, DMSO-d6) δ: 9.7 (1H, d,
J 6.8), 9.11 (1H, s, br), 9.09 (1H, s, br), 8.14 (1H, d, J 8.8),
7.82 (1H, t, J 8.0), 7.59 (1H, t, J 7.2). 13C NMR (100 MHz,
90% CDCl3 + 10% CF3CO2D) δ: 175.3, 168.8, 148.1, 147.3,
144.6, 142.9, 142.0, 131.2, 129.6, 129.0, 121.0, 119.7, 118.8,
111.0, 83.4. UV/vis λmax (EtOH, ε): 260 (10600), 347 (1900),
479 (700) nm. ESI-MS m/z: 275.0 [M + 1]+, 297.1 [M + Na]+.
Anal. Calc. for C15H6N4O2: C 65.70, H 2.21, N 20.43, O 11.67.
Found: C 65.71, H 2.24, N 20.42%.
The dichloro-substituted substrate 6 (503.8 mg, 2.2 mmol) was
dissolved in absolute ethanol (50 mL). The solution was heated
to 60◦C, and the pyridine derivative (6.8 mmol) and AMR
(2.6 mmol) such as ethyl acetoacetate, methyl acetoacetate, ethyl
cyanoacetate, acetylacetone, or nitroethane, were added drop-
wise. The reaction mixture was heated under reflux for 4 h, and
the dark-reddish suspension was concentrated under vacuum.
The residue was then subjected to flash column chromatography
(silica gel) to give the corresponding target compounds.
Ethyl 5,12-Dioxo-5,12-dihydroindolizino[2,3-g]quinoxaline-
11-carboxylate 7a
11-Methylindolizino[2,3-g]quinoxaline-5,12-dione 7e
Compound 6, pyridine (0.6 mL, 6.8 mmol) and ethyl aceto-
acetate (0.3 mL, 2.6 mmol) were used as reagents, and a mix-
ture of petroleum ether, ethyl acetate, and methanol (5:20:1) was
used as the eluent. A red solid 7a (238.0 mg) was obtained, yield
34%, mp 294–296◦C. 1H NMR (300 MHz, CDCl3) δ: 9.91 (1H,
Compound 6, pyridine (0.6 mL, 6.8 mmol), and nitroethane
(0.2 mL, 2.6 mmol) were used as reagents, and a mixture of
petroleum ether and ethyl acetate (1:9) was used as the eluent.
A red solid 7e (93.7 mg) was obtained, yield 16%, mp >300◦C.