Chemical compounds
The Beirut reaction was the general procedure used for synthesis of quinoxaline 1ˏ4-di-
N-oxide derivatives, as described in previous report (
16,
17). Quinoxaline 1ˏ4-di-
N-oxide derivatives (M1-M3, E1-E8 and P1-P3) synthesis was achieved by the reaction of the corresponding diketone derivative (10.6 mmol) with the appropriate benzofuroxane
N-oxide (2.4 mmol) in dry chloroform (35 mL). Triethylamine (TEA) was added (1 mL) and the reaction mixture was stirred at room temperature for 3–7 days. After evaporation to dryness at low pressure, crude solid or brown oil was obtained. This was then precipitated and washed by adding diethyl ether, affording the target compound. The residue was purified by column chromatography on silica gel, when necessary using dichloromethane: methanol (95:5). Quinoxaline di-reduced (DR1-DR3) was achieved by the reaction of the corresponding quinoxaline 1ˏ4-di-
N-oxide with sodium dithionite (
18). All compounds were characterized by infrared (IR), proton nuclear magnetic resonance (
1H-NMR) spectroscopy, and elemental analysis.
Methyl quinoxaline-7-carboxylate 1ˏ4-di-N-oxide derivatives
Methyl2-amide-3-methylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (M1)
This compound was obtained in 10% yield from methyl benzofuroxane-5-carboxylate N-oxide and acetoacetamide. IR (KBr): 3310 (NH), 2992 (ArC-H), 1702 (C=O), 1331 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 2.48 (s, 3H, CH3), 3.98 (s, 3H, CH3OOC), 8.25 (s, 2H, NH2), 8.37-8.42 (m, 1H, H5), 8.57-8.62 (m, 1H, H6), 8.94 (s, 1H, H8). Calculated analysis for C12H11N3O5: C, 51.98; H, 3.97; N, 15.16. Found: C, 51.72; H, 3.63; N, 14.86.
Dimethyl3-methylquinoxaline-2, 7-dicarboxylate 1, 4-di-N-oxide (M2)
This compound was obtained in 12% yield from methyl benzofuroxane-5-carboxylate N-oxide and methyl acetoacetate. IR (KBr): 1715.30 (C=O), 1333.57 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 2.44 (s, 3H, CH3), 3.97 (s, 3H, COOCH3), 4.03 (s, 3H, CH3OOC), 8.38 (d, J= 8.93 Hz, 1H, H5), 8.56 (d, J= 8.89 Hz, 1H, H6), 8.85(s, 1H, H8). Calculated analysis for C13H12N2O6: C, 53.43; H, 4.14; N, 9.59. Found: C, 53.29; H, 3.97; N, 9.45.
Methyl 2-acetyl-3 trifluoromethylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (M3)
This compound was obtained in 17.7% yield from methyl benzofuroxane-5-carboxylate N-oxide and 1,1, 1-trifluoro-2,4-pentanedione. IR (KBr): 2962 (Ar C-H), 1732 (C=O), 1337 (N - oxide), 1236 and 1173 (Ar-CF3) cm-1. 1H NMR (400 MHz, DMSO-d6) ppm: 2.62 (s, 3H, COCH3), 3.99 (s, 3H, CH3OOC), 8.51 (d, J= 8.95, Hz, 1H, H5), 8.58 (d, J= 8.94, 1H, H6), 8.92 (s, 1H, H8). Calculated analysis for C13H9F3N2O5: C, 47.28; H, 2.75; N, 8.48. Found: C, 47.01; H, 2.56; N 8.45.
Ethyl quinoxaline-7-carboxylate 1ˏ4-di-N-oxide derivatives
Ethyl2-acetyl-3-methyl-quinoxaline-7-carboxylate 1ˏ4-di-N-oxide (E1)
This compound was obtained in 28% yield from ethylbenzofuroxane-5-carboxylate N-oxide and 2, 4-pentanedione. IR (KBr): 2965 (ArC-H), 1722 (C=O), 1335 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.40 (t, J= 7.10 Hz, 3H, CH3CH2OOC), 2.38 (s, 3H, CH3), 2.66 (s, 3H, COCH3), 4.4 (q, J= 7.09 Hz, 2H, CH3CH2OOC), 8.37 (d, J= 8.93 Hz, 1H, H5), 8.5 (d, J= 8.94 Hz, 1H, H6), 8.92 (s, 1H, H8). Calculated analysis for C14H14N2O5: C, 57.93; H, 4.82; N, 9.65. Found: C, 57.68; H, 4.51; N, 9.18.
Ethyl2-benzoyl-3-methylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (E2)
This compound was obtained in 12.3% yield from ethyl benzofuroxane-5-carboxylate N-oxide and 1-phenyl-1, 3-butanedione. IR (KBr): 2979 (ArC-H), 1720 and 1684 (C=O), 1331 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.41 (t, J= 7.11 Hz, 3H, CH3CH2OOC), 2.32 (s, 3H, CH3), 4.46 (q, J1= 7.10 Hz, J2= 7.13 Hz, 2H, CH3CH2OOC), 7.6 (t, J= 7.8 Hz, 2H, H3 and H5, C6H5), 7.79 (t, J= 7.43 Hz, 1H, H4, C6H5), 8.1 (d, J= 7.34 Hz, 2H, H2 and H6, C6H5), 8.38 (d, J= 8.9 Hz, 1H, H5), 8.5 (d, J= 8.94 Hz, 1H, H6), 8.99 (s, 1H, H8). Calculated analysis for C19H16N2O5: C, 64.77; H, 4.58; N, 7.95. Found: C, 64.58; H, 4.32; N, 7.67.
Ethyl 2-phenylamide-3-methylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (E3)
This compound was obtained in 22.4% yield from ethyl benzofuroxane-5-carboxylate N-oxide and 3-oxo-N-phenylbutanamide. IR (KBr): 2981 (ArC-H), 1714 and 1661 (C=O), 1369 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.36 (m, 3H, CH3CH2OOC), 2.51 (s, 1H, CH3), 4.39-4.47 (q, J1= 7.10 Hz, J2= 7.22 Hz, 2H, CH3CH2O), 7.20 (t, J= 7.34 Hz, 1H, H4-NHC6H5), 7.41 (t, J= 7.16 Hz, 2H, H3 and H5, NHC6H5), 7.65 (d, J= 7.84 Hz, H2 and H6, NHC6H5), 8.39 (d, J= 8.98 Hz, 1H, H5), 8.59 (d, J= 8.97 Hz, 1H, H6), 8.96 (s, 1H, H8), 11.10 (s, 1H, NH). Calculated analysis for C19H17N3O5: C, 62.12; H, 4.66; N, 11.44. Found: C. 61.98; H, 4.49; N, 11.23.
Ethylmethyl-3-methyl-quinoxaline-2 ,7-dicarboxilate 1ˏ4-di-N-óxide (E4)
This compound was obtained in 10% yieldfromethylbenzofuroxane-5-carboxylate N-oxide and methyl acetoacetate. IR (KBr): 1715.30 and 1726.88 (C=O), 1327.65 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.35 (s, 3H, CH3CH2OOC), 2.44 (s, 3H, CH3), 4.03 (s, 3H, COOCH3), 4.48 (q, J1= 7.08 Hz, J2= 7.07 Hz, 2H, CH3CH2OOC), 8.39 (d, J= 8.99 Hz, 1H, H5), 8.56 (d, J= 8.99 Hz, 1H, H6), 8.84 (s, 1H, H8). Calculated analysis for C14H14N2O6: C, 54.90; H, 4.61; N, 9.15. Found: C, 54.76; H, 4.27; N, 9.13
Ethyl 2-acetyl-3-trifluoromethylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (E5)
This compound was obtained in 11.9% yield from ethyl benzofuroxane-5-carboxylate N-oxide and 1,1, 1-trifluoro-2,4-pentanedione. IR (KBr): 2978 (ArC-H), 1746 (C=O), 1355 (N-oxide), 1271 and 1158 (Ar-CF3) cm-1. 1H NMR (400 MHz, DMSO-d6) ppm: 1.40 (t, J= 7.11 Hz, 3H, CH3CH2OOC), 2.62 (s, 3H, COCH3), 4.45 (q, J1= 7.12 Hz, J2= 7.13 Hz, 2H, CH3CH2OOC), 8.52 (d, J= 8.95 Hz, 1H, H5), 8.58 (d, J= 8.96 Hz, 1H, H6), 8.92 (s, 1H, H8). Calculated analysis for C14H11 F3N2O5: C, 48.85; H, 3.22; N, 8.14. Found: C, 48.58; H, 3.15; N, 8.23.
Ethyl2-(thiophene-2-carbonyl)-3-trifluoromethylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (E6)
This compound was obtained in 23.2% yield from ethyl benzofuroxane-5-carboxylate N-oxide and 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione. IR (KBr): 2987 (ArC-H), 1726 and 1665 (C=O), 1336 (N-oxide), 1286 and 1161 (Ar-CF3) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.41 (t, J= 7.1 Hz, 3H, CH3CH2OOC), 4.47 (q, J1= 7.07 Hz, J2= 7.12 Hz, 2H, CH3CH2OOC), 7.32 (d, J= 4.7 Hz, 1H, H4, C4H3S), 8.24 (d, J= 4.59 Hz, H5, C4H3S), 8.3 (d, J= 4.8 Hz, H3, C4H3S), 8.51 (d, J= 8.95 Hz, 1H, H5), 8.56 (d, J= 8.96 Hz, 1H, H6), 8.96 (s, 1H, H8). Calculated analysis for C17H11F3N2O5S: C, 49.52; H, 2.69; N, 6.79. Found: C, 49.36; H, 2.45; N, 6.43.
Ethyl2-(naphthyl-2-carbonyl)-3-trifluoromethylquinoxaline-7-carboxylate1ˏ4-di-N-oxide (E7)
This compound was obtained in 11.3% yield from ethyl benzofuroxane-5-carboxylate N-oxide and 4, 4, 4-trifluoromethyl-1-(2-naphthyl)-1, 3-butanedione. IR (KBr): 2979 (ArC-H), 1725 and 1687 (C=O), 1349 (N-óxido), 1285 and 1174 (Ar-CF3) cm-1. 1H NMR (400 MHz, DMSO-d6) ppm: 1.42 (t, J= 7.10 Hz, 3H, CH3CH2OOC), 4.48 (q, J1= 7.08 Hz, J2= 7.11 Hz, 2H, CH3CH2OOC), 7.65 (t, J= 7.5 Hz, 1H, H3, C10H7), 7.75 (t, J= 7.2 Hz, 1H, H6, C10H7), 8.01 (d, J= 8.12 Hz, 1H, H7, C10H7), 8.07 (d, J= 8.14 Hz, 1H, H5, C10H7), 8.14 (s, 2H, H2, and H4 C10H7), 8.52-8.58 (m, 2H, H5 and H6), 8.88 (s, 1H, H8), 9.02 (s, 1H, H8, C10H7). Calculated analysis for C23H15F3N2O5: C, 60.53; H, 3.31; N, 6.14. Found: C, 60.23; H, 3.15; N, 5.89.
Ethyl 2-phenylamide-3-phenylquinoxaline-7-carboxylate 1, 4-di-N-oxide (E8)
This compound was obtained in 31.0% yield from ethyl benzofuroxane-5-carboxylate N-oxide and 3-oxo-N , 3-diphenylpropanamide. IR (KBr): 3110 (N-H), 2950 (ArC-H), 1718 and 1694 (C=O), 1334 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.41 (t, J= 7.11Hz, 3H, CH3CH2OOC), 4.45 (q, H= 7.12 Hz, 2H, CH3CH2OOC), 7.11 (t, J= 7.25 Hz, 1H, H4, NHC6H5), 7.31 (t, J= 7.88 Hz, 2H, H3 and H5, C6H5), 7.38 (d, J = 8.23 Hz, 2H, H3 and H5, NHC6H5), 7.48-7.50 (m, 3H, C6H5), 7.61-7.63 (m, 2H, H2 and H6, NHC6H5), 8.49 (d, J= 8.96 Hz, H5), 8.69 (d, J= 8.94 Hz, 1H, H6), 9.02 (s, 1H, H8), 10.86 (s, 1H, NH). Calculated analysis for C24H19N3O5: C, 67.13; H, 4.42; N, 9.79. Found: C, 66.95; H, 4.21; N, 9.52.
n-propil quinoxaline-7-carboxylate 1ˏ4-di-N-oxide derivatives
n-propyl 2-benzoyl-3-methylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (P1)
This compound was obtained in 8.3% yield from n-propyl benzofuroxane-5-carboxylate N-oxide and 1-phenyl-1, 3-butanedione. IR (KBr): 2978 (ArC-H), 1718 and 1685 (C=O), 1332 (N-oxide) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.02 (t, J= 7.38 Hz, 3H, CH3CH2CH2OOC), 1.81 (q, J1= 6.76 and J2= 14.12 Hz, 2H, CH3CH2CH2OOC), 4.39 (t, J= 6.62 Hz, 2H, CH3CH2CH2OOC), 7.61 (t, J= 7.82 Hz, 2H, H3 and H5, C6H5), 7.80 (t, J= 7.40 Hz, 1H, H4, C6H5), 8.12 (d, J= 7.30 Hz, 2H, H2 and H6, C6H5), 8.39 (d, J= 8.9 Hz, 1H, H5), 8.51 (d, J= 8.90 Hz, 1H, H6), 8.98 (s, 1H, H8). Calculated analysis for C20H18N2O5: C, 65.57; H, 4.91; N, 7.65. Found: C, 65.38; H, 4.63; N, 7.37.
n-propyl2-phenylamide-3methylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (P2)
This compound was obtained in 10.4% yield from n-propyl benzofuroxane-5-carboxylate N-oxide and 3-oxo-N-phenylbutanamide. IR (KBr): 2982 (ArC-H), 1716 and 1672 (C=O), 1332 (N-oxide), cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.03 (t, J= 7.40 Hz, 3H, CH3CH2CH2OOC), 1.82 (q, J1= 6.77 and J2= 14.11 Hz, 2H, CH3CH2CH2OOC), 4.38 (t, J= 6.60 Hz, 2H, CH3CH2CH2OOC), 7.21 (t, J= 7.32 Hz, 1H, H4-NHC6H5), 7.42 (t, J= 7.20 Hz, 2H, H3 and H5, NHC6H5), 7.64 (d, J= 7.80 Hz, H2 and H6, NHC6H5), 8.38 (d, J= 8.90 Hz, 1H, H5), 8.58 (d, J= 8.90 Hz, 1H, H6), 8.95 (s, 1H, H8), 11.12 (s, 1H, NH). Calculated analysis for C20H19N3O5: C, 62.99; H, 4.98; N, 11.02. Found: C. 62.58; H, 4.61; N, 10.87.
n-propyl2-benzoyl-3-trifluoromethylquinoxaline-7-carboxylate 1ˏ4-di-N-oxide (P3)
This compound was obtained in 5.9% yield from n-propyl benzofuroxane-5-carboxylate N-oxide and 4, 4,4-trifluoro-1-phenyl-1,3-butanedione. IR (KBr): 2982 (Ar C-H), 1728 and 1688 (C=O), 1336 (N-oxide), 1254 and 1166 (Ar-CF3) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 1.02 (t, J= 7.40 Hz, 3H, CH3CH2CH2OOC), 1.82 (q, J1= 6.77 and J2= 14.11 Hz, 2H, CH3CH2CH2OOC), 4.39 (t, J= 6.58 Hz, 2H, CH3CH2CH2OOC), 7.62 (t, J= 7.84 Hz, 2H, H3 and H5, C6H5), 7.79 (t, J= 7.43 Hz, 1H, H4, C6H5), 8.15 (d, J= 7.26 Hz, 2H, H2 and H6, C6H5), 8.52-8.54 (m, 2H, H5 and H6), 8.98 (s, 1H, H8). Calculated analysis for C20H15F3N2O5: C, 57.14; H, 3.57; N, 6.66. Found: C, 56.91; H, 3.39; N, 6.37.
Quinoxaline-7-carboxylate derivatives
Methyl2-amide-3-methylquinoxaline-7-carboxylate (DR1)
This compound was obtained in 4% yield from methyl 2 -amide-3-methylquinoxaline-7-carboxylate 1, 4-di-N-oxide by di-reduced using sodium dithionite. IR (KBr): 3312 (NH), 2994 (ArC-H), 1702 (C=O) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 2.48 (s, 3H, CH3), 3.98 (s, 3H, CH3OOC), 8.25 (s, 2H, NH2), 8.37-8.42 (m, 1H, H5), 8.57-8.62 (m, 1H, H6), 8.94 (s, 1H, H8). Calculated analysis for C12H11N3O3: C, 58.77; H, 4.48; N, 17.14. Found: C, 58.81; H, 4.65; N, 17.23.
Methyl 2-phenylamide-3-methylquinoxaline-7-carboxylate (DR2)
This compound was obtained in 6.5% yield from methyl 2-phenylamide-3-methylquinoxaline-7-carboxylate 1, 4-di-N-oxide by di-reduced using sodium dithionite. IR (KBr): 3081 (N-H), 2949 (ArC-H), 1722 and 1684 (C=O) cm-1. 1H NMR (400 MHz, DMSO-d6) δ ppm: 2.52 (s, 3H, CH3), 3.99 (s, 3H, CH3OOC), 7.20 (t, J= 7.38 Hz, 1H, H4, NHC6H5), 7.42 (t, J= 7.78 Hz, 2H, H3 and H5, NHC6H5), 7.67 (d, J = 7.92 Hz, H2 and H6, NHC6H5), 8.41 (d, J= 8.84 Hz, H5), 8.62 (d, J= 8.93 Hz, 1H, H6), 9.0 (s, 1H, H8), 11.01 (s, 1H, NH). Calculated analysis for C18H15N3O3: C, 67.28; H, 4.67; N, 13.08. Found: C, 67.15; H, 4.23; N, 12.86.
Ethyl2-(thiophene-2-carbonyl)-3-trifluoromethylquinoxaline-7-carboxylate (DR3)
This compound was obtained in 2.3% yield from ethyl 2-(thiophene-2-carbonyl)-3-trifluoromethylquinoxaline-7-carboxylate 1, 4-di-N-oxide by di-reduced using sodium dithionite. IR (KBr): 2991 (ArC-H), 1722 and 1672 (C=O), 1284 and 1162 (Ar-CF3) cm-1. 1H NMR (400 MHz, DMSO-d6) ppm: 1.41 (t, J= 7.1 Hz, 3H, CH3CH2OOC), 4.47 (q, J1= 7.07 Hz, J2= 7.12 Hz, 2H, CH3CH2OOC), 7.32 (d, J= 4.7 Hz, 1H, H4, C4H3S), 8.24 (d, J= 4.59 Hz, H5, C4H3S), 8.3 (d, J= 4.8 Hz, H3, C4H3S), 8.51 (d, J= 8.95 Hz, 1H, H5), 8.56 (d, J= 8.96 Hz, 1H, H6), 8.96 (s, 1H, H8). Calculated analysis for C17H11F3N2O3S: C, 53.61; H, 2.89; N, 7.35. Found: C, 53.46; H, 2.75; N,
7.23. Compounds derivatives from quinoxaline-7-carboxylate 1ˏ4-di-
N-oxide (M1-M3, E1-E8, and P1-P3) and quinoxaline di-reduced derivatives (DR1-DR3) are shown in
Table 1.
Biological assays
The National Cancer Institute (NCI) of the United States of America selected the 17 compounds cited above to be evaluated for their
in vitro antitumor activity. Initially, all compounds were tested at a single high dose (10
-5 M) according to NCI-60 human tumor cell line screen. The human tumor cell lines are grown in RPMI 1640 medium (5% fetal bovine serum and 2 mM L-glutamine). Cells are seeded into 96 well microtiter plates in 100 μL (5,000 to 40,000 cells/well). After, the microtiter plates are incubated at 37 °C, 5% CO
2, 95% air and 100% relative humidity for 24 h. Aliquots of 100 μL experimental drugs are added to the appropriate microtiter wells already containing 100 μL of medium, resulting in the required final drug concentration. After, the plates are incubated for an additional 48 h at 37 °C, 5% CO
2, 95% air, and 100% relative humidity. For adherent cells, the assay is terminated by the addition of cold TCA. Cells are fixed in situ by the addition of 50 μL of cold 50% (w/v) TCA (final concentration, 10% TCA) and incubated for 60 minutes at 4 °C. The supernatant is discarded, and the plates are washed five times with water and air dried. Sulforhodamine B (SRB) solution (100 μL) at 0.4% (w/v) in 1% acetic acid is added to each well, and plates are incubated for 10 minutes at room temperature. After staining, unbound dye is removed by washing five times with 1% acetic acid and the plates are air dried. Bound stain is subsequently solubilized with 10 mM trizma base, and the absorbance is read on an automated plate reader at a wavelength of 515 nm. After, only compounds M3, E5, E6, E7 and P3 were evaluated against the NCI-60 cell panel at five concentrations (0.01, 0.1, 1, 10 and 100 µm) and Growth Inhibition of 50% (GI50) was calculated. Total Growth Inhibition (TGI) and the Lethal Concentration 50 (LC50) were calculated for each cell line according to NCI methodology (
15). Data are express in Molar concentration. The GI50 value corresponds to the concentration of the compound causing 50% decrease in net cell growth, the TGI value or cytostatic activity reported is the concentration of the compound resulting in total growth inhibition and the LC50 value corresponds to the cytotoxic activity and it is the concentration of the compound causing 50% loss of initial cells at the end of the incubation period (
15).