Materials and methods
The solvents used were of HPLC reagent grade. Melting points were determined with a Mel-Temp apparatus. Fourier transform infrared spectroscopy (FT-IR) spectra were recorded on Nicolet 560. Nuclear magnetic resonance spectra (1H NMR and 13C NMR spectra) were recorded on a JOEL 400 MHz spectrometer with chemical shift values reported in δ units (ppm) relative to an internal standard. X-Ray data collection was carried out on Bruker SMART APEX II CCD diffractometer, cell refinement: SAINT; data reduction: SAINT; program used to solve structure: SHELXS; program used to refine structure: SHELXL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL [30] and PLATON [31]. The microwave irradiation employed a multimode reactor (Synthos 3000, Aton Paar GmbH, and 1400 W maximum magnetron). Elemental analyses were performed on Perkin-Elmer 2400 elemental analyzer, and the values found were within ±0.3% of the theoretical values. Follow-up of the reactions and checks of the purity of the compounds was done by TLC on silica gel-protected aluminum sheets (Type 60 GF254, Merck). The compounds were named using Chem. Draw Ultra version 11, Cambridge soft Corporation.
General method for synthesis of α-ketoamide and bis-(α-ketoamide) derivatives
Method A (Conventional Procedure)
To a solution of N-acetylisatin 1 or N-propionylisatin 2 (10 mmol) in acetonitrile (20 mL), secondary amine 3a-c or diamine 6a-e in ratio (1:1 and 2:1, respectively) was added at room temperature. The reaction mixture was stirred at room temperature for 12 h. On the next day, the solvent was removed under vacuum and the crude product was recrystallized from dichloromethane and hexane (1:2). In the case of diamine, the precipitate was filtered, washed with acetonitrile (5 mL), and dried under vacuum to afford the pure product.
Method B (Microwave-Irradiation)
The reaction was performed using a multimode reactor (Synthos 3000 Aton Paar, GmbH, 1400 W maximum magnetron). The initial step was conducted with 4-Teflon vessels rotor (MF 100) that allows the reactions to be processed 4 at a time under the same conditions. In each vessel N-acylisatin mixed with different amine or diamine in small amount of acetonitrile (2–5 mL). The individual vessels were purged with nitrogen gas for 2 min and then placed in the corresponding rotor. The vessels were heated for 3 min at 80°C and held at the same temperature for a further 2 min at 200 W. Cooling was accomplished by a fan (5 min); the final product was precipitated after cooling, filtered, dried under vacuum, and then recrystallized from dichloromethane-hexane (1:2).
N-[2-(2-Oxo-2-(piperidin-1-yl)acetyl)phenyl]acetamide 4a (1H NMR and 13C NMR attached as a supporting information; Additional file 1)
Light brown crystals; mp 132-133°C; yield (65% method A, Lit. [17] mp 130-132 °C); (91% method B); IR (KBr, cm−1): 3399 (NH), 1691 (α-COCON), 1630 (CO-amide), 1605 (CO-amide). 1H-NMR (CDCl3): δ = 1.55 (m, 2H, CH2), 1.70 (m, 4H, 2CH2), 2.25 (s, 3H, COCH3), 3.30 (m, 2H, CH2), 3.69 (m, 2H, CH2), 7.12 (t, J = 8.08 Hz, 1H, ArH), 7.65 (m, 2H, ArH), 8.88 (d, J = 8.80 Hz, 1H, ArH), 11.30 (s, 1H, NH, D2O exchangeable). 13C-NMR (CDCl3): δ = 24.3, 25.5, 25.7, 26.2, 42.3, 47.2, 117.9, 120.7, 122.8, 133.6, 136.9, 142.5, 164.5 (CO-amide), 169.6 (CO-amide), 196.2 (α-COCON). Anal. Calcd for C15H18N2O3: C, 65.68; H, 6.61; N, 10.21. Found: C, 65.56; H, 6.67; N, 10.33.
N-[2-(2-Morpholino-2-oxoacetyl)phenyl]acetamide 4b (1H NMR and 13C NMR attached as a supporting information; Additional file 1)
Light brown crystals; mp 111-113°C; yield (69% method A); (93% method B); IR (KBr, cm−1): 3399 (NH), 1693 (α-CO-CON), 1635 (CO-amide), 1608 (CO-amide). 1H-NMR (CDCl3): δ = 2.24 (s, 3H, COCH3), 3.34 (t, J = 5.12 Hz, 2H, CH2), 3.65 (t, J = 4.40 Hz, 2H, CH2), 3.77 (m, 4H, 2CH2), 7.13 (t, J = 7.36 Hz, 1H, ArH), 7.67 (m, 2H, ArH), 8.78 (d, J = 8.04 Hz, 1H, ArH), 11.21 (s, 1H, NH, D2O exchangeable) ppm; 13C-NMR (CDCl3): δ = 25.7, 41.3, 46.4, 66.7, 117.8, 120.8, 122.9, 133.53, 137.2, 142.6, 164.6 (CO-amide), 169.6 (CO-amide), 195.4 (α-COCON) ppm. Anal. Calcd for C14H16N2O4: C, 60.86; H, 5.84; N, 10.14. Found: C, 60.78; H, 5.77; N, 10.31.
N-[2-(2-(4-Methylpiperazin-1-yl)-2-oxoacetyl)phenyl]acetamide 4c (1H NMR and 13C NMR attached as a supporting information; Additional file 1)
Light brown crystals; mp 113-115°C; yield (64% method A); (89% method B); IR (KBr, cm−1): 3396 (NH), 1692 (α-CO-CON), 1633 (CO-amide), 1608 (CO-amide). 1H-NMR (CDCl3): δ 2.23 (s, 3H, COCH3), 2.30 (s, 3H, N-CH3), 2.35 (t, J = 5.01 Hz, 2H, CH2), 2.49 (t, J = 5.12 Hz, 2H, CH2), 3.33 (t, J = 5.12 Hz, 2H, CH2), 3.77 (t, J = 5.12 Hz, 2H, CH2), 7.12 (t, J = 7.32 Hz, 1H, ArH), 7.63 (m, 2H, ArH), 8.77 (d, J = 8.80 Hz, 1H, ArH), 11.24 (s, 1H, NH, D2O exchangeable) ppm; 13C-NMR (CDCl3): δ = 25.6, 41.3, 46.0, 46.1, 54.5, 54.9, 117.9, 120.7, 122.8, 133.6, 137.1, 142.5, 164.4 (CO-amide), 169.8 (CO-amide), 195.7 (α-COCON). Anal. Calcd for C15H19N3O3: C, 62.27; H, 6.62; N, 14.52. Found: C, 62.38; H, 6.71; N, 14.69.
N-[2-(2-Oxo-2-(piperidin-1-yl)acetyl)phenyl]propionamide 5a (1H NMR and 13C NMR attached as a supporting information; Additional file 2)
Light brown crystals; mp 102-103°C; yield (70% method A); (95% method B); IR (KBr, cm−1): 3396 (NH), 1695 (α-CO-CON), 1630 (CO-amide), 1608 (CO-amide). 1H-NMR (CDCl3): δ = 1.26 (t, J = 7.32 Hz, 3H, CH2CH3), 1.53 (m, 2H, CH2), 1.68 (m, 4H, 2CH2), 2.49 (q, J = 7.36 Hz, 2H, CH2CH3), 3.26 (t, J = 5.12 Hz, 2H, CH2), 3.68 (m, 2H, CH2), 7.12 (t, J = 8.08 Hz, 1H, ArH), 7.64 (m, 2H, ArH), 8.81 (d, J = 8.80 Hz, 1H, ArH), 11.31 (s, 1H, NH, D2O exchangeable) ppm; 13C-NMR (CDCl3): δ = 9.5, 24.4, 25.4, 25.7, 26.2, 31.8, 42.3, 47.2, 120.7, 118.0, 122.7, 133.5, 136.9, 142.6, 164.5 (CO-amide), 173.4 (CO-amide), 196.2 (α-COCON) ppm. Anal. Calcd for C16H20N2O3: C, 66.65; H, 6.99; N, 9.72. Found: C, 66.38; H, 6.81; N, 9.98.
N-[2-(2-Morpholino-2-oxoacetyl)phenyl]propionamide 5b (1H NMR and 13C NMR attached as a supporting information; Additional file 2)
Light brown crystals; mp 112-112°C; yield (69% method A); (93% method B); IR (KBr, cm−1): 3394 (NH), 1691 (α-CO), 1632 (CO-amide), 1610 (CO-amide). 1H-NMR (CDCl3): δ = 1.29 (t, J = 7.32 Hz, 3H, CH2CH3), 2.48 (q, J = 7.36Hz, 2H, CH2CH3), 3.36 (t, J = 5.12 Hz, 2H, CH2), 3.66 (t, J = 5.12 Hz, 2H, CH2), 3.78 (brs, 4H, 2CH2), 7.13 (t, J = 7.13 Hz, 1H, ArH), 7.67 (m, 2H, ArH), 8.83 (d, J = 8.80 Hz, 1H, ArH), 11.24 (s, 1H, NH, D2O exchangeable) ppm; 13C-NMR (CDCl3): δ = 9.5, 31.8, 41.7, 46.4, 66.7, 117.8, 120.9, 122.7, 133.5, 137.2, 142.8, 164.6 (CO-amide), 173.4 (CO-amide), 195.4 (α-COCON) ppm. Anal. Calcd for C15H18N2O4: C, 62.06; H, 6.25; N, 9.65. Found: C, 62.18; H, 6.17; N, 9.89.
N-[2-(2-(4-Methylpiperazin-1-yl)-2-oxoacetyl)phenyl]propionamide 5c (1H NMR and 13C NMR attached as a supporting information; Additional file 2)
Light brown crystals; mp 90-92°C; yield (72% method A); (89% method B); IR (KBr, cm−1): 3366 (NH), 1710 (α-CO), 1644 (CO-amide), 1581 (CO-amide). 1H-NMR (CDCl3): δ = 1.26 (s, 3H, CH2CH3), 2.30 (s, 3H, N-CH3), 2.35 (t, J = 5.12 Hz, 2H, CH2), 2.51 (m, 4H, CH2CH3, CH2), 3.35 (t, J = 4.80 Hz, 2H, CH2), 3.77 (t, J = 5.16 Hz, 2H, CH2), 7.12 (t, J = 8.08 Hz, 1H, ArH), 7.63 (m, 2H, ArH), 8.81 (d, J = 8.80 Hz, 1H, ArH), 11.27 (s, 1H, NH, D2O exchangeable) ppm; 13C-NMR (CDCl3): δ = 9.5, 31.8, 41.3, 46.0, 46.4, 54.5, 54.9, 117.9, 120.8, 122.7, 133.6, 137.1, 142.7, 164.5 (CO-amide), 173.4 (CO-amide), 195.7 (α-COCON) ppm. Anal. Calcd for C16H21N3O3: C, 63.35; H, 6.98; N, 13.85; Found: C, 63.21; H, 6.87; N, 14.03.
N, N'-(Ethane-1,2-diyl)bis[2-(2-acetamidophenyl)-2-oxoacetamide] 7a (1H NMR and 13C NMR attached as a supporting information; Additional file 3)
White solid; mp 220-221°C (dec.); yield (72% method A); (92% method B); IR (KBr, cm−1): 3351 (NH), 1685 (α-CO), 1653 (CO-amide), 1587 (CO-amide). 1H-NMR (DMSO-d6): δ = 2.06 (s, 6H,2 COCH3), 3.36 (m, 4H, 2CH2), 7.20 (t, J = 7.32 Hz, 2H, ArH), 7.65 (t, J = 8.08 Hz, 2H, 2 NH), 7.67(d, J = 8.08 Hz, 2H, 2ArH), 7.81 (d, J = 8.08 Hz, 2H, ArH), 8.84 (d, 2H, ArH), 11.55 (s, 2H, 2NH) ppm; 13C-NMR (DMSO-d6): δ = 24.5, 39.9, 122.1, 124.0, 124.8, 134.4, 138.8, 164.2 (CO-amide), 169.3 (CO-amide), 191.2 (α-COCON) ppm. Anal. Calcd for C22H22N4O6: C, 60.27; H, 5.06; N, 12.78; Found: C, 60.38; H, 5.11; N, 12.69.
N, N'-(Butane-1,4-diyl)bis[2-(2-acetamidophenyl)-2-oxoacetamide] 7b (1H NMR and 13C NMR attached as a supporting information; Additional file 3)
White solid; mp 205-207°C (dec.); yield (70% method A); (90% method B); IR (KBr, cm−1): 3258 (NH), 1698 (α-CO), 1663 (CO-amide), 1602 (CO-amide). 1H-NMR (DMSO-d6): δ 1.55 (m, 4H, 2CH2), 2.05 (s, 6H, 2COCH3), 3.23 (m, 4H, 2 CH2), 7.23 (t, J = 8.04 Hz, 2H, ArH), 7.64 (m, 4H, 2NH, 2ArH), 7.89 (d, J = 8.08 Hz, 2H, ArH), 8.75 (t, J = 5.16 Hz, 2H, ArH), 11.60 (s, 2H, 2NH) ppm; 13C-NMR (DMSO-d6): δ = 24.6, 26.8, 39.6, 121.9, 124.0, 124.2, 132.3, 134.7, 139.2, 164.3 (CO-amide), 169.4 (CO-amide), 192.4 (α-COCON) ppm. Anal. Calcd for C24H26N4O6: C, 61.79; H, 5.62; N, 12.01. Found: C, 61.87; H, 5.71; N, 12.19.
N, N'-(Hexane-1,6-diyl)bis[2-(2-acetamidophenyl)-2-oxoacetamide] 7c (1H NMR and 13C NMR attached as a supporting information; Additional file 3)
White solid; mp 176-178°C (dec.); yield (72% method A); (94% method B); IR (KBr, cm−1): 3257 (NH), 1698 (α-CO), 1662 (CO-amide), 1608 (CO-amide). 1H-NMR (DMSO-d6): δ = 1.33 (m, 4H, 2CH2), 1.51 (m, 4H, 2CH2), 2.07 (s, 6H, 2 COCH3), 3.21 (m, 4H, 2 CH2), 7.23 (t, J = 7.32 Hz, 2H, ArH), 7.62 (m, 4H, 2NH, 2ArH), 7.91 (d, J = 8.08 Hz, 2H, ArH), 8.73 (t, J = 5.88 Hz, 2H, ArH), 10.91 (s, 2H, 2NH) ppm; 13C-NMR (DMSO-d6): δ = 24.7, 26.6, 29.6, 39.1, 121.9, 124.0, 124.1, 132.3, 134.7, 139.3, 164.3 (CO-amide), 169.3 (CO-amide), 192.5 (α-COCON) ppm. Anal. Calcd for C26H30N4O6: C, 63.15; H, 6.11; N, 11.33. Found: C, 63.27; H, 5.98; N, 11.49.
1, 1'-(Piperazine-1,4-diyl)bis[2-(2-acetamidophenyl)ethane-1,2-dione] 7d (1H NMR and 13C NMR attached as a supporting information; Additional file 4)
White solid; mp 118-120°C (dec.); yield (69% method A); (93% method B); IR (KBr, cm−1): 3364 (NH), 1712 (α-CO), 1644 (CO-amide), 1580 (CO-amide). 1H-NMR (DMSO-d6): δ = 2.13 (s, 3H, COCH3), 2.18 (s, 3H, COCH3), 3.41 (m, 2H, CH2), 3.55 (m, 2H, CH2), 3.64 (m, 2H, CH2), 3.77 (m, 2H, CH2), 7.29 (m, 2H, ArH), 7.75 (m, 4H, ArH), 8.17 (d, J = 8.08 Hz, 1H, ArH), 8.31 (d, J = 8.08 Hz, 1H, ArH), 10.73 (s, 1H, NH), 10.83 (s, 1H, NH) ppm; 13C-NMR (DMSO-d6): δ = 25.1, 25.2, 41.1, 41.4, 45.4, 46.0, 121.8, 121.9, 122.1, 124.2, 124.2, 124.4, 133.4, 133.7, 136.5, 136.7, 140.6, 141.0, 164.6 (CO-amide), 164.7 (CO-amide), 169.9 (CO-amide), 193.4 (α-COCON), 193.9 (C = O) ppm. Anal. Calcd for C24H24N4O6: C, 62.06; H, 5.21; N, 12.06. Found: C, 62.31; H, 5.11; N, 12.29.
N, N'-(Cyclohexane-1,4-diyl)bis(2-(2-acetamidophenyl)-2-oxoacetamide] 7e (1H NMR and 13C NMR attached as a supporting information; Additional file 4)
Off White solid; mp 249-250°C; yield (68% method A); (89% method B); IR (KBr, cm−1): 3269 (NH), 1686 (α-CO), 1645 (CO-amide), 1588 (CO-amide). 1H-NMR (DMSO-d6): δ = 1.45 (m, 4H, CH2), 1.89 (m, 4H, CH2), 2.08 (s, 6H, 2 COCH3), 3.67 (m, 2H, CH), 7.26 (t, J = 7.36 Hz, 2H, 2ArH), 7.63 (m, 4H, 2NH, 2ArH), 7.97 (d, J = 8.08 Hz, 2H, ArH), 8.69 (d, J = 8.08 Hz, 2H, 2ArH), 10.64 (s, 2H, 2NH) ppm; 13C-NMR (DMSO-d6): δ = 24.7, 24.8, 31.1, 47.8, 121.8, 121.9, 123.7, 124.1, 132.3, 132.5, 134.7, 135.1, 139.5, 163.8 (CO-amide), 169.4 (CO-amide), 192.7 (α-COCON) ppm. Anal. Calcd for C26H28N4O6: C, 63.40; H, 5.73; N, 11.38. Found: C, 63.28; H, 5.81; N, 11.49.
N, N'-(Ethane-1,2-diyl)bis[2-(2-propionamidophenyl)-2-oxoacetamide] 8a (1H NMR and 13C NMR attached as a supporting information; Additional file 5)
White solid; mp 204-206°C (dec.); yield (70% method A); (91% method B); IR (KBr, cm−1): 3291 (NH), 1697 (α-CO), 1667 (CO-amide), 1607 (CO-amide). 1H-NMR (DMSO-d6): δ = 1.09 (t, J = 7.32 Hz, 6H, 2CH2CH3), 2.37 (q, J = 7.33 Hz, 4H, 2CH2CH3), 3.38 (m, 4H, 2CH2), 7.21 (t, J = 8.04 Hz, 2H, ArH), 7.62 (t, J = 7.32 Hz, 2H, 2NH), 7.69 (d, J = 7.32 Hz, 2H, ArH), 7.92 (d, J = 8.80 Hz, 2H, ArH), 8.88 (brs, 2H, ArH), 10.60 (s, 2H, 2NH) ppm; 13C-NMR (DMSO-d6): δ = 9.9, 30.4, 39.4, 121.8, 123.8, 124.0, 132.5, 134.7, 139.2, 164.3 (CO-amide), 172.9 (CO-amide), 191.9 (α-COCON) ppm. Anal. Calcd for C24H26N4O6: C, 61.79; H, 5.62; N, 12.01; O, 20.58. Found: C, 62.00; H, 5.51; N, 12.39.
1, 1'-(Piperazine-1,4-diyl)bis[2-(2-propionamidophenyl)ethane-1,2-dione] 8d (1H NMR and 13C NMR attached as a supporting information; Additional file 5)
White solid; mp 221-223°C; yield (72% method A); (93% method B); IR (KBr, cm−1): 3318 (NH), 1701 (α-CO), 1644 (CO-amide), 1581 (CO-amide). 1H-NMR (DMSO-d6): δ = 1.13 (m, 4H, 2CH2CH3), 2.48 (m, 4H, 2CH2CH3), 3.40 (m, 2H, CH2), 3.55 (m, 2H, CH2), 3.64 (m, 2H, CH2), 3.78 (m, 2H, CH2), 7.29 (m, 2H, ArH), 7.75 (m, 4H, ArH), 8.30 (d, J = 8.08 Hz, 1H, ArH), 8.44 (d, J = 8.04 Hz, 1H, ArH), 10.80 (s, 1H, NH), 10.90 (s, 1H, NH) ppm; 13C-NMR (DMSO-d6): δ = 9.8, 9.8, 30.8, 30.9, 41.1, 41.4, 45.4, 46.0, 120.4, 121.5, 121.7, 124.0, 124.1, 133.7, 134.0, 136.7, 136.9, 141.1, 141.5, 164.7 (CO-amide), 164.7 (CO-amide), 173.3, 193.9 (α-COCON), 194.3 (α-COCON) ppm. Anal. Calcd for C26H28N4O6; C, 63.40: H, 5.73; N, 11.38. Found: C, 63.31; H, 5.81; N, 11.19.
Synthesis of methyl 2-(2-acetamidophenyl)-2-oxoacetate (9a) and methyl 2-oxo-2-(2-propionamidophenyl)acetate (9b) using microwave irradiation
N-Acylisatin 1 or 2 (2 mmol) was dissolved in methanol (10 mL) and the reaction was microwave irradiated using a multimode reactor (Synthos 3000 Aton Paar, GmbH, 1400 W maximum magnetron) for 3 min at 80°C and hold at the same temperature for 2 min at 200 W. Cooling was accomplished by a fan (5 min) and the desired product was obtained after cooling with an excellent yield without further recrystallization.
Methyl 2-(2-acetamidophenyl)-2-oxoacetate 9a (1H NMR and 13C NMR attached as a supporting information; Additional file 6)
The product was obtained as yellow needles from methanol; mp 104-105°C; yield 91%. IR (KBr, cm−1): 3220.99 (NH), 1746.58 (CO-ester), 1696.22 (α-CO), 1656.79 (CO-amide). 1H NMR (CDCl3): δ = 2.25 (s, 3H, COCH3), 3.98 (s, 3H, COOCH3), 7.13 (t, J = 7.36 Hz, 1H, Ar), 7.62-7.68 (m, 2H, Ar), 8.78(d, J = 8.08 Hz, 1H, Ar), 11.06 (s, 1H, NH) ppm. 13C NMR (CDCl3): δ = 25.6, 53.1, 117.1, 120.8, 122.6, 133.6, 137.3, 142.8, 142.8, 164.0 (CO-amide), 169.6 (CO-ester), 190.3 (α-COCON) ppm. Anal. Calcd for C11H11NO4: C 59.73, H 5.01, N 6.33. Found C 60.00, H 5.18, N 6.44.
Methyl 2-(2-propionamidophenyl)-2-oxo-acetate 9b (1H NMR and 13C NMR attached as a supporting information; Additional file 7)
The product was obtained as yellow needles from methanol; mp 68-70°C; yield 89%. IR (KBr, cm−1): 3220.99 (NH), 1746.58 (CO-ester), 1696.22 (α-CO), 1656.79 (CONH). 1H NMR (CDCl3): δ 1.28 (t, J = 7.32 Hz, 3H, CH2CH3), 2.48 (q, J = 7.32 Hz, 2H, COCH2CH3), 3.98 (s, 3H, COOCH3), 7.13 (t, J = 8.04 Hz, 1H, Ar), 7.63-7.68 (m, 2H, Ar), 8.82 (d, J = 8.08 Hz, 1H, Ar), 11.10 (s, 1H, NH) ppm; 13C NMR (CDCl3): δ = 9.5, 31.8, 53.1, 117.1, 120.8, 122.5, 133.7, 137.3, 142.9, 164.0 (CO-amide), 173.4 (CO-ester), 190.4 (α-COCON) ppm. Anal. Calcd for C12H13NO4: C, 61.27; H, 5.57; N, 5.95. Found C 61.05, H 5.71, N 6.04.