A series of pyridopyridazin-3(2H)-one derivatives was synthesized in two facile steps. Mannich-type three-component condensation afforded the 2,6-diaryl piperidin-4-one derivatives, which underwent intramolecular cyclization in the presence of hydrazine or phenylhydrazine to yield the corresponding pyridopyridazin-3(2H)-one derivatives. All the derivatives of pyridopyridazin-3(2H)-one, except
Among the nitrogen containing six-member heterocylic compounds, the piperidine structural motif is often found in naturally occurring bioactive compounds such as alkaloids [
Another pharmacologically important heterocyclic structural motif is the pyridazin-3(2H)-one unit, which has been found to inhibit the activities of cGMP-phosphodiesterase (PDE3) and cAMP-phosphodiesterase (PDE4) enzymes [
Mannich-type condensation involving a ketone having two active methylene groups, an aromatic aldehyde, and ammonium acetate, resulting in the formation of 2,6-diarylpiperidin-4-one, was first reported by Noller and Baliah [
We, herein, report an improved method for the synthesis and complete characterization of different 4-oxo-2,6-diphenylpiperidin-3-yl-acetates (Scheme
Synthesis of piperidin-4-one derivatives. Reagents and conditions: methanol-acetic acid (70 mol%), 60°C, 2 h.
Synthesis of pyridopyridazin-3(2H)-one derivatives. Reagents and conditions: (i) N2H4·H2O, ethanol, reflux, 17 h; (ii) PhNHNH2, dry toluene, TFA (20 mol%), reflux, 2 days.
Three-component condensation of benzaldehyde, ammonium acetate, and ethyl levulinate in methanol at ~60°C afforded ethyl 4-oxo 2,6-diphenylpiperidin-3yl acetate in moderate yield (56%). After optimizing the reaction conditions (temperature, time, and amount of catalyst AcOH), various aryl aldehydes were allowed to react with ethyl levulinate and ammonium acetate in methanol-acetic acid medium at ~60°C to afford the corresponding ethyl 4-oxo-2,6-diarylpiperidin-3yl acetate derivatives in good yields. Typically, when benzaldehyde was used and the reaction was carried out in 70 mol% glacial acetic acid in methanol, the yield improved from 56% to 77%.
All the synthesized compounds were characterized using IR and NMR and ESI-MS techniques. For instance, the IR spectrum of compound
In view of the wide spectrum of biological activities documented for piperidine and pyridazinone pharmacophores, we reasoned that the combination of these two different pharmacophores into a single structural scaffold would confer synergistic properties on the new molecule. Accordingly, we synthesized pyrido[4,3-c]pyridazin-3(2H)-one derivatives using hydrazine and phenylhydrazine mediated cyclization as depicted in Scheme
The reaction of hydrazine hydrate with ethyl 4-oxo 2,6-diarylpiperidin-3yl acetates in ethanol under reflux condition yielded in due course the corresponding 4,4a,5,6,7,8-hexahydro-5,7-diarylpyrido[4,3-c]pyridazin-3(2H)-one derivatives
The structures of 4,4a,5,6,7,8-hexahydro-5,7-diarylpyrido[4,3-c]pyridazin-3(2H)-one derivatives
The structural elucidation of 4,4a,5,6,7,8-hexahydro-2,5,7-triarylpyrido[4,3-c]pyridazin-3(2H)-one derivatives
Several conformational isomers are possible for
ORTEP diagram of
The newly synthesized pyridopyridazin-3(2H)-one derivatives
Inhibitory effects of compounds
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In conclusion, three efficient methods for the syntheses of different derivatives of ethyl 4-oxo-2,6-diarylpiperidin-3yl acetate, 4,4a,5,6,7,8-hexahydro-5,7-diarylpyrido[4,3-c]pyridazin-3(2H)-one, and 4,4a,5,6,7,8-hexahydro-2,5,7-triarylpyrido[4,3-c]pyridazin-3(2H)-one are reported. The yields of ethyl 4-oxo-2,6-diarylpiperidin-3yl acetates (
All the chemicals used in this study were purchased from Sigma Aldrich without further purification. Melting points were determined in open capillary tubes and are uncorrected. IR spectra were taken as KBr pellets for solids on a Perkin Elmer Spectrum RXI FT-IR. 1H NMR (500 MHz) and 13C NMR (125 MHz) spectra were recorded in CDCl3 solutions with TMS as an internal standard on a JEOL instrument and Brucker Avance instrument. Mass spectra were recorded on a Thermo Finnigan LCQ Advantage MAX 6000 ESI spectrometer. Column chromatography was performed using neutral aluminium oxide, 150–200 mesh, and eluent, 7% ethyl acetate in hexane.
4-Oxo-2,6-diphenylpiperidin-3-yl-acetate (
To a solution of appropriate ethyl 4-oxo-2,6-diphenylpiperidin-3-yl-acetates (337 mg, 1.0 mmol) in ethanol was added hydrazine hydrate (0.053 mL, 1.2 mmol) and the resultant solution was refluxed for 17 h. The solvent was evaporated and the residue obtained was extracted with chloroform (3 × 20 mL). The combined organic layer was dried over sodium sulphate, concentrated under reduced pressure and the solid obtained was purified by crystallization using methanol.
Specifications are as follows: colourless solid; mp 153-154°C; yield 82%; IR (KBr cm−1): 3371, 3281, 3025, 2925, 2848, 1685, 1514, 1416, 1334, 1106, 1038, 823, 759; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: colourless solid; mp 183–185°C; yield 72%; IR (KBr cm−1): 3303, 3210, 3087, 2944, 2831, 1665, 1611, 1511, 1458, 1303, 1367, 1241, 1175, 1107, 1031, 834; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: colourless solid; mp 188–190°C; yield 76.7%; IR (KBr cm−1): 3318, 3222, 3090, 2920, 2849, 1664, 1439, 1414, 1370, 1305, 1230, 1174, 1091, 1014, 828; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: colourless solid, mp 185–187°C, yield 79%, IR (KBr cm−1): 3425, 3322, 3225, 3086, 2931, 2367, 2339, 1663, 1525, 1478, 1353, 1211, 1166; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: brown solid, mp 133–135°C, yield 75%, IR (KBr cm−1): 3236, 3097, 2922, 2854, 1674, 1485, 1439, 1412, 1345, 1305, 1230, 1102, 1070, 1008, 825; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: pale brown solid, mp 248–250°C, yield 69%, IR (KBr cm−1): 3417, 3322, 3227, 3091, 2926, 2853, 1665, 1523, 1353, 1453, 808, 735, 688; 1H NMR (500 MHz, CDCl3):
A mixture of ethyl 4-oxo-2,6-diphenylpiperidin-3-yl-acetates (337 mg, 1.0 mmol) in dry toluene were added to phenyl hydrazine (0.118 mL, 1.2 mmol) and trifluoroacetic acid (0.0155 mL, 0.20 mmol), and the solution was refluxed under nitrogen atmosphere for 2 days. After the reaction was complete the solvent was evaporated under reduced pressure, and the residue obtained was extracted with chloroform (3 × 20 mL). The combined organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure and the residue obtained was purified using column chromatography (neutral aluminium oxide, 150–200 mesh; eluent: 7% ethyl acetate in hexane).
Specifications are as follows: pale brown solid; mp 140–143°C; yield 79%; IR (KBr cm−1): 3304, 3030, 2960, 2887, 2806, 1680, 1595, 1492, 1454, 1326, 1305, 1227, 1160, 1107, 752; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: pale brown solid; mp 166-167°C; yield 72%; IR (KBr cm−1): 3320, 3021, 2919, 2878, 2815, 1688, 1594, 1492 1321, 1299, 1228, 1155, 1105, 821, 756; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: pink solid, mp 128–130°C; yield 74%; IR (KBr cm−1): 3415, 3306, 2954, 2832, 1682, 1606, 1506, 1449, 1302, 1242, 1175, 1105, 927, 833, 752; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: pale brown solid; mp 113–115°C; yield 77%; IR (KBr cm−1): 3315, 3061, 2853, 2810, 1676, 1593, 1491, 1442, 1413, 1359, 1329, 1304, 1227, 1202, 1158, 1093, 1014, 830; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: pale brown solid; mp 101-102°C; yield 71.6%; IR (KBr cm−1): 3300, 3041, 2923, 2814, 1679, 1593, 1488, 1410, 1328, 1305, 1227, 1201, 1159, 1106, 1069, 827; 1H NMR (500 MHz, CDCl3):
Specifications are as follows: brown solid; m.p 190-191°C; yield 67%; IR (KBr cm−1): 3418, 3085, 2922, 2852, 1679, 1596, 1522, 1345, 1103, 908, 810; 1H NMR (500 MHz, CDCl3):
Human breast adenocarcinoma (MCF-7) cell culture was procured from the National Centre for Cell Sciences (NCCS), Pune, India. The cells were grown in Dulbecco’s Modified Eagle Medium (DMEM) supplemented with 10% heat inactivated fetal bovine serum (FBS), penicillin (100 IU/mL), streptomycin (100
Cells were plated in 96-well flat bottom microtiter plate at a density of 1 × 104 cells per well and cultured for 24 h at 37°C in 5% CO2 atmosphere to allow cell adhesion. After 24 h, when partial monolayer was formed, medium was removed and cells were treated with different concentrations of standard drug (doxorubicin) and test compounds. Microscopic examination was carried out and observations recorded every 24 h. After the treatment, the solutions in the wells were discarded and 50
The authors declare that there is no conflict of interests regarding the publication of this paper.
One of the authors, Periasamy Selvakumar, thanks the Council of Scientific and Industrial Research, New Delhi, India, for the research fellowship. The authors would like to acknowledge the Department of Chemistry, IIT-Madras, India, for single crystal XRD analysis and the Department of Pharmaceutical Biotechnology, Manipal College of Pharmaceutical Sciences, Manipal, Karnataka, India, for MTT Assay. Financial support from CSC0201 project of CSIR is acknowledged.