Dichloromethane and chloroform was distilled from calcium hydride before use. All reactions were performed under an inert atmosphere with unpurified reagents and dry solvents. Analytical thin-layer chromatography (TLC) was performed using 0.25 mm silica gel-coated Kieselgel 60 F254 plates. Flash chromatography was performed using the indicated solvent and silica gel 60 (Merck, 230-400 mesh). All the microwave heating experiments were conducted under optimized reaction conditions of power and temperature in a closed vessel in a Biotage initiator model no: Initiator US, 355286, 10429-22T, using IR sensor as internal probe for the control of temperature and compressed air system for cooling. 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were recorded on a Bruker DX-300 spectrometer. Chemical shifts are reported in parts per million (ppm) on the δ scale from an internal standard. High-resolution mass spectra (HRMS) were recorded on a JEOL TMS-HX 110 mass spectrometer. Analytical HPLC analyses were recorded with UV detection at λ=254nm (column: Sphereclone 5μ Si (250 x 4.6 mm).
NO2
F O
O PEG
2.21. Experimental Section
General Procedure for the Synthesis of PEG bound 4-Fluoro-3-nitro benzoic acid 2.
4-Fluoro-3-nitro benzoic acid 1 (0.690 g, 3.73 mmol, 2.80 Equiv), PEG-4000 (5.30 g, 1.33 mmol, 1.0 Equiv) and N, N’-dimethylamino pyridine (DMAP) (0.005 g) are placed in a dry, nitrogen-purged 100 mL round-bottom flask containing dry CH2Cl2 (15 mL). To the mixtures were added dropwise N, N’-dicyclohexylcarbodiimide (DCC) (0.890 g, 4.32 mmol, 3.2 Equiv) dissolved in dry CH2Cl2 (5 mL) for a period of 5 minutes. The reaction mixtures were stirred for another 15 minutes at room temperature. Then this O-acylation reaction was carried out in a 80 ml sealed CEM microwave vessel using microwave irradiation at (85 °C) for 15 minutes. After the completion of the reaction, the insoluble DCU byproduct was allowed to settle, and the reaction mixtures were filtered and washed with CH2Cl2 (50 mLҳ3). The solvent was evaporated, and the residue was again precipitated with cold ether which was filtered through fritted funnel to remove any unreacted acid and DCC, finally collected and dried under vacuum. The crude product PEG bound 4-Fluoro-3-nitro benzoic acid 2 obtaind 5.4 gm as light yellow solid in high purity.
NH2
NH O
O PEG
General Procedure for the Substitution isobutyl amine on PEG bound 4-Fluoro-3-nitro benzoic acid 2.
Isobutyl amine (0.454 gm, 6.23 mmol, 5.0 Equiv) was added to the PEG bound 4-Fluoro-3-nitro benzoic acid 2 (5.40 gm, 1.25 mmol, 1.0 Equiv) solution in dry CH2Cl2 (10 mL) at room temperature for 5 minutes. The reaction mixtures were sealed and irradiated at 75
oC for 15 mins of on 80 ml CEM microwave vessel. After completion of the reaction time, the reaction mixtures were cool and precipitated with slow addition of cold ether (100 mL) which was filtered through a fritted funnel to obtain the PEG bound 4-alkyl amino-3-nitro benzoic acid 3, 5.5 gm as yellow solid in high purity.
General Procedure for the Reduction of the Aryl nitro group in PEG bound 4-isobutyl amino-3-nitro benzoic acid 3.
To a solution of 5 (5.50 gm, 1.24 mmol, 1.0 equiv) in dry methanol (10 mL), Zn (1.61 gm, 24.8 mmol, 20.0 equiv) and ammonium formate (1.21 gm, 18.6 mmol, and 15.0 equiv) were added. The reaction mixture was stirred at room temperature and subsequently irradiated in sealed microwave vial (80 ml) at 65 oC for 12 mins to obtain
NO2
NH O
O PEG
NH
NH O
O PEG
O O2N
F
the polymer bound conjugates. After completion, the mixtures were filtered with Celite to remove zinc and the filtrate was collected and concentrated under reduced pressure. Then dichloromethane (25 mL) was added to precipitate ammonium formate, and the mixture was again passed through a thin layer of Celite to remove ammonium formate and dried to yield the compound 4 in 5.2 gm colourless solid in high yield.
General Procedure for the Preparation of Polymer Bound 3-(4-Fluoro-3- nitrobenzamido)-4-(substituted amino) carboxylates 5.
Polymer bound o-phenylene diamine 4 (1.0 g, 0.23 mmol, 1.0 equiv) dissolved in (5 mL) of dichloromethane was added to a solution of 4-fluoro-3-nitrobenzoic acid (0.11 g, 0.60 mmol, 2.6 equiv) in dichloromethane (5 mL) in the presence of N,N′-dicyclohexylcarbodiimide (DCC) (0.12 g, 0.60 mmol, 2.6 equiv) and N,N′- dimethylamino pyridine (DMAP) (2 mg). The reaction mixture was stirred at room temperature and subsequently irradiated in sealed microwave vial (10 ml) for 85 oC 15 mins to obtain the polymer bound amide conjugates 5. After completion of the reaction, the suspensible dicyclohexyl urea (DCU) was filtered through filter paper. The reaction mixtures were precipitated by slow addition of cold ether and precipitated amide conjugate was filtered through fritted funnel. The crude product was washed successively with ether (50 mL × 3) to remove the undesired impurity and dried for further steps to obtain 5 as light brown solid.
O O PEG
N N
NO2 F
General Procedure for the Preparation of Polymer Bound 2-(4-fluoro-3-nitrophenyl)-1-alkyl-1H-benzo[d]imidazole carboxylates 6.
To a solution of 5 in 1, 2-dichloroethane, trifluoroacetic acid (0.5 mL) and MgSO4 (0.5 g) were added and irradiated under sealed microwave vial (10 ml) 100 oC for 15 mins. After completion of the reaction, MgSO4 was removed through celite. The reaction mixtures were cooled and precipitated by slow addition of excess of cold ether (100 mL) and filtered through a fritted funnel to obtain the compound 6 in high purity in quantitative yields as light green solid 5.3 gm.
General Procedure for the Preparation of Polymer Bound 1-alkyl-2-(3-nitro-4-(1H-pyrrol-1-yl)phenyl)-1H-benzo[d]imidazole-5-carboxylate 7.
Pyrrole (0.14 g, 2.14 mmol, 5 equiv) and Cs2CO3 (0.69 g, 2.14 mmol, 5 equiv) was added to the solution of 6 (2.0 g, 0.43 mmol, 1 equiv) in dimethyl formamide (10 mL) in a 20 mL microwave vial. The vial was sealed and the reaction mixtures were irradiated in a microwave reactor at 135 °C for 10 minutes to obtain the polymer conjugate 7. After being cooled to room temperature, the reaction mixtures were precipitated by slow
O O PEG
N N
NO2 N
O O PEG
N N
NH2 N
addition of cold ether and precipitated pyrrole bound polymer conjugates 7 were filtered through fritted funnel. The crude product was washed in succession with ether (100 mL×3) to remove the undesired impurity and dried for next steps.
General Procedure for the Preparation of Polymer Bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-alkyl-1H-benzo[d]imidazole-5-carboxylate 8.
To a solution of 7 (2.14 g, 0.45 mmol ) in methanol (10 ml), zinc dust (0.58 g, 9.0 mmol, 20.0 equiv) and ammonium formate (0.29 g, 4.50 mmol, and 10.0 equiv) were added in a 20 mL microwave vial. The vial was sealed and the reaction mixtures were irradiated in a microwave reactor at 60 °C for 10 minutes. After being cooled to ambient temperature, the reaction mixtures were then subjected to centrifugation for removal of Zn and filtered through fritted funnel and the supernatant liquid was concentrated by rotary evaporation.
Dichloromethane (10 mL) was then added to salt out ammonium formate. The reaction mixtures were filtered through fritted funnel again to remove ammonium formate to obtain the polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-alkyl-1H-benzo[d]imidazole-5-carboxylate 8.
General Procedure for the Preparation of Polymer Bound 2-(4,4-dialkyl-4,5-
dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1-methyl-1H-benzo[d]imidazole-5-carboxylate 9.
O O PEG
N N
N HN
To a stirred solution of polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-alkyl-1H-benzo[d]imidazole-5-carboxylate conjugates 8 in CHCl3 (10 mL), ketones (1.05 mmol, 5.0 equiv), trifluoro acetic acid (TFA) 0.05 ml and MgSO4 (20 mg) were added in 20 mL microwave vial. The vial was sealed and the reaction mixtures were irradiated in a microwave reactor at 85 °C for 12 minutes. After cooling to room tempaeratue, the crude product mixtures were purified by precipitation with cold ether (100 mL×3) and dried to obtain the conjugate 9 in high purity.
General Procedure for the Cleavage of Polymer Bound Substituted alkyl 2-(4,4- alkyl-4,5-dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1-methyl-1H-benzo[d]imidazole-5-carboxylate10.
To a solution of conjugates 10 in methanol (20 mL), KCN (100 mg) was added and stirred for 24 hours at room temperature. After completion of the reaction, excess of cold ether (100 mL) was added, the polymer was filtered off and filtrate was subjected to evaporation. The residue was dried under vacuum, and submitted to crude HPLC analysis with UV detection at λ = 254 nm (column: Sphereclone 5μ Si (250 x 4.6 mm);
gradient: 35 % ethyl acetate in hexane; flow rate: 1 mL/min.). The slurry obtained was loaded on silica gel column and eluted with a mixture of ethyl acetate and hexane (1:4) to get the title compounds 10 as a solid in 75-99 % overall yields.
O O
N N
N HN
General Procedure for the Preparation of Polymer Bound 1-isobutyl-2-(3-nitro-4-(1H-indole-1-yl)phenyl)-1H-benzo[d]imidazole-5-carboxylate 11.
Indole (0.24 g, 2.14 mmol, 5 equiv) and Cs2CO3 (0.69 g, 2.14 mmol, 5 equiv) was added to the solution of 6a (2.0 g, 0.43 mmol, 1 equiv) in dimethyl formamide (10 mL) in a 20 mL microwave vial. The vial was sealed and the reaction mixtures were irradiated in a microwave reactor at 135 °C for 10 minutes to obtain the polymer conjugate 11. After being cooled to room temperature, the reaction mixtures were precipitated by slow addition of cold ether and precipitated pyrrole bound polymer conjugates 11 were filtered through fritted funnel. The crude product was washed in succession with ether (100 mL×3) to remove the undesired impurity and dried for next steps.
General Procedure for the Preparation of Polymer Bound 2-(3-amino-4-(1H-indole-1-yl)phenyl)-1-isobutyl -1H-benzo[d]imidazole-5-carboxylate 12.
To a solution of 11 (2.00 g, 0.41 mmol ) in methanol (10 ml), zinc dust (0.53 g, 8.20 mmol, 20.0 equiv) and ammonium formate (0.27 g, 4.10 mmol, and 10.0 equiv) were added in a 20 mL microwave vial. The vial was sealed and the reaction mixtures were irradiated in a microwave reactor at 60 °C for 10 minutes. After being cooled to ambient temperature, the reaction mixtures were then subjected to centrifugation for removal of
O O PEG
N N
NO2 N
O O PEG
N N
NH2 N
Zn and filtered through fritted funnel and the supernatant liquid was concentrated by rotary evaporation. Dichloromethane (10 mL) was then added to salt out ammonium formate. The reaction mixtures were filtered through fritted funnel again to remove ammonium formate to obtain the polymer bound 2-(3-amino-4-(1H-indole-1-yl)phenyl)-1-isobutyl-1H-benzo[d]imidazole-5-carboxylate 12.
General Procedure for the Preparation of Polymer Bound 2-(4,4-dialkyl-4,5-
dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1-methyl-1H-benzo[d]imidazole-5-carboxylate 13.
To a stirred solution of polymer bound 2-(3-amino-4-(1H-indole-1-yl)phenyl)-1-isobutyl-1H-benzo[d]imidazole-5-carboxylate conjugates 12 in CHCl3 (10 mL), 4-methylcyclohexanone (1.05 mmol, 5.0 equiv), trifluoro acetic acid (TFA) 0.05 ml and MgSO4 (20 mg) were added in 20 mL microwave vial. The vial was sealed and the reaction mixtures were irradiated in a microwave reactor at 85 °C for 12 minutes. After cooling to room tempaeratue, the crude product mixtures were purified by precipitation with cold ether (100 mL×3) and dried to obtain the conjugate 13 in high purity.
PEGO O
N N
N HN
N O N
O
N N
15
General Procedure for the Cleavage of Polymer Bound Substituted alkyl 2-(4,4- alkyl-4,5-dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1-methyl-1H-benzo[d]imidazole-5-carboxylate 14.
To a solution of conjugates 13 in methanol (20 mL), KCN (100 mg) was added and stirred for 24 hours at room temperature. After completion of the reaction, excess of cold ether (100 mL) was added, the polymer was filtered off and filtrate was subjected to evaporation. The residue was dried under vacuum, and and was purified by silica gel column and eluted with a mixture of ethyl acetate and hexane (1:4) to get the title compounds 14 as a pale yellow solid in 94 % yield.
General Procedure for the synthesis of methyl
2-(12b-methyl-1,2,3,12b- tetrahydrodipyrrolo[1,2-a:2,1-c]quinoxalin-6-yl)-1-isobutyl-1H-benzo[d]imidazole-5-carboxylate 15.
To a stirred solution of polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-isobutyl-1H-benzo[d]imidazole-5-carboxylate conjugates 8a (1.5 gm, 0.32 mm, 1.0 equiv) in MeOH (10 mL), pent-4-yn-1-ol (0.08 gm, 0.95 mmol, 3.0 equiv), PtCl4 (5.3 mg, 5
mol-%) were added in 50 mL flask under argon atmosphere. The mixture was stirred at at 100
oC for 24 h. After completion of the reaction time, reaction mixture was filtered through
O O
N N
N HN
N O N
O
N N
16
celite pad. The crude product mixtures were purified by precipitation with cold ether (100 mL×3) and dried to obtain the polymer bound conjugate 15 in high purity. To a solution of conjugates 15 in methanol (20 mL), KCN (100 mg) was added and stirred for 24 hours at room temperature. After completion of the reaction, excess of cold ether (100 mL) was added, the polymer was filtered off and filtrate was subjected to evaporation.
The residue was dried under vacuum. The residue was purified by flash silica gel column chromatography as a white solid in 81 % yield.
General Procedure for the synthesis of methyl 1-isobutyl-2-(10-phenyl-15bH-isoquino[2,1-a]pyrrolo[2,1-c]quinoxalin-7-yl)-1H-benzimidazole-5-carboxylate 16.
To a stirred solution of polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-isobutyl-1H-benzo[d]imidazole-5-carboxylate conjugates 8a (1.5 gm, 0.32 mm, 1.0 equiv) in DCE (10 mL), 2-(phenylethynyl)benzaldehyde (0.19 gm, 0.95 mmol, 3.0 equiv), AuCl (3.6 mg, 5 mol-%) were added in 50 mL flask under nitrogen atmosphere. The mixture was stirred at room temperaturefor 12 h. After completion of the reaction time, reaction mixture was filtered through celite pad. The crude product mixtures were purified by precipitation with cold ether (100 mL×3) and dried to obtain the polymer bound conjugate 16 in high purity. To a solution of conjugates 15 in methanol (20 mL), KCN (100 mg) was added and stirred for 24 hours at room temperature. After completion of the reaction, excess of cold ether (100 mL) was added, the polymer was filtered off and filtrate was subjected to evaporation. The residue was dried under vacuum. The residue
N O N
O
N HN
17
was purified by flash silica gel column chromatography as a pale yellow solid in 79 % yield.
General Procedure for the synthesis of methyl 1-isobutyl-2-(4-methyl-4-phenyl-4,5-dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1H-benzimidazole-5-carboxylate 17.
To a stirred solution of polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-isobutyl-1H-benzo[d]imidazole-5-carboxylate conjugates 8a (1.5 gm, 0.32 mm, 1.0 equiv) in toluene (10 mL), phenyl acetylene (0.10 gm, 0.95 mmol, 3.0 equiv), AgOTf (8.1 mg, 10 mol-%) were added in 50 mL flask under nitrogen atmosphere. The mixture was heated with stirring for 24 h. After completion of the reaction time, reaction mixture was filtered through celite pad. The crude product mixtures were purified by precipitation with cold ether (100 mL×3) and dried to obtain the polymer bound conjugate 17 in high purity. To a solution of conjugates 15 in methanol (20 mL), KCN (100 mg) was added and stirred for 24 hours at room temperature. After completion of the reaction, excess of cold ether (100 mL) was added, the polymer was filtered off and filtrate was subjected to evaporation. The residue was dried under vacuum. The residue was purified by flash silica gel column chromatography as a white solid in 65 % yield.
O O PEG
N N
N N
O HO O
O PEG
N N
N NO2
O O
General Procedure for the Preparation of Polymer Bound methyl 1-isopentyl-2-4- [2-(methoxycarbonyl)-1H-1-pyrrolyl]-3-nitrophenyl-1H-benzo[d]imidazole-5-carboxylate (18d)
To a solution of 6 (5.3 g, 1.13 mmol, 1 equiv) in dimethyl formamide (10 mL) was added pyrrole 2-carboxylate (0.706 g, 5.65 mmol, 5 equiv) and Cs2CO3 (1.84 g, 5.65 mmol, 5 equiv) in a sequential order. Then the reaction mixtures were irradiated with stirring in a 20 mL microwave process vial for 10 minutes at 130oC (2 bar) to obtain the polymer conjugate 18. After completion of the reaction, the reaction mixtures were precipitated by slow addition of cold ether and precipitated pyrrole carboxylate bound polymer conjugates 18 were filtered through fritted funnel. The crude product was washed in succession with ether (100 mL×3) to remove the undesired impurity and dried for next steps.
General Procedure for the Preparation of Polymer Boundmethyl 2-(5-hydroxy-4- oxo-4,5-dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1-isopentyl-1H-benzo[d]imidazole-5-carboxylate 19d.
To a solution of 18 (5.40 g, 1.10 mmol ) in methanol, 10 % Pd/C (1.20 g, 11.00 mmol, 10.0 equiv) and ammonium formate (0.720 g, 11.00 mmol, and 10.0 equiv) were added.
O O PEG
N N
N N
O O
The reaction mixtures were exposed under pressured microwave irradiation for 10 minutes at 60 oC in 1 bar pressure. After completion, the reaction mixtures were filtered through Celite bed for removal of Pd/C and the supernatant liquid was concentrated by rotary evaporation. Dichloromethane (10 mL) was then added to salt out ammonium formate. The reaction mixtures were filtered through fritted funnel again to remove ammonium formate to obtain the polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-alkyl-1H-benzo[d]imidazole-5-carboxylate 19d.
General Procedure for the Preparation of Polymer Bound 2-(5-[(2E)-3,7-dimethyl- 2,6-octadienyl]oxy-4-oxo-4,5-dihydropyrrolo[1,2-a]quinoxalin-7-yl)-1-isopentyl-1H-benzo[d]imidazole-5-carboxylat 20d.
To a stirred solution of polymer bound 19d (5.40 g, 1.10 mmol) in DMF, NaH (1.20 g, 11.00 mmol, 5.0 equiv) was added. The reaction mixtures were cooled in ice bath. Alkyl bromide was added to the reaction mixture dropwise manner. The reaction mixture was stirred for 36 hrs. After completion of the reaction, the reaction mixtures were precipitated by slow addition of cold ether the precipitated compound were filtered throgh fritted funnel to obtain the polymer bound 2-(3-amino-4-(1H-pyrrol-1-yl)phenyl)-1-alkyl-1H-benzo[d]imidazole-5-carboxylate 20d.