All melting points were uncorrected and measured using capillary tubes on an Electrothermal digital apparatus. IR spectra were recorded on a Shimadzo(FT)-IR 300 spectrophotometer in KBr. NMR spectra were recorded on a Brucker 500 and 300 MHz spectrometer in CDCl
3 with TMS as an internal standard. The progress of the reaction was monitored by thin-layer chromatography TLC (Thin-Layer Chromatography) using CH
2Cl
2/EtOAc (3:1) as an eluent. The starting material tetrahydrobenzo[
b]pyrano drivatives 1(a-h) are easily obtained via one pot reaction of malonitrile, dimedone and aromatic aldehyde in presence of Alum (
18).
General procedure for synthesis of pyrano[2,3-d]pyrimidine derivatives2(a-h)
A solution of compound 1 (1 mmol) in Ac2O (1.5 mL) with catalytic amount of concentrated sulfuric acid (3-4 drops) was heated under reflux for 1 h. The reaction mixture was cooled at room temperature and kept for one day. The mixture was poured into water and the formed solid was filtrated, washed with water, and recrystallized from 2-propanol.
2,8,8-Trimethyl-5-phenyl-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2a)
White solid; m.p. 256-258 oC; Yield 60%; IR (KBr) νmax (cm-1): 3400 (NH), 2962 (CH), 1674, 1610 (C=O) and1452 (C=N). 1H NMR (CDCl3) δ ppm: 1.05, 1.12 (both s, 3H each, C(8) (CH3)2); 2.35 (s , 3H, C(2)-CH3); 2.26 (m, 2H, CH2); 2.58 (m. 2H, CH2); 4.92 (s, 1H, H-5)); 7.12-7.32 (m, 5H, C6H5) and 13.10 (s, 1H, NH). 13C NMR (CDCl3) δ ppm: 21.30, 27.74, 29.29, 32.51, 33.28, 41.12, 50.89, 103.02, 114.50, 127.02, 128.29, 128.66, 128.29, 143.32, 148.31, 158.56, 161.15, 165.44 and 196.62.
2,8,8-Trimethyl-5-(4-methylphenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2b)
White solid; m.p. 238-239 oC; Yield 50%; IR (KBr) νmax (cm-1): 3430 (NH), 2961 (CH), 1670, 1610 (C=O) and 1512 (C=N). 1H NMR (CDCl3) δ ppm: 1.05, 1.11 (both s, 3H each, C(8) (CH3)2); 2.24, 2.37 (both s, 3H each, C(5)-p-CH3-Phenyl, C(2)-CH3);; 2.28 (m, 2H, CH2); 2.57 (m, 2H, CH2); 4.88 (s, 1H, H(5)); 7.00-7.11 (m, 4H, Ar-H) and 13.10 (br, 1H, NH). 13C NMR (CDCl3) δ ppm: 21.40, 27.77, 29.30, 32.51, 32.83, 41.12, 50.92, 103.17, 114.98, 128.49, 129.021, 136.57 140.45, 158.45, 161.05, 163.40, 165.29 and 196.66.
2,8,8-Trimethyl-5-(3-nitrophenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2c)
Pale Yellow solid; m.p>285oC; Yield 81%; IR (KBr) νmax (cm-1): 3439(NH), 2961 (CH), 1674, 1632 (C=O) and 1526 (C=N). 1H NMR (CDCl3) δ ppm: 1.10, 1.16 (both s, 3H each, C(8) (CH3)2); 2.26 (s, 3H, C(2)-CH3); 2.40 (m, 2H, CH2); 2.65 (m, 2H, CH2); 5.04 (s, 1H, H(5)); 7.40-8.21 (m, 4H, Ar-H) and 13.35 (br, 1H, NH).13C NMR (CDCl3) δ ppm: 21.46, 27.76, 29.23, 32.56, 33.52, 41.10, 50.77, 101.74, 113.72, 122.16, 123.81, 129.07, 134.80, 145.33, 148.29, 159.36, 161.27 165.27 and 195.53.
2,8,8-Trimethyl-5-(2-chlorophenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2d)
White solid; m.p. 224-225 oC; Yield 50%; IR (KBr) νmax (cm-1): 3430 (NH), 2961 (CH), 1663, 1620 (C=O) and 1512 (C=N). 1H NMR (CDCl3) δ ppm: 1.07, 1.15 (both s, 3H each, C(8) (CH3)2); 2.21(m, 2H, CH2); 2.50(s, 3H, C(2)-CH3); 2.57 (m, 2H, CH2); 5.05 (s, 1H, H(5)); 7.01-7.50 (m, 4H, Ar-H) and 13.10 (br, 1H, NH). 13C NMR (CDCl3) δ ppm: 27.40, 29.52, 32.05, 32.25, 41.70, 40.09, 50.87, 113.87, 115.43, 126.56, 126.90, 127.91, 130.00, 130.37, 131.83, 133.12, 133.63, 140.06, 161.27 163.27 and 196.84.
2,8,8-Trimethyl-5-(4-nitrophenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2e)
White solid; m.p. 250-251 oC; Yield 70%; IR (KBr) νmax (cm-1): 3438 (NH), 2926 (CH), 1655, 1610 (C=O) and 1510 (C=N). 1H NMR (CDCl3) δ ppm: 1.05, 1.14 (both s, 3H each, C(8) (CH3)2); 2.31(m, 2H, CH2); 2.40 (s, 3H, C(2)-CH3); 2.61 (m, 2H, CH2); 5.02 (s, 1H, H(5)); 8.11-7.51 (m, 4H, Ar-H) and 13.10 (br, 1H, NH).
2,8,8-Trimethyl-5-(4-bromophenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2f)
Pale yellow solid; m.p. >310 oC; Yield 51%; IR (KBr) νmax (cm-1): 3431 (NH), 2959 (CH), 1667, 1611 (C=O) and 1485 (C=N). 1H NMR (CDCl3) δ ppm: 1.05, 1.13 (both s, 3H each, C(8) (CH3)2); 2.23 (m, 2H, CH2); 2.36 (s, 3H, C(2)-CH3); 2.58 (m, 2H, CH2); 4.88 (s, 1H, H(5)); 7.18-7.33 (m, 4H, Ar-H) and 13.10 (br, 1H, NH).
2,8,8-Trimethyl-5-(4-methoxyphenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione (2g)
Cream solid; m.p. 220-221 oC; Yield 60%; IR (KBr) νmax (cm-1): 3457 (NH), 2930 (CH), 1659, 1640 (C=O) and 1504 (C=N). 1H NMR (CDCl3) δ ppm: 1.11, 1.18 (both s, 3H each, C(8) (CH3)2); 2.25 (m, 2H, CH2); 2.33 (s, 3H, C(2)-CH3); 2.59 (m, 2H, CH2); 3.68 (s, 3H, O-CH3); 4.68 (s, 1H, H(5)); 7.07-7.11 (m, 4H, Ar-H) and 13.03 (br, 1H, NH).
2,8,8-Trimethyl-5-(3-hydroxyphenyl)-5,7,8,9-tetrahydro-4H-chromno-[2,3-d]pyrimidine-4,6(3H)-dione(2h)
White solid; m.p. 201-203 oC; Yield 67%; IR (KBr) νmax (cm-1): 3450 (NH), 2961 (CH), 1678, 1636 (C=O) and 1488 (C=N). 1H NMR (CDCl3) δ ppm: 1.06, 1.12 (both s, 3H each, C(8) (CH3)2); 2.24 (m, 2H, CH2); 2.36 (s, 3H, C(2)-CH3); 2.59 (m, 2H, CH2); 4.94 (s, 1H, H(5)); 6.68-7.27 (m, 4H, Ar-H); 7.02 (s, 1H, OH) and 13.30 (br, 1H, NH).
General procedure for synthesis of tetrahydro quinolone dione derivatives 3(a-g)
Compound 1 (1 mmol) was refluxed in a mixture of hydrochloric acid (1 mL) and acetic acid (3mL) for 3-5 h (monitored by TLC). After completion of the reaction, the reaction mixture was cooled, poured into water and the formed solid was filtrated. The obtained solid product was washed with water (3×15 mL) and recrystallized from ethanol.
3,4,7,8-Tetrahydro-7-7-dimethyl-4-phenyl-quinoline-2,5(1H,6H)-dione (3a)
White solid; m.p. 169-171 oC; Yield 48%; IR (KBr) νmax (cm-1): 3235 (NH), 2946 (CH), 1716, 1612 (C=O). 1H NMR (CDCl3) δ ppm: 1.07, 1.18 (both s, 3H each, C (7) (CH3)2); 2.33 (m, 2H, CH2); 2.49 (m, 2H, CH2); 2.81 (m. 2H, CH2); 4.38 (d, 1H, H (4)); 7.29 (m, 5H, C6H5) and 8.42 (s, 1H, NH). 13C NMR (CDCl3) δ ppm: 27.88, 29.25, 33.02, 33.94, 38.10, 41.07, 46.67, 50.79, 114.84, 126.83, 127.17, 129.01, 130.06, 142.22, 150.97, 172.87 and 196.10.
3,4,7,8-Tetrahydro-7-7-dimethyl-4-(4-methylphenyl)-quinoline-2,5(1H,6H)-dione (3b)
White solid; m.p. 201-203 oC; Yield 67%; IR (KBr) νmax (cm-1): 3219 (NH), 2960 (CH), 1695, 1645 (C=O). 1H NMR (CDCl3) δ ppm: 0.92, 1.03 (both s, 3H each, C (7) (CH3)2); 2.21 (s, 3H, C(4)-p-CH3-Phenyl); 2.27 (m, 2H, CH2); 2.39 (m, 2H, CH2); 2.87(m. 2H, CH2); 4.31(d, 1H, H(4)); 7.03-7.25 (m, 4H, C6H5) and 8.80 (s, 1H, NH). 13C NMR (CDCl3) δ ppm: 27.79, 29.04, 33.42, 32.83, 37.97, 41.12, 50.71, 115.03, 126.05, 129.47, 136.48, 139.12, 150.13, 172.23 and 195.49.
3,4,7,8-Tetrahydro-7-7-dimethyl-4-(3-Nitrophenyl)-quinoline-2,5(1H,6H)-dione (3c)
Pale Yellow solid; m.p. 194-195 oC; Yield 90%; IR (KBr) νmax (cm-1): 3105 (NH), 2960 (CH), 1707, 1620 (C=O). 1H NMR (CDCl3) δ ppm: 1.12, 1.80 (both s, 3H each, C(7) (CH3)2); 2.36 (m, 2H, CH2); 2.47 (m, 2H, CH2); 2.68 (m, 2H, CH2); 4.38 (d, 1H, H(4)); 7.60-8.09 (m, 4H, Ar-H) and 8.36 (s, 1H, NH). 13C NMR (CDCl3) δ ppm: 27.80, 29.30, 33.08, 33.97, 37.80, 41.29, 50.69, 113.68, 121.64, 122.41, 130.09, 133.61, 151.39, 171.31and 195.52.
3,4,7,8-Tetrahydro-7-7-dimethyl-4-(2-chlorophenyl)-quinoline-2,5(1H,6H)-dione (3d)
White solid; m.p. 240-241 oC; Yield 63%; IR (KBr) νmax (cm-1): 3247 (NH), 2961 (CH), 1715, 1645 (C=O). 1H NMR (CDCl3) δ ppm: 1.08, 1.18 (both s, 3H each, C (7) (CH3)2); 2.39 (m, 2H, CH2); 2.53 (m, 2H, CH2); 2.81 (m, 2H, CH2); 4.38 (d, 1H, H(4)); 7.47-8.11 (m, 4H, Ar-H) and 8.42 (s, 1H, NH).
3,4,7,8-Tetrahydro-7-7-dimethyl-4-(4-Nitrophenyl)-quinoline-2,5(1H,6H)-dione (3e)
White solid; m.p. 214-215 oC; Yield 55%; IR (KBr) νmax (cm-1): 3250 (NH), 2964 (CH), 1710, 1610 (C=O). 1H NMR (CDCl3) δ ppm: 1.06, 1.14 (both s, 3H each, C (7) (CH3)2); 2.32 (m, 2H, CH2); 2.45 (m, 2H, CH2); 2.90 (m, 2H, CH2); 4.31 (d, 1H, H (4)); 6.70-6.82 (m, 4H, Ar-H) and 8.32 (s, 1H, NH).
3,4,7,8-Tetrahydro-7-7-dimethyl-4-(4-bromophenyl)-quinoline-2,5(1H,6H)-dione (3f)
White solid; m.p. 173-174 oC; Yield 86%; IR (KBr) νmax (cm-1): 3208 (NH), 2945 (CH), 1667, 1636 (C=O). 1H NMR (CDCl3) (CDCl3) δ ppm: 1.11, 1.14 (both s, 3H each, C (7) (CH3)2); 2.31 (m, 2H, CH2); 2.47 (m, 2H, CH2); 2.92 (m, 2H, CH2); 4.32 (d, 1H, H (4)) and 7.10-7.40 (m, 4H, Ar-H).
3,4,7,8-Tetrahydro-7-7-dimethyl-4-(4-methoxyphenyl)-quinoline-2,5(1H,6H) dione (3g)
Pale yellow solid; m.p. 246-247 oC; Yield 67%; IR (KBr) νmax (cm-1): 3315 (NH), 2953 (CH), 1663, 1624 (C=O). 1H NMR (CDCl3) (CDCl3) δ ppm: 1.04, 1.13 (both s, 3H each, C(7) (CH3)2); 2.15 (m, 2H, CH2); 2.46 (m, 2H, CH2); 2.90 (m, 2H, CH2); 3.73 (s, 3H, O-CH3); 4.70 (d, 1H, H(4)); 6.75-7.22 (m, 4H, Ar-H) and 8.32 (s, 1H, NH).
Antibacterial activity
Antibacterial activity of synthesized compounds was assessed by the disc diffusion method (
19) using Mueller–Hinton Agar against
Escherichia Coli (ATTC-25922) as a gram negative bacteria as well as
Bacillus anthracic (ATTC-25924) and
Staphylococcus aureus (ATTC-25923) as gram positive bacteria. Cefazolin was used as a standard. Normal saline was used for preparation of inoculants having turbidity equal to 0.5 McFarland standards. The compounds were dissolved in dimethylformamide (DMF) for bioassay. The solvent control was included, although no inhibition zone was found. The plates were incubated at 37 C for 24 h. All samples were tested in triplicate and the average results of inhibitory effects are illustrated in
Table 1.
| Comp. No | E. Coli | Ba. anthracic | St. aureus |
|---|
| 2a | - | 15 | 10 |
| 2b | 11 | 15 | 17 |
| 2c | - | 14 | 20 |
| 2d | 13 | 10 | 3 |
| 2e | 18 | 14 | 5 |
| 2f | 15 | 18 | 4 |
| 2g | 16 | 15 | 10 |
| 2h | 12 | 10 | 10 |
| 3a | 18 | 17 | 23 |
| 3b | 10 | 15 | 7 |
| 3c | 10 | 11 | 17 |
| 3d | 10 | 15 | 10 |
| 3e | 14 | 15 | 3 |
| 3f | 13 | 10 | 17 |
| 3g | 12 | 10 | 7 |
| Cefazolin | 13 | 8 | 6 |
Determination of the minimum inhibitory concentration (MIC) values for synthesized compounds against three microorganisms was carried out using disc diffusion method (
20). In this method, concentrations of 1800, 900, 450, 225, 112.5, 56.2, 28.1, 14, 7, 3.5, 1.7 and 0.87 μg mL
-1 were used per disc and incubated at 37 ºC for 24 h.
Values of minimum inhibitor concentration (MIC) were recorded as the lowest concentration of substance, which gives no growth of inoculated bacteria. The Results are presented in
Table 2.
| Comp. No | MIC (μg.mL-1)
|
|---|
| E. Coli | Ba. anthracic | St. aureus |
|---|
| 2a | 225 | 450 | 112 |
| 2b | NP | 1800 | 1800 |
| 2c | 900 | 900 | 112 |
| 2d | 225 | 450 | 112 |
| 2e | 450 | 1800 | 900 |
| 2f | 450 | 1800 | 900 |
| 2g | 225 | 900 | 112 |
| 2h | 1800 | NP | 1800 |
| 3a | 900 | NP | 112 |
| 3b | 450 | 112 | 450 |
| 3c | 900 | NP | 1800 |
| 3d | 900 | NP | 1800 |
| 3e | 450 | 900 | 450 |
| 3f | 450 | 1800 | 900 |
| 3g | NP | NP | NP |
| Cefazolin | 450 | 900 | NP |