Synthesis of Aminoacetylcoumarins and Aminoacetylnaphthocoumarins and their Antibacterial activity study
Shubhangi S. Soman*, Tirth H. Thaker and Radhika D. Baloni
Department of Chemistry, Faculty of Science, The M.S. University of Baroda, India.
*Corresponding Author E-mail: shubhangiss@rediffmail.com
ABSTRACT:
Knoevenagel condensation of 2-hydroxy-1-naphthaldehyde with ethylacetoacetate gave 2-acetyl-benzo[f]chromen-3-one (1). Bromination of (1) with bromine in chloroform gave 2-(2-bromoacetyl)-benzo[f]chromen-3-one (2), which on condensation with different primary aromatic amines gave corresponding amino acetyl derivatives (3a-c). Similar series of reactions were carried out on salicylaldehyde and resorcaldehyde, which gave corresponding 3-aminoacetyl coumarin and 7-hydroxy-3-aminoacetyl coumarin derivatives. Screening of these compounds for antibacterial activity against Staphylococus aureus (Gram +ve), Micrococus leuteus (Gram +ve) and DH5α-Escherichia coli (Gram -ve) show good antibacterial activity.
KEYWORDS: acetylcoumarins, bromination, synthesis, antibacterial activity
Coumarins are naturally occuring compounds known to possess wide spectrum of physiological activities. Several natural products with the coumarin moiety exhibit interesting pharmacological properties such as antibacterial1, anticancer2, steroid 5α-reductase3 and human immunodeficiency virus HIV-1 protease4. Coumarin derivatives have been used as active components in the formulation of pesticides, additives in manufacture of pharmaceuticals, foods, laser dyes and fluorescent markers5. Many natural and synthetic derivatives of coumarin have been used as anticoagulants6. Desai and coworkers7 reported synthesis of amino methyl coumarin derivatives and their antibacterial activity. C.S.Reddy et.al8 reported synthesis of novel 6,6’-methylene-bis-[3-(2-anilinoacetyl-4-hydroxy] coumarin derivatives. Westwood et.al9 synthesized derivative of naphthocoumarin known as Cambinol analogs as Sirtuin inhibitors. Shang et.al10 synthesized 3-acetyl coumarins in ionic liquid by using L-proline as an efficient reusable promoter by Knoevenagel condensation. Looking towards pharmacological importance of naphthopyrones and in continuation with our research on design and synthesis of biologically active coumarins11, we have synthesized amino acetyl coumarins and amino acetyl naphthocoumarins.
MATERIALS AND METHODS:
All the materials are used of MERCK recognized. The melting points were determined in scientific open capillaries and are uncorrected. The IR spectra were determined as KBr pellets on a Schimadzu model IR-408 spectrophotometer. The 1H NMR spectra were recorded using Bruker DRX 400 MHz in CDCl3 or DMSO-d6 with tetramethylsilane as internal standard. Mass spectra were recorded on a GC-MS spectrometer. Elemental analyses were performed on Carlo Erba-1108 elemental analyzer.
RESULTS AND DISCUSSION:
Knoevenagel condensation of 2-hydroxy-1-naphthaldehyde with ethylacetoacetate gave 2-acetyl-benzo[f]chromen-3-one12 (1). The structure of (1) was confirmed by its IR and 1H NMR. In 1H NMR of (1), the presence of sharp singlet at δ 2.80 integrated for three protons clearly indicated -COCH3 protons. All other aromatic protons were observed in the range of δ 7.48-8.40. A downfield singlet at δ 9.34 integrated for one proton indicated C-1 proton. Bromination of (1) with bromine in chloroform gave 2-(2-bromoacetyl)-benzo[f]chromen-3-one (2)13. The structure of (2) was confirmed by its IR and 1H NMR. In 1H NMR of (2), sharp singlet at δ 2.80 integrated for three methyl protons which appeared in 1H NMR of (1) now disappeared, but singlet at δ 4.82 integrated for two protons indicated –COCH2 protons. A downfield singlet at δ 9.45 integrated for one proton indicated C-1 proton. All other aromatic protons were observed in the range of δ 7.50-8.41. 2-(2-bromoacetyl)benzo[f]chromen-3-one (2) was condensed with different primary aromatic amines to get corresponding amino acetyl derivatives.
Scheme-1
Scheme-2
(2) When refluxed with p-toludine in absolute ethanol gave 2-(2-p-tolylaminoacetyl)-benzo[f]-chromen-3-one (3a). (Scheme-1) The structure of 3a was confirmed by its IR, 1H NMR and Mass spectra. The IR spectrum of 3a showed one band at 3366 cm-1 for –NH and two bands at 1709 and 1597 cm-1 for >C=O (lactone) and keto group respectively. The 1H NMR of this compound showed singlet at δ 2.25 integrated for three protons indicated –CH3 protons, singlet at δ 4.78 integrated for two protons indicated -COCH2 protons. All other aromatic protons and –NH proton are observed clearly in the range of δ 6.68-9.51. Moreover mass spectrum of (3a) supported M+2 signals at 345.
Similar compounds 3b-c were obtained when different primary aromatic amines like p-nitroaniline and 2-hydroxyaniline were condensed with (2). (Scheme-1)
Similarly Knoevenagel condensation14 of salicylaldehyde with ethylacetoacetate gave 3-acetyl-chromen-2-one (4) (Scheme-2). Bromination of (4) with bromine in chloroform gave 3-(2-bromoacetyl)-chromen-2-one (5)13. The structure of (5) was confirmed by its IR and 1H NMR. Sharp singlet at δ 4.98 integrated for two protons indicated –COCH2 protons. All other aromatic protons are well observed in the range of δ 7.40-8.70.
3-(2-bromoacetyl)-chromen-2-one (5a) when refluxed with m-nitroaniline in absolute ethanol gave 3-[2-(3-nitrophenylamino)-acetyl]chromen-2-one (6b). The structure of (6b) was confirmed by its IR, 1H NMR and Mass spectra. IR showed two bands at 1710 and 1676 cm-1 for lactone carbonyl and keto group respectively. In 1H NMR, a doublet at δ 4.77-4.79 integrated for two protons indicated –COCH2 protons. A triplet at δ 6.83-6.85 integrated for one proton indicated –NH proton. All other aromatic protons are observed clearly in the range of δ 7.10-8.85. Moreover mass spectrum of (6b) also supports with signal at M+ 323.
Similar compounds 6a,c are obtained when different primary aromatic amines like p-toludine and 2-hydroxyaniline were condensed with (5). (Scheme-2)
Resorcaldehyde on Knoevenagel14 condensation with ethylacetoacetate gave 3-acetyl-7-hydroxy-chromen-2-one (4b), which on bromination with bromine in chloroform gave 3-(2-bromoacetyl)-7-hydroxychromen-2-one (5b). 5b on refluxing with different primary aromatic amines gave corresponding 3-aminoacetyl-7-hydroxychromen-2-ones (7a-c) (Scheme-2). The structures of all compounds were confirmed by its elemental analyses, IR and 1H NMR.
Biological Activity
All aminoacetyl coumarins and aminoacetyl naphthocoumarins were screened for their antibacterial activity.
Antibacterial activity: All the synthesized compounds were tested for their antibacterial activity against E. coli (gm -Ve), S. aureus (gm +Ve) and Micrococcus veuteus (gm +Ve) using cup-plate method15 at 100 ppm (10mg/ml) concentration in DMF solvent. Ampicillin was used as standard drug. All compounds showed excellent activity against all types of gm +Ve and gm-Ve bacteria (Table-1).
Pharmacology
Antibacterial activity of all the synthesized compounds was tested in vitro in these bacterial strains of Staphylococcus aureus (gm +ve), Escherichia coli (gm –ve) and Micrococcus leutius (gm +ve) were used, using serial agar dilution (cup plate method).
The microorganisms were cultured in dishes containing agar medium, cups (8 mm) were put onto the dishes and each synthesized compound dissolved in DMF (0.1ml of 10mg/ml) was added into the cups under aseptic condition. Then the dishes were incubated at 37°C for 24h. The zone of inhibition of the growth of the bacteria, which were produced by diffusion of the compounds from the cup into the surrounding medium, was measured to evaluate the antibacterial activity. Each experiment was repeated twice. DMF was used as a positive control for the experiments.
Table 1 Zone of inhibition in mm (Antibacterial Activity)
|
Compound (10mg/ml) |
S. aureus |
E. coli |
M. leutius |
|
3a |
11 |
09 |
19 |
|
3b |
09 |
07 |
20 |
|
3c |
12 |
07 |
15 |
|
6a |
08 |
10 |
14 |
|
6b |
08 |
08 |
16 |
|
6c |
21 |
08 |
14 |
|
7a |
09 |
05 |
11 |
|
7b |
10 |
05 |
10 |
|
7c |
22 |
05 |
11 |
|
Control |
05 |
04 |
05 |
EXPERIMENTAL:
2-Acetyl-benzo[f]chromen-3-one (1): A mixture of 2-hydroxy-1-naphthaldehyde (2gm, 0.01163 mol), ethylacetoacetate (1.51mL, 0.01163 mol), pyridine (10mL) and piperidine (0.1mL) (catalytic amount) was kept in light (100W bulb) for overnight. It was poured on Ice: HCl (90:10), crude product was filtered, dried and recrystallized from ethanol as yellow crystals.
Yield 81%, M.p.185°C (Lit.16, m.p. 190°C). IR (cm-1): 3065, 1736, 1675, 1597, 1557, 1511, 1463, 1360, 1342, 1242, 1220, 1209, 840, 760. 1H NMR: δ 2.80 (s, 3H, -COCH3), 7.48-7.50 (d, 1H, J = 9Hz, C6-H), 7.60-7.65 (m, 1H, C8-H), 7.74-7.78 (m, 1H, C9-H), 7.93-7.95 (d, 1H, J = 8Hz, C7-H), 8.11-8.13 (d, 1H, J = 9Hz, C5-H), 8.37-8.40 (d, 1H, J = 8.4Hz, C10-H), 9.34 (s, 1H, C1-H). Anal.Calcd. for C15H10O3: C, 75.63; H, 4.20 found C, 75.69; H, 4.07 %.
2-(2-Bromo-acetyl)benzo[f]chromen-3-one (2): 2-Acetyl-benzo[f]chromen-3-one (1) (1gm, 0.00420 mole) was dissolved in chloroform (30mL), liquid Br2 (0.22mL, 0.00420 mole) was added dropwise and stirred for 16h. at room temperature. Excess solvent was distilled off. Solid obtained was filtered, dried and recrystallized from ethanol as yellow crystals.
Yield 86%, m.p. 191°C (Lit.13). IR (cm-1): 3014, 2958, 1704, 1623, 1597, 1558, 1513, 1464, 1392, 1347, 1263, 1217, 1179, 829, 754. 1H NMR: δ 4.82 (s, 2H, -COCH2), 7.50-7.52 (d, 1H, J = 9Hz, C6-H), 7.63-7.67 (m, 1H, C8-H), 7.78-7.82 (m, 1H, C9-H), 7.95-7.97 (d, 1H, J = 8.0Hz, C7-H), 8.16-8.18 (d, 1H, J = 9.0Hz, C5-H), 8.39-8.41 (d, 1H, J = 8.5Hz, C10-H), 9.45 (s, 1H, C1-H). Anal. Calcd. for C15H9O3Br: C, 56.87; H, 2.84 found C, 56.49; H, 2.87 %.
General Procedure for the preparation of Aminoacetylnaphthocoumarins (3a-c): A mixture of 2-(2-Bromo-acetyl)benzo[f]chromen-3-one (2) (0.01mole), different aromatic amines (0.021 mole) and absolute ethanol (20 ml) was refluxed for 6h. It was allowed to cool and filtered. The crude product obtained was recrystallized from absolute ethanol. The physical and spectral data of the compounds 3a-c is as follows.
2-(2-p-Tolylamino-acetyl)benzo[f]chromen-3-one (3a): Yield 63%. m.p. 199°C IR (cm-1): 3366, 3039, 1709, 1597, 1547, 1514, 1482, 1210, 1047, 800, 744. 1H NMR: δ 2.25 (s, 3H, -CH3), 4.78 (s, 2H, -COCH2), 6.68-6.70 (d, J = 8.28Hz, 2H, C3’, C5’-H), 6.90-7.09 (m, 3H, C2’, C6’-H, -NH proton), 7.52-7.54 (d, 1H, J = 8.8Hz, C6-H), 7.63-7.67 (m, 1H, C8-H), 7.77-7.81 (m, 1H, C9-H), 7.95-7.97 (d, 1H, J = 8.0Hz, C7-H), 8.15-8.18 (d, 1H, J = 9.0Hz, C5-H), 8.41-8.43 (d, 1H, J = 8.5Hz, C10-H), 9.51 (s, 1H, C1-H). Mass: (M+2) 345, 167, 149, 129, 71, 57. Anal. Calcd. for C22H17NO3: C, 76.97; H, 4.96; N, 4.08 found C, 76.68; H, 4.87; N, 4.20 %.
2-[2-(4-Nitro-phenylamino-acetyl)benzo[f]chromen-3-one (3b): Yield 39%. m.p.248°C IR (cm-1): 3392, 3069, 1730, 1672, 1600, 1555, 1522, 1468, 1392, 1325, 1202, 1111, 1048, 977, 827. Anal. Calcd. for C21H14N2O5: C, 67.38; H, 3.74; N, 7.48 found C, 67.56; H, 3.89; N, 7.61%.
2-[2-(2-Hydroxy-phenylamino-acetyl)benzo[f]chromen-3-one (3c): Yield 39%. m.p. 214°C. Mass: (M+) 345, 329, 167, 149, 129, 71, 57. Anal. Calcd. for C21H15NO4: C, 73.04; H, 4.34; N, 4.05 found C, 73.05; H, 4.68; N, 3.81 %.
3-(2-Bromo-acetyl)chromen-2-one (5a): Compound (5a) was prepared according to the procedure described for (2). The title compound (5a) was obtained as colorless needles. Yield 63%. m.p. 168°C. (Lit.13, M.p. 163-165°C) IR (cm-1): 2926, 2855, 1731, 1686, 1614, 1557, 1500, 1452, 1273, 1180, 756, 670. 1H NMR: δ 4.98 (s, 2H, -COCH2), 7.40-7.45 (m, 2H, C5, C6-H), 7.72-7.74 (m, 2H, C7, C8-H), 8.70 (s, 1H, C4-H). Anal.Calcd. for C11H7O3Br: C, 49.53; H, 2.62 found C, 49.69; H, 2.45 %.
General Procedure for the preparation of Aminoacetylcoumarins (6a-c): A mixture of 3-(2-Bromo-acetyl)-chromen-2-one (5) (0.01mole), different aromatic amines (0.021 mole) and absolute ethanol (20 ml) was refluxed for 3h. It was allowed to cool and filtered. The crude product was recrystallized from absolute ethanol. The physical and spectral data of the compounds 6a-c is as follows.
3-(2-p-Tolylamino-acetyl) chromen-2-one (6a): It obtained as yellow solid. Yield 52.5%. m.p. 247°C. Anal.Calcd. for C18H15NO3: C, 73.72; H, 5.11; N, 4.78 found C, 73.69; H, 5.48; N, 4.90 %.
3-[2-(3-Nitro-phenylamino)-acetyl] chromen-2-one (6b): It obtained as orange crystals. Yield 48.4%. m.p. 228°C IR (cm-1): 3372, 3056, 1710, 1676, 1606, 1554, 1528, 1449, 1349, 1188, 986, 759, 736. 1H NMR: δ 4.77-4.79 (d, 2H, -COCH2), 6.83-6.85 (t, 1H,-NH), 7.10-7.12 (d, 1H, J = 8.0Hz, C3’-H), 7.37-7.45 (m, 2H, C5, C6-H), 7.48-7.54 (m, 2H, C7, C8 -H), 7.57-7.59 (d, 1H, J = 8.2Hz, C2’-H), 7.83-7.87 (m, 1H, C4’-H), 8.05-8.07 (d, 1H, C5’-H), 8.85 (s, 1H, C4-H). Mass: 323, 279, 167, 149, 81, 57. Anal. Calcd. for C17H12N2O5: C, 62.96; H, 3.70; N, 8.64 found C, 62.73; H, 3.91; N, 8.34 %.
3-[2-(2-Hydroxy-phenylamino)-acetyl]chromen-2-one (6c): It obtained as light green solid. Yield 58.5%. m.p. 177°C. IR (cm-1): 3383, 2920, 2851, 1710, 1607, 1501, 1456, 1375, 1189, 1107, 752. Anal. Calcd. for C17H13NO4: C, 69.15; H, 4.40; N, 4.74 found C, 69.29; H, 4.63; N, 4.60 %.
3-(2-Bromo-acetyl)-7-hydroxy-chromen-2-one (5b): Compound (5b) was prepared according to the procedure described for (2). The title compound (5b) was obtained as violet solid. Yield 72.5 %. m.p. 204°C. 1H NMR: δ 4.94 (s, 2H, -COCH2), 6.76-6.78 (m, 1H, C8-H), 6.85-6.89 (dd, 1H, C6-H), 7.63-7.66 (d, 1H, C5-H), 8.66 (s, 1H, C4-H). Anal. Calcd. for C11H7O4Br: C, 46.72; H, 2.48 found C, 46.81; H, 2.37 %.
General Procedure for the preparation of 7-Hydroxy-3-aminoacetylcoumarins (7a-c): A mixture of 3-(2-Bromo-acetyl)-7-hydroxy-chromen-2-one (5b) (0.01mole), different aromatic amines (0.021 mole) and absolute ethanol (20 mL) was refluxed for 4h. It was allowed to cool and filtered. The crude product was recrystallized from absolute ethanol. The physical and spectral data of the compounds 7a-c is as follows.
7-Hydroxy-3-(2-p-tolylamino-acetyl)chromen-2-one (7a): It obtained as yellow solid. Yield 37.5%. m.p. 189°C. IR (cm-1): 3423, 2923, 2854, 1706, 1615, 1512, 1456, 1380, 1249, 1156, 1021, 812. Anal. Calcd. for C18H15NO4: C, 69.90; H, 4.85; N, 4.53 found C, 69.83; H, 4.68; N, 4.71 %.
7-Hydroxy-3-[2-(3-nitro-phenylamino)-acetyl]chromen-2-one (7b): It obtained as light orange crystals. Yield 34.4%. m.p. 175°C IR (cm-1): 3383, 2921, 2852, 1684, 1617, 1526, 1346, 1242, 1187, 1139, 733, 670. 1H NMR: δ 4.72 (d, 2H, -COCH2), 6.86 (s, 1H,-NH), 6.93-6.95 (dd, 1H, J = 1.5, 8.6Hz, C6-H), 7.09-7.11 (d, 1H, J = 7.56Hz, C8-H), 7.32-7.47 (m, 4H, C2’, C3’, C4’, C6’-H), 7.89-7.91 (d, 1H, J = 8.6Hz, C5-H), 8.78 (s, 1H, C4-H), 11.29 (s, 1H, -OH). Anal. Calcd. for C17H12N2O6: C, 60.00; H, 3.52; N, 8.23 found C, 60.12; H, 3.71; N, 8.14 %.
7-Hydroxy-3-[2-(2-hydroxy-phenylamino)-acetyl]chromen-2-one (7c): It obtained as green solid. Yield 41.4%. m.p. 225°C. Anal. Calcd. for C17H13NO4: C, 65.59; H, 4.18; N, 4.50 found C, 65.43; H, 4.24; N, 4.64 %.
CONCLUSION:
All synthesized aminoacetylcoumarins and aminoacetyl naphthocoumarins are prepared in good yields and well characterized. All synthesized amino acetyl coumarins and naphthocoumarins show good antibacterial activity. Insertion of hydroxyl group in coumarin moiety enhances antibacterial activity.
ACKNOWLEDGEMENT:
The authors are thankful to the Head, Department of Chemistry, Faculty of Science, The M. S. University of Baroda for providing necessary facilities. One of the authors (THT) is thankful to UGC, New Delhi for financial assistance. The authors are thankful to Sun Pharma Advance Research Centre (SPARC) and SAIF, Panjab University for 1H NMR and mass spectra.
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Received on 26.08.2010 Modified on 02.09.2010
Accepted on 06.09.2010 © AJRC All right reserved
Asian J. Research Chem. 4(1): January 2011; Page 132-136