Synthesis and characterization of some new 4-hydroxy-coumarin derivatives.

Some novel coumarins were synthesized starting from 4-hydroxycoumarin and methyl bromoacetate. The structures of the newly obtained compounds were confirmed by elemental analysis, mass, IR and NMR spectra.

1. Introduction

<span class="Chemical">Coumarins or <class="Gene">span class="Chemical">benzo-2-pyrone derivatives are one of the most significant families of natural product compounds and are also important in synthetic organic chemistry. They have been widely used as starting materials or intermediates in the pharmaceutical, perfumery and agrochemical industries. Coumarins are also used as fluorescent brighteners, efficient laser dyes and additives in food and cosmetics [1]. The coumarins represent a large group of compounds that have been reported to possess a wide range of biological activities [2,3,4], including anticoagulant and antithrombotic properties [5,6,7]. Many coumarin derivatives, especially 4-hydroxycoumarin, show significant anticoagulant action by antagonizing the action of vitamin K. [8,9]. Recently, coumarins have attracted considerable attention for electronic and photonic applications [10,11] due to their inherent photochemical characteristics, reasonable stability and solubility in various organic solvents. Many coumarin derivatives have been commercialized as blue-green lasers for fluorescent labels, fluorescent probes [12,13,14] and enzymatic measurements [15]. They exhibit intense fluorescence upon substitution with various functional groups at different positions [16,17].

In view of the high degree of bioactivity shown by <span class="Chemical">4-aminoantipyrine, <class="Gene">span class="Chemical">thiazolidinones and hydroxycoumarin heterocyclic analogs, and in continuation of previous studies [18,19,20,21,22,23], we focus herein on the design of some novel structural entities that incorporate both of these moieties in a single molecular scaffold. We first report the synthesis of methyl 2-(coumarin-4-yloxy)acetate (1), which was then used as starting material for the synthesis of new molecules 2–11 (Scheme 1).

Scheme 1

Reaction sequences of the synthesized compounds.

Reagents and Conditions: a = <span class="Chemical">Ethyl bromoacetate/reflux; b = <class="Gene">span class="Chemical">hydrazine hydrate/refluxed; Ethylmethylketone/refluxed in ethanol; d = 2-methyl benzaldehyde/refluxed in ethanol; e = 4-aminoantipyrine/refluxed in ethanol; f = mercaptoacetic acid/refluxed in benzene; g = maleic anhydride/refluxed in benzene.

2. Results and Discussion

2.1. Chemistry

The reaction sequences for the synthesis of <span class="Chemical">coumarins 2–11 starting from <class="Gene">span class="Chemical">4-hydroxycoumarin are outlined in Scheme 1. Methyl 2-(coumarin-4-yloxy)acetate (1) was obtained by refluxing methyl bromoacetate with 4-hydroxycoumarin in anhydrous acetone in the presence of anhydrous potassium carbonate. The FT-IR spectrum of this compound showed an absorption band at 1,723.1 cm−1 (ester C=O carbonyl stretching). The 1H-NMR spectrum exhibited a singlet at δ 3.63 ppm due to the three CH3 protons. The reaction of 1 with hydrazine hydrate afforded hydrazide 2 in good yield. The FT-IR spectrum of compound 2 showed absorption bands at 3,233.3 and 3,210.0 cm−1 (hydrazide NH-NH2). The 1H-NMR spectrum exhibited a singlet at δ 4.45 ppm due to the two CH2 protons and a singlet due to the single NH proton at δ 8.21 ppm. The reaction of compound 2 with various carbonyl compounds (2-methylbenzaldehyde, 4-aminoantipyrine and ethyl methyl ketone) yielded the new Schiff bases N'-(2-methylbenzylidene)-2-[(coumarin-4-yl)oxy]acetohydrazide (3), N'-[4-amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-ylidene]-2-[(coumarin-4-yl)oxy]acetohydrazide (4) and N'-(butan-2-ylidene)-2-[(coumarin-4-yl)oxy]acetohydrazide (5), respectively. Schiff bases 3, 4 and 5 were cyclized by reaction with mercaptoacetic acid to yield novel coumarin compounds N-[4-oxo-2-(O-tolyl)thiazolidin-3-yl]-2-[(coumarin-4-yl)oxy]acetamide (6), N-(4-amino-2,3-dimethyl-8-oxo-1-phenyl-6-thia-1,2,9-triazaspiro[4.4]non-3-en-9-yl)-2-[(coumarin-4-yl)oxy]acetamide (7) and N-(2-ethyl-2-methyl-4-oxothiazolidin-3-yl)-2-[(coumarin-4-yl)oxy]acetamide (8), respectively. The FT-IR spectrum of compound 6 showed absorption bands at 3,191.4 cm−1 (NH) and 1,715.6 cm−1 (C=O, lactone) as well as 1,695 and 1,677 cm−1 (C=O, amide). The 1H-NMR spectrum exhibited a singlet due to the (S-CH) proton at δ 4.88 ppm and another singlet due to the O-CH2 proton at δ 5.11 ppm (2H). For compound 7, the FT-IR spectrum showed absorption bands at 3,388.3 cm−1 for NH2 and 3,189.1 cm−1 for N-H, and the C=N bands disappeared due to cyclization. The 1H-NMR spectrum exhibited a doublet due to the two protons at δ 4.89 and δ 4.12 ppm and singlet due to the single S-CH proton at δ 3.89 ppm. For compound 8, the FT-IR spectrum showed absorption bands at 3,199.0 cm−1 (NH) as well as 1,691 and 1,685 cm−1 (C=O, amide); the C=N bands disappeared due to cyclization. The 1H-NMR spectrum exhibited a doublet due to the S-CH2 proton at δ 3.86 and δ 8.02 ppm, and a singlet due to the NH proton. Another three novel compounds were synthesized by the cyclization of Schiff bases 3, 4 and 5 with maleic anhydride to yield N-[4,7-dioxo-2-(O-tolyl)-1,3-oxazepin-3(2H,4H,7H)-yl]-2-[(coumarin-4-yl)oxy] acetamide (9), N-[2-(4-amino-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-yl)4,7-dioxo-1,3-oxazepin-3(2H,4H,7H)-yl]-2-[(coumarin-4-yl)oxy] acetamide (10) and N-[2-ethylmethyl-4,7-dioxo-1,3-oxazepin-3(2H,4H,7H)-yl]-2-[(coumarin-4-yl)oxy] acetamide (11), respectively. For compound 9, the FT-IR spectrum showed absorption bands at 3,196.2 cm−1 (NH) and 1,667.9 cm−1 for the amide as well as 1,755 and 1,745 cm−1 for carbonyls. The 1H-NMR spectrum exhibited a singlet at δ 5.38 ppm due to the two O-CH2 protons. For compound 10, the FT-IR spectrum of showed absorption bands at 2,981.4 cm−1 (C-H, aliphatic), 1,765 and 1,734 cm−1 for the carbonyls, and 1,678 cm−1 for the amide. The 1H-NMR spectrum exhibited a singlet δ 4.89 ppm due to the two O-CH2 protons at. For compound 11, the FT-IR spectrum of showed absorption bands at 3,199 cm−1 (NH) and 1,669.2 cm−1 for the amides as well as 1,758 and 1,733 cm−1 for the carbonyls. The 1H-NMR spectrum exhibited a singlet due to the two O-CH2 protons at δ 4.65 ppm.

2.2. Geometrical Isomers of the Acylhydrazone of Coumarins

With respect to the C=N double bond, <span class="Chemical">N-acylhydrazones (<class="Gene">span class="Chemical">NAHs) may exist as Z/E geometrical isomers and syn/anti amide conformers [24,25]. In a study involving compounds 3, 4 and 5, energy calculations performed on the selected conformers according to the density functional theory (DFT) B3LYP method using the 6–31G basis set by means of the Gaussian 09, revision A.02 method indicated a slight difference in energy (ΔE = −10.383 Kcal/mol, −2.350 Kcal/mol and −13.918 Kcal/mol) respectively, between the syn-periplanar and anti-periplanar conformers in the favor of the former (Figure 1). Therefore, we concluded that the new derivatives 3, 4 and 5 were obtained as single E geometrical isomers.

Figure 1

Probable conformational isomers of the N-acylhydrazone of compound 3. (a) = 3dimetional structures; (b) = geometrical Isomers).

Probable conformational isomers of the <span class="Chemical">N-acylhydrazone of compound 3. (a) = 3dimetional structures; (b) = geometrical Isomers).

3. Experimental Section

3.1. General Information

The chemicals used during synthesis were supplied by Sigma-Aldrich (Selangor, Malaysia). The IR spectra were obtained on a Nicolet 6700 FT-IR spectrophotometer (Thermo Nicolet Corp., Madison, WI, USA), and the values are expressed in cm−1. Nuclear magnetic resonance (NMR) spectra were recorded using an AVANCE III 600 MHz spectrometer (Bruker, Billerica, MA, USA), using <span class="Chemical">DMSO as an internal standard and the values are expressed in δ ppm. Elemental microanalysis was performed on an Elementar Vario El III Carlo Erba 1108 elemental analyzer (Carlo Erba Reagenti SpA, Rodano, Italy).

3.2. Methyl 2-(coumarin-4-yloxy)acetate (

A suspension of <span class="Chemical">4-hydroxycoumarin (0.999 g, 6.17 mmol) in <class="Gene">span class="Chemical">acetone (30 mL) was refluxed with methyl bromoacetate (9.15 mmol) and K2CO3 (4.69 g, 33.91 mmol) for 12 h. After cooling, the mixture was evaporated to dryness and the residue was partitioned between CHCl3 (50 mL) and water (50 mL). The organic phase was dried using Na2SO4, filtered and evaporated to dryness. The residue was recrystallized from acetone; yield 85%; m.p. 84–85 °C; 1H-NMR (CDCl3): δ 3.6 (s, 3H, CH3), 4.79 (s, 2H, CH2) and 5.58 (s, 1H, -C=C-H), 7.3111, 7.555, 7.896 (three s, 1H each, aromatic ring); IR (cm−1): 2,960 (C-H, aliphatic), 3,083.4 (C-H, aromatic), 1,760.3 (C=O, ester), 1,723.1 (C=O, lactone), 1,624.5 (C=C, alkene), 1,567.2 (C=C, aromatic).

3.3. 2-(Coumarin-4-yloxy)acetohydrazide (

A solution of compound 2 (2.34 g, 10 mmol) in <span class="Chemical">ethanol 25 mL was refluxed with <class="Gene">span class="Chemical">hydrazine hydrate (15 mmol) for 4 h. After concentrating the reaction mixture an oily mass separated out and was recrystallized using ethanol, yield 55%; 1H-NMR (CDCl3): δ 4.45 (s, 2H, CH2), 4.75 (s, 2H, NH2), 5.43 (s, 1H, -C=C-H), 7.41–7.78 (m, 4H, aromatic ring), 8.21 (s, 1H, NH); IR (cm−1): 3,233.3, 3,210 (N-H), 2,959.0 (C-H, aliphatic), 3,083.9 (C-H, aromatic), 1,721.4 (C=O, lactone), 1,624.2 (C=O, amide).

3.4. Synthesis of Schiff bases 3–5

A solution of compound 2 (0.2 mmol) in <span class="Chemical">ethanol (25 mL) was refluxed with <class="Gene">span class="Chemical">2-methyl benzaldehyde, 4-aminoantipyrine or ethyl methyl ketone (0.2 mmol) for 20 h. After cooling to room temperature, a solid mass was filtered and the solid was recrystallized from ethanol.

N′-(2-Methylbenzylidene)-2-(<span class="Chemical">coumarin-4-yloxy)aceto<class="Gene">span class="Chemical">hydrazide (3). Yield 50%; 1H-NMR (CDCl3): δ 2.891 (s, 3H, CH3), 4.19 (s, 2H, CH2), 5.355 (s, 2H, O-CH2), 5.57 (s, 1H, -C=C-H), 7.270–7.75 (m, 4H, aromatic ring); 8.31 (s, 1H, N=CH), 8.01 (s, 1H, NH); IR (cm−1): 3,199.3 (N-H), 2,965.4 (C-H, aliphatic), 3,067.2 (CH, aromatic), 1,730.3 (C=O, lactone), 1,683.7 (C=O, amide), 1,627.7 (C=C).

<span class="Chemical">N'-(4-Amino-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-ylidene)-2-(coumarin-4-yloxy)acetohydrazide (4). Yield 60%; m.p 162-163 °C; 1H-NMR (CDCl3): 4.05 (s, 2H, assignment?), 4.67 (s, 2H, O-CH2), 5.23 (s, 1H, -C=C-H), 3.21 (s, 3H, CH3), 2.83 (s, 3H, CH3), 7.11–7.34 (m, 4H, aromatic ring), 8.0 (s, 1H, NH), 8.41 (s, 1H, N=CH); IR (cm−1): 3,432.8 (NH2), 3,328.0.3 (N-H), 2,989.9 (C-H, aliphatic), 3,077.3 (C-H, aromatic), 1,725.8 (C=O, <class="Gene">span class="Chemical">lactone), 1,651.9 (C=O, amide), 1,616.3 (C=N), 1,6229 (C=C); Analysis: Calc. for C21H21N5O4: C 61.91%, H 5.20%, N 17.19%. Found: C 60.057%, H 5.641%, N 16.685%.

N′-(Butan-2-ylidene)-2-(<span class="Chemical">coumarin-4-yloxy)aceto<class="Gene">span class="Chemical">hydrazide (5). Yield 50%; m.p 71–72 °C; 1H-NMR (CDCl3): δ 0.81 (t, 3H, CH3), 1.49 (q, 2H, CH2), 2.01 (s, 3H, CH3), 4.64 (s, 2H, O-CH2), 5.21 (s, 1H, -C=C-H), 6.95 (s, 1H, N=CH), 7.38–7.79 (m, 4H, aromatic ring); IR (cm−1): 3,198.2 (N-H), 2,922.9 (C-H, aliphatic), 3,068.4 (C-H, aromatic), 1,732.2 (C=O, lactone), 1,673.1 (C=O, amide), 1,615.3 (C=N), 1,621.5 (C=C); Analysis: Calc. for C15H16N2O4: C 62.49%, H 5.59%, N 9.72%. Found: C 61.70%, H 4.89%, N 9.11%.

3.5. Cyclization with Mercaptoacetic Acid: Synthesis of Compounds

A mixture of compound (3 or 4 or 5) (0.01 mole) with <span class="Chemical">mercaptoacetic acid (0.01 mole) in dry <class="Gene">span class="Chemical">benzene (50 mL) was refluxed in a water bath for 20 h, filtered off, washed with water, dried and recrystallized from dichloromethane.

<span class="Chemical">N-[4-Oxo-2-(o-tolyl)thiazolidin-3-yl)-2-(coumarin-4-yloxy]acetamide (6). Yield 45%; oil; 1H-NMR (CDCl3): δ 2.920 (s, 3H, CH3), 4.88 (s, S-CH), 4.67 (s, 1H, CH), 5.11 (s, 2H, O-CH2), 5.73 (s, 1H, -C=C-H), 7.270–7.820 (m, 4H, aromatic ring), 8.12 (s, 1H, NH); IR (cm−1): 3,191.4 (N-H), 2,930 (C-H, aliphatic), 3,043 (C-H, aromatic), 1,715.6 (C=O, <class="Gene">span class="Chemical">lactone), 1,695, 1677 (C=O, amide), 1,631.5 (C=C, aromatic).

N-{2-[(S)-4-Amino-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-yl]-4-oxothiazolidin-3-yl}-2-(<span class="Chemical">coumarin-4-yloxy)acet<class="Gene">span class="Chemical">amide (7). Yield 45%; oil; 1H-NMR (CDCl3): δ 2.24 (s, 3H, CH3), 3.06 (s, 3H, N-CH3), 3.89 (s, S-CH2), 4.67 (s, 2H, CH2), 4.69 (s, 2H, O-CH2), 5.26 (s, 1H, -C=C-H), 7.31, 7.52, 7.81 (s, 1H, aromatic ring), 6.84, 7.11, 7.29 (s, 1H, aromatic ring) 8.02 (s, 1H, NH), 8.32 (s, NH2); IR (cm−1): 3,388.3 (NH2), 3,189.1 (N-H), 2,928 (C-H, aliphatic), 3,057.7 (C-H, aromatic), 1,719.5 (C=O, lactone), 1,685, 1667 (C=O, amide), 1,633.7 (C=C, aromatic); Analysis: Calc. for C25H25N5O5S: C 59.16%, H 4.96%, N 13.80%. Found: C 58.91%, H 4.11%, N 12.92%.

<span class="Chemical">N-(2-Ethyl-2-methyl-4-oxothiazolidin-3-yl)-2-(coumarin-4-yloxy)acetamide (8). Yield 45%; oil; 1H-NMR (CDCl3): δ 0.89 (t, 3H, CH3), 1.59 (s, 3H, CH3), 1.78 (q, 2H, CH2), 3.86 (s, S-CH), 4.68 (s, 2H, O-CH2), 5.21 (s, 1H, -C=C-H), 7.36, 7.54, 7.71 (s, 1H, aromatic ring) 8.02 (s, 1H, NH); IR (cm−1): 3,199.0 (N-H), 2,931.3 (C-H, aliphatic), 3,040.5 (C-H, aromatic), 1,719 (C=O, <class="Gene">span class="Chemical">lactone), 1,691, 1,685 (C=O, amide), 1,632 (C=C, aromatic).

3.6. Cyclization with Maleic Anhydride; Synthesis of Compounds

A mixture of compound (3, 4 or 5) (1 mmol) and <span class="Chemical">maleic anhydride (1 mmol) in dry <class="Gene">span class="Chemical">benzene (50 mL) was refluxed in a water bath for 20 h. The solvent was removed and the precipitate was recrystallized from tetrahydrofuran.

<span class="Chemical">N-[4,7-Dioxo-2-(o-tolyl)-1,3-oxazepin-3(2H,4H,7H)-yl]-2-(coumarin-4-yloxy) acetamide (9). Yield 40%; m.p. 128–130 °C; 1H-NMR (CDCl3): δ 2.784 (s, 3H, CH3), 3.012 (d, 1H, CH), 3.69 and 4.02 (dd, 1H, CH=CH), 5.38 (s, 2H, O-CH2), 6.281 (s, 1H, -C=C-H), 7.329, 7.446, 7.964 (s, 1H, aromatic ring) 9.14 (s, 1H, NH); IR (cm−1): 3,196.2 (N-H), 2,970.5 (C-H, aliphatic), 3,087.2 (C-H, aromatic), 1,755, 1,745 (C=O), 1,667.9 (C=O, <class="Gene">span class="Chemical">amide), 1,630.1 (C=C, aromatic).

N-[2-(4-Amino-1,5-dimethyl-2-phenyl-2,3-dihydro-1H-pyrazol-3-yl)4,7-dioxo-1,3-oxazepin-3(2H,4H,7H)-yl]-2-(<span class="Chemical">coumarin-4-yloxy) acet<class="Gene">span class="Chemical">amide (10). Yield 35%; m.p 120–121 °C; 1H-NMR (CDCl3): δ 2.24 (s, 3H, CH3), 3.01 (s, 3H, CH3), 4.89 (s, 2H, O-CH2), 5.38 (s, 1H, -C=C-H), 6.89 and 6.39 (dd, 1H, CH=CH), 6.99, 7.11, 7.29 (s, 1H, aromatic ring); 8.14 (s, 1H, NH), 8.45 (s, NH2); IR (cm−1): 3,391.8 (NH2), 3,284.1 (N-H), 2,981.4 (C-H, aliphatic), 3,081.2.2 (C-H, aromatic), 1,765, 1,734 (C=O), 1,678 (C=O, amide), 1,629.6 (C=C, aromatic); Analysis: Calc. for C27H25N5O7: C 61.01%, H 4.74%, N 13.18%. Found: C 60.73%, H 4.01%, N 12.65%.

Synthesis of <span class="Chemical">N-[2-Ethylmethyl-4,7-dioxo-1,3-oxazepin-3(2H,4H,7H)-yl]-2-(coumarin-4-yloxy) acetamide (11). Yield 40%; m.p. 118–120 °C; 1H-NMR (CDCl3): δ 0.89 (t, 3H,CH3), 1.69 (s, 3H, CH3), 1.505 (q, 2H, CH2), 4.65 (s, 2H, O-CH2), 5.23 (s, 1H, -C=C-H), 6.82 and 6.41 (dd, 1H, <class="Gene">span class="Disease">HC=CH), 7.41, 7.453, 7.81 (s, 1H, aromatic ring), 8.12 (s, 1H, NH); IR (cm−1): 3,199.0 (N-H), 2,973.1 (C-H, aliphatic), 3,091.0 (C-H, aromatic), 1,758, 1,733 (C=O), 1,669.2 (C=O, amide), 1,630.3 (C=C, aromatic); Analysis: Calc. for C19H18N2O7: C 59.07%, H 4.70%, N 7.25%. Found: C 58.81%, H 4.12%, N 6.88%.

4. Conclusions

A series of new cyclic compounds based <span class="Chemical">4-hydroxycoumarin were successfully synthesized in high to acceptable yields (35%–85%). The proposed structures of the new <class="Gene">span class="Chemical">coumarins were confirmed by spectral analysis performed by IR, UV-Vis, 1H-NMR and elemental analysis. Coumarins 6, 7 and 8 were synthesized by the cyclization of Schiff bases 3, 4 and 5 using mercaptoacetic acid. The cyclization of Schiff bases 3–5 with maleic anhydride yielded new coumarins 9–11.