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Bleaching earth clay (pH 12.5): A novel and reusable catalyst for
rapid synthesis of 7-Hydroxy 4-Styryl coumarin derivatives and
their antihelmintic activity
Rahul D. Kamble1, Govind V. Jawadwar2, Snehalkumar D. Patil1, Shrikant
V. Hese1, Ashok P. Acharya1, Bhaskar S. Dawane1*
and Sanjay S. Pekamwar2*
1School of Chemical Sciences, Swami Ramanand Teerth Marathwada University, Nanded 2School of Pharmacuetucal Sciences, Swami Ramanand Teerth Marathwada University, (Received February 1, 2013; Revised February 27, 2013; Accepted June11, 2013) Abstract: 7-hydroxy 4-styryl coumarin derivatives were synthesized by Knovengel condensation of 7-hydroxy
4-methyl coumarin with aldehydes by using novel and reusable catalyst bleaching earth clay (pH12.5) in PEG-
400 as green reaction solvent, followed by the Mannich reaction. The synthesized compounds were evaluated for
their in vitro antihelmintic activity and it was found that the synthesized compounds showed good antihelmintic
Keywords: 7-hydroxy 4-styryl coumarin derivatives; bleaching earth clay (pH12.5); PEG-400; antihelmintic
The global burden of both human and domestic animal parasitic diseases coupled with the emergence of drug resistance has made the development of new chemotherapeutic agents, a critical need. Albendazole are still extensively used for the treatment of human pinworm infection1.Some antihelmintic drugs such as Praziquantel and Albendazole are avoided for certain groups of patients like pregnant and lactating women. Many natural products and their synthetic analogue have been reported for their biological applications. Coumarin is the naturally occurring compounds, which are widely distributed in the plantae kingdom and has also been produced synthetically2. Members of this group shows a wide range of applications, as fragrances, pharmaceuticals 3, food additives, anti-inflammatory activity4, biological activities like antihelmintic5, antitumor6, hypnotic7, insecticidal8, anticoagulant9 and antimicrobial activity10. The reported significance of coumarin derivatives generated the interest to exploit this valuable nucleus in the design and synthesis of 7-hydroxy 4-styryl coumarin derivatives via a green approach. * Corresponding author: Email: firstname.lastname@example.org; email@example.com The article was published by Academy of Chemistry of Globe Publications www.acgpubs.org/OC/index.htm Published 6/24/2013 EISSN:1307-6175 Kamble et al., Org. Commun. (2013) 6:2 95-101 The recovery of heterogeneous catalysts from the reaction mixture is simply by filtration
posses advantageous over the conventional homogeneous catalysts. Moreover, it can be reused after
activation, thereby making the process economically viable. Naturally occurring clay has unique
physical and chemical properties such as shape selectivity, acidic, basic nature and thermal stability.
The bleaching earth clay (pH 12.5) a highly efficient heterogeneous base catalyst is used for several
base-catalyzed organic transformations11-12. Use of green solvent is one of the aspects of green
synthesis. Liquid polymers or low melting polymers have recently emerged as alternative green
solvent with unique properties such as thermal stability, commercial availability, non-volatility,
miscibility with a number of organic solvents and recyclability. Poly ethylene glycols (PEGs) 13-15
are among the one of green solvents to overcome the toxic solvent effect on environment. Most of
reported methods for synthesis of 7-hydroxy 4-styryl coumarin derivatives suffer from different
drawbacks such as longer reaction times and/or the application of expensive toxic catalysts and
2. Results and discussion
With our recent success on the development of environmentally friendly methodologies using
polyethylene glycol (PEG-400)11-15 as a solvent for the preparation of biologically active compounds,
herein we report the synthesis of some 7-hydroxy 4-styryl coumarin (2 a-e) derivatives by the reaction
of 7-hydroxy 4-methyl coumarin with different substituted aromatic aldehydes using bleaching earth
clay (12.5) in PEG-400 as green reaction solvent (scheme 1) were synthesized by modifications of
reported method16 followed by the Mannich reaction yielding product (3 a-e).
Scheme 1. Synthesis of 7-hydroxy 4-styryl coumarin derivatives
Initially, we attempted the condensation of 7-hydroxy 4-methyl coumarin with aromatic aldehydes
using bleaching earth clay (pH 12.5) in polyethylene glycol (PEG-400) as reaction solvent. The
reaction went to completion within 25 min and corresponding product 2(a-e) was obtained in 90%
yield. In order to optimize the reaction conditions, we carried out the above reaction in different
solvents such as ethanol, acetic acid, dioxane, DMF and polyethylene glycol-400 (Table 1). We found
that polyethylene glycol-400 as an efficient reaction medium in terms of reaction time as well as yields
(above 80 %). Encouraged by the results, we turned our attention to variety of substituted aromatic
aldehydes. In all cases, the reaction proceeded efficiently in high yields at 60- 80 0C using PEG-400 as
an alternative reaction solvent. Further styrene derivatives undergo Mannich reaction with piperidine,
formaldehyde in methanol with few drop of acetic acid to yield 3(a-e) the physical data of synthesized
7-hydroxy4-styryl coumarin derivatives is shown in Table 2.
Table 1. Effect of solvent on the reaction of 7-hydroxy 4-methyl coumarin with aromatic aldehydes
Table 2. Physical data of synthesized 7-hydroxy 4-styryl coumarin derivatives
All synthesized compounds are well confirmed on the basis of spectral data. The absences of characteristic signals due to three protons of methyl of 4-methyl coumarin in 1H NMR spectrum of
compound 2 (a-e) confirms the formation of styryl derivatives of coumarin, further the presence of -
OH proton resonates between δ 10-11 ppm. The aromatic protons are observed at the expected
chemical shift and integral values. 7-Hydroxy 4-styryl coumarin (2 a-e) derivatives was further
supported by IR spectral data, picks due to (C-H aliphatic) stretching in (2930 cm-1–2960 cm-1) of 7-
hydroxy 4-methyl coumarin get disappeared and new pick observed at 3023 cm-1 due to (C=C-H)
stretching moreover the MS (EI) spectrum value corresponds to its an M + 1 peak of expected mass.
Yield and melting point are summarized in Table 2. These newly synthesized compounds were
screened for their antihelmintic activity.
3. Antihelmintic activity
The antihelmintic activity was performed according to the method reported by Ghosh et al, on
adult Indian earth worm Eisinea fetida (family: Lumbricidae) as it has anatomical and physiological
resemblance with the intestinal round worm parasites of human beings17. The worms were collected
from the Agricultural Science Center Pokharni, Nanded (MS) India. The worms were placed in fecal
mass before in vitro screening so as to prior use. Eisinea fetida (earth worms) were placed in petridish
containing three different concentrations (0.1, 0.5, 1%), one petridish was kept as a control (distilled
water) and one petridish contain standard drug Albendazole (1%) in distilled water. Each petridish
contains six worms (approximately equal length and diameter) and observed for paralysis and death
time. The mean time for paralysis was noted when no movement of any sort is observed, except when
the worm was shaken vigorously; the death time of worm (min) was recorded after ascertaining that
worms neither moved when shaken nor given external stimuli. The Test results were compared with
reference compound Albendazole (10mg/ml) treated samples.
Kamble et al., Org. Commun. (2013) 6:2 95-101 The antihelmintic screening of the 7-hydroxy 4-styryl coumarin derivatives and Albendazole showed
in Table 3. A closer inspection of data from tables indicates that compounds 3e and 3c showed
promising paralytic activity compared with standard Albendazole. Compound 3b showed moderate
paralysis activity with standard Albendazole. The transformation order of screened compounds for
paralysis time is 3e>3c>3b>3d>3a. Compounds 3e and 3c showed a moderate antihelmintic activity
with respect to death of worms than standard Albendazole. The transformation order of screened
compounds for death time is 3e>3c>3b>3a>3d.
Table 3. In vitro antihelmintic activity of various styrene derivatives
Death time (min)
All Values represent Mean+ SD; n=6 in each group.
In summary, we have developed a novel, efficient and environmentally benign methodology towards the synthesis of 7-hydroxy 4-styryl coumarin derivatives by the condensation reaction of 7-hydroxy 4-methyl coumarin derivatives with aldehydes using bleaching earth clay (pH: 12.5) as an efficient heterogeneous catalyst in polyethylene glycol (PEG-400) as a green reaction solvent is described. The advantages of the present protocol are the simplicity of operation, the high yields of products, and the recyclability of PEG-400, avoidance of expensive and toxic catalyst and usage of volatile organic solvents. The synthesized compounds exhibited moderate antihelmintic activity compared with standard Albendazole. From the present research work it is concluded that these 7-hydroxy 4-styryl coumarin derivatives can be the promising antihelmintic candidates for in vivo studies in future. 5. Experimental
All the melting points were uncorrected and determined in an open capillary tube. The chemicals and solvents used were of laboratory grade and were purified. Completion of the reaction was monitored by thin layer chromatography on precoated sheets of silica gel-G (Merck, Germany) using iodine vapour for detection. IR spectra were recorded in KBr pallets on FTIR Schimadzu spectrophotometer. 1H NMR and 13C NMR (70 MHz) spectra were recorded in DMSO-d6 with an Avance spectrometer (Bruker, Germany) at 400-MHz frequency using TMS as an internal standard. Mass spectra were recorded on an EI-Shimadzu QP 2010 PLUS GC-MS system (Shimadzu, Japan). Elemental analyses were performed on a Carlo Erba 106 Perkin-Elmer model 240 analyzer (Perkin-Elmer, USA).
General procedure for the preparation of compounds 2(a-e):
A mixture of 7-hydroxy-4-methyl-2-oxo-2H-chromene (1a) (10 mmol) and substituted aromatic
aldehydes (1.24 gm, 10 mmol) were dissolved in minimum quantity of PEG-400 along with catalytic
amount of bleaching earth clay (12.5). The reaction mixture was heated with stirred at 45oC
temperature. The progress and completion of the reaction was monitored by TLC. At the end of
reaction the solid product precipitated. It was filtered and thoroughly washed with chilled methanol
and crystallized from chloroform to give 7-hydroxy 4-styryl coumarin derivatives 2(a-e).
4-(2-chlorostyryl)-7-hydroxy-2H-chromen-2-one (2a): Colour (pale yellow); Purity by TLC >90% ;
IR (KBr) 3338 cm-1, 2944 cm-1, 1745 cm-1; 1H NMR (DMSO d6); δ 6.71(d,1H, J=7.5Hz), δ 6.86 (d,1H,
J=6.5 Hz), δ 6.91 (s 1H, J=6.2Hz) δ 7.11-7.82 (m, 8 H-Ar proton), δ 10.68 (s, 1H, OH); EIMS=298
4-(4-chlorostyryl)-7-hydroxy-2H-chromen-2-one (2b): Colour (white); Purity by TLC >90% ; IR
(KBr) 3332 cm-1, 2934 cm-1, 1739 cm-1; 1H NMR (DMSO d6); δ 6.70 (d, 1H, J=7.4Hz), δ 6.82 (d,1H,
J=6.5Hz), δ6.90 (s, 1H), δ 6.96-7.61 (m, 7H-Ar proton), δ 10.87 (s, 1H, OH); EIMS=298 (M+).
4-(4-bromostyryl)-7-hydroxy-2H-chromen-2-one (2c): Colour ( pale yellow); Purity by TLC >90% ;
IR (KBr) 3338 cm-1, 2944 cm-1, 1745 cm-1; 1H NMR (DMSO d6); δ 6.76 (d,1H, J=7.6 Hz), δ 6.91
(d,1H, J=6.4Hz), δ 6.99 (s, 1H) δ 7.19-7.81 (m, 7H-Ar proton), δ 10.67 (s, 1H, OH); EIMS=342 (M+).
7-hydroxy-4-(4-methylstyryl)-2H-chromen-2-one (2d): Colour ( pale brown); Purity by TLC >90%
; IR (KBr) 3328 cm-1, 2929 cm-1, 1749 cm-1; 1H NMR (DMSO d6) δ 1.32 (s, 3H), 6.69 (d,1H,
J=7.5Hz) , δ 6.72 (d,1H, J=6.8 Hz) , δ 6.92-7.512 (m, 8H-Ar proton), δ 10.321 (s, 1H, OH);
4-(4-flurostyryl)-7-hydroxy-2H-chromen-2-one (2a): Colour (yellow); Purity by TLC >90% ; IR
(KBr) 3348 cm-1, 2941 cm-1, 1748 cm-1; 1H NMR (DMSO d6); δ 6.81(d, 1H, J=7.5Hz), δ 6.92 (d,1H,
J=7.5Hz), δ7.21(s, 1H) δ 7.29-7.81 (m, 7H-Ar proton), δ 10.36 (s, 1H, OH); EIMS=282 (M+).
General procedure for the preparation of compounds 3:
Mixture of 2(a-e), formaldehyde and piperidine taken in an RBF containing methanol and few drop of
AcOH was refluxed for 3 hrs. After completion of reaction (monitored by TLC), the reaction mixture
was poured in ice cold water the precipitate obtained were filter and recrystalised from methanol to
4-[2-(2-Chloro-phenyl)-vinyl]-7-hydroxy-8-piperidin-1-yl-methyl-chromen-2-one (3a): Colour (
White); Purity by TLC >95 % ; IR (KBr) 3358 cm-1, 3118 cm-1, 2940 cm-1, 1755 cm-1; 1H NMR
(DMSO d6); δ 1.81 (m, 4H, piperidine), δ 2.13 (m ,6H, piperidine), δ 4.15 (s, 2H), δ 6.71 (d,1H,
J=7.2Hz), δ 6.91 (d,1H, J=6.6Hz), δ 6.93-7.19 (m, 7H, Ar proton), δ 10.68 (s, 1H, OH); 13C NMR;
24.1(CH2), 26.3 (CH2 × 2), 51.4 ( CH2), 57.1 (CH2× 2), 104.5 (CH × 2),115.2 (CH),125.7 (CH), 127.4
(CH × 2), 129.2 (CH × 3), 131.3 (CH), 133.6 (CH × 2), 155.2 (C-O × 2), 159.8 ( C=O), 162.4 (C);
4-[2-(4-Chloro-phenyl)-vinyl]-7-hydroxy-8-piperidin-1-yl-methyl-chromen-2-one (3b): Colour
( pale brown); Purity by TLC >95 % ; IR (KBr) 3328 cm-1, 3120 cm-1, 2929 cm-1, 1749 cm-1; 1H NMR
(DMSO d6); δ 1.71 (m, 4H, piperidine), δ 2.41 (m ,6H), δ 4.32 (s,2H), δ 6.69 (d,1H, J=7.5Hz) , δ 6.72
(d,1H, J=6.3Hz) , δ 6.92-7.58 (m, 7H, Ar proton), δ 10.21 (s, 1H, OH); 13C NMR; 23.9 (CH2), 27.1
(CH2 × 2), 50.8 ( CH2), 56.4 (CH2× 2), 102.9 (CH × 2),116.0 (CH),123.7 (CH), 128.4 (CH × 2), 129.1
(CH × 3), 132.6(CH), 135.7 (CH × 2), 156.2 (C-O × 2), 161.1 ( C=O), 163.4 (C); EIMS=396 (M+).
4-[2-(4-Bromo-phenyl)-vinyl]-7-hydroxy-8-piperidin-1-yl-methyl-chromen-2-one (3c): Colour
( pale brown); Purity by TLC >95 % ; IR (KBr) 3309 cm-1, 3109 cm-1, 2972 cm-1, 1748 cm-1; 1H NMR
(DMSO d6); δ 1.90 (m, 4H, piperidine), δ 2.32 (m,6H), δ 4.23 (s,2H), δ 6.70 (d,1H), δ 6.72 (d,1H) δ
6.91-7.74 (m, 7H, Ar proton), δ 10.64 (s, 1H, OH); 13C NMR; 23.9 (CH2), 26.8 (CH2 × 2), 51.3 ( CH2),
56.8 (CH2× 2), 103.4 (CH × 2),116.1 (CH),123.5 (CH), 128.2 (CH × 2), 129.2 (CH × 3), 132.8 (CH),
135.4 (CH × 2), 155.2 (C-O × 2), 161.5 ( C=O), 162.0 (C); EIMS=440 (M+).
4-[2-(4-Methyl-phenyl)-vinyl]-7-hydroxy-8-piperidin-1-yl-methyl-chromen-2-one (3d): Colour
(pale yellow); Purity by TLC >95 % ; IR (KBr) 3328 cm-1, 3123 cm-1, 2929 cm-1, 1749 cm-1; 1H NMR
Kamble et al., Org. Commun. (2013) 6:2 95-101 (DMSO d6); δ 1.43 (s, 3H), δ 1.69 (m, 4H, piperidine), δ 2.24 (m ,6H), δ 4.32 (s,2H), δ 6.69 (d,1H,
J=7.5Hz) , δ 6.72 (d,1H, J=6.8Hz) , δ 6.92-7.52 (m, 7H, Ar proton), δ 10.61 (s, 1H, OH); 13C NMR;
20.3(CH3), 24.9 (CH2), 27.2 (CH2 × 2), 51.1 ( CH2), 55.8 (CH2× 2), 104.4 (CH × 2),115.8 (CH),124.5
(CH), 127.2 (CH × 2), 128.8 (CH × 3), 131.8 (CH), 134.4 (CH × 2), 155.3 (C-O × 2), 160.5 ( C=O),
162.1 (C); EIMS=375 (M+).
4-[2-(4-Fluro-phenyl)-vinyl]-7-hydroxy-8-piperidin-1-yl-methyl-chromen-2-one (3e): Colour (pale
yellow); Purity by TLC >95 % ; IR (KBr) 3315 cm-1, 3118 cm-1, 2985 cm-1, 1739 cm-1; 1H NMR
(DMSO d6); δ 1.82 (m, 4H, piperidine), δ 2.16 (m ,6H), δ 4.23 (s,2H), δ 6.52 (d,1H, J=7.8Hz), δ 6.86
(d,1H, J=6.2Hz), δ 6.10-7.60 (m, 7H, Ar proton), δ 10.54 (s, 1H, OH); 13C NMR; 24.3(CH2), 27.3
(CH2 × 2), 51.7 ( CH2), 57.0 (CH2× 2), 104.1 (CH × 2),116.2 (CH),125.2 (CH), 126.4 (CH × 2), 128.2
(CH × 3), 138.3 (CH), 139.6 (CH × 2), 155.2 (C-O × 2), 159.8 ( C=O), 162.4 (C);EIMS=379 (M+).
Authors RDK and SDP are greatly acknowledging to CSIR, New Delhi for JRF.
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