Journal ITB
JETS

Journal of Engineering and Technological Sciences
  1. Home
  2. Archives
  3. Vol 53 (2021) Issue 1
  4. Articles

Microwave-Assisted Claisen-Schmidt Condensation Reaction of Ethyl p-methoxycinnamate to Synthesize p-Methoxystyryl Ketone Derivatives and Evaluate Anti-inflammatory Activity of Synthetic Products

Published: | DOI: 10.5614/j.math.fund.sci.2021.53.1.6 | Vol 53, Issue 1 (2021)

Authors

Abstract

The rhizome of Kaempferia galanga has been known to contain ethyl p-methoxycinnamate (EPMC) (1) as a main component, which has anti-inflammatory properties. Previously we have reported the structural modification of EPMC (1) to form another ester, nitrostyrene, and cinnammamide derivatives and then studied their structure-activity relationships as anti-inflammatory agent. In continuing our research, in this paper, we report the microwave-assisted Claisen-Schmidt condensation of EPMC (1) to synthesize a series of p-methoxystyryl ketones followed by a study of their anti-inflammatory activity. The reaction begins with microwave-assisted cleavage oxidation of hydrolyzed product of EPMC, p-methoxycinnamic acid (2) with Ca(NO3)2 for the synthesis of p-methoxybenzaldehyde (3). Furthermore, 3 was reacted with acetophenone, ethyl methyl ketone and acetone via microwave-assisted Claisen-Schmidt condensation for the synthesis of (E)-1-(4-methoxyphenyl)-3-phenylprop-2-en-1-one (5a) (E)-1-(4-methoxyphenyl)pent-1-en-3-one (5b) and (E)-4-(4-methoxyphenyl)but-3-en-2-one (5c), respectively. The reaction products were characterized using spectroscopic techniques and were then tested for anti-inflammatory activity using in vitro anti-denaturation of protein assay. It was found that converting EPMC (1) to 5a and 5b reduced anti-inflammatory activity, while 5c retained anti-denaturation activity with an IC50 of 72.8 µg/ml.

Keywords

Acetophenone; Chemistry; Ketone; Claisen condensation; Acetone; Condensation reaction; Organic chemistry; Stereochemistry; Catalysis

1 Introduction

Ethyl p-methoxycinnamate is a major volatile component of the rhizome of Kaempferia galanga and has been shown to possess anti-inflammatory

properties [1,2]. This compound has also been reported to have other pharmacological effects, such as antimicrobial, anti-cancer, larvicidal, antituberculosis, nematicidal, mosquito repellent, angiogenesis inhibition, anticarcinogenic, and anti-inflammatory activity [2]. Previously, we have reported the conversion of EPMC (1) to another ester, cinnamamide, and nitrostyrene derivatives followed by a study of the structure-activity relationship of these compounds to their anti-inflammatory activity [1,3,4]. It has been proposed that ethyl ester is part of EPMC (1), which causes anti-inflammatory activity, and that decreasing and increasing the number of carbon atoms in the ester group results in decreased activity [3]. The conversion of the structure to nitrostyrenes did not give a significantly different effect, while conversion to hydroxyl cinnnamamide derivatives tended to increase the anti-inflammatory activity [1]. The fact that the ester part of EPMC (1) is a functional group that plays an important role in its pharmacological action leads to a concern about the stability of this compound. It has been noticed that some ester drugs are unstable in blood, plasma and serum samples due to their ability to be hydrolyzed both in vitro and in vivo. The instability of drugs can cause a substantial underestimation of the actual drug concentration [5-7].

Curcumin is a promising natural pharmaceutically active compound that is extracted mainly from Curcuma longa L. [8,9]. Many curcumin activities are related to their ability to suppress acute and chronic inflammation [10]. Half of the curcumin structure is a styryl ketone moiety, a skeleton that possesses an aromatic and α,β-unsaturated ketone group. The styryl ketone derivatives themselves have been found to have various pharmacological effects, such as neuroprotective [11], antitumor [12], anti-inflammatory [13], antioxidant [14] and cytotoxic [15] activity. The conjugated system of the styryl ketones is expected to be one of the parts of the structure that is responsible for its biological activities [16]. Another part of styryl ketone compounds that also contributes to its biological activity is the halogenated phenyl part [13]. Various methods of synthesizing styryl ketones have been described in the literature, where Claisen-Schmidt condensation is one of the simplest methods to synthesize this compound [16].

As part of our research, which focuses on the study of the structure-activity relationship of EPMC as anti-inflammatory agent, in the current study we attempted to convert EPMC (1) to p-methoxystyryl ketone derivatives. The conversion was carried out through microwave-assisted Claisen-Schmidt condensation. The structure of the synthetic compounds was characterized by using spectroscopic data and comparison with previously reported data. In vitro anti-denaturation assay was used to further test the pharmacological activity of the synthetic products.

2 Material and Methods

2.1 Materials and Instrumentation

EPMC (1) was obtained from the extraction and purification of the rhizome of K. galanga [1]. The following chemicals used were purchased from Merck: acetone, acetophenone, ethyl acetate, ethyl methyl ketone, HCl, glacial acetic acid, H2SO4, NaCl, NaOH, Na2SO4, silica gel, TLC plate 60 F250. Bovine serum albumin and Na diclofenac were purchased from Sigma Aldrich. The melting point was measured using a Stuart SMP10 apparatus (without correction). The synthetic product was analyzed using an Agilent Technology GC/MS-MSD 7890A/5975C system [1,3]. The 1H-NMR was measured on a Jeol-500 MHz instrument. An unmodified oven microwave (Samsung) was used for the synthesis reaction.

2.2 Hydrolysis of 1

EPMC (1) was hydrolyzed as described previously to give 2 as colorless crystals [1], m.p. 175 °C (lit. 169 °C).

2.3 Conversion of 2 to 3

2.0 g p-Methoxycinnamic acid (2) and 5.0 g Ca(NO3)2 (Merck) were dissolved in 5 mL acetic acid glacial and irradiated for 2 minutes using an microwave oven at 300 W. Cold distilled water was added to the reaction product, which was then extracted with n-hexane to yield 0.95 g of yellow oil of (3) (45.7% yield) [18]. The 1H-NMR data was in agreement with previously reported data [19].

2.4 Claisen-Schmith Condensation

2.4.1 Synthesis of 5a

In an Erlenmeyer flask, 0.22 mg of p-methoxybenzaldehyde (3) (1.6 mmol), 5 mL of NaOH, and 195.8 µl of acetophenone (1.6 mmol) were mixed and irradiated for 7 minutes in a microwave oven at 600 W. During the reaction, the solution was taken from the oven every 30 minutes and put in an ice bath. When the color of the solution turned orange, the reaction was stopped, followed by extraction of the product with ethyl acetate and purification with chromatography to obtain 138 mg of 5a (62.2% yield), m.p. 71-72 °C, C16H14O2, GCMS: 238[M]+ , 207, 161, 133, 108, 77 and 51. The 1H-NMR spectra followed those previously reported and are tabulated in Table 2 [20].

2.4.2 Synthesis of 5b

In an Erlenmeyer flask, 214 mg of p-methoxybenzaldehyde (3) (1.6 mmol) and 8 ml of NaOH 5% were mixed, then 140 µl of ethyl methyl ketone (4b) (1.6 mmol) was added under continuous irradiation using a microwave oven at 600 W for 3 minutes. During the reaction, the mixture was removed from the oven every 30 seconds, followed by cooling in an ice bath. After the reaction was completed, the solution was poured into ice-cold water, neutralized with cold HCl and then extracted with ethyl acetate. Further purification of ethyl acetate extract using the chromatographic method gave 28 mg of 5b (13.5% yield), m.p. 49-51C, C12H14O2, GCMS: 190 [M]+ , 161 (base peak), 145, 133, 118, 103, 89, 76, 63. The 1H-NMR data is tabulated in Table 2.

2.4.3 Synthesis of 5c

In a test tube with cap, 60 mg of p-methoxybenzaldehyde (2) (0.44 mmol), 1.1 mL of NaOH 10% (0.44 mol), and 33.3 µL of acetone (4a) were combined and placed in a microwave oven and then irradiated for 20 minutes at 600 W. During irradiation, the mixture was removed from the oven every 10 seconds followed by cooling in an ice bath. After the reaction was completed, the product was poured into ice-cold water, neutralized with cold HCl and extracted with a mixture of ethyl acetate and n-hexane. Purification of ethyl acetate extract gave 40.4 mg of 5c (67.3% yield), m.p. 73-74 C, C11H12O2, GCMS: 176 [M]+ , 161 (base peak), 145, 118, 103, 89, 77, 63, 44. The 1H-NMR spectra were consistent with those previously reported and are tabulated in Table 2 [21].

2.5 Anti-denaturation Assay

Samples in concentrations of 0.1, 1, 10, 100 ppm were prepared and evaluated for anti-denaturation by using heated bovine serum albumin assay following our previous report [1,3,22]. Na diclofenac was used as standard.

3 Results and Discussion

Claisen-Schmidt condensation is a reaction that occurs when an aromatic carbonyl compound that does not have α-hydrogen reacts with aldehydes or ketones that have α-hydrogen. α,β-Unsaturated ketones such as chalcones, flavanones, and styryl ketones are typically synthesized using this reaction [16,23]. Recently, effective Claisen-Schmidt condensation reactions have been conducted through a microwave-assisted reaction between ketones and aromatic substituted aldehyde to synthesize α,β-unsaturated ketone compounds [16,24].

In this study, the conversion of EPMC (1) to α,β-unsaturated ketone, pmethoxystyryl ketones was carried out in two stages. The reaction begins with the conversion of EPMC (1) to p-methoxybenzaldehyde (3), followed by microwave-assisted Claisen-Schmidt condensation of 3 to pmethoxystyrylketones. At first, the conversion of EPMC (1) to pmethoxybenzaldehyde (3) was considered an undesirable product of the cold nitration reaction that was developed from the previous work of Bose et al. [25]. Instead of an electrophilic substitution reaction, the reaction between EPMC (1) and Ca(NO3)2 causes cleavage oxidation of the vinyl of EPMC (1) to give pmethoxybenzaldehyde (3). This reaction produces a mixture that needs to be further purified using a chromatographic method. As an alternative way of producing the reaction product as the major product, the hydrolyzed product of EPMC (1), p-methoxycinnamic acid (2) was reacted with Ca(NO3)2. This reaction succeeded in producing the major product of p-methoxybenzaldehyde (3) with a yield of 45.7% without using chromatography. The spectroscopic data of 3 followed previously reported data [19].

In adopting and modifying the previous work of Shakil et al. [24], the microwave-assisted Claisen-Schmidt condensation of EPMC (1) was started by conducting a reaction between 3 and acetophenone (4a) in a test tube with a cap. Variations of microwave-oven power and reaction time were used. The solution was removed from the oven and cooled in an ice bath every 30 seconds during the reaction. When the solution's color turned orange, the reaction was complete, and the solution was cooled in cold water before being neutralized with cold HCl. The reaction product was then extracted with an organic solvent and monitored using TLC. Reactions at 300 and 450 W for each 10, 15, 25 minutes did not give the targeted product. The synthesis product was formed as the major product when the mixture was irradiated at 600 W for 25 minutes, as seen on the TLC plate. Furthermore, we tried to use this condition to irradiate the mixture that was placed in an Erlenmeyer flask and irradiated at 600 W. Monitoring of the TLC showed a single spot of 5a within 7 minutes of irradiation. Further purification of the product reaction obtained 5a at a yield of 62.2%. The optimization of the Claisen-Schmidt condensation reaction is given in Table 1. The spectroscopic data of 5a was in agreement with previously reported data [20].

Other ketones were optimized by putting 3 and 4b in an Erlenmeyer flask and irradiating at 600 W for 3 and 5 minutes. The mixture was removed from the microwave oven and cooled in an ice bath every 30 seconds during the 3 minutes reaction to produce 5b at a yield of 13.3%. Extension of the reaction time to 5 minutes gave a mixture of the reaction product. To the best of our knowledge no spectroscopic data of this compound have been previously reported. According to the MS data of GCMS, the molecular weight of 5b is 190, which corresponds to the molecular formula of C12H14O2. A prominent peak appears at m/z 161, indicating the loss of C2H5 from the structure, where a peak at m/z 161 usually suggests the presence of p-methoxylcinnamic moiety in the structure [26]. The 1H-NMR spectrum exhibited the presence of four integrated protons at 6.91 (2H, d, J = 9 Hz, 2CH-Ar), 7.50 (2H, d, J = 9, 2CH-Ar), two trans-coupled peaks at 6.63 (1H, d, J = 16 Hz, =CH) and 7.52 (1H, d, J = 16 Hz, =CH), three integrated protons at 3.86 (3H, s, OCH3), indicating the presence of p-methoxy cinnamic acid moiety [26]. The peaks at 1.16 (3H, t, CH3) and 2.66 (2H. d, CH2) suggest the presence of C2H5. The H-NMR data of 5b is tabulated in Table 2. Hence, it is suggested that this compound is an (E)-1- (4-methoxyphenyl)pent-1-en-3-one.

Table 1 Optimization of Claisen-Schmidt condensation for synthesis of pmethoxystyryl ketone derivatives.

ReagentsMolar
Ratio
(3:4)		Power
(W)		Time
(minutes)		Product
(yield%)
30010-
1:1(In test tube)15-
25-
Acetophenone
(4a)		1:1450
(In test tube)		10-
15-
255a as minor
1:1600
(in a test tube)		10-
15-
255a as major
600
(in Erlenmeyer)		75a (62.2% )
Ethyl methyl600 W35b (13.3%)
ketone (4b)1:1(in Erlenmeyer)5-
3005-
(in a test tube)10-
Acetone
(4c)		1:120-
4505-
(in a test tube)10-
20-
600
(In test tube)		5-
10-
205c (67.3%)

(-): The product reaction was not formed.

In optimization reaction of 3 and 4c, the mixture of 3 and 4c was placed in a test tube with the cap and irradiated at 300, 450, and 600 W in 5, 10, 20 minutes. TLC analysis of the reaction results revealed that when the mixture was irradiated at 600 W for 20 minutes, the formation of 5c (67.3% yield) occurred. During the reaction, the mixture was removed from the microwave every 10 seconds and cooled in the ice bath. The spectroscopic data of 5c was consistent with the previously reported data [21]. The scheme of conversion of EPMC (1) to a series of p-methoxystyryl ketones is shown in Figure 1.

Note: MWI: Microwave irradiation

Figure 1 Scheme of synthesis of styryl ketones.

Table 2 1H-NMR data of 5a, 5b, and 5c in CDCl3.

5a5b5c
δ (ppm), J (Hz)δ (ppm), J (Hz)δ (ppm), J (Hz)
3.85 (3H, s; OCH3)1.16 (3H, t; CH3)2.36 (3H, s; CH3)
6.94 (2H, d, J = 9; 2CH-Ar)2.66 (2H. d; CH2)3,85 (3H ,s; OCH3)
7.42 (1H, d, J = 16; =CH)3.86 (3H, s; OCH3),6,61 (1H, d, J = 16; =CH)
7.50 (2H, t, J = 7; 2CH-Ar)6.63 (1H, d, J = 16; =CH)6,92 (2H, d, J = 9; 2CH-Ar)
7.56 (1H, tt, J1 = 7, J2 = 2; CH-Ar) 6.91 (2H, d, J = 9; 2CH-Ar)7,48 (1H, d, J = 16, =CH)
7.60 (2H, d, J = 9; 2CH-Ar)7.50 (2H, d, J = 9; 2CH-Ar)7.50 (2H, d, J = 9, 2CH-Ar)
7.78 (1H, d, J = 16; =CH)7.52 (1H, d, J = 16; =CH).
8.0 (2H, d, J = 7; 2CH-Ar)

Protein anti-denaturation assay was used to assess the anti-inflammatory activity of the synthetic products. Protein denaturation has been shown to increase the production of advanced glycation end products (AGEs), which are chemical mediators of inflammation, especially in rheumatoid arthritis. Therefore, compounds that have protein anti-denaturation activity are considered to have anti-inflammatory properties [27-29]. The result of the bioassay indicated that 5c showed anti-denaturation activity with an IC50 value of 72.48 µg/ml. Meanwhile, 5a and 5b were considered not to have antiinflammatory properties (Table 3). This study suggests that 5c still had antiinflammatory properties and that along with the increase of lipophilicity, the activity gradually decreased. This result is in line with our previous research, which reported that the increasing lipophilicity of the ester of EPMC (1) caused a decrease in anti-denaturation activity [3]. On the other hand, the conversion of EPMC (1) to hydroxyl cinnammamide derivative, which is more hydrophilic than EPMC (1), caused increased anti-denaturation activity [1]. EPMC (1) showed anti-denaturation activity with an IC50value of 53.3 µg/ml. Structurally, drugs that contain a ketone functional group are known to be more stable to hydrolysis than those containing an ester group [7]. Therefore, conversion of the ester EPMC (1) to p-methoxystyryl ketones provides more stable derivatives.

Table 3 Result of anti-denaturation assay.

CompoundIC50
Values (µg/ml)
153.3±4.3
3na*
5ana*
5b>100
5c72.8±4,7
Na Diclofenac5.04±1.1

*Did not inhibit heat BSA denaturation; IC50 values are expressed as mean ± SD (n = 3)

4 Conclusion

Microwave-assisted conversion of EPMC (1) to several p-methoxystyryl ketones was successfully conducted in 2 steps. First, EPMC (1) was converted to p-methoxybenzaldehyde (3), followed by the reaction of compound 3 with various ketones. The reaction of 3 with acetophenone (4a), ethyl methyl ketone (4b) and acetone (4c) succeeded in producing of (E)-1-(4-methoxyphenyl)-3 phenylprop-2-en-1-one (5a) (E)-1-(4-methoxyphenyl)pent-1-en-3-one (5b), and (E)-4-(4-methoxyphenyl)but-3-en-2-one (5c), respectively. The bioassay result indicated that 5c still had anti-inflammatory activity, with an IC50 value of 72.8 µg/ml. Meanwhile, both 5a and 5b were considered not to have antiinflammatory activity. The structure-activity study suggested that the increasing lipophilicity of p-methoxystyryl derivatives will decrease the anti-inflammatory activity.

Acknowledgments

The Center for Research and Publication, Institute for Research and Community Service, Universitas Islam Negeri Syarif Hidayatullah Jakarta, Indonesia funded this project with a research grant in 2016.

Research Intelligence

Data from OpenAlex ↗

Metrics

0.00
FWCIfield-weighted
26th
Percentilevs same year + field
Article
Work type
GOLD
Open Access

Topics

Ginger and Zingiberaceae research Primary
0.99
Pharmacology › Pharmacology, Toxicology and Pharmaceutics › Life Sciences
Synthesis of Organic Compounds
0.97
Synthesis of heterocyclic compounds
0.96

Related Research

Semantic Profile AI-classified research signals

Core Domains
Chemistry 0.78
level 0
Ketone 0.69
level 2
Acetone 0.58
level 2
Secondary Topics
Organic chemistry 0.39 Stereochemistry 0.39

Institution Network

  • Syarif Hidayatullah State Islamic University Jakarta ID
    Ismiarni Komala · Supandi Supandi · Nurmeilis Nurmeilis · Yardi Yardi · Ofa Suzanti Betha · Nurkhyati Putri Indriyani · Moethia Moethia · Muhamad Beny Setiawan · Ghilman Dharmawan · Putri Hayati Nufus · Noni Tri Utami

References

  1. Komala, I., Supandi, Nurhasni, Betha, O.S., Yardi, Mufidah, S., Reza, M., Ali, M.S., Aulia, N.S. & Sutar, Microwave-Assisted Synthesis of p-Methoxycinnamamides and p-Methoxy-b-Nitrosytrenes from Ethyl p-Methoxycinnamate and Screening Their Anti-inflammatory Activity, Natural Product Communication 12(8), pp. 1265-1268, 2017.
  2. Munda, S., Saikia, P. & Lal, M., Chemical Composition and Biological Activity of Essential Oil of Kaempferia galanga: A Review, Journal of Essential Oil Research, 30(5), pp. 303-308, 2018.
  3. Komala, I., Supandi, Nurhasni, Betha, O.S., Putri, E., Mufidah, S., Awaludin, M.F., Fahmi, M., Reza, M. & Indriyani, N.P., Structure-activity Relationship Study on the Ethyl p-Methoxycinnamate as an Anti-inflammatory Agent, Indonesian Journal of Chemistry, 18(1), pp. 60-65, 2018.
  4. Komala, I., Thantowi, A., Mas, A. & Putra, J., An Efficient Directly Conversion of the Ethyl p-Methoxycinnamate into N,N-dimethyl-p-Methoxycinnamamide and Study the Structure-activity Relationship on Anti-inflammatory Activity, Indonesian Journal of Pharmacy, 31(3), pp. 144-149, 2020. DOI: 10.22146/ijp.812
  5. Jornada, D.H., Fernandes, G.F.D.S., Chiba, D.E., Melo, T.R.F. De, Santos, J.L. Dos, & Chung, M.C., The Prodrug Approach: A Successful Tool for Improving Drug Solubility, Molecules, 21(1), p. 42, 2016
  6. Koitka, M., Höchel, J., Gieschen, H. & Borchert, H., Improving the Ex Vivo Stability of Drug Ester Compounds in Rat and Dog Serum : Inhibition of the Specific Esterases and Implications on their Identity, Journal of Pharmaceutical and Biomedical Analysis, 51(3), pp. 664-678, 2010.
  7. Waterman, K.C., Adami, R.C., Alsante, K.M., Antipas, A.S., Arenson, D.R., Carrier, R., Hong, J., Landis, M.S., Lombardo, F., Shah, J.C., Shalev, E., Smith, S.W., & Wang, H., Hydrolysis in Pharmaceutical Formulations, Pharmaceutical Development Technology, 7(2), pp. 113-146, 2002. DOI: 10.1081/pdt-120003494
  8. Arshad, L., Haque, M.A., Bukhari, S.N.A. Jantan, I., An Overview of Structure-activity Relationship Studies of Curcumin Analogs as Antioxidant and Anti-inflammatory Agents, Future Medicinal Chemistry, 9(6), pp. 605-626, 2017. DOI: 10.4155/fmc-2016-0223
  9. Priyadarsini, K.I., The Chemistry of Curcumin: From Extraction to Therapeutic Agent, Molecules 19(12), pp. 20091-20112, 2014. DOI: 10.3390/molecules191220091
  10. Hatcher, H., Planalp, R., Cho, J., Torti, F.M. &Torti, S. V., Curcumin: From Ancient Medicine to Current Clinical Trials, Cellular and Molecular Life Sciences, 65(11), pp. 1631-1652, 2008. DOI: 10.1007/s00018-008-7452-4
  11. Ning, X., Guo, Y., Ma, X., Zhu, R., Tian, C., Wang, X., Ma, Z., Zhang, Z. &Liu, J., Synthesis and Neuroprotective Effect of E-3,4-dihydroxy Styryl Aralkyl Ketones Derivatives Against Oxidative Stress and Inflammation, Bioorganic & Medicinal Chemistry Letter, 23(13), pp. 3700-3703, 2013.
  12. Motohashi, N., Yamagami, C., Tokuda, H., Konoshima, T., Okuda, Y., Okuda, M., Mukainaka, T., Nishino, H. & Saito, Y., Inhibitory Effects of Dehydrozingerone and Related Compounds on 12-O-tetradecanoylphorbol-13-acetate Induced Epstein-Barr Virus Early Antigen Activation, Cancer Letter, 134(11), pp. 37-42, 1998, DOI: 10.1016/s0304-3835(98)00239-0
  13. Nargund, L.V.G., Hariprasad, V., & Reddy, G.R.N., Synthesis and Anti-inflammatory Activity of Fluorinated Phenyl Styryl Ketones and N-Phenyl-5-substituted aryl-3-p (fluorophenyI) Pyrazolins and Pyrazoles, Journal of Pharmaceutical Science, 81(9), pp. 892-894, 1992.
  14. Rajakumar, D.V. & Rao, M.N.A., Antioxidant Properties of Phenyl Styryl Ketones, Free Radical Research, 22(4), pp. 309-317, 1995. DOI: 10.3109/10715769509145643
  15. Dimmock, J.R., Kumar, P., Quail, J.W., Pugazhenthi, U., Yang, J., Chen, M., Reid, R.S., Allen, T.M., Kao, G.Y., Cole, S.P.C., Batist, G., Balzarini., J., Clercq, E.D, Synthesis and Cytotoxic Evaluation of Some Styryl Ketones and Related Compounds, European Journal of Medicinal Chemistry, 30(3), pp. 209-217, 1995.
  16. Rayar, A., Veitía, M.S.-I. & Ferroud, C., An Efficient and Selective Microwave-assisted Claisen-Schmidt Reaction for the Synthesis of Functionalized Benzalacetones, Springer Plus, 4, p. 221, 2015
  17. Ekowati, J., Tejo, B.A., Sasaki, S., Highasiyama, K., Sukardiman, Siswandono, & Budiati, T., Structure Modification of Ethyl p-Methoxycinnamate and their Bioassay as Chemopreventive Agent Against Mice’s Fibrosarcoma, International Journal of Pharmacy and Pharmaceutical Sciences, 4(3), pp. 2012528-532, 2012.
  18. Bose, A.K., Ganguly, S.N., Manhas, M.S., He, W. & Speck, J., Cold Microwave Chemistry: Synthesis Using Pre-cooled Reagents, Tetrahedron Letters, 47(19), pp. 3213-3215, 2006. DOI: 10.1016/j.tetlet.2006.03.059
  19. Islam, M.K., Sohrab, M.H., & Jabbar, A. Caffeine and p-Anisaldehyde from the Fruits of Enterolobium Saman Prain, International Journal of Pharmaceutical Sciences and Research, 3(1), pp. 168-170, 2012.
  20. Cabrera, M., Simoens, M., Falchi, G., Lavaggi, M.L., Piro, O.E., Castellano, E.E., Vidal, A., Azqueta, A., Monge, A., de Cerain, A.L., et al., Synthetic Chalcones, Flavanones, and Flavones as Antitumoral Agents: Biological Evaluation and Structure-activity Relationships, Bioorganic and Medicinal Chemistry, 15(10), pp. 3356-3367, 2007.
  21. Jafari, A.A. & Ghadami, M. Efficient Synthesis of a,b-unsaturated Ketones with Trans-selective Horner-Wadsworth- Emmons Reaction in Water, Environmental Chemistry Letter, 14, pp. 223-228, 2016.
  22. Komala, I., Azrifitria, Yardi, Suzanti, B.O., Muliati, F., and Ni’mah, M., Antioxidant and anti-inflammatory activity of the Indonesian ferns, Nephrolepis Falcata and Pyrrosia Lanceolata, International Journal of Pharmacy and Pharmaceutical Sciences 7(12), pp. 162-165, 2015.
  23. Yadav, G.D., and Wagh, D.P., Claisen-Schmidt Condensation using Green Catalytic Processes: A Critical Review, ChemistrySelect, 5, pp. 9059-9085, 2020. DOI: 10.1002/slct.202001737
  24. Shakil, N.A., Singh, M.K., Kumar, J., Satthiyendiran, M., Kumar, G., Singh, M.K., Pandey, R.P., Pandey, A. & Parmar, V., Microwave Synthesis and Antifungal Evaluations of Some Chalcones and their Derived Diaryl-cyclohexenones Microwave Synthesis and Antifungal Evaluations of Some Chalcones and their Derived diaryl-cyclohexenone. Journal of Environmental Science and Health Part B Pesticide, Food Contaminant and Agriculture Waste, 45(6), pp. 524-530, 2010.
  25. Bose, A.K., Ganguly, S.N., Manhas, M.S., Rao, S., Speck, J., Pekelny, U., and Pombo-Villars, E., 2006, Microwave Promoted Rapid Nitration of Phenolic Compounds With Calcium Nitrate, Tetrahedron Lett. 47, pp. 1885-1888. DOI: 10.1002/chin.200626048
  26. Komala, I., Supandi, & Hardiansyah, M.M., Direct Amidation of Ethyl p-Methoxycinnamate to Produce N,N-bis-(2-hydroxyethyl)-p-methoxycinnamamide, Jurnal Kimia Valensi, 4(1), pp. 22-25, 2018.
  27. Williams, L.A.D., O’Connar, A., Latore, L., Dennis, O., Ringer, S., Whittaker, J.A., Conrad, J., Vogler, B., Rosner, H. & Kraus, W., The in vitro Anti-denaturation Effects Induced by Natural Products and Non-steroidal Compounds in Heat Treated (Immunogenic) Bovine Serum Albumin is Proposed as a Screening Assay for the Detection of Anti-inflammatory Compounds, Without the Use of Animals, West Indian Medical Journal, 57(4), pp. 327-331, 2008.
  28. Seidler, N.W., & Yeargans, G.S., Effects of Thermal Denaturation on Protein Glycation, Life Sciences, 70(15), pp. 1789-1799, 2002, DOI: 10.1016/s0024-3205(02)01474-1
  29. Groot, L. De, Hinkema, H., Westra, J., Smit, A.J., Kallenberg, C.G.M., Bijl, M., & Posthumus, M.D., Advanced Glycation Endproducts are Increased in Rheumatoid Arthritis Patients with Controlled Disease, Arthritis Research, and Therapy, 13(6), R205, 2011. DOI: 10.1186/ar3538