Original Article
457
Synthesis and Pharmacological Evaluation of New Chemical Entities from Ibuprofen as Novel Analgesic Candidates
Authors
A. Ahmadi1, N. Naderi2, M. Daniali1, S. Kazemi1, S. Aazami1, N. Alizadeh1, B. Nahri-Niknafs1
Affiliations
1
2
Key words ▶ NSAIDs ● ▶ ibuprofen ● ▶ analgesic ● ▶ modified aromatic and ● aliphatic moieties
Abstract
▼
Non-steroidal anti-inflammatory drugs (NSAIDs) are the first choice of drugs that are normally used for the treatment of pain and inflammation. Ibuprofen (I) and its analogues as the most widely used NSAIDs have been synthesized in recent years. In an effort to establish new candidates with improved analgesic properties, derivatives (II–VII) with substituted aromatic as
Introduction
▼
received 17.04.2014 accepted 05.05.2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1376976 Published online: May 28, 2014 Drug Res 2015; 65: 457–462 © Georg Thieme Verlag KG Stuttgart · New York ISSN 2194-9379 Correspondence Dr. A. Ahmadi, Associate professor Department of Chemistry Faculty of Science Islamic Azad University P.O.Box: 31485-313 Karaj Iran Tel.: + 98/26/34403 575 Fax: + 98/26/34403 575 [email protected] [email protected]
During the last 3 decades the development of non-steroidal anti-inflammatory drugs (NSAIDs) has shown to be one of the major advancements in chemotherapeutical research [1]. These agents are among the most widely used drugs worldwide and represent a mainstay in the therapy of acute and chronic pain, fever and inflammation by blocking the formation of Prostaglandins (PGs). PGs are well-known as the mediators of inflammation, pain and swelling. They are produced by the action of cyclooxygenase (COX) enzyme on arachidonic acid. COX is the principal target of NSAIDs. This enzyme exists as 2 isoforms of constitutive (COX-1) and inducible (COX-2). COX-1 is constitutively expressed and provides cytoprotection to the gastrointestinal (GI) tract while COX-2 is inducible and mediates inflammation. The traditional NSAIDs show greater selectivity for COX-1 than COX-2 [2–4]. The NSAIDs’ use is frequently associated with a broad spectrum of adverse effects of gastrointestinal (GI), renal and hepatic which are usually observed in patients undergoing long-term treatment. Therefore, the development of new NSAIDs without these side effects has long been awaited. Selective COX-2 inhibitors that ‘coxib’ with better safety profile have been marketed as the new generation of these drugs which were rapidly
well as aliphatic moieties were synthesized in this experiment and evaluated in formalin test with rats. The results were compared to ibuprofen and control groups. Findings indicated that derivatives with new alkylphenyl rings (VI and VII) had some similar or more analgesic activities relative to the control and ibuprofen groups, respectively; which could be justified as to more alkyl and phenyl groups instead of p-isobutylphenyl moiety in I.
introduced to the market and gained an impressive success. The serious cardiovascular effects by some, however, caused the drugs to become withdrawn from the market. Producing effective NSAIDs with an improved safety profile that eliminate the disadvantages of selective COX-2 inhibitors and spare the gastrointestinal mucosa remains as a compelling need. An alternative strategy to limit the risk of GI damage induced by NSAIDs is to enhance the protective mechanisms of the gastric mucosa [5, 6]. An important group of these drugs is the class of 2-arylpropionic acids (Profen family) which are able to reduce inflammation and pain. Ibuprofen (2-p-isobutylphenyl propionic acid, I) belongs to this class and uses to relieve the symptoms of a wide range of illness such as headache, backache, period pain, dental pain, neuralgia, rheumatic pain, muscular pain, migraine, cold and flu symptoms and arthritis [5, 7–10]. A broad variety of this compound has been synthesized with manifold synthetic methodologies [11–19] but its prolonged usage (similar to other NSAIDs) has been associated to gastrointestinal complications ranging from stomach irritation to life-threatening GI ulceration bleeding and nephrotoxicity. Therefore, the search for some brand new analgesic and anti-inflammatory agents devoid of side effects continues to be an active area of research in medicinal chemistry. Similarly, the synthetic approaches
Ahmadi A et al. New Chemical Entities from Ibuprofen … Drug Res 2015; 65: 457–462
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Department of Chemistry, Faculty of Science, Karaj Branch, Islamic Azad University, Karaj, Iran Department of Pharmacology and Toxicology, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran, Iran
458 Original Article
Experimental
▼
Material and equipments
All chemicals were purchased from Merck and Aldrich Chemical Companies. Melting points (uncorrected) were determined with a digital Electro Thermal Melting Point apparatus (model 9100, Electrothermal Engineering Ltd., Essex, UK). 1 H and 13C NMR spectra were recorded with a Bruker 400 MHz (AMX model, Karlsruhe, Germany) spectrometer. IR spectra were recorded with a Thermo Nicolet FT-IR (Nexus-870 model, Nicolet Instrument Corp, Madison, Wisconsin, USA) spectrophotometer. Mass spectra were recorded with an Agilent Technologies 5 973, Mass Selective Detector (MSD) spectrometer (Wilmington, USA). Elemental analyses were carried out with a Perkin-Elmer, CHN elemental analyzer model 2 400. Compound I was synthesized according to a published method [24]. ▶ Fig. 2) Preparations ( ● Compounds II–VII
To a solution of ethyl lactate, ethyl 2-hydroxyhexanoate, ethyl 2-hydroxyoctanoate, Ethyl mandelate or ethyl 2-hydroxy-2methylpropanoate (1–5) (8.47 mmol) and triethylamine (12.71 mmol) in 15 ml of dry dichloromethane was added portion-wise MsCl (9.32 mmol) at 0 °C. The resultant mixture was stirred at 0 °C for an hour and left at room temperature for 2 h. After completion of the reaction, as indicated by TLC, the reaction mixture was diluted with ethyl acetate, water-washed, dried over anhydrous Na2SO4 and concentrated under reduced pressure to give the crude compound ethyl-2-(alkylsulphonyloxy) alkanoate (6–10) which was used in the next step without any purification. AlCl3 (10.20 mmol) was added to isobutylbenzene, Neopentylbenzene or 2,3-dimethyl-2,3-diphenyl butane (11–
13) (20.41 mmol) at 0 °C. Ethyl-2-(alkylsulphonyloxy) alkanoate (6–10) was added to the cold solution portion-wise and the mixture warmed to the room temperature. It was heated to 80 °C for 8 h, cooled to room temperature, quenched with 5 % HCl solution, extracted with ethyl acetate, dried over anhydrous Na2SO4 and concentrated under the reduced pressure to give the crude compound ethyl 2-(4-alkylphenyl)-2-alkylalkanoate (14–20). Finally, KOH (479 mg, 8.55 mmol) in 5 ml of water was added to a solution of 14–20 (7 mmol) in 6 ml of MeOH. The resultant solution was stirred at room temperature for 4 h. Methanol was removed under reduced pressure, extracted with ethyl acetate, acidified, water-washed, dried over anhydrous Na2SO4 and concentrated under the reduced pressure to give the desired compounds 2-(4-alkylphenyl)-2-alkylalkanoic acid (II–VII).
Compound II
Dark brown viscous liquid; Yield 51 %; IR (KBr, νmax, cm − 1): 2 987, 1 750, 1 590, 1 443, 1 385, 1 232, 946, 774; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.82–1.96 (12 H, m), 2.37–2.52 (1 H, m), 3.13–4.02 (2 H, m), 7–7.33 (4 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 22.1, 27.4, 29.6, 44.1, 59.7, 126.2, 127.9, 129.2, 140.8, 179.2; Found ( %): C, 76.43; H, 9.2; C14H20O2. Anal. calcd. ( %): C, 76.33; H, 9.15; Mass spectrum, m/z (Irel, %): 220 (51), 205 (6), 177 (20), 175 (100), 161 (12), 147 (16), 133 (57), 131 (60), 119 (70), 105 (36), 91 (66), 73 (60), 57 (56).
Compound III
Dark brown viscous liquid; Yield 48 %; IR (KBr, νmax, cm − 1): 2 956, 1 737, 1 633, 1 465, 1 387, 1 211, 1 166, 1 045, 872; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.9–0.99 (9 H, m), 1.27–2.70 (9 H, m), 4.31–4.36 (1 H, m), 6.99–7.3 (4 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 13.9, 22.8, 28.1, 29.7, 30.3, 45.5, 76.6, 127.8, 129.4, 138.8, 146.7, 175.6; Found ( %): C, 77.46; H, 9.78; C16H24O2. Anal. calcd. ( %): C, 77.38; H, 9.74; Mass spectrum, m/z (Irel, %): 248 (84), 205 (33), 192 (13), 191 (11), 175 (23), 161 (100), 148 (39), 145 (40), 131 (39), 117 (86), 105 (64), 91 (92).
Compound IV
Dark brown solid; m. p. 71 °C; Yield 62 %; IR (KBr, νmax, cm–1): 2 956, 1 736, 1 574, 1 412, 1 376, 1 265, 1 168, 1 020, 934, 875; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.8–0.86 (4 H, m), 1.16–1.23 (9 H, m), 1.47–2.49 (4 H, m), 3.87–4.42 (5 H, m), 5.02 (1 H, m), 6.93–7.75 (4 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm):
C4H9 COOH
I
COOH
C6H13
II
COOH
III
Ph COOH
COOH
V
IV
COOH
COOH Ph VI
VII
Ahmadi A et al. New Chemical Entities from Ibuprofen … Drug Res 2015; 65: 457–462
Fig. 1 Structure formulas of 2-(p-isobutylphenyl) propionic acid (Ibuprofen, I), 2-(4-isobutylphenyl)2-methylpropanoic acid (II), 2-(4-isobutylphenyl) hexanoic acid (III), 2-(4-isobutylphenyl) octanoic acid (IV), 2-(4-isobutylphenyl)-2-phenylacetic acid (V), 2-(4-neopentylphenyl) propanoic acid (VI), 2-(4-(2,3-dimethyl-3-phenylbutan-2-yl)phenyl) propanoic acid (VII).
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based upon chemical modification of I are investigated with the aim of improving their safety profile [4, 7, 20–23]. In this research, the new analogues (II–V) with substituted acidic side chain (without changing the acidic groups) similar to ▶ Fig. the substituted aryl moiety (VI and VII) were synthesized ( ● 1). The analgesic effects of these novel compounds were evaluated in formalin (as a model of acute and chronic chemical pain) test on rats and the results were compared to the ibuprofen (the standard) and control (saline) groups.
Original Article
R1
Fig. 2 Synthesizing methods of final compounds (I–VII) and their intermediates (6–10 and 14–20).
OMs
OH
MsCl/Py
COOEt
R1
COOEt
R2
R2
1–5
6–10
459
+ R3 11–13
AlCl3 COOEt
COOH
R2
R2 R1
H+
R1
KOH / MeOH
R3
R3
R1
R2
R3
Intermediates
Final compounds
CH3
H
Isobutyl
6, 14
I
CH3
CH3
Isobutyl
7, 15
II
C4H9
H
Isobutyl
8, 16
III
C6H13
H
Isobutyl
9, 17
IV
Ph
H
Isobutyl
10, 18
V
CH3
H
Neopentyl
6, 19
VI
CH3
H
2,3-dimethyl-3-phenyl butyl
6, 20
VII
13.9, 22, 24.6, 28.4, 31.2, 34, 40.3, 69.5, 76.6, 126.7, 128.1, 134.5, 140.1, 175.9; Found ( %): C, 78.31; H, 10.26; C18H28O2. Anal. calcd. ( %): C, 78.21; H, 10.21. Mass spectrum, m/z (Irel, %): 276 (9), 233 (13), 205 (11), 191 (34), 175 (91), 161 (48), 147 (47), 131 (35), 117 (43), 105 (65), 91 (87), 57 (100).
Compound V
Dark brown viscous liquid; Yield 51 %; IR (KBr, νmax, cm–1): 2 965, 1 724, 1 570, 1 460, 1 362, 1 245, 1 184, 935, 718; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.87–1.27 (6 H, m), 2.44–2.46 (1 H, m), 3.41–4.21 (3 H, m), 5.37 (1 H, m), 7.21–7.5 (9 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 14.1, 22.4, 22.6, 29.7, 30.4, 45, 52.8, 127.9, 129.3, 135.5, 140.9, 178.2; Found ( %): C, 80.64; H, 7.55; C18H20O2. Anal. calcd. ( %): C, 80.56; H, 7.51; Mass spectrum, m/z (Irel, %): 268 (97), 223 (100), 225 (97), 207 (8), 191 (8), 181 (78), 167 (72), 165 (95), 145 (31), 133 (14), 115 (15), 105 (34), 91 (43), 77 (24), 57 (24).
Compound VI
Dark brown viscous liquid; Yield 41 %; IR (KBr, νmax, cm–1): 2 952, 1 708, 1 604, 1 461, 1 414, 1 364, 1 236, 1 077, 938, 726; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.88–0.98 (9 H, m), 1.37–1.44 (3 H, m), 2.48–2.81 (2 H, m), 3.39–3.73 (1 H, m), 7.05–7.26 (4 H, m); 13 1 C{ H}NMR spectrum in CDCl3 (δ, ppm): 15.6, 29.2, 30.6, 45.6, 50.5, 129.7, 130.4, 132.8, 141.5, 175.9; Found ( %): C, 76.42; H, 9.20; C14H20O2. Anal. calcd. ( %): C, 76.33; H, 9.15; Mass spectrum, m/z (Irel, %): 220 (23), 191 (5), 178 (20), 164 (90), 119 (84), 105 (9), 91 (44), 71 (19), 57 (100).
Compound VII
Light brown solid; m. p. 122 °C; Yield 52 %; IR (KBr, νmax, cm–1): 2 975, 1 707, 1 599, 1 496, 1 442, 1 379, 1 223, 1 029, 974, 774; 1 H NMR spectrum in CDCl3 (δ, ppm): 1.3 (15 H, m), 4.24–4.28 (1 H, m), 6.82–7.62 (9 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 25.7, 29, 30.6, 44.2, 126.2, 127.4, 128.2, 129.2, 132.4, 147.5, 152.1, 205.9; Found ( %): C, 81.35; H, 8.49; C21H26O2. Anal. calcd. ( %): C, 81.25; H, 8.44; Mass spectrum, m/z (Irel, %): 310 (5), 295 (5), 265 (16), 277 (8), 251 (16), 237 (32), 221 (16), 209 (12), 195 (16), 181 (16), 159 (18), 145 (20), 133 (24), 119 (100), 105 (60), 91 (90), 77 (13), 57 (8).
Animals
53 adult male wistar rats (Pasteur Institute, Tehran, Iran) weighing 220 ± 20 g at the beginning of the experiment were randomly housed 4 per cage in a temperature-controlled colony room under the 12 h light/dark cycle. Animals were given free access to water and standard laboratory rat chow (Pars Company, Tehran, Iran). All behavioral experiments were carried out between 9 am–4 pm under the normal room light and at 25 °C. This study was carried out in accordance with the guidelines set forth in the Guide for the Care and Use of Laboratory Animals (NIH) and those in the Research Council of Shahid Beheshti University of Medical Sciences, Tehran, Iran.
The formalin test
Rats were pretreated with the test compounds or vehicle (control group) 30 min before the initiation of the pain test. The test compounds were dissolved in DMSO. The volume of injection was 10 ml/kg. In the treatment groups, ibuprofen and their
Ahmadi A et al. New Chemical Entities from Ibuprofen … Drug Res 2015; 65: 457–462
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14–20
I–VII
460 Original Article
Statistical analysis
Data were presented as means ± S.E.M. Statistical analysis was conducted with Graphpad Prism software, Version 5. Comparisons were carried out using one-way Analysis of Variance (ANOVA) followed by Dunnett’s post test. A p-value less than 0.05 was considered as the level of significance.
Results
▼
Chemistry
The synthetic strategy of the title compounds was outlined in the ● ▶ Fig. 2. Ethyl-2-(alkylsulphonyloxy) alkanoates (6–10) were prepared according to the published method [24] using ethyl 2-hydroxyalkanoates and mesyl chloride (MsCl) in dry dichloromethane. Reaction of these intermediates with a mixture of various alkylbenzenes and AlCl3 yielded ethyl 2-(4-alkylphenyl)-2-alkylalkanoates (14–20) was examined. Finally the desired drugs (I–VII) were prepared with these intermediates reacting to KOH in MeOH and acidifying the ester products. In this research, 2-propanoic acid moiety was replaced by substituted alkyl and phenyl acids for obtaining II–V. Also isobutylbenzene was replaced by neopentylbenzene and 2,3-dimethyl-2,3-diphenyl butane for investigating the alkyl and phenyl increase in the hydrophobic terminal chain on the central aryl moiety of the molecule in analgesic activities of VI and VII. Spectroscopic (IR, 1 H and 13C-NMR, Mass) and elemental (CH) data confirmed the structure of the newly synthesized compounds. The purity of every compound was checked by TLC with ethyl acetate-hexane as the eluent.
Pharmacology Analgesic activity of ibuprofen and its newly synthesized derivatives in formalin test
One-way ANOVA revealed a significant change in the AUC of pain score between groups [F(7,45) = 3.83, p = 0.0024; ● ▶ Fig. 3. Further analysis in Dunnett’s multiple comparison post test showed that ibuprofen (I) and compound VII (p
457
Synthesis and Pharmacological Evaluation of New Chemical Entities from Ibuprofen as Novel Analgesic Candidates
Authors
A. Ahmadi1, N. Naderi2, M. Daniali1, S. Kazemi1, S. Aazami1, N. Alizadeh1, B. Nahri-Niknafs1
Affiliations
1
2
Key words ▶ NSAIDs ● ▶ ibuprofen ● ▶ analgesic ● ▶ modified aromatic and ● aliphatic moieties
Abstract
▼
Non-steroidal anti-inflammatory drugs (NSAIDs) are the first choice of drugs that are normally used for the treatment of pain and inflammation. Ibuprofen (I) and its analogues as the most widely used NSAIDs have been synthesized in recent years. In an effort to establish new candidates with improved analgesic properties, derivatives (II–VII) with substituted aromatic as
Introduction
▼
received 17.04.2014 accepted 05.05.2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1376976 Published online: May 28, 2014 Drug Res 2015; 65: 457–462 © Georg Thieme Verlag KG Stuttgart · New York ISSN 2194-9379 Correspondence Dr. A. Ahmadi, Associate professor Department of Chemistry Faculty of Science Islamic Azad University P.O.Box: 31485-313 Karaj Iran Tel.: + 98/26/34403 575 Fax: + 98/26/34403 575 [email protected] [email protected]
During the last 3 decades the development of non-steroidal anti-inflammatory drugs (NSAIDs) has shown to be one of the major advancements in chemotherapeutical research [1]. These agents are among the most widely used drugs worldwide and represent a mainstay in the therapy of acute and chronic pain, fever and inflammation by blocking the formation of Prostaglandins (PGs). PGs are well-known as the mediators of inflammation, pain and swelling. They are produced by the action of cyclooxygenase (COX) enzyme on arachidonic acid. COX is the principal target of NSAIDs. This enzyme exists as 2 isoforms of constitutive (COX-1) and inducible (COX-2). COX-1 is constitutively expressed and provides cytoprotection to the gastrointestinal (GI) tract while COX-2 is inducible and mediates inflammation. The traditional NSAIDs show greater selectivity for COX-1 than COX-2 [2–4]. The NSAIDs’ use is frequently associated with a broad spectrum of adverse effects of gastrointestinal (GI), renal and hepatic which are usually observed in patients undergoing long-term treatment. Therefore, the development of new NSAIDs without these side effects has long been awaited. Selective COX-2 inhibitors that ‘coxib’ with better safety profile have been marketed as the new generation of these drugs which were rapidly
well as aliphatic moieties were synthesized in this experiment and evaluated in formalin test with rats. The results were compared to ibuprofen and control groups. Findings indicated that derivatives with new alkylphenyl rings (VI and VII) had some similar or more analgesic activities relative to the control and ibuprofen groups, respectively; which could be justified as to more alkyl and phenyl groups instead of p-isobutylphenyl moiety in I.
introduced to the market and gained an impressive success. The serious cardiovascular effects by some, however, caused the drugs to become withdrawn from the market. Producing effective NSAIDs with an improved safety profile that eliminate the disadvantages of selective COX-2 inhibitors and spare the gastrointestinal mucosa remains as a compelling need. An alternative strategy to limit the risk of GI damage induced by NSAIDs is to enhance the protective mechanisms of the gastric mucosa [5, 6]. An important group of these drugs is the class of 2-arylpropionic acids (Profen family) which are able to reduce inflammation and pain. Ibuprofen (2-p-isobutylphenyl propionic acid, I) belongs to this class and uses to relieve the symptoms of a wide range of illness such as headache, backache, period pain, dental pain, neuralgia, rheumatic pain, muscular pain, migraine, cold and flu symptoms and arthritis [5, 7–10]. A broad variety of this compound has been synthesized with manifold synthetic methodologies [11–19] but its prolonged usage (similar to other NSAIDs) has been associated to gastrointestinal complications ranging from stomach irritation to life-threatening GI ulceration bleeding and nephrotoxicity. Therefore, the search for some brand new analgesic and anti-inflammatory agents devoid of side effects continues to be an active area of research in medicinal chemistry. Similarly, the synthetic approaches
Ahmadi A et al. New Chemical Entities from Ibuprofen … Drug Res 2015; 65: 457–462
Downloaded by: University of Liverpool. Copyrighted material.
Department of Chemistry, Faculty of Science, Karaj Branch, Islamic Azad University, Karaj, Iran Department of Pharmacology and Toxicology, School of Pharmacy, Shahid Beheshti University of Medical Sciences, Tehran, Iran
458 Original Article
Experimental
▼
Material and equipments
All chemicals were purchased from Merck and Aldrich Chemical Companies. Melting points (uncorrected) were determined with a digital Electro Thermal Melting Point apparatus (model 9100, Electrothermal Engineering Ltd., Essex, UK). 1 H and 13C NMR spectra were recorded with a Bruker 400 MHz (AMX model, Karlsruhe, Germany) spectrometer. IR spectra were recorded with a Thermo Nicolet FT-IR (Nexus-870 model, Nicolet Instrument Corp, Madison, Wisconsin, USA) spectrophotometer. Mass spectra were recorded with an Agilent Technologies 5 973, Mass Selective Detector (MSD) spectrometer (Wilmington, USA). Elemental analyses were carried out with a Perkin-Elmer, CHN elemental analyzer model 2 400. Compound I was synthesized according to a published method [24]. ▶ Fig. 2) Preparations ( ● Compounds II–VII
To a solution of ethyl lactate, ethyl 2-hydroxyhexanoate, ethyl 2-hydroxyoctanoate, Ethyl mandelate or ethyl 2-hydroxy-2methylpropanoate (1–5) (8.47 mmol) and triethylamine (12.71 mmol) in 15 ml of dry dichloromethane was added portion-wise MsCl (9.32 mmol) at 0 °C. The resultant mixture was stirred at 0 °C for an hour and left at room temperature for 2 h. After completion of the reaction, as indicated by TLC, the reaction mixture was diluted with ethyl acetate, water-washed, dried over anhydrous Na2SO4 and concentrated under reduced pressure to give the crude compound ethyl-2-(alkylsulphonyloxy) alkanoate (6–10) which was used in the next step without any purification. AlCl3 (10.20 mmol) was added to isobutylbenzene, Neopentylbenzene or 2,3-dimethyl-2,3-diphenyl butane (11–
13) (20.41 mmol) at 0 °C. Ethyl-2-(alkylsulphonyloxy) alkanoate (6–10) was added to the cold solution portion-wise and the mixture warmed to the room temperature. It was heated to 80 °C for 8 h, cooled to room temperature, quenched with 5 % HCl solution, extracted with ethyl acetate, dried over anhydrous Na2SO4 and concentrated under the reduced pressure to give the crude compound ethyl 2-(4-alkylphenyl)-2-alkylalkanoate (14–20). Finally, KOH (479 mg, 8.55 mmol) in 5 ml of water was added to a solution of 14–20 (7 mmol) in 6 ml of MeOH. The resultant solution was stirred at room temperature for 4 h. Methanol was removed under reduced pressure, extracted with ethyl acetate, acidified, water-washed, dried over anhydrous Na2SO4 and concentrated under the reduced pressure to give the desired compounds 2-(4-alkylphenyl)-2-alkylalkanoic acid (II–VII).
Compound II
Dark brown viscous liquid; Yield 51 %; IR (KBr, νmax, cm − 1): 2 987, 1 750, 1 590, 1 443, 1 385, 1 232, 946, 774; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.82–1.96 (12 H, m), 2.37–2.52 (1 H, m), 3.13–4.02 (2 H, m), 7–7.33 (4 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 22.1, 27.4, 29.6, 44.1, 59.7, 126.2, 127.9, 129.2, 140.8, 179.2; Found ( %): C, 76.43; H, 9.2; C14H20O2. Anal. calcd. ( %): C, 76.33; H, 9.15; Mass spectrum, m/z (Irel, %): 220 (51), 205 (6), 177 (20), 175 (100), 161 (12), 147 (16), 133 (57), 131 (60), 119 (70), 105 (36), 91 (66), 73 (60), 57 (56).
Compound III
Dark brown viscous liquid; Yield 48 %; IR (KBr, νmax, cm − 1): 2 956, 1 737, 1 633, 1 465, 1 387, 1 211, 1 166, 1 045, 872; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.9–0.99 (9 H, m), 1.27–2.70 (9 H, m), 4.31–4.36 (1 H, m), 6.99–7.3 (4 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 13.9, 22.8, 28.1, 29.7, 30.3, 45.5, 76.6, 127.8, 129.4, 138.8, 146.7, 175.6; Found ( %): C, 77.46; H, 9.78; C16H24O2. Anal. calcd. ( %): C, 77.38; H, 9.74; Mass spectrum, m/z (Irel, %): 248 (84), 205 (33), 192 (13), 191 (11), 175 (23), 161 (100), 148 (39), 145 (40), 131 (39), 117 (86), 105 (64), 91 (92).
Compound IV
Dark brown solid; m. p. 71 °C; Yield 62 %; IR (KBr, νmax, cm–1): 2 956, 1 736, 1 574, 1 412, 1 376, 1 265, 1 168, 1 020, 934, 875; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.8–0.86 (4 H, m), 1.16–1.23 (9 H, m), 1.47–2.49 (4 H, m), 3.87–4.42 (5 H, m), 5.02 (1 H, m), 6.93–7.75 (4 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm):
C4H9 COOH
I
COOH
C6H13
II
COOH
III
Ph COOH
COOH
V
IV
COOH
COOH Ph VI
VII
Ahmadi A et al. New Chemical Entities from Ibuprofen … Drug Res 2015; 65: 457–462
Fig. 1 Structure formulas of 2-(p-isobutylphenyl) propionic acid (Ibuprofen, I), 2-(4-isobutylphenyl)2-methylpropanoic acid (II), 2-(4-isobutylphenyl) hexanoic acid (III), 2-(4-isobutylphenyl) octanoic acid (IV), 2-(4-isobutylphenyl)-2-phenylacetic acid (V), 2-(4-neopentylphenyl) propanoic acid (VI), 2-(4-(2,3-dimethyl-3-phenylbutan-2-yl)phenyl) propanoic acid (VII).
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based upon chemical modification of I are investigated with the aim of improving their safety profile [4, 7, 20–23]. In this research, the new analogues (II–V) with substituted acidic side chain (without changing the acidic groups) similar to ▶ Fig. the substituted aryl moiety (VI and VII) were synthesized ( ● 1). The analgesic effects of these novel compounds were evaluated in formalin (as a model of acute and chronic chemical pain) test on rats and the results were compared to the ibuprofen (the standard) and control (saline) groups.
Original Article
R1
Fig. 2 Synthesizing methods of final compounds (I–VII) and their intermediates (6–10 and 14–20).
OMs
OH
MsCl/Py
COOEt
R1
COOEt
R2
R2
1–5
6–10
459
+ R3 11–13
AlCl3 COOEt
COOH
R2
R2 R1
H+
R1
KOH / MeOH
R3
R3
R1
R2
R3
Intermediates
Final compounds
CH3
H
Isobutyl
6, 14
I
CH3
CH3
Isobutyl
7, 15
II
C4H9
H
Isobutyl
8, 16
III
C6H13
H
Isobutyl
9, 17
IV
Ph
H
Isobutyl
10, 18
V
CH3
H
Neopentyl
6, 19
VI
CH3
H
2,3-dimethyl-3-phenyl butyl
6, 20
VII
13.9, 22, 24.6, 28.4, 31.2, 34, 40.3, 69.5, 76.6, 126.7, 128.1, 134.5, 140.1, 175.9; Found ( %): C, 78.31; H, 10.26; C18H28O2. Anal. calcd. ( %): C, 78.21; H, 10.21. Mass spectrum, m/z (Irel, %): 276 (9), 233 (13), 205 (11), 191 (34), 175 (91), 161 (48), 147 (47), 131 (35), 117 (43), 105 (65), 91 (87), 57 (100).
Compound V
Dark brown viscous liquid; Yield 51 %; IR (KBr, νmax, cm–1): 2 965, 1 724, 1 570, 1 460, 1 362, 1 245, 1 184, 935, 718; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.87–1.27 (6 H, m), 2.44–2.46 (1 H, m), 3.41–4.21 (3 H, m), 5.37 (1 H, m), 7.21–7.5 (9 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 14.1, 22.4, 22.6, 29.7, 30.4, 45, 52.8, 127.9, 129.3, 135.5, 140.9, 178.2; Found ( %): C, 80.64; H, 7.55; C18H20O2. Anal. calcd. ( %): C, 80.56; H, 7.51; Mass spectrum, m/z (Irel, %): 268 (97), 223 (100), 225 (97), 207 (8), 191 (8), 181 (78), 167 (72), 165 (95), 145 (31), 133 (14), 115 (15), 105 (34), 91 (43), 77 (24), 57 (24).
Compound VI
Dark brown viscous liquid; Yield 41 %; IR (KBr, νmax, cm–1): 2 952, 1 708, 1 604, 1 461, 1 414, 1 364, 1 236, 1 077, 938, 726; 1 H NMR spectrum in CDCl3 (δ, ppm): 0.88–0.98 (9 H, m), 1.37–1.44 (3 H, m), 2.48–2.81 (2 H, m), 3.39–3.73 (1 H, m), 7.05–7.26 (4 H, m); 13 1 C{ H}NMR spectrum in CDCl3 (δ, ppm): 15.6, 29.2, 30.6, 45.6, 50.5, 129.7, 130.4, 132.8, 141.5, 175.9; Found ( %): C, 76.42; H, 9.20; C14H20O2. Anal. calcd. ( %): C, 76.33; H, 9.15; Mass spectrum, m/z (Irel, %): 220 (23), 191 (5), 178 (20), 164 (90), 119 (84), 105 (9), 91 (44), 71 (19), 57 (100).
Compound VII
Light brown solid; m. p. 122 °C; Yield 52 %; IR (KBr, νmax, cm–1): 2 975, 1 707, 1 599, 1 496, 1 442, 1 379, 1 223, 1 029, 974, 774; 1 H NMR spectrum in CDCl3 (δ, ppm): 1.3 (15 H, m), 4.24–4.28 (1 H, m), 6.82–7.62 (9 H, m); 13C{1 H}NMR spectrum in CDCl3 (δ, ppm): 25.7, 29, 30.6, 44.2, 126.2, 127.4, 128.2, 129.2, 132.4, 147.5, 152.1, 205.9; Found ( %): C, 81.35; H, 8.49; C21H26O2. Anal. calcd. ( %): C, 81.25; H, 8.44; Mass spectrum, m/z (Irel, %): 310 (5), 295 (5), 265 (16), 277 (8), 251 (16), 237 (32), 221 (16), 209 (12), 195 (16), 181 (16), 159 (18), 145 (20), 133 (24), 119 (100), 105 (60), 91 (90), 77 (13), 57 (8).
Animals
53 adult male wistar rats (Pasteur Institute, Tehran, Iran) weighing 220 ± 20 g at the beginning of the experiment were randomly housed 4 per cage in a temperature-controlled colony room under the 12 h light/dark cycle. Animals were given free access to water and standard laboratory rat chow (Pars Company, Tehran, Iran). All behavioral experiments were carried out between 9 am–4 pm under the normal room light and at 25 °C. This study was carried out in accordance with the guidelines set forth in the Guide for the Care and Use of Laboratory Animals (NIH) and those in the Research Council of Shahid Beheshti University of Medical Sciences, Tehran, Iran.
The formalin test
Rats were pretreated with the test compounds or vehicle (control group) 30 min before the initiation of the pain test. The test compounds were dissolved in DMSO. The volume of injection was 10 ml/kg. In the treatment groups, ibuprofen and their
Ahmadi A et al. New Chemical Entities from Ibuprofen … Drug Res 2015; 65: 457–462
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14–20
I–VII
460 Original Article
Statistical analysis
Data were presented as means ± S.E.M. Statistical analysis was conducted with Graphpad Prism software, Version 5. Comparisons were carried out using one-way Analysis of Variance (ANOVA) followed by Dunnett’s post test. A p-value less than 0.05 was considered as the level of significance.
Results
▼
Chemistry
The synthetic strategy of the title compounds was outlined in the ● ▶ Fig. 2. Ethyl-2-(alkylsulphonyloxy) alkanoates (6–10) were prepared according to the published method [24] using ethyl 2-hydroxyalkanoates and mesyl chloride (MsCl) in dry dichloromethane. Reaction of these intermediates with a mixture of various alkylbenzenes and AlCl3 yielded ethyl 2-(4-alkylphenyl)-2-alkylalkanoates (14–20) was examined. Finally the desired drugs (I–VII) were prepared with these intermediates reacting to KOH in MeOH and acidifying the ester products. In this research, 2-propanoic acid moiety was replaced by substituted alkyl and phenyl acids for obtaining II–V. Also isobutylbenzene was replaced by neopentylbenzene and 2,3-dimethyl-2,3-diphenyl butane for investigating the alkyl and phenyl increase in the hydrophobic terminal chain on the central aryl moiety of the molecule in analgesic activities of VI and VII. Spectroscopic (IR, 1 H and 13C-NMR, Mass) and elemental (CH) data confirmed the structure of the newly synthesized compounds. The purity of every compound was checked by TLC with ethyl acetate-hexane as the eluent.
Pharmacology Analgesic activity of ibuprofen and its newly synthesized derivatives in formalin test
One-way ANOVA revealed a significant change in the AUC of pain score between groups [F(7,45) = 3.83, p = 0.0024; ● ▶ Fig. 3. Further analysis in Dunnett’s multiple comparison post test showed that ibuprofen (I) and compound VII (p
