Synthesis and pharmacological screening of some benzoxazole derivatives as an anti inflammatory agents

Publication Ref No.: IJPRD/2010/PUB/ARTI/VOV-2/ISSUE-9/NOV/024 ISSN 0974 – 9446

SYNTHESIS AND PHARMACOLOGICAL SCREENING OF SOME BENZOXAZOLE DERIVATIVES
AS AN ANTI-INFLAMMATORY AGENTS

Sunila T. Patil1* , Dr.Parloop A. Bhatt2
1
Research Scholar Jodhpur National University,
Jodhpur-342003, Rajasthan, India.
2
L. M. College of Pharmacy, Ahmedabad-380009,
Gujrat, India.
Sunila Patil Email:Devanshu31@gmail.com

ABSTRACT

The main objective of the medicinal chemistry is to synthesize the compounds that show promising
activity as therapeutic agents with lower toxicity. Benzoxazole derivatives are very useful compound
with well known biological activity. Notable among these are antibacterial, antiviral ,antifungal,
analgesic, anti-inflammatory and antitubercular. In the current research work, the title compounds
N`[substituted sulfonyl]-1,3-benzoxazole-5-carbohydrazide, were synthesized by electrophilic aromatic
substitution on p-hydroxy methyl benzoate (I) with concentrated nitric acid and concentrated sulfuric
acid under reflux condition. Compound (II) on reduction with sodium dithionate with alcohol gives 3-
amino-4-hydroxy-benzoic acid methyl ester (III). Reaction of compound (III) with two appropriate
aliphatic acids (formic acid and acetic acid) produced corresponding 2-subtituted benzoxazole-5-
carboxylic acid methyl esters. The reaction of compounds (IV) with hydrazine hydrate in ethanol on
refluxing yielded the corresponding 2-substituted benzoxazole-5-carboxylic acid hydrazides. On further
reaction of compounds (V) with the different sulfonyl chloride derivatives afforded the corresponding
eight N`[substituted sulfonyl]-1,3-benzoxazole-5-carbohydrazide. The identification and characterization
of the synthesized compounds were carried out by Elemental analysis, melting point,Thin Layer
Chromatography, FT-IR, NMR and Mass data to ascertain that all synthesized compounds were of
different chemical nature than the respective parent compound. The compounds were screened for
anti-inflammatory activity. The antiinflammatory activity of compounds was done by using carrageenan
induced rat paw edema method. The test compounds VIa, VId and VIe showed significant
antiinflammatory activity compared with the standard drug Ibuprofen.

Key Words: Anti-inflammatory activity. Benzoxazole, Carrageenan, Ibuprofen..

INTRODUCTION The main objective of the medicinal chemistry is
to synthesize the compounds that show

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promising activity as therapeutic agents with compounds were also subjected to C, H, N and
lower toxicity. Benzoxazoles have been S analysis(ThermoFinnigan) at IIT Mumbai.
reported to show a broad spectrum of biological scheme of synthesis
activities. Notable among these are
antihistaminic [1], antifungal[2], Cyclooxygenase COOCH3
Inhibiting[3], antitumor[4], antiulcer[5],
anticonvulsant[6], hypoglycemic[7], anti-
inflammatory[8,9] and antitubercular activity[10].
The pharmacological properties of HO
Benzoxazoles encouraged our interest in (I)
synthesizing several new compounds. In the Methyl p-hydroxy benzoate (I)
present study we synthesized a series of some
novel eight derivatives of N`[substituted
sulfonyl]-1,3-benzoxazole-5-carbohydrazide. H2SO4,HNO3
The compounds were screened for Anti- (0-15o)
inflammatory Activity.

CONHNHSO2R2 O2N COOCH3
N

R1

O HO
N`[substituted sulfonyl]-1,3-benzoxazole-5- (II)
carbohydrazide 4-Hydroxy-3-nitro-benzoic acid methyl ester (II)

MATERIALS AND METHODS Na2S2O4,H2O
Reflux,1.5h
All the reagents and solvents used were of
laboratory grade. The melting points of H2N COOCH3
synthesized compounds were determined by
open capillary method and were uncorrected.
The purity and homogeneity of compounds
were checked using TLC technique. IR HO
spectra[11] of compounds were recorded using (III)
KBr pellets on Perkin Elmer 337 3-Amino-4-hydroxy-benzoic acid methyl ester
spectrophotometer. 1H-NMR spectra[12] were (III)
recorded on Bruker Avance-300 MHz
R1COOH
Spectrophotometer using dimethyl sulfoxamide
as solvent at Indian Institute of Technology(IIT), Reflux, 2h
Mumbai. Mass Spectra of the synthesized
compounds were recorded on Liquid
Chromatography Mass Spectrometer at Indian
Institute of Technology(IIT), Mumbai. The

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COOCH3 N`[substituted sulfonyl]-1,3-benzoxazole-5-
N
carbohydrazide
R1 • Synthesis and Characterization of
Compounds:
O
(IV) 1) 4-Hydroxy-3-nitro-benzoic acid methyl
2-subtituted benzoxazole-5-carboxylic acid ester (II)
methyl ester (IV)
In a 1 lit. three necked round bottom
NH2NH2, H2O
Ethanol flask equipped with water condenser,
Reflux, 4h mechanical stirrer and thermometer, of p-
hydroxy methyl benzoate (10 g, 0.74 mol) was
CONHNH2 placed. A mixture of concentrated suphuric acid
N
(6.2 ml) and concentrated nitric acid (6.2 ml) in
R1 a dropping funnel, cool the flask in an ice bath
to 0-10ْ° and then run in the nitrating mixture in
O
p-hydroxy methyl benzoate with stirring, while
(V) maintaining the temperature of the reaction
2-substituted benzoxazole-5-carboxylic acid between 5 to 15° the addition continued upto 1
;
hydrazide (V) h. Poured the reaction mixture in to of crushed
R2SO2Cl ice (70 g). Filtered off the crude m-nitro, p-
Dry Pyridine hydroxy methyl benzoate at the pump and wash
0-10o, 2h with cold water. Transfer the solids into 500 ml
CONHNHSO2R2 flask and stirred it with ice cold methanol in
N
order to remove a small amount of ortho isomer
R1 and other impurities. The mixture was filtered
with suction and washed with little methanol and
O dried in the air. Then the product was
(VI) recrystallised using methanol as solvent.
Percentage Yield- 84%, M.P. 65-67° Rf-0.76
,
N`[substituted sulfonyl]-1,3-benzoxazole-5- (Ethyl acetate: methanol, 1:1),
carbohydrazide
۫2) 3-Amino-4-hydroxy-benzoic acid methyl
Lead Nucleus with Different substituents (R1 ester (III)
and R2) were summarized in Table No.1:
In a 500 ml three necked flat bottom flask
equipped with reflux condenser with guard tube,
compound II (10 g) was dissolved in boiling
alcohol (50%, 100 ml) and sodium dithionate
was added to this boiling alcohol solution until it
CONHNHSO2R2 becomes almost colorless. Then the alcohol
N
was reduced to one third of its volume by
R1 distillation and the residual liquid was triturated
with ice cold water. The resulting colorless,
O shiny product was filtered, washed with cold

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water, dried and recrystalise using methanol as b) 2-methyl-benzoxazole-5-carboxylic acid
solvent. hydrazide (Vb)
Percentage Yield- 70%, M.P. 110-112° Rf- , Percentage Yield- 80%, M.P. 144-146°C, R-
0.67 (Saturated methanol), f -0.7 (Methanol)

3) 2-subtituted benzoxazole-5-carboxylic 5) N`[substituted sulfonyl]-1,3-benzoxazole-
acid methyl ester (IV) 5-carbohydrazide (VIa-h)
Compound III (0.01mol) was heated with an To a cooled and stirred solution of compound
appropriate aliphatic acid (formic acid and VIa and VIb (4 g) in pyridine (25 ml) toluene
acetic acid) in excess under reflux for 2h. The sulfonyl chloride was slowly added (3.8 ml).
reaction mixture was cooled and poured in After two hours the solution was poured into
crushed ice (100 gm) with stirring. The product mixture of ice and concentrated hydrochloride
thus separated was filtered under suction and acid and water; the pale yellow colored
washed with cold water. The products were precipitate was recovered. Washed with dilute
recrystallised by using methanol as a solvent. hydrochloric acid and water, and was
The following two compounds were prepared by recrystallised using ethanol as a solvent.
the above mentioned procedure,

a) Benzoxazole-5-carboxylic acid methyl Compound (VIa)
ester (IVa) N`[(4-methyl phenyl)sulfonyl]-1,3-
Percentage Yield- 80%, M.P.74-76°C, Rf- benzoxazole-5-carbohydrazide.
0.7 (Saturated methanol), Percentage Yield- 38%, M.P. 72-74° , Rf-0.63
C
b) 2-methyl-benzoxazole-5-carboxylic acid (Ethanol:Ethyl acetate)
methyl ester (IVb) IR (KBr) cm-1: 3390 (-NH- str.), 1315 and 1398
Percentage Yield- 60%, M.P. 70-72°C, Rf- (-S-O str.), 1730 (-CO- str.), 1625 (C=N str.),
0.7 (Saturated methanol), 3085 (Ar–H str.), 835 (C=C bending), 1165
4) 2-substituted benzoxazole-5-carboxylic (ether group in ring);
acid hydrazide (V) 1
H NMR: (CDCl3) δ 7.34-7.95 (m, 8H), δ 8.0 (s,
A mixture of an appropriate 2-subtituted 2H), δ 2.35 (d, 3H).
benzoxazole-5-carboxylic acid methyl ester IV FAB-MS: (m/z, 100%): 331 (M+).
(0.001 mol) in alcohol (25 ml) and hydrazine
hydrate (99%, 0.015 mol) was heated under Compound (VIb)
reflux on water bath for 4 hours. The alcohol N`[(4-methyl phenyl)sulfonyl]-1,3-
was reduced to half of its volume and cooled. benzoxazole- 2-methyl-5-carbohydrazide.
The product separated was filtered and washed Percentage Yield- 57%, M.P. 78-80° , Rf-0.60
C
with small portions of cold alcohol and then with (Ethanol:Ethyl acetate)
cold water, repeatedly and dried. The resultant IR (KBr) cm-1: 3319 (-NH- str.), 1315 (-S-O
product was recrystallised using methanol as str.), 1730 (-CO- str.), 1625 (C=N str.), 3010
solvent. Using above mentioned procedure (Ar–H str.), 2230 (C-C str. );
following two compounds were synthesized. 1
H NMR: (CDCl3) δ 7.34-7.95 (m, 7H), δ 8.0 (s,
a) Benzoxazole-5-carboxylic acid hydrazide 2H), δ 2.35 (d, 6H).
(Va)
Percentage Yield- 90%, M.P. 108-110°C , R- Compound (VIc)
f -0.6 (Methanol)

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N`[(4-acetamido phenyl) sulfonyl]-1,3- N`[benzene sulfonyl]-1,3-benzoxazole-5-
benzoxazole-5-carbohydrazide. carbohydrazide.
Percentage Yield- 74%, M.P. 92-94° , Rf-0.57
C Percentage Yield- 30%, M.P. 68-70° , Rf-0.62
C
(Ethanol:Ethyl acetate) (Ethanol:Ethyl acetate)
IR (KBr) cm-1: 3327 (-NH- str.), 1352 (-S-O IR (KBr) cm-1: 3350 (-NH- str.), 1329 (-S-O
str.), 1730 (-CO- str.), 1116 and1172 (CONH str.), 1730 (-CO- str.), 3174 (CONH str.), 3097
str.), 3010 (Ar–H str.); (Ar–H str.), 674 (C-C bending).
1
H NMR: (CDCl3) δ 7.44-7.95(m, 8H), δ 8.0 (s, 1
H NMR: (CDCl3) δ 7.03-7.95 (m, Ar-H, 9H), δ
3H), δ 2.02 (d, 3H). 8.0 (s, 2H).

Compound (VId) Compound (VIh)
N`[(4-actamido phenyl) sulfonyl]-1,3- N`[benzene sulfonyl]-1,3-benzoxazole- 2-
benzoxazole-2-methyl-5-carbohydrazide. methyl-5-carbohydrazide.
Percentage Yield- 40%, M.P. 89-90° , Rf-0.54
C Percentage Yield- 40%, M.P. 66-68° , Rf-0.72
C
(Ethanol:Ethyl acetate) (Ethanol:Ethyl acetate)
IR (KBr) cm-1: 3324 (-NH- str.), 1322 (-S-O IR (KBr) cm-1: 3204 (-NH- str.), 1346 (-S-O
str.), 1730 (-CO- str.), 1629 (C=N str.), 3110 str.), 1730 (-CO- str.), 1625 (C=N str.), 3085
(Ar–H str.), 3180 (CONH str.), 1165 (ether in (Ar–H str.), 2990 (C-C str.), 1165 (ether group in
ring); ring);
1
H NMR: (CDCl3) δ 7.44-7.95 (m, 7H), δ 8.0 (s,
1
H NMR: (CDCl3) δ 7.03-7.95 (m, 8H), δ 8.0 (s,
3H), δ 2.02 and 2.35 (d, 6H). 2H), δ 2.35 (d, 3H).

Compound (VIe) • Physical data of compound. No. IIa-IIf were
N`[(4-chloro phenyl) sulfonyl]-1,3- summarized in Table No.2:
benzoxazole-5-carbohydrazide.
Percentage Yield- 75%, M.P. 110-112° , Rf- C • Elemental analysis of compound. No. IIa-IIl
0.53 (Ethanol:Ethyl acetate) were summarized in Table No.3:
IR (KBr): 3216 cm-1 (-NH- str.), 1339 cm-1 (-S-O
str.), 3090 cm-1 (Ar–H str.), 772 cm-1 (C-Cl str.)
Anti-inflammatory Activity:
1
H NMR: (CDCl3) δ 7.44-7.95 (m, Ar-H, 8H), δ
Carrageenan Induced Rat Paw Edema
8.0 (s, 2H).
Method[13]:
Compound (VIf)
Rats were divided into ten groups, each group
N`[(4-chloro phenyl) sulfonyl]-1,3-
contained six animals. They were starved
benzoxazole-2-methyl -5-carbohydrazide.
overnight with water prior to the day of
Percentage Yield- 72%, M.P. 102-104° , Rf-
C
experiment.
0.62 (Ethanol:Ethyl acetate)
The injection of 0.1ml of freshly prepared
IR (KBr) cm-1: 3204 (-NH- str.), 1354 and 1329
solution of carrageenan (1%) in physiological
(-S-O str.), 1730 (-CO- str.), 3180 (CONH str.),
saline (154 mmol/ml) NaCl was injected into
3097 (Ar–H str.), 767 (C-Cl str.),
subplantar region of the left hind paw of each
1
H NMR: (CDCl3) δ 7.44-7.95 (m, 7H), δ 8.0 (s, rat. Then, Selected compounds were
2H), δ 2.35 (d, 3H) suspended in 0.5% CMC and administered
orally (200 mg/kg) after 1h of carrageenan
Compound (VIg) dose.

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One group has been treated with Ibuprofen as
standard (50 mg/kg). The paw edema volume REFERENCES:
was measured with the help of plethysmograph
by mercury displacement method, at zero h 1] Kastura Y, Tnoue Y, Nishino S, Chem.
(Immediately after injecting carrageenan). Pharm.Bull., 40(6), 1992, 1424.
The same procedure was repeated at1h, 2 h 2] ismail Y, lkay O, Özlem T, Acta Biochimica
and 3 h. which was summarized in Table No.4. Polonica, 47, 2000, 481-486.
The difference between 1 h and subsequent 3] Shrinivasa R, Rao P, Kumar P, Bioorganic
hour readings was taken as actual edema and Medicinal Chemistry Letter, 13, 2003, 657-
volume. The percentage (%) inhibition of paw 660.
edema in the various treated groups was then 4] Aiello S, Wells G, Ston E, Kadri H, J. Med.
calculated by using the formula; Chem.,51, 2008, 5135-5139.
Percentage inhibition(%) = (1 – Vt/Vc ) X 100 5] Kastura Y, Inoue Y, Nishino S., Chem.
.... equation (1) Pharm. Bull., 40(6), 1992, 1424-1438.
Where, Vt = mean relative change in a paw 6] Siddiqui N, Sarafaroz M, Alam M, Ahsan W,
volume in test group. Polish Pharmaceiutical
Vc = mean relative change in paw Society, Acta Poloniae Pharmaceiutica-Drug
volume in control group Research, 65(4), 2008, 449-455.
7] Arakova K, Inamasu M, Masumoto M, Chem.
RESULTS AND DISCUSSION Pharm. Bull., 45(12), 1997, 1984.
8] Sondhi S, Singh N, Kumar A, Lozach O,
Antiinflammatory activity data were Bioorganic and Medicinal
summarized in Table No.5. Chemistry, 14(11), 2006, 3758-3765.
9] Unlu S, Baytas S, Kupeli E, Archives der
Inhibition of carrageenin-induced inflammation Pharmazie, 336(6-7), 2003, 310.
in rats is one of the most suitable test 10] Klimensova V, Koci J, Waisser K, Kaustova
procedures to screen anti-inflammatory agents. J, Dahse M, Bioorganic and
The development of carrageenin-induced Medicinal Chemistry Letters, 12, 2002,
oedema is bi-phasic, the first phase is attributed 3275-3278.
to the release of histamine, 5-HT and kinins, 11] Silverstein R.M, Morrill T.C,
while, the second phase is related to the Spectrophotometric Identification of Organic
release of prostaglandins. The test compounds Compounds, John Wiley and Sons, New
VIa, VId and VIe showed significant work, Edn.4th,1981,312.
antiinflammatory activity compared with the 12] Silverstein R.M, Morrill T.C,
standard drug Ibuprofen. Spectrophotometric Identification of Organic
Compounds, John Wiley and Sons, New
ACKNOWLEDGEMENT work, Edn.4th,1981,192.
13] Vogel H, Gehard H, Drug Discovery and
Authors are thankful to Jodhpur National Evaluation, Pharmacological
University, Jodhpur, Rajasthan, India for Assays, Springer-Verlag, Berlin Heidelberg,
providing necessary support for research New York, 2, 2002, 759.
purposed.

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TABLES AND FIGURES:

ILLUSTRATIONS

Table.No.1
COMPOUND R1 R2
VIa H Tosyl
VIb CH3 Tosyl
VIc H 4-aceta amido
VId CH3 4-aceta amido
VIe H 4-chloro
VIf CH3 4-chloro
VIg H Benzene
VIh CH3 Benzene

Table.No.2

Comp.
Rf value
No. R2 Molecular mp(0C) Yield(%)
VIa 4-methyl phenyl C15H13N3O4S 72-74 48% 0.63
VIb 4-methyl phenyl C16H15N3O4S 78-80 57% 0.60
VIc 4-aceta amido C16H14N4O5S 92-94 72% 0.57
VId 4-aceta amido C17H16N4O5S 88-90 40% 0.54
VIe 4-chloro C14H10ClN3O4S 110-112 75% 0.53
VIf 4-chloro C15H12ClN3O4S 102-104 72% 0.64
VIg Benzene C14H11N3O4S 69-70 38% 0.62
VIh Benzene C15H13N3O4S 66-68 40% 0.72

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Table.No.3

Elemental Analysis (%)
Compd R2 Molecular formula Calculated Found
No.
C H N C H N
VIa 4-methyl phenyl C15H13N3O4S 52.9 4.04 13.08 52.5 4.04 13.12
VIb 4-methyl phenyl C16H15N3O4S 55.6 4.34 12.07 55.2 4.38 12.11
VIc 4-aceta amido C16H14N4O5S 53.63 3.91 15.64 53.67 3.87 15.68
VId 4-aceta amido C17H16N4O5S 52.57 4.12 14.43 52.61 4.16 14.47
VIe 4-chloro C14H10ClN3O4S 45.94 2.94 12.37 45.90 2.98 12.41
VIf 4-chloro C15H12ClN3O4S 47.81 3.37 11.81 47.85 3,41 11.85
VIg Benzene C14H11N3O4S 51.31 3.28 13.81 51.35 3.32 13.85
VIh Benzene C15H13N3O4S 53.12 3.75 13.12 53.16 3.79 13.08

Table.No.4
No. of groups Treatment

Group- I Control
Group- II Ibuprofen 50 mg/kg
Group- III 1st derivative (200 mg/kg)
Group- IV 2nd derivative (200 mg/kg)
Group- V 3rd derivative (200 mg/kg)
Group- VI 4th derivative (200 mg/kg)
Group- VII 5th derivative (200 mg/kg)
Group- VIII 6th derivative (200 mg/kg)
Group- IX 7th derivative (200 mg/kg)
Group- X 8th derivative (200 mg/kg)

167

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Table.No.5

Group Test Material (dose) Mean increase in paw volume and % inhibition
1h 2h 3h
1. Control 0.44 + 0.00678 0.68 + 0.0091 0.76 + 0.0086

2. Standard 0.24 + 0.012 0.30 + 0.0085 0.38 + 0.0163
(Ibuprofen 50mg/kg) (43.1 %) (55.8 %) (49.3 %)
3. VIa 0.29 + 0.014 0.33 + 0.019 0.42 + 0.091
(200 mg/kg) (34.4 %) (51.5 %) (44.43 %)
4. VIb 0.27 + 0.0212 0.34 + 0.012 0.39 + 0.0192
(200 mg/kg) (36.3 %) (50.2 %) (48.2 %)
5. VIc 0.36 + 0.034 0.39 + 0.016 0.43 + 0.045
(200 mg/kg) (26%) (42.45%) (42.6%)
6. VId 0.26 + 0.0093 0,32 + 0.117 0.44 + 0.014
(200 mg/kg) (40.4 %) (52.4 %) (41.06%)
7. VIe 0.31 + 0.00961 0.31 + 0.0065 0.37 + 0.028
(200 mg/kg) (31.8 %) (54.4 %) (48.72%)
8. VIf 0.32 + 0.014 0.35 + 0.017 0.40 + 0.025
(200 mg/kg) (38.6 %) (48.5 %) (46.6 %)
9. VIg 0.30 + 0.012 0.42 + 0.096 0.41 + 0.059
(200 mg/kg) (29.34%) (29.67%) (45.3%)
10. VIh 0.28 + 0.012 0.45 + 0.072 0.51 + 0.063
(200 mg/kg) (36.3%) (26.45%) (33.45%)

168

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Synthesis and pharmacological screening of some benzoxazole derivatives as an anti inflammatory agents

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