New analgesic and antiinflammatory agents 4(1H)-pyridinone derivatives

Article abstract of DOI:10.1016/S0223-5234(02)01390-9

A series of 1,2,5-trisubstituted 4(1H)-pyridinone derivatives (7-14) were synthesised by using 4-pyrone derivatives with primary amines in ethanol. The structures of the synthesised compounds were confirmed by analytical and spectral data (UV, IR and 1H-NMR and microanalysis). Analgesic and antiinflammatory activities of the synthesised compounds were investigated by acetic acid-induced writhing syndrome and carrageenan rat paw edema tests. All of the test compounds exhibited higher analgesic activities than acetyl salicylic acid and showed higher antiinflammatory activities than indomethacin. The antiinflammatory activity and gastric ulceration potential of the compounds were tested using indomethacin as reference drug.

Full text of DOI:10.1016/S0223-5234(02)01390-9

European Journal of Medicinal Chemistry 37 (2002) 829ꢀ834
/
www.elsevier.com/locate/ejmech
Short communication
New analgesic and antiinflammatory agents 4(1H)-pyridinone
derivatives
a
Gulcan Ozturk , Dilek Demir Erol *, Mutlu Dilsiz Aytemir , Tayfun Uzbay
a,
a
b
¨
¨
¨
a Pharmaceutical Chemistry Department, Faculty of Pharmacy, Hacettepe University, 06100 S hh ye-Ankara, Turkey
ı
ı
b Military Medicinal Academy of Gulhane Pharmacology Department, Ankara, Turkey
¨
Received 10 August 2001; accepted 17 May 2002
Abstract
A series of 1,2,5-trisubstituted 4(1H)-pyridinone derivatives (7ꢀ
/
14) were synthesised by using 4-pyrone derivatives with primary
1
amines in ethanol. The structures of the synthesised compounds were confirmed by analytical and spectral data (UV, IR and H-
NMR and microanalysis). Analgesic and antiinflammatory activities of the synthesised compounds were investigated by acetic acid-
induced writhing syndrome and carrageenan rat paw edema tests. All of the test compounds exhibited higher analgesic activities
than acetyl salicylic acid and showed higher antiinflammatory activities than indomethacin. The anti-inflammatory activity and
gastric ulceration potential of the compounds were tested using indomethacin as reference drug.
´
# 2002 Published by Editions scientifiques et me´dicales Elsevier SAS.
Keywords: 4(1H)-pyridinones; Analgesic agents; Antiinflammatory agents; Synthesis; Kojic acid derivatives
1. Introduction
known for more than 90 years [7]. It has been utilised
for the preparation of a variety of these pyridinones [7ꢀ
/
A large number compounds with a 4(1H)-pyridinone
structure have been synthesised for biological screening
and variety of interesting pharmacological properties
9]; despite the fact that this reaction has somewhat
limited scope, being reliable only for small alkyl and aryl
amines. It is well known that 4(1H)-pyridinone deriva-
tives have shown various pharmacological effects such
as antibacterial [10,2], antifungal [11], antimalarial
[12,13], cardiotonic agents [14], antihypertensive [15],
were observed [1ꢀ3]. The most important activities
/
regarding their analgesic and anti-inflammatory actions
belong to their iron chelating properties. Moreover,
several 4(1H)-pyridinone compounds have shown an-
algesic and anti-inflammatory activities [1,4]. The most
prevalent side effects of the use of non-steroid antiin-
flammatory drugs are the occurrence of gastrointestinal
damage with gastric upset and irritation being the major
problems. Therefore, developing new agents with or
without minimal side effects is, at present, a diffuse
research area. Recently, in an effort to synthesise
analgesic and antiinflammatory drugs with minimal
gastrointestinal side effects, 4(1H)-pyridinones have
emerged as a promising group [5,6].
antineoplastic [16ꢀ/19], antiinflammatory [1], analgesic
[20ꢀ23], and treatment of Parkinson’s disease [3,24]. On
/
the other hand, 3-hydroxy-2-methyl-4(1H)-pyridinone
derivatives are of considerable interest because they may
be used as orally active iron (III) chelators in the
treatment of iron overload and acute iron poisoning
[25ꢀ29]. Hydroxypyridinones are undergoing develop-
/
ment for the treatment of Thalassemia disease [30,31].
This consideration led us to synthesise a series of 4-
pyridinone derivatives substituted with several cyclic
amines such as piperidine, pyridine, pyrrolidine and
morpholine by linking through an ethylene moiety (Fig.
1). The existence of the relationship between inhibition
of prostaglandin biosynthesis and analgesic or antiin-
flammatory activities was investigated in the case of 4-
pyridinone derivatives in comparison to acetyl salicylic
acid and indomethacin.
The reaction of primary amines with 4(1H)-pyrones
to form N-substituted-4(1H)-pyridinones has been
* Correspondence and reprints
E-mail address: derol@hacettepe.edu.tr (D.D. Erol).
´
0223-5234/02/$ - see front matter # 2002 Published by Editions scientifiques et me´dicales Elsevier SAS.
PII: S 0 2 2 3 - 5 2 3 4 ( 0 2 ) 0 1 3 9 0 - 9

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G. Ozturk et al. / European Journal of Medicinal Chemistry 37 (2002) 829ꢀ
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¨
of the corresponding hydrobromide salts for storage and
biological testing.
Since a convenient route to 4-pyridones is the
condensation of 4-pyrones with primary amines, com-
mercially available kojic acid was selected as starting
materials for the synthesis of the series of 4-pyridone
analogs (Fig. 2). Condensation of the benzyl ether of the
starting material with primary amines affords the
desired pyridones. The hydroxymethyl group required
conversion to benzyl kojic acid as a protection of
phenolic function. Formulas, melting points, % yields
of compounds are shown in Table 1.
The basic structures of these compounds were con-
1
firmed by IR and H-NMR spectral data Table 2. The
reaction products were assigned structures that were in
accord with their spectroscopic and chemical behaviour.
Thus all these compounds showed a strong band at 1632
Fig. 1. 1,2,5-Trisubstituted 4(1H)-pyridinone×
/
2HBr derivatives.
cmꢁ1 in their IR spectra assignable to a CÄ
/
O group,
and at 1234 cmꢁ1 which is characteristic of a CÃ
OÃ
band. The ethylene group protons in the 1H-NMR
spectra of all compounds appeared as a triplet at 4.70ꢀ
3.50 ppm for ÃNÃCH2Ã, a triplet signal at 3.90ꢀ2.90
/
/C
2. Chemistry
The synthesised compounds [7ꢀ
/
/14] were obtained by
/
/
/
/
reacting primary amines such as 1-(2-aminoethyl)piper-
idine, 2-(2-aminoethyl)pyridine, 2(2-aminoethyl)-l-
methylpyrrolidine and 4-(2-aminoethyl)morpholine
with 4-pyrone derivatives in ethanol. The desired sub-
stitited-4(1H)-pyridinones were catechol derivatives by
cleavage with BBr3 in dichloromethane. Susceptibility of
the free bases to air oxidation necessitated preparation
Table 1
Structures and chemical data of N-sustituted-2-methyl-5-hydroxy-
4(1H)-pyridinones×2HBr 7ꢀ/14 derivatives
a
Yields are those of the products obtained from the first
ctystallization (ethanolꢀ
/
ether).
Melting points were determined on a Thomas Hoover apparatus
b
Fig. 2. Synthesis of l,2,5-trisubstituted-4(1H)-pyridinone×
/2HBr deri-
and are uncorrected.
c
C,H,N were performed by Butterworth Co., UK.
vatives.

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G. Ozturk et al. / European Journal of Medicinal Chemistry 37 (2002) 829ꢀ
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831
¨
Table 2
Spectral data of N-substituted-2-methyl-5-benzyloxy-4(1H)-pyridinones (7ꢀ
(11ꢀ14) derivatives
/
10) and N-substituted 2-methyl-5-hydroxy-4(1H)-pyridinones×2HBr
/
a
b,c
1R (cmꢁl
)
lH-NMR (ppm)
Compound number
CÄO
CÃOÃC/OH*
CH3 [s]
NÃCH2 [t]
CH2 [t]
OÃCH2[s]
H3,2 [s,d]
H6 [s]
7
1634
1631
1631
1632
1229
1233
1229
1234
2.50
2.45
2.65
2.65
2.50
2.40
2.65
2.55
3.50
4.05
3.50
3.95
4.65
4.55
3.75
4.70
3.10
2.90
3.00
3.10
3.15
3.35
3.20
3.70
5.35
4.90
5.15
5.25
6.30
6.10
6.30
6.30
7.00
6.90
7.15
6.90
7.80
6.80
7.00
6.90
7.90
8.00
8.15
7.95
8
9
10
11
12
13
14
1614
1634
1636
1616
3500ꢀ
3200ꢀ
3400ꢀ
3500ꢀ
/
3400
3100
3100
3200
ꢀ/
ꢀ/
ꢀ/
ꢀ/
/
/
/
s, Singlet; d, dublet; t, triplet.
a
IR spectra were determined on a Perkinꢀ
/
Elmer FTIR Spectrometer 1720 X in KBr pellets.
1H-NMR spectra were charted on a Bruker AC 80 MHz FT.
b
c
Bruker AC 200 MHz FT and compounds were solved in CHCl3-d6 (7aꢀ
/
14a) and DMSO-d6 (7ꢀ14).
/
ppm for Ã
/
NÃ
/
CH2Ã
/
CH2Ã
/
. Characteristic doublets peak
was used as a reference analgesic drug and administered
according to the test protocol (100 mg kgꢁ1).
The analgesic activity was expressed in terms of %
inhibition;
of pyridones were observed at aromatic field.
% Analgesic Activityꢂnꢁn?=n100
3. Pharmacology
n is the mean number of writhes of control group, and
n? is the mean number of writhes of test group.
The experiments were carried out on male albino-
Swiss mice (body weight of 2092 g) and purchased
/
(local breed) from the University of Hacettepe Animal
House and maintained at a temperature between 20 and
23 8C. The animals were housed in groups of eight, with
food and water ad libitum and allowed to get accus-
tomed to their environment for at least 2 days before test
started. Motor coordination was measured according to
the method of Gross et al. [32] Mice were placed for 2
min on the rod rotating with the speed of 4 rpm. The
effects were evaluated 15, 30, 45, 60 and 75 min after the
administration of the investigated compounds. Animal
experiments have been practised under the supervision
of Veterinary Faculty of Ankara University, which is
responsible for the observation of the rules of guidelines
of animal experiments.
3.2. Antiinflammatory activity
Carrageenan induced mouse paw edema (CPE) was
measured using Peacock Thickness gauge (0.01ꢀ10
/
mm), eight mice per group were used. Sixty minutes
after i.p. administration of the compounds (100 mg
kgꢁ1), 2% carrageenan (0.01 mL) was injected subcuta-
neously into the plantar surface of the right hind paw.
Two hours later, the volume of the edema was mea-
sured. Indomethacin [100 mg/kg i.p. injection] was used
as a positive control [34].
3.3. Gastric ulceration studies
3.1. Analgesic activity
Active compounds were subjected to this experimen-
tal process. Animals were sacrified after last measure-
ment application of each test compounds, under ether
anesthesia and stomachs were removed, opened through
the greater curvature, washed and fixed in 5% formalin
solution. The stomachs were then examined for lesions
under a dissecting microscope.
Pain reactivity was measured by the ‘writhing syn-
drome’ test of Koster et al. [33]. The test was performed
in mice by i.p. injection of a 3% solution of acetic acid 60
min after the administration of compounds. Each
compound was administrated intraperitoneally (i.p.) as
a solution in Tween 80 of 100, 50 and 25 mg kgꢁ1
.
Control groups received an equal volume of vehicle.
Each experimental group consisted of eight animals.
Animals were placed in glass cages 5 min after acetic
acid injection and number of ‘writhes’ induced in each
mouse was observed for a 10 min period, starting 5 min
after injection of acetic acid. Acetylsalicylic acid (ASA)
3.4. Statistical values
Student t test and analysis of variance: ANOVA, two
factors [pharmacologic calculation system version 4.1]
were employed.

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4. Results and discussion
Therefore, we can conclude that the 1-pyrrolidi-
noethyl-2-methyl-5-hydroxy-4(1H)-pyridinone×
/
2HBr
Formulas, melting points, % yields of the compounds
are shown in Table 1. The synthesized compounds (7aꢀ
(compound 13) is the most active of the series as
analgesic and anti-inflammatory compound and further-
more, the ulcerogenic activity of the compound 13 was
lower than that of the reference compound and showing
almost no ulcerogenic activity.
/
14a) were obtained by reacting primary amines with 4-
pyrone derivatives in ethanol. The desired substituted-
4(1H)-pyridinones were cathechol derivatives by clea-
vage with BBr3 in dichloromethane. Susceptibility of the
free bases to air oxidation necessitated preparation of
the corresponding hydrobromide salts for storage and
biological studies.
5. Experimental protocols
Substituted 4(1H)-pyridinone derivatives were
screened for their analgesic and antiinflammatory activ-
ities. A modified Koster Test for screening analgesic
activity was employed, carrageenan-induced mousse
paw edema for screening antiinflammatory activity
was measured using Peacock Dial Thickness Gauge.
All tested compounds had no neurotoxic properties as
they did not affect the motor coordination in the rota-
rod test.
Melting points (Table 1) were determined in open
glass capillaries on a Thomas-Hoover (Philadelphia,
USA) apparatus and are uncorrected. The infrared
spectra (Table 2) were recorded on a PerkinꢀElmer
/
(Table 2) FTIR 1720 X IR (Beaconsfield, UK) spectro-
photometer using samples in potassium bromide disks.
1H-NMR spectra were measured on a Perkinꢀ
Elmer
/
R.32 90 MHz and Bruker AC 200 MHz FT NMR
(Karlsruhe, Germany) using tetramethylsilane as inter-
nal standard and dimethyl-d6 sulfoxide as solvent.
Chemical shift values are reported as d (ppm) values.
Mass spectra were obtained from V6 16F mass spectro-
meter with V6 data system 2000. Analyses indicated by
In the present study, acetic acid 3& (300 mg/kg) was
used to induce abdominal contractions (writhing) in the
mice. Koster et al. [33] used very low dose acetic acid (60
mg/kg) for evaluating writhing response in mice. In our
preliminary studies, we did not observe marked and
acceptable writhing responses by this low dose of acetic
acid. In some previous studies, acetic acid 3% (300 mg
kgꢁ1) has also been used for evaluating writhing
responses in mice [33,34]. Using different mice species
may be responsible for the discrepancy. As for the
analgesic activity, all the compounds were shown to be
equally potent in comparison with aspirin. The degree of
protection ranged from 51 to 88% at a dose of 100 mg
kgꢁ1. The most active compounds were 11, 13 and 14
which displayed a significant analgesic effect also at
dose of 50 mg kgꢁ1 (73.22, 75.94 and 68%, respectively)
and 25 mg kgꢁ1 (58.65, 53.87 and 49.67%, respectively).
Compound 13 is the more promising one and slightly
more potent than the others. Antiinflammatory activ-
ities of all the synthesised compounds were screened
using the carrageenan hind-paw edema test with in-
domethacin as standard. These results are disclosed in
Fig. 3. The edema inhibition of all compounds was
significant when compared with the inhibition obtained
by indomethacin. In Fig. 3 the activity of compound 13
is shown significantly high and potent in comparison
with indomethacin. The obtained results indicate that
the investigated 4(1H)-pyridinone derivatives have a
profile of action corresponding to new analgesic and
anti-inflammatory agents.
elemental symbols were within 90.4% of the theoretical
/
values and were performed by Butterworth, UK. The
purity of the compounds was determined by TLC on
silica gel HF 254 (Merk) (ChloroformꢀMethanol 95:5).
/
All chemicals were obtained from Aldrich Chemical Co.
(Steinheim, Germany).
5.1. 2-Chloromethyl-5-hydroxy-4-pyrone (1)
Kojic acid (142 g, 1 mol) was dissolved in thionyl
chloride (237 g, 2 mol), followed by stirring for 2 h at
room temparature. The yellow solid was filtered, washed
with cold petroleum ether (60ꢀ
from water gave light-yellow crystals (115 g, 72%),
melting point (m.p.) 146ꢀ147 8C.
/
70 8C). Recrystallisation
/
5.2. 2-Methyl-5-hydroxy-4-pyrone (2)
Compound 1 (20 g, 0.12 mol) was suspended in water
(500 mL). The temperature of the reaction mixture was
raised to 50 8C. Zinc dust (16 g, 0.24 mol) was added
and stirred at 70 8C for 0.5 h. Conc. HCl (13.6 g, 3 mol)
was added dropwise followed by stirring for 4 h at 70ꢀ
/
The stomachs of the animals were also examined for
gastric ulceration and in spite of the high gastric ulcer
incidence with the reference compound indomethacin
the synthesised active compounds 11, 13, 14 (25 and 50
mg kgꢁ1 doses, 0/6 ulcer score) were generally found
safe from the point of view of ulcer induction.
80 8C. The solution was filtered, poured into ice-water
and extracted with dichloromethane, dried with Na2SO4
and evaporated to dryness. Recrystallisation of the
resulting yellow solid from isopropanol provided com-
pound 2 as light-yellow needles (10.2 g, 64%) m.p. 125ꢀ
/
127 C.

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G. Ozturk et al. / European Journal of Medicinal Chemistry 37 (2002) 829ꢀ
/834
833
¨
Fig. 3. Pharmacological activity of N-substituted-4(1H)-pyridinone×
/
2HBr [7ꢀ14].
/
5.3. 5-Benzyloxy-2-methyl-4-pyrone (3)
evaporated. Recrystallisation from ethanolꢀ
/ether gave
pure 4-pyridinone derivatives as yellow-white powder.
Compound 2 (1 mol) was dissolved in methanol and
the solution of NaOH (2 mol) in 10 mL water and
benzyl chloride (2 mol) was added and heated under
reflux for 8 h, then evaporated to dryness and extracted
with dichloromethane, washed with 5% sodium hydrox-
ide and water, dried with Na2SO4 and evaporated to
dryness. Recrystallisation of the resulting tan solid from
ether provided 3 as white needles (76%), m.p. 48 8C.
Acknowledgements
This work has been supported partically with a grant
of the Scientific and Technical Research Council of
Turkey.
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