Synthesis of 4(1H)-pyridinone derivatives and investigation of analgesic and antiinflammatory activities

Article abstract of DOI:10.1016/S0014-827X(01)01083-7

This paper describes recent result of a research program aimed at the synthesis and pharmacological evaluation of new 4(1H)-pyridinone derivatives belonging to the 1,3-disubstituted series (4-11). These compounds were structurally planned by applying the molecular hybridization strategy on previously described 1,2-disubstituted-4(1H)-pyridinone derivatives, considered as lead compounds, which present potent analgesic properties (M. D. Aytemir, T. Uzbay, D. D. Erol, Arzneim. Forsch. (Drug Res.) 49 (1999) 250). Their chemical structures have been proved by means of their IR and 1H NMR data and by elemental analysis. The analgesic profile of the title compounds (4-11), evaluated by the model of abdominal constrictions induced by acetic acid, showed that all the 4(1H)-pyridinone derivatives were active, exhibiting an analgesic activity comparable with that of aspirin (acetyl salicylic acid) used as a standard. The antiinflammatory profile by the synthesized compounds, evaluated by the model of carrageenan rat paw edema, showed that all compounds were active and were comparable with indomethacin used as a standard.

Full text of DOI:10.1016/S0014-827X(01)01083-7

www.elsevier.nl/locate/farmac
Il Farmaco 56 (2001) 251–256
Synthesis of 4(1H)-pyridinone derivatives and investigation of
analgesic and antiinflammatory activities
a
a,
b
a
8
Gu¨lcan Oztu¨rk , Dilek Demir Erol *, Tayfun Uzbay , Mutlu Dilsiz Aytemir
a Pharmaceutical Chemistry Department, Faculty of Pharmacy, Hacettepe Uni6ersity, 06100 Sıhhıye, Ankara, Turkey
b Pharmacology Department, Military Medicinal Academy of Gu¨lhane, Ankara, Turkey
Received 20 March 2000; accepted 20 October 2000
Abstract
This paper describes recent results of a research program aimed at the synthesis and pharmacological evaluation of new
4(1H)-pyridinone derivatives belonging to the 1,3-disubstituted series (4–11). These compounds were structurally planned by
applying the molecular hybridization strategy on previously described 1,2-disubstituted-4(1H)-pyridinone derivatives, considered
as lead compounds, which present potent analgesic properties (M.D. Aytemir, T. Uzbay, D.D. Erol, Arzneim. Forsch. (Drug
Res.) 49 (1999) 250). Their chemical structures have been proved by means of their IR and 1H NMR data and by elemental
analysis. The analgesic profile of the title compounds (4–11), evaluated by the model of abdominal constrictions induced by acetic
acid, showed that all the 4(1H)-pyridinone derivatives were active, exhibiting an analgesic activity comparable with that of aspirin
(acetyl salicylic acid) used as a standard. The antiinflammatory profile of the synthesized compounds, evaluated by the model of
carrageenan rat paw edema, showed that all compounds were active and were comparable with indomethacin used as a standard.
© 2001 Elsevier Science S.A. All rights reserved.
Keywords: 4(1H)-Pyridinones; Analgesic properties; Antiinflammatory agents; Kojic acid derivatives
1. Introduction
antiinflammatory [1], analgesic [1,12–15] activity and
they are used for the treatment of Parkinson’s disease
[16,17].
The class of pyridinones includes compounds en-
dowed with pharmacological activities in different ani-
mal tests. Molecules containing the 4(1H)-pyridinone
nucleus possess antibacterial [2,3], antifungal [4], anti-
malarial [5,6], cardiotonic [7], antineoplastic [8–11],
Among the pharmacological properties of 4(1H)-
pyridinone derivatives, the analgesic effects [1,18] and
the antiinflammatory activity in the carrageenan-in-
duced rat paw edema could suggest inhibition of
prostaglandin E and arachidonic acid synthesis. On the
other hand, the 4(1H)-pyridinone based structures do
not feature molecular characteristics of known anal-
gesics and antiinflammatory agents.
These results led us to design new structurally related
derivatives, keeping the 4(1H)-pyridinone framework
and modifying the nature of the substituent on the
basic moiety. In this paper we describe the synthesis,
structural properties and pharmacological evaluation of
two new series of 1,3-disubtituted-4(1H)-pyridinone
derivatives (Fig. 1). The analgesic or antiinflammatory
activities were investigated for the 4(1H)-pyridinone
derivatives keeping acetyl salicylic acid and in-
domethacin as comparison compounds.
Fig. 1. 1,3-Disubstituted 4(1H)-pyridinone·2HBr derivatives.
* Corresponding author.
E-mail address: dilek erol@mail.com (D.D. Erol).
–
0014-827X/01/$ - see front matter © 2001 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(01)01083-7

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G. Oztu¨rk et al. / Il Farmaco 56 (2001) 251–256
Scheme 1. Synthesis of 1,3-disubstituted-4(1H)-pyridinone·2HBr derivatives.
2. Chemistry
phenolic function. Pyronecarboxylic acid 2 could be
converted to the benzyloxy-4-pyrone 3 by heating in
N-methylpyrrolidone that caused thermal decarboxyla-
tion. Formula, melting point and yield (%) of the
compounds are shown in Table 1. Susceptibility of the
free bases to air oxidation necessitated preparation of
the corresponding hydrobromide salts for storage and
biological studies. The structures of the newly pre-
pared compounds were assigned according to the reac-
tion mechanisms and analytical data and were
4(1H)-pyridinone derivatives (4–11) were prepared
as illustrated in Scheme 1 by means of nucleophilic
substitution on 4-pyrone derivatives by suitable cyclic
amines such as piperidine, pyridine, pyrrolidine and
morpholine.
The synthesized compounds (4–7) were obtained by
reacting primary amines with 4-pyrone derivatives in
absolute ethanol. The desired substituted-4(1H)-pyridi-
none derivatives (8–11) were obtained by cleavage
with BBr3 in dichloromethane. Since a convenient
route to 4-pyridones is the condensation of 4-pyrones
and primary amines, commercially available kojic acid
was selected as the starting material for the synthesis
of the 4-pyridone analogs (Scheme 1). Condensation
of the benzyl ether of the starting material with pri-
mary amines afforded the desired pyridinones. The
Jones’ oxidation of the hydroxymethyl group required
conversion to benzyl kojic acid, as a protection of the
1
confirmed by IR and H-NMR spectral data (Table 2).
Thus all these compounds showed in their IR spectra
a strong band at 1632 cm−1 assignable to a CꢀO
group, and a band at 1234 cm−1 that is characteristic
of a CꢁOꢁC group. The ethylene group protons in the
1H-NMR spectra of all compounds appeared as a
triplet at 4.70–3.50 ppm for ꢁNꢁCH2ꢁ and a triplet
signal at 3.90–2.90 ppm for ꢁNꢁCH2ꢁCH2ꢁ. The char-
acteristic doublets of pyridones were observed at aro-
matic fields.

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G. Oztu¨rk et al. / Il Farmaco 56 (2001) 251–256
253
Table 1
Structures and chemical data of N-substituted-3-benzyloxy-4(1H)-pyridinones (4–7) and N-substituted-3-hydroxy- 4(1H)-pyridinones (8–11)
3. Chemical experimental section
consfield, UK) spectrophotometer using samples in
potassium bromide disks. H-NMR spectra were mea-
1
Melting points were determined in open glass capil-
laries on a Thomas-Hoover (Philadelphia, USA) ap-
paratus and are uncorrected. The infrared spectra were
recorded on a Perkin–Elmer FT IR 1720 X IR (Bea-
sured on a Perkin–Elmer R 32 90 MHz and Bruker AC
200 MHz FT NMR (Karlsruhe, Germany) tetramethyl-
silane using as an internal standard. Chemical shift
values were reported as l (ppm) values. Analyses indi-

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G. Oztu¨rk et al. / Il Farmaco 56 (2001) 251–256
254
Table 2
Spectral data of N-substituted-3-benzyloxy-4(1H)-pyridinones (4–7) and N-substituted-3-hydroxy-4(1H)-pyridinones·2HBr (8–11) a
Comp. no.
IR (cm−1
)
1H NMR (ppm)
CꢀO
CꢁOꢁC/OH
NꢁCH2 (t)
CH2 (t)
OꢁCH2 (s)
H3,2 (s,d)
H6 (s)
4
5
6
7
8
9
10
11
1634
1635
1632
1635
1615
1614
1634
1617
1121
1227
1224
1234
3400–3300
3400–3300
3100–3300
3500–3200
3.50
3.40
3.85
4.10
4.65
4.75
4.70
4.70
3.05
2.85
3.00
3.70
3.20
3.05
3.60
3.65
5.00
5.20
5.00
5.20
6.10–5.30
7.05–6.40
5.95–6.50
5.95–6.30
7.00
7.00–7.85
6.90–7.90
7.10–7.90
7.70
7.20
7.90
7.70
8.15
8.15
8.40
8.20
a s: singlet; d: doublet; t: triplet. Compounds 4–7 were dissolved in CDCl3 and compounds 8–11 in DMSO-d6.
cated by 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 (Merck) (chloroform–
methanol 95:5). All chemicals were obtained from
Aldrich Chemical Co. (Steinheim, Germany).
the resulting yellow solid was recrystallized from tolu-
ene: (4.68 g, 56%), m.p. 85–86°C [3].
3.4. General procedure for N-substituted-4(1H)-
pyridinones (4–7)
Compound 3 (1 mol) was dissolved in ethanol and
the appropriate primary amine was added. The mixture
was heated under reflux for 40 h, the solvent evapo-
rated and the residue poured into the ice water and
extracted with chloroform. Organic phase was dried
with Na2SO4, filtered and evaporated in vacuo to yield
the title compounds as orange oil (Table 1).
3.1. 5-Benzyloxy-2-hydroxymethyl-4-pyrone (1)
Anhydrous K2CO3 (276.2 g, 2 mol) was suspended in
a solution of kojic acid (142 g, 1 mol) and benzyl
chloride (253.2 g, 2 mol) in dimethylformamide (700
ml). The temperature of the reaction mixture was raised
to 110°C and maintained for 3 h. The dark reaction
mixture was allowed to cool, poured into ice water (100
ml) and extracted with dichloromethane. The organic
phase was washed with water, dried with Na2SO4 and
evaporated. Recrystallization of the resulting solid from
chloroform provided compound 1 as white needles (125
g, 54%), m.p. 131–133°C [3].
3.5. General procedure for N-substituted hydroxy-
4(1H)-pyridinones (8–11)
Compounds (4–7) were dissolved in dry
dichloromethane. BBr3 in dichloromethane was added
dropwise under nitrogen and the reaction was stirred
for 3 h. The excess of BBr3 was destroyed at 15°C by
the addition of cold methanol and stirring was contin-
ued in an ice bath for 30 min. The mixture was concen-
trated to dryness in vacuum and the residue was
dissolved several times in methanol and evaporated.
Recrystallization from ethanol–ether gave the pure 4-
pyridinone derivatives as yellow–white powder (Table
1).
3.2. 5-Benzyloxy-4-pyrone-2-carboxylic acid (2)
Compound 1 (10 g, 43.2 mmol) was dissolved in
acetone (500 ml), cooled in an icebath and Jones
reagent was added (25 ml). The inorganic material was
removed by filtration and the filtrate evaporated to
dryness. Pure compound 2 was obtained by recrystal-
lization from methanol: (8.89 g, 89%) m.p. 194–196°C
[3].
4. Pharmacological experimental section
3.3. 3-Benzyloxy-4-pyrone (3)
Male Swiss Webster mice (2092 g) were purchased
(local breed) from the University of Hacettepe Animal
House and maintained at a temperature between 20 and
23°C. 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
the test. Motor coordination was measured according
to the method of Gross et al. [19]. The effects were
evaluated 15, 30, 45, 60 and 75 min after the adminis-
Benzylcomenic acid (2) (10 g, 40.6 mmol) was dis-
solved in N-methyl pyrrolidone and refluxed overnight.
After cooling 25 ml of dimethylformamide was added
to the reaction mixture and the solvent was evaporated
to give
a
residue, which was extracted with
dichloromethane. The organic layer was washed with
5% sodium hydroxide and water, dried and evaporated.
The residue was treated with charcoal in ethanol and

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G. Oztu¨rk et al. / Il Farmaco 56 (2001) 251–256
255
tration of the investigated compounds. Animal experi-
4.2. Antiinflammatory acti6ity
ments have been practiced under the supervision of the
Veterinary Faculty of the Ankara University, which is
responsible for the observation of the rules of guidelines
of animal experiments.
Carrageenan-induced mouse paw edema was mea-
sured using Peacock Dial Thickness gauge (0.01–10
mm). Eight mice per group were used. Sixty minutes
after i.p. administration of the compound (100 mg/kg)
2% carrageenan (0.01 ml) was injected s.c. into the
plantar surface of the right hind paw. Two hours later
the volume of the edema was measured. Indomethacin
(100 mg/kg i.p. injection) was used as a positive control
[20].
4.1. Analgesic acti6ity
Modified acetic acid writhing test for screening anal-
gesic activity was employed [18,20]. Each compound
(4–11) was i.p. administered to mice in groups of eight
at a dose level of 100 mg/kg. One hour later, 3% (w/w)
solution of acetic acid (300 mg/kg) was administered
i.p. Control groups (n=8) received an equal volume of
0.9% NaCl (10 ml/kg). Animals were placed in glass
cages 5 min after the acetic acid injection and the
number of ‘writhes’ induced in each mouse was ob-
served for a 10-min period. Acetylsalicylic acid was
used as a reference analgesic drug and administered
according to the test protocol (100 mg/kg).
4.3. Statistical analysis
Student’s t-test and two-factor analysis of variance,
(Pharmacologic calculation system version 4.1) was
employed.
5. Results and discussion
The analgesic activity was expressed in terms of %
inhibition;
The evaluation of the analgesic profile of all 1,3-di-
substituted-4(1H)-pyridinone derivatives (4–11) were
performed using the classical acetic acid-induced mice
abdominal contractions test with aspirin as the stan-
dard. In the present study, acetic acid 3% (300 mg/kg)
was used to induce abdominal contractions (writhing)
in the mice. Koster et al. [21] used very low dose of
acetic acid (60 mg/kg) for evaluating writhing response
in mice. In our preliminary studies, we did not observe
marked and acceptable writhing responses using this
low dose of acetic acid. In some previous studies, acetic
acid 3% (300 mg/kg) has also been used for evaluating
writhing responses in mice [19,20,22]. Using different
mice species may be responsible for the discrepancy.
With regard to the analgesic activity, all the compounds
were shown to be equally potent in comparison with
aspirin. The degree of protection ranged from 65 to
79% at a dose of 100 mg/kg. Compounds 8–10 were
most active and displayed a significant analgesic effect
at dose of 50 mg/kg (70, 61 and 61%, respectively) and
25 mg/kg (51, 48 and 45%, respectively). Compound 8
is the more promising one and slightly more potent
than the others.
% Analgesic activity=n−n%/n100
where n=mean number of writhes of control group,
n%=mean number of writhes of the test group.
Fig. 2. Analgesic and antiinflammatory activities of 4-pyridinone
derivatives.
Antiinflammatory activities of all the synthesized
compounds were screened using the carrageenan hind-
paw edema test with indomethacin as the standard.
These results are shown in Fig. 2. The edema inhibition
of all compounds was significant when compared to the
inhibition obtained by indomethacin. In Fig. 2 the
activity of compound 8 is shown to be significantly
higher and more potent in comparison with in-
domethacin. The results obtained indicate that the in-
vestigated 4(1H)-pyridinone derivatives have a profile
of action corresponding to new analgesic and anti-
inflammatory agents (Fig. 3).
Fig. 3. Action profile of 4-pyridinones.

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