Research on heterocyclic compounds, Part 40. 2-Phenylimidazo[1,2-a]pyridine-3-carboxylic acid derivatives: synthesis and antiinflammatory activity.

Article abstract of DOI:10.1002/(SICI)1521-4184(19989)331:9<273::AID-ARDP273>3.0.CO;2-R

A series of 2-phenylimidazo[1,2-a]pyridine-3-carboxylic esters, acids, and amides were synthesized and pharmacologically tested in order to evaluate their antiinflammatory and analgesic activity and their ulcerogenic action on the gastro-intestinal tract. The most active member of this series of compounds was found to be 6-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid (5c).

Full text of DOI:10.1002/(SICI)1521-4184(19989)331:9<273::AID-ARDP273>3.0.CO;2-R

2-Phenylimidazo[1,2-a]pyridine-3-carboxylic Acids
273
1)
Research on Heterocyclic Compounds, Part 40
2-Phenylimidazo[1,2-a]pyridine-3-carboxylic Acid Derivatives:
Synthesis and Antiinflammatory Activity
a)
a)
a)
a)
a)
b)
Anna Di Chiacchio , Maria Grazia Rimoli , Lucia Avallone *, Francesca Arena , Enrico Abignente , Walter Filippelli ,
b)
b)
Amelia Filippelli , and Giuseppe Falcone
a) Dipartimento di Chimica Farmaceutica e Tossicologica, Facoltà di Farmacia, Università di Napoli Federico II, Via Domenico Montesano 49,
I-80131 Napoli, Italy
b) Istituto di Farmacologia e Tossicologia, Facoltà di Medicina e Chirurgia, II Università di Napoli, Via Costantinopoli 16, I-80138 Napoli, Italy
Key Words: Imidazo[1,2-a]pyridines; antiinflammatory activity; analgesic activity; ulcerogenic activity.
biosynthesis plays a secondary role at the most in their mode
of action.
Summary
In this context, particularly interestingresults were obtained
on studying the structure-activity relationships in the series
of imidazo[1,2-a]pyridine acidic derivatives (Figure 2).
A series of 2-phenylimidazo[1,2-a]pyridine-3-carboxylic esters,
acids, and amides were synthesized and pharmacologically tested
in order to evaluate their antiinflammatory and analgesic activity
and their ulcerogenic action on the gastro-intestinal tract. The most
active member of this series of compounds was found to be
6-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid (5c).
Introduction
Figure 2. Imidazo[1,2-a]pyridines.
Our research on chemical and pharmacological properties
of heterocyclic compounds was originally based on the as-
sumption that molecules derived from the general structural
model 1 (Figure 1) could have antiinflammatory activity,
since this model was derived from the map proposed by Gund
We previously synthesized and pharmacologically tested a
2
number of imidazo[1,2-a]pyridine-2-carboxylic (R
=
2
COOH) and 2-acetic (R = CH COOH) acids, 2-methyl-3-
2
2
3
carboxylic (R = CH , R = COOH), and 2-methyl-3-acetic
3
2
3
[4,5]
[1]
(R = CH , R = CH COOH) acids
. In this series of
and Shen forthe active site ofcyclooxygenase: a compound
3
2
compounds, the most active one was found to be 6-
methylimidazo[1,2-a]pyridine-2-carboxylic acid. Antiin-
flammatory activity decreased or disappeared when the
methyl group was eliminated or shifted to another position,
and also when the carboxylic moiety was replaced by an
acetic acid group. In order to improve the activity, we synthe-
sized a number of2-phenylimidazo[1,2-a]pyridine-3-carbox-
related to the structure 1 should have the minimal structural
features which are required to act as a cyclooxygenase inhibi-
tor.
[6]
ylic acids of which the 6-methyl derivative 5c showed high
[7]
antiinflammatory activity . Since the introduction of phenyl
or p-chlorophenyl as a lipophilic moiety also increased the
pharmacological activity in other series of imidazo-deriva-
Figure 1. General structural model (X = 5- or 6-membered ring; R′ or R′′ =
acidic function; R = substituents).
[8]
tives, e.g. imidazo[1,2-b]pyridazines and imidazo[1,2-
[9]
a]pyrazines , we decided to synthesize a number of
2-phenylimidazo[1,2-a]pyridine-3-carboxylic esters, acids,
and amides in order to acquire a deeper knowledge of struc-
ture-activity relationships in this series of compounds and
possibly of their mechanism of action.
Many compounds related to 1 showed antiinflammatory
and/or analgesic activity , but the peculiar features of their
[2]
pharmacological profile (e.g. no parallelism between antiin-
flammatory and analgesic activities, low or negligible ulcero-
genic action on the rat gastric mucosa), and the lack of
inhibitory activity in vitro on the prostaglandin (PG) biosyn-
thesis of some compounds with high antiinflammatory activ-
Chemistry
The required compounds were prepared by means of the
synthetic method depicted in Figure 3: this method is closely
similar to the procedure normally used by us to obtain many
[3]
ity in vivo seem to indicate that the inhibition of PG
———
1)
Part 39: S. Laneri, A. Sacchi, M. Gallitelli, F. Arena, E. Luraschi,
E. Abignente, W. Filippelli, F. Rossi, Eur. J. Med. Chem. 1998, 33, 163–170.
series of bicyclic imidazo-derivatives with a bridgehead ni-
[2–5]
trogen atom, such as those cited in the Introduction
.
Arch. Pharm. Pharm. Med. Chem.
© WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
0365-6233/98/0909/0273 $17.50 +.50/0

274
Avallone and co-workers
Figure 3. Synthetic methods for ethyl esters 4a-f, acids 5a–f, and amides 6a–f.
2-Aminopyridines (2a–f) were refluxed with an equimolar
amount of ethyl 2-bromo-3-oxo-3-phenylpropionate 3 in
ethanolic solution to afford the corresponding ethyl ester 4.
The esters 4a–f were converted into the respective carboxylic
acids (5a–f) by alkaline hydrolysis, whereas the correspond-
ing carboxamides (6a–f) were prepared by ammonolysis.
Results and Discussion
The in vivo antiinflammatory, analgesic, and ulcerogenic
activities of the esters 4a,c–f, the acids 5a,c–f, and the amides
6a,c–f were determined, using indomethacin (IMA) as the
reference drug. Antiinflammatory activity was measured by
means of the carrageenan-induced rat paw edema: these
results are listed in Table 1. The most active compound was
6-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid
5c, which showed ED50 values sharply lower in comparison
with IMA. The corresponding ethyl ester 4c was much less
active and amide 6c was inactive. A fairly good activity was
displayed by both the ester 4d and the amide 6a, whereas the
remaining compounds showed moderate antiinflammatory
action.
Analgesic activity was determined using the acetic acid
writhing test in mice and the results obtained are summarized
in Table 2. In this assay, too, the acid 5c afforded the best
result, but its activity level was clearly not comparable with
that obtained in the edema test. The corresponding ethyl ester
4c was less active and the amide 6c almost inactive. Lower
or negligible analgesic activity was shown by the other com-
pounds.
1
13
All new compounds showed H and C-NMR spectra
coherent with the structures assigned and in good accordance
with available literature spectral data on 2-phenylimid-
[6]
azo[1,2-a]pyridines
.
1
The most peculiar feature of the H-NMR spectra of these
new compoundsisthe chemical shift ofH-5, which is strongly
deshielded by the presence of the -COOR group in the 3-po-
sition, with consequent large downfield shift of the signal of
this proton (δ 9.2–9.5 for esters 4 in CDCl , δ 10.2–10.5 for
3
acids 5 in CF COOD).This deshielding was already observed
3
[10, 11]
for similar compounds
by us and was first observed and
[12]
studied by Hand and Paudler
in a series of imidazo[1,2-
a]pyridines: this large downfield shift of the H-5 signal
appears when the 3-position bears a substituent -XY contain-
ing an electron-rich atom (Y) two bonds removed from C-3
(like COOEt).
13
The C-NMR spectrum of the ethyl ester 4a is reported in
The gastrointestinal irritative and ulcerogenic action (Ta-
the experimental part as an example.
ble 3) was negligible in the series of esters 4, a little higher in
Arch. Pharm. Pharm. Med. Chem. 331, 273–278 (1998)

2-Phenylimidazo[1,2-a]pyridine-3-carboxylic Acids
275
Table 1. Carrageenan rat paw edema: antiinflammatory activity of esters 4, acids 5, and amides 6.
————————————————————————————————————————————————————————————
Compound
Dose
mg/kg
% Edema inhibition relative
to control at the
ED50, mg/kg
(fiducial limits)
po
1st h
2nd h
3rd h
4th h
3rd h
4th h
————————————————————————————————————————————————————————————
4a
4c
4d
20
40
60
20
40
60
10
20
40
–11
–32
–82
–19
–40
–59
–27
–33
–82
–12
–26
–69
–20
–34
–51
–17
–25
–69
–11
–19
–50
–19
–29
–46
–12
–20
–63
–12
–33
–46
–20
–27
–42
–8
–17
–58
–
–
–
–
–
37.2
(31.4–44.0)
4e
4f
40
20
40
60
–59
0
–19
–40
–34
0
–20
–34
–19
0
–19
–47
–18
–17
–33
–41
–
–
–
–
5a
5c
25
40
50
1.25
2.5
5
–11
–32
–46
–40
–48
–59
–70
–82
–16
–3
–12
–26
–40
–38
–50
–60
–71
–83
–33
–18
–20
–11
–19
–42
–41
–53
–63
–73
–86
–25
–25
–18
–12
–17
–49
–40
–52
–66
–73
–80
–20
–30
–23
–
–
2.2
(1.5–3.3)
2.4
(1.4–3.35)
25
50
40
40
40
5d
5e
5f
–
–
–
–
–
–
–9
6a
10
20
40
40
20
40
60
20
40
60
40
5
–10
–17
–29
0
–11
–32
–33
–19
–24
–32
0
–10
–20
–51
–15
–12
–26
–67
–20
–26
–45
–18
–40
–33
–55
–10
–25
–58
–9
–10
–33
–63
–3
34.5
29.8
(28.8–41.4) (25.2–35.2)
6c
6d
–
–
–
–
–11
–19
–43
–19
–19
–56
–29
–37
–49
–67
–12
–17
–38
–20
–17
–58
–38
–35
–55
–79
6e
–
–
6f
IMA
–
7.0
(6.1–8.1)
–
6.5
(5.9–7.1)
–3
–16
–39
7.5
10
—————————————————————————————————————————————————————————————
the group of acids 5 and rather remarkable in the series of
amides 6, except 6c.
The ulcerogenic action of compounds 4, 5, and 6, summa-
rized in Table 3 shows an absolute lack of parallelism with
the antiinflammatory and analgesic data. Such an observation
is not surprising for us: in fact, we have observed this phar-
macological profile in almost all series of derivatives of fused
imidazole systems synthesized until now. In regard to the
most active compound, namely 5c, it should be noted that the
antiinflammatory activity is higher by far than the analgesic
one, whereas the ulcerogenic action is practically absent.
This is certainly not the pharmacological profile expected
from a compound hypothetically acting as inhibitor of the
prostaglandin biosynthesis.
Such results show that in the series of imidazo[1,2-a]pyri-
dines under examination a clear structure-activity relation-
ship is readily distinguishable: the contemporary presence of
a methyl group in the 6-position and a phenyl moiety in the
2-position largely increased the antiinflammatory activity,
leading to a compound (5c) more potent than indomethacin
in the edema test. In this connection, it must be noted that the
corresponding unsubstituted 2-carboxylic acid was found to
[4]
be completely devoid of pharmacological activity
.
In regard to analgesic action, similar results were obtained,
but the potency of the most active compound 5c is sharply
lower in comparison with its antiinflammatory activity.
In order to investigate this aspect of the problem, some
compounds were tested in vitro for their cyclooxygenase-in-
hibiting activity as detailed in the experimental part. We
Arch. Pharm. Pharm. Med. Chem. 331, 273–278 (1998)

276
Avallone and co-workers
Table 2. Acetic acid writhing test in mice: analgesic activity of com-
pounds 4, 5, and 6.
Table 3. Gastrointestinal lesions in rats.
——————————————————————————————
——————————————————————————————
Compound
(100 mg/kg po.)
Observations at the 6th hour
after treatment:
% animals with
———————————————
Compound Dose
% Decrease of
writhes relative
to control
ED50, mg/kg
mg/kg
po
(fiducial limits)
hyperaemia
ulcers
——————————————————————————————
——————————————————————————————
4a
4c
40
20
40
60
20
40
60
40
40
–3.6
–22.2
–45.3
–54.4
–27.8
–41.3
–59.9
29.3
–
49.9
(41.0–60.7)
4a
4c
4d
4e
4f
0
40
20
0
0
20
10
0
4d
46.7
(37.7–58.0)
10
0
5a
5c
5d
5e
5f
100
100
0
40
30
0
0
0
40
20
4e
4f
–
–
23.0
5a
5c
40
5
–16.1
–20.0
–33.0
–51.5
–60.0
–34.3
–18.0
–27.1
–27.5
–6.0
–30.4
–25.1
–8.4
–24.0
–56.0
–66.0
–81.0
–
39.1
(28.6–53.3)
25
40
50
40
40
40
40
40
40
40
40
6a
6c
6d
6e
6f
80
10
40
40
20
40
0
20
30
20
5d
5e
5f
6a
6c
6d
6e
–
–
–
–
–
–
–
–
4.7
IMAa)
80
50
——————————————————————————————
a) 5 mg/kg po.
6f
IMA
Elemental analyses indicated by the symbols of the elements were within
1
±0.4% of the theoretical values. H- and 13C-NMR spectra were recorded
2.5
5
7.5
10
(4.1–5.3)
using a Bruker WM-250 spectrometer or a Bruker AMX-500 instrument
equipped with a Bruker X-32 computer. Chemical shift values are reported
in δ units (ppm) relative to TMS used as internal standard.
——————————————————————————————
Ethyl 2-phenylimidazo[1,2-a]pyridine-3-carboxylates 4a–f
selected for this test three compounds which showed pharma-
cological activity in vivo (4d, 5c, 6a) and two inactive com-
pounds (4a, 5a): all five compounds showed very low
inhibitory activity, i.e. <10% relative to control, compared
with 90% of indomethacin at the same concentration
(10 µM).
It is logical to argue from these results that the in vivo
activity is independent from the cyclooxygenase inhibition
and therefore must be supported by different mechanisms of
action.
General procedure: a solution of equimolar amounts of a 2-aminopyridine
2 and ethyl 2-bromo-3-oxo-3-phenylpropionate (3) in anhydrous ethanol was
refluxed for 4–6 h. The solvent was then removed under reduced pressure,
the residue was treated with NaHCO3 saturated solution and extracted with
chloroform. The organic extract was washed with water, dried on Na2SO4,
concentrated in vacuo up to small volume and then chromatographed on a
silica gel column, eluting with n-hexane/diethyl ether mixtures with decreas-
ing percentage of n-hexane. The products so obtained were recrystallized
from n-hexane.
Ethyl 2-phenylimidazo[1,2-a]pyridine-3-carboxylate 4a (R5, R6, R7, R8 = H)
Prepared from 2-aminopyridine following a method previously de-
Acknowledgments
scribed [6]
.
13C-NMR (CDCl3): 160.97 (C=O), 153.47 (C-2), 146.98 (C-8a), 134.43
(C-1’), 130.15 (CH-2’, 6’), 128.58, 128.20, 127.80 (CH-4’, CH-5, CH-7),
127.46 (CH-3’, 5’), 117.33 (CH-8), 113.95 (CH-6), 111.50 (C-3), 60.35
(CH2), 13.91 (CH3).
The NMR spectra were performed at the “Centro di Ricerca Interdiparti-
mentale di Analisi Strumentale”, Università di Napoli Federico II, Naples.
The assistance of the staff is much appreciated. This research has been
financially supported by the National Research Council (CNR, Rome) and
the Italian Ministry of University and Scientific and Technological Research
(MURST, Rome).
Ethyl 5-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylate 4b (R5
=
CH3, R6, R7, R8 = H)
Experimental
Prepared from 2-amino-6-methylpyridine. Oil, yield 5%. Anal.
(C17H16N2O2) C, H, N. NMR (CDCl3): 7.68 (m, 2H) and 7.40 (m, 3H)
(phenyl protons), 7.50 (d, 1H, 8-H), 7.19 (dd, 1H, 7-H), 6.85 (d, 1H, 6-H),
4.30 (q, 2H, CH2), 2.48 (s, 3H, 5-CH3), 1.15 (t, 3H, CH3). J7,8 = 9.32 Hz, J6,7
= 7.05 Hz.
Chemistry
The course of reactions and the purity of products were controlled by TLC
using precoated silica gel plates (Merck 60 F254). Detection of components
was made by UV light and/or treatment with iodine vapors. Preparative
separations were performed in columns containing Merck 60 silica gel
(70–230 mesh ASTM). Melting points were determined with a Kofler hot
stage microscope and are uncorrected.
Ethyl 6-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylate 4c (R6
=
CH3, R5, R7, R8 = H)
Prepared from 2-amino-5-methylpyridine according to ref. [6]
.
Arch. Pharm. Pharm. Med. Chem. 331, 273–278 (1998)

2-Phenylimidazo[1,2-a]pyridine-3-carboxylic Acids
277
Ethyl 7-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylate 4d (R7
=
(t, 1H, 6-H), 8.01 (m, 2H) and 7.49 (m, 3H) (phenyl protons), 7.92 (bs, 1H)
CH3, R5, R6, R8 = H)
and 7.24 (bs, 1H) (CONH2). J5,6 = 6.7 Hz, J7,8 = 9 Hz, J5,7 = 1.5 Hz.
Prepared from 2-amino-4-methylpyridine. Mp 85 °C, 27%. Anal.
(C17H16N2O2) C, H, N. NMR (CDCl3): 9.22 (d, 1H, 5-H), 7.70 (m, 2H) and
7.37 (m, 3H) (phenyl protons), 7.44 (s, 1H, 8-H), 6.81 (d, 1H, 6-H), 4.23 (q,
2H, CH2), 2.41 (s, 3H, 7-CH3) 1.16 (t, 3H, CH3). J5,6 = 7.1 Hz.
6-Methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxamide 6c
Prepared from 4c. Mp 150°C, 44%. Anal. (C15H13N3O) C, H, N. NMR
(CD3OD): 8.17 (d, 1H, 5-H), 7.32 (d, 1H, 8-H), 7.16 (dd, 1H, 7-H), 7.87 (m,
2H) and 7.41 (m, 3H) (phenyl protons), 8.05 (bs, 1H) and 7.44 (bs, 1H)
(CONH2), 2.31 (s, 3H, 6-CH3). J7,8 = 9 Hz, J5,7 = 1.4 Hz.
Ethyl 8-methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylate 4e (R8
=
CH3, R5, R6, R7 = H)
Prepared from 2-amino-3-methylpyridine. Mp 75 °C, 22%. Anal.
(C17H16N2O2) C, H, N. NMR (CDCl3): 9.22 (dd, 1H, 5-H), 7.69 (m, 2H) and
7.36 (m, 3H) (phenyl protons), 7.18 (t, 1H, 7-H), 6.89 (t, 1H, 6-H), 4.22 (q,
7-Methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxamide 6d
Prepared from 4d. Mp 140°C, 56%. Anal. (C15H13N3O) C, H, N. NMR
(CDCl3): 7.94 (d, 1H, 5-H), 7.72 (s, 1H, 8-H), 6.57 (d, 1H, 6-H), 7.87 (m,
3H, two phenyl protons and one amide proton), 7.39 (bs, 1H, one amide
proton), 7.36 (m, 3H, phenyl protons), 2.34 (s, 3H, 7-CH3). J5,6 = 6.83 Hz.
2H, CH2), 2.63 (s, 3H, 8-CH3) 1.13 (t, 3H, CH3). J5,6 = J6,7 = 6.95 Hz, J5,7
=
1.62 Hz.
Ethyl 6-chloro-2-phenylimidazo[1,2-a]pyridine-3-carboxylate 4f (R6 = Cl,
R5, R7, R8 = H)
8-Methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxamide 6e
Prepared from 2-amino-5-chloropyridine. Mp 120 °C, 21%. Anal.
(C16H13ClN2O2) C, H, Cl, N. NMR (CDCl3): 9.55 (d, 1H, 5-H), 7.96(d, 1H,
8-H), 7.65 (m, 2H) and 7.43 (m, 3H) (phenyl protons), 7.53 (dd, 1H, 7-H),
4.28 (q, 2H, CH2), 1.16 (t, 3H, CH3). J7,8 = 9.46 Hz, J5,7 = 1.84 Hz.
Prepared from 4e. Mp 130°C, 44%. Anal. (C15H13N3O) C, H, N. NMR
(CD3OD): 8.25 (dd, 1H, 5-H), 7.35 (t, 1H, 7-H), 6.80 (t, 1H, 6-H), 7.94 (m,
2H) and 7.45 (m, 3H) (phenyl protons), 8.12 (bs, 1H) and 7.09 (bs, 1H)
(CONH2), 2.62 (s, 3H, 8-CH3). J5,6 = J6,7 = 7 Hz, J5,7 = 1.6 Hz.
2-Phenylimidazo[1,2-a]pyridine-3-carboxylic acids 5a,c–f
6-Chloro-2-phenylimidazo[1,2-a]pyridine-3-carboxamide 6f
General procedure. A mixture of 10 mmol of each ethyl ester, 50 ml of
10% NaOH and 60 ml of ethanol was refluxed for 1 h. Ethanol was then
removed under reduced pressure, the residual aqueous solution was adjusted
to pH 4–5 with HCl to obtain the precipitation of the acid which was then
recrystallized from methanol.
Prepared from 4f. Mp 195°C, 55%. Anal. (C14H10ClN3O) C, H, Cl, N.
NMR (CDCl3): 10.48 (d, 1H, 5-H), 8.81 (m, 2H, 8-H and one amide proton),
8.70 (dd, 1H, 7-H), 8.37 (m, 2H) and 8.24 (m, 3H) (phenyl protons), 8.34 (bs,
one amide proton). J5,7 = 1.7 Hz.
2-Phenylimidazo[1,2-a]pyridine-3-carboxylic acid 5a:
Pharmacology
Prepared from 4a according to ref. [6]
.
In regard to the experiments carried out in vivo, test compounds were
administered orally by gavage in 1% methylcellulose suspension at different
dose levels. In the edema and writhing tests, each compound was first tested
at 40 mg/kg. If a significant activity was observed, lower and/or higher doses
were then administered in order both to study dose-dependence of antiinflam-
matory and analgesic activity and to calculate ED50 values, if possible.
Gastric ulcerogenic action was studied in rats which were treated orally with
higher doses (100 mg/kg). Indomethacin was included in all tests for com-
parison purposes (IMA in Tables 1–3).
6-Methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid 5c
Prepared from 4c according to ref. [6]
.
7-Methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid 5d
Prepared from 4d. Mp 143°C, yield 54%. Anal. (C15H12N2O2) C, H, N.
NMR (CF3COOD): 10.17 (d, 1H, 5-H), 8.41 (s, 1H, 8-H), 8.25 (d, 1H, 6-H),
8.30 (m, 2H) and 8.16 (m, 3H) (phenyl protons), 3.29 (s, 3H, 7-CH3). J5,6
6.65 Hz.
=
A cyclooxygenase activity assay was carried out in vitro on rabbit colonic
microsomes. Microsomal fractions were incubated with test compounds or
IMA at the same concentration (10 µM).
8-Methyl-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid 5e
The following experimental procedures were employed.
Prepared from 4e. Mp 145°C, 55%. Anal. (C15H12N2O2) C, H, N. NMR
(CF3COOD): 10.26 (dd, 1H, 5-H), 8.63 (t, 1H, 7-H), 8.22 (t, 1H, 6-H), 8.34
(m, 2H) and 8.28 (m, 3H) (phenyl protons), 3.40 (s, 3H, 8-CH3). J5,6 = J6,7
= 7.0 Hz, J5,7 = 1.8 Hz.
Antiinflammatory Activity
[13]
The paw edema inhibition test
was used on rats. Groups of 5 rats of
both sexes (body weight 150–200 g), pregnant females excluded, were given
a dose of a test compound. After 30 min 0.2 ml 1% carrageenan suspension
in 0.9 % NaCl solution was injected subcutaneously into the plantar
aponeurosis of the hind paw and the paw volume was measured by the water
plethysmometer Socrel and then measured again 1, 2, 3, and 4 h later. The
mean increase of paw volume at each time interval was compared with that
of control group (5 rats treated with carrageenan, but not treated with test
compounds) at the same time intervals and percentage inhibition values were
calculated. The experimental results are listed in Table 1.
6-Chloro-2-phenylimidazo[1,2-a]pyridine-3-carboxylic acid 5f
Prepared from 4f. Mp 120°C, 55%. Anal. (C14H9ClN2O2) C, H, Cl, N.
NMR (CF3COOD): 10.49 (d, 1H, 5-H), 8.71 (d, 1H, 8-H), 8.26 (dd, 1H, 7-H),
8.52 (m, 2H) and 8.37 (m, 3H) (phenyl protons), J7,8 = 9.38 Hz, J5,7 = 1.88
Hz.
2-Phenylimidazo[1,2-a]pyridine-3-carboxamides 6a,c–f
General procedure: 10 mmol of the starting ethyl ester 4 was dissolved in
50 ml of methanol, added with 50 ml of 32% aqueous ammonia and heated
in a closed vessel under a pressure of 400 psi for 24 h. After cooling, the
solution was evaporated in vacuo. The residue was dissolved in a small
volume of chloroform and chromatographed on silica gel with n-hexane/di-
ethyl ether mixtures. The product was then recrystallized from methanol.
Analgesic Activity
Acetic acid writhing test [14]was used on mice. Groups of 5 mice of both
sexes (body weight 20–25 g), pregnant females excluded, were given a dose
of a test compound. After 30 min the animals were injected intraperitoneally
with 0.25 ml/mouse of 0.5 % acetic acid solution and writhes were counted
during the following 25 min. The mean number of writhes for each experi-
mental group and percentage decrease compared with the control group (5
mice not treated with test compounds) were calculated. The experimental
results are listed in Table 2.
2-Phenylimidazo[1,2-a]pyridine-3-carboxamide 6a
Prepared from 4a. Mp 130°C, yield 68%. Anal. (C14H11N3O) C, H, N.
NMR (CDCl3): 8.18 (d, 1H, 5-H), 7.72 (d, 1H, 8-H), 7.39 (t, 1H, 7-H), 6.85
Arch. Pharm. Pharm. Med. Chem. 331, 273–278 (1998)

278
Avallone and co-workers
Ulcerogenic Action
References
Groups of 10 rats of both sexes (body weight 200–220 g), pregnant females
excluded, fasted for 24 h, were given an oral dose of a test compound, except
the control group. All animals were sacrificed 6 h after dosing and their
stomachs and small intestines were macroscopically examined to assess the
incidence of hyperaemia and ulcers. The experimental results are listed in
Table 3.
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centrifuged again for 1 h at 100000 g. The microsomal pellet was used
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fractions (50 µl) were incubated with test agents for 5 min at 37°C in 30 µl
of Tris-HCl, pH 8.0, containing 2 mM reduced glutathione, 5mM L-trypto-
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amounts of [1-14C]arachidonic acid (220000 cpm), was then added and the
reaction proceeded for 3 min at 37°C. The reaction was stopped by the
addition of 0.2 ml of ethyl ether/methanol/citric acid 0.2 M (30:4:1), which
was precooled at –25°C. PGE2 was extracted twice into the same mixture.
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photometer (Model 100-40) equipped with a flow cell; the sample was
injected on a Ultrasphere column (Beckman) ODS 5 mm, 4.6 mm × 25 cm,
with 2 nmol unlabelled PGE2 as an internal standard. The PG chroma-
tographic profile was obtained by isocratic elution with 150 mM H3PO4 in
water, pH 3.5, containing 30% acetonitrile, at flow rate of 1 ml/min moni-
toring the UV absorption at 214 nm. Radioactivity that coeluted with authen-
tic PGE2 was quantified by liquid scintillation spectrometry. Test samples
were compared with paired control incubations. The percentage of inhibition
was calculated as follows:
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[17] V. Calderaro, A. Giovane, B. De Simone, G. Camussi, R. Rossiello, L.
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[(cpm control – cpm test)/(cpm control)] × 100
Received: May 11, 1998 [FP301]
Arch. Pharm. Pharm. Med. Chem. 331, 273–278 (1998)