Synthesis and pharmacological activity of some synthesized polyazacyclopenta[a]naphthalenes and pyrazolo[3,4-b]pyridines using 2-amino-6-methyl-4-phenylnicotinonitrile as synthon

Article abstract of DOI:10.1007/s00706-008-0091-5

A series of pyridines, pyrimidines, and their derivatives were synthesized using 2-amino-6-methyl-4-phenylnicotinonitrile as starting material. Thirteen new heterocyclics containing a pyridine ring were thus prepared. Pharmacological screening showed that many of these compounds have good anti-inflammatory and analgesic activity comparable with those of diclofenac potassium and valdecoxib as reference drugs. Assignment of the structures of the new compounds was based on chemical and spectroscopic evidence. Synthesis, spectroscopic data, and pharmacological properties of the compounds are reported in detail.

Full text of DOI:10.1007/s00706-008-0091-5

Monatsh Chem (2009) 140:573–579
DOI 10.1007/s00706-008-0091-5
ORIGINAL PAPER
Synthesis and pharmacological activity of some synthesized
polyazacyclopenta[a]naphthalenes and pyrazolo[3,4-b]pyridines
using 2-amino-6-methyl-4-phenylnicotinonitrile as synthon
Said Aly Said
Received: 16 October 2008 / Accepted: 21 October 2008 / Published online: 20 November 2008
Ó Springer-Verlag 2008
Abstract A series of pyridines, pyrimidines, and their
derivatives were synthesized using 2-amino-6-methyl-4-
phenylnicotinonitrile as starting material. Thirteen new
heterocyclics containing a pyridine ring were thus pre-
pared. Pharmacological screening showed that many of
these compounds have good anti-inflammatory and anal-
gesic activity comparable with those of diclofenac
potassium and valdecoxib as reference drugs. Assignment
of the structures of the new compounds was based on
chemical and spectroscopic evidence. Synthesis, spectro-
scopic data, and pharmacological properties of the
compounds are reported in detail.
work in heterocyclic chemistry, we synthesized some new
heterocyclic compounds containing the pyridine moiety
fused with other heterocyclic nuclei and tested their phar-
macological activity.
Results and discussion
Chemistry
In this paper we report the synthesis and a preliminary
pharmacological activity screening of several pyridine
derivatives based on 2-amino-6-methyl-4-phenylnicotino-
nitrile (1), which was prepared from 4-phenyl-but-3-en-2-
one and malononitrile in the presence of ammonium acetate
according to Ref. [9]. Reaction of 1 and 1,2-ethylenediamine
in the presence of carbon disulfide produced imidazoloa-
minopyridine 2, which was heated under reflux with carbon
disulfide or benzoyl chloride in pyridine to yield the corre-
sponding tetraazacyclopenta[a]naphthalenethione 3 and
tetraazacyclopenta[a]naphthalene 4. Compound 2 was
treated with sodium nitrite and hydrochloric acid in acetic
acid to give pentaazacyclopenta[a]naphthalene 5. When it
was heated under reflux in triethylorthoformate, it afforded
the corresponding tetraazacyclopenta[a]naphthalenethione
6 (Scheme 1).
Keywords 2-Amino-6-methyl-4-phenylnicotinonitrile Á
Polyazacyclopenta[a]naphthalenes Á Pyrazolopyridines Á
Anti-inflammatory and analgesic activity
Introduction
In previous work we prepared some substituted pyridines
and their derivatives [1–6]. In addition, the biological and
analgesic activity of many heterocyclic compounds con-
taining a pyridine moiety have been reviewed [7–9]. On the
other hand, pyrimidine derivatives have promising bio-
logical [10, 11] and anticancer activity [12, 13]. Recently,
some new pyridine and pyrimidine derivatives have been
synthesized and tested for androgenic–anabolic, antihy-
pertensive, and antiparkinsonian activity [14–16]. In view
of these observations and in continuation of our previous
Reaction of 1 with hydroxylamine hydrochloride in the
presence of anhydrous sodium acetate in glacial acetic acid
gave the corresponding pyrazolopyridine 7, which was
treated with acetylacetone or ethyl acetoacetate in acidic
medium to afford the corresponding trimethyltetraazafluo-
rene 8 and dimethyltetraazafluorenone 9. Heating of 7
under reflux with phenyl isothiocyanate in pyridine or
chloroacetyl chloride in dimethylformamide gave the cor-
responding pyrazolopyridine phenylthiourea 10 and
S. A. Said (&)
Chemistry Department, Faculty of Science, Zagazig University,
Zagazig, Egypt
e-mail: saidalysaid@yahoo.com
123

574
S. A. Said
Scheme 1
O
AcONH4
CN
H3C
+
C
CN
H2
O
NH2
H
N
Ph
CN
N
N
N
N
N
N
H3C
N
N
H3C
1
H3C
3
H2NCH2CH2NH2
H
4
NH2
N
CS2/Pyridine
PhCOCl
Pyridine
N
N
H3C
2
NaNO2/HCl
AcOH
Triethyl orthoformate
N
N
N
N
N
N
N
N
N
H3C
H3C
6
5
tetraazacyclopentaindenone 11. Condensation of 7 with 4-
nitrobenzaldehyde or cinnamaldehyde in ethanol under
reflux in the presence of piperidine as catalyst afforded the
corresponding the Schiff bases 12 and 13 (Scheme 2).
pharmacologically for their anti-inflammatory and analge-
sic activities.
Anti-inflammatory activity
Purpose and rationale
Pharmacological screening
For determination of the antiphlogistic potency of the
synthesized compounds, two standard tests were conducted
at doses 2.5 and 5 mg/kg body weight of the rats, namely,
protection against carrageenan-induced edema according to
Winter et al. [17] and inhibition of plasma PGE2. The latter
is known as a good confirming indicator for carrageenan-
induced rat paw edema [18]. Regarding protection against
All animals were obtained from the Animal House Colony,
Research Institute of Ophthalmology, Giza, Egypt. Ini-
tially, the acute toxicity of the compounds was assayed by
determining their LD50. Interestingly, all the synthesized
compounds were less toxic than valdecoxib (Table 1).
The newly synthesized compounds were then screened
123

Synthesis and pharmacological activity of naphthalenes and pyridines
575
Scheme 2
CH3
O
H
N
H
N
H
N
N
N
N
N
S
N
N
Ph
N
CH3
H3C
CH3
N
H
N
N
H
H
H3C
H3C
8
9
10
AcCH2COOEt
AcOH
AcCH2COCH3
EtOH
PhNCS
Pyridine
H
N
H
N
N
N
Cl
NH2OH.HCl
CH2COCl
N
NH2
N
N
O
1
H
AcONa/AcOH
H3C
H3C
7
11
O2N
CHO
Ph-CH=CH-CHO
H
N
H
N
N
N
N
N
N
N
H3C
NO2
H3C
13
12
carrageenan-induced edema, all tested compounds were
found to be more potent than diclofenac potassium. For
these compounds, a similar activity profile was obtained for
the inhibition of plasma PGE2. Concerning anti-inflam-
matory activity, the descending order of activity is 7, 2, 10,
1, 3, 11, 6, 5, 9, 4, 13, and 8. Compounds 7, 2, 10, 1, and 3
are the most active (Table 2).
Table 1 Acute toxicity (LD50) of the synthesized compounds
Compound no.
LD50/mg kg-1
1
2,213.78 0.19
2,100.89 0.17
1,456.09 0.12
1,249.87 0.12
2,134.89 0.10
1,720.00 0.11
2,112.55 0.11
1,620.14 0.24
2,612.56 0.16
2,213.87 0.18
1,272.87 0.17
1,345.98 0.14
1,180.01 0.23
2
3
4
Analgesic activity
5
6
All the compounds tested had analgesic activity in a hot-
plate assay (Table 3). Interestingly, the analgesic activity
of all the compounds 1–10, 12, and 13 was more potent
than that of valdecoxib as reference drug (Table 3) and,
compared with valdecoxib, after 120 min these analgesic
activities were increased. Compounds 7, 10, 2, 1, 3, 12, 6,
5, 9, 4, 13, and 8 are arranged in descending order of
analgesic potency. Compound 7 was three times more
active than valdecoxib, and compounds 1, 10, 2, and 3 were
twice as active as valdecoxib after 2 h.
7
8
9
10
11
13
ValdecoxibÒ
All results were significantly different from the normal control value
at P B 0.05
123

576
S. A. Said
Table 2 Anti-inflammatory
activity of some newly
synthesized compounds
Groups
Dose/mg kg-1
Protection against
edema/%
Inhibition of plasma
PGE2/%
1
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
2.5
5.0
96.45 0.052
97.89 0.042
98.12 0.077
98.09 0.063
92.90 0.073
97.76 0.062
82.10 0.077
93.00 0.060
80.94 0.074
96.00 0.062
85.06 0.055
96.10 0.066
89.88 0.091
99.34 0.080
78.80 0.090
91.94 0.060
91.10 0.064
95.18 0.075
90.26 0.034
98.55 0.035
86.14 0.053
98.16 0.052
79.28 0.081
92.90 0.098
70.14 0.061
76.23 0.082
79.26 0.040
81.48 0.052
83.14 0.040
85.05 0.030
74.70 0.040
79.05 0.060
58.00 0.030
73.55 0.040
62.10 0.040
78.87 0.030
60.13 0.040
76.10 0.040
62.15 0.030
85.15 0.070
56.56 0.050
75.05 0.040
72.43 0.048
77.55 0.040
61.10 0.050
82.05 0.048
58.42 0.050
80.08 0.054
56.91 0.040
76.10 0.041
53.05 0.040
70.05 0.051
2
3
4
5
6
7
8
9
10
11
13
All results were significantly
different from the standard and
normal control value at
P B 0.05
Diclofenac potassiumÒ
Table 3 Analgesic activity some newly synthesized compounds
Compound
Activity compared with that of valdecoxib after time:
10 min
20 min
30 min
60 min
90 min
120 min
1
0.60 0.02
0.65 0.02
0.54 0.01
0.46 0.01
0.46 0.02
0.46 0.01
0.73 0.02
0.41 0.01
0.48 0.01
0.66 0.01
0.50 0.01
0.42 0.01
1.00
0.60 0.05
0.75 0.07
0.55 0.03
0.46 0.03
0.46 0.03
0.48 0.04
0.84 0.07
0.42 0.03
0.48 0.03
0.62 0.06
0.54 0.05
0.42 0.04
1.00
0.89 0.03
0.80 0.06
0.86 0.05
0.52 0.04
0.60 0.04
0.61 0.05
0.97 0.08
0.45 0.04
0.56 0.05
0.96 0.07
0.81 0.06
0.50 0.05
1.00
1.00 0.01
1.15 0.15
0.88 0.08
0.64 0.06
0.74 0.07
0.76 0.07
1.20 0.12
0.58 0.05
0.67 0.09
1.00 0.01
0.85 0.08
0.61 0.06
1.00
1.18 0.10
1.43 0.12
1.12 0.12
0.80 0.08
0.99 0.09
0.99 0.09
1.63 0.16
0.89 0.08
0.87 0.09
1.24 0.12
1.11 0.11
0.97 0.09
1.00
2.34 0.12
2.45 0.14
2.22 0.21
1.30 0.08
1.58 0.04
1.63 0.06
3.55 0.13
1.11 0.07
1.47 0.14
2.56 0.11
1.89 0.08
1.28 0.16
1.00
2
3
4
5
6
7
8
9
10
12
13
Valdecoxib
All results were significantly different from the standard and normal control value at P B 0.05
123

Synthesis and pharmacological activity of naphthalenes and pyridines
Structure–activity relationship
577
(EI, 70 eV): m/z = 352 (M?, 12) and at 219 (100, base
peak).
The pyridine nucleus and poly nitrogen atoms in the mol-
ecule are essential for the anti-inflammatory and analgesic
activity. The fused ring at positions 2 and 3 with the sub-
stituents at positions 4 and 6 increases the activity.
7-Methyl-9-phenyl-2,5-dihydro-3H-1,3a,5,
6-tetraazacyclopenta[a]naphthalene-4-thione
(3, C16H14N4S)
A mixture of 1.26 g 2 (5 mmol) and 15 cm3 carbon disulfide
in 50 cm3 dry pyridine was heated under reflux for 10 h. The
solid obtained was isolated by filtration while still hot,
washed with water, dried, and crystallized to give 1.03 g 3
Experimental
Chemistry
(70%). Mp 172–174 °C (dioxane–H2O); IR (film):
-1
ꢀ
m = 3,331–3,213 (NH), 1,600 (C=N), 1,247 (C=S) cm
;
Melting points were determined in open glass capillaries
using an Electrothermal IA 9000 digital melting-point
apparatus. Elemental analyses were performed with an
Elementar Vario EL by the Microanalytical Unit, National
Research Center, Cairo Egypt and were found to be within
0.4% of the theoretical values. Infrared spectra were
recorded on Carl Zeiss model UR 10 spectrophotometer
using the KBr disc technique. 1H NMR spectra were
recorded on Varian Gemini 270 MHz spectrometer
(DMSO-d6) and chemical shifts are given in d (ppm)
downfield from tetramethylsilane (TMS) as internal stan-
dard. Mass spectra were measured using a Finnigan SSQ
7000 mass spectrometer. Follow up of the reactions and
checking of the purity of the compounds was performed by
TLC on silica gel-precoated aluminum sheets (type 60
1H NMR (DMSO-d6): d = 1.25–1.22 and 3.80–3.78 (2 m, 2
CH2), 2.48 (s, CH3), 7.05–7.40 (m, Ar-H), 7.50 (s, pyridyl-
H), 8.75 (s, NH, exchangeable with D2O) ppm; MS (EI,
70 eV): m/z = 294 (M?, 6) and at 279 (100, base peak).
7-Methyl-4,9-diphenyl-2,3-dihydro-1,3a,5,
6-tetraazacyclopenta[a]naphthalene (4, C22H18N4)
A mixture of 1.26 g 2 (5 mmol) and 0.7 g benzoyl chloride
(5 mmol) in 20 cm3 dry pyridine was heated under reflux
for 6 h. The reaction mixture was cooled, poured on to
water, and the solid formed was isolated by filtration,
washed with water, dried, and crystallized to give 1.0 g 4
ꢀ
(60%). Mp 128–130 °C (AcOH); IR (film): m = 3,070 (CH-
1
Ar), 1,610 (C=N) cm-1; H NMR (DMSO-d6): d = 1.90–
1.88 and 2.76–2.74 (2 m, 2 CH2), 2.46 (s, CH3), 7.18–7.46
(m, Ar-H), 7.55 (s, pyridyl-H) ppm; MS (EI, 70 eV): m/
z = 338 (M?, 16) and at 246 (100, base peak).
F
254; Merck, Darmstadt, Germany).
2-Amino-6-methyl-4-phenylnicotinonitrile (1, C13H11N3)
A mixture of 0.29 g 4-phenylbut-3-en-2-one (2 mmol),
0.13 g malononitrile (2 mmol), and 0.3 g ammonium
acetate (4 mmol) in 30 cm3 absolute ethanol was heated
under reflux for 5 h. After cooling, the product formed was
collected by filtration, washed with ethanol, dried, and
crystallized to give 0.31 g 1 (75%). Mp 140–142 °C
7-Methyl-9-phenyl-2,3-dihydro-1,3a,4,5,
6-pentaazacyclopenta[a]naphthalene (5, C15H13N5)
To a cold solution of 1.26 g 2 (5 mmol) in 15 cm3
hydrochloric acid and 15 cm3 acetic acid, 2 g sodium
nitrite in 15 cm3 water was added with stirring. After
complete addition the reaction mixture was stirred at room
temperature for 2 h. The solid product obtained was
isolated by filtration, washed with water, and crystallized
to give 0.8 g 5 (60%). Mp 185-183 °C (dioxane); IR (film):
ꢀ
(EtOH); IR (film): m = 3,341–3,223 (NH2), 2,209 (C:N),
1,604 (C=N) cm-1 1H NMR (DMSO-d6): d = 2.52 (s,
;
CH3), 4.50 (s, NH2, exchangeable with D2O), 7.10–7.48
(m, Ar-H and pyridyl-H) ppm; MS (EI, 70 eV): m/z = 209
(M?, 100, as a base peak).
m = 3,115 (CH-Ar), 1,608 (C=N) cm-1; 1H NMR (DMSO-
ꢀ
d6): d = 1.88–1.86 and 2.70–2.68 (2 m, 2 CH2), 2.46 (s,
CH3), 7.15–7.42 (m, Ar-H), 7.52 (s, pyridyl-H) ppm; MS
(EI, 70 eV): m/z = 263 (M?, 8) and at 248 (100, base
peak).
3-(4,5-Dihydro-1H-imidazol-2-yl)-6-methyl-4
-phenylpyridin-2-ylamine (2, C15H16N4)
To a mixture of 1.05 g 1 (5 mmol) and 7.5 cm3 ethylene-
diamine, 0.70 cm3 carbon disulfide was added dropwise
with stirring. The reaction mixture was heated under reflux
for 4 h. After cooling, it was poured on to ice-water. The
solid formed was isolated by filtration, washed with water,
dried, and crystallized to give 1.40 g 2 (80%). Mp 160–161
7-Methyl-9-phenyl-2,3-dihydro-1,3a,5,
6-tetraazacyclopenta[a]naphthalene (6, C16H14N4)
A mixture of 1.26 g 2 (5 mmol) and 15 cm3 triethylortho-
formate was heated under reflux for 3 h. After cooling, the
reaction mixture was poured on to cold water. The solid
precipitate was isolated by filtration, washed with water,
dried, and crystallized to give 0.65 g 6 (50%). Mp 240–242
ꢀ
°C (EtOH); IR (film): m = 3,336–3,211 (NH, NH2), 1,605
(C=N) cm-1 1H NMR (DMSO-d6): d = 1.80–1.78 and
;
2.71–2.68 (m, 2 CH2), 2.48 (s, CH3), 3.54 (s, NH2,
exchangeable with D2O), 7.00–7.45 (m, Ar-H), 7.52 (s,
pyridyl-H), 8.01 (s, NH, exchangeable with D2O) ppm; MS
°C (dioxane); IR (film):
ꢀm = 3,100 (CH-Ar), 1,604 (C=N)
cm-1; 1H NMR (DMSO-d6): d = 1.90–1.89 and 2.73–2.70
(2 m, 2 CH2), 2.45 (s, CH3), 7.17–7.46 (m, Ar-H and
123

578
S. A. Said
1
pyrimidinyl-H), 7.50 (s, pyridyl-H) ppm; MS (EI, 70 eV):
m/z = 262 (M?, 4) and at 170 (100, base peak).
3,219 (NH), 1,598 (C=N), 1,252 (C=S) cm-1; H NMR
(DMSO-d6): d = 2.44 (s, CH3), 7.03–7.42 (m, Ar-H), 7.51
(s, pyridyl-H), 8.69, 8.81 and 10.5 (3 s, 3NH exchangeable
with D2O) ppm; MS (EI, 70 eV): m/z = 359 (M?, 12) and
at 252 (100, base peak).
6-Methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridin-3-ylamine
(7, C13H12N4)
A mixture of 1.05 g 1 (5 mmol), 0.35 g hydroxylamine
hydrochloride (5 mmol), and 2 g anhydrous sodium acetate
in 30 cm3 glacial acetic acid was heated under reflux for
5 h. The reaction mixture was left overnight at room
temperature and then poured on to water. The solid
precipitate was isolated by filtration, washed with water,
and crystallized to give 0.85 g 7 (70%). Mp 188–190 °C
6-Methyl-4-phenyl-3a,8-dihydro-3H-3,7,8,
8a-tetraazacyclopenta[a]inden-2-one (11, C15H14N4O)
A mixture of 2.24 g 7 (10 mmol) and 1.13 g chloroacetyl
chloride (10 mmol) in 15 cm3 dimethylformamide with a
few drops of piperidine was heated under reflux for 6 h.
The reaction mixture was poured on to ice–water, and the
solid which separated was crystallized to give 1.7 g 11
ꢀ
(EtOH); IR (film): m = 3,450–3,320 (NH, NH2), 1,610
(C=N) cm-1 1H NMR (DMSO-d6): d = 2.50 (s, CH3),
;
(65%). Mp 172–174 °C (DMF–EtOH); IR (film):
-1
ꢀ
6.80 (s, NH2 exchangeable with D2O), 7.30–7.50 (m, Ar-
H), 7.52 (s, pyridyl-H), 8.62 (s, NH exchangeable with
D2O) ppm; MS (EI, 70 eV): m/z = 224 (M?, 12) and at
193 (100, base peak).
m = 3,350–3,260 (NH), 1,675 (C=O), 1,602 (C=N) cm ;
1H NMR (DMSO-d6): d = 2.54 (s, CH3), 3.35 and 3.42
(2d, CH2), 5.85 (s, CH), 7.05–7.46 (m, Ar-H), 7.45 (s,
pyridyl-H), 9.45 and 10.36 (2 s, 2NH exchangeable with
D2O) ppm; MS (EI, 70 eV): m/z = 266 (M?, 8) and at 194
(100, base peak).
2,6,8-Trimethyl-4-phenyl-4b,9-dihydro-1,5,8a,
9-tetraazafluorene (8, C18H18N4)
To a mixture of 1.12 g 7 (5 mmol) and 0.5 cm3 acetyl-
acetone (5 mmol) in 25 cm3 ethanol, a few drops of acetic
acid were added. The reaction mixture was heated under
reflux for 6 h, concentrated under reduced pressure, and
allowed to cool. The solid formed was isolated by filtration,
and crystallized to give 0.87 g 8 (60%). Mp 120–122 °C
Synthesis of the Schiff bases 12 and 13
A suspension of 1.12 g 7 (5 mmol) and 4-nitrobenzalde-
hyde or cinnamaldehyde (5 mmol) in 30 cm3 ethanol
containing a few drops of piperidine was heated under
reflux for 6 h. The reaction mixture was triturated with cold
water, and the solid product was isolated by filtration,
dried, and crystallized to give 0.98 g 12 (55%) and 1.0 g 13
(60%).
(EtOH); IR (film): m = 3,344 (NH), 1,605 (C=N) cm-1; 1H
ꢀ
NMR (DMSO-d6): d = 1.30, 1.90 and 2.50 (3 s, 3CH3),
3.34 (s, CH), 6.97–7.32 (m, Ar-H and CH-pyrimidine),
7.52 (s, pyridyl-H), 10.51 (s, NH exchangeable with D2O)
ppm; MS (EI, 70 eV): m/z = 290 (M?, 8) and at 168 (100,
base peak).
4-Nitrobenzylidene-(6-methyl-4-phenyl-1H-pyrazolo[3,4-
b]pyridin-3-yl)-amine (12, C20H15N5O2)
ꢀ
Mp 110–112 °C (dioxane); IR (film): m = 3,410 (NH),
2,6-Dimethyl-4-phenyl-4b,9-dihydro-5H-1,5,8a,
1
1,612 (C=N), 1545 (NO2) cm-1; H NMR (DMSO-d6):
9-tetraazafluoren-8-one (9, C17H16N4O)
d = 2.48 (s, CH3), 6.85–7.35 (m, Ar-H), 7.50 (s, pyridyl-
H), 8.15 (s, CH=N), 10.42 (s, NH exchangeable with D2O)
ppm; MS (EI, 70 eV): m/z = 357 (M?, 18) and at 208
(100, base peak).
A mixture of 1.12 g 7 (5 mmol) and 0.65 cm3 ethyl
acetoacetate (5 mmol) in 20 cm3 glacial acetic acid was
heated under reflux for 5 h. The solid product that formed
after cooling was collected by filtration, dried, and
crystallized to give 0.73 g 9 (50%). Mp 135–137 °C
(7-Methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridin-3-yl)-(3-
phenylallylidene)amine (13, C22H18N4)
ꢀ
(EtOH); IR (film): m = 3,343–3,216 (NH), 1,660 (C=O),
161 (C=N) cm-1; 1H NMR (DMSO-d6): d = 1.70 and 2.52
(2 s, 2CH3), 5.05 and 6.0 (2 s, 2CH), 7.10–7.40 (m, Ar-H),
7.49 (s, pyridyl-H), 9.50 and 10.42 (2 s, 2NH exchangeable
with D2O) ppm; MS (EI, 70 eV): m/z = 292 (M?, 8) and at
234 (100, base peak).
ꢀ
Mp 150–152 °C (DMF–EtOH); IR (film): m = 3,398 (NH),
1
1,660 (C=C), 1,608 (C=N) cm-1; H NMR (DMSO-d6):
d = 2.50 (s, CH3), 3.33 and 3.56 (2d, 2CH), 6.74-7.38 (m,
Ar-H), 7.52 (s, pyridyl-H), 8.14 (d, CH = N), 10.25 (s, NH
exchangeable with D2O) ppm; MS (EI, 70 eV): m/z = 338
(M?, 6) and at 235 (100, base peak).
1-(6-Methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridin-3-yl)-3-
phenylthiourea (10, C20H17N5S)
A mixture of 1.12 g 7 (5 mmol) and 0.66 cm3 phenyl
isothiocyanate (5 mmol) in 30 cm3 pyridine was heated
under reflux for 3 h. The precipitate that formed was
isolated by filtration, dried, and crystallized to give 1.1 g
Pharmacological screening
Determination of acute toxicity (LD50)
The LD50 was determined by using rats. They were
injected with different increasing doses of the synthesized
ꢀ
10 (60%). Mp 105–107 °C (dioxane); IR (film): m = 3,330–
123

Synthesis and pharmacological activity of naphthalenes and pyridines
579
compounds. The dose that killed 50% of the animals was
calculated according to Austen et al. [19] (Table 1).
(received saline), the second group received vehicle (gum
acacia), the third received valdecoxib as reference drug,
and the other groups received the test compounds (s.c.
administration; dose 5 mg/kg). Mice were dropped gently
into a dry glass beaker of 1 dm3 capacity maintained at
55.0–55.5 °C. Normal reaction time in seconds for all
animals was determined 10, 20, 30, 45, 60, 90, and
120 min after administration of the compound. The reac-
tion time was the time from the instant the mouse reached
the hot beaker until the animals licked its feet or jumped
out of the beaker [20]. The potencies relative to that of
valdecoxib were determined (Table 3).
Anti-inflammatory activity
Carrageenan-induced edema (rat’s paw test)
Groups of adult male albino rats (150–180 g), each of eight
animals, were orally dosed with tested compounds at a dose
of 2.5–5 mg/kg one hour before the carrageenan challenge.
Foot paw edema was induced by sub-plantar injection of
0.05 cm3 of a 1% suspension of carrageenan in saline
solution into the plantar tissue of one hind paw. An equal
volume of saline was injected to the other hind paw and
served as control. Four hours after drug administration, the
animals were decapitated, blood was collected, and the
paws were rapidly excised. The average weight of edema
was examined for the treated and control groups, and the
percentage inhibition of the weight of the edema was
evaluated. Diclofenac potassium (5 mg/kg) was employed
as standard reference to which the tested compounds were
compared (Table 2).
Acknowledgments The kind help of Dr Mohamed M. Abdulla,
Research Units, Hi-Care Pharmaceutical Co., Cairo, Egypt, for car-
rying out the pharmacological screening is highly appreciated.
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Analgesic activity
Sixty Webster mice of both sexes weighting 20–25 g were
divided into ten groups. One group was kept as control
123