2-Substituted-8-methyl-3,6-dihydroimidazo[4,5-c]pyrazolo[3,4-e] pyridazine as an anti-inflammatory agent

Article abstract of DOI:10.1007/s00044-009-9290-9

A series of 8-methyl-2-substituted-3,6-dihydroimidazo[ 4,5-c]pyrazolo[3,4- e]pyridazine compounds have been synthesized in the present investigation utilizing Philips condensation (Philips, J Chem Soc 2393-2399, 1928). The anti-inflammatory activity of the synthesized compounds was evaluated using a carrageenin rat model. Springer Science+Business Media, LLC 2010.

Full text of DOI:10.1007/s00044-009-9290-9

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:125–129
DOI 10.1007/s00044-009-9290-9
ORIGINAL RESEARCH
2-Substituted-8-methyl-3,6-dihydroimidazo[4,5-c]pyrazolo[3,4-e]
pyridazine as an anti-inflammatory agent
•
Ashish Kumar Tewari Rashmi Dubey
•
Anil Mishra
Received: 1 December 2008 / Accepted: 10 December 2009 / Published online: 22 January 2010
Ó Springer Science+Business Media, LLC 2010
Abstract A series of 8-methyl-2-substituted-3,6-dihy-
droimidazo[4,5-c]pyrazolo[3,4-e]pyridazine compounds
synthesis of pyridazines from 1,4-diketones and hydrazine
hydrate is one of the best known procedures (Hendrickson
et al., 1964). However, its major limitation is the avail-
ability of the required 1,4-dicarbonyl precursors (Huisgen
et al., 1968; Potts and Roy, 1968; Potts and Elliott, 1973).
This, in part, is due to the difficulty in the cycloaddition
procedure (Vogel, 1978), which involves ring closure of
vicinal dicarbonyl compounds, to synthesize the fused
pyridazine derivatives.
have been synthesized in the present investigation utilizing
Philips condensation (Philips, J Chem Soc 2393–2399,
1928). The anti-inflammatory activity of the synthesized
compounds was evaluated using a carrageenin rat model.
Keywords 8-Methyl-2-substituted-3,6-dihydroimidazo
[4,5-c]pyrazolo[3,4-e]pyridazine ꢀ Anti-inflammatory ꢀ
Philips condensation
The present paper reports the synthesis and biological
activity of a series of five tricyclic compounds: 8-methyl-2-
phenyldihydroimidazo[4,5-c]pyrazolo[3,4-e]pyridazine (6a),
8-methyl-2-[2-phenylethany]-3,6-dihydroimidazo[4,5-c]
pyrazolo[3,4-e]pyridazine (6b), 2-(8-methyl-3,6-dihydro-
imidazo[4,5-c]pyrazolo[3,4-e]pyridazin-2-yl)benzoicacid
(6c), 3-(8-methyl-3,6-dihydroimidazo[4,5-c]pyrazolo[3,4-
e]pyridazin-2-yl)propionic acid (6d), and 5-(8-methyl-3,6-
dihydroimidazo[4,5-c]pyrazolo[3,4-e]pyridazin-2-yl)penta-
noic acid (6e). The objective was achieved by using a unique
procedure of synthesizing 4,5-disubstituted-3-methyl-
1H-pyrazolo[3,4-c]pyridazin, staring from 5-methyl-2,4-
dihydro-3H-pyrazo-3-one, already synthesized by known
method (Winter et al., 1962).
Introduction
Heterocyclic systems containing pyrazole and imidazole
rings are characterized by several biological properties
(Avasthi et al., 2002, 2003) including a medicinal character
which can be utilized in the management of inflammation
(Deeb et al., 1990, 1991; Deeb and Said, 1990; Tisler and
Stanounic, 1973; Seada et al., 1989). Various synthetic
routes have been followed for synthesizing the fused ring
pyrazolo-pyridazine system and their derivatives (Druey,
1958; Caronna et al., 1986; Kobayashi et al., 1971; Kasuga
et al., 1974; Shawali, 1977; Kurihara et al., 1980). The
In Scheme 1, the synthesized 4-amino-3-methyl-1H-
pyrazolo [3,4-c]pyridazin-5-yl amine (5), was further
cyclized with different carboxylic acids (Scheme 2) to
obtain the final products.
A. K. Tewari (&)
Department of Chemistry, Faculty of Science, Banaras Hindu
Biological activity
University, Varanasi, India
e-mail: tashish2002@yahoo.com
All the reported compounds were tested for their anti-
inflammatory activities against carrageenin induced rats
paw edema.
R. Dubey ꢀ A. Mishra
Department of Chemistry, Lucknow University, Lucknow, India
e-mail: mishraanil101@hotmail.com
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Med Chem Res (2011) 20:125–129
Scheme 1 Synthesis of 4-
amino-3-methyl-1H-
pyrazolo[3,4-c]pyridazin-5-yl
amine
H C
3
H C
3
NH NH .H O
NH NH .H O
2
2
2
2
2
2
CH COCH COOC H
3
2
2
5
N
O
N
N
H
N.NH
2
N
H
Glacial Acetic Acid
in Ethanol
( 1 )
C H O
O
2
5
O
OC H
2
5
O
N
H C
3
Cl
N
H C
3
H C
3
OC H
2
OC H
2 5
5
SnCl2
Cl
N
POCl3
N
N
N
N
N
H
N
N
Nitro Benzene
N
N
O
C H O
2
5
H
H
( 4 )
( 3 )
( 2 )
NH3
NH
2
H C
3
NH
2
N
N
N
N
H
( 5 )
R
N
30 min after carrageenin treatment by the micropipette
method as described by Buttle et al. (1957). The increase in
the volume of the paw in each group was measured and
percent anti-inflammatory activity was calculated by fol-
lowing formula:
H
NH2
N
H3C
N
H3C
NH2
RCOOH
N
N
N
N
N
N
N
Percent anti-inflammatory activity ¼ ½1 ꢁ Vt=Vcꢂ ꢃ 100
H
H
( 5 )
( 6 a-e )
where Vt and Vc are the volume of the paw edema in drug
treated and control group, respectively, where Vc is vol-
ume of the paw edema of control - volume of the paw
edema of saline treated rats. Results in parentheses indi-
cate percentage change from respective control group
(Table 2).
Scheme 2 Synthesis of 2-substituted-8-methyl-3,6-dihydroimidazo
[4,5-c]pyrazolo[3,4-e]pyridazine
Anti-inflammatory activity against carrageenin induced
rats paw edema
The anti-inflammatory activity of the synthesized com-
pound was evaluated against carrageenin induced paw
edema in albino rats. The weight of the rats ranged between
80 and 180 g each. Food and water was given to the
experimental animals prior to the experiments. 0.05 ml of a
freshly prepared suspension of carrageenin (1.0%) in 0.9%
of saline was injected beneath the planter aponeurosis of
the right paw of the rats and saline was injected in the
opposite paw of the rat using the method of Winter (Segura
et al., 1998). Three sets of five rats each were maintained.
One set was kept as control and the other two sets were
pretreated with the test drug and standard drug, respec-
tively, at a dose (Olayemi and Ajaiyeoba, 2007) of
100 mg kg-1, orally 1 h before the carrageenin treatment
given (Table 1). Rat paw was measured in the interval of
Experimental section
Melting points were taken by an electrically heated
instrument and are uncorrected. Compounds were routinely
checked for their purity on silica gel G TLC plates and the
spots were visualized by iodine vapors. Column chroma-
tography was carried out by packing the column with
60–120 mesh silica gel G, used for purifying the com-
pound. IR spectra were recorded on Varian 3100 FT-IR
spectrometer. 1H and 13C-NMR spectra were recorded on a
JEOL AL 300 MHz FT NMR instrument. NMR data rep-
resented as follows: chemical shifts d (in ppm relative to
dTMS = 0), multiplicity, coupling constant J (quoted in
hertz, Hz) integration, and assignment.
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Med Chem Res (2011) 20:125–129
127
Table 1 Percentage edema growth relative to control at different time intervals (mean SEM)
Group
0 (min)
30 (min)
90 (min)
180 (min)
Control
100
100
100
100
100
100
100
0
130.1 6.54(30.1)
114.1 2.88(14.1)
103.9 2.59(3.9)
115.1 10.02(15.1)
106.5 3.67(6.5)
133.9 3.56(33.9)
101.7 2.11
138.7 4.47(38.7)
123.4 3.37(23.4)
106.2 3.98(6.2)
123.3 3.83(23.3)
118.4 3.86(18.4)
146.5 6.54(46.5)
108 3.27
122.3 5.17(22.3)
114.9 4.25(14.9)
99.6 2.54(0.4)
120.6 8.34(20.6)
121.4 4.55(21.4)
133.6 7.58(33.6)
11.6 4.19
6a
0
0
0
0
0
0
6b
6c
6d
6e
Ibuprofen
Table 2 Anti-inflammatory activity screening data of the compounds
30 ml of ethanol and 20 ml of water. Hydrazone deriva-
tives were added to the stirring mixture for about 1 h.
Then, temperature of stirrer was increased up to 20°C and
the whole mixture was stirred for 5 h. The solid material
was filtered to yield title compound. Yield: 48% m.p.
286°C; 1H NMR (CDCl3): d 0.3 (t, 3H, CH3, J = 6), d 0.9
(s, 3H, CH3), d 1.11 (t, 3H, CH3, J = 6), d 1.4 (s, 2H,
CH2), d 3.7 (q, 2H, CH2, J = 6.0), d 4.2 (q, 2H, CH2,
J = 6), d 7.0 (s, 1H, NH); 13C NMR (CDCl3); d 13.3
(CH3), d 14.5 (CH3), d 15.4 (CH3), d 30.0 (CH2), d 56.3
(CH2), d 59.6 (CH2), d 155.6 (CCH3), d 161 (CO), d 163
(CO), d 164 (C=N); IR (KBr): 3575 (O–H), 1718 (C=O),
1413 (C–N), 3413 (N–H); Elemental analysis for
C10H16N4O3: calcd: C; 50.00%, H; 6.66%, N; 23.33%
Found: C; 50.1%, H; 6.65%, N; 23.29%; M S: m/e 184.
Compound no.
Mean
difference
Percent activity
(100 mg/kg)
6a
28.76
30.17
22.31
29.08
28.73
18.76
30
35
41
33
31
49
6b
6c
6d
6e
Ibuprofen
5-Methyl-2,4-dihydro-3H-pyrazol-3-one hydrazone (1)
To a mixture of 60 ml of hydrazine hydrate, and 60 ml
of glacial acetic acid, about 30 ml of water and 5-methyl-
2,4-dihydro-3H-pyrazol-3-one (0.13 mol) was added in
fractions for about 30 min. The mixture was stirred con-
tinuously on a magnetic stirrer during the addition. After
complete addition, the mixture was warmed on a water
bath for 1 h. On cooling and scratching the sides of round-
bottom flask 1 was precipitated. Compound was recrys-
tallized from ethanol. yield: 54% m.p 241°C 1H NMR
(DMSO): d 0.91 (1H, s, CH3), d 1.34 (3H, s, CH2), d 7.10
(1H, s, NH) d 7.11 (2H, s, NH2); 13C NMR (DMSO): d
15.4 (CH3), d 36.1 (CH2), d 155.6 (CCH3), d 155 (C=N);
IR (KBr): 3513 (sym), 3316 (assy) (N–H), 1387 (C–N);
Elemental analysis for C4H8N4: calcd.: C; 42.85%, H;
7.14%, N; 50% Found: C; 43.27%, H; 7.87%, N; 48.98%;
MS: m/z 112.
4,5-Dihydroxy-3-methyl-1H–pyrazolo[3,4-c]pyridazine
(3)
4,5-Dihydroxy-3-methyl-1H-pyrazolo[3,4-c]pyridazine (3)
has been synthesized by refluxing ethyl-2-[2-(5-methyl-2,4-
dihydro-3H-pyrazol-3-ylidene) hydrazino]-2-oxoacetate (3)
(0.05 mol) with nitrobenzene (30 ml) and SnCl2 (10 g) for
5 h. The reaction was continued until a black jelly was
settled on the bottom of round-bottomed flask. On the
completion of cyclization nitrobenzene was distilled out.
The solid black material was shaken vigorously with water
in which insoluble material was filtered through suction.
Recrystallization from alcohol yielded the desired product
(4) Yield: 80%, m.p. 324°C; 1H NMR (DMSO d6): d 0.9 (s,
3H, CH3), d 1.11 (t, 3H, CH3, J = 6), d 2.2 (s, 3H, CH), d
3.57 (q, 2H, CH2, J = 6), d 5.2 (s, 1H, NH); 13C NMR
(DMSO d6): d 12.7 (CH3), d 14.5 (CH3), d 44.5 (CCC), d
56.4 (CH2), d 155.6 (CCH3), d 163 (NCO), d 164 (C=N) d
200 (CO); IR (KBr): 3575 (O–H), 1718 (C=O), 1413 (C–N),
3413 (N–H); Elemental analysis for C8H9N4O2: calcd: C;
49.74%, H; 4.66%, N; 29.01% Found: C; 49.71%, H;
4.62%, N; 29.15%; MS: m/e (%) 166 (M?, 100.0), 137
(84.9), 108 (19.3), 81 (33.8) and 56 (13.4).
Ethyl-2-[2-(5-methyl-2,4-dihydro-3H-pyrazol-3-
ylidene)hydrazine]-2-oxoacetate (2)
Ethyl-2-[2-(5-methyl-2,4-dihydro-3H-pyrazol-3-ylidene)
hydrazine]-2-oxoacetate (2) was synthesized by adding
5-methyl-2,4-dihydro-3H-pyrazol-3-one hydrazone (1)
(0.18 mol) in fractions to a well stirred mixture of diethyl
oxalate (0.18 mol) and 8 g of anhydrous sodium acetate in
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Med Chem Res (2011) 20:125–129
4,5-Dichloro-3-methyl-1H-pyrazolo[3,4-c]pyridazine (4)
C13H10N6: calcd.: C; 62.40%, H; 4.00%, N; 33.60% Found:
C; 62.82%, H; 4.32%, N; 32.82%; MS: m/e 250.
4,5-Dichloro-3-methyl-1H-pyrazolo[3,4-c]pyridazine (4)
has been synthesized by refluxing 4,5-dihydroxy-3-methyl-
1H-pyrazolo [3,4-c]pyridazine (3) (0.05 mol) with phos-
phorous oxychloride (200 ml) for 50 h. Excess POCl3 was
removed by vacuum distillation. The residual mixture was
poured into crushed ice to give 4 yields: 95.2%, m.p.
298°C; 1H NMR (DMSO d6): d 2.32 (s, 3H, CH3), d 12.67
(S, 1H, NH); 13C NMR (DMSO d6): d 12.43 (CH3), d104.6
(CCC), d 134.56 (CCl), d 135 (C=N), d 145 (C=N), d
154.21 (NCCl); Elemental analysis for C6H4N4Cl2: calcd.:
C; 35.64%, H; 1.98%, N; 27.72% Found: C; 35.63%, H;
1.94%, N; 27.70%; MS: m/z 202.
6b: R = –CH=CH–C6H5
1
Yield: 81.6% m.p. 138°C. H NMR (DMSO d6): d = 7.7
(m, 5H, Ph H), d 5.3 (s, 1H, NH), d 4.7 (s, 1H, NH), d 3.9
(d, J = 2.8, 1H, H10), d 3.4 (d, J = 2.8, 1H, H20), d 2.2 (s,
3 H CH3); 13C NMR (DMSO d6): d 10.46 (CH3), d 104.89
(CCC), d 121.56 (CCN), d 122 (NCN), d 124 (C=C), d
126.1 (ArCH), d 127.32 (ArCH), d 128.2 (ArCH), d 130.2
(C=C), d 134.76 (C–C), d 135.5 (NCN), d 135.87 (C–C), d
144.23 (C–CH3); Elemental analysis for C15H12N6: calcd.:
C; 65.21%, H; 4.35%, N; 30.44% Found: C; 66.78%, H;
4.82%, N; 30.12%; MS: m/e 276.
4-Amino-3-methyl-1H-pyrazolo[3,4-c]pyridazin-5-yl
amine (5)
6c: R = C6H4COOH
Yield: 79% 1H NMR (DMSO d6): d 2.2 (s, 3H, CH3), d 3.8
(s, 1H, OH), d 4.5 (s, 1H, NH), d 5.3 (s, 1H, NH), d 7.6 (m,
4H, PhH); 13C NMR (DMSO d6): d 10.46 (CH3), d 105.89
(CC), d 121.56 (CCN), d 122 (NCN), d 126.1 (ArCH), d
129 (CCO), d 128.7 (ArCH), d 130.21 (ArCH), d 134
(ArCH), d 136 (CC), d 139.21 (C–C), d 172 (CO), d 144.21
(C–CH3); IR (KBr): 1731 (C=O), 3512 (O–H), 3483 (N H),
1429 (C–N); Elemental analysis for C15H12N6: calcd.: C;
57.14%, H; 3.40%, N; 28.57% Found: C; 58.73%, H;
2.86%, N; 29.31%; MS: m/e 294.
4-Amino-3-methyl-1H-pyrazolo[3,4-c]pyridazin-5-yl amine
(5) was synthesized by stirring 5 (0.05 mol) with liquid
ammonia for 6 h. The product was filtered and recrystal-
lized from MeOH to 5. Yield: 90%; 1H NMR (DMSO d6):
d 2.56 (s, 3H, CH3), d 3.67 (S, 2H, NH2), d 3.67 (S, 2H,
NH2), d 12.67 (S, 1H, NH); 13C NMR (DMSO d6): d 11.46
(CH3), d 105 (CCC), d 132.56 (CNH2), d 134.87 (C=N), d
144.31 (C=N), d 150.10 (NCNH2); IR (KBr): 3548 (Sym),
3380 (Assy), (–NH2), 3489 (N–H), 1328 (C–N); Elemental
analysis for C6H8N6: calcd.: C; 43.90%, H; 4.87%, N;
51.21% Found: C; 43.1%, H; 4.89%, N; 51.00%; MS: m/e
164.
6d: R = –CH2CH2COOH
Yield: 86% m.p. 234°C 1H NMR (DMSO d6): d 6.2 (s, 1H,
OH), 5.3 (s, 1H, NH), 4.5 (s, 1H, NH), 3.1 (t, 2H, H-20), 2.8
(t, 2H, H-10), 2.2 (s, 3H, CH3); 13C NMR (DMSO d6): d
10.9 (CH3), d 36.78 (CH2CO), d 105.3 (CC), d 122.23
(CCN), d 122.67 (NCN), d 125.1 (CCH2), d 134.98 (NCN),
d 144.21 (C-CH3), d 148.67 (CCH2), d 177.0 (CO); IR
(KBr): 3513 (O–H), 3418 (N_H), 1692(C–O); Elemental
analysis for C10H10N6O2: calcd.: C; 48.78%, H; 4.06%, N;
34.14% Found: C; 49.26%, H; 3.96%, N; 33.82%; MS: m/e
248.
2-Substitued-8-methyl-3,6-dihydroimidazo[4,5-
c]pyrazolo[3,4-e]pyridazine (6a–e) general method
2-Substitued-8-methyl-3,6-dihydroimidazo[4,5-c]pyrazolo
[3,4-e]pyridazine (6a-e) have been synthesized by stirring
4-amino-3-methyl-1H-pyrazolo[3,4-c]pyridazin-5-yl amine
(5) (8.20 g, 0.05 mol) and carboxylic acids (0.05 mol) in
4 N hydrochloric acid (50 ml) for 4 h at 80°C. The reaction
mixture was made alkaline by adding liquor ammonia
solution. Precipitate obtain was filtered and purified by
column chromatography using CHCl3 and MeOH.
6e: R = –CH2CH2CH2CH2COOH
1
Yield: 83.3% m.p. 152°C H NMR (DMSO d6): d 6.7 (s,
6a: R = –C6H
1H, OH), 5.3 (s, 1H, NH), 4.5 (s, 1H, NH), 3.8 (t, 2H, H-
40), 3.1 (m, 4H, H-20, H-30), 2.6 (t, 2H, H-10), 2.1 (s, 3H,
CH3); 13C NMR (DMSO d6): d 10.59 (CH3), d 25.00
(CH2), d 29.4 (CH2), d 30.21 (CH2), d 31.78 (CH2), d 35.7
(CCO), d 105.36 (CC), d 122.12 (CCN), d 122.43 (NCN), d
135.8 (NCN), d 144 (C–CH3), d 148.57 (CCH2), d 176.78
(CO); IR (KBr): 1711 (C=O), 3445 (O–H), 3313 (N–H),
3396 (–H). Elemental analysis for C12H14N6O2: calcd.: C;
5
Yield: 74.44% 1H NMR (DMSO d6): d 7.6 (s, 5H, PhH), d
5.3 (s, 1H, NH), d 4.8 (s, 1H, NH), d 2.1 (s, 3H, CH3); 13
C
NMR (DMSO d6): d 10.46 (CH3), d 104.89 (CCC), d
121.56 (CCN), d 122 (NCN), d 127.1 (ArCH), d 128.32
(ArCH), d 129.2 (ArCH), d 135.5 (NCN), d 135.87 (C–C),
d 136 (CCN), d 144.23 (C–CH3); Elemental analysis for
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cyclization of N-aminodiazinium salts. Chem Pharm Bull
22:1814
Kobayashi Y, Kutsuma T, Morinaga K (1971) Studies on the
reactions of heterocyclic compounds. V. Syntheses of diazinium
ylides and their conversion to azaindolizines. Chem Pharm Bull
(Tokyo) 19:2106–2115
Kurihara T, Uno T, Sakomoto Y (1980) Reaction of ethyl 3-
thoxymethylene-2,4-dioxovalerate with monosubstituted hydra-
zines. J Heterocycl Chem 17:231–233
52.56%, H; 5.11%, N; 30.65% Found: C; 53.12%, H;
6.12%, N; 30.04%; MS: m/e 274.
Acknowledgment The authors acknowledge the help of RSCI,
CDRI Lucknow for providing the spectral analysis. Financial assis-
tance from UGC India grant no F.31-139/2005 (SR), India is also
gratefully acknowledged.
Olayemi JO, Ajaiyeoba EO (2007) Short communication—anti-
inflammatory studies of yam (Dioscorea esculenta) extract on
wistar rats. Afr J Biotechnol 6:1913–1915
References
Philips MA (1928) The formation of 2-substituted benziminazoles.
J Chem Soc 2393–2399. doi:10.1039/JR9280002393
Potts KT, Elliott AJ (1973) o-Dibenzoyl heterocycles via cycloaddi-
tion reactions. Convenient route to fused pyridazine systems.
J Org Chem 38:1769
Avasthi K, Tewari A, Rawat DS, Sharon A, Prakash R, Maulik PR
(2002) A stacked pyrazolo[3,4-d]pyrimidine-based flexible mol-
ecule: the effect of a bulky benzyl group on intermolecular
stacking in comparison with methyl and ethyl groups. Acta
Crystallogr Sect C 58:494–496
Avasthi K, Farooq SM, Tewari AK, Sharon A, Maulik PR (2003)
Intermolecular stacking in pyrazolo[3,4-d]pyrimidine-based pen-
tamethylene-linked flexible molecules. Acta Crystallogr Sect C
59:o42–o45
Buttle GAH, D’Arcy PF, Howard EM, Kellett DN (1957) Plethys-
mometric measurement of swelling in the feet of small
laboratory animals. Nature 179:629
Caronna S, Migliara O, Petruso S (1986) Synthesis of pyrazole(3,4-
a)pyridazine derivatives. Bull Chem Farm 125:114–116
Deeb A, Said SA (1990) Studies on polyazaindenes synthesis of
several new condensed pyridazine derivatives. Collect Czech
Chem Commun 55:2795
Deeb A, Said SA, Homed MM Yasine F (1990) J Chim Soc (Taipei)
37 287
Deeb A, Bayoumy B, Essawy AE, Fikry R (1991) Pyridazine
derivatives and related compounds part 5. Pyrazolo[3,4-c]pyrid-
azine: synthesis and some reactions. Heterocycles 32:895–900
Druey J (1958) Angew Chem 70:5
Hendrickson JB, Rees R, Templeton JF (1964) A new general
heterocycle synthesis; use of acetylenedicarboxylic esters. J Am
Chem Soc 86:107–111
Huisgen R, Gotthardt H, Groshey R (1968) Chem Ber 101:1062
Kasuga K, Hirobe M, Okamoto T (1974) Reaction of N-aminopyrid-
inium derivatives. XIII. Syntheses of pyrazolodiazines by
Potts KT, Roy DN (1968) 1,3-Dipolar cyclo-addition of mesoionic
hydroxides.
anhydro-2-aryl-5-hydroxy-3-methylthiazolium
Chem Commun 536:1061–1062
Seada M, Fawzy MM, Johine H, Magid MA, Saad RR (1989) J Chin
Soc (Taipei) 36:241
Segura L, Vila R, Gupta MP, Avella ME, Adzet T, Canigueral S
(1998) Antiinflammatory activity of Anthurium cerrocampan-
ense Croat in rats, mice. J Ethnopharm 61:243–248
Shawali AS (1977) Synthesis and tautomeric structure of some 2H-
pyrazolo[3,4-d]pyridazines. J Heterocycl Chem 14:375–381
Tewari AK, Mishra A (2001) Synthesis and anti-inflammatory
activities of N4, N5-isubstituted-3-methyl-1H-pyrazolo[3,4-
c]pyridazines. Bioorganic Med Chem 9:715–718
Tewari AK, Mishra L, Verma HN, Mishra A (2002) Synthesis and
antifungal activity of 4-substituted-3,7-dimethyl-pyrazolo[3,4-
e][1,2, 4]triazine. Indian J Chem 41B:664–667
Tisler M, Stanounic B (1973) In: Castle RN (ed) The chemistry of
heterocyclic compounds. Wiley, New York, p 785
Vogel AL (1978) Text-book of practical organic chemistry, 4th edn.
New York: Longman, p 595
Winter CA, Risley EA, Nuss GW (1962) Carrageenin-induced edema
in hind paw of the rat as an assay for antiinflammatory drugs.
Proc Soc Exp Biol Med 111:544–547
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