A. K. Tewari, A. Mishra /Bioorg. Med. Chem. 9 (2001) 715±718
717
Table 1. Anti-in¯ammatory activity of N4,N5-Diubstituted-3-methyl-
1H-pyrazolo[3,4-c]pyridazines
7.8 (m, 15H, ArH), 2.1 (s, 3H, CH3). CMR (DMSO-d6):
d 200 (OCO), 180 (NCO), 158 (C-8), 151 (C-5 and C-3),
144, 143, 141 (aromatic), 82 (C-4), 76 (C-9), 21 (3-CH3).
M/S (m/z): 478 (M+), 374 (C20H14N4O4), 254
(C13H10N4O2), 149 (C6H7N5), 134 (C6H6N4), 105
(C7H5O), 80 (C4H4N2) and 58 (C2H6N2). Anal.
(C27H18N4O5); calcd C, 67.78; H, 3.76; N, 11.71; found
C, 68.31; H, 4.17; N 11.92%.
Compound No.
Mean Dierence
Percent Activity
(100 mg/Kg)
4
5
6
7
8
9
10
26.14
22.01
24.35
21.19
17.73
23.18
25.63
36
45
39
32
49
40
40
3-Methyl-N4,N5-bis(4-methylphenyl)-1H-pyrazolo[3,4-c]-
pyridazine-4,5-diamine (7). 4,5-Dichloro-3-methyl-1H-
pyrazolo[3,4-c]pyridazine (5) (2 g, 0.01 mole) was re¯uxed
with p-toluedine (1.07 g, 0.01 mole) in tetrahydro furan
for 12 h. After the completion of the reaction the reac-
tion mixture was poured in cold water and ®ltered
through suction. The crude material was recrystallized
from a mixture of water and ethanol to give 7. Yield
2.9 g (83%). PMR (CD3OD): d 7.2 (m, 8H,ArH), 6.5 (s,
1H, 1-NH), 6.1 (s, 1H, 5-NH), 5.8 (s, 1H, 4NH), 2.4 (s,
6H, Ar-CH3), 2.1 (s, 3H, 3-CH3). CMR (CD3OD): d
154 (C-8), 150 (C-5 and C-3), 144, 143, 141 (aromatic),
82 (C-4), 46 (C-9), 26 (Ar-CH3), 21 (3-CH3). M/S (m/z):
344 (M+), 254 (C13H14N6), 164 (C6H8N6), 149
(C6H7N5), 134 (C6H6N4), 107 (C7H9N), 91 (C7H7) 80
(C4H4N2) and 58 (C2H6N2). Anal.: (C20H20N6); calcd C,
69.76; H, 5.81; N, 24.42; found C, 70.21; H, 6.32; N,
23.98%.
routinely checked for their purity on silica gel G TLC
plates and the spots were visualized by iodine vapors.
IR spectra were recorded on Shimadzu 8201 PC FTIR
spectrometer. PMR spectra were recorded on Bruker
DRX 300 MHz FT NMR spectrometer using TMS as
internal reference and chemical shift values are expres-
sed in d units. Mass spectra were run on Jeol SX-102
spectrometer.
4,5-Dihydroxy-3-methyl-1H-pyrazolo[3,4-c]pyridazine (4).
2-Ethoxy-N-(5-methyl-2,4-dihydro-3H-pyrazol-3yl-idene)-
2-oxoethanehydrazonic acid (3) (9.2 g, 0.05 mol) was
re¯uxed with nitrobenzene (30 mL) and SnCl4 (10 g) for
5 h. The reaction was continued until a black jelly was
settled on the bottom of round-bottomed ¯ask. On
completion of cyclization nitrobenzene was distilled out.
The solid black material was shaken well with water and
then ®ltered through suction. The resulting 4,5-dihydroxy-
3-methyl-pyrazolo[3,4-c] pyridazine (4) was recrys-
tallized from a mixture of methanol and water. Yield
6.52 g (80%). Mp 224 ꢀC. IR (KBr) cmÀ1: 3519 (O±H
stretching) 3312 (N±H stretching). PMR (CD3OD): d
6.8 (s, 1H, OH), d 6.3 (s, 1H, OH), 5.2 (s, 1H, NH), 2.1
(s, 3H, CH3). M/S (m/z): 166 (M+), 137 (C5H5N4O),
108 (C4H4N4), 81 (C3H3N3) and 56 (C2H4N2). Anal.
C6H6N4O2; calcd C, 43.37; H, 3.61; N, 33.76; found C,
43.14; H, 3.52; N, 34.14%.
4{[5-(4-Carboxyanilino)-3-methyl-1H-pyrazolo[3,4-c]pyr-
idazin-4yl}amino} benzoic acid (8). 4,5-Dichloro-3-
methyl-1H-pyrazolo[3,4-c]pyridazine (5) (2 g, 0.01 mol)
was re¯uxed with p-amino benzoic acid (1.37 g,
0.01 mole) for 12 h in tetrahydrofuran. On the comple-
tion of the reaction the reaction mixture was poured in
cold water and water insoluble material was ®ltered
through suction. The crude material was recrystallized
from a mixture of water and ethanol giving the desired
product. Yield 3.97 g (98%). IR (KBr) cmÀ1: 3518 (O-H
stretching), 3449 (N-H stretching), 3406 (N-H stretch-
ing), 1737 (CO stretching). PMR (CD3OD): d 7.6 (m,
8H, ArH), 6.5 (s, 1H, 1NH), 6.2 (s, 1H, 5NH), 5.8 (s,
1H, 4NH), 2.3 (s, 3H, CH3). CMR (CD3OD): d 172
(CO), 154 (C-8), 151 (C-5 and C-3), 141, 143, 145
(Aromatic), 82 (C-4),78 (C-9), 21 (3-CH3). M/S (m/z):
404(M+), 316 (C18H16N6), 240 (C12H12N6), 164
(C6H8N6), 149 (C6H7N5), 134 (C6H6N4), 93 (C6H7N),
80 (C4H4N2) and 58 (C2H6N2). Anal. (C20H16N6O4);
calcd C, 59.40; H, 3.96; N, 20.79; found: C, 60.31; H,
4.82; N, 18.17%.
4,5-Dichloro-3-methyl-1H-pyrazolo[3,4-c]pyridazine (5).
4,5-Dihydroxy-3-methyl-1H-pyrazolo[3,4-c]pyridazine (4)
(8.3 g, 0.05 mol) was re¯uxed with phosphorous oxy-
chloride (200 mL) for 50 h. Excess POCl3 was removed by
vacuum distillation. The residual mixture was poured
into crushed ice and on ®ltration 5 was obtained.
Yield 9.6 g (95%). Mp 298 ꢀC. M/S (m/z): 202(M+), 168
(C6H5N4Cl), 134 (C6H6N4), 105 (C5H5N3) and 80
(C4H4N2).
N-[5-(Benzoylamino)-3-methyl-1H-pyrazolo[3,4-c]pyridazin-
4-yl]benzamide (9). 4,5-Dichloro-3-methyl-1H-pyrazolo-
[3,4-c]pyridazine (5) (2 g, 0.01 mol) was re¯uxed with
benzamide (1.21 g, 0.01 mol) for 12 h in tetrahydrofuran
on a sand bath. The reaction mixture was ®ltered and
the crude product was then recrystallized from the mix-
ture of water and alcohol to give 9. Yield 3.22 g (87%).
IR (KBr) cmÀ1: 3515 (N-H stretching), 1723 (CO
stretching), 1433 (C-N stretching). PMR (CD3OD): d
7.2 (m, 10H, ArH), 6.3 (s, 1H, 1-NH), 5.9 (s, 1H, 5-
NH), 5.3 (s, 1H, 4-NH), 2.3 (s, 3H, CH3). CMR
(CD3OD): d 182 (CO), 154 (C-8), 150 (C-5 and C-3),
141, 143, 145 (aromatic), 82 (C-4), 78 (C-9), 21 (3-CH3).
4,-Benzoyloxy-3-methyl-1-benzoyl-1H-pyrazolo[3,4-c]pyr-
idazin-5yl benzoate (6). 4,5-Dihydroxy-3-methyl-1H-
pyrazolo[3,4-c]pyridazine (4) (11.6 g, 0.07 mol) was dis-
solved in 90 mL of 1% NaOH solution and to this
solution benzoyl chloride (12.6 mL, 0.09 mol) was intro-
duced. The mixture was shaken vigorously for about
30 min. When a solid substance was separated out
100 mL of water was added to this mixture and crude
benzoate was ®ltered, washed with cold water. The
compound was recrystallꢀized from methanol and water.
Yield 18 g (54%). Mp 88 C. IR (KBr) cmÀ1: 1735 (CO
stretching), 1418 (C±N stretching). PMR (DMSO-d6): d