Synthesis and antimicrobial activity of some new triazino-, triazolo-, and pyrazolopyridazine derivatives

Article abstract of DOI:10.1007/s10593-009-0381-9

The reaction of 3-hydrazino-4,5,6-triphenylpyridazine with phenacyl bromide afforded triazolopyridazine, while the reaction with different aldehydes gave the corresponding 3-arylidene hydrazinopyridazine derivatives which, on reaction with Br₂/

Full text of DOI:10.1007/s10593-009-0381-9

Chemistry of Heterocyclic Compounds, Vol. 45, No. 8, 2009
SYNTHESIS AND ANTIMICROBIAL ACTIVITY
OF SOME NEW TRIAZINO-, TRIAZOLO-, AND
PYRAZOLOPYRIDAZINE DERIVATIVES
F. A. Yassin1*
The reaction of 3-hydrazino-4,5,6-triphenylpyridazine with phenacyl bromide afforded
triazolopyridazine, while the reaction with different aldehydes gave the corresponding 3-arylidene
hydrazinopyridazine derivatives which, on reaction with Br2/Na2CO3, gave the corresponding
triazinopyridazines. Also, fusion with ethyl acetoacetate, ethyl benzoylacetate, diethyl malonate, or ethyl
phenylacetoacetate gave the corresponding pyrazolo- and triazinopyridazine derivatives. The
antimicrobial activity of some of the new compounds has been discussed.
Keywords: diethyl malonate, ethyl acetoacetate, ethylbenzoylacetate, ethyl cyanoacetate,
hydrazinopyridazine, phenacyl bromide, pyrazolopyridazine, triazinopyridazine, thiazolopyridazine.
Recently, it has been reported that some pyridazine derivatives display antihypertensive, anticancer, and
anti-HIV activities [1-3]. In addition, it is well documented that substituted pyridazines possess antimicrobial,
antifungal, and antiviral activities.[4-6]. On the other hand, triazoles, triazines, and pyrazoles possess
antimicrobial and antifungal activities [7-9]. On the basis of these findings and in continuation of our studies in
this field, the present investigation deals with the synthesis of some triazolo-, triazino-, and pyrazolopyridazine
derivatives likely possessing antimicrobial activity.
In the previous studies [10, 11] we have reported the synthesis of 4,5,6-triphenylpyridazin-3(2H)-one 1
via the reaction of benzylmonohydrazone with ethyl phenylacetate in the presence of sodium ethoxide/ethanol
solution. The reaction of compound 1 with POCl3/PCl5 mixture gave 3-chloro-4,5,6-triphenylpyridazine 2
which, on reaction with hydrazine hydrate in boiling ethanol, yielded 3-hydrazino-4,5,6-triphenylpyridazine (3)
as a starting material of the present work.
The reaction of compound 3 with phenacyl bromide in refluxing dry dioxane gave 3,7,8,9-tetraphenyl-
4H-pyridazino[6,1-c][1,2,4]triazine (4). The structure of compound 4 was confirmed from its analytical and
spectral data. The IR spectrum of compound 4 showed absorption bands at 1645 (C=N) and 1516 cm–1 (C=C); it
1
also revealed the absence of the band of NH and NH2 groups. The H NMR spectrum showed signals at δ 2.7
(2H, s, CH2) and 7.1-7.6 ppm (20H, m, aromatic protons).
_______
* To whom correspondence should be addressed, e-mail: fathy_yassin@yahoo.co.uk.
1Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1253-1259, August, 2009.
Original article submitted March 6, 2008.
0009-3122/09/4508-0997©2009 Springer Science+Business Media, Inc.
997

Condensation of 3-hydrazinopyridazine 3 with different aldehydes [12] such as benzaldehyde,
p-chlorobenzaldehyde, and anisaldehyde in boiling ethanol afforded the corresponding arylidene (4,5,6-tri-
phenylpyridazin-3-yl)hydrazones 5a-c, which, on oxidative cyclization using bromine/sodium carbonate, gave
3-substituted 6,7,8-triphenyl[1,2,4]triazolo[4,3-b]pyridazines 6a–c. The IR spectra of compounds 5a–c showed
absorption bands at 3349-3339 (NH), 1663-1646 (C=N), and 1520 (C=C) in addition to 1030 cm–1 (C–O–C) for
1
compound 5c. The H NMR spectrum of compound 5c showed signals at δ 3.7 (3H, s, CH3), 4.2 (1H, s, NH),
and 7.2-7.6 (19H, m, aromatic protons). The IR spectra of compounds 6a–c showed absorption bands at
1640-1645 (C=N) and 1510-1516 cm–1 (C=C), while the 1H NMR spectrum of compound 6c showed signals at δ
3.7 (3H, s, CH3) and 6.8-7.5 ppm (19H, m, aromatic protons).
The reaction of 3-hydrazinopyridazine 3 with ethyl cyanoacetate in boiling ethanol yielded N-(4,5,6-
triphenylpyridazin-3-yl)-2-cyanoacetohydrazide (7), which cyclized on heating in an oil bath to give 3-cyano-
methyl-6,7,8-triphenyl[1,2,4]triazolo[3,4-b]pyridazine (8). The IR spectrum of compound 7 revealed absorption
1
bands at 3313 (NH), 2263 (CN), 1689 (CO), 1645 (C=N), and 1519 cm–1 (C=C), while the H NMR spectrum
showed signals at δ 3.3 (2H, s, CH2), 4.0 (1H, s, NH), 7.2-7.7 (15H, m, aromatic protons), and 8.0 ppm (1H, s,
NHCO). IR spectrum of compound 8 showed absorption bands at 2263 (CN), 1645 (C=N), and 1519 cm–1
1
(C=C). The H NMR spectrum of compound 8 showed signals at δ 3.7 (2H, s, CH2) and 7.1-7.6 ppm (15H, m,
aromatic protons) (Scheme 1).
Scheme 1
Ph
Ph
Ph
Ph
Cl
Ph
Ph
POCl3
PCl 5
N
N
N
O
N
H
2
1
NH2NH2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
ArCHO
NCCH2COOEt
N
N
N
N
N
N
H
N
N
NHNH2
NHNHCOCH2CN
Ar
3
7
5a–c
PhCOCH2Br
Br2/Na2CO3
Fusion
Ph
N
Ph
Ph
N
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
N
N
N
N
N
N
N
NC
Ar
Ph
8
6a–c
4
a Ar = Ph, b Ar = p-ClC6H4, c Ar = p-MeOC6H4
The reaction of 3-hydrazinopyridazine 3 with each of ethyl acetoacetate and ethyl benzoylacetate [13] in
MeOH/CHCl3 at room temperature afforded ethyl N-(4,5,6-triphenylpyridazin-3-yl)-3-hydrazonobutanoate (9a)
and ethyl N-(4,5,6-triphenylpyridazin-3-yl)-3-hydrazono-3-phenylpropanoate (9b).
998

The IR spectra of compounds 9a,b showed absorption bands at 3449-3339 (NH), 1712-1710 (C=O),
1
1643-1626 (C=N), 1580 (C=C), and 1080-1056 cm–1 (C–O–C). The H NMR spectrum of compound 9a showed
signals at δ 1.4 (2H, t, CH2CH3), 2.3 (3H, s, N=CCH3), 3.4 (2H, s, CH2CO), 3.7 (1H, s, =CH), 4.5 (3H, q, CH2CH3),
7.1-7.5 (15H, m, aromatic protons), and 8.5 ppm (1H, s, NH). Fusion of compound 3 with ethyl acetoacetate in an oil
bath afforded the corresponding 3-methyl-6,7,8-triphenyl[1,2,4]triazolo[4,3-b]pyridazine (10).
Scheme 2
Ph
N
Ph
Ph
O
Ph
Ph
Ph
N
N
N
N
N
N
N
Ph
EtO
14
15
CH2(COOEt)2/Fusion
PhCH2COCH2COOEt
Ph
MeCOCH2COOEt
Fusion
MeCOCH2COOEt or
PhCOCH2COOEt/r. t.
Ph
Ph
N
N
NHNH2
Ph
Ph
N
3
Ph
Ph
Ph
Ph
PhCOCH2COOEt
Fusion
N
N
N
CH2COOEt
N
NH
N
Ph
N
R
N
9a,b
Ph
Ph
Me
10
+
N
–
PhN=N Cl
N
N
HNO2
Ph
HO
11
Ph
Ph
N
Ph
Ph
N
Ph
Ph
N
N
N
N
N
N
Ph
Ph
HO
HO
12
N
N
N
O
Ph
13
9 a R = Me, b R = Ph
The IR spectrum of compound 10 showed absorption bands at 1645 (C=N) and 1516 cm–1 (C=C),
whereas the 1H NMR spectrum showed signals at δ 2.3 (3H, s, CH3) and 7.2-7.5 (15H, m, aromatic protons). In
the present investigation compound 10 was also prepared by refluxing compound 9a in acetic anhydride. Fusion
of compound 3 with ethyl benzoylacetate in an oil bath gave the corresponding 3-phenyl-1-(4,5,6-
triphenylpyridazin-3-yl)-1H-pyrazol-5-ol 11. The IR spectrum of compound 11 revealed absorption bands at
1
3440 (br. OH enolic), 1681 (C=O), 1664 (C=N), and 1513 cm–1 (C=C), while the H NMR spectrum showed
999

TABLE 1. Characterization and Physical Data
Found, %
Calculated, %/
H
Com-
pound
Empirical
formula
mp, °C*
Yield, %
C
N
C22H16N2O
81.46
81.33
77.08
77.04
78.08
78.00
82.17
82.11
81.66
81.61
75.56
75.49
78.92
78.88
82.05
82.00
75.89
75.85
79.27
79.19
74.06
74.02
77.50
77.47
74.66
74.62
77.34
77.30
79.54
79.51
79.81
79.78
4.97
4.91
4.41
4.93
5.36
5.30
5.06
5.03
5.20
5.10
4.59
4.51
5.30
5.27
4.75
4.69
4.17
4.13
4.88
4.85
4.72
4.70
4.42
4.40
5.77
5.73
5.46
5.42
5.01
4.98
4.75
4.70
8.64
8.58
8.17
8.13
16.56
16.50
12.78
12.72
13.14
13.09
12.15
12.08
12.27
12.19
13.20
13.00
12.21
12.11
12.33
12.29
17.27
17.22
18.08
18.02
12.44
12.40
10.93
10.90
15.46
15.41
12.01
11.98
280
138
227
243
212
197
185
135
155
190
157
220
145
230
254
275
238
143
135
232
75
72
82
76
79
69
79
88
66
60
79
75
70
69
76
78
73
78
88
77
1
C22H15ClN2
C22H18N4
2
3
C30H22N4
4
C29H22N4
5a
5b
5c
6a
6b
6c
7
C29H21ClN4
C30H24N4O
C29H20N4
C29H19 ClN4
C30H22N4O
C25H19N5O
C25H17N5
8
C28H26N4O2
C33H28N4O2
C24H18N4
9a
9b
10
11
12
13
14
15
C31H22N4O
C37H26N6O
C31H21N5O2
C27H22N4O2
C30H22N4
77.88
77.82
75.14
75.10
74.64
74.60
82.17
82.12
4.59
4.56
4.27
4.22
5.10
5.07
5.06
5.04
14.73
14.70
14.13
14.09
12.89
12.85
12.78
12.74
_______
* Solvent: benzene (compounds 1, 6b,c, 11, 12), acetic acid (compound 2),
ethanol (compounds 3-5a-c, 6a, 7-9a,b, 13-15), petroleum ether (60-80°C)
(compound 10).
singlets at δ 3.7 (4-CH2), 6.0 (4-CH), 8.8 (OH), and a multiplet at 7.2-7.8 ppm (aromatic protons). The spectral
data of compound 11 showed that it exists in both keto-enol forms. For further evidence about the structure of
compound 11, the coupling of compound 11 with benzene diazonium chloride produced 4-phenylazopyrazol-
5-ol derivative 12, while the reaction of compound 11 with nitrous acid gave 4-nitroso-3-phenylpyrazol-5-ol
derivative (13). The IR spectra of compounds 12 and 13 revealed absorption bands at 3527-3501 (OH, enolic),
1666-1643 (C=N), 1590-1563 (C=C), and 1520 cm–1 (N=N in compound 12).
The treatment of 3-hydrazino-4,5,6-triphenylpyridazine 3 with diethyl malonate and ethyl phenylaceto-
acetate by fusion in an oil bath gave the corresponding ethyl (6,7,8-triphenyl[1,2,4]triazolo[3,4-b]pyridazin-
3-yl)acetate (14) and 3-benzyl-6,7,8-triphenyl[1,2,4]triazolo[3,4-b]pyridazine (15) (Scheme 2).
1000

TABLE 2. Antimicrobial activity
Compound
Candida albicans
Staphylococcus aureus
Escherichia coli
4
+
++
+
+++
++
+
++
++
+
++
+++
++
+
5a
6b
7
++
+
+++
++
+++
+
9a
10
12
13
15
+
++
+++
++
+
+
+++
++
The structure of compounds 14 and 15 was confirmed by their correct analytical and spectral data. The
IR spectrum of compound 14 showed absorption bands at 1715 (C=O, ester), 1610 (C=N), 1512 (C=C), and
1
1080-1056 cm–1 (C–O–C), while the H NMR spectrum showed signals at δ 1.3 (3H, t, CH2CH3), 4.2 (2H, q,
CH2CH3), 4.7 (2H, s, CH2), and 7.2-7.8 ppm (15H, m, aromatic protons).
The results of the antimicrobial studies presented in Table 2 revealed that most of the newly synthesized
compounds showed antimicrobial activity against the fungus Candida albicans and the gram-negative bacteria
Escherichia coli. However, they were less active against the gram-positive bacteria Straphylococcus aureus. The
most active compounds against C. albicans were compounds 7, 10, and 15.
EXPERIMENTAL
All melting points were uncorrected. The IR spectra were measured on KBr on a Bruker FT-IR ISS 25
1
spectrophotometer (νmax, cm–1). The H NMR spectra (DMSO-d6 and CDCl3) were measured on a Bruker Avance
300 MHz spectrometer using TMS as an internal reference.
3-Hydrazino-4,5,6-triphenylpyridazine (3). To a solution of 3-chloro-4,5,6-triphenylpyridazine 2
(0.01 mol) in n-butanol (10 ml), hydrazine hydrate (3 ml) was added. The reaction mixture was refluxed for 12 h.
The precipitated product was filtered off, dried, and recrystallized from ethanol.
3,7,8,9-Tetraphenyl-4H-pyridazino[6,1-c][1,2,4]triazine (4). To a solution of compound 3 (0.01 mol) in
dry dioxane (20 ml), phenacyl bromide (0.01 mol) was added. The reaction mixture was heated under reflux, a
reddish precipitate was formed during the first 5 min, the reflux was continued for 1 h, then the reaction mixture was
cooled. The crystalline product obtained was filtered off, dried, and crystallized from ethanol.
4-Substituted Benzaldehyde (4,5,6-Triphenylpyridazin-3-yl)hydrazones 5a-c. To a solution of
compound 3 (0.01 mol) in ethanol (30 ml), the appropriate aromatic aldehyde was added. The reaction mixture was
heated under reflux for 5 h, and then cooled to room temperature. The hydrazones precipitated were filtered off,
dried, and crystallized from the proper solvents (Table 1).
3-Substituted 6,7,8-Triphenyl[1,2,4]triazolo[4,3-b]pyridazines 6a-c. To a solution of each of compounds
5a-c (0.01 mol) and anhydrous Na2CO3 in CHCl3 (20 ml), bromine (0.5 ml) was added dropwise at room
temperature with continuous stirring for 3 h. The reaction mixture was left to stand overnight, then the solvent was
evaporated under vacuum. The residue was dried and crystallized from the proper solvents (Table 1).
N-(4,5,6-Triphenylpyridazin-3-yl)-2-cyanoacetohydrazide (7). A mixture of compound 3 (0.01 mol) and
ethyl cyanoacetate (0.01 mol) in ethanol (30 ml) was refluxed for 5 h. The reaction mixture was cooled, and the solid
precipitated was filtered off, dried, and crystallized from ethanol.
3-Cyanomethyl-6,7,8-triphenyl[1,2,4]triazolo[3,4-b]pyridazine (8). A mixture of compound 3 (0.01 mol)
and ethyl cyanoacetate (0.01 mol) was heated on an oil bath at 160-170°C for 1 h, then cooled, the residue was
triturated with ethanol, and the solid precipitated was filtered off, dried, and crystallized from ethanol.
1001

Ethyl N-(4,5,6-triphenylpyridazin-3-yl)-3-hydrazonobutanoate (9a) and Ethyl N-(4,5,6-Triphenyl-
pyridazin-3-yl)-3-hydrazono-3-phenylpropanoate (9b). To the solution of compound 3 (0.01 mol) in
MeOH/CHCl3 mixture (20 ml) (1:1), each of ethyl acetoacetate or ethyl benzoylacetate was added. The reaction
mixture was left at room temperature for 24 h, then the solvent was evaporated and the residue was triturated with
petroleum ether at 60-80°C; the solid precipitated was filtered off, dried, and crystallized from ethanol.
3-Methyl-6,7,8-triphenyl[1,2,4]triazolo[4,3-b]pyridazine (10). A mixture of compound 3 (0.01 mol) and
ethyl acetoacetate (0.01 mol) was heated on an oil bath at 160-170°C for 1 h, then cooled, the residue was triturated
with petroleum ether at 60-80°C, and the solid precipitated was filtered off, dried, and crystallized.
3-Phenyl-1-(4,5,6-triphenylpyridazin-3-yl)-1H-pyrazol-5-ol (11). A mixture of compound 3 (0.01 mol)
and ethyl benzoylacetate (0.01 mol) was heated on an oil bath at 160-170°C for 1 h, then cooled, the residue was
triturated with petroleum ether at 60-80°C, and the solid precipitated was filtered off, dried, and crystallized from
benzene.
4-Phenylazopyrazol-5-ol Derivative (12). To an ice cooled solution of compound 11 (0.46 g, 0.01 mol) in
ethanol (15 ml) containing NaOH (1 g) and sodium acetate (2 g), the benzene diazonium salt was added. The cooling
was continued for 1 h with stirring; the mixture was left to stand in a refrigerator overnight, then neutralized carefully
by dropwise addition of HCl. The formed orange precipitate was filtered off, dried, and crystallized from benzene.
4-Nitroso-3-phenylpyrazol-5-ol Derivative 13. To an ice cooled solution of compound 11 (0.46 g,
0.01 mol) in ethanol containing acetic acid (3 ml), a cold solution of NaNO2 (0.1 g) in H2O (1 ml) was added. The
mixture was left at room temperature overnight. The obtained orange precipitate was filtered off, dried, and
crystallized from ethanol.
Ethyl (6,7,8-triphenyl[1,2,4]triazolo[3,4-b]pyridazin-3-yl)acetate (14). A mixture of compound 3
(0.01 mol) and diethyl malonate (0.01 mol) was heated on an oil bath at 160-170°C for 1 h, then cooled, the residue
was triturated with ethanol, and the solid precipitated was filtered off, dried, and crystallized.
3-Benzyl-6,7,8-triphenyl[1,2,4]triazolo[3,4-b]pyridazine (15). A mixture of compound 3 (0.01 mol) and
ethyl phenylacetoacetate (0.01 mol) was heated on an oil bath at 160-170°C for 1 h, then cooled, the residue was
triturated with ethanol, and the solid precipitated was filtered off, dried, and crystallized.
Method for Testing of Biological Properties.
The biological activity of the tested compounds has been evaluated using the filter paper disk method after dissolving
the substances in ethanol. The inhibition zones of microbial growth surrounding the paper disk were measured in
millimeters at the end of incubation period [14] (18-24 h at 27oC ).
The author is thankful to Prof. Yassin Al-Ayouty, Botany Department, Faculty of Science, Zagazig
University, for help in studying the biological activity of some of the new compounds.
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