Synthesis and antifungal activity of 5-chloro-6-phenyl- pyridazin-3(2H)-one derivatives

Article abstract of DOI:10.3390/molecules14093676

An effective method has been developed for the preparation under mild conditions of novel pyridazine derivatives from the easily accessible starting materials mucochloric acid and benzene. All the synthesized compounds were fully characterized and some of

Full text of DOI:10.3390/molecules14093676

Molecules 2009, 14, 3676-3687; doi:10.3390/molecules14093676
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Antifungal Activity of 5-Chloro-6-Phenyl-
pyridazin-3(2H)-one Derivatives
Jian Wu, Baoan Song *, Hongjun Chen, Pinaki Bhadury and Deyu Hu
Key Laboratory of Green Pesticide and Agriculture Bioengineering, Ministry of Education, Research
and Development Center for Fine Chemicals, Guizhou University, Guiyang 550025, China;
E-Mails: jianwu2691@yahoo.com.cn (J.W.); chj020726@163.com (H-J.C.);
bhadury@gzu.edu.cn (P.B.); dyhu@gzu.edu.cn (D.H.)
* Author to whom correspondence should be addressed; E-Mail: songbaoan22@yahoo.com;
Tel.: +86 851 362 0521; Fax: +86 851 362 2211.
Received: 27 July 2009; in revised form: 13 September 2009 / Accepted: 16 September 2009 /
Published: 18 September 2009
Abstract: An effective method has been developed for the preparation under mild
conditions of novel pyridazine derivatives from the easily accessible starting materials
mucochloric acid and benzene. All the synthesized compounds were fully characterized
and some of them displayed good antifungal activities against G. zeae, F. oxysporum and
C. mandshurica in preliminary antifungal activity tests.
Keywords: pyridazine derivatives; synthesis; antifungal activity
1. Introduction
Many pyridazine derivatives are well known to possess a wide range of bioactivities and are often
employed as plant virucides [1,2], antitumor agents [3-5], fungicides [6-8], insecticides [9,10],
herbicides [11-15] and anti-inflammatory agents [16-17]. They have immense potential in agricultural
science as plant growth regulators and crop protection agents. Several derivatives of these compounds
incorporating 1,3,4-thiadiazole, 1,3,4-oxadiazole and oxazolidin-2-one rings have been shown to
display moderate to good antifungal activities [18-20]. Introduction of methyl N-methoxy-N-[2-(1,6-
dihydro-1-substitued-6-oxo-pyridazin-3-yloxymethyl) phenyl] carbonate base into pyrazole derived
pyraclostrolin has resulted in the development of compounds with appreciable fungicidal activities

Molecules 2009, 14
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against P. oryzae, B. cinerea and E. graminis [21]. In addition, a series of halogen and aryl substituted
pyridazine derivatives synthesized by Akio and Trah [22-23] exhibited high fungicidal activities at a
concentration of 50 µg/mL. Since oxadiazole and thiadiazole derivatives are associated with good
antifungal characteristics [24-26], we envisioned that modification of 5-chloro-6-phenylpyridazin-
3(2H)-one by suitable substituent replacement at the N-2 position, followed by incorporation of 1,3,4-
thiadiazole and 1,3,4-oxadiazole scaffolds into the pyridazin-3(2H)-one ring through a “-CH2S-”
moiety could result into the formation of lead structures with potent activity. The pyridazines 3a-3h
and 4 without the presence of any oxadiazole and thiadiazole moieties were prepared from
mucochloric acid and benzene as depicted in Scheme 1. Then 12 novel pyridazines 6a-6i and 7a-7c
derived from 4 incorporating the above structural features were prepared. The synthetic sequence is
shown in Scheme 2. All 21 compounds synthesized were unequivocally characterized by IR, NMR and
elemental analysis. Preliminary antifungal activity tests showed that most of the compounds exhibited
inhibitory activity against G. zeae, F. oxysporum and C. mandshurica to a certain extent. Among them,
compounds 3e, 3h, 7b, 7c exhibited slightly superior or similar activities as compared to the
commercial agent hymexazol on the corresponding fungi.
Scheme 1. Synthetic route to 3a-3h and 4.
Scheme 2. Synthetic route to 6a-6i and 7a-7c.

Molecules 2009, 14
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2. Results and Discussion
2.1. Chemistry
3,4-Dichloro-5-phenylfuran-2(5H)-one (1) was synthesized via Friedel-Crafts reaction by
employing mucochloric acid and benzene as starting materials in the presence of the Lewis acid AlCl3,
in accordance with the known synthetic protocols described in the literature [27,28].
Preparation of the compound 5-chloro-6-phenylpyridazin-3(2H)-one (2) has been described
previously [27,29], but unfortunately in our hands under the same reaction conditions the yield was
much lower (46%) compared to the one reported in the literature. It was observed that the type of
solvent, reaction temperature and reaction time were the most important parameters affecting the
purity and yield of the final product. The best result, affording a yield of 68%, was achieved when the
reaction was perfomed in the solvent DMF at 80°C for 40 min.
5-Chloro-6-phenyl-2-substituted-pyridazin-3(2H)-ones 3a-3h were then conveniently prepared in
good yields by treatment of 5-chloro-6-phenylpyridazin-3(2H)-one (2) with halide (XCH2R, X = Cl or
Br) in acetone, acetonitrile or N,N-dimethylformamide. Among these solvents, however, acetone
provided the best results and the reaction could be successfully conducted at room temperature. The
reaction was much faster and high yielding when X was bromine instead of chlorine. This kind of
substitution at the nitrogen atom of 2 in the presence of a base was also previously investigated [28] by
Estevez et al.
Compound 2 was also separately reacted (Scheme 1) with paraformaldehyde and thionyl chloride in
benzene to afford 5-chloro-2-(chloromethyl)-6-phenylpyridazin-3(2H)-one (4) in a single step in 73%
yield. In comparison with the two-step process as reported in the literature [30], the operation was
much more convenient and the reaction time was significantly shortened.
Finally, the pyridazine derivatives 6a-6i with 1,3,4-thiadiazole or 1,3,4-oxadiazole moieties were
easily obtained in 60-80% yields by the reaction of 5-chloro-2-(chloromethyl)-6-phenylpyridazin-
3(2H)-one (4) with 5 as depicted in Scheme 2. As the progress of the reaction was monitored by TLC,
the possibility of a side reaction through the chlorine atom at C-5 position of pyradazine ring could not
be ruled out. The reaction time and temperature were critical for this reaction. In general, the products
were obtained under mild conditions at 50 °C with a reaction time of 3-4 hours. The compounds 6a-6c
were eventually oxidized to 7a-7c by H2O2 and (NH4)6Mo7O24 as shown in Scheme 2.
The structures of the compounds 1, 2, 3a-3h, 4, 6a-6i and 7a-7c were established on the basis of
their spectroscopic data. The IR spectra showed absorption bands around 3,049-3,099 cm-1 for the Ar-
1
H stretching vibrations and near 1,662-1,678 cm-1 for the presence C=O functional groups. In the H-
NMR spectra of the pyradazine derivatives, the 4-H signal appeared as a singlet in 7.14-7.26 ppm
range, while the Ar-H peaks of all the derivatives were observed near 6.64-8.40 ppm as a multiplet.
The CH2 peaks were observed as singlets in 5.30-6.31 ppm range.
2.2. Antifungal activity bioassay
The in vitro antifungal screening data of the pyridazine derivatives are provided in Table 1. It was
observed that these synthesized compounds showed weak to good antifungal activities against the

Molecules 2009, 14
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tested fungi at 50 μg/mL. Compounds 3d, 3e and 6b were shown to inhibit the growth of G. zeae at
45.1%, 43.8%, and 40.4%, respectively; compounds 3d, 3f and 7c exhibited good activities on F.
oxysporum at 38.2%, 44.2% and 43.1%, respectively while compounds 3d, 3e and 3h inhibited the
growth of C. mandshurica at 43.5%, 40.6% and 47.8%, respectively. These figures were slightly lower
than those of hymexazol. It should be noted that compounds 3h, 7b and 7c showed good activities on
G. zeae at 50.3%, 57.9% and 60.5%, respectively; compounds 3e and 3h exhibited the growth of F.
oxysporum at 53.2% and 50.9% respectively and compound 7c exhibited good activity on C.
mandshurica. Amongst the four compounds 3e, 3h, 7b, 7c that exhibited similar activities as that of
hymexozole on their corresponding fungi, the last two showed considerable promise. Although, a
definite structure activity relationship could not be established with the limited experimental data and
available compounds, it appears that incorporation of oxadiazole or thiadiazole unit through thiol 5
into parent pyridazine derivative and subsequent oxidation of the resulting product to sulfone 7 might
have a positive influence to enhance antifungal activity of the designed compounds.
Table 1. Inhibition effects of pyridazine derivatives on phytopathogenic fungi.
Compd.( 50 µg/mL)
G. zeae
7.5
F. oxysporum
12.3
18.9
25.5
38.2
53.2
44.2
18.7
50.9
10.7
9.9
C. mandshurica
4.5
3a
3b
8.3
19.2
26.7
43.5
40.6
33.8
15.9
47.8
12.1
13.2
30.0
13.8
0.8
3c
33.7
45.1
43.8
24.2
22.3
50.3
17.8
12.1
40.4
16.2
26.2
29.0
16.6
35.3
11.2
22.1
35.5
57.9
60.5
50.4
3d
3e
3f
3g
3h
4
6a
6b
27.1
9.4
6c
6d
3.4
6e
9.14
8.1
1.5
6f
6.2
6g
32.9
-3.5
28.3
-2.5
6h
6i
3.8
2.0
7a
7b
32.6
35.3
43.1
52.4
34.6
26.3
52.1
54.1
7c
hymexazol
3. Experimental
3.1. General
Unless otherwise stated, all the reagents and reactants were purchased from commercial suppliers;
melting points were uncorrected and determined on a XT-4 binocular microscope (Beijing Tech

Molecules 2009, 14
3680
Instrument Co., China). The 1H-NMR and 13C-NMR spectra were recorded on a JEOL ECX 500 NMR
1
spectrometer at room temperature operating at 500 MHz for H-NMR and 125 MHz for 13C-NMR,
using CDCl3, CD3COCD3 or DMSO as solvents and TMS as an internal standard; infrared spectra
were recorded in KBr on a Bruker VECTOR 22 spectrometer; elemental analysis was performed on an
Elemental Vario-III CHN analyzer. The course of the reactions was monitored by TLC; analytical
TLC was performed on silica gel GF254; column chromatographic purification was carried out using
silica gel. 5-Subsititued phenyl-1,3,4-thiadiazoles (or oxadiazole)-2-thiols 5 were prepared according
to the literature procedure [25-26] from substituted benzoic acid as the starting material through
esterification, hydrazidation, salt formation, and cyclization. All compounds were synthesized under
mild conditions with moderate yields.
3.2. Preparation of 3, 4-dichloro-5-phenylfuran-2(5H)-one (1)
Mucochloric acid (33.0 g) was slowly added with stirring to a mixture of benzene (160 mL) and
anhydrous aluminum chloride (40.0 g). After completion of the addition, stirring was continued for 3 h
at room temperature. After addition of ice (60.6 g) and conc. HC1 (128 mL), the resulting mixture was
extracted with benzene (4 × 50 mL). The combined extract was dried on anhydrous Na2SO4 and
concentrated under vacuum to afford a crystalline solid which was filtered off and recrystallized from
methanol, m.p. 75-77 °C (lit. [27], m.p. 79-81 °C); yield 60%.
3.3. Preparation of 5-chloro-6-phenylpyridazin-3(2H)-one (2)
Hydrazine hydrate (80%, 6.0 g) was slowly added to a solution of 3,4-dichloro-5- phenylfuran-
2(5H)-one (5.0 g) dissolved in N,N-dimethylformamide (30 g). The resulting solution was stirred at 80
°C for 40 min; after cooling, the mixture was added to water (150 mL) to give a precipitate which was
filtered off, washed with water and recrystallized from dioxane to give a yellow solid. Yield, 68%;
m.p. 231-232 °C (lit. [27], m.p. 230-231°C).
3.4. Preparation of 5-chloro-6-phenyl-2-substitutedpyridazin-3(2H)-ones 3a-3h
To a well stirred solution of 5-chloro-6-phenylpyridazin-3(2H)-one (1.00 mmol) in acetone (8 mL)
anhydrous potassium carbonate (0.5 g) and halide (1.00 mmol) were added. The mixture was stirred at
room temperature and monitored by TLC. After completion of the reaction, the solid was filtered; the
solvent was evaporated and the crude product was purified by preparative TLC with a mixture of
petroleum ether and ethyl acetate (v:v = 1:1) as developing solvent to give title compounds 3a-3h.
Ethyl 2-(4-chloro-6-oxo-3-phenylpyridazin-1(6H)-yl)acetate (3a): Light yellow solid, yield 72%; m.p.
1
77.0-78.5 °C; H-NMR (CDCl3): δ 7.43-7.57 (m, 5H, Ph-H), 7.16 (s, 1H, pyridazine-H), 4.92 (s, 2H,
CH2), 2.25 (q, J = 7.45, 2H, CH2), 1.29 (t, J = 6.9Hz, 3H, CH3); 13C-NMR (CDCl3): δ 167.06, 158.85,
145.82, 140.48, 133.38, 129.73, 129.29, 128.79, 128.35, 62.00, 53.22, 14.21; IR: ν 3059.1, 3034.0,
2900.0, 1737.8, 1678.0 cm-1; Anal. Calc. for C14H13ClN2O3: C 57.44%, H 4.48%, N 9.57%. Found: C
57.73%, H 4.23%, N 9.98%.

Molecules 2009, 14
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2-(2-Nitrobenzyl)-5-chloro-6-phenylpyridazin-3(2H)-one (3b): White solid, yield 70%, m.p.
1
116-118 °C; H-NMR (CDCl3): δ 7.20-8.10 (m, 9H, Ph-H), 7.18 (s, 1H, pyridazine-H), 5.79 (s, 2H,
13
CH2); C-NMR (CDCl3): δ 158.92,148.65, 146.03, 140.27, 133.75, 133.22, 131.06, 129.80, 129.34,
129.24, 129.04, 128.85, 128.36, 125.36, 152.55; IR: ν 3030.0, 2943.3, 1662.6 cm-1; Anal. Calc. for
C17H12ClN3O3: C 59.75%, H 3.54%, N 12.30%. Found: C 59.43%, H 3.51%, N 12.02%.
2-(4-Nitrobenzyl)-5-chloro-6-phenylpyridazin-3(2H)-one (3c): White solid, yield 72%, m.p. 143-145
°C; 1H-NMR (CDCl3): δ 7.46-8.20 (m, 9H, Ph-H), 7.15 (s, 1H, pyridazine-H), 5.43 (s, 2H, CH2); 13C-
NMR (CDCl3): δ 158.74, 147.86, 145.99, 142.67, 140.24, 133.33, 129.86, 129.78, 129.24, 129.07,
128.42, 124.02, 56.64; IR: ν 3020.0, 2960.1, 1662.6 cm-1; Anal. Calc. for C17H12ClN3O3: C 59.75%, H
3.54%, N 12.30%. Found: C 59.85%, H 3.86%, N 12.21%.
5-Chloro-2-[(6-chloropyridin-3-yl)methyl]-6-phenylpyridazin-3(2H)-one (3d): Light yellow solid,
1
yield 68%, m.p. 121-123 °C; H-NMR (acetone-d6): δ 7.39-8.46 (m, 8H, Ar-H), 7.19 (s, 1H,
13
pyridazine-H), 5.35 (s, 2H, CH2); C-NMR (acetone-d6): δ 158.22, 150.55, 150.11, 145.20, 139.72,
139.47, 134.01, 131.53, 129.45, 129.35, 128.69, 128.20, 124.16, 51.69: IR: ν 3076.4, 3059.1, 2950.0,
1654.9 cm-1; Anal. Calc. for C16H11Cl2N3O: C 57.85%, H 3.34%, N 12.65%. Found: C 57.84%, H
3.63%, N 12.14%.
2-(2-Fluorobenzyl)-5-chloro-6-phenylpyridazin-3(2H)-one (3e): White crystals, yield 60%, m.p. 91.7-
1
93.8 °C; H-NMR (CDCl3): δ 7.05-7.58 (m, 10H, Ar-H) , 5.44 (s, 2H, CH2); 13C-NMR (CDCl3): δ
162.06, 160.08, 158.89, 139.80, 130.80, 130.00, 129.94, 129.61, 129.29, 128.92, 128.31, 124.30,
122.68, 115.75, 115.58, 49.29; IR: ν 3075.0, 3024.3, 1662.6 cm-1; Anal. Calc. for C17H12ClFN2O: C
64.87%, H 3.84%, N 8.90%. Found: C 64.84%, H 3.80%, N 8.87%.
2-(2-Iodobenzyl)-5-chloro-6-phenylpyridazin-3(2H)-one (3f): Light yellow solid, yield 70%, m.p.
1
78.1-79.6 °C; H-NMR (acetone-d6): δ 7.03-7.90 (m, 9H, Ph-H), 7.24 (s, 1H, Pyridazine-H), 5.34 (s,
13
2H, CH2); C-NMR (acetone-d6): δ 158.34, 145.00, 139.61, 139.41, 138.67, 134.02, 129.49, 129.39,
129.35, 128.67, 128.63, 128.53, 128.15, 97.82, 59.15; IR: ν 3041.7, 3026.4, 1668.4 cm-1; Anal. Calc.
for C17H12ClIN2O: C 48.31%, H 2.86%, N 6.63%: Found C 48.63%, H 2.37%, N 6.19%.
2-(4-Iodobenzyl)-5-chloro-6-phenylpyridazin-3(2H)-one (3g): White solid, yield 79%, m.p.
1
75.1-76.9 °C; H-NMR (CDCl3): δ 7.21-7.67 (m, 9H, Ph-H), 7.03-7.90 (m, 9H, Ph-H),5.28 (s, 2H,
CH2), 7.24 (s, 1H, pyridazine-H); 13C-NMR (CDCl3): δ 158.78, 145.51, 139.88, 137.88, 135.30,
133.53, 131.03, 129.98, 129.71, 129.29, 128.37, 94.18, 54.91; IR: ν 3057.2, 3026.3, 2950.5, 1666.5
cm-1; Anal. Calc. for C17H12ClIN2O: C 48.31%, H 2.86%, N 6.63%. Found C 48.14%, H 2.42%, N
6.36%.
2-(2-Methoxybenzyl)-5-chloro-6-phenylpyridazin-3(2H)-one (3h): White solid, yield 70%, m.p. 92.4-
1
94.0 °C; H-NMR (acetone-d6): δ 7.18 (s, 1H, pyridazine-H), 6.83-7.57 (m, 9H, Ph-H), 5.33 (s, 2H,
13
CH2), 3.83 (s, 3H, OCH3); C-NMR (acetone-d6): δ 158.36, 157.31, 144.47, 139.01, 134.21, 129.29,
129.31, 128.81, 128.45, 128.13, 124.50, 120.35, 110.64, 55.09, 49.75; IR: ν 3061.0, 2953.0, 2833.4

Molecules 2009, 14
3682
1666.5 cm-1; Anal. Calc. for C18H15ClN2O2: C 66.16%, H 4.63%, N 8.57%. Found: C 66.67%, H
4.64%, N 8.60%.
3.5. Preparation of 5-chloro-2-(chloromethyl)-6-phenylpyridazin-3(2H)-one (4)
To a round bottomed flask containing dry benzene (50 mL) was added 5-chloro-6- phenylpyridazin-
3(2H)-one (4, 2.2 g), paraformaldehyde (1.5 g) and thionyl chloride (3 mL). The resulting mixture was
heated under reflux for 1 hour, then cooled to room temperature and filtered. The filtrate was
evaporated to dryness under reduced pressure to give a crude solid, which was recrystallised from
1
anhydrous ethanol to afford white crystals, yield 73%, m.p. 108-110 °C; H-NMR (CDCl3): δ 7.48-
13
7.59 (m, 6H, Ar-H), 5.86 (s, 2H, CH2); C-NMR (CDCl3): δ 157.96, 146.92, 141.11, 132.96, 130.06,
129.27, 129.18, 128.45, 57.83; IR: ν 3057.1, 3024.3, 2933.7, 1674.21 cm-1; Anal. Calc. for
C11H8Cl2N2O: C 51.79%, H 3.16%, N 10.98%. Found: C 51.82%, H 3.24%, N 11.03%.
3.6. Preparation of 5-chloro-6-phenyl-2-[[5-substituted-phenyl-1,3,4-thiadiazol- (or oxadiazol)-2-
ylthio]methyl]pyridazin-3(2H)-ones 6a-6i
To a suspension of 5-subsititued phenyl-1,3,4-thiadiazole (or oxadiazole)-2-thiol 5 in acetone (or
acetonitrile), potassium carbonate (0.5 g) and 5-chloro-2-(chloromethyl)-6-phenylpyridazin-3(2H)-one
(4, 2 mmol) were added successively; the mixture was stirred and refluxed for 2 h. The solid was
filtered off, and the mother liquor was evaporated to give the crude product, which was purified by
chromatography on silica using a mixture of petroleum ether and ethyl acetate (v/v = 2:1) as an eluant
to provide the target compounds.
5-Chloro-6-phenyl-2-[[5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazol-2-ylthio]methyl]pyridazin-3(2H)-
1
one (6a), White solid, yield 65%, m.p. 97-99 °C; H-NMR (DMSO-d6): δ 7.25-7.49 (m, 7H, Ph-H),
7.17 (s, 1H, pyridazine-H), 5.85 (s, 2H, CH2), 3.79-3.89 (m, 9H, OCH3); 13C-NMR (DMSO-d6): δ
170.68, 166.57, 161.66, 157.64, 157.60, 154.09, 145.25, 140.07, 129.52, 129.27, 129.21, 128.57,
128.55, 128.13, 128.08, 125.08, 105.18, 104.22, 59.94, 55.91, 55.88, 55.12; IR: ν 3057.1, 3024.4,
2935.7, 2833.4, 1675.1 cm-1; Anal. Calc. for C22H19ClN4O4S2: C 52.53%, H 3.81%, N 11.14%. Found:
C 52.94%, H 3.29%, N 11.62%.
5-Chloro-6-phenyl-2-[(5-phenyl-1,3,4-oxadiazol-2-ylthio)methyl]pyridazin-3(2H)-one (6b): Light
yellow solid, yield 75% , 70.1-71.5 °C; 1H-NMR (acetone-d6): δ 7.32-7.93(m, 10H, Ph-H), 7.22 (s, 1H,
13
pyridazine-H), 5.85 (s, 2H, CH2); C-NMR (acetone-d6): δ 166.54, 161.58, 157.67, 145.53, 133.53,
132.00, 129.57, 129.29, 129.26, 128.59, 128.15, 126.69, 53.37; IR: ν 3062.9, 3035.9, 2968.4, 1662.6
cm-1; Anal. Calc. for C19H13ClN4O2S: C 53.21%, H 3.06%, N 13.06%. Found: C 53.00%, H 3.76%, N
12.64%.
5-Chloro-6-phenyl-2-[[5-phenyl-1,3,4-thiadiazol-2-ylthio]methyl]pyridazin-3(2H)-one (6c): Light
1
yellow solid, yield 75%, m.p. 87-88 °C; H-NMR (acetone-d6): δ 7.34-7.91 (m, 10H, Ph-H), 7.23 (s,
1H, pyridazine-H), 5.86 (s, 2H, CH2); 13C-NMR (acetone-d6): δ 170.69, 162.06, 157.59, 145.24,

Molecules 2009, 14
3683
140.06, 133.63, 131.51, 129.94, 129.50, 129.46, 129.25, 128.56, 128.12, 127.70, 53.01; IR: ν 3082.2,
3020.5, 2947.3, 1670.4 cm-1; Anal. Calc. for C19H13ClN4OS2: C 55.27%, H 3.17%, N 13.57%. Found:
C 55.74%, H 3.63%, N 13.92%.
5-Chloro-2-[[5-(2-chlorophenyl)-1,3,4-thiadiazol-2-ylthio]methyl]-6-phenylpyridazin-3(2H)-one (6d):
1
Yellow solid, yield 76%, m.p. 116.9-118.4 °C; H-NMR (DMSO-d6) δ: 7.37-7.68 (m, 10H, Ar-H),
13
5.87 (s, 2H, CH2); C-NMR (DMSO-d6): δ 165.90, 164.56, 157.99, 145.50, 140.17, 133.53, 133.23,
131.97, 131.25, 131.18, 120.08, 129.54, 129.09, 128.61, 128.36, 55.41; IR: ν 3066.8, 3026.3, 2966.5,
1676.1 cm-1; Anal. Calc. for C19H12Cl2N4OS2: C 51.01%, H 2.70%, N 12.52%. Found: C 51.49%, H
2.93%, N 12.82%.
5-Chloro-2-[[5-(2-chlorophenyl)-1,3,4-oxadiazol-2-ylthio]methyl]-6-phenylpyridazin-3(2H)-one (6e):
Yellow solid, yield 80%, m.p. 112.9-114.7 °C; 1H-NMR (CDCl3): δ 7.33-7.87 (m, 9H, Ph-H), 7.14 (s,
13
1H, pyridazine-H), 5.83 (s, 2H, CH2); C-NMR (CDCl3): δ 165.15, 162.32, 158.13, 146.31, 140.92,
133.22, 132.91, 132.64, 131.33, 131.16, 129.81, 129.18, 128.78, 128.28, 127.14, 122.73, 53.27; IR: ν
3061.0, 3041.7, 2980.0, 1678.0 cm-1; Anal. Calc. for C19H12Cl2N4O2S: C 52.91%, H 2.80%, N 12.99%.
Found: C 52.41%, H 3.29%, N 12.72%.
5-Chloro-2-[[5-(2-methoxyphenyl)-1,3,4-thiadiazol-2-ylthio]methyl]-6-phenylpyridazin-3(2H)-one
1
(6f): Yellow solid, yield 75%, m.p. 123.6-125.8 °C; H-NMR (CDCl3): δ 7.14-8.49 (m, 10H, Ar-H),
13
3.93 (s, 3H,OCH3), 5.84 (s, 2H, CH2); C-NMR (CDCl3): δ 164.62, 162.25, 158.19, 155.88, 145.75,
140.62, 133.06, 132.47, 129.64, 129.23,128.78, 128.44, 128.19, 121.42, 118.96, 111.32, 55.76, 55.25;
IR (KBr): ν 3061.0, 3028.2, 2937.6, 1670.3 cm-1; Anal. Calc. for C20H15ClN4O2S2: C 54.23%, H
3.41%, N 12.65%. Found: C 54.81%, H 3.02%, N 12.92%.
5-Chloro-2-[[5-(2-methoxyphenyl)-1,3,4-oxadiazol-2-ylthio]methyl]-6-phenylpyridazin-3(2H)-one
1
(6g): Light yellow solid, yield 70%, m.p. 89.2-90.6 °C; H-NMR (CDCl3): δ 6.9-7.8 (m, 10H, Ar-H),
13
3.88 (s, 3H, CH3), 5.80 (s, 2H, CH2); C-NMR (CDCl3): δ 165.63, 161.25, 158.14, 157.90, 146.17,
140.84, 133.39, 132.93, 130.49, 129.74, 129.21, 128.76, 128.25, 120.79, 112.56, 111.95, 56.02, 53.43;
IR: ν 3070.7, 3034.0, 2983.8,1664.6 cm-1; Anal. Calc. for C20H15ClN4O3S: C 56.27%, H 3.54%, N
13.12%. Found: C 56.69%, H 3.92%, N 13.60%.
5-Chloro-2-[[5-(2,4-dichlorophenyl)-1,3,4-thiadiazol-2-ylthio]methyl]-6-phenylpyridazin-3(2H)-one
1
(6h): Light yellow crystals, yield 75%, m.p. 142.5-144.1 °C; H-NMR (CDCl3): δ 7.36-8.26 (m, 8H,
13
Ph-H), 7.14 (s, 1H, pyridazine-H), 5.88 (s, 2H, CH2); C-NMR (CDCl3): δ 164.90, 164.09, 158.20,
146.02, 140.79, 137.53, 133.13, 133.00, 131.65, 130.41, 129.81, 129.20, 128.83, 128.30, 128.04,
127.33, 54.59; IR: ν 3068.7, 3022.4, 2953.0, 1674.2 cm-1; Anal. Calc. for C19H11Cl3N4OS2: C 47.36%,
H 2.30%, N 11.63%. Found: C 47.29%, H 2.68%, N 11.30%.
5-Chloro-2-[[5-(2,4-dichlorophenyl)-1,3,4-oxadiazol-2-ylthio]methyl]-6-phenylpyridazin-3(2H)-one
(6i): White solid, yield 73%, m.p. 134.5-136.1 °C; 1H-NMR (DMSO-d6): δ 7.36-7.93 (m, 9H, Ar-H),
13
5.87 (s, 2H, CH2); C-NMR (DMSO-d6): δ 163.96, 162.63, 158.04, 145.74, 140.22, 137.82, 133.50,

Molecules 2009, 14
3684
133.35, 132.75, 131.34, 130.06, 129.52, 129.07, 128.59, 121.44, 53.85; IR: ν 3057.1, 3026.3, 2933.7,
1676.1 cm-1; Anal. Calc. for C19H11Cl3N4O2S: C 49.00%, H 2.38%, N 12.03%. Found: C 48.73%, H
2.69%, N 12.39%.
3.7. Preparation of 5-chloro-6-phenyl-2-[(5-substituted-phenyl)-1,3,4-thiadiazol-2-ylsulfonyl]methyl)
pyridazin-3(2H)-ones 7a-7c
To a mixture of compound 6 (1.1 mmol) and ethanol (5 mL) was added 30% H2O2 (5.5 mmol) and
(NH4)6Mo7O24 (0.011 mmol). The mixture was stirred at 40 °C for 18 h and then filtered off to give a
crude product, which was recrystallized from a mixture of anhydrous ethanol and DMF (v/v = 3:1) to
afford the desired products.
5-Chloro-6-phenyl-2-[[5-(3,4,5-trimethoxyphenyl)-1,3,4-thiadiazol-2-ylsulfonyl]methyl]pyridazin-
3(2H)-one (7a): Yellow solid, yield 45%, m.p. 143.3-145.0 °C; 1H-NMR (CDCl3): δ 7.11-7.42 (m, 8H,
13
Ar-H), 5.90 (s, 2H, CH2), 3.94 (s, 9H, CH3); C-NMR (CDCl3): δ 174.34, 165.74, 158.15, 153.86,
147.10, 142.17, 141.28, 132.45, 130.01, 129.07, 129.01, 128.30, 123.66, 105.82, 69.11, 61.23, 56.56;
IR: ν 3066.8, 300.2, 2837.6, 2839.2, 1689.6 cm-1; Anal. Calc. for C22H19ClN4O6S2: C 49.39%, H
3.58%, N 10.47%. Found: C 52.94%, H 3.29%, N 11.62%.
5-chloro-6-phenyl-2-[(5-phenyl-1,3,4-oxadiazol-2-ylsulfonyl)methyl]pyridazin-3(2H)-one (7b): White
1
solid, yield 55%, m.p. 166-168 °C; H-NMR (DMSO-d6): δ 7.35-8.00 (m, 11H, Ar-H), 6.31 (s, 2H,
1
CH2); H-NMR (DMSO-d6): δ 167.15, 160.93, 158.48, 146.91, 140.80, 133.02, 130.33, 130.14,
129.48, 129.32, 128.65, 128.01, 122.35, 69.39; IR: ν 3095.7, 2999.3, 2914.4, 1672.3 cm-1; Anal. Calc.
for C19H13ClN4O4S: C 57.50%, H 3.30%, N 14.14%. Found: C 7.41%, H 3.54%, N 14.64%.
5-chloro-6-phenyl-2-[(5-phenyl-1,3,4-thiadiazol-2-ylsulfonyl)methyl]pyridazin-3(2H)-one (7c): White
1
solid, yield 60%, m.p. 154-156 °C; H-NMR (DMSO-d6): δ 7.37-8.03 (m, 11H, Ar-H), 6.20 (s, 2H,
CH2); 13C-NMR (DMSO-d6): δ 175.00, 166.00, 159.00, 158.26, 147.00, 140.50, 133.48, 133.05,
130.23, 130.12, 129.39, 128.93, 128.60, 69.36; IR: ν 3089.6, 3001.2, 2902.8, 1678.1 cm-1; Anal. Calc.
for C19H13ClN4O3S2: C 51.29%, H 2.95%, N 12.59%. Found: C 51.63%, H 2.69%, N 12.92%.
3.8. Antifungal bioassays
The antifungal activity of all synthesized compounds was tested against F. oxysporum, G. zeae, and
C. mandshurica by the poison plate technique [31]. All the compounds were dissolved in DMSO
(10 mL) before mixing with Potato Dextrose Agar (PDA, 90 mL). The final concentration of the
compounds in the medium was fixed at 50 μg/mL. The three kinds of fungi were incubated in PDA at
25 ± 1 °C for 5 days to get new mycelium for the antifungal assays, and then a mycelia disk of
approximately 0.45 cm diameter cut from the culture medium was picked up with a sterilized
inoculation needle and inoculated in the center of PDA plate. The inoculated plates were incubated at
25 ± 1 °C for 5 days. DMSO in sterilized distilled water served as control, while hymexazole was used
as positive control for each treatment with three replicates being conducted for each experiment. The

Molecules 2009, 14
3685
radial growth of the fungal colonies was measured on the sixth day and the data were statistically
analyzed. The in vitro inhibiting effects of the test compounds on the fungi were calculated by the
formula CV = (A − B)/A, where A represents the diameter of fungi growth on untreated PDA, B
represents the diameter of fungi on treated PDA, and CV represents the rate of inhibition.
4. Conclusions
In the present study, a mild and effective method for the preparation of 21 novel pyridazine
derivatives were undertaken by employing mucochloric acid and benzene as the starting materials. The
13
synthesized compounds were characterized by spectral data (1H-NMR, C-NMR, IR) and elemental
analysis. The compounds were subjected to fungicidal activities in vitro against G. zeae, F. oxysporum
and C. mandshurica. The results showed that the synthesized pyridazine compounds possessed weak
to good antifungal activities against the tested fungi, among which, compounds 3e, 3h, 7b, 7c
displayed good antifungal activities. Further studies are currently underway to establish a definite
structure activity relationship.
Acknowledgements
We are grateful to the National Natural Science Foundation of China (No. 20872021) and
Innovation Foundation for Graduate Students in Guizhou University (Grant No. 2009004) for
supporting the project.
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Sample Availability: Samples of the compounds are available from the authors.
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