Synthesis and antimicrobial activities of novel 1,2,4-triazolo [3,4-a] phthalazine derivatives

Article abstract of DOI:10.1016/j.bmcl.2013.12.010

A series of novel 1,2,4-triazolo [3,4-a] phthalazine derivatives were synthesized in five steps from a common precursor, phthalic anhydride. Most of synthesized phthalazine derivatives showed inhibitory activity against Staphylococcus aureus. One of phthalazine derivatives 5l showed inhibitory activity against all tested bacterial and fungal strains.

Full text of DOI:10.1016/j.bmcl.2013.12.010

Bioorganic & Medicinal Chemistry Letters 24 (2014) 1236–1238
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antimicrobial activities of novel 1,2,4-triazolo [3,4-a]
phthalazine derivatives
Qiu-Rong Zhang, Deng-Qi Xue, Peng He, Kun-Peng Shao, Peng-Ju Chen, Yi-Fei Gu, Jing-Li Ren,
⇑
⇑
Li-Hong Shan , Hong-Min Liu
New Drug Research & Development Center, School of Pharmaceutical Sciences, Zhengzhou University, No. 100, KeXue DaDao, Zhengzhou 450001, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 1,2,4-triazolo [3,4-a] phthalazine derivatives were synthesized in five steps from a com-
mon precursor, phthalic anhydride. Most of synthesized phthalazine derivatives showed inhibitory activ-
ity against Staphylococcus aureus. One of phthalazine derivatives 5l showed inhibitory activity against all
tested bacterial and fungal strains.
Received 8 August 2013
Revised 27 November 2013
Accepted 2 December 2013
Available online 7 December 2013
Ó 2014 Published by Elsevier Ltd.
Keywords:
Triazole
Phthalazine
Synthesis
Antimicrobial
The evolutionary adaptation of microorganisms has led to the
development of drug-resistant strains of bacteria and fungi. The
emergence of multidrug resistant organisms has become a major
public health problem, as they turn the management of infectious
diseases more precarious, so there is an urgent need for new active
compounds.1 Nitrogen-containing heterocyclic compounds have
received much attention as shown by the numerous studies pub-
lished on their applicability in different areas, especially as drugs.2
Phthalazine is an example of nitrogen heterocycles that showed a
series of biological activities, such as antimicrobial,3 antifungal,4
antibacterial,5 anticancer6 and antiepileptic.7 Triazole compounds
have attracted more and more attention because of its diversity
of biological activities. The different structures of the triazolo com-
pounds showed different biological activities. Triazolo showed a
series of biological activities, such as antibacterial,8 antiinflamma-
tory,9 antiHIV10 and antiplatelet11 activities. So we became inter-
ested in 1,2,4-triazolo [3,4-a] phthalazine.
We have designed and synthesized a series of 6-N-substituted-
1,2,4-triazolo [3,4-a] phthalazine derivatives. We also evaluated
the antimicrobial activities of the target compounds against some
bacterial and fungal strains.
The synthesis of the final target compounds were readily
obtained in five steps from commercially available phthalic
anhydride. The synthetic route was shown in Scheme 1. The start-
ing material phthalic anhydride reacted with hydrazine hydrate in
acetic acid to yield 2,3-dihydrophthalazine-1,4-dione (compound
1), which reacted further with the refluxing phosphorus oxychlo-
ride (POCl3) to yield 1,4-dichlorophthalazine (compound 2).12
The compound 2 reacted further with hydrazine hydrate in ethanol
to produce 1-chloro-4-hydrazinylphthalazine (compound 3).13 The
compound 3 reacted further with triethoxy methane in dioxane to
yield 6-chloro-1,2,4-triazolo [3,4-a] phthalazine (compound 4a).14
The compound 3 reacted further with acetyl chloride in dioxane to
produce 6-chloro-3-methyl-1,2,4-triazolo [3,4-a] phthalazine
(compound 4b).15 The compound 3 reacted further with benzoyl
chloride in dioxane to yield 6-chloro-3-phenyl-1,2,4-triazolo [3,4-
a] phthalazine (compound 4c).15 The compound 4 (4a, 4b, 4c) re-
acted further with appropriate amine in N,N-dimethylformamide
to yield the target compounds of 5a–5l. The results were summa-
rized in Table 1.
Antimicrobial activities of synthetic compounds were evaluated
versus Gram-positive bacteria: Staphylococcus aureus, Bacillus sub-
tilis; Gram-negative bacteria: Escherichia coli, Acinetobacter bau-
mannii, Stenotrophomonas maltophilia and Fungi: Candida albicans
by broth microdilution methods. Minimum inhibitory concentra-
tions (MICs) of compounds for bacteria and Fungi were determined
by microbroth dilution method according to Clinical and Labora-
tory Standards Institute (CLSI) guidelines (M100-S22 and M38-
A2). In brief, a series of concentrations ranging from 1 to 128
lg/
ml to a final volume of 200 l in plate was obtained by two-fold
l
dilutions. Each well except for the blank well was inoculated with
the test bacteria and incubated at 37 °C for 24 h. The minimum
inhibitory concentration (MIC) was determined as the lowest con-
centration of compound that inhibited visible growth. A mirror
⇑
Corresponding authors. Tel.: +86 371 67781896 (L.-H. S.); tel.: +86 371
67781739 (H.-M. L.).
E-mail addresses: shlh@zzu.edu.cn (L.-H. Shan), liuhm@zzu.edu.cn (H.-M. Liu).
0960-894X/$ - see front matter Ó 2014 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.bmcl.2013.12.010

Q.-R. Zhang et al. / Bioorg. Med. Chem. Lett. 24 (2014) 1236–1238
1237
Cl
N
N
d'
4a
N
N
O
O
Cl
Cl
Cl
Cl
O
a'
NH
NH
b'
N
N
N
N
N
N
c'
e'
f'
O
O
N
HN
N
NH2
phthalic anhydride
1
2
3
4b
Cl
N
N
R2
R2
1'- 5'
4a
N
N
3'; 4'; 6'; 7'
g'
N
N
4b
N
4c
N
g'
N
5a-5e
N
N
N
5f-5i
R2
1': 4-fluoroaniline
2': 4-chloroaniline
3': 4-methoxyaniline
4': 4-toluidine
5': piperazine
6': 2-chloroaniline
5a: R2= 4-fluoroanilino
5b: R2= 4-chloroanilino
5c: R2= 4-methoxyanilino
5d: R2= 4-toluidino
1'; 4'; 5'
4c
N
N
g'
5e: R2= piperazin-1-yl
5f: R2= 4-methoxyanilino
5g: R2= 4-toluidino
N
5j-5l
N
7': 3,5-dimethylpiperidine
5h: R2= 2-chloroanilino
5i: R2= 3,5-dimethylpiperidin-1-yl
5j: R2= 4-fluoroanilino
5k: R2= 4-toluidino
5l: R2= piperazin-1-yl
Scheme 1. Reagents and conditions: (a0): H2N-NH2ꢀH2O, CH3COOH, 120 °C, 89.8%; (b0): POCl3, 110 °C, 90.1%; (c0): C2H5OH, H2N-NH2ꢀH2O, 78 °C, 76.8%; (d0): CH(OC2H5),
dioxane, N(C2H5)3, 110 °C, 82.3%; (e0): CH3COCl, dioxane, N(C2H5)3, 110 °C, 75.7%; (f0): C6H5COCl, dioxane, N(C2H5)3, 110 °C, 78.2%; (g0): NaOH, DMF, 100 °C.
Table 1
Table 2
Structures of synthetic compound
Antimicrobial activities MIC data (
l
g/ml) of synthetic compounds
Bacteria
Compd
R2
Yield (%)
Compd
Fungal
C. af
5a
5b
5c
5d
5e
5f
5g
5h
5i
4-Fluoroanilino
4-Chloroanilino
4-Methoxyanilino
4-Toluidino
Piperazin-1-yl
4-Methoxyanilino
4-Toluidino
2-Chloroanilino
3,5-Dimethylpiperidin-1-yl
4-Fluoroanilino
4-Toluidino
69.6
70.3
68.5
65.6
83.2
66.4
72.8
84.7
75.2
62.5
61.4
74.8
S. aa
B. sb
E. cc
A. bd
S. me
5a
5b
5c
5d
5e
5f
5g
5h
5i
64
32
128
32
>128
16
64
32
32
16
32
32
0.5
/
>128
>128
>128
>128
>128
>128
>128
>128
64
>128
>128
64
1
/
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
64
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
32
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
32
5j
5k
5l
5j
Piperazin-1-yl
5k
5l
h
LEVg
FCZi
0.25
/
0.25
/
0.5
/
/
1
reader was used to assist in determining the MIC endpoint. (See
Table 2)
a
b
c
d
e
f
S.a: Staphylococcus aureus.
B.s: Bacillus subtilis.
E.c: Escherichia coli.
A.b: Acinetobacter baumannii.
S.m: Stenotrophomonas maltophilia.
C.a: Candida albicans.
LEV: levofloxacin, positive control drug.
No detection.
FCZ: fluconazole, positive control drug.
The results suggested that most of them showed inhibitory
activity against S. aureus with the MIC of 16–128
for compound 5e. Compound 5l showed inhibitory activity against
all bacterias and C. albicans, with the MIC of 32–128 g/ml.
lg/ml except
l
g
h
i
Among the synthetic derivatives, compound 5j containing 3-Ph
and 6-(4-fluoroanilino) showed better inhibitory activity against S.
aureus than that of compound 5a. Compounds 5l, 5e have the sim-
ilar SAR. The results showed that the 3-Ph is more beneficial for the
bioactivity than 3-H. Compound 5j showed the nearest approxima-
tion of inhibitory activity against S. aureus to Levofloxacin than
other compounds. Compound 5k containing 3-Ph and 6-(4-toluidi-
no) showed better inhibitory activity against S. aureus than that of
compound 5g. The results showed that the 3-Ph is more beneficial
for the bioactivity than 3-CH3. Compound 5l containing 3-Ph and
6-piperazin-1-yl activity showed inhibitory activity against S. aur-
eus with the MIC of 32
ml), A. baumannii (64
lg/ml, B. subtilis (64
l
g/ml), E. coli (128
lg/
l
g/ml), S. maltophilia (32
l
g/ml) and C. albi-

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To summary, a series of novel 1,2,4-triazolo [3,4-a] phthalazine
derivatives were synthesized. Most of synthetic compounds
showed inhibitory activity against S. aureus. Compound 5l showed
inhibitory activity against all bacterial strains and C. albicans.
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Acknowledgments
Financial supports by National Nature Science Foundation of
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013
.12.010.
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