Bioorganic & Medicinal Chemistry Letters 24 (2014) 1236–1238

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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

Article history: Received 8 August 2013 Revised 27 November 2013 Accepted 2 December 2013 Available online 7 December 2013

a b s t r a c t 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. 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 published 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 compounds showed different biological activities. Triazolo showed a series of biological activities, such as antibacterial,8 antiinflammatory,9 antiHIV10 and antiplatelet11 activities. So we became interested in 1,2,4-triazolo [3,4-a] phthalazine. We have designed and synthesized a series of 6-N-substituted1,2,4-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 starting material phthalic anhydride reacted with hydrazine hydrate in ⇑ Corresponding authors. Tel.: +86 371 67781896 (L.-H. S.); tel.: +86 371 67781739 (H.-M. L.). E-mail addresses: [email protected] (L.-H. Shan), [email protected] (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

acetic acid to yield 2,3-dihydrophthalazine-1,4-dione (compound 1), which reacted further with the refluxing phosphorus oxychloride (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 [3,4a] phthalazine (compound 4c).15 The compound 4 (4a, 4b, 4c) reacted further with appropriate amine in N,N-dimethylformamide to yield the target compounds of 5a–5l. The results were summarized in Table 1. Antimicrobial activities of synthetic compounds were evaluated versus Gram-positive bacteria: Staphylococcus aureus, Bacillus subtilis; Gram-negative bacteria: Escherichia coli, Acinetobacter baumannii, Stenotrophomonas maltophilia and Fungi: Candida albicans by broth microdilution methods. Minimum inhibitory concentrations (MICs) of compounds for bacteria and Fungi were determined by microbroth dilution method according to Clinical and Laboratory Standards Institute (CLSI) guidelines (M100-S22 and M38A2). In brief, a series of concentrations ranging from 1 to 128 lg/ ml to a final volume of 200 ll in plate was obtained by two-fold 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 concentration of compound that inhibited visible growth. A mirror

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Cl N N

d'

4a O

O O

a'

NH b' NH

O phthalic anhydride

Cl

O

N N

Cl

1

HN

2

3

R2 N

g'

N

4b

3'; 4'; 6'; 7'

N N 5a-5e R2 4c

1'; 4'; 5'

N N

g'

N

N N 5j-5l

N N

NH2

4b f'

Cl N N

N N

g'

N

e'

R2

1'- 5' 4a

Cl

Cl N c' N

N N

4c

N N

N N

5f-5i 1': 4-fluoroaniline 2': 4-chloroaniline

3': 4-methoxyaniline 4': 4-toluidine 5': piperazine 6': 2-chloroaniline 7': 3,5-dimethylpiperidine

5a: R 2= 4-f luoroanilino 5b: R 2= 4-chloroanilino 5c: R 2= 4-methoxyanilino 5d: R 2= 4-toluidino 5e: R 2= piperazin-1-yl 5f: R 2 = 4-methoxyanilino 5g: R 2= 4-toluidino 5h: R 2= 2-chloroanilino 5i: R 2= 3,5-dimethylpiperidin-1-yl 5j: R 2= 4-fluoroanilino 5k: R 2= 4-toluidino 5l: R 2= piperazin-1-yl

Scheme 1. Reagents and conditions: (a0 ): H2N-NH2H2O, CH3COOH, 120 °C, 89.8%; (b0 ): POCl3, 110 °C, 90.1%; (c0 ): C2H5OH, H2N-NH2H2O, 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 Structures of synthetic compound

Table 2 Antimicrobial activities MIC data (lg/ml) of synthetic compounds

Compd

R2

Yield (%)

5a 5b 5c 5d 5e 5f 5g 5h 5i 5j 5k 5l

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 Piperazin-1-yl

69.6 70.3 68.5 65.6 83.2 66.4 72.8 84.7 75.2 62.5 61.4 74.8

reader was used to assist in determining the MIC endpoint. (See Table 2) The results suggested that most of them showed inhibitory activity against S. aureus with the MIC of 16–128 lg/ml except for compound 5e. Compound 5l showed inhibitory activity against all bacterias and C. albicans, with the MIC of 32–128 lg/ml. 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 similar SAR. The results showed that the 3-Ph is more beneficial for the bioactivity than 3-H. Compound 5j showed the nearest approximation of inhibitory activity against S. aureus to Levofloxacin than other compounds. Compound 5k containing 3-Ph and 6-(4-toluidino) showed better inhibitory activity against S. aureus than that of compound 5g. The results showed that the 3-Ph is more beneficial

Compd

5a 5b 5c 5d 5e 5f 5g 5h 5i 5j 5k 5l LEVg FCZi a b c d e f g h i

Bacteria

Fungal

S. aa

B. sb

E. cc

A. bd

S. me

C. af

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 0.25 /

>128 >128 >128 >128 >128 >128 >128 >128 >128 >128 >128 64 0.25 /

>128 >128 >128 >128 >128 >128 >128 >128 >128 >128 >128 32 0.5 /

>128 >128 >128 >128 >128 >128 >128 >128 >128 >128 >128 32 /h 1

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.

for the bioactivity than 3-CH3. Compound 5l containing 3-Ph and 6-piperazin-1-yl activity showed inhibitory activity against S. aureus with the MIC of 32 lg/ml, B. subtilis (64 lg/ml), E. coli (128 lg/ ml), A. baumannii (64 lg/ml), S. maltophilia (32 lg/ml) and C. albi-

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cans (32 lg/ml). The result showed that this combination of functional group is beneficial for the bioactivity. Compound 5l showed the nearest approximation of inhibitory activity against C. albicans to Fluconazole than other compounds. Besides, compound 5i containing 3-CH3 and 6-(3, 5-dimethylpiperidin-1-yl) showed inhibitory activity against S. aureus (32 lg/ml), B. subtilis (64 lg/ml). 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. Acknowledgments Financial supports by National Nature Science Foundation of China, No.81172937. 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. References and notes 1. de Almeida, A. M.; Nascimento, T.; Ferreira, B. S.; de Castro, P. P.; Silva, V. L.; Diniz, C. G.; Hyaric, M. L. Bioorg. Med. Chem. Lett. 2013, 23, 2883. 2. El-hashash, M. A. A.; Soliman, A. Y.; El-Shamy, I. E. Turk. J. Chem. 2012, 36, 347. 3. (a) Kassem, E. M.; Kamel, M. M.; El-zahar, M. Pharmazie. 1990, 45, 215; (b) Dima, S.; Caprosu, M.; Ungureanu, M.; Grosu, G.; Petrovanu, M. Ann. Pharm. Fr. 1999, 57, 415.

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