In vitro Antibacterial Evaluation of 1,2,4-Triazole Compounds Containing Purine Moiety

Article abstract of DOI:10.1007/s10600-017-2217-7

9H-[1,2,4]Triazolo[4,3-g]purin-5-amine (2) was synthesized by reaction of 6-hydrazinyl-7H-purin-2-amine (1a) with formic acid under reflux conditions. Treating compound 1a in ethanol with CS₂ in the presence of KOH yielded 5-amino-3H-[1,2,4]tri

Full text of DOI:10.1007/s10600-017-2217-7

DOI 10.1007/s10600-017-2217-7
Chemistry of Natural Compounds, Vol. 53, No. 6, November, 2017
In vitro ANTIBACTERIAL EVALUATION OF 1,2,4-TRIAZOLE
COMPOUNDS CONTAINING PURINE MOIETY
Sevdije Govori
9H-[1,2,4]Triazolo[4,3-g]purin-5-amine (2) was synthesized by reaction of 6-hydrazinyl-7H-purin-2-amine
(1a) with formic acid under reflux conditions. Treating compound 1a in ethanol with CS in the presence
2
of KOH yielded 5-amino-3H-[1,2,4]triazolo[4,3-g]purine-3-thione (3). The new synthesized compounds
1
were characterized using IR, H NMR, and elemental analysis. The synthesized compounds have been screened
for antibacterial activity.
Keywords: 6-hydrazinyl-7H-purin-2-amine, 9H-[1,2,4]triazolo[4,3-g]purin-5-amine, 5-amino-3H-[1,2,4]triazolo[4,3-g]-
purine-3-thione, synthesis, antibacterial activity.
Triazoles are an important class of heterocyclic compounds that have received considerable attention for their biological
activity such as antimicrobial [1], antifungal [2, 3], antioxidant [4], antiinflammatory [5], antitubercular [6], and anticancer
activity [7]. Research articles that have been published during the last few years show that substituted 1,2,4-triazoles and their
N-bridged heterocycles have received considerable attention during the last two decades as they are endowed with a variety of
biological activities and have a wide range of therapeutic properties.
Considering this, we have synthesized 1,2,4-triazole compounds containing the purine moiety: 9H-[1,2,4]triazolo[4,3-g]-
purin-5-amine (2) and 5-amino-3H-[1,2,4]triazolo[4,3-g]purine-3-thione (3). The synthesized compounds have been screened
for in vitro antibacterial activity against Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Klebsiella
pneumoniae PR 23/07 by the cup plate method at concentrations of 1, 3, and 5 mg/mL (Table 1). DMF was used as solvent control.
2-Amino-6-chloropurine treated with hydrazine hydrate in ethanol under reflux conditions yielded 6-hydrazinyl-7H-
purin-2-amine (1a). Compound 1a is a useful starting material for synthesis of a variety of heterocycle–fused purines. Treating
compound 1a with HCOOH for 6 h yielded 9H-[1,2,4]triazolo[4,3-g] purin-5-amine (2). In addition, the reaction of 6-hydrazinyl-
7H-purin-2-amine (1a) with CS was a possible route to get the fused purino-1,2,4-triazole-3-thione ring (Scheme 1).
2
N
N
3
10
11
N
N
Cl
8
NHNH
N
H
N
2
H
N
5
6
b
7 N
H
5
4
N
NH
2
a
N
2
8
2
N
N
c
N
NH
2
N
NH
2
N
N
9
1
1a
S
N
N
N
8
N
NH
2
3
a. N H , EtOH; b. HCOOH; c. CS , KOH, EtOH
2
4
2
Scheme 1. The synthetic route for the preparation of compounds 2 and 3.
University of Pristina, Faculty of Natural Sciences, Department of Chemistry, Mother Teresa, 10000, Pristina, Republic
of Kosovo, e-mail: s_govori@yahoo.com; sevdije.govori@uni-pr.edu. Published in Khimiya Prirodnykh Soedinenii, No. 6,
November–December, 2017, pp. 966–967. Original article submitted April 25, 2016.
0009-3130/17/5306-1137 02017 Springer Science+Business Media New York
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TABLE 1. Antibacterial Activity – Diameters of Growth Inhibition Zones of Compounds 2 and 3, mm
2
3
Bacteria
Concentration, mg/mL
1
3
5
1
3
5
ATCC® 25922
–
2
4
4
2
5
4
5
6
3
3
–
4
3
–
6
3
3
Escheria coli
ATCC® 25923
PR 23/07
Staphylococcus aureus
Klebsiella pneumoniae
TLC was used for monitoring of the reaction, the structures of products 2 and 3 were assessed by IR and NMR and
elementaly analysis.
EXPERIMENTAL
General. All reactions were performed under an atmosphere of argon in oven-dried glassware. Anhydrous solvents
for reactions were obtained by filtration through activated alumina or by storage over molecular sieves (4A). Thin-layer
chromatography was performed on silicagel plates (Macherey–Nagel, 0.25 mm, UV254). Visualization was achieved either
under UV light or by staining in dip solutions [vanillin (15 g), ethanol (250 mL), and concentrated H SO (2.5 mL);
2
4
or p-anisaldehyde (10 mL), concentrated H SO (10 mL), concentrated acetic acid (2 mL), and ethanol (180 mL)] followed
2
4
by heating with a heat gun. Melting points were determined with a Buechi apparatus. The infrared (IR) spectra were recorded
as KBr pellets in a Bomem MB 100 mid FT-IR spectrophotometer. The nuclear magnetic resonance (NMR) spectra were
recorded using a Varian EM 360 with tetramethylsilane as internal standard.
9H-[1,2,4]Triazolo[4,3-g]purin-5-amine (2). A mixture of 6-chloro-7H-purin-2-amine (2.9 mmol) and hydrazine
hydrate (2.9 mmol) was heated under reflux for 15 min. The obtained crude product was filtered, allowed to cool, and then
dissolved in a formic acid (15 mL) under reflux conditions for 6 h. After the reaction was completed and cooled to room
temperature, the mixture was poured onto crushed ice (100 g) and 1 N NaOH solution. The crude white product was filtered
off, washed with alcohol, and recrystallized from the mixture of acetone–DMF (N,N-dimethylformamide) (1:1).
–1
Yield 87%, mp 298–300ꢀC. IR (KBr, ꢁ , cm ): 3400–3120 (N–H); 3080–3030 (C–H), 1612–1600 (C=N).
max
1
H NMR (DMSO-d , ꢂ, ppm): 8.00–8.75 (2H, aromatic), 10.3 (N–H), 3.90 (NH ). Elementary analysis: C H N : 175.06;
6
2
6 5 7
calcd %C, 41.14; %H, 2.88; %N, 55.98; experimentally: %C, 40.92; %H, 2.94; %N, 55.62.
5-Amino-3H-[1,2,4]triazolo[4,3-g]purine-3-thione (3). A mixture of 6-chloro-7H-purin-2-amine (2.9 mmol) and
hydrazine hydrate (2.9 mmol) was heated under reflux for 15 min. The obtained crude product 1a was allowed to cool. After
cooling, the precipitate was filtered off and dried. After 24 h, product 1a was dissolved in 25 mL ethanol, an alcohol solution
of KOH and 3.5 mL CS were added, and the whole refluxed for 25 min. After cooling, the crude yellow to brown product was
2
filtered off, washed with alcohol, and recrystallized from a mixture of methanol and DMF (1:1).
–1
Yield 73%, mp > 300ꢀC. IR (KBr, ꢁ , cm ): 3360–3160 (N–H), 3010 (C–H), 1608–1600 (C=N), 1220 (C=S).
max
1
H NMR (DMSO-d , ꢂ, ppm): 8.65 (1H, H-8), 4.20 (NH ). Elementary analysis: C H N S: 205.02. Experimentally: %C
6
2
6 3 7
35.33; %H 1.42; %N 47.52. calcd: %C 35.12; %H 1.47; %N 47.78.
Antibacterial Activity. Compounds 2 and 3 were screened for their antibacterial activity against Escherichia coli,
Staphylococcus aureus, and Klebsiella pseumoniae by the disc diffusion method of Kirby–Bayer at three concentrations
(1, 3, and 5 mg/mL) in DMF. These solutions were added to each filter disc, and the plates were incubated at 37ꢀC and
examined for zone of inhibition around each disc after 48 h. The results are summarized in Table 1.
The antibacterial activity of the synthesized compounds was found to be mild to moderate.
According to preliminary antibacterial screening by the paper disc method, compound 2 was found to be active
against all the bacterial strains except in a concentration 1 mg/mL in Escherichia coli. The antibacterial activity of compound 2 is
stronger in Staphylococcus aureus and Klebsiella pneumoniae PR 23/07. Results show that the antibacterial activity of
compound 3 in Escherichia coli is moderate, while the antibacterial activity of compound 3 is stronger in Staphylococcus
aureus (at concentrations of 1 and 3 mg/mL and did not change with increase in concentration) and weaker in Klebsiella
pneumoniae at the same concentration.
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1,2,4-Triazole compounds containing the purine moiety were synthesized and evaluated for in vitro antibacterial
activity. The biological evaluation of these purino-triazole derivatives generally showed mild to moderate activity against
Escherichia coli, Staphylococcus aureus, and Klebsiella pseumoniae.
ACKNOWLEDGMENT
Support for this study was provided by the Ministry for Education, Science and Technology of the Republic of
Kosovo. The author thanks Dr. Shuhreta Omeragiq from the Microbiological Laboratory of Regional Water Company, Pristina,
Republic of Kosovo, for antimicrobial testing of the compound prepared.
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