Synthesis, characterization and biological screening of some novel pyrazine associated 1,2,4-triazoles

Article abstract of DOI:10.14233/ajchem.2016.19860

A new and efficient method has been developed for the synthesis of some novel pyrazine associated 1,2,4-triazoles e.g., 2-methyl-5-(4-alkyl/aryl-5-methylsulfanyl-4H-[1,2,4]-triazol-3-yl)-pyrazine (5a-c). This novel method involves 5-methyl-2-pyrazinecarbo

Full text of DOI:10.14233/ajchem.2016.19860

Asian Journal of Chemistry; Vol. 28, No. 9 (2016), 1989-1991
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19860
Synthesis, Characterization and Biological Screening of
Some Novel Pyrazine Associated 1,2,4-Triazoles
1
2
1,*
3
PRASADA REDDY MEKA , PULLA RAO BOLLAM , RAVI CHANDRA BABU and SIVA RAMI REDDY
1
2
3
Department of Chemistry, Institute of Science, GITAM University, Visakhapatnam-530 045, India
Department of Chemistry, Acharya Nagarjuna University, Nagarjuna Nagar, Guntur-522 510, India
Maithili Life Sciences Private Limited, Plot No. 02, Gajulamandyam, APIIC, Tirupati- 517 520, India
*
Corresponding author: E-mail: prasadreddy.m83@gmail.com
Received: 27 January 2016; Accepted: 13 April 2016;
Published online: 1 June 2016;
AJC-17928
A new and efficient method has been developed for the synthesis of some novel pyrazine associated 1,2,4-triazoles e.g., 2-methyl-5-(4-
alkyl/aryl-5-methylsulfanyl-4H-[1,2,4]-triazol-3-yl)-pyrazine (5a-c). This novel method involves 5-methyl-2-pyrazinecarboxylic acid
(
1) as raw material and 5-methyl-2-pyrazinecarboxylic acid hydrazide (2), 5-methyl-2-pyrazinecarboxylic acid hydrazide N-alkyl/aryl
carbothioamide (3a-c) and 4-alkyl/aryl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-[1,2,4]-triazole-3-thione (4a-c) as intermediates in good
1
to excellent yields. The chemical structures of all these compounds are identified by IR, H NMR, mass spectroscopy and elemental
analysis. The antimicrobial activity of the target compounds has been also evaluated.
Keywords: Pyrazine, 1,2,4-Triazoles, Biological screening.
refluxed for 9 h on consistent stirring. After completion of the
reaction (monitored by the TLC), the reaction mixture is cooled
to room temperature, poured in ice-cold water (20 mL). Thus
the solid separated was filtered off and the crude product was
recrystallized from ethyl acetate to give pure 5-methyl-2-
pyrazinecarboxylic acid hydrazide (2).
INTRODUCTION
1
,2,4-Triazoles and their derivatives are important group
of heterocyclic compounds. The biological activity of 1,2,4-
triazoles have been demonstrated by various studies [1,2]. The
,2,4-triazole nucleus posses a wide range of pharmacological
activities such as analgesic [3], antibacterial [4], antifungal
5], anti-inflammatory [6] and antioxidant [7] properties.
Therefore, there is a continuing need for new antimicrobial
agents with more selectivity and lower side effect.
1
5
-Methyl-2-pyrazinecarboxylic acid hydrazide N-
[
alkyl/aryl carbothioamide (3a-c): A mixture of 5-methyl-2-
pyrazinecarboxylic acid hydrazide (2) (0.01 mol) and alkyl or
phenyl isocyanate in ethanol was refluxed on uniform stirring
for 4 h. After realization of the reaction (observed by the TLC),
the reaction mixture is cooled to ambient temperature, poured
in ice-cold water (20 mL) and the resulted solid was filtered
and the crude product was recrystallized from ethanol to offer
5-methyl-2-pyrazinecarboxylic acid hydrazide N-alkyl/aryl
carbothioamide (3a-c) in pure form.
4-Alkyl/aryl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-
[1,2,4]-triazole-3-thione (4a-c): A mixture of 5-methyl-2-
pyrazinecarboxylic acid hydrazide N-alkyl/aryl carbothio-
amides (3a-c) (0.01 mol) and 10 % sodium hydroxide (15
mL) in ethanol was heated at reflux temperature on constant
stirring for 3 h. After completion of the reaction (scanned by
the TLC), the reaction mixture is cooled to ambient temperature
and decanted in crushed ice (25 g). The resulted solution was
neutralized with conc. HCl and formed solid was isolated by
filtration, washed with ice-cold water, dried and recrystallized
EXPERIMENTAL
All reagents and solvents were used as purchased without
further purification. Melting points were determined on a
Fisher-Johns melting point apparatus and are uncorrected.
Crude products were purified by column chromatography on
silica gel of 60-120 mesh. IR spectra were obtained on a Perkin
Elmer BX series FT-IR 5000 spectrometer using KBr pellet.
1
H NMR spectra were recorded on a Varian 300 MHz spec-
trometer. The chemical shifts were reported as ppm down
field using TMS as an internal standard. Mass spectra were
recorded on a VG-Micromass 7070H spectrometer operating
at 70 eV.
-Methyl-2-pyrazinecarboxylic acid hydrazide (2): A
mixture of 5-methyl-2-pyrazinecarboxylic acid (1) (0.01 mol)
5
and hydrazine hydrate (0.025 mol) in ethanol (20 mL) was

1
990 Meka et al.
Asian J. Chem.
1
from ethanol to get 4-alkyl/aryl-5-(5-methyl-pyrazin-2-yl)-2,4-
(C=S); H NMR (300 MHz, DMSO-d
6
): δ 7.79 (s, 1H, Ar-H),
dihydro-[1,2,4]-triazole-3-thione (4a-c) in pure form.
7.29 (s, 1H, Ar-H), 7.46 (s, 1H, NH), 3.22 (s, 3H, CH
3
), 2.57
); MS: m/z 207 (M ); Elemental analysis: Calcd.
S: C 46.36, H 4.38, N 33.79, S 15.47. Found: C
+
2-Methyl-5-(4-alkyl/aryl-5-methylsulfanyl-4H-[1,2,4]-
(s, 3H, CH
for C
3
triazol-3-yl)-pyrazine (5a-c): A solution of iodomethane (0.01
8
H N
9 5
mol) and methanol (5 mL) is gradually added to a mixture of
46.08, H 4.36, N 33.12, S 15.25.
4
-alkyl/phenyl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-[1,2,4]-
triazole-3-thiones (4a-c) (0.01 mol) and sodium hydroxide
10 %, 10 mL) in methanol (10 mL) on steady stirring. The
4-Ethyl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-[1,2,4]-
triazole-3-thione (4b): Colour: Pale yellow;Yield: 77 %; m.p.:
-1
(
155-157 °C; IR (KBr, νmax, cm ): 3262 (N-H), 3028 (C-H,
Ar), 2975 (C-H, CH ), 1548 (C=C, Ar), 1434 (C=N), 1227
(C=S); H NMR (300 MHz, DMSO-d ): δ 7.72 (s, 1H, Ar-H),
7.36 (s, 1H, Ar-H), 7.49 (s, 1H, NH), 3.36 (q, 2H, J = 5.2 Hz,
CH ), 3.21 (s, 3H, CH ), 2.48 (t, 3H, J = 5.2 Hz, CH ); MS:
m/z 221 (M ); Elemental analysis: Calcd. for C S: C
48.85, H 5.01, N 31.65, S 14.49. Found: C 47.98, H 4.99, N
1.12, S 14.35.
-Phenyl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-
1,2,4]-triazole-3-thione (4c): Colour: Yellow; Yield: 76 %;
overall mixture refluxed for 3 h. After completion of the reac-
tion (examined by the TLC), the reaction mixture is cooled
and neutralized with conc. HCl and extracted with chloroform
3
1
6
and resulted solid was dried CaCl
2
to obtain pure 2-methyl-5-
2
3
3
+
(
4-alkyl/aryl-5-methylsulfanyl-4H-[1,2,4]-triazol-3-yl)-
9
H
11
N
5
pyrazine (5a-c).
3
Spectral data
4
5
-Methyl-2-pyrazinecarboxylic acid hydrazide (2):
[
Colour: White;Yield: 73 %; m.p.: 156-158 °C; IR (KBr, νmax
cm ): 3255 (N-H), 3020 (C-H, Ar), 2966 (C-H, CH
,
-1
m.p.: 123-125 °C; IR (KBr, νmax, cm ): 3255 (N-H), 3018 (C-H,
Ar), 2981 (C-H, CH ), 1559 (C=C, Ar), 1448 (C=N), 1225
C=S); H NMR (300 MHz, DMSO-d ): δ 7.55-7.25 (m, 5H,
Ar-H), 7.52 (s, 1H,Ar-H), 7.41 (s, 1H, NH), 7.45 (s, 1H,Ar-H),
-1
3
), 1670
3
1
(
C=O), 1572 (C=C, Ar), 1445 (C=N); H NMR (300 MHz,
DMSO-d ): δ 9.74 (s, 1H, NH), 7.77 (s, 1H, Ar-H), 7.36 (s,
H, Ar-H), 4.45 (s, 2H, NH ), 2.50 (s, 3H, CH ); MS: m/z 152
M ); Elemental analysis: Calcd. for C O: C 47.36, H
.30, N 36.82. Found: C 47.02, H 5.24, N 36.08.
-Methyl-2-pyrazinecarboxylic acid hydrazide N-
methyl carbothioamide (3a): Colour: Yellow; Yield: 75 %;
1
(
6
6
1
(
5
2
3
+
2
.58 (s, 3H, CH
Calcd. for C13
Found: C 57.36, H 4.08, N 25.87, S 11.58.
-Methyl-5-(4-methyl-5-methylsulfanyl-4H-[1,2,4]-
triazol-3-yl)-pyrazine (5a): Colour: White;Yield: 72 %; m.p.:
3
); MS: m/z 269 (M ); Elemental analysis:
+
6
H N
8 4
H
11
N
5
S: C 57.97, H 4.12, N 26.00, S 11.91.
5
2
-1
m.p.: 141-143 °C; IR (KBr, νmax, cm ): 3270 (N-H), 3030 (C-H,
Ar), 2966 (C-H, CH
-1
1
2
70-172°C; IR (KBr, νmax, cm ): 3262 (N-H), 3032 (C-H,Ar),
958 (C-H, CH ), 1562 (C=C, Ar), 1428 (C=N), 615 (C-S);
): δ 7.58 (s, 1H, Ar-H), 7.32 (s,
), 3.15 (s, 3H, S-CH ), 2.62 (s,
); MS: m/z 221 (M ); Elemental analysis: Calcd. for
S: C 48.85, H 5.01, N 31.65, S 14.49. Found: C 48.41,
H 4.99, N 31.36, S 14.40.
-Methyl-5-(4-ethyl-5-methylsulfanyl-4H-[1,2,4]-
3
1
), 1684 (C=O), 1577 (C=C, Ar), 1432
): δ 9.74
3
(
(
(
C=N), 1210 (C=S); H NMR (300 MHz, DMSO-d
6
1
H NMR (300 MHz, DMSO-d
6
s, 1H, CONH), 7.72 (s, 1H, Ar-H), 7.43 (s, 1H, CSNH), 7.36
s, 1H, Ar-H), 4.85 (s, 1H, NH-CH ), 3.28 (s, 3H, N-CH ),
); MS: m/z 225 (M ); Elemental analysis:
OS: C 42.65, H 4.92, N 31.09, S 14.23.
Found: C 42.14, H 4.88, N 30.87, S 14.12.
-Methyl-2-pyrazinecarboxylic acid hydrazide N-ethyl
carbothioamide (3b): Colour: Pale yellow;Yield: 70 %; m.p.:
1H, Ar-H), 3.23 (s, 3H, N-CH
3
3
3
3
+
3H, CH
3
+
2
.62 (s, 3H, CH
3
C
9
H
11
N
5
Calcd. for C
H
8 11
N
5
2
5
triazol-3-yl)-pyrazine (5b): Colour: Pale yellow;Yield: 74 %;
-1
m.p.: 153-155 °C; IR (KBr, νmax, cm ): 3020 (C-H, Ar), 2966
-1
1
38-140 °C; IR (KBr, νmax, cm ): 3278 (N-H), 3044 (C-H,
1
(
C-H, CH
3
), 1572 (C=C,Ar),1448 (C=N), 621 (C-S); H NMR
Ar), 2984 (C-H, CH
3
1
), 1670 (C=O), 1574 (C=C, Ar), 1428
): δ 9.74
(
3
3
300 MHz, DMSO-d
6
): δ 7.65 (s, 1H,Ar-H), 7.28 (s, 1H,Ar-H),
.28 (q, 2H, J = 5.6 Hz, CH ), 3.18 (s, 3H, S-CH ), 2.52 (t,
H, J = 5.6 Hz, CH ), 2.39 (s, 3H, CH
(
(
(
C=N), 1220 (C=S); H NMR (300 MHz, DMSO-d
6
2
3
s, 1H, CONH), 7.68 (s, 1H, Ar-H), 7.52 (s, 1H, CSNH), 7.29
s, 1H, Ar-H), 4.79 (s, 1H, NH-CH ), 3.30 (q, 2H, J = 5.4 Hz,
), 3.22 (t, 3H, J = 5.4 Hz, CH ), 2.58 (s, 3H, CH ); MS: m/z
39 (M ); Elemental analysis: Calcd. for C OS: C 45.17,
H 5.48, N 29.27, S 13.40. Found: C 44.87, H 5.43, N 29.11, S
3.28.
-Methyl-2-pyrazinecarboxylic acid hydrazide N-
phenyl carbothioamide (3c): Colour: Yellow; Yield: 71 %;
+
3
3
); MS: m/z 235 (M );
3
Elemental analysis: Calcd. for C10
H
13
5
N S: C 51.04, H 5.57, N
CH
2
2
3
3
2
9.67, S 13.67. Found: C 50.68, H 5.49, N 29.38, S 13.42.
-Methyl-5-(4-phenyl-5-methylsulfanyl-4H-[1,2,4]-
triazol-3-yl)-pyrazine (5c): Colour:Yellow;Yield: 70 %; m.p.:
+
H
9 13
N
5
2
1
-1
1
49-151 °C; IR (KBr, νmax, cm ): 3035 (C-H, Ar), 2959 (C-H,
5
1
CH
MHz, DMSO-d
.45 (s, 1H, Ar-H), 3.42 (s, 3H, S-CH
3
), 1584 (C=C, Ar),1429 (C=N), 628 (C-S); H NMR (300
): δ 7.85-7.42 (m, 5H,Ar-H), 7.69 (s, 1H,Ar-H),
), 2.85 (s, 3H, CH );
MS: m/z 283 (M ); Elemental analysis: Calcd. for C14 S:
C 59.34, H 4.62, N 24.72, S 11.32. Found: C 58.99, H 4.55, N
4.58, S 11.28.
6
-1
m.p.: 130.132 °C; IR (KBr, νmax, cm ): 3284 (N-H), 3040 (C-H,
Ar), 2977 (C-H, CH
7
3
3
3
1
), 1658 (C=O), 1560 (C=C, Ar), 1444
): δ 8.89
+
H
13
N
5
(
C=N), 1224 (C=S); H NMR (300 MHz, DMSO-d
6
(
s, 1H, CONH), 7.58-7.21 (m, 5H, Ar-H), 7.52 (s, 1H, Ar-H),
2
7
2
.49 (s, 1H,Ar-H), 7.34 (s, 1H, CSNH), 4.88 (s, 1H, NH-CH
3
),
); MS: m/z 287 (M ); Elemental analysis:
OS: C 54.34, H 4.56, N 24.37, S 11.16.
Found: C 53.98, H 4.52, N 24.12, S 11.04.
-Methyl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-
1,2,4]-triazole-3-thione (4a): Colour: White; Yield: 74 %;
+
.50 (s, 3H, CH
3
RESULTS AND DISCUSSION
The synthetic path of the target compounds, 2-methyl-5-
Calcd. for C13
H
13
N
5
(
4-alkyl/aryl-5-methylsulfanyl-4H-[1,2,4]-triazol-3-yl)-
4
pyrazine (5a-c) is involved 5-methyl-2-pyrazinecarboxylic
acid (1), 5-methyl-2-pyrazinecarboxylic acid hydrazide (2),
[
-1
m.p.: 162-164 °C; IR (KBr, νmax, cm ): 3274 (N-H), 3034 (C-H,
Ar), 2968 (C-H, CH ), 1555 (C=C, Ar), 1440 (C=N), 1230
5
-methyl-2-pyrazinecarboxylic acid hydrazide N-alkyl/aryl
3

Vol. 28, No. 9 (2016)
Compound
Synthesis and Biological Screening of Some Novel Pyrazine Associated 1,2,4-Triazoles 1991
TABLE-1
ANTIMICROBIAL ACTIVITY OF COMPOUNDS 4a-c AND 5a-c (ZONES OF INHIBITION IN mm)
Antibacterial activity
Antifungal activity
S. aureus
13.0
16.6
13.8
17.3
16.4
11.6
18.0
–
S. pyogenes
P. aureginosa
10.5
E. coli
15.6
14.8
15.1
13.6
15.2
12.3
16.0
–
C. albicans
10.4
16.9
13.2
12.5
17.4
13.4
–
4a
11.4
13.8
13.6
12.6
12.8
11.9
14.0
–
4b
12.9
11.2
12.8
13.1
12.6
14.0
–
4c
5a
5b
5c
Ampicilline
Fuoconazole
18.0
carbothioamide (3a-c) and 4-alkyl/aryl-5-(5-methyl-pyrazin-
-yl)-2,4-dihydro-[1,2,4]-triazole-3-thione (4a-c) as inter-
mediates (Scheme-I). Thus the initial intermediate, 5-methyl-
-pyrazinecarboxylic acid hydrazide (2) has been prepared
from 5-methyl-2-pyrazinecarboxylic acid (1) on reaction with
hydrazine hydrate in refluxing ethanol on constant stirring for
dihydro-[1,2,4]-triazole-3-thione (4a-c) and 2-methyl-5-(4-
alkyl/aryl-5-methylsulfanyl-4H-[1,2,4]-triazol-3-yl)-pyrazine
(5a-c) has been carried out with cup plate method [8] using
nutrient agar medium against four bacterial strains such as
Stapylococcus aureus, Streptococcus pyogenes, Escherichia
coli and Pseudomonas aureginosa and towards one fungal
organism like Candida albicans.Ampicilline and fluoconazole
were used as reference drugs for antibacterial and antifungal
study respectively. DMSO was used as sample solution and
the size of sample of all compounds was fixed at 0.1 mL and
the concentration is restricted at 100 µg/mL. The test compound
solution (0.1 mL) was added in the cups and the petri dishes
were subsequently incubated at 37 °C for 48 h. Zone of inhi-
bition produced by each compound was measured in mm and
the results are listed in Table-1. According to the results, com-
pounds 4b, 5a and 5b are highly active against all types of
tested bacteria. Compounds like 4a and 5b are also highly
active against C. albicans. Compounds 4a and 4c are highly
active against S. pyogenes and E. coli while compound 5c is
highly active against S. pyogenes and P. aeruginosa. The rest
of products were found to be moderately active against the
tested organisms. It is interesting to note that, none of the
compound is inactive towards any microorganism and this
outstanding property may be obtained to the target compound
by incorporating pyrazine rings into 1,2,4-triazole moiety.
2
2
9
5
h. Then compound 2 was turned into the next intermediate,
-methyl-2-pyrazinecarboxylic acid hydrazide N-alkyl/aryl
carbothioamide (3a-c) on reaction with isocyante in refluxing
ethanol under uniform stirring for 4 h. Further the final inter-
mediate, 4-alkyl/aryl-5-(5-methyl-pyrazin-2-yl)-2,4-dihydro-
[
1,2,4]-triazole-3-thione (4a-c) was obtained in better yield
when the cyclization reaction performed between compound
and sodium hydroxide solution on steady stirring for 3 h.
3
Finally the target compounds, 2-methyl-5-(4-alkyl/aryl-5-
methylsulfanyl-4H-[1,2,4]-triazol-3-yl)-pyrazine (5a-c) have
been achieved in good to excellent yields from the reaction
occurred between compound 4 with methyl iodide and sodium
hydroxide solution on steady stirring for 3 h. The chemical
structures of all the intermediates and products are readily
1
identified from their IR, H NMR, mass spectroscopy and
elemental analysis. Eventually, the target compounds were
evaluated for their antimicrobial activity.
S
N
N
N
NH2
NH
HN
NH
NH
R
(
i)
(ii)
REFERENCES
OH
N
N
N
1
O
2
O
3a-c
1. Y.A. Al-Soud, H.A. Mohammed and A. Abo-Amer, Jordan J. Chem.,
O
5, 119 (2010).
(
iii)
2. R. Agrawal and S.S. Pancholi, Der Pharma Chemica, 3, 32 (2011).
3
4
.
.
A. Cansiz, S. Servi, M. Koparir, M. Altintas and M. Digrak, J. Chem.
Soc. Pak., 23, 237 (2001).
S. Jantova, G. Greif, R. Pavlovicova and L. Cipak, Folia Microbiol.
N
N
R
N
R
N
(
iv)
S
S
N
a-c
N
4a-c
(Praha), 43, 75 (1998).
5
N
N
N
NH
5. B. Andrews and M. Ahmed, Inter. J. Chem. Technol. Res., 6, 1013
(2014).
6. Z. Rezaei, S. Khabnadideh, K. Pakshir, Z. Hossaini, F. Amiri and E.
Assadpour, Eur. J. Med. Chem., 44, 3064 (2009).
Scheme-I: (i) NH
h; (iii) NaOH, reflux, 3 h; (iv) CH
R a) = CH , b) = CH CH c) = C
2
NH
2
.H
2
O, EtOH, reflux, 9 h; (ii) RNCS, EtOH, reflux,
4
3
I, NaOH, reflux, 3h. 3-5
3
2
3
6 5
H
7
.
V. Mathew, D. Giles, J. Keshavayya and V. Vaidya, Arch Pharm., 342,
10 (2009).
2
Antimicrobial activity: The antimicrobial activity of the
newly prepared 4-alkyl/aryl-5-(5-methyl-pyrazin-2-yl)-2,4-
8
.
A.R. Sandane, K. Rudresh, N.D. Satyanarayan and S.P. Hiremath, Indian
J. Pharm. Sci., 60, 379 (1998).