Studies on pyrazine derivatives LII: Antibacterial and antifungal activity of nitrogen heterocyclic compounds obtained by pyrazinamidrazone usage

Article abstract of DOI:10.1002/hc.20751

Using reactivity of pyrazinamidrazones and their N′-substituted derivatives 1-8 in reaction with sulfonyl chlorides sulfone derivatives 9-17 were obtained, with orthoformate cyclized to sulfonyl compounds 18-20. Amidrazones in reaction with pyraziniminoesters gave dihydrazidines 21-23, which cyclized to 3,5-dipyrazine derivatives of 1,2,4-triazole 24-26. 1-Methyl- or 1-phenyl-3-pyrazine-1,2,4-triazole 27-38 was formed in reaction of amidrazones 1-8 with orthoformate and orthoacetate or benzoyl chloride. N′- Phenylamidrazones 3, 8 in reaction with thionyl chloride were transformed to 1,2,3,5-thiatriazole S-oxides 39, 40. Obtained compounds exhibited low antibacterial activity. Antifungal activity was affirmed for compounds 1,3,4,5,8,37,39, and 40, for which minimal inhibitory concentration (MIC) was in the concentration range of 16-128 μg/mL.

Full text of DOI:10.1002/hc.20751

Heteroatom Chemistry
Volume 23, Number 1, 2012
Studies on Pyrazine Derivatives LII:
Antibacterial and Antifungal Activity of
Nitrogen Heterocyclic Compounds Obtained
by Pyrazinamidrazone Usage
Henryk Foks,1 Lukasz Balewski,1 Katarzyna Gobis,1
Maria Dabrowska-Szponar,2 and Katarzyna Wisniewska2
1Department of Organic Chemistry, Medical University of Gdansk, 80-438 Gdansk, Poland
2Department of Medicinal Microbiology, Medical University of Gdansk, 80-438 Gdansk, Poland
Received 11 February 2011; revised 8 June 2011
INTRODUCTION
ABSTRACT: Using reactivity of pyrazinamidrazones
and their Nꢀ-substituted derivatives 1–8 in reaction
Pyrazine derivatives possess a wide range of bio-
with sulfonyl chlorides sulfone derivatives 9–17 were
obtained, with orthoformate cyclized to sulfonyl com-
pounds 18–20. Amidrazones in reaction with pyrazin-
iminoesters gave dihydrazidines 21–23, which cy-
clized to 3,5-dipyrazine derivatives of 1,2,4-triazole
24–26. 1-Methyl- or 1-phenyl-3-pyrazine-1,2,4-triazole
27–38 was formed in reaction of amidrazones 1–
8 with orthoformate and orthoacetate or benzoyl
chloride. Nꢀ-Phenylamidrazones 3, 8 in reaction
with thionyl chloride were transformed to 1,2,3,5-
thiatriazole S-oxides 39, 40. Obtained compounds
exhibited low antibacterial activity. Antifungal activ-
ity was affirmed for compounds 1, 3, 4, 5, 8, 37,
39, and 40, for which minimal inhibitory concentra-
tion (MIC) was in the concentration range of 16–128
logical activities. They are found in a variety of
naturally occurring compounds such as aspergillic
acid, hydroxyaspergillic acid, and other antibiotics
of similar structure, which possess antibacterial
activities [1–6]. Emimycin (3-hydroxypyrazine N-
oxide) has also antibacterial properties [7]. Synthetic
pyrazine derivatives exhibit a wide variety of phar-
macological properties, including hypoglycemic [8–
10] and diuretic [11,12] action. Sulfonamides with
pyrazine moiety are known to have high antibacte-
rial activity [13]. Pyrazinamide and its morpholino–
methylene derivative act as tuberculostatic agents
[14,15]. Nicotinic and isonicotinic amidrazones are
also reported in the literature as antibacterial agents
[16–18]. They also act as diuretic [19], antimycotic
[20], and circulatory system agents [21]. The ther-
apeutic potential activity of amidrazone derivatives
with pyrazine moiety can be developed as potential
antibacterial drugs.
ꢁ
C
μg/mL. 2011 Wiley Periodicals, Inc. Heteroatom Chem
23:49–58, 2012; View this article online at wileyonlineli-
brary.com. DOI 10.1002/hc.20751
CHEMISTRY
Pyrazinamidrazones for further reactions were ob-
tained by direct addition of respective hydrazines
to pyrazinenitriles or by reaction of pyrazinenitriles
Correspondence to: Katarzyna Gobis; e-mail: kgobis@amg
.gda.pl.
2011 Wiley Periodicals, Inc.
c
ꢀ
49

50 Foks et al.
noester, giving corresponding amidrazones. Then
hydrazine has acted with the remaining iminoester
in the presence of acid (PhSO3H), resulting in sym-
metric dihydrazidine 21 and 22 with facility. In these
conditions, p-toluenesulfonylhydrazide has behaved
similarly (Scheme 3).
Such a mechanism confirms obtaining dihy-
drazidines 21 and 23 in a reaction of iminoesters
with amidrazones in the presence of acetic acid. It
shows a capacity of synthesis of asymmetric dihy-
drazidines, using for reaction different amidrazones
and iminoesters (Scheme 4).
Dihydrazidines 21–23 have easily cyclized to ap-
propriate disubstituted 1,2,4-triazoles 24–26, giving
off ammonia. Cyclization has been carried out by
heating in diglyme or glacial acetic acid.
SCHEME 1
1
The H NMR spectrum of compound 25 shows
the splitting of signal at 15.29–15.41 ppm at-
tributable to the proton of the NH group of the tria-
zole ring. It indicates the existence of two structures
(Scheme 5). Lack of molecular symmetry causes
the formation of two energetic unequal hydrogen
bonds between the proton of the triazole NH group
with appropriate pyraziniminoesters (Scheme 1) ac-
cording to the methods described previously [22,23].
Some of the amidrazones were converted
into methane, benzenesulfone, and p-toluenesulfone
derivatives. Compounds 9, 12, and 13 were con-
verted into cyclic derivatives of benzene- and p-
toluene-1,2,4-triazole 18–20, by means of triethyl or-
thoformate (Scheme 2).
1
and nitrogen atoms of the pyrazine ring. H NMR
spectrum exhibits that hydrogen bond is more sta-
ble with nitrogen of substituted pyrazine with the
methoxy group (structure A). It allows the rotation
of another pyrazine ring about the single bound
with triazole ring. Addition of D2O causes disap-
pearance of the NH group proton signal and sharp-
ens proton bands of unsubstituted pyrazine. The
effect described above is not observed for symmetric
molecules of compounds 24 and 26, for which NMR
spectra show characteristic singlets of the triazole
ring.
At attempt of getting benzenesulfonylamidra-
zones 9 and 11 in reaction of pyraziniminoesters
with benzenesulfonylhydrazide in water–methanol
solution, unexpectedly dihydrazidines were re-
ceived, their structures were confirmed by means
1
of spectroscopic methods: IR, H NMR, and MS. It
can be explained on the basis of enhanced sensi-
tivity in the water environment, which has caused
decomposition to hydrazine and benzenesulfonic
acid. Free hydrazine has reacted with dissolved imi-
SCHEME 2
Heteroatom Chemistry DOI 10.1002/hc

Studies on Pyrazine Derivatives LII 51
SCHEME 5
Reaction yields, physical constants, and spectral
data of newly synthesized compounds are given in
Tables 1 and 2.
SCHEME 3
MICROBIOLOGY
All of obtained pyrazinamidrazone derivatives 1–
41 were evaluated for their in vitro antimicrobial
activity against Staphylococcus aureus, Escherichia
coli, Pseudomonas aeruginosae, and Candida albi-
cans strains (Table 3). Gramicidin was used as a ref-
erence drug in an antibacterial test. Unfortunately,
all tested compounds showed poor or no antibacte-
rial activity as the minimal inhibitory concentration
(MIC) obtained for the strains ranged from 128 to
256 μg/mL. Three of 41 derivatives (3, 5, and 12)
exhibited low activity against S. aureus (MIC 128
μg/mL) and both compounds 2 and 3 were active
toward P. aeruginosae in concentrations of 128 μ
and 256 μg/mL. The remaining agents showed no
antibacterial activity within the limits of used con-
centrations. MIC values determined for all of tested
compounds were much higher than for reference
gramicidin.
Nꢀ-Methyl and Nꢀ-phenyl substituted amidra-
zones were converted into corresponding di- and
tri-substituted derivatives (27–38) in reaction with
triethyl orthoformate, triethyl acetate, and benzoyl
chloride (Scheme 6).
Nꢀ-Phenyl substituted amidrazones 3 and 8 in
reaction with thionyl chloride in chloroform and an-
hydrous pyridine below 5◦C afforded 2,5-dihydro-
1,2,3,5-thiatriazole S-oxides 39 and 40 with very low
yield (Scheme 7). Analogous synthesis for Nꢀ-methyl
substituted amidrazones was carried out without
success.
Nꢀ-Substituted amidrazones could be a start-
ing material for synthesis of 1,2,4-triazoles with
methyl in ring position 1 and cycloamine in
position 4. It could be confirmed by reaction
of Nꢀ-methylpyrazinamidrazone with S-methylester
of 4-morpholinodithiocarbaminic acid. The anal-
ogous product 41 has been obtained from Nꢀ-
methylpyrazinehydrazide in aqueous solution of
potassium carbonate with a good yield (Scheme 8).
Eight (20%) derivatives (1, 3, 4, 5, 8, 37, 39, 40)
inhibited growth of the clinical strain of C. albicans
in a concentration 16–128 μg/mL exhibiting antifun-
gal activity. The most active derivatives were 3 and
SCHEME 4
Heteroatom Chemistry DOI 10.1002/hc

52 Foks et al.
TABLE 1 Characteristics of Compounds 2, 7–41
Calcd/Found
H
No.
Mp[◦C] Solvent
Molecular Formula MW
Yield [%]
C
N
2
7
8
9
108–109 EtOH
134–135 MeOH
149–150 MeOH
191–192 MeOH
157–158 MeOH
198–199 EtOH
184–185 EtOH
179–180 MeOH
167–168 EtOH
208–209 EtOH
180–181 MeOH
206–207 MeOH
171–172 MeOH
C6H9N5 151.17
C7H11N5O 181.20
C12H13N5O 243.26
38
58
30
35
60
78
20
44
45
28
16
48
79
59
73
24
28
64
58
98
98
88
95
72
54
56
80
96
77
73
39
28
58
68
72
40
47.67
46.40
59.25
47.64
49.47
48.59
42.38
49.47
48.59
50.14
36.67
37.06
50.17
44.80
50.75
49.58
47.68
48.53
53.33
51.76
50.53
52.17
50.26
64.56
61.65
55.93
54.85
52.67
65.81
62.91
57.47
72.23
69.29
50.95
49.82
47.47
47.56
46.28
59.32
47.62
49.53
48.56
42.32
49.51
48.63
50.17
36.71
37.12
50.21
44.83
50.78
49.56
47.71
48.50
53.29
51.78
50.47
52.21
50.29
64.63
61.62
56.05
54.88
52.71
65.87
62.95
57.43
72.41
69.35
50.97
49.71
47.52
6.00
6.12
5.39
4.00
4.50
4.70
3.23
4.50
4.70
5.11
4.84
5.05
3.16
2.51
3.95
4.16
4.67
4.44
3.13
3.55
3.89
4.38
4.74
4.06
4.38
3.13
5.18
5.40
4.67
4.90
3.71
4.38
4.59
3.50
3.83
5.07
5.99
6.10
5.38
4.01
4.52
4.71
3.23
4.49
4.71
5.12
4.83
5.04
3.16
2.51
3.96
4.17
4.68
4.45
3.13
3.55
3.89
4.39
4.75
4.06
4.39
3.13
5.19
5.41
4.66
4.89
3.71
4.38
4.59
3.50
3.83
5.08
46.33
38.65
28.79
25.26
24.04
21.27
22.46
24.04
21.79
20.88
30.55
27.01
24.38
21.77
21.14
46.26
37.07
41.16
43.54
38.41
34.37
43.45
36.63
31.37
27.65
27.18
39.98
34.13
29.53
26.20
25.78
23.40
21.26
27.01
24.21
30.19
46.28
38.68
28.75
25.28
23.97
21.22
22.48
24.07
21.81
20.90
30.57
27.03
24.41
21.78
21.18
46.31
37.04
41.13
43.51
38.45
34.41
43.47
36.68
31.35
27.67
27.15
39.92
34.14
29.51
26.24
25.73
23.42
21.24
27.05
24.23
30.18
C11H11N5O2S 277.30
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
C12H13N5O2S 291.33
C13H15N5O3S 321.35
C11H10ClN5O2S 311.75
C12H13N5O2S 291.33
C13H15N5O3S 321.35
C14H17N5O3S 335.38
C7H11N5O2S 229.26
C8H13N5O3S 259.29
C12H9N5O2S 287.30
C12H8ClN5O2S 321.74
C14H13N5O3S 331.35
155–157 (dec.) MeOH
159–160 MeOH
251–255 (dec.) DMF
252–258 (dec.) DMF
195–198 (dec.) Dioxan
274–276 (dec.) EtOH
209–210 MeOH
265–268 (dec.) EtOH
174–175 MeOH
133–134 EtOH
139–140 H2O
146–147 MeOH/H2O (1:1)
163–164 MeOH
C
10H10N8 242.24
C12H14N8O2 302.29
11H12N8O 272.27
C
C10H7N7 225.21
C11H N7O 255.24
C
12H119N7O 285.26
2
C7H7N5 161.16
C8H9N5O 191.19
C12H9N5 223.23
C13H11N5O 253.26
C12H8ClN5 257.68
C8H9N5 175.19
C9H11N5O 205.22
C13H11N5 237.26
C14H13N5O 267.28
173–174 MeOH
82–84 EtOH
125–126 H2O
144–145 MeOH/H2O (1:1)
142–144 (dec.) MeOH
177–178 MeOH
190–191 MeOH
204–205 (dec.) MeOH
179–180 MeOH
C13H10ClN5 271.70
C18H13N5 299.33
C19H15N5O 329.36
C11H9N5OS 259.29
C12H11N5O2S 289.31
221–222 EtOH
C11H14N6OS 278.33
SCHEME 6
Heteroatom Chemistry DOI 10.1002/hc

Studies on Pyrazine Derivatives LII 53
TABLE 2 IR and 1H NMR Spectra Data of Newly Synthesized Compounds
No.
2
IR [cm−1
]
1H NMR δ[ppm] (200 MHz, *500 MHz)
3392, 3314, 3092, 2868, 1651, 1521, 1423, 1365, 1134,
1016, 846, 768
CDCl3: 3.01 (s, 3H, CH3); 4.16 (s, 1H, NH); 5.03 (s, 2H,
NH2); 8.48 (d, J = 2.6 Hz, 1H, CH); 8.40 (d, J = 2.6
Hz, 1H, CH); 8.42 (d, J = 1.5 Hz, 1H, CH); 9.32 (d, J =
1.5 Hz, 1H, CH)
7
8
3203, 2950, 1634, 1534, 1411, 1369, 1301, 1208, 1030,
1009, 879, 797
CDCl3: 2.97 (s, 3H, CH3); 3.96 (s, 3H, OCH3); 4.07 (s,
1H, NH); 4.99 (s, 2H, NH2); 8.14 (s, 1H, CH); 8.84 (s,
1H, CH)
CDCl3: 4.02 (s, 3H, OCH3); 5.07 (s, 2H, NH2); 6.58 (s,
1H, NH); 6.91–7.34 (m, 5H, Ph); 8.20 (s, 1H, CH); 9.05
(s, 1H, CH)
3314, 3194, 1640, 1607, 1512, 1451, 1407, 1297, 1203,
1019, 867, 749, 690
9
3352, 3206, 1657, 1333, 1160, 1092, 1020, 727
DMSO-d6: 6.56 (s, 2H, NH2); 7.62–7.93 (m, 5H, Ph);
8.60–9.02 (m, 3H, CH); 9.76 (s, 1H, NH)
CDCl3: 2.86 (s, 3H, CH3); 6.59 (s, 2H, NH2); 7.55–7.95
(m, 5H, Ph); 8.56 (s, 1H, CH); 8.70 (s, 1H, CH); 9.39
(s, 1H, CH)
10
3295, 3254, 3191, 1648, 1575, 1446, 1339, 1162, 1018,
776, 683
11
3315, 1647, 1578, 1449, 1377, 1336, 1311, 1164, 824,
730
CDCl3: 2.84 (s, 3H, CH3); 4.02 (s, 3H, OCH3); 6.52 (s,
2H, NH2); 7.72-7.92 (m, 5H, Ph); 8.35 (s, 1H, CH);
8.92 (s, 1H, CH)
12
13
3329, 3202, 1645, 1451, 1331, 1165, 1091, 1010, 868,
734
3333, 3051, 2812, 1661, 1330, 1160, 815, 692
DMSO-d6: 6.54 (s, 2H, NH2); 7.63–7.92 (m, 5H, Ph);
8.80 (s, 1H, CH); 8.96 (s, 1H, CH); 9.86 (s, 1H, NH)
DMSO-d6: 2.35 (s, 3H, CH3); 6.53 (s, 2H, NH2);
7.40–7.80 (m, 4H, Ph); 8.63 (d, J = 9.7 Hz, 2H, CH);
9.03 (s, 1H, CH); 9.69 (s, 1H, NH)
14
15
3382, 3066, 2949, 1641, 1584, 1538, 1413, 1378, 1301,
1209, 1162, 1087, 1008, 813, 735
CDCl3: 2.48 (s, 3H, CH3); 4.03 (s, 3H, OCH3); 6.21 (s,
2H, NH2); 7.32-7.90 (m, 4H, Ph); 8.30 (s, 1H, CH);
8.79 (s, 1H, CH)
CDCl3: 2.47 (s, 3H, CH3); 2.82 (s, 3H, CH3); 4.02 (s, 3H,
OCH3); 6.46 (s, 2H, NH2); 7.38 (d, J = 8.2 Hz, 2H,
Ph); 7.78 (d, J = 8.2 Hz, 2H, Ph); 8.34 (s, 1H, CH);
8.90 (s, 1H, CH)
3310, 1640, 1577, 1543, 1447, 1377, 1333, 1210, 1159,
813, 720, 664
16
17
3298, 3252, 3024, 2973, 1641, 1586, 1326, 1143, 791
3347, 3244, 3181, 1642, 1335, 1154, 1008, 823, 757
CDCl3: 3.03 (s, 3H, CH3); 3.05 (s, 3H, CH3); 6.62 (s, 2H,
NH2); 8.57–9.53 (m, 3H, CH)
CDCl3: = 2.99 (s, 3H, CH3); 3.02 (s, 3H, CH3); 4.01 (s,
3H, OCH3); 6.40 (s, 2H, NH2); 8.35 (s, 1H, CH); 9.02
(s, 1H, CH)
18
3064, 1489, 1395, 1222, 1118, 763, 729
CDCl3: 7.59–8.19 (m, 5H, Ph); 8.65 (d, J = 2.5 Hz, 1H,
CH); 8.71 (d, J = 2.5 Hz, 1H, CH); 8.88 (s, 1H, CH);
9.38 (s, 1H, CH)
19
20
3127, 3064, 1391, 1188, 1172, 1112, 1008, 731
3065, 1593, 1510, 1439, 12227, 1196, 1178, 701
CDCl3: 7.70–8.17 (m, 5H, Ph); 8.66 (s, 1H, CH); 8.90 (s,
1H, CH); 9.27 (s, 1H, CH)
CDCl3: 2.45 (s, 3H, CH3); 7.40–8.03 (m, 4H, Ph); 8.64 (s,
1H, CH); 8.69 (s, 1H, CH); 8.80 (s, 1H, CH); 9.37 (s,
1H, CH)
21
22
3308, 1607, 1572, 1516, 1470, 1429, 1156, 1019, 862
3338, 1615, 1534, 1429, 1299, 1205, 1007, 876
DMSO-d6: 6.90 (s, 4H, NH2); 7.94–8.67 (m, 8H, CH)
DMSO-d6: 4.05 (s, 6H, OCH3); 6.80 (s, 4H, NH2); 8.34
(s, 2H, CH); 9.27 (s, 2H, CH)
23
24
25
26
27
28
3306, 2854, 1611, 1538, 1426, 1304, 1209, 1116, 1018,
871
DMSO-d6: 4.04 (s, 3H, OCH3); 6.82 (s, 4H, NH2);
8.32–9.74 (m, 5H, CH)
3059, 2916, 2807, 1524, 1378, 1141, 1018, 984, 861, 762 DMSO-d6:∗ 8.80 (d, J = 12.6 Hz, 4H, CH); 9.38 (s, 2H,
CH); 15.48 (s, 1H, NH)
3069, 3037, 2956, 1539, 1469, 1430, 1370, 1319, 1277,
1167, 1039, 1002, 894, 858, 764
3037, 3004, 2954, 1540, 1471, 1368, 1045, 1005, 901,
878, 766
DMSO-d6:∗ 4.08 (s, 3H, OCH3); 8.45-9.34 (m, 5H, CH);
15.29 (s, 1H, NH)
DMSO-d6:∗ 4.06 (s, 6H, OCH3); 8.44 (s, 2H, CH); 8.92 (s,
2H, CH); 15.19 (s, 1H, NH)
3091, 1495, 1390, 1334, 1223, 1157, 1017, 858, 761
CDCl3∗: 4.06 (s, 3H, CH3); 8.23 (s, 1H, CH); 8.62 (s, 1H,
CH); 8.68 (s, 1H, CH); 9.38 (s, 1H, CH)
3094, 2951, 1542, 1385, 1306, 1194, 1032, 1007, 873,
764
DMSO-d6: 2.48 (s, 3H, CH3); 2.49 (s, 3H, OCH3); 8.34
(s, 1H, CH); 8.63 (s, 1H, CH); 8.78 (s, 1H, CH)
(Continued)
Heteroatom Chemistry DOI 10.1002/hc

54 Foks et al.
TABLE 2 Continued
No.
IR [cm−1
]
1H NMR δ[ppm] (200 MHz, *500 MHz)
29
30
31
32
3100, 1598, 1510, 1498, 1479, 1332, 1253, 1126, 761,
688
3084, 2941, 1537, 1381, 1303, 1237, 1080, 1040, 1007,
758, 686
3096, 2888, 1596, 1509, 1376, 1336, 1153, 1128, 818,
760, 689
CDCl3: 7.43–7.82 (m, 5H, Ph); 8.60-8.69 (m, 3H, CH);
9.49 (s, 1H, CH)
CDCl3∗: 4.16 (s, 3H, OCH3); 7.47–7.80 (m, 5H, Ph); 8.32
(s, 1H, CH); 8.70 (s, 1H, CH); 9.04 (s, 1H, CH)
CDCl3∗: 7.49–7.81 (m, 5H, Ph); 8.67 (s, 1H, CH); 8.71 (s,
1H, CH); 9.38 (s, 1H, CH)
2949, 1537, 1384, 1354, 1140, 1018, 858, 761
CDCl3: 2.54 (s, 3H, CH3); 3.91 (s, 3H, CH3); 8.56 (d, J =
2.6 Hz, 1H, CH); 8.63 (d, J = 2.6 Hz, 1H, CH); 9.31 (s,
1H, CH)
33
34
35
36
37
38
39
40
41
3013, 2947, 1542, 1388, 1304, 1175, 1007, 898
CDCl3: 2.56 (s, 3H, CH3); 3.92 (s, 3H, CH3); 4.11 (s, 3H,
OCH3); 8.23 (s, 1H, CH); 8.87 (s, 1H, CH)
3066, 2937, 1534, 1388, 1360, 1179, 1131, 1015, 864,
789, 679, 674
2979, 1536, 1416, 1360, 1292, 1171, 1050, 1034, 776,
697, 679
3056, 1510, 1494, 1437, 1376, 1331, 1168, 1139, 1008,
825, 768, 697
3309, 3068, 1641, 1347, 1167, 688
CDCl3: 2.64 (s, 3H, CH3); 7.49–7.56 (m, 5H, Ph); 8.62 (d,
J = 2.5 Hz, 1H, CH); 8.69 (s, 1H, CH); 9.30 (s, 1H, CH)
CDCl3∗: 2.67 (s, 3H, CH3); 4.16 (s, 3H, OCH3); 7.50–7.59
(m, 5H, Ph); 8.29 (s, 1H, CH); 8.97 (s, 1H, CH)
CDCl3∗: 2.66 (s, 3H, CH3); 7.52–7.58 (m, 5H, Ph); 8.64
(s, 1H, CH); 9.32 (s, 1H, CH)
CDCl3: 7.21–7.71 (m, 10H, Ph); 8.53 (q, J = 2.5 Hz, 1H,
CH); 8.69 (d, J = 2.6 Hz, 1H, CH), 9.47 (s, 1H, CH)
CDCl3: 4.16 (s, 3H, OCH3); 7.33–7.61 (m, 10H, Ph); 8.31
(s, 1H, CH); 9.07 (s, 1H, CH)
3044, 3012, 2941, 1536, 1453, 1383, 1335, 1305, 1210,
1005, 781, 759, 702
3011, 1596, 1494, 1391, 1291, 1144, 1049, 747, 686
DMSO-d6∗: 7.19–7.60 (m, 5H, Ph); 8.79 (s, 1H, CH); 9.39
(s, 1H, CH); 12.26 (s, 1H, NH)
2947, 1593, 1539, 1466, 1381, 1317, 1142, 1125, 755,
687
2970, 2854, 1475, 1458, 1384, 1325, 1212, 1107, 847,
729
DMSO-d6: 4.12 (s, 3H, OCH3); 7.50-7.63 (m, 5H, Ph);
8.47 (s, 1H, CH); 8.95 (s, 1H, CH); 11.97 (s, 1H, NH)
CDCl3: 2.95 (d, J = 10.5 Hz, 2H, CH2); 3.66 (t, J = 11.4
Hz, 2H, CH2); 3.84 (s, 3H, CH3); 3.93 (d, J = 10.5 Hz,
2H, CH2); 4.85 (t, J = 11.4 Hz, 2H, CH2)8.75 (d, J =
5.6 Hz, 2H, CH); 9.20 (s, 1H, CH)
1HNMR spectra for compounds 24, 27, 30, 31, 35, 36 and 39 were performed at frequency 500 MHz.
SCHEME 7
SCHEME 8
8, which inhibited growth of C. albicans in a concen-
tration of 16 μg/mL.
Analyzing the structure–activity relationship,
it has been maintained that more active com-
pounds possessed an amidrazone group (3–5, 8).
Cyclization to 1,2,4-triazole caused loss of antibac-
terial activity. Only 2,5-dihydro-1,2,3,5-thiatriazole
S-oxides 39 and 40 exhibited tuberculostatic
activity in concentrations 62 and 31 μg/mL,
respectively.
Heteroatom Chemistry DOI 10.1002/hc

Studies on Pyrazine Derivatives LII 55
TABLE 3 In vitro Antimicrobial Activity of Pyrazinamidrazone Derivatives 1–41 a,b,c
MIC [μg/mL]
No.
S. aureus
E. coli
P. aeruginosae
C. albicans
1
>256
>256
128
>256
128
>256
>256
>256
>256
>256
>256
128
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
0.5
>256
256
>256
128
256
>256
32
2
3
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
0.5
256
4
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
2
128
5
32
6
>256
>256
16
7
8
9
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
>256
128
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
Gm
>256
32
64
>256
–
aMinimum inhibitory concentrations for microbial strains were determined by a two-fold classical test-tube method of successive dilution.
bGm, gramicidin.
cS. aureus ATCC 25923, E.coli ATCC 25922, P. aeruginosae ATCC 27853, C. albicans clinical strain.
EXPERIMENTAL
instruments. Mass spectra (MS) for compounds 21
and 22 were taken on Finigan MAT 95 (70 eV). The
results of elemental analysis (% C, H, N) for all of
obtained compounds were in agreement with calcu-
lated values within the 0.3% range.
Syntheses of amidrazones 1, 3–5 were described
elsewhere [24,25]. Reaction yields, physical con-
stants, and spectral data of the compounds are given
in Tables 1 and 2.
All materials and solvents were of analytical reagent
grade. Thin-layer chromatography was performed
on Merck silica gel 60F254 plates and visualized with
UV. Melting points were determined with Boethius
apparatus and were uncorrected. IR spectra were
taken on Satellite FT-IR spectrophotometer (KBr
1
pellets). H NMR spectra were recorded on Varian
Gemini (200 MHz) and Varian Unity Plus (500 MHz)
Heteroatom Chemistry DOI 10.1002/hc

56 Foks et al.
Nꢀ-Methylpyrazinamidrazone (2)
3-Pyrazine-1H-[1,2,4]triazoles (18–20, 27–36)
Cyanopyrazine (4.27 mL, 0.05 mol) was dissolved in
10 mL of anhydrous ethanol. Then 5.3 mL (0.1 mol)
of methylhydrazine was added. The mixture was re-
fluxed for 15 min and then left at room temperature
for 24 h. The product was filtered in the form of long
yellow needles and washed with cold ethanol.
General Procedure. To appropriate amidrazone
2–8, 9–17 (5 mmol), 5 mL of triethyl orthoformate
was added. The mixture was refluxed for 3 h. After
cooling, the precipitate was filtered and washed with
ethyl ether.
1,5-Diphenyl-3-pyrazine- and 1,5-Diphenyl-3-(6-
methoxypyrazine-2-yl)-1H-[1,2,4]triazoles
(37,38)
Nꢀ-Phenylpyrazinamidrazone 5 or 8 (5 mmol) was
refluxed with 0.6 mL (5 mmol) of benzoyl chloride
in 5 mL of anhydrous pyridine for 6 h. Then the
mixture was evaporated to dryness. The oily residue
was stirred with ice and the precipitate was filtered
and recrystallized.
6-Methoxypyrazinamidrazone (6)
6-Methoxypyrazine-2-iminoester [23] (3.3 g,0.02 mol)
was dissolved in 15 mL of methanol. Then 2 mL
(0.04 mol) of 98% hydrazine hydrate was added. The
mixture was heated to boiling. Product crystals were
filtered after cooling.
Nꢀ-Methyl-6-methoxypyrazinamidrazone (7)
To
a
solution of 3.3
g
(0.02 mol) of 6-
methoxypyrazine-2-methyliminoester [23] in 15 mL
of methanol, 2.1 mL (0.04 mol) of methylhydrazine
was added. The mixture was heated for 1 min and
left for crystallization.
Bis-(α-aminomethylenepyrazin-2-yl)hydrazine
(21)
Method A. 0.861 g (5 mmol) of benzenesulfonyl-
hydrazide was dissolved in 15 mL of methanol–water
mixture (1:1). Then 0.685 g (5 mmol) of pyrazin-
iminoester was added. The mixture became yellow
and an intensively yellow crystalline product precip-
itated. The product was filtered and recrystallized.
Nꢀ-Phenyl-6-methoxypyrazinamidrazone (8)
6-Methoxypyrazine-2-iminoester [23] (1.67 g, 0.01
mol) was dissolved in 10 mL of methanol. After ad-
dition of freshly distilled phenylhyrazine (1 mL, 10
mmol) the mixture was heated for 1 min and left for
crystallization. Precipitate was filtered and washed
with cold water.
Method B. 0.861 g (5 mmol) of pyrazinamidra-
zone and 0.685 g (5 mmol) pyrazinemethylester were
dissolved in the methanol–water mixture (1:1). The
mixture was acidified with acetic acid and a yel-
low product precipitated. The product was filtered,
washed with water, and recrystallized. MS: m/z 243.1
(100 MH+).
Nꢀ-Arylsulfonylpyrazinamidrazones (9–15)
General Procedure. 5 mmol of appropriate
pyrazine compound 3, 4, or 6 was dissolved in
10 mL of dioxane in the presence of 2 mL (14 mmol)
of triethylamine. Then 5 mmol of benzenesulfonyl
chloride was added and mixture was refluxed for 2 h.
The solvent was evaporated in vacuo and ice was
added to oily residue. The precipitate was filtered
and recrystallized.
Bis-(α-aminomethylene-6-methoxypyrazin-2-yl)
hydrazine (22)
It was synthesized according to the procedure
for 21 in method A from 0.861 g (5 mmol) of
benzenesulfonylhydrazide and 0.835 g (5 mmol)
of 6-methoxypyrazine-2-iminomethylester. MS: m/z
303.1 (100 MH+).
Nꢀ-Methyl-Nꢀ-methanesulfonylpyrazinamidra-
zone (16,17)
Appropriate pyrazinamidrazone (5 mmol) 2 or 7 was
dissolved in 4 mL of anhydrous pyridine. Then 5
mmol of methanesulfonyl chloride was added and
the mixture was heated for 1 min. The mixture was
left for over 1 h and evaporated under reduced pres-
sure. The residue was washed with water, filtered,
and recrystallized.
1,4-Diamine-(6-methoxypyrazin-2-yl)-4-pyra-
zine-2,3-diazabuta-1,3-diene (23)
It was synthesized according to the procedure
for 21 in method B from 0.861 g (5 mmol) of
Heteroatom Chemistry DOI 10.1002/hc

Studies on Pyrazine Derivatives LII 57
pyrazinamidrazone and 0.835 g (5 mmol) of 6-
methoxypyrazine-2-iminomethylester.
was examined. The susceptibility of the microor-
ganisms to the agents was determined by the broth
microdilution assay according to the procedures
outlined by the National Committee for Clinical
Laboratory Standards [26]. The final concentra-
tion of the agents prepared in 200 μL of Mueller–
Hinton broth (or Sabouraud’s medium for C. albi-
cans) ranged over 0.125–256 μg/mL. To prepare bac-
terial suspension, overnight a culture of bacteria in
3% Trypticase Soy Broth (or Sabouraud’s medium
for C. albicans) was diluted in sterile saline to the
final concentration of approximately 107 CFU/mL
of bacteria. Aliquots (5 μL) of bacterial suspension
were added to each agent solution. The MIC was de-
fined as the lowest concentration of the agent that
completely inhibited growth of the bacteria after 24
h incubation in 37◦C. The final results were the aver-
age values from the two independent experiments.
3,5-Dipyrazine-2-yl-4H-[1,2,4]triazoles (24–26)
Appropriate bis-(α-aminomethylenepyrazine)hydra-
zine 21 or 22 (1 mmol) was heated for 1 h in 5 mL
of glacial acetic acid. In the meantime, the mixture
became colorless. Then ice was added to the mixture
and product precipitated. It was filtered and recrys-
tallized.
2-Phenyl-4-pyrazin-2-yl-2,5-dihydro-[1,2,3,5]
thiatriazole 1-oxide (39, 40)
Appropriate amidrazone 3 or 8 (5 mmol) was dis-
solved in 4 mL of anhydrous pyridine and 5 mL of
chloroform. Then the solution of 0.92 mL (13 mmol)
of thionyl chloride in 5 mL of anhydrous chloroform
was added dropwise to the stirred mixture at a tem-
perature below 5◦C. The mixture was stirred at room
temperature overnight, then concentrated to dryness
and stirred with ice. The precipitate was filtered and
recrystallized.
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Heteroatom Chemistry DOI 10.1002/hc

58 Foks et al.
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Heteroatom Chemistry DOI 10.1002/hc