Synthesis and antibacterial activity of novel pyridine and pyrazine derivatives obtained from amidoximes

Article abstract of DOI:10.1002/jhet.251

(Chemical Equation Presented) The new pyridine, 4-pyridine N-oxide and pyrazine derivatives exhibiting an antibacterial activity have been synthesized. Amidoximes were transformed into N-hydroxyimidoyl chlorides and then into appropriate oximes. Upon treatment of pyridinecaboxamidoximes with methyl iodide 1-methylpyridynium iodides were formed. Reaction of amidoximes with various carbamoyl chlorides led to corresponding 5-aminocarbonyl-1,2,4-oxadiazoles. Some of carboxamides have undergone thermal decarboxylation to tertiary amines. The newly synthesized compounds were tested in vitro for their tuberculostatic activity. MIC of the most active compound 9 was 12.5 μg/mL for H ₃₇Rv strain. Their activity towards 25 strains of anaerobic and 25 strains of aerobic bacteria was also studied. Derivative 18 was active against both aerobic and anaerobic types of the bacteria.

Full text of DOI:10.1002/jhet.251

November 2009
Synthesis and Antibacterial Activity of Novel Pyridine and
Pyrazine Derivatives Obtained from Amidoximes
1271
Katarzyna Gobis,a* Henryk Foks,a Anna Ke˛dzia,b Maria Wierzbowska,b
and Zofia Zwolskac
aDepartment of Organic Chemistry, Medical University of Gdansk, Hallera, 80-438 Gdansk,
Poland
bDepartment of Oral Microbiology, Medical University of Gdansk, Hallera, 80-438 Gdansk, Poland
cDepartment of Microbiology, Institute of Tuberculosis and Pulmonary Diseases, Warsaw, Poland
*E-mail: kgobis@amg.gda.pl
Received May 4, 2009
DOI 10.1002/jhet.251
Published online 6 November 2009 in Wiley InterScience (www.interscience.wiley.com).
The new pyridine, 4-pyridine N-oxide and pyrazine derivatives exhibiting an antibacterial activity
have been synthesized. Amidoximes were transformed into N-hydroxyimidoyl chlorides and then into
appropriate oximes. Upon treatment of pyridinecaboxamidoximes with methyl iodide 1-methylpyridy-
nium iodides were formed. Reaction of amidoximes with various carbamoyl chlorides led to correspond-
ing 5-aminocarbonyl-1,2,4-oxadiazoles. Some of carboxamides have undergone thermal decarboxylation
to tertiary amines. The newly synthesized compounds were tested in vitro for their tuberculostatic activ-
ity. MIC of the most active compound 9 was 12.5 lg/mL for H37Rv strain. Their activity towards 25
strains of anaerobic and 25 strains of aerobic bacteria was also studied. Derivative 18 was active against
both aerobic and anaerobic types of the bacteria.
J. Heterocyclic Chem., 46, 1271 (2009).
INTRODUCTION
[2]. Thus antimicrobial therapy with a combination of
different drugs is required and new active compounds
for first-line therapy are needed.
Infections caused by Mycobacteria (M. tuberculosis,
M. avium, M. kansasaii, M. bovis) are known to express
multidrug-resistance toward most chemicals, disinfec-
tants and number of antibiotics and chemotherapeutics
as a consequence of single point mutations [1]. This
phenomenon is very dangerous especially for HIV-
infected individuals because of significantly increased
risk of the infection progress to active disease. Other
pathogenic strains, e.g. Streptococcus pneumonia, Staph-
ylococcus aureus, Enterococcus faecium, also exhibit
multidrug-resistance but mediated by other gene changes
In the last few years, many isoniazide and pyrazina-
mide derivatives have been synthesized. Few groups
demonstrate high activity against M. tuberculosis: 20-
monosubstituted isonicotinohydrazides [3], isonicotinoyl-
hydrazones [4], pyridine-2-carboxamidrazones [5,6] and
2-pyrazine or 3-pyridine-1,2,4-oxadiazole-5-ones [7].
Various pyridinium halides also exhibit antibacterial
activity [8–10]. In our previous papers, we reported
tuberculostatic activity of 4-mono- and 4-disubstituted
pyridoyl thiosemicarbazides [11] and some derivatives
C
V
2009 HeteroCorporation

1272
K. Gobis, H. Foks, A. Ke˛dzia, M. Wierzbowska, and Z. Zwolska
Vol 46
Scheme 1
performed for pyridine derivatives required an use of so-
dium hydrogen carbonate to isolate products from reac-
tion mixtures at pH 3. The obtained chlorides were used
for the synthesis of appropriate oximes 11–26. The reac-
tions with secondary amines were performed in mole ra-
tio 1:2 to neutralize hydrochloride generated during the
reactions. Anhydrous dioxane was used as the solvent
and reactions took about 15 min. In the case of oximes
synthesized as pyridine N-oxide derivatives 23–26
refluxing time was prolonged to 1.5 h.
Amidoximes 1–4 and 27 were also treated with triple
excess of appropriate carbamoyl chlorides in pyridine
environment giving expected 3,4-disubstituted 5-oxo-
[1,2,4]oxadiazoles 32–45 (Scheme 2) as a result of intra-
molecular nucleophilic attack of NH nitrogen electron
pair for carbonyl carbon of carbamoyl moiety bound to
OH oxygen instead proton. That attack followed substi-
tution of OH proton and one of NH2 protons by two car-
bamoyl moieties agreeably to mechanism proposed ear-
lier by Marquez and DiPersia [14]. In two cases, the
rate of that reaction was different resulting in formation
of 3-monosubstituted 1,2,4-oxadiazole-5(4H)-ones 30
and 31 (method A). Those products forms probably as
result of fast attack of NH2 nitrogen electron pair for
carbonyl carbon before NH2 proton was substituted by
carbamoyl (Scheme 3). Similar result was reached in
control reactions between corresponding amidoximes
and ethyl chloroformate (method B). Obtained com-
pounds 28 and 29 were next transformed to 3,4-disubsti-
tuted derivatives by substitution in N4 position. Two
amides 34 and 37 were undergone thermal decarboxyl-
ation at 215ꢀC to tertiary amines 46 and 47.
of 5-substituted 3-pyrazine-1,2,4-oxadiazoles [12]. Fur-
ther studies on antituberculosis agents active against
multidrug- resistant strains prompted us to synthesize a
series of new pyridine, pyridine-4-N-oxide and pyrazine
derivatives possessing substituted amidoxime group or
1,2,4-oxadiazole ring substituted with amide in 4-posi-
tion or amine group in 5-position. Both types of com-
pounds could be synthesized from the same substrates,
derivatives possessing carboxamidoxime functional
group [13]. We now report on the synthesis and in vitro
evaluation of their antibacterial and antituberculostatic
activities in vitro.
Scheme 2
RESULTS AND DISCUSSION
Carboxamidoximes 1–4 and 27 were obtained in reac-
tion of appropriate carbonitriles with hydroxylamine.
Methylation of 3- and 4-pyridinecarboxamidoximes 2, 3
on pyridine nitrogen atom was performed with methyl
iodide in anhydrous dioxane and resulted in 1-methyl-
pyridynium iodides 5, 6 formation (Scheme 1).
Compounds 2 and 3 also reacted with methyl iodide
in alkaline solution but both pyridine nitrogen and ami-
doxime oxygen underwent methylation. N-hydroxycar-
boximidoylchlorides 7–10 were prepared from corre-
sponding carboxamidoximes on treatment with sodium
nitrite in hydrochloric acid solution at 0ꢀC. Syntheses
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2009
Synthesis and Antibacterial Activity of Novel Pyridine and Pyrazine
Derivatives Obtained from Amidoximes
1273
Scheme 3
inhibition of Bacteroides vulgatus ATCC 8482 in con-
centration of 100 lg/mL. That compound also inhibited
the growth of two aerobic standard strains: Klebsiella
pneumoniae ATCC 13883 and Staphylococcus aureus
ATCC 25923 and MIC value for that derivative was
100 lg/mL in both casas.
The determined minimum concentrations inhibiting
the growth of tuberculous strains (MIC) for most of the
tested compounds were within the limits 12–100 lg/mL.
MIC of the most active compound 9 was 12.5 lg/mL
for H37Rv strain and 25 lg/mL for other strains.
In conclusion, the present research showed that reac-
tion between carboxamidoximes and carbamoyl chlor-
ides can occur according to two different rates. One de-
rivative (18) exhibited wide spectrum of antibacterial
activity but it did not performe better that metronidazole
against anaerobes and amikacin against aerobes. Other
compound (9) exhibited interesting tuberculostatic activ-
ity and it can be good lead structure for further
modifications.
Characteristics of newly synthesized compounds have
been presented in Table 1.
The investigations of aerobic and anaerobic bacteria
susceptibility to the synthesized pyridine derivatives are
summarized in Table 2. The results have been compared
with that obtained while testing the susceptibility of the
same bacteria to metronidazole (for anaerobes) and ami-
kacin (for aerobes).
Low metronidazole concentrations in range ꢁ0.1–3.1
lg/mL inhibited the growth of Gram-negative bacteria
except single strains of Bacteroides fragilis, B. forsythus
and Fusobacerium necrophorum. These results were
coincided with those obtained by other authors [15,16].
The lowest susceptibility to metronidazole exhibited
Gram-positive rods from Propionibacterium acnes spe-
cies (MIC > 12.5 lg/mL). Among 26 tested derivatives
24 (92%) exhibited differential activity against anaero-
bic bacteria (8–52% of the tested strains). The anaerobes
were the most susceptible at concentrations in ranges
from ꢁ6.2 to 100 lg/mL to derivatives 24 and 26 (52%
were susceptible) and to compound 9 (40% of suscepti-
ble strains). The aerobic bacteria were generally not sus-
ceptible to compounds 13 and 15 in mentioned range of
concentrations. Among 24 derivatives active towards an-
aerobic bacteria, 21 were more effective to Gram-posi-
tive strains. Compounds 30 (MIC 25–100 lg/mL, 100%
of susceptible strains), 9 and 24 (MIC ꢁ6.2–100 lg/mL,
89%) exhibited the highest activity. Derivatives 26, 27,
and 29 were more active against Gram-negative anaero-
bic rods. Compound 27 was the most active one (MIC
ꢁ6.2–100 lg/mL, 38%).
EXPERIMENTAL
All materials and solvents were of analytical reagent grade.
Thin-layer chromatography was performed on Merck silica gel
60F254 plates and visualized with UV. The results of elemental
analyses (%C, H, N) for all of obtained compounds were in
agreement with calculated values within 6 0.3 % range. 1H
NMR spectra in CDCl3 or DMSO-d6 were recorded on Varian
Unity Plus (500 MHz) and Varian Gemini (200 MHz) instru-
ments. IR Spectra (KBr) were determined as KBr pellets of
the solids on a Satellite FT-IR spectrophotometer. Mass spec-
tra for compounds 28, 29, and 46 were taken on Finingan
MAT 95 by a chemical ionization method with isobutane.
Melting points were determined on BOETIUS apparatus and
were uncorrected.
Pyridinecarboxamidoximes (1–3). To a stirred solution of
hydroxylamine hydrochloride (7 g, 0.1 mol) in methanol (50
mL) a solution of potassium hydroxide (6 g, 0.1 mol) in meth-
anol was added. The precipitated potassium chloride was fil-
tered off and appropriate pyridinecabonitrile (7 g, 60 mmol)
was added to the clear filtrate. Reaction mixture was refluxed
for 1 h and after cooling the final solid of 3 was filtered off,
washed with water and dried at room temperature. The crude
product was recrystallized to afford of bright leaflets (7.5 g).
To isolate two other isomers final reaction mixtures were
evaporated and 20 mL of water was added to the residue. The
crude products were filtered off after cooling and purified by
crystallization yielding 8 g of 1 and 6.7 g of 2.
Only one from 30 (3%) tested compounds was active
towards aerobic bacteria. Derivative 18 was active in
concentration 50–100 lg/mL and inhibited the growth
of 16% of the tested aerobic bacteria. Other compounds
did not inhibit the growth of aerobic bacteria in the
range of tested concentration (ꢁ6.2–200 lg/mL). Deriv-
ative 18 was active against both aerobic and anaerobic
types of bacteria.
2-Pyridinecarboxamidoxime (1). This compound was
obtained as colorless short needles. Yield 87%; m.p. 117–
118ꢀC. (ref. [17], m.p. 117ꢀC).
3-Pyridinecarboxamidoxime (2). This compound was
obtained as colorless small needles. Yield 73%; m.p. 131–
133ꢀC. (ref. [17], m.p. 131ꢀC).
4-Pyridinecarboxamidoxime (3). This compound was
obtained as colorless small needles. Yield 82%; m.p. 197–
199ꢀC. (ref. [17], m.p. 207ꢀC).
The standard strains of both types of bacteria exhib-
ited rather high resistance towards tested compounds
(MIC ꢂ 200 lg/mL). In the case of anaerobic Fusobac-
terium nucleatum, ATCC 25586 compounds 21 (MIC
100 lg/mL), 23 (MIC 100 lg/mL) and 15 (MIC 100
lg/mL) were active. Derivative 18 induced the growth
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1274
K. Gobis, H. Foks, A. Ke˛dzia, M. Wierzbowska, and Z. Zwolska
Vol 46
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2009
Synthesis and Antibacterial Activity of Novel Pyridine and Pyrazine
Derivatives Obtained from Amidoximes
1275
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DOI 10.1002/jhet

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Vol 46
(4.2 g). IR: 3098, 2520, 1603, 1550, 1476, 1444, 1232, 1213,
1
1-Oxy-isonicotincarboxamidoxime (4). A 7.2 g (60 mmol)
1183,1029, 959, 838, 623 cmꢃ1; H NMR (500 MHz, DMSO-
quantity of 4-cyanopyridine N-oxide was dissolved in 50 mL
of hot water and then water solution of hydroxylamine was
added in small portions with stirring. Hot reaction mixture was
left at room temperature for 1 h then cooled and precipitate
was filtered and recrystallized giving 6.85 g of small colorless
needles. Hydroxylamine solution was prepared by mixing 7 g
(0.1 mol) of hydroxylamine hydrochloride in 10 mL of water
with 6 g (0.1 mol) of potassium hydroxide in 10 mL of water.
IR: 3416, 3296, 3180, 2834, 1644, 1608, 1500, 1439, 1379,
d6): d 7.73 (d; 2H, 4-pyridyl, J 7.5 Hz) 8.26 (d;2H, 4-pyridyl,
J 20 Hz), 12.85 (s;1H, OH) ppm.
General procedure for the synthesis of pyridylmethanone
oximes (11–26). A 0.78 g (5mmol) quantity of carboximidoyl
chlorides 7–10 was dissolved in 10 mL of anhydrous dioxane.
Next 10 mmol of appropriate secondary amine was added
dropwise. Solid amines, 1-(4-flourophenyl)piperazine and 1-
piperonylpiperazine, were dissolved in a small volume of the
solvent (5 mL). The reaction mixture was heated under reflux
for 15 min. In the case of 1-oxy-isonicitin derivatives, 23–26
refluxing time was prolonged for 1.5 h. The solvent was
evaporated and 40 mL of ice-cold water was added to the resi-
due. The precipitate was filtered, washed with water and
recrystallized from suitable solvent yielding the solid.
4-Phenylpiperazin-1-yl-pyridin-2-yl-methanone oxime (11).
This compound was obtained as white powder. IR: 3457, 2844,
1615, 1595, 1502, 1448, 1382, 1340, 1276, 1236, 1167, 1153,
951, 789, 754, 685 cmꢃ1; 1H NMR (500 MHz, CDCl3): d 3.27 (s;
8H, NCH2), 6.89–7.00 (m; 3H, ArH), 7.28 (m; 3H, 2H ArH and
1H 2-pyridyl), 7.38 (M; 1H, 2-pyridyl), 7.61 (m; 1H, 2-pyridyl),
7.85 (m; 1H, 2-pyridyl), 8.72 (s; 1H, OH) ppm.
4-Benzylpiperazin-1-yl-pyridin-2-yl-methanone oxime (12).
This compound was obtained as white powder. IR: 3168,
3053, 2826, 1621, 1588, 1566, 1447, 1432, 1385, 1275, 1172,
1140, 966, 943, 791, 754, 704 cmꢃ1 1H NMR (500 MHz,
;
CDCl3): d 2.53 (s; 4H, NCH2), 3.09 (s; 4H, NCH2), 3.57 (s;
2H, NCH2Ar), 7.31 (s; 6H, 5H ArH and 1H 2-pyridyl), 7.53
(s; 1H, 2-pyridyl), 7.79 (s; 1H, 2-pyridyl), 8.69 (s; 1H, 2-pyri-
dyl), 9.18 (s;1H,OH) ppm.
1
1226, 1189, 1099, 1036, 946, 863 cmꢃ1; H NMR (200 MHz,
CDCl3): d 6.03 (s; 2H, NH2), 7.65 (m; 2H, 4-pyridyl), 8.20
(m; 2H, 4-pyridyl), 10.07 (s; 1H, OH) ppm.
N-hydroxycarbamimidoyl-1-methyl-pyridynium iodides
(5, 6). 1.3 g (10 mmol) of 2 or 3 was dissolved in hot anhy-
drous dioxane. After cooling to room temperature 2.5 mL (40
mmol) of methyl iodide was added. Reaction mixture was
refluxed for 1 h then left at room temperature for next 1 h. Af-
ter cooling precipitate was filtered and recrystallized to afford
2.6 g (5) and 2.7 g (6) of the product.
N-hydroxycarbamimidoyl-1-methyl-3-pyridynium iodide (5).
This compound was obtained as light yellow prisms. IR: 3389,
3286, 1639, 1592, 1506, 1462, 1416, 1361, 1299, 1206, 953,
898, 876, 669 cmꢃ1 1H NMR (200 MHz, DMSO-d6): d 4.37
;
(s; 3H, NþCH3), 6.33 (s; 2H, NH2), 8.14 (q; 1H, 3-pyridyl, J1
8.3 Hz, J2 6 Hz), 8.70 (d; 1H, 3-pyridyl, J 8.3 Hz), 8.96 (d;
1H, 3-pyridyl, J 6 Hz), 9.19 (s; 1H, 3-pyridyl), 10.39 (s;
1H,OH) ppm.
N-hydroxycarbamimidoyl-1-methyl-3-pyridynium iodide (6).
This compound was obtained as light yellow prisms. IR: 3462,
3342, 1649, 1624, 1557, 1525, 1410, 1360, 1289, 1225, 1196,
1
1081, 952, 839, 824 cmꢃ1; H NMR (200 MHz, DMSO-d6): d
4-(4-Fluorophenyl)piperazin-1-yl-pyridin-2-yl-methanone
oxime (13). This compound was obtained as white powder.
IR: 3207, 2828, 1631, 1512, 1455, 1434, 1390, 1236, 1170,
4.31 (s; 3H, NþCH3), 6.42 (s; 2H, NH2), 8.26 (d; 2H, 4-pyri-
dyl, J 6.4 Hz), 8.94 (d; 2H, 4-pyridyl, J 6.4 Hz), 10.92 (s; 1H,
OH) ppm.
1
988, 953, 818, 789 cmꢃ1; H NMR (500 MHz, CDCl3): 3.15–
3.23 (dd; 8H, NCH2, J1 38 Hz, J2 5 Hz), 6.90 (m; 4H, ArH),
7.50 (d; 3H, 2-pyridyl, J 7.8 Hz), 7.84 (m; 1H, 2-pyridyl),
8.72 (s; 1H, OH) ppm.
4-Piperonylpiperazin-1-yl-pyridin-2-yl-methanone oxime (14).
This compound was obtained as white powder. IR: 3179,
2831, 1608, 1590, 1487, 1439, 1370, 1244, 1169, 1141, 1039,
975, 799 cmꢃ1 1H NMR (500 MHz, CDCl3): d 2.49 (s; 4H,
;
NCH2), 3.08 (s; 4H, NCH2), 3.47 (s;2H, NCH2Ar), 5.93 (s;
2H, OCH2O), 6.73 (s; 2H, ArH), 6.87 (s; 1H, ArH), 7.33–7.53
(m; 2H, 2-pyridyl), 7.80 (s;1H, 2-pyridyl), 8,69 (s;1H, 2-pyri-
dyl), 9.07 (s; 1H, OH) ppm.
N-Hydroxy-pyridinecarboximidoyl
chlorides
(7–9).
Appropriate pyridinecarboxamidoxime 1–3 (2.8 g, 20 mmol)
was dissolved in a mixture of concentrated hydrochloric acid
(20 mL) and water (100 mL) at 0ꢀC. Sodium nitrite (1.6 g, 23
mmol) in 10 mL of water was added dropwise and reaction
mixture was stirred for 1 h at 0ꢀC. Next saturated solution of
sodium hydrogen carbonate was slowly added to the reaction
mixture until pH 3 was reached. The precipitate was filtered,
washed with ice-cold water and purified by crystallization giv-
ing 2.8 g (7), 1.6 g (8), and 2.5 g (9) of the product.
N-Hydroxy-2-pyridinecarboximidoyl chloride (7). This
compound was obtained as white small crystals. Yield: 80%;
m.p. 120–122ꢀC (ref. [18], m.p. 126–128ꢀC.
N-Hydroxy-2-pyridinecarboximidoyl chloride (8). This
compound was obtained as white small crystals. Yield: 80%;
m.p. 129–131ꢀC (ref. [18], m.p. 142–145ꢀC).
N-Hydroxy-2-pyridinecarboximidoyl chloride (9). This
compound was obtained as white small crystals 138–139ꢀC
(ref. [18], m.p. 148–150ꢀC).
1-Oxide-N-hydoxy-4-pyridinecarboximidoyl chloride (10).
5.6 g of 4 (10 mmol) was dissolved in 40 mL of concentrated
hydrochloric acid. The reaction mixture was cooled to temper-
ature 0ꢀC. Next sodium nitrite (5.5 g, 80 mmol) in water (10
mL) was added dropwise and mixture was stirred for 0.5 h.
The precipitate was filtered and washed with ice-cold water.
The crude product was recrystallized yielding bright needles
4-Phenylpiperazin-1-yl-pyridin-3-yl-methanone oxime (15).
This compound was obtained as white powder. IR: 3151,
3037, 2843, 1599, 1497, 1446, 1337, 1242, 1153, 1014, 923,
1
899, 765, 695 cmꢃ1; H NMR (500 MHz, CDCl3): d 3.21, (s;
4H, NCH2), 3.57 (s; 4H, NCH2), 6.89–6.95 (m; 3H, ArH),
7.28–7.41 (m;4H, 2H ArH and 2H 3-pyridyl), 7.86 (s; 1H,
OH), 8.75 (m; 2H, 3-pyridyl) ppm.
4-Benzylpiperazin-1-yl-pyridin-3-yl-methanone oxime (16).
This compound was obtained as white powder. IR: 3173,
2820, 1615, 1593, 1454, 1416, 1380, 1266, 1157, 1142, 1031,
1
1010, 965, 742, 714, 699 cmꢃ1; H NMR (500 MHz, CDCl3):
d 2.47 (s; 4H, NCH2), 3.05 (s; 4H, NCH2), 3.54 (s; 2H,
NCH2ArH), 7.25–7.37 (m; 6H, 5H ArH and 1H 3-pyridyl),
7.80 (m; 1H, 3-pyridyl), 8.37 (s; 1H, OH), 8.65 (m; 2H, 3-pyr-
idyl) ppm.
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Synthesis and Antibacterial Activity of Novel Pyridine and Pyrazine
Derivatives Obtained from Amidoximes
1277
oxide, J 6.5 Hz), 8.26 (d; 2H, 4-pyridine-N-oxide, J 6 Hz),
9.99 (s; 1H, OH) ppm.
4-(4-Fluorophenyl)piperazin-1-yl-1-oxide-pyridin-4-yl-meth-
anone oxime (25). This compound was obtained as white
powder. IR: 3174, 3059, 2848, 1637, 1614, 1442, 1375, 1361,
1221, 1186, 1147, 1037, 989, 965, 854, 834, 819 cmꢃ1 1H
;
NMR (500 MHz, DMSO-d6): d 3.07 (dd; 8H, NCH2, J1 28
Hz, J2 8 Hz), 6.94–7.06 (m; 4H, ArH), 7.45 (m; 2H, 4-pyri-
dine-N-oxide), 8.25 (m; 2H, 4-pyridine-N-oxide), 9.98
(s;1H,OH) ppm.
4-Piperonylpiperazin-1-yl-1-oxide-pyridin-4-yl-methanone
oxime (26). This compound was obtained as white powder.
IR: 3055, 2901, 2839, 1612, 1488, 1439, 1369, 1230, 1179,
;
1156, 1035, 970, 854 cmꢃ1 1H NMR (500 MHz, CDCl3): d
2.44 (m; 4H, NCH2), 2.89 (s; 2H, NCH2Ar), 3.42 (m; 4H,
NCH2), 5.97 (s; 2H, OCH2O), 6.73–6.87 (m;3H, ArH), 7.42
(dd; 2H, 4-pyridine-N-oxide, J1 25 Hz, J2 7 Hz), 8.20 (dd; 2H,
4-pyridine-N-oxide, J1 27 Hz, J2 7 Hz), 9.89 (s; 1H,OH) ppm.
Pyrazinecarboxamidoxime (27). This compound was
obtained as light beige needles according to method described
earlier [19]. Yield: 96%; m.p. 186–187ꢀC (lit. ref. [19], m.p.
186–187ꢀC).
1,2,4-Oxadiazol-5-ones (28, 29). Method A. In 10 mL of
dry pyridine 0.01 mol of appropriate carboxamidoxime was
dissolved and 0.03 mol of carbamoyl chloride was added. The
mixture was refluxed for 3 h. Then pyridine was evaporated
and residue was cooled. Precipitate was filtered, washed with
cold water and recrystallized. Method B. In 10 mL of dry pyri-
dine 5 mmol of appropriate carboxamidoxime was dissolved
and 0.956 mL (10 mmol) of ethyl chloroformate was added.
The mixture was refluxed for 6 h. Then pyridine was evapo-
rated and residue was cooled. Precipitate was filtered, washed
with cold water and recrystallized with addition of active
carbon.
4-(4-Fluorophenyl)piperazin-1-yl-pyridin-3-yl-methanone
oxime (17). This compound was obtained as white powder.
IR: 3176, 3056, 2839, 1624, 1592, 1510, 1417, 1382, 1267,
1235, 1152, 1025, 982, 957, 815, 713 cmꢃ1 1H NMR 500
;
MHz, CDCl3: 3.15 (d; 8H, NCH2, J 48 Hz), 6.87–6.90 (m;
4H, ArH), 7.42 (m; 1H, 3-pyridyl), 7.88 (d; 1H, 3-pyridyl, J 7
Hz), 8.22 (brs;1H,OH) 8.70 (d; 2H, 3-pyridyl, J 45 Hz).
4-Piperonylpiperazin-1-yl-pyridin-3-yl-methanone oxime (18).
This compound was obtained as white powder. IR: 3162,
2827, 1600, 1592, 1487, 1440, 1368, 1265, 1246, 1159, 1142,
1033, 969, 921, 869, 809, 714 cmꢃ1 1H NMR (500 MHz,
;
CDCl3): d 2.45 (s; 4H, NCH2), 3.04 (s; 4H, NCH2), 3.42 (s;
2H, NCH2Ar), 5.92 (s; 2H, OCH2O), 6.72 (s; 2H, ArH), 6.84
(s; 1H, ArH), 7.37 (s; 1H, 3-pyridyl), 7.81 (s; 1H, 3-pyridyl),
8.18 (brs; 1H, OH), 8.62–8.69 (d; 2H, 3-pyridyl, J 33 Hz)
ppm.
4-Phenylpiperazin-1-yl-pyridin-4-yl-methanone oxime (19).
This compound was obtained as light beige powder. IR: 3063,
2889, 2851, 1633, 1600, 1496, 1410, 1383, 1243, 1150, 1023,
1
962, 927, 830, 760, 692 cmꢃ1; H NMR (500 MHz, CDCl3): d
3.18 (s; 8H, NCH2), 6.89 (m; 3H, ArH), 7.25 (t; 2H, ArH, J
7.5 Hz), 7.42 (d; 2H, 4-pyridyl, J 4.5 Hz), 8.03 (s; 1H, OH),
8.74 (d; 2H, 4-pyridyl, J 4.5 Hz) ppm.
4-Benzylpiperazin-1-yl-pyridin-4-yl-methanone oxime (20).
This compound was obtained as small white crystals. IR:
3054, 2920, 2820, 1623, 1597, 1457, 1402, 1300, 1154, 1002,
1
967, 833, 743 cmꢃ1; H NMR (500 MHz, CDCl3): d 2.50 (s;
2H, NCH2), 2.60 (s; 2H, NCH2), 3.06 (s; 2H, NCH2), 3.45 (s;
2H, NCH2), 3.57 (s; 1H, NCH2Ar), 3.64 (s; 1H, NCH2Ar),
7.26–7.39 (m; 7H, 5H ArH and 2H 4-pyridyl), 8.10 (brs; 1H,
OH), 8.59 (d; 1H, 4-pyridyl, J 6 Hz), 8,68 (d; 1H, 4-pyridyl, J
5.5 Hz) ppm.
4-(4-Fluorophenyl)piperazin-1-yl-pyridin-4-yl-methanone
oxime (21). This compound was obtained as white powder.
IR: 3193, 3070, 2837, 1640, 1598, 1508, 1449, 1386, 1285,
1267, 1231, 1147, 1023, 959, 927, 825 cmꢃ1 1H NMR (500
;
MHz, CDCl3): d 3.15 (d; 8H, NCH2, J 43 Hz), 6.83–7.14 (m;
4H, ArH), 7.26–7.51 (m; 3H, 2H 4-pyridyl and 1H OH), 8.15
(brs; 1H, OH) 8.75 (m; 2H, 4-pyridyl) ppm.
4-Piperonylpiperazin-1-yl-pyridin-4-yl-methanone oxime (22).
This compound was obtained as white powder. IR: 3180,
3024, 2815, 1599, 1488, 1441, 1369, 1248, 1159, 1142, 1037,
;
973, 826 cmꢃ1 1H NMR (500 MHz, CDCl3): d 2.43 (s; 4H,
NCH2), 3.01 (s; 4H, NCH2), 3.43 (s; 2H, NCH2Ar), 5.92
(s; 2H, OCH2O), 6.72 (s; 2H, ArH), 6.83 (s; 1H, ArH), 7.35
(s; 2H,4-pyridyl), 8.25 (s; 1H, OH), 8,69 (s; 2H, 4-pyridyl)
ppm.
4-Phenylpiperazin-1-yl-1-oxide-pyridin-4-yl-methanone oxime
(23). This compound was obtained as white powder. IR: 3141,
3027, 2832, 1597, 1481, 1453, 1383, 1235, 1173, 1157, 1012,
;
971, 860, 735 cmꢃ1 1H NMR (500 MHz, DMSO-d6): d 2.49
(s; 4H, NCH2), 3.16 (s; 4H, NCH2), 6.78 (t; 1H, ArH, J 7 Hz),
6.94 (d; 2H, ArH, J 8.5 Hz), 7.21 (t; 2H, ArH, J1 8.5 Hz, J2 7
Hz), 7.50 (d; 2H, 4-pyridine-N-oxide, J 6.5 Hz), 8.17 (d; 2H,
4-pyridine-N-oxide, J 6.5 Hz), 10.49 (s; 1H, OH) ppm.
3-Pyridin-3-yl-4H-[1,2,4]oxadiazol-5-one (28). This com-
pound was obtained as small beige needles. IR: 3060, 2936,
1772, 1604, 1558, 1511, 1477, 1416, 1359, 1223, 1141, 1124,
1
1051, 1029, 915, 892, 761 cmꢃ1; H NMR (200 MHz, DMSO-
d6): d 7.63 (t; 1H, 3-pyridyl, J1 3.0 Hz, J2 5.0 Hz), 8.17 (q;
1H, 3-pyridyl, J1 4.7 Hz, J2 1.8 Hz), 8.79 (d; 1H, 3-pyridyl, J
4.9 Hz), 8.97 (s; 1H, 3-pyridyl), 12.8–13.4 (brs; 1H, NH) ppm.
MS: m/z 164 (100 MHþ), 120 (32.4).
3-Pyridin-4-yl-4H-[1,2,4]oxadiazol-5-one (29). This com-
pound was obtained as small white needles. IR: 3104, 3057,
1636, 1547, 1471, 1409, 1308, 1259, 1223, 1151, 1099, 1000,
1
933, 884, 846, 778 cmꢃ1; H NMR (200 MHz, DMSO-d6): d
7.75 (q; 2H, 4-pyridyl, J1 1.8 Hz, J2 2.7 Hz), 8.82 (q; 2H, 4-
pyridyl, J1 1.7 Hz, J2 2.8 Hz), 12.40–13.40 (brs; 1H, NH)
ppm. MS: m/z 164 (62.6 MHþ), 120 (100).
1,2,4-Oxadiazole-5-ones (30, 31). Synthesis was performed
according to procedure described above for compounds 28, 29
method B.
3-Pyrazin-2-yl-4H-[1,2,4]oxadiazol-5-one (30). This com-
pound was obtained as small beige crystals. Yield: 63%; m.p.
259–261ꢀC (ref. [12], m.p. 260–262ꢀC).
3-Pyridin-2-yl-4H-[1,2,4]oxadiazol-5-one (31). This com-
pound was obtained as small beige needles. IR: 3061, 1788,
1585, 1567, 1496, 1460, 1419, 1301, 1114, 1096, 990, 953,
4-Benzylpiperazin-1-yl-1-oxide-pyridin-4-yl-methanone oxime
(24). This compound was obtained as white powder. IR: 3139,
3078, 2845, 1623, 1596, 1481, 1453, 1408, 1336, 1226, 1177,
1
893, 798 cmꢃ1; H NMR (200 MHz, DMSO-d6): d 7.62–7.86
1
1156, 1012, 928, 763, 632 cmꢃ1; H NMR (500 MHz, DMSO-
(m; 1H, 2-pyridyl), 7.95–8.09 (m; 2H, 2-pyridyl), 8.75 (m; 1H,
2-pyridyl), 12.85–13.40 (brs; 1H, NH) ppm.
d6): d 3.05 (s; 4H, NCH2), 3.17 (s; 4H, NCH2), 3.33 (s; 2H,
NCH2Ar), 6.94–7.23 (m; 5H, ArH), 7.47 (d; 2H, 4-pyridine-N-
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1278
K. Gobis, H. Foks, A. Ke˛dzia, M. Wierzbowska, and Z. Zwolska
Vol 46
der. IR: 2983, 1798, 1716, 1534, 1419, 1375, 1308, 1246,
1200, 1027, 995, 901, 827, 794, 755 cmꢃ1 1H NMR (500
4-Aminocarbonyl-[1,2,4]oxadiazol-5-ones (32–41). Synthesis
was performed according to procedure described for com-
pounds 28, 29 method A.
;
MHz, CDCl3): d 1.26(d; 3H, CH3CH, J 6.8 Hz), 1.40 (d; 3H,
CH3CH, J 6.8 Hz), 1.47 (d; 6H, CH(CH3)2, J 6.8 Hz), 3.63–
3.82 (m; 1H, NCH(CH3)2), 4.07–4.12 (m; 1H, NCH(CH3)2),
7.56 (d; 2H, 4-pyridyl, J 5.4 Hz), 8.82 (d; 2H, 4-pyridyl, J 5.4
Hz) ppm.
4-Diethylaminocarbonyl-3-pyrazin-2-yl-4H-[1,2,4]oxadiazol-
5-one (32). This compound was obtained as small colorless
crystals. IR: 2981, 1790, 1733, 1584, 1568, 1474, 1453, 1425,
1
1378, 1268, 1181, 1166, 1147, 1018, 905, 857, 759 cmꢃ1; H
4-Dimethylaminocarbonyl-3-pyrazin-2-yl-4H-[1,2,4]oxadia-
zol-5-one (40). This compound was obtained as small white
needles. IR: 2931, 1784, 1725, 1587, 1484, 1450, 1384, 1274,
;
1193, 1144, 1059, 1019, 910, 868, 794, 765 cmꢃ1 1H NMR
NMR (200 MHz, CDCl3): d 1.31–1.39 (m; 6H, 2CH2CH3),
3.47–3.63 (m; 4H, 2NCH2CH3), 8.63 (t; 1H, pyrazinyl, J 1.8
Hz) 8,79 (d, 1H, pyrazinyl, J 2.5 Hz), 9.28 (d; 1H, pirazyna, J
1.5 Hz) ppm.
(200 MHz, CDCl3): d 3.17 (s; 3H, NCH3), 3.21 (s; 3H,
NCH3), 8.64 (m; 1H, pyrazinyl), 8.77 (d; 1H, pyrazinyl, J 2.5
Hz), 9.22 (d; 1H, pyrazinyl, J 1.5 Hz) ppm.
4-Dimethylaminocarbonyl-3-pyridin-2-yl-4H-[1,2,4]oxadia-
zol-5-one (41). Yield: 35%; m.p. 139–141ꢀC (ref. [13], m.p.
142–143ꢀC).
4-Aminocarbonyl-[1,2,4]oxadiazol-5-ones (42–45). In 5 mL
of dry pyridine 2.5 mmole of appropriate 1,2,4-oxadiazole-5-
one 28–31 was dissolved and 7.5 mmol of carbamoyl chloride
was added. The mixture was refluxed for 12–30 h. Reaction
progress was monitored by TLC analysis. Pyridine was evapo-
rated. Residue was cooled, filtered, washed, dried and
recrystallized.
4-Dimethylaminocarbonyl-3-pyridin-3-yl-4H-[1,2,4]oxadia-
zol-5-one (42). This compound was obtained as beige powder.
IR: 3060, 1772, 1728, 1604 1559, 1512, 1477, 1359, 1260,
1223, 1140, 1124, 1053, 1028, 910, 893, 829, 761 cmꢃ1 1H
;
NMR (200 MHz, DMSO-d6): d 3.01 (s; 3H, NCH3), 3.20 (s;
3H, NCH3), 7.59–7.66 (q; 1H, 3-pyridyl, J1 4.9 Hz, J2 3.1
Hz), 8.04 (d; 1H, 3-pyridyl, J 8.0 Hz), 8.81 (m; 2H, 3-pyridyl)
ppm.
4-Dimethylaminocarbonyl-3-pyridin-4-yl-4H-[1,2,4]oxadia-
zol-5-one (43). This compound was obtained as beige powder.
IR: 2943, 1785, 1718, 1586, 1548, 1492, 1417, 1382, 1269,
1140, 1060, 1000, 903, 835, 759 cmꢃ1 1H NMR (200 MHz,
;
CDCl3): d 3.18 (s; 3H, CH3), 3.25 (s; 3H, CH3), 7.56 (d, 2H,
4-pyridyl, J 6.2 Hz), 8.83 (d; 2H, 4-pyridyl, J 6.1 Hz) ppm.
4-(Morpholine-4-carbonyl)-3-pyrazin-2-yl-4H-[1,2,4]oxadia-
zol-5-one (44). This compound was obtained as white powder.
IR: 2922, 2867, 1808, 1735, 1584, 1421, 1377, 1263, 1233,
;
1178, 1114, 1017, 905, 840, 760 cmꢃ1 1H NMR (200 MHz,
DMSO-d6): d 3.64–3.74 (m; 8H, morpholine), 8.88–8.95 (m;
2H, pyrazinyl), 9.26 (d; 1H, pyrazinyl, J 1.4 Hz) ppm.
4-Diethylaminocarbonyl-3-pyridin-2-yl-4H-[1,2,4]oxadiazol-
5-one (33). This compound was obtained as small colorless
crystals. IR 2977; 1780; 1724; 1565, 1476; 1454; 1426; 1400;
1272; 1212; 1177; 1059; 903; 859; 756 cmꢃ1 1H NMR (200
;
MHz, CDCl3): 1.31–1.39 (m; 6H, 2CH2CH3), 3.44–3.55 (m;
4H, 2NCH2CH3), 7.46–7.53 (m; 1H, 2-pirydyl), 7.86–7.94 (m;
1H, 2-pyridyl), 8.62 (m; 1H, 2-pyridyl) ppm.
4-Diethylaminocarbonyl-3-pyridin-3-yl-4H-[1,2,4]oxadiazol-
5-one (34). This compound was obtained as small beige crys-
tals. IR: 2976, 1786, 1722, 1589, 1550, 1426, 1383, 1273,
1255, 1211, 1140, 1056, 1023, 901, 857, 814, 796, 758 cmꢃ1
;
1H NMR (200 MHz, CDCl3): d 1.23–1.34 (m, 6H, 2CH2CH3),
3.46–3.52 (m; 4H, 2NCH2CH3), 7,46–7,53 (q; 1H, 3-pyridyl,
J1 5.1 Hz, J2 3.0 Hz), 8.01–8.07 (m; 1H, 3-pyridyl), 8.81 (q;
2H, 3-pyridyl, J1 1.8 Hz, J2 3.3 Hz) ppm.
4-Diethylaminocarbonyl-3-pyridin-3-yl-4H-[1,2,4]oxadiazol-
5-one (35). This compound was obtained as small beige crys-
tals. IR: 2978, 1792, 1725, 1659, 1637, 1600, 1583, 1408,
1270, 1251, 1212, 1064, 991, 909, 859, 827, 780, 759 cmꢃ1
;
1H NMR (200 MHz, CDCl3): d 1.25–1.35 (q; 6H, 2CH2CH3,
J1 7.1 Hz, J2 6.3 Hz), 3.45 (m; 4H, 2NCH2CH3), 7.57 (d; 2H,
4-pyridyl, J 5.0 Hz), 8.83 (d; 2H, 4-pyridyl, J 6.2 Hz) ppm.
4-Diisopropylaminocarbonyl-3-pyrazin-2-yl-4H-[1,2,4]oxa-
diazol-5-one (36). This compound was obtained as beige pow-
der. IR: 2995, 1801, 1721, 1581, 1434, 1375, 1312, 1245,
1206, 1176, 1029, 1016, 900, 866, 825, 763 cmꢃ1 1H NMR
;
(200 MHz, CDCl3): d 1.27–1.49 (m; 12H, 2CH(CH3)2), 3,57–
3,71 (m; 1H, NCH(CH3)2), 4,05–4,19 (m; 1H, NCH(CH)3),
8,57 (q; 1H, pyrazinyl, J1 1.5 Hz, J2 1.0 Hz), 8.76 (d; 1H, pyr-
azinyl, J 2.5 Hz); 9,23 (d; 1H, pyrazinyl, J 1.5 Hz) ppm.
4-Diisopropylaminocarbonyl-3-pyridin-2-yl-4H-[1,2,4]oxa-
diazol-5-one (37). This compound was obtained as beige pow-
der. IR: 3004, 2986, 2969, 1792, 1717, 1565, 1480, 1436,
1400, 1375, 1317, 1251, 1209, 1171, 1137, 1034, 897, 827,
4-(Morpholine-4-carbonyl)-3-pyrazin-2-yl-4H-[1,2,4]oxadia-
zol-5-one (45). This compound was obtained as white powder.
IR: 2965, 2928, 1799, 1774, 1711, 1591, 1564, 1432, 1406,
1
789, 755 cmꢃ1; H NMR (200 MHz, CDCl3): d 1.28–1.38 (q;
6H, CH(CH3)2 J1 6.6 Hz, J2 7.2 Hz), 1,5 (t; 6H, CH(CH3)2 J
5.6 Hz), 3.49–3.71 (m; 1H; NCH(CH3)2), 4.06–4.19 (m; 1H;
NCH(CH3)2); 7.45 (m; 1H, 2-pyridyl), 7.82–7.91 (m; 1H, 2-
pyridyl); 7.99 (d; 1H, 2-pyridyl, J 7.9 Hz), 8.60 (q; 1H, 2-pyri-
dyl, J1 1.1 Hz, J2 3.7 Hz) ppm.
4-Diisopropylaminocarbonyl-3-pyridin-3-yl-4H-[1,2,4]oxa-
diazol-5-one (38). This compound was obtained as beige pow-
der. IR: 2994, 2973, 2938, 1797, 1716, 1588, 1433, 1378,
1309, 1247, 1152, 1029, 898, 852, 793, 755 cmꢃ1 1H NMR
;
(200 MHz, CDCl3): d 1.38 (d; 12H, 2CH(CH3)2, J 6.7 Hz),
4.11–4.25 (m; 2H, 2NCH(CH3)2), 7.43–7.50 (q; 1H, 3-pyridyl,
J1 5.1 Hz, J2 2.6 Hz), 8.38 (d; 1H, 3-pyridyl, J 8.0 Hz), 8.71
(d; 1H, 3-pyridyl, J 4.0 Hz), 9.26 (s; 1H, 3-pirydyl).
4-Diisopropylaminocarbonyl-3-pyridin-4-yl-4H-[1,2,4]oxa-
diazol-5-one (39). This compound was obtained as beige pow-
1
1392, 1292, 1262, 1109, 1020, 1000, 900, 797, 755 cmꢃ1; H
NMR (200 MHz, CDCl3): d 3.61 (t, 2H, NCH2, J 4.4 Hz),
3.76 (d; 2H, NCH2, J 4.9 Hz), 3.85 (d; 4H, 2 OCH2, J 3.3
Hz), 7.50 (t; 1H, 2-pyridyl, J 4.9 Hz); 7.85–8.02 (m; 2H, 2-
pyridyl), 8.65 (d; 1H, 2-pyridyl, J 4.7 Hz) ppm.
5-Alkylamino-[1,2,4]oxadiazoles (46, 47). 3 mmole of
compound 34 or 37 was heated in pressure vessel in silicon
bath gradually to 215ꢀC. Then vessel was cooled slowly. De-
carboxylation product was separated from substrate and puri-
fied by column chromatography on silica gel using chloro-
form–ethyl acetate as liquid phase.
5-Diethylamino-3-pyridin-3-yl-[1,2,4]oxadiazole (46). This
compound was obtained as beige powder. IR: 2972, 1636,
1594, 1579, 1519, 1439, 1355, 1261, 1214, 1137, 1083, 1022,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

November 2009
Synthesis and Antibacterial Activity of Novel Pyridine and Pyrazine
Derivatives Obtained from Amidoximes
1279
1
963, 883, 821, 759 cmꢃ1; H NMR (200 MHz, DMSO-d6): d
tuberculotic patients: one (Spec. 210) resistant to p-aminosali-
cic acid (PAS), isonicotinic acid hydrazide (INH), etambutol
(ETB) and rifampicine (RFP), another (Spec. 192) fully sensi-
tive to the administrated drugs. In vitro investigations were
performed by a classical test tube method of successive dilu-
tion with Youman’s liquid medium containing 10% of bovine
serum [22].
1.20 (t; 6H, 2CH2CH3, 7.0 Hz), 3.48–3.59 (q; 4H,
J
2NCH2CH3, J1 7.3 Hz, J2 7.0 Hz), 7.51–7.58 (q; 1H, 3-pyri-
dyl, J1 4,84 Hz, J2 3,14 Hz,), 8.23 (d; 1H, 3-pyridyl, J 7.9
Hz); 8.72 (d; 1H, 3-pyridyl, J 4.8 Hz), 9.05 (s; 1H, 3-pyridyl)
ppm. MS: m/z 219 (100MHþ).
5-Diisopropylamino-3-pyridin-2-yl-[1,2,4]oxadiazole (47).
This compound was obtained as beige powder. IR: 2976,
1610, 1523, 1410, 1391, 1368, 1298, 1197, 1160, 1123, 1024,
1
990, 925, 807, 757 cmꢃ1; H NMR (500 MHz, CDCl3): d 1.37
(d; 12H, 2CH(CH3)2, J 6.8 Hz), 4.26 (t; 2H, 2NCH(CH3)2, J
6.5 Hz); 7.39 (q; 1H, 2-pyridyl, J1 5.4 Hz, J2 1.5 Hz), 7.82 (t;
1H, 2-pyridyl, J 7.1 Hz), 8.07 (d; 1H, 2-pyridyl, J 7.8 Hz),
8.80 (d; 1H, 2-pyridyl, J 4.4 Hz) ppm.
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isolated from the oral cavity, respiratory system and abdominal
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to the following genera: Peptostreptococcus (5 strains), Actino-
myces (2), Propionibacterium (2), Prevotella (6), Porphyromo-
nas (2), Fusobacterium (3), Bacteroides (5), and standard
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experiments agar dilution technique with Miller-Hinton agar
was used. The derivatives were dissolved in 1mL of DMSO
immediately before the experiment. Sterile distilled water was
used for further dilutions. The following concentrations of
derivatives were used: 200, 100, 50, 25, 12.5, and 6.2 lg/mL.
The inoculum containing 106 CFU/spot applied to the agar
plates with Steers replicator. For aerobes the inoculated agar
plates and agar plates without derivatives were incubated for
24 h at 37ꢀC. For anaerobes agar plates were incubated in an-
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N2 with palladium catalyst and indicator for anaerobiosis. The
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Mycobacterium tuberculosis. The compounds were exam-
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet