Synthesis, reactions and biological activity of 2-substituted 3-cyano-4,6-dimethylpyridine derivatives

Article abstract of DOI:10.1007/s10593-009-0222-x

The reaction of 2-chloro-4,6-dimethylpyridine-3-carbonitrile with hydrazine hydrate, hydroxylamine, and anthranilic acid afforded the corresponding pyrazolo, isoxazolo, and pyridoquinazoline derivatives. Alkylation of 2-mercapto-4,6-dimethylpyridine-3-carbonitrile with ethyl chloroacetate or phenacyl bromide followed by cyclization in NaOH gave thienopyridine derivatives. Diazotization of ethyl 3-amino-4,6-dimethylthieno[2,3-b]pyridine-2- carboxylate followed by the reaction with thiourea, guanidine carbonate, and hydroxylamine hydrochloride gave the corresponding thienopyridine derivatives. The biological activity of some new compounds has been discussed.

Full text of DOI:10.1007/s10593-009-0222-x

Chemistry of Heterocyclic Compounds, Vol. 45, No. 1, 2009
SYNTHESIS, REACTIONS AND BIOLOGICAL
ACTIVITY OF 2-SUBSTITUTED 3-CYANO-
4,6-DIMETHYLPYRIDINE DERIVATIVES
F. A. Yassin1*
The reaction of 2-chloro-4,6-dimethylpyridine-3-carbonitrile with hydrazine hydrate, hydroxylamine,
and anthranilic acid afforded the corresponding pyrazolo, isoxazolo, and pyridoquinazoline derivatives.
Alkylation of 2-mercapto-4,6-dimethylpyridine-3-carbonitrile with ethyl chloroacetate or phenacyl
bromide followed by cyclization in NaOH gave thienopyridine derivatives. Diazotization of ethyl
3-amino-4,6-dimethylthiеno[2,3-b]pyridine-2-carboxylate followed by the reaction with thiourea,
guanidine carbonate, and hydroxylamine hydrochloride gave the corresponding thienopyridine
derivatives. The biological activity of some new compounds has been discussed.
Keywords: isoxazolopyridine, pyrazolopyridine, pyridine-3-carbonitrile, pyridoquinazoline,
antibacterial activity.
In continuation of our previous works [1, 2] on sulfur-containing compounds annulated with various
five- and six-membered heterocyclic compounds and the considerable biological activity of pyridine derivatives
as fungicidal, antibacterial, antifungal [3, 4], antimycotic [5], and antidepressant agents [6], as well as
thienopyridines as antithrombotic agents [7, 8] against the platelet aggregation, we study the synthesis of several
new pyridine derivatives.
In the present investigation 2-hydroxy-4,6-dimethylpyridine-3-carbonitrile (1) has been prepared via the
reaction of cyanoacetamide and acetylacetone in boiling n-butanol in the presence of a few drops of piperidine. The
treatment of compound 1 with POCl3 gave 2-chloro-4,6-dimethylpyridine-3-carbonitrile (2). IR spectrum of
compound 2 showed an absorption band at 2240 cm–1 (CN) with the absence of on OH group absorption band.
1H NMR spectrum of compound 2 showed signals at 2.3 (3H, s, CH3); 2.5 (3H, s, H3C−C=N), and 7.7 ppm (1H, s,
H-5).
The reaction of compound 2 with hydrazine hydrate in boiling n-butanol [9] gave 3-amino-4,6-di-
methylpyrazolo[3,4-b]pyridine (3). The structure of compound 3 was confirmed by its analytical and spectral
data. IR spectrum of compound 3 showed absorption bands at 1620 (C=N), 3300 (NH), and 3470 cm–1 (NH2),
while 1H NMR spectrum showed signals at 2.3 (3H, s, CH3); 2.5 (3H, s, H3C−C=N); 4.0 (1H, s, NH); 7.1 (1H, s,
H-5), and 12.5 ppm (2H, s, NH2).
_______
* To whom correspondence should be addressed, e-mail: fathy_yassin@yahoo.co.uk.
1Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 43-51, Januar, 2009. Original
article submitted April 9, 2008.
0009-3122/09/4501-0035©2009 Springer Science+Business Media, Inc.
35

The treatment of 2-chloro-4,6-dimethylpyridine-3-carbonitrile 2 with hydroxylamine hydrochloride in
refluxing dry toluene in the presence of a few drops of triethylamine afforded 3-amino-4,6-dimethylisoxazolo-
[3,4-b]pyridine (4). IR spectrum of compound 4 showed absorption bands at 3300–3430 (NH2) and 1620 cm–1
(C=N). 1 H NMR spectrum of compound 4 showed signals at 2.3 (3H, s, CH3); 2.5 (3H, s, H3C−C=N); 4.1 (2H, s,
NH2), and 7.1 ppm (1H, s, H-5). On the other hand, when compound 2 was allowed to react with anthranilic acid
it gave 1-cyano-2,4-dimethylpyrido[2,1-b]quinazolin-5-one (5). The structure of compound 5 was elucidated by
its correct analytical and spectral data. IR spectrum showed absorption bands in the regions of 2220 (CN), 1667
1
(C=O), and 1618 cm–1 (C=N), respectively. H NMR spectrum of compound 5 showed signals at 2.3 (3H, s,
CH3); 2.5 (3H, s, H3C−C=N); 7.3 (1H, s, H-3); and 7.1–7.5 ppm (4H, m, arom). Also, when compound 2 was
allowed to react with benzenesulfonylhydrazide in refluxing n-butanol [10] it yielded the corresponding
7-cyano-4,6-dimethyl(3-oxo-3-phenyl)thia[1,2,4]triazolo[4,5-a]pyridine (6) (Scheme 1).
Scheme 1
Me
CN
OH
Piperidine
O
O
O
NH2
+
Me
N
Me
Me
CN
1
POCl 3
Me
Me
Me
NH2
N
NH2
CN
Cl
H2NNH2
H2NOH · HCl
O
n-BuOH
N
N
Me
N
Me
N
Me
N
H
4
2
3
anthranilic acid
benzenesulphonyl-
hydrazide
thiourea
Me
Me
CN
O
CN
Me
N
Me
N
S
CN
SH
N
Me
N
N
O
Me
N
5
6
7
The structure of compound 6 was confirmed by its analytical and spectral data. IR spectrum of compound 6
1
showed absorption bands at 2220 (CN), 1610 (C=N), 1330 (S=O), and 1370 cm–1 (S=N), while its H NMR
spectrum showed signals at 2.4 (3H, s, CH3); 2.7 (3H, s, H3C−C=N); 7.3 (1H, s, H-5); and 7.5-8.0 ppm (5H, m,
arom).
The reaction of 2-chloro-4,6-dimethylpyridine-3-carbonitrile 2 with thiourea in n-butanol gave the
corresponding 2-mercapto-4,6-dimethylpyridine-3-carbonitrile (7). When compound 7 was allowed to react with
ethyl chloroacetate in the presence of sodium ethoxide [11] it yielded ethyl 2-(3-cyano-4,6-dimethylpyrid-
2-ylthio)acetate (8), which on cyclization in 10% ethanolic KOH afforded 3-amino-2-ethoxy-carbonyl-
4,6-dimethylthieno[2,3-b]pyridine (9). The structures of compounds 8 and 9 were confirmed by their correct
36

analytical and spectral data. IR spectrum of compound 8 showed absorption bands at 1620 (C=N), 1720 (C=O of
ester), and 2220 cm–1 (CN), while 1H NMR spectrum of compound 8 showed signals at 1.5 (3H, t, CH2CH3); 2.5
(3H, s, CH3); 2.9 (3H, s, H3C−C=N); 3.6 (2H, q, CH2CH3), and 7.2 ppm (1H, s, H-5). IR spectrum
of compound 9 showed the disappearance of (CN) band, while 1H NMR spectrum showed signals at 1.3 (3H, t,
CH2CH3); 2.3 (3H, s, CH3); 2.7 (3H, s, H3C−C=N); 4.1 (2H, q, CH2CH3), and 7.2 (1H, s, H-5). Chemically the
structure of compound 9 was confirmed through its reaction with hydrazine hydrate in refluxing ethanol to give
the corresponding 3-amino-2-(hydrazinocarbonyl)-4,6-dimethylthieno[2,3-b]pyridine (10).
IR spectrum of compound 10 showed absorption bands at 1620 (C=N), 1630 (CO, hydrazide), and
3470–3140 cm–1 (NH and two NH2), while its 1H NMR spectrum showed signals at 2.3 (3H, s, CH3); 2.7 (3H, s,
H3C−C=N); 3.6 (2H, s (br), CONHNH2); 5.5 (1H, s (br), CONHNH2), and 7.3 ppm (1H, H-5).
Analogously, alkylation of pyridinethione 7 with phenacyl bromide in the presence of sodium ethoxide
yielded 4,6-dimethyl-2-[(2-oxo-2-phenylethyl)thio]nicotinonitrile (11), which on cyclization in 10% KOH gave
3-amino-2-benzoyl-4,6-dimethylthieno[2,3-b]pyridine (12). IR spectrum of compound 11 showed absorption
1
bands at 1620 (C=N) and 2220 cm–1 (CN), while H NMR sprectrum of compound 11 showed signals at 2.3
(3H, s, CH3); 2.7 (3H, s, H3C−C=N); 4.1 (2H, s, CH2S); and 7.3 ppm (6H, m, arom). When compound 12 was
allowed to react with malononitrile in refluxing dimethylformamide in the presence of anhydrous potassium
carbonate, it yielded 2-amino-3-cyano-7,9-dimethyl-4-phenylpyrido[5,4-b]thieno[2,3-b]pyridine (13). IR spectra
Scheme 2
Me
CN
Me
N
SH
O
O
7
Cl
Br
Ph
OEt
O
NaOEt
NaOEt
Me
CN
Me
Me
CN
O
S
S
N
N
OEt
Me
11
8
KOH/EtOH
KOH/EtOH
NH2
Me
Me
N
NH2
O
O
OEt
S
S
Me
N
Me
12
9
H2NNH2
NH2
CH2(CN)2
N
NH2
CN
Me
N
Me
N
O
NHNH2
S
S
Me
Me
13
10
37

of compounds 9 and 12 were found free from the nitrile function and instead the bands of the newly born NH2
1
group were found. Moreover, the signals of methylene CH2 protons were not revealed in H NMR spectrum,
proving that they were involved in the cyclization step through addition to the nitrile group (Scheme 2).
Diazotization of compound 9 by adding sodium nitrite solution in water afforded the corresponding
3-diazo-2-ethylcarbonyl-4,6-dimethylthieno[2,3-b]pyridine (14), which on reaction with thiourea, guanidine
carbonate, and hydroxylamine hydrochloride gave the corresponding 7,9-dimethyl-2-thioxo-1,3-dihydro-
pyrido[5,4-b]thieno[3,2-d]pyrimidin-4-one (15), 2-amino-7,9-dimethylpyrido[5,4-b]thieno[3,2-d]pyrimidin-4-one
(16), and 6,8-dimethylisoxazolo[4,3-b]thieno[5,4-b]pyridin-3-one (17), respectively.
The structure of the tricyclic compounds 15, 16, and 17 was elucidated by their correct analytical and
spectral data. IR spectrum of compound 15 showed absorption bands at 3323 (NH−CO), 3188 (NH), and 1638
1
cm–1 (C=O). H NMR of compound 15 showed signals at 2.4 (3H, s, CH3); 2.6 (3H, s, H3C−C=N); 5.4 (1H, s,
HN−C=S); 7.1 (1H, s, H-8), and 10.6 (s, CONH), while IR spectrum of compound 16 showed absorption bands
at 3300–3160 (NH2), 3473 (NH), 1676 (C=O), and 1599 –1 (C=N). 1H NMR spectrum of compound 16 showed
signals at 2.3 (3H, s, CH3); 2.5 (3H, s, H3C−C=N); 7.2 (1H, s, arom); 8.2–8.8 (3H, br, NH and NH2). IR
–1
spectrum of compound 17 showed absorption bands in the regions of 3150 (NH), 1710 (C=O), 1593 (C=N).
1H NMR spectrum of compound 17 showed signals at 2.4 (3H, s, CH3); 2.6 (3H, s, H3C−C=N); 5.1 (1H, s, NH),
and 7.1 (1H, s, arom) (Scheme 3). Characterization and physical data of compounds 1−17 are listed in Table 1.
TABLE 1. Characterization and Physical Data of Compounds 1−17
Found, %
Calculated, %
——————
Com-
pound
Empirical
formula
mp, °C* Yield, %
C
H
N
S
1
C8H8N2O
64.54
64.58
57.60
57.64
59.01
59.24
58.79
58.88
72.26
72.05
59.11
59.19
58.44
58.51
57.54
57.58
57.55
57.58
50.22
50.38
68.00
68.06
68.02
68.06
69.85
69.90
50.14
50.17
53.58
53.64
54.47
54.53
5.40
5.44
4.02
4.03
6.11
6.21
5.53
5.56
4.43
4.45
4.20
4.22
4.87
4.91
5.60
5.64
5.58
5.64
5.04
5.12
5.00
5.00
5.00
5.00
4.17
4.20
3.39
3.44
4.07
4.09
3.61
3.66
18.78
18.91
16.76
16.81
34.35
34.54
25.59
25.75
16.79
16.86
19.69
19.72
17.00
17.06
11.00
11.19
11.11
11.19
23.66
23.71
9.82
9.92
9.85
9.92
16.92
16.96
15.90
15.96
22.69
22.75
12.69
12.72
288
90
85
82
80
73
70
75
59
80
63
65
62
72
78
59
66
77
2
C8H7ClN2
3
C8H10N4
280
252
230
198
180
90
4
C8H9N3O
5
C15H11N3O
C14H12N4OS
C8H8N2S
6
11.23
11.26
19.48
19.52
12.77
12.81
12.75
12.81
13.46
13.57
11.32
11.36
11.31
11.36
50.14
50.17
7
8
C12H14N2O2S
C12H14N2O2S
C10H12N4OS
C16H14N2OS
C16H14N2OS
C19H14N4S
C11H9N3OS2
C11H10N4OS
C10H8N2O2S
9
135
198
140
200
286
270
230
280
10
11
12
13
15
16
17
24.29
24.35
13.00
13.02
14.51
14.56
_______
* Solvent: EtOH (compounds 1, 3, 7, 9, 10, 17), MeOH (compound 2),
xylene (compounds 4−6), benzene (compounds 8, 16), AcOH (compounds
11, 12), CHCl3 (compound 13), BuOH (compound 15).
38

Scheme 3
+
N
–
Me
N
Cl
O
9
OEt
S
Me
N
14
Thiourea
NH2OH · HCl
Guanidine
carbonate
S
H
Me
N
Me
N
NH2
N
HN
S
O
NH
Me
N
N
O
NH
O
S
Me
Me
O
S
17
Me
15
16
TABLE 2. Antimicrobial Activity of Compounds 3−5, 9−13, 15
Inhibition zone diameter, mm
Com-
Solvent
Staphylo-
coccus aureus
Proteus
vulgaris
Klebsiella Pseudomonas Escherichia
pound
Spp
aeruginosa
coli
3
EtOH
8
12
8
12
12
—
8
12
12
18
18
18
18
18
12
18
12
18
8
18
12
12
18
8
12
12
12
12
8
4
EtOH
5
9
EtOH
EtOH
8
10
11
12
13
15
Acetone
Acetone
Acetone
Acetone
AcOEt
8
8
8
12
8
—
8
12
12
18
12
—
—
8
18
The biological effect of compounds 3−5, 9−13, and 15 against Gram-positive bacteria (Staphylococcus
aureus) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Klebsiella Spp, and Proteus
vulgaris) has been studied. The antimicrobial activity results are listed in Table 2.
EXPERIMENTAL
All melting points were uncorrected. IR spectra were measured in KBr on a Bruker FT-IR ISS 25
spectrophotometer (νmax, cm–1). 1H NMR spectra (DMSO-d6 and CDCl3) were determined on a Bruker Avance (300
MHz) spectrometer using TMS as an internal reference.
2-Hydroxy-4,6-dimethylpyridine-3-carbonitrile (1). A mixture of cyanoacetamide (2 g, 0.02 mol),
acetyl acetone (1.7 ml, 0.02 mol), and piperidine (3 ml) was refluxed for 6 h in n-butanol (20 ml) and the solid
precipitate was collected and recrystallized from ethanol to give a white crystalline solid.
2-Chloro-4,6-dimethylpyridine-3-carbonitrile (2). A mixture of compound 1 (0.01 mol) with excess
phosphorous oxychloride (30 ml) was refluxed for 4 h. The reaction mixture was left to cool; the excess POCl3
was evaporated under vacuo, the precipitate was washed several times with water, filtered off, and recrystallized
from methanol to give a white crystalline solid.
39

3-Amino-4,6-dimethylpyrazolo[3,4-b]pyridine (3). A mixture of compound 2 (0.01 mol) and
hydrazine hydrate (0.03 mol) was refluxed for 6 h in n-butanol (20 ml). The reaction mixture was left to cool,
and the precipitate was collected and recrystallized from ethanol to give a yellow crystalline solid.
3-Amino-4,6-dimethylisoxazolo[3,4-b]pyridine (4). A mixture of compound 4 (0.01 mol) and
hydroxylamine hydrochloride (0.01 mol) was refluxed for 6 h in dry toluene (20 ml) in the presence of
triethylamine (TEA) (3 ml). The reaction mixture was left to cool, and the precipitate was collected and
recrystallized from xylene to give white crystals.
1-Cyano-2,4-dimethylpyrido[2,1-b]quinazolin-5-one (5). A mixture of compound 2 (0.01 mol) and
anthranilic acid (0.01 mol) was refluxed for 10 h in n-butanol (30 ml). The reaction mixture was left to cool, and
the precipitate was collected and crystallized from xylene to give a brown crystalline solid.
7-Cyano-4,6-dimethyl(3-oxo-3-phenyl)thia[1,2,4]triazolo[4,5-a]pyridine (6). A mixture of compound
2 (0.01 mol) and benzenesulfonylhydrazide (0.01 mol) was refluxed for 10 h in n-butanol (30 ml). The reaction
mixture was left to cool, and the precipitate was collected and recrystallized from xylene to give a yellow solid.
2-Mercapto-4,6-dimethylpyridine-3-carbonitrile (7). A mixture of compound 2 (0.01 mol) and
thiourea 0.5 g (0.01 mol) in n-butanol (20 ml) was refluxed for 6 h. The precipitate was washed with n-butanol
and recrystallized from ethanol.
Ethyl 2-(3-Cyano-4,6-dimethylpyridine-2-ylthio)acetate (8). A mixture of compound 7 (0.01 mol)
and ethyl chloroacetate (0.01 mol) was treated with sodium metal (0.01 mol) in ethanol (30 ml) and stirred for
2 h, then poured gradually with stirring into ice-cold water; the solid formed was collected and recrystallized
from benzene to give compound 8.
3-Amino-2-ethoxycarbonyl-4,6-dimethylthieno[2,3-b]pyridine (9). Compound 8 (0.01 mol) was
treated with 10% KOH (0.01 mol) in ethanol (30 ml), stirred for 2 h, and neutralized with diluted HCl; the
precipitated solid formed after neutralization was collected by filteration, dried, and recrystallized from ethanol
to give compound 9.
3-Amino 2-(Hydrazinocarbonyl)-4,6-dimethylthieno[2,3-b]pyridine (10). A mixture of compound 9
(0.01 mol) and hydrazine hydrate (0.01 mol) in ethanol (30 ml) was heated under reflux for 5 h, and the reaction
mixture was left to cool. The precipitate was collected and recrystallized from ethanol to give compound 10.
4,6-Dimethyl-2-[(2-oxo-2-phenylethyl)thio]nicotinonitrile (11). A mixture of compound 7 (0.01 mol)
and phenacyl chloride (0.01 mol) was treated with sodium metal (0.01 mol) in ethanol (30 ml) and stirred for
2 h, then poured gradually with stirring into ice-cold water. The precipitate was collected and crystallized from
acetic acid to give compound 11.
3-Amino-2-benzoyl-4,6-dimethylthieno[2,3-b]pyridine (12). Compound 11 (0.10 mol) was treated with
10% KOH in ethanol (30 ml) and stirred for 2 h, and neutralized with diluted HCl; the precipitated solid formed
after neutralization was collected by filteration, dried, and recrystallized from acetic acid to give compound 12
in good yield.
2-Amino-3-cyano-7,9-dimethyl-4-phenylpyrido[5,4-b]thieno[2,3-b]pyridine (13). A mixture of
compound 12 (2.8 g, 0.01 mol) and malononitrile (0.5 ml, 0.01 mol) was heated under reflux for 9 h in
dimethylformamide (20 ml) and anhydrous potassium carbonate (1 g). The reaction mixture was left to cool and
then poured into ice-cold water. The precipitate was collected and crystallized from chloroform to give brown
crystals of compound 13.
3-Diazo-2-ethoxycarbonyl-4,6-dimethylthieno[2,3-b]pyridine (14). A solution of sodium nitrite (4 g)
in water (20 ml) was added slowly to an ice-cold solution of compound 9 (0.01 mol) in diluted hydrochloric acid
(25 ml). The resulting diazonium salt solution was stirred at 0°C for 15 min and the diazonium salt solution
formed was used in situ.
7,9-Dimethyl-2-thioxo-1,3-dihydropyrido[5,4-b]thieno[3,2-d]pyrimidin-4-one (15). A solution of
thiourea (0.5 g, 0.01 mol) was added to diazonium salt solution 14, and the mixture was stirred for 5 h, then
40

concentrated by evaporation. The separated solid produced was collected by filteration, dried, and crystallized
from n-butanol to give compound 15.
2-Amino-7,9-dimethylpyrido[5,4-b]thieno[3,2-d]pyrimidin-4-one (16). Diazonium salt solution 14 was
added to the solution of guanidine carbonate (0.15 g, 0.01 mol) in water (10 ml), and the reaction mixture was
stirred for 5 h; the obtained solid was collected by filtration, dried, and recrystallized from benzene to give a
yellow crystalline solid.
6,8-Dimethylisoxazolo[4,3-b]thieno[5,4-b]pyridin-3-one (17). Hydroxylamine hydrochloride (1 g,
0.03 mol) was added to diazonium salt solution 14, and the reaction mixture was stirred for 5 h; the solid
produced was collected and recrystallized from ethanol to give a white crystalline solid.
Method for Testing of Biological Activity.
The biological activity of the tested compounds has been evaluated using filter paper disk method after
dissolving the substances in the appropriate solvent indicated in Table 2. The inhibition zones of microbial growth
surrounding the paper disk were measured in millimeters at the end of the incubation period [12] (18–24 h at 27oC).
The author is thankful to Prof. Yassin Al-Ayouty, Botany Department, Faculty of Science, Zagazig
University for helping in the studies of biological activity of some compounds.
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