Synthesis and antimicobacterial activity of 2-substituted 4-arylamino-6-methylpyrimidines

Article abstract of DOI:10.1134/S1070363208100216

2-Substituted 4-arylamino-6-methylpyrimidines were synthesized by stepwise modification of the structure of 6-methyl-2-thiouracyl through the intermediate 2-(ar)alkylthio-6-methyl-4-chloropyrimidines. Some of the compounds synthesized exhibit expressed antimycobacterial activity.

Full text of DOI:10.1134/S1070363208100216

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 10, pp. 1944–1948. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © A.V. Erkin, V.I. Krutikov, E.B. Smirnova, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 10, pp. 1708–1712.
Synthesis and Antimicobacterial Activity
of 2-Substituted 4-Arylamino-6-methylpyrimidines
A. V. Erkin, V. I. Krutikov, and E. B. Smirnova
St. Petersburg State Technological Institute
Moskovskii pr. 26, St. Petersburg, 190013 Russia
e-mail:kruerk@yandex.ru
Received April 15, 2008
Abstract—2-Substituted 4-arylamino-6-methylpyrimidines were synthesized by stepwise modification of the
structure of 6-methyl-2-thiouracyl through the intermediate 2-(ar)alkylthio-6-methyl-4-chloropyrimidines.
Some of the compounds synthesized exhibit expressed antimycobacterial activity.
DOI: 10.1134/S1070363208100216
Biological screening of 4-arylamino-2-(2-acetoxy-
ethyl)amino-6-methylpyrimidines I obtained previously
by us permitted to reveal the compounds with the
expressed antimycobacterial properties. Most active in
vitro among them occured to be 2-(2-acetoxyethyl)
amino-4-(3-bromophenyl)amino-6-methylpyrimidine
(Ia) and 2-(2-acetoxyethyl)amino-4-(4-iodophenyl)
amino-6-methylpyrimidine (Ib) hydrochlorides which
by 100% inhibited reproduction of Mycobacterium
smegmatis cells in the concentration 0.0125 g l–1 [1].
Considering the analogy in structures of the
arylaminopyrimidines I and the guanin-cytosine pair of
the DNA of this strain the results obtained are not
unexpected. Analysis of dependence of the
antimycobacterial activity level expresses by the
logarithm of the reverse concentration log (1/C0)
which provides the complete suppression of the
biological object via the lipophilicity parameter log P
for the compounds I shows that these values vary
analogously (see the table). On the basis of the
established rule it could be proposed that introduction
of hydrophobic substituents in the position 2 of the 4-
arylamino-6-methylpyrimidines should cause an
increase in their antimycobacterial action. For the
checking this hypothesis we carried out the synthesis
of analogs of the compounds Ia and Ib, 4-arylamino-2-
benzylamino-6-methylpyrimidines (IIa, IIb), 4-aryl-
amino-2-benzylthio-6-methylpyrimidines (IIc, IId), and
4-arylamino-6-methyl-2-(4-methylphenyl) aminopyr-
imidines (IIe, IIf), and evaluated their biological ac-
tivity toward the above-mentioned mycobacterial culture.
Benzylaminopyrimidine hydrochlorides IIa, IIb
were synthesized by us by amination of 2-benzyl-
amino-6-methyl-4-chloropyrimidine (III) with the
equimolar amounts of 3-bromo- and 4-iodo-
phenylamines in the absence of a solvent at 140°C and
90°C respectively. Lower reaction temperature in the
second case is applied to avoid a significant tarring of
the reaction mixture causing more than a double
decrease in the yield of the compound IIb. Starting
benzylaminochloropyrimidine was synthesized by the
exchange chlorination of 2-benzylaminochloropyrim-
idin-4(3H)-one with phosphorus oxochloride, and
benzylisocytosine IV by amination of 6-methyl-2-
methylthiopyrimidin-4(3H)-one V with benzyl-amine
under rigid conditions. The complications in isolation
of the compound IV as a free base [2] were get over by
the complete removing of unreacted amine from the
reaction mixture.
Dependence of antimycobacterial activity of compounds I
on the lipophilicity parameter
Ar
log P
log 1/C0
4-FC6H4
1.79
2.12
2.12
2.17
2.17
2.44
2.91
4.08
4.08
3.78
4.11
4.11
4.47
4.52
4-MeC6H4
3-MeC6H4
4-ClC6H4
3-ClC6H4
3-BrC6H4
4-IC6H4
1944

SYNTHESIS AND ANTIMICOBACTERIAL ACTIVITY
O
1945
O
O
N
Me2SO4
PhCH2NH2
HN
HN
HN
MeS
Ph
N
N
Me
S
Me
N
Me
H
H
VIII
IV
V
PhCH2Cl
POCl3
Cl
O
N
HN
S
Ph
Ph
N
H
N
Me
Me
Ph
N
Me
III
VII
POCl3
ArNH2
Cl
NHAr
ArNH2
N
S
N
X
Ph
N
Me
N
VI
IIa_IId
Ar = 3-BrC6H4, X = NH (a), 4-IC6H4, NH (b), 3-BrC6H4, S (c), 4-IC6H4, S (d).
phenyl)amino-4-chloropyrimidine IX with 3-bromo-
phenylamine at 140°C. By the second procedure, the
crystallized substrate IX was treated with 4-iodo-
phenylamine at 90°C. Despite the low yield of diaryl-
aminopyrimidine IIf such procedure permits to isolate
this compound without admixture of the tarring prod-
ucts. Phenylaminochloropyrimidine IX was prepared by
the exchange chlorination of 6-me-thyl-2-(4-methyl-
phenyl)aminopyrimidin-4(3H)-one (X). The latter com-
pound was in turn prepared by the reaction of methyl-
thioether V with 4-methyl-phenylamine under rigid condi-
tions. Note that amination of compound V is not ac-
companied by complications marked by the workers [3].
Analogously, from 2-benzylthio-6-methyl-4-chloro-
pyrimidine VI and chosen haloanilines we prepared
thioaminopyrimidine hydrochlorides IIc, IId. Starting
thiochloropyrimidine VI was prepared by the exchange
chlorination of 2-benzylthio-6-methylpyrimidin-4(3H)-
one VI with phosphorus oxochloride. Benzylthioether
VII was synthesized by S-benzylation of 6-methyl-2-
thiouracyl VIII with benzyl chloride. As the com-
pound VI can not be distilled in a vacuum, we exposed
it to amination directly after extraction from the
reaction mixture. Diarylaminopyrimidines IId, IIe
were synthesized by two methods. One of them
included the amination of crude 6-methyl-2-(4-methyl-
O
N
Me
NH2
Me
HN
V
N
Me
H
X
POCl3
Cl
N
NHAr
N
Me
Me
ArNH2
N
N
N
H
Me
N
Me
H
IX
IIe, IIf
Ar = 3-BrC6H4 (e), 4-IC6H4 (f).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 10 2008

1946
ERKIN et al.
The structure of benzylthio- and diarylamino-
hydrochlorides display positive test at the treating with
the aqueous silver nitrate solution.
pyrimidines IIa–IIf is comfirmed by 1H NMR spectra.
In the case of benzylaminopyrimidines IIa, IIb they
contain characteristic signal of the amino group
protons at 8.5–8.7 ppm and 10.8–11.1 ppm and multi-
6-Methyl-2-merthylthiopyrimidin-4(3H)-one (V) and
6-methyl-2-thiouracyl (VIII) were synthesized by
means of the earlier described procedure [2].
1
plets of the aromatic ring protons at 7.2–8.0 ppm. H
Calculation of the lipophilicity parameter of
arylaminopyrimidines and the compounds IIa–IIf was
carried out using the HyperChemTM program package
Release for Windows Molecular Modelling System.
NMR spectra of thioaminopyrimidines IIc, IId contain
a singlet of the amino group proton at 11.1–11.4 ppm
1
and multiplets of the aryl protons at 7.2–8.0 ppm. H
NMR spectra of diarylaminopyrimidines IId, IIe are
characterized by the presence of singlets of the amino
group protons at 9.8–10.3 and 10.4–11.1 ppm and the
multiplets of the aromatic ring protons at 7.1–7.6 ppm.
In each of the above-mentioned cases integral intensity
of the signals observed corresponds to the needed one.
6-Benzylamino-4-(3-bromophenyl)amino-6-me-
thylpyrimidine (IIa). A mixture of 0.5 g of
benzylaminochloropyrimidine III and 0.37 g of 3-
bromophenylamine was heated at 140°C for 1 h.
Solidified reaction mass was grinded and crystallized
from ethanol. After drying in a vacuum over
phosphorus pentoxide, 0.52 g (60%) of compound IIa
By the results of biological testing, compounds
IIa–IIf reveal a significant increase in the anti-
mycobacterial activity of benzylaminopyrimidine IIb
as compared to the prototype Ib. Compound IIb 100%
inhibits reproduction of Mycobacterium smegmatis
cells at the concentration 0.0017 g l–1. Introduction of
sulfur atom into the benzylguanidine fragment of
benzylaminopyrimidine IIb instead of the amino group
(compound IId) leads to complete loss of biological
activity. Bensylaminopyrimidine IIa and thioamino-
pyrimidine IIc also reveal no antimycobacterial
activity. High activity is exhibited by compounds IIe,
IIf, the isosterical analogs of benzylaminopyrimidines
IIa, IIb. They suppress completely the reproduction of
cells of the above-mentioned line at the concentrations
0.0031 and 0.025 g l–1 respectively. The data obtained
show that antimycobacterial activity of compounds
IIa–IIe is determined not only by the parameters of
their lipophilicity varying in the range 3.8–4.3, but also
by some other characteristics, probably by the polariz-
ability and the lability of bond between the substituent
and the ring atom in the position 2 of the cycle.
1
was obtained, mp 260°C (decomp.), Rf 0.55 (A). H
NMR spectrum, δ, ppm: 2.31 s (3H, Me), 4.61 s (2H,
CH2), 6.23 s (1H, CH), 7.12-8.10 m (9H, Ar), 8.59 s
(1H, N2H), 11.05 s (1H, N4H). Found, %: C 52.45; H
4.18; N 13.52. C18H17BrN4·HCl. Calculated, %: C
53.29; H 4.47; N 13.81. Isolated as hydrochloride.
2-Benzylamino-4(4-iodophenyl)amino-6-methyl-
pyrimidine (IIb). This compound was prepared
analogously by the reaction of 0.5 g of benzylamino-
chloropyrimidine III with 0.47 g of 4-iodo-
phenylamine at 90°C, yield 0.49 g (51%), mp 284°C
1
(with decomposition), Rf 0.72 (A). H NMR spectrum,
δ, ppm: 2.31 s (3H, Me), 4.60 s (2H, CH2), 6.22 s (1H,
CH), 7.13-7.71 m (9H, Ar), 8.53 s (1H, N2H), 10.83 s
(1H, N4H). Found, %: C 47.02; H 3.88; N 12.21.
C18H17IN4·HCl. Calculated, %: C 47.76; H 4.01; N
12.38. Isolated as hydrochloride.
2-Benzylthio-4-(3-bromophenyl)amino-6-methyl-
pyrimidine (IIc). A mixture of 1 g of methylthioether
VII and 10 ml of freshly distilled phosphorus oxo-
chloride was boiled under reflux for 1 h. Then
phosphorus oxychloride excess was distilled off in a
vacuum, and the residue was mixed with finely
crushed ice and alkalized with 25% ammonium
hydroxide until the clear weakly alkaline reaction. The
oil obtained was extracted with dichloromethane. The
extract was dried over the anhydrous sodium sulfate
for a day, filtered, and evaporated to dryness at
atmospheric pressure. Chromatographically pure 2-
benzylthio-6-methyl-4-chloropyrimidine VI, 0.85 g
(79%) was obtained [Rf 0.55 (B)], which was used in
the second stage without the additional purification. A
mixture of 0.85 g of thiochloropyrimidine VI and 0.58 g
EXPERIMENTAL
The 1H NMR spectra were taken on a Bruker WM-
400 spectrometer (working frequency 400.13 MHz) in
DMSO-d6 against the signal of the residual DMSO
ptortons. The individuality of compounds was
controlled by TLC on Silufol UV-254 plates in the
2:1:1 butan-1-ol–acetic acid–water (A), 1:1 acetone–
hexane (B), and 2:1 acetone–hexane (C) systems.
Chromatograms were developed by the UV light. The
elemental analyses were carried out on a Hewlett-
Packard B-185 analyzer. The compounds IIa–IIf
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 10 2008

SYNTHESIS AND ANTIMICOBACTERIAL ACTIVITY
1947
of 3-bromophenylamine was kept at 140°C for 1 h.
Solidified reaction mixture was grinded and
crystallized from ethanol. After drying in a vacuum
over phosphorus pentoxide 0.44 g (31%) of compound
IIc was obtained, mp 244°C (decomp.), Rf 0.73 (A). 1H
NMR spectrum, δ, ppm: 2.39 s (3H, Me), 4.46 s (2H,
CH2), 6.70 s (1H, CH), 7.19–8.15 m (9H, Ar), 11.43 s
(1H, NH). Found, %: C 50.31; H 3.98; N 9.67.
C18H10BrN3S·HCl. Calculated, %: C 51.14; H 4.05; N
9.94. Isolated as hydrocloride.
Calculated, %: C 53.29; H 4.47; N 13.81. Isolated as
hydrochloride.
4-(4-Iodophenyl)amino-6-methyl-2-(4-methylphe-
nyl)aminopyrimidine (IIf). This compound was
prepared analogously to compound IIb by the reaction
of 0.21 g of phenylaminochloropyrimidine IX and
0.2 g of 4-iodophenylamine at 90°C, yield 0.0052 g
1
(13%), mp 298°C (decomp.), Rf 0.74 (A). H NMR
spectrum, δ, ppm: 2.26 s (3H, MeC6H4), 2.32 s (3H,
Me), 6.24 s (1H, CH), 7.01–7.70 m (8H, Ar), 9.96 s
(1H, NH), 10.46 s (1H, NH). Found, %: C 47.39; H
3.92; N 12.16. C18H17IN4·HCl. Calculated, %: C 47.76;
H 4.01; N 12.38. Isolated as hydrochloride.
2-Benzylthio-4-(4-iodophenyl)amino-6-methyl-
pyrimidine (IId). A mixture of 1.06 g of thiochloro-
pyrimidine VI prepared as described above and 0.93 g
of 4-iodophenylamine was kept at 90°C for 1.5 h.
Solidified reaction mixture was grinded and
crystallized from ethanol. After drying in a vacuum
over phosphorus pentoxide 0.68 g (34%) of compound
IId was obtained, mp 246°C (decomp.), Rf 0.72 (A).
1H NMR spectrum, δ, ppm: 2.37 s (3H, Me), 4.43 s
(2H, CH2), 6.62 s (1H, CH), 7.21–7.77 m (9H, Ar),
11.10 s (1H, NH). Found, %: C 45.71; H 3.45; N 8.68.
C18H17IN4·HCl. Calculated, %: C 46.02, H 3.55; N
8.94. Isolated as hydrochloride.
2-Benzylamino-6-methyl-4-chloropyrimidine (III).
A mixture of 1 g of benzylcytosine IV and 15 ml of
freshly distilled phosphorus oxychloride was refluxed
for 1 h. The oxychloride excess was distilled off in a
vacuum, and the residue was treated with the finely
crushed ice The liberated oily suspension was
alkalized with the 25% ammonium hydroxide and
triturated until the formation of crystals. The
precipitate obtained was filtered off, washed with
water and dried in a vacuum over phosphorus
pentoxide. Dry product was crystallized from ethanol,
and after drying in a vacuum over phosphorus
pentoxide 0.53 g (49%) of compound III was obtained,
mp 137°C (published mp 133–136°C [4]), Rf 0.68 (B).
1H NMR spectrum, δ, ppm: 2.22 s (3H, Me), 4.47 s
(2H, CH2), 6.50 s (1H, CH), 7.12-7.32 m (5H, Ph),
7.97 s (1H, NH).
4-(3-Bromophenyl)amino-6-methyl-2-(4-methyl-
phenyl)aminopyrimidine (IIe). A mixture of 1.5 g of
phenylisocytosine X and 14 ml of freshly distilled
phosphorus oxychloride was refluxed for 1 h, and the
excess POCl3 was distilled off in a vacuum. The
residue was mixed with the finely crushed ice and
alkalized with the 25% ammonium hydroxide until the
stable weakly alkaline reaction, and the isolated oil
was extracted with methylene chloride. The extract
was dried over the anhydrous sodium sulfate for a day,
and the drying agent was filtered off. The filtrate
obtained was evaporated to dryness at atmospheric
pressure to give 1.18 g (72%) of the chromato-
graphically pure 6-methyl-2-(4-methylphenyl)amino-
4-chloropyrimidine IX [Rf 0.67 (B)] which was used
on the next stage without the additional purification. A
mixture of 1.18 g of phenylaminochloropyrimidine IX
and 0.87 g of 3-bromophemylamine was kept at 140°C
for 1 h. The solidified reaction residue was grinded and
crystallized from ethanol. After drying in a vacuum
over phosphorus pentoxide 0.67 g (33%) of the
compound IIe was obtained, mp 252°C (decomp.), Rf
2-Benzylamino-6-methylpyrimidin-4(3H)-one (IV).
A mixture of 5 g of the methylthioether V and 5.14 g
of freshly distilled benzylamine was heated to 150°C
and kept at this temperature until the complete
evolution of methylmercaptane. Then the benzylamine
excess was distilled off in a vacuum. Solidified residue
was grinded and crystallized from the 70:1
acetonitrile–DMF mixture. After washing with
acetonitrile and drying in a vacuum 4.6 g (65%) of
compound IV was obtained, mp 151°C (published mp
1
132°C [5]), Rf 0.43 (B). H NMR spectrum, δ, ppm:
2.01 s (3H, Me), 4.46 s (2H, CH2), 5.43 s (1H, CH),
6.83 br.s (1H, NHexo), 7.21–7.37 m (3H, Ph), 10.55
br.s (1H, NH).
2-Benzylthio-6-methylpyrmidin-4(3H)-one (VII).
To a solution of 4.3 g of thiouracyl VIII in 20 ml of
water containing 1.2 g of sodium hydroxide 3.8 g of
benzyl chloride dissolved in 10 ml of ethanol was
added dropwise with stirring. After the addition was
1
0.76 (A). H NMR spectrum, δ, ppm: 2.32 s (3H,
MeC6H4), 2.38 s (3H, Me), 6.37 s (1H, CH), 7.21–8.11
m (8H, Ar), 10.36 s (1H, NH), 11.06 s (1H, NH).
Found, %: C 52.71; H 4.05; N 13.58. C18H17BrN4·HCl.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 10 2008

1948
ERKIN et al.
complete the mixture obtained was stirred at 80°C for
1.5 h. Cooled reaction mixture was neutralized with
the calculated amount of acetic acid. The precipitate
formed was filtered off, washed with water and
crystallized from ethanol. After drying in the stream of
warm air for 2 h 5.5 g (78%) of compound VII was
obtained, mp 186 (published mp 183–184°C [6], 170°C
[7]), Rf 0.72 (B).
mixture was grinded and crystallized from ethanol.
After washing with ethanol and drying in a vacuum
over phosphorus pentoxide 3.7 g (54%) of compound
1
X was obtained, mp 230°C, Rf 0.68 (B). H NMR
spectrum, δ, ppm: 2.11 s (3H, MeC6H4), 2.27 s (3H,
Me), 5.57 s (1H, CH), 7.04, 7.06 d (2H, Ar), 7.45, 7.47
d (2H, Ar), 8.55 br.s (1H, NHexo), 10.46 br.s (1H, NH).
Found, %: C 66.71; H 5.88; N 19.41. C12H13N3O.
Calculated, %: C 66.96; H 6.09; N 19.52.
6-Methyl-2-(4-methylphenyl)amino-4-chloropyr-
imidine (IX). A mixture of 1.5 g of phenylisocytosine
X and 15 ml of freshly distilled phosphorus
oxychloride was refluxed for 1 h. The excess
phosphorus oxychloride was distilled off in a vacuum.
The residue was treated with the finely crushed ice,
and the liberated oily suspension was alkalized with
25% ammonium hydroxide and triturated until the
formation of precipitate. The crystals obtained were
filtered off, washed with water and crystallized from
50% ethanol. After drying in a vacuum over
phosphorus pentoxide 0.38 g (23%) of compound IX
ACKNOWLEDGMENTS
The authors express their gratitude to prof. V.V.
Tets (Pavlov St. Petersburg State Medical University)
for performing the microbiological studies.
REFERENCES
1. Erkin, A.V. and Kruticov, V.I., Zh. Obshch. Khim.,
2007, vol. 77, no. 11, p. 1887.
2. Erkin, A.V., Krutikov, V.I., and Pavlovich, N.I., Zh.
Obshch. Khim., 2003, vol. 73, no. 3, p. 494.
1
was obtained, mp 108°C, Rf 0.75 (B). H NMR
spectrum, δ, ppm: 2.27 s (3H, MeC6H4), 2.35 s (3H,
Me), 6.69 s (1H, CH), 7.03, 7.05 d (2H, Ar), 7.56, 7.58
d (2H, Ar), 9.71 s (1H, NH). Found, %: C 61.42; H
5.02; N 17.81. C12H12ClN3. Calculated, %: C 61.67; H
5.18; N 17.98.
3. Sim, O.G., Novikov, M.S., and Ozerov, A.A., Usp.
sovremennogo estestvoznaniya, 2004, no. 4, p. 57.
4. Naito, T., Ouchi, G., Suzuki, K., and Nadase, O.,
J. Pharm. Soc. Japan, 1952, vol. 72, no. 3, p. 348.
5. Matsukawa, T. and Shirakawa, K., J. Pharm. Soc.
Japan, 1951, vol. 71, no. 9, p. 943.
6. Nishiwaki, T. and Goto, T., Bull. Chem. Soc. Japan,
1960, vol. 33, no. 1, p.26.
6-Methyl-2-(4-methylphenyl)aminopyrimidin-4-
(3H)-one (X). A mixture of 5 g of methylthioether V
and 3.43 g of 4-methylphenylamine was heated to 160°C
and kept at this temperature until the complete
evolution of methylmercaptane. Solidified reaction
7. Kuliev, F.A., Galtyan, K.A., and Babakhanov, R.A.,
Dokl. Akad. Nauk Azerb. SSR, 1985, vol. 51, no. 6, p. 27.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 10 2008