Electro-organic synthesis of new pyrimidine and uracil derivatives

Article abstract of DOI:10.1002/jhet.231

(Chemical Equation Presented) Electrochemical oxidations of catechols have been studied in the presence of 6-amino pyrimidine derivatives as nucleophiles in aqueous solution using cyclic voltammetry. The efficient electro-organic synthesis of products has

Full text of DOI:10.1002/jhet.231

40
Electro-Organic Synthesis of New Pyrimidine
and Uracil Derivatives
Vol 47
Saied Saeed Hosseiny Davarani,* Neda Sheijooni Fumani,
Siavash Vahidi, Mohammad-Ali Tabatabaei, and Hamid Arvin-Nezhad
Department of Chemistry, Faculty of Science, Shahid Beheshti University,
G.C. Tehran 1983963113, Iran
*E-mail: ss-hosseiny@cc.sbu.ac.ir
Received December 30, 2008
DOI 10.1002/jhet.231
Published online 21 December 2009 in Wiley InterScience (www.interscience.wiley.com).
Electrochemical oxidations of catechols have been studied in the presence of 6-amino pyrimidine
derivatives as nucleophiles in aqueous solution using cyclic voltammetry. The efficient electro-organic
synthesis of products has been successfully performed at carbon rod electrodes in an undivided cell
under controlled potential conditions in good yield and purity.
J. Heterocyclic Chem., 47, 40 (2010).
INTRODUCTION
friendly electrochemical method for synthesis of pyrimi-
dine derivatives (5a–5c) and uracil derivatives (8d–8f).
Pyrimidine and its derivatives are attracting the atten-
tion of an increasing number of synthetic organic chem-
ists because of their broad range of biological activity
and medicinal importance [1,2]. Numerous reports delin-
eate the antitumor [3], antiviral [4], antioxidant [5], anti-
fungal [6], and hepatoprotective [7], activities of these
compounds. Therefore, large efforts for the preparation
of these molecules have been directed toward the syn-
thetic manipulation of uracils [8]. The importance of py-
rimidine derivatives prompted us to synthesis a number
of these compounds from catechols and thiouracils. We
have investigated the electrochemical oxidation of cate-
chols (1a–1c) in the presence of 6-amino pyrimidine
derivatives (3a, 3b) as nucleophiles. This work has led
to the development of a facile and environmentally
RESULTS AND DISCUSSION
Cyclic voltammetry of 2 mM solution of catechol
(1a) in 0.2M sodium acetate solution containing 10%
acetonitrile as supporting electrolyte shows an anodic
(A1) and a corresponding cathodic peak (C1), which
correspond to the transformation of (1a) to o-quinone
(2a) and vice versa within a quasi-reversible two elec-
trons reaction (Fig. 1, curve a). A peak current ratio (ICP1/
IAP 1) of nearly unity can be considered as a criterion for
the stability of o-quinones (2a) produced at the surface of
the electrode under the experimental conditions [9,10]. In
other words, any hydroxylation [11,12], dimerization
C
V
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January 2010
Electro-Organic Synthesis of New Pyrimidine and Uracil Derivatives
41
Figure 1. Cyclic voltammogram of 2 mM catechol (1a): (a) in absence
of 6-amino-1-methyl-2-(methyl)2-(methylthio)pyrimidin-4(1H)-one (3a),
(b) in the presence of 6-amino-1-methyl-2-(methyl)2-(methylthio)pyrimi-
din-4(1H)-one, (c) cyclic voltammogram of 2 mM 6-amino-1-methyl-2-
(methyl)2-(methylthio)pyrimidin-4(1H)-one (3a) in the absence of
catechol, at glassy carbon electrode, in 0.2M sodium acetate solution
containing 10% acetonitrile. Scan rate: 100 mVsꢀ1, T ¼ ambient temper-
ature. [Color figure can be viewed in the online issue, which is available
at www.interscience.wiley.com.]
Figure 2. Cyclic voltammogram of 2 mM catechol: (a) in the presence
of 6-amino-1-methyl-2-(methyl)2-(methylthio)pyrimidin-4(1H)-one (first
cycle), (b) in the presence of 2 mM 6-amino-1-methyl-2-(methyl)2-(meth-
ylthio)pyrimidin-4(1H)-one (second cycle), at glassy carbon electrode, in
0.2M sodium acetate solution containing 10% acetonitrile. Scan rate: 100
mV sꢀ1, T ¼ ambient temperature. [Color figure can be viewed in the
online issue, which is available at www.interscience.wiley.com.]
3a/1a concentration ratio is decreases. Moreover, the
current function for A1 peak (IAP 1/v1/2) decreases slightly
with increasing scan rate (Fig. 3, curve g).
[13,14], or radical cations formation [15–18] are too slow
to be observed on the time scale of cyclic voltammetry.
To get further support on the electrochemical oxida-
tion of catechol (1a), it was studied in the presence of
3a as a nucleophile. Curve b in Figure 1 shows the
cyclic voltammogram obtained for a 2.0 mM solution of
1a in the presence of 2.0 mM 3a. The voltammogram
exhibits decreasing in cathodic counterpart (C1) of an-
odic peak (A1). This is due to the reactivity of 1a with
3a. The cyclic voltammogram of 2.0 mM of 3a is shown
in Figure 1 curve c, for comparison.
Controlled-potential coulometry was performed in an
aqueous solution containing 0.5 mmol of 1a and
0.5 mmol of 3a at the potential of A1 peak. At the end
of coulometry, it was specified that charge consumption
per molecules of 1a becomes about 2eꢀ.
The coulometry and voltammetry results allow us to
propose an EC mechanism[16,17] for the electro-oxida-
tion of 1a in the presence of 3a (Scheme 1). According
to our results, the Michael addition reaction of 3a to o-
quinone (2a) [eq. (2)] seems to occur much faster than
other side reactions, which leads to the product 5a. The
overoxidation of 5a was circumvented during the prepa-
rative reaction because of the almost insolubility of the
product in acetate buffer solution medium.
The multicyclic voltammogram of 1a in the presence
of 6-amino-1-methyl-2-(methyl)2-(methylthio)pyrimidin-
4(1H)-one (3a) are shown in Figure 2. In this figure, the
second scan exhibits a relatively intense decrease in an-
odic peak current A1 together with a potential shift in a
positive direction. The decrease in A1 peak current and
positive shift of this peak are probably due to the forma-
tion of a thin film of product at the surface of the elec-
trode inhibiting to a certain extent the performance of
electrode process [19,20].
The electro-organic synthesis of 5b and 5c has been
performed using oxidation of 1b and 1c in the presence
of 3a as described for 5a (Table 1).
The electro-oxidation of catechol (1a) in the presence of
6-amino-2,3-dihydro-2-thioxopyrimidin-4(1H)-one (3b) as
a nucleophile was studied by cyclic voltammetry and con-
trolled-potential coulometry in 0.2M sodium acetate solu-
tion containing 10% acetonitrile too. Figure 4, curve b,
shows the cyclic voltammogram obtained for a 2.0 mM
Furthermore, it was observed that the height of the C1
peak increased proportional to augmentation of potential
scan rate (Fig. 3, curve a–f). This confirms the reactivity
of 2a toward 3a. A similar situation was observed when
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DOI 10.1002/jhet

42
S. S. H. Davarani, N. S. Fumani, S. Vahidi, M.-A. Tabatabaei, and H. Arvin-Nezhad
Vol 47
Figure 3. Typical cyclic voltammogram of 2 mM catechol (1a) in the presence of 2 mM 6-amino-1-methyl-2-(methyl)2-(methylthio)pyrimidin-4(1H)-one
(3a) in 0.2M sodium acetate solution containing 10% acetonitrile at a glassy carbon electrode (1.8-mm diameter) at various scan rate. Scan rate from (a) to (f)
are 50, 100, 200, 400, 800, and 1600 mV sꢀ1, respectively. (g) Variation of peak current ratio (IAP1/v1/2) versus scan rate, T ¼ ambient temperature. [Color
figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]
solution of 1a in the presence of 2.0 mM 3b. The voltam-
mogram clearly exhibits an increase in anodic peak A1 and
a decrease in the cathodic peak C1. This is due to the reac-
tivity of 2a with 3b. For comparison, the cyclic voltammo-
gram of 2.0 mM solutions of catechol (1a) and 3b are
shown in Figure 4, curves a and c, respectively.
The possible reason for the observed large increase in
the A1 peak current could be the oxidation of
Scheme 1
Figure 4. Cyclic voltammogram of 2 mM catechol (1a): (a) in the ab-
sence of 6-amino-2,3-dihydro-2-thioxopyrimidin-4(1H)-one (3b), (b) in
the presence of 3b, (c) cyclic voltammogram of 2 mM 6-amino-2,3-
dihydro-2-thioxopyrimidin-4(1H)-one (3b) in the absence of catechol,
at glassy carbon electrode, in 0.2M sodium acetate solution containing
10% acetonitrile. Scan rate: 100 mV sꢀ1, T ¼ ambient temperature.
[Color figure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
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January 2010
Electro-Organic Synthesis of New Pyrimidine and Uracil Derivatives
43
Scheme 2
intermediate 5c at a potential close to that of the starting
catechol. This oxidation is due to solubility of the 5c in
the reaction medium. The most important differences
between this and previous cases are the large increase in
the A1 peak current (Fig. 4, curve b) and the number of
transferred electrons during controlled-potential coulometry.
The results demonstrate that contrary to the previous
cases, the consumed charge is about 4eꢀ per molecule
of catechol (1a). This is related to two two-electron
transfer processes [eqs. (1) and (4) in Scheme 2]. The
coulometry, voltammetry, and NMR results allow us to
propose an ECEC mechanism [21–24], indicated in
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S. S. H. Davarani, N. S. Fumani, S. Vahidi, M.-A. Tabatabaei, and H. Arvin-Nezhad
Vol 47
Table 1
Scheme 2 for the electro-oxidation of catechol (1a) in
the presence of 3b.
Electro-analytical and preparative data.
Applied
potential
(V) vs.
(Ag/AgCl)
Consumed
charge
(C)
Time of
electrolysis
(h)
CONCLUSIONS
Yield
(%)
Conversion
In conclusion, the results of this work show that cate-
chols (1a–1c) are oxidized to their respective o-benzo-
quinone (2a–2c). The formed o-benzoquinones are
attacked by nucleophiles 3a and 3b to form final prod-
ucts 5a–5c and 8d–8f. We observed an interesting diver-
sity in the electro-oxidation mechanism and products of
catechols (1a–1c) in the presence of (3a, 3b). In the
cases of 1a–1c in the presence of 3a, the final products
5a–5c are pyrimidine derivatives that were obtained af-
ter consumption of 2eꢀ per molecule 1a, 1b, and 1c. In
the case of 1a–1c in the presence of 3b, the final prod-
ucts 8d–8f are uracil derivatives that were obtained after
consumption of 4eꢀ per molecule 1a–1c, via intermolec-
ular and intramolecular Michael addition reactions. The
overall mechanism for anodic oxidation of catechols
(1a–1c) in the presence of 3a and 3b are presented in
Schemes 1 and 2. These mechanisms show a good di-
versity in anodic oxidation of 1a–1c in the presence of
3a and 3b.
1a–5a
1b–5b
1c–5c
1a–8d
1b–8e
1c–8f
0.3
0.3
68
72
69
64
67
62
98.1
97.8
16.3
16.2
16.4
33.4
33.1
33.8
0.3
98.2
0.25
0.25
0.25
196.2
196.8
196.5
interrupted during the electrolysis and the graphite anode was
washed in acetone to reactivate it. At the end of electrolysis, a
few drops of acetic acid were added to the solution and the
cell was placed in a refrigerator overnight. The precipitated
solid was collected by filtration and purified by washing with
hot water (Table 1).
Characteristics of products
6-Amino-5-(3,4-dihydroxyphenyl)-3-methyl-2-(methylthio)pyr-
imidin-4(3H)-one (5a). Mp > 270ꢂC; IR (KBr) (mmax cmꢀ1):
3438, 3324, 3225, 2931, 1635, 1590, 1537, 1505, 1418, 1359,
1223, 1092, 845. 1H NMR (DMSO-d6): d ¼ 3.30 (s, 3H,
CH3), 3.36 (s, 3H, CH3), 5.86 (s, 2H, NH2), 6.31 (d, J ¼
8Hz,1H, ArAH), 6.45 (s, 1H, ArAH), 6.59 (d, J ¼ 10Hz, 1H,
ArAH), 8.16 (s, 1H, OH), 8.79 (s, 1H, OH) ppm; 13C NMR
(DMSO-d6): d ¼ 14.6, 29.9, 95.1, 106.1, 111.7, 124.2, 133.3,
146.0, 148.6, 158.0, 159.8, 160.8 ppm; MS, m/z (%): 279
(Mþ, 100), 230 (10), 171 (40), 126 (30), 110 (50), 83 (46), 63
(50), 47 (90). Anal. Calcd. for C12H13N3O3S: C, 51.60; H,
4.69; N, 15.04. Found: C, 51.48; H, 4.73; N, 14.98.
EXPERIMENTAL
Chemical and solutions. Catechol derivatives were reagent-
grade materials, sodium acetate, and other solvents were of
proanalysis grade (all from E. Merck). These chemicals were
used without further purification. The stock solution of cate-
chols was prepared daily.
6-Amino-5-(3,4-dihydroxy-5-methylphenyl)-3-methyl-2-(meth-
ylthio)pyrimidin-4(3H)-one (5b). Mp > 270ꢂC; IR (KBr) (mmax
cmꢀ1): 3445, 3157, 2930, 1636, 1516, 1411, 1359, 1298, 1204,
Electrode and electrochemical instrument. A cyclic vol-
tammetry was performed using a micro-Autolab type III poten-
tiostat/galvanostat and millimole scale electrolysis was per-
formed using a pp-200 Zahrner potentiostat/galvanostat. The
working electrode used in voltammetry experiments was a
glassy carbon disc (2.7 mm2 area) and a platinum wire was
used as the counter electrode. The working electrode used in
controlled-potential coulometry and millimole scale electroly-
sis was assembly of three carbon rods (27 cm2 area) and large
platinum gauze constituted the counter electrode. The working
electrode potentials were measured versus 3M Ag/AgCl refer-
ence electrode (carbon rods from Azar electrode and other
electrodes from Metrohm).
Bruker IFS-66 FTIR spectrometer, Shimadzu QP 1100-EX
mass spectrometer operating at an ionization potential of
70 eV, and Bruker DRX-300 AVANCE NMR spectrometer
were used for recording different spectra.
Electrochemical synthesis of 5a–c and 8d–f. In a typical
procedure, 100 mL of 0.2M sodium acetate solution containing
10% acetonitrile was pre-electrolyzed at mentioned potential
(Table 1) versus 3M Ag/AgCl in an undivided cell. Then 2
mmol of catechols (1a–1c) and 2 mmol of nucleophiles (3a,
3b) were added to the cell. Initially, the current density was
ꢁ2 mA/cm2 and the electrolysis was terminated when the
decay of the current became more than 95%. The process was
1
1093, 1036, 906, 860. H NMR (DMSO-d6): d ¼ 2.09 (s, 3H,
CH3), 2.41 (s, 3H, CH3), 3.16 (s, 3H, CH3), 5.78 (s, 2H, NH2),
6.42 (s, 1H, H-Ar), 6.53 (s, 1H, H-Ar), 8.11 (s, 1H, OH), 9.09
(s, 1H, OH) ppm. 13C NMR (DMSO-d6): d ¼ 14.6, 16.5, 29.9,
95.1, 115.7, 123.5, 124.3, 124.5, 142.4, 145.0, 158.0, 159.7,
160.9 ppm; MS (EI, 70 eV): m/z (%) ¼ 293 (Mþ, 100), 243
(5), 171 (25), 124 (50), 105 (20), 88(50), 57 (55), 41 (50).
Anal. Calcd for C13H15N3O3S: C, 53.23 H, 5.15; N, 14.31.
Found: C, 53.18; H, 5.18; N, 14.31.
6-Amino-5-(3,4-dihydroxy-5-methoxyphenyl)-3-methyl-2-(meth-
ylthio)pyrimidin-4(3H)-one (5c). Mp > 270ꢂC; IR (KBr) (mmax
cmꢀ1): 3456, 1636, 1583, 1523, 1388, 1251, 1041, 998, 844,
1
800, 578. H NMR (DMSO-d6): d ¼ 3.21 (s, 3H, OCH3), 3.49
(s, 3H, CH3), 3.71 (s, 3H, CH3) 5.86 (s, 2H, NH2), 6.33 (s,
1H, H-Ar), 6.62 (s, 1H, H-Ar), 8.35 (s, 1H, OH), 9.85 (s, 1H,
OH) ppm.13C NMR (DMSO-d6): d ¼ 19.3, 23.4, 29.9, 90.2,
105.7, 121.4, 125.2, 145.4, 153.2, 157.2, 159.9, 161.0, 163.4
ppm; MS (EI, 70 eV): m/z (%) ¼ 309 (Mþ, 100), 236 (10),
171 (12), 140 (32), 88(25), 57 (30), 41 (50). Anal. Calcd for
C13H15N3O4S: C, 50.47 H, 4.89; N, 13.58. Found: C, 50.46;
H, 4.89; N, 13.60.
2,3-Dihydro-6,7-dihydroxy-2-thioxo-1H-pyrimido[4,5-b]indol-
4(9H)-one (8d). Mp > 270ꢂC; IR (KBr) (mmax cmꢀ1): 3415,
3343, 3173, 1639, 1566, 1481, 1450, 1366, 1309, 1201, 864.
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Electro-Organic Synthesis of New Pyrimidine and Uracil Derivatives
45
1H NMR (DMSO-d6): d ¼ 5.03 (s,1H, NH), 639 (s, 1H, H-
Ar), 6.70 (s, 1H, H-Ar), 7.20 (s, 1H, NH), 8.38 (s, 1H, NH),
9.37 (s, 1H, OH), 9.41 (s, 1H, OH) ppm; 13C NMR (DMSO-
d6): d ¼ 81.1, 106.4, 108.6, 112.3, 129.3, 144.9, 145.1, 161.0,
162.4, 163.0 ppm; MS (EI, 70 eV): m/z (%) ¼ 249 (Mþ, 80),
221 (25), 210 (25), 182(90), 155(10), 128 (10), 85 (30), 68
(100), 41 (55). Anal. Calcd for C10H7N3O3 S: C, 48.19; H,
2.83; N, 19.25. Found: C, 48.22; H, 2.85; N, 19.75.
[3] Sanghhvi, Y. S.; Larson, S. B.; Matsumoto, S. S.; Nord, L.
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2,3-Dihydro-6,7-dihydroxy-8-methyl-2-thioxo-1H-pyrimido[4,5-
b]indol-4(9H)-one (8e). Mp > 270ꢂC; IR (KBr) (mmax cmꢀ1):
3464, 3367, 2928, 1633, 1505 1452, 1361, 1297, 1228, 1033,
[7] Ram, V. J.; Goel, A.; Sarkhel, S.; Maulik, P. R. Bioorg
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1
804. H NMR (DMSO-d6) d ¼ 2.17 (s, 3H, CH3), 5.01 (s, 1H,
NH), 6.94 (s, 1H, H-Ar), 7.28 (s, 1H, NH), 8.22 (s, 1H, NH),
8.86 (s, 1H, OH), 9.97 (s, 1H, OH) ppm; 13C NMR (DMSO-
d6) d ¼ 14.6, 81.2, 105.7, 113.9, 117.3, 118.0, 128.2, 142.6,
144.9, 161.1, 162.4 ppm; MS (EI, 70 eV): m/z (%) ¼ 263
(Mþ, 100), 223 (15), 196 (75), 150 (10), 124 (25), 85 (30), 68
(60), 41 (100). Anal. Calcd for C11H9N3O3 S: C, 50.18; H,
3.44; N, 15.96. Found: C, 50.17; H, 3.45; N, 15.97.
2,3-Dihydro-6,7-dihydroxy-8-methoxy-2-thioxo-1H-pyri-
mido[4,5-b]indol-4(9H)-one (8f). Mp > 270ꢂC; IR (KBr)
(mmax cmꢀ1): 3435, 3336, 3339, 2924, 1659, 1565, 1463, 1394,
1278, 1020, 768. 1H NMR (DMSO-d6) d ¼ 2.93 (s, 3H,
OCH3), 4.91 (s, 1H, NH), 6.11 (s, 1H, H-Ar), 6.68 (s, 1H,
NH), 7.88 (s, 1H, NH), 8.35 (s, 1H, OH), 10.31 (s, 1H, OH)
ppm; 13C NMR (DMSO-d6) d ¼ 59.6, 91.5, 108.2, 121.4,
128.9, 132.2, 150.9, 152.6, 158.5, 166.3, 170.1 ppm; MS (EI,
70 eV): m/z (%) ¼ 279 (Mþ, 93), 251 (70), 223 (15), 157
(50), 140 (30), 110 (27), 60 (80), 41 (100). Anal. Calcd for
C11H9N3O4S: C, 47.31; H, 3.25; N, 15.05. Found: C, 47.29; H,
3.26; N, 15.06
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Acknowledgment. This work was supported by the Research
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DOI 10.1002/jhet