A mild and efficient copper-mediated N-arylation of 6-azauracil with corresponding boronic acids and their antibacterial activity

Article abstract of DOI:10.14233/ajchem.2018.21491

A convenient synthetic strategy is reported for the synthesis of N-arylated 6-azauracil through Chan-Lam cross-coupling. A variety of N-arylated 6-azauracil derivatives were synthesized in moderate to good yields by cross-coupling of 6-azauracil with arylboronic acids in the presence of Cu(OAc)2 and pyridine. However the arylation position is confirmed in the case of 2-(3,5-dichlorophenyl)-1,2,4-triazine-3,5(2H,4H)-dione (3a), by preparing the compound in a traditional method and compared the chemical shift of the NH proton at N-3 position. Further, the synthesized compounds were screened for their antibacterial activity using agar well diffusion method. The results revealed that most of the synthesized moieties possessing promising therapeutic nature.

Full text of DOI:10.14233/ajchem.2018.21491

Asian Journal of Chemistry; Vol. 30, No. 11 (2018), 2495-2501
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21491
A Mild and Efficient Copper-Mediated N-Arylation of 6-Azauracil with
Corresponding Boronic Acids and their Antibacterial Activity
1
1
2
1
KALI CHARAN GULIPALLI , SRINU BODIGE , PARAMESHWAR RAVULA , R. SEKHAR BOLLA ,
1
1
1,*
SRINIVAS ENDOORI , PURNA KOTESWARA RAO CHERUKUMALLI and NARESHVARMA SEELAM
1Department of Chemistry, Koneru Lakshmaiah Education Foundation, Green fields, Vaddeswaram, Guntur-522 502, India
2Department of Pharmaceutical Chemistry, Gurunanak Institutions Technical Campus, School of Pharmacy, Ibrahimpatnam-501 506, India
*Corresponding author: E-mail: nareshvarma.klu@gmail.com
Received: 1 June 2018;
Accepted: 19 July 2018;
Published online: 27 September 2018;
AJC-19101
A convenient synthetic strategy is reported for the synthesis of N-arylated 6-azauracil through Chan-Lam cross-coupling. A variety of
N-arylated 6-azauracil derivatives were synthesized in moderate to good yields by cross-coupling of 6-azauracil with arylboronic acids in
the presence of Cu(OAc)2 and pyridine. However the arylation position is confirmed in the case of 2-(3,5-dichlorophenyl)-1,2,4-triazine-
3,5(2H,4H)-dione (3a), by preparing the compound in a traditional method and compared the chemical shift of the NH proton at N-3
position. Further, the synthesized compounds were screened for their antibacterial activity using agar well diffusion method. The results
revealed that most of the synthesized moieties possessing promising therapeutic nature.
Keywords: 6-Azauracil, N-arylation, Chan-Lam cross-coupling, Copper acetate, Antibacterial activity.
O
N
O
N
INTRODUCTION
O
N
HN
HN
Azauracils have been extensively studied for their clinical
applications. For example, 6-azauracil and its derivatives have
been extensively used in chemotherapy of cancer [1,2], inhibit
viruses [3-5]. They are also used as a fungicide [6], chemother-
apeutic agents for psoriasis [7], for polyarthritis [8] and for
polycythemia vera [9]. It has been reported that 1-N position
of 6-azauracil is served as the best location to place a substi-
tuent to mimic the size and shape of the natural nucleoside
[10]. Attachment of substituted phenyl side chain at N-1 of
6-azauracil causes increasing its potency, which was related
in part to the acidity of the imide hydrogen. Therefore, substi-
tuents attached at N-1 position will affect the pharmacokinetics
and the binding properties of the drug. In addition, the polari-
zability of N-aryl-6-azauracil extends through out the molecule
and leads adaptation to the active site [11], therefore N-aryl 6-
azauracil derivatives are biologically active molecules [12-15]
(Fig. 1).
N
N
HN
O
O
N
O
O
HO
Cl
O
NC
OH
6-azauridine
HO
OH
PF-00277343
Fig. 1. Some biologically active N-aryl 6-azauracil derivatives
F
Cl
Clazuril
laborious workup process to get the pure material. There are
reports [17-19] about Chan-Lam cross-coupling of N-3 pro-
tected 6-azauracil and arylboronic acid in order to get the
specific arylation at N-1 position. Recently copper catalyzed
Unman coupling for N-arylation has been reported [14], the
method uses expensive diamine catalyst systems, high reaction
temperatures (170 °C) and inert conditions. In order to over-
come all the synthetic issues, we here report a simple, feasible
method to synthesize a range of N-aryl 6-azauracil derivatives
Traditionally N-aryl 6-azauracil derivatives were synthe-
sized [16] from corresponding anilines in 4 steps as shown in
Scheme-I. However, used harsh reaction conditions and
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2496 Gulipalli et al.
Asian J. Chem.
H
N
CN
O
O
H
H
N
Cl
NH2
Cl
N
O
CH
3 AcOH, NaOAc
NaNO2, HCl
N
Cl
N
N
CN
O
O
O
O
N
Cl
N
O
Cl
H
5
Cl
4
6
7
H
N
H
O
O
O
O
N
O
HS
conc. HCl
OH
Cl
N
Cl
N
N
COOH
N
Cl
Cl
8
9
Scheme-I: Traditional scheme for N-aryl 6-azauracil. Reagents and conditions: (a) 6 N HCl (10v), NaNO2 (1.0 equiv), 5 (1.0 equiv), Py
(10v), 5 °C to room temp., 1 h; 86 % (b) NaOAc (1.0 equiv), AcOH (10v), 120 °C, 2 h; 85 % (c) 6N HCl in 1,4-dioxane (10v), 110
°C, 16 h; (71 %) (d) 9 (1.0 equiv), tolune, 120 °C, 2 h; 83 %
using copper-mediated Chan-Lam coupling from N-3 unpro-
tected 6-azauracil and corresponding arylboronic acid.
Copper-mediated Chan-Lam coupling reactions play an
important role in heteroatom arylation and hetero arylation
[20,21]. The development of this new methodology has
attracted much attention as the reactions proceeds at lower
temperature in open air and works for many hetero arenes and
aryl boronic acids provides good yield of N-arylated hetero-
arenes. Therefore, by adopting Chan-Lam cross-coupling
protocol, a variety of N-aryl 6-azauracil derivatives were
synthesized and presenting for the first time.
1H and 100 MHz for 13C NMR. The 1H NMR and 13C NMR
chemical shifts were expressed in ppm with reference to
tetramethylsilane. High resolution mass spectroscopy (HRMS)
data were recorded on high resolution micr OTOF instrument
with electrospray ionization (ESI). Elemental analyses were
performed on a Perkin-Elmer 240 CHN elemental analyzer.
General procedure for the synthesis of title compounds
(3a-r): To a solution of 6-azauracil (100 mg, 0.88 mmol) in
DMF (10.0 mL) was added base (1.76 mmol) and Cu(OAc)2
(159 mg, 0.88 mmol) at room temperature. The resulting reation
mixture was degassed with oxygen for 10 min and then added
arylboronic acids (0.96 mmol) at room temperature and stirred
at appropriate temperature (Table-1) under oxygen atmosphere.
The reaction mixture was diluted with water (15 mL) and
extracted with dichloromethane (3 × 15 mL). The organic layer
washed with H2O (15 mL), brine solution (15 mL), dried over
Na2SO4 and concentrated. The obtained crude product was
purified by column chromatography (0 to 10 % CH3OH/CH2Cl2)
to afford the title compounds.
EXPERIMENTAL
All chemicals were purchased from Sigma-Aldrich; Merck
and Combi blocks were used without further purification. All
melting points were uncorrected and determined in one
end open capillary tubes using Guna Digital Melting Point
apparatus. 1H NMR and 13C NMR spectra were recorded on a
BrukerAMX 300 spectrometer operating at 400/300 MHz for
TABLE-1
PROTOCOL FOR THE SYNTHESIS OF THE TITLE COMPOUNDS (3a-r)
Entry
Product
Temp. (°C)
Base
Time (h)
2
Yield (%)
81
Substrate (2)
H
OH
O
N
O
Cl
B
OH
Cl
N
N
RT
Pyridine
3a
Cl
Cl
H
OH
O
N
O
B
OH
N
65
Et3N
4
62
3b
N
F3C
F3C
H
N
OH
B
O
O
O
O
OH
N
N
65
Et3N
4
2
68
79
3c
N
NC
Cl
NC
Cl
H
N
OH
B
RT
Pyridine
3d
OH
N

Vol. 30, No. 11 (2018)
Mild and Efficient Copper-Mediated N-Arylation of 6-Azauracil with Corresponding Boronic Acids 2497
H
O
N
N
O
OH
B
OH
N
N
RT
RT
65
Pyridine
Pyridine
Et3N
2
2
4
77
90
70
3e
F
F
H
OH
B
O
N
O
F
F
OH
F
3f
N
F
H
OH
O
O
N
B
OH
CF3
OH
N
3g
N
CF3
O
H
N
O
H3C
B
OH
H3C
RT
65
65
Pyridine
Et3N
2
4
4
80
72
64
3h
3i
N
N
H
OH
B
O
O
N
O
OH
N
N
H3 C
H3C
O
O
N
H3C
N
O
H
N
O
OH
B
O
N
Et3N
3j
OH
H3C
N
H
O
N
O
OH
B
OH
N
65
Et3N
4
60
3k
N
N
H3C
N
H3C
H
OH
B
O
N
O
OH
N
RT
65
65
Pyridine
Et3N
2
4
4
70
69
73
3l
3m
3n
N
Cl
Cl
H
N
OH
O
O
O
O
O
O
F3C
B
OH
F3C
N
N
N
N
H
N
OH
B
NC
OH
NC
Et3N
N
H
N
OH
Cl
Cl
B
OH
Cl
Cl
RT
6655
Pyridine
Et3N
2
75
75
3o
3p
N
H
O
O
N
OH
B
N
OH
4
4
N
Cl
Cl
H
N
OH
B
O
O
OH
N
65
80
Et3N
Et3N
4
6
60
65
3q
3r
N
CN
CN
O
H
N
OH
O
Cl
B
OH
Cl
N
N
N
N
Spectral data for compounds 3a-r
d6) δ 155.7, 148.4, 135.0, 134.1, 132.6, 130.2, 128.50,
128.25, 127.12; HRMS (ESI) m/z: calcd. for C9H5N3O2Cl2
[M+H]+ 256.9754, found 256.9748;Anal. Calcd. C9H5N3O2Cl2:
C, 41.89; H, 1.95; N, 16.28; Found: C, 41.86; H, 1.98; N,
16.25.
2-(3,5-Dichlorophenyl)-1,2,4-triazine-3,5(2H,4H)-dione
(3a) [22]: Off white solid; m.p.: 142-147 °C; 1H NMR (300
MHz, DMSO-d6) δ 12.75 (s, 1H), 7.76-7.75 (m, 1H), 7.65 (s,
1H), 7.557 (s, 1H), 7.551 (s, 1H); 13C NMR (100 MHz, DMSO-

2498 Gulipalli et al.
Asian J. Chem.
2-(4-(Trifluoromethyl)phenyl)-1,2,4-triazine-3,5(2H,4H)-
dione (3b): Off white solid; m.p.: 131-135 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.72 (s, 1H), 7.89 (d, 2H, J = 8.4 Hz),
7.64 (s, 1H), 7.61 (d, 2H, J = 8.0 Hz); 13C NMR (100 MHz,
DMSO-d6) δ 156.0, 148.7, 136.9, 135.4, 129.0, 126.0; HRMS
(ESI) m/z: calcd. for C10H6N3O2F3 [M+H]+ 257.0408, found
257.0422; Anal. Calcd. C10H6N3O2F3: C, 46.70; H, 2.35; N,
16.34; Found: C, 46.74; H, 2.37; N, 16.37.
4-(3,5-Dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)benzo-
nitrile (3c) [23]: Off white solid; m.p.: 293-297 °C; 1H NMR
(300 MHz, DMSO-d6) δ 12.73 (s, 1H), 8.00 (d, 2H, J = 8.4
Hz), 7.65 (s, 1H), 7.59 (d, 2H, J = 8.7 Hz); 13C NMR (100
MHz, DMSO-d6) δ 155.9, 148.5, 137.5, 135.4, 133.0, 129.8,
118.2, 111.6; HRMS (ESI) m/z: calcd. for C10H6N4O2 [M+H]+
214.0486, found 214.0481;Anal. Calcd. C10H6N4O2: C, 56.08;
H, 2.82; N, 26.16; Found: C, 56.11; H, 2.87; N, 26.12.
2-(3-Chlorophenyl)-1,2,4-triazine-3,5(2H,4H)-dione
(3d) [11]: Off white solid; m.p.: 212-215 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.69 (s, 1H), 7.62 (s, 1H), 7.53-7.37 (m,
3H), 7.36-7.31 (m, 1H); 13C NMR (100 MHz, DMSO-d6) δ
156.1, 148.7, 135.4, 134.5, 132.9, 130.5, 128.8, 128.5, 127.4;
HRMS (ESI) m/z: calcd. for C9H6N3O2Cl [M+H]+ 223.0143,
found 223.0134;Anal. Calcd. C9H6N3O2Cl: C, 48.34; H, 2.70;
N, 18.79; Found: C, 48.38; H, 2.76; N, 18.74.
2-(4-Fluorophenyl)-1,2,4-triazine-3,5(2H,4H)-dione
(3e) [11]: Off white solid; m.p.: 271-276 °C: 1H NMR (400
MHz, DMSO-d6) δ 12.67 (s, 1H), 7.60 (s, 1H), 7.39-7.37 (m,
2H), 7.33-7.31 (m, 2H); 13C NMR (100 MHz, DMSO-d6) δ
163.0, 160.5, 156.3, 148.9, 135.3, 130.6, 130.5, 115.9, 115.6;
HRMS (ESI) m/z: calcd. for C9H6N3O2F [M+H]+ 207.0438,
found 207.0439; Anal. Calcd. C9H6N3O2F: C, 52.18; H, 2.92;
N, 20.28; Found: C, 52.15; H, 2.96; N, 20.25.
2-(3,4-Difluorophenyl)-1,2,4-triazine-3,5(2H,4H)-
dione (3f): Off white solid; m.p.: 234-237 °C:1H NMR (300
MHz, DMSO-d6) δ 12.71 (s, 1H), 7.63 (s, 1H), 7.60-7.56 (m,
1H), 7.28-7.24 (m, 2H); 13C NMR (100 MHz, DMSO-d6) δ
156.1, 148.7, 136.4, 135.3, 126.07, 126.04, 126.01, 125.9, 118.3,
118.1, 117.7, 117.5; HRMS (ESI) m/z: calcd. for C9H5N3O2F2
[M+H]+ 225.0345, found 225.0341;Anal. Calcd. C9H5N3O2F2:
C, 48.01; H, 2.24; N, 18.66; Found: C, 48.05; H, 2.26; N, 18.61.
2-(2-(Trifluoromethyl)phenyl)-1,2,4-triazine-3,5(2H,4H)-
dione (3g): Off white solid; m.p.: 127-132 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.76 (s, 1H), 7.71-7.58 (m, 3H), 7.46-
7.29 (m, 2H); 13C NMR (100 MHz, DMSO-d6) δ; 155.2, 147.8,
135.4, 134.4, 128.78, 128.74, 128.66, 125.15, 125.12, 125.09,
125.05, 121.76, 121.73, 121.70, 117.41, 117.22, 116.84, 116.66;
HRMS (ESI) m/z: calcd. for C10H6N3O2F3 [M+H]+ 257.0407,
found 257.0412;Anal. Calcd. C10H6N3O2F3: C, 46.70; H, 2.35;
N, 16.34; Found: C, 46.74; H, 2.37; N, 16.37.
2-(6-Methoxypyridin-3-yl)-1,2,4-triazine-3,5(2H,4H)-
dione (3i): Off white solid; m.p.: 230-234 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.69 (s, 1H), 8.13 (d, 1H, J = 2.4 Hz),
7.68 (dd, 1H, J = 11.2 Hz, 2.4 Hz), 7.63 (s, 1H), 6.95 (d, 1H,
J = 8.8 Hz), 3.88 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ
163.1, 156.3, 149.0, 146.2, 139.3, 135.2, 123.7, 110.6, 53.55;
HRMS (ESI) m/z: calcd. for C9H8N4O3 [M+H]+ 220.0592,
found 220.0572; Anal. Calcd. C9H8N4O3: C, 49.09; H, 3.66;
N, 25.45; Found: C, 49.13; H, 3.63; N, 25.49.
2-(3-Acetylphenyl)-1,2,4-triazine-3,5(2H,4H)-dione
(3j): Off white solid; m.p.: 174-177 °C; 1H NMR (400 MHz,
DMSO-d6) δ 12.69 (s, 1H), 8.05-8.03 (m, 1H), 8.02 (d, 1H, J
= 1.6 Hz), 7.95 (t, 1H, J = 4.0 Hz), 7.68-7.62 (m, 2H), 2.59 (s,
3H); 13C NMR (100 MHz, DMSO-d6) δ 155.2, 147.9, 137.4,
134.4, 132.0, 128.3, 127.7, 127.6, 124.3, 19.71; HRMS (ESI)
m/z: calcd. for C11H9N3O3 [M+H]+ 231.0638, found 231.0619;
Anal. Calcd. C11H9N3O3: C, 57.14; H, 3.92; N, 18.17; Found:
C, 57.17; H, 3.96; N, 18.12.
2-(6-Methylpyridin-3-yl)-1,2,4-triazine-3,5(2H,4H)-
dione (3k): Off white solid; m.p.: 173-177 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.68 (s, 1H), 8.11 (d, 1H, J = 2.4 Hz),
7.67 (dd, 1H, J = 11.2 Hz, 2.4 Hz), 7.61 (s, 1H), 6.93 (d, 1H,
J = 8.8 Hz); 13C NMR (100 MHz, DMSO-d6) δ 162.7, 155.9,
148.6, 145.8, 138.9, 134.8, 123.2, 110.2, 53.15; HRMS (ESI)
m/z: calcd. for C9H8N4O2 [M+H]+ 204.0643, found 204.0637;
Anal. Calcd. C9H8N4O2: C, 52.94; H, 3.95; N, 27.44; Found:
C, 52.98; H, 3.93; N, 27.48.
2-(4-Chlorophenyl)-1,2,4-triazine-3,5(2H,4H)-dione
1
(3l) [11]: Off white solid; m.p.: 231-235 °C; H NMR (300
MHz, DMSO-d6) δ 12.56 (s, 1H), 7.82 (d, 2H, J = 8.4 Hz),
7.48 (s, 1H), 7.42 (d, 2H, J = 8.0 Hz); 13C NMR (100 MHz,
DMSO-d6) δ 155.3, 147.9, 136.1, 134.6, 128.89, 128.59,
128.27, 125.32, 125.28, 124.5, 121.8; HRMS (ESI) m/z: calcd.
for C9H6N3O2Cl [M+H]+ 223.0144, found 223.0124; Anal.
Calcd. C9H6N3O2Cl: C, 48.34; H, 2.70; N, 18.79; Found: C,
48.38; H, 2.76; N, 18.74.
2-(3-(Trifluoromethyl)phenyl)-1,2,4-triazine-3,5(2H,4H)-
dione (3m) [11]: Off white solid; m.p.: 123-127 °C; 1H NMR
(300 MHz, DMSO-d6) δ 12.50 (s, 1H), 7.93-7.85 (m, 2H),
7.77-7.72 (m, 2H), 7.67 (s, 1H); 13C NMR (100 MHz, DMSO-
d6) δ 157.1, 149.7, 137.9, 136.4, 130.7, 130.4, 130.0, 127.1,
127.0,126.7, 126.3, 123.6; HRMS (ESI) m/z: calcd. for
C10H6N3O2F3 [M+H]+ 257.0407, found 257.0412;Anal. Calcd.
C10H6N3O2F3: C, 46.70; H, 2.35; N, 16.34; Found: C, 46.74;
H, 2.37; N, 16.37.
3-(3,5-Dioxo-4,5-dihydro-1,2,4-triazin-2(3H)-yl)-
benzonitrile (3n) [11]: Off white solid; m.p.: 196-199 °C; 1H
NMR (400 MHz, DMSO-d6) δ 12.78 (s, 1H), 7.71 (s, 1H),
7.61-7.60 (m, 3H), 7.43-7.41 (m, 1H); 13C NMR (100 MHz,
DMSO-d6) δ 156.4, 149.1, 138.0, 136.0, 135.1, 133.6, 131.5,
130.4, 118.8, 112.2; HRMS (ESI) m/z: calcd. for C10H6N4O2
[M+H]+ 214.0486, found 214.0474; Anal. Calcd. C10H6N4O2:
C, 56.08; H, 2.82; N, 26.16; Found: C, 56.11; H, 2.87; N,
26.12.
2-(3,4-Dichlorophenyl)-1,2,4-triazine-3,5(2H,4H)-
dione (3o) [11]: Off white solid; m.p.: 224-227 °C; 1H NMR
(300 MHz, DMSO-d6) δ 12.78 (s, 1H), 7.79-7.78 (m, 1H),
7.68 (s, 1H), 7.59-7.58 (m, 2H); 13C NMR (100 MHz, DMSO-
2-m-Tolyl-1,2,4-triazine-3,5(2H,4H)-dione (3h) [24]:
Off white solid; m.p.: 134-136 °C; 1H NMR (300 MHz, DMSO-
d6) δ 12.63 (s, 1H), 7.59 (s, 1H), 7.38-7.33 (m, 1H), 7.24 (d,
1H, J = 7.8 Hz), 7.12-7.09 (m, 2H), 2.33(s, 3H); 13C NMR
(100 MHz, DMSO-d6) δ 156.3, 148.9, 138.4, 135.4, 133.0,
129.3, 128.7, 128.6, 125.3, 20.72; HRMS (ESI) m/z: calcd.
for C10H9N3O2 [M+H]+ 203.0690, found 203.0678; Anal.
Calcd. C10H9N3O2: C, 59.11; H, 4.46; N, 20.68; Found: C,
59.15; H, 4.48; N, 20.64.

Vol. 30, No. 11 (2018)
Mild and Efficient Copper-Mediated N-Arylation of 6-Azauracil with Corresponding Boronic Acids 2499
d6) δ 155.4, 148.0, 134.7, 133.8, 132.2, 129.8, 128.1, 127.8,
126.7; HRMS (ESI) m/z: calcd. for C9H5N3O2Cl2 [M+H]+
256.9754, found 256.9743; Anal. Calcd. C9H5N3O2Cl2: C,
41.89; H, 1.95; N, 16.28; Found: C, 41.86; H, 1.98; N, 16.25.
2-(2-Chlorophenyl)-1,2,4-triazine-3,5(2H,4H)-dione
(3p): Off white solid; m.p.: 213-216 °C; 1H NMR (300 MHz,
DMSO-d6) δ 12.39 (s, 1H), 7.81-7.73 (m, 2H), 7.66-7.61 (m,
2H), 7.56 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ 155.2,
147.8, 134.4, 133.6, 132.0, 129.6, 127.9, 127.6, 126.5; HRMS
(ESI) m/z: calcd. for C9H6N3O2Cl [M+H]+ 223.0144, found
223.0149; Anal. Calcd. C9H6N3O2Cl: C, 48.34; H, 2.70; N,
18.79; Found: C, 48.38; H, 2.76; N, 18.74.
2-(3,5-Dioxo-4,5-dihydro-1,2,4-triazine-2(3H)-yl)-
benzonitrile (3q): Off white solid; m.p.: 196-199 °C; 1H NMR
(300 MHz, DMSO-d6) δ 12.47 (s, 1H), 7.90-7.82 (m, 2H),
7.74-7.64 (m, 2H), 7.63 (s, 1H); 13C NMR (100 MHz, DMSO-
d6) δ 154.1, 146.8, 135.7, 133.7, 132.8, 131.3, 128.1, 116.5,
109.9; HRMS (ESI) m/z: calcd. for C10H6N4O2 [M+H]+
214.0486, found 214.0481;Anal. Calcd. C10H6N4O2: C, 56.08;
H, 2.82; N, 26.16; Found: C, 56.11; H, 2.87; N, 26.12.
2-(2-Chloropyridin-4-yl)-1,2,4-triazine-3,5(2H,4H)-
dione (3r): Off white solid; m.p.: 202-205 °C; 1H NMR (400
MHz, DMSO-d6) δ 12.66 (s, 1H), 8.10 (d, 1H, J = 2.4 Hz),
7.66 (dd, 1H, J = 11.2 Hz, 2.4 Hz), 7.59 (s, 1H), 6.91 (d, 1H,
J = 8.8 Hz); 13C NMR (100 MHz, DMSO-d6) δ 163.3, 156.6,
149.2, 146.4, 139.5, 123.9, 110.8, 53.77; HRMS (ESI) m/z:
calcd. for C8H5N4O2Cl [M+H]+ 224.0096, found 224.0072;
Anal. Calcd. C8H5N4O2Cl: C, 42.78; H, 2.24; N, 24.94; Found:
C, 42.75; H, 2.27; N, 24.91.
filtered and washed with water. The crude product was recrys-
tallized from ethanol to afford the 2-(3,5-dichlorophenyl)-3,5-
dioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carbonitrile (7) as an
1
off white solid. (1.10 g, 85 %). m.p.: 234-236 °C; H NMR
(300 MHz, DMSO-d6) δ 13.32 (bs, 1H), 7.78-7.74 (m, 3H);
MS (MM) m/z 280.9 [M–H]–; Anal. Calcd. C10H4N4O2Cl2: C,
42.43; H, 1.42; N, 19.79; Found: C, 42.40; H, 1.45; N, 19.74.
2-(3,5-Dichlorophenyl)-3,5-dioxo-2,3,4,5-tetrahydro-
1,2,4-triazine-6-carboxylic acid (8): 6 N HCl in 1,4-dioxane
(10 mL) was added to the 2-(3,5-dichlorophenyl)-3,5-dioxo-
2,3,4,5-tetrahydro-1,2,4-triazine-6-carbonitrile (7) (1.00 g,
3.54 mmol) at room temperature. The resulting suspension
was stirred for 110 °C for 16 h. After completion of starting
material by TLC analysis (90:10 dichloromethane/methanol)
the reaction mixture was poured into water. The solids were
filtered and washed with water. The crude product was recrys-
tallized from ethanol to afford the 2-(3,5-dichlorophenyl)-3,5-
dioxo-2,3,4,5-tetrahydro-1,2,4-triazine-6-carboxylic acid (8)
1
as an off white solid. (0.76 g, 71 %). m.p.: 257-259 °C; H
NMR (300 MHz, DMSO-d6) δ 7.89-7.85 (m, 2H), 7.74-7.72
(m, 1H); MS (MM) m/z 299.9 [M–H]–; Anal. Calcd.
C10H5N3O4Cl2: C, 39.76; H, 1.67; N, 13.91; Found: C, 39.72;
H, 1.63; N, 13.95.
2-(3,5-Dichlorophenyl)-1,2,4-triazine-3,5(2H,4H)-
dione (9): To a solution of 2-(3,5-dichlorophenyl)-3,5-dioxo-
2,3,4,5-tetrahydro-1,2,4-triazine-6-carboxylic acid (8) (0.50
g, 1.66 mmol) in toluene (5.0 mL) was added 2-mercaptoacetic
acid (0.10 mL) at room temperature. The resulting solution
was stirred for 120 °C for 2 h. After completion of starting
material by TLC analysis (80:20 hexanes/ethyl acetate) then
the reaction mixture was poured into water. The solids were
filtered and washed with water. The crude product was recrys-
tallized from toluene to afford to afford the 2-(3,5-dichloro-
phenyl)-1,2,4-triazine-3,5(2H,4H)-dione (9) as an off white
solid. (0.35 g, 83 %). m.p.: 142-146 °C; 1H NMR (300 MHz,
DMSO-d6) δ 12.75 (s, 1H), 7.76-7.75 (m, 1H), 7.65 (s, 1H),
7.557 (s, 1H), 7.551 (s, 1H); 13C NMR (100 MHz, DMSO-d6)
δ 155.7, 148.4, 135.0, 134.1, 132.6, 130.2, 128.50, 128.25,
127.12; HRMS (ESI) m/z: calcd. for C9H5N3O2Cl2 [M+H]+
256.9754, found 256.9742; Anal. Calcd. C9H5N3O2Cl2: C,
41.89; H, 1.95; N, 16.28; Found: C, 41.86; H, 1.98; N, 16.25
Antibacterial activity: Antibacterial activity of all the
synthesized compounds was screened by Agar well diffusion
method, as recommended by the National Committee for Clinical
Laboratory standards against Gram-positive bacteria such as
Staphylococcus aureus (NCIM 2079) and Gram-negative
bacteria Escherichia coli (NCIM 2068) at two concentrations
100 and 200 µg/mL. The obtained results were compared with
standard drug chloramphenicol. The fresh culture of bacteria
is obtained by inoculating bacteria into nutrient broth media
and incubated at 37 °C for 24 h. This culture mixed with nutrient
agar media was poured into petri dishes under aseptic condi-
tions. After solidification of media, bores are made by using
sterile cork borer (8 mm diameter). Into these cups, standard
drug and synthesized drugs are introduced; the plates were
placed in the refrigerator at 100 °C for proper diffusion of
drugs into the media.After 2 h, the petri plates were transferred
to an incubator and maintained at 37 2 °C for 24 h. After the
Experimental procedure for the compound 9 in a tradi-
tional method.
(E)-Ethyl 2-cyano-2-(2-(3,5-dichlorophenyl)hydrazono)-
acetylcarbamate (6): 6 N Hydrochloric acid (10 mL) was
added to 3,5-dichloroaniline (4) (1 g, 6.21 mmol) at a 10 °C.
The resulting slurry was cooled to 5 °C in an ice-bath and a
solution of sodium nitrite (0.42 g, 6.21 mmol) in water (2 mL)
was added at such a rate that the temperature does not rise
above 5 °C. Ethyl 2-cyanoacetylcarbamate (5) (0.96 g, 6.21 mmol)
and pyridine (10.0 mL) was added portion wise to the resulting
solution of the diazonium salt with vigorous stirring at 5 °C
and reaction mixture was raised to 5 °C and stirred at same tempe-
rature for 1 h. The solids were filtered and washed thoroughly
with water to remove alkaline impurities. The crude product
was recrystallized from toluene to afford (E)-ethyl 2-cyano-
2-(2-(3,5-dichlorophenyl)hydrazono)acetylcarbamate (6) as an
1
off white solid. (1.75 g, 86 %). m.p.: 194-196 °C; H NMR
(300 MHz, DMSO-d6) δ 12.16 (bs, 1H), 10.94 (s, 1H), 7.96-
7.72 (m, 3H), 4.20 (q, 2H), 1.26 (t, 3H, J = 7.2 Hz); MS (MM)
m/z 326.9 [M–H]–; Anal. Calcd. C12H10N4O3Cl2: C, 43.79; H,
3.06; N, 17.02; Found: C, 43.76; H, 3.09; N, 17.05.
2-(3,5-Dichlorophenyl)-3,5-dioxo-2,3,4,5-tetrahydro-
1,2,4-triazine-6-carbonitrile (7): To a solution of (E)-ethyl
2-cyano-2-(2-(3,5-dichlorophenyl)hydrazono)acetylcarbamate
(6) (1.50 g, 4.57 mmol) in acetic acid (15 mL) was added sodium
acetate (0.374 g, 4.57 mmol). The resulting reaction mixture
was stirred at 120 °C for 2 h. After completion of starting
material by TLC analysis (90:10 dichloromethane/methanol)
the reaction mixture was poured into water. The solids were

2500 Gulipalli et al.
Asian J. Chem.
incubation period, the petri plates were observed for the zone
of inhibition. The results are evaluated by comparing the zone
of inhibition shown by the synthesized compounds with standard
drug.
By utilizing the conditions that are employed to synthesize
3a, as shown in Scheme-II, several N-aryl 6-azouracils were
synthesized and showed in Table-1. Electron donating substi-
tuents on boronic acid afforded N-arylated products in good
yields at room temperature and pyridine as base, electron-with-
drawing substituents on boronic acids required 80 °C and triethyl
amine as base in order to proceed the reaction and afford in
relatively good yields.
The synthesized compounds were screened for their anti-
bacterial activity usingAgar well diffusion method [25] against
Escherichia coli (Gram-negative) and Staphylococcus aureus
(Gram-positive) strains. The screening data are shown inTable-3
indicated that the compounds 3b, 3g and 3m bearing trifluro-
methyl group showed significant antibacterial activity. The
introduction of chloro moiety on phenyl ring 3a, 3d, 3l and
3o exhibited more activity than fluorine containing compounds
3e and 3f. Remaining compounds were found to possess mode-
rate activity against Gram-positive and Gram-negative strains
when compared with standard drug chloramphenicol.
RESULTS AND DISCUSSION
The method used to synthesize derivatives of 6-azauracil
was shown in Scheme-II. Initially, the method was optimized
by the treatment of 6-azauracil with 3,5-dichlorophenyl boronic
acid in the presence of various copper sources, bases in DMF
as shown in Table-2. Among all of the conditions screened,
Cu(OAc)2 gives mono arylated product of 3a in good yield. In
addition, yield was improved furthermore when pyridine
was used as a base. With the higher equivalents of boronic
acid (~ 4 equiv) and increasing reaction temperature and time
(~ 12 h) resulted in large quantities of diaryl substitution. To
avoid diaryl products, boronic acid equivalents reduced to 1.1,
reaction temperature to room temperature and reaction time
to 2 h.
TABLE-3
H
ANTIBACTERIAL ACTIVITY OF THE
OH
B
O
N
O
H
N
O
O
Cu(OAc)2, Pyridine
DMF
TITLE COMPOUNDS (3a-3r)
+
OH
N
R
N
Zone of inhibition (mm)
HN
R
N
Escherichia coli
Gram-negative)
(conc. µg/mL)
Staphylococcus aureus
(Gram-positive)
1
2a-r
3a-r
Compound
Scheme-II: Reaction of 6-azauracil with phenylboronic acid
(conc. µg/mL)
100
16
26
9
17
13
14
25
12
8
200
19
29
10
19
15
17
28
15
12
13
14
21
28
13
17
19
15
16
30
100
18
23
11
18
14
15
22
8
200
23
27
15
21
15
18
26
17
16
15
19
20
27
13
25
21
15
13
29
TABLE-2
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
OPTIMIZATION OF CHAN-LAM COUPLING
TO ACCESS N-ARYL 6-AZAURACILa
Entry
Copper salt
CuI
Base
Et3N
Yieldb
15 %
18 %
N.R
N.R
N.R
N.R
80 %
81 %
1
2
3
4
5
6
7
8
CuI
CuBr
CuBr
Pyridine
Et3N
Pyridine
Et3N
Pyridine
Et3N
CuSO4
CuSO4
Cu(OAc)2
Cu(OAc)2
10
9
7
12
18
24
8
15
16
11
10
27
14
19
23
10
18
17
13
12
25
Pyridine
aReactions were performed with 6-azauracil 1 (1.0 mmol), Copper salt
(1.0 mmol), base (2.0 mmol), arylboronic acid 2 (1.1 mmol), DMF (10
mL) at room temperature for 2 h; bIsolated yield; N.R. = No reaction
In this method confirmation of exact position of arylation
is crucial as there is a chance of N-arylation at 3-N position.
In order to confirm the substituted position, we have synthe-
sized compound 3a using a traditional method as shown in
Scheme-I, where 3,5-dichloroaniline was treated with sodium
nitrite in presence of 6 N HCl to get the diazonium salt which
was then treated with ethyl (2-cyanoacetyl)carbamate (5) to
get the intermediate 6. The intermediate 6 was refluxed in acetic
acid in presence of sodium acetate to afford 1-(3,5-dichloro-
phenyl)-5-cyano-6-azauracil (7). The cyano group of compound
7 was hydrolyzed with 6N HCl in 1,4-dioxane to get the acid
compound 8. Decarboxylation of compound 8 was carried out
in 2-mercaptoacetic acid to afford the 1-(3,5-dichlorophenyl)-
6-azauracil (3a). The NH proton at N-3 position of 6-azouracils
prepared in both routes has showed same δ ppm values in 1H
NMR at δ12.6 ppm, which has confirmed unambiguously the
compound 3a prepared in both the routes are same.
3q
3r
Chloramphenicol
Conclusion
An efficient and mild synthetic procedure for the synthesis
of N-aryl 6-azauracil derivatives starting from corresponding
boronic acids was described and the position of N-arylation
for obtained N-aryl 6-azouracils were confirmed by 1H NMR
spectra of the same compound that was synthesized in tradi-
tional method.As it is a convenient and cost-effective method,
this can be utilized in the manipulations of 6-azauracil deriva-
tives to develop drugs based on azauracils. The synthesized
compounds were screened for their antibacterial activity using
agar well diffusion method against Escherichia coli and
Staphylococcus aureus strains. Most of the tested compounds
have shown moderate to good antibacterial activity.

Vol. 30, No. 11 (2018)
Mild and Efficient Copper-Mediated N-Arylation of 6-Azauracil with Corresponding Boronic Acids 2501
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The authors thank the Management of AMRI Hyderabad
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research. The authors are also thankful to Sai Innotech Labs
Pvt. Ltd. for providing synthesis facilities.
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CONFLICT OF INTEREST
The authors declare that there is no conflict of interests
regarding the publication of this article.
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