Cu-mediated N-arylation of 1,2,3-triazin-4-ones: Synthesis of fused triazinone derivatives as potential inhibitors of chorismate mutase

Article abstract of DOI:10.1016/j.bmcl.2011.11.096

A rapid and direct access to N-aryl substituted fused triazinone derivatives has been accomplished via N-arylation of 1,2,3-triazin-4-one ring involving a Cu-mediated coupling between triazinone derivatives and aryl boronic acids. A combination of Cu(OAc)

Full text of DOI:10.1016/j.bmcl.2011.11.096

Bioorganic & Medicinal Chemistry Letters 22 (2012) 1146–1150
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Bioorganic & Medicinal Chemistry Letters
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Cu-mediated N-arylation of 1,2,3-triazin-4-ones: Synthesis of fused
triazinone derivatives as potential inhibitors of chorismate mutase
K. Shiva Kumar a, Raju Adepu a, Sandhya Sandra a, D. Rambabu a, G. Rama Krishna b, C. Malla Reddy b,
Parimal Misra a, Manojit Pal a,
⇑
a Institute of Life Sciences, University of Hyderabad Campus, Gachibowli, Hyderabad 500 046, India
b Department of Chemical Sciences, Indian Institute of Science Education and Research, Kolkata, West Bengal 741252, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A rapid and direct access to N-aryl substituted fused triazinone derivatives has been accomplished via N-
arylation of 1,2,3-triazin-4-one ring involving a Cu-mediated coupling between triazinone derivatives
and aryl boronic acids. A combination of Cu(OAc)2–Et3N in 1,2-dichloroethane was found to be effective
and various fused triazinone derivatives have been prepared by using this methodology. Molecular struc-
ture of a representative compound was confirmed by single crystal X-ray diffraction study. The scope and
limitations of this reaction is discussed. Some of the compounds synthesized were tested for chorismate
mutase inhibitory properties in vitro. The in vitro dose response study of an active compound is
presented.
Received 14 September 2011
Revised 4 November 2011
Accepted 24 November 2011
Available online 2 December 2011
Keywords:
1,2,3-Triazin-4-one
Copper
Ó 2011 Elsevier Ltd. All rights reserved.
Coupling
Chorismate mutase
1,2,3-Triazin-4-ones being integral part of many bioactive
agents represent an important class of nitrogen containing hetero-
cycle and have attracted particular attention in the area of bioor-
ganic and medicinal chemistry.1 This is exemplified by a range of
pharmacological properties reported for this class of compounds
that include sedative,2 diuretic,3 anesthetic,4 antiarthritic5 and
antitumor activities.6 Indeed, the replacement of the pteridyl moi-
ety of folic acid with 1,2,3-benzotriazin-4-ones was achieved with-
out affecting its antitumor activity.6 Notably, not much known
about antitubercular properties of this class of compounds. Despite
the availability of a range of effective antibacterial agents, tubercu-
losis still remains a leading cause of death worldwide due to a
number of factors such as (a) long treatment duration (6–
9 months), (b) increased incidence of (multi or extensive) drug
resistance, (c) co-morbidity with HIV-AIDS and (d) declined effort
in anti-infective drug discovery research. Thus, discovery, develop-
ment and introduction of new treatments for tuberculosis require
immediate attention. Shikimate pathway for the biosynthesis of
aromatic amino acids such as phenylalanine and tyrosine involve
the Claisen rearrangement of chorismate to prephenate in the
presence of chorismate mutase or CM (EC 5.4.99.5). Due to the ab-
sence of this pathway in animals but not in bacteria CM is consid-
ered as an attractive target for the identification of effective
antibacterial agents.7 However, to our knowledge only few small
molecules8 have been reported as inhibitors of CM including the
2,3-diaryl acrylic acid A (Fig. 1). Our continuing interest8d,e in the
identification of novel small molecules as inhibitors of CM
prompted us to design the triazinone C from A via quinolone B
(Fig. 1). Herein we report for the first time the CM inhibitory prop-
erties of 1,2,3-triazin-4-one derivatives synthesis of which has
been carried out via a Cu-mediated N-arylation methodology.
Preparation of N-arylated 1,2,3-triazin-4-one derivatives usu-
ally involves the construction of the six-membered 1,2,3-triazin-
4-one ring9 with an aryl group at N-3 via a multi-step process or
a single-step N-arylation of 1,2,3-triazin-4-one ring at N-3 position
under Ullmann-type conditions10 (Scheme 1). However, all these
methods require tedious steps along with harsh reaction condi-
tions whereas Ullmann condensation of 1,2,3-benzotriazin-4-one
with iodobenzene provided the desired product only in 14%
yield.10 Moreover, only one example of N-arylation of 1,2,3-benzo-
triazin-4-one has been studied so far.
Copper promoted C–N bond formation between NH containing
heterocycles and organometalloids via cross coupling reactions
have emerged as a powerful synthetic tool for the generation of
N-(hetero)aryl derivatives.11 This efficient methodology is charac-
terized by mild reaction conditions for example the use of ambient
temperature, weaker base and the presence of air. A number of
extensions and applications of this methodology have been
reported.12,13 Notably, the use of 1,2,3-triazin-4-ones for successful
N-arylation by using this methodology is not common. In
continuation of our effort in the synthesis of bioactive molecules
via Cu-mediated reactions we became interested in generating a
small-molecule library based on 1,2,3-triazin-4-one scaffold where
⇑
Corresponding author. Tel.: +91 40 6657 1500; fax: +91 40 6657 1581.
E-mail addresses: manojitp@ilsresearch.org, manojitpal@rediffmail.com (M. Pal).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.11.096

K. Shiva Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1146–1150
1147
Cl
O
Cl
O
O
N
Ar
HO
N
N
Aryl /
MeO
MeO
Hetaryl
N
H
NO2
C
B
A
Figure 1. Design of novel inhibitors of chorismate mutase.
Table 1
O
O
N
Effect of reaction conditions on Cu-mediated coupling of 1a with 2aa
Ar
CO2R
NH2
c.f . Ref 9
Ref 10
NH
N
N
N
O
O
Cu salt
Solvent
N
N
N
NH
N
+
PhB(OH)2
Et3N
RT, air
Scheme 1. Reported synthetic approaches to N-arylation of 1,2,3-benzotriazin-4-
N
N
ones.
3a
2a
1a
Entry
Cu salts
Solvent
Time (h)
Yieldb (%)
Cu-mediated N-arylation was used as a key synthetic step. Thus,
aryl boronic acids were coupled with various 1,2,3-triazin-4-ones
in the presence of a Cu-salt (Scheme 2) to give the corresponding
N-arylated products. The preliminary results of this study are
presented.
1
3
3
4
5
6
7
8
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OTf)2
CuI
CH2Cl2
DMF
DCE
THF
DCE
DCE
DCE
DCE
3.0
3.0
1.0
4.0
3.0
2.5
4.0
6.0
80
70
90
70
75
75
60
50
Initially, the coupling of benzo[d][1,2,3]triazin-4(3H)-one (1a)
with phenyl boronic acid (2a, 1.5 equiv) was used to establish
the optimized reaction conditions. Thus 1a and 2a was reacted in
the presence of a number of Cu-salts in various solvents using
Et3N as a base at room temperature under anhydrous conditions
(Table 1). All the reactions were carried out in the presence of
air. The desired product that is 3-phenylbenzo[d][1,2,3]triazin-
4(3H)-one14 (3a) was isolated in 80% yield when Cu(OAc)2 (anhy-
drous) was used in dichloromethane (DCM) (Table 1, entry 1).
The reaction was completed within 3 h. The yield was decreased
marginally when DMF was used in place of DCM (Table 1, entry
2) but increased to 90% when 1,2-dichloroethane (DCE) was em-
ployed (Table 1, entry 3). The reaction was completed within 1 h
in DCE. The use of THF decreased the product yield (Table 1, entry
4). We then examined the use of other Cu-salts such as Cu(OTf)2,
CuI, and CuBr (Table 1, entries 5–7). While Cu(OTf)2 and CuI was
found to be equally effective the other salt was found to be inferior
in terms of product yields. Notably, a sharp decrease in yield was
observed when Cu(OAc)2ÁH2O was used as catalyst indicating
moisture sensitive nature of this methodology (Table 1, entry 8).
Overall, the combination of anhydrous Cu(OAc)2 and Et3N in DCE
was found to be optimum for the present N-arylation reaction.
Having established the optimum condition, we then decided to
examine the reactivity of other 1,2,3-triazin-4-ones with a variety
of aryl boronic acids. Accordingly, a number of boronic acids (2)
were reacted with 1 and the results are summarized in Table 2.
The reaction proceeded well irrespective of aryl (1a) or heteroaryl
(1b–c) moiety fused with 1,2,3-triazin-4-one ring. Thus 4,5,6,7-tet-
rahydrobenzothieno[2,3-d][1,2,3]triazin-4(3H)-one15 (1b) and 5-
CuBr
Cu(OAc)2ÁH2O
aAll the reactions were carried out using 1a (1.0 mmol), 2a (1.5 mmol), a Cu-salt
(1.0 mmol) and Et3N (2.0 mmol) in a solvent (10–15 mL) at room temperature
under anhydrous conditions in the presence of air (DCE = 1,2-dichloroethane).
b
Isolated yield.
methyl-7-propyl-3H-pyrazolo[4,3-d][1,2,3]triazin-4(5H)-one (1c)
were employed successfully to afford the desired products 3e–3l
in good yields (Table 2, entries 5–12). The presence of Cl, F and
MeO group in aryl boronic acids were well tolerated and the use
of naphthalen-2-ylboronic acid (entries 4, 8 and 12) was found to
be effective. However, no desired product was isolated when a het-
eroaryl boronic acid such as pyridin-2-yl boronic acid was reacted
with 1b under the reaction condition employed. Moreover, the use
of an alkyl boronic acid such as cyclopropylboronic acid was also
found to be ineffective in the present C–N bond forming reaction.
All the compounds synthesized were well characterized by spectral
data (NMR, MS and IR). Additionally, the molecular structure of a
representative compound 3e was established unambiguously by
single crystal X-ray diffraction study (Fig. 2).16
Some of the compounds synthesized were tested for CM inhib-
iting properties in vitro. The assay17,18 involved determination of
activity of enzyme CM which catalyzes the conversion of choris-
mate to prephenate. Thus determination of activity of CM is based
on the direct observation of conversion of chorismic acid to pre-
phenate spectrophotometrically at OD274. This reaction was per-
formed in the presence of test compounds to determine their CM
inhibiting activities. A known inhibitor of CM that is 4-(3,5-
dimethoxyphenethylamino)-3-nitro-5-sulfamoylbenzoic
was prepared and used as a reference compound the IC50 value
of which was found to be less than 10 M. Compounds 3d, 3h,
and 3l showed significant inhibition of CM in compared to other
molecules when tested at 50 M (Table 3) indicating the impor-
tance of naphthyl ring present in these molecules in CM inhibition.
Moreover, the maximum inhibition shown by the compound 3l
suggested that the pyrazole ring played a key role in CM inhibition.
The compound 3l showed dose dependent inhibition with an IC50
acid8a
O
N
O
N
Ar
H
HO
OH
l
Cu(OAc)2
N
N
N
N
B
Ar
2
Aryl /
Aryl /
+
Hetaryl
Hetaryl
ClCH2CH2Cl
RT
l
3
1
Scheme 2. Cu-mediated coupling of 1,2,3-triazin-4-ones (1) with arylboronic acids
(2).
value of 15.13 0.95 lM (Fig. 3).

1148
K. Shiva Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1146–1150
Table 2
Synthesis of N-aryl substituted fused triazinone derivatives (3) via Cu(OAc)2 mediated C–N bond forming reaction between 1 and 2 (Scheme 2)a
Entry
1,2,3-triazin-4-ones (1)
ArB(OH)2 (2)
Products (3)
Time (h)
Yieldb (%)
O
OH
HO
O
B
NH
N
N
N
1
1.0
90
N
N
1a
2a
3a
OH
F
HO
B
O
N
N
2
1a
1.0
90
N
3b
F
2b
OH
Cl
HO
B
O
N
3
1a
1.5
90
N
N
Cl
2c
3c
OH
B
OH
O
N
4
5
6
1a
1.5
1.0
2.0
85
85
81
N
N
2d
3d
O
F
O
NH
N
1b
N
N
2b
S
N
S
S
N
3e
1b
OH
OCH3
HO
B
O
1b
N
N
OCH3
N
3f
2e
Cl
O
7
8
1b
1b
2c
1.5
1.5
90
80
N
N
S
S
N
3g
O
N
N
2d
N
3h
N
N
N
NH
N
N
N
1c
N
9
2a
1.0
84
N
N
O
O
1c
3i

K. Shiva Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1146–1150
1149
Table 2 (continued)
Entry
1,2,3-triazin-4-ones (1)
ArB(OH)2 (2)
Products (3)
Time (h)
Yieldb (%)
N
N
N
N
10
1c
2b
1.0
86
N
O
F
3j
N
N
N
N
11
1c
2c
1.5
90
Cl
N
O
3k
N
O
N
N
N
12
1c
2d
1.5
88
N
3l
a
All the reactions were carried out using 1 (1.0 mmol), 2 (1.5 mmol), a Cu(OAc)2 (1.0 mmol) and Et3N (2.0 mmol) in DCE (10–15 mL) at room temperature under anhydrous
conditions in the presence of air.
b
Isolated yield.
Figure 2. ORTEP representation of the 3e (Thermal ellipsoids are drawn at 50% probability level).
Table 3
Inhibition of chorismate mutase by triazinones in vitro
Entry
Triazinones (3)
% Inhibitiona @ 50
lM
1
3
3
4
5
6
7
8
3a
3d
3e
3h
3i
3j
3k
3l
12
40
25
37
10
24
30
61
a
Average of three experiments.
In conclusion, a mild and efficient method has been developed for
direct N-arylation of 1,2,3-triazin-4-one ring which involves a
Cu-mediated coupling reaction between triazinone derivatives and
aryl boronic acids. Among all the Cu-salts tested Cu(OAc)2 was iden-
tified as the best catalyst and a combination of Cu(OAc)2–Et3N–DCE
was found to be optimum. A number of N-aryl substituted fused
Figure 3. Dose dependent inhibition of CM by compound 3l

1150
K. Shiva Kumar et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1146–1150
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tally simple and ligand-free process within short period of time and
molecular structure of a representative compound was confirmed
by single crystal X-ray diffraction study. The reaction however, did
not work with heteroaryl and alkyl boronic acids. Some of the com-
pounds synthesized were tested for chorismate mutase inhibitory
properties in vitro. The in vitro dose response study of an active com-
pound has been presented. Overall, this research has provided a ra-
pid and direct access to a library of compounds based on N-aryl
substitutedfused triazinone whichhas been identifiedas a new scaf-
fold for the development of novel inhibitors of chorismate mutase
for the potential treatment of tuberculosis.
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Acknowledgments
The authors thank Professor Seyed E. Hasnain and Professor J.
Iqbal for encouragement and DBT, New Delhi, India for financial
support (Grant NO BT/01/COE/07/02). KS thanks UGC, New Delhi,
India for a Dr. D. S. Kothari Post doctoral fellowship [No.F.4-2/
2006(BSR)/13-324/2010(BSR)]. RA thanks CSIR, New Delhi, India
for a Junior Research Fellowship.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.11.096.
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