Three-component, one-pot synthesis of novel 2,4-substituted 5-azolylthiopyrimidine library for screening against anti-influenza virus A

Article abstract of DOI:10.1016/j.bmcl.2007.11.117

A novel one-pot synthesis of 2,4-substituted 5-azolylthiopyrimidines is achieved by sequential Michael-addition of 3-iodochromones with mercaptoazole (or mercaptotriazoles) and then condensation with a variety of amidines. Compound A₁B₆

Full text of DOI:10.1016/j.bmcl.2007.11.117

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Bioorganic & Medicinal Chemistry Letters 18 (2008) 1177–1180
Three-component, one-pot synthesis of novel 2,4-substituted
5-azolylthiopyrimidine library for screening against
anti-influenza virus A
Gang Cheng, Shukun Li, Jingya Li and Youhong Hu*
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, China
Received 31 July 2007; revised 26 October 2007; accepted 30 November 2007
Available online 4 December 2007
Abstract—A novel one-pot synthesis of 2,4-substituted 5-azolylthiopyrimidines is achieved by sequential Michael-addition of 3-
iodochromones with mercaptoazole (or mercaptotriazoles) and then condensation with a variety of amidines. Compound
A1B6C1 exhibits a potent anti-influenza virus A activity with an IC50 value of 21.56 mg/mL and SI value of 9.
Ó 2007 Elsevier Ltd. All rights reserved.
Pyrimidine is widely found as a core structure in a large
variety of compounds that exhibit important biological
activity.1 The use of combinatorial approaches to the
high-throughput synthesis of this drug-like scaffold
would be a powerful advance in helping to speed up
drug discovery. Recently we have developed efficient
methods to generate heterocycle library by three-compo-
nent one-pot reaction.2 Since antiviral activity can be
associated with the presence of nitrogen heterocycle
(pyrimidine derivatives)3 or bis-heterocycle com-
pounds,4 this strategy leads us to explore the convenient
methodology to construct novel bis-heterocycle library
containing pyrimidine scaffold for antiviral screening.
Here, we report a combinatorial synthesis of 2,4-substi-
tuted-5-azolylthiopyrimidine library using a sequential
three-component, one-pot reaction and its anti-influenza
virus activity.
nucleophilic substitution of 5-iodopyrimidine with thiols
using copper, palladium chemistry or harsh condition.7
Initially, a consecutive one-pot process of iodochro-
mones (A-1), mercaptoazole (C-1), and acetamidine (B-
2) in the presence of K2CO3 as base in DMF only gave
the product D which is the directly condensed product
of iodochromone with acetamidine (Scheme 1, Eq. 1).
Refluxing of the mixture could not generate the desired
product (A1B1C1). This indicates acetamidine is a stron-
ger nucleophile than mercaptoazole. Then a sequential
process was applied. Iodochromone was first reacted
with mercaptoazole, followed by addition of acetamidine
to give the desired product (A1B1C1) in 68% yield
(Scheme 1, Eq. 2).8 Solvent systems were investigated,
THF and CH3CN as solvent led to low yields.
Through this powerful procedure, the bis-heterocycles
library containing pyrimidine scaffold can be generated
by parallel split-pool protocol. First a 18-compound li-
brary was synthesized by 2 different iodochromones, 9
amidines, and mercaptoazole in moderate to excellent
yield (Fig. 1).
According to Yokoe’s method,5 3-azolylthiochromone
E could be readily prepared by treatment of 3-iodochr-
omone with mercaptoazole under the basic conditions
(K2CO3). We envision the resulting 3-azolylthiochro-
mone E as 1,3-diketone equivalent6 could be further
condensed with amidines in situ to form 2,4-substi-
tuted-5-azolylthiopyrimidines. This protocol avoids the
Among them, we selected the universal compounds to
evaluate for inhibition of influenza virus H3N2 (A3 Chi-
na/15/90) replication in Madin-Darby canine Kidney
(MDCK) cells.9 The result is given in Table 1. Aryl sub-
stitutions of pyrimidine at 2-position did not show the
activity. Compounds A1B2C1 and A1B6C1 exhibit the
activity against influenza A virus, with IC50 values of
Keywords: One-pot synthesis; Michael-addition; Condensation;
5-Azolylthiopyridines; Heterocycle libraries; Anti-influenza.
*
Corresponding author. E-mail: yhhu@mail.shcnc.ac.cn
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.11.117

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G. Cheng et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1177–1180
O
O
I
HS
4 eq. K2CO3
DMF, rt
OH
N
N
N
NH
NH2
B-2
+
+
equation 1
N
I
A-1
C-1
D
O
O
O
I
I
H
HS
4 eq. K2CO3
DMF, rt
N
N
+
S
N
N
S
O
O
N
O
C-1
A-1
N
NH
NH2
OH
N
N
O
S
N
B-2
equation 2
N
S
N
O
rt
N
A1B2C1
E
Scheme 1. Sequential one-pot synthesis of 5-azolylthiopyrimidine.
A2B1C1 R1 = CH3O, R2 = H,
A2B2C1 R1 = CH3O, R2 = CH3,
A2B3C1 R1 = CH3O, R2 = C6H5,
A2B4C1 R1 = CH3O, R2 = 4-pyridinyl, 90%
A2B5C1 R1 = CH3O, R2 = 4-ClC6H4, 85%
A2B6C1 R1 = CH3O, R2 = tert-butyl, 91%
A2B7C1 R1 = CH3O, R2 = 4-NH2C6H4, 89%
A2B8C1 R1 = CH3O, R2 = methylthio, 40%
94%
85%
89%
A1B1C1 R1 = H, R2 = H,
85%
68%
54%
R2
A1B2C1 R1 = H, R2 = CH3,
A1B3C1 R1 = H, R2 = C6H5,
A1B4C1 R1 = H, R2 = 4-pyridinyl, 95%
A1B5C1 R1 = H, R2 = 4-ClC6H4, 19%
OH
R1
N
N
N
S
A1B6C1 R1 = H, R2
= tert-butyl, 70%
N
A1B7C1 R1 = H, R2 = 4-NH2C6H4, 60%
A1B8C1 R1 = H, R2 = methylthio, 48%
A2B9C1 R1 = CH3O, R2 = NH2,
70%
A1B9C1 R1 = H, R2 = NH2,
92%
Figure 1. First 18-compound library.
Table 1. Anti-influenza virus A, B activity and cytotoxicity of substituted pyrimidines in MDCK cellsa
R2
OH
R1
N
N
R3
b
CC50 (mg/mL)
Compound
Substituent
R2
Virus A
Virus B
R1
H
R3
c
IC50 (mg/mL)
c
IC50 (mg/mL)
N
N
CH3
A1B2C1
CH3
577.35
258.69
—
S
( C1)
C1
C1
C1
C1
C1
C1
C1
C1
C1
C1
A1B3C1
A1B4C1
A1B5C1
A1B6C1
A1B7C1
A1B9C1
A2B1C1
A2B6C1
A2B8C1
A3B6C1
H
C6H5
120.19
64.67
80.12
—
—
—
—
H
4-Pyridinyl
4-ClC6H4
tert-Butyl
4-NH2C6H4
NH2
H
—
—
—
H
194.01
80.12
21.56
—
—
H
—
—
H
388.03
618.39
115.56
7.19
CH3O
CH3O
CH3O
Cl
H
—
—
—
—
tert-Butyl
Methylthio
tert-Butyl
—
—
86.23
111.11
48.74

G. Cheng et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1177–1180
1179
Table 1 (continued)
b
CC50 (mg/mL)
Compound
Substituent
R2
Virus A
Virus B
R1
R3
c
IC50 (mg/mL)
c
IC50 (mg/mL)
A4B6C1
A1B6C2
CH3
tert-Butyl
C1
115.56
—
—
NH
N
H
H
tert-Butyl
160.25
—
—
—
N
S
C2
N
N
N
A1B6C3
tert-Butyl
160.25
—
S
CH3
C3
A1B6C4
A3B6C2
Ribavirin
H
Cl
tert-Butyl
tert-Butyl
H
C2
16.25
9.58
—
—
—
—
>500
2.06
4.27
a Abbeviations and strains used: MDCK, Madin-Darby canine kidney cells, influenza A H3N2 viruses (A3 China/15/90).
b Concentrations that cause microscopically detectable toxicity in virus-infected cultures.
c Concentrations required to reduce virus-induced CPE in MDCK cells by 50%.
258.69 and 21.56 mg/mL, respectively. These results indi-
cated that the steric hindrance and electron-donating
group in 2-position is favorable for activity. Based on
A1B6C1, compounds with thiotriazoles (A1B6C2 and
A1B6C3) or hydrogen (A1B6C4) substituted at 5-position
were synthesized and exhibited no inhibition for influenza
A virus.
Acknowledgment
The Shanghai Commission of Science and Technology
(06PJ14112) supported this work.
Supplementary data
We investigated the electron effect on substitution of
aromatic ring at 50-position. Only compound A3B6C1
showed the weaker activity (IC50 = 48.74 mg/mL) than
A1B6C1. Oxidation of A1B6C1 gave compound F which
showed no activity against influenza A. In addition, this
series of compounds did not exhibit the potent activity
against influenza B virus (see Scheme 2).
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.bmcl.2007.11.117.
References and notes
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In summary, we have developed a mild and convenient
method for the synthesis of 5-azolylthiopyridines based
upon a consecutive Michael-addition, condensation se-
quence. This method provides facile construction of
these bis-heterocycle libraries that are applicable for bio-
logical screening. Biological responses of these 5-azolyl-
thiopyridines against influenza virus
A
were
preliminarily evaluated, and the results showed that
compound A1B6C1 has inhibitory potency as lead for
the development of de novo antiviral agents. Further
studies on their structure–activity relationship and opti-
mization of these compounds are underway in our
group.
OH
N
N
OH
N
N
N
CH2Cl2
r.t
mCPBA
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Xing, Y.-C.; Nan, F.-J. Bioorg. Med. Chem. Lett. 2005, 15,
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Tkschuk, T. M.; Shevchuk, L. I. Chem. Nat. Compd. 2001,
S
O
N
S
N
N
43%
A1B6C1
Scheme 2. Oxidation of compound A1B6C1.
F

1180
G. Cheng et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1177–1180
37, 307; (c) Sosnovskikh, V. Y.; Usachev, B. I.; Sizov, A.
9. MDCK cells were grown as specified in Eagle’s minimum
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(FBS) plus antibiotics (penicillin, 100 U/mL; streptomycin,
100 U/mL). Influenza A H3N2 viruses (A3 China/15/90) were
propagated in the allantoic cavities of 10-day-old embryonated
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according to standard procedures. Confluent MDCK mono-
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8. Typical procedure for the synthesis of 2,4-substituted 5-
azolylthiopyrimidines:
a
mixture of substrate A-1
(0.2 mmol), C-1 (0.22 mmol), and K2CO3 (0.8 mmol) in
DMF (3 mL) was stirred at room temperature for 8 h, then
acetamidine (0.3 mmol) was added to the reaction mixture
and stirred at room temperature for 8 h. The reaction
mixture was concentrated. The residue was purified by flash
chromatography (silica gel, 30:1 CHCl3/CH3OH) to afford
40 mg (68%) of compound A1B2C1.