Arylazolyl(azinyl)thioacetanilides. Part 10: Design, synthesis and biological evaluation of novel substituted imidazopyridinylthioacetanilides as potent HIV-1 inhibitors

Article abstract of DOI:10.1016/j.bmc.2012.07.026

In continuation of our efforts toward the discovery of potent HIV-1 NNRTIs with novel structures, we have employed a scaffold hopping strategy to explore the chemically diversed space of bioactive compounds. The original arylazolylthioacetanilide platform

Full text of DOI:10.1016/j.bmc.2012.07.026

Bioorganic & Medicinal Chemistry 20 (2012) 5527–5536
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Arylazolyl(azinyl)thioacetanilides. Part 10: Design, synthesis and biological
evaluation of novel substituted imidazopyridinylthioacetanilides as potent
HIV-1 inhibitors q
Xiao Li a, Peng Zhan a, , Hong Liu a, Dongyue Li a, Liu Wang a, Xuwang Chen a, Huiqing Liu c,
⇑
Christophe Pannecouque b, Jan Balzarini b, Erik De Clercq b, Xinyong Liu a,
⇑
a Key Laboratory of Chemical Biology (Ministry of Education), School of Pharmaceutical Sciences, Shandong University, 44, West Culture Road, 250012 Jinan, Shandong, PR China
b Rega Institute for Medical Research, KU Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium
c Institute of Pharmacology, School of Medicine, Shandong University, 44, West Culture Road, 250012 Jinan, Shandong, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
In continuation of our efforts toward the discovery of potent HIV-1 NNRTIs with novel structures, we
have employed a scaffold hopping strategy to explore the chemically diversed space of bioactive com-
pounds. The original arylazolylthioacetanilide platform was replaced with different imidazopyridinyl-
thioacetanilide scaffolds to yield the optimal pharmacophore moieties in order to generate novel NNRTIs
with desirable potency. Some of the new compounds proved able to inhibit HIV-1 replication in the low
micromolar range. In particular, compound 5b16 displayed the most potent anti-HIV-1 activity
Received 6 June 2012
Revised 15 July 2012
Accepted 16 July 2012
Available online 24 July 2012
Keywords:
HIV
NNRTIs
Heterocycle
Synthesis
(EC50 = 0.21 0.06
dine (EC50 = 1.4 0.1
l
M), inhibiting HIV-1 IIIB replication in MT-4 cells more effectively than dideoxycyti-
M) and similarly with nevirapine (EC50 = 0.20 0.10 M). Preliminary structure–
l
l
activity relationship (SAR) of the newly synthesized congeners is discussed, and molecular modeling
study is performed to rationalize the SAR conclusions.
Ó 2012 Elsevier Ltd. All rights reserved.
Anti-HIV-1 activity
SAR
Imidazopyridine
Scaffold hopping
1. Introduction
Recently, arylazolylthioacetanilides, a particular series of five-
membered heterocyclic derivatives, have attracted lots of attention
Acquired inmmune deficiency syndrome (AIDS) mainly caused
by human immunodeficiency virus type-1 (HIV-1), continues to
be a major leading pandemic disease wordwide with approxi-
mately 40 million people living with HIV.1 Despite the meaningful
results having been achieved by highly active antiretroviral ther-
apy (HAART), definitive cure of AIDS by chemotherapeutics is still
a long way off.2 Non-nucleoside reverse transcriptase inhibitors
(NNRTIs) with their unique antiviral potency and high selectivity,
nowadays represent very potent anti-AIDS drugs that specifically
target the HIV-1 reverse transcriptase (RT).3 Nevertheless, the
long-term use of NNRTIs in the clinical leads to the emergence of
drug-resistant viruses and potentially severe side effects. As a con-
sequence, discovery of novel NNRTIs candidates, especially with
potency against the clinically relevant mutant strains of HIV-1, is
a continuous goal of drug development.4
to the development of novel NNRTIs because of their high potency
against wild-type and resistant HIV-1 strains, favorable bioavail-
ability and low toxicity.5–11 Among them, 1,2,4-triazole derivatives
VRX-480733 and RDEA80612, were chosen as candidates for fur-
ther studies. Especially, RDEA806, a potent and promising Ardea
Biosciences’ NNRTI lead, is currently in phase IIa clinical trials
(Fig. 1).
Meanwhile, during the course of our continued effort toward
the development of potent NNRTIs, we embarked on a chemical
evolution of lead compounds by ‘follow-on’-based drug discovery
strategies13, such as the structure-based bioisosterism principle.14
Herefrom, several series of new arylazolylthioacetanilide deriva-
tives were designed, synthesized and identified as promising NNR-
TIs with potent anti-HIV activities in cell lines infected with either
wild-type or mutant HIV-1 strains.15–23 Especially, 1,2,3-thiadia-
zole derivative ZP7 (Fig. 1) exhibited the most potent anti-HIV-1
activity (EC50 = 36.4 nM), inhibiting HIV-1 replication in MT-4 cells
with sevenfold and eightfold higher efficiency than nevirapine
(NVP) and delavirdine (DLV) respectively.16 Molecular modeling
studies demonstrated that the five-membered heterocycle portion
q
Parts 1–9 were reported in references 15–23.
⇑
Corresponding authors. Tel.: +86 531 88380270; fax: +86 531 88382731.
E-mail addresses: zhanpeng1982@163.com (P. Zhan), xinyongl@sdu.edu.cn (X. Liu).
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.07.026

5528
X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
Cl
Cl
Cl
N
N
N
N
N
S
N
H
N
H
N
H
N
S
S
N
S
Br
Br
N
N
O
O
O
Br
SO2NH2
COOK
VRX-480773
EC50 = 0.14 µM (WT)
EC50 = 0.23 µM (K103N/Y181C)
RDEA-806
ZP7
EC50 = 36.4 nM, SI > 6460
Br
Figure 1. Azolylthioacetanilide-based NNRTIs.
of these inhibitors could be acting as a scaffold which orients the
pharmacophores into the proper geometry for binding and being
a key structural element to form hydrogen bond with Lys101 in
the RT pocket.16
is outlined in Scheme 1. For the 5a series, the commercially available
2-chloro-3-nitropyridine 1a was converted to N-mesityl-3-nitropyri-
din-2-amine (2a) by reaction with 2,4,6-trimethyl-benzenamine in
the presence of KF at 120 °C for several hours.25 For the 5b series,
the commercially available 4-chloro-3-nitropyridine 1b was reacted
with 2,4,6-trimethyl-benzenamine and NaHCO3 in EtOH at ambient
temperature to obtain N-mesityl-3-nitropyridin-4-amine (2b).26 Un-
der the condition of Pd/C catalysis, the nitro group of 2a or 2b is
reducted by hydrogenation into amino group, which achieved the
intermediates N-mesitylpyridine-diamine 3a and 3b correspond-
ingly. The cyclization reaction of 3a or 3b with potassium O-ethyl car-
bonodithioate in the presence of NaHCO3 in refluxing EtOH, gave the
key compound N-mesityl-3-nitropyridin-2-amine 4a or N-mesityl-3-
nitropyridin-4-amine 4b after acidification.27 The final imidazopyri-
dine thioacetanilides 5a1–5a16 or 5b1–5b16 were obtained by reac-
tion of 4a or 4b with substituted anilines in the presence of K2CO3
in an easy, rapid and profitable way.28 Both analytical and spectral
data of all the newly synthesized compounds are in full agreement
with the proposed structures.
Encouraged by these promising results, and in order to further
explore the chemically diversed space and the SARs of arylazolyl-
thioacetanilides, we employed the scaffold hopping strategy, a use-
ful method to discover structurally novel compounds by modifying
the central core structure of the known active compounds.24 Using
this approach aimed at replacing the five-membered azole ring of
arylazolylthioacetanilides with a fused heterocyclic ring, we de-
signed two kinds of scaffolds (i.e. imidazo[4,5-b]pyridine and imi-
dazo[4,5-c]pyridine) for synthesis (Fig. 2), owing to their synthetic
accessibility and drug-like properties. Based on our previous SAR
results15–23, the other fragments which were considered to be
necessary for conserving anti-HIV-1 activity, such as the
‘‘-SCH2CONH-’’ linker and the substituted arylamines, were main-
tained. As a result, two series of novel imidazopyridinylthioacetan-
ilide derivatives were synthesized and evaluated in vitro for their
anti-HIV activities.
2.2. Biological activity
2. Results and discussion
2.1. Chemistry
2.2.1. Anti-HIV activity evaluation
The newly synthesized imidazopyridinylthioacetanilide deriva-
tives were evaluated for anti-HIV activity by determining their
ability to inhibit the replication of the HIV-1 IIIB strain, HIV-1 mu-
tant strain RES056 (K103 N/Y181C double RT mutant), and HIV-2
ROD strain in MT-4 cells in comparison with nevirapine (NVP),
zidovudine (azidothymidine, AZT), dideoxycytidine (DDC), delavir-
The general synthetic route utilized to obtain the desired com-
pounds 2-(3-mesityl-3H-imidazo[4,5-b]pyridin-2-ylthio)-N-phenyl-
acetamide (5a series) and 2-(1-mesityl-1H-imidazo[4,5-c]pyridin
-2-ylthio)-N-phenylacetamide (5b series) was straightforward and
R2
N
N
H
N
R1
S
N
X2
O
R2
N
R4
H
N
R
X1
Me
S
X3
N
Scaffold hopping
Triazole thioacetanilide
O
X4
Me
R4
R2
S
N
N
H
N
5a1-5a16: X1 = N, X2 = C
5b1-5b16: X1 = C, X2 = N
Target compounds
S
X3
Me
O
R4
R
X3 = CH, N
1,2,3-Thiadiazole thioacetanilide
Lead structures
Figure 2. The scaffold hopping replacement of azoles by imidazopyridines.

X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
5529
dine (DLV) and efavirenz (EFV) used as reference drugs. The cyto-
toxicity of the compounds was determined in parallel. Compari-
sons of inhibitory concentration (EC50), cytotoxic concentration
(CC50), and selective index (SI, given by the CC50/EC50 ratio) for dif-
ferent compounds are presented in Table 1 and Table 2.
As can be seen from Table 1 and Table 2, one third of the tested
compounds inhibited HIV-1 IIIB replication at micromolar concen-
trations. In particular, compounds 5a16 and 5b16 were the most
potent inhibitors against HIV-1 (IIIB) replication of these two series
revealed a principle that whenever the ortho substitution (such as
nitro and halogen) or the para substitution (such as nitro, acetyl
and sulfonamide) at the phenyl ring of the anilide moiety, the pres-
ence of electron-withdrawing groups is essential to improve the
potency against HIV-1. For instance, in the case of compounds
5b4 and 5b7 in the imidazo[4,5-c]pyridine series, introduction of
a methyl group in the para position at the phenyl ring of the anilide
moiety led to 5b5 and 5b6 with decreased activity, whereas intro-
duction of 4-acetyl and 4-sulfonamide in 5b4 led to 5b8 and 5b16,
respectively, with markedly improved activity, indicating that the
electronic nature or the steric-hindrance of the substituent at the
para position remarkably influenced the anti-HIV-1 activity. Simi-
lar SARs is also present in the imidazo[4,5-b]pyridine series. These
SAR conclusions are also grossly in agreement with the previously
reported results in the arylazolylthioacetanilide series.15,16
It is interesting to note that, compounds 5a16 and 5b16, with a
sulfonamide group at the para position of the anilide moiety pos-
sessed outstanding inhibitory activity comparing to their counter-
parts. Practically, the sulfonamide is a common privileged group
used in a lot of NNRTI scaffolds because its increased polarity can
accommodate the chemical environment in this region of RT, lead-
ing to the possibility of increasing affinity by generating hydrogen
bonding interactions.29
(EC50 = 0.75 0.14
were more effectively than DDC (EC50 = 1.39 0.05
possessed similar anti-HIV-1 inhibitory activity as that of NVP
(EC50 = 0.20 0.10 M). Some other compounds, 5a8, 5b4, 5b7,
lM and 0.21 0.06
l
M, respectively), which
l
M), and
l
5b8, 5b9, 5b13 and 5b14 also exhibited moderate to good activities
against HIV-1 strain IIIB with EC50 values in the range of 0.99–
5.7
lM, which reach the same order of magnitude as that of DDC
(1.39 0.05
l
M). These results indicated that the imidazopyridine
is an appropriate hopping scaffold instead of the five-membered
heterocycles in the lead compounds.
Compared with the results shown in Table 1 and Table 2, it was
found that substantial difference in antiviral activity against HIV-1
IIIB can be observed in the two series of compounds, with the fol-
lowing order of active sequence: imidazo[4,5-c]pyridine series
>imidazo[4,5-b]pyridine series. Therefore, the N atom position in
the imidazopyridine core is crucial for maintaining the antiviral
activity. Probably, a suitable position of the N atom was beneficial
for improving the binding affinity (hydrogen bonding interaction)
between the active binding site and the inhibitors, and thus
enhancing the biological activity. Besides, the results in each series
In general, the newly designed imidazopyridinylthioacetanilide
compounds had moderate activities against HIV-1 (IIIB), but were
less active than the previously reported 1,2,3-thiadiazole thioace-
tanilides16 and imidazole thioacetanilides.19 These results would
provide valuable information for further modification in the cen-
tral aromatic moietey of the arylazolylthioacetanilide NNRTI.
Table 1
Anti-HIV activity, cytotoxicity and selectivity indices of 2-(3-mesityl-3H-imidazo[4,5-b]pyridin-2-ylthio)-N-phenylacetamide derivatives (5a1–5a16) and positive drugs
N
H
N
N
S
Ar
N
O
Me
Me
5a1-5a16
Me
SIc
a
b
Compd
Ar
EC50
(
lM)
CC50 (lM)
HIV-1 IIIB
RES056
HIV-2 ROD
HIV-1 IIIB
5a1
5a2
5a3
5a4
5a5
5a6
5a7
5a8
Phenyl
2-Chlorophenyl
2-Fluorophenyl
2-Bromophenyl
>26
>3.9
>3.7
>5.6
>0.99
>144
P6.7
3.6 1.0
>6.0
>3.0
>15
8.9 0.29
9.9 4.1
>25
—
—
—
—
—
—
>39
>46
—
—
—
>80
>117
—
—
>22
>15
0.01 0.009
—
0.55 0.06
>36.19
>26
26 4.4
3.9 1.5
3.7 1.2
5.6 0.5
<1
<1
<1
<1
<1
<1
66
13
<1
<1
<1
9
12
<1
<1
30
>3.9
>3.7
>5.6
>0.99
>144
>39
2-Bromo-4-methylphenyl
4-Methyl-2-nitrophenyl
2-Nitrophenyl
4-Acetyl-2-bromophenyl
2-Chloropyridin-3-yl
2,4-Dichlorophenyl
o-tolyl
(Methyl 3-bromobenzoate)-4-yl
(Ethyl 3-bromobenzoate)-4-yl
2-Chloro-4-nitrophenyl
3-Bromo-5-methylpyridin-2-yl
2-Bromo-4-sulfonamidephenyl
0.99 0.1
144 35
39 17
46 29
6.0 0.8
3.9 0.2
15 6.9
80 42
117 46
25 1.5
102 46
22 2.6
>15
>46
5a9
>6.0
>3.0
>15
>80
>117
>25
>102
>22
—
0.007 0.0008
1.7 0.25
—
5a10
5a11
5a12
5a13
5a14
5a15
5a16
NVP
AZT
DDC
EFV
>102
0.75 0.14
200 105
6.0 0.57
1394 50
6.6 0.87
35 4.7
>75
P8295
>68
>964
>1034
P50
>95
>6.3
>36
DLV
—
In bold are the values of active compounds.
a
EC50: concentration of compound required to achieve 50% protection of MT-4 cells against HIV-1-induced cytotoxicity, as determined by the MTT method.
CC50: concentration required to reduce the viability of mock-infected cells by 50%, as determined by the MTT method.
SI: selectivity index (CC50/EC50). The SI values: X 1 stand for P1or <1.
b
c

5530
X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
Table 2
Anti-HIV activity, cytotoxicity and selectivity indices of 2-(1-mesityl-1H-imidazo[4,5-c]pyridin-2-ylthio)-N-phenylacetamide derivatives (5b1–5b16).
N
N
H
N
S
Ar
N
O
Me
Me
5b1-5b16
EC50
Me
Compd
Ar
(l
M)
CC50
(l
M)
SI
HIV-1IIIB
RES056
HIV-2 ROD
HIV-1 IIIB
5b1
5b2
5b3
5b4
5b5
5b6
5b7
5b8
Phenyl
2-Chlorophenyl
2-Fluorophenyl
2-Bromophenyl
>17
>19
>18
5.2 0.49
>5.9
P1.2
5.7 5.07
0.99 0.26
1.7 0.16
P1.1
>22
P2.5
4.7 0.39
1.4 0.6
>61
—
—
—
>22
—
>6.2
>9.9
>61
>22
>140
—
>27
>22
>29
—
>17
>19
>18
>22
>5.9
>6.2
>9.9
>61
>22
>140
>22
>27
>22
>29
>61
>9.7
17 0.5
19 0.6
18 0.7
22 6.2
5.9 0.5
6.2 1.7
9.9 1.9
61 29
22 6.3
140 26
22 9.6
27 9.1
22 2.1
29 2.6
61 63
9.7 3.7
<1
<1
<1
4
<1
65
2
61
12
6127
<1
611
5
20
<1
46
2-Bromo-4-methylphenyl
4-Methyl-2-nitrophenyl
2-Nitrophenyl
4-Acetyl-2-bromophenyl
2-Chloropyridin-3-yl
2,4-Dichlorophenyl
o-tolyl
(Methyl 3-bromobenzoate)-4-yl
(Ethyl 3-bromobenzoate)-4-yl
2-Chloro-4-nitrophenyl
3-Bromo-5-methylpyridin-2-yl
2-Bromo-4-sulfonamidephenyl
5b9
5b10
5b11
5b12
5b13
5b14
5b15
5b16
0.21 0.05
>9.7
In addition, all of the title compounds were evaluated for their
capability to inhibit HIV-2 (strain ROD) and HIV-1 RES056 mutant
strain replication in MT-4 cells, but no one was active against these
strains (Table 1 and Table 2). It can be concluded that two new ser-
ies of imidazopyridinylthioacetanilide derivatives were specific for
HIV-1 and thus belonged to the NNRTIs.
of Tyr188, Phe227, and Trp229. Detailed analysis of the binding
mode showed that phenyl ring interacts favorably with the
Tyr188 side chain, giving rise to a positive p-p stacking interaction.
The inhibitor’s amide carbonyl forms a key hydrogen bond with
the backbone N-H of Lys103, which is important for the affinity be-
tween inhibitor and RT. The 2-bromo-4-sulfonamidephenyl moiety
of 5b16 is close to Pro236, and the sulfonamide moiety points to-
ward the solvent exposed region. Therefore, 4-substituent at the
phenyl ring of the anilide moiety allows hydrophilic groups as
the preferred substituents, which can explain why 5b16 and
5a16 stand out of other congeners.
It is noteworthy to emphasize that, as shown in Fig. 3, although
imidazopyridine moiety is close to Lys101, the position of N atom
in pyridine did not favor forming the hydrogen binding interaction
with backbone of Lys101, which may rationalize the SAR conclu-
sion that anti-HIV activity is strongly dependent on the position
of the N atom of the pyridine ring, and also illustrate the reason
for their lost potency against the mutant RES056 strain.
According to our molecular modeling investigations on the
binding mode of 5b16 to the NNIBP of HIV-1 RT, together with
the SAR studies as described above, we postulate that keeping
favorable position of the heteroatom in this or alternative struc-
tural classes may be beneficial to enhance the interaction between
the inhibitors and the RT.
2.2.2. HIV-1 RT inhibition assay
With the aim to further confirm the drug target of imidazopy-
ridinylthioacetanilide derivatives, one selected title compound
5b16 was tested in enzymatic assays against highly purified re-
combinant HIV-1 RT using poly(rC)-oligo(dG) as template primer.
Compound 5b16 exhibited moderate inhibition of enzymatic activ-
ity with an IC50 value (50% of the inhibitory concentration of tested
compounds required to inhibit biotin deoxyuridine triphosphate
(biotin-dUTP) incorporation into the HIV-1 RT by 50%) of 4.4 lM,
which was slightly higher than that of NVP (1.2 lM).
2.3. Molecular modeling analysis
By means of Autodock Vina [http://vina.scripps.edu], molecular
modeling of compound 5b16 docked into the NNRTIs binding
pocket (NNIBP) of HIV-1 RT was employed to understand the inter-
actions between these inhibitors and the target. X-ray crystal
structure of HIV-1 RT with benzophenone taken from PDB
(3DLG) was used as the input structure for docking calculations be-
cause of the high degree of structural similarity between arylazol-
ylthioacetanilides and benzophenones.5 Default parameters were
used as described in the Autodock Vina manual unless otherwise
specified. The theoretical binding mode of 5b16 to the NNIBP is
shown in Fig. 3.
In summary, the results of the AutoDocking analysis seem to
support our newly designed and synthesized compounds. Further
structural optimization will consider these aspects in future design
attempts.
3. Conclusion
Results suggest that this class of compounds shares the similar
binding mode with previous arylazolylthioacetanilides.16 As illus-
trated in Fig. 3, the trimethylbenzene ring of 5b16 fits into the aro-
matic-rich binding pocket, surrounded by the aromatic side chains
In summary, the present work is an extension of our ongoing ef-
forts toward the development and the identification of new mole-
cules with anti-HIV activity. In the present investigation, the
‘‘scaffold hopping’’-based approach led to the identification of

X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
5531
Br
O
SO2NH2
N
S
N
H
N
N
5b16
Figure 3. Molecular model of 5b16 in the allosteric site of HIV-1 RT (PDB code: 3DLG). The docking result of 5b16 is showed by PyMOL.
imidazopyridinylthioacetanilide NNRTIs with potency against HIV-1
replication in the low micromolar concentration range. Among them,
compound 5b16 was identified as the most promising candidate with
favorable inhibitory activity against HIV-1 IIIB (EC50 = 0.21
were run in the same instrument at 150 or 100 MHz.Chemical
shifts are expressed in d units and TMS as internal reference. Mass
spectra were taken on a LC Autosampler Device: standard G1313A
instrument (Agilent Technologies, Company). TLC was performed
on Silica Gel GF254 for TLC (Merck) and spots were visualized by
iodine vapors or by irradiation with UV light (254 nm). Flash col-
umn chromatography was performed on column packed with Sil-
ica Gel 60 (200–300 mesh). Solvents were reagent grade and,
when necessary, were purified and dried by standard methods.
Concentration of the reaction solutions involved the use of rotary
evaporator at reduced pressure.
0.06
lM), which was more effective than DDC (EC50 = 1.4 0.05
lM)
and was similar to NVP (EC50 = 0.20 0.10
lM). Preliminary SAR re-
sults for the newly synthesized congeners and docking studies are
presented, providing insights for discovery of more potent NNRTIs
with diverse structures. Alternative structural classes derived from
arylazolylthioacetanilides have been studied in our laboratories and
will be reported in due course.
4.1.1. General procedure for the synthesis of 2-(3-mesityl-3H-
imidazo[4,5-b]pyridin-2-ylthio)-N-phenylacetamide (5a series)
4. Experimental
4.1. Chemistry
4.1.1.1. General Procedure for the synthesis of N-mesityl-3-
25
nitropyridin-2-amine (2a)
.
The reaction mixture of 2-
chloro-3-nitropyridine (1a) (1.58 g, 0.01 mol), 2,4,6-trimethylben-
zenamine (5.4 g, 0.04 mol), and KF (0.88 g, 0.015 mol) was slowly
heated to reflux temperature (120 °C) with stirring and continued
for 10 h (monitored by TLC). The suspension was cooled and then
poured into 150 mL water and 20 mL ammonia. The mixture was
then extracted with CH2Cl2 (30 mL), washed successively with
All melting points were determined on a micromelting point
apparatus and are uncorrected. Infrared spectra (IR) were recorded
with a Nexus 470FT-IR Spectrometer (Thermo Nicolet, Company).
1H NMR spectra were recorded on a Bruker Avance 600 or 400
spectrometer at 600 or 400 MHz, using DMSO-d6 as solvent and
tetramethylsilane (TMS) as internal standard. 13C-NMR spectra
NO2
N
NH
NO2
Cl
Me
Me
i (a)
i (b)
X2
X2
X2
R2
N
NH2
NH
N
N
H
N
X1
Me
X1
Me
X1
Me
S
X3
N
2a
1a
SH
Me
N
Me
ii
iv
iii
O
X4
Me
Me
N
R4
NO2
NH
N
NO2
Cl
Me
Me
Me
Me
Me
4a: X1 = N, X2 = C
3a: X1 = N, X2 = C
3b: X1 = C, X2 = C
5a: X1 = N, X2 = C
5b: X1 = C, X2 = C
1b
4b: X1 = C, X2 = C
2b
Me
Scheme 1. Reagentsc and conditions: (i) 2,4,6-trimethylbenzenamine, (a) KF, 120 °C; (b) NaHCO3, EtOH, 4; (ii) H2, Pd/C; (iii) NaHCO3, H2O, EtOH, CH3CH2OCS2K, reflux.
acidification; (iv) K2CO3, CH3COCH3, ClCH2CONHAr.

5532
X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
water (2 ꢀ 30 mL). The organic layer was dried (Na2SO4), filtered
and concentrated under reduced pressure to afford crude product
2a as a brown oil. Then, the pruduct was purified by recrystalliza-
tion from alcohol-petroleum ether to obtain yellow solid 2a,
Yellow needle crystals, yield: 65%, MS (ESI): m/z 258.12 (M+1).
(d, 1H, J = 7.8 Hz, C6-Ph0-H), 7.90 (d, 1H, J = 9.6 Hz, C7-imi-
dazo[4,5-b]pyridin-H), 7.29 (dd, 1H, J1 = 4.8 Hz, J2 = 9.6 Hz, C6-imi-
dazo[4,5-b]pyridin-H), 7.25 (m, 1H, C5-Ph0-H), 7.15 (m, 4H, C3,5-Ph-
H, C3,4-Ph0-H), 4.39 (s, 2H, S-CH2), 2.50 (s, 3H, Me), 1.85 (s, 6H,
2ꢀMe). ESI-MS: m/z 421.4 (M+1), 423.4 (M+3). C23H23FN4OS
(420.14).
C14H15N3O2 (257.12).
4.1.1.2. General procedure for the synthesis of 3-mesityl-3H-
imidazo[4,5-b]pyridine -2-thiol (4a). The reaction system
4.1.1.7.
N-(2-bromophenyl)-2-(3-mesityl-3H-imidazo[4,5-
White crystals, yield:
b]pyridin-2-ylthio)acetamide (5a4).
containing intermediate 2a (6 g, 0.023 mol), Pd/C (0.2 g) and
50 mL alcohol was vacuumed and fulled with excess hydrogen
gas. The reaction mixture was kept for 15 h and then evaporated
under reduced pressure. The obtained crude pruduct was washed
by petroleum ether and evaporated under reduced pressure again
to give purified compound 3a. Grey powder, yield: 65.6%.
mp:181–184 °C. MS (ESI): m/z 228.6. C14H17N3 (227.14).
Intermediate 3a (1.2 g, 5.3 mmol), EtOCS2K (1 g, 6.2 mmol) and
NaHCO3 (0.1 g, 1.2 mmol) were dissolved in alcohol (25 mL) and
water (5 ml), then the solution flowed back for 5 h with stirring.27
The reaction fluid was cooled to room temperature and then 50 ml
water and 15 mL NaOH solution (2 M) was added. The precipitate
that formed was removed by suction filtration and the filtrate
was modulated to ph 7 by adding acetic acid. Precipiteted com-
pond 4a was filtered by suction filtration and air-dried to a yellow-
ish-white powder. Grey powder, yield: 65.6%. mp:247–253 °C. MS
(ESI): m/z 270.7.C15H15N3S (269.1).
44.6%. mp: 188–191 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
9.96 (s, 1H, NH), 8.16 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyridin-
H), 8.07 (d, 1H, J = 7.8 Hz, C6-Ph0-H), 7.74 (d, 1H, J = 7.8 Hz, C3-
Ph0-H), 7.65 (d, 1H, J = 7.8 Hz, C7-imidazo[4,5-b]pyridin-H), 7.38
(t, 1H, J = 7.8 Hz, C5-Ph0-H), 7.29 (dd, 1H, J1 = 4.8 Hz, J2 = 7.8 Hz,
C6-imidazo[4,5-b]pyridin-H), 7.14 (s, 2H, C3,5-Ph-H), 7.11(t, 1H,
J = 7.8 Hz, C4-Ph0-H), 4.37 (s, 2H, S-CH2), 2.36 (s, 3H, Me), 1.85 (s,
6H, 2ꢀMe). ESI-MS: m/z 481.4 (M+1), 483.4(M+3), 485.4(M+5).
C23H21ClN4OS (480.06).
4.1.1.8.
N-(2-bromo-4-methylphenyl)-2-(3-mesityl-3H-imi-
White crys-
dazo[4,5-b]pyridin-2-ylthio)acetamide (5a5).
tals, yield: 67.6%. mp: 205-209 °C. 1H NMR (600 MHz, DMSO-d6,
ppm) d: 9.87 (s, 1H, NH), 8.16 (d, 1H, J = 5.4 Hz, C5-imidazo[4,5-
b]pyridin-H), 8.06 (d, 1H, J = 7.8 Hz, C6-Ph0-H), 7.57 (d, 1H,
J = 8.4 Hz C7-imidazo[4,5-b]pyridin-H), 7.47 (s, 1H, C3-Ph0-H),
7.31 (dd, 1H, J1 = 4.8 Hz, J2 = 7.8 Hz, C6-imidazo[4,5-b]pyridin-H),
7.17 (d, 1H, J = 7.8 Hz, C4-Ph0-H), 7.14 (m, 2H, C3,5-Ph-H), 4.34 (s,
2H, S-CH2), 2.50 (s, 3H, Me), 2.26 (s, 3H, Me), 1.84 (s, 6H,
2 ꢀ Me). ESI-MS: m/z 495.4 (M+1), 497.5 (M+3). 499.3 (M+5).
4.1.1.3. General procedure for the synthesis of 2-(3-mesityl-3H-
imidazo [4,5-b]pyridin- 2-ylthio)-N-phenyl-acetamide (5a1–
5a16).
mmol),
Compound 4a (0.15 g, 0.5 mmol), K2CO3 (0.14 g, 1.0
from different 2-chloro-N-(substituted aromatic
C24H25BrN4OS (494.08).
group)acetamides (0.05 mmol), was dissolved in acetone
(10 mL).28 The reaction mixture was stirred at ambient tempera-
ture for 2 h and then evaporated under reduced pressure. The
residue was dissovled with a small amount CH2Cl2 and chromato-
graphed on silica gel using ethyl acetate-petroleum ether system.
Pure fractions were collected and concentrated, giving the desired
compounds 5a1–5a16.
4.1.1.9. 2-(3-mesityl-3H-imidazo[4,5-b]pyridin-2-ylthio)-N-(4-
methyl-2-nitrophenyl)acetamide (5a6). Yellow crystals,
yield: 65.4%. mp: 230–233 °C. 1H NMR (600 MHz, DMSO-d6, ppm)
d: 10.52 (s, 1H, NH), 8.15 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyri-
din-H), 8.02 (d, 1H, J = 7.8 Hz, C6-Ph0-H), 7.81 (d, 1H, J = 1.8 Hz, C3-
Ph0-H), 7.71 (d, 1H, J = 8.4 Hz C7-imidazo[4,5-b]pyridin-H), 7.40
(dd, 1H, J1 = 7.8 Hz, J2 = 1.8 Hz, C5-Ph0-H), 7.28 (dd, 1H, J1 = 8.4 Hz,
J2 = 4.8 Hz, C6-imidazo[4,5-b]pyridin-H), 7.14 (s, 2H, C3,5-Ph-H),
4.34 (s, 2H, S-CH2), 2.36 (s, 6H, 2 ꢀ Me), 1.84 (s, 6H, 2ꢀMe). ESI-
MS: m/z 462.5(M+1). C24H23N5O3S (461.15).
4.1.1.4.
2-(3-mesityl-3H-imidazo[4,5-b]pyridin-2-ylthio)-N-
White crystals, yield: 54.7%. mp:
phenylacetamide (5a1).
174–176 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.42 (s, 1H,
NH), 8.14 (d, 1H, J = 4.2 Hz, C5-imidazo[4,5-b]pyridin-H), 8.00 (d,
1H, J = 7.8 Hz, C7-imidazo[4,5-b]pyridin-H), 7.56 (d, 2H, J = 7.8 Hz,
C6-Ph0-H, C2-Ph0-H), 7.30 (t, 2H, J = 7.8 Hz, C3-Ph0-H, C5-Ph0-H),
7.27 (dd, 1H, J1 = 4.2 Hz, J2 = 7.8 Hz, C6-imidazo[4,5-b]pyridin-H),
7.15 (s, 2H, C3,5-Ph-H), 7.05 (t, 1H, J = 7.8 Hz, C4-Ph0-H), 4.37 (s,
2H, S-CH2), 2.37 (s, 3H, Me), 1.86 (s, 6H, 2 ꢀ Me). ESI-MS: m/z
403.6 (M+1). C23H22N4OS (402.15).
4.1.1.10. 2-(3-mesityl-3H-imidazo[4,5-b]pyridin-2-ylthio)-N-(2-
nitrophenyl)acetamide (5a7).
White crystals, yield: 63.6%.
mp: 194–197 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.82 (s,
1H, NH), 8.15 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyridin-H), 8.03
(d, 1H, J = 8.4 Hz, C3-Ph0-H), 7.98 (d, 1H, J = 8.4 Hz, C6-Ph0-H), 7.84
(d, 1H, J = 8.4 Hz, C7-imidazo[4,5-b]pyridin-H), 7.73 (t, 1H,
J = 8.4 Hz, C5-Ph0-H), 7.38 (t, 1H, J = 8.4 Hz, C4-Ph0-H), 7.29 (dd,
1H, J1 = 4.8 Hz, J2 = 8.4 Hz, C6-imidazo[4,5-b]pyridin-H), 7.14 (s,
2H, C3,5-Ph-H), 4.36 (s, 2H, S-CH2), 2.36 (s, 3H, Me), 1.84 (s, 6H,
4.1.1.5.
N-(2-chlorophenyl)-2-(3-mesityl-3H-imidazo[4,5-
White crystals, yield:
b]pyridin-2-ylthio)acetamide (5a2).
2 ꢀ Me). ESI-MS: m/z 448.5 (M+1), 450.4(M+3).
C23H21N5O3-
64.5%. mp: 176–180 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
9.96 (s, 1H, NH), 8.16 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyridin-
H), 8.06 (d, 1H, J = 7.8 Hz, C6-Ph0-H), 7.74 (d, 1H, J = 7.8 Hz, C3-
Ph0-H), 7.64 (d, 1H, J = 7.8 Hz, C7-imidazo[4,5-b]pyridin-H), 7.37
(t, 1H, J = 7.8 Hz, C5-Ph0-H), 7.30 (dd, 1H, J1 = 4.8 Hz, J2 = 7.8 Hz,
C6-imidazo[4,5-b]pyridin-H), 7.14 (s, 2H, C3,5-Ph-H), 7.12(t, 1H,
J = 7.8 Hz, C4-Ph0-H), 4.37 (s, 2H, S-CH2), 2.36 (s, 3H, Me), 1.85 (s,
6H, 2ꢀMe). ESI-MS: m/z 437.6 (M+1), 439.5(M+3). C23H21ClN4OS
(436.11).
S(447.14).
4.1.1.11.
N-(4-acetyl-2-bromophenyl)-2-(3-mesityl-3H-imi-
White crys-
dazo[4,5-b]pyridin-2-ylthio)acetamide (5a8).
tals, yield: 67.8%. mp: 210–213 °C. 1H NMR (600 MHz, DMSO-d6,
ppm) d: 10.09 (s, 1H, NH), 8.17 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-
b]pyridin-H), 8.07 (m, 1H, C3-Ph0-H), 7.95 (d, 1H, J = 8.4 Hz, C6-
Ph0-H), 7.63 (d, 1H, J = 7.8 Hz, C7-imidazo[4,5-b]pyridin-H), 7.30
(dd, 1H, J1 = 4.8 Hz, J2 = 7.8 Hz, C6-imidazo[4,5-b]pyridin-H), 7.24
(t, 1H, J = 8.4 Hz, C5-Ph0-H), 7.14 (s, 2H, C3,5-Ph-H), 4.37 (s, 2H, S-
CH2), 2.50 (s, 3H, Me), 2.36 (s, 3H, Me), 1.85 (s, 6H, 2ꢀMe). ESI-
MS: m/z 523.4(M+1), 525.5(M+3). C25H23BrN4O2S (522.07). 13C-
NMR (100 MHz, DMSO-d6, ppm) d: 196.30 (Ph0-C=O), 167.33 (N-
C=O), 154.28, 149.36, 143.57, 140.49, 140.20, 136.83 (2 ꢀ C),
4.1.1.6. N-(2-fluorophenyl)-2-(3-mesityl-3H-imidazo[4,5-b]pyri-
din-2-ylthio)acetamide (5a3).
White crystals, yield: 55.6%.
mp:179–181 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.32 (s,
1H, NH), 8.16 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyridin-H), 8.02

X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
5533
135.37, 134.70, 133.08, 129.74 (2ꢀC), 129.18, 128.79, 125.77,
124.20, 119.00, 115.35, 35.54 (CH2-S), 27.06 (Me-C=O), 21.19
(CH3-Ph), 17.61 (2ꢀMe-Ph).
129.59, 129.18, 127.68, 125.77, 124.35, 118.99, 115.08, 61.54
(CH2-O), 35.53 (CH2-S), 21.19 (CH3-Ph), 17.60 (2 ꢀ Me-Ph), 14.56
(Me). ESI-MS: m/z 555.3 (M+3). C26H25BrN4O3S (552.38).
4.1.1.12. N-(2-chloropyridin-3-yl)-2-(3-mesityl-3H-imidazo[4,5-
4.1.1.17. N-(2-chloro-4-nitrophenyl)-2-(3-mesityl-3H-imidazo
b]pyridin-2-ylthio)acetamide (5a9).
White crystals, yield:
[4,5-b]pyridin-2-ylthio)acetamide (5a14).
White crystals,
57.7%. mp: 216–220 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
10.23 (s, 1H, NH), 8.27 (d, 1H, J = 7.8 Hz, C4-pyridine-H), 8.19 (d,
1H, J = 4.8 Hz, C6-pyridine-H), 8.16 (d, 1H, J = 4.8 Hz, C5-imi-
dazo[4,5-b]pyridin-H), 8.04 (d, 1H, J = 8.4 Hz, C7-imidazo
[4,5-b]pyridin-H), 7.44 (dd, 1H, J1 = 4.8 Hz, J2 = 8.4 Hz, C6-imi-
dazo[4,5-b]pyridin-H), 7.30 (dd, 1H, J1 = 4.8 Hz, J2 = 7.8 Hz, C5-pyr-
idine-H), 7.14 (s, 2H, C3,5-Ph-H), 4.41 (s, 2H, S-CH2), 2.36 (s, 3H,
Me), 1.85 (s, 6H, 2 ꢀ Me). ESI-MS: m/z 438.5 (M+1), 440.5 (M+3).
yield: 54.9%. mp:268–271 °C. ESI-MS: m/z 482.4 (M+1), 484.6
(M+3). C23H20ClN5O3S (481.1).
4.1.1.18.
N-(3-bromo-5-methylpyridin-2-yl)-2-(3-mesityl-3H-
(5a15). White
imidazo[4,5-b]pyridin-2-ylthio)acetamide
crystals, yield: 71.7%. mp:171–173 °C. 1H NMR (600 MHz, DMSO-
d6, ppm) d: 10.43 (s, 1H, NH), 8.37(d, J = 3.0 Hz, C5-pyridine-H),
8.22 (d, J = 3.0 Hz, C3-pyridine-H), 8.17 (d, 1H, J = 4.8 Hz, C5-imi-
dazo[4,5-b]pyridin-5H), 8.05 (dd, 1H, J1 = 8.4 Hz, J2 = 1.2 Hz,
C7-imidazo[4,5-b]pyridin-H) 7.31 (dd, 1H, J1 = 4.8 Hz, J2 = 8.4 Hz,
C6-imidazo[4,5-b]pyridin-H), 7.15 (s, 2H, C3,5-Ph-H), 4.41 (s, 2H,
S-CH2), 2.36 (s, 3H, Me), 1.85 (s, 6H, 2ꢀMe) 1.27 (s, 3H, Me). ESI-
MS: m/z 496.4 (M+1), 498.4 (M+3). C23H22BrN5OS (495.07).
C22H22ClN5OS(437.11).
4.1.1.13. N-(2,4-dichlorophenyl)-2-(3-mesityl-3H-imidazo[4,5-
b]pyridin-2-ylthio)acetamide (5a10). White crystals, yield:
62.6%. mp: 185–187 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
10.14 (s, 1H, NH), 8.16 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyri-
din-H), 8.04 (d, 1H, J = 7.8 Hz, C6-Ph0-H), 7.87 (d, 1H, J = 8.4 Hz,
C7-imidazo[4,5-b]pyridin-H), 7.66 (d, 1H, J = 1.8 Hz, C3-Ph0-H),
7.42 (dd, 1H, J1 = 7.8 Hz, J2 = 1.8 Hz, C5-Ph0-H), 7.30 (dd, 1H,
J1 = 4.8 Hz, J2 = 8.4 Hz, C6-imidazo[4,5-b]pyridin-H), 7.14 (s, 2H,
4.1.1.19. N-(2-bromo-4-sulfonamidephenyl)-2-(1-mesityl-1H-
imidazo[4,5-c]pyridin-2-ylthio) acetamide (5a16).
White
solid, yield: 75.8%. mp:173–175 °C. 1H NMR (600 MHz, DMSO-d6,
ppm) d: 10.15 (s, 1H, NH), 8.16 (d, 1H, J = 8.4 Hz, C5-Ph0-H), 8.08
(d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyridin-H), 8.03 (s, 1H, C3-Ph0-
H), 8.01(d, 1H, J = 8.4 Hz, C6-Ph0-H), 7.79 (d, 1H, J = 8.4 Hz, C7-imi-
C3,5-Ph-H), 4.38 (s, 2H, S-CH2), 2.36 (s, 3H, Me), 1.84 (s, 6H,
2 ꢀ Me). ESI-MS: m/z 471.4(M+1), 474.3(M+3).
C23H20Cl2N4OS
(470.07).
dazo[4,5-b]pyridin-H), 7.14 (s, 2H, C3,5-Ph-H), 7.30 (dd, 1H,
J1 = 8.4 Hz, J2 = 4.8 Hz, C6-imidazo[4,5-b]pyridin-H), 4.41 (s, 2H, S-
CH2), 2.36 (s, 3H, Me), 1.85 (s, 6H, 2ꢀMe). 13C-NMR (100 MHz,
DMSO-d6, ppm) d: 167.28 (N–C@O), 154.28, 149.37, 143.54,
141.81, 140.19, 139.41, 136.84 (2 ꢀ C), 135.39, 130.50, 129.74
(2 ꢀ C), 129.20, 126.09, 125.75, 125.28, 118.99, 115.72, 35.46
(CH2-S), 21.20 (Me-Ph), 17.62 (2 ꢀ Me-Ph). ESI-MS: m/z 560.3
(M+1), 562.2 (M+3), 564.3 (M+5). C23H22BrN5O3S2 (559.03).
4.1.1.14. 2-(3-mesityl-3H-imidazo[4,5-b]pyridin-2-ylthio)-N-o-
tolylacetamide (5a11). White crystals, yield: 62.6%. mp:
185–187 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 9.78 (s, 1H,
NH), 8.15 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyridin-H), 8.02 (d,
1H, J = 8.4 Hz, C7-imidazo[4,5-b]pyridin-H), 7.43 (d, 1H, J = 7.8 Hz,
C6-Ph0-H), 7.29 (t, 1H, J = 7.8 Hz, C5-Ph0-H), 7.19 (m, 2H, C6-imi-
dazo[4,5-b]pyridin-6H, C3-Ph0-H), 7.15 (s, 2H, C3,5-Ph-H), 7.07(t,
1H, J =7.8 Hz, C4-Ph0-H), 4.35 (s, 2H, S-CH2), 2.36 (s, 3H, Me), 1.85
(s, 6H, 2 ꢀ Me). ESI- MS: m/z 417.6(M+1). C24H24N4OS(416.17).
4.1.2. General procedure for the synthesis of 2-(1-mesityl-1H-
imidazo[4,5-c]pyridin-2-ylthio)-N-phenylacetamide (5b series)
4.1.2.1. General Procedure for the synthesis of N-mesityl-3-
4.1.1.15.
Methyl
3-bromo-4-(2-(3-mesityl-3H-imidazo[4,5-
White
nitropyridin-4-amine (2b).
Compound 4-chloro-3-nitropyri-
b]pyridin-2-ylthio)acetamido) benzoate (5a12).
dine (1b) (15.8 g, 0.1 mol), 2,4,6-trimethyl benzenamine (14.85 g,
0.11 mol), and NaHCO3 (25.2 g, 0.3 mol) was dissolved in alcohol
(250 mL) [26]. The reaction mixture was heated to reflux temper-
ature with stirring and kept for 10 h and then continued the reac-
tion at ambient tempreture for 12 h (monitored by TLC). The
reaction liquid was evaporated under reduced pressure. Then, the
residue was dissovled with a small amount CH2Cl2 and chromato-
graphed on silica gel using ethyl acetate-petroleum ether system.
Pure fractions were collected and concentrated, giving yellow solid
2b, yield: 57.8%, mp:133–139 °C. MS (ESI): m/z 258.12 (M+1).
crystals, yield: 59.9%. mp: 188–191 °C. 1H NMR (600 MHz,
DMSO-d6, ppm) d: 10.13 (s, 1H, NH), 8.17 (s, 1H, J = 4.2 Hz, C5-imi-
dazo[4,5-b]pyridin-H), 8.13 (d, 1H, J = 2.4 Hz, C3-Ph0-H), 8.07 (m,
2H, C6-Ph0-H, C5-Ph0-H), 7.95 (d, 1H, J = 8.4 Hz, C7-imidazo[4,5-
b]pyridin-H), 7.30 (dd, 1H, J1 = 4.8 Hz, J2 = 7.8 Hz, C6-imidazo[4,5-
b]pyridin-H), 7.14 (s, 2H, C3,5-Ph-H), 4.41 (s, 2H, S-CH2), 3.85(s,
3H, COCH3), 2.36 (s, 3H, Me), 1.84 (s, 6H, 2ꢀMe). 13C-NMR
(100 MHz, DMSO-d6, ppm) d: 167.36 (N-C=O), 165.03 (O–C@O),
154.29, 149.34, 143.56, 140.72, 140.20, 136.83 (2 ꢀ C), 135.35,
133.88, 129.74, 129.64 (2 ꢀ C), 129.16, 127.34, 125.78, 124.36,
119.01, 115.06, 52.85 (MeO), 35.50 (CH2-S), 21.20 (CH3-Ph),
C14H15N3O2 (257.12).
17.62 (2ꢀMe-Ph). ESI-MS: m/z 539.4(M+1), 543.5(M+5). C25H23
-
4.1.2.2. General Procedure for the synthesis of 1-mesityl-1H-
imidazo[4,5-c]pyridine-2-thiol (4b). With a similar proce-
BrN4O3S (538.07).
dure for compound 4a [27], the 1-mesityl-1H-imidazo[4,5-c]pyri-
dine-2-thiol (4b) was synthesized starting from N-mesityl-3-
nitropyridin-4-amine (2b).
Compound 3b: Brown powder, yield: 77.8%, mp:185–192 °C.
MS (ESI): m/z 228.6 (M+1). C14H17N3 (227.14). Compound 4b:
White powder, yield: 82.5%.
4.1.1.16. Ethyl 3-bromo-4-(2-(3-mesityl-3H-imidazo[4,5-b]pyri-
din-2-ylthio)acetamido) benzoate (5a13). White crystals,
yield: 63.9%. mp:181–183 °C. 1H NMR (600 MHz, DMSO-d6, ppm)
d: 10.10 (s, 1H, NH), 8.17 (d, 1H, J = 4.8 Hz, C5-imidazo[4,5-b]pyri-
din-5H), 8.16 (d, 1H, J = 1.8 Hz, C3-Ph0-H), 8.09 (m, 2H, C5-Ph0-H, C6-
Ph0-H), 7.95 (d, 1H, J = 8.4 Hz, C7-imidazo[4,5-b]pyridin-H), 7.30
(dd, 1H, J1 = 4.8 Hz, J2 = 8.4 Hz, C6-imidazo[4,5-b]pyridin-H), 7.14
(s, 2H, C3,5-Ph-H), 4.41 (s, 2H, S-CH2), 4.30 (q, 2H, J = 7.2 Hz,
OCH2CH3), 2.36 (s, 3H, Me), 1.85 (s, 6H, 2ꢀMe). 1.31 (t, 3H,
J = 7.2 Hz, OCH2CH3). 13C NMR (100 MHz, DMSO-d6, ppm) d:
167.33 (N–C@O), 164.52 (O–C@O), 154.28, 149.37, 143.56,
140.67, 140.43, 136.83 (2 ꢀ C), 135.37, 133.80, 129.74 (2 ꢀ C),
4.1.2.3. General Procedure for the synthesis of 2-(1-mesityl-1H-
imidazo[4,5-c]pyridin-2-yl
thio)-N-phenylacetamide
(5b1-
5b16). With a similar procedure for compounds 5a1–5a16
[28], the 2-(1-mesityl-1H-imidazo-[4,5-c]pyridin-2-ylthio)-N-
phenylacetamides (5b1–5b16) were synthesized starting from
1-mesityl-1H-imidazo[4,5-c]pyridine-2-thiol (4b).

5534
X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
4.1.2.4.
phenylacetamide (5b1).
2-(1-mesityl-1H-imidazo[4,5-c]pyridin-2-ylthio)-N-
White crystals, yield: 59.1%. mp:
4.1.2.10. 2-(1-mesityl-1H-imidazo[4,5-c]pyridin-2-ylthio)-N-(2-
nitrophenyl)acetamide (5b7). Yellow crystals, yield: 67.1%.
175–178 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.44 (s, 1H,
NH), 8.92 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.27 (d, 1H,
J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.57 (d, 2H, J = 7.8 Hz,
C6-Ph0-H, C2-Ph0-H), 7.31 (t, 2H, J = 7.8 Hz, C5-Ph0-H, C3-Ph0-H),
7.19 (s, 2H, C3,5-Ph-H), 7.05 (m, 1H, C4-Ph0-H), 6.98 (d, 1H,
J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-H), 4.41 (s, 2H, S-CH2), 2.37
(s, 3H, Me), 1.86 (s, 6H, 2 ꢀ Me). ESI-MS: m/z 403.5(M+1),
mp:192–195 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.82 (s,
1H, NH), 8.93 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.27 (d, 1H,
J = 4.8 Hz, C6-imidazo[4,5-c]pyridine-H), 7.98 (dd, 1H, J1 = 7.8 Hz,
J2 = 1.2 Hz, C3-Ph0-H), 7.82 (dd, 1H, J1 = 7.8 Hz, J2 = 0.6 Hz, C6-Ph0-
H), 7.73 (t, 1H, J = 7.8 Hz, C5-Ph0-H), 7.38 (t, 1H, J = 7.8 Hz, C4-Ph0-
H), 7.18 (s, 2H, C3,5-Ph-H), 6.99 (d, 1H, J = 4.8 Hz, C7-imidazo[4,5-
c]pyridine-H), 4.44 (s, 2H, S-CH2), 2.50 (s, 3H, Me), 1.85 (s, 6H,
2 ꢀ Me). ESI-MS: m/z 448.5 (M+1).C23H21N5O3S (447.14).
C23H22N4OS (402.15).
4.1.2.5. N-(2-chlorophenyl)-2-(1-mesityl-1H-imidazo[4,5-c]pyri-
din-2-ylthio)acetamide (5b2). White crystals, yield: 63.3%.
4.1.2.11.
N-(4-acetyl-2-bromophenyl)-2-(1-mesityl-1H-imi-
White crys-
dazo[4,5-c]pyridin-2-ylthio)acetamide (5b8).
mp:176–178 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.05 (s,
1H, NH), 8.94 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.28 (d, 1H,
J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.81 (d, 1H, J = 7.2 Hz,
C6-Ph0-H), 7.48 (d, 1H, J = 8.4 Hz, C3-Ph0-H), 7.32 (t, 1H, J = 7.2 Hz,
C5-Ph0-H), 7.18 (s, 3H, C4-Ph0-H, C3,5-Ph-H), 7.00 (d, 1H, J = 5.4 Hz,
C7-imidazo[4,5-c]pyridine-H), 4.41 (s, 2H, S-CH2), 2.37 (s, 3H,
Me), 1.85 (s, 6H, 2 ꢀ Me). ESI-MS: m/z 437.5(M+1), 439.5(M+3),
441.1(M+5), C23H23ClN4OS (436.11).
tals, yield: 70.7%. mp:242–244 °C. 1H NMR (600 MHz, DMSO-d6,
ppm) d: 10.09 (s, 1H, NH), 8.98 (s, 1H, C4-imidazo[4,5-c]pyridine-
H), 8.28 (d, 1H, J = 4.8 Hz, C6-imidazo[4,5-c]pyridine-H), 8.17 (s,
1H, C3-Ph0-H), 7.96 (d, 1H, J = 1.8 Hz, C6-Ph0-H), 7.95 (d, 1H,
J = 1.8 Hz, C5-Ph0-H), 7.19 (s, 2H, C3,5-Ph-H), 7.00 (d, 1H,
J = 4.8 Hz, C7-imidazo[4,5-c]pyridine-H), 4.44 (s, 2H, S-CH2), 2.50
(s, 3H, COCH3), 2.37 (s, 3H, Me), 1.85 (s, 6H, 2ꢀMe). 13C NMR
(100 MHz, DMSO-d6, ppm) d: 196.36 (Ph0–C@O), 167.18 (N–
C@O), 154.82, 142.74, 141.28, 140.66, 140.58, 140.47, 140.32,
136.64 (2 ꢀ C), 134.79, 133.12, 130.14, 128.79 (2 ꢀ C), 128.75,
124.48, 115.62, 105.16, 36.18 (CH2-S), 27.09 (Me-C@O), 21.22
(Me-Ph), 17.39 (2ꢀMe-Ph). ESI-MS: m/z 523.5 (M+1), 525.5
(M+3). C25H23BrN4O2S (522.07)
4.1.2.6. N-(2-fluorophenyl)-2-(1-mesityl-1H-imidazo[4,5-c]pyri-
din-2-ylthio)acetamide (5b3).
Grey crystals, yield: 70.3%.
mp:178–180 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.30 (s,
1H, NH), 8.92 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.28 (d, 1H,
J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.90 (m, 1H, C6-Ph0-H),
7.27 (m, 1H, C5-Ph0-H), 7.15 (m, 2H, C4-Ph0-H, C3-Ph0-H), 7.19 (s,
2H, C3,5-Ph-H), 6.99 (d, 1H, J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-
H), 4.43 (s, 2H, S-CH2), 2.37 (s, 3H, Me), 1.85 (s, 6H, 2 ꢀ Me). ESI-
MS: m/z 421.5 (M+1), 423.5 (M+3). C23H21FN4OS (420.14).
4.1.2.12. N-(2-chloropyridin-3-yl)-2-(1-mesityl-1H-imidazo[4,5-
c]pyridin-2-ylthio)acetamide (5b9).
White crystals, yield:
56.2%. mp:220–223 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
10.22 (s, 1H, NH), 8.94 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.29
(d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 8.25 (dd, 1H,
J1 = 7.8 Hz, J2 = 1.8 Hz, C6-pyridine-H), 8.20 (dd, 1H, J1 = 4.8 Hz,
J2 = 1.8 Hz, C4-pyridine-H), 7.44 (dd, 1H, J1 = 7.8 Hz, J2 = 4.8 Hz,
C5-pyridine-H), 7.19 (s, 2H, C3,5-Ph-H), 7.00 (s, 1H, J = 5.4 Hz, C7-
imidazo[4,5-c]pyridine-H), 4.44 (s, 2H, S-CH2), 2.50 (s, 3H, Me),
1.85 (s, 6H, 2 ꢀ Me). 13C NMR (100 MHz, DMSO-d6, ppm) d:
167.34 (N-C=O), 154.88, 145.74, 142.72, 142.66, 141.25, 140.64,
140.59, 140.21, 136.65 (2 ꢀ C), 133.43, 132.25, 130.12, 128.80
(2ꢀC), 123.99, 105.14, 36.01 (CH2-S), 21.21 (Me-Ph), 17.37
(2 ꢀ Me-Ph). ESI-MS: m/z 438.5 (M+1). C22H20ClN5OS (437.11).
4.1.2.7.
N-(2-bromophenyl)-2-(1-mesityl-1H-imidazo[4,5-
Grey solid, yield:
c]pyridin-2-ylthio)acetamide (5b4).
69,0%. mp:179–181 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
9.96 (s, 1H, NH), 8.96 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.28
(d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.71 (dd, 1H,
J1 = 7.2 Hz, J2 = 1.2 Hz, C6-Ph0-H), 7.65 (d, 1H, J = 7.2 Hz, C3-Ph0-H),
7.37 (t, 1H, J = 7.2 Hz, C5-Ph0-H), 7.18 (s, 2H, C3,5-Ph-H), 7.12 (t,
1H, J = 7.2 Hz, C4-Ph0-H), 7.00 (d, 1H, J = 5.4 Hz, C7-imidazo[4,5-
c]pyridine-H), 4.40 (s, 2H, S-CH2), 2.37 (s, 3H, Me), 1.85 (s, 6H,
2 ꢀ Me). ESI-MS: m/z 481.4 (M+1), 483.3 (M+3), 485.6 (M+5).
4.1.2.13. N-(2,4-dichlorophenyl)-2-(1-mesityl-1H-imidazo[4,5-
c]pyridin-2-ylthio)acetamide (5b10).
C23H21BrN4OS (480.06).
White crystals, yield:
63.7%. mp:250–254 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d:
10.11 (s, 1H, NH), 8.32 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.28
(d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.84 (d, 1H,
J = 8.4 Hz, C6-Ph0-H), 7.67 (d, 1H, J = 1.8 Hz, C3-Ph0-H), 7.42 (dd,
1H, J1 = 8.4 Hz, J2 = 1.8 Hz, C5-Ph0-H), 7.18 (s, 2H, C3,5-Ph-H), 6.99
(d, 1H, J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-H), 4.41 (s, 2H, S-
CH2), 2.37 (s, 3H, Me), 1.84 (s, 6H, 2 ꢀ Me). ESI-MS: m/z 471.8
(M+1). C23H20Cl2N4OS (470.07).
4.1.2.8. N-(2-bromo-4-methylphenyl)-2-(1-mesityl-1H-imidazo
[4,5-c]pyridin-2-ylthio)acetamide(5b5).
White
crystals,
yield: 75.5%. mp:191–195 °C. 1H NMR (600 MHz, DMSO-d6, ppm)
d: 9.88 (s, 1H, NH), 8.96 (s, 1H, C4-imidazo[4,5-c]pyridine-H),
8.31 (d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.55 (d, 1H,
J = 7.2 Hz, C6-Ph0-H), 7.45 (s, 1H, C3-Ph0-H), 7.17 (s, 3H, C5-Ph0-H,
C3,5-Ph-H), 6.98 (d, 1H, J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-H),
4.37 (s, 2H, S-CH2), 2.37 (s, 3H, Me), 2.27 (s, 3H, Me), 1.85 (s, 6H,
2 ꢀ Me). ESI-MS: m/z 495.3 (M+1), 497.5 (M+3), 599.2 (M+5).
4.1.2.14. 2-(1-mesityl-1H-imidazo[4,5-c]pyridin-2-ylthio)-N-o-
C
24H25BrN4OS (494.08).
tolylacetamide (5b11).
White solid, yield: 68.5%. mp:153–
156 °C. 1H NMR (600 MHz, DMSO-d6, ppm) d: 10.70 (s, 1H, NH),
8.93 (s, 1H, C4-imidazo[4,5-c]pyridine-H), 8.27 (d, 1H, J = 4.8 Hz,
C6-imidazo[4,5-c]pyridine-H), 7.81 (s, 1H, C6-Ph0-H), 7.68 (d, 1H,
J = 8.4 Hz, C5-Ph0-H), 7.54 (m, 2H, C4-Ph0-H, C3-Ph0-H), 7.18 (s, 2H,
C3,5-Ph-H), 6.98 (d, 1H, J = 4.8 Hz, C7-imidazo [4,5-c]pyridine-H),
4.36 (s, 2H, S-CH2), 2.36 (s, 6H, 2ꢀMe), 1.84 (s, 6H, 2 ꢀ Me). ESI-
MS: m/z 417.6 (M+1). C24H26N4OS (416.17).
4.1.2.9. 2-(1-mesityl-1H-imidazo[4,5-c]pyridin-2-ylthio)-N-(4-
methyl-2-nitrophenyl)acetamide (5b6). Yellow crystals,
yield: 71.1%. mp: 221–223 °C. 1H NMR (400 MHz, DMSO-d6,
ppm) d: 10.72 (s, 1H, NH), 8.94 (s, 1H, C4-imidazo[4,5-c]pyridine-
H), 8.29 (d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 7.82 (s,
1H, C3-Ph0-H), 7.73 (d, 1H, J = 8.4 Hz, C5-Ph0-H), 7.55 (d, 1H,
J = 8.4 Hz, C6-Ph0-H), 7.18 (s, 2H, C3,5-Ph-H), 6.99 (d, 1H,
J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-H), 4.38 (s, 2H, S-CH2), 2.37
(s, 3H, Me), 2.36 (s, 3H, Me) 1.85 (s, 6H, 2 ꢀ Me). ESI-MS: m/z
462.5 (M+1), 464.3 (M+3). C24H25N5O3S (461.15).
4.1.2.15.
c]pyridin-2-ylthio)acetamido)benzoate (5b12).
tals, yield: 69.7%. mp:202–205 °C. 1H NMR (600 MHz, DMSO-d6,
Methyl3-bromo-4-(2-(1-mesityl-1H-imidazo[4,5-
White crys-

X. Li et al. / Bioorg. Med. Chem. 20 (2012) 5527–5536
5535
ppm) d: 10.10 (s, 1H, NH), 8.97 (s, 1H, C4-imidazo[4,5-c]pyridine-
H), 8.28 (d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 8.14 (d,
1H, J = 1.8 Hz, C3-Ph0-H), 8.03 (d, 1H, J = 8.4 Hz, C6-Ph0-H), 7.94
(dd, 1H, J1 = 8.4 Hz, J2 = 1.8 Hz, C5-Ph0-H), 7.19 (s, 2H, C3,5-Ph-H),
6.99 (d, 1H, J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-H), 4.44 (s, 2H,
S-CH2), 3.34 (s, 3H, OCH3), 2.37 (s, 3H, Me), 1.85 (s, 6H, 2 ꢀ Me).
ESI-MS: m/z 539.4 (M+1), 541.4 (M+3), 543.5 (M+5).
cate wells to allow simultaneous evaluation of their effects on
mock- and HIV-infected cells at the beginning of each experiment.
Serial fivefold dilutions of test compounds were made directly in
flat-bottomed 96-well microtiter trays using a Biomek 3000 robot
(Beckman instruments, Fullerton, CA). Untreated control HIV- and
mock-infected cell samples were included for each sample.
HIV-1(IIIB)32 or HIV-2 (ROD)33 stock (50
lL) at 100–300 CCID50
C
25H23BrN4O3S (538.07).
(cell culture infectious dose) or culture medium was added to
either the infected or mock-infected wells of the microtiter tray.
Mock-infected cells were used to evaluate the effect of test com-
pound on uninfected cells in order to assess the cytotoxicity of
the test compound. Exponentially growing MT-4 cells34 were cen-
trifuged for 5 min at 1000 rpm and the supernatant was discarded.
4.1.2.16. Ethyl3-bromo-4-(2-(1-mesityl-1H-imidazo[4,5-c]pyri-
din-2-ylthio)acetamido)benzoate (5b13). White crystals,
yield: 56.7%. mp:201–203 °C. 1H NMR (600 MHz, DMSO-d6, ppm)
d: 10.09 (s, 1H, NH), 8.97 (s, 1H, C4-imidazo[4,5-c]pyridine-H),
8.28 (d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 8.14 (d, 1H,
J = 1.8 Hz, C3-Ph0-H), 8.02 (d, 1H, J = 8.4 Hz, C6-Ph0-H), 7.94 (dd,
1H, J1 = 8.4 Hz, J2 = 1.8 Hz, C5-Ph0-H), 7.19 (s, 2H, C3,5-Ph-H), 6.99
(d, 1H, J = 4.8 Hz, C7-imidazo[4,5-c]pyridine-7H), 4.44 (s, 2H, S-
CH2), 4.30 (q, 2H, J = 6.6 Hz, COCH2), 2.37 (s, 3H, Me), 1.85 (s, 6H,
2 ꢀ Me), 1.31 (t, 3H, J = 6.6 Hz, Me). ESI-MS: m/z 553.4 (M+1),
555.4 (M+3). C26H25BrN4O3S (552.08).
The MT-4 cells were resuspended at 6 ꢀ 105 cells/mL, and 50-
lL
volumes were transferred to the microtiter tray wells. Five days
after infection, the viability of mock- and HIV-infected cells was
examined spectrophotometrically by the MTT assay.
The MTT assay is based on the reduction of yellow colored
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide
(MTT) (Acros Organics, Geel, Belgium) by mitochondrial dehydro-
genase of metabolically active cells to a blue-purple formazan that
can be measured spectrophotometrically. The absorbances were
read in an eight-channel computer-controlled photometer (Multi-
scan Ascent Reader, Labsystems, Helsinki, Finland), at two wave-
lengths (540 and 690 nm). All data were calculated using the
median OD (optical density) value of three wells. The 50% cytotoxic
concentration (CC50) was defined as the concentration of the test
compound that reduced the absorbance (OD540) of the mock-in-
fected control samples by 50%. The 50% effective concentration
(EC50) was defined as the compound concentration required for
inhibiting virus-induced syncytium formation by 50%.
4.1.2.17.
N-(2-chloro-4-nitrophenyl)-2-(1-mesityl-1H-imi-
Grey crys-
dazo[4,5-c]pyridin-2-ylthio)acetamide (5b14).
tals, yield: 71.2%. mp:245–247 °C. 1H NMR (400 MHz, DMSO-d6,
ppm) d: 10.41 (s, 1H, NH), 8.94 (s, 1H, C4-imidazo[4,5-c]pyridine-
H), 8.38 (d, 1H, J = 2.4 Hz, C6-imidazo[4,5-c]pyridine-H), 8.31(d,
1H, J = 1.2 Hz, C5-Ph0-H), 8.29 (s, 1H, C3-Ph0-H), 8.22 (d, 1H,
J = 1.2 Hz, C6-Ph0-H), 7.19 (s, 2H, C3,5-Ph-H), 8.24 (d, 1H,
J = 2.4 Hz, C7-imidazo[4,5-c]pyridine-H), 4.50 (s, 2H, S-CH2), 2.37
(s, 3H, Me) 1.85 (s, 6H, 2 ꢀ Me). 13C NMR (100 MHz, DMSO-d6,
ppm) d: 167.13 (N–C@O), 154.29, 143.17, 142.23, 141.20, 140.73,
140.13, 139.97, 139.66, 136.07 (2 ꢀ C), 129.58 (2 ꢀ C), 128.20,
124.90, 123.87, 123.28, 122.87, 104.62, 35.69 (CH2-S), 20.65 (Me-
Ph), 16.79 (2ꢀMe-Ph). ESI-MS: m/z 482.2 (M+1), 484.12 (M+3).
4.3. HIV-1 RT inhibition assay
C23H20ClN5O3S (481.1).
Inhibition of HIV-1 RT was developed using nucleotides linked
to microtiter plate with colorimetric detection of incorporated bio-
tin-dUTP into homopolymer template primers.35 The incorporated
quantities of biotin-dUTP into the enzyme represented the activity
of HIV-1 RT. IC50 values corresponded to the concentration of the
imidazopyridinylthioacetanilide derivatives required to inhibit
biotin-dUTP incorporation into the HIV-1 RT by 50%.
4.1.2.18.
N-(3-bromo-5-methylpyridin-2-yl)-2-(1-mesityl-1H-
(5b15). White
imidazo[4,5-c]pyridin-2-ylthio)acetamide
crystals, yield: 60.0%. mp:155-157 °C. 1H NMR (600 MHz, DMSO-
d6, ppm) d: 10.41 (s, 1H, NH), 8.95 (s, 1H, imidazo[4,5-c]pyridine-
4H), 8.38 (d, 1H, J = 5.4 Hz, imidazo[4,5-c]pyridine-6H), 8.29 (m,
2H, pyridine-H), 7.19 (s, 2H, PhH), 7.00 (d, 1H, J = 5.4 Hz, imi-
dazo[4,5-c]pyridine-7H), 4.49 (s, 2H, S-CH2), 2.37 (s, 3H, Me),
1.85 (s, 6H, 2 ꢀ Me). ESI-MS: m/z 496.3 (M+1), 498.4 (M+3),
500.2 (M+5). C23H22BrN5OS (495.07).
Acknowledgment
The financial support from the National Natural Science
Foundation of China (NSFC No.81102320, No.30873133,
No.30772629, No.30371686), Key Project of NSFC for International
Cooperation (No.30910103908), Research Fund for the Doctoral
Program of Higher Education of China (No. 20110131130005,
20110131120037), Independent Innovation Foundation of Shan-
dong University (IIFSDU, No.2010GN044), Shandong Postdoctoral
Innovation Science Research Special Program (No.201002023),
China Postdoctoral Science Foundation funded project
(No.20100481282) and KU Leuven (GOA 10/014) is gratefully
acknowledged. We thank K. Erven, K. Uyttersprot and C. Heens
for technical assistance with the HIV assays.
4.1.2.19. N-(4-sulfonamide-2-bromophenyl)-2-(1-mesityl-1H-
imidazo[4,5-c]pyridin-2-ylthio)acetamide
(5b16).
White
crystals, yield: 62.2%. mp:190–192 °C. 1H NMR (600 MHz, DMSO-
d6, ppm) d: 10.15 (s, 1H, NH), 8.97 (s, 1H, C4-imidazo[4,5-c]pyri-
dine-H), 8.28 (d, 1H, J = 5.4 Hz, C6-imidazo[4,5-c]pyridine-H), 8.04
(s, 1H, C3-Ph0-H), 7.98 (d, 1H, J = 8.4 Hz, C5-Ph0-H), 7.79 (d, 1H,
J = 8.4 Hz, C6-Ph0-H), 7.46 (s, 2H, C3,5-Ph-H), 7.00 (d, 1H,
J = 5.4 Hz, C7-imidazo[4,5-c]pyridine-H), 4.44 (s, 2H, S-CH2), 2.50
(s, 3H, Me), 1.85 (s, 6H, 2ꢀMe). 13C-NMR (100 MHz, DMSO-d6,
ppm) d: 167.14 (N-C=O), 154.82, 142.72, 141.87, 141.27, 140.65,
140.60, 140.30, 139.39, 136.65 (2ꢀC), 130.51, 130.13, 128.79
(2ꢀC), 126.06, 125.54, 115.97, 105.14, 36.09 (CH2-S), 21.22 (Me-
Ph), 17.40 (2 ꢀ Me-Ph). ESI-MS: m/z 560.3 (M+1), 562.2 (M+3),
564.3 (M+5). C23H22BrN5O3S2 (559.03).
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