Synthesis and antiviral activity of N-phenylbenzamide derivatives, a novel class of enterovirus 71 inhibitors

Article abstract of DOI:10.3390/molecules18033630

A series of novel N-phenylbenzamide derivatives were synthesized and their anti-EV 71 activities were assayed in vitro. Among the compounds tested, 3-amino-N-(4- bromophenyl)-4-methoxybenzamide (1e) was active against the EV 71 strains tested at low micromolar concentrations, with IC₅₀ values ranging from 5.7 ± 0.8-12 ± 1.2 μM, and its cytotoxicity to Vero cells (TC₅₀ = 620 ± 0.0 μM) was far lower than that of pirodavir (TC₅₀ = 31 ± 2.2 μM). Based on these results, compound 1e is a promising lead compound for the development of anti-EV 71 drugs.

Full text of DOI:10.3390/molecules18033630

Molecules 2013, 18, 3630-3640; doi:10.3390/molecules18033630
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Antiviral Activity of N-Phenylbenzamide
Derivatives, a Novel Class of Enterovirus 71 Inhibitors
Xing-Yue Ji †, Hui-Qiang Wang †, Lan-Hu Hao, Wei-Ying He, Rong-Mei Gao, Yan-Ping Li *,
Yu-Huan Li *, Jian-Dong Jiang and Zhuo-Rong Li
Institute of Medicinal Biotechnology, Chinese Academy of Medical Science and Peking Union
Medical College, Beijing 100050, China
†
These authors contributed equally to this work.
* Authors to whom correspondence should be addressed; E-Mails: liyanping08@hotmail.com (Y.-P.L.);
yuhuanlibj@126.com (Y.-H.L.); Tel.: +86-10-6316-5267 (Y.-P.L.); +86-10-6301-0984 (Y.-H.L.);
Fax: +86-10-6301-7302 (Y.-P.L. & Y.-H.L.).
Received: 6 January 2013; in revised form: 14 March 2013 / Accepted: 18 March 2013 /
Published: 21 March 2013
Abstract: A series of novel N-phenylbenzamide derivatives were synthesized and their
anti-EV 71 activities were assayed in vitro. Among the compounds tested, 3-amino-N-(4-
bromophenyl)-4-methoxybenzamide (1e) was active against the EV 71 strains tested at low
micromolar concentrations, with IC50 values ranging from 5.7 ± 0.8–12 ± 1.2 μM, and its
cytotoxicity to Vero cells (TC50 = 620 ± 0.0 μM) was far lower than that of pirodavir
(TC50 = 31 ± 2.2 μM). Based on these results, compound 1e is a promising lead compound
for the development of anti-EV 71 drugs.
Keywords: synthesis; EV 71; N-phenylbenzamide
1. Introduction
Enterovirus 71 (EV 71) is a single-strained and positive sense RNA virus that belongs to the
Picornaviridae family. It was first isolated and identified from patients with central nervous system
(CNS) diseases in California between 1969 and 1974 [1]. Since then, outbreaks of EV 71 have been
reported in several countries, especially in the Asia Pacific region [2–4]. Diseases caused by an EV 71
infection include hand-foot-mouth disease (HFMD), herpangina (HA) and CNS involvement with fatal

Molecules 2013, 18
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pulmonary edema [5]. EV 71 infections are a global public health problem causing severe clinical
illness and even death in young children. However, there are currently no antiviral drugs or vaccines
available in the clinic against EV 71, and the majority of treatments are simply supportive symptom
management treatments. Consequently, there is an increasing need for the discovery of effective drugs
against EV 71. Additionally, due to the high mutation rate of EV 71, several genotypes have been
isolated in the clinic [6], and, at times, more than one genotype has been associated with both complicated
and uncomplicated diseases [7]. Therefore, pinpointing the active strain has been unsuccessful.
Consequently, the development of anti-EV 71 drugs should be mainly focused on the discovery of
compounds with activity against several genotypes of EV 71.
Antiviral screening of our privileged structure library was carried out, and compound 2a (Figure 1)
exhibited moderate activity against EV 71 virus (strain H, C2 genotype) in vitro with an IC50 value of
18 ± 1.2 μM. In order to obtain compounds with more potent activity and superior physicochemical
profiles, we synthesized a series of N-phenylbenzamide derivatives and evaluated their antiviral
activity against four strains (SZ-98, JS-52-3, H, BrCr) of EV 71 in Vero cells. The structure
modification was mainly made to the substituents at the C-3 position of the benzene ring A to
investigate the importance of amide group for the anti-EV 71 activity. Meanwhile, because there was
no substituent on the ring B of compound 2a, which possibly made it vulnerable to metabolism, we
also synthesized derivatives with substituents on the ring B to make them metabolically stable, and
also to explore the structure-activity relationships on the ring B. This is the first report of the anti-EV
71 activity of the N-phenylbenzamide scaffold, to the best of our knowledge.
Figure 1. The structure of compound 2a.
O
HN
MeO
F
H
A
N
B
O
2a
2. Results and Discussion
2.1. Chemistry
As shown in Schemes 1 and 2, a series of N-phenylbenzamide derivatives were designed and
synthesized according to our previous reported method [8]. In Scheme 1, 3-amino-4-methoxybenzoic
acid was chosen as the starting material and was condensed with a variety of amines, using
N,N′-diisopropylcarbodiimide (DIC) as the coupling reagent and N-hydroxybenzotriazole (HOBt) as
the activating reagent [9], to yield the intermediate compounds 1a–e. Under the same conditions,
compounds 1a, b were condensed with 2-fluoropropionic acid, which was obtained by the hydrolysis
of methyl 2-fluoropropanoate, to afford the target compounds 2a, b. Alkylation of the amine groups of
compounds 1a, c and d was accomplished by a nucleophilic substitution reaction. To avoid cleavage of

Molecules 2013, 18
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the amide bond during the reaction, a mild base (NaHCO3) was employed as the acid-binding agent.
When iodomethane (MeI) was used as the alkylating agent in excess, dialkylation products 3b, d were
also obtained in addition to monoalkylated products. Additionally, by a similar method used to
synthesize compounds 2a, b, we also synthesized compound 2c using 3-methoxy-4-aminobenzoic acid
as the starting material.
Scheme 1. The synthetic route to compounds 2a–c and 3a–g.
O
HN
MeO
F
NHR1
NH2
NH2
O
MeO
MeO
(i)
2a: R1 = phenyl
2b: R1 = cyclohexyl
OH
NHR1
O
O
R2
R3
1a: R1 = phenyl
1b: R1 = cyclohexyl
1c: R1 = 4-chlorophenyl
1d: R1 = 3,4,5-trimethoxyphenyl
1e: R1 = 4-bromophenyl
N
MeO
NHR1
O
3a: R1 = phenyl, R2 = Me, R3 = H
3b: R1 = 4-chlorophenyl, R2 = R3 = Me
3c: R1 = 3,4,5-trimethoxyphenyl, R2 = Me, R3 = H
3d: R1 = 3,4,5-trimethoxyphenyl, R2 = R3 = Me
3e: R1 = phenyl, R2 = n-Pr, R3 = H
3f: R1 = 4-chlorophenyl, R2 = n-Pr, R3 = H
3g: R1 = 3,4,5-trimethoxyphenyl, R2 = n-Pr, R3 = H
F
OMe
OMe
OMe
H
N
H2N
H2N
(ii)
(i)
H
H
O
N
N
OH
O
O
O
2c
1f
Reagents and conditions: (i) DIC, HOBt, R1NH2, CH2Cl2, rt, 5 h, 60–70%, (ii) 2-fluoropropionic
acid, DIC, HOBt, CH2Cl2, rt, 5 h, 60–70%, (iii) MeI/PrI, NaHCO3, CH2Cl2, rt, 12 h, 30–50%.
Scheme 2. The synthetic route to compounds 5a–f.
O
O
X
R4
O
X
R4
XH
MeO
MeO
(i)
(ii)
MeO
R6
N
OH
OH
O
O
R5
5a: R4 = Et, R5 = H, R6 = H, X = NH
5b: R4 = Et, R5 = Cl, R6 = H, X = NH
5c: R4 = Et, R5 = Br, R6 = H, X = NH
5d: R4 = Et, R5 = Cl, R6 = Me, X = O
5e: R4 = Me, R5 = Cl, R6 = H, X = O
5f: R4 = Me, R5 = H, R6 = H, X = O
4a: R4 = Et, X = NH
4b: R4 = Et, X = O
4c: R4 = Me, X= O
Reagents and conditions: (i) TEA, CH2Cl2, R4COCl, 0 °C-rt, 6 h, 70–80%, (ii) DIC, HOBt, amines,
CH2Cl2, rt, 5 h, 60–70%, or SOCl2, reflux 1 h, then CH2Cl2, TEA, amines , 0 °C-rt, 6 h, 60–70%.

Molecules 2013, 18
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As depicted in Scheme 2, we also synthesized several derivatives with propionyloxy (acetoxy) and
propionylamino substituents on the benzene ring A. 3-Hydroxyl/amino-4-methoxybenzoic acid was
first reacted in dichloromethane with propionyl chloride or acetyl chloride using triethylamine (TEA)
as the base to afford compounds 4a–c. By using a similar method to that used for compounds 1a–e,
compounds 5a–f were thus obtained. Alternatively, compounds 4a–c were first reacted with thionyl
chloride under refluxing conditions to give intermediate chloride products, which were condensed with
a substituted arylamine to yield the target compounds 5a–f. Ultimately, compounds 5a–f were obtained
in overall yields of 40–60%.
2.2. Anti-EV 71 Activity
The EV 71 was divided into three genotypes A, B and C based on nucleotide sequence
comparisons, and genotypes B and C were subdivided into B1-B5 and C1-C5 [6,10]. Genotype C is
the most common genotype found in mainland China, especially the C4 subgenotype [4,11].
Consequently, the intermediate compounds 1a, 1c and 1e, and the final products 2a–c, 3a–g, and 5a–f
were evaluated for their anti-EV 71 activity in Vero cells against genotypes C4 (strains SZ-98 and
JS-52-3), C2 (strain H) and A (strain BrCr). Pirodavir (Figure 2) is a rather potent and broad-spectrum
picornavirus inhibitor. It was reported to be effective against 80% of 16 enteroviruses tested at the
concentration of 1.3 μg/mL [12]. Therefore, we employed pirodavir as positive control to validate our
model. The IC50 values were calculated by the Reed and Muench method, and the cytotoxicity was
monitored by the CPE method.
Figure 2. The chemical structure of pirodavir.
N
N
O
N
O
O
Pirodavir
As indicated in Table 1, the cytotoxicity of all the synthesized compounds was far lower than that
of pirodavir, and most of the synthesized N-phenylamide derivatives exhibited some activity against
several strains of EV 71 simultaneously, especially compound 1e, which was active against all the
strains tested at low micromolar concentrations (5.7 ± 0.80–12 ± 1.2 μM). In addition to compound 1e,
other compounds also showed moderate levels of inhibitory activity with IC50 values of approximately
15 μM including, compound 1c against strain SZ-98, compound 3g against strains H and BrCr, 3e
against strain H, 5c against strains SZ-98, JS-52-3 and H, and compound 5e against strain SZ-98.
Moreover, the selectivity index (SI) values of compounds 1c (10–36), 1e (51–110), 3g (16–35), 5b
(>16 – >27), 5c (16–63) and 5e (15–37) were also comparable or superior to those of pirodavir
(25–52).

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Table 1. The activity of the synthesized N-phenylbenzamide derivatives against several
strains of EV 71.
SZ-98
IC50
(μM)
JS-52-3
IC50
(μM)
H
BrCr
IC50
(μM)
TC50
Cpds
IC50
(μM)
SI
SI
SI
SI
(μM)
1a
1c
1e
2a
2b
2c
3a
3b
3c
3d
3e
3f
>820
350 ± 24 2.3 160 ± 7.9 5.2 190 ± 14 4.3 160 ± 12 5.2
520 ± 29 15 ± 0.6
620 ± 0.0 12 ± 1.1
36
51
-
46 ± 5.7
9.8 ± 0.4
12
64
34 ± 3.6
5.7 ± 0.8 110 9.1 ± 1.4
>630
16
56 ± 4.2
10
68
-
630 ± 0.0
>620
>630
>620
160 ± 5.7 >3.9 18 ± 1.2 >35
-
210 ± 0.0 >3.0 430 ± 36 >1.4 360 ± 26 >1.7
41 ± 2.9 >16 90 ± 9.5 >7.0
260 ± 0.0 3.0 260 ± 0.0 3.0 180 ± 14 4.3
>630
110 ± 12 >5.8 34 ± 2.8
>260
780 ± 0.0
-
510 ± 38 73 ± 8.6 7.0
280 ± 5.9 64 ± 0.0 4.3
42 ± 3.1
37 ± 1.9
>560
12
7.5
-
31 ± 4.3
37 ± 1.2
16
50 ± 3.8
44 ± 1.0
10
7.5
6.2
>560
410 ± 22
120
320 ± 32 >1.7
190 ± 0.0 >3.0 190 ± 0.0 >3.0
>78
>70
>59
>75
-
-
-
-
34 ± 4.6
>70
12
-
20 ± 1.2
>70
20
-
45 ± 0.0
>70
9.0
-
3g
5a
5b
5c
5d
5e
5f
530
34 ± 2.5
16
15 ± 0.0
35
20 ± 3.1
27
9.0
-
>670
>600
58 ± 4.9 >12
96 ± 10 >7.0 45 ± 10
38 ± 2.9 > 16 39 ± 1.9 >16 22 ± 2.9 >27
>67
530 ± 0.0 11 ± 0.8
47
20 ± 3.1
44 ± 3.7
32 ± 3.6
98 ± 4.7
1.0 ± 0.2
27
6.2
14
8.4 ± 1.2
65 ± 0.0
22 ± 4.7
47 ± 6.1
0.6 ± 0.1
63
4.3
21
34 ± 0.0
53 ± 2.4
32 ± 3.9
95 ± 9.0
1.0 ± 0.2
16
5.2
15
3.8
30
280 ± 21 190 ± 12 1.4
470 ± 22 13 ± 2.4
360 ± 39 90 ± 11
37
4.0
3.7
30
7.6
52
Pirodavir 31 ± 2.2 1.2 ± 0.2 25
TC50 was defined as the concentration that inhibits 50% cellular growth in comparison with untreated controls
and calculated by Reed and Muench method. IC50 (50% inhibitory concentration) was calculated by Reed
& Muench method. The selectivity index (SI) was calculated as the ratio of TC50/IC50. “-” stands for no
antiviral selectivity.
In terms of structure-activity relationships, benzene ring B was essential for anti-EV 71 activity. For
example, when benzene ring B was replaced by a cyclohexyl group (2b), no anti-EV 71 activity was
observed. On the basis of the activity of compounds 1c, 1e, 5b, 5c and 5e against EV 71, it was
concluded that the introduction of electron-withdrawing groups (Cl and Br, especially Br) at the para
position of benzene ring B increased anti-EV 71 activity. Substitution of acetoxy groups (5e, f) for the
propionylamino group (5a, b) on benzene ring A had little influence on anti-EV 71 activity. Because
the activity of compounds with propionyl substituent at the amino group (5b, c) was slightly inferior to
their unsubstituted counterparts (1c, e), it can be concluded that the propionyl substituent at the amino
group disfavors the anti-EV 71 activity. Compound 5d presented less potent activity against EV 71 in
comparison to 5e. Therefore, it is possible that H-bond donor group at the position of R6 substituent
favors the anti-EV 71 activity.

Molecules 2013, 18
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3. Experimental
3.1. General
All reagents and solvents were purchased from J&K and Alfa Aesar Chemicals, and were used
without purification. 1H-NMR and 13C-NMR spectra were recorded in CDCl3 or DMSO-d6 on a Varian
Inova 400/500 MHz spectrometer (Varian, San Francisco, CA, USA). Chemical shift was reported in
parts per million relative to tetramethylsilane as the internal standard. Melting points were determined
with a X6 microscope melting point apparatus and were uncorrected. Electrospray ionisation (ESI)
high-resolution mass spectra (HRMS) were obtained on an MDS SCIEX Q-Trap mass spectrometer.
The area normalization purities of the tested compounds were >95% as determined using analytical
high-performance liquid chromatography (HPLC method for all compounds: detector wavelength: 260 nm,
column temperature: 25 °C, column: ODS (5 μm, 4.6 × 250 mm), mobile phase: methanol/water =
75/25, flow rate = 1 mL/min). For the synthesis and spectral data of compounds 1a, 2a, 4a, 4b, 5a and
5c, please refer to our previous paper [8].
3.1.1. General Procedure for the Synthesis of Compound 1b–f, 5b, 5e, 5f
3-Amino-4-methoxybenzoic acid/4a, c (1.20 mmol) was dissolved in CH2Cl2 (20 mL), and DIC
(1.82 mmol) and HOBt (1.82 mmol) was added to the solution. The resulting mixture was stirred for
0.5 h at room temperature, after which amines (1.68 mmol) was added. After approximately 12 h, the
reaction was quenched by the addition of 0.5 N NaOH solution (20 mL), and the organic layer was
separated and washed with dilute hydrochloric acid (10%, 30 mL) and brine (30 mL), successively.
The solution was then dried over anhydrous MgSO4, filtered and concentrated, and the crude residue
was purified over silica gel (petroleum/ethyl acetate = 3/2) to give the corresponding compounds.
3-Amino-N-cyclohexyl-4-methoxybenzamide (1b). White solid, yield: 65%. mp: 171–172 °C. 1H-NMR
(400 MHz, DMSO-d6) δ: 1.13 (1H, m), 1.24 (4H, m), 1.62 (1H, m), 1.75 (4H, m), 3.63 (1H, m), 3.79
(3H, s), 4.79 (2H, br), 6.80 (1H, d, J = 8.4 Hz), 7.07 (1H, d, J = 8.4 Hz), 7.12 (1H, s), 8.25 (1H, s).
ESI-HRMS m/z: 249.16018 (M+H+) (Calcd for C14H21N2O2: 249.16030).
3-Amino-N-(4-chlorophenyl)-4-methoxybenzamide (1c). White solid, yield: 66%. mp 152–154 °C.
1H-NMR (400 MHz, DMSO-d6) δ: 3.84 (s, 3H), 5.46 (2H, br), 6.88 (d, 1H, J = 6.8 Hz), 7.19 (m, 2H),
7.37 (d, 2H, J = 8.0Hz), 7.78 (d, 2H, J = 8.0Hz), 10.07 (s, 1H). 13C-NMR (100 MHz, CDCl3) δ: 55.6,
109.6, 113.4, 117.4, 121.2, 124.7, 128.9, 129.2, 136.5, 150.1, 156.9. ESI-HRMS m/z: 277.07487
(M+H+) (Calcd for C14H14ClN2O2: 277.07438).
3-Amino-4-methoxy-N-(3,4,5-trimethoxyphenyl)benzamide (1d). White solid, yield: 65%. mp: 140–142 °C.
1H-NMR (500 MHz, DMSO-d6) δ: 3.62 (3H, s), 3.76 (6H, s), 3.83 (3H, s), 4.92 (2H, s), 6.88 (1H, d,
J = 8.0 Hz), 7.22 (4H, m), 9.85 (1H, s). ESI-HRMS m/z: 333.14778 (M+H+) (Calcd for C17H21N2O5:
333.14505).
3-Amino-N-(4-bromophenyl)-4-methoxybenzamide (1e). White solid, yield: 68%. mp 190–192°C.
1H-NMR (500 MHz, DMSO-d6) δ: 3.84 (s, 3H), 4.97 (s, 2H), 6.90 (d, 1H, J = 8.0 Hz), 7.21 (m, 2H),

Molecules 2013, 18
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7.51 (d, 2H, J = 8.0 Hz), 7.74 (d, 2H, J = 8.0 Hz), 10.10 (s, 1H). 13C-NMR (100 MHz, CDCl3) δ: 55.6,
109.6, 113.6, 116.6, 117.3, 121.5, 127.3, 131.9, 136.5, 137.3, 150.1, 165.5. ESI-HRMS m/z: 321.02365
(M+H+) (Calcd for C14H14BrN2O2: 321.02387).
4-Amino-3-methoxy-N-phenylbenzamide (1f). White solid, yield: 70%. mp: 174–176°C. 1H-NMR (400
MHz, DMSO-d6) δ: 3.82 (s, 3H), 5.37 (2H, s), 6.66 (1H, d, J = 8.0 Hz), 7.03 (1H, d, J = 8.0 Hz), 7.32
(2H, m), 7.45 (2H, m), 7.73 (2H, d, J = 7.6 Hz), 9.77 (1H, s). ESI-HRMS m/z: 243.11329 (M+H+)
(Calcd for C14H15N2O2: 243.11335).
N-(4-Chlorophenyl)-4-methoxy-3-propionamidobenzamide (5b). White solid, yield: 70%. mp: 130–132 °C.
1H-NMR (400 MHz, CDCl3) δ: 1.07 (3H, t, J = 7.6 Hz), 2.42 (2H, q, J = 7.6 Hz), 3.96 (3H, s), 6.98
(1H, d, J = 8.0 Hz), 7.32 (1H, d, J = 8.0 Hz), 7.62 (2H, d, J = 8.0 Hz), 7.79 (1H, dd, J = 8.0 and
2.0 Hz), 7.82 (1H, s), 8.09 (1H, s), 8.87 (1H, s). ESI-HRMS m/z: 333.10200 (M+H+) (Calcd for
C17H18ClN2O3: 333.10059).
N-(4-Chlorophenyl)-4-methoxy-3-acetoxybenzamide (5e). White solid, yield: 58%. mp: 177–179 °C.
1H-NMR (400 MHz, DMSO-d6) δ: 2.34 (3H, s), 3.89 (3H, s), 6.73 (1H, d, J = 8.0 Hz), 7.01 (2H, d,
J = 8.4 Hz), 7.13 (1H, d, J = 8.0 Hz), 7.22 (2H, d, J = 8.4 Hz), 8.30 (1H, s), 9.01 (1H, s). ESI-HRMS
m/z: 320.06891 (M+H+) (Calcd for C16H15ClNO4: 320.06896).
1
4-Methoxy-N-phenyl-3-acetoxybenzamide (5f). White solid, yield: 61%. mp: 153–155 °C. H-NMR
(400 MHz, DMSO-d6) δ: 2.29 (3H, s), 3.85 (3H, s), 7.08 (1H, t, J = 8.0 Hz), 7.26 (1H, d, J = 8.4 Hz),
7.33 (2H, t, J = 8.0 Hz), 7.73 (3H, m), 7.92 (d, 1H, J = 8.4 Hz), 10.11 (1H, s). ESI-HRMS m/z:
286.10799 (M+H+) (Calcd for C16H16NO4: 286.10793).
3.1.2. General Procedure for the Synthesis of Compounds 2b, c
2-Fluoropropanoic acid (2.40 mmol) was dissolved in CH2Cl2 (20 mL), and DIC (3.60 mmol) and
HOBt (3.60 mmol) was added to the solution. The resulting mixture was stirred for 0.5 h at room
temperature, after which compound 1b/1e (1.71 mmol) was added. After approximately 12 h, the
reaction was quenched by the addition of 0.5 N NaOH solution (20 mL), and the organic layer was
separated and washed with dilute hydrochloric acid (10%, 30 mL) and brine (30 mL), successively.
The solution was then dried over anhydrous MgSO4, filtered and concentrated, and the crude residue
was purified over silica gel (petroleum/ethyl acetate = 4/1) to give compounds 2b, c.
N-Cyclohexyl-3-(2-fluoropropanamido)-4-methoxybenzamide (2b). White solid, yield: 73%. mp:
192–194 °C. 1H-NMR (400 MHz, DMSO-d6) δ: 1.15 (1H, m), 1.26 (4H, m), 1.55 (3H, dd, J = 6.4 and
16.8 Hz), 1.61 (1H, m), 1.72 (4H, m), 3.73 (1H, m), 3.93 (3H, s), 5.34 (1H, qq, J = 6.4 and 48.8 Hz),
7.15 (1H, d, J = 8.0 Hz), 8.06 (1H, d, J = 8.0 Hz),8.33 (1H, s), 9.16 (1H, s), 13.63 (1H, s). ESI-HRMS
m/z: 323.17695 (M+H+) (Calcd for C17H24FN2O3: 323.17710).
4-(2-Fluoropropanamido)-3-methoxy-N-phenylbenzamide (2c). White solid, yield: 59%. mp: 142–143 °C.
1H-NMR (500 MHz, DMSO-d6) δ: 1.55 (3H, dd, J = 6.5 and 20.0 Hz), 3.96 (3H, s), 5.34 (1H, qq,
J = 7.0 and 48.5 Hz), 7.09 (1H, t, J = 8.0 Hz), 7.35 (2H, t, J = 8.0 Hz), 7.61 (2H, m), 7.74 (2H, d,

Molecules 2013, 18
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J = 8.0 Hz), 8.17 (1H, d, J = 8.0 Hz), 9.22 (1H, s), 10.12 (1H, s). ESI-HRMS m/z: 317.13087 (M+H+)
(Calcd for C17H18FN2O3: 317.13015).
3.1.3. General Procedure for the Synthesis of Compound 3a–g
Compound 1a/1c/1d (2.2 mmol) was dissolved in CH2Cl2 (15 mL), and NaHCO3 (2.5 mmol) and
MeI/n-PrI (22 mmol) were added. The resulting mixture was stirred for 12 h at room temperature. The
mixture was filtered, and the filtrate was concentrated in vacuo to give a residue which was purified
over silica gel (petroleum/ethyl acetate = 2/1) to give the target compounds 3a–g.
4-Methoxy-3-methylamino-N-phenylbenzamide (3a). White solid, yield: 33%. mp: 170–172 °C.
1H-NMR (400 MHz, DMSO-d6) δ: 2.77 (d, 3H, J = 5.2 Hz), 3.84 (s, 3H), 5.19 (q, 1H, J = 5.2 Hz), 6.88
(d, 1H, J = 8.0 Hz), 7.05 (m, 2H), 7.23 (d, 1H, J = 8.0 Hz), 7.32 (t, 2H, J = 8.0 Hz), 7.74 (d, 2H,
J = 8.0 Hz), 9.93 (s, 1H). 13C-NMR (100 MHz, CDCl3) δ: 30.2, 55.6, 107.8, 108.2, 115.0, 119.9,
124.1, 128.1, 129.0, 138.3, 139.5, 149.6, 166.1. ESI-HRMS m/z: 257.12934 (M+H+) (Calcd for
C15H17N2O2: 257.12900).
N-(4-Chlorophenyl)-3-dimethylamino-4-methoxybenzamide (3b). White solid, yield: 40%. mp:
1
160–162 °C. H-NMR (400 MHz, DMSO-d6) δ: 2.77 (6H, s), 3.86 (3H, s), 7.03 (1H, d, J = 8.0 Hz),
7.37 (2H, d, J = 8.0 Hz), 7.43 (1H, s), 7.60 (1H, d, J = 8.0 Hz), 7.79 (2H, d, J = 8.0 Hz), 10.12 (1H, s).
13C-NMR (100 MHz, DMSO-d6) δ: 23.8, 56.2, 111.4, 117.7, 122.2, 127.2, 127.4, 128.8, 138.9, 142.3,
155.1, 157.3, 165.9. ESI-HRMS m/z: 305.10524 (M+H+) (Calcd for C16H18ClN2O2: 305.10568).
4-Methoxy-3-methylamino-N-(3,4,5-trimethoxyphenyl)benzamide (3c). White solid, yield: 30%. mp:
1
147–148 °C. H-NMR (400 MHz, DMSO-d6) δ: 2.77 (3H, s), 3.62 (3H, s), 3.75 (6H, s), 3.84 (3H, s),
5.21 (1H, br), 6.89 (1H, d, J = 8.0 Hz), 7.01 (1H, s), 7.24 (3H, m), 9.84 (1H, s). 13C-NMR (100 MHz,
CDCl3) δ: 30.2, 55.6, 56.1, 60.9, 65.8, 97.6, 107.8, 108.6, 114.9, 127.9, 134.4, 134.5, 139.5, 149.6,
153.3, 166.1. ESI-HRMS m/z: 347.16079 (M+H+) (Calcd for C18H23N2O5: 347.16070).
3-Dimethylamino-4-methoxy-N-(3,4,5-trimethoxyphenyl)benzamide (3d). White solid, yield: 21%. mp:
1
120–122 °C. H-NMR (400 MHz, DMSO-d6) δ: 2.76 (6H, s), 3.62 (3H, s), 3.75 (6H, s), 3.87 (3H, s),
13
7.08 (1H, d, J = 8.0 Hz), 7.20 (2H, s), 7.48 (1H, s), 7.82 (1H, d, J = 8.0 Hz), 9.98 (1H, s). C-NMR
(100 MHz, CDCl3) δ: 30.2, 55.6, 56.1, 56.1, 60.9, 97.9, 107.8, 108.4, 110.2, 115.2, 116.4, 124.8, 127.2,
127.8, 134.2, 153.2, 166.3. ESI-HRMS m/z: 361.17621 (M+H+) (Calcd for C19H25N2O5: 361.17635).
4-Methoxy-N-phenyl-3-(propylamino)benzamide (3e). White solid, yield: 46%. mp: 121–123 °C.
1H-NMR (400 MHz, DMSO-d6) δ: 0.94 (3H, t, J = 7.2 Hz), 1.62 (2H, m), 3.09 (2H, m), 3.84 (3H, s),
4.93 (1H, t, J = 5.6 Hz), 6.88 (1H, d, J = 8.4 Hz), 7.05 (2H, m), 7.23 (1H, d, J = 8.4 Hz), 7.31 (2H, t,
J = 8.0 Hz), 7.73 (2H, d, J = 8.0 Hz), 9.93 (1H, s). 13C-NMR (100 MHz, DMSO-d6) δ: 11.6, 21.7, 40.1,
55.6, 107.8, 108.6, 115.6, 120.3, 123.2, 127.4, 128.5, 137.8, 139.4, 148.9, 165.7. ESI-HRMS m/z:
285.15975 (M+H+) (Calcd for C17H21N2O2: 285.16006).
N-(4-Chlorophenyl)-4-methoxy-3-propylaminobenzamide (3f). White solid, yield: 37%. mp: 168–171 °C.
1H-NMR (500 MHz, DMSO-d6) δ: 0.93 (3H, t, J = 7.0 Hz), 1.59 (2H, m), 3.09 (2H, m), 3.84 (3H, s),

Molecules 2013, 18
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4.93 (1H, t, J = 5.0 Hz), 6.89 (1H, d, J = 8.0 Hz), 7.05 (1H, s), 7.24 (1H, dd, J = 1.5 and 8.0 Hz), 7.36
(2H, d, J = 8.0 Hz), 7.79 (2H, d, J = 8.0 Hz), 10.05 (1H, s). 13C-NMR (100 MHz, DMSO-d6) δ: 11.6,
21.7, 39.9, 55.6, 107.8, 108.7, 115.7, 121.8, 126.8, 127.2, 128.4, 137.9, 138.5, 149.0, 165.9.
ESI-HRMS m/z: 319.12139 (M+H+) (Calcd for C17H20ClN2O2: 319.12133).
4-Methoxy-3-(propylamino)-N-(3,4,5-trimethoxyphenyl)benzamide (3g). White solid, yield: 41%. mp:
164–167 °C. 1H-NMR (500 MHz, DMSO-d6) δ: 0.92 (3H, t, J = 7.0 Hz), 1.60 (2H, m), 3.09 (2H, m),
3.62 (3H, s), 3.75 (6H, s), 3.84 (3H, s), 4.93 (1H, br), 6.89 (1H, d, J = 8.0 Hz), 7.06 (1H, s), 7.23 (3H,
m), 9.84 (1H, s). 13C-NMR (100 MHz, CDCl3) δ: 11.5, 22.5, 45.2, 55.5, 56.0, 60.9, 97.6, 108.2, 108.3,
114.6, 127.8, 134.5, 134.5, 138.7, 149.4, 153.3, 166.1. ESI-HRMS m/z: 375.19227 (M+H+) (Calcd for
C20H27N2O5: 375.19200).
3-Acetoxy-4-methoxybenzoic acid (4c). To a solution of 3-hydroxy-4-methoxybenzoic acid (5.0 g,
30 mmol) and Et3N (4.5 g, 45 mmol) in CH2Cl2 (100 mL) was added acetyl chloride (3.5 g, 45 mmol)
at 0 °C, and the resulting mixture was warmed to room temperature and then stirred for another 2 h.
The reaction mixture was then washed with water (100 mL), and brine (100 mL) successively. The
organic layer was dried over anhydrous MgSO4, filtered and concentrated, and the crude residue was
purified over silica gel (petroleum/ethyl acetate = 4/1) to give compounds 4c (3.8 g, yield: 60%), white
1
solid, mp: 230–231 °C. H-NMR (400 MHz, DMSO-d6) δ: 2.23 (3H, s), 3.85 (3H, s), 7.35 (1H, d,
J = 8.0 Hz), 7.83 (1H, s), 7.90 (1H, d, J = 8.0 Hz), 12.21 (1H, s). ESI-HRMS m/z: 209.04513 (M−H−)
(Calcd for C10H9O5: 209.04500).
N-(4-Chlorophenyl)-N-methyl-4-methoxy-3-propionyloxybenzamide (5d). A mixture of compound 4b
(0.5 g, 2.23 mmol) and SOCl2 (15 mL, 206 mmol) was heated under reflux for 1 h. The excess SOCl2
was evaporated and the corresponding chloride product was obtained as yellow oil, which was
dissolved in CH2Cl2 (5 mL) and used without further purification. N-methyl-4-chlorobenzenamine
(0.38 g, 2.68 mmol) was dissolved in CH2Cl2 (20 mL), and Et3N (0.34 g, 3.34 mmol) was added, and
the mixture was cooled to 0 °C (ice bath). A solution of the acid chloride product in CH2Cl2 (5 mL)
was added to the solution dropwise. The resulting mixture was warmed to room temperature and then
stirred for another 4 h, after which water (20 mL) was added, and the organic layer was separated,
washed with brine (30 mL), and dried over anhydrous MgSO4. It was then filtered and concentrated to
give a residue, which was purified over silica gel (petroleum/ethyl acetate = 1/1) to yield compound 5d as a
white solid (0.5 g, yield: 64%). mp: 139–141 °C. 1H-NMR (400 MHz, CDCl3) δ: 1.23 (3H, t, J = 7.6 Hz),
2.55 (2H, q, J = 7.6 Hz), 3.44 (3H, s), 3.77 (3H, s), 6.72 (1H, d, J = 8.4 Hz), 6.98 (1H, d, J = 8.4 Hz),
7.06 (1H, s), 7.11 (1H, d, J = 8.8 Hz), 7.22 (2H, d, J = 8.8 Hz). ESI-HRMS m/z: 348.10021 (M+H+)
(Calcd for C18H19ClNO4: 348.10026).
3.2. Biological Activity Test Procedures
Vero cells were purchased from the American Type Culture Collection and cultured in Minimum
Essential Medium (MEM) supplemented with 10% Fetal Bovine Serum (FBS) and antibiotics
(100 U/mL penicillin G, 100 μg/mL streptomycin). Enterovirus 71 (EV 71) strain SZ-98 was kindly
provided by Dr. Qi Jin, Institute of Pathogen Biology, Chinese Academy of Medical Science and

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Peking Union Medical School. Enterovirus 71 (EV 71) strain BrCr (VR-1775) was purchased from the
American Type Culture Collection. Enterovirus 71 (EV 71) strain JS-52-3 was kindly provided by
Dr. Xiang-zhong Ye, Beijing Wantai Biological Pharmacy Enterprise Co., Ltd. All Enterovirus 71
strains were propagated in Vero cells.
All compounds were dissolved in DMSO at 20 mg/mL as a stock solution and further diluted in
culture medium prior to use. The initial concentration in all cytotoxicity assay was 200 µg/mL, and
inhibition assay for anti-EV71 experiments was from maximum non-toxic concentration, and
proceeded serially 3-fold dilution with culture medium. All cytotoxicity and activity assay for each
compound was repeated for three times, and the data was indicated as average ± SD.
3.2.1. Cytotoxicity Determination
The cytotoxicity of compounds in the presence of Vero cells was monitored by cytopathic effect
(CPE). Vero cells (2.5 × 104/well) were plated into a 96-well plate. A total of 24 h later, the monolayer
cells were incubated in the presence of various concentrations of test compounds. After 48 h of culture
at 37 °C and 5% CO2 in a carbon-dioxide incubator, the cells were monitored by CPE. The median
toxic concentration (TC50) was calculated by Reed & Muench analyses.
3.2.2. Anti EV 71 Activity Assay
Confluent Vero cells grown in 96-well microplates were infected respectively with 100 median
tissue culture infective dose (TCID50) EV 71. After 1 h adsorption at 37 °C, the monolayers were
washed by PBS and incubated at 37 °C in the maintenance medium with or without different
concentrations of test compounds. Viral cytopathic effect (CPE) was observed when the viral control group
reached 4 and the antiviral activity of tested compounds was determined by the Reed & Muench analyses.
4. Conclusions
In summary, a series of N-phenylbenzamide derivatives were synthesized and their anti-EV 71
activities were evaluated in vitro. All of the synthesized compounds were less toxic to Vero cells in
comparison to pirodavir, and several compounds were comparable or superior to pirodavir in terms of SI
values, especially compound 1e. This compound has a molecular weight and an ALogP of 321.169 g/mol
and 2.6 (data obtained from Discovery Studio 3.0), respectively, and shows potential for optimization
to improve its activity against EV 71 without sacrificing its druggability. Consequently, compound 1e
is a promising lead compound for the development of a new anti-EV 71 agent, and further lead
optimization based on compound 1e will be performed.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant 30873138
and 81202414).

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3640
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Sample Availability: Samples of the compounds 1a, 1c, 1e, 2a–c, 3a–g, and 5a–f are available from
the authors.
© 2013 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).