Synthesis and anti-HIV activity evaluation of 2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-acetamides as novel non-nucleoside HIV-1 reverse transcriptase inhibitors

Article abstract of DOI:10.1016/j.ejmech.2009.06.037

A series of 2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)acetamide (TTA) derivatives were synthesized and evaluated as potent inhibitors of HIV-1. Among the newly disclosed TTAs, compounds 7f, 7g and 7c were the most potent inhibitors of HIV-1 replication of the series (EC₅₀ = 0.17 ± 0.02, 0.36 ± 0.19 and 0.39 ± 0.05 μM, respectively), coupled with a reasonable selectivity index (SI > 1452, >845, and >774, respectively). They possess improved or similar HIV-1 inhibitory activity compared with NVP (EC₅₀ = 0.208 μM) and DLV (EC₅₀ = 0.320 μM). The preliminary structure-activity relationships among the newly synthesized congeners are discussed briefly and rationalized by docking studies. Crown Copyright

Full text of DOI:10.1016/j.ejmech.2009.06.037

European Journal of Medicinal Chemistry 44 (2009) 4648–4653
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and anti-HIV activity evaluation of 2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)-N-acetamides as novel non-nucleoside HIV-1
reverse transcriptase inhibitors
,
a
a
b
b
Peng Zhan a, Xinyong Liu a , Zengjun Fang , Zhenyu Li , Christophe Pannecouque , Erik De Clercq
*
a Institute of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, No. 44 Wenhuaxi Road, Jinan 250012, PR China
b Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)acetamide (TTA) derivatives were synthe-
sized and evaluated as potent inhibitors of HIV-1. Among the newly disclosed TTAs, compounds 7f, 7g
and 7c were the most potent inhibitors of HIV-1 replication of the series (EC50 ¼ 0.17 ꢀ 0.02, 0.36 ꢀ 0.19
Received 8 June 2009
Received in revised form
29 June 2009
Accepted 30 June 2009
Available online 4 July 2009
and 0.39 ꢀ 0.05
mM, respectively), coupled with a reasonable selectivity index (SI > 1452, >845, and
>774, respectively). They possess improved or similar HIV-1 inhibitory activity compared with NVP
M). The preliminary structure–activity relationships among
(EC50 ¼ 0.208
m
M) and DLV (EC50 ¼ 0.320
m
the newly synthesized congeners are discussed briefly and rationalized by docking studies.
Keywords:
HIV-1
Crown Copyright Ó 2009 Published by Elsevier Masson SAS. All rights reserved.
AIDS
NNRTIs
Thiadiazole thioacetanilides
Heterocycle
Antiviral activity
1. Introduction
of our work on the search of novel NNRTIs [14,15], we thought it
worthwhile to synthesize new compounds of TTAs having 4-(2-
The reverse transcriptase (RT) of the human immunodeficiency
virus type 1 (HIV-1) is a key target for inhibition of HIV-1 replica-
tion. The RTcan be inhibited by two classes of drug belonging either
to the nucleoside reverse transcriptase inhibitors (NRTIs) or to the
non-nucleoside reverse transcriptase inhibitors (NNRTIs). NNRTIs
have proved to be an important component of cocktail therapy [1–
4]. However, the long-term usage of NNRTIs in HIV/AIDS patients
may eventually lead to the development of virus-drug resistance.
Therefore, it is imperative to look for novel NNRTIs with potent and
broad spectrum anti-HIV mutant activity that are also safe and have
excellent pharmacokinetic profiles [5].
Among the representatives of the NNRTIs, sulfanyltriazoles (I)
and sulfanyltetrazoles (II) (Fig. 1) have interesting structures and
offer various opportunities on the skeleton of sulfanylazoles as
lead compounds [6–11]. Initially, we developed a series of 2-(4-
(2,4-dichlorophenyl)-1,2,3-thiadiazol-5-ylthio)-N-acetamide (TTA)
analogues (III, Fig. 1), which exhibited significant anti-HIV-1 activ-
ities [12,13]. Inspired by these promising results and in continuation
naphthoyl) moiety attached to 1,2,3-thiadiazole, with the aim to
strengthen the stacking interaction between the inhibitors and
aromatic residues (such as Tyr188 or Tyr181) of RTand to obtain new
biologically active compounds (Fig. 2).
p–p
Molecular modeling studies of the sulfanyltriazole/tetrazoles
family [6,10,11,13] revealed that the N-substituted anilide phenyl
ring extends from the NNRTI binding pocket to the protein/solvent
interface, which presents an attractive site (a tolerant region) for
introducing structurally diverse moieties to generate novel mole-
cules with reasonable anti-HIV activity (Fig. 2).
These backgrounds prompted us to further explore novel 4-(2-
naphthoyl) TTAs bearing substituted anilide phenyl ring or
heterocycles linked with the amide. In this paper, a series of novel
TTA analogues were synthesized and evaluated for anti-HIV activity
in MT-4 cell culture.
2. Results and discussion
2.1. Chemistry
* Corresponding author. Tel.: þ86 531 88380270; fax: þ86 531 88382731.
E-mail addresses: zhanpeng1982@163.com (P. Zhan), xinyongl@sdu.edu.cn
(X. Liu).
A modified synthetic route of 1,2,3-thiadiazole thioacetanilides
which requires the salt of 5-thiol-1,2,3-thiadiazole as one of the
0223-5234/$ – see front matter Crown Copyright Ó 2009 Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.06.037

P. Zhan et al. / European Journal of Medicinal Chemistry 44 (2009) 4648–4653
4649
X
previously reported analogues further confirmed the above
structures [12].
X
N
N
N
N
H
H
N
N
N
S
S
R'
N
N
O
O
2.2. Anti-HIV evaluation
Y
Y
R
R
II
I
All designed compounds were evaluated for cytotoxicity and
anti-HIV activity in MT-4 cells, in comparison with nevirapine
(NVP), delavirdine (DLV), efavirenz (EFV) and zidovudine (azido-
thymidine, AZT) used as reference drugs. The results, expressed as
CC50, EC50 and SI, are summarized in Table 1.
As can be seen from Table 1, nearly half of the test compounds
inhibited HIV-1 replication at the lower micromolar concentration
range. Itisworthnotingthatastrikinglylowcytotoxicityofthesenew
TTAs was observed. In fact, the majority of them were non-cytotoxic
N
X
S
III-1: X= NO2, Y= H.
H
N
N
EC50 = 0.059 μM, SI > 4883
III-2: X= Br, Y= CO2Et.
EC50 = 0.099 μM, SI > 2298
III-3: X= Cl, Y= H.
EC50 = 0.118 μM, SI = 943
III-4: X= Br, Y= H.
S
O
Cl
Y
III
EC50 = 0.149 μM, SI > 981
III-5: X= Br, Y= Me.
for MT-4 cells at doses as high as 253 mM. Among all the newly dis-
Cl
closed TTAs, compounds 7f, 7g and 7c were the most potent inhibi-
tors of HIV-1 replication of the series (EC50 ¼ 0.17 ꢀ 0.02, 0.36 ꢀ 0.19
EC50 = 0.204 μM, SI > 1265
and 0.39 ꢀ 0.05
mM, respectively), coupled with the highest selec-
tivity index (SI > 1452, >845, and >774, respectively). They possess
Fig. 1. Sulfanylazoles based NNRTIs.
similar HIV-1 inhibitory activity compared with NVP
(EC50 ¼ 0.208
compounds, 7b, 7d, 7e, 7i, and 7r, also showed reasonable anti-HIV-1
potency (EC50 < 4.5 M) and moderate selectivity indices.
Besides, the results shown in Table 1 revealed some important
SAR information on the role of different substitutions in the aromatic
ring linked with amide. In the case of 2-monosubstituted analogues
(7a, 7b, 7d, 7g and 7i), a clear order of 2-substition for anti-HIV
activity was observed by direct comparison: NO2 > Br > Cl > Me > F.
This conclusion is in agreement with the previous SAR studies
grossly [12].
Furthermore, additional substitution with methyl at the para-
position of anilide phenyl ring in compounds 7d and 7g led to
derivatives 7e and 7h with reduced or deprived antiviral potency,
respectively, suggesting that the nature (probably hydrophobicity)
of methyl did not accommodate the chemical environment in this
region of RT. In contrast, the increased activity against HIV-1 for 7c
(versus 7b) and 7f (versus 7d) might suggest the detrimental effect
of introducing a polar atom or moiety in the anilide phenyl ring to
enhance antiviral activity. The above findings are also in agreement
with the results of earlier SAR studies [12].
m
M) and DLV (EC50 ¼ 0.320
mM). Some other
key intermediates is developed as shown in Scheme 1. In this
approach, the commercially available 1-(naphthalen-2-yl)etha-
none (1) was utilized as starting material. 2-Bromo-1-(naph-
thalen-2-yl)ethanone (2), synthesized by direct bromination of 1,
was reacted with methyl 3-mercaptopropanoate in EtOH at
ambient temperature for several hours to obtain the methyl 3-(1-
(naphthalen-2-yl)ethanone)propanoate (3). The compound 4 was
synthesized from semicarbazide by reaction with the compound
3. Ring-closure reaction of 4 with SOCl2 was carried out according
to the similar methods reported in the literatures [16–18],
producing the methyl 3-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-5-
ylthio)propanoate (5), which was purified by flash chromatog-
raphy. Treatment of compound 5 with sodium methoxide afforded
the desired sodium salt of 1,2,3-thiadiazole-5-thiolate 6 as a result
m
of the b-elimination of the propyl ester group at the C5–S group
[19]. The final 1,2,3-thiadiazole thioacetanilides 7 were synthe-
sized by the reaction of 6 with various 2-chloro-N-(substituted
aromatic group)acetamides in high yields. All the synthesized
compounds 7a–r were characterized by NMR, MS and IR. Both
analytical and spectral data of all the compounds are in full
agreement with the proposed structures. Moreover, comparison
of the spectroscopic data of the new compounds with those of the
Moreover, it is worth noting that only compound 7r demon-
strated moderate antiviral activity (EC50 ¼ 4.42 ꢀ 0.09
mM) among
the N-substituted heterocycle derivatives 7o–r, indicating that this
region was structurally sensitive to modifications with the diverse
heterocyclic substitutions.
All the compounds were evaluated for their, but did not show
any, activity against HIV-2 (ROD) in MT-4 cells. These findings
showed that this new series of TTAs was specific for HIV-1 and
belonged to typical NNRTIs.
N
S
H
N
N
Tolerant
region
Ar (Ph or Het)
S
2.3. Molecular modeling analysis
O
π-π stacking
interaction
In order to investigate the binding mode of our newly synthesized
compounds and rationalize the SAR data, a molecular modeling of
compound 7f docked into the NNRTIs binding pocket (NNIBP) of
HIV-1 RT was performed by means of Autodock Vina [http://vina.
scripps.edu]. X-ray crystal structure of HIV-1 RT with benzophe-
none was taken from PDB (3DLG) and used for docking studies for
the high degree of similarity between sulfanyltriazole/tetrazole leads
and benzophenones [13]. Default parameters were used as described
in the AutoDock manual unless otherwise specified. The theoretical
binding mode of 7f to the NNIBP is shown in Fig. 3.
O
H
N
OH
HO
Y181
K103
HN
W229
Y188
Our studies suggest that this class of compounds shares the
similar binding mode with sulfanyltriazoles [6] and sulfanylte-
trazoles-basedNNRTIs[10,11]. AsillustratedinFig. 3, thenaphthalene
Fig. 2. Structure and proposed binding mode for newly designed TTAs to NNIBP.

4650
P. Zhan et al. / European Journal of Medicinal Chemistry 44 (2009) 4648–4653
O
O
O
S
O
Br
i
ii
iii
O
1
2
3
O
N
S
S
N
N
S
NNHCONH2
S
H
N
N
N
N
O
S
R
iv
S
O
SNa
vi
v
O
O
4
5
6
7
Scheme 1. Reagents and conditions: (i) Br2/AcOH; (ii) HSCH2CH2COOCH3, TEA, DCM; (iii) NH2NHCONH2$HCl, AcONa, EtOH; (iv) SOCl2; (v) CH3ONa/CH3OH; (vi) ClCH2CONHR, EtOH.
ring of 7f fits into the aromatic-rich binding pocket, surrounded by
the aromatic side chains of Tyr188, Phe227, and Trp229. Detailed
analysis of the binding mode shows that one phenyl ring is parallel to
Tyr188 side chain and is orthogonal to the indole ring of Trp229,
results of the AutoDocking analysis seem to support our proposed
binding mode for newly designed TTAs to NNIBP (Fig. 2). Further
optimization of TTA analogues will consider these aspects in further
design attempts.
giving rise to a positive p-stacking interaction and CH–p interaction,
respectively. The inhibitor’s amide carbonyl forms a key hydrogen
bond with the backbone N–H of Lys103 (not shown). The anilide
moiety of 7f is close to Pro236, and the 4-acetyl points toward the
solvent exposed region. Thus, introduction of hydrophilic groups or
heteroatoms in the anilide moiety led a dramatic increase in potency,
which can explain the SAR conclusion at this region. In summary, the
3. Conclusions
A
new series of 2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-5-
ylthio) acetamide (TTA) derivatives was synthesized and evaluated
as potent HIV-1 inhibitors. Among them, the most potent HIV-1
inhibitors were 7f (EC50 ¼ 0.17
m
M), 7g (EC50 ¼ 0.36
mM) and 7c
Table 1
Anti-HIV activities, cytotoxicities and selectivity indices of 2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)acetamide derivatives (7a–r).
N
S
H
N
N
S
R
O
SIc
a
b
No.
R
EC50
(
m
M)
CC50 (mM)
HIV-1 IIIB
HIV-2 ROD
HIV-1 IIIB
HIV-2 ROD
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
7n
7o
7p
7q
2-Fluorophenyl
2-Chlorophenyl
>257.92
>257.92
>229.04
>302.72
>211.88
>265.73
>250.79
>295.87
>182.36
>257.98
>248.09
>319.28
>125.70
>308.23
>308.23
>253.92
>239.35
>163.14
>283.09
ꢁ257.92
< or ꢂ1
79
>774
‡154
>98
>1452
>845
<1
< or ꢂ1
<1
2.91 0.39
0.39 0.05
1.38 0.20
2.72 0.28
0.17 0.02
0.36 0.19
>182.36
4.24
229.04 ꢀ 13.50
>302.72
2-Chloropyridin-3-yl
2-Bromophenyl
2-Bromo-4-methylphenyl
4-Acetyl-2-bromophenyl
2-Nitrophenyl
4-Methyl-2-nitrophenyl
o-Tolyl
Phenyl
p-Tolyl
4-Chlorophenyl
2,3-Dimethylphenyl
2,6-Dimethylphenyl
Pyridin-2-yl
ꢂ1
ꢁ211.88
< or ꢂ1
ꢂ1
>265.73
>250.79
>295.87
ꢂ1
ꢂ1
182.36 ꢀ 3.78
<1
‡257.98
‡61
ꢃ10
ꢂ1
< or ꢂ1
ꢁ24.45
248.09 ꢀ 13.09
>319.28
<1
>319.28
>125.70
>308.23
>308.23
>253.92
>239.35
>163.14
4.42 0.09
0.208
ꢂ1
125.70 ꢀ 17.62
<1
<1
>308.23
ꢂ1
ꢂ1
>308.23
ꢂ1
ꢂ1
253.92 ꢀ 7.42
239.35 ꢀ 16.18
163.14 ꢀ 7.91
>283.09
>15.02
>3.827
<1
<1
Thiazol-2-yl
5-Methylbenzo[d]thiazol-2-yl
3-Methyl acetate-thiophen-2-yl
<1
<1
64
>72
>12
>1434
>6192
<1
<1
ꢂ1
7r
NVPd
DLVd
EFVd
AZTd
0.320
0.00440
0.0151
>6.336
>93.55
a
EC50: concentration of compound required to achieve 50% protection of MT-4 cell from 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: ꢂ1 stand for ꢁ1 or <1.
b
c
d
The antiviral properties of these compounds were previously described [12].

P. Zhan et al. / European Journal of Medicinal Chemistry 44 (2009) 4648–4653
4651
bromo-1-(naphthalen-2-yl)ethanone (2), which was used without
any further concentration or purification.
Methyl 3-mercaptopropanoate (11.4 ml, 0.1 mol) was added
dropwise to the dichloromethane (DCM) solution of 2-bromo-1-
(naphthalen-2-yl)ethanone (2, about 0.1 mol) obtained in the above
step in ice bath. When the addition was finished with further stir-
ring for 10 min, 0.1 mol of triethylamine (TEA) in 20 ml dichloro-
methane was added to the mixture, which was then stirred at room
temperature overnight (checked by TLC). The mixture was diluted
with CH2Cl2 (100 ml), washed with 0.1 N HCl solution, aqueous
saturated NaHCO3, water and brine, successively. The organic layer
was dried with Na2SO4, filtered and concentrated under reduced
pressure to afford crude product 3 as a light yellow oil.
A mixture of semicarbazide hydrochloride (12.2 g, 0.12 mol) and
sodium acetate (8.2 g, 0.1 mol) was dissolved in absolute ethanol
(50 ml). The mixture was heated for 60 min under reflux, then
filtered while hot to remove precipitated sodium chloride. The
filtrate was then mixed with compound 3 (30 g, 0.1 mol), and the
resulting mixture was heated to reflux. Subsequently, a few drops of
concentrated hydrochloric acid were added and heated under reflux
with continuous removal of the generated water was continued
overnight. Finally, the solution was cooled and filtered. The obtained
solid was washed successively with water and diethyl ether and
dried to give compound 4 as white solid, yield: 75.1%, m.p.162–
164 ꢄC. MS (ESI): m/z 346.3 (M þ 1).
Fig. 3. Molecular model of 7f in the allosteric site of HIV-1 RT (PDB code: 3DLG). The
docking result of 7f is showed by PyMOL.
10 ml of thionyl chloride was added to the cooled suspension
0 ꢄC of hydrazone 4 (3.5 g, 0.01 mol) in 10 ml of dry dichloro-
methane with vigorous stirring and cooling. The mixture was
allowed to warm up to room temperature with continuous stirring.
Monitoring of reaction progress with TLC showed that reaction was
completed in 12 h at which time the solvent was removed under
vacuum. The residue was diluted with ethyl acetate (50 ml), filtered
and the filtrate was evaporated to a residue which was chromato-
graphed on silica gel using ethyl acetate:petroleum ether (1:4).
Fractions were collected and evaporated, giving the desired
compound 5 as brilliant yellow oil, yield: 71.5%, MS (ESI): m/z 331.3
(M þ 1).
(EC50 ¼ 0.39
m
M), which possess similar HIV-1 inhibitory activity
compared with NVP (EC50 ¼ 0.208
mM) and DLV (EC50 ¼ 0.320
mM).
The preliminary structure–activity relationships among the newly
disclosed congeners are discussed. Molecular modeling studies
were employed to understand the interactions between these
inhibitors and the RT, and to guide further SAR studies.
4. Experimental section
4.1. Chemistry
A solution of sodium methoxide (0.54 g, 0.01 mol) in 15 ml of
methanol was added to a solution of methyl 3-(4-(naphthalen-2-
yl)-1,2,3-thiadiazol-5-ylthio)propanoate (5) (3.3 g, 0.01 mol) in
100 ml of methanol. After about 1 h, the reaction solution was
evaporated in vacuo to about 10 ml. 50 ml of dry methylene chlo-
ride was added, causing precipitation of a red solid. This solid was
collected, washed with methylene chloride, giving the desired
product sodium 4-(naphthalen-2-yl)-1,2,3-thiadiazole-5-thiolate
(6), yield: 92.4%, m.p.138–140 ꢄC.
All melting points were determined on a micromelting point
apparatus and are uncorrected. Infrared spectra (IR) were recorded
with a Nexus 470FT-IR Spectrometer. 1H NMR spectra were obtained
on a Bruker Avance-600 NMR-spectrometer in the indicated
solvents. Chemical shifts are expressed in d units and TMS as internal
reference. Mass spectra were taken on an LC Autosampler Device:
Standard G1313A instrument. 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 column chromatography
was performed on column packed with silica gel 60 (230–400 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.
4.1.2. General procedure for the synthesis of 2-(4-(naphthalen-2-
yl)-1,2,3-thiadiazol-5-ylthio) acetamide (7a–r)
To the solution of sodium 4-(naphthalen-2-yl)-1,2,3-thiadiazole-
5-thiolate (6) (1.05 mmol, 0.28 g) in ethanol (30 ml) were added 2-
chloro-N-(substituted aromatic group)acetamides (1.0 mmol). The
reaction mixture was stirred at room temperature overnight. Upon
completion of the reaction, the solvent was evaporated, leaving
a residue which was treated with methylene chloride (30 ml) and
washed with water (3 ꢂ 30 ml). The organic layer was dried over
anhydrous sodium sulfate, the drying agent was filtered off, and the
solvent was removed in vacuo. The residue was purified by recrys-
tallisation using ethanol to yield the title compounds (7a–r).
4.1.1. General procedure for the synthesis of sodium 4-(naphthalen-
2-yl)-1,2,3-thiadiazole-5-thiolate (6)
To a solution of 1-(naphthalen-2-yl)ethanone (1, 17.0 g, 0.1 mol)
in glacial acetic acid (200 ml) was added at room temperature
a solution of Br2 (16.0 g, 0.1 mol) in glacial acetic acid (30 ml) over
a period of 30 min. The reaction mixture was stirred at room
temperature for 6 h (monitored by TLC). Then the mixture was
poured into ice water (100 g), extracted with dichloromethane
(3 ꢂ 50 ml). The combined organic phase was washed with cold
water (3 ꢂ 150 ml), 10% NaHCO3 solution (3 ꢂ 50 ml), successively,
and then dried over anhydrous Na2SO4. The drying agent was
filtered off to give the dichloromethane solution (about 150 ml) of 2-
4.1.3. N-(2-Fluorophenyl)-2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-
5-ylthio)acetamide (7a)
Light yellow needle crystals, yield: 58.9%. mp: 163–165 ꢄC. 1H
NMR (CDCl3, ppm)
d: 11.07 (br s, 1H, NH), 8.41–7.55 (m, 7H, naph-
thalene–H), 8.19 (t, 1H, Ph0H), 7.20 (m, 3H, Ph0H), 3.91 (s, 2H, S–CH2).

4652
P. Zhan et al. / European Journal of Medicinal Chemistry 44 (2009) 4648–4653
IR (KBr, cmꢅ1): 3247 (yNH),1658 (yC]O),1541,1492,1457 (yN]N),1256,
1199, 756 (yC–S). MS (ESI): m/z 396.2 (M þ 1). C20H14FN3OS2 (395.06).
Ph0H), 8.43–7.52 (m, 7H, naphthalene–H), 8.07 (dd, 1H, J ¼ 1.8 Hz,
J ¼ 8.4 Hz, Ph0H), 7.38 (m, 1H, Ph0H), 3.90 (s, 2H, S–CH2), 2.36 (s, 3H,
CH3). IR (KBr, cmꢅ1): 3313 (yNH), 1696 (yC]O), 1516 ðyas NO Þ, 1446
2
4.1.4. N-(2-Chlorophenyl)-2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-
5-ylthio)acetamide (7b)
(
yN]N), 1340 ðys NO Þ, 1278, 825, 751 (yC–S). MS (ESI): m/z 437.3
2
(M þ 1). C21H16N4O3S2 (436.07).
White needle crystals, yield: 84.7%. mp: 179–180 ꢄC. 1H NMR
(CDCl3, ppm)
d
: 8.58 (br s, 1H, NH), 8.51–7.57 (m, 7H, naphthalene–
4.1.11. 2-(4-(Naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-o-
tolylacetamide (7i)
H), 7.41 (d, 1H, J ¼ 2.4 Hz, Ph0H), 7.31 (d, 1H, J ¼ 7.8 Hz, Ph0H), 7.25
(t, 1H, Ph0H), 7.07 (t, 1H, Ph0H), 3.92 (s, 2H, S–CH2). IR (KBr, cmꢅ1):
3296 (yNH), 1685 (yC]O), 1594, 1525, 1438 (yN]N), 1233, 744 (yC–S).
MS (ESI): m/z 412.3 (M þ 1), 414.3 (M þ 3). C20H14ClN3OS2 (411.03).
White needle crystals, yield: 80.7%. mp: 138–140 ꢄC. 1H NMR
(CDCl3, ppm) d: 9.72 (br s, 1H, NH), 8.40–7.56 (m, 7H, naphthalene–
H), 7.71 (d,1H, J ¼ 8.4 Hz, Ph0H), 7.21 (t,1H, Ph0H), 7.18 (m, 2H, Ph0H),
3.94 (s, 2H, S–CH2), 2.01 (s, 3H, CH3). IR (KBr, cmꢅ1): 3213 (yNH),
3051, 2969, 2912, 2855, 1649 (yC]O), 1539, 1457 (yN]N), 1228, 748
4.1.5. N-(2-Chloropyridin-3-yl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7c)
(yC–S). MS (ESI): m/z 392.2 (M þ 1). C21H17N3OS2 (391.08).
Light yellow needle crystals, yield: 81.7%. mp: 161–163 ꢄC. 1H
NMR (CDCl3, ppm)
d
: 8.60 (d,1H, J ¼ 8.4 Hz, pyridine–H), 8.53 (s,1H,
4.1.12. 2-(4-(Naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-
phenylacetamide (7j)
NH), 8.43–7.56 (m, 7H, naphthalene–H), 8.18 (dd, 1H, J ¼ 1.8 Hz,
J ¼ 4.2 Hz, pyridine–H), 7.27 (m, 1H, pyridine–H), 3.93 (s, 2H, S–
CH2). IR (KBr, cmꢅ1): 3439 (yNH), 1683 (yC]O), 1520, 1453 (yN]N),
1394, 748 (yC–S). MS (ESI): m/z 413.4 (M þ 1), 415.3 (M þ 3).
C19H13ClN4OS2 (412.02).
White needle crystals, yield: 76.1%. mp: 171–173 ꢄC. 1H NMR
(CDCl3, ppm) d: 10.24 (br s, 1H, NH), 8.41–7.56 (m, 7H, naphtha-
lene–H), 7.43 (d, 2H, J ¼ 7.8 Hz, Ph0H), 7.30 (dt, 2H, Ph0H), 7.11
(dt, 1H, Ph0H), 3.86 (s, 2H, S–CH2). IR (KBr, cmꢅ1): 3285 (yNH), 1653
(yC]O), 1530, 1445 (yN]N), 756, 749 (yC–S). MS (ESI): m/z 378.3
4.1.6. N-(2-Bromophenyl)-2-(4-(naphthalen-2-yl)-1,2,3-thiadiazol-
5-ylthio)acetamide (7d)
(M þ 1). C20H15N3OS2 (377.07).
White needle crystals, yield: 69.8%. mp: 164–166 ꢄC. 1H NMR
4.1.13. 2-(4-(Naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-p-
tolylacetamide (7k)
(CDCl3, ppm)
d
: 8.62 (br s, 1H, NH), 8.24 (d, 1H, J ¼ 7.8 Hz, Ph0H),
8.41–7.55 (m, 7H, naphthalene–H), 7.47 (d, 1H, J ¼ 7.8 Hz, Ph0H),
7.32 (dd, 1H, Ph0H), 7.00 (dt, 1H, Ph0H), 3.95 (s, 2H, S–CH2). IR (KBr,
cmꢅ1): 3214 (yNH), 1653 (yC]O), 1533, 1435 (yN]N), 1227, 748 (yC–S).
MS (ESI): m/z 456.3 (M þ 1). C20H14BrN3OS2 (454.98).
White needle crystals, yield: 78.4%. mp: 163–165 ꢄC. 1H NMR
(CDCl3, ppm) d
: 10.27 (s, 1H, NH), 8.37 (s, 1H, naphthalene–10-H),
8.17 (dd, 1H, J1 ¼1.8 Hz, J2 ¼ 8.4 Hz, naphthalene–40-H), 8.01 (dd,
1H, J ¼ 8.4 Hz, naphthalene–30-H), 7.91–7.86 (m, 2H, naphthalene–
50, 80-H), 7.57 (m, 2H, naphthalene–60, 70-H), 7.18 (d, 2H, J ¼ 8.4 Hz,
Ph0H), 7.06 (d, 2H, J ¼ 8.4 Hz, Ph0H), 3.86 (s, 2H, S–CH2), 2.29 (s, 3H,
CH3). IR (KBr, cmꢅ1): 3244 (yNH), 3052, 2915, 1651 (yC]O), 1541, 1405
4.1.7. N-(2-Bromo-4-methylphenyl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7e)
White needle crystals, yield: 70.8%. mp: 143–145 ꢄC. 1H NMR
(
yN]N), 1227, 813, 751
(
yC–S). MS (ESI): m/z 391.9 (M þ 1).
(CDCl3, ppm) d: 8.52 (br s, 1H, NH), 8.44–7.55 (m, 7H, naphthalene–
C21H17N3OS2 (391.08).
H), 7.84 (d, 1H, J ¼ 8.4 Hz, Ph0H), 7.28 (s, 1H, Ph0H), 7.10 (dd, 1H,
Ph0H), 3.92 (s, 2H, S–CH2), 2.28 (s, 3H, CH3). IR (KBr, cmꢅ1): 3234
4.1.14. N-(4-Chlorophenyl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7l)
(
(
yNH), 3042, 2967, 2916, 1659 (yC]O), 1526, 1444 (yN]N), 814, 747
yC–S). MS (ESI): m/z 470.2 (M þ 1), 472.2 (M þ 3). C21H16BrN3OS2
White crystals, yield: 69.0%. mp: 147–149 ꢄC. 1H NMR (CDCl3,
(468.99).
ppm) d
: 10.33 (s, 1H, NH), 8.39 (s, 1H, naphthalene–10-H), 8.16
(dd, 1H, J1 ¼1.8 Hz, J2 ¼ 8.4 Hz, naphthalene–40-H), 8.05 (dd, 1H,
J ¼ 8.4 Hz, naphthalene–30-H), 7.94–7.81 (m, 2H, naphthalene–50,
80-H), 7.59 (m, 2H, naphthalene–60, 70-H), 7.20 (d, 2H, J ¼ 9 Hz,
Ph0H), 7.15 (d, 2H, J ¼ 9 Hz, Ph0H), 3.86 (s, 2H, S–CH2). IR (KBr, cmꢅ1):
3241 (yNH), 1652 (yC]O), 1595, 1539, 1491 (yN]N), 827, 746 (yC–S). MS
(ESI): m/z 412.3 (M þ 1), 414.3 (M þ 3). C20H14ClN3OS2 (411.03).
4.1.8. N-(4-Acetyl-2-bromophenyl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7f)
White crystals, yield: 85.7%. mp: 172–174 ꢄC. 1H NMR (CDCl3,
ppm) d: 8.77 (s, 1H, NH), 8.54–7.55 (m, 7H, naphthalene–H), 8.40
(d, 1H, J ¼ 8.4 Hz, Ph0H), 8.07 (d, 1H, J ¼ 2.4 Hz, Ph0H), 7.83 (dd, 1H,
J ¼ 2.4 Hz, J ¼ 8.4 Hz, Ph0H), 3.89 (s, 2H, S–CH2), 2.55 (s, 3H, CH3). IR
(KBr, cmꢅ1): 3233 (yNH),1675 (yC]O),1595 (yC]O),1527,1386 (yN]N),
1266, 748 (yC–S). MS (ESI): m/z 498.2 (M þ 1). C22H16BrN3O2S2
(496.99).
4.1.15. N-(2,3-Dimethylphenyl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7m)
White needle crystals, yield: 68.7%. mp: 171–173 ꢄC. 1H NMR
(CDCl3, ppm) d: 9.69 (br s, 1H, NH), 8.39–7.55 (m, 7H, naphthalene–
4.1.9. 2-(4-(Naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-(2-
nitrophenyl)acetamide (7g)
H), 7.35 (d, 1H, J ¼ 7.8 Hz, Ph0H), 7.07 (t, 1H, Ph0H), 7.00 (d, 1H,
J ¼ 7.8 Hz, Ph0H), 3.92 (s, 2H, S–CH2), 2.22 (s, 3H, CH3), 1.93 (s, 3H,
CH3). IR (KBr, cmꢅ1): 3246 (yNH), 3050, 2966, 2915, 2852, 1652
Light yellow needle crystals, yield: 67.4%. mp: 151–153 ꢄC. 1H
NMR (CDCl3, ppm)
d
: 11.12 (br s, 1H, NH), 8.65 (d, 1H, J ¼ 8.4 Hz,
(yC]O), 1538, 1472 (yN]N), 777, 745 (yC–S). MS (ESI): m/z 406.4
(M þ 1). C22H19N3OS2 (405.1).
Ph0H), 8.44–7.53 (m, 7H, naphthalene–H), 8.32 (dd, 1H, J ¼ 1.8 Hz,
J ¼ 8.4 Hz, Ph0H), 7.19 (m, 2H, Ph0H), 3.89 (s, 2H, S–CH2). IR
(KBr, cmꢅ1): 3339 (yNH), 1699 (yC]O), 1588 ðyas NO Þ, 1437 (yN]N),
4.1.16. N-(2,6-Dimethylphenyl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7n)
2
1339 ðys NO Þ, 1271, 1148, 740 (yC–S). MS (ESI): m/z 423.3 (M þ 1).
2
C20H14N4O3S2 (422.05).
White needle crystals, yield: 74.2%. mp: 188–190 ꢄC. 1H NMR
(CDCl3, ppm)
d
: 8.38 (s,1H, naphthalene–10-H), 8.17 (dd,1H, J1 ¼1.8 Hz,
4.1.10. N-(4-Methyl-2-nitrophenyl)-2-(4-(naphthalen-2-yl)-1,2,3-
thiadiazol-5-ylthio)acetamide (7h)
J2 ¼ 8.4 Hz, naphthalene–40-H), 8.07 (dd, 1H, J ¼ 8.4 Hz, naphthalene–
30-H), 7.95–7.90 (m, 2H, naphthalene–50, 80-H), 7.57 (m, 2H, naphtha-
lene–60, 70-H), 7.50 (br s, 1H, NH), 7.09 (t, 1H, Ph0H), 7.03 (m, 2H, Ph0H),
3.97 (s, 2H, S–CH2), 2.06 (s, 6H, CH3). IR (KBr, cmꢅ1): 3235 (yNH), 3034,
Light yellow needle crystals, yield: 84.3%. mp: 159–161 ꢄC. 1H
NMR (CDCl3, ppm)
d
: 10.96 (br s, 1H, NH), 8.48 (d, 1H, J ¼ 8.4 Hz,

P. Zhan et al. / European Journal of Medicinal Chemistry 44 (2009) 4648–4653
4653
2960, 2922, 2852, 1655 (yC]O), 1533, 1474, 1440 (yN]N), 1224, 760, 747
yC–S). MS (ESI): m/z 406.4 (M þ 1). C22H19N3OS2 (405.1).
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 coloured 3-
(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
(Acros Organics, Geel, Belgium) by mitochondrial dehydrogenase 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 (Multiscan Ascent
Reader, Labsystems, Helsinki, Finland), at two wavelengths
(540 and 690 nm). All data were calculated using the median OD
(optical density) value of three wells. The 50% cytotoxic concen-
tration (CC50) was defined as the concentration of the test
compound that reduced the absorbance (OD540) of the mock-
infected control sample by 50%. The concentration achieving 50%
protection from the cytopathic effect of the virus in infected cells
was defined as the 50% effective concentration (EC50).
4.1.17. 2-(4-(Naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-
(pyridin-2-yl)acetamide (7o)
White solids, yield: 59.7%. mp: 186–188 ꢄC. 1H NMR (CDCl3,
ppm) d: 8.76 (s, 1H, NH), 8.42–7.54 (m, 7H, naphthalene–H), 8.20
(d, 1H, J ¼ 4.2 Hz, pyridine–H), 8.13 (d, 1H, J ¼ 8.4 Hz, pyridine–H),
7.73 (m, 1H, pyridine–H), 7.06 (dd, 1H, J ¼ 4.8 Hz, J ¼ 7.2 Hz, pyri-
dine–H), 3.87 (s, 2H, S–CH2). IR (KBr, cmꢅ1): 3215 (yNH),1683 (yC]O),
1585, 1539, 1445 (yN]N), 1314, 1163, 785, 747 (yC–S). MS (ESI): m/z
351.3 (M–N2 þ1), 379.3 (M þ 1), 401.3 (M þ Na). C19H14N4OS2
(378.06).
4.1.18. 2-(4-(Naphthalen-2-yl)-1,2,3-thiadiazol-5-ylthio)-N-
(thiazol-2-yl)acetamide (7p)
White powder, yield: 35.8%. mp: 219–221 ꢄC. 1H NMR (CDCl3,
ppm) d: 12.56 (br s,1H, NH), 8.41–7.61 (m, 7H, naphthalene–H), 7.51
Acknowledgements
(d, 1H, J ¼ 3.6 Hz, thiazole–H), 7.27 (d, 1H, J ¼ 3.6 Hz, thiazole–H),
4.33 (s, 2H, S–CH2). IR (KBr, cmꢅ1): 3193 (yNH), 1687 (yC]O), 1589,
1403 (yN]N), 1325, 1229, 1172, 1162, 969, 750 (yC–S). MS (ESI): m/z
385.2 (M þ 1), 407.3 (M þ Na). C17H12N4OS3 (384.02).
Research work in the Chinese authors’ laboratory has been
supported by the National Natural Science Foundation of China
(NSFC No. 30371686, No. 30772629, No. 30873133), Key Project of
The International Cooperation, Ministry of Science and Technology
of China (2003DF000033) and Research Fund for the Doctoral
Program of Higher Education of China (070422083). We are grateful
to Kristien Erven and Kris Uyttersprot for technical assistance.
4.1.19. N-(5-Methylbenzo[d]thiazol-2-yl)-2-(4-(naphthalen-2-yl)-
1,2,3-thiadiazol-5-ylthio)acetamide (7q)
White needle crystals, yield: 58.7%. mp: 196–198 ꢄC. 1H NMR
(CDCl3, ppm) d: 12.71 (br s, 1H, NH), 8.42–7.59 (m, 7H, naphtha-
lene–H), 7.77 (s, 1H, Ph0H), 7.65 (d, 1H, J ¼ 8.4 Hz, Ph0H), 7.27 (d, 1H,
J ¼ 8.4 Hz, Ph0H), 4.36 (s, 2H, S–CH2), 2.50 (s, 3H, CH3). IR
(KBr, cmꢅ1): 3207 (yNH), 2997, 2919, 2854, 1698 (yC]O), 1608, 1553,
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