Design, microwave-assisted synthesis and HIV-RT inhibitory activity of 2-(2,6-dihalophenyl)-3-(4,6-dimethyl-5-(un)substituted-pyrimidin-2-yl)th iazolidin-4-ones

Article abstract of DOI:10.1016/j.bmc.2009.04.024

A series of novel thiazolidin-4-ones bearing a hydrophobic substituent at 5-position on the 4,6-dimethyl-pyrimidine ring at N-3 (5c-i and 6c-i) were designed on the prediction of QSAR studies, synthesized in good yields of 60.1-85.3% by microwave-assisted one-pot protocol with the combination of using dicyclohexylcarbonimide (DCC) as the promotor, and evaluated as HIV-1 reverse transcriptases inhibitors. The results of in vitro HIV-1 RT kit assay showed that some of the new compounds, such as 5c, 6c, 5d, 6d, 5g, 5h and 6i, could effectively inhibit RT activity. Among them, compounds 5c and 6c where ethyl group existed at 5-position on N-3 pyrimidine ring were the best ones with the IC₅₀ value of 0.26 μM and 0.23 μM, respectively. Structure-activity relationship analysis of these analogues suggested that the overall hydrophobicity and steric factor were important to the anti-HIV RT activity. The mechanism of the intramolecular cycloamidation promoted by DCC was also investigated with the key uncyclized intermediate 13.

Full text of DOI:10.1016/j.bmc.2009.04.024

Bioorganic & Medicinal Chemistry 17 (2009) 3980–3986
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Design, microwave-assisted synthesis and HIV-RT inhibitory activity of
2-(2,6-dihalophenyl)-3-(4,6-dimethyl-5-(un)substituted-pyrimidin-2-yl)-
thiazolidin-4-ones
*
*
Hua Chen , Jie Bai, Lingling Jiao, Zaihong Guo, Qingmei Yin, Xiaoliu Li
Key Laboratory of Chemical Biology of Hebei Province, Key Laboratory of Medicinal Chemistry and Molecular Diagnosis, Ministry of Education, College of Chemistry and
Environmental Science, Hebei University, Baoding 071002, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel thiazolidin-4-ones bearing a hydrophobic substituent at 5-position on the 4,6-dimethyl-
pyrimidine ring at N-3 (5c–i and 6c–i) were designed on the prediction of QSAR studies, synthesized in
good yields of 60.1–85.3% by microwave-assisted one-pot protocol with the combination of using dic-
yclohexylcarbonimide (DCC) as the promotor, and evaluated as HIV-1 reverse transcriptases inhibitors.
The results of in vitro HIV-1 RT kit assay showed that some of the new compounds, such as 5c, 6c, 5d,
6d, 5g, 5h and 6i, could effectively inhibit RT activity. Among them, compounds 5c and 6c where ethyl
Received 21 January 2009
Revised 4 April 2009
Accepted 6 April 2009
Available online 18 April 2009
Keywords:
group existed at 5-position on N-3 pyrimidine ring were the best ones with the IC50 value of 0.26
lM
Thiazolidin-4-one
Microwave-assisted
Synthesis
and 0.23 M, respectively. Structure-activity relationship analysis of these analogues suggested that
l
the overall hydrophobicity and steric factor were important to the anti-HIV RT activity. The mechanism
of the intramolecular cycloamidation promoted by DCC was also investigated with the key uncyclized
intermediate 13.
Anti-HIV-RT activity
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
ture–activity relationship (SAR) study and the anti-HIV drug dis-
covery. Therefore, in this paper the compounds possessing para-
2,3-(Diaryl-substituted)-1,3-thiozolidin-4-one scaffold, a mimic
of thiazolobenzimidazole (TBZ) (1 and 2) (Fig. 1) has drawn many
attentions due to its’ potent and selective inhibition against the
HIV-1 and low toxicity by binding to the allosteric site of the re-
alkyl substituent of N-3-pyrimidine moiety (5c–i and 6c–i) were
designed, synthesized and evaluated for HIV-RT inhibitory activity
for further investigating the SAR analysis between the RT inhibi-
tory activity and the hydrophobicity of the thiazolidin-4-one
derivatives.
verse transcriptase (RT) as
a non-nucleoside RT inhibitor
(NNRTI).1–8 Recently, the systematic QSAR study revealed that
the overall hydrophobicity of the molecule, and steric and elec-
tronic features of meta-/para-substituents on N-3-aryl moiety were
important to enhance the biological activity.9–14 For examples, the
thiazolidin-4-ones bearing a lipophilic adamantyl substituent have
exhibited good anti-HIV activity,15,16 and a series of 2-(2,6-dihal-
ophenyl)-3-(4,6-dimethyl-pyrimidin-2-yl) thiazolidin-4-ones (3–
6) have been observed with higher anti-HIV activity compared to
the other aryl substituted ones (Fig. 1).17–21 Among them, 4a, 5b
and 6b exhibited the most activity and high selectivity index (4a:
2,3-Diaryl-1,3-thiozolidin-4-one derivatives have been conve-
niently synthesized by the three component one-pot reaction with
aromatic amine, aromatic aldehyde and mercaptoacetic acid in
refluxing toluene.22 Some new synthetic methods and reagents
such as microwave-assisted,23–25 DCC,26 Hünig’s base,27 ion liq-
uids,28 and KSF clay29 have been used for effectively improving
the synthesis of such compounds. For instance, in the case of 3–6
bearing a 4,6-dimethylpyrimidinyl group, while the reaction could
not provide satisfactory result with moderate yields in refluxing
toluene for long time (24–48 h) probably due to the low reactivity
of the 2-aminopyrimidine,1,18 under microwave-irradiation the
synthesis could produce 5a in yield of 56% within 12 min.23 More
recently, we have also reported an efficient microwave assisted
synthesis of 2,3-diaryl-1,3-thiozolidin-4-ones.30,31 Herein, we
would like to present an improved microwave assisted synthesis
of 2-(2,6-dihalophenyl)-3-(5-(un)substitued-4,6-dimethyl pyrimi-
din-2-yl)thiazolidin-4-ones (5 and 6) in good yields promoted by
DCC (Scheme 1), and the reaction process of such intramolecular
cycloamidation via the key uncyclized intermediate 13.
EC50 = 0.02 0.01
EC50=0.03 0.02
0.01 M, CC50 = 216.2 53.5
l
l
M, CC50 = 184.76 42.22
M, CC50 > 320 M, SI > 11456; 6b: EC50 = 0.02
M, SI = 8669), implying that they
lM, SI = 7123; 5b:
l
l
l
would be potential anti-HIV drug candidates.17,18 These promising
antiviral activities of 3–6 demanded to synthesize their novel
derivatives to meet the ever-growing requirements for the struc-
* Corresponding authors. Tel./fax: +86 312 5971116 (X.L.).
E-mail addresses: hua-todd@hbu.cn (H. Chen), lixl@hbu.cn (X. Li).
0968-0896/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2009.04.024

H. Chen et al. / Bioorg. Med. Chem. 17 (2009) 3980–3986
3981
CH3
R
X1
X1
N
N
3 X1=X2=F
4 X1=X2=Br
5 X1=X2=Cl
a: R=H; b: R=CH3
a: R=H; b: R=CH3
a: R=H; b: R=CH3
1 TBZ1, X1=X2=F
2 TBZ2, X1=X2=Cl
N
H3C
N
X2
N
X2
6 X1=Cl, X2=F a: R=H; b: R=CH3
S
S
O
Figure 1. Structures of TBZ (1 and 2) and 2-(2,6-dihalorophenyl)-3-(pyrimidin-2-yl) thiazolidin-4-ones (3–6).
R
Cl
N
Cl
OHC
Cl
N
N
a R=H
S
Cl
O
b R=CH3
c R=CH2CH3
d R=CH2CH2CH3
e R=CH2(CH2)2CH3
R
5a-i
+
8
N
a
+
NH2
+
HSCH2COOH
N
Cl
f
R=CH2(CH2)3CH3
10
R
Cl
N
g R=CH2CH=CH2
h R=CH2CH2C≡ N
i R=Br
OHC
F
7a-i
N
N
S
F
O
9
6a-i
Scheme 1. Synthesis of 5 and 6. Reagents and conditions (a) (1) MW, 140 °C in sealed tube, 10 min, 7a:8:10 = 1:1:2; (2) MW, 140 °C in sealed tube, 2 equiv DCC, 5 min.
fied with (5a) using 7a, 8 and 10 as the starting materials under
microwave irradiation following our reported procedure30,31
(Scheme 3 and Table 1). However, the reaction could not proceed
effectively with a poor yield of the desired product 5a, insteadly,
an uncyclized addition intermediate 13 was obtained as a predom-
inant product.
According to the proposed mechanism of the reaction (Scheme
3), the intermediate 13 was produced from the nucleophilic addi-
tion of mercaptoacetic acid 10 to the imine in situ generated from
7a and 8, and further intramolecular condensation of 13 would af-
ford the desired product 5a. The results (Table 1) indicated that the
reactivity for 13 to form the target product 5a was not so high pos-
sibly because of the existence of the electron deficient pyrimidine
2. Result and discussion
2.1. Chemistry
The 2-aminopyrimidines (7a–h) were prepared by refluxing an
ethanolic solution of free base guanidine (12) with different 1,3-
dicarbonyl compounds (11a–h) as shown in Scheme 2 according
to the literature,32 and the synthesis of 2-amino-4,6-dimethyl-5-
bromopyrimidine (7i) was carried out according to the reported
procedure (Scheme 2).33
The synthesis of 2-(2,6-dihalophenyl)-3-(4,6-dimethyl-5-
(un)substituted-pyrimidin-2-yl) thiazolidin-4-ones (5 and 6) was
firstly examined for optimizing the reaction condition as exampli-
a R=H
b R=CH3
R
O
c R=CH2CH3
NH2
N
a
+
R
d R=CH2CH2CH3
e R=CH2(CH2)2CH3
HN
NH2
O
N
NH2
f
R=CH2(CH2)3CH3
g R=CH2CH=CH2
h R=CH2CH2C≡ N
7a-h
11a-h
12
Br
N
N
b
N
NH2
N
NH2
7a
7i
Scheme 2. Synthesis of 2-aminopyrimidines 7. Reagents and conditions: (a) anhydrous EtOH, reflux, 8 h, 8.8–85.2% yields; (b) Br2, anhydrous CHCl3, rt, stirred in the dark,
20 h, 65.1% yields.
Cl
Cl
Cl
N
N
OHC
Cl
N
+
II
N
N
+
NH2
+
HSCH2COOH
N
N
H
I
S
O
Cl
S
Cl
N
10
O
HO
5a
7a
8
13
Scheme 3. Synthesis of compound 5a.

3982
H. Chen et al. / Bioorg. Med. Chem. 17 (2009) 3980–3986
Table 1
were optimized by examining the equivalent of DCC, the reaction
time and the temperature (Table 2).
The microwave assisted synthesis of 5a
Entry
Temperature (°C)
140 °C in sealed tubeb
Reflux
Time (min)
Yielda of 5a (%)
Yielda of 13 (%)
Thus, the one-pot three component synthesis could proceed
effectively firstly with the reactant ratio of 7a:8:10 = 1:1:2 at
140 °C in dry toluene in sealed tube under microwave irradiation
for 10 min, subsequently, DCC (2 equiv) was added and some dry
toluene was added again which made the concentration of the
reaction mixture to be in 0.25 mmol/mL, and then the reaction
solution was irradiated for another 5 min. After simply work up
and purification by silica gel column chromatography, the product
5a was obtained in the high yield of 73.7%. Under the same condi-
tions, the compounds 5 and 6 were synthesized in the yields of
60.1–85.3% within 15 min, providing a convenient and practical
one pot procedure for accessing to 2-(2,6-dihalophenyl)-3-(4,6-di-
methyl-5-(un)substituted-pyrimidin-2-yl)thiazolidin-4-ones (Ta-
ble 3).
1
2
3
10
13.6
10.5
33.7
67.8
63.2
31.5
20
140 °C in sealed tube
10c
a
Isolated yield.
b
All the reaction could proceeded with the reactant ratio of 7a:8:10 = 1:1:2 in
dry toluene under microwave irradiation.
c
Total reaction time: after the condensation of 7a and 8 was carried out at 140 °C
in sealed tube stirring for 5 min, mercaptoacetic acid 10 was added for other 5 min.
group. Accordingly, we examined the cycloamidation of 13 by
using Lewis acid catalysts, condensation agent and microwave irra-
diation for promotion (Table 2). Although Lewis acids could not
catalyze the cyclo-condensation, DCC has remarkably promoted
the reaction. Furthermore by using the combination of the conden-
sation agent (DCC) and microwave irradiation the cycloamidation
of 13 could proceed very effectively and provided 5a in excellent
yield of 80.2% (Table 2, entry 4). Subsequently, we approached
the microwave assisted one-pot three components reaction with
7a, 8 and 10 in the presence of DCC, but the yield of 5a was
18.5% without detecting the intermediate 13 (entry 5). Considering
above results, the one-pot synthesis would take place with two
steps as shown in Scheme 3. Firstly, the mixture of 7a, 8 and 10
was irradiated to form the intermediate 13 with minor product
5a (Scheme 3 step I), then a certain amount of DCC was added to
the reaction mixture and the reaction mixture was exposured to
microwave irradiation again for a given time to afford the product
5a in good yield (Scheme 3 step II). It should be noted that the
additional solvent should be added to dissolve DCC and to decrease
the concentration of the final mixture solution from 1.0 mmol/mL
to 0.25 mmol/mL. With this procedure, the reaction conditions
All the synthesized compounds were characterized by spectro-
scopic methods and elemental analysis.
2.2. HIV-RT inhibitory activity evaluation
All the new compounds (5c–i and 6c–i) were evaluated for HIV-
RT inhibitory activity in HIV-RT kit34 by comparison with the doc-
umented compounds 5b and 6b (the most active ones among the
reported thiozolidin-4-one derivatives), and the results are showed
in Table 4.
It could be seen from the table that most of the new compounds
showed notable HIV-RT inhibitory activity, such as 5c, 6c, 5d, 6d,
5g, 5h and 6i. Among them, compound 5c and 6c where ethyl
group existed at 5-position on the pyrimidine ring at N-3 showed
a more significant HIV-RT inhibitory activity and their IC50 values
were 0.26
lM and 0.23
lM, respectively, even better than those
of the known analogues 5b and 6b (IC50: 0.83
l
M and 0.38 M,
l
Table 2
The synthesis of 5a
Entry
Lewis acid (equiv)
Condensation agent (equiv)
Solvent
Conditions
Time (min)
Yield of 5a (%)
1a
2a
3a
4a,b
5c
6d
7
8
9
10
11
Na2SO4 (1)
ZnCl2 (1)
—
—
—
THF
THF
THF
rt
rt
rt
30
30
30
10
10
10
5
2.5
5
5
Trace
Trace
41.8
80.2
18.5
56.3
73.7
48.8
50.5
71.2
65.5
DCC (1)
DCC (1)
DCC (2)
DCC (2)
DCC (2)
DCC (2)
DCC (2)
DCC (2)
DCC (2)
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
140 °C, MW
140 °C, MW
140 °C, MW
140 °C, MW
140 °C, MW
150 °C, MW
130 °C, MW
120 °C, MW
—
—
—
—
—
—
—
5
a
The reaction was carried out with the pure 13 as the starting material.
The reaction was performed in sealed tube under MW.
All the reactants were added at the same time. The reaction conditions were same with those in entry 1 (Table 1).
DCC was added in step II in Scheme 3 and the corresponding conditions were discussed. The reactions were performed in sealed tube under MW. The conditions of step I
b
c
d
were also same with those in entry 1 (Table 1).
Table 3
The microwave assisted synthesis of 5 and 6
R
Yield of 5 (lit.) (%)
Mp of 5 (lit.) (°C)
Yield of 6 (lit.) (%)
Mp of 6 (lit.) (°C)
a
b
c
d
e
f
73.7 (5623
73.8 (5618
70.2
67.0
71.4
)
)
208.5–210.5 (200–20223
208.5–210.5 (202–20418
174.5–176.5
139.5–141.0
139.5–141.5
)
)
85.3(221)
162.0–164.0 (165–1661)
178.0–179.5 (199–20014
127.0–128.5
154.0–155.5
110.0–112.5
82.5(5018
80.8
)
)
71.1
70.6
63.2
63.7
128.5–130.0
129.5–131.5
g
h
i
66.1
60.1
71.5
135.5–137.5
195.3–197.2
199.0–201.0
67.8
67.3
70.9
110.0–111.5
182.6–184.2
153.5–155.0

H. Chen et al. / Bioorg. Med. Chem. 17 (2009) 3980–3986
3983
Table 4
HIV-RT kit assay for compounds (5b–i and 6b–i)
Compounds
R
IC50
(lM) (HIV-RT kit assay)
Compounds
IC50
(lM) (HIV-RT kit assay)
5b
5c
5d
5e
5f
5g
5h
5i
CH3
CH2CH3
0.83 0.03
0.26 0.02
0.77 0.35
4.29 3.57
74.39 4.42
1.22 0.15
1.02 0.13
9.82 2.67
6b
6c
6d
6e
6f
6g
6h
6i
0.38 0.09
0.23 0.04
0.85 0.35
15.96 3.99
16.15 4.95
2.92 0.14
2.01 0.57
1.52 0.25
CH2CH2CH3
CH2(CH2)2CH3
CH2(CH2)3CH3
CH2CH@CH2
CH2 CH2C„N
Br
respectively), implying that 5c and 6c may be better accommo-
dated into the HIV-1 RT allosteric binding site. It’s also suggested
that the compounds with high hydrophobicity would be better
for the HIV-RT inhibitory activity. However, as the alkyl chain of
R group at 5-position on the pyrimidine ring prolonged, the RT
inhibitory activity decreased. For instance, the introduction of 5-
pentyl (5f and 6f) led to a markedly loss in the activity, which indi-
cated that the bulky substituents at this position, such as butyl and
pentyl group, would be a detrimental effect in anti-HIV-RT activity.
In the cases of 5-propyl (5d and 6d), 5-allyl (5g and 6g) and 5-pro-
panenitrile group (5h and 6h), their activity were lightly decreased.
Furthermore, compounds 5h and 6h with nitrile group are more
active than 5g and 6g bearing a double bond, respectively,
although the former have the more bulky substituent
(CH2CH2C„N) then that (CH2CH@CH2) of the later at 5-position
on the pyrimidine ring at N-3. The inhibitory activity of com-
pounds 5i and 6i is less active than those of 5b and 6b, suggesting
that the hydrophobic but electron withdrawing halo atom such as
Br at 5-position on the pyrimidine ring at N-3 may be unfavorable
to anti-HIV-RT activity. The above structure–activity relationships
(SAR) analysis may be helpful to guide further modification of thia-
zolidinone analogs.
inhibition was measured on a BioRad Model 3550 microplate spec-
trophotometer. The silica gel (300–400 mesh) for flash column
chromatography was from Qingdao Marine Chemical (China).
3.2. The synthesis of compounds 7a–i
The synthesis of compounds 7a–h was carried out according to
the reported procedure,32 and the synthesis compound 7i was pro-
ceeded as the literature.33
3.2.1. 2-Amino-4,6-dimethylpyrimidine (7a)
White solid, 85.2%, mp 152–153 °C, lit. mp 152–154 °C,35 1H
NMR (CDCl3, 400 MHz) d: 4.52 (s, 2H, NH2), 2.35 (s, 6H, 2CH3),
6.22 (s, 1H, Ar-H).
3.2.2. 2-Amino-4,5,6-trimethylpyrimidine (7b)
White solid, 70.5%, mp 206–208 °C, lit. mp 208 °C,32 1H NMR
(CDCl3, 400 MHz) d: 5.03 (s, 2H, NH2), 2.28 (s, 6H, 2CH3), 2.05 (s,
3H, CH3).
3.2.3. 2-Amino-4,6-dimethyl-5-ethylpyrimidine (7c)
White solid, 32.8%, mp 142–144 °C, lit. mp 148–149 °C,32 1H
NMR (CDCl3, 400 MHz) d: 4.97 (s, 2H, NH2), 2.32 (s, 6H, 2CH3),
1.07 (t, 3H, J = 7.2 Hz, CH3), 2.54–2.48 (q, 2H, J = 7.2 Hz, CH2).
In conclusion, this paper presented an improved microwave-as-
sisted one-pot protocol combining with the use of DCC for
synthesizing 2-(2,6-dihalophenyl)-3-(4,6-dimethyl-5-(un)substi-
tuted-pyrimidin-2-yl) thiazolidin-4-ones in good yields. A majority
of the new compounds, such as 5c, 6c, 5d, 6d, 5g, 5h and 6i,
showed notable HIV-1 RT inhibitory activity and compound 5c
and 6c were the best ones with the IC50 value of RT inhibitory
3.2.4. 2-Amino-4,6-dimethyl-5-propylpyrimidine (7d)
White solid, 26.3%, mp 160-162 °C, lit. mp 165–167 °C,36 1H
NMR (CDCl3, 400 MHz) d: 4.90 (s, 2H, NH2), 2.33 (s, 6H, 2CH3),
0.99 (t, 3H, J = 7.2 Hz, CH3), 1.52–1.42 (m, 2H, CH2), 2.47(t, 2H,
J = 7.6 Hz, CH2).
activities of 0.26 lM and 0.23 lM, respectively, higher than those
of 5b and 6b. SAR analysis indicated that the results were in agree-
ment with those predicted by molecular modeling studies9–14
which suggested the overall hydrophobicity of the analogues, and
steric and electronic features of meta-/para-substituents of 3-het-
ero-aryl moiety on thiazolidin-4-one led to a substantial increase
in antiviral activity. The further synthesis and biological activity
measurement are under way.
3.2.5. 2-Amino-4,6-dimethyl-5-butylpyrimidine (7e)
White solid, 24.1%, mp 109–110 °C, 1H NMR (CDCl3, 400 MHz)
d: 4.85 (s, 2H, NH2), 2.33 (s, 6H, 2CH3), 0.96 (t, 3H, J = 7.2 Hz,
CH3), 1.41–1.45 (m, 4H, 2CH2), 2.48 (t, 2H, J = 7.6 Hz, CH2). MS
(ESI) m/z: 180.2 ([M+H]+).
3.2.6. 2-Amino-4,6-dimethyl-5-pentylpyrimidine (7f)
White solid, 15.7%, mp 150–151 °C, 1H NMR (CDCl3, 400 MHz)
d: 4.88 (s, 2H, NH2), 2.33 (s, 6H, 2CH3), 0.91 (t, 3H, J = 6.8 Hz,
CH3), 1.35–1.44 (m, 6H, 3CH2), 2.48 (t, 2H, J = 7.6 Hz, CH2). MS
(ESI) m/z: 194.4 ([M+H]+).
3. Experimental
3.1. General experimental procedures
All microwave-assisted reactions were carried out on a CEM
Discover S-Class Synthesizer (CEM Co. Ltd, USA). Melting points
were measured in an open capillary on a SGWÒ X-4 melting point
apparatus and are uncorrected. 1H NMR and 13C NMR spectra were
recorded at 400 MHz in CDCl3 solutions on a AC-P400 Bruker FT-
NMR spectrometer. The chemical shifts are as parts per million (d
ppm) from TMS as an internal standard. ESI-MS were determined
using a Quayyro mass spectrometer, and signals were recorded
in m/z. IR spectra were determined on a WQF-510 as KBr tablets
for solid samples and were expressed in cmꢀ1 scale. Element anal-
ysis was performed using a Hekaeus (CHNO, rapid) elemental ana-
lyzer. The optical densities for examining the activities of HIV-RT
3.2.7. 2-Amino-4,6-dimethyl-5-allylpyrimidine (7g)
White solid, 22.4%, mp 129–131 °C, lit. mp 131–134 °C,36 1H
NMR (CDCl3, 400 MHz) d: 4.85 (s, 2H, NH2), 2.34 (s, 6H, 2CH3),
3.27 (d, 2H, J = 4.8 Hz, CH2), 4.78 (d, 1H, J = 17.2 Hz, @CH2), 5.02
(d, 1H, J = 10.4 Hz, @CH2), 5.72–5.82 (m, 1H, @CH).
3.2.8. 2-Amino-4,6-dimethyl-5-propanenitrilepyrimidine (7h)
White solid, 8.8%, mp decomposed at 209 °C, 1H NMR (CDCl3,
400 MHz) d: 2.68 (t, 2H, J = 4.8 Hz, CH2), 2.46 (t, 2H, J = 4.8 Hz,
CH2), 2.21 (s, 6H, CH3). MS (ESI) m/z: 177.1 ([M+H]+).

3984
H. Chen et al. / Bioorg. Med. Chem. 17 (2009) 3980–3986
3.2.9. 2-Amino-4,6-dimethyl-5-bromopyrimidine (7i)
White solid, 65.1%, mp 180–182 °C, lit. mp 186–188 °C,33 1H
NMR (CDCl3, 400 MHz) d: 5.10 (s, 2H, NH2), 2.43 (s, 6H, 2CH3).
2.0 Hz, CH2), 3.93 (d, 1H, J = 15.7 Hz, CH2), 2.50–2.43 (m, 2H,
CH2), 2.38 (s, 6H, CH3), 1.49–1.39 (q, 2H, J = 7.2 Hz, CH2), 1.08–
1.04 (t, 3H, J = 7.2 Hz, CH3). MS (ESI) m/z: 419.3 ([M+Na]+). Anal.
Calcd for C18H19Cl2N3OS: C, 54.55; H, 4.83; N, 10.60. Found: C,
54.62; H, 4.81; N, 10.55.
3.3. The synthesis of compound 13
A mixture of 2-amino-4,6-dimethylpyrimidine compound (7a)
(0.5 mmol), 2,6-dichlorophenyl aldehyde 8 (0.5 mmol) and mer-
captoacetic acid 10 (1.0 mmol) were stirred at 140 °C using dry tol-
uene (0.5 mL) as solvent in sealed tube by irradiating in a CEM
Discover S-Class Synthesizer for 10 min. After cooled to room tem-
perature, a yellow solid was precipitated, which was crystallized
from ethanol to afford compound.
3.4.5. 2-(2,6-Dichlorophenyl)-3-(5-butyl-4,6-dimethylpyrimidin-
2-yl)thiazolidin-4-one (5e)
IR (KBr) m
: 1722 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.45 (d, 1H,
J = 1.9 Hz, CH), 7.28–7.05 (m, 3H, Ar-H), 4.15 (dd, 1H, J = 15.7 Hz,
2.0 Hz, CH2), 3.92 (d, 1H, J = 15.7 Hz, CH2), 2.50–2.46 (m, 2H,
CH2), 2.37 (s, 6H, CH3), 1.38–1.36 (m, 4H, CH2), 0.94–0.90 (t, 3H,
J = 6.8 Hz, CH3). MS (ESI) m/z: 433.0 ([M+Na]+). Anal. Calcd for
C19H21Cl2N3OS: C, 55.61; H, 5.16; N, 10.24. Found: C, 55.58; H,
5.10; N, 10.31.
3.3.1. 2-((4,6-Dimethylpyrimidin-2-ylamino)(2,6-dichloro-
phenyl)methylthio)acetic acid (13)
White solid, 67.8%, mp: decomposed at 190 °C, IR (KBr)
m:
3.4.6. 2-(2,6-Dichlorophenyl)-3-(5-pentyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (5f)
1702 cmꢀ1 (C@O); 3279 cmꢀ1 (NH); 3458 cmꢀ1 (OH), 1H NMR
(DMSO-d6, 400 MHz) d: 12.56 (brs, 1H, COOH), 7.45 (m, 2H, CH;
NH), 7.01–7.33 (m, 3H, Ar-H), 6.49 (s, 1H, pyrimidinyl-H), 3.70
(d, 1H, J = 16.2 Hz, CH2), 3.93 (d, 1H, J = 16.2 Hz, CH2), 2.22 (s, 6H,
CH3). MS (ESI) m/z: 372.4 ([M+H]+). Anal. Calcd for C15H15Cl2N3O2S:
C, 48.40; H, 4.06; N, 11.29; Found: C, 48.32; H, 4.10; N, 11.32.
IR (KBr) m
: 1722 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.46 (d, 1H,
J = 1.9 Hz, CH), 7.28–7.06 (m, 3H, Ar-H), 4.16 (dd, 1H, J = 15.7 Hz,
2.0 Hz, CH2), 3.93 (d, 1H, J = 15.7 Hz, CH2), 2.53–2.42 (m, 2H,
CH2), 2.38 (s, 6H, CH3), 1.41–1.32 (m, 6H, CH2), 0.87–0.91 (t, 3H,
J = 6.8 Hz, CH3). MS (ESI) m/z: 447.4 ([M+Na]+). Anal. Calcd for
C20H23Cl2N3OS: C, 56.60; H, 5.46; N, 9.90. Found: C, 56.52; H,
5.47; N, 9.86.
3.4. General procedure for the synthesis of compounds 5 and 6
A mixture of 5-(un)substituted-2-amino-4,6-dimethylpyrimi-
dine compounds (7a-i) (0.5 mmol), aromatic aldehydes (0.5 mmol)
and mercaptoacetic acid (1.0 mmol) were firstly stirred at 140 °C
using dry toluene (0.5 mL) as solvent in sealed tube by irradiating
in a CEM Discover S-Class Synthesizer for 10 min. Subsequently,
DCC (206 mg) and additional dry toluene were added and the last
concentration was 0.25 mmol/mL. The mixture were stirred at
140 °C in sealed tube by irradiating microwave for 5 min reaction.
Then, after cooled to room temperature, DCU was removed by fil-
tration and the mixture was neutralized with solid K2CO3. Solvent
was removed under reduced pressure to get a crude product,
which was isolated by silica gel column chromatography eluting
with cyclohexane–ethyl acetate as eluent. Compounds 5 and 6
were obtained as white solids.
3.4.7. 2-(2,6-Dichlorophenyl)-3-(5-allyl-4,6-dimethylpyrimidin-
2-yl)thiazolidin-4-one (5g)
IR (KBr) m
: 1710 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.47 (s, 1H, CH),
7.27–7.07 (m, 3H, Ar-H), 5.72–5.82 (m, 1H, @CH), 5.02 (d, 1H,
J = 10.4 Hz, @CH2), 4.78 (d, 1H, J = 17.2 Hz, @CH2), 4.15 (dd, 1H,
J = 15.6 Hz, 1.6 Hz, CH2), 3.93 (d, 1H, J = 14.8 Hz, CH2), 3.26–3.27
(m, 2H, CH2), 2.36 (s, 6H, CH3). MS (ESI) m/z: 416.8 ([M+Na]+). Anal.
Calcd for C18H17Cl2N3OS: C, 54.83; H, 4.35; N, 10.66. Found: C,
54.91; H, 4.34; N, 10.71.
3.4.8. 2-(2,6-Dichlorophenyl)-3-(5-propanenitrile-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (5h)
IR (KBr) m
: 1718 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.44 (s, 1H, CH),
7.30–7.07 (m, 3H, Ar-H), 4.19 (dd, 1H, J = 16.0 Hz, 2.0 Hz, CH2), 3.93
(d, 1H, J = 15.6 Hz, CH2), 2.95 (t, 2H, J = 7.6 Hz, CH2), 2.48 (t, 2H,
J = 7.6 Hz, CH2), 2.44 (s, 6H, CH3). MS (ESI) m/z: 428.3 ([M+Na]+).
Anal. Calcd for C20H18Cl2N2OS: C, 59.26; H, 4.48; N, 6.91. Found:
C, 59.41; H, 4.40; N, 6.99.
3.4.1. 2-(2,6-Dichlorophenyl)-3-(4,6-dimethylpyrimidin-2-
yl)thiazolidin-4-one (5a)
1H NMR (CDCl3, 400 MHz) d: 7.47 (s, 1H, CH), 7.28–7.05 (m, 3H,
Ar-H), 6.72 (s, 1H, pyrimidinyl-H), 4.16 (d, 1H, J = 15.8 Hz, CH2),
3.93 (d, 1H, J = 15.8 Hz, CH2), 2.36 (s, 6H, CH3).
3.4.9. 2-(2,6-Dichlorophenyl)-3-(5-bromo-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (5i)
3.4.2. 2-(2,6-Dichlorophenyl)-3-(4,5,6-trimethylpyrimidin-2-
yl)thiazolidin-4-one (5b)
IR (KBr) m
: 1727 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.42 (d, 1H,
1H NMR (CDCl3) d: 7.47 (d, 1H, J = 1.7 Hz, CH), 7.28–7.06 (m, 3H,
Ar-H), 4.16 (dd, 1H, J = 15.7 Hz, 2.0 Hz, CH2), 3.93 (d, 1H, J =15.7 Hz,
CH2), 2.36 (s, 3H, CH3), 2.10 (s, 6H, CH3).
J = 1.6 Hz, CH), 7.31–7.08 (m, 3H, Ar-H), 4.16 (dd, 1H, J = 15.6 Hz,
1.6 Hz, CH2), 3.93 (d, 1H, J = 15.8 Hz, CH2), 2.48 (s, 6H, CH3). MS
(ESI) m/z: 456.1 ([M+Na]+). Anal. Calcd for C15H12BrCl2N3OS: C,
41.59; H, 2.79; N, 9.70. Found: C, 41.54; H, 2.77; N, 9.68.
3.4.3. 2-(2,6-Dichlorophenyl)-3-(5-ethyl-4,6-dimethylpyrimidin-
2-yl)thiazolidin-4-one (5c)
3.4.10. 2-(2-Chloro-6-fluorophenyl)-3-(4,6-dimethylpyrimidin-
2-yl)thiazolidin-4-one (6a)
IR (KBr) m
: 1710 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.46 (d, 1H,
J = 1.8 Hz, CH), 7.29–7.06 (m, 3H, Ar-H), 4.16 (dd, 1H, J = 15.7 Hz,
2.0 Hz, CH2), 3.92 (d, 1H, J = 15.7 Hz, CH2), 2.54 (q, 2H, J = 7.2 Hz,
CH2), 2.39 (s, 6H, CH3), 1.06 (t, 3H, J = 7.2 Hz, CH3). MS (ESI) m/z:
404.9 ([M+Na]+). Anal. Calcd for C17H17Cl2N3OS: C, 53.41; H, 4.48;
N, 10.99. Found: C, 53.37; H, 4.41; N, 11.05.
1H NMR (CDCl3) d: 7.15–7.12 (m, 3H, Ar-H; CH), 6.93–6.90 (m,
1H, Ar-H), 6.72 (s, 1H, pyrimidinyl-H), 4.17 (d, 1H, J = 15.8 Hz,
CH2), 3.84 (d, 1H, J = 14.7 Hz, CH2), 2.36 (s, 6H, CH3).
3.4.11. 2-(2-Chloro-6-fluorophenyl)-3-(4,5,6-dimethylpyrimidin-
2-yl)thiazolidin-4-one (6b)
3.4.4. 2-(2,6-Dichlorophenyl)-3-(5-propyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (5d)
IR (KBr)
J = 1.8 Hz, CH), 7.29–7.06 (m, 3H, Ar-H), 4.16 (dd, 1H, J = 15.7 Hz,
1H NMR (CDCl3) d: 7.17–7.13 (m, 3H, Ar-H; CH), 6.95–6.90 (m,
1H, Ar-H), 4.18 (d, 1H, J = 15.7 Hz, CH2), 3.85 (d, 1H, J = 14.8 Hz,
CH2), 2.37 (s, 3H, CH3), 2.11 (s, 6H, CH3).
m
: 1710 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.46 (d, 1H,

H. Chen et al. / Bioorg. Med. Chem. 17 (2009) 3980–3986
3985
3.4.12. 2-(2-Chloro-6-fluorophenyl)-3-(5-ethyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (6c)
IR (KBr)
: 1714 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.17–7.13 (m,
3H, Ar-H; CH), 6.95–6.90 (m, 1H, Ar-H), 4.18 (d, 1H, J = 15.7 Hz,
CH2), 3.85 (d, 1H, J = 14.1 Hz, CH2), 2.56 (q, 2H, J = 7.6 Hz, CH2),
2.40 (s, 6H, CH3), 1.07 (t, 3H, J = 7.6 Hz, CH3). MS (ESI) m/z: 389.2
([M+Na]+). Anal. Calcd for C17H17ClFN3OS: C, 55.81; H, 4.68; N,
11.49. Found: C, 55.73; H, 4.62; N, 11.54.
3.5. In vitro HIV-RT kit assay34
m
The HIV-RT inhibition assay was performed by using an RT as-
say kit (Roche), and the procedure for assaying RT inhibition was
performed as described in the kit protocol. Briefly, the reaction
mixture consists of template/primer complex, 20-deoxy-nucleo-
tide-50-triphosphates (dNTPs) and reverse transcriptase (RT) en-
zyme in the lysis buffer with or without inhibitors. After 1 h
incubation at 37 °C the reaction mixture was transferred to strep-
tavidine-coated microtitre plate (MTP). The biotin labeled dNTPs
that are incorporated in the template due to activity of RT were
bound to streptavidine. The unbound dNTPs were washed using
wash buffer and antidigoxigenin-peroxidase (DIG-POD) was added
in MTP. The DIG-labeled dNTPs incorporated in the template was
bound to anti-DIG-POD antibody. The unbound anti-DIG-POD
was washed and the peroxide substrate (ABST) was added to the
MTP. A colored reaction product was produced during the cleavage
of the substrate catalyses by a peroxide enzyme. The absorbance of
the sample was determined at OD 405 nM using microtiter plate
ELISA reader. The resulting color intensity is directly proportional
to the actual RT activity. The percentage inhibitory activity of RT
inhibitors was calculated by comparing to a sample that does not
contain an inhibitor. The percentage inhibition was calculated by
formula as given below: % Inhibition = 100 ꢀ [(OD 405 nm with
inhibitor/OD 405 nm without inhibitor) ꢁ 100].
3.4.13. 2-(2-Chloro-6-fluorophenyl)-3-(5-propyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (6d)
IR (KBr) m
: 1712 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.15–7.13 (m,
3H, Ar-H; CH), 6.95–6.90 (m, 1H, Ar-H), 4.18 (d, 1H, J = 15.7 Hz,
CH2), 3.85 (d, 1H, J = 15.3 Hz, CH2), 2.49 (t, 2H, J = 7.8 Hz, CH2),
2.39 (s, 6H, CH3), 1.45 (q, 2H, J = 7.2 Hz, CH2), 0.97 (t, 3H,
J = 7.2 Hz, CH3). MS (ESI) m/z: 402.9 ([M+Na]+). Anal. Calcd for
C18H19ClFN3OS: C, 56.91; H, 5.04; N, 11.06. Found: C, 56.95; H,
5.12; N, 11.07.
3.4.14. 2-(2-Chloro-6-fluorophenyl)-3-(5-butyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (6e)
IR (KBr) m
: 1712 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.17–7.14 (m,
3H, Ar-H; CH), 6.95–6.90 (m, 1H, Ar-H), 4.18 (dd, 1H, J = 15.7 Hz,
1.6 Hz, CH2), 3.84 (d, 1H, J = 14.9 Hz, CH2), 2.55–2.48 (m, 2H,
CH2), 2.39 (s, 6H, CH3), 1.40–1.38 (m, 4H, CH2), 0.93 (t, 3H,
J = 6.8 Hz, CH3). MS (ESI) m/z: 417.6 ([M+Na]+). Anal. Calcd for
C19H21ClFN3OS: C, 57.93; H, 5.37; N, 10.67. Found: C, 57.90; H,
5.34; N, 10.62.
Acknowledgements
The financial supports from the National Natural Science Foun-
dation of China (NSFC) (20672027), the Natural Science Foundation
of Hebei (2008000588), the Research Foundation of the Ministry of
Education of China (206013) and the Postdoctoral Foundation of
China are gratefully acknowledged.
3.4.15. 2-(2-Chloro-6-fluorophenyl)-3-(5-pentyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (6f)
IR (KBr) m
: 1718 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.12–7.10 (m,
3H, Ar-H; CH), 6.92–6.87 (m, 1H, Ar-H), 4.15 (d, 1H, J = 15.7 Hz,
CH2), 3.82 (d, 1H, J = 15.4 Hz, CH2), 2.50–2.486 (m, 2H, CH2), 2.37
(s, 6H, CH3), 1.40–1.30 (m, 6H, CH2), 0.87 (t, 3H, J = 6.87 Hz, CH3).
MS (ESI) m/z: 432.3 ([M+Na]+). Anal. Calcd for C20H23ClFN3OS: C,
58.89; H, 5.68; N, 10.30. Found: C, 58.85; H, 5.67; N, 10.36.
References and notes
1. Rao, A.; Balzarini, J.; Carbone, A.; Chimirri, A.; De Clercq, E.; Monforte, A. M.;
Monforte, P.; Pannecouque, C.; Zappalà, M. Antivir. Res. 2004, 63, 79.
2. Rao, A.; Balzarini, J.; Carbone, A.; Chimirri, A.; De Clercq, E.; Monforte, A. M.;
Monforte, P.; Pannecouque, C.; Zappalà, M. Il Farmaco 2004, 59, 33.
3. Barreca, M. L.; Chimirri, A.; De Clercq, E.; De Luca, L.; Monforte, A. M.; Monforte,
P.; Rao, A.; Zappalà, M. Il Farmaco 2003, 58, 259.
3.4.16. 2-(2-Chloro-6-fluorophenyl)-3-(5-allyl-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (6g)
IR (KBr) m
: 1713 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.16–7.15 (m,
4. Rao, A.; Carbone, A.; Chimirri, A.; De Clercq, E.; Monforte, A. M.; Monforte, P.;
Pannecouque, C.; Zappalà, M. Il Farmaco 2003, 58, 115.
3H, Ar-H; CH), 6.96–6.90 (m, 1H, Ar-H), 5.75–5.82 (m, 1H, @CH),
5.04 (d, 1H, J = 10.4 Hz, @CH2), 4.80 (d, 1H, J = 17.2 Hz, @CH2)
4.18 (d, 1H, J = 15.6 Hz, CH2), 3.85 (d, 1H, J = 14.8 Hz, CH2), 3.28–
3.29 (m, 2H, CH2), 2.39 (s, 6H, CH3). MS (ESI) m/z: 401.3
([M+Na]+). Anal. Calcd for C18H17ClFN3OS: C, 57.21; H, 4.53; N,
11.12. Found: C, 57.29; H, 4.48; N, 11.07.
5. Barreca, M. L.; Balzarini, J.; Chimirri, A.; De Clercq, E.; De Luca, L.; Höltje, H. D.;
Höltje, M.; Monforte, A. M.; Monforte, P.; Pannecouque, C.; Rao, A.; Zappalà, M.
J. Med. Chem. 2002, 45, 5410.
6. Rao, A.; Carbone, A.; Chimirri, A.; De Clercq, E.; Monforte, A. M.; Monforte, P.;
Pannecouque, C.; Zappalà, M. Il Farmaco 2002, 57, 747.
7. Barreca, M. L.; Chimirri, A.; De Luca, L.; Monforte, A. M.; Monforte, P.; Rao, A.;
Zappala, M.; Balzarini, J.; De Clercq, E.; Pannecouque, C.; Witvrouw, M. Bioorg.
Med. Chem. Lett. 2001, 11, 1793.
8. Rawal, R. K.; Tripathi, R.; Katti, S. B.; Pannecouque, C.; De Clercq, E. Bioorg. Med.
Chem. 2007, 15, 1725.
9. Rawal, R. K.; Solomon, V. R.; Prabhakar, Y. S.; Katti, S. B.; De Clercq, E. Comb.
Chem. High Throughput Screening 2005, 8, 439.
10. Prabhakar, Y. S.; Solomon, V. R.; Rawal, R. K.; Gupta, M. K.; Katti, S. B. QSAR
Comb. Sci. 2004, 23, 234.
11. Prabhakar, Y. S.; Rawal, R. K.; Gupta, M. K.; Solomon, V. R.; Katti, S. B. Comb.
Chem. High Throughput Screening 2005, 8, 431.
12. Roy, K.; Leonard, J. T. QSAR Comb. Sci. 2005, 24, 579.
13. Ravichandran, V.; Prashantha Kumar, B. R.; Sankar, S.; Agrawal, R. K. Eur. J. Med.
Chem. 2009, 44, 1180.
14. Murugesan, V.; Prabhakar, Y. S.; Katti, S. B. J. Mol. Graphics Modell. 2009, 27, 735.
15. Balzarini, J.; Orzeszko-Krzesin´ ska, B.; Maurin, J. K.; Orzeszko, A. Eur. J. Med.
Chem. 2009, 44, 303.
3.4.17. 2-(2-Chloro-6-fluorophenyl)-3-(5-propanenitrile-4,6-
dimethylpyrimidin-2-yl) thiazolidin-4-one (6h)
IR (KBr) m
: 1715 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.15 (m, 3H,
CH, Ar-H), 6.93 (m, 1H, Ar-H), 4.19 (d, 1H, J = 15.6 Hz, CH2), 3.85
(d, 1H, J = 14.4 Hz, CH2), 2.96 (t, 2H, J = 7.2 Hz, CH2), 2.49 (t, 2H,
J = 7.6 Hz, CH2), 2.46 (s, 6H, CH3). MS (ESI) m/z: 388.9 ([M+H]+).
Anal. Calcd for C20H18ClFN2OS: C, 61.77; H, 4.67; N, 7.20. Found:
C, 61.82; H, 4.61; N, 7.09.
3.4.18. 2-(2-Chloro-6-fluorophenyl)-3-(5-bromo-4,6-dimethyl-
pyrimidin-2-yl)thiazolidin-4-one (6i)
16. Balzarini, J.; Orzeszko-Krzesin´ ska, B.; Maurin, J. K.; Orzeszko, A. Eur. J. Med.
Chem. 2007, 42, 993.
IR (KBr) m
: 1736 cmꢀ1 (C@O), 1H NMR (CDCl3) d: 7.17–7.12 (m,
17. Rawal, R. K.; Tripathi, R.; Katti, S. B.; Pannecouque, C.; De Clercq, E. Eur. J. Med.
Chem. 2008, 43, 2800.
18. Rawal, R. K.; Tripathi, R.; Katti, S. B.; Pannecouque, C.; De Clercq, E. Bioorg. Med.
Chem. 2007, 15, 3134.
19. Rawal, R. K.; Prabhakar, Y. S.; Katti, S. B.; De Clercq, E. Bioorg. Med. Chem. 2005,
13, 6771.
3H, Ar-H; CH), 6.96–6.91 (m, 1H, Ar-H), 4.18 (d, 1H, J = 15.8 Hz,
CH2), 3.85 (d, 1H, J = 15.4 Hz, CH2), 2.53 (s, 6H, CH3). MS (ESI) m/
z: 438.9 ([M+Na]+). Anal. Calcd for C15H12BrClFN3OS: C, 43.24; H,
2.90; N, 10.08. Found: C, 43.27; H, 2.89; N, 10.05.

3986
H. Chen et al. / Bioorg. Med. Chem. 17 (2009) 3980–3986
20. Rawal, R. K.; Tripathi, R. K.; Katti, S. B.; Pannecouque, C.; De Clercq, E. Med.
Chem. 2007, 3, 355.
29. Dandia, A.; Singh, R.; Khaturia, S.; Me-rienne, C.; Morgantc, G.; Loupyd, A.
Bioorg. Med. Chem. 2006, 14, 2409.
21. Rawal, R. K.; Tripathi, R.; Kulkarni, S.; Paranjape, R.; Katti, S. B.; Pannecouque,
C.; De Clercq, E. Chem. Biol. Drug. Des. 2008, 72, 147.
30. Chen, H.; Bai, J.; Zhao, L.; Yuan, X. G.; Li, X. L.; Cao, K. Q. Chin. J. Org. Chem. 2008,
28, 1092 (in Chinese).
22. Verma, A.; Saraf, S. K. Eur. J. Med. Chem. 2008, 43, 897.
23. Rao, A.; Chimirri, A.; Ferro, S.; Monforte, A. M.; Monforte, P.; Pannecouque, C.;
Zappalà, M. Arkivoc 2004, 147.
24. Sriram, D.; Yogeeswari, P.; Kumar, T. G. A. J. Pharm. Pharm. Sci. 2005, 8, 426.
25. Bolognese, A.; Correale, G.; Manfra, M.; Lavecchia, A.; Novellino, E.; Barone, V.
Org. Biomol. Chem. 2004, 2, 2809.
26. Srivastava, T.; Haq, W.; Katti, S. B. Tetrahedron 2002, 58, 7619.
27. Gududuru, V.; Nguyen, V.; Dalton, J. T.; Miller, D. D. Synlett 2004, 2357.
28. Fraga-Dubreuil, J.; Bazureau, J. P. Tetrahedron 2003, 59, 6121.
31. Chen, H.; Bai, J.; Zhao, L.; Yuan, X. G.; Li, X. L.; Cao, K. Q. Chin. J. Org. Chem. 2009,
29, 94 (in Chinese).
32. Stewart, R.; Thomas, W. S. L. J. Org. Chem. 1982, 47, 2075.
33. Nasielski, J.; Standaert, A.; Nasielski-Hinkens, R. Synth. Commun. 1991, 21, 901.
34. Reverse Transcriptase Assay, Colorimetric kit, Roche Diagnostics GmbH, Roche
Applied Science, Sandhofer Strasse 116, D-68305 Mannheim, Germany.
35. Haley, C. A. C.; Maitland, P. J. Chem. Soc. 1951, 3155.
36. Brown, D. J.; England, B. T. J. Chem. Soc. 1967, 1922.