Design, synthesis, and biological activity of a novel series of 2,5-disubstituted furans/pyrroles as HIV-1 fusion inhibitors targeting gp41

Article abstract of DOI:10.1016/j.bmcl.2011.08.081

Based on molecular docking analysis of earlier results, we designed a series of 2,5-disubstituted furans/pyrroles (5a-h) as HIV-1 entry inhibitors. Compounds were synthesized by Suzuki-Miyaura cross coupling, followed by a Knoevenagel condensation or Witt

Full text of DOI:10.1016/j.bmcl.2011.08.081

Bioorganic & Medicinal Chemistry Letters 21 (2011) 6895–6898
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis, and biological activity of a novel series
of 2,5-disubstituted furans/pyrroles as HIV-1 fusion inhibitors
targeting gp41
Shibo Jiang a, , Srinivasa R. Tala b, , Hong Lu a, Peng Zou a, Ilker Avan b,c, Tarek S. Ibrahim b,d
,
⇑
b,f,
Nader E. Abo-Dya b,d, Abdelmotaal Abdelmajeid b,e, Asim K. Debnath a, , Alan R. Katritzky
⇑
⇑
a Lindsley F. Kimball Research Institute, New York Blood Center, NY 10065, USA
b Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
c Department of Chemistry, Anadolu University, 26470 Eskißsehir, Turkey
d Department of Pharmaceutical Organic Chemistry, Faculty of Pharmacy, Zagazig University, Zagazig 44519, Egypt
e Department of Chemistry, Faculty of Science, Benha University, Benha, Egypt
f Department of Chemistry, King Abdulaziz University, Jeddah 21589, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 July 2011
Revised 15 August 2011
Accepted 17 August 2011
Available online 5 September 2011
Based on molecular docking analysis of earlier results, we designed a series of 2,5-disubstituted
furans/pyrroles (5a–h) as HIV-1 entry inhibitors. Compounds were synthesized by Suzuki–Miyaura cross
coupling, followed by a Knoevenagel condensation or Wittig reaction. Four of these compounds were
found to be effective in inhibiting HIV-1 infection, with the best compounds being 5f and 5h, which
exhibited significant inhibition on HIV-1IIIB infection at micromolar levels with low cytotoxicity. These
compounds are also effective in blocking HIV-1 mediated cell-cell fusion and the gp41 six-helix bundle
formation, suggesting that they are also HIV-1 fusion inhibitors targeting gp41 and have potential to
be developed as a new class of anti-HIV-1 agents.
Keywords:
HIV-1 fusion inhibitors
Gp41
Ó 2011 Elsevier Ltd. All rights reserved.
Furans
Pyrroles
ELISA
Human immunodeficiency virus type 1 (HIV-1) entry into a tar-
get cell is initiated by the binding of the viral envelope glycopro-
tein (Env) surface subunit gp120 to the primary receptor CD4
and a coreceptor CXCR4 or CCR5, which triggers a series of confor-
mational changes in gp41 to expose the inner trimeric coiled-coil
formed by three parallel N-terminal heptad repeat (NHR) units of
gp41. There is a deep hydrophobic cavity in each of the grooves
on the surface of NHR-trimer, which is an attractive target for
development of small molecule HIV fusion/entry inhibitors.1 Bind-
ing of the gp41 C-terminal heptad repeat (CHR) units to the NHR-
trimer results in formation of a six-helix bundle (6-HB) core, which
brings the viral and target cell membranes into close proximity for
fusion.2–4
as N-substituted pyrrole derivatives 1 and 2 (NB-2 and NB-64),5
2-aryl 5-(4-oxo-3-phenethyl-2-thioxothiazolidin-ylidenemethyl)
furans (3a–o),6 and 5-((arylfuran/1H-pyrrol-2-yl) methylene)-2-
thioxo-3-(3-(trifluoromethyl)phenyl)thiazolidin-4-ones (4a–o),7
(Fig. 1). These compounds could effectively inhibit HIV-1 infection,
HIV-1 Env-mediated cell–cell fusion and gp41 six-helix bundle for-
mation and have the potential for the development of a new class of
anti-HIV drugs.
In order to expand the chemical diversity within the series, we
have now designed and synthesized a novel series of 2,5-disubsti-
tuted furans/pyrroles 5a–h (Fig. 2) and tested their biological activ-
ity against HIV-1 infection, HIV-1 mediated cell–cell fusion and the
gp41 six-helix bundle (6-HB) core formation, including 3d, one of
the most active compounds in the series of 2-aryl 5-(4-oxo-
We previously identified several series of small molecule HIV-1
fusion inhibitors that were expected to target the gp41 cavity, such
3-phenethyl-2-thioxothiazolidin-ylidenemethyl) furans6 as
control (Table 1).
a
2,5-Disubstituted furans/pyrroles (5a–h) were synthesized by
Suzuki–Miyaura cross couplings and subsequent condensations.
The inhibitory activities of 5a–h on HIV-1IIIB replication in MT-2
cells were assessed using an enzyme-linked immunosorbent assay
(ELISA) for p24 measurement as previously described.6 Two of the
compounds, 5f and 5h inhibited HIV-1IIIB infection with EC50
⇑
Corresponding authors. Tel.: +1 212 570 3058; fax: +1 212 570 3099 (S.J.);
tel.: +1 212 5703373; fax: +1 212 570 3168 (A.K.D.); tel.: +1 352 392 0554;
fax: +1 352 392 9199 (A.R.K.).
E-mail addresses: sjiang@nybloodcenter.org (S. Jiang), adebnath@nybloodcenter.
org (A.K. Debnath), katritzky@chem.ufl.edu (A.R. Katritzky).
Present address: Department of Medicinal Chemistry, College of Pharmacy,
University of Minnesota, Minneapolis, MN 55455, USA.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.08.081

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S. Jiang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 6895–6898
COOH
N
Cl
N
O
OH
HO
HOOC
O
OH
R1
S
R
R
N
S
O
X
X
O
O
H3C
CH3
6a-c
6a
R = H, X = NH for
R = Cl, X = NH for 6b
R = Cl, X = O for 6c
3a-o:
3d:
X= C or N
R = Cl, R = H, X = CH
2
1
1
S
X
Figure 3. 2-Aryl-5-formylpyrroles 6a–b and 2-aryl-5-formylfuran 6c.
F
R
R1
N
O
S
F
F
Y
Br
O
O
4a-o:
X= COOH or Tetrazolyl; Y= O or NH
K2CO3, DMF
90 oC, 10 h
HN
HN
N
NH
Figure 1. Previously identified small molecule HIV-1 fusion inhibitors.
O
O
8
9
7a, 86%
O
O
OH
Scheme 1. Synthesis of 3-phenethylimidazolidine-2,4-dione 7a.
Z
COOH
N
Cl
R
N
N
Y
N
S
X
O
O
O
Br
O
O
5a-g
S
Na2CO3, (CH3)2CO
reflux, 4 h
S
5h
N
NH
O
Figure 2. Novel 2,5-disubstituted furans/pyrroles 5a–h.
O
10
9
7b
, 80%
values (effective concentration for 50% inhibition) of 6.9 and
16.8 M, respectively. The cytotoxicity of these compounds on
Scheme 2. Synthesis of 3-phenethylthiazolidine-2,4-dione 7b.
l
MT-2 cells was tested by a colorimetric XTT assay as previously
described.6 The CC50 (concentration causing 50% cytotoxicity) val-
ues of the compounds 5f and 5h were 118 and >320 lM, giving SI
NH2
O
O
i) (CH3CH2)2O,
20 oC, 2 h
(selectivity index) values of 17.2 and >19.1, respectively (Table 1).
Compounds 5f and 5h also inhibited HIV-1-mediated cell–cell fu-
sion and the gp41 6-HB formation, respectively (Table 1). The re-
sults suggest that the compounds inhibit HIV-1 fusion by
targeting the HIV-1 gp41 and blocking gp41 6-HB core formation.
Notably, the compounds 5a and 5e had higher solubility in PBS
used in 6-HB formation assay than that in FBS-containing culture
media used in virus inhibition assay and cell–cell fusion assays,
which may be an explanation why these compounds are effective
in inhibiting 6-HB formation, but not effective against HIV-1 infec-
tion and
PPh3, CH3COOH
100 oC, 1 h
O
N
ii) p-TsOH, toluene,
reflux, 5 h
O
O
13
11
12
, 83%
O
N
Ph
P
O
Ph
Ph
7c
, 72%
cell–cell fusion. 2-Aryl 5-formylpyrroles 6a,3 6b3 and 2-aryl
5-formylfuran 6c6 ( Fig. 3) were synthesized by our previously
reported procedures.
Scheme 3. Synthesis of 1-phenethyl-3-(triphenylphosphoranylidene)-pyrrolidine-
2,5-dione 7c.
Table 1
Inhibitory activity on HIV-1IIIB infection, cell–cell fusion and 6-HB formation, cytotoxicity and selectivity indexes of the 2,5-disubstituted furans/pyrroles 5a–ha and 3dc
Product
X
Y
Z
R
CC50
(
lM)
EC50
(l
M) for inhibiting
SIb
HIV-1 infection
Cell fusion
6-HB formation
5a
5b
5c
5d
5e
5f
5g
5h
3dc
NH
O
O
NH
NH
O
O
NH
NH
S
CH2
CH2
CH2
O
O
O
O
O
O
O
S
H
75.15 5.61
78.45 9.25
68.22 1.23
126.99 0.00
74.08 2.19
118.45 5.63
282.40 11.44
>320
>100
35.89 0.28
>100
26.89 1.15
>100
3.05 0.36
18.96 1.31
29.65 4.24
>100
5.50 1.31
15.55 2.84
27.81 0.69
12.89 1.78
1.27 0.23
—
Cl
Cl
H
Cl
Cl
Cl
54.21 34.10
15.11 0.48
>100
1.5
4.5
—
>100
>100
—
6.90 0.73
31.03 1.72
16.79 3.10
0.050 0.007
43.55 0.87
49.59 2.30
45.92 1.19
0.75 0.02
17.2
9.1
>19.1
406
(as in Fig. 2)
O
S
S
Cl
20.30 1.14
a
b
c
Each compound was tested in triplicate; the data are presented as the mean SD.
SI was calculated based on the CC50 for MT-2 cells and EC50 for inhibiting infection of HIV-1IIIB
.
Reported.6

S. Jiang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 6895–6898
6897
O
OH
O
OH
O
O
R
N
R
N
Y
Y
O
X
X
O
O
7a,b
base, reflux
5a-c
6a,c
Scheme 4. Synthesis of 2,5-disubstituted pyrrole/furans 5a–c.
Table 3
Table 2
Preparation of 2,5-disubstituted pyrrole/furans 5a–c
Preparation of 2,5-disubstituted pyrrole/furans 5d–f
Yielda (%)
Product 5
X
R
Reaction time (h)
Yielda (%)
Product 5
X
R
Y
Reaction time (h)
Base
5d
5e
5f
NH
NH
O
H
Cl
Cl
24
24
12
39
48
57
5a
5b
5c
NH
O
O
H
Cl
Cl
NH
NH
S
5
10
18
Pyrrolidine
56
49
45
Pyrrolidine
b
a
a
Isolated yields.
Isolated yields.
2,2,6,6-Tetramethylpiperidine.
b
acetic anhydride, acetic acid and sodium acetate under micro-
waves at 50 W to afford (Z)-2-chloro-5-(5-((4-oxo-3-phenethyl-
2-thioxooxazolidin-5-ylidene)methyl)furan-2-yl)-benzoic acid 5g
in 21% yield (Scheme 6).
2-Chloro-5-(5-formylfuran-2-yl)benzoic acid 6c was treated
with 3-mercapto-6-phenyl-1,2,4-triazin-5(4H)-one 14 in the pres-
ence of chloroacetic acid and sodium acetate to afford (Z)-2-chloro-
5-(5-((3,7-dioxo-6-phenyl-3,7-dihydro-2H-thiazolo[3,2-b]
[1,2,4]triazin-2-ylidene)methyl)furan-2-yl)benzoic acid 5h in 53%
yield (Scheme 7).
3-Phenethylimidazolidine-2,4-dione 7a was synthesized in 86%
yield by the reaction of imidazolidine-2,4-dione 8 with (2-bromo-
ethyl)benzene 9 in the presence of potassium carbonate in DMF at
90 °C for 10 h (Scheme 1).
3-Phenethylthiazolidine-2,4-dione 7b was synthesized in 80%
yield by the reaction of thiazolidine-2,4-dione 10 with (2-bromo-
ethyl)benzene 9 in the presence of sodium carbonate in acetone
under reflux for 4 h (Scheme 2).
In conclusion, we report the design and synthesis of 2,5-disub-
stituted pyrrole/furans 5a–h by Knoevenagel condensation or Wit-
tig reactions. Two of these compounds 5f and 5h exhibited
significant inhibitory activity against HIV-1IIIB infection, HIV-1-
mediated cell–cell fusion and the gp41 six-helix bundle formation,
suggesting that this new series of compounds can be used for
developing small molecule HIV-1 fusion/entry inhibitors targeting
gp41.
The in vitro cytotoxicity of compounds on MT-2 cells, the inhib-
itory activity of compounds on HIV-1IIIB replication in MT-2 cells,
on HIV-1-mediated cell–cell fusion, and on the gp41 six-helix bun-
dle (6-HB) formation were determined as previously described.5
The CC50 (concentration for 50% cytotoxicity) and EC50 values were
calculated using CalcuSyn program.10
Treatment of maleic anhydride 11 with 2-phenylethylamine in
diethyl ether at 20 °C for 2 h, followed by heating the precipitated
solid in toluene with p-toluenesulfonic acid for 5 h, gave 1-phen-
ethyl-1H-pyrrole-2,5-dione 13 in 83% yield. Treatment of 1-phen-
ethyl-1H-pyrrole-2,5-dione 13 with triphenylphosphine in acetic
acid at 100 °C for 1 h gave 1-phenethyl-3-(triphenylphosphorany-
lidene)-pyrrolidine-2,5-dione 7c (Scheme 3).
3-Phenethyl-2-thioxooxazolidin-4-one 7d8 and 3-mercapto-
6-phenyl-1,2-4-triazin-5(4H)-one 149 were synthesized according
to literature procedures.
Knoevenagel condensation of 2-aryl 5-formylpyrrole/furans
6a,c with active methylene compounds 7a,b in the presence of pyr-
rolidine or 2,2,6,6-tetramethylpiperidine gave 2,5-disubstituted
pyrrole/furans 5a–c (45À56%) (Scheme 4, Table 2), characterized
by 1H, 13C NMR spectroscopy and elemental analysis. In the prep-
aration of 5b, the reaction mixture was first treated with
1,1,1,3,3,3-hexamethyldisilazane for 5 h at 90 °C, followed by
treatment with pyrrolidine for 5 h at 90 °C.
Detailed information regarding the syntheses and spectroscopic
characterization of 2,5-disubstituted pyrrole/furans 5a–h pre-
sented in this Letter can be found in the Supplementary data
provided.
Reaction of 1-phenethyl-3-(triphenylphosphoranylidene)pyrr-
olidine-2,5-dione 7c with 2-aryl 5-formylpyrrole/furans 6a–c at
room temperature in THF gave 2,5-disubstituted pyrrole/furan
5d–f (39À57%) (Scheme 5, Table 3), characterized by 1H, 13C
NMR spectroscopy and elemental analysis.
Acknowledgments
We thank the University of Florida, The Kenan Foundation and
King Abdulaziz University, Jeddah, Saudi Arabia for financial sup-
port. This study was supported by NIH grant AI046221. We thank
Dr. C. D. Hall for helpful discussions.
2-Chloro-5-(5-formylfuran-2-yl)benzoic acid 6c was treated
with 3-phenethyloxazolidine-2,4-dione 7d in the presence of
O
O
OH
O
OH
N
O
Ph
Ph
R
R
N
P
O
Ph
O
7c
THF, rt
X
X
O
6a-c
5d-f
Scheme 5. Synthesis of 2,5-disubstituted pyrrole/furans 5d–f.

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S. Jiang et al. / Bioorg. Med. Chem. Lett. 21 (2011) 6895–6898
S
COOH
COOH
O
Cl
Cl
N
O
MW, 50W, NaOAc
Ac2O, CH3COOH
N
O
+
O
O
O
O
S
6c
7d
5g, 21%
Scheme 6. Synthesis of 2,5-disubstituted furan 5g.
O
COOH
COOH
Cl
N
Cl
N
N
Ph
O
COOH
Cl
N
N
S
O
O
+
O
HS
N
H
NaOAc, CH3COOH
O
6c
14
5h, 53%
Scheme 7. Synthesis of 2,5-disubstituted furan 5h.
3. Moore, J. P.; Doms, R. W. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 10598.
4. Liu, S.; Wu, S.; Jiang, S. Curr. Pharm. Des. 2007, 13, 143.
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Chemother. 2004, 48, 4349.
6. Katritzky, A. R.; Tala, S. R.; Lu, H.; Vakulenko, A. V.; Chen, Q. Y.; Sivapackiam, J.;
Pandya, K.; Jiang, S.; Debnath, A. K. J. Med. Chem. 2009, 52, 7631.
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Supplementary data
Supplementary data (synthetic procedures and compounds
characterization data) associated with this article can be found,
in the online version, at doi:10.1016/j.bmcl.2011.08.081.
8. Kouzou H., Mitsubishi Paper Mills, Ltd, JP 56,034,675, 1981.
9. Arndt, F.; Franke, W.; Klose, W.; Lorenz, J.; Schwarz, K. Liebigs Ann. der Chem.
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