Design, synthesis, and biological evaluation of novel 4-hydroxypyrone derivatives as HIV-1 protease inhibitors

Article abstract of DOI:10.1016/j.bmcl.2005.04.057

Twenty-four 4-hydroxypyrone derivatives were synthesized with a facile synthetic method to develop novel HIV protease inhibitors. Most of them were shown to display good antiviral activities in SIV-infected CEM cells. The introduction of α-naphthylmethyl group to C-6 of 5,6-dihydropyran-2-ones led to an effective antiviral compound that showed an EC₅₀ value at 1.7 μM with a therapeutic index of 46.

Full text of DOI:10.1016/j.bmcl.2005.04.057

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3257–3262
Design, synthesis, and biological evaluation of novel
-hydroxypyrone derivatives as HIV-1 protease inhibitors
4
Chun-Lai Sun, Rui-Fang Pang, Hang Zhang and Ming Yang*
National Research Laboratory of Natural and Biomimetic Drugs, Peking University, Beijing 100083, PeopleÕs Republic of China
Received 18 March 2005; accepted 26 April 2005
Available online 31 May 2005
Abstract—Twenty-four 4-hydroxypyrone derivatives were synthesized with a facile synthetic method to develop novel HIV protease
inhibitors. Most of them were shown to display good antiviral activities in SIV-infected CEM cells. The introduction of a-naph-
thylmethyl group to C-6 of 5,6-dihydropyran-2-ones led to an effective antiviral compound that showed an EC50 value at
1
ꢀ
.7 lM with a therapeutic index of 46.
2005 Elsevier Ltd. All rights reserved.
1
. Introduction
antiviral therapy. Intense research into the therapeutic
intervention of AIDS has brought to market several
2
,3
HIV protease plays an important role in post-transla-
tional processing of the precursor polyproteins Gay
and Gay/Pol, which is essential for maturation of the
virus. And now HIV-1 protease has become an attrac-
tive target for the design of inhibitors for effective
effective HIV protease inhibitors. The clinical effec-
tiveness of the HIV protease inhibitors in combination
with reverse transcriptase inhibitors for the treatment
1
4
of AIDS has been well established. However, the
currently marketed HIV protease inhibitors which are
Figure 1. 4-Hydropyrone HIV protease inhibitors.
Keywords: 4-Hydroxypyrone; Antiviral activity; Protease inhibitor.
*
Corresponding author. Tel.: +86 10 82801569; fax: +86 10 82802062; e-mail: yangm@bjmu.edu.cn
0
960-894X/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.04.057

3258
C.-L. Sun et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3257–3262
Table 1. The structures of 4-hydroxypyrones
Table 1 (continued)
1
R
2
3
4
R
Entry
R
R
5
A
H
H
1
R
2
R
3
R
4
R
Entry
5B
CH
3
H
1A
1B
1C
1D
2A
2B
2C
2D
3A
H
H
5
5
6
6
6
6
C
D
A
B
C
D
C
2
H
5
H
CH
3
H
CH
H
3
CH
3
C
2
H
5
H
O
H
CH
3
CH
3
CH
3
H
H
H
C
2
H
5
H
CH
3
H
CH
3
CH
3
C
2
H
5
H
peptidomimetics have serious problems associated with
,6
5
CH
3
CH
3
low bioavailability and high toxicity.
Additionally,
the emergence of HIV-1 resistant strains necessitates
continued research for novel inhibitors of viral
7,8
replications.
H
H
Since the 4-hydroxycoumarin phenprocoumon I (Fig. 1)
was previously identified as a non-peptidic protease
3B
3C
3D
CH
3
H
9
inhibitor from a broad screening program, many 4-
hydroxypyrones have been synthesized by different re-
1
0,11
10
C
2
H
5
H
search groups.
Suvit Thaisrivongs and co-workers
have synthesized a series of 5,6-dihydro-4-hydroxy-py-
ran-2-ones containing two substituents at C-6. The X-
ray crystal structure of compound II (Fig. 1) bound to
HIV-1 protease displayed that its side chains filled four
CH
3
CH
3
0
0
2
binding pockets (S , S , S , S ) of the HIV-1 protease. So
1
2
1
pyrones II showed very good enzyme inhibitory activity
(k = 35 nM), but exhibited low antiviral activity in the
HIV-1IIIB-infected MT cells.
4
4
A
B
H
H
H
i
The 4-hydroxy-3-thiosubstituted-pyran-2-one III (Fig. 1)
is similar in structure to the carbon branched com-
4
CH
3
1
2
pounds of Upjohn, but is generally more potent and
does not have a chiral center at position 3. Great ef-
1
1,13
forts
were focused on adding thiosubstitutes to C-3
of 5,6-dihydro-4-hydroxy-pyran-2-ones. As a result,
4
4
C
D
C
2
H
5
H
11
compound IV (Fig. 1) was identified to be a potent
HIV protease inhibitor with a very low IC50 value of
1
.1 nM. But it also showed low antiviral activity
(EC50 = 15 lM). Thus, we became interested in prepar-
CH
3
CH
3
ing 5,6-dihydro-4-hydroxy-3-thiosubstituted-pyrones.
We modified the known 5,6-dihydropyrones at C-3 with
thiosubstitutes to get compounds 1A–D, 3A–D, 6A–D

C.-L. Sun et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3257–3262
3259
1
5
and changed different groups at C-6 to get compounds
A–D, 4A–D, 5A–D (Table 1).
ride in the presence of a single drop DMF, and then
reacted with the compound (9), lithium di-n-propylcup-
rate(I), to get the appropriate ketone (10) possessing a n-
2
1
6
The structures of these compounds were confirmed by
propyl group. a-Phenoxyacetophenone (11) was syn-
thesized from a-bromoacetophenone and phenol in the
presence of potassium carbonate.
1
14
EI-MS and H NMR. Most of them were shown to
display good antiviral activities in SIV-infected CEM
cells. Compound 4C (Fig. 1) was the most potent in this
study, with an EC50 value at 1.7 lM and a therapeutic
index of 46.
1
7
2. Results and discussion
1
0
1
.1. Chemistry
It is reported in the literature that 4-hydroxypyrones
with a spirocycle at C-6 exhibited some inhibitory activ-
ity of HIV protease. The compound with the six-mem-
bered ring was the most potent (IC50 ꢀ 1 lM). The
crystallographic structure of the HIV protease com-
plexed with the pyrone possessing the six-membered ring
The title compounds for this study were synthesized
1
3
using the methods shown in Scheme 1. The dihydropy-
rone cores (1–6) were prepared from the requisite ke-
tones and the dianion of methyl acetoacetate. The
synthesis of the dihydropyrone targets involved prepara-
tion of the 3-bromodihydropyrone derivatives with NBS
in the dark and then displacement of the bromide by the
appropriately substituted thiophenol.
demonstrated that the cyclohexyl ring at C-6 folded into
the S pocket of the HIV protease. We modified the pyr-
one at C-3 with thiosubstitutes, which resulted in achiral
compounds 1A–D (Table 1). They showed good antivi-
1
ral activities in SIV-infected CEM cells and low cyto-
0
2
8
The synthetic pathway for the necessary ketones is
shown in Scheme 2. Acyl chloride (8) was prepared by
reaction of the corresponding acid (7) with thionyl chlo-
toxicity (TC50 > 100 lM) except for compound 1A. To
discover whether adding a large group to C-8 of
0
the spiro ring system could fill the S pocket of the
2
Scheme 1. Reagents and conditions: (a) (1) NaH, (2) n-BuLi, dry THF, followed by ketone addition, 0 ꢁC; (b) (1) NaOH, CH
for two steps); (c) NBS, dry t-BuOH, reflux; (d) Corresponding thiophenol, piperidine, CH Cl , 50–65% (for two steps).
3
OH, (2) H+, 50–70%
(
2
2
Scheme 2. Reagents and conditions: (e) SOCl
2
2 3
, DMF, EtoAc; (f) dry ether, ꢁ40 ꢁC; (g) ꢁ78 ꢁC; (h) K CO , acetone.

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C.-L. Sun et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3257–3262
HIV protease more closely and result in enhanced anti-
viral activity, we synthesized compounds 2A–D (Table
studies were conducted. All the compounds except
1A–D, 2A–D in Table 1 were docked in the binding
site of HIV protease structure using AutoDock3.0
program to get predicted binding free energy. The
results demonstrated that all the compounds in the
naphthylmethyl series (4A–D, 5A–D) had lower
predicted binding free energy than that of compounds
in the phenylethyl series (3A–D). We synthesized them
all and got the EC50 values in a cell culture assay using
SIV-infected CEM cells (Table 2).
1
9
1
). Contrary to our expectation, all four compounds dis-
played lower antiviral activities but higher toxicity. These
0
results showed that the S pocket of the HIV protease
probably could not accommodate such a large group.
2
To further explore the interaction between the pyrone
derivatives and the HIV proteases, molecular modeling
Table 2. The antiviral activities (EC50) and toxicities (TC50) of
4-hydroxypyrones
Among the 6-phenylethyl series, all the inhibitors showed
similar antiviral activities in the range from 3.7 to 4.6 lM,
though the alkyl group on thiophenol of C-3 varied, for
example, methyl(3B), ethyl(3C), dimethyl(3D), and they
showed low toxicity (TC50 > 100 lM). 5,6-Dihydropy-
ran-2-ones containing a 6-position naphthylmethyl group
a
b
c
d
Entry
Mp (ꢁ)
EC50 (M)
TC50 (M)
TI
1A
1B
1C
1D
2A
2B
2C
2D
3A
3B
3C
3D
4A
4B
4C
4D
5A
5B
5C
5D
6A
6B
6C
6D
155–157
123–125
135–136
146–147
174–176
132–133
55–57
12.3
3.3
3.9
3.6
>5.0
6.7
8.1
8.3
4.6
3.7
4.1
4.3
4.3
3.8
1.7
4.6
3.2
2.0
1.8
4.0
13.0
8.2
5.6
9.2
52
>100
>100
>100
5.0
4
>30
>26
>28
1
(
4A–D, 5A–D), showed a different structure–activity rela-
56.1
20.1
>100
>100
>100
>100
>100
54
8
tionship compared to the 6-phenylethyl series. Thus, as
the bulk of the alkyl group at the a-position of thiophenol
was increased, the antiviral activities were enhanced ex-
cept for the compounds possessing a dimethyl on thiophe-
nol (4D, 5D). Moreover, the toxicity was increased
compared with the phenylethyl series, especially for the
b-naphthylmethyl series. The most potent inhibitor in
the naphthylmethyl series (4C) showed EC50 of 1.7 lM
with a therapeutic index of 46, which exhibited 2-fold
enhancement in antiviral activities compared to the most
potent one in the phenylethyl series (compound 3B,
EC50 = 3.7 lM). These results showed that the naph-
thylmethyl group at C-6 could possibly occupy the S2
pocket of the HIV protease more closely than the phenyl-
ethyl group, although the phenylethyl group was more
flexible and theoretically it should be conventional to fill
3
82–83
Syrup
>12
>22
>27
>24
>23
13
Syrup
Syrup
37–38
49–51
33–34
>100
78.9
49.7
32.1
34.8
61.5
40.1
31.8
>100
45.3
47.3
>26
46
152–153
127–128
39–40
11
10
32–34
43–45
17
34
42–44
55–57
10
2
157–158
54–55
47–48
>12
8
5
the S pocket of the HIV protease.
2
a
b
c
All compounds are racemic mixtures except for achiral molecules
A–D, 2A–D.
EC50 is the effective concentration at which 50% of the CEM cells are
Molecular modeling studies showed that compound 4C,
1
which was docked in the HIV protease binding sites (S ,
1
18
0
0
2
protected from SIV infection and is the average of at least two runs.
TC50 is the concentration that elicits cytotoxicity in 50% of uninfected
CEM cells.
S , S , S pockets) using program AutoDock3.0, was
overlaid with Tipranavir, a nonpeptidic inhibitor, in
its bound conformation in the X-ray crystal structure
2
1
20
d
TI, therapeutic index = TC50/EC50
.
(
Fig. 2).
0
0
Figure 2. Compound 4C docked in the HIV protease binding sites (S
1
, S
2
, S , S pockets) using program AutoDock3.0 was overlaid with Tipranavir,
1
2
a nonpeptidic inhibitor, in its bound conformation in the X-ray crystal structure. The protein was from the docking experiment and was colored blue.
Compound 4C was colored red and green and Tipranavir was colored white.

C.-L. Sun et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3257–3262
3261
+
14. 1A: MS(EI) m/z 290 (M ). H NMR (CDCl
1
In conclusion, we have synthesized 24 compounds of 4-
hydroxy-pyran-2-one derivatives as new HIV-1 protease
inhibitors. Most of them were shown to display good
antiviral activities in SIV-infected CEM cells. The intro-
duction of a-naphthylmethyl group to C-6 of 5,6-dihyd-
ropyran-2-ones leads to an effective antiviral compound
3
) 1.25–1.53 (m,
6
7
H), 1.64–1.83 (m, 2H), 1.85–2.03 (m, 2H), 2.77 (s, 2H),
.19–7.41 (m, 5H); 1B: MS(EI) m/z 304 (M ). H NMR
+
1
(
CDCl
3
) d 1.28–1.78 (m, 10H), 2.44 (s, 2H), 3.88 (s, 3H),
+
1
7
.22–7.25 (m, 4H); 1C: MS(EI) m/z 318 (M ). H NMR
) d 1.30 (t, 3H, J 7.5 Hz), 1.33–1.41 (m, 1H), 1.47–
(
CDCl
3
1
2
4
.53 (m, 2H), 1.58–1.65 (m, 3H), 1.77–1.85 (m, 2H), 2.00–
.04 (m, 2H), 2.79 (s, 2H), 2.83–2.88 (m, 2H), 6.95–7.18 (m,
H); 1D: MS(EI) m/z 318 (M ). H NMR (CDCl ) d 1.36–
3
4
C (EC50 = 1.7 lM, TI = 46), which can be easily syn-
+
1
thesized from the corresponding ketone in 4 steps with
about 40% yield.
1.66 (m, 6H), 1.68–1.86 (m, 2H), 2.04–2.09 (m, 2H), 2.23 (s,
3
H), 2.40 (s, 3H), 2.8 (s, 2H), 6.75 (s, 1H), 6.90 (d, 1H, J
+
.8 Hz), 7.04 (d, 1H, J 7.8 Hz); 2A: MS(EI) m/z 346 (M ).
7
1
H NMR (CDCl
3
) d 0.87 (s, 9H), 1.20–1.82 (m, 7H), 2.08–
.22 (m, 2H), 2.69 (s, 1H), 2.87 (s, 1H), 7.11–7.31 (m, 5H);
Acknowledgments
2
2
1
+
B: MS(EI) m/z 360 (M ). H NMR (CDCl
1
3
) d 0.87 (s, 9H),
We are grateful to the National Natural Science Foun-
dation of China (No. 30370323) and the Doctoral Pro-
gram Foundation of China (No. 20030001041) for
financial support.
.24–1.28 (m, 2H), 1.51–1.55 (m, 4H), 1.99–2.03 (m, 3H),
2.38 (s, 2H), 3.88 (s, 3H), 7.20–7.31 (m, 4H); 2C: MS(EI) m/
+
1
z 374 (M ). H NMR (CDCl
7.5 Hz), 1.10–1.81 (m, 7H), 2.12–2.16 (m, 2H), 2.70–2.90
(
) d 0.88 (s, 9H), 1.30 (t, 3H, J
3
+
m, 4H), 6.94–7.27 (m, 4H); 2D: MS(EI) m/z 374 (M ). H
1
NMR (CDCl ) d 0.88 (s, 9H), 1.10–1.80 (m, 9H), 2.15 (s,
3
3
H), 2.24 (s, 3H), 2.73 (s, 1H), 2.90 (s, 1H), 6.75–7.04 (m,
+
1
References and notes
3
3H); 3A: MS(EI) m/z 368 (M ). H NMR (CDCl ) d 0.95 (t,
3
2.11 (m, 2H), 2.68–2.81 (m, 4H), 7.13–7.32 (m, 10H); 3B:
MS(EI) m/z 382 (M ). H NMR (CDCl ) d 0.93 (t, 3H, J
3
H, J 7.2 Hz), 1.41–1.44 (m, 2H), 1.77–1.83 (m, 2H), 1.99–
1
2
3
4
5
. Redshaw, S. Exp. Opin. Invest. Drugs 1994, 3, 273.
. Ghosh, A. K.; Bilcer, G.; Schiltz, G. Synthesis 2001, 2203.
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. Barry, M.; Gibbons, S.; Back, D.; Mulcahy, F. Clin.
Pharmacokinet. 1997, 32, 194.
+
1
7.35 Hz), 1.32–1.38 (m, 2H), 1.64–1.71 (m, 2H), 1.91–1.98
(m, 2H), 2.49 (s, 2H), 2.63–2.71 (m, 2H), 3.86 (s, 3H), 7.15–
+
1
7.32 (m, 9H); 3C: MS(EI) m/z 396 (M ). H NMR (CDCl )
3
d 0.94–1.00 (m, 3H), 1.27–1.32 (m, 3H), 1.41–1.47 (m, 2H),
1.83–1.86 (m, 2H), 2.03–2.12 (m, 2H), 2.71–2.91 (m, 6H),
6
. Sommadossi, J. P. AIDS (London) 1999, 13(Suppl. 1),
S29.
+
6.96–7.33 (m, 9H); 3D: MS(EI) m/z 396 (M ). H NMR
1
7
. Mascolini, M. J. Int. Assoc. Physicians AIDS Care 1995,
(CDCl ) d 0.97 (t, 3H, J 7.35 Hz), 1.44–1.58 (m, 2H), 1.83–
3
1
. Erickson, J. W. Nat. Struct. Biol. 1995, 2, 523.
129.
1.93 (m, 2H), 2.07–2.17 (m, 5H), 2.42 (s, 3H), 2.72–2.86 (m,
4H), 6.76 (s, 1H), 6.90 (d, 1H, J 7.5 Hz), 7.04 (d, 1H, J
8
+
1
9
. Romines, K. R.; Chrusciel, R. A. Curr. Med. Chem. 1995,
, 825.
7.5 Hz), 7.17–7.33 (m, 5H); 4A: MS(EI) m/z 404 (M ). H
NMR (CDCl ) d 0.93–0.98 (m, 3H), 1.54–1.62 (m, 2H),
1.85–1.90 (m, 2H), 2.69–2.71 (m, 2H), 3.45–3.65 (m, 2H),
2
3
1
1
0. Thaisrivongs, S.; Romero, D. L.; Tommasi, R. A.;
Janakiraman, M. N.; Strohbach, J. W.; Turner, S. R.;
Biles, C.; Morge, R. R.; Johnson, P. D.; Aristoff, P. A.;
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Hinshaw, R. R.; Howe, W. J.; Finzel, B. C.; Watenpaugh,
K. D. J. Med. Chem. 1996, 39, 4630.
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Ellsworth, E. L.; Gajda, C.; Hamilton, H. W.; Hagen, S.
E.; Markoski, L. J.; Steinbaugh, B. A.; Tait, B. D.;
Humblet, C.; Lunney, E. A.; Pavlovsky, A.; Rubin, J. R.;
Ferguson, D.; Graham, N.; Holler, T.; Hupe, D.; Nouhan,
C.; Tummino, P. J.; Urumov, A.; Zeikus, E.; Zeikus, G.;
Gracheck, S. J.; Saunders, J. M.; VanderRoest, S.;
Brodfuehrer, J.; Iyer, K.; Sinz, M.; Gulnik, S. V. Bioorg.
Med. Chem. 1999, 7, 2775.
2. Skulnick, H. I.; Johnson, P. D.; Howe, W.; Tomich, P. K.;
Chong, K. T.; Watenpaugh, K. D.; Janakiraman, M. N.;
Dolak, L. A.; McGrath, J. P.; Lynn, J. C.; Horng, M. M.;
Hinshaw, R. R.; Zipp, G. L.; Ruwart, M. J.; Schwende, F.
J.; Zhong, W. Z.; Padbury, G. E.; Dalga, R. J.; Shiou, L.;
Possert, P. L.; Rush, B. D.; Wilkinson, K. F.; Howard, G.
M.; Toth, L. N.; Williams, M. G.; Kakuk, T. J.; Cole, S.
L.; Zaya, R. M.; Lovasz, K. D.; Morris, J. K.; Romines,
K. R.; Thaisrivongs, S.; Aristoff, P. A. J. Med. Chem.
+
1
7.15–7.89 (m, 12H); 4B: MS(EI) m/z 418 (M ). H NMR
(CDCl ) d 0.94 (t, 3H, J 7.35 Hz), 1.49–1.54 (m, 2H),1.73–
1.75 (m, 2H), 2.38 (s, 3H), 3.33–3.78 (m, 4H), 7.04–7.88 (m,
3
+
1
3
11H); 4C: MS(EI) m/z 432 (M ). H NMR (CDCl ) d 0.95
(t, 3H, J 7.25 Hz), 1.26 (t, 3H, J 7.5 Hz), 1.54–1.66 (m, 2H),
1.83–1.93 (m, 2H), 2.65–2.84 (m, 4H), 3.47–3.64 (m, 2H),
+
1
6.90–7.87 (m, 11H); 4D: MS(EI) m/z 432 (M ). H NMR
(CDCl ) d 0.98 (t, 3H, J 7.25 Hz), 1.55–1.68 (m, 2H), 1.87–
2.04 (m, 2H), 2.18 (s, 3H), 2.38 (s, 3H), 2.66–2.76 (m, 2H),
3
3.51–3.67 (m, 2H), 6.74–7.88 (m, 10H); 5A: MS(EI) m/z 404
+
(M ). H NMR (CDCl
1
3
) d 0.93–0.98 (m, 3H), 1.56–1.60
(m, 2H), 1.76–1.81 (m, 2H), 2.69–3.33 (m, 4H), 7.21–7.89
+
1
(m, 12H); 5B: MS(EI) m/z 418 (M ). H NMR (CDCl ) d
3
0.93 (t, 3H, J 7.2 Hz), 1.47–1.68 (m, 4H), 2.36–2.48 (m,
2H), 2.97–3.16 (m, 2H), 3.79 (s, 3H), 7.09–7.83 (m, 11H);
1
+
1
5C: MS(EI) m/z 432 (M ). H NMR (CDCl
3
) d 0.95 ꢁ1.00
(m, 3H), 1.28–1.33 (m, 3H), 1.61–1.83 (m, 4H), 2.71–2.90
(m, 4H), 3.17–3.37 (m, 2H), 6.95–7.84 (m, 11H); 5D:
+
1
3
MS(EI) m/z 432 (M ). H NMR (CDCl ) d 0.95–1.00 (m,
3H), 1.62–1.85 (m, 4H), 2.20 (s, 3H), 2.41 (s, 3H), 2.77–2.84
(m, 2H), 3.24–3.38 (m, 2H), 6.80–7.84 (m, 10H); 6A:
+
1
3
MS(EI) m/z 404 (M ). H NMR (CDCl ) d 3.44 (d, 1H, J
17.7 Hz), 3.82 (d, 1H, J 17.7 Hz), 4.06 (d, 1H, J 9.9 Hz),
4.35 (d, 1H, J 10.2 Hz), 6.60–7.60 (m, 15H); 6B: MS(EI) m/
1
995, 38, 4968.
+
1
1
3. Tait, B. D.; Domagala, J. M.; Ellsworth, E. L.; Gajda,
C.; Hagen, S. E.; Hamilton, H.; Vara Prasad, J. V. N.;
Ferguson, D.; Graham, N.; Hupe, D.; Nouhan, C.;
Tummino, P. J.; Humblet, C.; Lunney, E. A.; Pavlov-
sky, A.; Rubin, R. J.; Baldwin, E. T.; Bhat, T. N.;
Erickson, J. W.; Gulnik, S.; Liu, B. S. J. Med. Chem.
3
z 418 (M ). H NMR (CDCl ) d 3.11 (d, 1H, J 17.7 Hz),
3.51–3.57 (m, 3H), 3.76 (d, 1H, J 12.9 Hz), 3.98 (d, 1H, J
9.9 Hz), 4.25 (d, 1H, J 9.9 Hz), 6.87–7.55 (m, 14H); 6C:
+
1
MS(EI) m/z 432 (M ). H NMR (CDCl ) d 1.23 (t, 3H, J
3
7.5 Hz), 2.70–2.78 (m, 2H), 3.46 (d, 1H, J 17.4 Hz), 3.83 (d,
1H, J 17.7 Hz), 4.06 (d, 1H, J 9.9 Hz), 4.35 (d, 1H, J
+
9.9 Hz), 6.83–7.67 (m, 14H); 6D: MS(EI) m/z 432 (M ). H
1
1
997, 40, 3781.

3262
C.-L. Sun et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3257–3262
NMR (CDCl
1
4
3
) d 1.92 (s, 3H), 2.30 (s, 3H), 3.43 (d, 1H, J
7.7 Hz), 3.84 (d, 1H, J 17.7 Hz), 4.03 (d, 1H, J 10.2 Hz),
.353 (d, 1H, J 10.2 Hz), 6.78–7.61 (m, 13H).
compounds. After 5 days of incubation at 37 ꢁC in 5%
CO containing humidified air, CEM giant (syncytium)
cell formation was examined microscopically (COIC). The
EC50 was defined as the compound concentration required
to protect cells against the cytopathogenicity of SIV by
50%.
2
1
5. Stoner, E. J.; Cooper, A. J.; Dickman, D. A.; Kolacz-
kowski, L.; Lallaman, J. E.; Liu, J.-H.; Oliver-Shaffer, P.
A.; Patel, K. M.; Paterson, J. B.; Plata, D. J.; Riley, D. A.;
Sham, H. L.; Stengel, P. J.; Tien, J. J.-H. Org. Process Res.
Dev. 2000, 4, 264.
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Chem. 1998, 19, 1639; (b) Huang, X. Q.; Xu, L. S.; Luo, X.
M.; Fan, K. N.; Ji, R. Y.; Pei, G.; Chen, K. X.; Jiang, H.
L. J. Med. Chem. 2002, 45, 333.
20. Turner, S. R.; Strohbach, J. W.; Tommasi, R. A.; Aristoff,
P. A.; Johnson, P. D.; Skulnick, H. I.; Dolak, L. A.; Seest,
E. P.; Tomich, P. K.; Bohanon, M. J.; Horng, M. M.;
Lynn, J. C.; Chong, K. T.; Hinshaw, R. R.; Watenpaugh,
K. D.; Janakiraman, M. N.; Thaisrivongs, S. J. Med.
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1
1
6. Posner, G. H.; Whitten, C. E.; McFarland, P. E. J. Am.
Chem. Soc. 1972, 94, 5106.
7. Dorrestijn, E.; Hemmink, S.; Hulstman, G.; Monnier, L.;
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607.
1
8. Inhibition of SIV-induced syncytium in CEM174 cell
cultures was measured in a 96-well microplate containing
5
2
well and containing appropriate dilutions of the tested
· 10 CEM cells/ml infected with 100 TCID50 of SIV per