6-Hydroxy-1,3-dioxin-4-ones as non-peptidic HIV protease inhibitors

Article abstract of DOI:10.1016/S0960-894X(00)00534-5

HIV protease inhibitors containing 6-hydroxy-1,3-dioxin-4-one ring system as a new scaffold have been prepared. Among them, compound 4d showed potent HIV protease inhibitory activity (IC₅₀=0.01 μM) and antiviral activity in cell culture (EC

Full text of DOI:10.1016/S0960-894X(00)00534-5

Bioorganic & Medicinal Chemistry Letters 10 (2000) 2625±2627
6-Hydroxy-1,3-dioxin-4-ones as Non-Peptidic HIV
Protease Inhibitors
Yong Sup Lee,a,* Yong Sil Lee,a Jae Yeol Lee,a Sun Nam Kim,a
Chong-Kyo Leeb and Hokoon Parka
aDivision of Life Sciences, Korea Institute of Science & Technology, PO Box 131, Cheongryang, Seoul 130-650, South Korea
bPharmaceutical Screening Center, Korea Research Institute of Chemical Technology, Daejeon 305-606, South Korea
Received 28 July 2000; accepted 14 September 2000
AbstractÐHIV protease inhibitors containing 6-hydroxy-1,3-dioxin-4-one ring system as a new sca€old have been prepared.
Among them, compound 4d showed potent HIV protease inhibitory activity (IC50=0.01 mM) and antiviral activity in cell culture
(EC50=0.96 mM, SI=65.69). # 2000 Elsevier Science Ltd. All rights reserved.
The alarming spread of the acquired immunode®ciency
syndrome (AIDS) epidemic has stimulated the discovery
of therapeutic agents to inhibit the replication of the
causative virus, human immunodi®ciency virus (HIV).1
The advanced understanding of viral cell cycle has made
it possible to de®ne the targets to interrupt the life cycle
of virus. Among them, one such target is the virally
encoded protease which is essential for viral matura-
tion.2 Although a number of compounds with potent
activity have been reported as the protease inhibitors,3,4
most of them are peptidomimetic compounds and
therefore often possess pharmacological problems,5
such as low oral bioavailability, rapid excretion, or
synthetic diculty of multi steps.
knowledge of X-ray crystal structure of the HIV pro-
tease complexed with 4-hydroxypyrone compound 3
(Fig. 2); the lactone carbonyl of pyrone ring forms
hydrogen bonds with the backbone amide groups of
isoleucine 50 and isoleucine 500 on the ¯ap of the
enzyme, and the 4-hydroxy functionality forms hydro-
gen bonds with the carboxylic acids of the catalytic 25
and 250 aspartic acid (Fig. 2).11 We expected that a
similar core binding mode would occur in 6-hydroxy-
1,3-dioxin-4-one 4 as an isostere of 4-hydroxy-5,6-dihy-
dropyrone and that additional hydrogen bonds might
be possible via interaction of the oxygen atom at the 1
position of the dioxinone ring with HIV-1 protease
residues (Fig. 2). Therefore, we wished to examine the
in¯uence of oxygen atom on the HIV protease inhibi-
tory activity and antiviral activity in the cell culture.
Since the discovery of phenprocoumon (1, Fig. 1) as a
non-peptidic HIV protease inhibitor using a random
screening approach,6 various 4-hydroxypyrones have
been synthesized by many research groups.7 9 As a
result, tipranavir (PNU-140690: 2, Fig. 1) was identi®ed
to be a potent HIV protease inhibitor exhibiting low
toxicity, acceptable drug delivery and distribution
characteristics. It is currently undergoing clinical trials
as a therapeutic agent for treatment of AIDS.10
With this in mind, we embarked on the synthesis of 6-hy-
droxy-1,3-dioxin-4-one derivatives (4a±f) for non-pepti-
dic HIV protease inhibitor. Our synthetic e€ort was
focused on the variation of the m-sulfonamide sub-
stituent of the phenyl ring at the C-5a position while the
ethyl group in the C-5a position and C-2 side chains of
6-hydroxy-1,3-dioxin-4-one were ®xed as shown in the
structure of compounds 4aꢀf because these side
chains in 4-hydroxypyrone are well known0 to ®ll ®ve
During a continuous e€ort in our laboratory to develop
new potent small molecules of the protease inhibitors,
we designed 6-hydroxy-1,3-dioxin-4-one 4 as a possible
sca€old of HIV-1 protease inhibitor based on the
0
binding pockets (S1, S2, S3, S1 , and S2 ) of HIV
protease (Scheme 1).10
As illustrated in Scheme 1, the reaction of 1-phenyl-3-
hexanone (5) with malonic acid (18 equiv) in acetic
anhydride in the presence of concd sulfuric acid a€or-
*Corresponding author. Tel.: +82-2-958-5167; fax: +82-2-958-
5189;
ded 1,3-dioxane-4,6-dione ring system
6 in 32%
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00534-5

2626
Y. S. Lee et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2625±2627
yield with the recovered 1-phenyl-3-hexanone (31%).
Aluminum trichloride-catalyzed condensation of 1,3-
dioxane-4,6-dione ring with m-nitrobenzaldehyde a€or-
ded a benzylidene intermediate, which was not isolated
and directly reacted with triethylaluminum in the pre-
sence of copper(I) bromide±dimethyl sul®de to give the
fully functionalized 6-hydroxy-1,3-dioxin-4-one 7 as a
racemic mixture in 47% yield.10 Reduction of the nitro
group in compound 7 was accomplished using a cataly-
tic hydrogenation in methanol to a€ord the free amine
compound 8, which was coupled with various arylsul-
fonyl chlorides in the presence of pyridine to provide the
®nal sulfonamides 4a±f in good yields.12 Compound 4f
was obtained from 4e by a catalytic hydrogenation on
palladium±charcoal in 94% yield.
The resulting 6-hydroxy-1,3-dioxin-4-one derivatives 4a±
f have been assayed on inhibition of HIV protease.
Shown in Table 1 are IC50 values on HIV-1 protease and
CC50 and EC50 values in a cell culture assay using HIV-
IIIIB infected MT-4 cells. For the purpose of comparison
of biological activity, we prepared a racemic form of 2
(rac-2) as a reference by using a known procedure.10
In general, all compounds 4a±f showed good HIV pro-
tease inhibitory activities with IC50 values in the 0.003±
0.065 mM range, as compared to rac-2 (IC50=0.05 mM).
This result explains more ecient binding of 6-hydroxy-
1,3-dioxin-4-one derivatives to the active site of HIV
protease. With respect to cytotoxicity, all compounds
except 4e (5-nitopyridine; CC50=14.79 mM) were found
Figure 1. 4-Hydroxypyrone protease inhibitors.
Figure 2. Potential 4-hydroxy-5,6-dihydropyrone (3) and 6-hydroxy-1,3-dioxin-4-one (4) core interactions.
Scheme 1. (a) Malonic acid (18 equiv), Ac2O, concd H2SO4, 32%; (b) m-nitrobenzaldehyde, AlCl3, THF; (c) Et3Al, CuBr±Me2S, THF, 47% (for
two steps); (d) H2, Pd/C, MeOH, 99%; (e) ArSO2Cl, pyr., CH2Cl2.

Y. S. Lee et al. / Bioorg. Med. Chem. Lett. 10 (2000) 2625±2627
2627
Table 1. Yields and biological activity of 6-hydroxy-1,3-dioxin-4-one
protease inhibitors 4a±f
References and Notes
Compda
Ar
Yieldsb IC50
(mM)c,d (mM)c,e (mM)c,e (CC50/EC50
EC50
CC50
SI
1. Barre-Sinoussi, F.; Chermann, J.-C.; Rey, F.; Nugeyre, M.
T.; Chemaret, S.; Gruest, J.; Dauguet, C.; Axler-Blin, C.;
Byun-Vezinet, F.; Rouzioux, C.; Rozenbaum, W.; Mon-
tagnier, L. Science 1983, 220, 868.
)
4a
52
0.015 >66.53
66.53
<1
2. Navia, M. A.; Fitzgerald, P. M. D.; McKeever, B. M.; Leu,
C.-T.; Heimbach, J. C.; Herber, W. K.; Sigal, I. S.; Darke, P.
L.; Springer, J. P. Nature 1989, 337, 615.
4b
4c
4d
4e
37
50
70
51
0.013
0.003
0.010
86.71 >178
>2.05
6.77
3. Hu€, J. R. J. Med. Chem. 1991, 34, 2305.
4. Chong, K. T. Exp. Opin. Invest. Drugs 1996, 5, 115.
5. Plattner, J. J.; Norbeck, D. W. In Drug Discovery Technol-
ogies; Clark, C. R., Moos, W. H., Eds.; Ellis Horwood Ltd:
Chichester, 1990; Chapter 5, pp 92±126.
6. Romines, K. R.; Chrusciel, R. A. Curr. Med. Chem. 1995,
2, 825.
7. Skulnick, H. I.; Johnson, P. D.; Howe, W. J.; Tomich, P.
K.; Chong, K.-T.; Watenpaugh, K. D.; Janakiraman, M. N.;
Hinshaw, R. R.; Zipp, G. L.; Ruwart, M. J.; Schwende, F. J.;
Zhong, W.-Z.; Padbury, G. E.; Dalga, R. J.; Shiou, L.; Pos-
ssert, P. I.; Rush, B. D.; Wilkinson, K. F.; Howard, G. M.;
Tpth, L. N.; Williams, M. G.; Kakuk, T. J.; Cole, S. L.; Zaya,
R. M.; Thaisrivongs, S.; Aristof, P. A. J. Med. Chem. 1995, 38,
4968.
11.37
0.96
76.96
63.01
14.79
65.69
<1
0.065 >14.79
0.013 >69.97
4f
rac-2f
94
Ð
69.97
18.60
<1
26.57
Ð
0.050
0.70
aAll compounds are racemic mixtures.
bYields from compound 8.
cAll values are averages of at least two runs.
dHIV protease inhibitory activity.
eAntiviral activity in HIV-1IIIB infected MT-4 cells.
fRacemic compound prepared by means of known procedure.10
8. Tummino, P. J.; Ferguson, D.; Hupe, D. Biochem. Biophys.
Res. Commun. 1994, 201, 290.
9. Tummino, P. J.; Ferguson, D.; Hupe, L.; Hupe, D. Bio-
chem. Biophys. Res. Commun. 1994, 200, 1658.
to be less cytotoxic than compound rac-2 (CC50=18.60
mM). However, they unexpectedly showed no antiviral
activities in HIV-1IIIB infected MT-4 cells under non-
toxic concentration except (5-cyanopyridine)-sulfona-
mide- and (5-tri¯uoromethylpyridine) sulfonamide-
substituted 6-hydroxy-1,3-dioxin-4-one derivatives (4c,
4d). Compound 4d exhibited good antiviral activity
(EC50=0.96 mM) comparable to compound rac-2
(EC50=0.7 mM), and showed a 2.5-fold lower cytotoxic
e€ect (CC50=63.01 mM, SI=65.69) than rac-2
(SI=26.57). This overall result implies that the com-
pound 4d would be a promising HIV-1 protease inhi-
bitor because of potent enzyme inhibitory activity,
antiviral activity, and lower cytotoxicity.
10. Turner, S. R.; Strohbach, J. W.; Tommasi, R. A.; Aristo€,
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. Chem. 1998, 41,
3467.
11. Lunney, E. A.; Hagen, S. E.; Domagala, J. M.; Humblet,
C.; Kosinski, J.; Tait, B. D.; Warmus, J. S.; Wilson, M.; Fer-
guson, D.; Hupe, D.; Tummino, P. J.; Baldwin, E. T.; Bhat, T.
N.; Liu, B.; Erickson, J. W. J. Med. Chem. 1994, 37, 2664.
12. Selected 1H NMR spectroscopic data. 4a: 1H NMR
(CD3OD, 300 MHz) d 7.85±7.65 (m, 3H), 7.63 (d, 1H, J=8.6
Hz), 7.16±6.78 (m, 9H), 3.21 (m, 1H), 2.73 (m, 1H), 2.10±1.98
(m, 3H), 1.83±1.74 (m, 2H), 1.49±1.20 (m, 2H), 1.04 (m, 1H),
1
0.86±0.45 (m, 7H). 4b: H NMR (CD3OD, 300 MHz) d 8.59±
8.48 (m, 1H), 7.89±7.78 (m, 2H), 7.47±7.16 (m, 1H), 7.15±6.77
(m, 9H), 3.38 (m, 1H), 2.55 (m, 1H), 2.10±1.87 (m, 4H), 1.74
(m, 1H), 1.46 (m, 1H), 1.30 (m, 1H), 0.94 (m, 1H), 0.85±0.45
(m, 7H). 4c: 1H NMR (CD3OD, 300 MHz) d 8.96±0.74 (m,
1H), 8.31±8.12 (m, 1H), 8.03±7.90 (m, 1H), 7.15±6.90 (m, 9H),
3.38 (m, 1H), 2.55 (m, 1H), 2.06±1.97 (m, 3H), 1.82±1.71 (m,
2H), 1.47 (m, 1H), 1.31 (m, 1H), 0.97 (m, 1H), 0.85±0.49 (m,
In conclusion, we have synthesized 6-hydroxy-1,3-
dioxin-4-one derivatives 4a±f as new HIV-1 protease
inhibitors. The introduction of an oxygen atom in the
dihydropyrone ring enhanced remarkably HIV protease
inhibitory activity. Even though the antiviral activity
was not improved, cytotoxicity was slightly lowered
when compared to the parent dihydropyrone-based
HIV protease inhibitor, rac-2.
1
7H). 4d: H NMR (CD3OD, 300 MHz) d 8.95±8.82 (m, 1H),
8.28±8.12 (m, 1H), 8.07±7.97 (m, 1H), 7.15±6.80 (m, 9H), 3.21
(m, 1H), 2.52 (m, 1H), 2.10±1.90 (m, 3H), 1.80±1.68 (m, 2H),
1.45±1.41 (m, 2H), 1.00±0.90 (m, 1H), 0.83±0.45 (m, 7H). 4e:
1H NMR (CD3OD, 300 MHz) d 9.42±9.22 (m, 1H), 8.70±8.50
(m, 1H), 8.11±7.96 (m, 1H), 7.18±6.80 (m, 9H), 3.37 (m, 1H),
2.47 (m, 1H), 2.07±1.90 (m, 3H), 1.79±1.97 (m, 2H), 1.47 (m,
1H), 1.26 (m, 1H), 1.8 (m, 1H), 0.97±0.50 (m, 7H). 4f: 1H
NMR (CD3OD, 300 MHz) d 7.87±7.76 (m, 1H), 7.61±7.45 (m,
1H), 7.15±6.73 (m, 10H), 3.38 (m, 1H), 2.55 (m, 1H), 2.17±1.65
(m, 5H), 1.30±1.15 (m, 3H), 0.85±0.46 (m, 7H).
Acknowledgements
We are grateful for the support of this work by the
Ministry of Science and Technology, Korea (N20110).