Novel cyclourethane-derived HIV protease inhibitors: A ring-closing olefin metathesis based strategy

Article abstract of DOI:10.1016/S0960-894X(02)00300-1

A series of novel macrocyclic urethanes incorporating a (R)-hydroxyethylamine isostere was designed and synthesized. Ring size and substituent efffects have been investigated. Cyclourethanes containing 14- to 16-membered rings exhibited low nanomolar inhibitory potencies against HIV-1 protease.

Full text of DOI:10.1016/S0960-894X(02)00300-1

Bioorganic & Medicinal Chemistry Letters 12 (2002) 1993–1996
Novel Cyclourethane-Derived HIV Protease Inhibitors:
A Ring-Closing Olefin Metathesis Based Strategy
Arun K. Ghosh,a,* Lisa M. Swanson,a Chunfeng Liu,a Khaja Azhar Hussain,a
Hanna Cho,a D. Eric Walters,b Louis Hollandc and Jim Buthodc
aDepartment of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607, USA
bDepartment of Biological Chemistry, Finch University of Health Sciences/The Chicago Medical School, North Chicago, IL 60064, USA
cIIT Research Institute, Life Science Department, Chicago, IL 60616, USA
Received 11 January 2002; accepted 16 April 2002
Abstract—A series of novel macrocyclic urethanes incorporating a (R)-hydroxyethylamine isostere was designed and synthesized.
Ring size and substituent efffects have been investigated. Cyclourethanes containing 14- to 16-membered rings exhibited low
nanomolar inhibitory potencies against HIV-1 protease. # 2002 Elsevier Science Ltd. All rights reserved.
The current treatment regimen for AIDS consists of HIV
protease and reverse transcriptase inhibitors.1 In the con-
text of design and synthesis of protease inhibitors, a
number of structurally diverse acyclic urethane derived
inhibitors with improved pharmacological properties
have been reported.2 Unlike acyclic urethanes, the bio-
logical importance of cyclourethanes has been hitherto
unexplored. We recently reported a series of very potent
nonpeptide HIV protease inhibitors incorporating
structure-based designed novel, high affinity P2-ligands
and (R)-(hydroxyethylamino)sulfonamide isosteres.3 Of
particular note, inhibitor 1 (UIC-PI also known as
TMC-126)4 incorporating bis-tetrahydrofuran as the P2-
ligand has shown remarkable enzyme inhibitory and
antiviral potencies (Ki=15ꢀ1 pM, n=4 and ID50=
1.4ꢀ0.25 nM, n=5) compared to inhibitor 2, which
contains the hydroxyethylamine isostere of saquinavir
(Ki=2 nM and ID50=50 nM).5,6 In an effort to intro-
duce further structural diversity as well as to explore the
biological potential of cyclourethanes, we have designed
our preliminary results of these investigations. Cyclour-
ethanes are generally more potent than their acyclic
counterparts and a number of cyclourethanes exhibited
low nanomolar inhibitory potencies against HIV-1 pro-
tease. Various cyclourethanes were conveniently prepared
by N,N0-disuccinimidyl carbonate (DSC) promoted
alkoxycarbonylation of amines followed by efficient
ring-closing metathesis of the resulting dienes utilizing
Grubbs’ catalyst.8
The general synthesis of various acyclic urethanes con-
taining (R)-hydroxyethylamine isosteres is illustrated in
Scheme 1. Enantiomerically pure azido epoxide 3 has
been prepared in multigram quantities as described pre-
viously.9 Regioselective opening of epoxide 3 with allyl-
amine and 3-butenylamine in isopropanol at reflux
provided amino alcohols 4 and 5 (80 and 85%, respec-
tively). For preliminary investigation, we have prepared
unsubstituted and substituted cyclourethanes derived
from commercially available 9-decene-1-ol 6 and corre-
sponding derivative 7. Alcohol 7 was prepared by Swern
oxidation of 6 followed by reaction of the resulting
aldehyde with phenyl magnesium bromide (85%, two
steps). Alcohols 6 and 7 were converted to the respective
mixed carbonates 8 and 9 by using N,N0-disuccinimidyl
carbonate in the presence of triethylamine. Reaction of
these carbonates with amines 4 and 5 furnished the
corresponding azido urethanes which, upon reduction
with triphenylphosphine in aqueous THF, provided
respective amines 10 and 11 (70–74%, two steps).10
Amine 11 contains a 1:1 mixture of diastereomers at the
0
0
macrocyclic urethanes as P1 –P2 -ligands for these inhi-
bitors. Preliminary modeling studies of various cyclour-
ethanes based upon the X-ray structure of saquinavir-
bound7 HIV protease reveal that 14- to 16-membered
cyclourethane carbonyls could effectively hydrogen
bond with the crit0ical0 tight-bound water molecule as
well as fill in the S1 –S2 binding sites. Herein, we report
*Corresponding author. Tel.: +1-312-996-9672; fax: +1-312-996-
2183; e-mail: arunghos@uic.edu
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00300-1

1994
A. K. Ghosh et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1993–1996
Figure 1.
Scheme 1. (a) H2N(CH2)nCH¼CH2, iPrOH, 65 ꢁC; (b) Swern oxida-
tion, ꢂ60 ꢁC; (c) PhMgBr, THF, 0 ꢁC; (d) N,N0-disucc-
inimidylcarbonate, Et3N, acetonitrile, 23 ꢁC; (e) Et3N, CH2Cl2, 23 ꢁC;
(f) Ph3P, THF/H2O (10:1), 23 ꢁC.
Scheme 2. (a) Et3N, CH2Cl2, 23 ꢁC; (b) Cl2(PCy3)2¼CHPh (10 mol%),
Ti(OiPr)4 (30 mol%), CH2Cl2 (0.002 M solution), 23 ꢁC; (c) H2, 10%
Pd/C, MeOH.
phenyl bearing center as racemic alcohol 7 was
employed for urethane formation.
Preparations of the acyclic and corresponding cyclic
macrourethanes derived from amines 10 and 11 are
shown in Scheme 2. Alkoxycarbonylation of these
amines with known optically active bis-tetrahydro-
furanyl carbonate 12 afforded acyclic inhibitors 13 and
14 (1:1 mixture of diastereomers).
against HIV protease. The saturated cyclourethanes are
generally more potent than their corresponding unsatu-
rated counterparts. Furthermore, ring size and sub-
stituents on the ring have pronounced effects on the
inhibitory potencies. Both the 14- and 15-membered
unsubstituted rings exhibited Ki values of 80nM (17) and
14nM (24), respectively. All alcohol 7-derived 14- to 16-
membered cyclourethanes have shown significant reduc-
tion in their respective Ki values. Since 15-membered
cyclourethanes were the most potent, we have investigated
the substituent effects of the corresponding a-alkyl
cyclourethanes. The saturated a-methyl derivative is less
Exposure of acyclic urethanes 13 and 14 to commercial
Grubbs’ catalyst (10 mol%) in the presence of titanium
isopropoxide (30 mol%) in CH2Cl2 (0.003 M solution)
for 20 h at 23 ꢁC afforded cyclourethanes 15 and 16 (1:1
1
cis/trans by H NMR) after silica gel chromatography
(69–78%).11 Unsaturated cyclourethane 15 containing
a 14-membered ring was obtained mainly as a single
cis-isomer. Catalytic hydrogenation of the unsaturated
cyclourethanes furnished saturated cyclic inhibitors 17
and 18. Other inhibitors in Table 1 were prepared by
analogous procedures.
0
potent than unsubstituted derivative 24. Since the P1 -iso-
butyl substitutent is optimum for inhibitors containing
(R)-hydroxymethylsulfonamide isosteres, we have exam-
ined the substituent effect of the b-methyl cyclourethanes.
For initial screening, a mixture of diastereomers (1:1) at
the methyl bearing center of the cyclourethanes was
evaluated in the HIV protease inhibition assay. Unsatu-
rated (1:1 cis/trans) mixture 32 displayed a Ki value of
11nM. The corresponding 15-membered saturated
cyclourethanes 33, containing a mixture of diastereomers
The inhibitory potencies of various acyclic and cyclic ure-
thanes in Table 1 were measured by the assay protocol of
Toth and Marshall.12 As can be seen, the acyclic inhibitors
have shown very little inhibition. In contrast, the corre-
sponding cyclic urethanes have shown significant activity

A. K. Ghosh et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1993–1996
Table 1. Structure and inhibitory potencies of various acyclic and cyclic inhibitorsa
1995
Compd
Ki (nM)
Compd
Ki (nM)
Compd
Ki (nM)
13 R=H
19 R=Ph
>1000
>1000
15 R=H
20 R=Ph
125
229
17 R=H
21 R=Ph
80
189
22 R=H
14 R=Ph
>1000
>1000
23 R=H
16 R=Ph
88
167
24 R=H
18 R=Ph
14
357
25
28
31
444
>1000
>1000
26
29
32
162
53
27
30
33
268
30
11
6.1
aIn-house prepared saquinavir6 displayed Ki=0.12ꢀ0.01 nM (n=3) in this assay.
at the methyl center (Ki value of 6.1 nM), are significantly
more potent than unsubstituted 15-membered cyclour-
Acknowledgements
ethane 24. Subsequently, stereodefined syntheses of both
diastereomers of 33 were carried out from known 2-(R)-
and 2-(S)-methyl-4-penten-1-ol.13 The diastereomer-con-
taining S-methyl configuration (Ki=8.9nM) is nearly 3-
fold more potent than the R-isomer (Ki=25.8nM). Inhi-
bitor 33 prevented the spread of HIV-1 in MT4 human T-
lymphoid cells infected with IIIB isolate at a concentration
of 2.5 mM (ID50).14
Financial support of this work by the National Insti-
tutes of Health (GM 53386) is gratefully acknowledged.
References and Notes
1. (a) Flexner, C. N. Engl. J. Med. 1998, 338, 1281. (b) Cih-
lar, T.; Bischofberger, N. Annu. Rep. Med. Chem. 2000, 35,
177.
2. (a) Ghosh, A. K.; Shin, D. W.; Swanson, L.; Krishnan, K.;
Cho, H.; Hussain, K. A.; Walters, D. E.; Holland, L.; Buthod,
J. Il Farmaco 2001, 56, 29. (b) Kim, E. E.; Baker, C. T.;
Dwyer, M. D.; Murcko, M. A.; Rao, B. G.; Tung, R. D.;
Navia, M. A. J. Am. Chem. Soc. 1995, 117, 1181. (c) Ghosh,
A. K.; Thompson, W. J.; McKee, S. P.; Duong, T. T.; Lyle,
T. A.; Chen, J. C.; Darke, P. L.; Zugay, J. A.; Emini, E. A.;
Schleif, W. A.; Huff, J. R.; Anderson, P. S. J. Med. Chem.
1993, 36, 292, and references cited therein.
In summa0ry, incorporation of cyclourethane function-
0
ality at P1 –P2 resulted in a novel series of structurally
diverse protease inhibitors. Interestingly, cyclourethanes
in general are considerably more potent than their
acyclic counterparts. A substituent at the a-position on
the ring appears detrimental to potency. Saturated 15-
membered cyclourethane 33 is thus by far the most
potent in this series with a Ki value of 6.1 nM. Chemical
modifications of these inhibitors and further design are
currently underway.
3. Ghosh, A. K.; Kincaid, J. F.; Cho, W.; Walters, D. E.;
Krishnan, K.; Hussain, K. A.; Koo, Y.; Cho, H.; Rudall, C.;

1996
A. K. Ghosh et al. / Bioorg. Med. Chem. Lett. 12 (2002) 1993–1996
Holland, L.; Buthod, J. Bioorg. Med. Chem. Lett. 1998, 8, 687,
and references cited therein.
4. Yoshimura, K.; Kato, R.; Kavlick, M. F.; Nguyen, A.;
Maroun, V.; Maeda, K.; Hussain, K. A.; Ghosh, A. K.; Gul-
nik, S. V.; Erickson, J. W.; Mitsuya, H. J. Virol. 2002, 76,
1349.
5. Ghosh, A. K.; Kincaid, J. F.; Walters, D. E.; Chen, Y.;
Chaudhuri, N. C.; Thompson, W. J.; Culberson, C.; Fitzger-
ald, P. M. D.; Lee, H. Y.; McKee, S. P.; Munson, P. M.;
Duong, T. T.; Darke, P. L.; Zugay, J. A.; Schleif, W. A.; Axel,
M. G.; Lin, J.; Huff, J. R. J. Med. Chem. 1996, 39, 3278.
6. Roberts, N. A.; Martin, J. A.; Kinchington, D.; Broad-
hurst, A. V.; Craig, J. C.; Duncan, I. B.; Galpin, S. A.; Handa,
B. K.; Kay, J.; Krohn, A.; Lambert, R. W.; Merrett, J. H.;
Mills, J. S.; Parkes, K. E. B.; Redshaw, S.; Ritchie, A. J.;
Taylor, D. L.; Thomas, G. J.; Machin, P. J. Science 1990, 248,
358, and references cited therein.
Wai, J. M.; Darke, P. L.; Zugay, J. A.; Emini, E. A.; Schleif,
W. A.; Huff, J. R.; Anderson, P. S. J. Med. Chem. 1993, 36,
2300.
10. (a) Ghosh, A. K.; Duong, T. T.; McKee, S. P. Tetrahedron
Lett. 1991, 32, 4251. (b) Ghosh, A. K.; Duong, T. T.; McKee,
S. P.; Thompson, W. J. Tetrahedron Lett. 1992, 33, 2781.
11. Ghosh, A. K.; Hussain, K. A. Tetrahedron Lett. 1998, 39,
1881.
12. Toth, M. V.; Marshall, G. R. Int. J. Pep. Prot. Res. 1990,
36, 544.
13. The corresponding amine was prepared by mesylation
of alcohol, reaction of mesylate with NaH and di-tert-butyl
iminodicarboxylate in DMf at 0 ꢁC to give 80 ꢁC followed by
BOC deprotection with CF3CO2H in CH2Cl2 at 23 ꢁC. For
preparation of optically active alcohol, see: Evans, D. A.;
Ennis, M. D.; Mathre, D. J. J. Am. Chem. Soc. 1982, 104,
1737.
7. (a) Munshi, S.; Chen, Z.; Yan, Y.; Li, Y.; Olsen, D. B.;
Scock, H. B.; Galvin, B. B.; Dorsey, B.; Kuo, L. Acta Crys-
tallogr. 2000, D56, 381. (b) Dohnalek, J.; Hasek, J.; Duskova,
J.; Petrokova, H.; Hradilek, M.; Soucek, M.; Konvalinka, J.;
Jiri, B.; Sedlack, J.; Fabry, M. Acta Crystallogr. 2001, D57,
472.
14. In-house prepared saquinavir exhibited ID50 value of
18 nM. For Ro 31 8959, Craig and coworkers have reported
IC90 values of 6–30 nM in cell culture assay.15 However, the
assay protocol differs widely in that syneytia formation rather
than p24 production was monitored as endpoint, and cell types
other than MT4 were employed.
8. Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413.
9. Ghosh, A. K.; Thompson, W. J.; Holloway, M. K.; McKee,
S. P.; Duong, T. T.; Lee, H. Y.; Munson, P. M.; Smith, A. M.;
15. Craig, J. C.; Duncan, I. B.; Hockley, D.; Grief, C.;
Roberts, N. A.; Mills, J. S. Antiviral Res. 1991, 16, 295, and
references cited therein.