Design of HIV-1 protease inhibitors with C3-substituted hexahydrocyclopentafuranyl urethanes as P2-ligands: Synthesis, biological evaluation, and protein-ligand X-ray crystal structure

Article abstract of DOI:10.1021/jm200649p

We report the design, synthesis, biological evaluation, and the X-ray crystal structure of a novel inhibitor bound to the HIV-1 protease. Various C3-functionalized cyclopentanyltetrahydrofurans (Cp-THF) were designed to interact with the flap Gly48 carbonyl or amide NH in the S2-subsite of the HIV-1 protease. We investigated the potential of those functionalized ligands in combination with hydroxyethylsulfonamide isosteres. Inhibitor 26 containing a 3-(R)-hydroxyl group on the Cp-THF core displayed the most potent enzyme inhibitory and antiviral activity. Our studies revealed a preference for the 3-(R)-configuration over the corresponding 3-(S)-derivative. Inhibitor 26 exhibited potent activity against a panel of multidrug-resistant HIV-1 variants. A high resolution X-ray structure of 26-bound HIV-1 protease revealed important molecular insight into the ligand-binding site interactions.

Full text of DOI:10.1021/jm200649p

ARTICLE
pubs.acs.org/jmc
Design of HIV-1 Protease Inhibitors with C3-Substituted
Hexahydrocyclopentafuranyl Urethanes as P2-Ligands: Synthesis,
Biological Evaluation, and ProteinꢀLigand X-ray Crystal Structure†
Arun K. Ghosh,*,‡ Bruno D. Chapsal,‡ Garth L. Parham,‡ Melinda Steffey,‡ Johnson Agniswamy,§
Yuan-Fang Wang,§ Masayuki Amano,|| Irene T. Weber,§ and Hiroaki Mitsuya||,^
‡Departments of Chemistry and Medicinal Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
§Department of Biology, Molecular Basis of Disease, Georgia State University, Atlanta, Georgia 30303, United States
Departments of Hematology and Infectious Diseases, Kumamoto University Graduate School of Medical and Pharmaceutical Sciences,
Kumamoto 860-8556, Japan
^Experimental Retrovirology Section, HIV and AIDS Malignancy Branch, National Cancer Institute, National Institutes of Health,
Bethesda, Maryland 20892, United States
S Supporting Information
b
ABSTRACT: We report the design, synthesis, biological evaluation, and the X-ray crystal
structure of a novel inhibitor bound to the HIV-1 protease. Various C3-functionalized
cyclopentanyltetrahydrofurans (Cp-THF) were designed to interact with the flap Gly48
carbonyl or amide NH in the S2-subsite of the HIV-1 protease. We investigated the
potential of those functionalized ligands in combination with hydroxyethylsulfonamide
isosteres. Inhibitor 26 containing a 3-(R)-hydroxyl group on the Cp-THF core displayed
the most potent enzyme inhibitory and antiviral activity. Our studies revealed a
preference for the 3-(R)-configuration over the corresponding 3-(S)-derivative. Inhibitor 26 exhibited potent activity against a
panel of multidrug-resistant HIV-1 variants. A high resolution X-ray structure of 26-bound HIV-1 protease revealed important
molecular insight into the ligand-binding site interactions.
’ INTRODUCTION
retained full potency against a range of multidrug-resistant HIV-1
variants.12 The X-ray structural studies of 4-bound HIV-1
protease evidenced enhanced backbone interactions with the
Gly270 carbonyl at the S10-subsite. The Cp-THF ligand appears
to fit within the S2-subsite, and the cyclic ether oxygen is involved
in a close hydrogen bonding interaction with the backbone NH
of Asp29 (2.8 Å). On the basis of this molecular insight, we have
now investigated structural modifications of the Cp-THF ligand
to further optimize ligand binding, particularly hydrogen bond-
ing ability, in the S2-subsite. The X-ray structure of 3-bound
HIV-1 protease indicated that the C3 methylene of the Cp-THF
is in proximity to the protease flap region. In fact, the X-ray data
Human immunodeficiency virus 1 (HIV-1) protease inhibi-
tors are critical components of antiretroviral therapies.1,2 How-
ever, the emergence of drug resistance has raised serious
questions about long-term treatment options.3,4 Our structure-
based design of inhibitors targeting the protein backbone has led
to the discovery of a variety of novel HIV-1 protease inhibitors
(PIs) with broad-spectrum activity against multidrug-resistant
HIV-1 variants.5,6 One of these inhibitors, darunavir (1, Figure 1),
was approved by the FDA for the treatment of HIV/AIDS
patients.7ꢀ9 In an effort to address drug resistance, our inhibitor
design strategy focused on maximizing active site interactions
with the protease, particularly by promoting extensive hydro-
gen bonding interactions with backbone atoms throughout the
active site.5,6
We have recently reported a number of potent inhibitors
incorporating a stereochemically defined (3aS,5R,6aR)-hexahydro-
2H-cyclopenta[b]furan-5-yl (Cp-THF) as the P2-ligand with
a modified hydroxyethylsulfonamide isostere as in inhibitor 3.10
The X-ray crystal structure of 3-bound HIV-1 protease revealed
the formation of an extensive hydrogen-bonding network be-
tween the inhibitor and the active site. On the basis of this
molecular insight, we subsequently incorporated a stereochemi-
cally defined lactam at the P10-position to further enhance
backbone interactions.11 Interestingly, the resulting inhibitor 4
suggested a weak C3ꢀH O interaction with the Gly48 back-
3 3 3
bone carbonyl group.10 We therefore envisioned that introduc-
tion of a polar substituent at the C3 position may lead to
additional interactions of the Cp-THF ligand with the protease
flap residues. Furthermore, an inhibitor that makes tight inter-
actions with the protease flap region could conceivably delay its
dissociation via opening of the flaps. Herein, we report the
design, synthesis, and biological evaluation of a series of protease
inhibitors that incorporate a stereochemically defined function-
ality at the C3 position of the Cp-THF ligand. Inhibitor 26,
Received: May 20, 2011
Published: July 29, 2011
r
2011 American Chemical Society
5890
dx.doi.org/10.1021/jm200649p J. Med. Chem. 2011, 54, 5890–5901
|

Journal of Medicinal Chemistry
ARTICLE
Scheme 2. Syntheses of Ligands 11 and 12
Figure 1. Structures of potent HIV-1 protease inhibitors 1ꢀ4 and 26.
Scheme 1. Syntheses of Optically Pure P2 Ligands 7 and 8
Scheme 3. Syntheses of C3-Methyl-Substituted Ligands 14
and 18
incorporating a 3-(R)-hydroxyl group, was the most potent PI
(Ki = 5 pM; antiviral IC50 = 2.9 nM). This inhibitor also
maintained excellent potency against a range of multidrug-
resistant HIV-1 variants. The proteinꢀligand X-ray structure of
26-bound HIV-1 protease revealed important insights into the
ligand-binding site interactions of the inhibitor with the flap
region as well as other regions of the HIV-1 protease active site.
’ CHEMISTRY
NaH and 2-bromoacetic acid in THF provided the correspond-
ing alkylated acid. The resulting acid was reacted with methyl
iodide in the presence of NaHCO3 to provide methyl ester 9 in
76% yield (two steps). DIBAL-H reduction of ester 9 followed by
radical cyclization15 of the resulting alkene using a catalytic
amount of (n-Bu3Sn)2O, Ph2SiH2 and ethanol (2 equiv) in the
presence of a catalytic amount of AIBN in benzene provided
3-(R)-hydroxy derivative 10 in 64% yield, in two steps. The 1H
NMR results showed a diastereomeric ratio of 10:1. The major
isomer was separated by silica gel chromatography and used for
the subsequent reactions. Reaction of alcohol 10 with acetic
anhydride and triethylamine in the presence of a catalytic amount
of DMAP afforded the corresponding acetate. The removal of the
silyl group with TBAF in THF provided ligand 11 in 73% yield, in
two steps. Alcohol 10 was converted to methoxy derivative 12 by
The syntheses of 3-keto and 3-(S)-methoxy Cp-THF ligands
are shown in Scheme 1. Optically active alcohol 5 was prepared
in multigram quantities as described previously.13,14 This was
efficiently converted to ketone 6 as reported by us.14 The
removal of TBS ether by exposure to HFꢀpyridine afforded
keto alcohol 7 in 94% yield. Ketone 6 was converted to 3-(S)-
methoxy derivative 8 in a three-step sequence involving (1)
reduction of the ketone with NaBH4 in ethanol at ꢀ25 ꢀC to
provide the corresponding alcohol as a single diastereomer, (2)
methylation of the resulting alcohol with MeI in the presence of
Ag2O in acetonitrile, and (3) removal of the silyl group with
TBAF in THF to provide 8 in 66% yield, in three steps.
The syntheses of 3-(R)-acetoxy and 3-(R)-methoxy ligands 11
and 12 are outlined in Scheme 2. Treatment of alcohol 5 with
5891
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
Scheme 4. Syntheses of Activated Mixed Carbonates 19aꢀf
Scheme 5. Syntheses of Inhibitors 21ꢀ32
alkylation with NaH and MeI in THF followed by removal of the
silyl group in 71% yield (two steps).
We also planned to synthesize stereochemically defined
3-methyl derivatives to compare with the effects of alkoxy and
hydroxy groups. Toward this goal, we have carried out stereoselective
syntheses of 3-(S)- and 3-(R)-methyl derivatives, and the syn-
thetic routes are shown in Scheme 3. Optically active olefin 13
was synthesized as described previously.14 Catalytic hydrogena-
tion of 13 in the presence of Wilkinson’s catalyst under a
hydrogen filled balloon at 23 ꢀC for 3 h followed by removal
of the silyl group using TBAF afforded 3-(S)-methyl derivative
14.16 For the synthesis of the 3-(R)-methyl derivative, commer-
cially available optically active lactone (+)-15 was methylated
using LDA and MeI at ꢀ78 ꢀC to provide methyl derivative 16
with high diastereoselectivity (dr = 20:1) and in 95% yield. Olefin
16 was then subjected to oxymercuration condition with Hg-
(OAc)2 and HClO4. The resulting organomercurial derivative
was treated with aqueous sodium hydroxide solution followed by
NaBH4 reduction to afford endo-alcohol 17 in 64% yield. The
lactone was then reduced to the corresponding lactol with
DIBAL-H. Further reduction of the resulting lactol using Et3SiH
and TiCl4 furnished 3-(R)-methyl derivative 18 in 68% yield.
The inhibitor structures are shown in Table 1. Inhibitors 25 and
28ꢀ30 were prepared by reactions of amine 20a with mixed
carbonates 19b and 19dꢀf, respectively. The synthesis of
inhibitors 26 and 27 was carried out by reactions of mixed
carbonate 19c with amines 20a and 20b followed by removal of
the acetyl group with K2CO3 in methanol. All inhibitors were
prepared in good to excellent overall (41ꢀ96%) yields. The
synthesis of inhibitor 31 containing a dimethylamine function-
ality was carried out by reductive amination of ketone 21 with
+
Me2NH2 OAcꢀ in the presence of NaHB(OAc)3. We have also
attempted to prepare the corresponding methylamine derivative
by reductive amination with MeNH3 OAcꢀ. However, the
+
resulting 3-(S)-methylamine derivative 32 turned out to be
unstable.
1
Results from the H NMR NOESY experiments fully corrobo-
rated the assignment of 3-(S)- and 3-(R)-stereochemistry of
methyl derivatives 14 and 18, respectively.
’ RESULTS AND DISCUSSION
As mentioned previously, inhibitors were designed to make
additional interactions in the S2-subsite of the protease, espe-
cially with the Gly48 backbone atoms in the flap region of the
enzyme. All inhibitors in Table 1 were first evaluated in enzyme
inhibitory assay developed by Toth and Marshall.18 Inhibitors
that exhibited potent Ki were subsequently evaluated for in vitro
antiviral assays. As can be seen in the Table 1, all inhibitors
displayed subnanomolar to low picomolar inhibitory potencies.
Inhibitor 22, with a 3-(S)-hydroxy group on the Cp-THF, was
significantly more potent than the keto derivative 21 (entries 1
and 2). The 3-(S)-hydroxy Cp-THF ligand was also investigated
in combination with other phenylsulfonamide substituents.
Inhibitor 23 with a p-aminophenylsulfonamide as the P20-ligand
displayed impressive inhibitory potency; however, its antiviral
Various optically active ligand alcohols 7, 8, 11, 12, 14, and 18
were converted to the respective mixed activated carbonates. As
shown in Scheme 4, reactions of ligand alcohols with 4-nitro-
phenyl chloroformate in the presence of pyridine in CH2Cl2
provided activated carbonates 19aꢀf in 50ꢀ96% yield.17 The
syntheses of designed inhibitors were carried out by coupling these
activated carbonates with various hydroxyethylsulfonamide iso-
steres containing functionalized P20-phenylsulfonamide ligands.
As shown in Scheme 5, amines 20aꢀc were readily prepared as
described previously.10,17 Reaction of amine 20a with carbonate
19a provided inhibitor 21. Inhibitors 22ꢀ24 were prepared by
reaction of carbonate 19a with respective amines 20aꢀc fol-
lowed by NaBH4 reduction of the resulting ketone derivatives.
5892
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
Table 1. Enzymatic Inhibitory and Antiviral Activity of Inhibitors 21ꢀ31
a Values are the mean of at least two experiments. Human T-lymphoid (MT-2) cells (2 ꢁ 103) were exposed to 100 TCID50 of HIV-1LAI and cultured in
the presence of each PI, and IC50 values were determined using the MTT assay. The IC50 values of amprenavir (APV), saquinavir (SQV), indinavir
(IDV), and darunavir (DRV) were 0.03, 0.015, 0.03, and 0.003 μM, respectively.
activity was 3-fold lower than 22. Inhibitor 24 with a p-hydroxy-
methylphenylsulfonamide as the P20-ligand has shown a reduc-
tion in potency. Inhibitor 25, which contains a 3-(S)-methoxy
substituent, exhibited a significant loss of potency and a near
5-fold loss of antiviral activity compared to 22. Interestingly,
inhibitor 26 with 3-(R) configuration displayed an impressive
enzyme inhibitory and antiviral activity. Inhibitor 27 with the
4-aminophenylsulfonamide isostere also showed comparable
enzyme inhibitory activity. Inhibitor 28, with a 3-(R)-methoxy
group, also exhibited comparable inhibitory potency.
In order to probe the importance of the C3- oxygen on the Cp-
THF ring, inhibitors 29 and 30 with a methyl group in place of a
C3-hydroxyl were synthesized. Inhibitor 29, which contains a
3-(S)-methyl group, showed a significant reduction in potency
compared to 22. Similarly, inhibitor 30 with a 3-(R)-methyl
group has shown a reduction in enzyme Ki compared to the
corresponding hydroxy derivative 26. We have also investigated
an amine substitution on the Cp-THF ligand. Inhibitor 31 with
C3-dimethylamine exhibited a substantially lower enzyme in-
hibitory potency compared to the corresponding hydroxy or
methoxy derivatives.
PIs including APV and DRV. The results are shown in Table 2.
All inhibitors in Table 2 exhibited high antiviral activity against
the wild-type HIV-1 laboratory strain, HIV-1ERS104pre, isolated
from a drug-naive patient.7 Compound 26 provided the most
potent activity with an IC50 of 2.9 nM, comparable to that of
DRV. When tested against various multidrug-resistant HIV-1
strains, the IC50 of inhibitor 26 remained in the low nanomolar
range (2.9ꢀ29 nM) and fold-change in IC50 did not exceed 10.
Interestingly, isomeric inhibitor 22 displayed lower activity
against the wild-type viral strain (IC50 = 20 nM). It also
exhibited a much larger IC50 fold change and in some cases
only marginal activity against multidrug-resistant HIV-1 var-
iants. Such a stark contrast in antiviral activity of 22 compared
to 26 emphasizes the importance of the stereochemistry at the
C3-position of the Cp-THF ligand. Inhibitor 26 displayed a
superior profile compared to another approved PI, APV. Over-
all, inhibitor 26 maintained impressive potency against all
tested multidrug-resistant HIV-1 strains. It compared favorably
with DRV, which is the leading PI for the treatment of multi-
drug resistant HIV infection.
In order to gain molecular insight into the ligand/binding-site
interactions responsible for the activity of inhibitor 26, we have
determined the X-ray crystal structure of the inhibitor-bound
wild-type HIV-1 protease that was refined to a 1.45 Å resolution.
The protease dimer binds with the inhibitor in two orientations
Inhibitors 22 with a 3-(S)-hydroxyl group and 26 with a
3-(R)-hydroxyl group on the Cp-THF ligand were tested
against a panel of multidrug-resistant HIV-1 variants. Their
antiviral activity was compared against other clinically available
5893
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
Table 2. Comparison of the Antiviral Activity of 22, 26, and Other PIs against Multidrug Resistant HIV-1 Variants
IC50 ( SD, μM (fold change)b
virusa
APV
DRV
22
26
HIV-1ERS104pre(wt)
HIV-1MDR/B
0.030 ( 0.006
0.0037 ( 0.0001
0.020 ( 0.004
>1 (>50)
0.0029 ( 0.0008
0.93 ( 0.28 (31)
0.26 ( 0.03 (9)
0.38 ( 0.03 (12)
0.19 ( 0.06 (6)
0.036 ( 0.013 (10)
0.013 ( 0.0004 (4)
0.0023 ( 0.0006 (1)
0.0019 ( 0.0003 (1)
0.029 ( 0.007 (10)
0.022 ( 0.003 (7)
0.0045 ( 0.0007 (2)
0.0031 ( 0.002 (1)
HIV-1MDR/C
>1 (>50)
HIV-1MDR/G
0.27 ( 0.02 (13)
0.041 ( 0.004 (2)
HIV-1MDR/TM
a Amino acid substitutions identified in the protease-encoding region compared to the consensus type B sequence cited from the Los Alamos database:
L10I, L33I, M36I, M46I, F53L, K55R, I62 V, L63P, A71 V, G73S, V82A, L90M, and I93L in HIV-1MDR/B; L10I, I15 V, K20R, L24I, M36I, M46L, I54
V, I62 V, L63P, K70Q, V82A, and L89 M in HIV-1MDR/C; L10I, V11I, T12E, I15 V, L19I, R41K, M46L, L63P, A71T, V82A, and L90 M in HIV-
1MDR/G; L10I, K14R, R41K, M46L, I54V, L63P, A71V, V82A, L90M, I93L in HIV-1MDR/TM. HIV-1ERS104pre served as a source of wild-type HIV-1.
b IC50 values were determined by using PHA-PBMs as target cells, and inhibition of p24 Gag protein production by each drug was used as an end point.
Numbers in parentheses represent n-fold changes of IC50 for each isolate compared to IC50 for the wild-type HIV-1ERS104pre. All assays were conducted
in duplicate or triplicate, and data shown represent mean values ((1 standard deviation) derived from results of three independent experiments. PHA-
PBMs were derived from a single donor in each independent experiment. DRV: darunavir. APV: amprenavir.
Figure 2. Stereoview of the X-ray structure of inhibitor 26 bound to the active site of the wild-type HIV-1 protease.
related by a 180ꢀ rotation with a 0.55/0.45 ratio. The protease
backbone structure showed a very low rms deviation of 0.15 Å
for all CR atoms compared to protease complexes of 2 or
darunavir.19,20 The inhibitor makes extensive interactions from
the P2 to P20 ligands with the protease atoms and most notably
displays favorable polar interactions including hydrogen bonds,
weaker CꢀH O and CꢀH π interactions, as shown in
orientation. Also, the Cp-THF ether oxygen forms a strong
hydrogen bond with the backbone amide NH of Asp29. These
new interactions with the backbone atoms of Gly48 are likely to
be responsible for the impressive antiviral activity and drug
resistance properties of this inhibitor. The C3-functionality on
the Cp-THF appears to enhance the affinity of the inhibitor. The
new water-mediated interaction with the backbone NH of Gly48
on the protease flap may promote thermodynamic stabilization
of the closed conformation of the proteaseꢀligand complex. This
may slow the kinetics of dissociation of the inhibitor through
flexible opening of the protease flap.
3 3 3
3 3 3
Figure 2. The central hydroxyl group forms hydrogen bonds with
the side chain carboxylate oxygen atoms of the catalytic Asp25
and Asp250 residues. The inhibitor hydrogen-bonds with the
protease backbone atoms of the amide of Asp300, the carbonyl
oxygen of Gly27, and forms water-mediated interactions with
the amides of Ile50 and Ile500, which are generally conserved in
the majority of protease complexes with inhibitors21 or substrate
analogues.22,23 The inhibitor interactions with atoms in the
binding cavity resemble those of darunavir and 2 (TMC-126)
with the exception of the interactions of the new P2-ligand that
replaces the bis-THF group. The 3-(R)-hydroxyl of the Cp-THF
ligand extends toward the flap region and forms a new water-
mediated hydrogen bond interaction with the backbone amide
NH of Gly48, with interatomic distances of 2.5 and 3.1 Å for
the major inhibitor orientation or 2.7 and 3.1 Å for the minor
’ CONCLUSION
In summary, we have designed a number of C3-substituted
hexahydrocyclopentafuranylurethanes as P2-ligands to enhance
interactions with the protein backbone in the S2-subsite. The
ligands were stereoselectively synthesized in optically active
form. Incorporation of these ligands in (R)-hydroxyethylsulfo-
namide isosteres resulted in a series of novel and highly potent
HIV-1 protease inhibitors. In particular, inhibitor 26 displayed
remarkable enzyme inhibitory and antiviral potency. Also, in-
hibitor 26 has shown excellent activity against multi-PI-resistant
5894
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
variants compared to other FDA approved inhibitors. A pro-
teinꢀligand X-ray structure of 26-bound HIV-1 protease was
determined at 1.45 Å resolution. The inhibitor appeared to make
extensive interactions throughout the active site. Of particular
interest, the 3-(R)-hydroxyl of the Cp-THF ligand formed a new
water-mediated hydrogen bond interaction with the backbone
amide NH of Gly48, and the Cp-THF ether oxygen formed a
strong hydrogen bond with backbone amide NH of Asp29. The
extensive interactions with the protein backbone may be respon-
sible for inhibitor 26’s impressive antiviral activity and drug
resistance profile. The design of inhibitors targeting the protein
backbone has led us to develop inhibitors characterized by high
potency against both wild-type and multidrug-resistant HIV-1
strains. Further design and optimization of inhibitors utilizing
this molecular insight are in progress.
hexanes/EtOAc (5:1) as the eluent provided the corresponding alcohol
(32.2 mg, 90%) as a colorless oil. TLC, Rf = 0.22 (hexanes/EtOAc =
5:1); [R]2D0 +21.5 (c 1.05, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 4.55
(br s, 1H), 4.42 (t, J = 7.0 Hz, 1H), 4.34 (t, J = 4.5 Hz, 1H), 4.11 (m, 1H),
3.87 (d, J = 9.9 Hz, 1H), 3.48 (dd, J = 3.6, 9.9 Hz, 1H), 2.89 (dt, J = 7.8,
10.2 Hz, 1 H), 2.13 (dd, J = 2.4, 14.7 Hz, 1H), 1.99 (dd, J = 2.4, 14.7 Hz,
1H), 1.78ꢀ1.65 (m, 2 H), 0.89 (s, 9H), 0.11 (s, 3H), 0.10 (s, 3H); 13C
NMR (CDCl3, 75 MHz) δ 85.3, 77.3, 74.9, 72.9, 48.1, 41.8, 34.8, 25.7,
18.0, ꢀ4.7, ꢀ5.2. HRMS-CI (m/z): [M + H]+ calcd for C13H27O3Si
259.1729, found 259.1731. To a solution of the above alcohol (27 mg,
0.1 mmol) in CH3CN (1 mL) was added MeI (0.3 mL, excess) followed
by Ag2O (50 mg, 0.2 mmol). The mixture was gently refluxed for 12 h
under argon, and then additional MeI (0.3 mL) and Ag2O (50 mg) were
added. Reflux was continued for an additional 12 h until all SM
disappeared. The resulting mixture was diluted in Et2O and filtered on
Celite. After evaporation of the solvent, the residue was purified by
column chromatography on silica gel using hexanes/EtOAc (8:1) as the
eluent to yield the corresponding 3-(S)-methoxy intermediate as a clear
oil (23 mg, 85%). TLC, Rf = 0.38 (hexanes/EtOAc = 5:1); [R]2D0 +42.6
(c 1.02, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 4.41 (dt, J = 5.1, 7.2 Hz,
1H), 4.12 (m, 1H), 3.93 (m, 1H), 3.87ꢀ3.70 (m, 2H), 3.32 (s, 3H), 2.61
(m, 1H), 2.18 (m, 1H), 1.90ꢀ1.75 (m, 2H), 1.63 (m, 1H), 0.88 (s, 9H),
0.05 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 82.5, 81.1, 73.5, 69.0, 57.8,
42.6, 33.5, 25.8, 18.1, ꢀ4.8. To a solution of the above intermediate (16
mg, 0.059 mmol) in THF (1 mL) was added TBAF (1 M solution in
THF, 0.1 mmol, 100 μL). The solution was stirred at room temperature
for 2 h. The solvent was evaporated and the residue purified by flash
column chromatography on silica gel using hexanes/EtOAc (1:1 and
then 1:2.5) to furnish 8 as a colorless oil (8 mg, 86%). TLC, Rf = 0.32
(CHCl3/3% EtOH); 1H NMR (CDCl3, 500 MHz) δ 4.41 (t, J = 4.4 Hz,
1H), 4.21 (dt, J = 5.1, 10.1 Hz, 1H), 4.08 (d, J = 10.3 Hz, 1H), 3.85 (dd,
J = 3.0, 7.3 Hz, 1H), 3.83 (d, J = 10.3 Hz, 1H), 3.42 (s, 3H), 2.94ꢀ2.86
(m, 1H), 2.13 (d, J = 14.5 Hz, 1H), 2.08 (dd, J = 2.4, 15.1 Hz, 1H), 1.81
(ddd, J = 5.3, 10.6, 14.5 Hz, 1H), 1.74 (ddd, J = 5.3, 6.0, 15.0 Hz, 1H);
13C NMR (CDCl3, 125 MHz) δ 86.0, 82.1, 73.6, 71.6, 57.4, 47.2,
42.0, 34.0.
’ EXPERIMENTAL SECTION
General. All anhydrous solvents were obtained according to the
following procedures. Diethyl ether and tetrahydrofuran (THF) were
distilled from sodium/benzophenone under argon. Toluene, methanol,
acetonitrile, and dichloromethane were distilled from calcium hydride,
and benzene was distilled from sodium. Other solvents were used
without purification. All moisture-sensitive reactions were carried out
in flame-dried flasks under argon atmosphere. Reactions were moni-
tored by thin layer chromatography (TLC) using Silicycle 60A-F254
silica gel precoated plates. Flash column chromatography was performed
using Silicycle 230ꢀ400 mesh silica gel. Yields refer to chromatogra-
phically and spectroscopically pure compounds. Optical rotations were
recorded on a Perkin-Elmer 341 polarimeter. 1H NMR and 13C NMR
spectra were recorded on a Varian Inova-300 (300 and 75 MHz,
respectively), Bruker Avance ARX- 400 (400 and 100 MHz), and Bruker
Avance ARX-500 (500 and 125 MHz). High and low resolution mass
spectra were carried out by the Mass Spectroscopy Center at Purdue
University, IN. The purity of all test compounds was determined by
HRMS and HPLC analyses in the different solvent systems. All test
compounds showed g95% purity.
Methyl 2-{(1R,4S)-4-[(tert-Butyldimethylsilyl)oxy]cyclopent-
2-en-1-yloxy}acetate (9). To an ice-cold suspension of NaH (60%
suspension in oil, 360 mg, 9 mmol) in dry THF (5 mL) under argon was
slowly added a solution of 2-bromoacetic acid (520 mg, 3.75 mmol) in dry
THF (3 mL + 3 mL rinse). The resulting mixture was stirred at room
temperature for 30 min and then cooled back to 0 ꢀC. Desymmetrized meso-
cyclopentenediol 5 (642 mg, 3 mmol) in dry DMF (10 mL) was slowly
added to this solution, and the mixture was allowed to warm to room
temperature and was stirred for 24 h. A pH 4 phosphate buffer solution was
added at 0 ꢀC, and the aqueous phase was extracted with EtOAc (ꢁ4). The
combined organic phase was dried (Na2SO4), filtered, and evaporated in
vacuo to give the corresponding crude carboxylic acid along with residual
DMF. The acid was diluted with additional DMF (10 mL). The solution
was cooled to 0 ꢀC, and NaHCO3 (630 g, 7.5 mmol) was added at once
followed by MeI (14 mmol, 1.98 g, 871 μL). After the mixture was stirred at
room temperature for 12 h, saturated aqueous NH4Cl solution was added
(10 mL), then water (10 mL), and the aqueous phase was successively
extracted with hexanes/Et2O, 1:1 (ꢁ3). The combined organic phase was
dried (Na2SO4), filtered, and evaporated. The residue was purified by flash
chromatography on silica gel using hexanes/EtOAc (20:1 and then 15:1) to
give methyl ester 9 as a colorless oil (654 mg, 76%, two steps). TLC, Rf =
0.45 (hexanes/EtOAc = 3:1); 1H NMR (CDCl3, 300 MHz) δ5.92 (s, 2H),
4.63 (dd, J = 4.8, 7.0 Hz, 1H), 4.53 (dd, J = 5.1, 7.2 Hz, 1H), 4.10 (s, 2H),
3.74 (s, 3H), 2.64 (dt, J = 7.2, 13.8 Hz, 1H), 1.60 (dt, J = 4.9, 13.7 Hz, 1H),
0.87 (s, 9H), 0.065 (s, 3H), 0.06 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ
171.2, 138.4, 131.9, 82.4, 74.6, 64.7, 51.8, 40.5, 25.8, 18.0, ꢀ4.7.
(3aS,5R,6aR)-5-Hydroxytetrahydro-2H-cyclopenta[b]furan-
3(3aH)-one (7). A solution of ketone 6 (23 mg, 0.09 mmol) in CH3CN
(0.5 mL) was cooled to 0 ꢀC under argon. Pyridine (50 μL) was added
followed by dropwise addition of HFꢀpyridine (0.18 mL). The solution
was stirred at 0 ꢀC for 4 h. The reaction was quenched by addition of
saturated aqueous NaHCO3 solution followed by solid NaHCO3. The
aqueous phase was extracted multiple times with EtOAc, and the
combined organic layer was dried over Na2SO4. Following careful
evaporation of the solvent, the residue was purified by column chroma-
tography on silica gel using hexanes/EtOAc (1:1 and then 1:2) as the
eluenttoyieldthedesiredketone7(12 mg, 94%) asacolorless oil. TLC, Rf
= 0.32 (hexanes/EtOAc = 1:2); [R]2D0 +96.1 (c 0.86, CHCl3); 1H NMR
(CDCl3, 400 MHz) δ5.04 (t, J =6.6 Hz, 1H), 4.38 (t, J = 4.0 Hz, 1H), 4.20
(d, J = 17.0 Hz, 1H), 3.97 (d, J = 17.0 Hz, 1H), 2.85 (t, J = 8.4 Hz, 1H),
2.21 (d, J = 13.9 Hz, 1H), 2.15 (d, J = 15.2 Hz, 1H), 2.01(ddd, J = 3.9, 10.5,
14.1 Hz, 1H), 1.95 (ddd, J = 4.5, 6.0, 15.1 Hz, 1H), 1.90 (br s, 1H); 13C
NMR (CDCl3, 100 MHz) δ 217.7, 84.0, 72.9, 70.8, 48.8, 43.4, 40.7.
(3S,3aS,5R,6aR)-3-Methoxyhexahydro-2H-cyclopenta-
[b]furan-5-ol (8). Ketone 6 (35.6 mg, 0.14 mmol) was dissolved in
EtOH (1 mL) under argon and cooled to ꢀ25 ꢀC. To the solution was
added NaBH4 (10 mg, 0.26 mmol) in one protion, and the resulting
mixture was stirred at this temperature for 20 min. Saturated aqueous
NH4Cl solution was added and the volume of solvent reduced under
vacuum. Additional water was added, and the aqueous phase was
extracted several times with EtOAc. The combined organic layer was
washed with brine, dried (Na2SO4), and evaporated in vacuo. Purifica-
tion of the crude alcohol by column chromatography on silica gel using
(3R,3aR,5R,6aR)-5-[(tert-Butyldimethylsilyl)oxy]hexahydro-
2H-cyclopenta[b]furan-3-ol (10). A solution of methyl ester 9(87.2mg,
5895
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
0.304 mmol) in dry CH2Cl2 (8 mL) was cooled to ꢀ78 ꢀC under argon.
DIBAL-H (1 M solution in hexanes, 0.40 mL) was added slowly, and the
reaction mixture was stirred for 1 h at this temperature. The reaction was
quenched by addition of MeOH (100 μL), and the mixture was warmed to
room temperature. A pH 7 phosphate buffer (0.5 M solution, 2 mL) was
added. The aqueous phase was extracted with CH2Cl2 (ꢁ3) and the
combined organic phase washed with brine, dried (Na2SO4), filtered, and
evaporated in vacuo. The crude aldehyde solution was passed through a short
plug of silica gel, deactivated with 1% Et3N using hexanes/EtOAc (5:1) as the
eluent. After evaporation, the crude product was directly submitted to the next
step. The residue was dissolved in dry benzene (degassed, 2 mL) under argon
and the solution transferred into a sealable tube. (n-Bu3Sn)2O (22.5 μL, 26.3
mg, 44 μmol), Ph2SiH2 (42 μL, 41.6 mg, 0.22 mmol), EtOH (45 μL), and
AIBN (10 mg) were successively added. The sealed tube was placed with
stirring in an oil bath at 80 ꢀC for 6 h. After cooling to room temperature, the
reaction mixture was diluted with Et2O (2 mL) and aqueous 0.5 M HCl
solution (2 mL) was added. After the mixture was stirred at room temperature
for 15 min, the aqueous phase was extracted with Et2O (ꢁ3). The combined
organic phase was washed with saturated aqueous NaHCO3 solution, brine,
dried (MgSO4), filtered, and evaporated. The residue was purified by flash
chromatography on silica gel using hexanes/EtOAc (6:1 to 2:1) to afford the
(R)-alcohol 10 (50 mg, 64%, over two steps) as a white solid; 5 mg of the
other 3-(S)-diastereoisomer was also isolated, and only traces of 1,2 reduction
product was observed. TLC, Rf = 0.46 (hexanes/EtOAc = 3:1); [R]2D0 +22.3
(c 0.67, CHCl3); 1H NMR (CDCl3, 300 MHz) δ 4.69 (dt, J = 3.8, 7.2 Hz,
1H), 4.19ꢀ4.02 (m, 3H), 3.72 (d, J = 9.8 Hz, 1H), 2.48 (q, J = 7.5 Hz, 1H),
2.13ꢀ1.96 (m, 2H), 1.70ꢀ1.55 (m, 1H), 1.47ꢀ1.25 (m, 1H), 0.86 (s, 9H),
0.03 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 82.2, 78.3, 73.1, 72.7, 50.9, 42.4,
39.0, 25.8, 17.5, ꢀ4.8, ꢀ4.9.
was washed with brine, dried (Mg2SO4), filtered, and evaporated in
vacuo. The residue was purified by flash chromatography on silica gel
using hexanes/EtOAc (10:1 and then 8:1) to afford the corresponding
TBS-protected methoxy compound (28.6 mg, 86%) as a clear oil. TLC,
Rf = 0.61 (hexanes/EtOAc = 3:1); [R]2D0 +20.6 (c 1.52, CHCl3); H
1
NMR (CDCl3, 400 MHz) δ 4.63 (dt, J = 3.6, 7.2 Hz, 1H), 4.11 (m, 1H),
4.05 (dd, J = 4.1, 9.9 Hz, 1H), 3.81 (dd, J = 1.3, 9.9 Hz, 1H), 3.74 (m,
1H), 3.31 (s, 3H), 2.54 (td, J = 7.7, 8.3 Hz, 1H), 2.10ꢀ1.96 (m, 2H),
1.70ꢀ1.60 (m, 1H), 1.47 (m, 1H), 0.87 (s, 9H), 0.04 (6H); 13C NMR
(CDCl3, 100 MHz) δ 87.7, 82.5, 72.9, 70.3, 56.6, 47.4, 42.5, 39.5, 25.8,
18.0, ꢀ4.8, ꢀ4.9. To an ice-cold solution of the above methoxy
intermediate (27 mg, 0.1 mmol) in THF (2 mL) under argon was
added TBAF (1 M solution in THF, 0.2 mL, 0.2 mmol). The mixture
was stirred for 1.5 h. The solvent was evaporated, and the crude residue
was purified by flash column chromatography on silica gel using
hexanes/EtOAc (1:1) as the eluent to furnish alcohol 12 as a clear oil
(13 mg, 82%). TLC, Rf = 0.17 (hexanes/EtOAc = 1:2); 1H NMR
(CDCl3, 300 MHz) δ 4.63 (t, J = 5.5 Hz, 1H), 4.26 (m, 1H), 4.20 (dd, J =
5.3, 9.7 Hz, 1H), 3.89 (dt, J = 2.0, 4.8 Hz, 1H), 3.65 (dd, J = 4.4, 9.7 Hz,
1H), 3.34 (s, 3H), 2.64ꢀ2.54 (m, 1H), 2.40 (br s, 1H), 2.16 (ddd, J = 5.5,
10.6, 14.3 Hz, 1H), 2.02 (dd, J = 1.7, 14.7 Hz, 1H), 1.87 (dt, J = 5.1, 14.7
Hz, 1H), 1.77ꢀ1.61 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 88.4, 85.1,
74.0, 71.9, 57.0, 48.4, 41.8, 40.2.
(3S,3aR,5R,6aR)-3-Methylhexahydro-2H-cyclopenta[b]furan-
5-ol (14). To a solution of olefin 13 (29.7 mg, 0.12 mmol) in toluene
(3 mL) was added Wilkinson’s catalyst, RhCl(PPh3)3 (18 μmol, 17 mg).
The resulting solution was then placed under a hydrogen atmosphere
and stirred for 3 h. After dilution with additional toluene, the solution
was filtered on a Celite pad, and the pad was rinsed with toluene.
Evaporation of the solvent and purification of the residue on silica gel
using hexanes/EtOAc (100:1 and then 50:1) as the eluent furnished the
corresponding 3-(S)-methyl compound (29 mg, 97%). TLC, Rf = 0.28
(hexanes/EtOAc = 20:1); [R]2D0 +22.7 (c 1.01, CHCl3); 1H NMR
(CDCl3, 400 MHz) δ 4.43 (m, 1H), 4.03 (m, 1H), 3.81 (dd, J = 7.4, 8.0
Hz, 1H), 3.42 (dd, J = 8.0, 10.7 Hz, 1H), 2.43 (m, 1H), 2.32ꢀ2.18 (m,
2H), 1.72 (m, 1H), 1.51 (ddd, J = 4.8, 8.6, 13.5 Hz, 1H), 1.44 (m, 1H),
0.95 (d, J = 6.8 Hz, 3H), 0.88 (s, 9H), 0.05 (s, 6H); 13C NMR (CDCl3,
100 MHz) δ 82.6, 73.2, 71.6, 44.5, 43.2, 36.2, 34.7, 25.9, 18.2, 11.3, ꢀ4.7,
ꢀ4.8. HRMS-CI (m/z): [M + H]+ calcd for C14H29O2Si 257.1937,
found 257.1936. A solution of methyl-based ligand (28 mg, 0.1 mmol) in
THF (2 mL) was treated with TBAF (1 M solution in THF, 150 μL) and
stirred at room temperature for 2.5 h. The reaction mixture was diluted
with Et2O and filtered on a short silica pad. The solvent containing the
alcohol was carefully reduced, and essentially pure alcohol 14 was
directly used in the next step without purification (>99% pure). TLC,
Rf = 0.26 (hexanes/EtOAc = 1:1); 1H NMR (CDCl3, 400 MHz) δ 4.46
(dt, J = 2.7, 5.5 Hz, 1H), 4.20 (m, 1H), 3.88 (t, J = 7.8 Hz, 1H), 3.48 (t,
J = 9.2 Hz, 1H), 2.59ꢀ2.40 (m, 2H), 2.22 (d, J = 6.9 Hz, 1H), 2.08 (dt,
J = 5.9, 14.1 Hz, 1H), 1.87 (ddd, J = 6.0, 9.5, 13.7 Hz, 1H), 1.83 (m, 1H),
1.68ꢀ1.54 (m, 1H), 1.01 (d, J = 6.8 Hz, 3H); 13C NMR (CDCl3, 100
MHz) δ 85.3, 73.8, 72.9, 46.3, 42.4, 36.5, 34.5, 12.7.
(3R,3aS,5R,6aR)-5-Hydroxyhexahydro-2H-cyclopenta-
[b]furan-3-yl Acetate (11). Alcohol 10 (45 mg, 0.175 mmol) was
diluted in CH2Cl2 (5 mL), and the solution was cooled to 0 ꢀC under
argon. Et3N (0.525 mmol, 53 mg, 75 μL) and DMAP (1 crystal) were
added followed by acetic anhydride (25 μL, 0.23 mmol). The mixture
was warmed to room temperature and stirred overnight. The solution
was evaporated to dryness, and purification of the residue by flash
column chromatography on silica gel using hexanes/EtOAc (20:1)
furnished the corresponding acetate derivative (38 mg, 73%). TLC, Rf
= 0.24 (hexanes/EtOAc = 10:1); 1H NMR (CDCl3, 300 MHz) δ 5.02
(d, J = 3.8 Hz, 1H), 4.69 (dt, J = 3.2, 7.2 Hz, 1H), 4.22 (dd, J = 4.0, 10.4
Hz, 1H), 4.11 (m, 1H), 3.80 (d, J = 10.4 Hz, 1H), 2.56 (m, 1H),
2.09ꢀ1.97 (m, 2H), 2.04 (s, 3H), 1.71 (m, 1H), 1.68ꢀ1.54 (m, 1H),
0.86 (s, 9H), 0.03 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 170.8, 82.9,
81.2, 72.8, 70.9, 48.5, 42.7, 39.2, 25.8, 21.2, 18.0, ꢀ4.9. The acetate (28
mg, 0.093 mmol) was diluted in THF (1.5 mL). TBAF (1 M solution of
THF, 200 μL, 0.2 mmol) was added at 0 ꢀC, and the mixture was stirred
for 2.5 h while warming to 23 ꢀC. The solvent was evaporated and the
residue purified by flash column chromatography on silica gel using
hexanes/EtOAc (3:1 to 1:1) to give pure alcohol 11 as a colorless oil
(17.5 mg, quant). TLC, Rf = 0.18 (EtOAc, 100%); 1H NMR (CDCl3,
300 MHz) δ 5.11 (m, 1H), 4.70ꢀ4.62 (m, 1H), 4.32 (dd, J = 5.0, 10.4
Hz, 1H), 4.28ꢀ4.20 (m, 1H), 3.71 (dd, J = 3.2, 10.4 Hz, 1H), 2.65ꢀ2.56
(m, 1H), 2.30ꢀ2.13 (m, 2H), 2.06 (s, 3H), 1.99ꢀ1.88 (m, 1H),
1.77ꢀ1.68 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 170.8, 84.8, 81.1,
73.4, 71.9, 48.9, 41.9, 39.5, 21.1.
(3R,3aR,6aR)-3-Methyl-3,3a,6,6a-tetrahydro-2H-cyclopenta-
[b]furan-2-one (16). To a solution of lithium diisopropylamide, pre-
pared by adding n-BuLi (2.5 M solution in hexanes, 1.36 mL, 3.39 mmol) to
diisopropylamine (477 μL, 3.39 mmol) in THF (15 mL) at 0 ꢀC, was added
(3R,3aS,5R,6aR)-3-Methoxyhexahydro-2H-cyclopenta-
[b]furan-5-ol (12). A solution of alcohol 10 (30 mg, 0.116 mmol) in
dry DMF (1 mL) was cooled to 0 ꢀC under argon, and NaH (60%
suspension in oil, 15 mg, 0.348 mmol) was added in one portion. The
mixture was warmed to room temperature, stirred for 30 min, and then
cooled to 0 ꢀC. MeI (22 μL, 50 mg, 0.35 mmol) was added to the
solution, and the mixture was warmed to 23 ꢀC and stirred for 3.5 h.
Saturated aqueous NH4Cl solution was added, and the aqueous phase
was extracted with Et2O/hexanes (1:1). The combined organic phase
a precooled solution of known (3aS,6aR)-3,3a,6,6a-tetrahydro-2H-
cyclopenta[b]furan-2-one (+)-15 (350 mg, 2.82 mmol) in THF (5 mL +
3 mL rinse) at ꢀ78 ꢀC, dropwise. The reaction mixture was stirred at this
temperature for 30 min. Then methyl iodide (352 μL, 5.65 mmol) was
added dropwise and the reaction mixture was stirred at ꢀ78 ꢀC for 6 h. The
reaction mixture was quenched with 2 M aqueous HCl. The aqueous phase
was extracted with Et2O (ꢁ3). The combined organic layer was dried
(Na2SO4), filtered, and concentrated under vacuum. The residue was
purified by column chromatography on silica gel using hexanes/Et2O (5:1)
5896
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
to yield lactone 16 (369 mg, 95%) as a brown oil. TLC, Rf = 0.54 (hexanes/
EtOAc = 2:1); [R]2D0 +54.2 (c1.0, CHCl3); 1HNMR(CDCl3, 400 MHz) δ
5.74 (m, 1H), 5.59 (m, 1H), 5.12 (t, J = 5.6 Hz, 1H), 3.13 (dd, J = 3.8, 1.8
Hz, 1H), 2.65 (m, 2H), 2.52 (q, J = 7.6 Hz, 1H), 1.33 (d, J = 7.6 Hz, 3H);
13C NMR (CDCl3, 100 MHz) δ 180.0, 130.9, 129.4, 81.3, 53.8, 39.9,
39.2, 17.4.
dryness and the residue purified by column chromatography on silica gel
using hexanes/EtOAc (3:1 and then 2:1) as eluent to furnish pure mixed
carbonate 19a (39 mg, 92%) as a white solid. TLC, Rf = 0.25 (hexanes/
EtOAc = 2:1); 1H NMR (CDCl3, 400 MHz) δ 8.27 (d, J = 9.2 Hz, 2H),
7.34 (d, J = 9.2 Hz, 2H), 5.23 (t, J = 4.2 Hz, 1H), 5.13 (t, J = 6.9 Hz, 1H),
4.19 (d, J = 17.1 Hz, 1H), 4.06 (d, J = 17.1 Hz, 1H), 2.99 (dd, J = 8.7, 8.8
Hz, 1H), 2.54ꢀ2.41 (m, 2H), 2.22ꢀ2.08 (m, 2H); 13C NMR (CDCl3,
100 MHz) δ 216.8, 155.3, 151.5, 145.4, 125.3, 121.9, 82.4, 81.0, 70.6,
48.5, 41.2, 37.1.
(3S,3aS,5R,6aR)-3-Methoxyhexahydro-2H-cyclopenta[b]-
furan-5-yl (4-nitrophenyl)carbonate (19b). The title compound
was obtained from 8 in 82% yield as described for 7 after purification by
column chromatography on silica gel using hexanes/EtOAc (3:1 to 2:1)
as the eluent (white solid). TLC, Rf = 0.25 (hexanes/EtOAc = 2:1); 1H
NMR (CDCl3, 300 MHz) δ 8.27 (d, J = 9.2 Hz, 2H), 7.38 (d, J = 9.2 Hz,
2H), 5.15 (tt, J = 4.5, 6.2 Hz, 1H), 4.56 (dt, J = 2.8, 6.1 Hz, 1H), 4.04 (dt,
J = 6.3, 7.5 Hz, 1H), 3.87 (AB, dd, J = 5.2, 9.1 Hz, 1H), 3.86 (AB, dd, J =
6.6, 9.1 Hz, 1H), 3.34 (s, 3H), 2.83 (m, 1H), 2.38ꢀ2.02 (m, 4H); 13C
NMR (CDCl3, 75 MHz) δ 155.6, 152.1, 145.2, 125.2, 121.8, 83.7, 81.4,
77.2, 70.3, 57.9, 44.2, 39.6, 30.2.
(3R,3aS,5R,6aR)-5-((4-Nitrophenoxy)carbonyloxy)hexa-
hydro-2H-cyclopenta[b]furan-3-yl Acetate (19c). The title
compound was obtained from 11 in 96% yield as described for 7 after
purification by column chromatography on silica gel using hexanes/
EtOAc (6:1 and then 4:1) as the eluent (white solid). TLC, Rf = 0.26
(hexanes/EtOAc = 3:1); 1H NMR (CDCl3, 300 MHz) δ 8.27 (d, J = 9.1
Hz, 2H), 7.37 (d, J = 9.1 Hz, 2H), 5.20ꢀ5.12 (m, 1H), 5.12ꢀ5.08 (m,
1H), 4.76 (dt, J = 2.0, 6.0 Hz, 1H), 4.27 (dd, J = 4.6, 10.4 Hz, 1H), 3.80
(dd, J = 2.5, 10.4 Hz, 1H), 2.79ꢀ2.70 (m, 1H), 2.37 (ddd, J = 6.0, 10.2,
15.0 Hz, 1H), 2.29ꢀ2.19 (m, 1H), 2.15 (dt, J = 5.6, 15.6 Hz, 1H), 2.07
(s, 3H), 2.02ꢀ1.92 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 170.7, 155.4,
151.9, 145.3, 125.3, 121.8, 83.2, 81.0, 80.5, 71.7, 48.8, 39.6, 35.9, 21.1.
(3R,3aS,5R,6aR)-3-Methoxyhexahydro-2H-cyclopenta[b]-
furan-5-yl (4-Nitrophenyl)carbonate (19d). The title was ob-
tained from 12 in 93% yield as described for 7 after purification by
column chromatography on silica gel using hexanes/EtOAc (6:1 to 4:1)
as the eluent (white solid). TLC, Rf = 0.40 (hexanes/EtOAc = 3:1); 1H
NMR (CDCl3, 400 MHz) δ 8.27 (d, J = 9.2 Hz, 2H), 7.37 (d, J = 9.2 Hz,
2H), 5.19ꢀ5.12 (m, 1H), 4.74ꢀ4.67 (m, 1H), 4.13 (dd, J = 5.4, 5.5 Hz,
1H), 3.84ꢀ3.78 (m, 2H), 3.35 (s, 3H), 2.75ꢀ2.68 (m, 1H), 2.36 (ddd,
J = 6.1, 10.0, 14.8 Hz, 1H), 2.25ꢀ2.11 (m, 2H), 1.82 (dddd, J = 1.2, 3.8,
5.5, 14.7 Hz, 1H); 13C NMR (CDCl3, 100 MHz) δ 155.5, 151.9, 145.3,
125.3, 121.8, 87.5, 83.0, 81.3, 71.3, 56.9, 48.2, 39.4, 36.2.
(3S,3aR,5R,6aR)-3-Methylhexahydro-2H-cyclopenta[b]-
furan-5-yl (4-Nitrophenyl)carbonate (19e). The title compound
was obtained from 14 in 83% yield as described for 7 after purification by
column chromatography on silica gel using hexanes/EtOAc (10:1 and
then 7:1) as the eluent (white solid). TLC, Rf = 0.25 (hexanes/EtOAc =
3:1); 1H NMR (CDCl3, 300 MHz) δ 8.27 (d, J = 9.0 Hz, 2H), 7.37 (d,
J = 9.0 Hz, 2H), 5.09 (m, 1H), 4.57 (dt, J = 2.8, 6.2 Hz, 1H), 3.93 (t, J =
8.1 Hz, 1H), 3.51 (dd, J = 8.1, 10.4, 1H), 2.65 (m, 1H), 2.46 (m, 1H),
2.38 (m, 1H), 2.11 (m, 1H), 2.02 (ddd, J = 2.7, 5.5, 14.8 Hz, 1H), 1.81
(m, 1H), 1.02 (d, J = 6.9 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 155.5,
152.0, 145.3, 125.3, 121.8, 83.4, 80.8, 72.3, 45.8, 39.7, 36.5, 31.0, 11.8.
(3R,3aR,5R,6aR)-3-Methylhexahydro-2H-cyclopenta[b]-
furan-5-yl (4-Nitrophenyl)carbonate (19f). The title compound
was obtained from 18 in 50% yield as described for 7 following column
chromatography on silica gel using hexanes/EtOAc (10:1 and then 7:1)
as the eluent (white solid). TLC, Rf = 0.29 (hexanes/EtOAc = 3:1);
[R]2D0 +40.6 (c 1.0, CHCl3); 1H NMR (CDCl3, 400 MHz) δ 8.26 (d, J =
9.3 Hz, 2H), 7.39 (d, J = 9.3 Hz, 2H), 5.19ꢀ5.12 (m, 1H), 4.57 (dt, J =
2.0, 6.8 Hz, 1H), 4.07 (dd, J = 6.3, 8.6 Hz, 1H), 3.31 (dd, J = 7.1, 8.6 Hz,
1H), 2.35ꢀ2.25 (m, 1H), 2.23ꢀ2.17 (m, 2H), 2.17ꢀ2.07 (m, 2H), 1.88
(ddd, J = 3.8, 5.3, 14.5 Hz, 1H), 1.05 (d, J = 6.8 Hz, 3H); 13C NMR
(3R,3aR,5R,6aR)-5-Hydroxy-3-methylhexahydro-2H-cyclo-
penta[b]furan-2-one (17). To an ice-cold yellow solution of
Hg(OAc)2 (1.45 g, 4.57 mmol) in THF/H2O (2.5:1 ratio, 23 mL) was
added perchloric acid (∼0.7 mL) until the solution became colorless. A
solution of lactone 16 (350 mg, 2.54 mmol) in THF (7 mL) was then
added at 0 ꢀC, and the mixture was stirred for 1 h. Additional Hg(OAc)2
(646 mg, 2.03 mmol) similarly pretreated with perchloric acid in THF/
H2O (2.5:1, 10 mL) was added, and stirring was continued for 2 h at 0 ꢀC.
The pH of the mixture was then adjusted to ∼10 by addition of a 1 M
aqueous NaOH solution. Stirring was then continued for 1 h at room
temperature. The solution was cooled to 0 ꢀC, and NaBH4 (145 mg, 3.81
mmol) was added in small portions. After 1 h, the reaction mixture was
acidified to pH 2 with concentrated HCl, and stirring was continued for 1
h. The reaction solution was saturated with NaCl and the aqueous phase
extracted several times with EtOAc. The combined organic phase was
dried (Na2SO4), filtered, and concentrated under vacuum. The residue
was purified by column chromatography on silica gel using 2% MeOH in
CH2Cl2 to yield alcohol 17 (252 mg, 64%) as a colorless oil. TLC, Rf =
0.31 (CHCl3/MeOH = 9/1); [R]2D0 +53.5 (c 1.0, CHCl3); H NMR
1
(CDCl3, 400 MHz) δ 4.98 (dt, J = 8.0, 14.9 Hz, 1H), 4.55 (m, 1H), 2.69
(qd, J = 3.9, 7.6 Hz, 1H), 2.58 (m, 1H), 2.55 (m, 1H), 2.09 (d, J = 15.0 Hz,
1H), 1.94 (m, 2H), 1.83 (m, 1H), 1.26 (d, J = 7.6 Hz, 3H); 13C NMR
(CDCl3, 100 MHz) δ 181.0, 83.8, 74.6, 51.2, 45.5, 43.9, 41.3, 18.4.
(3R,3aR,5R,6aR)-3-Methylhexahydro-2H-cyclopenta[b]furan-
5-ol (18). To a solution of lactone 17 (205 mg, 1.31 mmol) in CH2Cl2
(9 mL) was added DIBAL-H (1 M solution in CH2Cl2, 1.45 mL, 1.45
mmol) dropwise at ꢀ78 ꢀC. The mixture was stirred for 3 h and then
quenched with saturated Rochelle’s salt solution. After the mixture was
stirred overnight at room temperature, the phases were separated and
the aquoues phase was extracted with EtOAc (ꢁ3). The combined
organic phase was dried (Na2SO4), filtered, and concentrated under
reduced pressure. The residue was purified by column chromatography
on silica gel using 2% MeOH in CH2Cl2 to yield the corresponding
lactol (150 mg, 72%). To a solution of this lactol (143 mg, 0.9 mmol) in
CH2Cl2 (9 mL) at ꢀ78 ꢀC was added TiCl4 (100 μL, 0.9 mmol)
dropwise, and the mixture was stirred for 20 min. Et3SiH (289 μL, 1.81
mmol) was then added, and the solution was stirred for an additional 1 h.
The reaction was quenched with saturated NaHCO3 solution once
completion was reached as observed by TLC. The aqueous phase was
extracted with Et2O, dried (Na2SO4), filtered, and concentrated under
reduced pressure at 25 ꢀC. The residue was purified by column
chromatography on silica gel using 2% MeOH in CH2Cl2 to yield
alcohol 18 (122 mg, 95%) as a colorless oil. TLC, Rf = 0.38 (CHCl3/
1
MeOH = 9/1); [R]2D0 +12.6 (c 1.0, CHCl3); H NMR (CDCl3, 400
MHz) δ 4.47 (t, J = 5.7 Hz, 1H), 4.22 (m, 1H), 4.06 (dd, J = 6.5, 8.7 Hz,
1H), 3.18 (t, J = 8.4 Hz, 1H), 2.60 (d, J = 7.2 Hz, 1H), 2.27ꢀ2.18 (m,
1H), 2.18ꢀ2.12 (m, 1H), 2.00 (dd, J = 1.5, 16.2 Hz, 1H), 1.98ꢀ1.91 (m,
1H), 1.80 (dt, J = 5.2, 14.6 Hz, 1H), 1.69 (ddd, J = 2.3, 5.4, 13.9 Hz, 1H),
1.03 (d, J = 6.7 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 85.4, 75.1,
74.7, 50.3, 43.2, 41.6, 41.5, 17.6.
Synthesis of Activated Mixed Carbonates. (3aS,5R,6aR)-3-
Oxohexahydro-2H-cyclopenta[b]furan-5-yl (4-nitrophenyl)-
carbonate (19a). To a solution of ketone 7 (20 mg, 0.14 mmol) in
CH2Cl2 (1 mL) was added pyridine (30 μL). The solution was cooled to
0 ꢀC under argon, and 4-nitrophenyl chloroformate (42 mg, 0.21 mmol)
was added at once. A white suspension formed. The solution was stirred
at this temperature and slowly warmed to room temperature until all
starting material was consumed. The reaction mixture was evaporated to
5897
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
(CDCl3, 100 MHz) δ 155.6, 151.9, 145.2, 125.2, 121.8, 83.3, 82.2, 74.9,
50.4, 41.8, 39.5, 37.3, 17.5.
129.6, 129.5, 128.5, 126.5, 126.3, 114.1, 82.9, 76.3, 72.2, 70.6, 58.9, 55.0,
53.8, 48.7, 41.2, 37.3, 35.2, 27.3, 20.2, 19.9. HRMS-ESI (m/z): [M +
Na+] calcd for C28H37N3O7SNa 582.2250, found 582.2246. The title
compound was obtained in 82% yield by reduction of the above ketone
intermediate as described for 22, followed by column chromatography
on silica gel using hexanes/EtOAc (1:2 to 1:5) as the eluent. Off-white
solid. TLC, Rf = 0.12 (hexanes/EtOAc = 1:2); 1H NMR (CDCl3, 500
MHz) δ 7.54 (d, J = 8.8 Hz, 2H), 7.34ꢀ7.18 (m, 5H), 6.68 (d, J = 8.8 Hz,
2H), 5.07 (m, 1H), 4.87 (d, J = 7.2 Hz, 1H), 4.38 (t, J = 6.8 Hz, 1H),
4.24ꢀ4.19 (m, 1H), 4.14 (s, 2H), 3.86 (br s, 1H), 3.85ꢀ3.75 (m, 3H),
3.55 (dd, J = 3.6, 9.6 Hz, 1H), 3.10 (dd, J = 8.2, 15.0 Hz, 1H), 3.04ꢀ2.79
(m, 5H), 2.76 (dd, J = 6.8, 13.2 Hz, 1H), 2.37 (d, J = 11.6 Hz, 1H), 2.10
(t, J = 14.4 Hz, 2H), 1.94ꢀ1.75 (m, 3H), 0.90 (d, J = 6.8 Hz, 3H), 0.86
(d, J = 6.4 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ 155.3, 150.6, 137.6,
129.6, 129.5, 128.5, 126.5, 126.4, 114.1, 84.9, 78.0, 70.3, 73.0, 72.2, 58.8,
55.2, 53.7, 47.3, 39.1, 35.5, 31.3, 27.3, 20.2, 19.9. HRMS-ESI (m/z): [M
+ Na]+ calcd for C28H39N3O7SNa 584.2406, found 584.2410.
(3S,3aR,5R,6aR)-3-Hydroxyhexahydro-2H-cyclopenta[b]-
furan-5-yl {(2S,3R)-3-Hydroxy-4-[4-(hydroxymethyl)-N-iso-
butylphenylsulfonamido]-1-phenylbutan-2-yl}carbamate
(24). The ketone intermediate was first synthesized from the coupling of
19a with isostere 20c as described for 21. Purification of the crude
compound by column chromatography on silica gel using hexanes/
EtOAc (2:1 to 1:2) as the eluent afforded the corresponding ketone
inhibitor in 49% yield as a white solid. TLC, Rf = 0.38 (hexanes/EtOAc =
1:3); 1H NMR (CDCl3, 500 MHz) δ 7.76 (d, J = 8.2 Hz, 2H), 7.51 (d,
J = 8.2 Hz, 2H), 7.34ꢀ7.28 (m, 2H), 7.25ꢀ7.20 (m, 3H), 5.02 (t, J = 6.9
Hz, 1H), 4.96 (m, 1H), 4.79 (s, 2H), 4.67 (d, J = 8.4 Hz, 1H), 3.98ꢀ3.93
(m, 2H), 3.84ꢀ3.75 (m, 2H), 3.75ꢀ3.67 (m, 1H), 3.10 (dd, J = 8.2, 15.1
Hz, 1H), 3.07ꢀ2.80 (m, 5H), 2.83 (dd, J = 6.9, 13.5 Hz, 1H), 2.23ꢀ2.15
(m, 2H), 2.04ꢀ1.96 (m, 2H), 1.88ꢀ1.76 (m, 1H), 0.90 (dd, J = 6.6 Hz,
3H), 0.87 (d, J = 6.6 Hz, 3H). The title compound was obtained in 83%
yield by reduction of the above ketone intermediate as described for 22,
followed by column chromatography on silica gel using hexanes/EtOAc
(1:1 to 1:3 and then 100% EtOAc) as the eluent. White solid. TLC, Rf =
0.23 (hexanes/EtOAc = 1:3); 1H NMR (CDCl3, 400 MHz) δ 7.76 (d, J
= 8.2 Hz, 2H), 7.51 (d, J = 8.2 Hz, 2H), 7.34ꢀ7.27 (m, 2H), 7.24ꢀ7.20
(m, 3H), 5.06 (m, 1H), 4.82 (d, J = 7.8 Hz, 1H), 4.76 (s, 2H), 4.38 (t, J =
7.0 Hz, 1H), 4.21 (m, 1H), 3.85ꢀ3.68 (m, 4H), 3.55 (dd, J = 3.5, 9.8 Hz,
1H), 3.11 (dd, J = 8.3, 15.1 Hz, 1H), 3.05ꢀ2.79 (m, 6H), 2.38 (d, J = 8.3
Hz, 1H), 2.15ꢀ1.99 (m, 2H), 1.94ꢀ1.80 (m, 3H), 0.91 (d, J = 6.6 Hz,
3H), 0.87 (d, J = 6.6 Hz, 3H). HRMS-ESI (m/z): [M + Na]+ calcd for
C29H40N2O8SNa 599.2403, found 599.2401.
General Method for the Synthesis of HIV-Protease Inhibi-
tors. (3aS,5R,6aR)-3-Oxohexahydro-2H-cyclopenta[b]furan-
5-yl[(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxyphenylsulfo-
namido)-1-phenylbutan-2-yl]carbamate (21). The N-Boc-pro-
tected isostere 20a (82 mg, 0.16 mmol) was dissolved in a 2:1 mixture
CH2Cl2/TFA and stirred at room temperature for 2 h. The solution was
then evaporated and dried in vacuo. The residue was redissolved in
CH3CN (1 mL) and the solution cooled down to 0 ꢀC under argon.
Et3N (100 μL) was added followed by a solution of activated carbonate
19a (40 mg, 0.13 mmol) in THF (1 mL). The solution was stirred for 36
h and the solution evaporated in vacuo. The residue was purified by
column chromatography on silica gel using hexanes/EtOAc (3:1 to
1.5:1) as the eluent to furnish inhibitor 21 (46 mg, 61%) as a white solid.
TLC, Rf = 0.23 (hexanes/EtOAc = 1:1); 1H NMR (CDCl3, 500 MHz) δ
7.70 (d, J = 8.8 Hz, 2H), 7.34ꢀ7.28 (m, 2H), 7.25ꢀ7.19 (m, 3H), 6.98
(d, J = 8.8 Hz, 2H), 5.03 (t, J = 6.9 Hz, 1H), 4.99 (m, 1H), 4.71 (d, J = 8.7
Hz, 1H), 3.97 (s, 2H), 3.87 (s, 3H), 3.89ꢀ3.85 (m, 1H), 3.83ꢀ3.70 (m,
2H), 3.09 (dd, J = 8.0, 15.2 Hz, 1H), 3.00 (dd, J = 3.0, 15.1 Hz, 1H),
2.99ꢀ2.89 (m, 3H), 2.89ꢀ2.82 (m, 1H), 2.79 (dd, J = 6.8, 13.4 Hz, 1H),
2.24ꢀ2.12 (m, 2H), 2.06ꢀ1.94 (m, 2H), 1.81 (m, 1H), 0.90 (d, J = 6.4
Hz, 3H), 0.86 (d, J = 6.4 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ
216.2, 163.0, 155.4, 137.5, 129.8, 129.6, 129.5, 128.5, 126.6, 114.3, 82.9,
76.3, 72.2, 70.6, 58.8, 55.6, 55.1, 53.7, 48.7, 41.2, 37.3, 35.1, 27.3, 20.1,
19.9. HRMS-ESI (m/z): [M + Na]+ calcd for C29H38N2O8SNa
597.2247, found 597.2251.
(3S,3aR,5R,6aR)-3-Hydroxyhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxy-
phenylsulfonamido)-1-phenylbutan-2-yl]carbamate (22). A
solution of keto inhibitor 21 (10 mg, 17 μmol) in EtOH was cooled to
ꢀ25 ꢀC, and NaBH4 (6 mg) was added at once. The solution was stirred
for 30 min. Then saturated aqueous NH4Cl solution was added. The
aqueous phase was extracted with EtOAc (ꢁ4). The combined organic
layer was dried, filtered, and evaporated under reduced pressure. The
residue was purified by column chromatography on silica gel using
hexanes/EtOAc (2:1, 1:1, then 1:2) as the eluent to afford the desired
inhibitor 22 (8 mg, 80%) as a white solid. TLC, Rf = 0.39 (hexanes/
EtOAc = 1:5); 1H NMR (CDCl3, 500 MHz) δ 7.70 (d, J = 8.8 Hz, 2H),
7.32ꢀ7.19 (m, 5H), 6.97 (d, J = 8.8 Hz, 2H), 5.07 (m, 1H), 4.89 (d, J =
7.2 Hz, 1H), 4.38 (t, J = 6.8 Hz, 1H), 4.21 (m, 1H), 3.87 (s, 3H),
3.88ꢀ3.74 (m, 4H), 3.54 (dd, J = 3.2, 9.6 Hz, 1H), 3.10 (dd, J = 7.8, 15.0
Hz, 1H), 3.05ꢀ2.82 (m, 5H), 2.78 (dd, J = 6.8, 13.4 Hz, 1H), 2.42 (br s,
1H), 2.18ꢀ2.04 (m, 2H), 1.94ꢀ1.76 (m, 3H), 0.90 (d, J = 6.6 Hz, 3H),
0.86 (d, J = 6.6 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ 163.0, 155.3,
137.6, 129.9, 129.6, 129.5, 128.6, 126.5, 114.3, 84.9, 78.1, 76.3, 73.0, 72.2,
58.7, 55.6, 55.3, 53.7, 47.3, 39.1, 35.4, 31.3, 27.2, 20.1, 19.9; LRMS-ESI
(m/z): [M + Na]+ 599.3.
(3S,3aS,5R,6aR)-3-Methoxyhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxy-
phenylsulfonamido)-1-phenylbutan-2-yl]carbamate (25).
The title compound was obtained in 73% yield from 19b and 20a as
described for 21 following column chromatography on silica gel using
hexanes/EtOAc (1:1) as the eluent. White solid. TLC, Rf = 0.21
(hexanes/EtOAc = 1:1); 1H NMR (CDCl3, 500 MHz) δ 7.70 (d, J =
8.9 Hz, 2H), 7.33ꢀ7.19 (m, 5H), 6.97 (d, J = 8.9 Hz, 2H), 4.97ꢀ4.90
(m, 1H), 4.78 (d, J = 7.5 Hz, 1H), 4.47ꢀ4.42 (m, 1H), 3.99 (q, J = 6.9
Hz, 1H), 3.87 (s, 3H), 3.88ꢀ3.82 (m, 2H), 3.81ꢀ3.76 (m, 2H), 3.70
(dd, J = 6.9, 9.0 Hz, 1H), 3.30 (s, 3H), 3.14ꢀ3.06 (dd, J = 7.8, 14.9 Hz,
1H), 3.04ꢀ2.88 (m, 4H), 2.78 (dd, J = 6.7, 13.4 Hz, 1H), 2.70 (m, 1H),
2.14 (m, 1H), 1.93 (dd, J = 6.3, 8.6 Hz, 2H), 1.86ꢀ1.76 (m, 2H), 0.90 (d,
J = 6.6 Hz, 3H), 0.86 (d, J = 6.6 Hz, 3H); 13C NMR (CDCl3, 125 MHz)
δ 163.0, 156.3, 137.5, 129.9, 129.6, 129.5, 128.5, 126.5, 114.3, 83.5, 81.3,
76.3, 72.3, 70.0, 58.7, 57.8, 55.6, 54.9, 53.7, 43.8, 39.5, 35.5, 30.4, 27.2,
(3S,3aR,5R,6aR)-3-Hydroxyhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-4-(4-Amino-N-isobutylphenylsulfo-
namido)-3-hydroxy-1-phenylbutan-2-yl]carbamate
(23).
The ketone intermediate was first synthesized from the coupling of
19a with isostere 20b as described for 21 after stirring 48 h at room
temperature in a CH2Cl2/THF (1:1) mixture. Purification of the crude
compound by column chromatography on silica gel using chloroform
with 1ꢀ3% EtOH as the eluent afforded the corresponding ketone
inhibitor (60%, white solid). TLC, Rf = 0.18 (chloroform/3% EtOH);
1H NMR (CDCl3, 500 MHz) δ 7.54 (d, J = 8.6 Hz, 2H), 7.34ꢀ7.28 (m,
2H), 7.25ꢀ7.18 (m, 3H), 6.68 (d, J = 8.6 Hz, 2H), 5.02 (t, J = 6.9 Hz,
1H), 4.99 (m, 1H), 4.68 (d, J = 8.8 Hz, 1H), 4.14 (br s, 2H), 3.98 (s, 2H),
3.91 (m, 1H), 3.84ꢀ3.72 (m, 2H), 3.08 (dd, J = 8.4, 15.1 Hz, 1H),
3.00ꢀ2.83 (m, 5H), 2.76 (dd, J = 8.7, 13.4 Hz, 1H), 2.22ꢀ2.15 (m, 2H),
2.05ꢀ1.97 (m, 2H), 1.80 (m, 1H), 0.90 (d, J = 6.6 Hz, 3H), 0.86 (d, J =
6.6 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ 216.9, 155.4, 150.6, 137.5,
+
20.1, 19.9. HRMS-ESI (m/z): [M + H] calcd for C30H43N2O8S
591.2740, found 591.2742.
(3R,3aR,5R,6aR)-3-Hydroxyhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxyphe-
nylsulfonamido)-1-phenylbutan-2-yl]carbamate (26). The
5898
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
acetyl intermediate was first synthesized in 84% yield by coupling of 19c
with 20a as described for 21 followed by purification by column
chromatography on silica gel using hexanes/EtOAc (3:1 to 1:1) as the
eluent. White solid. TLC, Rf = 0.23 (hexanes/EtOAc = 1:2); 1H NMR
(CDCl3, 300 MHz) δ 7.71 (d, J = 8.9 Hz, 2H), 7.34ꢀ7.19 (m, 5H), 6.97
(d, J = 8.9 Hz, 2H), 4.91 (m, 1H), 4.88 (m, 1H), 4.75 (d, J = 8.2 Hz, 1H),
4.67 (m, 1H), 3.98 (dd, J = 4.1, 10.4 Hz, 1H), 3.87 (s, 3H), 3.85ꢀ3.77
(m, 3H), 3.73 (dd, J = 1.5, 10.4 Hz, 1H), 3.19ꢀ2.92 (m, 4H), 2.90ꢀ2.72
(m, 2H), 2.67ꢀ2.55 (m, 1H), 2.23ꢀ2.09 (m, 1H), 2.06 (s, 3H),
2.04ꢀ1.76 (m, 3H), 1.50ꢀ1.43 (m, 1H), 0.91 (d, J = 6.6 Hz, 3H),
0.87 (d, J = 6.6 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 170.6, 163.0,
156.0, 137.6, 129.8, 129.5, 128.5, 126.6, 114.3, 83.5, 80.6, 76.1, 72.6, 71.6,
58.8, 55.6, 54.9, 53.7, 48.5, 39.6, 36.2, 35.7, 27.2, 21.1, 20.1, 19.9. The
acetate intermediate (18 mg, 0.029 mmol) was diluted in MeOH
(1.5 mL) at 0 ꢀC. K2CO3 (5 mg, 0.04 mmol) was added, and the
solution was stirred for 6 h. Saturated aqueous NH4Cl solution (1 mL)
was added, and the solvent was reduced under vacuum. The aqueous
phase was diluted and extracted with EtOAc (ꢁ4). The combined
organic phase was dried (MgSO4), filtered, and evaporated. The residue
was purified by column chromatography on silica gel using
(chloroform)/(0.5ꢀ3% EtOH) as the eluent to provide inhibitor 26
(15.9 mg, 94%) as a white solid. TLC, Rf = 0.26 (hexanes/EtOAc = 1:5);
1H NMR (CDCl3, 500 MHz) δ 7.71 (d, J = 8.9 Hz, 2H), 7.33ꢀ7.25 (m,
1H), 7.24ꢀ7.19 (m, 3H), 6.98 (d, J = 8.9 Hz, 2H), 4.86 (m, 1H), 4.81 (d,
J = 8.3 Hz, 1H), 4.69 (t, J = 5.4 Hz, 1H), 4.01 (m, 1H), 3.91ꢀ3.76 (m,
4H), 3.87 (s, 3H), 3.64 (dd, J = 2.0, 9.7 Hz, 1H), 3.12 (dd, J = 8.2, 15.1
Hz, 1H), 3.11ꢀ3.05 (m, 1H), 3.03 (dd, J = 2.7, 15.2 Hz, 1H), 2.95 (dd,
J = 8.3, 13.4 Hz, 1H), 2.85ꢀ2.75 (m, 2H), 2.52 (m, 1H), 2.12 (ddd, J =
6.1, 10.0, 14.7 Hz, 1H), 1.99 (dt, J = 6.1, 15.0 Hz, 1H), 1.93ꢀ1.79 (m,
3H), 1.35 (m, 1H), 0.91 (d, J = 6.6 Hz, 3H), 0.87 (d, J = 6.6 Hz, 3H); 13C
NMR (CDCl3, 125 MHz) δ 163.0, 156.0, 137.8, 129.8, 129.5, 128.4,
126.4, 114.3, 83.1, 78.3, 76.3, 73.8, 72.7, 58.8, 55.6, 54.8, 53.7, 51.3, 39.5,
36.1, 35.8, 27.2, 20.1, 19.9. HRMS-ESI (m/z): [M + H]+ calcd for
C29H41N2O8S 577.2584, found 577.2572.
1H), 2.00 (dt, J = 6.1, 15.1 Hz, 1H), 1.93ꢀ1.85 (m, 1H), 1.85ꢀ1.76 (m,
2H), 1.35 (m, 1H), 0.91 (d, J = 6.6 Hz, 3H), 0.87 (d, J = 6.6 Hz, 3H); 13
C
NMR (CDCl3, 125 MHz) δ 156.0, 150.7, 137.8, 129.5, 128.4, 126.4,
126.2, 114.1, 83.1, 78.3, 76.2, 73.7, 72.7, 58.9, 54.8, 53.8, 51.3, 39.5, 36.0,
35.8, 27.3, 20.2, 19.9. HRMS-ESI (m/z): [M + H]+ calcd for
C28H39N3O7S 584.2406, found 584.2398.
(3R,3aS,5R,6aR)-3-Methoxyhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxy-
phenylsulfonamido)-1-phenylbutan-2-yl]carbamate (28).
The title compound was obtained in 57% yield from 19d and 20a as
described for 21 following purification by column chromatography on
silica gel using hexanes/EtOAc (2:1 to 1:1) as the eluent. White solid.
TLC, Rf = 0.34 (hexanes/EtOAc = 1:2); 1H NMR (CDCl3, 500 MHz) δ
7.71 (d, J = 8.8 Hz, 2H), 7.33ꢀ7.25 (m, 2H), 7.26ꢀ7.20 (m, 3H), 6.98
(d, J = 8.8 Hz, 2H), 4.89 (m, 1H), 4.78 (d, J = 8.3 Hz, 1H), 4.61 (t, J = 5.7
Hz, 1H), 3.93ꢀ3.85 (m, 1H), 3.88 (s, 3H), 3.85ꢀ3.79 (m, 2H), 3.73 (d,
J = 2.7, 9.8 Hz, 1H), 3.60 (m, 1H), 3.31 (s, 3H), 3.13 (dd, J = 8.3, 15.2
Hz, 1H), 3.10ꢀ3.00 (m, 2H), 2.95 (dd, J = 8.4, 13.4 Hz, 1H), 2.88ꢀ2.77
(m, 1H), 2.80 (dd, J = 7.0, 13.3 Hz, 1H), 2.62ꢀ2.53 (m, 1H), 2.19ꢀ2.09
(m, 1H), 1.99 (dt, J = 6.0, 15.1 Hz, 1H), 1.92 (m, 1H), 1.90ꢀ1.78 (m,
2H), 1.47ꢀ1.38 (m, 1H), 0.92 (d, J = 6.6 Hz, 3H), 0.88 (d, J = 6.6 Hz,
3H); 13C NMR (CDCl3, 125 MHz) δ 163.0, 156.1, 137.7, 129.9, 129.5,
128.5, 126.5, 114.3, 87.6, 83.3, 76.5, 72.7, 71.1, 58.8, 56.7, 55.6, 54.9,
53.7, 48.0, 39.5, 36.6, 35.8, 27.2, 20.1, 19.9. HRMS-ESI (m/z): [M +
Na]+ calcd for C30H42N2O8SNa 613.2560, found 613.2555.
(3S,3aR,5R,6aR)-3-Methylhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxy-
phenylsulfonamido)-1-phenylbutan-2-yl]carbamate (29).
The title compound was obtained from 19e and 20a in 78% yield as
described for 21 following purification by column chromatography on
silica gel using hexanes/EtOAc (3:1 to 2:1) as the eluent. White solid.
TLC, Rf = 0.32 (hexanes/EtOAc = 1:1); 1H NMR (CDCl3, 300 MHz) δ
7.71 (d, J = 8.9 Hz, 2H), 7.34ꢀ7.19 (m, 5H), 6.98 (d, J = 8.9 Hz, 2H),
4.84 (m, 1H), 4.75 (d, J = 8.2 Hz, 1H), 4.49ꢀ4.40 (m, 1H), 3.87 (s, 3H),
3.86ꢀ3.76 (m, 4H), 3.32 (dd, J = 8.3, 10.5 Hz, 1H), 3.11 (dd, J = 7.8,
15.1 Hz, 1H), 3.06ꢀ2.84 (m, 4H), 2.79 (dd, J = 6.7, 13.4 Hz, 1H),
2.54ꢀ2.45 (m, 1H), 2.40ꢀ2.31 (m, 1H), 2.18 (dt, J = 6.5, 14.8 Hz, 1H),
1.90ꢀ1.77 (m, 2H), 1.74ꢀ1.66 (m, 1H), 1.50ꢀ1.40 (m, 1H), 0.91
(d, J = 6.8 Hz, 3H), 0.90 (d, J = 6.6 Hz, 3H), 0.86 (d, J = 6.6 Hz, 3H);
13C NMR (CDCl3, 75 MHz) δ 162.7, 156.3, 137.6, 129.8, 129.5, 128.5,
126.5, 114.3, 83.5, 76.0, 72.6, 72.2, 58.7, 55.6, 54.9, 53.7, 45.6, 39.8, 36.4,
35.6, 31.3, 27.2, 20.1, 19.8, 11.8. LRMS-ESI (m/z): [M + Na]+ 597.3,
[M + H]+ 575.1.
(3R,3aR,5R,6aR)-3-Methylhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-methoxy-
phenylsulfonamido)-1-phenylbutan-2-yl]carbamate (30).
The title compound was obtained from 19f and 20a in 96% yield as
described for 21 following purification by column chromatography on
silica gel using hexanes/EtOAc (5:1) as the eluent. White solid. TLC, Rf
= 0.50 (hexanes/EtOAc = 1:1); [R]2D0 +24.5 (c 1.0, CHCl3); 1H NMR
(CDCl3, 400 MHz) δ 7.70 (d, J = 8.8 Hz, 2H), 7.30ꢀ7.16 (m, 5H), 6.96
(d, J = 8.8 Hz, 2H), 4.88 (m, 1H), 4.80 (d, J = 7.1 Hz, 1H), 4.46 (m, 1H),
3.91 (dd, J = 6.1, 8.5 Hz, 1H), 3.86 (s, 3H), 3.80 (m, 3H), 3.22 (dd, J =
7.5, 14.8 Hz, 1H), 3.15ꢀ2.99 (m, 3H), 2.94 (dd, J = 8.2, 13.4 Hz, 1H),
2.87ꢀ2.75 (m, 2H), 2.14 (m, 1H), 2.00ꢀ1.77 (m, 5H), 1.50 (d, J =
12.3 Hz, 1H), 0.98 (d, J = 6.6 Hz, 3H), 0.90 (d, J = 6.6 Hz, 3H), 0.85 (d,
J = 6.6 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 162.9, 156.2, 137.7,
129.8, 129.4, 128.4, 126.4, 114.3, 83.7, 77.2, 74.7, 72.5, 58.7, 55.6, 54.8,
53.7, 50.2, 41.8, 39.4, 37.7, 35.7, 27.2, 20.1, 19.8, 17.6. LRMS-ESI (m/z):
[M + Na]+ 597.1, [M + H]+ 575.3.
(3R,3aR,5R,6aR)-3-Hydroxyhexahydro-2H-cyclopenta[b]-
furan-5-yl [(2S,3R)-4-(4-Amino-N-isobutylphenylsulfo-
namido)-3-hydroxy-1-phenylbutan-2-yl]carbamate
(27).
The acetyl intermediate was first synthesized in 63% yield by coupling
of 19c with 20b as described for 21 followed by purification by column
chromatography on silica gel using (CHCl3)/(0.25ꢀ1.5% EtOH) as the
eluent. White solid. TLC, Rf = 0.44 (hexanes/EtOAc = 1:3); 1H NMR
(CDCl3, 500 MHz) δ 7.54 (d, J = 8.7 Hz, 2H), 7.32ꢀ7.27 (m, 2H),
7.25ꢀ7.19 (m, 3H), 6.67 (d, J = 8.7 Hz, 2H), 4.94 (m, 1H), 4.90ꢀ4.85
(m, 1H), 4.75 (d, J = 8.7 Hz, 1H), 4.66 (t, J = 5.4 Hz, 1H), 4.16 (br s,
2H), 3.99 (dd, J = 4.1, 10.4 Hz, 1H), 3.88ꢀ3.77 (m, 3H), 3.74 (d, J =
10.3 Hz, 1H), 3.11 (dd, J = 8.5, 15.1 Hz, 1H), 3.05 (dd, J = 4.0, 14.1 Hz,
1H), 2.98 (dd, J = 1.5, 15.2 Hz, 1H), 2.93 (dd, J = 8.4, 13.2 Hz, 1H), 2.84
(dd, J = 8.8, 13.9 Hz, 1H), 2.77 (dd, J = 6.7, 13.3 Hz, 1H), 2.64ꢀ2.56 (m,
1H), 2.20ꢀ2.12 (m, 1H), 2.07 (s, 3H), 2.00 (dt, J = 6.1, 15.2 Hz, 1H),
1.95ꢀ1.88 (m, 1H), 1.81 (m, 1H), 1.51ꢀ1.44 (m, 1H), 0.91 (d, J = 6.6
Hz, 3H), 0.87 (d, J = 6.6 Hz, 3H); 13C NMR (CDCl3, 125 MHz) δ
170.6, 155.9, 150.6, 137.7, 129.5, 128.5, 126.5, 126.2, 114.1, 83.5, 80.6,
76.0, 72.6, 71.5, 58.9, 54.9, 53.8, 48.5, 39.6, 36.2, 35.7, 27.3, 21.1, 20.2,
19.9. The title compound was obtained from the above acetate inter-
mediate in 88% yield as described for 26 following purification by
column chromatography on silica gel using a gradient, 1ꢀ5% EtOH in
CHCl3, as the eluent. White solid. TLC, Rf = 0.4 (CHCl3/10% EtOH);
1H NMR (CDCl3, 500 MHz) δ 7.55 (d, J = 8.7 Hz, 2H), 7.31ꢀ7.26 (m,
2H), 7.24ꢀ7.19 (m, 3H), 6.67 (d, J = 8.7 Hz, 2H), 4.89ꢀ4.83 (m, 1H),
4.79 (d, J = 8.9 Hz, 1H), 4.69 (t, J = 5.4 Hz, 1H), 4.16 (br s, 2H), 4.01 (m,
1H), 3.88 (dd, J = 3.7, 9.9 Hz, 1H), 3.87ꢀ3.76 (m, 3H), 3.65 (dd, J = 1.4,
9.8 Hz, 1H), 3.14ꢀ3.04 (m, 2H), 2.99 (dd, J = 2.9, 15.1 Hz, 1H), 2.92
(dd, J = 8.3, 13.3 Hz, 1H), 2.81 (dd, J = 9.1, 14.0 Hz, 1H), 2.78 (dd, J =
6.8, 13.3 Hz, 1H), 2.54ꢀ2.47 (m, 1H), 2.11 (ddd, J = 6.2, 10.2, 14.6 Hz,
(3S,3aR,5R,6aR)-3-(Dimethylamino)hexahydro-2H-cyclo-
penta[b]furan-5-yl [(2S,3R)-3-Hydroxy-4-(N-isobutyl-4-meth-
oxyphenylsulfonamido)-1-phenylbutan-2-yl]carbamate (31).
To a solution of AcOH (∼15 μL) in dichloromethane (1 mL), a slow
5899
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
stream of Me2NH gas was bubbled briefly at 0 ꢀC for 5 min. After the
flask was flushed with argon, a solution of ketone inhibitor 21 (13 mg,
0.02 mmol) in dichloroethane (0.5 mL) was added at 0 ꢀC, and after 15
min, NaBH(OAc)3 (10 mg, 0.05 mmol) was added. The resulting
solution was warmed to room temperature. After 24 h, another 10 mg
portion of NaBH(OAc)3 was added and the solution stirred for 48 h.
The reaction was quenched by addition of saturated aqueous NaHCO3
solution, adjusting the pH to 10 with 1 M NaOH solution. The aqueous
phase was extracted multiple times with EtOAc. The combined organic
phase was dried (Na2SO4), filtered, and evaporated under reduced
pressure. The residue was purified by column chromatography on silica
gel using ethanol (0.5ꢀ2%) in CHCl3 to furnish the corresponding
dimethylamine inhibitor 31 (11.3 mg, 82%) as a white solid. TLC, Rf =
0.35 (CHCl3/8% EtOH); 1H NMR (CDCl3, 500 MHz) δ 7.70 (d, J =
8.9 Hz, 2H), 7.32ꢀ7.26 (m, 2H), 7.25ꢀ7.19 (m, 3H), 6.97 (d, J = 8.9
Hz, 2H), 4.92 (m, 1H), 4.86 (m, 1H), 4.55 (m, 1H), 3.90ꢀ3.85 (m, 1H),
3.87 (s, 3H), 3.83ꢀ3.75 (m, 2H) 3.70ꢀ3.63 (m, 1H), 3.30ꢀ3.20 (m,
1H), 3.10 (dd, J = 3.14, 3.06 Hz, 1H), 3.04ꢀ2.88 (m, 4H), 2.79 (dd, J =
6.9, 13.4 Hz, 1H), 2.64ꢀ2.55 (m, 1H), 2.23ꢀ2.18 (m, 1H), 2.24 (br s,
6H), 2.18ꢀ2.10 (m, 1H), 2.06ꢀ1.97 (m, 1H), 1.88ꢀ1.75 (m, 2H), 0.90
(d, J = 6.6 Hz, 3H), 0.85 (d, J = 6.6 Hz, 3H); 13C NMR (CDCl3, 125
MHz) δ 163.0, 156.4, 137.6, 130.0, 129.6, 129.5, 128.5, 126.5, 114.3,
83.8, 77.2, 76.0, 72.3, 69.4, 58.7, 55.6, 55.0, 53.7, 45.4, 45.3, 40.1, 35.5,
31.4, 27.2, 20.1, 19.9. LRMS-ESI (m/z): [M + H]+ 604.3
Determination of X-ray Structure of HIV-1 Protease
Inhibitor Complex. The optimized HIV-1 protease was expressed
and purified as previously described.23 The proteaseꢀinhibitor complex
was crystallized by the hanging drop vapor diffusion method with well
solutions of 1.2 M ammonium chloride and 0.1 M sodium acetate buffer
(pH 4.8). Diffraction data were collected on a single crystal cooled to 90
K at SER-CAT BM beamline 22, Advanced Photon Source, Argonne
National Laboratory (Chicago, IL, U.S.), with an X-ray wavelength of 1.0
Å and processed by HKL-200024 with Rmerge of 7.2%. The PR structure
was used in molecular replacement by PHASER25,26 in the CCP4i
suite27,28 and refined to 1.45 Å resolution using SHELX-9729,30 and
COOT31 for manual modification. PRODRG-232 was used to construct
the inhibitor and the restraints for refinement. Alternative conforma-
tions were modeled, anisotropic atomic displacement parameters
(B factors) were applied for all atoms including solvent molecules,
and hydrogen atoms were added in the final round of refinement. The
final refined solvent structure comprised two Clꢀ ions and 142 water
molecules. The crystallographic statistics are listed in Table 3 in the
Supporting Information. The coordinates and structure factors of the PR
with 26 complex have been deposited in Protein Data Bank33 with code
3ST5.
’ ACKNOWLEDGMENT
This research was supported by the National Institutes of
Health (Grant GM53386 to A.K.G. and Grant GM62920 to I.T.
W.). This work was also supported by the Intramural Research
Program of the Center for Cancer Research, National Cancer
Institute, National Institutes of Health, and in part by a Grant-in-
Aid for Scientific Research (Priority Areas) from the Ministry of
Education, Culture, Sports, Science, and Technology of Japan
(Monbu Kagakusho), a Grant for Promotion of AIDS Research
from the Ministry of Health, Welfare, and Labor of Japan, and the
Grant to the Cooperative Research Project on Clinical and
Epidemiological Studies of Emerging and Reemerging Infectious
Diseases (Renkei Jigyo) of Monbu-Kagakusho.
’ ABBREVIATIONS USED
bis-THF, bis-tetrahydrofuran; Cp-THF, hexahydrocyclopenta-
furan; PI, protease inhibitor; APV, amprenavir; DRV, darunavir;
SQV, saquinavir; IDV, indinavir; TBS, tert-butyldimethylsilyl;
DIBAL, diisobutylaluminum hydride
’ REFERENCES
(1) Palella, F. J., Jr.; Delaney, K. M.; Moorman, A. C.; Loveless,
M. O.; Fuhrer, J.; Satten, G. A.; Aschman, D. J.; Holmberg, S. D.
Declining Morbidity and Mortality among Patients with Advanced
Human Immunodeficiency Virus Infection. N. Engl. J. Med. 1998,
338, 853–860.
(2) Sepkowitz, K. A. AIDS—The First 20 Years. N. Engl. J. Med.
2001, 344, 1764–1772.
(3) Gupta, R.; Hill, A.; Sawyer, A. W.; Pillay, D. Emergence of Drug
Resistance in HIV Type 1-Infected Patients after Receipt of First-Line
Highly Active Antiretroviral Therapy: A Systematic Review of Clinical
Trials. Clin. Infect. Dis. 2008, 47, 712–722.
(4) Wainberg, M. A.; Friedland, G. Public Health Implications of
Antiretroviral Therapy and HIV Drug Resistance. JAMA, J. Am. Med.
Assoc. 1998, 279, 1977–1983.
(5) Ghosh, A. K.; Chapsal, B. D.; Weber, I. T.; Mitsuya, H. Design of
HIV Protease Inhibitors Targeting Protein Backbone: An Effective
Strategy for Combating Drug Resistance. Acc. Chem. Res. 2008,
41, 78–86.
(6) Ghosh, A. K.; Sridhar, P. R.; Kumaragurubaran, N.; Koh, Y.;
Weber, I. T.; Mitsuya, H. Bis-Tetrahydrofuran: A Privileged Ligand for
Darunavir and a New Generation of HIV Protease Inhibitors That
Combat Drug Resistance. ChemMedChem. 2006, 1, 939–950.
(7) Koh, Y.; Nakata, H.; Maeda, K.; Ogata, H.; Bilcer, G.; Devasa-
mudram, T.; Kincaid, J. F.; Boross, P.; Wang, Y.-F.; Tie, Y.; Volarath, P.;
Gaddis, L.; Harrison, R. W.; Weber, I. T.; Ghosh, A. K.; Mitsuya, H.
Novel Bis-tetrahydrofuranylurethane-Containing Nonpeptidic Protease
Inhibitor (PI) UIC-94017 (TMC114) with Potent Activity against
Multi-PI-Resistant Human Immunodeficiency Virus in Vitro. Antimi-
crob. Agents Chemother. 2003, 47, 3123–3129.
’ ASSOCIATED CONTENT
S
Supporting Information. HPLC, LRMS, and HRMS
b
(8) Ghosh, A.; Chapsal, B.; Mitsuya, H. In Aspartic Acid Proteases as
Therapeutic Targets; Ghosh, A., Ed.; Wiley-VCH Verlag GmbH & Co.
KGaA: Weinheim, Germany, 2010; pp 245ꢀ262.
data of inhibitors 21ꢀ31; crystallographic data collection and
refinement statistics for inhibitor 26. This material is available
free of charge via the Internet at http://pubs.acs.org.
(9) Ghosh, A. K.; Dawson, Z. L.; Mitsuya, H. Darunavir, a Con-
ceptually New HIV-1 Protease Inhibitor for the Treatment of Drug-
Resistant HIV. Bioorg. Med. Chem. Lett. 2007, 15, 7576–7580.
(10) Ghosh, A. K.; Sridhar, P. R.; Leshchenko, S.; Hussain, A. K.; Li,
J.; Kovalevsky, A. Y.; Walters, D. E.; Wedekind, J. E.; Grum-Tokars, V.;
Das, D.; Koh, Y.; Maeda, K.; Gatanaga, H.; Weber, I. T.; Mitsuya, H.
Structure-Based Design of Novel HIV-1 Protease Inhibitors To Combat
Drug Resistance. J. Med. Chem. 2006, 49, 5252–5261.
Accession Codes
†The PDB accession code for 26-bound HIV-1 protease X-ray
structure is 3ST5.
’ AUTHOR INFORMATION
Corresponding Author
*Phone: (765) 494-5323. Fax: (765) 496-1612. E-mail: akghosh@
purdue.edu.
(11) Ghosh, A. K.; Leshchenko-Yashchuk, S.; Anderson, D. D.;
Baldridge, A.; Noetzel, M.; Miller, H. B.; Tie, Y. F.; Wang, Y.-F.; Koh,
Y.; Weber, I. T.; Mitsuya, H. Design of HIV-1 Protease Inhibitors with
5900
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901

Journal of Medicinal Chemistry
ARTICLE
Pyrrolidinones and Oxazolidinones as Novel P10-Ligands To Enhance
Backbone-Binding Interactions with Protease: Synthesis, Biological
Evaluation, and ProteinꢀLigand X-ray Studies. J. Med. Chem. 2009,
52, 3902–3914.
(28) Potterton, E.; Briggs, P.; Turkenburg, M.; Dodson, E. A
Graphical User Interface to the CCP4 Program Suite. Acta Crystallogr.,
Sect. D: Biol. Crystallogr. 2003, 59, 1131–1137.
(29) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr.,
(12) Koh, Y.; Das, D.; Leschenko, S.; Nakata, H.; Ogata-Aoki, H.;
Amano, M.; Nakayama, M.; Ghosh, A. K.; Mitsuya, H. GRL-02031, a
Novel Nonpeptidic Protease Inhibitor (PI) Containing a Stereochemi-
cally Defined Fused Cyclopentanyltetrahydrofuran Potent against Mul-
ti-PI-Resistant Human Immunodeficiency Virus Type 1 in Vitro.
Antimicrob. Agents Chemother. 2009, 53, 997–1006.
Sect. A: Found. Crystallogr. 2008, 64, 112–122.
(30) Sheldrick, G. M.; Schneider, T. R. SHELXL: High Resolution
Refinement. Methods Enzymol. 1997, 277, 319–343.
(31) Emsley, P.; Cowtan, K. Coot: Model-Building Tools for
Molecular Graphics. Acta Crystallogr., Sect. D: Biol. Crystallogr. 2004, 60,
2126–2132.
(13) Deardorff, D. R.; Windham, C. Q.; Craney, C. L. Org. Synth.,
Collect. Vol. 1998, 9, 487.
(14) Ghosh, A. K.; Chapsal, B. D.; Baldridge, A.; Ide, K.; Koh, Y.;
Mitsuya, H. Design and Synthesis of Stereochemically Defined Novel
Spirocyclic P2-Ligands for HIV-1 Protease Inhibitors. Org. Lett. 2008,
10, 5135–5138.
(32) Schuettelkopf, A. W.; van Aalten, D. M. F. PRODRG: A Tool
for High-Throughput Crystallography of ProteinꢀLigand Complexes.
Acta Crystallogr., Sect. D: Biol. Crystallogr. 2004, 60, 1355–1363.
(33) Berman, H. M.; Westbrook, J.; Feng, Z.; Gilliland, G.; Bhat,
T. N.; Weissig, H.; Shindyalov, I. N.; Bourne, P. E. The Protein Data
Bank. Nucleic Acids Res. 2000, 28, 235–242.
(15) Hays, D. S.; Fu, G. C. Organotin Hydride Catalyzed Car-
bonꢀCarbon Bond Formation: Radical-Mediated Reductive Cycliza-
tion of Enals and Enones. J. Org. Chem. 1996, 61, 4–5.
(16) Bueno, J. M.; Coterꢀon, J. M.; Chiara, J. L.; Fernꢀandez-Mayoralas,
A.; Fiandor, J. M.; Valle, N. Stereoselective Synthesis of the Antifungal
GM222712. Tetrahedron Lett. 2000, 41, 4379–4382.
(17) Ghosh, A. K.; Chapsal, B. D.; Baldridge, A.; Steffey, M. P.;
Walters, D. E.; Koh, Y.; Amano, M.; Mitsuya, H. Design and
Synthesis of Potent HIV-1 Protease Inhibitors Incorporating Hex-
ahydrofuropyranol-Derived High Affinity P2 Ligands: Structure
ꢀActivity Studies and Biological Evaluation. J. Med. Chem. 2011,
54, 622–634.
(18) Toth, M. V.; Marshall, G. R. A Simple Continuous Fluorometric
Assay for HIV Protease. Int. J. Pept. Protein Res. 1990, 36, 544–550.
(19) Ghosh, A. K.; Kulkarni, S.; Anderson, D. D.; Hong, L.;
Baldridge, A.; Wang, Y.-F.; Chumanevich, A. A.; Kovalevsky, A. Y.;
Tojo, Y.; Amano, M.; Koh, Y.; Tang, J.; Weber, I. T.; Mitsuya, H. Design,
Synthesis, ProteinꢀLigand X-ray Structure, and Biological Evaluation of
a Series of Novel Macrocyclic Human Immunodeficiency Virus-1
Protease Inhibitors To Combat Drug Resistance. J. Med. Chem. 2009,
52, 7689–7705.
(20) Kovalevsky, A. Y.; Liu, F.; Leshchenko, S.; Ghosh, A. K.; Louis,
J. M.; Harrison, R. W.; Weber, I. T. Ultra-High Resolution Crystal
Structure of HIV-1 Protease Mutant Reveals Two Binding Sites for
Clinical Inhibitor TMC114. J. Mol. Biol. 2006, 363, 161–173.
(21) Gustchina, A.; Sansom, C.; Prevost, M.; Richelle, J.; Wodak,
S. Y.; Wlodawer, A.; Weber, I. T. Energy Calculations and Analysis of
HIV-1 ProteaseꢀInhibitor Crystal Structures. Protein Eng. 1994,
7, 309–316.
(22) Tie, Y.; Boross, P. I.; Wang, Y. F.; Gaddis, L.; Liu, F.; Chen, X.;
Tozser, J.; Harrison, R. W.; Weber, I. T. Molecular Basis for Substrate
Recognition and Drug Resistance from 1.1 to 1.6 Å Resolution Crystal
Structures of HIV-1 Protease Mutants with Substrate Analogs. FEBS J.
2005, 272, 5265–5277.
(23) Mahalingam, B.; Louis, J. M.; Hung, J.; Harrison, R. W.; Weber,
I. T. Structural Implications of Drug-Resistant Mutants of HIV-1
Protease: High Resolution Crystal Structures of the Mutant Protease/
Substrate Analog Complexes. Proteins 2001, 43, 455–464.
(24) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. Macromolecular Crystallography, Part A;
Carter, C. W., Jr., Sweet, R. M., Eds.; Methods in Enzymology, Vol. 276;
Academic Press: San Diego, CA, 1997; pp 307ꢀ326.
(25) Shen, C. H.; Wang, Y. F.; Kovalevasky, A. Y.; Harrison, R. W.;
Weber, I. T. Amprenavir Complexes with HIV-1 Protease and Its Drug-
Resistant Mutants Altering Hydrophobic Clusters. FEBS J. 2010, 277
(18), 3699–3714.
(26) McCoy, A. J.; Grosse-Kunstleve, R. W.; Adams, P. D.; Winn,
M. D.; Storoni, L. C.; Read, R. J. Phaser Crystallographic Software.
J. Appl. Crystallogr. 2007, 40, 658–674.
(27) Collaborative Computational Project, Number 4. The CCP4
Suite: Programs for Protein Crystallography. Acta Crystallogr., Sect. D:
Biol. Crystallogr., 1994, 50, 760ꢀ763.
5901
dx.doi.org/10.1021/jm200649p |J. Med. Chem. 2011, 54, 5890–5901