Hydroxyethylene sulfones as a new scaffold to address aspartic proteases: Design, synthesis, and structural characterization

Article abstract of DOI:10.1021/jm050224y

Hydroxyethylene sulfones were developed as novel scaffolds against aspartyl proteases. A diastereoselective synthesis has been established to introduce the required side chain decoration with desired stereochemistry. Depending on the substitution of the h

Full text of DOI:10.1021/jm050224y

J. Med. Chem. 2005, 48, 6607-6619
6607
Hydroxyethylene Sulfones as a New Scaffold To Address Aspartic Proteases:
Design, Synthesis, and Structural Characterization
Edgar Specker, Jark Bo¨ttcher, Andreas Heine, Christoph A. Sotriffer, Hauke Lilie,† Andreas Schoop,‡
Gerhard Mu¨ller,§ Nils Griebenow,|| and Gerhard Klebe*
Institut fu¨r Pharmazeutische Chemie, Philipps-Universita¨t Marburg, Marbacher Weg 6, D-35032 Marburg, Germany, Institut
fu¨r Biotechnologie, Martin-Luther-Universita¨t Halle-Wittenberg, Kurt-Mothes-Strasse 3, D-06120 Halle (Saale), Germany,
Boehringer Ingelheim, Wien, Austria, Axxima Pharmaceuticals AG, Mu¨nchen, Germany, and Bayer AG, Elberfeld, Germany
Received March 11, 2005
Hydroxyethylene sulfones were developed as novel scaffolds against aspartyl proteases. A
diastereoselective synthesis has been established to introduce the required side chain decoration
with desired stereochemistry. Depending on the substitution of the hydroxyethylene sulfone
core, micro- to submicromolar inhibition of HIV-1 protease is achieved for the S-configuration
at P1 and R-configuration at the hydroxy-group-bearing backbone atom. This stereochemical
preference is consistent with the S,R configuration of amprenavir. The racemic mixture of the
most potent derivative (Ki ) 80 nM) was separated by chiral HPLC, revealing the S,R,S-
enantiomer to be more active (Ki ) 45 nM). Docking studies suggested this isomer as the more
active one. The subsequently determined crystal structure with HIV-1 protease, cocrystallized
from a racemic mixture, exclusively reveals the S,R,S-enantiomer accommodated to the binding
pocket. The transition state mimicking hydroxy group of the inhibitor is centered between
both catalytic aspartates, while either its carbonyl or sulfonyl group forms H-bonds to the
structurally conserved water mediating interactions between ligand and Ile50NH/Ile50NH′ of
both flaps. Biological testing of the stereoisomeric hydroxyethylene sulfones against cathepsin
D and â-secretase did not reveal significant inhibition. Most likely, the latter proteases require
inverted configuration at the hydroxy group.
Introduction
Aspartic acid proteases constitute a therapeutically
relevant class of enzymes that play an important role
in the regulation of various physiological processes, such
as the control of blood pressure (renin),1 digestion
(pepsin),2 or degradation of endocytosed proteins (cathep-
sin D).3 Further, they actively propagate the progression
of severe diseases caused either by parasites, such as
malaria (plasmepsin),4 or viruses, such as HIV (HIV
protease),5 or neurodegenerative disorders including
Figure 1. Examples of transition state isosteres with a
hydroxy group incorporated in stable peptide bond replace-
Alzheimer disease (â-secretase).6 On the basis of the
mechanism of peptide bond hydrolysis employed by
ments.
aspartate proteases, several structurally diverse transi-
encompassing a noncleavable peptide bond replacement
tion state analogues have been designed by replacing
embedded in the corresponding dipeptide mimetic.
the dipeptide-encoded scissile bond within the specific
In the present contribution, we introduce a series of
substrates. A key structural element in most transition
hydroxyethylene sulfones as novel transition state
state isosteres is a hydroxy moiety that interacts with
analogues. The hydroxyethylene sulfones have been
the catalytic site aspartic acid side chains via hydrogen
synthesized and evaluated for their potential to inhibit
bonds. This secondary hydroxy group further replaces
aspartic proteases. The binding mode of one representa-
the catalytic water molecule normally bound between
tive of the series has been crystallographically charac-
both aspartates and simultaneously mimics the tetra-
terized together with HIV-1 protease. The novel lead
hedral geometry that is intermediately formed in the
structural motif has been derived from different scaf-
initial steps of the amide bond hydrolysis of a peptide
folds, already realized in known inhibitors targeting
substrate. Consequently, this type of inhibitor has been
distinct aspartic proteases. The design of the novel
termed collected-substrate inhibitor.7 Figure 1 shows six
structural motif is based on blending structural ele-
well-established examples of transition state isosteres
ments from known inhibitor principles into a novel
structural entity. The hydroxyethylene sulfones can be
traced back to four skeletons found in different aspar-
tate protease inhibitors, as shown in Figure 2.
In comparison to the hydroxyethylene sulfone, the
hydroxyethylamine core of the HIV protease inhibitor
* Corresponding author. Tel: +49 6421 282 1313. Fax: +49 6421
282 8994. E-mail: klebe@mailer.uni-marburg.de.
† Martin-Luther-Universita¨t Halle-Wittenberg.
‡ Boehringer Ingelheim.
§ Axxima Pharmaceuticals AG.
|| Bayer AG.
10.1021/jm050224y CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/16/2005

6608 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21
Specker et al.
Figure 2. Analogy of hydroxyethylene sulfones with the scaffolds of four different aspartic protease inhibitors, 1-4. Functional
groups of the four inhibitors, colored in red, are exchanged with a methylenesulfone moiety, highlighted in red, in the
hydroxyethylene sulfone.
amprenavir (1) is altered by replacing the alkylated
nitrogen atom with a carbon atom, whereas the sulfone
core of the renin inhibitor 2 lacks a substitution in the
R-position as the P1′ portion.8,9 The central scaffolds of
the cathepsin D inhibitor 3 and the â-secretase inhibitor
4 are modified by replacing an amide bond or carbonyl
group, respectively, with a methylenesulfone moiety in
the hydroxyethylene sulfones.10,11
To evaluate the viability of the hydroxyethylene
sulfones as novel scaffold for aspartic acid protease
inhibitors, synthetic procedures for prototype com-
pounds have been established in which the decoration
of the novel core is reminiscent of already optimized side
chains found in inhibitors 1-4 (Figure 2) addressing the
subsites S2 to S2′ flanking the scissile peptide bond. A
further synthetic challenge resulted from the stereo-
chemical control of the three stereocenters contained in
the hydroxyethylene sulfones. A diastereoselective syn-
thesis is described to introduce the desired relative
configuration of the stereocenters.
Chemistry
Scheme 1 illustrates the procedure to synthesize
aldehyde 9 as a precursor to address P1. Reaction of
3-bromobenzyl bromide with deprotonated acetamido-
malonic acid diethyl ester resulted in the formation of
the substituted malonic acid diethyl ester 5. Decarboxy-
lation of 5 with HCl to the nonnatural amino acid 6 was
followed by protection with the Boc group to 7. N-
Protected 7 was activated as an anhydride for the
reduction with NaBH4 to yield the primary alcohol 8.12
Swern oxidation afforded the racemic aldehyde 9 with
an overall yield of 49%.13
In Scheme 2 the generation of the methanesulfonates
13a-c is outlined. To decorate the inhibitor core frag-
ment, shown in Figure 2 with different side chains R1
to address the distinct S1′ subsites of the three aspartic
proteases HIV protease, cathepsin D and â-secretase,
three methyl ketones with distinct substitution [R1 )
acetone, 4-methylpentan-2-one, 4-(2,4-dichlorophenyl)-

Hydroxyethylene Sulfones as a Novel Scaffold
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21 6609
Scheme 1a
a (a) NaOEt/EtOH, (b) concd HCl, (c) (Boc)2O, NEt3, (d) ClCOOMe, NEt3, NaBH4, (e) (COCl)2, DMSO, NEt3.
Scheme 2a
a (a) LDA, -78 °C, (b) BBu3, rt, 2 h; -78 °C, NaBH4, (c) NaH, THF, (d) NEt3, ClSO2CH3.
butane-2-one] were applied. The action of LDA afforded
the lithiumenolates that preferentially added to the less
hindered diastereotopic face of the nonchelated aldehyde
carbonyl 9 to give rac-(S,R)-anti-â-hydroxy ketones
S2 subsite followed by oxidation of the corresponding
sulfides with m-chloroperoxybenzoic acid (mCPBA)
revealed the desired final products 17 and 18 (Table 2)
with rac-(S,R,S) configuration. Introduction of one
further orthogonal functionality was possible through
nucleophilic substitution of the fluorine atom in 18a and
18b with amines or by the replacement of the aromatic
bromine with palladium chemistry.
To examine whether the correct rac-(S,R,S) stereo-
chemistry is produced, the thioether 14c was oxidized
with mCPBA to the corresponding sulfone 19 prior to
the cleavage of the oxazolidinone (Figure 3). Crystal
structure analysis of 19 revealed that the desired
racemate was obtained.
Biological Testing of HIV-1 Protease Inhibition.
Compounds 17 and 18 were tested against HIV-1
protease inhibition, because their S-configuration at the
P1 site and R-configuration at the hydroxy group are
consistent with the S,R-configuration of the HIV-1
protease inhibitor amprenavir (1). Additionally, Vazquez
10a-c following the model of Felkin and Anh.14,15
A
diastereoselective 1,3 asymmetric induction has been
achieved by the syn-selective reduction of 10a-c to rac-
(S,R,R)-11a-c 1,3-diols via boron chelates.16 Treatment
with NaH proceeded via an intramolecular cyclization
to oxazolidinones 12a-c followed by mesylation to
methanesulfonates 13a-c.
The introduction of side chains to address the S2 and
S2′ subsites is described in Scheme 3. Upon treatment
of 13a-c with distinct thiolates (R2) for addressing the
S2′ subsite (3-methylbutane-1-thiolate for 13a and 4-flu-
orothiophenolate for 13b-c), SN2 substitution took place
by inversion of the configuration to thioethers 14a-c.
Cleavage of the oxazolidinone with Ba(OH)2 led to the
â-amino alcohols 15a-c. Coupling 15a-c with distinct
carboxylic acids to 16a-e (Table 1) for addressing the

6610 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21
Specker et al.
Scheme 3a
a (a) NaH, HSR2, (b) Ba(OH)2, (c) EDC, R3COOH, (d) mCPBA, reflux, (e) HNMeR4, THF, 160°C, 2 bar.
Table 1. Decorations of 16a-e
et al. confirmed for a series of HIV-1 protease inhibitors
containing the hydroxyethylsulfonamide isostere the
preference for the S,R-configuration of these stereo-
centers.17
Inhibition constants were determined using a stan-
dard assay wherein the initial rate of enzymatic cleav-
age of the synthetic, fluorophore-labeled substrate Abz-
Thr-Ile-p-nitrophenylalanine-Phe-Gln-Arg-NH2 was mea-
sured in the presence of varying concentrations of
inhibitors 17 and 18. Ki and IC50 values are presented
in Table 3.
The most potent inhibitor in the series is 17b. It is
decorated with similar side chains as the HIV-1 protease
inhibitor amprenavir (1), addressing the S1, S1′ and S2′
pockets of the enzyme. To replace the tetrahydrofuranyl
group in 1, the 2,6-dimethylphenoxy fragment was
introduced as an achiral and specifically optimized P2
residue for HIV-1 protease.18 The reduced affinity for
17c-e is not surprising, since the decorations tested
were originally optimized for cathepsin D. Facing the
biological data of 17b and 17c, a drop in affinity by a
factor of about 100 is indicated. We explain this differ-

Hydroxyethylene Sulfones as a Novel Scaffold
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21 6611
Table 2. Decorations of the Hydroxyethylene Sulfones
ence by the fact that the decoration of 17c at P1 is too
large to optimally fill the S1 pocket of the protease. The
dichlorophenethyl moiety is significantly larger than
any side chain found in one of the peptidic substrates
recognized at the cleavage site. Nucleophilic substitution
of the fluorine atom in 17b by methylamine and
dimethylamine groups provided inhibitors 18a,b, which,
however, exhibit lower affinities toward HIV-1 protease.
Compound 17a, decorated with alkyl groups, taken from
the â-secretase inhibitor 4 as reference, did not show
any affinity toward HIV-1 protease.
To verify whether any of the distinct stereosisomers
shows deviating affinity toward HIV-1 protease, the
racemic mixture of 17b and the diastereomers of 17e
were separated via chiral HPLC. The absolute stereo-
chemistry of the S,R,S-enantiomer of 17b was deter-
mined by cocrystallization in complex with HIV-1
protease. The stereochemistry of 17e isomers was
assigned accordingly. Table 4 shows the Ki and IC50
values of the stereochemically pure forms of 17b and
17e.
of 17e, a higher affinity was observed compared to the
((2R),1R,2S,4R)-stereoisomer.
Modeling and Crystal Structure Analysis. To
rationalize these observations, prior to successful crys-
tallization and structure determination, a modeling
study has been performed, using AutoDock for docking
and DrugScore for scoring.19-22 Both enantiomers of 17b
were flexibly docked to HIV-1 protease, using the
complex structure with amprenavir (1) (PDB code 1hpv)
as reference.8 Docking of the S,R,S-enantiomer of 17b
suggested as top-ranked solution a binding mode in
excellent agreement with the experimentally deter-
mined binding mode of 1, as illustrated in Figure 4.
In contrast to the S,R,S-enantiomer, the R,S,R-
enantiomer of 17b achieved no such reasonable binding
modes upon docking, properly addressing the catalytic
dyad. In addition, the average docking scores for these
docking solutions were significantly less favorable for
the latter enantiomer. Nevertheless, the best scored
docking solution exhibits a fair overlap with the side
chains of amprenavir. To assess the reliability of the
applied docking protocol, amprenavir (1) was redocked
into HIV-1 protease. The top-ranked docking solution
showed virtually perfect overlap with the crystallo-
graphically determined binding mode (rmsd ) 0.99 Å).
After the modeling studies, we succeeded in cocrys-
tallizing 17b with HIV-1 protease. A racemic mixture
The results show that the enantiomer with the same
S-configuration at P1, as present in the natural amino
acids, and the R-configuration at the hydroxy group
(similar to the S,R-configuration in 1) exhibits a sig-
nificantly higher affinity compared to the R,S-enanti-
omer of 17e. Also for the ((2R),1S,2R,4S)-stereoisomer

6612 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21
Specker et al.
Figure 3. Crystal structure of the R,S,R-enantiomer of 19.
Table 3. Ki and IC50 Values of Several Racemic
Hydroxyethylene Sulfones for HIV-1 Protease Inhibition
Ki
(µM)
IC50
(µM)
Ki
(µM)
IC50
(µM)
compd
compd
17a
17b
17c
17d
>40
0.08
7.0
>40
0.14
10
17e
18a
18b
3.9
0.37
0.54
5.6
0.53
0.79
3.1
4.5
Table 4. Ki and IC50 Values of Resolved Stereoisomers of 17b
and 17e toward HIV-1 Protease
stereoisomers of
17b and 17e
Ki (µM)
IC50 (µM)
S,R,S-17b
0.045
1.4
0.085
2
R,S,R-17b
((2R),1S,2R,4S)-17e
((2R),1R,2S,4R)-17e
2.9
4.2
Figure 4. Predicted binding mode of S,R,S-17b in the binding
pocket of HIV-1 protease, as suggested by docking. The ligand
is color-coded by atom types and superimposed with the
experimentally determined binding mode of amprenavir (1)
(PDB ID 1hpv), shown in green. The protein backbone trace
is schematically illustrated, and the catalytic aspartic acids
and Asp30 are displayed in pink.
>40
>40
of 17b was added to the crystallization buffer. In
agreement with the predictions of modeling, the crystal
structure shows that the S,R,S-enantiomer exhibits
better binding to the protein. Exclusively, this stereo-
isomer is found in the binding site of HIV-1 protease
(Figure 5). Figure 6 shows the superposition of S,R,S-
17b with amprenavir (1) in the corresponding complex.
Both inhibitors bind with their central hydroxy groups
centered between the two aspartates, and both the
carbonyl and sulfonyl groups form hydrogen bonds to
the structural water which mediates interactions be-
tween bound ligand and Ile50NH or Ile50NH′ in the flap
region. With respect to the previously solved complex
structure of amprenavir (PDB code 1hpv), the protease
adopts a very similar conformation in the complex with
S,R,S-17b (rmsd ) 0.78 Å). No remarkable induced-fit
adaptations are observed. As expected, the inhibitor
occupies the four specificity pockets of the protease. Its
bromobenzyl moiety is found in the S1 pocket. It adopts
a nearly identical binding mode as the phenylalanine
side chain in amprenavir. The additional bulky m-bromo
substitutent is oriented toward the adjacent solvent
environment and thus does not provoke any induced-
fit adaptations. However, in the adopted binding mode
it remains partially exposed to solvent. This might be
to some degree detrimental to binding affinity due to
unsatisfactory burial of the hydrophobic bromo group.
The S2′ pocket accommodates the p-fluorophenyl group
of S,R,S-17b. It is found in very similar geometry as
the p-aminophenyl group of amprenavir. Different to the
latter, S,R,S-17b cannot form a similar hydrogen bond
to the carboxy group of Asp30. Supposedly, this differ-
ence also contributes to the slightly reduced affinity of

Hydroxyethylene Sulfones as a Novel Scaffold
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21 6613
Biological Evaluation for Cathepsin D and
â-Secretase
Although compounds 17a and 17c-e were decorated
with side chains that are also present in potent inhibi-
tors of cathepsin D and â-secretase, no inhibition could
be detected in cathepsin D nor in â-secretase assays.
The lack of affinity might be explained by the unfavor-
able S,R,S- and R,S,R-configurations of the stereo-
centers in the hydroxyethylene sulfones for cathepsin
D and â-secretase. In comparison to the more favorable
S,R-configurations, realized in the HIV-1 protease
inhibitor amprenavir 1, Baldwin et al.23 solved the
crystal structure of cathepsin D in complex with the
oligopeptide pepstatin (Ki ) 3.8 pM). The latter inhibitor
bears a statine core with S,S-configuration, whereas the
S,R-stereoisomer turned out to be a much weaker
inhibitor.24 In addition, Lee et al.10 reported for 3 (Figure
2) that the diastereomer with the nonnatural R-config-
uration at the P1 site together with an S-configuration
at the hydroxy group did not inhibit cathepsin D. In
contrast, the S,S configuration in 3 revealed inhibition
with a Ki of 0.7 nM. The â-secretase inhibitor 4 and
related active derivatives also possess a hydroxyethyl-
ene core solely with S-configuration at P1 and S-
configuration at the hydroxy group.11
Figure 5. Crystal structure of S,R,S-17b in complex with
HIV-1 protease. The protein backbone trace is schematically
illustrated in gray and the catalytic aspartic acids are pink,
whereas the isoleucines 50 and 50′ of the flaps are displayed
in salmon. The 2Fo - Fc density for the ligand and the
structural water is displayed in blue at a σ level of 1.0.
Future work will be focused on an aldole reaction with
aldehyde 9 under chelate control, following methods
described by Kempf or Reetz,25,26 to invert the stereo-
centers to produce the obviously more favorable S,S-
configuration for cathepsin D and â-secretase inhibition.
Summary and Conclusion
Hydroxyethylene sulfones have been developed as a
new, privileged skeleton to address the target family-
wide commonality of aspartic acid proteases in substrate
binding and processing. The novel motif for a transition
state analogue has been derived from four different
scaffolds already present in known aspartic protease
inhibitors. It is ideally suited for subsequent decoration
with appropriate side chain substitutions to address the
structurally distinct specificity pockets in various mem-
bers of the aspartic proteases family. A synthesis
strategy has been established that allows stereochemical
control of three stereocenters introduced into the hy-
droxysulfones. The actually produced stereochemistry
has been confirmed by crystal structure analysis of one
final product. Enzyme kinetics revealed submicro- to
micromolar inhibition of HIV protease by the racemic
products. Docking of both enantiomeric forms of the
most potent inhibitor suggested the S,R,S-enantiomer
to be of higher affinity. Testing of the enantiomerically
pure form separated by chromatography proves the
latter enantiomer to be significantly more potent (Table
4). X-ray structure analysis of crystals prepared from a
racemic mixture of the best lead compound together
with HIV-1 protease confirms the stereochemistry and
the binding mode suggested by docking. Even though a
new stereocenter is created at the position next to the
SO2 group, the attached isobutyl substituent shows very
similar occupation of the S1′ pocket. The observed
reduced affinity of our best lead compound compared
to amprenavir can be explained by the unsatisfactory
desolvation of a hydrophobic bromo substituent in S1
and the fact that the p-fluorophenyl compared to the
Figure 6. Crystal structure of S,R,S-17b in complex with
HIV-1 protease (colored in green) superimposed with the
corresponding crystal structure of amprenavir (1) (PDB ID
1hpv) shown in gray. The protein backbones trace, the catalytic
aspartic acids, and Asp30 are illustrated in the corresponding
colors.
S,R,S-17b compared to 1. In both complexes the isobu-
tyl groups of the inhibitors attached either to the amino
group of 1 or to the methylenesulfone group of S,R,S-
17b fill the S1′ subsite in very similar fashion. This fact
explains the, on a first glance, surprising similarity of
this side chain, even though attached with different
stereochemistry to the ligand skeleton. The largest
difference is observed for the occupancy of the S2 pocket.
While amprenavir exhibits a terminal tetrahydrofuran
moiety, S,R,S-17b has been decorated by an achiral 2,6-
dimethylphenoxy moiety. The latter extends deeper into
this subsite and achieves nearly optimal filling of the
pocket. In a direct comparison, both moieties adopt an
opposing orientation in the S2 subsite. At its far end,
the dimethylphenoxy group of S,R,S-17b reaches the
surrounding solvent environment.
In summary, S,R,S-17b adopts the expected binding
mode. The reduced binding affinity compared to 1
possibly arises from either the unsatisfactory burial of
the bromo substituent or the lack of a hydrogen bond
to the carboxy group of Asp30. Further optimization of
S,R,S-17b will consider these aspects in future design
attempts.

6614 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21
Specker et al.
Table 5. Crystal Data of S,R,S-17b Complexed with HIV-1
p-aminophenyl group in amprenavir cannot form a
strong hydrogen bond to the adjacent carboxylate of Asp
30. Biological testing of the synthesized stereoisomers
with respect to cathepsin D and â-secretase did not
reveal satisfactory binding. Most likely, the latter
proteases require inverted configuration at the hydroxy
group in the portion mimicking the geometry of the
transition state. Similar observations have been de-
scribed for other series of aspartic protease inhibitors.
This discrimination due to inverted stereochemistry at
the central privileged scaffold can be exploited to achieve
the desired selectivity toward different members of the
aspartic protease family.
Protease
S,R,S-17b-HIV-1 protease
resolution (Å)
space group
cell dimensions
(Å)
25-1.73
P21212
a ) 57.9
b ) 85.8
c ) 46.8
1.76-1.73
101892
24462
highest resolution shell (Å)
no. of measured reflections
no. of independent reflections
completeness (%)
I/σ
Rsym (%)
refined residues
refined ligand atoms
refined water molecules
refined chlorids
97.6 [79.2]a
12.8 [1.7]
7.8 [45.2]
198
40
Material and Methods
207
3
Kinetic Assay. Inhibition data for HIV protease were
determined as follows. IC50 values were taken from plots of
Vi/V0 vs inhibitor concentration, where Vi and V0 are the
catalytic rates in the presence or absence of the inhibitor. The
fluorogenic substrate Abz-Thr-Ile-p-nitrophenylalanine-Phe-
Gln-Arg-NH2 was purchased from Bachem. To convert IC50
values to Ki values, the following equation was applied:
resolution in refinement (Å)
Rcryst (F > 4σFo; Fo)
Rfree(F > 4σFo; Fo)
mean B-factor (Å2)
(peptide chain A; B)
main chain (Å2)
8-1.73
16.7; 20.1
21.0; 24.7
17.2; 14.6
12.8; 11.4
22.1; 18.0
23.0
28.1
18.27
side chains (Å2)
ligand (Å2)
water (Å2)
Ki ) [IC50 - (Et/2)][1 + (S/Km)]-1
Cl ions (Å2)
Ramachandran plot
most favorite geometry (%)
additionally allowed (%)
generously allowed (%)
disallowed (%)
where Et is the total enzyme concentration (40 nM), Km the
Michaelis-Menten constant (39 µM), and S the substrate
concentration (20 µM). Recombinant HIV-1 protease was
expressed from Escherichia coli and purified as previously
described.27 Enzymatic assays were performed in 402.2 µL
assay buffer (100 mM MES, 300 mM KCl, 5 mM EDTA, 1 mg/
mL BSA, pH 5.5) by addition of substrate dissolved in 8.4 µL
DMSO, and distinct inhibitor concentrations were dissolved
in 8.4 µL DMSO and 1 µL HIV-1 protease to a final volume of
420 µL (final DMSO concentration 4%). The hydrolysis of the
substrate was recorded as an increase of the fluorescence
intensity (extinction wavelength 337 nm, emission wavelength
410 nm) over a 10-min time period, during which the rate
increased in a linear fashion with time.28
Computational Docking. Docking was carried out using
version 3.0 of the program AutoDock.20,21 Instead of the
implemented AutoDock scoring function, DrugScore was used
for calculating the required grids and for scoring, as previously
described.19,22 The Lamarckian genetic algorithm was applied,
following a standard protocol of 10 independent runs per ligand
with an initial population of 50 randomly placed individuals,
a maximum number of 1.5 × 106 energy evaluations, a
mutation rate of 0.02, a crossover rate of 0.80, and an elitism
value of 1. The probability of performing local searches on an
individual in the population was 0.06, using a maximum of
300 iterations per local search.
95.6
4.4
0
0
a Values in brackets refer to the shell of highest resolution.
ture was determined by the molecular replacement method
with AmoRe,30 and the 1.79 Å structure of the HIV-1 protease
in complex with the inhibitor Bea403 (PDB code 1EC0)31 was
used as the search model. Refinement was continued with
SHELXL-97;32 for each refinement step at least 10 cycles of
conjugate gradient minimization were performed, with re-
straints on bond distances, angles, and B-values. Intermittent
cycles of model building were done with the program O.33 The
coordinates have been deposited in the PDB (http://www.
rcsb.org/pdb/) with access code 1XL5.
Crystal Structure Determination of 19: C26H23BrCl2-
FNO4S, Mr ) 615.32, monoclinic space group C2/c, a ) 34.013
(2) Å, b ) 5.800 (1) Å, c ) 26.610 (1) Å, â ) 101.98 (1)°, V )
5134.9 (5) Å3, Z ) 8, dcalc ) 1.592 Mg m-3, F(000) ) 2496, λ )
0.71073 Å, T ) 153 K, µ(Mo KR) ) 1.93 mm-1. Data were
collected on a CAD4 diffractometer, and intensities on a cooled
crystal (dimensions 0.01 × 0.03 × 0.4 mm) were collected at
153(2) K in the θ range 1.22-30.63°. Of a total of 22 554
reflections, 7835 were independent with Rint ) 0.077; R1
)
The coordinates of HIV protease in complex with am-
prenavir (1) (PDB code 1hpv) were used as reference in
docking.7 Ligand and solvent molecules were removed from
the PDB file and DrugScore grids (16 Å × 14 Å × 22 Å, with
1 Å grid spacing) were calculated using AutoDock, as de-
scribed.22 Ligand structures were constructed with Sybyl and
set up for flexible docking using AutoTors, with 13 rotatable
bonds for both enantiomers of 17b and 12 for 1.
Crystal Structure Analyses: Crystallization and Struc-
ture Determination of S,R,S-17b with HIV Protease. The
HIV protease (7 mg/mL) in complex with the hydroxyethylene
sulfone crystallizes at 18 °C in 2.7 M NaCl, 0.1 M BisTris, pH
6.5 in space group P21212 (crystal data, Table 5). The crystals
were obtained by cocrystallization of the enzyme with the
inhibitor at 1.9 mmol/L. For cryoprotection, the crystals were
briefly soaked in mother liquor containing 20% glycerol. The
data set was collected at the synchrotron BESSYII in Berlin
on PSF beamline I equipped with a MAR-CCD detector. In
total, 221 frames with δæ ) 0.5° at a crystal to detector
distance of 120 mm were collected at -170 °C. Data were
processed and scaled with Denzo and Scalepack.29 The struc-
0.043, and wR2 ) 0.0892 (I > 2 σ(I)), with largest difference
maximum and minimum being 0.58 and -0.87 e Å-3, respec-
tively. Further details of the crystal structure determination
are available upon request from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK, on quoting the full journal citation and the deposition
number CCDC 256954.
Analytic Part. 1H and 13C NMR spectra were recorded on
a JEOL Eclipse + 500 instrument, using DMSO-d6 or CDCl3
with TMS as internal standard. Chemical shifts are given in
ppm (δ scale). Reactions were monitored by thin-layer chro-
matography (TLC) on precoated Alugram SIL G/UV plates
from Macherey-Nagel, and spots were visualized with UV light
or with a mixture of 6 g of molybdatophosphoric acid, 2.5 g of
cerium(IV) sulfate, 470 mL of water, and 30 mL of concen-
trated H2SO4. Flash column chromatography was performed
using silica gel (particle size 0.040-0.063 mm) supplied by
Merck. Diethyl ether and THF were freshly distilled from
LiAlH4 under argon. Triethylamine, N,N-dimethylformamide
(DMF), and dichloromethane were purchased from Aldrich and
used without purification. High-resolution mass spectra (HRMS,

Hydroxyethylene Sulfones as a Novel Scaffold
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21 6615
EI and ESI) were performed on either a Micromass 7070 H or
a Micromass Autospec spectrometer. Analytical high perfor-
mance liquid chromatography (HPLC) was carried out with a
KROMASIL 100 column, type 1050 from Hewlett-Packard,
C18/3.5 µm, 125.3 mm. Chiral resolution using preparative
HPLC was achieved with a Semiprep HPLC of Shimadzu
(column, Daicel Chiralcel OD, 30 cm length; injector, SIL-10
AD-VP). Elemental analyses were performed on a Charm-
homat 5-ADG from Wo¨sthoff or HP-185. The HIV-1 protease
assay was performed on a RF-5301 PC spectrofluorophotom-
eter by Shimadzu.
Synthesis. rac-2-Acetylamino-2-(3-bromobenzyl)ma-
lonic Acid Diethyl Ester (5). To a solution of 2-acetylami-
nomalonic acid diethyl ester (86.9 g, 0.4 mol) and NaEtOAc
(27.2 g, 0.4 mol) in 1.2 L of EtOH was added 1-bromo-3-
bromomethylbenzene (100 g, 0.4 mol) in dropwise fashion.
After being stirred under reflux for 5 h, the solution was
evaporated under reduced pressure and the crude product was
recrystallized in MeOH to give 113 g of 5 (75%) as a white
solid. 1H NMR (δ/ppm, 500 MHz, CDCl3): 1.30 (t, J ) 7.1 Hz,
6H), 2.05 (s, 3H), 3.62 (s, 2H), 4.28 (q, J ) 7.1 Hz), 6.56 (s,
1H), 6.94 (d, J ) 7.7 Hz, 1H), 7.14 (t, J ) 7.8 Hz, 1H), 7.17
(m, 1H), 7.34 (d, J ) 7.7 Hz, 1H). 13C NMR (δ/ppm, 125 MHz,
CDCl3): 14.0, 23.0, 37.4, 62.8, 67.1, 122.3, 128.5, 129.8, 130.3,
132.9, 137.6, 167.3, 169.2. Anal. C16H20BrNO5: C, H, N.
brine. The organic layer was dried (MgSO4), filtered, and
concentrated. Column chromatography (cyclohexane/EtOAc
3:1) of the residue provided 9.59 g (29 mmol, 96%) of 9 as a
white solid: 1H NMR (δ/ppm, 500 MHz, CDCl3): 1.45 (s, 9H),
3.05 (dd, J ) 14.1, 6.7 Hz, 2H), 3.14 (dd, J ) 14.1, 6.4 Hz,
2H), 4.39 (m, 1H), 5.08 (d, J ) 5.6 Hz, 1H), 7.10 (d, J ) 7.7
Hz, 1H), 7.19 (t, J ) 7.8 Hz, 1H), 7.33 (s, 1H), 7.64 (d, J ) 7.8
Hz, 1H). 13C NMR (δ/ppm, 125 MHz, CDCl3): 28.6, 35.3, 61.0,
80.8, 123.1, 128.3, 130.6, 130.6, 132.8, 138.6, 155.6, 199.1.
Anal. C14H18BrNO3: C, H, N.
rac-(1S,2R)-[1-(Bromobenzyl)-2-hydroxy-4-oxopentyl]-
carbamic Acid tert-Butyl Ester (10a). To a solution of LDA
(54 mL, 1 M in THF) in 100 mL of anhydrous THF at -78 °C
was added acetone (1.22 g, 21 mmol) dropwise. After being
stirred for 30 min at -78 °C, the solution was treated by
dropwise addition of 9 (6.9 g, 21 mmol) solved in 200 mL of
THF at -78 °C. The reaction mixture was warmed to room
temperature and quenched with 300 mL of saturated NH4Cl.
The solution was extracted with CH2Cl2 (3 × 100 mL), dried
over MgSO4, and evaporated under reduced pressure. The
diastereomeric mixture (de ) 92:8 determined by HPLC) could
be purified by column chromatography (cyclohexane/EtOAc
1:1) to give the rac-(S,R)-isomers of 10a (4.25 g, 52%). 1H NMR
(δ/ppm, 500 MHz, DMSO-d6): 1.39 (m, 9H), 2.01 (s, 3H), 2.50
(m, 3H), 3.01 (dd, J ) 13.7, 3.2 Hz, 1H), 3.45 (m, 1H), 3.82 (m,
1H), 4.98 (d, J ) 6.6 Hz, 1H), 6.65 (d, J ) 9.6 Hz, 1H) 7.19 (m,
2H), 7.33 (d, J ) 3.3 Hz, 1H), 7.38 (s, 1H). 13C NMR (δ/ppm,
125 MHz, DMSO-d6): 28.7, 31.1, 36.3, 48.8, 57.2, 70.3, 78.1,
121.8, 128.2, 128.4, 129.8, 131.8, 143.8, 155.8, 208.1. Anal.
C17H24BrNO4: C, H, N.
rac-[3-(3-Bromophenyl)-2-tert-butoxycarbonylamino-
propionic Acid (7). To a solution of 5 (113 g, 0.30 mol) in
900 mL of HCl was added 300 mL of acetic acid, and the
reaction mixture was stirred under reflux for 16 h. The mixture
was cooled to room temperature and the pH was adjusted to
6 by addition of 800 mL of NaOH. The product 6 was filtrated
and dried under reduced pressure. The crude material was
dissolved in 500 mL of 5% NaHCO3, and 67 g of Boc2O (0.30
mol) dissolved in 300 mL of dioxane was added in one portion.
After being stirred for 3 h at room temperature, the solution
was acidified with 2 N HCl to a pH of 2. The reaction mixture
was extracted with Et2O (3 × 300 mL). The combined organic
layer was dried (MgSO4) and evaporated to give 72 g of 7 (70%)
rac-(1S,2R)-[1-(Bromobenzyl)-2-hydroxy-6-methyl-4-
oxoheptyl]carbamic Acid tert-Butyl Ester (10b) was
prepared analogously to 10a using 4-methylpentan-2-one as
alkyl methyl ketone (2.1 g, 21 mmol) with 57% yield (de )
94:6). 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.86 (d, J ) 6.7
Hz, 6H), 1.22 (m, 9H), 1.98 (m, 1H), 2.28 (m, 2H), 2.47 (m,
3H), 2.98 (dd, J ) 13.9, 3.2 Hz, 1H), 3.42 (m, 1H), 3.79 (m,
1H), 5.03 (d, J ) 6.7 Hz, 1H), 6.64 (d, J ) 9.6 Hz, 1H), 7.19
(m, 2H), 7.32 (m, 1H), 7.37 (s, 1H). 13C NMR (δ/ppm, 125 MHz,
DMSO-d6): 22.3, 23.6, 28.1, 35.6, 47.6, 51.6, 56.5, 69.6, 77.4,
121.2, 128.2, 128.4, 129.8, 131.8, 142.5, 155.2, 209.0. Anal.
C20H30BrNO4: C, H, N.
1
as a white foam. H NMR (δ/ppm, 500 MHz, CDCl3): 1.42 (s,
9H), 3.02 (dd, J ) 13.4, 6.7 Hz, 1H), 3.18 (dd, J ) 13.6, 5.0
Hz, 1H), 4.59 (m, 1H), 5.03 (d, J ) 8.0 Hz, 1H), 7.13 (d, J )
7.7 Hz, 1H), 7.17 (t, J ) 7.7 Hz, 1H), 7.34 (s, 1H), 7.39 (d, J )
7.7 Hz, 1H). 13C NMR (δ/ppm, 125 MHz, CDCl3): 28.3, 37.5,
54.2, 80.5, 122.5, 128.0, 130.1, 130.2, 132.5, 138.3, 155.3, 175.8.
Anal. C14H18BrNO4: C, H, N.
rac-(1S,2R)-[1-(Bromobenzyl)-6-[2,4-dichlorophenyl)-
2-hydroxy-4-oxohexyl]carbamic Acid tert-Butyl Ester
(10c) was synthesized following the above procedure in
analogy to 10a by addition of 4-(2,4-dichlorophenyl)butan-2-
rac-[2-(3-Bromophenyl)-1-hydroxymethylethyl]carbam-
ic Acid tert-Butyl Ester (8). To a cold (-15 °C) solution of 7
(15.9 g, 69.1 mmol) in 400 mL of THF were added N-
methylmorpholine (7.67 mL, 69.1 mmol) and isobutyl chloro-
formate (9.39 mL, 69.1 mmol) successively. The precipitated
N-methylmorpholine hydrochloride was removed by filtration
and washed with THF (3 × 50 mL). The combined organic
layers were cooled to 0 °C, and sodium borohydride (3.9 g, 103
mmol) was added sequentially. The reaction mixture was
quenched with 400 mL of water and extracted with EtOAc (3
× 100 mL). The solution was dried over MgSO4, filtrated,
evaporated under reduced pressure, and purified by recrys-
tallization with EtOAc to provide 8 (22.3 g, 98%) as a white
solid: 1H NMR (δ/ppm, 500 MHz, CDCl3): 1.42 (s, 9H), 2.82
(m, 2H), 3.56 (dd, J ) 10.9, 5.0 Hz, 1H), 3.67 (dd, J ) 11.0,
3.8 Hz, 1H), 3.83 (m, 1H), 4.78 (d, J ) 8.1 Hz, 1H), 7.18 (m,
2H), 7.36 (m, 2H). 13C NMR (δ/ppm, 125 MHz, CDCl3): 28.7,
37.4, 53.9, 64.4, 80.3, 122.4, 128.3, 130.1, 130.5, 132.7, 140.7,
155.1. Anal. C14H20BrNO3: C, H, N.
rac-[2-(Bromophenyl)-1-formylethyl]carbamic Acid tert-
Butyl Ester (9). To a solution of oxalyl chloride (5.7 g, 45
mmol, 1.5 equiv) in 100 mL of CH2Cl2 at -78 °C was added
7.02 g DMSO (90 mmol, 3 equiv) under argon in a dropwise
fashion. The reaction mixture was stirred for 30 min by
dropwise addition of 8 (10 g, 300 mmol) solved in 400 mL of
CH2Cl2. The reaction was kept at -78 °C for 30 min, and TEA
(23.3 g, 0.18 mol, 6 equiv) was added subsequently. The
reaction was allowed to warm to room temperature and
washed sequentially with 1 N HCl, saturated NaHCO3, and
1
one (4.55 g, 21 mmol) in 80% yield (de ) 94:6). H NMR (δ/
ppm, 500 MHz, CDCl3): 1.25 (s, 9H), 2.51 (m, 3H), 2.78 (m,
2H), 2.85 (m, 2H), 3.00 (m, 1H), 3.45 (m, 1H), 3.83 (m, 1H),
5.06 (d, J ) 6.6 Hz, 1H), 6.69 (d, J ) 9.5 Hz, 1H), 7.20 (m,
2H), 7.36 (m, 4H), 7.57 (s, 1H). 13C NMR (δ/ppm, 125 MHz,
CDCl3): 26.1, 28.0, 35.6, 41.8, 47.3, 56.6, 69.7, 77.4, 121.4,
127.2, 128.2, 128.4, 128.4, 129.9, 131.3, 131.7, 131.8, 133.7,
137.6, 142.4, 155.2, 208.1. Anal. C24H28BrCl2NO4: C, H, N.
rac-(1S,2R,4R)-[1-(3-Bromobenzyl)-2,4-dihydroxypen-
tyl]carbamic Acid tert-Butyl Ester (11a). A THF (200 mL)
solution of tributylborane (2 g, 11 mmol) and 10a (3.86 g, 10
mmol) was stirred for 2 h at room temperature under argon
atmosphere. Subsequently, the solution was cooled to -78 °C,
and solid NaBH4 (440 mg, 11 mmol) was added in one portion.
It was essential for the asymmetric reduction to stir the
reaction mixture at -78 °C for at least 7 h. The solution was
quenched with a mixture of 30% H2O2 (50 mL), Na2HPO4/
NaH2PO4 buffer (pH 7, 100 mL), and MeOH (150 mL). The
organic solvent was evaporated under reduced pressure and
the residual solution was extracted with CH2Cl2 (3 × 100 mL).
The combined organic layers were dried over MgSO4 and
condensed in vacuo. To decompose the remaining boronic acid
ester, 40 mL of 1% HCl in MeOH was added, and the solution
was stirred at room temperature overnight, evaporated (de )
99:1 determined by HPLC), and flash chromatographed on
silica gel (cyclohexane/EtOAc 1:1) to give rac-(S,R,R)-11a
(2.87 g, 74%). 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.06 (d,
J ) 6.1 Hz, 3H), 1.29 (m, 9H), 1.49 (m, 1H), 2.50 (m, 1H), 2.99

6616 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21
Specker et al.
(dd, J ) 13.9, 2.0 Hz, 1H), 3.48 (m, 2H), 3.82 (m, 1H), 4.53 (d,
J ) 4.1 Hz, 1H), 4.78 (d, J ) 4.8 Hz, 1H), 6.58 (d, J ) 8.7 Hz,
1H), 7.19 (m, 2H), 7.34 (d, J ) 3.3 Hz, 1H), 7.38 (s, 1H). 13C
NMR (δ/ppm, 125 MHz, DMSO-d6): 23.3, 28.1, 35.5, 42.6, 56.6,
64.9, 71.5, 77.3, 121.2, 128.2, 128.4, 129.8, 131.8, 142.7, 155.2.
HRMS (ESI) m/z: C17H27BrNO4 (MH+) calcd, 388.1123, found,
388.1143.
rac-(1S,2R,4R)-[1-(3-Bromobenzyl)-2,4-dihydroxy-6-
methylheptyl]carbamic Acid tert-Butyl Ester (11b) was
obtained in same manner as 11a with 70% yield (de ) 99:1).
1H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.86 (m, 6H), 1.24 (m,
2H), 1.24 (m, 9H), 1.36 (m, 1H), 1.39 (m, 1H), 1.75 (m, 1H),
2.50 (m, 1H), 2.98 (dd, J ) 13.8, 3.1 Hz, 1H), 3.47 (m, 1H),
3.47 (m, 1H), 3.68 (m, 1H), 4.46 (d, J ) 5.0 Hz, 1H), 4.83 (d, J
) 4.6 Hz, 1H), 6.58 (d, J ) 9.1 Hz, 1H), 7.20 (m, 2H), 7.32 (m,
1H), 7.38 (s, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 21.9,
23.5, 23.8, 28.1, 35.3, 41.5, 46.4, 56.5, 67.1, 71.7, 77.3, 121.1,
128.2, 128.3, 129.8, 131.8, 142.9, 155.2. Anal. C20H32BrNO4:
C, H, N.
rac-(1S,2R,4R)-[1-(3-Bromobenzyl)-6-(2,4-dichloro-
phenyl)-2,4-dihydroxyhexyl]carbamic Acid tert-Butyl
Ester (11c) was prepared in same manner as 11a with 76%
yield (de ) 99:1). 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.26
(s, 9H), 1.52 (m, 2H), 1.65 (m, 2H), 2.50 (m, 1H), 2.67 (m, 1H),
2.80 (m, 1-H), 2.97 (m, 1H), 3.44 (m, 2H), 3.68 (m, 1H), 4.70
(d, J ) 4.6 Hz, 1H), 4.85 (d, J ) 5.2 Hz, 1H), 6.63 (d, J ) 8.9
Hz), 7.19 (m, 2H), 7.35 (m, 4H), 7.55 (s, 1H). 13C NMR (δ/ppm,
125 MHz, DMSO-d6): 28.0, 28.4, 35.3, 36.3, 40.8, 56.6, 66.0,
67.9, 77.3, 121.1, 127.2, 128.2, 128.4, 128.5, 129.9, 131.0, 131.7,
131.8, 133.7, 139.0, 142.6, 155.1. HRMS (ESI) m/z: C24H30-
BrCl2NO4 + Na+ calcd, 568.0627; found, 568.0624. Anal.
C24H30BrCl2NO4: C, H, N.
rac-(4S,5R,1R)-Methanesulfonic Acid 2-[4-(3-Bromoben-
zyl)-2-oxooxazolidin-5-yl]-1-methylethyl Ester (13a). A
solution of 12a (1.39 g, 3.9 mmol) and triethylamine (2.36 g,
23.4 mmol) in 200 mL of CH2Cl2 was cooled to 0 °C and treated
by dropwise addition of mesyl chloride (1.32 g, 11.7 mmol).
After being stirred for 2 h at 0 °C, the solution was quenched
with 0.5 N HCl (3 × 50 mL) and washed with NaHCO3 (3 ×
50 mL) and brine solution (3 × 50 mL). The organic solution
was dried (MgSO4), evaporated, and flash chromatographed
(cyclohexane/EtOAc 1:1) to give 1.3 g (84%) of 13a as a white
1
powder. H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.39 (d, J )
6.5 Hz, 3H), 1.99 (m 1H), 2.15 (m, 1H), 2.60 (dd, J ) 13.6,
10.0 Hz, 1H), 2.90 (dd, J ) 13.8, 4.3 Hz, 1H), 3.18 (s, 3H),
4.05 (m, 1H), 4.71 (ddd, J ) 10.5, 6.7, 3.8 Hz, 1H), 4.81 (m,
1H), 7.26 (m, 2H), 7.43 (m, 1H), 7.52 (s, 1H), 7.66 (s, 1H). 13C
NMR (δ/ppm, 125 MHz, DMSO-d6): 20.3, 31.7, 35.4, 37.8, 55.2,
75.2, 76.9, 121.6, 128.2, 129.1, 130.4, 131.8, 140.5, 157.5. Anal.
C14H18BrNO5S: C, H, N.
rac-(4S,5R,3R)-Methanesulfonic Acid 1-[4-(3-Bromoben-
zyl)-2-oxooxazolidin-5-ylmethyl]-3-methylbutyl Ester (13b)
was prepared from 12b in the same manner as 13a with yield
1
of 80%. H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.90 (d, J )
6.6 Hz, 6H), 1.51 (ddd, J ) 13.1, 7.3, 3.0 Hz, 1H), 1.60 (ddd, J
) 14.2, 8.6, 4.9 Hz, 1H), 1.72 (m, 1H), 2.05 (ddd, J ) 14.3, 6.9,
3.1 Hz, 1H), 2.16 (ddd, J ) 14.9, 10.3, 4.9 Hz, 1H), 2.63 (dd, J
) 13.7, 9.2 Hz, 1H), 2.88 (dd, J ) 13.9, 4.8 Hz, 1H), 3.18 (s,
3H), 4.08 (m, 1H), 4.72 (ddd, J ) 10.2, 7.4, 3.0 Hz, 1H), 4.80
(m, 1H), 7.25 (m, 2H), 7.42 (m, 1H), 7.47 (s, 1H), 7.68 (s, 1H).
13C NMR (δ/ppm, 125 MHz, DMSO-d6): 21.6, 22.9, 23.6, 31.5,
34.2, 35.3, 44.6, 55.3, 75.3, 79.1, 121.5, 128.2, 129.2, 130.4,
131.8, 140.4, 157.6. HRMS (ESI) m/z: C17H24BrNO5S + Na+
calcd, 456.0456; found, 456.0494. Anal. C17H24BrNO5S: C, H,
N.
rac-(4S,5R,2R)-4-(3-Bromobenzyl)-5-(2-hydroxypropyl)-
1,3-oxazolidin-2-one (12a). To a mixture of NaH (0.5 g, 20.7
mmol) in 50 mL of THF was added a solution of 11a (2.68 g,
6.9 mmol) in 50 mL of THF in a dropwise fashion. The reaction
mixture was stirred at room temperature for 2 h and poured
into a saturated solution of NH4Cl (100 mL). The aqueous layer
was extracted with Et2O (3 × 50 mL), and the combined
extracts were washed with brine (3 × 50 mL). The organic
layer was dried (MgSO4), filtered, and concentrated in vacuo.
Flash chromatography (cyclohexane/EtOAc 1:1) afforded 12a
(1.41 g, 66% yield) as a white solid: 1H NMR (δ/ppm, 500 MHz,
DMSO-d6): 1.08 (d, J ) 6.2 Hz, 3H), 1.66 (ddd, J ) 14.0, 6.5,
5.0 Hz, 1H), 1.84 (ddd, J ) 13.9, 8.7, 5.7 Hz, 1H), 2.58 (dd, J
) 12.9, 9.1 Hz, 1H), 2.87 (dd, J ) 13.7, 4.6 Hz, 1H), 4.60 (d, J
) 4.8 Hz, 1H), 4.03 (m, 1H), 4.64 (m, 1H), 7.26 (m, 2H), 7.41
(m, 1H), 7.49 (s, 1H), 7.57 (s, 1H). 13C NMR (δ/ppm, 125 MHz,
DMSO-d6): 22.8, 35.6, 35.6, 38.1, 55.3, 63.1, 76.4, 121.6, 128.2,
129.1, 130.4, 131.8, 140.6, 157.9. Anal. C13H16BrNO3: C, H,
N.
rac-(4S,5R,2R)-4-(3-Bromobenzyl)-5-(2-hydroxy-4-
methylpentyl)-1,3-oxazolidin-2-one (12b) was obtained in
the same manner as 12a with 67% yield. 1H NMR (δ/ppm, 500
MHz, DMSO-d6): 0.81 (d, J ) 6.8 Hz, 3H), 0.86 (d, J ) 6.8
Hz, 3H), 1.14 (m, 1H), 1.26 (m, 1H), 1.75 (m, 1H), 1.75 (m,
2H), 2.58 (dd, J ) 14.0, 5.0 Hz, 1H), 2.84 (dd, J ) 13.8, 8.9
Hz, 1H), 3.52 (m, 1H), 4.05 (m, 1H), 4.47 (d, J ) 5.8 Hz, 1H),
4.67 (m, 1H), 7.25 (m, 2H), 7.41 (m, 1H), 7.47 (s, 1H), 7.56 (s,
1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 21.7, 23.6, 23.8,
35.6, 37.6, 45.7, 55.3, 64.8, 78.6, 121.6, 128.2, 129.1, 130.4,
131.8, 140.6, 158.0. HRMS (ESI) m/z: C16H22BrNO3 + Na+
calcd, 378.0681; found, 378.0677. Anal. C16H22BrNO3: C, H,
N.
rac-(4S,5R,3R)-Methanesulfonic Acid 1-[4-(3-Bromoben-
zyl)-2-oxooxazolidin-5-ylmethyl]-3-(2,4-dichlorophenyl)-
propyl Ester (13c) was obtained from 12c in the same
manner as 12a with 82% yield. 1H NMR (δ/ppm, 500 Hz,
DMSO-d6): 1.92 (m, 1H), 2.01 (m, 1H), 2.15 (ddd, J ) 14.8,
6.8, 3.3 Hz, 1H), 2.22 (ddd, J ) 14.6, 9.8, 5.3 Hz, 1H), 2.65
(dd, J ) 13.7, 9.5 Hz, 1H), 2.80 (m, 2H), 2.91 (dd, J ) 13.7,
4.5 Hz, 1H), 3.22 (s, 3H), 4.11 (m, 1H), 4.76 (m, 1-H), 4.85 (m,
1H), 7.28 (m, 2H), 7.42 (m, 3H), 7.49 (s, 1H), 7.59 (s, 1H), 7.72
(s, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 27.6, 31.4,
33.2, 35.3, 37.9, 55.2, 75.1, 79.5, 121.7, 127.4, 128.2, 128.6,
129.2, 130.4, 131.5, 131.8, 131.8, 133.7, 137.6, 140.4, 157.6.
Anal. C21H22BrCl2NO5S: C, H, N.
rac-(4S,5R,2S)-4-(3-Bromobenzyl)-5-[2-(3-methylbutyl-
sulfanyl)propyl]-1,3-oxazolidin-2-one (14a). To a 0 °C
solution of NaH (65 mg, 2.7 mmol) in 50 mL of THF was added
3-methyl-butane-1-thiol (281 mg, 2.7 mmol) in one portion. The
mixture was treated by dropwise addition of 13a dissolved in
20 mL of THF. The reaction mixture was stirred for 1 h at
room temperature and then distributed between 35 mL of CH2-
Cl2 and 35 mL of brine. The organic layer was dried with
MgSO4 and evaporated. The residue was chromatographed on
silica gel eluting with cyclohexane/EtOAc (2:1) to give 880 mg
(83%) of 14a. 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.86 (d,
J ) 1.0 Hz, 3H), 0.88 (d, J ) 1.2 Hz, 3H), 1.32 (d, J ) 6.9 Hz,
3H), 1.38 (m, 2H), 1.63 (m, 1H), 1.68 (ddd, J ) 14.6, 9.7, 3.0
Hz, 1H), 2.15 (ddd, J ) 14.9, 10.4, 4.4 Hz, 1H), 2.49 (m, 2H),
2.63 (dd, J ) 13.8, 9.1 Hz, 1H), 2.82 (m, 1H), 2.89 (dd, J )
13.9, 4.9 Hz, 1H), 4.14 (m, 1H), 4.80 (ddd, J ) 10.4, 7.8, 3.4
Hz, 1H), 7.26 (m, 2H), 7.41 (m, 1H), 7.47 (s, 1H), 7.59 (s, 1H).
13C NMR (δ/ppm, 125 MHz, DMSO-d6): 21.9, 22.5, 27.6, 27.7,
35.2, 36.5, 36.7, 38.2, 54.9, 76.7, 121.5, 127.9, 128.8, 130.2,
132.1, 140.4, 157.3. HRMS (ESI) m/z: C18H27BrNO2S (MH+)
calcd, 400.0964; found, 400.0945. Anal. C18H26BrNO2S: C, H,
N.
rac-(4S,5R,2R)-4-(3-Bromobenzyl)-5-[4-(2,4-dichloro-
phenyl)-2-hydroxybutyl]-1,3-oxazolidin-2-one (12c) was
prepared analogously to 12a with 64% yield. 1H NMR (δ/ppm,
500 MHz, DMSO-d6): 1.58 (m, 1 H), 1.68 (m, 1H), 1.82 (m,
2H), 2.62 (m, 2H), 2.84 (m, 2H), 3.55 (m, 1H), 4.06 (m, 1H),
4.73 (m, 1H), 4.80 (s, 1H), 7.26 (m, 2H), 7.36 (m, 2H), 7.42 (m,
1H), 7.47 (s, 1H), 7.55 (s, 1H), 7.61 (s, 1H). 13C NMR (δ/ppm,
125 MHz, DMSO-d6): 28.8, 35.6, 36.2, 36.5, 55.4, 66.4, 76.4,
121.8, 127.4, 128.4, 128.7, 129.3, 130.6, 131.3, 132.0, 132.0,
133.9, 139.0, 140.8, 158.2. Anal. C20H20BrCl2NO3: C, H, N.
rac-(4S,5R,2S)-4-(3-Bromobenzyl)-5-[2-(4-fluorophen-
ylsulfanyl)-4-methylpentyl]-1,3-oxazolidinon-2-one (14b)
was synthesized following the above procedure by addition of
4-fluorobenzenethiol (346 mg, 2.7 mmol) and 13b with 80%
yield.1H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.82 (d, J ) 3.0
Hz, 3H), 0.84 (d, J ) 3.2 Hz, 3H), 1.37 (m, 2H), 1.53 (ddd, J )

Hydroxyethylene Sulfones as a Novel Scaffold
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21 6617
14.7, 10.5, 2.0 Hz, 1H), 1.88 (m, 1H), 1.95 (ddd, J ) 14.7, 11.5,
3.4 Hz, 1H), 2.64 (dd, J ) 14.0, 8.8 Hz, 1H), 2.83 (dd, J ) 14.0,
5.3 Hz, 1H), 3.06 (m, 1H), 4.20 (m, 1H), 4.99 (ddd, J ) 11.7,
7.8, 2.0 Hz, 1H), 7.20 (m, 4H), 7.40 (m, 4H), 7.65 (s, 1H). 13C
NMR (δ/ppm, 125 MHz, DMSO-d6): 22.1, 22.3, 24.8, 34.3, 35.3,
44.5, 44.7, 57.8, 76.3, 116.1, 121.5, 128.0, 128.3, 129.1, 130.4,
131.8, 135.5, 140.5, 157.8, 161.7. HRMS (ESI) m/z: C22H26-
BrFNO2S (MH+) calcd, 466.0852; found, 466.0885. Anal.
C22H25BrFNO2S: C, H, N.
rac-(4S,5R,2S)-4-(3-Bromobenzyl)-5-[4-(2,4-dichloro-
phenyl)-2-(4-fluorophenylsulfanyl)butyl]-1,3-oxazolidin-
2-one (14c) was produced following the above procedure by
addition of 4-fluorobenzenethiol (346 mg, 2.7 mmol) and 13c
in 80% yield. 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.65 (m,
1H), 1.79 (m, 2H), 2.08 (m, 1H), 2.67 (m, 1H), 2.87 (m, 3H),
3.17 (m, 1H), 4.21 (m, 1H), 4.99 (m, 1H), 7.18 (m, 2H), 7.28
(m, 2H), 7.36 (m, 2H), 7.43 (s, 3H), 7.48 (s, 1H), 7.55 (s, 1H),
7.70 (s, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 29.8, 34.1,
35.3, 35.7, 46.5, 55.3, 76.7, 116.5, 122.1, 127.8, 128.5, 128.7,
129.0, 129.6, 130.8, 131.8, 132.1, 132.4, 134.1, 135.6, 138.4,
141.0, 158.1, 162.1. Anal. C26H23BrCl2FNO2S: C, H, N.
gel chromatography, eluting with cyclohexane/EtOAc 2:1 to
afford 133 mg (81%) of 16a as a white solid. 1H NMR (δ/ppm,
500 MHz, DMSO-d6): 0.86 (d, J ) 0.9 Hz, 3H), 0.88 (d, J )
1.0 Hz, 3H), 1.27 (d, J ) 6.9 Hz, 3H), 1.41 (m, 3H), 1.63 (m,
2H), 1.99 (s, 3H), 2.25 (m, 2H), 2.49 (m, 5H), 2.92 (m, 1H),
2.99 (dd, J ) 13.8, 3.3 Hz, 1H), 3.59 (m, 1H), 3.78 (m, 1H),
4.77 (d, J ) 6.7 Hz, 1H), 7.20 (m, 2H), 7.34 (m, 1H), 7.41 (s,
1H), 7.71 (d, J ) 9.0 Hz, 1H). 13C NMR (δ/ppm, 125 MHz,
DMSO-d6): 14.5, 22.0, 23.0, 26.9, 27.0, 39.4, 35.3, 35.6, 36.9,
38.6, 40.1, 55.1, 70.6, 121.1, 128.1, 128.5, 128.8, 131.8, 142.4,
170.5. HRMS (ESI) m/z: C21H35BrNO2S2 (MH+) calcd, 476.1254;
found, 476.1292. Anal. C21H34BrNO2S2: C, H, N.
rac-(1S,2R,4S)-N-[1-(3-Bromobenzyl)-4-(4-fluorophen-
ylsulfanyl)-2-hydroxy-6-methylheptyl]-2-(2,6-dimethyl-
phenoxy)acetamide (16b). Coupling of 15b (145 mg, 0.33
mmol) with (2,6-dimethylphenoxy)acetic acid (63 mg, 0.35
mmol) was used to prepare 16b with 75% yield, as described
1
for 16a. H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.82 (d, J )
6.5 Hz, 3H), 0.84 (d, J ) 6.4 Hz, 3H), 1.35 (m, 2H), 1.57 (m,
2H), 1.84 (m, 1H), 2.16 (s, 6H), 2.79 (dd, J ) 13.7, 10.7 Hz,
1H), 3.07 (dd, J ) 13.9, 3.0 Hz, 1H), 3.30 (m, 1H), 3.96 (m,
1H), 3.96 (m, 1H), 3.96 (d, J ) 14.3 Hz, 1H), 4.11 (d, J ) 14.3
Hz, 1H), 5.10 (d, J ) 6.4 Hz, 1H), 6.93 (dd, J ) 7.2, 6.7 Hz,
1H), 7.02 (d, J ) 7.3 Hz, 2H), 7.20 (m, 4H), 7.44 (m, 4H), 7.95
(m, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 15.7, 22.1,
22.3, 24.7, 35.0, 38.7, 44.1, 45.3, 55.9, 59.6, 70.1, 116.5, 121.1,
124.2, 128.1, 128.6, 128.7, 128.7, 129.3, 129.9, 130.1, 131.8,
133.5, 135.1, 142.3, 154.3, 161.4,167.3. Anal. C31H37Br-
FNO3S: C, H, N.
rac-(2S,3R,5S)-2-Amino-1-(3-bromophenyl)-5-(3-meth-
ylbutylsulfanyl)hexan-3-ol (15a). A solution of 14a (0.8 g,
2 mmol) and barium hydroxide octahydrate (1.1 g, 4 mmol) in
dioxane (100 mL) and water (60 mL) was heated at reflux
under N2 overnight. The solid barium carbonate was filtered
and the filtrate was diluted with water. The resulting solution
was extracted with Et2O (3 × 50 mL), and the combined
organic extracts were washed with brine, dried over MgSO4,
and evaporated to a residue. Flash chromatography on silica
Synthesis of Compounds 16c-e. rac-(1S,2R,4S)-N-[1-(3-
Bromobenzyl)-6-(2,4-dichlorophenyl)-4-(4-fluorophenylsulfanyl)-
2-hydroxyhexyl]-2-(2,4-dichlorophenoxy)acetamide (16c), rac-
(1S,2R,4S)-N-[1-(3-bromobenzyl)-6-(2,4-dichlorophenyl)-4-
(4-fluorophenylsulfanyl)-2-hydroxyhexyl]-4,5-dimethoxy-
benzamide(16d),andadiastereomericmixtureof((2R),1S,2R,4S)-
and ((2R),1R,2S,4R)-tetrahydrofuran-2-carboxylic acid [1-(3-
bromobenzyl)-6-(2,4-dichlorophenyl)-4-(4-fluorophenylsulfanyl)-
2-hydroxyhexyl]amide (16e) were prepared in analogous fash-
ion as 16a, coupling 15c with three distinct carboxylic acids
as R3-fragments (0.35 mmol) with 84% (16c), 81% (16d), and
77% (16e) yield.
1
gel eluting with EtOAc gave 560 mg (75%) of 15a. H NMR
(δ/ppm, 500 MHz, DMSO-d6): 0.86 (d, J ) 0.8 Hz, 3H), 0.88
(d, J ) 0.9 Hz, 3H), 1.24 (d, J ) 6.7 Hz, 3H), 1.40 (m, 2H),
1.47 (m, 1H), 1.64 (m, 2H), 2.36 (dd, J ) 12.8, 7.8 Hz, 1H),
2.49 (m, 2H), 2.74 (m, 2H), 2.93 (m, 1H), 3.27 (s, 2H), 4.48 (m,
J ) 5.7 Hz, 1H), 7.23 (m, 2H), 7.37 (m, 1H), 7.44 (s, 1H). 13C
NMR (δ/ppm, 125 MHz, DMSO-d6): 21.9, 23.0, 26.7, 26.8, 38.5,
39.0, 39.1, 39.2, 57.5, 71.7, 121.4, 128.1, 128.3, 129.9, 131.7,
143.3. HRMS (ESI) m/z: C17H29BrNOS (MH+) calcd, 374.1181;
found, 374.1153.
rac-(2S,3R,5S)-2-Amino-1-(3-bromophenyl)-5-(4-fluo-
rophenylsulfanyl)-7-methyloctan-3-ol (15b) was synthe-
sized from 14b as described for 15a with 72% yield. 1H NMR
(δ/ppm, 500 MHz, DMSO-d6): 0.81 (d, J ) 6.7 Hz, 3H), 0.83
(d, J ) 6.7 Hz, 3H), 1.37 (m, 2H), 1.58 (m, 2H), 1.81 (m, 1H),
2.35 (dd, J ) 12.9, 9.4 Hz, 1H), 2.73 (m, 1H), 2.97 (dd, J )
13.4, 4.3 Hz, 1H), 3.27 (m, 1H), 3.67 (m, 1H), 4.68 (d, J ) 6.1
Hz, 1H), 7.20 (m, 4H), 7.40 (m, 4H). 13C NMR (δ/ppm, 125
MHz, DMSO-d6): 22.1, 22.3, 24.8, 37.3, 38.9, 44.5, 45.6, 57.7,
71.3, 116.5, 121.3, 128.3, 128.4, 128.7, 129.9, 130.0, 131.8,
134.7, 142.3, 161.4. Anal. C21H27BrFNOS: C, H, N.
rac-(2S,3R,5S)-2-Amino-1-(3-bromophenyl)-7-(2,4-dichlo-
rophenyl)-5-(4-fluorophenylsulfanyl)heptan-3-ol (15c) was
obtained from 14c in the same manner as 15a with 80% yield.
1H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.70 (m, 2H), 1.80 (m,
1H), 2.39 (dd, J ) 12.9, 8.9 Hz, 1H), 2.78 (m, 2H), 2.84 (m,
2H), 3.34 (m, 1H), 3.57 (m, 1H), 4.63 (d, J ) 5.72 Hz, 1H),
7.14 (m, 2H), 7.24 (m, 2H), 7.31 (m, 2H), 7.37 (m, 2H), 7.46
(m, 2H), 7.50 (m, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6):
29.6, 35.6, 37.0, 38.7, 46.2, 57.7, 71.6, 115.8, 121.4, 127.2, 128.3,
128.4, 128.5, 130.0, 130.1, 131.3, 131.8, 131.9, 133.7, 134.3,
138.2, 143.4, 161.4. Anal. C25H25BrCl2FNOS: C, H, N.
rac-(1S,2R,4S)-N-[1-(3-Bromobenzyl)-2-hydroxy-4-(3-
methylbutylsulfanyl)pentyl]-3-methylsulfanylpropion-
amide (16a). A solution of 3-methylsulfanylpropionic acid (42
mg, 0.35 mmol) and 15a (125 mg, 0.33 mmol) in 40 mL of
anhydrous THF was cooled to 0 °C. Hydroxybenzotriazole (53
mg, 0.39 mmol) and EDC (70 mg, 0.35 mmol) were then added
sequentially. The reaction mixture was stirred for 2 h at 0 °C,
warmed to 25 °C, and stirred for a further 2 h. The organic
phase was quenched with saturated NaHCO3 and washed with
brine. After extraction with Et2O (3 × 50 mL), the combined
organic layers were dried with MgSO4, filtered, and evaporated
in vacuo. The resulting material was submitted to flash silica
1
16c. H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.63 (m, 2H),
1.76 (m, 2H), 2.66 (dd, J ) 14.0, 10.6 Hz, 1H), 2.83 (m, 2H),
3.06 (dd, J ) 14.0, 3.4 Hz, 1H), 3.29 (m, 1H), 3.87 (m, 1H),
3.96 (m, 1H), 4.47 (s, 2H), 5.01 (d, J ) 7.0 Hz, 1H), 6.75 (d, J
) 8.9 Hz, 1H), 7.16 (m, 2H), 7.20 (m, 2H), 7.33 (m, 2H), 7.38
(m, 2H), 7.47 (m 1H), 7.42 (s, 1H), 7.47 (m, 2H), 7.50 (s, 1H),
7.53 (d, J ) 9.1 Hz, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-
d6): 29.5, 35.2, 35.3, 38.1, 45.8, 54.9, 67.7, 69.8, 115.1, 115.8,
121.2, 122.5 125.0, 127.2, 127.6, 128.0, 128.5, 128.6, 129.0,
129.3, 129.9, 130.2, 130.7, 130.7, 134.8, 138.0, 142.0, 152.3,
161.5, 166.2. HRMS (ESI) m/z: C33H30BrCl4FNO3S (MH+)
calcd, 757.9833; found, 757.9867.
1
16d. H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.79 (m, 3H),
1.89 (m, 1H), 2.66 (dd, J ) 14.2, 11.1 Hz, 1H), 2.83 (m, 2H),
3.20 (m, 1H), 3.39 (m, 1H), 3.74 (s, 3H), 3.78 (s, 3H), 3.88 (m,
1H), 4.15 (m, 1H), 5.00 (d, J ) 6.9 Hz, 1H), 6.52 (s, 1H), 7.10
(m, 3H), 7.30 (m, 4H), 7.38 (m, 1H), 7.48 (m, 4H), 8.06 (d, J )
6.9 Hz, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 29.4, 35.5,
35.7, 38.5, 46.0, 55.6, 55.7, 56.1, 70.7, 109.4, 112.0, 115.7, 116.5,
121.2, 128.2 128.5, 128.6, 129.7, 130.0, 130.9, 131.1, 131.8,
131.9, 133.7, 134.4, 134.5, 138.1, 142.6, 147.7, 149.9, 161.4,
166.3. HRMS (ESI) m/z: C34H33Br2Cl2FNO4S (MH+) calcd,
797.9813; found, 797.9858. Anal. C34H32Br2Cl2FNO4S: C, H,
N.
16e (ratio of diastereomers 1:1). 1H NMR (δ/ppm, 500 MHz,
DMSO-d6): 1.41 (m, 1H), 1.68 (m, 6H), 1.98 (m, 1H), 2.72 (m,
1H), 2.84 (m, 2H), 3.07 (m, 1H), 3.29 (m, 1H), 3.47 (m, 1H),
3.85 (m, 3H), 4.03 (m, 1H), 5.00 (d, J ) 6.5 Hz, 1H), 7.17 (m,
2H), 7.34 (m, 3H), 7.39 (m, 4H), 7.48 (m, 3H). 13C NMR (δ/
ppm, 125 MHz, DMSO-d6): 25.0, 29.1, 29.2, 34.6, 38.8, 45.3,
53.9, 67.3, 68.7, 76.9, 115.3, 120.5, 126.6, 127.3, 127.8, 127.9,
129.2, 130.7, 131.3, 133.0, 133.2, 134.0, 134.6, 137.4, 141.8,
161.0,171.3. Anal. C30H32BrCl2FNO3S: C, H, N.

6618 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21
Specker et al.
rac-(1S,2R,4S)-N-[1-(3-Bromobenzyl)-2-hydroxy-4-(3-
methylbutane-1-sulfonyl)pentyl]-3-methanesulfonylpro-
pionamide (17a). To a solution of 16a (100 mg, 0.21 mmol)
in 50 mL of CHCl3 was added mCPBA (200 mg, 1.26 mmol, 6
equiv) sequentially. The reaction mixture was heated for 2 h
under reflux. The reaction was quenched by pouring into
saturated NaHCO3, and the product was extracted with CH2-
Cl2. The organic layer was washed with NaHCO3 (6 × 50 mL)
and then with brine. After drying (MgSO4), the solvent was
evaporated and the residue purified by flash chromatography
on silica gel using 3:1 cyclohexane/EtOAc to give 95 mg (89%)
Br2Cl2FNO6S (MH+) calcd, 829.9736; found, 829.9756. Anal.
C34H32Br2Cl2FNO6S: C, H, N.
The diastereomeric mixture of 17e was separated into the
((2R),1S,2R,4S)- and ((2R),1R,2S,4R)-diastereomers via chiral
HPLC. Assignment of the absolute configuration to the dif-
ferent diastereomers was performed with respect to their IC50
valuesintheHIVproteaseassay(4.2µMforthe((2R),1S,2R,4S)-
diastereomer and > 40 µM for the ((2R),1R,2S,4R)-diastere-
omer) and similarity to the crystallographically fully charac-
terized 17b and the small molecule crystal structure of rac-
19.
1
of 17a. H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.91 (d, J )
1
((2R),1S,2R,4S)-17e. H NMR (δ/ppm, 300 MHz, CDCl3):
6.5 Hz, 6H), 1.34 (d, J ) 6.8 Hz, 3H), 1.43 (ddd, J ) 15.2, 8.2,
7.0 Hz, 1H), 1.57 (m, 2H), 1.68 (m, 2H), 2.17 (ddd, J ) 14.8,
4.5, 4.0 Hz, 1H), 2.46 (m, 2H), 2.55 (dd, J ) 13.0, 10.3 Hz,
1H), 2.87 (s, 3H), 2.96 (dd, J ) 13.9, 3.4 Hz, 1H), 3.15 (m, 2H),
3.27 (m, 1H), 3.62 (m, 1H), 3.86 (m, 1H), 5.04 (m, 1H), 7.22
(m, 2H), 7.36 (m, 1H), 7.43 (s, 1H), 8.01 (d, J ) 9.0 Hz, 1H).
13C NMR (δ/ppm, 125 MHz, DMSO-d6): 14.7, 21.9, 26.7, 27.9,
29.2, 33.2, 34.6, 46.9, 49.8, 54.9. 55.1, 62.7, 71.0, 121.2, 128.2,
128.6, 130.0, 131.8, 142.1, 168.4. HRMS (ESI) m/z: C21H34-
BrNO6S2 calcd, 540.1058; found, 540.1089. Anal. C21H34-
BrNO6S2: C, H, N.
Synthesis of Compounds 17 b-e. rac-(1S,2R,4S)-N-
[1-(3-Bromobenzyl)-4-(4-fluorobenzenesulfonyl)-2-hydroxy-6-
methylheptyl]-2-(2,6-dimethylphenoxy)acetamide (17b), rac-
(1S,2R,4S)-N-[1-(3-bromobenzyl)-6-(2,4-dichlorophenyl)-4-(4-
fluorobenzenesulfonyl)-2-hydroxyhexyl]-2-(2,4-dichlorophen-
oxy)acetamide (17c), rac-(1S,2R,4S)-2-bromo-N-[1-(3-bromoben-
zyl)-6-(2,4-dichlorophenyl)-4-(4-fluorobenzenesulfonyl)-2-hy-
droxyhexyl]-4,5-dimethoxybenzamide (17d), and the separated
diastereomers ((2R),1S,2R,4S)- and ((2R),1R, 2S,4R)-tetrahy-
drofuran-2-carboxylic acid [1-(3-bromobenzyl)-6-(2,4-dichlo-
rophenyl)-4-(4-fluorophenylsulfanyl)-2-hydroxyhexyl]amide (17e)
were prepared analogously as 17a, however, with only 3 equiv
of mCPBA (0.63 mmol) oxidizing 16b-e to give 80% (17b),
89% (17c), 90% (17d), and 87% (17e) yields, respectively.
1.87 (m, 6H), 2.28 (m, 2H), 2.56 (ddd, J ) 13.8, 9.3, 7.2 Hz,
1H), 2.90 (m, 3H), 3.32 (m, 1H), 3.82 (m, 2H), 3.89 (m, 1H),
4.06 (m, 1H), 4.27 (dd, J ) 8.1, 5.8 Hz, 1H), 5.56 (m, 1H), 6.86
(d, J ) 7.2 Hz, 1H), 7.17 (m, 7H), 7.34 (s, 1H), 7.39 (m, 1H),
7.83 (m, 2H). 13C NMR (δ/ppm, 125 MHz, CDCl3): 25.2, 29.6,
29.8, 30.2, 31.9, 35.3, 57.3, 60.4, 69.5, 71.9, 78.2, 116.8, 122.7,
127.2, 127.8, 129.4, 130.0, 130.3, 131.4, 131.5, 131.6, 132.3,
132.9, 133.5, 134.3, 136.3, 140.0, 164.9,174.9. Anal. C30H32-
BrCl2FNO5S: C, H, N.
1
((2R),1R,2S,4R)-17e. H NMR (δ/ppm, 300 MHz, CDCl3):
1.50 (m, 1H), 1.75 (m, 4H), 2.02 (m, 1H), 2.17 (m, 2H), 2.57
(ddd, J ) 13.7, 9.3, 7.3 Hz, 1H), 2.71 (dd, J ) 14.0, 10.7 Hz,
1H), 2.84 (ddd, J ) 13.8, 9.3, 4.7 Hz, 1H), 3.03 (dd, J ) 14.2,
4.5 Hz, 1H), 3.36 (m, 1H), 3.66 (m, 1H), 3.79 (m, 1H), 4.03 (m,
1H), 4.14 (m, 1H), 4.28 (dd, J ) 8.3, 5.3 Hz, 1H), 6.72 (d, J )
7.7 Hz, 1H), 7.17 (m, 7H), 7.37 (s, 1H), 7.40 (m, 1H), 7.83 (m,
2H). 13C NMR (δ/ppm, 125 MHz, CDCl3): 25.5, 29.9, 30.2, 30.5,
32.2, 36.2, 56.3, 60.8, 69.9, 72.2, 78.5, 116.8, 123.0, 127.6, 128.2,
129.8, 130.3, 130.7, 131.9, 132.0, 132.6, 133.3, 133.7, 134.8,
136.7, 140.3, 164.9, 175.0. HRMS (ESI) m/z: C30H32BrCl2-
FNO5S (MH+) calcd, 686.0549; found, 686.0545. Anal. C30H32-
BrCl2FNO5S: C, H, N.
rac-(1S,2R,4S)-N-[1-Bromobenzyl)-2-hydroxy-6-meth-
yl-4-(4-methylaminobenzenesulfonyl)heptyl]-2-(2,6-di-
methylphenoxy)acetamide (18a). To a solution of 17b (50
mg, 0.08 mmol) was added 10 mL (1 M in THF) of MeNH2.
The reaction mixture was transferred to an autoclave and
heated to 160 °C and 2 bar. After being stirred for 5 h, the
reaction was quenched with 50 mL of water and extracted with
Et2O (3 × 40 mL). The combined organic layers were dried
(MgSO4), filtrated, and evaporated under reduced pressure.
The crude product was flash chromatographed with cyclohex-
ane/EtOAc (3:1) to give 45 mg (87%) of 18a as a light brown
solid. 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.78 (d, J ) 6.3
Hz, 3H), 0.85 (d, J ) 6.6 Hz, 3H), 1.16 (m, 1H), 1.36 (m, 1H),
1.48 (m, 1H), 1.65 (m, 1H), 2.04 (ddd, J ) 15.3, 2.8, 7.2 Hz,
1H), 2.17 (s, 6H), 2.71 (d, J ) 4.7 Hz, 3H), 2.76 (dd, J ) 13.6,
2.5 Hz, 1H), 3.03 (dd, J ) 14.0, 2.7 Hz, 1H), 3.22 (m, 1H), 3.77
(m, 1H), 3.96 (m, 1H), 3.96 (d, J ) 14.6 Hz, 1H), 4.12 (d, J )
14.6 Hz, 1H), 5.14 (d, J ) 6.6 Hz, 1H), 6.62 (d, J ) 8.9 Hz,
2H), 6.66 (d, J ) 4.7 Hz, 1H), 6.94 (dd, J ) 8.2, 7.0 Hz, 1H),
7.01 (dd, J ) 7.3, 6.6 Hz, 2H), 7.22 (m, 2H), 7.35 (dd, J ) 7.6,
1.3 Hz, 1H), 7.48 (s, 1H), 7.49 (d, J ) 9.0 Hz, 2H), 7.75 (d, J
) 9.7 Hz, 1H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 15.6,
21.1, 23.2, 24.3, 28.9, 33.7, 34.9, 35.1, 54.9, 59.2, 70.0, 70.9,
110.5, 121.3, 124.2, 128.2, 128.6, 128.7, 129.9, 130.2, 130.3,
130.4, 131.8, 142.3, 153.6, 154.3, 167.2. Anal. C32H41-
BrN2O5S: C, H, N.
rac-(1S,2R,4S)-N-[1-Bromobenzyl)-4-(4-(dimethylami-
no)benzenesulfonyl)-2-hydroxy-6-methylheptyl]-2-(2,6-
dimethylphenoxy)acetamide (18b) was prepared in the
same manner from 17b, however, using Me2NH (10 mL, 1 M
in THF) for nucelophilic substitution to give 47 mg of 18b
(90%) as a light brown solid: 1H NMR (δ/ppm, 500 MHz,
DMSO-d6): 0.78 (d, J ) 6.3 Hz, 3H), 0.85 (d, J ) 6.5 Hz, 3H),
1.16 (m, 1H), 1.36 (m, 1H), 1.48 (m, 1H), 1.66 (m, 1H), 2.04
(m, 1H), 2.16 (s, 6H), 2.75 (dd, J ) 16.2, 2.9 Hz, 1H), 2.99 (s,
6H), 3.03 (dd, J ) 13.6, 3.2 Hz, 1H), 3.23 (m, 1H), 3.76 (m,
1H), 3.96 (m, 1H), 3.96 (d, J ) 14.3 Hz, 1H), 4.11 (d, J ) 14.2
Hz, 1H), 5.14 (s, 1H), 6.78 (d, J ) 9.2 Hz, 2H), 6.94 (dd, J )
8.0, 7.0 Hz, 1H), 7.01 (dd, J ) 7.3, 7.3 Hz, 2H), 7.22 (m, 2H),
7.36 (dd, J ) 7.6, 1.9 Hz, 1H), 7.44 (s, 1H), 7.56 (d, J ) 9.0
17b. 1H NMR (δ/ppm, 500 MHz, DMSO-d6): 0.75 (d, J )
6.4 Hz, 3H), 0.85 (d, J ) 6.7 Hz, 3H), 1.26 (m, 2H), 1.44 (m,
1H), 1.66 (m, 1H), 2.08 (m, 1H), 2.16 (s, 6H), 2.75 (dd, J )
11.0, 2.5 Hz, 1H), 3.03 (dd, J ) 13.9, 3.4 Hz, 1H), 3.41 (m,
1H), 3.76 (m, 1H), 3.96 (m, 1H), 3.96 (d, J ) 14.5 Hz, 1H),
4.10 (d, J ) 14.5 Hz, 1H), 5.25 (d, J ) 6.9 Hz, 1H), 6.94 (d, J
) 7.1 Hz, 1H), 7.01 (d, J ) 7.1 Hz, 2H), 7.21 (m, 2H), 7.36 (dd,
J ) 7.4, 1.4 Hz, 1H), 7.44 (s, 1H), 7.51 (d, J ) 9.0 Hz, 2H),
7.93 (m, 3H). 13C NMR (δ/ppm, 125 MHz, DMSO-d6): 15.6,
20.9, 23.1, 24.3, 33.3, 34.9, 38.8, 54.9, 59.0, 70.0, 70.6, 116.5,
121.1, 124.2, 128.1, 128.6, 128.7, 129.9, 130.2, 131.6, 131.8,
133.7, 142.3, 154.2, 165.0, 167.3. Anal. C31H37BrFNO5S: C,
H, N.
1
17c. H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.65 (m, 2H),
1.99 (m, 1H), 2.10 (ddd, J ) 15.2, 7.2, 2.7 Hz, 1H), 2.61 (dd, J
) 13.6, 10.7 Hz, 1H), 2.70 (m, 2H), 3.01 (dd, J ) 13.9, 3.0 Hz,
1H), 3.42 (m, 1H), 3.69 (m, 1H), 3.96 (m, 1H), 4.48 (s, 2H),
5.18 (d, J ) 6.7 Hz, 1H), 6.74 (d, J ) 8.9 Hz, 1H), 7.20 (m,
3H), 7.33 (m, 2H), 7.38 (m, 2H), 7.47 (m, 3H), 7.54 (d, J ) 2.6
Hz, 1H), 7.81 (d, J ) 9.3 Hz, 1H), 7.92 (m, 2H). 13C NMR (δ/
ppm, 125 MHz, DMSO-d6): 28.8, 29.0, 32.2, 34.6, 54.5, 60.0,
67.4, 70.5, 114.9, 116.2, 121.0, 122.3, 124.8, 127.0, 127.5, 127.8,
128.3, 128.4, 128.9, 129.0, 129.7, 131.2, 131.3, 131.5, 131.6,
133.4, 136.9, 141.5, 152.9, 164.7, 166.0. HRMS (ESI) m/z:
C33H30BrCl4FNO5S (MH+) calcd, 789.9755; found, 789.9766.
Anal. C33H29BrCl4FNO5S: C, H, N.
1
17d. H NMR (δ/ppm, 500 MHz, DMSO-d6): 1.65 (m, 1H),
1.73 (ddd, J ) 14.9, 10.7, 4.0 Hz, 1H), 1.94 (m, 1H), 2.42 (ddd,
J ) 15.3, 7.8, 2.5 Hz, 1H), 2.65 (m, 2H), 3.18 (dd, J ) 14.0, 3.2
Hz, 1H), 3.46 (m, 1H), 3.75 (m, 1H), 3.75 (s, 3H), 3.78 (s, 3H),
4.03 (m, 1H), 5.23 (d, J ) 7.1 Hz, 1H), 6.59 (s, 1H), 7.10 (s,
1H), 7.27 (m, 2H), 7.33 (m, 3H), 7.38 (m, 3H), 7.49 (m, 1H),
7.89 (m, 2H), 8.17 (d, J ) 9.4 Hz, 1H). 13C NMR (δ/ppm, 125
MHz, DMSO-d6): 29.0, 29.5, 32.6, 35.4, 55.5, 55.7, 56.0, 60.0,
71.5, 109.3, 111.7, 115.7, 116.5, 121.2, 127.3, 128.2, 128.6,
128.6, 130.0, 130.7, 131.4, 131.5, 131.6, 131.9, 133.6, 137.2,
142.3, 147.6, 149.8, 166.0, 166.5. HRMS (ESI) m/z: C34H33-

Hydroxyethylene Sulfones as a Novel Scaffold
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 21 6619
Hz, 2H), 7.85 (d, J ) 9.7 Hz, 1H). 13C NMR (δ/ppm, 125 MHz,
DMSO-d6): 15.6, 21.1, 23.2, 24.3, 33.7, 34.9, 39.4, 54.9, 59.2,
70.1, 70.7, 110.7, 121.3, 124.1, 128.2, 128.6, 128.7, 129.9, 130.1,
130.2, 130.3, 131.8, 142.3, 153.0, 154.3, 167.2. Anal. C33H43-
BrN2O5S: C, H, N.
rac-(4S,5R,2S)-4-(3-Bromobenzyl)-5-[-(2,4-dichlorophen-
yl)-2-(4-fluorobenzenesulfonyl)butyl]-1,3-oxazolidin-2-one
(19) was prepared by oxidation of 14 c (100 mg, 0.17 mmol)
with mCPBA (80 mg, 0.51 mmol, 3 equiv) in the same manner
as 17b to give 77 mg (74%) of 19. 1H NMR (δ/ppm, 500 MHz,
DMSO): 1.72 (m, 1H), 1.96 (m, 1H), 2.12 (m, 2H), 2.70 (m,
2H), 2.87 (m, 2H), 3.44 (m, 1H), 4.19 (m, 1H), 4.76 (m, 1H),
7.31 (m, 2H), 7.37 (m, 2H), 7.49 (m, 5H), 7.74 (s, 1H), 7.89 (m,
2H). 13C NMR (δ/ppm, 125 MHz, DMSO): 27.7, 28.7, 28.9, 34.7,
54.9, 60.0, 76.7, 116.7, 121.7, 127.4, 128.1, 128.6, 129.2, 130.5,
131.6, 131.7, 131.7, 132.0, 133.0, 133.6, 137.1, 140.3, 157.4,
165.2. Anal. C26H23BrCl2NO4S: C, H, N.
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Acknowledgment. The authors are grateful to
Bayer AG, Wuppertal, Germany, for financial support.
We thank also Prof. Dieter Hoppe, Department of
Organic Chemistry, University of Mu¨nster, Mu¨nster,
Germany, for his supervision and helpful discussions
during the first stages of the project. Additionally our
thanks go to Prof. Andreas Pfaltz and Dr. Frederik
Menges, Department of Organic Chemistry, University
of Basel, Basel, Switzerland, for the permission to use
their chiral HPLC. The clone of the protease was kindly
provided by Prof. Helena Danielson, Department of
Biochemistry, University of Uppsala, Uppsala, Sweden.
We would also like to thank the beamline staff at Bessy
II.
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Supporting Information Available: Results from ele-
mental analysis and crystallographic data for 19. This material
is available free of charge via the Internet at http://pubs.
acs.org.
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