Design and synthesis of potent C2-symmetric diol-based HIV-1 protease inhibitors: Effects of fluoro substitution

Article abstract of DOI:10.1021/jm001134q

Implementation of derivatized carbohydrates as C₂-symmetric HIV-1 protease inhibitors has previously been reported. With the objective of improving the anti-HIV activity of such compounds, we synthesized a series of fluoro substituted P1/P1′ an

Full text of DOI:10.1021/jm001134q

J . Med. Chem. 2001, 44, 3083-3091
3083
Design a n d Syn th esis of P oten t C2-Sym m etr ic Diol-Ba sed HIV-1 P r otea se
In h ibitor s: Effects of F lu or o Su bstitu tion
David Pyring,† J immy Lindberg,§ Åsa Rosenquist,† Guido Zuccarello,† Ingemar Kvarnstro¨m,† Hong Zhang,∇
Lotta Vrang,∇ Torsten Unge,§ Bjorn Classon,∇,‡ Anders Hallberg, and Bertil Samuelsson*,∇,‡
Department of Chemistry, Linko¨ping University, SE-581 83 Linko¨ping, Sweden, Department of Cell and Molecular Biology,
BMC, Uppsala University, Box 596, SE-751 24 Uppsala, Sweden, Medivir AB, Lunastigen 7, SE-141 44 Huddinge, Sweden,
Department of Organic Pharmaceutical Chemistry, Uppsala University, BMC, Box 574, SE-751 23 Uppsala, Sweden, and
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
Received December 15, 2000
Implementation of derivatized carbohydrates as C2-symmetric HIV-1 protease inhibitors has
previously been reported. With the objective of improving the anti-HIV activity of such
compounds, we synthesized a series of fluoro substituted P1/P1′ analogues. These compounds
were evaluated for antiviral activity toward both wild type and mutant virus. The potency of
the analogues in blocking HIV-1 protease was moderate, with Ki values ranging from 1 to 7
nM. Nonetheless, compared to the parent nonfluorous inhibitors, a majority of the compounds
exhibited improved antiviral activity, for example the 3-fluorobenzyl derivative 9b, which had
a Ki value of 7.13 nM and displayed one of the most powerful antiviral activities in the cellular
assay of the series. Our results strongly suggest that fluoro substitution can substantially
improve antiviral activity. The X-ray crystal structures of two of the fluoro substituted inhibitors
(9a and 9f) cocrystallized with HIV-1 protease are discussed.
In tr od u ction
The human immunodeficiency virus (HIV) is the
causative agent of acquired immunodeficiency syndrome
(AIDS).1-3 The RNA genome of HIV encodes a dimeric
aspartyl protease that processes the viral gag and
gag-pol polyproteins into structural and functional
units. The HIV-1 protease (HIV-1 PR) has been shown
to be essential for formation of mature and infectious
virions;4,5 hence inhibition of this enzyme has become
an attractive target in the quest for effective antiviral
agents, and numerous reports have been published
describing potent inhibitors of HIV-1 PR.6-11 Despite
the success of the FDA-approved HIV-1 PR inhibitors
saquinavir,12 ritonavir,13 indinavir,14 nelfinavir,15
amprenavir,16 and lopinavir,17 there is an urgent need
for new and improved drugs against HIV-1 PR due to
increasing viral resistance, a matter that is now of great
concern.6,7,18-21
Our research group has focused on utilization of
carbohydrates as building blocks in the design and
synthesis of C2-symmetric HIV-1 PR inhibitors.22-26 The
N- and C-termini of a substrate or inhibitor bind to
identical subsites of the C2-symmetric dimeric protease.
A symmetric core unit can be produced by deleting
either the N- or C-terminus and then duplicating the
remaining portion.27,28 We applied this methodology,
placing the C2-symmetry axis in the center of an
asymmetric inhibitor (Figure 1) and deleting the N-
terminus and duplicating the C-terminus, which gave
F igu r e 1. Design of C2-symmetric inhibitor core unit.
F igu r e 2.
us a core unit with stereochemical demands that were
met by L-mannaric acid (Figure 2). Benzylation of the
hydroxy groups at C-2 and C-5 and subsequent coupling
with amino acids or amines gave a series of C2-
symmetric diol-based inhibitors with the general struc-
ture shown in Figure 2. Optimization of the P2/P2′
substituents provided the inhibitors 1 and 2 (Figure 3),
which show good inhibitory profiles.25
Having succeeded in developing highly active protease
inhibitors, we focused on modifying the P1/P1′ benzyloxy
groups by fluoro substitution in an effort to further
improve the anti-HIV activity of HIV wild type and of
resistant mutant strains. The substitution of hydrogen
by fluorine would introduce a minor increase in molec-
ular weight and minimal steric changes, accompanied
by a slight increase in lipophilicity.29-32 Here we de-
scribe the efficient synthesis and biological evaluation
of a series of fluoro inhibitors that, despite moderate
* To whom correspondence should be addressed. Phone: +46 8 608
31 00. Fax: +46 8 608 31 99. E-mail: bertil.samuelsson@medivir.se.
† Linko¨ping University.
§ Department of Cell and Molecular Biology, Uppsala University.
∇ Medivir AB.
Department of Organic Pharmaceutical Chemistry, Uppsala Uni-
versity.
‡ Stockholm University.
10.1021/jm001134q CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/15/2001

3084 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19
Pyring et al.
Sch em e 2a
a
Reagents: (a) HNO3; (b) 4a -i, trifluoromethanesulfonic acid,
dioxane; (c) for 8a -i: l-valine methylamide, 2-hydroxypyridine,
C2H4Cl2; (d) for 9a -i: (1S,2R)-(-)-cis-1-amino-2-indanol, 2-hy-
droxypyridine, C2H4Cl2.
F igu r e 3. Parent inhibitors 1 and 2.
Sch em e 1. Preparation of Benzyl
Trichloroacetimidatesa
Biologica l Resu lts. In Tables 1 and 2 the HIV-1 PR
inhibitor values and the anti-HIV-1 activity toward wild
type and mutant virus of the synthesized compounds
are shown. HIV-1 PR was cloned and heterologously
expressed in Escherichia coli as described elsewhere.40
A fluorometric assay was used to determine inhibition
of HIV-1 PR (Ki values).41 Anti-HIV activity (ED50
values) was analyzed in vitro in MT4 cells according to
a previously reported procedure that uses the colori-
metric XTT assay to monitor cytopathogenic effects.41
Selection of drug-resistant virus in vitro was done as
follows: MT4 cells seeded in 96-well microplates were
treated with sub-ED50 concentrations of respective drugs
and infected with 20-50 times the 50% tissue culture
infectious doses of HIV-1 (IIIb).
a
Reagents: (a) CCl3CN, 50% KOH, n-Bu4NHSO4, CH2Cl2.
inhibitory potencies as HIV-PR inhibitors, exhibit sub-
stantial antiviral activities.
Resu lts a n d Discu ssion
Virus replication was monitored by determining levels
of p24 antigen in MT4 cell supernatants. Cell-free virus
was further passaged in 5-fold serially increased con-
centrations of the drug. When virus was growing in
concentrations of the drug that exceeded the ED50
concentration for wild-type virus more than 50-fold, the
supernatant was divided into aliquots, which were used
as virus stock in cross-resistance studies. Proviral DNA
from infected cells in the final passage was analyzed
with respect to nucleotide sequence in the protease
coding region.
Str u ctu r e-Activity Rela tion sh ip s. The present
series of fluoro substituted compounds shows moderate
to good protease inhibition (Ki values in the low nano-
molar range), albeit poorer than the parent unsubsti-
tuted benzyl compounds 1 and 2. Notably, in some cases,
however, the cellular ED50 values were markedly im-
proved compared to the parent inhibitors and even
compared to the reference drugs ritonavir, saquinavir,
and nelfinavir. This tendency can in part be rationalized
by an improvement in cellular permeability attributed
to the higher lipophilicity of the fluoro substituted
compounds.29,31
Ch em istr y. Using the commercially available fluoro-
benzyl alcohols 3a -i, various mono- and difluoro sub-
stituted benzyl trichloroacetimidates 4a -i were
prepared in excellent yields by reaction with trichloro-
acetonitrile under basic conditions (Scheme 1).33 L-
Mannaro-1,4:3,6-di-γ-lactone (6) was synthesized from
L-mannonic-γ-lactone (5) via an aqueous nitric acid
oxidation (Scheme 2), as previously described.25 The
dilactone 6 was benzylated with the crude fluorobenzyl
trichloroacetimidates 4a -i using a catalytic amount of
trifluoromethanesulfonic acid in dry dioxane to give the
dibenzylated lactones 7a -i.34-37 Subsequent opening of
these dilactones with l-valine methylamide38 in the
presence of 2-hydroxypyridine39 in 1,2-dichloroethane
afforded the diamide derivatives 8a -i in 30-92% yield.
Similarly, opening with (1S,2R)-(-)-cis-1-amino-2-
indanol and 2-hydroxypyridine in 1,2-dichloroethane
generated the corresponding diamide derivatives 9a -i
in 47-72% yield. An undesired â-elimination attributed
to the basicity of the amines constituted the major side
reaction. The competing elimination process was coun-
tered to some extent by addition of the bifunctional
catalyst 2-hydroxypyridine, which has previously been
shown to improve yields in formation of amides from
esters.39
Examination of the ED50 values for the monosubsti-
tuted derivatives reveals that the 2-fluoro substituted
derivatives were the most potent over all. Thus, in the

Synthesis of C2-Symmetric HIV-1 PR Inhibitors
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19 3085
Ta ble 1. HIV-1 Protease Inhibitory Activities of l-Valine Methylamide Compounds
ED50 MT4/mutant HIV-1 (µM)
D30N, S37N,
K45I, M46I,
A71V, L90Me
Kia
(nM)
ED50 WT
(µM)
V32I, M46I,
A71V, V82Ab
M46I, V82F,
I84Vc
A71V, I84V,
L90Md
compd
X-
Y-
1
H
H
H
H
H
3-F
4-F
5-F
6-F
4-F
5-F
0.80
1.92
1.83
1.79
1.28
1.12
1.98
1.73
1.98
1.98
0.82
0.23
0.23
1.32
0.28
0.68
1.17
0.66
0.72
0.65
1.35
0.67
0.42
0.06
0.01
0.02
8.13
9.34
1.84
7.82
1.54
3.35
10.73
>15
>15
7.45
1.69
0.97
2.26
1.89
10.92
>15
1.22
1.40
2.47
0.01
0.11
6.1
>15
1.15
1.10
1.32
0.34
0.48
1.38
7.14
0.85
0.34
0.15
0.03
2.44
8a
8b
8c
8d
8e
8f
8g
8h
8i
2-F
3-F
4-F
2-F
2-F
2-F
2-F
3-F
3-F
0.63
1.04
3.65
1.11
1.17
1.38
8.14
0.81
1.64
0.41
0.08
0.12
2.84
1.32
0.98
0.01
0.07
r iton a vir
sa qu in a vir
n elfin a vir
a
b
d
Standard error 20%. Mutation selected with compound 1. c Mutation selected with ritonavir. Mutation selected with saquinavir.
e Mutation selected with nelfinavir.
Ta ble 2. HIV-1 Protease Inhibitory Activity of (1S,2R)-(-)-cis-1-Amino-2-indanol Compounds
ED50 MT4/mutant HIV-1 (µM)
D30N, S37N,
Kia
(nM)
ED50 WT
(µM)
V32I, M46I,
A71V, V82Ab
M46I, V82F,
I84Vc
A71V, I84V,
L90Md
K45I, M46I,
compd
X-
Y-
A71V, L90Me
2
H
H
H
H
H
3-F
4-F
5-F
6-F
4-F
5-F
1.22
3.26
7.13
5.39
4.00
1.65
3.29
1.64
3.90
5.00
0.82
0.23
0.23
0.10
0.05
0.06
0.25
0.03
0.11
0.02
0.06
0.13
0.05
0.06
0.01
0.02
0.46
0.27
0.18
1.13
0.24
0.67
0.16
0.31
1.05
0.23
0.98
0.01
0.07
1.28
0.51
0.53
1.13
0.88
1.73
0.71
1.39
1.30
1.06
2.47
0.01
0.11
0.07
0.08
0.95
ndf
0.05
0.37
0.08
0.13
0.16
0.09
0.41
0.08
0.12
0.10
0.21
0.21
0.56
0.06
0.25
0.10
0.25
0.30
0.24
0.15
0.03
2.44
9a
9b
9c
9d
9e
9f
9g
9h
9i
2-F
3-F
4-F
2-F
2-F
2-F
2-F
3-F
3-F
r iton a vir
sa qu in a vir
n elfin a vir
a
b
d
Standard error 20%. Mutation selected with compound 1. c Mutation selected with ritonavir. Mutation selected with saquinavir.
e Mutation selected with nelfinavir. f nd, not determined.
valine series the 2-, 3-, and 4-fluoro derivatives (8a -c,
respectively) were equipotent in the enzyme essay,
whereas the 2-fluoro compound exhibited the most
pronounced activity in the cell system. This tendency
can also be discerned in the indanolamine series (9a -
c), but in that case the analysis is complicated by

3086 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19
Pyring et al.
group points away from the active site and is hydrogen
bonded to one of the carbonyls. This interaction pattern
of the diol results in asymmetric binding of this class
of compounds.25
In compounds 9a and 9f, the 2-fluoro substituent is
positioned in range for hydrophobic contacts with P81,
V82, and I50. As deduced from the 3D structure, it is
possible that the 5-fluoro substituent of 9f participates
in a hydrogen bond interaction with the R8 side chain
(2.9 Å) at the water interface of the S1/S1′ subsites
(Figure 5). However, the Ki values do not indicate that
such a favorable interaction is established (cf. 9a and
9f, with Ki values of 3.26 and 3.29 nM, respectively).
Compounds 9a and 9f exhibit a minor conformational
difference in the P1′ orientation, but this slight dis-
similarity seems to have only a minor effect on the
positioning of the fluorine substituents in the S1′ subsite
and is related to the asymmetric positioning of the
central diols. As a consequence of close packing inter-
actions to the P2/P2′ arms and S1/S1′ subsites, the
phenyl rings are held coplanar in both the mono- and
disubstituted compounds.
F igu r e 4. Superimposition of compound 9a (black) and 9f
(gray) bound to the active site of HIV-1 PR. The mono- and
disubstituted fluoro compounds have the same overall binding
conformation. However, there is a small conformational dif-
ference in the P1′ orientation between compounds 9a and 9f.
This difference has only a minor effect on the positioning of
the fluorine substituents in the S1′ subsite, and it is related
to the asymmetric positioning of the central diols. The image
was compiled using the protein modeling software O42 and the
Web-based imaging program MOLRAY.43
variations in the Ki values. It is notable that in the
indanolamine series, but not the valine series (cf. 8b
and 9b), the 3-fluoro benzyl group was apparently less
well accommodated in the enzyme. Considering the
disubstituted derivatives, a 2-fluoro substitution was
again favorable, and the most potent of all were the
indanolamine 9d (2,3-difluoro) and especially 9f (2,5-
difluoro). The latter compound had an ED50 value of 0.02
µM, despite its moderate Ki value of 3.29 nM (cf.
nelfinavir in the same assays, which had an ED50 of 0.02
µM and a Ki of 0.23 nM). However, the most convincing
results regarding the ability of fluorine substitution to
improve antiviral activity in cell assays was observed
for 9b, which had an ED50 value of 0.06 µM and a Ki
value as high as 7.13 nM.
Con clu sion
In summary, we discovered two P1/P1′ fluoro substi-
tuted benzyl analogues (9d and 9f) with very potent
anti-HIV activity on wild type and a wide range of
mutant HIV-1 strains. Closer examination of the sub-
stitution pattern and antiviral activity shows that the
2-position in combination with substitution at the 3- or
5-position is most favorable for fluoro substitution. Our
results strongly suggest that fluoro substitution might
provide an efficient tool for improvement of antiviral
activity.
X-r a y Cr ysta llogr a p h y. The monofluoro substituted
compound 9a and the difluoro substituted analogue 9f
were cocrystallized with HIV-1 PR, and their structures
were determined. When associated to the active site, 9a
and 9f adopt a similar overall binding conformation
(Figure 4). The hydroxy group of the indanolamine in
P2/P2′ forms a hydrogen bond to the backbone nitrogen
of D29 (3.0 Å). Furthermore, the structures reveal that
one of the hydroxyls of the central diol points toward
the D25/D125 residues in the active site and is hydrogen
bonded to both carboxyl oxygens. The other hydroxyl
Exp er im en ta l Section
Ch em istr y. Gen er a l In for m a tion . 1H and 13C NMR
spectra were recorded on a Bruker AF-250 instrument, using
DMSO-d6 or CDCl3 with Me4Si as an internal standard, as
solvents. Chemical shifts are given in ppm (δ scale). Thin-layer
chromatography was performed on Merck precoated 60 F-254
plates, and spots were visualized with UV light and by
charring with EtOH/H2SO4/HOAc/p-anisaldehyde 90:3:1:2.
Column chromatography was performed using silica gel 60
(0.040-0.063 mm, Merck). Melting points were recorded on
an electrothermal melting point apparatus and are uncor-
F igu r e 5. Stereoview of compound 9f bound to the active site of HIV-1 PR. This orientation visualizes the interactions between
the disubstituted phenyl ring of the P1 arm and the S1 subsite. The residues P81, V84, and I50 are within 4.0 Å of the 2-fluoro
substituent, suggesting the presence of hydrophobic interactions. The 5-fluoro substituent might form a hydrogen bond to the
guanidine group of R8 at the water interface of S1 (2.9 Å). The P1/P1′ arms are positioned for optimal hydrophobic interactions
with the P2/P2′ arms and the S2/S2′ subsites. The image was compiled using the protein modeling software O42 and the Web-
based imaging program MOLRAY.43

Synthesis of C2-Symmetric HIV-1 PR Inhibitors
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19 3087
rected. Optical rotations were obtained on a Perkin-Elmer 141
polarimeter. Specific rotations ([R]D) are reported in deg/dm,
the concentration (c) values are given in g/100 mL of the
specified solvent and were recorded at 21 ( 2 °C. Samples were
lyophilized from p.a. dioxane prior to elemental analysis and
biological testing. Elemental analyses were performed by
Analytische Laboratorien, Lindlar, Germany, and the results
are within (0.4% of calculated values.Samples sent for
elemental analysis were lyophilized from p.a. dioxane or water.
Standard workup: organic layers were dried over anhydrous
MgSO4 and concentrated in vacuo.
(2-F lu or oben zyl)-2,2,2-tr ich lor oa cetim id a te (4a ). Tetra-
butylammonium hydrogen sulfate (10 mg) was added to a
stirred and cooled (0 °C) mixture of 2-fluorobenzyl alcohol 3a
(0.510 g, 4.04 mmol) in CH2Cl2 and 50% aqueous KOH (20 mL,
1:1). After 5 min, trichloroacetonitrile (0.49 mL, 4.85 mmol)
was added. The mixture was stirred for 30 min at 0 °C and 2
h at room temperature. The layers were separated, and the
aqueous layer was extracted with CH2Cl2 (2 × 10 mL). The
combined organic layers were dried and concentrated to give
4a (0.973 g, 89%), as a yellow oil. The formed trichloroace-
timidate was used without further purification. 1H NMR (250
MHz, CDCl3) δ 5.41 (s, 2H), 7.05-7.19 (m, 2H), 7.28-7.42 (m,
2H), 7.46-7.57 (m, 2H), 8.44 (s, 1H); 13C NMR (62.9 MHz,
7.27-7.36 (m, 1H), 8.45 (s, 1H); 13C NMR (62.9 MHz, CDCl3)
δ 58.9, 91.1, 117.0 (m, 3C), 124.0 (m), 132.5 (m), 150.1 (m, 2C),
162.3.
(3,5-Diflu or ob en zyl)-2,2,2-t r ich lor oa cet im id a t e (4i).
Compound 4i was prepared from 3,5-difluorobenzyl alcohol 3i
in 99% yield by the same procedure as described for 4a . 1H
NMR (250 MHz, CDCl3) δ 5.3 (s, 2H), 6.7-6.8 (m, 1H), 6.9-
7.05 (m, 2H), 8.45 (s, 1H); 13C NMR (62.9 MHz, CDCl3) δ 69.0,
91.0, 103.6 (t, J CF ) 25.9), 110.1 (d, 2C, J CF ) 25.9), 139.4 (m),
162.2, 162.6 (m, 2C).
L-Ma n n a r o-1,4:3,6-d ila cton e (6). 6 was prepared from
L-mannonic-γ-lactone 5 by the procedure described by Alter-
man.25 The title compound was obtained as a white solid in
1
40% yield. H NMR (250 MHz, DMSO-d6) δ 4.77 (d, 2H, J )
4.02), 5.05 (d, 2H, J ) 4.02), 6.43 (brs); 13C NMR (62.9 MHz,
DMSO-d6) δ 69.0, 75.7, 174.1.
2,5-O-Bis-(2-flu or ob e n zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7a ). Compound 6 (0.200 g, 1.15 mmol) and 2-fluoroben-
zyl trichloroacetimidate 4a (0.930 g, 3.44 mmol) were dissolved
in dry dioxane (20 mL) with vigorous stirring in an N2
atmosphere. Trifluoromethanesulfonic acid (107 µL) was slowly
added. Within 1-2 h the color changed to a reddish-brown.
After 6 h the reaction mixture was filtered through a plug of
SiO2/NaHCO3/SiO2, eluated with dioxane (20 mL), and then
concentrated and dried under vacuum overnight. The resulting
solid was suspended in hot Et2O, and the Et2O was decanted.
This procedure was repeated twice, filtering the final time to
obtain the bisbenzylated dilactone. The resulting solid was
crystallized from CHCl3 to give 0.303 g (68%) of the title
compound as a white solid: mp 172-173 °C; [R]D ) -128.32
CDCl3) δ 64.7, 64.8, 91.2, 115.4 (d, J CF ) 20.3), 122.6 (d, J CF
)
14.8), 124.1 (d, J CF ) 3.7), 130.1 (m, 2C), 160.7 (d, J CF ) 247.9),
162.4.
(3-F lu or oben zyl)-2,2,2-tr ich lor oa cetim id a te (4b). Com-
pound 4b was prepared from 3-fluorobenzyl alcohol 3b in 95%
yield by the same procedure as described for 4a . 1H NMR (250
MHz, CDCl3) δ 5.29 (s, 2H), 7.00-7.13 (m, 3H), 7.31-7.44 (m,
1H), 8.4 (s, 1H); 13C NMR (62.9 MHz, CDCl3) δ 69.6, 91.2, 114.3
(d, J CF ) 21.3), 114.9 (d, J CF ) 22.2), 123.0 (m), 130.0 (d, J CF
) 7.4), 138.1 (d, J CF ) 7.4), 162.0 (d, J CF ) 243.0), 162.2.
(4-F lu or oben zyl)-2,2,2-tr ich lor oa cetim id a te (4c). Com-
pound 4c was prepared from 4-fluorobenzyl alcohol 3c in 94%
yield by the same procedure as described for 4a . 1H NMR (250
MHz, CDCl3) δ 5.31 (s, 2H), 6.94-7.16 (m, 2H), 7.41-7.49 (m,
2H), 8.4 (s, 1H); 13C NMR (62.9 MHz, CDCl3) δ 70.0, 90.4, 115.4
(d, 2C, J CF ) 22.2), 129.7 (d, 2C, J CF ) 7.4), 131.2 (m), 162.6
(d, J CF ) 247.8), 162.4.
1
(c ) 1.01, DMSO); H NMR (250 MHz, DMSO-d6) δ 4.80 and
4.85 (q, 4H, J AB ) 19.9), 4.97 (d, 2H, J ) 3.7), 5.30 (d, 2H, J )
3.8), 7.13-7.24 (m, 4H), 7.36-7.55 (m, 4H); 13C NMR (62.9
MHz, DMSO-d6) δ 65.7, 65.8, 74.2, 75.0, 115.2 (d, J CF ) 20.3),
123.7 (d, J CF ) 14.8), 124.4 (d, J CF ) 3.7), 130.4 (m, 2C), 160.2
(d, J CF ) 246.0), 171.4. Anal. (C20H16F2O6) C, H.
2,5-O-Bis-(3-flu or ob e n zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7b). Compound 7b was obtained as a white solid (57%
yield) from 4b by the same procedure as reported for 7a : mp
174-175 °C; [R]D ) -137.96 (c ) 0.98, DMSO); 1H NMR (250
MHz, DMSO-d6) 4.76 and 4.81 (q, 4H, J AB ) 18.3), 4.92 (d,
2H, J ) 3.7), 5.24 (d, 2H, J ) 4.0), 7.10-7.25 (m, 6H), 7.39-
7.50 (m, 2H); 13C NMR (62.9 MHz, DMSO-d6) δ 71.1, 74.3, 74.7,
114.0 (d, J CF ) 20.3), 114.1 (d, J CF ) 22.3), 123.3 (m), 130.0
(d, J CF ) 7.4), 140.1 (d, J CF ) 7.4), 162.0 (d, J CF ) 243.0), 171.6.
Anal. (C20H16F2O6) C, H.
(2,3-Diflu or oben zyl)-2,2,2-t r ich lor oa cet im id a t e (4d ).
Compound 4d was prepared from 2,3-difluorobenzyl alcohol
3d in 96% yield by the same procedure as described for 4a .
1H NMR (250 MHz, CDCl3) δ 5.42 (s, 2H), 7.05-7.18 (m, 2H),
7.21-7.30 (m, 1H), 8.45 (s, 1H); 13C NMR (62.9 MHz, CDCl3)
2,5-O-Bis-(4-flu or ob e n zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7c). Compound 7c was obtained as a white solid (54%
yield) from 4c by the same procedure as reported for 7a : mp
δ 64.2, 91.1, 117.3 (d, J CF ) 16.6), 124.1 (m), 124.6 (d, J CF
3.7), 125.1 (d, J CF ) 11.1), 149.6 (m, 2C), 162.3.
)
(2,4-Diflu or ob en zyl)-2,2,2-t r ich lor oa cet im id a t e (4e).
Compound 4e was prepared from 2,4-difluorobenzyl alcohol
3e in 98% yield by the same procedure as described for 4a . 1H
NMR (250 MHz, CDCl3) δ 5.33 (s, 2H), 6.74-6.89 (m, 2H),
7.41-7.56 (m, 1H), 8.5 (s, 1H); 13C NMR (62.9 MHz, CDCl3) δ
64.1, 91.1, 104.0 (t, J CF ) 24.9), 111.2 (dd, J CF ) 3.7, 20.3),
1
157-158 °C; [R]D ) -77.17 (c ) 0.92, DMSO); H NMR (250
MHz, DMSO-d6) δ 4.72 and 4.77 (q, 4H, J AB ) 18.9), 4.91 (d,
2H, J ) 4.0), 5.26 (d, 2H, J ) 4.0), 7.13-7.22 (m, 4H), 7.38-
7.49 (m, 4H); 13C NMR (62.9 MHz, DMSO-d6) δ 71.2, 74.3, 74.7,
115.1 (m, 2C), 129.7 (m, 2C), 133.3 (m), 161.8 (d, J CF ) 247.8),
171.6. Anal. (C20H16F2O6) C, H.
118.7 (dd, J CF ) 3.7, 18.5), 131.5 (m), 161.9 (dd, 2C, J CF
112.7, 246.0), 162.3.
)
2,5-O-Bis-(2,3-d iflu or oben zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7d ). Compound 7d was obtained as a white solid (86%
yield) from 4d by the same procedure as reported for 7a : mp
213-214 °C; [R]D ) -132.95 (c ) 1.05, DMSO); 1H NMR (250
MHz, DMSO-d6) δ 4.89 (m, 4H), 5.00 (d, 2H, J ) 4.0), 5.35 (s,
2H, J ) 4.0), 7.21-7.52 (m, 6H); 13C NMR (62.9 MHz, DMSO-
(2,5-Diflu or ob en zyl)-2,2,2-t r ich lor oa cet im id a t e (4f).
Compound 4f was prepared from 2,5-difluorobenzyl alcohol 3f
in 97% yield by the same procedure as described for 4a . 1H
NMR (250 MHz, CDCl3) δ 5.40 (s, 2H), 6.94-7.11 (m, 2H),
7.20-7.32 (m, 1H), 8.5 (s, 1H); 13C NMR (62.9 MHz, CDCl3) δ
64.0, 91.0, 116.2 (m, 3C), 124.5 (m), 157.4 (dd, 2C, J CF ) 242.3,
138.7), 162.2.
d6) δ 65.5, 74.2, 75.0, 117.4 (d, J CF ) 16.6), 124.9 (d, J CF
)
7.4), 125.6 (d, J CF ) 3.7), 126.3 (d, J CF ) 11.1), 148.6 (m, 2C),
171.3. Anal. (C20H14F4O6) C, H.
(2,6-Diflu or ob en zyl)-2,2,2-t r ich lor oa cet im id a t e (4g).
Compound 4g was prepared from 2,6-difluorobenzyl alcohol
3g in 93% yield by the same procedure as described for 4a . 1H
NMR (250 MHz, CDCl3) δ 5.41 (s, 2H), 6.83-7.02 (m, 2H),
7.28-7.40 (m, 1H), 8.45 (s, 1H); 13C NMR (62.9 MHz, CDCl3)
δ 58.8, 91.1, 111.4 (m, 3C), 131.0 (m), 161.6 (m, 2C), 162.5.
(3,4-Diflu or ob en zyl)-2,2,2-t r ich lor oa cet im id a t e (4h ).
Compound 4h was prepared from 3,4-difluorobenzyl alcohol
3h in 98% yield by the same procedure as described for 4a .
1H NMR (250 MHz, CDCl3) δ 5.29 (s, 2H), 7.10-7.22 (m, 2H),
2,5-O-Bis-(2,4-d iflu or oben zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7e). Compound 7e was obtained as a white solid (71%
yield) from 4e by the same procedure as reported for 7a . For
7e-i, the product precipitates from the reaction mixture and
was filtered off to give a white solid prior to filtration through
NaHCO3/SiO2. The filtrate was treated in the same manner
as for 7a : mp 203-204 °C; [R]D ) -138.24 (c ) 1.02, DMSO);
1H NMR (250 MHz, DMSO-d6) δ 4.77 and 4.83 (q, 4H, J AB
)
20.1), 4.92 (d, 2H, J ) 2.2), 5.29 (d, 2H, J ) 4.0), 7.04-7.16
(m, 2H), 7.20-7.35 (m, 2H), 7.51-7.59 (m, 2H); 13C NMR (62.9

3088 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19
Pyring et al.
MHz, DMSO-d6) δ 65.4, 74.2, 74.9, 103.9 (t, J CF ) 24.9), 111.4
(dd, J CF ) 3.7, 20.3), 120.3 (dd, J CF ) 3.7, 18.5), 132.1 (m),
161.2 (dd, 2C, J CF ) 112.8, 246.0) 171.3. Anal. (C20H14F4O6)
C, H.
2,5-O-Bis-(2,5-d iflu or oben zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7f). Compound 7f was obtained as a white solid (59%
yield) from 4f by the same procedure as reported for 7e: mp
195-196 °C; [R]D ) -109.25 (c ) 1.06, DMSO); 1H NMR (250
MHz, DMSO-d6) δ 4.80 and 4.86 (q, 4H, J AB ) 19.7), 5.01 (d,
2H, J ) 4.0), 5.34 (d, 2H, J ) 4.0), 7.20-7.42 (m, 6H); 13C
NMR (62.9 MHz, DMSO-d6) δ 65.5, 74.2, 75.1, 116.6, (m, 3C),
125.6 (m), 157.8 (m, 2C), 171.3. Anal. (C20H14F4O6) C, H.
2,5-O-Bis-(2,6-d iflu or oben zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7g). Compound 7g was obtained as a white solid (93%
yield) from 4g by the same procedure as reported for 7e: mp
220-221 °C; [R]D ) -140.41 (c ) 0.98, DMSO); 1H NMR (250
MHz, DMSO-d6) δ 4.81 (m, 4H), 4.90 (d, 2H, J ) 3.7), 5.28 (d,
2H, J ) 3.7), 7.09-7.22 (m, 4H), 7.43-7.57 (m, 2H); 13C NMR
(62.9 MHz, DMSO-d6) δ 59.6, 74.2, 75.0, 111.6, (m, 3C), 131.0
(m), 160.1 (m, 2C), 171.2. Anal. (C20H14F4O6) C, H.
2,5-O-Bis-(3,4-d iflu or oben zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7h ). Compound 7h was obtained as a white solid (71%
yield) from 4h by the same procedure as reported for 7e: mp
192-193 °C; [R]D ) -136.17 (c ) 0.94, DMSO); 1H NMR (250
MHz, DMSO-d6) 4.72 and 4.76 (q, 4H, J AB ) 18.7), 4.92 (d, 2H,
J ) 3.7), 5.24 (d, 2H, J ) 3.7), 7.20-7.31 (m, 2H), 7.39-7.54
(m, 4H); 13C NMR (62.9 MHz, DMSO-d6) δ 70.6, 74.3, 74.8,
116.9 (m, 2C), 124.6 (m), 134.6 (m), 149.9 (m, 2C), 171.5. Anal.
(C20H14F4O6) C, H.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-bis-(4-flu or oben zyloxy)-3,4-d ih yd r oxy-
h exa n ed ia m id e (8c). The title compound was prepared in
43% yield from 7c by the same procedure as described for 8a :
mp 237-238 °C; [R]D ) +9.26 (c ) 0.68, DMSO). 1H NMR (250
MHz, DMSO-d6) δ 0.79 (dd, 12H, J ) 4.6, 6.5), 1.96 (m, 2H),
2.59 (d, 6H, J ) 4.1), 3.83 (dd, 2H, J ) 6.9), 4.01 (d, 2H, J )
7.3), 4.17 (q, 2H, J ) 2.0, 6.7), 4.52 (m, 4H), 4.91 (d, 2H, J )
7.1), 7.09-7.44 (m, 8H), 7.71 (d, 2H, J ) 9.0), 7.89 (d, 2H, J )
4.6). 13C NMR (62.9 MHz, DMSO-d6) δ 18.0, 19.1, 25.3, 30.4,
57.5, 69.6, 70.3, 79.2, 114.8 (d, 2C, J CF ) 20.3), 129.6 (d, 2C,
J CF ) 7.4), 134.2 (m), 161.6 (d, J CF ) 242.3), 170.3, 171.0. Anal.
(C32H44F2N4O8) C, H, N.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-b is-(2,3-d iflu or ob en zyloxy)-3,4-d ih y-
d r oxyh exa n ed ia m id e (8d ). The title compound was pre-
pared in 31% yield from 7d by the same procedure as described
for 8a : mp 204-205 °C; [R]D ) +7.5 (c ) 0.40, DMSO); 1H
NMR (250 MHz, DMSO-d6) δ 0.80 (dd, 12H, J ) 4.0, 6.6), 1.92
(m, 2H), 2.59 (d, 6H, J ) 4.8), 3.78 (dd, 2H, J ) 7.0), 4.00 (d,
2H, J ) 7.7), 4.23 (dd, 2H, J ) 7.0, 8.8), 4.61 (m, 4H), 4.83 (d,
2H, J ) 7.0), 7.11-7.46 (m, 6H), 7.74 (d, 2H, J ) 9.1), 7.91 (d,
2H, J ) 4.8); 13C NMR (62.9 MHz, DMSO-d6) δ 18.0, 19.1, 25.3,
30.4, 57.6, 64.3, 69.5, 79.2, 116.7 (d, J CF ) 16.6), 124.6 (d, J CF
) 7.4), 125.2 (d, J CF ) 3.7), 127.4 (d, J CF ) 11.1), 148.3 (dd,
J CF ) 116.5, 247.9), 148.5 (dd, J CF ) 117.4, 246.9), 170.0, 171.0.
Anal. (C32H42F4N4O8) C, H, N.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-b is-(2,4-d iflu or ob en zyloxy)-3,4-d ih y-
d r oxyh exa n ed ia m id e (8e). The title compound was prepared
in 58% yield from 7e by the same procedure as decribed for
8a : mp 223-224 °C; [R]D ) +8.26 (c ) 0.69, DMSO); 1H NMR
(250 MHz, DMSO-d6) δ 0.89 (dd, 12H, J ) 4.8, 6.2), 2.03 (m,
2H), 2.61 (d, 6H, J ) 4.4), 3.79 (t, 2H, J ) 7.3), 3.99 (d, 2H, J
) 7.7), 4.20 (dd, 2H, J ) 6.6, 8.4), 4.61 (m, 4H), 4.84 (d, 2H, J
) 7.3), 7.04-7.23 (m, 4H), 7.48 (m, 2H), 7.77 (d, 2H, J ) 8.8),
7.92 (d, 2H, J ) 4.8); 13C NMR (62.9 MHz, DMSO-d6) δ 17.9,
19.1, 25.3, 30.4, 57.5, 64.4, 69.6, 79.2, 103.6 (t, J CF ) 24.9),
111.2 (q, J CF ) 3.7, 20.3), 121.1 (d, J CF ) 18.5), 131.5 (m), 160.9
(dd, J CF ) 112.8, 246.0), 161.0 (dd, J CF ) 112.8, 246.0), 170.1,
171.0. Anal. (C32H42F4N4O8) C, H, N.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-b is-(2,5-d iflu or ob en zyloxy)-3,4-d ih y-
d r oxyh exa n ed ia m id e (8f). The title compound was prepared
in 36% yield from 7f by the same procedure as described for
8a : mp 249-250 °C; [R]D ) +5.88 (c ) 0.68, DMSO); 1H NMR
(250 MHz, DMSO-d6) δ 0.82 (q, 12H, J ) 3.3), 1.93 (m, 2H),
2.61 (d, 6H, J ) 4.4), 3.84 (dd, 2H, J ) 7.0), 4.07 (d, 2H, J )
7.7), 4.16 (dd, 2H, J ) 7.0, 8.8), 4.48 (m, 4H), 4.91 (d, 2H, J )
7.0), 7.09-7.36 (m, 6H), 7.81 (d, 2H, J ) 8.8), 7.88 (d, 2H, J )
4.8); 13C NMR (62.9 MHz, DMSO-d6) δ 17.9, 19.1, 25.3, 30.4,
57.6, 64.1, 64.2, 69.5, 79.4, 116.0, (m, 3C), 127.0 (m), 156.8
(dd, 2C, J CF ) 242.3, 147.9), 170.0, 171.0. Anal. (C32H42F4N4O8)
C, H, N.
2,5-O-Bis-(3,5-d iflu or oben zyl)-L-m a n n a r o-1,4:3,6-d ila c-
ton e (7i). Compound 7i was obtained as a white solid (59%
yield) from 4i by the same procedure as reported for 7e: mp
221-222 °C; [R]D ) -127.63 (c ) 0.80, DMSO); 1H NMR (250
MHz, DMSO-d6) δ 4.78 (m, 4H), 4.95 (d, 2H, J ) 3.3), 5.32 (d,
2H, J ) 3.7), 7.12-7.24 (m, 6H); 13C NMR (62.9 MHz, DMSO-
d6) δ 70.6, 74.3, 75.0, 103.2 (t, J CF ) 26.0), 110.3 (d, 2C, J CF
)
25.9), 141.6 (m), 162.0 (m, 2C), 171.4. Anal. (C20H14F4O6) C,
H.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-bis-(2-flu or oben zyloxy)-3,4-d ih yd r oxy-
h exa n ed ia m id e (8a ). l-Valine methylamide38 (38 mg, 0.29
mmol) in dry 1,2-dichloroethane (3 mL) was added to a solution
of 7a (47 mg, 0.12 mmol) and 2-hydroxypyridine (10 mg, 0.12
mmol) in dry 1,2-dichloroethane (2 mL). The resulting mixture
was stirred at 70 °C overnight and concentrated. The residue
was dissolved in CH2Cl2 (9 mL) and MeOH (1 mL), and the
organic phase was washed with 1 M HCl (5 mL), followed by
saturated aqueous NaHCO3 (5 mL), and then dried, filtered,
and concentrated. Column chromatography (CH2Cl2-MeOH
24:1 f 14:1) gave 34 mg (44%) of the title compound as a white
1
solid: mp 220-221 °C; [R]D ) +10.91 (c ) 0.55, DMSO); H
NMR (250 MHz, DMSO-d6) δ 0.93 (dd, 12H, J ) 6.0), 2.16 (m,
2H), 2.68 (d, 6H, J ) 4.4), 3.81 (dd, 2H, J ) 6.9), 4.03 (d, 2H,
J ) 7.3), 4.17 (q, 2H, J ) 2.1, 6.7), 4.60 (m, 4H), 4.89 (d, 2H,
J ) 7.1), 7.13-7.47 (m, 8H), 7.67 (d, 2H, J ) 9.0), 7.92 (d, 2H,
J ) 4.6); 13C NMR (62.9 MHz, DMSO-d6) δ 18.2, 19.7, 26.2,
31.7, 59.8, 67.4, 72.4, 81.6, 116.2 (d, J CF ) 22.2), 125.4 (d, J CF
) 3.7), 125.7 (d, J CF ) 22.2), 131.5 (d, J CF ) 48.1), 131.6 (d,
J CF ) 44.4), 159.8 (d, J CF ) 246.0), 173.3, 173.8. Anal.
(C32H44F2N4O8) C, H, N.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-b is-(2,6-d iflu or ob en zyloxy)-3,4-d ih y-
d r oxyh exa n ed ia m id e (8g). The title compound was pre-
pared in 42% yield from 7g by the same procedure as described
1
for 8a : mp 211-212 °C; [R]D ) +19.90 (c ) 1.00, DMSO); H
NMR (250 MHz, DMSO-d6) δ 0.82 (dd, 12H, J ) 7.0), 1.93 (m,
2H), 2.58 (d, 6H, J ) 4.4), 3.67 (dd, 2H, J ) 5.9), 4.01(d, 2H,
J ) 6.6), 4.13 (dd, 2H, J ) 6.6, 8.8), 4.54 (m, 4H), 4.85 (d, 2H,
J ) 5.9), 7.11 (m, 4H), 7.42 (m, 2H), 7.63 (d, 2H, J ) 9.1), 7.87
(d, 2H, J ) 4.8); 13C NMR (62.9 MHz, DMSO-d6) δ 17.8, 19.1,
25.3, 30.5, 57.3, 59.1, 70.1, 79.6, 111.5, (m, 2C), 112.8 (m), 131.0
(m), 161.5 (m, 2C), 169.9, 170.7. Anal. (C32H42F4N4O8) C, H,
N.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-bis-(3-flu or oben zyloxy)-3,4-d ih yd r oxy-
h exa n ed ia m id e (8b). The title compound was prepared in
30% yield from 7b by the same procedure as described for 8a :
mp 230-231 °C; [R]D ) +11.17 (c ) 0.94, DMSO); 1H NMR
(250 MHz, DMSO-d6) δ 0.85 (q, 12H, J ) 3.3), 2.02 (m, 2H),
2.6 (d, 6H, J ) 4.4), 3.86 (dd, 2H, J ) 7.5), 4.04 (d, 2H, J )
8.0), 4.21 (dd, 2H, J ) 6.9, 8.7), 4.48 (m, 4H), 4.86 (d, 2H, J )
7.7), 7.07-7.24 (m, 6H), 7.29-7.43 (m, 2H), 7.76 (d, 2H, J )
8.8), 7.95 (d, 2H, J ) 4.8); 13C NMR (62.9 MHz, DMSO-d6) δ
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-b is-(3,4-d iflu or ob en zyloxy)-3,4-d ih y-
d r oxyh exa n ed ia m id e (8h ). The title compound was pre-
pared in 92% yield from 7h by the same procedure as for 8a :
mp 227-228 °C; [R]D ) +9.22 (c ) 0.64, DMSO); 1H NMR (250
MHz, DMSO-d6) δ 0.77 (dd, 12H, J ) 2.9, 6.6), 1.94 (m, 2H),
2.61 (d, 6H, J ) 4.4), 3.80 (dd, 2H, J ) 7.7), 4.02 (d, 2H, J )
17.9, 19.1, 25.3, 30.4, 57.6, 69.5, 70.1, 79.3, 113.9 (d, J CF
)
22.2), 114.0 (d, J CF ) 20.3), 123.1 (m), 130.0 (d, J CF ) 7.4),
140.9 (d, J CF ) 7.4), 162.0 (d, J CF ) 242.2), 170.2, 171.0. Anal.
(C32H44F2N4O8) C, H, N.

Synthesis of C2-Symmetric HIV-1 PR Inhibitors
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19 3089
8.0), 4.13 (dd, 2H, J ) 6.9, 8.8), 4.39 (m, 4H), 4.79 (d, 2H, J )
7.7), 7.12-7.23 (m, 2H), 7.29-7.46 (m, 4H), 7.73 (d, 2H, J )
9.1), 7.87 (d, 2H, J ) 4.8); 13C NMR (62.9 MHz, DMSO-d6) δ
18.0, 19.1, 25.3, 30.4, 57.6, 69.5, 79.1, 116.7 (m, 2C), 124.0 (m),
135.7 (m), 148.9 (m, 2C), 170.2, 171.0. Anal. (C32H42F4N4O8)
C, H, N.
N1,N6-Bis-[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-b is-(3,5-d iflu or ob en zyloxy)-3,4-d ih y-
d r oxyh exa n ed ia m id e (8i). The title compound was prepared
in 31% yield from 7i by the same procedure as described for
8a : mp 234-235 °C; [R]D ) +10.20 (c ) 0.50, DMSO); 1H NMR
(250 MHz, DMSO-d6) δ 0.86 (dd, 12H, J ) 2.2, 6.6), 1.94 (m,
2H), 2.62 (d, 6H, J ) 4.4), 3.84 (dd, 2H, J ) 7.3), 3.98 (d, 2H,
J ) 8.1), 4.18 (dd, 2H, J ) 7.0, 8.8), 4.5 (m, 4H), 4.83 (d, 2H,
J ) 6.9), 7.02-7.14 (m, 6H), 7.82 (d, 2H, J ) 8.8), 7.94 (d, 2H,
J ) 4.8); 13C NMR (62.9 MHz, DMSO-d6) δ 18.0, 19.1, 25.3,
30.4, 57.6, 69.4, 79.2, 102.6 (m, J CF ) 25.9), 110.0 (m, 2C), 142.8
(m), 162.0 (m, 2C), 170.1, 171.0. Anal. (C32H42F4N4O8) C, H,
N.
2H, J ) 6.0), 4.42 (m, 2H), 4.63 and 4.68 (q, 4H, J AB ) 15.0),
4.91 (d, 2H, J ) 7.3), 5.13 (d, 2H, J ) 4.0), 5.28 (2d, 2H, J )
4.8, 8.4), 7.10-7.34 (m, 14H), 7.87 (d, 2H, J ) 8.8); 13C NMR
(62.9 MHz, DMSO-d6) δ 40.2 (hidden in DMSO), 56.6, 64.5,
69.7, 70.4, 72.0, 79.4, 116.7 (d, J CF ) 16.6), 124.2, 124.6 (d,
J CF ) 7.4), 124.7, 125.2 (d, J CF ) 3.7), 126.1, 127.2, 127.4 (d,
J CF ) 11.1), 140.6, 141.9, 148.3, (dd, J CF ) 116.5, 247.9), 148.5
(q, J CF ) 117.4, 246.9), 170.5. Anal. (C38H36F4N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-bis-(2,4-d iflu or oben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (9e). The title compound was prepared in 59% yield
from 7e by the same procedure as reported for 9a : mp 87-88
°C; [R]D ) +23.82 (c ) 1.10, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.88 (d, 2H, J ) 16.5), 3.17 (2d, 2H, J ) 16.4,
5.2), 3.96 (t, 2H, J ) 7.7), 4.16 (d, 2H, J ) 7.7), 4.45 (m, 2H),
4.55 and 4.60 (q, 4H, J AB ) 15.0), 4.85 (d, 2H, J ) 7.3), 5.15
(d, 2H, J ) 4.4), 5.23 (m, 2H), 7.01-7.21 (m, 12H), 7.48-7.55
(m, 2H), 7.82 (d, 2H, J ) 8.8); 13C NMR (62.9 MHz, DMSO-d6)
δ 40.3 (hidden in DMSO), 56.6, 64.5, 69.7, 70.4, 72.0, 79.4,
103.6 (t, J CF ) 25.8), 111.2 (dd, J CF ) 3.7, 20.3), 121.2 (m)
124.2, 124.7, 126.1, 127.2, 131.6 (m), 140.6, 141.9, 160.9 (dd,
J CF ) 112.8, 246.0), 161.0 (dd, J CF ) 112.8, 246.0), 170.8. Anal.
(C38H36F4N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-bis-(2,5-d iflu or oben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (9f). The title compound was prepared in 70% yield
from 7f by the same procedure as reported for 9a : mp 86-87
°C; [R]D ) +25.16 (c ) 0.64, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.80 (d, 2H, J ) 16.5), 3.11 (2d, 2H, J ) 16.4,
5.2), 3.95 (m, 2H), 4.21 (d, 2H, J ) 7.7), 4.42 (m, 2H), 4.59
and 4.64 (q, 4H, J AB ) 8.4), 4.92 (d, 2H, J ) 7.3), 5.07 (d, 2H,
J ) 4.0), 5.27 (m, 2H), 7.04-7.34 (m, 14H), 7.88 (d, 2H, J )
8.8); 13C NMR (62.9 MHz, DMSO-d6) δ 40.2 (hidden in DMSO),
56.6, 64.2, 69.7, 72.0, 79.5, 115.4, (m, 3C), 124.2, 124.7, 126.1,
126.6 (m), 127.2, 140.6, 141.9, 156.8 (dd, 2C, J CF ) 242.3,
147.9), 170.4. Anal. (C38H36F4N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-bis-(2,6-d iflu or oben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (9g). The title compound was prepared in 72% yield
from 7g by the same procedure as reported for 9a : mp 91-92
°C; [R]D ) +28.82 (c ) 0.93, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.80 (d, 2H, J ) 16.5), 3.06 (2d, 2H, J ) 16.3,
4.8), 3.85 (m, 2H), 4.11 (d, 2H, J ) 7.7), 4.41 (m, 2H), 4.59
and 4.64 (q, 4H, J AB ) 18.6), 4.82 (d, 2H, J ) 7.3), 5.08 (d, 2H,
J ) 4.0), 5.25 (m, 2H), 7.03-7.25 (m, 12H), 7.48 (m, 2H), 7.70
(d, 2H, J ) 8.8); 13C NMR (62.9 MHz, DMSO-d6) δ 40.3 (hidden
in DMSO), 56.4, 59.0, 69.9, 71.9, 79.6, 111.4, (m, 2C), 112.8
(m), 124.2, 124.7, 126.1, 127.2, 131.0 (m), 140.4, 141.9, 161.1
(m, 2C), 170.4. Anal. (C38H36F4N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-bis-(3,4-d iflu or oben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (9h ). The title compound was prepared in 50% yield
from 7h by the same procedure as reported for 9a : mp 72-73
°C; [R]D ) +29.48 (c ) 0.96, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.79 (d, 2H, J ) 16.2), 3.08 (dd, 2H, J ) 16.7,
4.8), 3.87 (m, 2H), 4.21 (m, 2H), 4.49 (m, 6H), 4.91 (m, 2H),
5.12 (d, 2H, J ) 4.4), 5.28 (m, 2H), 7.09-7.45 (m, 14H), 7.78
(d, 2H, J ) 8.7); 13C NMR (62.9 MHz, DMSO-d6) δ 40.2 (hidden
in DMSO), 58.5, 59.9, 73.0, 74.0, 118.0 (m, 2C), 124.2, 124.7,
125.4 (m), 126.1, 127.2, 135.7 (m), 148.9 (m, 2C), 173.8. Anal.
(C38H36F4N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-bis-(3,5-d iflu or oben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (9i). The title compound was prepared in 60% yield
from 7i by the same procedure as reported for 9a : mp 74-75
°C; [R]D ) +38.46 (c ) 0.78, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.84 (d, 2H, J ) 16.1), 3.07 (dd, 2H, J ) 4.6, 16.6),
4.02 (m, 2H), 4.13 (d, 2H, J ) 8.0), 4.42 (m, 2H), 4.55 and 4.61
(q, 4H, J AB ) 18.2), 4.93 (d, 2H, J ) 7.7), 5.05 (d, 2H, J ) 4.0),
5.25 (m, 2H), 7.06-7.21 (m, 14H), 7.85 (d, 2H, J ) 8.8); 13C
NMR (62.9 MHz, DMSO-d6) δ 40.3 (hidden in DMSO), 56.6,
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-b is -(2-flu o r o b e n zy lo x y )-3,4-d ih y d r o x y h e x a n e d i-
a m id e (9a ). (1S,2R)-(-)-cis-1-Amino-2-indanol (40 mg, 0.26
mmol) in dry 1,2-dichloroethane (3 mL) was added to a solution
of 7a (48 mg, 0.12 mmol) and 2-hydroxypyridine (12 mg, 0.13
mmol) in dry 1,2-dichloroethane (2 mL). The reaction mixture
was stirred overnight at 70 °C and then concentrated. The
residue was dissolved in EtOAc (10 mL) and washed with 1
M HCl (5 mL), followed by saturated aqueous NaHCO3 (5 mL),
and thereafter dried, filtered, and concentrated. Column
chromatography (CH2Cl2-MeOH 24:1) gave 50 mg (61%) of
the title compound as a white solid: mp 76-77 °C; [R]D
)
+23.19 (c ) 0.94, DMSO); 1H NMR (250M Hz, DMSO-d6) δ
2.74-3.15 (m, 4H), 3.95 (t, 2H, J ) 7.3), 4.17 (d, 2H, J ) 7.7),
4.43 (q, 2H, J ) 3.8, 4.4), 4.61 and 4.65 (q, 4H, J AB ) 15.4),
4.89 (d, 2H, J ) 7.2), 5.11 (d, 2H, J ) 4.1), 5.31 (q, 2H, J )
3.6, 5.5), 7.13-7.49 (m, 16H), 7.78 (d, 2H, J ) 8.7); 13C NMR
(62.9 MHz, DMSO-d6) δ 40.3 (hidden in DMSO), 56.6, 64.9,
69.8, 72.0, 79.5, 114.9 (d, J CF ) 22.2), 124.4 (d, J CF ) 33.3),
124.7 (d, J CF ) 4.0), 126.1, 127.2, 129.8 (d, J CF ) 33.3), 129.9
(d, J CF ) 31.4), 140.6, 141.9, 159.8 (d, J CF ) 246.0), 170.6. Anal.
(C38H38F2N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-b is -(3-flu o r o b e n zy lo x y )-3,4-d ih y d r o x y h e x a n e d i-
a m id e (9b). The title compound was prepared in 67% yield
from 7b by the same procedure as reported for 9a : mp 77-78
°C; [R]D ) +35.16 (c ) 0.95, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.87 (d, 2H, J ) 16.2), 3.16 (dd, 2H, J ) 4.6, 16.2),
3.97 (t, 2H, J ) 7.6), 4.20 (d, 2H, J ) 7.8), 4.42 (d, 2H, J )
4.0), 4.55 and 4.59 (q, 4H, J AB ) 17.9), 4.89 (d, 2H, J ) 7.2),
5.13 (d, 2H, J ) 2.5), 5.31 (m, 2H), 7.02-7.37 (m, 16H), 7.93
(d, 2H, J ) 8.7); 13C NMR (62.9 MHz, DMSO-d6) δ 40.3 (hidden
in DMSO), 56.6, 69.7, 70.2, 72.0, 79.5, 114.0 (d, J CF ) 20.3),
114.1 (d, J CF ) 22.2), 123.2 (m), 124.2, 124.7, 126.1, 127.2,
130.0 (d, J CF ) 7.4), 140.6, 141.0 (d, J CF ) 7.4), 141.9, 162.0
(d, J CF ) 242.2), 170.7. Anal. (C38H38F2N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-b is -(4-flu o r o b e n zy lo x y )-3,4-d ih y d r o x y h e x a n e d i-
a m id e (9c). The title compound was prepared in 47% yield
from 7c by the same procedure as reported for 9a : mp 79-80
°C; [R]D ) +26.40 (c ) 0.75, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.8-3.1 (m, 4H), 3.93 (t, 2H, J ) 7.6), 4.09 (d,
2H, J ) 8.0), 4.44 (m, 2H), 4.49 (m, 4H), 4.90 (d, 2H, J ) 7.45),
5.12 (d, 2H, J ) 4.2), 5.29 (2d, 2H, J ) 3.6, 5.0), 7.14-7.78
(m, 16H), 8.27 (d, 2H, J ) 8.8); 13C NMR (62.9 MHz, DMSO-
d6) δ 40.3 (hidden in DMSO), 56.5, 69.7, 70.4, 72.0, 79.4, 114.8
(d, 2C, J CF ) 20.3), 124.2, 124.7, 126.1, 127.2, 129.6 (d, 2C,
J CF ) 7.4), 134.1, 140.6, 141.9, 161.6 (d, J CF ) 242.3), 170.8.
Anal. (C38H38F2N2O8) C, H, N.
N1,N6-Bis-[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-bis-(2,3-d iflu or ob en zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (9d ). The title compound was prepared in 49% yield
from 7d by the same procedure as reported for 9a : mp 84-85
°C; [R]D ) +27.53 (c ) 0.81, DMSO); 1H NMR (250 MHz,
DMSO-d6) δ 2.8-3.1 (m, 4H), 3.98 (t, 2H, J ) 7.6), 4.14 (d,
66.2, 69.5, 72.0, 79.4, 102.6 (t, J CF ) 25.9), 110.0 (d, 2C, J CF
)
25.9), 124.2, 124.6, 126.0, 127.2, 140.5, 141.8, 142.8 (m), 162.1
(m, 2C), 170.5. Anal. (C38H36F4N2O8) C, H, N.

3090 J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19
Pyring et al.
(16) Navia, M. A.; Sato, V. L.; Tung, R. D. Design of VX-478, a Potent
Inhibitor of HIV Protease. Int. Antiviral News 1995, 3, 143-
145.
(17) Sham, H. L.; Kempf, D. J .; Molla, A.; Marsh, K. C.; Kumar, G.
N.; Chen, C.-M.; Kati, W.; Stewart, K.; Lal, R.; Hsu, A.;
Betebenner, D.; Korneyeva, M.; Vasavanonda, S.; McDonald, E.;
Saldivar, A.; J apour, A. J .; Leonard, J . M.; Plattner, J .; Norbeck,
D. ABT-378, a Highly Potent Inhibitor of the Human Immuno-
deficiency Virus Protease. Antimicrob. Agents Chemother. 1998,
42, 3218-3224.
(18) Schinzai, R. F.; Larder, B. A.; Mellors, J . W. Mutations in
retroviral genes associated with drug resistance. Int. Antiviral
News 1996, 4, 95-107.
(19) Molla, A.; Korneyeva, M.; Gao, Q.; Vasavanonda, S.; Schipper,
P. J .; Mo, H.-M.; Markowitz, M.; Chernyavskiy, T.; Niu, P.;
Lyons, N.; Hsu, A.; Granneman, G. R.; Ho, D. D.; Boucher, A.
B. B.; Leonard, J . M.; Norbeck, D. W.; Kempf, D. J . Ordered
accumulation of mutations in HIV protease confers resistance
to ritonavir. Nature Med. 1996, 2, 760-766.
Cr ysta llogr a p h y. The details of the crystallization and
structure determinations will be published elsewhere. Briefly,
the complexes of HIV-1 PR, 9a , and 9f were crystallized in
space group P21212 and determined to 1.8 and 1.9 Å resolu-
tions, respectively.
Ack n ow led gm en t. We are grateful to the Swedish
National Board for Technical Development (NUTEK)
and the Swedish Foundation for Strategic Research
(SSF) for financial support and to Medivir AB, Hud-
dinge, Sweden, for financial support and biological
testing. We also thank Seved Lo¨wgren, Department of
Cell and Molecular Biology, BMC, Uppsala University,
Sweden, for preparation of the HIV-1 protease and the
protease/inhibitor crystals.
(20) Condra, J . H.; Schleif, W. A.; Blahy, O. M.; Gabryelski, L. J .;
Graham, D. J .; Quintero, J . C.; Rhodes, A.; Robbins, H. L.; Roth,
E.; Shivaprakash, M.; Tius, D.; Yang, T.; Teppler, H.; Squires,
K. E.; Deutsch, P. J .; Emini, E. A. In vivo emergence of HIV-1
variants resistant to multiple protease inhibitors. Nature 1995,
374, 569-571.
(21) Coffin, J . M. HIV population dynamics in vivo: Implications for
genetic variation, pathogenesis, and therapy. Science 1995, 267,
483-489.
(22) Wachtmeister, J .; Mu¨hlman, A.; Classon, B.; Kvarnstro¨m, I.;
Hallberg, A.; Samuelsson, B. Impact of the Central Hydroxyl
Groups on the activity of Symmetrical HIV-1 Protease Inhibitors
Derived From L-Mannaric Acid. Tetrahedron 2000, 56, 3219-
3225.
(23) Oscarsson, K.; Classon, B.; Kvarnstro¨m, I.; Hallberg, A.; Sam-
uelsson, B. Solid phase assisted synthesis of HIV-1 protease
inhibitors. Expedient entry to unsymmetrical substitution of a
C2 symmetric template. Can. J . Chem. 2000, 78, 829-837.
(24) Alterman, M.; Andersson, H. O.; Garg, N.; Ahlse´n, G.; Lo¨vgren,
S.; Classon, B.; Danielsson, H.; Kvarnstro¨m, I.; Vrang, L.; Unge,
T.; Samuelsson, B.; Hallberg, A. Design and Fast Synthesis of
C-Terminal Duplicated Potent C2-Symmetric P1/P1′-Modified
HIV-1 Protease Inhibitors. J . Med. Chem. 1999, 42, 3835-3844.
(25) Alterman, M.; Bjo¨rsne, M.; Mu¨hlman, A.; Classon, B.; Kvarn-
stro¨m, I.; Danielsson, H.; Markgren, P.-O.; Nillroth, U.; Unge,
T.; Hallberg, A.; Samuelsson, B. Design and Synthesis of New
Potent C2-Symmetric HIV-1 Protease Inhibitors. Use of L-
Mannaric Acid as a Peptidomimetic Scaffold. J . Med. Chem.
1998, 41, 3782-3792.
(26) Zucarello, G.; Bouzide, A.; Kvarnstro¨m, I.; Niklasson, G.; Svens-
son, S. C. T.; Brisander, M.; Danielsson, H.; Nillroth, U.; Karle´n,
A.; Hallberg, A.; Classon, B.; Samuelsson, B. HIV-1 Protease
Inhibitors Based on Acyclic Carbohydrates. J . Org. Chem. 1998,
63, 4898-4906.
(27) Erickson, J .; Kempf, D. Structure-based design of symmetric
inhibitors of HIV-1 protease. Arch. Virol. 1994, 9, 19-29.
(28) Kempf, D. J . Design of Symmetry-Based, Peptidomimetic Inhibi-
tors of Human Immunodeficiency Virus Protease. Methods
Enzymol. 1994, 334-354.
(29) Patani, G. A.; LaVoie, E. J . Biosterism: A Rational Approach
in Drug Design. Chem. Rev. 1996, 96, 3147-3176.
(30) Ojima, I.; Welch, J . T.; McCarthy, J . R. Biomedical frontiers of
fluorine chemistry; American Chemical Society: Washington,
DC, 1996.
(31) Filler, R.; Kobayashi, Y.; Yagupolski, L. M. Organofluorine
Compounds in Medicinal Chemistry and Biomedical Applica-
tions; Elsevier Science Publishers B. V.: Amsterdam, 1993.
(32) Filler, R.; Kobayashi, Y. Biomedicinal aspects of fluorine chem-
istry; Elsevier Biomedical Press: Amsterdam, 1982.
(33) Patil, V. J . A Simple Access to Trichloroacetimidates. Tetrahe-
dron Lett. 1996, 37, 1481-1484.
Refer en ces
(1) Gallo, R. C.; Salahuddin, S. Z.; Popovic, M.; Shearer, G. M.;
Kaplan, M.; Haynes, B. F.; Palker, T. J .; Redfield, R.; Oleske,
J .; Safai, B.; White, G.; Foster, P.; Markham, P. D. Frequent
Detection and Isolation of Cytopathic Retroviruses (HTLV-III)
from Patients with AIDS and at Risk for AIDS. Science 1984,
224, 500-503.
(2) Gallo, R. C.; Sarin, P. S.; Gelmann, E. P.; Robert-Guroff, M.;
Richardson, E.; Kalyanaraman, V. S.; Mann, D.; Sidhu, G. D.;
Stahl, R. E.; Zolla-Pazner, S.; Leibowitch, J .; Popovic, M.
Isolation of Human T-Cell Leukemia Virus in Acquired Immune
Deficiency Syndrome (AIDS). Science 1983, 220, 865-867.
(3) Barre´-Sinoussi, F.; C., C. J .; Rey, F.; Nugeyre, M. T.; Chamaret,
S.; Gruest, J .; Dauguet, C.; Axler-Blin, C.; Ve´zinet-Brun, F.;
Rouzioux, C.; Rozenbaum, W.; Montagnier, L. Isolation of a
T-lymphocytic Retrovirus from a Patient at Risk for Acquired
Immune Deficiency Syndrome (AIDS). Science 1983, 220, 868-
871.
(4) Peng, C.; Ho, B. K.; Chang, T. W.; Chang, N. T. Role of Human
Immunodeficiency Virus Type 1-Specific Protease in Core Pro-
tein Maturation and Viral Infectivity. J . Virol. 1989, 63, 2550-
2556.
(5) Kohl, N. E.; Emini, E. A.; Schleif, W. A.; Davis, L. J .; Heimbach,
J . C.; Dixon, R. A. F.; Scolnick, E. M.; Sigal, I. S. Active human
immunodeficiency virus protease is required for viral infectivity.
Proc. Natl. Acad. Sci. U.S.A. 1988, 85, 4686-4690.
(6) Flexner, C. J . HIV Protease Inhibitors. N. Engl. J . Med. 1998,
338, 1281-1292.
(7) Molla, A.; Granneman, G. R.; Sun, E.; Kempf, D. J . Recent
developments in HIV protease inhibitor therapy. Antiviral Res.
1998, 1-23.
(8) Kempf, D. J .; Sham, H. L. HIV Protease Inhibitors. Curr. Pharm.
Des. 1996, 2, 225-246.
(9) De Clercq, E. Toward Improved Anti-HIV Chemotherapy: Thera-
peutic Strategies for Intervention with HIV Infections. J . Med.
Chem. 1995, 38, 2491-2517.
(10) Wlodawer, A.; Erickson, J . W. Structure-Based Inhibitors of
HIV-1 Protease. Annu. Rev. Biochem. 1993, 62, 543-585.
(11) Huff, J . R. HIV Protease: A Novel Chemotherapeutic Target
for AIDS. J . Med. Chem. 1991, 34, 2305-2314.
(12) Roberts, N. A.; Martin, J . A.; Kinchington, D.; Broadhurst, A.
V.; Craig, J . C.; Duncan, I. B.; Galpin, S. A.; Handa, B. K.; Kay,
J .; Kro¨hn, A.; Lambert, R. W.; Merrett, J . H.; Mills, J . S.; Parkes,
K. E. B.; Redshaw, S.; Ritchie, A. J .; Taylor, D. L.; Thomas, G.
J .; Machin, P. J . Rational Design of Peptide-Based HIV Pro-
teinase Inhibitors. Science 1990, 248, 358-361.
(13) Kempf, D. J .; Marsh, K. C.; Denissen, J . F.; McDonald, E.;
Vasavanonda, S.; Flentge, C. A.; Green, B. E.; Fino, L.; Park, C.
H.; Kong, X.-P.; Wideburg, N. E.; Saldivar, A.; Ruiz, L.; Kati,
W. M.; Sham, H. L.; Robins, T.; Stewart, K. D.; Hsu, A.; Plattner,
J . J .; Leonard, J . M.; Norbeck, D. W. ABT-538 is a Potent
Inhibitor of Human Immunodeficiency Virus Protease and has
High Oral Bioavailability in Humans. Proc. Natl. Acad. Sci.
U.S.A. 1995, 92, 2484-2488.
(14) Vacca, J . P.; Dorsey, B. D.; Schleif, W. A.; Levin, R. B.; McDaniel,
S. L.; Darke, P. L.; Zugay, J .; Quintero, J . C.; Blahy, O. M.; Roth,
E.; Sardana, V. V.; Schlabach, A. J .; Graham, P. I.; Condra, J .
H.; Gotlib, L.; Holloway, M. K.; Lin, J .; Chen, I.-W.; Vastag, K.;
Ostovic, D.; Anderson, P. S.; Emini, E. A.; Huff, J . R. L-735,-
524: An Orally Bioavailable Human Immunodeficiency Virus
Type 1 Protease Inhibitor. Proc. Natl. Acad. Sci. U.S.A. 1994,
91, 4096-4100.
(15) Kalish, V.; Kaldor, S.; Shetty, B.; Tatlock, J .; Davies, J .;
Hammond, M.; Dressman, B.; Fritz, J .; Appelt, K.; Reich, S.;
Musick, L.; Wu, B.-W.; Su, K. Iterative Protein Structure-Based
Drug Design and Synthesis of HIV Protease Inhibitors. Eur. J .
Med. Chem. 1995, 30 (Suppl), S201-S214.
(34) J ensen, H. S.; Limberg, G.; Pedersen, C. Benzylation of Aldono-
lactones with benzyl trichloroacetimidate. Carbohydr. Res. 1997,
109-112.
(35) Eckenberg, P.; Groth, U.; Huhn, T.; Richter, N.; Schmeck, C. A
Useful Application of Benzyl Trichloroacetimidate for the Ben-
zylation of Alcohols. Tetrahedron 1993, 49, 1619-1624.
(36) Wessel, H.-P.; Iversen, T.; Bundle, D. R. Acid-catalysed Benzy-
lation and Allylation by Alkyl Trichloroacetimidates. J . Chem.
Soc., Perkin Trans. 1 1985, 2247-2250.
(37) Iversen, T.; Bundle, D. R. Benzyl Trichloroacetimidate,
a
Versatile Reagent for Acid-catalysed Benzylation of Hydroxy-
groups. J . Chem. Soc., Chem. Commun. 1981, 1240-1241.
(38) Poirier, V.; Calleman, C. J . The Nucleophilic Reactivity of Valine
Methylamide. A Model of the N-Terminal valine Residues of
Hemoglobin. Acta Chem. Scand. Ser. B 1983, 37, 817-822.

Synthesis of C2-Symmetric HIV-1 PR Inhibitors
J ournal of Medicinal Chemistry, 2001, Vol. 44, No. 19 3091
(39) Oppenshaw, H. T.; Whittaker, N. The Synthesis of Emetine and
Related Compounds. Part VII. The Utility of Bifunctional
catalysts in Amine-Ester Interactions. J . Chem. Soc. 1969, 89-
91.
(40) Danielsson, U. H.; Lindgren, M. T.; Markgren, P. O.; Nillroth,
U. Investigation of an Allosteric Site of HIV-1 Proteinase
Involved in Inhibition by Cu2+. Adv. Exp. Med. Biol. 1998, 436,
99-103.
(42) J ones, T. A.; Zou, J .-Y.; Cowan, S. W.; Kjeldgaard, M. Improved
Methods for Building Protein Models in Electron Density Maps
and the Location of Errors in These Models. Acta Crystallogr.
1991, A47, 110-119.
(43) Harris, M.; J ones, T. A. Molray: A Web-based Interface to POV-
Ray for Production of High-quality Molecular-graphics Images
from O Plot Files and Other Sources, 2000.
(41) Nillroth, U.; Vrang, L.; Markgren, P.-O.; Hulte´n, J .; Hallberg,
A.; Danielsson, U. H. Human Immunodeficiency Virus Type 1
Proteinase Resistance to Symmetric Cyclic Urea Inhibitor
Analogs. Antimicrob. Agents Chemother. 1997, 41, 2383-2388.
J M001134Q