A new class of HIV-1 protease inhibitors containing a tertiary alcohol in the transition-state mimicking scaffold

Article abstract of DOI:10.1021/jm050790t

Novel HIV-1 protease inhibitors encompassing a tertiary alcohol as part of the transition-state mimicking unit have been synthesized. Variation of the P₁′-P₃′ residues and alteration of the tertiary alcohol absolute stereochemistry a

Full text of DOI:10.1021/jm050790t

8098
J. Med. Chem. 2005, 48, 8098-8102
Brief Articles
A New Class of HIV-1 Protease Inhibitors Containing a Tertiary Alcohol in the
Transition-State Mimicking Scaffold
Jenny K. Ekegren,† Torsten Unge,‡ Mayada Zreik Safa,† Hans Wallberg,§ Bertil Samuelsson,§ and
Anders Hallberg*,†
Department of Medicinal Chemistry, Organic Pharmaceutical Chemistry, BMC, Uppsala University, Box 574,
SE-751 23 Uppsala, Sweden, Department of Cell and Molecular Biology, Structural Biology, BMC, Uppsala University,
Box 596, SE-751 24 Uppsala, Sweden, and Medivir AB, Lunastigen 7, SE-141 44 Huddinge, Sweden
Received August 10, 2005
Novel HIV-1 protease inhibitors encompassing a tertiary alcohol as part of the transition-
state mimicking unit have been synthesized. Variation of the P1′-P3′ residues and alteration
of the tertiary alcohol absolute stereochemistry afforded 10 inhibitors. High potencies for the
compounds with (S)-configuration at the carbon carrying the tertiary hydroxyl group were
achieved with Ki values down to 2.4 nM. X-ray crystallographic data for a representative
compound in complex with HIV-1 protease are presented.
Introduction
Since the first cases of AIDS were identified in 1981,
followed by isolation of the HIV virus a few years later,
the epidemic has expanded worldwide, leaving almost
no region unaffected by the disease.1,2 Recent figures
from UNAIDS reveal that almost 5 million people were
newly infected with HIV in 2004 and a total of 39 million
people were living with HIV/AIDS.3 For patients with
access to therapy, most of whom live in the developed
world, drugs and accurate medical care have turned the
former fatal infection into a treatable, chronic infectious
disease.4-6 With the use of antiretroviral therapy, a new
threat in the battle against HIV has appeared: drug
resistance. In the U.S., about 50% of the patients
receiving therapy are infected with viruses resistant to
at least one of the available anti-HIV drugs on the
market.7-10 Taking these different aspects into account,
the need for new drugs is obvious.11
Figure 1. Atazanavir (top left), indinavir (top right), and the
generic structure of the new class of inhibitors (bottom).
All inhibitors in clinic encompass a secondary hy-
droxyl group as part of the transition-state mimicking
unit. There are only a few examples reported where
tertiary alcohols have been used as parts of transition-
state mimics in protease inhibitors.21-25 In those cases,
introduction of the tertiary alcohol generally provided
less potent inhibitors compared to the corresponding
compounds with a secondary alcohol. In one study of
aspartyl protease inhibitors (not including HIV protease
inhibitors) by Rich et al., the most potent compound
with a tertiary hydroxyl group had the opposite stereo-
chemistry compared to the most potent compound
comprising a secondary hydroxyl group.21-23 We were
encouraged to explore the transition-state mimic present
in the generic structure shown in Figure 1, as initial
modeling suggested that a tertiary alcohol built into this
core structure could favorably interact with Asp25 and
Asp125 of the HIV protease. Furthermore, we speculate
that a hydroxyl group in R-position to an amide could
enable partial masking of the amide functionality and
the hydroxyl group via internal hydrogen bonding that
in principle should improve transcellular transport. This
HIV protease inhibitors used in combination therapy
with reverse transcriptase inhibitors are important as
significant suppression of viral loads in HIV patients
has been accomplished.12-15 Seven HIV protease inhibi-
tors have reached the market so far. However, the
therapy is far from being free of complications; severe
side effects such as dyslipidaemia, hypersensitivity, and
lipodystrophy are limiting adherence and therefore
clinical efficacy.16 The oral bioavailability of the HIV
protease inhibitors is generally low. However, the
development of atazanavir led to the first drug in which
high oral bioavailability was achieved (Figure 1). Fur-
thermore, this drug exhibits excellent antiviral activity
against wild-type and saquinavir- and indinavir-resis-
tant strains of HIV.17-20
* To whom correspondence should be addressed. Phone: +46-18-
4714284. Fax:
orgfarm.uu.se.
+46-18-4714474. E-mail:
Anders.Hallberg@
† Department of Medicinal Chemistry, Uppsala University.
‡ Department of Cell and Molecular Biology, Uppsala University.
§ Medivir AB.
10.1021/jm050790t CCC: $30.25 © 2005 American Chemical Society
Published on Web 11/16/2005

Brief Articles
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 25 8099
Scheme 1a
acids were coupled with benzylhydrazine using EDC,
NMM, and HOBT, affording the desired hydrazides in
50-67% yield after column chromatography (4-9,
Scheme 2). However, the urea derivative 9 turned out
to be unstable, and after filtration through a short silica
column the crude product was used without further
purification in the inhibitor synthesis. To investigate
the effect of a larger substituent in the inhibitor P1′ side
chain, two brominated hydrazides were synthesized (10
and 11, Scheme 2). Starting from 4-bromobenzylhydra-
zine,32 prepared according to a published procedure from
4-bromobenzyl bromide and hydrazine monohydrate,33
the two bromohydrazides were produced in 54% and
79% yields, respectively.
a Reagents: (a) (1S,2R)-1-amino-2-indanol, EDC, NMM, HOBT,
EtOAc, room temp, 68%; (b) mCPBA, CH2Cl2, reflux, 53%.
Scheme 2a
Two different strategies were used for the synthesis
of the HIV protease inhibitors from epoxide 3 and the
hydrazides 4-11 (Table 1). In the first approach the two
reagents were stirred in iPrOH at 80 °C for 3-7 days,
and the reactions were monitored by RPLC-MS (method
A). Later, an improved procedure was used where
Ti(OiPr)434,35 catalyzed the ring opening of 3 in THF and
a reaction time of only 3 h was now required (method
B). Purification by preparative RPLC-MS resulted in
highly pure products; however, this also seemed to have
a negative effect on the isolated yields compared to
purification by column chromatography only. To estab-
lish which stereochemistry of the transition-state mim-
icking tertiary alcohol generated the most potent in-
hibitors, two pairs of inhibitors were synthesized having
an opposite absolute configuration at the carbon bearing
the tertiary hydroxyl group. Hydrazide 4 was used to
ring-open epoxides (S)-3 and (R)-3, affording the dia-
stereomeric inhibitors 12 and 13. Likewise, hydrazide
7 was utilized to afford inhibitors 16 and 17 (Table 1).
a Reagents: (a) benzylhydrazine‚2HCl/Et3N or 4-bromobenzyl-
hydrazine and EDC, HOBT, NMM, EtOAc, room temp, 50-79%.
concept, which takes advantage of intramolecular hy-
drogen bonds to increase apparent lipophilicity and to
increase membrane penetration, was successfully ap-
plied by Ashwood et al. in NK1 receptor antagonists.26
In the generic structure in Figure 1 the tertiary alcohol
unit on the prime side is linked to the ethyl(hydrazine)
moiety found in atazanavir and on the nonprime side
to the (1S)-amino-(2R)-hydroxyindane structure origi-
nating from indinavir.27-29 We herein report the syn-
thetic protocols, HIV-1 protease inhibition data, and
anti-HIV activities for these new HIV protease inhibi-
tors in cell assays. Furthermore, we present X-ray
crystallographic data for a representative compound of
this class.
HIV Protease Inhibition, MT4 Cell-Based Anti-
HIV Activity, Permeability, and Metabolic Stabil-
ity in Vitro. The Ki and EC50 values for 12-21 are in
Table 1. The Ki values for the diastereomer pairs 12/13
and 16/17 revealed that the compounds with (S)-
configuration were at least 40 times more potent than
the compounds with (R)-configuration. The N-methoxy-
carbonyl group in the P3′ position clearly gave more
potent inhibitors than the N-benzyloxycarbonyl group
and the sulfonamide and urea derivatives (cf. 16 with
14, 18, and 19; Table 1). Incorporation of a bromo atom
in the para position of the P1′ benzyl group provided
the most potent inhibitor with Ki ) 2.4 nM (20, Table
1). EC50 values below 10 µM were achieved for all
compounds with an N-methoxycarbonyl group in the P3′
position and (S)-configuration at the carbon bearing the
tertiary alcohol, while the N-benzyloxycarbonyl com-
pounds exhibited values above that limit (cf. 16/14 and
15/12, Table 1). A tert-butyl group in the P2′ position
combined with the favorable N-methoxycarbonyl at the
P3′ position rendered a compound twice as active as the
corresponding isopropyl derivative in the cell assay (cf.
16 and 15, Table 1). The most potent compound within
this series was 20 as it also had the best cell activity
data with an EC50 of 1.1 µM. 16 and 20 were evaluated
in selected in vitro resistant HIV-1 isolates from serial
passages of a symmetric diol-based inhibitor36 and
ritonavir, respectively (Table 1). The two compounds
exhibited equipotent activity in these mutant MT4/
HIV-1 protease assays (V32I, M46I, V82A and V32I,
Results
Chemistry. The transition-state mimicking tertiary
alcohol utilized in the new HIV protease inhibitors
originated from the optically active 2,2-disubstituted
epoxide 3, which was readily available in both diaster-
eomeric forms (Scheme 1). The synthesis of 3 started
from 2-benzylacrylic acid 130 and (1S,2R)-1-amino-2-
indanol, which were coupled using 1-(3-dimethylami-
nopropyl)-3-ethylcarbodiimide hydrochloride (EDC), N-
methylmorpholine (NMM), and 1-hydroxybenzotriazole
(HOBT). The resulting R,â-unsaturated amide 2 was
epoxidized by 3-chloroperoxybenzoic acid (mCPBA),
yielding the two diastereomers of epoxide 3 in a 50:50
mixture, here denoted (S)-3 and (R)-3 where S and R
refer to the absolute configuration of the asymmetric
carbon in the epoxide ring. The two diastereomers
readily separated upon column chromatography, yield-
ing the pure isomers.
The synthetic strategy was to ring-open 3 with
different hydrazides to obtain a series of inhibitors.17,18,31
The hydrazides were synthesized from L-valine or L-tert-
leucine to assess the impact of an isopropyl versus a
tert-butyl group as P2′ side chains (Scheme 2). Different
P3′ substituents were incorporated into the scaffold by
starting from commercially available Cbz-protected
L-valine/L-tert-leucine or from the corresponding unpro-
tected amino acids, which were first N-derivatized.
Functionalization with an N-methoxycarbonyl group
was described previously.17,18 The functionalized amino

8100 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 25
Table 1. Synthesis of Inhibitors 12-21 and Biological Data
Brief Articles
Figure 2. X-ray crystal structure of 15 cocrystallized with
HIV-1 protease. Hydrogen-bonding interactions between the
inhibitor and key residues of the enzyme are represented by
green dashed lines.
Figure 3. Superimposition of the X-ray structures of inhibitor
15 (gray) and indinavir (orange) in the active site of HIV-1
protease.
X-ray Crystallographic Data. Cocrystallization of
inhibitor 15 with HIV-1 protease followed by X-ray
diffraction data provided a 3D structure with 1.8 Å
resolution (PDB code 2bqv). The hydrogen-bonding
interactions between the inhibitor and the enzyme are
shown in Figure 2. The tertiary alcohol forms a hydro-
gen bond to one of the active site aspartates, Asp125.
Furthermore, the â-nitrogen of the hydrazido group was
found to form a weak hydrogen bond to the other active
site aspartate residue, Asp25 (3.2 Å). A distinct hydro-
gen bond pattern was also observed between the P3′
carbamate group and Asp129 and Gly148 as well as
Gly149.
Superimposition of the X-ray structures of 15 and
indinavir (PDB code 1hsg) reveals significant differences
between the two inhibitors (Figure 3). Whereas the
positions of the P2 aminoindanol and the P2′ isopropyl
groups overlap well with the corresponding residues in
indinavir, the positions of the P1/P1′ groups differ
considerably in 15. Both groups penetrate less deeply
into the enzyme subsites, and the discrepancies are
about 1.4 Å on the P1 side and 4.5 Å on the P1′ side
compared to indinavir. In addition, the angle at which
the P1′ benzyl group penetrates into the S1′ pocket is
different from that of indinavir. The most striking
differences appear when the hydrogen bond pattern
between the enzyme catalytic aspartates and the transi-
tion-state mimicking scaffolds of 15 and indinavir is
analyzed (Figure 4). Whereas indinavir positions the
central hydroxyl group in close contact (within 2.6-3.0
Å) with all four oxygen atoms of the active site aspartate
residues, 15 positions the tertiary alcohol and the
â-nitrogen of the hydrazido group symmetrically over
the active site. This arrangement leads to the tertiary
alcohol forming a less tight hydrogen bond to Asp125
(3.1 Å) compared to indinavir. In addition, the tertiary
a All compounds were synthezised according to method A except
20, which was prepared according to method B (see Supporting
Information). b Purification methods: (1) column chromatography,
silica; (2) RPLC-MS. c Indinavir: Ki ) 0.31 nM14 and EC50 ) 0.041
µM.13,38 d Mutations in MT4/HIV-1 protease: V32I, M46I, V82A.
e Mutations in MT4/HIV-1 protease: V32I, M46I, A71V, V82A.f 16
Papp(Caco-2) ) 35 × 10-6 cm/s; 20 Papp(Caco-2) ) 42 × 10-6 cm/
s. g 16 Clint ) 527 µL min-1 mg-1; 20 Clint ) 266 µL min-1 mg-1
.
M46I, A71V, V82A, respectively) as in the wild-type
MT4/HIV-1 protease assay. The in vitro DMPK profile
for 16 and 20 was also evaluated. As we hoped, 16 (Papp
) 35 × 10-6 cm/s) and 20 (Papp ) 42 × 10-6 cm/s) were
found to exhibit excellent permeability in the Caco-2 cell
assay, more than 6 times better than atazanavir (Papp
) 5.3 × 10-6 cm/s) in the same assay. We propose that
the high permeability is attributed to the masking of
the amide and tertiary hydroxyl functionalities by an
intramolecular hydrogen bond network. The fast intrin-
sic clearance of 16 (Clint ) 527 µL min-1 mg-1) and 20
(Clint ) 266 µL min-1 mg-1) is believed to be due to
metabolic hydroxylation of the benzylic position of the
aminoindanol.37

Brief Articles
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 25 8101
afforded indinavir a Ki of 0.31 nM in the HIV-1 protease
assay and an EC50 of 41 nM in the MT4 cell assay.13,14,38
Thus, indinavir is 10 times better than 20 in the enzyme
assay and ∼25 times more effective in the cell assay.
The data from the Caco-2 cell assay (16 Papp ) 35 ×
10-6 cm/s; 20 Papp ) 42 × 10-6 cm/s) predict excellent
cell membrane penetration for these compounds. As a
comparison, atazanavir exhibited a Papp of 5.3 × 10-6
cm/s and indinavir a Papp of 1.7 × 10-6 cm/s in the same
assay. With the exception of the reports from Rich et
al.,21-23 there seems to be few studies addressing the
potential of tertiary alcohols as part of transition-state
substitutes. The data presented herein suggest that
further efforts could be devoted to more extensive
elaboration of this structural element as a central core
in inhibitors of aspartyl proteases. Carboxylic acid
derivatives with an R-hydroxyl group are prone to form
intramolecular hydrogen bonds in solution.39 The present
investigation, as deduced from the Papp values from the
Caco-2 assay, supports the hypothesis that compounds
with an inherent ability to form intramolecular hydro-
gen bonds are more likely to exhibit high permeability.
However, the compounds herein do not seem to be
efficiently transported into the intracellular compart-
ments of HIV-1 infected MT4 cells and the moderate
antiviral activities observed are not easy to rationalize.
Figure 4. Comparison of hydrogen bond pattern in complexes
of HIV-1 protease and inhibitor 15 (A) and indinavir (B).
Hydrogen bonds are represented by green dashed lines.
hydroxyl group is hydrogen-bonded to the main chain
oxygen of Gly27 (3.0 Å), a feature not observed with
indinavir.
Discussion
The observed lowering of Ki when the benzyl group
of the P1′ residue was elongated with a p-bromo sub-
stituent (cf. 20 and 16, Table 1) might be explained by
favorable interactions at the enzyme surface. The exten-
sion of this residue approaches the enzyme/solvent
interface, and a more efficient displacement of solvent
molecules at the enzyme surface, mediated by the polar
bromine compared to the hydrophobic phenyl lacking a
para substituent, can occur. Large P3′ residues will
occupy parts of the S3′-S1′ spanning pocket and could
interfere negatively with the phenyl P1′ group, as
deduced from modeling. It was therefore less surprising
that a P3′ benzyl group resulted in less efficient inhibi-
tors, as was also observed in the atazanavir series.17,18
In contrast, the relatively small (and more easily
solvated) methyl carbamate group that gave lower Ki
and EC50 values (below 10 µM) can be well accom-
modated in the S3′-S1′ pocket (cf. 16/14 and 15/12,
Table 1). The 3D structure revealed that the carbamate
group in 15 is in a hydrogen bond network where the
three heteroatoms of the carbamate participate (Figure
2). We replaced the carbamate with the powerful
hydrogen bond accepting/donating urea fragment and
hoped that lower Ki values could be achieved in the
enzyme assay by this manipulation. However, no im-
provement was encountered (cf. 14 and 19, Table 1). An
unfavorable alignment of the urea imposed by the large
benzyl group present in 19 when binding to the enzyme
could account for this observation. Modeling suggested
that a methyl sulfonamide could provide an alternative
and proper substitute for the methyl carbamate in 15.
This alteration was also largely unsuccessful. Hence,
18 was 10 times less potent than 16 (Table 1), but more
importantly it did not exhibit any inhibitory effect in
the cell assay. The fact that only the methyl carbamates
and not the methylsulfonamide compound are efficient
in the cell assays is difficult to rationalize. The increased
cellular potency achieved when switching from valine
to tert-leucine for the P3′ methyl carbamate compounds
(cf. 16 and 15, Table 1) was in agreement with previ-
ously reported observations from the atazanavir series.18
Even though the tert-leucine compounds 16 and 20, with
Ki of 6 and 2.4 nM, exert antiviral activities in the cell
assay, it is notable that the EC50 values are not
impressive (1.9 and 1.1 µM). The same types of assay
Conclusion
In summary, new HIV-1 protease inhibitors encom-
passing a rarely used tertiary alcohol based transition-
state mimicking scaffold have been synthesized. Varia-
tions at the P1′-P3′ side chains of the inhibitors resulted
in compounds with Ki values in the low nanomolar
range (down to 2.4 nM). Results from the enzyme assay
established that the compounds comprising the tertiary
alcohol with (S)-configuration were more potent enzyme
inhibitors than those with (R)-configuration. The abso-
lute stereochemistry was confirmed by X-ray crystal-
lography data obtained from ligand 15 cocrystallized
with the HIV-1 protease at a resolution of 1.8 Å. The
results confirm that a tertiary alcohol can serve as part
of a transition-state mimicking scaffold in HIV-protease
inhibitors. The moderate antiviral activities encountered
in HIV-1 infected MT4 cells are difficult to explain, in
particular since excellent Papp values from Caco-2
assays support the assumption that masking of the
hydroxyl group and the adjacent amide bond by in-
tramolecular hydrogen bonds should render compounds
with high cell membrane permeability. It is notable that
the best compound (20) in cell assays was equally potent
toward two common mutated HIV proteases as toward
the wild-type protease. An optimization of the com-
pounds within this series aiming at inhibitors with
improved cellular potency is in progress.
Experimental Section
General Procedures for Synthesis of Inhibitors.
Method A. Epoxide 3 and hydrazide were dissolved in iPrOH,
and the mixture was stirred at 80 °C for 72-168 h. Evapora-
tion of the solvent followed by purification (column chroma-
tography and/or RPLC-MS) afforded the products in 13-55%
yield.
Method B. Epoxide 3 and hydrazide were dissolved in dry
THF, and Ti(OiPr)4 was added under N2 atmosphere. Stirring
at room temperature for 2.5 h and then at 40 °C for 30 min

8102 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 25
Brief Articles
(21) Rich, D. H.; Bernatowicz, M. S.; Agarwal, N. S.; Kawai, M.;
Salituro, F. G.; Schmidt, P. G. Inhibition of aspartic proteases
by pepstatin and 3-methylstatine derivatives of pepstatin.
Evidence for collected-substrate enzyme inhibition. Biochemistry
1985, 24, 3165-3173.
(22) Rich, D. H. Pepstatin-derived inhibitors of aspartic proteinases.
A close look at an apparent transition-state analog inhibitor. J.
Med. Chem. 1985, 28, 263-273.
was followed by the addition of saturated NaHCO3 (aq) and
Et2O. The resulting mixture was stirred at room temperature
for 10 min. Filtration and separation of the two phases, drying
of the organic phase (Na2SO4), and evaporation followed by
purification by column chromatography afforded the product
in 55% yield.
(23) Agarwal, N. S.; Rich, D. H. Inhibition of cathepsin D by substrate
analogs containing statine and by analogs of pepstatin. J. Med.
Chem. 1986, 29, 2519-2524.
(24) Godfrey, J. D., Jr.; Gordon, E. M.; Von Langen, D. J. Synthesis
of peptide-derived amino alcohols II. Synthetic methodology for
the preparation of tertiary alcohols. Tetrahedron Lett. 1987, 28,
1603-1606.
(25) Kim, B. M.; Guare, J. P.; Hanifin, C. M.; Arford-Bickerstaff, D.
J.; Vacca, J. P.; Ball, R. G. A convergent synthesis of novel
conformationally restricted HIV-1 protease inhibitors. Tetrahe-
dron Lett. 1994, 35, 5153-5156.
(26) Ashwood, V. A.; Field, M. J.; Horwell, D. C.; Julien-Larose, C.;
Lewthwaite, R. A.; McCleary, S.; Pritchard, M. C.; Raphy, J.;
Singh, L. Utilization of an intramolecular hydrogen bond to
increase the CNS penetration of an NK1 receptor antagonist.
J. Med. Chem. 2001, 44, 2276-2285.
(27) Lyle, T. A.; Wiscount, C. M.; Guare, J. P.; Thompson, W. J.;
Anderson, P. S.; Darke, P. L.; Zugay, J. A.; Emini, E. A.; Schleif,
W. A.; Quintero, J. C.; Dixon, R. A. F.; Sigal, I. S.; Huff, J. R.
Benzocycloalkyl amines as novel C-termini for HIV protease
inhibitors. J. Med. Chem. 1991, 34, 1228-1230.
(28) Askin, D.; Eng, K. K.; Rossen, K.; Purick, R. M.; Wells, K. M.;
Volante, R. P.; Reider, P. J. Highly diastereoselective reaction
of a chiral, non-racemic amide enolate with (S)-glycidyl tosylate.
Synthesis of the orally active HIV-1 protease inhibitor L-735,-
524. Tetrahedron Lett. 1994, 35, 673-676.
(29) Dorsey, B. D.; Levin, R. B.; McDaniel, S. L.; Vacca, J. P.; Guare,
J. P.; Darke, P. L.; Zugay, J. A.; Emini, E. A.; Schleif, W. A.;
Quintero, J. C.; Lin, J. H.; Chen, I.-W.; Holloway, M. K.;
Fitzgerald, P. M. D.; Axel, M. G.; Ostovic, D.; Anderson, P. S.;
Huff, J. R. L-735,524: The design of a potent and orally
bioavailable HIV protease inhibitor. J. Med. Chem. 1994, 37,
3443-3451.
Acknowledgment. We gratefully acknowledge the
Swedish Foundation for Strategic Research (SSF) and
the Swedish Research Council (VR) for financial support
and Johan Gising for preparative work.
Supporting Information Available: Experimental de-
tails and spectroscopic data for compounds 2-21 (1H NMR,
13C NMR, MS, optical rotation), procedures for enzyme and
Caco-2 assays and liver microsome stability evaluation, and
table of elemental analysis data and X-ray structure determi-
nation details. This material is available free of charge via the
Internet at http://pubs.acs.org.
References
(1) Barre-Sinoussi, F.; Chermann, J. C.; Rey, F.; Nugeyre, M. T.;
Chamaret, S.; Gruest, J.; Dauguet, C.; Axler-Blin, C.; Vezinet-
Brun, F.; Rouzioux, C.; Rozenbaum, W.; Montagnier, L. Isolation
of a T-lymphotropic retrovirus from a patient at risk for acquired
immune deficiency syndrome (AIDS). Science 1983, 220, 868-
871.
(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) AIDS Epidemic Update: December 2004; Joint United Nations
Programme on HIV/AIDS (UNAIDS)/WHO, 2004.
(4) Pomerantz, R. J.; Horn, D. L. Twenty years of therapy for HIV-1
infection. Nat. Med. 2003, 9, 867-873.
(5) Peterlin, B. M.; Trono, D. Hide, shield and strike back: how HIV-
infected cells avoid immune eradication. Nat. Rev. Immunol.
2003, 3, 97-107.
(30) Liu, X.; Hu, E.; Tian, X.; Mazur, A.; Ebetino, F. H. Enantio-
selective synthesis of phosphinyl peptidomimetics via an asym-
metric Michael reaction of phosphinic acids with acrylate
derivatives. J. Organomet. Chem. 2002, 646, 212-222.
(31) Sham, H. L.; Zhao, C.; Stewart, K. D.; Betebenner, D. A.; Lin,
S.; Park, C. H.; Kong, X.-P.; Rosenbrook, W., Jr.; Herrin, T.;
Madigan, D.; Vasavanonda, S.; Lyons, N.; Molla, A.; Saldivar,
A.; Marsh, K. C.; McDonald, E.; Wideburg, N. E.; Denissen, J.
F.; Robins, T.; Kempf, D. J.; Plattner, J. J.; Norbeck, D. W. A
novel, picomolar inhibitor of human immunodeficiency virus type
1 protease. J. Med. Chem. 1996, 39, 392-397.
(6) 2004 Report on the Global AIDS Epidemic; Joint United Nations
Programme on HIV/AIDS (UNAIDS), 2004.
(7) Clavel, F.; Hance, A. J. HIV drug resistance. N. Engl. J. Med.
2004, 350, 1023-1035.
(8) Werber, Y. HIV drug market. Nat. Rev. Drug Discovery 2003,
2, 513-514.
(9) Mene´ndez-Arias, L. Targeting HIV: antiretroviral therapy and
development of drug resistance. Trends Pharmacol. Sci. 2002,
23, 381-388.
(32) Savin, V. I. N-Nitrenes. IV. Synthesis of unsymmetrical bi-
benzyls. Zh. Org. Khim. 1992, 28, 43-50.
(10) de Mendoza, C.; Soriano, V. Resistance to HIV protease inhibi-
tors: mechanisms and clinical consequences. Curr. Drug Metab.
2004, 5, 321-328.
(33) Otteneder, M.; Plastaras, J. P.; Marnett, L. J. Reaction of
malondialdehyde-DNA adducts with hydrazinessdevelopment
of a facile assay for quantification of malondialdehyde equiva-
lents in DNA. Chem. Res. Toxicol. 2002, 15, 312-318.
(34) Chong, J. M.; Sharpless, K. B. Nucleophilic openings of 2,3-epoxy
acids and amides mediated by Ti(O-i-Pr)4. Reliable C-3 selectiv-
ity. J. Org. Chem. 1985, 50, 1560-1563.
(11) De Clercq, E. New approaches toward anti-HIV chemotherapy.
J. Med. Chem. 2005, 48, 1297-1313.
(12) Abdel-Rahman, H. M.; Al-Karamany, G. S.; El-Koussi, N. A.;
Youssef, A. F.; Kiso, Y. HIV protease inhibitors: peptidomimetic
drugs and future perspectives. Curr. Med. Chem. 2002, 9, 1905-
1922.
(35) Caron, M.; Sharpless, K. B. Ti(O-i-Pr)4-mediated nucleophilic
openings of 2,3-epoxy alcohols. A mild procedure for regioselec-
tive ring-opening. J. Org. Chem. 1985, 50, 1557-1560.
(36) Alterman, M.; Bjoersne, M.; Muehlman, A.; Classon, B.; Kvarn-
stroem, I.; Danielson, 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.
(37) Balani, S. K.; Arison, B. H.; Mathai, L.; Kauffman, L. R.; Miller,
R. R.; Stearns, R. A.; Chen, I. W.; Lin, J. H. Metabolites of
L-735,524, a potent HIV-1 protease inhibitor, in human urine.
Drug Metab. Dispos. 1995, 23, 266-270.
(38) Molla, A.; Vasavanonda, S.; Kumar, G.; Sham, H. L.; Johnson,
M.; Grabowski, B.; Denissen, J. F.; Kohlbrenner, W.; Plattner,
J. J.; Leonard, J. M.; Norbeck, D. W.; Kempf, D. J. Human serum
attenuates the activity of protease inhibitors toward wild-type
and mutant human immunodeficiency virus. Virology 1998, 250,
255-262.
(39) Carrell, H. L.; Glusker, J. P.; Piercy, E. A.; Stallings, W. C.;
Zacharias, D. E.; Davis, R. L.; Astbury, C.; Kennard, C. H. L.
Metal chelation versus internal hydrogen bonding of the R-hy-
droxy carboxylate group. J. Am. Chem. Soc. 1987, 109, 8067-
8071.
(13) Randolph, J. T.; DeGoey, D. A. Peptidomimetic inhibitors of HIV
protease. Curr. Top. Med. Chem. 2004, 4, 1079-1095.
(14) Rodr´ıguez-Barrios, F.; Gago, F. HIV protease inhibition: limited
recent progress and advances in understanding current pitfalls.
Curr. Top. Med. Chem. 2004, 4, 991-1007.
(15) Bursavich, M. G.; Rich, D. H. Designing non-peptide peptido-
mimetics in the 21st century: inhibitors targeting conforma-
tional ensembles. J. Med. Chem. 2002, 45, 541-558.
(16) Carr, A. Toxicity of antiretroviral therapy and implications for
drug development. Nat. Rev. Drug Discovery 2003, 2, 624-634.
(17) Fa¨ssler, A.; Bold, G.; Capraro, H.-G.; Cozens, R.; Mestan, J.;
Poncioni, B.; Ro¨sel, J.; Tintelnot-Blomley, M.; Lang, M. Aza-
peptide analogs as potent human immunodeficiency virus type-1
protease inhibitors with oral bioavailability. J. Med. Chem. 1996,
39, 3203-3216.
(18) Bold, G.; Fa¨ssler, A.; Capraro, H.-G.; Cozens, R.; Klimkait, T.;
Lazdins, J.; Mestan, J.; Poncioni, B.; Ro¨sel, J.; Stover, D.;
Tintelnot-Blomley, M.; Acemoglu, F.; Beck, W.; Boss, E.; Esch-
bach, M.; Hurlimann, T.; Masso, E.; Roussel, S.; Ucci-Stoll, K.;
Wyss, D.; Lang, M. New aza-dipeptide analogues as potent and
orally absorbed HIV-1 protease inhibitors: candidates for clinical
development. J. Med. Chem. 1998, 41, 3387-3401.
(19) Wang, F.; Ross, J. Atazanavir: a novel azapeptide inhibitor of
HIV-1 protease. Formulary 2003, 38, 691-702.
(20) Raja, A.; Lebbos, J.; Kirkpatrick, P. Fresh from the pipeline:
Atazanavir sulphate. Nat. Rev. Drug Discovery 2003, 2, 857-
858.
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