Design and synthesis of new potent C2-symmetric HIV-1 protease inhibitors. Use of L-mannaric acid as a peptidomimetic scaffold

Article abstract of DOI:10.1021/jm970777b

A study on the use of derivatized carbohydrates as C₂-symmetric HIV-1 protease inhibitors has been undertaken. L-Mannaric acid (6) was bis-O- benzylated at C-2 and C-5 and subsequently coupled with amino acids and amines to give C₂-s

Full text of DOI:10.1021/jm970777b

3782
J . Med. Chem. 1998, 41, 3782-3792
Design a n d Syn th esis of New P oten t C2-Sym m etr ic HIV-1 P r otea se In h ibitor s.
Use of L-Ma n n a r ic Acid a s a P ep tid om im etic Sca ffold
Mathias Alterman,† Magnus Bjo¨rsne,‡ Anna Mu¨hlman,‡ Bjo¨rn Classon,‡ Ingemar Kvarnstro¨m,§
Helena Danielson,| Per-Olof Markgren,| Ulrika Nillroth,| Torsten Unge, Anders Hallberg,† and
Bertil Samuelsson*,‡,∇
Department of Chemistry, Linko¨ping University, S-581 83 Linko¨ping, Sweden, Arrhenius Laboratory, Department of Organic
Chemistry, Stockholm University, S-106 91 Stockholm, Sweden, Department of Biochemistry, Uppsala University, BMC,
S-751 23 Uppsala, Sweden, Department of Molecular Biology, Uppsala University, BMC, Box 590, S-751 24 Uppsala, Sweden,
and Department of Organic Pharmaceutical Chemistry, Uppsala University, BMC, S-751 23 Uppsala, Sweden
Received November 14, 1997
A study on the use of derivatized carbohydrates as C2-symmetric HIV-1 protease inhibitors
has been undertaken. L-Mannaric acid (6) was bis-O-benzylated at C-2 and C-5 and
subsequently coupled with amino acids and amines to give C2-symmetric products based on
C-terminal duplication. Potent HIV protease inhibitors, 28 Ki ) 0.4 nM and 43 Ki ) 0.2 nM,
have been discovered, and two synthetic methodologies have been developed, one whereby these
inhibitors can be prepared in just three chemical steps from commercially available materials.
A remarkable increase in potency going from IC50 ) 5000 nM (23) to IC50 ) 15 nM (28) was
observed upon exchanging -COOMe for -CONHMe in the inhibitor, resulting in the net
addition of one hydrogen bond interaction between each of the two -NH- groups and the HIV
protease backbone (Gly 48/148). The X-ray crystal structures of 43 and of 48 have been
determined (Figures 5 and 6), revealing the binding mode of these inhibitors which will aid
further design.
In tr od u ction
structures it has been shown that the HIV-1 protease
exists as a C2-symmetric dimer. Recognizing that both
the N- and C-terminal of a substrate or inhibitor binds
into identical subsites of the HIV protease and that
duplication of either the N- or the C-terminal produces
a C2-symmetric compound has led to the design and
synthesis of new inhibitors.5 A successful exploration
of the N-terminal duplication concept was demonstrated
for the (3R,4R)-diaminodiol 5 and for a related series
of compounds.6
The human immunodeficiency virus (HIV) has been
identified as the etiologic agent of acquired immunode-
ficiency syndrome (AIDS).1 The pol gene of the human
immunodeficiency virus type 1 (HIV-1) encodes for the
aspartic protease which mediates proteolytic processing
of the gag and the gag-pol viral gene products liberating
functional enzymes and structural proteins which are
essential for the formation of the mature, infectious
virus.2 Inactivation of the aspartic protease leads to the
formation of noninfectious virions.3 As a result the
HIV-1 protease has become one of the major targets for
therapeutic intervention in AIDS and in HIV infection.
Recently four protease inhibitors, saquinavir (1), ritonavir
(2), indinavir (3), and nelfinavir (4) were approved for
clinical use by the FDA (Figure 1). Despite the clinical
efficacy the benefits from long-term treatment with
these agents remains to be demonstrated. Selection of
a drug resistant mutant virus is likely to occur after
prolonged treatment reducing efficacy of therapy. The
high cost of synthesis is today a barrier to the wide-
spread use of the currently approved protease inhibitors,
notably in less developed countries. It is thus important
that new improved protease inhibitors accessible at low
costs are developed.4
We have recently explored D-mannitol as a linear
peptidomimetic scaffold7 and have shown that D-man-
nitol based C2-symmetric protease inhibitors of the
general structure 6 have antiviral activities similar to
the diaminodiol inhibitors 5 (Figure 2).8 Cyclic protease
inhibitors derived from D-mannitol and L-mannitol have
also been recently disclosed by us and others.9
In h ibitor Design . The present work describes the
use of carbohydrates in the design and synthesis of
structurally new C2-symmetric protease inhibitors in-
corporating C-terminal duplication (Figure 3). From
molecular modeling L-mannaric acid (7) was selected as
a C2-symmetric backbone where O-benzylation of the
hydroxyls at C-2 and C-5 of 7 and subsequent coupling
with amino acids or amines gives inhibitors of the
general structure 8 (Figure 3). While inhibitors based
on N-terminal duplication have been extensively stud-
ied, there are fewer reports on C2-symmetric inhibitors
based on C-terminal duplication.10 The absolute ster-
eochemistry of the P1/P1′ substituents and of the central
diol varies from one class of inhibitors to another, cf.
A-759256 (9) and DMP 323,11 (10) (Figure 4). We have
used computer-assisted molecular modeling to build and
conformationally refine potential inhibitors in extended
Numerous reports describing potent protease inhibi-
tors have been disclosed.5 On the basis of X-ray crystal
* Corresponding author.
† Department of Organic Pharmaceutical Chemistry, Uppsala Uni-
versity.
‡ Stockholm University.
§ Linko¨ping University.
| Department of Biochemistry, Uppsala University.
Department of Molecular Biology, Uppsala University.
∇ Additional address: Astra Ha¨ssle AB, Department of Medicinal
Chemistry, S-431 83 Mo¨lndal, Sweden.
S0022-2623(97)00777-2 CCC: $15.00 © 1998 American Chemical Society
Published on Web 08/26/1998

Design of New C2-Symmetric HIV-1 Protease Inhibitors
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20 3783
F igu r e 4.
Sch em e 1. Synthesis of Protected L-Mannaric Acid
ing into the lipophilic S2/S2′ pockets of the HIV-1
protease and/or hydrogen bonding to the inhibitor
backbone. It is noteworthy that with the present
inhibitor design strategy diverse P1 and P2 substituents
in 8 are synthetically readily available making optimi-
zation of potential inhibitors feasible.
Resu lts a n d Discu ssion
F igu r e 1. FDA-approved HIV-1 protease inhibitors.
Ch em istr y. For the synthesis of inhibitors of the
general structure 8 two synthetic routes were developed.
In the first route (synthetic route 1) a suitably protected
2,5-di-O-benzylated L-mannaric acid was prepared and
coupled to a set of amines and amino acid derivatives.
In the second synthetic route developed (synthetic route
2), which is substantially shorter, 2,5-di-O-benzyl-L-
mannaro-1,4:3,6-di-γ-lactone (36) was prepared and
subsequently in one step reacted with various amines
and amino acid derivatives giving bisamides 8 by
nucleophilic ring opening of the bislactone 36.
F igu r e 2.
Syn th etic Rou te 1. (Schemes 1 and 2) The mono-
acetonide 12 was prepared using a modified procedure
as described for the corresponding D-mannitol ace-
tonide.14 Reduction of L-mannonic γ-lactone (11) with
lithium borohydride in dry MeOH gave L-mannitol
which, after azeotropic removal of the boric acid and
without further purification, was protected using 2,2-
dimethoxypropane in acetone containing camphorsul-
fonic acid to give the triacetonide in 78% overall yield.
Partial hydrolysis with aqueous HOAc (70%) provided
the monoacetonide 12 in 64% yield after recrystalliza-
tion. Subsequent selective protection of the primary
hydroxyls with tert-butyldimethylsilyl chloride in pyri-
dine, containing p-(dimethylamino)pyridine, afforded
F igu r e 3.
conformations12 and to match these with X-ray crystal
structures.13 This analysis indicated that inhibitors
derived from substituted L-mannaric acid would give a
good fit with respect to (a) the spacial direction of the
P1/P1′ substituents (benzyloxy), (b) the carbonyl oxy-
gens of 8 hydrogen bonding to the structural water, and
(c) the stereochemistry of the central hydroxyl groups
forming hydrogen bonds to the carboxylic acid residues
of Asp 25 and Asp 125. The amino acids or amines
providing the P2/P2′ substituents were modeled extend-

3784 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20
Sch em e 2. Synthesis of L-Mannaric Diamides
Alterman et al.
compound 13 in 96% yield.15 Benzylation of the 2,5-
diol using benzyl bromide, sodium hydride, and a
catalytic amount of tetrabutylammonium iodide in THF
gave 14 in 76% yield. Desilylation of 14 using tetrabu-
tylammonium fluoride in THF delivered compound 15
in 98% yield. For the oxidation of primary hydroxyls
to the corresponding dicarboxylic acid, the majority of
published methods gives lactones when applied to 1,4-,
1,5-, or 1,6-diols. Attempted oxidation of compound 15
with J ones oxidation16 resulted in a complex product
mixture, and attempts to oxidize the 1,6-diol using PDC
and acetic acid anhydride17 produced a slightly more
polar product which decomposed upon workup. The
reagent system 2,2,6,6-tetramethylpiperidine 1-oxyl
radical (TEMPO)-NaOCl has previously been employed
for the direct conversion of alcohols to carboxylic acids
and for the preparation of lactones from 1,4- and 1,5-
diols.18 However with this reagent system, it is reported
that oxidation of 1,6-diols to the corresponding lactone
results in the formation of polymerization products.18
Notably, by using 0.05 molar equivalents of TEMPO and
an excess of NaOCl at 0 °C, compound 15 was oxidized
directly to the dicarboxylic acid 16 in 67% yield (Scheme
1). The successful implementation of this oxidation
procedure seems to rely upon the presence of the cyclic
3,4-O-isopropylidene group which effectively prevents
intramolecular side reactions. In the absence of the
cyclic protection groups the dicarboxylic acid could not
be isolated.
For introducing the amino acids and amines (Scheme
2) corresponding to the P2/P2′ substituents of the
inhibitor, compound 16 was dissolved in CH2Cl2-THF
and condensed with the corresponding amino acid
derivatives with HOBT-EDC. The condensation prod-
ucts, compounds 17-21, were isolated in yields ranging
from 34% to 73%. The 3,4-O-isopropylidene group was
cleaved off with 4% HCl in MeOH, giving the corre-
sponding diol products 23-27 in approximately 70%
yield (Table 1). Compounds 28-31 were prepared from
16 (Scheme 2, route A) in the same manner as that for
the preparation of 23-27, but the intermediate mono-
acetonide was not isolated in this case. Valin methyl-
amide, used in the preparation of 28, was synthesized
through amidation of Z-Val-OSu in dry THF followed
by hydrogenolysis to furnish the methyl amide in 78%
overall yield.19
In an alternative coupling procedure L-mannaric acid
16 was activated with N,N-disuccinimidyl carbonate20
to give the corresponding activated bissuccinimidyl ester
22 in 88% yield, which conveniently could be stored
prior to use. This protocol avoids repeating the activa-
tion step before coupling with the appropriate amines
(Scheme 2, route B). Other synthetic routes21 examined
to prepare the active ester 22 gave lower yields, and
attempts to prepare the corresponding pentafluorophen-
yl diester were not successful.22 Coupling of 22 with
three hydroxy anilines in CH2Cl2 followed by cleavage
of the isopropylidene group with 4% HCl in MeOH
delivered the diamide products 32-34 in 27-38%
overall yield.
The cleavage step of the 3,4-O-isopropylidene groups
in the synthesis of compounds 23-34 was very sensitive
to the reaction conditions and other cleavage conditions
examined, i.e., using TFA-H2O mixtures or PTS in
dioxane-H2O gave complex product mixtures. Alter-
natively the hydrolysis was successfully executed with
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in 9:1
CH3CN-H2O.23
Syn th etic Rou te 2. (Scheme 3) Oxidation of L-
mannonic γ-lactone (11) with aqueous nitric acid pro-
vided, after workup, L-mannaro-1,4:3,6-di-γ-lactone (35)
in 60% yield.24 Benzylation of bislactone 35 was per-
formed using benzyltrichloroacetimidate25 with a cata-
lytic amount of trifluoromethanesulfonic acid in dry
dioxane furnishing the dibenzylated product 36 in 72%
yield. Numerous other solvents besides dioxane were
examined, but either yields were low or compound 35
could not be dissolved in the solvent. Benzylation
procedures employing basic conditions including ben-
zylation with benzylbromide and silveroxide were also
examined, but all failed to give the desired product in
reasonable yields probably attributed due to the base
lability of 35.
Nucleophilic ring opening of dilactone 36 with amines
gave the bisamide derivatives 28, 37-48 in 22-76%
yields (Scheme 3). Best yields were obtained in CH2-
Cl2 at reflux while moderate yields were obtained in
chloroform, CH3CN, dioxane, or THF. Low yields were
obtained in dimethylformamide and in ethanol. The
major side product of the reaction results from â-elim-
ination of 36 to give 49 (Scheme 4). The formation of

Design of New C2-Symmetric HIV-1 Protease Inhibitors
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20 3785
Ta ble 1. Structures, Yields, Methods of Preparation, and HIV-1 Protease Inhibititory Activity of L-Mannaric Diamides with
2R,3R,4R,5R Configuration
a
Method I: see Scheme 2, route A. Method II: see Scheme 2, route A (overall yields from 16). Method III: see Scheme 2, route B (yields
from 22). Method IV: see Scheme 3 (amine opening of bislactone 36). ni ) no inhibition at 10 µM. c nd ) not determined. 3,4-O-
isoprypylidene protected coupling product.
b
d
49 is favored in polar solvents and in reactions involving
basic amines. This interesting elimination product 49
can be produced in high yield (95%) by reacting the
bislactone 36 with 1 M NaOH in dioxane (Scheme 4).
was isolated from the product mixture when an excess
of amine is used.
HIV-1 P r otea se In h ibition . (Table 1) HIV-1 pro-
tease was cloned and heterologously expressed in Es-
cherichia coli as described elsewhere.26 The inhibitory
effect of the synthesized compounds was initially de-
termined with purified HIV-1 protease in a standardized
spectrophotometric assay.27 The results are presented
as IC50 values, i.e., the concentration of inhibitor result-
A notable feature of the bislactone 36 is that the
reaction rate for opening of the first lactone ring is
considerably slower than the rate for opening of the
second lactone ring. Thus only a minor amount of the
monolactone product was traced during the reaction or

3786 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20
Sch em e 3. Synthesis of L-Mannaric Acid Diamides
Alterman et al.
F igu r e 5. Schematic drawing showing the hydrogen bonds
between the HIV-1 protease and the C2-symmetric inhibitor
48.
Sch em e 4. A High Yielding Ring Opening Elimination
Product
125 residues and is hydrogen bonded to both carboxyl
oxygens. The other hydroxyl group points away from
the active site but is still hydrogen bonded to one of the
Asp residues. This difference in usage of the hydroxyls
results in an asymmetric positioning of the inhibitor in
the center of the protease. The P1/P1′ benzyloxy groups
are positioned in the S1/S1′ pockets. The 1,6-dicarbonyl
oxygens of the L-mannaric acid backbone and the amide
nitrogens of the residues Ile 50/150 coordinate a struc-
tural water molecule in a distorted tetrahedral arrange-
ment. The carbonyl oxygen of Ile (Figure 5) binds to
the backbone amide nitrogens of Asp 29/129 in the S3/
S3′ site, and the nitrogen of the N-methyl amide binds
to the Gly 48/148 carbonyl. The aliphatic Ile side chains
are placed in the S2/S2′ pockets in close packing
distances to Val 32/132. From this structural informa-
tion it is apparent that the S2/S2′ pockets of the Ile
inhibitor are not optimally filled up and that conforma-
tionally restricted side chains might induce improved
fit to the S2/S2′ pockets.
ing in 50% inhibition in this assay. For subsequent
compounds and those that exhibited significant inhibi-
tory effects, Ki values were determined by a more
sensitive fluorometric assay.28
Str u ctu r e-Activity Relation sh ip an d X-r ay Cr ys-
ta llogr a p h ic Da ta . For compounds 23-25 and 27
each having lipophilic P2/P2′ amino acid methyl ester
side chains, only compound 23 showed any enzyme
inhibitory activity. A dramatic increase in inhibitory
activity (IC50) going from 5000 nM to 15 nM was
obtained when the methyl ester of compound 23 was
changed to the corresponding N-methyl amide (28).
Thus duplication of one additional hydrogen bond
between the C2-symmetric inhibitor and the HIV pro-
tease backbone results in this substantial increase in
inhibitory activity.
To explore hydrophilic interactions to the enzyme
backbone or to groups lining the hydrophobic S2/S2′
pockets, a number of amines each containing hydrogen
bond donating or accepting functionalities were selected
and coupled to give compounds 26, 29-34, and 45-47.
However, these compounds exhibited only weak or no
HIV-1 protease inhibitory activity. Efforts were then
turned to optimizing the P2/P2′ side chains of the
methyl amide 28. Compounds 37-42 and 48 were
prepared where enzyme inhibition data indicated that
only lipophilic substituents at this position produced
active inhibitors, Ki (nM) ) 660, 140, 81, 2.3, and 0.9
for inhibitors 40 (Met), 37 (Phe), 42 (m-F-phenylGly),
41 (phenylGly), and 48 (Ile) where compounds 28 and
48 were the most potent in this series.
1(S)-Amino-2(R)-hydroxyindan has successfully been
incorporated in HIV-1 protease inhibitors by, for ex-
ample, researchers at Merck (Figure 1, indinavir). As
deduced from molecular modeling experiments, 1(S)-
amino-2(R)-hydroxyindan excellently fit with respect to
filling the S2/S2′ subsite pockets and with respect to
hydrogen bonding between the hydroxyl group and the
protease backbone. Compound 43, having the 1(S)-
amino-2(R)-hydroxyindan moiety, was thus synthesized
and found to be twice as active as compound 28 (Ki 0.2
nM). As expected the corresponding enantiomer of 1(S)-
amino-2(R)-hydroxyindan (44) exhibited no enzyme
inhibition activity.
The X-ray crystal structure of HIV-1 protease com-
plexed with inhibitor 43 (Figure 6) was determined,
and reveled that both inhibitors 43 and 48 bind simi-
larly.29 The hydroxyl group of 1(S)-amino-2(R)-hy-
droxyindan in inhibitor 43 binds to the backbone amide
nitrogens of Asp 29/129 in the S3/S3′ site. The aromatic
portion of the 1(S)-amino-2(R)-hydroxyindan groups in
inhibitor 43 are positioned such that they truly form
the intended expansion of the Ile groups, nicely filling
out the S2/S2′ pockets.
The X-ray crystal structure of HIV-1 protease com-
plexed with the isoleucine inhibitor 48 (Figure 5) was
determined.29 It reveals that one of the hydroxyls of
the central diol points toward the active site Asp 25/

Design of New C2-Symmetric HIV-1 Protease Inhibitors
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20 3787
for a peptidomimetic enabled the design of a number of
potent HIV-1 protease inhibitors. One of the com-
pounds, 43, also demonstrated promising anti-HIV
activity in cell culture. Two synthetic routes leading
up to these inhibitors have been developed, one of which
gives access to these inhibitors in just three chemical
steps from commercially available starting materials.
The structure-activity relationships for these C2-
symmetric inhibitors have been rationalized with the
aid of X-ray crystal structures. An IC50 going from 5000
nM to 15 nM was observed upon changing -OMe (23)
into -NHMe (28), resulting in the net addition of one
more hydrogen bond interaction from each NHMe group
to the enzyme backbone. By sacrificing this important
hydrogen bonding interaction but by optimizing binding
to the S2/S2′ subsite pockets, an even more potent
inhibitor was discovered (43). Further studies of this
class of compounds are currently under way.
F igu r e 6. Schematic drawing showing the hydrogen bonds
between the HIV-1 protease and the C2-symmetric inhibitor
43.
Exp er im en ta l Section
Ta ble 2. In Vitro Anti-HIV-1 Activity30
Thin layer chromatography was performed using silica gel
60 F-254 (Merck) plates with detection by UV and/or charring
with 8% sulfuric acid. Column chromatography was performed
on silica gel (Matrix Silica Si 60A, 35-70 µm, Amicon) eluting
with CH3Cl-MeOH (gradient 5-20% MeOH) if not otherwise
stated. Organic phases were dried over anhydrous sodium
sulfate or magnesium sulfate. Concentrations were performed
under reduced pressure. Optical rotations were recorded on
a Perkin-Elmer 241 polarimeter. Infrared spectra were re-
corded on a Perkin-Elmer 1600 series FTIR instrument. NMR
spectra were recorded on a J EOL GSX-270 instrument; 13C
NMR 67 MHz and 1H NMR 270 MHz. Chemical shifts are
reported in ppm (δ) downfield from tetramethylsilane in
CDCl3, unless otherwise stated.
Accurate mass measurements were recorded on a J EOL SX
102 mass spectrometer/MS-MP7000 data system.
3,4-O-Isop r op ylid en e-L-m a n n itol (12). To a stirred and
cooled (0 °C) solution of L-mannonic γ-lactone (20.0 g, 112
mmol) in dry MeOH (700 mL) was added lithium borohydride
(4.80 g, 225 mmol) in four portions. The reaction mixture was
stirred at room temperature for 30 min, cooled to 0 °C, and
acidified with HOAc. After the mixture was stirred for 15 min,
it was concentrated until dryness and the residue dissolved
in MeOH (200 mL). Another portion of HOAc and MeOH was
added and the acidic solution was again concentrated. Drying
in a vacuum gave L-mannitol as a white foam which was
suspended in dry acetone (600 mL) to which 2,2-dimethoxy-
propane (100 mL, 821 mmol) and camphorsulfonic acid (60.0
g, 260 mmol) were added. The reaction mixture was stirred
overnight and concentrated. EtOAc (300 mL) was added, and
the organic layer was washed with saturated aqueous NaCO3
(300 mL), dried, and concentrated. Purification by column
chromatography (toluene:EtOAc, 10:1) gave the triacetonide
as a white solid (26.5 g, 87.6 mmol, 78%).
The triacetonide (25.1 g, 83.0 mmol) was dissolved in 70%
HOAc (500 mL) and stirred at 40 °C for 1.5 h. The solution
was concentrated, the residue extracted with acetone (L-
mannitol remains as a solid residue), and the extract concen-
trated. The remaining traces of HOAc were removed by
coevaporation with added toluene. The solid residue was
recrystallized from warm acetone to give compound 12 (11.7
g, 53 mmol, 64%) as white crystals. 1H NMR was in agreement
with that previously reported9b (patent WO 93/07128).
1,6-Di-O-ter t-bu tyld im eth ylsilyl-3,4-O-isop r op ylid en e-
L-m a n n itol (13). tert-Butyldimethylsilyl chloride (814 mg, 5.4
mmol) was added to a stirred solution of compound 12 (566
mg, 2.57 mmol) in pyridine (10 mL) containing (dimethyl-
amino)pyridine (7 mg, 0.05 mmol). The mixture was stirred
at 40 °C for 1.5 h and then concentrated to dryness by
coevaporation with added toluene. The residue was dissolved
in CH2Cl2 (30 mL) and washed with saturated aqueous NaCO3,
In Vitr o An ti-HIV Activity. (Table 2) The anti-HIV
activity was assayed by an HIV cytopathic assay in
MT-4 cells where the effect was quantified using vital
dye XTT.30 The 50% inhibitory concentrations (ED50)
were calculated from the percent cytoprotection for
individual compounds.
As can be seen in Table 2, compound 43 has an anti-
HIV-1 activity in cell culture which is comparable to
that of ritonavir and indenavir whereas compounds 28
and 48 are more than 10 times less active in the assay.
Con clu sion
Application of the concept of C-terminal duplication
with a carbohydrate, L-mannaric acid, as a new template

3788 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20
Alterman et al.
dried, concentrated, and purified by column chromatography
(toluene:EtOAc, 10:1) to give 13 as a clear oil (1.10 g, 2.47
mmol, 96%). 13C NMR (CDCl3): δ 5.2, 18.5, 26.0, 27.1, 64.6,
79.6, 109.4. Anal. (C21H46O6Si2) C, H.
17.8, 19.0, 27.0, 31.2, 52.0, 56.7, 73.9, 77.6, 79.4, 110.4, 128.2,
128.3, 136.8, 169.0, 171.8. Anal. (C35H48N2O10‚1H2O) C, H,
N.
N1,N6-Di[(1S)-2-p h en yl-1-(m et h oxyca r b on yl)et h yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxy-3,4-O-iso-
2,5-Di-O-ben zyl-1,6-d i-O-ter t-bu tyld im eth ylsilyl-3,4-O-
isop r op ylid en e-L-m a n n itol (14). To a cold (0 °C), stirred
suspension of NaH (290 mg, 12.1 mmol) in dry THF (30 mL)
under an atmosphere of argon was added 13 (2.27 g, 5.06
mmol) over 10 min. The ice bath was removed, and the
resulting tan solution was stirred at room temperature for 15
min. Tetrabutylammonium iodide (15 mg) and benzyl bromide
(1.32 mL, 11.1 mmol) were added, and the reaction mixture
was stirred at room temperature for 15 h. H2O (3 mL) was
added, and the resulting mixture was concentrated. The
residue was taken up in Et2O (40 mL) and washed with H2O
(3 × 40 mL). The combined organic extracts were dried,
concentrated, and purified by column chromatography (light
petroleum ether-EtOAc, 17:1) to give compound 14 as a clear
oil (2.43 g, 3.85 mmol, 76%). 13C NMR (CDCl3): δ 5.4, 18.2,
25.9, 27.2, 63.8, 73.1, 78.3, 81.1, 109.5, 127.7, 128.1, 138.8.
Anal. (C35H58O6Si2) H,C.
p r op ylid en eh exa n ed ia m id e (18). 13C NMR (CDCl3):
δ
27.0, 37.9, 52.1, 52.6, 73.6, 78.1, 79.8, 110.6, 128.4, 128.5, 128.7,
129.2, 135.6, 136.5, 169.0, 171.6. Anal. (C43H48N2O10‚0.5H2O)
C, H, N.
N1,N6-Di[(1S)-2-m eth yl-1-(ben zyloxyca r bon yl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxy-3,4-O-iso-
p r op ylid en eh exa n ed ia m id e (19). 13C NMR (CDCl3):
δ
17.67, 19.0, 27.0, 31.3, 56.7, 66.9, 73.9, 77.5, 79.5, 110,4, 128.2,
128.3, 128.6, 129.5, 135.5, 136.9, 169.1, 171.2. Anal. (C47H56N3-
O10‚0.5H2O) C, H, N.
N 1,N 6-Di[(1S )-2-m e t h yl-1-(h yd r oxym e t h yl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxy-3,4-O-iso-
p r op ylid en eh exa n ed ia m id e (20). Compound 20 was di-
rectly subjected to deprotection. 13C NMR (CDCl3): δ 18.2,
19.4, 27.3, 30.2, 56.9, 63.3, 75.1, 77.5, 79.3, 110.4, 128.3, 128.8,
129.0, 136.7, 169.6.
N1,N6-Di[(1S)-3-m et h yl-1-(m et h oxyca r b on yl)b u t yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxy-3,4-O-iso-
p r op ylid en eh exa n ed ia m id e (21). Compound 21 was di-
rectly subjected to deprotection. 13C NMR (CDCl3): δ 21.9,
23.0, 24.9, 27.1, 41.7, 50.3, 52.3, 74.0, 77.8, 79.6, 110,5; 128.4,
128.7, 129.1, 136.9, 169.2, 173.0.
2,5-Di-O-ben zyl-3,4-O-isop r op ylid en e-L-m a n n itol (15).
Compound 14 (2.10 g, 3.3 mmol) was dissolved in THF (15
mL), a solution of tetrabutylammonium fluoride in THF (7.2
mL, 1.1 M) was added, and the reaction mixture was stirred
at room temperature for 1 h. Most of the solvent was removed
under reduced pressure, and the residue was flashed through
a short column of silica gel with CH3CN as eluent, concen-
trated, and purified by column chromatography (light petro-
leum ether-EtOAc, 1:1) to give compound 15 as a clear oil
(1.29 mg, 3.2 mmol, 98%) which solidified upon standing. 13C
NMR (CDCl3): δ 27.3, 61.4, 80.0, 110.1, 128.1, 128.7, 137.9.
Anal. (C23H30O6) C, H.
N1,N6-Disu ccin im idyl-(2R,3R,4R,5R)-2,5-di(ben zyloxy)-
3,4-d ih yd r oxyh exa n ed ia m id e (22). A mixture of compound
16 (1.01 g, 2.35 mmol), N,N-disuccinimidyl carbonate (2.41 g,
9.4 mmol) and pyridine (1.15 mL, 14.1 mmol) in CH3CN (15
mL) was stirred at ambient temperature overnight. The
mixture was concentrated and the residue dissolved in EtOAc.
The organic phase was washed with H2O, dried, and concen-
trated, and the residue was purified by column chromathograpy
to give 22 (1.29 g, 2.07 mmol, 88%) as a white foam. A small
portion was crystallized from 2-propanol. [R]D ) +53.8° (c )
0.935, CHCl3). 1H NMR (CDCl3): δ 1.4 (s, 6H), 2.8 (s, 8H),
4.4-4.65 (m, 6H), 4.85 (d, 2H), 7.2-7.4 (m, 10H). 13C NMR
(CDCl3): δ 25.6, 27.0, 73.0, 77.0, 77.8, 112.2, 128.2, 128.5,
136.1, 165.5, 168.4. Anal. (C31H32N2O12) C, H, N.
P r oced u r e for P r ep a r a t ion of Com p ou n d s 23-27.
Meth od I. Compounds 17-21 were dissolved in MeOH (15
mL) acidified with HCl (4%, w:w) and stirred at room tem-
perature for 2 h. The clear solution was concentrated and
purified by column chromatography (toluene-EtOAc, 1:1; CH2-
Cl2-MeOH, 95:5 for compound 26) to give compounds 23-27
in 70-74% yield (see Table 1).
2,5-Di-O-ben zyl-3,4-O-isop r op ylid en e-L-m a n n a r ic a cid
(16). To a stirred solution of compound 15 (1.080 g, 2.68 mmol)
in CH2Cl2 (36 mL) was added TEMPO (2,2,6,6-tetramethyl-
1-piperidinyloxy, free radical) (22 mg, 0.14 mmol) and a
solution of saturated aqueous NaCO3 (11 mL), KBr (59 mg,
0.50 mmol), and tetrabutylammonium bromide (90 mg, 0.28
mmol). The mixture was cooled to 0 °C, and a solution of
sodium hypochlorite (17.4 mL, 1.2 M), saturated aqueous
NaCO3 (5.9 mL), and brine (11.8 mL) was added over 45 min.
After the mixture was stirred at 0 °C for an additional 45 min,
the organic layer was separated and washed with H2O (3 ×
20 mL). The combined aqueous phases were acidified with 4
M HCl, extracted with EtOAc (3 × 20 mL), dried, and
concentrated to give compound 16 as a white solid (775 mg,
1.80 mmol, 67%). 13C NMR (DMSO-d6): δ 27.0, 71.7, 78.4,
79.1, 110.0, 127.6, 128.3, 137.5, 170.6. A small portion was
recrystallized from EtOAc and light petroleum ether to give
the dicarboxylic acid as white crystals which were subjected
to elementary analysis. Anal. (C23H26O8) C, H.
N1,N6-Di[(1S)-2-m eth yl-1-(m eth oxyca r bon yl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (23). 13C NMR (CDCl3): δ 17.6, 19.0, 31.3, 52.1, 56.6,
71.6, 74.2, 78.0, 128.3, 128.5, 136.4, 171.7, 172.1. [R]D
)
+20.53° (c ) 1.13, CHCl3). Anal. (C32H44N2O10‚0.5H2O) C, H,
N.
P r oced u r e for P r ep a r a t ion of Com p ou n d s 17-21.
Meth od I. Compound 16 (200-300 mg, 0.46-0.70 mmol),
amino acid derivative (2.2 equiv, 1.01-1.54 mmol), and 1-hy-
droxybenzotriazole hydrate (3.0 equiv, 186-284 mg, 1.38-2.10
mol) were dissolved in 6-8 mL CH2Cl2-THF (2:1) under an
atmosphere of argon. The pH of the stirred reaction mixture
was adjusted to 7.5 by dropwise addition of triethylamine. The
temperature was lowered to 0 °C, and 1-(3-dimethylamino-
propyl)-3-ethylcarbodiimide hydrochloride (2.4 equiv, 211-322
mg, 0.96-1.68 mmol) was added in one portion. After 1 h,
the temperature was raised to room temperature, and the
reaction mixture was stirred for 2-4 h, depending on the
amino acid derivative used. CH2Cl2 (20 mL) was added, and
the organic layer was washed with saturated aqueous NaCO3.
The organic layer was separated, dried, and concentrated.
Column chromatography (toluene-EtOAc, 3:1-4:1) furnished
compounds 17-21. Details about yields and amino acid
derivatives used are listed in Table 1.
N1,N6-Di[(1S)-2-p h en yl-1-(m et h oxyca r b on yl)et h yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (24). [R]D ) +44.21° (c ) 1.07, CHCl3). 13C NMR
(CDCl3): δ 37.7, 52.6, 53.0, 70.9, 74.0, 79.1, 128.3, 128.7, 128.8,
129.2, 135.8, 136.8, 171.5, 172.3. Anal. (C40H44N2O10‚1H2O)
C, H, N.
N1,N6-Di[(1S)-2-m eth yl-1-(ben zyloxyca r bon yl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (25). [R]D ) +16.11° (c ) 0.95, CHCl3). 13C NMR
(CDCl3): δ 17.5, 18.9, 31.0, 56.9, 67.0, 70.8, 74.0, 78.4, 128.4,
128.6, 128.7, 129.6, 135.3, 136.8, 171.0, 172.6. Anal. (C44H52N2-
O10‚1H2O) C, H, N.
N 1,N 6-Di[(1S )-2-m e t h yl-1-(h yd r oxym e t h yl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (26). 13C NMR (CDCl3): δ 18.9, 19.6, 29.0, 56.9, 62.9,
71.8, 73.2, 81.1, 128.1, 128.3, 128.6, 136.8, 171.7. Anal.
(C30H44N2O8‚1H2O) C, H, N.
N1,N6-Di[(1S)-2-m eth yl-1-(m eth oxyca r bon yl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxy-3,4-O-iso-
N1,N6-Di[(1S)-3-m et h yl-1-(m et h oxyca r b on yl)b u t yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (27). 13C NMR (CDCl3): δ 21.7, 23.0, 24.9, 27.1, 41.7,
p r op ylid en eh exa n ed ia m id e (17). 13C NMR (CDCl3):
δ

Design of New C2-Symmetric HIV-1 Protease Inhibitors
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20 3789
50.4, 52.3, 70.9, 74.0, 78.8, 128.2, 128.3, 128.7, 136.9, 172.4,
172.7. Anal. (C34H48N2O10) C, H, N.
Gen er a l Meth od for th e P r ep a r a tion of Com p ou n d s
32-34. Meth od III. The succinimidyl diester 22 (1.0 equiv)
and the amine (2.5 equiv) were dissolved in dichloroethane.
The mixture was stirred for 16 h under argon at 65 °C. After
concentration the mixture was dissolved in CH2Cl2 and washed
with saturated aqueous NaHCO3, dried, and concentrated, and
the residue was subjected to column chromathograpy. The
purified l-mannaric amides were dissolved in 5 mL of 4% HCl
in MeOH, and the reaction mixture was stirred at ambient
temperature until TLC indicated complete reaction. The
mixture was partitioned between CH2Cl2 and saturated aque-
ous NaHCO3 (2×), dried, concentrated, and purified by column
chromatography to give title compounds 32-34.
N1,N6-Di(3-h yd r oxy-2-m et h ylp h en yl)-(2R,3R,4R,5R)-
2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (32). The
title compound was prepared in 25% yield (40 mg, 0.067 mmol)
according to method III, using 3-amino-o-cresol. [R]D ) +37.8°
(c ) 0.54, MeOH). 13C NMR (CD3OD and CDCl3): δ 10.0, 71.5,
73.9, 80.4, 112.8, 115.4, 118.0, 126.6, 128.6, 128.9, 135.8, 137.1,
155.7, 170.8. HRMS calcd for C34H36N2O8 600.2472, found
600.2508.
N1,N6-Di(2-h yd r oxy-4-m et h ylp h en yl)-(2R,3R,4R,5R)-
2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (33). The
title compound was prepared in 32% yield (75 mg, 0.13 mmol)
according to method III, using 6-amino-m-cresol. [R]D ) +46.2°
(c ) 0.75, MeOH). 13C NMR (CD3OD): δ 21.2, 72.4, 74.1, 81.7,
116.9, 121.0, 122.4, 124.2, 129.0, 129.4, 129.5, 136.4, 138.6,
148.9, 171.7. Anal. (C34H36N2O8) C, H, N.
N1,N6-Di(4-h yd r oxy-2-m et h ylp h en yl)-(2R,3R,4R,5R)-
2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (34). The
title compound was prepared in 38% yield (96 mg, 0.16 mmol)
Va lin e Meth yla m id e. To a cooled (-15 °C) solution of
Z-Val-OSu (348 mg, 1 mmol) in dry THF (5 mL) was added
methylamine (2 mmol, 2 M solution in THF). The reaction
mixture was brought to room temperature and stirred for 4 h.
The N-hydroxysuccinimide was filtered off and the residue
concentrated, dissolved in EtOAc (25 mL), washed with
NaHCO3 (2 × 15 mL), dried, and concentrated to give the crude
methylamide which was crystallized from EtOAc. The product
was dissolved in EtOAc and hydrogenated over Pd/C for 6 h.
The catalyst was removed and the residue concentrated to give
the desired methylamide in 78% yield (102 mg, 0.78 mmol).
Spectral data were in agreement with those previously re-
ported.19
N1,N6-Di[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (28). Compound 16 (181 mg, 0.42 mmol), valine
methylamide (121 mg, 0.93 mmol), and 1-hydroxybenzotriazole
hydrate (170 mg, 1.26 mmol) were dissolved in 6 mL of CH2-
Cl2-THF (2:1) under an atmosphere of argon. The pH of the
stirred reaction mixture was adjusted to 7.2 by dropwise
addition of triethylamine. The temperature was lowered to 0
°C, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hy-
drochloride (191 mg, 1.0 mmol) was added in one portion. After
1 h, the temperature was raised to room temperature and the
reaction mixture was stirred 4 h. CH2Cl2 (20 mL) was added,
and the organic layer was washed with saturated aqueous
NaCO3. The organic layer was separated, dried, and concen-
trated. The residue was dissolved in MeOH (15 mL) acidified
with HCl (4%, w:w) and stirred at room temperature for 2 h.
The clear solution was concentrated and purified by column
chromatography (toluene-EtOAc, 1:1) to give 28 in 88% yield.
[R]D ) -6.27° (c ) 1.03, CHCl3). 13C NMR (CDCl3-CD3OD,
7:3): δ 17.5, 19.6, 26.0, 30.2, 58.5, 72.1, 73.2, 80.5, 128.4, 128.6,
137.2, 172.1, 172.4. Anal. (C32H46N4O8‚1H2O) C, H, N.
Gen er a l Meth od for th e P r ep a r a tion of Com p ou n d s
29-31. Meth od II. The l-mannaric acid 16 (1.0 equiv), the
amine (2.2 equiv), and HOBT (3.0 equiv) were dissolved in 2:1
CH2Cl2-THF with stirring under argon. The pH was adjusted
to 7.5 by dropwise addition of triethylamine, and the temper-
ature was adjusted to 0 °C. EDC (2.4 equiv) was added, and
stirring was continued for 1 h at 0 °C and then for 16 h at
ambient temperature. The reaction mixture was diluted with
CH2Cl2 (2× volume), washed with saturated aqueous NaHCO3,
dried, and concentrated, and the residue was purified by
column chromatography. The purified l-mannaric amides
were dissolved in 5 mL of 4% HCl in MeOH, and the reaction
mixture was stirred at ambient temperature until TLC
indicated complete reaction. The mixture was partitioned
between CH2Cl2 and saturated aqueous NaHCO3, dried,
concentrated, and purified by column chromatography to give
the target compounds 29-31.
according to method III, using 4-amino-3-methylfenol. [R]D
)
+30.3° (c ) 0.75, DMSO). 13C NMR (DMSO-d6): δ 18.0, 70.0,
71.5, 80.2, 112.6, 116.6, 127.2, 127.5, 127.6, 127.8, 128.2, 134.1,
138.0, 155.1, 169.9. Anal. (C34H36N2O8) C, H, N.
L-Ma n n a r o-1,4:3:6-d i-γ-la cton e (35). L-Mannonic γ-lac-
tone (11) (1.0 equiv, 3.0 g, 17.0 mmol), HNO3 (9 mL, concen-
trated), and H2O (1.7 mL) were heated to 85 °C under stirring
with the evolution of nitrous gases. The reaction mixture was
refluxed for 16 h and concentrated twice with addition of H2O
(30 mL). The residue was lyophilized from H2O (40 mL). The
resulting white solid was suspended in ethanol (5 mL) and
diethyl ether (30 mL). After filtration and drying 35 was
obtained as a white solid (1.76 g, 10.1 mmol, 60%). [R]D
)
-158.81° (c ) 1.18, MeOH). 1H NMR (DMSO-d6): δ 4.75 (d,
2H), 5.1 (d, 2H), 6.4 (broad s, 2H). 13C NMR (DMSO-d6): δ
69.2, 75.9, 174.3. IR (KBr): 1799.4 cm-1. Anal. (C6H6O6) C,
H.
2,5-Di-O-ben zyl-L-m a n n a r o-1,4:3,6-d i-γ-la cton e (36). To
a stirred solution of L-mannaro-1,4:6,3-di-γ-lactone (300 mg,
1.72 mmol) and benzyl-2,2,2-trichloroacetimidate (0.96 mL,
5.17 mmol) in dry dioxane was added trifloromethanesulfonic
acid (240 µL) dropwise under nitrogen. Within 1-2 h the color
changed to red-brown. After an additional 30 min the reaction
mixture was filtered through 2 cm of NaCO3 on 2 cm of silica
in a glass filter-funnel and subsequently evaporated under
reduced pressure. Warm diethyl ether was added to the crude
product, the mixture was stirred for 1 min, and the diethyl
ether was thereafter decanted. Recrystalization from CH2Cl2
gave white crystals of 2,5-di-O-benzyl-L-mannaro-1,4:3,6-di-
γ-lactone (439.5 mg, 72%). [R]D ) -125.58° (c ) 1.04, CH2-
Cl2). IR (KBr) 1785 cm-1. Mp 184-186 °C. 13C NMR (DMSO-
d6): δ 72.04, 74.39, 74.82, 127.97, 128.04, 128.4, 136.92, 171.76.
Anal. (C20H18O6) C, H.
Gen er a l Meth od for th e P r ep a r a tion of Com p ou n d s
28, 37-40. Meth od IV. Bislactone 36 (40 mg, 0.11 mmol)
was dissolved in CH2Cl2 (4 mL). Six equivalents of the amino
acid derivative was added to the solution, and the mixture was
stirred at reflux for 16 h. The solvent was removed under
reduced pressure and the crude product purified by silica gel
chromatography.
N1,N6-Di(2-p yr id ylm et h yl)-(2R,3R,4R,5R)-2,5-d i(b en -
zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (29). The title com-
pound was prepared in 29% yield (50 mg, 0.088 mmol)
according to method II, using 2-aminomethyl pyridine [R]D
)
+21.7° (c ) 1.34, CHCl3). 13C NMR (CDCl3): δ 43.9, 71.3, 73.7,
79.5, 121.9, 122.4, 128.1, 128.3, 128.5, 137.0, 148.9, 156.1,
172.4. Anal. (C32H34N4O6‚0.5H2O) C, H, N.
N1,N6-Di(3-p yr id ylm et h yl)-(2R,3R,4R,5R)-2,5-d i(b en -
zyloxy)-3,4- d ih yd r oxyh exa n ed ia m id e (30). The title com-
pound was prepared in 30% yield 30 (62 mg, 0.109 mmol)
according to method II, using 3-aminomethyl pyridine. [R]D
) +49.2° (c ) 1.34, CHCl3). 13C NMR (CD3OD): δ 40.5, 40.6,
71.2, 73.3, 80.3, 124.2, 128.4, 128.7, 134.7, 136.4, 137.1, 148.0,
148.5, 172.6, 172.7. Anal. (C32H34N4O6) C, H, N.
N1,N6-Di(4-p yr id ylm et h yl)-(2R,3R,4R,5R)-2,5-d i(b en -
zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (31). The title com-
pound was prepared in 21% (94 mg, 0.165 mmol) according to
method II, using 4-aminomethyl pyridine. [R]D ) +31.4° (c )
0.36, MeOH). 13C NMR (CDCl3): δ 41.8, 71.5, 73.8, 79.8, 122.2,
128.3, 128.5, 128.7, 136.6, 147.2, 149.6, 172.3. Anal. (C32H34N4-
O6‚0.5H2O) C, H, N.
N1,N6-Di[(1S)-2-m eth yl-1-(m eth ylca r ba m oyl)p r op yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (28). The title compound was prepared using valine

3790 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20
Alterman et al.
methylamide19 according to method IV using CH2Cl2-MeOH
(20: 1) as eluent to give 28 (48.6 mg, 70%).
Anal. Calcd for C38H42N4O8: C, 66.85; H, 6.20; N, 8.21.
Found: C, 66.74; H, 6.34; N, 8.12.
N1,N6-Di[(1S)-2-p h en yl-1-(m et h ylca r b a m oyl)et h yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (37). The title compound was prepared using phenyl-
alanine methylamide31 according to method IV using CH2Cl2-
MeOH (20:1) as eluent to give product 37 (60.9 mg, 76%). [R]D
N1,N6-Di[1-(3-flu or oph en yl)-1-(m eth ylcar bam oyl)m eth -
yl]- (2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh ex-
a n ed ia m id e (42). The title compound was prepared in 20%
yield (49 mg, 0.068 mmol) according to method IV, using
3-fluorophenylglycine methyl amide (220 mg, 1.21 mmol) in
CH3CN (1 mL) at 70 °C for 16 h. 13C NMR (CD3OD and
CDCl3): δ 26.5, 57.4, 57.6, 71.7, 71.9, 72.2, 73.6, 73.7, 80.2,
80.3, 80.9, 115.0, 115.2, 115.4, 115.5, 115.7, 116.0, 124.0, 124.3,
128.7, 128.9, 129.2, 131.2, 131.3, 138.1, 140.9, 162.1, 165.7,
171.7, 172.8, 173.0. Anal. (C38H40N4O8F2) C, H, N.
N1,N6-Di[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (43). The
title compound was prepared according to method IV, using
(1S,2R)-(-)-cis-1-amino-2-indanol (0.915 g, 6.2 mmol) in CHCl3
(12 mL) at 45 °C for 4. The reaction mixture was concentrated
and partitioned between CHCl3 and saturated aqueous NH4-
Cl and H2O. The organic layer was separated, dried (MgSO4),
and concentrated. Crystallization from MeOH gave 43 (0.65
g, 0.996 mmol, 35%). [R]D ) -20.7° (c ) 0.68, CHCl3). 13C
NMR (CDCl3): δ 39.2, 57.8, 71.6, 72.5, 73.5, 81.5, 124.0, 125.3,
127.0, 128.2, 128.3, 128.6, 136.7, 139.8, 140.8, 171.6. Anal.
(C38H40N2O8) C, H, N.
N1,N6-Di[(2R)-h yd r oxy-1(S)-in d a n yl]-(2R,3R,4R,5R)-
2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (44). The
title compound was prepared in 22% yield (60 mg, 0.092 mmol)
according to method IV using (1R,2S)-(+)-cis-1-amino-2-in-
danol (370 mg, 2.5 mmol) in CH3CN (1 mL) at 70 °C for 16 h.
[R]D ) +3.2° (c ) 0.53, CH3OH). 13C NMR (CD3OD and
CDCl3): δ 40.1, 57.9, 71.6, 73.1, 73.5, 80.4, 124.8, 125.6, 127.5,
128.6, 128.8, 128.9, 137.6, 140.9, 173.2. Anal. (C38H40N2O8)
C, H, N.
N1,N6-Di(2-h yd r oxyet h yl)-(2R,3R,4R,5R)-2,5-d i(b en -
zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (45). The title com-
pound was prepared in 49% yield (105 mg, 0.296 mmol)
according to method IV using 2-hydroxyethylamine (43 µL,
0.78 mmol) in CHCl3 (2 mL) at 40 °C for 1 h. [R]D ) +64.0° (c
) 0.69, CHCl3). 13C NMR (CD3OD): δ 42.5, 61.4, 71.6, 73.6,
81.2, 128.8, 129.2, 138.5, 174.0. Anal. (C24H32N2O8) C, H, N.
5-Am in om eth yl Th ia zole. 5-Hydroxymethyl thiazole (1.0
equiv, 315 mg, 2.74 mmol), triphenyl phosphine (1.4 equiv, 995
mg, 3.79 mmol), and LiN3 (6.3 equiv, 855 mg, 17.5 mmol) were
suspended in DMF (15 mL). CBr4 (1.4 equiv, 1.25 g, 3.78
mmol) was added, and the reaction mixture was stirred at
room temperature for 23 h after which MeOH (3 mL) was
added. The mixture was partitioned between toluene and H2O
(4×), dried, and concentrated. The residue was purified using
column chromathograpy eluting with toluene-EtOAc (5:1) to
give 5-azidomethyl thiazole (297 mg, 2.12 mmol, 77%) as a
yellow viscous oil. 1H NMR (CDCl3): δ 4.58, 7.74, 8.84. 13C
NMR (CDCl3): δ 46.3, 132.4, 142.7, 154.3. Anal. (C4H4N4S)
C, H, N. 5-Azidomethyl thiazole (1.0 equiv, 229 mg, 1.63
mmol) was dissolved in ethanol (20 mL), and Pd/C (0.2 g) was
added. The suspension was stirred under hydrogen atmo-
sphere for 20 h, filtered through Celite, and concentrated to
give 5-aminomethyl thiazole (138 mg, 1.21 mmol, 74%) as a
yellow syrup which was used without further purification. 1H
NMR (CD3OD): δ 4.04, 4.71, 7.76, 8.89. 13C NMR (CD3OD):
δ 38.5, 140.9, 141.7, 154.6.
N1,N6-Di(5-th ia zolylm eth yl)-(2R,3R,4R,5R)-2,5-d i(ben -
zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (46). The title com-
pound was prepared in 65% yield (106 mg, 0.182 mmol)
according to method IV using 5-aminomethyl thiazole (138 mg,
1.21 mmol) in CH3CN (1 mL) at 70 °C for 1 h. [R]D ) +29.0°
(c ) 0.38, CH3OH). 13C NMR (CD3OD and CDCl3): δ 35.5,
71.3, 73.4, 80.6, 128.6, 128.9, 129.0, 137.7, 137.8, 141.6, 155.0,
173.4. Anal. (C28H30N4O6S2) C, H, N.
N1,N6-Di(2-ch lor o-6-flu or oben zyl)-(2R,3R,4R,5R)-2,5-
d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed ia m id e (47). The
title compound was prepared in 59% yield (114 mg, 0.169
mmol) according to method IV using 2-chloro-6-fluorobenzyl-
amine (282 mg, 1.77 mmol) in CH3CN (1 mL) at 70 °C for 21
h. [R]D ) +15.6° (c ) 0.93, CHCl3). 13C NMR (CD3OD and
) +5.59° (c ) 1.02, CHCl3); IR (KBr): 3324, 1650, 1525 cm-1
.
13C NMR (CDCl3): δ 26.20, 37.02, 54.03, 72.83, 73.67, 81.87,
127.07, 127.81, 128.42, 128.65, 128.78, 129.00, 136.38, 134.98,
170.00, 172.06. Anal. (C40H46N4O8) C, H, N.
N1,N6-Di[(1S)-2-(p-h yd r oxy)p h en yl-1-(m eth ylca r ba m -
oyl)eth yl]-(2R,3R,4R,5R)-2,5-di(ben zyloxy)-3,4-dih ydr oxy-
h exa n ed ia m id e (38). The title compound was prepared
using tyrosine methylamide31 according to method IV using
CH2Cl2-MeOH (9:1) as eluent to give product 38 (60.0 mg,
60%). [R]D ) +7.13° (c ) 0.87, EtOH). IR (KBr): 3320, 1651,
1514 cm-1 13C NMR (CD3OD): δ 26.13, 37.07, 55.32, 72.86,
.
72.93, 81.13, 116.14, 128.83, 129.15, 130.93, 138.32, 157.18,
172.92, 173.59. Anal. (C40H46N4O10) C, H, N.
N1,N6-Di[(1S,2R)-2-h yd r oxy-1-(m eth ylca r ba m oyl)p r o-
p yl]-(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh ex-
a n ed ia m id e (39). The title compound was prepared accord-
ing to method IV using threonine methylamide using CH2Cl2-
MeOH (9:1) to give product 39 (42.9 mg, 61%). [R]D ) -3.24°
(c ) 1.02, MeOH). IR (KBr): 3393, 1651, 1518 cm-1 13C NMR
.
(CD3OD): δ 20.59, 26.18, 59.53, 67.09, 73.13, 81.02, 128.90,
129.08, 129.24, 138.39, 172.69, 173.21. Anal. (C30H42N4O10
C, H, N.
)
N1,N6-Di[(1S)-3-th iom eth yl-1-(m eth ylca r ba m oyl)p r o-
p yl]-(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh ex-
a n ed ia m id e (40). The title compound was prepared using
methionine methylamide32 according to method IV using CH2-
Cl2-MeOH (20:1) as eluent to give product 40 (55.0 mg, 72%).
[R]D ) -13.84° (c ) 1.51, MeOH). IR (KBr): 3303, 1636, 1541
cm-1 13C NMR (CD3OD): δ 15.37, 26.58, 31.42, 32.21, 53.73,
.
72.72, 73.64, 81.55, 129.16, 129.41, 129.60, 138.86, 174.02,
174.22. Anal. (C32H46N4S2O8) C, H, N.
Gen er a l Meth od for th e P r ep a r a tion of Com p ou n d s
41-48. Meth od IV. A mixture of the amine (2.2-6 equiv)
in specified solvent was heated at 40-70 °C with stirring. The
benzylated bislactone 36 (1.0 equiv) was added, and the
mixture was stirred for 1-16 h at elevated temperature. The
solvent was evaporated, and the crude product was purified
by silica gel column chromatography and/or crystallization to
give the target compounds 41-48.
L-P h en ylglycin e Meth yl Am id e. Z-PhGly-OSu (1 equiv,
2.01 g, 5.26 mmol) was suspended in THF (20 mL) under argon
at -10 °C. Methylamine (1.6 equiv, 4.2 mL as a 2.0 M solution
in THF, 8.4 mmol) was added dropwise during 20 min.
Stirring was continued at -10 °C for 2 h and at room
temperature for 1.5 h. The mixture was filtered through
Celite, concentrated, and partitioned between CHCl3, H2O, and
NH4Cl, dried, and concentrated. Crystallization from EtOAc
gave Z-L-phenylglycine methyl amide (649 mg, 2.18 mmol,
42%) as a white solid. 13C NMR (CD3OD and CDCl3): δ 26.3,
26.5, 58.7, 67.2, 127.2, 128.0, 128.3, 128.5, 128.6, 129.0, 136.2,
138.1, 156.3, 171.3.
Z-L-P h en ylglycin e Meth yl Am id e (1.0 equiv, 607 mg, 2.03
mmol) was dissolved in EtOAc (12 mL). Pd/C (44 mg) was
added, and the suspension was stirred under hydrogen for 21
h, filtered through Celite, and concentrated to give L-phenyl-
glycine methyl amide (274 mg, 1.67 mmol, 77%) as a yellow
oil which was used in the next step without further purifica-
tion. 13C NMR (CD3OD): δ 26.4, 59.8, 128.2, 129.3, 129.8,
140.9, 174.9.
N1,N6-Di[(1S)-1-p h en yl-1-(m eth ylca r ba m oyl)m eth yl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (41). The title compound was prepared in 31% yield
(89 mg, 0.130 mmol) according to method IV, using l-phenyl-
glycine methyl amide (274 mg, 1.67 mmol) in CH3CN (1 mL)
at 65 °C for 14 h. [R]D ) +75.7° (c ) 0.39, CH3OH). 13C NMR
(CD3OD and CDCl3): δ 26.3, 26.4, 57.1, 71.8, 73.4, 80.3, 127.4,
128.3, 128.4, 128.5, 128.6, 129.0, 136.5, 137.2, 170.3, 171.3.

Design of New C2-Symmetric HIV-1 Protease Inhibitors
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 20 3791
shaw, S. Inhibitors of HIV proteinase. Exp. Opin. Invest. Drugs
1994, 3, 273-286. (d) Wlodawer, A.; Erickson, J . Structure-based
inhibitors of HIV-1 protease. W. Annu. Rev. Biochem. 1993, 62,
543-585. (e) Meek, T. D. Inhibitors of HIV-1 protease. J . Enzyme
Inhib. 1992, 6, 65-98. (f) Norbeck, D. W.; Kempf, D. HIV
protease inhibitors. J . Annu. Rep. Med. Chem. 1991, 26, 141-
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1996, 2, 225-246.
CDCl3): δ 34.8, 71.0, 73.7, 80.0, 114.5, 114.9, 123.3, 123.6,
125.8, 125.9, 128.5, 128.6, 128.8, 130.3, 130.4, 135.9, 137.2,
160.2, 163.9, 172.3, 172.4. Anal. (C34H32N2O6Cl2F2) C, H, N.
N1,N6-Di[(1S,2S)-2-m eth yl-1-(m eth ylcar bam oyl)bu tyl]-
(2R,3R,4R,5R)-2,5-d i(ben zyloxy)-3,4-d ih yd r oxyh exa n ed i-
a m id e (48). Prepared using isolucine methylamide33 accord-
ing to method IV using chloroform-methanol (20:1) as eluent
to give (34.4 mg, 46%). [R]D ) -6.8° (c ) 0.50, CHCl3). IR
(KBr): 3324, 1650, 1541 cm-1 13C (CD3OD): δ 11.67, 16.07,
.
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Harada, Y.; Swaminathan, S.; Bischofberger, N.; Chen, M. S.;
Cherrington, J . M.; Xiong, S. F.; Griffin, L.; Cundy, K. C.; Lee,
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25.13, 26.34, 37.20, 58.46, 72.26, 73.39, 80.84, 128.72, 129.13,
137.72, 172.68, 173.12. Anal. (C34H50N4O8) C, H, N.
(5R)-5-[(R)-(Ben zyloxy)-(h yd r oxyca r bon yl)m eth yl]-2-
ben zyloxy-2(5H)-fu r a n on e (49). Bislactone 36 (40 mg,
0.113 mmol) was dissolved in dioxane (6 mL). NaOH (1 M, 2
mL) was added, and the reaction mixture was stirred for 5
min. The solvent was removed under reduced pressure, and
the crude product was dissolved in saturated NaCO3 (20 mL).
The solution was extracted with CH2Cl2 (3 × 20 mL). The
combined organic phase was dried with MgSO4, filtered, and
concentrated under reduced pressure to give product 49 (38
mg, 95%). [R]D ) -16.8° (c ) 1.06, MeOH). IR (KBr): 3428.7,
1781.3, 1651.0, 1590.2 cm-1 1H NMR (CD3OD): δ 4.43 (d, J
.
) 3.9, 1H), 4.49 (d, J ) 11.6, 1H), 4.74 (d, J ) 11.6, 1H), 4.95
(s, 2H), 5.32 (dd, J ) 2.3, J ) 3.8, 1H), 6.31 (d, J ) 2.3, 1H),
7.32 (m, 10H). 13C NMR (CD3OD): δ 73.74, 74.19, 78.27, 79.60,
115.75, 128.72, 128.95, 129.19, 129.37, 136.43, 138.15, 147.53,
169.02, 171.75. HRMS calcd for C20H18O6 355.1182, found
355.1170.
Ack n ow led gm en t. We gratefully acknowledge sup-
port from the Swedish National Board for Technical
Development (NUTEK), from the Swedish Research
Council for Engineering Sciences (TFR), and from
Medivir AB, Huddinge, Sweden.
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