Nonpeptidal P2 ligands for HIV protease inhibitors: structure-based design, synthesis, and biological evaluation.

Article abstract of DOI:10.1021/jm960128k

Design and synthesis of nonpeptidal bis-tetrahydrofuran ligands based upon the X-ray crystal structure of the HIV-1 protease-inhibitor complex 1 led to replacement of two amide bonds and a 10 pi-aromatic system of Ro 31-8959 class of HIV protease inhibitors. Detailed structure-activity studies have now established that the position of ring oxygens, ring size, and stereochemistry are all crucial to potency. Of particular interest, compound 49 with (3S,3aS,6aS)-bis-Thf is the most potent inhibitor (IC50 value 1.8 +/- 0.2 nM; CIC95 value 46 +/- 4 nM) in this series. The X-ray structure of protein-inhibitor complex 49 has provided insight into the ligand-binding site interactions. As it turned out, both oxygens in the bis-Thf ligands are involved in hydrogen-bonding interactions with Asp 29 and Asp 30 NH present in the S2 subsite of HIV-1 protease. Stereoselective routes have been developed to obtain these novel ligands in optically pure form.

Full text of DOI:10.1021/jm960128k

3278
J . Med. Chem. 1996, 39, 3278-3290
Non p ep tid a l P 2 Liga n d s for HIV P r otea se In h ibitor s: Str u ctu r e-Ba sed Design ,
Syn th esis, a n d Biologica l Eva lu a tion
Arun K. Ghosh,*,† J ohn F. Kincaid,† D. Eric Walters,§ Yan Chen,† Narayan C. Chaudhuri,† Wayne J . Thompson,‡
Chris Culberson,‡ Paula M. D. Fitzgerald,‡ Hee Yoon Lee,‡ Sean P. McKee,‡ Peter M. Munson,‡ Tien T. Duong,‡
Paul L. Darke,‡ J oan A. Zugay,‡ William A. Schleif,‡ Melinda G. Axel,‡ J uinn Lin,‡ and J oel R. Huff‡
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, Department of
Biological Chemistry, Finch University of Health Sciences/ The Chicago Medical School, North Chicago, Illinois 60616, and
Merck Research Laboratories, West Point, Pennsylvania 19486, and Rahway, New J ersey 07065
Received February 9, 1996X
Design and synthesis of nonpeptidal bis-tetrahydrofuran ligands based upon the X-ray crystal
structure of the HIV-1 protease-inhibitor complex 1 led to replacement of two amide bonds
and a 10π-aromatic system of Ro 31-8959 class of HIV protease inhibitors. Detailed structure-
activity studies have now established that the position of ring oxygens, ring size, and
stereochemistry are all crucial to potency. Of particular interest, compound 49 with (3S,3aS,-
6aS)-bis-Thf is the most potent inhibitor (IC50 value 1.8 ( 0.2 nM; CIC95 value 46 ( 4 nM) in
this series. The X-ray structure of protein-inhibitor complex 49 has provided insight into the
ligand-binding site interactions. As it turned out, both oxygens in the bis-Thf ligands are
involved in hydrogen-bonding interactions with Asp 29 and Asp 30 NH present in the S2 subsite
of HIV-1 protease. Stereoselective routes have been developed to obtain these novel ligands
in optically pure form.
The understanding of protein-ligand interactions has
been greatly advanced by the unprecedented advances
in molecular biology and modern spectroscopic and
X-ray crystallographic techniques. Concurrent to these
remarkable achievements, structure-based design and
synthesis of molecular probes for biologically important
peptides and proteins has become a subject of great
interest in contemporary bioorganic and medicinal
chemistry.1 Because of the therapeutic potential for the
treatment of AIDS, the structure-based design and
synthesis of HIV protease inhibitors perhaps has at-
tracted the most attention.2 An impressive number of
X-ray crystal sturctures of the protein-ligand complexes
of HIV protease have been resolved to obtain molecular
31-8959 inhibitor.5a Furthermore, we presumed that
due to considerable rotational freedom about the four
bonds connecting the two carbonyls involved, such
constrained ligands may provide additional gains in
binding energy and thereby offset the loss of the P3
hydrophobic binding of the quinoline ring. Indeed, as
described8 in a recent communication, the structure-
based design of a stereochemically defined fused bicyclic
tetrahydrofuran effectively replaced two amide bonds
and a 10π-aromatic system of 1 (Ro 31-8959).5a Sub-
sequently, structure-activity studies established that
the position of ring oxygens, ring size, and stereochem-
istry are all important to effective binding. In this
article, we report the structure-based design, synthesis,
and structure-activity studies of a new class of protease
inhibitors incorporating novel nonpeptidal ligands which
interact specifically at the HIV protease substrate-
binding site.
insight into the ligand-binding site interaction.3
A
number of therapeutically promising HIV protease
inhibitors have already resulted from structure-based
design strategies.4,5
We recently reported a number of nonpeptidal high-
affinity ligands for the HIV protease substrate-binding
site.6-10 These ligands are designed based upon various
available three-dimensional structures of the protein-
ligand complexes. The key feature in our ligand design
is the incorporation of a conformationally constrained
functionality that replaces a peptide bond and mimics
the biological mode of action. As exemplified, a stereo-
chemically defined tetrahydrofuran ring can serve as a
surrogate (inhibitor 2) for the asparagine side chain of
Ro 31-8959-based HIV protease inhibitors.7 An exami-
nation of the X-ray crystal structure of inhibitor Ro 31-
8959 bound to HIV protease led us to further speculate
that a fused bicyclic ligand with oxygens positioned
properly could effectively hydrogen bond to the NH of
the Asp 29 and 30 residues corresponding to the
quinaldic amide-asparagine amide fragment of the Ro
Ch em istr y
The enantioselective synthesis of bis-tetrahydrofuran
(bis-Thf) 7 is illustrated in Scheme 1. Allylation of 3(R)-
diethyl malate (3) according to Seebach’s procedure11
afforded the desired diasteoreomer 4 as the major
(selectivity 12:1) product after distillation (85% yield).
The above mixture was reduced by LAH in diethyl ether,
and the resulting triol was treated with a catalytic
amount of p-TsOH in acetone to provide the isopropyl-
idene derivative 5 (74% yield). Swern oxidation of 5
provided the aldehyde which upon treatment with
camphorsulfonic acid (CSA) in methanol furnished the
methyl acetal 6 as a mixture (ratio 4:1) in 50% yield.
The acetal mixture 6 was converted to bis-Thf ligand 7
by the following reaction sequence: (1) ozonolytic cleav-
age of the terminal olefin, (2) NaBH4 reduction of the
resulting aldehyde in ethanol at 0 °C, and (3) exposure
of the corresponding alcohol with CSA in methylene
chloride at 23 °C for 12 h (74% from 6). The mixed
acetal 6 was also converted to the bicyclic ligand 8 by
† University of Illinois at Chicago.
‡ Merck Research Laboratories.
§ Finch University of Health Sciences/The Chicago Medical School.
X Abstract published in Advance ACS Abstracts, J uly 15, 1996.
S0022-2623(96)00128-8 CCC: $12.00 © 1996 American Chemical Society

Nonpeptidal Ligands for HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3279
Sch em e 1. Enantioselective Synthesis of the Bicyclic
Sch em e 2. Synthesis and Optical Resolution of the
Ligandsa
Bicyclic Ligandsa
+_
a
Key: (a) N-iodosuccinimide, propargyl alcohol, CH2Cl2, 0-23
a
°C; (b) cobaloxime (cat), NaBH4, EtOH; (c) O3, CH2Cl2-MeOH,
Me2S, -78-23 °C; (d) NaBH4, EtOH, -15 °C; (e) immobilized
lipase 30, Ac2O, DME, 23 °C; (f) aqueous LiOH, THF-H2O; (g)
immobilized lipase 30, pH 7 buffer, 23 °C.
Key: (a) LDA, CHdCHCH2Br; (b) LAH, Et2O; (c) acetone,
pTsOH; (d) Swern oxidation; (e) CSA, MeOH; (f) ozonolysis then
NaBH4; (g) CSA, CH2Cl2; (h) 9-BBN, THF, aqueous NaOH, H2O2.
hydroboration with 9-BBN followed by reaction of the
resulting alcohol with CSA in methylene chloride.
Similarly, enantiomeric bicyclic ligands 10 and 11 were
synthesized, starting from optically pure 3(S)-diethyl
malate (9) following the sequence of reactions described
above.
alcohol 7 (95% ee, [R]23D -11.9°, MeOH) was determined
by formation of Mosher ester and 19F-NMR analysis.19
The acylated alcohol 16 was hydrolyzed by treatment
with aqueous lithium hydroxide to provide optically
active 11 (87% ee, [R]23 +11.7°, MeOH). Similarly,
D
Alternatively, racemic synthesis of these ligands
followed by their enzymatic resolution provided an easy
access to these ligands in optically active form.12 As
shown in Scheme 2, reaction of commercial 2,3-dihy-
drofuran (12) with N-iodosuccinimide and propargyl
alcohol in methylene chloride at 0-23 °C for 3 h resulted
in the iodo ether 13 in excellent yields (91-95%).
Radical cyclization of the iodo ether 13 with tributyltin
hydride13 in refluxing toluene in the presence of a
catalytic amount of AIBN afforded the bicyclic acetal
14 in good yield (70-80%) after silica gel chromatog-
raphy. This radical cyclization was more conveniently
effected with sodium borohydride reduction in the
presence of a catalytic amount (10 mol %) of cobaloxime
(Scheme 2)14 in 95% ethanol at 65 °C for 3 h affording
the bicyclic acetal 14 in comparable yield (70-75%).
Ozonolytic cleavage followed by the reduction of the
resulting ketone with sodium borohydride in ethanol at
-15 °C furnished the racemic endo alcohol 15 (74-78%)
after chromatography.16 The optical resolution of the
racemic alcohol 15 was carried out efficiently by expo-
sure to Amano lipase17-mediated acylation as well as
the hydrolysis of the corresponding acetate. Thus,
acylation of 15 with immobilized18 lipase PS-30 (25%
by weight with respect to lipase PS30) in the presence
of acetic anhydride in dimethoxyethane at 23 °C for 3 h
afforded the unacylated alcohol 7 (42% yield) and the
acylated alcohol 16 (45% yield) which were separated
by silica gel chromatography. The optical purity of the
racemic 17 was synthesized utilizing dihydropyran as
the starting material. The resolution of 17 was effected
by formation of the corresponding acetate 18 followed
by the enzymatic hydrolysis with immobilized lipase PS-
30 in phosphate buffer (pH ) 7.0) at 23 °C for 24 h.
The hydrolyzed alcohol 10 (yield 34%, 90% ee) and the
acetate 19 (40%) were separated by silica gel chroma-
tography. Ester hydrolysis of 19 furnished the alcohol
8 in optically active form (94% ee). The represented
absolute configurations of the resolved alcohols were
assigned based on comparison of their optical rotation
with the ligands synthesized utilizing 3(S)- and 3(R)-
diethyl malates as described above.
Enantiomerically pure fused tetrahydrofuran 23
was synthesized from commercial cis-(-)-3,3a,6,6a-
tetrahydro-2H-cyclopenta[b]furan-2-one (20) according
to Scheme 3. As shown, reduction of 20 with LAH in
tetrahydrofuran at 23 °C afforded the diol 21 (isolated
yield 96%). Treatment of the diol 21 with iodine and
potassium iodide in methylene chloride at 23 °C fur-
nished the iodo ether 22.20 Radical dehalogenation of
the iodine with tributyltin hydride in refluxing dioxane
in the presence of a catalytic amount of AIBN provided
the bicyclic ligand 23 with defined absolute configura-
tion.
Synthesis of symmetric bicyclic ligand 26 is outlined
in Scheme 4. Reaction of 2,3-dihydrofuran (12) with
mCPBA in 1-butanol at -15-0 °C for 2 h afforded the
alcohol 24 after distillation (65%). Oxidation of 24 with

3280 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Ghosh et al.
Sch em e 5. Synthesis of Racemic Bicyclic Ligandsa
Sch em e 3. Enantioselective Synthesis of the Bicyclic
Ligandsa
a
a
Key: (a) LiAlH4, THF, 23 °C; (b) KI, I2, NaHCO3, CH2Cl2, 23
Key: (a) N-bromosuccinimide, propargyl alcohol, CH2Cl2, 0-23
°C; (c) nBu3SnH, AIBN, dioxane, reflux.
°C; (b) nBu3SnH, AIBN, PhH, reflux; (c) O3, CH2Cl2-MeOH, Me2S,
-78-23 °C; (d) NaBH4, EtOH, -15 °C.
Sch em e 4. Synthesis of the Symmetric Bicyclic Liganda
Sch em e 6. Synthesis of the Bicyclic Liganda
a
Key: (a) mCPBA, n-butanol, 0 °C; (b) Pyr‚SO3, DMSO, Et3N;
a
(c) allylmagnesium bromide, Et2O, 0-23 °C; (d) O3, CH2Cl2-
MeOH, -78-0 °C, then NaBH4, EtOH, 0 °C; (e) pTsOH, CH2Cl2,
23 °C; (f) COCl2, pyridine, PhCH3, then N-hydroxysuccinimide,
CH3CN, Et3N, 23 °C.
Key: (a) PhOC(S)Cl, Et3N, CH2Cl2; (b) separated by silica gel
chromatography; (c) nBu3SnH, AIBN, PhMe, reflux.
Sch em e 7
pyridine‚SO3 complex in methylene chloride gave the
corresponding ketone which was reacted with allylmag-
nesium bromide in diethyl ether at 0-23 °C for 4 h to
furnish the alcohol 25.21 Ozonolysis of the terminal
olefin followed by reduction of the ozonide with sodium
borohydride in ethanol at 0 °C provided the correspond-
ing alcohol which was treated with p-TsOH in methyl-
ene chloride to afford the symmetric ligand 26. Reaction
of 26 with phosgene and pyridine in toluene followed
by reaction with N-hydroxysuccinimide in acetonitrile
furnished the mixed active carbonate 27 after silica gel
chromatography.22
Racemic bicyclic ligands 34 and 35 were prepared
(Scheme 5) utilizing a similar synthetic route as de-
scribed for racemic 15. Reaction of cyclopentene with
N-bromosuccinimide and propargyl alcohol provided
good yield of the corresponding bromo ether 30 (yield
72%). However, the reaction with 2,5-dihydrofuran
proceeded with modest yield (35%) of the corresponding
bromo ether 31. Tributyltin hydride-mediated radical
cyclization of 30 and 31 provided the bicyclic olefins 32
and 33 which were converted to racemic bicyclic ligands
34 and 35 for structure-activity studies.
Bicyclic ligand 39 with oxygens in a vicinal relation-
ship was synthesized in enantiomerically pure form
starting from commercially available 1,4:3,6-dianhydro-
D-sorbitol (36) (Scheme 6). Treatment of 36 with
commercial chlorothionoformate and triethylamine in
methylene chloride at 23 °C for 4 h afforded a mixture
(2:1) of thionocarbonates 37 and 38. The isomers were
separated on silica gel by column chromatography, and
the major isomer 37 was exposed to the radical deoxy-
genation23 conditions to provide the ligand 39.
Synthesis of various inhibitors with bicyclic ethers as
the P2 ligands and decahydroisoquinolinecarboxamide
as the P1′ ligand was carried out according to Scheme
7. The previously described6,7 hydroxyethylamine iso-
stere 42 was transformed into the various target inhibi-
tors listed in Tables 1 and 2 by an alkoxycarbonylation
of the respective alcohol.24 For example, reaction of bis-
Thf ligand 7 with dipyridyl carbonate (40) and triethyl-
amine in methylene chloride afforded the active car-
bonate 41 after chromatography. Reaction of the mixed
carbonate 41 with amine 42 in methylene chloride

Nonpeptidal Ligands for HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3281
Ta ble 1. Structure and Inhibitory Potencies of Various
Heterocyclic Derivatives
afforded only the inhibitor 49 (white solid, mp 98-101
°C) by 1H-NMR and HPLC analysis (isolated yield 76%).
For the preparation of inhibitor 55, the mixed active
carbonate 27 was reacted with amine 42 in methylene
chloride in the presence of 3 equiv of triethylamine at
23 °C for 12 h to provide 55 after silica gel chromatog-
raphy. Similarly, various nonpeptidal ligands were
converted to other inhibitors in Tables 1 and 2.
Resu lts a n d Discu ssion
As described previously,9 the preliminary X-ray crys-
tal structure of the enzyme-inhibitor complex of 43 and
HIV-1 protease25 has suggested a number of structural
changes on the tetrahydrofuran ring that could lead to
improved binding. The urethane of 3(S)-hydroxysul-
folane (46) has exhibited nearly a 2-fold potency en-
hancement compared to 43, presumably due to the close
proximity of the sulfolane oxygen cis to the 3-hydroxyl
group to Asp 29 and Asp 30 NH. It is evident in the
crystal structure that the oxygen atom of the tetrahy-
drofuran ring in 43 is oriented toward the Asp 29 and
Asp 30 NH. Recently, researchers from Vertex Labo-
ratories have reported a similar observation in their
X-ray crystal structure of protein-ligand complex con-
taining an inhibitor with 3(S)-tetrahydrofuranyloxy
group as the P2 ligand.26 The protein-ligand structure
of inhibitor 43 further provided rationale for incorpora-
tion of the cis-2-alkyl substitutent of the sulfolane ring
of inhibitor 46. Optimization of these findings resulted
in inhibitors with reduced molecular weight and com-
parable in vitro potency to 1 (Ro 31-8959). A detailed
account of these investigations has been reported re-
cently.8 Subsequently, during the introduction of a cis-
2-methoxymethyl substitutent of the sulfolane ring of
inhibitor 46, we have observed a very intriguing struc-
ture-activity relationship. As evident in Table 1,
replacement of the ring oxygen in 43 with sulfur
(inhibitor 45) resulted in no change in inhibitory
potency. Oxidation of the ring sulfur to sulfone has
provided nearly a 2-fold improvement over 45. Thus
far, our observation is that the ring sulfones, in general,
are 2-5-fold more potent than their corresponding ring
sulfides.27 Consistent with our earlier observation,
incorporation of a cis-2-methoxymethyl substitutent in
cyclic sulfide 45 afforded inhibitor 47 with a 6-fold
potency enhancement. However, in contrast, oxidation
of ring sulfur to the corresponding sulfone resulted in
inhibitor 48 with reduction in potency (IC50 23.8 nM).
To gain insight into the molecular binding properties,
an energy-minimized active model of inhibitors 46 and
47 was created28 utilizing the X-ray crystal structure
of the enzyme-inhibitor complex of L-689,502 bound to
HIV-1 protease (2.25 Å resolution).30 On the basis of
superimposition of these modeled structures (Figure 1),
it appeared that in addition to filling the hydrophobic
pocket in the S2 region, the methoxyl oxygen of inhibitor
47 is in close proximity to hydrogen bonding with the
Asp 29 and Asp 30 NH. Thus, the methoxyl oxygen is
effectively competing for the same binding site as the
sulfolane oxygen cis to the 3-hydroxyl group of inhibitor
46. Therefore, oxidation of the ring sulfide in inhibitor
47 did not provide any additional potency enhancement
as was observed earlier. These findings subsequently
provided the basis for a conformationally constrained
and structurally new class of ligand design.
As can be seen from the superimposed stereoviews of
46 and 47 (Figure 1), the conformation of methoxy-
methyl side chain of 47 can be further restricted to form
another ring cycle to the existing five-membered ring.
On the basis of this possible molecular insight, we
speculated that a bicyclic ligand with oxygens positioned
appropriately in the ring would interact effectively with
the Asp 29 and Asp 30 residues of the enzyme active
site. Also, superimposition of the X-ray crystal struc-
ture of the protein-ligand complex31 of Ro 31-8959 and
the modeled structure of 47 (Figure 2) revealed the
potential benefit of such ligand design. It appears that
a fused bicyclic tetrahydrofuran not only could replace
the quinaldic amide and asparagine amide of Ro 31-
8959 inhibitor, but it may also provide additional
binding energy to offset the loss of P3-hydrophobic
binding corresponding to the quinoline ring. Indeed,
incorporation of bis-tetrahydrofuran as the P2 ligand
with 3(R),3a(S),6a(R)-configurations (inhibitor 49), as
speculated from the ligand-binding site interactions of
inhibitors 47 and 1, has shown impressive in vitro
potencies.9 As presented in Table 2, inhibitor 49 has
shown an enzyme inhibitory potency (IC50) of 1.8 ( 0.2
nM (n ) 6). In comparison, the inhibitor with 3(S),3a-
(R),6a(S)-bis-Thf as the P2 ligand (inhibitor 50, IC50 6.4
nM) is less potent than 49. The difference in enzyme
inhibitory potencies is also reflected in their antiviral
activities. Inhibitor 49 has prevented the spread of
HIV-1 in MT4 human T-lymphoid cells infected with
IIIb isolate32 at an average concentration (n ) 4) of 46
( 4 nM (CIC95). Inhibitor 50, in contrast, has shown
an antiviral potency of 200 nM. In head to head

3282 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Ghosh et al.
F igu r e 1. Stereoview of the optimized bound conformations of inhibitors 46 (magenta) and 47 (green) superimposed in the HIV-1
protease active site.30
F igu r e 2. Stereoview of the X-ray structure of inhibitor 1 (magenta) bound to HIV-1 protease and optimized bound conformation
of inhibitor 47 (green).
comparison, inhibitor 49 was shown to be equipotent
to 1 (Ro 31-8959; CIC95 23 ( 7 nM).33 The enhanced
inhibitory potency as well as the stereochemical prefer-
ence for 3(R),3a(S),6a(R)-configurations in bis-Thf ligand
(inhibitor 49) indicated a specific hydrogen-bonding
interaction with the residues of the S2 region of the
enzyme active site. Incorporation of 3-hexahydrofuro-
pyran as the P2 ligand has shown reversal of stereo-
chemical trends. Inhibitor 52 with 3(S),3a(R),7a(S)-
configurations has shown an IC50 value of 1.2 nM, a
greater than 3-fold potency increase over inhibitor 51
(IC50 4.2 nM). Antiviral potency of this inhibitor
(compound 50; CIC95 50 nM) is also comparable to that
of Ro 31-8959 or inhibitor 49. Evaluation of compounds
53 and 54 established that both oxygens are involved
in binding. Incorporation of symmetric bis-Thf ligand
(inhibitor 55) resulted in at least a 225-fold loss (IC50
410 nM) in inhibitory potency. Similarly, change of the
ring oxygen positions (inhibitors 56 and 57) also re-
sulted in significant loss of potency. Various substitu-
tion at the bicyclic ring (inhibitors 58-60) did not
improve enzyme inhibitory or antiviral potencies. Thus,
the above structure-activity studies provided ample
evidence that in the bis-Thf ligand of inhibitor 49, the
ring stereochemistry, ring size, and position of ring
oxygens all are critical to effective binding in the S2
region of the substrate-binding site.
X-ray diffraction at a resolution of 2.2 and 2.10 Å,
respectively.34 A superimposed stereoview of these
inhibitors (Figure 3) was then created by superimposi-
tion of the X-ray crystal structure of 1 (green) on the
X-ray crystal structure of 49 (magenta) bound to HIV-1
protease in the same frame of reference. The (R)-
hydroxyl group of inhibitor 49 is positioned sym-
metrically between the catalytic aspartates of the HIV-1
protease. The P1 benzyl side chain and the P1′ decahy-
droisoquinoline moiety of 49 are located at the S1 and
S1′ regions, respectively, in the enzyme active site. The
N-tert-butyl group is positioned in the S2′ subsite. A
comparison of binding properties of the bis-Thf ligand
of 49 and the asparagine of 1 is very intriguing. As
shown, both the bis-Thf oxygen-1 and asparagine car-
bonyl of 1 are within hydrogen-bonding distance (3.2
and 3.5 Å, respectively, between the heavy atoms) to
the Asp 30 NH of the HIV-1 protease. The bis-Thf
oxygen-6 and the P3 quinoline amide carbonyl of 1 are
also appropriately positioned for hydrogen-bonding
interaction with the Asp 29 NH (bonding distance 3.0
and 3.3 Å, respectively, between the heavy atoms)
present in the S2-binding domain of the enzyme. Like
most reported protein-ligand complex structures, the
P2 bis-Thf urethane carbonyl and the tert-butyl amide
carbonyl of 49 hydrogen bond to the structural water
molecule that interacts with the flap Ile 50 NH resi-
dues.35 Thus, incorporation of a stereochemically de-
fined bis-Thf or fused Thf-Thp ligand into the Ro 31-
8959-based hydroxyethylamine isostere provided
To gain further insight into the molecular binding
properties, the three-dimensional structure of both
inhibitors 1 (Ro 31-8959) and 49 was determined by

Nonpeptidal Ligands for HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3283
Ta ble 2. Structure and Inhibitory Potencies of Inhibitors
Containing Novel Bicyclic P2 Ligands
essentially replaces two amide bonds and a 10π-
aromatic system of the Ro 31-8959 inhibitor which is
currently in advanced clinical trials.36
In addition to reduction of molecular weight and
replacement of amide bonds, inhibitors incorporating
the fused cyclic ethers as P2 ligands have shown
significant improvement in aqueous solubility compared
to the Ro 31-8959 class of inhibitors. As can be seen in
Table 3, inhibitor 49 has shown an aqueous solubility
of 0.235 mg/mL in phosphate buffer (pH ) 7.4), a greater
than 23-fold improvement over 1 (Ro 31-8959; aqueous
solubility less than 0.01 mg/mL). The 3(S)-tetrahydro-
furanyl carbamate in inhibitor 43 also exhibited solubil-
ity enhancement (aqueous solublity 0.15 mg/mL). The
inhibitor containing bis-Thf ligand (inhibitor 49) also
shows a decreased log P value compared to inhibitor 1.
The log P values of inhibitors 1 and 49 were measured
to be 5.7 and 3.5, respectively. Pharmacokinetic studies
in dogs with inhibitor 52 are encouraging. Inhibitor 52
was administered in dogs at an oral dose of 10 mg/kg
dissolved in a 10% citric acid solution. The average (two
dogs) Cmax was 4380 nM after 20 min. After 3 h, the
plasma level was above 200 nM, more than 4-fold over
its CIC95 value. Oral bioavailability was estimated by
comparing the area under the curve following oral
administration with that of iv administration at a dose
of 2 mg/kg in DMSO. The oral bioavailability was
determined to be 17% in dogs under the formulation
protocol described above.37
Con clu sion
In summary, on the basis of X-ray crystal structures
of various protein-ligand complexes, we have designed
and synthesized a novel class of nonpeptidal high-
affinity P2 ligands for the HIV-1 protease substrate-
binding site. The designed ligands are conformationally
constrained with a fused bicyclic ether-like feature. The
inhibitor incorporating a 3(R),3a(S),6a(R)-bis-Thf as the
P2 ligand (inhibitor 49) is the most potent compound in
the series. This inhibitor has exhibited in vitro antiviral
activities comparable to inhibitors in the Ro 31-8959
(inhibitor 1)-based hydroxyethylamine series with both
P2 and P3 ligands. Based on the inhibitor-bound X-ray
crystal structures of 1 and 49 with the HIV-1 protease,
it appears that the bis-Thf ring oxygens essentially
compete for the same binding site as the P2 asparagine
carboxamide and the P3 quinaldic amide carbonyls of
inhibitor 1 (Ro 31-8959). Through various structure-
activity studies, we have also shown that the stereo-
chemistry, position of oxygens, substitution in the ring,
and ring size all are critical to optimum binding.
Incorporation of bis-Thf ligand (inhibitor 49) not only
provided a protease inhibitor with reduced molecular
weight but also led to improved aqueous solubility and
decreased log P value (Figure 4). Basically, fusion of a
tetrahydrofuran ring to inhibitor 44 resulted in inhibitor
49 (Figure 4) with an impressive 300-fold enhancement
in its inhibitory potency and more than 30-fold enhance-
ment of its antiviral potency. The molecular weight of
the bis-Thf is essentially one-half the combined molec-
ular weight of the P2 asparagine and P3 quinoline
ligands of inhibitor 1. Further molecular design is
currently underway in our laboratories.
inhibitors (compounds 49 and 52) with comparable in
vitro antiviral potencies to inhibitors with both P2 and
P3 ligands. As shown in Figure 3, the bis-Thf ligand
Exp er im en ta l Section
All melting points were recorded on a Thomas-Hoover
capillary melting point apparatus and are uncorrected. Proton

3284 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Ghosh et al.
F igu r e 3. Stereoview of the X-ray structure of the inhibitors 1 (green) and 49 (magenta) bound to HIV-1 protease.
Ta ble 3. Aqueous Solubilities of Selected Inhibitors
were recorded on a VG Model 7070 mass spectrometer, and
relevant data are tabulated as m/z. Elemental analyses were
performed by the Analytical Department, Merck Research
Laboratories, West Point, PA, and were within (0.4% of the
theoretical values. Anhydrous solvents were obtained as
follows: methylene chloride, distillation from P4O10; tetrahy-
drofuran, distillation from sodium/benzophenone; dimethyl-
formamide and pyridine, distillation from CaH2. All other
solvents were HPLC grade. Column chromatography was
performed with E. Merck 240-400 mesh silica gel under a low
pressure of 5-10 psi. Thin-layer chromatography (TLC) was
carried out with E. Merck silica gel 60 F-254 plates.
inhibitors
solubility (mg/mL)
1
43
49
50
52
0.01
0.15
0.235
0.130
0.107
(2R,3S)-Eth yl 2-Hyd r oxy-3-a llylsu ccin a te (4). (-)-Di-
ethyl (2R,3S)-3-allyl-2-hydroxysuccinate (7.2 g) was prepared
according to the procedure of D. Seebach, J . Aebi, and D.
Wasmuth, Organic Syntheses 1985, 63, 109-120. Compound
4: 1H-NMR (CDCl3) δ 5.8 (m, 1 H), 5.15 (m, 2 H), 4.3 (m, 1 H),
4.1-4.2 (m, 4 H), 3.0 (m, 1 H), 2.4-2.7 (m, 2 H), 1.25 (t, 3 H,
J ) 7.0 Hz), 1.2 (t, 3 H, J ) 6.9 Hz).
(2R,3R)-1,2-O-Isop r op ylid en e-3-a llylbu ta n e-1,4-d iol (5).
A solution of 9.4 g (40.8 mmol) of (2R,3S)-ethyl 2-hydroxy-3-
allylsuccinate (2) in 15 mL of diethyl ether was added dropwise
to a suspension of 3.1 g (81.6 mmol) of LiAlH4 in ether (70
mL) at 0 °C. The resulting mixture was stirred at room
temperature for 12 h. After this period, the mixture was
heated to reflux for 1 h and then cooled to 0 °C. The reaction
was quenched by sequential dropwise addition of water (3.1
mL), 20% aqueous NaOH (3.1 mL), and then water (8 mL).
The mixture was stirred for 1 h, and THF (50 mL) and
anhydrous Na2SO4 were added. The mixture was filtered
through Celite, and the filter cake was throughly washed with
THF. Evaporation of the solvents gave 6.3 g of the corre-
sponding triol, as a colorless oil which was utilized directly
without further purification.
The resulting triol was dissolved in acetone (500 mL), and
150 mg of p-toluenesulfonic acid monohydrate was added. The
resulting mixture was stirred at 24 °C for 3 h. After this
period, the mixture was concentrated under reduced pressure,
and the resulting residue was taken up in ethyl acetate and
washed with saturated aqueous NaHCO3. The layers were
separated, and the organic layer was dried over Na2SO4.
Filtration and evaporation of the solvent provided a residue
which was chromatographed over silica gel (50% ethyl acetate/
hexane) to furnish 4.1 g (59% yield) of the title compound as
a colorless oil: 1H-NMR (CDCl3) δ 5.75 (m, 1 H), 5.1 (m, 2 H),
F igu r e 4.
magnetic resonance spectra were recorded on a Varian XL-
300 spectrometer using tetramethylsilane as the internal
standard. Significant 1H-NMR data for representative com-
pounds are tabulated in the following order: multiplicity (s,
singlet; d, doublet; t, triplet; q, quartet; m, multiplet), number
of protons, coupling constant(s) in hertz. FAB mass spectra

Nonpeptidal Ligands for HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3285
4.1 (m, 2 H), 3.7 (m, 4 H), 2.0 (m, 1 H), 2.0 (m, 1 H), 1.45 (s, 3
H), 1.4 (s, 3 H).
for 24 h. The reaction was quenched with a mixture of 1 mL
of 30% H2O2 and 1 mL of 20% NaOH. The resulting mixture
was heated to 50 °C for 1.5 h and then cooled to 24 °C and
extracted with three portions of ethyl acetate. The combined
extracts were dried over anhydrous Na2SO4, filtered, and
concentrated under reduced pressure. The residue was puri-
fied by silica gel chromatography (75% ethyl acetate/hexanes)
to afford a mixture of (2R,3S,4R)- and (2S,3S,4R)-2-methoxy-
3-(3′-hydroxypropyl)-4-hydroxytetrahydrofuran (140 mg) as a
clear colorless oil.
A solution of 140 mg of (2R,3S,4R)- and (2S,3S,4R)-2-
methoxy-3-(3′-hydroxypropyl)-4-hydroxytetrahydrofuran and
camphorsulfonic acid (100 mg) in 100 mL of CH2Cl2 was stirred
at 24 °C for 12 h. The reaction was quenched with 3 mL of
saturated aqueous NaHCO3 and the mixture stirred for 10
min. The layers were separated, and the aqueous layer was
extracted with ethyl acetate (3 × 10 mL). The combined
organic layers were dried over Na2SO4, filtered, and concen-
trated under reduced pressure. Purification of the residue by
chromatography over silica gel (75% ethyl acetate/hexanes)
(2SR,3S,4R)-2-Meth oxy-3-a llyl-4-h yd r oxytetr a h yd r ofu -
r a n (6). To a stirred solution of oxalyl chloride (1.1 mL) in
CH2Cl2 (40 mL) at -50 °C was added a mixture (1:2) of
dimethyl sulfoxide and CH2Cl2 (6 mL). The resulting mixture
was stirred for 3 min, and a solution of 2.0 g of (2R,3R)-1,2-
O-isopropylidene-3-allylbutane-1,4-diol in CH2Cl2 (6 mL) was
added dropwise over a period of 5 min. The mixture was
allowed to warm to -20 °C over a period of 1.5 h, and
triethylamine (10 mL) was added. The reaction mixture was
stirred at -20 °C to room temperature for 1 h, and water (30
mL) was added. The layers were separated, and the aqueous
layer was extracted with ethyl acetate (2 × 20 mL). The
combined organic layers were dried over anhydrous Na2SO4
and concentrated under reduced pressure. The residue was
chromatographed over silica gel (25% ethyl acetate/hexane)
to provide 1.56 g of the corresponding aldehyde as a colorless
oil.
To a stirred solution of 1.3 g of the aldehyde in methanol
(25 mL) was added camphorsulfonic acid (300 mg), and the
resulting mixture was stirred at 24 °C for 12 h. The reaction
was quenched by addition of saturated aqueous NaHCO3 (5
mL), and the mixture was concentrated under reduced pres-
sure. The residue was partitioned between ethyl acetate and
brine solution. The layers were separated, and the aqueous
layer was extracted with ethyl acetate (50 mL). The combined
organic layers were dried over anhydrous Na2SO4 and con-
centrated under reduced pressure to give a residue which was
chromatographed over silica gel (25% ethyl acetate/hexane)
to provide (815 mg) the methyl acetal 6 (4:1 mixture) as an
oil.
afforded the title compound 8 (100 mg) as a clear colorless oil;
1
[R]23 +10.1°, MeOH; H-NMR (CDCl3) δ 5.0 (s, 1 H), 4.3 (m,
D
1 H), 3.8-4.1 (m, 3 H), 3.5 (m, 1 H), 3.0 (br s, 1 H), 2.5 (br d,
1 H), 1.8-2.2 (m, 3 H), 1.4 (m, 1 H); MS (70 eV) m/ z 145 (M+
+ H).
(3S,3aR,7aS)-3-Hydr oxyh exah ydr ofu r o[2,3-b]pyr an (10).
From (+)-diethyl (2S,3R)-3-allyl-2-hydroxysuccinate using the
procedure substantially as described above for preparation of
(3R,3aS,7aR)-3-hydroxyhexahydrofuro[2,3-b]pyran, there was
1
obtained a clear colorless oil: [R]23 -10.8°, MeOH; H-NMR
D
(CDCl3) δ 5.0 (s, 1 H), 4.3 (m, 1 H), 3.8-4.1 (m, 3 H), 3.5 (m,
1 H), 3.0 (br s, 1 H), 2.5 (br d, 1 H), 1.8-2.2 (m, 3 H), 1.4 (m,
1 H); MS (70 eV) m/ z 145 (M+ + H).
(3R,3aS,6aR)-3-Hyd r oxyh exa h ydr ofu r o[2,3-b]fu r a n (7).
To a stirred solution of 500 mg (3.2 mmol) of (2R,3S,4R)-2-
methoxy-3-allyl-4-hydroxytetrahydrofuran (4) in a mixture (1:
1) of methanol and methylene chloride (25 mL) at -78 °C was
bubbled through a stream of ozonized oxygen until the blue
color persisted (1 h). After the solution was flushed with
nitrogen for 5 min, dimethyl sulfide (3 mL) was added. The
cooling bath was removed, and the mixture was allowed to
warm to room temperature. Evaporation of the solvent gave
the crude aldehyde as a colorless oil. The resulting aldehyde
was dissolved in absolute ethanol (20 mL) and cooled to 0 °C,
and solid NaBH4 (180 mg, 4.7 mmol) was added in three
portions. The mixture was stirred for 15 min, and the reaction
was quenched with 10% aqueous citric (3 mL) acid. The
mixture was concentrated under reduced pressure, and the
residue was partitioned between ethyl acetate and brine
solution. The layers were separated, and the aqueous layer
was extracted with ethyl acetate (25 mL). The combined
organic layers were dried over anhydrous Na2SO4 and con-
centrated under reduced pressure to give a residue which was
chromatographed over silica gel (75% ethyl acetate/hexane)
to provide 430 mg of (2R,3S,4R)-2-methoxy-3-(2′-hydroxy-
ethyl)-4-hydroxytetrahydrofuran as a colorless oil.
(3S,3aR,6aS)-3-Hydr oxyh exah ydr ofu r o[2,3-b]fu r an (11).
From (+)-diethyl (2S,3R)-3-allyl-2-hydroxysuccinate using the
procedure substantially as described above for preparation of
(3R,3aS,6aR)-3-hydroxyhexahydrofuro[2,3-b]furan, there was
1
obtained a clear colorless oil: [R]23 +12.1°, MeOH; H-NMR
D
(CDCl3) δ 5.7 (d, 1H, J ) 5.1 Hz), 1.85 (m, 2 H), 4.45 (dd, 1H,
J ) 6.8, 14.6 Hz), 3.9-4.0 (m, 3 H), 3.65 (dd, 1 H, J ) 7, 9
Hz), 2.9 (m, 1 H), 2.3 (m, 1 H); MS (70 eV) m/ z 131 (M+ + H).
tr a n s-2-(P r opar gyloxy)-3-iodotetr ah ydr ofu r an (13). To
a stirred, ice cold suspension of 15 g (66.6 mmol) of N-
iodosuccinimide in 150 mL of CH2Cl2 was added a mixture of
dihydrofuran (66.6 mmol, 4.67 g, 5.1 mL) and propargyl alcohol
(100 mmol, 5.0 g, 5.2 mL) in 50 mL of CH2Cl2 over 20 min.
After warming to 24 °C with stirring over 2 h, 200 mL of water
was added, and the stirring was continued for 1 h. The layers
were separated and the aqueous layer extracted with 2 × 100
mL of CH2Cl2. The combined organic extracts were washed
with brine solution containing a small amount of Na2S2O3 (70
mg), dried over anhydrous Na2SO4, filtered, and concentrated.
Chromatography over silica gel using 30% ethyl acetate in
hexane afforded (15.4 g, 92%) the title iodo ether as an oil:
1H-NMR (CDCl3) δ 5.4 (br s, 1 H), 4.0-4.3 (m, 5 H), 2.7 (m, 1
H), 2.48 (br s, 1 H), 2.25 (m, 1 H); IR (neat) 2956, 2180, 1621,
To stirred a solution of 400 mg of (2R,3S,4R)-2-methoxy-3-
(2′-hydroxyethyl)-4-hydroxytetrahydrofuran in dry CH2Cl2 (100
mL) was added camphorsulfonic acid (200 mg). The resulting
mixture was stirred at 23 °C for 12 h. After this period, the
reaction was quenched by additon of saturated aqueous
NaHCO3 (5 mL). The layers were separated, and the aqueous
layer was extracted with ethyl acetate (3 × 30 mL). The
combined organic layers were dried over anhydrous Na2SO4,
filtered, and concentrated under reduced pressure. The
residue was chromatographed over silica gel (75% ethyl
1440 cm-1
.
(3a R,6a S)- a n d (3a S,6a R)-3-Meth ylen e-4H-h exa h yd r o-
fu r o[2,3-b]fu r a n (14) (Tr ibu tyltin h yd r id e p r oced u r e). To
a refluxing solution of tributyltinhydride (20.7 mL, 77 mmol)
containing AIBN (100 mg) in toluene (200 mL) was added
dropwise a solution of 15.4 g (61 mmol) of iodotetrahydrofuran
13 in toluene (50 mL) over a period of 1 h. The resulting
mixture was stirred at reflux for an additional 4 h (monitored
by TLC). The mixture was then cooled to 23 °C and concen-
trated under reduced pressure. The residue was partitioned
between petroleum ether and acetonitrile (200 mL of each),
and the acetonitrile (lower) layer was concentrated. The
residue was purified by chromatography on silica gel, using
10% ethyl acetate in hexane as the eluent to provide the title
product 14 (5.84 g, 76%) as an oil: 1H-NMR (CDCl3) δ 5.7 (d,
1 H, J ) 4.9 Hz), 4.9-5.1 (m, 2 H), 4.3-4.6 (m, 2 H), 3.7-4.0
(m, 2 H), 3.3 (m, 1 H), 1.8-2.2 (m, 2 H); IR (neat) 2970, 1645,
acetate/hexanes) to give 350 mg of 7 as a colorless oil; [R]23
D
1
-12.4°, MeOH; H-NMR (CDCl3) δ 5.7 (d, 1 H, J ) 5.13 Hz),
4.45 (dd, 1 H, J ) 6.8, 14.6 Hz), 3.9-4.0 (m, 3 H), 3.65 (dd, 1
H, J ) 7, 9.1 Hz), 2.9 (m, 1 H), 2.3 (m, 1 H), 1.85 (m, 2 H); MS
(70 eV) m/ z 131 (M+ + H).
(3R,3aS,7aR)-3-Hydr oxyh exah ydr ofu r o[2,3-b]pyr an (8).
To a stirred solution of 225 mg of (2R,3S,4R)- and (2S,3S,4R)-
2-methoxy-3-allyl-4-hydroxytetrahydrofuran (6) in 5 mL of
THF cooled to -10 °C was added dropwise 4.3 mL of 0.5 M
9-BBN in THF. After stirring at 24 °C for 12 h, another 2.5
mL of 0.5 M 9-BBN was added, and stirring was continued
1430 cm-1
.
(3a R,6a S)- a n d (3a S,6a R)-3-Meth ylen e-4H-h exa h yd r o-
fu r o[2,3-b]fu r a n (14) (Ca ta lytic coba loxim e p r oced u r e).

3286 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Ghosh et al.
To a solution of iodo ether 13 (6.4 g, 25.4 mmol) in 95% ethanol
(80 mL) were added solid NaBH4 (1.06 g, 28 mmol) and 10 N
NaOH (2.6 mL, 26 mmol). The solution was flushed with N2,
and several portions of finely powered cobaloxime (611 mg,
1.5 mmol) were added during a 1 h period at 50 °C (bath
temperature 65 °C). The resulting mixture was stirred for an
additional 1 h, and the reaction mixture was concentrated
under reduced pressure. The resulting residue was diluted
with brine, and the mixture was thoroughly extracted with
ether (3 × 150 mL). The combined organic layers were washed
with water and brine and dried over anhydrous Na2SO4.
Evaporation of the solvent gave a residue which was chro-
matographed over silica gel to provide the title product (2.3 g,
73%) as an oil: 1H-NMR (CDCl3) δ 5.7 (d, 1 H, J ) 4.9 Hz),
4.9-5.1 (m, 2 H), 4.3-4.6 (m, 2 H), 3.7-4.0 (m, 2 H), 3.3 (m,
1 H), 1.8-2.2 (m, 2 H); IR (neat) 2970, 1645, 1430 cm-1; MS
(70 eV) m/ z 126 (m+).
(3S,3a R,6a S)- a n d (3R,3a S,6a R)-3-Hyd r oxy-4H-h exa h y-
d r ofu r o[2,3-b]fu r a n (15). A stream of ozone was dispersed
into a solution of 14 (5.84 g, 46.4 momol) in methanol (150
mL) and CH2Cl2 (150 mL) at -78 °C for 30 min. The resulting
blue solution was purged with nitrogen until colorless, then
the reaction was quenched with 20 mL of dimethyl sulfide,
and the resulting mixture was allowed to warm to 23 °C. The
mixture was concentrated under reduced pressure to afford
the crude ketone. This ketone was dissolved in ethanol (50
mL) and cooled to 0 °C, and sodium borohydride (2.1 g, 55.6
mmol) was added. The reaction mixture was stirred for an
additional 2 h at 0 °C, and then the reaction was quenched
with 10% aqueous citric acid (10 mL). The resulting mixture
was concentrated under reduced pressure, and the residue was
partitioned between ethyl acetate and brine. The layers were
separated, and the aqueous layer was extracted with ethyl
acetate (2 × 100 mL). The combined organic layers were dried
over anhydrous Na2SO4 and concentrated carefully under
reduced pressure. The resulting residue was chromatographed
over silica gel using 30% ethyl acetate in hexane as the eluent
to furnish (4.52 g, 75%) the title racemic alcohol 15 as an oil:
1H-NMR (CDCl3) δ 5.7 (d, J ) 5.13 Hz, 1 H), 4.45 (dd, J ) 6.8,
14.6 Hz, 1 H), 3.9-4.0 (m, 3 H), 3.65 (dd, 1 H, J ) 7 Hz, 9.1),
2.9 (m, 1 H), 2.3 (m, 1 H), 1.85 (m, 2 H); IR (neat) 2951, 1640,
1346, 1210 cm-1; MS (70 eV) m/ z 131 (M+ + H).
of commercial cis-(-)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]-
furan-2-one (1.09 g, 8.78 mmol) in THF (15 mL) over 15 min.
The mixture was brought to room temperature, and after 4 h
acetone (2 mL) was added followed by aqueous NaOH (8%,
1.2 mL) and water (1 mL). The mixture was diluted with ethyl
acetate (50 mL), and anhydrous sodium sulfate was added.
The resulting mixture was stirred for 30 min and filtered. The
filter cake was washed with ethyl acetate, and the solvent was
evaporated under reduced pressure. The resulting residue was
purified by column chromatography (EtOAc/hexane) over silica
gel to yield the title compound (1.08 g, 96.4%) as a white oil:
1H-NMR (400 MHz, CDCl3) δ 5.74 (dt, J ) 2.4, 8.2 Hz, 1 H),
5.55 (d, J ) 4.1 Hz, 1 H), 4.48 (dt, J ) 3.0, 10.0 Hz, 1 H), 3.83
(m, 1 H), 3.70 (dt, J ) 4.8, 15.8 Hz, 1 H), 2.60-2.79 (m, 3 H),
2.36 (br d, J ) 17.1 Hz, 1 H), 1.71-1.95 (m, 3 H).
(3a S,4S,6S,6a S)-4-Hyd r oxy-6-iod oh exa h yd r o-2H-cyclo-
p en ta [b]fu r a n (22). To a vigorously stirring heterogeneous
mixture of 21 (0.517 g, 4.04 mmol) dissolved in CH2Cl2 (20
mL) and water (2 mL) was added solid NaHCO3 (1.35 g, 16.07
mmol) followed by solid KI (1.34 g, 8.07 mmol) and I2 (2.04 g,
8.04 mmol). The mixture was stirred overnight at room
temperature, diluted with CH2Cl2 (25 mL), and washed with
sodium thiosulfate solution (2 × 20 mL), water (15 mL), and
brine (15 mL). Evaporation of CH2Cl2 followed by column
chromatogrophy (EtOAc/hexane) yielded the title compound
(0.882 g, 86%) as a yellow oil: 1H-NMR (400 MHz, CDCl3) δ
4.74 (d, 1 H, J ) 6.6 Hz), 4.67 (m, 1 H), 4.23 (br s, 1 H), 3.76-
3.90 (m, 2 H), 2.95 (br s, 1 H), 2.26-2.35 (dd, 1 H, J ) 2.8, 5.8
Hz), 2.02-2.21 (m, 2 H), 1.6-2.0 (m, 2 H).
(3a S,4S,6a R)-4-Hyd r oxyh exa h yd r o-2H-cyclop en ta [b]-
fu r a n (23). To a vigorously refluxing mixture of n-tributyltin
hydride (0.572 g, 1.97 mmol) and AIBN (10 mg) in dioxane
(10 mL) under nitrogen was added dropwise a solution of 22
(0.25 g, 0.984 mmol) in dioxane (1.8 mL). The mixture was
refluxed overnight, diluted with acetonitrile (50 mL), and
washed with hexane (2 × 25 mL). Evaporation of the solvents
followed by column chromatography (1:1 EtOAc/hexane) over
silica gel yielded the title compound (0.102 g, 81%) as a pale
yellow oil: 1H-NMR (400 MHz, CDCl3) δ 4.35 (t, 1 H, J ) 6.2
Hz), 4.19 (m, 1 H), 3.95 (m, 1 H), 3.62 (q, 1 H, J ) 1.7, 8.35
Hz), 2.69 (m, 1 H), 1.98-2.09 (m, 1 H), 1.76-1.90 (m, 3 H),
1.57-1.73 (m, 3 H); IR (neat) 3410, 2982, 1500 cm-1
.
P r ep a r a tion of Im m obilized Am a n o Lip a se 30. Com-
mercially available Celite 521 (4 g; Aldrich) was loaded on a
Buchner funnel and washed successively with 50 mL of
deionized water and 50 mL of 0.05 N phosphate buffer (pH )
7.0; Fisher Scientific). The washed Celite was then added to
a suspension of 1 g of Amano lipase 30 in 20 mL of 0.05 N
phosphate buffer. The resulting slurry was spread on a glass
dish and allowed to dry in the air at 23 °C for 48 h (weight 5.4
g, water content about 2% by Fisher method).
Hexa h yd r ofu r o[2,3-b]fu r a n -3a -ol (26). Into a stirred
solution of (2-n-butyloxy)-3-allyltetrahydrofuran-3-ol (25) (10
g; prepared as described by J alali-Naini and co-workers21) in
methanol (10 mL) and methylene chloride (220 mL) at -78
°C was passed a stream of ozone until a blue color persisted.
The mixture was purged with nitrogen, warmed to 0 °C, and
diluted with ethanol (100 mL). To this mixture was added
NaBH4 (5 g), and the resulting mixture was stirred at 23 °C
for 6 h. After this period, the solvents were removed under
reduced pressure and the residue was partitioned between 10%
citric acid (50 mL) and CH2Cl2 (100 mL). The layers were
separated, the aqueous layer was extracted with additional
CH2Cl2 (2 × 100 mL), and the combined organic extracts were
dried over anhydrous MgSO4 and concentrated. The residue
was dissolved in CH2Cl2 (100 mL), and p-toluenesulfonic acid
monohydrate (0.10 g) was added. The resulting mixture was
heated at reflux for 24 h and then concentrated to a small
volume under reduced pressure. Distillation of the residue
(110-130 °C, at 0.1 mmHg) furnished (2 g) the title compound
as an oil: 1H-NMR (300 MHz, CDCl3) δ 5.4 (s, 1 H), 4.0-4.2
(m, 4 H), 3.0 (br s, 1 H), 2.2 (m, 4 H); IR (neat) 2948, 1656,
1460, 1210 cm-1; MS (70 eV) m/ z 131 (M+ + H).
(3R,3a S,6a R)-3-Hyd r oxyh exa h yd r ofu r o[2,3-b]fu r a n (7)
by Im m obilized Lip a se-Ca ta lyzed Acyla tion . To a stirred
solution of racemic alcohol 15 (2 g, 15.4 mmol) and acetic
anhydride (4 g, 42.4 mmol) in 100 mL of DME was added 2.7
g (about 25% by weight of lipase PS30) of immobilized Amano
lipase, and the resulting suspension was stirred at 23 °C. The
reaction was monitored by TLC and 1H-NMR analysis until
50% conversion was reached. The reaction mixture was
filtered, and the filter cake was washed repeatedly with ethyl
acetate. The combined filtrate was carefully concentrated in
a rotary evaporator, keeping the bath temperature below 15
°C. The residue was chromatographed over silica gel to
provide 843 mg (42%) of 7 (95% ee; [R]23 -11.9°, c 1.24,
D
MeOH); 1H-NMR (CDCl3) δ 5.7 (d, 1 H, J ) 5.1 Hz), 4.45 (dd,
1 H, J ) 6.8, 14.6 Hz), 3.85-4.0 (m, 3 H), 3.65 (dd, 1 H, J )
7.0, 9.1 Hz), 2.9 (m, 1 H), 2.3 (m, 1 H), 1.85 (m, 2 H). Also,
1.21 g of 16 was obtained after washing with 5% aqueous
sodium carbonate (45%; [R]23D +31.8°, c 1.86, MeOH); 1H-NMR
(CDCl3) δ 5.7 (d, 1 H, J ) 5.2 Hz), 5.2 (dd, 1 H, J ) 6.4, 14.5
Hz), 3.8-4.1 (m, 3 H), 3.75 (dd, 1 H, J ) 6.6, 9.2 Hz), 3.1 (m,
1 H), 2.1 (s, 3 H), 1.85-2.1 (m, 2 H); IR (neat) 2947, 1750,
Hexa h yd r ofu r o[2,3-b]fu r a n -3a -yl Su ccin im id yl Ca r -
bon a te (27). To a stirred solution of 1 g of hexahydrofuro-
[2,3-b]furan-3a-ol in 25 mL of 12.5% phosgene in toluene cooled
to -10 °C was added 1 mL of pyridine. The mixture was
allowed to warm to 25 °C and stir for 4 h and then was
concentrated to dryness under reduced pressure. The oily
residue after drying under vacuum (1.3 g) was dissolved in 30
mL of anhydrous acetonitrile and then cooled in an ice bath.
To this cold solution were added 1.14 g of N-hydroxysuccin-
imide and 1.3 mL of triethylamine. The mixture was aged
for 48 h at 25 °C and then concentrated to dryness. The
residue was dissolved in 200 mL of ethyl acetate, washed with
1630, 1338, 1220 cm-1
.
(1S,2R)-2-(2′-Hyd r oxyeth yl)-3-cyclop en ten -1-ol (21). To
a stirring mixture of LiAlH4 (0.667 g, 17.58 mmol) in dry THF
(12 mL) at 0 °C under nitrogen was added dropwise a solution

Nonpeptidal Ligands for HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3287
2 × 50 mL of water, dried over MgSO4, and concentrated to
dryness under reduced pressure. Chromatography of the
residue with 20% ethyl acetate in methylene chloride gave 0.49
g of product as a white solid: 1H-NMR (300 MHz, CDCl3) δ
5.7 (s, 1 H), 4.0-4.25 (m, 4 H), 2.85 (s, 4 H), 2.5 (m, 4 H); MS
(70 eV) m/ z 272 (M+ + H).
an additional 24 h. Following the workup and chromatography
according to the procedure described for compound 32, the
bicyclic olefin 33 (1.21 g, 16%) was obtained as an oil: 1H-
NMR (300 MHz, CDCl3) δ 5.0 (br s, 2 H), 4.75 (m, 1 H), 4.5
(m, 1 H), 4.3 (m, 1 H), 4.05 (br d, 1 H, J ) 10 Hz), 3.8-3.95
(m, 2 H), 3.4 (dd, 1 H, J ) 4.1, 10 Hz), 3.2 (m, 1 H).
tr a n s-3-(P r op a r gyloxy)-4-br om ocyclop en ta n e (30). To
a stirred suspension of 26.1 g (0.14 mol) of N-bromosuccinimide
and propargyl alcohol (61 mL) in CH2Cl2 (25 mL) at -30 °C
was added a solution of cyclopentene (64 mmol, 5.0 g, 6.5 mL)
in 25 mL of CH2Cl2 over a period of 2 h. The resulting mixture
was warmed to 23 °C and stirred at that temperature for 24
h. After this period, aqueous NaOH solution (10%, 100 mL)
was added and the mixture was stirred for 15 min. The layers
were separated and the aqueous layer extracted with CH2CL2
(2 × 100 mL). The combined organic extracts were washed
with brine containing a small amount of Na2S2O3 (70 mg) and
dried over anhydrous Na2SO4. Evaporation of the solvent
afforded a residue which was chromatographed over silica gel
(10% ethyl acetate in hexane) to provide (9.6 g, 92%) the title
bromo ether 30 as an oil: 1H-NMR (300 MHz, CDCl3) δ 4.2-
4.35 (m, 2 H), 4.18 (m, 2 H), 2.45 (m, 1 H), 2.1-2.4 (m, 2 H),
1.7-2.1 (m, 4 H).
Bicyclic Olefin 32. To a refluxing solution of 17.3 mL (64
mmol) of tributyltin hydride containing AIBN (400 mg) in
toluene (200 mL) was added dropwise a solution of 9.6 g (54
mmol) of bromocyclopentane 30 in toluene (200 mL) over a
period of 1 h. The resulting mixture was stirred at reflux for
an additional 24 h. The mixture was then cooled to 23 °C and
concentrated under reduced pressure. The residue was par-
titioned between petroleum ether and acetonitrile (200 mL of
each), and the acetonitrile (lower) layer was concentrated. The
residue was purified by chromatography on silica gel, using
10% ethyl acetate in hexane as the eluent to provide the exo-
olefin 32 (1.48 g, 22%) as an oil: 1H-NMR (300 MHz, CDCl3)
δ 4.8 (br s, 2 H), 4.5 (m, 1 H), 2.2-2.4 (m, 2 H), 3.0 (m, 1 H),
1.4-1.8 (m, 6 H).
Bicyclic Alcoh ol 34. A stream of ozone was dispersed into
a solution of 32 (1.48 g, 11.9 mmol) in methanol (40 mL) and
CH2Cl2 (40 mL) at -78 °C for 30 min. The resulting blue
solution was purged with nitrogen until colorless, then the
reaction was quenched with 5 mL of dimethyl sulfide at -78
°C, and the resulting mixture was allowed to warm to 23 °C.
The mixture was concentrated under reduced pressure to
afford the crude ketone. The resulting crude ketone was
dissolved in ethanol (30 mL), the solution was cooled to 0 °C,
and sodium borohydride (1.05 g, 27.6 mmol) was added. The
reaction mixture was stirred for an additional 2 h at 0 °C and
then the reaction quenched with 10% aqueous citric acid (10
mL). The resulting mixture was concentrated under reduced
pressure, and the residue was partitioned between ethyl
acetate and brine. The layers were separated, and the aqueous
layer was extracted with ethyl acetate (2 × 50 mL). The
combined organic layers were dried over anhydrous Na2SO4
and concentrated carefully under reduced pressure. The
resulting residue was chromatographed over silica gel (30%
ethyl acetate in hexane) to furnish (193 mg, 14%) the title
racemic alcohol 34 as an oil: 1H-NMR (300 MHz, CDCl3) δ
4.4 (m, 1 H), 4.35 (br s, 1 H), 3.75 (dd, 1 H, J ) 4.5, 8 Hz),
3.65 (dd, 1 H, J ) 8, 11 Hz), 2.65 (m, 1 H), 1.8-2.0 (m, 2 H),
1.4-1.8 (m, 4 H).
tr a n s-3-Br om o-4-(p r op a r gyloxy)tetr a h yd r ofu r a n (31).
To a stirred suspension of N-bromosuccinimide (50.8 g, 0.28
mol) and propargyl alcohol (120 mL) at -30 °C was added a
solution of dihydrofuran (140 mmol, 10 g) in CH2Cl2 (50 mL)
over a period of 2 h. The resulting mixture was warmed to 23
°C and stirred at that temperature for 24 h. Following the
workup and chromatography according to the procedure
described for compound 30, the bromo ether 31 (10.2 g, 35%)
was obtained as an oil: 1H-NMR (300 MHz, CDCl3) δ 4.6-
4.75 (m, 3 H), 4.45 (m, 2 H), 4.2-4.35 (m, 3 H), 2.5 (m, 1 H).
Bicyclic Olefin 33. To a refluxing solution of tributyltin
hydride (16.9 mL, 63 mmol) containing AIBN (400 mg) in
toluene (200 mL) was added dropwise a solution of 10.2 g (40
mmol) of bromotetrahydrofuran 31 in toluene (50 mL) over a
period of 1 h. The resulting mixture was stirred at reflux for
Bicyclic Alcoh ol 35. A stream of ozone was dispersed into
a solution of 33 (1.21 g, 10.5 mmol) in methanol (40 mL) and
CH2Cl2 (40 mL) at -78 °C for 30 min. The resulting blue
solution was purged with nitrogen until colorless, then the
reaction was quenched with 5 mL of dimethyl sulfide at -78
°C, and the resulting mixture was allowed to warm to 23 °C.
The mixture was concentrated under reduced pressure to
afford the crude ketone. The resulting crude ketone was
dissolved in ethanol (30 mL), the solution was cooled to 0 °C,
and sodium borohydride (1.2 g, 31 mmol) was added. The
reaction mixture was stirred for an additional 2 h at 0 °C and
then the reaction quenched with 10% aqueous citric acid (10
mL). Following the workup and chromatography according
to the procedure described for compound 34, racemic bicyclic
alcohol 35 (150 mg, 10%) was obtained as an oil: 1H-NMR (300
MHz, CDCl3) δ 4.6 (m, 1 H), 4.3-4.4 (m, 2 H), 4.05 (br d, 1 H,
J ) 11 Hz), 3.9 (d, 1 H, J ) 8.8 Hz), 3.6 (dd, 1 H, J ) 2.1, 8.8
Hz), 3.45 (m, 2 H), 2.9 (m, 1 H), 2.2 (br, 1 H).
Th ion oca r bon a tes 37 a n d 38. To a mixture of isosorbide
(36) (7.31 g, 50.0 mmol) and triethylamine (607.2 mg, 6.0
mmol) in dry methylene chloride (25 mL) was added phenyl
chlorothionoformate (863.2 mg, 692 mL, 5.0 mmol) over a
period of 10 min at 23 °C, and the resulting mixture was
stirred under nitrogen atmosphere for 12 h. The reaction was
quenched with aqueous NaHCO3 solution, and the layers were
separated. The aqueous layer was extracted with methylene
chloride (2 × 20 mL). The combined extracts were washed
successively with water and brine and dried with anhydrous
Na2SO4. Removal of the solvent under reduced pressure
furnished a thick oil which was purified by flash chromatog-
raphy over silica gel (1:1 ethyl acetate/hexanes) to afford pure
thionocarbonates 37 (577 mg, 41%) and 38 (273 mg, 19%) as
white solids: 1H-NMR (CDCl3) (37) δ 7.55-7.41 (m, 2 H), 7.31
(t, 1 H, J ) 7.5 Hz), 7.11 (d, 2 H, J ) 7.65 Hz), 5.69 (d, 1 H, J
) 3.38 Hz), 4.76-4.71 (m, 2 H), 4.39-4.32 (m, 2 H), 4.13 (dd,
1 H, J ) 3.55, 11.16 Hz), 3.94 (dd, 1 H, J ) 5.96, 9.51 Hz),
3.63 (dd, 1 H, J ) 5.86, 9.52 Hz), 2.58 (d, 1 H, J ) 7.15 Hz);
(thionocarbonate 38) δ 7.44-7.4 (m, 2 H), 7.3 (t, 1 H, J ) 7.43
Hz), 7.13 (d, 2 H, J ) 7.84 Hz), 5.66 (dd, 1 H, J ) 5.37, 10.59
Hz), 5.03 (t, 1 H, J ) 5.03 Hz), 4.47 (d, 1 H, J ) 4.6 Hz), 4.4
(d, 1 H, J ) 5.38 Hz), 4.06-3.98 (m, 4 H), 1.83 (d, 1 H, J )
5.57 Hz).
Bicyclic F u r a n ofu r a n 39. To a refluxing solution of tri-
n-butyltin hydride (277 mg, 0.95 mmol) and 2,2′-azobis-
(isobutyronitrile) (8 mg, 0.048 mmol) in dry toluene (3 mL)
under nitrogen atmosphere was added dropwise a solution of
thionocarbonate 37 (130 mg, 0.46 mmol) in toluene (2 mL) over
a period of 1 h. The resulting mixture was heated under reflux
for 4 h. The mixture was cooled to 23 °C, and toluene was
removed under reduced pressure. The residue was partitioned
between acetonitrile (15 mL) and hexanes (15 mL). After
separating the acetonitrile layer, the hexane layer was ex-
tracted with additional acetonitrile (15 mL). The combined
acetonitrile layers were evaporated under reduced pressure
to obtain a residue which was purified by flash chromatogra-
phy over silica gel (1:3 ethyl acetate/hexanes) to obtain 39 (40
mg, 67%): 1H-NMR (CDCl3) δ 4.59 (dt, 1 H, J ) 1.1, 4.7 Hz),
4.46 (t, 1 H, J ) 5.15 Hz), 4.3-4.18 (m, 1 H), 4.05 (dt, 1 H, J
) 2.72, 8.2 Hz), 3.89-3.76 (m, 2 H), 3.69-3.62 (m, 1 H), 2.78
(d, 1 H, J ) 6.35 Hz), 2.2-1.9 (m, 2 H).
(3R,3a S,6a R)-3-Hyd r oxyh exa h yd r ofu r o[2,3-b]fu r a n yl
2-P yr id yl Ca r bon a te (41). To a stirred solution of 380 mg
(2.9 mmol) of (3R,3aS,6aR)-3-hydroxyhexahydrofuro[2,3-b]-
furan in dry CH2Cl2 (25 mL) at 23 °C was added di-2-pyridyl
carbonate (950 mg, 4.4 mmol) and triethylamine (0.62 mL).
The resulting mixture was stirred for 12 h and the reaction
quenched with saturated aqueous NaHCO3 (15 mL). The
layers were separated, and the organic layer was washed with
brine (15 mL) and dried over anhydrous Na2SO4. Evaporation
of the solvent under reduced pressure gave a residue which

3288 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Ghosh et al.
was chromatographed over silica gel (75% ethyl acetate/
hexane) to furnish 460 mg of (3R,3aS,6aR)-3-hydroxyhexahy-
drofuro[2,3-b]furanyl 2-pyridyl carbonate (41) as a brown oil.
Unreacted starting alcohol (120 mg) was also recovered from
this reaction. Carbonate 41: 1H-NMR (CDCl3) δ 8.5 (m, 1 H),
7.8 (m, 1 H), 7.3 (m, 1 H), 7.1 (m, 1 H), 5.75 (m, 1 H), 5.25 (m,
1 H), 4.2 (m, 1 H), 4.0 (m, 3 H), 3.1 (m, 1 H), 2.2 (m, 1 H), 2.0
(m, 1 H).
Inhibitor 53: MS (70 eV) m/ z 556 (m+ + H). Anal.
(C32H49N3O5‚0.25EtOAc) C, H, N.
(3S,4a S,8a S,2′R,3′S,3′′a S,4′′S,6′′a R)-N-ter t-Bu t yl-2-[2′-
h yd r oxy-4′-p h en yl-3′-[[[(4′′-h exa h yd r o-2H-cyclop en ta [b]-
fu r a n y l)o x y ]c a r b o n y l]a m i n o ]b u t y l]d e c a h y d r o i s o -
q u in olin e-3-ca r b oxa m id e (54). From (3aS,4S,6aR)-4-
hydroxyhexahydro-2H-cyclopenta[b]furan using the procedure
substantially as described above for preparation of compound
1
(3S,4a S,8a S,2′R,3′S,3′′R,3′′a S,6′′a R)-N-ter t-Bu t yl-2-[2′-
h yd r oxy-4′-p h en yl-3′-[[[(3′′-h exa h yd r ofu r o[2,3-b]fu r a -
n yl)oxy]ca r bon yl]a m in o]bu tyl]d eca h yd r oisoqu in olin e-
3-ca r b oxa m id e (49). To a stirred solution of 400 mg (1.6
mmol) of (3R,3aS,6aR)-3-hydroxyhexahydrofuro[2,3-b]furanyl
2-pyridyl carbonate in dry CH2Cl2 (30 mL) was added decahy-
droisoquinoline-3-carboxamide derivative 42 (430 mg, 1.1
mmol). The resulting solution was stirred at 23 °C for 12 h.
After this period, the reaction was quenched with saturated
aqueous NaHCO3 (20 mL) and the mixture diluted with CH2-
Cl2 (25 mL). The layers were separated, and the organic layer
was washed with brine (15 mL) and dried over anhydrous Na2-
SO4. Evaporation of the solvent under reduced pressure
afforded a residue which was purified by silica gel chroma-
tography (75% ethyl acetate/hexane) to furnish 620 mg of
49, there was obtained a white solid: mp 87-8 °C; H-NMR
(300 MHz, CDCl3) δ 7.2-7.4 (m, 5 H), 5.8 (s, 1 H), 5.35 (m, 1
H), 4.8 (m, 1 H), 4.35 (m, 1 H), 3.6-4.0 (m, 3 H), 3.5 (m, 1 H),
2.8-3.2 (m, 3 H), 2.5-2.8 (m, 3 H), 2.25 (m, 1 H), 2.0 (m, 1 H),
1.2-1.9 (m, 18 H), 1.34 (s, 9 H); MS (70 eV) m/ z 556 (m+
H). Anal. (C32H49N3O5‚0.5EtOAc) C, H, N.
+
(3S,4aS,8aS,2′R,3′S)-N-ter t-Bu tyl-2-[2′-h ydr oxy-4′-p h en -
yl-3′-[[[(3a ′′-h exa h yd r ofu r o[2,3-b]fu r a n yl)oxy]ca r bon yl]-
am in o]bu tyl]decah ydr oisoqu in olin e-3-car boxam ide (55).
From hexahydrofuro[2,3-b]furan-3a-yl succinimidyl carbonate
(27) using the procedure substantially as described above for
preparation of compound 49, there was obtained inhibitor 55
as a white solid: 1H-NMR (300 MHz, CDCl3) δ 7.2-7.4 (m, 5
H), 5.8 (br s, 1 H), 5.4 (m, 1 H), 3.7-4.0 (m, 6 H), 2.8-3.2 (m,
3 H), 2.2-2.6 (m, 4 H), 1.95-2.1 (m, 2 H), 1.2-1.9 (m, 16 H),
1.34 (s, 9 H); MS (70 eV) m/ z 558 (m+ + H). Anal.
(C31H47N3O6) C, H, N.
In h ibitor 56. To a stirred solution of bicyclic alcohol 35
(150 mg, 1.1 mmol) in dry CH2Cl2 (5 mL) at 23 °C were added
di-2-pyridyl carbonate (368 mg, 1.7 mmol) and triethylamine
(0.24 mL). The resulting mixture was stirred for 12 h and
then the reaction quenched with saturated aqueous NaHCO3
(5 mL). The layers were separated, and the organic layer was
washed with brine (5 mL) and dried over anhydrous Na2SO4.
Evaporation of the solvent under reduced pressure gave a
residue which was chromatographed over silica gel (75% ethyl
acetate/hexane) to furnish the corresponding mixed carbonate
of 35 (79 mg) as a brown oil. From the above mixed carbonate
(79 mg) and decahydroisoquinoline-3-carboxamide derivative
42 (124 mg, 0.31 mmol) using the procedure substantially as
described above for preparation of compound 49, there was
obtained inhibitor 56 (140 mg) as a mixture (1:1) of diaster-
eomers after silica gel chromatography (25% ethyl acetate in
hexane). The mixture was assayed for enzyme inhibitory
potency. Inhibitor 56: MS (70 eV) m/ z 558 (m+ + H). Anal.
(C31H47N3O6) C, H, N.
(3R,3a S,5S,6a R)- a n d (3R,3a S,5R,6a R)-3-H yd r oxy-5-
m eth ylh exa h yd r ofu r o[2,3-b]fu r a n for In h ibitor s 59 a n d
60: (1S,3S,4R,1′R,2′′SR)-, (1S,3S,4R,1′S,2′′SR)-, (1S,3S,4R,-
1′R,2′′SR)-, a n d (1R,3S,4R,1′S,2′′SR)-2-Meth oxy-3-(1′-ox-
ir a n ylm e t h yl)-4-[(2′′-t e t r a h yd r op yr a n yl)oxy]t e t r a h y-
d r ofu r a n . To a stirred solution of (2R,3S,4R)- and (2S,3S,4R)-
2-methoxy-3-allyl-4-hydroxytetrahydrofuran (6) (0.5 g, 3.2
mmol) and dihydropyran (0.87 mL, 9.6 mmol) in dry THF (25
mL) was added p-toluensulfonic acid (10 mg). The resulting
solution was stirred at 23 °C for 12 h. After this period, the
reaction was quenched with saturated NaHCO3 solution. The
layers were separated, and the aqueous layer was extracted
with ethyl acetate. The combined layers were dried over
anhydrous Na2SO4 and concentrated under reduced pressure.
The residue was chromatographed over slilica gel (50% ethyl
acetate/hexane as eluent) to furnish the tetrahydropyranyl
ether (625 mg) as an oil. To a solution of the above tetrahy-
dropyranyl ether (300 mg) in CH2Cl2 (25 mL) was added
mCPBA (60%, 461 mg, 1.6 mmol), and the resulting mixture
was stirred at 23 °C for 12 h. The reaction was quenched with
aqueous NaHCO3 solution, the layers were separated, and the
aqueous layer was extracted with an additional amount of CH2-
Cl2 (25 mL). The combined extracts were dried over Na2SO4
and concentrated. Chromatography of the residue over silica
gel (50% ethyl acetate/hexane) afforded the corresponding
epoxide (238 mg) as an oil.
1
inhibitor 49 as a white crystalline solid: mp 98-101 °C; H-
NMR (CDCl3) δ 7.18-7.3 (br m, 5 H), 5.77 (s, 1 H), 5.61 (d, 1
H), 5.59 (d, 1 H), 5.0 (br q, 1 H), 4.05 (br m, 1 H), 3.75-3.95
(br m, 3 H), 3.7 (m, 2 H), 3.1-3.2 (m, 1 H), 2.8-3.0 (br m, 4
H), 2.5-2.7 (br m, 2 H), 2.25 (br d, 2 H), 1.4-1.9 (br m, 14 H),
1.35 (s, 9 H); MS (70 eV) m/ z 558 (m+ + H). Anal.
(C31H47N3O6) C, H, N.
(3S,4a S,8a S,2′R,3′S,3′′S,3′′a R,6′′a S)-N-ter t-Bu t yl-2-[2′-
h yd r oxy-4′-p h en yl-3′-[[[(3′′-h exa h yd r ofu r o[2,3-b]fu r a -
n yl)oxy]ca r bon yl]a m in o]bu tyl]d eca h yd r oisoqu in olin e-
3-ca r b oxa m id e (50). From (3S,3aR,6aS)-3-hydroxyhexa-
hydrofuro[2,3-b]furan using the procedure substantially as
described above for preparation of compound 49, there was
obtained a white solid: mp 85-9 °C; 1H-NMR (300 MHz,
CDCl3) δ 7.2-7.3 (br m, 5 H), 5.8 (s, 1 H), 5.7 (m, 1 H), 5.4 (m,
1 H), 5.0 (br q, 1 H), 3.95 (m, 3 H), 3.8-3.9 (m, 2 H), 3.5 (m,
1 H), 2.8-3.1 (m, 4 H), 2.6 (m, 2 H), 2.3 (m, 2 H), 2.0 (m, 1 H),
1.4-1.9 (br m, 14 H), 1.3 (s, 9 H); MS (70 eV) m/ z 558 (m+
H). Anal. (C31H47N3O6) C, H, N.
+
(3S,4a S,8a S,2′R,3′S,3′′R,3′′a S,7′′a R)-N-ter t-Bu t yl-2-[2′-
h ydr oxy-4′-ph en yl-3′-[[[(3′′-h exah ydr o-4′′H-fu r o[2,3-b]pyr -
a n yl)oxy]ca r bon yl]a m in o]bu tyl]d eca h yd r oisoqu in olin e-
3-ca r b oxa m id e (51). From (3R,3aS,7aR)-3-hydroxy-4H-
hexahydrofuro[2,3-b]pyran using the procedure substantially
as described above for preparation of compound 49, there was
1
obtained a white solid: mp 147-53 °C; H-NMR (300 MHz,
CDCl3) δ 7.3-7.4 (m, 5 H), 6.9 (s, 1 H), 5.5 (br d, 1 H), 5.25
(m, 2 H), 5.0 (br d, 1 H), 4.1 (m, 1 H), 3.9 (m, 4 H), 3.8 (m, 2
H), 3.4 (m, 1 H), 2.9-3.1 (m, 4 H), 2.5-2.7 (m, 2 H), 2.3 (m, 2
H), 2.1 (m, 2 H), 1.6-2.0 (m, 6 H), 1.3-1.5 (m, 6 H), 1.3 (s, 9
H); MS (70 eV) m/ z 572 (m+ + H). Anal. (C32H49N3O6) C, H,
N.
(3S,4a S,8a S,2′R,3′S,3′′S,3′′a R,7′′a S)-N-ter t-Bu t yl-2-[2′-
h ydr oxy-4′-ph en yl-3′-[[[(3′′-h exah ydr o-4′′H-fu r o[2,3-b]pyr -
a n yl)oxy]ca r bon yl]a m in o]bu tyl]d eca h yd r oisoqu in olin e-
3-ca r b oxa m id e (52). From (3S,3aR,7aS)-3-hydroxy-4H-
hexahydrofuro[2,3-b]pyran (10) using the procedure substan-
tially as described above for preparation of compound 49, there
was obtained a white solid: mp 82-6 °C; 1H-NMR (300 MHz,
CDCl3) δ 7.3 (m, 5 H), 6.85 (s, 1 H), 5.2 (m, 1 H), 5.05 (m, 3
H), 4.1 (m, 1 H), 3.8 (m, 4 H), 3.85-4.0 (m, 4 H), 2.95 (m, 4
H), 2.6 (m, 2 H), 2.3 (m, 2 H), 2.15 (m, 1 H), 1.6-2.0 (m, 6 H),
1.3-1.5 (m, 6 H), 1.3 (s, 9 H); MS (70 eV) m/ z 572 (m+ + H).
Anal. (C32H49N3O6) C, H, N.
(3S,4a S,8a S,2′R,3′S,4′′R,3′′a R,6′′a S)-N-ter t-Bu t yl-2-[2′-
h yd r oxy-4′-p h en yl-3′-[[[(3′′-h exa h yd r o-2H-cyclop en ta [b]-
fu r a n y l)o x y ]c a r b o n y l]a m i n o ]b u t y l]d e c a h y d r o i s o -
qu in olin e-3-car boxam ide (53). From racemic bicyclic alcohol
34 (100 mg, 0.78 mmol) using the procedure substantially as
described above for preparation of compound 49, there was
obtained a 1:1 mixture of diastereomers which were separated
by silica gel chromatography (25% ethyl acetate in hexane) to
afford 53 (40 mg, Rf ) 0.45) and diastereomer (Rf ) 0.6).
(2R,3S,4R,2′SR,2′′SR)-2-Meth oxy-3-(2′-h yd r oxyp r op yl)-
4-[(2-tetr ah ydr opyr an yl)oxy]tetr ah ydr ofu r an . To a stirred,
ice cold suspension of LiAlH4 (50 mg, 1.4 mmol) in THF (10
mL) was added a solution of the above epoxide (230 mg) in
THF (2 mL). The resulting mixture was warmed to 23 °C and
stirred for 12 h. After this period, the reaction was quenched

Nonpeptidal Ligands for HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17 3289
Inhibitors. Annu. Rep. Med. Chem. 1991, 26, 141-50. (h)
Tomasselli, A. G.; Howe, W. J .; Sawyer, T. K.; Wlodawer, A.;
Heinrikson, R. L. The complexities of AIDS: An Assessment of
the HIV Protease as a Therapeutic Target. Chimicaoggi 1991,
6-27.
with water (0.1 mL) and then 20% NaOH (0.1 mL) and the
resulting mixture was stirred for 30 min. The mixture was
then filtered through diatomaceous earth, and the filtrate was
concentrated under reduced pressure. The residue was chro-
matographed over silica gel (75% ethyl acetate/hexane) to
provide a mixture of the corresponding mixture of secondary
alcohols (180 mg) as an oil.
(3) Wlodawer, A.; Erickson, J . W.; Structure-based Inhibitors of
HIV-1 Protease. Annu. Rev. Biochem. 1993, 62, 543-85.
(4) (a) 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 I Protease Inhibitor. Proc. Natl. Acad. Sci. U.S.A.
1994, 91, 4096-100. (b) Dorsey, B. D.; Levin, R. B.; McDaniel,
S. L.; Vacca, J . P.; Guare, J . P.; Darke, P. L.; Zugay, J .; 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, 3443-51. (c) Kempf, D. J .; Marsh, K. C.; Denissen, J .;
McDonald, E.; Vasavononda, S.; Flentge, C.; Green, B. G.; Fino,
L.; Park, C.; 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 .; Norbeck, D. ABT-538 is a Potent
Inhibitor of Human Immunodeficiency Virus Protease with High
Oral Bioavailability in Humans. Proc. Natl. Acad. Sci. U.S.A.
1995, 92, 2484-8. (d) Lam, P. Y. S.; J adhav, P. K.; Eyermann,
C. J .; Hodge, C. N.; Ru, Y.; Bacheler, L. T.; Meek, J . L.; Otto, M.
J .; Rayner, M. M.; Wong, Y. N.; Chang, C.-H.; Weber, P. C.;
J ackson, D. A.; Sharpe, T. R.; Erickson-Viitanen, S. Rational
Design of Potent, Bioavailable, Nonpeptide Cyclic Ureas as HIV
Protease Inhibitors. Science 1994, 263, 380-4.
(5) (a) 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 .; Krohn, 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 Proteinase Inhibitors. Science 1990, 248, 358-61. (b)
Williams, P. E. O.; Muirhead, G. J .; Madigan, M. J .; Mitchell,
A. M.; Shaw, T. Disposition and Bioavailability of the HIV
Proteinase Inhibitor, R0 31-8959, After Single doses in Healthy
Volunteers. Proceedings of British Pharmacology Society Meet-
ing, Univ. of Newcastle, Upon Tyne, Apr. 8-10, 1992. (c)
Thaisrivongs, S.; Tomich, P. K.; Watenpaugh, K. D.; Chong, K.
T.; Howe, W. J .; Yang, C.-P.; Strohbach, J . W.; Turner, S. R.;
McGrath, J . P.; Bohanon, M. J .; Lynn, J . C.; Mulichack, A. M.;
Spinelli, P. A.; Hinshaw, R. R.; Pagano, P. J .; Moon, J . B.;
Ruwart, M. J .; Wilkinson, K. F.; Rush, B. D.; Zipp, G. L; Dalga,
R. J .; Schwende, F. J .; Howard, G. M.; Padbury, G. E.; Toth, L.
N.; Zhao, Z.; Koeplinger, K. A.; Kakuk, T. J .; Cole, S. L.; Zaya,
R. M.; Piper, R. C.; J effery, P. Structure-based Design of HIV
Protease Inhibitors: 4-Hydroxycoumarins and 4-Hydroxy-2-
pyrones as Non-peptidic Inhibitors. J . Med. Chem. 1994, 37,
3200-4.
(3R,3a S,5S,6a R)- a n d (3R,3a S,5R,6a R)-3-H yd r oxy-5-
m eth ylh exa h yd r ofu r o[2,3-b]fu r a n . To a stirred solution
of the above alcohols (180 mg) in a mixture (10:1) of CH2Cl2
and methanol (50 mL) was added camphorsulfonic acid (50
mg), and the resulting mixture was stirred at 23 °C for 14 h.
After this period, the mixture was concentrated to dryness,
the residue was redissolved in CH2Cl2 (70 mL), and the
resulting solution was stirred for an additional 12 h. It was
then washed with saturated aqueous NaHCO3 solution, dried
over Na2SO4, and concentrated under reduced pressure. Chro-
matography of the residue over silica gel (75% ethyl acetate/
hexane) provided (3R,3aS,5R,6aR)-3-hydroxy-5-methylhexa-
hydrofuro[2,3-b]furan (60 mg, for inhibitor 59) and (3R,-
3aS,5S,6aR)-3-hydroxy-5-methylhexahydrofuro[2,3-b]furan (60
mg for inhibitor 60) as oils.
(3S,4a S,8a S,2′R,3′S,3′′R,3′′a S,5′′R,6′′a R)-N-ter t-Bu tyl-2-
[2′-h yd r oxy-4′-p h en yl-3′-[[[(5′′-m eth yl-3′′-h exa h yd r ofu r o-
[2,3-b]fu r a n yl)oxy]ca r bon yl]a m in o]bu tyl]d eca h yd r oiso-
qu in olin e-3-ca r boxa m id e (59). From (3R,3aS,5R,6aR)-3-
hydroxy-5-methylhexahydrofuro[2,3-b]furan using the procedure
substantially as described above for preparation of compound
49, there was obtained a white solid: mp 100-2 °C; 1H-NMR
(300 MHz, CDCl3) δ 7.3-7.4 (m, 5 H), 5.75 (s, 1 H), 5.5-5.6
(m, 3 H), 4.9 (m, 1 H), 3.8-4.0 (m, 4 H), 3.7 (m, 1 H), 3.2 (m,
1 H), 2.9 (m, 4 H), 2.6 (m, 3 H), 2.3 (m, 2 H), 1.5-2.0 (m, 6 H),
1.4-1.6 (m, 6 H), 1.3 (s, 9 H), 1.28 (d, 3 H, J ) 6.9 Hz); MS
(70 eV) m/ z 572 (m+ + H). Anal. (C32H49N3O6‚0.1CHCl3) C,
H, N.
(3S,4a S,8a S,2′R,3′S,3′′R,3′′a S,5′′S,6′′a R)-N-ter t-Bu tyl-2-
[2′-h yd r oxy-4′-p h en yl-3′-[[[(5′′-m eth yl-3′′-h exa h yd r ofu r o-
[2,3-b]fu r a n yl)oxy]ca r bon yl]a m in o]bu tyl]d eca h yd r oiso-
qu in olin e-3-ca r boxa m id e (60). From (3R,3aS,5S,6aR)-3-
hydroxy-5-methylhexahydrofuro[2,3-b]furan using the procedure
substantially as described above for preparation of compound
49, there was obtained a white solid: mp 105-7 °C; 1H-NMR
(300 MHz, CDCl3) δ 7.3-7.4 (m, 5 H), 5.8 (s, 1 H), 5.6 (m, 3
H), 5.0 (m, 1 H), 4.05 (m, 4 H), 3.9 (m, 2 H), 3.65 (m, 1 H), 2.2
(m, 1 H), 2.95 (m, 4 H), 2.6 (m, 2 H), 2.25 (m, 2 H), 1.5-2.9
(m, 4 H), 1.4-1.6 (m, 6 H), 1.3 (s, 9 H), 1.2 (m, 3 H); MS (70
eV) m/ z 572 (m+ + H). Anal. (C32H49N3O6‚0.35CHCl3) C, H,
N.
(6) Ghosh, A. K.; Thompson, W. J .; McKee, S. P.; Duong, T. T.; Lyle,
T. A.; Chen, J . C.; Darke, P. L.; Zugay, J . A.; Emini, E. A.; Schleif,
W. A.; Huff, J . R.; Anderson, P. S. 3-Tetrahydrofuran and Pyran
Urethanes as High Affinity P2-Ligands for HIV-1 Protease
Inhibitors. J . Med. Chem. 1993, 36, 292-4.
Ack n ow led gm en t. Financial support of this re-
search by the National Institute of Health (GM 53386-
01) and Merck Research Laboratories is gratefully
acknowledged. We would like to thank Professor George
Gould for helpful discussion. The authors also thank
Mr. Matthew Zrada and Mr. Kenneth D. Anderson of
MRL for log P and solubility determination.
(7) (a) Ghosh, A. K.; Thompson, W. J .; Holloway, M. K.; Mckee, S.
P.; Duong, T. T.; Lee, H. Y.; Munson, P. M.; Smith, A. M.; Wai,
J . M.; Darke, P. L.; Zugay, J . A.; Emini, E. A.; Schleif, W. A.;
Huff, J . R.; Anderson, P. S. Potent HIV Protease Inhibitors: The
Development of Tetrahydrofuranylglycines as Novel P2-Ligands
and Pyrazine Amides as P3-Ligands. J . Med. Chem. 1993, 36,
2300-10. (b) Thompson, W. J .; Ghosh, A. K.; Holloway, M. K.;
Lee, H. Y.; Munson, P. M.; Schwering, J . E.; Wai, J . M.; Darke,
P. L.; Zugay, J . A.; Emini, E. A.; Schleif, W. A.; Huff, J . R.;
Anderson, P. S. 3′-Tetrahydrofuranylglycine as a Novel, Un-
natural Amino Acid Surrogate for Asparagine in the Design of
Inhibitors of the HIV Protease. J . Am. Chem. Soc. 1993, 115,
801-3.
Refer en ces
(1) Erickson, J . W.; Fesik, S. W. Macromolecular X-Ray Crystal-
lography and NMR as Tools for Structure-based Drug Design.
Annu. Rep. Med. Chem. 1992, 26, 271 and references cited
therein.
(8) (a) Ghosh, A. K.; Lee, H. Y.; Thompson, W. J .; Culberson, C.;
Holloway, M. K.; McKee, S. P.; Munson, P. M.; Duong, T. T.;
Smith, A. M.; Darke, P. L.; Zugay, J . A.; Emini, E. A.; Schleif,
W. A.; Huff, J . R.; Anderson, P. S. The Development of Cyclic
(2) (a) Thaisrivongs, S. HIV Protease Inhibitors. Annu. Rep. Med.
Chem. 1994, 29, 133. (b) Darke, P. L.; Huff, J . R. HIV Protease
as an Inhibitor Target for the Treatment of AIDS. In Advances
in Pharmacology; August, J . T., Anders, M. W., Murad, F., Eds.;
Academic Press: San Diego, CA, 1994; Vol. 25, pp 399-454. (c)
Clare, M. HIV Protease: Structure-based Design. Perspect. Drug
Discovery Des. 1993, 1, 49-68. (d) Debouck, C. The HIV-1
Protease as a Therapeutic Target for AIDS. AIDS Res. Hum.
Retroviruses 1992, 8 (2), 153-64. (e) Martin, J . A. Recent
Advances in the Design of HIV Protease Inhibitors. Antiviral
Res. 1992, 17, 265-78. (f) Huff, J . R. HIV Protease: A Novel
Chemotherapeutic Target for AIDS. J . Med. Chem. 1991, 34,
2305-14. (g) Norbeck, D. W.; Kempf, D. J . HIV Protease
Sulfolanes as Novel and High Affinity P
2-Ligands for HIV-1
Protease Inhibitors. J . Med. Chem. 1994, 37, 1177-88. (b)
Ghosh, A. K.; Thompson, W. J .; Lee, H. Y.; McKee, S. P.; Munson,
P. M.; Duong, T. T.; Darke, P. L.; Zugay, J . A.; Emini, E. A.;
Schleif, W. A.; Huff, J . R.; Anderson, P. S. Cyclic Sulfolanes as
Novel and High Affinity Ligands for HIV-1 Protease Inhibitors.
J . Med. Chem. 1993, 36, 924-7.
(9) Ghosh, A. K.; Thompson, W. J .; Fitzgerald, P. M. D.; Culberson,
C. J .; Axel, M. G.; McKee, S. P.; Huff, J . R.; Anderson, P. S.
Structure-Based Design of HIV-1 Protease Inhibitors: Replace-
ment of Two Amides and a 10π-Aromatic System by a Fused
Bis-tetrahydrofuran. J . Med. Chem. 1994, 37, 2506-8.

3290 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 17
Ghosh et al.
(10) Ghosh, A. K.; Thompson, W. J .; Munson, P. M.; Liu, W.; Huff,
J . R. Cyclic Sulfone-3-carboxamides as Novel P2-Ligands for Ro
31-8959 Based HIV-1 Protease Inhibitors. Biorg. Med. Chem.
Lett. 1995, 5, 83-8.
(11) Seebach, D.; Aebi, J .; Wasmuth, D. Diastereoselective R-Alky-
lation of â-Hydroxycarboxylic Esters Through Alkoxide Eno-
lates: (+)-Diethyl (2s, 3R)-3-Allyl-2-Hydroxysuccinate from (-)-
Diethyl-S-Malate. Org. Synth. 1985, 63, 109-20.
(12) Ghosh, A. K.; Chen, Y. Synthesis and Optical Resolution of High
Affinity P2-Ligands for HIV-1 Protease Inhibitors. Tetrahedron
Lett. 1995, 36, 505-8.
(13) Dulcere, J . P.; Rodriguez, J .; Santelli, M.; Zahra, J . P. Prepara-
tion D'acyl-4-Methylene-3-Tetrahydrofurans: Un Acces Aux
R-Methylene γ-Lactones et Butenolides Fonctionnalies. (Prepa-
ration of 4-acyl-3-methylenetetrahydrofurans: an access to
functionalized R-methylene-γ-lactones and butenolides.) Tetra-
hedron Lett. 1987, 28, 2009-12 and references cited therein.
(14) Okabe, M.; Abe, M.; Tada, M. Reductive Cyclization of 2-[(2-
Propynyl)oxy]ethyl Bromides by a Cobalt Complex, Cobaloxime
(I). A New Method for the Synthesis of R-Methylene-γ-butyro-
lactones. J . Org. Chem. 1982, 47, 1775-7. For preparation of
cobaloxime, see ref 15.
(28) The structure was energy minimized in the active site using the
Merck molecular force field, OPTIMOL, which is a variant of
the MM2 program; see ref 29.
(29) Halgren, T. A. Merck Sharp and Dohme Research Laboratories,
Rahway, NJ . Unpublished work on the development of the force
field program OPTIMOL. OPTIMOL differs from MM2 mainly
in the use of partial charges on atoms, instead of bond dipoles,
and in the absence of unshared pairs of electrons on certain
nitrogen and oxygen atoms. Also, see: Allinger, N. L.; Confor-
mational Analysis. 130. MM2. A Hydrocarbon Force Field
Utilizing V1 and V2 Torsional Terms. J . Am. Chem. Soc. 1977,
99, 8127-34.
(30) Thompson, W. J .; Fitzgerald, P. M. D.; Holloway, M. K.; Emini,
E. A.; Darke, P. L.; McKeever, B. M.; Schleif, W. A.; Quintero,
J . C.; Zugay, J . A.; Tucker, T. J .; Schwering, J . E.; Homnick, C.
F.; Nunberg, J .; Springer, J . P.; Huff, J . R. Synthesis and
Antiviral Activity of a Series of HIV-1 Protease Inhibitors with
Functionality Tethered to the P1 or P1′ Phenyl Substituents :
X-ray Crystal Structure Assisted Design. J . Med. Chem. 1992,
35, 1685-1701.
(31) A complex between 1 (Ro 31-8959) and HIV-1 protease was
crystallized in the space group P61, a ) b ) 63.33 Å, c ) 83.31
Å. A model for the complex was partially refined against data
extending from 8.0 to 2.2 Å in resolution; the R-value for the
current model is 0.196, and deviations from ideal bond distances
are 0.018 Å. Full details of the crystallographic analysis will be
published elswhere.
(15) Schrauzer, G. N. Bis(dimethylglyoximato)cobalt Complexes.
Inorg. Synth. 1968, 11, 62-4.
(16) The stereochemical assignment of alcohol 15 was made based
on comparison with alcohol 7.
(17) Purchased from Amano International Enzyme Co., Troy, VA.
(18) A slightly modified procedure was used; see: Bianchi, D.; Cesti,
P.; Battistel, E. Anhydrides as Acylating Agents in Lipase-
Catalyzed Stereoselective Esterification of Racemic Alcohols. J .
Org. Chem. 1988, 53, 5531-34.
(32) For details of the assay protocol, see ref 30.
(33) Craig, J . C.; Duncan, I. B.; Hockley, D.; Grief, C.; Roberts, N.
A.; Mills, J . S.; Antiviral Res. 1991, 16, 295-305 and references
cited therein. These authors report IC90 values of 6-30 nM in
cell culture. However, the assay protocol differs widely in that
syneytia formation rather than p24 production was monitored
as end point, and cell types other than MT4 were employed.
(34) A complex between 49 and HIV-1 protease was crystallized in
the space group P61, a ) b ) 63.40 Å, c ) 83.48 Å. A model for
the complex was refined to completion against data extending
from 8.0 to 2.1 Å in resolution; the R-value for the final model
is 0.166, and deviations from ideal bond distances are 0.018 Å.
Full details of the crystallographic analysis will be published in
due course.
(35) Vazquez, M. L.; Bryant, M. L.; Clare, M.; DeCrescenzo, G. A.;
Doherty, E. M.; Freskos, J . N.; Getman, D. P.; Houseman, K.
A.; J ulien, J . A.; Kocan, G. P.; Mueller, R. A.; Shieh, H.-S..;
Stallings, W. C.; Stegeman, R. A.; Talley, J . J . Inhibitors of HIV-1
Protease Containing the Novel and Potent (R)-(Hydroxyethyl)-
sulfonamide Isostere. J . Med. Chem. 1995, 38, 581-4. Also, see
ref 3.
(19) Enantiomeric excess (90% ee) was determined by 19F-NMR
spectroscopy using the Mosher ester; see: Dale, J . A.; Dull, D.
L.; Mosher, H. S. R-Methyl-R-trifluoromethylphenylacetic Acid,
a
Versatile Reagent for the Determination of Enantiomeric
Composition of Alcohols and Amines. J . Org. Chem. 1969, 34,
2543-9.
(20) Tokoroyama, T.; Matsuo, K.; Kanazawa, R. Synthetic Studies
on Terpenic compounds. XII. Selective Degradation of the Side
Chain in Portulal. Bull. Chem. Soc. J pn. 1980, 53, 3383-4.
(21) J alali-Naini, M.; Lallemand, J . Y. Iodocyclization of Unsaturated
Lactols and Acetals, a New Route to Furo-2,3-b-Furans and
Pyrans. Tetrahedron Lett. 1986, 497-500.
(22) Shute, R.; Rich, D. H. Synthesis and Evaluation of Novel
Activated Mixed carbonate Reagents for the Introduction of the
2-(Trimethylsilyl)ethoxycarbonyl(Teoc)-Protecting Group. Syn-
thesis 1987, 346.
(23) Barton, D. H. R.; Motherwell, W. B. New and Selective Reactions
and Reagents in carbohydrate Chemistry. Pure Appl. Chem.
1981, 53, 15-31.
(36) (a) Delfraissy, J . F.; Sereni, D.; Brun-Vezinet, F.; Dussaix, E.;
Krivine, A.; Dormont, J .; Bragman, K. A Phase I-II Dose Ranging
Study of the Safety and Activity of Ro 31-8959 (HIV Proteinase
Inhibitor) in Previously Zidovudine (ZDV) Treated HIV-Infected
Individuals. Skinner, C.; Sedwick, A.; Bragman, K.; Pinching,
A. J .; Weber, J . A Phase I-II Dose Ranging Study of the Safety
and Activity of Ro 31-8959 (HIV Proteinase Inhibitor) in As-
ymptomatic or Mildly Symptomatic HIV-Infection. Abstracts at
the 9th Int. Conf. on AIDS, Berlin, 1993. (b) Teppler, H.;
Pomerantz, R.; Bjornsson, T.; Pientka, J .; Osborne, B.; Woolfe,
E.; Yeh, K.; Duetsch, P.; Emini, E.; Squires, K.; Saag, M.;
Waldman, S. 1st Natl. Conf. on Human Retroviruses and Related
Infections, Washington, DC, Dec. 12-16, 1993; Session 77, L8.
(37) Personal communication: Dr. J uinn Lin, Department of Animal
Pharmacology, Merck Research Laboratories, West Point, PA.
Details of these experiments will be published elsewhere.
(24) (a) Ghosh, A. K.; Duong, T. T.; McKee, S. P. Di(2-Pyridyl)
Carbonate Promoted Alkoxycarbonylation of Amines: A Con-
venient Synthesis of Functionalized Carbamates. Tetrahedron
Lett. 1991, 32, 4251-4. (b) Ghosh, A. K.; Duong, T. T.; McKee,
S. P.; Thompson, W. J . N,N′-Disuccinimidyl Carbonate: A Useful
Reagent for Alkoxycarbonylation of Amines. Tetrahedron Lett.
1992, 33, 2781-4.
(25) A preliminary model of the X-ray crystal structure of the
inhibitor 43 complexed with the HIV-1 protease at 2.5
Å
resolution has been provided by Dr. Paula Fitzgerald, Depart-
ment of Biophysical Chemistry. The final coordinates of the fully
refined structure will be published elsewhere.
(26) Kim, E. E.; Baker, C. T.; Dwyer, M. D.; Murcko, M. A.; Rao, B.
G.; Tung, R. D.; Navia, M. A. Crystal Structure of HIV-1 Protease
in Complex with VX-478, a Potent and Orally Bioavailable
Inhibitor of the Enzyme. J . Am. Chem. Soc. 1995, 117, 1181-2.
(27) The ligands corresponding to the inhibitors 47 and 48 were
prepared according to the procedure described in Scheme 4 in
ref 8a.
J M960128K