Structure-activity relationship of small-sized HIV protease inhibitors containing allophenylnorstatine

Article abstract of DOI:10.1021/jm980637h

We designed and synthesized a new class of peptidomimetic human immunodeficiency virus (HIV) protease inhibitors containing a unique unnatural amino acid, allophenylnorstatine [Apns; (2S,3S)-3-amino-2-hydroxy- 4-phenylbutyric acid], with a hydroxymethylcarbonyl (HMC) isostere as the active moiety. A systematic evaluation of structure - activity relationships for HIV protease inhibition, anti-HIV activities, and pharmacokinetic profiles has led to the delineation of a set of structural characteristics that appear to afford an orally available HIV protease inhibitor. Optimum structures, exemplified by 21f (JE-2147), incorporated 3-hydroxy-2- methylbenzoyl groups as the P2 ligand, (R)-5,5-dimethyl-1,3-thiazolidine-4- carbonyl (Dmt) residue at the P1' site, and 2-methylbenzylcarboxamide group as the P2' ligand. The present study demonstrated that JE-2147 has potent antiviral activities in vitro and exhibits good oral bioavailability and plasma pharmacokinetic profiles in two species of laboratory animals.

Full text of DOI:10.1021/jm980637h

J . Med. Chem. 1999, 42, 1789-1802
1789
Str u ctu r e-Activity Rela tion sh ip of Sm a ll-Sized HIV P r otea se In h ibitor s
Con ta in in g Allop h en yln or sta tin e
Tsutomu Mimoto, Ryohei Kato, Haruo Takaku, Satoshi Nojima, Keisuke Terashima, Satoru Misawa,
Tominaga Fukazawa, Takamasa Ueno, Hideharu Sato, Makoto Shintani, Yoshiaki Kiso,† and Hideya Hayashi*
Pharmaceuticals & Biotechnology Laboratory, J apan Energy Corporation, Toda-shi, Saitama 335-8502, J apan, and
Department of Medicinal Chemistry, Kyoto Pharmaceutical University, Yamashina-ku, Kyoto 607-8414, J apan
Received November 9, 1998
We designed and synthesized a new class of peptidomimetic human immunodeficiency virus
(HIV) protease inhibitors containing a unique unnatural amino acid, allophenylnorstatine [Apns;
(2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid], with a hydroxymethylcarbonyl (HMC) isostere
as the active moiety. A systematic evaluation of structure-activity relationships for HIV
protease inhibition, anti-HIV activities, and pharmacokinetic profiles has led to the delineation
of a set of structural charateristics that appear to afford an orally available HIV protease
inhibitor. Optimum structures, exemplified by 21f (J E-2147), incorporated 3-hydroxy-2-
methylbenzoyl groups as the P2 ligand, (R)-5,5-dimethyl-1,3-thiazolidine-4-carbonyl (Dmt)
residue at the P1′ site, and 2-methylbenzylcarboxamide group as the P2′ ligand. The present
study demonstrated that J E-2147 has potent antiviral activities in vitro and exhibits good
oral bioavailability and plasma pharmacokinetic profiles in two species of laboratory animals.
In tr od u ction
The alarming spread of human immunodeficiency
virus (HIV), the etiologic agent of acquired immunode-
ficiency syndrome (AIDS), has initiated an urgent
pursuit to comprehend and control this disease. Ad-
vances in molecular, viral, and cell biology have defined
numerous targets for potential drug intervention. The
virally encoded homodimeric aspartyl protease, which
is responsible for processing the gag and gag/ pol gene
products that allow for the organization of core struc-
tural proteins and release of viral enzymes, is one such
target.1 Inhibition of this enzyme prevents the matura-
tion and replication of the virus in cell culture. Inhibi-
F igu r e 1. Structures of KNI-227 (1) and KNI-272 (2).
tors of HIV protease are presently being used in therapy
life was very short (t1/2â ) 23 min upon intravenous
for the treatment of AIDS.2 The HIV-1 protease can
recognize Phe-Pro and Tyr-Pro sequences as the retro-
virus-specific cleavage site, but mammalian aspartic
proteases such as renin, pepsin, and cathepsin D do not
have such specificity. These features provided a basis
for the rational design of selective HIV protease-
targeted drugs for the treatment of AIDS and related
diseases. Previously, we reported a series of peptide
mimetic HIV protease inhibitors containing allophenyl-
norstatine [Apns, (2S,3S)-3-amino-2-hydroxy-4-phenyl-
butyric acid] with a hydroxymethylcarboxamide (HMC)
isostere based on the transition-state mimic concept.3,4
The compounds containing a thiazolidine ring, a bio-
isostere of proline, at the P1′ portion showed highly
potent HIV protease inhibitory activity.5,6 The com-
pounds containing a 5-isoquinolinyloxyacetyl group at
the P3 site, represented by KNI-227 (1) and KNI-272
(2), (Figure 1), showed highly potent anti-HIV activity,
and KNI-272 was well-absorbed from the digestive tract
in rats and dogs. Although KNI-272 showed a good oral
bioavailability in a human clinical trial, the plasma half-
administration),7 and tid or qid regimen was needed to
maintain a plasma concentration for over 90% inhibition
of HIV replication.8
In the present study, we describe our continuing effort
to generate novel small-sized HIV protease inhibitors
bearing desirable antiviral activity and pharmacokinetic
profiles, which ultimately resulted in J E-2147, a potent
and orally bioavailable HIV protease inhibitor.
Design Ra tion a le
Information on the interaction between KNI-272 and
HIV-1 protease based on studies of X-ray crystal-
lography of the complex,9 NMR in the solution state,10
and molecular modeling11 gave us the basic structure
to design novel small-sized HIV protease inhibitors. The
hydroxymethylcarbonyl group of Apns (P1) interacts
with the aspartic acid carbonyl groups of the HIV-1
protease active site in essentially the same hydrogen-
bonding mode as occurs in the transition state and
contributes to the high activity of KNI-272.10 The P2
and P1′ carbonyl moieties in KNI-272 are in position to
maintain a critical hydrogen bond to a water molecule,
which hydrogen bonds to the backbone of both flaps
* Corresponding author.
† Kyoto Pharmaceutical University.
10.1021/jm980637h CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/24/1999

1790 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10
Mimoto et al.
272 series molecules might show improved plasma
stability while maintaing its highly potent antiviral
activity. Two types of small-sized lead compounds
(Figure 2, 9d , 12e) were designed, and a SAR study of
P2 and P1′ sites was performed. On the other hand, the
retroviral proteases in general, and HIV protease in
particular, have been shown to exist in their active
forms as C2-symmetric homodimers with each monomer
contributing a catalytic triad to a single active site. The
high degree of symmetry of the HIV protease structure
offers a unique opportunity for the design of C2-
symmetric inhibitors that match the characteristics of
the enzyme structure. Many inhibitors based on this
character were synthesized, and some of them showed
excellent antiviral properties.19-21 This character
prompted us to introduce an aryl group as the P2′
ligand. The C2 operation along the axis in the Apns-
Thz site of compound 12e generated the benzylcarboxa-
mide group as a novel P2′ ligand (Figure 3). The amide
nitrogen of P2′ was expected to interact with the HIV-1
protease in a similar manner as the amide nitrogen of
the tert-butyl (P2′) of KNI-272. Thus, in addition to the
benzoyl (P2)-type compounds, another type of lead
compound (21a ) was obtained.
F igu r e 2. Structures of small-sized lead compounds.
(Ile50 and Ile50′). Moreover, the amide nitrogen of tert-
butyl (P2′) binds to a water molecule, which forms
bridging hydrogen bonds between the amide nitrogen
atom of the P2′ group and the backbone nitrogen of
Asp29. This causes the 10-fold preference in inhibitory
potency of the amide linkage over the ester linkage of
KNI-272 analogues. Another feature that may relate to
the high potency of KNI-272 is that the conformationally
constrained P1-P1′ linkage binds in a low-energy trans
conformation. In contrast to most peptidomimetic in-
hibitors of HIV protease, which exhibit a high degree
of conformational flexibility, KNI-272 appears to be
structurally preorganized to bind in an energetically
preferred conformation. Therefore the basic structure
(surrounded by the dashed line in Figure 1) was
selected, and P2 and P2′ ligands were mainly tested in
the course of our structure-activity relationship (SAR)
study on HIV-1 protease inhibition.
Recently, a variety of ligands optimized for binding
to the S2 subsite of HIV protease have been reported
for hydroxyethylamine inhibitors. In particular, the
3-hydroxy-2-methylbenzoyl group12-16 and 2,6-dimeth-
ylphenoxyacetyl group17,18 provide attractive P2 ligands
due to their lack of stereocenters and ease of synthesis.
Therefore, we hypothesized that a small-sized inhibitor
incorporating these groups into the backbone of KNI-
Ch em istr y
Boc-Apns-OH22,23 and 2-alkyl-3-hydroxybenzoic ac-
ids24 were prepared according to the methods described
previously.
Scheme 1 illustrates the procedures to synthesize
dipeptide tert-butylamide derivatives 6a ,b. Boc-protect-
ed 1,3-thiazolidine-4-carboxylic acid derivatives 4a ,b
were prepared from the corresponding cysteine ana-
logues 3a ,b by cyclization with formaldehyde, followed
by tert-butoxycarbonylation with Boc2O in a one-pot
reaction. The amide bond formation here was prepared
by use of N,N′-dicyclohexylcarbodiimide/1-hydroxyben-
zotriazole (DCC/HOBt) or diphenylphosphoryl chloride
(DPP-Cl) as
a condensation reagent. The mixed
anhydride prepared with DPP-Cl was effective for
preparation of Boc-protected 5,5-dimethyl-1,3-thiazoli-
dine-4-carboxamides.
The inhibitors in Table 1 (8a ,b,e and 9c,d ,f-i) were
obtained as shown in Scheme 2. The 3-hydroxyl group
F igu r e 3. Design of symmetric type compounds.

SAR of Small-Sized HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10 1791
Sch em e 1a
Ta ble 1. HIV-1 Protease Inhibitory Activity of Benzoyl-Type
Compounds
structure
R2
HIV-1 protease inhibition (%)
compd
R1
R3
at 5 µM
at 50 nM
Ki (nM)
8a
8b
9c
9d
8e
9f
H
H
H
Me
H
H
H
H
H
H
H
H
52
75
76
97
81
98
92
99
99
nta
nt
nt
36
nt
46
17
88
84
nt
nt
nt
24.9
nt
22.2
nt
5.14
2.24
OH
OH
NH2 Me
OH
OH
a
Me
Conditions: (a) HCHOaq; (b) Boc2O, NaOHaq, THF; (c) DCC-
HOBt, tert-butylamine, CH2Cl2; or DPP-Cl, triethylamine, tert-
butylamine, ethyl acetate; (d) methanesulfonic acid/CH2Cl2; (e)
Boc-Apns-OH, EDC-HOBt, DMF; (f) methanesulfonic acid/CH2Cl2.
Et
Pr
9g
9h (J E-533) OH
9i
Me Me
Et Me
Sch em e 2a
OH
a
nt, not tested.
was obtained by chlorination of the corresponding
benzyl alcohol with trimethylsilyl chloride (TMS-Cl) in
the presence of dimethyl sulfoxide (DMSO),25 was
converted to 2,6-dimethylbenzylamine (16a ) by the use
of a Gabriel-type reaction. Reduction of 2,6-dimethyl-
benzamide with LiAlH4 in tetrahydrofuran (THF) under
reflux condition gave the corresponding benzyl alcohol,
not benzylamine. The synthesis of inhibitors shown in
Table 3 (21a -i) was conducted by the same method
used for the inhibitors in Table 1 (Scheme 5).
Resu lts a n d Discu ssion
SAR Stu d y on HIV-1 P r otea se In h ibition . The
compounds synthesized in this study were first tested
for HIV-1 protease inhibitory activity. HIV-1 protease
activity was determined by an HPLC method using
recombinant HIV-1 protease (NY-5) and synthetic pep-
tide H-Ser-Gln-Asn-Tyr-Pro-Ile-Val-OH as a substrate.
Table 1 shows the results of the SAR study on HIV-1
protease inhibition by the benzoyl-type compounds. The
compound 9d bearing both o-methyl group and m-
hydroxyl group of the phenyl ring at the P2 site
exhibited high HIV protease inhibitory activity (Ki )
24.9 nM). The compounds having only one of these
groups, either the methyl group (8b) or the hydroxyl
group (9c), showed weak activity. These results are
supported by the observation of Kalish et al.12 that the
methyl group provides additional binding over the
corresponding unsubstituted analogue through in-
creased hydrophobic interactions with the S2 pocket and
that the methyl group induces repulsion between the
aromatic ring and the amide carbonyl, such that the
hydroxyl group at the 3 position is oriented in a
favorable position for hydrogen-bonding interaction with
Asp30. Replacement of the o-methyl group with an ethyl
group (9f) resulted in a slightly increased enzyme
inhibitory activity, but the replacement with the bulkier
propyl group (9g) did not increase the activity. An amino
group at the R1 caused a decrease in the enzyme
inhibitory activity (8e). The amino group, a weaker
hydrogen bond donor than the hydroxyl group, is
considered to not make a good hydrogen bond with
a
Conditions: (a) EDC, HOBt, DMF; or DPP-Cl, triethylamine,
ethyl acetate; (b) NaOHaq, methanol.
on the benzoic acids was protected with an acetyl group
during the course of the coupling step and were saponi-
fied in the final stage.
Scheme 3 illustrates the procedures to synthesize the
aryloxyacetyl-type compounds shown in Table 2 (12a -
i). All phenoxyacetic acids 11a -i were obtained by the
reaction of phenols and methyl chloroacetate in the
presence of K2CO3, followed by saponification. The
coupling step for these compounds was performed by
the N-ethyl-N′-[3-(dimethylamino)propyl]carbodiimide
(EDC)-HOBt method.
The methods for synthesis of the benzylamide-type
compounds (Table 3) are shown in Schemes 4 and 5.
All commercially available benzylamines were pur-
chased. 2,6-Dimethylbenzylamine (16a ) was synthesized
according to Scheme 4. 2,6-Dimethylbenzoic acid (13)
was converted to the corresponding benzyl alcohol 14
by esterification with methyl iodide, followed by reduc-
tion with LiAlH4. 2,6-Dimethylbenzyl chloride, which

1792 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10
Mimoto et al.
Sch em e 3a
a
Conditions: (a) Cl-CH2COOMe, K2CO3, DMF; (b) NaOHaq, methanol; (c) EDC, HOBt, DMF.
Sch em e 4a
a
Conditions: (a) methyl iodide, K2CO3, DMF; (b) LiAlH4, THF; (c) trimethylsilyl chloride, DMSO; (d) potassium phthalimide, DMF; (e)
NH2NH2, ethanol, and then concd HCl.
Ta ble 2. HIV-1 Protease Inhibitory Activity of
Phenoxyacetyl-Type Compounds
Asp30. We previously found that the methyl substitu-
tion at the 5 position of the thiazolidine ring at the P1′
portion of the tripeptide inhibitors remarkably enhanced
the protease inhibitory activity (KNI-272 (2) vs KNI-
227 (1), Ki values were 0.74 and 0.088 nM, respectively).
These results prompted us to introduce methyl groups
at the thiazolidine ring of 9d or 9f. The resulting
compounds, 9h (J E-533) and 9i, containing 5,5-di-
methyl-1,3-thiazolidine-4-carbonyl (Dmt) at the P1′
position, showed more potent HIV protease inhibitory
activity, and the Ki values were 5.14 and 2.24 nM,
respectively (Table 1).
HIV-1 protease
inhibition (%)
structure
compd
R1 R2 R3 R4 R5 at 5 µM at 50 nM Ki (nM)
Table 2 presents the results of the SAR study on
phenoxyacetyl-type compounds. At first, we examined
the effect of a methyl group introduced at various
positions of the phenoxyacetyl group of compound 12a .
The substitution by the methyl group at the ortho
position (R1) enhanced the HIV protease inhibitory
activity (12b), but neither meta nor para substitution
increase the inhibitory activity (12c,d ). These data
indicated that the o-methyl group is essential for the
increase in binding affinity for the enzyme and that
there was no hydrophobic space in the meta position.
Additionally, we found that o-methyl substitution at R4
generated a potent HIV protease inhibitor having a 2,6-
dimethylphenoxyacetyl group (12e). Compounds 12f,g
having a bulkier group (ethyl or propyl) at R4 showed
slightly decreased protease inhibitory activity. Com-
pound 12h with ethyl groups at both R1 and R4 showed
12a
12b
12c
12d
12e
12f
12g
12h
H
Me
H
H
H
Me
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
Me
Et
Pr
Et
H
H
H
H
H
H
H
H
48
82
38
44
95
94
97
62
97
nta
nt
nt
nt
nt
nt
nt
21.7
nt
nt
nt
1.40
H
nt
Me
Me
Me
Et
56
32
35
nt
12i (J E-1482) Me
Me Me
96
a
nt, not tested.
little inhibitory activity. Thus the presence of a rela-
tively small hydrophobic pocket at both ortho positions
and a 2,6-dimethylphenoxyacetyl group17 provided the
best ligand of our HMC-type compounds. In the case of
the compounds of this type, the introduction of the Dmt
residue at the P1′ enhanced the enzyme inhibitory
activity, and the Ki value was 1.40 nM (12i).

SAR of Small-Sized HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10 1793
Sch em e 5a
a
Conditions: (a) EDC, HOBt, DMF; or DPP-Cl, triethylamine, ethyl acetate; (b) methanesulfonic acid/CH2Cl2; or HCl/dioxane; (c)
Boc-Apns-OH, EDC, HOBt, DMF; (d) methanesulfonic acid/CH2Cl2; or HCl/dioxane; (e) DPP-Cl, triethylamine, ethyl acetate; (f) NaOHaq
methanol.
,
Ta ble 3. HIV-1 Protease Inhibitory Activity of
Benzylamide-Type Compounds
Ta ble 4. Inhibitory Activity against HIV-1 Protease,
Anti-HIV-1 IIIB Activity, and Cellular Toxicity of HIV Protease
Inhibitors
HIV-1 protease inhibition
HIV-1 IIIB
IC50 (nM)a TC50 (µM)b
compd
Ki (nM)
9d
9h
9i
24.9
5.14
2.24
21.7
1.40
8.91
0.33
0.29
0.16
0.088
0.74
>200
19
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
>20
92
12e
12i
21c
21f (J E-2147)
21g
21i (J E-1520)
1 (KNI-227)
2 (KNI-272)
>200
>200
>200
7
HIV-1 protease
inhibition (%)
structure
34
11
6
34
compd
R1 R2 R3 R4 R5 R6 at 50 nM Ki (nM)
21a
21c
21d
21e
21a
H
Me
H
H
Me
H
H
Me
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
43
70
18
13
75
96
95
88
97
59
8.9
nta
nt
4.8
0.33
0.29
nt
a
Antiviral activities were determined based on the HIV-1 IIIB-
induced cytopathic effects evaluated by the use of the tetrazolium
reagent as described in the Experimental Section. Each value
21f (J E-2147) Me
21g
21h
Me Me
Me Me
Me Me
Me Et
b
represents the mean of duplicate determinations. The value
shown is the 50% toxic concentration of the test compound.
Cl
CF3
21i (J E-1520) Me
0.19
the phenyl ring provided a compound more potent than
the corresponding unsubstituted analogue 21c (Ki ) 8.9
nM). On the other hand, the m- or p-methyl substituent
at the phenyl ring unexpectedly resulted in decreased
inhibitory activity (21d ,e). Furthermore, compound 21a
having an additional o-methyl substituent, i.e., the 2,6-
dimethylbenzyl group, showed only slightly improved
potency. These results were almost the same as in the
case of the P2 phenoxyacetyl group. However, the
increase in potency of benzylamide (P2′)-type com-
pounds upon introduction of Dmt at the P1′ site (27-
fold increase in comparison with 21c,f, in Table 3) was
easily unexpected base on the results of SAR of tert-
a
nt, not tested.
Table 3 shows the results of our SAR study on the
benzylamide (P2′)-type compounds. Although the com-
pounds bearing the 2,6-dimethylphenoxyacetyl group
exerted a potent HIV protease inhibitory activity (Table
2), this activity was not translated into an anti-HIV
activity, as described later (Table 4, 12i). Therefore
benzyl groups were introduced into the benzoyl-type
compounds. Compound 21b, bearing an unsubstituted
benzyl group at the P2′ site, showed HIV-1 protease
inhibitory activity comparable to that of the tert-butyl
compound (9d ). Substitution by an o-methyl group at

1794 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10
Mimoto et al.
Ta ble 5. Pharmacokinetic Profiles of HIV Protease Inhibitors
after Intravenous or Intraduodenal Administration in Ratsa
iv injection
id administration
compd
t
1/2â (min) Cmax (µM) Tmax (min)
F (%)
9d
9h
9f
9i
21c
59
83
74
84
41
2.91 ( 0.21
2.60 ( 0.85
1.73 ( 0.04
1.16 ( 0.18
0.77 ( 0.07
0.70 ( 0.20
0.23 ( 0.09
30
30
30
30
30
60
10
33.9 ( 3.4
39.4 ( 16.1
36.2 ( 1.2
37.0 ( 2.8
32.3 ( 10.0
41.6 ( 10.7
10.0 ( 1.0
21f (J E-2147)
21i (J E-1520)
93
126
a
The values represent the mean ( standard error of the mean
for three rats. F (%) was determined by comparing the mean areas
under the curves (AUC) after intravenous and intraduodenal
doses. t1/2â, plasma half-life; Cmax, maximum plasma concentration;
T
max, time of maximum plasma concentration; F (%), percent
bioavailability.
F igu r e 4. Plasma concentrations of J E-2147 after dosing at
25 mg/kg by intravenous or oral administration to dogs. J E-
2147 was formulated in 50% PEG. The plasma concentration
was measured by the HPLC method as described in the
Experimental Section. Each point represents the mean ( SE
of six dogs: b, iv injection; O, po administration (fed); 4, po
administration (fasted 16 h).
butylamide (P2′)-type compounds (5-fold increase in
potency in comparison with 9d ,h , in Table 1). Introduc-
tion of a Dmt residue at the P1′ site resulted in the
highly potent protease inhibitor 21f (J E-2147), which
had Ki ) 0.33 nM. The two methyl substituents of the
thiazolidine ring presumably oriented the benzyl group
to a more favorable position for interacting with the
protease. Although replacement of the methyl group
with chlorine (21g) had no effect on the activity,
replacement with the bulkier CF3 group (21h ) decreased
the activity.
An tivir a l Activity. Antiviral activity for selected
analogues in Tables 1-3 was determined in cell culture
against HIV-1 strain IIIB in CEM-SS cells (Table 4).
The compounds containing a Dmt residue at the P1′ site,
except for 12i, showed potent antiviral activity with IC50
values below 100 nM, and their 50% toxic concentrations
were more than 20 µM. Especially, benzylamide-type
compounds 21f (J E-2147) and 21i (J E-1520), which had
low Ki values, showed a highly potent activity equal to
that of the tripeptide compounds KNI-227 (1) and KNI-
272 (2). Although the compounds bearing the 2,6-
dimethylphenoxyacetyl group (12e,i) showed potent
HIV-1 protease inhibitory activity equal to that of the
benzoyl-type compounds, this action did not translate
into anti-HIV activity in CEM-SS cells. The discrepancy
between protease inhibitory activity and antiviral effect
has not yet been clarified.
solution (10 mg/kg). The 2-methyl-3-hydroxybenzoyl-
type compounds maintained higher maximum plasma
concentration (Cmax) than the 2-ethyl-3-hydroxybenzyl-
type compounds (9d vs 9f, 9h vs 9i, and 21f vs 21i).
The tert-butylcarboxamide-type compounds were ab-
sorbed more quickly than the benzylcarboxamide ones.
The slow absorption of the benzylcarboxamide-type
compound (e.g., 21f) contributed to the maintenance of
the plasma level for a long period after id administra-
tion. Unfortunately, compound 21i, which had excellent
antiviral potency and a long plasma half-life, did not
show an acceptable plasma concentration by id admin-
istration of this formulation. In the pharmacokinetic
study in dogs (Table 6 and Figure 4), the experiment
confirmed that 21f (J E-2147) had a favorable pharma-
cokinetic profile. J E-2147 showed an elimination half-
life with 94 min after iv administration, and the oral
bioavailability was estimated to be 33% and 37% in the
nonfasting and fasting conditions, respectively. The
maximum plasma concentration achieved was 4.02-
5.30 µM when J E-2147 was orally administered at a
dose of 25 mg/kg to dogs (Table 6). In addition, a single
oral dose (25 mg/kg) of J E-2147 exhibited plasma levels
exceeding the in vitro antiviral IC95 (52 nM) for more
than 12 h in dogs (Figure 4). Additional antiviral testing
demonstrated that J E-2147 was effective against the
replication of HIV-1 IIIB in various cells (T cell, B cell,
macrophage, and PBMC) with IC50 values ranging from
31 to 160 nM and also had antiviral activity against
simian immunodefidiency virus and HIV-2 as effective
as that of other HIV protease inhibitors and reverse
transcriptase inhibitors.26 Moreover, the resistance
P h a r m a cok in etics. A representative set of com-
pounds (9d -21i) was examined for pharmacokinetics
in rats, and the results are summarized in Table 5. After
intravenous (iv) administration (10 mg/kg), the elimina-
tion half-life of these compounds ranged from 41 to 126
min, which was more than 3 times longer than that of
KNI-272. The plasma levels of these compounds, except
compound 21i, reached 0.70-2.91 µM, and the bioavail-
ability was over 30% when intraduodenally (id) admin-
istered to rats as a 50% poly(ethylene glycol) (PEG)
Ta ble 6. Oral Pharmacokinetics of J E-2147 in Dogs under Various Feeding Conditionsa
feeding
dose
AUC
F
Cmax
Tmax
CL
Vdss
condition
route
(mg/kg)
(µM‚min)
(%)
(µM)
(min)
t
1/2â (min)
94
(L/h/kg)
(L/kg)
iv
po
po
25
25
25
3095
1009
1149
0.88 ( 0.09
1.58
fed
32.6 ( 0.06
37.1 ( 0.08
4.02 ( 0.72
5.30 ( 1.13
90
60
fastedb
a
b
The values represent the mean ( standard error of the mean for six dogs. The animals were fasted overnight. F (%) was determined
by comparing the mean areas under the curves (AUC) after intravenous and oral doses. CL, plasma clearance rate; Vdss, volume of
distribution; t1/2â, plasma half-life; Cmax, maximum plasma concentration; Tmax, time of maximum plasma concentration; F (%), percent
bioavailability via oral route.

SAR of Small-Sized HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10 1795
compound and HIV-1 IIIB for 6 days at 37 °C in a 5% CO2
incubator. The virus was added to each well as a titer sufficient
to give complete cell killing at 6 days postinfection. After
incubation, HIV IIIB-induced cytopathic effects were analyzed
by staining with the tetrazolium dye XTT.29 The antiviral
activity and cytotoxicity of a given compound are expressed
as 50% inhibitory concentration (IC50) and 50% toxic concen-
tration (TC50), respectively.
P h a r m a cok in etics. Pharmacokinetic parameters of the
protease inhibitors were studied in rats and dogs. In the rat
iv or id administration studies, three male Sprague-Dawley
rats (300-400 g) received the compound at 10 mg/kg in 50%
PEG (1 mL/kg) under anesthesia in combination with Ketaral
(Sankyo Co., Ltd, Tokyo)/Selactal (Bayer AG, Germany). The
iv administration was made via a femoral vein. In the id dosing
study, rats were incised subphrenically for ca. 3 cm along the
abdominal median line, a poly(ethylene) tube (Intramedic,
PE10) was inserted into duodenum, and then the test solution
was injected into the duodenum through the tube.
The pharmacokinetic behavior of J E-2147 in beagle dogs
was evaluated following a single oral or iv dose. Eighteen male
beagle dogs (7-10 kg; HRP, Inc., Cumberland, MD) were
randomly assigned to one of three groups, with each group
containing six animals. J E-2147 was administered intrave-
nously as a bolus via the cephalic vein at a dose of 25 mg/kg
(2 mL/kg) and orally by gavage at a dose of 25 mg/kg (5 mL/
kg). J E-2147 was prepared as a 12.5 mg/mL solution in a 50%
PEG-in-water vehicle.
In all of the animal studies, heparinized blood samples (0.5
mL) were obtained after dosing at appropriate times, and
plasma (0.2 mL) was obtained by immediate centrifugation
and kept frozen (-80 °C) until analyzed.
Sa m p le An a lysis. A plasma aliquot (0.2 mL) was combined
with 4 mL of tert-butylmethyl ester containing an appropriate
internal standard (0.5 mg/mL KNI-748, (R)-N-tert-butyl-3-
[(2S,3S)-3-(4-carbamoyl-2,6-dimethylphenoxyacetyl)amino-2-
hydroxy-4-phenylbutanoyl]-1,3-thiazolidine-4-carboxamide).
Samples were vortexed vigorously for 10 s and shakened for 1
h at room temperature followed by centrifugation at 2500g for
15 min at 4 °C. The organic layer (3.6 mL) was evaporated to
dryness at 40 °C, and then samples were reconstituted in 0.3
mL of 50% methanol with vortexing. The analytical method
for the quantification of J E-2147 in dog plasma samples was
similar to that described above.
The parent inhibitors and a respective internal standard
were separated from plasma contaminants on a Capcellpak
C18 column (4.6 × 150 mm; Shiseido Ltd., Tokyo). The elution
condition was a linear gradient of 45-60% acetonitrile in 0.1%
TFA for 12 min at a flow rate of 1.0 mL/min with UV detection
at 210 nm. The drug concentration in each plasma sample was
calculated by the internal standard method. Standard plasma
samples spiked with specified amounts of each compound were
analyzed, and the calibration curve was prepared by plotting
the concentration of test compound and its ratio to the internal
standard.
The assays for each inhibitor were linear (correlation
coefficients, >0.999) over the concentration range of 0-10 µg/
mL, and the detection limit of quantification was 0.01 µg/mL.
P h a r m a cok in etic An a lysis. Pharmacokinetic parameters
for inhibitors were estimated by a noncompartmental method.
Maximum plasma concentration (Cmax), and time of maximum
plasma concentration (Tmax) were determined by inspection of
individual subject concentration-time curves, and the mean
area under the plasma concentration-time curve (AUC) was
determined by the linear trapezoidal rule. The apparent
plasma half-life (t1/2â) was estimated from the slope of the
terminal phase fitted to the log plasma concentration-time
data by the method of least squares. The apparent distribution
volume (Vdss) of the inhibitor was determined by eq 2:
profile of J E-2147 was different from that of other HIV
protease inhibitors that have been approved for market-
ing.26,27
Con clu sion
In summary, we designed and synthesized a series
of novel dipeptide HIV protease inhibitors containing
Apns-Thz based on the transition-state isostere concept.
From our SAR study on HIV protease inhibition by
three different types of compounds, a combination of
Dmt (P1′) and benzylamide group (P2′) led to an
increase in the inhibitory activity of HMC-type com-
pounds. Among them, 21f (J E-2147) and 21i (J E-1520)
were highly potent inhibitors of HIV-1 protease with Ki
values of 0.16-0.33 nM and also exerted a potent
antiviral activity against HIV-1 IIIB-infected CEM cells
with IC50 values ranging from 7 to 11 nM. Furthermore,
the additional evidence of the pharmacokinetic profiles
of these compounds indicated that 21f (J E-2147) is an
orally available and thus favorable HIV protease inhibi-
tor.
Exp er im en ta l Section
HIV P r otea se In h ibition . HIV protease substrate (SQNY-
PIV) was synthesized by solid-phase methods using an Applied
Biosystems model 430A. Recombinant HIV-1 protease (NY5-
type sequence) was expressed in Escherichia coli and purified
to a single band on sodium dodecyl sulfate-polyacrylamide
gel electrophpresis.
In the inhibition assay, 25 µL of 200 mM 2-(N-morpholino-
)ethanesulfonic acid (MES)-NaOH buffer, pH 6.0, containing
2 mM dithiothreitol (DTT) and 2 mM EDTA-2Na was mixed
with 5 µL of inhibitor (50 nM or 0.5 µM) dissolved in DMSO
and 10 µL of titrated HIV-1 protease (10.5 nM) in 50 mM
MES-NaOH, pH 6.0, containing 2.5 mM DTT, 1 mM EDTA-
2Na, 0.2% Nonidet P-40, and 15% glycerol. The mixture of
protease and inhibitor was preincubated for 5 min at 37 °C,
and the enzymic reaction was initiated by addition of 10 µL of
a 75 mM substrate solution in the above-described assay
buffer. After incubation for 60 min at 37 °C, the reaction was
terminated by addition of 75 µL of 4% trifluoroacetic acid
(TFA), and the C-terminal cleavage fragment (PIV) was
separated by reverse-phase HPLC on a C18 column with linear
gradient of water to acetonitrile (both solutions containing
0.1% TFA), detected by absorbance at 215 nm, and quantified
by comparison with a synthetic product standard.
For some highly potent inhibitors, their Ki values were
analyzed by a mathematical model for tight-binding inhibi-
tors,28 in which the concentration of inhibitor is less than or
approximately equal to the enzyme concentration. The initial
velocity data of HIV protease in the presence of various
inhibitor concentrations were fitted by nonlinear regression
analysis to eq 1 with KaleidaGraph (Version 3.08d) for
Macintosh, where V is the initial velocity with an inhibitor,
V0 is the measured initial velocity in the absence of the
inhibitor, the substrate Km is estimated to be 21.4 mM, and
S, Et, and It are the concentrations of substrate, active enzyme,
and inhibitor, respectively.
V0
2
1/2
S
Km
S
Km
V )
Ki 1 +
+ It - Et + 4Ki 1 +
Et
-
({
(
)
(
) }
[
]
2Et
S
Km
Ki 1 +
+ It - Et
(1)
(
)
)
]
[
An tivir a l Activity. Antiviral activity of test compounds
was determined based on inhibition of HIV-1 IIIB-induced
cytopathic effects in CEM-SS cells in vitro. The CEM-SS cells
(2.5 × 104 cells/mL) were incubated in a total volume of 200
µL of tissue culture medium (RPMI-1640 medium plus 10%
fetal calf serum with 50 µg of gentamicin/mL) containing test
Vdss ) dose iv × AUMC(0-∞)/AUC iv(0-∞)
(2)
where AUMC(0-∞) is the total area under the first moment
of the drug concentration curve from zero to infinity. The

1796 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10
Mimoto et al.
plasma clearance (CL) was calculated as the dose divided by
product by silica gel column chromatography (CH2Cl2/metha-
∞
the AUC from zero to infinity, [AUC]0
.
nol), and reprecipitation from n-hexane/ethyl acetate gave 296
1
mg of the title compound, yield 63%: mp 85-87 °C; H NMR
Ch em istr y. In general, reagents and solvents were used
as purchased without further purification. Column chroma-
tography was performed on Wakogel C-200 (Wako, 70-150
µm) or Wakogel C-300 (Wako, 45-75 µm). Melting points were
measured with a Yanagimoto melting point apparatus and are
uncorrected. Proton and carbon NMR spectra were recorded
on a J EOL GSX270 FT NMR spectrometer. Chemical shifts
are expressed in δ (ppm) from the internal standard tetram-
ethylsilane. TOFMS were recorded on a Kompact MALDI III
spectrometer. Elemental analyses were performed by the
Toray Research Center and are within 0.4% of the calculated
values unless otherwise noted.
Abbr evia tion s: Boc, tert-butoxycarbonyl; Thz, (R)-1,3-
thiazolidine-4-carbonyl; HOBt, 1-hydroxybenzotriazole; DCC,
N,N′-dicyclohexylcarbodiimide; TOFMS, time-of-flight mass
spectrometry; DMF, N,N-dimethylformamide; Apns, (2S,3S)-
3-amino-2-hydroxy-4-phenylbutanoyl; EDC, N-ethyl-N′-[3-
(dimethylamino)propyl]carbodiimide; tBu, tert-butyl; DPP-Cl,
diphenylphosphoryl chloride; HOSu, N-hydroxysuccinimide;
THF, tetrahydrofuran; Dmt, (R)-5,5-dimethyl-1,3-thiazolidine-
4-carbonyl; DMSO, dimethyl sulfoxide; TMS-Cl, trimethylsilyl
chloride.
(R)-N-ter t-Bu tyl-1,3-th ia zolid in e-4-ca r boxa m id e (5a ).
To a solution of Boc-Thz-OH (11.65 g, 50 mmol) and HOBt
(6.75 g, 50 mmol) in CH2Cl2 (80 mL) was added DCC (11.33 g,
55 mmol) in an ice-bath. After 30 min, tert-butylamine (13.75
mL, 150 mmol) in CH2Cl2 (60 mL) was dropped to the reaction
mixture and stirred overnight. The reaction mixture was
washed with 3% K2CO3, 1 N HCl, and brine, dried over MgSO4,
and then evaporated. The residue was redissolved in CH2Cl2
(125 mL), and 4 N HCl in dioxane (125 mL) was added and
stirred for 2 h. The reaction mixture was concentrated, and
then the residue was dissolved in H2O and filtrated. The
filtrate was washed with CH2Cl2, adjusted to pH 8 with K2CO3,
and extracted with CH2Cl2. After drying and concentrating,
the obtained solid was recrystallized from n-hexane/toluene
to give 7.87 g of the title compound, yield 84%: mp 63-65 °C;
1H NMR (DMSO-d6) δ 1.26 (s, 9H), 2.75-2.82 (m, 1H), 2.91-
2.98 (m, 1H), 3.10-3.21 (m, 1H), 3.62-3.71 (m, 1H), 4.01 (t,
1H, J ) 9.7 Hz), 4.14 (t, 1H, J ) 8.8 Hz), 7.56 (s, 1H); MS
(TOF) m/z ) 189 (M+ + H). Anal. (C8H16N2OS) C, H, N.
(R )-N -t er t -B u t y l-3-[(2S ,3S )-3-a m in o -2-h y d r o x y -4-
p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r boxa m id e (6a ). To
a solution of 5a (1.05 g, 5.59 mmol) in DMF (10 mL) were
added Boc-Apns-OH (1.50 g, 5.09 mmol), HOBt (0.69 g, 5.09
mmol), and EDC•HCl (1.07 g, 5.60 mmol), and the mixture
was stirred overnight. To the reaction mixture were added
CH2Cl2 and 1 N HCl, and then the organic layer was washed
with 3% K2CO3 and brine, dried over MgSO4, and evaporated
to give Boc-Apns-Thz-NHtBu. To the solution of Boc-Apns-Thz-
NHtBu in CH2Cl2 (13 mL) was added 4 N HCl in dioxane (13
mL), and the mixture was stirred for 2 h. The reaction mixture
was concentrated, and then the residue was dissolved in H2O,
washed with CH2Cl2, and adjusted to pH 8 with K2CO3, to give
a solid. The obtained solid was washed with hot methanol to
give 1.57 g of the title compound, yield 85%: mp 208-210 °C;
1H NMR (DMSO-d6) δ 1.19 (s, 9H), 1.40 (br, 2H), 2.31-2.40
(m, 1H), 2.90 (t, 1H, J ) 8.1 Hz), 3.01-3.07 (m, 2H), 3.16-
3.26 (m, 1H), 4.11 (t, 1H, J ) 7.6 Hz), 4.60 (d, 1H, J ) 8.9
Hz), 4.77-4.82 (m, 1H), 4.89 (d, 1H, J ) 8.6 Hz), 5.20 (d, 1H,
J ) 7.8 Hz), 7.16-7.31 (m, 5H), 7.57 (s, 1H); MS (TOF) m/z )
366 (M+ + H). Anal. (C18H27N3O3S) C, H, N.
(DMSO-d6) δ 1.26 (s, 9H), 2.72-2.76 (m, 1H), 2.85-2.94 (m,
1H), 2.99-3.05 (m, 1H), 3.31-3.38 (m, 1H), 4.31-4.38 (m, 1H),
4.60-4.64 (m, 1H), 4.73-4.82 (m, 2H), 5.08 (d, 1H, J ) 9.2
Hz), 5.22 (d, 1H, J ) 6.8 Hz), 7.08-7.14 (m, 1H), 7.22 (t, 2H,
J ) 7.3 Hz), 7.40-7.53 (m, 5H), 7.70 (s, 1H), 7.81 (d, 1H, J )
7.0 Hz), 8.54 (d, 1H, J ) 7.8 Hz); MS (TOF) m/z ) 470 (M+
H). Anal. (C25H31N3O4S) C, H, N.
+
(R)-N-ter t-Bu tyl-3-[(2S,3S)-2-h yd r oxy-3-(2-m eth ylben -
zoyl)a m in o-4-p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r box-
a m id e (8b). Compound 8b was prepared from 2-methylben-
zoic acid and compound 6a in a manner similar to that
described for compound 8a , yield 61%: mp 90-92 °C; 1H NMR
(DMSO-d6) δ 1.25 (s, 9H), 2.05 (s, 3H), 2.7-2.9 (m, 2H), 2.98-
3.05 (m, 1H), 3.28-3.33 (m, 1H), 4.3-4.5 (br, 1H), 4.55-4.65
(m, 1H), 4.7-4.9 (m, 2H), 5.06 (d, 1H, J ) 9.4 Hz), 5.27 (d,
1H, J ) 7.3 Hz), 7.14-7.27 (m, 7H), 7.40 (d, 2H, J ) 6.8 Hz),
7.66 (s, 1H), 8.33 (d, 1H, J ) 8.9 Hz); MS (TOF) m/z ) 484
(M+ + H). Anal. (C26H33N3O4S•0.25EtOAc) C, H, N.
(R)-N-ter t-Bu tyl-3-[(2S,3S)-2-h yd r oxy-3-(3-h yd r oxyben -
zoyl)a m in o-4-p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r box-
a m id e (9c). To a solution of 3-acetoxybenzoic acid (180 mg,
1.1 mmol) and triethylamine (167 µL, 1.2 mmol) in ethyl
acetate (3 mL) was added DPP-Cl (228 µL, 1.1 mmol) in an
ice-bath, and the mixture was stirred for 1 h. Then to the
reaction mixture, compound 6a (365 mg, 1.00 mmol) and
triethylamine (209 µL, 1.5 mmol) were added in an ice-bath
and stirred overnight. The reaction mixture was washed
sequentially with 1 N HCl, 3% K2CO3, and brine and concen-
trated. To the solution of the resulting residue in methanol (5
mL), was added 1 N NaOH (1.5 mL, 1.5 mmol), and the
mixture was stirred for 1 h. The mixture was acidified with 1
N HCl, and the aqueous phase was extracted with ethyl
acetate. The organic extract was washed sequentially with 1
N HCl, 3% K2CO3, and brine, dried over MgSO4, filtered, and
concentrated. Purification of the crude product by silica gel
column chromatography (CH2Cl2/methanol) and reprecipita-
tion from n-hexane/ethyl acetate gave 321 mg of the title
1
compound, yield 66%: mp 115-118 °C; H NMR (DMSO-d6)
δ 1.25 (s, 9H), 2.7-2.8 (m, 1H), 2.84-2.93 (m, 1H), 2.98-3.05
(m, 1H), 3.30-3.37 (m, 1H), 4.2-4.4 (br, 1H), 4.57-4.60 (m,
1H), 4.71-4.81 (m, 2H), 5.07 (d, 1H, J ) 9.2 Hz), 5.20 (d, 1H,
J ) 7.0 Hz), 6.86-6.90 (m, 1H), 7.09-7.23 (m, 6H), 7.44 (d,
2H, J ) 7.3 Hz), 7.68 (s, 1H), 8.42 (d, 1H, J ) 8.4 Hz), 9.60 (s,
1H); MS (TOF) m/z ) 486 (M+ + H). Anal. (C25H31N3O5S) C,
H, N.
(R)-N-ter t-Bu t yl-3-[(2S,3S)-2-h yd r oxy-3-(3-h yd r oxy-2-
m eth ylben zoyl)am in o-4-ph en ylbu tan oyl]-1,3-th iazolidin e-
4-ca r boxa m id e (9d ). Compound 9d was prepared from
3-acetoxy-2-methylbenzoic acid and compound 6a in a manner
similar to that described for compound 9c, yield 76%: mp 220-
1
223 °C; H NMR (DMSO-d6) δ 1.26 (s, 9H), 1.82 (s, 3H), 2.74
(m, 2H), 3.02 (m, 1H), 3.32 (m, 1H), 4.35 (bs, 1H), 4.58 (bs,
1H), 4.78 (m, 2H), 5.09 (d, 1H), 5.21 (d, 1H), 6.56 (d, 1H), 6.77
(d, 1H), 6.94 (t, 1H), 7.15 (t, 1H), 7.23 (t, 2H), 7.38 (d, 2H),
7.64 (s, 1H), 8.22 (d, 1H), 9.38 (s, 1H); MS (TOF) m/z ) 500
(M+ + H). Anal. (C26H33N3O5S•0.25 H2O) C, H, N.
(R)-N-ter t-Bu t yl-3-[(2S,3S)-3-(3-a m in o-2-m et h ylb en z-
oyl)am in o-2-h ydr oxy-4-ph en ylbu tan oyl]-1,3-th iazolidin e-4-
ca r boxa m id e (8e). Compound 8e was prepared from 3-amino-
2-methylbenzoic acid and compound 6a in a manner similar
to that described for compound 8a , yield 31%: mp 114-117
(R)-N-ter t-Bu tyl-3-[(2S,3S)-ben zoyla m in o-2-h yd r oxy-4-
p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r boxa m id e (8a ). To
a solution of compound 6a (365 mg, 1.00 mmol), benzoic acid
(122 mg, 1.00 mmol), and HOBt•H2O (153 mg, 1.00 mmol) in
DMF (3 mL) was added EDC•HCl (191 mg, 1.00 mmol) in an
ice-bath, and the mixture was stirred overnight. The reaction
mixture was concentrated under reduced pressure and then
redissolved in ethyl acetate. The organic layer was washed
sequentially with 3% K2CO3, 1 N HCl, and brine, dried over
MgSO4, filtered, and concentrated. Purification of the crude
1
°C; H NMR (DMSO-d6) δ 1.26 (s, 9H), 1.72 (s, 3H), 2.7-2.8
(m, 2H), 2.98-3.05 (m, 1H), 3.28-3.33 (m, 1H), 4.3-4.4 (m,
1H), 4.5-4.6 (m, 1H), 4.7-4.9 (m, 4H), 5.05 (d, 1H, J ) 9.2
Hz), 5.19 (d, 1H, J ) 7.3 Hz), 6.33 (d, 1H, J ) 7.6 Hz), 6.60 (d,
1H, J ) 7.3 Hz), 6.84 (t, 1H, J ) 7.8 Hz), 7.16-7.26 (m, 3H),
7.39 (d, 1H, J ) 6.8 Hz), 7.66 (s, 1H), 8.16 (d, 1H, J ) 8.1 Hz);
MS (TOF) m/z ) 499 (M+ + H). Anal. (C26H34N4O4S•0.5 H2O)
Calcd: C, 61.51; H, 6.95; N, 11.04. Found: C, 61.00; H, 6.96;
N, 10.74.

SAR of Small-Sized HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10 1797
(R)-N-ter t-Bu t yl-3-[(2S,3S)-3-(2-et h yl-3-h yd r oxyb en z-
oyl)am in o-2-h ydr oxy-4-ph en ylbu tan oyl]-1,3-th iazolidin e-4-
ca r boxa m id e (9f). Compound 9f was prepared from 3-ac-
etoxy-2-ethylbenzoic acid and compound 6a in a manner
similar to that described for compound 9c, yield 62%: mp 216-
218 °C; 1H NMR (DMSO-d6) δ 0.85 (t, 3H, J ) 7.5 Hz), 1.25 (s,
9H), 2.35 (m, 2H), 2.74 (m, 2H), 3.00 (m, 1H), 3.2-3.4 (m, 1H),
4.35 (bs, 1H), 4.55 (bs, 1H), 4.77 (m, 2H), 5.05 (d, 1H, J ) 9.3
Hz), 5.25 (d, 1H, J ) 7.1 Hz), 6.55 (d, 1H, J ) 7.1 Hz), 6.78 (d,
1H, J ) 8.6 Hz), 6.94 (dd, 1H, J ) 7.9 Hz, 7.9 Hz), 7.18 (d, 1H,
J ) 6.6 Hz), 7.22 (t, 2H, J ) 7.1 Hz), 7.38 (d, 2H, J ) 7.5 Hz),
7.63 (s, 1H), 8.21 (d, 1H, J ) 7.9 Hz), 9.31 (s, 1H); MS (TOF)
m/z ) 514 (M+ + H). Anal. (C27H35N3O5S•0.25 H2O) C, H, N.
6b in a manner similar to that described for compound 9c,
yield 67%: mp 203-205 °C; 1H NMR (DMSO-d6) δ 1.27 (s, 9H),
1.40 (s, 3H), 1.49 (s, 3H), 1.80 (s, 3H), 2.75 (m, 2H), 3.2-3.4
(m, 1H), 4.35 (bs, 1H), 4.52 (bs and s, 2H), 4.98 (d, 1H), 5.18
(d, 1H), 5.27 (d, 1H), 6.55 (d, 1H), 6.76 (d, 1H), 6.94 (t, 1H),
7.13 (t, 1H), 7.23 (t, 2H), 7.36 (d, 2H), 7.63 (s, 1H), 8.22 (d,
1H), 9.36 (s, 1H); MS (TOF) m/z ) 528 (M+ + H). Anal.
(C28H37N3O5S) C, H, N.
(R)-N-ter t-Bu t yl-3-[(2S,3S)-3-(2-et h yl-3-h yd r oxyb en z-
oyl)am in o-2-h ydr oxy-4-ph en ylbu tan oyl]-5,5-dim eth yl-1,3-
th ia zolid in e-4-ca r boxa m id e (9i). Compound 9i was pre-
pared from 3-acetoxy-2-ethylbenzoic acid and compound 6b in
a manner similar to that described for compound 9c, yield
88%: mp 144-146 °C; 1H NMR (DMSO-d6) δ 0.84 (t, 3H, J )
7.3 Hz), 1.27 (s, 9H), 1.41 (s, 3H), 1.49 (s, 3H), 2.3-2.6 (m,
2H), 2.7-2.9 (m, 2H), 4.3-4.4 (m, 1H), 4.53 (s, 2H), 4.97 (d,
1H, J ) 8.9 Hz), 5.17 (d, 1H, J ) 8.6 Hz), 5.26 (d, 1H, J ) 7.0
Hz), 6.55 (d, 1H, J ) 7.8 Hz), 6.78 (d, 1H, J ) 7.8 Hz), 6.95 (t,
1H, J ) 7.6 Hz), 7.16-7.26 (m, 3H), 7.39 (d, 1H, J ) 6.8 Hz),
7.64 (s, 1H), 8.22 (d, 1H, J ) 8.9 Hz), 9.33 (s, 1H); MS (TOF)
m/z ) 542 (M+ + H). Anal. (C29H39N3O5S) C, H, N.
(R )-N -t er t -Bu t yl-3-[(2S ,3S )-2-h yd r oxy-3-(p h e n oxy-
a c e t y l)a m in o -4-p h e n y lb u t a n o y l]-1,3-t h ia zo lid in e -4-
ca r boxa m id e (12a ). To a solution of compound 6a (365 mg,
1.00 mmol), phenoxyacetic acid (167 mg, 1.10 mmol), and
HOBt•H2O (153 mg, 1.00 mmol) in DMF (3 mL) was added
EDC•HCl (210 mg, 1.10 mmol) in an ice bath, and the mixture
was stirred overnight. The reaction mixture was concentrated
under reduced pressure and then redissolved in ethyl acetate.
The organic layer was washed sequentially with 3% K2CO3, 1
N HCl, and brine, dried over MgSO4, filtered, and concen-
trated. Purification of the crude product by silica gel column
chromatography (CH2Cl2/methanol) and reprecipitation from
n-hexane/ethyl acetate gave 300 mg of the title compound,
yield 60%: mp 68-69 °C; 1H NMR (DMSO-d6) δ 1.26 (s, 9H),
2.6-2.8 (m, 2H), 2.95-3.02 (m, 1H), 3.29-3.36 (m, 1H), 4.1-
4.3 (m, 1H), 4.39 (s, 2H), 4.48-4.52 (m, 1H), 4.62 (d, 1H, J )
9.2 Hz), 4.77 (t, 1H, J ) 7.2 Hz), 4.96 (d, 1H, J ) 9.2 Hz), 5.29
(d, 1H, J ) 6.8 Hz), 6.77 (d, 2H, J ) 8.4 Hz), 6.93 (t, 1H, J )
7.4 Hz), 7.17-7.25 (m, 5H), 7.34 (d, 2H, J ) 6.8 Hz), 7.70 (s,
1H), 8.24 (d, 1H, J ) 8.4 Hz); MS (TOF) m/z ) 500 (M+ + H).
Anal. (C26H33N3O5S) C, H, N.
(R )-N -t er t -Bu t yl-3-[(2S ,3S )-2-h yd r oxy-3-(2-m e t h yl-
phenoxyacetyl)amino-4-phenylbutanoyl]-1,3-thiazolidine-4-
ca r boxa m id e (12b). Compound 12b was prepared from
2-methylphenoxyacetic acid and compound 6a in a manner
similar to that described for compound 12a , yield 39%: mp
69-72 °C; 1H NMR (DMSO-d6) δ 1.26 (s, 9H), 2.19 (s, 3H),
2.6-2.8 (m, 2H), 2.96-3.02 (m, 1H), 3.29-3.36 (m, 1H), 4.1-
4.3 (m, 1H), 4.41 (d, 2H, J ) 5.9 Hz), 4.47-4.51 (m, 1H), 4.60
(d, 1H, J ) 9.5 Hz), 4.76 (t, 1H, J ) 7.0 Hz), 4.96 (d, 1H, J )
9.2 Hz), 5.33 (d, 1H, J ) 7.0 Hz), 6.58 (d, 1H, J ) 7.8 Hz),
6.83 (t, 1H, J ) 7.3 Hz), 6.99-7.02 (m, 1H), 7.12-7.26 (m, 4H),
7.34 (d, 2H, J ) 7.0 Hz), 7.70 (s, 1H), 8.17 (d, 1H, J ) 8.4 Hz);
MS (TOF) m/z ) 514 (M+ + H). Anal. (C27H35N3O5S) C, H, N.
(R)-N-ter t-Bu tyl-3-[(2S,3S)- 2-h yd r oxy-3-(3-h yd r oxy-2-
pr opylben zoyl)am in o-4-ph en ylbu tan oyl]-1,3-th iazolidin e-
4-ca r boxa m id e (9g). Compound 9g was prepared from
3-acetoxy-2-propylbenzoic acid and compound 6a in a manner
similar to that described for compound 9c, yield 25%: mp 205-
1
207 °C; H NMR (DMSO-d6) δ 0.69 (t, 3H, J ) 7.0 Hz), 1.2-
1.4 (br, 2H), 1.26 (s, 9H), 2.2-2.3 (m, 1H), 2.3-2.4 (m, 1H),
2.7-2.8 (m, 1H), 3.0-3.1 (m, 1H), 3.28-3.34 (m, 1H), 4.2-4.4
(m, 1H), 4.5-4.6 (m, 1H), 4.75-4.82 (m, 2H), 5.02 (d, 1H, J )
9.4 Hz), 5.18 (d, 1H, J ) 7.3 Hz), 6.57 (d, 1H, J ) 7.3 Hz),
6.78 (d, 1H, J ) 7.5 Hz), 6.96 (t, 1H, J ) 7.7 Hz), 7.15-7.26
(m, 3H), 7.40 (d, 1H, J ) 7.3 Hz), 7.66 (s, 1H), 8.23 (d, 1H, J
) 8.4 Hz), 9.29 (s, 1H); MS (TOF) m/z ) 528 (M+ + H). Anal.
(C28H37N3O5S•0.5H2O) C, H, N.
(R)-N-ter t-Bu t yl-5,5-d im et h yl-1,3-t h ia zolid in e-4-ca r -
boxa m id e (5b). To a solution of Boc-Dmt-OH (15.0 g, 58.37
mmol) and HOSu (7.38 g, 64.21 mmol) in THF (50 mL) was
added DCC (13.23 g, 64.21 mmol) in THF (50 mL) in an ice-
bath. After 60 min, tert-butylamine (30.64 mL, 291.85 mmol)
in THF (100 mL) was dropped into the reaction mixture and
stirred overnight. The reaction mixture was filtered, and the
filtrate was evaporated. The residue was redissolved in ethyl
acetate, washed with 5% citric acid, 3% K2CO3, and brine, dried
over MgSO4, and evaporated. The residue was redissolved in
CH2Cl2 (146 mL); 4 N HCl in dioxane (146 mL) was added
and stirred for 2 h. The reaction mixture was concentrated,
and then the residue was dissolved in H2O and filtered. The
filtrate was washed with CH2Cl2, adjusted to pH 8 with K2CO3,
and extracted with CH2Cl2. After drying and concentrating,
the obtained solid was recrystallized from n-heptane to give
9.80 g of the title compound, yield 79%: mp 75-77 °C; 1H NMR
(DMSO-d6) δ 1.16 (s, 3H), 1.27 (s, 9H), 1.52 (s, 3H), 3.16 (d,
1H, J ) 13.2 Hz), 3.46-3.58 (m, 1H), 3.99 (dd, 1H, J ) 11.8
Hz, 9.2 Hz), 4.26 (dd, 1H, J ) 7.3 Hz, 9.2 Hz), 7.47 (s, 1H);
MS (TOF) m/z ) 217 (M+ + H). Anal. (C10H20N2OS) C, H, N.
(R )-N -t er t -B u t y l-3-[(2S ,3S )-3-a m in o -2-h y d r o x y -4-
p h e n y lb u t a n o y l]-5,5-d i m e t h y l-1,3-t h i a z o li d i n e -4-
ca r boxa m id e (6b). To a solution of 5b (3.00 g, 14.15 mmol)
in DMF (30 mL) were added Boc-Apns-OH (4.17 g, 14.15
mmol), HOBt (1.91 g, 14.15 mmol), and DCC (3.21 g, 15.57
mmol), and the mixture was stirred overnight. To the reaction
mixture were added toluene (100 mL) and 5% citric acid, and
then the solution was filtrated. The organic layer was washed
with 3% K2CO3 and brine, dried over MgSO4, and evaporated.
The residue was redissolved in CH2Cl2 (18 mL); 4 N HCl in
dioxane (18 mL) was added and stirred for 2 h. The reaction
mixture was concentrated, and then the residue was dissolved
in H2O and filtrated. The filtrate was washed with CH2Cl2,
adjusted to pH 8 with K2CO3, and extracted with CH2Cl2. After
drying with MgSO4 and concentrating, the obtained solid was
recrystallized from n-heptane/ethanol to give 3.60 g of the title
(R )-N -t er t -Bu t yl-3-[(2S ,3S )-2-h yd r oxy-3-(3-m e t h yl-
phenoxyacetyl)amino-4-phenylbutanoyl]-1,3-thiazolidine-4-
ca r boxa m id e (12c). Compound 12c was prepared from
3-methylphenoxyacetic acid and compound 6a in a manner
similar to that described for compound 12a , yield 53%: mp
59-60 °C; 1H NMR (DMSO-d6) δ 1.26 (s, 9H), 2.24 (s, 3H),
2.6-2.8 (m, 2H), 2.95-3.02 (m, 1H), 3.2-3.4 (m, 1H), 4.1-4.3
(m, 1H), 4.37 (s, 2H), 4.48-4.52 (m, 1H), 4.61 (d, 1H, J ) 9.2
Hz), 4.77 (t, 1H, J ) 7.0 Hz), 4.96 (d, 1H, J ) 9.2 Hz), 5.29 (d,
1H, J ) 7.3 Hz), 6.59 (m, 1H), 6.67 (s, 1H), 6.75 (d, 1H, J )
7.3 Hz), 7.07-7.24 (m, 4H), 7.33 (d, 2H, J ) 6.5 Hz), 7.70 (s,
1H), 8.19 (d, 1H, J ) 8.1 Hz); MS (TOF) m/z ) 514 (M+ + H).
Anal. (C27H35N3O5S) C, H, N.
(R )-N -t er t -Bu t yl-3-[(2S ,3S )-2-h yd r oxy-3-(4-m e t h yl-
phenoxyacetyl)amino-4-phenylbutanoyl]-1,3-thiazolidine-4-
ca r boxa m id e (12d ). Compound 12d was prepared from
4-methylphenoxyacetic acid and compound 6a in a manner
similar to that described for compound 12a , yield 80%: mp
68-70 °C; 1H NMR (DMSO-d6) δ 1.26 (s, 9H), 2.22 (s, 3H),
1
compound, yield 65%: mp 177-180 °C; H NMR (DMSO-d6)
δ 1.23 (s, 9H), 1.35 (s, 3H), 1.3-1.5 (m, 2H), 1.49 (s, 3H), 2.30-
2.38 (m, 1H), 2.88-3.04 (m, 2H), 4.10 (t, 1H, J ) 7.3 Hz), 4.36
(s, 1H), 4.90 (s, 1H), 5.19 (d, 1H, J ) 7.3 Hz), 7.16-7.31 (m,
5H), 7.52 (s, 1H); MS (TOF) m/z ) 394 (M+ + H). Anal.
(C20H31N3O3S) C, H, N.
(R)-N-ter t-Bu t yl-3-[(2S,3S)-2-h yd r oxy-3-(3-h yd r oxy-2-
m eth ylben zoyl)a m in o-4-p h en ylbu ta n oyl]-5,5-d im eth yl-
1,3-th ia zolid in e-4-ca r boxa m id e (9h ). Compound 9h was
prepared from 3-acetoxy-2-methylbenzoic acid and compound

1798 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10
Mimoto et al.
2.6-2.8 (m, 2H), 2.95-3.02 (m, 1H), 3.29-3.36 (m, 1H), 4.1-
4.3 (m, 1H), 4.35 (s, 2H), 4.48-4.52 (m, 1H), 4.61 (d, 1H, J )
9.5 Hz), 4.77 (t, 1H, J ) 7.0 Hz), 4.96 (d, 1H, J ) 9.2 Hz), 5.29
(d, 1H, J ) 7.6 Hz), 6.68 (d, 2H, J ) 8.4 Hz), 7.02 (d, 2H, J )
8.4 Hz), 7.16-7.25 (m, 3H), 7.33 (d, 2H, J ) 6.5 Hz), 7.70 (s,
1H), 8.19 (d, 1H, J ) 8.6 Hz); MS (TOF) m/z ) 514 (M+ + H).
Anal. (C27H35N3O5S) C, H, N.
(R)-N-ter t-Bu t yl-3-[(2S,3S)-3-(2,6-d im et h ylp h en oxy-
a ce t yl)a m in o-2-h yd r oxy-4-p h e n ylb u t a n oyl]-1,3-t h ia -
zolid in e-4-ca r boxa m id e (12e). Compound 12e was prepared
from 2,6-dimethylphenoxyacetic acid and compound 6a in a
manner similar to that described for compound 12a , yield
66%: mp 81-83 °C; 1H NMR (DMSO-d6) δ (ppm): 1.26 (S,
9H), 2.15 (S, 6H), 2.76-2.78 (m, 2H), 3.02 (dd, 1H, J ) 7.1
Hz, 10.6 Hz), 3.2-3.4 (m, 1H), 3.98 (d, 1H, J ) 14.3 Hz), 4.18
(d, 1H, J ) 14.3 Hz), 4.3-4.4 (m, 1 H), 4.5-4.6 (br, 1H), 4.63
(d, 1H, J ) 9.6 Hz), 4.77 (t, 1H, J ) 7.1 Hz), 5.00 (d, 1H, J )
9.6 Hz), 5.33 (d, 1H, J ) 6.6 Hz), 6.92 (m, 1H), 7.00 (d, 2H, J
) 6.6 Hz), 7.1-7.3 (m, 3H), 7.36 (d, 2H, J ) 7.5 Hz), 7.68 (s,
1H), 8.11(d, 1H, J ) 8.8 Hz); MS (TOF) m/z ) 528 (M+ + H).
Anal. (C28H37N3O5S) C, H, N.
7.00 (d, 2H, J ) 6.6 Hz), 7.1-7.3 (m, 3H), 7.35 (d, 2H, J ) 7.5
Hz), 7.66 (s, 1H), 8.11(d, 1H, J ) 8.8 Hz); MS (TOF) m/z )
556 (M+ + H). Anal. (C30H41N3O5S•0.5EtOAc) C, H, N.
2,6-Dim et h ylben zyl Alcoh ol (14). To a solution of 2,6-
dimethylbenzoic acid (1.50 g, 10.0 mmol) and K2CO3 (1.38 g,
10 mmol), in DMF (10 mL), was added methyl iodide (1.24
mL, 20 mmol) in an ice bath, and the mixture was stirred
overnight. To the reaction mixture were added toluene and
water, and the organic layer was washed with 3% K2CO3, 1 N
HCl, and brine, dried over MgSO4, filtered, and concentrated.
The oily residue was redissolved in THF (20 mL), added to
LiAlH4 (0.57 g, 15 mmol), and stirred for 4 h in an ice bath.
To the reaction mixture were added 1 N HCl and ethyl acetate,
and the organic phase was washed with brine, dried over
MgSO4, filtered, and concentrated. The residue was recrystal-
lized from n-hexane to give 0.88 g of the title compound, yield
1
65%: mp 78-80 °C; H NMR (DMSO-d6) δ 2.34 (s, 6H), 4.47
(d, 2H, J ) 5.1 Hz), 4.67 (t, 1H, J ) 5.1 Hz), 6.96 (d, 2H, J )
6.6 Hz), 7.03 (dd, 1H, J ) 6.6 Hz). Anal. (C9H12O) C, H.
N-(2,6-Dim eth ylben zyl)p h th a lim id e (15). To a solution
of compound 14 (0.68 g, 5.0 mmol) in DMSO (1.77 mL) was
added TMS-Cl (1.90 mL, 15 mmol), and the mixture was
stirred for 30 min. To the reaction mixture were added ethyl
acetate and water and the organic layer was washed with
brine, dried over MgSO4, filtered, and concentrated. The oily
residue was redissolved in DMF (10 mL), added to potassium
phthalimide (1.11 g, 6.0 mmol), and stirred overnight. To the
reaction mixture was added ethyl acetate and organic phase
was washed with 3% Na2CO3, 1 N HCl, and brine, dried over
MgSO4, filtered, and concentrated. The residue was recrystal-
lized from n-hexane to give 0.90 g of the title compound, yield
68%: mp 158-160 °C; 1H NMR (DMSO-d6) δ 2.34 (s, 6H), 4.47
(s, 2H), 6.9-7.1 (m, 3H), 7.82 (s, 4H). Anal. (C17H15NO2) C, H,
N.
(R)-N-ter t-Bu tyl-3-[(2S,3S)- 3-(2-eth yl-6-m eth ylph en oxy-
a cetyl)a m in o-2-h yd r oxy-4-p h en ylbu ta n oyl]-1,3-th ia zoli-
d in e-4-ca r boxa m id e (12f). Compound 12f was prepared from
2-ethyl-6-methylphenoxyacetic acid and compound 6a in a
manner similar to that described for compound 12a , yield
1
42%: mp 72-74 °C; H NMR (DMSO-d6) δ 1.12 (t, 3H, J )
7.3 Hz), 1.26 (s, 9H), 2.49-2.57 (m, 2H), 2.7-2.8 (m, 2H), 2.98-
3.05 (m, 1H), 3.30-3.37 (m, 1H), 3.98 (d, 1H, J ) 14.0 Hz),
4.18 (d, 1H, J ) 14.0 Hz), 4.2-4.4 (m, 1H), 4.51-4.54 (m, 1H),
4.63 (d, 1H, J ) 9.2 Hz), 4.77 (t, 1H, J ) 7.0 Hz), 5.01 (d, 1H,
J ) 9.4 Hz), 5.34 (d, 1H, J ) 7.3 Hz), 6.98-7.06 (m, 3H), 7.17-
7.27 (m, 3H), 7.37 (d, 2H, J ) 7.0 Hz), 7.70 (s, 1H), 8.10 (d,
1H, J ) 8.9 Hz); MS (TOF) m/z ) 542 (M+ + H). Anal.
(C29H39N3O5S•0.5EtOAc) C, H, N.
(R)-N-(2,6-Dim eth ylben zyl)-1,3-th ia zolid in e-4-ca r boxa -
m id e (18a ). To a solution of compound 14 (0.90 g, 3.40 mmol)
in ethanol (10 mL) was added hydrazine monohydrate (0.25
mL, 5.09 mmol), and the mixture was stirred for 3 h under
reflux condition. To the reaction mixture was added c HCl to
pH 1, and the mixture was stirred for 2 h under the same
conditions. After water was added and filtered, the filtrate was
evaporated and adjusted to pH 10 with 2 N NaOH and
extracted with CH2Cl2. The organic layer was washed with
brine, dried over MgSO4, filtered, and concentrated. The oily
residue was redissolved in CH2Cl2 (10 mL), added to Boc-Thz-
OH (0.87 g, 3.74 mmol), HOBt (0.50 g, 3.74 mmol), and
EDC•HCl (0.78 g, 4.08 mmol), and stirred overnight. The
reaction mixture was washed with 3% K2CO3, 1 N HCl, and
brine, dried over MgSO4, filtered, and concentrated. The
residue was purified by silica gel column chromatography
(CH2Cl2/methanol). The oily residue was redissolved in CH2Cl2
(10 mL), added to 4 N HCl in dioxane (10 mL), and stirred for
3 h. The reaction mixture was concentrated under reduced
pressure and then redissolved CH2Cl2. The organic phase was
washed with 3% K2CO3 and brine, dried over MgSO4, filtered,
and concentrated. The crude product was recrystallized from
n-hexane to give 0.54 g of the title compound, yield 64%: mp
146-148 °C; 1H NMR (DMSO-d6) δ 2.30 (S, 6H), 2.74-2.81
(m, 1H), 2.93-2.99 (m, 1H), 3.1-3.3 (br, 1H), 3.6-3.8 (br, 1H),
3.98 (t, 1H, J ) 9.7 Hz), 4.14 (t, 1H, J ) 8.4 Hz), 4.2-4.4 (m,
2H), 7.00-7.11 (m, 3H), 8.03 (br, 1H); MS (TOF) m/z ) 251
(M+ + H). Anal. (C13H18N2OS) C, H, N.
(R)-N-(2,6-Dim et h ylb en zyl)-3-[(2S,3S)-3-a m in o-2-h y-
d r oxy-4-p h en ylb u t a n oyl]-1,3-t h ia zolid in e-4-ca r b oxa m -
id e (19a ). To a solution of compound 18a (0.23 g, 1.05 mmol)
were added Boc-Apns-OH (0.30 g, 1.00 mmol), HOBt (0.14 g,
1.00 mmol) in ethyl acetate (5 mL), and DCC (0.22 g, 1.10
mmol) in an ice bath, and the mixture was stirred overnight.
The reaction mixture was filtrated, washed sequentially with
3% K2CO3, 1 N HCl, and brine, dried over MgSO4, filtered,
and concentrated. The oily residue was redissolved in CH2Cl2
(5 mL), added to 4 N HCl in dioxane (5 mL), and stirred for 3
h. The reaction mixture was concentrated under reduced
pressure and then redissolved in water. The aqueous phase
(R)-N-ter t-Bu t yl-3-[(2S,3S)-2-h yd r oxy-3-(2-m et h yl-6-
p r op ylp h en oxya cetyl)a m in o-4-p h en ylbu ta n oyl]-1,3-th ia -
zolid in e-4-ca r boxa m id e (12g). Compound 12g was prepared
from 2-methyl-6-propylphenoxyacetic acid and compound 6a
in a manner similar to that described for compound 12a , yield
1
84%: mp 68-71 °C; H NMR (DMSO-d6) δ 0.88 (t, 3H, J )
7.3 Hz), 1.26 (s, 9H), 1.50-1.58 (m, 2H), 2.14 (s, 3H), 2.47-
2.53 (m, 2H),, 2.7-2.9 (m, 2H), 2.98-3.05 (m, 1H), 3.2-3.4
(m, 1H), 3.99 (d, 1H, J ) 14.0 Hz), 4.17 (d, 1H, J ) 14.0 Hz),
4.2-4.4 (m, 1 H), 4.5-4.6 (br, 1H), 4.62 (d, 1H, J ) 9.2 Hz),
4.77 (t, 1H, J ) 7.0 Hz), 5.01 (d, 1H, J ) 9.2 Hz), 5.35 (d, 1H,
J ) 7.0 Hz), 6.96-7.04 (m, 3H), 7.17-7.27 (m, 3H), 7.36 (d,
2H, J ) 6.8 Hz), 7.70 (s, 1H), 8.11(d, 1H, J ) 8.6 Hz); MS
(TOF) m/z ) 556 (M+ + H). Anal. (C30H41N3O5S•0.5EtOAc) C,
H, N.
(R )-N -t er t -B u t y l-3-[(2S ,3S )-3-(2,6-d ie t h y lp h e n o xy-
a ce t yl)a m in o-2-h yd r oxy-4-p h e n ylb u t a n oyl]-1,3-t h ia -
zolid in e-4-ca r boxa m id e (12h ). Compound 12h was pre-
pared from 2,6-diethylphenoxyacetic acid and compound 6a
in a manner similar to that described for compound 12a , yield
1
63%: mp 65-67 °C; H NMR (DMSO-d6) δ 1.12 (t, 6H, J )
7.6 Hz), 1.26 (s, 9H), 2.49-2.57 (m, 4H), 2.7-2.8 (m, 2H), 2.98-
3.05 (m, 1H), 3.30-3.37 (m, 1H), 3.97 (d, 1H, J ) 14.0 Hz),
4.17 (d, 1H, J ) 14.0 Hz), 4.3-4.4 (m, 1H), 4.5-4.6 (m, 1H),
4.64 (d, 1H, J ) 9.2 Hz), 4.77 (t, 1H, J ) 7.0 Hz), 5.02 (d, 1H,
J ) 9.2 Hz), 5.34 (d, 1H, J ) 7.3 Hz), 7.05 (s, 3H), 7.18-7.28
(m, 3H), 7.36 (d, 2H, J ) 7.0 Hz), 7.69 (s, 1H), 8.09 (d, 1H, J
) 8.9 Hz); MS (TOF) m/z ) 556 (M+ + H). Anal. (C30H41N3O5S‚
0.5EtOAc) C, H, N.
(R)-N-ter t-Bu t yl-3-[(2S,3S)-3-(2,6-d im et h ylp h en oxy-
acetyl)amino-2-hydroxy-4-phenylbutanoyl]-5,5-dimethyl-1,3-
th ia zolid in e-4-ca r boxa m id e (12i). Compound 12i was pre-
pared from 2,6-dimethylphenoxyacetic acid and compound 6b
in a manner similar to that described for compound 12a , yield
1
92%: mp 87-89 °C; H NMR (DMSO-d6) δ 1.27 (S, 9H), 1.40
(S, 3H), 1.49 (S, 3H), 2.14 (S, 6H), 2.7-2.9 (m, 2H), 3.98 (d,
1H, J ) 14.1 Hz), 4.19 (d, 1H, J ) 14.1 Hz), 4.3-4.4 (m, 1H),
4.4-4.5 (br, 1H), 4.52 (S, 1H), 4.92 (d, 1H, J ) 10.2 Hz), 4.97
(d, 1H, J ) 10.2 Hz), 5.34 (d, 1H, J ) 7.2 Hz), 6.92 (m, 1H),

SAR of Small-Sized HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10 1799
1
was filtered, washed with toluene, neutralized with 2 N NaOH,
and extract with CH2Cl2. The organic phase was washed with
brine, dried over MgSO4, filtered, and concentrated. The crude
product was recrystallized from n-hexane/ethyl acetate gave
115-117 °C; H NMR (DMSO-d6) δ 1.83 (s, 3H), 2.7-2.9 (m,
2H), 3.07-3.14 (m, 1H), 3.31-3.38 (m, 1H), 4.1-4.5 (m, 4H),
4.78-4.88 (m, 2H), 5.05 (d, 1H, J ) 9.2 Hz), 5.50 (d, 1H, J )
7.0 Hz), 6.56 (d, 1H, J ) 7.3 Hz), 6.78 (d, 1H, J ) 7.3 Hz),
6.94 (t, 1H, J ) 7.3 Hz), 7.16-7.34 (m, 10H), 8.14 (d, 1H, J )
8.4 Hz), 8.45 (br, 1H), 9.39 (s, 1H); MS (TOF) m/z ) 534 (M+
+ H). Anal. (C29H31N3O5S•0.5H2O) C, H, N.
(R)-N-(2-Met h ylb en zyl)-1,3-t h ia zolid in e-4-ca r b oxa m -
id e (18c). Compound 18c was prepared from Boc-Thz-OH and
2-methylbenzylamine in a manner similar to that described
for compound 18b, yield 85%: mp 114-116 °C; 1H NMR
(DMSO-d6) δ 2.56 (S, 3H), 2.85-3.05 (m, 3H), 3.2-3.4 (m, 1H),
3.86 (m, 1H), 4.0-4.2 (m, 2H), 4.2-4.3 (br, 2H), 7.0-7.2 (br,
4H), 8.34 (br, 1H); MS (TOF) m/z ) 237 (M+ + H). Anal.
(C12H16N2OS) C, H, N.
1
0.20 g of the title compound, yield 45%: mp 150-153 °C; H
NMR (DMSO-d6) δ 0.6-0.8 (br, 2H), 2.10 (s, 6H), 2.1-2.3 (m,
1H), 2.40-2.51 (m, 1H), 3.07-3.16 (m, 2H), 3.21-3.33 (m, 1H),
3.97 (t, 1H, J ) 8.8 Hz), 4.12 (d, 2H, J ) 4.1 Hz), 4.70 (s, 2H),
4.86-4.89 (m, 1H), 5.26 (d, 1H, J ) 8.9 Hz), 6.62-6.71 (m,
3H), 7.05 (d, 2H, J ) 6.8 Hz), 7.27-7.37 (m, 3H), 8.37 (s, 1H);
MS (TOF) m/z ) 428 (M+ + H). Anal. (C23H29N3O3S) C, H, N.
(R)-N-(2,6-Dim eth ylben zyl)-3-[(2S,3S)-2-h yd r oxy-3-(3-
h yd r oxy-2-m eth ylben zoyl)a m in o-4-p h en ylbu ta n oyl]-1,3-
th ia zolid in e-4-ca r boxa m id e (21a ). Compound 21a was
prepared from 3-acetoxy-2-methylbenzoic acid and compound
19a in a manner similar to that described for compound 9c,
yield 83%: mp 124-127 °C; 1H NMR (DMSO-d6) δ 1.83 (s, 3H),
2.30 (s, 6H), 2.7-2.8 (m, 2H), 2.9-3.1 (m, 1H), 3.29-3.36 (m,
1H), 4.21-4.27 (m, 1H), 4.3-4.5 (m, 2H), 4,5-4.6 (br, 1H), 4.7-
4.9 (m, 2H), 5.07 (d, 1H, J ) 9.2 Hz), 5.23 (d, 1H, J ) 6.8 Hz),
6.57 (d, 1H, J ) 7.3 Hz), 6.79 (d, 1H, J ) 7.8 Hz), 6.93-7.07
(m, 4H), 7.17-7.29 (m, 3H), 7.40 (d, 2H, J ) 6.8 Hz), 8.15 (t,
1H, J ) 4.9 Hz), 8.25 (d, 1H, J ) 8.6 Hz), 9.39 (s, 1H); MS
(TOF) m/z ) 562 (M+ + H). Anal. (C31H35N3O5S•0.5H2O) C,
H, N.
(R)-N-(2-Meth ylben zyl)-3-[(2S,3S)-3-a m in o-2-h yd r oxy-
4-p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r boxa m id e (19c).
Compound 19c was prepared from Boc-Apns-OH and com-
pound 18c in a manner similar to that described for compound
1
19b, yield 52%: mp 144-146 °C; H NMR (CDCl3) δ 0.2-1.4
(br, 2H), 2.20 (s, 3H), 2.2-2.4 (m, 1H), 2.4-2.6 (m, 1H), 3.14
(d, 2H, J ) 16.8 Hz), 3.21 (t, 1H, J ) 5.4 Hz), 3.48 (d, 1H, J )
9.6 Hz), 3.94 (d, 1H, J ) 9.6 Hz), 4.1-4.3 (m, 1H), 4.3-4.5 (m,
1H), 4.55 (d, 1H, J ) 7.5 Hz), 6.8-7.1 (m, 3H), 7.9-8.1 (br,
1H);MS (TOF)m/z)414 (M+ +H).Anal.(C22H27N3O3S•0.25H2O)
C, H, N.
(R)-N-Ben zyl-1,3-th ia zolid in e-4-ca r boxa m id e (18b). To
a solution of Boc-Thz-OH (2.33 g, 10.0 mmol), benzylamine
(1.20 mL, 11.0 mmol), and HOBt•H2O (1.53 g, 10.0 mmol) in
CH2Cl2 (30 mL) was added EDC•HCl (2.10 g, 11.0 mmol) in
an ice bath, and the mixture was stirred for 2 h. The reaction
mixture was washed sequentially with 3% K2CO3, 1 N HCl,
and brine, dried over MgSO4, filtered, and concentrated. The
oily residue was redissolved in CH2Cl2 (25 mL), added to 4 N
HCl in dioxane (25 mL), and stirred for 3 h. The reaction
mixture was concentrated under reduced pressure and then
redissolved in water. The aqueous phase was washed with
CH2Cl2, neutralized with K2CO3, and extracted with CH2Cl2.
The organic phase was washed with brine, dried over MgSO4,
filtered, and concentrated. The crude product was recrystal-
lized from n-hexane/ethyl acetate gave 1.75 g of the title
(R)-N-(2-Met h ylb en zyl)-3-{(2S,3S)-2-h yd r oxy-3-(3-h y-
d r oxy-2-m et h ylb en zoyl)a m in o-4-p h en ylb u t a n oyl]-1,3-
t h ia zolid in e-4-ca r boxa m id e (21c). Compound 21c was
prepared from 3-acetoxy-2-methylbenzoic acid and compound
19c in a manner similar to that described for compound 9c,
yield 91%: mp 112-115 °C; 1H NMR (DMSO-d6) δ 1.83 (s, 3H),
2.23 (s, 3H), 2.78 (m, 2H), 3.10 (m, 1H), 3.2-3.4 (m, 1H), 4.18
(d, 1H, J ) 6.0 Hz), 4.30 (d, 1H, J ) 7.1 Hz), 4.38 (m, 2H),
4.78 (d, 1H, J ) 8.7 Hz), 4.87(t, 1H, J ) 6.4 Hz), 5.03 (d, 1H,
J ) 10.0 Hz), 5.45 (d, 1H, J ) 6.4 HZ), 6.55 (d, 1H, J ) 7.2
Hz), 6.77 (d, 1H, J ) 8.1 Hz), 6.93 (dd, 1H, J ) 6.4 Hz), 7.12
(br, 4H), 7.23(br, 3H), 7.32 (d, 2H, J ) 6.0 Hz), 8.15 (d, 1H, J
) 7.9 Hz), 8.35 (br, 1H), 9.37 (s, 1H); MS (TOF) m/z ) 548
(M+ + H). Anal. (C30H33N3O5S•0.5EtOAc) C, H, N.
(R)-N-(3-Met h ylb en zyl)-1,3-t h ia zolid in e-4-ca r b oxa m -
id e (18d ). Compound 18d was prepared from Boc-Thz-OH and
3-methylbenzylamine in a manner similar to that described
for compound 18b, yield 79%: mp 77-79 °C; 1H NMR (DMSO-
d6) δ 2.28 (S, 3H), 2.91-2.97 (m, 3H), 3.28-3.38 (m, 1H), 3.85-
3.93 (m, 1H), 4.10 (d, 2H, J ) 9.7 Hz), 4.15-4.34 (m, 2H),
7.01-7.12 (br, 3H), 7.17-7.22 (m, 1H), 8.51 (br, 1H); MS (TOF)
m/z ) 237 (M+ + H). Anal. (C12H16N2OS) C, H, N.
(R)-N-(3-Meth ylben zyl)-3-[(2S,3S)-3-a m in o-2-h yd r oxy-
4-p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r boxa m id e (19d ).
Compound 19d was prepared from Boc-Apns-OH and com-
pound 18d in a manner similar to that described for compound
19b, yield 68%: mp 145-147 °C; 1H NMR (DMSO-d6) δ 1.4-
1.6 (br, 2H), 2.19 (s, 3H), 2.2-2.4 (m, 1H), 2.7-2.9 (m, 1H),
3.1-3.4 (m, 3H), 4.05-4.22 (m, 3H), 4.76 (d, 1H, J ) 8.6 Hz),
4.82 (d, 1H, J ) 8.6 Hz), 4.95-4.98 (m, 1H), 5.36 (d, 1H, J )
7.8 Hz), 6.89-7.31 (m, 9H), 8.96 (t, 1H, J ) 5.4 Hz); MS (TOF)
m/z ) 414 (M+ + H). Anal. (C22H27N3O3S) C, H, N.
(R)-N-(3-Met h ylb en zyl)-3-[(2S,3S)-2-h yd r oxy-3-(3-h y-
d r oxy-2-m et h ylb en zoyl)a m in o-4-p h en ylb u t a n oyl]-1,3-
th ia zolid in e-4-ca r boxa m id e (21d ). Compound 21d was
prepared from 3-acetoxy-2-methylbenzoic acid and compound
19d in a manner similar to that described for compound 9c,
yield 40%: mp 112-117 °C; 1H NMR (DMSO-d6) δ 1.83 (s, 3H),
2.25 (s, 3H), 2.7-2.9 (m, 2H), 3.0-3.2 (m, 1H), 3.3-3.5 (m,
1H), 4.0-4.5 (m, 4H), 4.78-4.87 (m, 2H), 5.05 (d, 1H, J ) 8.9
Hz), 5.46 (br, 1H), 6.56 (d, 1H, J ) 7.3 Hz), 6.78 (d, 1H, J )
7.3 Hz), 6.92-7.34 (m, 10H), 8.13 (d, 1H, J ) 8.4 Hz), 8.41
(br, 1H), 9.39 (s, 1H); MS (TOF) m/z ) 548 (M+ + H). Anal.
(C30H33N3O5S•0.5EtOAc) C, H, N.
1
compound, yield 79%: mp 80-82 °C; H NMR (DMSO-d6) δ
3.23-3.39 (m, 1H), 3.86-3.94 (m, 1H), 4.10 (d, 2H, J ) 9.7
Hz), 4.22-4.37 (m, 3H), 7.20-7.37 (m, 5H), 8.55 (br, 1H); MS
(TOF) m/z ) 223 (M+ + H). Anal. (C11H14N2OS) C, H, N.
(R)-N-Ben zyl-3-[(2S,3S)-3-a m in o-2-h yd r oxy-4-p h en ylb-
u ta n oyl]-1,3-th ia zolid in e-4-ca r boxa m id e (19b). To a solu-
tion of compound 18b (0.73 g, 3.3 mmol) were added Boc-Apns-
OH (0.89 g, 3.0 mmol), HOBt (0.41 g, 3.0 mmol) in DMF (15
mL), and EDC•HCl (0.63 g, 3.3 mmol) in an ice bath, and the
mixture was stirred overnight. To the reaction mixture was
added ethyl acetate, and the organic phase was washed
sequentially with 3% K2CO3, 1 N HCl, and brine, dried over
MgSO4, filtered, and concentrated. The oily residue was
redissolved in CH2Cl2 (25 mL), added to 4 N HCl in dioxane
(25 mL), and stirred for 3 h. The reaction mixture was
concentrated under reduced pressure and then redissolved in
water. The aqueous phase was washed with toluene, neutral-
ized with 2 N NaOH, and extracted with CH2Cl2. The organic
phase was washed with brine, dried over MgSO4, filtered, and
concentrated. Purification of the crude product by silica gel
column chromatography (CH2Cl2/methanol) and recrystalliza-
tion from n-hexane/ethyl acetate gave 0.40 g of the title
1
compound, yield 33%: mp 91-93 °C; H NMR (DMSO-d6) δ
1.3-1.6 (br, 2H), 2.29-2.38 (m, 1H), 2.75-2.82 (m, 1H), 3.13-
3.34 (m, 3H), 4.10 (t, 1H, J ) 7.3 Hz), 4.16-4.31 (m, 2H), 4.77
(d, 1H, J ) 8.9 Hz), 4.83 (d, 1H, J ) 8.9 Hz), 4.95-4.99 (m,
1H), 5.37 (d, 1H, J ) 7.8 Hz), 7.09-7.31 (m, 10H), 9.02 (t, 1H,
J ) 5.9 Hz); MS (TOF) m/z ) 400 (M+ + H). Anal. (C21H25N3O3S)
C, H, N.
(R)-N-Ben zyl-3-[(2S,3S)-2-h yd r oxy-3-(3-h yd r oxy-2-m e-
th ylben zoyl)a m in o-4-p h en ylbu ta n oyl]-1,3-th ia zolid in e-
4-ca r boxa m id e (21b). Compound 21b was prepared from
3-acetoxy-2-methylbenzoic acid and compound 19b in a man-
ner similar to that described for compound 9c, yield 56%: mp
(R)-N-(4-Met h ylb en zyl)-1,3-t h ia zolid in e-4-ca r b oxa m -
id e (18e). Compound 18e was prepared from Boc-Thz-OH and
4-methylbenzylamine in a manner similar to that described
for compound 18b, yield 85%: mp 122-124 °C; 1H NMR

1800 J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10
Mimoto et al.
(DMSO-d6) δ 2.27 (s, 3H), 2.95 (d, 2H, J ) 6.5 Hz), 3.26-3.37
(m, 1H), 3.83-3.91 (m, 1H), 4.09 (d, 2H, J ) 9.7 Hz), 4.17-
4.32 (m, 3H), 7.12 (s, 4H), 8.49 (br, 1H); MS (TOF) m/z ) 237
(M+ + H). Anal. (C12H16N2OS) C, H, N.
d im eth yl-1,3-th ia zolid in e-4-ca r boxa m id e (21f). To a so-
lution of 3-acetoxy-2-methylbenzoic acid (4.27 g, 22.0 mmol)
and triethylamine (3.06 mL, 22.0 mmol) in ethyl acetate (100
mL) was added DPP-Cl (4.55 mL, 22.0 mmol) in an ice bath,
and the mixture was stirred for 1 h. Then to the reaction
mixture were added compound 19f (8.82 g, 20.0 mmol) and
triethylamine (3.34 mL, 24.0 mmol) in an ice bath, and the
mixture was stirred overnight. The reaction mixture was
washed sequentially with 3% K2CO3, 1 N HCl, and brine and
concentrated. To the solution of the resulting residue in
methanol (50 mL) was added 1 N NaOH (22 mL, 22.0 mmol),
and the mixture was stirred for 1 h. The mixture was acidified
with 1 N HCl, and the aqueous phase was extracted with ethyl
acetate. The organic extract was washed sequentially with 1
N HCl, 3% K2CO3, and brine, dried over MgSO4, filtered, and
concentrated. The crude product was recrystallized from
n-hexane/ethyl acetate and gave 9.70 g of the title compound,
yield 84%: mp 137-139 °C; 1H NMR (DMSO-d6) δ 1.35 (s, 3H,
Dmt-5-CH3), 1.50 (s, 3H, Dmt-5-CH3), 1.83 (s, 3H, benzoyl-
CH3), 2.26 (s, 3H, benzylamine-CH3), 2.7-2.9 (m, 2H, Apns-
4-CH2), 4.10 (dd, 1H, J ) 5.0 Hz, 15.0 Hz, benzylamine-CH2),
4.3-4.5 (m, 4H, benzylamine-CH2, Dmt-4-CH, Apns-2-CH, and
Apns-3-CH), 5.01 (d, 1H, J ) 9.2 Hz, Dmt-2-CH2), 5.14 (d, 1H,
J ) 9.2 Hz, Dmt-2-CH2), 5.46 (d, 1H, J ) 6.6 Hz, Apns-2-OH),
6.55 (d, 1H, J ) 7.5 Hz, aromatic), 6.77 (d, 1H, J ) 7.5 Hz,
aromatic), 6.94 (t, 1H, J ) 7.5 Hz, aromatic), 7.0-7.4 (m, 9H,
aromatic), 8.13 (d, 1H, J ) 8.7 Hz, Apns-NH), 8.31 (t, 1H,
benzylamine-NH), 9.36 (s, 1H, benzoyl-OH); 13C NMR (DMSO-
d6) δ 12.23, 18.67, 24.57, 30.27, 33.72, 40.42, 47.73, 51.08,
52.83, 71.50, 72.06, 115.14, 117.45, 121.41, 125.61, 125.68,
125.80, 126.87, 127.62, 127.82, 127.86, 128.01, 129.52, 129.78,
135.64, 136.73, 139.03, 139.30, 155.30, 167.96, 169.07, 170.12;
MS (TOF) m/z ) 576 (M+ + H). Anal. (C32H37N3O5S) C, H, N.
(R)-N-(4-Meth ylben zyl)-3-[(2S,3S)-3-a m in o-2-h yd r oxy-
4-p h en ylbu ta n oyl]-1,3-th ia zolid in e-4-ca r boxa m id e (19e).
Compound 19e was prepared from Boc-Apns-OH and com-
pound 18e in a manner similar to that described for compound
19b, yield 58%: mp 153-155 °C; 1H NMR (DMSO-d6) δ 1.5-
1.7 (br, 2H), 2.21 (s, 3H), 2.26-2.38 (m, 1H), 2.79 (t, 1H, J )
8.4 Hz), 3.1-3.4 (m, 3H), 4.07-4.20 (m, 3H), 4.75 (d, 1H, J )
8.4 Hz), 4.82 (d, 1H, J ) 8.4 Hz), 4.93-4.97 (m, 1H), 5.37 (d,
1H, J ) 7.8 Hz), 6.97-7.32 (m, 9H), 8.95 (t, 1H, J ) 5.5 Hz);
MS (TOF) m/z ) 414 (M+ + H). Anal. (C22H27N3O3S•0.5H2O)
C, H, N.
(R)-N-(4-Met h ylb en zyl)-3-[(2S,3S)-2-h yd r oxy-3-(3-h y-
d r oxy-2-m et h ylb en zoyl)a m in o-4-p h en ylb u t a n oyl]-1,3-
th ia zolid in e-4-ca r boxa m id e (21e). Compound 21e was
prepared from 3-acetoxy-2-methylbenzoic acid and compound
19e in a manner similar to that described for compound 9c,
yield 57%: mp 113-116 °C; 1H NMR (DMSO-d6) δ 1.83 (s, 3H),
2.24 (s, 3H), 2.7-2.9 (m, 2H), 3.0-3.2 (m, 1H), 3.3-3.4 (m,
1H), 4.28-4.48 (m, 4H), 5.05 (d, 1H, J ) 9.2 Hz), 5.48 (d, 1H,
J ) 6.2 Hz), 6.56 (d, 1H, J ) 7.0 Hz), 6.78 (d, 1H, J ) 7.8 Hz),
6.95 (t, 1H, J ) 7.8 Hz), 7.06-7.34 (m, 9H), 8.13 (d, 1H, J )
7.8 Hz), 8.39 (br, 1H), 9.39 (s, 1H); MS (TOF) m/z ) 548 (M+
+ H). Anal. (C30H33N3O5S•0.5EtOAc) C, H, N.
(R)-N-(2-Meth ylben zyl)-5,5-d im eth yl-1,3-th ia zolid in e-
4-ca r boxa m id e (18f). To a solution of Boc-Dmt-OH (5.22 g,
20.0 mmol) and triethylamine (3.06 mL, 22.0 mmol) in ethyl
acetate (50 mL) was added DPP-Cl (4.55 mL, 22.0 mmol) in
an ice bath, and the mixture was stirred for 1 h. Then to the
reaction mixture were added 2-methylbenzylamine (2.73 mL,
22.0 mmol) and triethylamine (3.06 mL, 22.0 mmol) in an ice
bath, and the mixture was stirred overnight. The reaction
mixture was washed sequentially with 1 N HCl, 3% K2CO3,
and brine, dried over MgSO4, filtered, and concentrated. The
residue was redissolved in CH2Cl2 (30 mL), added to 4 N HCl
in dioxane (30 mL), and stirred for 2 h. To the reaction mixture
was added water, and aqueous phase was washed with
toluene, neutralized with 2 N NaOH, and extracted with ethyl
acetate. The organic phase was washed with brine, dried over
MgSO4, filtered, and concentrated to give a crude product.
Recrystallization from n-hexane/ethyl acetate gave 3.75 g of
the title compound, yield 71%: mp 77-79 °C; 1H NMR (DMSO-
d6) δ 1.15 (s, 3H), 1.52 (s, 3H), 2.28 (s, 3H), 3.27 (s, 3H), 3.66
(s, 1H), 4.03 (d, 1H, J ) 9.6 Hz), 4.22-4.33 (m, 3H), 7.12-
(R)-N-(2-Ch lor oben zyl)-5,5-d im eth yl-1,3-th ia zolid in e-
4-ca r boxa m id e (18g). Compound 18g was prepared from
Boc-Dmt-OH and 2-chlorobenzylamine in a manner similar to
that described for compound 18f, yield 46%: mp 93-96 °C;
1H NMR (DMSO-d6) δ 1.14 (s, 3H), 1.54 (s, 3H), 3.28-3.34 (m,
1H), 3.6-3.8 (br, 1H), 4.05 (t, 1H, J ) 10.3 Hz), 4.26-4.49 (m,
3H), 7.27-7.47 (m, 4H), 8.51 (br, 1H); MS (TOF) m/z ) 285
(M+ + H). Anal. (C13H17ClN2OS) C, H, N.
(R)-N-(2-Ch lor oben zyl)-3-[(2S,3S)-3-a m in o-2-h yd r oxy-
4-p h en ylb u t a n oyl]-5,5-d im et h yl-1,3-t h ia zolid in e-4-ca r -
boxa m id e (19g). Compound 19g was prepared from Boc-
Apns-OH and compound 18g in a manner similar to that
1
described for compound 19f, yield 59%: mp 175-178 °C; H
NMR (DMSO-d6) δ 1.33 (s, 3H), 1.4-1.5 (m, 2H), 1.53 (s, 3H),
2.31-2.39 (m, 1H), 2.79-2.87 (m, 1H), 3.08-3.14 (m, 1H), 4.11
(t, 1H, J ) 7.7 Hz), 4.26-4.36 (m, 2H), 4.39 (s, 1H), 4.95 (s,
2H), 5.38 (d, 1H, J ) 7.8 Hz), 7.17-7.39 (m, 9H), 8.85 (t, 1H,
J )5.7 Hz);MS (TOF)m/z)462 (M+ +H). Anal. (C23H28ClN3O3S)
C, H, N.
7.22 (m, 4H), 8.32-8.33 (br, 1H); MS (TOF) m/z ) 265 (M+
H). Anal. (C14H20N2OS) C, H, N.
+
(R)-N-(2-Meth ylben zyl)-3-[(2S,3S)-3-a m in o-2-h yd r oxy-
4-p h en ylb u t a n oyl]-5,5-d im et h yl-1,3-t h ia zolid in e-4-ca r -
boxa m id e (19f). To a solution of compound 18f (15.0 g, 56.8
mmol) were added Boc-Apns-OH (16.0 g, 54.1 mmol), HOBt
(7.30 g, 54.1 mmol) in DMF (150 mL), and EDC•HCl (11.4 g,
59.5 mmol) in an ice bath, and the mixture was stirred
overnight. To the reaction mixture was added ethyl acetate,
and the organic layer was washed sequentially with 3% K2CO3,
1 N HCl, and brine, dried over MgSO4, filtered, and concen-
trated. The residue was redissolved in CH2Cl2 (100 mL), added
to 4 N HCl in dioxane (100 mL), and stirred for 3 h. The
reaction mixture was concentrated under reduced pressure and
then redissolved in water. The aqueous phase was washed with
toluene, neutralized with 2 N NaOH, and gave the precipitate.
The crude product was recrystallized from ethyl acetate and
gave 11.0 g of the title compound, yield 46%: mp 205-208
°C; 1H NMR (DMSO-d6) δ 1.15-1.25 (br, 2H), 1.34 (s, 3H), 1.52
(s, 3H), 2.23-2.31 (m, 1H), 2.70 (t, 1H, J ) 10.0 Hz), 3.09 (d,
1H, J ) 12.3 Hz), 4.04-4.08 (br, 1H), 4.11 (dd, 1H, J ) 5.0
Hz, 15.3 Hz), 4.22 (dd, 1H, J ) 5.0 Hz, 15.0 Hz), 4.36 (s, 1H),
4.90 (s, 2H), 5.31 (d, 1H, J ) 6.6 Hz), 6.95 (s, 3H), 7.12-7.31
(R)-N-(2-Ch lor ob en zyl)-3-[(2S,3S)-2-h yd r oxy-3-(3-h y-
d r oxy-2-m et h ylb en zoyl)a m in o-4-p h en ylb u t a n oyl]-5,5-
d im et h yl-1,3-t h ia zolid in e-4-ca r b oxa m id e (21g). Com-
pound 21h was prepared from 3-acetoxy-2-methylbenzoic acid
and compound 19g in a manner similar to that described for
compound 21f, yield 82%: mp 147-149 °C; 1H NMR (DMSO-
d6) δ 1.36 (s, 3H), 1.52 (s, 3H), 1.83 (s, 3H), 2.6-2.9 (m, 2H),
4.2-4.4 (m, 1H), 4.4-4.6 (m, 4H), 5.03 (d, 1H, J ) 9.2 Hz),
5.16 (d, 1H, J ) 8.9 Hz), 5.51 (d, 1H, J ) 6.8 Hz), 6.55 (d, 1H,
J ) 7.0 Hz), 6.78 (d, 1H, J ) 7.3 Hz), 6.95 (t, 1H, J ) 7.6 Hz),
7.1-7.3 (m, 7H), 7.39-7.50 (m, 2H), 8.14 (d, 1H, J ) 8.4 Hz),
8.52 (br, 1H), 9.38 (s, 1H); MS (TOF) m/z ) 596 (M+ + H).
Anal. (C31H34ClN3O5S•0.5EtOAc) C, H, N.
(R)-N-(2-Tr iflu or om eth ylben zyl)-5,5-d im eth yl-1,3-th ia -
zolid in e-4-ca r boxa m id e (18h ). Compound 18h was pre-
pared from Boc-Dmt-OH and 2-trifluoromethylbenzylamine in
a manner similar to that described for compound 18f, yield
36%: mp 118-120 °C; 1H NMR (DMSO-d6) δ 1.17 (s, 3H), 1.55
(s, 3H), 3.31-3.36 (m, 1H), 3.69-3.78 (m, 1H), 4.03-4.10 (m,
1H), 4.29 (t, 1H, J ) 8.0 Hz), 4.50 (t, 2H, J ) 5.1 Hz), 7.46-
7.55 (m, 2H), 7.65-7.74 (m, 2H), 8.56 (t, 1H, J ) 5.5 Hz); MS
(TOF) m/z ) 319 (M+ + H). Anal. (C14H17F3N2OS) C, H, N.
(m, 6H), 8.48 (t, 1H, J ) 4.8 Hz); MS (TOF) m/z ) 442 (M+
H). Anal. (C24H31N3O3S) C, H, N.
+
(R)-N-(2-Met h ylb en zyl)-3-[(2S,3S)-2-h yd r oxy-3-(3-h y-
d r oxy-2-m et h ylb en zoyl)a m in o-4-p h en ylb u t a n oyl]-5,5-

SAR of Small-Sized HIV Protease Inhibitors
J ournal of Medicinal Chemistry, 1999, Vol. 42, No. 10 1801
(8) Humphrey, R. E.; Wyvill, K. M.; Nguyen, B.-Y.; Shay, L. E.;
Kohler, D. R.; Steinberg, S. M.; Ueno, T.; Fukazawa, T.; Shintani,
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the Pharmacokinetics, Toxicity, and Activity of KNI-272, an
Inhibitor of HIV-1 Protease, in Patients with AIDS or Symp-
tomatic HIV Infection. Antiviral Res., in press
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590.
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(R)-N-(2-Tr iflu or om eth ylben zyl)-3-[(2S,3S)-3-a m in o-2-
h ydr oxy-4-ph en ylbu tan oyl]-5,5-dim eth yl-1,3-th iazolidin e-
4-ca r boxa m id e (19h ). Compound 19h was prepared from
Boc-Apns-OH and compound 18h in a manner similar to that
1
described for compound 19f, yield 55%: mp 192-195 °C; H
NMR (DMSO-d6) δ 1.34 (s, 3H), 1.4-1.5 (m, 2H), 1.54 (s, 3H),
2.31-2.39 (m, 1H), 2.79-2.85 (m, 1H), 3.07-3.33 (m, 1H), 4.12
(t, 1H, J ) 8.1 Hz), 4.40 (s, 3H), 4.96 (s, 2H), 5.40 (d, 1H, J )
8.4 Hz), 7.16-7.39 (m, 6H), 7.49-7.63 (m, 3H), 8.90 (t, 1H, J
)
5.5 Hz); MS (TOF) m/z
(C24H28F3N3O3S) C, H, N.
) + H). Anal.
496 (M+
(R)-N-(2-Tr iflu or om eth ylben zyl)-3-[(2S,3S)-3-(3-h ydr oxy-
2-m eth ylben zoyl)a m in o-4-p h en ylbu ta n oyl]-5,5-d im eth yl-
1,3-th ia zolid in e-4-ca r boxa m id e (21h ). Compound 21h was
prepared from 3-acetoxy-2-methylbenzoic acid and compound
19h in a manner similar to that described for compound 21f,
yield 89%: mp 142-145 °C; 1H NMR (DMSO-d6) δ 1.38 (s, 3H),
1.54 (s, 3H), 1.82 (s, 3H), 2.65-2.85 (m, 2H), 4.3-4.7 (m, 5H),
5.04 (d, 1H, J ) 8.9 Hz), 5.20 (d, 1H, J ) 8.9 Hz), 5.51 (d, 1H,
J ) 7.0 Hz), 6.55 (d, 1H, J ) 7.3 Hz), 6.78 (d, 1H, J ) 8.4 Hz),
6.94 (t, 1H, J ) 7.8 Hz), 7.13-7.27 (m, 5H), 7.40 (t, 1H, J )
7.7 Hz), 7.55 (t, 1H, J ) 7.6 Hz), 7.68 (d, 1H, J ) 7.8 Hz), 8.18
(d, 1H, J ) 8.4 Hz), 8.63 (t, 1H, J ) 5.5 Hz), 9.38 (s, 1H); MS
(TOF) m/z ) 630 (M+ + H). Anal. (C32H34F3N3O5S) C, H, N.
(R)-N-(2-Meth ylben zyl)-3-[(2S,3S)-3-(2-eth yl-3-h yd r ox-
yb en zoyl)a m in o-2-h yd r oxy-4-p h en ylb u t a n oyl]-5,5-d im -
eth yl-1,3-th ia zolid in e-4-ca r boxa m id e (21i). Compound 21i
was prepared from 3-acetoxy-2-ethylbenzoic acid and com-
pound 19f in a manner similar to that described for compound
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1
21f, yield 85%: mp 164-167 °C; H NMR (DMSO-d6) δ 0.87
(t, 3H, J ) 7.4 Hz), 1.36 (s, 3H), 1.50 (s, 3H), 2.26 (s, 3H),
2.2-2.4 (m, 2H), 2.7-2.9 (m, 2H), 4.05-4.20 (m, 1H), 4.37-
4.50 (m, 4H), 5.01 (d, 1H, J ) 9.2 Hz), 5.15 (d, 1H, J ) 9.5
Hz), 5.46 (d, 1H, J ) 6.8 Hz), 6.55 (d, 1H, J ) 6.8 Hz), 6.78 (d,
1H, J ) 7.3 Hz), 6.95 (t, 1H, J ) 7.6 Hz), 7.09-7.35 (m, 9H),
8.14 (d, 1H, J ) 8.1 Hz), 8.33 (br, 1H), 9.34 (s, 1H); MS (TOF)
m/z ) 590 (M+ + H). Anal. (C33H39N3O5S) C, H, N.
Ack n ow led gm en t. We appreciate assistance from
Mr. Mitsuhiko Sugawara and Mr. Hideo Omukai for the
chemical synthesis of HIV protease inhibitors and the
determination of HIV-1 protease inhibitory activity,
respectively.
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