Structure-activity relationship of HIV-1 protease inhibitors containing AHPBA. Part III: Modification of P2 site

Article abstract of DOI:10.1016/S0968-0896(98)00004-2

The structure-activity relationship of HIV-1 protease (HIV-1 PR) inhibitors containing AHPBA (3-amino-2-hydroxy-4-phenylbutanoic acid) is discussed. In order to solve the problem of poor oral bioavailability, small-sized dipeptide HIV-1 protease inhibitors containing cyclic urethanes or benzamides at the P₂ site were designed and prepared. The substitution patterns of the benzamides contributed significantly to their HIV-1 PR inhibitory activities, and it was shown that the choice of P₂-residues was very important. Highly potent inhibitors possessing subnanomolar IC₅₀ values and exhibiting good antiviral potency have been identified. In this class, inhibitor 18 was the most potent (IC₉₀ (CEM/HIV-1 IIIb) 0.11μM) and showed good oral bioavailability in dogs. Copyright (C) 1998 Elsevier Science Ltd.

Full text of DOI:10.1016/S0968-0896(98)00004-2

BIOORGANIC &
MEDICINAL
CHEMISTRY
Bioorganic & Medicinal Chemistry 6 (1998) 595±604
Structure±Activity Relationship of HIV-1 Protease Inhibitors
Containing AHPBA. Part III: Modi®cation of P2 Site
Eiji Takashiro,a,* Takashi Watanabe,a Tamayo Nitta,a Atsushi Kasuya,a
Shuichi Miyamoto,a Yuji Ozawa,b Ryuichi Yagi,b Takashi Nishigaki,b
Takahiro Shibayama,c Akihiko Nakagawa,c Aikichi Iwamotod
and Yuichiro Yabea,*
aExploratory Chemistry Research Laboratories, Sankyo Co. Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140, Japan
bBiological Research Laboratories, Sankyo Co. Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140, Japan
cAnalytical and Metabolic Research Laboratories, Sankyo Co. Ltd., 1-2-58 Hiromachi, Shinagawa-ku, Tokyo 140, Japan
dInstitute of Medical Science, University of Tokyo, Shiroganedai, Minato-ku, Tokyo 108, Japan
Received 18 September 1997; accepted 25 December 1997
AbstractÐThe structure±activity relationship of HIV-1 protease (HIV-1 PR) inhibitors containing AHPBA (3-amino-
2-hydroxy-4-phenylbutanoic acid) is discussed. In order to solve the problem of poor oral bioavailability, small-sized
dipeptide HIV-1 protease inhibitors containing cyclic urethanes or benzamides at the P2 site were designed and pre-
pared. The substitution patterns of the benzamides contributed signi®cantly to their HIV-1 PR inhibitory activities,
and it was shown that the choice of P2-residues was very important. Highly potent inhibitors possessing subnanomolar
IC50 values and exhibiting good antiviral potency have been identi®ed. In this class, inhibitor 18 was the most potent
(IC90 (CEM/HIV-1 IIIb) 0.11 mM) and showed good oral bioavailability in dogs. # 1998 Elsevier Science Ltd. All
rights reserved.
Introduction
tory. In order to improve this, we replaced the P3±P2
region with groups which are smaller in size (Figure 1).
Treatment of acquired immunode®ciency syndrome
(AIDS) continues to be one of the most challenging
obstacles in chemotherapy. HIV-1 protease is an
aspartic protease which is essential for viral replication,
processing the gag and the gag±pol polyproteins to per-
mit formation of mature protein.1 Inhibition of HIV-1
protease o€ers an attractive target for the treatment of
AIDS.2 Numerous inhibitors have been developed and
several of them are now on the market or undergoing
clinical trial.3,4
Ghosh et al. reported that inhibitors incorporating cyc-
lic ligands at the P2 site showed high potency.6 This
result prompted us to synthesize compounds with cyclic
urethanes as P2 ligands. Benzamide groups were proved
0
to be desirable P2/P2 -ligands in symmetric inhibitors by
two groups,7 and Kalish et al. disclosed that they were
also very good P2-ligands for hydroxyethylamine-type
inhibitors.8a These results encouraged us to incorporate
substituted benzoyl groups into the backbone structure
of our HIV-1 PR inhibitors.
In the previous paper, we reported that AHPBA-
de0rived HIV-1 PR inhibitors having 4(S)-Cl-Pro at the
P1 site showed potent inhibitory activity against HIV-1
PR, and some of them showed good anti-HIV activity.5
Unfortunately, their oral bioavailability was unsatisfac-
Results and Discussion
Chemistry
All alcohols used were either purchased or prepared
according to known procedures. 5(S)-hydroxy-5,6-
*Corresponding author.
0968-0896/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved
PII: S0968-0896(98)00004-2

596
E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
Figure 1. Design of reduced size inhibitors.
dihydro-2H-pyran, 5(S)-hydroxy-6(R)-methoxy-5,6-di-
hydro-2H-pyrane and their antipols were synthesized by
Fleet's procedure.9
diimide-hydrochloride (EDCI), 1-hydroxybenzotriazole
(HOBt) and (2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu in
tetrahydrofuran (THF), in quantitative yield.
All commercially available benzoic acids were purch-
ased, and others were prepared as follows. 3- Hydr-
oxy-2-methylbenzoic acid,10 2,6-dimethyl-3-hydroxy-
benzoic acid11 and 2-ethyl-3-hydroxybenzoic acid12
were prepared according to known methods. 2-Bromo-
3-hydroxybenzoic acid was obtained by oxidation13 of
the corresponding aldehyde.14 3-Hydroxy-2-n-propyl-
benzoic acid was synthesized according to Scheme 1.
Structure±activity relationship
Table 1 shows the inhibitory activities of AHPBA-based
inhibitors possessing cyclic urethanes.
Among compounds 5, 6, 7, 8 and 9, inhibitor 6 was the
most potent. The superior potency of 6 clearly showed
that an oxygen atom is more e€ective than sulfur or
nitrogen as a hetero ring atom. Because inhibitor 6,
which has a racemic alcohol, was equipotent to diaster-
eomerically pure 10, and compounds 12 and 13 were of
similar potency, it was concluded that the con®guration
of the cyclic urethanes is not important.17 The presence
of unsaturated bonds in the six-membered ring
increased the activity (14 versus 15)(13 versus 17).
Although compound 6 showed good oral absorption in
rats (data not shown), its anti-HIV activity was weak
(IC90 (CEM/HIV-1 IIIb) 4.8 mM). Therefore, compound
6 did not satisfy our criteria, so we attempted to remove
the oxygen atom from the urethanes. Compounds which
have benzamide structure at the P2 site were synthesized
(Table 2).
Regioselective lithiation of aldehyde 1, followed by
alkylation of the corresponding aryllithium, a€orded
aldehyde 2 in good yield.15 Oxidation of 2 with NaClO2
gave benzoic acid,13 which was then converted to methyl
ester 3 in quantitative yield. Deprotection of the benzyl
group in 3, followed by alkaline hydrolysis of the methyl
ester, gave desired benzoic acid 4.
The formation of urethane- and benzamide-bearing
structures was carried out in the following ways. (2S,
3S)-AHPBA-(4S)-Cl-Pro-NH-t-Bu was coupled with
cyclic alcohols using DSC16(N,N0-disuccinimidyl car-
bonate) to a€ord cyclic urethanes in good yield. Benz-
amide-bearing compounds, which included the most
potent inhibitor 18, were synthesized by treatment with
benzoic acid, 1-(3-dimethylaminopropyl)-3-ethylcarbo-
Among these compounds, 18 that has 3-hydroxy-2-
methylbenzoyl group was the most potent.7,8a We were
Scheme 1. (a) MeHNCH2CH2NMe2, n-BuLi/THF then 1, PhLi, n-propyl±l (72%); (b) NaClO2, Na2H2PO4, 2-methyl-2-butene/acet-
one±H2O; (c) TMSCHN2/MeOH±benzene (83%, 2 steps); (d) H2, Pd-black/MeOH (50%); (e) LiOH/MeOH, re¯ux (86%).

E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
597
Table 1. HIV-1 PR inhibitory activity of urethane-type compounds
No.
2
R
IC50 (nM)
19
No
10
R
IC50 (nM)
5.1
No
14
R
IC50 (nM)
4.5
6
7
8
9
4.9
>1000
7.7
11
12
13
25
35
29
15
16
17
14
>1000
37
11
interested in investigating the relationship between sub-
stitution pattern and inhibitory activity. It was shown
that ortho-substitution of the benzene ring is very
important for high potency (19 versus 20ꢀ28) and that
inhibitors having an alkyl group or a halogen atom at
this position were potent.
On the other hand, compounds 26 and 27 exhibited very
poor activity. The low-®eld singlet (d 12.0 in 26 and 11.2
in 27, respectively) in their respective H NMR spectra
1
suggests that hydrogen bondings occur between the
ortho-hydroxyl groups and the amide carbonyls. It is
concluded that this hydrogen bonding decreases the
interactions between `¯ap' water and the amide carbon-
yls.19 Interestingly, compound 28 showed moderate
activity. In 28, the ortho-amino group possibly forms a
hydrogen bond with the amide carbonyl, but this
hydrogen bonding seems to be very weak because the
aniline proton in 28 is less acidic than the phenolic pro-
ton in 26 or 27 (pKa values of phenol and aniline are
10.0 and 30.7, respectively). Thus, the di€erence
between the inhibitory activity of 26 and that of 28
could be explained in this way.20
Randad et al. reported on inhibitors which showed
strong activities when the aromatic ring and the amide
carbonyl were not co-planar.7a Kaldor et al. found that
0
ortho-substitution at the P1 site a€ected amide con-
formation.8b Our computational studies on 18 showed
that the benzamide carbonyl group is almost at right
angle to the benzene ring.18 In 18 and 20±23, ortho-sub-
stitutions seemed to induce a repulsion between the
aromatic ring and the amide carbonyl. Because of this
repulsion, aromatic rings might occupy favorable posi-
tions in inhibitor±protease complexes. With the inten-
tion of enhancing the substituent-induced repulsion, we
synthesized inhibitors 24 and 25, which have a n-propyl
group and a dimethyl group, respectively, at the ortho-
position. Comparing these two compounds, two small
substituents were found to be more e€ective than one
large substituent.
We also investigated the position of the hydroxyl group.
According to our computational studies on 18, the
hydroxyl group seems to form a hydrogen bond with
Asp29 or Asp30 in protease. This is consistent with the
results of Randad et al.7a and Kalish et al.8a Inhibitors
with hydroxyl group at the meta-position were generally
more e€ective than the regioisomers or non-substituted

598
E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
Table 2. HIV-1 PR Inhibitory activity of benzamide-type compounds
No.
18
R
IC50 (nM)
No
26
R
IC50 (nM)
>1000
No
33
R
IC50 (nM)
0.8
1.5
19
20
21
22
23
26
5.1
11
12
14
27
28
29
30
31
32
>1000
34
35
36
37
38
39
0.9
1.6
2.5
5.4
9.0
50
39
9.0
33
20
24
25
29
5.6
3.6

E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
599
Table 3. Anti-HIV activity of AHPBA-based inhibitors 18, 32,
34, 35, 36 and 37
substitution as judged by the above results (20 versus 24,
18 versus 35).
Comparing 37 with 18, a hydroxyl group is more e€ec-
tive than an amino group for the formation of a hydro-
gen bond to Asp29 or Asp30. Moreover, compound 38
was more potent than compound 39, suggesting that the
boldface bond in 38 might work in a similar way to the
methyl group in 18.
No.
18
R
CEM/HIV-1 III, B
IC90 (nM)
Anti-HIV-1 activity
It is well known that protease inhibition is not always
compatible with anti-HIV activity. Table 3 summarizes
the anti-HIV activities of selected inhibitors.5b
110
Compound 18 with a 3-hydroxy-2-methylbenzoyl group
was the best candidate among the compounds in this
class. Although 34 and 35 showed almost equipotent
protease inhibitory activities as 18, they were much less
potent than 18 in terms of anti-HIV activities. Interest-
ingly, although 36 was less potent than 18 in protease
inhibition, they were of similar potency in anti-HIV
activity. These results suggest that the 2,6-dimethyl-3-
hydroxybenzamide moiety is important not only for
interaction with protease, but also for cellular penetra-
tion. However, the reason for superior penetration abil-
ity of the 2,6-dimethyl-3-hydroxybenzamide moiety
compared to the other benzamide-bearing compounds is
not clearly understood, nor is its cell penetration
mechanism known.
32
34
>500*
120
35
230
105
Inhibitor 18 showed good oral bioavailability in dogs.
When inhibitor 18 (10 mg/kg) was administered orally
to dogs, the Cmax, AUC and bioavailability were as fol-
lows: 5.0 mM, 8.7 mM hr and 27%, respectively.
36
34
Conclusion
We have succeeded in developing small-sized dipeptide
HIV-1 protease inhibitors. During the course of this
study, we found that inhibitors with benzamides as P2-
ligands in the peptide-based structure showed high
potency. We also discovered that ortho-substitutions of
benzene rings are crucial for biological activities. Fur-
ther work to develop more active compounds is now in
progress.
>500*
*IC50 (nM)
compounds (e.g. 18 versus 20, 19 versus 29, 29 versus
30, 22 versus 33). Replacement of the methyl group with
an ethyl group (34) or a n-propyl group (35) gave com-
pounds with potent enzyme inhibitory activities, but
their antiviral activities were less potent than that of 18
(Table 3). 2,6-Dimethyl-3-hydroxybenzamide 36 was
also a good inhibitor, but it was a little less potent than
18. A n-propyl group proved to be too large as a ortho-
Experimental
Melting points were determined with a Yanagimoto
melting point apparatus and are not corrected. Infrared
(IR) spectra were measured with a Nic 5SXC FT-IR
1
spectrophotometer. H NMR spectra were recorded on

600
E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
a JEOL JNM-GX 270 FT-NMR spectrophotometer.
Chemical shifts are expressed in d ppm from the internal
standard tetramethylsilane. EI- and FAB-MS were
taken on a JEOL JMS-D 300 mass spectrometer and
relevant data are tabulated as m/z. Column chromato-
graphy was carried out using SK-34 (Kishida, 70±230
mesh). Preparative thin-layer chromatography was per-
formed using 60 F254 plates (Merck art. 5744).
for 5 min at room temperature. To this solution was
added phenyllithium (40.4 mL, 1.0 M solution in cyclo-
hexane) and THF (10 mL), and stirred for 30 min at
room temperature. The reaction mixture was cooled to
78 ꢁC and n-propyliodide (8.90 mL, 91.3 mmol) was
added and then stirred for 17 h. After quenching by
adding H2O, the product was extracted with EtOAc and
the combined organic layer was washed with brine.
After removal of the solvent in vacuo, the residue was
puri®ed by ¯ash column chromatography (hexane/
Preparation of urethane-type inhibitors (5±17)
1
CH2Cl2/Et2O=8/1/1) to give 2 in 72% yield: H NMR
The representative compound 13 was prepared by the
following method. A solution of 5(S)-hydroxy-6(R)-
methoxy-5,6-dihydro-2H-pyrane (153 mg, 1.17 mmol),
d 0.96 (t, 3H, J=7.4 Hz), 1.75±1.88 (m, 1H), 1.95±2.09
(m, 1H), 3,11 (t, 2H, J=7.8 Hz), 5.12 (s, 2H), 7.09±7.50
(m, 8H), 9.88 (s, 1H); MS m/z 254 (M+).
DSC
(N,N0-disuccinimidyl
carbonate)
(450 mg,
1.76 mmol) and triethylamine (355 mg, 3.51 mmol) in
acetonitrile (5 mL) was stirred for 5 h at room tempera-
ture. After removal of the solvent in vacuo, the residue
was dissolved with CH2Cl2 (2 mL). To this was added
Methyl(3-benzyloxy-2-n-propyl)benzoate (3). To the
stirred solution of 2 (2.24 g, 8.80 mmol) and 2-methyl-
2-butene (2.60 g, 37.0 mmol) in acetone (40 mL), was
added a solution of NaClO2 (2.45 g, 27.1 mmol) and
Na2H2PO4 (3.49 g, 29.1 mmol) in H2O (20 mL), and the
mixture was stirred for 18 h. The solution was acidi®ed
with 0.3 N HCl aq and extracted with EtOAc. The
combined organic layer was successively washed with
saturated aq Na2S2O3 and brine. After removal of solvent
in vacuo, the residue was used without puri®cation in the
next step.
a
solution of (2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(580 mg, 1.17 mmol) in CH2Cl2 (2 mL) and a solution of
triethylamine (180 mg, 1.78 mmol) in CH2Cl2 (2 mL),
and the resulting solution was stirred for 1 day. The
reaction was quenched with brine and the reaction mix-
ture was extracted with EtOAc. The combined organic
layer was successively washed with saturated aqueous
NaHCO3 and brine, and dried over Na2SO4. After
removal of the solvent in vacuo, the residue was puri®ed
by ¯ash column chromatography (hexane/EtOAc=2/8
then EtOAc only) to a€ord 13 (343 mg) in 55% yield.
To the stirred solution of the above crude benzoic acid
in benzene/MeOH (20/10 mL) was added trimethyl-
silyldiazomethane (20 mL, 10% n-hexane solution) at
room temperature. The reaction was stirred for 5 min
and evaporated in vacuo. The resulting residue was
puri®ed by ¯ash column chromatography (hexane/
Preparation of benzamide-type inhibitors (18±39)
1
The representative compound 18 was coupled with (2S,
3S)-AHPBA-4S-Cl-Pro-NH-t-Bu in the following way.
The solution of 3-hydroxy-2-methylbenzoic acid (1.51 g,
9.92 mmol), 1-(3-dimethylaminopropyl)-3-ethylcarbodi-
EtOAc=9/1) to give 3 in 83% yield: H NMR (CDCl3)
d 0.98 (t, 3H, J=7.3 Hz), 1.81±1.87 (m, 1H), 1.96±2.08
(m, 1H), 2.96 (t, 2H, J=7.9 Hz), 3.89 (s, 3H), 5.10 (s,
2H), 6.99±7.70 (m, 8H); MS m/z 284 (M+).
.
imide hydrochloride (EDCI) (3.05 g, 15.9 mmol), 1-hydroxy-
benzotriazole (HOBt) (1.35 g, 9.96 mmol) and (2S,3S)-
AHPBA-4(S)-Cl-Pro-NH-t-Bu (3.45 g, 9.02 mmol) in
THF (80 mL) was stirred for 1 day at room temperature.
The reaction was quenched with brine and this reaction
mixture was extracted with EtOAc. The organic layer
was washed with brine and dried over Na2SO4. After
removal of the solvent in vacuo, the residue was puri®ed
by ¯ash column chromatography (CH2Cl2/MeOH=9/1)
to a€ord 18 (4.25 mg) in 91% yield.
3-Hydroxy-2-n-propylbenzoic acid (4). A suspension of
the methyl ester 3 (578 mg, 2.0 mmol) and Pd-black
(50 mg) in MeOH (5 mL) was stirred for 2 days under
hydrogen (1 atm) at room temperature. After changing
the atmosphere to N2, the mixture was diluted with
CH2Cl2 and ®ltered through a Celite pad (washed with
CH2Cl2). After removal of the solvent in vacuo, the
residue was used without puri®cation in the next step
(200 mg, 50%, as crude product): mp 80 ꢁC; H NMR
1
(CDCl3) d 1.00 (t, 3H, J=7.4 Hz), 1.54±1.69 (m, 2H),
2.86±2.92 (m, 2H), 3.89 (s, 3H), 5.12 (s, 1H), 6.93 (d,
1H, J=7.9 Hz), 7.11 (dd, 1H, J1=J2=7.9 Hz), 7.39 (d,
1H, J=7.9 Hz); IR (KBr) 3413, 1698 cm 1; Anal. Calcd
for C11H14O3: C, 68.02; H,717; Found: C,67.85; H, 7.53.
3-Benzyloxy-2-n-propylbenzaldehyde (2). To the stirred
solution of N,N,N0-trimethylethylenediamine (1.46 g,
14.3 mmol) in toluene (13 mL) was added n-butyllithium
(5.46 mL, 2.5 M solution in n-hexane) at 20 ꢁC. The
cooling bath was removed and this solution was stirred
for 10 min at room temperature. The reaction mixture
was cooled to 20 ꢁC and to this a THF solution
(10 mL) of 1 (2.76 g, 13.0 mmol) was added and stirred
The resulting crude methyl ester (116 mg, 596 mmol) and
.
LiOH H2O (125 mg, 299 mmol) in MeOH±H2O (1 mL/
1 mL) was stirred for 3 h at 100 ꢁC. The reaction was

E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
601
cooled to room temperature and acidi®ed with 3 N
aqueous HCI. The reaction mixture was extracted with
EtOAc and washed with brine. After the removal of
solvent in vacuo, the residue was puri®ed with pre-
parative TLC (EtOAc only) to give acid 4 (91.4 mg) in
85% yield: mp, 144±145 ꢁC; 1H NMR (DMSO-d6) d
0.89 (t, 3H, J=7.8 Hz), 1.49 (tq, 2H, J1=J2=7.8 Hz),
2.80 (t, 2H, J=7.8 Hz), 6.94 (d, 1 H, J=8.2 Hz), 7.05
(dd, 1H, J1=J2=8.2 Hz), 7.13 (d, 1H, J=8.2 Hz), 9.51
(s, 1H), 12.6 (br,1H); IR(KBr) 3386, 1699 cm 1, Anal.
Calcd for C10H12O3: C, 66.65; 11,6.71; Found: C, 66.41;
H, 6.81.
2H), 2.62±2.77 (m, 3H), 3.04±3.28 (m, 4H), 3.66±3.81
(m, 2H), 4.07±4.33 (m, 4H), 4.45±4.56 (m, 2H), 5.27±
5.38 (m, 2H), 6.18 (br, 1H), 7.22±7.36 (m, 5H); MS m/z
544 (M+).
[3(S)-(Tetrahydrofuranyl)oxy]carbonyl-(2S,3S)-AHPBA-
4(S)-Cl-Pro-NH-t-Bu (10). Mp 73±86 ꢁC; 1H NMR
(CD3OD) d 1.32 (s, 9H), 1.95±2.05 (m, 1H), 2.07±2.18
(m, 2H), 2.60±2.74 (m, 2H), 2.94 (dd, 1H, J1=13.9,
J2=3.3 Hz), 3.52 (d, 1H, J=10.6 Hz), 3.50±3.84 (m,
5H), 4.01±4.06 (m, 1H), 4.31±4.44 (m, 4H), 5.00±5.04
(m, 1H), 7.16±7.33 (m, 5H); IR (KBr) 3414, 3343, 2970,
2478, 1683, 1534, 1367, 1226, 1033, 702 cm 1; Anal.
1
.
[(Cyclopentyl)oxy]carbonyl - (2S,3S) - AHPBA - 4(S) - Cl-
Pro-NH-t-Bu (5). Mp 70±79 ꢁC; 1H NMR (CD3OD) d
1.32 (s, 9H), 1.47±1.67 (m, 9H), 2.14±2.18 (m, 1H),
2.61±2.74 (m, 2H), 2.93 (dd, 1H, J1=13.9, J2=3.3 Hz),
3.78 (q, 1H, J=10.6 Hz), 4.03±4.04 (m, 1H), 4.31±4.44
(m, 4H), 7.16±7.32 (in, 5H); IR (KBr).3339, 2968, 2489,
1655, 1528, 1455, 1227 cm 1; MS m/z 495 (M+).
Calcd for C24H34N3O6C1 2H2O: C, 57.08; H, 6.99; N,
8.32; Cl, 7.02; Found: C, 57.33; H, 6.96; N, 8.36; Cl,
7.31.
(1,4:3,6-Dianhydro-D-sorbitol)carbonyl-(2S,3S)-AHPBA-
4(S)-Cl-Pro-NH-t-Bu (11). Mp 104±106 ꢁC; 1H NMR
(CD3OD) d 1.32 (s, 9H), 2.13±2.18 (m, 1H), 2.64±2.74
(m, 3H), 2.89 (dd, 1H, J1=13.9, J2=3.3 Hz), 3.50 (t,
1H, J=8.6 Hz), 3.66±3.93 (m, 5H), 3.99±4.04 (m, 1H),
4.17±4.22 (m, 1H), 4.31±4.49 (m, 5H), 4.63 (t, 1H,
J=5.3 Hz), 4.88±4.90 (m, 1H), 7.16±7.32 (m, 5H); IR
(KBr) 3417, 3344, 2969, 1717, 1652, 1531, 1427, 1265,
[3(R,S)-(Tetrahydrofuranyl)oxy]carbonyl-(2S,3S)-AHPBA-
4(S)-Cl-Pro-NH-t-Bu (6). Mp, 85±91 ꢁC; 1H NMR
(CD3OD) d 1.35 (s, 9H), 1.96±2.18 (m, 3H), 2.61±2.72
(m, 3H), 2.94 (dd, 1H, J1=13.9, J2=3.3 Hz), 3.54±3.84
(m, 6H), 4.03±4.04 (m, 1H), 4.31±4.44 (m, 4H), 5.00±
5.02 (m, 1H),7.16±7.32 (m, 5H); IR (KBr) 3339, 2970,
1
2
.
751, 701 cm ; Anal. Calcd for C26H36N3O8C1 3H2O: C,
55.17; H, 6.65; N, 7.42; Cl, 6.26; Found: C, 55.06; H,
6.61; N, 7.45; Cl, 6.1 1; MS m/z 554 (M++1).
2875, 2489, 1706, 1426, 1226, 702 cm 1; Anal. Calcd for
1
.
C24H34N3O6Cl 2H2O: C, 57.08; H, 6.99; N, 8.32; Cl,
7.02; Found: C, 57.09; H, 6.90; N, 8.29; Cl, 7.02; MS m/
z 496 (M+).
[5(R)-[6(S)-Methoxy-5,6-dihydro-2H-pyranyl]oxy]carbonyl-
(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (12). Mp 88±
90 ꢁC; H NMR (CDCl3) d 1.30 (s, 9H), 2.57±2.76 (m,
1
[3(R,S)-(Pyrrolidyl)oxy]carbonyl-(2S, 3S)-AHPBA-4(S)-
Cl-Pro-NH-t-Bu HCl (7). Mp 112 ꢁC; 1H NMR
4H), 3.50 (s, 3H), 3.71±3.84 (m, 2H), 4.02±4.34 (m, 4H),
4.49±4.58 (m, 2H), 4.82±5.33 (m, 3H), 5.50 (dd, 1H,
J1=10.5, J2=1.5 Hz), 5.87 (dd, 1H, J1=10.5,
J2=2.0 Hz), 6.33 (s, 1H), 7.13±7.37 (m, 5H); IR (KBr)
3335, 2968, 2935, 1762, 1710, 1687, 1651, 1531, 1455,
1392, 1367, 1250, 1230, 1206, 1128, 1101, 1057, 967, 937,
888, 820, 752, 702 cm 1; MS m/z 538 (M++1).
.
(CD3OD) d 1.35 (s, 9H), 1.96±2.18 (m, 3H), 2.61±2.72
(m, 3H), 2.94 (dd, 1H, J1=13.9, J2=3.3 Hz), 3.54±3.84
(m, 6H), 4.03±4.04 (m, 1H), 4.31±4.44 (m, 4H), 5.00±
5.02 (m, 1H), 7.16±7.32 (m, 5H); IR (KBr) 3293, 2970,
1718, 1651, 1534, 1455, 1228, 1032, 752, 702 cm 1; Anal.
.
.
Calcd for C24H35N4O5C1 HCl H2O: C, 52.46; H, 6.79;
N, 10.20; Cl, 12.90; Found: C, 52.38; H, 7.3 1; N, 9.98;
Cl, 13.68; MS m/z 494 (M++1).
[5(S)-[6(R)-Methoxy-5,6-dihydro-2H-pyranyl]oxy]carbonyl-
(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (13). Mp 90±
92 ꢁC; H NMR (CDCl3) d 1.31 (s, 9H), 2.54±2.79 (m,
1
[3(R, S) - (Tetrahydrothiophenyl)oxy]carbonyl - (2S, 3S) -
AHPBA-4(S)-Cl-Pro-NH-t-Bu (8). Mp 85±91 ꢁC; 1H
NMR (CDCl3) d 1.31 (s, 9H), 1.78±1.98 (m, 1H), 2.03±
2.28 (m, 1H), 2.62±3.08 (m, 7H), 3.64±3.89 (m, 3H),
4.03±4.32 (m, 3H), 4.49±4.58 (m, 2H), 5.14 (br, 1H),
5.31 (br, 1H), 6.28 (br, 1H), 7.20±7.32 (m, 5H); Anal.
4H), 3.39 (s, 3H), 3.33±3.95 (m, 1H), 3.99±4.50 (m, 6H),
4.52±4.88 (m, 3H), 5.16 (s, 1H), 5.29 (d, 1H, J=8.7 Hz),
5.69 (dd, 1H, J1=10.5, J2=1.8 Hz), 5.96 (dd, 1H,
J1=10.5, J2=2.1 Hz), 6.36 (s, 1H), 7.13±7.38 (m, 5H);
IR (KBr) 3366, 2965, 2934, 1762, 1700, 1688, 1650,
1128, 1102, 1059, 968, 937, 888, 753, 702 cm 1; MS m/z
538 (M++1).
1
.
Calcd for C24H34N3O5SCl 2H2O: C, 54.38; H, 6.66; N,
7.92; Cl, 6.69; S, 6.05; Found: C, 54.69; H, 6.34; N, 7.73;
Cl, 6.72; S, 6.08; MS m/z 512 (M+).
[5(R)-(5,6-Dihydro-2H-pyranyl)oxy]carbonyl-(2S,3S)-
AHPBA-4(S)-Cl-Pro-NH-t-Bu (14). Mp 88±90 ꢁC; d
1.30 (s, 9H), 2.56±2.76 (m, 4H), 3.36 (s, 3H), 3.41±3.90
(m, 1H), 4.00±4.48 (m, 6H), 4.49±4.88 (m, 3H), 5.14 (s,
1H), 5.28 (d, 1H, J=8.7 Hz), 5.63 (dd, 1H, J1=10.5,
[3(R,S) - (1,1 - Dioxo - tetrahydrothiophenyl)oxy]carbonyl-
(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (9). Mp 90±
ꢁ
1
94 C; H NMR (CDCl3) d 1.35 (s, 9H), 2.01±2.43 (m,

602
E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
J2=1.8 Hz), 5.90 (dd, 1H, J1=10.5, J2=2.1 Hz), 6.31
(s, 1H), 7.13±7.35 (m, 5H); MS m/z 508 (M++1).
7.34 (m, 9H); IR (KBr) 3322, 2968, 1649, 1530, 1455,
1392, 1366, 1270, 1207, 1112, 746, 700 cm 1; Anal.
1
.
Calcd for C27H34N3O4Cl 2H2O: C, 63.71; H, 6.93; N,
8.25; Cl, 6.96. Found: C, 63.39; H, 6.52; N, 7.90; Cl,
[3(S)-(Tetrahydropyranyl)oxy]carbonyl-(2S,3S)-AHPBA-
4(S)-Cl-Pro-NH-t-Bu (15). Mp 73±86 ꢁC; 1H NMR
(CD3OD) d 1.32 (s, 9H), 1.95±2.05 (m, 2H), 2.07±2.20
(m, 2H), 2.55±2.98 (m, 5H), 3.50±3.84 (m, 7H), 4.01±4.12
(m, 1H), 4.31±4.44 (m, 4H), 5.00±5.04 (m, 1H), 7.16±
7.33 (m, 5H); IR (KBr) 3414, 3343, 2970, 2478, 1683,
1534, 1367, 1226, 1033, 702 cm 1; MS m/z 510 (M++1).
7.08; MS m/z 500 (M++1).
2-Chlorobenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(21). Mp 85 ꢁC; H NMR (CDCl3) d 1.30 (s, 9H), 2.41±
1
2.93 (m, 4H), 3.61±4.17 (m, 3H), 4.31±4.75 (m, 4H), 6.28
(s, 1H), 6.69 (d, 1H, J=8.2 Hz), 7.17±7.48 (m, 9H);
IR (KBr) 3341, 3324, 2968, 1652, 1530, 1391, 1365,
1
1
2
.
1205, 751 cm ; Anal. Calcd for C26H31N3O4Cl2 H2O:
[3(S)-[2(R)-methoxy-(4(S),5(R)-methoxymethylene)tetra-
hydropyranyl]oxy]carbonyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-
C, 58.98; H, 6.09; N, 7.93; Cl, 13.39. Found: C,
58.62; H, 6.01; N, 7.64; Cl, 13.38; MS m/z 520
(M++1).
NH-t-Bu (16). Mp 88±90 ꢁC; H NMR (CDCl3) d 1.30
1
(s, 9H), 2.56±2.89 (m, 4H), 3.29±3.49 (m, 6H), 3.68±4.73
(m, 13H), 5.40 (d, 1H, J=9.0 Hz), 5.79 (s, 1H), 6.30 (s,
1H), 7.15±7.39 (m, 5H); MS m/z 652 (M++K).
2-Bromobenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(22). Mp 91 ꢁC; H NMR (CDCl3) d 1.30 (s, 9H), 2.40±
1
[3(S) - [2(R) - Methoxy - tetrahydropyranyl]oxy]carbonyl-
(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (17). Mp 89±
2.92 (m, 3H), 3.64±4.10 (m, 4H), 4.31±4.74 (m, 4H),
6.26±6.61 (m, 2H), 7.18±7.35 (m, 8H), 7.51±7.59 (m,
93 ꢁC; H NMR (CDCl3) d 1.29 (s, 9H), 1.36±1.87 (m,
1H); IR (KBr) 3403, 3326, 2969, 2932, 2877, 1652, 1530,
1
1
3H), 2.41±3.29 (m, 4H), 3.34 (s, 1H), 3.37±3.52 (m, 3H),
3.61±3.73 (m, 2H), 3.81±3.90 (m, 1H), 4.07±4.33 (m,
3H), 4.49±4.64 (m, 3H), 5.22 (d, 1H, J=8.6 Hz), 6.30 (s,
1H), 7.00±7.32 (m, 5H); IR (KBr) 3338, 2965, 2880,
1455, 1392, 1366, 1268, 1226, 1119, 1029, 750, 701 cm
MS m/z 564 (M++1).
;
2-Iodobenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(23). Mp 93±94 ꢁC; 1H NMR (CDCl3) d 1.30 (s, 9H),
2.40±2.93 (m, 3H), 3.64±4.10 (m, 4H), 4.31±4.75 (m,
4H), 6.22±6.53 (m, 2H), 7.03±7.13 (m, 2H), 7.19±7.38
(m, 6H), 7.78±7.85 (m, 1H); IR (KBr) 3319, 2966, 1652,
1533, 1454, 1118, 1016, 872, 749, 700 cm 1; MS m/z 612
(M++1).
1707, 1690, 1648, 1535, 1455, 1392, 1366, 1320, 1265,
1
1225, 1156, 1126, 1086, 1058, 1031, 969, 752, 701 cm
;
1
.
Anal. Calcd for C26H38N3O7Cl 2H2O: C, 56.88; H, 7.16;
N, 7.65; Cl, 6.46; Found: C, 56.63; H, 7.27; N, 7.53; Cl,
6.72; MS m/z 540 (M+).
(3-Hydroxy-2-methyl)benzoyl-(2S,3S)-AHPBA-4(S)-Cl-
Pro-NH-t-Bu (18). Mp 117 ꢁC; 1H NMR (CDCl3) d 1.30
(s, 9H), 1.96 (s, 3H), 2.21±2.77 (m, 4H), 3.48±4.18 (m,
2H), 4.30±4.73 (m, 4H), 5.94 (s, 1H), 6.17±6.84 (m, 3H),
6.93±7.03 (m, 1H), 7.14±7.33 (m, 5H); IR (KBr) 3325,
2969, 2931, 1648, 1586, 1526, 1455, 1367, 1282, 1225,
2-n-Propylbenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-
Bu (24). Mp 73±75 ꢁC; H NMR (CDCl3) d 0.80 (t, 3H,
J=7.7 Hz), 1.30 (s, 9H), 1.42 (q, 2H, J=7.7 Hz), 2.41±
2.91 (m, 6H), 3.65±4.14 (m, 3H), 4.32±4.73 (m, 4H),
6.04±6.46 (m, 2H), 6.99±7.36 (m, 9H); IR (KBr) 3409,
3326, 1648, 1527, 1455, 1367, 1116, 700 cm 1; Anal.
1
1208, 1176, 1112, 1093, 700 cm 1; Anal. Calcd for
1
.
.
Calcd for C29H38N3O4Cl H2O: C, 63.78; H, 7.38; N,
C27H34N3O5Cl 2H2O: C, 61.77; H, 6.72; N, 8.00; Cl,
6.75. Found: C, 61.46; H, 6.77; N, 7.85; Cl, 6.64; MS m/
z 515 (M+).
7.69; Cl, 6.49. Found: C, 64.00; H, 7.20; N, 7.56; Cl,
6.83; MS m/z 528 (M++1).
Benzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (19).
Mp 84±85 ꢁC; H NMR (CDCl3) d 1.31 (s, 9H), 2.40±
2.94 (m, 4H), 3.60±4.07 (m, 3H), 4.30±4.40 (m, 2H),
4.51±4.72 (m, 2H), 6.30 (s, 1H), 6.53 (d, 1H, J=8.0 Hz),
7.17±7.70 (m, 10H); IR (KBr) 3413, 3340, 2968, 2931,
1648, 1531, 1488, 1454, 1391, 1366, 1272, 1226, 1113,
2,6-Dimethylbenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-
t-Bu (25). Mp 93±97 ꢁC; 1H NMR (CDCl3) d 1.30 (s,
9H), 2.00 (s, 6H), 2.61±2.91 (m, 3H), 3.60±4.21 (m, 4H),
1
4.31±4.83 (m, 4H), 6.13 (d, 1H, J=8.1 Hz), 6.27 (s, 1H),
3
.
6.99±7.36 (m, 10H); Anal. Calcd for C28H36N3O4Cl 2H2O:
C, 62.15; H, 7.26; N, 7.77; Cl, 6.55. Found: C, 62.34; H,
1
1
1074, 700 cm ; Anal. Calcd for C26H32N3O4Cl 2H2O:
C, 63.09; H, 6.72; N, 8.49; Cl, 7.16. Found: C, 63.23; H,
6.75; N, 8.49; Cl, 6.89; MS m/z 486 (M++1).
6.98; N, 7.44; Cl, 6.72; MS m/z 514 (M++1).
.
2-Hydroxybenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-
Bu (26). Mp 100 ꢁC; H NMR (CDCl3) d 1.33 (s, 9H),
1
2-Methylbenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(20). Mp 83±84 ꢁC; 1H NMR (CDCl3) d 1.30 (s, 9H),
2.18 (s, 3H), 2.41±2.93 (m, 4H), 3.61±4.14 (m, 3H), 4.32±
5.06 (m, 4H), 6.08 (d, 1H, J=8.4 Hz), 6.27 (s, 1H), 7.10±
2.43±3.00 (m, 4H), 3.62±3.94 (m, 4H), 4.05±4.66 (m,
4H), 6.20 (s 1H), 6.77±7.06 (m, 2H), 7.14±7.43 (m, 7H),
12.0 (s, 1H); IR (KBr) 3350, 2970, 1644, 1603, 1536, 1494,
1454, 1226, 754 cm 1; Anal. Calcd for C26H32N3O5-

E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
603
1
.
C1 H2O: C, 60.05; H, 6.59; N, 8.08; Cl, 6.82. Found: C,
1225, 1115, 830, 752, 700 cm
;
Anal. Calcd for
1
60.05; H, 6,38; N, 7.72; Cl, 6.48; MS m/z 501 (M+).
C27H33N3O4FCl 2H2O: C, 61.53; H, 6.51; N, 7.97; F,
3.60; Cl, 7.97. Found: C, 61.18; H, 6.71; N, 7.68; F,
3.47; Cl, 6.62; MS m/z 517 (M+).
.
(2-Hydroxy-3-methoxy)benzoyl-(2S,3S)-AHPBA-4(S)-
Cl-Pro-NH-t-Bu (27). Mp 120±126 ꢁC; 1H NMR
(CDCl3) d 1.32 (s, 9H), 2.41±2.94 (m, 3H), 3.65±3.74 (m,
3H), 3.82±4.09 (m, 4H), 4.27±4.67 (m, 4H), 6.14±6.27
(m, 1H), 6.77±6.88 (m, 1H), 6.94±7.06 (m, 2H), 7.10±
7.56 (m, 6H), 11.2 (s, 1H); IR (KBr) 3353, 2969, 2935,
1671, 1587, 1534, 1462, 1367, 1253, 1119, 936, 873, 835,
779, 747, 702 cm 1; MS m/z 531 (M+).
(2-Bromo-3-hydroxy)benzoyl-(2S,3S)-AHPBA-4(S)-Cl-
Pro-NH-t-Bu (33). Mp 117±118 ꢁC; 1H NMR (CDCl3) d
1.30 (s, 9H), 2.39±2.99 (m, 3H), 3.43±4.24 (m, 3H), 4.31±
4.53 (m, 2H), 4.60±5.06 (m, 3H), 6.22±7.34 (m, 10H); IR
(KBr) 3321, 2968, 2931, 1652, 1569, 1530, 1458, 1439,
1
1367, 1296, 1225, 1118, 1031, 873, 795, 750, 701 cm
MS m/z 580 (M++1).
;
2-Aminobenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(28). Mp 93±94 ꢁC; 1H NMR (CDCl3) d 1.31 (s, 9H),
2.44±2.94 (m, 3H), 3.70±4.16 (m, 4H), 4.29±4.38 (m,
2H), 4.50±4.60 (m, 3H), 6.27±6.32 (m, 1H), 6.46 (d, 1H,
J=8.2 Hz), 6.60±6.71 (m, 3H), 7.13±7.32 (m, 7H); IR
(KBr) 3348, 2968, 1644, 1521, 1453, 1366, 1266, 1118,
(2-Ethyl-3-hydroxy)benzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-
NH-t-Bu (34). Mp 111±116 ꢁC; 1H NMR (CDCl3) d 1.00
(t, 3H, J=7.6 Hz), 1.30 (s, 9H), 2.38±2.93 (m, 5H), 3.61±
4.12 (m, 4H), 4.31±4.71 (m, 4H), 6.10 (d, 1H,
J=7.4 Hz), 6.43 (s, 1H), 6.64±7.34 (m, 8H); IR (KBr)
1
5
.
750, 702 cm ; Anal. Calcd for C26H33N4O4C1 4H2O: C,
59.65; H, 6.84; N, 10.70; Cl, 6.77. Found: C, 60.36; H,
6.51; N, 10.28; Cl, 6.62; MS m/z 501 (M+).
3326, 2967, 1648, 1522, 1455, 1367, 1287, 1099, 749,
1
.
700 cm ; Anal. Calcd for C28H36N3O5Cl H2O: C,
61.36; H, 6.99; N, 7.67; Cl, 6.47. Found: C, 61.31; H,
6.01; N, 7.41; Cl, 6.35; MS m/z 5 30 (M++1).
3-Hydroxybenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-
Bu (29). Mp 112 ꢁC; H NMR (CDCl3) d 1.23 (s, 9H),
1
(3-Hydroxy-2-n-propyl)benzoyl-(2S,3S)-AHPBA-4(S)-
Cl-Pro-NH-t-Bu (35). Mp 108±112 ꢁC; 1H NMR
(CDCl3) d 1.00 (t, 3H, J=7.4 Hz), 1.30 (s, 9H), 2.38±
2.94 (m, 3H), 3.61±4.12 (m, 4H), 4.31±4.71 (m, 4H), 5.42
(s, 1 H), 6.10 (d, 1H, J=7.6 Hz), 6.25 (s, 1 H), 6.63±7.34
(m, 8H); IR (KBr) 3327, 2964, 2871, 1648, 1584, 1522,
1455, 1367, 1290, 1223, 1105, 791, 742, 700 cm 1; Anal.
2.35±4.61 (m, 8H), 4.61±5.06 (m, 3H), 6.46±8.25 (m,
11H); IR (KBr) 3406, 2968, 1648,1585, 1530, 1454,
1367, 1272, 1226, 1116, 811, 751, 700 cm 1; Anal. Calcd
1
.
for C26H32N3O5Cl 2H2O: C, 61.11; H, 6.52; N, 8.22; Cl,
6.94. Found: C, 61.25; H, 6.55; N, 7.95; Cl, 7.05; MS m/z
501 (M+).
.
Calcd for C29H38N3O5Cl H2O: C, 61.97; H, 7.17; N,
4-Hydroxybenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(30). Mp 100 ꢁC; 1H NMR (CDCl3) d 1.31 (s, 9H), 2.43±
2.95 (m, 4H), 3.60±4.09 (m, 3H), 4.20±4.69 (m, 5H),
5.97±8.13 (m, 11H); IR (KBr) 3327, 2969, 2876, 1652,
1609, 1536, 1503, 1455, 1392, 1366, 1272, 1226, 1174,
1113, 851, 750 cm 1; Anal. Calcd for C26H32N3O5-
7.48; Cl, 6.3 1. Found: C, 62.14; ¯, 6.93; N, 7.22; Cl,
6.60; MS m/z 544 (M+).
(2,6-Dimethyl-3-hydroxy)benzoyl-(2S,3S)-AHPBA-4(S)-
Cl-Pro-NH-t-Bu (36). Mp 134±136 ꢁC; 1H NMR
(CDCl3) d 1.30 (s, 9H), 1.91 (s, 3H), 1.97 (s, 311), 2.36±
2.90 (m, 3H), 3.71±4.19 (m, 4H), 4.31±4.85 (m, 3H),
5.04±7.00 (m, 3H), 7.11±7.52 (m, 7H); IR (KBr) 3335,
.
C1 H2O: C, 60.05; H, 6.59; N, 8.08; Cl, 6.82. Found: C,
60.19; H, 6.78; N, 8.41; Cl, 6.98; MS m/z 501 (M+).
2968, 1645, 1532, 1455, 1276, 1223, 1118, 872, 749,
1
.
700 cm ; Anal. Calcd for C28H36N3O5Cl 1.78H2O: C,
3-Fluorobenzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu
(31). Mp 81±82 ꢁC; 1H NMR (CDCl3) d 1.31 (s, 9H),
2.41±2.75 (m, 2H), 2.78±2.92 (m, 2H), 3.62±4.08 (m,
3H), 4.29±4.69 (m, 4H), 6.25 (s, 1H), 6.54 (d, 1H,
59.84; H, 7.09; N, 7.47; Cl, 6.31. Found: C, 60.07; H,
6.75; N, 7.09; Cl, 6.57; MS m/z 529 (M+).
J=8.1 Hz), 7.13±7.49 (m, 9H); IR (KBr) 3337, 2969,
1
(3-Amino-2-methyl)benzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-
NH-t-Bu (37). Mp 106±108 ꢁC; 1H NMR (CDCl3) d 1.30
(s, 9H), 1.90 (dd, 2H, J1=J2=22.5 Hz), 2.40±3.18 (m,
3H), 3.63±4.14 (m, 6H), 4.30±4.71 (m, 4H), 6.09±6.72
(m, 4H), 6.93±7.33 (m, 6H); IR (KBr) 3350, 1648, 1522,
2932, 1649, 1455, 1366, 1271, 1224, 806, 751, 701 cm
;
1
.
Anal. Calcd for C26H31N3O4FCl 4H2O: C, 61.41; H,
6.24; N, 8.26; F, 3.74; Cl, 6.97. Found: C, 61.40; H, 6.40; N,
8.20; F, 3.66; Cl, 6.74; MS m/z 504 (M++1).
1454, 1225, 1119, 873, 751, 701 cm 1; Anal. Calcd for
3
.
(3-Fluoro-2-methyl)benzoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-
NH-t-Bu (32). Mp 86±88 ꢁC; H NMR (CDCl3) d 1.30
C27H35N4O4Cl 4H2O: C, 61.35; H, 6.96; N, 10.60; Cl,
1
6.70. Found: C, 61.48; H, 6.98; N, 9.69; Cl, 6.33; MS m/
z 515 (M++1).
(s, 9H), 2.05 (s, 3H), 2.42±2.89 (m, 3H), 3.68±4.16 (m,
3H), 4.31±4.71 (m, 4H), 6.09 (d, 1H, J=8.4 Hz), 6.22 (s,
1H), 6.90 (d, 1H, J=7.4 Hz), 6.97±7.34 (m, 8H); IR
(KBr) 3321, 2969, 2932, 1652, 1530, 1456, 1393, 1243,
ꢀ-Naphthoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (38).
Mp 89±91 ꢁC; 1H NMR (CDCl3) d 1.31 (s, 9H),

604
E. Takashiro et al./Bioorg. Med. Chem. 6 (1998) 595±604
2.42±2.94 (m, 3H), 3.60±4.19 (m, 4H), 4.33±4.82 (m,
4H), 6.28±6.65 (m, 2H), 7.21±7.51 (m, 9H), 7.77±
7.99 (m, 3H); IR (KBr) 3350, 1648, 1522, 1454,
Thompson, W. L.; Culberson, C.; Holloway, M. K.; McKee, S.
R.; Munson, P. M.; Duong, T. T.; Smith, A. M.; Darke, P. L.;
Zugay, J. A.; Emilio, E. A.; Scheif, W. A.; Hu€, J. R.; Ander-
son, P. S. J. Med. Chem. 1994, 37, 1177.
1
1225, 1119, 873, 751, 701 cm
; Anal. Calcd for
3
.
7. (a) Randad, R. S.; Lubkowska, L.; Bhat, T. N.; Munshi, S.;
Gulnik, S. V.; Yu, B.; Erickson, J. W. Bioorg. Med. Chem. Lett.
1995, 5, 1707. (b) Kempf, D. L.; Flentge, C. A.; Wideburg, N.
E.; Saldivar, A.; Vasavanonda, S.; Norbeck, D. W. Bioorg.
Med. Chem. Lett. 1995, 5, 2725.
C30H34N3O4C1 4H2O: C, 65.56; H, 6.5 1; N, 7.65; Cl,
6.45. Found: C, 65.53; H, 6.23; N, 7.57; Cl, 6.57; MS m/
z 536 (M++1).
ꢁ-Naphthoyl-(2S,3S)-AHPBA-4(S)-Cl-Pro-NH-t-Bu (39).
8. (a) Kalish, V. L.; Tatlock, J. H.; Davis, II, J. R.; Kaldor, S.
W.; Dressman, B. A.; Reich, S.; Pino, M.; Nyugen, D.; Appelt,
K.; Musick, L.; Wu, B-W. Bioorg. Med. Chem. Lett. 1995, 5,
727. (b) Kaldor S. W.; Hammond, M.; Dressman, B. A.; Fritz,
J. E.; Crowell, T. A.; Hermann, R. A. Bioorg. Med. Chem. Lett.
1994, 4, 1385.
ꢁ
1
Mp 95 C; H NMR (CDCl3) d 1.32 (s, 9H), 2.42±5.06
(m, 11H), 6.29±8.19 (m, 14H); IR (KBr) 3334, 2968, 1648,
1531, 1455, 1391, 1366, 1269, 1228, 1205, 1136, 1115,
1
3
.
778, 761, 701 cm ; Anal. Calcd for C30H34N3O4C1 4H2O:
C, 65.57; H, 6.5 1; N, 7.65; Cl, 6.45. Found: C, 65.69; H,
6.3 1; N, 7.52; Cl, 6.29; MS m/z 536 (M++1).
9. Fleet, G. W. L; Gough, M. L.; Shing, T. K. M. Tetrahedron
Lett. 1983, 24, 3661.
10. Houbion, J. A.; Miles, J. A.; Paton, J. A. Org. Prep. Proc.
Int. 1979, 11, 27.
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where.
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20. The conclusion described by Kempf et al. was that ortho is
not a suitable position for interaction with Asp 29 or 30 (see
Ref. 7b). But the hydrogen bond interaction between the car-
bonyls and the ortho hydroxyl groups is presumed to be more
important than aforesaid interaction.
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