Structure-based design of nonpeptide inhibitors of interleukin-1β converting enzyme (ICE, Caspase-1)

Article abstract of DOI:10.1016/S0968-0896(01)00250-4

A novel class of reversible inhibitors of Interleukin-1β-converting enzyme (ICE, caspase-1) were discovered by iterative structure-based design. Guided by the X-ray crystal structure of analogues 1, 7 and 10 bound to ICE, we have designed a non-peptide series of small molecule inhibitors. These compounds incorporate an arylsulfonamide moiety which replaces Val-His unit (P3-P2 residues) amino acids of the native substrate. The synthesis of the core structure, structure-activity relationships (SARs), and proposed binding orientation based on molecular modeling studies for this serie of ICE inhibitors are described. Copyright

Full text of DOI:10.1016/S0968-0896(01)00250-4

Bioorganic & Medicinal Chemistry 10 (2002) 31–40
Structure-Based Design of Nonpeptide Inhibitors of Interleukin-1ꢀ
Converting Enzyme (ICE, Caspase-1)
Aurash B. Shahripour,a,* Mark S. Plummer,a Elizabeth A. Lunney,a Hans P. Albrecht,b
Sheryl J. Hays,a Catherine R. Kostlan,a Tomi K. Sawyer,a Nigel P. C. Walker,b,y
Kenneth D. Brady,c Hamish J. Allen,c Robert V. Talanian,c
Winnie W. Wongc and Christine Humbletb
aDepartment of Medicinal Chemistry, Pfizer Global Research & Development, 2800 Plymouth Road, Ann Arbor, MI 48105, USA
bDepartment of Chemistry BASF AG, Carl-Bosch-Str. 38, 67056 Ludwigshafen, Germany
cDepartment of Biochemistry, BASF Bioresearch Corporation, Worcester, MA 01609, USA
Received 9 April 2001; accepted 29 June 2001
Abstract—A novel class of reversible inhibitors of Interleukin-1b-converting enzyme (ICE, caspase-1) were discovered by iterative
structure-based design. Guided by the X-ray crystal structure of analogues 1, 7 and 10 bound to ICE, we have designed a non-
peptide series of small molecule inhibitors. These compounds incorporate an arylsulfonamide moiety which replaces Val-His unit
(P3-P2 residues) amino acids of the native substrate. The synthesis of the core structure, structure–activity relationships (SARs),
and proposed binding orientation based on molecular modeling studies for this series of ICE inhibitors are described. # 2001
Elsevier Science Ltd. All rights reserved.
Interleukin-1 (IL-1) is the general term for two distinct
proteins, IL-1a and IL-1b; the latter is the predominant
species released by monocytes.1 The mature cytokine
IL-1b plays a key role in inflammation, septic shock,
and in a variety of other physiological and pathological
processes, including wound healing and the growth of
certain leukemias. The cysteinyl protease interleukin-1b
converting enzyme2 (ICE) has been shown to cleave the
31 kDa IL-1b precursor (pro-IL-1b) at Asp116–Ala117
to generate the 17.5 kDa mature form of IL-1b.3 Like-
wise the mature active form of human ICE is derived
from a 404 amino acid precursor (p45) by proteolytic
cleavage at Asp103, Asp119, Asp297 and Asp316. The
active enzyme is a heterotetramer which consists of two
subunits, p20 (residues 120–297) and p10 (residues 317–
404), which are non-covalently bound. ICE has been
characterized as a cysteine protease,4 with cysteine285
of the p20 subunit serving as the catalytic residue.4 The
structure of ICE bound to a tetrapeptide aldehyde inhi-
bitor (Ac-Tyr-Val-Ala-Asp-H) has been determined by
X-ray diffraction.5,6 ICE has the unique requirement for
aspartic acid in the P1 position.7,8 Exploiting this unu-
sual specificity, two general inhibition strategies have
been reported. The first utilizes peptidomimetic alde-
hydes, nitriles, and ketones, as covalent reversible inhi-
bitors of ICE.9,10 The second approach employs
peptidomimetic a-substituted ketones of the general
structure R-CO-CH2-X, where X is a leaving group.
These are covalent irreversible inhibitors.9,10 Potent and
selective tetrapeptide inhibitors have been reported that
inhibit the production of IL-1b in monocytes.4 Our goal
is to employ structure-based design to identify low
molecular weight, nonpeptidic, reversible inhibitors of
ICE, as potential therapeutic agents for inflammatory
diseases.
In an effort to develop more bioavailable, nonpeptidic
inhibitors for assessing the effects of ICE inhibition in
vivo, we simplified the known potent peptide inhibitor,
Ac-Tyr-Val-Ala-Asp-CO–(CH2)5–Ph (1, Ki=19 nM),11
by replacing the Ac-Tyr-Val-Ala tripeptide with a ben-
zyloxycarbonyl (CBZ) group providing 3 (Ki=119 mM).
Molecular modeling12 of 3, using the X-ray structure of
1 and manual docking, indicated that the CBZ would
*Corresponding author. Fax: +1-734-622-3107; e-mail: aurash.
shahripour@pfizer.com
yCorresponding author on X-ray crystallography at present address:
Tularic Inc., Two Corporate Drive, South San Francisco, CA 94080,
USA.
0968-0896/02/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0968-0896(01)00250-4

32
A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
occupy the S2 site and the phenylpentyl group would be
directed toward the prime side pocket. This prediction
was based on the steric compatibility of the ligand with
the enzyme binding region. In an attempt to understand
the functionality contributing to the activity of 3, with
the aim of increasing the potency, analogues 5, 7, and 10
(Table 1, vide infra) were synthesized.13 In designing our
target molecule, we decided to replace the P10 b-methy-
lene in compound 3 with a sulfur atom, based on similar
replacements in peptide ketone inhibitors,14 to provide
5. Such a replacement was expected to increase potency
and indeed a 5-fold increase in potency compared to 3
was observed (5, Ki=25 mM). Replacement of the CBZ
group in 3 with a functionality predicted to interact with
ICE forming hydrogen bonds with the Arg341 side
chain and backbone carbonyl led us to incorporate a
phenyl sulfonamide moiety giving inhibitor 7. The
binding affinity of 7 was enhanced by 5-fold relative to 3
(7, Ki=24 mM). An attempt to further improve the
potency of 7 by combining the potency enhancing thio-
methylketone moiety with the phenyl sulfonamide to
give 10, surprisingly, resulted in no potency increase, as
10 was found to be equipotent with 5 and 7.
is that the phenyl ring of the arylsulfonamide group
which points towards solvent is within hydrophobic
contact of the Trp340 indole ring and the prime side
polymethylene chain.
Examination of the X-ray crystal structure of 7 indi-
cates that an ortho hydrogen atom of the phenylsulfo-
namide group is in close proximity to prime side
methylene units of the phenylpentyl side chain extend-
ing from the aspartic acid-ketone. It is possible that this
favorable binding mode is pre-organized by hydro-
phobic collapse. The X-ray crystal structure of 10
bound to ICE, indicates however, that the sulfur in the
phenyl-thiomethyl side chain is oriented further away
from the phenyl group than the corresponding methyl-
ene in 7, perhaps to avoid a steric clash. An overlay of
the bound crystal structures of 7 and 10 is shown in
Figure 1.
On the basis of the X-ray structures of compounds 7
and 10, it was surmised that if this C-terminal side chain
in 10 was truncated to an aldehyde, then substitution of
the ortho position of the phenyl sulfonamide group with
a phenyl ring would provide an analogue with produc-
tive binding. The resulting ortho biphenyl sulfonamide
was designed to provide a hydrophobic cap over the
imidazole of the active site His237, partially blocking
the oxyanion hole from bulk water while providing
favorable van der Waals contact with the protein. We
now describe the structure–activity relationship of these
designed nonpeptide, sulfonamide-containing, aspartic
acid aldehyde ICE inhibitors.
In an effort to understand this lack of cooperative
potency enhancement between the P side phenyl sulfo-
nyl group and the prime side thiomethylketone func-
tionality in 10, the crystal structures of 7 and 10 were
obtained (Fig. 1). As observed in the structure of 7
complexed with ICE, both oxygen atoms of the phenyl
sulfonamide are hydrogen bonded to the protein. In this
orientation, the sulfonamide N–H is hydrogen bonded
to the carbonyl of Ser339 (2.83 A), the in-plane sulfonyl
oxygen atom is hydrogen bonded to the guanidino NH2
of Arg341 (2.69 A) while the other sulfonyl oxygen
forms a hydrogen bond with the main chain amide of
Arg341 (2.98 A). The consequence of these interactions
The preparation of a representative sulfonamide-con-
taining aspartic acid aldehyde, VII, is shown in Scheme
1. We were gratified to find that the biphenyl sulfona-
mide aspartic acid aldehyde 12 was 15-fold more potent
than the thioketone containing inhibitor 10 (12,
Ki=1.6 mM). For comparison, the aldehyde derivative
11 which lacks the pendent ortho phenyl ring of 12, is
nearly 6-fold less potent than 12 (11, Ki=9.4 mM).
Table 1. Reversible inhibitors and their assay values tested against
ICE PRin vitro a
Compd
no.
Reversible inhibitors
Ki (mM) IC50 (mM)
Compound 12, was studied in its ICE bound state via
X-ray crystallography to verify that the proposed bind-
ing mode of 12 was responsible for its potency increase
(Fig. 2). This complex confirmed our original hypothesis
regarding the mode of binding and the active site inter-
actions of 12. In this complex however, a second con-
formation of His237 side chain which was not predicted
is populated. Specifically, His237 side chain has rotated
from the previously observed +gauche orientation to a
trans orientation creating a large pocket adjacent to the
S1 site.15
1
Ac-Tyr-Val-Ala-Asp-CO-(CH2)5-Ph
0.011
119
0.078
1034
3
5
25
24
24
141
166
176
The X-ray structure of compound 12 guided further
design efforts to increase the binding affinity of this
small nonpeptide inhibitor. We realized an improved
potency by modifying the biphenyl ring system in the
extended S1 site. Relative to the parent inhibitor 12, two
compounds were designed and synthesized to changed the
torsion angle of the pendant aromatic ring: compound 13
with the methyl substituent on the phenyl ring at C-6
position and compound 14 with the methyl substituent on
7
10
aFor a description of the assay, see ref 6. Values are the average of at
least two determinations.

A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
33
Figure 1. Overlay of the crystal structures of 7 (green thick lines) and 10 (orange thick lines) bound to the active site of ICE. The inhibitors are
colored according to atom type [blue for nitrogens, red for oxygens, yellow for sulfurs, green (7) and orange (10) for carbons]. Enzyme residues are
depicted in pink. The hydrogen bonds between the inhibitors sulfonamide (SO2NH) and Arg341 (NH2CNH) Ser339 (CO), and between the acid
(CO2) and Arg179 (NH2CNH) are shown. His237 is shown in cyan.
Scheme 1. Preparation of sulfonamide-containing l-aspartic acid aldehyde. Reagents: (a) Ar-B(OH)2, Pd0(Ph3P)4, 2 N Na2CO3, DME, 100 ꢀC, 12 h;
(b) H2 at 50 psi, Raney nickel, MeOH/THF (1:1), 6 h; (c) (i) HCl, H2O, AcOH, (ii) 1.2 equiv NaNO2, H2O, ꢁ5 to 0 ꢀC, (iii) 0.5 mol% CuCl, H2O
AcOH, SO2, 50 ꢀC, 12 h; (d) pyridine, CH2Cl2, Asp-(OtBu)–O–CH3N(OCH3); (e) LiAlH4, Et2O, ꢁ65 ꢀC, (f) 20% TFA/CH2Cl2.
the phenyl ring at C-20 position. The designed inhibi-
tors, 13 and 14, were based on the expectation that the
methyl groups on the phenyl rings would re-orient the
distal phenyl ring toward Arg341. The constrained ana-
logues of 12 showed a loss in binding affinity with
respect to 12, (13, Ki=1.9 mM and 14, Ki=6.8 mM).
stitutions are tolerated, increases in potency were not
observed.
Analysis of the X-ray structure (inhibitor 12) indicated
that replacing the distal phenyl ring in this series with a
1-naphthyl substituent was tolerated, although
improved potency was not realized, as illustrated by 17
(Ki=6.9 mM). The X-ray crystallographic structure of
17 complexed with ICE was obtained, confirming that
the His237 again moves from the standard +gauche
conformation to a trans conformation. Subsequent
molecular modeling indicated that replacing the second
phenyl ring of the naphthyl group in 17 with an acet-
amide moiety could possibly provide a hydrogen bond
donor to the Pro177(CO). This carbonyl normally forms
The X-ray structure of the inhibitor 12 showed a major
conformational change of His237 (vide supra), which
created a large hydrophobic pocket adjacent to the S1
site. It was hoped that the substitutions appended from
the phenylsulfonamide would serve to further fill this
new pocket by employing methyl groups on the phenyl
ring at C-30 and C-40 position, for example 15
(Ki=3.1 mM) and 16 (Ki=7.2 mM). Although these sub-

34
A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
Figure 2. X-ray crystal structure of 12 in the ICE active site. The inhibitor is colored according to atom type (blue for nitrogens, red for oxygens,
yellow for sulfurs, and white for carbons). The hydrogen bonds between the inhibitor sulfonamide (SO2NH) and Arg341 (NH2CNH) Ser339 (CO),
and between the acid (CO2) and Arg179 (NH2CNH) are shown. His237 is shown in cyan.
a hydrogen bond with His237, when the His237 side chain
is positioned in the standard +gauche orientation. This
concept was tested by preparing an analogue containing a
NHCOCH3 substituent at the C-30 position of the phenyl
ring giving 18 (Ki=2.3 mM). Disappointingly, the resulting
amide 18, was 1.5 times less active relative to 12 (Table 2)
perhaps due to desolvation penalty.
against human ICE. Further efforts aimed at improving
compound potency as well as an investigation of their
selectivity for specific members of the ICE family are
under way and will be reported in due course.
Experimental
General comments
Conclusions
Analytical data were recorded for the compounds
described below using the following general procedures.
Proton NMRspectra of the compounds were recorded
on Varian, Gemini 2000 (300 MHz) or Unity
(400 MHz); chemical shifts were recorded in ppm (d)
from an internal tetramethylsilane standard in deuter-
iochloroform or deuteriodimethyl sulfoxide or deuter-
iomethyl alcohol as specified below. Combustion
analyses were performed by Quantitative Technologies
Inc., Whitehouse, NJ, USA, and are within ꢂ0.4% of
the theoretical values. Positive and negative ion atmo-
spheric pressure chemical ionization (APCI) mass spec-
tra (MS) were recorded on a Micromass Platform LC
mass spectrometer operating in open access mode.
Samples were introduced by loop injection using a Gil-
son 215 autosampler into a mobile phase of 80:20 ace-
tonitrile/water flowing at 200 mL/min delivered by a
Hewlett-Packard HP1100 HPLC. The mass spectro-
meter source and probe temperatures were 150 and
The X-ray crystal structure of 1 proved to be very useful
in guiding the synthetic effort. Starting from a tetra-
peptide (1) lead and a predicted mode of binding, fol-
lowed by peptide-derived inhibitor structure–activity
relationship analysis and molecular modeling, we have
advanced a novel, low molecular weight class of inhibi-
tors. The X-ray structure of 12 complexed with ICE has
been determined. In this X-ray structure a major con-
formational change has been observed in which the cata-
lytic His237 side chain has been rotated from a +gauche to
a trans orientation creating a large hydrophobic pocket
adjacent to the P1 site. Synthetic efforts are now directed
toward increased potency in this series of non-peptidic ICE
inhibitor. Taking advantage of the information gained
with the X-ray structures, we have designed and synthe-
sized more potent ICE inhibitors relative to our initial
inhibitors 3, 5, 7, and 10. Compound 12 is the most
potent inhibitor in this class and displays a Ki=1.6 mM

A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
Table 2. Evaluation of inhibitors against ICE
35
After an additional 5 min and cooling to 0 ꢀC benzyl
chloroformate (0.23 mL 0.315 g, 1.8 mmol) and N-
methylmorpholine (0.20 mL, 0.18 g, 1.8 mmol) were
added simultaneously. The reaction mixture was stirred
for 15 h at room temperature. The solvent was removed
under reduced pressure and the residue was taken up in
the ethyl acetate. The organic phase was washed suc-
cessively with aqueous citric acid, aqueous sodium
hydrogencarbonate and water, dried over sodium sul-
fate and concentrated under reduced pressure. Purifica-
tion of the residue over silica (elution with
dichloromethane/acetone 100:1) gave 0.125 g (31%) of
2. 1H NMR(400 MHz, DMSO- d6) d 7.75 (d, 1H), 7.35–
7.1 (m, 10H), 5.0 (s, 2H), 4.3 (dd, 1H), 2.65 (dd, 1H),
2.55–2.35 (m, 7H), 1.6–1.1 (m, 6H), 1.35(s, 9H).
Compd no.
RICE
ICE
Ki (mM)
IC50 (mM)
11
9.4
86.8
12
13
14
15
16
17
18
1.6
1.9
6.8
3.1
7.2
6.9
2.3
20.3
34.4
28.0
37.0
66.2
11.40
49.80
(S)-3-Benzyloxycarbonylamino-4-oxo-9-phenyl-nonanoic
acid, 3. A solution of 2 (0.11 g, 0.243 mmol) was treated
with CH2Cl2/TFA (8 mL, 1:1) for 30 min at room tem-
perature. Evaporation under reduced pressure followed
by crystallization from dichloromethane/ether/hexane
yielded 0.088 g (91%) of 3. 1H NMR(400 MHz,
DMSO-d6) d 7.8 (d, 1H), 7.4–7.15 (m, 10H), 5.05 (dd,
2H), 4.35 (dd, 1H), 2.7 (dd, 1H), 2.6–2.4 (m, 5H), 1.6–
1.4 (m, 4H), 1.35–1.15 (m, 2H)
(S)-3-Benzyloxycarbonylamino-4-oxo-5-(3-phenyl-propyl-
sulfanyl)-pentanoic acid tert-butyl ester, 4. A mixture of
(S)-3-Benzyloxycarbonylamino-5-bromo-4-oxo-pentanoic
tert-butyl ester (1.0 g, 2.5 mmol) and 3-phenylpropyl-
mercaptan (0.38 g, 2.5 mmol) were dissolved in anhy-
drous DMF (1 mL). Potassium carbonate (0.173 g,
2.5 mmol) was added and the reaction was stirred at
25 ꢀC under a nitrogen atmosphere for 16 h. The reac-
tion was partitioned between EtOAc and H2O. The
organic layer was then washed with additional H2O
(3ꢃ50 mL), dried (Na2SO4), filtered and concentrated.
The crude product was chromatographed on a silica gel
column eluted with hexane/EtOAc/CH2Cl2 (7:1.5:1.5).
The product 4 was isolated as yellow oil (0.89 g, 75%).
450 ꢀC, respectively. The cone voltage was 15V while the
corona pin was held at 3.5 kV in positive ion and 3.0 kV
in negative ion mode.
Reagents were purchased from commercial sources.
Chromatography was performed on silica gel using the
solvent systems indicated below. For mixed solvent sys-
tems, the volume ratios are given. All reactions were
performed under a nitrogen atmosphere using magnetic
stirring. Commonly used abbreviations are: EtOAc
(ethyl acetate), MeOH (methanol), DMF (N,N-dime-
thylformamide), DMAP (dimethylaminopyridine),
HOAc (acetic acid), THF (tetrahydrofuran).
1H NMR(400 MHz, CDCl ) d 7.35 (m, 4H), 7.23 (m,
3
3H), 7.18 (m, 3H), 5.82 (d, 1H), 5.10 (s, 2H), 4.75 (m,
1H), 3.38 (dd, 2H), 2.88 (dd, 1H), 2.70 (dd, 1H), 2.65 (t,
2H), 2.45 (t, 2H), 1.85 (q, 2H), 1.38 (s, 9H).
General procedures
(S)-3-Benzyloxycarbonylamino-4-oxo-9-phenyl-nonanoic
acid tert-butyl ester, 2. To a solution of (S)-3-Allyloxy-
carbonylamino-4-oxo-9-phenyl-nonanoic acid tert-butyl
ester (0.36 g, 0.89 mmol) and bis(triphenylphosphine)
palladium (II) chloride (0.03 g) in CH2Cl2/DMF (5 mL,
1:1) was added tri-n-butyltin hydride (97%, 0.4 g,
1.33 mmol) dropwise over 2 min at room temperature.
(S)-3-Benzyloxycarbonylamino-4-oxo-5-(3-phenyl-propyl-
sulfanyl)-pentanoic acid, 5. To a solution of 4 (0.38 g,
0.80 mmol) in CH2Cl2 (10 mL) was added TFA (2 mL).
The reaction was stirred at 25 ꢀC for 18 h and the sol-
vent was removed in vacuo. The reaction mixture was

36
A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
diluted with toluene (5 mL) and concentrated to elim-
inate the excess TFA. The crude product was chroma-
tograph on a silica gel column and eluted with CH2Cl2/
EtOAc (1:4) to produce the product as a semi-solid
paste. The purified material was slurred in Et2O to
(S)-3-tert-Butoxycarbonylamino-4-oxo-5-(3-phenyl-pro-
pylsulfanyl)-pentanoic acid 9 H-fluoren-9-ylmethyl ester,
8. To a suspension of sodium hydride (60% suspension
in oil, 4.5 mmol, 0.18 g) in DMF (2 mL) at 0 ꢀC under an
atmosphere of dry nitrogen was added dropwise 3-
phenyl-propane-1-thiol (4.5 mmol, 0.68 g). The reaction
mixture was stirred at 0 ꢀC until bubbling had ceased
and the resulting solution was added dropwise to a
solution of (S)-3-tert-Butoxycarbonylamino-4-oxo-hex-
anoic acid 9H-fluoren-9-ylmethyl ester (4.6 mmol,
2.25 g) in DMF (5 mL) at 0 ꢀC under an atmosphere of
dry nitrogen. The reaction mixture was stirred at room
temperature for 3 h and the DMF was removed under
reduced pressure. The residue was taken up in ethyl
acetate (50 mL) and washed with water (5ꢃ50 mL). The
organic layer was evaporated and the residue purified by
flash chromatography (silica gel) eluting with CHCl3.
Further purification was obtained by triturating the
product with isopropyl ether/hexane until it solidified,
and the product 8 (0.780 g, 31%) was collected by fil-
1
afford the product 5 as a beige solid (0.072 g, 22%). H
NMR(400 MHz, CDCl ) d 7.38 (m, 4H), 7.20 (m, 3H),
3
7.12 (m, 3H), 5.80 (d, 1H), 5.05 (s, 2H), 4.98 (m, 1H),
3.32 (dd, 2H), 3.0 (dd, 1H), 2.82 (dd, 1H), 2.61 (t, 2H),
2.40 (t, 2H), 1.80 (q, 2H); MS (APCI) m/z 416.30
(M+1). Anal. calcd for C22H25N1O5S1 (M=415.50): C
63.60; H 6.06; N 3.37. Found: C 63.20; H 6.06; N 3.26.
HPLC [Vydac C-18, 250ꢃ4.6 mm, acetonitrile in water
(0.1% trifluoroacetic acid) at 1.50 mL/min 0–100% over
30 min], tR=6.25 min, 100% purity.
1
(S)-3-Benzenesulfonylamino-4-oxo-9-phenyl-nonanoic acid
tert-butyl ester, 6. To a stirred solution of CH2Cl2/DMF
(6.0 mL, 1:1) containing (S)-3-amino-4-oxo-9-phenyl-
nonanoic acid tert-butyl ester (0.36 g, 0.89 mmol) pre-
pared according to ref 11 and bis(triphenylphosphine)
palladium(II) chloride (0.030 g) was added tri-n-butyltin
hydride (97%, 0.40 g, 1.33 mmol) dropwise over 2 min at
room temperature. After an additional 5 min and cool-
ing to 0 ꢀC benzensulfonyl chloride (0.23 mL, 0.315 g,
tration. H NMR(400 MHz, CDCl 3) d 7.73 (d, 2H),
7.53 (m, 2H), 7.38 (t, 2H), 7.30 (t, 2H), 7.22 (m, 3H),
7.12 (m, 2H), 5.46 (d, 1H), 4.65 (m, 1H), 4.36 (m, 2H),
4.18 (t, 1H), 3.52 (d, 1H), 3.28 (d, 1H), 3.05 (dd, 1H),
2.82 (d, 1H), 2.65 (t, 2H), 2.42 (t, 2H), 1.84 (q, 2H), 1.40
(s, 9H).
1.8 mmol)
and
N-methylmorpholine
(0.20 mL,
1.80 mmol) were added simultaneously. The reaction
was stirred for 15 h at room temperature. The solvent
was removed under reduced pressure and the residue
was taken up in ethyl acetate. The organic phase was
washed successively with aqueous citric acid, aqueous
sodium hydrogencarbonate and water, dried over
sodium sulfate and concentrated under reduced pres-
sure. Purification of the residue over silica (elution with
CH2Cl2/acetone 100:1) gave 0.11 g (27%) of 6, which
was used without further purification for the next step.
(S)-3-Benzenesulfonylamino-4-oxo-5-(3-phenyl-propylsul-
fanyl)-pentanoic acid 9H-fluoren-9-ylmethyl ester, 9.
Compound 8 (0.350 g, 0.630 mmol) was dissolved in a
solution of HCl (1 M) in ethyl acetate and the reaction
mixture was allowed to stand at room temperature
overnight. The solvent was evaporated. The residue was
taken up in acetonitrile (35 mL), and treated dropwise
with phenylsulfonyl chloride (0.120 g) in acetonitrile
followed by dropwise treatment with a solution of
DMAP (5 mg) and diisopropylethylamine (0.182 g). The
reaction mixture was stirred at room temperature for 3 h
and the solvent was evaporated. The residue was parti-
tioned between ethyl acetate and water, and the aqueous
layer was acidified to pH=2 with 1 N HCl. The organic
layer was collected, dried (MgSO4) and evaporated.
(S)-3-Benzenesulfonylamino-4-oxo-9-phenyl-nonanoic
acid, 7. A solution of 6 (0.11 g, 0.24 mmol) was treated
with CH2Cl2/TFA (10 mL, 1:1) for 30 min at room
temperature. Evaporation under reduced pressure fol-
lowed by crystallization from ether/hexane yielded
0.69 g (72%) of 7. 1H NMR(400 MHz, DMSO- d6) d 8.3
(bs, 1H), 7.8 (m, 2H), 7.65–7.55 (m, 3H), 7.3 (m, 2H),
7.15 (m, 3H), 4.05 (dd, 1H), 2.6-2.2 (m, 6H), 1.5 (m,
2H), 1.4 (m, 2H), 1.15 (m, 2H).
Purification by flash chromatography gave the desired
1
product 9 (0.110 g, 30%). H NMR(400 MHz, CDCl )
3
d 7.78 (m, 4H), 7.55 (m, 3H), 7.46 (m, 4H), 7.31 (m,
4H), 7.18 (m, 3H), 5.62 (d, 1H), 4.40 (m, 3H), 4.18 (t,
1H), 3.22 (d, 1H), 3.15 (d, 1H), 2.86 (dd, IH), 2.60 (m,
3H), 2.22 (t, 2H), 1.78 (q, 2H), 1.52 (s, 2H).

A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
37
(S)-3-Benzenesulfonylamino-4-oxo-5-(3-phenyl-propylsul-
fanyl)-pentanoic acid, 10. A solution of 9 (0.084 g,
0.14 mmol) in dioxane (2 mL) and methanol (2 mL) was
treated with a solution of 1.2 N NaOH (0.224 mL) dilu-
ted in 1 mL of methanol. The reaction mixture was stir-
red at room temperature overnight. The solvent was
evaporated and the residue triturated with hexane. The
residue was taken up in water (0.5 mL), extracted with
hexane (5 mL). The aqueous layer was acidified and the
product extracted into ethyl acetate. The organic layer
was dried (MgSO4) and evaporated. The residue was
purified by flash chromatography (silica gel) eluting
with CHCl3/MeOH (95:5) followed by recrystalization
from hexane/isopropyl ether) to afford 10 (0.019 g,
1H); MS (APCI) m/z 334 (M+H)+. Anal. calcd for:
C16H15N1O5S1 (M=333.36): C 57.92; H 4.50; N 4.19.
Found: C 57.65, H 4.54, N 4.20.
General procedure for the synthesis of biphenyl-2-sulfo-
nylamino)-4-oxo-butyric acids 13–18 (Table 2).
32%): mp 70–73 ꢀC. H NMR(400 MHz, MeOH- d4) d
1
7.88 (d, 2H), 7.60 (t, 2H), 7.58 (t, 2H), 7.24 (t, 2H), 7.17
(d, 2H), 5.50 (m, 1H), 3.42 (d, 2H), 2.62 (t, 2H), 2.52
(dd, 1H), 2.32 (t, 2H), 1.78 (q, 2H); MS (CI) m/z 422
(M+1). Anal. calcd for C20H23N1O5S2 0.38 H20
(M=423.145): C 56.77; H 5.52; N 3.31. Found: C 56.38;
H 5.428; N 3.259.
6-Methyl-2-nitro-biphenyl, 19. To a stirred solution of 2-
bromo-3-nitrotoluene (5.0 g, 23.10 mmol) in toluene
(70 mL), 2M aqueous sodium carbonate (23.0 mL,
46.20 mmol) and tetra-n-butylammonium bromide
(0.37 g, 1.20 mmol) under nitrogen was added benzene-
boronic acid (2.82 g, 23.10 mmol) in 70 mL of absolute
ethanol via addition funnel. The reaction mixture was
.
degassed
for
30 min.
Tetrakis(triphenylpho-
sphine)palladium(0) (0.14 g, 5% by wt) was added.
After 7 h at 100 ꢀC, the reaction mixture was cooled,
and ethyl acetate (200 mL) was added. The layers were
separated, the aqueous layer was extracted with ethyl
acetate (2ꢃ100 mL), and the combined organic phases
were washed with water, brine, and dried with MgSO4,
filtered, and concentrated. The residue was purified by
column chromatography on silica gel (elution with 10%
EtOAc/hexanes) to give 4.80 g (97%) of 19 as a white
solid: 1H NMR(300 MHz, CDCl 3) d 7.65 (d, 1H, ArH),
7.50–7.35 (m, 5H, ArH), 7.18 (d, 2H, ArH), 2.14 (s, 3H).
(S)-3-Benzenesulfonylamino-4-oxo-butyric acid, 11. Ben-
zenesulfonyl chloride was employed to acylate the
amine of Asp(OtBu)–NMe(OMe), 23, as described for
the synthesis of 24. From the resulting sulfonamide, the
final product was obtained as a colorless foam employ-
1
ing the methods described for the synthesis of 13. H
NMR(300 MHz, MeOH- d4) as the hemiacetal d 7.87 (m,
2H), 7.58 (m, 3H), 4.44, 4.38 (d, 1H), 3.74 (m, 1H); MS
(APCI) m/z 240 (M–OH)+. Anal. calcd for C10H11NO5S1
(M=257.26): C 46.69; H 4.31; N 5.44. Found: C 46.74; H
4.18; N 5.10. HPLC [Vydac C-18, 250ꢃ4.6 mm, aceto-
nitrile in water (0.1% trifluoroacetic acid) at 1.50 mL/min
0–66% over 22 min] tR=11.8 min, 100% purity.
6-Methyl-biphenyl-2-ylamine, 20. A solution of 19
(4.80 g, 22.5 0 mmol) in THF (100 mL) was shaken with
Raney nickel (1.50 g) under H2 (50 psi) for 3.5 h using
Parr apparatus. The reaction mixture was filtered
through Celite and concentrated. The crude product of
1
20 was obtained (4.00 g, 98%) as an off white solid. H
NMR(400 MHz, CDCl ) d 7.44 (t, 2H, ArH), 7.31 (t,
3
1H, ArH), 7.21 (d, 2H, ArH), 7.03 (t, 2H, ArH), 6.67 (d,
2H, ArH), 6.59 (d, 1H, ArH), 1.97 (s, 3H).
(S)-3-(Biphenyl-2-sulfonylamino)-4-oxobutryic acid, 12.
Biphenyl-2-sulfonyl chloride16 was employed to acylate
the amine of Asp(OtBu)–NMe(OMe), 23, as described
for the synthesis of 24. From the resulting sulfonamide,
the final product was obtained as a colorless foam
employing the methods described for the synthesis of 13.
1H NMR(300 MHz, MeOH- d4) as the hemiacetal d 8.18
(m, 1H), 7.62 (t, 1H), 7.53 (t, 1H), 7.40, (m, 5H), 7.30 (d,
1H), 4.43 (d, 1H), 3.82 (m, 1H), 2.53 (dt, 1H), 2.30 (m,

38
A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
6-Methyl-biphenyl-2-sulfonyl chloride, 21. 6-Methyl-
biphenyl-2-ylamine 20 (4.0 g, 21.17 mmol) was dissolved
in glacial acetic acid (20 mL) and then added concd HCl
(7 mL). The stirred solution was diazotised at ꢁ10 ꢀC
with NaNO2 (1.95 g, 28.30 mmol) in water (5 mL). The
solution was allowed to stirred at ꢁ10 ꢀC for 30 min.
The diazonium salt solution was poured into a mixture
of 30% SO2ꢁ glacial acetic acid (20 mL) and benzene
been suspended and which was at ꢁ5 ꢀC initially. The
reaction mixture was stirred at 0 ꢀC for 2 h. The mixture
was then heated to 50 ꢀC using oil bath, and maintained
at this temperature for 12 h. The mixture was then
cooled and poured into water (200 mL) and the
resultant oil was extracted into ethyl acetate
(500 mL). The organic layer was washed with water
(2ꢃ200 mL), saturated NaHCO3, dried over MgSO4
and the solvents were removed in vacuo. The crude oil
was crystallized from hexanes/ether to give product 21
as yellow solid (0.750 g, 14%): 1H NMR(400 MHz,
CDCl3) d 8.05 (d, 1H, ArH), 7.59 (d, 1H, ArH), 7.42–
7.12 (m, 4H, ArH), 8.05 (d, 1H, ArH), 6.42 (d, 1H,
ArH); MS (APCI) (M+1) m/z 267.0.15
100% over 30 min], tR=18.2 min, 100% purity.
(S)-3-Amino-N-methoxy-N-methyl-succinamic acid tert-
butyl ester, 23. To
a solution of 22 (11.55 g,
31.50 mmol) in EtOH (100 mL) and concd HCl (3 mL)
was added 20% Pd/C (0.50 g), and the mixture was
stirred for 3 h under a hydrogen atmosphere at atmo-
spheric pressure. The catalyst was filtered and the sol-
vent removed. The resulting oil solidified upon the
addition of ether. The solid was dried to give 8.40 g
(99%) of 23 as an off-white solid. The solid was used
immediately in the next step. It is important to solidify
.
(20 mL) in which CuCl2 2H2O (1.2 g, 6.5 mmol) had
1
this intermediate before submitting to the next step. H
NMR(300 MHz, CDCl ) d 8.59 (br s, 1H), 4.68 (m,
3
1H), 3.84 (s, 3H), 3.28 (s, 3H), 3.05 (d, 2H), 1.25 (s, 9H);
HPLC [Vydac C-18, 250ꢃ4.6 mm, acetonitrile in water
(0.1% trifluoroacetic acid) at 1.50 mL/min 0–100% over
30 min], tR=10.80 min, 100% purity.
(S)-3-Benzyloxycarbonylamino-N-methoxy-N-methyl-
succinamic acid tert-butyl ester, 22. To a solution of the
acid (S)-2-benzyloxycarbonylamino-succinic acid 4-tert-
butyl ester (50.0 g, 154.6 mmol) in dry dichloromethane
(200 mL)
and
N-methylmorpholine
(42.5 mL,
386.5 mmol) at ꢁ75 ꢀC was added dropwise isobutyl-
chloroformate (24.1 mL, 185.5 mmol) followed by stir-
A solution (N,O-
hydrochloride (18.10 g,
(S)-N-Methoxy-N-methyl-3-(6-methyl-biphenyl-2-sulfo-
nylamino)-succinamic acid tert-butyl ester, 24. To a
solution of 21 (0.75 g, 2.80 mmol) in dry dichloro-
methane (15 mL) and Asp(OtBu)–NMe(OMe) 23
(0.50 g, 1.90 mmol) was added pyridine (1.0 mL,
8.40 mmol). The resulting solution was stirred at room
temperature for 12 h. The resulting solution was taken
into ethyl acetate (100 mL), washed with 5% citric acid,
saturated sodium bicarbonate, dried (MgSO4), and the
solvent was removed. The resulting oil was chromato-
ring at ꢁ75 ꢀC for 30 min.
dimethylhydroxylamine)
185.5 mmol) in dry dichloromethane (50 mL) and N-
methylpiperidine (22.55 mL, 185.5 mmol) was added.
The solution was allowed to warm to room temperature
and stirred for 1 h, quenched by addition of 10% H2SO4
and extracted into ethyl acetate. The organic layer was
washed sequentially with 10% H2SO4, H2O, and brine.
The solution was dried and the solvent removed. The
resulting oil crystallized upon the addition of 20%
ether/hexane and was collected and dried to give the
corresponding amide 22 45.0 g (80%): 1H NMR
(400 MHz, CDCl3) d 7.30 (s, 5H), 5.62 (d,1H), 5.05 (s,
2H), 4.95 (m, 1H), 3.78 (s, 3H), 3.20 (s, 3H), 2.65 (dd,
1H), 2.55 (dd, 1H), 1.39 (s, 9H); MS (APCI) (M+1) m/z
367; HPLC [Vydac C-18, 250ꢃ4.6 mm, acetonitrile in
water (0.1% trifluoroacetic acid) at 1.50 mL/min 0–
graph (20% EtOAc/hexanes) to give 0.59 g (45%) of 24
1
as off white foam. H NMR(300 MHz, CDCl ) d 7.94
3
(s, 1H, ArH), 7.51–7.31 (m, 6H, ArH), 4.72 (br s, 2H),
3.65 (s, 3H), 3.05 (s, 3H), 2.58 (dd, 1H), 2.38 (dd, 1H),
1.98 (s, 3H), 1.38 (s, 9H); HPLC [Vydac C-18,
250ꢃ4.6 mm, acetonitrile in water (0.1% trifluoroacetic
acid) at 1.50 mL/min 0–100% over 30 min],
tR=21.60 min, 100% purity.

A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
39
(S)-3-(6-Methyl-biphenyl-2-sulfonylamino)-4-oxo-butyric
acid tert-butyl ester, 25. To weinreb amide 24 (0.56 g,
1.10 mmol) solution in dry Et2O (20 mL) at ꢁ65 ꢀC was
added LiAlH4 (0.062 g, 1.6 mmol). The reaction mixture
temperature was maintained for 2 h. The excess
hydride was quenched by the addition of potassium
hydrogen sulfate (2 equiv) dissolved in water. After
warming to room temperature, Et2O was added
(100 mL) and the organic layer was washed with
water and then with brine. The solvent was dried
(MgSO4), filtered, and evaporated to dryness. The
resulting crude product was purified on silica gel
flash chromatography (15% EtOAc in hexanes) to
give 25 as an off white foam (0.18 g, 40%). 1H
(S)-3-(20-Methyl-biphenyl-2-sulfonylamino)-4-oxo-butyric
acid, 14. Yield 0.070 g (46%), 1H NMR(400 MHz,
MeOH-d4) d 8.12 (m, 1H, ArH), 7.62 (m, 1H, ArH),
7.58 (m, 1H, ArH), 7.28 (m, 5H, ArH), 4.58, 4.41 (dd,
1H), 3.71 (m, 1H), 2.58 (dd, 1H), 2.46 (dd, 1H), 2.05 (s,
3H). MS (APCI) m/z 348.4 (M+1). Anal. calcd for
C17H17N1O5S1 (M=347.393): C 58.78; H 4.93; N 4.03.
Found: C 58.53; H 5.17; N 4.08. HPLC [Vydac C-18,
250ꢃ4.6 mm, acetonitrile in water (0.1% trifluoroacetic
acid) at 1.50 mL/min 0–100% over 30 min],
tR=16.57 min, 100% purity.
NMR(300 MHz, CDCl ) d 9.46 (s, 1H), 7.95 (t, 1H,
Compound 15 was synthesized using the method
described for 13.
3
ArH), 7.52–7.31 (m, 6H, ArH), 7.22 (d, 1H, ArH), 5.11
(d, 1H), 3.82 (m, 1H), 2.88 (dd, 1H), 2.62 (dd, 1H), 2.02
(s, 3H), 1.38 (s, 9H); HPLC [Vydac C-18, 250ꢃ4.6 mm,
acetonitrile in water (0.1% trifluoroacetic acid) at
1.50 mL/min 0–100% over 30 min], tR=18.36 min,
100% purity.
(S)-3-(30-Methyl-biphenyl-2-sulfonylamino)-4-oxo-butyric
acid, 15. Yield 0.16 g (76%), 1H NMR(400 MHz,
MeOH-d4) d 8.06 (m, 1H, ArH), 7.60 (t, 1H, ArH), 7.52
(t, 1H, ArH), 7.25 (m, 5H, ArH), 4.42 (dd, 1H), 3.62 (m,
1H), 2.51 (dd, 1H), 2.39 (s, 3H), 2.34 (dd, 1H), MS
(APCI) m/z 346.4 (Mꢁ1). Anal. calcd for
C17H17N1O5S1 (M=347.393): C 58.78; H 4.93; N 4.03.
Found: C 58.82; H 5.25; N 4.17. HPLC [Vydac C-18,
250ꢃ4.6 mm, acetonitrile in water (0.1% trifluoroacetic
acid) at 1.50 mL/min 0–100% over 30 min],
tR=16.55 min, 100% purity.
(S)-3-(6-Methyl-biphenyl-2-sulfonylamino)-4-oxo-butyric
acid, 13. A solution of 25 (0.18 g, 0.60 mmol) in TFA
(2 mL) and CH2Cl2 (20 mL) was stirred for 3 h. After
the solvent was removed under vacuum, the residue was
subjected to preparative reverse-phase HPLC (Vydac,
C18) using linear gradient of (A) water containing 0.1%
TFA and (B) acetonitrile containing 0.1% TFA (10–
45% B, in 120 min) at a flow rate of 20 mL/min. Frac-
tions containing the major peak were pooled and lyo-
philized to yield 0.120 g (86%) of 13. 1H NMR
(400 MHz, MeOH-d4) d 7.93 (dd, 1H, ArH), 7.55 (d,
1H, ArH), 7.42 (m, 4H, ArH), 7.32 (t, 1H, ArH), 7.21 (t,
1H, ArH), 4.46 (m, 1H), 3.65 (m, 1H), 2.52 (dd, 1H),
2.36 (dd, 1H), 1.98 (s, 3H); MS (APCI) m/z 348 (M+1).
Anal. calcd for C17H17N1O5S1 (M=347.393): C 58.78;
H 4.93; N 4.03. Found: C 58.57; H 5.60; N 3.31. HPLC
[Vydac C-18, 250ꢃ4.6 mm, acetonitrile in water (0.1%
trifluoroacetic acid) at 1.50 mL/min 0–100% over
30 min], tR=16.88 min, 100% purity.
Compound 16 was synthesized using the method
described for 13.
Compound 14 was synthesized using the method
described for 13.

40
A. B. Shahripour et al. / Bioorg. Med. Chem. 10 (2002) 31–40
(S)-3-(40-Methyl-biphenyl-2-sulfonylamino)-4-oxo-butyric
acid, 16. Yield 0.073 g (70%), 1H NMR(400 MHz,
MeOH-d4) d 8.07 (m, 1H, ArH), 7.60 (t, 1H, ArH), 7.28
(t, 3H, ArH), 7.22 (d, 2H, ArH), 4.41 (dd, 1H), 3.61 (m,
1H), 2.45 (dd, 1H), 2.41 (s, 3H), 2.28 (dd, 1H), MS
(APCI) m/z 348.5 (M+1). Anal. calcd for
C17H17N1O5S1 (M=347.393): C 58.78; H 4.93; N 4.03.
Found: C 58.88; H 5.37; N 4.28. HPLC [Vydac C-18,
250ꢃ4.6 mm, acetonitrile in water (0.1% trifluoroacetic
acid) at 1.50 mL/min 0–100% over 30 min],
tR=20.12 min, 100% purity.
2H, ArH), 7.50 (m, 2H, ArH), 7.37 (d, 2H, ArH), 7.17
(d, 1H) 4.48 (dd, 1H), 3.71 (m, 1H), 2.55 (dd, 1H), 2.41
(dd, 1H), 2.12 (s, 3H), MS (APCI) m/z 390.8 (M+1).
Anal. calcd for C18H18N2O6S1 (M=390.418): C 55.38;
H 4.65; N 7.18. Found: C 55.28; H 4.62; N 7.16. HPLC
[Vydac C-18, 250ꢃ4.6 mm, acetonitrile in water (0.1%
trifluoroacetic acid) at 1.50 mL/min 0–100% over
30 min], tR=13.01 min, 100% purity.
References and Notes
Compound 17 was synthesized using the method
described for 13.
1. Dinarello, C. A. Blood 1991, 77, 1627.
2. Dinarello, C. A.; Wolff, S. M. N. Engl. J. Med. 1993, 328,
106.
3. Black, R. A.; Kronheim, S. R.; Sleath, P. R. FEBS Lett.
1989, 247, 386.
4. Thornberry, N. A.; Bull, H. G.; Calaycay, J. R.; Chapman,
K. T.; Howard, A. D.; Kostura, M. J.; Miller, D. K.; Moli-
neaux, S. M.; Weidner, J. R.; Aunins, J.; Elliston, K. O.;
Ayala, J. M.; Casano, F. J.; Chin, J.; Ding, G. J.-F.; Egger,
L. A.; Gaffney, E. P.; Limjuco, G.; Palyha, O. C.; Raju, S. M.;
Rolando, A. M.; Salley, J. P.; Yamin, T.-T.; Lee, T. D.;
Shively, J. E.; MacCross, M.; Mumford, R. A.; Schmid, J. A.;
Tocci, M. J. Nature 1992, 356, 768.
5. Wilson, K. P.; Black, J. F.; Thomson, J. A.; Kim, E. E.;
Griffith, J. P.; Navia, M. A.; Murcko, M. A.; Chambers, S. P.;
Aldape, J. P.; Raybuck, S. A.; Livingston, D. J. Nature 1994,
370, 270.
6. Walker, N. P. C.; Talanian, R. V.; Brady, K. D.; Dang,
L. C.; Bump, N. J.; Ferenz, C. R.; Franklin, S.; Ghayur, T.;
Hackett, M. C.; Hammill, L. D.; Herzog, L.; Hugunin, M.;
Houy, W.; Mankovick, J. A.; McGuiness, L.; Orlewicz, E.;
Paskind, M.; Pratt, C. A.; Reis, P.; Summani, A.; Terranova,
M.; Welch, J. P.; Moller, A.; Tracey, D. E.; Kamen, R.; Wong,
W. W. Cell 1994, 78, 343.
(S)-3-(2-Naphthalen-1-yl-benzenesulfonylamino)-4-oxo-
butyric acid, 17. Yield 0.110 g (35%), 1H NMR
(400 MHz, MeOH-d4) d 8.19 (m, 1H, ArH), 7.92 (d, 2H,
ArH), 7.66 (m, 2H, ArH), 7.50 (m, 3H, ArH), 7.32 (m,
3H, ArH), 4.41, 4.39 (dd, 1H), 3.65 (m, 1H), 3.31 (s,
3H), 2.50 (dd, 1H), 2.28 (dd, 1H), MS (APCI) m/z 384.4
(M+1). Anal. calcd for C20H17N1O5S1 (M=383.426):
C 62.65; H 4.47; N 3.65. Found: C 62.36; H 4.67; N
3.50. HPLC [Vydac C-18, 250ꢃ4.6 mm, acetonitrile in
water (0.1% trifluoroacetic acid) at 1.50 mL/min 0–
100% over 30 min], tR=16.14 min, 100% purity.
7. Howard, A. D.; Kostura, M. J.; Thornberry, N. A.; Ding,
J. F.; Limjuco, G.; Weidner, J.; Salley, J. P.; Hogquist, K. A.;
Chaplin, D. D.; Mumford, R. D.; Schmidt, J. A.; Tocci, M. J.
J. Immunol. 1991, 147, 2964.
8. Sleath, P. R.; Hendrickson, R. C.; Kronheim, S. R.; March,
C. J.; Black, R. A. J. Biol. Chem. 1990, 265, 14526.
9. Rich, D. H. In Proteinase Inhibitors; Barrett, A. J., Salve-
sen, G., Eds.; Elsevier Science: Amsterdam, 1986; Chapter 4, p
153.
Compound 18 was synthesized using the method
described for 13
10. Shaw, E. Adv. Enzymol. 1990, 63, 271.
11. Mjalli, A. M. M.; Chapman, K. T.; MacCoss, M.;
Thornberry, N. A. Bioorg. Med. Chem. Lett. 1993, 3, 2689.
12. Molecular modeling studies were performed using
SYBYL, version 6.0, commercially available from Tripos
Associates, Inc., 1699 Hanley Rd., Suite 303, St. Louis, MO
63144, USA.
13. Compounds 3 and 5 were prepared according to ref 11.
14. Mjalli, A. M. M.; Chapman, K. T.; MacCoss, M.;
Thornberry, N. A.; Peterson, E. P. Bioorg. Med. Chem. Lett.
1994, 4, 1965.
15. Yoshinori, O.; Hideki, A.; Eiichi, N.; Koichiro, M.;
Yasuhiro, Y.; Hiroyuki, K.; Hitoshi, S.; Yoshiya, T.; Makoto,
T.; Tadao, S.; Yasuo, I. Chem. Pharm. Bull. 1999, 47, 11.
16. Neale, A. J.; Rawlings, T. J.; McCall, E. B. Tetrahedron
1965, 1299.
(S)-3-(30-Acetylamino-biphenyl-2-sulfonylamino)-4-oxo-
butyric acid, 18. Yield 0.060 g (77%), 1H NMR
(400 MHz, MeOH-d4) d 8.07 (m, 1H, ArH), 7.63 (m,