Dipeptidyl aspartyl fluoromethylketones as potent caspase inhibitors: Peptidomimetic replacement of the P2 α-amino acid by a α-hydroxy acid

Article abstract of DOI:10.1016/j.bmcl.2005.01.007

As a continuation of our SAR studies of dipeptidyl aspartyl-fmk as caspase inhibitors, we explored the replacement of the P₂ α-amino acid by a peptidomimetic α-hydroxy acid. These α-carbamoyl-alkylcarbonyl- aspartyl fluoromethylketones were found to be potent caspase inhibitors, and the SAR of these compounds is similar to the corresponding dipeptidyl aspartyl-fmk. MX1153, (S)-3-methyl-2-(phenylcarbamoyl)butanoyl-Asp-fmk, is identified as a potent broad-spectrum caspase inhibitor, and is selective for caspases versus other proteases. MX1153 also has good activity in the cell apoptosis protection assays and is active in the mouse liver apoptosis model.

Full text of DOI:10.1016/j.bmcl.2005.01.007

Bioorganic & Medicinal Chemistry Letters 15 (2005) 1379–1383
Dipeptidyl aspartyl fluoromethylketones as potent
caspase inhibitors: peptidomimetic replacement of the
P2 a-amino acid by a a-hydroxy acid
Yan Wang, Lufeng Guan, Shaojuan Jia, Ben Tseng, John Drewe and Sui Xiong Cai*
Maxim Pharmaceuticals, 6650 Nancy Ridge Drive, San Diego, CA 92121, USA
Received 1 November 2004; revised 4 January 2005; accepted 6 January 2005
Available online 25 January 2005
Abstract—As a continuation of our SAR studies of dipeptidyl aspartyl-fmk as caspase inhibitors, we explored the replacement of the
P2 a-amino acid by a peptidomimetic a-hydroxy acid. These a-carbamoyl-alkylcarbonyl-aspartyl fluoromethylketones were found to
be potent caspase inhibitors, and the SAR of these compounds is similar to the corresponding dipeptidyl aspartyl-fmk. MX1153,
(S)-3-methyl-2-(phenylcarbamoyl)butanoyl-Asp-fmk, is identified as a potent broad-spectrum caspase inhibitor, and is selective
for caspases versus other proteases. MX1153 also has good activity in the cell apoptosis protection assays and is active in the mouse
liver apoptosis model.
Ó 2005 Elsevier Ltd. All rights reserved.
Caspases is a group of cysteine proteases with strict sub-
strate specificity for aspartic acid as the P1 amino acid.1
Caspases can be divided into two groups. One group,
represented by caspase-1, plays an important function
in cytokine maturation.2 The other group, including cas-
pase-3, -8, and -9, plays a critical role in apoptosis by
cleaving numerous important proteins.3 Excessive apop-
tosis is known to be involved with various diseases,
including acute diseases such as brain ischemia4 and
myocardial infarction,5 as well as chronic diseases such
as HuntingtonÕs disease and AlzheimerÕs disease.6 Due
to the important function of caspases in both inflamma-
tion and apoptosis, the discovery and development of
caspase inhibitors could result in novel anti-inflamma-
tory and anti-apoptotic drugs for the treatment of a
variety of diseases.7
pase inhibitors have advanced into clinical trials. VX-
740 (Pralnacasan) is a peptidomimetic, reversible, and
selective caspase-1 inhibitor, and was in clinical trial
for the potential treatment of inflammatory diseases.13
IDUN-6556 is a dipeptide based, irreversible, and
broad-spectrum caspase inhibitor, and is in clinical trail
for liver diseases.14,15
We have reported the discovery of MX1013 (Cbz-Val-
Asp-fmk) as a potent and broad-spectrum caspase inhib-
itor, with potent in vivo activities in several animal models
of apoptosis.16–18 The crystal structures of caspase-1, -3,
-7, and -8 in complex with tetrapeptide based inhibitors
have been determined by X-ray crystallography,19 and
no hydrogen bonding between the P2 NH of the inhibitors
with the enzymes was found. Therefore the P2 nitrogen
contributes little to the binding of the inhibitors to the
caspases. To maintain the preferred dipeptide scaffold
of MX1013 and to reduce the peptide characteristics of
the inhibitor, we elected to explore the replacement of
the P2 a-amino acid by a a-hydroxy acid (Chart 1). Herein
we report the synthesis and biological evaluation of a
group of a-hydroxy acid derivatives, a-carbamoyl-alkyl-
carbonyl-Asp-fmk, as caspase inhibitors.
Many caspase inhibitors have been designed and synthe-
sized based on substrate specificity of caspases. These in-
clude peptide based inhibitors,8–10 and peptidomimetic-
based inhibitors,11 as well as non-peptide inhibitors dis-
covered through screening of compound libraries.12
Some of these are selective for specific caspases, while
others are broad-spectrum caspase inhibitors. Two cas-
(S)-2-(Phenylcarbamoyl)propionyl-Asp-fmk (5a) was
prepared similar to the dipeptide-fmk inhibitors as
reported previously.17 (S)-(À)-2-(phenylcarbamoyl)propionic
acid (1a) was coupled with amine 220 to give amide 3a.
Keywords: Caspase inhibitor; Apoptosis.
*
Corresponding author. Tel.: +1 858 202 4006; fax: +1 858 202
4000; e-mail: scai@maxim.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.01.007

1380
Y. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1379–1383
CO2H
CH2F
O
O
O
H
N
O
H
N
HO
Ph
O
R1NCO
R1
OH
OH +
N
H
pyridine
O
R2
R2
O
O
O
1b, R1 = Ph, R2 = 2-propyl
6b, R2 = 2-propyl
6c, R2 = cyclohexyl
6d, R2 = Me
7a, R1 = Ph
1c, R1 = Ph, R2 = cyclohexyl
1d, R1 = PhCH2, R2 = Me
MX1013
7b, R1 = PhCH2
7f-k, R1 = RPh
CO2H
O
1e, R1 = PhCH2, R2 = 2-propyl
1f-k, R1 = RPh, R2 = 2-propyl
H
N
O
CH2F
R1
N
H
R2
O
Scheme 2.
Chart 1.
CO2-t-Bu
CO2-t-Bu
1b
O
H
N
O
Oxidation of compound 3a by Dess–Martin reagent
produced the corresponding ketone 4a. The t-Bu ester
was then cleaved by TFA to give the free acid 5a
(Scheme 1). Other a-carbamoyl-alkylcarbonyl-Asp-fmk
5b–k were prepared similarly from the carbamoyl pro-
tected a-hydroxy acids 1b–k.
H2N
X
Ph
N
H
X
EDCI/HOBT
O
O
O
9, 11
8, 10
O
Cl
O
8, 9, 5l, X =
CO2H
O
The carbamoyl protected a-hydroxy acids 1b–k were
prepared by reaction of the corresponding a-hydroxy
acid with the corresponding phenyl or benzyl isocyanate
(Scheme 2). Reaction of (S)-(+)-2-hydroxy-3-methylbu-
tyric acid (6b) with phenyl isocyanate (7a) in pyridine
H
N
Cl
TFA
O
CF3
N
Ph
N
H
X
O
O
10, 11, 5m, X =
N
O
Ph
5l, 5m
produced
(S)-3-methyl-2-(phenylcarbamoyl)butanoic
acid (1b), and (S)-2-cyclohexyl-2-(phenylcarbamoyl)ace-
tic acid (1c) was produced by reaction of (S)-(+)-hexa-
hydromandelic acid (6c) with phenyl isocyanate. (S)-2-
(Benzylcarbamoyl)propionic acid (1d) was prepared by
reaction of L-(+)-lactic acid (6d) with benzyl isocyanate
(7b), and (S)-2-(benzylcarbamoyl)-3-methylbutanoic
acid (1e) was prepared similarly from reaction of (S)-
(+)-2-hydroxy-3-methylbutyric acid (6b) with 7b. Substi-
tuted (S)-3-methyl-2-(phenylcarbamoyl)butanoic acids
1f–k were prepared similarly by reaction of (S)-(+)-2-hy-
droxy-3-methylbutyric acid (6b) with the corresponding
commercial available substituted phenyl isocyanates 7f–k.
Scheme 3.
(1b) produced the amide 9, and the t-Bu ester was re-
moved by TFA to produce the acid 5l. (S)-3-Methyl-2-
(phenylcarbamoyl)butanoyl-Asp-CH2PTP (1-phenyl-3-
(trifluoromethyl)pyrazol-5-yloxy) (5m) was prepared
similarly as shown in Scheme 3, by coupling of NH2-
Asp(O-t-Bu)-CH2PTP22 (10) with acid 1b to produce
amide 11, followed by removal of the t-Bu ester.
The activity of these compounds to inhibit human re-
combinant caspase-3 was determined using a standard
fluorometric assay,16,23 and the results are summarized
in Table 1. Compound 5a, with a P2 side chain equiva-
lent to Ala, had an IC50 value of 66 nM against cas-
pase-3. Compound 5b, with a P2 side chain equivalent
(S)-3-Methyl-2-(phenylcarbamoyl)butanoyl-Asp-CH2DCB
(2,6-dichlorobenzoyloxy) (5l) was prepared as shown in
Scheme 3. Coupling of NH2-Asp(O-t-Bu)-CH2DCB21
(8) with (S)-3-methyl-2-(phenylcarbamoyl)butanoic acid
O
CO2-t-Bu
CH2F
OH
CO2-t-Bu
H
N
O
O
H
N
EDCI
Ph
OH
O
CH2F
+
H2N
Ph
N
H
HOBt, DMAP
O
O
OH
3a
1a
2
CO2-t-Bu
CH2F
CO2H
CH2F
O
O
TFA
H
N
H
Dess-Martin
O
N
O
Ph
N
H
Ph
N
H
O
O
O
O
5a
4a
Scheme 1.

Y. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1379–1383
1381
of Z-V-D-fmk (MX1013),24 those compounds also are
equal or slightly more potent than MX1013 in a cas-
pase-3 assay. Interestingly, compound 5k, with a phen-
oxy group substituted in the 4-position of the Ph
group, is about as potent as 5b, indicating that a large
group is tolerated in that position.
Table 1. Caspase-3 inhibiting activity and cell apoptosis protection
activity of a-carbamoyl-alkylcarbonyl-aspartyl-CH2X
CO2H
O
H
N
O
CH2X
R1
N
H
O
R2
O
We also explored the incorporation of large DCB9,21
and PTP22 as the leaving groups, which were first suc-
cessfully used for the preparation of caspase-1 inhibi-
tors. Compound 5l, with the DCB as the leaving
group, was found to have similar potency as that of
compound 5b, in agreement with results obtained from
other series of caspase inhibitors that a large group like
DCB can be tolerated in the PÕ side.9,21 Compound 5m,
with a PTP group, was found to be about 3.5-fold less
active than 5l. It is known that as a caspase-1 inhibitor,
Z-Val-Asp-CH2DCB is about 2-fold more active than
Z-Val-Asp-CH2PTP.9,22
a
Entry
R1
R2
X
IC50 50% cell
(nM) protectione
(nM)
5a
5b
Ph
Ph
Ph
Me
2-Pr
F
F
F
F
F
F
F
F
F
F
F
66
17
50
70
20
6
1400
200
5c
5d
Cyclohexyl
Me
2-Pr
NDf
ND
ND
ND
ND
ND
100
PhCH2
PhCH2
3-F–Ph
4-F–Ph
5e
5f
5g
2-Pr
2-Pr
19
14
14
5
5h
5i
3,4-DiF–Ph 2-Pr
2,4-DiCl–Ph 2-Pr
2,5-DiCl–Ph 2-Pr
5j
ND
ND
1000
1100
250
5k
5l
4-PhOPh
Ph
Ph
2-Pr
2-Pr
2-Pr
NAd
12
Selected compounds were tested in the HeLa cell apop-
tosis protection assay,16 which measures the protecting
effects of caspase inhibitors against apoptosis induced
by TNF-a. The viability of the cells was quantified by
calcein AM uptake, and the concentration of inhibitor
that provided 50% of cell protection is summarized in
Table 1. Compound 5b was found to protect 50% of
the TNF-a treated cells at a concentration of 200 nM,
which is similar to that of MX1013. Compound 5a
was 7-times less potent than compound 5b in the cell
protection assay, slightly more than the 4-fold difference
observed from the caspase-3 enzyme assay. This is prob-
ably due to the larger P2 side chain group in 5b
(cLog P = 1.43), which makes the compound more
hydrophobic with increased cLog P value, and thus
more cell permeable relative to compound 5a
(cLog P = 0.51). Compound 5i (cLog P = 2.58), with a
di-chloro substituted Ph group, and similar caspase-3
enzyme activity as that of 5b, was found to be 2-fold
more potent than 5b in the cell protection assay, con-
firming that the increased hydrophobicity can increase
cell permeability of the inhibitors, similar to what was
observed for analogs of MX1013 with Cl and F substi-
tuted on the Ph group.24 Compound 5l (cLog P = 3.96)
and 5m (cLog P = 6.51), with a large and more hydro-
phobic groups in the PÕ side, and very high cLog P val-
ues, were ꢀ5-times less active than 5b in the cell
protection assay.
DCBb 20
PTPc 70
30
5m
MX1013
a IC50 is determined as described in Ref. 16.
b DCB, 2,6-dichlorobenzoyloxy.
c PTP, 1-phenyl-3-(trifluoromethyl)pyrazol-5-yloxy.
d NA, not applied.
e Concentration of inhibitor that provided 50% of cell protection is
determined as described in Ref. 16.
f Not determined.
to Val, which is preferred for caspase-3, had an IC50
value of 17 nM, suggested that replacement of the P2
a-amino acid by a a-hydroxy acid did not change the
preference of the P2 side chain. Compound 5c, with a
cyclohexyl group as the P2 side chain, was about 3-fold
less potent than 5b, similar to what is observed from the
dipeptide-fmk that valine is preferred over cyclohexyl-
glycine as the P2 amino acid for caspase-3 inhibitors.17
Compound 5e was >3-fold more potent than 5d, further
supporting the above conclusion that the preference of
the P2 side chain was maintained with replacement of
the P2 NH by an O. Interestingly, compound 5e, with
a structure almost identical to MX1013 except the rever-
sal of the carbamate group, has similar potency as
MX1013 as a caspase-3 inhibitor. These results are in
agreement with the crystal structure of caspase-3, which
shows that the P2 backbone nitrogen is not important
for interaction with the enzyme.
Compounds 5b (MX1153) was then tested against other
caspases and proteases for selectivity and the results are
summarized in Table 2. Compound 5b was found to
have high activity in caspase-1, -3, -6, -7, -8, and -9, with
IC50 values between 11–50 nM. This is in agreement
with the crystal structure of caspase-1, -3, -7, and -8
in complex with tetrapeptide inhibitors that the P2 back-
bone nitrogen does not form hydrogen bonding with the
enzymes and contributes little to the binding of the
inhibitors to the enzymes. Testing against other prote-
ases, compound 5b was found to be inactive against
other cysteine proteases, Calpain-1, Cathepsin B, as well
as the serine protease, Factor Xa, at up to the high con-
centration of 100,000 nM. Therefore 5b is >5000-fold
We then explored analogs of compound 5b with fluoro,
chloro, or phenoxy substituted on the Ph group, with
the goal of increasing the hydrophobicity of the com-
pounds. Due to the presence of the free carboxylic acid,
these dipeptide inhibitors in general have relatively low
hydrophobicity and cLog P values. For example, com-
pound 5b and MX1013 have cLog P values of 1.43
and 1.60, respectively. As shown in Table 1, these ana-
logs 5f–k have similar potency as, or are slightly more
potent than 5b, in the caspase-3 assay with IC50 values
ranged between 5–19 nM. This is similar to what was
observed with Cl and F substitutions on the Ph group

1382
Y. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1379–1383
Table 2. Inhibiting activity of compound 5b (MX1153) against
different proteases
sults indicate that the in vivo protecting effects of 5b is
relatively short and a high dose of 5b is needed to pro-
vide long lasting protection. Compound 5i, which has
similar caspase-3 inhibition potency as 5b, and is about
2-fold more active than 5b in the cell protection assay,
also was tested in the in vivo model. Compound 5i
was slightly more active than 5b in vivo, providing
100% protection at all time points at a dose of 10 mg/
kg, and 66% protection at 6 h time point at a dose of
1 mg/kg. In comparison, MX1013 provided 100% pro-
tection in the same model at all time points at a dose
of 1 mg/kg.16 Since 5b and MX1013 have similar activity
in the caspase enzyme assays as well as in the cell pro-
tecting assays, the in vivo activity difference suggested
that 5b might have a shorter PK half-life. In fact, com-
pound 5b was found to have a relatively short plasma
t1/2 of about 0.2 h.
a
IC50 (nM)
Enzyme
Caspase-1
Caspase-3
Caspase-6
Caspase-7
Caspase-8
Caspase-9
Calpain-1
Cathepsin B
Factor Xa
12
17
50
11
17
30
>100,000
>100,000
>100,000
a IC50 is determined as described in Ref. 16.
selective for caspase-3 versus these three non-caspase
proteases. Similar to MX101317 and MX1122,24 com-
pound 5b is a broad-spectrum caspase inhibitor and is
selective for caspases versus other proteases. It is known
that the free carboxylic acid in the P1 aspartic acid of
peptide based inhibitors is key for the specificity of casp-
ases versus other proteases. Our data suggest that the
non-specificity reported recently for several irreversible
caspase inhibitors, including Z-DEVD-fmk, Z-YVAD-
fmk, and Z-VAD-fmk,25 most probably is because the
inhibitors used for the assays were methyl esters, and
not due to the irreversible fmk group.26
In conclusion, based on the crystal structure of caspases
bound with tetrapeptide based inhibitors, we have de-
signed and synthesized a group of novel peptidomimetic
based caspase inhibitors by replacement of the P2 a-ami-
no acid with a a-hydroxy acid. These a-carbamoyl-
alkylcarbonyl-Asp-fmks were found to have similar
SAR and to be as potent as that of dipeptidyl aspartyl-
fmk, in agreement with the discovery from the crystal
structure of caspases that the P2 backbone nitrogen of
caspase inhibitors does not contribute to the binding
with the enzymes. Substitution of chloro and fluoro
groups in the phenylcarbamoyl capping group had little
effect on their potency as caspase-3 inhibitors. In the cell
apoptosis protecting assays, compounds that are more
hydrophobic were found to be more active, suggesting
that the increased hydrophobicity makes them more cell
permeable. Compound 5b (MX1153) is identified as a
potent and broad-spectrum caspase inhibitor. It is selec-
tive for caspases versus other proteases and is highly ac-
tive in the cell apoptosis protection assays. Compound
5b also was found to be active in the mouse liver apop-
tosis model.
Compound 5b was also tested in a mouse liver apoptosis
model16,27 to determine the in vivo anti-apoptotic effi-
cacy of this novel caspase inhibitor. Mice were injected
intravenously with anti-Fas monoclonal antibody, fol-
lowed 5 min later by IV administration of various doses
of compound 5b formulated in an aqueous vehicle con-
taining 50 mM Tris–HCl. The number of surviving ani-
mals in each group was determined at 1, 3, 6, 24 h and
3 days post-injection, and reported as a percentage of
the total number of animals in each group (Table 3).
Control mice, injected with 8 lg (microgram) of anti-
Fas antibody and without treatment, were all dead by
the 1 h time point. Compound 5b, tested at 0.25 mg/
kg, was able to protected 100% of the mice from the
lethal effects of anti-Fas antibody at the 1 and 3 h time
point, but none of the mice were protected at the 6 h
time point. At 1 mg/kg, all the animals were protected
at the 1 and 3 h time point, and 50% of the mice were
protected at the 6 h time point. At 10 mg/kg dose, 5b
protected 100% of the mice at the 1, 3, and 6 h time
points, and 83% at 24 h and 3 days time point. These re-
References and notes
1. Denault, J. B.; Salvesen, G. S. Chem. Rev. 2002, 102, 4489.
2. Livingston, D. J. J. Cell. Biochem. 1997, 64, 19.
3. Thornberry, N. A. Chem. Biol. 1998, 5, R97.
4. Han, B. H.; Xu, D.; Choi, J.; Han, Y.; Xanthoudakis, S.
R.; Tam, J.; Vaillancourt, J.; Colucci, J.; Siman, R.;
Giroux, A.; Robertson, G. S.; Zamboni, R.; Nicholson, D.
W.; Holtzman, D. M. J. Biol. Chem. 2002, 277, 30126.
5. Haunstetter, A.; Izumo, S. Circ. Res. 1998, 82, 1111.
6. Wellington, C. L.; Hayden, M. R. Clin. Genet. 2000, 57, 1.
7. Talanian, R. V.; Brady, K. D.; Cryns, V. L. J. Med. Chem.
2000, 43, 3351.
Table 3. Survival of mice with compound 5b (MX1153) treatment
after induction of apoptosis by anti-Fas antibody
Dose of 5b (mg/kg)
% Survival (n = 6)
1 h
3 h
6 h
24 h
3 days
8. Nicholson, D. W.; Ali, A.; Thornberry, N. A.; Vaillan-
court, J. P.; Ding, C. K.; Gallant, M.; Gareau, Y.; Griffin,
P. R.; Labelle, M.; Lazebnik, Y. A.; Munday, N. A.; Raju,
S. M.; Smulson, M. E.; Yamin, T. T.; Yu, V. L.; Miller, D.
R. Nature 1995, 376, 37.
0
100
100
100
100
0
0
0
0
0
0
0.25
1
100
100
100
0
50
0
83
0
83
10
100
Mice were injected intravenously (IV) with 8 lg of anti-Fas antibody
(clone JO-2; Pharmingen), followed 5 min later with IV injection of
compound 5b at the indicated doses or by vehicle. Six mice were
treated in each group and the number of surviving mice was monitored
for up to 3 days, when the experiment was terminated.
9. (a) Dolle, R. E.; Hoyer, D.; Prasad, C. V.; Schmidt, S. J.;
Helaszek, C. T.; Miller, R. E.; Ator, M. A. J. Med. Chem.
1994, 37, 563; (b) Han, Y.; Giroux, A.; Grimm, E. L.;
Aspiotis, R.; Francoeur, S.; Bayly, C. I.; Mckay, D. J.;
Roy, S.; Xanthoudakis, S.; Vaillancourt, J. P.; Rasper, D.

Y. Wang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 1379–1383
1383
M.; Tam, J.; Tawa, P.; Thornberry, N. A.; Paterson, E. P.;
Garcia-Calvo, M.; Becker, J. W.; Rotonda, J.; Nicholson,
D. W.; Zamboni, R. J. Bioorg. Med. Chem. Lett. 2004, 14,
805.
Becker, J. W. Nat. Struct. Biol. 1996, 3, 619; (b) Wei, Y.;
Fox, T.; Chambers, S. P.; Sintchak, J.; Coll, J. T.;
McGolec, J.; Swenson, L.; Wilson, K. P.; Charifson, P.
S. Chem. Biol. 2000, 7, 423; (c) Chereau, D.; Kodanda-
pani, L.; Tomaselli, K. J.; Spada, A. P.; Wu, J. C.
Biochemistry 2003, 42, 4151.
10. Linton, S. D.; Karanewsky, D. S.; Ternansky, R. J.; Wu,
J. C.; Pham, B.; Kodandapani, L.; Smidt, R.; Diaz, J.-L.;
Fritz, L. C.; Tomaselli, K. J. Bioorg. Med. Chem. Lett.
2002, 12, 2969.
11. Karanewsky, D. S.; Bai, X.; Linton, S. D.; Krebs, J. F.;
Wu, J.; Pham, B.; Tomaselli, K. J. Bioorg. Med. Chem.
Lett. 1998, 8, 2757.
12. Lee, D.; Long, S. A.; Murray, J. H.; Adams, J. L.; Nuttall,
M. E.; Nadeau, D. P.; Kikly, K.; Winkler, J. D.; Sung, C.
M.; Ryan, M. D.; Levy, M. A.; Keller, P. M.; DeWolf, W.
E., Jr. J. Med. Chem. 2001, 43, 2015.
13. Siegmund, B.; Zeitz, M. I. Drugs 2003, 6, 154.
14. Hoglen, N. C.; Chen, L. S.; Fisher, C. D.; Hirakawa, B. P.;
Groessl, T.; Contreras, P. C. J. Pharmacol. Exp. Ther.
2004, 309, 634.
15. Valentino, K. L.; Gutierrez, M.; Sanchez, R.; Winship, M.
J.; Shapiro, D. A. Int. J. Clin. Pharmacol. Ther. 2003, 41,
441.
16. Yang, W.; Guastella, J.; Huang, J.-C.; Wang, Y.; Zhang,
L.; Xue, D.; Tran, M.; Woodward, R.; Kasibhatla, S.;
Tseng, B.; Drewe, J.; Cai, S. X. Br. J. Pharmacol. 2003,
140, 402.
17. Wang, Y.; Huang, J.-C.; Zhou, Z.-L.; Yang, W.; Gua-
stella, J.; Drewe, J.; Cai, S. X. Bioorg. Med. Chem. Lett.
2004, 14, 1269.
18. Jaeschke, H.; Farhood, A.; Cai, S. X.; Tseng, B. Y.; Bajt,
M. L. Toxicol. Appl. Pharmacol. 2000, 169, 77.
19. (a) Rotonda, J.; Nicholson, D. W.; Fazil, K. M.; Gallant,
M.; Gareau, Y.; Labelle, M.; Peterson, E. P.; Rasper, D.
M.; Ruel, R.; Vaillancourt, J. P.; Thornberry, N. A.;
20. Revesz, L.; Briswalter, C.; Heng, R.; Leutwiler, A.;
Mueller, R.; Wuethrich, H. J. Tetrahedron Lett. 1994,
35, 9693.
21. Dolle, R. E.; Prouty, C. P.; Prasad, C. V.; Cook, E.; Saha,
A.; Ross, T. M.; Salvino, J. M.; Helaszek, C. T.; Ator, M.
A. J. Med. Chem. 1996, 39, 2438.
22. Dolle, R. E.; Singh, J.; Rinker, J.; Hoyer, D.; Prasad, C.
V.; Graybill, T. L.; Salvino, J. M.; Helaszek, C. T.; Miller,
R. E.; Ator, M. A. J. Med. Chem. 1994, 37, 3863.
23. Thornberry, N. A.; Peterson, E. P.; Zhao, J. J.; Howard,
A. D.; Griffin, P. R.; Chapman, K. T. Biochemistry 1994,
33, 3934.
24. Cai, S. X.; Guan, L.; Jia, S.; Wang, Y.; Yang, W.; Tseng,
B.; Drewe, J. Bioorg. Med. Chem. Lett. 2004, 14, 5295.
25. Rozman-Pungercar, J.; Kopitar-Jerala, N.; Bogyo, M.;
Turk, D.; Vasiljeva, O.; Stefe, I.; Vandenabeele, P.;
Bromme, D.; Puizdar, V.; Fonovic, M.; Trstenjak-Pre-
banda, M.; Dolenc, I.; Turk, V.; Turk, B. Cell Death
Differ. 2003, 10, 881.
26. (a) James, K. E.; Asgian, J. L.; Li, Z. Z.; Ekici, O. D.;
Rubin, J. R.; Mikolajczyk, J.; Salvesen, G. S.; Powers, J.
C. J. Med. Chem. 2004, 47, 1553; (b) Ekici, O. D.; Gotz,
M. G.; James, K. E.; Li, Z. Z.; Rukamp, B. J.; Asgian, J.
L.; Caffrey, C. R.; Hansell, E.; Dvorak, J.; McKerrow, J.
H.; Potempa, J.; Travis, J.; Mikolajczyk, J.; Salvesen, G.
S.; Powers, J. C. J. Med. Chem. 2004, 47, 1889.
27. Rodriguez, I.; Matsuura, K.; Ody, C.; Nagata, S.; Vassalli,
P. J. Exp. Med. 1996, 184, 2067.