Potent transglutaminase inhibitors, dithio β-aminoethyl ketones

Article abstract of DOI:10.1016/j.bmcl.2010.10.136

Potent transglutaminase inhibitors were obtained from disulfide compounds, cystamine, dimethyl cystine, and dimethyl homocystine. The disulfide bond and thiophene ring play an important role in inhibitory activity of synthesized aryl β-amino ketones.

Full text of DOI:10.1016/j.bmcl.2010.10.136

Bioorganic & Medicinal Chemistry Letters 21 (2011) 377–379
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Potent transglutaminase inhibitors, dithio b-aminoethyl ketones
Shoichiro Ozaki a, Etsuko Ebisui a, Kozo Hamada a,b, Akinobu Z. Suzuki a, Akiko Terauchi a,b
,
Katsuhiko Mikoshiba a,b,
⇑
a Laboratory for Developmental Neurobiology, Brain Development Research Group, Brain Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
b Calcium Oscillation Project, ICORP-SORST, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Potent transglutaminase inhibitors were obtained from disulfide compounds, cystamine, dimethyl
cystine, and dimethyl homocystine. The disulfide bond and thiophene ring play an important role in
inhibitory activity of synthesized aryl b-amino ketones.
Received 30 July 2010
Revised 26 October 2010
Accepted 28 October 2010
Available online 31 October 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Transglutaminase inhibitors
Dithio b-aminoethyl ketones
Alzheimer’s disease
Huntington’s disease
Parkinson’s disease
Celiac disease
Transglutaminases (TGases)1–5 are ubiquitous enzymes involved
in various post-translational modifications, including protein cross-
linking, amine incorporation, and deamidation. TGases catalyze
protein cross-linking by forming isopeptide bonds between the
propyl N-benzyl) aminoethyl ketone,47 gluten peptide analogs,48
epigallocatechin gallates,49 chlorogenic acid,50,51 peptide and
peptidemimetic Michael systems,52 glucosamine and its deriva-
tives,53 milk-derived inhibitors,54 nordihydroguaiaretic acid,55
carboxamide group of glutamine residues and the
of lysine residues to produce N-( -glutamyl)- -lysine upon loss of
ammonia.2,6,7 Strong intra- and intermolecular
-bonds play an
e
-amino group
cystamine,56 IkB -derived peptides,57 and dihydroisoxazole and
a
c
L
isatin derivatives.58 We have also reported aryl b-amino ketones
as potent transglutaminase inhibitors.59
r
important role in biological phenomena, such as blood clotting upon
As an extension of our previous report, we have synthesized
aryl b-amino ketones starting from disulfide compounds, including
cystamine, dimethyl cystine ester, and dimethyl homocystine es-
ter, because disulfide compounds are well-known transglutamin-
ase inhibitors,60,61 in particular, cystamines.22,23,62–64 In this
report, we found that the resulting dithio aryl b-amino ketones
(Fig. 1) were approximately 300 times more active than the start-
ing disulfides.
fibrin cross-linking and cornified envelope formation.8 In addition,
unregulated high TGase activities result in numerous N-(
yl)- -lysine isopeptide bonds which may partly contribute to protein
aggregates, such as amyloid b (Ab) deposits,9 tau protein,10,11 polyg-
lutaminylated proteins, and -synuclein that are commonly
c-glutam-
L
a
observed in many neurodegenerative diseases, including Alzhei-
mer’s,10,12–19 Huntington’s,3,20–25 and Parkinson’s disease,24 as well
as progressive supranuclear palsy.26,27 TGases are also involved in
the pathogenesis of ear comedogenesis,28,29 cataractous lens,30 pso-
riasis,31 cancer metastasis,32 and injuries of the liver,33 fibrin,34,35
and immune system.36 The deamidation function of TGase is also
known to play a pathogenetic role in celiac disease by modifying
the gluten peptide intake.37–42 These cumulative reports suggest
thatthe development of inhibitorsfor TGase may beclinically useful.
Many TGase inhibitors have been described, such as thienopyri-
midonine-4-one acylhydrazides,43 peptidyl methyl ketones,44
dihydrooxazoles,45 cinnamoyl derivatives,46 2-naphtyl 2-(N-iso-
Dithio b-aminoethyl ketone derivatives 1, 5–41 (Table 1) were
prepared using the conventional Mannich reaction.59,65–67 Aryl
methyl ketone derivatives 2, disulfide compounds 3, and parafor-
maldehyde were gradually heated from room temperature to
123 °C for 1 h and then kept at 123 °C for 10 min (Fig. 1). The
resulting dithio b-aminoethyl ketones formed viscous oils68 and
were evaluated for TGase inhibitory activities using liver tissue
transglutaminase (TGase 2), as reported previously.59 Briefly, we
monitored the velocity of the enzymatic reaction by measuring
fluorescent intensity of monodansyl cadaverine using a Functional
Drug Screening System (Hamamatsu Photonics, Shizuoka, Japan).
IC50 values of the dithio b-aminoethyl ketones shown in Table 1
were calculated by fitting experimental data at 0.03, 0.1, 1, 3, 10,
⇑
Corresponding author. Tel.: +81 48 467 9745; fax: +81 48 467 9744.
E-mail address: mikosiba@brain.riken.jp (K. Mikoshiba).
and 30 l
M of compounds.59
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.10.136

378
S. Ozaki et al. / Bioorg. Med. Chem. Lett. 21 (2011) 377–379
Figure 1. Representative structures of dithio b-aminoethyl ketones (1 and 4) and synthetic scheme.
Table 1
Table 1 (continued)
IC50 values of dithio b-aminoethyl ketones
(R1COCH2CH2)2R2
R2
(R1COCH2CH2)2R2
R2
R1
R1
9.7
38
0.12
5
0.19
6
0.12
7
4.0
39
0.12
8
0.18
1
0.099
9
0.17
10
0.24
11
0.10
12
2.0
40
19
41
0.51
13
0.40
14
3.6
15
In each row, upper and lower values correspond to IC50 value (lM) and compound
number, respectively.
1.6
16
0.29
17
Comparison of dithio b-aminoethyl ketones with the R1 aryl
group showed that the compound bearing the 2-thienyl group
was more potent than phenyl, naphthyl, and other hetero aryl
groups. The activities of the dithio b-aminoethyl ketones were
not changed significantly by changing the substituents of the 2-thi-
enyl group from hydrogen to chloro, bromo, iodo, methyl, and ben-
zo groups. Furyl, 4-bromophenyl, and 4-iodophenyl groups were
also effective, as shown by their IC50 values which were below
0.21
18
5.7
19
0.33
20
0.17
21
0.90
22
0.12
23
1 l
M. Comparison of the disulfide backbones (R2) revealed that
0.42
24
2.9
25
cystamine (X = H, n = 1), dimethyl cystine (X = CO2Me, n = 1), and
dimethyl homocystine (X = CO2Me, n = 2) derivatives exhibited al-
most the same inhibitory activities.
2.2
26
0.12
27
11
28
1.6
29
The IC50 values of cystamine, dimethyl cystine ester, and di-
methyl homocystine ester were calculated as 31, 35, and 40 lM,
respectively. Comparison between dithio b-aminoethyl ketones
0.89
30
and starting disulfide compounds revealed that active compounds
1.1
1.3
31
32
with IC50 values in the range of 0.1–0.2 lM (1, 5–10, 12, 21, and
23) were approximately 300 times more effective than the starting
disulfide compounds. These potencies were comparable to those of
3.4
33
1.4
34
LDDN-80042 (IC50 = 0.13 lM), a thienopyrimidine derivative de-
scribed by Duval et al.43, and aryl b-aminoethyl ketones that we re-
ported previously.59 The disulfide bonds have previously been
proposed to deactivate TGase by sulfide/disulfide interchange with
an active site cysteine,60 and the thienyl b-aminoethyl ketone moi-
ety has been shown to strongly inhibit TGase.59 Thus, incorporating
these two elements within our synthesized compounds may addi-
tively contribute to the potent inhibition of TGase.
2.6
35
1.1
36
5.5
37

S. Ozaki et al. / Bioorg. Med. Chem. Lett. 21 (2011) 377–379
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