Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
J. Wang, Z. Cao, F. Wang et al.
European Journal of Medicinal Chemistry 225 (2021) 113799
Abbreviations
Bcl-2
DMSO
TGItw
THF
B-cell lymphoma-2
Dimethyl sulfoxide;
tumor growth inhibition by weight
Tetrahydrofuran
HDAC
ACE
histone deacetylase
angiotensin-converting enzyme
HMG-CoA 3-hydroxy-3-methylglutaryl-coenzyme A
TFA
trifluoroacetic acid
HTS
high-throughput screening
G-protein coupled receptors
suberanilohydroxamic acid
zinc binding group;
L-2-amino-7-carboxamidoheptanoic acid
L-S-(3-carboxamidopropyl) cysteine;
benzyloxycarbonyl
DCM
PE
EA
dichloromethane
petroleum ether
ethyl acetate
GPCRs
SAHA
ZBG
L-ACAH
L-CAPC
Cbz
HBTU
O-Benzotriazole-N,N,N0,N0-tetramethyl-uronium-
hexaf
DIEA
TEA
N,N-Diisopropylethylamine;
triethylamine;
tPSA
Nrot
topological polar surface area
rotatable bonds
IBCF
isobutyl chlorocarbonate
while chidamide [15] have been approved by China Food and Drug
Administration (CFDA) for treating T-cell lymphoma (Fig. 1A).
Additionally, these five approved HDAC inhibitors along with many
pre-clinical HDAC inhibitors are structurally featured with three
parts, a cap group, linker, and a zinc binding group (ZBG) [10].
Among all approved HDAC inhibitors, there is still not available for
treating solid tumor cancers in clinic yet [10e15]. Therefore, to
discover more HDAC inhibitors for exploring the therapeutic po-
tentials in solid tumor cancers is still highly desired.
derivatives of L-CAPC can be the substrate mimics of acetyl lysine
that are expected to inhibit HDAC activity very well.
2.2. Chemistry
The synthetic routes for the cysteine derivatives were shown in
Scheme 1 and Scheme 2. All candidate compounds were synthe-
sized from cysteine derivative 1, which was obtained from unpro-
tected cysteine according to our reported procedure [26]. In
While many HDAC inhibitors have been reported, surprisingly
there are only several reports of HDAC inhibitors developed that
closely mimics the substrate Nε-acetyl lysine [16e25]. Considering
that we and others have many successful experiences for devel-
oping sirtuin (Class III HDACs) inhibitors by mimicking Nε-acyl
lysine (sirtuin substrate) [26e30], we have previously designed and
developed a series of Nε-acetyl lysine analogs containing amide
acetyl groups with the hybridization of ZBG group as HDAC in-
hibitors by the strategy of substrate mimics (Fig. 1B) [18]. To further
fulfil the strategy of substrate mimics, we herein report the rational
design, synthesis, biological evaluation and molecular docking
studies of a series of novel HDAC inhibitors using cysteine-derived
Nε-acetyl lysine mimics with potent antitumor activities and
further exploration for treating solid tumor in a A549 xenograft
mice model (Fig. 1B).
Scheme
1,
compound
1
was
condensed
with
3-
fluorobenzenesulfonyl chloride or N-(benzyloxycarbonyloxy) suc-
cinimide to give compound 2 and compound 5, respectively.
Further condensation of compound 2 with -tryptophan cyclobutyl
amide or compound 5 with aniline and then deprotection of tert-
butyl group gave the intermediates 3 and 6, respectively. A series of
candidate compounds 4a-d were obtained by the assemble of
different amines from intermediate 3 while another series of
candidate compounds 7a-h were also accomplished by the
assemble of various amines from intermediate 6.
L
In Scheme 2, with similar procedures, compound 10 was readily
achieved by condensation of compound
1
with N-(9-
fluorenylmethoxycarbonyloxy) succinimide. Different amines
were furnished at the C-terminal of compound 5 to give interme-
diate 8, which was decorated with hydroxylamine to afford
hydroxamates 9a-j. Another series of hydroxamates 13a-i were
obtained through the condensation of hydroxylamine with inter-
mediate 12, which was prepared by condensation of compound 10
with aniline followed by the removal of the Fmoc group.
2. Results and discussion
2.1. HDAC inhibitors designed from acetyl lysine
According to the crystal structure of the HDAC8-substrate
(acetyl lysine) complex (PDB entry: 2V5W) [31], His180, Asp178
and Asp267 of HDAC8 and the acetyl lysine of the substrate directly
interact with the catalytic zinc ion (Fig. 2A). Similarly, the crystal
structure of the HDAC8 in complex with SAHA complex (PDB entry:
1t69) shows that the hydroxamate moiety of SAHA coordinate the
zinc ion (Fig. 2B) [32]. Furthermore, the alignment of these two
crystal structures shows that they possess almost the same binding
mode with good superimposition of the HDAC8 substrate and in-
hibitor (Fig. 2C). This provoked us to design HDAC inhibitors
directly by switching acetyl group on lysine to zinc binding group.
To achieve this, based on L-2-amino-7-carboxamidoheptanoic acid
(L-ACAH) containing acetyl lysine analogs with an “inverted amide”
by isosteric swapping of the NH and methyl groups of the acetyl
amide, we could simply replace the methylene group with the
Sulphur atom to give a L-S-(3-carboxamidopropyl) cysteine (L-
CAPC) scaffold, which could be further decorated with different
substituents to become zinc binding groups (Fig. 1B) [26]. Thus, the
2.3. Biological evaluation
In compounds 4a-d, C-terminal of cysteine is coupled to -
L
tryptophan cyclobutyl amide and N-terminal of cysteine containing
3-fluorobenzenesulfonyl group that were used in the acyl lysine
mimics of SIRT5 (one of Class III HDACs) inhibitors [33]. Compounds
7a-h contain benzyloxycarbonyl at N-terminal of cysteine and an-
iline at C-terminal, which were used in other acyl lysine mimics of
sirtuin (Class III HDACs) inhibitors [26e30].
We first evaluated the ZBG effect in series of compounds 4a-
d and 7a-h at the concentration of 1 mM using HeLa nuclear extract
as HDACs source. As shown in Table S1 in the Supporting Infor-
mation, it was not surprising that hydroxamic acid, a classic ZBG
group, was superior over all others including amino benzamide,
thiol, and heterocyclic groups. Among those hydroxamic acids, 7a
with the moieties of benzyloxycarbonyl at N-terminal and aniline
at C-terminal only showed slightly better HDAC inhibition (84%)
than that of 4a (82%). Among a series of hydroxamic acids 9a-j with
2