Bioorganic & Medicinal Chemistry Letters
Discovery of N-(2,3,5-triazoyl)mycophenolic amide and
mycophenolic epoxyketone as novel inhibitors of human IMPDH
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Kazuhiro Sunohara, Shinya Mitsuhashi, Kengo Shigetomi, Makoto Ubukata
Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan
a r t i c l e i n f o
a b s t r a c t
Syntheses of ten derivatives of mycophenolic acid (MPA) at C-60 position, and structure–activity relation-
ship study among these derivatives, MPA and mycophenolic hydroxamic acid (MPHA) led to discovery of
N-(2,3,5-triazolyl)mycophenolic amide 4, (70S) mycophenolic epoxyketone 9 and (70R) mycophenolic
epoxyketone 10 having potent inhibitory activity against human inosine-50-monophosphate dehydroge-
nase (IMPDH) type I and II as well as antiproliferative activity on human leukemia K562 cells. Compounds
4, 9, and 10 showed induction activity of erythroid differentiation in K562 cells. Inhibitory effects of 4 and
10 against IMPDH were attenuated by supplemental guanosine in K562 cells. In contrast, attenuation
effect by supplemental guanosine was not significant in the case of 9. Compound 9 weakly inhibited
Article history:
Received 13 May 2013
Revised 5 July 2013
Accepted 12 July 2013
Available online 19 July 2013
Keywords:
Mycophenolic acid
Erythroid differentiation
Mycophenolic hydroxamic acid
Inosine-50-monophosphate dehydrogenase
(IMPDH)
the enzyme activity of HDAC in the nuclear lysate of K562 cells at 10 lM. These observations suggest that
the primary target of 4, 9, and 10 is IMPDH, whereas compound 9 partially inhibits a certain type of
HDAC.
Histone deacetylase (HDAC)
Ó 2013 Elsevier Ltd. All rights reserved.
Inosine-50-monophosphate dehydrogenase (IMPDH) is an en-
zyme that catalyzes the NAD-dependent oxidation of inosine
monophosphate (IMP) to xanthosine monophosphate (XMP), the
first committed and rate-limiting step in guanine nucleotide bio-
synthesis.1 We found mycophenolic acid (1), known as an inhibitor
of IMPDH, to be a latent agonist of peroxisome proliferator acti-
K562 cell proliferation, inductive activity on erythroid differentia-
tion in K562 cells, and inhibitory activity against human IMPDH
in vitro.
Since one of the molecular targets for cancer therapy is zinc
dependent HDAC16 and Zn2+ is classified as borderline acid in
HASB rule,7 substitution of hydroxyl group as hard base of
hydroxamic acid in 2 with heterocyclic group might afford excel-
lent dual inhibitor for HDAC1 and IMPDH II. Six MPA derivatives
3–8, each having heterocyclic group were designed for dual inhib-
itor having the zinc binding moiety. Other MPA derivatives de-
signed here were compounds 9 and 10 which have terminus
epoxyketone known as zinc binding group in trapoxin,8 and com-
pound 12 having thiol group recognized as zinc binding group in
FK228.9 Thioacetate 11 was also selected as a candidate of a
masked dual-inhibitor for HDAC and IMPDH (Fig. 1).
7-O-TBS-mycophenolic acid (13) was obtained by treating 1
with 3 equiv of TBSOTf in the presence of Et3N in CH2Cl2, followed
by selective hydrolysis using AcOH/THF/H2O (1:9:1) in 95% yield.
The condensation reaction of 13 with each heterocyclic amine fol-
lowed by deprotection using TBAF afforded desired products 3–8
as shown in Table 1. The reaction of 13 with 2-aminopyridine gave
corresponding amide in 39.6% yield, when 1-ethyl-3-(3-dimethyl-
aminopropyl) carbodiimide hydrochloride (EDC) was used as a
condensation reagent, and deprotection of TBS group afforded 3
as a final product in 78.6%. The result suggests that more effective
activation of carboxylic acid is needed due to poor nucleophilicity
of heterocyclic amine. We therefore used ethyl chlorocarbonate
(ClCOOEt) for syntheses of 4, 6, and 7, oxalyl chloride [(COCl)2]
vated receptor
c (PPARc
).2 This finding led us to perform a chal-
lenge for conversion of molecular target of 1 by derivatization.
To develop dual inhibitors for human IMPDH and histone deacetyl-
ase (HDAC), we synthesized hydroxamic acid derivatives of 1,
mycophenolic hydroxamic acid (MPHA, 2), 7-O-acetyl MPHA, and
7-O-lauroyl MPHA which were found to be new tubulin-specific
HDAC inhibitors in culture cells (Fig. 1).3 The inhibitory effect of
2 on IMPDH was however 1-order of magnitude less than that of
1, and the selectivity of 1 toward human IMPDH type II was lost
after such derivatization (selectivity index of 1: 1.6, 2: 0.83, IMPDH
I/IMPDH II IC50 ratio).4 Transplantation therapy and chemotherapy
could be improved with IMPDH II specific inhibitors.5 Therefore,
discovery of new type of dual inhibitor for HDAC and IMPDH II
would provide important information for drug discovery for trans-
plantation therapy and chemotherapy. Herein, we describe design,
syntheses of new MPA heterocyclic amide derivatives 3, 4, 5, 6, 7, 8,
terminus epoxide derivatives 9, 10, thiol derivatives 11, 12, and
their structure–activity relationships for inhibitory effect on
⇑
Corresponding author. Tel./fax: +81 11 706 3638.
(M. Ubukata).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.