Published on the web June 7, 2013
1051
Discovery of Synthetic Methoxy-substituted 4-Phenylbutyric Acid Derivatives
as Chemical Chaperones
Seisuke Mimori,1 Yasunobu Okuma,2 Masayuki Kaneko,3 Koichi Kawada,2
Yasuyuki Nomura,4 Yasuoki Murakami,1 and Hiroshi Hamana*1
1Department of Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Chiba Institute of Science,
15-8 Shiomi-cho, Choshi, Chiba 288-0025
2Department of Pharmacology, Faculty of Pharmaceutical Sciences, Chiba Institute of Science,
15-8 Shiomi-cho, Choshi, Chiba 288-0025
3Medical Therapeutics and Molecular Therapeutics, Gifu Pharmaceutical University,
1-25-4 Daigaku-nishi, Gifu 501-1196
4Laboratory of Pharmacotherapeutics, Yokohama College of Pharmacy,
601 Matano-cho, Totsuka-ku, Yokohama, Kanagawa 245-0066
(Received May 2, 2013; CL-130419; E-mail: hhamana@cis.ac.jp, smimori@cis.ac.jp)
In this study, we evaluated the chemical chaperone activity
of synthetic 4-phenylbutyric acid (4-PBA) derivatives. These
CO2H
derivatives have a methoxy group at the benzene ring and/or
longer or shorter fatty acid portions. Several 4-PBA derivatives
1
demonstrated higher antiaggregation activity than 4-PBA.
Moreover, 4-(4-methoxyphenyl)butanoic acid (7b) showed
protective effects against endoplasmic reticulum stress-induced
neuronal cell death.
Figure 1. Structure of 4-PBA.
(CH2)nCHO
(CH2)nCH2OH
Y
(CH2)nCH=CHCOOC2H5
(CH2)nCH2CH2COOC2H5
Y
Y
Y
PCC
(C2H5O)2P(O)CH2COOC2H5
H2/Pd-C
AcOEt
CH2Cl2
NaH / THF
X
X
X
X
2
3
4
5
4-Phenylbutyric acid (4-PBA), 1 (Figure 1), is a terminal
aromatic-substituted fatty acid and a well-known chemical
chaperone. It has been used to treat disorders of the urea cycle.
We reported that 4-PBA protects against cerebral ischemic injury
and endoplasmic reticulum (ER) stress-induced neuronal death,
demonstrates chemical chaperone activity, and prevents the
aggregation of reduced ¡ (alpha)-lactalbumin (r-LA) with
denatured bovine serum albumin (BSA).1,2 Moreover, we
reported that the chemical chaperone activity and protective
effects of ER stress-induced neuronal death are dependent on the
number of carbon atoms bound to the benzene ring.3
4-PBA has remarkable potential as a novel therapeutic agent
for type-2 diabetes and familial hypercholesterolemia.4 Further-
more, 4-PBA exerts significant neuroprotective effects in mouse
models of Parkinson’s disease (PD) and Alzheimer’s disease
(AD).5-7 Although these effects are valuable, a high dose of 4-
PBA is required. Therefore, reducing the dose of 4-PBA when
using it as a drug is an important limitation that should be
overcome. Conversely, the chemical chaperone activity of 4-
PBA derivatives has not been reported. Hence, we evaluated
certain synthetic 4-PBA derivatives for their chemical chaperone
activity against denatured proteins.
The synthetic routes to 4-PBA derivatives are illustrated in
Scheme 1. General experiments are shown in the Supporting
Information. We had thought that chemical chaperone activity is
dependent on the benzene ring, because in a previous paper,
butyrate had showed the very weak chemical chaperone
activity.3 Therefore, we focused on the benzene ring substituted
with fatty acids, not on the fatty acid in 4-PBA.
First, we examined the effects of compounds as chemical
chaperones in in vitro aggregation of ¡-LA with BSA.
Experimental details are shown in the Supporting Information.
As a representative of the compounds, we have shown the
1) 10% NaOH/EtOH
2) 10% HCl
1) 10% NaOH/EtOH
2) 10% HCl
LiAlH4/THF
CH2CH2CH2OH
(CH2)nCH=CHCOOH
Y
(CH2)nCH2CH2COOH
Y
(n=0)
Y
X
8
X
6
X
7
2
(n=2)
6a: n= 0, X= OCH3, Y= H (64, 2)
6b: n= 1, X= OCH3, Y= H (27 ,3)
6c: n= 2, X= OCH3, Y= H (51, 6)
6d: n= 0, X= H, Y= OCH3 (99, 2)
6e: n= 1, X= H, Y= OCH3 (38, 3)
6f : n= 2, X= H, Y= OCH3 (36, 6)
7a: n= 0, X= OCH3, Y= H (92, 3)
7b: n= 1, X= OCH3, Y= H (37, 4)
7c: n= 2, X= OCH3, Y= H (35, 7)
7d: n= 0, X= H, Y= OCH3 (60, 3)
7e: n= 1, X= H, Y= OCH3 (28, 4)
7f : n= 2, X= H, Y= OCH3 (33, 7)
overall yields (%, steps)
Scheme 1. Synthetic scheme of 4-PBA derivatives.
inhibitory effect of 6a on the protein aggregation (Figure 2
upper). Moreover, the chemical chaperone activities of 0.3, 1,
and 3 mM 4-PBA derivatives were compared with that of 3 mM
4-PBA (Figure 2 lower). All derivatives inhibited the aggrega-
tion of denatured BSA and r-LA in a concentration-dependent
manner. In particular, six derivatives 6b, 6e, 7a, 7b, 7c, and 7f
suppressed aggregation more strongly than 4-PBA at the same
concentration. This result showed that 4-PBA, available as a
seed compound, may be used against neurodegenerative diseases
if a minor structural change is induced in it.
With respect to the structure-activity relationship, inhibitory
effects increased if the methoxy group was substituted in the
para position (fourth/sixth) of the benzene ring. However, for
derivatives having a methoxy-substituted benzene ring, the
relationship between chemical chaperone activity and the
number of carbon atoms bound to the benzene ring was not
investigated. Chemical chaperone activity was dependent on the
Chem. Lett. 2013, 42, 1051-1052
© 2013 The Chemical Society of Japan