Evaluation of synthetic naphthalene derivatives as novel chemical chaperones that mimic 4-phenylbutyric acid

Article abstract of DOI:10.1016/j.bmcl.2014.12.080

The chemical chaperone 4-phenylbutyric acid (4-PBA) has potential as an agent for the treatment of neurodegenerative diseases. However, the requirement of high concentrations warrants chemical optimization for clinical use. In this study, novel naphthalene derivatives with a greater chemical chaperone activity than 4-PBA were synthesized with analogy to the benzene ring. All novel compounds showed chemical chaperone activity, and 2 and 5 possessed high activity. In subsequent experiments, the protective effects of the compounds were examined in Parkinson's disease model cells, and low toxicity of 9 and 11 was related to amphiphilic substitution with naphthalene.

Full text of DOI:10.1016/j.bmcl.2014.12.080

Bioorganic & Medicinal Chemistry Letters 25 (2015) 811–814
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Evaluation of synthetic naphthalene derivatives as novel
chemical chaperones that mimic 4-phenylbutyric acid
Seisuke Mimori a, , Yukari Koshikawa , Yu Mashima , Katsuyoshi Mitsunaga , Koichi Kawada ,
⇑
a
a
b
c
d
c
e
a
f
Masayuki Kaneko , Yasunobu Okuma , Yasuyuki Nomura , Yasuoki Murakami , Tetsuto Kanzaki ,
a
Hiroshi Hamana
a
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomicho, Choshi, Chiba 288-0025, Japan
Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
Department of Pharmacology, Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomi-cho, Choshi, Chiba 288-0025, Japan
Department of Biochemistry, Graduate School of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan
Department of Pharmacology, Faculty of Medicine, Kurume University, 67 Asahimachi, Kurume, Fukuoka 830-0011, Japan
Department of Clinical Medicine, Faculty of Pharmacy, Chiba Institute of Science, 15-8 Shiomicho, Choshi, Chiba 288-0025, Japan
b
c
d
e
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a r t i c l e i n f o
a b s t r a c t
Article history:
The chemical chaperone 4-phenylbutyric acid (4-PBA) has potential as an agent for the treatment of
neurodegenerative diseases. However, the requirement of high concentrations warrants chemical
optimization for clinical use. In this study, novel naphthalene derivatives with a greater chemical chap-
erone activity than 4-PBA were synthesized with analogy to the benzene ring. All novel compounds
showed chemical chaperone activity, and 2 and 5 possessed high activity. In subsequent experiments,
the protective effects of the compounds were examined in Parkinson’s disease model cells, and low
toxicity of 9 and 11 was related to amphiphilic substitution with naphthalene.
Received 18 October 2014
Revised 22 December 2014
Accepted 24 December 2014
Available online 5 January 2015
Keywords:
Chemical chaperone
Ó 2015 Elsevier Ltd. All rights reserved.
4
-Phenylbutyric acid (4-PBA)
Naphthalene
Parkinson’s disease (PD)
Endoplasmic reticulum (ER) stress
Aggregation of insoluble proteins is common to neurodegener-
ative diseases such as Alzheimer’s disease (AD) and Parkinson’s
disease (PD), involving phosphorylated tau and amyloid-b (Ab)
peptides, and
a-synuclein, respectively. Dysfunctions associated
with these aggregates have prompted the discovery of genetic pre-
dispositions and inhibitors for use as prophylactics or treatments.
In particular, geldanamycin induces molecular chaperones and
1
,2
suppresses neurodegeneration in a drosophila model of PD.
Molecular chaperones such as heat shock proteins (Hsps) are
required for the functional folding of nascent proteins and the
repair of higher-order protein structure. In particular, Hsp70
reduces the overexpression of Ab, which is the major component
of neurofibrillary tangles in AD, and protects neuronal cells from
3,4
Ab-dependent neurotoxicity in vivo and in vitro.
Moreover,
inducible Hsp70 is protective against ischemic injury in vivo and
5
in vitro.
Although chemical chaperones are low molecular weight com-
pounds, their actions are similar to those of molecular chaperones,
and the well-known molecular chaperone 4-PBA prevents the
Figure 1. Strategy for synthesis of novel chemical chaperones.
aggregation of denatured proteins. In previous studies, 4-PBA has
been shown to protect against cerebral ischemic injury and endo-
plasmic reticulum (ER) stress-induced neuronal cell death,6 and
⇑
Corresponding author. Tel./fax: +81 479 30 4549.
E-mail address: smimori@cis.ac.jp (S. Mimori).
,7
http://dx.doi.org/10.1016/j.bmcl.2014.12.080
960-894X/Ó 2015 Elsevier Ltd. All rights reserved.
0

8
12
S. Mimori et al. / Bioorg. Med. Chem. Lett. 25 (2015) 811–814
Scheme 1. Reagents and conditions: (a) pyridinium chlorochromate (PCC), methylene chloride, RT, 2–4 h, 64–72%; (b) ethyl diethylphosphonoacetate, NaH, THF, RT, 66–99%;
c) alkaline hydrolysis, EtOH, 10% NaOH, RT, 83–97%; (d) H , 5% palladium carbon, AcOEt, RT, 56–90%; (e) alkaline hydrolysis, EtOH, 10% NaOH, RT, 80–98%; (f) LiAH , THF, RT,
.5–3 h, 91–97%.
(
2
4
1
Figure 2. Structures of synthetic naphthalene analogs.
significant neuroprotective effects are shown in mouse models of
Previous data indicate that the benzene ring of 4-PBA is essen-
tial for chemical chaperone activity, suggesting that hydrophobic
amino acids are involved in protein aggregation (Fig. 1). Thus, we
assumed that the electron clouds of benzene rings interact with
the aggregates of denatured proteins, and intended to expand the
electron cloud area by synthesizing 4-PBA analogs based on
naphthalene.
8
–10
AD and PD.
Moreover, 4-PBA has been approved for clinical
use as an ammonia scavenger in children with urea cycle disor-
1
1
ders. Recently, 4-PBA has also shown remarkable potential as a
novel therapeutic agent for type
diabetes12 and familial
2
1
3
hypercholesterolemia.
Although these effects are promising, the required doses of 4-
PBA are prohibitively high. Thus, we designed synthetic 4-PBA ana-
logs to optimize chemical chaperone activity against denatured
proteins.
Chemistry: Naphthalene derivatives were synthesized according
1
5
to a previous study as shown in Scheme 1. Additional details of
the synthetic process are presented in Supporting information15
and all synthesized compounds are shown in Figure 2. All deriva-
In a recent study, we showed that chemical chaperone activities
and protective effects against ER stress-induced neuronal cell
death are dependent on the numbers of fatty acid carbon atoms
tives were characterized using spectrometric methods,17 and 1
H
NMR experiments were performed using a Unity 400 MHz spec-
trometer. Silica gel column chromatography was conducted using
a Merck Silica gel 60 (0.040–0.063; 230–400 mesh ASTM).
Biology: Initially, we examined the effects of chemical chaper-
1
4
on 4-PBA derivatives. In further studies, we evaluated the chem-
ical chaperone activities of synthetic methoxy-substituted 4-PBA
1
5
derivatives.
Subsequently, we showed that although 4-PBA
inhibits histone deacetylase (HDAC), it acts as a chemical chaper-
one and protects against ER stress-induced neuronal cell death.
ones on the aggregation of r-LA with BSA in vitro, as previously
1
6
14,16
described.
All compounds inhibited the aggregation of

S. Mimori et al. / Bioorg. Med. Chem. Lett. 25 (2015) 811–814
813
work was supported by Grants-in-Aid for Scientific Research
24790085, 245901119, and 24300135) from the Ministry of Edu-
(
cation, Culture, Sports, Science and Technology, Japan.
References and notes
1.
Sittler, A1.; Lurz, R.; Lueder, G.; Priller, J.; Lehrach, H.; Hayer-Hartl, M. K.; Hartl,
F. U.; Wanker, E. E. Hum. Mol. Genet. 2001, 10, 1307.
2
3
4
.
.
.
Auluck, P. K.; Bonini, N. M. Nat. Med. 2002, 8, 1185.
Jordi, M.; Roy, C. S.; Kenneth, W.; Henry, W. Q. J. Neurosci. 2004, 24, 1700.
Hoshino, T.; Murao, N.; Namba, T.; Takehara, M.; Adachi, H.; Katsuno, M.;
Sobue, G.; Matsushima, T.; Suzuki, T.; Mizushima, T. J. Neurosci. 2011, 31,
5225.
5
6
.
.
Yunjuan, S.; Yi-Bing, O.; Lijun, X.; Ari, M.-Y. C.; Robin, A.; James, G. H.; Rona, G.;
Giffard, J. Cereb Blood Flow Metab. 2006, 267, 937.
Qi, X.; Hosoi, T.; Okuma, Y.; Kaneko, M.; Nomura, Y. Mol. Pharm. 2004, 66, 899.
Figure 3. Inhibitory effects of naphthalene analogs on the aggregation of reduced
-lactalbumin. Experiments were conducted as previously described.14–16 Briefly, r-
7. Kubota, K.; Niinuma, Y.; Kaneko, M.; Okuma, Y.; Sugai, M.; Omura, T.; Uesugi,
M.; Uehara, T.; Hosoi, T.; Nomura, Y. J. Neurochem. 2006, 97, 1259.
a
8
9
.
.
Inden, M.; Kitamura, Y.; Takeuchi, H.; Yanagida, T.; Takata, K.; Kobayashi, Y.;
Taniguchi, T.; Yoshimoto, K.; Kaneko, M.; Okuma, Y.; Taira, T.; Ariga, H.;
Shimohama, S. J. Neurochem. 2007, 101, 1491.
Ono, K.; Ikemoto, M.; Kawarabayashi, T.; Ikeda, M.; Nishinakagawa, T.;
Hosokawa, M.; Shoji, M.; Takahashi, M.; Nakashima, M. Parkinsonism Relat.
Disord. 2009, 15, 649.
LA was prepared by incubating -LA with 5 mM dithiothreitol and 2.5 mM
a
ethylenediamine tetraacetic acid at 25 °C for 30 min. Aggregation of r-LA was
induced by the addition of denatured bovine serum albumin at 37 °C. Protein
aggregation was monitored by measuring optical density at 488 nm (turbidity) after
the addition of a vehicle (DMSO), 0.3 mM test compound, or 3 mM 4-PBA; NT
indicates no treatment. Turbidities in the presence of naphthalene derivatives are
expressed relative to corresponding controls and are presented as means ± SE of
four independent experiments.
10. Ricobaraza, A.; Cuadrado, T. M.; Pérez, M. A.; Frechilla, D.; Del, R. J.; García, O. A.
Neuropsychopharmacology 2009, 34, 1721.
1
1
1. Brusilow, S. W.; Maestri, N. E. Adv. Pediatr. 1996, 43, 127.
2. Ozcan, U.; Yilmaz, E.; Ozcan, L.; Furuhashi, M.; Vaillancourt, E.; Smith, R. O.;
Görgün, C. Z.; Hotamisligil, G. S. Science 2006, 313, 1137.
1
1
1
1
1
3. Tveten, K.; Holla, Ø. L.; Ranheim, T.; Berge, K. E.; Leren, T. P.; Kulseth, M. A. FEBS
J. 2007, 274, 1881.
4. Mimori, S.; Okuma, Y.; Kaneko, M.; Kawada, K.; Hosoi, T.; Ozawa, K.; Nomura,
Y.; Hamana, H. Biol. Pharm. Bull. 2012, 35, 84.
5. Mimori, S.; Okuma, Y.; Kaneko, M.; Kawada, K.; Nomura, Y.; Murakami, Y.;
Hamana, H. Chem. Lett. 2013, 42, 1051.
6. Mimori, S.; Ohtaka, H.; Koshikawa, Y.; Kawada, K.; Kaneko, M.; Okuma, Y.;
Nomura, Y.; Murakami, Y.; Hamana, H. Bioorg. Med. Chem. Lett. 2013, 23, 6015.
7. Spectral data for representative compounds: 3-(2-Methoxynaphthalen-1-
1
yl)propanoic acid (1): H NMR (400 MHz; CDCl
3
): d 4.13 (2H, t, J = 16 Hz,
-H), 6.90 (3H, s, –OCH ), 7.62–7.86 (1H, m,
naph-H), 8.24 (2H, m, naph-H), 8.31 (1H, d, J = 8.3 Hz, naph-C -H), 8.64 (1H,
d, J = 16 Hz, naph-C -H) HRMS (EI method): Calcd for
30.0943. Found: 230.0943. Mp: 132–133 °C. 3-(4-Methoxynaphthalen-1-
C
2
-H), 6.54 (2H, t, J = 16 Hz, C
3
3
5
+
8
14 14 3
C H O (M ):
2
1
yl)propanoic acid (2): H NMR (400 MHz; CDCl
2H, t, J = 16 Hz, C -H), 6.89 (3H, s, J = 8.1 Hz, –OCH
H), 8.24 (2H, m, naph-H), 8.25 (1H, d, J = 8.3 Hz, naph-C
J = 16 Hz, naph-C -H) HRMS (EI method): Calcd for C14
Found: 230.0943. Mp: 170–172 °C. 3-(6-Methoxynaphthalen-2-yl)acrylic acid
(3): 1H NMR (400 MHz; CDCl
): d 2.76 (2H, t, J = 8.0, C -H), 3.09 (2H, t,
J = 8.0 Hz, C -H), 3.91 (3H, s, –OCH ), 7.10–7.69 (6H, m, naph-H) HRMS (EI
method): Calcd for C14 (M ): 230.0943. Found: 230.0943. Mp: 158–
61 °C. 3-(2-Methoxynaphthalen-1-yl)acrylic acid (4): 1
NMR (400 MHz;
CDCl ): d 4.03 (3H, s, –OCH ), 6.84 (1H, d, J = 16 Hz, C -H), 7.29–7.54 (3H, m,
naph-H), 7.80 (1H, d, J = 8.0 Hz, naph-H), 7.88 (1H, d, J = 9.0 Hz, naph-H), 8.21
1H, d, J = 8.6 Hz, naph-H), 8.48 (1H, d, J = 16 Hz, C -H) HRMS (EI method):
(M ): 228.0787. Found: 228.0788. Mp: 162–164 °C. 3-(4-
3
): d 4.05 (2H, m, C
) 7.55–7.84 (1H, m, naph-
-H), 8.60 (1H, d,
2
-H), 6.53
Figure 4. Protective effects of synthetic naphthalene derivatives on Pael-R-induced
cell death in human neuroblastoma SH-SY5Y cells. Experiments were conducted as
we previously described.14 Briefly, SH-SY5Y cells stably expressing Pael-R–FLAG
were incubated in the presence or absence of indicated naphthalene derivatives at
(
3
3
5
+
8
14 3
H O (M ): 230.0943.
0
.1, 0.5, or 1.0 mM for 48 h. About 10% of control Pael-R overexpressing cells died.
3
2
Cell viability was determined using crystal violet assays; Data are presented as
means ± SE of three independent experiments.
3
3
+
14 3
H O
1
H
3
3
3
denatured BSA and r-LA (Fig. 3), and although 4-PBA was active at
(
2
3
mM, synthetic compounds were active at 0.3 mM. However, fur-
+
Calcd for C14
Methoxynaphthalen-1-yl)acrylic acid (5): H NMR (400 MHz; CDCl
(3H, s, –OCH ), 6.46 (1H, d, J = 16 Hz, naph-C -H), 6.88 (1H, d, J = 8.1 Hz),
12 3
H O
ther studies are required to elucidate the associated structure–
activity relationships.
1
3
): d 4.06
3
3
Pael-R is a substrate of the protein Parkin,18 which is a PD-asso-
7
.53–7.82 (2H, m, naph-H), 8.20 (1H, d, J = 8.4 Hz, naph-H), 8.32 (1H, d,
J = 8.3 Hz, naph-H), 8.57 (1H, d, J = 16 Hz, naph-C -H) HRMS (EI method):
(M ): 228.0787. Found: 228.0789. Mp: 216–220 °C. 3-(6-
ciated ubiquitin ligase E3.19 Thus, in subsequent experiments, we
investigated the protective effects of the naphthalene derivatives
8
+
Calcd for C14
12 3
H O
1
Methoxynaphthalen-2-yl)propanoic acid (6): H NMR (400 MHz; CDCl ): d
3
on Pael-R-induced cell death in SH-SY5Y cells using crystal violet
3.49 (3H, s, –OCH
7.14–8.26 (6H, m, naph-H) HRMS (EI method): Calcd for C
28.0787. Found: 228.0788. Mp: 215–217 °C. 5-(2-Methoxynaphthalen-1-
3
), 3.95 (1H, d, J = 8.0 Hz, C
2
-H), 6.53 (1H, d, J = 8.0 Hz, C
3
-H),
+
assays, as previously described.14 At 0.1 mM, the present synthetic
H O
14 12 3
(M ):
2
analogs were not significantly more effective than 4-PBA (Fig. 4).
Moreover, naphthalene has been used as an insecticide and may
have exerted some toxicity.
1
yl)pentanoic acid (7): H NMR (400 MHz; CDCl
J = 7.4 Hz, C -H), 3.10 (2H, t, J = 7.6 Hz, C -H), 3.93 (3H, s, –OCH
-H), 7.27–7.47 (2H, m, naph-H), 7.73 (1H, m, naph-C -H), 7.79 (1H, m,
-H), 7.93 (1H, d, J = 8.6 Hz, naph-C -H) HRMS (EI method): Calcd for
(M ): 258.1256. Found: 258.1256. Mp: 87–89 °C. 5-(4-
3
): d 1.69 (4H, m), 2.42 (2H, t,
2
5
3
), 7.25 (1H, d,
naph-C
naph-C
3
5
4
8
In conclusion, we have developed naphthalene based analogs of
+
16 18 3
C H O
1
4
-PBA that have wider electron clouds and exhibit chemical chap-
Methoxynaphthalen-1-yl)pentanoic acid (8): H NMR (400 MHz; CDCl
.75–1.79 (2H, m), 2.40 (2H, m), 3.01 (2H, m, C -H), 3.98 (3H, s, –OCH ), 6.73
1H, d, J = 7.8 Hz, naph-C -H), 7.21 (1H, d, J = 7.8 Hz, naph-C -H), 7.46 (2H, m),
.94 (1H, d, J = 8.0 Hz, naph-C -H), 8.28 (1H, d, J = 1.3 Hz, naph-C -H) HRMS
(M ): 258.1256. Found: 258.1257. Mp: 141–
3
): d
1
(
7
5
3
erone activity. Among the tested naphthalene derivatives, 9 had
the weakest toxicity and may protect against Pael-R-induced cell
death. However, no significant protective effects were observed
in PD model cells. Thus, in further studies, we will examine atomic
substitutes for carbon in chemical chaperones.
3
2
5
8
+
(EI method): Calcd for C16
43 °C. 5-(6-Methoxynaphthalen-2-yl)pentanoic acid (9): H NMR (400 MHz;
CDCl ): 1.25–1.72 (4H, m), 2.39 (2H, t, J = 5.0 Hz, -H), 2.76 (2H, t,
J = 6.3 Hz, C -H), 3.91 (3H, s, –OCH ), 7.10 (2H, m, naph-H), 7.29 (1H, m,
naph-H), 7.53 (1H, s, naph-H), 7.66 (2H, m, naph-H) HRMS (EI method): Calcd
18 3
H O
1
1
3
d
C
2
5
3
+
for
Methoxynaphthalen-1-yl)-2-pentenoic acid (10): H NMR (400 MHz; CDCl
d 2.66 (2H, m, C -H), 3.16 (2H, t, J = 7.8 Hz, C -H), 3.98 (3H, s, –OCH ), 5.89
(1H, d, J = 16 Hz, C -H), 7.16–7.22 (2H, m, naph-H), 7.48–7.55 (2H, m, naph-
C H O (M ): 258.1256. Found: 258.1257. Mp: 130–133 °C. 5-(4-
16 18 3
Acknowledgments
1
3
):
4
5
3
This work was partly supported by a Sasakawa Scientific
Research Grant from The Japan Science Society. In addition, this
2
5 8
H), 7.90 (1H, d, J = 8.0 Hz, naph-C -H), 8.30 (1H, d, J = 1.2 Hz, naph-C -H)

8
14
S. Mimori et al. / Bioorg. Med. Chem. Lett. 25 (2015) 811–814
+
+
HRMS (EI method): Calcd for C16
55–158 °C. 5-(6-Methoxynaphthalen-2-yl)-2-pentenic acid (11):
400 MHz; CDCl ): d 2.62 (2H, q, J = 7.3 Hz, C -H), 2.90 (2H, t, J = 7.5 Hz, C
.91 (3H, s, –OCH ), 5.87 (1H, d, J = 16 Hz, C -H), 7.14 (3H, m, naph-H), 7.26
-H), 7.68 (2H, m, naph-H) HRMS (EI
H
16
O
3
(M ): 256.1100. Found: 256.1100. Mp:
16 3
method): Calcd for C16H O (M ): 256.1100. Found: 256.1101. Mp: 149–
151 °C.
1
1
(
3
(
H
NMR
-H),
3
4
5
18. Imai, Y.; Soda, M.; Inoue, H.; Hattari, N.; Mizuno, Y.; Takahashi, R. Cell 2001,
105, 891.
19. Imai, Y.; Soda, M.; Takahashi, R. J. Biol. Chem. 2000, 275, 35661.
3
2
2H, m, naph-H), 7.55 (1H, s, naph-C
1