Synthesis of Denosomin-Vitamin D3 Hybrids and Evaluation of Their Anti-Alzheimer's Disease Activities

Article abstract of DOI:10.1021/acs.orglett.5b03138

As an extension of previously conducted studies on developing an anti-Alzheimer's disease agent, denosomin (1-deoxy-24-norsominone, an artificial inducer of neurite elongation), derivatives were designed and synthesized based on the hypothesis that our denosomin would exhibit axonal extension activity via a 1,25D₃-membrane-associated, rapid response steroid-binding protein (1,25D₃-MARRS) pathway. The biological assay revealed that the hybridization of characteristic δ-lactone in denosomin and the triene moiety in VD₃ was effective to enhance the nerve re-extension activity in amyloid β (Aβ)-damaged neurons.

Full text of DOI:10.1021/acs.orglett.5b03138

Letter
pubs.acs.org/OrgLett
Synthesis of Denosomin−Vitamin D3 Hybrids and Evaluation of Their
Anti-Alzheimer’s Disease Activities
Kenji Sugimoto,† Hisanari Yajima,† Yusuke Hayashi,† Daishiro Minato,† Sayuri Terasaki,‡ Chihiro Tohda,‡
and Yuji Matsuya*,†
†Graduate School of Medicine and Pharmaceutical Sciences, and ‡Institute of Natural Medicine, University of Toyama, 2630 Sugitani,
Toyama 930-0194, Japan
S
* Supporting Information
ABSTRACT: As an extension of previously conducted studies on developing an anti-Alzheimer’s disease agent, denosomin (1-
deoxy-24-norsominone, an artificial inducer of neurite elongation), derivatives were designed and synthesized based on the
hypothesis that our denosomin would exhibit axonal extension activity via a 1,25D3-membrane-associated, rapid response steroid-
binding protein (1,25D3-MARRS) pathway. The biological assay revealed that the hybridization of characteristic δ-lactone in
denosomin and the triene moiety in VD3 was effective to enhance the nerve re-extension activity in amyloid β (Aβ)-damaged
neurons.
ntering the era of an aging population, dementia has
Ebecome one of the most serious problems in the world,
and the number of affected patients has increased each year.
The most common form of dementia is Alzheimer’s disease
(AD), and the number of patients in 2050 is predicted to reach
114 million worldwide, a 4-fold increase from 25 million in
2000.1 Against such problems, several acetylcholinesterase
inhibitors have been developed and prescribed for the clinical
treatment of AD; however, those only address symptomatic
treatment. Although recent studies revealed that amyloid β
(Aβ) in the brain causes AD, Aβ targeting therapy could not
recover from the advanced memory disorder. From the point of
view of improving the injured brain function by reactivation
and re-establishment of the damaged neuron network,
neurotrophic agents are desirable, and a large number of
potent natural products have been reported2 since the isolation
Figure 1. Denosomin and related compounds.
of lactacystin by Omura and co-workers.3 In recent decades,
steroids such as NGA01874 and withanolide A5 were reported
denosomin and the triene part mimicking VD3 would possibly
have a higher affinity with 1,25D3-MARRS and would exhibit
enhanced biological activity. In this manuscript, we describe the
synthesis of a novel denosomin−VD3 hybrid and the evaluation
of axonal extension activity on Aβ-damaged neurons.
Our synthetic plan for denosomin−VD3 hybrids (1: R = OH,
2: R = H) is outlined in Scheme 1. A conjugated triene moiety
would be constructed by a Trost coupling reaction8 between
CD-ring fragment 3 and known enyne 49 (or 5). Vinyl bromide
3 could be established from trans-hydrindan 610 with
to exhibit potent neurite outgrowth activities. In the course of
our studies on an Ayurvedic tonic medicine Ashwagandha, we
also found that natural steroid sominone and its artificial, but
more potent, derivative denosomin (1-deoxy-24-norsominone,
Figure 1) showed significant axonal extension activity in Aβ-
damaged neurons.6 Recently, Tohda, one of the authors,
revealed that diosgenin, a steroidal sapogenin, improved
memory in AD model mice through the activation of the
1,25D3-membrane-associated, rapid response steroid-binding
protein (1,25D3-MARRS).7 Thus, we hypothesized that our
denosomin also exhibited axonal extension activity via the
1,25D3-MARRS pathway. If the hypothesis were correct, the
CD-ring core equipped with a characteristic δ-lactone moiety in
Received: October 30, 2015
Published: November 20, 2015
© 2015 American Chemical Society
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Letter
Despite the highly basic conditions included in the Wittig
transformation from 11 to 12, the trans-hydrindane scaffold in
11, which occasionally isomerizes into thermodynamically
stable cis-hydrindane under basic conditions,13 was proven to
be untouched through the process (Scheme 3). For stereo-
Scheme 1. Synthetic Plan for Denosomin−VD3 Hybrids
Scheme 3. Stereochemical Verification of Hydrindanes
modification of our previous work on the synthesis of
denosomin.6a A ring precursor 4 and 5 could be prepared
following the report by Takayama and co-workers.9
Hydrogenation of 6, which was prepared from the Hajos
Ketone (7) via known eight steps,10 gave 8 in a
diastereoselective manner (Scheme 2).11 The primary hydroxyl
Scheme 2. Preparation of Diene 16
chemical verification by 1H NMR, cis-hydrindane 12′ was
prepared by the consistent Wittig reaction/acidic deprotection
sequence after the exposure of 11 to NaOMe/MeOH.13 While
the signal of the methyl group on the ring juncture in 12′
appears at 0.97 ppm as in the case of typical cis-hydrindanes,
that for 12 was found at 0.78 ppm, which is typically observed
in trans-hydrindanes.
Next, we examined a δ-lactone formation reaction of diene
16 by ring closing metathesis (RCM) with Ru-based catalysts
(Table 1). Though Grubbs’ second generation catalyst (cat-1)
Table 1. Ring Closing Metathesis for δ-Lactone
entry
catalyst
time (h)
yield (%)
1
2
3
4
cat-1
cat-2
cat-3
cat-4
20
7
23
57
29
61
20
5
group was then oxidized with IBX, and subsequent asymmetric
allylation of the resultant aldehyde afforded homoallylalcohol 9.
The ketone 11, the precursor for vinyl bromide 12, was
obtained via MOM-protection of the secondary hydroxyl
group, desilylation, and IBX oxidation. Wittig reaction of 11
with bromomethyltriphenylphosphonium bromide followed by
acidic hydrolysis of MOM ether afforded 12.12 Silyloxy-
methacrylic acid 14, which was readily prepared from ethyl
acrylate through a Morita−Baylis−Hillman reaction, was
condensed with 12, and removal of the TBDPS group under
neutral conditions gave diene 16.
gave the δ-lactone 3 in low yield (entry 1), Hoveyda−Grubbs’
second generation catalyst (cat-2) smoothly afforded 3 in 57%
yield. With sterically less demanding catalysts cat-314 and cat-
4,14 which were derivatives with the bis(o-tolyl) NHC ligand,
the chemical yields were improved and desired 3 was furnished
in 61% yield with cat-4.
On the other hand, enynes 4 and 5 were prepared from 3-
buten-1-ol according to the procedures described by Takayama
and co-workers (Scheme 4).9 An eight-step transformation
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Scheme 4. Preparation of A Ring Precursors
from 3-butene-1-ol including Sharpless asymmetric dihydrox-
ylation afforded the pivotal aldehyde 17. Enyne 4, the precursor
of the dihydroxy A-ring unit, was synthesized through the
literature methods, and monohydroxyenyne 5 could be
obtained through chain elongation reactions of 17 via aldehyde
18.
With the corresponding counterparts, a Trost-coupling
reaction was examined between CD-ring core 3 and A ring
precursor 4 or 5 (Scheme 5). In the presence of Pd(OAc)2 and
Figure 2. Biological evaluation of denosomin−VD3 hybrids. (A)
Effects on axonal density. (B) Representative fluorescent images of
axons.
neurons. The result suggests that our anti-Alzheimer’s disease
agents exhibit nerve re-extension activity in Aβ-damaged
neurons via the 1,25D3-MARRS pathway. Based on these
findings, further derivatizations and evaluations of denosomin−
VD3 hybrids are ongoing in our laboratory.
Scheme 5. Synthesis of Denosomin−VD3 Hybrids
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.5b03138.
1
Experimental procedure, spectral data, and copies of H
and 13C NMR spectra for all novel compounds (PDF)
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: matsuya@pha.u-toyama.ac.jp.
Notes
PPh3, the domino reaction proceeded smoothly to furnish
desired coupling products, respectively. Removal of the TBS
group with aqueous HF solution gave the hybrids 1 and 2.
Finally, we evaluated the nerve re-extension activity of the
hybrids in Aβ-damaged neurons compared with denosomin.
Denosomin and hybrids 1 and 2 (0.1 μM or 1 μM each) were
exposed to rat cortical neurons on the third day after treatment
with 10 μM of Aβ (25−35), and the axonal densities were
measured after further incubation for 4 days. As a result, we
proved our hybrids exhibit more potent axonal re-extension
activities than parent denosomin, especially in lower concen-
tration, 0.1 μM (Figure 2A and B). These phenomena were
consistent with our hypothesis that denosomin demonstrated
the axonal extension activity via the 1,25D3-MARRS pathway.
In conclusion, we designed and synthesized novel anti-
Alzheimer’s disease agents, denosomin−VD3 hybrids, and
proved their potency on axonal re-extension in rat cortical
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported in part by the KAKENHI, a Grant-in-
Aid for Scientific Research (C) (25460010) for Y.M.
■
REFERENCES
■
(1) Moreira, P. I.; Zhu, X.; Smith, M. A.; Perry, G. In Encyclopedia of
Neuroscience; Larry, R. S., Ed.; Academic Press: Oxford, 2009; pp 259−
263.
(2) (a) Xu, J.; Lacoske, M. H.; Theodorakis, E. A. Angew. Chem., Int.
Ed. 2013, 52, 2−34. (b) Silva, T.; Teixeira, J.; Remiao, F.; Borges, F.
Angew. Chem., Int. Ed. 2013, 52, 1110−1121.
(3) (a) Omura, S.; Fujimoto, T.; Otoguro, K.; Matsuzaki, K.;
Moriguchi, R.; Tanaka, H.; Sasaki, Y. J. Antibiot. 1991, 44, 113−116.
(b) Omura, S.; Matsuzaki, K.; Fujimoto, T.; Kosuge, K.; Furuya, T.;
Fujita, S.; Nakagawa, A. J. Antibiot. 1991, 44, 117−118.
̃
5912
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Org. Lett. 2015, 17, 5910−5913

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Letter
(4) (a) Nozawa, Y.; Sakai, N.; Matsumoto, K.; Mizoue, K. J. Antibiot.
2002, 55, 629−634. (b) Hua, Z. H.; Carcache, D. A.; Tian, Y.; Li, Y.
M.; Danishefsky, S. J. J. Org. Chem. 2005, 70, 9849−9856.
(5) (a) Zhao, J.; Nakamura, N.; Hattori, M.; Kuboyama, T.; Tohda,
C.; Komatsu, K. Chem. Pharm. Bull. 2002, 50, 760−765.
(b) Kuboyama, T.; Tohda, C.; Komatsu, K. Br. J. Pharmacol. 2005,
144, 961−971. (c) Jana, C. K.; Hoecker, J.; Woods, T. M.; Jessen, H.
J.; Neuburger, M.; Gademann, K. Angew. Chem., Int. Ed. 2011, 50,
8407−8411. (d) Liffert, R.; Hoecker, J.; Jana, C. K.; Woods, T. M.;
Burch, P.; Jessen, H. J.; Neuburger, M.; Gademann, K. Chem. Sci.
2013, 4, 2851−2857. During a preparation of this manuscript, the
common trans-hydrindane dehydro-δ-lactone scaffold was found to be
̌
novel modulators of Hedgehog signaling; see: (e) Svenda, J.;
Sheremet, M.; Kremer, L.; Maier, L.; Bauer, J. O.; Strohmann, C.;
Ziegler, S.; Kumar, K.; Waldmann, H. Angew. Chem., Int. Ed. 2015, 54,
5596−5602.
(6) (a) Matsuya, Y.; Yamakawa, Y.; Tohda, C.; Teshigawara, K.;
Yamada, M.; Nemoto, H. Org. Lett. 2009, 11, 3970−3973.
(b) Teshigawara, K.; Kuboyama, T.; Shigyo, M.; Nagata, A.;
Sugimoto, K.; Matsuya, Y.; Tohda, C. Br. J. Pharmacol. 2013, 168,
903−919.
(7) (a) Tohda, C.; Urano, T.; Umezaki, M.; Nemere, I.; Kuboyama,
T. Sci. Rep. 2012, 2, 535. (b) Tohda, C.; Lee, Y.-A.; Goto, Y.; Nemere,
I. Sci. Rep. 2013, 3, 3395.
(8) Trost, B. M.; Dumas, J.; Villa, M. J. Am. Chem. Soc. 1992, 114,
9836−9845.
(9) Fujishima, T.; Konno, K.; Nakagawa, K.; Kurobe, M.; Okano, T.;
Takayama, H. Bioorg. Med. Chem. 2000, 8, 123−134.
(10) Blæhr, L. K. A.; Bjorkling, F.; Calverley, M. J.; Binderup, E.;
̈
Begtrup, M. J. Org. Chem. 2003, 68, 1367−1375.
(11) Mascarenas, J. L.; Mourino, A.; Castedo, L. J. Org. Chem. 1986,
̃
̃
51, 1269−1272.
(12) The geometry of bromo olefin was determined by the chemical
shifts of the corresponding olefinic proton. Trost and co-workers
synthesized similar bromo olefins. While their minor (Z)-isomer had
the signal at 5.92 ppm, the major (E)-isomer had the signal at 5.62
ppm.8 Similarly, our major isomer showed 5.58−5.55 ppm (multiplet)
for the corresponding olefinic proton.
(13) Sawada, D.; Katayama, T.; Tsukuda, Y.; Saito, N.; Saito, H.;
Takagi, K.; Ochiai, E.; Ishizuka, S.; Takenouchi, K.; Kittaka, A.
Tetrahedron 2010, 66, 5407−5423.
(14) Stewart, I. C.; Ung, T.; Pletnev, A. A.; Berlin, J. M.; Grubbs, R.
H.; Schrodi, Y. Org. Lett. 2007, 9, 1589−1592.
5913
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Org. Lett. 2015, 17, 5910−5913