Angewandte
Chemie
DOI: 10.1002/anie.201405109
Amyloid Inhibitors
Hot Paper
Rational Design and Identification of a Non-Peptidic Aggregation
Inhibitor of Amyloid-b Based on a Pharmacophore Motif Obtained
from cyclo[-Lys-Leu-Val-Phe-Phe-]**
Tadamasa Arai, Takushi Araya, Daisuke Sasaki, Atsuhiko Taniguchi, Takeshi Sato,
Youhei Sohma,* and Motomu Kanai*
Abstract: Inhibition of pathogenic protein aggregation may be
an important and straightforward therapeutic strategy for
curing amyloid diseases. Small-molecule aggregation inhib-
itors of Alzheimerꢀs amyloid-b (Ab) are extremely scarce,
however, and are mainly restricted to dye- and polyphenol-type
compounds that lack drug-likeness. Based on the structure-
activity relationship of cyclic Ab16–20 (cyclo-[KLVFF]), we
identified unique pharmacophore motifs comprising side-
chains of Leu2, Val3, Phe4, and Phe5 residues without involve-
ment of the backbone amide bonds to inhibit Ab aggregation.
This finding allowed us to design non-peptidic, small-molecule
aggregation inhibitors that possess potent activity. These
molecules are the first successful non-peptidic, small-molecule
aggregation inhibitors of amyloids based on rational molecular
design.
generated in the aggregation processes (that is, oligomers,
protofibrils, and fibrils) contribute to disease development.[1]
Specifically, AD is an age-related neurodegenerative disor-
der, and affected individuals exhibit progressive memory loss
and cognitive impairment.[2] Thirty million people worldwide
are estimated to have the disease, and the number is predicted
to increase to 106 million by 2050.[3] Although the precise
etiology of AD remains unclear, the aggregation of 40- and
42-residue amyloid-b peptides (designated Ab1–40 and Ab1–
42, respectively), produced by proteolytic processing of
amyloid precursor protein, is critically involved in AD.[2]
Both oligomers[4] and fibrils[5] of Ab are neurotoxic, and
Ab1–42 is far more aggregative and toxic than Ab1–40.[6]
Aggregation inhibitors of Ab are therefore candidate
drugs for the treatment (or prevention) of AD.[7] To date,
a number of natural products possessing inhibitory activities
against Ab aggregation have been identified.[8] Most of those
compounds are dye- or polyphenol-derivatives and, because
these compounds bind non-selectively to a wide range of
biomolecules, there is high potential for various side-effects.
Structural optimization to enhance Ab specificity is very
difficult, however, owing to both the unknown three-dimen-
sional structures of Ab aggregates (oligomers and protofi-
brils) and the lability of Ab conformation during aggregation.
Fragment peptides of Ab bind to full-length Ab and
inhibit its aggregation.[9–12] An Ab sequence-based approach
will be advantageous in logical potentiation of aggregation
inhibitors. KLVFF peptide (1) corresponding to the Ab16–20
fragment, a region that plays a critical role in generating Ab
fibrils by forming a core b-strand structure,[13] was intensively
derivatized.[14–20] Use of this approach led to the identification
of an analogue of 1, d-[chGly-Tyr-chGly-chGly-mLeu]-NH2
(ch = cyclohexyl, m = N-methyl), that is more than 30 times
more potent than 1.[20] To date, however, all of the reported
analogues resulting from this approach are peptidic mole-
cules, and thus have inherent disadvantages, such as poor
bioavailability and a high propensity to aggregate into
deposits. To the best of our knowledge, no non-peptidic,
small-molecule aggregation inhibitors of amyloids have yet
been rationally designed from the lead peptide. Here, we
report the first non-peptidic small molecules with potent Ab
aggregation inhibitory activities based on rational derivatiza-
tion.
P
rotein aggregation is intimately related to several human
diseases, including currently intractable neurodegenerative
diseases such as Alzheimerꢀs disease (AD), Parkinsonꢀs
disease, and Huntingtonꢀs disease. More than 20 proteins
have been identified to aggregate into so-called amyloid
fibrils containing extensive b-sheet structures, and species
[*] T. Arai,[+] T. Araya,[+] Dr. D. Sasaki, Dr. A. Taniguchi, Dr. Y. Sohma,
Prof. M. Kanai
Graduate School of Pharmaceutical Sciences
The University of Tokyo, Bunkyo-ku
Tokyo 113-0033 (Japan)
E-mail: ysohma@mol.f.u-tokyo.ac.jp
T. Arai,[+] T. Araya,[+] Dr. D. Sasaki, Dr. A. Taniguchi, Dr. Y. Sohma,
Prof. M. Kanai
ERATO (Japan) Science and Technology Agency (JST)
Kanai Life Science Catalysis Project
Tokyo 113-0033 (Japan)
Dr. T. Sato
Institute for Protein Research, Osaka University
Suita, Osaka 565-0871 (Japan)
[+] These authors contributed equally to this work.
[**] This work was supported in part by ERATO from JST, the Takeda
Science Foundation, and the Suzuken Memorial Foundation. We are
grateful to Ms. Y. Kobayashi for technical assistance and Dr. S.
Matsunaga for fruitful discussions. We are grateful to Dr. T. Ikegami
(Institute for Protein Research, Osaka University) for providing
guidance on NMR experiments. We thank Prof. T. Katada and Dr. K.
Kontani for access to the ultracentrifuge and Dr. M. Kato for access
to atomic force microscopy.
To develop non-peptidic inhibitors, the contribution of
backbone amide moieties to Ab binding affinity must be
reduced relative to that of the side-chain functional groups.
We first synthesized 3 (Figure 1), a cyclic analogue of 1, to
Supporting information for this article is available on the WWW
Angew. Chem. Int. Ed. 2014, 53, 1 – 5
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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