Isoindol-1,3-dione and isoindol-1-one derivatives with high binding affinity to β-amyloid fibrils

Article abstract of DOI:10.1016/j.bmcl.2008.01.066

Based on the structural features of Indoprofen and PIB, a series of isoindol-1,3-diones 1a-k and isoindol-1-ones 2a-l were designed and synthesized. These 23 compounds were evaluated by competitive binding assay against aggregated Aβ42 fibrils using [¹²⁵I]TZDM. All the isoindolone derivatives showed very good binding affinities with K_i values in the subnanomolar range (0.42-0.94 nM). Among them, isoindol-1,3-diones 1i and 1k and isoindol-1-ones 2c and 2i exhibited excellent binding affinities (K_i = 0.42-0.44 and 0.46-0.49 nM) than those of Indoprofen (K_i = 0.52 nM) and PIB (K_i = 0.70 nM). These results suggest that isoindolones could be served as a scaffold for potential AD diagnostic probes to monitor Aβ fibrils.

Full text of DOI:10.1016/j.bmcl.2008.01.066

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Bioorganic & Medicinal Chemistry Letters 18 (2008) 1628–1631
Isoindol-1,3-dione and isoindol-1-one derivatives with high
binding affinity to b-amyloid fibrils
Hyu Ji Lee,a,b Soo Jeong Lim,c Seung Jun Oh,c Dae Hyuk Moon,c
Dong Jin Kim,a Jinsung Taeb and Kyung Ho Yooa,*
aLife Sciences Research Division, Korea Institute of Science and Technology, PO Box 131,
Cheongryang, Seoul 130-650, Republic of Korea
bDepartment of Chemistry, Yonsei University, Seodaemun-gu, Seoul 120-749, Republic of Korea
cDepartment of Nuclear Medicine, Asan Medical Center, 388-1, Pungnap-2-Dong, Songpa-Gu, Seoul 138-736, Republic of Korea
Received 17 October 2007; revised 14 January 2008; accepted 16 January 2008
Available online 19 January 2008
Abstract—Based on the structural features of Indoprofen and PIB, a series of isoindol-1,3-diones 1a–k and isoindol-1-ones 2a–l were
designed and synthesized. These 23 compounds were evaluated by competitive binding assay against aggregated Ab42 fibrils using
[
125I]TZDM. All the isoindolone derivatives showed very good binding affinities with Ki values in the subnanomolar range (0.42–
0.94 nM). Among them, isoindol-1,3-diones 1i and 1k and isoindol-1-ones 2c and 2i exhibited excellent binding affinities (Ki = 0.42–
0.44 and 0.46–0.49 nM) than those of Indoprofen (Ki = 0.52 nM) and PIB (Ki = 0.70 nM). These results suggest that isoindolones
could be served as a scaffold for potential AD diagnostic probes to monitor Ab fibrils.
ꢀ 2008 Elsevier Ltd. All rights reserved.
Alzheimer’s disease (AD) is a progressive neuro degen-
erative disease that is characterized by the presence of
extracellular amyloid plaques and intraneuronal neuro-
fibrillary tangles in the brain of AD patients.1–3 Fibrillar
b-amyloid (Ab), which is one of the main components of
senile plaques, is cleaved from b-amyloid precursor pro-
tein (APP) by secretase to produce Ab40 and Ab42,
resulting in neurotoxic activity both in vitro and it
in vivo.4,5
exhibited high affinity for Ab, good brain entry and
clearance. For early diagnosis or monitoring of b-amy-
loid formation and aggregation in AD brain, a variety
of radiolabeled compounds as imaging probes have been
developed.13–18 The development of ligands specifically
binding to b-amyloid aggregates is very important for
labeling agents as in vivo diagnostic tools.
In an effort to develop the small molecules with high
affinity to Ab aggregates, isoindolones based on the
structural combination of Indoprofen as a NSAID and
PIB were designed as shown in Figure 1. We report here
the synthesis and evaluation of a series of isoindol-1,3-
dione and isoindol-1-one derivatives with high affinities
for b-amyloid fibrils.
It has suggested that the chronic use of non-steroidal
anti-inflammatory drugs (NSAIDs) from epidemiologi-
cal studies reduces the relative risk6–8 or delays the
onset of AD.9 Since then, 2-(1-{6-[(2-[18F]fluoro ethyl)
(methyl)amino]-2-naphthyl}ethylidene)malono nitrile
([18F]FDDNP) as a molecular imaging probe was devel-
oped for detection of senile plaques and neurofibrillary
tangles in the living brain of AD patients using positron
emission tomography (PET).10 Recently, N-methyl-
[11C]2-(40-methylaminophenyl)-6-hydroxy benzothiazole
([11C]PIB)11,12 as an in vivo PET b-sheet imaging agent
The synthesis of isoindol-1,3-dione derivatives 1a–k was
outlined in Scheme 1. Phthalic acids 3a and 3b with thio-
nyl chloride in the presence of 1,4-diazabicy-
clo[2.2.0]octane gave phthalic anhydrides 4a and 4b
(4c–e, commercially available), which were then treated
with aminobenzene compounds 7 to afford the corre-
sponding 1a–k, respectively. Compounds 7b–d (7a, com-
mercially available) were obtained in good yields by first
reductive amination of nitrobenzenes 5b–d with p-form-
aldehyde and sodium cyanoborohydride19,20 and subse-
Keywords: Alzheimer’s disease; Ab42 fibrils; Isoindolones; Binding
affinity.
*
Corresponding author. Tel.: +82 2 958 5152; fax: +82 2 958 5189;
e-mail: khyoo@kist.re.kr
0960-894X/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.01.066

H. J. Lee et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1628–1631
1629
(Scheme 3). Conversion of 8a–e, 8g and 8h to ester com-
pounds 9a–e, 9g and 9h followed by bromination with
N-bromosuccinimide provided bromomethylbenzoic es-
ters 10a–e, 10g and 10h, which were transformed into
the corresponding 2a–l, respectively.22 Compound 9f,
which was prepared by bromination of 8f with N-bro-
mosuccinimide in the presence of benzoyl peroxide,
was esterified to give 10f for the synthesis of 2f.
NC
CN
11CH3
NH
N
S
18F
HO
N
O
11C]PIB
[
18F]FDDNP
[
O
O
R2
R1
OH
N
N
A
R3
Table 1 shows the in vitro binding affinities (Ki values)
of isoindol-1,3-diones 1a–k and isoindol-1-ones
2a–l against aggregated Ab42 fibrils together with
those of Indoprofen and PIB as reference compounds.
All the synthesized compounds were evaluated by com-
petitive binding assays against Ab42 fibrils using
R4
1a-k: A=CO
2a-l: A=CH2
Indoprofen
Figure 1. Structures of FDDNP, PIB, Indoprofen and isoindolone
derivatives.
[
125I]TZDM.23
quent reduction of nitro group with tin chloride21
(Scheme 2).
Binding affinities of the evaluated isoindolones ranged
from 0.42 to 0.94 nM, and 13 compounds displayed
higher affinity (lower Ki values) to Ab42 fibrils than that
of PIB (Ki = 0.70 nM). Especially, isoindol-1,3-diones 1i
Isoindol-1-one derivatives 2a–l were prepared in three
steps using benzoic acids 8a–h as starting materials
O
O
O
R2
R2
R1
R2
R1
i
7, ii
OH
OH
N
R3
O
R1
R4
O
O
O
3a: R1=NMe2, R2=H
3b: R1=MeO, R2=H
4a: R1=NMe2, R2=H
4b: R1=MeO, R2=H
4c: R1=Me, R2=H
4d: R1=H, R2=H
1a-k
4e: R1=F, R2=H
Scheme 1. Reagents and reaction conditions: (i) 1,4-diazabicyclo[2.2.2]octane, SOCl2, CH2Cl2, 0 ꢁC–rt, 1 h, 75% (for 4a), 77% (for 4b); (ii) acetic
acid, reflux, 3–4 h, 46–99% (for 1a–k).
i
ii
O2N
R5
O2N
R3
H2N
R3
R6
R4
R4
6b: R3=NMe2, R4=MeO
6c: R3=H, R4=NMe2
6d: R3=MeO, R4=NMe2
5b: R5=NH2, R6=MeO
5c: R5=H, R6=NH2
5d: R5=MeO, R6=NH2
7a: R3=NMe2, R4=H
7b-d
Scheme 2. Reagents and reaction conditions: (i) (CH2O)n, NaBH3CN, AcOH, 0 ꢁC–rt, 3 h, 75–99% (for 6b–d); (ii) SnCl2, EtOH, reflux, 3 h, 79–95%
(for 7b–d).
O
O
O
R2
R1
R2
R1
R2
R1
i
ii
OH
OMe
OMe
Br
8a: R1=MeO, R2=H
8b: R1=H, R2=H
8c: R1=F, R2=H
8d: R1=Cl, R2=H
8e: R1=Br, R2=H
8f: R1=H, R2=Me
8g: R1=H, R2=F
8h: R1=H, R2=Cl
9a-e,g,h
10a-h
iv
iii
7, v
O
O
R2
R1
R2
R1
OH
Br
N
R3
R4
9f
2a-l
Scheme 3. Reagent and reaction conditions : (i) SOCl2, MeOH, reflux, 4 h, 79–97%; (ii) N-bromosuccinimide, CCl4, reflux, 6 h, 34–59% (for 10a–e,
10g and 10h); (iii) N-bromosuccinimide, CCl4, benzoyl peroxide, reflux, 1 h, 36%; (iv) THF, MeOH, 2 M trimethylsilyl diazomethane–hexane
solution, rt, 4 h, 61% (for 10f); (v) acetic acid, reflux, 3–4 h, 9–33% (for 2a–l).

1630
H. J. Lee et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1628–1631
Table 1. In vitro binding affinities of isoindol-1,3-diones 1a–k and isoindol-1-ones 2a–l against Ab42 fibrils using [125I]TZDM
Compound
A
R1
R2
R3
R4
Kia (nM)
1a
1b
CO
CO
NMe2
MeO
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
F
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
H
H
0.70
0.71
0.50
0.69
0.56
0.66
0.78
0.70
0.42
0.46
0.44
0.94
0.58
0.49
0.76
0.81
0.76
0.93
0.50
0.46
0.90
0.57
0.65
0.52
0.70
H
1c
1d
CO
CO
H
H
1e
CO
CO
F
H
1f
1g
H
MeO
MeO
MeO
MeO
NMe2
NMe2
H
CO
CO
F
1h
Cl
Br
H
1i25
1j
CO
CO
1k25
2a
CO
H
MeO
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
H
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
CH2
—
MeO
H
2b
H
2c25
2d
F
H
Cl
Br
H
H
2e
H
2f
2g
H
H
H
2h
H
Cl
Me
H
H
H
—
—
H
2i25
2j
H
MeO
MeO
NMe2
NMe2
—
H
2k
2l
H
H
MeO
—
—
Indoprofen
PIB
—
—
—
—
a Ki was calculated by the Cheng–Prusoff equation (Ki = IC50/(1 = [L]/Kd)24 using Graphpad Prism software.
4. Behl, C.; Davis, J. B.; Cole, G. M.; Schbert, D. Biochem.
Biophys. Res. Commun. 1992, 186, 944.
5. Corder, E. H.; Saunders, A. M.; Strittmatter, W. J.;
Schmechel, D. E.; Gaskell, P. C.; Small, G. W.; Roses, A.
D.; Haines, J. L.; Paticak-Vance, M. A. Science 1993, 261,
921.
6. Breitner, J. C. S.; Welsh, K. A.; Helms, M. J.; Gaskell, P.
C.; Gau, B. A.; Roses, A. D.; Pericak-Vance, M. A.;
Saunders, A. M. Neurobiol. Aging 1995, 16, 523.
7. Stewart, W. F.; Kawas, C.; Corrada, M.; Metter, E. J.
Neurology 1997, 48, 626.
8. in t’ Veld, B. A.; Ruitenberg, A.; Hofman, A.; Launer, L.
J.; van Duijn, C. M.; Stijnen, T.; Breteler, M. M.; Stricker,
B. H. N. Engl. J. Med. 2001, 345, 1515.
9. Rogers, J.; Kirby, L. C.; Hempelman, S. R.; Berry, D. L.;
McGeer, P. L.; Kaszniak, A. W.; Zalinski, J.; Cofield, M.;
Mansukhani, L.; Willson, P.; Kogan, F. Neurology 1993,
43, 1609.
10. Shoghi-Jadid, K.; Small, G. W.; Agdeppa, E. D.; Kepe,
V.; Ercoli, L. M.; Siddarth, P.; Read, S.; Satyamurthy, N.;
Petric, A.; Huang, S. C.; Barrio, J. R. Am. J. Geriatr.
Psychiatry 2002, 10, 24.
and 1k and isoindol-1-ones 2c and 2i exhibited excellent
binding affinities (Ki = 0.42–0.44 and 0.46–0.49 nM,
respectively) compared to reference compounds. In gen-
eral, isoindol-1,3-diones 1 showed slightly better po-
tency in binding to Ab42 fibrils than isoindol-1-ones 2.
Positional effect according to R1 and R2 substituents
and modification of electron-donating groups to elec-
tron withdrawing groups at isoindolone nucleus did
not make any significant difference of binding affinity.
Compounds 1d, 1f and 2b, 2i having NMe2, OMe at
R3, R4 positions possessed slightly lower affinities as
compared to compounds 1j, 1k and 2k, 2l with OMe,
NMe2 at R3, R4 positions, respectively.
In conclusion, all the isoindolone derivatives based on
the structural features of Indoprofen and PIB exhibited
very good binding affinities to aggregated Ab42 fibrils.
These isoindolones with high affinity provide the possi-
bility of a scaffold for potential molecular imaging
agents to monitor Ab fibrils in the brain of AD patients.
11. Mathis, C. A.; Wang, Y.; Holt, D. P.; Huang, G.-f.;
Debnath, M. L.; Klunk, W. E. J. Med. Chem. 2003, 46,
2740.
Acknowledgment
12. Klunk, W. E.; Engler, H.; Nordberg, A.; Wang, Y.;
Blomqvist, G.; Holt, D. P.; Bergstrom, M.; Savitcheva, I.;
Huan, G.-f.; Estrada, S.; Ausen, B.; Debnath, M. L.;
Barletta, J.; Price, J. C.; Sndell, J.; Lopresti, B. J.; Wall,
A.; Koivisto, P.; Antoni, G.; Mathis, C. A.; Langstrom, B.
Ann. Neurol. 2004, 55, 306.
We are grateful to the Ministry of Science and Technol-
ogy (MOST) and Ministry of Commerce, Industry and
Energy (MCIE) of Korea for financial support.
13. Klunk, W. E.; Debnath, M. L.; Pettegrew, J. W. Neuro-
biol. Aging 1994, 15, 691.
References and notes
14. Mathis, C. A.; Mahmood, K.; Debnath, M. L.; Klunk, W.
E. J. Labelled Compd. Radiopharm. 1997, 40, 94.
15. Skovronsky, D.; Zhang, B.; Kung, M.-P.; Kung, H. F.;
Trojanowski, J. Q.; Lee, V. M.-Y. Proc. Natl. Acad. Sci.
U.S.A. 2000, 97, 7609.
1. Hardy, J.; Selkoe, D. J. Science 2002, 297, 353.
2. Meyer-luemen, M. Nat. Neurosci. 2003, 6, 1.
3. Nussbaum, R. L.; Ellis, C. E. N. Engl. J. Med. 2003, 348,
1356.

H. J. Lee et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1628–1631
1631
16. Agdeppa, E. D.; Kepe, V.; Liu, J.; Shoughi-Jadid, K.;
Satyamurthy, N.; Small, G. W.; Petric, A.; Vinters, H. V.;
Huang, S. C.; Barrio, J. R. J. Labelled Compd. Radiop-
harm. 2001, 44, S242.
17. Ono, M.; Haratake, M.; Nakayama, M.; Kaneko, Y.;
Kawabata, K.; Mori, H.; Kung, M.-P.; Kung, H. F. Nucl.
Med. Biol. 2005, 32, 329.
18. Zeng, F.; Southerland, J. A.; Voll, R. J.; Williams, L.;
Ciliax, B. J.; Levey, A. I.; Goodman, M. J. Bioorg. Med.
Chem. Lett. 2006, 16, 3015.
19. Gribble, G. W.; Nutaitis, C. F. Synthesis 1987, 709.
20. Ono, M.; Kung, M.-P.; Hou, C.; Kung, H. F. Nucl. Med.
Biol. 2002, 29, 633.
regression analysis using software Graphpad Prism by Ki
values was calculated.
24. Cheng,Y.;Prusoff,W.H.Biochem. Pharmacol. 1973,22, 3099.
25. Selected data 1i: Mp 167.5–168.5 ꢁC; IR (KBr): 3678,
1724, 1514, 1334, 1252 cmꢀ1; 1H NMR (CDCl3, 300 MHz)
d 8.09 (d, J = 1.2 Hz, 1H), 7.93 (dd, J = 7.9, 7.9 Hz, 1H),
7.82 (dd, J = 7.9, 0.3 Hz, 1H), 7.03 (d, J = 8.4 Hz, 1H),
6.95 (dd, J = 8.4, 2.2 Hz, 1H), 6.87 (d, J = 2.2 Hz, 1H); 13
C
NMR (DMSO-d6, 75 MHz) d 166.80, 166.26, 152.45,
137.36, 133.45, 130.42, 129.25, 127.01, 125.03, 119.06,
118.16, 109.77, 55.61, 43.15; MS m/z 375 (M+).
Compound 1k: Mp 154.0–155.0 ꢁC; IR (KBr): 3671, 1716,
1512, 1389, 1246 cmꢀ1 1H NMR (CDCl3, 300 MHz) d
;
21. Ono, M.; Wilson, A.; Nobrega, J.; Westaway, D.;
Verhoeff, P.; Zhung, Z.-P.; Kung, M.-P.; Kung, H. F.
Nucl. Med. Biol. 2003, 30, 565.
22. Prasad, C. S. N.; Varala, R.; Adapa, S. R. Heterocycl.
Commun. 2002, 8, 281.
7.97–7.94 (m, 2H), 7.81–7.78 (m, 2H), 7.02 (dd, J = 8.6,
2.2 Hz, 1H), 6.95 (d, J = 2.1 Hz, 1H), 3.94 (s, 3H), 2.83 (s,
6H); 13C NMR (DMSO-d6, 75 MHz) d 167.71, 152.16,
143.02, 134.26, 131.90, 124.42, 123.62, 120.65, 117.03,
111.14, 55.63, 43.15; MS m/z 296 (M+).
23. We estimated Kd value (0.13 nM) of [125I]TZDM for Ab42
aggregates. For inhibition studies, the reaction mixture
contained 50 lL of Ab42 aggregates (11.5 nM in the final
conc.), 50 lL of inhibitors (10ꢀ6–10ꢀ12 M in DMSO),
50 lL of [125I]TZDM (in 40% EtOH, 0.05 nM in the final
conc.) and 10% EtOH in a final volume of 1 mL. Non-
specific binding was defined by adding 2 lM Th–T for
Compound 2c: Mp 238.5–239.5 ꢁC; IR (KBr): 3674, 1673,
1527, 1357, 1250 cmꢀ1 1H NMR (CDCl3, 300 MHz) d
;
7.88 (dd, J = 9.1, 5.1 Hz, 1H), 7.61 (dd, J = 6.9, 2.2 Hz,
2H), 7.21–7.16 (m, 2H), 6.78 (dd, J = 6.9, 2.2 Hz, 2H),
4.78 (s, 2H), 2.96 (s, 6H); 13C NMR (DMSO-d6, 75 MHz)
d 166.83, 166.09, 163.50, 148.24, 142.64, 142.50, 129.59,
128.88, 126.00, 125.87, 121.70, 116.20, 115.89, 113.00,
110.08, 109.76, 51.01, 50.98, 40.80; MS m/z 270 (M+).
Compound 2i: Mp 153.0–154.0 ꢁC; IR (KBr): 3671, 1678,
[
125I]TZDM binding. The mixture was incubated at room
temperature for 3 h and the bound and the free radioac-
tivity were separated by a vacuum filtration through
Whatman GF/B filters using a Brandel M-24R cell
harvester followed by 2· 3 mL washes of 10% EtOH at
room temperature. Filters containing the bound radioli-
gand were counted in a gamma-counter (Cobra-II). The
result of inhibition assays was subjected to nonlinear
1514, 1392, 1219 cmꢀ1 1H NMR (CDCl3, 300 MHz) d
;
7.90 (s, 1H), 7.69 (s, 1H), 7.38 (s, 2H), 6.70 (s, 2H), 4.78 (s,
2H), 3.96 (s, 3H), 2.81 (s, 6H), 2.46 (s, 3H); 13C NMR
(DMSO-d6, 75 MHz) d 167.54, 152.64, 138.41, 137.30,
135.16, 133.44, 132.99, 124.12, 122.27, 118.25, 110.86,
104.19, 55.54, 50.90, 43.50, 21.40; MS m/z 296 (M+).