Multidentate 18F-polypegylated styrylpyridines As imaging agents for Aβ plaques in cerebral amyloid angiopathy (CAA)

Article abstract of DOI:10.1021/jm2009106

β-Amyloid plaques (Aβ plaques) in the brain are associated with cerebral amyloid angiopathy (CAA). Imaging agents that could target the Aβ plaques in the living human brain would be potentially valuable as biomarkers in patients with CAA. A new series of ¹⁸F styrylpyridine derivatives with high molecular weights for selectively targeting Aβ plaques in the blood vessels of the brain but excluded from the brain parenchyma is reported. The styrylpyridine derivatives, 8a-c, display high binding affinities and specificity to Aβ plaques (K_i = 2.87, 3.24, and 7.71 nM, respectively). In vitro autoradiography of [¹⁸F]8a shows labeling of β-amyloid plaques associated with blood vessel walls in human brain sections of subjects with CAA and also in the tissue of AD brain sections. The results suggest that [¹⁸F]8a may be a useful PET imaging agent for selectively detecting Aβ plaques associated with cerebral vessels in the living human brain.

Full text of DOI:10.1021/jm2009106

Article
pubs.acs.org/jmc
18
Multidentate F-Polypegylated Styrylpyridines As Imaging Agents
for Aβ Plaques in Cerebral Amyloid Angiopathy (CAA)
Zhihao Zha,† Seok Rye Choi,§ Karl Ploessl,† Brian P. Lieberman,† Wenchao Qu,† Franz Hefti,§
Mark Mintun,§ Daniel Skovronsky,†,§ and Hank F. Kung*,†,‡
‡
†Departments of Radiology and Pharmacology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
§Avid Radiopharmaceuticals Inc., Philadelphia, Pennsylvania 19104, United States
S
* Supporting Information
ABSTRACT: β-Amyloid plaques (Aβ plaques) in the brain are
associated with cerebral amyloid angiopathy (CAA). Imaging agents
that could target the Aβ plaques in the living human brain would be
potentially valuable as biomarkers in patients with CAA. A new series
of 18F styrylpyridine derivatives with high molecular weights for
selectively targeting Aβ plaques in the blood vessels of the brain but
excluded from the brain parenchyma is reported. The styrylpyridine
derivatives, 8a−c, display high binding affinities and specificity to Aβ plaques (Ki = 2.87, 3.24, and 7.71 nM, respectively). In vitro
autoradiography of [18F]8a shows labeling of β-amyloid plaques associated with blood vessel walls in human brain sections of
subjects with CAA and also in the tissue of AD brain sections. The results suggest that [18F]8a may be a useful PET imaging
agent for selectively detecting Aβ plaques associated with cerebral vessels in the living human brain.
β-amyloid. One of the leading protocols is [11C]PIB ([11C]1)
INTRODUCTION
■
(Pittsburgh compound B)/PET imaging of Aβ plaques in the
Cerebral amyloid angiopathy (CAA) is a common cause of
stroke and dementia in older people. Patients typically present
pathological symptoms associated with lobar intracranial macro-
hemorrhages or microbleeds. Post-mortem studies suggest that
there are distinctive morphological changes in the cerebral
vessels including the deposition of β-amyloid (Aβ) peptide
living brain.13−16 Recently, several reports on [11C]1/PET imaging
in CAA and post-stroke patients suggested that Aβ depositions
could be detected in the brain tissue as well as in the blood
vessels.6,13,17−19 Because 1 is a small molecule, it readily
penetrates the intact blood−brain barrier; therefore, [11C]1/
PET images of the Aβ deposition represents the map
aggregates, of which Aβ peptides are the most common.1,2 The
of total Aβ deposition in the brain, as well as in the cerebral
depositions are located in small to medium-sized cerebral and
leptomeningeal arteries and less prominently in the walls of
capillaries and veins. Similar to the deposition of Aβ in the
parenchymal brain tissue in Alzheimer’s disease (AD), the Aβ
peptides form Aβ aggregates and neurofibrillary plaques are
accumulated in the cerebral blood vessels. As the deposition of
Aβ aggregates increases with time, they become hardened.
vessels.
To improve the availability of PET tracers for routine clinical
practice, several 18F Aβ-plaque imaging agents, including
[18F]florbetapir f 18 ([18F]AV-45, [18F]5),20−24 [18F]-
florbetaben f 18 ([18F]AV-1, BAY-94−9172, [18F]4),25−28
[18F]flutemetamol f 18 ([18F]FPIB, GE067, [18F]6)29−33 and
2-(2-([18F]fluoro)-6-methylaminopyridin-3-yl)benzofuran-5-ol
These changes in the cerebral blood vessels lead to micro-
([18F]AZD4694, [18F]7)34 have been developed and found to
bleeds.3−6 It has been estimated that CAA is present in 55−59%
be useful PET agents for targeting Aβ plaques in the brain
of dementia patients. At least 30% of the dementia patients
showed severe CAA, as compared to 7−24% in nondemented
(Figure 1). The phase III clinical trial for [18F]5 has been
completed,24 and this Aβ-plaque targeting imaging agent is
currently under regulatory review for approval. Similar to
[11C]1, [18F]5 labels all Aβ plaques, those deposited in the
parenchymal of the brain, as well as those in the cerebrovascular
vessels. To differentially diagnose the CAA related accumu-
lation of Aβ plaques, a [18F] labeled Aβ-plaque imaging agent
for specifically detecting Aβ deposition located on the wall of
cerebral blood vessels is needed.
patients.7,8 In general, there is a very close, but not parallel,
relationship between CAA and Alzheimer’s disease (AD). They
also share a set of common genetic risk factors. It is believed
that there are specific mechanism(s) which put age-related
cerebrovascular degeneration at a critical point in the patho-
genesis of AD.9,10 Evidence collected from post-mortem
examination of brain tissues from CAA and AD patients
found Aβ deposition in the parenchymal and cortical arteries of
the brains of AD subjects, while in CAA patients the same
deposition was visible predominantly in the blood vessels.11,12
Imaging Aβ plaques in the brain is generally accepted as a
potential useful tool for studying the pathophysiology of
neurodegenerative diseases associated with the formation of
To be able to differentiate between Aβ plaques in the brain
and those on the wall of cerebrovascular vessels, a series of
Received: July 14, 2011
Published: October 19, 2011
© 2011 American Chemical Society
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Figure 1. The chemical structures and binding affinities of imaging agents targeting Aβ plaques in the brain are listed. All of these agents are small,
neutral molecules showing high binding affinity and the ability to penetrate intact blood−brain barrier in vivo (previously published values *,22 **34).
Figure 2. Multidentate (bidentate and tridentate) ligands, 8a, 8b, 8c, 9, and 10, based on styrylpyridine cores aiming at multiple binding sites within
the repeated β-sheet structure are shown. These novel ligands are designed to bind to the Aβ aggregates via a divalent or a trivalent attachment
(binding) sites.
[18F] imaging agents containing two styrylpyridine cores
separated by long pegylated chains (n > 8) was prepared and
tested. We reasoned that the “bivalent or trivalent ligands”
containing two or three styrylpyridine binding cores would
retain a high binding affinity toward the Aβ plaques due to the
presence of multiple binding sites within the repeated β-sheet
structure (Figure 2). It is probable that the multidentate
styrylpyridine derivatives with the appropriate spacing between
the binding moieties would display good binding to the Aβ
aggregates and that they would be unable to penetrate the
intact blood−brain barrier (BBB) in vivo due to their high
molecular weights, which exceed 600, a general cutoff point for
a simple and neutral molecule to penetrate the BBB by
diffusion.21 Therefore, the “bidentate or tridentate ligands”, 8,
9, and 10, would likely bind only to the Aβ aggregates located
outside of the blood−brain barrier on the vessel walls in CAA
patients.
therefore may specifically target Aβ aggregates located on the
cerebrovascular vessel walls outside of the BBB of CAA
subjects.
RESULTS
■
Chemical Synthesis of Bivalent and Trivalent Styryl-
pyridine Derivatives, 8a, 8b, 8c, 9, and 10. The synthesis
of the 5 derivatives, 8a, 8b, 8c, 9, and 10, with two (bivalent
ligand) or three (trivalent ligand) styrylpyridine binding
moieties tethered by a polyethylene glycol chain was
successfully achieved as described in Schemes 1, 2, 3, and 4.
For the first series of bivalent ligands, compound 8, the binding
core, styrylpyridine, was attached with different chain lengths
of polyethylene glycol (8a, 8b, 8c, n = 4, 5, or 6). The hydroxyl
ends of the polyethylene glycol tethered with styrylpyridines
were attached to the 1- and 3-hydroxy positions of a glycerol.
The 2-hydroxyl group of the glycerol was linked to an ethylene
glycol group, leaving one free hydroxyl group, through which
the fluorine atom was end-capped. The molecule has an achiral
center and the hydroxyl groups of the glycerol provided a
Reported herein is the synthesis and characterization of
several Aβ aggregate-binding ligands, 8a, 8b, 8c, 9, and 10,
which do not cross the intact blood−brain barrier, and
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a
Scheme 1
a
Reagents and conditions: (a) (Boc)2O, H2O, 35 °C; (b) NaH, CH3I, DMF, rt; (c) triethylene glycol, CsCO3, DMF, 150 °C; (d) K2CO3, Bu4NBr,
Pd(OAc)2, DMF, 60 °C; (e) TsCI, Et3N, DMAP, DCM, rt; (f) diethylene glycol ditosylate, NaH, DMF, rt; (g) DHP, PPTS, EtOH, rt; (h) K2CO3
Bu4NI, Bu4NOAc, ACN; (i) NH3, CH3OH.
a
Scheme 2
a
Reagents and conditions: (a) NaH, 2 equiv 15, DMF, rt; (b) PPTS, EtOH; (c) NaH, 2-(2-bromoethoxy)-tetrahydro-2H-pyran, DMF, rt; (d) TsCI,
Et3N, DMAP, DCM, rt; (e) TBAF, THP, 70 °C; (f) TFA, rt.
convenient way of stretching between the two styrylpyridine
cores with polypegylated chains while leaving one more site for
an additional ethylene glycol group for [18F] labeling. We chose
to use ether linkage (for 8a, 8b, 8c) or amide linkage (for 9)
instead of carboxyl esters, in consideration of in vivo stability.
However, the character of the linkage bond, ether vs amide,
apparently has a dramatic effect on the in vitro binding affinity
to the Aβ plaques, see Discussion below. We also used “click
chemistry” to explore the feasibility of constructing a tridentate
ligand, 10, in which three styrylpyridine cores would be
included in one single molecule.
The intermediates 11−19, 26, and 35 were readily prepared
according to similar reported methods.35−37 Using the
Williamson ether synthesis method, dialcohol 19 and tosylates
15 were stitched together (Scheme 1) and the key bivalent inter-
mediates 20a−c were synthesized in good yields. Following a
six-step transformation, fluoroethoxy group tethered bivalent
styrylpyridine derivatives, 8a−c, were obtained (Scheme 2). For
the synthesis of the other bivalent styrylpyridine derivative, 9,
linked via amide bonds, the key intermediates, amine 32 and
diacid 30, were prepared first, followed by a 1-hydroxybenzo-
triazole hydrate/N-(3-dimethylaminopropyl)-N′-ethylcarbodi-
imide hydrochloride (HOBt/EDCI) promoted coupling reac-
tion. The intermediate 33 was employed as the starting material
for fluorination, and subsequently the Boc protection group was
removed to give 9 in an acceptable yield.
For preparation of a tridentate ligand, we decided to use
pentaerythritol as the backbone structure (Scheme 4). Three of
the hydroxyl groups were reacted with propargyl bromide,
leaving one hydroxyl group for additional pegylation (n = 3).
The end of the triglycolated hydroxyl group was capped with a
fluorine atom. To assemble the targeted tridentate ligand, 10,
containing three 1,2,3-triazole rings, “click chemistry” between
azide and alkyne was carried out. The desired intermediate 37
was first prepared through a simple three-step sequence. At this
stage, copper-catalyzed “click chemistry”38 was utilized to
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a
Scheme 3
a
Reagents and conditions: (a) N2CHCO2C2H5, BF3 Et2O, DCM, 0 °C; (b) NBS, PPh3, DCM, 0 °C; (c) NaOH, THF, rt; (d) HOBt, EDCI, DIPEA,
di-tert-butyl iminodiacetate, DMF, rt; (e) TFA, rt; (f) NaN3, DMF, 60 °C; (g) PPh3, H2O, THF, 60 °C; (h) DCC, DMAP, DCM, rt; (i) TBAF,
THF, 70 °C.
a
Scheme 4
a
Reagents and conditions: (a) 40% NaOH, DMSO, rt; (b) NaH, triethylene glycol di(p-toluenesulfonate), DMF, rt; (c) TBAF, THF, 70 °C;
(d) sodium ascorbate, CuSO4, t-BuOH, H2O, rt; (e) TFA, rt.
assemble the styrylpyridine polyethylene glycol-trimerized
intermediates 38 and 39. The final product, trivalent ligand
10, was obtained by a simple acidic deprotection of
intermediate 39.
Two HPLC conditions were used to test the purity of the
final compounds, 8a, 8b, 8c, 9, and 10. Using a Phenomenex
Luna 5 μ C18 250 mm × 4.60 mm column, eluted with
ACN/water, 8/2, 1 min/mL or a Phenomenex Luna 5 μ C18
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250 mm × 4.60 mm column, eluted with MeOH/water, 9/1,
1 min/mL. All of the final tested samples showed a purity >95%.
The HPLC profiles are included in the Supporting Information.
In Vitro Binding Studies of [18F]5 to Aβ-Aggregates in
the AD Brain Tissue Homogenates. An in vitro binding
assay was employed to measure the inhibition of [18F]5 binding
to Aβ-aggregates in the AD brain tissue homogenates (see
Supporting Information). Inhibition constants (Ki, nM) of
various agents against the binding of [18F]5 to Aβ-aggregates
are shown in Table 1. In addition, standard ligands, such as 1, 4,
cerebral blood vessels contained Aβ plaques; therefore the [18F]
8a only accumulated in these areas. For comparison, AD and
healthy control (HC) brain sections were also labeled with
[18F]5 or [18F]8a. As expected, in the AD brain sections, which
contained Aβ plaques in both the parenchymal tissue and the
blood vessels, the sections were labeled intensely by both
tracers. Because of a lack of Aβ plaques, both tracers showed
very low labeling in the healthy control (HC) brain sections
(Figure 4 lower panel).
To further confirm the nature of the Aβ plaque-labeling of
CAA brain sections, a comparison experiment between auto-
radiography of [18F]8a (Figure 5A,B) and fluorescent staining
with thioflavin S (Figure 5C,D) was performed using
neighboring CAA occipital brain sections. The results clearly
indicate that the same labeling of the major blood vessels was
observed with thioflavin S as with [18F]8a. The data support
the conclusion that [18F]8a labeled Aβ plaques located on the
major blood vessels in the CAA brain (Figure 5).
In Vivo Biodistribution in Mice. After an iv injection in
normal mice, [18F]8a, 8b, and 8c showed relatively low brain
uptake ranging between 0.3 and 0.4% dose/gram at 2 min
(Table 2). In comparison to the brain uptake of [18F]5, which
showed 7.8% dose/gram at 2 min, the bidentate ligands, [18F]
8a, 8b, and 8c, clearly displayed a very low brain penetration.
The low brain penetration of these new tracers would enable
the selective labeling of Aβ plaques located on the major blood
vessels in the CAA brain.
Table 1. Inhibition Constants (Ki, nM) of Aβ Plaques
Targeting Ligands against Binding of [18F]5 to Aβ Plaques in
a
Post-Mortem AD Brain Homogenates
compd
Ki (nM)
compd
Ki (nM)
PIB, 1
0.87 ± 0.18
3.18 ± 1.04
1.29 ± 0.46
2.22 ± 0.54
2.87 ± 0.17
0.74 ± 0.38
8a (n = 4)
8b (n = 5)
8c (n = 6)
25a
3.24 ± 1.92
7.71 ± 3.56
3.86 ± 1.05
>1000
SB-13, 2
IMPY, 3
florbetaben (AV-1), 4
florbetapir (AV-45), 5
9 (n = 3)
10
71.2 ± 16.8
468
flutemetamol
(3-FPIB), 6
a
Reference 22.
5, and 6, were tested in the same binding assay (see Table 1).
As expected, high binding affinities were obtained for the
known compounds within the range of <5 nM. The glycerol-
based bivalent ligands, 8a, 8b, and 8c, displayed excellent
binding affinities (Ki = 3.24, 7.71, and 3.86 nM, respectively). It
appears that the chain length of the pegylation has no affect on
the binding affinity. The Ki values (3−7 nM) were comparable
when the chain length was 4, 5, or 6. However, the amide-based
bivalent ligand, 9, showed a significantly lower affinity, Ki =
71.2 nM. The amide linkage is apparently not suitable for
designing this series of bivalent ligand. The trivalent ligand, 10,
also displayed a dramatically low binding affinity, Ki = 468 nM.
Radiolabeling of Bivalent and Trivalent Styrylpyridine
Derivatives, [18F]8a, 8b, 8c, 9, and 10. The radiolabeling
of the bidentate and tridentate ligands, 8a−c, 9, and 10, was
successfully performed using the same protocol as reported for
the preparation of [18F]5 (see Scheme 5 and Figure 3).22 The
labeling yields (about 30% EOS) were comparable to that
observed for [18F]5, and the radiochemical purity was >98%.
Autoradiography of Post-Mortem Brain Tissue Sec-
tions with [18F]5 and [18F]8a. When confirmed CAA brain
sections were incubated with [18F]8a, the resulting autoradio-
gram clearly demonstrated a selective and highly dense labeling
of the Aβ plaques of cerebral blood vessels with low labeling
in the other areas of the brain sections (see Figure 4, upper
panel). The labeling in the CAA brain sections was highly
discrete. It is likely that in the CAA brain only the walls of
DISCUSSION
■
Cerebral amyloid angiopathy (CAA) and Alzheimer’s disease
(AD) share common risk factors, mainly the accumulation of
Aβ aggregates. It is generally believed that the pathology of
CAA is associated with the deposit of β-amyloid on the walls
of the cortical and leptomeningeal blood vessels. In addition to
being a disease-defining pathological marker of AD, Aβ plaques
are believed to play a significant role in the pathophysiological
mechanisms associated with cerebral amyloid angiopathy. The
ability to use PET imaging to determine the location and
concentration of Aβ aggregates would be useful for diagnostic
purposes.
There are two major prerequisites for imaging agents
targeting Aβ plaques associated with cerebral blood vessel
walls: (1) High binding affinity to Aβ plaques. To evaluate the
feasibility of new ligands targeting the Aβ plaques of cerebral
blood vessel walls suitable as CAA imaging agents, we employed
an in vitro assay using AD brain tissue homogenates against the
binding of [18F]5 to measure the binding affinity. (2) Selective
labeling of Aβ plaques on cerebral blood vessel walls and not
in the cerebral parenchymal tissue: Preliminary testing of this
requirement was based on biodistribution (brain uptake at
2 min after an iv injection) of [18F] labeled ligands in normal
a
Scheme 5
a
Reagents and conditions: (a) Na[18F]floride, K[2,2,2]/K2CO3; (b) 6N HCI.
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Figure 3. HPLC profiles of [18F]8a and coinjected cold standard 8a on a reversed phase Gemini C18 column (250 mm × 4.6 mm) with the
following gradient and a flow rate of 1 mL/min: 0−2 min 100% ammonium format buffer (10 mM); 2−5 min ammonium formate buffer 100% to
30%, ACN 0−70%; 5−10 min ammonium formate buffer 30% to 0%, ACN 70−100%; 10−15 min 0−100% ammonium formate buffer, 100% to 0%
ACN; 15−18 min 100% ammonium formate buffer.
Figure 4. In the upper panel the autoradiography of post-mortem human brain sections of occipital samples from cerebral amyloid angiopathy
(CAA) using the new bivalent ligand, [18F]8a, showed a highly distinctive labeling at the blood vessels. Other brain parenchymal regions displayed
very little labeling, which suggests that there was a selective accumulation of Aβ plaques in the vessel walls in this CAA patient. The lower panel
shows brain sections of AD and healthy control (HC) subjects using either [18F]AV-45 ([18F]5) or [18F]8a. The AD brain section showed highly
significant labeling of Aβ plaques, while both tracers showed little or no binding in the HC sections.
mice. We reasoned that the inability of the new ligands to
penetrate the intact blood−brain barrier (BBB) supported the
conclusion that they would label only Aβ plaques on cerebral
blood vessel walls, located outside of the BBB. It will be useful in
the future to evaluate the distribution of Aβ plaque labeling in
various transgenic mice reported recently.1,39,40 One important
consideration is the total number of Aβ plaques on cerebral
blood vessel walls, i.e. the Bmax for these new ligands. Because
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Figure 5. Autoradiography of post-mortem human brain samples of cerebral amyloid angiopathy (CAA) using [18F]8a (A,B), which displayed
excellent labeling of Aβ aggregates of the blood vessel walls. There was prominent labeling of major blood vessels only in the CAA brain sections. It
is apparent that the parenchymal brain tissue had no Aβ plaques, therefore no labeling was observed. When the neighboring sections were labeled
with thioflavin S (C,D), the fluorescent images displayed a matching staining of blood vessel walls comparable to the images from the
autoradiography of [18F]8a. The results strongly suggest that [18F]8a labeled the Aβ aggregates of the blood vessel walls. The white bars represent a
scale of 500 μm.
humans are physically larger and have an increased number of
Aβ plaques on their cerebral blood vessel walls, it may be
possible to efficiently detect such differences.
Multidentate ligands have been utilized in various biological
systems. Dimeric and multimeric ligands targeting αvβ3-integrin
binding sites have been very useful for tumor imaging.41−47
However, it is likely due to structural limitations of the parallel
β-sheets of Aβ aggregates, as compared to that of the αvβ3-
integrin binding sites, that the structure−activity-relationship for
binding would be very different. In this report, we have prepared
and examined the multidentate Aβ aggregate-binding affinity of
8a, 8b, 8c, 9, and 10. Surprisingly, only the bidentate ligands 8a,
8b, and 8c showed the desired high binding affinity comparable
to that of [18F]5. The structural difference between the
bidentate ligands 8a−c and 9 was the linkage for the pegylated
styrylpyridines, i.e. ether vs amide linkage, which may have
caused the big difference in binding affinity (Ki = 3−7 nM vs 71
nM). The binding affinity of the tridentate ligand, 10, also
showed a dramatic reduction (Ki = 468 nM). This decrease may
have been caused by changes in the geometry of the new ligand.
These observations suggest that there are space limitations for
multidentate ligands to insert themselves into β-amyloid and to
bind to neighboring target sites.
The initial data from in vitro labeling of human brain sections
also show that similar to [18F]5, [18F]8a is capable of labeling
Aβ aggregates in human AD brain sections (Figure 4). It is
important to note that the in vitro autoradiography of confirmed
CAA brain sections showed successful labeling of major blood
vessels by [18F]8a and the labeling was confirmed by costaining
with thioflavin S (Figure 5). The results strongly suggest that it
will be feasible to use [18F]8a in imaging the accumulation of
Aβ aggregates on the walls of major cerebral blood vessels in
CAA patients. A buildup of Aβ aggregates in cerebral blood
vessels also occurs in patients at risk of stroke and Alzheimer’s
disease.19 CAA discriminating Aβ imaging agents, due to the
location of Aβ aggregates on the wall of cerebral blood vessels,
We prepared the desired ligands by stitching together
multiple styrylpyridine cores (selective core for binding Aβ
aggregates) using pegylation chains with chain lengths of n = 4,
5, and 6. It was assumed that Aβ aggregates composed of
parallel β-sheets would likely contain repetitive and neighboring
binding sites. These molecules were thus expected to show
good binding to β-amyloid and to be excluded from the brain
because of their large sizes.
Table 2. Comparison of the Biodistributions of [18F]8a,
a
[18F]8b, [18F]8c, and [18F] 5) in Normal Mice (% dose/g)
[18F]8a
[18F]5
organ
2 min n = 6
30 min n = 6 2 min* n = 3 30 min* n = 3
blood
muscle
kidney
liver
4.77 ± 1.25
0.82 ± 0.16
8.13 ± 0.73
21.2 ± 1.58
0.40 ± 0.03
1.30 ± 0.23
1.54 ± 0.12
1.21 ± 0.15
9.36 ± 0.42
21.4 ± 2.24
0.40 ± 0.05
2.34 ± 0.80
3.14 ± 0.69
1.06 ± 0.39
10.9 ± 2.63
21.5 ± 1.07
7.77 ± 1.70
1.43 ± 0.09
2.80 ± 0.44
1.78 ± 0.34
6.31 ± 0.58
12.9 ± 0.72
1.59 ± 0.22
1.22 ± 0.17
brain
bone
[18F]8b
[18F]8c
organ
2 min n = 6
30 min n = 6
2 min n = 6
30 min n = 6
blood
muscle
kidney
liver
2.55 ± 0.21
1.30 ± 0.70
14.9 ± 0.86
33.5 ± 6.60
0.40 ± 0.10
1.64 ± 0.44
1.32 ± 0.04
1.62 ± 0.39
13.4 ± 1.84
20.0 ± 6.48
0.34 ± 0.07
1.80 ± 0.57
3.12 ± 0.17
0.65 ± 0.22
13.7 ± 2.15
30.2 ± 3.47
0.29 ± 0.06
1.06 ± 0.11
1.40 ± 0.10
1.29 ± 0.12
11.7 ± 0.57
16.0 ± 1.91
0.38 ± 0.04
1.36 ± 0.12
brain
bone
a
About 925 KBq of each ligand in a saline solution was injected. Mice
were sacrificed at 2 and 30 minutes post injection.22
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2-(2-Fluoroethoxy)-1,3-di((E)-2-(2-(2-(5-(4-(methylamino)styryl)-
pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)propane
(8c). Compound 8c was prepared from 25c (0.0950 g, 0.074 mmol)
in 0.9 mL of TFA and 0.1 mL of dimethyl sulfide, with the same
procedure described for compound 8a. Compound 8c: 0.074 g (yield:
may provide selective diagnostic tools that would be useful in
teasing out the accumulation of Aβ aggregates in different areas,
which can be associated with different clinical manifestations.
Currently, it is assumed that the Aβ aggregates on the walls of
major cerebral blood vessels in CAA are similar to those Aβ
plaques in the brain (parenchymal). The new bidentate ligand,
[18F]8a, will likely bind to Aβ aggregates on the blood vessels in
a similar binding mechanism as it would bind to Aβ plaques in
the brain. Further studies will be required to confirm that this
assumption is true.
One other key factor for consideration is the number of
binding sites associated with Aβ plaques on the blood vessels
walls. These may not be as high as those reported for AD brain
Kd = 3.72 ± 0.30 nM, Bmax = 8811 ± 1643 fmol/mg protein.22
However, the Aβ plaques located in the blood vessels may be
more accessible and readily exposed to the CAA binding agent
in the blood circulation. Therefore, the Aβ plaques in CAA may
show higher apparent binding sites. This is a critical factor that
warrants further investigation.
1
92%). H NMR (200 MHz, CDCl3) δ: 8.13 (d, 2H, J = 2.2 Hz), 7.75
(dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.34 (d, 4H, J = 8.6 Hz), 6.85 (d, 4H,
J = 8.0 Hz), 6.76 (d, 2H, J = 8.6 Hz), 6.58 (d, 4H, J = 8.6 Hz), 4.64 (t,
1H, J = 4.3 Hz), 4.47 (t, 4H, J = 4.8 Hz), 4.40 (t, 1H, J = 4.2 Hz),
3.81−3.96 (m, 6H), 3.54−3.79 (m, 45H), 2.85 (s, 6H). 13C NMR
(200 MHz, CDCl3) δ: 162.7, 149.2, 145.1, 135.2, 128.5, 127.7, 126.6,
120.5, 112.6, 111.4, 85.1, 81.7, 78.8, 71.7, 71.0, 70.8, 70.2, 69.9, 69.8,
65.4, 30.0. HRMS (ESI) calculated for C57H84FN4O15 (M + H+),
1083.5917; found, 1083.5890.
2-(2-(2-(2-Fluoroethoxy)ethoxy)ethoxy)-N,N-bis(14-(5-((E)-4-
(methylamino)styryl)pyridin-2-yloxy)-2-oxo-6,9,12-trioxa-3-
azatetradecyl)acetamide (9). A solution of 34 (0.0400 g, 0.031
mmol) in 0.9 mL of TFA and 0.1 mL of dimethyl sulfide was stirred at
rt for 1 h. The reaction mixture was evaporated in vacuo, and the
residue was purified by FC (DCM/MeOH = 92.5/7.5) to give 0.021 g
yellowish oil 8a (yield: 62%). 1H NMR (200 MHz, CDCl3) δ: 8.14 (d,
2H, J = 2.2 Hz), 7.76 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.35 (d, 4H, J =
8.4 Hz), 6.86 (d, 4H, J = 8.8 Hz), 6.76 (d, 2H, J = 7.2 Hz), 6.60 (d,
4H, 8.6 Hz), 4.68 (t, 1H, J = 4.2 Hz), 4.42−4.51 (m, 5H), 4.17 (s,
2H), 4.12 (s, 2H), 3.97 (s, 2H), 3.79−3.88 (m, 6H), 3.54−3.70 (m,
28H). 3.43−3.50 (m, 4H), 2.87 (s, 6H). 13C NMR (200 MHz, CDCl3)
δ: 170.7, 169.3, 169.1, 162.7, 149.3, 145.2, 135.4, 128.6, 127.8, 126.7,
120.5, 112.7, 111.4, 85.0, 81.7, 70.9, 70.8, 70.6, 70.5, 70.0, 69.6, 65.4,
39.6, 30.9. HRMS (ESI) calculated for C56H79FN7O14 (M + H+),
1092.5669; found, 1092.5557.
CONCLUSION
■
In summary, multidentate binding ligands targeting Aβ
aggregates on cerebral vessels have been prepared and tested.
They may provide useful tools for selective diagnosis of cerebral
amyloid angiopathy (CAA), a significant risk factor in the older
patient population.
1,3-Di(E)-(1-(2-(2-(2-(2-(5-(4-(methylamino)styryl)pyridin-2-
yloxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)methoxy-2-
(((E)-(1-(2-(2-(2-(2-(5-(4-(methylamino)styryl)pyridin-2-yloxy)-
ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)methoxy)-
methyl)-2-((2-(2-(2-fluoroethoxy)ethoxy)ethoxy)methyl)propane
(10). A solution of 39 (0.0900 mg, 0.046 mmol) in 0.6 mL of TFA
and 0.06 mL of dimethyl sulfide was stirred at rt for 1 h. The reaction
mixture was evaporated in vacuo, and the residue was purified by FC
(DCM/MeOH = 95/5) to give 0.063 g yellowish oil 8a (yield: 82%).
1H NMR (200 MHz, CDCl3) δ: 8.12 (d, 3H, J = 2.2 Hz), 7.69−7.76
(m, 6H), 7.33 (d, 6H, J = 8.6 Hz), 6.84 (d, 6H, J = 8.6 Hz), 6.73 (d,
3H, J = 8.6 Hz), 6.58 (d, 6H, J = 8.6 Hz), 4.64 (t, 1H, J = 4.2 Hz),
4.38−4.58 (m, 19H), 3.75−3.88 (m, 13H), 3.42−3.72 (m, 41H), 2.84
(s, 9H). 13C NMR (200 MHz, CDCl3) δ: 162.7, 149.2, 145.4, 145.1,
135.3, 128.5, 127.8, 126.7, 123.7, 120.4, 112.6, 111.3, 85.0, 81.6, 71.2,
71.0, 70.8, 70.8, 70.7, 70.5, 70.3, 69.9, 69.6, 69.5, 65.3, 65.2, 50.3, 45.6,
30.8. HRMS (ESI) calculated for C86H116FN15O18Na (M + Na+),
1688.8505; found, 1688.8490.
tert-Butyl 4-Vinylphenylcarbamate (11). To a solution of amino-
styrene (1.19 g, 10 mmol) in 10 mL of water (H2O) was added di-tert-
butyl dicarbonate (Boc2O, 2.40 g, 11 mmol). After vigorously stirring
at 35 °C for 4 h, the mixture was extracted with dichloromethane
(DCM, 25 mL × 2). The organic layer was dried by anhydrous sodium
sulfate (Na2SO4) and filtered. The filtrate was concentrated, and the
residue was purified by flash chromatography (FC) (ethyl acetate
(EtOAc)/hexane = 2/8) to give 2.18 g white solid 11 (yield: 99%). 1H
NMR (200 MHz, CDCl3) δ: 7.34 (s, 4H), 6.67 (dd, 1H, J = 10.8 Hz,
J = 17.6 Hz), 6.47 (br, 1H), 5.66 (d, 1H, J = 17.6 Hz), 5.17 (d, 1H, J =
11 Hz), 1.53 (s, 9H).
EXPERIMENTAL SECTION
■
1. General. All reagents used for chemical synthesis were
commercial products and were used without further purification.
CD-1 mice (20−26 g) were used for the biodistribution studies. All
protocols requiring the utilization of mice were reviewed and approved
by the Institutional Animal Care and Use Committee (University of
Pennsylvania and University of the Sciences in Philadelphia). Post-
mortem human samples were obtained from phase III clinical trials of
[18F]5. The synthesis of precursors and bidentate and tridentate
styrylpyridine derivatives, 8a, 8b, 8c, 9, and 10, was accomplished by
the following schemes (Schemes 1−4).
2-(2-Fluoroethoxy)-1,3-di((E)-2-(2-(2-(5-(4-(methylamino)styryl)-
pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)propane (8a). A solution of
25a (0.0338 g, 0.031 mmol) in 0.9 mL of trifluoroacetic acid (TFA)
and 0.1 mL of dimethyl sulfide was stirred at rt for 1 h. The reaction
mixture was evaporated in vacuo, and the residue was purified by FC
(DCM/MeOH = 92.5/7.5) to give 0.024 g yellowish oil 8a (yield:
1
87%). H NMR (200 MHz, CDCl3) δ: 8.14 (d, 2H, J = 2.2 Hz), 7.76
(dd, 2H, J = 2.4 Hz, J = 8.8 Hz), 7.35 (d, 4H, J = 8.4 Hz), 6.86 (d, 4H,
J = 8.0 Hz), 6.77 (d, 2H, J = 8.6 Hz), 6.60 (d, 4H, J = 8.6 Hz), 4.65 (t,
1H, J = 4.2 Hz), 4.49 (t, 4H, J = 4.8 Hz), 4.41 (t, 1H, J = 4.2 Hz),
3.78−3.97 (m, 6H), 3.63−3.74 (m, 25H), 3.55−3.59 (m, 4H), 2.88 (s,
6H). 13C NMR (200 MHz, CDCl3) δ: 162.9, 149.3, 145.2, 135.3,
128.6, 127.8, 126.8, 120.7, 112.7, 111.5, 85.2, 81.8, 79.0, 71.82, 71.14,
70.9, 70.9, 70.8, 70.2, 70.0, 69.8, 65.5, 30.9. HRMS (ESI) calculated for
C49H68FN4O11 (MH+), 907.4869; found, 907.4870.
2-(2-Fluoroethoxy)-1,3-di((E)-2-(2-(2-(5-(4-(methylamino)styryl)-
pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)propane (8b). Com-
pound 8b was prepared from 25b (0.0650 g, 0.054 mmol) in 0.5
mL of TFA and 0.05 mL of dimethyl sulfide, with the same procedure
tert-Butyl Methyl(4-vinylphenyl)carbamate (12). To a suspension
of NaH (60%, 0.600 g, 15 mmol) in 30 mL of N,N-
dimethylformamide (DMF) was slowly added 11 (2.19 g, 10 mmol)
in 20 mL of DMF followed by iodomethane (CH3I, 7.10 g, 50 mmol).
After stirring at room temperature (rt) for 6 h, the reaction mixture
was quenched with 40 mL satd ammonium chloride (NH4Cl) at 0 °C.
The mixture was then extracted with 120 mL of EtOAc. The organic
layer was washed with H2O (40 mL × 2) as well as brine (40 mL),
dried by Na2SO4, and filtered. The filtrate was concentrated, and the
residue was purified by FC (EtOAc/hexane = 2/8) to give 2.32 g white
1
described for compound 8a. Compound 8b: 0.050 g (yield: 93%). H
NMR (200 MHz, CDCl3) δ: 8.14 (d, 2H, J = 2.2 Hz), 7.75 (dd, 2H,
J = 2.4 Hz, J = 8.6 Hz), 7.34 (d, 4H, J = 8.6 Hz), 6.86 (d, 4H, J = 8.0
Hz), 6.76 (d, 2H, J = 8.6 Hz), 6.59 (d, 4H, J = 8.6 Hz), 4.65 (t, 1H, J =
4.3 Hz), 4.48 (t, 4H, J = 4.8 Hz), 4.41 (t, 1H, J = 4.3 Hz), 3.80−3.96
(m, 6H), 3.52−3.77 (m, 37H), 2.86 (s, 6H). 13C NMR (200 MHz,
CDCl3) δ: 162.8, 149.2, 145.2, 135.3, 128.5, 127.8, 126.7, 120.6, 112.7,
111.4, 85.1, 81.8, 78.9, 71.8, 71.1, 70.8, 70.7, 70.2, 70.0, 69.8, 65.4,
30.8. HRMS (ESI) calculated for C53H76FN4O13 (MH+), 995.5393;
found, 995.5371.
1
solid 12 (yield: 99%). H NMR (200 MHz, CDCl3) δ: 7.37 (d, 2H,
J = 8.6 Hz), 7.20 (d, 2H, J = 8.6 Hz), 6.70 (dd, 1H, J = 11 Hz,
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J = 17.6 Hz), 5.72 (d, 1H, J = 17.6 Hz), 5.24 (d, 1H, J = 11 Hz), 3.26
(s, 3H), 1.46 (s, 9H).
di(p-toluenesulfonate) (1.87 g, 4.5 mmol) and 15 mL of DMF, with
the same procedure described for compound 15b. Compound 15c:
0.759 g (yield: 68%). 1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 1H, J =
2.4 Hz), 7.78−7.83 (m, 3H), 7.45 (d, 2H, J = 8.6 Hz), 7.34 (d, 2H, J =
8.0 Hz), 7.24 (d, 2H, J = 8.6 Hz), 6.98 (s, 2H), 6.80 (d, 1H, J = 8.6
Hz), 4.50 (t, 2H, J = 4.8 Hz), 4.17 (t, 2H, J = 4.8 Hz), 3.87 (t, 2H, J =
4.8 Hz), 3.59−3.75 (m, 18H), 3.28 (s, 3H), 2.45 (s, 3H), 1.47 (s, 9H).
(E)-tert-Butyl 4-(2-(6-(2-(2-(2-(2-Hydroxyethoxy)ethoxy)ethoxy)-
pyridin-3-yl)vinyl)phenyl(methyl)carbamate (16). A mixture of 12
(0.710 g, 3.0 mmol), 13a (0.706 g, 2.0 mmol), potassium carbonate
(K2CO3, 0.690 g, 5.0 mmol), tetrabutylammonium bromide (1.29 g,
4.0 mmol), and palladium acetate (Pd(OAc)2, 0.0224 g, 0.10 mmol) in
15 mL of DMF was deoxygenated by purging into nitrogen for 15 min
and then heated at 65 °C for 2 h. The mixture was cooled to RT,
diluted with 80 mL of EtOAc, and washed with H2O (20 mL × 2) as
well as brine (20 mL). The organic layer was dried by Na2SO4 and
filtered. The filtrate was concentrated, and the residue was purified by
FC (EtOAc/hexane = 8/2) to give 0.753 g white solid 16 (yield: 82%).
1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 1H, J = 2.4 Hz), 7.80 (dd,
2-(2-(2-(5-Iodopyridin-2-yloxy)ethoxy)ethoxy)ethanol (13a). In a
20 mL Biotage microwave reaction vial, 2-chloro-5-iodopyridine
(2.39 g, 10 mmol), tetraethylene glycol (3.00 g, 20 mmol), cesium
carbonate (Cs2CO3, 4.89 g, 15 mmol), and DMF (10 mL) were mixed
and capped. After microwave heating at 150 °C for 55 min, the
mixture was cooled to rt and diluted with 150 mL of EtOAc and
washed with H2O (40 mL × 2) as well as brine (40 mL). The organic
layer was dried by Na2SO4 and filtered. The filtrate was concentrated,
and the residue was purified by FC (EtOAc/hexane = 7/3) to give
2.37 g white solid 4 (yield: 67%). 1H NMR (200 MHz, CDCl3) δ: 8.31
(d, 1H, J = 2.4 Hz), 7.79 (dd, 1H, J = 2.4 Hz, J = 8.6 Hz), 6.65 (d, 1H,
J = 8.6 Hz), 4.45 (t, 2H, J = 4.8 Hz), 3.85 (t, 2H, J = 4.8 Hz), 3.60−
3.76 (m, 8H).
2-(2-(2-(2-(5-Iodopyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethanol
(13b). Compound 13b was prepared from 2-chloro-5-iodopyridine
(3.59 g, 15 mmol), triethylene glycol (5.83 g, 30 mmol), Cs2CO3
(7.34 g, 22.5 mmol), and DMF (10 mL), with the same procedure
described for compound 13a. Compound 13b: 3.27 g (yield: 55%). 1H
NMR (200 MHz, CDCl3) δ: 8.31 (d, 1H, J = 2.4 Hz), 7.78 (dd, 1H,
J = 2.4 Hz, J = 8.6 Hz), 6.64 (d, 1H, J = 8.6 Hz), 4.45 (t, 2H, J = 4.8
Hz), 3.85 (t, 2H, J = 4.8 Hz), 3.60−3.74 (m, 12H).
1H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 2H, J = 8.4 Hz), 7.23 (d, 2H, J =
8.4 Hz), 6.98 (s, 2H), 6.80 (d, 1H, J = 8.6 Hz), 4.52 (t, 2H, J = 4.8
Hz), 3.89 (t, 2H, J = 4.8 Hz), 3.61−3.80 (m, 8H), 3.28 (s, 3H), 2.46
(t, 1H, J = 6.0 Hz), 1.47 (s, 9H).
(E)-tert-Butyl 4-(2-(6-(2-(2-(2-(2-Hydroxyethoxy)ethoxy)ethoxy)-
ethoxy)pyridin-3-yl)vinyl)phenyl(methyl)carbamate (14a). Com-
pound 14a was prepared from 12 (2.33 g, 10 mmol), 13b (2.66 g,
6.7 mmol), K2CO3 (2.31 g, 16.75 mmol), tetrabutylammonium
bromide (4.31 g, 13.4 mmol), Pd(OAc)2 (0.0750 g, 0.34 mmol), and
50 mL of DMF, with the same procedure described for compound 16.
Compound 14a: 3.07 g (yield: 91%). 1H NMR (200 MHz, CDCl3) δ:
8.19 (d, 1H, J = 2.4 Hz), 7.80 (dd, 1H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d,
2H, J = 8.4 Hz), 7.23 (d, 2H, J = 8.6 Hz), 6.98 (s, 2H), 6.80 (d, 1H, J =
8.6 Hz), 4.51 (t, 2H, J = 4.8 Hz), 3.88 (t, 2H, J = 4.8 Hz), 3.60−3.78
(m, 12H), 3.28 (s, 3H), 2.56 (t, 1H, J = 6.0 Hz), 1.47 (s, 9H).
(E)-2-(2-(2-(2-(5-(4-(tert-Butoxycarbonyl(methyl)amino)styryl)-
pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethyl 4-Methylbenzenesulfo-
nate (15a). To a solution of 14a (3.07 g, 6.1 mmol) and
triethylamine (3.03 g, 30 mmol) in 30 mL of DCM was added
p-toluenesulfonyl chloride (2.29 g, 12 mmol) and 4-(dimethylamino)-
pyridine (DMAP, 0.0732 g, 0.6 mmol) at 0 °C. The solution was
allowed to warm to rt. After 50 min, the mixture was diluted with 80
mL of DCM, washed with H2O (30 mL × 2) as well as brine (30 mL).
The organic layer was dried by Na2SO4 and concentrated to give an oil
that was purified by FC (EtOAc/hexane = 1/1) to give 3.21 g white
solid 15a (80%). 1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 1H, J = 2.4
Hz), 7.78−7.83 (m, 3H), 7.45 (d, 2H, J = 8.6 Hz), 7.34 (d, 2H, J = 8.4
Hz), 7.24 (d, 2H, J = 8.6 Hz), 6.98 (s, 2H), 6.80 (d, 1H, J = 8.6 Hz),
4.50 (t, 2H, J = 4.8 Hz), 4.17 (t, 2H, J = 4.8 Hz), 3.86 (t, 2H, J = 4.8
Hz), 3.63−3.72 (m, 10H), 3.28 (s, 3H), 2.45 (s, 3H), 1.47 (s, 9H).
(E)-14-(5-(4-(tert-Butoxycarbonyl(methyl)amino)styryl)pyridin-2-
yloxy)-3,6,9,12-tetraoxatetradecyl 4-Methylbenzenesulfonate
(15b). NaH (60% in mineral oil, 0.08 g, 2 mmol) was placed in a
two-neck flask and washed with hexane. Four mL of DMF was added
to form a suspension. A solution of 16 (0.459 g, 1 mmol) in 3 mL of
DMF was added dropwise at 0 °C. After stirring at rt for 30 min, the
mixture was cooled to 0 °C, and a solution of diethylene glycol
di(p-toluenesulfonate) (1.24 g, 3 mmol) in 3 mL of DMF was added.
The reaction mixture was stirred at rt overnight. The mixture was then
poured into 10 mL of cold 10% NaHCO3 and extracted with DCM
(20 mL × 2). The organic layer was washed with H2O (10 mL × 2)
and brine (10 mL), dried over Na2SO4, concentrated, and purified by
FC (DCM/MeOH = 98/2) to give 0.470 g clear oil 15b (yield: 67%).
1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 1H, J = 2.4 Hz), 7.78−7.83
2-(1,3-Dibromopropan-2-yloxy)-tetrahydro-2H-pyran (17). To a
solution of 1,3-dibromopropane-2-ol (2.18 g, 10 mmol) in 20 mL of
tetrahydrofuran (THF) was added pyridinum p-toluenesulfonate
(PPTS, 0.25 g, 1 mmol) and 3,4-dihydro-2H-pyran (1.68 g,
20 mmol). After stirring at rt for 3 h, the mixture was diluted with
100 mL of EtOAc and washed with H2O (30 mL × 2) as well as brine
(30 mL). The organic layer was dried by Na2SO4 and filtered. The
filtrate was concentrated, and the residue was purified by FC (EtOAc/
1
hexane = 5/95) to give 2.72 g of clear oil 17 (yield: 90%). H NMR
(200 MHz, CDCl3) δ: 4.78−4.82 (m, 1H), 3.89−4.06 (m, 2H), 3.51−
3.74 (m, 5H), 1.55−1.85 (m, 6H).
2-(Tetrahydro-2H-pyran-2-yloxy)propane-1,3-diyl Diacetate
(18). A mixture of 17 (3.83 g, 12.6 mmol), tetrabutylammonium
acetate (11.4 g, 37.8 mmol), tetrabutylammonium iodide (0.923 g,
2.5 mmol), and K2CO3 (0.345 g, 2.5 mmol) in 20 mL of anhydrous
acetonitrile was stirred at rt overnight. The mixture was filtered, and
the filtrate was concentrated. The residue was purified by FC (EtOAc/
1
hexane = 5/95) to give 2.81 g of clear oil 18 (yield: 86%). H NMR
(200 MHz, CDCl3) δ: 4.79−4.81 (m, 1H), 4.03−4.31 (m, 5H), 3.88−
3.97 (m, 1H), 3.49−3.57 (m, 1H), 2.09 (s, 3H), 2.08 (s, 3H), 1.55−
1.84 (m, 6H).
2-(Tetrahydro-2H-pyran-2-yloxy)propane-1,3-diol (19). A mix-
ture of 18 (1.30 g, 5 mmol) and 25 mL of ammonia solution
(2.0 M in methanol) was stirred at rt overnight. The mixture was
then concentrated in vacuo to afford 0.81 g of yellow oil 19 (yield:
1
91%). H NMR (200 MHz, CDCl3) δ: 4.60−4.63 (m, 1H), 4.01−
4.06 (m, 1H), 3.53−3.80 (m, 6H), 1.84−1.96 (m, 2H), 1.56−1.59
(m, 4H).
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)propan-
2-yloxy)-tetrahydro-2H-pyran (20a). NaH (60% in mineral oil, 0.160
g, 4 mmol) was placed in a two-neck flask and washed with hexane.
Five mL of DMF was added to form a suspension. A solution of 19
(0.176 g, 1 mmol) in 5 mL of DMF was added dropwise at 0 °C. After
stirring at rt for 30 min, the mixture was cooled to 0 °C, and a solution
of 15a (1.31 g, 2 mmol) in 3 mL of DMF was added dropwise, and the
reaction mixture was stirred at rt overnight. The mixture was then
poured into 50 mL of cold satd NH4Cl and extracted with DCM (50
mL × 2). The organic layer was washed with H2O (30 mL) and brine
(30 mL), dried over Na2SO4, concentrated, and purified by FC
(m, 3H), 7.45 (d, 2H, J = 8.6 Hz), 7.34 (d, 2H, J = 8.0 Hz), 7.24 (d,
2H, J = 8.6 Hz), 6.98 (s, 2H), 6.80 (d, 1H, J = 8.6 Hz), 4.50 (t, 2H, J =
4.8 Hz), 4.17 (t, 2H, J = 4.8 Hz), 3.7 (t, 2H, J = 4.8 Hz), 3.59−3.76
(m, 14H), 3.28 (s, 3H), 2.45 (s, 3H), 1.47 (s, 9H).
(E)-17-(5-(4-(tert-Butoxycarbonyl(methyl)amino)styryl)pyridin-2-
yloxy)-3,6,9,12,15-pentaoxaheptadecyl 4-Methylbenzenesulfonate
(15c). Compound 15c was prepared from NaH (60% in mineral
oil, 0.120 g, 3 mmol), 14a (0.754 g, 1.5 mmol), diethylene glycol
1
(EtOAc: 100%) to give 0.835 g of a clear oil 20a (yield: 73%). H
NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.4 Hz), 7.80 (dd, 2H,
J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz), 7.23 (d, 4H, J = 8.4
Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.73−4.82 (m, 1H), 4.50
(t, 4H, J = 4.8 Hz), 3.85−4.02 (m, 6H), 3.50−3.71 (m, 29H), 3.28 (s,
6H), 1.56−1.96 (m, 6H), 1.47 (s, 18H).
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2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-yloxy)-tetrahydro-2H-pyran (20b). Compound 20b was
prepared from NaH (60% in mineral oil, 0.052 g, 1.3 mmol), 19
(0.0581 g, 0.33 mmol), and 15b (0.469 g, 0.67 mmol) in 8 mL of
DMF, with the same procedure described for compound 20a.
Compound 20b: 0.310 g (yield: 76%):. 1H NMR (200 MHz,
CDCl3) δ: 8.19 (d, 2H, J = 2.4 Hz), 7.80 (dd, 2H, J = 2.4 Hz, J = 8.6
Hz), 7.45 (d, 4H, J = 8.4 Hz), 7.23 (d, 4H, J = 8.4 Hz), 6.97 (s, 4H),
6.80 (d, 2H, J = 8.6 Hz), 4.79−4.81 (m, 1H), 4.50 (t, 4H, J = 4.8 Hz),
3.84−4.05 (m, 6H), 3.62−3.71 (m, 37H), 3.28 (s, 6H), 1.56−1.96 (m,
6H), 1.47 (s, 18H).
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
ethoxy)propan-2-yloxy)-tetrahydro-2H-pyran (20c). Compound
20c was prepared from NaH (60% in mineral oil, 0.080 g, 2 mmol),
19 (0.0851 g, 0.48 mmol), and 15c (0.745 g, 1 mmol) in 10 mL of
DMF, with the same procedure described for compound 20a.
Compound 20c: 0.522 g (yield: 82%). 1H NMR (200 MHz,
CDCl3) δ: 8.19 (d, 2H, J = 2.4 Hz), 7.80 (dd, 2H, J = 2.4 Hz, J =
8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz), 7.23 (d, 4H, J = 8.6 Hz), 6.97 (s,
4H), 6.80 (d, 2H, J = 8.6 Hz), 4.79−4.81 (m, 1H), 4.50 (t, 4H, J = 4.8
Hz), 3.85−4.05 (m, 6H), 3.45−3.71 (m, 45H), 3.28 (s, 6H), 1.56−
1.96 (m, 6H), 1.47 (s, 18H).
1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)amino)-
styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)propan-2-ol
(21a). A mixture of 20a (0.841 g, 0.73 mmol) and PPTS (0.0183 g,
0.073 mmol) in 7 mL of EtOH was stirred at 55 °C for 3 h. The
mixture was concentrated, and the residue was purified by FC
(EtOAc/MeOH = 9/1) to give 0.732 g colorless oil 21a (yield: 94%).
1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.4 Hz), 7.80 (dd,
2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz), 7.23 (d, 4H, J =
8.6 Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.50 (t, 4H, J = 4.8
Hz), 3.84−4.05 (m, 6H), 3.45−3.80 (m, 28H), 3.28 (s, 6H), 1.47 (s,
18H).
J = 8.4 Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.62−4.65 (m, 1H),
4.50 (t, 4H, J = 4.8 Hz), 3.55−3.89 (m, 39H), 3.28 (s, 6H), 1.56−1.96
(m, 6H), 1.47 (s, 18H).
2-(2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-yloxy)ethoxy)-tetrahydro-2H-pyran (22b). Compound
22b was prepared from NaH (60% in mineral oil, 0.0180 g, 0.45
mmol), 21b (0.172 g, 0.15 mmol), and 2-(2-bromoethoxy)-tetrahydro-
2H-pyran (0.0627 g, 0.3 mmol) in 2.5 mL of DMF, with the same
procedure described for compound 22a. Compound 22b: 0.130 g
1
(yield: 68%). H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.4
Hz), 7.80 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz),
7.23 (d, 4H, J = 8.4 Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.62−
4.65 (m, 1H), 4.50 (t, 4H, J = 4.8 Hz), 3.52−3.89 (m, 47H), 3.28 (s,
6H), 1.56−1.96 (m, 6H), 1.47 (s, 18H).
2-(2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-yloxy)ethoxy)-tetrahydro-2H-pyran (22c). Compound
22c was prepared from NaH (60% in mineral oil, 0.022 g, 0.55
mmol), 21c (0.333 g, 0.27 mmol), and 2-(2-bromoethoxy)-tetrahydro-
2H-pyran (0.115 g, 0.55 mmol) in 4 mL of DMF, with the same
procedure described for compound 22a. Compound 22c: 0.310 g
1
(yield: 83%). H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.4
Hz), 7.80 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz),
7.23 (d, 4H, J = 8.4 Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.62−
4.65 (m, 1H), 4.50 (t, 4H, J = 4.8 Hz), 3.57−3.89 (m, 55H), 3.28 (s,
6H), 1.56−1.96 (m, 6H), 1.47 (s, 18H).
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)propan-
2-yloxy)ethanol (23a). A mixture of 22a (0.570 g, 0.48 mmol) and
PPTS (0.0120 g, 0.048 mmol) in 6 mL of EtOH was stirred at 55 °C
for 6 h. The mixture was concentrated, and the residue was purified by
FC (EtOAc/MeOH = 9/1) to give 0.477 g of a colorless oil 23a
1
(yield: 90%). H NMR (200 MHz, CDCl3) δ: 8.18 (d, 2H, J = 2.4
Hz), 7.79 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz),
7.23 (d, 4H, J = 8.6 Hz), 6.96 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.49 (t,
4H, J = 4.8 Hz), 3.86 (t, 4H, J = 4.8 Hz), 3.64−3.79 (m, 29H), 3.49−
3.58 (m, 4H), 3.27 (s, 6H), 1.47 (s, 18H).
1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)amino)-
styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)propan-
2-ol (21b). Compound 21b was prepared from 20b (0.295 g,
0.24 mmol) and PPTS (0.0060 g, 0.024 mmol) in 3 mL of EtOH,
with the same procedure described for compound 21a. Compound
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-yloxy)ethanol (23b). Compound 23b was prepared from
22b (0.128 g, 0.1 mmol) and PPTS (0.0025 g, 0.01 mmol) in 1 mL of
EtOH, with the same procedure described for compound 23a.
1
21b: 0.177 g (yield: 62%). H NMR (200 MHz, CDCl3) δ: 8.19 (d,
2H, J = 2.4 Hz), 7.80 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J =
8.4 Hz), 7.23 (d, 4H, J = 8.4 Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6
Hz), 4.48−4.52 (m, 4H), 3.84−4.05 (m, 6H), 3.45−3.80 (m, 36H),
3.28 (s, 6H), 1.47 (s, 18H).
1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)amino)-
styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-ol (21c). Compound 21b was prepared from 20c (0.524 g,
0.4 mmol) and PPTS (0.0100 g, 0.04 mmol) in 4 mL of EtOH, with
the same procedure described for compound 21a. Compound 21c:
0.340 g (yield: 69%). 1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J =
2.4 Hz), 7.80 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz),
7.23 (d, 4H, J = 8.4 Hz), 6.97 (s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.50 (t,
4H, J = 4.8 Hz), 3.84−4.05 (m, 6H), 3.45−3.80 (m, 44H), 3.28 (s,
6H), 1.47 (s, 18H).
1
Compound 23b: 0.116 g (yield: 98%). H NMR (200 MHz, CDCl3)
δ: 8.19 (d, 2H, J = 2.2 Hz), 7.80 (dd, 2H, J = 2.6 Hz, J = 8.8 Hz), 7.45
(d, 4H, J = 8.6 Hz), 7.23 (d, 4H, J = 8.6 Hz), 6.97 (s, 4H), 6.80 (d, 2H,
J = 8.6 Hz), 4.50 (t, 4H, J = 4.8 Hz), 3.87 (t, 4H, J = 4.8 Hz), 3.65−
3.79 (m, 37H), 3.51−3.55 (m, 4H), 3.28 (s, 6H), 1.47 (s, 18H).
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
ethoxy)propan-2-yloxy)ethanol (23c). Compound 23c was prepared
from 22c (0.314 g, 0.23 mmol) and PPTS (0.00577 g, 0.023 mmol) in
2 mL of EtOH, with the same procedure described for compound 23a.
1
Compound 23c: 0.235 g (yield: 80%). H NMR (200 MHz, CDCl3)
δ: 8.19 (d, 2H, J = 2.2 Hz), 7.80 (dd, 2H, J = 2.4 Hz, J = 8.8 Hz), 7.45
(d, 4H, J = 8.6 Hz), 7.23 (d, 4H, J = 8.6 Hz), 6.97 (s, 4H), 6.80 (d, 2H,
J = 8.6 Hz), 4.50 (t, 4H, J = 4.8 Hz), 3.87 (t, 4H, J = 4.8 Hz), 3.64−
3.71 (m, 45H), 3.51−3.55 (m, 4H), 3.28 (s, 6H), 1.47 (s, 18H).
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)propan-
2-yloxy)ethyl-4-methylbenzene Sulfonate (24a). To a solution of
23a (0.395 g, 0.36 mmol) and triethylamine (0.180 g, 1.79 mmol) in
5 mL of DCM was added p-toluenesulfonyl chloride (0.135 g,
0.71 mmol) and DMAP (0.0044 g, 0.036 mmol) at 0 °C. The solution
was allowed to warm to rt. After 1 h, the mixture was diluted with
30 mL of DCM, washed with H2O (10 mL × 2) as well as brine
(10 mL). The organic layer was dried by Na2SO4 and concentrated to
give an oil that was purified by FC (DCM/MeOH = 95/5) to give
2-(2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl) pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-yloxy)ethoxy)-tetrahydro-2H-pyran (22a). NaH (60% in
mineral oil, 0.0552 g, 1.38 mmol) was placed in a two-neck flask and
washed with hexane. Four mL of DMF was added to form a
suspension. A solution of 21a (0.73 g, 0.69 mmol) in 3 mL of DMF
was added dropwise at 0 °C. After stirring at rt for 30 min, the mixture
was cooled to 0 °C, and a solution of 2-(2-bromoethoxy)-tetrahydro-
2H-pyran (0.288 g, 1.38 mmol) in 3 mL DMF was added dropwise.
The reaction mixture was stirred at rt overnight. The mixture was then
poured into 50 mL of cold satd NH4Cl and extracted with DCM
(30 mL × 2). The organic layer was washed with H2O (20 mL) and
brine (20 mL), dried over Na2SO4, concentrated, and purified by FC
(EtOAc/MeOH = 98/2) to give 0.574 g of a colorless oil 22a (yield:
1
0.444 g of a yellowish solid 24a (yield: 97%). H NMR (200 MHz,
1
70%). H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.0 Hz), 7.80
CDCl3) δ: 8.18 (d, 2H, J = 2.0 Hz), 7.77−7.82 (m, 4H), 7.45 (d, 4H,
J = 8.6 Hz), 7.33 (d, 2H, J = 8.0 Hz), 7.23 (d, 4H, J = 8.6 Hz),
(dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz), 7.23 (d, 4H,
8094
dx.doi.org/10.1021/jm2009106|J. Med. Chem. 2011, 54, 8085−8098

Journal of Medicinal Chemistry
Article
1
6.97 (s, 4H), 6.79 (d, 2H, J = 8.6 Hz), 4.50 (t, 4H, J = 4.8 Hz), 4.15 (t,
2H, J = 4.8 Hz), 3.80−3.89 (m, 6H), 3.55−3.74 (m, 25H), 3.44−3.51
(m, 4H), 3.28 (s, 6H), 2.44 (s, 3H), 1.47 (s, 18H).
(yield: 50%). H NMR (200 MHz, CDCl3) δ: 4.16−4.28 (m, 4H),
3.60−3.76 (m, 12H), 2.43 (t, 1H, J = 6.2 Hz), 1.30 (t, 3H, J = 7.2 Hz).
Ethyl 2-(2-(2-(2-Bromoethoxy)ethoxy)ethoxy)acetate (27). To
a solution of triphenylphosphine (2.16 g, 8.25 mmol) and
N-bromosuccinimide (1.47 g, 8.25 mmol) in 30 mL of DCM was
slowly added 26 (1.30 g, 5.5 mmol) in 20 mL of DCM at 0 °C. The
reaction mixture was stirred at 0 °C for 2 h and then washed with H2O
(10 mL × 2) and brine (10 mL). The organic layer was dried by
Na2SO4 and concentrated to give 1.39 g of yellow oil 27 (yield: 85%).
1H NMR (200 MHz, CDCl3) δ: 4.16−4.28 (m, 4H), 3.68−3.86 (m,
10H), 3.48 (t, 2H, J = 6.4 Hz), 1.29 (t, 3H, J = 7.2 Hz).
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
propan-2-yloxy)ethyl-4-methylbenzene Sulfonate (24b). Com-
pound 24b was prepared from 23b (0.125 g, 0.11 mmol), triethyl-
amine (0.0525 g, 0.5 mmol), p-toluenesulfonyl chloride (0.0400 g,
0.21 mmol), and DMAP (0.0012 g, 0.01 mmol) in 2 mL of DCM, with
the same procedure described for compound 24a. Compound 24b:
0.134 g (yield: 96%). 1H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J =
2.0 Hz), 7.77−7.82 (m, 4H), 7.45 (d, 4H, J = 8.6 Hz), 7.34 (d, 2H, J =
8.4 Hz), 7.23 (d, 4H, J = 8.8 Hz), 6.97 (s, 4H), 6.79 (d, 2H, J = 8.6
Hz), 4.50 (t, 4H, J = 4.8 Hz), 4.14 (t, 2H, J = 4.8 Hz), 3.80−3.89
(m, 6H), 3.60−3.74 (m, 33H), 3.46−3.51 (m, 4H), 3.28 (s, 6H), 2.44
(s, 3H), 1.47 (s, 18H).
2-(2-(2-(2-Bromoethoxy)ethoxy)ethoxy)acetic Acid (28). A sol-
ution of 27 (1.39 g, 4.6 mmol) in 15 mL of sodium hydroxide (NaOH,
1 M)/THF (v/v, 1/1) was stirred at rt for 2 h. Hydrochloric acid
(HCl, 0.9 mL) was then added to the mixture. The solvent was
removed in vacuo, and the residue was taken up in DCM. The mixture
was filtered, and the filtrate was concentrated to give 0.810 g of clear
2-(1,3-Di((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)-
ethoxy)propan-2-yloxy)ethyl-4-methylbenzenesulfonate
(24c). Compound 24c was prepared from 23c (0.230 g, 0.18 mmol),
triethylamine (0.0909 g, 0.9 mmol), p-toluenesulfonyl chloride (0.0686
g, 0.36 mmol), and DMAP (0.0022 g, 0.018 mmol) in 3 mL of DCM,
with the same procedure described for compound 24a. Compound
1
oil 28 (yield: 65%). H NMR (200 MHz, CDCl3) δ: 4.17 (s, 2H),
3.75−3.88 (m, 10H), 3.52 (t, 2H, J = 6.4 Hz).
tert-Butyl 14-Bromo-3-(2-tert-butoxy-2-oxoethyl)-4-oxo-6,9,12-
trioxa-3-azatetradecan-1-oate (29). To a solution of 28 (0.810 g,
2.9 mmol) in 15 mL of DMF was added di-tert-butyl iminodiacetate
(0.711 g, 2.9 mmol), 1-hydroxybenzotriazole hydrate (0.882 g, 5.22
mmol), N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochlor-
ide (1.0 g, 5.22 mmol), and N,N-diisopropylethylamine (0.674 g,
5.22 mmol). After stirring at rt overnight, the mixture was poured into
100 mL of EtOAc and washed with H2O (30 mL × 2) and brine
(30 mL). The organic layer was dried by Na2SO4 and filtered. The
filtrate was concentrated, and the residue was purified by FC (EtOAc/
1
24c: 0.240 g (yield: 98%). H NMR (200 MHz, CDCl3) δ: 8.1 8
(d, 2H, J = 2.2 Hz), 7.78−7.82 (m, 4H), 7.45 (d, 4H, J = 8.6 Hz), 7.34
(d, 2H, J = 8.0 Hz), 7.23 (d, 4H, J = 8.2 Hz), 6.97 (s, 4H), 6.79
(d, 2H, J = 8.6 Hz), 4.50 (t, 4H, J = 4.8 Hz), 4.14 (t, 2H, J = 4.8 Hz),
3.80−3.89 (m, 6H), 3.46−3.75 (m, 41H), 3.44−3.51 (m, 4H), 3.28
(s, 6H), 2.45 (s, 3H), 1.47 (s, 18H).
2-(2-Fluoroethoxy)-1,3-di((E)-2-(2-(2-(2-(5-(4-(tert-
butoxycarbonyl(methyl)amino)styryl)pyridin-2-yloxy)ethoxy)-
ethoxy)ethoxy)ethoxy) Propane (25a). A mixture of 24a (0.126 g,
0.1 mmol) and tetrabutylammonium fluoride (TBAF, 0.25 mL, 1.0 M
in THF) in 1.5 mL of THF was stirred at 70 °C overnight. The
reaction mixture was evaporated in vacuo, and the residue was purified
by FC (EtOAc/MeOH = 9/1) to give 0.054 g of a colorless oil 25a
1
hexane = 1/1) to give 0.931 g of clear oil 29 (yield: 64%). H NMR
(200 MHz, CDCl3) δ: 4.24 (s, 2H), 4.14 (s, 2H), 4.05 (s, 2H), 3.64−
3.86 (m, 10H), 3.48 (t, 2H, J = 6.4 Hz), 1.49 (s, 9H), 1.47 (s, 9H).
14-Bromo-3-(carboxymethyl)-4-oxo-6,9,12-trioxa-3-azatetrade-
can-1-oic Acid (30). A solution of 29 (0.157 g, 0.3 mmol) in 3 mL of
TFA/DCM (v/v, 1/1) was stirred at rt for 2 h. Removal of solvent
gave clear oil. After several times of coevaporation with methanol,
0.112 g of 30 (yield: 97%) was given as a clear oil. H NMR (200
MHz, CDCl3) δ: 4.49 (s, 2H), 4.34 (s, 2H), 4.28 (s, 2H), 3.74−3.92
(m, 10H), 3.49 (t, 2H, J = 6.0 Hz).
1
(yield: 49%). H NMR (200 MHz, CDCl3) δ: 8.17 (d, 2H, J = 2.2
1
Hz), 7.78 (dd, 2H, J = 2.2 Hz, J = 8.6 Hz), 7.43 (d, 4H, J = 8.6 Hz),
7.22 (d, 4H, J = 8.6 Hz), 6.96 (s, 4H), 6.78 (d, 2H, J = 8.6 Hz), 4.64 (t,
1H, J = 4.2 Hz), 4.48 (t, 4H, J = 4.8 Hz), 4.40 (t, 1H, J = 4.2 Hz), 3.94
(t, 1H, J = 4.3 Hz), 3.85 (t, 4H, J = 4.8 Hz), 3.79 (t, 1H, J = 4.3 Hz),
3.62−3.73 (m, 25H), 3.54−3.58 (m, 4H), 3.26 (s, 6H), 1.46 (s, 18H).
2-(2-Fluoroethoxy)-1,3-di((E)-2-(2-(2-(2-(5-(4-(tert-
butoxycarbonyl(methyl)amino)styryl)pyridin-2-yloxy)ethoxy)-
ethoxy)ethoxy)ethoxy)ethoxy)propane (25b). Compound 25b was
prepared from 24b (0.100 g, 0.074 mmol) and TBAF (0.15 mL, 1.0 M
in THF) in 1 mL THF, with the same procedure described for
(E)-tert-Butyl 4-(2-(6-(2-(2-(2-(2-Azidoethoxy)ethoxy)ethoxy)-
ethoxy)pyridin-3-yl)vinyl)phenyl(methyl)carbamate (31). Sodium
azide (0.566 g, 8.7 mmol) was added to a solution of 15a (1.91 g,
2.9 mmol) in 20 mL of DMF. After stirring at 60 °C for 3 h, the
mixture was then poured into 100 mL of EtOAc and washed with H2O
(30 mL × 2) as well as brine (30 mL). The organic layer was dried by
Na2SO4 and filtered. The filtrate was concentrated, and the residue was
purified by FC (EtOAc/hexane = 1/1) to give 1.33 g of white solid 31
1
compound 25a. Compound 25b: 0.0726 g (yield: 82%). H NMR
1
(200 MHz, CDCl3) δ: 8.18 (d, 2H, J = 2.2 Hz), 7.79 (dd, 2H, J = 2.4
Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.6 Hz), 7.23 (d, 4H, J = 8.6 Hz), 6.97
(s, 4H), 6.79 (d, 2H, J = 8.6 Hz), 4.65 (t, 1H, J = 4.2 Hz), 4.50 (t, 4H,
J = 4.8 Hz), 4.41 (t, 1H, J = 4.2 Hz), 3.95 (t, 1H, J = 4.3 Hz), 3.78−
3.89 (m, 5H), 3.53−3.77 (m, 37H), 3.28 (s, 6H), 1.47 (s, 18H).
2-(2-Fluoroethoxy)-1,3-di((E)-2-(2-(2-(2-(5-(4-(tert-
butoxycarbonyl(methyl)amino)styryl)pyridin-2-yloxy)ethoxy)-
ethoxy)ethoxy)ethoxy)ethoxy)ethoxy)propane (25c). Compound
25c was prepared from 24c (0.171 g, 0.12 mmol) and TBAF (0.24
mL, 1.0 M in THF) in 2 mL THF, with the same procedure described
(yield: 87%). H NMR (200 MHz, CDCl3) δ: 8.20 (d, 1H, J = 2.6
Hz), 7.80 (dd, 1H, J = 2.2 Hz, J = 8.6 Hz), 7.45 (d, 2H, J = 8.4 Hz),
7.23 (d, 2H, J = 8.6 Hz), 6.98 (s, 2H), 6.81 (d, 1H, J = 8.4 Hz), 4.51
(t, 2H, J = 4.8 Hz), 3.88 (t, 2H, J = 4.8 Hz), 3.66−3.72 (m, 10H), 3.39
(t, 2H, J = 4.8 Hz), 3.28 (s, 3H), 1.47 (s, 9H).
(E)-tert-Butyl 4-(2-(6-(2-(2-(2-(2-Aminoethoxy)ethoxy)ethoxy)-
ethoxy)pyridin-3-yl)vinyl)phenyl(methyl)carbamate (32). Triphe-
nylphosphine (0.472 g, 1.8 mmol) was added to a solution of 31
(0.379 g, 0.72 mmol) in 12.6 mL of THF. After stirring at rt for 2 h,
1.4 mL of H2O was added and the mixture was heated at 60 °C
overnight. The reaction mixture was evaporated in vacuo, and the
residue was purified by FC (DCM/MeOH/NH4OH = 90/9/1) to
1
for compound 25a. Compound 25c: 0.123 g (yield: 80%). H NMR
(200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.2 Hz), 7.80 (dd, 2H, J = 2.4
Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.6 Hz), 7.23 (d, 4H, J = 8.6 Hz), 6.98
(s, 4H), 6.80 (d, 2H, J = 8.6 Hz), 4.65 (t, 1H, J = 4.2 Hz), 4.50 (t, 4H,
J = 4.8 Hz), 4.42 (t, 1H, J = 4.2 Hz), 3.96 (t, 1H, J = 4.3 Hz), 3.78−
3.89 (m, 5H), 3.53−3.77 (m, 45H), 3.28 (s, 6H), 1.47 (s, 18H).
Ethyl 2-(2-(2-(2-Hydroxyethoxy)ethoxy)ethoxy)acetate (26). To
a solution of tetraethylene glycol (3.02 g, 20 mmol) and boron
trifluoride−diethyl ether (0.1 mL) in 40 mL of DCM was slowly
added ethyl diazoacetate (1.14 g, 10 mmol) in 10 mL of DCM at 0 °C.
The reaction mixture was stirred at rt for 2 h and then washed with
H2O (10 mL × 2) as well as brine (10 mL). The organic layer was
dried by Na2SO4 and concentrated to give 1.19 g of a clear oil 26
1
give 0.360 g of white solid 32 (yield: 100%). H NMR (200 MHz,
CDCl3) δ: 8.19 (d, 1H, J = 2.4 Hz), 7.81 (dd, 1H, J = 2.4 Hz, J = 8.6
Hz), 7.45 (d, 2H, J = 8.4 Hz), 7.23 (d, 2H, J = 8.6 Hz), 6.98 (s, 2H),
6.81 (d, 1H, J = 8.8 Hz), 4.50 (t, 2H, J = 4.8 Hz), 3.88 (t, 2H, J = 4.8
Hz), 3.67−3.72 (m, 8H), 3.56 (t, 2H, J = 5.2 Hz), 3.28 (s, 3H), 2.890
(t, 2H, J = 5.2 Hz), 1.47 (s, 9H).
2-(2-(2-(2-Bromoethoxy)ethoxy)ethoxy)-N,N-bis(2-(((E)-2-(2-(2-
(2-(5-(4-(tert-butoxycarbonyl(methyl)amino)styryl)pyridin-2-yloxy)-
ethoxy)ethoxy)ethoxy)ethoxy) amino)-2-oxoethyl)acetamide
(33). To a solution of 30 (0.116 g, 0.3 mmol) in 6 mL of DCM was
added N,N′-dicyclohexylcarbodiimide (0.247 g, 1.2 mmol), 32 (0.301 g,
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0.6 mmol), and 4-(dimethylamino)pyridine (0.0073 g, 0.06 mmol).
The mixture was stirred at rt for 3 h and filtered with Celite. The
filtrate was concentrated, and the residue was purified by FC (DCM/
MeOH/NH4OH = 95/5/0.5) to give 0.161 g of clear oil 33 (yield:
The organic layer was dried by Na2SO4 and filtered. The filtrate was
concentrated, and the residue was purified by FC (EtOAc/MeOH =
9/1) to give 0.110 g clear oil 38 (yield: 90%). H NMR (200 MHz,
CDCl3) δ: 8.17 (d, 3H, J = 2.2 Hz), 7.76−7.82 (m, 5H), 7.71 (s, 3H),
7.45 (d, 6H, J = 8.6 Hz), 7.33 (d, 2H, J = 8.2 Hz), 7.23 (d, 6H, J = 8.6
Hz), 6.97 (s, 6H), 6.77 (d, 3H, J = 8.6 Hz), 4.46−4.59 (m, 18H),
4.11−4.16 (m, 2H), 3.83−3.90 (m, 12H), 3.61−3.71 (m, 26H), 3.38−
3.56 (m, 16H), 3.28 (s, 9H), 2.43 (s, 3H), 1.47 (s, 27H).
1
1
40%). H NMR (200 MHz, CDCl3) δ: 8.19 (d, 2H, J = 2.2 Hz), 7.80
(dd, 2H, J = 2.2 Hz, J = 8.6 Hz), 7.45 (d, 4H, J = 8.4 Hz), 7.23 (d, 4H,
J = 8.4 Hz), 6.97 (s, 4H), 6.79 (dd, 2H, J = 3.4 Hz, J = 8.8 Hz), 4.50 (t,
4H, J = 4.8 Hz), 4.18 (s, 2H), 4.12 (s, 2H), 3.97 (s, 2H), 3.78−3.86
(m, 6H), 3.58−3.70 (m, 28H), 3.44−3.50 (m, 6H), 3.28 (s, 6H), 1.47
(s, 18H).
1,3-Di(E)-(1-(2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-
triazol-4-yl)methoxy-2-(((E)-(1-(2-(2-(2-(2-(5-(4-(tert-
butoxycarbonyl(methyl)amino)styryl)pyridin-2-yloxy)ethoxy)-
ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)methoxy)methyl)-2-((2-
(2-(2-fluoroethoxy)ethoxy)ethoxy)methyl)propane (39). Com-
pound 39 was prepared from 37 (0.0486 g, 0.126 mmol), 31
(0.201 g, 0.38 mmol), sodium ascorbate (0.0376 g, 0.19 mmol), and
CuSO4 (0.0061 g, 0.038 mmol) in 4 mL of t-BuOH/H2O (v/v, 1/1),
with the same procedure described for compound 38. Compound 39:
N,N-Bis(2-(((E)-2-(2-(2-(2-(5-(4-(tert-butoxycarbonyl(methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethoxy)amino)-
2-oxoethyl)-2-(2-(2-(2-fluoroethoxy)ethoxy)ethoxy)acetamide
(34). A mixture of 33 (0.100 g, 0.074 mmol) and TBAF (0.15 mL,
1.0 M in THF) in 1 mL of THF was stirred at 70 °C overnight. The
reaction mixture was evaporated in vacuo, and the residue was purified
by FC (DCM/MeOH/NH4OH = 95/5/0.5) to give 0.045 g clear oil
34 (yield: 47%). 1H NMR (200 MHz, CDCl3) δ: 8.17 (d, 2H, J = 2.2
Hz), 7.79 (dd, 2H, J = 2.4 Hz, J = 8.6 Hz), 7.44 (d, 4H, J = 8.6 Hz),
7.22 (d, 4H, J = 8.4 Hz), 6.96 (s, 4H), 6.78 (dd, 2H, J = 2.2 Hz, J = 8.6
Hz), 4.67 (t, 1H, J = 4.1 Hz), 4.41−4.51 (m, 5H), 4.17 (s, 2H), 4.12
(s, 2H), 3.97 (s, 2H), 3.50−3.88 (m, 34H), 3.43−3.48 (m, 4H), 3.27
(s, 6H), 1.46 (s, 18H).
1
0.208 g (yield: 84%). H NMR (200 MHz, CDCl3): 8.17 (d, 3H, J =
2.4 Hz), 7.79 (dd, 3H, J = 2.4 Hz, J = 8.6 Hz), 7.71 (s, 3H), 7.45 (d,
6H, J = 8.6 Hz), 7.23 (d, 6H, J = 8.6 Hz), 6.97 (s, 6H), 6.77 (dd, 3H,
J = 8.6 Hz), 4.65 (t, 1H, J = 4.2 Hz), 4.39−4.60 (m, 19H), 3.77−3.90
(m, 13H), 3.43−3.73 (m, 41H), 3.28 (s, 9H), 1.47 (s, 27H).
2. Radiosynthesis of [18F]8a−c. Preparation of [18F]8a−c was
achieved by using a modified method reported previously (see Scheme
5).27 Briefly, the 18F-fluoride ions were trapped on an activated QMA
anion exchange cartridge and eluted with 1 mL of Kryptofix222/
K2CO3 acetonitrile/water solution (22 mg Kryptofix222/1.8 mg
K2CO3/0.84 mL ACN/0.16 mL water). The solution was azeotropi-
cally dried twice with acetonitrile at 110 °C under a stream of argon.
Approximately 1 mg of O-tosylated precursor (24a−c) was dissolved
in 1 mL of DMSO and added to the anhydrous Kryptofix/K2CO3/
[18F]fluoride. The reaction was heated for 10 min at 110 °C and
allowed to cool at room temperature for 5 min. One mL of a 10%
(∼4 N) HCl solution was added and heated at 80 °C for 7 min. The
reaction was cooled in an ice bath, neutralized with a NaOH solution,
and diluted with water to about 8 mL total volume. The mixture was
pushed through an activated C4 mini column (Vydac Bioselect
214SPE3000 reversed-phase C4), washed twice with 3 mL of water
and [18F]8a−c was eluted with 1 mL of ethanol (decay corrected
radiochemical yields were 29%, 29%, and 30%, respectively; radio-
chemical purity was >98%). To ensure an accurate detection of free
fluoride, other impurities and the desired products, [18F]8a−c, two
HPLC systems were employed: (a) Gemini C18 150 mm × 4.6 mm,
acetonitrile/10 mM ammonium format buffer 8/2 and flow rate of
1 mL/min and (b) Gemini C18 250 mm × 4.6 mm with a solvent
gradient at a flow rate of 1 mL/min according to the following:
0−2 min 100% 10 mM ammonium formate buffer; 2−5 min
ammonium formate buffer 100% to 30%, ACN 0% to 70%;
5−10 min ammonium formate buffer 30% to 0%, ACN 70% to
100%, 10−15 min ammonium formate buffer 0% to 100%, 15−18 min
100% ammonium formate buffer.
3-(Prop-2-ynyloxy)-2,2-bis((prop-2-ynyloxy)methyl)propan-1-ol
(35). An aqueous solution of NaOH (40 wt %, 10 mL) was added
to a solution of pentaerythritol (2.00 g, 14.7 mmol) in 15 mL of
dimethylsulfoxide (DMSO). The solution was stirred at rt for 30 min.
Propargyl bromide (97%, 9.8 mL, 110 mmol) was then added, and the
solution was kept at rt for an additional 10 h. The reaction mixture was
then poured into 150 mL of EtOAc and washed with H2O (50 mL ×
2) as well as brine (50 mL). The organic layer was dried by Na2SO4
and filtered. The filtrate was concentrated, and the residue was purified
by FC (EtOAc/hexane = 1/4) to give 2.29 g of yellowish oil 35 (yield:
1
62%). H NMR (200 MHz, CDCl3) δ: 4.13 (d, 6H, J = 2.4 Hz), 3.69
(d, 2H, J = 6.4 Hz), 3.56 (s, 6H), 2.43 (t, 3H, J = 2.4 Hz).
11,11-Bis((prop-2-ynyloxy)methyl)-3,6,9,13-tetraoxahexadec-15-
ynyl 4-Methylbenzenesulfonate (36). NaH (60% in mineral oil,
0.120 g, 3.0 mmol) was placed in a two-neck flask and washed with
hexane. Six mL of DMF was added to form a suspension. A solution of
35 (0.500 g, 2.0 mmol) in 4 mL of DMF was added dropwise at 0 °C.
After stirring at rt for 30 min, the mixture was cooled to 0 °C, and
a solution of triethylene glycol di(p-toluenesulfonate) (1.38 g,
3.0 mmol) in 3 mL of DMF was added dropwise. After stirred at rt
overnight, the mixture was poured into 50 mL cold satd NH4Cl and
extracted with DCM (30 mL × 2). The organic layer was washed with
H2O (20 mL) and brine (20 mL), dried over Na2SO4, concentrated,
and purified by FC (EtOAc/hexane = 3/7) to give 0.501 g colorless oil
36 (yield: 47%). 1H NMR (200 MHz, CDCl3) δ: 7.81 (d, 2H, J = 8.4
Hz), 7.35 (d, 2H, J = 8.4 Hz), 4.11−4.20 (m, 8H), 3.71 (t, 2H, J = 4.8
Hz), 3.58−3.60 (m, 8H), 3.52 (s, 6H), 3.45 (s, 2H), 2.46 (s, 3H), 2.41
(t, 3H, J = 2.4 Hz).
1-Fluoro-11,11-bis((prop-2-ynyloxy)methyl)-3,6,9,13-tetraoxa-
hexadec-15-yne (37). A mixture of 36 (0.200 g, 0.37 mmol) and
TBAF (1.12 mL, 1.0 M in THF) in 4 mL of THF was stirred at 70 °C
overnight. The reaction mixture was evaporated in vacuo, and the
residue was purified by FC (EtOAc/hexane = 3/7) to give 0.122 g of
clear oil 37 (yield: 86%). 1H NMR (200 MHz, CDCl3) δ: 4.69 (t, 1H,
J = 4.2 Hz), 4.46 (t, 1H, J = 4.2 Hz), 4.13 (d, 6H, J = 2.4 Hz), 3.84 (t,
1H, J = 4.2 Hz), 3.67−3.71 (m, 5H), 3.59−3.64 (m, 4H), 3.54 (s, 6H),
3.47 (s, 2H), 2.41 (t, 3H, J = 2.4 Hz).
2-(2-(2-(3-(E)-(1-(2-(2-(2-(2-(5-(4-(tert-Butoxycarbonyl (methyl)-
amino)styryl)pyridin-2-yloxy)ethoxy)ethoxy)ethoxy)ethyl)-1H-1,2,3-
triazol-4-yl)methoxy-2,2-bis((E)-(1-(2-(2-(2-(2-(5-(4-(tert-
butoxycarbonyl(methyl)amino)styryl)pyridin-2-yloxy)ethoxy)-
ethoxy)ethoxy)ethyl)-1H-1,2,3-triazol-4-yl)methoxymethyl)-
propoxy)ethoxy)ethoxy)ethyl 4-Methylbenzenesulfonate (38). A
solution of 36 (0.0313 g, 0.058 mmol), 31 (0.0923 g, 0.175 mmol),
sodium ascorbate (0.0174 g, 0.088 mmol), and copper sulfate (CuSO4,
0.0028 g, 0.0175 mmol) in 2 mL of t-BuOH/H2O (v/v, 1/1) was
stirred at rt for 4 h. The reaction mixture was then poured into 10 mL
of EtOAc and washed with H2O (3 mL × 2) and brine (3 mL).
3. In Vitro Autoradiography of AD Brain Sections. Frozen
brains from confirmed CAA, AD, and control subjects were cut into
20 μm sections. The sections were incubated with the 18F labeled
tracer in 40% ethanol for 1 h. The sections were then dipped in
saturated Li2CO3 in 40% ethanol (2 min wash, twice) and washed with
40% ethanol (2 min wash, once), followed by rinsing with water for
30 s. After drying, the sections were exposed to Kodak Biomax MR film
for 12−18 h. After the film was developed, the images were digitized.
4. Thioflavin S Staining. Brain sections were immersed in 10%
neutral buffered formalin for 1 h and then treated with 0.05% KMnO4
and bleached in 0.2% K2S2O5/0.2% oxalic acid in order to quench
autofluorescence. Quenched tissue sections were stained with 0.025%
thioflavin S in 40% ethanol for 3−5 min. The sections were
differentiated in 50% ethanol and viewed using a Nikon E800
fluorescence microscope with a CCD digital camera.
5. In Vivo Biodistribution Study in ICR Mice. To test [18F]8a−c
as PET imaging agents for cerebral amyloid angiopathy, we
first tested the biodistribution of these tracers in normal ICR mice
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(20−25 g). A group of 5−6 mice were used for each time point of the
biodistribution studies. After the mice were put under anesthesia with
isoflurane (2−3%), 0.15 mL of saline solution containing 925 KBq
(25 μCi) of the tracer was injected via the lateral tail vein. The mice
were sacrificed at 2 and 30 min postinjection by cardiac excision while
under isoflurane anesthesia. The organs of interest were removed,
weighed, and the radioactivity was counted with a γ counter (Packard
Cobra). The percent dose per gram was calculated by a comparison
of the tissue activity counts to counts of 1% of the initial dose. The initial
dose was measured by aliquots of the injected material diluted 100 times
and measured at the same time (0.5 min/sample, 80% efficiency).
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ASSOCIATED CONTENT
* Supporting Information
■
S
Method for in vitro binding assay and HPLC profiles of final
tested compounds. This material is available free of charge via
the Internet at http://pubs.acs.org.
(13) Jack, C. R. Jr.; Wiste, H. J.; Vemuri, P.; Weigand, S. D.; Senjem,
M. L.; Zeng, G.; Bernstein, M. A.; Gunter, J. L.; Pankratz, V. S.; Aisen,
P. S.; Weiner, M. W.; Petersen, R. C.; Shaw, L. M.; Trojanowski, J. Q.;
Knopman, D. S. Brain beta-amyloid measures and magnetic resonance
imaging atrophy both predict time-to-progression from mild cognitive
impairment to Alzheimer’s disease. Brain 2010, 133, 3336−3348.
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W.; Mathis, C.; Blennow, K.; Barakos, J.; Okello, A.; Rodriguez
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Shaw, L.; Saykin, A.; Morris, J.; Cairns, N.; Beckett, L.; Toga, A.;
Green, R.; Walter, S.; Soares, H.; Snyder, P.; Siemers, E.; Potter, W.;
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C. A.; Price, J. C.; Tsopelas, N. D.; Lopresti, B. J.; Ziolko, S.; Bi, W.;
Paljug, W. R.; Debnath, M. L.; Hope, C. E.; Isanski, B. A.; Hamilton,
R. L.; Dekosky, S. T. Post-mortem correlates of in vivo PiB-PET
amyloid imaging in a typical case of Alzheimer’s disease. Brain 2008,
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(17) Mok, V.; Leung, E.; Chu, W.; Chen, S.; Wong, A.; Xiong, Y.;
Lam, W.; Ho, C.; Wong, K. Pittsburgh compound B binding in
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(18) Ly, J.; Donnan, G.; Villemagne, V.; Zavala, J.; Ma, H.; O’Keefe,
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AUTHOR INFORMATION
Corresponding Author
*Phone: (215) 662-3096. Fax: (215) 349-5035. E-mail:
kunghf@gmail.com. Address: Hank F. Kung, Ph.D., 3700
Market Street, Suite 305, Department of Radiology, University
of Pennsylvania School of Medicine, Philadelphia, PA 19104.
■
ACKNOWLEDGMENTS
■
This work was supported by grants from the National Institutes
of Health (RO1-AG-022559 (H.F.K.) and R43AG032206
(D.S.)) and Avid Radiopharmaceuticals Inc. We thank Dr.
Carita Huang for editing and reviewing this manuscript. The
authors thank Dr. Nick Bryan for his encouragement and
helpful discussion.
ABBREVIATIONS USED
■
AD, Alzheimer’s disease; Aβ, β-amyloid; CAA, cerebral amyloid
angiopathy; APP, β-amyloid precursor protein; PET, positron
emission tomography; PIB, Pittsburgh compound B; SB-13,
4-N-methylamino-4′-hydroxystilbene; IMPY, 6-[iodo-2-(4′-
N,N-dimethylamino)-phenylimidazo[1,2-a]pyridine; [18F]AV-
1, BAY-94−9172, [18F]florbetaben f 18; [18F]AV-45, [18F]-
florbetapir f 18; [18F]FPIB, GE067, [18F]flutemetamol f 18;
[18F]AZD4694, 2-(2-([18F]fluoro)-6-methylaminopyridin-3-
yl)benzofuran-5-ol
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