Curcumin and dehydrozingerone derivatives: Synthesis, radiolabeling, and evaluation for β-amyloid plaque imaging

Article abstract of DOI:10.1021/jm0607193

Alzheimer's disease (AD) is pathologically characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain, and thus, the in vivo imaging of plaques and tangles would be beneficial for the early diagnosis of AD. It has been s

Full text of DOI:10.1021/jm0607193

J. Med. Chem. 2006, 49, 6111-6119
6111
Curcumin and Dehydrozingerone Derivatives: Synthesis, Radiolabeling, and Evaluation for
â-Amyloid Plaque Imaging†
Eun Kyoung Ryu, Yearn Seong Choe,* Kyung-Han Lee, Yong Choi, and Byung-Tae Kim
Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan UniVersity School of Medicine, 50 Ilwon-dong, Kangnam-ku,
Seoul 135-710, Korea
ReceiVed June 15, 2006
Alzheimer’s disease (AD) is pathologically characterized by the accumulation of amyloid plaques and
neurofibrillary tangles in the brain, and thus, the in vivo imaging of plaques and tangles would be beneficial
for the early diagnosis of AD. It has been suggested that 5-hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)-
1,4,6-heptatrien-3-one (curcumin) may be responsible for low age-adjusted prevalence of AD in India. In
the present study, eight novel derivatives of curcumin and 4-(4-hydroxy-3-methoxyphenyl)-3-buten-2-one
(dehydrozingerone) were synthesized and their binding affinities for â-amyloid (Aâ) aggregates were
measured. Of these ligands, fluoropropyl-substituted curcumin (8) showed the highest binding affinity (Ki
) 0.07 nM), and therefore, 8 was radiolabeled and evaluated as a potential probe for Aâ plaque imaging.
Partition coefficient measurement and biodistribution in normal mice demonstrated that [18F]8 has a suitable
lipophilicity and reasonable initial brain uptake. Metabolism studies also indicated that [18F]8 is metabolically
stable in the brain. These results suggest that [18F]8 is a suitable radioligand for Aâ plaque imaging.
Introduction
uptake; diazo groups and a biphenyl group were replaced by
vinyl groups and a phenyl group, respectively, in 1,4-bis(3-
hydroxycarbonyl-4-hydroxyphenylethenyl)benzene (X-34, Ki )
17.8 nM),4,13 1-bromo-2,5-bis(3-hydroxycarbonyl-4-hydroxy)-
styrylbenzene (BSB, Ki ) 400 nM),14 1-iodo-2,5-bis(3-hydroxy-
carbonyl-4-hydroxy)styrylbenzene (ISB, Kd ) 0.08 nM), and
1-iodo-2,5-bis(3-hydroxycarbonyl-4-methoxy)styrylbenzene (IM-
SB, Ki ) 0.17 nM; Figure 1).15 Radioiodine-labeled ISB and
IMSB showed lower initial brain uptakes in normal mice (0.27%
ID/organ and 0.14% ID/organ at 5 min after injection) than
radioiodinated thioflavin-T derivatives (0.6-3.5% ID/organ at
2 min), despite their potent binding affinities for Aâ ag-
gregates.15 This may be because that the carboxylic acids of
CG derivatives would be mostly ionized in the physiological
pH range, which would reduce their abilities to cross the BBB.
A neutral and lipophilic fluorescent dye, 2-(1-{6-[dimethyl-
amino]-2-naphthyl}ethylidene)malononitrile (DDNP) was also
modified for 18F labeling. A fluoromethyl derivative of DDNP
(FDDNP) was found to have a Kd of 0.12 nM for high binding
sites on Aâ aggregates and a Kd of 1.86 nM for low binding
sites. [18F]FDDNP was found to easily traverse the BBB due
to its high lipophilicity (log P ) 3.92). This radioligand was
found to label both senile plaques and neurofibrillary tangles
in the brains of AD patients with positron emission tomography
(PET).16,17
A charged molecule, thioflavin-T, was structurally modified
to improve its brain permeability;4,18,19 the neutral benzothiazole
derivatives obtained include 2-[4′-(dimethylamino)phenyl]-6-
iodobenzothiazole (TZDM, Ki ) 1.9 nM),15 2-(4′-dimethylami-
nophenyl)-6-iodobenzoxazole (IBOX, Ki ) 0.8 nM),20 6-iodo-
2-(4′-(dimethylamino)-)phenyl-imidazo[1,2-a]pyridine (IMPY,
Ki ) 15 nM),21 and 2-(4′-(methylamino)phenyl-6-hydroxyben-
zothiazole (6-OH-BTA-1, Ki ) 4.3 nM; Figure 1),22 However,
although [125I]TZDM and [125I]IBOX labeled Aâ in postmortem
AD brain sections, they showed slow washout from normal
mouse brain.15,20 Radioiodine-labeled benzofuran derivatives
also showed slow radioactivity washout from normal mouse
brain, indicating a high level of nonspecific binding in vivo.23
However, [125I]IMPY showed good initial brain uptake (2.88%
Alzheimer’s disease (AD)a is a progressive neurodegenerative
disorder and a leading cause of dementia. AD is characterized
by abundant senile plaques composed of Aâ peptides and
numerous neurofibrillary tangles formed from filaments of
highly phosphorylated tau proteins, which are invariably
observed in the postmortem brain tissues of AD patients.1-3
Therefore, the monitoring of Aâ plaques and neurofibrillary
tangles may be beneficial for the diagnosis, staging, and
treatment of AD.
Many specific ligands have been developed for the imaging
of Aâ plaques. These are based on fluorescent dyes that are
used to stain Aâ plaques and neurofibrillary tangles in vitro
and include highly conjugated symmetric compounds, such as
Congo red (CR) and chrysamine-G (CG), and a smaller
molecule, such as thioflavin-T (Figure 1).4 However, radioio-
dine-labeled CR has low brain uptake, probably because of the
hydrophilic nature of its sulfonate groups.5 The more lipophilic
CG has been labeled with 125I or 99mTc-monoamine-monoa-
mide bisthiol (MAMA), but studies showed low brain uptake
in rodents.6-8 Lansbury and co-workers synthesized the posi-
tively charged 99mTc(bipyridyl)(t-butylisonitrile)4 derivatives of
CR and CG, and found that they had Kd values for Aâ(1-40)
comparable to those of CR for insulin amyloid fibrils and of
CG for Aâ(10-43).9 This group further prepared neutral Re-
(dO)-MAMA-CR and CG complexes and a Tc(dO)-
MAMA-CR complex. The Re complexes showed affinities for
Aâ(40) comparable to those of CR and CG and stained amyloid
plaques in AD brain sections.10 However, the complexes may
exceed the physicochemical and molecular weight limitations
(700 Daltons) imposed by the blood-brain barrier (BBB).4,11,12
In other studies, CG was further modified to increase brain
* Corresponding author. Tel.: +82-2-3410-2623. Fax: +82-2-3410-
2639. E-mail: ysnm.choe@samsung.com.
† Presented in part at the International Chemical Congress of Pacific Basin
Societies, Honolulu, HI, December 15-20, 2005.
a Abbreviations: AD, Alzheimer’s disease; Aâ, â-amyloid; BBB, blood-
brain barrier; PET, positron emission tomography; SPECT, single photon
emission computed tomography.
10.1021/jm0607193 CCC: $33.50 © 2006 American Chemical Society
Published on Web 09/14/2006

6112 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Ryu et al.
Figure 1. Chemical structures of CR, CG, styrylbenzene derivatives, FDDNP, thioflavin-T derivatives, and stilbene derivative.
Scheme 1a
ID/organ at 2 min) and rapid washout from normal mouse
brain,21 and labeled regions containing Aâ in transgenic PSAPP
mouse brain sections and also in postmortem AD brain
sections.24,25 [11C]6-OH-BTA-1 (PIB), a benzothiazole-aniline
derivative, was also found to have high initial uptake and rapid
clearance from normal mouse and baboon brains,22 and human
trials with this radioligand showed high uptake in brains of AD
patients and significant retention in frontal and temporoparietal
cortex, the anterior and posterior cingulated cortex, and the
striatum, which is consistent with the known pattern of Aâ
plaque distribution in the AD brain.4,26,27
a Reagents and conditions: (a) acetone, 2.5 M NaOH, rt, 24 h, 54%.
In the present study, curcumin and dehydrozingerone deriva-
tives were synthesized and evaluated in vitro and in vivo as
Aâ plaque imaging probes for PET or single photon emission
computed tomography (SPECT).
Stilbene derivatives were also found to have good binding
affinities for Aâ aggregates in vitro (Ki ) 1.2-151 nM). In
particular, 11C-labeled 4-N-methylamino-4′-hydroxystilbene (SB-
13 (Figure 1), Ki ) 6.0 nM) displayed moderate lipophilicity
(log P ) 2.36), high initial brain uptake in the normal rat cortex
(1.51% ID/g at 2 min), and rapid washout (0.42% ID/g at 30
min). This radioligand also showed specific labeling of Aâ
plaques in brain sections from transgenic (TgCRDN8) mice.28
Results and Discussion
Chemistry. The syntheses of dehydrozingerone and curcumin
derivatives are shown in Schemes 1-4. Dehydrozingerone
derivatives, 1-3, were prepared by aldol condensations of the
vanillin derivatives and acetone in the presence of 2.5 M NaOH
(Schemes 1 and 2).36 Recrystallization from ethanol and water
yielded orange-colored products. Fluoroalkyl derivatives of
dehydrozingerone, 2 and 3, were prepared as in Scheme 2.
Compounds 9 and 10 were prepared in high yields from the
O-alkylation of vanillin with the corresponding dibromoalkanes
in the presence of K2CO3. The bromo groups of 9 and 10 were
converted into tosyl groups, as in 11 and 12, using silver
p-toluenesulfonate under reflux overnight, and these were further
substituted with fluorine atoms using n-Bu4NF to give 13 and
14. Aldol condensation of the resulting aldehyde and acetone,
followed by dehydration, afforded the dehydrozingerone deriva-
tives 2 and 3.
Aldol condensation of acetylacetone-boron complex and
vanillin derivatives is a key step in acetylation of the dehy-
drozingerone in ligands 4-6.37 Keto-enol compounds (4, 5, 6,
15, and 16) were synthesized by reacting the corresponding
aldehydes with 2 equiv of acetylacetone-boron complex.
Recrystallization from ethanol and water gave products that were
visualized by fluorescence and UV illumination.
5-Hydroxy-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,4,6-hep-
tatrien-3-one (curcumin) has been extensively studied for its
anticancer, antioxidant, and anti-inflammatory activities.29-31
Moreover, it has also been reported that the age-adjusted
prevalence of AD patients in India is 4.4-fold less than that in
the U.S.A.,32 and it was suggested that this may be explained
by the fact that curcumin, a major ingredient of the curry spice
turmeric, is used as a food preservative and herbal medicine in
India.33 Moreover, it has a favorable toxicity profile in mice
and was found to cause no adverse effects in cancer patients
during clinical studies.29,33 In addition, curcumin has been
reported to have favorable brain permeability, and satisfactory
Aâ plaque binding properties have been predicted from the
fluorescence staining of Aâ plaques in brain sections from
APPsw transgenic mice administered curcumin by injection or
in diet.34 4-(4-Hydroxy-3-methoxyphenyl)-3-buten-2-one (de-
hydrozingerone), a partial structure of curcumin, is also known
to have antioxidant properties.35
Curcumin derivatives, 7, 8, and 17 were synthesized by
coupling keto-enol compounds and the corresponding vanillin

Curcumin and Dehydrozingerone DerViatiVes
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20 6113
Scheme 2a
a Reagents and conditions: (a) Br(CH2)nBr, K2CO3, DMF, 80 °C, 1 h, 65-99%; (b) AgOTs, CH3CN, reflux, overnight, 66-85%; (c) n-Bu4NF, THF,
reflux, 4 h, 74-91%; (d) acetone, 2.5 M NaOH, rt, 24 h, 68-83%; (e) 2,4-pentanedione, B2O3, (n-BuO)3B, ethyl acetate, 80 °C, 30 min, n-BuNH2, 100 °C,
30 min, 1 N HCl, 50 °C, 30 min, 48-53%.
Scheme 3a
a Reagents and conditions: (a) 2,4-pentanedione, B2O3, (n-BuO)3B, ethyl acetate, 80 °C, 30 min, n-BuNH2, 100 °C; 30 min, 1 N HCl, 50 °C, 30 min,
59-85%; (b) vanillin, B2O3, (n-BuO)3B, ethyl acetate, 80 °C, piperidine, 80 °C, 30 min, 0.4 N HCl, 50 °C, 30 min, 50-58%.
Scheme 4a
a Reagents and conditions: (a) 15, B2O3, (n-BuO)3B, ethyl acetate, 80 °C, piperidine, 80 °C, 30 min, 0.4 N HCl, 50 °C, 30 min, 37.6%; (b) AgOTs,
CH3CN, reflux, overnight, 62%; (c) n-Bu4NF, THF, reflux, 4 h, 23%; (d) 15, B2O3, (n-BuO)3B, ethyl acetate, 80 °C, piperidine, 80 °C, 30 min, 0.4 N HCl,
50 °C, 30 min, 54%.
Scheme 5a
derivative-boron complexes in the presence of piperidine,
which was found to give better yields than when n-butylamine
was used (Schemes 3 and 4).37 Direct iodination of curcumin
to produce 7 yielded a side product that probably resulted from
iodination at the C4 position. To prepare the radioligands ([125I]-
6 and [125I]7) with high specific activity, bromo compounds
were used instead of iodo compounds to synthesize the
precursors shown in Schemes 5 and 6. Bromo groups were
converted to the tributylstannyl precursors, 20 and 21, using
bis(tributyltin) in the presence of Pd(PPh3)4.
The fluoropropyl derivative of curcumin was synthesized
using two different methods, as shown in Scheme 4. The tosylate
precursor 19 was prepared by coupling 10 and the 15-boron
complex, and this was followed by substituting the bromo group
with a tosyl group. However, the subsequent substitution with
n-Bu4NF to give ligand 8 was only achieved in a yield of 23%.
As an alternative pathway, the hydroxyl group of 18 was
protected as an acetyl ester with acetic anhydride in pyridine
in high yield, and this was followed by substitution of the bromo
group with a tosyl group. However, fluorination of the tosylate
a Reagents and conditions: (a) Pd(PPh3)4, (SnBu3)2, toluene, 110 °C,
overnight, 20%; (b) Na125I, 1 N HCl, 3% H2O2, ethanol, rt, 10 min, 10-
14%.
precursor also had a low yield (13%), and therefore, 14 was
coupled with 15 to prepare the product 8 (32%).
Radiolabeling. [125I]6 and [125I]7 were prepared by radio-
iododestannylation of the corresponding tributylstannyl precur-

6114 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Ryu et al.
Scheme 6a
a Reagents and conditions: (a) Pd(PPh3)4, (SnBu3)2, toluene, 110 °C, overnight, 19%; (b) Na125I, 1 N HCl, 3% H2O2, rt, 10 min, 35-40%.
Scheme 7a
a Reagents and conditions: (a) n-Bu4N18F, CH3CN, 105 °C, 10 min, >85%; (b) 15, B2O3, (n-BuO)3B, piperidine, ethyl acetate, 105 °C, 15 min, 0.4 N
HCl, 90 °C, 5 min, 16-25%; (c) n-Bu4N18F, THF, 95 °C, 20 min, 0-17%.
Table 1. Ki (nM) of Ligands for Aâ(1-40) Aggregates
sors, 20 and 21, respectively, using Na[125I]I in the presence of
ligand
[
125I]IMPY
[
125I]IMSB
3% H2O2 at room temperature for 10 min (Schemes 5 and 6).
The reaction was quenched with saturated NaHSO3, and the
mixture was purified by HPLC. Decay-corrected radiochemical
yields of [125I]6 and [125I]7 were 10-14% and 35-40% and
specific activities were 72.6 GBq/µmol and 87.3 GBq/µmol,
respectively.
Radioligand [18F]8 was synthesized as shown in Scheme 7.
When precursor 19 was used for 18F-labeling, [18F]8 was
synthesized in variable yields (0-17%). As an alternative
pathway, nucleophilic [18F]fluorination of acetyl protected
tosylate precursor also gave the product in low yield (13%) and
with low effective specific activity. Therefore, [18F]14, which
was prepared from 12 and n-Bu4N[18F]F (>85%), was used for
the preparation of [18F]8. The subsequent aldol condensation
with acetylacetone-boron complex, followed by HPLC puri-
fication, gave the product in overall decay-corrected radio-
chemical yield of 16-25% and with an effective specific activity
of 37.6 GBq/µmol.
Binding Assays. In vitro binding assays using Aâ(1-40)
aggregates were performed as described in the literature,15,18
and radiolabeled standards, [125I]IMSB and [125I]IMPY, were
prepared as previously described.15,21 Their Kd values for binding
to Aâ(1-40) aggregates were similar to those reported, that is,
0.18 nM versus 0.13 nM (reported) for [125I]IMSB and 17.3
nM versus 5.4 nM (reported value obtained using the gray matter
homogenates of AD brains) for [125I]IMPY.15,25 The binding
affinities of ligands described here were determined using Aâ
aggregates and the radiolabeled standards, [125I]IMSB or [125I]-
IMPY, depending on the structures of the ligands tested, and
nonspecific binding was measured in the presence of CG or
thioflavin-T (Table 1). [125I]IMSB and CG were used for
curcumin derivatives, but [125I]IMPY and thioflavin-T were used
for dehydrozingerone derivatives.
Dehydrozingerone derivatives, including 1-6, showed lower
affinities for Aâ aggregates than curcumin derivatives. In
particular, 2-fluoroalkyl ligands, 2-5, exhibited Ki values higher
than 200 nM for the Aâ aggregates. On the other hand, the
iodine-substituted ligands, 1 and 6, showed reasonable Ki values
(36.6 nM and 24.9 nM, respectively) for Aâ aggregates.
Dehydrozingerone was found to have similar affinities for Aâ
aggregates upon using [125I]IMPY or [125I]IMSB (55.9 nM vs
54.2 nM, respectively) as the radiolabeled standards, and ligand
dehydrozingerone
1
2
3
55.9 ( 4.0
36.6 ( 1.2
232.7 ( 16
839.2
54.24
19.97 ( 2.7
4
5
6
CG
958.1 ( 93
316.3 ( 69
24.9 ( 0.9
0.16 ( 0.04
0.20 ( 0.06
9.37 ( 1.0
0.07 ( 0.01
curcumin
7
8
1 competed better with [125I]IMSB binding than [125I]IMPY
binding to Aâ aggregates (19.97 nM vs 36.6 nM).
CG showed a similar Ki value (0.16 nM) to that reported (0.14
nM) for binding to Aâ(1-40) aggregates.15 Curcumin exhibited
potent binding affinity for Aâ(1-40) aggregates (Ki ) 0.20 nM),
but the introduction of an iodine into its phenyl ring (7)
significantly decreased its binding affinity by 47-fold, whereas
O-fluoropropylation of its hydroxyl group (8) increased binding
affinity 2.9-fold, giving a Ki value of 0.07 nM. These results
demonstrate that a highly conjugated dimeric structure is
required for high Aâ aggregate binding affinity.
Partition Coefficient Measurement. The partition coef-
ficients of some ligands were measured using radiolabeled
forms, that is, [125I]6, [125I]7, and [18F]8 had log Po/w values of
1.35, 0.94, and 1.84, respectively, predicting a favorable brain
permeability for all three. Of these radioligands, [18F]8 is most
preferable for in vivo evaluations because of its high binding
affinity and suitable lipophilicity.
Metabolism Studies. Radioligand [18F]8 was analyzed using
mouse brain and blood and remained intact in the brain during
the time of the study (60 min), whereas an unidentified polar
metabolite appeared in blood samples within 2 min after
injection and [18F]8 was completely converted into the metabo-
lite at 60 min (Figure 2). This polar radioactive metabolite did
not seem to cross the BBB because of its high polarity. These
results demonstrate that [18F]8 is metabolically stable in the
mouse brain after being taken up.
Biodistribution. Radioligands ([125I]6 and [18F]8) were
evaluated in normal mice to assess their ability to cross the BBB.
Radioligand [125I]6 showed a similar initial brain uptake (0.69%
ID/g) to [18F]8, but lower radioactivity accumulation in liver,

Curcumin and Dehydrozingerone DerViatiVes
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20 6115
Table 3. Biodistribution of [18F]8 (A) and of [18F]8 Co-Injected with
Piperine (B) in Normal Mice
(A)
organ
2 min
30 min
60 min
blood
heart
lung
7.34 ( 1.29
4.05 ( 0.40
30.91 ( 4.43
38.99 ( 2.80
16.32 ( 1.99
8.64 ( 0.35
0.89 ( 0.12
3.23 ( 0.29
0.52 ( 0.08
1.24 ( 0.01
0.57 ( 0.08
7.23 ( 0.34
41.06 ( 5.41
42.94 ( 1.19
2.71 ( 1.11
0.28 ( 0.16
2.68 ( 0.11
0.11 ( 0.03
0.61 ( 0.45
0.64 ( 0.08
10.55 ( 1.73
37.06 ( 6.24
36.05 ( 9.45
2.07 ( 0.58
0.27 ( 0.09
3.43 ( 0.48
0.11 ( 0.02
liver
spleen
kidney
muscle
bone
brain
(B)
30 min
organ
2 min
60 min
120 min
blood
heart
lung
11.18 ( 3.41
5.24 ( 1.10
0.90 ( 0.05
0.70 ( 0.06
0.82 ( 0.11
0.57 ( 0.03
7.88 ( 0.62
0.75 ( 0.16
0.38 ( 0.08
3.48 ( 1.26
34.26 ( 6.81 13.61 ( 1.33
Figure 2. Metabolism of [18F]8 in mouse brain and blood. Data are
presented as % parent radioligand in brain (b) and in blood (9) as
determined by radio-TLC as a function of time (2, 30, and 60 min).
liver
35.39 ( 3.93 43.13 ( 4.97 37.02 ( 4.77 18.53 ( 7.85
28.68 ( 7.26 36.25 ( 8.36 41.07 ( 1.66 21.49 ( 15.0
8.69 ( 1.04
1.12 ( 0.18
0.77 ( 0.10
spleen
kidney
muscle
brain
2.81 ( 0.73
0.36 ( 0.07
0.14 ( 0.02
1.70 ( 0.41
0.28 ( 0.03
0.09 ( 0.02
0.99 ( 0.22
0.20 ( 0.12
0.07 ( 0.02
Table 2. Biodistribution of [125I]6 in Normal Mice
organ
2 min
30 min
60 min
120 min
significantly increased if the solubility of piperine can be
enhanced in an injection solution.
blood
thyroid
heart
lung
liver
spleen
kidney
muscle
brain
17.92 ( 7.65
2.05 ( 0.47
0.87 ( 0.05
0.64 ( 0.09
4.60 ( 0.70 10.25 ( 1.44 23.18 ( 4.05 27.63 ( 13.0
An initial brain uptake higher than 0.5% ID/organ at 2 min
after injection is preferred for Aâ plaque imaging probes, and
this initial uptake should remain at less than 30% at 30 min in
normal mouse brain because of the absence of Aâ plaques.21,24
Although the initial brain uptakes of [125I]6 and [18F]8 fall
slightly short of these criteria (0.24-0.34% ID/organ at 2 min),
these radioligands showed rapid washout at 30 min. Thus, taken
together with other in vitro and in vivo results, [125I]6 may be
unsuitable for Aâ plaque imaging because of its severe in vivo
deiodination. In contrast, [18F]8 has promise as an Aâ plaque
imaging probe because it is metabolically stable in the brain
and, therefore, it would strongly bind to Aâ plaques due to its
excellent in vitro binding affinity (Ki ) 0.07 nM) once taken
up by the brain. Moreover, the fluorescence of curcumin
derivatives aids locating Aâ plaques in vitro and, thus, offers
an additional advantage.
5.23 ( 0.87
14.78 ( 9.86
18.28 ( 0.60
4.61 ( 1.31
11.82 ( 1.37
1.35 ( 0.13
0.69 ( 0.08
0.72 ( 0.13
1.30 ( 0.35
4.64 ( 1.23
1.93 ( 0.46
9.63 ( 1.17
0.54 ( 0.14
0.11 ( 0.05
0.31 ( 0.02
0.57 ( 0.06
2.85 ( 0.51
1.81 ( 0.44
2.34 ( 0.34
0.26 ( 0.07
0.05 ( 0.01
0.20 ( 0.05
0.57 ( 0.20
2.53 ( 0.42
1.37 ( 0.40
1.03 ( 0.10
0.13 ( 0.04
0.02 ( 0.01
spleen, and lungs (Table 2). The high thyroid uptake of [125I]6
indicated that this radioligand was deiodinated in vivo (4.6%
ID/g at 2 min, 10.3% ID/g at 30 min, and 23.2% ID/g at 60
min).
Biodistribution studies on [18F]8 demonstrated that high and
persistent radioactivity accumulation occurred in the liver and
spleen and that its lung uptake decreased with time. Brain uptake
of [18F]8 was 0.52% ID/g at 2 min postinjection, and its
radioactivity was rapidly washed out from the brain at 30 min
(0.11% ID/g) (Table 3A). In addition, [18F]8 did not appear to
undergo metabolic defluorination due to a constant level of bone
uptake with time (2.7-3.4% ID/g). However, despite its suitable
lipophilicity and reasonable molecular size (mol wt 428.45),
its initial brain uptake was relatively low, which may be
explained by its rapid metabolism in the liver and in the
intestinal wall, like curcumin.38 Piperine, a major component
of black pepper, is a known inhibitor of hepatic and intestinal
glucuronidation and is also shown to increase the bioavailability
of curcumin. This effect of piperine on the pharmacokinetics
of curcumin has been shown to be much greater in humans than
in rats; in humans, curcumin bioavailability was increased by
2000% at 45 min after co-administering curcumin orally with
piperine, whereas in rats, curcumin bioavailability was increased
by only 154% between 1 and 2 h after co-administration.38
Therefore, the effect of piperine on the uptake of [18F]8 was
assessed after co-injecting [18F]8 with piperine. As shown in
Table 3B, initial brain uptake (0.77% ID/g at 2 min) was
increased by 48% (p value < 0.05) relative to that without
piperine, although other organ uptakes were similar to those
without piperine (Table 3A,B). However, the effect of piperine
was limited, possibly due to its poor solubility in 10% ethanol-
saline. Therefore, the initial brain uptake of [18F]8 would be
Conclusion
Eight novel curcumin and dehydrozingerone derivatives were
synthesized and evaluated in vitro and in vivo. The curcumin
derivatives showed higher binding affinities for Aâ(1-40)
aggregates than dehydrozingerone derivatives, with 8 being the
most potent ligand. Moreover, [18F]8 showed suitable lipophi-
licity, reasonable initial brain uptake, and metabolic stability
in the normal mouse brain. These results suggest that [18F]8 is
a promising candidate for Aâ plaque imaging.
Experimental Section
Chemicals were purchased from Sigma-Aldrich (St. Louis, MO)
and CG from Merck Biosciences (San Diego, CA). Aâ(1-40)
peptide was obtained from Biosource, Inc. (Camarillo, CA), and
Na[125I]I from PerkinElmer Life and Analytical Sciences (Boston,
MA). Dehydrozingerone and curcumin were synthesized as de-
scribed in the literature.36,37 1H NMR spectra were obtained using
a Varian UnityInoVa 500NB (500 MHz) spectrometer (Palo Alto,
CA), and chemical shifts (δ) were reported in ppm downfield from
tetramethylsilane. Electron impact (EI) and fast atom bombardment
(FAB) mass spectra were obtained using a JMS-700 Mstation
instrument (JEOL, Ltd., Tokyo, Japan). Elemental analysis was
performed on a Flash EA 1112 (ThermoQuest CE Instruments,
Milan, Italy). Purification of radioligand was carried out on a HPLC

6116 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Ryu et al.
(Thermo Separation Products System, Fremont, CA) equipped with
a semipreparative column (YMC-Pack C18, 5 µ, 10 × 250 mm),
and eluant was simultaneously monitored using a UV detector (254
nm) and a NaI(T1) radioactivity detector. Radio-thin-layer chro-
matography (TLC) was performed on Merck F254 silica plates and
analyzed using a Bioscan scanner (Washington DC, U.S.A.).
[18F]Fluoride was produced using the 18O(p,n)18F reaction on a
PETtrace cyclotron (GE Healthcare, Uppsala, Sweden). Radioactiv-
ity was measured in a dose calibrator (Biodex Medical Systems,
Shirley, NY), and tissue radioactivity was measured in a Wallac
automated gamma counter (Boston, MA). All animal experiments
complied with the rules of the Samsung Medical Center Laboratory
Animal Care, which are based on NIH guidelines.
4-(2-Bromoethoxy)- and 4-(3-Bromopropoxy)-3-methoxyben-
zaldehyde (9 and 10). Vanillin (0.5 g, 3.29 mmol) and K2CO3
(0.64 g, 4.6 mmol) were added to 1,2-dibromoethane or 1,3-
dibromopropane (9.79 mmol) in DMF (20 mL). The reaction
mixture was then stirred at 80 °C for 1 h, cooled to 0 °C on an ice
bath, quenched with 1 N HCl, and extracted with ethyl acetate.
The organic layer was washed with water and dried over Na2SO4.
Flash column chromatography (2:1 hexanes-ethyl acetate) afforded
9 (550 mg, 65%) or 10 (890 mg, 99%) as white solids.
by flash column chromatography (3:1 hexanes-ethyl acetate) to
afford 13 (140 mg, 74%), a white solid, or 14 (184.6 mg, 91%), a
colorless oil.
4-(2-Fluoroethoxy)-3-methoxybenzaldehyde (13): mp 82.1-
1
84.2 °C; H NMR (CDCl3) δ 3.96 (s, 3H), 4.35-4.37 (m, 1H),
4.40-4.42 (m, 1H), 4.79-4.81 (m, 1H), 4.88-4.90 (m, 1H), 7.02
(d, J ) 8.0 Hz, 1H), 7.46 (d, J ) 8.0 Hz, 2H), 9.89 (s, 1H); MS
(EI) m/z 198 (M+); HRMS calcd for C10H11FO3, 198.0692; found,
198.0691. Anal. (C10H11FO3) C, H.
4-(3-Fluoropropoxy)-3-methoxybenzaldehyde (14): 1H NMR
(CDCl3) δ 2.22-2.32 (m, 2H), 3.93 (s, 3H), 4.25 (t, J ) 6.5 Hz,
2H), 4.63 (t, J ) 5.5 Hz, 1H), 4.72 (t, J ) 5.5 Hz, 1H), 7.00 (d, J
) 8.0 Hz, 1H), 7.42-7.45 (m, 2H), 9.86 (s, 1H); MS (EI) m/z 212
(M+); HRMS calcd for C11H13FO3, 212.0849; found, 212.0850.
4-(3-Methoxyphenyl)-3-buten-2-one Derivatives (1, 2, and 3).
5-Iodovanillin, 13, or 14 (1.64 mmol) was dissolved in acetone (1
mL) in a pressure tube (ACE glass, 13 × 102 mm). To this solution
was carefully added 2.5 M NaOH (1 mL), and the mixture was
stirred at room temperature for 24 h. This was then treated with 3
M HCl (5 mL) and then stirred until yellow crystals formed.
Products were filtered, washed with water, and then dried. The
products, 1 (280.4 mg, 54%), 2 (323.1 mg, 83%), or 3 (280.5 mg,
68%), were obtained as yellow solids after recrystallization from
ethanol and water.
4-(2-Bromoethoxy)-3-methoxybenzaldehyde (9): mp 71.4-
1
72.1 °C; H NMR (CDCl3) δ 3.71 (t, J ) 7.0 Hz, 2H), 3.96 (d, J
) 5.0 Hz, 3H), 4.43 (t, J ) 7.0 Hz, 2H), 7.00 (d, J ) 8.5 Hz, 1H),
7.46 (dd, J ) 5.8, 2.0 Hz, 2H), 9.89 (s, 1H); MS (EI) m/z 260
(M+, 81Br), 258 (M+, 79Br); HRMS calcd for C10H1181BrO3,
259.9872; found, 259.9875.
4-(3-Bromopropoxy)-3-methoxybenzaldehyde (10): mp 58.4-
59.9 °C; 1H NMR (CDCl3) δ 2.39-2.44 (m, 2H), 3.64 (t, J ) 6.5
Hz, 2H), 3.92 (s, 3H), 4.25 (t, J ) 6.0 Hz, 2H), 7.01 (d, J ) 8.0
Hz, 1H), 7.42-7.46 (m, 2H), 9.86 (s, 1H); MS (EI) m/z 274 (M+,
81Br), 272 (M+, 79Br); HRMS calcd for C11H1381BrO3, 274.0029;
found, 274.0006. Anal. (C11H13BrO3) C, H.
4-(4-Hydroxy-3-iodo-5-methoxyphenyl)-3-buten-2-one (1): mp
149.1-151.6 °C; 1H NMR (CD3OD) δ 2.36 (s, 3H), 3.92 (s, 3H),
6.66 (d, J ) 16.0 Hz, 1H), 7.23 (d, J ) 2.0 Hz, 1H), 7.51 (d, J )
16.0 Hz, 1H), 7.58 (d, J ) 1.5 Hz, 1H); MS (EI) m/z 318 (M+);
HRMS calcd for C11H11IO3, 317.9753; found, 317.9751. Anal.
(C11H11IO3) C, H.
4-[4-(2-Fluoroethoxy)-3-methoxyphenyl]-3-buten-2-one (2):
1
mp 109.6-113.9 °C; H NMR (CDCl3) δ 3.39 (s, 3H), 3.93 (s,
3H), 4.30 (t, J ) 4.5 Hz, 1H), 4.36 (t, J ) 4.5 Hz, 1H), 4.77 (t, J
) 4.5 Hz, 1H), 4.86 (t, J ) 4.5 Hz, 1H), 6.63 (d, J ) 16 Hz, 1H),
6.92 (d, J ) 8.5 Hz, 1H), 7.10-7.14 (m, 2H), 7.47 (d, J ) 16.0
Hz, 1H); MS (EI) m/z 238 (M+); HRMS calcd for C13H15FO3,
238.1005; found, 238.1001.
4-(2-Tosyloxyethoxy)- and 4-(3-Tosyloxypropoxy)-3-meth-
oxybenzaldehyde (11 and 12) and 5-Hydroxy-7-(4-hydroxy-3-
methoxyphenyl)-1-[3-methoxy-4-(3-tosyloxypropoxy)phenyl]-
1,4,6-heptatrien-3-one (19). To 9, 10, or 18 (2.93 mmol) in CH3CN
(15 mL) was added silver p-toluenesulfonate (2 g, 7.17 mmol), and
the reaction mixtures were stirred under reflux overnight. After
removing solvent in vacuo, the resulting residues were extracted
with CH2Cl2, washed with water, and dried over Na2SO4. Flash
column chromatography (3:1 hexanes-ethyl acetate) gave 11 (680
mg, 66%), 12 (910 mg, 85%), or 19 (1.1 g, 62%) as white solids.
4-(2-Tosyloxyethoxy)-3-methoxybenzaldehyde (11): mp 105.5-
4-[4-(3-Fluoropropoxy)-3-methoxyphenyl]-3-buten-2-one (3):
mp 73.7-75.2 °C; 1H NMR (CDCl3) δ 2.19-2.26 (m, 1H), 2.26-
2.39 (m, 1H), 2.39 (s, 3H), 3.92 (s, 3H), 4.21 (t, J ) 6.0 Hz, 2H),
4.64 (t, J ) 6.0 Hz, 1H), 4.73 (t, J ) 6.0 Hz, 1H), 6.62 (d, J )
16.0 Hz, 1H), 6.92 (d, J ) 8.5 Hz, 1H), 7.12 (td, J ) 8.5, 2.0 Hz,
2H), 7.48 (d, J ) 16.0 Hz, 1H); MS (EI) m/z 252 (M+); HRMS
calcd for C14H17FO3, 252.1162; found, 252.1163.
5-Hydroxy-1-(3-methoxyphenyl)-1,4-hexadien-3-one Deriva-
tives (4, 5, 6, 15, and 16). 2,4-Pentanedione (0.81 mL, 7.92 mmol)
and B2O3 (500 mg, 7.18 mmol) were dissolved in ethyl acetate (5
mL), and the solution was stirred at 80 °C for 30 min. To this
mixture was added an ethyl acetate solution (10 mL) of the vanillin
derivative (13, 14, 5-iodovanillin, vanillin, or 5-bromovanillin (3.6
mmol)) and (n-BuO)3B (0.4 mL, 1.48 mmol). After stirring for 30
min at 80 °C, n-butylamine (0.14 mL, 1.43 mmol) was added
dropwise to the mixtures, which were allowed to stir at 100 °C for
1 h. They were then treated with 1 N HCl (10 mL) at 50 °C and
stirred at the same temperature for 30 min. Reaction mixtures were
extracted with ethyl acetate, washed with water, and then dried
over Na2SO4. Flash column chromatography (2:1 hexanes-ethyl
acetate), followed by recrystallization from ethanol and water, gave
4 (534.8 mg, 53%), 5 (508.6 mg, 48%), 6 (1.1 g, 85%), 15 (607.2
mg, 72%), or 16 (665.1 mg, 59%) as yellow solids.
1
107.2 °C; H NMR (CDCl3) δ 2.45 (s, 3H), 3.92 (s, 3H), 4.32-
4.34 (m, 2H), 4.43-4.45 (m, 2H), 6.93 (d, J ) 8.0 Hz, 1H), 7.34
(d, J ) 8.0 Hz, 2H), 7.42-7.43 (m, 2H), 7.83 (d, J ) 8.5 Hz, 2H),
9.87 (s, 1H); MS (EI) m/z 350 (M+); HRMS calcd for C17H18O6S,
350.0824; found, 350.0825. Anal. (C17H18O6S) C, H.
4-(3-Tosyloxypropoxy)-3-methoxybenzaldehyde (12): mp 97.6-
1
98.2 °C; H NMR (CDCl3) δ 2.19-2.24 (m, 4H), 2.37 (s, 3H),
3.87 (s, 3H), 4.10 (t, J ) 6.0 Hz, 2H), 4.29 (t, J ) 6.0 Hz, 2H),
6.88 (d, J ) 8.0 Hz, 1H), 7.25 (d, J ) 5.0 Hz, 2H), 7.38-7.43 (m,
2H), 7.75 (dd, J ) 3.3, 2.0 Hz, 2H), 9.86 (s, 1H); MS (FAB) m/z
387 (M+ + Na); HRMS calcd for C18H20O6SNa, 387.0878; found,
387.0872. Anal. (C18H20O6S) C, H.
5-Hydroxy-7-(4-hydroxy-3-methoxyphenyl)-1-[3-methoxy-4-
(3-tosyloxypropoxy)phenyl]-1,4,6-heptatrien-3-one (19): 1H NMR
(CDCl3) δ 1.21-1.27 (m, 2H), 2.38 (s, 3H), 3.85 (s, 3H), 3.95 (s,
3H), 4.00-4.05 (m, 2H), 4.27-4.32 (m, 2H), 5.82 (s, 1H), 5.86
(s, 1H), 6.49 (dd, J ) 16.0, 5.5 Hz, 2H), 6.77 (d, J ) 13.5 Hz,
1H), 6.94 (d, J ) 8.0 Hz, 1H), 7.02-7.13 (m, 4H), 7.40 (d, J )
9.0 Hz, 2H), 7.59 (d, J ) 13.0 Hz, 2H), 7.76 (d, J ) 3.5 Hz, 2H);
MS (EI) m/z 580 (M+); HRMS calcd for C31H32O9S, 580.1767;
found, 580.1766.
4-(2-Fluoroethoxy)- and 4-(3-Fluoropropoxy)-3-methoxyben-
zaldehyde (13 and 14). Compound 11 or 12 (0.96 mmol) was
dissolved in THF (10 mL), and to this solution was added n-Bu4-
NF (1 M in THF, 6 mL, 6 mmol). Reaction mixtures were refluxed
for 4 h. After removing solvent in vacuo, products were purified
1-[4-(2-Fluoroethoxy)-3-methoxyphenyl]-5-hydroxy-1,4-hexa-
dien-3-one (4): mp 105.1-107.1 °C; 1H NMR (CDCl3) δ 2.18 (s,
3H), 3.93 (s, 3H), 4.30 (t, J ) 4.5 Hz, 1H), 4.52 (t, J ) 4.5 Hz,
1H), 4.76-4.77 (m, 1H), 4.85-4.87 (m, 1H), 5.66 (s, 2H), 6.37
(d, J ) 16.5 Hz, 1H), 6.91 (d, J ) 4.0 Hz, 1H), 7.10 (td, J ) 8.3,
2.0 Hz, 1H), 7.56 (d, J ) 15.5 Hz, 1H); MS (EI) m/z 280 (M+);
HRMS calcd for C15H17FO4, 280.1111; found, 280.1112. Anal.
(C15H17FO4) C, H.
1-[4-(3-Fluoropropoxy)-3-methoxyphenyl]-5-hydroxy-1,4-hexa-
1
dien-3-one (5): mp 70.0-71.2 °C; H NMR (CD3Cl) δ 2.18 (s,
3H), 2.22-2.24 (m, 1H), 2.27-2.30 (m, 1H), 3.92 (s, 1H), 4.21 (t,

Curcumin and Dehydrozingerone DerViatiVes
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20 6117
J ) 6.5 Hz, 2H), 4.64 (t, J ) 6.0 Hz, 1H), 4.73 (t, J ) 6.0 Hz,
1H), 5.66 (s, 2H), 6.36 (d, J ) 15.5 Hz, 1H), 6.91 (d, J ) 8.5 Hz,
1H), 7.06-7.12 (m, 2H), 7.56 (d, J ) 15.5 Hz, 1H); MS (EI) m/z
294 (M+); HRMS calcd for C16H19FO4, 294.1267; found, 294.1266.
5-Hydroxy-1-(4-hydroxy-3-iodo-5-methoxyphenyl)-1,4-hexa-
dien-3-one (6): mp 178.2-180.0 °C; 1H NMR (CDCl3) δ 2.16 (s,
3H), 3.94 (s, 3H), 5.63 (s, 1H), 6.30 (dd, J ) 15.5, 8.0 Hz, 2H),
6.96 (d, J ) 2.0 Hz, 1H), 7.43 (d, J ) 15.5 Hz, 2H), 7.52 (d, J )
1.5 Hz, 2H); MS (FAB) m/z 361 (M+ + H); HRMS calcd for
C13H14IO4, 360.9937; found, 360.9937. Anal. (C13H13IO4) C, H.
flash column chromatography (2:1 hexanes-ethyl acetate) to afford
8 (10 mg, 23%) as a yellow solid.
1-[4-(3-Fluoropropoxy)-3-methoxyphenyl]-5-hydroxy-7-(4-hy-
droxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (8): mp 92.6-
1
93.2 °C; H NMR (CDCl3) δ 2.22-2.33 (m, 2H), 3.91 (s, 3H),
3.94 (s, 3H), 4.20 (t, J ) 6.0 Hz, 2H), 4.62 (t, J ) 5.5 Hz, 1H),
4.72 (t, J ) 5.5 Hz, 1H), 5.81 (s, 1H), 6.47 (dd, J ) 15.5, 7.8 Hz,
2H), 6.93 (dd, J ) 20.0, 9.9 Hz, 2H), 7.02-7.12 (m, 4H), 7.59 (d,
J ) 15.5 Hz, 2H); MS (EI) m/z 428 (M+); HRMS calcd for C24H25-
FO6, 428.1635; found, 428.1638. Anal. (C24H25FO6) C, H.
1-[4-(3-Bromopropoxy)-3-methoxyphenyl]-5-hydroxy-7-(4-hy-
5-Hydroxy-1-(4-hydroxy-3-methoxyphenyl)-1,4-hexadien-3-
1
1
droxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (18): H NMR
one (15): mp 143.5-145.5 °C; H NMR (CDCl3) δ 2.15 (s, 3H),
(CDCl3) δ 2.36-2.41 (m, 2H), 3.62-3.71 (m, 2H), 3.76 (s, 3H),
3.80 (s, 3H), 4.20 (t, J ) 5.5 Hz, 2H), 5.87 (s, 1H), 5.89 (s, 1H),
6.48 (dd, J ) 15.8, 7.5 Hz, 2H), 6.87-6.94 (m, 2H), 7.02-7.26
(m, 2H), 7.59 (d, J ) 16.0 Hz, 2H); MS (EI) m/z 490 (M+, 81Br),
488 (M+, 79Br); HRMS calcd for C24H2581BrO6, 490.0818; found,
490.0792.
3.94 (s, 3H), 5.63 (s, 1H), 5.84 (s, 1H), 6.32 (d, J ) 16.0 Hz, 1H),
6.93 (d, J ) 15.5 Hz, 1H), 7.09 (d, J ) 10.5 Hz, 2H), 7.53 (d, J )
16.0 Hz, 1H); MS (EI) m/z 234 (M+); HRMS calcd for C13H14O4,
234.0892; found, 234.0891.
1-(3-Bromo-4-hydroxy-5-methoxyphenyl)-5-hydroxy-1,4-hexa-
1
dien-3-one (16): mp 158.8-161.4 °C; H NMR (CDCl3) δ 1.97
5-Hydroxy-1-(4-hydroxy-3-methoxy-5-tributylstannylphenyl)-
1,4-hexadien-3-one (20) and 5-Hydroxy-7-(4-hydroxy-3-meth-
oxyphenyl)-1-(4-hydroxy-3-methoxy-5-tributylstannylphenyl)-
1,4,6-heptatrien-3-one (21). A mixture of the bromo compounds
16 or 17 (0.37 mmol), bis(tributyltin) (1.1 mL, 2.18 mmol), and
Pd(Ph3P)4 (84.4 mg, 0.037 mmol) in toluene (10 mL) was stirred
at 110 °C overnight. At the end of the reactions, solvent was
removed in vacuo and the crude products were purified by flash
column chromatography (2:1 hexanes-ethyl acetate) to give 20
(38.7 mg, 20%) as an orange-colored oil or 21 (45 mg, 18%) as an
orange-colored solid.
5-Hydroxy-1-(4-hydroxy-3-methoxy-5-tributylstannylphenyl)-
1,4-hexadien-3-one (20): 1H NMR (CDCl3) δ 0.78-0.96 (m, 9H),
1.03-1.19 (m, 6H), 1.26-1.42 (m, 6H), 1.48-1.69 (m, 6H), 2.17
(s, 3H), 3.94 (s, 3H), 5.66 (s, 1H), 5.98 (s, 1H), 6.33 (d, J ) 17.5
Hz, 1H), 7.01 (d, J ) 2.0 Hz, 1H), 7.13 (d, J ) 2.0 Hz, 1H), 7.58
(d, J ) 16.0 Hz, 1H); MS (FAB) m/z 547 (M+ + Na); HRMS
calcd for C25H40O4SnNa, 547.1851; found, 547.1860.
5-Hydroxy-7-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxy-3-
methoxy-5-tributylstannylphenyl)-1,4,6-heptatrien-3-one (21):
mp 95.1-97.5 °C; 1H NMR (CDCl3) δ 0.85-0.98 (m, 9H), 1.12-
1.47 (m, 18H), 3.94 (d, J ) 8.0, 6H), 5.91 (s, 2H), 6.46 (d, J )
16.0 Hz, 2H), 6.93 (d, J ) 9.5 Hz, 2H), 7.00-7.14 (m, 2H), 7.52-
7.59 (m, 3H), 7.71 (dd, J ) 8.8, 5.0 Hz, 1H); MS (FAB) m/z 659
(M+ + H); HRMS calcd for C33H47O26Sn, 659.2395; found,
659.2407.
(s, 3H), 3.74 (s, 3H), 6.17 (d, J ) 16.0 Hz, 1H), 6.80 (d, J ) 2.0
Hz, 2H), 7.12 (d, J ) 2.0 Hz, 1H), 7.25 (d, J ) 16.0 Hz, 2H); MS
(FAB) m/z 315 (M+ + H, 81Br), 313 (M+ + H, 79Br); HRMS calcd
for C13H1481BrO4, 315.0056; found, 315.0048.
5-Hydroxy-1-(4-hydroxy-3-iodo-5-methoxyphenyl)-7-(4-hy-
droxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (7) and 1-(3-
Bromo-4-hydroxy-5-methoxyphenyl)-5-hydroxy-7-(4-hydroxy-
3-methoxyphenyl)-1,4,6-heptatrien-3-one (17). Vanillin (374 g,
2.46 mmol) and B2O3 (427 mg, 6.13 mmol) were dissolved in ethyl
acetate (5 mL) at 80 °C, and to this mixture was added an ethyl
acetate solution (5 mL) of 6 or 16 (3.07 mmol) and (n-BuO)3B
(1.65 mL, 6.12 mmol). After stirring for 30 min, mixtures were
treated with piperidine (121.7 µL, 1.23 mmol) at 80 °C for 30 min
and then with 0.4 N HCl (5 mL) at 50 °C for 30 min. Reaction
mixtures were extracted with ethyl acetate, washed with water, and
then dried over Na2SO4. Flash column chromatography (2:1
hexanes-ethyl acetate) gave 7 (700 mg, 58%) or 17 (549.3 mg,
50%) as orange-colored solids.
5-Hydroxy-1-(4-hydroxy-3-iodo-5-methoxyphenyl)-7-(4-hy-
droxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (7): mp 209.9-
212.4 °C; 1H NMR (CD3OD) δ 3.95 (s, 6H), 5.82 (d, J ) 18.0 Hz,
2H), 6.48 (d, J ) 15.5 Hz, 2H), 6.93 (d, J ) 8.0 Hz, 1H), 7.05 (d,
J ) 2.0 Hz, 2H), 7.12 (dd, J ) 8.0, 2.0 Hz, 2H), 7.59 (d, J ) 15.5
Hz, 2H); MS (FAB) m/z 495 (M+ + H); HRMS calcd for C21H20-
IO6, 495.0305; found, 495.0312.
5-Hydroxy-1-(4-hydroxy-3-[125I]iodo-5-methoxyphenyl)-1,4-
hexadien-3-one([125I]6) and 5-Hydroxy-1-(4-hydroxy-3-[125I]iodo-
5-methoxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-1,4,6-hep-
tatrien-3-one ([125I]7). To 100 µL of the tributylstannyl precursor
20 or 21 (1 mg/mL ethanol) were added 1 N HCl (100 µL) and
Na[125I]I (185 MBq). Reactions were initiated by adding 100 µL
of H2O2 (3% w/v) and stirring at room temperature for 10 min.
After adding saturated NaHSO3 (300 µL, aq), radiolabeled products
were extracted using ethyl acetate and passed through an anhydrous
Na2SO4 plug. Solvent was then removed under a gentle stream of
N2, and reaction mixtures were purified by HPLC using a
semipreparative column eluted with a 60:40 mixture of CH3CN
and trifluoroacetic acid (0.1%, aq) at a flow rate of 3.0 mL/min.
The desired fraction of [125I]6 was eluted between 19 and 20 min,
whereas [125I]7 was eluted between 18 and 19 min using a 55:45
mixture of CH3CN and trifluoroacetic acid (0.1%, aq) at a flow
rate of 4.0 mL/min. Specific activities were determined by
comparing UV peak areas of the desired radioactive peak and the
UV peak areas of different concentrations of unlabeled standard 6
or 7 on HPLC. Aliquots of radioligand ([125I]6 or [125I]7) were co-
injected with unlabeled ligand into the HPLC system to confirm
identities.
1-(3-Bromo-4-hydroxy-5-methoxyphenyl)-5-hydroxy-7-(4-hy-
droxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (17): mp 207.6-
1
211.1 °C; H NMR (CD3OD) δ 3.92 (dd, J ) 7.8, 4.0 Hz, 6H),
6.53 (dd, J ) 15.5, 1.5 Hz, 2H), 6.85 (d, J ) 8.0 Hz, 1H), 7.08
(ddd, J ) 20.0, 10.0, 2.0 Hz, 3H), 7.34 (d, J ) 2.0 Hz, 1H), 7.47
(d, J ) 2.0 Hz, 1H), 7.55 (d, J ) 3.0 Hz, 2H); MS (FAB) m/z 449
81
(M+ + H, 81Br), 447 (M+ + H, 79Br); HRMS calcd for C21H20
BrO6, 449.0426; found, 449.0421.
-
1-[4-(3-Fluoropropoxy)-3-methoxyphenyl]-5-hydroxy-7-(4-hy-
droxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one (8) and 1-[4-(3-
Bromopropoxy)-3-methoxyphenyl]-5-hydroxy-7-(4-hydroxy-3-
methoxyphenyl)-1,4,6-heptatrien-3-one (18). Compound 15 (337.8
mg, 1.44 mmol) and B2O3 (148 mg, 2.13 mmol) were dissolved in
ethyl acetate (5 mL) at 80 °C. To this mixture was added an ethyl
acetate solution (5 mL) of 10 or 14 (180 mg, 0.85 mmol) and (n-
BuO)3B (0.57 mL, 2.11 mmol). After stirring for 30 min, the
mixture was treated with piperidine (50 µL, 0.51 mmol) at 80 °C
for 30 min, and then with 0.4 N HCl (5 mL) at 50 °C for 30 min.
After the reaction mixtures were extracted with ethyl acetate,
washed with water, and then dried over Na2SO4, the products were
purified by flash column chromatography (2:1 hexanes-ethyl
acetate) to give 8 (197.4 mg, 54%) or 18 (155.6 mg, 38%) as yellow
solids.
1-[4-(3-[18F]Fluoropropoxy)-3-methoxyphenyl]-5-hydroxy-7-
(4-hydroxy-3-methoxyphenyl)-1,4,6-heptatrien-3-one ([18F]8).
[18F]Fluoride (1110 MBq) was placed in a Vacutainer containing
n-Bu4NOH (3.2 µL, 4.88 µmol). Three azeotropic distillations were
then performed using 100-200 µL aliquots of CH3CN at 90 °C
In another experiment, 19 (59 mg, 0.10 mmol) was dissolved in
THF (5 mL), and to this solution was added n-Bu4NF (1 M in THF,
1 mL, 1.00 mmol). The reaction mixture was refluxed for 4 h,
solvent was removed in vacuo, and the product was purified by

6118 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 20
Ryu et al.
(oil bath) under a gentle stream of N2. The resulting n-Bu4N[18F]F
was then dissolved in CH3CN (200 µL) and transferred to a reaction
vial containing precursor 12 (2 mg, 5.49 µmol). The reaction
mixture was then stirred at 105 °C for 10 min to give [18F]14. The
resulting mixture was added to an ethyl acetate solution (200 µL)
of 15 (2.5 mg, 10.7 µmol) and B2O3 (2 mg, 28.7 µmol), and to this
solution were added (n-BuO)3B (10 µL, 37.1 µmol) in ethyl acetate
(200 µL) and piperidine (1 µL, 10.1 µmol). This reaction mixture
was stirred at 105 °C for 15 min and then treated with 0.4 N HCl
(300 µL) at 90 °C for 5 min. The mixture was cooled, diluted with
water (2 mL), and extracted with ethyl acetate (2 mL). The organic
layer was washed with water and passed through a 3-cm Na2SO4
plug, and solvent was removed under a stream of N2 at 50 °C (water
bath). The reaction mixture was then purified by HPLC using a
semipreparative column eluted with a 60:40 mixture of CH3CN
and trifluoroacetic acid (0.1%, aq) at a flow rate of 3.0 mL/min.
The desired product eluted between 23 and 24 min. [18F]8 was
identified and its effective specific activity was determined as
described above.
brain, and thyroid (or bone) were removed, weighed, and counted.
Data are expressed as the percent injected dose per gram of tissue
(% ID/g).
In another experiment, mice were injected with a mixture of
radioligand [18F]8 and piperine (2 mg/kg) in 0.2 mL of 10%
ethanol-saline via a tail vein. The remainder of the procedure was
as described above.
Acknowledgment. We thank Ms. Hyun Jung Jeon for
performing the biodistribution studies and Mr. Dong Hyun Kim
and Iljung Lee for their technical assistance. The tributylstannyl
precursor of [125I]IMSB was a generous gift from the University
of Pennsylvania (PA). This study was supported by a grant of
the Korea Health 21 R&D Project, Ministry of Health &
Welfare, Republic of Korea (A050329).
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