Synthesis, radiosynthesis, and biological evaluation of fluorine-18-labeled 2β-carbo(fluoroalkoxy)-3β-(3′-((Z)-2-haloethenyl)phenyl) nortropanes: Candidate radioligands for in vivo imaging of the serotonin transporter with positron emission tomography

Article abstract of DOI:10.1021/jm800781a

The meta-vinylhalide fluoroalkyl ester nortropanes 1-4 were synthesized as ligands of the serotonin transporter (SERT) for use as positron emission tomography (PET) imaging agents. In vitro competition binding assays demonstrated that 1-4 have a high affinity for the SERT (K_i values = 0.3-0.4 nM) and are selective for the SERT over the dopamine and norepinephrine transporters (DAT and NET). MicroPET imaging in anesthetized cynomolgus monkeys with [¹⁸F]1-[¹⁸F]4 demonstrated that all four tracers behave similarly with peak uptake in the SERT-rich brain regions achieved after 45-55 min, followed by a steady washout. An awake monkey study was performed with [¹⁸F]1, which demonstrated that the uptake of [¹⁸F]1 was not influenced by anesthesia. Chase studies with the SERT ligand 15 displaced [¹⁸F]1-[¹⁸F]4, but chase studies with the DAT ligand 16 did not displace [¹⁸F]1-[¹⁸F]4 thus indicating that the tracers were binding specifically to the SERT.

Full text of DOI:10.1021/jm800781a

7788
J. Med. Chem. 2008, 51, 7788–7799
Synthesis, Radiosynthesis, and Biological Evaluation of Fluorine-18-Labeled
2ꢀ-Carbo(fluoroalkoxy)-3ꢀ-(3′-((Z)-2-haloethenyl)phenyl)nortropanes: Candidate Radioligands
for In Vivo Imaging of the Serotonin Transporter with Positron Emission Tomography
Jeffrey S. Stehouwer,† Nachwa Jarkas,† Fanxing Zeng,† Ronald J. Voll,† Larry Williams,† Vernon M. Camp,†
Eugene J. Malveaux,† John R. Votaw,† Leonard Howell,‡ Michael J. Owens,§ and Mark M. Goodman*,†,§
Department of Radiology, Department of Psychiatry and BehaVioral Sciences, and Yerkes National Primate Research Center, Emory
UniVersity, Atlanta, GA
ReceiVed June 27, 2008
The meta-vinylhalide fluoroalkyl ester nortropanes 1-4 were synthesized as ligands of the serotonin transporter
(SERT) for use as positron emission tomography (PET) imaging agents. In vitro competition binding assays
demonstrated that 1-4 have a high affinity for the SERT (Ki values ) 0.3-0.4 nM) and are selective for
the SERT over the dopamine and norepinephrine transporters (DAT and NET). MicroPET imaging in
anesthetized cynomolgus monkeys with [18F]1-[18F]4 demonstrated that all four tracers behave similarly
with peak uptake in the SERT-rich brain regions achieved after 45-55 min, followed by a steady washout.
An awake monkey study was performed with [18F]1, which demonstrated that the uptake of [18F]1 was not
influenced by anesthesia. Chase studies with the SERT ligand 15 displaced [18F]1-[18F]4, but chase studies
with the DAT ligand 16 did not displace [18F]1-[18F]4 thus indicating that the tracers were binding specifically
to the SERT.
Introduction
the development of new SERT therapeutics by allowing for
occupancy measurements of the therapeutic.23-28
The human serotonin transporter (SERT)a is a 630 amino acid
transmembrane protein located in the brain, peripheral organs,
and blood platelets.3-6 Within the central nervous system (CNS),
the SERT is localized on the presynaptic terminals of seroton-
ergic neurons and functions to terminate neurotransmission by
removing serotonin from the synapse. Serotonergic neurons
originate primarily in the median and dorsal raphe nuclei of
the brainstem and innervate discrete areas that include the
hypothalamus, thalamus, striatum, and cerebral cortex.4,7-10
Thus, the SERT can serve as a specific marker for serotonergic
neuronal anatomy and integrity. Dysregulation of serotonin
neurotransmission has been implicated in the pathophysiology
of major depression and a reduction in SERT density has been
observed postmortem in the tissues of depressed patients and
suicide victims.7,11-14 Therefore, the SERT is the target of the
selective serotonin reuptake inhibitor (SSRI) class of antidepres-
sants. The ability to image CNS SERT in vivo using positron
emission tomography (PET) 15-17 may provide insight into the
pathophysiology of depression and suicide by enabling the
SERT density of specific brain regions to be measured, thereby
indicating which regions of the brain have SERT density altered
by the disease, as well as allow for improved diagnostic
techniques and monitoring of antidepressant therapy.18-22
Furthermore, the availability of SERT PET tracers may aid in
This need for a SERT PET tracer has led to extensive research
into the development of new tracers for this target17 with the
majority of these new compounds belonging to the diarylsul-
fide24,29-43 or nortropane44-46 classes. Many of the initial SERT
PET tracers are 11C-labeled compounds and therefore are limited
to use in the location where they are prepared due to the short
half-life of 11C (t1/2 ) 20.4 min). Tracers labeled with 18F are
desirable because the longer half-life of 18F (t1/2 ) 109.8 min)
allows for longer radiosynthesis times and transport of 18F-
labeled tracers to sites away from the production facility which
thus enables PET imaging centers without onsite cyclotrons to
utilize these tracers. Furthermore, 18F positrons have a lower
maximum energy than 11C positrons (0.64 vs 0.97 MeV)17 and
therefore deposit less energy into tissue, and they also have a
shorter linear range47,48 that allows for higher spatial resolution.
These properties of 18F are fortuitous because of the valuable
role that 19F plays in medicinal chemistry49-51 and numerous
methods have now been developed to incorporate 18F or 19F
into molecules.52-54
The goal of developing a viable SERT PET tracer is an
important, but not easy, task as evidenced by the numerous
compounds that have been and continue to be reported. Several
criteria need to be met for a candidate molecule to become a
useful tracer. The desirable properties for a candidate SERT
PET tracer include (exceptions may exist) (1) high binding
affinity55 (Ki ) ∼0.1-0.5 nM) for the SERT with high
selectivity (>50:1) over the norepinephrine transporter (NET)
and dopamine transporter (DAT); (2) moderate lipophilicity (log
P ) ∼1-3)56-58 for good initial brain entry and low nonspecific
binding; (3) high uptake ratios versus cerebellum59 (g1.7) in
SERT-rich brain regions, such as thalamus, hypothalamus, and
raphe, with uptake ratios g1.3 in low density regions such as
anterior cingulate to enable delineation of specific SERT
binding; (4) specific binding to brain SERT reaching peak
equilibrium at e60 min, followed by washout for both 11C-
* To whom correspondence should be addressed. Address: Department
of Radiology, Emory University, 1364 Clifton Road NE, Atlanta, GA 30322.
Phone: (404) 727-9366. Fax: (404) 727-3488. E-mail: mgoodma@
emory.edu.
†
Department of Radiology.
Department of Psychiatry and Behavioral Sciences.
Yerkes National Primate Research Center.
§
‡
a Abbreviations: PET, positron emission tomography; SUV, standardized
uptake value;1,2 SPECT, single-photon emission computed tomography;
TAC, time-activity curve; HRRT, high resolution research tomograph; EOB,
end-of-bombardment; CNS, central nervous system; SSRI, selective sero-
tonin reuptake inhibitor; SERT, serotonin transporter; DAT, dopamine
transporter; NET, norepinephrine transporter.
10.1021/jm800781a CCC: $40.75
2008 American Chemical Society
Published on Web 11/24/2008

Imaging of the Serotonin Transporter
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24 7789
Scheme 1
Table 1. Octanol/Water Partition Coefficients
Scheme 2
a
compound
log P7.4
n
[
[
[
[
18F]1
18F]2
18F]3
18F]4
1.69 ( 0.01
1.40 ( 0.03
1.64 ( 0.14
1.87 ( 0.03
7
4
12
8
a Average value of n determinations ( the standard deviation.
and 18F-tracers to allow quantification of SERT occupancy; (5)
lack of radiolabeled metabolites generated in the brain; and (6)
lack of lipophilic radiolabeled metabolites in peripheral organs
that may enter brain and bind specifically or nonspecifically to
SERT-rich regions and cerebellum.
combined and the product was isolated by solid phase extraction
according to a previously reported procedure.75 We were able
to obtain higher decay-corrected radiochemical yields with
[18F]FEtOBs than with [18F]FPrOBs in our radiosyntheses (see
Experimental Section). This is presumably because the carbon
atom bonded to the brosylate leaving group bears a larger partial
positive charge in [18F]FEtOBs than [18F]FPrOBs due to the
electron-withdrawing properties of the fluorine atom which is
two bonds away in [18F]FEtOBs but three bonds away in
[18F]FPrOBs. The octanol/water partition coefficients56-58 of
[18F]1-[18F]4 were measured according to a known procedure76,77
and are shown in Table 1. These values are all in the range56
that will allow for diffusion of the tracer across the blood-brain-
barrier.
As part of an ongoing research project in our laboratories to
develop SERT-selective tropane and nortropane PET and single-
photon emission computed tomography (SPECT) imaging agents
labeled with 11C or 18F (PET) or 123I (SPECT) for human
diagnostic applications we have been exploring the effect of
placing a vinyl halide60-66 or furyl substituent67 on the 3ꢀ-
phenyl ring. We report here the synthesis and biological
evaluation of 2ꢀ-carbo(2-fluoroethoxy)-3ꢀ-(3′-((Z)-2-iodoethe-
nyl)phenyl)nortropane (1, FEmZIENT),68 2ꢀ-carbo(2-fluoroet-
hoxy)-3ꢀ-(3′-((Z)-2-bromoethenyl)phenyl)nortropane (2, FEm-
ZBrENT),69 2ꢀ-carbo(3-fluoropropoxy)-3ꢀ-(3′-((Z)-2-iodoeth-
enyl)phenyl)nortropane (3, FPmZIENT),70 and 2ꢀ-carbo(3-flu-
oropropoxy)-3ꢀ-(3′-((Z)-2-bromoethenyl)phenyl)nortropane (4,
FPmZBrENT),70 along with the radiosynthesis and microPET
imaging of [18F]1-[18F]4 in anesthetized nonhuman primates and
the PET imaging of [18F]1 in an awake nonhuman primate.
In Vitro Competition Binding Assays
Vinylhalide nortropanes 1-4 and trans-1 were screened for
binding to human monoamine transporters using in vitro
competition binding assays with transfected SERT, DAT, or
NET according to our previously reported procedure.61,78 The
binding affinities for each transporter were determined using
[3H](R,S)-citalopram·HBr78,79 ([3H]15) (SERT), [125I]RTI-5580
(DAT), or [3H]Nisoxetine81 (NET). The data in Table 2 indicate
that 1-4 all have a high affinity for the SERT and are selective
for the SERT over the DAT and NET.55 trans-1 has a reduced
affinity at all three transporters as expected based on previous
reports.60,74
Chemistry
The synthesis of target compounds 1-4 is shown in Scheme
1. 2ꢀ-Carbomethoxy-3ꢀ-(3′-bromophenyl)tropane (5)63 was
hydrolyzed in refluxing 1,4-dioxane/H2O71 to give the acid 6
which was converted to the acid chloride and then esterified to
afford the 2-fluoroethyl ester 7 or the 3-fluoropropyl ester 8.
N-demethylation72 afforded the nortropanes 9 and 10, which
were coupled to (Z)-1,2-bis(trimethylstannyl)ethene73,74 to give
the vinyl-tin nortropanes 11 and 12 in varying cis/trans ratios
with the major product being the cis isomer (∼3:1). Halodestan-
nylation then afforded the vinyl iodides 1 and 3 and the vinyl
bromides 2 and 4 (after separation of the cis/trans isomers by
semipreparative HPLC).
In Vivo Nonhuman Primate MicroPET Imaging
The in vivo regional brain uptake of [18F]1-[18F]4 was
determined in anesthetized cynomolgus monkeys (a total of 4
different cynomolgus monkeys) using a Concorde microPET
P4 according to our previously reported procedure.61 Baseline
studies were initially performed to determine the extent of uptake
of [18F]1-[18F]4 in the SERT-rich regions of the brain. The
baseline time-activity curves (TACs) for [18F]1 are shown in
Figure 1. Compound [18F]1 enters the brain rapidly and achieves
peak uptake in the SERT-rich brain regions after ∼ 45 min
(Table S1, Supporting Information) with the highest uptake
observed in the midbrain followed by the putamen, thalamus,
medulla, and caudate. This rank order of uptake is similar to
that observed with previously reported 11C-labeled diarylsul-
Radiochemistry
The radiolabeling procedure is depicted in Scheme 2. N-Boc
acid 13 or 1463 was dissolved in DMF, deprotonated with 0.1
M Bu4OH(aq), added to [18F]fluoroalkylbrosylate, and heated.
The N-Boc group was cleaved under acidic conditions, the
solution was neutralized, and the mixture was purified by
semipreparative HPLC. The desired HPLC fractions were

7790 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24
Stehouwer et al.
Table 2. Results of In Vitro Competition Binding Assays with Transfected Human Monoamine Transporters
Ki (nM)a
SERT selectivity
compd
hSERT
hDAT
hNET
DAT/SERT
NET/SERT
1
2
3
4
0.43 ( 0.01b
0.33 ( 0.10b
0.26 ( 0.03b
0.33 ( 0.03b
15.2 ( 3.9b
87.6 ( 10.2b
109.9 ( 6.3c
101.3 ( 2.5b
67.5 ( 5.6b
30.2 ( 0.4b
1180 ( 426b
∼204
∼108
∼691
∼360
∼18
∼256
∼307
∼260
∼92
35.5 ( 5.9b
179.7 ( 17.8b
118.7 ( 13.8b
274.0 ( 9.3b
trans-1
∼78
a Average value of n determinations ( SEM (each determination performed in triplicate). b n ) 2. c n ) 3.
Figure 3. Metabolite analysis of [18F]1 in an anesthetized cynomolgus
monkey.
Figure 1. MicroPET baseline TACs obtained by injection of [18F]1
into an anesthetized cynomolgus monkey.
Figure 2. MicroPET images (summed 0-235 min) obtained by
injection of [18F]1 into an anesthetized cynomolgus monkey.
fides30,31,33,34,37 and is consistent with the known distribution
of SERT in the brain.34,59,82,83 Lesser uptake is observed in the
pons and the occipital and frontal cortices. The uptake in the
midbrain, putamen, thalamus, medulla, and caudate remains
nearly constant for ∼20 min (∼45-65 min postinjection) and
then begins to steadily wash out. In the cerebellum, a region
with low SERT density,59 peak uptake is achieved after ∼27
min, followed by a rapid washout of radioactivity down to
uptake levels similar to that observed in the occipital and frontal
cortices. Between 65-175 min postinjection the washout from
the SERT-rich brain regions remains nearly parallel with the
washout from the cerebellum indicating that a quasi-equilibrium
(a condition where the ratio of radioactivity uptake in the region
of interest to reference region stays relatively constant)37 has
been established. The microPET images from this baseline study
are shown in Figure 2.
Figure 4. HRRT baseline TACs obtained by injection of [18F]1 into
an awake rhesus monkey.
each time point is shown in Table S15, Supporting Information,
and was in the range of 5.6-8.5% during the course of the study.
It has been previously shown that anesthesia during PET
imaging can interfere with radioligand binding.85-88 We
therefore performed a baseline study in an awake rhesus monkey
with [18F]1 using a Siemens/CTI High Resolution Research
Tomograph (HRRT) to determine if there was a difference in
the behavior of [18F]1 in an awake versus an anesthetized state.
The TACs are shown in Figure 4 and the PET images are shown
in Figure 5. High uptake is observed in the thalamus, putamen,
midbrain, and caudate with peak uptake achieved after ∼ 45
min (Table S2, Supporting Information). The behavior of [18F]1
in an awake monkey is very similar to its behavior in an
anesthetized monkey thus demonstrating that the imaging
properties of [18F]1 are not affected by anesthesia. We were
not able to follow the washout of [18F]1 in the awake study for
the same amount of time as with the anesthetized study because
of the difficulty of keeping an awake monkey motionless for
an extended period of time.
Metabolite analysis of [18F]1 (Figure 3) was performed with
arterial plasma samples and determined by an HPLC method
with radioactivity detection as previously described.61 The initial
arterial plasma sample was taken at 1 min postinjection of [18F]1
and consisted of 93% of the total plasma radioactivity as
unmetabolized [18F]1. The percent of total plasma radioactivity
then decreased over time during the course of the study to 13%
unmetabolized [18F]1 after 180 min. The radioactive metabolite
eluted immediately after the void volume during HPLC analysis
and is believed to be [18F]fluoroethanol (or one of its metabolic
oxidation products [18F]fluoroacetaldehyde or [18F]fluoroacetic
acid) that would result from hydrolysis of the [18F]fluoroethyl
ester.84 The percentage of protein-bound [18F]1 in plasma at
The TACs for the baseline studies with [18F]2-[18F]4 are
shown in Figures 6-8, respectively. Compound [18F]2 reaches
peak uptake after 55-65 min in the SERT-rich brain regions
followed by a steady washout (Table S3, Supporting Informa-
tion). Peak uptake in the cerebellum is achieved after ∼30 min,

Imaging of the Serotonin Transporter
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24 7791
Figure 8. MicroPET baseline TACs obtained by injection of [18F]4
into an anesthetized cynomolgus monkey.
Figure 5. HRRT PET images (left, summed 60-120 min) obtained
by injection of [18F]1 into an awake rhesus monkey. Composite MRI’s
of several rhesus monkeys (right) and overlaid images (center).
Table 3. Comparison of Uptake of [18F]1-[18F]4 in SERT-Rich Brain
Regions to Cerebellum Uptake at 115 and 215 min Post-Injection
115 min
215 min
brain
region
[
18F]1a 18F]1 [18F]2 [18F]3 [18F]4 [18F]1 [18F]2 [18F]3 [18F]4
[
caudate
1.6
1.4
1.7
1.6
1.9
1.3
1.5
0.9
1.0
1.5
1.7
1.5
1.7
1.6
1.5
1.1
1.0
1.2
1.4
1.4
1.5
1.3
1.5
1.0
0.8
1.4
1.5
1.5
1.7
1.3
1.5
1.1
1.0
1.5
1.8
1.7
2.2
1.5
1.7
0.9
1.1
1.6
1.8
1.6
2.1
1.8
1.7
1.1
1.1
1.2
1.5
1.5
1.8
1.5
1.8
1.0
1.0
1.7
1.7
1.7
2.2
1.5
1.8
1.3
1.0
putamen 1.6
thalamus 1.8
midbrain 1.9
pons
medulla 1.3
occipital N/A
1.8
frontal
1.2
a HRRT awake rhesus study.
Figure 6. MicroPET baseline TACs obtained by injection of [18F]2
into an anesthetized cynomolgus monkey.
Figure 9. MicroPET TACs showing the results of injection of 15 (1.5
mg/kg) into an anesthetized cynomolgus monkey at 120 min postin-
jection of [18F]1.
of individual differences between the monkeys studied rather
than differences between the performance of each tracer. The
uptake ratios for [18F]1 after 115 min in awake and anesthetized
monkeys are also very similar which provides further evidence
that isoflurane anesthesia does not influence the in vivo behavior
of [18F]1.
To demonstrate that the observed uptake in the baseline
studies with [18F]1-[18F]4 is the result of preferential binding
to the SERT and not the DAT, chase studies were performed
with the SERT ligand 15, and the DAT ligands (()-
methylphenidate·HCl89 (16) and RTI-113 ·HCl71,90,91 (17).
Figures 9-12 show the TACs for the chase studies with 15 at
120 min postinjection of the tracer for compounds [18F]1-[18F]4,
respectively. For all four chase studies the amount of radioactiv-
ity in the SERT-rich brain regions decreases to nearly the level
of the cortices and cerebellum thus indicating that the observed
uptake is the result of binding to the SERT. These results also
indicate that [18F]1-[18F]4 can be used for occupancy studies
of SERT-selective therapeutics.26 Graphs of the uptake ratio
Figure 7. MicroPET baseline TACs obtained by injection of [18F]3
into an anesthetized cynomolgus monkey.
followed by a rapid washout to a level of uptake slightly less
than that observed in the occipital and frontal cortices. Peak
uptake in the SERT-rich brain regions for [18F]3 was achieved
after 45-55 min (Table S4, Supporting Information) and for
[18F]4 peak uptake was achieved after 35-45 min (Table S5,
Supporting Information) with both compounds showing a steady
washout. The ratio of uptake in the SERT-rich brain regions vs
cerebellum uptake for compounds [18F]1-[18F]4 at 115 and 215
min postinjection is shown in Table 3 (the complete data is
shown in Tables S6-S10, Supporting Information, along with
graphs of the uptake ratios versus time in Figures S1-S5,
Supporting Information). The ratios for each tracer are very
similar at these two time points thus indicating that these tracers
all behave very similarly in vivo. The differences between the
data in Table 3 are believed to be the result, at least partially,

7792 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24
Stehouwer et al.
Table 4. Comparison of the Times of Peak Uptake between [18F]1 and
[
18F]19 for Anesthetized and Awake Monkey Studiesa
time (min)
anesthetized
awake
brain region
[
18F]1
[
18F]19
[
18F]1
[
18F]19
caudate
putamen
thalamus
midbrain
pons
55
45
45
45
45
35
28
105
95
85
95
115
85
45
45
45
45
85
35
45
85
85
>75
>75
>75
85
medulla
cerebellum
45
35
a See Tables S1, S2, S11, and S13, Supporting Information, for the
complete data.
Figure 10. MicroPET TACs showing the results of injection of 15
(1.5 mg/kg) into an anesthetized cynomolgus monkey at 120 min
postinjection of [18F]2.
Table 5. Comparison of the Uptake Ratios between [18F]1 and [18F]19
for Anesthetized and Awake Monkey Studies at Selected Time Pointsa
anesthetized
115 min
awake
55 min
225 min
95 min
brain
region
[
18F]1 [18F]19 [18F]1 [18F]19 [18F]1 [18F]19 [18F]1 [18F]19
caudate
1.1
1.1
1.6
1.5
1.6
1.2
1.5
1.4
1.7
1.6
1.9
1.3
1.5
1.7
2.4
2.2
2.5
2.0
2.1
1.6
1.9
1.8
2.4
1.6
1.9
2.5
3.5
3.1
4.2
3.1
3.0
1.5
1.7
1.7
1.6
1.5
1.1
2.0
2.1
2.4
2.0
1.6
1.5
putamen 1.2
thalamus 1.2
midbrain 1.4
pons
medulla
0.9
1.1
a See Tables S6, S7, S12, and S14, Supporting Information, for the
complete data. Also see Figures S1, S2, S16, and S18, Supporting
Information.
because 18 also has an affinity for the SERT60 and we have
previously demonstrated that 18 will displace SERT PET
tracers.63,64
Figure 11. MicroPET TACs showing the results of injection of 15
(1.5 mg/kg) into an anesthetized cynomolgus monkey at 120 min
postinjection of [18F]3.
We have recently reported the microPET and HRRT PET
imaging properties of [18F]19 in nonhuman primates (anesthe-
tized and awake, respectively).64 Compound 19 is the para-
substituted isomer of 1 and has a higher affinity at all three
transporters than 1 (Ki ) 0.08 nM SERT, 13 nM DAT, and 28
nM NET) but a lower SERT versus DAT selectivity (∼162).
Comparison between [18F]19 and [18F]1 will reveal the effect
of placing the vinyl iodide group in the para- or meta-position.
The microPET baseline TACs for [18F]19 are reproduced in
Figure S15, Supporting Information, and the awake rhesus
monkey HRRT baseline TACs are reproduced in Figure S17,
Supporting Information. Table 4 compares the times of peak
uptake between [18F]19 and [18F]1 for the microPET and HRRT
studies with each compound. In both the anesthetized and awake
studies [18F]1 reaches peak uptake significantly faster than
[18F]19 and [18F]1 also shows a greater washout (also see Tables
S1, S2, S11, and S13, Supporting Information). Thus, [18F]1
has superior imaging kinetics relative to [18F]19. Table 5
compares the ratio of uptake in SERT-rich brain regions to
Figure 12. MicroPET TACs showing the results of injection of 15
(1.5 mg/kg) into an anesthetized cynomolgus monkey at 120 min
postinjection of [18F]4.
versus time for these chase studies are shown in Figures S6-S9,
Supporting Information. Figure S10, Supporting Information,
shows the results of chasing [18F]1 with the DAT ligand 16,
and Figure S11, Supporting Information, shows the results of
chasing [18F]1 with the DAT ligand 17. We chose to perform
chase studies with both 16 and 17 because we wanted to chase
[18F]1 with a tropane-based DAT ligand (17) and a nontropane-
based DAT ligand (16). In neither case did the amount of
radioactivity uptake decrease after administration of the chase
compound (other than normal washout) thus indicating that
[18F]1 is not bound to the DAT. Chase studies using 16 were
also performed with [18F]2-[18F]4 (Figures S12-S14, Support-
ing Information, respectively) and, similarly to what was
observed with [18F]1, the radioactivity was not displaced. We
did not perform any chase studies with the NET ligand 1892,93

Imaging of the Serotonin Transporter
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24 7793
cerebellum uptake for [18F]1 and [18F]19 (also see Tables S6,
S7, S12, and S14, Supporting Information). Compound [18F]19
shows higher uptake ratios than [18F]1 in both anesthetized and
awake states, and for both compounds the uptake ratios increase
with time throughout the course of the studies (This is
represented by Figures S1, S2, S16, and S18, Supporting
Information, where the uptake ratio is plotted vs time). The
differences in uptake ratio are a result of the differences in
kinetics for each tracer. For compound [18F]1 (Figure 1) washout
from the cerebellum begins after ∼27 min and washout from
the SERT-rich brain regions begins after ∼65 min. This washout
then remains fairly steady and the uptake ratios slowly increase
until finally stabilizing after ∼175 min (Figure S1, Supporting
Information). In contrast, [18F]19 reaches peak uptake in the
cerebellum after 45 min and then begins to wash out, while
uptake in the SERT-rich brain regions continues to increase until
85-105 min followed by a very slow washout. This results in
a continuously increasing uptake ratio with time (Figure S16,
Supporting Information). Similar differences between [18F]1 and
[18F]19 are also observed in the awake monkey studies (Figures
S2 and S18, Supporting Information). Therefore, [18F]1 may
be more ideally suited for measuring SERT density in humans
because of its superior kinetics and the ability to achieve a quasi-
equilibrium. Alternatively, as shown in Figure S19, Supporting
Information, chasing [18F]19 with 15 produces a more drastic
displacement of [18F]19 than occurs with [18F]1 (Figure 9) which
suggests that [18F]19 may be better suited to be used for
occupancy determination studies of SSRI’s.15,25-27 Thus, com-
pounds [18F]1 and [18F]19 each have their own unique imaging
properties and are both promising candidates for use in human
PET studies. The decision of which tracer to use, [18F]1 or
[18F]19, would therefore have to be determined by the objective
of the pending study.
tively, with [18F]19. Similar effects are observed in the midbrain
and thalamus. Alternatively, the ratio of uptake in the SERT-
rich brain regions to the cerebellum is higher with [18F]19 than
with [18F]1. Both [18F]1 and [18F]19 are, therefore, promising
candidates for advancement to human studies because [18F]1
offers faster kinetics than [18F]19 but [18F]19 offers higher
uptake ratios than [18F]1 and it will be interesting to see if these
differences are maintained in human subjects. Additionally, each
compound can be radiolabeled as [123I]1 or [123I]19 for SPECT
imaging which will further expand the possible uses of these
two tracers. We have, therefore, chosen to further pursue [18F]1
out of this series of tracers reported above in combination with
[18F]19 due to the higher radiochemical yields that can be
obtained by O-alkylation with [18F]FEtOBs, the ability to use
both [18F]1 and [18F]19 and to make direct comparisons between
the two, and the possibility of radiolabeling each with 123I for
SPECT imaging. Thus, we intend to evaluate both [18F]1 and
[18F]19 in healthy normal human volunteers under baseline
conditions as well as perform test-retest variability in dose-
dependent blocking studies to determine their suitability for
measuring occupancy in subjects with neuropsychiatric disorders.
Experimental Section
General. Solvents were purchased from VWR and had originated
from EMD or Burdick and Jackson. Anhydrous solvents (100-mL
septum-capped bottles) were purchased from Aldrich. TLC plates
used were EMD glass-backed Silica Gel 60 F254, 20 × 20 cm, 250
µm. Preparatory TLC plates used were Analtech Uniplate Silica
Gel GF 20 × 20 cm, 2000 µm. Silica gel used was EMD Silica
Gel 60, 40-63 µm. Radial chromatography was performed with a
Harrison Research Chromatotron. Semipreparatory HPLC: Waters
XTerra Prep RP18, 5 µm, 19 × 100 mm + guard cartridge (19 ×
10 mm), 60:40:0.1 v/v/v MeOH/H2O/NEt3. Analytical HPLC:
Waters NovaPak 3.9 × 150 mm, 75:25:0.1 v/v/v MeOH/H2O/NEt3.
HRMS was performed by the Emory University Mass Spectrometry
Center. NMR spectrometry was performed on Varian Inova and
Unity spectrometers at the specified frequencies.
Summary
3ꢀ-(3′-Bromophenyl)tropane-2ꢀ-carboxylic acid (6). 2ꢀ-Car-
bomethoxy-3ꢀ-(3′-bromophenyl)tropane (5) (0.74 g, 2.19 mmol),
1,4-dioxane (15 mL), and H2O (15 mL) were stirred at reflux for
16 h. The solvent was removed azeotropically with EtOH to give
a white solid that was dried under vacuum for 3 h. The solid was
suspended in CHCl3 (5 mL), cooled to 0 °C, and the precipitate
was isolated by filtration and dried under vacuum to afford 0.48 g
The SERT ligands 1-4 were synthesized from m-bromophe-
nyl tropane 5 and evaluated for binding to the SERT, DAT,
and NET with in vitro competition binding assays using
transfected cells. Compounds 1-4 have a high and nearly equal
affinity for the SERT and are selective for the SERT over the
DAT and NET. Radiolabeling afforded tracers [18F]1-[18F]4
with higher decay-corrected radiochemical yields obtained with
[18F]FEtOBs than with [18F]FPrOBs. Tracers [18F]1-[18F]4
1
(68%) of a white solid: H NMR (600 MHz, CD3OD) δ 7.51 (br
s, 1 H), 7.36 (d, 1 H, J ) 7.8 Hz), 7.31 (d, 1 H, J ) 7.8 Hz), 7.20
(dd, 1 H, J ) 7.8 Hz), 3.94 (m, 2 H), 3.36 (dt, 1 H, J ) 6.0 Hz, J
) 13.8 Hz), 2.81 (m, 1 H), 2.79 (s, 3 H), 2.69 (m, 1 H), 2.40 (m,
2 H), 2.17 (m, 2 H), 1.84 (m, 1 H); HRMS (APCI) [MH]+ Calcd
for C15H19O2N79Br 324.0594, Found 324.0593; Calcd for
C15H19O2N81Br 326.0578, Found 326.0574.
were found to have lipophilicities in the range log P7.4
)
1.4-1.9. MicroPET imaging studies in anesthetized cynomolgus
monkeys demonstrated that [18F]1-[18F]4 behave very similarly
in vivo with peak uptake achieved after 45-55 min, followed
by a steady washout. The ratios of uptake in SERT-rich brain
regions to cerebellum uptake for [18F]1-[18F]4 were also very
similar. An HRRT study was performed with [18F]1 in an awake
rhesus monkey to determine if anesthesia was influencing the
behavior of [18F]1. The time to peak uptake and the uptake ratio
of [18F]1 were similar between anesthetized and awake states
indicating that anesthesia does not affect the imaging properties
of [18F]1. Chase studies with the SERT ligand 15 displaced
tracers [18F]1-[18F]4 but chase studies with the DAT ligand
16 did not displace tracers [18F]1-[18F]4 thus indicating that
the observed uptake in the brain is a result of preferential binding
to the SERT and not the DAT. Comparison between [18F]1 and
the para-substituted isomer [18F]19 demonstrates that the
position of the vinyl iodide group can have a significant affect
on the tracer properties of the two compounds. Peak uptake in
the putamen and caudate is achieved after 45 and 55 min,
respectively, with [18F]1 but it takes 95 and 105 min, respec-
2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-bromophenyl)tropane (7). 3ꢀ-
(3′-Bromophenyl)tropane-2ꢀ-carboxylic acid (6) (0.43 g, 1.33
mmol) was suspended in anhydrous CH2Cl2 (25 mL) under Ar,
followed by addition of anhydrous NEt3 (0.30 mL, 2.15 mmol, 1.6
equiv.) and cooling to -4 °C. Oxalyl chloride (1.0 mL, 2 M CH2Cl2,
2.0 mmol, 1.5 equiv.) was diluted with anhydrous CH2Cl2 (5 mL)
and added dropwise through the condenser to the reaction flask
over a period of 5 min. The reaction mixture was stirred under Ar
at -4 °C for 20 min, warmed to rt, and the solvent was removed
to give a brown solid that was dried under vacuum for 20 min.
The solid was dissolved in anhydrous CH2Cl2 (25 mL) and cooled
to -4 °C under Ar. FEtOH (0.80 mL, 13.62 mmol 10.2 equiv.)
and anhydrous NEt3 (0.30 mL, 2.15 mmol, 1.6 equiv) were
dissolved in anhydrous CH2Cl2 (10 mL) and added dropwise
through the condenser to the acid chloride solution over a period
of 3 min. The reaction mixture was stirred under Ar at -4 °C for
5 min, warmed to rt, and stirred at rt for 80 min, and then the
solvent was removed to give a brown solid that was dried under

7794 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24
Stehouwer et al.
vacuum for 20 min. The solid was dissolved in CH2Cl2, poured
onto dry silica (43 mm h × 43 mm i.d.), and eluted under vacuum:
CH2Cl2 (100 mL), v/v/v hexane/EtOAc/NEt3 75:20:5 (300 mL),
50:45:5 (100 mL) to afford 0.31 g (63%) of a colorless syrup: TLC
Rf ) 0.38 (50:45:5 v/v/v hexane/EtOAc/NEt3); 1H NMR (600 MHz,
give 0.18 g (72%) of a light yellow oil: TLC Rf ) 0.10 (50:45:5
1
v/v/v hexane/EtOAc/NEt3); H NMR (600 MHz, CDCl3) δ 7.35
2
(s, 1 H), 7.33 (m, 1 H), 7.15 (m, 2 H), 4.36 (dddd, 1 H, JHF
)
2
3
3
46.8 Hz, JHH ) 10.8 Hz, JHH ) 2.4 Hz, JHH ) 5.4 Hz), 4.23
(dddd, 1 H, 2JHF ) 48.0 Hz, 2JHH ) 10.8 Hz, 3JHH ) 2.4 Hz, 3JHH
) 6.6 Hz), 4.12 (dddd, 1 H, 3JHF ) 26.4 Hz, 2JHH ) 13.2 Hz, 3JHH
) 2.4 Hz, 3JHH ) 6.6 Hz), 4.01 (dddd, 1 H, 3JHF ) 30.0 Hz, 2JHH
CDCl3) δ 7.39 (s, 1 H), 7.29 (d, 1 H, J ) 7.8 Hz), 7.21 (d, 1 H, J
2
) 7.8 Hz), 7.14 (dd, 1 H, J ) 7.8 Hz), 4.45 (dddd, 2 H, JHF
)
)
46.8 Hz, 3JHH ) 5.8 Hz, 3JHH ) 2.6 Hz), 4.29 (dddd, 1 H, 3JHF
) 13.2 Hz, JHH ) 2.4 Hz, JHH ) 5.4 Hz), 3.75 (m, 2 H), 3.25
(dt, 1 H, J ) 6.0 Hz, J ) 12.6 Hz), 2.82 (m, 1 H), 2.37 (td, 1 H,
J ) 3.0 Hz, J ) 13.2 Hz), 2.12 (m, 1 H), 2.01 (m, 1 H), 1.76 (m,
1 H), 1.67 (m, 3 H); 13C NMR (150 MHz, CDCl3) δ 172.98, 144.85,
3
3
2
3
3
29.4 Hz, JHH ) 13.2 Hz, JHH ) 5.2 Hz, JHH ) 2.6 Hz), 4.08
(dddd, 1 H, 3JHF ) 28.2 Hz, 2JHH ) 12.6 Hz, 3JHH ) 5.9 Hz, 3JHH
) 2.4 Hz), 3.63 (m, 1 H), 3.36 (m, 1 H), 2.98 (m, 2 H), 2.53 (td,
1 H, J ) 3.0 Hz, J ) 12.3 Hz), 2.22 (s, 3 H), 2.20 (m, 1 H), 2.11
(m, 1 H), 1.70 (m, 2 H), 1.60 (m, 2 H); 13C NMR (150 MHz,
CDCl3) δ 171.29, 145.79, 130.73, 129.69, 129.16, 126.10, 122.38,
81.74 (d, 1JCF ) 169.2 Hz), 65.47, 62.91 (d, 2JCF ) 20.6 Hz), 62.33,
52.65, 42.08, 34.04, 33.71, 25.95, 25.45; HRMS (APCI) [MH]+
calcd for C17H22O2N79Br 370.0813, found 370.0812; calcd for
C17H22O2N81Br 372.0797, found 372.0793.
1
130.64, 130.00, 129.82, 126.21, 122.61, 81.25 (d, JCF ) 169.2
Hz), 62.99 (d, 2JCF ) 20.7 Hz), 56.54, 53.76, 51.08, 35.44, 33.60,
29.33, 27.89; HRMS (APCI) [MH]+ Calcd for C16H20O2N79BrF
356.0656, Found 356.0656; Calcd for C16H20O2N81BrF 358.0635,
Found 358.0636.
2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-bromophenyl)nortro-
pane (10). 2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-bromophenyl)tropane
(8) (78 mg, 2.03 × 10-4 mol), 2,2,2-trichloroethyl chloroformate
(0.30 mL, 2.18 mmol, 10.7 equiv.), Na2CO3(s) (11 mg, 0.10 mmol,
0.5 equiv.), and toluene (5 mL) were stirred at reflux under Ar for
4 h, cooled, poured onto dry silica (25 mm h × 33 mm i.d.), and
eluted under vacuum with CH2Cl2 (25 mL) and then 75:20:5 v/v/
v/ hexane/EtOAc/NEt3 (100 mL). The solvent was removed to give
a colorless residue that was dried under vacuum (0.11 g). To the
residue was added Zn dust (0.13 g), AcOH (4 mL), and H2O (0.1
mL), and the mixture was stirred at rt for 21 h. The reaction mixture
was filtered; the filtrate was diluted with CH2Cl2 (25 mL) and H2O
(25 mL) and cooled to 0 °C. The aqueous phase was basified to
pH 10 with conc. NH4OH(aq); the layers were separated, and the
aqueous layer was extracted with CH2Cl2 (10 mL × 2). The
combined CH2Cl2 layers were dried over MgSO4 and the solvent
was removed to give a colorless oil. The oil was dissolved in
CH2Cl2, poured onto dry silica (26 mm h × 33 mm i.d.), and eluted
under vacuum: CH2Cl2 (75 mL), then v/v/v hexane/EtOAc/NEt3
75:20:5 (50 mL), 50:45:5 (75 mL), 20:75:5 (100 mL). The solvent
was removed to give 44 mg (59%) of a light yellow oil: 1H NMR
(600 MHz, CDCl3) δ 7.33 (m, 2 H), 7.15 (m, 2 H), 4.17 (ddd, 2 H,
2JHF ) 47.4 Hz, JHH ) 5.7 Hz), 4.01 (m, 1 H), 3.91 (m, 1 H), 3.73
(m, 2 H), 3.24 (dt, 1 H, J ) 5.9 Hz, J ) 13.2 Hz), 2.73 (d, 1 H, J
) 5.4 Hz), 2.36 (td, 1 H, J ) 2.4 Hz, J ) 13.2 Hz), 2.13 (m, 1 H),
2.02 (m, 1 H), 1.69 (m, 6 H); 13C NMR (150 MHz, CDCl3) δ
173.30, 144.95, 130.74, 130.04, 129.83, 126.21, 122.61, 80.46 (d,
2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-bromophenyl)tropane (8).
3ꢀ-(3′-Bromophenyl)tropane-2ꢀ-carboxylic acid (6) (0.11 g, 0.34
mmol) was suspended in anhydrous CH2Cl2 (8 mL) under Ar,
followed by addition of anhydrous NEt3 (0.08 mL, 0.57 mmol, 1.7
equiv.) and cooling to -4 °C. Oxalyl chloride (0.27 mL, 2 M
CH2Cl2, 0.54 mmol, 1.6 equiv.) was diluted with anhydrous CH2Cl2
(2 mL) and added dropwise to the reaction flask over a period of
90 s. The reaction mixture was stirred under Ar at -4 °C for 20
min, warmed to rt, and the solvent was removed to give a brown
solid that was dried under vacuum for 20 min. The solid was
dissolved in anhydrous CH2Cl2 (10 mL) and cooled to -4 °C under
Ar. FPrOH (0.32 g, 4.10 mmol 12.1 equiv.) and anhydrous NEt3
(0.08 mL, 0.57 mmol, 1.7 equiv.) were dissolved in anhydrous
CH2Cl2 (5 mL) and added dropwise to the acid chloride solution.
The reaction mixture was stirred under Ar at -4 °C for 5 min,
warmed to rt, and the solvent was removed to give a brown solid
that was dried under vacuum for 10 min. The solid was dissolved
in CH2Cl2, poured onto dry silica (39 mm h × 43 mm i.d.), and
eluted under vacuum: CH2Cl2 (100 mL), v/v/v hexane/EtOAc/NEt3
75:20:5 (300 mL), 50:45:5 (100 mL) to afford 88 mg (67%) of a
colorless syrup: TLC Rf ) 0.41 (50:45:5 v/v/v hexane/EtOAc/NEt3);
1H NMR (600 MHz, CDCl3) δ 7.36 (s, 1 H), 7.29 (d, 1 H, J ) 7.8
Hz), 7.19 (d, 1 H, J ) 7.8 Hz), 7.14 (dd, 1 H, J ) 7.8 Hz), 4.37
(2 m, 2 H, 2JHF ) 47.1 Hz), 4.14 (m, 1 H), 3.98 (m, 1 H), 3.58 (m,
1 H), 3.35 (m, 1 H), 2.98 (dt, 1 H, J ) 5.7 Hz, J ) 12.0 Hz), 2.91
(m, 1 H), 2.50 (td, 1 H, J ) 2.4 Hz, J ) 12.6 Hz), 2.21 (s, 3 H),
3
1JCF ) 165.2 Hz), 60.11 (d, JCF ) 5.9 Hz), 56.45, 53.67, 51.00,
2
3
35.62, 33.56, 29.68 (d, JCF ) 20.7 Hz), 29.22, 27.79; HRMS
2.18 (m, 1 H), 2.11 (m, 1 H), 1.85 (2 m, 2 H, JHF ) 24.6 Hz),
(APCI) [MH]+ Calcd for C17H22O2N79BrF 370.0813, Found
370.0814; Calcd for C17H22O2N81BrF 372.0792, Found 372.0793.
(Z)-1,2-Bis(trimethylstannyl)ethane. Purified acetylene (passed
successively through a -78 °C cold trap, conc. H2SO4(aq), NaOH(s),
CaCl2(s), and then Drierite) was bubbled through a solution of
hexamethylditin (2.52 g, 7.69 mmol), Pd(PPh3)4 (0.89 g, 0.77
mmol), and 1,4-dioxane (20 mL, purged with Ar for 45 min prior
to use) at 65 °C for 4 h. The solution was cooled to rt, stirred at rt
for 20 min, and filtered. The filtrate was poured onto silica gel (14
cm high × 4 cm i.d.) that had been pretreated with 10% NEt3/
hexane (100 mL) and then 1% NEt3/hexane (100 mL). The product
was eluted under vacuum with 1% NEt3/hexane (200 mL), and the
solvent was removed to give a dark orange oil that was briefly
dried under vacuum (2.48 g, 91%). TLC Rf ) 0.66 (1% NEt3/
Hexane); 1H NMR (400 MHz, CDCl3) δ 7.33 (s, 2 H), 0.17 (t, 18
H, 2JSnH ) 26.6 Hz); 13C NMR (150 MHz, CDCl3) δ 155.17, -8.10.
(Z)-1,2-Bis(trimethylstannyl)ethene was found to be stable (by
1H NMR spectroscopy) for at least 1 year when stored at -15 °C
under Ar and protected from moisture and light (the vial was flushed
with Ar, capped, wrapped with Parafilm, completely wrapped in
Al foil, and then stored in a resealable plastic bag in a freezer).
2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-((Z)-2-trimethylstannylethe-
nyl)phenyl)nortropane (11). 2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-
bromophenyl)nortropane (9) (0.23 g, 6.46 × 10-4 mol), (Z)-1,2-
bis(trimethylstannyl)ethene (0.72 g, 2.04 mmol, 3.2 equiv),
Pd(PPh3)4 (80 mg, 6.92 × 10-5 mol, 0.1 equiv), and toluene (25
1.70 (m, 2 H), 1.60 (m, 1 H); 13C NMR (150 MHz, CDCl3) δ
171.62, 146.01, 130.57, 129.72, 129.09, 125.98, 122.38, 80.89 (d,
3
1JCF ) 165.0 Hz), 65.55, 62.29, 59.96 (d, JCF ) 6.2 Hz), 52.80,
42.10, 34.11, 33.61, 29.94 (d, 2JCF ) 20.6 Hz), 26.00, 25.43; HRMS
(APCI) [MH]+ Calcd for C18H24O2N79BrF 384.0969, Found
384.0971; Calcd for C18H24O2N81BrF 386.0954, Found 386.0953.
2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-bromophenyl)nortropane (9).
2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-bromophenyl)tropane (7) (0.26 g,
7.02 × 10-4 mol), 2,2,2-trichloroethyl chloroformate (1.0 mL, 7.27
mmol, 10.4 equiv.), Na2CO3(s) (36 mg, 0.34 mmol, 0.5 equiv.), and
toluene (15 mL) were stirred at reflux under Ar for 4 h, cooled,
poured onto dry silica (43 mm h × 43 mm i.d.), and eluted under
vacuum with CH2Cl2 (75 mL) and then 75:20:5 v/v/v/ hexane/
EtOAc/NEt3. The solvent was removed to give a colorless residue
that was dried under vacuum (0.37 g). To the residue was added
Zn dust (0.46 g), AcOH (10 mL), and H2O (0.3 mL), and the
mixture was stirred at rt for 21 h. The reaction mixture was filtered,
the filtrate was diluted with CH2Cl2 (50 mL) and H2O (50 mL),
and cooled to 0 °C. The aqueous phase was basified to pH 11 with
conc. NH4OH(aq); the layers were separated, and the aqueous layer
was extracted with CH2Cl2 (20 mL × 2). The combined CH2Cl2
layers were dried over MgSO4, and the solvent was removed to
give a colorless oil. The oil was dissolved in CH2Cl2, poured onto
dry silica (35 mm h × 43 mm i.d.), and eluted under vacuum:
CH2Cl2 (75 mL), then v/v/v hexane/EtOAc/NEt3 75:20:5 (50 mL),
50:45:5 (50 mL), 20:75:5 (500 mL). The solvent was removed to

Imaging of the Serotonin Transporter
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24 7795
mL, purged with Ar for 2 h) were stirred at reflux under Ar for
18 h. The reaction mixture was cooled to rt, stirred at rt for 1.5 h,
poured onto dry silica (40 mm h × 43 mm i.d.), and eluted under
vacuum: CH2Cl2 (100 mL), hexane (50 mL), v/v/v hexane/EtOAc/
NEt3 75:20:5 (100 mL), 50:45:5 (100 mL), 20:75:5 (300 mL). The
solvent was removed to give an orange oil that was radially
chromatographed (4 mm silica, v/v/v hexane/EtOAc/NEt3 90:8:2
(300 mL), 75:20:5 (1 L)) to afford 0.13 g of a colorless syrup that
was ∼73:27 cis/trans by integration of the 1H NMR vinyl
resonances. The product was again radially chromatographed (2
mm silica, v/v/v hexane/EtOAc/NEt3 95:4:1 (1 L), 90:8:2 (800 mL),
75:20:5 (200 mL), 50:45:5 (200 mL)) to afford 64 mg (21%) of a
colorless syrup that was ∼93:7 cis/trans, 29 mg (10%) of a colorless
syrup that was ∼76:24 cis/trans, and 29 mg (10%) of a colorless
syrup that was ∼47:53 cis/trans. TLC Rf ) 0.28 (20:75:5 v/v/v
and the aqueous phase extracted with CHCl3 (5 mL × 2). The
combined CHCl3 layers were dried over MgSO4, the solvent was
removed, and the residue was purified by preparative TLC (20:
75:5 v/v/v hexane/EtOAc/NEt3 × 2) to give 23 mg (71%) of a
colorless residue that was ∼95:5 cis/trans by integration of the 1H
NMR vinyl resonances. Separation of the isomers by semiprepara-
tive HPLC (cis tR ) 19.7 min, 8.8 mL/min) afforded 16 mg (50%)
1
of 1 as a white residue: H NMR (600 MHz, CDCl3) δ 7.47 and
7.46 (overlapping resonances, 2 H), 7.30 (m, 2 H), 7.20 (d, 1 H, J
) 7.8 Hz), 6.56 (d, 1 H, J ) 8.4 Hz), 4.31 (dddd, 1 H, 2JHF ) 47.1
Hz, 2JHH ) 10.6 Hz, 3JHH ) 5.2 Hz, 3JHH ) 2.4 Hz), 4.20 (partially
2
3
3
resolved ddd, 0.5 H, JHH ) 10.6 Hz, JHH ) 7.1 Hz, JHH ) 2.4
Hz), 4.11 (overlapping resonances, 0.5 H + 0.5 H, 3JHH ) 2.4 Hz),
4.06 (ddd, 0.5 H, 2JHH ) 12.9 Hz, 3JHH ) 7.1 Hz, 3JHH ) 2.4 Hz),
3.97 (dddd, 1 H, 3JHF ) 30.3 Hz, 2JHH ) 12.9 Hz, 3JHH ) 5.2 Hz,
3JHH ) 2.4 Hz), 3.77 (m, 2 H), 3.32 (dt, 1 H, J ) 6.0 Hz, J ) 12.6
Hz), 2.88 (m, 1 H), 2.44 (td, 1 H, J ) 13.2 Hz, J ) 3.0 Hz), 2.14
(m, 1 H), 2.03 (m, 1 H), 1.80 (m, 1 H), 1.71 (overlapping m + br
1
hexane/EtOAc/NEt3); H NMR (600 MHz, CDCl3) δ 7.54 (td, 1
H, 3JHH ) 13.8 Hz, 3JSnH ) 75.0 Hz), 7.23 (dd, 1 H, J ) 7.8 Hz),
3
2
7.11 (m, 3 H), 6.18 (td, 1 H, JHH ) 13.8 Hz, JSnH ) 32.0 Hz),
4.33 (dddd, 1 H, 2JHF ) 46.9 Hz, 2JHH ) 10.8 Hz, 3JHH ) 5.4 Hz,
3JHH ) 2.4 Hz), 4.20 (dddd, 1 H, 2JHF ) 47.7 Hz, 2JHH ) 10.8 Hz,
3JHH ) 6.9 Hz, 3JHH ) 2.4 Hz), 4.10 (partially resolved dddd, 1 H,
3JHH ) 2.4 Hz), 3.95 (dddd, 1 H, 3JHF ) 30.1 Hz, 2JHH ) 13.0 Hz,
s, 2 H + 1 H); 13C NMR (150 MHz, CDCl3) δ 172.90, 141.59,
1
138.68, 136.93, 128.37, 127.55, 127.45, 126.93, 81.26 (d, JCF
)
2
170.1 Hz), 79.79, 63.26 (d, JCF ) 18.7 Hz), 56.27, 53.91, 50.76,
35.28, 32.84, 28.71, 27.31; HRMS (ESI) [MH]+ calcd for
C18H22O2NF127I 430.0674, found 430.0660.
3
3JHH ) 5.4 Hz, JHH ) 2.4 Hz), 3.74 (m, 2 H), 3.27 (dt, 1 H, J )
1
5.4 Hz, J ) 13.2 Hz), 2.83 (m, 1 H), 2.43 (td, 1 H, J ) 3.0 Hz, J
) 12.9 Hz), 2.13 (m, 1 H), 2.02, (m, 1 H), 1.77 (m, 1 H), 1.68 (m,
trans-1. H NMR (600 MHz, CDCl3) δ 7.40 (d, 1 H, J ) 15.0
Hz), 7.24 (dd, 1 H, J ) 7.8 Hz), 7.14 (s, 1 H), 7.13 (m, 2 H), 6.82
2
2
2
2 H), 1.61 (br s, 1 H), 0.08 (t, 9 H, JSnH ) 27.3 Hz); 13C NMR
(d, 1 H, J ) 15.0 Hz), 4.31 (dddd, 1 H, JHF ) 47.2 Hz, JHH )
3 3
(100 MHz, CDCl3) δ 173.18, 147.41, 142.29, 141.13, 133.71,
128.30, 126.86, 126.47, 125.57, 81.22 (d, 1JCF ) 169.1 Hz), 62.85
(d, 2JCF ) 20.5 Hz), 56.53, 53.84, 51.24, 35.75, 33.84, 29.37, 27.88,
-7.89; HRMS (ESI) [M + H]+ Calcd for C21H31O2NF120Sn
468.1355, Found 468.1354.
10.7 Hz, JHH ) 5.5 Hz, JHH ) 2.4 Hz), 4.19 (partially resolved
ddd, 0.5 H, 2JHH ) 10.7 Hz, 3JHH ) 6.7 Hz, 3JHH ) 2.4 Hz), 4.11
(overlapping resonances, 0.5 H + 0.5 H, 3JHH ) 2.4 Hz), 4.06 (ddd,
0.5 H, 2JHH ) 12.9 Hz, 3JHH ) 6.7 Hz, 3JHH ) 2.4 Hz), 3.95 (dddd,
1 H, 3JHF ) 30.1 Hz, 2JHH ) 12.9 Hz, 3JHH ) 5.5 Hz, 3JHH ) 2.4
Hz), 3.77 (m, 2 H), 3.27 (dt, 1 H, J ) 12.6 Hz, J ) 6.0 Hz), 2.83
(m, 1 H), 2.62 (br s, 1 H, NH), 2.41 (td, 1 H, J ) 12.9 Hz, J ) 3.0
Hz), 2.15 (m, 1 H), 2.04 (m, 1 H), 1.78 (m, 1 H), 1.68 (m, 2 H);
semipreparative HPLC (tR ) 26.9 min, 8.8 mL/min).
2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-((Z)-2-trimethylstannylethe-
nyl)phenyl)nortropane (12). 2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-
bromophenyl)nortropane (10) (0.15 g, 4.05 × 10-4 mol), (Z)-1,2-
bis(trimethylstannyl)ethene (0.54 g, 1.53 mmol, 3.8 equiv),
Pd(PPh3)4 (73 mg, 6.32 × 10-5 mol, 0.16 equiv), and toluene (15
mL) were stirred at reflux under Ar for 16 h. The reaction mixture
was cooled to rt, poured onto dry silica (40 mm h × 43 mm i.d.)
that had been pretreated with 10% NEt3/hexane (50 mL), and eluted
under vacuum: CH2Cl2 (50 mL), hexane/EtOAc/NEt3 v/v/v 75:20:5
(50 mL), 50:45:5 (50 mL), 20:75:5 (400 mL). The solvent was
removed to give a brown oil (0.17 g) that was ∼78:22 cis/trans (+
impurities) by integration of the 1H NMR vinyl resonances.
Purification by radial chromatography (2 mm silica, v/v/v hexane/
EtOAc/NEt3 95:4:1 (100 mL), 90:8:2 (700 mL), 85:12:3 (100 mL),
80:16:4 (100 mL), and 75:20:5 (300 mL)) afforded 52 mg (27%)
of a faint yellow syrup that was ∼91:9 cis/trans and 41 mg (21%)
of a faint yellow syrup that was ∼68:32 cis/trans. TLC Rf ) 0.24
2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-((Z)-2-bromoethenyl)phenyl)-
nortropane (2). 2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-((Z)-2-trimeth-
ylstannylethenyl)phenyl)nortropane (11) (∼80:20 cis/trans, 38 mg,
8.15 × 10-5 mol) was dissolved in CH2Cl2 (4 mL) and cooled to
0 °C under Ar. Br2 (35 mg, 0.22 mmol) was dissolved in CH2Cl2
(1 mL) and added dropwise until a faint yellow color remained.
The reaction mixture was stirred at 0 °C under Ar for 6 min and
then quenched by addition of Na2S2O3 ·5H2O (0.57 g in 4 mL H2O).
The reaction mixture was diluted by addition of CH2Cl2 (10 mL)
and H2O (10 mL), the layers were separated, and the aqueous layer
was extracted with CH2Cl2 (5 mL × 2). The combined CH2Cl2
layers were dried over MgSO4 and the solvent was removed to
give a colorless residue that was purified by preparative TLC (silica,
20:75:5 v/v/v hexane/EtOAc/NEt3) to afford 21 mg (67%) of a
colorless residue that was ∼91:9 cis/trans by integration of the 1H
NMR vinyl resonances. The isomers were separated by semi-
preparative HPLC (9 mL/min, cis tR ) 15.9 min, trans tR ) 20.4
1
(silica, 20:75:5 v/v/v hexane/EtOAc/NEt3); H NMR (600 MHz,
3
3
CDCl3) δ 7.52 (td, 1 H, JHH ) 13.8 Hz, JSnH ) 73.4 Hz), 7.22
(dd, 1 H, J ) 7.5 Hz), 7.10 (s, 1 H), 7.08 (m, 2 H), 6.17 (td, 1 H,
3JHH ) 13.8 Hz, 2JSnH ) 32.1 Hz), 4.17 and 4.09 (dm, 1 H + 1 H,
2JHF ) 46.8 Hz), 3.92 (m, 2 H), 3.73 (m, 1 H), 3.70 (m, 1 H), 3.25
(dt, 1 H, J ) 5.9 Hz, J ) 13.2 Hz), 2.73 (m, 1 H), 2.62 (br s, 1 H,
NH s conc. dependent), 2.41 (td, 1 H, J ) 13.2 Hz, J ) 2.6 Hz),
2.11 (m, 1 H), 2.02 (m, 1 H), 1.76-1.58 (m, 5 H), 0.08 (t, 9 H,
2JSnH ) 27.0 Hz); 13C NMR (150 MHz, CDCl3) δ 173.53, 147.32,
142.42, 141.09, 133.71, 128.35, 126.86, 126.50, 125.69, 80.53 (d,
1
min) to afford 16 mg (51%) of 2 as a colorless residue: H NMR
(600 MHz, CDCl3) δ 7.53 (d, 1 H, J ) 7.8 Hz), 7.49 (s, 1 H), 7.30
(dd, 1 H, J ) 7.8 Hz), 7.18 (d, 1 H, J ) 7.2 Hz), 7.04 (d, 1 H, J
) 8.4 Hz), 6.42 (d, 1 H, J ) 7.8 Hz), 4.30 (dddd, 1 H, 2JHF ) 47.1
Hz, 2JHH) 10.7 Hz,3JHH) 2.4 Hz, 3JHH) 5.3 Hz), 4.15 (unresolved
dddd, 1 H, 2JHF ) 47.1 Hz, 2JHH ) 2.4 Hz), 4.09 (unresolved dddd,
1 H, 2JHH ) 2.4 Hz), 3.96 (dddd, 1 H, 3JHF ) 30.6 Hz, 2JHH) 12.9
3
1JCF ) 165.5 Hz), 59.97 (d, JCF ) 6.2 Hz), 56.52, 53.79, 51.20,
35.97, 33.90, 29.68 (d, 2JCF )19.9 Hz), 29.33, 27.86, -7.84; HRMS
(ESI) [M + H]+ Calcd for C22H33O2NF120Sn 482.1512, found
482.1513.
Hz,3JHH) 2.4 Hz, JHH) 5.3 Hz), 3.82 (br s, 1 H), 3.31 (dt, 1 H,
3
J ) 6.0 Hz, J ) 13.2 Hz), 2.87 (m, 1 H), 2.45 (unresolved td, 1 H,
J ) 12.6 Hz), 2.19 (m, 1 H), 2.07 (m, 1 H), 1.80 (m, 1 H), 1.72
(m, 2 H); 13C NMR (150 MHz, CDCl3) δ 173.13, 142.03, 135.13,
2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-((Z)-2-iodoethenyl)phenyl)-
nortropane (1). 2ꢀ-Carbo(2-fluoroethoxy)-3ꢀ-(3′-((Z)-2-trimeth-
ylstannylethenyl)phenyl)nortropane (11) (∼96:4 cis/trans, 35 mg,
7.51 × 10-5 mol) was dissolved in CHCl3 (5 mL) and cooled to
-2 °C under Ar. ICl (0.11 mL, 1.0 M CH2Cl2, 0.11 mmol, 1.5
equiv) was added dropwise, the reaction mixture was stirred at -2
°C under Ar for 15 min, and quenched by addition of Na2S2O3 ·5
H2O (0.307 g, 1.24 mmol, in 5 mL H2O). The mixture was diluted
with CHCl3 (5 mL) and H2O (5 mL); the layers were separated,
1
132.51, 128.40, 128.10, 127.56, 127.47, 106.71, 81.27 (d, JCF
)
2
169.2 Hz), 63.08 (d, JCF ) 18.6 Hz), 56.42, 53.89, 51.00, 35.47,
33.31, 29.07, 27.64; Analytical HPLC (tR ) 4.4 min, 1 mL/min);
HRMS (ESI) [MH]+ Calcd for C18H22O2NF79Br 382.0813, Found
382.0815; Calcd for C18H22O2NF81Br 384.0792, Found 384.0796.
2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-((Z)-2-iodoethenyl)phenyl)-
nortropane (3). 2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-((Z)-2-trimeth-
ylstannylethenyl)phenyl)nortropane (12) (∼ 95:5 cis/trans, 84 mg,

7796 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 24
Stehouwer et al.
1.75 × 10-4 mol) was dissolved in CHCl3 (10 mL) and cooled to
-7 °C under Ar(g). ICl (0.27 mL, 1.0 M CH2Cl2, 0.27 mmol, 1.5
equiv.) was added dropwise, the reaction mixture was warmed to
rt, stirred at rt for 10 min, and quenched by addition of
Na2S2O3 ·5H2O (0.683 g, 2.75 mmol, in 10 mL H2O). The reaction
mixture was diluted with CHCl3 (25 mL) and H2O (25 mL), the
layers were separated, and the aqueous layer was extracted with
CHCl3 (10 mL × 2). The combined CHCl3 layers were dried over
MgSO4, and the solvent was removed to give a yellow residue (85
mg) that was purified on Waters silica Sep-Pak Classics (2 in series):
loaded with CH2Cl2 (1 mL), eluted with CH2Cl2 (1 mL), then
hexane/EtOAc/NEt3 v/v/v 90:8:2 (2 mL), 75:20:5 (5 mL), 50:45:5
(10 mL), 20:75:5 (25 mL). The desired fractions were combined,
and the solvent was removed to give 43 mg (55%) of a yellow oil
that was ∼86:14 cis/trans by integration of the 1H NMR vinyl
resonances. The isomers were separated by semipreparative HPLC
(8.8 mL/min; cis tR ) 25.2 min; trans tR ) 34.3 min) to afford 26
mg (34%) of 3 as an opaque residue: 1H NMR (600 MHz, CDCl3)
δ 7.47 and 7.46 (overlapping resonances, 2 H, J ) 8.4 Hz), 7.29
(m, 2 H), 7.18 (d, 1 H, J ) 7.8 Hz), 6.56 (d, 1 H, J ) 8.4 Hz),
4.14 (m, 1 H), 4.06 (m, 1 H), 3.98 (quintet, 1 H, J ) 6.0 Hz), 3.87
(m, 1 H), 3.76 (m, 1 H), 3.73 (m, 1 H), 3.31 (dt, 1 H, J ) 13.2 Hz,
J ) 5.4 Hz), 2.78 (d, 1 H, J ) 5.4 Hz), 2.53 (br s, 1 H, NH), 2.43
(td, 1 H, J ) 2.4 Hz, J ) 12.9 Hz), 2.14 (m, 1 H), 2.03 (m, 1 H),
1.78 (m, 1 H), 1.68 (m, 3 H), 1.58 (m, 1 H); 13C NMR (150 MHz,
CDCl3) δ 173.52, 142.47, 138.64, 136.79, 128.32, 127.63, 126.78,
80.55 (d, 1JCF ) 165.0 Hz), 79.56, 59.97 (d, 3JCF ) 4.5 Hz), 56.47,
53.75, 51.19, 35.73, 33.58, 29.70 (d, 2JCF ) 20.6 Hz), 29.31, 27.83;
HRMS (ESI) [MH]+ Calcd for C19H24O2NF127I 444.0830, found
444.0825.
in a 110 °C oil bath, the solvent was evaporated under a N2(g) flow,
and CH3CN (3 mL) was added and evaporated in order to
azeotropically dry the Kryptofix 222/ K18F. 1,2-Dibrosylethane (4
mg in 1 mL CH3CN) was added, the reaction mixture was heated
at 90 °C for 10 min, and the [18F]fluoroethylbrosylate was trapped
on a Waters silica Sep-Pak Classic (WAT051900) (previously
prepped with 10 mL EtOEt). The [18F]fluoroethylbrosylate was
eluted with EtOEt, the EtOEt solution was transferred to a hot cell
under N2(g) pressure and collected in a V-tube to give [18F]fluo-
roethylbrosylate in 74% radiochemical yield (decay corrected from
transfer of H18F(aq) to the CPCU). The V-tube was placed in an 80
°C oil bath and the EtOEt was evaporated with an Ar(g) flow. The
solution of radiolabeling precursor was then added to this V-tube
(see below).
[18F]Fluoropropylbrosylate. Prepared in an analogous manner
as [18F]fluoroethylbrosylate using 1,3-dibrosylpropane.
2ꢀ-Carbo(2-[18F]fluoroethoxy)-3ꢀ-(3′-((Z)-2-iodoethenyl)phe-
nyl)nortropane ([18F]1). N-(t-butoxycarbonyl)-3ꢀ-(3′-((Z)-2-iodo-
ethenyl)phenyl)nortropane-2ꢀ-carboxylic acid (13) (∼ 1.1 mg,
∼98:2 cis/trans) was dissolved in DMF (0.3 mL), deprotonated by
addition of 0.1 M Bu4NOH(aq) (16 µL, 0.7 equiv), and added to
[18F]fluoroethylbrosylate. The solution was heated at 90 °C for 10
min, 6 M HCl(aq) (∼0.16 mL, ∼422 equiv) was added, the solution
was heated at 90 °C for 10 min, cooled to 0 °C, and neutralized by
addition of 6 M NH4OH(aq) (∼0.16 mL, ∼422 equiv). The solution
was diluted with HPLC solvent and purified by semipreparative
HPLC (tR (range) ) 15-19 min, 9.2 mL/min). The desired fractions
were combined, diluted 1:2 v/v with H2O and loaded onto a Waters
C
18 Sep-Pak. The Sep-Pak was washed with 0.9% NaCl(aq) (40 mL)
and then EtOH (0.5 mL). The product was eluted from the Sep-
Pak with EtOH (1.5 mL) and collected in a sealed sterile vial
containing 0.9% NaCl(aq) (3.5 mL). This solution was passed
successively through a 1 µm filter and then a 0.2 µm filter (Acrodisc
PTFE) under Ar-pressure and collected in a sealed sterile dose vial
containing 0.9% NaCl(aq) (10 mL). The total synthesis time was
∼80 min from the delivery of [18F]fluoroethylbrosylate to the hot
cell with a 6.3 ( 1.8% (n ) 4) radiochemical yield (decay
corrected). The product was then analyzed by analytical HPLC (tR
) 4.9 min, 1 mL/min) to determine the radiochemical purity (97
( 2%, n ) 4).
2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-((Z)-2-bromoethenyl)phe-
nyl)nortropane (4). 2ꢀ-Carbo(3-fluoropropoxy)-3ꢀ-(3′-((Z)-2-tri-
methylstannylethenyl)phenyl)nortropane (12) (∼ 91:9 cis/trans, 52
mg, 1.08 × 10-4 mol) was dissolved in CHCl3 (5 mL) and cooled
to 0 °C under Ar. Br2 (58 mg, 3.63 × 10-4 mol, 3.4 equiv.) was
dissolved in CHCl3 (1 mL) and added dropwise until a faint yellow
color persisted (not all of the solution was added). The reaction
mixture was stirred at 0 °C under Ar for 15 min and then quenched
by addition of Na2S2O3 ·5 H2O (98 mg, 3.95 × 10-4 mol, dissolved
in 10 mL H2O). The mixture was diluted with CHCl3 (10 mL) and
H2O (10 mL); the layers were separated, and the aqueous layer
was extracted with CHCl3 (10 mL × 2). The combined CHCl3
layers were dried over MgSO4, and the solvent was removed to
give a colorless syrup that became an opaque residue when dried
under vacuum. The residue was dissolved in CH2Cl2, poured onto
dry silica (26 mm h × 33 mm i.d.), and eluted under vacuum:
CH2Cl2 (25 mL), hexanes/EtOAc/NEt3 v/v/v 75:20:5 (25 mL), 50:
45:5 (50 mL), 20:75:5 (250 mL). The isolated product was further
purified by preparative TLC (20:75:5 v/v/v hexanes/EtOAc/NEt3)
to give a faint yellow syrup (26 mg) that was ∼93:7 cis/trans by
integration of the 1H NMR vinyl resonances. The isomers were
separated by semipreparative HPLC (cis tR ) 20.3 min, 9.0 mL/
min) to afford 21 mg (49%) of a colorless residue: 1H NMR (600
MHz, CDCl3) δ 7.53 (d, 1 H, J ) 7.2 Hz), 7.49 (s, 1 H), 7.30 (dd,
1 H, J ) 7.2 Hz), 7.15 (d, 1 H, J ) 7.2 Hz), 7.04 (d, 1 H, J ) 8.4
Hz), 6.44 (d, 1 H, J ) 8.4 Hz), 4.11 (m, 1 H), 4.03 (m, 1 H), 3.97
(quintet, 1 H, J ) 5.9 Hz), 3.87 (m, 2 H), 3.82 (m, 1 H), 3.32 (dt,
1 H, J ) 6.0 Hz, J ) 12.6 Hz), 2.80 (overlapping resonances: br
s + m, 2 H), 2.46 (td, 1 H, J ) 2.4 Hz, J ) 13.2 Hz), 2.25 (m, 1
H), 2.14 (m, 1 H), 1.82 (m, 1 H), 1.74 (m, 2 H), 1.65 (m, 1 H),
1.54 (m, 1 H); 13C NMR (150 MHz, CDCl3) δ 173.55, 141.61,
135.24, 132.32, 128.51, 128.11, 127.69, 127.51, 106.90, 80.41 (d,
2ꢀ-Carbo(2-[18F]fluoroethoxy)-3ꢀ-(3′-((Z)-2-bromoethenyl)phe-
nyl)nortropane ([18F]2). N-(t-butoxycarbonyl)-3ꢀ-(3′-((Z)-2-bro-
moethenyl)phenyl)nortropane-2ꢀ-carboxylic acid (14) (∼0.6 mg,
∼95:5 cis/trans) was dissolved in DMF (0.3 mL), deprotonated by
addition of 0.1 M Bu4NOH(aq) (10 µL, 0.7 equiv), and added to
[18F]fluoroethylbrosylate. The solution was heated at 90 °C for 10
min, 6 M HCl(aq) (∼0.11 mL, ∼480 equiv) was added, the solution
was heated at 90 °C for 10 min, cooled to 0 °C, and neutralized by
addition of 6 M NH4OH(aq) (∼0.11 mL, ∼480 equiv). The solution
was diluted with HPLC solvent and purified by semipreparative
HPLC (tR (range) ) 10-16 min, 9.2 mL/min). The desired fractions
were combined, diluted 1:2 v/v with H2O and loaded onto a Waters
C
18 Sep-Pak. The Sep-Pak was washed with 0.9% NaCl(aq) (40 mL)
and then EtOH (0.5 mL). The product was eluted from the Sep-
Pak with EtOH (1.5 mL) and collected in a sealed sterile vial
containing 0.9% NaCl(aq) (3.5 mL). This solution was passed
successively through a 1 µm filter and then a 0.2 µm filter (Acrodisc
PTFE) under Ar-pressure and collected in a sealed sterile dose vial
containing 0.9% NaCl(aq) (10 mL). The total synthesis time was
∼75 min from the delivery of [18F]fluoroethylbrosylate to the hot
cell with a 4.2 ( 2.7% (n ) 3) radiochemical yield (decay
corrected). The product was then analyzed by analytical HPLC (tR
) 4.4 min, 1 mL/min) to determine the radiochemical purity (95
( 2%, n ) 3).
3
1JCF ) 166.0 Hz), 60.38 (d, JCF ) 4.2 Hz), 56.31, 53.86, 50.64,
35.63, 33.00, 29.57 (d, 2JCF ) 18.7 Hz), 28.63, 27.34; HRMS (ESI)
[M + H]+ Calcd for C19H24O2FN79Br 396.0969, found 396.0974.
[18F]Fluoroethylbrosylate. H18F was produced with a Siemens
11-MeV RDS 112 cyclotron by employing the 18O(p,n)18F reaction
in H218O. The H18F(aq) was transferred to a chemical processing
control unit (CPCU), collected on a trap/release cartridge, released
with K2CO3(aq) (0.9 mg in 0.6 mL H2O), and added to a CH3CN
solution of Kryptofix 222 (5 mg in 1 mL). The solution was placed
2ꢀ-Carbo(3-[18F]fluoropropoxy)-3ꢀ-(3′-((Z)-2-iodoethenyl)phe-
nyl)nortropane ([18F]3). N-(t-butoxycarbonyl)-3ꢀ-(3′-((Z)-2-iodo-
ethenyl)phenyl)nortropane-2ꢀ-carboxylic acid (13) (∼0.6 mg) was
dissolved in DMF (0.3 mL), deprotonated by addition of 0.1 M
Bu4NOH(aq) (11 µL, 0.9 equiv), and added to [18F]fluoropropyl-
brosylate. The solution was heated at 105 °C for 10 min, and 6 M
HCl(aq) (∼0.12 mL, ∼ 580 equiv) was added. The solution was

Imaging of the Serotonin Transporter
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heated at 105 °C for 10 min, cooled to 0 °C, and neutralized by
addition of 6 M NH4OH(aq) (∼0.12 mL, ∼580 equiv). The solution
was diluted with HPLC solvent and purified by semipreparative
HPLC (tR (range) ) 21-25 min, 9.2 mL/min). The desired fractions
were combined, diluted 1:2 v/v with H2O, and loaded onto a Waters
C18 Sep-Pak. The Sep-Pak was washed with 0.9% NaCl(aq) (40 mL)
and then EtOH (0.5 mL). The product was eluted from the Sep-
Pak with EtOH (1.5 mL) and collected in a sealed sterile vial
containing 0.9% NaCl(aq) (3.5 mL). This solution was passed
successively through a 1 µm filter and then a 0.2 µm filter (Acrodisc
PTFE) under Ar-pressure and collected in a sealed sterile dose vial
containing 0.9% NaCl(aq) (10 mL).
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[18F]fluoropropylbrosylate to the hot cell with a 1.9 ( 0.8% (n )
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3245.
and then EtOH (0.5 mL). The product was eluted from the Sep-
Pak with EtOH (1.5 mL) and collected in a sealed sterile vial
containing 0.9% NaCl(aq) (3.5 mL). This solution was passed
successively through a 1 µm filter and then a 0.2 µm filter (Acrodisc
PTFE) under Ar-pressure and collected in a sealed sterile dose vial
containing 0.9% NaCl(aq) (10 mL). The total synthesis time was
∼77 min from the delivery of [18F]fluoropropylbrosylate to the hot
cell with a 1.7 ( 0.3% (n ) 3) radiochemical yield (decay
corrected). The product was then analyzed by analytical HPLC (tR
) 6.0 min, 1 mL/min) to determine the radiochemical purity (93
( 7%, n ) 3).
Acknowledgment. This research was sponsored by the
NIMH (1-R21-MH-66622-01). We acknowledge the use of
shared instrumentation provided by grants from the NIH and
the NSF.
Note Added after ASAP Publication. This manuscript was
released ASAP on November 24, 2008 with incorrect labeling for
the last two tables. The correct version was posted on December
18, 2008.
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Supporting Information Available: Additional microPET data
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