Synthesis of carbon-11-labeled 5-HT6R antagonists as new candidate PET radioligands for imaging of Alzheimer's disease

Article abstract of DOI:10.1016/j.bmcl.2018.04.014

Carbon-11-labeled serotonin (5-hydroxytryptamine) 6 receptor (5-HT₆R) antagonists, 1-[(2-bromophenyl)sulfonyl]-5-[¹¹C]methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole (O-[¹¹C]2a) and 1-[(2-bromophenyl)sulfonyl]-5-metho

Full text of DOI:10.1016/j.bmcl.2018.04.014

Accepted Manuscript
Synthesis of carbon-11-labeled 5-HT6R antagonists as new candidate PET ra-
dioligands for imaging of Alzheimer’s disease
Xiaohong Wang, Fugui Dong, Caihong Miao, Wei Li, Min Wang, Mingzhang
Gao, Qi-Huang Zheng, Zhidong Xu
PII:
S0960-894X(18)30312-3
https://doi.org/10.1016/j.bmcl.2018.04.014
BMCL 25761
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
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Revised Date:
Accepted Date:
6 March 2018
4 April 2018
6 April 2018
Please cite this article as: Wang, X., Dong, F., Miao, C., Li, W., Wang, M., Gao, M., Zheng, Q-H., Xu, Z., Synthesis
of carbon-11-labeled 5-HT6R antagonists as new candidate PET radioligands for imaging of Alzheimer’s disease,
Bioorganic & Medicinal Chemistry Letters (2018), doi: https://doi.org/10.1016/j.bmcl.2018.04.014
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Synthesis of carbon-11-labeled 5-HT6R antagonists as new
candidate PET radioligands for imaging of Alzheimer’s disease
Xiaohong Wanga, Fugui Donga, Caihong Miaoa, Wei Lia, Min Wangb, Mingzhang Gaob,
Qi-Huang Zhengb,*, Zhidong Xua,c,*
aKey Laboratory of Medicinal Chemistry and Molecular Diagnosis of Ministry of Education, College of Chemistry and
Environmental Science, Hebei University, Baoding, Hebei 071002, China
bDepartment of Radiology and Imaging Sciences, Indiana University School of Medicine, 1345 West 16th Street, Room 202,
Indianapolis, IN 46202, USA
cShijiazhuang Vince Pharmatech Co., Ltd., Shijiazhuang, Hebei 050030, China
*Corresponding authors. E-mail address: qzheng@iupui.edu (Q.-H. Zheng); zhidongxu@hbu.edu.cn (Z. Xu).
This is where the receipt/accepted dates will go; Received Month XX, 2018; Accepted Month XX, 2018 [BMCL RECEIPT]
Abstract—Carbon-11-labeled serotonin (5-hydroxytryptamine) 6 receptor (5-HT6R) antagonists, 1-[(2-bromophenyl)sulfonyl]-5-
[11C]methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole
(O-[11C]2a)
and
1-[(2-bromophenyl)sulfonyl]-5-methoxy-3-[(4-
[11C]methyl-1-piperazinyl)methyl]-1H-indole (N-[11C]2a), 5-[11C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-
indole (O-[11C]2b) and 5-methoxy-3-((4-[11C]methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-indole (N-[11C]2b), 1-((4-
isopropylphenyl)sulfonyl)-5-[11C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole
(O-[11C]2c)
and
isopropylphenyl)sulfonyl)-5-methoxy-3-((4-[11C]methylpiperazin-1-yl)methyl)-1H-indole (N-[11C]2c), 1-((4-fluorophenyl)sulfonyl)-5-
[11C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole (O-[11C]2d)
and 1-((4-fluorophenyl)sulfonyl)-5-methoxy-3-((4-
1-((4-
[11C]methylpiperazin-1-yl)methyl)-1H-indole (N-[11C]2d), were prepared from their O- or N-desmethylated precursors with [11C]CH3OTf
through O- or N-[11C]methylation and isolated by HPLC combined with SPE in 40-50% radiochemical yield, based on [11C]CO2 and
decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (MA) at EOB was 370-740
GBq/µmol with a total synthesis time of ~40-minutes from EOB.
Keywords: Serotonin (5-hydroxytryptamine) 6 receptor (5-HT6R); Carbon-11-labeled 5-HT6R antagonists; Radiosynthesis;
Positron emission tomography (PET); Alzheimer’s disease (AD).
Alzheimer’s disease (AD) is the most common form of
dementia and affects close to 50 million people
worldwide in 2017.1 The disease is divided into four
stages, including predementia, early dementia, moderate
AD and advanced AD.2 The cause for most AD cases is
still unknown, and there are several competing
hypotheses like genetic, cholinergic hypothesis, amyloid
hypothesis, and tau hypothesis, trying to explain it.3 AD
might be treated by symptomatic treatments and
disease-modifying therapies such as neuroprotective and
neurorestorative therapies, however, none effective
strategy is approved for preventing, curing and slowing
the progress of AD.4 The current available medications
can only be used to treat the cognitive problems of AD,
focused on acetylcholinesterase inhibitors (AChEIs)
including tacrine, rivastigmine, galantamine, and
donepezil, as well as a N-methyl-D-aspartate (NMDA)
receptor antagonist memantine.5 The benefit from these
approved cognitive enhancing drugs for AD is small,
and novel alternate therapy for treating cognitive
disorders is eagerly needed.6 Since the clinical trial of
the disease-modifying therapies in AD is an extremely
complex process with very high failure rate, the
researchers have turned their focus to symptomatic

treatment, and serotonin (5-hydroxytryptamine)
receptor (5-HT6R) has become a promising alternative
target.7 5-HT6R is a subtype of 5-HT receptor, and it is a
6
methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-indole
(2c) and 1-((4-fluorophenyl)sulfonyl)-5-methoxy-3-((4-
methylpiperazin-1-yl)methyl)-1H-indole (2d), exhibited
high binding affinity to human 5-HT6R with Ki value
2.0, 4.3, 1.6 and 5.0 nM, respectively, and high
selectivity over 100 target sites.24 These compounds
possesses the combination of favorable binding affinity
and selectivity to 5-HT6R, and O- and N-methyl
positions amenable to labeling with carbon-11,
therefore, their carbon-11-labeled radioligands are
expected to have high specific binding. Here, we report
the synthesis of carbon-11-labeled 5-HT6R antagonists
labeled at oxygen or nitrogen positions O-[11C]2a-d and
N-[11C]2a-d (Figure 2) as new potential PET
radioligands for imaging of AD.
G
protein-coupled receptor (GPCR). 5-HT6R
antagonists have been hypothesized to improve
cognition, learning, and memory.8
To discover more effective treatments, reliable
diagnostic tools are really needed. Neuroimaging of AD
becomes one of the most active as well as most
challenging areas in neuroscience.9 Advanced
biomedical imaging technique positron emission
tomography (PET) is a promising modality for AD, and
significant advances have occurred in this field of
molecular imaging.10 The development of PET imaging
probes for in vivo detection of Alzheimer’s brains is
critical for early and accurate diagnosis and for the
successful discovery of AD therapies.11 Previous PET
AD imaging agent development is based on cholinergic
hypothesis, amyloid hypothesis, and tau hypothesis. The
representative PET tracers in clinical evaluations such
as carbon-11-labeled AChEIs [11C]AMP ([11C]MP4A),
[11C]PMP ([11C]MP4P), and [11C]Donepezil;12-14 β-
amyloid plaques (Aβ) tracers [11C]PIB and [18F]Amyvid
([18F]AV-45);15,16 and tau tracers [11C]PBB3 and
[18F]T807 ([18F]AV-1451)17,18 are listed in Figure 1.
The success and limitations of Aβ imaging and tau
imaging have spurred efforts worldwide to develop new
selective PET tracers for different imaging targets. Our
efforts toward the development of PET agents for AD
diagnosis have been ongoing quite some time, and a
series of enzyme- or receptor-based PET agents have
been developed in this laboratory. In our previous work,
we have targeted the enzyme glycogen synthase kinase-
3 (GSK-3) and developed carbon-11-labeled GSK-3
inhibitors19,20 as PET AD imaging agents (Figure 1). In
this ongoing study, we target 5-HT6R, which is a novel
and attractive molecular target for treatment and PET
imaging of AD.8 Several 5-HT6R PET tracers such as
[18F]12ST05, [11C]GSK215083 and [11C]SB399885, as
shown in Figure 2, have been previously developed,
however, preclinical and clinical evaluation indicated
these radioligands have significant drawbacks like no
specific binding, high non-specific binding, poor brain
entry and inconsistent brain uptake compared to known
5-HT6R distribution.21-23 Thus an ideal 5-HT6R
radioligand that can be used in the clinical setting to
study 5-HT6R expression levels in AD remains to be
Figure 1. PET radiotracers for imaging of AD.
discovered. Recently
a
novel series of 3-
(piperazinylmethyl) indole derivatives have been
developed as 5-HT6R antagonists for potential treatment
of AD, and the representative compounds, 1-[(2-
bromophenyl)sulfonyl]-5-methoxy-3-[(4-methyl-1-
piperazinyl)methyl]-1H-indole (2a), 5-methoxy-3-((4-
methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-1H-
Figure 2. 5-HT6R PET radioligands.
indole
(2b),
1-((4-isopropylphenyl)sulfonyl)-5-

3c: R = 4-iPr; 3d: R = 4-F) in 88-94% yield.
Compounds 5 (5a: R = 2-Br; 5b: R = H; 5c: R = 4-iPr;
5d: R = 4-F) were prepared from commercially
procured aryl sulfonyl or substituted aryl sulfonyl by
condensation with compound 4 in the presence of
ground KOH in THF with 90-96% yield. The
deprotecting reaction of compounds 5 (5a: R = 2-Br;
5b: R = H; 5c: R = 4-iPr; 5d: R = 4-F) with
trifluoroacetic acid (TFA) in THF gave N-
desmethylated precursors 6 (6a: R = 2-Br; 6b: R = H;
6c: R = 4-iPr; 6d: R = 4-F) in 91-96% yield.
CH3
CH2O, HOAc
CH3OH
N
H3CO
N
HN
N CH3
+
H3CO
N
H
N
H
1
O
S
Cl
R
O
KOH, THF
CH3
N
CH3
N
N
N
O
HO
H3CO
48% HBr
N
S
N
O
O
R
3a: R=2-Br
3b: R=H
3c: R=4-iPr
3d: R=4-F
S
2a: R=2-Br
2b: R=H
2c: R=4-iPr
2d: R=4-F
O
R
Scheme 1. Synthesis of reference standards 2a-d and O-desmethylated
precursors 3a-d.
CH2O, HOAc
CH3OH
N(Boc)
H3CO
N
HN
N(Boc)
+
H3CO
Scheme 3. Synthesis of target tracers (O-[11C]2a-d) labeled at oxygen
position.
N
H
N
H
4
O
S
Cl
R
O
KOH, THF
NH
N
N(Boc)
N
O
H3CO
H3CO
TFA, THF
N
N
Scheme 4. Synthesis of target tracers (N-[11C]2a-d) labeled at nitrogen
position.
O
S
O
R
6a: R=2-Br
: R=H
S
5a: R=2-Br
5b: R=H
5c: R=4-iPr
5d: R=4-F
O
R
6b
6c: R=4-iPr
: R=4-F
6d
Synthesis of the target tracer (O-[11C]2a-d and N-
[11C]2a-d) labeled at oxygen or nitrogen positions is
shown in Scheme 3 and Scheme 4. O-Desmethylated
precursors 3a-d and N-desmethylated precursors 6a-d
underwent O- or N-[11C]methylation30,31 using the
reactive [11C]methylating agent [11C]methyl triflate
([11C]CH3OTf)32,33 in acetonitrile at 80 °C under basic
conditions (2 M KOH). The product was isolated by
semi-preparative reverse-phase (RP) high performance
liquid chromatography (HPLC) with a C-18 column,
and then concentrated by solid-phase extraction
(SPE)34,35 with a disposable C-18 Light Sep-Pak
cartridge to produce the corresponding pure
radiolabeled compound O-[11C]2a-d or N-[11C]2a-d in
40-50% radiochemical yield, decay corrected to end of
bombardment (EOB), based on [11C]CO2.
Scheme 2. Synthesis of N-desmethylated precursors 6a-d.
The reference standards 2 (2a: R = 2-Br; 2b: R = H; 2c:
R = 4-iPr; 2d: R = 4-F), their O-desmethylated
precursors 3 (3a: R = 2-Br; 3b: R = H; 3c: R = 4-iPr;
3d: R = 4-F) and N-desmethylated precursors 6 (6a: R =
2-Br; 6b: R = H; 6c: R = 4-iPr; 6d: R = 4-F) were
synthesized as depicted in Scheme 1 and Scheme 2
according
to
the
reported
procedure
with
modifications.24-29 The main modifications included the
use of different reagents, reactions and methods to
synthesize new compounds O- and N-desmethylated
precursors.
5-Methoxy-3-((4-methylpiperazin-1-yl)
methyl)-1H-indole (1) and tert-butyl 4-((5-methoxy-1H-
indol-3-yl)methyl)piperazine-1-carboxylate (4) were
achieved by well-known Mannich reaction from
commercially available 5-methoxy-1H-indole and 1-
methylpiperazine or tert-butyl piperazine-1-carboxylate
in 92% and 91% yield, respectively. Reference
standards 2 (2a: R = 2-Br; 2b: R = H; 2c: R = 4-iPr; 2d:
R = 4-F) was prepared from commercially procured aryl
sulfonyl or substituted aryl sulfonyl by condensation
with compound 1 in the presence of ground KOH in
THF with 76-94% yield. Compounds 2 (2a: R = 2-Br;
2b: R = H; 2c: R = 4-iPr; 2d: R = 4-F) were treated with
48% HBr to provide the corresponding O-
desmethylated precursors 3 (3a: R = 2-Br; 3b: R = H;
The radiosynthesis includes three stages: 1) labeling
reaction; 2) purification; and 3) formulation. We
employed more reactive [11C]CH3OTf, instead of
commonly used [11C]methyl iodide ([11C]CH3I),36 in O-
or N-[11C]methylation to improve radiochemical yield
of O-[11C]2a-d or N-[11C]2a-d from 30-40% to 40-50%.
We used an Eckert & Ziegler Modular Lab C-11 Methyl
Iodide/Triflate module to produce [11C]methylating
agent either [11C]CH3OTf or [11C]CH3I ([11C]CH3Br
passed through a NaI column). The direct comparison

between [11C]CH3OTf and [11C]CH3I confirmed the
result. The labeling reaction was conducted using a V-
vial method. Addition of aqueous NaHCO3 to quench
the radiolabeling reaction and to dilute the radiolabeling
mixture prior to the injection onto the semi-preparative
HPLC column for purification gave better separation of
O-[11C]2a-d or N-[11C]2a-d from its O-desmethylated
precursors 3a-d or N-desmethylated precursors 6a-d.
We used Sep-Pak trap/release method instead of
rotatory evaporation for formulation to improve the
chemical purity of radiolabeled products O-[11C]2a-d or
N-[11C]2a-d. In addition, a C18 Light Sep-Pak to
replace a C18 Plus Sep-Pak allowed final product
formulation with ≤5% ethanol.37 Overall, it took ~40
min for synthesis, purification and dose formulation.
practice perspective have been provided in our previous
works.42 At the end of synthesis (EOS), the MA of
[11C]-tracer was determined again by analytical RP
HPLC, calculated, decay corrected to EOB, and based
on [11C]CO2, which was in agreement with the ‘on line’
determined value. In this work, semi-preparative HPLC
was used for purification, thus the MA of [11C]-tracer
was assessed by both semi-preparative HPLC (during
synthesis) and analytical HPLC (EOS).
Chemical purity and radiochemical purity were
determined by analytical HPLC.43 The chemical purity
of the precursor and reference standard was >95%. The
radiochemical purity of the target tracer was >99%
determined by radio-HPLC through γ-ray (PIN diode)
flow detector, and the chemical purity of the target
tracer was >95% determined by reversed-phase HPLC
through UV flow detector.
The radiosynthesis was performed in a home-built
automated
multi-purpose
[11C]-radiosynthesis
module.38-40 This radiosynthesis module facilitated the
overall design of the reaction, purification and
reformulation capabilities in a fashion suitable for
adaptation to preparation of human doses. In addition,
the module is designed to allow in-process measurement
of [11C]-tracer molar activity (MA, GBq/µmol at EOB)
using a radiation detector with a UV detector at the
outlet of the HPLC-portion of the system. In the HPLC
chromatogram, peak analysis of the chromatographic
data utilized PeakSimple software (SRI Instruments,
Las Vegas, NV). Immediately following elution of the
product peak, the chromatographic data are exported to
PeakSimple readable files, and the area of the
radioactivity peak is converted to GBq - mCi at EOB by
comparison to a reference calibration curve previously
constructed using the same detector, loop column,
mobile phase and flow rate. The mass peak from the
UV chromatogram (without decay correction) is
similarly compared to a standard curve made at the
same UV wavelength, mobile phase and flow rate.
Simple division of the total EOB radioactivity peak (in
GBq - mCi) by the total mass peak (in nmoles) gives
specific activity at EOB in GBq - Ci/µmol. For the
reported syntheses, product MA was in a range of 370-
740 GBq/µmol at EOB. The factors that affect the EOB
MA significantly to lead to such a wide range have been
discussed in our previous works.41 The general methods
to increase SA have been described as well, and the SA
of our [11C]-tracers is significantly improved.41 The
‘wide range’ of MA we reported is for the same [11C]-
tracer produced in different days, because very different
[11C]-target and [11C]-radiosynthesis unit situations
would make MA in a wide range. For a [11C]-tracer
produced in the same day, the MA of the same tracer in
different production runs will be in a small range,
because [11C]-target and [11C]-radiosynthesis unit would
not be much different in the same day. Likewise, the
methods to minimize such wide range of MA from
The octanol-water partition coefficient (commonly
expressed as Log P) is an important physical parameter
directly correlated with the biological activities of a
wide variety of organic compounds.42 Log P provides an
assessment of lipophilicity that often correlates with a
compound’s ability to penetrate the blood brain barrier
(BBB). We obtained Log P and calculated Log P (CLog
P) values of carbon-11-labeled 5-HT6R antagonists O-
[11C]2a-d and N-[11C]2a-d (Figure 2) in comparison
with [11C]PIB, [18F]Amyvid, [11C]PBB3 and [18F]T807
(Figure 1) from ChemDraw Professional 15.1
(ChemOffice) as listed in Table 1. Log P data of O-
[11C]2a-d and N-[11C]2a-d (2.59 - 3.83) are similar to
those of [11C]PIB, [18F]Amyvid, [11C]PBB3 and
[18F]T807 (2.25 – 4.09), which are PET AD imaging
agents in clinical evaluation. These data suggest the O-
[11C]2a-d and N-[11C]2a-d have appropriate
lipophilicity for brain uptake.
Table 1. Log P and CLog P values of carbon-11-labeled
5-HT6R antagonists 2a-d in comparison with [11C]PIB,
[18F]Amyvid, [11C]PBB3 and [18F]T807.
Compound
O- or N-[11C]2a
O- or N-[11C]2b
O- or N-[11C]2c
O- or N-[11C]2d
[11C]PIB
Log P
3.42
2.59
3.83
2.75
3.41
3.16
4.09
2.25
CLog P
4.92
4.05
5.48
4.20
3.99
3.91
4.05
3.18
[18F]Amyvid
[11C]PBB3
[18F]T807
The stability of the labeled tracers O-[11C]2a-d and N-
[11C]2a-d was evaluated by analytical HPLC from EOS
up to 3 h, one injection of the tracer solution in
EtOH/saline onto HPLC column per hour. The HPLC

chromatograms showed O-[11C]2a-d and N-[11C]2a-d
were stable without decomposition.
4. Cummings JL. Defining and labeling disease-
modifying treatments for Alzheimer's disease.
Alzheimer’s Dement. 2009;5:406-418.
5. Hung SY, Fu WM. Drug candidates in clinical trials
for Alzheimer's disease. J Biomed Sci. 2017;24:47.
The experimental details and characterization data for
compounds 1-6 and for the tracers O-[11C]2a-d and N-
[11C]2a-d are given.44
6. Kamkwalala
AR,
Newhouse
PA.
Beyond
acetylcholinesterase inhibitors: Novel cholinergic
treatments for Alzheimer's disease. Curr Alzheimer
Res. 2017;14:377-392.
In summary, synthetic routes with moderate to high
yields have been developed to produce the reference
standard 2a-d, O-desmethylated precursor 3a-d, N-
desmethylated precursor 6a-d, and target tracer O-
[11C]2a-d and N-[11C]2a-d. The radiosynthesis
employed [11C]CH3OTf for O- or N-[11C]methylation at
O- or N-position of 3-(piperazinylmethyl) indole
desmethylated precursor, followed by product
purification and isolation using a semi-preparative RP
HPLC combined with SPE. O-[11C]2a-d and N-[11C]2a-
7. de Jong IEM, Mørk A. Antagonism of the 5-HT6
receptor - Preclinical rationale for the treatment of
Alzheimer's
2017;125:50-63.
disease.
Neuropharmacology.
8. Benhamú B, Martín-Fontecha M, Vázquez-Villa H,
Pardo L, López-Rodríguez ML. Serotonin 5-HT6
receptor antagonists for the treatment of cognitive
deficiency in Alzheimer's disease. J Med Chem.
2014;57:7160-7181.
d
were obtained in high radiochemical yield,
9. Rathore S, Habes M, Iftikhar MA, Shacklett A,
Davatzikos C. A review on neuroimaging-based
classification studies and associated feature extraction
methods for Alzheimer's disease and its prodromal
stages. Neuroimage. 2017;155:530-548.
radiochemical purity and chemical purity, with a
reasonable short overall synthesis time, and high molar
activity. This will facilitate studies to evaluate carbon-
11-labeled 5-HT6R antagonists O-[11C]2a-d and N-
[11C]2a-d as new candidate PET radioligands for
imaging of AD.
10. Frisoni GB, Boccardi M, Barkhof F, Blennow K,
Cappa S, Chiotis K, Démonet JF, Garibotto V,
Giannakopoulos P, Gietl A, Hansson O, Herholz K,
Jack CR Jr, Nobili F, Nordberg A, Snyder HM, Ten
Kate M, Varrone A, Albanese E, Becker S, Bossuyt P,
Carrillo MC, Cerami C, Dubois B, Gallo V, Giacobini
E, Gold G, Hurst S, Lönneborg A, Lovblad KO,
Mattsson N, Molinuevo JL, Monsch AU, Mosimann
U, Padovani A, Picco A, Porteri C, Ratib O, Saint-
Aubert L, Scerri C, Scheltens P, Schott JM, Sonni I,
Teipel S, Vineis P, Visser PJ, Yasui Y, Winblad B.
Strategic roadmap for an early diagnosis of
Alzheimer's disease based on biomarkers. Lancet
Neurol. 2017;16:661-676.
Acknowledgments
This work was partially supported by the Hebei
Province Major Science and Technology Program (No.
17392605D), the Hundred-Talent Program of Hebei
Province (No. E2015100012), and the High Level
Scientific and Technological Innovation and
Entrepreneurial Talent Plan of Shijiazhuang in China.
This work was also partially supported by the Advanced
Imaging Research and Technology Development
(AIRTD) grants from the Indiana University
Department of Radiology and Imaging Sciences in the
United States.
11. Okamura N, Harada R, Furukawa K, Furumoto S,
Tago T, Yanai K, Arai H, Kudo Y. Advances in the
development of tau PET radiotracers and their clinical
applications. Ageing Res Rev. 2016;30:107-113.
12. Ota T, Shinotoh H, Fukushi K, Nagatsuka S, Namba
H, Iyo M, Aotsuka A, Tanaka N, Sato K, Shiraishi T,
Tanada S, Arai H, Irie T. A simple method for the
detection of abnormal brain regions in Alzheimer's
disease patients using [11C]MP4A: comparison with
References and notes
1. Jakki SL, Senthil V, Yasam VR, Chandrasekar MJN,
Vijayaraghavan C. The blood brain barrier and its role
in Alzheimer's therapy: An overview. Curr Drug
Targets. 2018;19:155-169.
[
123I]IMP SPECT. Ann Nucl Med. 2004;18:187-193.
2. Chételat G, Villemagne VL, Pike KE, Ellis KA, Ames
D, Masters CL, Rowe CC; Australian Imaging
Biomarkers and Lifestyle Study of Ageing Research
Group. Relationship between memory performance
and β-amyloid deposition at different stages of
Alzheimer's disease. Neurodegener Dis. 2012;10:141-
144.
13. Sato K, Fukushi K, Shinotoh H, Nagatsuka S, Tanaka
N, Aotsuka A, Ota T, Shiraishi T, Tanada S, Iyo M,
Irie T. Evaluation of simplified kinetic analyses for
measurement of brain acetylcholinesterase activity
using N-[11C]Methylpiperidin-4-yl propionate and
positron emission tomography. J Cereb Blood Flow
Metab. 2004;24:600-611.
3. Kozlov S, Afonin A, Evsyukov I, Bondarenko A.
Alzheimer's disease: as it was in the beginning. Rev
Neurosci. 2017;28:825-843.
14. Mochida I, Shimosegawa E, Kanai Y, Naka S,
Matsunaga K, Isohashi K, Horitsugi G, Watabe T,
Kato H, Hatazawa J. Whole-body distribution of
donepezil as an acetylcholinesterase inhibitor after
oral administration in normal human subjects: A 11C-

donepezil PET Study. Asia Ocean J Nucl Med Biol.
2017;5:3-9.
bromophenyl)sulfonyl]-5-methoxy-3-[(4-methyl-1-
piperazinyl)methyl]-1H-indole
dimesylate
15. Klunk WE, Engler H, Nordberg A, Bacskai BJ, Wang
Y, Price JC, Bergström M, Hyman BT, Långström B,
Mathis CA. Imaging the pathology of Alzheimer's
disease: amyloid-imaging with positron emission
tomography. Neuroimaging Clin N Am. 2003;13:781-
789.
16. Carpenter AP Jr, Pontecorvo MJ, Hefti FF,
Skovronsky DM. The use of the exploratory IND in
the evaluation and development of 18F-PET
radiopharmaceuticals for amyloid imaging in the
brain: a review of one company's experience. Q J Nucl
Med Mol Imaging. 2009;53:387-393.
monohydrate (SUVN-502): A novel, potent, selective
and orally active serotonin 6 (5-HT6) receptor
antagonist for potential treatment of Alzheimer's
disease. J Med Chem. 2017;60:1843-1859.
25. Bursavich MG, Zhang N, Ayral-Kaloustian S,
Anderson JT, Nguyen TH, Lombardi S, Malwitz D,
Brooijmans N, Cole DC, Gilbert AM, Nowak PW,
Park K, Das S, Tsou HR, Venkatesan AM, Otteng
MA, Birnberg GH, MacEwan GJ. 3-Substituted-1H-
indole compounds, their use as MTOR kinase and PI3
kinase inhibitors, and their synthesis. US Patent No.
20090311217, 2009.
17. Hashimoto H, Kawamura K, Igarashi N, Takei M,
Fujishiro T, Aihara Y, Shiomi S, Muto M, Ito T,
Furutsuka K, Yamasaki T, Yui J, Xie L, Ono M,
Hatori A, Nemoto K, Suhara T, Higuchi M, Zhang
26. Ayral-Kaloustian S, Mansour TS, Tsou HR, Zhang N,
Venkatesan AM, Di L, Kerns EH. 3-Substituted-1H-
pyrrolo[3,2-B] pyridine compounds, their use as
MTOR kinase and PI3 Kinase inhibitors, and their
synthesis. US Patent No. 20100061982, 2010.
27. Ramakrishna VSN, Shirsath VS, Kambhampati RS,
Rao VSVV, Jasti, V. N-Arylsulfonyl-3-substituted
indoles having serotonin receptor affinity, process for
their preparation and pharmaceutical composition
containing them. WO 2004048330, 2004.
28. Ramakrishna VSN, Shirsath VS, Kambhampati RS,
Rao VSVV, Jasti, V. Tetracyclic 3-substituted indoles
having serotonin receptor affinity. WO 2004055026,
2004.
29. Nirogi R, Kambhampati RS, Shinde AK, Jasti V.
Process for large scale production of 1-[(2-
bromophenyl)sulfonyl]-5-methoxy-3-[(4-methyl-1-
MR.
Radiosynthesis,
photoisomerization,
biodistribution, and metabolite analysis of 11C-PBB3
as a clinically useful PET probe for imaging of tau
pathology. J Nucl Med. 2014;55:1532-1538.
18. Chien DT, Bahri S, Szardenings AK, Walsh JC, Mu F,
Su MY, Shankle WR, Elizarov A, Kolb HC. Early
clinical PET imaging results with the novel PHF-tau
radioligand [F-18]-T807.
2013;34:457-468.
J
Alzheimers Dis.
19. Wang M, Gao M, Miller KD, Sledge GW, Hutchins
GD, Zheng Q.-H. The first synthesis of [11C]SB-
216763, a new potential PET agent for imaging of
glycogen synthase kinase-3 (GSK-3). Bioorg Med
Chem Lett. 2011;21:245-249.
20. Gao M, Wang M, Zheng Q.-H. Synthesis of carbon-
11-labeled isonicotinamides as new potential PET
agents for imaging of GSK-3 enzyme in Alzheimer's
disease. Bioorg Med Chem Lett. 2017;27:740-743.
21. Tang S, Verdurand M, Joseph B, Lemoine L, Daoust
A, Billard T, Fournet G, Le Bars D, Zimmer L.
Synthesis and biological evaluation in rat and cat of
[18F]12ST05 as a potential 5-HT6 PET radioligand.
Nucl Med Biol. 2007;34:995-1002.
22. Parker CA, Gunn RN, Rabiner EA, Slifstein M,
Comley R, Salinas C, Johnson CN, Jakobsen S, Houle
S, Laruelle M, Cunningham VJ, Martarello L.
Radiosynthesis and characterization of 11C-
GSK215083 as a PET radioligand for the 5-HT6
receptor. J Nucl Med. 2012;53:295-303.
23. Liu F, Majo VJ, Prabhakaran J, Milak MS, John Mann
J, Parsey RV, Kumar JS. Synthesis and in vivo
evaluation of [O-methyl-11C] N-[3,5-dichloro-2-
(methoxy)phenyl]-4-(methoxy)-3-(1-
piperazinyl)methyl]-1H-indole
monohydrate. WO 2015083179, 2015.
dimesylate
30. Wang M, Gao M, Xu Z, Zheng Q.-H. Synthesis of
[11C]HG-10-102-01 as a new potential PET agent for
imaging of LRRK2 enzyme in Parkinson's disease.
Bioorg Med Chem Lett. 2017;27:1351-1355.
31. Wang M, Gao M, Xu Z, Zheng Q.-H. Synthesis of a
PET tau tracer [11C]PBB3 for imaging of Alzheimer's
disease. Bioorg Med Chem Lett. 2015;25:4587-4592.
32. Jewett DM. A simple synthesis of [11C]methyl triflate.
Int J Rad Appl Instrum A. 1992;43:1383-1385.
33. Mock BH, Mulholland GK, Vavrek MT. Convenient
gas phase bromination of [11C]methane and production
of [11C]methyl triflate. Nucl Med Biol. 1999;26:467-
471.
34. Wang M, Gao M, Miller KD, Zheng Q.-H. Synthesis
of [¹¹C]PBR06 and [¹⁸F]PBR06 as agents for positron
emission tomographic (PET) imaging of the
translocator protein (TSPO). Steroids. 2011;76:1331-
1340.
piperazinyl)benzenesulfonamide as an imaging probe
for 5-HT6 receptors. Bioorg Med Chem.
2011;19:5255-5259.
35. Wang M, Gao M, Miller KD, Sledge GW, Zheng Q.-
H. [11C]GSK2126458 and [18F]GSK2126458, the first
radiosynthesis of new potential PET agents for
imaging of PI3K and mTOR in cancers. Bioorg Med
Chem Lett. 2012;22:1569-1574.
36. Allard M, Fouquet E, James D, Szlosek-Pinaud M.
State of art in 11C labelled radiotracers synthesis. Curr
Med Chem. 2008;15:235-277.
24. Nirogi R, Shinde A, Kambhampati RS, Mohammed
AR, Saraf SK, Badange RK, Bandyala TR, Bhatta V,
Bojja K, Reballi V, Subramanian R, Benade V,
Palacharla RC, Bhyrapuneni G, Jayarajan P, Goyal V,
Jasti V. Discovery and development of 1-[(2-

37. Zheng Q.-H, Glick-Wilson BE, Steele B, Shaffer M,
Corbin L, Green MA. A simplified conventional
manual C18 Light Sep-Pak system for purification and
reformulation of carbon-11 PET tracers. J Labelled
Compd Radiopharm. 2015;58:S392.
38. Wang M, Gao M, Zheng Q.-H. Fully automated
synthesis of PET TSPO radioligands [11C]DAA1106
and [18F]FEDAA1106. Appl Radiat Isot. 2012;70:965-
973.
39. Mock BH, Zheng Q.-H, DeGrado TR. A multi-
purpose 11C-radio-synthesis system. J Labelled Compd
Radiopharm. 2005;48:S225.
40. Mock BH, Glick-Wilson BE, Zheng Q.-H, DeGrado
TR. Automated measurement of specific activity of
radiolabeled ligands during synthesis. J Labelled
Compd Radiopharm. 2005;48:S224.
5 µm C-18 column, 4.6 × 250 mm, a gradient mobile
phase (40-80%) CH3CN/3 mM HCOONH4, flow rate
1.6 mL/min; UV (254 nm) and γ-ray (PIN diode) flow
detectors. Semi-preparative RP HPLC column was
performed using a Prodigy (Phenomenex) 5 µm C-18
column, 10 × 250 mm; 57% CH3CN:43% 0.1 M
NaHCO3 mobile phase; 5, 4, 7, and 5 mL/min flow
rate for O-[11C]2a and N-[11C]2a, O-[11C]2b and N-
[11C]2b, O-[11C]2c and N-[11C]2c, O-[11C]2d and N-
[11C]2d, respectively; UV (254 nm) and γ-ray (PIN
diode) flow detectors. C18 Light Sep-Pak cartridges
were obtained from Waters Corporation (Milford,
MA). Sterile Millex-FG 0.2 µm filter units were
obtained from Millipore Corporation (Bedford, MA).
(b).
5-Methoxy-3-[(4-methyl-1-piperazinyl)methyl]-
1H-indole (1): The formaldehyde solution (20 mL,
30% w/v, 0.2 mol) was added to the stirred mixture of
1-methylpiperazine (15.0 g, 0.15 mol) and acetic acid
(6.0 g, 0.1 mol) in water (20 mL) at 10 ºC. The
reaction mixture was stirred at 10 ºC for 15 min, it was
warmed to room temperature (RT) and stirred for
another 2 h. After the thick syrup was formed, it was
added slowly to a stirred solution of 5-methoxy-1H-
indole (20 g, 0.13 mol) in MeOH (125 mL) at 5 ºC.
The reaction mixture was warmed and stirred at RT
for another 3 h. The mixture was poured into ice
water, the pH was adjusted to 10-12 with aqueous 5 N
NaOH solution, and extracted with EtOAc. The
combined organic layer was washed with water, brine,
dried over anhydrous Na2SO4 and filtered. The solvent
was evaporated under vacuum. The crude product was
purified by silica gel column chromatography with
CH2Cl2/MeOH (100:1 to 10:1) as eluent to afford 1 as
41. Gao M, Wang M, Green MA, Hutchins GD, Zheng
Q.-H. Synthesis of [11C]GSK1482160 as a new PET
agent for targeting P2X7 receptor. Bioorg Med Chem
Lett. 2015;25:1965-1970.
42. Gao M, Wang M, Zheng Q.-H. Synthesis of [11C]MK-
1064 as a new PET radioligand for imaging of orexin-
2 receptor. Bioorg Med Chem Lett. 2016;26:3694-
3699.
43. Zheng Q.-H, Mock BH. Purification of carbon-11 PET
radiotracers from unlabeled precursors by preparative
HPLC and SPE. Biomed Chromatogr. 2005;19:671-
676.
44. (a). General: All commercial reagents and solvents
were purchased from Sigma-Aldrich and Fisher
Scientific, and used without further purification.
[11C]CH3OTf was prepared according to a literature
procedure.33 Melting points were determined on WRR
apparatus and were uncorrected. 1H NMR spectra
were recorded on a Bruker Avance II 600 MHz NMR
Fourier transform spectrometer. Chemical shifts (δ)
are reported in parts per million (ppm) relative to an
internal standard tetramethylsilane (TMS, δ 0.0), and
coupling constants (J) are reported in hertz (Hz).
Liquid chromatography-mass spectra (LC-MS)
analysis was performed on AB Sciex 4000Q Trap
instrument, consisting of an 1100 series HPLC
connected to a diode array detector and a 1946D mass
spectrometer configured for positive-ion/negative-ion
electrospray ionization (ESI). The high resolution
1
a white solid (32.5 g, 92%), mp 79.5-80.4 ºC. H
NMR (600 MHz, CDCl3): δ 9.55 (s, 1H), 7.15 (d, J =
2.4 Hz, 1H), 7.13 (d, J = 8.8 Hz, 1H), 6.95 (d, J = 1.9
Hz, 1H), 6.81 (dd, J = 2.4, 8.8 Hz, 1H), 3.86 (s, 3H),
3.71 (s, 2H), 2.48 (s, 8H), 2.30 (s, 3H). LC-MS (ESI,
m/z): Calcd for C15H22N3O ([M+H]+) 260.2, found:
260.2.
(c).
1-[(2-Bromophenyl)sulfonyl]-5-methoxy-3-[(4-
methyl-1-piperazinyl)methyl]-1H-indole (2a): To a
stirred mixture of finely ground KOH solid (0.93 g,
16.6 mmol) and 1 (2.0 g, 7.7 mmol) in THF (8.0 mL),
2-bromobenzenesulphonyl chloride (2.6 g, 10.0 mmol)
in THF (5.0 mL) was added at 15 ºC. After the
reaction mixture was stirred at RT for 3 h, the mixture
was poured into ice water and the pH was adjusted to
9.5-10 with aqueous 2 N KOH solution. The mixture
was extracted with EtOAc. The combined organic
layer was washed with water, brine, dried over
anhydrous Na2SO4 and filtered. The solvent was
evaporated under vacuum. The crude product was
purified by silica gel column chromatography with
CH2Cl2/MeOH (200:1 to 20:1) as eluent to afford 2a
mass spectra (HRMS) were obtained using
a
Waters/Micromass LCT Classic spectrometer.
Chromatographic solvent proportions are indicated as
volume: volume ratio. Thin-layer chromatography
(TLC) was run using HS silica gel GF254 uniplates (5
× 10 cm2). Plates were visualized under UV light.
Normal phase flash column chromatography was
carried out on Combiflash Rf 150 silica gel 60 (300-
400 mesh) with a forced flow of the indicated solvent
system in the proportions described below. All
moisture- and air-sensitive reactions were performed
under a positive pressure of nitrogen maintained by a
direct line from a nitrogen source. Analytical RP
HPLC was performed using a Prodigy (Phenomenex)
1
as a white solid (3.3 g, 90%), mp 127.7-128.8 ºC. H
NMR (600 MHz, CDCl3): δ 8.04 (dd, J = 1.5, 8.0 Hz,
1H), 7.64 (t, J = 5.7 Hz, 2H), 7.54 (d, J = 9.0 Hz, 1H),

7.43 (t, J = 7.6 Hz, 1H), 7.36 (dd, J = 1.5, 7.6 Hz, 1H),
7.19 (d, J = 2.4 Hz, 1H), 6.84 (dd, J = 2.4, 8.9 Hz,
1H), 3.62 (s, 2H), 3.83 (s, 3H), 2.32-2.50 (br, 8H),
2.29 (s, 3H). LC-MS (ESI, m/z): Calcd for
C21H25BrN3O3S ([M+H]+) 479.4, found: 479.9.
Compounds 2b, 2c, and 2d were prepared with the
same procedure according to 2a, and the data were
listed as below. 5-Methoxy-3-((4-methylpiperazin-1-
yl)methyl)-1-(phenylsulfonyl)-1H-indole (2b): White
solid (2.8 g, 90%), mp 125.1-125.4 ºC. 1H NMR (600
MHz, CDCl3): δ 7.87 (d, J = 9.0 Hz, 1H), 7.81 (d, J =
7.6 Hz, 2H), 7.44 (t, J = 7.4 Hz, 2H), 7.35 (t, J = 7.6
Hz, 2H), 7.14 (d, J = 2.0 Hz, 1H), 6.91 (dd, J = 2.0,
9.0 Hz, 1H), 3.79 (s, 3H), 3.55 (s, 2H,), 2.45 (br, 8H),
2.26 (s, 3H). LC-MS (ESI, m/z): Calcd for
C21H26N3O3S ([M+H]+) 400.2, found: 400.0. 1-((4-
Isopropylphenyl)sulfonyl)-5-methoxy-3-((4-
211.3-212.8 ºC. 1H NMR (600 MHz, CDCl3): δ 7.86
(d, J = 7.5 Hz, 2H), 7.67 (d, J = 8.9 Hz, 1H), 7.63 (t, J
= 7.5 Hz, 2H), 7.61 (br, 1H), 7.55 (t, J = 8.0 Hz, 2H),
7.08 (d, J = 2.1 Hz, 1H), 6.85 (dd, J = 2.1, 8.9 Hz,
1H), 4.23 (s, 2H), 3.47 (br, 8H), 2.60 (s, 3H). HRMS
(ESI, m/z): Calcd for C20H24N3O3S ([M+H]+)
386.1538,
found:
386.1538.
1-((4-
Isopropylphenyl)sulfonyl)-3-((4-methylpiperazin-1-
yl)methyl)-1H-indol-5-ol (3c): White solid (1.6 g,
94%), mp 211.4-212.8 ºC. 1H NMR (600 MHz,
CDCl3): δ 7.79 (d, J = 8.8 Hz, 1H), 7.72 (d, J = 8.4
Hz, 2H), 7.40 (s, 1H), 7.22 (d, J = 8.4 Hz, 2H), 6.96
(d, J = 2.0 Hz, 1H), 6.78 (dd, J = 2.0, 8.8 Hz, 1H),
3.51 (s, 2H), 2.88-2.83 (m, 1H), 2.49 (s, 8H), 2.26 (s,
3H), 1.16 (d, J = 6.9 Hz, 6H). HRMS (ESI, m/z):
Calcd for C23H30N3O3S ([M+H]+) 428.2008, found:
428.2043.
methylpiperazin-1-yl)methyl)-1H-indol-5-ol (3d): Pale
1-((4-Fluorophenyl)sulfonyl)-3-((4-
methylpiperazin-1-yl)methyl)-1H-indole (2c): White
solid (2.6 g, 76%), mp 126.6-128.8 ºC. H NMR (600
1
1
yellow solid (1.5 g, 88%), mp 210.8-212.8 ºC. H
MHz, CDCl3): δ 7.88 (d, J = 9.0 Hz, 1H), 7.74 (d, J =
8.4 Hz, 2H), 7.44 (s, 1H), 7.21 (d, J = 8.4 Hz, 2H),
7.16 (d, J = 2.1 Hz, 1H), 6.92 (dd, J = 2.1, 9.0 Hz,
1H), 3.79 (s, 3H), 3.57 (s, 2H), 2.86-2.81 (m, 1H),
2.46 (br, 8H), 2.26 (s, 3H), 1.13 (d, J = 7.0 Hz, 6H).
LC-MS (ESI, m/z): Calcd for C24H32N3O3S ([M+H]+)
442.2, found: 442.0. 1-((4-Fluorophenyl)sulfonyl)-5-
methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-
indole (2d): White solid (3.0 g, 94%), mp 130.6-134.0
ºC. 1H NMR (600 MHz, CDCl3): δ 7.85 (t, J = 8.8 Hz,
3H), 7.40 (s, 1H), 7.11 (d, J = 2.0 Hz, 1H), 7.08 (t, J =
8.5 Hz, 2H), 6.93 (dd, J = 2.0, 9.0 Hz, 1H), 3.83 (s,
3H), 3.60 (s, 2H), 2.59 (br, 8H), 2.42 (s, 3H). LC-MS
(ESI, m/z): Calcd for C21H25FN3O3S ([M+H]+) 418.2,
found: 417.9.
NMR (600 MHz, CDCl3): δ 7.97 (dd, J = 4.9, 8.8 Hz,
2H), 7.70 (d, J = 8.8 Hz, 1H), 7.56 (s, 1H), 7.41 (t, J =
8.8 Hz, 2H), 6.99 (d, J = 2.3 Hz, 1H), 6.81 (dd, J =
2.3, 8.8 Hz, 1H), 3.51 (s, 2H), 2.39 (s, 8H), 2.28 (s,
3H). HRMS (ESI, m/z): Calcd for C20H23FN3O3S
([M+H]+) 404.1444, found: 404.1419.
(e).
yl)methyl)piperazine-1-carboxylate
tert-Butyl
4-((5-methoxy-1H-indol-3-
(4): The
formaldehyde solution (1.60 mL, 30% w/v, 0.02 mol)
was added to the stirred mixture of tert-butyl
piperazine-1-carboxylate (1.50 g, 0.015 mol) and
acetic acid (0.62 g, 0.01 mol) in water (1.6 mL) at 10
℃. The reaction mixture was stirred at 10 ℃ for 15
min, it was warmed to RT and stirred for another 2 h.
After the thick syrup was formed, it was added slowly
to a stirred solution of 5-methoxy-1H-indole (2.0 g,
0.013 mol) in methanol (13 mL) at 5 ℃. The reaction
mixture was warmed to RT and stirred for another 3 h.
The reaction mixture was poured into ice water, and
the pH was adjusted to 10-12 with aqueous 5 N NaOH
solution and extracted with EtOAC. The combined
organic layers were washed with water, brine, dried
over anhydrous Na2SO4, and filtered. The solvent was
evaporated under vacuum. The crude product was
purified by silica gel column chromatography with
CH2Cl2/MeOH (100:1 to 10:1) as eluent to afford 4 as
(d).
1-((2-Bromophenyl)sulfonyl)-3-((4-
methylpiperazin-1-yl)methyl)-1H-indol-5-ol (3a): To a
solution of HBr (7 mL, 48% wt), 2a (2.0 g, 4.8 mmol)
was added at RT under stirring, the resulting mixture
was heated to 80 ºC and reaction continued for 12 h.
The reaction mixture was poured into water (40 mL)
after cooled to 25 ºC, and then extracted with CHCl3
(3 × 40 mL) after the pH was adjusted to 10 with
ammonia solution (17%). The combined organic layer
was washed with water and brine, dried over
anhydrous Na2SO4 and filtered. The solvent was
evaporated under vacuum. The crude product was
purified by silica gel column chromatography with
CHCl3/CH3OH (100:10) as eluent to afford 3a as a
pale yellow solid (1.8 g, 93%), mp 212.0-212.8 ºC. 1H
NMR (600 MHz, CDCl3): δ 8.03 (d, J = 8.0 Hz, 1H),
7.59 (d, J = 5.0 Hz, 2H), 7.42 (dd, J = 7.7, 8.8 Hz,
2H), 7.34 (t, J = 7.7 Hz, 1H), 7.07 (s, 1H), 6.77 (d, J =
8.8 Hz, 1H), 3.56 (s, 2H), 2.69-2.62 (m, 8H), 2.39 (s,
3H). HRMS (ESI, m/z): Calcd for C20H23BrN3O3S
([M+H]+) 464.0643, found: 464.0633. Compounds 3b,
3c, and 3d were prepared with the same procedure
according to 3a, and the data were listed as below. 3-
((4-Methylpiperazin-1-yl)methyl)-1-(phenylsulfonyl)-
1H-indol-5-ol (3b): White solid (1.5 g, 94%), mp
1
a white solid (4.1 g, 91%), mp 132.8-134.0 ºC. H
NMR (600 MHz, CDCl3): δ 7.31 (d, J = 8.8 Hz, 1H),
7.09 (d, J = 2.2 Hz, 1H), 6.86 (dd, J = 2.2, 8.8 Hz,
1H), 6.83 (s, 1H), 3.83 (s, 3H), 3.54 (s, 2H), 3.29 (t, J
= 4.5 Hz, 4H), 2.36 (t, J = 4.5 Hz, 4H), 1.42 (s, 9H).
LC-MS (ESI, m/z): Calcd for C19H27N3O3([M+Na]+)
368.2, found: 368.0.
(f). tert-Butyl 4-((1-((2-bromophenyl)sulfonyl)-5-
methoxy-1H-indol-3-yl)methyl)piperazine-1-
carboxylate (5a): To a stirred mixture of finely ground
KOH solid (0.93 g, 16.6 mmol) and 4 (2.7 g, 7.7
mmol) in THF (8.0 mL), 2-bromobenzenesulphonyl
chloride (2.6 g, 10.0 mmol) in THF (5.0 mL) was
added at 15 ℃. After the reaction mixture was stirred

at RT for 3 h, the mixture was poured into ice water
and the PH was adjusted to 9.5-10 with aqueous 2 N
KOH solution. The mixture was extracted with
EtOAC. The combined organic layer was washed with
water, brine, dried over anhydrous Na2SO4 and
filtered. The solvent was evaporated under vacuum.
The crude product was purified by silica gel column
chromatography with CH2Cl2/MeOH (200:1 to 20:1)
as eluent to afford 5a as a white solid (3.9g, 89.7%),
eluent to afford 6a as a pale yellow solid (0.8 g, 96%),
mp 57.6-58.3 ºC. 1H NMR (600 MHz, CDCl3): δ 8.07
(d, J = 6.8 Hz, 1H), 7.64 (d, J = 10.0 Hz, 2H), 7.54 (d,
J = 9.0 Hz, 1H), 7.45 (t, J = 7.5 Hz, 1H), 7.37 (t, J =
7.6 Hz, 1H), 7.18 (d, J = 2.0 Hz, 1H), 6.85 (dd, J =
2.0, 8.9 Hz, 1H), 3.81 (s, 3H), 3.63 (s, 2H), 2.98 (s,
4H), 2.55 (s, 4H). HRMS (ESI, m/z): Calcd for
C20H22BrN3O3S ([M+H]+) 464.0638, found: 464.0639.
Compounds 6b, 6c, and 6d were prepared with the
same procedure according to 6a, and the data were
listed as below. 5-Methoxy-1-(phenylsulfonyl)-3-
(piperazin-1-ylmethyl)-1H-indole (6b): White solid
1
mp 136.9-138.7 ºC. H NMR (600 MHz, CDCl3): δ
8.09 (d, J = 6.4 Hz, 1H), 7.66 (d, J = 7.7 Hz, 2H), 7.54
(d, J = 9.0 Hz, 1H), 7.46 (t, J = 7.7 Hz, 1H), 7.39 (t, J
= 7.4 Hz, 1H), 7.20 (s, 1H), 6.85 (dd, J = 2.0, 9.0 Hz,
1H), 3.82 (s, 3H), 3.66 (s, 2H), 3.44 (s, 4H), 2.45 (s,
4H), 1.45 (s, 9H). LC-MS (ESI, m/z): Calcd for
C25H30BrN3O5S ([M+Na]+) 526.2, found: 526.4.
Compounds 5b, 5c, and 5d were prepared with the
same procedure according to 5a, and the data were
listed as below. tert-Butyl 4-((5-methoxy-1-
(phenylsulfonyl)-1H-indol-3-yl)methyl)piperazine-1-
carboxylate (5b): White solid (2.7 g, 90%), mp 59.8-
61.2 ºC. 1H NMR (600 MHz, CDCl3): δ 7.87 (d, J =
9.0 Hz, 1H), 7.82 (d, J = 7.5 Hz, 2H), 7.49 (t, J = 7.5
Hz, 1H), 7.39 (t, J = 7.7 Hz, 3H), 7.13 (d, J = 2.4 Hz,
1H), 6.93 (dd, J = 2.4, 9.0 Hz, 1H), 3.80 (s, 3H), 3.56
(s, 2H), 3.39 (t, J = 4.3 Hz, 4H), 2.34 (t, J = 4.8 Hz,
4H), 9.05 (s, 9H); LC-MS (ESI, m/z): Calcd for
C25H31N3O5S ([M+H]+) 486.2, found: 486.2. tert-Butyl
4-((1-((4-isopropylphenyl)sulfonyl)-5-methoxy-1H-
1
(0.7 g, 91%), mp 49.8-50.2 ºC. H NMR (600 MHz,
CDCl3): δ 7.86 (d, J = 9.0 Hz, 1H), 7.83 (d, J = 7.5
Hz, 2H), 7.50 (t, J = 7.5 Hz, 1H), 7.40 (dd, J = 3.2, 7.6
Hz, 3H), 7.14 (d, J = 2.2 Hz, 1H), 6.92 (dd, J = 2.2,
9.0 Hz, 1H), 3.81 (s, 3H), 3.54 (s, 2H), 2.85 (s, 4H),
2.39 (s, 4H). HRMS (ESI, m/z): Calcd for
C20H23N3O3S ([M+H]+) 386.1533, found: 386.1530. 1-
((4-Isopropylphenyl)sulfonyl)-5-methoxy-3-(piperazin-
1-ylmethyl)-1H-indole (6c): Pale yellow solid (0.76 g,
94%), mp 50.2-51.8 ºC. 1H NMR (600 MHz, CDCl3):
δ 7.87 (d, J = 9.0 Hz, 1H), 7.75 (d, J = 8.3 Hz, 2H),
7.42 (s, 1H), 7.23 (d, J = 8.3 Hz, 2H), 7.15 (d, J = 2.1
Hz, 1H), 6.93 (dd, J = 2.2, 9.0 Hz, 1H), 3.81 (s, 3H),
3.55 (s, 2H), 3.09 (s, 1H), 2.87 (s, 4H), 2.42 (s, 4H),
1.16 (d, J = 6.8 Hz, 6H). HRMS (ESI, m/z): Calcd for
C23H29N3O3S ([M+H]+) 428.2002, found: 428.1999. 1-
((4-Fluorophenyl)sulfonyl)-5-methoxy-3-(piperazin-1-
ylmethyl)-1H-indole (6d): White solid (0.72 g, 94 %),
mp 56.5-58.3 ºC. 1H NMR (600 MHz, CDCl3): δ 7.85
(dd, J = 5.1, 8.9 Hz, 3H), 7.38 (s, 1H), 7.10 (d, J = 2.0
Hz, 1H), 7.08 (d, J = 8.4 Hz, 2H), 6.94 (dd, J = 2.0,
8.9 Hz, 1H), 3.81 (s, 3H), 3.59 (s, 2H), 3.02 (s, 4H),
2.56 (s, 4H). HRMS (ESI, m/z): Calcd for
C20H22FN3O3S ([M+H]+) 404.1432, found: 404.1439.
(h). 1-[(2-Bromophenyl)sulfonyl]-5-[11C]methoxy-3-
indol-3-yl)methyl)piperazine-1-carboxylate
(5c):
White solid (3.9 g, 96%), mp 51.3-51.7 ºC. 1H NMR
(600 MHz, CDCl3): δ 7.88 (d, J = 9.0 Hz, 1H), 7.74
(d, J = 12.2 Hz, 2H), 7.41 (s, 1H), 7.25 (t, J = 7.3 Hz,
2H), 7.13 (d, J = 2.4 Hz, 1H), 6.93 (dd, J = 2.4, 9.0
Hz, 1H), 3.81 (s, 3H), 3.57 (s, 2H), 3.39 (s, 4H), 2.90 -
2.85 (m, 1H), 2.36 (s, 4H), 1.45 (s, 9H), 1.18 (d, J =
7.0 Hz, 6H). LC-MS (ESI, m/z): Calcd for
C28H37N3O5S ([M+Na]+) 550.2, found: 550.1. tert-
Butyl 4-((1-((4-fluorophenyl)sulfonyl)-5-methoxy-1H-
[(4-methyl-1-piperazinyl)methyl]-1H-indole
(O-
[11C]2a) and 1-[(2-bromophenyl)sulfonyl]-5-methoxy-
3-[(4-[11C]methyl-1-piperazinyl)methyl]-1H-indole
(N-[11C]2a), 5-[11C]methoxy-3-((4-methylpiperazin-1-
yl)methyl)-1-(phenylsulfonyl)-1H-indole (O-[11C]2b)
indol-3-yl)methyl)piperazine-1-carboxylate
(5d):
White solid (3.6 g, 93%), mp 138.0-139.3 ºC. 1H
NMR (600 MHz, CDCl3): δ 7.84 (dd, J = 5.5, 8.9 Hz,
3H), 7.38 (s, 1H), 7.14 (d, J = 2.2 Hz, 1H), 7.07 (t, J =
8.4 Hz, 2H), 6.93 (dd, J = 2.2, 8.9 Hz, 1H), 3.81 (s,
3H), 3.57 (s, 2H), 3.40 (s, 4H), 2.36 (s, 4H), 1.45 (s,
9H). LC-MS (ESI, m/z): Calcd for C25H30FN3O5S
([M+H]+) 504.6, found: 504.6.
and
5-methoxy-3-((4-[11C]methylpiperazin-1-
yl)methyl)-1-(phenylsulfonyl)-1H-indole (N-[11C]2b),
1-((4-isopropylphenyl)sulfonyl)-5-[11C]methoxy-3-((4-
methylpiperazin-1-yl)methyl)-1H-indole (O-[11C]2c)
and 1-((4-isopropylphenyl)sulfonyl)-5-methoxy-3-((4-
(g).
1-((2-Bromophenyl)sulfonyl)-5-methoxy-3-
[11C]methylpiperazin-1-yl)methyl)-1H-indole
[11C]2c),
1-((4-fluorophenyl)sulfonyl)-5-
(N-
(piperazin-1-ylmethyl)-1H-indole (6a): To a solution
of TFA, 5a (1.0 g, 1.8 mmol) was added at RT under
stirring, the reaction mixture was stirred at RT for 12
h. The resulted mixture was poured into water (10
mL), and then extracted with CH2Cl2 after the pH was
adjusted to 7-8 with aqueous 5 N KOH solution, The
combined organic layer was washed with water, brine,
dried over anhydrous Na2SO4, and filtered. The
solvent was evaporated under vacuum. The crude
product was purified by silica gel column
chromatography with CH2Cl2/CH3OH (100:10) as
[11C]methoxy-3-((4-methylpiperazin-1-yl)methyl)-1H-
indole (O-[11C]2d) and 1-((4-fluorophenyl)sulfonyl)-
5-methoxy-3-((4-[11C]methylpiperazin-1-yl)methyl)-
1H-indole (N-[11C]2d): [11C]CO2 was produced by the
14N(p,α)11C nuclear reaction in the small volume (9.5
cm3) aluminum gas target provided with the Siemens
RDS-111 Eclipse cyclotron. The target gas consisted
of 1% oxygen in nitrogen purchased as a specialty gas
from Praxair, Indianapolis, IN. Typical irradiations
used for the development were 58 µA beam current

and 20 min on target. The production run produced
approximately 37.0 GBq of [11C]CO2 at EOB. The
precursor 3a-d or 6a-d (0.1-0.3 mg) was dissolved in
CH3CN (300 µL). To this solution was added aqueous
KOH (2 M, 2 µL). The mixture was transferred to a
small reaction vial. No-carrier-added (high molar
activity) [11C]CH3OTf that was produced by the gas-
phase production method33 within 12 min from
[11C]CO2 through [11C]CH4 and [11C]CH3Br with
AgOTf column was passed into the reaction vial at RT
until radioactivity reached a maximum (2 min), and
then the reaction vial was isolated and heated at 80 °C
for 3 min. The contents of the reaction vial were
diluted with aqueous NaHCO3 (0.1 M, 1 mL). The
reaction vial was connected to a 3-mL HPLC injection
loop. The labeled product mixture solution was
injected onto the semi-preparative HPLC column for
purification. The product fraction was collected in a
recovery vial containing 30 mL water. The diluted
tracer solution was then passed through a C-18 Light
Sep-Pak cartridge, and washed with water (3 × 10
mL). The cartridge was eluted with EtOH (3 × 0.4
mL) to release the labeled product, followed by saline
(10-11 mL). The eluted product was then sterile-
filtered through a Millex-FG 0.2 µm membrane into a
sterile vial. Total radioactivity was assayed and total
volume (10-11 mL) was noted for tracer dose
dispensing. The overall synthesis time including
HPLC-SPE purification and reformulation was ~40
min from EOB. The decay corrected radiochemical
yield was 40-50%. Retention times in the analytical
HPLC system were: tR 3a = 5.23 min, tR 6a = 6.84
min, tR 2a = 7.44 min, tR O-[11C]2a = 7.51 min, tR N-
[11C]2a = 7.49 min; tR 3b = 4.71 min, tR 6b = 6.21
min, tR 2b = 6.81 min, tR O-[11C]2b = 6.86 min, tR N-
[11C]2b = 6.88 min; tR 3c = 6.76 min, tR 6c = 8.93 min,
tR 2c = 9.46 min, tR O-[11C]2c = 9.58 min, tR N-[11C]2c
= 9.61 min; and tR 3d = 5.03 min, tR 6d = 6.58 min, tR
2d = 7.12 min, tR O-[11C]2d = 7.19 min, tR N-[11C]2d
= 7.23 min. Retention times in the preparative HPLC
system were: tR 3a = 6.54 min, tR 6a = 7.25 min, tR 2a
= 13.53 min, tR O-[11C]2a = 13.72 min, tR N-[11C]2a =
13.81 min; tR 3b = 6.32 min, tR 6b = 7.85 min, tR 2b =
12.01 min, tR O-[11C]2b = 12.27 min, tR N-[11C]2b =
12.23 min; tR 3c = 6.85 min, tR 6c = 9.59 min, tR 2c =
17.75 min, tR O-[11C]2c = 17.94 min, tR N-[11C]2c =
17.99 min; and tR 3d = 5.88 min, tR 6d = 7.24 min, tR
2d = 11.04 min, tR O-[11C]2d = 11.27 min, tR N-
[11C]2d = 11.25 min.

Synthesis of carbon-11-labeled 5-HT6R
antagonists as new candidate PET radioligands
for imaging of Alzheimer’s disease
Xiaohong Wang, Fugui Dong, Caihong Miao, Wei
Li, Min Wang, Mingzhang Gao, Qi-Huang Zheng*,
Zhidong Xu*
CH3
N
11CH3
N
N
N
O
H311CO
H3CO
N
N
11
11
O
O
O
O
O
2a
-[ C] : R=2-Br
2a
N
N
N
N
-[ C] : R=2-Br
S
S
O
R
O
R
11
11
2b
-[ C] : R=H
2b
-[ C] : R=H
11
11
2c
i
-[ C] : R=4- Pr
2c
i
-[ C] : R=4- Pr
11
11
2d
-[ C] : R=4-F
2d
-[ C] : R=4-F
Carbon-11-labeled 5-HT6R antagonists

Synthesis of carbon-11-labeled 5-HT6R
antagonists as new candidate PET
radioligands for imaging of Alzheimer’s
disease
Xiaohong Wanga, Fugui Donga, Caihong Miaoa,
Wei Lia, Min Wangb, Mingzhang Gaob,
Qi-Huang Zhengb,*, Zhidong Xua,c,*
aKey Laboratory of Medicinal Chemistry and
Molecular Diagnosis of Ministry of Education,
College of Chemistry and Environmental
Science, Hebei University, Baoding, Hebei
071002, China
bDepartment of Radiology and Imaging Sciences,
Indiana University School of Medicine, 1345
West 16th Street, Room 202, Indianapolis, IN
46202, USA
cShijiazhuang Vince Pharmatech Co., Ltd.,
Shijiazhuang, Hebei 050030, China
• New carbon-11-labeled 5-HT6R antagonists
were synthesized.
• A fully automated multi-purpose [11C]-
radiosynthesis module was built up.
•
A semi-preparative RP HPLC-SPE technique
was employed in radiosynthesis.