Facile radiosynthesis of new carbon-11-labeled propanamide derivatives as selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging

Article abstract of DOI:10.1016/j.steroids.2011.08.005

The androgen receptor (AR) is an attractive target for the treatment and molecular imaging of prostate cancer. New carbon-11-labeled propanamide derivatives were first designed and synthesized as selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging using the biomedical imaging technique positron emission tomography (PET). The target tracers, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-[¹¹C] methoxyphenoxy)-2-methylpropanamide ([¹¹C]8a), (S)-2-hydroxy-3-(2- [¹¹C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl) propanamide ([¹¹C]8e), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2- hydroxy-3-(4-[¹¹C]methoxyphenoxy)-2-methylpropanamide ([ ¹¹C]8c) and (S)-2-hydroxy-3-(4-[¹¹C]methoxyphenoxy)-2- methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide ([¹¹C]8g), were prepared by O-[¹¹C]methylation of their corresponding precursors, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2- hydroxyphenoxy)-2-methylpropanamide (9a), (S)-2-hydroxy-3-(2-hydroxyphenoxy)-2- methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide (9b), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-hydroxyphenoxy) -2-methylpropanamide (9c) and (S)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methyl-N-(4- nitro-3-(trifluoromethyl)phenyl)propanamide (9d), with [¹¹C]CH ₃OTf under basic conditions and isolated by a simplified C-18 solid-phase extraction (SPE) method in 55 ± 5% (n = 5) radiochemical yields based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The overall synthesis time from EOB was 23 min, the radiochemical purity was >99%, and the specific activity at end of synthesis (EOS) was 277.5 ± 92.5 GBq/μmol (n = 5).

Full text of DOI:10.1016/j.steroids.2011.08.005

Steroids 76 (2011) 1505–1512
Contents lists available at SciVerse ScienceDirect
Steroids
journal homepage: www.elsevier.com/locate/steroids
Facile radiosynthesis of new carbon-11-labeled propanamide derivatives
as selective androgen receptor modulator (SARM) radioligands
for prostate cancer imaging
Mingzhang Gao a, Min Wang a, Kathy D. Miller b, Qi-Huang Zheng a,
⇑
a Department of Radiology and Imaging Sciences, Indiana University School of Medicine, 1345 West 16th Street, L3-202, Indianapolis, IN 46202-2111, USA
b Department of Medicine, Indiana University School of Medicine, Indianapolis, IN 46202, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 July 2011
Received in revised form 8 August 2011
Accepted 11 August 2011
Available online 17 August 2011
The androgen receptor (AR) is an attractive target for the treatment and molecular imaging of prostate
cancer. New carbon-11-labeled propanamide derivatives were first designed and synthesized as
selective androgen receptor modulator (SARM) radioligands for prostate cancer imaging using the
biomedical imaging technique positron emission tomography (PET). The target tracers, (S)-N-(4-
cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-[11C]methoxyphenoxy)-2-methylpropanamide ([11C]8a),
(S)-2-hydroxy-3-(2-[11C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide
([11C]8e), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-[11C]methoxyphenoxy)-2-methyl-
propanamide ([11C]8c) and (S)-2-hydroxy-3-(4-[11C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluo-
romethyl)phenyl)propanamide ([11C]8g), were prepared by O-[11C]methylation of their corresponding
precursors, (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-hydroxyphenoxy)-2-methylpropan-
amide (9a), (S)-2-hydroxy-3-(2-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propan-
amide (9b), (S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methyl-
propanamide (9c) and (S)-2-hydroxy-3-(4-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)-
phenyl)propanamide (9d), with [11C]CH3OTf under basic conditions and isolated by a simplified C-18
solid-phase extraction (SPE) method in 55 5% (n = 5) radiochemical yields based on [11C]CO2 and decay
corrected to end of bombardment (EOB). The overall synthesis time from EOB was 23 min, the radio-
Keywords:
Carbon-11-labeled propanamide derivatives
Androgen receptor (AR)
Positron emission tomography (PET)
Prostate cancer
Imaging
chemical purity was >99%, and the specific activity at end of synthesis (EOS) was 277.5 92.5 GBq/lmol
(n = 5).
Ó 2011 Elsevier Inc. All rights reserved.
1. Introduction
are slow-growing and may never cause problems. Uncertain or
false test results also could cause confusion and worry. Doctors
and patients are still struggling for the treatment, since the avail-
able treatments still fail to cure a significant number of patients
and can lead to other problems like urinary, bowel or sex problem.
In general, earlier detection and treatment provide the best oppor-
tunity for cures or prolonged survival of the patients. Rapid and
accurate early detection is highly desirable so that various thera-
peutic regiments can be given before the primary tumors become
widely spread to other organs [2,3]. The improved therapies with
fewer side effects and early detection with advanced imaging tech-
nology will help to decrease the overall death rate of prostate can-
cer. Novel strategies are eagerly needed.
In the diagnosis and treatment of prostate cancer, the biomed-
ical imaging technique positron emission tomography (PET) has
become a clinically valuable and accepted new medical imaging
tool for the diagnosis and staging of primary tumors, detection of
subclinical disease, assessment of therapy response, and detection
of recurrence [4–6]. At present, the clinically used PET prostate
Prostate cancer is the most commonly diagnosed cancer and is
the second leading cause of cancer death in men. More than
200,000 new cases of prostate cancer in the United States in the
year 2010 will be diagnosed and more than 30,000 men will die
of this disease [1]. The exact cause of prostate cancer is not fully
understood. Most prostate cancer patients will survive after con-
ventional treatment modalities such as surgery, radiation therapy,
endocrine therapy, chemotherapy and/or a combination thereof if
prostate cancer can be detected at the early stage. The early detec-
tion of prostate cancer includes prostate-specific antigen (PSA)
blood test, digital rectal exam (DRE), and transrectal ultrasound
(TRUS) test. However, these tests are not perfect, because they can-
not tell how dangerous the cancer is, and some prostate cancers
⇑
Corresponding author. Tel.: +1 317 278 4671; fax: +1 317 278 9711.
E-mail address: qzheng@iupui.edu (Q.-H. Zheng).
0039-128X/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved.
doi:10.1016/j.steroids.2011.08.005

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M. Gao et al. / Steroids 76 (2011) 1505–1512
cancer imaging agent is only 2-[18F]fluoro-2-deoxy-
D
-glucose
divided into steroidal and nonsteroidal ligands, two main chemical
structural classes; or androgenic and antiandrogenic ligands, two
different functional classes [14]. Likewise, AR radioligands can be
divided into two classes: steroidal and nonsteroidal radioligands,
or androgenic and antiandrogenic radioligands. The most well-
([18F]FDG). However, [18F]FDG is not in all cases satisfactory, there
are some well-known limitations to its use such as the inability of
[
18F]FDG-PET to visualize very small size prostate tumor in early
stage and the low cellular uptake rate in prostate cancer, relatively
low sensitivity and specificity. Obviously, [18F]FDG-PET is not an
ideal imaging tool for both primary and metastatic prostate cancer
[7,8]. In addition, only a limited number of PET studies using other
radiotracers have been conducted to image prostate cancer and
monitor its response to treatment, due to the limited accessibility
of radiotracers. The other well-known PET prostate cancer imaging
agents are [11C]choline and [18F]choline [9,10]. Both tracers target
choline kinase in prostate cancer. The limited accessibility of radio-
tracers has motivated the development of new prostate cancer PET
imaging agents [11]. More effective molecular imaging probes are
urgently needed to improve the detection accuracy of primary,
metastatic and recurrent prostate cancer.
known PET radioligand for AR visualization is 16b-[18F]fluoro-5
a-
dihydrotestosterone ([18F]FDHT, Fig. 1), an androgenic steroid
derivative of 5
-DHT [17–20]. [18F]FDHT-PET human study results
a
indicated this radioligand had rapid metabolic rate, fast prostate
tumor uptake and prolonged retention of radioactivity [18–20].
Androgenic steroid compounds have high affinity to the AR, how-
ever, at the same time, they do not have adequate AR selectivity
and they tend to bind to additional steroid receptors [18–20]. Thus,
recent efforts have turned to the search for nonsteroidal AR
ligands, or selective androgen receptor modulators (SARMs)
[21–23]. Subsequently, the search for nonsteroidal AR radioligands
also has become a widely competitive area of research [14,24].
Recently a novel series of propanamide derivatives with nanomo-
lar Ki binding affinity has been developed as potent selective
androgen receptor modulators (SARMs) for antiandrogen therapy
of prostate cancer [21,25–27]. The representative compound
(S)-2-hydroxy-3-(4-methoxyphenoxy)-2-methyl-N-(4-nitro-3-(tri-
fluoromethyl)phenyl)propanamide (8g, Fig. 1) displayed Ki value of
13.69 0.68 nM. These compounds were synthesized and tested in
the prostate cancer cell lines LNCaP, DU145, PC-3, PPC-1, and a
bladder cancer cell line TSU-Pr1 as well as a normal monkey kidney
cell line CV-1, and the results suggested they are selective
AR-dependent prostate cancer inhibitors with strong AR binding
affinity and no cytotoxicity on normal cell lines [27]. Obviously
these compounds exhibited selective uptake in the target areas
and rapid clearance from non target areas. These data enable the
prediction that the compounds, besides a good affinity, will exhibit
other specific features of good imaging agents such as specific
binding to the receptor target and rapid metabolic rate. In addition,
To this end, the androgen receptor (AR) [12] has attracted our
interest. AR is a member of the steroid/thyroid hormone receptor
superfamily of ligand-dependent intracellular transcription factors
and is predominantly activated by testosterone (T) and its metab-
olite 5a-dihydrotestosterone (5a-DHT) [13] (Fig. 1.). AR plays a
critical role in prostate cancer, since approximately 80–90% of
prostate cancers are androgen dependent at initial diagnosis, and
some very aggressive prostate cancers were shown loss of the
expression of the AR and are insensitive to inhibition of the AR
[14]. Therefore, it is very important to determine and understand
the role of the AR in prostate cancer, and noninvasive molecular
imaging modality PET should have this function [15]. PET coupled
with appropriate radiopharmaceuticals would be able to guide and
monitor the treatment. AR has become an attractive target for the
treatment and molecular imaging of prostate cancer. The strategy
is to develop new and potent AR ligands and radioligands for the
therapy and detection of prostate cancer [16]. AR ligands can be
OH
OH
H
H
H
H
H
H
O
O
H
5α-Dihydrotestosterone (5α-DHT)
Testosterone (T)
OH
18F
H
H
H
O
H
16β-[18F]Fluoro-5α-dihydrotestosterone ([18F]FDHT)
O
O
OCH3
O2N
F3C
N
H
OH
H3C
(S)-2-Hydroxy-3-(4-methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide (8g)
Ki 13.69 nM
O
O
O11CH3
O2N
F3C
N
H
OH
H3C
(S)-2-Hydroxy-3-(4-[11C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)propanamide ([11C]8g)
Fig. 1. Chemical structures of AR ligands and radioligands.

M. Gao et al. / Steroids 76 (2011) 1505–1512
1507
they possess O-methyl position amenable to labeling with a
positron emitting radionuclide carbon-11. This study was designed
to label nonsteroidal AR ligands propanamide derivatives with car-
bon-11 as SARM radioligands for prostate cancer imaging.
rated in vacuo at 40 °C to remove acetone. The residual solution
was washed with ether and acidified to pH 2 with concentrated
HCl. The acidic mixture was saturated with NaCl and extracted
with EtOAc (3 ꢀ 120 mL). The combined EtOAc extracts were dried
over Na2SO4, concentrated by evaporation in vacuo, mixed with
hexanes (with about 1:1 ratio), and further concentrated until
the beginning of crystallization to give 2 (13.66 g, 75%) as a white
solid, Rf = 0.38 (7% MeOH/CH2Cl2), m.p. 102–103 °C. 1H NMR
(DMSO-d6) d: 1.78 (s, 3H, CH3), 1.80–1.94 (m, 3H, aliphatic CH2
and CH), 2.18–2.29 (m, 1H, aliphatic CH), 3.40–3.56 (m, 2H, ali-
phatic CH2), 4.23–4.47 (2q, J = 4.0 Hz, 1H, tertiary CH), 5.04, 5.16
and 5.29 (3s, 2H, vinyl CH2), 12.52 (s, 1H, COOH). MS (ESI): 184
([M+H]+, 100%).
We are interested in the development of new PET prostate
cancer imaging agents, and a series of PET agents have been syn-
thesized and evaluated in this laboratory [28–31]. Here we report
the design, synthesis and radiosynthesis of novel nonsteroidal
SARM radioligands, carbon-11-labeled propanamide derivatives,
(S)-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-[11C]-
methoxyphenoxy)-2-methylpropanamide ([11C]8a), (S)-2-hydro-
xy-3-(2-[11C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoro-
methyl)phenyl)propanamide
([11C]8e),
(S)-N-(4-cyano-3-
(trifluoromethyl)phenyl)-2-hydroxy-3-(4-[11C]methoxyphenoxy)-2-
methylpropanamide ([11C]8c) and (S)-2-hydroxy-3-(4-[11C]-
methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)phenyl)-
propanamide ([11C]8g).
2.3. (3R,8aR)-3-(Bromomethyl)-3-methyltetrahydro-1H-pyrrolo[2,1-
c][1,4]oxazine-1,4(3H)-dione (3)
A solution of N-bromosuccinimide (NBS) (17.8 g, 0.10 mol) in
N,N-dimethylformamide (DMF) (100 mL) was added to a stirred
solution of compound 2 (9.16 g, 50 mmol) in DMF (100 mL) under
N2 at RT. The reaction mixture was stirred for 20 h, and then evap-
orated to dryness in vacuo. The residue was diluted with water
(300 mL), and extracted with EtOAc (3 ꢀ 200 mL). The combined
EtOAc extracts were washed with brine, dried over Na2SO4 and
evaporated to dryness. The residue was crystallized from EtOAc
to give 3 (9.95 g, 76%) as a white solid, Rf = 0.35 (1:1 EtOAc/Hex-
anes), m.p. 152–154 oC. 1H NMR (DMSO-d6) d: 1.57 (s, 3H, CH3),
1.82–1.84 (m, 1H, aliphatic CH), 1.91–2.01 (m, 2H, aliphatic CH2),
2.23–2.28 (m, 1H, aliphatic CH), 3.37–3.42 (m, 1H, aliphatic CH),
3.48–3.53 (m, 1H, aliphatic CH), 3.86 (d, J = 11.5 Hz, 1H, CHHBr),
4.01 (d, J = 11.5 Hz, 1H, CHHBr), 4.70 (dd, J = 7.0, 10.0 Hz, 1H, ter-
2. Methods
2.1. General
All commercial reagents and solvents were purchased from Sig-
ma–Aldrich and Fisher Scientific and used without further purifica-
tion. [11C]Methyl triflate ([11C]CH3OTf) was prepared according to
a literature procedure [32]. Melting points were determined on a
MEL-TEMP II capillary tube apparatus and were uncorrected. 1H
NMR and 13C NMR spectra were recorded on Bruker Avance II
500 MHz NMR spectrometers using tetramethylsilane (TMS) as
an internal standard. Chemical shift data for the proton resonances
were reported in parts per million (ppm, d scale) relative to inter-
nal standard TMS (d 0.0), and coupling constants (J) were reported
in hertz (Hz). Liquid chromatography–mass spectra (LC–MS) anal-
ysis was performed on an Agilent system, consisting of an 1100
series high performance liquid chromatography (HPLC) connected
to a diode array detector and a 1946D mass spectrometer config-
ured for positive-ion/negative-ion electrospray ionization. The
high resolution mass spectra (HRMS) were obtained using a
Waters/Micromass LCT Classic spectrometer. Chromatographic sol-
vent proportions are indicated as volume: volume ratio. Thin-layer
chromatography (TLC) was run using Analtech silica gel GF uni-
plates (5 ꢀ 10 cm2). Plates were visualized under UV light. Normal
phase flash column chromatography was carried out on EM Sci-
ence silica gel 60 (230–400 mesh) with a forced flow of the indi-
cated solvent system in the proportions described below. All
moisture- and/or air-sensitive reactions were performed under a
positive pressure of nitrogen maintained by a direct line from a
nitrogen source. Analytical HPLC was performed using a Prodigy
tiary CH). MS (ESI): 262 ([M+H]+, 100%). ½a D26
ꢁ
+ 124.5° (c = 1.3,
CHCl3) (lit. [25]).
2.4. (R)-3-Bromo-2-hydroxy-2-methylpropanoic acid (4)
A mixture of compound 3 (15.7 g, 60 mmol) in 28% HBr
(180 mL) was heated at reflux for 3 h. The cooled reaction mixture
was diluted with brine (150 mL), and extracted with EtOAc
(3 ꢀ 120 mL). The combined EtOAc extracts were washed with sat-
urated NaHCO3 (3 ꢀ 120 mL). The NaHCO3 extracts were acidified
with concentrated HCl to pH 2, and extracted with EtOAc
(3 ꢀ 120 mL). The EtOAc extracts were dried over Na2SO4, and
evaporated to dryness. The residue was crystallized from toluene
to afford 4 (8.56 g, 78%) as a white solid, Rf = 0.17 (7% MeOH/
CH2Cl2), m.p. 107–109 °C. 1H NMR (CDCl3) d: 1.62 (s, 3H, CH3),
3.51 (d, J = 10.5 Hz, 1H, CHH), 3.76 (d, J = 10.5 Hz, 1H, CHH).
½
a 2D5
+ 10.5° (c = 2.6, MeOH) (lit. [25]).
ꢁ
(Phenomenex)
CH3CN:MeOH:20 mM, pH 6.7 phosphate (buffer solution) mobile
phase; 1.5 mL/min flow rate; and UV (254 nm) and -ray (PIN
diode) flow detectors. C-18 Plus Sep-Pak cartridges were obtained
from Waters Corporation, Milford, MA. Sterile Millex-GS 0.22
5
l
m
C-18 column, 4.6 ꢀ 250 mm; 3:1:1
2.5. (R)-3-Bromo-N-(4-cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-
2-methylpropanamide (6a)
c
Thionyl chloride (1.73 g, 14.5 mmol) was added to a stirred
solution of compound 4 (1.83 g, 10.0 mmol) in CH3CN (50 mL) at
ꢂ5 to ꢂ10 °C. The resulting mixture was stirred under the same
temperature for 2 h, and Et3N (2.52 g, 25.0 mmol) was added
slowly into above mixture for 20 min. Then a solution of 4-cya-
no-3-(trifluoromethyl)aniline (1.49 g, 8.0 mmol) in CH3CN
(15 mL) was added into the reaction mixture at ꢂ5 to ꢂ10 °C.
The reaction was stirred under the same temperature for 3 h and
allowed to warm to RT for additional 3 h. After the reaction mix-
ture was evaporated, the residue was extracted with EtOAc
(3 ꢀ 100 mL). The combined EtOAc extracts were washed with
NaHCO3, brine, and dried over Na2SO4. The EtOAc solution was
evaporated to give brownish oil, which crystallized when it cooled.
The solid was recrystallized from a mixture of hexanes and toluene
l
m
vented filter unit was obtained from Millipore Corporation, Bed-
ford, MA.
2.2. (R)-1-Methacryloylpyrrolidine-2-carboxylic acid (2)
D
-Proline (1) (11.51 g, 0.10 mol) was dissolved in 2 N NaOH
(60 mL) and cooled in an ice bath, and resulting alkaline solution
was diluted with acetone (60 mL). An acetone solution (60 mL) of
methacryloyl chloride (15.68 g, 0.15 mol) and 2 N NaOH (80 mL)
were simultaneously added over 50 min to the aqueous solution
of
D-proline with stirring in an ice bath. After the stirring was con-
tinued for 3 h at room temperature (RT), the mixture was evapo-

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M. Gao et al. / Steroids 76 (2011) 1505–1512
1
2
to give 6a as a brownish solid. The crude oil also can be purified by
column chromatography on silica gel with eluent (1:7 EtOAc/hex-
anes) to afford 6a (1.83 g, 65%) as a brownish solid, Rf = 0.62 (1:1
EtOAc/hexanes), m.p. 106–107 °C. 1H NMR (DMSO-d6) d: 1.48 (s,
3H, CH3), 3.57 (d, J = 10.5 Hz, 1H, CHH), 3.81 (d, J = 10.5 Hz, 1H,
CHH), 6.40 (s, 1H, OH), 8.10 (d, J = 8.5 Hz, 1H, Ph–H), 8.29 (dd,
J = 2.0, 8.5 Hz, 1H, Ph–H), 8.54 (d, J = 2.0 Hz, 1H, Ph-H), 10.53 (s,
NH). MS (ESI): 349 ([MꢂH]+, 100%).
F = 5.0 Hz), 121.13 (q, JC–F = 272.5 Hz), 121.95, 133.94 (q, JC–
F = 32.7 Hz), 135.92, 136.35, 141.70, 151.94, 154.79, 173.26. MS
(ESI): 395 ([M+H]+, 100%). HRMS (ESI): calcd. for C19H17N2O4F3Na
417.1038 ([M+Na]+), found 417.1021.
(S)-3-(4-(Benzyloxy)phenoxy)-N-(4-cyano-3-(trifluoromethyl)-
phenyl)-2-hydroxy-2-methylpropanamide (8d). White solid, m.p.
95–97 °C, 39% yield. 1H NMR (CDCl3) d: 1.58 (s, 3H, CH3), 3.46 (s,
1H, OH), 3.91 (d, J = 9.0 Hz, 1H, CHH), 4.39 (d, J = 9.0 Hz, 1H,
CHH), 5.00 (s, 2H, CH2O), 6.83 (dd, J = 2.5, 7.0 Hz, 2H, Ph–H), 6.88
(dd, J = 2.5, 7.0 Hz, 2H, Ph–H), 7.31–7.41 (m, 5H, Ph–H), 7.78 (d,
J = 8.5 Hz, 1H, Ph–H), 7.94 (dd, J = 2.0, 8.5 Hz, 1H, Ph–H), 8.09 (d,
J = 2.0 Hz, 1H, Ph–H), 9.12 (s, 1H, NH). MS (ESI): 471 ([M+H]+,
100%).
(S)-2-Hydroxy-3-(2-methoxyphenoxy)-2-methyl-N-(4-nitro-3-
(trifluoromethyl)phenyl)propanamide (8e). Yellowish oil, 33%
yield, 96.9% HPLC purity. 1H NMR (CDCl3) d: 1.56 (s, 3H, CH3),
3.87 (s, 3H, OCH3), 3.91 (d, J = 9.5 Hz, 1H, CHH), 4.47 (d,
J = 9.5 Hz, 1H, CHH), 4.67 (s, 1H, OH), 6.91–6.94 (m, 2H, Ph–H),
6.98–7.05 (m, 2H, Ph–H), 7.95 (d, J = 8.5 Hz, 1H, Ph–H), 8.03 (d,
J = 2.0 Hz, 1H, Ph–H), 8.06 (dd, J = 2.0, 8.5 Hz, 1H, Ph–H), 9.44 (s,
1H, NH). 13C NMR (CDCl3) d: 23.37, 55.98, 75.19, 75.44, 112.24,
2.6. (R)-3-Bromo-2-hydroxy-2-methyl-N-(4-nitro-3-
(trifluoromethyl)phenyl)propanamide (6b)
6b Was obtained from 4 and 4-nitro-3-(trifluoromethyl)aniline
by the same method used for the preparation of 6a as a brown solid
in 62% yield, Rf = 0.63 (1:1 EtOAc/hexanes), m.p. 101–102 °C. 1H
NMR (DMSO-d6) d: 1.49 (s, 3H, CH3), 3.58 (d, J = 10.5 Hz, 1H,
CHH), 3.82 (d, J = 10.5 Hz, 1H, CHH), 6.41 (s, 1H, OH), 8.19 (d,
J = 9.0 Hz, 1H, Ph–H), 8.35 (dd, J = 2.0, 9.0 Hz, 1H, Ph–H), 8.55 (d,
J = 2.0 Hz, 1H, Ph–H), 10.58 (s, NH). MS (ESI): 369 ([MꢂH]+, 100%).
2.7. General procedure for preparation of compounds 8
3
1
116.86, 118.51 (q, JC–F = 5.7 Hz), 120.80 (q, JC–F = 271.8 Hz),
2
The mixture of 6 (1.0 mmol) and K2CO3 (0.41 g, 3.0 mmol) in
acetone (50 mL) was heated to reflux for 2 h. Then the solvent
was evaporated under reduced pressure to give a yellowish residue
of epoxide intermediate. Substituted phenol 7 (1.0 mmol), addi-
tional amount of K2CO3 (0.28 g, 2.0 mmol) and solvent 2-butanone
(50 mL) were added to above residue. The reaction mixture was re-
fluxed for 4 h. The solvent was removed under reduced pressure.
The residue was extracted with EtOAc (2 ꢀ 100 mL). The EtOAc ex-
tract was dried over Na2SO4, concentrated and purified by column
chromatography on silica gel with elute (1:5 EtOAc/hexanes) to
give 8 as colorless or yellowish oil. The overall reaction was carried
out in one-pot two-step process, and the yields varied from 28% to
50%. Rf = 0.69–0.74 (1:1 EtOAc/hexanes).
121.66, 122.30, 123.62, 125.18 (q, JC–F = 33.8 Hz), 127.17, 141.96,
143.19, 147.35, 149.70, 173.84. MS (ESI): 415 ([M+H]+, 100%).
HRMS (ESI): calcd. for C18H17N2O6F3Na 437.0936 ([M+Na]+), found
437.0924.
(S)-3-(2-(Benzyloxy)phenoxy)-2-hydroxy-2-methyl-N-(4-nitro-
3-(trifluoromethyl)phenyl)propanamide (8f). Yellowish oil, 28%
yield, 96.2% HPLC purity. 1H NMR (CDCl3) d: 1.50 (s, 3H, CH3),
3.90 (d, J = 9.5 Hz, 1H, CHH), 4.50 (d, J = 9.5 Hz, 1H, CHH), 4.59 (s,
1H, OH), 5.02 (d, J = 11.0 Hz, 2H, CHHO), 5.05 (d, J = 11.0 Hz, 1H,
CHHO), 6.94–7.02 (m, 4H, Ph–H), 7.29–7.31 (m, 3H, Ph–H), 7.36–
7.37 (m, 2H, Ph–H), 7.80 (dd, J = 2.0, 8.5 Hz, 1H, Ph–H), 7.85 (d,
J = 8.5 Hz, 1H, Ph–H), 7.91 (d, J = 2.0 Hz, 1H, Ph–H), 9.17 (s, 1H,
NH). MS (ESI): 491 ([M+H]+, 100%).
(S)-N-(4-Cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-
methoxyphenoxy)-2-methylpropanamide (8a). Colorless oil, 41%
yield, 97.5% HPLC purity. 1H NMR (CDCl3) d: 1.55 (s, 3H, CH3), 3.86
(s, 3H, OCH3), 3.91 (d, J = 9.0 Hz, 1H, CHH), 4.46 (d, J = 9.0 Hz, 1H,
CHH), 4.68 (s, 1H, OH), 6.90–6.94 (m, 2H, Ph–H), 6.97–7.04 (m,
2H, Ph–H), 7.76 (d, J = 8.5 Hz, 1H, Ph–H), 7.99 (dd, J = 2.0, 8.5 Hz,
1H, Ph–H), 8.04 (d, J = 2.0 Hz, 1H, Ph–H), 9.41 (s, 1H, NH). 13C
(S)-2-Hydroxy-3-(4-methoxyphenoxy)-2-methyl-N-(4-nitro-3-
(trifluoromethyl)phenyl)propanamide (8g). Yellowish oil, 40%
yield, 97.7% HPLC purity. 1H NMR (CDCl3) d: 1.57 (s, 3H, CH3),
3.60 (s, 1H, OH), 3.75 (s, 3H, OCH3), 3.92 (d, J = 9.0 Hz, 1H, CHH),
4.39 (d, J = 9.0 Hz, 1H, CHH), 6.80–6.85 (m, 4H, Ph–H), 7.95 (d,
J = 9.0 Hz, 1H, Ph–H), 8.00 (dd, J = 2.0, 9.0 Hz, 1H, Ph–H), 8.09 (d,
J = 2.0 Hz, 1H, Ph–H), 9.22 (s, 1H, NH). MS (ESI): 415 ([M+H]+,
100%).
(S)-3-(4-(Benzyloxy)phenoxy)-N-(4-cyano-3-(trifluoromethyl)-
phenyl)-2-hydroxy-2-methylpropanamide (8h). Yellowish oil, 32%
yield, 96.3% HPLC purity. 1H NMR (CDCl3) d: 1.57 (s, 3H, CH3), 3.52
(s, 1H, OH), 3.91 (d, J = 9.0 Hz, 1H, CHH), 4.39 (d, J = 9.0 Hz, 1H,
CHH), 5.00 (s, 2H, CH2O), 6.83 (d, J = 9.0 Hz, 2H, Ph–H), 6.88 (d,
J = 9.0 Hz, 2H, Ph–H), 7.31–7.41 (m, 5H, Ph–H), 7.96 (d, J = 9.0 Hz,
1H, Ph–H), 8.01 (dd, J = 2.5, 9.0 Hz, 1H, Ph–H), 8.09 (d, J = 2.0 Hz,
1H, Ph–H), 9.18 (s, 1H, NH). MS (ESI): 513 ([M+Na]+, 100%).
3
NMR (CDCl3) d: 23.27, 55.92, 75.25, 75.37, 104.39 (q, JC–
3
F = 1.8 Hz), 112.22, 115.65, 116.65, 117.47 (q, JC–F = 4.8 Hz),
1
2
121.15 (q, JC–F = 272.5 Hz), 121.62, 122.04, 123.49, 133.52 (q, JC–
F = 32.6 Hz), 135.89, 141.90, 147.34, 149.61, 173.84. MS (ESI): 395
([M+H]+, 100%). HRMS (ESI): calcd. for C19H17N2O4F3Na 417.1038
([M+Na]+), found 417.1021.
(S)-3-(2-(Benzyloxy)phenoxy)-N-(4-cyano-3-(trifluoromethyl)-
phenyl)-2-hydroxy-2-methylpropanamide (8b). White oil, 34%
yield, 96.4% HPLC purity. 1H NMR (CDCl3) d: 1.50 (s, 3H, CH3),
3.89 (d, J = 9.5 Hz, 1H, CHH), 4.50 (s, 1H, OH), 4.52 (d, J = 9.5 Hz,
1H, CHH), 5.03 (d, J = 11.0 Hz, 1H, CHHO), 5.07 (d, J = 11.0 Hz, 1H,
CHHO), 6.94–7.02 (m, 4H, Ph–H), 7.31–7.33 (m, 3H, Ph–H), 7.37–
7.38 (m, 2H, Ph–H), 7.66 (d, J = 8.5 Hz, 1H, Ph–H), 7.73 (dd,
J = 2.0, 8.5 Hz, 1H, Ph–H), 7.91 (d, J = 2.0 Hz, 1H, Ph–H), 9.12 (s,
1H, NH). MS (ESI): 469 ([MꢂH]+, 100%).
2.8. General procedure for preparation of compounds 9
Boron trifluoride diethyl etherate (BF3ꢃOEt2) (0.7 mL) and di-
methyl sulfide (0.8 mL) were added to a solution of 8b, 8d, 8f, or
8h (0.5 mmol) in dichloromethane (30 mL) at 0 °C. The resulting
mixture was stirred for 2 h at 0 °C, and then 2 h at RT. The reaction
mixture was evaporated to dryness in vacuo. The residue was par-
titioned with EtOAc and aqueous NaHCO3; the organic layer was
washed with brine, and dried over Na2SO4. After the EtOAc extract
was concentrated, the residue was purified by column chromatog-
raphy on silica gel with eluent (1:4 EtOAc/hexanes) to give corre-
sponding 9a, 9c, 9b, or 9d. Rf = 0.58–0.62 (1:1 EtOAc/hexanes).
(S)-N-(4-Cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-
hydroxyphenoxy)-2-methylpropanamide (9a). Colorless oil, 91%
(S)-N-(4-Cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-
methoxyphenoxy)-2-methylpropanamide (8c). Colorless oil, 50%
yield, 97.3% HPLC purity. 1H NMR (CDCl3) d: 1.57 (s, 3H, CH3), 3.73
(s, 1H, OH), 3.75 (s, 3H, OCH3), 3.92 (d, J = 9.0 Hz, 1H, CHH), 4.39 (d,
J = 9.0 Hz, 1H, CHH), 6.80 (d, J = 9.0 Hz, 2H, Ph–H), 6.84 (d,
J = 9.0 Hz, 2H, Ph–H), 7.75 (d, J = 8.5 Hz, 1H, Ph–H), 7.93 (dd,
J = 2.0, 8.5 Hz, 1H, Ph–H), 8.12 (d, J = 2.0 Hz, 1H, Ph–H), 9.23 (s,
1H, NH). 13C NMR (CDCl3) d: 22.97, 55.79, 73.49, 75.95, 104.49
3
3
(q, JC–F = 1.8 Hz), 114.85, 115.66, 116.08, 117.41 (q, JC–

M. Gao et al. / Steroids 76 (2011) 1505–1512
1509
yield, 97.1% HPLC purity. 1H NMR (CDCl3) d: 1.58 (s, 3H, CH3), 3.99
(d, J = 9.5 Hz, 1H, CHH), 4.45 (d, J = 9.5 Hz, 1H, CHH), 4.60 (board s,
1H, OH), 6.83–6.86 (m, 1H, Ph–H), 6.89–6.93 (m, 3H, Ph–H), 7.67
(d, J = 8.5 Hz, 1H, Ph–H), 7.86 (dd, J = 2.0, 8.5 Hz, 1H, Ph–H), 7.99
(d, J = 2.0 Hz, 1H, Ph–H), 9.26 (s, 1H, NH). MS (ESI): 381 ([M+H]+,
100%). HRMS (ESI) calcd. for C18H16N2O4F3 381.1062 ([M+H]+),
found 381.1068.
(2 ꢀ 2 mL), and then passed onto a rotatory evaporator. The solvent
was removed by evaporation (3 min) under vacuum. The final vol-
ume of ethanol after evaporation was ꢄ1 mL. The labeled product
[
11C]8a, [11C]8e, [11C]8c, or [11C]8g was reformulated with saline
(10 mL), sterile-filtered through
a sterile vented Millex-GS
0.22 m cellulose acetate membrane and collected into a sterile
l
vial. Total radioactivity (5.9–7.1 GBq) was assayed and the total
volume (10–11 mL) was noted for tracer dose dispensing. The
overall synthesis time including SPE purification and reformulation
was 23 min. The radiochemical yields decay corrected to end of
bombardment (EOB), from [11C]CO2, were 55 5% (n = 5). Reten-
tion times in the analytical HPLC system were: tR 9a = 2.40 min,
(S)-2-Hydroxy-3-(2-hydroxyphenoxy)-2-methyl-N-(4-nitro-
3-(trifluoromethyl)phenyl)propanamide (9b). Yellowish oil, 89%
yield, 96.7% HPLC purity. 1H NMR (CDCl3) d: 1.61 (s, 3H, CH3),
4.00 (d, J = 9.5 Hz, 1H, CHH), 4.13 (s, 1H, OH), 4.45 (d, J = 9.5 Hz,
1H, CHH), 6.58 (s, 1H, Ph–OH), 6.83–6.86 (m, 1H, Ph–H), 6.90–
6.94 (m, 3H, Ph–H), 7.90 (d, J = 8.5 Hz, 1H, Ph–H), 7.97 (dd,
J = 2.0, 8.5 Hz, 1H, Ph–H), 7.99 (d, J = 2.0 Hz, 1H, Ph–H), 9.25 (s,
1H, NH). MS (ESI): 423 ([M+Na]+, 100%). HRMS (ESI) calcd. for
tR 8a = 4.49 min, tR
[
11C]8a = 4.49 min; tR 9b = 2.55 min, tR
8e = 4.73 min, tR
8c = 4.34 min, tR
[
11C]8e = 4.73 min; tR 9c = 2.43 min, tR
11C]8c = 4.34 min; and tR 9d = 2.57 min, tR
[
C
17H15N2O6F3Na 423.0780 ([M+Na]+), found 423.0779.
8g = 4.48 min, tR [
11C]8g = 4.48 min.
(S)-N-(4-Cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-
hydroxyphenoxy)-2-methylpropanamide (9c). White solid, m.p.
165–167 °C, 92% yield. 1H NMR (CDCl3) d: 1.56 (s, 3H, CH3), 3.52
(s, 1H, OH), 3.90 (d, J = 9.0 Hz, 1H, CHH), 4.38 (d, J = 9.0 Hz, 1H,
CHH), 5.00 (s, 1H, Ph–OH), 6.73 (d, J = 9.0 Hz, 2H, Ph–H), 6.77 (d,
J = 9.0 Hz, 2H, Ph–H), 7.78 (d, J = 8.5 Hz, 1H, Ph–H), 7.94 (dd,
J = 2.0, 8.5 Hz, 1H, Ph–H), 8.09 (d, J = 2.0 Hz, 1H, Ph–H), 9.16 (s,
1H, NH). MS (ESI): 381 ([M+H]+, 100%). HRMS (ESI) calcd. for
3. Results and discussion
3.1. Chemistry
Four title compounds (8a, 8e, 8c, 8g) were selected as target
compounds for carbon-11 labeling. The four compounds include
two different aromatic methoxy regioisomers of two different pro-
panamide non-steroidal anti-androgens. Compound 8g has been
reported previously [26], and compounds 8a, 8e and 8c are new
compounds. Synthesis of propanamide derivative reference stan-
dards (8a, 8e, 8c, 8g) and their corresponding precursors (9a, 9b,
9c, 9d) is shown in Scheme 1. The authentic standards were syn-
thesized according to slight modifications of the published syn-
thetic procedures [14,25–27]. The coupling reaction of chiral
C
18H16N2O4F3 381.1062 ([M+H]+), found 381.1062.
(S)-2-Hydroxy-3-(4-hydroxyphenoxy)-2-methyl-N-(4-nitro-3-
(trifluoromethyl)phenyl)propanamide (9d). Yellowish solid, m.p.
104–106 °C, 90% yield. 1H NMR (acetone-d6) d: 1.51 (s, 3H, CH3),
3.95 (d, J = 9.0 Hz, 1H, CHH), 4.27 (d, J = 9.0 Hz, 1H, CHH), 5.28 (s,
1H, OH), 6.71 (d, J = 7.5 Hz, 2H, Ph–H), 6.76 (d, J = 7.5 Hz, 2H, Ph–
H), 7.88 (s, 1H, Ph–H), 8.12 (d, J = 9.0 Hz, 1H, Ph–H), 8.35 (d,
J = 9.0 Hz, 1, Ph–H), 8.54 (s, 1H, NH), 10.06 (s, 1H, Ph–OH). MS
(ESI): 401 ([M+H]+, 100%). HRMS (ESI): calcd. for C17H15N2O6F3Na
423.0780 ([M+Na]+), found 423.0770.
auxiliary, D-proline (1), with methacryloyl chloride in aqueous ace-
tone at 0 °C under basic condition formed (R)-prolineamide 2 in
75% yield. 1H NMR data of compound 2 list 3 singlets 5.04, 5.16,
and 5.29 to represent the 2 terminal vinyl protons. This would ex-
pect the two protons to have different chemical shifts and couple
to each other. This signal is really two doublets. There was an over-
lap at the singlet 5.16, and its integrated height is taller than both
the singlet 5.04 and the singlet 5.29. Thus, the signal became 3
singlets. 1H NMR assignment of 2 has three signals for CH. There
is only one CH (tertiary) in the molecule; the other CH must be
the aliphatic CH2 wherein the two have different chemical shifts.
Compound 2 was then converted to its corresponding (R)-bromo-
lactone 3 using 2 equiv of NBS in DMF in 76% yield. Hydrolysis of
3 in 28% HBr at reflux gave (R)-bromoacid 4 in 78% yield. Unlike
the published procedure [25], we used 28% HBr instead of concen-
trated HCl for hydrolysis of 3 to avoid the formation of a side prod-
uct of 4, (R)-chloroacid, which appeared to be difficult to separate.
This modification gave the similar chemical yield of 4 and signifi-
cantly improved the chemical purity of 4. Coupling of 4 with differ-
ent aniline derivatives 5 [4-cyano-3-(trifluoro-methyl)benzenamine
(5a) and 4-nitro-3-(trifluoro-methyl)benzenamine (5b)] yielded R-
enantiomers of 6a and 6b in 65% and 62% yield, respectively. In-
stead of high boiling point solvent N,N-dimethylacetamide
(DMA), lower boiling point solvent CH3CN and base Et3N were used
in the reaction. Our modified procedures significantly simplified
the work-up procedures and slightly improved the chemical yield
of 6. Compound 6 was converted into an epoxide intermediate
by treatment with K2CO3 in acetone. The epoxide, without purifica-
tion, was directly reacted with substituted phenol 7 (2-methoxy-
phenol, 2-benzyloxyphenol, 4-methoxyphenol and 4-benzyl
oxyphenol) in additional K2CO3 and 2-butanone to provide pro-
panamide derivatives 8 in 28–50% yield. The process was a two-
step-one-pot reaction. Synthesis of the appropriate precursors is
more challenging. Attempts to generate desmethyl precursors 9
2.9. (S)-N-(4-Cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(2-
[
11C]methoxyphenoxy)-2-methylpropanamide ([11C]8a)
(S)-2-hydroxy-3-(2-[11C]methoxyphenoxy)-2-methyl-N-(4-ni-
tro-3-(trifluoromethyl)phenyl)propanamide ([11C]8e), (S)-N-(4-
cyano-3-(trifluoromethyl)phenyl)-2-hydroxy-3-(4-[11C]methoxy-
phenoxy)-2-methylpropanamide ([11C]8c) and (S)-2-hydroxy-3-
(4-[11C]methoxyphenoxy)-2-methyl-N-(4-nitro-3-(trifluoromethyl)-
phenyl)propanamide ([11C]8g)
[
11C]CO2 was produced by the
14N(p, 11C nuclear reaction in the small volume (9.5 cm3) alumi-
a)
num gas target provided with the Siemens RDS-111 Eclipse cyclo-
tron. 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 50
target. The production run produced approximately 25.9 GBq of
11C]CO2 at EOB. The phenolic hydroxyl precursor 9a, 9b, 9c, or
9d (0.1–0.3 mg) was dissolved in CH3CN (300 L). To this solution
was added 2 N NaOH (2 L). The mixture was transferred to a small
lA beam current and 15 min on
[
l
l
reaction vial. No-carrier-added (high specific activity) [11C]CH3OTf
(13.9 GBq) that was produced by the gas-phase production method
[32] within 11 min from [11C]CO2 (25.9 GBq) through [11C]CH4
(21.8 GBq) and [11C]CH3Br (13.9 GBq) with silver triflate (AgOTf)
column was passed into the reaction vial at RT until radioactivity
reached a maximum (2 min), and then the reaction vial was iso-
lated and heated at 80 °C for 3 min. The contents of the reaction
vial were diluted with NaHCO3 (0.1 M, 1 mL). The reaction vial
was connected to a C-18 Plus Sep-Pak cartridge. The labeled prod-
uct mixture solution was passed onto the cartridge for solid-phase
extraction (SPE) purification by gas pressure. The cartridge was
washed with H2O (2 ꢀ 3 mL), and the aqueous washing was dis-
carded. The product was eluted from the cartridge with EtOH

1510
M. Gao et al. / Steroids 76 (2011) 1505–1512
O
CO2H
HOOC
H3C
Br
OH
N
i
CO2H
ii
N
iii
N
H
1
O
O
O
H3C
Br
4
2
3
R2
R2
R1
F3C
NH2
O
O
HO
R3
7
O
R3
Br
OH
R1
F3C
N
H
5
R1
N
H
H3C
OH
iv
H3C
v
F3C
6a, R1 = CN
6b, R1 = NO2
8a, R1 = CN, R2 = OCH3, R3 = H
8b, R1 = CN, R2 = Benzyloxy, R3 = H
8c, R1 = CN, R2 = H, R3 = OCH3
8d, R1 = CN, R2 = H, R3, = Benzyloxy
8e, R1 = NO2, R2 = OCH3, R3 = H
8f, R1 = NO2, R2 = Benzyloxy, R3 = H
8g, R1 = NO2, R2 = H, R3 = OCH3
8h, R1 = NO2, R2 = H, R3 = Benzyloxy
HO
O
O
R1
F3C
N
H
vi
O
OH
R1
N
O
H
OH
H3C
OH
H3C
9a, R1 = CN (from 8b)
F3C
9c, R1 = CN (from 8d)
9d, R1 = NO2 (from 8h)
9b, R1 = NO2 (from 8f)
Scheme 1. Synthesis of propanamide derivatives. Reagents and conditions: (i) Methacryloyl chloride, NaOH (aq), 5 °C; 75%. (ii) NBS, DMF; 76%. (iii) 28% HBr, reflux; 78%. (iv)
Thionyl chloride, CH3CN, Et3N, 5, ꢂ5 °C; 65% and 62%. (v) a. acetone/K2CO3, reflux; b. 2-butanone/K2CO3, 7, reflux; 28–50%. (vi) BF3ꢃOEt2, Me2S; 89–92%.
H311CO
HO
O
O
R1
F3C
N
H
O
R1
F3C
N
H
O
OH
OH
H3C
H3C
9a, R1 = CN
[
[
11C]8a, R1 = CN
11C]8e, R1 = NO2
i
9b, R1 = NO2
O
O
R1
F3C
N
O
O11CH3
R1
F3C
N
O
OH
H
H
OH
OH
H3C
H3C
9c, R1 = CN
9d, R1 = NO2
[
[
11C]8c, R1 = CN
11C]8g, R1 = NO2
Scheme 2. Synthesis of carbon-11-labeled propanamide derivatives. Reagents and conditions: (i) [11C]CH3OTf, CH3CN, 2 N NaOH, 80 °C; 55 5%.
for radiolabeling from their corresponding methoxy compounds 8
via direct O-demethylation were unsuccessful. Thus, an alternative
strategy was explored and designed. The preparation of phenolic
hydroxyl precursors 9a–d required a protecting group method
[33]. We found that benzyl group was a good protecting group
for this reaction scheme. Benzyloxy compounds 8b, 8d, 8f and 8h
were obtained using the same method as standard compounds
8a, 8c, 8e and 8g. The demethylated precursors 9 were prepared
by the deprotecting reaction of their corresponding compounds 8
with BF3ꢃOEt2 and Me2S in 89–92% yield.
and [11C]8g in 55 5% (n = 5) radiochemical yields, decay corrected
to EOB, based on [11C]CO2. The large polarity difference between
the phenolic hydroxyl precursor and the corresponding labeled
O-methylated ether product permitted the use of SPE technique
for purification of the labeled product from the radiolabeling reac-
tion mixture. A C-18 Plus Sep-Pak cartridge was used in SPE puri-
fication technique. The crude reaction mixture was treated with
sodium bicarbonate and loaded onto the cartridge by gas pressure.
The pH of freshly prepared 0.1 M NaHCO3 might be too low to
effectively deprotonate a phenol. However, an excess of 2 N NaOH
used in the reaction provided a final pH after addition of the 0.1 M
NaHCO3 high enough to deprotonate all the phenol. Any non-re-
acted phenolic hydroxyl precursor was actually converted to the
corresponding sodium salt, and any non-reacted [11C]CH3OTf was
actually hydrolyzed to [11C]CH3OH, which would not stick to the
C-18 Sep-Pak. The cartridge was washed with water to remove
non-reacted [11C]CH3OTf, phenolic hydroxyl precursor and reac-
tion solvent, and total 6 mL (2 ꢀ 3 mL) volume of water was en-
ough to wash off all phenol. The final labeled product was eluted
with ethanol. Overall synthesis time was 23 min from EOB, includ-
3.2. Radiochemistry
Synthesis of carbon-11-labeled propanamide derivatives,
[
11C]8a, [11C]8e, [11C]8c and [11C]8g, is indicated in Scheme 2. Phe-
nolic hydroxyl precursors 9a, 9b, 9c and 9d were labeled by a reac-
tive [11C]methylating agent, [11C]CH3OTf [32,34] prepared from
[
11C]CO2, under basic conditions (2 N NaOH) in acetonitrile
through the O-[11C]methylation and isolated by a simplified SPE
method [35,36] to provide target tracers [11C]8a, [11C]8e, [11C]8c

M. Gao et al. / Steroids 76 (2011) 1505–1512
1511
ing approximately 11 min for [11C]CH3OTf production, 5 min for O-
11C]methylation reaction, and 7 min for SPE purification, evapora-
References
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from 370 to 925 GBq/
The specific activity of carbon-11-labeled propanamide derivatives
was estimated in a range of 185–370 GBq/ mol at the end of syn-
lmol at EOB according to our previous works.
l
thesis (EOS) based on other compounds produced in our facility
using the same targetry conditions which have been measured
by the on-the-fly technique or the same SPE purification method
[38,39]. The actual measurement of specific activity at EOS was
performed by analytical HPLC [40] and calculated. The exact values
were 277.5 92.5 GBq/lmol (n = 5), which are in agreement with
the estimated values and the ‘‘on line’’ determined values. Chemi-
cal purity and radiochemical purity were determined by analytical
HPLC [40]. The chemical purity of the precursors and reference
standards was >96%. The radiochemical purity of the target tracers
was >99% determined by radio-HPLC through
c-ray (PIN diode)
flow detector, and the chemical purity of the target tracers was
>95% determined by reversed-phase HPLC through UV flow
detector.
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An efficient and convenient synthesis of new SARM radioli-
gands, carbon-11-labeled propanamide derivatives, has been
developed. The synthetic methodology employed multiple step
organic reactions to prepare a series of propanamide derivatives,
phenolic hydroxyl precursors and their corresponding ether
standard compounds. The target tracers were easily prepared by
O-[11C]methylation of their corresponding precursors using a reac-
tive [11C]methylating agent, [11C]CH3OTf, and isolated by a simpli-
fied SPE purification procedure in high radiochemical yields, short
overall synthesis time, and high specific radioactivities. These
chemistry results combined with the reported in vitro biological
data [14,21,25–27] encourage further in vivo biological evaluation
of new carbon-11-labeled propanamide derivatives as candidate
PET agents to image AR in prostate cancer.
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