Synthesis of 2-[11C]methoxy-3,17β-O,O-bis(sulfamoyl) estradiol as a new potential PET agent for imaging of steroid sulfatase (STS) in cancers

Article abstract of DOI:10.1016/j.steroids.2012.04.007

Steroid sulfatase (STS) catalyzes the hydrolysis of steroid sulfates to estrones, the main source of estrogens in tumors. Carbonic anhydrase II (CAII) is highly expressed in red blood cells through a coordination of the monoanionic form of the sulfamate moiety to the zinc atom in the enzyme active site, and CAII is highly expressed in several tumors. 2-Methoxy-3,17β-O,O- bis(sulfamoyl)estradiol (5) is a dual-function STS-CAII inhibitor inhibited STS with 39 nM IC₅₀ value selectively over CAII with 379 nM IC ₅₀ value. This compound exhibited potent antiproferative activity with mean graph midpoint value of 87 nM in the NCI 60-cell-line panel, and antiangiogenic in vitro and in vivo activity in an early-stage Lewis lung model as well. The compound has been recently developed as a multitargeted anticancer agent. Both STS and CAII are over-expressed in cancers and have become attractive targets for cancer treatment and molecular imaging of cancer. Here we report the first design and synthesis of 2-[¹¹C]methoxy-3,17β- O,O-bis(sulfamoyl)estradiol ([¹¹C]5) as a new potential imaging agent for biomedical imaging technique positron emission tomography (PET) to image STS in cancers. The authentic standard 5 was synthesized from 17β-estradiol by published procedures in 5 steps with 40% overall chemical yield. The precursor 2-hydroxy-3,17β-O,O-bis(sulfamoyl)estradiol (14a) for radiolabeling was synthesized from 17β-estradiol in 10 steps with 5% overall chemical yield. The target tracer [¹¹C]5 was prepared from the precursor 14a with [¹¹C]CH₃OTf through O-[ ¹¹C]methylation and isolated by HPLC combined with solid-phase extraction (SPE) purification in 40-50% radiochemical yields based on [ ¹¹C]CO₂ and decay corrected to end of bombardment (EOB), with 370-740 GBq/μmol specific activity at EOB.

Full text of DOI:10.1016/j.steroids.2012.04.007

Steroids 77 (2012) 864–870
Contents lists available at SciVerse ScienceDirect
Steroids
journal homepage: www.elsevier.com/locate/steroids
Synthesis of 2-[11C]methoxy-3,17b-O,O-bis(sulfamoyl)estradiol as a new
potential PET agent for imaging of steroid sulfatase (STS) in cancers
Min Wang a, Lu Xu a, Mingzhang Gao a, Kathy D. Miller b, George W. Sledge 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, 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 1 March 2012
Received in revised form 30 March 2012
Accepted 10 April 2012
Available online 19 April 2012
Steroid sulfatase (STS) catalyzes the hydrolysis of steroid sulfates to estrones, the main source of estro-
gens in tumors. Carbonic anhydrase II (CAII) is highly expressed in red blood cells through a coordination
of the monoanionic form of the sulfamate moiety to the zinc atom in the enzyme active site, and CAII is
highly expressed in several tumors. 2-Methoxy-3,17b-O,O-bis(sulfamoyl)estradiol (5) is a dual-function
STS-CAII inhibitor inhibited STS with 39 nM IC50 value selectively over CAII with 379 nM IC50 value. This
compound exhibited potent antiproferative activity with mean graph midpoint value of 87 nM in the NCI
60-cell-line panel, and antiangiogenic in vitro and in vivo activity in an early-stage Lewis lung model as
well. The compound has been recently developed as a multitargeted anticancer agent. Both STS and CAII
are over-expressed in cancers and have become attractive targets for cancer treatment and molecular
imaging of cancer. Here we report the first design and synthesis of 2-[11C]methoxy-3,17b-O,O-bis(sulfa-
moyl)estradiol ([11C]5) as a new potential imaging agent for biomedical imaging technique positron
emission tomography (PET) to image STS in cancers. The authentic standard 5 was synthesized from
17b-estradiol by published procedures in 5 steps with 40% overall chemical yield. The precursor
2-hydroxy-3,17b-O,O-bis(sulfamoyl)estradiol (14a) for radiolabeling was synthesized from 17b-estradiol
in 10 steps with 5% overall chemical yield. The target tracer [11C]5 was prepared from the precursor 14a
with [11C]CH3OTf through O-[11C]methylation and isolated by HPLC combined with solid-phase extrac-
tion (SPE) purification in 40–50% radiochemical yields based on [11C]CO2 and decay corrected to end of
Keywords:
Steroid sulfatase (STS)
Carbonic anhydrase II (CAII)
2-[11C]Methoxy-3,17b-O,O-
bis(sulfamoyl)estradiol
Positron emission tomography (PET)
Radiosynthesis
Cancer imaging
bombardment (EOB), with 370–740 GBq/
l
mol specific activity at EOB.
Ó 2012 Elsevier Inc. All rights reserved.
1. Introduction
highly active reversible CAII inhibitor with 379 nM IC50 value [3].
Although compound 5 is a dual-function STS and CAII inhibitor, its
selectivity to inhibit STS over CAII is ꢀ10-fold. This compound
exhibited potent antiproferative activity with mean graph midpoint
The enzyme steroid sulfatase (STS) catalyzes the hydrolysis of
steroid sulfates to estrones, the main source of estrogens in tumors
[1]. The enzyme carbonic anhydrase (CA) catalyzes the production
of acid in tumors, and so far more than 10 enzymatically active CA
isoenzymes have been identified [2]. CAII is highly expressed in sev-
eral tumors, and is highly expressed in red blood cells through a
coordination of the monoanionic form of the sulfamate moiety to
the zinc atom in the enzyme active site [3]. Both STS and CAII are
over-expressed in cancers and have become attractive clinical
targets for the treatment of cancers [1–3], and dual-function STS-
CAII inhibitors have been developed, because the sulfamate-bearing
steroidal and nonsteroidal STS inhibitors may also interact with CAII
[4]. Recently a novel series of 2-substituted estradiol bis-sulfamates
has been developed as multitargeted antitumor agents, and the lead
compound 2-methoxy-3,17b-O,O-bis(sulfamoyl)estradiol (5) is a
potent irreversible STS inhibitor with 39 nM IC50 value, and also a
value of 87 nM in the NCI 60-cell-line panel, and GI50 (lM) values
were 0.25 (breast MCF-7), 0.051 (lung HOP-62), 0.045 (colon
HCT-116), 0.036 (CNS SF-539), <0.01 (melanoma UACC-62), <0.01
(ovarian OVCAR-3), 0.126 (renal SN12-C), 0.083 (prostate DU-145)
and <0.01 (breast MDA-MB-435), respectively, [3]. Compound 5 also
exhibited antiangiogenic in vitro and in vivo activity in an early-
stage Lewis lung model as well; in addition, X-ray crystallography
of the cocrystallization of compound 5 with CAII revealed unex-
pected coordination of the 17b-O-sulfamate of 5 to the active site
zinc and a probable additional lower affinity binding site [3]. Both
STS and CAII are attractive targets for molecular imaging of cancer.
We are interested in the development of enzyme- and/or receptor-
based cancer imaging agents for biomedical imaging technique
positron emission tomography (PET), especially in dual-function
imaging agents. However, the low nanomolar IC50 value of 5 for
STS is likely on the usable range to label this compound as an imag-
ing agent, the high nanomolar IC50 value of 5 for CAII is almost too
⇑
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 2012 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.steroids.2012.04.007

M. Wang et al. / Steroids 77 (2012) 864–870
865
large to be useful although the enzyme CAII is abundant, and the
biological activity of 5 is not appropriate to detect/image both en-
zymes STS and CAII with a single agent. Therefore, we hypothesized
2-substituted estradiol bis-sulfamates labeled with a positron-
emitting radionuclide such as carbon-11 or fluorine-18 may enable
non-invasive monitoring of the enzyme STS and cancer response to
NMR and 13C NMR spectra were recorded at 500 and 125 MHz,
respectively, on a Bruker Avance II 500 MHz NMR spectrometer
using tetramethylsilane (TMS) as an internal standard. Chemical
shift data for the proton resonances were reported in parts per mil-
lion (ppm, d scale) relative to internal standard TMS d 0.0), and cou-
pling constants (J) were reported in hertz (Hz). The high resolution
mass spectra (HRMS) were obtained using a Thermo MAT 95XP-
Trap spectrometer. Chromatographic solvent proportions are indi-
cated in a volume: volume ratio. Thin-layer chromatography (TLC)
was run using Analtech silica gel GF uniplates (5 Â 10 cm2). Plates
were visualized under UV light. Preparative TLC was run using
Analtech silica gel UV 254 plates (20 Â 20 cm2). Normal phase flash
column chromatography was carried out on EM Science silica gel 60
(230–400 mesh) with a forced flow of the indicated solvent system
in the proportions described below. All moisture- and/or air-sensi-
tive reactions were performed under a positive pressure of nitrogen
maintained by a direct line from a nitrogen source. Analytical high
performance liquid chromatography (HPLC) was performed using
enzyme inhibitor treatment using PET. Steroidal compound 16a-
[18F]fluoro-17b-estradiol ([18F]FES), as shown in Fig. 1, has been
previously developed as a PET tracer to identify estrogen-recep-
tor-positive (ER+) breast tumors that are likely to respond to anti-
estrogen therapy in patients [5], to delineate the ER expression in
primary and metastatic breast cancer and to evaluate the therapeu-
tic efficacy of breast cancer treated with aromatase inhibitors (AIs)
[6]. In our previous works, we have synthesized carbon-11-labeled
nonsteroidal sulfamate derivatives (Fig. 1) as potential PET agents
for imaging of steroid biosynthetic enzymes aromatase and STS
expression in breast cancer [7]. In this ongoing studies, the repre-
sentative 2-substituted estradiol bis-sulfamate 5 was selected as
the target compound for radiolabeling, due to its excellent biologi-
cal activity and O-methyl position amendable to labeling with
carbon-11, and we report here the first design and synthesis of
2-[11C]methoxy-3,17b-O,O-bis(sulfamoyl)estradiol ([11C]5) (Fig. 1)
as a new potential imaging agent for PET to image the enzyme STS
in cancers.
a Prodigy (Phenomenex) 5
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. Semi-preparative HPLC was performed using
a Prodigy (Phenomenex) 5
m, 10 Â 250 mm C-18 column; 52:48
CH3CN/H2O mobile phase; 4.0 mL/min flow rate; UV (254 nm) and
-ray (PIN diode) flow detectors. C18 Plus Sep-Pak cartridges were
obtained from Waters Corporation (Milford, MA). Sterile
Millex-FG 0.2 m filter units were obtained from Millipore Corpora-
lm C-18 column, 4.6 Â 250 mm; 3:1:1
c
l
c
2. Experimental
l
tion (Bedford, MA).
2.1. General
2.2. 3,17b-O,O-Bis(methoxymethyl)estradiol (1)
All commercial reagents and solvents were purchased from
Sigma–Aldrich and Fisher Scientific and used without further puri-
fication. [11C]Methyl triflate ([11C]CH3OTf) was prepared according
to a literature procedure [8]. Melting points were determined on a
MEL-TEMP II capillary tube apparatus and were uncorrected. 1H
Compound 1 was prepared from 17b-estradiol as a colorless oil
in 94% yield. 1H NMR (CDCl3): d 7.20 (d, J = 8.5 Hz, 1H), 6.82 (dd,
J = 2.5, 8.5 Hz, 1H), 6.77 (d, J = 7.5 Hz, 1H), 5.14 (s, 2H), 4.67, 4.65
(ABq, J = 6.5 Hz, 2H), 3.61 (t, J = 8.5 Hz, 1H), 3.47 (s, 3H), 3.37 (s,
3H), 2.86–2.83 (m, 2H), 2.29–2.26 (m, 1H), 2.22–2.16 (m, 1H),
2.08–2.04 (m, 1H), 2.01–1.97 (m, 1H), 1.89–1.85 (m, 1H), 1.70–
1.18 (m, 8H), 0.81 (s, 3H).
OH
OH
18F
2.3. 2-Hydroxy-3,17b-O,O-bis(methoxymethyl)estradiol (2)
HO
Compound 2 was prepared from 1 as a pale yellow oil in 84%
yield. 1H NMR (CDCl3): d 6.88 (s, 1H), 6.78 (s, 1H), 5.87 (br s, 1H),
5.15 (s, 2H), 4.67, 4.64 (ABq, J = 6.5 Hz, 2H), 3.61 (t, J = 8.5 Hz,
1H), 3.51 (s, 3H), 3.37 (s, 3H), 2.78–2.73 (m, 2H), 2.23–2.04 (m,
3H), 2.00–1.96 (m, 1H), 1.87–1.83 (m, 1H), 1.70–1.16 (m, 8H),
0.80 (s, 3H).
HO
16α-[18F]Fluoro-17β-estradiol
17β-Estradiol
N
N
N
N
11
H2NO2SO
N
H3 CO
N
N
N
2.4. 2-Methoxy-3,17b-O,O-bis(methoxymethyl)estradiol (3)
11
H3 CO
H2NO2SO
Compound 3 was prepared from 2 as a white solid in 93% yield,
mp 74–75 °C (lit. 73–75 °C [9]). 1H NMR (CDCl3): d 6.86 (s, 1H),
6.84 (s, 1H), 5.19 (s, 2H), 4.67, 4.65 (ABq, J = 6.5 Hz, 2H), 3.85 (s,
3H), 3.62 (t, J = 8.5 Hz, 1H), 3.51 (s, 3H), 3.38 (s, 3H), 2.81–2.77
(m, 2H), 2.28–2.01 (m, 4H), 2.00–1.85 (m, 1H), 1.71–1.19 (m,
8H), 0.82 (s, 3H).
CN
CN
Carbon-11-labeled sulfamate derivatives
OSO2NH2
H311CO
2.5. 2-Methoxyestradiol (4)
Compound 4 was prepared from 3 as a white solid in 83% yield,
mp 186–187 °C (lit. 186–187 °C [10]). 1H NMR (DMSO-d6): d 8.58
(s, 1H), 6.78 (s, 1H), 6.43 (s, 1H), 4.49 (d, J = 3.5 Hz, 1H), 3.71 (s,
3H), 3.54–3.50 (m, 1H), 2.65–2.59 (m, 2H), 2.27 (d, J = 11.0 Hz,
1H), 2.09–2.05 (m, 1H), 1.92–1.75 (m, 3H), 1.61–1.56 (m,
1H),1.39–1.06 (m, 7H), 0.67 (s, 3H).
H2NO2SO
2-[11C]Methoxy-3,17β-O,O-bis(sulfamoyl)estradiol
Fig. 1. Chemical structures of 17b-estradiol, 16a
-[18F]fluoro-17b-estradiol, carbon-
11-labeled nonsteroidal sulfamate derivatives, and 2-[11C]methoxy-3,17b-O,O-
bis(sulfamoyl)estradiol.

866
M. Wang et al. / Steroids 77 (2012) 864–870
2.6. 2-Methoxy-3,17b-O,O-bis(sulfamoyl)estradiol (5)
60 °C for 1 h, MeOH was evaporated in vacuo. The residue was di-
luted with cold water, acidified with 1 N HCl, and extracted with
CH2Cl2. The combined organic layers were washed with brine,
dried over anhydrous Na2SO4, filtered and concentrated. The crude
product was purified by column chromatography (8:1 hexanes/
CH3COCH3) to afford 10 (1.46 g, 96%) as a white solid, mp 105–
106 °C. 1H NMR (CDCl3): d 7.41–7.23 (m, 10H), 6.90 (s, 1H), 6.64
(s, 1H), 5.45 (br s, 1H), 5.04(s, 2H), 4.57 (s, 2H), 3.49 (t, J = 8.5 Hz,
1H), 2.82–2.71 (m, 2H), 2.23–2.00 (m, 3H), 1.86–1.83 (m, 1H),
1.69–1.17 (m, 9 H), 0.86 (s, 3H).
Compound 5 was prepared from 4 as a white solid in 74% yield,
mp 180–182 °C (lit. 180–182 °C [3]). 1H NMR (CD3OD): d 7.00 (s,
1H), 6.98 (s, 1H), 4.43 (t, J = 8.5 Hz, 1H), 3.82 (s, 3H), 2.79–2.77
(m, 2H), 2.38–2.35 (m, 1H), 2.29–2.24 (m, 2H), 2.08–2.05 (m,
1H), 1.91–1.87 (m, 1H), 1.84–1.74 (m, 2H), 1.54–1.41 (m, 4H),
1.36–1.24 (m, 2H), 0.86 (s, 3H). 13C NMR (CD3OD): d 151.2, 140.6,
138.6, 130.2, 124.8, 111.5, 90.0, 56.5, 50.4, 45.7, 44.3, 39.7, 37.6,
29.6, 28.9, 28.2, 27.3, 24.0, 12.1. HRMS (ESI, m/z): calcd for
C
19H28N2O7S2Na ([M + Na]+) 483.1236; found 483.1242.
2.12. 2-Triisopropylsilyloxy-3,17b-O,O-bis(benzyloxy)estradiol (11)
2.7. 2-Formyl-3,17b-O,O-bis(methoxymethyl)estradiol (6)
To a solution of compound 10 (1.0 g, 2.14 mmol) and DMAP
(564 mg, 4.62 mmol) in pyridine (20 mL) was added triisopropylsi-
lyl triflate (TIPSOTf) (4.0 mL, 14.9 mmol) dropwise at 0 °C under
nitrogen atmosphere. The resulting pale yellow solution was al-
lowed to warm up to RT. After the reaction mixture was stirred
at RT overnight, the reaction was quenched with MeOH (8 mL).
The mixture was diluted with Et2O, and then washed with 5%
aqueous HCl, saturated aqueous NaHCO3 and brine. The organic
layer was dried over anhydrous Na2SO4, filtered and concentrated.
The crude product was purified by column chromatography (8:1
hexanes/Et2O) to afford 11 (1.26 g, 95%) as a pale yellow oil. 1H
NMR (CDCl3): d 7.43–7.24 (m, 10H), 6.80 (s, 1H), 6.59 (s, 1H),
5.00 (s, 2H), 4.58 (s, 2H), 3.49 (t, J = 8.5 Hz, 1H), 2.80–2.68 (m,
2H), 2.18–2.01 (m, 4H), 1.85–1.81 (m, 1H), 1.70–1.17 (m, 11 H),
1.34 (d, J = 7.0 Hz, 18H), 0.87 (s, 3H). 13C NMR (CDCl3): d 147.8,
143.7, 139.5, 137.7, 133.0, 129.1, 128.4, 128.4, 127.9, 127.8,
127.4, 127.4, 117.5, 114.7, 88.4, 71.8, 71.1, 50.4, 44.1, 43.6, 38.6,
38.2, 29.3, 28.2, 27.5, 26.7, 23.3, 18.2, 13.0, 12.0. HRMS (ESI, m/z):
calcd for C41H56O3SiNa ([M + Na]+) 647.3896; found 647.3903.
Compound 6 was prepared from 5 as a white solid in 81% yield,
mp 88–89 °C. 1H NMR (CDCl3): d 10.43 (s, 1H), 7.77 (s, 1H), 6.91 (s,
1H), 5.26 (s, 2H), 4.67, 4.65 (ABq, J = 6.5 Hz, 2H), 3.63 (t, J = 8.5 Hz,
1H), 3.52 (s, 3H), 3.38 (s, 3H), 2.91–2.88 (m, 2H), 2.40–2.37 (m, 1H),
2.17–1.88 (m, 4H), 1.70–1.32 (m, 7H), 1.22–1.18 (m, 1H), 0.80 (s,
3H).
2.8. 2-Formylestradiol (7)
Compound 7 was prepared from 6 as a white solid in 98% yield,
mp 231–233 °C (lit. 231–233 °C [11]; lit. 230–232 °C [12]). 1H NMR
(DMSO-d6): d 10.42 (s, 1H), 10.13 (s, 1H), 7.56 (s, 1H), 6.67 (s, 1H),
4.51 (d, J = 4.5 Hz, 1H), 3.54–3.50 (m, 1H), 2.83–2.78 (m, 2H), 2.29–
2.26 (m, 1H), 2.11–2.06 (m, 1H), 1.92–1.85 (m, 2H), 1.80–1.77 (m,
1H), 1.60–1.55 (m, 1H), 1.42–1.33 (m, 2H), 1.31–1.07 (m, 5H), 0.66
(s, 3H).
2.9. 2-Formyl-3,17b-O,O-bis(benzyloxy)estradiol (8)
Compound 8 was prepared from 7 as a white solid in 66% yield,
mp 123–125 °C (lit. 124–125 °C [12]). 1H NMR (CDCl3): d 10.48 (s,
1H), 7.78 (s, 1H), 7.44–7.27 (m, 10H), 6.74 (s, 1H), 5.14 (s, 2H), 4.57
(s, 2H), 3.50 (t, J = 8.5 Hz, 1H), 2.89–2.87 (m, 2H), 2.39–2.36 (m,
1H), 2.16–2.03 (m, 4H), 1.90–1.87 (m, 1H), 1.68–1.17 (m, 7H),
0.86 (s, 3H).
2.13. 2-Triisopropylsilyloxyestradiol (12a) and 3-triisopropylsilyloxy-
2-hydroxyestradiol (12b)
A solution of compound 11 (1.0 g, 1.60 mmol) in EtOAc (5 mL)
was hydrogenated over 20% Pd(OH)2/C (360 mg) at 60 psi H2 for
8 h. The catalyst was filtered through a layer of Celite, and then
the solvent was evaporated in vacuo. The crude product was puri-
fied by column chromatography (8:1–4:1, then 1:1 hexanes/Et2O)
to afford a mixture of two isomers 12a and 12b (357 mg, 50%) as
a white solid. 1H NMR (CDCl3): d 6.86, 6.76, 6.63, 6.52 (s, 2H),
5.43, 5.41 (s, 1H), 3.72 (t, J = 8.5 Hz, 1H), 2.78–2.63 (m, 2H), 2.26–
2.07 (m, 4H), 1.95–1.93 (m, 1H), 1.86–1.82 (m, 1H), 1.72–1.66
(m, 1H), 1.52–1.26 (m, 11H), 1.13–1.11 (m, 18H), 0.78 (s, 3H). 13C
NMR (CDCl3): d 144.8, 144.7, 140.7, 140.6, 133.7, 131.7, 130.0,
127.9, 117.5, 114.7, 114.4, 111.7, 82.0, 82.0, 50.2, 50.1, 44.2, 44.1,
43.4, 38.9, 38.8, 36.9, 36.8, 30.8, 30.7, 29.2, 29.1, 27.6, 27.5, 26.6,
26.4, 23.2, 18.1, 18.1, 12.9, 12.2.
2.10. 3,17b-O,O-Bis(benzyloxy)estradiol-2-yl formate (9)
To a solution of compound 8 (2.6 g, 5.41 mmol) in CH2Cl2
(50 mL) was added m-CPBA (containing 77% peracid, 1.58 g,
7.04 mmol) in portions, followed by p-TsOHꢁH2O (25 mg) under
nitrogen atmosphere. After the resulting yellow solution was stir-
red at room temperature (RT) for 3 h, it was diluted with water and
extracted with CH2Cl2. The organic layers were washed with 10%
aqueous Na2SO3, brine, dried over anhydrous Na2SO4, filtered and
concentrated. The crude product was purified by column chroma-
tography (8:1 hexanes/CH3COCH3) to afford 9 (1.91 g, 71%) as a
white solid, mp 137–138 °C. 1H NMR (CDCl3): d 8.26 (s, 1H),
7.37–7.27 (m, 10H), 7.01 (s, 1H), 6.74 (s, 1H), 5.05 (s, 2H), 4.57
(s, 2H), 3.50 (t, J = 8.5 Hz, 1H), 2.83–2.78 (m, 2H), 2.20–2.13 (m,
2H), 2.09–2.03 (m, 2H), 1.88–1.85 (m, 1H), 1.68–1.17 (m, 8H),
0.86 (s, 3H). 13C NMR (CDCl3): d 159.8, 147.7, 139.4, 137.1, 136.8,
135.9, 133.8, 128.7, 128.4, 128.1, 127.4, 119.7, 114.5, 88.4, 71.8,
70.9, 50.3, 44.0, 43.5, 38.3, 37.9, 29.7, 28.2, 27.2, 26.5, 23.2, 11.9.
HRMS (ESI, m/z): calcd for C33H36O4Na ([M + Na]+) 519.2511; found
519.2527.
2.14. 2-Triisopropylsilyloxy-3,17b-O,O-bis(sulfamoyl)estradiol (13a)
and 3-triisopropylsilyloxy-2,17b-O,O-bis(sulfamoyl)estradiol (13b)
To a cold (0 °C) solution of a mixture of compounds 12a and 12b
(280 mg, 0.63 mmol) in dimethylacetamide (DMA) (2 mL) was
added sulfamoyl chloride (435 mg, 3.78 mmol) in potions at 0 °C
under nitrogen atmosphere. The reaction mixture was allowed to
warm up to RT. After the resulting yellow solution was stirred at
RT overnight, it was poured into ice-water and extracted with
EtOAc. The combined organic layers were washed with brine, dried
over anhydrous Na2SO4, filtered and concentrated. The crude prod-
uct was purified by preparative TLC plate (4:1 CHCl3/CH3COCH3) to
afford 13a (137 mg, 36%) and 13b (146 mg, 38%) as white solids.
13a, mp 79–80 °C. 1H NMR (CDCl3): d 7.05 (s, 1H), 6.88 (s, 1H),
4.89 (s, 2H), 4.84 (s, 2H), 4.51 (t, J = 8.5 Hz, 1H), 2.81–2.79 (m,
2.11. 2-Hydroxy-3,17b-O,O-bis(benzyloxy)estradiol (10)
To a solution of compound 9 (1.6 g, 3.22 mmol) in MeOH
(40 mL) was added 10% aqueous NaOH (8.0 mL) under nitrogen
atmosphere. After the reaction mixture was heated and stirred at

M. Wang et al. / Steroids 77 (2012) 864–870
867
2H), 2.31–2.24 (m, 1H), 2.21–2.17 (m, 2H), 2.10–2.08 (m, 1H),
1.91–1.84 (m, 2H), 1.80–1.73 (m, 1H), 1.51–1.42 (m, 4H), 1.32–
1.22 (m, 5H), 1.11 (dd, J = 1.5, 7.5 Hz, 18H), 0.87 (s, 3H). 13C NMR
(CDCl3): 145.6, 140.0, 138.4, 130.5, 124.2, 118.0, 90.7, 49.3, 44.1,
43.4, 38.1, 36.5, 28.7, 27.8, 27.0, 26.1, 23.1, 18.0, 12.8, 11.8. HRMS
(ESI, m/z): calcd for C27H46N2O7S2SiNa ([M + Na]+) 625.2413; found
625.2424. 13b, mp 101–103 °C. 1H NMR (CDCl3): d 7.19 (s, 1H),
6.63 (s, 1H), 5.23 (s, 2H), 5.18 (s, 2H), 4.46 (t, J = 8.5 Hz, 1H),
2.77–2.74 (m, 2H), 2.27–2.22 (m, 2H), 2.04–2.02 (m, 2H), 1.86–
1.82 (m, 2H), 1.72–1.70 (m, 1H), 1.47–1.35 (m, 4H), 1.30–1.22
(m, 5H), 1.09 (d, J = 7.5 Hz, 18H), 0.84 (s, 3H). 13C NMR (CDCl3): d
145.7, 138.5, 136.5, 133.7, 120.8, 120.8, 90.3, 49.1, 43.6, 43.3,
38.1, 36.3, 29.2, 27.7, 26.9, 25.9, 23.1, 22.9, 17.9, 12.8, 11.8. HRMS
(ESI, m/z): calcd for C27H46N2O7S2SiNa ([M + H]+) 603.2594; found
603.2623.
(2
was produced by the gas-phase production method [8] from
11C]CO2 through [11C]CH4 and [11C]CH3Br with silver triflate
l
L). No carrier-added (high specific activity) [11C]CH3OTf that
[
(AgOTf) column was passed into the reaction vial at RT, until radio-
activity 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 NaHCO3 (0.1 M, 1 mL), and injected
onto the semi-preparative HPLC column with 3 mL injection loop
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 Sep-Pak Plus cartridge, and washed with
water (5 mL Â 4). The cartridge was eluted with EtOH (1 mL Â 2),
followed by 10 mL saline, to release [11C]5. The eluted product
was then sterile-filtered through a Millex-FG 0.2 lm membrane
into a sterile vial. Total radioactivity was assayed and total volume
was noted for tracer dose dispensing. Retention times in the semi-
preparative HPLC system were: tR 14a = 4.85 min, tR 5 = 7.53 min,
2.15. 2-Hydroxy-3,17b-O,O-bis(sulfamoyl)estradiol (14a)
tR [
11C]5 = 7.53 min. Retention times in the analytical HPLC system
To a cold (0 °C) solution of compound 13a (80 mg, 0.13 mmol)
in THF (1.5 mL) was added n-Bu4NF (1 M in THF, 0.4 mL, 0.4 mmol)
dropwise at 0 °C under nitrogen atmosphere. The reaction mixture
was allowed to warm up to RT. After the resulting yellow solution
was stirred at RT overnight, it was poured into ice-water and ex-
tracted with EtOAc. The combined organic layers were washed
with brine, dried over anhydrous Na2SO4, filtered and concen-
trated. The crude product was purified by preparative TLC plate
(4:1:0.1 CHCl3/CH3COCH3/MeOH) to afford 14a (47 mg, 79%) as a
white solid, mp 74–75 °C. 1H NMR (CD3OD): d 6.98 (s, 1H), 6.89
(s, 1H), 4.43 (t, J = 8.5 Hz, 1H), 2.77–2.76 (m, 2H), 2.32–2.24 (m,
2H), 2.19–2.17 (m, 1H), 2.06–2.02 (m, 1H), 1.90–1.74 (m, 3H),
1.50–1.36 (m, 4H), 1.35–1.23 (m, 2H), 0.86 (s, 3H). 13C NMR
(CD3OD): d 148.2, 140.7, 137.3, 129.3, 124.3, 115.2, 90.1, 50.4,
45.3, 44.2, 39.6, 37.5, 29.5, 28.8, 28.2, 27.2, 24.0, 12.1. HRMS (ESI,
were: tR 14a = 3.12 min, tR 5 = 5.34 min, tR [
11C]5 = 5.34 min. The
decay corrected radiochemical yields of [11C]5 from [11C]CO2 were
40–50%.
3. Results and discussion
3.1. Chemistry and lipophilicity
The reference standard 5 was synthesized from 17b-estradiol
according to reported methods [3,9,13,14] in 5 steps with 40%
overall chemical yield, as shown in Scheme 1.
The measured HPLC lipophilicity coefficient (octanol–water
partition coefficient, Log P) is an important parameter in selecting
PET radioligand candidates (small organic molecules) for further
evaluations [15–18]. Since biodistributions of labeled compounds
are very dependent on the lipid solubility and the more lipid solu-
ble a compound is the longer it takes to clear from the background
tissue. PET radionuclide carbon-11 does not give the long half-life
to observe the process and a high Log P can give very slow clear-
ance rates. It is a common phenomenon that an increase in lipo-
philicity is correlated to increasing nonspecific binding affinity of
a ligand to its target protein, and when the ligand is an enzyme
inhibitor, an increase in in vitro inhibitory activity is often ex-
pected when the lipophilicity of the inhibitor is increased [19].
Log P of 5 measured by analytical HPLC is 2.54, and Log P of 5 cal-
culated from ChemDraw Ultra 9.0 (ChemOffice 2005) is 2.69. Both
measured and calculated Log P values of 5 are comparable to what
had reported for the STS inhibitors [19] and appropriate for 5 to be
labeled as a radioligand, based on our previous experiences in radi-
oligand development [15–18].
Direct demethylation of the standard 5 to the desmethylated
precursor for radiolabeling was failed and a multiple-step synthe-
sis of desmethylated precursor was employed, which is outlined in
Scheme 2. This synthetic strategy was allowed to differentiate 2-,
3- and 17b-hydroxyl functions with different protecting groups be-
fore executing core synthetic transformations. As depicted in
Scheme 2, bis-methoxymethyl (MOM) protected ether 1 was
ortho-lithiated predominately at 2-position over 4-position with
s-BuLi, and the resulting anion was quenched with DMF [20] to de-
liver the 2-formylated estradiol 6 in 81% yield. Deprotection of the
bis-MOM groups of 6 with 6 N HCl in THF [20] produced 2-formy-
lestradiol 7 in 98% yield. Estradiol 7 was protected with 3- and 17b-
benzyl ether groups by treatment with BnBr in the presence of NaH
and a catalytic amount of n-Bu4NI in DMF to afford bis-benzylated
compound 8 in 66% yield. For this reaction to be successful, it was
essential to azeotropically dry compound 7 with toluene just prior
to use, then add BnBr slowly to a stirred suspension of 7 and NaH in
m/z): calcd for
C
18H26N2O7S2Na ([M + Na]+) 469.1079; found
469.1097.
2.16. 3-Hydroxy-2,17b-O,O-bis(sulfamoyl)estradiol (14b)
To a cold (0 °C) solution of compound 13b (110 mg, 0.18 mmol)
in THF (2 mL) was added n-Bu4NF (1 M in THF, 0.55 mL,
0.55 mmol) dropwise at 0 °C under nitrogen atmosphere. The reac-
tion mixture was allowed to warm up to RT. After the resulting yel-
low solution was stirred for 30 min, it was poured into ice-water
and extracted with EtOAc. The combined organic layers were
washed with brine, dried over anhydrous Na2SO4, filtered and con-
centrated. The crude product was purified by preparative TLC plate
(2:1:0.3 CHCl3/CH3COCH3/MeOH) to afford 14b (56 mg, 69%) as a
white solid, mp 162–163 °C. 1H NMR (CD3OD): d 7.18 (s, 1H),
6.64 (s, 1H), 4.42 (t, J = 8.0 Hz, 1H), 2.79–2.77 (m, 2H), 2.30–2.22
(m, 2H), 2.19–2.17 (m, 1H), 2.06–2.01 (m, 1H), 1.90–1.75 (m,
3H), 1.49–1.22 (m, 6H), 0.86 (s, 3H). 13C NMR (CDCl3): d 148.3,
137.5, 137.2, 133.0, 121.5, 118.1, 90.1, 50.4, 45.0, 44.3, 39.8, 37.5,
30.1, 28.9, 28.2, 27.2, 24.0, 12.1. HRMS (ESI, m/z): calcd for
C
18H26N2O7S2Na ([M + Na]+) 469.1079; found 469.1096.
2.17. 2-[11C]Methoxy-3,17b-O,O-bis(sulfamoyl)estradiol ([11C]5)
[
11C]CO2 was produced by the 14N(p,
a)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 50 lA beam current and 15 min on target. The production
run produced approximately 25.9 GBq of [11C]CO2 at EOB. In a
small reaction vial (5 mL), the precursor 14a (0.3–0.5 mg) was dis-
solved in CH3CN (400 lL). To this solution was added 2 N NaOH

868
M. Wang et al. / Steroids 77 (2012) 864–870
OMOM
OMOM
OH
a
b
HO
MOMO
MOMO
HO
2
1
OH
OMOM
d
e
H3CO
HO
c
H3CO
MOMO
4
3
OSO2NH2
H3CO
H2NO2SO
5
Scheme 1. Synthesis of 2-methoxy-3,17b-O,O-bis(sulfamoyl)estradiol (5). Reagents, conditions and yields: (a) N, N-diisopropylethylamine, CH3OCH2Cl, THF, reflux, 94%; (b)
(1) s-BuLi, THF, À78 °C; (2) (MeO)3B, À78 °C-RT; (3) NaBO3, RT; 84%; (c) K2CO3, CH3I, n-Bu4NI, DMF, RT, 93%; (d) 6 N HCl, THF, RT, 74%; (e) sulfamoyl chloride, DMA, 0 °C-RT,
74%.
DMF at 0 °C, followed by n-Bu4NI. Baeyer–Villiger oxidation of 8
with m-CPBA (77%) and a catalytic amount of p-TsOHꢁH2O in
CH2Cl2 following the procedure of Cushman et al. [12] failed to di-
rectly give phenol 10, but gave formyl ester 9 instead in 71% yield.
We noticed that Cushman et al. probably did not attempt to isolate
the intermediate formate ester 9 and hydrolyzed it in situ to the
phenol 10. At the beginning, we thought the reason could be they
used 80–90% m-CPBA in the reaction, and commercially available
m-CPBA we purchased was only 77%. Then we purified the pur-
chased m-CPBA to increase the concentration of peracid to 80–
90% and exactly repeated the reported procedure [12] again, the
product was still formate ester 9, and no phenol 10 was identified.
It is likely the basic condition is necessary for the hydrolysis of 9 to
10. The reported procedure for Baeyer–Villiger oxidation was con-
ducted under acidic condition (p-TsOH). It might not be possible to
hydrolyze 9 in situ to the phenol 10. Compound 9 was then hydro-
lyzed by treatment with 10% NaOH in MeOH to afford phenol 10 in
96% yield. Access to precursor compound 14a required a sequence
of silyl protection of 2-hydroxy group and debenzylation of 3- and
17b-benzyl ether groups of compound 10. Considering that triiso-
propylsilyl (TIPS) group is less prone to migrate to proximate hy-
droxyl group than the tert-butyldimethylsilyl (TBDMS) group [7]
for the following hydrogenolysis, attempt to protect 2-hydroxyl
group of compound 10 with triisopropylsilyl chloride (TIPSCl) as
silylating agent proved unsuccessful. TIPS protected ether 11 was
achieved with another silylating agent TIPSOTf in the presence of
DMAP in pyridine in 95% yield. Debenzylation of the bis-benzyl
groups by hydrogenolysis with 10% Pd/C as catalyst only removed
3-benzyl protecting group. Cleavage of the bis-benzyl groups was
accomplished over another catalyst 20% Pd(OH)2/C in EtOAc to
yield a mixture of two regioisomers 12a and 12b in 50% yield,
which were difficult to separate by column chromatography. The
ratio of the resulting regioisomers 12a and 12b was determined
by 1H NMR as 1:1, this indicated that 12b is the product of 1,2-
O,O-TIPS migration of 12a [7]. Without isolation, the phenols mix-
ture was sulfamoylated with sulfamoyl chloride in DMA to give
sulfamate regioisomers 13a and 13b, which were readily separated
by column chromatography in 36% and 38% yield, respectively.
Desilylation of 13a and 13b with tetrabutylammonium fluoride
(TBAF, n-Bu4NF) in THF gave 14a and 14b in 79% and 69% yield,
respectively. The overall chemical yield for the precursor 14a start-
ing from 17b-estradiol in 10 steps was 5%.
3.2. Radiochemistry
Synthesis of the target tracer carbon-11-labeled bis-sulfamate
[
by
11C]5 is indicated in Scheme 3. The precursor 14a was labeled
[
11C]CH3OTf [8,21] through O-[11C]methylation [22,23] at
80 °C under basic condition (2 N NaOH) and isolated by a semi-pre-
parative HPLC with a C-18 column and a solid-phase extraction
(SPE) with a disposable C-18 Plus Sep-Pak cartridge (a second puri-
fication or isolation process) [24–26] to produce the corresponding
pure radiolabeled compound [11C]5 in 40–50% radiochemical yield,
decay corrected to end of bombardment (EOB), based on [11C]CO2.
[
11C]CH3OTf is a proven methylation reagent with greater reactiv-
ity than commonly used [11C]methyl iodide ([11C]CH3I) [27], and
thus, the radiochemical yield of [11C]5 was relatively high. Addition
of NaHCO3 to quench the radiolabeling reaction and to dilute the
radiolabeling mixture prior to the injection onto the semi-prepara-
tive HPLC column for purification gave better separation of [11C]5
from its phenol hydroxyl precursor 14a [24–26,28]. The radiosyn-
thesis was performed in a home-built automated multi-purpose
11C-radiosynthesis module, allowing measurement of specific
radioactivity during synthesis [29,30]. This 11C-radiosynthesis
module includes the overall design of the reaction, purification
and reformulation capabilities of the prototype system. In addition,
11C-tracer specific activity (GBq/
lmol at EOB) can be automatically
determined prior to product delivery for compounds purified by
the HPLC-portion of the system. The overall synthesis, purification
and reformulation time was 30–40 min from EOB. The specific
radioactivity was in a range of 370–740 GBq/lmol at EOB. Chemi-
cal purity and radiochemical purity were determined by analytical
HPLC [31]. The chemical purity of the precursor 14a and reference
standard 5 was >96%. The radiochemical purity of the target tracer
[
11C]5 was >99% determined by radio-HPLC through
c-ray (PIN
diode) flow detector, and the chemical purity of [11C]5 was >93%
determined by reverse-phase HPLC through UV flow detector. A
C-18 Plus Sep-Pak cartridge was used to significantly improve

M. Wang et al. / Steroids 77 (2012) 864–870
869
OMOM
OH
OMOM
c
a
b
OHC
OHC
HO
MOMO
MOMO
1
7
6
OBn
OBn
OBn
O
d
f
e
O
HO
OHC
BnO
H
BnO
BnO
10
9
8
OH
OBn
OH
g
HO
TIPSO
BnO
TIPSO
TIPSO
HO
11
12a
12b
h
OSO2NH2
OSO2NH2
TIPSO
H2NO2SO
TIPSO
H2NO2SO
13a
13b
i
i
OSO2NH2
OSO2NH2
HO
H2NO2SO
HO
H2NO2SO
14a
14b
Scheme 2. Synthesis of 2-hydroxy-3,17b-O,O-bis(sulfamoyl)estradiol (14a). Reagents, conditions and yields: (a) (1) s-BuLi, THF, -78 °C; (2) DMF, -78 °C-RT; 81%; (b) 6 N HCl,
THF, RT, 98%; (c) NaH, BnBr, n-Bu4NI, DMF, 0 °C-RT, 66%; (d) m-CPBA, p-TsOHꢁH2O, CH2Cl2, RT, 71%; (e) 10% NaOH, MeOH, 60 °C, 96%; (f) DMAP, TIPSOTf, pyridine, 0 °C-RT,
95%; (g) H2, 20% Pd(OH)2/C, EtOAc, 60 psi, RT, 50% (1:1 12a/12b); (h) sulfamoyl chloride, DMA, 0 °C-RT, 36% (13a), 38% (13b); (i) n-Bu4NF, THF, RT, 79% (14a), 69% (14b).
OSO2NH2
OSO2NH2
H311CO
a
HO
H2NO2SO
H2NO2SO
[11C]5
14a
Scheme 3. Synthesis of 2-[11C]methoxy-3,17b-O,O-bis(sulfamoyl)estradiol ([11C]5). Reagents, conditions and yields: (a) [11C]CH3OTf, CH3CN, 2 N NaOH, 80 °C, 3 min, 40–50%.
the chemical purity of the tracer solution. Initial HPLC purification
was employed to separate the labeled product from its un-reacted
excess precursor and other labeled by-products. The second SPE
purification with Sep-Pak [24–26,31] was employed, instead of
rotary evaporator, to remove potential impurities from the HPLC
co-elution with the precursor and from the residual solvents
including HPLC mobile phase solvents and module set-up cleaning
solvents. Rotary evaporation was unable to perform in this regard.
Moreover, it could result in the decomposition of the labeled prod-
uct such as desmethylation during the heating. The chemical purity
of the [
11C]5 tracer solution with Sep-Pak purification was
increased higher 10–20% than that without Sep-Pak purification
[24–26].
4. Conclusion
In summary, an efficient and convenient synthesis of a new car-
bon-11-labeled 2-substituted estradiol bis-sulfamate, 2-[11C]meth-
oxy-3,17b-O,O-bis(sulfamoyl)estradiol, has been developed. The

870
M. Wang et al. / Steroids 77 (2012) 864–870
[11] Pert DJ, Ridley DD. Formylation of oestrogens. Aust J Chem 1989;42:405–19.
[12] Cushman M, He HM, Katzenellenbogen JA, Lin CM, Hamel E. Synthesis,
antitubulin and antimitotic activity, and cytotoxicity of analogs of 2-
methoxyestradiol, an endogenous mammalian metabolite of estradiol that
inhibits tubulin polymerization by binding to the colchicine binding site. J Med
Chem 1995;38:2041–9.
reference standard, the precursor for labeling, and new 2-substi-
tuted estradiol derivatives have been synthesized. The target radio-
tracer was prepared by the O-[11C]methylation of its corresponding
phenolic precursor using
a reactive [
11C]methylating agent,
[
11C]CH3OTf, and isolated by a HPLC combined with SPE procedure
[13] Paaren HE, Duff SR. Synthesis of 2-hydroxyestradiol derivatives. US Patent No.
6448419 B1;2002.
in high radiochemical yields, short overall synthesis time, and great
specific radioactivity. These chemistry results combined with the
reported in vitro and in vivo biological data [3] encourage further
in vivo biological evaluation of new carbon-11-labeled 2-substi-
tuted estradiol bis-sulfamate as a candidate PET agent for imaging
of STS in cancers.
[14] Lee I, Seong Choe Y, Jung KH, Lee KH, Young Choi J, Choi Y, et al. 2-
[methyl-11C]methoxyestradiol: synthesis, evaluation and pharmacokinetics
for in vivo studies on angiogenesis. Nucl Med Biol 2007;34:625–31.
[15] Fei X, Zheng Q-H. Lipophilicity coefficients of [
11C]Me-halo-CGS 27023A
analogs determined by HPLC. J Liq Chromatogr Rel Technol 2005;28:939–45.
[16] Liu X, Wang J-Q, Zheng Q-H. Lipophilicity coefficients of potential tumor
imaging agents, positron-labeled O6-benzylguanine derivatives. Biomed
Chromatogr 2005;19:379–84.
[17] Gao M, Mock BH, Hutchins GD, Zheng Q-H. Synthesis and initial PET imaging of
new potential NK1 receptor radioligands 1-[2-(3,5-bis-trifluoromethyl-
benzyloxy)-1-phenyl-ethyl]-4-[11C]methyl-piperazine and {4-[2-(3,5-bis-
Acknowledgments
This work was partially supported by the Breast Cancer Re-
search Foundation. 1H NMR and 13C NMR spectra were recorded
on a Bruker Avance II 500 MHz NMR spectrometer in the Depart-
ment of Chemistry and Chemical Biology at Indiana University
Purdue University Indianapolis (IUPUI), which is supported by a
NSF-MRI grant CHE-0619254. The referees’ criticisms and editors’
comments for the revision of the manuscript are greatly
appreciated.
trifluoromethyl-benzyloxy)-1-phenyl-ethyl]-piperazine-1-yl}-acetic
acid
[
11C]methyl ester. Nucl Med Biol 2005:543–52.
[18] Gao M, Wang M, Hutchins GD, Zheng Q-H. [11C]Dimebon, radiosynthesis and
lipophilicity of a new potential PET agent for imaging of Alzheimer’s disease
and Huntington’s disease. Bioorg Med Chem Lett 2010;20:2529–32.
[19] Woo LW, Fischer DS, Sharland CM, Trusselle M, Foster PA, Chander SK, et al.
Anticancer steroid sulfatase inhibitors: synthesis of
a potent fluorinated
second-generation agent, in vitro and in vivo activities, molecular modeling,
and protein crystallography. Mol Cancer Ther 2008;7:2435–44.
[20] Lovely CJ, Gilbert NE, Liberto MM, Sharp DW, Lin YC, Brueggemeier RW. 2-
(Hydroxyalkyl)estradiols: synthesis and biological evaluation. J Med Chem
1996;39:1917–23.
References
[21] Jewett DM. A simple synthesis of [11C]methyl triflate. Int J Rad Appl Instrum A
1992;43:1383–5.
[1] Stanway SJ, Delavault P, Purohit A, Woo LW, Thurieau C, Potter BV, et al.
Steroid sulfatase: a new target for the endocrine therapy of breast cancer.
Oncologist 2007;12:370–4.
[2] Parkkila S, Rajaniemi H, Parkkila AK, Kivela J, Waheed A, Pastorekova S, et al.
Carbonic anhydrase inhibitor suppresses invasion of renal cancer cells in vitro.
Proc Natl Acad Sci USA 2000;97:2220–4.
[3] Leese MP, Leblond B, Smith A, Newman SP, Di Fiore A, De Simone G, et al. 2-
substituted estradiol bis-sulfamates, multitargeted antitumor agents:
synthesis, in vitro SAR, protein crystallography, and in vivo activity. J Med
Chem 2006;49:7683–96.
[22] Wang M, Yoder KK, Gao M, Mock BH, Xu XM, Saykin AJ, et al. Fully automated
synthesis and initial PET evaluation of [11C]PBR28. Bioorg Med Chem Lett
2009;19:5636–9.
[23] Wang M, Gao M, Hutchins GD, Zheng Q-H. Synthesis of [11C]FEDAA1106 as a
new PET imaging probe for peripheral benzodiazepine receptor expression.
Eur J Med Chem 2009;44:2748–53.
[24] Gao M, Wang M, Mock BH, Glick-Wilson BE, Yoder KK, Hutchins GD, et al. An
improved synthesis of dopamine D2/D3 receptor radioligands [11C]fallypride
and [18F]fallypride. Appl Radiat Isot 2010;68:1079–86.
[25] Wang M, Gao M, Miller KD, Zheng Q-H. Synthesis of
18F]PBR06 as agents for positron emission tomographic (PET) imaging of the
translocator protein (TSPO). Steroids 2011;76:1331–40.
[26] 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
[
11C]PBR06 and
[4] Reed MJ, Purohit A, Woo LWL, Newman SP, Potter BVL. Steroid sulfatase:
molecular biology, regulation and inhibition. Endocr Rev 2005;26:171–202.
[5] McGuire AH, Dehdashti F, Siegel BA, Lyss AP, Brodack JW, Mathias CJ, et al.
[
Positron tomographic assessment of 16a
-[18F] fluoro-17b-estradiol uptake in
[
metastatic breast carcinoma. J Nucl Med 1991;32:1526–31.
imaging of PI3K and mTOR in cancers. Bioorg Med Chem Lett
2012;22:1569–74.
[6] Dehdashti F, Mortimer JE, Trinkaus K, Naughton MJ, Ellis M, Katzenellenbogen
JA, et al. PET-based estradiol challenge as a predictive biomarker of response to
endocrine therapy in women with estrogen-receptor-positive breast cancer.
Breast Cancer Res Treat 2009;113:509–17.
[7] Wang M, Mickens J, Gao M, Miller KD, Sledge GW, Hutchins GD, et al. Design
and synthesis of carbon-11-labeled dual aromatase-steroid sulfatase inhibitors
as new potential PET agents for imaging of aromatase and steroid sulfatase
expression in breast cancer. Steroids 2009;74:896–905.
[27] Allard M, Fouquet E, James D, Szlosek-Pinaud M. State of art in 11C labelled
radiotracers synthesis. Curr Med Chem 2008;15:235–77.
[28] Gao M, Wang M, Hutchins GD, Zheng Q-H. Synthesis of new carbon-11-labeled
carboxamide derivatives as potential PET dopamine D3 receptor radioligands.
Appl Radiat Isot 2008;66:1891–7.
[29] Mock BH, Zheng Q-H, DeGrado TR.
A
multi-purpose 11C-radio-synthesis
system. J Labelled Compd Radiopharm 2005;48:S225.
[30] 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.
[31] Zheng Q-H, Mock BH. Purification of carbon-11 PET radiotracers from
unlabeled precursors by preparative HPLC and SPE. Biomed Chromatogr
2005;19:671–6.
[8] Mock BH, Mulholland GK, Vavrek MT. Convenient gas phase bromination of
[
11C]methane and production of 11C]methyl triflate. Nucl Med Biol
[
1999;26:467–71.
[9] Hou Y, Meyers CY, Akomeah M.
A short, economical synthesis of 2-
methoxyestradiol, an anticancer agent in clinical trials.
2009;74:6362–4.
J Org Chem
[10] Kiuru PS, Wähälä K. Short synthesis of 2-methoxyestradiol and 2-
hydroxyestradiol. Steroids 2003;68:373–5.