Synthesis and in vitro evaluation of 2-[11C]methoxyestradiol-3, 17β-O,O-bissulfamate for in vivo studies of angiogenesis

Article abstract of DOI:10.1002/jlcr.1930

In the present study, 2-methoxyestradiol-3,17β-O,O-bissulfamate (1), a known angiogenesis inhibitor, was prepared in a radiolabeled form by ¹¹C-methylation of 2-hydroxyestradiol-3,17β-O,O-bis(N-trityl) sulfamate (6) followed by detritylation. S

Full text of DOI:10.1002/jlcr.1930

Research Article
Received 13 June 2011,
Revised 29 July 2011,
Accepted 31 July 2011
Published online 4 October 2011 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.1930
Synthesis and in vitro evaluation of 2-[11C]
methoxyestradiol-3,17b-O,O-bissulfamate for
in vivo studies of angiogenesis
*
Choong Mo Kang, Yearn Seong Choe, Kyung-Ho Jung, Joon Young Choi,
Kyung-Han Lee, and Byung-Tae Kim
In the present study, 2-methoxyestradiol-3,17b-O,O-bissulfamate (1), a known angiogenesis inhibitor, was prepared in a
radiolabeled form by 11C-methylation of 2-hydroxyestradiol-3,17b-O,O-bis(N-trityl)sulfamate (6) followed by detritylation.
Synthesis of precursor 6 required a rather long step because of the presence of two sulfamoyl groups. The decay-corrected
radiochemical yield of [11C]1 was 19 Æ 2% based on [11C]CH3I, and the specific activity was 34–39 GBq/mmol. Although 1 is
known to significantly inhibit the proliferation of human umbilical vascular endothelial cells (HUVECs), its radiolabeled
form, [11C]1 was not avidly taken up by HUVECs, and the uptake increased slightly in a time-dependent manner (156%
at 60 min relative to a value of 100% at 5 min). These results suggest that further studies are warranted to determine
the molecular target for [11C]1.
Keywords: 2-[11C]methoxyestradiol-3,17b-bissulfamate; angiogenesis; carbonic anhydrase; steroid sulfatase
for treatment of hormone-dependent tumors. Later, sulfamates
Introduction
were found to have inhibitory activity against carbonic
2-Methoxyestradiol (2-ME), an endogenous estrogen metabolite,
anhydrases (CA), which catalyze the interconversion between
is known to inhibit angiogenesis. It has potent inhibitory activity
CO2 and bicarbonate, by binding of the sulfamate moiety to
the catalytic zinc ion of the enzymes.7 Some sulfamates are
against endothelial cell proliferation and migration in vitro and
known to be dual inhibitors of CA and STS.7,8 It was reported that
also inhibits the growth and neovascularization of solid tumors
in mice by oral administration.1 We previously synthesized
16a-fluoroestradiol-3,17b-bissulfamate is a potent inhibitor of
human CAI (hCAI; IC50 = 288 nM) and hCAII (IC50 = 54 nM), which
2-[11C]ME (Figure 1) for in vivo angiogenesis studies, which
showed high and specific uptake by human umbilical vascular
endothelial cells (HUVECs) in vitro but low tumor uptake in
shows similar inhibitory activities to acetazolamide, a clinically
used CA inhibitor (IC50 = 219 nM for hCAI and 30 nM for hCAII).9
C57BL/6 mice implanted with Lewis lung carcinoma (LLC) cells.2
This result may be attributed to the rapid disappearance of
2-ME from the plasma after intravenous or oral administration.3
Sulfamoylation of 2-ME, however, showed enhanced anti-
proliferative effects compared with 2-ME on human breast
cancer cells.4 Among sulfamate derivatives, 2-ME-3,17b-O,
O-bissulfamate (1) showed more potent anti-proliferative effects
than 2-ME on MCF-7 and HUVECs by 10- and 60-fold, respec-
tively.4 On the basis of the in vitro data, 1 was further evaluated
in mice implanted with LLC cells (5 mg/kg intraperitoneally,
10 mg/kg intraperitoneally, or 30 mg/kg intravenously) and
in nude mice implanted with MDA-MB-435 cells (20 mg/kg,
oral), and results showed significant inhibition of tumor growth
in both models.3,5 Moreover, 1 had favorable bioavailability
(85%) and underwent little metabolism after intravenous or
oral administration.3
Biodistribution studies of 16a-[18F]fluoroestradiol-3, 17b-bissulfamate
demonstrated that this radioligand bound to both STS and CA
in rats, tumor-bearing nude mice, and piglets; however, the
binding affinities were not high enough for tumor imaging.10,11
It was reported that steroid sulfamate 1 has potent in-
hibitory effect on the proliferation of MCF-7 (IC50 = 250 nM)
and HUVECs (IC50 = 50 nM) and also has inhibitory activity
against hCAII (IC50 = 379 nM) as well as STS (IC50 = 39 nM).4,8 In
the present study, we synthesized 2-[11C]methoxyestradiol-3,
17b-O,O-bissulfamate ([11C]1) (Figure 1) and evaluated it in vitro
for in vivo studies of angiogenesis.
Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan
University School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul 135-710,
Steroid sulfamates were initially found to be inhibitors of South Korea
steroid sulfatase (STS).6 Many tumors in which steroid sulfatase
plays an important role, such as breast tumors, are hormone
dependent because this enzyme converts estrogen sulfates to
*Correspondence to: Yearn Seong Choe, Department of Nuclear Medicine,
Samsung Medical Center, Sungkyunkwan University School of Medicine, 50
Ilwon-dong, Kangnam-ku, Seoul 135-710, South Korea.
estrogens. Thus, steroid sulfamates may be good candidates E-mail: ysnm.choe@samsung.com
J. Label Compd. Radiopharm 2011, 54 783–787
Copyright © 2011 John Wiley & Sons, Ltd.

C. M. Kang et al.
OH
OSO2NH2
step was carried out manually after the product eluted from the
tC18 Sep-Pak cartridge using EtOH. However, we expect to con-
duct the whole process using an automated system if a higher
dose of [11C]CH4 were to be used.
H311CO
H311CO
HO
H2NO2SO
2-[11C]ME
[
11C]1
For the 11C-methylation, use of base including NaH, DIPEA, or
K2CO3 resulted in cleavage of the sulfamoyl groups of 6.
Therefore, NaOH, which was unreactive with the sulfamoyl
groups, was the base of choice. Furthermore, reaction solvents
(DMF, 2-butanone, or acetone) other than DMSO resulted in by-
product formation. Removal of the trityl protecting groups from
the sulfamoyl groups was carried out in 80% trifluoroacetic acid
(300 mL) and 33% HBr-acetic acid (20 mL) (80 ꢀC, 5 min). Although
trityl groups are generally removed with trifluoroacetic acid, more
harsh conditions were required for this one-pot reaction because
the reaction mixture contained DMSO and NaOH.
Figure 1. Structures of 2-[11C]ME and 2-[11C]ME-3,17 b-O,O-bissulfamate ([11C]1).
Results and discussion
Chemistry
Compound 1 was synthesized using a previously described
method (Scheme 1).12,13 Synthesis of precursor 6 required a
rather long step from 3,17b-estradiol because of the presence
of two sulfamoyl groups at the C3 and 17b positions (Scheme 2).
Introduction of a hydroxyl group to C2 of 3,17b-estradiol-3,
17b-O,O-bis(methoxymethyl)ether to give the 2-hydroxy com-
pound 2 was carried out by boronylation using s-butyl lithium
and trimethyl borate, followed by oxidation using sodium perbo-
rate.14 It was reported that tritylated sulfamoyl groups are labile
for sulfamoyl NH and trityl C bond cleavage under acidic condi-
tions and for sulfamoyl O and sulfur bond cleavage with nucleo-
philic treatment.15,16 Therefore, the hydroxyl group at the C2
position was first protected as benzyl ether, and then the
methoxymethyl groups at the C3 and 17b positions were removed
under acidic conditions. Sulfamoyl groups were introduced into
the C3 and 17b positions using a procedure described in the litera-
ture,12,17 and then the sulfamoyl amine groups were protected by
tritylation prior to debenzylation at C2 position.
The total synthesis time after [11C]CH4 production was
45–48 min. The decay-corrected radiochemical yield of [11C]1
was 19 Æ 2% based on [11C]CH3I, and its specific activity was
34–39 GBq/mmol. Long-term use of [11C]CH4 target would
increase the specific activity of the radioligand. Co-elution with
1 on HPLC confirmed the identity of [11C]1.
Partition coefficient
[11C]1 was found to have lower lipophilicity (log Po/w = 2.25) than
2-[11C]ME (log Po/w = 2.95).18
Uptake of [11C]1 by HUVECs
HUVECs are an in vitro model of angiogenesis, and 1 is known to
inhibit HUVEC proliferation significantly.4,19 Therefore, we inves-
tigated the uptake of [11C]1 by HUVECs. Small fraction of [11C]1
Radiochemical synthesis
Radiochemical synthesis of [11C]1 was carried out in a one-pot was found to be taken up by HUVECs (0.31% ID at 5 min and
reaction (Scheme 2). Although 11C labeling and purification were 0.48% ID at 60 min), and this uptake slightly increased in a
conducted using an automated system, the final reformulation time-dependent manner: 128 Æ 4.6% at 15min, 151Æ 5.3% at
30min, and 156 Æ 7.4% at 60 min (relative to a value of
100 Æ 5.9% at 5 min) (Figure 2A). In addition, [11C]1 uptake by
HUVECs at 60 min was inhibited in the presence of 1 (10 mM)
OH
OSO2NH2
by 23% (Figure 2B). In contrast, 2-[11C]ME was taken up avidly by
HUVECs (2.96% ID at 5 min and 6.9% ID at 60min) and in a time-
dependent manner (i.e., 160% at 15 min, 220% at 30 min, and
240% at 60 min; relative to a value of 100% at 5 min), and the
uptake was inhibited in the presence of 2-ME by 70% at 60 min.
However, tumor uptake of 2-[11C]ME was not significantly high
(1.04% ID/g) in C57BL/6 mice implanted with LLC cells.2 This result
a
H3CO
H3CO
HO
H2NO2SO
1
Scheme 1. Reagents and conditions: (a) H2NSO2Cl, DMA, room temperature, 1.5 h,
90%.
OMOM
OMOM
a
OH
c, d
b
HO
BnO
BnO
HO
MOMO
MOMO
2
3
4
OSO2NHTr
OSO2NH2
OSO2NHTr
e
f
BnO
TrHNO2SO
HO
TrHNO2SO
H311CO
H2NO2SO
[
11C]1
5
6
Scheme 2. Reagents and conditions: (a) K2CO3, acetone, benzyl bromide, 40 ꢀC, 12 h, 93%; (b) 6 N HCl, THF, room temperature (rt), 7 h, 88%; (c) H2NSO2Cl, DMA, rt, 2 h,
75%; (d) trityl chloride, DIPEA, CH2Cl2, rt, 20 h, 56%; (e) H2, 10% Pd/C, 1:5 THF–EtOH, rt, 6 h, 85%; (f) [11C]CH3I, 5 N NaOH, DMSO, 80 ꢀC, 5 min; 80% trifluoroacetic acid, 33%
HBr-acetic acid, 80 ꢀC, 5 min.
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Copyright © 2011 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2011, 54 783–787

C. M. Kang et al.
Chemistry
Synthesis of 2-methoxyestradiol 3,17b-O,O-bissulfamate (1)
2-Methoxyestradiol (25 mg, 0.083 mmol) in ice-cold DMA (400mL)
was slowly added to a solution of sulfamoyl chloride (1.05 mmol)12
in DMA (400 mL) at 0 ꢀC. The reaction mixture was allowed to
stir at room temperature for 1.5 h. The resulting mixture was
diluted with water (1mL) and extracted with ethyl acetate
(1mL Â 2). The organic layer was washed with water and
saturated NaCl and was dried over anhydrous Na2SO4. Flash
column chromatography (1:1 hexane–ethyl acetate) yielded 1 as
a white solid (34 mg) in 90% yield: 1H NMR (DMSO-d6) d 7.80
(s, 2H), 7.38 (s, 2H), 6.99 (s, 2H), 4.35 (t, 1H, J = 8.5 Hz), 3.77 (s, 3H),
2.75–2.73 (m, 2H), 2.39–1.16 (m, 13H), 0.78 (s, 3H); MS (ESI) m/z
459.6 ((M À H)À). The NMR and MS data agreed with
literature values.20
Synthesis of 2-hydroxyestradiol-3,17b-O,O-bis(methoxymethyl)
ether (2)
Compound 2 was synthesized according to a method described
in the literature.14 s-Butyl lithium (1.4 M in cyclohexane, 2.2 mL,
3.08 mmol) was slowly added to a solution of estradiol-3,17b-O,
O-bis(methoxymethyl)ether (640 mg, 7.08 mmol) in THF (4 mL)
at À75 ꢀC under N2, and the mixture was stirred at the same tem-
perature for 2 h. Trimethylborate (804.5 mL, 7.08 mmol) was then
slowly added, and the mixture was stirred at À75 ꢀC for 15 min
and then warmed to 0 ꢀC. The reaction was quenched with
10% ammonium chloride (aq., 8 mL), and the mixture was stirred
at room temperature for 1 h. Sodium perborate tetrahydrate
(1.07 g, 7 mmol) was then carefully added in portions, and the
mixture was stirred at room temperature for 15 h before filtering
to remove inorganic salts. The filter cake was washed with ethyl
acetate, and the filtrate was extracted with ethyl acetate. The
combined organic layers were washed with saturated brine
and were dried over anhydrous Na2SO4. Flash column chroma-
tography (6:1 hexane–ethyl acetate) yielded 2 as a yellow oil
(421 mg) in 63% yield: 1H NMR (CDCl3) d 6.91 (s, 1H), 6.80
(s, 1H), 5.75 (s, 1H), 5.17 (s, 2H), 4.67 (ABq, 2H, J = 6.5 Hz), 3.63
Figure 2. (A) Uptake of [11C]1 by HUVECs as a function of time. Uptake levels are
expressed relative to a value of 100% at 5 min. (B) Inhibition of [11C]1 uptake by
compound 1 in HUVECs after incubation for 60 min. Data are expressed as the
mean of three measurements Æ SD. *P < 0.05, compared to control level.
may be explained by the fact that 2-ME was rapidly removed from
rat plasma 15 min after an intravenous injection.3 It should be
noted that 1 lasted much longer in rat plasma.3 Ligand 1 has been
known to have multiple targets for its antitumor activity, including
inhibition of CA, STS, and angiogenesis. Therefore, it would be
worthwhile to further investigate the molecular targets for [11C]1,
such as CA and STS.
Experimental
Materials and equipment
Chemicals were obtained from Sigma-Aldrich (St. Louis, MO, USA). (t, 1H, J = 8.5 Hz), 3.53 (s, 3H), 3.39 (s, 3H), 2.80–2.77 (m, 2H),
1H NMR spectra were obtained on a Varian UnityInova 500NB 2.26–1.77 (m, 13H), 0.82 (s, 3H); MS (EI) m/z 376 (M+); HRMS cal-
(500MHz) spectrometer (Palo Alto, CA, USA) at the Cooperative culated for C22H32O5 376.2250, found 376.2250. The NMR and
Center for Research Facilities, Sungkyunkwan University (Suwon, MS data agreed with literature values.2,21
Korea). Chemical shifts (d) are reported as ppm downfield from
tetramethylsilane internal standard. Electron impact (EI) mass
Synthesis of 2-O-benzyloxyestradiol-3,17b-O,O-bis(methoxymethyl)
spectra were obtained on a JMS-700 Mstation (JEOL Ltd, Tokyo,
ether (3)
Japan), and electrospray ionization (ESI) mass spectra were
obtained on a LCQ-DECA-XP (Thermo Scientific, Waltham, MA, Potassium carbonate (588.77 mg, 4.26 mmol) was added to com-
USA) at the Korea Basic Science Institute (Seoul, Korea). For pound 2 (321 mg, 0.852 mmol) in acetone (6 mL). The reaction
radioligand purification and analysis, HPLC was conducted using mixture was stirred at room temperature for 10 min, and benzyl
a SpectraSystem (Thermo Scientific) equipped with a semi- bromide (303.67 mL, 2.56 mmol) was slowly added. The resulting
preparative column (YMC-Pack C18, 5 mm, 10 Â 250 mm) or an solution was stirred at 40 ꢀC for 12 h, diluted with water (5 mL),
analytical column (YMC-Pack C18, 5 mm, 4.6 Â 250 mm). The eluant and extracted with ethyl acetate (5 mL Â 3). The combined
was monitored simultaneously by UV (280nm) and NaI(T1) radio- organic layers were washed with water and saturated NaCl and
activity detectors.
were dried over anhydrous Na2SO4. Flash column chromatogra-
[11C]CH4 was produced by the 14N(p,a)11C reaction using a phy (6:1 hexane–ethyl acetate) yielded 3 as a colorless oil
1
cyclotron (GE Healthcare, Uppsala, Sweden), and the radiochemi- (370 mg) in 93% yield. H NMR (DMSO-d6) d 7.30–7.45 (m, 5H),
cal synthesis of [11C]1 was carried out using a TRACERlab FXc Pro 6.94 (s, 1H), 6.76 (s, 1H), 5.75 (s, 1H), 5.10 (ABq, 2H, J = 6.5 Hz),
module (GE Healthcare, Uppsala, Sweden). Radioactivity was 5.06 (s, 2H), 4.58 (ABq, 2H, J = 6.5 Hz), 3.54 (t, 1H, J = 8.3 Hz), 3.37
measured in a dose calibrator (Biodex Medical Systems, Shirley, (s, 3H), 3.25 (s, 3H), 2.71–2.68 (m, 2H), 2.26–1.16 (m, 13H), 0.74
NY, USA), and cell uptake was measured using a 2480 WIZARD2 (s, 3H); MS (EI) m/z 466 (M+); HRMS calculated for C22H32O5
Automatic Gamma Counter (PerkinElmer, Waltham, MA, USA).
466.2719, found 466.2706.
J. Label Compd. Radiopharm 2011, 54 783–787
Copyright © 2011 John Wiley & Sons, Ltd.
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C. M. Kang et al.
Synthesis of 2-O-benzyloxyestradiol (4)
25 ꢀC. This mixture was then stirred at 80 ꢀC for 5 min and then
treated with 80% trifluoroacetic acid (aq., 300 mL) and 33% HBr-
acetic acid (20 mL) at 80 ꢀC for 5 min. The solution was cooled
to 40 ꢀC, neutralized with 4 M sodium acetate (670 mL), and then
injected onto a semi-preparative HPLC column, which was eluted
with a 43:57 mixture of ethanol and water at a flow rate of
3.5 mL/min. The desired fraction, eluting at 12.8–13.8 min, was col-
lected in a round flask and diluted with 30mL of water. The pro-
duct was trapped onto a tC18 Sep-Pak cartridge, which was rinsed
with 10mL of water and then with 1 mL of EtOH. The EtOH fraction
was then transferred via a 1/16-in. tubing into a vial, which was
placed in a drawer-type shielded port of the hot cell. The vial was
then transferred to a separate hot cell. After EtOH was removed
using a rotary evaporator, the product was redissolved in ethanol
and was diluted with saline to give a final solution of 10% ethanol
Compound 3 (266 mg, 0.57 mmol) was dissolved in THF (5.6 mL),
and 6 N HCl (3.7mL, 22.23 mmol) was added to the solution. The
reaction mixture was stirred at room temperature for 7 h, diluted
with saturated sodium bicarbonate (5mL), and extracted with
ethyl acetate (4mLÂ 2). The combined organic layers were
washed with water (5mLÂ 2) and then saturated NaCl and were
dried over anhydrous Na2SO4. Flash column chromatography (2:1
hexane–ethyl acetate) yielded 4 as a colorless oil (189 mg) in 88%
1
yield. H NMR (DMSO-d6) d 8.65 (s, 1H), 7.47–7.29 (m, 5H), 6.83
(s, 1H), 6.48 (s, 1H), 5.04 (s, 2H), 4.46 (s, 1H), 3.53–3.49(m, 1H),
2.65–2.59 (m, 2H), 2.21–0.85 (m, 13H), 0.66 (s, 3H); MS (EI) m/z 378
(M+); HRMS calculated for C25H30O3 378.2195, found 378.2190.
Synthesis of 2-O-benzyloxyestradiol-3,17b-O,O-bis(N-trityl)sulfamate (5) in saline. For specific activity determination, an aliquot of [11C]1
was injected onto an analytical column, which was eluted with a
Compound 4 (184 mg, 0.486 mmol) in ice-cold DMA (5mL) was
55:45 mixture of ethanol and water at a flow rate of 0.8 mL/min
slowly added to a solution of sulfamoyl chloride (10.5mmol)11 in
(tR = 8.2–9.0min). Specific activity determinations were carried
DMA (5mL) at 0 ꢀC. The reaction mixture was allowed to stir at
out by comparing the HPLC UV peak area of the desired radioac-
room temperature for 2 h and then cooled to 0 ꢀC. The resulting
tive peak with those of different concentrations of unlabeled com-
mixture was diluted with water (10 mL) and extracted with ethyl
pound 1. An aliquot of [11C]1 was co-injected with 1 onto the HPLC
acetate (10 mLÂ 2). The organic layer was washed with water
system to confirm its identity.
and saturated NaCl and was dried over anhydrous Na2SO4. Flash
column chromatography (5:4 hexane–ethyl acetate) yielded
Partition coefficient
2-O-benzylestradiol-3,17b-O,O-bissulfamate as
a white solid
(195 mg) in 75% yield. 1H NMR (DMSO-d6) d 7.86 (s, 2H), 7.50–7.31
(m, 7H), 7.03 (s, 2H), 5.15 (s, 2H), 4.34 (t, 1H, J= 8Hz), 2.75–2.73
(m, 2H), 2.28–1.16 (m, 13H), 0.76 (s, 3H); MS (ESI) m/z 535.3 ((M À H)À).
Bis-sulfamate (237 mg, 0.442mmol) was dissolved in anhydrous
dichloromethane (12 mL); DIPEA (923 mL, 5.29 mmol) was added;
and the mixture was stirred at room temperature for 10 min. To
the reaction mixture was added trityl chloride (369mg, 1.32 mmol),
and stirring was continued at room temperature for 20 h. After the
reaction mixture was treated with saturated ammonium chloride
(15 mL), the organic layer was washed with water and saturated
NaCl and was dried over anhydrous Na2SO4. Flash column chroma-
tography (3.5:1 hexane–ethyl acetate) yielded 5 as a white solid
(518 mg) in 56% yield. 1H NMR (DMSO-d6) d 9.09 (s, 1H), 8.71
(s, 1H), 7.43–7.22 (m, 35H), 6.96 (s, 1H), 6.64 (s, 1H), 5.05 (s, 2H),
4.19 (t, 1H, J = 8 Hz), 2.64–2.57 (m, 2H), 2.23–0.85 (m, 13H), 0.54
(s, 3H); MS (ESI) m/z 1019.3 ((M À H)À).
Radioligand [11C]1 was added to premixed suspensions containing
600 mL of octanol and 600 mL of water, and the mixture was vor-
texed vigorously for 3 min and centrifuged at 2000 rpm for 5 min.
After two layers had separated, 100-mL aliquots of the octanol
and aqueous layers were removed and counted. Samples from
the octanol and aqueous layers were repartitioned until consistent
values were obtained. The experiment was carried out in triplicate.
Log Po/w was expressed as the logarithm of the ratio of the counts
per minute from octanol versus water.22
Uptake of [11C]1 by HUVECs
HUVECs were cultured at 37 ꢀC under 5% CO2 in EBM-2 medium
containing endothelial growth supplements, 10% fetal bovine
serum, and antibiotics. The cells were grown to 80–90% conflu-
ence, harvested with trypsin, and washed twice with 1 mL of phos-
phate buffered saline (PBS, pH7.4) containing 1% bovine serum
albumin (BSA). Cells (105–106) were subsequently transferred into
Eppendorf tubes. Radioligand [11C]1 (555 kBq/5 mL) was dissolved
in 10% ethanol–saline and incubated with HUVECs (50mL of PBS,
pH7.4) at 37 ꢀC for 5, 15, 30, and 60 min (n = 3). Cells were then
washed twice with PBS (pH 7.4) containing BSA (1%), and counted.
To investigate inhibition of [11C]1 uptake by 1, HUVECs were
incubated with [11C]1 (555 kBq/5 mL) in the presence of 10 mM
of 1 (5 mL in 10% ethanol–saline) at 37 ꢀC for 60 min. Cells were
then washed as described above and counted.
Synthesis of 2-hydroxyestradiol-3,17b-O,O-bis(N-trityl)sulfamate (6)
A mixture of compound 5 (50 mg, 0.049 mmol) and 10% Pd/C
(10 mg) in 1:5 THF–ethanol (2.4 mL) was stirred under a H2 atmo-
sphere at room temperature for 6 h. The reaction mixture was fil-
tered, and the filtrate was diluted with water (3 mL) and
extracted with ethyl acetate (3 mL Â 2). The combined organic
layers were washed with water and saturated NaCl and were
dried over anhydrous Na2SO4. Flash column chromatography
(3:1 hexane–ethyl acetate) yielded 6 as a white solid (39 mg) in
All experiments were performed in triplicate, and the results
were analyzed using unpaired two-tailed Student’s t-test. Differ-
ences at the 95% confidence level (P < 0.05) were considered
significant.
1
85% yield. H NMR (DMSO-d6) d 9.12 (br s, 1H), 8.80 (br s, 1H),
8.75 (s, 1H), 7.35–7.22 (m, 30H), 6.78 (s, 1H), 6.55 (s, 1H), 4.18
(t, 1H, J = 8.5), 2.58–2.57 (m, 2H), 2.18–0.84 (m, 13H), 0.54 (s, 3H);
MS (ESI) m/z 929.3 ((M À H)À).
Conclusions
Steroid sulfamate [11C]1 was prepared by 11C-methylation of the
Radiochemical synthesis
[11C]CH4 was converted into [11C]CH3I using I2 at 740 ꢀC. The 2-hydroxy precursor followed by detritylation. Synthesis of the
resulting [11C]CH3I was trapped in a mixture of 6 (4 mg, 2-hydroxy precursor required seven steps from 3,17b-estradiol.
4.30 mmol) and 5 N NaOH (7 mL, 35 mmol) in 300 mL of DMSO at Although 1 is known to significantly inhibit the proliferation of
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J. Label Compd. Radiopharm 2011, 54 783–787

C. M. Kang et al.
HUVECs, the low uptake of [11C]1 by HUVECs suggests that
further studies are warranted to determine the molecular
target for [11C]1.
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This work was supported by a grant from the Nuclear Research
and Development Program of the Korea Science and Engineering
Foundation (KOSEF), funded by the Korean government (MEST)
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