18F-Labelled vorozole analogues as PET tracer for aromatase

Article abstract of DOI:10.1002/jlcr.1502

One- and two-step syntheses for the ¹⁸F-labelling of 6-[(S)-(4-chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-(2-[¹⁸F] fluoroethyl)-1H-benzotriazole, [¹⁸F]FVOZ, 1 and 6-[(S)-(4- chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-[2-(2-[¹⁸F] fluoroethoxy)ethyl]-1H-benzotriazole, [¹⁸F]FVOO, 2 were developed. In the two-step synthesis, the nucleophilic fluorination step was performed by reacting (S)-6-[(4-chlorophenyl)-(1H-1,2,4-triazol-1-yl)methyl]-1H-benzotriazole (VOZ) with either the ¹⁸F-labelled ethane-1,2-diyl bis(4-methylbenzenesulfonate) or the oxydiethane-2,1-diyl bis(4- methylbenzenesulfonate). The radiochemical yields were in the range of 9-13% after the 110-120 min total syntheses and the specific radioactivities were 175 ± 7 GBq/μmol and 56 GBq/μmol for compounds 1 and 2, respectively. In the one-step synthesis, the precursor 2-{6-[(4-chlorophenyl)(1H-1,2,4- triazol-1-yl)methyl]-1H-1,2,3-benzotriazol-1-yl}ethyl 4-methylbenzenesulfonate (7) or 1-[2-(2-bromoethoxy)ethyl]-6-[(4-chlorophenyl)(1H-1,2,4-triazol-1-yl) methyl]-1H-benzotriazole (8) was directly labelled via an ¹⁸F nucleophilic substitution to give the corresponding tracer. The labelled compounds were obtained in 36-99% radiochemical yield after 75-min syntheses. The specific radioactivities are 100 GBq/μmol for compound 1 and 80 GBq/μmol for compound 2. In vitro autoradiography using frozen rat brains illustrated specific binding in the medial amygdala, the bed nucleus of stria terminalis and the preoptic area, all of which corresponded well to the result of ¹¹C-labelled vorozole. Copyright

Full text of DOI:10.1002/jlcr.1502

Research Article
Received 22 December 2007,
Revised 22 January 2008,
Accepted 22 January 2008
Published online 26 March 2008 in Wiley Interscience
(www.interscience.wiley.com) DOI: 10.1002/jlcr.1502
18F-Labelled vorozole analogues as PET tracer
for aromatase
Maria Erlandsson,a Farhad Karimi,b Kayo Takahashi,b,c
a,b
Ã
˚
and Bengt Langstrom
¨
One- and two-step syntheses for the 18F-labelling of 6-[(S)-(4-chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-(2-[18F]fluoroethyl)-
1H-benzotriazole, [18F]FVOZ, 1 and 6-[(S)-(4-chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-[2-(2-[18F]fluoroethoxy)ethyl]-1H-
benzotriazole, [18F]FVOO, 2 were developed. In the two-step synthesis, the nucleophilic fluorination step was performed
by reacting (S)-6-[(4-chlorophenyl)-(1H-1,2,4-triazol-1-yl)methyl]-1H-benzotriazole (VOZ) with either the 18F-labelled
ethane-1,2-diyl bis(4-methylbenzenesulfonate) or the oxydiethane-2,1-diyl bis(4-methylbenzenesulfonate). The radio-
chemical yields were in the range of 9–13% after the 110–120 min total syntheses and the specific radioactivities were
17577 GBq/lmol and 56 GBq/lmol for compounds 1 and 2, respectively. In the one-step synthesis, the precursor 2-{6-[(4-
chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1H-1,2,3-benzotriazol-1-yl}ethyl 4-methylbenzenesulfonate (7) or 1-[2-(2-bro-
moethoxy)ethyl]-6-[(4-chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1H-benzotriazole (8) was directly labelled via an 18F
nucleophilic substitution to give the corresponding tracer. The labelled compounds were obtained in 36–99% radiochemical
yield after 75-min syntheses. The specific radioactivities are 100 GBq/lmol for compound 1 and 80 GBq/lmol for compound
2. In vitro autoradiography using frozen rat brains illustrated specific binding in the medial amygdala, the bed nucleus of
stria terminalis and the preoptic area, all of which corresponded well to the result of 11C-labelled vorozole.
Keywords: n. c. a nucleophilic 18F-fluorination; 18F-labelled VOZ analogues; aromatase
Introduction
Results and discussion
Two-step labelling
Aromatase is an enzyme that converts androgens (C19 steroids)
to estrogens (C18) and may play a role in mood and mental
The 18F-labelled analogues were synthesized in two steps. In
the first step of the synthesis of compound 1, [18F]fluoride was
reacted with ethane-1,2-diyl bis(4-methylbenzenesulfonate) to
give 3,6 which in the second step was reacted with the pre-
status.1
(S)-6-[(4-Chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-
methyl-1H-benzotriazole, VOZ, is a nonsteroidal aromatase
inhibitor that reversibly binds to the heme domain of aromatase.
[N-Methyl-11C]vorozole, [11C]VOZ, is an interesting high-affinity
aromatase-binding radiotracer2 used in positron emission
tomography (PET). The radiotracer has previously shown high
and specific binding to aromatase-rich tumor reference placen-
ta2 and ovarian tissues.3 Recently, [11C]VOZ has also demon-
strated a high affinity for brain aromatase in the amygdala.1
Finally, 11C-labelled vorozole can be used to study the
alternation of aromatase expression in the brain by anaboli-
c–androgenic steroid treatment in vivo.4 Although [11C]VOZ has
good biological properties, we were interested in developing
18F-labelled analogues. Owing to longer half-life, these could
thus be used as tools for visualizing the aromatase enzyme in a
variety of applications, e.g. such as for depression or Alzheimer’s
disease, which might be influenced by steroid hormones.5
In this paper, we report the one- and two-step radiolabelling
syntheses of 18F-labelled vorozole analogues, i.e. 6-[(S)-(4-
chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-(2-[18F]fluoroethyl)-
1H-benzotriazole, [18F]FVOZ, 1 and 6-[(S)-(4-chlorophenyl)(1H-
1,2,4-triazol-1-yl)methyl]-1-[2-(2-[18F]fluoroethoxy)ethyl]-1H-ben-
zotriazole, [18F]FVOO, 2. The two tracers have been evaluated in
some preclinical studies using in vitro autoradiography and
metabolite studies.
treated precursor
5
to obtain the 18F-labelled product
(Schemes 1 and 2). Efficient alkylation was achieved when
the substrate was deprotonated using KOH. The reaction was
heated to 701C for 15 min during the first step and to 1501C for
15 min during the second step. The 18F-labelled product 2 was
synthesized from the intermediate 2-(2-[18F]fluoroethoxy)ethyl
4-methylbenzenesulfonate7 (4a) or 1-bromo-2-(2-[18F]fluor-
oethoxy)ethane (4b), which were synthesized from oxy-
diethane-2,1-diyl bis(4-methylbenzenesulfonate) (a) or 2-
bromoethyl ether (b), respectively (Schemes 1 and 2). The
aDepartment of Biochemistry and Organic Chemistry, Uppsala University, Box
576, Husargatan 3, BMC, S-751 23 Uppsala, Sweden
bUppsala Imanet, GE Healthcare, Box 967, S-751 09 Uppsala, Sweden
cMolecular Imaging Research Program, RIKEN, 6-7-3 Minatojima Minamimachi,
Chuo-ku, Kobe, 650-0047, Japan
˚
¨
*Correspondence to: Bengt Langstrom, Department of Biochemistry and Organic
Chemistry, Uppsala University, Box 576, Husargatan 3, BMC, S-751 23 Uppsala,
Sweden.
E-mail: bengt.langstrom@biorg.uu.se
J. Label Compd. Radiopharm 2008, 51 207–212
Copyright r 2008 John Wiley & Sons, Ltd.

M. Erlandsson et al.
O
S
18F
O
S
O
S
18F
O
O
O
O
O
O
(3)
18F
O
S
O
S
O
S
18F
O
O
O
O
O
O
O
O
(a)
(4a)
Br
18F
Br
18F
Br
O
O
(b)
(4b)
Scheme 1. 18F-Labelled intermediates.
N
18F
N
N
N
N
N
N
Cl
(3)
N
(1)
N
H
N
18F
N
N
N
Cl
(4a or b)
O
N
N
(5)
N
N
N
Cl
(2)
Scheme 2. Two-step synthesis of 18F-labelled analogues.
Table 1. Radiochemical yields of compound 2
One-step labelling
Precursor
Radiochemical yield (%)
In order to perform the radiolabelling in one step, relevant
precursors were synthesized (Scheme 3). Precursor 7 was
synthesized in two steps. In the first step, 2-iodoethanol was
reacted with 5, which had been pre-treated with potassium
hydroxide, to obtain the corresponding alcohol 6. Then, 4-
methylbenzenesulfonyl chloride was added to give 7. Precursor
8 was synthesized by adding 2-bromoethyl ether to compound
4a
4b
1573 (n = 2)
571 (n = 3)
n = Number of experiments.
analytical yield of the first step was between 76 and 84%. The 5, which had been pre-treated with potassium hydroxide. The
highest decay-corrected (d.c.) radiochemical yield for com- precursors were 18F-labelled with no-carrier-added [18F]fluoride
pound 2 was obtained with 4a (Table 1), due to tosylate’s (Scheme 4). In the one-step synthesis the radiochemical yields
better leaving group character.8 The radiochemical purity of (d.c.) for compounds 1 and 2 were 36–99%, after 75-min
compounds 1 and 2, determined by analytical HPLC, was syntheses from EOB (Table 2). The specific radioactivities,
496%. The radiochemical yields (d.c.) were in the range of measured at the end of the labelling syntheses, were 100 GBq/
9–13% after 110–120 min synthesis from EOB (Table 2). The mmol for compound 1 and 80 GBq/mmol for compound 2.
specific radioactivity, measured at the end of the labelling
In the two-step 18F-alkylation reaction, two significant
synthesis was 17577 GBq/mmol for compound 1 and 56 GBq/ products were formed, as alkylation occurred on the first
mmol for compound 2, respectively.
and third nitrogen atoms of the triazole ring. The major
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Copyright r 2008 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2008, 51 207–212

M. Erlandsson et al.
Table 2. Radiochemical yields for compounds 1 and 2
Compound
Reaction steps
Radiochemical yielda (%)
Specific activity (GBq/mmol)b
1
1
2
2
One
Two
One
Two
499 (n = 1)
1172 (n = 7)
36713 (n = 4)
1573 (n = 2)
100 (n = 1)
17577 (n = 2)
80 (n = 1)
56 (n = 1)
n = Number of experiments.
aDecay-corrected based on [18F]fluoride at the start and radioactivity of HPLC-purified product.
bRatio of radioactivity to amount of substance, decay-corrected to time at the start of synthesis.
O
N
N
N
N
O
S
OH
N
N
O
N
N
N
N
N
N
Cl
N
Cl
N
N
H
N
(7)
(6)
N
N
Cl
Br
N
N
(5)
O
N
N
N
N
Cl
(8)
Scheme 3. Precursor synthesis.
O
N
N
18F
O
S
N
N
N
O
N
N
N
N
N
N
N
Cl
Cl
(7)
(1)
18F
Br
N
N
O
O
N
N
N
N
N
N
N
N
N
N
Cl
Cl
(8)
(2)
Scheme 4. One-step 18F-labelling.
product was the desired product. This may be due to the synthesized references. The structures of the precursors 7
delocalization of negative charge in the base-generated anion and 8, used in the one-step 18F-labelling synthesis, were
in the triazole ring, with the major electron densities on the identified by NOE diff, HSQC and HMBC NMR analysis and
first and third nitrogen atoms. The identities of 18F-labelled shown to have the alkyl chains on the first nitrogen atom in
analogues 1 and 2 were assessed by HPLC comparison with both cases.
J. Label Compd. Radiopharm 2008, 51 207–212
Copyright r 2008 John Wiley & Sons, Ltd.
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M. Erlandsson et al.
elektriska AB, Sweden). When analyzing the 18F-labelled
compounds, unlabelled reference substances were used for
comparison in LC runs. Synthesis of the references was
conducted under nitrogen atmosphere using dried glassware
and magnetic stirring. All anhydrous solvents were bought from
commercial suppliers. Mass spectra were recorded at a Quattro
Premier from Waters, which has a triple quadrupole with
electrospray ionization, operated in positive mode or on
Finnigan AQA using mobile phases MeCN (0.1% formic acid)
[18F]FVOZ
[18F]FVOO
and H2O (0.1% formic acid).
A Gilson 322 pump and
Phenomenexs Gemeni 5 mm C18 110A 150 mm ꢀ 3.00 mm
1
column were also used. H, 13C, 19F, NOE diff, HMBC and HSQC
NMR spectra were recorded in CDCl3 (7.26 ppm 1H, 77.0 ppm
13C) on a Varian Unity 400 spectrometer (400 MHz for 1H,
100.6 MHz for 13C and 376.3 MHz for 19F nuclei) or on a Varian
Inova spectrometer (500 MHz for 1H and 125 MHz for 13C nuclei).
19F NMR spectra were recorded in CDCl3, with CFCl3 as the
reference.
[11C]VOZ
Bed nucleus
of stria terminalis
Amygdala
Figure 1. Autoradiographic images of [18F]FVOZ, [18F]FVOO and [11C]VOZ in the
male rat brain. This figure is available in colour online at www.interscience.wiley.-
com/journal/jlcr.
18F-production
[18F]Fluoride was produced at Uppsala Imanet using the
Scanditronix MC17 Cyclotron and the 18O(p, n) 18F nuclear
reaction through proton irradiation of 18O-enriched water (95%,
Rotem). The product solution of [18F]fluoride in water was
transferred from the cyclotron target by an HPLC pump and
trapped on a QMA filter (ABX, advanced biochemical compounds,
Pre-conditioned Sep-PAKs, Light QMA Cartridge with CO23ꢁ as
counter ions, Radeberg). The column was purged with helium for
1 min. The [18F]fluoride adsorbed on the resin was eluted into a
reaction vial with 2 ml of the following solution: 12ml of a 96:4
(by volume) acetonitrile:water mixture containing 55.8570.37mg
(n = 4) of K2.2.2 and 12.7370.13mg (n = 4) of K2CO3. The solution
was then evaporated and co-evaporated with anhydrous
acetonitrile to dryness in a nitrogen stream at 1101C.
Analysis of radiolabelled metabolites in plasma
A metabolite study was performed on [18F]FVOZ and [18F]FVOO.
For each radioligand one male rat was injected via the
tail vein with 50 MBq. After 40 min, blood was collected and
the protocol developed for metabolite analysis of [11C]VOZ was
followed.1 Metabolite analysis of plasma revealed that 30% of
[18F]FVOZ and 9% of [18F]FVOO were intact after 40 min of
injection.
Autoradiography
Rat brain autoradiography was used to demonstrate the
distribution of [18F]FVOZ, [18F]FVOO and [11C]VOZ (Figure 1).
The distribution patterns were similar for all tracers, with specific
binding in the medial amygdala, bed nucleus of stria terminalis
and preoptic area. By adding vorozole, binding of labelled
vorozole in these regions was blocked. This result is consistent
with an earlier report9 that showed high amounts of aromatase
activity in these regions of rat brain.
General method for two-step/one-vessel 18F-labelling
The dried complex [K/K2.2.2]118Fꢁ was dissolved in anhydrous
DMF (0.2 ml). A solution of the first reagent ethane-1,2-diyl bis(4-
methylbenzenesulfonate) was used in the synthesis of 1 and
oxydiethane-2,1-diyl bis(4-methylbenzenesulfonate) was used in
the synthesis of 2 in anhydrous MeCN (0.2 ml), and the reaction
mixture was heated in a closed vessel at 701C for 15 min.
Following this reaction, a solution of the precursor 5 in
anhydrous DMF (0.3 ml) and 1 M KOH (10 ml) was added. The
reaction mixture was heated for another 15 min at 1501C. The
crude product was dissolved in nanopure H2O (2 ml) and
injected onto the semi-preparative LC (1 and 2; tR = 9.3 and
10.2 min, respectively), mobile phase C:D (55:45). The product
was formulated with propylene glycol and phosphate buffer (pH
7.5, 1:16). Radiochemical purity (498%) and analytical radio-
chemical yield (14–60%) were determined by analytical LC.
Analytical LC (1 and 2; tR = 4.3 and 4.9 min, respectively), mobile
phase A:B (55:45).
Experimental
General
Liquid chromatographic analysis was performed with a Hitachi
LaChromElite, pump L-2130, injector L-220 and an L-2400 UV-
detector in series with a b1-flow detector. The following mobile
phases were used: MeCN:H2O (50:7) (A), 25 mM KH2PO4 (B),
0.05 M ammonium formate pH 3.5 (C) and MeCN (D). For
analytical LC, a Discovery ODS, 5 mm ꢀ 250 mm ꢀ 4.6 mm col-
umn and an ACE 5 C18-HL 250 mm ꢀ 4.6 mm column were used
at a flow rate of 1.5 ml/min. For semi-preparative LC, an ACE 5
C18-HL 250 mm ꢀ 10 mm column was used at a flow of 5 ml/
min. Synthias, an automated synthesis system, was used for LC
injection and fraction collection. Data collection and LC control
were performed with the use of a Beckman System Gold
chromatography software package (USA). Radioactivity was
measured in an ion chamber (Veenstra Instrumenten bv, VDC-
202, Holland). For coarse estimations of radioactivity during
General method for one-step 18F-labelling
The dried complex [K/K2.2.2]118Fꢁ was dissolved in anhydrous
DMF (0.2ml). The precursor 7 or 8 dissolved in anhydrous DMF
(0.3ml) was added and the reaction mixture was heated in a
closed vessel at 1501C for 15min. The crude product was
dissolved in nanopure H2O (2 ml) and injected onto the semi-
˚
synthesis, a portable dose-rate meter was used (Langenas
¨
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J. Label Compd. Radiopharm 2008, 51 207–212

M. Erlandsson et al.
preparative LC (1 and 2; tR = 9.3 and 10.2 min, respectively) (eluents C:D, 55:45) to give the title compound 1 (2.9 mg, 63%).
mobile phase C:D (55:45). The product was formulated in Analytical LC (tR = 4.3 min), eluents A:B (55:45). 1H NMR (CDCl3): d
propylene glycol and phosphate buffer (pH 7.5, 1:16). Radio- 8.07 (s, 1H), 8.03 (s, 1H), 7.81–7.78 (m, 1H), 7.64–7.60 (m, 1H),
chemical purity (498%) and analytical radiochemical yield 7.42–7.34 (m, 3H), 7.15–7.09 (m, 2H), 6.90 (s, 1H), 4.94–4.90 (m,
(21–59%) were determined by analytical LC. Analytical LC (1 2H), 4.88–4.79 (m, 2H). 13C NMR (CDCl3): d 152.9, 143.7, 138.0,
and 2; tR = 4.3 and 4.9 min, respectively), mobile phase A:B (55:45). 136.3, 135.9, 135.2, 129.8, 129.6, 128.1, 124.4, 120.9, 110.8, 82.3
(3JC,F = 174.8 Hz), 67.0, 49.0 (2JC,F = 21.6 Hz). 19F NMR (CFCl3): d
ꢁ219.8 (m, F). LC-MS (ESI1): m/z 357 [M1H]1.
Precursor and reference compounds
6-[(S)-(4-Chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-[2-(2-fluoro-
ethoxy)ethyl]-1H-benzotriazole (2)
1-[2-(2-Bromoethoxy)ethyl]-6-[(4-chlorophenyl)(1H-1,2,4-triazol-
1-yl)methyl]-1H-benzotriazole (8)
To a solution of 8 (4.9 mg, 0.011 mmol) in THF, 1 M TBAF (31 ml in
THF) was added, and the mixture was stirred for 4 h. The crude
product was extracted with CH2Cl2 and H2O. The product was
purified by preparative HPLC to give the title compound 2
1
(2.6 mg, 61%). Analytical LC (tR = 4.9 min), eluents A:B (55:45). H
NMR (CDCl3): d 8.54 (m, 1H), 8.06–7.99 (m, 2H), 7.71–7.68 (m, 2H),
7.38–7.32 (m, 2H), 7.13–7.09 (m, 2H), 6.89 (s, 1H), 4.85–4.78 (m,
2H), 4.25–4.18 (m, 2H), 4.03–3.94 (m, 2H), 3.68–3.54 (m, 2H). 13C
NMR (CDCl3): d 152.0, 143.2, 142.1, 141.3, 134.7, 134.4, 133.7,
131.5, 125.1, 124.1, 114.0, 81.0, 68.2, 68.0, 64.5, 40.7. 19F NMR
(CFCl3): d ꢁ223.0 (m, F). LC-MS (ESI1): m/z 401 [M1H]1.
To a solution of 5 (25 mg, 0.08 mmol) in DMF, KOH (1 M, 80 ml)
was added. The solution was cooled to 01C and 2-bromoethyl
ether (100 ml, 0.8 mmol) was added. The mixture was brought to
room temperature and stirred for 3.5 h. The crude product was
extracted with CH2Cl2 and H2O and further purified by
preparative HPLC (CH2Cl2:MeOH, 9.5:0.5) to give the title
compound 8 as an oil (11.8 mg, 31%). 1H NMR (CDCl3): d
8.05–8.00 (m, 2H), 7.73–7.69 (m, 1H), 7.45–7.44 (m, 1H), 7.37–7.34
(m, 2H), 7.18–7.15 (m, 1H), 7.13–7.08 (m, 2H), 6.90 (s, 1H), 4.81
(dt, 2H), 3.96 (dt, 2H), 3.67 (dt, 2H), 3.27 (dt, 2H). 13C NMR (CDCl3):
d 152.8, 143.8, 137.4, 136.3, 129.9, 129.6, 127.7, 124.3, 120.7,
119.8, 111.9, 110.9, 71.3, 70.2, 67.2, 48.97, 30.4. LC-MS (ESI1): m/z
462 [M1H]1.
Biology
Frozen rat brains were sectioned (25 mm) with a cryomicrotome
(Microm HM 560, Microm, Germany) and put on superfrost glass
slides. The slides were kept in a freezer (ꢁ201C) until they were
used. At the start of the experiment, the slides were pre-
incubated for 10min in TRIS-HCl buffer (50 mM, pH 7.4). They
were then transferred to containers containing [18F]FVOZ,
[18F]FVOO or [11C]VOZ in TRIS buffer. In a duplicate set of
containers, 1 mM of unlabelled vorozole was added to block
specific binding. After incubation for 50min ([18F]FVOZ and
[18F]FVOO) or 30min ([11C]VOZ), the slides were washed 3 ꢀ 2 min
in buffer. The slides were dried in an oven (371C) and then
exposed to phosphor imaging plates (Molecular Dynamics, USA)
for 4 h ([18F]FVOZ and [18F]FVOO) or 40min ([11C]VOZ) and
scanned in a Phosphor Imager Model 400S (Molecular Dynamics).
2-f6-[(4-Chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1H-benzotria-
zol-1-ylgethanol (6)
To a solution of 5 (50 mg, 0.16 mmol) in DMF, KOH (1 M, 160 ml)
was added. The solution was cooled to 01C and 2-iodoethanol
(13 ml, 0.16 mmol) was added. The mixture was heated to 801C
and stirred for 2 h. The crude product was extracted with CH2Cl2
and NaHCO3 (sat.) and purified by preparative TLC (CH2Cl2/
MeOH 9.5:0.5) to give the title compound 6 as an oil (17 mg,
30%). 1H NMR (CDCl3): d 7.88–7.78 (m, 3H), 7.27–7.21 (m, 3H),
7.03–6.97 (m, 3H), 6.77 (s, 1H), 4.61 (dt, 2H), 4.07 (dt, 2H). 13C
NMR (CDCl3): d 152.4, 143.5, 137.5, 133.9, 129.6, 129.4, 127.6,
124.1, 120.5, 119.6, 110.8, 109.8, 66.9, 61.3, 50.8. LC-MS (ESI1):
m/z 355 [M1H]1.
Metabolite study
2-f6-[(4-Chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1H-1,2,3-ben-
zotriazol-1-ylgethyl 4-methylbenzenesulfonate (7)
The metabolite analyses of [18F]FVOZ and [18F]FVOO in plasma
were performed with one rat each 40 min after injection. The
plasma was obtained using the reported method for [11C]VOZ.1
The sample was analyzed by HPLC to separate the radioligands
from their radioactive metabolites. The sample (90 ml) was
injected on an ACE 5 C18-HL 250 mm ꢀ 10 mm column, and the
tracer and its metabolite were eluted with the solvents mixture
C:D (1 and 2; 45:55 and 55:45 vol/vol, respectively) at a flow
rate of 5 ml/min. The eluent from the column was collected in
two fractions. The metabolite eluted in the first fraction
(metabolites for compounds 1 and 2; tR = 1.9 and 1.9 min,
respectively) and the tracer in the second fraction (1 and 2;
tR = 3.4 and 5.0 min, respectively). Observation of the UV peak
from the unlabelled standard as well as the peak of labelled
vorozole on a radio detector indicated that [18F]FVOZ eluted in
the second fraction. Even if no detectable radiopeak co-eluted
with the unlabelled standard of FVOO, the fraction was
collected and the radioactivity of the second fraction was
measured in a g-counter. After 40 min, 30% [18F]FVOZ and 9%
To a solution of 6 (29 mg, 0.08 mmol) in pyridine at 01C, 4-
methylbenzenesulfonyl chloride (17 mg, 0.09 mmol) was added.
The solution was stirred for 2.5 h. CH2Cl2 was added and the
crude product was extracted with H2O and further purified by
preparative TLC (CH2Cl2/MeOH 9:1) to give the title compound 7
1
as a yellow solid (9.1 mg, 22%). H NMR (CDCl3): d 8.08–8.01 (m,
2H), 7.53–7.47 (m, 2H), 7.41–7.33 (m, 4H), 7.26–7.12 (m, 5H), 6.90
(s, 1H), 4.87 (dt, 2H), 4.47 (dt, 2H), 2.39 (d, 3H). 13C NMR (CDCl3): d
152.8, 146.0, 145.7, 145.5, 143.7, 135.8, 134.3, 133.9, 131.9, 130.0,
129.6, 127.8, 124.5, 120.9, 110.7, 68.3, 67.1, 47.5, 21.8. LC-MS
(ESI1): m/z 509 [M1H]1.
6-[(S)-(4-Chlorophenyl)(1H-1,2,4-triazol-1-yl)methyl]-1-(2-fluoro-
ethyl)-1H-benzotriazole (1)
To a solution of 5 (3.8 mg, 0.013 mmol) in anhydrous DMF
(0.3 ml) and 1 M KOH (12.8 ml), 1-bromo-2-fluoroethane (1 ml,
0.013 mmol) was added. The reaction mixture was heated at
1501C for 30 min. The product was purified by preparative TLC
[
18F]FVOO were intact in the plasma.
J. Label Compd. Radiopharm 2008, 51 207–212
Copyright r 2008 John Wiley & Sons, Ltd.
www.jlcr.org

M. Erlandsson et al.
References
Conclusions
The 18F-labelled vorozole analogues are tracers that can be used
in PET for detection of the enzyme aromatase. [18F]FVOO was
metabolized more quickly than [18F]FVOZ. The described one-
and two-step syntheses give general methods to synthesize 18F-
labelled analogues. The developed one-step 18F-fluorination
method provides higher reproducibility and radiochemical yield
and might easily be automated in the future.
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Janssen Research Foundation.
www.jlcr.org
Copyright r 2008 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2008, 51 207–212