Synthesis and in vivo evaluation of [18F]-4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide as a PET imaging probe for COX-2 expression

Article abstract of DOI:10.1016/j.bmc.2006.11.033

Synthesis of [¹⁸F]4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide ([¹⁸F]celecoxib), a selective COX-2 inhibitor, is achieved via a bromide to [¹⁸F]F^- exchange reaction. Synthesis of the precursor for radiolabeling was achieved from 4′-methylacetophenone in four steps with 22% overall yield. Under non-radioactive conditions, fluorination was achieved using TBAF in DMSO at 135 °C in 80% yield. Synthesis of [¹⁸F]celecoxib was achieved using [¹⁸F]TBAF in DMSO at 135 °C in 10 ± 2% yield (EOS) with >99% chemical and radiochemical purities. The specific activity was 120 ± 40 mCi/μmol (EOB). [¹⁸F]celecoxib was found to be stable in ethanol, however, de[¹⁸F]fluorination (6.5%) was observed after 4 h in 10% ethanol-saline solution. Rodent PET studies show bone labeling indicating in vivo de[¹⁸F]fluorination of [¹⁸F]celecoxib. PET studies in baboon indicated a lower rate of de[¹⁸F]fluorination than rat and retention of radioactivity in brain regions consistent with the known distribution of COX-2. A radiolabeling method that can generate consistent high specific activity is needed for routine human use.

Full text of DOI:10.1016/j.bmc.2006.11.033

Bioorganic & Medicinal Chemistry 15 (2007) 1802–1807
Synthesis and in vivo evaluation of [18F]-4-[5-(4-methylphenyl)-
3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide
as a PET imaging probe for COX-2 expression
Jaya Prabhakaran,a Mark D. Underwood,a,b Ramin V. Parsey,a,b Victoria Arango,a,b
Vattoly J. Majo,a Norman R. Simpson,b,c Ronald Van Heertum,c
J. John Manna,b,c and J. S. Dileep Kumara,b,
*
aDepartment of Psychiatry, Columbia University College of Physicians and Surgeons, NY, USA
bDivision of Neuroscience, New York State Psychiatric Institute, New York, NY 10032, USA
cDepartment of Radiology, Columbia University College of Physicians and Surgeons, NY, USA
Received 2 August 2006; revised 13 November 2006; accepted 19 November 2006
Available online 29 November 2006
Abstract—Synthesis of [18F]4-[5-(4-methylphenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide ([18F]celecoxib), a selec-
tive COX-2 inhibitor, is achieved via a bromide to [18F]Fꢀ exchange reaction. Synthesis of the precursor for radiolabeling was
achieved from 40-methylacetophenone in four steps with 22% overall yield. Under non-radioactive conditions, fluorination was
achieved using TBAF in DMSO at 135 ꢀC in 80% yield. Synthesis of [18F]celecoxib was achieved using [18F]TBAF in DMSO at
135 ꢀC in 10 2% yield (EOS) with >99% chemical and radiochemical purities. The specific activity was 120 40 mCi/lmol
(EOB). [18F]celecoxib was found to be stable in ethanol, however, de[18F]fluorination (6.5%) was observed after 4 h in 10% etha-
nol–saline solution. Rodent PET studies show bone labeling indicating in vivo de[18F]fluorination of [18F]celecoxib. PET studies
in baboon indicated a lower rate of de[18F]fluorination than rat and retention of radioactivity in brain regions consistent with
the known distribution of COX-2. A radiolabeling method that can generate consistent high specific activity is needed for routine
human use.
ꢁ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
Efforts undertaken thus far to develop a specific PET
probe for COX-2 expression have been unsuccessful.12–19
Recently, synthesis and in vivo evaluation of [125I]IMTP
and [125I]IATP are reported as potential SPECT tracers
for COX-2 expression in rats.20 The COX-2 IC50 values
of these ligands are 5.16 and 8.20 lM and have a COX-
1/COX-2 selectivity ratio of 19 and 13, respectively. The
micromolar affinity and poor selectivity of [125I]IMTP
and [125I]IATP would not qualify them as PET tracer
candidates. The biodistribution studies of these ligands
also show uniform retention of radioactivity in all areas
examined indicating a lack of measurable specific bind-
ing. Moreover, the affinity of IMTP and IATP for other
enzymes, biogenic amines, transporters, and receptors is
not reported. Hence the retention of radioactivity of
The discovery of cyclooxygenase-2 (COX-2) and its role
in inflammation led to the recognition that COX-2 selec-
tive inhibitors might have an anti-inflammatory effect
without the gastrointestinal side effects of non-selective
COX inhibitors.1–6 Subsequent discoveries suggesting
an involvement of COX-2 in many diseases or disease
processes7–9 raised the possibility that quantification of
COX-2 expression might be a useful biological marker
for early diagnosis, monitoring disease progression,
and an indicator of effective treatment. Positron emis-
sion tomography (PET) is a non-invasive imaging tech-
nique used in nuclear medicine to study various
biochemical and biological processes in vivo because it
can detect targets at subnanomolar concentrations.10,11
[
125I]IMTP and [125I]IATP in various tissues may be
due to the contribution of non-specific binding and per-
haps some binding to other sites where the ligands may
have higher binding affinity. Hence, currently no specific
imaging agent is available for COX-2. In this report, we
Keywords: [18F]Fluorine; PET; Radiotracer; Inflammation.
*
Corresponding author. Tel.: +1 212 543 1163; fax: +1 212 543
1054; e-mail: dk2038@columbia.edu
0968-0896/$ - see front matter ꢁ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2006.11.033

J. Prabhakaran et al. / Bioorg. Med. Chem. 15 (2007) 1802–1807
1803
present the [18F]radiolabeling of 4-[5-(4-methylphenyl)-
3-(trifluoromethyl)-1H-pyrazol-1-yl]benzenesulfonamide
(celecoxib), a selective COX-2 inhibitor, and the results of
in vivo imaging studies in rats and baboons. COX-2 and
COX-1 Ki values of celecoxib are 40 and 17,000 nM,
respectively, with a COX-1/COX-2 selectivity ratio of
425.4 These properties coupled with known safe toxicity
data of celecoxib in human subjects suggest that celecoxib
can be a suitable candidate PET tracer for the in vivo
quantification of COX-2.
as dimethoxytrityl (DMT) derivative 5, in 82% yield.18,19
The pharmacologic screen from NIMH-Psychoactive
Drug Screening Program (PDSP) shows that celecoxib
has no significant affinity (Ki > 10 lM) for brain biogenic
amines, receptors or transporters. To derive conditions of
radiolabeling for obtaining optimum yield in minimum
time, experiments were first performed under non-radio-
active conditions. After reacting precursor 5 with KF-
Kryptofixꢂ at elevated temperature, in solvents such as
acetonitrile or dimethylsulfoxide, only negligible amount
(<3%) of celecoxib 6 was formed after deprotecting the
sulfonamide group (1:1; TFA/DCM). Whereas, heating
5 with tetrabutylammonium fluoride at 135 ꢀC (TBAF)
in DMSO for 40 min followed by sulfonamide deprotec-
tion afforded 6 in good yield (80%, Scheme 1).
2. Results and discussion
2.1. Chemistry
Synthesis of N-[bis(4-methoxyphenyl)phenylmethyl]-4-
[3-(bromodifluoromethyl)-5-p-tolylpyrazol-1-yl]benzene-
sulfonamide (5), the precursor for radiolabeling of
celecoxib, and standard celecoxib was achieved as de-
scribed in Scheme 1. The synthesis of 2-bromo-2,2-diflu-
oro-1-imidazol-1-yl-ethanone (2) has been achieved via
the N-acylation of N,N0-carbonyldiimidazole (1) with
2-bromo-2,2-difluoroacetyl chloride in 90% yield.21 Reac-
tion of 40-methyl acetophenone with 2 afforded bromo-
4,4-difluoro-1-p-tolylbutane-1,3-dione (3). The coupling
reaction proceeded smoothly in 1 h to afford 65% of the
dione 3 in presence of compound 2,22 whereas using
bromodifluoroacetyl chloride as the coupling agent the
reaction resulted in poor yield of 3. A subsequent conden-
sation reaction of 3 with 4-hydrazinobenzenesulfonamide
by refluxing in ethanol resulted in the formation of 4-[3-
(bromodifluoro-methyl)-5-p-tolyl-pyrazol-1-yl]benzene-
sulfonamide (4) in 45% yield. Compound 4 was protected
2.2. Radiochemistry
Incorporation of [18F]fluorine to precursor 5 was also
not effective using [18F]KF-Kryptofixꢂ as the radiolabel-
ing reagent, even under rigorous conditions such as
using high temperature and microwave irradiation.
Optimum yield of [18F]6 was obtained while heating pre-
cursor 5 with [18F]TBAF22 in DMSO for 20 min at
135 ꢀC followed by treating with a 1:1 mixture of TFA
and DCM (Scheme 2). The reaction mixture was puri-
fied by RP-HPLC followed by passing through a C-18
Sep-Pakꢂ cartridge. The radiochemical yield of [18F]6
was 10 2% (n = 6) at the end of synthesis (EOS). The
chemical identity of [18F]6 was confirmed by co-injecting
the radio-product with non-radioactive celecoxib on an
analytical RP-HPLC. The chemical and radiochemical
purities of [18F]6 were found to be >99% with a specific
activity of 120 40 mCi/lmol at EOB. Multiple mobile
phases were used to determine the purities of the
radioligand. Our efforts to improve the yield and specific
activity of [18F]6 were not effective. We observed that
lowering the temperature or decreasing the time of
experiment did not improve the outcome of the reaction.
O
O
N
b
N
CF2Br
a
NH
N
O
CF2Br
We hypothesize that in the reaction mixture,
a
3
1
2
competitive [19F]ꢀ to [18F]ꢀ exchange may compete with
[18F]ꢀ incorporation, resulting in low yield and specific
activity of [18F]celecoxib.23
c
d
CF2Br
CF2Br
N
N
2.3. In vitro stability
N
N
O
O
In vitro stability of [18F]celecoxib was determined in
ethanol and 10% ethanol–saline using silica gel TLC,
in which [18F]fluoride stays at the origin and [18F]cele-
coxib stays at the solvent front.18 No significant
S
S
H2N
HN
DMT
O
O
4
5
e
CF3
N
N
O
a, b, c
CF218F
S
5
N
N
H2N
O
O
6
S
H2N
O
Scheme 1. Synthesis of celecoxib and radiolabeling precursor.
Reagents and conditions: (a) 2-bromo-2,2-difluoroacetyl chloride, rt,
THF, 90%; (b) p-tolylethanone, THF, reflux, 65%; (c) 4-hydrazino-
benzenesulfonamide, ethanol, reflux, 45%; (d) DMT/Cl, TEA, CH2Cl2,
82%; (e) 1—TBAF (4 equiv), DMSO, 135 ꢀC, 40 min; 2—TFA/DCM
(1:1), 60 ꢀC, 5 min, 80%.
[
18F]6
Scheme 2. Radiosynthesis of [18F]celecoxib. Reagents and conditions:
(a) 1—[18F]TBAF, DMSO, 135 ꢀC, 20 min; (b) TFA/DCM (1:1),
60 ꢀC, 5 min; (c) Semipreparative HPLC purification.

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J. Prabhakaran et al. / Bioorg. Med. Chem. 15 (2007) 1802–1807
Figure 3. Time–activity curves of the radioactivity in rat after the
injection of [18F]celecoxib (CER, cerebellum; HT, heart; SK, skeleton;
ROB, rest of brain).
Figure 1. In vitro stability of [18F]celecoxib. Data points presented are
the average determinations from representative experiments repeated
at least on two-independent occasions with similar results.
eton at 112 min was found to be 0.70, 0.54 and 0.45,
respectively (Fig. 3).
de[18F]fluorination was observed for [18F]celecoxib for-
mulation in ethanol up to 4 h, but a low rate of
de[18F]fluorination (6.5% in 4 h) was observed for the
radiotracer formulation in saline containing 10% etha-
nol (Fig. 1).
2.5. PET studies in baboon
PET studies in anesthetized baboon show that [18F]cele-
coxib (dose = 2.0 0.4 mCi, specific activity = 120
40 mCi/lmol) penetrated the BBB and accumulated in
brain (Fig. 4).25 The TACs of several brain regions
and skull were examined and show relatively poor skull
uptake indicating a low degree of in vivo de[18F]fluori-
nation of radioligand (Fig. 5) in baboon. Uptake of
[18F]6 peaked in most regions within 3.5–13 min and
then declined relatively slowly. The fastest washout
was observed in skull followed by cerebellum,
hippocampus, cingulate cortex, putamen, caudate, and
thalamus. The distribution of [18F]6 accumulation in ba-
boon brain is consistent with known distribution of
COX-2.26–29 The binding ratios of thalamus, caudate,
putamen, cingulate, hippocampus, and cerebellum in
comparison to skull are 1.60, 1.48, 1.46, 1.43, 1.41,
and 1.20, respectively, at 115 min. The brain to skull
ratio of baboon is 3–4 times higher than the ratio ob-
tained for rats indicating a lower rate of de[18F]fluorina-
tion in non-human primates in comparison to rodents.
The metabolite analyses show that [18F]celecoxib
undergoes fast metabolism.25 Polar metabolites were
found in baboon plasma and the % of unmetabolized
fractions at 2, 4, 12, 30, and 60 min are 93.2%, 84.9%,
47.5%, 30.2%, and 17.0%, respectively (Fig. 6).24
2.4. In vivo imaging in rats
Since the in vitro de[18F]fluorination rate of [18F]cele-
coxib was relatively slow in the imaging time-frame
(2–3% in 90–120 min), in vivo imaging was performed
in rats using a small animal PET Scanner (microPET).
PET images in a rat during 0–20 min (A) and
60–120 min (B) are shown in Figure 2. The PET images
show significant bone uptake, most likely be attributed
to in vivo de[18F]fluorination of [18F]6 (Fig. 2B). The
time–activity curves (TACs) generated from the PET
studies show higher skeleton uptake of [18F]6 compared
to brain or heart, regions where COX-2 is known to be
present (Fig. 3).24 The uptake ratio of [18F]6 in heart,
cerebellum, and rest of the brain with reference to skel-
3. Conclusion
Synthesis of [18F]celecoxib was achieved via a bromide
to [18F]fluoride displacement reaction in 10 2% yield
(EOS) and a specific activity of 120 40 mCi/ lmol.
Poor specific activity of [18F]celecoxib obtained from
the bromine to [18F]fluorine displacement reaction may
be attributed to the competitive defluorination from 5,
which may dilute the [18F]anion during the labeling
Figure 2. microPET images of [18F]celecoxib in rat. PET images of
[
18F]celecoxib in rat (images are normalized to the injected dose). (A)
Sum of 0–20 min PET images; (B) sum of 60–120 min PET images.

J. Prabhakaran et al. / Bioorg. Med. Chem. 15 (2007) 1802–1807
1805
Figure 4. Sum of the (0–120 min) PET images of baboon brain after the injection of 1.2 mCi [18F]celecoxib. First column, sagittal; middle column,
coronal; last column, axial views.
mal rats the ligand is unlikely to allow imaging of
COX-2 expression in rats. However, the de[18F]fluorina-
tion rate is lower in baboon and could be much slower in
human subjects due to a slower metabolism. Further
studies are required to demonstrate the utility of
[18F]celecoxib in human subjects as a PET tracer for
the in vivo imaging of COX-2 expression, and specifical-
ly an improved radiolabeling method is needed for rou-
tine human use.
4. Experimental
4.1. General
The commercial chemicals used in the synthesis were
purchased from Sigma–Aldrich Chemical Co. or Fisher
Scientific Inc. and were used without further purifica-
tion. Melting points were determined on a Fisher melt-
ing point apparatus and are uncorrected. 1H NMR
Figure 5. Time–activity curves of the radioactivity in baboon after the
injection of [18F]celecoxib (CIN, cingulate; CER, cerebellum; CAU,
caudate; HIP, hippocampus; PUT, putamen; THA, thalamus).
spectra were recorded on a Bruker PPX 300 and
400 MHz spectrometer. 19F NMR spectra were generat-
ed on Bruker PPX 282.5 MHz spectrometer. Spectra are
obtained in CDCl3 and chemical shifts are reported in
ppm relative to TMS for 1H and CFCl3 for 19F as inter-
nal standards. The mass spectra were recorded on JKS-
HX 11UHF/HX110 HF Tandem Mass Spectrometer in
the FAB+ and EI+ mode. Semipreparative HPLC anal-
yses were performed using a Waters 1525 HPLC system.
Semipreparative analyses were performed by Phenome-
nex, Prodigy ODS(3) 10 · 250 mm, 10 l column and
analytical studies were performed by Phenomenex,
Prodigy
ODS(3)
4.6 · 250 mm,
5 l
column
(k = 254 nm). Flash column chromatography was per-
formed on silica gel (Fisher 200–400 mesh) using the sol-
vent system indicated in the experimental procedure for
each compound. [18F]Fluoride was generated from
RDS112 cyclotron (Siemens, Knoxville,). The radio-
TLC was performed on silica gel plates (EM science, sil-
ica gel 60 F254) using Bioscan, AR-2000 Instrument and
ethanol as the mobile phase. microPET studies were per-
formed with Seimens R4, Microsystem Inc.
Figure 6. Unmetabolized parent fraction of [18F]celecoxib in baboon
plasma. Filled circles represent the average of two studies.
4.2. Chemistry
process. The radiotracer was found to be stable in etha-
nol solution, but de[18F]fluorinated slowly in 10% etha-
nol–saline solution. microPET studies in rat show that
[18F]celecoxib has uptake in heart and brain. Due to
the in vivo de[18F]fluorination of [18F]celecoxib in nor-
4.2.1. 4-Bromo-4,4-difluoro-1-p-tolylbutane-1,3-dione (3).
At 0 ꢀC, bromodifluoroacetyl chloride (386 mg,
2 mmol) was added to a solution of imidazole
(285 mg, 4.2 mmol) in 2.5 mL anhydrous THF. The

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J. Prabhakaran et al. / Bioorg. Med. Chem. 15 (2007) 1802–1807
solution was warmed to room temperature and stirred
for an additional hour. The precipitate formed was
filtered off and the filtrate was washed with ether (2·
5 mL), the combined filtrates were evaporated and
ed for C38H32O4N3BrF2S, C, 61.29; H, 4.33; N, 5.10.
Found: C, 61.41; H, 4.62; N, 5.38.
4.2.4. Synthesis of celecoxib (6) from bromoderivative 5.
Compound 5 (51 mg, 0.07 mmol) was dissolved in
DMSO (2 mL) and 0.27 mL (0.27 mmol) TBAF in
THF was added to it. The solution was heated at
135 ꢀC for 40 min after which it was cooled to room
temperature and 5 mL of 20% TFA in DCM was added.
The solution was stirred for 5 min and treated with
water (2 mL). The product was extracted into ethyl ace-
tate (3· 5 mL), washed with water and brine, and puri-
fied by silica gel column chromatography using 40%
ethyl acetate in hexane to afford celecoxib (6) (21 mg,
dried under high vacuum to give compound
2
2
(400 mg, 90%). The imidazole derivative thus
obtained was dissolved in anhydrous THF (1 mL)
and added to a previously stirred solution of 40-methyl
acetophenone (268 mg, 2 mmol) in 10 mL THF treated
with NaHMDS solution (1 M in THF, 3 mL, 3 mmol)
at ꢀ78 ꢀC. After the addition of 2, the reaction mixture
was warmed to room temperature and stirred for 1 h.
The reaction was quenched by adding saturated ammo-
nium chloride solution and diluted with water (10 mL).
The products were extracted into ethyl acetate (3·
25 mL), washed with water and brine, and dried over
anhydrous magnesium sulfate. Solvent was evaporated
under reduced pressure and the product was purified
using silica gel column chromatography using 15%
ethyl acetate in hexane to afford dione 3 (380 mg,
65%) as a viscous liquid.
1
80% yield). H and 19F NMR of synthesized 6 are iden-
tical to the reported data.4
4.3. Radiosynthesis of [18F]celecoxib
The aqueous solution of [18F]fluoride generated from
RDS 112 cyclotron is passed through an activated
QMA and eluted with a mixture of 50 lmol of tetrabu-
tylammonium bicarbonate in 1 mL of acetonitrile to a
reaction vial. The reaction mixture was heated at
110 ꢀC under a stream of argon while it dried azeotrop-
ically with the addition of acetonitrile (3· 0.4 mL). A
solution of 3 0.5 mg of precursor 5 in 0.5 mL of ana-
hydrous DMSO was added to the reaction vial, sealed,
mixed well, and heated for 20 min. The reaction mixture
was allowed to cool at room temperature and 1 mL of
50% TFA in DCM was slowly added. The solution
was purged with argon at 60 ꢀC for 5 min to remove
DCM. The reaction mixture was then treated with
0.5 mL of 1:1 methanol/water, mixed well and further
diluted with 4 mL water. The reaction mixture was sub-
sequently passed through a classic C-18 Sep-Pak car-
tridge, washed with 20 mL water to remove unreacted
[18F]fluoride and other polar impurities, eluted with
1 mL of acetonitrile, and injected onto a semiprepara-
tive RP-HPLC (mobile phase; 60:39:1, acetonitrile/
water/acetic acid, flow rate 5 mL/min). The product
fraction with a retention time (tR) of 11 min based on
c-detector was collected, diluted with 100 mL of deion-
ized water, and passed through a classic C-18 Sep-
Pakꢂ cartridge. The DMT-deprotected precursor ap-
pears at 12–14 min. Reconstitution of the product in
1 mL of absolute ethanol afforded [18F]celecoxib. A por-
tion of the ethanol solution was analyzed by analytical
HPLC (mobile phase; 60:39:1, acetonitrile/water/acetic
acid, flow rate 1 mL/min, tR = 10 min) to determine
the specific activity, chemical and radiochemical puri-
ties. The chemical and radiochemical purities of
[18F]celecoxib were confirmed by RP-HPLC (mobile
phase; 1:1 acetonitrile/50 mM sodium phosphate, flow
rate: 2 mL/min, tR = 14 min).
1
Compound 3: H NMR (300 MHz, CDCl3) d: 7.83 (d,
J = 9, 2H), 7.26 (d, J = 9, 2H), 6.55 (s, 1H), 2.43 (s,
3H); HRMS (EI+) calculated for C11H10O2BrF2:
289.9754. Found: 289.9759.
4.2.2. 4-[3-(Bromodifluoromethyl)-5-p-tolylpyrazol-1-yl]-
benzenesulfonamide (4). 1,3-Dione (3, 291 mg, 1 mmol)
and 4-hydrazino-sulfonamide (224 mg, 1 mmol) were
dissolved in anhydrous ethanol (20 mL) and the mixture
was refluxed for 16 h. Ethanol was evaporated, and the
residue was dissolved in ethyl acetate, washed with
water and brine. The organic layer was dried over anhy-
drous MgSO4, concentrated, and the product was puri-
fied by silica gel column chromatography using 20%
ethyl acetate in hexane to afford sulfonamide 4 as a
white solid (200 mg, 45%), mp 184–185 ꢀC.
1
Compound 4: H NMR (300 MHz, CDCl3) d: 7.95 (d,
J = 9, 2H), 7.51 (d, J = 9, 2H), 7.15 (m, 4H), 6.76 (s,
1H), 4.98 (s, 2H), 2.39 (s, 3H); 19F NMR (282.5 MHz,
CDCl3) d: ꢀ42.31 (s); HRMS (EI+) calculated for
C17H15O2N3BrF2S: 443.0017. Found; 443.0064.
4.2.3. N-[Bis(4-methoxyphenyl)phenylmethyl]-4-[3-(bro-
mo-difluoromethyl)-5-p-tolylpyrazol-1-yl] benzenesulfona-
mide (5). To a solution of sulfonamide 4 (256 mg,
0.6 mmol) in dichloromethane (10 mL) at 0 ꢀC was add-
ed dimethoxytrityl chloride (245 mg, 0.72 mmol) in
dichloromethane (5 mL). Triethylamine (0.2 mL,
1.45 mmol) was added to the above solution and stirred
at room temperature for 1 h after which the solution was
evaporated under reduced pressure and the residue was
directly charged onto a silica gel column. The product
was eluted using 15% ethyl acetate in hexane (350 mg,
82%) as a colorless solid; mp 135–136 ꢀC.
4.4. PET studies of [18F]celecoxib in rodent
Compound 5: 1H NMR (400 MHz, CDCl3) d: 7.20–7.12
(m, 17H), 6.71 (m, 4H), 5.79 (s, 1H), 3.75 (s, 6H), 2.35 (s,
3H); 19F NMR (282.5 MHz, CDCl3) d: ꢀ42.10 (s);
HRMS (FAB+) calculated for C38H32O4N3BrF2S:
744.1343. Found; 744.1343. Elemental analysis calculat-
All animal experiments were carried out with the
approval of the Institutional Animal Care and Use
Committees of Columbia University Medical Center
and the New York State Psychiatric Institute. Spra-
gue–Dawley rats (male) weighing 300–400 g (Hilltop

J. Prabhakaran et al. / Bioorg. Med. Chem. 15 (2007) 1802–1807
1807
6. Talley, J. J.; Brown, D. L.; Carter, J. S.; Graneto, M. J.;
Koboldt, C. M.; Masferrer, J. L.; Perkins, W. E.; Rogers,
R. S.; Shaffer, A. F.; Zhang, Y. Y.; Zweifel, B. S.; Seibert,
K. J. Med. Chem. 2000, 43, 775–777.
7. Fitz, G. A. Nat. Rev. Drug Disc. 2003, 2, 879–890.
8. Gately, S. T. Prog. Drug Res. 2005, 63, 207–225.
9. Giovannini, M. G.; Scali, C.; Prosperi, C.; Bellucci, A.;
Pepeu, G.; Casamenti, F. Int. J. Immunopathol. Pharma-
col. 2003, 16, 31–40.
10. Massoud, T. F.; Gambhir, S. S. Genes Dev. 2003, 17, 545–
580.
11. Phelps, M. E. Proc. Natl. Acad. Sci. U.S.A. 2000, 97,
9226–9233.
Lab Animals, NY) were anesthetized with isoflurane (1–
5%) and positioned head and upper thorax at the center
of the field of view of a microPET R4 camera (Seimen’s
Microsystems, Inc., Model R4). A polyethylene catheter
(PE90, 1.27 mm od, Intramedic) filled with heparinized
saline was inserted into the left femoral vein for radioli-
gand injection and a terminal KCl (4 M) injection at the
conclusion of the experiment. The femoral arteries were
cannulated (PE50, 0.965 mm od, Intramedic) for mea-
surement of arterial pressure, blood gases, and hemato-
crit. A tracheotomy was performed (PE360, Intramedic)
for artificial ventilation. Transmission scans were ac-
quired with a rotating germanium-68 point source and
used attenuation correction. [18F]6 (0.2 mCi) was inject-
ed into the left femoral vein and initiated camera acqui-
sition. List-mode data were collected for 120 min and
reconstructed using attenuation correction and Fourier
rebinning. The dynamic images were reconstructed
using a filtered back-projection algorithm and interpo-
lated to give nCi/cc (microPET Manager, Concorde
Microsystems Inc.). The regions of interest (ROIs) were
drawn on the PET images. Time–activity curves were
generated for ROIs including heart, bone, and
brain.30,31
12. Isakson, P. C.; Clarkson, V.; Seibert, K.; Talley, J. J. PCT
Int. Appl. 2000, 6045773.
13. McCarthy, T. J.; Sheriff, A. U.; Graneto, M. J.; Talley, J.
J.; Welch, M. J. J. Nucl. Med. 2002, 43, 117–124.
14. de Vries, E. F. J.; van Waarde, A.; Buursma, A. R.;
Vaalburg, W. J. Nucl. Med. 2003, 44, 1700–1706.
15. Toyokuni, T; Satyamurthy, N; Herschman, H. R; Phelps,
M. E; Barrio, J. R. PCT Int. Appl. WO 2003089013, 2003,
60 pp.
16. Mann, J. J.; Kumar, J. S. D. WO 2005120584, 2005, 51 pp.
17. Majo, V. J.; Prabhakaran, J.; Simpson, N. R.; Van
Heertum, R. L.; Mann, J. J.; Kumar, J. S. D. Bioorg. Med.
Chem. Lett. 2005, 15, 4268–4271.
18. Toyokuni, T.; Kumar, J. S. D.; Walsh, J. C.; Shapiro, A.;
Talley, J. J.; Phelps, M. E.; Herschman, H. R.; Barrio, J.
R.; Satyamurthy, N. Bioorg. Med. Chem. Lett. 2005, 15,
4699–4702.
Acknowledgments
19. Prabhakaran, J.; Majo, V. J.; Simpson, N. R.; Van
Heertum, R. L.; Mann, J. J.; Kumar, J. S. D. J. Labelled
Compd. Radiopham. 2005, 48, 887–895.
20. Yuji, K.; Yumiko, K.; Sayaka, S.; Takashi, T.; Hiroyuki,
K.; Yasushi, K.; Chiaki, Y.; Kazuo, M.; Koh-ichi, S.;
Nagara, T.; Kazue, O.; Hideo, S. Nucl. Med. Biol. 2006,
33, 21–27.
Pfizer Inc. provided funding for this investigator initiat-
ed grant request. The authors thank the NIMH-PDSP
for the pharmacologic screen of celecoxib. Ms. Anna
R. Cooper provided technical assistance for the micro-
PET studies.
21. Staab, H. A.; Walther, G. Ber. 1962, 95, 2070–2072.
22. Alauddin, M. M.; Conti, P. S.; Mathew, T.; Fissekis, J. D.;
Surya Prakash, G. K.; Watanabe, K. A. J. Fluorine Chem.
2000, 106, 87–91.
23. Das, M. K.; Mukherjee, Y. Appl. Radiat. Isot. 1993, 44,
835–842.
References and notes
1. Lipsky, P. E. Am. J. Med. 1999, 106, 15473–15480.
2. Masferrer, J. L. Proc. Natl. Acad. Sci. U.S.A. 1994, 91,
3228–3232.
24. Yasojima, K.; Schwab, C.; McGeer, E. G.; McGeer, P. L.
Brain Res. 1999, 830, 226–236.
25. Kumar, J. S. D.; Majo, V. J.; Sullivan, G. M.; Prabhak-
aran, J.; Van Heertum, R. L.; Parsey, R. V.; Mann, J. J.
Bioorg. Med. Chem. 2006, 14, 4029–4034.
26. Kaufmann, W. E.; Worley, P. F.; Peggi, J.; Bremer, M.;
Peter Isakson, P. Proc. Nat. Acad. Sci. U.S.A. 1996, 93,
2317–2321.
3. Talley, J. J. Prog. Med. Chem. 1999, 36, 201–234.
4. Penning, T. D.; Talley, J. J.; Bertenshaw, S. R.; Carter, J.
S.; Collins, P. W.; Docter, S.; Graneto, M. J.; Lee, L. F.;
Malecha, J. W.; Miyashiro, J. M.; Rogers, R. S.; Rogier,
D. J.; Yu, S. S.; Anderson, G. D.; Burton, E. G.; Cogburn,
J. N.; Gregory, S. A.; Koboldt, C. M.; Perkins, W. E.;
Seibert, K.; Veenhuizen, A. W.; Zhang, Y. Y.; Isakson, P.
C. J. Med. Chem. 1997, 40, 1347–1365.
27. Minghetti, L. J. Neuropathol. Exp. Neurol. 2004, 63, 901–
910.
28. Breder, C. D.; Dewitt, D.; Kraig, R. P. J. Comp. Neurol.
1995, 355, 296–315.
29. Ho, L.; Pieroni, C.; Winger, D.; Purohit, D. P.; Aisen, P.
S.; Pasinetti, G. J. Neurosci. Res. 1999, 57, 295–303.
30. Watson, C. C.; Newport, D.; Casey, M. E. Aix-les-bains,
France, 1995, pp 215–219.
31. Woods, R. P.; Cherry, S. R.; Mazziotta, J. C. J. Comput.
Assist. Tomogr. 1992, 16, 620–633.
5. Chan, C.-C.; Boyce, S.; Brideau, C.; Charleson, S.;
Cromlish, W.; Ethier, D.; Evans, J.; Ford-Hutchinson,
A. W.; Forrest, M. J.; Gauthier, J. Y.; Gordon, R.;
Gresser, M.; Guay, J.; Kargman, S.; Kennedy, B.;
Leblanc, Y.; Leger, S.; Mancini, J.; O’Neill, G. P.; Ouellet,
M.; Patrick, D.; Percival, M. D.; Perrier, H.; Prasit, P.;
Rodger, I.; Tagari, P.; Therien, M.; Vickers, P.; Visco, D.;
Wang, Z.; Webb, J.; Wong, E.; Xu, L.-J.; Young, R. N.;
Zamboni, R.; Riendeau, D. J. Pharm. Exp. Ther. 1999,
290, 551–560.