N3-Substituted thymidine analogues III: Radiosynthesis of N 3-[(4-[18F]fluoromethyl-phenyl)butyl]thymidine ([ 18F]-FMPBT) and N-[(4-[18F]fluoromethyl-phenyl)pentyl] thymidine ([18F]-FMPPT)

Article abstract of DOI:10.1002/jlcr.1425

Radiosyntheses of two N³-substituted thymidine analogues, N ³-[(4[¹⁸F]fluoromethyl-phenyl)butyl]thymidine ([ ¹⁸F]-FMPBT) and N³-[(4[¹⁸F]fluoromethyl-phenyl) pentyl]thymidine ([¹⁸

Full text of DOI:10.1002/jlcr.1425

Journal of Labelled Compounds and Radiopharmaceuticals
J Label Compd Radiopharm 2007; 50: 1185–1191.
Published online 9 August 2007 in Wiley InterScience
(www.interscience.wiley.com). DOI: 10.1002/jlcr.1425
JLCR
Research Article
N3-Substituted thymidine analogues III: radiosynthesis of
N3-[(4-[18F]fluoromethyl-phenyl)butyl]thymidine ([18F]-FMPBT)
and N3-[(4-[18F]fluoromethyl-phenyl)pentyl] thymidine
([18F]-FMPPT) for PET
PRADIP GHOSH, JURI G. GELOVANI and MIAN M. ALAUDDIN*
Department of Experimental Diagnostic Imaging, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA
Received 6 March 2007; Revised 7 June 2007; Accepted 7 June 2007
Abstract: Radiosyntheses of two N3-substituted thymidine analogues, N3-[(4[18F]fluoromethyl-phenyl)butyl]thymi-
dine ([18F]-FMPBT) and N3-[(4[18F]fluoromethyl-phenyl)pentyl]thymidine ([18F]-FMPPT), are reported. The precursor
compounds 9 and 10 were synthesized in six steps and the standard compounds 13 and 14 were synthesized from
these precursors. For radiosynthesis, compounds 9 and 10 were fluorinated with n-Bu4N[18F] to produce [18F]-11
and [18F]-12, which by acid hydrolysis yielded [18F]-13 and [18F]-14, respectively. The crude products were purified
by high-performance liquid chromatography to obtain [18F]-FMPBT and [18F]-FMPPT. The average decay-corrected
radiochemical yield for [18F]-13 was 15% in five runs, and that for [18F]-14 was 10% in four runs. The radiochemical
purity was >99% and the specific activity was >74 GBq/mmol at the end of synthesis. The synthesis time was 80–
90 min from the end of bombardment. Copyright # 2007 John Wiley & Sons, Ltd.
Keywords: fluorine-18; N3-substituted thymidine; TK1; PET
Introduction
in a
variety of types of cancer.16–18 20-Deoxy-20-
fluoro-5-methyl-1-b-d-ribofuranosyluracil (FMRU) and
5-substituted analogues have also been synthesized
and tested for their ability to visualize tumor prolifera-
tion.19,20 Nucleoside analogues radiolabeled in the
30-position reported to date are 30-[18F]-fluoro-30-deoxy-
thymidine ([18F]-FLT)11 and 30-deoxy-30-[18F]fluoro-
Since the late 1970s, many fluorinated analogues of
pyrimidine nucleosides have been synthesized and
studied for their antitumor and antiviral activities.1–5
Among these compounds, 20-deoxy-20-fluoro-5-methyl-
1-b-d-arabinofuranosyluracil (FMAU) and other 5-sub-
stituted derivatives are known to be phosphorylated by
human and other mammalian nucleoside kinases,
including the thymidine kinases TK1 and TK2, and
are effective against viruses such as herpes simplex
virus (HSV) type 1 and 2, and the hepatitis B-virus.6–8
We and others have been developing and testing several
radiofluorinated pyrimidine nucleoside analogues for
use in imaging tumor proliferation, DNA synthesis, and
5-methyl-1-b-d-xylofuranosyluracil
18F]-FLT is currently under clinical investigation for
([18F]-FMXU).21
[
tumor proliferation by positron emission tomography
(PET).22,23 Although both [18F]-FMAU and [18F]-FLT are
in clinical investigation, their rates of phosphorylation
by TK1 are relatively low compared with that of
thymidine. Therefore, there is a desire for radiotracers,
which are substrates for TK1 with high rates of
phosphorylation and being stable in vivo.
HSV-tk reporter gene expression.6,9–15 11C]- and [18F]-
[
labeled FMAU are currently in clinical trials at several
centers for imaging tumor proliferation or DNA synthesis
During the past decade, a series of N3-substituted
thymidine analogues carrying a carboranyl moiety at
the N3-position, with spacers of various lengths, have
been developed as boron delivery agents for boron
neutron capture therapy.24–28 Some of these N3-sub-
stituted thymidine analogues are phosphorylated by
TK1 at an efficacy of 50–89% of that of thymidine but
are poor substrates for thymidine phosphorylase.26–28
*Correspondence to: Mian M. Alauddin, Department of Experimental
Diagnostic Imaging, UT M. D. Anderson Cancer Center, 1515 Holcombe
Blvd., T8.3895, Box 059, Houston, TX 77030, USA.
E-mail: alauddin@di.mdacc.tmc.edu
Contract/grant sponsor: The University of Texas M. D. Anderson
Cancer Center; contract/grant number: CA016672
Copyright # 2007 John Wiley & Sons, Ltd.

1186 P. GHOSH ET AL.
These favorable characteristics of N3-substituted thy-
midine analogues make them attractive candidates for
development as radiolabeled agents for imaging
proliferative activity. Some simple N3-substituted thy-
midine derivatives with simple substitutions at the
N3-position, e.g. ethyl, n-butyl and acetylenic have also
been shown to be effective substrates for TK1, with
high phosphorylation rates.26,27,29 These favorable
properties of N3-substituted thymidine analogues
prompted us to explore the development of [18F]-labeled
N3-substituted thymidine analogues for use in PET
imaging of TK1 activity. Recently, we and others have
reported a few [18F]-labeled N3-substituted thymidine
analogues with open chains of different lengths at the
N3-position.30,32 We hypothesize that a bulky lipophilic
group, such as a phenyl group, at the end of the tether
may mimic the carboranyl group of the previously
reported compounds, which have been reported to be
substrates for TK1 with 50–89% efficiency relative to
thymidine but do not react with thymidine phosphor-
ylase. Such compounds, radiolabeled with [18F], would
thus be good candidates for PET imaging of cellular
proliferation. Here, we report the synthesis and radio-
synthesis of two new N3-substituted thymidine analo-
gues with chains of different lengths containing
an aromatic substituent at the end of the spacer:
N3-[(4-[18F]-fluoromethyl-phenyl)butyl]thymidine ([18F]-
FMPBT) and N3-[4-([18F]-fluoromethyl-phenyl)pen-
tyl]thymidine ([18F]-FMPPT). Our synthesis produced
these tracers in good yields with high purity and high
specific activity.
Results and Discussion
The scheme for synthesizing the N3-substituted thymi-
dine analogues [18F]-FMPBT and [18F]-FMPPT is shown
in Figure 1. Compound 1 was prepared from thymidine
according to a published method, with 95% yield.32
Compound 2 was prepared by reaction of 4-bromo-
benzyl alcohol with tert-butyldimethylsilyl chloride
(TBDMSCl) in dichloromethane in the presence of
triethylamine. Compound 2 was purified by column
chromatography and isolated in 79% yield. The 1H
NMR spectrum of 2 was consistent with that published
in the literature.33 Compounds 3 and 4 were prepared
by treating 2 with n-butyllithium in dry tetrahydrofur-
an (THF) at ꢀ788C followed by addition of 1-chloro-4-
iodobutane and 1-chloro-5-iodopentane, respectively.
Compounds 3 and 4 were both purified by flash
chromatography on silica gel columns. Yields in this
step were 73% and 61% for 3 and 4, respectively.
But Li
n I
OTBDMS
Cl
OTBDMS
OH
Br
TBDMSCl
n
Br
Cl
3 n = 4
4 n = 5
2
O
O
H3C
NH
H3C
THPO
N
n
OTBDMS
+
O
O
THPO
N
N
DMSO, K2CO3
n
O
O
Cl
OTBDMS
3 n = 4
4 n = 5
5 n = 4
6 n = 5
OTHP
OTHP
i TBAF
1
ii CH2Cl2, Et3N
MsCl
O
N
O
N
O
N
H3C
H3C
n
N
N
n
H3C
HO
MeCN
HCl
N
n
F- THPO
O
O
O
THPO
O
O
X
O
F
F
OTHP
OTHP
OH
13 n = 4
14 n = 5
7
8
9
X = OH, n = 4
X = OH, n = 5
X = Cl, n = 4
11 n = 4
12 n = 5
10 X = Cl, n = 5
Figure 1 Synthetic scheme for N3-[(4-[18F]fluoromethyl-phenyl)butyl]thymidine ([18F]-FMPBT); compound [18F]-13 and N3-[(4-
[
18F]fluoromethyl-phenyl)pentyl]thymidine ([18F]-FMPPT); compound [18F]-14.
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 1185–1191
DOI: 10.1002.jlcr

[
18F]-N3-SUBSTITUTED THYMIDINE ANALOGUES III 1187
Compounds 5 and 6 were prepared by reacting 3 and
4 with thymidine tetrahydropyranyl ether (THP) 1 in
acetone and dimethylsulfoxide (DMSO) (1:1) and po-
compounds. The retention times for both products,
11.5–12.5 min, were quite similar under these solvent
systems. Pure products [18F]-13 and [18F]-14 showed a
single radioactive peak that co-eluted with their cold
standard in analytical HPLC. The radiochemical yields
were 14–17% decay corrected (d.c.) for [18F]-13, with an
average of 15% in five runs, and 8–12% (d.c.) for [18F]-
14, with an average of 10% in four runs. The radio-
chemical purity was >99%, and the specific activity was
>74 GBq/mmol. The synthesis time was 80–90 min from
the end of bombardment (EOB).
tassium carbonate at 508C following
a published
method.24 Purified yields in this step were 69% for 5
and 59% for 6. Compounds 5 and 6 were hydrolyzed by
Bu4NF in THF and purified by flash chromatography to
obtain compound 7 in 66% yield, and 8 in 68% yield.
Compounds 9 and 10 were prepared by reaction of 7
and 8 with methanesulfonyl chloride in dichloro-
methane in the presence of triethylamine and N,N-
dimethyl aminopyridine (DMAP). Although our aim was
to prepare mesylate derivatives, the reaction at room
temperature eventually produced the respective chlor-
oderivatives 9 and 10. The mesylates were quite
unstable to isolate; they were readily converted to the
respective chlorides. Small amount of the mesylate was
isolated in some reactions. Yields in this step were 42%
and 47% for compounds 9 and 10, respectively.
Experimental
Reagents and instrumentation
All reagents and solvents were purchased from Aldrich
Chemical Co. (Milwaukee, WI), and used without
further purification. Solid-phase extraction cartridges
(silica gel, 900 mg) were purchased from Alltech
Associates (Deerfield, IL). n-Bu4NHCO3 solution was
prepared by bubbling CO2 gas into a solution of n-
Bu4NOH (1% by wt) to pH 7.0.
Compounds 11 and 12 were prepared by reacting 9
and 10 with n-Bu4NF in dry acetonitrile at 908C for
25 min. Yields in this step were 31% and 26% for 11
and 12, respectively. These compounds were charac-
terized by 19F NMR spectroscopy in addition to 1H NMR
and mass spectrometry. The 19F NMR spectra (coupled)
of compounds 11 and 12 showed multiplets centered at
ꢀ204.08 ppm and ꢀ203.92 ppm, respectively.
Compounds 13 and 14 were prepared by acid
hydrolysis of compounds 11 and 12, respectively,
followed by purification with high-performance liquid
chromatography (HPLC). Yields in this step were 70% for
13 and 66% for 14. These compounds were also
characterized by 1H and 19F NMR spectroscopy and by
high-resolution mass spectrometry. The 1H NMR spec-
trum of compound 13 showed a peak (d) at 5.35ppm
with J ¼ 48:3 Hz, a typical geminal coupling constant
between fluorine and hydrogen. Similarly, compound 14
Thin-layer chromatography (TLC) was performed on
pre-coated Kieselgel 60 F254 (Merck) glass plates. Proton
and 19F NMR spectra were recorded on a Brucker
300 MHz spectrometer with tetramethylsilane used as an
internal reference and hexafluorobenzene as an external
reference at The University of Texas M. D. Anderson
Cancer Center. Low-resolution mass spectral analysis was
performed in house with an HPLC-mass spectrometer
(Applied Biosystems Q-Trap LC/MS/MS). High-resolution
mass spectra were obtained on a Bruker BioTOF II mass
spectrometer at the University of Minnesota by using
electrospray ionization (ESI) technique.
HPLC was performed with an 1100 series pump
(Agilent, Germany), with a built-in UV detector oper-
ated at 254 nm, and a radioactivity detector with single-
channel analyzer (Bioscan, Washington, DC) with a
semi-preparative C18 reverse-phase column (Alltech,
Econosil, 10 ꢁ 250 mm, Deerfield, IL) and an analytical
C18 column (Rainin, Microsorb-MV, 4.6 ꢁ 250 mm,
Emeryville, CA). An acetonitrile/water (MeCN/H2O)
solvent system (35% MeCN/H2O for FMPBT and 40%
MeCN for FMPPT) was used for purification of the
radiolabeled products at a flow of 4 mL/min. Quality
control analyses were performed on an analytical HPLC
with the same solvents at a flow of 1 mL/min.
showed
a peak at 5.36ppm (d) with the similar
characteristic F–H geminal coupling constant of 48.0 Hz.
Radiolabeled compounds 13 and 14 were prepared
by radiofluorination of precursors 9 and 10 separately
with n-Bu4N[18F] followed by acid hydrolysis and HPLC
purification. After radiofluorination of the precursors,
the crude reaction mixture was passed through a silica
gel cartridge (900 mg, Alltech), and the crude product
was eluted with ethyl acetate. The recovered [18F]-
labeled intermediate compounds 11 and 12 were
readily hydrolyzed with acid to remove the protecting
groups, and the desired labeled N3-substituted thymi-
dine derivatives [18F]-13 ([18F]-FMPBT) and [18F]-14
([18F]-FMPPT) were isolated by HPLC purification. Two
different HPLC solvent systems were required, 35%
MeCN in water for 13 and 40% MeCN in water for 14,
because of the difference in lipophilicity between the
Preparation of 30,50-O-Bis-tetrahydropyranyl-thymi-
dine: 1
30,50-O-bis-tetrahydropyranyl-thymidine
pared according to a published method.32
1 was pre-
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 1185–1191
DOI: 10.1002.jlcr

1188 P. GHOSH ET AL.
(quint, 2H, C4H), 1.46 (m, 2H, C3H), 0.96 (s, 9H, tert-
but), 0.12 (s, 6H, CH3). MS: M þ NH4, calculated
344.18, found 344.36.
Preparation of 4-bromobenzyl tert-butyldimethylsilyl
ether: 2
4-Bromobenzylalcohol (0.5 g, 2.67 mmol) was dissolved
in dichloromethane (15 mL) in a dry flask under argon;
triethylamine (1.9 mL, 13.35 mmol) was added, fol-
lowed by addition of DMAP (98 mg, 0.80 mmol).
TBDMSCl (0.605 g, 4.0 mmol) was added and the
reaction mixture was stirred for 3 h at room tempera-
ture, when TLC showed that no starting material
remained. The solvent was evaporated under vacuum,
the residue was dissolved in CH2Cl2 (60 mL), and the
solution was washed with H2O (3 ꢁ 60 mL). The organic
phase was dried (MgSO4), evaporated to dryness and
the crude product was purified on a silica gel column
by using 10% ethyl acetate in hexane as eluent. This
afforded product 2 as a colorless oil (630 mg, 79%
yield). 1H NMR (CDCl3) d: 7.48 (d, 2H, J ¼ 8:4 Hz,
aromatic), 7.22 (d, 2H, J ¼ 8:7 Hz, aromatic), 4.71
(s, 2H, benzylic H), 0.97 (s, 9H, tert-but), 0.12 (s, 6H,
CH3). MS: M þ 1, calculated 301.10, found 301.24.
Preparation of 30,50-O-bis-tetrahydropyranyl-N3-[4-
(4-tert-butyl-dimethylsilyl-benzyl)butyl]thymidine
and 30,50-O-bis-tetrahydropyranyl-N3-[5-(4-tert-bu-
tyl-dimethylsilyl-benzyl)pentyl]thymidine: 5, 6
Compounds 5 and 6 were prepared by the same
methodology; a representative procedure is described
below. Compound 3 (0.400 g, 1.28 mmol) was dissolved
in a mixture of acetone and DMSO (20 mL, 1:1) under
argon. Potassium carbonate (0.634 g, 6.4 mmol) and
thymidine THP ether
1 (0.525 g, 1.28 mmol) were
added, and the reaction mixture was heated with
stirring at 508C for 27 h, when TLC showed that no
significant starting material remained. The reaction
mixture was filtered and evaporated under vacuum, and
the residue was dissolved in CH2Cl2 (60 mL). The solution
was washed with H2O (3ꢁ 60 mL). The organic phase was
dried (MgSO4), evaporated to dryness, and purified on a
silica gel column using 25% acetone in hexane. The pure
compound 5 (605 mg) was obtained in 69% yield.
Compound 6 was obtained in 59% yield. 1H NMR 5
(CDCl3) d: 7.68–7.52 (4s, 1H, C6H), 7.23 (d, 2H,
J ¼ 7:8 Hz, aromatic), 7.14 (d, 2H, J ¼ 8:1 Hz, aromatic),
6.44–6.33 (m, 1H, 10H), 4.78–3.48 (m, 14H, benzylic H,
N3–C1H, THP and 30–50 H), 2.70–2.60 (m, 2H, N3–C4H),
2.58–2.01 (m, 2H, 20H), 1.94 and 1.92 (2s, 3H, CH3),
1.89–1.77 (m, 4H, N3–C2,3H), 1.72–1.49 (m, 12H, THP),
0.95 (s, 9H, tert-but), 0.11(s, 6H, CH3). MS: M þ 1,
calculated 687.95, found 687.83.
1H NMR 6 (CDCl3) d: 7.65–7.52 (4s, 1H, C6H), 7.23 (d,
2H, J ¼ 7:5 Hz, aromatic), 7.14 (d, 2H, J ¼ 8:1 Hz,
aromatic), 6.44–6.33 (m, 1H, 10H), 4.78–3.49 (m, 14H,
benzylic H, N3–C1H, THP and 30–50H), 2.65–2.55 (m,
2H, N3–C5H), 2.53–2.00 (m, 2H, 20H), 1.96 and 1.93
(2s, 3H, CH3), 1.89–1.77 (m, 4H, N3–C2,4H), 1.71–1.51
(m, 12H, THP), 1.48–1.38 (m, 2H, N3–C3H), 0.95 (s, 9H,
tert-but), 0.10 (s, 6H, CH3). MS: M þ NH4, calculated
718.41, found 718.93.
Preparation of 1-chloro-4-(4-tert-butyl-dimethylsilyl-
benzyl)butane
and
1-chloro-5-(4-tert-butyl-di
methylsilyl-benzyl)pentane: 3, 4
Compounds 3 and 4 were prepared with the same
method; a representative procedure is described below.
A solution of compound 2 (0.5 g, 1.67 mmol) in dry THF
(7 mL) was cooled to ꢀ788C for 15 min under argon.
n-Butyllithium (1.6 M in hexanes, 1.7 mL, 2.67 mmol)
was slowly added using a syringe over a period of 5 min.
After the mixture was stirred at the same temperature
for 3 min, a solution of 1-chloro-4-iodobutane (0.27 mL,
2.17 mmol) in THF (0.5 mL) was added dropwise using
a syringe over 5 min. The reaction mixture was stirred
at ꢀ788C for 20 min, warmed to room temperature, and
continued stirring for another 20 min, and then
quenched with H2O (50 mL). The solvent was evaporated
under vacuum; the residue was purified on a silica gel
column using 5% acetone in hexane as eluent. The
pure compound 3 (380 mg) was obtained in 73% yield.
Compound 4 was obtained in 61% yield. 1H NMR 3
(CDCl3) d: 7.23 (d, 2H, J ¼ 8:4 Hz, aromatic), 7.16 (d,
2H, J ¼ 8:1 Hz, aromatic), 4.73 (s, 2H, benzylic H), 3.56
(t, 2H, J ¼ 4:8 Hz, C1H), 2.65 (t, 2H, J ¼ 6:3 Hz, C4H),
1.80 (t, 4H, J ¼ 3:0 Hz, C2,3H), 0.95 (s, 9H, tert-but),
0.11 (s, 6H, CH3). MS: M þ NH4, calculated 330.23,
found 330.30.
Preparation of 30,50-O-bis-tetrahydropyranyl-N3-[(4-
hydroxybenzyl)butyl]thymidine and 30,50-O-bis-tet-
rahydropyranyl-N3-[(4-hydroxybenzyl)pentyl]thymi-
dine: 7, 8
Compounds 7 and 8 were prepared by the same
method. Compound 5 (800 mg, 1.16 mmol) was taken
in a round-bottom flask and dissolved in THF (15 mL).
Bu4NF solution (1 M, 2.33 mL) was added to the above
solution and stirred for 2 h at room temperature, when
TLC showed that no starting material remained.
1H NMR
4 (CDCl3) d: 7.26 (d, 2H, J ¼ 8:4 Hz,
aromatic), 7.16 (d, 2H, J ¼ 8:1 Hz, aromatic), 4.73
(s, 2H, benzylic H), 3.54 (t, 2H, J ¼ 6:9 Hz, C1H), 2.63
(t, 2H, J ¼ 7:5 Hz, C5H), 1.82 (quint, 2H, C2H), 1.66
Copyright # 2007 John Wiley & Sons, Ltd.
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DOI: 10.1002.jlcr

[
18F]-N3-SUBSTITUTED THYMIDINE ANALOGUES III 1189
Solvent was evaporated and the residue was purified on
a silica gel column using 30% acetone in hexane to
isolate 7 (440 mg) in 66% yield. Compound 8 was
obtained in 68% yield. 1H NMR 7 (CDCl3) d: 7.66–7.52
(4s, 1H, C6H), 7.29 (d, 2H, J ¼ 7:8 Hz, aromatic), 7.17
(d, 2H, J ¼ 8:1 Hz, aromatic), 6.43–6.32 (m, 1H, 10H),
4.78–3.51 (m, 14H, benzylic H, N3–C1H, THP and
30–50H), 2.66 (t, 2H, N3–C4H), 2.58–2.01 (m, 2H, 20H),
1.95 and 1.92 (2s, 3H, CH3), 1.90–1.76 (m, 4H, N3–
(2s, 3H, CH3), 1.89–1.78 (m, 4H, N3–C2,4H), 1.73–1.50
(m, 12H, THP), 1.48–1.30 (m, 2H, N3–C3H). High-
resolution MS: M þ Na, calculated 627.2808, found
627.2819.
Preparation of 30,50-O-bis-tetrahydropyranyl-N3-
[(4-fluoromethyl-phenyl)butyl]thymidine and 30,50-O-
bis-tetrahydropyranyl-N3-[(4-fluoromethyl-phenyl)-
pentyl]thymidine: 11, 12
C
2,3H), 1.72–1.51 (m, 12H, THP). MS: M þ 1, calculated
573.69, found 573.74.
As the fluorination reactions of both precursor com-
1H NMR 8 (CDCl3) d: 7.67–7.51 (4s, 1H, C6H), 7.27 (d,
2H, J ¼ 7:8 Hz, aromatic), 7.16 (d, 2H, J ¼ 7:8 Hz,
aromatic), 6.43–6.32 (m, 1H, 10H), 4.77–3.48 (m, 14H,
benzylic H, N3–C1H, THP and 30–50H), 2.68–2.58 (m,
2H, N3–C5H), 2.49–2.23 (m, 2H, 20H), 1.95 and 1.92
(2s, 3H, CH3), 1.90–1.76 (m, 4H, N3–C2,4H), 1.69–1.51
(m, 12H, THP) 1.49–1.35 (m, 2H, N3–C3H). MS: M þ 1,
calculated 587.30, found 587.61.
pounds 9 and 10 were similar, a representative
procedure is described here. Compound 9 (40 mg,
0.07 mmol) was dissolved in dry MeCN (1.0 mL) in a
sealed v-vial under argon. To the above solution, n-
Bu4NF (1 M, 50 mL) was added and the mixture was
heated at 908C for 25 min in a heating block. The
reaction mixture was cooled to room temperature and
the solvent was evaporated under a stream of air. The
residue was purified on a short silica gel column using
25% acetone in hexane as the eluent. Pure compound
11 (12 mg) was obtained in 31% yield. Compound 12
was obtained in 26% yield. 1H NMR 11 (CDCl3) d: 7.64–
7.53 (4s, 1H, C6H), 7.30 (d, 2H, J ¼ 8:1 Hz, aromatic),
7.22 (d, 2H, J ¼ 8:4 Hz, aromatic), 6.44–6.33 (m, 1H,
10H), 5.35 (d, 2H, J ¼ 48:0 Hz, benzylic H), 4.77–3.50
(m, 12H, N3–C1H, THP and 30–50H), 2.75–2.60 (m, 2H,
N3–C4H), 2.58–2.00 (m, 2H, 20H), 1.96 and 1.92 (2s,
3H, CH3), 1.87–1.75 (m, 4H, N3–C2,3H), 1.71–1.53 (m,
12H, THP). 19F NMR (CDCl3) (d): ꢀ204.08 (t, J ¼ 51 Hz,
coupled). MS: M þ 1, calculated 575.72, found 575.65.
1H NMR 12 (CDCl3) d: 7.65–7.52 (4s, 1H, C6H), 7.30
(d, 2H, J ¼ 8:1 Hz, aromatic), 7.17 (d, 2H, J ¼ 8:4 Hz,
aromatic), 6.44–6.33 (m, 1H, 10H), 5.35 (d, 2H,
J ¼ 48:3 Hz, benzylic H), 4.78–3.49 (m, 12H, N3–C1H,
THP and 30–50H), 2.68–2.59 (m, 2H, N3–C5H), 2.57–2.00
(m, 2H, 20H), 1.96 and 1.92 (2s, 3H, CH3), 1.90–1.78
(m, 4H, N3–C2,4H), 1.74–1.50 (m, 12H, THP), 1.48–1.36
(m, 2H, N3–C3H). 19F NMR (d): ꢀ203.92 (t, J ¼ 51 Hz,
coupled). MS: M þ 1, calculated 589.34, found 589.60.
Preparation of 30,50-O-bis-tetrahydropyranyl-N3-[(4-
chloro-benzyl)butyl]thymidine and 30,50-O-bis-tetra-
hydropyranyl-N3-[(4-chloro-benzyl)pentyl]thymidine:
9, 10
Compounds 9 and 10 were prepared by the same
method. Compound 7 (0.650 g, 1.13 mmol) was dis-
solved in dichloromethane (15 mL) under argon, and
triethylamine (0.8 mL, 5.65 mmol) was added, followed
by addition of DMAP (42 mg, 0.33 mmol). The reaction
mixture was cooled to 08C, and then methane sulfonyl
chloride (265 mL, 3.40 mmol) was added. The reaction
mixture was warmed to room temperature and stirred
for 2 h, when TLC showed that no starting material
remained. The solvent was evaporated under vacuum,
the residue was dissolved in CH2Cl2 (60 mL), and the
solution was washed with H2O (3 ꢁ 60 mL). The organic
phase was dried (MgSO4), evaporated to dryness, and
purified on a silica gel column. Appropriate fractions
were combined and evaporated to produce 280 mg of
the compound 9 in 47% yield. Compound 10 was
obtained in 34% yield. 1H NMR 9 (CDCl3) d: 7.65–7.53
(4s, 1H, C6H), 7.30 (d, 2H, J ¼ 8:1 Hz, aromatic), 7.18
(d, 2H, J ¼ 7:8 Hz, aromatic), 6.44–6.33 (m, 1H, 10H),
4.78–3.50 (m, 14H, benzylic H, N3–C1H, THP and 30–
50H), 2.66 (t, J ¼ 6:9 Hz, 2H, N3–C4H), 2.48–2.01 (m,
2H, 20H), 1.96 and 1.92 (2s, CH3), 1.89–1.76 (m, 4H,
N3–C2,3H), 1.73–1.59 (m, 12H, THP). High-resolution
MS: M þ Na, calculated 613.2651, found 613.2658.
1H NMR 10 (CDCl3) d: 7.63–7.52 (4s, 1H, C6H), 7.28
(d, 2H, J ¼ 8:1 Hz, aromatic), 7.16 (d, 2H, J ¼ 7:8 Hz,
aromatic), 6.43–6.32 (m, 1H, 10H), 4.77–3.48 (m, 14H,
benzylic H, N3–C1H, THP and 30–50H), 2.67–2.55 (m,
2H, N3–C5H), 2.29–2.00 (m, 2H, 20H), 1.96 and 1.92
Preparation of N3-[(4-fluoromethyl-phenyl)butyl]thy-
midine and N3-[(4-fluoromethyl-phenyl) pentyl]
thymidine: 13, 14
Compounds 13 and 14 were prepared by the same
method; a representative procedure is described here
for 13. Compound 11 (15 mg, 0.03 mmol) was placed in
a small flask and dissolved in MeOH (1 mL). Hydro-
chloric acid (1 M in MeOH, 0.1 mL) was added to the
above solution and the reaction mixture was refluxed
for 5 min at 808C. The reaction mixture was cooled and
the solvent evaporated. The residue was purified on a
short silica gel column using 40% acetone in hexane as
Copyright # 2007 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2007; 50: 1185–1191
DOI: 10.1002.jlcr

1190 P. GHOSH ET AL.
the eluent. The pure compound 13 (7.4 mg) was
obtained in 70% yield. Compound 14 was obtained in
66% yield.
Conclusion
We have synthesized two new radiolabeled N3-substi-
tuted analogues of thymidine, N3-[(4-[18F]fluoromethyl-
phenyl)butyl] thymidine ([18F]-FMPBT) and N3-
1H NMR 13 (CDCl3) d: 7.32 (s, 1H, C6H), 7.30 (d, 2H,
J ¼ 8:1 Hz, aromatic), 7.22 (d, 2H, J ¼ 8:1 Hz, aro-
matic), 6.18 (t, 1H, J ¼ 6:9 Hz, 10H), 5.35 (d, 2H,
JHF ¼ 48:3 Hz, benzylic H), 4.63–4.58 (m, 1H, 30H),
4.03–3.82 (m, 5H, N3–C1H, 40 and 50H), 2.67 (bs, 2H,
N3–C4H), 2.51–2.26 (m 2H, 20H), 1.94 (s, 3H, CH3),
1.72–1.64 (m, 4H, N3–C2,3H). 19F NMR (d): ꢀ203.92 (t,
J ¼ 51 Hz; coupled). High-resolution MS: M þ Na, cal-
culated 429.1796, found 429.1802.
[(4-[18F]fluoromethyl-phenyl)pentyl]thymidine
([18F]-
FMPPT) in good yields, with high purity and high specific
activity. These compounds may be useful agents for PET
imaging of tumor proliferation and DNA synthesis.
Acknowledgements
This work was supported by start-up funds from The
University of Texas M. D. Anderson Cancer Center.
NMR spectra were obtained at the NMR facility of M. D.
Anderson Cancer Center supported by CCSG core
Grant CA016672.
1H NMR 14 (CDCl3) d: 7.29 (s, 1H, C6H), 7.31 (d, 2H,
J ¼ 8:4 Hz, aromatic), 7.21 (d, 2H, J ¼ 8:1 Hz; aro-
matic), 6.16 (t, 1H, J ¼ 7:2 Hz, 10H), 5.36 (d, 2H,
JHF ¼ 48:0 Hz, benzylic H), 4.64–4.62 (m, 1H, 30H),
4.04–3.83 (m, 5H, N3–C1H, 40 and 50H), 2.64 (t, 2H,
J ¼ 6:9 Hz, N3–C5H), 2.54–2.44 (m, 2H, 20H), 1.94 (s,
3H, CH3), 1.74–1.60 (m, 4H, N3–C2,4H), 1.45–1.34 (m,
2H, N3–C5H). 19F NMR (d): ꢀ203.73 (t, J ¼ 51 Hz,
coupled). High-resolution MS: M þ Na, calculated
443.1953, found 443.1960.
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