Synthesis of [18F]-labeled N-3(substituted) thymidine analogues: N-3([18F]fluorobutyl) thymidine ([18F]-FBT) and N-3([18F]fluoropentyl) thymidine ([18F]-FPT) for PET

Article abstract of DOI:10.1002/jlcr.1127

Syntheses of N-3(substituted) analogues of thymidine, N-3([ ¹⁸F]fluorobutyl)thymidine ([¹⁸F]-FBT) and N-3([ ¹⁸F]fluoropentyl)thymidine ([¹⁸F]-FPT) are reported. 1,4-Butane diol and 1,5 pentane diol were converte

Full text of DOI:10.1002/jlcr.1127

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS
J Label Compd Radiopharm 2006; 49: 1079–1088.
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jlcr.1127
Research Article
Synthesis of [18F]-labeled N-3(substituted) thymidine
analogues: N-3([18F]fluorobutyl) thymidine ([18F]-FBT)
and N-3([18F]fluoropentyl) thymidine ([18F]-FPT) for
PET
Mian M. Alauddin*, Pradip Ghosh and Juri G. Gelovani
Department of Experimental Diagnostic Imaging, University of Texas MD Anderson
Cancer Center, Houston, TX, USA
Summary
Syntheses of N-3(substituted) analogues of thymidine, N-3([18F]fluorobutyl)thymidine
([18F]-FBT) and N-3([18F]fluoropentyl)thymidine ([18F]-FPT) are reported. 1,4-Butane
diol and 1,5 pentane diol were converted to their tosyl derivatives 2 and 3 followed by
conversion to benzoate esters 4 and 5, respectively. Protected thymidine 1 was coupled
separately with 4 and 5 to produce 6 and 7, which were hydrolyzed to 8 and 9, then
converted to their mesylates 10 and 11, respectively. Compounds 10 and 11 were
fluorinated with n-Bu4N[18F] to produce 12 and 13, which by acid hydrolysis yielded
14 and 15, respectively. The crude products were purified by HPLC to obtain [18F]-
FBT and [18F]-FPT. The radiochemical yields were 58–65% decay corrected (d.c.) for
14 and 46–57% (d.c.) for 15 with an average of 56% in three runs per compound.
Radiochemical purity was >99% and specific activity was >74 GBq/mmol at the end
of synthesis (EOS). The synthesis time was 65–75 min from the end of bombardment
(EOB). Copyright # 2006 John Wiley & Sons, Ltd.
Received 2 June 2006; Revised 3 August 2006; Accepted 4 August 2006
Key Words: fluorine-18; thymidine; TK1; PET
*Correspondence to: Mian M. Alauddin, 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 MD Anderson Cancer Center
Contract/grant sponsor: CCSG; contract/grant number: CA016672
Copyright # 2006 John Wiley & Sons, Ltd.

1080
M. M. ALAUDDIN ET AL.
Introduction
We and others have been developing and testing several radiofluorinated
pyrimidine nucleoside analogues as potential agents for imaging tumor
proliferative activity or HSV-tk reporter gene expression.1ꢀ8 Initially, many
fluorinated analogues of pyrimidine nucleosides have been synthesized and
studied as potential antitumor and antiviral agents.9ꢀ13 Among these,
20-deoxy-20-fluoro-5-methyl-1-b-D-arabinofuranosyl-uracil (FMAU) and
other 5-substituted derivatives are known to be phosphorylated by human
and other mammalian nucleoside kinases including thymidine kinase TK1 and
TK2, as well as viral kinase such as herpes simplex virus (HSV) type 1 and 2,
and hepatitis B-virus.14,15 In particular, 11C and 18F radiolabeled FMAU are
currently undergoing clinical studies in multiple centers for imaging tumor
proliferation in a variety of cancer types16,17 and DNA synthesis.18 Also,
20-deoxy-20-fluoro-5-methyl-1-b-D-ribofuranosyl-uracil (FMRU) and 5-sub-
stituted analogues have been synthesized and tested as potential imaging
agents for tumor proliferation.19,20 The nucleoside analogues radiolabeled in
the 30-position reported to date are 30-[18F]-fluoro-30-deoxy-thymidine ([18F]-
FLT)4 and 30-deoxy-30-[18F]fluoro-5-methyl-1-b-D-xylo-furanosyluracil ([18F]-
FMXU).21 [18F]-FLT is currently under clinical investigation as a PET
imaging agent for tumor proliferation.22,23 Although both [18F]-FMAU and
[18F]-FLT are in clinical investigation, their phosphorylation rates by TK1 are
relatively low compared to that of thymidine.
Recently a series of N-3(substituted)thymidine analogues carrying a
carborane moiety at the N-3-position with various spacer length have
drawn attention in boron neutron capture therapy.24–28 It has been reported
that some of the N-3(substituted)thymidine analogues are phosphorylated
by TK1 with 50–89% efficiency as compared to thymidine, while being
poor substrates for thymidine phosphorylase.25–27 Furthermore, some simple
N-3(substituted)thymidine derivatives such as ethyl, n-butyl, acetylenic, etc.
have also been shown to be substrates of TK1 with high phosphorylation
rates.25,26,29 This prompted us to synthesize 18F-labeled N-3(substituted)
thymidine analogues for PET imaging of TK1 activity and DNA synthesis
during tumor proliferation. Here we report synthesis and radiosynthesis of
two N-3(substituted)thymidine analogues, N-3([18F]-fluorobutyl)thymidine
([18F]-FBT) and N-3([18F]-fluoropentyl)thymidine ([18F]-FPT) in high yield,
high specific activity and purity.
Results and discussion
Figure 1 represents the scheme for synthesis of N-3(substituted)thymidine
analogues, [18F]-FBT and [18F]-FPT. Compound 1 was prepared from
thymidine following a literature method in 95% yield.30 Compounds 2 and
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

[
18F]-N-3 (SUBSTITUTED) THYMIDINE ANALOGUES FOR PET
1081
CH2Cl2, Et3N
(BzO)2O
CH2Cl2, Et3N
TsCl
n
n
OH
OH
HO
TsO
nOBz
TsO
2 n = 4
3 n = 5
4 n = 4
5 n = 5
O
N
O
H3C
H3C
NH
O
n
OBz
N
DMSO, K2CO3
THPO
nOBz
TsO
+
O
N
THPO
O
O
4 n = 4
5 n = 5
OTHP
OTHP
6 n = 4
7 n = 5
1
i NaOH
ii CH2Cl2, Et3N
MsCl
O
O
N
O
N
N
H3C
HO
H3C
H3C
n
F
N
n
n
OR
F
N
MeOH
HCl
MeCN
F- THPO
O
O
O
N
THPO
O
O
O
OH
OTHP
OTHP
8 R=H, n = 4
9 R=H, n = 5
10 R=Ms, n = 4
11 R=Ms, n = 5
12 n = 4
13 n = 5
14 n = 4
15 n = 5
Figure 1. Synthetic scheme of N-3([18F]fluorobutyl)thymidine ([18F]-FBT) and
N-3([18F]fluoropentyl)thymidine ([18F]-FPT)
3 were prepared following literature methods,31,32 in 33 and 40% yields,
respectively.
Compounds 4 and 5 were prepared from 2 and 3 by reaction with benzoic
anhydride in dichloromethane in the presence of triethylamine at 508C. Yields
in this step were 63 and 76% for 4 and 5, respectively.
Compounds 6 and 7 were prepared by reaction of 4 and 5 with thymidine
THP ether 1 following a literature method.28 Yields in this step were 80% for 6
and 85% for 7, respectively. Basic hydrolysis of the benzoate esters 6 and 7
produced 8 and 9 in 92% and 95% yields, respectively.
Compounds 10 and 11 were prepared by reaction of 8 and 9 with
methanesulfonyl chloride in dichloromethane in the presence of triethylamine
and N,N-dimethyl aminopyridine (DMAP) at 08C. Cooling the reaction
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

1082
M. M. ALAUDDIN ET AL.
mixture to 08C was necessary to obtain high yields. Yields in this step were 86
and 91% for compounds 10 and 11, respectively.
Compounds 12 and 13 were prepared by the reaction of 10 and 11 with n-
Bu4NF in dry acetonitrile at 908C for 25 min. Yields in this step were 70 and
76% for compounds 12 and 13, respectively. These compounds were
1
characterized by 19F NMR spectroscopy in addition to H NMR, and high
resolution mass spectrometry. 19F NMR spectra (coupled) showed multiplets
centered at ꢀ218.26 and ꢀ218.30 ppm for 12 and 13, respectively.
Compounds 14 and 15 were prepared by acid hydrolysis of the compounds
12 and 13, respectively, followed by HPLC purification, and characterized by
1H and 19F NMR spectroscopy, and high-resolution mass spectrometry.
1H NMR spectrum of 14 showed a peak (dt) at 4.48 ppm with J=47.4 Hz,
a typical geminal coupling constant between fluorine and hydrogen. Similarly,
compound 15 showed a peak at 4.46 ppm (dt) with the similar characteristic
F-H geminal coupling constant 47.1Hz. Interestingly, the C6 proton and the
methyl (CH3) protons showed as doublets with small coupling constants in the
range of 0.9 to 1.2 Hz for both compounds. 19F NMR spectrum (coupled) of 14
and 15 showed multiplets centered at ꢀ218.30 and ꢀ218.36 ppm, respectively,
due to long range coupling between fluorine and hydrogen in addition to their
1
geminal coupling, which was also observed in H NMR spectra.
Radiolabeled compounds 14 and 15 were prepared by fluorination of the
precursors 10 and 11 separately with n-Bu4N18F followed by acid hydrolysis and
HPLC purification. n-Bu4N18F was prepared in situ from n-Bu4NHCO3 and
aqueous H18F using 0.40ml (1% solution, ꢁ7 mmol) of n-Bu4NHCO3 to elute
the activity from the ion exchange cartridge.1,2 Following 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 12 and 13 were readily
hydrolyzed with acid to remove the protecting groups, and the desired labeled
N-3(substituted)thymidine derivatives 14 and 15 isolated by HPLC purification.
Two different HPLC solvent systems, 25 and 30% MeCN in water for 14 and
15, respectively, were required due to the difference in lipophilicity between the
compounds. The radiochemical yields were 58–65% (d.c.) for 14 and 46–57%
(d.c.) for 15 with an average of 56%, in three runs per compound. The
radiochemical purity was >99% with specific activity >74GBq/mmol. The
synthesis time was 65–75 min from the end of bombardment (EOB).
Experimental
Reagents and instrumentation
All reagents and solvents were purchased from Aldrich Chemical Co.
(Milwaukee, WI), and used without further purification. Solid phase
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

[
18F]-N-3 (SUBSTITUTED) THYMIDINE ANALOGUES FOR PET
1083
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.
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 using tetramethylsilane as an internal
reference and hexafluorobenzene as an external reference, respectively, at The
University of Texas MD Anderson Cancer Center. High resolution mass
spectra were obtained on a Bruker BioTOF II mass spectrometer at the
University of Minnesota using electrospray ionization (ESI) technique.
High performance liquid chromatography (HPLC) was performed on a
1100 series pump (Agilent, Germany), with built in UV detector operated at
254 nm, and a radioactivity detector with single-channel analyzer (Bioscan,
Washington DC) using a semi-preparative C18 reverse phase column (Alltech,
Econosil, 10 ꢂ 250 mm, Deerfield, IL) and an analytical C18 column (Rainin,
Microsorb-MV, 4.6 ꢂ 250 mm, Emeryville, CA). A acetonitrile/water (MeCN/
H2O) solvent system (25% MeCN for FBT and 30% MeCN for FPT) was
used for purification of the radiolabeled products. For quality control analysis
on analytical HPLC, 20% MeCN and 25% MeCN were used for FBT and
FPT, respectively.
Preparation of 1-p-toluenesulfonyl-4-benzoyl-n-butane and 1-p-toluenesulfonyl-
5-benzoyl-n-pentane-: 4; 5
Both compounds 4 and 5 were prepared using the same methodology, a
representative procedure is described below. Compound 2 (0.375 g, 1.5 mmol)
was dissolved in dichloromethane (7 ml) under argon. Triethylamine (1.0 ml,
7.7 mmol) was added followed by addition of benzoic anhydride (0.45 mg,
2.0 mmol). The reaction mixture was refluxed at 508C for 1.2 h when TLC
showed no starting material remained. Solvent was evaporated under vacuum,
the residue was re-dissolved in CH2Cl2 (50 ml) and washed with H2O
(3 ꢂ 50 ml). The organic phase was dried (MgSO4), evaporated to dryness
and purified by flash column chromatography using 20% acetone in hexane as
eluent. The pure compound 4, 332 mg was obtained in 63% yield. Compound
1
5 was obtained in 76% yield. H NMR 4 (CDCl3) d: 8.02 (d, 2 H, J=7.2 Hz,
aromatic), 7.81 (d, 2 H, J=8.1 Hz, aromatic), 7.64–7.55 (m, 1 H, aromatic),
7.48 (d, 2 H, J=7.2 Hz, aromatic), 7.35 (d, 2 H, J=8.1 Hz, aromatic), 4.30 (t,
2 H, J=6.0 Hz, C4H), 4.12 (t, 2 H, J=6 Hz, C1H), 2.45 (s, 3 H, CH3), 1.84
1
(quint, 4 H, C2ꢀ3H). MS: M+1, 349.50. H NMR 5 (CDCl3) d: 8.04 (d, 2 H,
J=8.4 Hz, aromatic), 7.80 (d, 2 H, J=8.4 Hz, aromatic), 7.61–7.55 (m, 1 H,
aromatic), 7.48–7.43 (m, 2 H, aromatic), 7.34 (d, 2 H, J=8.4 Hz, aromatic),
4.29 (t, 2 H, J=6.3 Hz, C5H), 4.07 (t, 2 H, J=12.6 Hz, C1H), 2.44 (s, 3 H,
CH3), 1.76 (quint, 4 H, C2,4H), 1.52 (quint, 2 H, C3H). MS: M+1, 363.30.
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

1084
M. M. ALAUDDIN ET AL.
Preparation of 30,5-0-O-bis-tetrahydropyranyl-N-3(4-benzoyl-n-butyl)thymidine
and 30,50-O-bis-tetrahydropyranyl-N-3(5-benzoyl-n-pentyl)thymidine: 6; 7
Both compounds 6 and 7 were prepared using the same methodology, a
representative procedure is described below. Compound 4 (0.10 g, 0.29 mmol)
was dissolved in acetone (3 ml) and DMSO (3 ml) (1:1) under argon.
Potassium carbonate (0.144 g, 1.45 mmol) and thymidine THP ether 1
(0.119 g, 0.29 mmol) were added and the reaction mixture heated with stirring
at 508C for 30 h when TLC showed no significant starting material remained.
The reaction mixture was filtered and evaporated under vacuum, and the
residue was dissolved in CH2Cl2 (30 ml). The solution was washed with H2O
(3 ꢂ 30 ml). The organic phase was dried (MgSO4), evaporated to dryness and
purified on a silica gel column using 20% acetone in hexane. The pure
compound 6 (136 mg) was obtained in 80% yield. Compound 7 was obtained
1
in 85% yield. H NMR 6 (CDCl3) d: 8.06–8.03 (m, 2 H, aromatic), 7.66–7.50
(m, 2 H, C6H and aromatic), 7.46–7.38 (m, 2 H, aromatic), 6.41–6.37 (m, 1 H,
10H), 4.75–3.52 (m, 14 H, N-3C1,4H, THP and 30-50H), 2.59–2.0 (m, 2 H, 20H),
1.96, 1.95, 1.93, 1.92 (4 s, 3 H, CH3), 1.90–1.48 (m, 16 H, N-3C2,3H and THP).
1
High resolution MS: M+Na, calculated 609.2783; found 609.2799. H NMR
7 (CDCl3) d: 8.05 (d, 2 H, J=8.1 Hz, aromatic), 7.65–7.51 (m, 2 H, C6H and
aromatic), 7.47–7.44 (m, 2 H, aromatic), 6.41–6.37 (m, 1 H, 10H), 4.78–3.48 (m,
14 H, N-3C1,5H, THP and 30-50H), 2.59–2.00 (m, 2 H, 20H) 1.96, 1.95, 1.93,
1.92 (4 s, 3 H, CH3), 1.98–1.48 (m, 18 H, N-3C2ꢀ4H and THP). MS: M+1,
601.60.
Preparation of 30,50-O-bis-tetrahydropyranyl-N-3(4-hydroxy-n-butyl)thymidine
and 30,50-O-bis-tetrahydropyranyl-N-3(5-hydroxy-n-pentyl)thymidine: 8; 9
Both compounds 8 and 9 were prepared in the same methodology. Compound
6 (80 mg, 0.14 mmol) was placed in a small flask and dissolved in MeOH
(2 ml). Aqueous sodium hydroxide solution (1 M, 0.2 ml) was added to the
above solutions and refluxed for 30 min at 708C when TLC showed no starting
material remained. The reaction mixture was cooled and solvent evaporated.
The residue was purified on a silica gel column and eluted with 30% acetone in
hexane to produce 8 (62 mg) in 92% yield. Compound 9 was obtained in 95%
yield. 1H NMR 8 (CDCl3) d: 7.66, 7.60, 7.56, 7.54 (4d, J= 1.2 Hz, 1 H, C6H),
6.43–6.34 (m, 1 H, 10H), 4.72–3.48 (m, 14 H, N-3C1,4H, THP and 30-50H),
2.58–2.10 (m, 2 H, 20H), 1.96, 1.95, 1.93, 1.92 (4 s, 3 H, CH3), 1.89–1.48
1
(m, 16 H, N-3C2,3H and THP). MS: M+1, 483.40. H NMR 9 (CDCl3) d:
7.65, 7.59, 7.55, 7.53 (4d, 1 H, J=1.2 Hz, C6H), 6.41–6.37 (m, 1 H, 10H),
4.76–3.48 (m, 14 H, N-3C1,5H, THP and 30-50H), 2.58–2.00 (m, 2 H, 20H), 1.96,
1.95, 1.93, 1.92 (4 s, 3 H, CH3), 1.89–1.39 (m, 18 H, N-3C2ꢀ4 and THP). High
resolution MS: M+Na, calculated 519.2677; found 519.2686.
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

[
18F]-N-3 (SUBSTITUTED) THYMIDINE ANALOGUES FOR PET
1085
Preparation of 30,50-O-bis-tetrahydropyranyl-N-3(4-methane-sulfonyl-n-butyl)
thymidine and 30,50-O-bis-tetrahydropyranyl-N-3(5-methanesulfonyl-n-pentyl)
thymidine: 10; 11
Both compounds 10 and 11 were prepared using the same methodology, a
representative procedure is described below. Compound 8 (0.150 g, 0.31 mmol)
was dissolved in dichloromethane (5 ml) under argon and triethylamine
(0.30 ml, 2.2 mmol) was added, followed by addition of dimethyl aminopyr-
idine (38 mg, 0.31 mmol). The reaction mixture was cooled to 0oC then
methane sulfonyl chloride (34 ml, 0.43 mmol) was added. The reaction mixture
was stirred for 40 min at 08C when TLC showed no starting material remained.
Solvent was evaporated under vacuum, the residue was dissolved in CH2Cl2
(25 ml) and the solution washed with H2O (3 ꢂ 25 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 149 mg of
the compound 10 in 86% yields. Compound 11 was obtained in 91% yield. 1H
NMR 10 (CDCl3) d: 7.66, 7.60, 7.56, 7.54 (4d, 1 H, J=1.2 Hz, C6H), 6.39–6.35
(m, 1 H, 10H), 4.74–3.48 (m, 14 H, N-3C1,4H, THP and 30-50H), 3.01 (s, 3 H,
S-CH3), 2.58–2.00 (m, 2 H, 20H), 1.95, 1.94, 1.91, 1.90 (4 s, 3 H, CH3), 1.89–
1.49 (m, 16 H, N-3C2,3H andTHP). High resolution MS: M+Na, calculated
1
583.2296; found 583.2300. H NMR 11 (CDCl3) d: 7.65, 7.59, 7.55, 7.53
(4d, J=1.2 Hz, 1 H, C6H), 6.42–6.31 (m, 1 H, 10H), 4.78–3.50 (m, 14 H,
N-3C1,5H, THP and 30-50H), 3.01 (s, 3 H, S-CH3), 2.51–2.00 (m, 2 H, 20H),
1.96, 1.95, 1.93,1.92 (4 s, 3 H, CH3), 1.59-1.40 (m, 18 H, N-3C2ꢀ4H and THP).
High resolution MS: M+Na, calculated 597.2452; found 597.2465.
Preparation of 30,50-O-bis-tetrahydropyranyl-N-3(4-fluoro-n-butyl)thymidine
and 30,50-O-bis-tetrahydropyranyl-N-3(5-fluoro-n-pentyl)thymidine: 12; 13
The fluorination reactions of both precursor compounds 10 and 11 are similar,
and a representative procedure is described. Compound 10 (30 mg, 0.05 mmol)
was dissolved in dry MeCN (3 ml) in a sealed v-vial under argon. To the above
solution, n-Bu4NF (1 M, 30 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 20% acetone in hexane as
eluent. The pure compound 12 (20 mg) was obtained in 70% yield. Compound
1
13 was obtained in 76% yield. H NMR 12 (CDCl3) d: 7.66, 7.60, 7.56, 7.54
(4d, J=0.9 Hz, 1 H, C6H), 6.41–6.37 (m, 1 H, 10H), 4.76–3.48 (m, 14 H,
N-3C1,4H, THP and 30-50H), 2.60–2.00 (m, 2 H, 20H), 1.96, 1.95, 1.93, 1.92
(4 s, 3 H, CH3), 1.85–1.41 (m, 16 H, N-3C2ꢀ3H and THP). 19F NMR 12 (d):
ꢀ218.26 (s, decoupled), ꢀ218.09 to ꢀ218.43 (m, coupled). High resolution
1
MS: M+K, calculated 523.2216; found 523.2213. H NMR 13 (CDCl3) d:
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

1086
M. M. ALAUDDIN ET AL.
7.65, 7.59, 7.55, 7.53 (4d, J=0.9 Hz, 1 H, C6H), 6.41–6.37 (4 s, 1 H, 1H), 4.79–
3.52 (m, 14 H, N-3C1,5H, THP and 30-50H), 2.61–2.00 (m, 2 H, 20H), 1.96, 1.95,
1.93, 1.92 (4 s, 3 H, CH3), 1.90–1.40 (m, 18 H, N-3C2ꢀ4H and THP). 19F NMR
13 (d): ꢀ218.33 (s, decoupled), ꢀ218.16 to ꢀ218.58 (m, coupled). High
resolution MS: M+Na, calculated 521.2634; found 521.2654.
Preparation of N-3(4-fluoro-n-butyl)thymidine and N-3(5-fluoro-n-pentyl)
thymidine: 14; 15
Compounds 14 and 15 were prepared in the same methodology and a
representative preparation is described below. Compound 12 (15 mg,
0.03 mmol) was placed in a small flask and dissolved in MeOH (1 ml).
Hydrochloric 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 solvent evaporated. The crude product was diluted with 25%
MeCN in water (1.2 ml) and purified by HPLC. After solvent evaporation
6.7 mg of the product was obtain in 68% yield. Compound 15 was purified
with 30% MeCN/H2O to obtain 73% yields. 1H NMR 14 (CDCl3) d: 7.34 (d,
1 H, J=1.2 Hz, C6H), 6.19 (t, 1 H, J=6.9 Hz, 10H), 4.62–4.59 (m, 1 H, 30H),
4.48 (dt, 2 H, JHF=47.4 Hz and JHꢀH=5.7 Hz, N-3C4H), 4.04–3.83 (m, 5 H,
N-3C1H, 40 and 50H), 2.51–2.42 (m, 2 H, 20H), 1.95 (d, 3 H, J= 1.2 Hz, CH3),
1.81–1.69 (m, 4 H, N-3C2ꢀ3H). 19F NMR 14 (d): ꢀ218.30 (s, decoupled),
ꢀ218.04 to ꢀ218.55 (m, coupled). High resolution MS: M+Na, calculated
1
339.1327; found 339.1347. H NMR 15 (CDCl3) d: 7.32 (d, 1 H, J=1.2 Hz,
C6H), 6.18 (t, 1 H, J=6.9 Hz, 10H), 4.64–4.61 (m, 1 H, 3H), 4.46 (dt, 2 H,
JHF=47.1 Hz and JHꢀH=6.0 Hz, N-3C5H), 4.04–3.85 (m, 5 H, N-3C1H,
40 and 50H), 2.52–2.43 (m, 2 H, 20H), 1.94 (d, 3 H, J=0.9 Hz, CH3), 1.85–1.65
(m, 6 H, N-3C2ꢀ4H). 19F NMR 15 (d): ꢀ218.36 (s, decoupled), ꢀ218.11 to
ꢀ218.62 (m, coupled). High resolution MS: M+Na, calculated 353.1483;
found 353.1486.
Preparation of N-3(4-[18F]fluoro-n-butyl)thymidine and N-3(5-[18F]fluoro-
n-pentyl)thymidine
The aqueous [18F]fluoride was trapped in anion exchange cartridge (ABX,
Germany) and eluted with a solution of n-Bu4NHCO3 (400 ml, 1% by wt) into
a v-vial, and the solution evaporated azeotropically with acetonitrile (1.0 ml)
to dryness at 79–808C under a stream of argon. To the dried n-Bu4N18F, a
solution of 10 or 11 (5–6 mg) in anhydrous acetonitrile (0.5 ml) was added, and
the mixture was heated at 908C for 25 min. The reaction mixture was cooled,
passed through a silica gel cartridge (Alltech), and eluted with ethyl acetate
(2.5 ml). After evaporation of the solvent under a stream of argon at 808C, the
residue was dissolved in methanol (0.4 ml). Hydrochloric acid solution in
methanol (1 N, 0.1 ml) was added and the mixture was refluxed for 5 min. The
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

[
18F]-N-3 (SUBSTITUTED) THYMIDINE ANALOGUES FOR PET
1087
crude mixture was neutralized with 1 N sodium bicarbonate solution (0.1 ml),
diluted with HPLC solvent (1.0 ml) and purified by HPLC. The desired
product was isolated and radioactivity was measured in a dose calibrator
(Capintec, Ramsey, NJ). Solvent was evaporated and the product was
redissolved in saline. The final product was analyzed onto an analytical
column and co-injected with an authentic standard compound to confirm its
identity.
Conclusion
We have synthesized two new radiotracers, N-3(substituted) analogues of
thymidine, N-3([18F]fluorobutyl)thymidine ([18F]-FBT) and N-3([18F]fluoro-
pentyl)thymidine ([18F]-FPT) with high yield, high specific activity and purity.
The described method may be suitable for the preparation of other
N-3(substituted) analogues of thymidine.
Acknowledgements
This work was supported by start up funds from The University of Texas MD
Anderson Cancer Center. NMR spectra were taken at the NMR facility
supported by CCSG core grant CA016672.
References
1. Alauddin MM, Conti PS, Fissekis JD. J Label Compd Radiopharm 2002; 45:
583–590.
2. Alauddin MM, Conti PS, Fissekis JD. J Label Compd Radiopharm 2003; 46:
285–289.
3. Mangner TJ, Klecker RW, Anderson L, Shields AF. Nucl Med Biol 2003; 30:
215–224.
4. Grierson JR, Shields AF. Nucl Med Biol 2000; 27: 143–156.
5. Alauddin MM, Shahinian A, Gordon EM, Conti PS. Mol Imaging 2002; 1: 74–81.
6. Alauddin MM, Shahinian A, Park R, Tohme M, Fissekis JD, Conti PS. Nucl Med
Biol 2004; 31: 399–405.
7. Alauddin MM, Shahinian A, Gordon EM, Conti PS. Mol Imaging 2004; 3: 76–84.
8. Alauddin MM, Shahinian A, Park R, Tohme M, Fissekis JD, Conti PS. J Nucl
Med 2005; 45: 2063–2069.
9. Watanabe KA, Reichman U, Hirota K, Lopez C, Fox JJ. J Med Chem 1979; 22:
21–24.
10. Perlman ME, Watanabe KA, Schinazi RF, Fox JJ. J Med Chem 1985; 28:
741–748.
11. Tann CH, Brodfuehrer PR, Brunding SP, Sapiro C, Howell HG. J Org Chem
1985; 50: 3644–3647.
12. Fox JJ, Watanabe KA, Chou TC, Schinazi RF, Soike KF, Fourel I, Hantz G,
Trepo C. In Fluorinated Carbohydrates, Chapter 10, Taylor NF (ed.). American
Chemical Society: Washington DC, 1998; 176–190.
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr

1088
M. M. ALAUDDIN ET AL.
13. Watanabe KA, Su T-L, Reichman U, Greenberg N, Lopez C, Fox JJ. J Med
Chem 1984; 27: 91–92.
14. Horn DM, Neeb LA, Colacino JM, Richardson FC. Antiviral Res 1997; 34:
71–74.
15. Colacino JM. Antiviral Res 1996; 29: 125–139.
16. Conti PS, Alauddin MM, Fissekis JD, Watanabe KA. Nucl Med Biol 1995; 22:
783–789.
17. Conti PS, Bading JR, Alauddin MM, Fissekis JD, Berenji B. (Abstract). RSNA,
Chicago, IL, 5–9 December 2002.
18. Sun H, Sloan A, Mangner TJ, Vaishampayan U, Muzik O, Collins JM, Douglas
K, Shields AF. Eur J Nucl Med Mol Imaging 2005; 32: 15–22.
19. Mercer JR, Knaus EE, Weibe LI. J Med Chem 1987; 30: 670–675.
20. Shields AF, Grierson JR, Kazawa SM, Zheng M. Nucl Med Biol 1996; 23: 17–22.
21. Alauddin MM, Balatoni J, Gelovani J. J Label Compd Radiopharm 2005; 48:
941–950.
22. Buck AK, Halter G, Schirrmeister H, Kotzerke J, Wuriger I, Glatting G,
Mattfeldt T, Neumaier B, Reske SN, Hetxel M. J Nucl Med 2003; 44: 1426–1431.
23. Sugiyama M, Sakahara H, Sato K, Harada N, Jukumoto D, Kakiuchi T, Hirano
T, Kohno E, Tsukada H. J Nucl Med 2004; 45: 1754–1758.
24. Lunato AJ, Wang J, Woollard JE, Anisizzaman AKM, Ji W, Rong F-G, Ikeda S,
Soloway AH, Eriksson S, Tjarks W. J Med Chem 1999; 42: 3373–3389.
25. Al-Madhoun AS, Johnsamuel J, Yan J, Ji W, Wang J, Zhou J, Lunato A,
Woollerd JE, Hawk AE, Blue TE, Tjarks W, Eriksson S. J Med Chem 2002; 45:
4018–4028.
26. Byun Y, Yan J, Al-Madhoun AS, Johnsamuel J, Yang W, Barth RF, Eriksson S,
Tjarks W. Appl Radiat Isot 2004; 61: 1125–1130.
27. Al-Madhoun AS, Johnsamuel J, Barth RF, Tjarks W, Eriksson S. Cancer Res
2004; 64: 6280–6286.
28. Byun Y, Yan J, Al-Madhoun AS, Johnsamuel J, Yang W, Barth RF, Eriksson S,
Tjarks W. J Med Chem 2005; 48: 1188–1198.
29. Bandyopadhyaya AK, Johnsamuel J, Al-Madhoun AS, Erikson S, Tjarks W.
Bioorg Med Chem 2005; 13: 1681–1689.
30. Alauddin MM, Conti PS. Tetrahedron 1994; 50: 1699–1706.
31. Choudary BM, Chowdari NS, Kantam ML. Tetrahedron 2000; 56: 7291–7298.
32. Borjesson L, Csoregh I, Welch C. J Org Chem 1995; 60: 2989–2999.
Copyright # 2006 John Wiley & Sons, Ltd.
J Label Compd Radiopharm 2006; 49: 1079–1088
DOI: 10.1002/jlcr