N. Turkman et al.
Preparation of N3-Boc-30,50-O-1,1,3,3-tetraisopropyl-1,3-disiloxane- Preparation of N3-Boc-30,50-O-bis-tetrahydropyranyl-20-O-methyl-
5-methyluridine 4
sulfonyloxy-5-methyluridine 7
Compound 3 (2.29 g, 4.0 mmol) was dissolved in tetrahydrofuran To a solution of compound 6 (62.0 mg, 0.14mmol) in dry THF
(THF, 50mL), then di-tert-butyl dicarbonate (1.0g, 4.8 mmol) and (5mL) and a catalytic amount of TsOH (10.0 mg) was added 3,4-
N,N-dimethylaminopyridine (DMAP, 0.49g, 4.0 mmol) were dihydro-2H-pyrane (DHP, 0.36mL, 0.4 mmol). The reaction mixture
added. The reaction mixture was stirred at room temperature was stirred at room temperature for 16h, and then neutralized by
for 12h, when TLC showed a complete reaction (Rf = 0.7: 20% the addition of triethyl amine (20.0 mL), and the solvent was
ethylacetate in hexane). To the above solution was added evaporated. The residue was purified by flash chromatography on
p-toluenesulfonic acid (TsOH) (1.52 g, 8.0 mmol), and the mixture a silica gel column with 20% ethyl acetate in hexane to give
was stirred at room temperature for 30min. The reaction mixture 7 (a mixture of diasteriomers) as a colorless oil in 48% yield. Based
was then cooled to 01C, and triethylamine (2.2mL, 16.0mmol) on HPLC chromatogram, the compound was 498% pure.
was added dropwise; and the reaction mixture was stirred for 1H NMR (CDCl3)d: 7.79, 7.78, 7.68, 7.67 (4s, 1H, C6–H), 6.06, 5.98
another 10min. The solution was filtered and diluted with 1 M (2d, J = 3.3 Hz, 2.4 Hz, 1H, 10-H), 4.55ꢁ4.47 (m, 1H, 20-H), 4.72ꢁ3.54
aqueous NaHCO3 (15mL) and extracted with ethyl acetate (m, 10H, 30-50-H and THP), 3.23, 3.22 (2s, 3H, Ms), 2.43ꢁ2.37
(3ꢀ 50mL). The organic layers were combined, dried over (m, 1H, 20-H), 1.96, 1.92 (2s, 3H, CH3), 1.83ꢁ1.70 (m, 4H, THP), 1.62
Na2SO4, and concentrated to give a colorless oil that was purified (m, 9H), 1.63ꢁ1.58 (m, 8H, THP). High-resolution MS (m/z):
by flash chromatography on a silica gel column using 0–50% [M1Na] for C26H40N2O12S, calculated, 627.2200; found, 627.2235.
ethyl acetate in hexane with gradient elution. The appropriate
Preparation of [18F]FMAU 8
fractions were combined and evaporated to give a colorless thick
oil, which was re-dissolved in CH2Cl2 and evaporated under high
The aqueous [18F]fluoride produced from the cyclotron by the
reaction of 18O(p, n)[18F] was trapped on an ion-exchange
cartridge (Chromafix 30-PS-HCO3, ABX) and eluted with an
aqueous solution of K2CO3 (2.75 mg/mL) into a V-vial contaning
kryptofix 2.2.2 solution (12.0 mg/mL) in acetonitrile. Water was
removed by an azeotropic evaporation at 801C with acetonitrile
(1.0mL) under a stream of argon. A solution of 7 (2–3mg) in
acetonitrile (0.3mL) was added to the dried K18F/kryptofix 2.2.2.
The reaction mixture was heated at 801C for 20min. The crude
reaction mixture was passed through a silica Sep-Pak cartridge
followed by elution with two portions of ethyl acetate (2.5mL,
total) which was evaporated at 801C under a stream of argon. The
residue was dissolved in methanol (0.3mL), 1M methanol/HCl
solution (0.1mL) was added, and the mixture was heated at 801C
for 10min. The solvent was evaporated, and the residue was
dissolved in HPLC solvent (9% acetonitrile/water, 1.0 mL) and
purified by HPLC using a semipreperative column. The product
was eluted with 9% acetonitrile/water at a flow of 4 mL/min. The
appropriate fraction (radioactive) was collected between 11.5 and
12.5min, and the solvent was evaporated under reduced
pressure. The product was dissolved in saline, and an aliquot of
the product [18F]FMAU 8 was analyzed on an analytical HPLC
column to verify its identity and purity by coinjection with the
nonradioactive authentic samples FMAU and FMRU.
vacuum to give 4 as a white foam in 83% yield. Based on 1H NMR
spectrum, the compound was 498% pure. 1H NMR (CDCl3)d: 7.40
(d, 1H, J = 1.2 Hz, C6–H), 5.78 (s, 1H, 10-H), 4.40 (m, 1H), 4.20
(m, 2H), 4.11 (m, 1H), 4.03 (m, 1H), 2.79 (d, 1H, J = 0.7 Hz, –OH),
1.94 (d, 3H, J = 1.0 Hz, CH3–H), 1.62 (s, 9H, N-Boc), 1.06–1.09
(m, 28H, i-Pr-H). High-resolution MS (m/z): [M1Na] for
C27H48N2O9Si2, calculated, 623.2796; found, 623.2830.
Preparation of N3-Boc-30,50-O-1,1,3,3-tetraisopropyl-1,3-disiloxane-
20-O-methylsulfonyloxy-5-methyluridine 5
Compound 4 (0.50 g, 0.83 mmol) was dissolved in 5 mL of THF
and cooled to 01C, then triethylamine (0.56 mL, 4.1 mmol) was
added, followed by the addition of methanesulfonyl chloride
(0.15 mL, 1.9 mmol). The mixture was stirred at 01C for 10 min,
warmed to room temperature, and stirred for an additional 1.5 h.
The reaction mixture was filtered, and THF was removed under
reduced pressure to give a colorless oil that was purified by flash
chromatography on a silica gel column with 20% ethyl acetate
in hexane to give 5 as a white foam in 90% yield. Based on
1H NMR spectrum, the compound was 498% pure. 1H NMR
(CDCl3) d: 7.53 (s, 1H, C6–H), 5.78 (s, 1H), 5.04 (d, 1H, J = 4.5 Hz),
4.40 (m, 1H), 4.20 (m, 1H), 4.11 (m, 1H), 4.03 (m, 1H), 3.25
(s, 3H, -Ms), 1.94 (s, 3H, CH3), 1.63 (s, 9H), 1.06–1.09 (m, 28H).
High-resolution MS (m/z): [M1Na] for C28H50N2O11SSi2, calcu-
lated, 701.2572; found, 701.2605.
A carrier-added synthesis was performed following the above
method, and the product [18/19F]FMAU 8 was saved for decay.
Two days later, the product [19F]FMAU 8 was submitted for
analysis by mass spectrometry. MS (m/z): [M1H] for
C10H14N2O5F, 261.12.
Preparation of N3-Boc-20-O-methylsulfonyloxy-5-methyluridine 6
To a solution of 5 (0.27 g, 0.4 mmol) in THF (10 mL) was added
n-Bu4NF (1M in THF, 1.0 mL, 1.0 mmol). The reaction mixture was
stirred at room temperature for 30 min, when TLC showed no
starting material remained. The reaction mixture was concen-
trated and the residue purified by flash chromatography on a
silica gel column with 10% methanol in dichloromethane to give
6 as a white foam in 97% yield and 98% purity.1H NMR (CDCl3)d:
7.49 (s, 1H, C6–H) 5.89 (d, 1H, J = 4.5 Hz,10-H), 5.27 (t, 1H,
J = 4.5 Hz, 20-H), 4.60 (t, 1H, J = 5.2 Hz, 30-H), 4.20 (m, 1H, 40-H),
4.08ꢁ3.83 (m, 2H, 50-H), 3.23, (s, 3H, -Ms), 2.20–2.80 (broad s, 2H,
–OH), 1.95 (s, 3H, CH3), 1.62 (s, 9H, N-Boc). High-resolution MS
(m/z): [M1H] for C16H24N2O10S, calculated, 437.1224; found,
437.1222.
Results and discussion
Figure 2 presents the synthetic scheme for the preparation of
[18F]FMAU 8. The synthesis began with a selective sequence of
protection and deprotection on 5-methyluridine functionalities.
We first prepared the 30,50-O-1,1,3,3-tetraisopropyl-1,3-disilox-
ane-5-methyluridine 2 from the 5-methyluridine according to
published methods.24,29 Compound 2 was obtained in 80%
1
yield. The H NMR spectrum was in agreement with previously
published results.29 This one-step protection of the 30- and 50-
hydroxyl groups turned out to be advantageous; it allowed for
Copyright r 2010 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2010, 53 782–786