Synthesis of 2′-deoxy-2′-fluoro-1-β-D-arabinofuranosyl uracil derivatives: A method suitable for preparation of [18F]-labeled nucleosides

Article abstract of DOI:10.1081/SCC-120004272

N-glycosylation of 2,4-bis-O-(trimethylsilyl)-pyrimidine bases with 2-deoxy-2-fluoro-3,5-di-O-benzoyl-l-(Br, OBz)-α-D-arabinose derivatives are reported. 1-Bromo-arabinose provides high yield and a favorable anomeric ratio (β/α) of pyrimidine nucleoside i

Full text of DOI:10.1081/SCC-120004272

This article was downloaded by: [Moskow State Univ Bibliote]
On: 28 October 2013, At: 10:42
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsyc20
SYNTHESIS OF 2′-DEOXY-2′-FLUORO- 1-β-d-
ARABINOFURANOSYL URACIL DERIVATIVES: A METHOD
SUITABLE FOR PREPARATION OF [18F]-LABELED
NUCLEOSIDES
Mian M. Alauddin a , Peter S. Conti a , John D. Fissekis a & Kyoihci A. Watanabe b c
a PET Imaging Science Center , University of Southern California , 2250 Alcazar St., Suite
101, Los Angeles, CA, 90033, U.S.A.
b Laboratory of Organic Chemistry , Memorial Sloan-Kettering Cancer Center , New York, NY,
10021, U.S.A.
c Pharmasset, Inc. , 1860 Montreal Road, Tucker, GA, 30084, U.S.A.
Published online: 16 Aug 2006.
To cite this article: Mian M. Alauddin , Peter S. Conti , John D. Fissekis & Kyoihci A. Watanabe (2002) SYNTHESIS OF 2′-
DEOXY-2′-FLUORO- 1-β-d-ARABINOFURANOSYL URACIL DERIVATIVES: A METHOD SUITABLE FOR PREPARATION OF [18F]-LABELED
NUCLEOSIDES, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
32:11, 1757-1764, DOI: 10.1081/SCC-120004272
To link to this article: http://dx.doi.org/10.1081/SCC-120004272
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
SYNTHETIC COMMUNICATIONS, 32(11), 1757–1764 (2002)
SYNTHESIS OF 20-DEOXY-20-FLUORO-
1-b-D-ARABINOFURANOSYL
URACIL DERIVATIVES: A METHOD
SUITABLE FOR PREPARATION OF
[18F]-LABELED NUCLEOSIDES
Mian M. Alauddin,1 Peter S. Conti,1,
*
John D. Fissekis,1 and Kyoihci A. Watanabe2,y
1University of Southern California, PET Imaging
Science Center, Los Angeles, CA 90033, USA
2Laboratory of Organic Chemistry,
Memorial Sloan-Kettering Cancer Center,
New York, NY 10021, USA
ABSTRACT
N-glycosylation of 2,4-bis-O-(trimethylsilyl)-pyrimidine bases
with 2-deoxy-2-fluoro-3,5-di-O-benzoyl-1-(Br, OBz)-ꢀ-D-ara-
binose derivatives are reported. 1-Bromo-arabinose provides
high yield and a favorable anomeric ratio (ꢁ/ꢀ) of pyrimi-
dine nucleoside in either MeCN or CH2Cl–CH2Cl. This
method should be suitable for the synthesis of 20-deoxy-20-
[18F]fluoro-1-ꢁ-D-arabinofuranosyluracil derivatives.
*Corresponding author. USC PET Imaging Science Center, 2250 Alcazar St., Suite
101, Los Angeles, CA 90033. Fax: (323) 442 5778; E-mail: pconti@hsc.usc.edu
yCurrent address: Pharmasset, Inc., 1860 Montreal Road, Tucker, GA 30084.
1757
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
1758
ALAUDDIN ET AL.
20-Deoxy-20-fluoro-5-[11C-methyl]-1-ꢁ-D-arabinofuranosyluracil (11C-
FMAU), first synthesized in our laboratory, is being studied as a marker
for cell proliferation by positron emission tomography (PET).[1–3] However,
the short half-life of 11C (t1/2 ¼ 20 min) limits the clinical application of the
compound. The corresponding analogue labeled with fluorine-18 (t1/2
110 min) would be more advantageous.
¼
Attempted syntheses of 20-deoxy-20-fluoro-1-ꢁ-D-arabinofuranosylura-
cils by the direct introduction of fluorine have hitherto failed.[4,5] However,
the incorporation of fluorine in the arabino configuration at C-2 of the
sugar followed by coupling with the pyrimidine base has been successful
toward the synthesis of these nucleosides.[6–8] The most common method
involves conversion of the protected sugar to its 1-bromo-derivative, which
is then treated with a protected pyrimidine base over a lengthy period of
time ranging from 16 h to 7 d.[7,8] These conditions are not suitable for
radiochemical synthesis with short half-life isotopes such as 18F. Another
method of coupling the glycosyl moiety to the pyrimidine base involves
the use of a Friedel-Crafts catalyst and 2-substituted ribofuranose, which
produced, exclusively, the ꢁ-anomer of the nucleoside.[9]
Very limited work has been done on pyrimidine glycosylation with a
protected 2-deoxy sugar.[9,10] In our effort toward the synthesis of 18F-
FMAU, we have investigated reactions of 2,4-bis-O-(trimethylsilyl)uracil
derivatives 1a and 1b with 2-deoxy-2-fluoro-1,3,5-tri-O-benzoyl-ꢀ-D-
arabinofuranose 2a using several catalysts under a variety of experimental
conditions. In addition, we have investigated the preparation of 1-bromo-2-
deoxy-2-fluoro-3,5-di-O-benzoyl-arabinofuranose 2b in short time, and its
subsequent coupling with a protected pyrimidine.
2,4-Bis-O-(trimethylsilyl)uracil derivatives 1a and 1b were prepared
in high yields following a literature method.[10] Compound 2a was
prepared either by a literature method[11] or by one developed in our
laboratory.[12] Through careful optimization of solvent and reaction con-
ditions we have developed the synthesis of 2b in high yield with a reduction
of time from 16 to 0.5 h. Compound 2b was exclusively the ꢀ-anomer as
observed by 1H NMR spectroscopy (J1,2 ¼ 0).
Figure 1 represents the coupling reactions of protected pyrimidine
base and protected sugar.
Tables 1 and 2 represent the coupling of 1a and 2b, and 1a and 2a in
various conditions, respectively.
The reactions of 1a with 2b in MeCN at 80ꢀC resulted in 80–86%
chemical yield of the coupled product in the ratio of 65 : 35 (ꢁ : ꢀ). In
CH2Cl–CH2Cl, these reactions produced a higher yield, and the anomeric
ratio was further enhanced to 10 : 1 (Table 1, Entry 5). The required reaction
time for the coupling of 1a with 2b at 80ꢀC was longer in CH2Cl–CH2Cl

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
PREPARATION OF [18F]-LABELED NUCLEOSIDES
1759
Figure 1.
Table 1.
Entry
Solvent
Catalyst
SnCl4
Temp/Time
Yield
Product (ꢁ : ꢀ)
1
MeCN
MeCN
2Cl–CH2Cl
CH2Cl–CH2Cl
CH2Cl–CH2Cl
80ꢀC/50 min
70ꢀC/50 min
97ꢀC/1 h
86–90%
58%
90–95%
70–75%*
95%
65 : 35
40 : 60
85 : 15
85 : 15
91 : 9
2
3CH
4
5
97ꢀC/1 h
80ꢀC/3.25 h
*Started from 1-benzoate ester, yield in two steps.
(3.25 h) than in MeCN (50 min). However, the temperature of the reaction in
CH2Cl–CH2Cl could be increased up to 97ꢀC to achieve high yield in a
relatively shorter time maintaining the high anomeric selectivity. Thus in
1h at 97ꢀC the chemical yield was similar as those obtained in 3.25 h at 80ꢀC,
while the anomeric ratio (ꢁ : ꢀ) was only slightly lower at the higher tem-
perature (Table 1, Entry 3). The two step process, i.e., preparation of 2b and
its and subsequent coupling, leads to an overall yield of 70–75% with an
anomeric ratio of 85 : 15 (ꢁ : ꢀ) (Table 1, Entry 4).
We have also carried out the coupling of 1a with 2a using Friedel-
Crafts catalysts. In these reactions, solvent plays a very important role in
determining the anomeric selectivity. In the highly polar solvent MeCN the
formation of the ꢀ anomer predominates. Thus reactions of 2a with 1a in
MeCN/SnCl4 produced the two anomers in the ratio of 28 : 72 (ꢁ : ꢀ) in
70–76% combined chemical yield. In CH2Cl–CH2Cl/SnCl4 the anomeric
ratio was reversed to 70 : 30 (ꢁ : ꢀ) (Table 2, Entry 2); however, the combined
yield was reduced to 30–32%. The addition of catalyst to the reactions of
1-bromo-sugar (2b) with 1a in MeCN/SnCl4 resulted in a lower chemical

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
1760
ALAUDDIN ET AL.
Table 2.
Entry
Solvent
MeCN
CH2Cl–CH2Cl SnCl4
Catalyst Temp./Time
Yield
Product (ꢁ : ꢀ)
1
SnCl4
80ꢀC/45 min
80ꢀC/1 h
80ꢀC/1 h
80ꢀC/1 h
80ꢀC/1 h
80ꢀC/1 h
70–76%
30–32%
20%
14%
5%
28 : 72
70 : 30
67 : 33
29 : 71
29 : 71
2
3CCl
4
5
6
SnCl4
BF3
4
MeCN
MeCN
MeCN
TiCl4
ZnCl2
No reaction
yield (58%) and a ratio of 40 : 60 (ꢁ : ꢀ) (Table 1 Entry 2). It appears that in
both instances (2a and 2b), the catalyst (SnCl4) influences the course of
reaction through a SN1 mechanism by the formation of a carbocation as
suggested earlier.[8] Tin tetrachloride (SnCl4) was found to be the best cat-
alyst compared to others (ZnCl2, BF3-etherate and TiCl4) used in this study.
In comparison to the direct, one step coupling of 2a (Method 2) the two step
procedure (Method 1) that involves the conversion of 2a to 2b prior to
coupling, lengthens the overall reaction time by 40 min. Although Method
2 requires 40 min additional time the overall yield of the desired anomer is
much higher, and therefore has an advantage over the other method.
Experiments with 1b produced similar results as in the case of 1a.
The protected coupled product could be hydrolyzed in 5 min using
sodium methoxide at 80ꢀC. Analysis by HPLC of this free nucleoside
showed a mixture of two products, ꢀ and ꢁ, co-eluted with authentic
samples (Figure 2), and consistent with the literature.[7] The ratio of the
anomers was consistent with that estimated by 1H NMR spectra.
Preparation and subsequent coupling of 2b with a protected pyrimidine
base in CH2Cl–CH2Cl should be suitable to the synthesis of 20-deoxy-20-
[18F]fluoro-1-ꢁ-D-arabinofuranosyluracil derivatives for PET imaging.
EXPERIMENTAL
Proton NMR spectra were recorded on a Brucker 360 or 500 MHz
spectrometer using tetramethylsilane as an internal reference at the
University of Southern California. Mass spectra were obtained on a
Finnigan 400 mass spectrometer at the University of Minnesota using an
ammonia chemical ionization technique. High performance Liquid
Chromatography (HPLC) was performed on a system using a 510 pump
(Waters Associates), a UV detector (Isco) operated at 254 nm and a C18

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
PREPARATION OF [18F]-LABELED NUCLEOSIDES
1761
Figure 2.
reverse phase analytical column (Alltech). A MeCN/H2O solvent system
(7.5% MeCN) was used as eluent.
1-Bromo-2-deoxy-2-fluoro-3,5-di-O-benzoyl-
a-D-arabinofuranose 2b
The fluorosugar 2a (50 mg, 0.11 mmol) was dissolved in 1,2-dichloro-
ethane (3ml) under argon. Hydrogen bromide (HBr) in acetic acid (30%,
0.5 ml) was added, and the reaction mixture was heated at 80ꢀC for 30 min.
The reaction mixture was cooled to room temperature, diluted with CH2Cl2
(15 ml), washed with saturated NaHCO3 soln (15 ml), dried and evaporated
to dryness. After flash chromatography on silica gel using 12% acetone in
hexane as eluent, 40 mg of pure product 2b was obtained (88% yield).
1H NMR: (ꢂ): 8.1–8.2 (m, 4H, aromatic), 7.5–7.7 (m, 2H, aromatic), 7.4–
7.5 (m, 4H, aromatic), 6.65 (d, 1H, 10H, J ¼ 12 Hz), 5.55 (dm, 1H, 30H,
J ¼ 20 Hz), 5.61 (d, 1H, 20H, J ¼ 50 Hz), 4.6–4.9 (m, 3H, 40H & 50H).
High resolution MS : M þ H, Calculated 423.0223; found 423.0223.
2-Deoxy-2-fluoro-3,5-di-O-benzoyl-1-
b-D-arabinofuranosyluracil Derivative
Method 1: Compound 2b (25–30 mg) was dissolved in either acetonitrile
or 1,2-dichloroethane (0.5 ml) under argon in a V-vial. Freshly prepared 2,4-
bis-O-(trimethylsilyl)uracil derivative 1a (8–9 equiv.) was dissolved in either
MeCN or CH2Cl–CH2Cl (1.5 ml) and added to the reaction vial and the

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
1762
ALAUDDIN ET AL.
mixture heated at 80–81ꢀC for 50 min, when TLC (30% acetone in hexane)
showed no remaining starting material. The reaction mixture was cooled to
room temperature and the solvent was evaporated. The residue was dissolved
in CH2Cl2, the solution washed with water, dried and evaporated to dryness.
The crude product was purified on silica gel using 25% acetone in hexane as
eluent. Pure product (by TLC) was obtained in 80–86% yield, as a mixture of
1
ꢀ and ꢁ anomers. H NMR: (ꢀ): (ꢂ): 9.26 (s, 1H, NH), 8.0–8.2 (m, 4H,
aromatic), 7.5–7.7 (m, 2H, aromatic), 7.2–7.5 (m, 4H, aromatic), 6.16 (d,
1H, 10H, J ¼ 15.5 Hz), 5.69 (d, 1H, 30H, J ¼ 15 Hz), 5.49 (d, 1H, 20H,
J ¼ 48 Hz), 4.2–5.0 (m, 3H, 40H and 50H), 1.86 (s, 3H, methyl). H NMR:
1
(ꢁ): (ꢂ): 9.10 (s, 1H, NH), 8.0–8.2 (m, 4H, aromatic), 7.5–7.7 (m, 2H,
aromatic), 7.2–7.5 (m, 4H, aromatic), 6.34 (dd, 1H, 10H, J ¼ 22.5 Hz and
2.8 Hz), 5.62 (dt, 1H, 30H, J ¼ 17.5 Hz and 2.8 Hz), 5.30 (dd, 1H, 20H,
J ¼ 50 Hz), 4.7–4.8 (m, 1H, 40H), 4.5–4.6 (m, 2H, 50H), 1.73(s, 3H, methyl).
Method 2: Compound 2a (25–30 mg) was dissolved in either MeCN or
CH2Cl–CH2Cl (0.5 ml) under argon in a V-vial. The protected uracil deriva-
tive 1a (8–9 equiv.) was dissolved in appropriate solvents (1.5 ml) and
the solution added to the reaction vial followed by addition of SnCl4
(10 equiv.). The vial was heated at 80–81ꢀC for 45 min, when TLC showed
absence of starting material. The reaction mixture was cooled to room
temperature, worked up and purified as described in Method 1. Pure product
(by TLC) was obtained in 70–76% yield. 1H NMR spectrum showed a
mixture of ꢀ and ꢁ anomers.
2-Deoxy-2-fluoro-1-b-D-arabinofuranosyluracil Nucleoside
The protected-coupled product (5 mg) was dissolved in methanol (2 ml).
Sodium methoxide (1M, 0.1 ml) was added, and the mixture was heated for
5 min at 80ꢀC when TLC showed that no starting material remained. The
reaction mixture was neutralized with dil. HCl, filtered and analyzed by
HPLC using a C18 reverse phase analytical column and 7.5% MeCN in
water as eluting solvent at a flow of 1.5 ml/min. HPLC chromatogram
(Figure 2) showed to be a mixture of two products ꢀ and ꢁ in the ratio as
observed by 1H NMR spectra, and co-eluted with the known product.
ACKNOWLEDGMENT
The authors wish to thank Mr. Allan D. Kershaw for assisting with
the NMR spectra. This work was supported by the National Cancer
Institute grant CA 72896.

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
PREPARATION OF [18F]-LABELED NUCLEOSIDES
REFERENCES
1763
1. Conti, P.S.; Alauddin, M.M.; Fissekis, J.D.; Schmall, B.; Watanabe,
K.A. Synthesis of 20-fluoro-5-[11C] methyl-1-ꢁ-D-arabinofuranosylura-
cil ([11C]-FMAU): A Potential Nucleoside Analogue for In Vivo Study
of Cellular Proliferation with PET. Nucl. Med. Biol. 1995, 22, 783–789.
2. Conti, P.S.; Anderson, J.H.; Wong, D.F.; Bading, J.R.; Alauddin,
M.M.; Ravert, H.T.; Mathews, W.B.; Musachio, J.L.; Dannals, R.F.;
Scheffel, U. Pre-clinical studies of 20-fluoro-5-[C-11]-methyl-1-ꢁ-D-
arabinofuranosylurcil (FMAU): A Potential PET Indicator of
Tumor Proliferation. J. Nucl. Med. 1996, 37, 107P.
3. Bading, J.R.; Alauddin, M.M.; Fissekis, J.D.; Kirkman, E.; Vail, A.;
Conti, P.S. Pharmacokinetics of 20-Fluoro-5-[11C]-methyl-1-ꢁ-D-
arabinofuranosyluracil ([11C]-FMAU) in Monkeys. J. Nucl. Med.
2000, 41, 234P.
4. Reichman, U.; Watanabe, K.A.; Fox, J.J. A Practical Synthesis of
2-Deoxy-2-fluoro-D-arabinofuranose Derivatives. Carbohydrate Res.
1975, 42, 233–240.
5. Pankiewicz, K.W.; Nawrot, B.; Gadler, H.; Price, R.W.; Watanabe,
K.A. Nucleosides. 146. 1-Methyl-5-(2-deoxy-2-fluoro-ꢁ-D-arabino-
furanosyl)uracil, the C-nucleoside Isostere of the Potential Antiviral
Agent 1-(2-deoxy-2-fluoro-ꢁ-D-arabinofuranosyl)thymine (FMAU).
Studies Directed Towards the Synthesis of 20-deoxy-20-Substituted
Arabino Nucleosides. J. Med. Chem. 1987, 30, 2314–2316.
6. Watanabe, K.W.; Su, T.L.; Klein, R.S.; Riechman, U.; Greenberg, N.;
Lopez, C.; Fox, J.J. Nucleosides 129. Synthesis of Antiviral
Nucleosides: 5-alkenyl-1-(2-deoxy-2-fluoro-ꢁ-D-arabinofurabosyl)ura-
cils. J. Med. Chem. 1984, 27, 91–94.
7. Tann, C.H.; Brodfuehrer, P.R.; Brundidge, S.P.; Sapino, C.; Howell,
H.G. Fluorocarbohydrates in Synthesis. An Efficient Synthesis of
1-(2-deoxy-2-fluoro-ꢁ-D-arabinofuranisyl)-5-iodouracil (ꢁ-FIAU) and
1-(2-deoxy-2-fluoro-ꢁ-D-arabinofuranosyl)thymine (ꢁ-FMAU). J. Org.
Chem. 1985, 50, 3644–3647.
8. Howell, H.G.; Brodfuehrer, P.R.; Brundidge, S.P.; Beningni, D.A.;
Sapino, C. Jr. Antiviral Nucleosides.
A Stereospecific, Total
Synthesis of 20-Fluoro-20-deoxy-ꢁ-D-arabinofuranosyl Nucleosides.
J. Org. Chem. 1988, 53, 85–88.
9. Niedballa, U.; Vorbruggen, H. A General Synthesis of N-Glycosides. I.
Synthesis of Pyrimidine Nucleosides. J. Org. Chem. 1974, 39,
3654–3660.
10. Hubbard, A.J.; Jones, A.S.; Waker, R.T. An Investigation by 1H NMR
Spectroscopy into the Factors Determining the ꢁ : ꢀ Ratio of the

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016
©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
1764
ALAUDDIN ET AL.
Product in 20-Deoxynucleoside Synthesis. Nucleic Acids Res. 1984, 12,
6827–6837.
11. Chou, T.S.; Becke, L.M.; O’Toole, J.C.; Carr, M.A.; Parker, B.E.
Triethylamine Poly(hydrogen fluorides) in the Synthesis of a Fluori-
nated Nucleoside Glycon. Tetrahedron Lett. 1996, 37, 17–20.
12. Alauddin, M.M.; Conti, P.S.; Mathew, T.; Fissekis, J.D.; Prakash,
G.K.S.; Watanabe, K.A. Stereospecific Fluorination of 1,3,5-tri-O-
benzoyl-ꢀ-D-ribofuranose-2-sulfonate Esters: Preparation of
a
Versatile Intermediate for Synthesis of 20-[18F]-fluoro-arabinonucleo-
sides. J. Fluorine Chem. 2000, 106, 87–91.
Received in the USA June 23, 2001