A facile one-pot synthesis of N4-alkyloxycarbonyl cytosine nucleosides

Article abstract of DOI:10.1081/SCC-200030544

N⁴-Alkyloxycarbonyl cytosine nucleosides can be easily prepared by reacting cytosine nucleosides with triphosgene and alcohols.

Full text of DOI:10.1081/SCC-200030544

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A Facile One‐Pot Synthesis of
N 4‐Alkyloxycarbonyl Cytosine
Nucleosides
Yue‐Lei Chen a & Jun‐Da Cen a
a Department of Chemistry, Shanghai Institute of
Pharmaceutical Industry, Shanghai, 200437, P.R.
China
Published online: 10 Jan 2011.
To cite this article: YueLei Chen & JunDa Cen (2004) A Facile One‐Pot Synthesis
of N 4‐Alkyloxycarbonyl Cytosine Nucleosides, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry,
34:18, 3273-3279, DOI: 10.1081/SCC-200030544
To link to this article: http://dx.doi.org/10.1081/SCC-200030544
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 18, pp. 3273–3279, 2004
A Facile One-Pot Synthesis of
N4-Alkyloxycarbonyl Cytosine Nucleosides
*
Yue-Lei Chen and Jun-Da Cen
Department of Chemistry, Shanghai Institute of Pharmaceutical Industry,
Shanghai, P.R. China
ABSTRACT
N4-Alkyloxycarbonyl cytosine nucleosides can be easily prepared by
reacting cytosine nucleosides with triphosgene and alcohols.
Key Words: N4-Alkyloxycarbonyl cytosine nucleoside; Triphosgene;
Cytosine nucleoside; Isocyanate.
In the medicinal chemistry of nucleosides, using alkyloxycarbonyl group
to mask the 4-amino group of cytosine nucleoside has been proved to be an
important tactic in the design of nucleoside prodrugs.[1] The desired active
*
Correspondence: Yue-Lei Chen, Department of Chemistry, Shanghai Institute of
Pharmaceutical Industry, Shanghai, 200437, P.R. China; E-mail: yuelei_chen@
yahoo.com.
3273
DOI: 10.1081/SCC-200030544
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3274
Chen and Cen
nucleoside species will be released after cleavage of the inert carbamate struc-
ture by enzymes in vivo. The reported synthetic methods toward N4-alkyloxy-
carbonyl cytosine nucleosides mainly focused on the reaction between the
cytosine nucleosides and alkyl chloroformates.[1,2] But to our knowledge,
most alkyl chloroformates are not commercially available and have to be pre-
pared prior to use. In screening of a large number of bio-active compounds, the
preparation of various of chloroformates, especially the complex ones, will be
a tedious work. Hattori has reported on an improved method,[3] in which cyto-
sine nucleoside derivatives were reacted with triphosgene and alcohols in the
presence of N,N-diisopropyl ethylamine at room temperature. But this patent
method is only suitable for mg-scale preparation. Herein we report a con-
venient method for preparing them in gram-scale from cytosine nucleoside
derivatives and the corresponding alcohols without a base via unseparated
cytosine nucleoside isocyanate intermediates to meet the requirement for in
vivo screening of N4-alkyloxycarbonyl cytosine nucleosides.
In our work, it was found that the classical reaction condition for aryl
isocyanate from aryl amine is suitable to cytosine nucleosides. Reacting the
nucleosides 1 with triphosgene in refluxing toluene gives the unprecedentedly
reported cytosine nucleoside isocyanates 2, which are sensitive to moisture
and cannot be purified by chromatography on silica gel. We confirmed the
existence of this intermediate by crystallization and mass spectroscopy. For-
tunately, the separation of these isocyanates is not necessary for the synthesis
of target compounds. The carbamates 3 will be produced easily in one pot by
adding the corresponding alcohols to the reacting vessel directly.
In scaling up this reaction, we found the main essentials were that the yield
and the purity of the product are variable to the concentration of the reactants
Scheme 1.

Facile One-Pot Synthesis of N4-Alkyloxycarbonyl Cytosine Nucleosides
3275

3276
Chen and Cen
in toluene and the initial heating rate. After optimization, it was found that
keeping the concentration of the nucleoside substrate in toluene less than
0.1M and heating the reaction mixture rapidly to reflux are crucial points to
obtain high yield of pure product.
Application of 30,50-dibenzoyl-4-amino thymidine 1A and a synthetic
intermediate 1B for Lamivudine (an antiviral agent) exemplified the use of
the synthesis tactic (Sch. 1, Table 1).
Further examples are demonstrated by the synthesis of several Capecit-
abine (an antitumor agent) analogues 30(C–F) (Sch. 2, Table 2) using this
method. The carbamates 3(C–F) obtained are very pure and the protection
groups of the free hydroxyls on the sugar moiety of 3(C–F) are finally
removed to afford the desired compounds 30(C–F). Some of the products
have been subjected to bioactivity test.
EXPERIMENTAL
All melting points were uncorrected. H1 NMR were recorded on INOVA-
400 spectrometer in CDCl3 or (CD3)SO using tetramethylsilane (TMS) as an
internal standard. Mass spectra were performed on Micro Mass Q-Tof Micro
high performance liquid chromatography (HPLC)-MS. Data of H1 NMR
shown in Tables 1 and 2 do not contain peaks of all protons exchangeable
with D2O.
GENERAL PROCEDURE
Mix 2.2 mmol cytosine nucleoside derivative 1 and 0.75 g (2.5 mmol)
triphosgene in 40 mL toluene. Rapidly heat the mixture to reflux and keep
Scheme 2.

Facile One-Pot Synthesis of N4-Alkyloxycarbonyl Cytosine Nucleosides
3277

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Chen and Cen
boiling for 1 hr (here the isocyanate intermediate 2 could be isolated by crys-
tallization from proper solvents after removing toluene). To this clear boiling
solution, add 5 mmol alcohol in one portion. The reaction completes in 10 min
by thin layer chromotography (TLC) (silica gel, GF254). After evaporating
the solvent in vacuo, the residue could be crystallized in suitable solvent to
get 3.
If the deprotected product is desired, taking the benzoyl protection as an
example, the retained residue is dissolved in 50 mL methanol and cooled to
08C. Two mL of 5N sodium methoxide in methanol is added and the
mixture is stirred at room temperature for 1 hr. Then the mixture is neutralized
with HCl-EtOH and the solvent is removed in vacuo. The residue could be
crystallized in suitable solvent or purified by chromatography on silica gel
column to get 30.
REFERENCES
1. (a) Hattori, K.; Kohchi, Y.; Oikawa, N.; Suda, H.; Ura, M.; Ishikawa, T.;
Miwa, M.; Endoh, M.; Eda, H.; Tanimura, H.; Kawashima, A.; Horii, I.;
Ishitsuka, H.; Shimma, N. Design and synthesis of the tumor-activated
prodrug of dihydropyrimidine dehydrogenase (DPD) inhibitor, RO
094889 for combination therapy with capecitabine. Bioorg. Med.
Chem. Lett. 2003, 13 (5), 867–872; (b) Kim, K.; Kim, J.; Lee, K.-H.;
Noh, M.; Kim, Y.; Park, H. Synthesis and biological activity of the new
5-fluorocytosine derivatives, 50-deoxy-N-alkyloxycarbonyl-5-fluorocyto-
sine-50-carboxylic acid. Bioorg. Med. Chem. Lett. 2002, 12 (3),
483–486; (c) Shimma, N.; Umeda, I.; Arasaki, M.; Murasaki, C.;
Masubuchi, K.; Kohchi, Y.; Miwa, M.; Ura, M.; Sawada, N.;
Tahara, H.; Kuruma, I.; Horii, I.; Ishitsuka, H. The design and synthesis
of a new tumor-selective fluoropyrimidine carbamate, Capecitabine.
Bioorg. Med. Chem. 2000, 8 (7), 1697–1706.; (d) Arasaki, M.N.R.;
Ishitsuka, H.; Kuruma, I.; Miwa, M.; Murasaki, C.; Shimma, N.;
Umeda, I.I.H. N-Oxycarbonyl-substituted 50-deoxy-5-fluorocytidines as
antitumor agents. EP 602,454, June 22, 1994.; (d) Hertel, L.W.;
Kroin, J.S. 20-Deoxy-20,20-difluoro-(4-substituted pyrimidine) nucleosides
having antiviral and anti-cancer activity and intermediates. EP 576,230,
December 29, 1993.
2. (a) Kobori, A.; Miyata, K.; Ushioda, M.; Seio, K.; Sekine, M. A new
method for the synthesis of oligodeoxyribonucleotides containing 4-N-
alkoxycarbonyldeoxycytidine derivatives and their hybridization proper-
ties. J. Org. Chem. 2002, 67 (2), 476–485; (b) Merk, C.; Reiner, T.;
Kvasyuk, E.; Pfleiderer, W. Nucleotides part LXVII the 2-cyanoethyl

Facile One-Pot Synthesis of N4-Alkyloxycarbonyl Cytosine Nucleosides
3279
and (2-cyanoethoxy)carbonyl group for base protection in nucleoside and
nucleotide chemistry. Helv. Chim. Acta 2000, 83 (12), 3198–3210;
(c) Alvarez, K.; Vasseur, J.; Beltran, T.; Imbach, J. Photo-cleavable
protecting groups as nucleobase protections allowed the solid-phase
synthesis of base-sensitive SATE-prooligodeoxyribonucleotides. J. Org.
Chem. 1999, 64 (17), 6319–6328; (d) Wagner, T.; Pfleiderer, W. Nucleo-
tides. Part 50. Aglycon protection by the (2-dansylethoxy)carbonyl [(2-
f[5-(dimethylamino)naphthalen-1-yl]sulfonyl)ethoxygcarbonyl; dnseoc]
group. A new variation in oligodeoxyribonucleotide synthesis. Helv.
Chim. Acta 1997, 80 (1), 200–212; (e) Hotoda, H.; Saito, R.;
Sekine, M.; Hata, T. Synthesis of cytidyl(30-50)adenosine bearing 20(30)-
O-leucyl ester via a phosphorothioate triester intermediate. Tetrahedron
1990, 46 (4), 1181–1190; (f) Hayakawa, Y.; Wakabayashi, S.; Kato, H.;
Noyori, R. The allylic protection method in solid-phase oligonucleotide
synthesis. An efficient preparation of solid-anchored DNA oligomers.
J. Am. Chem. Soc. 1990, 112 (5), 1691–1696; (g) Koole, L.H.;
Moody,
H.M.;
Broeders,
N.L.H.L.;
Quaedflieg,
P.J.L.M.;
Kuijpers, W.H.A.; Van Genderen, M.H.P.; Coenen, A.J.J.M.; Van der
Wal, S.; Buck, H.M. Synthesis of phosphate-methylated DNA fragments
using 9-fluorenylmethoxycarbonyl as transient base protecting group.
J. Org. Chem. 1989, 54 (7), 1657–1664.
3. Hattori, K.; Ishikawa, T.; Ishitsuka, H.; Kohchi, Y.; Oikawa, N.;
Shimma, N.; Suda, H. Preparation of 50-deoxycytidines as antitumor
agents. WO 9,940,099, August 12, 1999.
Received in Japan April 22, 2004