A novel synthesis of new antineoplastic 2′-deoxy-2′-substituted-4′-thiocytidines

Full text of DOI:10.1021/jo9519423

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J . Org. Chem. 1996, 61, 822-823
Ch a r t 1
A Novel Syn th esis of New An tin eop la stic
2′-Deoxy-2′-su bstitu ted -4′-th iocytid in es
Yuichi Yoshimura,*,† Kenji Kitano,† Hiroshi Satoh,†
Mikari Watanabe,† Shinji Miura,† Shinji Sakata,†
Takuma Sasaki,‡ and Akira Matsuda§
Research and Development Division, Yamasa Corporation,
2-10-1 Araoicho, Choshi, Chiba 288, J apan,
Cancer Research Institute, Kanazawa University,
13-1 Takara-machi, Kanazawa 920, J apan, and
Faculty of Pharmaceutical Sciences, Hokkaido University,
Kita-12, Nishi-6, Kita-ku, Sapporo 060, J apan
Received November 2, 1995
Nucleosides containing sulfur atoms instead of lactol
oxygen have been the focus of much recent research
because of their potent biological activity. Walker1 and
Secrist2 independently reported that 2′-deoxy-4′-thiopy-
rimidine nucleosides (1) have antiviral and cytotoxic
effects. 2′,3′-Dideoxy-3′-thiacytidine (3TC, 2) has been
shown to have potent anti-human immunodeficiency
virus (HIV) activity4 and anti-human hepatitis B virus
activity.5,6 Furthermore, new antineoplastic cytidine
analogues having various 2′-substituents, 2′-deoxy-2′,2′-
difluorocytidine7 (Gemcitabine, 3), 2′-deoxy-2′-methyl-
enecytidine8 (DMDC, 4), and 2′-deoxy-2′(E)-(fluorometh-
ylene)cytidine (5)9 have been described.
The specific properties of 4′-thionucleosides and potent
cytotoxicity of 2′-substituted cytidine analogues prompted
us to synthesize 4′-thioDMDC (6) and 4′-thiogemcitabine
(7) (Chart I). Since the first synthesis of 4′-thionucleo-
sides was described in 1964,10 several alternate synthetic
methods have been reported.1-3,11-14 These procedures
are not optimal, however, due to a lengthy manipu-
lation3,10-12 and limitation to the use of 2′-deoxy deriva-
tives.1,2,13 Thus, a new synthetic strategy utilizing more
generally available compounds would increase the suc-
cess of this synthesis. Recent progress was made in this
regard by Chu et al.,6 in the synthesis of 3TC. These
results led us to synthesize the title compounds employ-
ing an anhydrothiosugar as a key intermediate. In the
present study, we describe a novel synthesis of 4′-
thiocytidines originating from D-glucose.
In four steps, diisopropylideneglucose 8 was converted
to 3-benzylxylose 9, which was then subjected to acidic
methanolysis to produce an anomeric mixture of 1-O-
methyl-3-O-benzylxylose (10) with a high yield. Anomers
were easily separated by a silica gel column. The
separated R- and â-anomers of 10 were mesylated,
producing R- and â-11, followed by treatment with
sodium sulfide in DMF to yield bicyclic R- and â-12 at
78% and 73% yield, respectively. Acid hydrolysis and
hydride reduction of R,â-12 produced 1,4-anhydro-4-
thioarabinitol 13 with a 90% yield.15 The primary alcohol
of 13 was selectively protected with a tert-butyldiphen-
ylsilyl (TBDPS) group to produce 14, which was oxidized
with DMSO-Ac2O, giving 15. The Wittig reaction of 15
yielded 16 (efficiency: 74% of 14). A reaction with boron
trichloride (BCl3) effectively deprotected the benzyl group
of 16 to yield 17 at over 90% efficiency.
Pioneering works of Kita et al. led to application of
Pummerer reaction for the synthesis of C-C bond at the
R-position of sulfoxides.16 O’Neil and Hamilton also
reported the syntheses of a tetrahydrothienylthymine
and other derivatives using TMSOTf as a catalyst under
similar reaction conditions.17 On the basis of this, we
designed the synthesis of the 4′-thiocytidine utilizing
sulfoxide 18 obtained from m-CPBA oxidation of 17. The
compound 18 was treated with 3 equiv of the silylated
N-acetylcytosine and 2 equiv of TMSOTf producing the
4′-thiocytidine derivative R,â-19 (Scheme 1) with a 74%
yield (R:â ) 2.5:1).18 The reaction conditions have not
† Yamasa Corporation.
‡ Kanazawa University.
§ Hokkaido University.
(1) Dyson, M. R.; Coe, P. L.; Walker, R. T. J . Med. Chem. 1991, 34,
2782-2786.
(2) Secrist, J . A.; Tiwari, K. N.; Riordan, J . M.; Montgomery, J . A.
J . Med. Chem. 1991, 34, 2361-2366.
(3) Tiwari, K. N.; Secrist, J . A.; Montgomery, J . A. Nucleosides
Nucleotides 1994, 13, 1819-1828.
(4) (a) Schinazi, R. F.; Chu, C. K.; Peck, A.; McMillan, A.; Mathis,
R.; Cannon, D.; J eong, L.-S.; Beach, J . W.; Choi, W.-B.; Yeola, S.; Liotta,
D. C. Antimicrob. Agents Chemother. 1992, 36, 672-676. (b) Coates,
J . A. V.; Cammack, N.; J enkinson, H. J .; J owett, A. J .; J owett, M. I.;
Pearson, B. A.; Penn, C. R.; Rouse, P. L.; Viner, K. C.; Cameron, J . M.
Antimicrob. Agents Chemother. 1992, 36, 733-739.
(5) Doong, S.-L.; Tsai, C.-H.; Schinazi, R. F.; Liotta, D. C.; Chen,
Y.-C. Proc. Natl. Acad. Sci. USA 1991, 88, 8495-8499.
(6) Beach, J . W.; J eong, L. S.; Alves, A. J .; Pohl, D.; Kim, H. O.;
Chang, C.-N.; Doong, S.-L.; Schinazi, R. F.; Cheng, Y.-C.; Chu, C. K.
J . Org. Chem. 1992, 57, 2217-2219.
(7) (a) Hertel, L. W.; Kroin, J . S.; Misner, J . W.; Tustin, J . M. J .
Org. Chem. 1988, 53, 2406-2409. (b) Hertel, L. W.; Boder, G. B.; Kroin,
J . S.; Rinzel, S. M.; Poore, G. A.; Todd, G. C.; Grindey, G. B. Cancer
Res. 1990, 50, 4417-4420.
(8) Yamagami, K.; Fujii, A.; Arita, M.; Okumoto, T.; Sakata, S.;
Matsuda, A.; Ueda, T. Cancer Res. 1991, 51, 2319-2323.
(9) Bitonti, A. J .; Dumont, J . A.; Bush, T. L.; Cashman, E. A.; Cross-
Doersen, D. E.; Wright, P. S.; Matthews, D. P.; McCarthy, J . R.; Kaplan,
D. A. Cancer Res. 1994, 54, 1485-1490.
(14) Fluorine substituted derivatives and dideoxy analogues, includ-
ing AZT, of 4′-thionucleosides were reported. Fluorine substituted
derivatives: (a) J eng, L. S.; Nicklaus, M. C.; George, C.; Marquez, V.
E. Tetrahedron Lett. 1994, 35, 7569-7572. (b) J eng, L. S.; Nicklaus,
M. C.; George, C.; Marquez, V. E. Tetrahedron Lett. 1994, 35, 7573-
7576. Dideoxy derivatives: (c) Secrist, J . A.; Riggs, R. M.; Tiwari, K.
N.; Montgomery, J . A. J . Med. Chem. 1992, 35, 533-538. (d) Tber, B.;
Fahmi, N.-E.; Ronco, G.; Villa, P.; Ewing, D. F.; Mackenzie, G.
Carbohydr. Res. 1995, 267, 203-215.
(10) Reist, E. J .; Gueffroy, D. E.; Goodman, L. J . Am. Chem. Soc.
1964, 86, 5658-5663.
(11) Bobek, M.; Bloch, A.; Parthasarathy, R.; Whistler, R. L. J . Med.
Chem. 1975, 18, 784-787.
(12) Leydier, C.; Bellon, L.; Barascut, J .-L.; Deydier, J .; Maury, G.;
Pelicano, H.; El Alaoui, M. A.; Imbach, J .-L. Nucleosides Nucleotides,
1994, 13, 2035-2050.
(13) Uenishi and his co-workers reported an elegant synthesis of
2′-deoxy-4′-thionucleosides using Sharpless asymmetric epoxidation:
(a) Uenishi, J .; Motoyama, M.; Nishiyama, Y.; Wakabayashi, S. J .
Chem. Soc. Chem. Commun. 1991, 1421-1422. (b) Uenishi, J .; Taka-
hashi, K.; Motoyama, M.; Akashi, H.; Sasaki, T. Nucleosides Nucle-
otides 1994, 13, 1347-1361.
(15) During the course of our investigation, the synthesis of 13 was
independently reported by another group: Yuasa, H.; Kajimoto, T.;
Wong, C.-H. Tetrahedron Lett. 1994, 35, 8243-8246.
(16) Kita, Y.; Tamura, O.; Yasuda, H.; Itoh, F.; Tamura, Y. Chem.
Pharm. Bull. 1985, 33, 4235-4241.
(17) O’Neil, I. A.; Hamilton, K. M. Synlett 1992, 791-792.
0022-3263/96/1961-0822$12.00/0 © 1996 American Chemical Society

Communications
J . Org. Chem., Vol. 61, No. 3, 1996 823
Sch em e 1a
a
(a) BnBr, NaH, DMF, THF; (b) 2 M HCl, THF; (c) NaIO4, H2O, MeOH; (d) NaBH4, MeOH, 82% from 8; (e) 5% HCl/MeOH, 91%; (f)
MsCl, pyridine; (g) Na2S, DMF, 100 °C, 78% (R-anomer) and 73% (â-anomer) from 10; (h) 4 M HCl, THF; (i) NaBH4, MeOH. 90% from 12;
(j) TBDPSCl, imidazole, DMF, 87%; (k) DMSO, Ac2O; (l) Ph3P+CH3Br-, NaH, tert-amyl alcohol, THF, 74% from 14; (m) BCl3, CH2Cl2,
-78 °C, then MeOH, pyridine. 92%; (n) m-CPBA, CH2Cl2, -78 °C; (o) silylated N-acetylcytosine, TMSOTf, ClCH2CH2Cl, 0 °C, 74% from
17; (p) TBAF, THF; (q) aqueous NH3, MeOH, then HPLC separation, 34% (R-anomer) and 13% (â-anomer) from 19.
Sch em e 2a
been optimized yet; â-selectivity remains a problem.
Finally, the R,â-mixture of 19 was deprotected by tet-
rabutylammonium fluoride (TBAF) followed by aqueous
ammonia in methanol. Pure R- and â- anomers of 6 were
obtained from the mixture by HPLC (R; 34%, â; 13%).
The method described above was applied to the syn-
thesis of 4′-thiogemcitabine. (Diethylamido)sulfur tri-
fluoride (DAST) treatment19 of ketone 15 produced the
2-deoxy-2,2-difluoro derivative 20 with a 48% yield.
Compound 20 was simultaneously deprotected and ben-
zoylated to give 21, which was oxidized to produce 22.
The Pummerer type glycosylation of 22 resulted in a 57%
yield of the protected 4′-thiogemcitabine 23 (Scheme 2)
as an anomeric mixture (R:â ) 2.6:1).20 Deprotection of
23, followed by HPLC separation, produced the R- and
â-derivatives of 4′-thiogemcitabine (7).
We evaluated the antineoplastic properties of 6 and 7
against human T-cell leukemia (CCRF-HSB-2) and KB
a
cells. None of the R-4′-thionucleosides had any measur-
able activity, whereas â-4′-thioDMDC (6) exhibited a
potent antitumor activity against CCRF-HSB-2 cells (IC50
) 0.0091 µg/mL). In contrast, â-4′-thiogemcitabine (7)
was only weakly active in the same cell line (IC50 ) 1.5
µg/mL). â-4′-Thio-DMDC (6) was also effective against
a solid tumor, KB cells (IC50 ) 0.12 µg/mL). The activity
was higher than that of DMDC 4 (KB cell; IC50 ) 0.44
µg/mL). It is noteworthy that 4′-thioDMDC (6) had
potent antineoplastic activity, but 4′-thiogemcitabine (7)
did not, while both 3 and 4 were highly active.7,8
(a) DAST, benzene, 0 °C, and then room temperature 48%;
(b) BCl3, CH2Cl2, -78 °C, and then MeOH, pyridine; (c) Bz2O,
Et3N, DMAP, CH3CN, 79% from 20; (d) m-CPBA, CH2Cl2, -78
°C; (e) silylated N-acetylcytosine, TMSOTf, ClCH2CH2Cl, 0 °C, 57%
from 21; (f) TBAF, THF; (g) aqueous NH3, MeOH, then HPLC
separation, 36% (R-anomer) and 15% (â-anomer) from 23.
Ack n ow led gm en t. The authors are grateful to Dr.
K. Horita, Health Science University of Hokkaido, for
useful suggestions. The authors thank Dr. A. Kuni-
naka, Yamasa Corporation, for his critical reading of
the manuscript. The authors also acknowledge Mr. M.
Morozumi and Dr. H. Machida, Yamasa Corporation,
for their helpful discussions.
(18) The stereochemistry of the anomeric carbon was determined
by an NOE analysis of the free nucleoside 6 (minor isomer). It showed
7.1% NOE at the H-3′ proton when irradiated at H-6.
(19) An, S.-H.; Bobek, M. Tetrahedron Lett. 1986, 27, 3219-3222.
(20) The stereochemistry at the 1′-position was determined, after
deprotection, by comparison of coupling constants of H-1′ with that of
gemcitabin described in ref 7a.
Su p p or tin g In for m a tion Ava ila ble: Experimental pro-
cedures and characterization data (9 pages).
J O9519423