Synthesis and biological evaluation of novel D-2′-azido-2′,3′-dideoxyarabinofuranosyl-4′- thiopyrimidines and purines

Article abstract of DOI:10.1016/S0960-894X(02)00394-3

Novel D-2′-azido-2′,3′-dideoxyarabinofuranosyl-4′- thiopyrimidines and purines have been synthesized, starting from L-xylose via azidation at the 2′-position as a key step. Most of the final nucleosides exhibited toxicity-dependent anti-HIV-1 activity, among which D-α-adenine analogue 3h was found to be the most cytotoxic.

Full text of DOI:10.1016/S0960-894X(02)00394-3

Bioorganic & Medicinal Chemistry Letters 12 (2002) 2403–2406
Synthesis and Biological Evaluation of Novel
D-20-Azido-20,30-dideoxyarabinofuranosyl-40-thiopyrimidines
and Purines
Hea Ok Kim,a Yong Hee Park,b Hyung Ryong Moonb and Lak Shin Jeongb,*
aDivision of Chemistry and Molecular Engineering, Seoul National University, Seoul 151-742, Republic of Korea
bLaboratory of Medicinal Chemistry, College of Pharmacy, Ewha Womans University, Seoul 120-750, Republic of Korea
Received 27 March 2002;accepted 22 May 2002
Abstract—Novel d-20-azido-20,30-dideoxyarabinofuranosyl-40-thiopyrimidines and purines have been synthesized, starting from
l-xylose via azidation at the 20-position as a key step. Most of the final nucleosides exhibited toxicity-dependent anti-HIV-1 activity,
among which d-a-adenine analogue 3h was found to be the most cytotoxic. # 2002 Elsevier Science Ltd. All rights reserved.
Introduction
Herein, we report the synthesis and antiviral activity
of novel d-20-‘up’-azido-20,30-dideoxy-40-thiopyrimidine
and purine nucleosides (3), starting from l-xylose via
azidation as a key step.
Substitution of the 20- or 30-position of the d-20,30-
dideoxynucleosides with fluorine or azide has led to the
development of potent anti-HIV agents.1 Among them,
20-‘up’-fluoro-20,30-dideoxyadenosine (1, 20-F-ddA)2 has
been undergoing clinical trials for the treatment of
AIDS and AIDS-related complex (ARC) and 20-‘up’-
azido-20,30-dideoxyadenosine (2)3 has also been reported
to show potent anti-HIV-1 activity (Fig. 1).
Results and Discussion
For the synthesis of the desired pyrimidine and purine
nucleosides 3, the glycosyl donor 9 (Scheme 1) was first
prepared and then condensed with nucleobases.
40-Thionucleosides in bioisosteric relationships with
40-oxonucleosides have also been paid great attention by
medicinal chemists for the development of new antiviral
and antitumor agents since they are metabolically stable
as well as biologically active.4 Recently, along with the
development of the efficient synthetic pr0oc0edures of
4-thiosugar,5 20-deoxy-20-substituted-6 and 2 ,3 -dideoxy-
20-fluoro-40-thionucleosides7 have been synthesized and
reported to show promising antiviral and antitumor
activities. More recently, our laboratory has reported
the structure–activity relationships of d- and l-20-
‘down’-azido-20,30-dideoxy-40-thionucleosides as anti-
viral and antitumor agents.8 Based on these findings, it
was of interest to design and synthesize the target
40-thionucleosides 3 shown in Fig. 1, since sulfur of the
40-thionucleosides is in bioisosteric relationship with
oxygen of the corresponding 40-oxonucleosides.
l-Xylose was converted to compound 4 according to an
efficient procedure developed by our laboratory.8 The
standard Mitsunobu reaction was employed to invert
the stereochemistry of the hydroxyl group of 4, giving
the benzoate 5 in 70% yield without the participation of
sulfur atom.9 Treatment of 5 with methanolic ammonia
gave 6, which was subjected to another Mitsunobu
reaction using diphenylphosphoryl azide (DPPA) as a
nucleophile to afford the ‘up’ azido derivative 7 in good
yield. As in the case of the synthesis of ‘down’ azido
sugar,8 no sulfur participation was observed in Mitsu-
nobu reaction with DPPA, proceeding in a pure SN2
reaction. It is also interesting to note that in the case of
the preparation of ‘down’ azido derivative, the same
Mitsunobu reaction failed to give the desired azido
derivative, requiring two-step conversion (mesylation
and substitution with sodium azide).8 Oxidation of 7
with mCPBA followed by heating the resulting sulfoxide
8 with acetic anhydride yielded the key intermediate 9,
which is ready for the condensation with nucleobases.
*Corresponding author. Tel.: +82-2-3277-3466;fax: +82-2-3277-
2851;e-mail: lakjeong@ewha.ac.kr
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00394-3

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H. O. Kim et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2403–2406
Figure 1. The rationale for the design of the desired nucleosides 3.
Scheme 2. Reagents and conditions: (a) silylated thymine, TMSOTf,
ClCH2Cl2Cl, rt, 12 h;(b) n-Bu4NF, THF, rt, 1.5 h;(c) BzCl, pyridine,
70 ꢀC, 48 h;(d) NaOMe, MeOH, rt, 15 h.
Scheme 1. Reagents and conditions: (a) Ph3P, DEAD, BzOH, THF,
50 ꢀC, 15 h;(b) NH 3, MeOH, rt, 15 h;(c) Ph 3P, DEAD, DPPA, THF,
0 ꢀC, 1 h;(d) mCPBA, CH2Cl2, ꢁ78 ꢀC, 2 h;(e) Ac 2O, 100 ꢀC, 15 h.
For the synthesis of thymine derivatives, 3a and 3b
(Scheme 2), acetate 9 was condensed with silylated thy-
mine in the presence of TMSOTf as a Lewis acid to give
10 as an inseparable anomeric mixture (75%). Since
desilylation of 10 with n-tetrabutylammonium fluoride
also produced an inseparable anomeric mixture, the
desilylated product was treated with excess benzoyl
chloride in pyridine at 70ꢀC to afford b-anomer 11 and
a-anomer 12 in 1:2 ratio after the purification on silica
gel. The major formation of a-anomer 12 over b-anomer
11 during the condensation is believed to be attributed to
the presence of bulky azido group on the b-side since
condensation of 20-azido-20,30-dideoxyribosyl acetate
with silylated thymine in the presence of TMSOTf pro-
duced b-anomer and a-anomer in 3:1 ratio.8 Anomeric
in the case of compound 12, resulting in a-anomer. In
addition to NOE effect, similar H NMR patterns of 11
1
and 12 were observed to those of 20-azido-20,30-dideoxy-40-
thioribofuranosylnucleosides.8 For example, the 40-pro-
ton of a-anomer 12 appeared further downfield than that
of b-anomer 11 because of the deshielding effect by cyto-
sine and the 50-protons of 11 appeared further downfield
than those observed for 12 due to the same deshielding
1
1
effect. These typical H NMR patterns and similar H
NOE effects were consistently maintained in other pyr-
imidine and purine nucleoside derivatives synthesized in
Schemes 3 and 4. Treatment of each of 11 and 12 with
sodium methoxide in methanol yielded the final nucleo-
sides, 3a and 3b, respectively.
1
configurations of 11 and 12 were readily assigned by H
Other pyrimidine nucleosides, cytosine derivatives 3c
and 3d, were synthesized as depicted in Scheme 3.
Condensation of acetate 9 with silylated N4-benzoylcy-
tosine in the presence of TMSOTf gave the b-anomer 13
(23%) and a-anomer 14 (49%) after the purification on
NMR NOE experiments as shown in Scheme 2. Irradia-
tion of 20-H of compound 11 gave a large NOE effect
(5.0%) on its 10-H, indicating b-anomer, while a small
NOE effect (1.8%) was observed on the same experiment

H. O. Kim et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2403–2406
2405
silica gel. Both anomers 13 and 14 were deproteced under
the standard conditions to afford 3c and 3d, respectively.
9 with silylated 6-chloropurine in the presence of
TMSOTf yielded 15 as an inseparable anomeric mix-
ture. As in the case of 20-‘down’ azido derivative,8 the
N3-isomer formed initially during the condensation
cleanly migrated to the N9-isomer on heating. Desilyla-
tion of 15 with n-tetrabutylammonium fluoride gave the
b-anomer 16 and a-anomer 17 in about 1:3 ratio after
the isolation by silica gel column chromatography. The
b-anomer 16 was converted to N6-methyladenine deri-
vative 3e10 and adenine derivative 3f by heating with
methanolic methylamine and methanolic ammonia,
respectively. Similarly, N6-methyladenine derivative
3g11 and adenine derivative 3h were obtained from the
a-anomer 17.
The synthetic route to the purine nucleoside analogues,
3e–3h, is shown in Scheme 4. Condensation of the acetate
All the synthesized nucleosides 3a–3h were tested against
several viruses such as HIV-1, HSV-1, and HSV-2.
As shown in Table 1, most of the compounds were
found to exhibit toxicity-dependent anti-HIV-1 activity
in MT-4 cells, among which a-adenine derivative 3h was
the most cytotoxic. Unlike the nontoxic and potent
antiviral activity of 20-azido-20,30-di-deoxy-40-oxonucleo-
sides, all the corresponding 40-thionucleosides exhibited
cytotoxicity, indicating that small change from oxygen
to sulfur led to a big difference in biological activity
(antiviral versus cytotoxic), despite their bioisosteric
relationship. On the basis of the cytotoxicity of 3h, its
anticancer assay is in progress in our laboratory and the
results will be reported elsewhere. However, all the syn-
thesized compounds did not exhibit antiviral activity
against HSV-1 and HSV-2.
Scheme 3. Reagents and conditions: (a) silylated N4-benzoylcytosine,
TMSOTf, ClCH2Cl2Cl, rt, 12 h;(b) n-Bu4NF, THF, rt, 1.5 h;(c) NH 3,
MeOH, rt, 15 h.
In summary, we have completed the synthesis of
novel d-20-azido-20,30-dideoxyarabinofuranosyl-40-thio-
pyrimidines and purines, starting from l-xylose via azi-
dation at the 20-position as a key step. Since most of the
final nucleosides exhibited toxicity-dependent anti-HIV-1
activity, it is believed that in terms of medicinal chem-
istry, this class of nucleosides can act as a new template
for the design of anticancer agents, instead of antiviral
agents.
Table 1. Antiviral activities and cytotoxicity of the synthesized
nucleosides
Compd
HIV-1a
EC50
Cytotoxicityb
CC50
HSV-1
EC50
HSV-2
EC50
(mg/mL)
(mg/mL)
(mg/mL)
(mg/mL)
3a
3b
3c
3d
3e
3f
3g
>56.5
>63.5
>41.7
>100
>48.1
>66.6
>61.5
>17.3
0.0005
ND
56.1
63.5
41.7
>100
48.1
66.6
61.5
17.3
>100
>100
>100
>100
>100
>100
>100
>100
0.52
>100
>100
>100
>100
>100
>100
>100
>100
>100
0.88
3h
AZT
Acyclovir
0.52
>76.6 (HSV-1)
>11.4 (HSV-2)
0.13
aIndicative of 50% cytopathic concentration in virus-infected MT-4
cells.
bIndicative of 50% survival concentration in virus-uninfected MT-4
cells.
Scheme 4. Reagents and conditions: (a) silylated 6-chloropurine,
TMSOTf, ClCH2Cl2Cl, rt to 40 ꢀC, 15 h;(b) n-Bu4NF, THF, AcOH,
rt, 1 h;(c) MeNH 2, MeOH, 80 ꢀC, 24 h;(d) NH 3, MeOH, 80 ꢀC, 24 h.

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H. O. Kim et al. / Bioorg. Med. Chem. Lett. 12 (2002) 2403–2406
Miura, S.;Sakata, S.;Sasaki, T.;Matsuda, A. J. Org. Chem.
Acknowledgements
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This work was supported by a grant from the Korea
Health 21 R&D Project, Ministry of Health & Welfare,
Republic of Korea (01-PJ2-PG6–01NA01–0002). The
authors thank Dr. C.-K. Lee (KRICT) for the antiviral
testing.
7. (a) Jeong, L. S.;Nicklaus, M. C.;George, C.;Marquez,
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Tetrahedron
References and Notes
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10. Compound 3h: UV (MeOH) lmax 260 nm;IR (KBr) 2115
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1
cmꢁ1 (N3); H NMR (CDCl3, 400 MHz) d 8.40 (s, 1H, H-8),
8.08 (s, 1H, H-2), 5.99 (d, 1H, J=6.0 Hz, 10-H), 5.58 (br s, 2H,
NH2), 4.78 (td, 1H, J=5.6, 8.0 Hz, 20-H), 4.11 (quintet, 1H,
J=6.0 Hz, 40-H), 3.85 (dd, 1H, J=4.8, 11.2 Hz, 50-Ha), 3.78
(dd, 1H, J=6.0, 11.2 Hz, 50-Hb), 3.16 (s, 1H, OH), 2.50 (m,
1H, 30-Ha), 2.19 (m, 1H, 30-Hb). Anal. calcd for C10H12N8OS:
C, 41.09;H, 4.14;N, 38.33;S, 10.97. Found: C, 41.45;H, 4.33;
N, 38.69;S, 10.73.
11. Compound 3f: UV (MeOH) lmax 260 nm;IR (KBr)
2114.50 cmꢁ1 (N3); 1H NMR (CDCl3, 400 MHz) d 8.38 (s, 1H,
H-8), 8.32 (s, 1H, H-2), 6.21 (d, 1H, J=6.0 Hz, 10-H), 5.54 (br
s, 2H, NH2), 4.40 (td, 1H, J=5.2, 10.8 Hz, 20-H), 4.01 (d, 1H,
J=4.0 Hz, 50-Ha), 4.00 (d, 1H, J=4.0 Hz, 50-Hb), 3.83 (m, 1H,
40-H), 3.50 (br s, 1H, OH), 2.53–2.46 (m. 2H, 30-H). Anal.
calcd for C10H12N8OS: C, 41.09;H, 4.14;N, 38.33;S, 10.97.
Found: C, 41.21;H, 4.10;N, 38.06;S, 10.89.
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