Synthesis and anti-HIV activity of triazolo-fused 3′,5′-cyclic nucleoside analogues derived from an intramolecular Huisgen 1,3-dipolar cycloaddition

Article abstract of DOI:10.1002/hlca.201100366

Triazolo-fused 3′,5′-cyclic nucleoside analogues were synthesized by an intramolecular 1,3-dipolar cycloaddition of nucleoside-derived azido-alkynes in a regio- and stereospecific manner. The thymine nucleoside base in these target compounds was transform

Full text of DOI:10.1002/hlca.201100366

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Synthesis and Anti-HIV Activity of Triazolo-Fused 3’,5’-Cyclic Nucleoside
Analogues Derived from an Intramolecular Huisgen 1,3-Dipolar
Cycloaddition
by Jingbo Sun, Xinyu Liu, Hongming Li, Ronghui Duan, and Jinchang Wu*
College of Chemistry, Jilin University, Changchun 130012, P. R. China
(phone: þ 86-15044068371; fax: þ 86-0431-85195516; e-mail: jcwu@jlu.edu.cn)
Triazolo-fused 3’,5’-cyclic nucleoside analogues were synthesized by an intramolecular 1,3-dipolar
cycloaddition of nucleoside-derived azido-alkynes in a regio- and stereospecific manner. The thymine
nucleoside base in these target compounds was transformed successfully into the corresponding 5-
methylcytosine component. The synthesized compounds were examined in a MAGI assay for exploring
the anti-HIV activity and in a H9 T lymphocytes assay for measuring the cell toxicity.
Introduction. – Modification of nucleosides has been demonstrated as one of the
most promising pathways in searching for new therapeutic agents for the past decades
[1]. Nucleoside reverse transcriptase inhibitors (NRTIs), structurally featured as 2’,3’-
dideoxynucleoside analogs, constitute an important class of antiviral drugs that
mechanistically act as chain terminators for the production of viral genomic material in
its life cycle [2]. It has been revealed that the conformation of the sugar ring has a
profound impact on the biological activity of nucleosides, and many cyclic nucleoside
analogues with restricted conformation have been designed and synthesized to probe
the conformational preference demanded by the specific enzyme, aiming at finding new
and better drugs with improved profiles in drug resistance and delayed toxicity after
long-term treatment [3][1c].
The Huisgen 1,3-dipolar cycloaddition between azides and alkynes as one of the
most powerful click reactions has gained considerable attention and has found many
applications in recent years [4]. Noteworthy, the five-membered 1,2,3-triazole moiety
formed in this reaction has been employed as a widespread pharmacophore associated
with anti-HIV, anti-allergic, antifungal, antimicrobial, and other biological activities
[5]. Thus, the structural features and physiochemical properties of the triazole fragment
are of great interest in drug design and discovery [6].
As our efforts in the development of synthetic methods for the construction of
cyclic nucleoside analogues, we have previously reported the synthesis of 2’,3’-fused
uridines via intramolecular Michael addition and of 4’-spironucleosides via 1,5-
hydrogen translocation reactions [7]. We envisioned that enclosing a triazole moiety
into cyclic nucleosides would lead to a type of unexplored and unique compounds that
will combine a conformational-restriction concept with a triazole-structure feature in
the drug design. Herein, we report the synthesis of triazolo-fused tricyclic nucleosides
via intramolecular 1,3-dipolar cycloaddition between a 3’-a- or 3’-b-azido and a 5’-
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alkyne moiety and, alternatively, between a 5’-azido and 3’-a- or 3’-b-alkyne moiety of
thymidine and its 3’-epimer, respectively, and the subsequent transformation of the
cyclized products into the corresponding 5-methylcytosine nucleosides (thymine ¼ 5-
methylpyrimidine-2,4(1H,3H)-dione; cytosine ¼ 4-aminopyrimidin-2(1H)-one). Fur-
thermore, the anti-HIV activities of all the target compounds are also described.
Results and Discussion. – We started our synthesis from azide 1 which was derived
from thymidine following a literature procedure [8]. Selective propargylation (¼ prop-
2-ynylation) of the 5’-OH group was conducted with propargyl bromide (¼ 3-
bromoprop-1-yne) employing NaH as a base in THF under ultrasonic irradiation [9]
to give the precursor 2 in 85% yield. The azido-alkyne derivative 2 was then heated
under reflux in toluene [10] to afford the desired triazolo-fused cyclic compound 3 in
87% yield. The polar addition product was normally precipitated and purified by an
easy procedure. Furthermore, the nucleobase thymine in the resulting cyclic nucleoside
3 was successfully transformed into 5-methylcytosine to give compound 4 in a moderate
yield by means of a two-step procedure [11], firstly, by treatment with POCl3 and 1H-
1,2,4-triazole in the presence of Et3N, and then by treatment with ammonia in dioxane
(Scheme 1).
Scheme 1
a) NaH, THF, propargyl bromide (¼ 3-bromoprop-1-yne), ultrasound; 85%. b) Toluene, reflux; 87%. c)
1. POCl3, 1H-1,2,4-triazole, MeCN, Et3N; 2. dioxane, NH3 · H2O; 65% (2 steps).
To study the steric effect for the cycloaddition and to produce other novel
compounds, we synthesized the 3’-b-azido compound 6 from 5 following a literature
method [12] (Scheme 2). Selective propargylation of the 5’-hydroxy group was
achieved under the same conditions as for the preparation of 2 to give precursor 7,
which was then cyclized to the triazolo-fused compound 8 and transformed to the 5-
methylcyctosine compound 9 under the conditions shown in Scheme 2. Interestingly, we
detected some amount of the cyclization product when compound 7 was placed at room
temperature for a period of time. It is reasoned that the steric proximity of the azido
and alkynyl groups in cis configuration in 7 made the cycloaddition with compound 7
more feasible in comparison to that with compound 2.
Next, we synthesized compounds 10 [13] and 14 [14] as precursors, in which an azido
group was introduced at the 5’ position while the propargyl functionality was attached
at the 3’-a- or 3’-b position as ether appendage (Scheme 3). The precursors 11 and 15
were heated under reflux in toluene to produce the corresponding cyclic products 12

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Scheme 2
a) 1. MsCl (¼ MeSO2Cl), THF, Et3N; 2. LiN3, DMF, 1008; 3. 80% AcOH, 508; 72% (3 steps). b)
Propargyl bromide, THF, NaH; 75%. c) Toluene, reflux; 78%. d) 1. POCl3, 1H-1,2,4-triazole, MeCN,
Et3N; 2. dioxane, NH3 · H2O; 64% (2 steps).
and 16 which were transformed into the 5-methylcytosine products 13 and 17,
respectively. Similarly as with compound 7, we observed that a cycloaddition reaction
took place spontaneously when compound 15 was left standing at room temperature.
Scheme 3
a) Propargyl bromide, THF, NaH; 75%. b) Toluene, reflux; 78%. c) 1. POCl3, 1H-1,2,4-triazole, MeCN,
Et3N; 2. dioxane, NH3 · H2O; 50% (2 steps). d) 1. Ph3P, DIAD (¼diisopropyl azodicarboxylate ¼ di-
isopropyl diazenedicarboxylate), DMF; 2. 1n NaOH (aq.), EtOH; 70% (2 steps).

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The structures of the triazolo-fused nucleosides were established on the basis of
their spectroscopic data. For example, a s at d(H) 7.71 in the 1H-NMR spectrum of 12
indicated the H-atom of triazole ring. In addition, in the 13C-NMR spectrum, the
triazole C(4) and C(5) resonances were observed at d(C) 136.59 and 133.50 which is in
accordance with characteristic 13C-NMR shifts of 1,5-regioisomers [15]. Furthermore,
compound 12 was crystallized from MeOH and AcOEt, and was subjected to X-ray
crystal-structure analysis. The crystal structure (Fig.) unambiguously showed that the
triazole moiety of the fused nucleoside was indeed 1,5-disubstited, and additionally,
that the sugar ring was locked in the south conformation (C(2’) (¼ C7) up and C(3’)
(¼ C8) down corresponding to OꢀC(4’) (¼ O3)).
Figure. Crystal structure of compound 12. Arbitrary atom numbering.
The antiviral activity of the newly designed and synthesized triazolo-fused
nucleoside analogues were tested in a MAGI assay by the published procedure [16].
The viral infectivity was measured in MAGI-CCR5 cells infected by HIV-1 NL4-3
particles upon treatment with 50 mm of each compound. The cell toxicity of these
compounds was evaluated with H9 T lymphocytes. The 3’-azido-3’-deoxythymidine
(AZT; 1) was selected as the reference compound in the tests. Although the biological
results indicated that compounds 9 and 16 possessed the most significant antiviral
activity with relatively low cell toxicity among the synthesized compounds, all the
tested triazolo-fused cyclic compounds offered inferior anti-HIV activity compared
with the reference compound 1 under the test conditions.
Conclusions. – We demonstrated that an intramolecular 1,3-dipolar cycloaddition of
an azido and an alkyne moiety is a powerful means to synthesize triazolo-fused cyclic
nucleosides. The triazole moiety of these analogues tolerated a standard transformation
procedure of the 4-carbonyl into a 4-amino group in pyrimidine nucleosides. Some of
the novel compounds showed moderate anti-HIV activity in the test assay. Further
expansions of the presented methodology to the synthesis of other relevant triazolo-
fused cyclic nucleosides in searching for antiviral agents are under investigation in this
laboratory and will be disclosed in due course.
We thank the National Natural Science Foundation of China (No. 20572034). We thank Dr. W. Gao
for helping with the crystal structural analysis.
Experimental Part
General. All reactions were carried out under N2. CH2Cl2 was dried (anh. CaCl2). All other
commercial reagents were used as received without additional purification. Column chromatography

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(CC): silica gel G (SiO2; 200 – 300 mesh; Qingdao Haiyang Chemical Company, P. R. China). Anal. TLC:
2.5 ꢁ 5 cm plates coated with a 0.25 mm thickness of SiO2 GF 254. 1H- and 13C-NMR Spectra: Mercury
300BB; at 300 (1H) and 75 MHz (13C); in CDCl3 or (D6)DMSO; d in ppm rel. to Me4Si as internal
standard, J in Hz. HR-MS: Bruker micrOTOF-Q-II mass spectrometer equipped with an electrospray-
ionization (ESI) source; in m/z. MS: Applied-Biosystems-ABI-Q-Trap mass spectrometer equipped with
an atmospheric-pressure chemical-ionization (APCI) source; in m/z.
3’-Azido-3’-deoxy-5’-O-(prop-2-yn-1-yl)thymidine (2) [9]. To a soln. of 3’-azido-3’-deoxythymidine
(1; 2.67 g, 10 mmol) in dry THF (100 ml) was added NaH (60%; 600 mg, 15 mmol), and the mixture was
activated at r.t. by ultrasound irradiation (30 min). Propargyl bromide (1.30 ml, 15.0 mmol) was added,
and the reaction was continued at r.t. under ultrasound irradiation (50 min). After the reactants were
consumed, MeOH (2 ml) and then H2O (100 ml) were added to the mixture, which was extracted with
AcOEt (3 ꢁ 50 ml). The combined extract was dried (Na2SO4) and concentrated, and the crude product
1
was purified by CC (SiO2, CH2Cl2/MeOH 80 :1): pure 2 (2.58 g, 85%). H-NMR (CDCl3, 300 MHz):
10.10 (s, 1 H); 7.52 (s, 1 H); 6.18 (t, J ¼ 6.3, 1 H); 4.19 – 4.25 (m, 1 H); 4.17 (s, 2 H); 3.98 (t, J ¼ 1.8, 1 H);
3.82 (dd, J ¼ 2.4, 2.1, 1 H); 3.66 (dd, J ¼ 2.4, 2.1, 1 H); 2.49 (s, 1 H); 2.23 – 2.28 (m, 2 H); 1.84 (s, 3 H).
13C-NMR (CDCl3, 75 MHz): 164.1; 150.4; 135.5; 110.8; 84.6; 82.9; 78.5; 75.5; 68.9; 60.5; 58.4; 37.6; 12.4.
APCI-MS: 306.2 ([M þ H]þ, C13H16N5O4þ ; calc. 306.1).
5-Methyl-1-[(6aS,8R,9aS)-6a,8,9,9a-tetrahydro-4H,6H-furo[2,3-c][1,2,3]triazolo[1,5-e][1,4]oxazep-
in-8-yl]pyrimidine-2,4(1H,3H)-dione (3). A soln. of 2 (1 g, 3.3 mmol) in toluene (25 ml) was heated to
reflux for 24 h and then cooled to r.t. The mixture was concentrated and the crude product purified by CC
1
(SiO2 (short column), AcOEt/MeOH 15 :1): pure 3 (0.87 g, 87%). H-NMR ((D6)DMSO, 300 MHz):
11.39 (s, 1 H); 7.76 (s, 1 H); 7.54 (d, J ¼ 1.2, 1 H); 6.34 (dd, J ¼ 2.4, 2.1, 1 H); 5.25 – 5.35 (m, 1 H); 5.07 (d,
J ¼ 15, 1 H); 4.65 (d, J ¼ 15, 1 H); 4.27 (dd, J ¼ 3.3, 3.6, 1 H); 3.89 (t, J ¼ 10.2, 1 H); 3.64 – 3.71 (m, 1 H);
3.36 – 3.47 (m, 1 H); 2.86 – 2.90 (m, 1 H); 1.82 (s, 3 H). 13C-NMR ((D6)DMSO, 75 MHz): 163.7; 150.3;
136.9; 136.6; 132.9; 110.2; 83.2; 78.1; 72.4; 61.1; 60.5; 32.7; 12.1. ESI-HR-MS: 306.1197 ([M þ H]þ,
C13H16N5Oþ4 ; calc. 306.1209).
4-Amino-5-methyl-1-[(6aS,8R,9aS)-6a,8,9,9a-tetrahydro-4H,6H-furo[2,3-c][1,2,3]triazolo[1,5-e]-
[1,4]oxazepin-8-yl]pyrimidin-2(1H)-one (4). To a soln. of 3 (0.87 g, 2.84 mmol) in MeCN (30 ml) was
added 1H-1,2,4-triazole (3.09 g, 44.87 mmol) and Et3N (7.81 ml, 56.09 mmol) at 08 under N2. POCl3
(1.04 ml, 11.21 mmol) was then added, and the resulting mixture was stirred at r.t. for 24 h. The mixture
was filtrated and the solid washed with Et3N/MeCN 1:4 (50 ml). The filtrate was concentrated and the
residue dissolved in dioxane (5 ml) and treated with sat. NH3 · H2O (2 ml). After stirring for 12 h, the
mixture was concentrated and the crude product purified by CC (SiO2, 10 ! 40% MeOH/AcOEt): pure
1
4 (0.56 g, 65%). White solid. H-NMR ((D6)DMSO, 300 MHz): 7.76 (s, 1 H); 7.47 (s, 1 H); 7.43 (br. s,
1 H); 6.92 (br. s, 1 H); 6.32 (dd, J ¼ 2.4, 2.1, 1 H); 5.26 – 5.35 (m, 1 H); 5.07 (d, J ¼ 15, 1 H); 4.68 (d, J ¼ 15,
1 H); 4.28 (dd, J ¼ 3.6, 3.6, 1 H); 3.92 (t, J ¼ 9.9, 1 H); 3.64 – 3.71 (m, 1 H); 3.36 – 3.48 (m, 1 H); 2.72 – 2.80
(m, 1 H); 1.89 (s, 3 H). 13C-NMR ((D6)DMSO, 75 MHz): 165.5; 154.9; 138.8; 137.0; 132.9; 102.1; 84.2;
78.2; 72.5; 61.1; 60.6; 33.4; 13.2. ESI-HR-MS: 305.1380 ([M þ H]þ, C13H17N5O4þ ; calc. 305.1357).
1-(3’-Azido-2’,3’-dideoxy-b-d-threo-pentofuranosyl)thymine (6). To a soln. of 5 (9.68 g, 20 mmol) in
anh. THF (200 ml) was added Et3N (15.4 ml, 100 mmol). The mixture was cooled to 08 (ice bath), and
MsCl (3.3 ml, 24 mmol) in anh. THF (20 ml) was added dropwise during 20 min. After the reactants were
consumed, the mixture was filtrated, and the filtrate was concentrated. The residue was dissolved in
AcOEt (200 ml), the soln. washed with brine (3 ꢁ 100 ml), dried (Na2SO4), and concentrated, and the
crude product dissolved in anh. DMF (200 ml). To this soln., LiN3 (1.82 g, 37. 2 mmol) was added. The
mixture was heated at 1008 for 8 h, cooled to r.t. and poured into ice water (400 ml). The mixture was
extracted with AcOEt (3 ꢁ 150 ml), the combined org. layer washed with brine and concentrated, and
the crude product purified by CC (SiO2, AcOEt/petroleum ether 1:2) to afford a white solid. This solid
was subsequently treated with 80% aq. AcOH (300 ml) at r.t. overnight, and the volatile matters were
then evaporated. The residue was triturated with AcOEt and CHCl3 to give the crude detritylation
product 6 (3.86 g, 72%). 1H-NMR (CDCl3, 300 MHz): 9.20 (s, 1 H); 7.60 (s, 1 H); 6.20 (dd, J ¼ 3.6, 7.5);
4.25 – 4.34 (m, 1 H); 4.09 – 4.18 (m, 1 H); 3.98 – 4.09 (m, 2 H); 2,72 – 2.81 (m, 1 H); 2.18 – 2.24 (m, 1 H);
1.87 – 1.96 (m, 3 H). 13C-NMR (CDCl3): 164.50; 152.61; 135.47; 111.36; 83.23; 82.38; 64.78; 62.69; 39.16;
12.56. APCI-MS: 268.2 ([M þ H]þ, C10H14N5O4þ ; calc. 268.1).

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1-[3’-Azido-2’,3’-dideoxy-5’-O-(prop-2-yn-1-yl)-b-d-threo-pentofuranosyl]thymine (7). As descri-
bed for 2, with crude 6 (3.86 g, 14 mmol), THF (140 ml), NaH (60%; 894 mg, 22.4 mmol), and propargyl
1
bromide (1.9 ml, 22.4 mmol): pure 7 (3.31 g, 75%). H-NMR (CDCl3, 300 MHz): 8.83 (s, 1 H); 7.51 (s,
1 H); 6.21 (dd, J ¼ 3.9, 7.8, 1 H); 4.27 (s, 3 H); 4.16 – 4.27 (m, 1 H); 3.87 – 3.89 (m, 2 H); 2.69 – 2.78 (m,
1 H); 2.51 (s, 1 H); 2.12 – 2.18 (m, 1 H); 1.95 (s, 3 H). 13C-NMR (CDCl3): 164.00; 150.61; 135.40; 110.95;
83.65; 80.38; 78.67; 75.31; 67.58; 60.84; 58.57; 38.06; 12.62. ESI-HR-MS: 306.1210 ([M þ H]þ,
C13H16N5Oþ4 ; calc. 306.1197).
5-Methyl-1-[(6aS,8R,9aR)-6a,8,9,9a-tetrahydro-4H,6H-furo[2,3-c][1,2,3]triazolo[1,5-e][1,4]-oxaze-
pin-8-yl]pyrimidine-2,4(1H,3H)-dione (8). As described for 3: 8 (78%). 1H-NMR ((D6)DMSO,
300 MHz): 11.28 (s, 1 H); 7.63 (s, 1 H); 6.92(d, J ¼ 0.9, 1 H); 6.10 (dd, J ¼ 4.2, 6.6, 1 H); 5.50 (dd, J ¼
4.8, 10.8, 1 H); 5.15 (d, J ¼ 15, 1 H); 4.77 (d, J ¼ 15, 1 H); 4.38 – 4.40 (m, 1 H); 4.26 – 4.32 (m, 1 H);
3.95 (dd, J ¼ 7.2, 14.8, 1 H); 3.18 – 3.26 (m, 1 H); 2.89 – 2.96 (m, 1 H); 1.54 (s, 3 H). 13C-NMR
((D6)DMSO, 75 MHz): 163.49; 150.13; 136.48; 134.41; 132.13; 108.38; 82.83; 79.42; 70.40; 62.70; 59.69;
37.09; 12.56. ESI-HR-MS: 306.1205 ([M þ H]þ, C13H16N5O4þ ; calc. 306.1197).
4-Amino-5-methyl-1-[(6aS,8R,9aR)-6a,8,9,9a-tetrahydro-4H,6H-furo[2,3-c][1,2,3]triazolo[1,5-e]-
[1,4]oxazepin-8-yl]pyrimidin-2(1H)-one (9). As described for 4: 9 (64%). 1H-NMR ((D6)DMSO,
300 MHz): 7.61 (s, 1 H); 7.17 (s, 1 H); 6.80 (s, 1 H); 6.71 (s, 1 H); 6.09 – 6.12 (m, 1 H); 5.46 – 5.49 (m, 1 H);
5.13 (d, J ¼ 14.1, 1 H); 4.79 (d, J ¼ 6.9,1 H); 4.28 – 4.37 (m, 2 H); 4.00 (d, J ¼ 14.1, 1 H); 3.15 – 19 (m, 1 H);
2.87 – 2.92 (m, 1 H); 1.61 (s, 3 H). 13C-NMR ((D6)DMSO, 75 MHz): 164.84; 154.43; 137.85; 137.60;
132.97; 101.53; 84.55; 80.63; 71.38; 63.49; 60.80; 38.34; 14.12. ESI-HR-MS: 305.1365 ([M þ H]þ,
C13H17N5Oþ4 ; calc. 305.1357).
5’-Azido-5’-deoxy-3’-O-(prop-2-yn-1-yl)thymidine (11). As described for 2: 11 (75%). 1H-NMR
(CDCl3, 300 MHz): 9.80 (s, 1 H); 7.30 (s, 1 H); 6.21 (t, J ¼ 6.9, 1 H); 4.28 (t, J ¼ 3, 1 H); 4.15 – 4.19 (m,
2 H); 4.09 – 4.11 (m, 1 H); 3.71 (dd, J ¼ 2.4, 13.2, 1 H); 3.58(dd, J ¼ 3.3, 13.2, 1 H); 2.40 – 2.50 (m, 2 H);
2.16 – 2.18 (m, 1 H); 1.91 (s, 3 H). 13C-NMR (CDCl3, 75 MHz): 164.00; 150.46; 135.27; 111.37; 84.91;
82.21; 78.80; 78.13; 75.35; 56.89; 52.17; 36.88; 12.56. APCI-MS: 306.1 ([M þ H]þ, C13H16N5O4þ ; calc.
306.1).
5-Methyl-1-[(5aS,7R,8aR)-5a,6,8a,9-tetrahydro-4H,7H-furo[3,2-b][1,2,3]triazolo[1,5-e][1,4]-oxaze-
pin-7-yl]pyrimidine-2,4(1H,3H)-dione (12). As described for 3: 12 (78%). 1H-NMR ((D6)DMSO,
300 MHz): 11.35 (s, 1 H); 7.71 (s, 1 H); 7.47 (d, J ¼ 1.2, 1 H); 6.17 – 6.21 (m, 1 H); 5.09 (d, J ¼ 14.4, 2 H);
4.62 – 4.70 (m, 2 H); 4.42 – 4.51 (m, 1 H); 3.49 – 3.56 (m, 1 H); 2.37 – 2.44 (m, 2 H); 1.83 (s, 3 H).
13C-NMR ((D6)DMSO, 75 MHz): 163.45; 150.28; 136.59;136.28; 133.50; 110.25; 83.87; 81.92; 76.68; 61.47;
50.86; 35.86; 12.09. ESI-HR-MS: 306.1209 ([M þ H]þ, C13H16N5O4þ ; calc. 306.1197).
4-Amino-5-methyl-1-[(5aS,7R,8aR)-5a,6,8a,9-tetrahydro-4H,7H-furo[3,2-b][1,2,3]triazolo[1,5-e]-
[1,4]oxazepin-7-yl]pyrimidin-2(1H)-one (13). As described 4: 13 (50%). 1H-NMR ((D6)DMSO,
300 MHz): 7.71 (s, 1 H); 7.41 (s, 1 H); 7.37 (br. s, 1 H); 6.89 (br. s, 1 H); 6.19 – 6.22 (m, 1 H); 5.07 –
5.13 (m, 2 H); 4.64 – 4.74 (m, 2 H); 4.42 (dd, J ¼ 4.8, 5.1, 1 H); 3.50 – 3.57 (m, 1 H); 2.32 – 2.40 (m,
2 H); 1.89 (s, 3 H). 13C-NMR ((D6)DMSO, 75 MHz): 165.45; 154.97; 138.44; 136.71; 133.55; 102.31;
83.80; 82.73; 76.81; 61.49; 51.00; 36.40; 13.21. ESI-HR-MS: 305.1348 ([M þ H]þ, C13H17N5O4þ ; calc.
305.1357).
1-(5’-Azido-2’,5’-dideoxy-b-d-threo-pentofuranosyl)thymine (14) [17]. DIAD (3.8 ml, 18.8 mmol)
was added dropwise to a soln. of Ph3P (4.98 g, 18.8 mmol) in DMF (100 ml) at 08, and the mixture was
stirred for 30 min at 08. After addition of 10 (5 g, 18.8 mmol), the reaction was continued for 2 h at r.t.
The mixture was poured into cold Et2O to produce a white precipitate which was collected by filtration to
give 1-(2,3’-anhydro-5’-azido-2’,5’-dideoxy-b-d-threo-pentofuranosyl)thymine. This compound was dis-
solved in EtOH (50 ml) and was treated with aq. 1n NaOH (25 ml) for 3 h. The mixture was neutralized
with 1n HCI and all volatile matters were evaporated. The crude product was purified by CC (SiO2
AcOEt/CH2Cl2 1:1): 14 (3.49 g, 86%). 1H-NMR (CDCl3, 300 MHz): 9.91 (s, 1 H); 7.52 (s, 1 H); 6.03 (dd,
J ¼ 2.1, 2.1, 1 H); 4.45 (d, J ¼ 2.7, 1 H); 3.98 – 4.08 (m, 2 H); 3.73 (d, J ¼ 6.3, 1 H); 2.42 – 2.51 (m, 2 H);
1.86 (s, 3 H). APCI-MS: 268.3 ([M þ H]þ, C10H14N5O4þ ; calc. 268.1).
1-[5’-Azido-2’,5’-dideoxy-3’-O-(prop-2-yn-1-yl)-b-d-threo-pentofuranosyl]thymine (15). As de-
scribed for 2: 15 (75%). 1H-NMR (CDCl3, 300 MHz): 8.89 (s, 1 H); 7.52 (d, J ¼ 1.2, 1 H); 6.31 (dd,
J ¼ 3.0, 8.1, 1 H); 4.27 (m, 1 H); 4.20 (d, J ¼ 2.4, 2 H); 4.04 – 4.11 (m, 1 H); 3.69 (d, J ¼ 6.3, 2 H); 2.53 –

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2.61 (m, 1 H); 2.49 (t, J ¼ 2.4, 1 H); 2.25 – 2.31 (m, 1 H); 1.94 (d, J ¼ 1.2, 3 H). 13C-NMR ((D6)DMSO,
75 MHz): 163.96; 150.65; 136.00; 110.93; 83.91; 81.55; 78.47; 76.76; 75.44; 56.74; 49.44; 37.41; 13.60.
APCI-MS: 306.2 ([M þ H]þ, C13H16N5O4þ ; calc. 306.1).
5-Methyl-1-[(5aR,7R,8aR)-5a,6,8a,9-tetrahydro-4H,7H-furo[3,2-b][1,2,3]triazolo[1,5-e][1,4]oxaze-
pin-7-yl]pyrimidine-2,4(1H,3H)-dione (16). As described for 3: 16 (78%). 1H-NMR ((D6)DMSO,
300 MHz): 11.25 (s, 1 H); 7.76 (s, 1 H); 6.43 (d, J ¼ 1.2,1 H); 5.96 (dd, J ¼ 1.8, 8.1, 1 H); 5.17 (dd, J ¼ 4.5,
15.3, 1 H); 5.02 (dd, J ¼ 1.8, 15.3, 1 H); 4.93 (d, J ¼ 14.4, 1 H); 4.75 (d, J ¼ 14.4, 1 H); 4.51 (dd, J ¼ 2.1, 4.5,
1 H); 4.49 – 4.52 (m, 1 H); 2.65 – 2.74 (m, 1 H); 1.91 (dd, J ¼ 1.5, 15.3, 1 H); 1.49 (d, J ¼ 1.2, 3 H).
13C-NMR ((D6)DMSO, 75 MHz): 163.64; 150.23; 136.77; 135.30; 132.11; 108.07; 83.23; 79.33; 76.58;
58.38; 47.37; 39.81; 12.27. ESI-HR-MS: 306.1210 ([M þ H]þ, C13H16N5O4þ ; calc. 306.1197).
4-Amino-5-methyl-1-[(5aS,7R,8aR)-5a,6,8a,9-tetrahydro-4H,7H-furo[3,2-b][1,2,3]triazolo[1,5-
1
e][1,4]oxazepin-7-yl]pyrimidin-2(1H)-one (17). As described for 4: 17 (50%). H-NMR ((D6)DMSO,
300 MHz): 7.75 (s, 1 H); 7.17 (br. s, 1 H); 6.66 (br. s, 1 H); 6.17 (s, 1 H); 5.88 (d, J ¼ 7.8, 1 H); 5.15 – 5.21
(m, 1 H); 5.04 (d, J ¼ 15.3, 1 H); 4.87 (d, J ¼ 14.1, 1 H); 4.72 (d, J ¼ 14.4, 1 H); 4.48 (s, 1 H); 4.17 (s, 1 H);
2.50 – 2.69 (m, 1 H); 1.84 (d, J ¼ 14.1, 1 H); 1.53 (s, 3 H). 13C-NMR ((D6)DMSO, 75 MHz): 165.11;
154.83; 137.18; 136.81; 132.01; 99.68; 83.94; 79.49; 76.55; 58.21; 47.42; 40.23; 13.18. ESI-HR-MS: 305.1369
([M þ H]þ, C13H17N6Oþ3 ; calc. 305.1357).
Crystallographic Data of 12. C13H15N5O5 , Mr 321.30, orthorhombic, space group P3(2), a ¼
12.1795(8), b ¼ 12.1795(8), c ¼ 8.9404(12) ꢂ, V ¼ 1148.54(19) ꢂ3, Z ¼ 3, Dcalc ¼ 1.394 g cmꢀ3, T
293(2) K, m ¼ 0.110 mmꢀ1, F(000) ¼ 504, l ¼ MoKa, a ¼ 0.71073 ꢂ, 6533 reflections measured, 2694
unique, observed with I > 2s(I); final R1 ¼ 0.0412, wR2 ¼ 0.0978. CCDC-817212 contains the supple-
mentary crystallographic data for compound 12. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/data_request.cif.
REFERENCES
[1] a) E. De Clercq, J. Clin. Virol. 2004, 30, 115; b) E. De Clercq, Biochem. Pharmacol. 2007, 73, 911;
c) E. De Clercq, Biochim. Biophys. Acta 2002, 1587, 258; d) E. De Clercq, Biochem. Pharmacol.
2004, 68, 2301; e) R. C. Brady, D. I. Bernstein, Antiviral Res. 2004, 61, 73; f) G. V. Papatheodoridis,
E. Dimou, V. Papadimitropoulos, Am. J. Gastroenterol. 2002, 97, 1618; g) M. V. Blagosklonny, Cell
Cycle 2004, 3, 1035; h) T. Robak, A. Korycka, M. Kasznicki, A. Wrzesien-Kus, P. Smolewski, Curr.
Cancer Drug Targets 2005, 5, 421; i) S. Miura, S. Izuta, Curr. Drug Targets 2004, 5, 191.
[2] J. Balzarini, Pharm. World Sci. 1994, 16, 113; D. S. Stein, K. H. Moore, Pharmacotherapy 2001, 21, 11;
E. De Clercq, Int. J. Antimicrob. Agents 2009, 33, 307; E. De Clercq, Antiviral Res. 2005, 67, 56.
[3] D. F. Ewing, N.-E. Fahmi, C. Len, G. Mackenzie, A. Pranzo, J. Chem. Soc., Perkin Trans. 1 2000,
3561; C. Len, G. Mackenzie, Tetrahedron 2006, 62, 9085; J. J. Barchi Jr., R. G. Karki, M. C. Nicklaus,
M. A. Siddiqui, C. George, I. A. Mikhailopulo, V. E. Marquez, J. Am. Chem. Soc. 2008, 130, 9048;
K. I. Shaikh, S. Kumar, L. Lundhus, A. D. Bond, P. K. Sharma, P. Nielsen, J. Org. Chem. 2009, 74,
1557.
[4] H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem., Int. Ed. 2001, 40, 2004; V. D. Bock, H.
Hiemstra, J. H. van Maarseveen, Eur. J. Org. Chem. 2006, 51; W. H. Binder, C. Kluger, Curr. Org.
Chem. 2006, 10, 1791; W. H. Binder, R. Sachsenhofer, Macromol. Rapid Commun. 2007, 28, 15;
W. H. Binder, R. Sachsenhofer, Macromol. Rapid Commun. 2008, 29, 952.
[5] R. Alvarez, S. Velazquez, A. San-Felix, S. Aquaro, E. De Clercq, C.-F. Perno, A. Karlsson, J.
Balzarini, M. J. Camarasa, J. Med. Chem. 1994, 37, 4185; D. R. Buckle, C. J. M. Rockell, H. Smith,
B. A. Spicer, J. Med. Chem. 1986, 29, 2269; M. J. Genin, D. A. Allwine, D. J. Anderson, M. R.
Barbachyn, D. E. Emmert, S. A. Garmon, D. R. Graber, K. C. Grega, J. B. Hester, D. K. Hutchinson,
J. Morris, R. J. Reischer, C. W. Ford, G. E. Zurenko, J. C. Hamel, R. D. Schaadt, D. Stapert, B. H.
Yagi, J. Med. Chem. 2000, 43, 953; W. G. Lewis, L. G. Green, F. Grynszpan, Z. Radic, P. R. Carlier, P.
Taylor, M. G. Finn, K. B. Sharpless, Angew. Chem., Int. Ed. 2002, 41, 1053; H. C. Kolb, K. B.
Sharpless, Drug Discovery Today 2003, 8, 1128; G. C. Tron, T. Pirali, R. A. Billington, P. L. Canonico,
G. Sorba, A. A. Genazzani, Med. Res. Rev. 2008, 28, 278.

Helvetica Chimica Acta – Vol. 95 (2012)
779
[6] J.-F. Lutz, Z. Zarafshani, Adv. Drug Delivery Rev. 2008, 60, 958; A. D. Moorhouse, J. E. Moses,
ChemMedChem 2008, 3, 715; E. De Clercq, Clin. Microbiol. Rev. 1997, 10, 674; E. De Clercq, Nat.
Rev. Drug Discovery 2002, 1, 13.
[7] J. Sun, J.Wu, H. Yang, Helv. Chim. Acta 2007, 90, 1917; J.-B. Sun, H. Yang, J.-C. Wu. Acta Crystallogr.,
Sect. E 2007, E63, o724; J.-B. Sun, H. Yang, J.-C. Wu, Acta Crystallogr., Sect. E 2007, E63, o978; S.-F.
Dang, J.-B. Sun, X.-X. Xu, P. Wang, J.-C. Wu, Chem. Res. Chin. Univ. 2008, 24, 473.
´
[8] S. Czernecki, J. M. Valery, Synthesis 1991, 239.
[9] K. Teste, L. Colombeau, A. Hadj-Bouazza, R. Lucas, R. Zerrouki, P. Krausza, Y. Champavier,
Carbohydr. Res. 2008, 343, 1490.
[10] S. Hotha, R. I. Anegundi, A. A. Natu, Tetrahedron Lett. 2005, 46, 4585; R. I. Anegundi, V. G.
Puranik, S. Hotha, Org. Biomol. Chem. 2008, 6, 779.
[11] A. Matsuda, J. Yasuoka, T. Ueda, Chem. Pharm. Bull. 1989, 37, 1659.
[12] Y. F. Shealy, C. A. OꢃDell, W. M. Shannon, G. Arnett, J. Med. Chem. 1986, 29, 483.
[13] A. Van Aerschot, P. Herdewijn, J. Balzarini, R. Pauwels, E. De Clercq, J. Med. Chem. 1989, 32, 1743.
[14] K. Agyei-Aye, S. Yan, A. K. Hebbler, D. C. Baker, Nucleosides Nucleotides 1989, 8, 327.
´
[15] A. Krasinski, V. V. Fokin, K. B. Sharpless, Org. Lett. 2004, 6, 1237; A. I. Oliva, U. Christmann, D.
`
Font, F. Cuevas, P. Ballester, H. Buschmann, A. Torrens, S. Yenes, M. A. Pericas, Org. Lett. 2008, 10,
1617; U. Pradere, V. Roy, T. R. McBrayer, R. F. Schinazi, L. A. Agrofoglio, Tetrahedron 2008, 64,
9044.
[16] X. Yu, Y. Yu, B. Liu, K. Luo, W. Kong, P. Mao, X.-F. Yu, Science (Washington, DC, U.S.) 2003, 302,
1056; J. Kimpton, M. Emerman, J. Virol. 1992, 66, 2232; C. Tian, X. Yu, W. Zhang, T. Wang, R. Xu,
X.-F. Yu, J. Virol. 2006, 80, 3112.
[17] D. Katalenic, M. Zinic, Nucleosides Nucleotides 1998, 17, 1231; R. C. Reynolds, P. A. Crooks, W. B.
Parker, J. A. Maddry, J. A. Montgomery, J. A. Secrist, J. Biopharm. Sci. 1991, 2, 195.
Received September 15, 2011