Synthesis of Novel 2',3'-Linked Bicyclic Thymine Ribonucleosides

Full text of DOI:10.1021/jo972239c

2778
J . Org. Chem. 1998, 63, 2778-2781
Syn th esis of Novel 2′,3′-Lin k ed Bicyclic
Th ym in e Ribon u cleosid es
Alexei A. Koshkin and J esper Wengel*
Department of Chemistry, Chemical Laboratory II,
University of Copenhagen, Universitetsparken 5, DK-2100
Copenhagen, Denmark
Received December 10, 1997
With the aim of efficient nucleic acid recognition, a
variety of oligonucleotide mimics have been synthesized
in recent years.1 Though a number of promising ana-
logues have been reported, e.g., PNA,2 phosphorami-
dates,3 and anhydrohexitol nucleic acid,4 no synthetic
oligonucleotide analogue has so far exhibited the desired
combination of high-affinity, straightforward oligomer-
ization and DNA/RNA-like structure. In this context, we
believe that oligonucleotides containing bicyclic pento-
furanose building blocks and a natural 5′-O- to 3′-O-
linked phosphodiester backbone are attractive novel
candidates.5,6 Thus, we have recently reported strong
binding of an oligonucleotide of type C (2′,3′-BcNA,
Figure, B ) nucleobase) toward complementary RNA.5
To evaluate the possibility of further improving the
nucleic acid recognition properties of this class of com-
pounds, we have developed a synthetic route to the
nucleoside building blocks suitable for preparation of
novel oligonucleotides of type D. Our interest in this type
of structural modification was further stimulated by the
improved properties of 2′-O-alkyl oligonucleotides of type
B compared to those of the parent type A, e.g., enhanced
RNA-binding because of N-type conformational prefer-
ence and improved 3′-exonucleolytic stability.1e,7 In ad-
dition, the novel nucleosides 5a ,b and 10, and derivatives
thereof, are direct analogues of the ribonucleoside con-
stituents of RNA and may exhibit interesting biological
activities.
configured thymine derivatives 1a ,b (Scheme 1) as key
intermediates. They were prepared from 1,2-di-O-iso-
propylidine-R-D-xylofuranose as previously described.5
Selective silylation of the primary hydroxy groups of
compounds 1a and 1b using tert-butyldimethylsilyl chlo-
ride (TBDMSCl) in anhydrous pyridine afforded nucleo-
sides 2a and 2b in 89% and 92% yield, respectively, after
column chromatographic purification. During oxidation
of 2a , precautions had to be taken to avoid overoxidation.
Thus, when cooling was omitted the major product (yield
∼60%) was assigned (MS, 1H NMR, 13C NMR) as the 3′,5′-
di-O-benzoylated nucleoside corresponding to 2′-ulose 3a .
Oxidation using pyridinium dichromate (PDC) yielded 2′-
uloses 3a and 3b in yields of 84% and 91%, respectively,
after column chromatographic purification. Compounds
3a and 3b were converted to the bicyclic nucleosides 4a
and 4b simply by removing the silyl protection group
from the 3′-C-hydroxyethyl or 3′-C-hydroxypropyl sub-
stituents. Both acid- and fluoride-mediated desilylation
proved effective, allowing the preparation of compounds
4a ,b in 94% yield. As clearly evidenced by 13C NMR,
compounds 4a ,b existed exclusively as the bicyclic hemi-
acetals. Palladium hydroxide-assisted catalytic removal
of the benzyl protection groups of 4a and 4b afforded the
targeted bicyclic thymidine derivatives 5a and 5b in
yields of 82% and 79%, respectively, after column chro-
matographic purification (Scheme 1).
For stereoselective synthesis of the novel bicyclic
nucleosides analogues 5a ,b and 10, we chose â-D-ribo
* To whom correspondence should be addressed. Tel.: 45 35 32 01
70. Fax 45 35 32 02 12. E-mail: wengel@kiku.dk.
(1) (a) Wagner, R. W. Nature 1994, 372, 333. (b) De Mesmaeker,
A.; Ha¨ner, R.; Martin, P.; Moser, H. E. Acc. Chem. Res. 1995, 28, 366.
(c) Akhtar, S.; Agrawal, S. Trends Pharmacol. Sci. 1997, 18, 12. (d)
Herdewijn, P. Liebigs Ann. 1996, 1337. (e) Freier, S. M.; Altmann,
K.-H. Nucleic Acids Res. 1997, 25, 4429.
(2) (a) Hyrup, B.; Nielsen, P. E. Bioorg. Med. Chem. 1996, 4, 5. (b)
Nielsen, P. E.; Haiima, G. Chem. Soc. Rev. 1997, 73.
(3) Schultz, D. G., Gryaznov, S. M. Nucleic Acids Res. 1996, 24, 2966.
(4) (a) Van Aershot, A.; Verheggen, I.; Hendrix, C.; Herdewijn, P.
Angew. Chem., Int. Ed. Engl. 1995, 34, 1338. (b) Hendrix, C.;
Rosemeyer, H.; Verheggen, I.; Seela, F.; Van Aershot, A.; Herdewijn,
P. Chem. Eur. J . 1997, 3, 110.
Theoretically, two possibilities exist for hemiacetal
formation in compounds 5a ,b, namely attack on the 2′-
keto function from the 3′-C-hydroxyalkyl or the 5′-
hydroxy groups. To prove the existence of free 5′-hydroxy
groups, we selectively acetylated the free primary hy-
droxy groups of compounds 5a and 5b using acetic
anhydride in anhydrous pyridine, affording derivatives
6a and 6b in yields of 52% and 75%, respectively. The
structures of nucleosides 6a ,b were confirmed by 1H and
1H-1H COSY NMR experiments. By the process of
acetylation, the resonance signals of the 5′-protons were
shifted downfield by approximately 0.5 ppm, proving that
the acetylation took place at the 5′-hydroxy groups of 5a
and 5b. No traces of acetylation at the 3′-C-hydroxyalkyl
branches were detected even after 24 h reaction.
(5) (a) Nielsen, P.; Pfundheller, H. M.; Wengel, J . Chem. Commun.
1997, 9, 825. (b) Nielsen, P.; Pfundheller, H. M.; Olsen, C. E.; Wengel,
J . J . Chem. Soc., Perkin Trans. 1 1997, 3423.
(6) A number of bicyclic nucleosides have been incorporated into
oligonucleotides. See, e.g.: (a) Bolli, M.; Litten, J . C.; Schu¨ltz, R.;
Leumann, C. J . Chem. Biol. 1996, 3, 197. (b) Altmann, K.-H.;
Kesselring, R.; Francotte, E.; Rihs, G. Tetrahedron Lett. 1994, 35, 2331.
(c) Altmann, K.-H.; Imwinkelried, R.; Kesselring, R.; Rihs, G. Tetra-
hedron Lett. 1994, 35, 7625. (d) Marquez, V. E.; Siddiqui, M. A.;
Ezzitouni, A.; Russ, P.; Wang, J .; Wagner, R. W.; Matteucci, M. D. J .
Med. Chem. 1996, 39, 3739. (e) Zou, R.; Matteucci, M. Tetrahedron
Lett. 1996, 37, 941. (f) Wang, J .; Matteucci, M. D. Bioorg. Med. Chem.
Lett. 1997, 7, 229.
(7) Cummins, L. L.; Owens, S. R.; Risen, L. M.; Lesnik, E. A.; Freier,
S. M.; McGee, D.; Guinosso, C. J .; Cook, P. D. Nucleic Acids Res. 1995,
23, 2019.
S0022-3263(97)02239-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 04/01/1998

Notes
J . Org. Chem., Vol. 63, No. 8, 1998 2779
trimethylsilyl triflate),10 and acetalization in the presence
of chlorotrimethylsilane.11 Eventually, compound 9 was
synthesized in 62% yield by direct alkylation of the 2′-
hydroxy group of 4a by reaction with methyl iodide in
anhydrous dichloromethane in the presence of sodium
hydride. This approach was, however, complicated by
3-N-alkylation, resulting in the formation of byproducts
7 and 8 in yields of 4% and 9%, respectively. The
structural assignment of compounds 7-9 was based on
13C NMR spectra, especially the appearance of signals
corresponding to N- and/or O-methyl derivatives (at
approximately 28 and 51 ppm, respectively). The depro-
tected bicyclic nucleoside analogue 10 was finally ob-
tained in 79% yield by catalytic hydrogenation of nucle-
oside 9 (Scheme 2).
Sch em e 1a
In summary, synthesis of three novel 2′,3′-linked
bicyclic nucleoside analogues 5a ,b and 10 has been
accomplished by ring closure of 2′-ketonucleosides.
A
similar strategy should prove viable for synthesis of other
bicyclic nucleosides. Efforts are underway transforming
5a and 10 into building blocks for automated oligomer-
ization and evaluating the biological activity of this novel
class of ribonucleoside analogues.
a
Reagents and conditions: (a) 1.2 equiv of TBDMSCl, pyridine,
2 h, rt, 92% (2a ); 1 equiv of TBDMSCl, pyridine, 2 h, rt, 90% (2b);
(b) 1.1 equiv of PDC, Ac2O, 3 Å molecular sieve powder, 1.5 h, rt,
CH2Cl2 , 84% (3a ); 1.7 equiv of PDC, Ac2O, 3 Å molecular sieve
powder, CH2Cl2, 1.5 h, rt, 91% (3b); (c) 0.5% HCl in methanol, 30
min, rt, 94% (4a ); 3.1 equiv of triethylamine trihydrofluoride, THF,
12 h, rt, 94% (4b); (d) 20% Pd(OH)2, H2, methanol, 12 h, rt, 82%,
5a ; 20% Pd(OH)2, H2, methanol, 24 h, rt, 79%, 5b; (e) 1.4 equiv of
Ac2O, pyridine, 16 h, 7 °C, 52%, 6a ; 1.5 equiv of Ac2O, pyridine, 4
h, rt, 75%, 6b.
Exp er im en ta l Section
Gen er a l Meth od s. Chemicals and solvents were purchased
from commercial suppliers and used as such. Silica gel 60
(0.040-0.063 mm) was used for chromatography. Silica gel
HPLC was performed by use of PrepPAK-500/silica cartridges
(flow rate 60 mL/min). NMR spectra were recorded at 400 MHz
(1H spectra) or 100 MHz (13C spectra) using tetramethylsilane
as internal reference. Chemical shifts δ are reported in parts
per million (ppm) and coupling constants J in Hz. 1H-1H COSY
NMR spectra were recorded for compounds 6a ,b. Fast-atom
bombardment mass spectra (FAB-MS) were recorded in positive
ion mode.
Sch em e 2a
1-[3-C-[2-O-[(ter t-Bu tyld im eth ylsilyl)oxy]eth yl]-3,5-d i-O-
ben zyl-â-D-r ibofu r a n osyl]th ym in e (2a ). A mixture of nucleo-
side 1a 5 (1.80 g, 3.4 mmol) and TBDMSCl (0.585 g, 3.9 mmol)
was dissolved in anhydrous pyridine (20 mL). After being stirred
for 2 h at room temperature, the reaction mixture was evapo-
rated, coevaporated with toluene (2 × 10 mL), and redissolved
in dichloromethane (150 mL). The solution was washed with a
saturated aqueous solution of sodium hydrogen carbonate (2 ×
50 mL), and the separated organic phase was evaporated to give
a foam. This material was purified by preparative silica gel
HPLC (0-3% methanol in dichloromethane, v/v) to give nucleo-
side 2a as a white solid material (1.86 g, 92%): 1H NMR (CDCl3)
7.61 (1H, d, J ) 1.1), 7.35-7.20 (10H, m), 6.27 (1H, d, J ) 7.9),
4.65-4.40 (4H, m), 4.37 (1H, s), 4.28 (1H, t, J ) 7.9), 4.10-3.55
(4H, m), 2.30-2.05 (2H, m), 1.46 (3H, s), 0.90 (9H, m), 0.08 (6H,
m); 13C (CDCl3) 163.6, 151.0, 137.5, 136.6, 135.8, 128.3, 128.1,
127.8, 127.2, 127.1, 126.8, 126.7, 110.7, 86.8, 82.5, 81.2, 78.3,
73.3, 69.8, 64.5, 58.2, 32.9, 25.6, 25.4, 17.9, 11.6, -3.9, -5.7;
FAB-MS m/z 597 [M + H]+, 619 [M + Na]+. Anal. Calcd for
a
Reagents and conditions: (a) 2 equiv of NaH, 7.4 equiv of CH3I,
CH2Cl2, 23 h, 36 °C, 4% (7), 9% (8), 62% (9); (b) 9, 20% Pd(OH)2,
H2, methanol, rt, 12 h, 79%.
Compound 4a was additionally utilized as an inter-
mediate for synthesis of the 2′-O-alkylated bicyclic nu-
cleoside 10 (Scheme 2). The key reaction was alkylation
to give the bicyclic acetal 9. A wide variety of O-
glycosylation methods have been described,8 but all
attempts to prepare derivative 9 by the use of reactions
involving carbocation intermediates were unsuccessful.
Thus, we failed to produce the desired product using the
method of Ficher-Helferich (up to 5% HCl in anhydrous
methanol was used), p-toluenesulfonic acid/2,2-dimethox-
ypropane,9 Noyori’s acetalization under aprotic conditions
(methoxytrimethylsilane in dichloromethane catalyzed by
C
32H44O7N2Si: C, 64.4; H, 7.4; N, 4.7. Found: C, 64.2; H, 7.4;
N, 4.2.
1-[3-C-[2-O-[(ter t-Bu tyld im eth ylsilyl)oxy]p r op yl]-3,5-d i-
O-ben zyl-â-D-r ibofu r a n osyl]th ym in e (2b). The same proce-
dure as decribed above for 2a was used: nucleoside 1b5 (3.64 g,
7.34 mmol), anhydrous pyridine (25 mL), TBDMSCl (1.12 g, 7.42
mmol), reaction time 2 h at room temperature, toluene (2 × 50
mL), dichloromethane (300 mL), a saturated aqueous solution
of sodium hydrogen carbonate (2 × 150 mL). The residue
obtained after evaporation of the organic phase was purified by
preparative silica gel HPLC (0-5% methanol in dichloromethane,
v/v) to give nucleoside 2b as a white solid material (4.01 g,
90%): 1H NMR (CDCl3) 7.60 (1H, d, J ) 1.2), 7.38-7.25 (10H,
(8) (a) Schmidt, R. R. Angew. Chem., Int. Ed. Engl. 1986, 25, 212.
(b) Toshima, K.; Tatsuta, K. Chem. Rev. 1993, 93, 1503.
(9) Rupprecht, K. M.; Boger, J .; Hoogsteen, K.; Nachbar, R. B.;
Springer, J . P. J . Org. Chem. 1991, 56, 6180.
(10) Tsunoda, T.; Suzuki, M.; Noyori, R. Tetrahedron Lett. 1980, 21,
1357.
(11) Chan, T. H.; Brook, M. A.; Chaly, T. Synthesis 1983, 203.

2780 J . Org. Chem., Vol. 63, No. 8, 1998
Notes
m), 6.14 (1H, d, J ) 7.9), 4.62-4.54 (4H, m), 4.37 (1H, d, J )
1.3), 4.18 (1H, m), 3.84 (1H, m), 3.75-3.57 (2H, m), 3.55 (1H,
m), 2.20-1.65 (4H, m), 1.47 (3H, d, J ) 1.1), 0.90 (9H, m), 0.06
(6H, m); 13C NMR (CDCl3) 163.5, 151.1, 137.3, 136.8, 136.1,
128.7, 128.5, 128.3, 127.9, 127.7, 127.5, 127.4, 111.2, 87.5, 82.7,
81.3, 79.3, 73.7, 70.0, 64.3, 63.0, 26.6, 26.1, 26.0, 18.3, 11.9, -5.3,
-5.3; FAB-MS m/z 611 [M + H]+. Anal. Calcd for C33H46O7N2-
Si: C, 64.9; H, 7.6; N, 4.6. Found: C, 64.9; H, 7.5; N, 4.5.
1-[3-C-[2-O-[(ter t-Bu tyld im eth ylsilyl)oxy]eth yl)-3,5-d i-O-
ben zyl-â-D-er yth r o-p en tofu r a n -2-u losyl]th ym in e (3a ). Nu-
cleoside 2a (2.14 g, 3.59 mmol), pyridinium dichromate (1.48 g,
3.95 mmol), and activated 3A molecular sieve powder (4 g) was
suspended in anhydrous dichloromethane (80 mL). After the
mixture was cooled to -10 °C, acetic anhydride (10 mL, 98 mmol)
was added dropwise under vigorous stirring. The mixture was
allowed to warm to room temperature, and stirring was contin-
ued for 1.5 h, whereupon triethylamine (20 mL) was added. The
mixture was diluted with dichloromethane to 300 mL and was
washed with water (2 × 200 mL). The organic phase was
evaporated, and the residue was purified by flash silica gel
chromatography (2.5 × 20 cm column) in a steplike gradient of
1.0, 1.2, 1.3, 1.4, and 1.5% methanol in dichloromethane (v/v,
250 mL each) to give nucleoside 3a (1.89 g, 84%) as a white solid
material: 1H NMR (CDCl3) 9.21 (1H, br s), 7.35-7.20 (11H, m),
6.40 (1H, s), 4.57 (1H, s), 4.52 (1H, s), 4.46 (1H, d, J ) 11.0),
4.29 (1H, d, J ) 11.0), 4.07 (1H, dd, J ) 10.5, 2.2), 3.95-3.70
(4H, m), 2.42 (1H, m), 2.05 (1H, m), 1.42 (3H, d, J ) 1.1), 0.86
(9H, s), 0.01 (6H, s); 13C NMR (CDCl3) 202.6, 163.7, 151.2, 137.7,
136.6, 136.5, 128.7, 128.5, 128.2, 128.1, 127.7, 126.4, 126.3, 110.9,
84.5, 81.3, 80.2, 73.6, 70.4, 66.0, 57.6, 27.3, 25.9, 25.7, 18.2, 11.7,
-5.8, -5.9; FAB-MS m/z 595 [M + H]+. Anal. Calcd for
6.2 mmol), and the mixture was stirred for 12 h at room
temperature. Dichloromethane (100 mL) was added, and the
mixture was washed with a saturated aqueous solution of
sodium hydrogen carbonate (2 × 100 mL) and water (100 mL).
The organic phase was concentrated, and the residue was
purified by silica gel HPLC (eluent: 0-8% methanol in dichlo-
romethane (v/v) during 60 min) to yield compound 4b (0.91 g,
94%) as a white solid material: 1H NMR (CDCl3) 9.79 (1H, br
s), 7.38-7.25 (11H, m), 6.13 (1H, s), 4.68-4.54 (5H, m), 4.03-
3.88 (1H, m), 3.83-3.74 (2H, m), 3.72-3.60 (1H, m), 2.30-2.18
(1H, m), 2.07-1.90 (1H, m), 1.87 (3H, d, J ) 1.0), 1.72-1.54
(2H, m); 13C NMR (CDCl3) 164.3, 151.9, 138.0, 137.5, 137.0,
128.6, 128.4, 128.0, 127.6, 127.2, 109.4, 99.5, 89.0, 83.6, 80.2,
73.6, 70.5, 64.9, 58.9, 23.4, 21.2, 12.7; FAB-MS m/z 495 [M +
H]+. Anal. Calcd for C27H30O7N2: C, 65.6; H, 6.1; N, 5.7.
Found: C, 64.9; H, 6.0; N, 5.5.
(1S,5R,6R,8R)-1,5-Dih ydr oxy-6-(h ydr oxym eth yl)-8-(th ym -
in -1-yl)-2,7-d ioxa bicyclo[3.3.0]octa n e (5a ). A mixture of
nucleoside 4a (192 mg, 0.40 mmol) and 20% palladium hydroxide
on carbon (40 mg) was suspended in methanol (5 mL). The
mixture was degassed under reduced pressure and placed in a
hydrogen atmosphere with a balloon. After being stirred for 12
h at room temperature, the reaction mixture was evaporated.
The residue was purified by silica gel chromatography (2 × 5
cm column) using methanol in dichloromethane (6-14%, v/v)
as eluent to give a glass after evaporation of the solvents.
A
solution of this glass in 5% methanol in benzene (5 mL, v/v) was
frozen and lyophilized to give compound 5a (98 mg, 82%) as a
white solid material: 1H NMR (CD3OD) 7.44 (1H, d, J ) 1.2),
5.83 (1H, s), 4.10-3.80 (5H, m), 2.39-2.25 (1H, m), 2.00-1.90
(1H, m), 1.87 (3H, d, J ) 1.2); 13C NMR (CD3OD) 166.2, 152.6,
139.7, 109.9, 109.6, 87.8, 84.6, 84.6, 68.8, 61.6, 35.6, 12.4; FAB-
MS m/z 301 [M + H]+.
(1S,6R,7R,9R)-1,6-Dih ydr oxy-7-(h ydr oxym eth yl)-9-(th ym -
in -1-yl)-2,8-d ioxa bicyclo[4.3.0]n on a n e (5b). The same pro-
cedure as described above for 5a was used: nucleoside 4b (650
mg, 1.31 mmol), 20% palladium hydroxide on carbon (100 mg),
methanol (15 mL), reaction time 24 h at room temperature. After
evaporation, the residue was purified by silica gel chromatog-
raphy (1.5 × 10 cm column) using 3-12% methanol in dichlo-
romethane as eluent to give a glass after evaporation of the
solvents. A solution of this glass in 5% methanol in benzene
(21 mL, v/v) was frozen and lyophilized to give compound 5b
(325 mg, 79%) as a white solid material: 1H NMR (CD3OD) 7.58
(1H, d, J ) 1.3), 6.11 (1H, s), 4.14-4.11 (1H, m), 3.92-3.82 (3H,
m), 3.66-3.62 (1H, m), 2.03-2.00 (1H, m), 1.88 (3H, d, J ) 1.2),
1.77-1.54 (3H, m); 13C NMR (CD3OD) 166.4, 153.4, 139.6, 109.8,
100.5, 90.5, 89.6, 75.9, 63.7, 59.7, 27.8, 22.2, 12.5; FAB-MS m/z
315 [M + H]+.
(1S,5R,6R,8R)-6-[(Acet yloxy)m et h yl]-1,5-d ih yd r oxy-8-
(th ym in -1-yl)-2,7-d ioxa bicyclo[3.3.0]octa n e (6a ). Acetic an-
hydride (0.026 mL, 0.27 mmol) was added dropwise at room
temperature to a stirred solution of nucleoside 5a (55 mg, 0.18
mmol) in anhydrous pyridine (5 mL). After 16 h at 7 °C, the
reaction mixture was evaporated. The residue was coevaporated
with toluene (2 × 5 mL), and extraction was performed in a 1:1(v/
v) mixture of dichloromethane and saturated aqueous sodium
hydrogen carbonate (60 mL). The separated organic phase was
concentrated, and the residue was purified by silica gel flash
chromatography (1 × 25 cm column) using 2-4% methanol in
dichloromethane as eluent. The monoacetylated product 6a (32
mg, 52%) was isolated as a white solid material: 1H NMR (CD3-
OD) 7.40 (1H, d, J ) 1.1, 6-H), 5.84 (1H, s, 1′-H), 4.43-4.35 (2H,
m, 5′-H), 4.14-3.98 (3H, m, 2′′-H, 4′-H), 2.34-2.26 (1H, m, 1′′-
H), 2.08 (3H, s, acetyl), 2.06-1.96 (1H, m, 1′′-H), 1.87 (3H, d, J
) 1.1, 5-CH3); 13C NMR (CD3OD) 172.4, 166.2, 152.6, 139.6,
110.1, 109.5, 87.8, 84.7, 81.4, 68.8, 63.7, 35.8, 20.7, 12.4.
(1S,6R,7R,9R)-7-[(Acet yloxy)m et h yl]-1,6-d ih yd r oxy-9-
(th ym in -1-yl)-2,8-d ioxa bicyclo[4.3.0]n on a n e (6b). The same
procedure as described above for 6a was used: acetic anhydride
(0.082 mL, 0.81 mmol), nucleoside 5b (170 mg, 0.54 mmol),
anhydrous pyridine (5 mL), reaction time 4 h at room temper-
ature, toluene (2 × 5 mL), a 1:1 (v/v) mixture of dichloromethane
and H2O (100 mL). The residue obtained after evaporation of
the organic phase was purified by silica gel flash chromatogra-
phy (1.5 × 30 cm column) using methanol in dichloromethane
(2-4%) as eluent, affording monoacetylated compound 6b (145
C
32H42O7N2Si: C, 64.6; H, 7.1; N, 4.7. Found: C, 64.1; H, 6.9;
N, 4.5.
1-[3-C-[2-O-[(ter t-Bu tyld im eth ylsilyl)oxy]p r op yl]-3,5-d i-
O-ben zyl-â-D-er yth r o-p en tofu r a n -2-u losyl]th ym in e (3b). To
suspension of 3A molecular sieve powder (360 mg) and
a
pyridimium dichromate (275 mg, 0.73 mmol) in anhydrous
dichloromethane (5 mL) was added a solution of nucleoside 2b
(280 mg, 0.46 mmol, in 2 mL of dichloromethane). Acetic
anhydride (0.12 mL, 1.17 mmol) was added dropwise at room
temperature under vigorous stirring. After 1.5 h at room
temperature, the reaction mixture was subjected to column
chromatographic purification (2 × 15 cm column, silica gel, 0-2%
methanol in dichloromethane, v/v), affording nucleoside 3b as
a white solid material (254 mg, 91%): 1H NMR (CDCl3) 9.43
(1H, br s), 7.41-7.22 (11 H, m), 6.26 (1H, s), 4.58-4.48 (4H, m),
4.29 (1H, d, J ) 10.8), 3.87 (1H, dd, J ) 10.9, 2.7), 3.73 (1H, dd,
J ) 10.8, 2.9), 3.68-3.58 (2H, m), 2.33-2.26 (1H, m), 1.87-1.73
(2H, m), 1.61-1.54 (1H, m), 1.47 (3H, d, J ) 1.0), 0.88 (9H, m),
0.04 (6H, m); 13C NMR (CDCl3) 202.4, 163.6, 151.0, 137.8, 136.7,
136.6, 128.6, 128.5, 128.1, 128.0, 127.8, 127.7, 127.6, 127.4, 111.2,
83.7, 82.2, 80.5, 73.6, 69.6, 65.7, 62.7, 25.9, 25.7, 21.4, 18.3, 11.7,
-5.3; FAB-MS m/z 609 [M + H]+. Anal. Calcd for C33H44O7N2-
Si: C, 65.1; H, 7.3; N, 4.6. Found: C, 64.8; H, 7.2; N, 4.6.
(1S,5R,6R,8R)-5-(Ben zyloxy)-6-(ben zyloxym eth yl)-1-h y-
d r oxy-8-(th ym in -1-yl)-2,7-d ioxa bicyclo[3.3.0]octa n e (4a ).
Compound 3a (1.80 g, 3.03 mmol) was dissolved in 0.5% HCl in
methanol (20 mL, w/w) and the mixture was stirred for 30 min
at room temperature. After evaporation, the residue was
dissolved in dichloromethane (100 mL) and washed with a
saturated aqueous solution of sodium hydrogen carbonate (2 ×
40 mL). The organic phase was evaporated, and the residue was
purified by flash silica gel chromatography (2.5 × 20 cm column),
eluting with 2% methanol in dichloromethane (v/v) to yield
nucleoside 4a (1.35 g, 94%) as a white solid material: 1H NMR
(CDCl3) 9.54 (1H, br s), 7.37-7.27 (11H, m), 5.87 (1H, s), 4.71
(2H, s), 4.64 (1H, d, J ) 12.0), 4.56 (1H, d, J ) 12.0), 4.36 (1H,
t, J ) 5.7), 4.16 (1H, m), 3.96 (1H, m), 3.74 (2H, m), 2.35-2.15
(2H, m), 1.88 (3H, s, J ) 1.1); 13C NMR (CDCl3) 163.7, 151.4,
137.8, 137.3, 136.7, 128.5, 128.4, 128.0, 127.8, 127.5, 109.9, 108.6,
88.8, 87.1, 80.9, 73.6, 68.5, 68.1, 67.9, 30.9, 12.6; FAB-MS m/z
481 [M + H]+, 503 [M + Na]+. Anal. Calcd for C26H28O7N2: C,
65.0; H, 5.9; N, 5.8. Found: C, 64.6; H, 5.8; N, 5.7.
(1S,6R,7R,9R)-6-(Ben zyloxy)-7-(ben zyloxym eth yl)-1-h y-
d r oxy-9-(th ym in -1-yl)-2,8-d ioxa bicyclo[4.3.0]n on a n e (4b).
To a solution of nucleoside 3b (1.2 g, 1.97 mmol) in anhydrous
THF (20 mL) was added triethylamine trihydrofluoride (1 mL,

Notes
J . Org. Chem., Vol. 63, No. 8, 1998 2781
mg, 75%) as a white solid material: 1H NMR (CD3OD) 7.54 (1H,
d, J ) 1.1, 6-H), 6.16 (1H, s, 1′-H), 4.68 (1H, dd, J ) 11.9, 10.1,
4′-H), 4.26-4.22 (2H, m, 5′-H), 3.94-3.66 (2H, m, 3′′-H), 2.10
(3H, s, acetyl), 1.87 (3H, s, 5-CH3), 2.07-1.55 (4H, m, 1′′-H, 2′′-
H); 13C NMR (CD3OD) 172.5, 166.3, 153.3, 139.7, 109.9, 100.3,
89.1, 87.3, 76.1, 65.7, 59.6, 27.9, 22.5, 20.8, 12.5.
d, J ) 1.1); 13C NMR (CDCl3) 163.2, 150.1, 138.2, 137.9, 137.3,
128.4, 128.2, 127.8, 127.6 127.4, 127.1, 110.8, 109.3, 89.2, 84.2,
79.6, 73.6, 68.5, 68.3, 67.4, 50.8, 32.6, 12.5; FAB-MS m/z 495
[M + H]+, 517 [M + Na]+.
(1S,5R,6R,8R)-5-Hyd r oxy-6-(h yd r oxym eth yl)-1-m eth oxy-
8-(th ym in -1-yl)-2,7-d ioxa bicyclo[3.3.0]octa n e (10). To a
solution of nucleoside 9 (1.20 g, 2.43 mmol) in methanol (10 mL)
was added 20% palladium hydroxide over charcoal (250 mg), and
the mixture was degassed under reduced pressure. An atmo-
sphere of hydrogen was applied, and stirring was continued for
12 h at room temperature. The catalyst was removed by
filtration through a glass column (1 × 8 cm) packed with silica
gel in methanol. The column was additionally washed with
methanol (20 mL). All fractions were collected, evaporated, and
coevaporated with petroleum ether to yield a glasslike solid. This
residue was purified by silica gel chromatography (5 × 15 cm
column), eluting with a gradient of 5-10% methanol in dichlo-
romethane (v/v). The fractions containing the product were
collected, combined, and evaporated. The residue was dissolved
in anhydrous methanol (5 mL), and anhydrous benzene (100 mL)
was added. The solution was frozen and lyophilized under
reduced pressure to give nucleoside 10 (0.61 g, 79%) as a white
solid material: 1H NMR (CD3OD) 7.45 (1H, s), 5.93 (1H, s), 4.15-
3.81 (5H, m), 3.43 (3H, s), 2.47-2.40 (1H, m), 2.03-1.93 (1H,
m), 1.92 (3H, s); 13C NMR (CD3OD) 166.0, 152.0, 140.2, 111.5,
86.3, 86.0, 84.3, 70.0, 61.4, 51.5, 36.0, 12.4; FAB-MS m/z 315
[M + H]+, 337 [M + Na]+. Anal. Calcd for C13H18O7N2: C, 49.7;
H, 5.8; N, 8.9. Found: C, 49.9; H, 5.7; N, 8.3.
(1S,5R,6R,8R)-5-(Ben zyloxy)-6-(ben zyloxym eth yl)-1-m eth -
oxy-8-(3-N -m e t h ylt h ym in -1-yl)-2,7-d ioxa b icyclo[3.3.0]-
octa n e (7), (1S,5R,6R,8R)-5-(Ben zyloxy)-6-(ben zyloxym e-
t h y l)-1-h y d r o x y -8-(3-N -m e t h y lt h y m in -1-y l)-2,7-d io x a -
bicyclo[3.3.0]octa n e (8), a n d (1S,5R,6R,8R)-5-(Ben zyloxy)-
6-(b e n z y lo x y m e t h y l)-1-m e t h o x y -8-(t h y m in -1-y l)-2,7-
d ioxa b icyclo[3.3.0]oct a n e (9). A mixture of nucleoside 4a
(1.035 g, 2.16 mmol) and a 60% suspension of sodium hydride
(171 mg, 4.30 mmol) in mineral oil was dissolved in anhydrous
dichloromethane (4 mL). Methyl iodide (1 mL, 16 mmol) was
added, and the reaction mixture was stirred for 23 h at 36 °C.
After evaporation of the solvents in vacuo, the residue was
purified by silica gel chromatography (4 × 35 cm column) using
0.4-2.4% methanol in dichloromethane (v/v) as eluent to give
products 7-9 and starting material 4a (212 mg, 21%). Com-
1
pound 7: yield 47 mg (4%); H NMR (CDCl3) 7.25-7.37 (11H,
m), 6.15 (1H, s), 4.74 (1H, d, J ) 11.5), 4.67 (1H, d, J ) 11.3),
4.62 (1H, d, J ) 12.1), 4.55 (1H, d, J ) 11.9), 4.34 (1H, t, J )
5.6), 4.22 (1H, m), 3.99, (1H, m), 3.72 (2H, m), 3.41 (3H, s), 3.35
(3H, s), 2.27 (1H, m), 2.41 (1H, m), 1.93 (3H, s); 13C NMR (CDCl3)
163.3, 151.0, 138.2, 137.3, 135.7, 128.3, 128.2, 127.8, 127.6, 127.4,
126.9, 110.8, 108.5, 89.1, 84.8, 79.5, 73.5, 68.4, 68.2, 67.3, 50.8,
32.6, 27.9, 13.2; FAB-MS m/z 509 [M + H]+. Compound 8: yield
97 mg (9%); 1H NMR (CDCl3) 7.37-7.28 (11H, m), 5.86 (1H, s),
4.72 (2H, s), 4.64 (1H, d, J ) 11.9), 4.58 (1H, d, J ) 11.9), 4.37
(1H, t, J ) 5.6), 4.13 (1H, m), 3.93 (1H, m), 3.75 (2H, m), 3.34
(3H, s), 2.32-2.16 (2H, m), 1.93 (3H, s); 13C NMR (CDCl3) 163.2,
151.9, 137.5, 137.1, 134.0, 128.4, 128.3, 128.1, 127.9 127.7, 127.6,
127.3, 108.8, 108.5, 88.7, 88.0, 81.0, 73.5, 68.3, 67.9, 67.7, 30.6,
27.8, 13.2; FAB-MS m/z 495 [M + H]+, 517 [M + Na]+.
Compound 9: yield 665 mg (62%); 1H NMR (CDCl3) 8.71 (1H,
br s), 7.35-7.25 (11H, m), 6.06 (1H, s), 4.73 (1H, d, J ) 11.5),
4.66 (1H, d, J ) 11.3), 4.61 (1H, d, J ) 11.9), 4.55 (1H, d, J )
12.0), 4.34 (1H, t, J ) 5.6), 4.20 (1H, m), 3.98 (1H, m), 3.72 (2H,
m), 3.40 (3H, s), 2.45-2.35 (1H, m), 2.30-2.20 (1H, m), 1.90 (3H,
Ack n ow led gm en t. The Danish Natural Science
Research Council is thanked for financial support.
Su p p or tin g In for m a tion Ava ila ble: Copies of 13C NMR
spectra for compounds 5a ,b, 6a ,b, 7-9 (7 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
J O972239C