Efficient synthesis of protected 3′-deoxyadenosine and 3′-deoxyguanosine from adenosine and guanosine

Article abstract of DOI:10.1016/S0040-4039(00)02041-4

Highly efficient synthesis of protected 3′-deoxyadenosine and 3′-deoxyguanosine from adenosine and guanosine were described. The 2′,3′-diol of protected adenosine and guanosine were reacted with α-acetoxyisobutyryl bromide to yield 9-(2′-O-acetyl-3′-bromo

Full text of DOI:10.1016/S0040-4039(00)02041-4

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 561–563
Efficient synthesis of protected 3%-deoxyadenosine and
3%-deoxyguanosine from adenosine and guanosine
Zhiyong Cui, Lei Zhang and Biliang Zhang*
Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605, USA
Received 8 November 2000; accepted 14 November 2000
Abstract—Highly efficient synthesis of protected 3%-deoxyadenosine and 3%-deoxyguanosine from adenosine and guanosine were
described. The 2%,3%-diol of protected adenosine and guanosine were reacted with a-acetoxyisobutyryl bromide to yield 9-(2%-O-
acetyl-3%-bromo-5%-O-tert-butyldiphenylsilyl-3%-deoxy-b-D-xylofuranosyl)-6-N-benzoyl adenine and 9-(2%-O-acetyl-3%-bromo-5%-O-
tert-butyldiphenylsilyl-3%-deoxy-b-D-xylofuranosyl)-2-N-(N%,N%-dimethylaminomethylene) guanine and subsequently heated with
tri-n-butyltin hydride in the presence of 2,2%-azobisisobutyronitrile to afford the protected 3%-deoxyadenosine and 3%-
deoxyguanosine in 66–73% over all yield. © 2001 Elsevier Science Ltd. All rights reserved.
Modified nucleosides play an important role in the
development of genetic therapies such as antigene and
antisense strategies.1 3%-Deoxyribonucleosides are
known to posses potential antiviral and antitumor
activities.2 The first isolated nucleotide antibiotic was
3%-deoxyadenosine, that is known as cordycepin which
inhibits Bacillus subtilis, avian tubercle bacillus and
Ehrlich ascites tumor cells.2a 3%-Deoxynucleotides have
been incorporated into oligonucleotides to form 2%,
5%-linked oligodeoxynucleotide that selectively binds
with complementary DNA or RNA.3 The 2%, 5%-linked
oligonucleotides are stable to most of the nucleases that
hydrolyze the natural DNA, making them potential
candidates for diagnostic and therapeutic antisense
applications.4 A number of methods to prepare 3%-
deoxyadenosine and several synthetic approaches for
3%-deoxyguanosine have been described.5 The most
efficient route of 3%-deoxyguanosine synthesis in five
steps with 50% overall yield from guanosine was
reported by He and Bischofberger.6 The efficient route
of 3%-deoxyadenosine synthesis in three steps with 53%
overall yield from adenosine was reported by Robins et
al.7 Norman and Reese have described that the prepa-
ration of 2%, 5%-di-O-acetyl-3%-deoxyadenosine was in
41% overall yield from adenosine.8 Herein, we report
an efficient synthetic route to prepare protected 3%-
deoxyadenosine and 3%-deoxyguanosine in very high
yield from corresponding nucleosides.
Moffatt et al. reported that adenosine reacted with
a-acetoxyisobutyryl bromide to generate 2%-O-acetyl-
3%(2%)-deoxy-3%(2%)-bromo-5%-dioxolone-adenosine mix-
tures.9 We modified the Moffatt’s reaction by
protecting 5%-hydroxy and exo-amino groups of ribonu-
cleotides prior reacting with a-acetoxyisobutyryl bro-
mide. The tert-butyldiphenylsilyl (TBDPS) group was
chosen as a protection group for 5%-hydroxy and ben-
zoyl group for the 6-amino group of adenosine. The
adenosine (1) was first converted into 6-N-benzoyl-
adenosine 2 in 96% yield10 by treating with trimethylsi-
lyl chloride, benzoyl chloride, and 1.0 M ammonium
hydroxide, respectively and then treated with tert-
butyldiphenylsilyl chloride to give 6-N-benzoyl-5%-O-
tert-butyldiphenylsilyl-adenosine (3) in 99% yield. To a
suspension of 3 (915 mg, 1.5 mmol) in acetonitrile (45
ml) containing a trace amount of water (22 ml, 1.2
mmol), a-acetoxyisobutyryl bromide (0.66 ml, 4.5
mmol) was added slowly at 0°C. The mixture was
stirred at 0°C for 2.5 h and at room temperature for 7
h when the reaction gave a clear solution. The mixture
was concentrated to about 5 ml under reduced pressure
and 150 ml of ethyl acetate was added. The solution
was washed with cold saturated sodium bicarbonate
(2×50 ml), water (50 ml), and brine (50 ml). The
aqueous solution was extracted with dichloromethane
(2×50 ml) and the combined organic layers were dried
over anhydrous sodium sulfate. After evaporation, the
crude product was purified by flash silica gel column
eluted with a gradient (0–5%) methanol–chloroform to
give 4 as a white foam solid (900 mg, yield=84.1%).11
Several methods, such as H2/Raney Ni and H2/Pd-C
(10%), have been tried for the reductive cleavage of
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)02041-4

562
Z. Cui et al. / Tetrahedron Letters 42 (2001) 561–563
Scheme 1.
3%-bromo group of 4 but gave poor yield or side prod-
ucts. When 4 was heated with an excess tri-n-butyltin
hydride in the presence of 2,2%-azobisisobutyronitrile
(AIBN) in toluene solution, a protected 3%-deoxy-
adenosine (5) was obtained in high yield but a trace
amount of N-benzoyl cleaved product was formed after
prolonged heating. The compound 4 (500 mg, 0.7
mmol) was first dissolved in dry toluene (10 ml) under
an atmosphere of argon and then tri-n-butyltin hydride
(0.57 ml, 2.1 mmol) and 2,2%-azobisisobutyronitrile (9.8
mg, 0.06 mmol) were added at room temperature. The
stirred reaction mixture was heated to 95°C. After 50
min, the starting material was disappeared monitored
by ESI-MS. The solvent was removed under reduced
pressure, the crude product was purified by flash silica
gel column eluted with 0.1–3% methanol–methylene
chloride to afford 5 as a white solid (410 mg, 92% yield)
(73% from 1) (Scheme 1).12
n-butyltin hydride and a catalytic amount of AIBN to
give the desired product (Scheme 2). Briefly, guanosine
6 was reacted with N,N-dimethylformamide dimethyl
acetal in acetonitrile to give 2-(N,N-dimethyl-
aminomethylene) guanosine in 97% yield and then
treated with tert-butyldiphenylsilyl chloride to give 7 in
90% yield. Compound 7 was reacted with a-acetoxy-
isobutyryl bromide to yield 8 (83%).14 The compound 8
(190 mg, 0.28 mmol) was dissolved in toluene (10 ml)
under an atmosphere of argon and tri-n-butyltin
hydride (0.23 ml, 0.84 mmol) and 2,2%-azobisisobuty-
ronitrile were added, and heated to 95°C for 2 h. The
pure product 9 (154 mg, 91%) was obtained after silica
gel chromatography purification (66% overall from 6).15
TBDPS or acetyl group of 5 and 9 can be selectively
deprotected with appropriate reagent. 5%-TBDPS group
of 5 and 9 was removed quantitatively with 1.0 M
tetra-n-butylammonium fluoride (TBAF) in THF at
0°C. 2%-Acetyl group of 5 and 9 was deprotected with
0.5–1.0N ammonia in methanol in ꢀ100% yield. Thus,
the 5 and 9 can be easily converted to corresponding
phosphoramidites for solid-phase oligonucleotide syn-
thesis using standard coupling protocols.16 This syn-
thetic route can be enhanced to preparative scale for
preparing 3%-deoxynucleosides.
9-(2%-O-Acetyl-5%-O-tert-butyldiphenylsilyl-3%-b-D-2-(N%,
N%-dimethylaminomethylene) xylofuranosyl) guanine
(9) was prepared by a similar synthetic route as
described above for 5. Guanosine was first protected by
N,N-dimethylaminomethylene at 2-amino of guanine
and TBDPS at 5%-hydroxy group, and then reacted with
a-acetoxyisobutyryl bromide,13 finally treated with tri-
Scheme 2.

Z. Cui et al. / Tetrahedron Letters 42 (2001) 561–563
563
9. Russell, A. F.; Greenberg, S.; Moffatt, J. G. J. Am.
Chem. Soc. 1973, 95, 4025–4030.
Acknowledgements
10. Ti, G. S.; Gaffney, B. L.; Jones, R. A. J. Am. Chem. Soc.
1982, 104, 1316–1319.
This work was partially supported by grants from the
CFAR development grant of UMass Medical School
and Biomedical Research Annual Research Fund Inno-
vation Grant of Worcester Foundation.
11. Compound 4: Rf=0.50 (chloroform: methanol=95:5); 1H
NMR (400 MHz, CDCl3): l 1.09 (s, 9H), 2.19 (s, 3H),
4.04 (m, 2H), 4.47–4.39 (m, 2H), 5.75 (s, 1H), 6.28 (d,
J=2.0 Hz, 1H), 8.01–7.37 (m, 15H), 8.33 (s, 1H), 8.74 (s,
1H), 9.51 (s, 1H). 13C NMR (100 MHz, CDCl3): l 19.2,
20.7, 26.8, 50.2, 64.5, 81.5, 82.8, 88.0, 123.3, 127.9, 128.0,
128.6, 130.0, 132.6, 132.7, 133.7, 135.5, 141.1, 149.8,
151.5, 152.8, 165.2, 169.1; ESI-Mass (m/e): 736.2 (M+
Na)+; 738.2 (M+Na+2)+.
References
1. (a) Uhlmann, E.; Peyman, A. Chem. Rev. 1990, 90,
544–584. (b) De Mesmaeker, A.; Haener, R.; Martin, P.;
Moser, H. E. Acc. Chem. Res. 1995, 28, 366–372. (c) Dan
Cook, P. Nuckleosides & Nucleotides 1999, 1141–1162
2. (a) Suhadolnik, R. J. Nucleoside Antibiotics.; New York:
Wiley-Interscience, 1970. (b) Suhadolnik, R. J. Nucleoside
as Biological Probes; New York: Wiley-Interscience,
1979. (c) Cameron, J. M. New Developments in Antiviral
Therapy, Control of Virus Diseases for General Microbi-
ology Symposium 45; eds. Dimmock et al., p. 341, 1990.
3. (a) Hashimoto, H.; Switzer, C. J. Am. Chem. Soc. 1992,
114, 6256–6257. (b) Jin, R.; Chapman, W. H., Jr.; Srini-
vasan, A. R.; Olson, W. K.; Breslow, R.; Breslauer, K. J.
Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 10568–10572. (c)
Jung, K.-E.; Switzer, C. J. Am. Chem. Soc. 1994, 116,
6059–6061. (d) Robinson, H.; Jung, K.-E.; Switzer, C.;
Wang, A. H.-J. J. Am. Chem. Soc. 1995, 117, 837–838. (e)
Kierzek, R.; He, L.; Turner, D. H. Nucleic Acids Res.
1992, 20, 1685–1690. (f) Breslow, R. C; Sheppard, T. L.
Pure & Appl. Chem. 1996, 68, 2037–2041.
12. Compound 5: Rf=0.45 (chloroform: methanol=20:1); 1H
NMR (400 MHz, CDCl3): l 1.05 (s, 9H), 2.12 (s, 3H),
2.14–2.18 (m, 1H), 2.66–2.73 (m, 1H), 3.77 (dd, J=4.03,
11.74 Hz, 1H), 4.02 (dd, J=3.30, 11.74 Hz, 1H), 4.51 (m,
1H), 5.67 (m, 1H), 6.20 (d, J=1.47 Hz, 1H), 7.30–7.55
(m, 9H), 7.61–7.64 (m, 4H), 8.00 (m, 2H), 8.28 (s, 1H),
8.73 (s, 1H), 9.46 (s, 1H). 13C NMR (100 MHz, CDCl3):
l 19.4, 21.2, 27.1, 32.4, 64.7, 78.3, 81.6, 89.7, 123.6, 128.0,
128.1, 128.9, 130.1, 132.9, 133.0, 134.0, 135.7, 141.7,
149.9, 151.4, 153.0, 165.11, 170.3; ESI-MS positive ion
636.1 (M +1)+, 658.3 (M+Na)+.
13. Matulic-Adamic, J.; Beigelman, L. Helv. Chim. Acta
1999, 82, 2141–2150.
14. Compound 8: Rf=0.65 (chloroform: methanol=85:15);
1H NMR (400 MHz, CDCl3): l 1.08 (s, 9H), 2.22 (s, 3H),
3.10 (s, 3H), 3.18 (s, 3H), 4.03 (m, 2H), 4.37 (d, J=3.6
Hz, 1H), 4.43 (m, 1H), 5.94 (d, J=1.8 Hz, 1H), 6.12 (s,
1H), 7.72–7.38 (m, 10H), 7.83 (s, 1H), 8.64 (s, 1H), 8.81
1
(br, 1H). The H NMR spectrum is coincident with that
4. Sheppard, T. L.; Breslow, R. C. J. Am. Chem. Soc. 1996,
40, 9810–9811.
reported in the literature.13
15. Compound 9: Rf=0.44 (chloroform: methanol=10:1); 1H
NMR (400 MHz, CDCl3): l 1.05 (s, 9H), 2.02–2.07 (m,
1H), 2.12 (s, 3H), 2.34–2.41 (m, 1H), 3.06 (s, 3H), 3.13 (s,
3H), 3.76 (dd, J=4.03, 11.37 Hz, 1H), 3.93 (dd, J= 3.66,
11.37 Hz, 1H), 4.49 (m, 1H), 5.82 (m, 1H), 5.96 (d, J=1.1
Hz, 1H), 7.33–7.41 (m, 6H), 7.61–7.66 (m, 4H), 7.81 (s,
1H), 8.62 (s, 1H), 9.72 (br, s, 1H). 13C NMR (100 MHz,
CDCl3): l 19.4, 21.3, 27.1, 32.3, 35.3, 41.6, 65.0, 77.7,
81.6, 89.4, 121.1, 128.1, 130.1, 133.0, 135.7, 136.1, 149.7,
157.2, 158.4, 159.0, 170.0; ESI-MS positive ion: 603.2
(M+1)+, 625.3 (M+Na)+; negative ion, 601.4 (M−1)−.
16. Vinayak, R. Methods: A Companion to Methods in Enzy-
mol. 1993, 5, 7–18.
5. (a) Ogilvie, K. K.; Hakimelahi, G. H.; Proba, Z. A.,
Usman, N. Tetrahedron Lett. 1983, 24, 865–868. (b)
Bazin, H.; Chattopadhyaya, J. Synthesis 1985, 26, 1108–
1111. (c) Rizzo, C. J.; Dougherty, J. P.; Breslow, R.
Tetrahedron Lett. 1992, 33, 4129–4132. (d) Dougherty, J.
P.; Rizzo, C. J.; Breslow, R. J. Am. Chem. Soc. 1992, 114,
6254–6255. (e) Sheppard, T. L.; Rosenblatt, A. T.;
Breslow, R. J. Org. Chem. 1994, 59, 7243–7248.
6. He, G. X.; Bischofberger, N. Tetrahedron Lett. 1995, 36,
6991–6994.
7. Robins, M. J., et al. J. Org. Chem. 1995, 60, 7902–7908.
8. Norman, D. G.; Reese, C. B. Synthesis 1983, 304–306.
.
.