An efficient synthesis of 3′-amino-3′-deoxyguanosine from guanosine

Article abstract of DOI:10.1002/hlca.200390069

3′-Amino-3′-deoxyguanosine was synthesized from guanosine in eight steps and 58% overall yield. The 2′,3′-diol of 5′-O-[(tert-butyl)diphenylsilyl]-2-N-[(dimethylamino) methylidene]guanosine was reacted with α-acetoxyisobutyryl bromide and treated with 0.5N NH₃ in MeOH to yield 9-[2′-O-acetyl-3′-bromo-5′-O-[(tertbutyl) diphenylsilyl]-3′-deoxy-β-D-xylofuranosyl]-2-N- [(dimethylamino)methylidene]guanine, which was reacted with benzyl isocyanate, NaH, and then 3.0N NaOH, and finally with Pd/C (10%) and HCO₂NH₄ in EtOH/AcOH to afford 3′-amino-3′-deoxyguanosine.

Full text of DOI:10.1002/hlca.200390069

Helvetica Chimica Acta Vol. 86 (2003)
703
An Efficient Synthesis of 3'-Amino-3'-deoxyguanosine from Guanosine
by Lei Zhang, Zhiyong Cui, and Biliang Zhang*
Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA 01605 USA
(phone: (508) 856-6673; fax: (508) 856-4289; e-mail: biliang.zhang@umassmed.edu)
3'-Amino-3'-deoxyguanosine was synthesized from guanosine in eight steps and 58% overall yield. The
2',3'-diol of 5'-O-[(tert-butyl)diphenylsilyl]-2-N-[(dimethylamino)methylidene]guanosine was reacted with a-
acetoxyisobutyryl bromide and treated with 0.5n NH3 in MeOH to yield 9-{2'-O-acetyl-3'-bromo-5'-O-[(tert-
butyl)diphenylsilyl]-3'-deoxy-b-d-xylofuranosyl]-2-N-[(dimethylamino)methylidene]guanine, which was react-
ed with benzyl isocyanate, NaH, and then 3.0n NaOH, and finally with Pd/C (10%) and HCO2NH4 in EtOH/
AcOH to afford 3'-amino-3'-deoxyguanosine.
Introduction.
Unnatural nucleotide derivatives have been shown to possess
antibacterial, anticancer, and biosynthetic-inhibition activities [1 3]. 3'-Amino-3'-
deoxynucleosides are very important bioactive molecules. 3'-Amino-3'-deoxyadeno-
sine, known as puromycin, is an analogue of the 3'-terminus of aminoacyl charge-
transfer RNA and a good acceptor in the peptidyl transferase reaction in the ribosome
[4][5]. 3'-Amino-3'-deoxynucleosides are also the key intermediates in the synthesis of
several backbone-modified oligonucleotides. For example, the phosphodiester in the
natural oligonucleotides can be replaced by guanidine [6 9], amide [10][11], urea
[12], carbamate [13], and aminoalkyl derivatives [14][15]. Such antisense oligonucleo-
tides may have great potential as therapeutic and diagnostic agents. The oligonucleo-
tide N(3')ÀP(5') phosphoramidates that can inhibit the telomerase have been shown to
have potential therapeutic application [16][17], and they have been also used as
substrate-analog inhibitors for ribozyme [18]. Bruice and co-workers have reported the
synthesis of ribonucleic (A and U) guanidines for biological and biochemical studies
[8][9]. Several synthetic routes have been suggested for the synthesis of 3'-amino-3'-
deoxynucleosides. There are two major methods to approach the synthesis of sugar-
modified nucleosides: a) modifications on the intact nucleosides [19 21]; b) attach-
ment of the heterocyclic base to a modified glycosyl unit [22 26]. The coupling
reactions of suitably protected purine bases with glucose or xylose derivatives usually
gave low yields (overall yield < 20%). Samano and Robins [27] have reported a nine-
stepsynthetic route to 3 '-amino-3'-deoxyadenosine in 66% overall yield, and Pfleiderer
and co-workers [28] have repeated the synthetic procedure of Samano and Robins to
prepare 3'-amino-3'-deoxyadenosine. Robins et al. [29] have reported another
improved method for the synthesis of 3'-amino-3'-deoxyadenosine. There were also
several other reported methods to prepare 3'-amino-3'-deoxyguanosine by the attach-
ment of the protecting guanine to 3'-azido-3'-deoxy-d-ribofuranose [30 33]. However,
to our knowledge, there is so far no report on the preparation of the title compound
directly from guanosine. In this paper, we report an efficient route for the synthesis of
3'-amino-3'-deoxyguanosine directly from guanosine.

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Results and Discussion. Synthesis of 3'-Amino-3'-deoxyadenosine (8). We have
modified the nine-steproute of Samone and Robins for synthesis of 3'-amino-3'-
deoxyadenosine to a seven-steproute with 55% overall yield ( Scheme 1). Briefly,
adenosine (1) was first protected with (t-Bu)Ph2Si (TBDPS) at C(5'), to avoid
formation of 5'-dioxolone, when treated with 2-acetoxyisobutyryl bromide to yield 2'-
O-acetyl-3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxyadenosine (3). The Moffatt
reaction [13] of adenosine with 2-acetoxyisobutyryl bromide (AcOCMe2COBr)
produced 2'-O-acetyl-3'-bromo-3'-deoxyadenosine. To avoid the formation of the 5'-
dioxolone product, the 5'-OH groupof adenosine was selectively protected by the acid-
stable TBDPS group. The reaction of adenosine with slight excess of (t-Bu)Ph2SiCl was
carried out in dry pyridine for 40 h at room temperature in the presence of a catalytic
amount of 4-(dimethylamino)pyridine (DMAP). The reaction of 5'-O-TBDPS-
adenosine with 2-acetoxyisobutyryl bromide was performed in MeCN and 1.0 equiv.
of H2O to give 2'-O-acetyl-3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxyadeno-
sine (3). Deprotection of 2'-O-Ac groupof 2 '-O-acetyl-3'-bromo-5'-O-[(tert-butyl)di-
phenylsilyl]-3'-deoxyadenosine in dilute NH3/MeOH solution led to the formation of
3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxyadenosine (4). The addition of NH3/
MeOH solution to a solution of 2'-O-acetyl-3'-bromo-3'-deoxyadenosine in MeOH was
controlled at 08, and the final concentration of NH3 in MeOH was ca. 0.5 1.0n. No
2',3'-anhydroadenosine was formed under these reaction conditions, but it was formed
when the reaction was run in concentrated NH3 in MeOH or aqueous solution for a
longer time. Compound 3 was treated with 0.5n NH3 in MeOH and then reacted with
PhCH2NCO to yield 5, which was reacted with NaH and then 1.0n NaOH, and, finally
Scheme 1. Synthesis of 3'-Amino-3'-deoxyadenosine (8)
NH2
N
NH2
N
NH2
N
N
N
N
N
N
N
TBDPSO
Br
OH
HO
TBDPSO
AcOCMe2COBr
TBDPS-Cl
O
O
N
N
O
N
MeCN, 1 equiv. H2O
0°
Py, DMAP
99%
80%
OH
HO
OH
OAc
1
3
2
NH2
N
NH2
N
N
TBDPSO
Br
N
N
PhCH2NCO,
Et3N, THF, r.t.
N
TBDPSO
O
N
NaH
NH3/MeOH
87%
O
N
THF, -20°
94%
95%
Br
O
H
N
OH
5
C
PhCH2
4
O
NH2
N
NH2
N
NH2
N
N
N
N
N
HO
TBDPSO
H2/Pd-C(10%)
92%
HO
N
O
N
1.0N NaOH
98%
O
N
N
O
N
OH
H2N
O
N
OH
NH
PhCH2
C
O
PhCH2
8
6
7

Helvetica Chimica Acta Vol. 86 (2003)
705
deprotected by hydrogenation with PdÀC (10%) in EtOH to afford 3'-amino-3'-
deoxyadenosine (8).
Synthesis of 3'-Amino-3'-deoxyguanosine. Adenosine could react with 2-acetox-
yisobutyryl bromide to give 3'-bromo-2'-deoxyadenosine; however, guanosine yielded
a mixture, presumably because of the 2-NH2 group of purine. After the protection of 2-
NH2 group, guanosine can react with 2-acetoxyisobutyryl bromide to yield the desired
product [34][35]. The synthesis of 3'-amino-3'-deoxyguanosine is outlined in
Scheme 2. Guanosine 9 (2.0 g, 7.06 mmol) was reacted with N,N-dimethylformamide
dimethyl acetal in MeOH to give 2-N-[(dimethylamino)methylidene]guanosine
(2.22 g, 93%) [36], which was then treated with (t-Bu)Ph2SiCl in pyridine to yield 10
(3.3 g, 96%) [35]. To a suspension of 10 (2.3 g, 4.0 mmol) in MeCN (80 ml) containing
a trace amount of H2O (64 ml, 3.6 mmol), 2-acetoxyisobutyryl bromide (2.2 ml,
15.2 mmol) was slowly added under Ar at 08. The mixture was stirred at 08 for 2 h.
After stirring at room temperature for an additional 4 h, the mixture was concentrated
Scheme 2. Synthesis of 3'-Amino-3'-deoxyguanosine (16)
O
N
O
N
N
N
N
NH
NH2
NH
1) Me2NCH(OMe)2,
MeOH
93%
TBDPSO
HO
AcOCMe2COBr
CH-NMe2
N
N
O
O
MeCN, 1 equiv. H2O
2) TBDPS-Cl, pyridine,
DMAP
0°
83%
HO
OH
HO
OH
96%
9
10
O
N
O
N
N
NH
N
NH
TBDPSO
Br
NH3/MeOH
90%
TBDPSO
Br
CH-NMe2
N
O
N
CH-NMe2
N
N
O
OAc
OH
11
12
O
O
N
N
N
NH
NH
PhCH2NCO, TBDPSO
Et3N, THF
HO
N
N
CH-NMe2
N
O
CH-NMe2
NaH, DMF
N
N
O
Br
94%
–15° to r.t.
14
O
H
N
13
O
N
C
O
PhCH2
C
PhCH2
O
O
O
N
N
N
NH
NH2
N
NH
NH2
HO
HO
N
O
Pd-C (10%), EtOH, AcOH
N
3.0N NaOH, MeOH
O
HCO2NH4
98%
95% from 13
HN
PhCH2
OH
15
16
H2N
OH
Exact Mass: 282.1077
Mol. Wt.: 282.2562
C 42.55, H 5.00, N 29.77, O 22.67
Exact Mass: 372.1546
Mol. Wt.: 372.3787
C 54.83, H 5.41, N 22.57, O 17.19

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Helvetica Chimica Acta Vol. 86 (2003)
under reduced pressure. The residue was dissolved in CH2Cl2 and washed with
saturated NaHCO3 (2 Â 50 ml) and brine (2 Â 50 ml). The organic layer was dried (anh.
Na2SO4). After evaporating the solvent, the crude product was purified with a flash
silica-gel column, eluting with a gradient from CH2Cl2 to MeOH/CH2Cl2 95 :5 to give 11
as a white solid (2.3 g, 83%). Reaction of 11 (820 mg, 1.2 mmol) in MeOH (30 ml) with
7.0n NH3 in MeOH (0.85 ml) for 1.5 h at room temperature yielded 9-{3'-bromo-5'-O-
[(tert-butyl)diphenylsilyl]-3'-deoxy-b-d-xylofuranosyl}-2-N-[(dimethylamino)methyl-
ene]guanine (12; 690 mg, 90%). Compound 12 (487 mg, 0.76 mmol) was dissolved in
5 ml of anhydrous THF and Et3N (318 ml, 2.28 mmol), and PhCH2NCO (282 ml,
2.28 mmol) was added under Ar. The mixture was stirred at room temperature for
2.5 d. MeOH (5 ml) was added, and the mixture was stirred for additional 2 h. After
removing the solvent, the solid residue was purified with a silica-gel column eluted with
a gradient of CHCl3 and CHCl3/MeOH 95 :5 to give the desired compound 13 as a
white solid (550 mg, 94%).
When 13 was reacted with NaH in anhydrous THF at À208 and room temperature
for 2 d, as described for adenosine, no reaction was observed. We repeated the reaction
once more, but no ring-closing reaction had been observed. However, when the ring-
closing reaction was performed in anhydrous DMF, the desired product 14 was
obtained in very high yield. A solution of 13 (355 mg, 0.46 mmol) in 15 ml of anhydrous
DMF was cooled with an ice/EtOH bath (À158), and NaH (36 mg, 1.48 mmol) was
added. The mixture was stirred for 4 h between À158 and 08, and for 24 h at room
temperature. The reaction was monitored by TLC (CHCl3/MeOH 9 :1). After the
disappearance of the starting material, the mixture was filtered, and the solution was
evaporated under reduced pressure. The residue was dissolved in AcOEt (200 ml) and
washed with H2O (20 ml), saturated NaHCO3 (2 Â 25 ml), and brine (50 ml). The
organic layer was dried (Na2SO4). By evaporation of the solvent, compound 14 was
obtained and used for the next step of reaction without further purification. Compound
14 was treated with a solution of 3.0n NaOH (aq.) MeOH 1:1 to yield 3'-
(benzylamino)-3'-deoxyguanosine (15). The pure compound 15 (207 mg, 95% from
13) was obtained by the C18 reversed-phase chromatography eluted with a gradient
from H2O to MeOH/H2O 1:1. Compound 15 was dissolved in MeOH. The mixture with
Pd/C (10%) catalyst was sealed in a stainless steel reaction vessel under 50 psi H2
pressure and shaken at room temperature for a week. The mixture was filtered through
Celite, and the filtrate was evaporated to dryness and worked up as usual to give 3'-
amino-3'-deoxyguanosine (16) in very low yield because of the poor solubility of 15 in
EtOH. Other deprotection methods to remove PhCH2 grouphave also been tested.
According to one of the successful methods compound 15 was dissolved in a mixture of
EtOH and AcOH, and a catalytic amount of 10% Pd/C and an excess of ammonium
formate were added. The suspension was stirred for 24 h at room temperature. The
reaction was monitored by TLC. After removing the solid materials, the solvents were
evaporated under reduced pressure. The residue was purified with a C18 reversed-
phase column eluted with a gradient of H2O and MeOH to give a white solid 16 (98%).
The final product was confirmed by 1H- and 13C-NMR spectroscopy, and mass spectrometry.
This synthetic route can be scaled upfor a large-scale synthesis of 3 '-amino-3'-
deoxyguanosine (16). We are currently using these 3'-amino-3'-deoxy-nucleosides as
building blocks to prepare backbone-modified oligonucleotides for biological studies.

Helvetica Chimica Acta Vol. 86 (2003)
707
This work was partially supported by grants from the CFAR development grant and start-up fund of
University of Massachusetts Medical School.
Experimental Part
1. General. All solvents, org. and inorg. chemicals were purchased from ACROS or Aldrich. Solvents were
dried according to standard methods. CH2Cl2, MeCN, and pyridine were refluxed over CaH2 and freshly distilled
before use. Reactions were run under Ar. TLC: pre-coated silica-gel thin-layer sheets 60 F 254 from Merck;
Flash chromatography (FC): silica gel 60, 180 240 mesh from Merck. 1H-NMR: Varian VNMR 400
spectrometer, with CDCl3 or (D6)DMSO as solvents and trace solvent peak as reference, data were recorded
as d in ppm. ESI-MS: Finnigan LCQDUO spectrometry.
2. 5'-O-[(tert-Butyl)diphenylsilyl]adenosine (2). To a suspension of adenosine (1; 13.4 g, 50 mmol) in
250 ml of dry pyridine were added 4-(dimethylamino)pyridine (0.3 g, 2.5 mmol) and (t-Bu)Ph2SiCl (15.6 ml,
60 mmol) under Ar. The mixture was stirred at r.t. for 40 h. After the disappearance of the starting material
(TLC), 10 ml of MeOH was added to the mixture, and the mixture was stirred at r.t. for 0.5 h. After removing
the solvent, the residue was dissolved in CHCl3 (50 ml) and precipitated with Et2O (200 ml) to form a white
solid. After filtration, the solid was washed with Et2O and H2O, and dried (P2O5) to give 2 (25.0 g, 98.8%). White
solid. TLC (CHCl3/MeOH 85 :15): Rf 0.43. 1H-NMR ((D6)DMSO): 8.46 (s, 1 H); 8.31 (s, 1 H); 7.61 7.33
(m, 10 H); 5.96 (d, J ˆ 4.58, 1 H); 4.59 (t, J ˆ 4.85, 1 H); 4.32 (t, J ˆ 4.94, 1 H); 4.06 (dt, J ˆ 3.85, 4.40, 1 H); 3.85
(m, 2 H); 0.97 (s, 9 H).
3. 2'-O-Acetyl-3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxyadenosine (3). To a suspension of 2 (20 g,
40 mmol) in MeCN (400 ml) containing a trace amount of H2O (0.65 ml, 3.6 mmol) was added a soln. of 2-
acetoxyisobutyryl bromide (17.5 ml, 0.12 mol) in dry MeCN (100 ml) at 08 over 1 h. A clear soln. was formed
first after 2.5 h, and, then, a solid precipitate was formed when the reaction progressed. The mixture was stirred
at 08 for 5 h. Sat. NaHCO3 soln. was added dropwise at 08 until the pH of the soln. reached 8, and, then, the soln.
was neutralized with AcOH to pH 5. The solid was filtered and washed with cold H2O (150 ml), MeCN (50 ml),
and Et2O (50 ml). The solid product was dried (P2O5) to yield 11.56 g of 3. The mother liquor was concentrated
to a small volume and extracted with CHCl3 (600 ml). The org. layer was washed with sat. NaHCO3 soln. (2 Â
50 ml) and brine (200 ml) and dried (Na2SO4). After evaporation, the residue was submitted to FC (silica gel;
hexane/CHCl3) 1:1 to 1:3 and CHCl3/MeOH (0 5%)) to yield pure 3 (total 19.2 g, 79.5%), and a mixture of 3
and the 3'-acetyl-2'-bromo-2'-deoxy isomer. TLC (CHCl3/MeOH 85 :15): Rf 0.61. TLC (CHCl3/MeOH 9 :1):
Rf 0.52. 1H-NMR (CDCl3): 8.34 (s, 1 H); 8.15 (s, 1 H); 7.71 7.37 (m, 10 H); 6.21 (d, J ˆ 2.0, 1 H); 5.74 (t, J ˆ 2.0,
1 H); 5.62 (br., 2 H); 4.44 (dd, J ˆ 1.6, 4.0, 1 H); 4.36 (m, 1 H); 4.02 (m, 1 H); 2.20 (s, 3 H); 1.08 (s, 9 H).
4. 3'-Bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxyadenosine (4). A suspension of 3 (10.6 g, 17.3 mmol)
in 750 ml of MeOH was cooled to 08 in an ice-bath, and 7.0n NH3/MeOH soln. (5 ml, 35 mmol) was added
dropwise. The mixture was stirred overnight at 48, and then at room temperature for 3 h. The white precipitate
was filtered and washed with cold MeOH (50 ml). The solid product was dried (P2O5) to yield 7.0 g of pure 4.
The mother liquor was neutralized with AcOH (2 ml) to pH 5 and evaporated to dryness. The solid was washed
with cold H2O, dried (P2O5), and submitted to FC (silica gel; CH2Cl2/MeOH (0 5%)). The collected fractions
were evaporated to give 1.5 g of 4 (total 8.6 g, 87.4%) and a mixture of 4 and the 2',3'-epoxide compound (0.5 g).
5. 2'-O-[(Benzylamino)carbonyl]-3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxyadenosine (5). To a
soln. of 4 (6.82 g, 12 mmol) in 150 ml of anh. THF were added Et2O (3.75 ml, 27 mmol) and PhCH2NCO
(4.5 ml, 36 mmol). The mixture was stirred at r.t. until the disappearance of the starting material for 3 d. MeOH
(10 ml) was added, and the mixture was stirred for 0.5 h. After evaporating the solvent, the residue was
submitted to FC (silica gel; CH2Cl2, CHCl3, and CHCl3/MeOH 95 :5). The desired fractions were collected and
evaporated to yield 5 (8.0 g, 95.0%). White foam. TLC (AcOEt/MeOH 95 :5): Rf 0.68. 1H-NMR (CDCl3): 8.27
(s, 1 H); 8.14 (s, 1 H); 7.71 7.27 (m, 15 H); 6.23 (d, J ˆ 2.4, 1 H); 6.10 (br., 2 H); 5.71 (s, 1 H); 5.67 (t, J ˆ 6.0,
1 H); 4.53 (dd, J ˆ 4.0, 1.2, 1 H); 4.37 (m, 3 H); 4.01 (m, 1 H); 1.07 (s, 9 H).
6. 3'-(Benzylamino)-5'-O-[(tert-butyl)diphenylsilyl]-3'-N,2'-O-carbonyl-3'-deoxyadenosine (6). To a soln.
of 5 (8.0 g, 11.4 mmol) in 225 ml of anh. THF was added NaH powder (547 mg, 22.4 mmol) at À158 (ice/EtOH
bath). The suspension was stirred at À15 to À108 for 1 h. When the reaction took place at À158, H2 bubbles
were observed. The reaction was completed after 1 h at À108. After filtering through Celite, the filtrate was
neutralized with AcOH (ca. 1 ml) and evaporated under reduced pressure. The residue was dissolved in CHCl3
(500 ml) and washed with H2O (50 ml), sat. NaHCO3 soln. (3 Â 50 ml), and brine (2 Â 50 ml). The combined aq.
layers were re-extracted with CHCl3 (2 Â 50 ml), and the combined org. layers were dried (Na2SO4). After

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Helvetica Chimica Acta Vol. 86 (2003)
evaporation, the residue was submitted to FC (silica gel; MeOH/CHCl3 2 :98) to yield 6 (6.67 g, 94.3%). White
foam. TLC (AcOEt/MeOH 95 :5): Rf 0.64. 1H-NMR (CDCl3): 8.07 (s, 1 H); 7.86 (s, 1 H); 7.52 7.18 (m, 15 H);
6.14 (d, J ˆ 2.8, 1 H); 5.92 (dd, J ˆ 8.4, 2.8, 1 H); 5.68 (s, 2 H); 4.70 (d, J ˆ 15.2, 1 H); 4.57 (dd, J ˆ 8.4, 2.8, 1 H);
4.28 (m, 3 H); 3.60 (m, 2 H); 0.97 (s, 9 H).
7. 3'-(Benzylamino)-3'-deoxyadenosine (7). To a soln. of 6 (6.2 g, 10 mmol) in MeOH (200 ml) was added
an aq. NaOH soln. (2.0n, 200 ml) in five portions. Each addition was stopped, when the soln. became cloudy, and
then more NaOH (aq.) was added after the soln. became clear. The reaction was complete after 3 d. The mixture
was neutralized with AcOH to pH 6. The soln. was filtered through Celite, and the filtrate was evaporated under
reduced pressure. The residue was co-evaporated with EtOH to afford a white solid. The crude product was
purified by FC (silica gel; MeOH/CHCl3 (0 10%)). The collected fractions were evaporated to give 7 (3.45 g,
96.7%). White solid. TLC (CHCl3/MeOH 9 :1): Rf 0.37. TLC (i-PrOH/aq. NH3/H2O 8 :1 :1): Rf 0.83. 1H-NMR
((D6)DMSO): 8.36 (s, 1 H); 8.12 (s, 1 H); 7.36 7.19 (m, 8 H); 5.96 (d, J ˆ 3.8, 1 H); 4.57 (dd, J ˆ 5.1, 3.8, 1 H);
3.92 (m, 1 H); 3.80 3.70 (m, 3 H); 3.56 3.33 (m, 2 H).
8. 3'-Amino-3'-deoxyadenosine (8). A mixture of 7 (3.0 g, 8.4 mmol) and 10% Pd/C (0.3 g) in EtOH/H2O
(150 ml/150 ml) was sealed in a stainless steel reactor and shaken under H2 (30 psi) at r.t. for 5 d. The mixture
was filtered through Celite and washed with hot DMSO. The combined soln. was evaporated under reduced
pressure to yield white crystals, which were washed with Et2O. The solid product was dried (P2O5) to yield 8
1
(2.05 g, 91.8%). White solid. TLC (i-PrOH/aq. NH3/H2O 8 :1 :1): Rf 0.52. H-NMR (D2O): 8.16 (s, 1 H); 8.06
(s, 1 H); 5.97 (d, J ˆ 4.7, 1 H); 4.83 (dd, J ˆ 6.6, 4.7, 1 H); 4.29 (m, 1 H); 3.96 (t, J ˆ 6.0, 1 H); 3.82 3.65
(m, 2 H).
9. 2-[(Dimethylamino)methylidene]guanosine. To a suspension of guanosine 9 (2.0 g, 7.06 mmol) in 20 ml of
abs. MeOH was added N,N-(dimethylamino)formamide dimethyl acetal (3.4 ml, 25.2 mmol). The mixture was
stirred at r.t. for 5 d. The solid precipitate was filtered off and washed with cold MeOH and Et2O, and dried to
yield the product (2.22 g, 93.3%). White solid. 1H-NMR ((D6)DMSO): 3.01 (s, 1 H); 3.13 (s, 1 H); 3.56
(m, 2 H); 3.88 (q, J ˆ 6.8, 4.0, 1 H); 4.09 (q, J ˆ 8.0, 4.8, 1 H); 4.46 (q, J ˆ 11.2, 6.0, 1 H); 5.01 (t, J ˆ 5.6, 1 H);
5.17 (d, J ˆ 3.6, 1 H); 5.40 (d, J ˆ 6.4, 1 H); 5.78 (d, J ˆ 6.4, 1 H); 8.02 (s, 1 H); 8.51 (s, 1 H); 11.33 (br., 1 H).
‡
‡
ESI-MS: 361.3 ([M ‡ Na] ); calc. for M : 338.1).
10. 5'-O-[(tert-Butyl)diphenylsilyl]-2-[(dimethylamino)methyledene)guanosine (10). A suspension of 2-
[(dimethylamino)methylidene]guanosine (2.2 g, 6.5 mmol) in 80 ml of dry pyridine was stirred with
(t-Bu)Ph2SiCl (1.9 ml, 7.1 mmol) and DMAP (45 mg, 0.37 mmol) for 3 d to give a clear soln. A MeOH
(10 ml) was added, and the mixture was stirred for an additional 0.5 h and evaporated under reduced pressure.
The residue was washed with cold H2O and dried under vacuum. The solid was stirred with Et2O, filtered, and
washed with Et2O. The solid product was dried in vacuum to give 10 (3.3 g, 96.2%). White solid. TLC (CHCl3/
‡
‡
MeOH 9 :1): Rf 0.28. ESI-MS: 599.4 ([M ‡ Na] ); calc. for M : 576.3).
11. 2'-O-Acetyl-3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxy-2-[(dimethylamino)methylidene]guano-
sine (11). To a suspension of 10 (2.3 g, 4.0 mmol) in 80 ml of MeCN was added 64 ml of H2O. The mixture was
cooled to 08 in an ice-H2O bath, and 1-(bromocarbonyl)-1-methyl acetate (2.2 ml, 15.2 mmol) was added
dropwise under Ar. The mixture was stirred at 08 for 2 h to give a clear soln. After stirring for an additional 4 h at
r.t., the mixture was evaporated to dryness. The residue was dissolved in CHCl3 (150 ml) and washed carefully
with cold H2O (20 ml), NaHCO3 soln. (3 Â 30 ml), and brine (50 ml). The aq. layers were re-extracted with
CHCl3 (3 Â 30 ml), and the combined org. layers were dried (Na2SO4) and evaporated under reduced pressure.
The residue was submitted to FC (silica gel; MeOH/CHCl3 (0 5%)) to afford 11 (2.3 g, 82.8%). White foam.
TLC (CHCl3/MeOH 9 :1): Rf 0.52. 1H-NMR (CDCl3, 400 MHz): 1.08 (s, 9 H); 2.21 (s, 3 H); 3.06 (s, 3 H); 3.18
(s, 3 H); 4.02 (m, 2 H); 4.38 (d, 4.4, 1 H); 4.43 (m, 1 H); 5.95 (d, J ˆ 1.8, 1 H); 6.07 (s, 1 H); 7.38 7.71 (m, 10 H);
7.84 (s, 1 H); 8.61 (s, 1 H); 9.71 (br., 1 H). 13C-NMR (CDCl3): 19.4; 21.1; 27.0; 35.4; 41.6; 50.3; 64.8; 81.9; 82.2;
‡
88.8; 120.6; 128.1; 130.2; 132.9; 133.0; 135.8; 136.4; 150.0; 157.4; 158.3; 159.0; 169.1. ESI-MS: 703.3 ([M ‡ Na] ),
‡
‡
705.3 ([M ‡ Na ‡ 2] ); calc. for M : 680.2.
12. 3'-Bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxy-2-[(dimethylamino)methylidene]guanosine (12). To
a soln. of 11 (820 mg, 1.2 mmol) in 30 ml of MeOH was added dropwise a 7.0n soln. of NH3 in MeOH (0.85 ml,
6 mmol). The mixture was stirred at r.t. for 1.5 h. AcOH (1 ml) was added, and the solvent was evaporated
under reduced pressure. The residue was dissolved in CHCl3 (100 ml) and washed with H2O (20 ml), NaHCO3
soln. (2 Â 20 ml), and brine (2 Â 20 ml). The aq. layers were extracted with CHCl3 (2 Â 20 ml), and the
combined org. layers were dried (Na2SO4). After evaporation, the residue was submitted to FC to yield 12
(690 mg, 89.7%). White solid. TLC (CHCl3/MeOH 9 :1): Rf 0.42. 1H-NMR (CDCl3): 1.03 (s, 9 H); 3.06 (s, 3 H);
3.17 (s, 3 H); 3.97 (m, 2 H); 4.44 (q, J ˆ 9.9, 5.1, 1 H); 4.54 (dd, J ˆ 5.1, 3.7, 1 H); 5.17 (br., 1 H); 5.78 (br., 1 H);
5.85 (d, J ˆ 3.3, 1 H); 7.35 7.69 (m, 10 H); 7.79 (s, 1 H); 8.51 (s, 1 H); 8.82 (br., 1 H). 13C-NMR (CDCl3): 19.5;

Helvetica Chimica Acta Vol. 86 (2003)
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27.1; 30.0; 35.4; 41.8; 54.5; 65.0; 81.0; 82.7; 90.7; 119.2; 128.0; 130.1; 133.2; 135.8; 137.6; 150.6; 157.0; 158.7. ESI-
‡
‡
‡
MS: 661.3 ([M ‡ Na] ), 663.3 ([M ‡ Na ‡ 2] ); calc. for M : 638.2.
13. 2'-O-[(Benzylamino)carbonyl]-3'-bromo-5'-O-[(tert-butyl)diphenylsilyl]-3'-deoxy-2-[(dimethylami-
no)methylidene]guanosine (13). A soln. of 12 (487 mg, 0.76 mmol), Et3N (318 ml, 2.28 mmol), and PhCH2NCO
(282 ml, 2.28 mmol) in 8 ml of anh. THF was stirred at r.t. for 2.5 d. MeOH (5 ml) was added and the mixture was
stirred for 2 h. After removal of solvent, the residue was submitted to FC (silica gel; MeOH/CHCl3) (0 5%)) to
give 13 (550 mg, 93.7%). White solid. TLC (AcOEt/MeOH 9 :1): Rf 0.30. 1H-NMR (CDCl3): 1.08 (s, 9 H); 3.01
(s, 3 H); 3.04 (s, 3 H); 3.02 (m, 2 H); 4.43 (m,4 H); 5.45 (t, J ˆ 5.9, 1 H); 5.96 (d, J ˆ 1.5, 1 H); 6.11 (s, 1 H);
7.29 7.47 (m, 15 H); 7.81 (s, 1 H); 8.65 (s, 1 H); 8.95 (s, 1 H). 13C-NMR (CDCl3): 19.4; 27.0; 35.2; 41.4; 45.5;
51.0; 64.8; 81.7; 83.3; 88.7; 120.5; 127.7; 127.9; 128.1; 128.9; 133.0; 133.1; 135.7; 135.8; 136.3; 138.1; 150.2; 154.7;
‡
‡
‡
157.4; 158.4; 159.0. ESI-MS: 794.2 ([M ‡ Na] ), 796.2 ([M ‡ Na ‡ 2] ); calc. for M : 771.2.
14. 3'-(Benzylamino)-2'-O,3'-N-carbonyl-3'-deoxy-2-[(dimethylamino)methylidene]guanosine (14). A soln.
of 13 (355 mg, 0.46 mmol) in 15 ml of anh. DMF was cooled to À158 in an ice-EtOH bath. NaH (36 mg,
1.48 mmol) was added under Ar. The suspension was stirred at À15 to 08 for 4 h, and at r.t. for 24 h, leading to
disappearance of starting material. The solution was filtered and evaporated to dryness. The residue was
dissolved in AcOEt (150 ml) and washed with H2O (20 ml), NaHCO3 soln. (2 Â 25 ml), and brine (50 ml). The
aq. layers were extracted with CHCl3 (3 Â 20 ml), and the combined org. layers were dried (Na2SO4). After
removing the solvent, the residue was used directly for the next stepwithout further purification. In another
reaction with 100 mg (0.13 mmol) of 6, 53 mg (91.4%) of 14 was isolated by FC (silica gel). TLC (CHCl3/MeOH
9 :1): Rf 0.32. 1H-NMR (CDCl3): 3.00 (s, 3 H); 3.07 (s, 3 H); 3.51 (m, 1 H); 3.85 (m, 1 H); 4.29 (d, J ˆ 6.2, 1 H);
4.31 (s, 1 H); 4.52 (dd, J ˆ 8.4, 2.5, 1 H); 4.75 (d, J ˆ 6.2, 1 H); 5.35 (br., 1 H); 5.45 (dd, J ˆ 8.2, 3.9, 1 H); 6.07
(d, J ˆ 3.9, 1 H); 7.28 7.34 (m, 5 H); 7.86 (s, 1 H); 8.45 (s, 1 H); 9.80 (br., 1 H). 13C-NMR (CDCl3): 35.4; 41.7;
47.6; 60.7; 62.5; 80.2; 85.5; 91.3; 120.7; 128.6; 128.7; 129.3; 135.1; 137.8; 150.0; 157.0; 157.5; 158.2; 158.8. ESI-MS:
‡
‡
476.3 ([M ‡ Na] ); calc. for M : 453.2.
15. 3'-(Benzylamino)-3'-deoxyguanosine (15). To a soln. of 14 (crude product without purification) in 20 ml
of MeOH was added 20 ml of 3.0n NaOH soln. The mixture was stirred at r.t. for 3 d. The mixture was
neutralized with AcOH to pH 5. After evaporating the solvent, a white solid was obtained and washed with
Et2O. The solid was dried (P2O5) to yield 133 mg of 15. The aq. soln. was concentrated to a small volume and was
loaded on a C18 reversed-phase column and eluted with H2O/MeOH. After evaporation, a total amount of
1
207 mg (95% from 13) of 15 was obtained. TLC (i-PrOH/NH3/H2O 8 :1:1). Rf 0.60. H-NMR ((D6)DMSO):
3.29 (m, 1 H); 3.50 (dd, J ˆ 3.5, 11.6, 1 H); 3.65 (m, 1 H); 3.73 (d, J ˆ 7.7, 2 H); 3.82 (m, 1 H); 4.39 (t, J ˆ 4.6,
1 H); 5.08 (br., 1 H); 5.75 (d, J ˆ 3.7, 1 H); 5.85 (br., 1 H); 7.03 (br., 2 H); 7.19 7.35 (m, 5 H); 7.86 (s, 1 H).
13C-NMR ((D6)DMSO): 51.7; 59.5; 62.2; 73.1; 84.3; 88.8; 117.3; 127.3; 135.6; 141.4; 151.7; 155.4; 158.4. ESI-MS:
‡
‡
395.3 ([M ‡ Na] ); calc. for M : 372.2.
16. 3'-Amino-3'-deoxyguanosine (16). To a soln. of 15 (60 mg, 0.16 mmol) in 10 ml of EtOH and 2 ml of
AcOH were added 10% Pd/C (140 mg, 50% wet) and ammonium formate (760 mg). The suspension was stirred
overnight at r.t. The reaction was monitored by TLC. After filtration, the solvents were removed by evaporation
under reduced pressure. The residue was purified by a C18 reversed-phase column with H2O/MeOH. After
evaporation, 16 (45 mg, 98%) was obtained. White solid. 1H-NMR (400 MHz, (D6)DMSO): 1.82 (br., 2 H); 3.40
(dd, J ˆ 5.2, 5.6, 1 H); 3.54 (dd, J ˆ 3.3, 3.6, 1 H); 3.64 (m, 1 H); 3.68 (m, 1 H); 4.10 (dd, J ˆ 3.2, 2.4, 1 H); 5.71
(d, J ˆ 2.4, 1 H); 6.66 (br., 2 H); 7.93 (s, 1 H). 13C-NMR (100 MHz, (D6)DMSO): 52.5; 60.9; 75.0; 85.1; 88.0;
‡
‡
116.6; 135.2; 150.8; 153.9; 156.9. ESI-MS: 283.1 ([M ‡ H] ); calc. for M : 282.1.
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Received October 14, 2002