Novel and efficient syntheses of 3′,5′-diamino derivatives of 2′,3′,5′-trideoxycytidine and 2′,3′,5′-trideoxyadenosine. Protonation behavior of 3′,5′-diaminonucleosides

Article abstract of DOI:10.1016/S0040-4020(03)00870-6

High yielding synthetic routes to 3′,5′-diamino-2′,3′,5′-trideoxycytidine and 3′,5′-diamino-2′,3′,5′-trideoxyadenosine are described. In addition, the protonation behavior of 3′,5′-diamino-2′,3′,5′-trideoxycytidine, 3′,5′-diamino-2′,3′,5′-trideoxyadenosin

Full text of DOI:10.1016/S0040-4020(03)00870-6

Tetrahedron 59 (2003) 5449–5456
Novel and efficient syntheses of 30,50-diamino derivatives of
20,30,50-trideoxycytidine and 20,30,50-trideoxyadenosine.
Protonation behavior of 30,50-diaminonucleosides
*
´ ´
Ivan Lavandera, Susana Fernandez, Miguel Ferrero and Vicente Gotor
´ ´ ´ ´
Departamento de Quımica Organica e Inorganica, Facultad de Quımica, Universidad de Oviedo, 33006 Oviedo, Spain
Received 11 April 2003; revised 13 May 2003; accepted 28 May 2003
Abstract—High yielding synthetic routes to 30,50-diamino-20,30,50-trideoxycytidine and 300,50-diamino-200,300,50-trideoxyadenosine are
described.0 In addition, the protonation behavior of 030,50-diamino-20,30,50-trideoxycytidine, 30,5 -diamino-20,3 ,5 -trideoxyadenosine, 30,50-
diamino-3 ,50-dideoxythymidine, and 30,50-diamino-2 ,30,50-trideoxyuridine has been studied by means of pH-metric measurements and NMR
spectroscopy. The ionization constants and the sequence of protonation sites have been determined. q 2003 Elsevier Science Ltd. All rights
reserved.
1. Introduction
min0d, we descri0be0here for the first time the preparation of
30,5 -diamino-2 ,3 ,50-trideoxycytidine and an efficient
alternative synthesis to N-benzoyl-30,50-diamino-20,30,50-
trideoxyadenosine. Additionally, we perform pro0tonation
studies of 300,50-diaminonucleoside derivatives of 2 -deoxy-
cytidine, 2 -deoxyadenosine, thymidine, and 20-deoxy-
uridine with the aim of finding the ionization constants
and the sequence of protonation sites on these molecules.
In the last few years the ever-growing interest in the field of
nucleosides and nucleotides has led to renewed efforts in the
synthesis of analogues.1 Modifications in the sugar moiety
are one of the most important kind of nucleoside derivatives
that can lead to promising chemotherapeutic agents.2 These
compounds have attracted much attention as potential
antiviral and anticancer agents.3 Due to their use as
building-blocks to prepare anti-sense and anti-gene oligo-
nucleotides, they also emerge as potential and selective
inhibitors of gene expression.4 Particularly, amino sugar
nucleosides a0re import0ant bioactive molecules,5 of which
puromycin (3 -amino-2 ,30-dideoxyadenosine) is one of the
most important examples. One of the major strategies for the
synthesis of sugar-modified nucleosides is the modification
of the intact nucleosides.6 Although there has been a
growing demand for the develop0ment of nucleoside-base
therapeutics, 30,50-diamino-20,3 ,50-trideoxynucleosides
remains to some extent unexplored mainly due to the
difficult synthetic accessibility. There is very little in the
literature concerning the synthesis of such nucleosides.7
2. Results and discussion
Starting from 20-deoxyuridine (1) we previously synthesized
30,50-diazido-20,30,50-trideoxyuridine (2) through a simple
and efficient three step procedure.8 This diazido compound
was treated9 with phosphorus oxychloride, 1,2,4-triazole,
and triethylamine in acetonitrile at room temperature for 1 h
to afford the 4-triazolylpyrimidinone derivative 3
(Scheme 1). Subsequent treatment with aqueous ammonia
in 1,4-dioxane solution give the cytidine derivative 4.
Hydrogenat0ion of 4 in 0Et0OH in the presence of 10% Pd/C
yielded 30,5 -diamino-2 ,3 ,50-trideoxycytidine (5) with 29%
overall yield.
In our ongoing study to elucidate the effects of amino-
derivatized nucleosides on critical biosynthetic pathways as
well as their use as monomers for the preparation of
anti0sense oligonucleotides, we first reported the synthesis of
300,50-d0iamino-30,50-dideoxythymidine and 30,50-diamino-
2 ,3 ,5 -trideoxyuridine.8 With these considerations in
For the synthesis of N-benzoyl-30,50-diamino-20,30,50-tri-
deoxyadenosine (12), 50-O-protected adenosine derivative 6
(commercially available) was subjected to Mitsunobu
conditions (Scheme 2). Thus, esterification of the hydroxyl
group at 30 position takes place with inversion of
configuration giving place to ester 7. Methanolysis of the
p-nitrobenzoate ester and cleavage of the dimethoxytrityl
group with catalytic amounts of formic acid in CHCl3
afforded N-benzoyl-20-deoxyxyloadenosine (9). Mesylation
Keywords: 30,50-diaminonucleosides; protonation studies; ionization
constants.
*
Corresponding author. Tel.: þ34-985-103-448; fax: þ34-985-103-451;
e-mail: vgs@sauron.quimica.uniovi.es
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00870-6

5450
I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
Scheme 1. Synthesis of 30,50-diamino-20-deoxycytidine.
Scheme 2. Synthesis of 30,50-diamino-20-deoxyadenosine N-benzoylated.

I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
5451
Scheme 3. Mesilation reaction with model nucleoside, 20-deoxyadenosine N-benzoylated.
Table 1. Mesylation reaction of N-benzoyl-20-deoxyadenosine (13)
Entry
Base (equiv.)
Equiv. of MsCl
t (h)
13 (%)a
14 (%)a
50
70
30
20
12c
Complex
15 (%)a
16 (%)a
1
2
3
4
5
6
7
Et3Nb
Et3N (6)
Et3N (1:1 v/v)
Et3N (1:2 v/v)
Et3N (1:4 v/v)
Imidazol (10)
DMAP (10)
4
4
6
6
6
6
6
13
23
66
66
66
72
2
50
30
30
40
65c
Mixture
99c
40
40
a
1
Calculated by H NMR.
As base and solvent.
Isolated yields after flash chromatography.
b
c
of 9 proved difficult, the 50-O-mesyl derivative and
fragments corresponding to the hydrolysis of the glycosidic
bond being observed when the reaction was carried out with
2.2 equiv. of mesyl chloride in pyridine at 08C.
(Scheme 2). Subsequent treatment of 10 with sodium
azide in DMF solution afforded diazido 11. Hydrogenation
of the latter0 in EtOH in the0 p0resence of Pd black gave
N-benzoyl-3 ,50-diamino-20,3 ,5 -trideoxyadenosine (12).
This efficient six-step procedure from readily available
starting material gave 12 in 29% overall yield.
This hydrolysis could be explained by initial protonation of
the base moiety followed by dissociation of the protonated
nucleoside to a glycosyl oxocarbenium ion and the free
purine.10
Additi0onally, we report here the protonation behavior of
both 3 ,50-diamino nucleosides 5 and 12, and the previously
reported8 30,50-diamino-30,50-dideoxythymidine (17) and
30,50-diamino-20,30,50-trideoxyuridine (18) (Fig. 1) using
pH-metric measurements and NMR spectroscopy. To
determine the stepwise protonation sites we recorded their
1H and 13C NMR spectra at different pD values
(pD¼pHþ0.4). As a general rule, when pD is decreased,
proton atoms in the a-position to the protonated nitrogen
move downfield while b-C signals move upfield.11
Although the pKa of pyridine (5.29) is greater than the pKa
of adenine (4.25), it seems that the difference is not enough
to shift the equilibrium toward the protonation of pyridine.
For this reason, we carried out the reaction in a medium of
triethylamine (pKa¼10.75). As the model nucleoside we
choose N-benzoyl-20-deoxyadenosine (13, Scheme 3).
However, the process was slower than before, and a mixture
of starting material and 50-O-mesyl derivative 14 was
obtained (entry 1, Table 1). Next, the reaction was carried
out with Et3N as base and pyridine as solvent (entries 2–5,
Table 1). The best result was observed with a ratio Et3N/Py
1:4 (v/v), the desired compound 15 being isolated in 65%
yield after flash chromatography. In addition, monomesyl
derivative 14 was obtained in 12% yield. The use of
imidazol (pKa¼7.0) as base gave rise to a complex mixture
(entry 6, Table 1). However, when the process was
performed with 10 equiv. of DMAP (pKa¼9.7) in pyridine
solution and 6 equiv. of MsCl, 30,50-di-O-mesyl nucleoside
15 was achieved exclusively after 2 h in quantitative yield
(entry 7, Table 1). DMAP makes the reaction faster and this
avoids the hydrolysis of the glycosidic bond in solution.
For all diaminonucleosides, in the range pD 12–10, no
1
appreciable variations in the chemical shifts of H and 13C
NMR spectra occurred, but between pD 10 and 8 a
significant downfield of H-50 and an upfield of C-40 were
observed (Figs. 2 and 3). The shift of C-40 can be as0cribed to
protonation at N-50 or N-30, but the fact that C-2 did not
Figure 1. 30,50-Diamino-30,50-dideoxythymidine and 30,50-diamino-20,30,50-
trideoxyuridine.
Extension of this reaction to the xylonucleoside 9 led to the
formation of di-O-mesyl derivative 10 in 75% yield

5452
I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
Figure 3. 13C NMR chemical shift of: (a) diamino-dC, 5; (b) N-Bz-
diamino-dA, 12; (c) diamino-T, 17; (d) diamino-dU, 18 as a function of pD.
Figure 2. 1H NMR chemical shift of: (a) diamino-dC, 5; (b) N-Bz-diamino-
dA, 12; (c) diamino-T, 17; (d) diamino-dU, 18 as a function of pD.
main species in solution is the monoprotonated form. Below
pH 5, the diprotonated form exists for dA, T, and dU
derivatives (Fig. 4(b), (c) and (d)) almost exclusively. This
is also the main species at pH¼4.5–6 in 30,50-diamino-dC
(5), which predominates in its fully protonated form (LHþ3 )
at pH,3 (Fig. 4(a)).
experience a clear shift suggests that the first proton binding
to the molecule occurs mainly at the amino group of the
50-position. In the p0D range 8–5, the0 most significant shifts
are shown by H-3 , C-40, and C-2 , which confirms the
second protonation to be predominantly at the N-30 position.
An additional protonation is expected for 30,50-diamino-20-
deoxycytidine (5) due to the presence of an extra amino
group on the base. Nucleoside 5 lacks a hydrogen in the
a-position to this amino group. However, a downfield of
H-5 (b-position) was observed at pD,5. Since in 18 no
appreciable shift of that hydrogen was evident, the shift of
H-5 in 5 can be imputed to the base protonation. This fact is
confirmed by a slight upfield of C-5 (Fig. 3(a)).
The distribution of protonated species at different pHs can
be used as a guide to chemical reactivity. Thus, when we
carried out the enzymatic acylation of 30,50-diamino-
thymidine (17), a poor yield of acylated derivative was
obtained. However, if the process was performed in the
p0resence of molecular sieves, the isolated yield of
5 -acetylnucleoside was increased up to 80%.8 To explain
this fact, a measurement of pH to a water solution of 17
before and after the addition of molecular sieves (1:1 w/w)
was carried out. We observed a slight increase of pH from
8.8 to 9.2, in which at least 50% of free amine was present.
The addition of molecular sieves to the enzymatic acylation
The potentiometric titrations were carried out in 0.1 M
Me4NCl aqueous solution at 298 K. In Table 2, the basicity
constants of 5, 12, 17, and 18 are presented. The comparison
of the pKa values indicated that the basicity is similar for
purine and pyrimidine nucleosides. In the case of 30,50-
diamino-20,30,50-trideoxycytidine a third pKa of 3.67
appears, corresponding to protonation at the exocyclic
amino base, in addition to the pKas for protonation at N-30
and N-50.
Table 2. Logarithms of the protonation constants of 5, 12, 17, and 18
log Kb
Reactiona
5
12
17
18
From the ionization constants the distributions of the
protonated species of the diaminonucleoside derivatives
formed as a function of pH were calculated using the
computer program SUPERQUAD12 (Fig. 4). The free amine
predominates at pH.10 whereas at a pH of ca. 7.5–8.5 the
LþH¼HL
8.74 (7)
6.49 (7)
3.67 (7)
9.21 (4)
6.57 (4)
8.99 (3)
6.59 (3)
9.06 (5)
6.78 (5)
HLþH¼H2L
H2LþH¼H3L
a
Charges have been omitted for clarity.
Values in parentheses are standard deviation in the last significant figure.
b

I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
5453
and analysis of 1H and 13C NMR at different pD values. The
first protonation takes place mainly at the 50-amino group,
giving the monoprotonated form as the predominant species
at ca. pH 8. The diprotonated species is present mainly at pH
5. In the case of 30,50-diaminocytidine, the base protonation
occurs at pH values below 3. The distribution diagrams of
protonated species allows us to determine the predominant
form at different pHs to plan the best way to perform a
process. Aminonucleosides 5, 12, 16, and 17 are subjected
to biological assays and under investigation as monomers
for antisense oliogonucleotides.
3. Experimental
3.1. General
Melting points were taken on samples in open capillary
tubes and are uncorrected. IR spectra were recorded on an
Infrared Fourier Transform spectrophotometer using
KBr pellets. Flash chromatography was performed
1
using silica gel 60 (230–400 mesh). H, 13C NMR, and
DEPT were obtained using AC-200 (1H, 200.13 MHz and
13C, 50.3 MHz), and AC-300 (1H, 300.13 MHz and 13C,
75.5 MHz), or DPX-300 (1H, 300.13 MHz and 13C,
75.5 MHz) spectrometers for routine experiments. An
AMX-400 spectrometer operating at 400.13 and
1
100.61 MHz for H and 13C, respectively, was used for
1
1
the acquisition of H–1H and H–13C correlation experi-
ments. The chemical shifts are given in delta (d) values and
the coupling constants (J) in Hertz (Hz). ESIþ was used to
record mass spectra (MS). Microanalyses were performed
on a Perkin–Elmer model 2400 instrument. For the NMR
titrations, the samples were prepared with known amounts
of the diaminonucleoside, the pD was adjusted by addition
of DCl or NaOD solutions in D2O and the correction
pD¼pHpþ0.4 was used, where pHp is the direct measure-
ment of a pH-meter calibrated with non-deuterated buffer
solutions. For the pH-metric titrations, a Metrohm TITRO-
PROCESSOR-636 titrimeter was used, the reference
electrode was an Ag/AgCl electrode in sat. aq. KCl, the
cell was thermostated at 298^0.1 K, and the measurements
were performed under nitrogen atmosphere. The protona-
tion constants were determined by titration with 0.1N NaOH
of a solution containing 1023 M of the HCl salt of the
diamine in the presence of Me4NCl (0.1 M). The measure-
ments were carried out twice, and the data analysis was
performed with the computer program SUPERQUAD.12
3.1.1. 30,50-Diazido-4-(1,2,4-triazol-1-yl)-20,30,50-trideoxy-
cytidine (3). POCl3 (293 mL, 3.15 mmol) was added to a
suspension of 1,2,4-triazole (1.7 g, 25.16 mmol) in dry
acetonitrile (21 mL). Triethylamine (3.86 mL, 27.68 mmol)
and a solution of 28 (350 mg, 1.26 mmol) in 4 mL of dry
acetonitrile were added at 08C. Then, the reaction was
stirred for 1 h at room temperature. After that, 2.4 mL of
Et3N and 0.7 mL of water were added and stirred for
10 min. Later, the solvent was evaporated in vacuo and the
crude residue was redissolved in a saturated solution of
NaHCO3 and extracted with CHCl3 (3£15 mL). The organic
layer was dried with Na2SO4, filtered off and the solvent was
evaporated under reduced pressure, affording 384 mg (93%)
of an hygroscopic solid corresponding to compound 3. Rf
Figure 4. Distribution diagram of protonated species of: (a) diamino-dC, 5
(¼L); (b) N-Bz-diamino-dA, 12 (¼L); (c) diamino-T, 17 (¼L); (d) diamino-
dU, 18 (¼L) as a function of pH.
reaction shifts the equilibrium toward the free amine, and
this favors the above process. The acid–base effects of
molecular sieves are previously reported in the literature.13
In summary, efficient syntheses of 30,50-diamino derivatives
of 20-deoxycytidine and 20-deoxyadenosine have been
described. The sequence of the protonation sites and the
ionization constants of a series of four diaminonucleoside
derivatives has been determined by potentiometric study

5454
I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
(EtOAc): 0.54; IR (KBr): n 3235, 3065, 2932, 2105, 1637
1
room temperature, the solvent was evaporated in vacuo and
the crude residue was purified by flash chromatography
column (EtOAc) affording 432 mg (70%) of a yellow solid
corresponding to compound 7. Rf (EtOAc): 0.68; mp: 109–
1118C; IR (KBr): n 3413, 2929, 1731, 1638, 1617, 1507, and
and 1616 cm21; H NMR (CDCl3, 200 MHz): d 2.46 (m,
0
1H, H2 ), 2.77 (m, 1H, H2 ), 3.67–3.96 (m, 2H, H5 ), 4.07 (m,
0
0
3
0
0
3
0
1H, H4 ), 4.18 (m, 1H, H3 ), 6.15 (dd, 1H, H1 , JHH¼6.7,
4.9 Hz), 7.12 (d, 1H, H5, JHH¼7.2 Hz), 8.12 (s, 1H), 8.38
(d, 1H, H6, JHH¼7.2 Hz), and 9.25 (s, 1H); 13C NMR
1249 cm21; H NMR (CDCl3, 200 MHz): d 3.07 (m, 2H,
3
1
2
0
(CDCl3, 75.5 MHz): d 38.5 (C2 ), 51.1 (C5 ), 59.2 (C3 ), 82.6
0
0
0
0
0
H2 ), 3.46 (dd, 1H, H5 , JHH¼9.0, 7.4 Hz), 3.69 (dd, 1H, H5 ,
(C4 ), 87.3 (C1 ), 94.7 (C5), 143.1 (CH), 145.9 (C6), 153.9
(2C, C2þCH), and 159.3 (C4); MS (ESIþ, m/z): 368
[(MþK)þ, 4%] and 352 [(MþNa)þ, 100]. Anal. calcd (%)
for C11H11N11O2: C, 40.11; H, 3.37; N, 46.80. Found: C,
39.9; H, 3.5; N, 46.6.
2JHH¼9.0, 7.4 Hz), 3.74 (s, 3H, MeO), 3.75 (s, 3H, MeO),
0
0
0
4.67 (m, 1H, H4 ), 5.96 (m, 1H, H3 ), 6.55 (dd, 1H, H1 ,
0
0
3
0
0
JHH¼5.4 Hz), 6.71 (m, 4H, Hm ), 7.18–7.28 (m, 7H, Ho þ
00
00
00
Hm þHp ), 7.35 (m, 2H, Ho ), 7.48–7.67 (m, 5H, HmþHpþ
000
000
Ho ), 8.01 (m, 2H, Ho), 8.20 (m, 3H, H8þHm ), 8.61 (s, 1H,
H2), and 9.01 (s, 1H, NH); 13C NMR (CDCl3, 75.5 MHz): d
3.1.2. 30,50-Diazido-20,30,50-trideoxycytidine (4). A sol-
ution of 3 (860 mg, 2.61 mmol) in dry 1,4-dioxane (50 mL)
was cooled at 08C under nitrogen, and then an aqueous
solution of NH3 (33%, 15 mL) was added. After reaction for
2 h at room temperature, the solvent was evaporated in
vacuo and the crude residue was purified by flash
chromatography column (gradient eluent 10% to 15%
MeOH/EtOAc) affording 640 mg (89%) of a white solid
corresponding to compound 4. Rf (20% MeOH/EtOAc):
0.28; mp: 138–1418C; IR (KBr): n 3479, 3414, 3236, 2105,
0
38.5 (C2 ), 54.6 (2C, 2MeO), 60.2 (C5 ), 72.9 (C3 ), 82.0
0
0
0
(C4 ), 84.0 (C1 ), 86.0 (Ct), 112.5 (Cm ), 123.1 (2C,
0
0
000
C5þCm ), 126.4 (CH), 127.3 (CH), 128.3 (CH), 129.4
(CH), 129.5 (CH), 129.9 (CH), 132.4 (Cp), 132.8 (C), 133.5
00
(C), 134.4 (C), 134.7 (C), 140.2 (C8), 143.6 (Ci ), 148.9 (C),
0
150.0 (C), 150.8 (C), 151.9 (C2), 157.9 (Cp ), 162.7 (Ce), and
164.1 (Ca); MS (ESIþ, m/z): 845 [(MþK)þ, 37%], 829
[(MþNa)þ, 33], and 807 [(MþH)þ, 100]. Anal. calcd (%)
for C45H38N6O9: C, 66.98; H, 4.75; N, 10.42. Found: C,
67.0; H, 4.6; N, 10.2.
1
1637, 1617, 1483, and 1277 cm21; H NMR (MeOH-d4,
300 MHz): d 2.53–2.72 (m, 1H, H2 ), 3.79–3.93 (m, 2H,
3.1.5. N 6-Benzoyl-50-O-(4,40-dimethoxytrityl)-20-deoxy-
xyloadenosine (8).15 Compound 7 (360 mg, 0.45 mmol)
was dissolved in dry MeOH (50 mL) under nitrogen, and
was cooled at 08C. Then, a solution 0.2 M of NaOMe in
MeOH (1.8 mL, 0.36 mmol) was added. After reaction for
1.5 h at 08C, the solvent was evaporated in vacuo and the
crude residue was purified by flash chromatography column
(gradient eluent EtOAc-50% MeOH/EtOAc) affording
284 mg (97%) of a white solid corresponding to compound
8.
0
0
H5 ), 4.18 (m, 1H, H4 ), 4.50 (m, 1H, H3 ), 6.12 (d, 1H, H5,
0
0
3
3
0
JHH¼7.4 Hz), 6.35 (dd, 1H, H1 , JHH¼6.3 Hz), and 7.94
(d, 1H, H6, JHH¼7.4 Hz); 13C NMR (MeOH-d4,
3
0
0
0
0
75.5 MHz): d 38.3 (C2 ), 53.1 (C5 ), 62.3 (C3 ), 83.8 (C4 ),
0
87.4 (C1 ), 96.4 (C5), 142.4 (C6), 158.0 (C2), and 167.7 (C4);
MS (ESIþ, m/z): 316 [(MþK)þ, 11%], 300 [(MþNa)þ,
100], and 278 [(MþH)þ, 32]. Anal. calcd (%) for
C9H11N9O2: C, 38.97; H, 4.00; N, 46.48. Found: C, 39.2;
H, 4.1; N, 46.3.
3.1.3. 30,50-Diamino-20,30,50-trideoxycitydine (5). A sol-
ution of compound 4 (100 mg, 0.36 mmol) in EtOH (6 mL)
was exposed to a positive pressure of hydrogen gas
(balloon) at room temperature for 4 h in the presence of
10% palladium on charcoal (20 mg). The catalyst was
removed by filtration on Celite and the filtrate was
evaporated to dryness. The crude was purified by flash
chromatography column [4% NH3(aq.)/MeOH] to afford
after vacuum drying 58 mg (71%) of a white solid
corresponding to compound 5. Rf [10% NH3(aq.)/MeOH]:
0.39; mp: 186–1878C (decomposed); IR (KBr): n 3550,
3.1.6. N 6-Benzoyl-20-deoxyxyloadenosine (9).7c
A
catalytic amount of formic acid (3–4 drops) was added to
a solution of compound 8 (133 mg, 0.20 mmol) in CHCl3
(14 mL). The reaction was stirred for 24 h at room
temperature. Then, a few drops of 1N KOH were added,
the solvent was evaporated in vacuo, and the crude residue
was purified by flash chromatography (gradient eluent
10–20% MeOH/EtOAc) affording 70 mg (94%) of a white
solid corresponding to compound 9.
3.1.7. N 6-Benzoyl-30,50-di-O-methanesulfonyl-20-deoxy-
xyloadenosine (10). DMAP (688 mg, 5.63 mmol) was
added to a solution of compound 9 (200 mg, 0.56 mmol)
in dry pyridine (8 mL) under N2. Then, dry methane-
sulphonyl chloride (261 mL, 3.38 mmol) was added. After
reaction for 2 h at room temperature, the solvent was
evaporated in vacuo, and the crude residue was purified by
flash chromatography (8% MeOH/EtOAc) to afford 216 mg
(75%) of a white solid corresponding to compound 10. Rf
(20% MeOH/EtOAc): 0.65; mp: 75–778C; IR (KBr): n
1
3480, 3413, 3239, 1638, 1617 and 1490 cm21; H NMR
0
(D2O, 200 MHz): d 2.04–2.29 (m, 1H, H2 ), 2.72–2.98 (m,
0
0
0
2H, H5 ), 3.24 (m, 1H, H4 ), 3.66 (m, 1H, H3 ), 5.87 (d, 1H,
3
3
0
H5, JHH¼7.6 Hz), 6.01 (dd, 1H, H1 , JHH¼7.0, 5.0 Hz),
and 7.53 (d, 1H, H6, JHH¼7.6 Hz); 13C NMR (D2O,
3
0
0
0
0
75.5 MHz): d 39.5 (C2 ), 42.3 (C5 ), 51.7 (C3 ), 85.7 (C4 ),
0
86.2 (C1 ), 96.1 (C5), 141.8 (C6), 157.6 (C2), and 166.2 (C4);
MS (ESIþ, m/z): 264 [(MþK)þ, 25%], 248 [(MþNa)þ, 33],
and 226 [(MþH)þ, 100]. Anal. calcd (%) for C9H15N5O2: C,
47.97; H, 6.72; N, 31.10. Found: C, 47.8; H, 6.7; N, 31.1.
1
3494, 1602, 1566, and 1251 cm21; H NMR (MeOH-d4,
0
200 MHz): d 3.18–3.35 (m, 8H, H2 þMeS), 4.82 (s, 3H,
3.1.4. N 6-Benzoyl-50-O-(4,40-dimethoxytrityl)-30-O-(p-
nitrobenzoyl)-20-deoxyxyloadenosine (7).14 p-Nitro-
benzoic acid (254 mg, 1.52 mmol) was added to a solution
of 6 (500 mg, 0.76 mmol) in dry THF (50 mL) under
nitrogen. Then, Ph3P (400 mg, 1.52 mmol) and DEAD
(237 mL, 1.52 mmol) were added. After reaction for 2 h at
H5 þH4 ), 5.74 (m, 1H, H3 ), 6.83 (dd, 1H, H1 , JHH¼7.1,
3.0 Hz), 7.71–7.85 (m, 3H, HmþHp), 8.28 (m, 2H, Ho), 8.78
(s, 1H, H8), and 8.91 (s, 1H, H2); 13C NMR (MeOH-d4,
0
50.3 MHz): d 37.4 (MeS), 38.3 (MeS), 40.2 (C2 ), 68.3 (C5 ),
0
80.0 (CH), 81.8 (CH), 85.4 (C1 ), 125.1 (C5), 129.4 (CH),
129.8 (CH), 133.9 (Cp), 134.9 (Ci), 143.4 (C8), 151.1 (C6),
3
0
0
0
0
0

I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
5455
153.1 (C4), 153.3 (C2), and 168.1 (C¼O); MS (ESIþ, m/z):
512 [(MþH)þ, 100%]. Anal. calcd (%) for C19H21N5O8S2:
C, 44.61; H, 4.14; N, 13.70. Found: C, 44.6; H, 4.2; N, 13.4.
We thank Robin Walker for his revision of the English of
the manuscript.
3.1.8. N 6-Benzoyl-30,50-diazido-20,30,50-trideoxyadeno-
sine (11).7c Sodium azide (382 mg, 5.87 mmol) was added
to a solution of compound 10 (500 mg, 0.98 mmol) in dry
DMF (15 mL) under nitrogen. The reaction was stirred for
5 h at 658C, then 2 mL of water were added, and the solvent
was evaporated in vacuo. The crude residue was purified by
flash chromatography (EtOAc) affording 297 mg (75%) of a
white solid corresponding to compound 11.
References
1. (a) Robins, R. K.; Revankar, G. R. In Antiviral Drug
Development; De Clercq, E., Walker, R. T., Eds.; Plenum:
New York, 1998; p 11. (b) Nucleosides and Nucleotides as
Antitumor and Antiviral Agents; Chu, C. K., Baker, D. C.,
Eds.; Plenum Press: New York, 1993. (c) MacCoss, M.;
Robins, M. J. In Chemistry of Antitumor Agents; Wilman, D. E.
V., Ed.; Blackie and Son: UK, 1990; p 261. (d) Robins, R. K.;
Kini, G. D. In Chemistry of Antitumor Agents; Wilman, D. E.
V., Ed.; Blackie and Son: UK, 1990; p 299. (e) Chemistry of
Nucleosides and Nucleotides; Townsend, L. B., Ed.; Plenum:
New York, 1988.
3.1.9. N 6-Benzoyl-30,50-diamino-20,30,50-trideoxyadeno-
sine (12).16
A solution of compound 11 (50 mg,
0.12 mmol) in EtOH (4 mL) was exposed to a positive
pressure of hydrogen gas (balloon) at room temperature for
4 h in the presence of Pd black (20 mg). The catalyst was
removed by filtration on Celite and the filtrate was
evaporated to dryness. The crude was purified by flash
chromatography [1% NH3(aq.)/MeOH] to afford after
vacuum drying 35 mg (81%) of a white solid corresponding
to compound 12. Rf [5% NH3(aq.)/MeOH]: 0.33; mp: 74–
768C (decomposed); IR (KBr): n 3454, 3364, 2936, 1636,
2. (a) Ferrero, M.; Gotor, V. Chem. Rev. 2000, 100, 4319–4347.
(b) Kool, E. T. Chem. Rev. 1997, 97, 1473–1487.
3. (a) Vince, R.; Hua, M. J. Med. Chem. 1990, 33, 17–21.
(b) Ozaki, S.; Akiyama, T.; Ike, Y.; Mori, H.; Hoshi, A. Chem.
Pharm. Bull. 1990, 37, 3405–3417.
4. (a) Singh, I.; Hecker, W.; Prasad, A. K.; Parmar, V. S.; Seitz,
O. Chem. Commun. 2002, 500–501. (b) Singh, S. K.; Kumar,
R.; Wengel, J. Org. Chem. 1998, 63, 10035–10039.
(c) Uhlman, E.; Peyman, A. Chem. Rev. 1990, 90, 543–584.
5. (a) Suhadolnik, R. J. Nucleosides as Biological Probes; Wiley:
New York, 1979. (b) Suhadolnik, R. J. Nucleoside Antibiotics;
Wiley: New York, 1970.
1
1603, 1567, and 1488 cm21; H NMR (D2O, 300 MHz): d
0
0
0
2.32 (m, 1H, H2 ), 2.64 (m, 1H, H2 ), 2.90–3.09 (m, 2H, H5 ),
0
0
0
3.54 (m, 1H, H3 ), 3.86 (m, 1H, H4 ), 6.23 (dd, 1H, H1 ,
3JHH¼5.7 Hz), 7.22 (m, 2H, Hm), 7.36 (m, 1H, Hp), 7.61 (d,
13
3
2H, Ho, JHH¼7.7 Hz), 8.22 (s, 1H, H8), and 8.35 (s, 1H,
0
H2); C NMR (D2O, 75.5 MHz): d 39.4 (C2 ), 42.6 (C5 ),
0
0
0
0
52.4 (C3 ), 84.6 (C4 ), 85.8 (C1 ), 123.7 (C5), 128.2 (CH),
128.9 (CH), 132.7 (Ci), 133.4 (Cp), 143.3 (C8), 149.6 (C),
151.2 (C), 152.0 (C2), and 168.2 (CvO); MS (ESIþ, m/z):
376 [(MþNa)þ, 5%] and 354 [(MþH)þ, 100]. Anal. calcd
(%) for C17H19N7O2: C, 57.76; H, 5.42; N, 27.76. Found: C,
57.6; H, 5.6; N, 27.9.
6. (a) Robins, M. J.; Zou, R.; Hansske, F.; Wnuk, S. F. Can.
´
J. Chem. 1997, 75, 762–767. (b) Garcıa-Alles, L. F.;
Magdalena, J.; Gotor, V. J. Org. Chem. 1996, 61,
6980–6986. (c) Robins, M. J.; Hawrelak, S. D.; Hernandez,
A. E.; Wnuk, S. F. Nucleos. Nucleot. 1992, 11, 821–834.
(d) Samano, M. C.; Robins, M. J. Tetrahedron Lett. 1989, 30,
2329–2332. (e) Herdewijn, P.; Balzarini, J.; Masanori, B.;
Pauwels, R.; Van Aerschot, A.; Janssen, G.; De Clercq, E.
J. Med. Chem. 1988, 31, 2040–2048. (f) Mengel, R.; Wiedner,
H. Chem. Ber. 1976, 109, 433–443.
3.1.10. N 6-Benzoyl-30,50-di-O-methanesulfonyl-20-deoxy-
adenosine (15). The same procedure as the one described
for 10 yielded 15 (white solid, 97%). Rf (20% MeOH/
EtOAc): 0.78; mp: 57–598C; IR (KBr): n 3470, 2942, 1699,
1603, 1566, 1356, 1250, and 1175 cm21; 1H NMR (DMSO-
7. (a) Pannecouque, C.; Busson, R.; Balzarini, J.; Claes, P.; De
Clercq, E.; Herdewijn, P. Tetrahedron 1995, 51, 5369–5380.
(b) Pannecouque, C.; Van Poppel, K.; Balzarini, J.; Claes, P.;
De Clercq, E.; Herdewijn, P. Nucleos. Nucleot. 1995, 14,
541–544. (c) Herdewijn, P.; Balzarini, J.; Pauwels, R.;
Janssen, G.; Van Aerschot, A.; De Clercq, E. Nucleos.
Nucleot. 1989, 8, 1231–1257. (d) Lin, T.; Zhou, R.-X.;
Scanlon, K. J.; Brubaker, W. F., Jr.; Lee, J. J. S.; Woods, K.;
Humphreys, C.; Prusoff, W. H. J. Med. Chem. 1986, 29,
681–686. (e) Lin, T.-S.; Prusoff, W. H. J. Med. Chem. 1978,
21, 109–112.
0
d6, 300 MHz): d 2.85 (m, 1H, H2 ), 3.17 (s, 3H, MeS), 3.24–
0
0
0
3.38 (m, 4H, H2 þMeS), 4.52 (s, 3H, H5 þH4 ), 5.58 (m, 1H,
3
0
0
H3 ), 6.59 (dd, 1H, H1 , JHH¼7.0 Hz), 7.54 (m, 2H, Hm),
3
7.64 (m, 1H, Hp), 8.04 (d, 2H, Ho, JHH¼7.3 Hz), 8.69 (s,
1H, H8), 8.78 (s, 1H, H2), and 11.26 (s, 1H, NH); 13C NMR
0
(DMSO-d6, 50.3 MHz): d 36.0 (C2 ), 36.8 (MeS), 37.8
0
(MeS), 68.4 (C5 ), 79.9 (CH), 81.5 (CH), 83.7 (CH), 125.9
(C5), 128.5 (2C, CoþCm), 132.5 (Cp), 133.3 (Ci), 143.2 (C8),
150.6 (C6), 151.8 (2C, C4þC2), and 165.7 (CvO); MS
(ESIþ, m/z): 512 [(MþH)þ, 100%], and 534 [(MþNa)þ,
5%]. Anal. calcd (%) for C19H21N5O8S2: C, 44.61; H, 4.14;
N, 13.70. Found: C, 44.8; H, 3.9; N, 13.5.
´
8. Lavandera, I.; Fernandez, S.; Ferrero, M.; Gotor, V. J. Org.
Chem. 2001, 66, 4079–4082.
9. Divakar, K. J.; Reese, C. B. J. Chem. Soc., Perkin Trans. 1
1982, 1171–1176.
10. (a) Garrett, E. R.; Mehta, P. J. J. Am. Chem. Soc. 1972, 94,
8532–8541. (b) Zoltewicz, J. A.; Clarck, D. F. J. Org. Chem.
1972, 37, 1193–1197. (c) Romero, R.; Stein, R.; Cordes, H. G.;
Cordes, E. H. J. Am. Chem. Soc. 1978, 100, 7620–7624.
11. Gunter, H. In NMR Spectroscopy: Basic Principles Concepts
and Applications in Chemistry; 2nd ed. Wiley: New York,
1995.
Acknowledgements
This work has been supported by grants from MCYT
(Spain; Project PPQ-2001-2683) and the Principado de
Asturias (Spain; Project GE-EXP01-03). S. F. thanks
´
MCYT for a personal grant (Ramon y Cajal Program).
I. L. thanks MCYT (Spain) for a pre-doctoral fellowship.

5456
I. Lavandera et al. / Tetrahedron 59 (2003) 5449–5456
12. Gans, P.; Sabatini, A.; Vacca, A. J. Chem. Soc., Dalton Trans.
1985, 1195–1200.
15. Chen, J.-K.; Schultz, R. G.; Lloyd, D. H.; Gryanov, S. M.
Nucleic Acids Res. 1995, 23, 2661–2668.
13. Fontes, N.; Partridge, J.; Halling, P. J.; Barreiros, S.
Biotechnol. Bioeng. 2002, 77, 296–305.
14. Structure of compound 7 is labelled as follows:
16. Linkletter, B. A.; Szabo, I. E.; Bruice, T. C. Nucleic Acids Res.
2001, 29, 2370–2376.
.