A new class of phosphanucleosides containing a 3-hydroxy-1- hydroxymethylphospholane 1-oxide ring

Article abstract of DOI:10.1016/j.tet.2013.08.021

Novel phosphanucleosides containing a 3-hydroxy-1-hydroxymethylphospholane 1-oxide ring were synthesized as compounds with potential biological activity. A double Arbuzov reaction was employed to prepare a phospholene precursor, which was then converted into an epoxide and subsequently into racemic phosphanucleoside via nucleobase construction.

Full text of DOI:10.1016/j.tet.2013.08.021

Tetrahedron 69 (2013) 9120e9129
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A new class of phosphanucleosides containing a 3-hydroxy-1-
hydroxymethylphospholane 1-oxide ring
a
a
,
b
,
y
, Milo ꢀs Bud eꢀ ꢀs ínsk yꢁ , Ivan Rosenberg a
a
,
Ond ꢀr ej P aꢁ v , Eva Zborníkov aꢁ
*
a
Institute of Organic Chemistry and Biochemistry AS CR, v.v.i., Flemingovo nam. 2, 16610 Prague, Czech Republic
Department of Analytical Chemistry, Faculty of Science, Charles University in Prague, Albertov 2030, 128 43 Prague, Czech Republic
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2013
Received in revised form 26 July 2013
Accepted 12 August 2013
Available online 15 August 2013
Novel phosphanucleosides containing a 3-hydroxy-1-hydroxymethylphospholane 1-oxide ring were
synthesized as compounds with potential biological activity. A double Arbuzov reaction was employed to
prepare a phospholene precursor, which was then converted into an epoxide and subsequently into
racemic phosphanucleoside via nucleobase construction.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Phosphanucleoside
Nucleoside analogue
Phospholane
Conformation
1. Introduction
Given the potential of phosphanucleosides and phosphanu-
cleotides as novel therapeutic agents, the preparation of these
Sugar-modified nucleosides and nucleotides represent an im-
compounds is an attractive area of medicinal research. Moreover,
due to their novelty, the synthesis of phosphanucleosides is of in-
terest to the field of organic synthesis. Therefore, we report herein
the synthesis of a novel set of phosphanucleoside analogues 4
portant group of antimetabolites, which exhibit a variety of bi-
1
,2
3,4
5
ological properties. Carba-, aza-, and thianucleosides, in which
the furanose oxygen is replaced by a carbon, nitrogen, or sulfur
atom, respectively, were found to exhibit very interesting antibac-
containing
a 3-hydroxy-1-hydroxymethylphospholane 1-oxide
6
,7
terial, antiviral, and antitumor properties.
However, the rapid
ring (Fig. 1). The aimed compounds 4 exhibit the structural simi-
0
evolution of drug resistance has recently become a serious issue;
therefore, the search for new compounds with various chemical,
biological, and pharmacological properties is becoming in-
creasingly required.
larity with 3 -deoxynucleosides.
2. Results and discussion
In the field of phosphasugars, several classes of furanose
and pyranose analogues whose hemiacetal ring oxygen was
Our strategy for the synthesis of phosphanucleosides 4 con-
8
e10
replaced by phosphorus atom have been prepared.
Among
sisted of a multistep synthesis of a suitable phospholane precursor
and subsequent introduction of a nucleobase. There are three
general routes to introduce a nucleobase: (i) alkylation of a nucle-
these analogues, several compounds with anticancer activity
11e13
have recently been discovered.
Surprisingly, phosphanu-
cleosides have not received significant attention, and only
17e19
obase with a protected reactive compound, such as a mesylate,
a few types of these compounds have been reported in the
20e24
(
(
ii) nucleobase construction using an amino compound
and
literature8
,14e16
(Fig. 1). Compounds 1e3 were prepared from
iii) Mitsunobu reaction of a hydroxy compound with a purine
nucleobase.
Considering our previous syntheses of pyrrolidine and piper-
the appropriate 2-aminophospholane or 2-azidophospholane
-oxide derivatives using nucleobase construction or
17e19
1
1
14e16
,3-dipolar cycloaddition.
17e19,21,23
idine derivatives of nucleobases
and the known ten-
dency of 2-O-alkyl/arylsulfonyl- and 2-haloethylphosphonates to
undergo elimination reactions, we decided to employ a phos-
pholane 3,4-epoxide as a starting synthon for the synthesis of
phosphanucleosides. We expected this compound to be more
stable towards elimination than the corresponding 3-O-mesyl- or
*
Corresponding author. Tel.: þ420 220 183 381; fax: þ420 220 183 531; e-mail
address: ivan@uochb.cas.cz (I. Rosenberg).
y
Tel.: þ420 221 951 236.
0
040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.021

O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
9121
(
)
(
)
( )
Fig. 1. Known (1e3) and novel (4) phosphanucleosides.
3
-halophospholane derivatives. This synthetic protocol afforded
and in 79% yield (Scheme 2). This mixture of diastereomers was
easily separated by chromatography on silica gel. The faster eluting
isomer was identified as racemate 12, wherein the hydroxymethyl
group and bromine atom are in a trans configuration. The slower
eluting isomer was identified as racemate 11, wherein the
hydroxymethyl group and bromine atom are in a cis configuration.
The structures of diastereomers 11 and 12 were assigned using 2D-
H and H-ROESY spectra. Phosphanucleosides derived from the cis
the target compounds as racemic mixtures.
It is well established that phosphines and phosphites react with
alkyl halides or epoxides to form PeC bonds. Therefore, we
employed a double Arbuzov reaction to prepare the phosphol-3-
ene 1-oxide ring.25 Reaction of cis-1,4-dichlorobut-2-ene 5 with
bis(trimethylsilyl) hypophosphite afforded phosphinic acid 6. Our
improved protocol, which uses N,O-bis(trimethylsilyl)acetamide
(
BSA) instead of hexamethyldisilazane, provided the desired
series exhibit structural similarity to naturally occurring
osides, while phosphanucleosides derived from the trans series
resemble -nucleosides.
Epoxides 13 and 16 were prepared by the reactions of bromo-
hydrins 11 and 12 with potassium carbonate. Next, we attempted to
prepare the desired phosphanucleosides by the reactions of epox-
ides 13 and 16 with a nucleobase in the presence of sodium hydride
or cesium carbonate, or with a persilylated nucleobase in the pre-
b-nucle-
phosphinic acid 6 in 65% yield (Scheme 1). We subsequently fol-
lowed a previously established protocol for the preparation of 2,5-
a
2
6
diphenyl-1-hydroxyphospholane 1-oxides, which was based on
the transformation of phosphinic acids to H-phosphinates. Finally,
the reaction of H-phosphinate 8 with formaldehyde followed by
protection of the primary hydroxyl provided the desired starting
synthon 10 in 35% overall yield (Scheme 1).
ꢀ
, DCM, rt 16 h (iii) DIBAL, DCM, ꢁ78 ꢀC 2 h (iv) CH
ꢀ
Scheme 1. (i) NH
4
2
H PO
2
, BSA, 110 C 72 h (ii) (COCl)
2
2
O, TEA, MeOH, rt 16 h (v) TreCl, pyridine, 70 C 36 h.
4 3 2
sence of a Lewis acid (SnCl , BF $Et
O).17e19,28 Unfortunately, these
The epoxidation of phosphol-3-ene derivative 10 using MCPBA
2
7
afforded in agreement with the literature data diastereomer 16 as
a major product in 90% yield. Because we were interested in the
synthesis of both diastereomers 13 and 16, we decided to prepare
the desired epoxide precursors using a known two-step protocol.
The reaction of 10 with NBS in acetone/water afforded a mixture of
two racemic bromohydrins,11 and 12, in an approximately 1:1 ratio
alkylations all afforded the corresponding 3-hydroxyphosphol-2-
ene derivatives, i.e., the products of elimination. Meanwhile, the
reactions with a Lewis acid led to the decomposition of the starting
compounds.
Instead, we converted the epoxides 13 and 16 to phospholane
azides 14 and 17, respectively, via treatment with sodium azide in
(
)
( )
(
)
(
)
(
)
(
)
ꢀ
Scheme 2. (i) NBS, H
2
O, acetone, rt 16 h (ii) K
2
CO
3
, acetone, rt 16 h (iii) NaN
3
4
, NH Cl, EtOH/H
2
O, 80 C 16 h (iv) H
2
, Pd/C, EtOH, rt 16 h.

9122
O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
the presence of ammonium chloride. These reactions proceeded in
good yield (11 to 14: 53% overall yield, 12 to 17: 62% overall yield)
The prepared compounds were tested for their cytostatic
(HepG2, HL60, HeLa S3, CCRF-CEM) and antimicrobial (Escher-
ichia coli CCM 3954, Enterococcus faecalis CCM 4224, Pseudomo-
nas aeruginosa CCM 3955, Staphylococcus aureus CCM 4223,
Bacillus subtilis, Streptococcus agalactiae, Candida albicans, and
Candida krusei) activities, but no significant effects were
observed.
(Scheme 2). Azides 14 and 17 were hydrogenated at atmospheric
pressure in the presence of catalytic Pd/C to provide the corre-
sponding amines as starting compounds for nucleobase construc-
tion. Under these reaction conditions, no cleavage of the trityl
group was observed.
To build the uracil nucleobase, we utilized 4-nitrophenyl-3-
ethoxyacryloylcarbamate 20, a reagent previously invented in our
laboratory (Scheme 3).21 The reaction of phospholane amines 15
and 18 with 20 provided acyclic products, which were immediately
cyclized by heating with Dowex H to form uracil derivatives 4a
and 19a in a one-pot reaction sequence.
The structures of phosphanucleosides 4aed and 19aed were
confirmed by H, C, and P NMR spectra in DMSO and D O. These
2
data are summarized in Tables 2e4 in the Experimental section.
The numbering scheme for the atoms in these five-membered rings
is shown in Fig. 2. The standard atom numbering of nucleobases is
used.
1
13
31
þ
(
)
( )
(
)
( )
Scheme 3. (i) B¼U (1) 20, dioxane, rt 2 h (2) DOWEX H , 90 C 4 h; B¼A (1) 21, DIPEA, n-BuOH, 130 ꢀC 16 h (2) aq NH
þ
ꢀ
, dioxane, rt 48 h (3) 80% AcOH, 60 C 16 h; B¼G (1) 22, DIPEA,
ꢀ
3
ꢀ
ꢀ
n-BuOH, 130 C 16 h (2) 1 M HCl, MeOH 60 C 16 h; B¼C (1) 4a, 19a, BzCN, TEA, acetonitrile, rt 16 h (2) TIPS-Cl, TEA, DMAP, acetonitrile, rt 16 h (3) aq NH
3
, acetonitrile, rt 16 h.
Fig. 2. Numbering of atoms and torsion angles in the five-membered rings of phosphanucleosides 4aed, 19aed.
Cytosine derivatives 4d and 19d were prepared from the ap-
propriate uracil derivatives. Compounds 4a and 19a were protected
with benzoyl groups, and they were then converted to 4-O-TIPS
derivatives. These compounds were then treated with aqueous
ammonia to afford cytosine derivatives 4d and 19d.
Table 3 in Experimental part highlights the very similar values of
the vicinal coupling constants and, therefore, indicates that these
compounds have very similar conformations in both DMSO and
2
D O. Additionally, the effect of the type of nucleobase in both series
4aed and 19aed seems to be negligible. Large values (w10 Hz) of
3
For the syntheses of the adenine (4b, 19b) and guanine (4c, 19c)
J(3,4) indicate the pseudoaxial positions of H-3 and H-4 and
phosphanucleosides
formamidopyrimidine
formamidopyrimidine 20, respectively (Scheme 3).
agents showed several advantages over the commonly used 5-
amino-4,6-dichloro- and 2,5-amino-4,6-dichloropyrimidine.
we
19
employed
and 2-amino-4,6-dichloro-5-
4,6-dichloro-5-
therefore the pseudoequatorial positions of the 3-OH and nucleo-
2
9
base. Quantum chemical calculations (Gaussian 09, DFT B3LYP 6-
31Gd in vacuo) were used to scan the energy profile of phospha-
nucleoside 19a during pseudorotation of its five-membered ring.
2
2,24
These re-
2
3
ꢀ
ꢀ
For the two maximum puckers (
f
max¼40 and 50 ) the phase an-
(0)
max) and the others allowed to opti-
ꢀ
First, the purine rings were formed in one-pot reactions under
conditions of heating at 130 C. The addition of a ring-closing re-
gles (P) were changed in 18 steps with fixed torsion angles
f
ꢀ
and
f
(3) (defined by P and
f
ꢀ
agent, such as diethoxymethyl acetate or triethyl orthoformate, was
mize. This calculation showed two energy minima around 0 and
not required.2
2e24
Second, the reactions were complete in less time
180 with a slightly lower energy for
ꢀ
f
max¼50 . Geometry opti-
ꢀ
ꢀ
ꢀ
ꢀ
(
16 h compared to 40 h using 5-amino reagents). Third, the re-
mizations for P¼0 and 180 and
f
max¼50 were then performed
actions using these reagents provided the desired products in ap-
proximately 45% yield compared to approximately 20% yield using
the corresponding 5-amino reagents.
The 6-chloropurine derivatives were converted into adenine
phosphanucleotides 4b and 19b by treatment with aqueous am-
monia followed by treatment with acetic acid to remove the trityl
group. The 2-amino-6-chloropurine derivatives were treated with
hydrochloric acid in methanol to afford guanine phosphanucleo-
tides 4c and 19c.
for all compounds 4aed and 19aed. Surprisingly, the conformers
with their 3-OH group and nucleobase in pseudoaxial positions
provided somewhat lower energy than those with these groups in
pseuoequatorial positions, in contrast with the observed vicinal
J(H,H). The inspection of models suggested that H-bonding be-
tween the 3-OH and the nucleobase, possible only in their pseu-
doequatorial position, could decrease the energy and stabilize such
a conformation. This hypothesis was confirmed by a new set of
calculations where the starting orientations of the OH and

O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
9123
nucleobase were turned to allow an H-bond between the 3-OH and
the C(2)]O in the pyrimidine phosphanucleosides (4a, 4d, 19a,
9d) or N(3) in the purine phosphanucleosides (4b, 4c, 19b, 19c).
1
Calculations of geometry-optimized conformers with H-bonds
provided markedly lower energy (2e6 kcal/mol) and confirmed the
very high preference (>95%) of the forms with pseudoequatorial
substituents, which is in agreement with preliminary estimations
from the vicinal J(H,H) values.
The quantum chemical calculations of J(H,H) (again with DFT
B3LYP 6-31Gd) for these H-bonded conformers showed satisfactory
agreement with the observed vicinal J(H,H)s (average difference
Fig. 3. Schematic representation of the highly preferred conformations 3
T
(com-
4
4
pounds 4aed) and
3
T
(compounds 19aed).
1
.0 Hz). Similar levels of agreement (average difference 0.9 Hz)
3
were obtained when J(H,H) were estimated using calculated pro-
ton torsion angles and a generalized Karplus-type relation.
comparison of the calculated and observed J(H,H) values is shown
in Table 1. The preferred conformation of phosphanucleosides 4aed
3
0
A
3
3
4
4 3
and 19aed can be described as T and T (Fig. 3) containing the
nucleobase and hydroxyl groups in pseudoequatorial positions. The
values of the endocyclic torsion angles have nearly the same ab-
solute values, but they differ in sign (Table 1). Maximum pucker in
ꢀ
both conformations is close to 50 . The calculated lowest energy
conformations with the H-bond of phosphanucleosides 4a, 4b, 19a,
and 19b are shown in Fig. 4.
Table 1
Observed values of vicinal J(H,H), theoretically calculated (DFT B3LYP 6-31Gd) tor-
sion angles and J(H,H)
Fig. 4. Calculated conformations of phosphanucleosides 4a, 19a, 4b, and 19b (hydro-
gen bonds are indicated with dotted lines).
Coupled nuclei 4a
4b
4c
4d
19a 19b
19c
19d
Observed vicinal J(H,H) in D
2
O
2
2
3
4
4
a, 3
b, 3
, 4
, 5a
, 5b
10.6
7.3
10.3
8.5
10.4
6.7
10.0
8.3
10.6
7.2
10.2
8.1
10.5 7.6
7.5
10.3
10.4
11.7
7.4
7.5
10.6
9.9
11.5
7.9
7.6
7.2 10.6
10.3 10.2
8.5 12.0
11.9 7.9
10.4
10.3
11.9
7.6
H5b
5
H5b
5
6
6
HO-CH2
B
HO-CH2
(2)
(3)
H4
(2)
H2b
(3)
12.2
12.0
12.1
4
H5a
4
H5a
DFT calculated endocyclic torsion angles in H-bonded structures
P
H2b
1
P
OH
1
H3
4
4
4
4
4
P
(0)
(1)
(2)
(3)
(4)
52
46
ꢁ37
16
48
ꢁ37
14
52 ꢁ51
ꢁ38 36
13 ꢁ12
15 ꢁ16
ꢁ40 41
ꢁ44
ꢁ47
ꢁ51
O
O
(1)
ꢁ38
32
36
ꢁ13
ꢁ14
37
35
ꢁ11
ꢁ17
41
(4) H4
(1)
(4)
3
2
3
2
13
ꢁ11
ꢁ14
35
(0)
(0)
B
H2a
OH
H2a
H3
15
9
12
ꢁ40
ꢁ33
ꢁ36
4
a - 4d
19a - 19d
ꢁ1.4
4.4
1.2
ꢁ1.4 176.7 177.5 179.2 175.6
4
(max)
52
46
48
52 ꢁ51
ꢁ44
ꢁ47
ꢁ51
Fig. 5. Numbering of atoms and torsion angles in compounds 4aed and 19aed used
for the comparison with standard nucleosides.
3
4
Conf. type
T
4
3
T
DFT calculated torsion angles of hydrogen atoms in H-bonded structures
2
2
3
4
4
a, 3
b, 3
, 4
, 5a
, 5b
ꢁ166 ꢁ165 ꢁ165 ꢁ166 42
39
157
42
161
42
161
0
ribonucleosides and 2 -deoxyribo-
b
-
D
-nucleosides provided cluster
ꢁ46
179
ꢁ44
ꢁ46
171
ꢁ37
ꢁ46
173
ꢁ40
ꢁ47 162
ꢀ
ꢀ
179 ꢁ179 ꢁ169 ꢁ173 ꢁ178
of ‘north’ conformers (ꢁ1 <P
N
<34 ) and ‘south’ conformers
fmax<46 . The limited amount of the
ꢀ
ꢀ
ꢀ ꢀ
31
ꢁ44 171
165
42
166
44
172
48
(
137 <P
S
<194 ) with 30 <
-nucleosides showed somewhat shifted
ꢁ167 ꢁ158 ꢁ162 ꢁ168 47
X-ray structures of
a
DFT calculated vicinal J(H,H) in H-bonded structures
2
2
3
4
4
a, 3
b, 3
, 4
, 5a
, 5b
9.3
6.7
9.5
7.3
12.7
10.1
6.9
7.4
8.8
9.8
10.2
7.0
7.9
8.3
10.3
9.2 7.5
6.7 8.8
9.3 9.4
7.0 12.8
12.8 6.3
8.2
9.0
7.0
10.5
7.3
7.8
9.6
7.7
10.6
7.2
7.6
8.6
9.2
13.0
6.1
Calculated vicinal J(H,H) using torsion angles and generalized Karplus relation
2
2
3
4
4
a, 3
b, 3
, 4
, 5a
, 5b
11.0
6.3
9.3
6.1
11.8
10.9
6.2
8.8
7.3
10.7
10.9
6.3
8.9
6.8
11.1
11.1 7.0
6.1 10.5
9.3 9.3
6.1 12.1
11.8 5.5
7.5
9.8
8.6
11.5
6.4
7.0
10.3
8.9
11.6
6.1
7.0
10.4
9.2
12.2
5.4
The comparison of preferred conformations of five-membered
rings of compounds 4aed and 19aed with standard nucleosides
required renumbering of atoms and torsion angles as shown in
Fig. 5.
Schematic graphical representation of the conformation ranges
Fig. 6. Schematic representation of the conformation ranges of different types of
of standard nucleosides is shown in Fig. 6. The X-ray data on
b-
D-
nucleosides.

9124
O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
ꢀ
ꢀ
clusters of ‘north’ conformers (ꢁ18 <P
N
ꢀ
<19 ) and ‘south’ con-
product was eluted with 3% HCl in water. In the end, the phosphinic
acid 6 was treated with charcoal in refluxed methanol. Charcoal
was filtered off and solvent evaporated to afford phosphinic acid 6
ꢀ
ꢀ
31
formers (168 <P
S
<224 ) with
f
max<49 . The vicinal J(H, H)
-adenosine indicated preferred ‘north’ form
0
values of 3 -deoxy-
b
-D
ꢀ
32
0
(P
N
wꢁ4 ), whereas applicable data on 3 -deoxy-
a
-D
-adenosine
4 6 2
as yellow oil. Yield 15.3 g (65%). HRMS (FAB) calcd for C H O P
ꢁ
1
were not found in the literature. For more details on the confor-
mation of five-membered rings of various nucleosides see
Supplementary data.
(MꢁH) 117.0111, found 117.0108. H NMR (600.1 MHz, CDCl
¼10.99 (b, 1H, PeOH); 5.92 (dt, J(P,H)¼33.4 Hz, J(H,H)¼1.0 Hz, 2H,
H-3 and H-4); 2.50 (dd, J(P,H)¼12.9 Hz, J(H,H)¼1.0 Hz, 4H, H-2 and
3
):
d
1
3
The projection of phosphanucleosides into the pseudorotation
wheel (Fig. 6) showed that the compounds 4aed preferred ‘south’
H-5). C NMR (150.9 MHz, CDCl
and C-4); 30.16 (d, J(P,C)¼93.2 Hz, C-2 and C-5).
(202.3 MHz, CDCl ):
3
):
d¼126.84 (d, J(P,C)¼15.9 Hz, C-3
31
P NMR
2
ꢀ
ꢀ
ꢀ
ꢀ
T
1
conformation (141 <P
S
<148 and 44 <
f
max<49 ), whereas the
3
d
¼76.78.
1
ꢀ
ꢀ
compounds 19aed ‘north’
4
2
T
conformation (ꢁ42 <P
N
<ꢁ37 and
Caution: Bis(trimethylsilyl)hypophosphite is potentially pyro-
phoric compound.
ꢀ ꢀ
2 <fmax<48 ). The counterclockwise shift of the positions of the
compounds 4aed and 19aed was probably due to presence of
P(]O)CH OH group and H-bond interactions between the hy-
droxyl and a nucleobase (shown in Fig. 4).
>
2
4.3. 1-Trityloxymethylphosphol-3-ene 1-oxide (10)
ꢀ
Oxalyl chloride (22.0 mL; 0.26 mol) was added at 0 C to a so-
3
. Conclusions
lution of 1-hydroxyphosphol-3-ene 1-oxide 6 (15.3 g; 0.13 mol) in
DCM (1 L). The reaction mixture was left to warm up gradually to rt,
and then stirred for 16 h at rt. After that, the mixture was evapo-
rated and coevaporated with toluene (3ꢂ300 mL). The crude 1-
chlorophosphol-3-ene 1-oxide 7 was used without further purifi-
In summary, we have developed a synthetic route leading to a new
class of nucleoside analogues, the phosphanucleosides containing 3-
hydroxy-1-hydroxymethylphospholane 1-oxide rings. We employed
nucleobase construction to prepare phosphanucleosides bearing all
four nucleobases in good yields. Up to now, we did not find any sig-
nificant biological activity of these compounds. Nevertheless, thor-
ough studies on the antiviral, antibacterial, and antitumoractivities of
these phosphanucleosides are in progress. Moreover, phosphanu-
cleosides provide possibilities for the transformation into the nucle-
otide analogues via phosphorylation or phosphonylation of the
primary hydroxyl of 1-hydroxymethylphospholane ring. The prepa-
31
cation. P NMR (202.3 MHz, CDCl
3
):
d
¼83.5.
DIBAL (130 mL of 1 M solution in hexane; 0.13 mol) was added
ꢀ
under nitrogen at ꢁ78 C to a solution of 1-chlorophosphol-3-ene
1-oxide 7 in DCM (1 L). The reaction mixture was stirred for 2 h
ꢀ
under nitrogen at ꢁ78 C. The reaction mixture was quenched at
ꢀ
ꢁ78 C by the addition of methanol (15 mL) and extracted with 10%
acetic acid in water (500 mL). Water layer was extracted with
chloroform (6ꢂ200 mL). Organic layers were collected, dried over
anhydrous sodium sulfate and evaporated. The crude phosphol-3-
0
ration of series of phosphanucleosides related to 2 -deoxynucleosides
and ribonucleosides is also of our interest.
1
ene 1-oxide 8 was used without further purification. H NMR
(
600.1 MHz, CDCl
3
):
d
¼7.47 (dttt, J(P,H)¼467.3 Hz, J(H,H)¼4.9, 2.8,
4
4
. Experimental
1.2 Hz, 1H, PeH); 5.92 (dm, J(P,H)¼28.1 Hz, SJ(H,H)¼6.5 Hz, 2H, H-3
and H-4); 2.68 (m, 2H, H-2a and H-5a); 2.60 (m, 2H, H-2b and H-
13
.1. General
5b). C NMR (150.9 MHz, CDCl
and C-4); 29.93 (d, J(P,C)¼64.6 Hz, C-2 and C-5).
(202.3 MHz, CDCl ):
¼44.4.
3
):
d
¼126.27 (d, J(P,C)¼12.8 Hz, C-3
31
P NMR
Unless stated otherwise, all used solvents were anhydrous. Re-
3
d
agent 18 was prepared according to Ref. 21. Reagent 19 was pre-
pared according to Ref. 24. Reagent 20 was purchased from TCI Co.,
Ltd., Japan. Mass spectra were recorded on a ZAB-EQ (VG Analytical)
instrument using FAB (ionization with Xe, accelerating voltage
Formaldehyde (19.4 mL of 36e38% solution in water; 0.26 mol)
and triethylamine (18.1 mL; 0.13 mol) were added to a solution of
phosphol-3-ene 1-oxide 8 in methanol (1 L). The reaction mixture
was stirred for 16 h at rt and evaporated. The crude mixture was
treated with chloroform (1 L) and anhydrous sodium sulfate was
added. The solution was filtered, evaporated and coevaporated with
8
kV; glycerol and thioglycerol as matrices) and on LTQ Orbitrap XL
(
Thermo Fisher Scientific) using ESI ionization. NMR spectra were
1
13
measured on Bruker AVANCE 400 ( H at 400 MHz, C at
pyridine (3ꢂ300 mL). The crude 1-hydroxymethylphosphol-3-ene
1
13
1
1
00.6 MHz), Bruker AVANCE 500 ( H at 500 MHz, C at 125.7 MHz,
1-oxide
9
was used without further purification.
H NMR
3
1
1
13
P at 202.3 MHz) and Bruker AVANCE 600 ( H at 600.1 MHz, C at
(600.1 MHz, CDCl
2H, H-3 and H-4); 4.01 (d, J(P,H)¼1.8 Hz, 2H, PeCH
2H, H-2a and H-5a); 2.48 (m, 2H, H-2b and H-5b). C NMR
(150.9 MHz, CDCl ):
¼127.14 (d, J(P,C)¼11.2 Hz, C-3 and C-4); 59.51
(d, J(P,C)¼75.0 Hz, PeCH
NMR (202.3 MHz, CDCl
3
):
d
¼5.86 (dm, J(P,H)¼27.9 Hz, SJ(H,H)¼5.3 Hz,
1
50.9 MHz) spectrometers. The complete assignment of protons
2
eO); 2.65 (m,
13
and carbons was performed by the analysis of correlated homo-
nuclear 2D-COSY and heteronuclear He C HSQC and He
HMBC spectra. Relative configuration was checked using the
DPFGSE-NOE and 2D-ROESY techniques. IR spectra were recorded
using KBr pellets on Nicolet 6700 (Thermo Electron Corp.).
1
13
1
13
C
3
d
31
2
eO); 28.52 (d, J¼63.2 Hz, C-2 and C-5).
P
3
):
d
¼70.64.
Trityl chloride (43.5 g; 0.156 mol) was added to a solution of 1-
hydroxymethylphosphol-3-ene 1-oxide 9 in pyridine (1 L). The
ꢀ
4
.2. 1-Hydroxyphosphol-3-ene 1-oxide 6
reaction mixture was stirred for 36 h at 70 C, quenched by the
addition of methanol (20 mL) and evaporated. The residue was
dissolved in chloroform (1 L) and extracted with saturated solution
of sodium hydrogencarbonate (3ꢂ200 mL). The organic layer was
dried over anhydrous sodium sulfate and evaporated. 1-
Trityloxymethyl-phosphol-3-ene 1-oxide 10 was purified by chro-
matography on silica gel (elution with gradient of 0e50% acetone in
toluene) to yield 26.3 g (54%) of white foam. HRMS (FAB) calcd for
N,O-Bis(trimethylsilyl)acetamide (146.7 mL; 0.6 mol) was added
under nitrogen to ammonium hypophosphite (16.6 g; 0.2 mol) and
ꢀ
the mixture was left to dissolve under 25 C (30 min with occa-
sional cooling in an ice bath to avoid overheating). After that, cis-
1
,4-dichlorobut-2-ene (23.1 mL; 0.22 mol) was added and the re-
ꢀ
action mixture was heated for 72 h at 110 C under nitrogen. The
þ
1
reaction mixture was quenched by the addition of 1% HCl in water
24 24
C H O
2
P (MþH) 375.1514, found 375.1518. H NMR (600.1 MHz,
¼7.39 (m, 6H, ortho-ArH); 7.31 (m, 6H, meta-ArH); 7.26 (m,
3H, para-ArH); 5.93 (dm, J(P,H)¼28.6 Hz, SJ(H,H)¼5.3 Hz, 2H, H-3
and H-4); 3.64 (d, J(P,H)¼8.2 Hz, 2H, PeCH eO); 2.65 (bdd, J(H,H)¼
17.7 Hz, J(P,H)¼6.4 Hz, 2H, H-2a and H-5a); 2.52 (bdd, J(H,H)¼
(
500 mL) and extracted with ethyl acetate (3ꢂ300 mL). The water
3
CDCl ): d
þ
layer was treated with Dowex H (0.5 kg), filtered, and evaporated.
ꢁ
The crude product was purified on Dowex OH (1 kg). After being
2
washed with water (3ꢂ500 mL) and methanol (3ꢂ500 mL), the

O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
9125
1
CDCl
7.7 Hz, J(P,H)¼15.0 Hz, 2H, H-2b and H-5b). 13C NMR (150.9 MHz,
purified by chromatography on silica gel (elution with gradient of
3
):
d¼142.58 (3C, ipso-ArC); 128.57 (6C, ortho-ArC); 128.03 (6C,
0e10% ethanol in chloroform) to yield 5.7 g (53%) of white foam.
þ
meta-ArC); 127.44 (3C, para-ArC); 127.36 (d, J(P,C)¼11.0 Hz, C-3 and
C-4); 84.45 (d, J(P,C)¼12.3 Hz, >C<); 59.86 (d, J(P,C)¼81.4 Hz,
HRMS (FAB) calcd for C24
434.1631. H NMR (600.1 MHz, DMSO-d
H
25
N
3
O
3
P (MþH) 434.1634, found
1
6
):
d
¼7.39 (m, 12H, ortho-
31
PeCH
2
eO); 30.13 (d, J(P,C)¼65.1 Hz, C-2 and C-5). P NMR
ArH and meta-ArH); 7.31 (m, 3H, para-ArH); 5.78 (d, J(H,H)¼5.1 Hz,
OH); 4.06 (m, 1H, H-4); 3.89 (m, 1H, H-3); 3.40 (dd, J(P,H)¼7.4 Hz,
J(H,H)¼12.5 Hz, 1H, P-CHa-O); 3.36 (dd, J(P,H)¼7.4 Hz, J(H,H)¼
12.5 Hz, 1H, P-CHb-O); 2.22 (dt, J(P,H)¼6.7 Hz, J(H,H)¼15.0 and
6.7 Hz, 1H, H-2a); 2.15 (ddd, J(P,H)¼15.5 Hz, J(H,H)¼15.2 and 7.6 Hz,
1H, H-5a); 1.83 (dt, J(P,H)¼8.9 Hz, J(H,H)¼15.2 and 8.8 Hz, 1H, H-
5b); 1.68 (ddd, J(P,H)¼17.8 Hz, J(H,H)¼15.0 and 8.1 Hz, 1H, H-2b).
(
202.3 MHz, CDCl
3
):
d¼66.90.
4
.3.1. (3S,4R,1S and 3R,4S,1R) 3-Bromo-4-hydroxy-1-trityloxy-
methylphospholane 1-oxide (11), (3R,4S,1S and 3S,4R,1R) 3-bromo-
4-hydroxy-1-trityloxymethylphospholane 1-oxide (12). NBS (13.8 g;
7
7.3 mmol) in acetone (150 mL) was added to a solution of 1-
1
3
trityloxymethyl-phosphol-3-ene 1-oxide 10 (26.3 g; 70.3 mmol)
in acetone/water 2/1 (450 mL). The reaction mixture was stirred for
8
roform (1 L) was added and the mixture was extracted with satu-
rated solution of sodium hydrogencarbonate (3ꢂ200 mL). The
organic layer was dried over anhydrous sodium sulfate and evap-
orated. The diastereoisomers were separated by chromatography
on silica gel (elution with gradient of 0e10% ethanol in chloroform)
as faster eluting racemate 12 (14.6 g; 44%; white foam) and slower
eluting racemate 11 (11.6 g; 35%; white foam). HRMS (FAB) calcd for
C NMR (150.9 MHz, DMSO-d
6
):
d
¼142.83 (3C, ipso-ArC); 128.50
(6C, ortho-ArC); 128.37 (6C, meta-ArC); 127.65 (3C, para-ArC); 88.20
(d, J(P,C)¼11.9 Hz, >C<); 72.99 (d, J(P,C)¼10.1 Hz, C-3); 64.61 (d,
h at rt and then evaporated to a volume of about 200 mL. Chlo-
J(P,C)¼10.6 Hz, C-4); 61.79 (d, J(P,C)¼81.4 Hz, PeCH
2
eO); 33.48 (d,
31
J(P,C)¼59.0 Hz, C-2); 28.65 (d, J(P,C)¼59.2 Hz, C-5). P NMR
(202.3 MHz, DMSO-d ):
6
d
¼51.44.
4.3.3. (4R,3R,1R and 4S,3S,1S) 4-Azido-3-hydroxy-1-trityloxy-
methylphospholane 1-oxide (17). Potassium carbonate (4.7 g;
34.1 mmol) was added to a solution of racemic bromohydrin 12
(14.6 g; 31.00 mmol) in acetone (500 mL). The reaction mixture was
stirred for 16 h at rt and then evaporated. The residue was dissolved
in chloroform (1 L) and extracted with saturated solution of sodium
chloride (3ꢂ200 mL). The organic layer was dried over anhydrous
sodium sulfate and evaporated. The crude epoxide 16 was used
without further purification.
79
P (MþH)þ 471.0725; found (11) 471.0729, (12)
24 25 3
C H ( Br)O
471.0718.
1
1
1: H NMR (600.1 MHz, CDCl
m, 6H, meta-ArH); 7.28 (m, 3H, para-ArH); 4.37e4.42 (m, 2H, H-3
and H-4); 3.67 (dd, J(P,H)¼7.7, J(H,H)¼12.7 Hz, 1H, P-CHa-O); 3.64
dd, J(P,H)¼7.9, J(H,H)¼12.7 Hz, 1H, P-CHb-O); 2.69 (ddd, J(P,H)¼
5.8 Hz, J(H,H)¼15.6 and 6.6 Hz, 1H, H-5a); 2.46 (dt, J(P,H)¼7.8 Hz,
J(H,H)¼15.6 and 7.8 Hz,1H, H-5b); 2.35 (ddd, J(P,H)¼6.3 Hz, J(H,H)¼
5.5 and 5.7 Hz, 1H, H-5a); 2.06 (ddd, J(P,H)¼16.3 Hz, J(H,H)¼15.5
3
):
d¼7.42 (m, 6H, ortho-ArH); 7.34
(
(
1
Sodium azide (10.1 g; 155 mmol) and ammonium chloride
(3.3 g; 62 mmol) were added to a solution of epoxide 16 in ethanol/
water 8/2 (500 mL). The reaction mixture was stirred for 16 h at
1
13
ꢀ
and 7.0 Hz, 1H, H-5a); C NMR (150.9 MHz, CDCl
ipso-ArC); 128.59 (6C, ortho-ArC); 128.20 (6C, meta-ArC); 127.64
3C, para-ArC); 89.09 (d, J(P,C)¼12.4 Hz, >C<); 76.50 (d, J(P,C)¼
3
):
d
¼142.29 (3C,
80 C and then evaporated. The residue was dissolved in chloro-
form (500 mL) and extracted with saturated solution of sodium
hydrogencarbonate (3ꢂ200 mL). The organic layer was dried over
anhydrous sodium sulfate and evaporated. The product was puri-
fied by chromatography on silica gel (elution with gradient of
(
9
.0 Hz, C-4); 61.22 (d, J(P,C)¼83.8 Hz, PeCH eO); 51.36 (d, J(P,C)¼
2
1
0.1 Hz, C-3); 33.90 (d, J(P,C)¼56.4 Hz, C-2); 32.44 (d, J(P,C)¼
3
1
6
2.0 Hz, C-5). P NMR (202.3 MHz, CDCl
3
):
¼7.39 (m, 6H, ortho-ArH); 7.34
m, 6H, meta-ArH); 7.29 (m, 3H, para-ArH); 4.50 (dddd, J(P,H)¼
d
¼55.71.
0e10% ethanol in chloroform) to yield 8.3 g (62%) of white foam.
1
þ
1
2: H NMR (600.1 MHz, CDCl
3
):
d
HRMS (FAB) calcd for C24
434.1639. H NMR (600.1 MHz, DMSO-d
H
25
N
3
O
3
P (MþH) 434.1634, found
1
(
6
):
d
¼7.41 (m, 6H, ortho-
1
0.0 Hz, J(H,H)¼8.0, 7.2 and 7.0 Hz, 1H, H-4); 4.11 (tdd, J(P,H)¼
ArH); 7.37 (m, 6H, meta-ArH); 7.30 (m, 3H, para-ArH); 5.73 (d,
J(H,H)¼4.9 Hz, OH); 4.12 (ddtd, J(P,H)¼10.6 Hz, J(H,H)¼7.9, 6.9, 6.8
and 4.9 Hz, 1H, H-3); 3.79 (ddt, J(P,H)¼9.8 Hz, J(H,H)¼8.1, 6.9 and
6.9 Hz,1H, H-4); 3.43 (dd, J(P,H)¼7.0 Hz, J(H,H)¼12.3 Hz, 1H, P-CHa-
O); 3.41 (dd, J(P,H)¼6.7 Hz, J(H,H)¼12.3 Hz, 1H, P-CHb-O); 2.31
(ddd, J(P,H)¼7.8 Hz, J(H,H)¼15.3 and 6.9 Hz, 1H, H-5a); 2.05 (td,
J(P,H)¼15.4 Hz, J(H,H)¼15.2 and 6.8 Hz, 1H, H-2a); 1.90 (dt, J(P,H)¼
7.9 Hz, J(H,H)¼15.2 and 7.9 Hz, 1H, H-2b); 1.68 (ddd, J(P,H)¼16.8 Hz,
9
.6 Hz, J(H,H)¼9.6, 8.9 and 7.2 Hz,1H, H-3); 3.69 (m, 2H, PeCH
2
eO);
2
.64 (dt, J(P,H)¼7.0 Hz, J(H,H)¼15.6 and 7.1 Hz, 1H, H-2a); 2.43 (td,
J(P,H)¼15.4 Hz, J(H,H)¼15.6 and 7.0 Hz, 1H, H-5a); 2.30 (ddd,
J(P,H)¼17.4 Hz, J(H,H)¼15.6 and 8.9 Hz, 1H, H-2b); 2.07 (dt, J(P,H)¼
13
8
.0 Hz, J(H,H)¼15.6 and 8.0 Hz, 1H, H-5b). C NMR (150.9 MHz,
CDCl
meta-ArC); 127.78 (3C, para-ArC); 89.60 (d, J(P,C)¼12.1 Hz, >C<);
6.01 (d, J(P,C)¼10.9 Hz, C-4); 59.86 (d, J(P,C)¼83.5 Hz, PeCH eO);
1.03 (d, J(P,C)¼9.6 Hz, C-3); 35.07 (d, J(P,C)¼55.5 Hz, C-2); 31.48 (d,
3
):
d
¼142.04 (3C, ipso-ArC); 128.51 (6C, ortho-ArC); 128.29 (6C,
1
3
7
5
2
J(H,H)¼15.3 and 8.1 Hz, 1H, H-5b). C NMR (150.9 MHz, DMSO-d
6
):
d
¼142.92 (3C, ipso-ArC); 128.56 (6C, ortho-ArC); 128.33 (6C, meta-
31
J(P,C)¼61.6 Hz, C-5). P NMR (202.3 MHz, CDCl
3
):
d
¼55.94.
ArC); 127.61 (3C, para-ArC); 88.12 (d, J(P,C)¼11.9 Hz, >C<); 72.75 (d,
J(P,C)¼9.3 Hz, C-3); 64.83 (d, J(P,C)¼10.6 Hz, C-4); 62.64 (d, J(P,C)¼
4
.3.2. (4S,3S,1R and 4R,3R,1S) 4-Azido-3-hydroxy-1-trityloxy-
81.0 Hz, PeCH
2
eO); 32.11 (d, J(P,C)¼59.3 Hz, C-2); 29.62 (d, J(P,C)¼
31
methylphospholane 1-oxide (14). Potassium carbonate (3.7 g;
7.1 mmol) was added to a solution of racemic bromohydrin 11
11.6 g; 24.6 mmol) in acetone (500 mL). The reaction mixture was
59.3 Hz, C-5). P NMR (202.3 MHz, DMSO-d
6
):
d¼52.64.
2
(
4.3.4. (4S,3S,1R and 4R,3R,1S) 4-Amino-3-hydroxy-1-trityloxy-
methylphospholane 1-oxide (15). Azido derivative 14 (5.7 g;
13.1 mmol) and 10% Pd/C catalyst (0.3 g) were suspended in ethanol
(200 mL). The mixture was hydrogenated at atmospheric pressure
for 16 h at rt. The reaction mixture was filtered through a layer of
Celite and the solvent was evaporated. The crude amino derivative
15 was used without further purification (yellow oil). ESI-MS calcd
stirred for 16 h at rt and then evaporated. The residue was dissolved
in chloroform (1 L) and extracted with saturated solution of sodium
chloride (3ꢂ200 mL). The organic layer was dried over anhydrous
sodium sulfate and evaporated. The crude epoxide 13 was used
without further purification.
Sodium azide (8.0 g; 123 mmol) and ammonium chloride (2.6 g;
9.2 mmol) were added to a solution of epoxide 13 in ethanol/
4
for C24
H
27NO
3
P (MþH)þ 408.2, found 408.3.
water 8/2 (500 mL). The reaction mixture was stirred for 16 h at
8
form (500 mL) and extracted with saturated solution of sodium
hydrogencarbonate (3ꢂ200 mL). The organic layer was dried over
anhydrous sodium sulfate and evaporated. The product was
ꢀ
0
C and then evaporated. The residue was dissolved in chloro-
4.3.5. (4R,3R,1R and 4S,3S,1S) 4-Amino-3-hydroxy-1-trityloxy-
methylphospholane 1-oxide (18). Azido derivative 17 (8.3 g;
19.1 mmol) and 10% Pd/C catalyst (0.4 g) were suspended in ethanol
(200 mL). The mixture was hydrogenated at atmospheric pressure

9126
O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
ꢀ
for 16 h at rt. The reaction mixture was filtered through a layer of
Celite and the solvent was evaporated. The crude amino derivative
derivative was treated for 16 h at 60 C with 80% acetic acid in water
þ
(100 mL), diluted with water (100 mL) and treated with Dowex H
1
8 was used without further purification (yellow oil). ESI-MS calcd
(10 g). The resin was filtered off and washed with methanol
(100 mL) and water (100 mL). The product was washed off of the
resin with 5% aqueous ammonia (100 mL), evaporated, purified by
preparative HPLC (elution with gradient of 0e20% methanol in
þ
for C24
3
H27NO P (MþH) 408.2, found 408.0.
4.3.6. (4S,3S,1R and 4R,3R,1S) 4-(Uracil-1-yl)-3-hydroxy-1-hydroxy-
methylphospholane 1-oxide (4a). 4-Nitrophenyl-3-ethoxyacryloyl-
carbamate 20 (0.8 g; 2.9 mmol) was added to a solution of 4-
water) and freeze-dried from water to yield 0.29 g (41%) of white
þ
15 5 3
lyofilisate. HRMS (FAB) calcd for C10H N O P (MþH) 284.0913,
amino-3-hydroxy-1-trityloxymethylphospholane
1-oxide
15
found 284.0910. IR
nmax (KBr) 3328, 3266, 3178, 1648, 1603, 1572,
(
1.0 g; 2.5 mmol) in dioxane (25 mL). The reaction mixture was
1507, 1485, 1419, 1331, 1309, 1218, 1157, 1072, 1050, 795, 726, 644.
NMR datadsee Tables 2e4.
þ
stirred for 4 h at rt. After that, 5 g of Dowex H was added and the
suspension was stirred for 2 h at 90 C. The resin was filtered off and
ꢀ
washed with dioxane (100 mL). The product was washed off of the
resin with water (100 mL), evaporated, purified by preparative
HPLC (isocratically water) and freeze-dried from water to yield
4.3.8. (4S,3S,1R and 4R,3R,1S) 4-(Guanin-9-yl)-3-hydroxy-1-hydroxy-
methylphospholane
1-oxide
(4c). 2-Amino-4,6-dichloro-5-
formamidopyrimidine (0.8 g; 3.8 mmol) and DIPEA (1.7 mL;
10.0 mmol) were added to a solution of 4-amino-3-hydroxy-1-
trityloxymethylphospholane 1-oxide 15 (1.0 g; 2.5 mmol) in n-bu-
0
.47 g (73%) of white lyofilisate. HRMS (FAB) calcd for C
9
H
14
N
2
O
5
P
þ
(
MþH) 261.0640, found 261.0643. IR
nmax (KBr) 3424, 3349, 3192,
ꢀ
3156, 3100, 3050, 1709, 1674, 1621, 1467, 1422, 1414, 1398, 1388,
tanol (25 mL). The reaction mixture was stirred for 16 h at 130 C
ꢀ
1263, 1170, 1084, 1049, 1043, 767, 718. NMR datadsee Tables 2e4.
and evaporated. The residue was treated 16 h at 60 C with con-
Table 2
2
Proton chemical shifts of phosphanucleosides in DMSO and D O
Comp.
H-2a
H-2b
H-3
H-4
H-5a
H-5b
H-6a
H-6b
H-2a
H-5a
H-6a
H-8a
In DMSO
4
4
4
4
1
1
1
1
a
1.66
ddd
1.75
ddd
1.71
ddd
1.66
ddd
2.06
m
2.15
ddd
2.11
ddd
2.04
ddd
2.59
dt
w2.69
m
2.67
dt
2.58
dt
1.94
dt
2.04
dt
1.99
dt
1.92
dt
4.16
m
4.50
m
4.37
m
4.24
tt
4.55
m
4.85
m
4.76
m
4.60
m
4.69
ddd
4.81
ddd
4.62
ddd
4.64
ddd
4.42
ddd
4.52
m
2.03
td
2.25
btd
2.22
dt
1.99
dt
2.10
m
2.68
dt
2.48
ddd
2.10
ddd
2.20
ddd
w2.69
m
2.38
ddd
2.20
ddd
2.45
dt
2.63
ddd
2.61
dt
2.43
dt
3.82 (2H)
m
3.88 (2H)
bm
3.87 (2H)
m
3.81 (2H)
m
3.83
dt
3.88
dt
3.86
dt
d
5.64
d
7.59
d
d
b
8.12
s
d
d
8.15
s
7.74
s
c
d
d
d
d
d
d
5.70
d
5.57
d
7.51
d
7.82
d
d
9a
9b
9c
9d
3.79
dt
3.84
dt
3.82
dt
3.77 ddd
d
8.13
s
d
d
8.25
s
7.83
s
4.33
ddd
4.36
ddd
d
d
d
3.81
dt
d
d
5.67
d
7.66
d
d
2
In D O
4
4
4
4
1
1
1
1
a
2.05
dddt
2.17
ddd
2.11
bddd
2.04
ddd
2.90
dtd
3.00
dt
2.95
bdt
2.89
m
4.54
tdd
4.74
m
4.68
tdd
4.58
m
4.87
dddd
5.06
m
4.90
m
w4.81
m
4.59
dddd
4.75
m
2.42 dddd
2.59 dddd
4.18
dd
4.26
dd
4.23
dd
4.17
dd
4.19
dd
4.25
dd
4.22
dd
4.19
dd
4.14 ddd
5.89
d
7.65
d
d
b
2.66
ddd
2.59
m
2.40
m
2.36
dddd
2.67
ddd
2.69
ddd
2.35
bddd
2.83
ddd
2.83
dddd
2.60
m
2.82
m
3.05
dt
4.23
dd
4.20
dd
4.14
dd
4.16 ddd
8.16
s
d
d
8.28
s
7.89
s
c
d
d
d
d
d
d
6.03
d
5.91
7.59
d
7.75
d
9a
9b
9c
9d
2.50 dddd
2.17 dddd
4.84
tdd
d
2.58 dddd
2.30
dtd
2.24
m
2.18
dtd
5.07
dddd
5.02
dddd
4.86
m
4.22
dd
4.19
dd
4.15
dd
8.22
s
d
d
d
d
8.29
s
7.94
s
2.54
m
2.49
dddd
4.57
dddd
4.60
m
2.97
dt
2.80
dt
d
d
6.06
d
7.69
d
d
a
Nucleobase proton.
4
.3.7. (4S,3S,1R and 4R,3R,1S) 4-(Adenin-9-yl)-3-hydroxy-1-hydroxy-
methylphospholane 1-oxide (4b). 4,6-Dichloro-5-
formamidopyrimidine (0.7 g; 3.8 mmol) and DIPEA (1.7 mL;
0.0 mmol) were added to a solution of 4-amino-3-hydroxy-1-
centrated hydrochloric acid/methanol 1/10 (25 mL), diluted with
water (100 mL) and treated with Dowex H (10 g). The resin was
filtered off and washed with methanol (100 mL) and water (100 mL).
The product was washed off of the resin with 5% aqueous ammonia
(100 mL), evaporated, purified by preparative HPLC (isocratically
þ
1
trityloxymethylphospholane 1-oxide 15 (1.0 g; 2.5 mmol) in n-bu-
tanol (25 mL). The reaction mixture was stirred for 16 h at 130 C
and evaporated. The residue was treated 5 days at rt with aqueous
ammonia/dioxane 1/1 (25 mL) and evaporated. The crude adenine
ꢀ
water) and freeze-dried from water to yield 0.34 g (45%) of white
þ
lyofilisate. HRMS (FAB) calcd for C10
H
15
N
5
O
4
P (MþH) 300.0862,
found 300.0865. IR
n
max (KBr) 3403, 3322, 3200, 3161, 3113, 1736,

O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
9127
Table 3
2.4 mmol) was added to a mixture of 4-(uracil-1-yl)-3-hydroxy-1-
hydroxymethylphospholane 1-oxide 4a (0.26 g; 1.0 mmol) and TEA
(0.33 mL; 2.4 mmol) in acetonitrile (10 mL). The reaction mixture
was stirred for 16 h at rt, quenched by the addition of methanol
(1 mL) and evaporated. The residue was dissolved in chloroform
Proton coupling constants J(H,H) and J(P,H) in phosphanucleosides
Coupled nuclei 4a
4b
4c
4d
19a
19b
19c
19d
In DMSO
H-2a, H-2b
H-2a, H-3
H-2, H-3
H-3, H-4
H-4, H-5a
H-4, H-5b
H-5a, H-5b
H-6a, H-6b
P, H-2a
P, H-2b
P, H-3
P, H-4
P, H-5a
14.6 14.8
10.3 10.4
14.7 14.5
10.4 10.4
6.1
10.2 10.4
7.8 8.2
12.4 12.2
14.7 14.9 14.9 14.7
7.7 7.6 7.7 7.6
10.4 10.4 10.4 10.2
10.3 10.1 9.8 10.2
12.1 11.6 12.0 11.9
7.4 7.6 7.4 7.5
14.3 14.6 14.6 14.4
13.9 13.8 13.9 13.9
13.0 12.6 12.7 12.9
10.4 10.4 10.4 10.2
(100 mL) and extracted with saturated solution of sodium hydro-
7.2
10.3 10.0
8.1 7.7
12.5 12.4
14.7 w14.2 14.8 14.6
a
7.0
gencarbonate (3ꢂ20 mL). The organic layer was dried over anhy-
drous sodium sulfate and evaporated. The crude dibenzoyl
derivative was used without further purification. ESI-MS calcd for
þ
C
23
H
2
22
N
2
O
7
P (MþH) 469.1, found 469.5.
a
a
a
a
,4,6-Triisopropylbenzenesulfonyl chloride (0.91 g; 3.0 mmol)
was added to a mixture of dibenzoyl derivative, TEA (0.84 mL;
mmol) and DMAP (0.12 g; 1.0 mmol) in acetonitrile (10 mL). The
19.2 18.9
19.2 19.2
7.2
a
6.8
a
a
a
a
a
6.7
a
a
6
a
a
a
a
1.3
<1
w0
w0
a
reaction mixture was stirred for 16 h at rt. After that, 5 mL of
aqueous ammonia was added. The reaction mixture was stirred for
13.6 w14.2 13.4 14.0
19.1 18.2 18.8 18.9
P, H-5b
P, H-6a
P, H-6b
10.5
a
a
a
a
a
9.8
a
a
10.4
a
a
7.5
5.6
4.6
7.8
5.6
5.1
7.3
5.3
4.9
7.4
w5.3
w4.5
16 h at rt and evaporated. The crude cytosine derivative was dis-
solved in 50% methanol in water (100 mL) and treated with Dowex
þ
2
In D O
H
(10 g). The resin was filtered off and washed with methanol
H-2a, H-2b
H-2a, H-3
H-2b, H-3
H-3, H-4
H-4, H-5a
H-4, H-5b
H-5a, H-5b
H-6a, H-6b
P, H-2a
15.4 15.4
10.6 10.4
15.4 15.2
10.6 10.5
15.5 15.6 15.4 15.4
7.6 7.5 7.5 7.6
10.6 10.3 10.6 10.4
10.2 10.4 9.9 10.3
12.0 11.7 11.5 11.9
7.9 7.4 7.9 7.6
15.4 15.7 15.6 15.4
14.6 14.5 14.5 14.6
19.6 19.0 15.4 13.6
(100 mL) and water (100 mL). The product was washed off of the
resin with 5% aqueous ammonia (100 mL), evaporated, purified by
preparative HPLC (isocratically water) and freeze-dried from water
7.3
10.3 10.0
8.5 8.3
6.7
7.2
10.2 10.3
8.1 8.5
7.2
to yield 0.14 g (54%) of white lyofilisate. HRMS (FAB) calcd for
þ
12.2 12.0
15.8 15.8
14.6 14.5
20.1 19.8
12.1 11.9
15.8 15.6
14.6 14.6
19.7 20.0
C
3
9
H
15
N
3
O
4
P (MþH) 260.0800, found 260.0804. IR
nmax (KBr) 3336,
194, 1647, 1607, 1527, 1487, 1398, 1296, 1153, 1071, 1045, 786. NMR
datadsee Tables 2e4.
P, H-2b
P, H-3
P, H-4
P, H-5a
P, H-5b
P, H-6a
P, H-6b
6.7
0.8
0.8
14.3 14.1
10.8 9.8
6.7
a
a
6.4
a
a
14.2 14.4
10.1 10.4
4.5
4.1
6.8
w0.6
a
15.5 7.4
10.2 10.4
a
a
2.0
1.5
1.8
0.8
4.3.10. (4R,3R,1R and 4S,3S,1S) 4-(Uracil-1-yl)-3-hydroxy-1-hydroxy-
1.6
2.1
methylphospholane
cryloylcarbamate 20 (0.8 g; 2.9 mmol) was added to a solution of
-amino-3-hydroxy-1-trityloxymethylphospholane 1-oxide 18
1-oxide
(19a). 4-Nitrophenyl-3-ethoxya-
13.7 13.6 13.4 19.4
10.3 10.3 7.0
7.4
4.7
4.4
4
4.4
4.1
4.4
4.1
4.3
3.8
4.8
4.2
4.6
4.2
4.6
4.4
(
1.0 g; 2.5 mmol) in dioxane (25 mL). The reaction mixture was
þ
stirred for 4 h at rt. After that, 5 g of Dowex H was added and the
adThe J value was not determined.
Table 4
1
3C and 31P chemical shifts in phosphanucleosides (coupling constants J(P,C) are given in brackets)
Atom
4a
4b
4c
4d
19a
19b
19c
19d
In DMSO
C-2
C-3
C-4
C-5
33.61 (54.8)
69.77 (9.1)
60.66 (10.6
26.86 (55.2)
59.89 (79.8)
151.40
163.37
101.77
142.67
d
28.28 (55.6)
70.95 (9.2)
59.77 (10.4)
33.94 (54.8)
59.78 (80.0)
152.32
149.76
119.48
156.20
140.33
34.21 (54.9)
71.04 (9.2)
58.54 (10.1)
28.97 (55.1)
59.82 (80.0)
153.55
151.63
116.88
157.00
135.86
33.88 (54.9)
69.55 (9.7)
62.04 (10.4)
27.24 (55.3)
59.98 (79.3)
165.53
156.05
93.99
143.67
d
30.79 (55.8)
69.73 (8.4)
60.71 (9.6)
28.90 (55.2)
59.40 (81.0)
151.41
163.36
101.68
143.06
d
31.21 (55.8)
71.05 (8.8)
59.92 (10.4)
30.29 (55.5)
59.41 (81.0)
152.27
149.77
119.48
156.23
140.48
31.22 (55.7)
71.10 (8.7)
59.31 (10.4)
30.47 (55.4)
59.40 (81.0)
153.38
151.49
117.26
156.99
136.97
31.17 (55.8)
69.67 (8.6)
62.28 (6.3)
29.11 (55.3)
59.60 (80.4)
165.49
156.06
93.98
144.00
d
C-6
C-2
C-4
C-5
C-6
C-8
a
a
a
a
a
P-1
47.79
48.76
49.73
48.46
48.80
49.48
49.63
49.73
In D
C-2
C-3
C-4
C-5
C-6
2
O
34.40 (56.3)
72.64 (11.2)
64.84 (11.5)
27.87 (7.6)
61.04 (81.8)
154.83
168.91
105.13
146.96
d
34.70 (56.3)
74.27 (10.7)
62.05 (10.7)
30.04 (57.7)
61.08 (81.8)
155.19
151.86
121.57
158.24
143.54
34.59 (56.5)
74.14 (9.1)
61.73 (10.8)
29.62 (57.8)
60.92 (81.6)
156.26
154.74
119.10
161.72
141.08
34.44 (54.9)
72.67 (11.7)
65.86 (10.3)
28.21 (57.5)
61.19 (81.2)
168.67
160.82
99.14
147.00
d
32.16 (57.2)
72.55 (9.5)
64.23 (12.5)
29.96 (57.1)
60.88 (81.6)
154.91
168.87
105.22
146.48
d
32.40 (57.2)
74.08 (9.7)
62.11 (9.6)
31.81 (57.0)
61.08 (81.5)
155.28
151.94
121.61
158.36
143.44
32.30 (57.4)
73.97 (10.0)
61.94 (11.4)
31.46 (57.4)
60.92 (81.9)
156.32
154.74
119.16
161.84
141.11
32.24 (57.3)
72.70 (9.6)
64.89 (10.4)
30.37 (57.0)
60.94 (81.6)
168.52
160.82
99.27
146.24
d
a
C-2
C-4
C-5
C-6
C-8
P-1
a
a
a
a
58.49
59.07
59.05
58.81
58.57
58.90
59.15
58.87
a
Nucleobase carbon.
ꢀ
1
689, 1633,1610,1572,1539,1484, 1408,1390,1324,1218,1152, 1073,
suspension was stirred for 2 h at 90 C. The resin was filtered off and
washed with dioxane (100 mL). The product was washed off of the
resin with water (100 mL), evaporated, purified by preparative HPLC
(isocratically water) and freeze-dried from water to yield 0.46 g
1054, 784, 777, 729, 639. NMR datadsee Tables 2e4.
4
.3.9. (4S,3S,1R and 4R,3R,1S) 4-(Cytosin-1-yl)-3-hydroxy-1-
hydroxymethylphospholane 1-oxide (4d). Benzoyl cyanide (0.31 g;
(71%) of white lyofilisate. HRMS (FAB) calcd for C
H N O
9 14 2 5
P (MþH)þ

9128
O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
2
1
61.0640, found 261.0638. IR
425, 1409, 1384, 1261, 1149, 1065, 1052, 765, 720. NMR datadsee
Tables 2e4.
n
max (KBr) 3376, 3262,1688,1622,1467,
to yield 0.18 g (69%) of white lyofilisate. HRMS (FAB) calcd for
þ
C
9
H
15
N
3
O
4
P (MþH) 260.0800, found 260.0802. IR
nmax (KBr) 3444,
3414, 3292, 3201, 1658, 1645, 1623, 1610, 1532, 1492, 1416, 1394,
1300, 1291, 1145, 1066, 1048, 782. NMR datadsee Tables 2e4.
4
.3.11. (4R,3R,1R and 4S,3S,1S) 4-(Adenin-9-yl)-3-hydroxy-1-
hydroxymethylphospholane 1-oxide (19b). 4,6-Dichloro-5-
formamidopyrimidine (0.7 g; 3.8 mmol) and DIPEA (1.7 mL;
0.0 mmol) were added to a solution of 4-amino-3-hydroxy-1-
Acknowledgements
1
The support by grants No. 202/09/0193 and 13-24880S (Czech
Science Foundation) under the IOCB’s research project RVO:
1388963 is gratefully acknowledged. This work was also sup-
ported by Charles University in Prague, project No. SVV267215.
trityloxymethylphospholane 1-oxide 18 (1.0 g; 2.5 mmol) in n-
butanol (25 mL). The reaction mixture was stirred for 16 h at 130 C
and evaporated. The residue was treated 5 days at rt with aqueous
ammonia/dioxane 1/1 (25 mL) and evaporated. The crude adenine
ꢀ
6
ꢀ
derivative was treated 16 h at 60 C with 80% acetic acid in water
Supplementary data
þ
(
(
(
100 mL), diluted with water (100 mL) and treated with Dowex H
10 g). The resin was filtered off and washed with methanol
100 mL) and water (100 mL). The product was washed off of the
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.08.021.
resin with 5% aqueous ammonia (100 mL), evaporated, purified by
preparative HPLC (elution with gradient of 0e20% methanol in
References and notes
water) and freeze-dried from water to yield 0.33 g (47%) of white
þ
lyofilisate. HRMS (FAB) calcd for C10
found 284.0914. IR
606, 1573, 1515, 1483, 1423, 1405, 1396, 1335, 1303, 1295, 1226,
221, 1156, 1071, 1041, 795, 713, 653. NMR datadsee Tables 2e4.
H
15
N
5
O
3
P (MþH) 284.0913,
1
. Zhu, X. Nucleosides, Nucleotides Nucleic Acids 2000, 19, 651e690.
2. Schneller, S. W. Curr. Top. Med. Chem. 2002, 10, 1087e1092.
. Yokoyama, M.; Momotake, A. Synthesis 1999, 1541e1554.
. Merino, P.; Tejero, P.; Delso, P. Curr. Med. Chem. 2008, 15, 954e967.
. Yokoyama, M. Modified Nucleosides In Biochemistry, Biotechnology and Medi-
cine; Wiley-VCH: Weinheim, 2008; pp 173e221.
n
max (KBr) 3419, 3331, 3265, 3214, 3133, 1659,
3
4
5
1
1
4
.3.12. (4R,3R,1R and 4S,3S,1S) 4-(Guanin-9-yl)-3-hydroxy-1-
hydroxymethylphospholane 1-oxide (19c). 2-Amino-4,6-dichloro-
-formamidopyrimidine (0.8 g; 3.8 mmol) and DIPEA (1.7 mL;
0.0 mmol) were added to a solution of 4-amino-3-hydroxy-1-
6. De Clercq, E. Antiviral Drug Strategies; Wiley-VCH: Weinheim, 2011.
. Modified Nucleosides In Biochemistry, Biotechnology and Medicine; Herdewijn, P.,
Ed.; Wiley-VCH: Weinheim, 2008.
8. Yamashita, M. In Topics in Heterocyclic ChemistrydBioactive Heterocycles II;
Springer: Heidelberg: 2007; pp 173e222.
7
5
1
9. Yamamoto, H.; Hanaya, T.; Kawamoto, H.; Inokawa, S.; Yamashita, M.; Armour,
trityloxymethylphospholane 1-oxide 18 (1.0 g; 2.5 mmol) in n-
butanol (25 mL). The reaction mixture was stirred for 16 h at 130 C
and evaporated. The residue was treated 16 h at 60 C with con-
centrated hydrochloric acid/methanol 1/10 (25 mL), diluted with
water (100 mL) and treated with Dowex H (10 g). The resin was
filtered off and washed with methanol (100 mL) and water
M. A.; Nakashima, T. T. J. Org. Chem. 1985, 50, 3516e3521.
ꢀ
10. Hanaya, T.; Noguchi, A.; Armour, M. A.; Hogg, A. M.; Yamamoto, H. J. Chem. Soc.,
ꢀ
Perkin Trans. 1 1992, 295e301.
1
1. Yamaoka, M.; Yamashita, M.; Yamada, M.; Fujie, M.; Kiyofuji, K.; Ozaki, N.; Asai,
K.; Niimi, T.; Suyama, T.; Yamashita, J.; Sawada, A.; Makita, R.; Sugiyama, M.;
Toda, M.; Nakamura, S.; Ohnishi, K. Pure Appl. Chem. 2012, 84, 37e48.
12. Yamada, M.; Yamashita, M.; Suyama, T.; Yamashita, J.; Asai, K.; Niimi, T.; No-
buhisa, O.; Fujie, M.; Maddali, K.; Nakamura, S.; Ohnishi, K. Bioorg. Med. Chem.
Lett. 2010, 20, 5943e5946.
þ
(
100 mL). The product was washed off of the resin with 5% aqueous
ammonia (100 mL), evaporated, purified by preparative HPLC
13. Ito, S.; Yamashita, M.; Niimi, T.; Fujie, M.; Reddy, V. K.; Totsuka, H.; Haritha, B.;
(
(
(
3
1
isocratically water) and freeze-dried from water to yield 0.36 g
Maddali, K.; Nakamura, S.; Asai, K.; Suyama, T.; Yamashita, J.; Iguchi, Y.; Yu, G.;
Oshikawa, T. Heterocycl. Commun. 2009, 15, 23e30.
14. Yamashita, M.; Reddy, V. K.; Reddy, P. M.; Kato, Y.; Haritha, B.; Suzuki, K.; Ta-
kahashi, M.; Oshikawa, T. Tetrahedron Lett. 2003, 44, 3455e3458.
15. Yamashita, M.; Reddy, P. M.; Kato, Y.; Reddy, V. K.; Suzuki, K.; Oshikawa, T.
Carbohydr. Res. 2001, 336, 257e270.
48%) of white lyofilisate. HRMS (FAB) calcd for C10
H
15
N
5
O
4
P
þ
MþH) 300.0862, found 300.0861. IR
nmax (KBr) 3480, 3438, 3318,
215, 3138, 3119, 2732, 1747, 1688, 1658, 1641, 1628, 1589, 1578,
544,1480,1421,1400,1386,1324,1224,1166,1062,1050,1036, 778,
34, 634. NMR datadsee Tables 2e4.
1
6. Yamashita, M.; Suzuki, K.; Kato, Y.; Iida, A.; Ikai, K.; Reddy, P. M.; Oshikawa, T. J.
Carbohydr. Chem. 1999, 18, 915e935.
7
1
7. Ko ꢀc alka, P.; Pohl, R.; Rejman, D.; Rosenberg, I. Nucleosides, Nucleotides Nucleic
Acids 2005, 24, 805e808.
4
.3.13. (4R,3R,1R and 4S,3S,1S) 4-(Cytosin-1-yl)-3-hydroxy-1-
1
8. Ko ꢀc alka, P.; Pohl, R.; Rejman, D.; Rosenberg, I. Tetrahedron 2006, 62, 5763e5774.
9. Rejman, D.; Ko ꢀc alka, P.; Bud eꢀ ꢀs ínsk yꢁ , M.; Pohl, R.; Rosenberg, I. Tetrahedron 2007,
3, 1243e1253.
20. H ꢀr ebabeck yꢁ , H.; Masojídkov aꢁ , M.; Hol yꢁ , T. Collect. Czech. Chem. Commun. 2005,
0, 103e123.
1. Rejman, D.; Kova ꢀc kov ꢁa , S.; Pohl, R.; Dra ꢀc ínsk yꢁ , M.; Fiedler, P.; Rosenberg, I.
hydroxymethylphospholane
0.31 g; 2.4 mmol) was added to a mixture of 4-(uracil-1-yl)-3-
hydroxy-1-hydroxymethylphospholane 1-oxide 19a (0.26 g;
.0 mmol) and TEA (0.33 mL; 2.4 mmol) in acetonitrile (10 mL). The
1-oxide
(19d). Benzoyl
cyanide
1
(
6
7
1
2
reaction mixture was stirred for 16 h at rt, quenched by the addition
of methanol (1 mL) and evaporated. The residue was dissolved in
chloroform (100 mL) and extracted with saturated solution of so-
dium hydrogencarbonate (3ꢂ20 mL). The organic layer was dried
over anhydrous sodium sulfate and evaporated. The crude diben-
Tetrahedron 2009, 65, 8513e8523.
22. Dejmek, M.; Kovackova, S.; Zbornikova, E.; Hrebabecky, H.; Sala, M.; Dracinsky,
M.; Nencka, R. RSC Adv. 2012, 2, 6970e6980.
3. Kova ꢀc kov aꢁ , S.; Dra ꢀc ínsk yꢁ , M.; Rejman, D. Tetrahedron 2011, 67, 1485e1500.
4. Harnden, M. R.; Wyatt, P. G.; Boyd, M. R.; Sutton, D. J. Med. Chem. 1990, 33,
187e196.
5. Montchamp, J.-L.; Tian, F.; Frost, J. W. J. Org. Chem. 1995, 60, 6076e6081.
26. Guillen, F.; Rivard, M.; Toffano, M.; Legros, J. Y.; Daran, J. C.; Fiaud, J. C. Tetra-
hedron 2002, 58, 5895e5904.
27. Pakulski, Z.; Koprowski, M.; Pietrusiewicz, K. M. Tetrahedron 2003, 59,
2
2
2
zoyl derivative was used without further purification. ESI-MS calcd
þ
for C23
22
H N
2
O
7
P (MþH) 469.1, found 469.5.
2
,4,6-Triisopropylbenzenesulfonyl chloride (0.91 g; 3.0 mmol)
was added to a mixture of dibenzoyl derivative, TEA (0.84 mL;
mmol) and DMAP (0.12 g; 1.0 mmol) in acetonitrile (10 mL). The
8
219e8226.
8. Liboska, R.; Masojidkova, M.; Rosenberg, I. Collect. Czech. Chem. Commun. 1996,
1, 778e790.
2
6
6
reaction mixture was stirred for 16 h at rt. After that, 5 mL of
aqueous ammonia was added. The reaction mixture was stirred for
29. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Na-
katsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng,
G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery,
J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K.
N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.;
Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene,
M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
16 h at rt and evaporated. The crude cytosine derivative was dis-
solved in 50% methanol in water (100 mL) and treated with Dowex
þ
H
(10 g). The resin was filtered off and washed with methanol
(
100 mL) and water (100 mL). The product was washed off of the
resin with 5% aqueous ammonia (100 mL), evaporated, purified by
preparative HPLC (isocratically water) and freeze-dried from water

O. P aꢁ v et al. / Tetrahedron 69 (2013) 9120e9129
9129
Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dan-
nenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, Revision A.02; Gaussian: Wallingford CT.
0. Haasnoot, C. A. G.; de Leeuw, F. A. A. M.; Altona, C. Tetrahedron 1980, 36,
31. Thibaudeau, C.; Chattopadhyaya, Y. In Stereoelectronic Effects in Nucleosides and
Nucleotides and then Structural Implications; Uppsala Univ: Uppsala, 1999;
pp 28e30.
32. Westhof, E.; Plach, H.; Cuno, I.; Ludemann, H. D. Nucleic Acids Res. 1977, 4,
939e953.
3
2783e2792.