Bifunctional acyclic nucleoside phosphonates: synthesis of chiral 9-{3-hydroxy[1,4-bis(phosphonomethoxy)]butan-2-yl} derivatives of purines

Article abstract of DOI:10.1016/j.tetasy.2007.09.021

We report herein a general method for the synthesis of new types of chiral acyclic nucleoside four-carbon bisphosphonates. The alkylation of 2-amino-6-chloropurine and adenine was performed with (2S,3S)- or (2R,3R)-1,4-[bis(diisopropoxyphosphoryl)methoxy]]-3-[(methylsulfonyl)oxy]butan-2-yl benzoate. Alkylations provided (2R,3R) or (2S,3S) N⁹-substituted nucleobases, which were further converted to other derivatives. These conversions included either a modification of the nucleobase or transformation of the bisphosphonate chain. Subsequent deprotection of the diisopropyl esters with bromotrimethylsilane provided the resulting (2R,3R)- or (2S,3S)-bisphosphonic acids.

Full text of DOI:10.1016/j.tetasy.2007.09.021

Available online at www.sciencedirect.com
Tetrahedron: Asymmetry 18 (2007) 2233–2247
Bifunctional acyclic nucleoside phosphonates: synthesis of chiral
9-{3-hydroxy[1,4-bis(phosphonomethoxy)]butan-2-yl}
derivatives of purines
*
´
ˇ´
´
´
´
Silvie Vrbkova, Martin Dracınsky and Antonın Holy
Centre for Novel Antivirals and Antineoplastics, Gilead Sciences and IOCB Research Center,
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
Flemingovo na´m. 2, 166 10 Prague 6, Czech Republic
Received 4 August 2007; accepted 14 September 2007
Abstract—We report herein a general method for the synthesis of new types of chiral acyclic nucleoside four-carbon bisphosphonates.
The alkylation of 2-amino-6-chloropurine and adenine was performed with (2S,3S)- or (2R,3R)-1,4-[bis(diisopropoxyphosphoryl)meth-
oxy]]-3-[(methylsulfonyl)oxy]butan-2-yl benzoate. Alkylations provided (2R,3R) or (2S,3S) N9-substituted nucleobases, which were fur-
ther converted to other derivatives. These conversions included either a modification of the nucleobase or transformation of the
bisphosphonate chain. Subsequent deprotection of the diisopropyl esters with bromotrimethylsilane provided the resulting (2R,3R)-
or (2S,3S)-bisphosphonic acids.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
The discovery of PMEA was the beginning of a search for
other similar biologically active compounds. A study of
structure–activity relationships (SAR) in the series of newly
synthesized phosphonomethoxyalkyl purine and pyri-
midine derivatives revealed that several nucleobases
substituted by 3-hydroxy-2-(phosphonomethoxy)propyl
(HPMP) or a 2-phosphonomethoxypropyl (PMP) moiety
[(R)-PMPA or (S)-HPMPC, respectively; (see Fig. 1)],
show a broad spectrum of potent antiviral activity.12–17
Most of the antiviral compounds that are currently used in
the treatment of the herpes simplex virus (HSV), human
immunodeficiency virus (HIV), hepatitis B virus (HBV),
varicella zoster virus (VZV), and cytomegalovirus (CMV)
infections can be described as acyclic nucleoside or nucleo-
tide analogues.1–3 The activity of this class of chemical sub-
stances is currently behind ongoing intensive research
aimed at cancer therapy and viral diseases treatment.4,5 It
is worth mentioning that the absolute configuration of
the compounds studied often play an important role and
significantly influences their biological potency.6
Recently, attention has turned to the synthesis of a new
type of ANPs originating from 2-substituted 4-amino-6-
hydroxypyrimidines.18 In these investigations, a significant
activity of 6-[2-(phosphonomethoxy)ethoxy]pyrimidine
derivatives, compounds derived from 2,4-diaminopyrimi-
dine19 and 2-amino-4-hydroxypyrimidine,19 and their C5-
substituted congeners20,21 was discovered.
Among the acyclic nucleoside analogues bearing
a
phosphonomethyl ether group, 9-(2-phosphonomethoxy-
ethyl)adenine (PMEA, adefovir) was approved as an
antiviral agent7 active both against DNA viruses and
retroviruses, including HIV.8–11
Among the products isolated in these studies, bisphospho-
nates I and II were also identified (Fig. 2).18 Despite the
fact that these compounds constitute a new class of possi-
ble antiviral agents, they have not yet received much atten-
tion. The aim of this work was to explore the potential
biological activity of such substances, which could also
be considered as analogues of nucleotide bisphosphate
*
Corresponding author. Tel.: +420 220183262; fax: +420 220183560;
e-mail addresses: vrbkova@uochb.cas.cz; dracinsky@uochb.cas.cz;
holy@uochb.cas.cz
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.09.021

2234
S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
NH2
N
NH2
N
NH2
N
N
N
N
N
N
O
OH
P
O
OH
O
OH
O
O
P
P
N
N
O
O
HO
HO
HO
HO
(R)-PMPA (Tenofovir)
(S)-HPMPC (Cidofovir)
PMEA (Adefovir)
Figure 1.
O
O
P(O)(OH)2
O
O
P(O)(OH)2
O
N
O
N
OH
N
N
N
H2N
H2N
H2N
N
OH
O
P(O)(OH)2
O
P(O)(OH)2
I
II
Figure 2.
antagonists of the P2Y1 receptor.22,23a,b Additional goal
was to study the effect of the introduction of stereogenic
centers onto the synthesized compounds, since the chirality
seems to play an important role in EI-complex formation
in certain enzymes.
to prepare an appropriate chiral bisphosphonate building
block and use it as a common alkylation reagent for vari-
ous nucleobases. The synthesis of this building block made
use of our earlier experience on synthesis of threo- and
erythro-butyl analogues of acyclic nucleosides,24 it differed
for (2S,3S)- and (2R,3R)-bisphosphonate enantiomers.
While (2S,3S)-bisphosphonate was prepared from (+)-
diethyl L-tartrate 1 (Scheme 1), D-mannitol was used as
starting compound for the opposite enantiomer (2R,3R)
(Scheme 2).
2. Results and discussion
As an outcome of our research, we proposed the following
synthetic pathway leading to a novel type of chiral four-
carbon acyclic nucleoside bisphosphonates, derivatives of
L-threitol and D-mannitol. The strategy of our work was
The starting (4S,5S)-(2,2-dimethyl-1,3-dioxolane-4,5-diyl)-
dimethanol 324 was prepared from commercially available
O
P
O
O
P
O
EtOOC
COOEt
(ii)
HO
OH
H
OH
O
O
O
EtOOC
O
(iii)
(i)
COOEt
O
O
O
O
H
OH
O
O
3 (90 %)
2 (85 %)
1
4 (65 %)
(iv)
O
O
O
O
O
O
P
(v)
P
P
(vi)
HO
MsO
O
HO
O
O
O
O
O
O
O
O
O
O
O
O
OH
5 (95 %)
OBz
7 (95 %)
OBz
6 (65 %)
P
P
P
O
O
O
O
O
Scheme 1. The synthesis of (2S,3S)-bisphosphonate. Reagents and conditions: (i) HC(OEt)3, 4.5 M HCl/DMF, acetone, rt; (ii) LiAlH4, ether, rt; (iii)
NaH, DMF, TsOCH2OP(O)(OiPr)2, 0 ꢁC, then rt; (iv) Dowex 50 · 8 (H+ form), 80% isopropyl alcohol; (v) BzCl, pyridine, 0 ꢁC; (vi) MsCl, pyridine, 0 ꢁC.

S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
2235
OH
OH
OBz
OH
CH2OH
H
CH2OBz
H
OH
O
OH
O
HO
HO
HO
H
BzO
HO
HO
H
HO
OH
(iii)
(iv)
(i)
(ii)
H
OH
OH
H
OH
OH
O
O
O
O
H
H
CH2OH
CH2OBz
10 (95 %)
12 (77 %)
11 (93 %)
8
9 (67 %)
(v)
O
O
O
O
P
P
O
O
O
HO
O
HO
(vi)
(vii)
O
P
O
O
P
O
O
O
O
O
OH
O
OBz
O
O
O
P
O
O
P
O
O
O
O
14 (95 %)
15 (65 %)
13 (65 %)
(viii)
O
O
P
O
O
BzO
OMs
16 (95 %)
O
O
P
O
O
Scheme 2. The synthesis of (2R,3R)-bisphosphonate. Reagents and conditions: (i) BzCl, pyridine, 0 ꢁC; (ii) HC(OEt)3, 4.5 M HCl/DMF, acetone, rt; (iii)
MeONa/MeOH, MeOH, rt; (iv) NaIO4, Ba(OAc)2Æ2H2O, then NaBH4, H2O, acetone; (v) TsOCH2P(O)(OiPr)2, NaH, DMF, 0 ꢁC; (vi) Dowex 50 · 8 (H+
form), 80% isopropyl alcohol; (vii) BzCl, pyridine, 0 ꢁC; (viii) MsCl, pyridine, 0 ꢁC.
(+)-diethyl L-tartrate 1 as described in Scheme 1. The
thus-obtained diol intermediate 3 was alkylated with
(diisopropoxyphosphoryl)methyl tosylate25 and isopropyl-
idene protecting group was subsequently removed with
Dowex 50 · 8 (H+ form) to give compound 5. The resulting
chiral bisphosphonate agent 7 was prepared by mono
benzoylation of 5 and subsequent mesylation of 6. No race-
mization was observed during this multistep reaction
(NMR analysis, specific rotation), so we assumed that the
configuration of final chiral four-carbon bisphosphonate
was as (2S,3S).
Alkylation of 2-amino-6-chloropurine 17 and adenine 18
with both chiral four-carbon bisphosphonates 7 and 16
provided N9-substituted derivatives as the only product.
However, the mechanism of alkylation and the final config-
uration at stereocenter C2 could not be unambiguously
determined (Scheme 4). We used the benzoyl-protected
moiety on stereocenter C3, which is generally used as a par-
ticipating group for glycosylations in the chemistry of car-
bohydrates.27,28 The formation of
a single product
indicated the possibility of either an SN2 or SN1 mecha-
nism. It is known that the participation of the benzoyl
group during the glycosylation reaction (SN1) on the rigid
carbohydrate moiety affords the formation of cyclic inter-
mediate IV, which allows the nucleophile (e.g., R1OH) to
attack the anomeric carbon only from the opposite side
and thus create the highly stereoselective trans-product V
(Scheme 3).
A multistep synthesis of (2R,3R)-bisphosphonate was
started by the protection of primary hydroxyls of com-
pound 8 (D-mannitol) with benzoyl groups (Scheme 2).
cis-Oriented hydroxyl groups were then protected by an
isopropylidene group. This reaction step was followed by
debenzoylation. Cleavage of 1126 with NaIO4 in the pres-
ence of Ba(OAc)2Æ2H2O and NaBH4 reduction gave 3,4-
di-O-isopropylidene protected 1,4-diol 12.26 Alkylating bis-
phosphonate agent 16 was prepared in the following four
steps: attachment of the phosphonate moiety to 12 formed
compound 13, which was then transformed to 14 with
Dowex 50 · 8 (H+ form). Its monobenzoylation provided
compound 15, which gave the final alkylating agent 16 by
mesylation. No racemization was observed during this
multistep reaction according to NMR analysis, and the
specific rotation; therefore, we assigned the configuration
of the final chiral four-carbon bisphosphonate as (2R,3R).
In spite of the fact that free rotation of bisphosphonate
chains 7 and 16 probably occurred in our case (Scheme
4), the participation of the benzoyl group could not be
excluded.
The mechanism of the alkylation reaction was clarified
after the replacement of the participating benzoyl group
with a non-participating tert-butyldimethylsilyl group
(Scheme 5). For this purpose compound 33 was prepared
and used as the alkylating agent. Alkylation of adenine un-
der the same conditions as used for bisphosphonate 7

2236
S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
R1OH
An NMR study of both measured derivatives proved that
they are identical. Specific rotation analysis also confirmed
that 35 was indeed compound 24a.
(S)O
O(S)
O
OR1
(S)O
O
(R)
(S)
ZO
ZO
(R)
ZO
O
X
+
O
O
O
OBn
OR
NMR spectroscopy, the specific rotation and exclusion of
the participation of the silyl group, therefore, revealed that
the alkylation of compounds 7, 16, and 33 (Schemes 4 and
5) had proceeded by the SN2 mechanism; that is, the nucleo-
phile (nucleobase) attacks the C2 of bisphosphonates 7, 16,
and 33 from the opposite side after which the mesyl group
leaves and it causes the conversion of configuration on
stereocenter C2. As an outcome of this study, this can be
said that the alkylation of (2S,3S)-bisphosphonate 7 gave
(2R,3R)-alkylated derivatives 19a and 20a, while opposite
enantiomers 19b and 20b were formed during the alkyl-
ation with (2R,3R)-bisphoshonate building block 16
(Scheme 4).
OBn
III
V
IV
Z = the system of protecting groups on a saccharide skeleton
X = leaving group
Scheme 3. Glycosylation reaction using participating benzoyl group.
(DMSO, Cs2CO3, 110 ꢁC) provided N9-substituted deriva-
tive 34. Since only one product was isolated, the mecha-
nism was still not certain. Therefore, the protecting silyl
group was removed with 1 M TBAF in THF. The structure
of the thus-obtained compound 35 was compared with 24a.
R1
N
O
O
N
R1
P
O
N
O
N
N
N
R2
i)
a)(2R,3R)-
b)(2S,3S)-
R2
N
N
H
O
OBz
O
P
O
O
17 R1 = Cl, R2 = NH2
18 R1 = NH2, R2 = H
19a,b R1 = Cl, R2 = NH2 (15 %)
20a,b R1 = NH2, R2 = H (17 %)
R1
Cl
O
N
O
O
N
O
P
N
P
N
O
O
N
O
N
O
N
N
H2N
H2N
ii)
O
X
O
OBz
O
O
O
O
21a,b R1 = OH, X = OBz (64 %)
22a,b R1 = NH2, X = OH (62 %)
23a,b R1 = cypr, X = OBz (75 %)
P
P
O
O
19a,b
R1
O
N
O
P
N
24a,b R1 = NH2, R2 = H (86%)
25a,b R1 = OH, R2 = NH2 (80%)
26a,b R1 = cypr, R2 = NH2 (79%)
O
N
O
20a,b
21a,b
23a,b
iii)
N
R2
O
OH
O
P
O
O
R1
27a,b R1 = NH2, R2 = NH2 (83 %)
28a,b R1 = NH2, R2 = H (93 %)
29a,b R1 = OH, R2 = NH2 (63 %)
30a,b R1 = cypr, R2 = NH2 (84 %)
OH
N
O
P
N
22a,b
24a,b
25a,b
26a,b
OH
N
O
N
R2
O
OH
O
P
OH
HO
Scheme 4. Alkylation of nucleobases with (2S,3S) or (2R,3R) bisphosphonate. Reagents and conditions: (i) 7 or 16, Cs2CO3, DMF or DMSO, 110 ꢁC; (ii)
for compounds 21a,b: 80% CH3COOH, reflux; for compounds 22a,b: methanolic ammonia, 100 ꢁC; for compounds 23a,b: cyclopropylamine, dioxane,
reflux; (iii) 1 M CH3ONa/CH3OH, rt; (iv) TMSBr, CH3CN, rt.

S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
2237
O
O
O
O
O
O
P
P
BzO
P
O
O
BzO
HO
O
O
O
O
O
i)
O
OH
ii)
O
O
O
O
OTBDS
P
OTBDS
P
P
O
O
O
O
O
O
6
32 (97 %)
31 (98 %)
iii)
H2N
N
O
N
H2N
N
O
O
O
P
N
O
O
P
O
P
N
O
v)
O
iv)
MsO
N
O
O
N
O
N
O
OH
O
O
O
OTBDS
33 (99 %)
O
OTBDS
P
P
O
O
O
P
O
O
O
O
35 (quant.)
34 (11 %)
Scheme 5. The synthesis of (2S,3S)-bisphosphonate with non-participating group. (i) TBDSCl, imidazole, DMF, rt; (ii) 1 M MeONa/MeOH, rt; (iii)
MsCl, pyridine, 0 ꢁC; (iv) adenine 18, Cs2CO3, DMSO, 110 ꢁC; (v) 1 M TBAF/THF, rt.
2
1.5
1
1
0. 8
0. 6
0. 4
0. 2
0
-28a
-28b
CD
CD
CD
CD
-
-
27a
27b
0.5
0
220
270
320
370
220
270
320
370
-0.2
-0.4
-0.6
-0.5
-1
-1.5
-2
-0.8
-1
nm
nm
1.5
1
0.6
CD-30a
CD-30b
CD-29a
CD-29b
0.4
0.2
0
0.5
0
220
-0.5
270
320
370
220
270
320
370
-0.2
-0.4
-0.6
-1
-1.5
nm
nm
Figure 3. CD spectra of enantiomeric free bisphosphonic acids.

2238
S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
Figure 4. Capillary zone electrophoresis of compounds 27a and 27b.
As found by NMR analysis the C3 stereocenter was un-
changed during the alkylation (no formation of diastereo-
mer congener was observed).
tra (see Fig. 3) or capillary zone electrophoresis (CZE,
Figs. 4 and 5).29
Transformation of the C–Cl bond of purines 19a,b under
standard conditions23a afforded the bisphosphonates
21a,b–23a,b (Scheme 4). Methanolysis catalyzed by sodium
methoxide provided compounds 24a,b–26a,b. Deprotection
of the diisopropyl esters with bromotrimethylsilane in aceto-
nitrile, followed by hydrolysis, gave their chiral (2R,3R)-
bisphosphonic acids 27a–30a and (2S,3S)-bisphosphonic
acids 28b and 29b, which were isolated from the deionized
product by ion exchange chromatography.
3. Conclusion
Chiral four-carbon bisphosphonate alkylating agents were
prepared from optically active (+)-diethyl L-tartrate and
D-mannitol. These were then used for the synthesis of
N9-alkylated nucleobases, 2-amino-6-chloropurine, and
adenine, respectively. As verified in the attempts with
non-participating silyl group, the alkylation proceeds via
an SN2 mechanism, which causes an inversion of configura-
tion at the C2 stereocenter. No racemization at the C3
stereocenter took place during the reactions. Therefore,
we predicted the configuration of the final bisphosphonic
acids to be (2R,3R) when starting from (2S,3S)-bis-
phosphonate, or (2S,3S) when starting from (2R,3R)-
bisphosphonate.
Purification of compounds 27b and 30b was slightly differ-
ent. The crude products were applied onto Dowex 50 · 8
(H+ form) and washed with water, followed by dilute aque-
ous ammonia. The thus-obtained ammonium salts were
transformed into sodium salts of bisphosphonic acids by
Dowex 50 · 8 (Na+ form) ion exchange chromatography.
Free bisphosphonic acids of original sodium salts of com-
pounds 27b and 30b were obtained after the treatment with
HCl in water. The enantiomeric purity of final free bisphos-
phonic acids was among others demonstrated by CD spec-
The enantiomeric purity was confirmed with NMR, CD, or
CZE analysis. CZE analyses of compounds 27a,b and 28a,b
provided single peaks both in the non-chiral BGE and chi-
ral BGE 2 (see Figs. 4 and 5). No enantioseparation was

S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
2239
Figure 5. Capillary zone electrophoresis of compounds 28a and 28b.
achieved in the case of enantiomeric pairs 29a,b and 30a,b,
despite the fact that several chiral BGEs were tested for
their separation. This is probably due to the fact that the
chiral selector used, b-cyclodextrin, was not able to distin-
guish among these, because the strength of interactions in
both enantiomer–cyclodextrin complexes was the same.
When the interaction differs among the enantiomers, it is
possible to separate them by means of electrophoresis, as
observed for the enantiomeric pairs 27a,b and 28a,b.
apparatus and are uncorrected. NMR spectra were mea-
sured on a Bruker Avance-500 instrument (500.0 MHz
1
for H and 125.7 MHz for 13C). Chemical shifts are given
in ppm (d-scale), and coupling constants (J) in Hz. Mass
spectra were measured on a ZAB-EQ spectrometer (Micro-
mass, Manchester, UK) using FAB (ionization by Xe,
accelerating voltage 8 kV) or using EI (electron energy
70eV). UV spectra (k in nm) were taken on a Beckman
CoulterTM, DUꢂ 800 spectrophotometer. Elemental analy-
ses were carried out on a Perkin–Elmer 2400 Series II
CHNS/O Analyser. Optical rotations were measured on
Autopol IV (Rudolph Research Analytical). CD spectra
were recorded on Jasco J-810 spectrometer in silicon cells
with thickness 0.5–1.0mm. Aqueous solution with approx-
imate concentration of 0.002 mol/L was used. The results
were averaged over three scans (point spacing 0.5 nm, time
constant 2s) due to unfavorable CD signal/absorption ra-
tio. Capillary zone electrophoresis analyses were performed
in a commercial P/ACE MDQ apparatus (Beckman Coul-
terTM, Fullerton, CA, USA), equipped with an internally
non-coated fused silica capillary with outer polyimide coat-
ing (Polymicro Technologies, Phoenix, AR, USA). The
analyses were performed both in non-chiral and chiral
background electrolytes (BGEs). Chemicals were pur-
chased from Sigma–Aldrich (Prague, Czech Republic).
The CD spectra and specific rotation indicate that in all
cases, the respective enantiomeric pairs were obtained.
For all compounds the spectra correspond also
quantitatively.
All synthesized compounds are currently undergoing
screening for their potential antiviral and cytostatic
activity.
4. Experimental
Unless otherwise stated, solvents were evaporated at 40 ꢁC/
2 kPa, and compounds were dried over P2O5 at 2 kPa.
Melting points were determined on a Buchi melting point
¨

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S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
Dimethylformamide and acetonitrile were distilled from
P2O5 and stored over molecular sieves (4 A). Acetone was
iPr); 78.99 (2C, O–CH); 62.14 (2C, O–CH2); 27.31 (2C,
CH3).
˚
dried over anhydrous CuSO4. Diethylether was distilled
from LiAlH4. Pyridine was dried over KOH and distilled
with KMnO4. Methanol was distilled over magnesium pel-
lets.
4.3. (4S,5S)-[4,5-Bis(diisopropoxyphosphoryl)methoxy-
methyl]-2,2-dimethyl-1,3-dioxolane 4
A
solution of (4S,5S)-(2,2-dimethyl-1,3-dioxolane-4,5-
Numbering for NMR analysis
R1
diyl)dimethanol 3 (20 g, 124 mmol) in dry DMF (200 mL)
was added dropwise to a stirred suspension of NaH
(12.4 g of 60% suspension in mineral oil, prewashed with
n-hexane, 310 mmol) in dry DMF (300 mL) at 0 ꢁC under
a CaCl2 protecting tube. (Diisopropoxyphosphoryl)methyl
tosylate (91 g, 260 mmol) was added dropwise and the mix-
ture stirred at room temperature overnight. The reaction
mixture was neutralized with 4.5 M HCl in DMF and the
solvent evaporated. The residue was co-evaporated with
toluene, dissolved in ethyl acetate (300 mL), and washed
with water (3 · 300 mL). The organic layer was dried over
anhydrous MgSO4, filtered, and evaporated. The residue
was purified by silica gel column chromatography, using
OR
N
O
P
1
N
OR
N
O
N
R2
3
2
4
5
6
O
OBz (OH)
O
P
OR
RO
4.1. (4R,5R)-Diethyl 2,2-dimethyl-1,3-dioxolane-4,5-dicar-
boxylate 2
A mixture of (+)-diethyl L-tartrate (309 g; 1.5 mol), dry
acetone (450 mL), ethyl orthoformate (332 mL; 1.3 equiv),
and 4.5 M HCl in DMF (9 mL) was set aside at room tem-
perature under a CaCl2 cap for 3 days. After neutralization
with Et3N, the mixture was evaporated. The residue was di-
luted with diethylether (900 mL), washed with water
(2 · 300 mL), dried over MgSO4, filtrated, and evaporated.
chloroform–methanol gradient 0–2%, to yield 42 g (65%)
20
of pure 4 as a yellowish oil. ½aꢀD ¼ þ39:4 (c 0.43, MeOH);
FABMS: 519.0 (MH+) (100). 1H NMR (500 MHz, DMSO-
d6): 4.60 (m, 4H, CH-iPr); 3.91 (m, 2H, O–CH); 3.78 (dd,
4H, JP,CH = 8.3, P–CH2); 3.67 (dd, 2H, J = 3.1 and 10.7,
O–CH2); 3.62 (dd, 2H, J = 5.1 and 10.7, O–CH2); 1.31 (s,
6H, CH3); 1.25 and 1.24 (4 · d, 24H, JCH ;CH ¼ 6:2,
3
Distillation in vacuo afforded 310 g (85%) of pure 2 as a
CH3). 13C NMR (125.7 MHz, DMSO-d6): 108.99 (C-iPr);
76.50 (2C, O–CH); 72.67 (d, 2C, JP,C = 11.7, O–CH2);
70.31 (d, 4C, JP,C = 6.4, CH-iPr); 65.48 (d, 2C,
JP,C = 164.5, P–CH2); 27.01 (2C, CH3); 23.99 (d, 4C,
JP,C = 3.9, CH3); 23.88 (d, 4C, JP,C = 4.4, CH3).
20
yellowish oil, bp 84–86 ꢁC/0.1Torr. ½aꢀD ¼ þ41:2 (c 1,
MeOH). FABMS: 247.2 (MH+) (55). 1H NMR
(500 MHz, DMSO-d6): 4.81 (s, 2H, O–CH); 4.18 (q, 4H,
JCH ;CH ¼ 7:1, O–CH2); 1.38 (s, 6H, CH3); 1.21 (t, 6H,
2
3
JCH ;CH ¼ 7:1, CH3). 13C NMR (125.7 MHz, DMSO-d6):
3
2
169.60 (2C, CO); 113.04 (C-iPr); 76.74 (2C, O–CH); 61.46
(2C, O–CH2); 26.48 and 14.08 (2C and 2C, CH3-iPr and
CH3).
4.4. (2S,3S)-[1,4-Bis(diisopropoxyphosphoryl)methoxy]-
butane-2,3-diol 5
A solution of (4S,5S)-[4,5-bis(diisopropoxyphosphoryl)-
4.2. (4S,5S)-(2,2-Dimethyl-1,3-dioxolane-4,5-diyl)dimetha-
nol 3
methoxymethyl]-2,2-dimethyl-1,3-dioxolane
4
(42 g,
81 mmol) in 80% isopropanol (300 mL) was refluxed with
Dowex 50 · 8 in H+ form (5 g) for 12 h. The resin was fil-
tered off, the solution neutralized with aqueous ammonia
and the solvent evaporated. The crude product was purified
by silica gel column chromatography, using chloroform–
(4R,5R)-Diethyl 2,2-dimethyl-1,3-dioxolane-4,5-dicarbox-
ylate 2 (269 g, 1.1 mol) in dry diethylether (300 mL) was
added dropwise to a stirred and ice-cooled solution of
Red-Al (564 mL, 65wt % solution in toluene) in absolute
diethylether (500 mL). The temperature was held below
35 ꢁC. The mixture was then stirred at room temperature
for 3 h. The excess hydride was decomposed with ethyl ace-
tate, ethanol, water, and 4 M NaOH. The solids were fil-
tered off and the solution evaporated. The residue was
diluted with hot water and neutralized with HCl. The solids
were again filtered through the Celite pad and the filtrate
washed twice with diethylether. The water layer was evap-
orated and co-evaporated with ethanol. The residue was di-
luted with ethyl acetate and the solids filtered through the
Celite pad. The organic layer was dried over MgSO4, fil-
tered, and evaporated. The residue was distilled, yielding
methanol gradient 0–5%, to yield 37.5 g (95%) of pure 5
20
as a colorless oil. ½aꢀD ¼ þ2:2 (c 0.35, MeOH); FABMS:
479.0 (MH+) (100). 1H NMR (500 MHz, DMSO-d6):
4.62 (br s, 2H, OH); 4.60 (m, 4H, CH-iPr); 3.74 and 3.71
(dd, 4H, JP,C = 8.2, Jgem = 13.9, P–CH2); 3.57 (m, 4H,
OCH2); 3.43 (m, 2H, OCH); 1.24 and 1.23 (2 · d, 24H,
JCH ;CH ¼ 6:2 and 6.3, CH3). 13C NMR (125.7 MHz,
3
DMSO-d6): 74.16 (d, 2C, JP,C = 11.2, OCH2); 70.28 and
70.27 (d, 4C, JP, C = 6.4, CH-iPr); 69.57 (2C, OCH);
65.38 (d, 2C, JP,C = 164.5, PCH2); 24.03 (d, 4C,
JP,C = 3.9, CH3); 23.92 (d, 4C, JP,C = 4.4, CH3).
4.5. (2S,3S)-3-Hydroxy-1,4-[bis(diisopropoxyphosphoryl)-
methoxy]butan-2-yl benzoate 6
108 g (90%) of 3 as a yellowish oil; bp 91–93 ꢁC/0.1 Torr.
20
½aꢀD ¼ þ10:8 (c 0.5, MeOH); FABMS: 163.0 (MH+) (50).
1H NMR (500 MHz, DMSO-d6): 4.65 (br s, 2H, OH);
3.74 (m, 2H, O–CH); 3.51 (dd, 2H, J = 4.1 and 11.6, O–
CH2); 3.47 (dd, 2H, J = 5.2 and 11.6, O–CH2); 1.30 (s,
6H, CH3). 13C NMR (125.7 MHz, DMSO-d6): 108.20 (C-
Benzoyl chloride (8.7 g, 62 mmol) was added dropwise to a
stirred solution of 5 (37.0 g, 77 mmol) in dry pyridine
(300 mL) at 0 ꢁC with a CaCl2 protecting tube. The mixture
was stirred for 2 h at 0 ꢁC and then at room temperature

S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
2241
overnight. The solvent was evaporated and the residue was
purified by column chromatography on silica gel, using
(500 MHz, CDCl3): 8.04 (m, 2H, Bz-2); 7.56 (m, 1H, Bz-
4); 7.44 (m, 2H, Bz-3); 5.34 (m, 1H, H-3); 4.70 (m, 4H,
CH-iPr); 4.13 (m, 1H, H-4); 3.89 (m, 2H, H-2); 3.84–3.69
(m, 4H, H-1 and H-6); 3.65 (m, 2H, H-5); 1.34–1.23 (m,
24H, CH3-iPr); 0.88 (s, 9H, C–(CH3)3); 0.11 and 0.09
(2 · s, 6H, CH3–Si). 13C NMR (125.7 MHz, CDCl3):
165.69 (CO); 133.06 (Bz-4); 130.02 (Bz-1); 129.74 (Bz-2);
128.32 (Bz-3); 74.61 (d, J5,P = 10.6, C-5); 73.43 (C-3);
71.25 (d, J2,P = 11.8, C-2); 71.03 (m, 4 · CH-iPr); 70.33
(C-4); 66.49 and 66.04 (2 · d, JC,P = 167.2 and 167.6, C-1
and C-6); 25.74 (C–(CH3)3); 24.00 (m, 8 · CH3-iPr); 17.98
(C–(CH3)3); ꢂ4.48 (CH3–Si).
chloroform–methanol gradient 0–5%, to yield 29.2 g
20
(65%) of pure 6 as a yellowish oil. ½aꢀD ¼ þ5:0 (c 0.1,
MeOH); FABMS: 583.1 (MH+) (100). 1H NMR
(500 MHz, DMSO-d6): 8.05 (d, 2H, Harom.); 7.66 (t, 1H,
Harom.); 7.53 (t, 2H, Harom.); 5.26 (br s, 1H, OH); 5.22
(m, 1H, OCH); 4.58 and 4.52 (m, 4H, CH-iPr); 3.88 (m,
1H, OCH); 3.81 (d, 2H, J = 5.0, OCH2); 3.58 (dd, 1H,
J = 4.8 and 10.2, OCH2); 3.53 (dd, 1H, J = 6.2 and 10.2,
OCH2); 3.77 (dd, 1H, JP,C = 8.2, Jgem = 13.9, P–CH2);
3.75 (d, 2H, JP,C = 7.8, P–CH2); 3.73 (dd, 1H, JP,C = 8.2,
Jgem = 13.9,
P–CH2);
1.23–1.13
(8 · d,
24H,
JCH ;CH ¼ 6:2, CH3). 13C NMR (125.7 MHz, DMSO-d6):
4.8. (2S,3S)-1,4-[Bis(diisopropoxyphosphoryl)methoxy]-3-
(tert-butyldimethylsilyloxy)-butane-2-ol 32
3
165.40 (CO); 133.49; 129.99; 129.58 (2C), 128.77 (2C);
73.80 (d, JP,C = 10.2, OCH2); 73.17 (OCH); 71.30 (d,
JP,C = 12.2, OCH2); 70.34 and 70.30 (2 · d, JP,C = 5.9,
CH-iPr); 65.48 and 65.19 (2 · d, JP,C = 164.1, P–CH2);
23.99 (d, 4C, JP,C = 3.9, CH3); 23.80 (d, 4C, JP,C = 4.4,
CH3).
See general procedure for debenzoylation. Column chro-
matography (silica gel, chloroform–methanol gradient 1–
5%) afforded product 32 as a yellowish oil (4.4 g, yield
20
97%). ½aꢀD ¼ þ8:5 (c 0.50, MeOH); FABMS: 593.7
1
(MH+) (90). H NMR (500 MHz, CDCl3): 4.75 (m, 4H,
4.6. (2S,3S)-3-(Benzoyloxy)-1,4-[bis(diisopropoxyphos-
phoryl)methoxy]butan-2-yl mesylate 7
CH-iPr); 3.90 (m, 1H, H-4); 3.84 (m, 1H, H-3); 3.75 (m,
4H, H-1 and H-6); 3.67 (dd, 1H, Jgem = 9.5, J5,4 = 6.0,
H-5); 3.64 (dd, 1H, Jgem = 9.9, J2,3 = 5.3, H-2); 3.59 (dd,
Mesyl chloride (7.8 g, 68 mmol) was added dropwise to a
stirred solution of 6 (28.5 g, 49 mmol) in dry pyridine
(200 mL) at 0 ꢁC with a CaCl2 protecting tube. The mixture
was stirred for 2 h at 0 ꢁC and then at room temperature
overnight. The solvent was evaporated and the residue
was purified by column chromatography on silica gel, using
1H, Jgem = 9.9, J2 ,3 = 6.9, H-20); 3.57 (dd, 1H, Jgem = 9.5,
0
J5 ,4 = 5.9, H-50); 1.34 (m, 24H, CH3-iPr); 0.89 (s, 9H, C–
0
(CH3)3); 0.10 and 0.09 (2 · s, 6H, CH3–Si). 13C NMR
(125.7 MHz, CDCl3): 74.39 and 74.37(2 · d, JC,P = 10.6
and 10.4, C-5 and C-2); 71.02 (m, 4 · CH-iPr); 70.60 (C-
4); 70.24 (C-3); 66.23 and 66.22 (2 · d, JC, P = 167.4 and
167.7, C-1 and C-6); 25.81 (C–(CH3)3); 24.00 (m,
8 · CH3-iPr); 18.05 (C–(CH3)3); ꢂ4.38 and ꢂ5.03 (CH3–
Si).
chloroform–methanol gradient 0–3%, to yield 29.8 g (95%)
20
of pure 7 as a yellowish oil. ½aꢀD ¼ þ27:5 (c 0.2, MeOH);
For C26H46O13P2S (660.65) calcd: C, 47.27; H, 7.02; P,
9.38; S, 4.85. Found: C, 47.23; H, 7.14; P, 9.55; S 4.92.
1
FABMS: 661.20 (M+) (40). H NMR (500 MHz, CDCl3):
4.9. (2S,3S)-1,4-[Bis(diisopropoxyphosphoryl)methoxy]-3-
(tert-butyldimethylsilyloxy)butan-2-yl mesylate 33
8.08 (m, 2H, Harom.); 7.59 (m, 1H, Harom.); 7.46 (m,
2H, Harom.); 5.48 (q, 1H, JCH–Bz,CH–Ms ꢁ JCH–Bz,CHa
ꢁ
JCH–Bz,CHb = 4.8, CH–Bz); 5.16 (m, 1H, CH–Ms); 4.72
(m, 4H, CH-iPr); 4.00–3.87 (m, 4H, OCH2); 3.88–3.68
(m, 4H, P–CH2); 3.18 (s, 3H, Ms–CH3); 1.34–1.27 (m,
24H, CH3); 13C NMR (125.7 MHz, CDCl3): 166.45 (CO);
135.54; 129.95 (2C); 129.15; 128.50 (2C); 79.05 (CH–Ms);
72.09 (d, JC,P = 11.9, OCH2); 71.33–71.13 (m, CH-iPr);
70.78 (d, JC,P = 10.6, OCH2); 70.77 (C–Bz); 66.31 (d,
JC,P = 167.4 and 168.6, P–CH2); 38.82 (Ms–CH3); 24.06–
23.93 (m, CH3).
See mesylation of compound 6. Column chromatography
(silica gel, chloroform–methanol gradient 0–2%) afforded
product 33 as
a yellowish oil (4.7 g, yield 99%).
20
½aꢀD ¼ þ25:0 (c 0.43, MeOH); FABMS: 671.7 (MH+)
(90). For C25H56O12P2SSi (670.8) calcd: C, 44.76; H,
8.41; P, 9.23; S, 4.78; Si, 4.19. Found: C, 44.68; H, 8.39;
1
P, 9.19; S, 4.86. H NMR (500 MHz, CDCl3): 4.74 (m,
5H, CH-iPr and H-3); 4.03 (m, 1H, H-4); 3.84 (m, 2H,
H-2); 3.79 and 3.71 (2 · m, 4H, H-1 and H-6); 3.65 (m,
1H, H-5); 3.14 (s, 3H, Ms–CH3); 1.33 (m, 24H, CH3-iPr);
0.89 (s, 9H, C–(CH3)3); 0.11 (s, 6H, CH3–Si). 13C NMR
(125.7 MHz, CDCl3): 81.42 (C-3); 73.27 and 71.91 (2 · d,
JC,P = 10.8 and 13.3, C-5 and C-2); 71.06 (m, 4 · CH-
iPr); 70.77 (C-4); 66.36 and 66.22 (2 · d, JC,P = 167.5 and
169.3, C-1 and C-6); 38.54 (Ms–CH3); 25.73 (C–(CH3)3);
24.04 (m, 8 · CH3-iPr); 17.98 (C–(CH3)3); ꢂ5.08 and
ꢂ4.60 (CH3–Si).
4.7. (2S,3S)-1,4-[Bis(diisopropoxyphosphoryl)methoxy]-3-
(tert-butyldimethylsilyloxy)butan-2-yl benzoate 31
A
solution of tert-butyldimethylsilyl chloride (5.2 g,
34.4 mmol) in dry DMF (50 mL) was slowly added to a
solution of 6 (5.0 g, 8.6 mmol) and imidazole (4.1 g,
60.0 mmol) in dry DMF (150 mL). The reaction mixture
was stirred overnight at room temperature. It was then
concentrated under reduced pressure, dissolved in chloro-
form, and washed with 0.1 M aq HCl (twice). The organic
layer was dried over MgSO4, filtered, and concentrated un-
der reduced pressure. Column chromatography (silica gel,
4.10. 1,6-Di-O-benzoyl-D-mannitol 9
Benzoyl chloride (308.6 g, 2196 mmol) was added dropwise
to a stirred solution of D-mannitol 8 (200 g, 1098 mmol) in
dry pyridine (850 mL) at 0 ꢁC with a CaCl2 protecting
tube. The mixture was stirred at 0 ꢁC for 2 h and then at
room temperature overnight. The solvent was evaporated
chloroform–methanol gradient 1–5%) afforded product 31
20
as a yellowish oil (5.87 g, yield 98%). ½aꢀD ¼ þ5:0 (c 0.25,
MeOH); FABMS: 697.7 (MH+) (90). 1H NMR

2242
S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
and co-evaporated with toluene. The residue was slowly
poured into vigorously stirred water. The white precipitate
was filtered and dried in air. Crystallization from ethanol
4.13. (4R,5R)-(2,2-Dimethyl-1,3-dioxolane-4,5-diyl)dimeth-
anol 12
yielded 288 g (67%) of 9 as a white powder. Mp 180–
NaIO4 (225 g) was dissolved in hot water (830 mL) and
then cooled to 40 ꢁC. Acetone (1000 mL) was added and
the reaction mixture was cooled to 15 ꢁC. 3,4-Di-O-isoprop-
ylidene-D-mannitol 11 (115 g, 517 mmol) was added and
the reaction mixture stirred at 10–15 ꢁC for 2 h. The sus-
pension was filtered off and washed with acetone. Acetone
was evaporated from the water–acetone solution and
Ba(OAc)2Æ2H2O (11 g dissolved in minimum water) was
added. The precipitate was filtered through the Celite pad
and the residue was cooled to 5 ꢁC. NaBH4 (24 g) was
added portionwise while keeping the temperature under
20 ꢁC. The reaction mixture was stirred at 15 ꢁC for 2 h
and at room temperature overnight. The solution was neu-
tralized with acetic acid, evaporated to 150 mL of final vol-
ume, and continually extracted with chloroform for 15 h to
20
181 ꢁC (lit. 182 ꢁC); ½aꢀD ¼ þ15:4 (c 0.5, acetone). For
C20H22O8 (390.38) calcd: C, 61.53; H, 5.68. Found: C,
1
61.63; H, 5.67. FABMS: 391.12 (MH+) (100). H NMR
(500 MHz, DMSO-d6): 7.95 (d, 4H, Harom.); 7.56 (t, 2H,
Harom.); 7.40 (t, 4H, Harom.); 4.47 and 4.45 (2 · dd, 2H,
J = 1.4 and 11.4, Hb-1,6); 4.30 and 4.27 (2 · dd, 2H,
J = 5.8 and 11.4, Ha-1,6); 3.82 and 3.80 (2 · m, 2H, H-
2,5); 3.75 and 3.73 (2 · d, 2H, J = 9.4, H-3,4); 13C NMR
(125.7 MHz, DMSO-d6): 165.92 (CO); 132.89, 130.10,
129.15, 128.75, 70.56 (2C, CH-3,4); 68.54 (2C, CH2);
67.15 (CH-2,5).
4.11. 1,6-Dibenzoyl-3,4-di-O-isopropylidene-D-mannitol 10
yield 65 g (77%) of 12 as a colorless oil. The analysis data
A mixture of 9 (287 g; 735 mmol), dry acetone (600 mL),
ethyl orthoformate (159 mL; 1.3 equiv) and 4.5 M HCl in
DMF (5 mL) was set aside for 7 days at room temperature
under a CaCl2 protecting tube. After neutralization with
Et3N, the mixture was evaporated, the residue diluted with
ethyl acetate (900 mL) and washed with water
(2 · 300 mL), dried over MgSO4, filtrated, and evaporated.
Crystallization from ethylacetate–petrolether afforded
20
correspond with compound 3. ½aꢀD ¼ ꢂ11:2 (c 0.52,
MeOH).
4.14. (4R,5R)-[4,5-Bis(diisopropoxyphosphoryl)methoxy-
methyl]-2,2-dimethyl-1,3-dioxolane 13
The synthetic procedure and analysis data correspond with
20
compound 4. ½aꢀD ¼ ꢂ38:9 (c 0.50, MeOH).
242 g (95%) of 10 as a white powder. Mp 95–96 ꢁC.
20
½aꢀD ¼ þ32:3 (c 1, MeOH); For C23H26O8 (430.45) calcd:
C, 64.18; H, 6.09. Found: C, 63.92; H, 6.05. FABMS:
431.2 (MH+) (100). 1H NMR (500 MHz, DMSO-d6):
8.02 (d, 4H, Harom.); 7.65 (t, 2H, Harom.); 7.52 (t, 4H, Har-
om.); 5.59 (d, 1H, JOH,CH = 5.4, OH); 4.47 and 4.45 (2 · dd,
2H, J = 3.2 and 11.4, Hb-1,6); 4.30 and 4.26 (2 · dd, 2H,
J = 6.7 and 11.4, Ha-1,6); 4.10 and 4.05 (2 · d, 2H,
J = 9.4, H-3,4); 3.94 and 3.92 (2 · m, 2H, H-2,5); 1.34 (s,
3H, CH3); 13C NMR (125.7 MHz, DMSO-d6): 165.97
(CO); 133.49, 130.01, 129.48 (2C); 128.87 (2C); 109.44
(C-iPr); 79.54 and 69.82 (2C, CH–OH); 66.59 (O–CH2);
27.55 (CH3).
4.15. (2R,3R)-[1,4-Bis(diisopropoxyphosphoryl)methoxy]-
butane-2,3-diol 14
The synthetic procedure and analysis data correspond with
20
compound 5. ½aꢀD ¼ ꢂ2:4 (c 0.25, MeOH).
4.16. (2R,3R)-3-Hydroxy-1,4-[bis(diisopropoxyphosphor-
yl)methoxy]butan-2-yl benzoate 15
The synthetic procedure and analysis data correspond with
20
compound 6. ½aꢀD ¼ ꢂ5:2 (c 0.30, MeOH).
4.12. 3,4-Di-O-isopropylidene-D-mannitol 11
4.17. (2R,3R)-3-(Benzoyloxy)-1,4-[bis(diisopropoxyphos-
phoryl)methoxy]butan-2-yl mesylate 16
A catalytic amount of sodium methoxide (1 M) in metha-
nol (10 mL) was added to a solution of 10 (241 g;
560 mmol) in dry methanol (500) and stirred at room tem-
perature for 5 h. After neutralization with Dowex 50 · 8
(H+ form), the mixture was filtered, and Dowex was
washed with hot methanol. The solution was evaporated
and the residue was diluted with water and washed with
diethylether. The water layer was evaporated and co-evap-
The synthetic procedure and analysis data correspond with
20
compound 7. ½aꢀD ¼ ꢂ27:8 (c 0.45, MeOH).
5. General procedure for alkylation of nucleobases
orated with ethanol to give 115.6 g (93%) of 11 as a white
A solution of an appropriate nucleobase (17, 18, 2 equiv) in
dry DMF or DMSO (50 mL) was treated with Cs2CO3
(1 equiv) at room temperature under a CaCl2 protecting
tube for 1 h. The reaction mixture was then heated at
60 ꢁC and bisphosphonate 7, 16, or 33 (0.5 equiv) was
added portionvise. The mixture was stirred at 110 ꢁC for
48 h. The solvent was evaporated and the residue co-evapo-
rated with toluene (twice). The residue in 10% MeOH in
chloroform was filtered through a Celite pad, evaporated,
and purified on a silica gel column in chloroform–
methanol.
20
powder. Mp 86–87 ꢁC (lit. 85–88 ꢁC). ½aꢀD ¼ þ31:2 (c 0.8,
MeOH). For C9H18O6 (222.24) calcd: C, 48.64; H, 8.16.
Found: C, 48.58; H, 8.27. FABMS: 223.12 (MH+) (100).
1H NMR (500 MHz, DMSO-d6): 5.08 (d, 2H,
JOH,CH = 4.6, OH); 4.46 (t, 2H, JOH;CH ¼ 5:7, OH); 3.85
2
and 3.47 (2 · dd, 2 · 2H, O–CH-3,4); 3.54 (ddd, 2H,
J = 3.1 and 5.6 and 11.2, O–CH2); 3.35 (dt, 2H, J = 6.0
and 6.0 and 11.2, O–CH-2,5); 1.28 (s, 6H, CH3); 13C
NMR (125.7 MHz, DMSO-d6): 108.48 (C-iPr); 79.25 and
73.07 (4C, OCH); 63.18 (2C, OCH2); 27.44 (CH3).

S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
2243
5.1. (2R,3R)-2-Amino-6-chloro-9-{3-(benzoyloxy)-1,4-
[bis(diisopropoxyphosphoryl)methoxy]butan-2-yl}purine 19a
5.5. (2R,3R)-9-{1,4-[Bis(diisopropoxyphosphoryl)meth-
oxy]butan-2-yl-3-(tert-butyldimethylsilyloxy)}adenine 34
Column chromatography (silica gel, chloroform–methanol
Column chromatography (silica gel, chloroform–methanol
gradient 1–3%) afforded product 19a as a yellowish oil (2 g,
gradient 2–3%) afforded product 34 as a yellowish oil
20
20
yield 15%). ½aꢀD ¼ þ21:8 (c 0.3, MeOH); FABMS: 735.21
(0.31 g, yield 11%). ½aꢀD ¼ þ18:2 (c 0.59, MeOH); FABMS:
(MH+) (100). 1H NMR (500 MHz, CDCl3): 8.05–8.02
(m, 3H, Pu-8 and Bz-2); 7.64–7.59 (m, 1H, Bz-4); 7.49–
700.2 (MH+) (90). H NMR (500 MHz, CDCl3): 8.31 (s,
1
1H, Pu-2); 8.04 (s, 1H, Pu-8); 5.70 (br s, 2H, NH2); 4.87
0
0
7.45 (m, 2H, Bz-3); 5.75 (dt 1H, J4,5 ꢁ J4,5 = 3.7,
(ddd 1H, J3,2 = 3.7, J3,2 ꢁ J3,4 = 6.8 and 8.2, H-3); 4.72–
J4,3 = 8.2, H-4); 5.30 (br s, 2H, NH2); 5.23 (dt, 1H,
4.60 and 4.61–4.54 (2 · m, 4H, CH-iPr); 4.38 (m, 2H, H-2
and H-4); 3.97 (dd, 1H, Jgem = 10.1, J2 ,3 = 3.7, H-20);
0
0
J3,4 ꢁ J3,2 = 7.7, J3,2 = 3.4; H-3); 4.78-4.57 (m, 4H, CH-
iPr); 4.40 (dd, 1H, Jgem = 10.2, J2,3 = 7.4, H-2); 4.02 (dd,
3.69–3.54 (m, 4H, H-1 and H-6); 3.47 (dd, 1H, Jgem = 10.3,
1H, Jgem = 10.2, J2 ,3 = 3.4, H-20); 3.84 (dd, 1H,
J5,4 = 4.6, H-5); 3.28 (dd, 1H, Jgem = 10.3, J5 ,4 = 4.8, H-50);
0
0
Jgem = 11.1, J5,4 = 3.6, H-5); 3.70–3.59 (m, 4H, H-1 and
1.29–1.12 (m, 24H, CH3-iPr); 0.90 (s, 9H, C–(CH3)3); 0.07
and ꢂ0.04 (2 · s, 6H, CH3–Si). 13C NMR (125.7 MHz,
CDCl3): 155.26 (Pu-6); 152.64 (Pu-2); 150.05 (Pu-4);
141.35 (Pu-8); 119.39 (Pu-5); 74.34 (d, J5,P = 9.7, C-5);
71.00 (m, 4 · CH-iPr); 70.25 (C-4); 70.00 (d, J2,P = 11.5,
C-2); 66.31 and 65.98 (2 · d, JC,P = 167.1 and 168.1, C-1
and C-6); 56.91 (C-3); 25.77 (C-(CH3)3); 23.90 (m,
8 · CH3-iPr); ꢂ4.36 and ꢂ5.28 (CH3–Si).
H-6); 3.41 (dd, 1H, Jgem = 11.1, J5 ,4 = 3.8, H-50); 1.30–
0
1.17 (m, 24H, CH3-iPr). 13C NMR (125.7 MHz, CDCl3):
165.19 (CO); 159.10 (Pu-2); 153.90 (Pu-4); 151.40 (Pu-6);
142.63 (Pu-8); 133.63 (Bz-4); 129.81 (Bz-2); 129.25 (Bz-1);
128.59 (Bz-3); 125.02 (Pu-5); 71.42–71.18 (m, 4 · CH-iPr);
70.60 (C-4); 70.59 (d, J5,P = 12.2, C-5); 70.26 (d,
J2,P = 9.8, C-2); 66.38 and 66.24 (2 · d, JC,P = 169.0 and
167.5, C-1 and C-6); 54.68 (C-3); 24.03–23.90 (m,
8 · CH3-iPr).
5.6. (2R,3R)-9-{3-(Benzoyloxy)-1,4-[bis(diisopropoxyphos-
phoryl)methoxy]butan-2-yl}guanine 21a
5.2. (2S,3S)-2-Amino-6-chloro-9-{3-(benzoyloxy)-1,4-
[bis(diisopropoxyphosphoryl)methoxy]butan-2-yl}purine 19b
A solution of 19a (0.6 g, 0.8 mmol) in 80% acetic acid
(25 mL) was refluxed for 6 h. The solution was neutralized
with Et3N and the volatiles were evaporated in vacuo. Col-
umn chromatography (silica gel, chloroform–methanol
The synthetic procedure and analysis data correspond with
20
compound 19a. ½aꢀD ¼ ꢂ21:2 (c 0.4, MeOH).
gradient 1–12%) afforded compound 21a as a yellowish
20
oil (0.37 g, yield 64%). ½aꢀD ¼ þ20:3 (c 0.3, MeOH); FAB-
MS: 716.32 (MH+) (50). 1H NMR (500 MHz, CDCl3):
11.78 (br s, 1H, NH); 8.10–8.01 (m, 2H, Bz-2); 7.78 (s,
1H, Pu-8); 7.64–7.56 (m, 1H, Bz-4); 7.50–7.43 (m, 2H, Bz-
5.3. (2R,3R)-9-{3-(Benzoyloxy)-1,4-[bis(diisopropoxyphos-
phoryl)methoxy]butan-2-yl}adenine 20a
0
3); 6.54 (br s, 2H, NH2); 5.72 (dt 1H, J4,5 ꢁ J4,5 = 3.8,
Column chromatography (silica gel, chloroform–methanol
J4,3 = 8.2, H-4); 5.09 (dt, 1H, J3,4 ꢁ J3,2 = 7.3,
0
gradient 1–6%) afforded product 20a as a yellowish oil
J3,2 = 3.3; H-3); 4.77-4.59 (m, 4H, CH-iPr); 4.33 (dd, 1H,
20
(0.42 g, yield 17%). ½aꢀD ¼ þ18:7 (c 0.32, MeOH); FAB-
Jgem = 10.2, J2,3 = 6.8, H-2); 4.02 (dd, 1H, Jgem = 10.2,
MS: 700.45 (MH+) (90). 1H NMR (500 MHz, DMSO-
d6): 8.17 (s, 1H, Pu-8); 8.09 (s, 1H, Pu-2); 7.97 (m, 2H,
Bz-2); 7.69 (m, 1H, Bz-4); 7.54 (m, 2H, Bz-3); 7.25 (br s,
J2 ,3 = 3.3, H-2); 3.84 (dd, 1H, Jgem = 11.0, J5,4 = 4.0,
0
H-5); 3.53 (dd, 1H, Jgem = 11.0, J5,4 = 4.1, H-5); 3.71 and
3.69 (2 · d, 2 · 2H, JH,P = 8.7 and 8.2, H-1 and H-6);
1.29–1.19 (m, 24H, 8 · CH3-iPr). 13C NMR (125.7 MHz,
CDCl3): 165.18 (CO); 158.91 (Pu-6); 153.74 (Pu-2);
151.70 (Pu-4); 137.34 (Pu-8); 133.56 (Bz-4); 129.82 (Bz-2);
129.35 (Bz-1); 128.57 (Bz-3); 116.92 (Pu-5); 71.55–71.27
(m, 4 · CH-iPr); 70.88 (d, J2,P = 9.7, C-2); 70.85 (C-4);
70.78 (d, J5,P = 12.6, C-5); 66.38 and 66.24 (2 · d,
JC,P = 169.4 and 167.5, C-1 and C-6); 53.94 (C-3); 23.87,
23.88–24.05 (m, 8 · CH3-iPr).
0
2H, NH2); 5.77 (dt 1H, J4,5 ꢁ J4,5 = 3.3, J4,3 = 6.4, H-4);
0
5.14 (dt, 1H, J3,4 ꢁ J3,2 = 7.3, J3,2 = 3.3; H-3); 4.55 (m,
4H, CH-iPr); 4.37 (dd, 1H, Jgem = 10.2, J2,3 = 6.8, H-2);
4.06 (dd, 1H, Jgem = 10.5, J2 ,3 = 4.0, H-20); 3.83 (dd, 1H,
0
Jgem = 11.0, J5,4 = 4.0, H-5); 3.72 (dd, 1H, Jgem = 11.0,
0
J5 ,4 = 4.1, H-5); 3.70 and 3.67 (2 · d, 2 · 2H, JH,P = 8.7
and 8.2, H-1 and H-6); 1.15–1.04 (m, 24H, CH3-iPr). 13C
NMR (125.7 MHz, DMSO-d6): 164.89 (CO); 156.17 (Pu-
6); 152.53 (Pu-2); 149.77 (Pu-4); 140.25 (Pu-8); 133.76
(Bz-4); 129.60 (Bz-2); 129.29 (Bz-1); 128.80 (Bz-3); 118.91
(Pu-5); 71.01 (C-4); 70.72 (d, J5,P = 10.7, C-5); 70.37–
70.27 (m, 4 · CH-iPr); 69.46 (d, J2,P = 11.7, C-2); 65.25
and 64.99 (2 · d, JC,P = 164.1 and 163.6, C-1 and C-6);
54.38 (C-3); 23.90–23.58 (m, 8 · CH3-iPr).
5.7. (2S,3S)-9-{3-(Benzoyloxy)-1,4-[bis(diisopropoxyphos-
phoryl)methoxy]butan-2-yl}guanine 21b
The synthetic procedure and analysis data correspond with
20
compound 19a. ½aꢀD ¼ ꢂ20:2 (c 0.35, MeOH).
5.8. (2R,3R)-2,6-Diamino-9-{3-(hydroxy)-1,4-[bis(diisoprop-
oxyphosphoryl)methoxy]butan-2-yl}purine 22a
5.4. (2S,3S)-9-{3-(Benzoyloxy)-1,4-[bis(diisopropoxyphos-
phoryl)methoxy]butan-2-yl}adenine 20b
A solution of 19a (0.6 g, 0.8 mmol) in methanolic ammonia
(50 mL) was heated (100 ꢁC) in an autoclave for 13 h. The
solvent was then evaporated. Purification of the residue by
The synthetic procedure and analysis data correspond with
compound 20a. ½aꢀD ¼ ꢂ18:8 (c 0.4, MeOH).
20

2244
S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
column chromatography (silica gel, chloroform–methanol
6. General procedure for debenzoylation
gradient 1–11%) afforded compound 22a as a yellowish
20
foam (0.30, yield 62%). ½aꢀD ¼ þ17:3 (c 0.23, MeOH + 2
A catalytic amount of 1 M sodium methoxide in methanol
was added to a well-dried benzoylated compound (20a,b;
21a,b; 23a,b; 0.5–0.6 mmol) in dry methanol and stirred
at rt under CaCl2 protecting tube until the full conversion
of the starting compound. The mixture was neutralized
with HCl or CH3COOH, evaporated, and purified on a sil-
ica gel column in chloroform–methanol.
drops CHCl3); FABMS: 611.58 (MH+) (90). 1H NMR
(500 MHz, CDCl3): 7.63 (s, 1H, Pu-8); 6.04 (br s, 1H,
OH); 5.62 (br s, 2H, 6-NH2); 4.81 (br s, 2H, 2-NH2);
4.80–4.62 (m, 4H, CH-iPr); 4.59 (dt, 1H, J3,4 ꢁ J3,2 = 7.5,
0
0
J3,2 = 3.4; H-3); 4.32 (dt 1H, J4,5 ꢁ J4,5 = 3.7, J4,3 = 8.2,
H-4); 4.13 (dd, 1H, Jgem = 10.3, J2,3 = 7.7, H-2); 3.99 (dd,
1H, Jgem = 10.2, J2 ,3 = 3.3, H-20); 3.83 and 3.77 (2 · d,
0
2 · 2H, JH,P = 8.7 and 8.2, H-1 and H-6); 3.72 (dd, 1H,
Jgem = 11.0, J5,4 = 4.0, H-5); 3.65 (dd, 1H, Jgem = 11.0,
6.1. (2R,3R)-9-{3-(Hydroxy)-1,4-[bis(diisopropoxyphosphor-
yl)methoxy]butan-2-yl}adenine 24a
J5 ,4 = 4.1, H-50); 1.34–1.24 (m, 24H, CH3-iPr). 13C NMR
0
(125.7 MHz, CDCl3): 159.08 (Pu-2); 156.00 (Pu-6); 151.08
(Pu-4); 139.04 (Pu-8); 114.38 (Pu-5); 74.16 (d, J5,P = 10.0,
C-5); 71.24–71.09 (m, 4 · CH-iPr); 70.83 (d, J2,P = 10.5,
C-2); 70.20 (C-4); 66.41 and 66.05 (2 · d, JC, P = 165.0
and 163.6, C-1 and C-6); 57.68 (C-3); 24.08–23.87 (m,
8 · CH3-iPr).
Column chromatography (silica gel, chloroform–methanol
gradient 1–8%) afforded product 24a as a yellowish oil
20
(0.31 g, yield 86%). ½aꢀD ¼ þ12:4 (c 0.60, MeOH); FAB-
MS: 596.35 (MH+) (80). 1H NMR (500 MHz, DMSO-
d6): 8.12 (s, 1H, Pu-8); 8.10 (s, 1H, Pu-2); 7.20 (br s, 2H,
NH2); 5.63 (d, 1H, JOH,4 = 5.8, OH); 4.72 (ddd, 1H,
0
J3,2 = 3.8, J3,4 = 6.6, J3,2 = 9.2, H-3); 4.58 and 4.38
5.9. (2S,3S)-2,6-Diamino-9-{3-(hydroxy)-1,4-[bis(diisoprop-
oxyphosphoryl)methoxy]butan-2-yl}purine 22b
0
(2 · m, 4H, CH-iPr); 4.25 (t, 1H, J2,3 = J2,2 = 9.8, H-2a);
0
0
4.13 (m, 1H, H-4); 4.01 (dd, 1H, J2 ,2 = 10.5, J2 , 3 = 3.7,
H-20); 3.80–3.64 (2 · d, 2 · 2H, JH,P = 8.8 and 8.4, H-1
and H-6); 3.45 (dd, 1H, Jgem = 11.2, J5,4 = 4.0, H-5); 3.36
The synthetic procedure and analysis data correspond with
20
compound 22a. ½aꢀD ¼ ꢂ17:5 (c 0.20, MeOH).
(dd, 1H, Jgem = 11.2, J5 ,4 = 4.1, H-50); 1.23–1.02 (m,
0
24H, CH3-iPr). 13C NMR (125.7 MHz, DMSO-d6):
156.17 (Pu-6); 152.32 (Pu-2); 149.68 (Pu-4); 140.38 (Pu-8);
118.91 (Pu-5) 74.21 (d, J5,P = 10.0, C-5); 70.34 (m,
4 · CH-iPr); 70.22 (d, J2,P = 12.2, C-2); 68.86 (C-4); 65.44
(d, J6,P = 163.5, C-6); 64.94 (d, J1,P = 163.6, C-1); 55.93
(C-3); 24.02–23.67 (m, 8 · CH3-iPr).
5.10. (2R,3R)-2-Amino-9-{3-(benzoyloxy)-1,4-[bis(diiso-
propoxyphosphoryl)methoxy]butan-2-yl}-6-(cycloprop-
yl)aminopurine 23a
A solution of 19a (0.5 g, 0.68 mmol) in dry dioxane (20 mL)
was refluxed with cyclopropylamine (0.38 mL, 5.44 mmol)
for 13 h. The solvent was then evaporated. Purification of
the residue by column chromatography (silica gel, chloro-
6.2. (2S,3S)-9-{3-(Hydroxy)-1,4-[bis(diisopropoxyphosphor-
yl)methoxy]butan-2-yl}adenine 24b
form–methanol gradient 1–4%) afforded compound 23a as
20
a yellowish oil (0.38 g, yield 75%). ½aꢀD ¼ þ24:5 (c 0.25,
CHCl3); FABMS: 755.54 (MH+) (90). 1H NMR
(500 MHz, CDCl3): 8.06 (s, 1H, Bz-2); 7.69 (s, 1H, Pu-8);
7.60 (m, 1H, Bz-4); 7.47 (m, 2H, Bz-3); 5.80 (dt 1H,
The synthetic procedure and analysis data correspond with
compound 24a. ½aꢀD ¼ ꢂ12:6 (c 0.60, MeOH).
20
0
J4,5 ꢁ J4,5 = 3.8, J4,3 = 8.3, H-4); 5.09 (ddd, 1H,
0
J3,4 = 8.4, J3,2 = 7.4, J3,2 = 3.4; H-3); 4.83 (br s, 2H,
6.3. (2R,3R)-9-{3-(Hydroxy)-1,4-[bis(diisopropoxyphosphor-
yl)methoxy]butan-2-yl}guanine 25a
NH2); 4.74–4.55 (m, 4H, CH-iPr); 4.35 (dd, 1H, Jgem = 10.1,
J2,3 = 7.4, H-2); 3.97 (dd, 1H, Jgem = 10.1, J2 ,3 = 3.4, H-20);
0
3.80 (dd, 1H, Jgem = 11.0, J5,4 = 3.3, H-5); 3.70 and 3.65
(2 · d, 2 · 2H, JH,P = 8.7 and 8.2, H-1 and H-6); 3.42
Column chromatography (silica gel, chloroform–methanol
gradient 1–8%) afforded product 25a as a yellowish
20
(dd, 1H, Jgem = 11.0, J5 ,4 = 4.2, H-50); 2.98 (br s, 1H,
oil (0.26 g, yield 80%). ½aꢀD ¼ þ18:2 (c 0.2, CHCl3);
0
CHcyclopropyl); 1.29–1.16 (m, 24H, CH3-iPr); 0.90–0.82 (m,
2H, CH2); 0.64–0.59 (m, 2H, CH2). 13C NMR
(125.7 MHz, CDCl3): 165.26 (CO); 159.91 (Pu-2); 156.19
(Pu-6); 151.05 (Pu-4); 137.62 (Pu-8); 133.49 (Bz-4); 129.81
(Bz-2); 129.39 (Bz-1); 128.51 (Bz-3); 114.25 (Pu-5); 71.26–
71.07 (m, 4 · CH-iPr); 70.80 (d, J5,P = 12.3, C-5); 70.77
(d, J2,P = 11.3, C-2); 70.75 (C-4); 66.21 and 66.15 (2 · d,
JC,P = 168.1 and 167.1, C-1 and C-6); 54.07 (C-30); 24.02–
23.77 (m, 8 · CH3, CHcyclopropyl); 7.32 and 6.47 (2 · CH2).
FABMS: 612.23 (MH+) (50). 1H NMR (500 MHz,
DMSO-d6): 10.73 (br s, 1H, NH); 7.68 (s, 1H, Pu-8); 6.59
(br s, 2H, NH2); 5.60 (d, 1H, JOH,H-4 = 5.8, OH); 4.62–
4.52 (m, 4H, CH-iPr); 4.40 (dt, 1H, J3,4 ꢁ J3,2 = 7.5,
0
J3,2 = 3.4; H-3); 4.12 (dd, 1H, Jgem = 10.4, J2,3 = 6.6, H-
0
2); 4.03 (dt 1H, J4,5 ꢁ J4,5 = 3.7, J4,3 = 8.2, H-4); 3.94
(dd, 1H, Jgem = 10.5, J2 ,3 = 3.6, H-20); 3.77 and 3.61
0
(2 · d, 2 · 2H, JH,P = 8.7 and 8.2, H-1 and H-6); 3.45
(dd, 1H, Jgem = 11.0, J5,4 = 4.0, H-5); 3.40 (dd, 1H,
0
Jgem = 11.0, J5 ,4 = 4.1, H-5); 1.23–1.10 (m, 24H, CH3-
5.11. (2S,3S)-2-Amino-9-{3-(benzoyloxy)-1,4-[bis(diisoprop-
oxyphosphoryl)methoxy]butan-2-yl}-6-(cyclopropyl)amino-
purine 23b
iPr). 13C NMR (125.7 MHz, DMSO-d6): 156.83 (Pu-6);
153.63 (Pu-2); 151.16 (Pu-4); 136.72 (Pu-8); 116.54 (Pu-5);
74.13 (d, JC,P = 12.6, C-5); 70.50–70.20 (m, 4 · CH-iPr,
C-2); 68.86 (C-4); 65.48 and 65.01 (2 · d, JC,P = 165.0
and 163.6, C-1 and C-6); 55.52 (C-3); 24.00–23.60 (m,
8 · CH3-iPr).
The synthetic procedure and analysis data correspond with
20
compound 23a. ½aꢀD ¼ ꢂ24:6 (c 0.20, CHCl3).

S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
2245
6.4. (2S,3S)-9-{3-(Hydroxy)-1,4-[bis(diisopropoxyphosphor-
yl)methoxy]butan-2-yl}guanine 25b
evaporated to dryness, and the residue dissolved in water
applied onto a column of Dowex 50 · 8 in H+ form and
washed with water.
The synthetic procedure and analysis data correspond with
20
compound 25a. ½aꢀD ¼ ꢂ18:9 (c 0.20, CHCl3).
(A) Elution with water, evaporation in vacuo, and crys-
tallization from water/ethanol afforded free bisphos-
phonic acids 27a; 28a,b; 29a,b; 30a.
(B) Elution with dilute ammonia and evaporation
afforded ammonium salts, which were applied onto
Dowex 50 (Na+ form). Elution with water and evap-
oration gave bisphosphonic acids 27b and 30b as tet-
rasodium salts. Precipitation of free bisphosphonic
acids was obtained after the treatment of sodium
salts with HCl in water.
6.5. (2R,3R)-2-Amino-6-(cyclopropyl)amino-9-{3-(hydroxy)-
1,4-[bis(diisopropoxyphosphoryl)methoxy]butan-2-yl}purine
26a
Column chromatography (silica gel, chloroform–methanol
gradient 1–5%) afforded product 26a as a yellowish oil
20
(0.26 g, yield 79%). ½aꢀD ¼ þ19:9 (c 0.22, CHCl3); FABMS:
651.45 (MH+) (80). H NMR (500 MHz, CDCl3): 7.63 (s,
1
1H, Pu-8); 6.07 (br s, 1H, OH); 5.67 (br s, 2H, NH2);
4.80–4.62 (m, 4H, CH-iPr); 4.60 (ddd, 1H, J3,4 ꢁ J3,2
=
7.1. (2R,3R)-2,6-Diamino-9-{3-(hydroxy)-1,4-[bis(phospho-
nomethoxy)]butan-2-yl}purine 27a
0
0
7.5, J3,2 = 3.4, H-3); 4.26 (dt, 1H, J4,5 ꢁ J4,5 = 3.7,
J4,3 = 8.2, H-4); 4.15 (dd, 1H, Jgem = 10.1, J2,3 = 7.5, H-
2); 4.01 (dd, 1H, Jgem = 10.2, J2 ,3 = 3.3, H-20); 3.83 and
White solid (0.18 g, yield 83%), mp 142.1 ꢁC (D).
0
20
3.77 (2 · d, 2 · 2H, JH,P = 8.7 and 8.2, H-1 and H-6);
½aꢀD ¼ þ19:2 (c 0.34, H2O). For C11H20N6O9P2 (442.26)
3.72 (dd, 1H, Jgem = 11.0, J5,4 = 4.0, H-5); 3.65 (dd, 1H,
calcd: C, 29.87; H, 4.56; N, 19.00; P, 14.01. Found: C,
29.95; H, 4.62; N, 19.12; P, 13.95. FABMS: 443.3 (MH+)
Jgem = 11.0, J5 ,4 = 4.1, H-50); 2.95 (br s, 1H, CHcyclopropyl);
0
1
1.34-1.24 (m, 24H, CH3-iPr); 0.85 (m, 2H, CH2); 0.60
(m, 2H, CH2). 13C NMR (125.7 MHz, CDCl3): 159.72
(Pu-2); 156.35 (Pu-6); 151.18 (Pu-4); 139.24 (Pu-8); 114.48
(Pu-5) 74.14 (d, J5,P = 10.0, C-5); 71.11 (m, 4 · CH-iPr);
70.81 (d, J2,P = 10.5, C-2); 70.20 (C-4); 66.41 (d,
J6,P = 163.5, C-6); 66.05 (d, J1,P = 163.6, C-1); 57.68 (C-
3); 24.05–23.87 (m, 8 · CH3, CHcyclopropyl); 7.31 and 6.49
(2 · CH2).
(40). H NMR (500 MHz, D2O): 8.20 (s, 1H, Pu-8); 4.82
0
(dt, 1H, J3,4 ꢁ J3,2 = 7.4, J3,2 = 3.2, H-3); 4.32 (ddd, 1H,
0
J4,3 = 7.2, J4,5 = 5.2, J4,5 = 3.8, H-4); 4.30 (dd, 1H,
Jgem = 11.0, J2,3 = 7.7, H-2); 4.09 (dd, 1H, Jgem = 11.0,
J2 ,3 = 3.3, H-20); 3.80 (dd, 1H, Jgem = 13.3, J1,P = 8.8, H-
0
1); 3.73 (dd, 1H, Jgem = 13.3, J1 ,P = 9.0, H-10); 3.65–3.61
0
(m, 3H, 6, 60, 5); 3.44 (dd, 1H, Jgem = 10.8, J5 ,4 = 5.2, H-
0
50). 13C NMR (125.7 MHz, D2O): 153.03 (Pu-2); 151.02
(Pu-6); 150.94 (Pu-4); 142.27 (Pu-8); 111.17 (Pu-5) 73.74
(d, J5,P = 12.3, C-5); 70.53 (d, J2,P = 12.7, C-2); 69.22 (C-
4); 67.52 and 67.47 (2 · d, JC,P = 157.8 and 157.5, C-1
and C-6); 56.85 (C-3). UV spectrum: (0.01 M HCl)
6.6. (2S,3S)-2-Amino-6-(cyclopropyl)amino-9-{3-(hydroxy)-
1,4-[bis(diisopropoxyphosphoryl)methoxy]butan-2-yl}purine
26b
k
max = 250 nm (emax = 7804); (H2O)
k
k
max = 251 nm
max = 254 nm
The synthetic procedure and analysis data correspond with
compound 26a. ½aꢀD ¼ ꢂ20:1 (c 0.20, CHCl3).
(emax = 7286);
(emax = 6562).
(0.01 M
NaOH)
20
6.7. (2R,3R)-9-{3-(Hydroxy)-1,4-[bis(diisopropoxyphosphor-
yl)methoxy]butan-2-yl}adenine 35
7.2. (2S,3S)-2,6-Diamino-9-{3-(hydroxy)-1,4-[bis(phospho-
nomethoxy)]butan-2-yl}purine 27b
An oven-dried round bottomed flask under an argon atmo-
sphere was charged with 34 (110mg, 0.15 mmol) and 1 M
solution of TBAF in THF (0.85 mL, 0.85 mmol). The reac-
tion was aged at rt for 2 h and concentrated. Purification
on thin layer chromatography with UV silica gel sorbent
The synthetic procedure (followed by method B), NMR
and UV data correspond with compound 27a. White solid
20
(0.12 g, yield 88%). ½aꢀD ¼ ꢂ19:0 (c 0.20, H2O).
7.3. (2R,3R)-9-{3-(Hydroxy)-1,4-[bis(phosphonomethoxy)]-
butan-2-yl}adenine 28a
(eluent 10% MeOH in CHCl3) afforded pure 35 as a yellow-
20
ish oil (90mg, quant. yield). ½aꢀD ¼ þ12:7 (c 0.71, MeOH).
For C23H43N5O9P2 (595.56) calcd: C, 46.38; H, 7.28; N,
11.76; P, 10.40. Found: C, 46.43; H, 7.35; N, 11.72; P,
10.50. Other analysis data (FABMS and NMR) corre-
spond with compound 24a.
White solid (0.21 g, yield 93%), mp 147.2 ꢁC (D).
20
½aꢀD ¼ þ12:2 (c 0.26, H2O). For C11H19N5O9P2 (427.24)
calcd: C, 30.92; H, 4.48; N, 16.39; P, 14.50. Found: C,
30.98; H, 4.56; N, 16.35; P, 14.61. FABMS: 428.3 (MH+)
1
(40). H NMR (500 MHz, D2O): 8.56 (s, 1H, Pu-8); 8.41
0
(s, 1H, Pu-2); 5.04 (dt, 1H, J3,4 ꢁ J3,2 = 7.5, J3,2 = 3.3,
0
7. Transformation of esters to free phosphonic acids—
general procedure
H-3); 4.44 (ddd, 1H, J4,3 = 7.6, J4,5 = 5.2, J4,5 = 3.7, H-
4); 4.34 (dd, 1H, Jgem = 11.1, J2,3 = 7.4, H-2); 4.10 (dd,
1H, Jgem = 11.0, J2 ,3 = 3.4, H-20); 3.73 (dd, 1H,
0
The dried esters (22a,b;24a,b;25a,b;26a,b; 0.4–0.5 mmol),
acetonitrile (15 mL) and BrSiMe3 (2–3 mL) were stirred
at room temperature overnight. After evaporation and
co-distillation with acetonitrile, the residue was treated
with water and aqueous ammonia. The mixture was
Jgem = 13.4, J1,P = 8.8, H-1); 3.69 (dd, 1H, Jgem = 13.4,
0
J1 ,P = 8.8, H-10); 3.63 (m, 1H, H-5); 3.58 (m, 2H, 6 and
60); 3.45 (dd, 1H, Jgem = 10.8, J5 ,4 = 5.2, H-50). 13C
0
NMR (125.7 MHz, D2O): 150.54 (Pu-6); 149.27 (Pu-4);
145.07 (Pu-8); 144.94 (Pu-2); 118.55 (Pu-5) 73.86

2246
S. Vrbkova´ et al. / Tetrahedron: Asymmetry 18 (2007) 2233–2247
(d, J5,P = 11.7, C-5); 70.76 (d, J2,P = 12.2, C-2); 69.26
(C-4); 67.50 and 67.38 (2 · d, JC,P = 158.2 and 157.7,
C-1 and C-6); 57.36 (C-3). UV spectrum: (0.01 M HCl)
k
max = 253 nm and 292 nm (emax = 9216 and 11,408);
(H2O) max = 253 nm and 290 nm (emax = 9156 and
k
11,394); (0.01 M NaOH) kmax = 258 nm and 282 nm
(emax = 7590 and 12,546).
k
max = 257 nm (emax = 12,992); (H2O)
kmax = 258 nm
(emax = 13,274); (0.01 M NaOH) kmax = 259 nm (emax
=
13,122).
7.8. (2S,3S)-2-Amino-6-(cyclopropyl)amino-9-{3-(hydroxy)-
1,4-[bis(phosphonomethoxy)]butan-2-yl}-purine 30b
7.4. (2S,3S)-9-{3-(Hydroxy)-1,4-[bis(phosphonomethoxy)]-
butan-2-yl}adenine 28b
The synthetic procedure (followed by method B), NMR
and UV data correspond with compound 30a. White solid
(0.11 g, yield 88%). ½aꢀD ¼ ꢂ13:1 (c 0.16, H2O).
The synthetic procedure and analysis data correspond with
compound 28a. ½aꢀD ¼ ꢂ11:9 (c 0.2, H2O).
20
20
7.5. (2R,3R)-9-{3-(Hydroxy)-1,4-[bis(phosphonomethoxy)]-
butan-2-yl}guanine 29a
Acknowledgments
White solid (0.12 g, yield 63%), mp 163.3 ꢁC (D).
20
This work is a part of the research project Z4 055 0506. It
was supported by the ‘Centre for New Antivirals and
Antineoplastics’ (1M0508), by the Program of Targeted
Projects of Academy of Sciences of the Czech Republic
(1QS400550501) and by Gilead Sciences, Inc. (Foster City,
CA, USA). We would like to thank the team of Dr. P.
½aꢀD ¼ þ10:9 (c 0.23, H2O). For C11H19N5O10P2 (443.24)
calcd: C, 29.81; H, 4.32; N, 15.80; P, 13.98. Found: C,
29.92; H, 4.36; N, 15.85; P, 13.87. FABMS: 444.2 (MH+)
1
(60). H NMR (500 MHz, D2O): 9.08 (br s, 1H, Pu-8);
0
5.00 (dt, 1H, J3,4 ꢁ J3,2 = 6.9, J3,2 = 3.3, H-3); 4.38 (dt,
0
1H, J4,3 = 7.1, J4,5 ꢁ J4,5 = 4.6, H-4); 4.29 (dd, 1H,
Malonˇ for measurement of CD spectra, and also to Dr.
Jgem = 11.0, J2,3 = 6.6, H-2); 4.04 (dd, 1H, Jgem = 11.0,
J2 ,3 = 3.3, H-20); 3.74 (m, 2H, H-1); 3.70 (dd, 1H,
ˇ
0
´
´
V. Kasˇicˇka and Dr. V. Solınova for performing the CZE
measurements.
Jgem = 10.7, J5,4 = 4.2, H-5); 3.65 (d, 2H, J = 6.6, H-6);
3.58 (dd, 1H, Jgem = 10.7, J5 ,4 = 5.0, H-50). 13C NMR
0
(125.7 MHz, D2O): 155.98 and 155.96 (Pu-6 and Pu-2);
150.86 (Pu-4); 138.34 (Pu-8); 108.26 (Pu-5) 73.77 (d,
J5,P = 12.1, C-5); 69.98 (d, J2,P = 12.5, C-2); 68.80 (C-4);
67.43 and 67.39 (2 · d, JC,P = 158.3 and 158.0, C-1 and
C-6); 57.76 (C-3). UV spectrum: (0.01 M HCl)
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20
½aꢀD ¼ þ12:9 (c 0.25, H2O). For C14H24N6O9P2 (482.32)
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