Electrophile-promoted addition of hydroxymethylphosphonate to 4′,5′-didehydronucleosides: a way to novel isosteric analogues of 5′-nucleotides

Article abstract of DOI:10.1016/j.tet.2007.03.059

An electrophile-promoted addition of dialkyl-hydroxymethylphosphonate to the protected 4′,5′-didehydronucleosides resulted in an epimeric mixture of 4′-dialkylphosphonomethoxy derivatives of 2′,5′-dideoxynucleosides, novel analogues of 2′-deoxynucleoside 5′-monophosphates. Several types of electrophiles (pyridinium tosylate, NIS, NBS, MCPBA and others) were evaluated in addition reactions with 4′,5′-didehydrothymidine. Out of them, pyridinium tosylate was found to have a practical usefulness in these transformations. Its use has led to the preparation of a series of 4′-phosphonomethoxy derivatives of common 2′-deoxynucleosides. On biological screening, these free phosphonic acids exerted no significant cytostatic or antiviral activity.

Full text of DOI:10.1016/j.tet.2007.03.059

Tetrahedron 63 (2007) 4516–4534
Electrophile-promoted addition of hydroxymethylphosphonate
to 40,50-didehydronucleosides: a way to novel isosteric
analogues of 50-nucleotides
*
Zdenek Tocık, Ivana Dvorakova, Radek Liboska, Milos Budesınsky,
ˇ
ˇ
ꢁ
ˇ
ꢀꢁ
ꢀꢁ
ꢁ
ꢀ
ꢁ
*
ꢁ
Milena Masojıdkova and Ivan Rosenberg
ꢁ
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo 2,
16610 Prague 6, Czech Republic
Received 18 July 2006; revised 19 February 2007; accepted 8 March 2007
Available online 12 March 2007
Abstract—An electrophile-promoted addition of dialkyl-hydroxymethylphosphonate to the protected 40,50-didehydronucleosides resulted in
an epimeric mixture of 40-dialkylphosphonomethoxy derivatives of 20,50-dideoxynucleosides, novel analogues of 20-deoxynucleoside 50-
monophosphates. Several types of electrophiles (pyridinium tosylate, NIS, NBS, MCPBA and others) were evaluated in addition reactions
with 40,50-didehydrothymidine. Out of them, pyridinium tosylate was found to have a practical usefulness in these transformations. Its use
has led to the preparation of a series of 40-phosphonomethoxy derivatives of common 20-deoxynucleosides. On biological screening, these
free phosphonic acids exerted no significant cytostatic or antiviral activity.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
activity of these compounds.3,4 This was proved on finding
remarkable antiviral properties of a family of acyclic nu-
cleoside phosphonic acids,5–7 analogues of 50-nucleotides.
Among them, three phosphonate drugs bearing just the P–
C–O moiety are in clinical use (Fig. 1): Vistide [(S)-1-(1-cy-
tosinyl)-3-hydroxy-2-propoxymethylphosphonic acid (1)]
for the treatment of CMV-induced retinitis, Viread [(R)-1-
(9-adeninyl)-2-propoxymethylphosphonic acid (2)] for the
treatment of HIVand Hepsera [2-(9-adeninyl)ethoxymethyl-
phosphonic acid (3)] for the treatment of chronic Hepatitis B.
In addition, the isosteric phosphonate analogues of 20-di-
deoxynucleoside 50-phosphate 4a and 20,30-dideoxydide-
hydronucleoside 50-phosphate 5a,4,8 bearing 40C–O–C–P
linkagewere found to possess antiretroviral activity, and their
There have been numerous attempts to accomplish structural
alterations of the phosphate moiety in nucleotides and
oligonucleotides, stimulated especially by the need to over-
come its inherent susceptibility to in vivo cleavage by
phosphomonoesterases, nucleotidases and nucleases.1,2 The
phosphonate analogues containing the enzyme-stable ether
P–C–O moiety instead of the ester P–O emerged as promis-
ing candidates in this respect. Isopolarity and isostericity of
these compounds with natural 50-nucleotides, as well as the
presence of an oxygen atom-containing moiety mimicking
the phosphoester oxygen atom in the proximity of the phos-
phoryl residue, seems to be of key importance for biological
C
A
A
(HO)2P
O
O
(HO)2P
O
(HO)2P
O
(HO)2P
O
O
O
(HO)2P
O
O
B
O
B
X
X
a X=O
5a,b
CH3
1
4a,b
2
3
b X=CH2
OH
O
(HO)2P
O
(HO)2P
O
B
O
B
H3C
O
B
O
O
O
O
H3C
H3C
(HO)2P
6
21b-25b
OH
OH
21a-25a
OH
Figure 1. Examples of structurally diverse nucleoside phosphonic acids.
Keywords: Phosphonate analogues; 40-Phosphonomethoxy derivatives; Isosteric phosphonates; Electrophile-promoted addition.
* Corresponding authors. Tel.: +420 220 183 381; fax: +420 220 183 578; e-mail addresses: tocik@uochb.cas.cz; ivan@uochb.cas.cz
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.03.059

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4517
carba congeners 4b and 5b9 were also prepared (Fig. 1). Over
recent years we have been dealing extensively with both the
synthetic methods leading to a range of novel phosphonate-
based analogues of mono- and oligonucleotides,10–17 and
with their biochemical and biophysical evaluation.18–22 We
describe here the compounds 21–25 (Fig. 1) isosteric
with 40-methyl-20-deoxynucleoside 50-phosphates 623 and
bearing 40-phosphonomethoxy moiety (P–C–O), similar to
compound 4a.
nucleosides was seen, therefore, in the exploitation of
40,50-didehydronucleosides 9 (Schemes 1 and 2)24 studied
by Moffatt,25,26 and also by Prisbe,27 Lerner,28 Robins,29
and Reese.30 We expected compounds 9, in keeping with re-
sults of reactions performed earlier with nucleosidic com-
pounds having the acyclic type of vinyl ether linkage,31
cyclic type,4,8 or exocyclic double bond of the vinyl ether
moiety,32,33 to be suitable for an electrophile-promoted
addition of hydroxymethylphosphonate. In our study, we
explored the use of pyridinium p-toluenesulfonate (PTS),
N-iodosuccinimide (NIS), N-bromosuccinimide (NBS) and
m-chloroperoxybenzoic acid (MCPBA) as electrophiles,
and dialkyl-hydroxymethylphosphonates as nucleophiles.
2. Results and discussion
In general, electrophilic addition (Scheme 1) of a nucleophile
to 40,50-didehydronucleosides proceeds via electrophile-
mediated formation of 40-epimeric three-membered spiro-
intermediates, which subsequently undergo an attack by
a nucleophile on the 40-position to provide the desired prod-
uct as a mixture of 40-epimers. A plausible synthetic route to
the preparation of 40-phosphonomethoxy derivatives of
2.1. Phosphonylation reactions in thymidine series
The starting compounds 1-(2,5-dideoxy-b-D-glycero-pent-
4-enofuranosyl)thymine (40,50-didehydrothymidine) 9a27
(Scheme 2) and the 30-O-tert-butyldimethylsilyl derivative
9b27 reacted smoothly with an excess of dialkyl-
Nu
B
E
E
B
B
Nu
B
B
O
O
O
O
O
E
E
E
E
Nu
OR
Nu
OR
OR
OR
OR
E = H+, I+, Br+
Scheme 1. Electrophile-mediated addition of nucleophile to exocyclic vinyl ether moiety.
X
B
B
HO
B
PTS
O
O
O
-HX
R2O
P
O
OH
R2O
10
R1O
R1O
R1O
8
7
9
a B=A, R1=TBDPS
b B=C, R1=TBDPS
c B=GiBu, R1=H
a B=T, R1=H
a B=A, R1=TBDPS, X=Br; 48%
b B=C, R1=TBDPS, X=Br; 66%
c B=GiBu, R1=H, X=I; 40%
a R2=CH3
b B=T, R1=TBDMS
b R2=i-C3H7
c B=T, R1=TBDPS; 79%
d B=U, R1=H
e B=U, R1=TBDMS; 65%
f B=A, R1=TBDPS; 55%
g B=C, R1=TBDPS; 67%
h B=GiBu, R1=H; 32%
i B=GiBu, R1=TBDMS; 70%
R2O
P
O
O
B
H3C
B
O
R2O
O
+
O
P
R2O
H3C
O
b
OR1
R2O
OR1
a
H3C
B
(HO)2P
O
O
B
O
O
+
11 B=T, R1=H, R2=i-C3H7; 35%
O
H3C
12 B=T, R1=TBDMS, R2=i-C3H7; 51%
13 B=T, R1=H, R2=CH3; 73%
(HO)2P
O
a
HO
b
HO
14 B=T, R1=TBDMS, R2=CH3; 78%
15 B=U, R1=TBDMS, R2=CH3; 68%
16 B=C, R1=TBDPS, R2=CH3; 53%
17 B=A, R1=TBDPS, R2=CH3; 47%
18 B=GiBu, R 1=TBDMS, R2=CH3; 38%
21 B=T; 21a 38%, 21b 35%
22 B=U; 22a,b 75%
23 B=C; 23a 43%, 23b 73%
24 B=G; 24a,b 21%
25 B=A; 25a,b 48%
N
N
N
N
NH2
N
N
N
O P
N
N
O
O
N
CH3O
CH3O
CH3O
P
3
P
O
15a
O
O
23a
O
O
CH3O
O
50%
H3C
19a
H3C
20a
NH3
OTBDMS
OTBDMS
41%, from 15a
Scheme 2. Synthesis of 40-C-phosphonomethoxynucleosides.

4518
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
(R2O)2P(O)CH2O
hydroxymethylphosphonate 10a or 10b in dichloromethane
at rt in the presence of PTS as a proton source added as the
last component, to provide expected phosphonates 11–14 as
40-epimeric mixtures. Considerably better yields of the prod-
ucts were obtained with dimethyl ester 10a. A slight advan-
tage over the use of the unprotected starting compound 9a
has been observed (somewhat better yields) in the use of
30-O-silylated derivative 9b (may be due to a better solubility
of 9b than 9a in dichloromethane). Resulting pairs of diaste-
reoisomers 11a,b–14a,b were all separable on silica gel. The
yields and isomeric ratios for the products 11–14, along with
the data obtained with non-thymidine compounds 15–18
(see below) are provided in Table 1.
B
2'
B
3'
CH3
4'
O
O
1'
4'
1'
OR1
CH3
(R2O)2P(O)CH2O
β-
OR1
-threo
D
-erythro
α-
L
80-95% of C2'-endo
70-90% of C3'-endo
Figure 3. Preferred conformations of pentose ring for a-L-threo and b-
D-erythro diastereoisomers 11–18.
%S ¼ ½ðJð10;20Þ þ Jð10;200Þ ꢀ 9:8Þ=5:9ꢁ ꢂ 100
ð1Þ
It is worth mentioning that compounds 14a and 14b proved
exploitable for obtaining the building blocks for the prepara-
tion of modified thymidine oligonucleotides.35
The assignments of the 30-O-silylated diastereoisomers with
the configuration a-L-threo and b-D-erythro, respectively,
was made by 2D-ROESY NMR spectroscopy, as is shown
for compounds 14a and 14b in Figure 2. The observed
NOE contacts between H-6 of the base and pentose proton
H-20 and H-30confirm b-orientation of base in both diaste-
reoisomers 14a, 14b, and allow for distinguishing the hydro-
gens H-20 and H-200. Configuration of the C(4)-methyl group
could be derived from NOE contacts of its protons with H-10
and H-20 in diastereoisomer 14a and/or with H-30 and H-6 in
diastereoisomer 14b. The vicinal coupling pattern of the
pentose ring protons shows significant difference in diaste-
reoisomeric pairs. Although the absence of H-40 does not al-
low for the use of complete pseudorotational conformation
calculation for the pentose ring, the application of empirical
relation (Eq. 1) suggested by Rinkel and Altona34 and ap-
plied under similar conditions by Chattopadhyaya33 allowed
us to estimate the S-type (80–95% of C20-endo) as preferred
for all a-L-threo diastereoisomers and the N-type (70–90%
of C30-endo) for b-D-erythro diastereoisomers 11–18, as it
is illustrated in Figure 3.
Attempts to employ tetrazole, BF3–etherate, or N-methyl-
imidazolium trifluoromethanesulfonate in the role of PTS
did not afford the phosphonate compounds, and led to
decomposition of the starting 40,50-didehydrothymidine
derivative. An attempt to convert the 40,50-didehydro-20,30-
dideoxythymidine (26)27 and (2-methylene-5(R)-(thymin-
1-yl))-2,5-dihydrofuran (27)36 into the corresponding
40-phosphonomethoxy derivatives using PTS and 10a com-
pletely failed (Scheme 3). Only 2-methyl-5-(thymin-1-yl)-
furan (28) as a predominant product, along with thymine
as a minor product, were identified by 1H NMR. It is known
that ddTand d4Tare acid-sensitive compounds; in the case of
compound 27, Reese37 reported its lability in both basic and
acidic conditions, with formation of furan derivative 28 in
a high yield in both cases. Assuming this, and the results ob-
served, we did not go into further studies and quantification
of the reactions with 26 and 27.
T
T
PTS
10a
PTS
10a
O
O
O
H3C
T
Table 1. Yields and 40-epimeric ratios of dimethyl-phosphonates 11–18
27
26
28
Compound
Base
Yield (%)
Ratio (a:b)a
Scheme 3.
11
12
13
14
15
16
17
18
T
T
T
T
U
C
35
51
73
78
68
53
47
38
17:83b
44:56b
29:71b
40:60b
49:51b
20:80c
8:92c
In general, PTS activation was clearly the most straightfor-
ward, considering the practical accessibility of the desired
phosphonate compounds. It was found difficult to modulate
favourably the yield and epimeric composition by the condi-
tions influencing the PTS-mediated electrophilic addition,
e.g., by increasing the acidity of the PTS (prolonged drying
in vacuo), the presence of molecular sieves in the reactions,
etc. No conclusions on the positive role of such changes
could be drawn.
A
Gi-Bu
40:60c
a
Epimers assigned from NMR spectra.
Silica gel separable.
Silica gel unseparable.
b
c
In a similar way as with the PTS activation, though with
somewhat lower overall yields (26–48%), the reactions of
9a–c with 10a and 10b promoted by NIS were carried out
to give (Scheme 4) the desired 50-deoxy-50-halo derivatives
29–33, and in the same way, 9b afforded 34a,b in reaction
promoted by NBS (41%). The principal difference from
the above-mentioned reactions using PTS was the high pre-
dominance of the b-D-erythro isomers 29b–33b over a-L-
threo isomers 29a–33a. Actually, with a single exception
of the 50-bromo derivative 34 (with the ratio of isomers
34a–34b¼1:5) all other minor isomers 29a–33a could not
be fully characterized by NMR spectra due to their too low
O
O
H3C
H3C
H
NH
NH
H
N
H
O
N
H
O
O
P
CH3O
O
CH3
H
CH2
O
O
O
P
H
H
H
H
H
OCH3
H3C
TBDMSO
CH3O
CH2
O
TBDMSO
14a
14b
OCH3
Figure 2. The observed proton NOE contacts (shown with arrows) impor-
tant for structure determination of diastereoisomers 14a and 14b.

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4519
R2O
R2O
minor
major
O
CH3O
CH3O
I
P
P
O
O
T
T
T
O
T
O
O
O
+
MCPBA
10a
O
NIS
10a or
10b
O
P
R2O
O
I
HO
OR1
R2O
OR1
b
R1O
R1O
37
a
9
NBS
a B=T, R1=H
29 B=T, R1=H, R2=i-C3H7; 29b: 36%
10b
b B=T, R1=TBDMS
c B=T, R1=TBDPS
30 B=T, R1=TBDMS, R2=i-C3H7; 30b: 26%
31 B=T, R1=TBDPS, R2=i-C3H7; 31b: 35%
32 B=T, R1=TBDMS, R2=CH3; 32b: 48%
33 B=T, R1=TBDPS, R2=CH3; 33b: 37%
minor
O
major
O
iPrO
Br
P
O
T
T
+
iPrO
iPrO
O
O
P
O
Br
OTBDMS iPrO
34a
OTBDMS
34b
mixt., 41%
N3
I
T
T
O
O
O
P
O
P
NaN3
NaCN
33b
iPrO
iPrO
HO
NaN3
NaN3
32b
29b
30b
O
O
36
OR1
OR1
CH3O
35
a R1=TBDMS; 51%
a R1=H
b R1=TBDMS; 29%
b R1=TBDPS; 46%
Scheme 4. Reaction of 40,50-didehydrothymidine derivatives with various electrophiles.
population (<10%). Obviously, the predominant type of the
supposed epiiodonium (epibromonium) intermediate
(Scheme 1) strongly favours the form with halogen atom ori-
entated to b-face, which governs the opening of the three-
membered cycle from a-face by the hydroxy function of
10. The presence of iodine atom at C-50 in compounds 29–
33 is manifested by characteristic upfield signal of CH2–I
in the 13C NMR spectra around 5 ppm. A characteristic fea-
ture in the 1H NMR spectra for the compounds 29–33 is the
coupling pattern of the pentose protons in positions 10,20 and
30, which corresponds to that observed for b isomers (b-D-er-
ythro) of the above discussed series 11–18, and indicates
a preference of N-type pentose conformer (60–70% of
C30-endo). The bromine atom at C-50 in diastereoisomeric
pair 34a, 34b is evidenced in the 13C NMR spectra
azido compound 35c. In case of product 35b, obtained in
a low yield and contaminated, the IR, 1H and 13C NMR spec-
tra were obtained and could be interpreted; in the latter,
dCH ꢀN at 50.22 ppm confirms the presence of the azido de-
2
rivative. On treatment of dimethyl ester 32b with sodium
azide in DMSO at rt, as well as of 33b with sodium cyanide
in DMF at elevated temperature, no substitution of the iodo
group was observed and the reactions afforded only the
appropriate monoesters 36a and 36b.
Finally, a possibility was checked to accomplish the
MCPBA-promoted phosphonylation reaction, and thus
achieve the formation of a product 37 that would possess
the both 40-phosphonomethoxy and 40-hydroxymethyl moie-
ties. In our hands, reaction of 40,50-didehydrothymidine de-
rivatives 9a–c with 10a and MCPBA provided thymine in
all cases and no expected products 37. To this point, neither
purification of MCPBA to remove m-chlorobenzoic acid
nor the use of base (K2CO3) to suppress acidity was any
help in attempts to obtain 37 (recently, Haraguchi et al.
reported38 the dimethyldioxirane epoxidation of 40,50 double
bond in 9a). The failure of this reaction to provide the desired
product is in contrast to the successful preparation of several
40-alkoxythymidine derivatives using the same methodol-
ogy.27,33 Obviously there is a considerable difference
between the reactivity of simple alcohols and dialkyl-
hydroxymethylphosphonate 10a as a nucleophile with
40,50-oxirane intermediate, and with longer reaction times,
the competing side reactions (decomposition) finally prevail.
ðdCH ꢀBrw31:5Þ.
2
Unfortunately, with the reactions employing NIS/NBS, the
obtained mixtures were very difficult to separate, although
both silica gel and reversed-phase separations were used. In
addition, the products 29–34, although providing (for single
main isomers b) the MS FAB (molecular ions) and NMR data
as expected, underwent gradual decomposition on attempted
deblocking reactions, further purifications, and even on stor-
age. That was also why we were not able to proceed in this
case to the preparation of the free 50-iodo and 50-bromo com-
pounds 29–34 as free phosphonic acids. Attempts were
made, nevertheless, to find out whether the prepared 50-de-
oxy-50-iodo derivatives 29b–31b (diisopropyl esters; their
better stability over dimethyl esters assumed) could be con-
verted to the corresponding azido derivatives 35a–35c on
substitution reaction with sodium azide (Scheme 4). After
several days in DMF at elevated temperature, the reaction
2.2. PTS-mediated phosphonylation reactions in the
dA, dC, dG and dU series
1
mixtures still showed, as seen from H NMR spectra, the
In general, the so far reported ways to the synthesis of 40,50-
didehydronucleosides 9 as starting compounds were based
on a simple scheme involving 50-halogenation of the nucleo-
side 7 and subsequent basic elimination of 8 (Scheme 2).
Maag et al.27 described the Ph3P/I2 iodination–MeONa elim-
ination approach as usable for all 20-deoxynucleosides (ex-
cept for dC, which was not mentioned). In turning to this
presence of the starting compound, which was not separable
by means of chromatography. The formation of 35a from 29b
was supported only by finding azido group bands at 2112 and
1
1288 cmꢀ1 in the IR spectrum while interpretation of H
NMR spectrum was not successful. Likewise, reaction of
31b with sodium azide yielded no spectrally characterizable

4520
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
approach, however, we found its use straightforward in the
case of 40,50-didehydrodeoxyuridine 9d only and prepared
its 30-O-TBDMS derivative 9e; it proved necessary to adjust
the syntheses of starting compounds first (Scheme 4).
derivative (45%), which in turn furnished the N-deblocked
compound 8a (31%) on treatment with methanolic ammonia
(Scheme 2).
In Method B using an altered reaction sequence, 50-O-dime-
thoxytrityl-30-O-tert-butyldiphenylsilyl-20-deoxyadenosine40
was treated with 80% aq acetic acid to remove the 50-protect-
ing group to give compound 7a (89%). This was converted to
the desired 50-bromo derivative 8a on reaction with Ph3P–
CBr4 in dioxane (48%). Compound 8a was subsequently
subjected to the elimination by prolonged treatment with
DBU in DMF (47%), giving the 40,50-didehydro derivative
9f. No anomerization was observed.
With N-protected 20-deoxyguanosine, iodination–elimina-
tion reactions gave complex mixtures under varied condi-
tions, and we failed to obtain any preparatively sufficient
yields of 40,50-didehydrodeoxyguanosine (much later, we
found that direct iodination of 20-deoxyguanosine with
Ph3P–I2 followed by elimination using sodium methoxide
in methanol at elevated temperature gives satisfactory yield
of unprotected 20-deoxy-40,50-didehydroguanosine). We par-
tially succeeded in starting with 20-deoxy-N-isobutyryl gua-
nosine (7c), converting it to the 50-iodo derivative 8c with
Ph3P–I2, and subsequently using t-BuOK in DMF for elim-
ination at low temperature and short reaction time to obtain
the product 9h (32%), which was then silylated to afford 9i
(70%) as a starting compound for phosphonylation. Elimina-
tion of HI can be a tricky reaction accompanied by elimina-
tion of the nucleobase.
In the 20-deoxycytidine case, the 50-bromo derivative 8b was
obtained by reaction sequence starting from 4-N-benzoyl-20-
deoxy-50-O-dimethoxytritylcytidine. This compound was
first silylated to produce the 30-O-tert-butyldiphenylsilyl de-
rivative, which was debenzoylated in methanolic ammonia,
and then dimethoxytrityl group was removed in 80% aq
acetic acid to afford compound 7b (75%, three steps), which
was brominated in 50-position with CBr4/Ph3P in dioxane to
give 8b (66%). This compound, on prolonged treatment with
DBU–DMF at rt, afforded the 40,50-didehydro precursor 9g
smoothly, also without anomerization.
With deoxyadenosine, similarly, the reported27 iodination
yield of 29% proved to be inaccessible. The product was
difficult to purify, and in turn the subsequent MeONa elimi-
nation (16 h heating) gave very unsatisfactory results. Fol-
lowing the report by Lerner28 on the use of DBU in DMF
at rt for the elimination reaction with 30-O-acetyl-50-
bromo-20,50-dideoxyadenosine (53%), and an earlier com-
munication by Moffatt26 on the use of Ph3P–CBr4 in
dimethylacetamide when brominating 4-N-benzoyl-20-
deoxycytidine, we therefore tested the combination of the
bromination of the readily available 6-N-benzoyl-30-O-tert-
butyldiphenylsilyl-20-deoxyadenosine with Ph3P–CBr4 in
dioxane and the DBU–DMF elimination, but found that the
obtained 40,50-didehydro product was repeatedly anomerized
(to ca. 20–30%; the use of t-BuOK caused the same, and
partial decomposition was observed). The anomerization,
as evidenced on the 1H NMR spectra, was attributable to the
elimination step. Similarly, we observed partial anomeriza-
tion and decomposition when carrying out the same reactions
Phosphonylation reactions with the 30-silylated precursors
9e, 9f, 9g and 9i (Scheme 2) using 10a and PTS were carried
out as described above for thymidine compounds 9a,b. Thus,
the dA derivative 9f furnished a 47% yield of phosphonate
mixture of 17a and 17b showing (on NMR checking) the
predominance of 12:1 of the b-D-erythro compound 17b
over the a-L-threo isomer 17a. The isomers were not separa-
ble either on silica gel or on reversed-phase chromatography,
but both were characterized by NMR spectroscopy. They
were submitted for further deprotection treatment as a
mixture.
The deoxycytidine precursor 9g afforded two expected iso-
mers 16a and 16b, which were separated by column chroma-
tography on silica. They gave a combined yield of 53%, and
were characterized by NMR. The isomer of the b-D-erythro
configuration 16b showed a more pronounced predominance
in this case (ratio 4:1). In connection with the initial difficul-
ties in dC series in preparing a suitable derivative for the
elimination reaction and subsequent phosphonylation, we
also sought help in the utilization of the dU-precursor for
the preparation of deoxycytidine phosphonate. Thus, the de-
oxyuridine derivative 9e was phosphonylated, and a dia-
stereoisomeric mixture of 15a and 15b (1:1 ratio, as of
HPLC) was obtained, from which we were able to isolate
the more desired a-L-threo isomer 15a in pure form (while
the remaining mixture was left for final deblocking). Com-
pound 15a was then converted to a triazolide intermediate
19a by the reaction with triazole–POCl3 according to the ap-
proach described by Brown,41 which in turn was converted
on treatment with aq ammonia, without isolation, to the 20-
deoxycytidine compound 20a in 40% overall yield. It was
submitted for deblocking (see below) as a separate sample.
with
4-N-benzoyl-30-O-tert-butyldiphenylsilyl-20-deoxy-
cytidine. This may relate to the comment in the paper by
Verheyden and Moffatt26 that 4-N-benzoyl-1-(2,5-dideoxy-
b-D-glycero-pent-4-enofuranosyl)cytosine, which they
prepared, was characterized as just ‘essentially pure’. The
NMR spectra were not provided; the authors described its
further alkaline deblocking to the free 40,50-didehydro deriv-
ative, unless they mentioned anomerization, but the ambigu-
ous term ‘essentially pure’ may refer to the fact that the purity
of the compound could have been affected by the presence of
certain amount of the anomerized product. We concluded
that the observed partial anomerization/decomposition was
probably due to the presence of N-protecting groups, since
we finally succeeded in obtaining the correct products from
the N-unprotected starting compounds, as follows. To pre-
pare the key 50-halogeno compound for elimination, two
approaches were used (as an alternative to procedure28 de-
scribing 29% yield of bromination by thionyl bromide).
In Method A, the described 6-N-benzoyl-30-O-tert-butyl-
diphenylsilyl-20-deoxyadenosine39 was converted, using
bromination with Ph3P–CBr4 in dioxane, to its 50-bromo
The dG derivative 9i provided a mixture of 40-diastereoiso-
mers 18a and 18b in 30% overall yield, with a 1.5:1 majority
of the b-D-erythro isomer 18b, as revealed by HPLC. The

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4521
O
CH3
N
CH3O
CH3O
OTBDMS
O
OTBDMS
O
R1O
O
T
T
N
P
O
O
H3C
O
T
OH-
PTS/MS
10a
Ph3P/DIAD
O
O
+
9a
O
P
CH3O
H3C
a R1=H
38
39
CH3O
40b
40a
89%
b R1=TBDMS; 47%
25%
51%
Scheme 5.
compounds could not be fully separated by repeated chroma-
tography on silica and, in order to avoid losing and decom-
posing the material, the isomeric mixture was left
unresolved for further deblocking steps. Both 40-epimers
18a,b were analyzed by 1H NMR in the mixture.
derivative 18), then the removal of the methylester groups of
the phosphonate moiety with bromotrimethylsilane in ace-
tonitrile in the presence of 2,6-lutidine, and finally, the
splitting of the 30-O-silyl group with tetrabutylammonium
fluoride in tetrahydrofuran. The use of 2,6-lutidine during
the bromotrimethylsilane treatment was absolutely neces-
sary to avoid the rapid cleavage of nucleosidic bond. After
complete deprotection, the compounds were subjected to
ion-exchange purification on DEAE-Sephadex with a gradi-
ent of triethylammonium hydrogen carbonate, followed by
reversed-phase column re-purification and desalting. The
obtained phosphonate compounds were converted, after re-
versed-phase treatment, into sodium salts by Dowex 50
(Na+) and adjusted by lyophilization from water. These sam-
ples were submitted to the confirmation of structure by MS
and NMR spectra. All compounds provided the expected
HRMS data from the respective molecular ions, and the 1H
and 13C NMR spectra in D2O were all interpretable and in
accordance with the expected structures. No anomerization
was observed. The configuration at C-40 in diastereoisomeric
pairs 21–25 was derived from 2D-ROESY spectra and
showed characteristic coupling pattern of pentose ring pro-
tons, as with the above discussed compounds 11–18. NMR
spectra of 40-epimers of dT-phosphonates 21a,b and dC-
phosphonates 23a,b were recorded from the pure epimers,
while the remaining ones (dU-phosphonates, 22a,b; dG-
phosphonates, 24a,b; dA-phosphonates, 25a,b) were ob-
tained from the respective epimeric mixtures.
Apart from testing the accessibility of 40-phosphonomethoxy
derivatives 11–18, i.e. those originating from the natural nu-
cleosidic precursors possessing the b-D-erythro configu-
ration of the pentofuranose ring, we also attempted the
preparation of analogues with reverse configuration of the
30-hydroxy group, i.e. b-D-threo or a-L-erythro compounds,
for potential further exploitation in oligonucleotide chemis-
try. To achieve this (Scheme 5), we made use of the thymidine
derivative 9a, which was converted in a high yield (w85%)
to the 2,30-cyclonucleoside 38 under Mitsunobu conditions,
using triphenyl phosphine and diisopropyl-azodicarboxylate
in DMF. This compound was treated with alkali to afford
1-(2,5-dideoxy-b-D-threo-pent-4-enofuranosyl)thymine
(39a),42 and this in turn was immediately silylated to give the
derivative 39b (47%, in two steps) as the starting compound
for phosphonylation in the presence of PTS (39b was re-
ported43 recently, without data, as obtainable from 1-(2,5-di-
deoxy-5-iodo-b-D-threo-pentofuranosyl)thymine in four
steps). With 10a, the reaction furnished (in the presence of
molecular sieves) the phosphonates 40a and 40b in a 1:2 ratio
(76%), separable on silica. In an attempt to accomplish
formation of 2,30-anhydro bridge with the phosphonate 13a
via Mitsunobu reaction, we obtained 3-N-methylated
phosphonate 13a without the 2,30-anhydro bridge, as single
product.
2.4. Screening for biological activity
The free 40-phosphonomethoxy compounds 21a,b and
23a,b, as individual isomers, and 22a,b, 24a,b and 25a,b,
as mixtures of the a-L-threo and b-D-erythro isomers, were
evaluated for potential cytostatic and antiviral activity. It
was found in tests (Dr. I. Votruba, IOCB, Prague) with
L929, L1210 and HeLa cells that none of the compounds ex-
erted any significant cytostatic effect. Likewise, no activity
was found (Prof. E. DeClercq, Rega Inst., Leuven) on the
screening with CMV, VZV, HSV and HIV viruses.
The configuration at carbon atom C-40 in the isomers 40a
and 40b was derived from their 2D-ROESY spectra. In com-
pound 40a the observed NOE contacts between the C40-
methyl protons and protons H-30, H-200 and H-10 indicate
the cis-orientation of C40-methyl group. On the other hand,
in compound 40b the C40-methyl protons show NOE contact
with proton H-6 of thymine, which indicates the cis-orienta-
tion of C40-methyl group and thymine base. Additional NOE
contacts support the above suggested configurations in both
isomers. Further exploitation of these compounds is under-
way.
3. Conclusion
2.3. Deprotection
We have succeeded in the verification of the practical utility
of the general reaction leading to 40-dialkylphosphono-
methoxy derivatives of 20,50-dideoxynucleosides (Schemes
1 and 2). The novel structural features introduced in 40-posi-
tion were considered worth examining as plausible modify-
ing elements in nucleotide (and potentially, oligonucleotide)
analogues. The syntheses elaborated with 40,50-didehydro-
thymidine derivatives were applied to analogous reactions
All the 30-silylated phosphonate dimethyl esters in dT, dC,
dA, dU and dG series 11–18, and 20 were subjected to a
standard procedure leading to completely deblocked phos-
phonate derivatives 21–25 (Scheme 2). The deprotection
included, first, the removal of the nucleobase-acyl protecting
groups using ammonia-saturated methanol (case of the dGib

4522
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
with the corresponding 40,50-didehydro derivatives of the
protected 20-deoxycytidine, 20-deoxyuridine, 20-deoxygua-
nosine and 20-deoxyadenosine, whereby the preparative
availability of these didehydronucleosides was evaluated
and revised. New knowledge concerning the use of the indi-
vidual electrophiles (showing positive results with PTS, NIS
and NBS activation, and negative results on attempts with
MCPBA) for the addition of dialkyl-hydroxymethylphos-
phonates to the 40,50-didehydronucleosides was obtained.
The deprotected compounds of the most promising (PTS-
promoted) series (21–25) submitted for biological testing
showed no significant cytostatic effect or antiviral activity,
and thus the assumption on the possible biological activity
was not confirmed. It seems that the mere presence of the
isopolar, isosteric phosphonomethoxy group in the molecule
of such a nucleotide analogue may not be sufficient for exert-
ing activity, although this grouping was found to be the key
structural feature in some antivirals.4,8,9 When considering
the absence of antiviral and cytostatic activity, nevertheless,
we cannot exclude the possibility that the tested compounds
are not transported into cells and phosphorylated to the 50-
triphosphates. It would be of interest to prepare a suitable
prodrug to evaluate the biological properties at such a stage
as well. In addition, in vitro experiments with triphosphate
analogues and DNA polymerases should provide informa-
tion on substrate or inhibitory properties of the compounds.
These studies are underway.
methanol–water mixture at pH 2, pH 7 and pH 12. Mass
spectra (m/z) were recorded on a ZAB-EQ (VG Analytical)
instrument, using FAB in both positive and negative mode
(ionization by Xe, accelerating voltage 8 kV) with glyc-
erol–thioglycerol (3:1) and 2-hydroxyethyldisulfide as ma-
trices. Infrared spectra (cmꢀ1) were measured on a Nicolet
740 spectrometer in chloroform or in KBr pellet. Elemental
analyses were carried out on a PE 2400 Series II analyzer. In
cases of compounds where the elemental analyses are not
presented and the HRMS data are used instead, it is under-
stood that no peaks were observed in their NMR spectra ad-
ditional to those expected for the target compounds; the
HRMS values thus refer to the uncontaminated species.
The optical rotations (aD values) were measured on an
Autopol IV polarimeter (Rudolph Research Analytical) at
20 ꢃC. 1H and 13C NMR spectra were measured on a Varian
Unity 500 instrument (1H at 500 MHz, 13C at 125.7 MHz) in
DMSO-d6 (referenced to the solvent signal dH¼2.50,
dC¼39.7) and/or CDCl3 (referenced to TMS). Sodium salts
of phosphonic acids were measured in deuterium oxide,
free phosphonic acids in deuterium oxide containing sodium
deuteroxide, with DSS as internal standard. Signals in the 1H
NMR spectra were assigned to protons on the basis of chem-
ical shifts, observed multiplicities and homonuclear 2D-
COSY experiments. Chemical shifts and coupling constants
were obtained by a first-order analysis of spectra. The ex-
change of hydroxy protons for deuterium was carried out
by addition of several drops of tetradeuterioacetic acid. As-
signments of signals in 13C NMR spectra were accomplished
on the basis of J-modulated spectra (APT) enabling to dis-
criminate between C, CH, CH2 and CH3 signals, character-
4. Experimental
4.1. General
1
istic chemical shifts and in some cases confirmed by H,
13C-correlated HMQC spectra. Pyridinium p-toluenesul-
fonate (PTS) was prepared according to Miyashita et al.,44
and m-chloroperoxybenzoic acid containing a 95% active
species was prepared according to Schwartz and Blum-
bergs.45 1-(2,5-Dideoxy-b-D-glycero-pent-4-enofuranosyl)-
thymine (9a) was repeatedly prepared according to Ref. 27
in 70–80% yields. 1-(3-O-tert-Butyldimethylsilyl-2,5-di-
deoxy-b-D-glycero-pent-4-enofuranosyl)thymine (9b), de-
scribed without experimental details by Reese,30 was
prepared in repeated yields of 70–75% by silylation of 9a
using the procedure provided for 9-(3-O-tert-butyldimethyl-
silyl-2,5-dideoxy-b-D-glycero-pent-4-enofuranosyl)adenine.27
Unless stated otherwise, the solvents were concentrated at
40 ꢃC using a rotatory evaporator. The products were dried
over phosphorus pentoxide at 40–50 ꢃC and 13 Pa. The
course of the reactions was followed by TLC on silica gel
Silufol UV 254 foils (Kavalier Glassworks, Votice, Czech
Republic) and the products were visualized both by UV
monitoring and (where applicable) by spraying with a 1%
ethanolic solution of 4-(4-nitrobenzyl)pyridine which, after
short heating and exposing to ammonia vapours, showed
the di- (and partly mono-) alkyl phosphonates as blue spots.
Preparative column chromatography (PLC) was performed
on silica gel (40–60 mm, Fluka) whereby the amount of ad-
sorbent used was 20–40 times the weight of the mixture sep-
arated. Elution was performed under a 50 kPa overpressure
at the rate of 40 mL minꢀ1. For TLC and PLC runs, the
following solvent systems were used (v/v): toluene–ethyl
acetate 1:1 (T1), chloroform–ethanol 9:1 (C1), chloroform–
ethanol 95:5 (C2), ethyl acetate–acetone–ethanol–water
4:1:1:1 (H1), 12:2:2:1 (H3), H3–ethyl acetate 1:4 (E1), 2-
propanol–concd aq ammonia–water 7:1:2 (IPAW, for
charged compounds). The HPLC analyses were performed
on a DuPont 850 Liquid Chromatograph instrument using
a column of reverse phase (4.6ꢂ150 mm) Nucleosil 100-5
C18 (Macherey-Nagel), either isocratically at various con-
centrations of methanol in 0.1 M triethylammonium acetate
(TEAA) or by gradients of methanol in the same buffer. The
electrophoresis was made on Whatman No. 1 paper in 0.1 M
triethylammonium hydrogen carbonate (pH 7.5) at
20 V cmꢀ1. The UV spectra were recorded on a Pye-Unicam
SP 8000 spectrophotometer in water or in a 1:1 (v/v)
4.2. Deblocking of the fully protected phosphonate
derivatives—general procedures
(a) Removal of phosphorus protecting groups: The phos-
phonate diesters 11–17, 20a and the deacylated (by 16 h
treatment with satd ammonia in methanol) 18 in dry acetoni-
trile (10 mL mmolꢀ1) were treated with 2,6-lutidine (2-fold
molar equivalent of trimethylbromosilane), and then trime-
thylbromosilane (6 M equiv per mmol of diester) was added
dropwise under stirring at rt. The mixture was stirred over-
night (TLC in IPAW and H1), then evaporated in the pres-
ence of triethylamine (1.5 equiv of bromotrimethylsilane),
and the residue was co-evaporated with 5% triethylamine
in acetonitrile.
(b) Removal of silyl protecting groups: The residue obtained
in (a) was treated with 0.5 M TBAF in tetrahydrofuran
(5 equiv, based on starting phosphonate diester) at rt

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4523
overnight (TLC in IPAW; completion of reaction was
checked by electrophoretic comparison with AMP or UMP
as reference). The solvent was evaporated with several drops
of triethylamine.
15.4 mmol) at rt for 4 d (after 2 d, half portions of both
reagents were added). The reaction mixture was quenched
by methanol (1 mL), the solution was concentrated in vacuo
to one third, diluted with ethyl acetate (300 mL), and the or-
ganic layer was washed with satd aq sodium hydrogen car-
bonate (3ꢂ100 mL), dried over Na2SO4 and evaporated.
Gradient chromatography of the residue on silica gel
(0–10% of acetone in toluene) afforded 5.4 g (8.2 mmol,
45%) of 6-N-benzoyl-50-bromo-30-O-tert-butyldiphenyl-
silyl-20,500-dideoxyadenosine as TLC-pure compound, which
was used for further reaction without characterization. It was
treated with satd (0 ꢃC) ammonia in anhydrous methanol
(150 mL) at rt for 48 h, the solvent was evaporated, and the
residue chromatographed on silica gel in chloroform–ethanol
(0–10%). Yield: 1.4 g (2.5 mmol, 31%) of 8a as a solid.
(c) Anion exchange chromatography: The products from (b)
containing crude free phosphonic acids 21–25 were applied
onto a column of DEAE-Sephadex A25 (16ꢂ200 mm), the
column was washed with water (150 mL), and then a gradi-
ent elution with aq triethylammonium hydrogen carbonate
(0–0.2 M, 2ꢂ1000 mL) was applied. Fractions (10 mL) con-
taining the product were pooled and evaporated repeatedly
with several drops of triethylamine, and finally co-evapo-
rated three times with 1% triethylamine–methanol. In cases
when TLC checking of the residue (IPAW) showed, on
gentle heating of the eluted TLC sheet, the presence of a
carbonized by-product not detectable in UV light, the anion
exchange chromatography was repeated with somewhat
slower elution to remove it.
Method B: 30-O-tert-butyldiphenylsilyl-20-deoxyadenosine
(7a) (21.8 g, 44.5 mmol) was brominated with triphenyl
phosphine and tetrabromomethane in the same manner as
described for N-benzoyl derivative in Method A, and the
product was chromatographed on silica gel (0–10% ethanol
in chloroform). Yield: 11.81 g (21.4 mmol, 48%) of crystal-
line 8a (crystallized from ethanol). Mp 172 ꢃC (decomp.).
For C26H30N5O2SiBr calcd C 56.52%, H 5.47%, N
12.67%, Br 14.46%; found C 56.54%, H 5.67%, N
12.34%, Br 14.79%. IR spectrum (KBr): nmax (cmꢀ1) 3300
(s), 3280 (s, sh), 3246 (s), 3160 (s, br), 3133 (s), 3121 (s)
and 1643 all NH2; 3075 (s) ]C–H; 1605 (vs), 1574 (s),
1514 (w), 1472 (m), 1370 (m) and 1335 (s) all adenine
ring; 1302 (s), 1252 (m), 1237 (m), 1216 (m), 1050 (vs),
1035 (m, sh), 824 (m), 797 (m) and 724 (m) all adenine;
1472 (m), 1391 (w) and 1363 (w, sh) all CH3 from TBDPS;
1426 (s), 1112 (vs), 1105 (s), 995 (m), 744 (m), 701 (vs), 692
(s), 622 (m), 616 (m), 504 (s) and 490 (m) all ring from
TBDPS; 1078 (m, sh) COSi; 648 (w, sh) and 606 (w, sh)
(d) Reversed-phase chromatography: The free phosphonic
acids from (c) were subjected to preparative chromato-
graphy on octadecyl silica column (25ꢂ300 mm, 20–
40 mm, IOCB Prague); compounds were eluted with a linear
gradient of methanol in water at a rate of 10 mL minꢀ1. Frac-
tions with product were evaporated.
(e) Adjustment of phosphonic acids 21–25: The pure phos-
phonic acids from (d) were converted into the sodium salt
by passing through a Dowex 50 (Na+) column. Final adjust-
ment was made by lyophilization of the compound from
water and drying over phosphorus pentoxide in vacuo.
4.2.1. 30-O-tert-Butyldiphenylsilyl-20-deoxyadenosine
(7a). 50-O-Dimethoxytrityl-30-O-tert-butyldiphenylsilyl-20-
deoxyadenosine40 (39.6 g, 50 mmol) was treated with 80%
aq acetic acid (400 mL) for 4 h at rt, the solution was evapo-
rated to dryness, and the residue was chromatographed on
silica gel using gradient elution from A to 8:92 A–B (where
A¼ethyl acetate, B¼ethyl acetate–H3 9:1). Obtained:
21.82 g (44.5 mmol, 89%) of 7a as an amorphous solid. 1H
NMR (DMSO): 8.09 and 8.29 (2ꢂs, 2ꢂ1H, H-2 and H-8),
7.43–7.51 m, 6H and 7.64 m, 4H (2ꢂC6H5), 5.30 (dd,
1
all C–Br. H NMR (DMSO): 8.29 and 8.12 (2ꢂs, 2ꢂ1H,
H-2 and H-8), 7.66 m, 4H and 7.50 m, 6H (2ꢂC6H5), 7.30
0
00
0
0
(br s, 2H, NH2), 6.49 (dd, 1H, J1 ,2 ¼6.1, J1 ,2 ¼8.3 Hz, H-
10), 4.63 (dt, 1H, J3 ,2 ¼2.4, J3 ,4 ¼2.0, J3 ,2 ¼5.4 Hz, H-3 ),
0
0
00
0
0
0
0
0
0
0
0
0
0
00
4.17 (td, 1H, J4 ,3 ¼2.0, J4 ,5 ¼6.8, J4 ,5 ¼6.1 Hz, H-4 ),
0
0
0
0
00
3.49 (dd, 1H, J5 ,4 ¼6.8, J5 ,5 ¼10.5 Hz, H-5 ), 3.42 (dd,
00
00
0
00
0
0
0
1H, J5 ,4 ¼6.1, J5 ,5 ¼10.5 Hz, H-5 ), 2.95 (ddd, 1H, J2 ,3
¼
0
0
0
0
00
5.4, J2 ,1 ¼8.3, J2 ,2 ¼13.7 Hz, H-2 ), 2.36 (ddd, 1H,
00
0
0
00
00
0
00
0
00
0
000
1H, JOH,5 ¼7.0, JOH,5 ¼4.7 Hz, OH), 6.45 (dd, 1H, J1 ,2
¼
J2 ,3 ¼2.4, J2 ,1 ¼6.1, J2 ,2 ¼13.7 Hz, H-2 ), 1.08 s, 9H,
t-Bu. HRMS FAB+ calcd for C26H31BrN5O2Si (M+H)+
552.1430, found 552.1492.
0
0
0
00
0
0
5.8, J1 ,2 ¼8.8 Hz, 0H-1 ), 4.57 (dt, 1H, J3 ,2 ¼1.8, J3 ,2 ¼5.3,
0
0
0
0
0
0
J3 ,4 ¼1.6 Hz, H-30), 4.02 (ddd, 1H, J4 ,3 ¼1.6, J4 ,5 ¼3.8,
0
00
00
0
00
0
J4 ,5 ¼4.3 Hz, H-4 ), 3.43 (ddd, 1H, J5 ,4 ¼4.3, J5 ,5 ¼12.0,
J5 ,OH¼4.7 Hz, H-500), 3.18 (ddd, 1H, J5 ,4 ¼3.8, J5 ,5
¼
¼
4.2.3. 50-Bromo-30-O-tert-butyldiphenylsilyl-20,50-dide-
oxycytidine (8b). 30-O-tert-Butyldiphenylsilyl-20-deoxycy-
tidine (7b): 4-N-benzoyl-20-deoxy-50-O-dimethoxytrityl-
cytidine (15.8 g, 25 mmol) and dried imidazole (3.4 g,
50 mmol) in pyridine (100 mL) were treated with tert-butyl-
chlorodiphenylsilane (8.25 g, 30 mmol) at rt for 16 h (TLC
in 50% ethyl acetate–toluene). The reaction was quenched
with methanol (2 mL) and the solution was evaporated.
The solution of the residue in ethyl acetate (300 mL) was
washed with satd aq sodium hydrogen carbonate
(3ꢂ100 mL), dried (Na2SO4) and evaporated. The residue
was treated with satd (0 ꢃC) ammonia in anhydrous metha-
nol (300 mL) in a stoppered vessel at rt for 16 h, and the
solvent was carefully evaporated. The residue was co-evap-
orated with toluene (2ꢂ100 mL), treated with 80% aq acetic
acid (300 mL) at rt for 1 h to remove the dimethoxytrityl
00
0
0
0
00
12.0, J5 ,OH¼7.0 Hz, H-50), 2.68 (ddd, 1H, J2 ,1 ¼8.8, J2 ,2
0
0
0
0
00
0
0
0
00
0
13.2, J2 ,3 ¼5.3 Hz, H-2 ), 2.29 (ddd, 1H, J2 ,1 ¼5.8,
J2 ,2 ¼13.2, J2 ,3 ¼1.8 Hz, H-2 ), 1.07 (s, 9H, t-Bu). 13C
NMR (DMSO): 156.30 (C-6), 152.48 (C-2), 148.98 (C-4),
139.75 (C-8), 128.12 (4), 130.21 (2), 133.11 (2) and 135.45
(4) (2ꢂC6H5), 119.47 (C-5), 88.43 (C-10), 84.36 (C-40),
74.52 (C-30), 61.74 (C-50), w39.7 (C-20, overlapped with
DMSO), 18.83 and 26.92 (t-Bu). HRMS FAB+ calcd for
C26H32N5O3Si (M+H)+ 490.2274, found 490.2260.
00
00
0
00
0
4.2.2. 50-Bromo-30-O-tert-butyldiphenylsilyl-20,50-dide-
oxyadenosine (8a). Method A: 6-N-benzoyl-30-O-tert-butyl-
diphenylsilyl-20-deoxyadenosine39 (10.7 g, 18.1 mmol) in
dioxane (130 mL) was treated with triphenyl phosphine
(5.3 g, 19.9 mmol) and tetrabromomethane (5.1 g,

4524
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
group, and the solution concentrated to dryness. Gradient
chromatography of the residue on silica gel (0–10% of eth-
anol in chloroform) afforded a TLC-pure silyl derivative 7b
(8.7 g, 18.7 mmol, 75%), which was used without character-
ization for subsequent reactions.
0.2 equiv of both tert-butyldimethylchlorosilane and imid-
azole were added to complete the reaction (8 h). Abs metha-
nol was then added (0.5 mL) and after 30 min, the solvent
was evaporated, the residue co-evaporated with toluene,
and partitioned between chloroform (2ꢂ150 mL) and satd
aq sodium hydrogen carbonate (150 mL). The organic layer
was dried with MgSO4, the solvent evaporated and the resi-
due chromatographed on silica using a gradient of 0–3.5%
ethanol in chloroform. Yield: 3.53 g (65%) of 9e as a foam.
IR spectrum (KBr): nmax (cmꢀ1) 3117 (w) NH; 1688 (vs)
C]O; 1472 (w, sh), 1463 (w), 1388 (m), 1363 (w), 1268
(m), 1253 (w, sh) and 837 (m) all CH3 from TBDMS; 1418
Bromination: Compound 7b (1.9 g, 4.08 mmol) was treated
with triphenyl phosphine (1.31 g, 5 mmol) and tetrabromo-
methane (1.72 g, 5.2 mmol) in dioxane (40 mL) at rt for
16 h. The reaction was quenched with methanol (0.5 mL),
the solution concentrated in vacuo, then ethyl acetate
(100 mL) was added, and the organic layer was washed
with satd aq sodium hydrogen carbonate (3ꢂ60 mL), dried
over Na2SO4 and evaporated. Gradient chromatography of
the residue on silica gel (0–10% of ethanol in chloroform) af-
forded TLC-pure title compound 8b (1.43 g, 2.7 mmol, 66%)
as an amorphous solid. 1H NMR (DMSO): 7.62 m, 4H and
7.48 m, 6H (2ꢂC6H5), 7.53 (d, 1H, J6,5¼7.6 Hz, H-6); 7.22
1
(w) ring; 873 (w) ]CH2; 764 (w, sh) ]CH. H NMR
(DMSO): 11.41 (br s, 1H, NH), 7.57 (d, 1H, J6,5¼8.2 Hz,
0
0
0
0
00
H-6), 6.34 (dd, 1H, J1 ,2 ¼5.9, J1 ,2 ¼7.0 Hz, H-1 ), 5.65 (d,
1H, J5,6¼8.2 Hz, H-5), 4.91 (m, 1H, H-30), 4.34 (dd, 1H,
0
0
0
0
00
00
0
J5 ,3 ¼1.2, J5 ,5 ¼1.8 Hz, H-5 ), 4.10 (dd, 1H, J5 ,3 ¼1.2,
00
00
0
0
0
0
0
J5 ,5 ¼1.8 Hz, H-5 ), 2.49 (ddd, 1H, J2 ,1 ¼5.9, J2 ,3 ¼6.8,
0
0
00
0
00
00
0
00
0
and 7.19 (2ꢂbr s,0 2ꢂ1H, NH2), 6.35 (dd, 1H, J1 ,2 ¼5.6,
J2 ,2 ¼13.7 Hz, H-2 0)0, 2.21 (ddd, 1H, J2 ,3 ¼4.2, J2 ,1 ¼7.0,
0
0
00
0
J1 ,2 ¼8.8 Hz, H-1 ), 5.71 (d, 1H, J5,6¼7.6 Hz, 0H-5), 4.35
J2 ,2 ¼13.7 Hz, H-2 ), 0.88 (s, 9H, t-Bu), 0.12 and 0.11
(2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR (DMSO): 164.60 (C-4),
163.98 (C-40), 150.58 (C-2), 141.29 (C-6), 102.59 (C-5),
86.07 (C-10), 83.51 (C-50), 70.66 (C-30), 37.16 (C-20), 25.86
(3ꢂCH3 (t-Bu)), 17.99 (pCo(t-Bu)), ꢀ4.60 (Si(CH3)2).
HRMS FAB+ calcd for C15H25N2O4Si (M+H)+ 325.1584,
found 325.1571.
0
00
0
0
0
0
(dt, 1H, J3 ,2 ¼2.2, J3 ,4 ¼2.0, J3 ,2 ¼5.4 Hz, H-3 ), 4.08 (td,
0
0
0
0
0
0
00
1H, J4 ,3 ¼2.0, J4 ,5 ¼6.2, J4 ,5 ¼0 5.6 Hz, H-4 ), 3.37 (dd, 1H,
0
0
0
00
00
0
J5 ,4 ¼6.2, J5 ,5 ¼10.7 Hz, H-5 ), 3.31 (dd, 1H, J5 ,4 ¼5.6,
00
00
0
00
0
00
0
J5 ,5 ¼10.7 Hz, H-5 ), 2.13 (ddd, 1H, J2 ,3 ¼2.2, J2 ,1 ¼5.6,
00
00
0
0
0
0
0
J2 ,2 ¼13.7 Hz, H-2 ), 2.03 (ddd, 1H, J2 ,3 ¼5.4, J2 ,1 ¼8.8,
0
0
00
J2 ,2 ¼13.7 Hz, H-2 ), 1.05 (s, 9H, t-Bu). HRMS FAB+ calcd
for C25H31BrN3O3Si (M+H)+ 528.1318, found 528.1313.
4.2.6. 9-(3-O-tert-Butyldiphenylsilyl-2,5-dideoxy-b-D-
glycero-pent-4-enofuranosyl)adenine (9f). Using the pro-
cedure described for preparation of 9g, the deoxyadenosine
compound was prepared from 8a (3.0 g, 5.44 mmol) in DMF
(30 mL) by treatment with DBU (4 equiv) for 4 d (checked
by HPLC). Work-up and column chromatography on silica
gel using gradient elution from A to 8:92 A–B (where
A¼ethyl acetate, B¼ethyl acetate–H3 9:1) afforded 1.41 g
(2.99 mmol, 55%) of 9f as a solid foam. IR spectrum
(KBr): nmax (cmꢀ1) 3421 (s, br), 3358 (s), 3310 (s) and
3161 (s) all NH2, H2O, OH; 3074 (m) ]C–H; 1641 (s)
NH2; 1604 (vs), 1573 (s), 1511 (w), 1472 (m), 1371 (m)
and 1333 all adenine ring; 1303 (m) adenine; 1076 (s);
1472 (m) and 1391 (w, sh) all CH3; 1427 (s), 1113 (s), 999
(w, sh), 743 (m), 703 (vs), 693 (m, sh), 617 (m), 505 (s)
4.2.4. 1-(3-O-tert-Butyldiphenylsilyl-2,5-dideoxy-b-
D-glycero-pent-4-enofuranosyl)thymine (9c). To a solution
of compound 9a27 (2.24 g, 10 mmol) and imidazole (6.15 g,
90 mmol) in dimethylformamide (20 mL), tert-butyldiphe-
nylsilyl chloride (10.24 mL, 40 mmol) was gradually added
and the whole was stirred at rt overnight. On checking the
end of reaction by TLC (in C2 and T1), methanol (2 mL)
was added and the stirring continued for 1 h. The mixture
was then diluted with ethyl acetate (200 mL) and washed
with a satd solution of sodium hydrogen carbonate
(270 mL). The organic phase was separated and the aqueous
layer washed with ethyl acetate (2ꢂ100 mL). The pooled ex-
tracts were washed with a satd solution of NaCl (80 mL),
dried over anhydrous MgSO4 and evaporated. The resulting
mixture was chromatographed on a silica gel column
(120 g) with chloroform as an eluent. Yield: 3.63 g (79%)
of product 9c in the form of a solid foam, Rf¼0.87 (C2).
For C26H30N2O4Si (462.61) calcd 67.65% C, 6.54% H,
6.06% N; found, 68.02% C, 6.66% H, 5.73% N. MS
1
and 482 (m) all arom. ring of TBDPS. H NMR (DMSO):
8.26 and 8.03 (2ꢂs, 2ꢂ1H, H-2 and H-8), 7.68 and 7.47
(2ꢂm, 4H and 6H, 2ꢂC6H5), 7.32 (br s, 2H, NH2), 6.64
0
0
0
0
00
(dd, 1H, J1 ,2 ¼6.2, J1 ,2 ¼6.8 Hz, H-1 ), 5.25 (m, 1H, H-
30), 4.20 (dd, 1H, J5 ,3 ¼1.5, J5 ,5 ¼1.8 Hz, H-5 ), 3.80 (dd,
0
0
0
0
00
1
(FAB): 463.4 (M+H)+. H NMR (DMSO): 11.40 (br s, 1H,
1H, J5 ,3 ¼1.0, J5 ,5 ¼1.8 Hz, H-5 ), 2.90 (dt, 1H, J2 ,1
¼
¼
00
00
0
00
0
0
0
0
0
0
0
0
00
00
NH), 7.64 and 7.45–7.50 (2ꢂm, 4H and 6H, 2ꢂC6H5), 7.38
6.2, J2 ,3 ¼6.4, J2 ,2 ¼13.2 Hz, H-2 ), 2.51 (ddd, 1H, J2 ,3
00
0
0
00
0
00
0
(q, 1H, J6;CH ¼ 1:2 Hz, H-6), 6.47 (br t, 1H, J1 ,2 ¼6.7 Hz,
4.4, J2 ,1 ¼6.8, J2 ,2 ¼13.2 Hz, H-2 ), 1.08 (s, 9H, t-Bu).
13C NMR (DMSO): 162.69 (C-40), 156.31 (C-6), 152.86
(C-2), 149.06 (C-4), 140.21 (C-8), 135.66(2), 135.65(2),
133.04, 132.96, 130.34, 130.31, 128.19(2) and 128.11(2)
(2ꢂC6H5), 119.45 (C-5), 84.09 (C-10), 83.57 (C-50), 71.82
(C-30), 37.95 (C-20), 26.98 (3ꢂCH3 (t-Bu)), 19.01 (pCo(t-
Bu)), ꢀ4.60 (Si(CH3)2). HRMS FAB+ calcd for
C26H30N5O2Si (M+H)+ 472.2169, found 472.2207.
3
H-10), 4.83 (dd, 1H, J3 ,2 ¼2.9, J3 ,2 ¼6.3 Hz, H-3 ), 4.23
0
0
00
0
0
0
0
00
00
0
(br d, 1H, J5 ,5 ¼2.0 Hz, H-5 ), 3.72 (d, 1H, J5 ,5 ¼2.0 Hz,
H-500), 2.36 (ddd, 1H, J2 ,1 ¼7.1, J2 ,3 ¼6.3, J2 ,2 ¼13.7 Hz,
0
0
0
0
0
00
H-20), 2.27 (ddd, 1H, J2 ,1 ¼6.3, J2 ,3 ¼2.9, J2 ,2 ¼13.7 Hz,
00
0
00
0
00
0
H-200), 1.76 (d, 3H, JCH ;6 ¼ 1:2 Hz, CH3), 1.03 (s, 9H, t-Bu).
3
4.2.5. 1-(3-O-tert-Butyldimethylsilyl-2,5-dideoxy-b-D-
glycero-pent-4-enofuranosyl)uracil (9e). Compound 9d27
(3.99 g, 16.75 mmol) was co-evaporated with pyridine,
then pyridine (120 mL) and imidazole (3.42 g, 50.3 mmol,
3 equiv) were added followed by tert-butyldimethylchloro-
silane (3.03 g, 20.1 mmol, 1.2 equiv), and the whole was
left to react at rt overnight. On TLC checking (C1), additional
4.2.7. 1-(3-O-tert-Butyldiphenylsilyl-2,5-dideoxy-b-D-
glycero-pent-4-enofuranosyl)cytosine (9g). To the 50-
bromo compound 8b (1.13 g, 2.14 mmol) in dry DMF
(23 mL), DBU (1.28 mL, 8.55 mmol, 4 equiv) was added
and the whole was stirred at rt for 4 d (HPLC) until

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4525
completion. Solvent was evaporated in vacuo at 45 ꢃC and
the chloroform solution (100 mL) of the residue was washed
with 5% aq citric acid (2ꢂ100 mL). The chloroform layer
was washed with 0.5 M aq triethylammonium hydrogen car-
bonate (100 mL), separated, dried (MgSO4) and evaporated.
Chromatography of the residue on silica gel using a gradient
elution with 0–7% ethanol in chloroform afforded 0.641 g
(67%) of 9g as an amorphous solid. IR spectrum (KBr):
nmax (cmꢀ1) 3412 (w, br) and 3177 (w, br) all NH2; 3072
(w) and 3051 (w) ]C–H; 1647 (vs) NH2 and C]O; 1610
(m) C]C; 1525 (w) and 1404 (w) all cytosine ring; 1280
(w) C–N; 823 (w), 856 (w), 788 (w), 1473 (m, sh), 1465
(w, sh), 1393 (w) and 1362 (w) all CH3; 1428 (m), 1113
(s), 1105 (m, sh), 1029 (m), 999 (w), 742 (w), 703 (m),
615 (w), 507 (w) and 491 (w) all arom. ring of TBDPS;
1563 (m), 1402 (w) and 1391 (w) all ring; 1688 (vs) amide
I, 1538 (w, sh) amide II, 1102 (m) and 1054 (w) all C–OH.
1H NMR (DMSO): 12.10 (br s, 1H, NH), 11.65 (br s, 1H,
0
0
0
00
NH), 8.21 (s, 1H, H-8), 6.46 (dd, 1H, J1 ,2 ¼6.2, J1 ,2
¼
6.6 Hz, H-10), 5.63 (d, 1H, JOH,3 ¼4.9 Hz, OH), 4.93 (m,
0
1H, H-30), 4.27 (t, 1H, J5 ,3 ¼1.5, J5 ,5 ¼1.5 Hz, H-5 ), 4.17
0
0
0
0 00 00
00
0
00
0
0
0
(t, 1H, J5 ,3 ¼1.5, J5 ,5 ¼1.5 Hz, H-5 ), 2.87 (dt, 1H, J2 ,1
¼
0
0
0
0
00
J2 ,3 ¼6.3, J2 ,2 ¼13.4 Hz, H-2 ), 2.73 (sept, 1H, J¼6.8 Hz,
00
0
00
0
00
0
CH), 2.40 (ddd, 1H, J2 ,3 ¼4.9, J2 ,1 ¼6.6, J2 ,2 ¼13.4 Hz,
H-200), 1.12 (d, 6H, J¼6.8 Hz, CH3). HRMS FAB+ calcd
for C14H18N5O4 (M+H)+ 320.1357, found 320.2005.
4.2.9. 9-(3-O-tert-Butyldimethylsilyl-2,5-dideoxy-b-D-
glycero-pent-4-eno-furanosyl)-2-N-isobutyrylguanine
(9i). Compound 9h (1.58 g, 4.95 mmol) was co-evaporated
with pyridine and silylated with tert-butyldimethylchloro-
silane in pyridine in the presence of imidazole in the same
manner as described for 9e. Chromatography on silica gel
using a gradient of 0–8% ethanol in chloroform yielded
1
1080 (m) COSi. H NMR (DMSO): 7.65 and 7.50 (2ꢂm,
4H and 6H, 2ꢂC6H5), 7.39 (d, 1H, J6,5¼7.4 Hz, H-6), 7.26
0
00
and 7.23 (2ꢂbr s, 2ꢂ1H, NH2), 6.47 (t, 1H, J1 ,2 ¼6.6,
0
0
0
J1 ,2 ¼6.6 Hz, H-1 ), 5.69 (d, 1H, J5,6¼7.4 Hz, H-5), 4.84
1
0
0
00
0
0
(br dd, 1H, J3 ,2 ¼3.4, J3 ,2 ¼6.0 Hz, H-3 ), 4.22 (br d, 1H,
1.51 g (3.48 mmol, 70%) of 9i as an amorphous solid. H
NMR (DMSO): 12.12 (s, 1H, NH), 11.67 (s, 1H, NH), 8.26
0
0
0
0
00
00
0
J5 ,3 ¼1.0, J5 ,5 ¼1.7 Hz, H-5 ), 3.73 (br d, 1H, J5 ,3 ¼1.0,
00
0
00
0
00
0
00
0
0
0
0
00
J5 ,5 ¼1.7 Hz, H-5 ), 2.26 (ddd, 1H, J2 ,3 ¼3.4, J2 ,1 ¼6.6,
(s, 1H, H-8), 6.45 (t, 1H, J1 ,2 ¼6.4, J1 ,2 ¼6.4 Hz, H-1 ),
00
00
0
0
0
0
0
0
00
0
0
0
00
0
00
0
00
J2 ,2 ¼13.6 Hz, H-2 ), 2.19 (dt, 1H, J2 ,1 ¼J2 ,3 ¼6.3, J2 ,2
¼
5.02 (ddt, 1H, J3 ,5 ¼1.0, J3 ,5 ¼1.0, J3 ,2 ¼4.2, J3 ,2 ¼6.2 Hz,
13.6 Hz, H-20), 1.04 (s, 9H, t-Bu). 13C NMR (DMSO):
165.82 (C-4), 162.84 (C-40), 154.91 (C-2), 141.56 (C-6),
94.96 (C-5), 135.60(4), 133.01, 132.95, 130.36, 130.30,
128.22(2) and 128.11(2) (2ꢂC6H5), 86.87 (C-10), 83.76
(C-50), 72.04 (C-30), 39.17 (C-20), 26.92 (3ꢂCH3 (t-Bu)),
18.94 (pCo(t-Bu)). HRMS FAB+ calcd for C25H30N3O3Si
(M+H)+ 448.2056, found 448.2005.
H-30), 4.31 (dd, 1H, J5 ,3 ¼1.0, J5 ,5 ¼2.0 Hz, H-5 ), 4.13 (dd,
0
0
0
00 00
00
0
00
0
0
0
1H, J5 ,3 ¼1.0, J5 ,5 ¼2.0 Hz, H-5 ), 2.93 (dt, 1H, J2 ,1
¼
0
0
0
0
00
6.4, J2 ,3 ¼6.2, J2 ,2 ¼13.6 Hz, H-2 ), 2.77 (sept, 1H,
00
0
00
0
J¼6.8 Hz, CH), 2.44 (ddd, 1H, J2 ,3 ¼4.2, J2 ,1 ¼6.4,
00
00
0
J2 ,2 ¼13.6 Hz, H-2 ), 1.125 and 1.12 (2ꢂd, 2ꢂ3H,
J¼6.8 Hz, 2ꢂCH3), 0.90 (s, 9H, t-Bu), 0.16 and 0.15 (2ꢂs,
2ꢂ3H, Si(CH3)2).
4.2.8. 9-(2,5-Dideoxy-b-D-glycero-pent-4-enofuranosyl)-
2-N-isobutyrylguanine (9h). 20,50-Dideoxy-50-iodo-2-N-
isobutyrylguanosine (8c): Iodine (7.61 g, 60 mmol) was
added at 0 ꢃC to a stirred mixture of 20-deoxy-2-N-isobu-
tyrylguanosine (16.87 g, 50 mmol), triphenyl phosphine
(15.74 g, 60 mmol) and pyridine (5 mL) in DMF (200 mL),
and the reaction mixture was further stirred at rt for 16 h. Wa-
ter (10 mL) was added and the mixture was concentrated in
vacuo. The residue was shortly refluxed in methanol
(200 mL), silica gel (100 g) was added and methanol was
removed in vacuo. Silica gel with adsorbed compound was
applied on a dry column of silica gel (300 g) and the com-
pound was eluted using a linear gradient of H1 in ethyl ace-
tate. The obtained TLC- and HPLC-pure 8c (17.9 g, 40%)
was used for further reactions without characterization.
13C NMR (DMSO): 180.50 (C]O (iBu)), 162.91 (C-40),
155.02 (C-6), 148.93 (C-4), 141.84 (C-2), 137.75 (C-8),
120.64 (C-5), 83.83 (C-50), 83.22 (C-10), 70.65 (C-30),
38.41 (C-20), 25.94 (3ꢂCH3 (t-Bu)), 17.92 (pCo(t-Bu)),
ꢀ4.59 and ꢀ4.57 (Si(CH3)2). HRMS FAB+ calcd for
C20H32N5O4Si (M+H)+ 434.2224, found 434.2188.
4.2.10. Diisopropyl-(1-thymin-1-yl-1,2,5-trideoxy-a-L-
threo-pentofuranos-4-yloxy)methylphosphonate (11a)
and diisopropyl-(1-thymin-1-yl-1,2,5-trideoxy-b-D-ery-
thro-pentofuranos-4-yloxy)methylphosphonate (11b).
To a solution of compound 9a (436 mg, 1.946 mmol; co-
evaporated with dioxane–dichloromethane) in dry dichloro-
methane (20 mL), 10b (1.144 g, 5.838 mmol) was added and
then, under stirring, PTS (1.465 g, 5.838 mmol). The whole
was stirred at rt for 3 h (TLC in C2 and E1). The mixture was
then diluted with dichloromethane (50 mL) and washed with
water (50 mL). The aqueous layer was extracted with di-
chloromethane (3ꢂ30 mL), and the pooled organic wash-
ings were dried with Na2SO4 and evaporated. The residue
was chromatographed on a silica gel column (50 g) using
a 0–5% chloroform–ethanol gradient. Overall yield of the
obtained isomers 11a and 11b, 290 mg (35%) as colourless
sirups; ca. 1:5 weight ratio. HRMS FAB+ calcd for
C17H30N2O8P (M+H)+ 421.1740, found 421.1755.
Elimination reaction: Compound 8c (6.96 g, 15.56 mmol) in
DMF (15 mL) was treated with potassium tert-butoxide
(2.34 g, 20.9 mmol; in 8 mL of DMF) under stirring at 0 ꢃC
for 5 min, and then the reaction was quenched by adding
Dowex 50 (Et3N)+ in 50% aq ethanol. The pooled washings
were evaporated, and the residue was submitted to a short
column of Dowex 1X8 (HCO3)ꢀ. The bound product was re-
leased from the resin by washing with a 30:70 mixture of 1 M
aq triethylammonium hydrogen carbonate–ethanol, the
washings were concentrated, and the aq solution of the resi-
due was applied onto preparative reversed-phase column.
Elution with water afforded the traces of starting product
while 10% aq methanol eluted the title product. Yield of
the amorphous solid 9h: 1.59 g (4.98 mmol, 32%). IR spec-
trum (KBr): nmax (cmꢀ1) 3500 (m, br, sh) OH, 3454 (s, br)
H2O, 3227 (w, br) NH, 1721 (m, br, sh) C]O, 1608 (s),
Isomer 11a: 48 mg, Rf¼0.17 in C2. 1H NMR (DMSO): 11.35
(br s, 1H, NH), 7.50 (br q, 1H, J¼1.0 Hz, H-6), 6.48 (dd, 1H,
0
0
0
0
00
0
J1 ,2 ¼9.0, J1 ,2 ¼6.3 Hz, H-1 ), 5.62 (d, 1H, JOH,3 ¼4.9 Hz,
30-OH), 4.63 (m, 2H, 2ꢂP–OCH), 4.01 (br t, 1H, H-30), 3.74
(dd, 1H, JP,CHa¼11.5, Jgem¼12.9 Hz, P–CHa), 3.62 (dd, 1H,
JP,CHb¼10.7, Jgem¼12.9 Hz, P–CHb), 2.26 (ddd, 1H,

4526
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
0
0
0
0
0
0
00
J2 ,1 ¼9.0, J2 ,3 ¼4.4, J2 ,2 ¼13.4 Hz, H-2 ), 2.11 (br dd, 1H,
(2ꢂd sept, 2ꢂ1H, JH,H¼6.1, JP,OCH¼7.6 Hz, 2ꢂP–OCH),
00
0
00
0
00
0
00
0
0
0
0
00
J2 ,1 ¼6.3, J2 ,3 ¼1.0, J2 ,2 ¼13.4 Hz, H-2 ), 1.87 (d, 3H,
J¼1.0 Hz, CH3), 1.26, 1.25 and 1.23 (3ꢂd, 6H, 3H and
3H, J¼6.1 Hz, 4ꢂCH3), 1.36 (s, 3H, CH3). 13C NMR
(DMSO): 163.86 (C-4), 151.01 (C-2), 135.59 (C-6),
111.48 (d, JC,P¼13.7 Hz, C-40), 111.18 (C-5), 84.33 (C-10),
75.17 (C-30), 70.77 and 70.61 (2ꢂd, JC,P¼6.8 Hz, 2ꢂP–
OCH), 56.21 (d, JC,P¼172.9 Hz, P–C), 37.52 (C-20), 23.96
(d, 2C, JC,P¼3.9 Hz, 2ꢂCH3), 23.86 and 23.83 (2ꢂd,
JC,P¼4.9 Hz, 2ꢂCH3), 16.37 (CH3), 11.86 (CH3).
4.45 (t, 1H, J3 ,2 ¼J3 ,2 ¼9.0 Hz, H-3 ), 3.74 (dd, 1H, JP,CHa
¼
15.4, Jgem¼13.4 Hz, P–CHa), 3.72 (t, 1H, JP,CHb¼13.4,
Jgem¼13.4 Hz, P–CHb), 2.15–2.25 (m, 2H, H-20 and H-
200), 1.81 (d, 3H, J¼1.2 Hz, CH3) 1.27 and 1.26 (2ꢂd,
2ꢂ3H, J¼6.1 Hz, 4ꢂCH3), 1.40 (s, 3H, CH3), 0.87 (s, 9H,
t-Bu), 0.10 and 0.07 (2ꢂs, 2ꢂ3H, Si(CH3)2).
4.2.12. Dimethyl-(1-thymin-1-yl-1,2,5-trideoxy-a-L-
threo-pentofuranos-4-yloxy)methylphosphonate (13a)
and dimethyl-(1-thymin-1-yl-1,2,5-trideoxy-b-D-erythro-
pentofuranos-4-yloxy)methylphosphonate (13a). Com-
pound 9a (1.345 g, 6 mmol) was co-evaporated with
dichloromethane–dioxane, dichloromethane (25 mL) and
the finely powdered molecular sieves A3 (1 g) were added,
and the whole was stirred. To the mixture, 10a (2.52 g,
18 mmol) and then PTS (4.52 g, 18 mmol) were added.
The whole was stirred at rt for 36 h (TLC in C1, HPLC).
The mixture was treated with water (0.3 mL), filtered
through Celite, the washings were evaporated and co-dis-
tilled with toluene. The residue was chromatographed on sil-
ica gel using a gradient of ethyl acetate to 10% H3 in ethyl
acetate. Obtained: 0.457 g of the faster product a-L-threo
13a and 1.144 g of slower b-D-erythro 13b as colourless sir-
ups; total yield, 1.601 g (73%); ratio, ca. 1:2.5. HRMS FAB+
calcd for C13H22N2O8P (M+H)+ 365.1114, found 365.1115.
1
Isomer 11b: 242 mg, Rf ¼0.22 in C2. H NMR (DMSO):
11.30 (br s, 1H, NH), 7.36 (br q, 1H, J¼1.0 Hz, H-6),
0
00
0
0
0 0
6.11 (dd, 1H, J1 ,2 ¼8.5, J1 ,2 ¼2.9 Hz, H-1 ), 5.11 (d, 1H,
0
JOH,3 ¼6.1 Hz, 3 -OH), 4.65 and 4.63 (2ꢂd sept, 2ꢂ1H,
JH,H¼6.1, JP,OCH¼7.6 Hz, 2ꢂP–OCH), 4.29 (br td,
1H, J3 ,2 ¼9.5, J3 ,2 ¼8.8, J3 ,OH¼6.1 Hz, H-30), 3.74 (dd,
0
00
0
0
0
1H, JP,CHa¼12.2, Jgem¼13.4 Hz, P–CHa), 3.67 (dd, 1H,
JP,CHb¼8.3, Jgem¼13.4 Hz, P–CHb), 2.23 (ddd, 1H,
00
00
0
00
0
00
0
J2 ,1 ¼8.5, J2 ,3 ¼9.5, J2 ,2 ¼13.2 Hz, H-2 ), 2.13 (ddd,
0
0
0
0
0
0
00
1H, J2 ,1 ¼2.9, J2 ,3 ¼8.8, J2 ,2 ¼13.2 Hz, H-2 ), 1.80 (d,
3H, J¼1.0 Hz, CH3), 1.27 (d, 12H, J¼6.1 Hz, 4ꢂCH3),
1.41 (s, 3H, CH3). 13C NMR (DMSO): 163.96 (C-4),
150.48 (C-2), 136.58 (C-6), 110.39 (C-5), 106.18 (d,
JC,P¼11.7 Hz, C-40), 81.79 (C-10), 74.27 (C-30), 70.50
and 70.45 (2ꢂd, JC,P¼6.8 Hz, 2ꢂP–OCH), 55.80 (d,
JC,P¼170.9 Hz, P–C), 36.23 (C-20), 24.03, 24.00, 23.93 and
23.88 (4ꢂd, JC,P¼4.9 Hz, 4ꢂCH3), 18.49 (CH3), 12.20
(CH3).
1
Isomer a-L-threo 13a: H NMR (DMSO): 11.31 (br s, 1H,
0
00
NH), 7.45 (br q, 1H, J¼1.2 Hz, H-6), 6.47 (dd, 1H, J1 ,2
¼
0
0
0
0
6.2, J1 ,2 ¼9.1 Hz, H-1 ), 5.62 (d, 1H, JOH,3 ¼4.8 Hz, OH),
4.04 (br t, 1H, J3 ,2 w1.0, J3 ,2 ¼4.8, J3 ,OH¼4.8 Hz, H-30),
3.87 (dd, 1H, JP,CHa¼11.0, Jgem¼13.2 Hz, P–CHa), 3.74
(dd, 1H, JP,CHb¼10.8, Jgem¼13.2 Hz, P–CHb), 3.69 and
0
00
0
0
0
4.2.11. Diisopropyl-(3-O-tert-butyldimethylsilyl-1-thy-
min-1-yl-1,2,5-trideoxy-a-L-threo-pentofuranos-4-yl-
oxy)methylphosphonate (12a) and diisopropyl-(3-O-tert-
butyldimethylsilyl-1-thymin-1-yl-1,2,5-trideoxy-b-D-
erythro-pentofuranos-4-yloxy)methylphosphonate (12b).
Compound 9b (100 mg, 0.296 mmol), co-evaporated with
dioxane–dichloromethane, was dissolved in dichlorome-
thane (5 mL). Compound 10b (175 mg, 0.888 mmol) was
added and then, under stirring, PTS (223 mg, 0.888 mmol).
The mixture was stirred for 4 h (TLC in C2 and T1) and
then partitioned between dichloromethane (40 mL) and
water (40 mL). Aqueous layer was extracted with dichloro-
methane (3ꢂ30 mL), the organic washings were combined,
dried with Na2SO4 and evaporated. The residue was chroma-
tographed on a silica gel column (40 g) using a 0–2.5%
ethanol–chloroform gradient. Combined yield of isomers
12a and 12b (in 1:1.25 ratio), 81 mg (51%); solid foams.
HRMS FAB+ calcd for C23H44N2O8PSi (M+H)+ 535.2604,
3.68 (2ꢂd, 2ꢂ3H, JP,H¼10.6 Hz, P(OCH3)2), 2.28 (ddd,
0
0
0
0
0
0
00
1H, J2 ,3 ¼4.8, J2 ,1 ¼9.1, J2 ,2 ¼13.4 Hz, H-2 ), 2.11 (ddd,
00
00
0
00
0
00
0
1H, J2 ,3 ¼1.0, J2 ,1 ¼6.2, J2 ,2 ¼13.4 Hz, H-2 ), 1.84 (d,
3H, J¼1.2 Hz, CH3), 1.36 (s, 3H, CH3).
Isomer b-D-erythro 13b: 1H NMR (DMSO): 11.31 (br s, 1H,
0
0
NH), 7.36 (br q, 1H, J¼1.2 Hz, H-6), 6.08 (dd, 1H, J1 ,2
¼
0
0
00
0
3.1, J1 ,2 ¼8.5 Hz, H-1 ), 5.14 (d, 1H, JOH,3 ¼6.4 Hz, OH),
0
0
0
00
0
0
4.29 (td, 1H, J3 ,OH¼6.4, J3 ,2 ¼9.6, J3 ,2 ¼8.8 Hz, H-3 ),
3.88 (dd, 1H, JP,CHa¼12.0, Jgem¼13.7 Hz, P–CHa), 3.80
(dd, 1H, JP,CHb¼8.3, Jgem¼13.7 Hz, P–CHb), 3.715 and
3.71 (2ꢂd, 2ꢂ3H, JP,OCH¼10.6 Hz, P(OCH3)2), 2.23 (ddd,
00
00
0
00
0
00
0
1H, J2 ,1 ¼8.5, J2 ,3 ¼9.6, J2 ,2 ¼13.4 Hz, H-2 ), 2.15
0
0
0
0
0
0
00
(ddd, 1H, J2 ,1 ¼3.1, J2 ,3 ¼8.8, J2 ,2 ¼13.4 Hz, H-2 ), 1.79
(d, 3H, J¼1.2 Hz, CH3), 1.40 (s, 3H, CH3).
1
found 535.2626. Isomer 12a: 36 mg, Rf ¼0.27 in C2. H
NMR (DMSO): 11.37 (br s, 1H, NH), 7.50 0(br s, 1H, H-6),
4.2.13. Dimethyl-(3-O-tert-butyldimethylsilyl-1-thymin-
1-yl-1,2,5-trideoxy-a-L-threo-pentofuranos-4-yloxy)me-
thylphosphonate (14a) and dimethyl-(3-O-tert-butyldi-
methylsilyl-1-thymin-1-yl-1,2,5-trideoxy-b-D-erythro-
pentofuranos-4-yloxy)methylphosphonate (14b). To a
solution of 9b (1.69 g, 5 mmol, co-evaporated with dioxane–
dichloromethane) in dichloromethane (30 mL), 10a (2.1 g,
15 mmol) was added and then, under stirring, PTS (3.76 g,
15 mmol). The mixture was stirred at rt overnight (TLC in
C2), dichloromethane was added (30 mL), and the whole
washed with water (100 mL). On re-extraction of the aque-
ous layer with dichloromethane (2ꢂ50 mL), the organic
washings were combined, dried with Na2SO4 and evapo-
rated. The syrupy residue was subjected to column
0
0
0
00
6.43 (dd, 1H, J1 ,2 ¼9.0, J1 ,2 ¼6.1 Hz, H-1 ), 4.63 (m, 2H,
0
0
0
0
00
2ꢂP–OCH), 4.18 (br d, 1H, J3 ,2 ¼4.2, J3 ,2 ¼1.0 Hz, H-3 ),
3.78 (dd, 1H, JP,CHa¼11.5, Jgem¼12.9 Hz, P–CHa), 3.64
(dd, 1H, JP,CHb¼11.0, Jgem¼12.9 Hz, P–CHb), 2.32 (ddd,
0
0
0
0
0
0
00
1H, J2 ,1 ¼9.0, J2 ,3 ¼4.2, J2 ,2 ¼13.4 Hz, H-2 ), 2.08 (br dd,
00
00
0
00
0
00
0
1H, J2 ,1 ¼6.1, J2 ,3 ¼1.0, J2 ,2 ¼13.4 Hz, H-2 ), 1.86 (br s,
3H, CH3), 1.26, 1.255 and 1.23 (3ꢂd, 6H, 3H and 3H,
J¼6.1 Hz, 4ꢂCH3), 1.35 (s, 3H, CH3), 0.89 (s, 9H, t-Bu),
0.11 and 0.10 (2ꢂs, 2ꢂ3H, Si(CH3)2).
1
Isomer 12b: 45 mg, Rf¼0.14 in C2. H NMR (DMSO):
11.31 (br s, 1H, NH), 7.40 (br q, 1H, J¼1.2 Hz, H-6), 6.08
0
0
0
0
00
(dd, 1H, J1 ,2 ¼3.7, J1 ,2 ¼8.0 Hz, H-1 ), 4.65 and 4.63

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4527
chromatography on silica gel (100 g) and the elution by
a gradient of 0–2.5% methanol in chloroform provided
a 1.860 g (78%) combined yield of isomers 14a (0.76 g)
and 14b (1.10 g) as solid foams; weight ratio, ca. 1:1.5.
For C19H35O8N2PSi (478.55) calcd 47.69% C, 7.37% H,
5.85% N; found: 47.75% C, 7.39% H, 5.56% N. MS
(FAB): 479.3 (M+H)+.
the aqueous layer with dichloromethane (50 mL), the or-
ganic washings were dried with Na2SO4 and evaporated.
The residue was subjected to column chromatography on sil-
ica gel and the elution by a gradient of 0–6% ethanol in chlo-
roform provided isomers 15a and 15b in a 1:1 ratio (TLC in
C1, HPLC) of which the faster-moving compound was iso-
lated (in the form of a solid foam) and characterized as
pure a-L-threo isomer 15a (0.783 g, 33%), while the remain-
ing sirupy mixture of isomers 15a,b (0.830 g, 35%) was not
further resolved and brought to additional NMR character-
ization in the form of fully deprotected isomers 22a,b.
Isomer 14a: Rf¼0.56 in C2. [a]2D0 ꢀ45.3 (c 0.063, CHCl3). IR
spectrum (KBr): nmax (cmꢀ1) 3180 (w, br) NH; 2897 (w),
1472 (m), 1464 (m, sh), 1389 (w, sh), 1364 (w), 1261 (s)
and 837 (s) all CH3 from TBDMS; 1718 (s, sh) and 1693
(vs) all C]O; 1648 (m, sh) C]C; 1432 (m, sh), 1404 (w),
1289 (m), 1007 (m) and 764 (m, sh) all ring; 1381 (w) CH3
from thymine; 1107 (s) C–O–C; 1047 (s), 1030 (s) and 780
1
Isomer a-L-threo 15a: Rf¼0.53 in C2. H NMR (DMSO):
11.38 (d, 1H, JNH,5¼2.0 Hz, NH), 7.69 (d, 1H, J6,5
¼
0
0
00
0
0
8.2 Hz, H-6), 6.39 (dd, 1H, J1 ,2 ¼6.2, J1 ,2 ¼8.8 Hz, H-1 ),
1
(m) all P–O–C. H NMR (DMSO): 11.37 (br s, 1H, NH),
0
5.63 (dd, 1H, J5,NH¼2.0, J5,6¼8.2 Hz, H-5), 4.21 (dd, 1H,
0
0
0
00
0
00
0
0
7.46 (br s, 1H, H-6), 6.42 (dd, 1H, J1 ,2 ¼9.3, J1 ,2 ¼6.1 Hz,
J3 ,2 ¼1.5, J3 ,2 ¼4.5 Hz, H-3 ), 3.90 (dd, 1H, JP,CHa¼10.5,
H-10), 4.22 (br d, 1H, J3 ,2 ¼4.0, J3 ,2 ¼1.0 Hz, H-3 ), 3.91
(dd, 1H, JP,CHa¼11.0, Jgem¼13.2 Hz, P–CHa), 3.77 (dd,
1H, JP,CHb¼11.2, Jgem¼13.2 Hz, P–CHb), 3.70 and 3.695
Jgem¼13.4 Hz, P–CHa), 3.77 (dd, 1H, JP,CHb¼11.5, Jgem
¼
¼
0
0
0
0
00
13.4 Hz, P–CHb), 3.70 and 3.69 (2ꢂd, 2ꢂ3H, JP;OCH
3
0
0
0
0
10:6 Hz, P(OCH3)2), 2.33 (ddd, 1H, J2 ,3 ¼4.5, J2 ,1 ¼8.8,
0
0
00
00
0
00
0
(2ꢂd, 2ꢂ3H, JP,OCH¼10.5 Hz, P(OCH3)2), 2.34 (ddd, 1H,
J2 ,2 ¼13.6 Hz, H-2 ), 2.12 (ddd, 1H, J2 ,3 ¼1.5, J2 ,1 ¼6.2,
0
00
0
0
0
0
0
00
00
0
J2 ,1 ¼9.3, J2 ,3 ¼4.0, J2 ,2 ¼13.4 Hz, H-2 ), 2.06 (br dd, 1H,
J2 ,2 ¼13.6 Hz, H-2 ), 1.36 (s, 3H, CH3), 0.89 (s, 9H,
t-Bu); 0.12 and 0.10 (2ꢂs, 2ꢂ3H, Si(CH3)2). HRMS FAB+
calcd for C18H34 N2O8PSi (M+H)+ 465.1822, found
465.1852.
00
00
0
00
0
00
0
J2 ,1 ¼6.1, J2 ,3 ¼1.0, J2 ,2 ¼13.4 Hz, H-2 ), 1.84 (br s, 3H,
CH3), 1.36 (s, 3H, CH3), 0.89 (s, 9H, t-Bu), 0.12 and 0.11
(2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR (DMSO): 163.79 (C-4),
150.98 (C-2), 135.44 (C-6), 111.33 (d, JC,P¼13.7 Hz, C-
40), 111.10 (C-5), 84.23 (C-10), 76.59 (C-30), 55.02 (d,
JC,P¼169.9 Hz, P–C), 53.04 and 52.99 (2ꢂd, JC,P¼6.8 and
5.9 Hz, P(OCH3)2), 37.83 (C-20), 25.73 and 17.81 (t-Bu),
16.58 (CH3), 11.82 (CH3), ꢀ4.81 and ꢀ5.03 (Si(CH3)2).
4.2.15. Dimethyl-(3-O-tert-butyldiphenylsilyl-1-cytosin-
1-yl-1,2,5-trideoxy-a-L-threo-pentofuranos-4-yloxy)me-
thylphosphonate (16a) and dimethyl-(3-O-tert-butyldi-
phenylsilyl-1-cytosin-1-yl-1,2,5-trideoxy-b-D-erythro-
pentofuranos-4-yloxy)methylphosphonate (16b). Com-
pound 9g (0.240 g, 0.536 mmol) was co-evaporated with di-
oxane, and dichloromethane was added (7 mL) followed by
10a (0.225 g, 1.608 mmol, 3 equiv) and then by PTS
(0.404 g, 1.608 mmol, 3 equiv). The mixture was stirred at
rt for 2 d (TLC in C2, HPLC), and 1 equiv each of the re-
agents were added to completion (8 h). Dichloromethane
was added (30 mL), and the whole washed with water
(50 mL). On re-extraction of the aqueous layer with di-
chloromethane (40 mL), the organic washings were dried
(Na2SO4) and evaporated. The residue was chromato-
graphed on silica gel using a gradient of 0–10% ethanol in
chloroform to afford isomers 16a (32 mg) as the faster,
and 16b (132 mg) as the slower moving product (ratio
1:4); overall yield, 164 mg (53%) in the form of solid foams.
Isomer 14b: Rf¼0.46 in C2. [a]2D0 +10.1 (c 0.188; CHCl3). IR
spectrum (KBr): nmax (cmꢀ1) 3180 (w, br) NH, 2898 (w),
1473 (m), 1464 (m, sh), 1363 (w, sh), 1251 (s), 1185 (m),
939 (w) and 840 (s) all CH3 from TBDMS, 1705 (vs) and
1687 (vs) all C]O, 1646 (m, sh) C]C, 1424 (w), 1317
(w), 1288 (m, sh) and 1066 (s) all ring, 1385 (m) and 1368
(w) all CH3 from thymine, 1260 (s) P]O, 1134 (s) C–O–
C, 1101 (w, sh) C–O–Si, 1041 (s), 802 (m) and 778 (m) all
1
P–O–C, 765 (m) ]CH. H NMR (DMSO): 11.32 (br s,
1H, NH), 7.41 (br q, 1H, J¼1.2 Hz, H-6), 6.06 (dd, 1H,
0
0
0
0
00
0
0
0
00
J1 ,2 ¼3.4, J1 ,2 ¼8.3 Hz, H-1 ), 4.48 (t, 1H, J3 ,2 ¼8.8, J3 ,2
¼
8.8 Hz, H-30), 3.88 (dd, 1H, JP,CHa¼11.2, Jgem¼13.7 Hz, P–
CHa), 3.85 (dd, 1H, JP,CHb¼9.5, Jgem¼13.7 Hz, P–CHb),
3.72 and 3.71 (2ꢂd, 2ꢂ3H, JP,OCH¼10.5 Hz, P(OCH3)2),
2.16–2.30 (m, 2H, H-20 and H-200), 1.81 (d, 3H, J¼1.2 Hz,
CH3), 1.41 (s, 3H, CH3), 0.86 (s, 9H, t-Bu), 0.10 and 0.07
(2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR (DMSO): 163.96 (C-4),
150.38 (C-2), 137.14 (C-6), 110.17 (C-5), 105.97 (d,
JC,P¼11.7 Hz, C-40), 82.68 (C-10), 75.42 (C-30), 54.97 (d,
JC,P¼168.0 Hz, P–C), 53.17 and 53.11 (2ꢂd, JC,P¼7.8 and
6.8 Hz, P(OCH3)2), 36.73 (C-20), 25.75 and 17.80 (t-Bu),
18.59 (CH3), 12.22 (CH3), ꢀ4.59 and ꢀ4.71 (Si(CH3)2).
Isomer a-L-threo 16a: Rf ¼0.50 in C2. [a]2D0 +5.0 (c 0.039,
CHCl3). IR spectrum (KBr): nmax (cmꢀ1) 3073 (w) ]C–
H; 1651 (s) NH2 and C]O, 1612 (m, sh) C]C, 1530 (w)
and 1291 (m) all cytosine ring, 1590 (w, sh), 1486 (w),
1428 (m), 1113 (s), 1105 (s), 998 (w, sh), 740 (w), 704
(m), 613 (m), 514 (s) and 488 (m) all arom. ring of TBDPS;
1468 (m), 1392 (w), 1365 (w) and 1379 (w) all CH3, 1260
(m) and 1207 (m) all P]O, 1046 (s) POC. 1H NMR
(DMSO): 7.62 and 7.45 (2ꢂm, 4H and 6H, 2ꢂC6H5), 7.55
(d, 1H, J6,5¼7.5 Hz, H-6), 7.23 and 7.20 (2ꢂbr s,02ꢂ1H,
4.2.14. Dimethyl-(3-O-tert-butyldimethylsilyl-1,2,5-tri-
deoxy-1-uracil-1-yl-a-L-threo-pentofuranos-4-yloxy)me-
thylphosphonate (15a). To the compound 9e (1.657 g,
5.11 mmol) co-evaporated with dry dioxane–dichlorome-
thane was added dichloromethane (35 mL) followed by
10a (2.15 g, 15.33 mmol) and then, under stirring, by PTS
(3.85 g, 15.33 mmol). The mixture was stirred at rt overnight
(TLC in C2), dichloromethane was added (60 mL) and the
whole washed with water (100 mL). On re-extraction of
0
0
0
00
NH2), 6.58 (dd, 1H, J1 ,2 ¼8.8, J1 ,2 ¼6.5 Hz, H-1 ), 5.72
0
0
0
00
(d, 1H, J5,6¼7.5 Hz, H-5), 4.23 (dd, 1H, J3 ,2 ¼4.7, J3 ,2
¼
1.5 Hz, H-30), 3.83 (dd, 1H, JP,CHa¼10.5, Jgem¼13.4 Hz,
P–CHa), 3.70 (dd, 1H, JP,CHb¼11.4, Jgem¼13.4 Hz, P–
CHb), 3.63 (d, 6H, JP,OCH¼10.7 Hz, P(OCH3)2), 2.02 (ddd,
0
0
0
0
0
0
00
1H, J2 ,3 ¼4.7, J2 ,1 ¼8.8, J2 ,2 ¼13.4 Hz, H-2 ), 1.95 (ddd,
00
00
0
00
0
00
0
1H, J2 ,3 ¼1.5, J2 ,1 ¼6.5, J2 ,2 ¼13.4 Hz, H-2 ), 1.39 (s,

4528
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
1
3H, CH3), 1.07 (s, 9H, t-Bu). 13C NMR (DMSO): 165.54 (C-
2), 141.21 (C-6), 135.58(2), 135.54(2), 132.92, 132.42,
130.50, 130.46, 128.31(2) and 128.27(2) (2ꢂC6H5),
111.40 (C-40), 84.90 (C-10), 77.96 (C-30), 54.89 d,
J(C,P)¼169.8 Hz (P–CH2–O), 53.05 d, J(C,P)¼6.2 Hz and
53.00 d, J(C,P)¼6.2 Hz (P(OCH3)2), 38.20 (C-20), 26.92
(3ꢂCH3 (t-Bu)), 19.05 (pCo(t-Bu)), 17.12 (C-50). HRMS
FAB+ calcd for C28H39N3O7PSi (M+H)+ 588.2295, found
588.2270.
Isomer b-D-erythro 17b: H NMR (DMSO): 8.08 and 7.97
(2ꢂs, 2ꢂ1H, H-2 and H-8), 7.73, 7.69 and 7.45 (3ꢂm, 2H,
2H and 6H, 2ꢂC6H5), 7.24 (s, 2H, NH2), 6.23 (dd, 1H,
0
0
0
0
00
0
0
J1 ,2 ¼2.0, J1 ,2 ¼8.7 Hz, H-1 ), 5.16 (dd, 1H, J3 ,2 ¼8.3,
0
0
00
J3 ,2 ¼9.2 Hz, H-3 ), 3.99 (dd, 1H, JP,CHa¼11.1, Jgem
¼
13.6 Hz, P–CHa), 3.93 (dd, 1H, JP,CHb¼9.6, Jgem¼13.6 Hz,
P–CHb), 3.80 and 3.78 (2ꢂd, 2ꢂ3H, JP;OCH ¼ 10:5 Hz,
3
00
0
00
0
00
0
P(OCH3)2), 2.56 (ddd, 1H, J2 ,1 ¼8.7, J2 ,3 ¼9.2, J2 ,2
¼
12.9 Hz, H-200), 2.37 (ddd, 1H, J2 ,1 ¼2.0, J2 ,3 ¼8.3,
0
0
0
0
0
0
00
J2 ,2 ¼12.9 Hz, H-2 ), 1.18 (s, 3H, CH3); 1.06 (s, 9H, t-Bu).
Isomer b-D-erythro 16b: Rf¼0.40 in C2. IR spectrum (KBr):
nmax (cmꢀ1) 3072 (m) and 3049 (m) all ]C–H, 1653 (vs)
NH2 and C]O, 1527 (m) and 1291 (m) all cytosine ring;
1590 (m), 1480 (m), 1428 (m), 113 (vs), 1105 (s, sh), 999
(m), 742 (m) 703 (s), 612 (m), 507 (s) and 489 (s) all arom.
ring of TBDPS; 1472 (m), 1465 (m), 1390 (m), 1381 (m)
and 1362 (m) all CH3, 1272 (m), 1225 (s, sh) P]O, 1078
4.2.17. Dimethyl-(3-O-tert-butyldimethylsilyl-1-guanin-
9-yl-1,2,5-trideoxy-a-L-threo-pentofuranos-4-yloxy)me-
thylphosphonate (18a) and dimethyl-(3-O-tert-butyldi-
methylsilyl-1-guanin-9-yl-1,2,5-trideoxy-b-D-erythro-
pentofuranos-4-yloxy)methylphosphonate (18b). Using
the procedure described for 16a,b, compound 9i (1.273 g,
2.94 mmol) was phosphonylated with 4 equiv of both 10a
and PTS for 2 d to completion (TLC in C1, HPLC). After
work-up, the silica gel chromatography using a gradient of
0–6% ethanol in chloroform, which was repeated once
more with a 0–4% run, afforded 0.635 g (1.107 mmol,
38%) of 18a,b as unresolved mixture of isomers in the
form of a sirupy residue. They were identified by 1H NMR
spectra, using the enriched fractions, as the faster-moving
a-L-threo 18a isomer and the slower b-D-erythro 18b isomer
in ca. 1:1.5 ratio. HRMS FAB+ calcd for C23H41N5O8PSi
(M+H)+ 574.2462, found 574.2494.
1
(s, sh) COSi, 1047 (vs), 760 (m) and 545 (m) all POC. H
NMR (DMSO): 7.65 and 7.45 (2ꢂm, 4H and 6H,
2ꢂC6H5), 7.32 (d, 1H, J6,5¼7.6 Hz, H-6), 7.17 and 7.12
0
0
0
00
(2ꢂbr s, 2ꢂ1H, NH2), 5.99 (dd, 1H, J1 ,2 ¼2.9, J1 ,2 ¼8.4 Hz,
H-10), 5.64 (d, 1H, J5,6¼7.6 Hz, H-5), 4.43 (t, 1H, J3 ,2 ¼8.8,
0
00
0
0
0
J3 ,2 ¼8.4 Hz, H-3 ), 3.92 (dd, 1H, JP,CHa¼11.1, Jgem
¼
13.6 Hz, P–CHa), 3.88 (dd, 1H, JP,CHb¼9.5, Jgem¼13.6 Hz,
P–CHb), 3.75 and 3.745 (2ꢂd, 2ꢂ3H, JP,OCH¼10.6 Hz,
00
0
00
0
00
0
P(OCH3)2), 2.28 (dt, 1H, J2 ,1 ¼8.4, J2 ,3 ¼8.8, J2 ,2
¼
13.4 Hz, H-200), 1.78 (ddd, 1H, J2 ,1 ¼2.9, J2 ,3 ¼8.4 Hz,
0
0
0
0
H-20), 1.25 (s, 3H, CH3), 1.02 (s, 9H, t-Bu).
4.2.16. Dimethyl-(1-adenin-9-yl-3-O-tert-butyldiphenyl-
silyl-1,2,5-trideoxy-a-L-threo-pentofuranos-4-yloxy)me-
thylphosphonate (17a) and dimethyl-(1-adenin-9-yl-3-O-
tert-butyldiphenylsilyl-1,2,5-trideoxy-b-D-erythro-pento-
furanos-4-yloxy)methylphosphonate (17b). Compound 9f
(1.40 g, 2.97 mmol) was phosphonylated following the pro-
cedure described for 16a,b under the use of 4 equiv of both
10a and PTS for 4 d (TLC in C1, HPLC). After work-up,
the silica gel chromatography using a gradient of 0–8% eth-
anol in chloroform afforded the isomeric mixture of 17a
(faster moving, minor product) and 17b (slower, major prod-
uct) in a 1:12 ratio (NMR reading). The mixture remained un-
resolved after an attempt for separation on preparative RP
column (elution, 100% water to 100% methanol). Yield of
17a,b: 0.86 g (47%); amorphous solid. IR spectrum (KBr):
nmax (cmꢀ1) 3072 (w) ]C–H, 1642 (m, sh) NH2, 1611 (vs),
1566 (m), 1517 (w), 1437 (m) all adenine ring; 1314 (w),
1216 (m), 1160 (m, sh), 824 (m), 798 (w) and 648 (w) all ad-
enine; 1590 (m, sh), 1488 (w, sh), 1428 (m), 1113 (s), 742 (w),
703 (s), 622 (m), 613 (m), 508 (m), 504 (m) and 487 (m) all
arom. ring of TBDPS; 1365 (w, sh) CH3, 1230 (m) P]O,
1082 (m) COSi, 1039 (w) POC. HRMS FAB+ calcd for
C29H39N5O6PSi (M+H)+ 612.2407, found 612.2379.
Isomer a-L-threo 18a: 1H NMR (DMSO): 12.09 (s, 1H, NH),
0
00
11.64 (s, 1H, NH), 8.17 (s, 1H, H-8), 6.33 (dd, 1H, J1 ,2 ¼6.4,
0
0
0
0
00
0
0
J1 ,2 ¼8.6 Hz, H-1 ), 4.31 (dd, 1H, J3 ,2 ¼1.0, J3 ,2 ¼4.5 Hz,
H-30); 3.82 (dd, 1H, JP,CHa¼11.0, Jgem¼13.4 Hz, P–CHa),
3.675 and 3.67 (2ꢂd, 2ꢂ3H, JP;OCH ¼ 10:7 Hz,
3
P(OCH3)2), 3.47 (dd, 1H, JP,CHb¼10.6, Jgem¼13.4 Hz, P–
0
0
0
0
0
00
CHb), 2.96 (ddd, 1H, J2 ,3 ¼4.5, J2 ,1 ¼8.6, J2 ,2 ¼13.9 Hz,
H-20), 2.76 (sept, 1H, J¼6.8 Hz, CH), 2.35 (ddd, 1H,
00
00
0
00
0
00
0
J2 ,3 ¼1.0, J2 ,1 ¼6.4, J2 ,2 ¼13.9 Hz, H-2 ), 1.35 (s, 3H,
CH3), 1.12 (d, 6H, J¼6.8 Hz, 2ꢂCH3), 0.91 (s, 9H, t-Bu),
0.15 and 0.13 (2ꢂs, 2ꢂ3H, Si(CH3)2).
1
Isomer b-D-erythro 18b: H NMR (DMSO): 12.09 (s, 1H,
NH), 11.64 (s, 1H, NH), 8.260 (s, 1H, H-8), 6.18 (dd, 1H,
0
0
0
00
0
00
J1 ,2 ¼3.4, J1 ,2 ¼7.0 Hz, H-1 ), 4.64 (t, 1H, J3 ,2 ¼8.8,
0
0
0
J3 ,2 ¼8.4 Hz, H-3 ), 3.91 (d, 2H, JP,CH2¼10.5 Hz, P–CH2),
3.75 and 3.71 (2ꢂd, 2ꢂ3H, JP;OCH ¼ 10:7 Hz, P(OCH3)2),
3
2.77 (sept, 1H, J¼6.8 Hz, CH), 2.50 (m, 2H, H-20 and H-
200), 1.44 (s, 3H, CH3), 1.12 (d, 6H, J¼6.8 Hz, 2ꢂCH3),
0.87 (s, 9H, t-Bu), 0.14 and 0.10 (2ꢂs, 2ꢂ3H, Si(CH3)2).
4.2.18. Dimethyl-(3-O-tert-butyldimethylsilyl-1,2,5-tri-
deoxy-1-cytosin-1-yl-a-L-threo-pentofuranos-4-yloxy)-
methylphosphonate (20a). Phosphorylchloride (0.69 mL,
7.4 mmol) followed by triethylamine (5.45 mL, 74 mmol)
were added to an ice-cold suspension of triazole (2.26 g,
33 mmol) in dry acetonitrile (55 mL). After 30 min stirring,
compound 15a (0.773 g, 1.664 mmol) in acetonitrile (8 mL)
was added dropwise. The whole was stirred for 5 h (TLC in
C2), evaporated to dryness, and the residue partitioned be-
tween chloroform and a satd solution of sodium hydrogen
carbonate. The organic washings were pooled, evaporated
and the residue submitted to short-column chromatography
on silica (gradient of 0–7% ethanol in chloroform) to give
1
Isomer a-L-threo 17a: H NMR (DMSO): 8.22 and 8.14
(2ꢂs, 2ꢂ1H, H-2 and H-8), 7.67 and 7.45 (2ꢂm, 4H and
0
00
6H, 2ꢂC6H5), 7.31 (s, 2H, NH2), 6.53 (dd, 1H, J1 ,2 ¼6.9,
0
0
0
0
00
0
0
J1 ,2 ¼7.6 Hz, H-1 ), 4.45 (dd, 1H, J3 ,2 ¼1.5, J3 ,2 ¼4.5 Hz,
H-30), 3.77 (dd, 1H, JP,CHa¼10.6, Jgem¼13.4 Hz, P–CHa),
3.59 (d, 6H, JP;OCH ¼ 10:5 Hz, P(OCH3)2), 3.40 (dd,
3
1H, JP,CHb¼11.4, Jgem¼13.4 Hz, P–CHb), 2.59 (ddd, 1H,
0
0
0
0
0
0
00
J2 ,3 ¼4.5, J2 ,1 ¼7.6, J2 ,2 ¼13.4 Hz, H-2 ), 2.26 (ddd, 1H,
00
00
0
00
0
00
0
J2 ,3 ¼1.5, J2 ,1 ¼6.9, J2 ,2 ¼13.4 Hz, H-2 ), 1.42 (s, 3H,
CH3), 1.09 (s, 9H, t-Bu).

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4529
the residue of a single main product, which was immediately
used, without characterization, for treatment in satd (0 ꢃC)
ammonia-dry dioxane (15 mL) in a sealed vessel for 80 ꢃC
for 2d (TLC in H1). The mixture, upon cooling, was carefully
evaporated, the residue partitioned between chloroform and
a satd solution of sodium hydrogen carbonate, the organic
washings collected and evaporated, and the residue chroma-
tographed on a silica gel column (gradient, 0–5% ethanol in
chloroform). Obtained: 0.316 g of 20a (0.682 mmol, 41%) as
a solid foam. UV spectrum (nm): pH2: nmax¼275, nmin¼244;
pH7: nmax¼265, nmin¼253; pH12: nmax¼270, nmin¼255. 1H
NMR (DMSO): 7.66 (d, 1H, H-6), 7.23 and 7.19 (2ꢂbr 0s,
H-30), 3.57 (dd, 1H, Jgem¼12.3, JCH,P¼9.4 Hz, P–CHaHb–
O), 3.68 (dd, 1H, Jgem¼12.3, JCH,P¼11.5 Hz, P–CHaHb–
00
0
00
0
00
0
O), 2.54 (ddd, 1H, J2 ,1 ¼8.5, J2 ,2 ¼13.8, J2 ,3 ¼9.3 Hz,
H-200), 2.45 (ddd, 1H, J2 ,1 ¼3.0, J2 ,2 ¼13.8, J2 ,3 ¼8.9 Hz,
0
0
0
00
0
0
H-20), 1.88 (d, 3H, JCH ;6 ¼ 1:2 Hz, 5-CH3), 1.53 (s, 3H, 40-
3
CH3). 13C NMR (D2O): 169.41 (C-4), 154.32 (C-2), 141.22
(C-6), 114.59 (C-5), 108.93 (d, JC,P¼11.2 Hz, C-40), 86.80
(C-10), 77.61 (C-30), 60.13 (d, JC,P¼163.7 Hz, P–CH2–O),
38.40 (C-20), 20.27 (40-CH3), 14.30 (5-CH3). HRMS FAB+
calcd for C11H18N2O8P (M+H)+ 337.0801, found 337.0819.
4.2.21. 1,2,5-Trideoxy-1-uracil-1-yl-pentofuranos-4-
yloxymethylphosphonic acid (22a,b). Standard deprotec-
tion of epimeric mixture 15a,b (0.283 g, 0.609 mmol) af-
forded 0.147 g (0.456 mmol, 75%) of epimeric mixture
22a,b in the form of a solid lyophilisate from water. IR spec-
trum (KBr): nmax (cmꢀ1) 3427 (s, br), 3250 (m, br, sh) and
2805 (w, br) all OH, NH, H2O; 1697 (s) and 1685 (s, sh) all
C]O, 1628 (m, sh) C]C, 1473 (w), 1437 (w), 1398 (w)
and 1282 (m) all ring, 1387 (w) CH3, 1072 (m) C–OH,
1040 (m), 1015 (m), 985 (w, sh), 911 (w), 891 (w), 541 (w)
and 472 (w, br) all [PO3]2ꢀ, 817 (w) and 767 (w) ]C–H.
HRMS FAB+ calcd for C10H16N2O8P (M+H)+ 323.0644,
0
0
0
00
2ꢂ1H, NH2), 6.51 (dd, 1H, J1 ,2 ¼8.9, J1 ,2 ¼6.1 Hz, H-1 ),
0
0
0
00
5.78 (d, J5,6¼7.4 Hz, H-5), 4.18 (br d, 1H, J3 ,2 ¼4.4, J3 ,2
w
1.0 Hz, H-30), 3.89 (dd, 1H, JP,CHa¼10.5, Jgem¼13.3 Hz, P–
CHa), 3.77 (dd, 1H, JP,CHb¼11.6, Jgem¼13.3 Hz, P–CHb),
3.70 and 3.69 (2ꢂd, 2ꢂ3H, JP,OCH¼10.6 Hz, P(OCH3)2),
0
0
0
0
0
0
00
2.22 (ddd, 1H, J2 ,3 ¼4.4, J2 ,1 ¼8.9, J2 ,2 ¼13.4 Hz, H-2 ),
00
0
00
0
00
0
2.08 (br dd, 1H, J2 ,3w1.0, J2 ,1 ¼6.1, J2 ,2 ¼13.4 Hz, H-
200), 1.35 (s, 3H, CH3), 0.89 (s, 9H, t-Bu), 0.12 and 0.105
(2ꢂs, 2ꢂ3H, Si(CH3)2). Product was further characterized
in its fully deprotected form 23a.
1
4.2.19. 1-Thymin-1-yl-1,2,5-trideoxy-a-L-threo-pentofur-
anos-4-yloxymethylphosphonic acid (21a). On application
of the general deprotection procedure provided above, com-
pound 14a (0.900 g, 1.88 mmol) afforded the free phos-
phonic acid 21a (0.243 g, 0.723 mmol) in 38% yield as
a solid lyophilisate from water. [a]2D0 +24.8 (c 0.177, H2O).
IR spectrum (KBr): nmax (cmꢀ1) 3437 (vs, br), 3260 (w, br,
sh) and 2795 all OH, NH, H2O; 1696 (vs, br) C]O; 1476
(w) and 1284 (m) all ring; 1040 (m, sh), 1016 (m), 972 (m),
908 (w), 564 (m) and 480 (w, br) all [PO3]2ꢀ, 1388 (w) and
found 323.0829. Isomer a-L-threo 22a: H NMR (D2O):
0
0
7.98 (d, 1H, J6,5¼08.0 Hz, H-6); 6.57 (dd, 1H, J1 ,2 ¼8.5,
0
00
J1 ,2 ¼6.6 Hz, H-1 ), 5.95 (d, 1H, J5,6¼8.0 Hz, H-5), 4.33
0
0
00
0
0
(dd, 1H, J3 ,2 ¼1.0, J3 ,2 ¼5.0 Hz, H-3 ), 3.54 (dd, 1H, Jgem
¼
¼
12.4, JCH,P¼10.5 Hz, P–CHaHb–O), 3.66 (dd, 1H, Jgem
12.4, JCH,P¼5.8 Hz, P–CHaHb–O), 2.62 (ddd, 1H,
0
0
0
0
00
0
0
J2 ,1 ¼8.5, J2 ,2 ¼14.3, J2 ,3 ¼5.0 Hz, H-2 ), 2.37 (ddd, 1H,
00
00
0
00
0
00
0
J2 ,2 ¼14.3, J2 ,1 ¼6.6, J2 ,3 ¼1.0 Hz, H-2 ), 1.50 (s, 3H,
40-CH3). 13C NMR (D2O): 169.04 (C-4), 154.94 (C-2),
145.68 (C-6), 115.17 (d, JC,P¼12.7 Hz, C-40), 106.06 (C-
5), 87.86 (C-10), 78.60 (C-30), 61.16 (d, JC,P¼160.3 Hz, P–
CH2–O), 39.87 (C-20), 18.23 (40-CH3). Isomer b-D-erythro
1379 (w) all CH3, 1107 (m) C–O–C, 1079 (s) C–OH, 769 (w)
]C–H. H NMR (D2O): 7.78 (q, 1H, J6;OCH ¼ 1:3 Hz,
1
3
1
0
0
0
0
00
0
H-6), 6.56 (dd, 1H, J1 ,2 ¼8.5, J1 ,2 ¼6.5 Hz, H-1 ), 4.21 (br
22b: H NMR (D2O): 7.64 (d, 1H, J6,5¼8.1 Hz, H-6), 6.12
0
0
0
0
00
0
0
0
00
d, 1H, J3 ,2 ¼6.0, J3 ,2 <1 Hz, H-3 ), 3.66 (dd, 1H, JP,CHa
¼
(dd, 1H, J1 ,2 ¼2.9, J1 ,2 ¼8.5 Hz, H-1 ), 5.86 (d, 1H, J5,6
¼
0
0
0
0
00
11.5, JCHa,CHb¼12.2 Hz, P–CHa), 3.53 (dd, 1H, JP,CHb¼10.0,
8.1 Hz, H-5), 4.35 (dd, 1H, J3 ,2 ¼8.7, J3 ,2 ¼9.4 Hz, H-3 ),
3.63 (dd, 1H, Jgem¼12.0, JCH,P¼11.2 Hz, P–CHaHb–O),
0
0
JCHb,CHa¼12.2 Hz, P–CHb), 2.66 (ddd, 1H, J2 ,1 ¼8.5,
0
0
00
0
0
00
0
J2 ,2 ¼14.2, J2 ,3 ¼5.0 Hz, H-2 ), 2.35 (bdd, 1H, J2 ,1 ¼6.5,
3.53 (dd, 1H, Jgem¼12.0, JCH,P¼9.7 Hz, P–CHaHb–O),
00
0
H-200),
1.89
(d,
3H,
2.58 (ddd, 1H, J2 ,1 ¼8.5, J2 ,2 ¼13.8, J2 ,3 ¼9.4 Hz, H-2 ),
00
0
00
0
00
0
00
0
00
0
J2 ,2 ¼14.2,
J
2 ,3 <1 Hz,
JCH ;6 ¼ 1:2 Hz, 5-CH3), 1.50 (s, 3H, 40-CH3). 13C NMR
2.45 (ddd, 1H, J2 ,1 ¼2.9, J2 ,2 ¼13.8, J2 ,3 ¼8.7 Hz, H-2 ),
1.53 (s, 3H, 40-CH3). 13C NMR (D2O): 170.20 (C-4),
154.42 (C-2), 145.84 (C-6), 114.88 (d, JC,P¼12.7 Hz, C-
40), 104.96 (C-5), 88.03 (C-10), 76.74 (C-30), 60.42 (d,
JC,P¼159.3 Hz, P–CH2–O), 40.98 (C-20), 17.91 (40-CH3).
0
0
0
00
0
0
3
(D2O): 169.52 (C-4), 154.64 (C-2), 141.55 (C-6), 114.66
(d, JC,P¼11.7 Hz, C-40), 114.35 (C-5), 87.77 (C-10), 76.98
(C-30), 61.04 (d, JC,P¼157.2 Hz, P–CH2–O), 40.92 (C-20),
18.06 (40-CH3), 14.47 (5-CH3). HRMS FAB+ calcd for
C11H18N2O8P (M+H)+ 337.0801, found 337.0813.
4.2.22. 1-Cytosin-1-yl-1,2,5-trideoxy-a-L-threo-pento-
furanos-4-yloxymethylphosphonic acid (23a). From 16a:
On standard deblocking, compound 16a (0.027 g,
0.058 mmol) afforded 0.008 g (0.025 mmol, 43%) of 23a
as a solid lyophilisate from water.
4.2.20. 1-Thymin-1-yl-1,2,5-trideoxy-b-D-erythro-pento-
furanos-4-yloxymethylphosphonic acid (21b). On stan-
dard deprotection of 14b (0.220 g, 0.606 mmol), product
21b 0.071 g (0.211 mmol) was obtained in 35% overall yield
as a solid lyophilisate from water. [a]2D0 +80.0 (c 0.074,
H2O).
From 20a: On standard deblocking, 0.306 g of compound
20a (0.660 mmol) afforded 0.106 g (0.330 mmol, 50%) of
23a (lyophilisate from water). [a]2D0 ꢀ7.8 (c 0.348, H2O).
IR spectrum (KBr): nmax (cmꢀ1) 3430 (vs, br) and 3205 (m,
br, sh) all OH, NH2, H2O, 1722 (w, sh) C]O, 1645 (s)
C]O, NH2, 1607 (m, sh), 1531 (w), 1485 (w), 1423 (w),
and 1335 (w) all ring, 1380 (w) CH3, 1290 (w, br), 1206
(w), 1155 (m), 1043 (w), 1102 (m) C–O–C; 1080 (m, br,
sh) C–OH; 1043 (w), 1013 (w), 970 (w), 945 (w), 899 (w,
IR spectrum (KBr): nmax (cmꢀ1) 3425 (s, br), 3260 (br, sh)
and 2816 (w, vbr) all OH, NH, H2O, 1692 (vs, br) C]O,
1477 (m) and 1282 (m) all ring; 1387 (w) and 1383 (w) all
CH3, 1108 (s) COC, 1087 (m, sh) C–OH, 1041 (s), 1014
(m, sh), 960 (m), 908 (m), 551 (m) and 477 (m, sh) all
[PO3]2ꢀ, 766 (w) ]C–H. 1H NMR (D2O): 7.39 (q,
0
0
1H, J6;CH ¼ 1:2 Hz, H-6), 6.14 (dd, 1H, J1 ,2 ¼3.0,
3
0
0
00
0
0
0
00
J1 ,2 ¼8.5 Hz, H-1 ), 4.39 (dd, 1H, J3 ,2 ¼8.9, J3 ,2 ¼9.3 Hz,
br), 570 (w, br, sh), 536 (w, br) and 467 (w, br) all [PO3]2ꢀ
,

4530
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
799 (w) ]C–H. 1H NMR (D2O): 7.99 (d, 1H, J6,5¼7.5 Hz,
J3 ,2 ¼8.6, J3 ,2 ¼9.5 Hz, H-3 ), 3.58 (dd, 1H, Jgem¼12.2,
JCHa,P¼9.2 Hz, P–CHaHb–O), 3.72 (dd, 1H, Jgem¼12.2,
0
0
0
0
00
0
0
00
0
0
H-6), 6.60 (dd, 1H, J1 ,2 ¼6.5, J1 ,2 ¼8.4 Hz, H-1 ), 6.13 (d,
0
00
0
0
00
0
1H, J5,6¼7.5 Hz, H-5), 4.33 (dd, 1H, J3 ,2 ¼1.2, J3 ,2
¼
JCHb,P¼11.4 Hz, P–CHaHb–O), 2.71 (ddd, 1H, J2 ,1 ¼8.0,
4.8 Hz, H-30), 3.50 (dd, 1H, Jgem¼12.0, JCHa,P¼10.4 Hz,
J2 ,2 ¼13.8, J2 ,3 ¼9.5 Hz, H-2 ), 2.67 (ddd, 1H, J2 ,1 ¼3.3,
00
0
00
0
00
0
0
0
P–CHaHb–O), 3.60 (dd, 1H, Jgem¼12.0, JCHb,P¼11.2 Hz,
J2 ,2 ¼13.8, J2 ,3 ¼8.6 Hz, H-2 ), 1.51 (s, 3H, 4 -CH3). 13C
NMR (D2O): 161.78 (C-6), 156.64 (C-2), 119.16 (C-5),
109.04 (C-40), 83.84 (C-10), 77.65 (C-30), 60.27 (d,
JC,P¼158.7 Hz, P–CH2–O), 38.78 (C-20), 20.45 (40-CH3),
signals of C-4 and C-8 were not detected. HRMS FAB+
calcd for C11H17N5O7P (M+H)+ 362.0866, found 362.0856.
0
0
00
0
0
0
0
0
00
P–CHaHb–O), 0 2.58 (ddd, 1H, J2 ,1 ¼8.4, J2 ,2 ¼14.2,
0
0
00
00
0
00
J2 ,3 ¼4.8, H-2 ), 2.37 (ddd, 1H, J2 ,1 ¼6.5, J2 ,2 ¼14.2,
J2 ,3 ¼1.2 Hz, H-2 ), 1.50 (s, 3H, 4 -CH3). 13C NMR
(D2O): 168.93 (C-2), 160.82 (C-4), 145.64 (C-6), 115.07
(d, JC,P¼13.2 Hz, C-40), 100.18 (C-5), 88.65 (C-10), 78.76
(C-30), 61.44 (d, JC,P¼157.2 Hz, P–CH2–O), 40.40 (C-20),
18.37 (40-CH3). HRMS FAB+ calcd for C10H17N3O7P
(M+H)+ 322.0804, found 322.0902.
00
00
0
4.2.25. 1-Adenin-9-yl-1,2,5-trideoxypentofuranos-4-
yloxymethylphosphonic acid (25a,b). Standard deprotec-
tion of compound mixture 17a,b (0.350 g, 0.572 mmol) af-
forded 0.095 g (0.275 mmol, 48%) of epimeric mixture
25a,b as a solid lyophilisate from water. IR spectrum
(KBr): nmax (cmꢀ1) 3435 (vs, br) and 3180 (m, br, sh) all
OH, NH2, H2O, 1644 (s) NH2, 1607 (m), 1579 (w), 1579
(w), 1506 (w), 1480 (w), 1423 (w) and 1335 (w) all ring,
1305 (w), 1210 (w) and 647 (w) all C–NH2, 1386 (w,
CH3), 1230 (w, br), 1176 (w), 1106 (m, C–O–C), 1085 (m,
sh, C–OH); 1040 (m), 951 (w), 903 (w), 565 (w, br) and
464 (w, br) all [PO3]2ꢀ, 798 (w), 734 (w) ]C–H.
4.2.23. 1-Cytosin-1-yl-1,2,5-trideoxy-b-D-erythro-pento-
furanos-4-yloxymethylphosphonic acid (23b). On stan-
dard deblocking, 0.127 g (0.216 mmol) of 16b afforded
0.051 g (0.159 mmol, 73%) of 23b as a solid lyophilisate
from water. [a]2D0 +64.0 (c 0.033, H2O). IR spectrum (KBr):
nmax (cmꢀ1) 3427 (vs, br) OH, NH2, H2O, 1722 (w) C]O,
1651 (s) C]O and NH2, 1613 (m, sh), 1530 (w), 1493 (w)
and 1411 (w) all ring, 1388 (vw) CH3, 1289 (w), 1210 (w,
sh), 1093 (m) C–O–C, C–OH, 1044 (m), 960 (w), 907 (w),
570 (m, br), 481 (m, br) all [PO3]2ꢀ, 784 (w) ]C–H.
Isomer a-L-threo 25a: 1H NMR (D2O): 8.17 and 8.49 (2ꢂs,
1H NMR (D2O): 7.60 (d, 1H, J6,5¼7.5 Hz, H-6), 6.10 (dd,
2ꢂ1H, H-2 and H-8), 6.56 (dd, 1H, J1 ,2 ¼7.0, J1 ,2 ¼7.8 Hz,
0
00
0
0
1H, J1 ,2 ¼2.6, J1 ,2 ¼8.4 Hz, H-10), 6.02 (d, 1H,
H-10), 4.47 (dd, 1H, J3 ,2 w1.0, J3 ,2 ¼5.2 Hz, H-3 ), 3.17 (dd,
0
0
0
0
00
0
00
0
0
0
0
0
00
J5,6¼7.5 Hz, H-5), 4.33 (dd, 1H, J3 ,2 ¼8.5, J3 ,2 ¼9.6 Hz,
H-30), 3.58 (dd, 1H, Jgem¼12.2, JCHa,P¼9.4 Hz, P–
CHaHb–O), 3.69 (dd, 1H, Jgem¼12.2, JCHb,P¼11.4 Hz, P–
1H, Jgem¼12.2, JCHa,P¼9.3 Hz, P–CHaHb–O), 3.53 (t,
1H, Jgem¼JCHb,P¼12.2 Hz, P–CHaHb–O), 3.13 (ddd, 1H,
0
0
0
0
00
0
0
J2 ,1 ¼7.8, J2 ,2 ¼14.3, J2 ,3 ¼5.2 Hz, H-2 ), 2.62 (ddd, 1H,
00
00
0
00
0
00
0
00
0
00
0
CHaHb–O), 2.56 (ddd, 1H, J2 ,1 ¼8.4, J2 ,2 ¼13.6,
J2 ,1 ¼7.0, J2 ,2 ¼14.3, J2 ,3w1.0 Hz, H-2 ), 1.51 (s, 3H,
13
00
J2 ,3 ¼9.6 Hz, H-2 0), 2.39 (ddd, 1H, J2 ,1 ¼2.6, J2 ,2 ¼13.6,
40-CH3). C NMR (D2O): 85.64 (C-10), 78.76 (C-30),
00
0
0
0
00
00
J2 ,3 ¼8.5 Hz, H-2 ), 1.52 (s, 3H, 4 -CH3). 13C NMR
(D2O): 169.07 (C-2), 160.12 (C-4), 145.29 (C-6), 108.99
(d, JC,P¼12.2 Hz, C-40), 99.17 (C-5), 87.72 (C-10), 77.53
(C-30), 60.16 (d, JC,P¼159.2 Hz, P–CH2–O), 39.06 (C-20),
20.39 (40-CH3). HRMS FAB+ calcd for C10H17N3O7P
(M+H)+ 322.0804, found 322.0922.
40.70 (C-20), 18.17 (40-CH3).
0
0
1
Isomer b-D-erythro 25b: H NMR (D2O): 8.17 and 8.22
0
0
(2ꢂs, 2ꢂ1H, H-2 and H-8), 6.35 (dd, 1H, J1 ,2 ¼3.0,
0
0
00
0
0
0
00
J1 ,2 ¼8.0 Hz, H-1 ), 4.58 (dd, 1H, J3 ,2 ¼8.4, J3 ,2 ¼9.6 Hz,
H-30), 3.59 (dd, 1H, Jgem¼12.2, JCHa,P¼9.4 Hz, P–CHaHb–
O), 3.73 (t, 1H, Jgem¼12.2, JCHb,P¼12.2 Hz, P–CHaHb–O),
00
0
00
0
00
0
00
0
4.2.24. 1-Guanin-9-yl-1,2,5-trideoxypentofuranos-4-
yloxymethylphosphonic acid (24a,b). Standard deprotec-
tion of compound mixture 18a,b (0.618 g, 1.077 mmol) af-
forded 0.080 g (0.221 mmol, 21%) of epimeric mixture
24a,b in the form of a solid lyophilisate from water. IR spec-
trum (KBr): nmax (cmꢀ1) 3433 (vs, br) and 3132 (w, br, sh) all
OH, NH, NH2, H2O, 1694 (m) C]O, 1627 (m, br) NH2,
1605 (m, sh), 1532 (w), 1484 (w), 1412 (vw, sh) and 1324
(w) all ring, 1177 (w), 1381 (w) CH3, 1110 (w) C–O–C,
1082 (w, sh) C–OH, 1040 (w), 970 (w, sh), 907 (w, br),
560 (w, br), 470 (w, br) all [PO3]2ꢀ, 783 (vw) ]C–H.
2.77 (ddd, 1H, J2 ,1 ¼8.0, J2 ,2 ¼13.5, J2 ,3 ¼9.6 Hz, H-2 ),
0
0
0
00
0
0
2.73 (ddd, 1H, J2 ,1 ¼3.0, J2 ,2 ¼13.5, J2 ,3 ¼8.4 Hz, H-2 ),
1.54 (s, 3H, 40-CH3). 13C NMR (D2O): 158.35 (C-6),
155.61 (C-2), 151.21 (C-4), 143.01 (C-8), 121.61 (C-5),
109.08 (d, JC,P¼11.7 Hz, C-40), 84.12 (C-10), 77.62 (C-30),
60.49 (d, JC,P¼158.3 Hz, P–CH2–O), 38.89 (C-20), 20.55
(40-CH3). HRMS FAB+ calcd for C11H17N5O6P (M+H)+
346.0917, found 346.0883.
4.2.26. Diisopropyl-(5-iodo-1-thymin-1-yl-1,2,5-tri-
deoxy-b-D-erythro-pentofuranos-4-yloxy)methylphosph-
onate (29b). To a solution of 9a (1.120 g, 5 mmol; dried by
co-evaporation with toluene) in 20 mL of dichloromethane,
1.96 g (10 mmol) of 10b was added. Then NIS (1.463 g,
6.5 mmol) was added under stirring and the mixture was
stirred at rt overnight (TLC in C2, HPLC). After the starting
compound had disappeared, the mixture was diluted with di-
chloromethane (150 mL) and washed with aq sodium thio-
sulfate (150 mL). The aqueous layer was washed with
dichloromethane (2ꢂ80 mL), the pooled organic washings
were treated with satd NaCl solution (150 mL), dried with
anhydrous MgSO4 and evaporated. The residue was purified
using the preparative reversed-phase chromatography under
elution with a linear gradient of water–methanol (0–50% in
1
Isomer a-L-threo 24a: H NMR (D2O): 8.15 (s, 1H, H-8),
0
0
00
0
0
6.38 (dd, 1H, J1 ,2 ¼7.0, J1 ,2 ¼8.0 Hz, H-1 ), 4.43 (dd, 1H,
0
0
00
0
0
J3 ,2 <1.0, J3 ,2 ¼5.0 Hz, H-3 ), 3.20 (dd, 1H, Jgem¼12.2,
JCHa,P¼9.3 Hz, P–CHaHb–O), 3.55 (t, 1H, Jgem¼12.2,
0
0
JCHb,P¼12.2 Hz, P–CHaHb–O0), 3.06 (ddd, 1H, J2 ,1 ¼8.0,
0
00
0
0
00
0
J2 ,2 ¼14.4, J2 ,3 ¼5.0 Hz, H-2 ), 2.55 (bdd, 1H, J2 ,1 ¼7.0,
J2 ,2 ¼14.4, J2 ,3 <1.0 Hz, H-2 ), 1.50 (s, 3H, 4 -CH3). 13C
NMR (D2O): 85.44 (C-10), 78.74 (C-30), 40.37 (C-20),
18.16 (40-CH3).
00
0
00
0
00
0
Isomer b-D-erythro 24b: 1H NMR (D2O): 7.89 (s, 1H, H-8),
0
0
0
0
00
6.19 (dd, 1H, J1 ,2 ¼3.3, J1 ,2 ¼8.0 Hz, H-1 ), 4.62 (dd, 1H,

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4531
150 min, 50–100% in 150 min, 10 mL minꢀ1) to furnish
984 mg (36%) of 29b as an amorphous solid. MS (FAB):
(M+H)+. 1H NMR (DMSO): 11.32 (br s, 1H, NH), 7.69 and
7.46 (2ꢂm, 4H and 6H, 2ꢂC6H5), 7.03 (br q, 1H,
1
547.2 (M+H)+. H NMR (DMSO): 11.36 (br s, 1H, NH),
J6;CH ¼ 1:0 Hz, H-6), 6.15 (dd, 1H, J1 ,2 ¼8.3, J1 ,2
¼
0
00
0
0
3
7.49 (br q, 1H, J6;CH ¼ 1:2 Hz, H-6), 6.22 (dd, 1H, J1 ,2
¼
3.2 Hz, H-10), 4.71 (t, 1H, J3 ,2 ¼J3 ,2 ¼8.3 Hz, H-3 ), 4.65
0
0
0
0
0
0
00
3
0
0
0
00
0
3.7, J1 ,2 ¼8.0 Hz, H-1 ), 5.32 (d, 1H, JOH,3 ¼5.9 Hz, 3 -
(m, 2H, P(OCH)2), 3.89 (d, 2H, JP,CH¼10.3 Hz, P–CH2),
OH), 4.65 (d sept, 2H, JCH;CH ¼ 6:1, JP,OCH¼7.6 Hz,
3.75 and 3.22 (2ꢂd, 2ꢂ1H, Jgem¼11.5 Hz, I–CH2), 2.28
3
0
00
0
0
00
0
00
0
00
0
P(OCH)2), 4.59 (t, 1H, J3 ,2 ¼8.8 Hz, H-3 ), 3.85 (dd, 1H,
(dt, 1H, J2 ,1 ¼J2 ,3 ¼8.3, J2 ,2 ¼13.4 Hz, H-2 ), 1.92 (ddd,
0
0
0
0
0
0
00
JP,CHa¼12.0, Jgem¼13.4 Hz, P–CHa), 3.79 (dd, 1H, JP,CHb
¼
1H, J2 ,1 ¼3.2, J2 ,3 ¼8.3, J2 ,2 ¼13.4 Hz, H-2 ), 1.67 (d,
8.8, Jgem¼13.4 Hz, P–CHb), 3.75 and 3.45 (2ꢂd, 2ꢂ1H,
Jgem¼11.2 Hz, I–CH2), 2.18–2.40 (m, 2H, H-20 and H-200),
3H, JCH ;6 ¼ 1:0 Hz, CH3), 1.29, 1.28 and 1.275 (3ꢂd, 3H,
3
3H and 6H, JCH ;CH ¼ 6:1 Hz, 4ꢂCH3), 1.04 (s, 9H, t-Bu).
3
1.80 (d, 3H, JCH ;6 ¼ 1:2 Hz, 5-CH3), 1.27 (d, 12H,
3
JCH ;CH ¼ 6:3 Hz, 4ꢂCH3); 13C NMR (DMSO): 163.96 (C-
4.2.29. Dimethyl-(3-O-tert-butyldimethylsilyl-5-iodo-1-
thymin-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-4-
yloxy)methylphosphonate (32b). Compound 9b (1.69 g,
5 mmol) was co-evaporated with dioxane, dissolved in di-
chloromethane (20 mL), and treated with dimethyl hydr-
oxymethylphosphonate (1.4 g, 10 mmol). NIS (1.463 g,
6.5 mmol) was added under stirring and after 90 min (TLC
in C2 and T1) of stirring at rt, the mixture was worked up
as described for 29a. Column chromatography on silica
(100 g; elution with 0–3% chloroform–ethanol) afforded
1.451 g (48%) of 32b as an amorphous solid, along with
a minor product (ca. 1:20, as from NMR; its spectrum not re-
solved). MS (FAB) 603.1 (M+H)+. 1H NMR (DMSO): 11.40
3
4), 150.60 (C-2), 136.87 (C-6), 110.36 (C-5), 104.47 (d,
JC,P¼11.7 Hz, C-40), 82.66 (C-10), 72.40 (C-30), 70.94 and
70.87 (2ꢂd, JC,P¼6.8 Hz, P(OCH)2), 56.40 (d, JC,P
¼
169.9 Hz, P–C), 36.51 (C-20), 24.15, 24.10, 24.06 and
24.02 (4ꢂd, JC,P¼4.9 Hz, 4ꢂCH3), 12.37 (CH3), 5.34
(CH2–I).
4.2.27. Diisopropyl-(3-O-tert-butyldimethylsilyl-5-iodo-
1-thymin-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-
4-yloxy)methylphosphonate (30b). Compound 9b
(845 mg, 2.5 mmol) was co-evaporated with dioxane–di-
chloromethane, dissolved in dichloromethane (10 mL), and
10b (980 mg, 5 mmol) was added. Then 730 mg
(3.25 mmol) of NIS was added, and the reaction and subse-
quent work-up were carried out as described for 29b. Chro-
matography of the residue on silica (100 g) using a 0–5%
ethanol–chloroform gradient followed by rechromatography
in the same system (0–2.5%) afforded 424 mg (26%) of 30b
as a sirup besides 50 mg of a mixture of three compounds un-
resolved by NMR. For C23H42N2O8ISiP (660.55) calcd
41.82% C, 6.41% H, 4.24% N; found, 41.77% C, 6.23% H,
(br s, 1H, NH), 7.48 (br q, 1H, J6;CH ¼ 10:2 Hz, H-6), 6.18
3
0
0
0
00
(dd, 1H, J1 ,2 ¼4.1, J1 ,2 ¼08.1 Hz, H-1 ), 4.72 (t, 1H,
0
0
0
00
J3 ,2 ¼8.3, J3 ,2 ¼7.8 Hz, H-3 ), 3.96 (d, 2H, JP,CH¼10.0 Hz,
P–CH2), 3.73 and 3.40 (2ꢂd, 2ꢂ1H, Jgem¼11.2 Hz, I–CH2),
3.73 and 3.72 (2ꢂd, 2ꢂ3H, JP;OCH ¼ 10:5 Hz, P(OCH3)2),
3
0
0
0
0
0
0
00
2.48 (ddd, 1H, J2 ,1 ¼4.1, J2 ,3 ¼8.3, J2 ,2 ¼12.7 Hz, H-2 ),
00
00
0
00
0
00
0
2.23 (dt, 1H, J2 ,1 ¼J2 ,3 ¼7.8, J2 ,2 ¼12.7 Hz, H-2 ), 1.80
(d, 3H, JCH ;6 ¼ 1:2 Hz, CH3), 0.88 (s, 9H, t-Bu), 0.15 and
3
0.11 (2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR (DMSO): 163.89
(C-4), 150.43 (C-2), 137.12 (C-6), 110.02 (C-5), 104.56
(d, JC,P¼12.7 Hz, C-40), 83.51 (C-10), 73.82 (C-30), 55.44
(d, JC,P¼167.0 Hz, P–C), 53.25 and 53.19 (2ꢂd,
JC,P¼6.8 Hz, P(OCH3)2), 37.36 (C-20), 25.78 and 17.78 (t-
Bu), 12.29 (CH3), 5.13 (CH2–I), ꢀ4.50 and ꢀ4.57
(Si(CH3)2).
1
4.47% N. MS (FAB) 661.3 (M+H)+. H NMR (DMSO):
11.37 (br s, 1H, NH), 7.48 (br q, 1H, J6;CH ¼ 1:2 Hz, H-6),
3
0
0
0
00
00
6.19 (dd, 1H, J1 ,2 ¼3.2, J1 ,2 ¼8.3 Hz, H-1 ), 4.71 (t, 1H,
0
0
J3 ,2 ¼8.2 Hz, H-3 ), 4.65 and 4.63 (2ꢂd sept, 2ꢂ1H,
JCH;CH ¼ 6:1, JP,OCH¼7.8 Hz, P(OCH)2), 3.84 (dd, 1H,
3
JP,CHa¼11.2, Jgem¼13.4 Hz, P–CHa), 3.835 (dd, 1H,
JP,CHb¼9.8, Jgem¼13.4 Hz, P–CHb), 3.78 and 3.35 (2ꢂd,
0
0
2ꢂ1H, Jgem¼11.5 Hz, I–CH2), 2.44 (ddd, 1H, J2 ,1 ¼3.2, J
4.2.30. Dimethyl-(3-O-tert-butyldiphenylsilyl-5-iodo-1-
thymin-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-4-
yloxy)methylphosphonate (33b). Using the same procedure
and stoichiometry as for 32b (reaction time, 90 min), com-
pound 9c (693 mg, 1.5 mmol) was treated with 10a and
NIS to afford, after similar work-up and column chromato-
graphy (50 g silica, 0–3% chloroform–ethanol gradient),
410 mg (37%) of 33b (Rf¼0.25 in C2) as a thick oil, along
0
0
0
0
00
00
0
¼8.1, J2 ,2 ¼13.2 Hz, H-2 ), 2.21 (dt, 1H, J2 ,1 ¼8.3,
2 ,3
00
00
0
00
0
J2 ,3 ¼8.3, J2 ,2 ¼13.2 Hz, H-2 ), 1.275, 1.270 and 1.26
(3ꢂd, 3H, 3H and 6H, JCH ;CH ¼ 6:1 Hz, 4ꢂCH3), 0.88 s,
3
9H, t-Bu), 0.15 and 0.10 (2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR
(DMSO): 164.11 (C-4), 150.86 (C-2), 138.11 (C-6), 110.35
(C-5), 104.41 (d, JC,P¼11.7 Hz, C-40), 82.59 (C-10), 72.48
(C-30), 71.06 and 70.96 (2ꢂd, JC,P¼5.9 Hz, P(OCH)2),
56.31 (d, JC,P¼169.0 Hz, P–C), 36.45 (C-20), 24.16, 24.13,
24.08 and 24.04 (4ꢂd, JC,P¼4.0 Hz, 4ꢂCH3), 26.12 and
18.09 (t-Bu), 12.38 (CH3), 5.23 (CH2–I), ꢀ2.92 (SiCH3).
1
with a minor (ca. 1:10, NMR) product (the signals in H
NMR were not fully resolvable). MS (FAB): 728.3
1
(M+H)+. H NMR (DMSO): 11.35 (br s, 1H, NH), 7.66–
7.72 and 7.30–7.52 (2ꢂm, 4H and 6H, 2ꢂC6H5), 7.12 (br
0
0
00
0
00
4.2.28. Diisopropyl-(3-O-tert-butyldiphenylsilyl-5-iodo-
1-thymin-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-
4-yloxy)methylphosphonate (31b). Compound 9c (924 mg,
2 mmol) was co-evaporated with dioxane, dissolved in di-
chloromethane (5 mL), treated with 10b (784 mg, 4 mmol),
and then NIS (585 mg, 2.6 mmol) was added under stirring.
On carrying out the reaction and work-up as described for
29b, the obtained syrupy residue was chromatographed on
silica (gradient, 0–3% chloroform–methanol) to give
530 mg (35%) of 31b as an amorphous solid, besides trace
by-products unresolved by NMR. MS (FAB): 785.3
s, 1H, H-6), 6.15 (dd, 1H, J1 ,2 ¼8.3, J1 ,2 ¼3.4 Hz, H-1 ),
0
0
0
00
4.75 (t, 1H, J3 ,2 ¼8.1, J3 ,2 ¼8.1 Hz, H-3 ), 4.03 (d, 2H,
JP,CH¼10.5 Hz, P–CH2), 3.76 (d, 6H, JP;OCH ¼ 10:5 Hz,
3
P(OCH3)2), 3.65 and 3.22 (2ꢂd, 2ꢂ1H, Jgem¼11.2 Hz, I–
00
0
00
0
00
0
CH2), 2.28 (dt, 1H, J2 ,1 ¼8.3, J2 ,3 ¼8.3, J2 ,2 ¼13.4 Hz,
H-200), 2.04 (ddd, 1H, J2 ,1 ¼3.4, J2 ,3 ¼8.1, J2 ,2 ¼13.4 Hz,
H-20), 1.70 (br s, 3H, 5-CH3), 1.04 (s, 9H, t-Bu). 13C NMR
(DMSO): 163.72 (C-4), 150.28 (C-2), 136.69 (C-6),
132.91, 132.74, 135.66, 135.64, 130.39, 130.36, 128.16
(arom. C), 109.99 (C-5), 104.50 (d, JC,P¼11.7 Hz, C-40),
83.21 (C-10), 74.37 (C-30), 55.13 (d, JC,P¼167.0 Hz, P–C),
0
0
0
0
0
00

4532
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
53.22 and 53.12 (2ꢂd, JC,P¼5.9 Hz, P(OCH3)2), 36.75
(C-20), 26.79 and 19.93 (t-Bu), 12.23 (5-CH3), 4.85 (CH2–I).
The organic layer was dried (Na2SO4), evaporated and chro-
matographed on silica (50 g) under elution with a 0–5%
chloroform–ethanol gradient.
4.2.31. Diisopropyl-(5-bromo-3-O-tert-butyldimethyl-
silyl-1-thymin-1-yl-1,2,5-trideoxy-a-L-threo-pentofura-
nos-4-yloxy)methylphosphonate (34a) and diisopropyl-
(5-bromo-3-O-tert-butyldimethylsilyl-1-thymin-1-yl-
1,2,5-trideoxy-b-D-erythro-pentofuranos-4-yloxy)-
methylphosphonate (34b). Compound 9b (563 mg,
1.67 mmol) was co-evaporated with dioxane, dissolved in
dichloromethane (10 mL), and 10b (655 mg, 3.34 mmol)
was added. NBS (386 mg, 2.17 mmol) was added under stir-
ring and the whole was left to react for 5 h at rt (TLC in C2).
The mixture was diluted with dichloromethane (150 mL)
and washed with a 5% solution of NaHCO3 (150 mL). The
aqueous layer was treated with dichloromethane
(2ꢂ50 mL), the combined organic washings were washed
with water (100 mL), dried with MgSO4 and evaporated.
The residue was purified by preparative reversed-phase chro-
matography under elution with a linear gradient of water–
methanol (0–50% in 180 min, 50–100% in 120 min,
10 mL minꢀ1). The obtained product was rechromato-
graphed on silica gel column (50 g) using a 0–3% chloro-
form–ethanol gradient elution. Yield: 423 mg (41%) of
a 5:1 34b–34a isomeric mixture (as of NMR) in the form
of a thick oil, MS (FAB) 614.1 (M+H)+.
The desired azido derivative 35b (58.5 mg, 29%), obtained
as a thick oil, was contaminated by the starting compound
and could not be separated from it by reversed-phase purifi-
cation. MS (FAB): 598.2 (M++Na). IR spectrum (cmꢀ1):
3392, 3178 (NH); 2960, 2900, 1254, 844, 1411 (CH3,
SiMe2); 2109 (–N3); 1692, 1713 (C]O); 1382, 1374
(CH3, isopropyl); 1361 (CH3, t-Bu); 1144, 1133 (C–O);
1
999, 1055 (C–O–P–O–C). H NMR (DMSO): 11.36 (br s,
1H, NH), 7.42 (br q, 1H, J6;CH ¼ 1:2 Hz, H-6), 6.21 (dd,
3
1H, J1 ,2 ¼3.2, J1 ,2 ¼8.8 Hz, H-10), 4.74 (t, 1H,
0
0
0
00
0
0
0
0
00
J3 ,2 ¼J3 ,2 ¼8.5 Hz, H-3 ), 4.64 (m, 2H, P(OCH)2), 3.68–
3.94 (m, 4H, P–CH2 and N–CH2), 2.22–2.44 (m, 2H, H-20
and H-200), 1.79 (d, 3H, JCH ;6 ¼ 1:2 Hz, 5-CH3), 1.27 and
3
1.26 (2ꢂd, 2ꢂ6H, JCH ;CH ¼ 6:3 Hz, 4ꢂCH3), 0.87 (s, 9H,
3
t-Bu), 0.10 and 0.08 (2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR
(DMSO): 163.98 (C-4), 150.41 (C-2), 137.50 (C-6),
109.99 (C-5), 105.98 (d, JC,P¼11.7 Hz, C-40), 84.38 (C-10),
72.39 (C-30), 70.51 (d, JC,P¼5.9 Hz, P(OCH)2), 56.20 (d,
JC,P¼169.0 Hz, P–C), 50.22 (CH2–N), 36.63 (C-20), 25.74
and 17.81 (t-Bu), 24.10 and 23.96 (2ꢂd, JC,P¼4.9 Hz,
4ꢂCH3), 12.23 (5-CH3), ꢀ4.52 and ꢀ4.69 (Si(CH3)2).
4.2.33. Methyl-(3-O-tert-butyldimethylsilyl-5-iodo-1-thy-
min-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-4-
yloxy)methylphosphonate (36a). Compound 32b (604 mg,
1 mmol) was dissolved in dry DMSO (10 mL) and 650 mg
(10 mmol) of sodium azide was added. The mixture was
stirred and on disappearance of the starting product (3 d,
TLC in C2), the solvent was removed and the residue was
chromatographed on preparative reversed phase column us-
ing a water–methanol linear gradient (0–50% in 30 min,
50–100% in 240 min, 10 mL minꢀ1). Obtained: 302 mg
Isomer 34a, a-L-threo, minor: 1H NMR (DMSO): 11.12 (br
s, 1H, NH), 7.64 (br q, 1 H, J6;CH ¼ 1:0 Hz, H-6), 6.20 (dd, 1
3
0
0
00
0
0
0
H, J1 ,2 ¼6.3, J1 , ¼9.0 Hz, H-1 ), 5.87 (br d, 1H, J3 ,
2
0
00
0
0
<0.5, J3 , 2 ¼5.0 Hz, H-3 ), 4.60 (m, 2H, P(OCH)2), 3.90
2
and 3.51 (2ꢂd, 2ꢂ1H, Jgem¼11.2 Hz, CH2–Br), 3.68 (dd,
1H, JP,CHa¼11.5, Jgem¼13.2 Hz, P–CHa), 3.61 (dd, 1H,
JP,CHb¼7.1, Jgem¼13.2 Hz, P–CHb), 2.54 and 2.10 (2ꢂm,
2ꢂ1H, H-20 and H-200), 1.87 (d, 3H, JCH ;6 ¼ 1:0 Hz, 5-
3
CH3), further CH3 signals overlapped.
1
(51%) of 36a as an oil. MS (FAB): 613.2 (M++Na). H
Isomer 34b, ß-D-erythro, major: 1H NMR (DMSO): 11.37 (br
NMR (DMSO): 11.40 (br s, 1H, NH), 7.45 (br q, 1H,
0
0
0
00
s, 1H, NH), 7.46 (br q, 1H, J6;CH ¼ 1:2 Hz, H-6), 6.25 (dd,
J6;CH ¼ 1:2 Hz, H-6), 6.20 (t, 1H, J1 ,2 ¼J1 ,2 ¼6.3 Hz, H-
3
3
0
0
0
0
0
0
00
0
0
0
00
1H, J1 ,2 ¼3.7, J1 ,2 ¼8.3 Hz, H-1 ), 4.57–4.70 (m, 3H, H-3
10), 4.66 (t, 1H, J3 ,2 ¼J3 ,2 ¼8.5 Hz, H-3 ), 3.73 and 3.26
and P(OCH)2), 3.92 and 3.68 (2ꢂd, 2ꢂ1H, Jgem¼11.2 Hz,
Br–CH2), 3.89 (dd, 1H, JP,CHa¼12.0, Jgem¼13.2 Hz, P–
(2ꢂd, 2ꢂ1H, Jgem¼11.5 Hz, I–CH2), 3.48 (br t, 1H, JP,CHa
¼
Jgem¼12.0 Hz, P–CHa), 3.43 (d, 3H, JP;OCH ¼ 9:8 Hz, P–
3
CHa), 3.80 (dd, 1H, JP,CHb¼8.7, Jgem¼13.2 Hz, P–CHb),
OCH3), 3.39 (dd, 1H, JP,CHb¼8.5, Jgem¼12.2 Hz, P–CHb),
0
00
0
0
0
0
0
00
0
0
00
0
0
0
00
0
2.32 (ddd, 1H, J2 ,1 ¼3.7, J
¼8.3, J2 ,2 ¼13.4 Hz, H-2 ),
2.29 (dd, 2H, J2 ,1 ¼J2 ,1 ¼6.3, J2 ,3 ¼J2 ,3 ¼8.5 Hz, H-
2 ,3
00
0
00
0
00
0
2.27 (dt, 1H, J2 ,1 ¼8.3, J2 ,3 ¼8.3, J2 ,2 ¼13.4 Hz, H-2 ),
20+H-200), 1.80 (d, 3H, JCH ;6 ¼ 1:2 Hz, 5-CH3), 0.87 (s,
3
1.79 (d, 3H, JCH ;6 ¼ 1:2 Hz, 5-CH3), 1.27 and 1.26 (2ꢂd,
9H, t-Bu), 0.14 and 0.10 (2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR
(DMSO): 164.07 (C-4), 150.53 (C-2), 137.09 (C-6), 109.92
(C-5), 103.27 (d, JC,P¼8.8 Hz, C-40), 82.63 (C-10), 73.41
(C-30), 58.48 (d, JC,P¼155.3 Hz, P–C), 51.93 (d,
JC,P¼4.9 Hz, OCH3), 36.81 (C-20), 25.91 and 17.89 (t-Bu),
12.41 (5-CH3), 4.69 (CH2–I), ꢀ4.41 and ꢀ4.44 (Si(CH3)2).
3
2ꢂ6H, JCH ;CH ¼ 6:3 Hz, 4ꢂCH3). 13C NMR (DMSO):
3
163.85 (C-4), 150.50 (C-2), 136.52 (C-6), 110.16 (C-5),
104.75 (d, JC,P¼10.7 Hz, C-40), 82.66 (C-10), 71.38 (C-30),
70.66 and 70.61 (2ꢂd, JC,P¼5.9 Hz, P(OCH)2), 56.47 (d,
JC,P¼169.9 Hz, P–C), 36.23 (C-20), 31.60 (CH2–Br), 23.91
and 23.88 (2ꢂd, JC,P¼3.9 Hz, 2ꢂCH3), 25.0 and 18.0 (t-
Bu), 12.25 (5-CH3), ꢀ5.0 (Si(CH3)2).
4.2.34. Methyl-(3-O-tert-butyldiphenylsilyl-5-iodo-1-thy-
min-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-4-
yloxy)methylphosphonate (36b). Compound 33b (259 mg,
0.36 mmol) in dry DMF (5 mL) was heated with 176 mg
(3.6 mmol) of sodium cyanide at 100 ꢃC for 3 d (TLC in
C2). The solvent was removed, and the residue chromato-
graphed on preparative reversed phase column using a wa-
ter–methanol linear gradient (0–50% in 90 min, 50–100%
in 150 min, 10 mL minꢀ1). Obtained: 118 mg (46%) of title
product in the form of an oil. MS (FAB): 737.1 (M++Na).
1H NMR (DMSO): 11.35 br s, 1H, NH), 7.70 and
4.2.32. Diisopropyl-(5-azido-3-O-tert-butyldimethylsilyl-
1-thymin-1-yl-1,2,5-trideoxy-b-D-erythro-pentofuranos-
4-yloxy)methylphosphonate (35b). Compound 30b
(234 mg, 0.35 mmol) was co-evaporated with dioxane, dis-
solved in dry DMF (15 mL) and sodium azide (300 mg,
4.61 mmol) was added. The mixture was heated at 100 ꢃC
for 48 h (TLC in C2), then the solvent was removed under
reduced pressure at 50 ꢃC, and the residue partitioned be-
tween dichloromethane (50 mL) and water (2ꢂ50 mL).

Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
4533
7.42–7.52 (2ꢂm, 4H and 6H, 2ꢂC6H5), 6.91 (br s, 1H, H-6),
NMR (CDCl3): 9.71 (br s, 1H, NH), 7.44 (q, 1H,
0
0
0
0
0
0
0
00
000
6.22 (dd, 1H, J1 ,2 ¼2.5, J1 ,2 ¼9.0 Hz, H-1 ), 4.61 (t, 1H,
J6;CH ¼ 1:2 Hz, H-6), 6.47 (dd, 1H, J1 ,2 ¼3.3, J1 ,2
¼
3
J3 ,2 ¼8.8, J3 ,2 ¼8.8 Hz, H-3 ), 3.72 and 3.15 (2ꢂd, 2ꢂ1H,
7.1 Hz, H-10), 4.68 (ddt, 1H, J3 ,2 ¼3.3, J3 ,2 ¼6.7, J3 ,5
¼
0
00
0
0
0
0
0
00
0
0
0
0
00
0
00
0
0
Jgem¼11.5 Hz, I–CH2), 3.51 (dd, 1H, JP,CHa¼11.0, Jgem
¼
J3 ,5 w1.0 Hz, H-3 ), 4.25 (dd, 1H, J5 ,5 ¼2.2, J5 ,3w1.0 Hz,
00
00
H-50), 4.57 (dd, 1H, J5 ,5 ¼2.2, J5 ,3 ¼J5 ,3w1.0 Hz, H-5 ),
0
00
0
0
00
00
0
12.2 Hz, P–CHa), 3.50 (d, 3H, JP;OCH ¼ 9:5 Hz, P–OCH3),
3
00
0
00
0
0
3.44 (dd, 1H, JP,CHb¼8.0, Jgem¼12.2 Hz, P–CHb), 2.37 (dt,
2.65 (dt, 1H, J2 ,1 ¼7.1, J2 ,2 ¼14.2, J2 ,3 ¼6.7 Hz, H-2 0),
00
00
0
00
0
00
0
0
0
0
00
0
0
1H, J2 ,1 ¼9.0, J2 ,3 ¼8.8, J2 ,2 ¼13.2 Hz, H-2 ), 1.71 (m,
1H, H-20), 1.66 (br s, 3H, 5-CH3), 1.02 (s, 9H, t-Bu). 13C
NMR (DMSO): 164.95 (C-4), 151.18 (C-2), 135.98 (C-6),
132.99, 132.92, 135.72, 135.65, 128.13, 128.10, 130.28 and
130.24 (arom. C), 110.09 (C-5), 103.21 (d, JC,P¼8.8 Hz,
C-40), 81.83 (C-10), 73.95 (C-30), 58.61 (d, JC,P¼155.3 Hz,
P–C), 51.97 (d, JC,P¼4.9 Hz, P–OCH3), 36.28 (C-20), 26.85
and 18.94 (t-Bu), 12.50 (5-CH3), 4.85 (CH2–I).
2.04 (dt, 1H, J2 ,1 ¼3.3, J2 ,2 ¼14.2, J2 ,3 ¼3.3 Hz, H-2 ),
1.92 (d, 3H, JCH ;6 ¼ 1:2 Hz, 5-CH3), 0.88 s, 9H, t-Bu),
3
0.11 and 0.14 (2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR (CDCl3):
164.01 (C-4), 163.09 (C-40), 150.54 (C-2), 135.72 (C-6),
110.77 (C-5), 85.36 (C-50), 85.03 (C-10), 69.83 (C-30),
40.22 (C-20), 17.87 and 25.49 (t-Bu), 12.56 (5-CH3), 4.78
and ꢀ5.04 (Si(CH3)2).
4.2.37. Dimethyl-(3-O-tert-butyldimethylsilyl-1-thymin-
1-yl-1,2,5-trideoxy-a-L-threo-pentofuranos-4-yloxy)me-
thylphosphonate (40a) and dimethyl-(3-O-tert-butyldi-
methylsilyl-1-thymin-1-yl-1,2,5-trideoxy-b-D-erythro-
pentofuranos-4-yloxy)methylphosphonate (40b). To a so-
lution of 39b (169 mg, 0.5 mmol) in dichloromethane
(3 mL), 10a (140 mg, 1 mmol, 2 equiv) and A3 molecular
sieves (Merck) (0.7 g) were added followed by PTS
(377 mg, 1.5 mmol) and the whole was stirred overnight un-
der argon (TLC in C2). The solids were filtered off on Celite,
thewashingswerepooled,thesolventevaporatedandtheresi-
due chromatographed on a silica gel column using elution by
a 0–5% chloroform–ethanol gradient to provide 60 mg
(25%) of 40a and 122 mg (51%) of 40b as solid foams.
4.2.35. 2,30-Anhydro-1-(3-O-tert-butyldimethylsilyl-2,5-
dideoxy-b-L-glycero-pent-4-enofuranosyl)thymine (38).
To the compound 9a (2.24 g, 10 mmol) in DMF (10 mL), tri-
phenyl phosphine (3.93 g, 15 mmol) was added and then,
under stirring, diisopropyl-azodicarboxylate (2.93 mL,
15 mmol; in 10 mL of DMF) was added dropwise while
keeping the reaction temperature below 20 ꢃC. The whole
was then stirred at rt for 30 min (TLC in H-1). The product
was then precipitated by dropping the mixture into stirred
ether (400 mL), and the solid was collected on sintered glass
and washed with ether. On evaporating the solvents from the
filtrate, the residue was re-precipitated in ether (100 mL). To-
tal yield from two crops, 1.848 g (89%) of 38 as awhite amor-
phous solid. HRMS FAB+ calcd for C10H11N2O3 (M+H)+
1
207.0770, found 207.0799. H NMR (DMSO): 7.65 (br q,
0
Isomer 40a: HRMS FAB+ calcd for C19H36N2O8SiP
478.1900, found 479.1979 (M+H)+. 1H NMR (CDCl3):
0
0
00
1H, J6;CH ¼ 1:2 Hz, H-6), 6.18 (dd, 1H, J1 ,2 ¼1.0, J1 ,2
¼
3
4.0 Hz, H-10), 5.54 (dt, 1H, J3 ,2 ¼J3 ,5 ¼1.2, J3 ,2 ¼2.9 Hz,
9.40 (br s, 1H, NH), 7.71 (q, 1H, J6;CH ¼ 1:2 Hz, H-6),
0
0
0
00
0
00
3
0
H-30), 4.69 (br d, 1H, Jgem¼2.5 Hz, H-50), 4.61 (dd, 1H,
6.36 (dd, 1H, J1 ,2 ¼6.4, J1 ,2 ¼8.7 Hz, H-1 ), 4.07 (ddd,
0
0
0
00
00
0
00
0
00
0
0
0
0
0
0
00
0
J5 ,3 ¼1.2, J5 ,5 ¼2.5 Hz, H-5 ), 2.66 (br d, 1H, J2 ,1
¼
1H, J3 ,2 ¼6.5, J3 ,2 ¼10.2, J3 ,P¼1.1 Hz, H-30), 3.91 (dd,
1H, Jgem¼12.8, JP,CHa¼11.0 Hz, P–CHa), 4.00 (dd, 1H,
Jgem¼12.8, JP–CHb¼11.6 Hz, P–CHb), 3.86 and 3.82 (2ꢂd,
0
0
0
00
00
0
J2 ,3 ¼1.1, J2 ,2 ¼13.2 Hz, H-2 ), 2.47 (ddd, 1H, J2 ,3 ¼2.9,
J2 ,1 ¼4.0, J2 ,2 ¼13.2 Hz, H-200), 1.76 (d, 3H,
00
0
00
0
JCH ;6 ¼ 1:2 Hz, 5-CH3). 13C NMR (DMSO): 170.70 (C-4),
2ꢂ3H, JP;OCH ¼ 10:6 Hz, P(OCH3)2), 0 2.45 (dt, 1H,
3
3
158.97 (C-2), 136.94 (C-6), 116.62 (C-5), 89.55 (C-40),
J2 ,1 ¼6.4, J2 ,2 ¼12.3, J2 ,3 ¼6.5 Hz, H-2 ), 2.25 (dt, 1H,
0
0
0
00
0
0
00
87.43 (C-10), 75.77 (C-30), 32.92 (C-20), 13.15 (CH3).
J2 ,1 ¼8.7, J2 ,2 ¼12.3, J2 ,3 ¼10.2 Hz, H-2 ), 2.03 (d, 3H,
00
0
00
0
00
0
J6;CH ¼ 1:2 Hz, 5-CH3), 1.47 (s, 3H, 40-CH3), 0.92 (s, 9H,
3
4.2.36. 1-(3-O-tert-Butyldimethylsilyl-2,5-dideoxy-b-L-
glycero-pent-4-enofuranosyl)thymine (39b). Compound
38 (1.031; 5 mmol) was set with 0.1 M NaOH (60 mL,
6 mmol) for 36 h at rt. A single reaction product was then
detected on TLC checking in H3. For work-up, first the
Na+ ions were exchanged for py+ by treatment with Dowex
50 (py+) in cooled (0 ꢃC) 50% aq pyridine. The solvents
were evaporated, and the residue 39a (ca. 0.90 g, 4 mmol)
was immediately used for subsequent reaction without fur-
ther purification to avoid decomposition. It was made anhy-
drous by repeated co-vaporation with pyridine, then dry
pyridine (4 mL) was added followed by tert-butyldimethyl-
silyl imidazole (2.19 g, 12 mmol, 3 equiv) and the mixture
was stirred for 3 h at rt (TLC in C2). After quenching with
anhydrous methanol (0.5 mL) and stirring for 30 min, the
solvents were evaporated and the residue partitioned between
2 M triethylammonium hydrogen carbonate and chloroform.
The organic layer was dried by MgSO4, the solvent evapo-
rated, and the resulting sirup chromatographed on silica gel
(50 g) using elution with toluene to 1:1 toluene–acetone gra-
dient. Obtained: 634 mg of compound 39b (47%, based on
38) as an amorphous solid. HRMS FAB+ calcd for
C16H27N2O4Si (M+H)+ 339.1740, found 339.1727. 1H
t-Bu), 0.12 and 0.09 (2ꢂs, 2ꢂ3H, Si(CH3)2). 13C NMR
(CDCl3): 163.85 (C-4), 150.97 (C-2), 136.03 (C-6), 112.20
(C-5), 105.54 (d, JC,P¼14.2 Hz, C-40), 80.89 (C-10), 76.53
(C-30), 56.75 (d, JC,P¼172.4 Hz, P–CH2–O), 53.48 and
52.83 (2ꢂd, JC,P¼6.4 Hz, P(OCH3)2), 36.35 (C-20), 19.34
(40-CH3), 17.91 and 25.51 (t-Bu), 11.95 (5-CH3), ꢀ4.91
and ꢀ5.07 (Si(CH3)2).
Isomer 40b: 1H NMR (CDCl3): 9.75 (br s, 1H, NH), 7.56 (q,
0
0
1H, J6;CH ¼ 1:2 Hz, H-6), 6.33 (dd, 1H, J1 ,2 ¼2.2,
3
0
0
00
0
0
0
00
J1 ,2 ¼8.5 Hz, H-1 ), 4.11 (d, 1H, J3 ,2w0, J3 ,2 ¼5.4 Hz,
H-30), 3.73 (dd, 1H, Jgem¼13.6, JP,CHa¼8.0 Hz, P–CHa),
3.95 (dd, 1H, Jgem¼13.6, JP,CHb¼12.9 Hz, P–CHb), 3.82
(d, 6H, JP;OCH ¼ 10:8 Hz, P(OCH3)2), 2.91 (ddd, 1H,
3
00
00
0
00
0
00
0
J2 ,1 ¼8.5, J2 ,2 ¼14.5, J2 ,3 ¼5.4 Hz, H-2 ), 1.90 (d, 3H,
0
0
JCH ;6 ¼ 1:2 Hz, 5-CH3), 01.74 (dd, 1H,0 J2 ,1 ¼2.2,
3
0
00
0
0
J2 ,2 ¼14.5, J2 ,3w0 Hz, H-2 ), 1.48 (s, 3H, 4 -CH3), 0.90
(s, 9H, t-Bu), 0.11 and 0.07 (2ꢂs, 2ꢂ3H, Si(CH3)2).
13C NMR (CDCl3): 163.97 (C-4), 150.57 (C-2), 136.41 (C-
6), 111.61 (d, JC,P¼10.8 Hz, C-40), 110.98 (C-5), 83.76 (C-
10), 75.34 (C-30), 54.33 (d, JC,P¼173.4 Hz, P–CH2–O), 53.06
and 53.01 (2ꢂd, JC,P¼6.6 Hz, P(OCH3)2), 40.28 (C-20),

4534
Z. Tocꢀꢁık et al. / Tetrahedron 63 (2007) 4516–4534
17.85 and 25.53 (t-Bu), 16.13 (40-CH3), 12.45 (5-CH3),
ꢀ5.00 and ꢀ5.06 (Si(CH3)2).
ꢁꢀ
19. Rejman, D.; Snasel, J.; Liboska, R.; Tocık, Z.; Paces, O.;
Kralıkova, S.; Rinnova, M.; Kois, P.; Rosenberg, I.
ꢀꢁ
ꢀ
ꢀ
ꢁꢁ
ꢁ
ꢁ
ꢀ
Nucleosides Nucleotides Nucleic Acids 2001, 20, 819–823.
ꢀ
20. Hanus, J.; Barvık, I.; Ruszova-Chmelova, K.; Stepanek, J.;
ꢀ
ꢁ
ꢁ
ꢁ
ˇ ꢁ
Turpin, P.-Y.; Bok, J.; Rosenberg, I.; Petrova-Endova, M.
Acknowledgements
ꢁ
ꢁ
Nucleic Acids Res. 2001, 29, 5182–5194.
The work was supported by grants 203/05/0827 and 202/05/
0628 (Czech Science Foundation), and by the Centre for
Biomolecules and Complex Molecular Systems (LC512),
Centre LC06-invasion (LC06061) and Centre ChemGen
(LC06077) under research project Z40550506. Our thanks
are due to Prof. E. De Clercq (Rega Institute, Catholic Uni-
versity, Leuven, Belgium) for the tests for antiviral activity,
and to Dr. I. Votruba (IOCB, Prague) for the measurement of
cytostatic effect.
ꢁ
ꢁ
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