Diastereoselective synthesis of cyclosaligenyl-nucleosyl-phosphotriesters

Article abstract of DOI:10.1002/chem.201002657

A diastereoselective synthesis of cycloSal-phosphotriesters (cycloSal=cycloSaligenyl) based on chiral auxiliaries has been developed that allows the synthesis of single diastereomers of the cycloSal-pronucleotides. In previously described synthesis routes, the cycloSal-compounds were always obtained as 1:1 diastereomeric mixtures that could be separated in only rare cases. However, it was shown that the diastereomers have different antiviral activity, toxicity, and hydrolysis stabilities. Here, first a chiral thiazoline derivative was used to prepare nonsubstituted and 5-methyl-cycloSal- phosphotriesters in 48 and ≥95%a de (de=diastereomeric excess). However, this approach failed to give the important group of 3-substituted cycloSal-nucleotides. Therefore, two other chiral groups were discovered that allowed the synthesis of (R_P)- and (S_P)-3-methyl-cycloSal- phosphotriesters as well. The antiviral activity was found to be five- to 20-fold different between the two individual diastereomers, which proved the importance of this approach. Chiral chemical Trojan horses: cycloSal-nucleotides (cycloSal=cycloSaligenyl) of thymidine and cycloSal-pronucleotides of 3′-azido-3′-deoxythymidine (AZT) and 3′-deoxy-2′, 3′-didehydrothymidine (d4T) were prepared by a diastereoselective route for the first time by using a chiral auxiliary approach with up to ≥95%a de (see scheme). The procedure is suitable to synthesize cycloSal-phosphotriesters with different substitution patterns in the aromatic residue.

Full text of DOI:10.1002/chem.201002657

FULL PAPER
DOI: 10.1002/chem.201002657
Diastereoselective Synthesis of cycloSaligenyl-Nucleosyl-Phosphotriesters
Edwuin H. Rios Morales,[a] Jan Balzarini,[b] and Chris Meier*[a]
Abstract: A diastereoselective synthe-
sis of cycloSal-phosphotriesters (cyclo-
Sal=cycloSaligenyl) based on chiral
auxiliaries has been developed that
allows the synthesis of single diastereo-
mers of the cycloSal-pronucleotides. In
previously described synthesis routes,
the cycloSal-compounds were always
obtained as 1:1 diastereomeric mix-
tures that could be separated in only
rare cases. However, it was shown that
the diastereomers have different antivi-
ral activity, toxicity, and hydrolysis sta-
bilities. Here, first a chiral thiazoline
derivative was used to prepare nonsub-
stituted and 5-methyl-cycloSal-phos-
photriesters in 48 and ꢀ95% de (de=
diastereomeric excess). However, this
approach failed to give the important
group of 3-substituted cycloSal-nucleo-
tides. Therefore, two other chiral
groups were discovered that allowed
the synthesis of (RP)- and (SP)-3-
methyl-cycloSal-phosphotriesters
as
well. The antiviral activity was found
to be five- to 20-fold different between
the two individual diastereomers,
which proved the importance of this
approach.
Keywords: antiviral agents · chiral
phosphates · nucleotides · cyclosali-
genyl · stereoselective synthesis
Introduction
(RT) proved to be efficient for the treatment of AIDS.[3] For
their antiviral activity, the intracellular activation into the 5’-
mono-, 5’-di-, and the ultimately biological active 5’-triphos-
phates by cellular nucleoside kinases or 5’-nucleotidases is
necessary after cell penetration of the nucleoside ana-
logues.[4,6]
Chiral phosphorus compounds are important target struc-
tures. It has been proven that the configuration at the phos-
phorus atom has an influence on the biological activity
while interacting with biomolecules. Therefore, the stereose-
lective synthesis of such compounds is an important aim to
achieve. One application of chiral phosphorus compounds
are pronucleotides that act as lipophilic nucleotide precur-
sors, for example, in antiviral chemotherapy. Since the dis-
covery of a new disease in 1981[1] called Acquired Immuno-
deficiency Syndrome (AIDS) which is caused by the Human
Immunodeficiency Virus (HIV),[2] many efforts have been
made to inhibit its replication in infected cells. The use of
nucleoside analogues, such as 3’-azido-3’-deoxythymidine
(AZT; 1) and 3’-deoxy-2’,3’-didehydrothymidine (d4T; 2),
for the inhibition of the virus-encoded reverse transcriptase
However, these phosphorylation steps represent a critical
point because the first phosphorylation step of d4T (2) into
3’-deoxy-2’,3’-didehydrothymidine-5’-monophosphate
(d4TMP) catalyzed by thymidine kinase (TK) is the rate-
limiting step in human cells and the conversion of 3’-azido-
3’-deoxythymidine-5’-monophosphate (AZTMP) into AZT
diphosphate (AZTDP) mediated by thymidylate kinase is
the metabolic bottleneck in the case of AZT.[7,9] In principle,
the direct administration of nucleotides, such as d4TMP,
should bypass the limiting step in the thymidine kinase-
[a] Dr. E. H. Rios Morales, Prof. Dr. C. Meier
Organic Chemistry, Department of Chemistry
Faculty of Sciences, University of Hamburg
Martin-Luther-King-Platz 6
20146 Hamburg (Germany)
Fax : (+49)40428385592
E-mail: chris.meier@chemie.uni-hamburg.de
[b] Prof. Dr. J. Balzarini
Rega Institute for Medical Research
Katholieke Universiteit Leuven
Minderbroedersstraat 10, 3000 Leuven (Belgium)
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mediated anabolism and thus improve their biological activi-
ty. However, nucleotides are very polar molecules and do
not passively pass cellular membranes. Therefore, strategies
have been developed to mask the charged phosphate by
using (bio)degradable lipophilic carrier groups that release
the 5’-nucleotides after cellular uptake (pronucleotide ap-
proach).[10] Thus, pronucleotides are membrane-permeable
nucleotide precursors. Several pronucleotide strategies have
been reported for nucleotide delivery, for example, the
mixed-SATE compounds,[11] the HepDirect technique,[12] the
phosphoramidates,[13] the cycloSal-phosphate triesters 3,[14]
and recently a first approach for the intracellular delivery of
nucleoside diphosphates.[15] Due to their synthesis, all P-
chiral pronucleotides are obtained as 1:1 mixtures of diaste-
reomers with respect to the configuration at the phosphorus
center.[13,14] The mixtures of diastereomers can be separated
in only rare cases. However, it has been shown that the indi-
vidual diastereomers of the pronucleotides showed signifi-
cantly different antiviral activity, toxicity, and hydrolysis sta-
bilities, for example, in the case of the cycloSal compounds
3.[14] It was found that one isomer of 3-methyl-cycloSal-
d4TMP 4 was 11-fold more active against HIV than the
other one.[16] Moreover, only one isomer of 4 was found to
be a strong inhibitor of the enzyme butyrylcholinesterase.[17]
Although in previous studies a few cycloSal-triesters could
be separated by using semipreparative HPLC,[16,18] currently
there is no synthesis route to prepare isomerically pure cy-
cloSal-pronucleotides.
Here, we report on a convergent synthesis leading to cy-
cloSal-pronucleotides 3 with very high diastereoselectivities
based on the chiral auxiliary strategy. First, the studies were
focused on the synthesis of both diastereomers of cycloSal-
(3’-O-acetyl)-thymidine monophosphate (cycloSal-(3’-OAc)-
dTMP; 5) as model compounds (Scheme 1). The approach
was later applied to the synthesis of (RP)- and (SP)-3-
methyl-cycloSal-3’-azido-3’-deoxythymidine monophosphate
(3-Me-cycloSal-AZTMP; 6). It should be noted, that all cy-
cloSal-AZTMP derivatives prepared in the past proved to
be inseparable even by HPLC chromatography. Finally, also
the diastereoselective preparation of the important (RP)-
and (SP)-3-methyl-cycloSal-derivatives of d4TMP 4 will be
reported.
Scheme 1. Stereoselective synthesis of cycloSal-nucleotide (SP)/(RP)-5 by
starting from thiazoline 7. Reagents: i) P(O)Cl3, CH2Cl2, NEt3; ii) 1) sali-
cylalcohol 9, DBU, acetone, 2) chromatographic separation; iii) dTOAc 10,
tert-BuMgCl. DBU=1,8-diazabicycloACTHNUTRGNEUNG[5.4.0]undec-7-ene.
chromatographically separable diastereomers in the second
step and 2) it has to be replaced selectively by the nucleo-
side (or an analogue) in the last step of the reaction se-
quence under mild reaction conditions. Briefly, first prolinol
derivatives followed by oxazolidinone derivatives of the
Evans-type were investigated as chiral auxiliaries. Despite
very good stereoselectivities obtained with the first group of
compounds, these groups could not be substituted by the nu-
cleoside without degradation due to the harsh reaction con-
ditions that were necessary. The second group of compounds
also gave very good stereoselectivities and some of them
proved to be suitable for replacement in the nucleophilic re-
action introducing the nucleoside 10. However, the chiral in-
termediates were found to be inseparable by chromatogra-
phy and hence these compounds 11 could not be used as ste-
reochemically pure starting materials in the last step (ste-
p iii, Scheme 1). Finally, the use of (S)-4-isopropyl-2-mercap-
to-2-thiazoline (7) as a potentially suitable chiral auxiliary
was the result of an in-depth developing process that will be
summarized in a further publication.
The thiazoline 7 was reacted with P(O)Cl3 to give the di-
chlorophosphoramidate 8, which was too unstable to be pu-
rified by column chromatography. Nevertheless, the crude
product was pure enough to be used in the following reac-
tion. The dichloridate 8 was then reacted with salicylalcohol
9 to yield the cycloSal-phosphoramidate 11 in 43% chemical
yield in a ratio of 94:6 (88% de) as determined by 31P NMR
spectroscopy. By silica gel column chromatography, the ste-
reochemically pure “major” and “minor” diastereomers
were obtained. The (SP)-configuration of the minor diaste-
reomer was attributed by X-ray crystal structure analysis
(Figure 1). Thus, the major diastereomer had the (RP)-con-
figuration. The chirality at phosphorus was assigned accord-
ing to the Cahn–Ingold–Prelog rules.
Results and Discussion
The developed synthesis route for diastereomerically pure
cycloSal-phosphotriesters is based on chiral auxiliaries and
consists of three steps: 1) the reaction of (S)-4-isopropyl-2-
mercapto-2-thiazoline (7) with P(O)Cl3 to introduce the
chiral auxiliary in the earliest step, 2) esterification of the
formed dichlorophosphoramidate 8 with salicylalcohol 9 to
give the chiral phosphoramidate 11, and 3) the substitution
The displacement of 7 from the diastereomerically pure
cycloSal-phosphoramidates (RP)-11 with dTOAc 10 led to the
corresponding cycloSal-nucleotide (SP)-5 in 46% yield and a
diastereomeric excess of ꢀ95% de (Scheme 1). The assign-
ment of the configuration at the phosphorus atom in prod-
of the chiral auxiliary by the protected nucleoside 3’-OAc-
[19]
thymidine (dTOAc
)
10 (Scheme 1).
Besides the stereochemical induction, the auxiliary has to
fulfill two further important criteria: 1) it should lead to
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Synthesis of cycloSaligenyl-Nucleosyl-Phosphotriesters
FULL PAPER
was not used as an auxiliary but helps to achieve the separa-
tion of the diastereomers and acts as a good leaving group
in the last step. The retrosynthesis for the preparation of iso-
merically pure 3-alkylated cycloSal-pronucleotides is sum-
marized in Scheme 2.
3-Methyl-salicylic acid was reduced with LiAlH4 leading
to the corresponding salicylalcohol 12 in 80% yield.[20] Com-
pounds 18 and 13 were obtained as a racemic mixture after
esterification of two salicylalcohols 9 and 12 with P(O)Cl3 in
61 and 76% yields (Scheme 3).
The coupling of thiazoline 7 with the cycloSal-derivative
rac-(13) led to chromatographically separable diastereomers
11. However, due to the bulky iso-propyl group and the 3-
methyl group in the aromatic ring the following substitution
by the nucleoside 10 proceeded very slowly with formation
of small amounts of the product 11 within several weeks.
Thus, more appropriate chiral leaving groups have to be
used for this reaction. The chiral group 14 was prepared by
the reaction of d-norephedrine (19) with dimethylcyanodi-
thioiminocarbonate (21) (Scheme 4).
Figure 1. ORTEP illustration of the (SP)-11-diastereomer.
uct (SP)-5 was done by the as-
sumption that the substitution
reaction took place with inver-
sion of the configuration (SNP
reaction). Hence, in this case
the chiral auxiliary fulfilled all
three requirements mentioned
above.
The same pathway was also
successfully used for the synthe-
sis of 5-substituted cycloSal-
pronucleotides (e.g. a 5-methyl-
cycloSal-(3’-OAc)-dTMP, 45%
yield, ꢀ95% de). However, the
synthesis of the 3-methyl-cyclo-
Sal-derivative failed when using
Scheme 2. Retrosynthesis of the route to the cycloSal-phosphotriesters 17.
this reaction sequence because surprisingly the second step
did not led to the expected chiral cycloSal-phosphoramidate
11. Presumably, the substituent at the 3-position caused un-
favorable steric interactions in this reaction and after some
unsuccessful variations of the reaction conditions it became
clear that 7 is not suitable for the synthesis of the 3-substi-
tuted cycloSal-counterparts. However, because particularly
3-substituted cycloSal-pronucleotides of nucleoside ana-
logues showed very interesting antiviral activities by intra-
cellular nucleotide delivery, enzyme-inhibition, and hydroly-
sis properties a different synthetic strategy was developed
that allows access to these important compounds.
Scheme 3. Synthesis of the phosphochloridates rac-18 and rac-13. TEA=
triethylamine.
The following concept was envisaged: The 3-methyl sali-
cylalcohol 12 should be first reacted with P(O)Cl3 to give cy-
cloSal-phosphorochlorides rac-(13). The reaction of the thia-
zoline 7 and chiral N-cyaniminooxazolidines 14 and 15 with
the cycloSal derivative rac-(13) should lead to a diastereo-
meric mixture of the cycloSal-amidate 11 or 16. This mixture
has to be easily separable into the individual diastereomers.
Finally, the nucleoside will be introduced. Again, dTOAc 10
was used first. As a consequence, here the chiral compound
Scheme 4. Synthesis of the chiral group 14 and preparation of the single
diastereomers (SP)-22 and (RP)-22.
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C. Meier et al.
Interestingly, compound 14 precipitated during the reac-
tion and the pure product was isolated by simple filtration
in 95% yield. The X-ray crystal structure analysis of the
chiral compound 14 confirmed the absolute 4R,5S configura-
tion. The following coupling of 14 with the cycloSal-phos-
phorchloridates rac-(18) led to the formation of the corre-
sponding 1:1 diastereomeric mixture (SP)/(RP)-22 in 59%
yield (Scheme 4). The crude mixture of 22 displayed two
baseline separated signals in the 31P NMR spectra as depict-
ed in Figure 2. The diastereomers could be easily separated
by column chromatography to give the isomerically pure
diastereoisomers (SP)-22 and (RP)-22.
the addition of a strong base, such as alkylmagnesium
halide, the reaction conditions used by Jones et al., or a
combination of both were successful (Scheme 5).[22] The abil-
ity of copper(II)triflate (CuACHTNUGRTENUNG(OTf)2) in combination with a
Scheme 5. Diastereoselective synthesis of (RP)-cycloSal-(3’-OAc)-dTMP
(5).
ligand like N,N’-ethylenebis(benzaldiimine) (BEN) to cata-
lyze phosphorylation of primary, secondary, and tertiary al-
cohols with achiral dialkylphosphoamidates was reported by
Jones and Smanmoo.[22] In our case, the combination of Cu-
AHCTUNGRTEG(NNUN OTf)2, BEN, as well as the addition of a base for the depro-
tonation of the nucleoside led to the formation of (RP)-cy-
cloSal-(3’-OAc)-dTMP 5 in 53% yield and with ꢀ95% de
(Scheme 5).
Since (RP)-cycloSal-triester 5 could not be crystallized, no
X-ray data were available proving the absolute configura-
tion at the phosphorus atom. However, assuming that the
reaction took place with inversion of configuration, com-
pound 5 must have a (RP)-configuration because the great
majority of the substitution reactions at the phosphate pro-
ceed by following an addition–elimination mechanism with
inversion of configuration (SN2-type reaction).[23]
Several base, Lewis acid, and solvent combinations were
studied. To our surprise in most of the reactions we ob-
served that the stereochemical purity of the product de-
creased significantly. The reaction conditions and the corre-
sponding results are summarized in Table 1. The diastereo-
Figure 2. 31P NMR spectrum of the crude diastereomeric mixture of (SP)-
22 and (RP)-22.
Interestingly, during chromatography on silica gel by
using petroleum ether/ethyl acetate (1:2) as the eluent it was
observed that one diastereomer of the diastereomeric mix-
ture (SP)/(RP)-22 was chemically less stable than the second
one. The more stable (SP)-isomer 22 crystallized from a mix-
ture of petroleum ether and ethyl acetate and the (SP)-con-
figuration of the phosphorus center was assigned from the
X-ray analysis (Figure 3).[21] The difference in stability was
confirmed by DFT calculations (B3LYP/6-311G). The re-
sults obtained showed that the (SP)-isomer 22 was about
39 kcalmolÀ1 more stable than the (RP)-isomer 22.
Table 1. Reaction conditions used for the synthesis of (RP)-cycloSal-
phosphotriester 5.
Promoter (1.0 equiv)
Base
Solvent
de [%]
1
2
3
4
5
6
7
8
9
–
–
–
–
NEt3
CH2Cl2
THF/CH3CN
CH3CN
THF/CH3CN
CH2Cl2
CH2Cl2
CH2Cl2/CH3CN
THF/CH3CN
CH2Cl2
58
86–90
77
76
8
63
47
83
ꢀ95
Taking the individual diastereomers of (SP)-22 or (RP)-22,
in the last step the chiral leaving group was substituted by
dTOAc 10. Several attempts have been tried and among those
tBuMgCl
tBuMgCl
iPropMgCl
NEt3
NEt3
NEt3
Eu
Mg
Cu(OTf)2/BEN/DCI
Cu(OTf)2/BEN
Cu(OTf)2/BEN
U
A
E
N
iPropMgCl
NEt3
G
meric excess was calculated from the 31P NMR spectra of
the crude reaction mixtures. As an example, the 31P NMR
spectrum of the crude material from reaction 9 (Table 1) is
shown in Figure 4. According to these results, the [Cu-
ACHUTNGRENU(NG BEN)]ACHTUNGTREN(NUGN OTf)2 complex in combination with NEt3 was found
to be optimal for promoting the diastereoselective synthesis
Figure 3. ORTEP illustration of the (SP)-isomer 22.
to yield (RP)-cycloSal-phosphotriester 5. It should be men-
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Synthesis of cycloSaligenyl-Nucleosyl-Phosphotriesters
FULL PAPER
Finally, the chiral compound 15 that was synthesized from
l-phenylalaninol (20) and dimethylcyanodithioiminocarbon-
ate (21) in 86% yield proved to be suitable to achieve the
goal (Scheme 6). As observed with compound 14, the chiral
product 15 precipitated during the reaction and was isolated
by simple filtration.
Figure 4. 31P NMR spectroscopic signals of the crude material of (RP)-
and (SP)-cycloSal-phosphotriesters 5 (reaction 9, Table 1).
tioned that in all reactions summarized in Table 1 always the
same diastereomer was formed preferentially although to
different extents.
We do not have a solid explanation for the isomerization
process that occurred during some of these phosphorylation
reactions. According to the literature there are three possi-
ble mechanisms for such nucleophilic substitutions at phos-
Scheme 6. Syntheses of the chiral group 15, (SP)-26 and (RP)-26, and (SP)-
cycloSal-phosphotriester 5.
phorus,
1) SN1(P),
2) addition–elimination,
and
3) SN2(P).[24,25] Based on this, it was assumed that in the
cases of isomerization the reactions proceeded by a SN1(P)
mechanism by which dissociation of the leaving group pro-
duced a planar, tri-coordinate metaphosphate intermediate
making this species achiral.
Compound 15 was then coupled with cycloSal-phosphoro-
chloridate rac-(18) to the corresponding diastereomer mix-
ture (SP)/(RP)-26 (Scheme 6). The formed diastereomers
(SP)-26 and (RP)-26 were separated by using silica gel
column chromatography. After reaction of the now more
stable isomer (RP)-26 with dTOAc 10, the (SP)-cycloSal-triest-
er 5 was obtained (Scheme 6). The reaction was carried out
by using the reaction conditions summarized in Table 2.
The isomerization observed in the majority of cases could
also be explained by an addition–elimination mechanism
that involves the formation of a pentavalent intermediate
with trigonal bipyramidal (TBP) geometry with two apical
positions and three equatorial positions. Polytopal isomeri-
zation (pseudorotation) may occur, re-sorting the positions
of the residues at the phosphorus in the TBP intermediate.
To synthesize (SP)-cycloSal-(3’-OAc)-dTMP 5, (RP)-22 was
treated under identical conditions as described above for
(SP)-22. Surprisingly, the reaction gave very low yields of
6%, a diastereoselectivity of 93% de, and in addition de-
composition of the starting material was observed. Again,
this confirms that (RP)-22 is chemically less stable than its
(SP)-counterpart for unknown reasons. Therefore, another
chiral leaving group was needed that forms after coupling
with the cycloSal-phosphorochloridates rac-(18) chromato-
graphically separable diastereoisomers. In addition to this,
the more stable diastereoisomer should lead to the desired
(SP)-cycloSal-triester 5. Several chiral compounds analogous
to 14 were synthesized by starting from cheap l-amino
acids. However, compounds 23, 24, and 25 failed to give sep-
arable diastereomers at the cycloSal-phosphoramidate level.
Table 2. Reaction conditions used for the synthesis of (SP)-cycloSal-phos-
photriester 5.
Cu
(OTf)2/BEN
solvent
t [d]
de [%]
Yield [%]
[a]
1
2
3
4
5
–
CH2Cl2
CH2Cl2
CH2Cl2/CH3CN 1:1
CH2Cl2
CH3CN
2
7
5
5–7
8
24
83
85
91
ꢀ95
–
9
12
0.2 equiv
0.5 equiv
1.0 equiv
1.0 equiv
17–24
13–18
[a] Not determined.
Triethylamine was used as a base in all reactions. Moreover,
variable equivalents of the [Cu(BEN)](OTf)2 complex as
A
ACHTUNGTRENNUNG
well as two solvents were studied. Interestingly, we observed
a higher degree of isomerization when employing small
amounts of the promoter complex and the best diastereo-
meric excess was obtained when using one equivalent of the
promoter and CH3CN as the solvent.
The 31P NMR spectrum of the product obtained in reac-
tion 5, Table 2 is depicted in Figure 5. After having identi-
fied chiral groups as well as a suitable promoter system, the
synthesis of cycloSal-nucleotides of the antivirally active nu-
cleoside analogues AZT (1) and d4T (2) was started. As
mentioned above in particular 3-methyl- or 3,5-dimethyl-
substituted cycloSal-compounds showed interesting antiviral
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C. Meier et al.
Each stable isomer (SP)-27 or (RP)-28 was reacted with
AZT (1) to give the corresponding 3-methyl-cycloSal-
AZTMP (RP)-6 and (SP)-6 in 30 and 21% yields, respective-
1
ly (Scheme 8), which were characterized by means of H-,
13C-, IR-, and 31P NMR spectroscopy as well as HR fast-
atom bombardment (HR-FAB) MS after chromatographic
purification. The observed diastereomeric excess for both
compounds (SP)-6 and (RP)-6 was ꢀ95% de as shown in the
31P NMR spectra of the crude mixture (Figures 6 and 7).
Again, the conversion of the less stable diastereomers 27
and 28 with AZT (1) produced a complex mixture of prod-
ucts and decomposition of the starting phosphoroamide. Ac-
cording to the 31P NMR spectra and TLC a small amount of
the desired products (RP)-6 and (SP)-6 was also formed but
their purification was not successful.
Figure 5. 31P NMR spectroscopic signals of the (SP)-cycloSal-triesters 5
with a very small amount of the (RP)-isomer 5.
activities and hydrolysis proper-
ties at simulated physiological
pH values (7.3).[14] Therefore,
the following reactions were fo-
cused on the synthesis of such
compounds.
For this purpose, both chiral
leaving groups 14 and 15 were
coupled with the cycloSal-phos-
phorochloridate rac-(13) to give
the corresponding diastereo-
meric mixtures (SP)/(RP)-27 and
(SP)/(RP)-28 (Scheme 7). Both
mixtures were easily separated
into the individual diastereo-
mers by using silica gel column
Scheme 8. Synthesis of the title compounds (RP)-6, (SP)-6, (RP)-4, and (SP)-4.
Scheme 7. Preparation of the single diastereomers (SP)-27, (RP)-27, (SP)-
28, and (RP)-28.
Figure 6. 31P NMR spectroscopic signals of the crude mixture of 3-
methyl-cycloSal-AZTMP (RP)-6 and (SP)-6.
chromatography and petroleum ether/ethyl acetate (1:2) as
the eluent. Again, it was observed that one diastereomer
was more stable than the other one.
One possibility to distinguish the diastereomers was the
chemical stability properties and the chemical shift of the
31P NMR spectroscopic signals. The correlation of the
31P NMR spectroscopic signal of the stable diastereomer
(SP)-22 with the signal of the stable diastereomer 27 led us
to the assumption that this compound 27 has the (SP)-config-
uration as well.
Next, (RP)- and (SP)-3-methyl-cycloSal-d4TMPs 4 were
prepared by using the same chiral entities and the same re-
action conditions. Compounds (SP)-27 and (RP)-28 were re-
acted with d4T (2) to give the corresponding 3-methyl-cyclo-
Sal-d4TMP (RP)-4 and (SP)-4 in 33 (94% de) and 28% (ꢀ
95 de) yield, respectively. Analogous reactions by using 3,5-
dimethyl-salicylalcohol led by the same route to the corre-
sponding diastereomers of 3,5-dimethyl-cycloSal-d4TMP
(SP)/(RP)-29 (data not shown).
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Synthesis of cycloSaligenyl-Nucleosyl-Phosphotriesters
FULL PAPER
and 29. In both HIV-infected CEM/0 and CEM/TKÀ assays,
the (RP)-diastereomer was found to be 5- to 20-fold more
active as compared to the (SP)-diastereomer. Moreover,
both diastereomers of the cycloSal-d4TMP triesters fully
kept antiviral activity in the HIV-2-infected CEM/TKÀ cell
cultures compared to CEM/0 cells. This effect of the cyclo-
Sal-d4TMP triesters has been studied earlier in more
detail.[26] In conclusion, this data perfectly agrees with our
earlier observation that the (RP)-diastereomers always
showed higher antiviral activity relative to the (SP)-isomer.
The configurational correlation perfectly agrees with the
earlier attribution of configuration, which was based on CD-
effects of chromatographically separated cycloSal-d4TMP
triesters.[16]
Figure 7. 31P NMR spectroscopic signals of the crude mixture of 3-
methyl-cycloSal-AZTMP (RP)-6 and (SP)-6.
Antiviral evaluation: 3-Methyl-cycloSal-AZTMP (RP)-6 and
(SP)-6 and 3-methyl-cycloSal-d4TMP (RP)-4 and (SP)-4 were
evaluated for their antiviral potencies against HIV-1- and
HIV-2-infected CEM/0 and HIV-2-infected CEM/TKÀ cells
(Table 3). In addition, the values of 3,5-dimethyl-cycloSal-
d4TMP (SP)/(RP)-29[16] and for comparison the values for
the parent nucleoside analogues AZT (1) and d4T (2) are
also given.
Conclusion
First results for the stereospecific synthesis of cycloSal-pro-
nucleotide triesters (SP)-4 and (RP)-4, (SP)-5 and (RP)-5, and
(SP)-6 and (RP)-6, by using a chiral auxiliary or suitable
chiral leaving groups are disclosed. In the last step of the se-
quence, the auxiliary or the leaving group is replaced by a
nucleoside analogue in a Lewis acid promoted reaction lead-
ing to almost diastereomerically pure target compounds al-
though the chemical yields require further improvement.
Two different chiral groups were necessary to prepare all
possible substitution patterns within the cycloSal-residue
and RP or SP configuration at the phosphorus atom. The an-
tiviral activity of each diastereomer against HIV-1- and
HIV-2-infected CEM/0 and HIV-2-infected CEM/TKÀ cells
were evaluated. All diastereomers with the (RP)-configura-
tion showed significantly higher antiviral activity than the
diastereomers with the (SP)-configuration. Particularly a sig-
nificant difference between diastereomers 4 and 29 was ob-
served in HIV-2-infected CEM/TKÀ cells. Thus, these assays
verify the importance of the phosphorus configuration on
the antiviral activity. Perspectively, we believe that we have
developed a new general access to chiral phosphate deriva-
tives. At least in one further example we have shown that
this is indeed the case.[27]
Table 3. Anti-HIV activity of (RP)- or (SP)-cycloSal-nucleotides 4, 6, and
29 in CEM/0 cells and in thymidine kinase-deficient CEM/TKÀ cells.
Comp.
Antiviral Activity EC50 [mm][a]
CEM/0
CEM/TKÀ
HIV-2 HIV-2
Cytostatic activity
CC50 [mm][b]
HIV-1
(RP)-6
(SP)-6
(RP)-4
(SP)-4
0.065Æ0.02 0.14Æ0.007 20Æ3.5
>50
119Æ3.0
109Æ2.0
0.091Æ0.07 0.16Æ0.028
0.08Æ0.0
0.067Æ0.03 0.063Æ0.015 11Æ2.0
0.42Æ0.18
1.1Æ0.78
0.70Æ0.30
0.08Æ0.0
0.38Æ0.37
>250
76Æ40
17.4Æ5.0
22Æ4.0
>250
(RP)-29 0.093Æ0.02 0.17Æ0.10
(SP)-29
AZT 1
d4T 2
0.50Æ0.17
0.016Æ0.0
0.80Æ0.03
0.80Æ0.10
0.084Æ0.08
0.82Æ0.05
250Æ0.0
ꢀ250
[a] 50% effective concentration. [b] 50% cytostatic concentration.
The parent AZT 1 proved to be very active against HIV-1
and HIV-2 in CEM/0 cells (EC50 =0.016 and 0.084 mm, re-
spectively). As expected, AZT 1 lost its antiviral activity
against HIV-2 in CEM/TKÀ cells due to the absence of thy-
midine-kinase. The individual (SP)- and (RP)-diastereomers
of 3-methyl-cycloSal-AZTMP 6 also showed antiviral activi-
ty against HIV-1 and HIV-2 in CEM/0 cells in virtually the
same concentration range as AZT. Interestingly, the antivi-
ral potency of the diastereomers (SP)/(RP)-6 markedly, but
partially, lost antiviral potency (~150- to 300-fold) in the
CEM/TKÀ cell assay, whereas AZT completely lost its anti-
viral activity (>3,000- to 10,000-fold), thus proving the re-
lease of limited but significant amounts of AZTMP from
the pronucleotide into the cell. The reason for this loss of
activity in the TK-deficient cell line has been studied before
in detail.[26] However, a much more beneficial outcome has
been observed for the two cycloSal-d4TMP derivatives 4
Experimental Section
General: All experiments involving water-sensitive compounds were con-
ducted under scrupulously dry conditions and a nitrogen atmosphere. All
solvents were dried over an appropriate drying agent. Triethylamine, di-
chloromethane, and acetonitrile were dried by heating under reflux over
calcium hydride for several days followed by distillation. Dichlorome-
thane was stored over activated 4 ꢁ molecular sieves and acetonitrile
over 3 ꢁ molecular sieves. THF was dried by heating under reflux over
potassium and benzophenone followed by distillation. Ethyl acetate, pe-
troleum ether 50–70, dichloromethane, and methanol for chromatography
were distilled before use. Evaporation of solvents was carried out on a
rotary evaporator under reduced pressure or by using a high-vacuum
pump. Column chromatography was performed by using Merck silica gel
60, 230–400 mesh. Analytical TLC was performed on Merck precoated
aluminum plates 60F254 with a 0.2 mm layer of silica gel containing a fluo-
Chem. Eur. J. 2011, 17, 1649 – 1659
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1655

C. Meier et al.
rescent indicator; sugar-containing compounds were visualized with the
sugar spray reagent (0.5 mL of 4-methoxybenzaldehyde, 9 mL of ethanol,
0.1 mL of glacial acetic acid, and 0.5 mL of concentrated sulphuric acid)
by heating with a fan. The coupling product of the cycloSal-mask and the
leaving groups was visualized with a 10% solution of potassium perman-
ganate in sodium hydroxide. For some separations a chromatotron (Har-
rison Research 7924T) with glass plates coated with 1, 2, or 4 mm layers
of VWR 60 PF254 silica gel containing a fluorescent indicator (VWR no.
crude product was purified by column chromatography on silica gel (pe-
troleum ether 50–70/ethyl acetate 1:1).
General procedure B
Preparation of the leaving groups 14 and 15: 2-Amino alcohol 19 or 20
(1.0 equiv) was added to a solution of dimethylcyanodithioiminocarbon-
ate (21) (1.0 equiv) in methanol. The reaction mixture was heated for 3 h
under reflux and then stirred at room temperature for 15 h. The originat-
ing methanethiol was oxidized to methanesulfonic acid by using nitric
acid. The product was filtered, washed with cold petroleum ether, and
dried under reduced pressure.
7749) was used.
1
Instrumentation:
H NMR spectroscopy was carried out by using a
Bruker AMX 400 at 400 MHz, Bruker DMX 500 at 500 MHz, or Bruker
AV 400 at 400 MHz with CDCl3 or [D6]DMSO as the internal standard.
13C NMR spectra were recorded on a Bruker AMX 400 at 101 MHz or
Bruker AV 400 at 101 MHz (CDCl3 or [D6]DMSO as the internal stan-
General procedure C
Preparation of the diastereomeric mixtures as precursors: A solution of 2-
chloro(4H)-1,3,2-benzodioxaphosphorin-2-oxide derivative rac-13 or rac-
18 (1.0–1.5 equiv) in dichloromethane was added to a suspension of the
leaving group 14 or 15 (1.0 equiv) and triethylamine (1.1 equiv) in di-
chloromethane at room temperature. The reaction mixture was stirred
for 5–10 h at room temperature. The solvent was removed under reduced
pressure by using a high-vacuum pump. Ethyl acetate was added, the re-
action mixture was stirred for 30 min at room temperature and stored for
2 h at 08C. The precipitated salt was filtered, the solvent removed, and
the crude product was purified by column chromatography on silica gel
(petroleum ether 50–70/ethyl acetate 1:2).
dard). 31P NMR spectra were recorded on
a Bruker AMX 400 at
162 MHz (H3PO4 as the internal standard). All 1H, 31P, and 13C NMR
chemical shifts are quoted in ppm. All 13C and 31P NMR spectra were re-
corded in the proton-decoupled mode. HRMS were obtained with a VG
Analytical VG/70–250F spectrometer (FAB, matrix was m-nitrobenzyl al-
cohol). For the X-ray crystal structure analyses, data collection was done
with a Bruker Smart APEX CCD area detector diffractometer. Analyti-
cal HPLC: LiChroCART 250–4 with LiChrospher 100 RP-18 (5 mm)
standard gradient (Gradient I: 18–100% CH3CN in water (0–16 min),
100% CH3CN (16–19 min), 18% CH3CN (19–31), flow rate
0.5 mLminÀ1; UV detection at 269 nm). Gradient II: 0–100% CH3CN (0–
18 min), 100% CH3CN (18.1–20 min), 0% CH3CN (20.1–33 min); flow
rate 0.5 mLminÀ1; UV detection at 265 nm The purity of cycloSal-nucleo-
tides was checked by means of HPLC and was in all cases ꢀ95%.
General procedure D
Preparation of the cycloSal-phosphotriesters: A solution of isomerically
pure diastereomer (1.0 equiv), copper(II)triflate (1.0 equiv), and BEN
(1.0 equiv) in dichloromethane or acetonitrile was stirred for 30 min and
added to a solution of AZT (1) or d4T (2) (3.0 equiv) and triethylamine
(3.0 equiv) in dichloromethane at room temperature. The reaction mix-
ture was stirred for days and quenched with saturated ammonium chlo-
ride solution and extracted with dichloromethane three times. The com-
bined organic layers were dried over sodium sulfate and concentrated
under reduced pressure. The crude product was purified by column chro-
matography on silica gel (dichloromethane/methanol 19:1).
Preparation of [(S)-4-isopropylthiazolidine-2-thione]phosphorodichlori-
date (8): A solution of (S)-4-isopropylthiazolidine-2-thione (7) (0.52 g,
3.2 mmol, 1.0 equiv) and phosphoryl chloride (0.91 mL, 9.7 mmol,
3.0 equiv) in CH2Cl2 (20 mL) was cooled to 08C. NEt3 (0.49 mL,
3.5 mmol, 1.1 equiv) in CH2Cl2 (10 mL) was added dropwise. Following
the addition, the reaction mixture was allowed to warm to room tempera-
ture and stirred for 12 h. The solvent was removed under reduced pres-
sure and the residue was suspended in CH2Cl2 (1 mL) and Et2O (15 mL).
The precipitated triethylammonium chloride was filtered under nitrogen
and washed with Et2O (5 mL). The solvent of the filtrate was removed
under reduced pressure to give the crude product 8 as an oil. Further pu-
rification was not possible due to high reactivity but the 31P NMR spec-
trum in CDCl3 showed only one signal at d=4.4 ppm.
2-Chloro(4H)-1,3,2-benzodioxaphosphorin-2-oxide (rac-(18)): General
procedure A with salicylalcohol (9) (6.00 g, 48.3 mmol), triethylamine
(14.1 mL, 0.101 mol) dissolved in THF (90 mL), and phosphoryl chloride
(8.15 g, 53.2 mmol) in THF (70 mL). The product rac-(18) (7.53 g, 76%)
was obtained as a colorless solid. 1H NMR (400 MHz, CDCl3): d=7.41–
7.33 (m, 1H; H-arom.), 7.25–7.19 (m, 1H; H-arom.), 7.16–7.07 (m, 2H;
H-arom.), 5.55–5.42 ppm (m, 2H; H-4); 31P NMR(162 MHz, CDCl3): d=
À6.00 ppm.
Preparation of 2-(4’-isopropyl-thiazolidin-2’-thion-3’-yl)(4H)-1,3,2-benzo-
dioxaphosphorin-2-oxide ((RP)-11): A solution of [(S)-4-isopropylthiazo-
lidine-2-thione]phosphorodichloridate (8) (0.89 g, 3.2 mmol, 1.0 equiv)
and salicylalcohol (9) (0.40 g, 3.2 mmol, 1.0 equiv) in acetone was cooled
to À918C. DBU (0.48 mL, 3.2 mmol, 1.0 equiv) was added dropwise.
After 1 to 12 h at À918C, the reaction was quenched with saturated am-
monium chloride solution and extracted with CH2Cl2 three times. The
combined organic layers were dried over magnesium sulfate and concen-
trated under reduced pressure. The resulting residue was purified by
column chromatography on silica gel (petroleum ether 50–70/EtOAc
1:2). The product (RP)-11 (0.45 g, 1.4 mmol, 43%) was obtained as a
2-Chloro-8-methyl(4H)-1,3,2-benzodioxaphosphorin-2-oxide
(rac-(13)):
General procedure A with 3-methyl-salicylalcohol 12 (2.50 g, 18.1 mmol),
triethylamine (5.29 mL, 38.0 mol) dissolved in THF (40 mL), and phos-
phoryl chloride (3.05 g, 19.9 mmol) in THF (40 mL). The product rac-
1
(13) (2.39 g, 61%) was obtained as a colorless solid. H NMR (400 MHz,
CDCl3): d=7.25–7.20 (m, 1H; H-7), 7.11 (dd, 1H, 3JHÀH =7.6, JHÀH
=
3
7.6 Hz; H-6), 6.94 (d, 1H, 3JHÀH =7.6 Hz; H-5), 5.51–5.43 (m, 2H; H-4),
2.31 ppm (s, 3H; CH3); 31P NMR (162 MHz, CDCl3): d=À5.01 ppm.
AHCTUNGTRENNUNG
B
pale-yellow solid. 1H NMR (400 MHz, CDCl3): d=7.30–7.28 (m, 1H; H
32.8 mmol) and dimethylcyanodithioiminocarbonate (21) (4.80 g,
32.8 mmol) in methanol (30 mL). The product 14 (6.32 g, 95%) was ob-
tained as a colorless solid. 1H NMR (400 MHz, [D6]DMSO): d=9.56 (s,
1H; N-H), 7.50–7.35 (m, 3H; H-arom.), 7.33–7.26 (m, 2H; H-arom.),
6.05 (d, 1H, 3JHÀH =8.5 Hz; H-5), 4.50–4.38 (m, 1H; H-4), 0.68 ppm (d,
3
arom.), 7.15–7.03 (m, 3H; H arom.), 5.62 (dd, 1H, 2JHÀH =14.0, JHÀP
=
2
3
14.0 Hz; H-4), 5.52 (dd, 1H, JHÀH =14.0, JHÀP =14.0 Hz; H-4’), 4.92–4.86
(m, 1H; H-13), 3.76 (dd, 1H, 3JHÀH =11.5, 3JHÀH =8.3 Hz; H-12), 3.18
(ddd, 2H, 3JHÀH =11.5, 3JHÀH =1.8, 4JHÀP =0.8 Hz; H-12’), 2.59–2.45 (m,
3
1H; H-14), 1.14 (d, 3H, 3JHÀH =6.8 Hz; H-15), 1.13 ppm (d, 3H, JHÀH
=
3
3H, JHÀH =6.6 Hz; H-6).
7.1 Hz; H-15’); 31P NMR (162 MHz, CDCl3): d=À11.0 ppm.
General procedure A
(S)-4-Benzyl-2-(N-cyanimino)oxazolidine (15): General procedure B with
l-phenylalaninol (20) (2.59 g, 17.1 mmol) and dimethylcyanodithioimino-
carbonate (21) (2.50 g, 17.1 mmol) in methanol (25 mL). The product 15
(2.92 g, 86%) was obtained as a colorless solid. 1H NMR (400 MHz,
[D6]DMSO): d=9.55 (s; N-H), 7.37–7.22 (m, 5H; H-arom.), 4.63–4.56
(m, 1H; H-5), 4.40–4.31 (m, 2H; H-5’, H-4), 2.93–2.80 ppm (m, 2H; H-
7).
Preparation of 2-chloroACHTUNGTRENNUNG(4H)-1,3,2-benzodioxaphosphorin-2-oxide deriva-
tives rac-(13) and rac-(18): A solution of the cycloSal-alcohol 12 or 9
(1.0 equiv) and triethylamine (2.1 equiv) in THF was added dropwise
within 1 h to a stirred solution of P(O)Cl3 (1.1 equiv) in THF at À708C.
The reaction was allowed to warm to À508C and stirred for 1 h. The re-
action mixture was then allowed to warm to room temperature and
stirred for 4 h. The triethylammonium chloride was filtered. The solvent
was removed under reduced pressure by using a high-vacuum pump. The
(RP,4’RC,5’SC)- and (SP,4’RC,5’SC)-2-(4’-Methyl-5’-phenyl-2’-N-cyanimino-
oxazo-lidin-3’-yl)(4H)-1,3,2-benzodioxaphosphorin-2-oxide (22): General
procedure C with (4R,5S)-4-methyl-5-phenyl-2-(N-cyanimino)oxazolidine
1656
www.chemeurj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 1649 – 1659

Synthesis of cycloSaligenyl-Nucleosyl-Phosphotriesters
FULL PAPER
(14) (0.804 g, 4.00 mmol) in dichloromethane (40 mL), 2-chloro(4H)-
1,3,2-benzodioxaphosphorin-2-oxide (rac-(18)) (0.820 g, 4.00 mmol) in di-
chloromethane (15 mL), and triethylamine (0.61 mL, 0.445 g, 4.40 mmol).
The product (SP)/(RP)-22 (0.860 g, 59%) was obtained as a colorless foam
as a diastereomeric mixture, which was then separated by column chro-
matography.
C
with
(S)-4-benzyl-2-(N-cyanimino)oxazolidine
(15)
(0.380 g,
1.89 mmol) in dichloromethane (30 mL), 2-chloro-8-methyl(4H)-1,3,2-
benzodioxaphosphorin-2-oxide (rac-(13)) (0.620 g, 2.84 mmol) in di-
chloromethane (15 mL), and triethylamine (0.29 mL, 0.210 g, 2.08 mmol).
The product (SP)/(RP)-28 (0.325 g, 45%) was obtained as a colorless foam
and as a diastereomeric mixture, which was then separated by column
chromatography.
1
Product (SP,4’RC,5’SC)-22: H NMR (400 MHz, CDCl3): d=7.49–7.34 (m,
1
Product (SP,4’SC)-28: H NMR (400 MHz, CDCl3): d=7.40–7.31 (m, 3H;
4H; H-arom.), 7.32–7.29 (m, 2H; H-arom.), 7.23–7.18 (m, 1H; H-arom.),
7.16–7.12 (m, 1H; H-arom.), 7.11–7.09 (m, 1H; H-arom.), 6.04 (d, 1H,
3JHÀH =7.3 Hz; H-12), 5.84 (dd, 1H, 2JHÀH =13.3, 3JHÀP =10.7 Hz; H-4),
5.39 (dd, 1H, 2JHÀH =13.4, 3JHÀP =18.8 Hz; H-4’), 4.88–4.77 (m, 1H; H-
13), 1.09 ppm (d, 3H, 3JHÀH =6.7 Hz; H-14); 31P NMR (162 MHz,
CDCl3): d=À14.43 ppm.
3
H-arom.), 7.28–7.24 (m, 2H; H-arom.), 7.22 (d, 1H, JHÀH =7.6 Hz; H-7),
7.09 (dd, 1H, 3JHÀH =7.6, 3JHÀH =7.5 Hz; H-6), 6.97 (d, 1H, JHÀH
=
3
7.5 Hz; H-5), 5.85 (dd, 1H, 2JHÀH =13, 3JHÀP =11 Hz; H-4), 5.39 (dd, 1H,
2JHÀH =13, JHÀP =19.7 Hz; H-4’), 4.89–4.77 (m, 1-H; H-14), 4.58 (dd, 1H,
3
3JHÀH =7.8, 2JHÀH =9.0 Hz; H-13), 4.51 (ddd, 1H, 4JHÀP =1.6, 3JHÀH =2.8,
2JHÀH =9.2 Hz; H-13’), 3.43 (dd, 1H, 3JHÀH =3.5, 2JHÀH =13.6 Hz; H-15),
2.99 (dd, 1H, 3JHÀH =9.6, 2JHÀH =14 Hz, 1H; H-15’), 2.30 ppm (s, 3H; H-
9); 31P NMR (162 MHz, CDCl3): d=À12.87 ppm.
Product (RP,4’RC,5’SC)-22: 1H NMR (400 MHz, CDCl3): d=7.49–7.34
(m, 4H; H-arom.), 7.32–7.28 (m, 2H; H-arom.), 7.23–7.16 (m, 1H; H-
arom.), 7.15–7.12 (m, 1H; H-arom.), 7.11–7.08 (m, 1H; H-arom.), 6.03
(d, 1H, 3JHÀH =7.3 Hz; H-12), 5.84 (dd, 1H, 2JHÀH =13.3, 3JHÀP =10.8 Hz;
1
Product (RP,4’SC)-28: H NMR (400 MHz, CDCl3): d=7.40–7.28 (m, 5H;
H-arom.) 7.23 (d, 1H, 3JHÀH =7.6 Hz; H-7), 7.09 (dd, 1H, 3JHÀH =7.6,
3JHÀH =7.6 Hz; H-6), 6.97 (d, 1H, 3JHÀH =7.6 Hz; H-5), 5.74 (dd, 1H,
2
3
H-4), 5.39 (dd, 1H, JHÀH =13.4, JHÀP =18.8 Hz; H-4’), 4.84–4.80 (m, 1H;
H-13), 1.09 ppm (d, 3H, 3JHÀH =6.7 Hz; H-14); 31P NMR (162 MHz,
CDCl3): d=À14.14 ppm.
2JHÀH =13, JHÀP =13 Hz; H-4), 5.43 (dd, 1H, JHÀH =14, JHÀP =17 Hz; H-
3
2
3
3
2
4’), 4.82–4.74 (m, 1H; H-14), 4.55 (dd, 1H, JHÀH =7.8, JHÀH =9.0 Hz; H-
13), 4.52–4.47 (m, 1H; H-13’), 3.43 (dd, 1H, 3JHÀH =3.0, 2JHÀH =13.6 Hz;
H-15), 3.09 (dd, 1H, 3JHÀH =9.1, 2JHÀH =14 Hz; H-15’), 2.34 ppm (s, 3H;
H-9); 31P NMR: (162 MHz, CDCl3): d=À13.05 ppm.
A
and
(SP,4’SC)-2-(4’-Benzyl-2’-N-cyanimino-oxazolidin-3’-
yl)(4H)-1,3,2-benzodioxaphosphorin-2-oxide (26): General procedure C
with (S)-4-benzyl-2-(N-cyanimino)oxazolidine (15) (0.760 g, 3.78 mmol)
in dichloromethane (40 mL), 2-chloro(4H)-1,3,2-benzodioxaphosphorin-
2-oxide (rac-(18)) (0.774 g, 3.78 mmol) in dichloromethane (15 mL), and
triethylamine (0.58 mL, 0.451 g, 4.16 mmol). The product (SP)/(RP)-26
(0.940 g, 67%) was obtained as a colorless foam as a diastereomeric mix-
ture, which was then separated by column chromatography.
cycloSal-3’-O-acetyl-thymidine monophosphates (RP)- and (SP)-5:
Product (RP)-5: General procedure D with (SP,4’RC,5’SC)-2-(4’-methyl-5’-
phenyl-2’-N-cyanimino-oxazolidin-3’-yl)(4H)-1,3,2-benzodioxaphosphor-
in-2-oxide ((SP)-22) (50.0 mg, 0.135 mmol), BEN (31.9 mg, 0.135 mmol),
copper(II)triflate (48.8 mg, 0.135 mmol) in dichloromethane (3 mL), 3’-
O-acetyl-thymidine 10 (0.115 g, 0.405 mmol), and triethylamine (54 mL,
41.0 mg, 0.405 mmol) in dichloromethane (3 mL). The product (RP)-5
(32 mg, 53%, ꢀ95% de) was obtained as a colorless foam. 1H NMR
(400 MHz, CDCl3): d=8.13 (brs, 1H; NH), 7.46 (d, 1H, 4JHÀH =1.0 Hz;
H-6), 7.38–7.31 (m, 1H; H-arom.), 7.20–7.14 (m, 1H; H-arom.), 7.12 (dd,
1H, 4JHÀH =1.4, 3JHÀH =7.7 Hz; H-arom.), 7.08 (dd, 1H, 4JHÀH =0.6,
1
Product (RP,4’SC)-26: H NMR (400 MHz, CDCl3): d=7.41–7.11 (m, 9H;
H-arom.), 5.79 (dd, 1H, 2JHÀH =12.9, 3JHÀP =12.2 Hz; H-4), 5.47 (dd, 1H,
2JHÀH =13.4, 3JHÀP =16.8 Hz; H-4’), 4.81–4.71 (m, 1H; H-13), 4.58–4.50
(m, 1H; H-12), 4.50–4.45 (m, 1H; H-12’), 3.50 (dd, 1H, 2JHÀH =13.6,
3JHÀH =3.6 Hz; H-14), 3.01 ppm (dd, 1H, 2JHÀH =13.6, 3JHÀH =9.6 Hz; H-
14’); 31P NMR (162 MHz, CDCl3): d=À14.33 ppm.
1
Product (SP,4’SC)-26: H NMR (400 MHz, CDCl3): d=7.39–7.28 (m, 5H;
3JHÀH =8.2 Hz; H-arom.), 6.35 (dd, 1H, 3JHÀH =9.1, 3JHÀH =5.4 Hz; H-1’),
H-arom.), 7.27–7.23 (m, 1H; H-arom.), 7.23–7.17 (m, 1H; H-arom.),
5.47 (dd, 1H, 2JHÀH =14.0, 3JHÀP =14.2 Hz; H-10), 5.32 (dd, 1H, JHÀH
=
2
7.16–7.11 (m, 1H; H-arom.), 7.10–7.05 (m, 1H; H-arom.), 5.87 (dd, 1H,
13.7, 3JHÀP =13.8 Hz; H-10’), 5.26–5.22 (m, 1H; H-3’), 4.49–4.44 (m, 2H;
H-5’a, H-5’b), 4.19–4.15 (m, 1H; H4’), 2.41 (ddd, 3JHÀH =1.2, 3JHÀH =5.4,
2JHÀH =14.1 Hz, 1H; H-2’a), 2.10 (s, 3H; H-9), 2.12–2.03 (m, 1H; H-2’b),
1.87 ppm (d, 3H, 4JHÀH =1.1 Hz; H-7); 31P NMR (162 MHz, CDCl3): d=
À9.23 ppm.
3
2JHÀH =13.3, 3JHÀP =10.5 Hz; H-4), 5.43 (dd, 1H, 2JHÀH =13.4, JHÀP
=
19.0 Hz; H-4’), 4.83–4.74 (m, 1H; H-13), 4.60–4.52 (m, 1H; H-12), 4.52–
4.45 (m, 1H; H-12’), 3.40 (dd, 1H, 2JHÀH =13.6, 3JHÀH =3.5 Hz; H-14),
2.99 ppm (dd, 1H, 2JHÀH =13.6, 3JHÀH =9.4 Hz; H-14’); 31P NMR
(162 MHz, CDCl3): d=À14.17 ppm.
Product (SP)-5: General procedure D with (RP,4’SC)-2-(4’-benzyl-2’-N-cy-
animino-oxazolidin-3’-yl)(4H)-1,3,2-benzodioxaphosphorin-2-oxide (RP)-
26 (23.0 mg, 0.0622 mmol), BEN (14.7 mg, 0.0622 mmol), copper(II)tri-
flate (22.5 mg, 0.0622 mmol) in acetonitrile (3 mL), 3’-O-acetyl-thymidine
10 (53.1 mg, 0.187), and triethylamine (26 mL, 18.9 mg, 0.187 mmol) in
acetonitrile (3 mL). The product (SP)-5 (4.90 mg, 18%, ꢀ95% de) was
obtained as a colorless foam. 1H NMR (400 MHz, CDCl3): d=7.94 (brs,
(RP,4’RC,5’SC)- and (SP,4’RC,5’SC)-8,4’-Dimethyl-2-(5’-phenyl-2’-N-cyani-
mino-oxazolidin-3’-yl)(4H)-1,3,2-benzodioxaphosphorin-2-oxide
General procedure with (4R,5S)-4-methyl-5-phenyl-2-(N-cyanimi-
no)oxazolidine (14) (0.500 g, 2.49 mmol) in dichloromethane (20 mL), 2-
chloro-8-methyl(4H)-1,3,2-benzodioxaphosphorin-2-oxide (rac-(13))
(27):
C
(0.817 g, 3.74 mmol) in dichloromethane (20 mL), and triethylamine
(0.42 mL, 0.302 g, 2.99 mmol). The product (SP)/(RP)-27 (0.582 g, 61%)
was obtained as a colorless foam and as a diastereomeric mixture, which
was then separated by column chromatography.
4
1H; NH), 7.46 (d, 1H, JHÀH =1.2 Hz; H-6), 7.38–7.31 (m, 1H; H-arom.),
7.20–7.14 (m, 1H; H-arom.), 7.12 (dd, 1H, 4JHÀH =1.4, JHÀH =7.6 Hz; H-
3
arom.), 7.08 (dd, 1H, 4JHÀH =0.6, 3JHÀH =8.2 Hz; H-arom.), 6.33 (dd, 1H,
1
3JHÀH =9.1, 3JHÀH =5.4 Hz; H-1’), 5.44 (dd, 1H, 2JHÀH =14.2, JHÀP
=
3
Product (SP,4’RC,5’SC)-27: H NMR (400 MHz, CDCl3): d=7.49–7.40 (m,
14.6 Hz; H-10), 5.34 (dd, 1H, 2JHÀH =13.3, 3JHÀP =13.8 Hz; H-10’), 5.28–
5.23 (m, 1H; H-3’), 4.49–4.43 (m, 2H; H-5’), 4.21–4.16 (m, 1H; H4’), 2.44
(ddd, 3JHÀH =1.4, 3JHÀH =5.4, 2JHÀH =14.1 Hz, 1H; H-2), 2.10 (s, 3H; H-
9), 2.14–2.04 (m, 1H; H-2’), 1.92 ppm (d, 3H, 4JHÀH =1.2 Hz; H-7);
31P NMR (162 MHz, CDCl3): d=À9.06 ppm.
3H; H-arom.), 7.34–7.29 (m, 2H; H-arom.), 7.24–7.20 (m, 1H; H-arom.),
7.09 (dd, 1H, 3JHÀH =7.6, 3JHÀH =7.6 Hz; H-6), 6.99–6.95 (m, 1H; H-
arom.), 6.01 (d, 1H, 3JHÀH =7.1 Hz; H-13), 5.78 (dd, 1H, 2JHÀH =12.9,
3JHÀP =12.8 Hz; H-4), 5.43 (dd, 1H, 2JHÀH =13.3, 3JHÀP =17.0 Hz; H-4’),
3
4.87–4.75 (m, 1H; H-14), 2.28 (s, 3H; H-9), 1.15 ppm (d, 3H, JHÀH
=
6.7 Hz; H-15); 31P NMR (162 MHz, CDCl3): d=À13.25 ppm.
3-Methyl-cycloSal-3’-azido-3’-deoxythymidine monophosphates (SP)- and
(RP)-6
1
Product (RP,4’RC,5’SC)-27: H NMR (400 MHz, CDCl3): d=7.49–7.40 (m,
3H; H-arom.), 7.34–7.29 (m, 2H; H-arom.), 7.25–7.20 (m, 1H; H-arom.),
7.08 (dd, 1H, 3JHÀH =7.5, 3JHÀH =7.7 Hz; H-6), 6.99–6.94 (m, 1H; H-
arom.), 6.06 (d, 1H, 3JHÀH =7.3 Hz; H-13), 5.80 (dd, 1H, 2JHÀH =13.2,
Product (RP)-6: General procedure D with (SP,4’RC,5’SC)-8,4’-dimethyl-2-
(5’-phenyl-2’-N-cyanimino-oxazolidin-3’-yl)-4H-1,3,2-benzodioxaphos-
phorin-2-oxide ((SP)-27) (74 mg, 0.193 mmol), BEN (45.6 mg,
0.193 mmol), copper(II)triflate (69.8 mg, 0.193 mmol) in dichloromethane
(3 mL), AZT (1) (0.155 g, 0.579 mmol), and triethylamine (81 mL,
58.6 mg, 0.579 mmol) in dichloromethane (3 mL). The product (RP)-6
(26.3 mg, 30%, ꢀ95% de) was obtained as a colorless foam. 1H NMR
(500 MHz, CDCl3): d=8.24 (brs, 1H; N-H), 7.32 (q, 1H, 4JHÀH =1.0 Hz;
3JHÀP =11.5 Hz; H-4), 5.34 (dd, 1H, 2JHÀH =13.3, 3JHÀP =19.2 Hz; H-4’),
3
4.89–4.79 (m, 1H; H-14), 2.32 (s, 3H; H-9), 1.09 ppm (d, 3H, JHÀH
=
6.7 Hz; H-15); 31P NMR (162 MHz, CDCl3): d=À12.88 ppm.
ACHTUNGTRENNUNG
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1657

C. Meier et al.
H-6), 7.20 (dd, 1H, 3JHÀH =7.6, 4JHÀH =0.6 Hz; H-12), 7.06 (dd, 1H,
CEM cells/mL were infected with HIV-1
(IIIB) or HIV-2
N
4
3JHÀH =7.6, 3JHÀH =7.6 Hz; H-13), 6.95 (dd, 1H, 3JHÀH =7.6, JHÀH
=
CCID50 (50% cell culture infective dose) per mL of cell suspension. The
0.6 Hz; H-14), 6.18 (dd, 1H, 3JHÀH =6.5, 3JHÀH =6.6 Hz; H-1’), 5.42 (dd,
thymidine kinase-deficient CEM/TKÀ cell cultures were also infected
1H, 2JHÀH =14.1, 3JHÀP =14.8 Hz; H-8a), 5.30 (dd, 1H, 2JHÀH =13.6,
with HIV-2ACTHNUTRGENUG(N ROD). Then, 100 mL of the infected cell suspensions was
3JHÀP =13.6 Hz, 1H; H-8b), 4.45 (ddd, 1H, 3JHÀP =11.5, 2JHÀH =7.3,
transferred to 96-well microtiter plate wells and mixed with 100 mL of the
appropriate dilutions of the test compounds. After 4–5 days, giant cell
formation was recorded microscopically in the HIV-infected cell cultures.
The 50% effective concentration is defined as the compound concentra-
tion required to inhibit virus-induced cytopathicity by 50%. The 50% cy-
tostatic concentration is defined as the compound concentration required
to inhibit CEM cell proliferation by 50%, as derived by counting the cell
numbers in the presence of different compound concentrations by use of
a Coulter Particle Counter ZI (Analysis, Gent, Belgium).
3
3JHÀH =3.1 Hz; H-5’a), 4.35 (ddd, 1H, 3JHÀP =14.7, 2JHÀH =7.3, JHÀH
=
3.1 Hz; H-5’b), 4.34–4.30 (m, 1H; H-3’), 4.07–4.00 (m, 1H; H-4’), 2.45
(ddd, 1H, 2JHÀH =13.9, 3JHÀH =4.5, 3JHÀH =6.3 Hz; H-2’a), 2.34–2.27 (m,
1H; H-2’b), 2.28 (s, 3H; H-15), 1.82 ppm (d, 3H, 4JHÀH =1.1 Hz; H-7);
31P NMR (162 MHz, CDCl3): d=À8.41 ppm.
Product (SP)-6: General procedure
D with (RP,4’SC)-8-methyl-2-(4’-
benzyl-2’-N-cyanimino-oxazolidin-3’-yl)(4H)-1,3,2-benzodioxaphosphor-
in-2-oxide ((RP)-28) (46 mg, 0.120 mmol), BEN (28.4 mg, 0.120 mmol),
copper(II) triflate (43.4 mg, 0.120 mmol) in dichloromethane (3 mL),
AZT (1) (96.2 g, 0.360 mmol), and triethylamine (50 mL, 36.4 mg,
0.36 mmol) in dichloromethane (3 mL). The product (SP)-6 (11.3 mg,
21%, ꢀ95% de) was obtained as a colorless foam. 1H NMR (500 MHz,
CDCl3): d=8.39 (brs, 1H; N-H), 7.29 (q, 1H, 4JHÀH =1.0 Hz; H-6), 7.20
(d, 1H, 3JHÀH =7.6 Hz; H-12), 7.06 (dd, 1H, 3JHÀH =7.6, 3JHÀH =7.6 Hz;
H-13), 6.95 (d, 1H, 3JHÀH =7.6 Hz; H-14), 6.17 (dd, 1H, 3JHÀH =6.5,
3JHÀH =6.5 Hz; H-1’), 5.42 (dd, 1H, 2JHÀH =14.2, 3JHÀP =14.2 Hz; H-8a),
5.29 (dd, 1H, 2JHÀH =14.2, 3JHÀP =13.9 Hz, 1H; H-8b), 4.43–4.38 (m, 2H;
H-5’), 4.38–4.33 (m, 1H; H-3’), 4.07–4.02 (m, 1H; H-4’), 2.47 (ddd, 1H,
2JHÀH =14.0, 3JHÀH =4.8, 3JHÀH =6.3 Hz; H-2’a), 2.36–2.27 (m, 1H; H-2’b),
2.29 (s, 3H; H-15), 1.85 ppm (d, 3H, 4JHÀH =1.0 Hz; H-7); 31P NMR:
(162 MHz, CDCl3): d=À8.04 ppm.
Acknowledgements
We thank I. Nevoigt for solving the X-ray crystal structures and L. Ingels
and L. van Berckelaer for excellent technical assistance. C.M. thanks sup-
port from the Deutsche Forschungsgemeinschaft (DFG; ME 1161/9–1)
and the University of Hamburg. J.B. received a grant from the K.U.
Leuven (GOA 10/14).
[1] J. W. Curran, W. M. Morgan, A. M. Hardy, H. W. Jaffe, W. W.
Darrow, D. R. Dowdle, Science 1985, 229, 1352–1357.
3-Methyl-cycloSal-3’-deoxy-2’,3’-didehydrothymidine
(SP)- and (RP)-4
monophosphates
[2] F. Barre-Sinoussi, J. C. Cherman, F. Rey, M. T. Nugeyre, S. Chamar-
et, T. Gruest, C. Dauguet, C. Axler-Blin, F. Vezin-Brun, C. Rou-
tioux, W. Rosenbaum, L. Montagnier, Isolation of a T-lymphotropic
Retrovirus from a Patient at Risk for Acquired Immune Deficiency
Syndrome ACTHNUGTRNEUNG(AIDS), Science 1983, 220, 868–871.
[3] E. De Clercq, J. Med. Chem. 1995, 38, 2491.
[4] a) J. Balzarini, Pharm. World Sci. 1994, 16, 113–126; b) E. De
Clercq, Nat. Rev. Drug Discovery 2002, 1, 13–25.
[5] P. Herdewijn, J. Balzarini, E. De Clercq in Advances in Antiviral
Drug Design, Vol. 1 (Ed.: E. De Clercq), JAI Press Inc., Greenwich
(Connecticut), London (England), 1993, pp. 233–318.
[6] P. A. Furman, J. A. Fyfe, M. H. St. Clair, K. J. Weinhold, J. L. Ride-
out, G. A. Freeman, S. N. Lehrmann, D. Bolognesi, S. Broder, Proc.
Natl. Acad. Sci. USA 1986, 83, 8333–8337.
[7] S. A. Riddler, R. E. Anderson, J. W. Mellors, Antiviral Res. 1995, 27,
189–203.
[8] a) M. J. M. Hitchcock, Antiviral Chem. Chemother. 1991, 2, 125–
132; b) J. P. Sommadossi, J. Infect. Dis. (Suppl. 2) 1995, 171, 88–92.
[9] J. Balzarini, P. Herdewijn, E. De Clercq, J. Biol. Chem. 1989, 264,
6127–6133.
[10] Whole issue: “Pro-Nucleotide Development and Delivery of Biolog-
ically Active Nucleotide analogues”, Mini-Rev. Med. Chem. 2004, 4,
341–459.
[11] a) S. Peyrottes, D. Egron, I. Lefebvre, G. Gosselin, J.-L. Imbach, C.
Perigaud, Mini-Rev. Med. Chem. 2004, 4, 395–408; b) J.-L. Girardet,
C. Pꢃrigaud, A.-M. Aubertin, G. Gosselin, A. Kim, J.-L. Imbach,
Bioorg. Med. Chem. Lett. 1995, 5, 2981–2984.
[12] a) K. R. Reddy, S. H. Boyer, M. D. Erion, Tetrahedron Lett. 2005,
46, 4321–4324; b) M. D. Erion, J. Am. Chem. Soc. 2004, 126, 5154–
5163.
[13] a) C. McGuigan, M.-J. Camarasa, H. Egberink, K. Hartmann, A.
Karlsson, C. F. Perno, J. Balzarini, Int. Antiviral News 1997, 5, 19–
21; b) C. McGuigan, D. Cahard, H. M. Sheeka, E. De Clercq, J. Bal-
zarini, J. Med. Chem. 1996, 39, 1748–1753.
[14] a) C. Meier, Eur. J. Org. Chem. 2006, 1081–1102; b) C. Meier, E. De
Clercq, J. Balzarini, Eur. J. Org. Chem. 1998, 837–846; c) H. J.
Jessen, J. Balzarini, C. Meier, J. Med. Chem. 2008, 51, 6592–6598;
d) N. Gisch, F. Pertenbreiter, J. Balzarini, C. Meier, J. Med. Chem.
2008, 51, 8115–8123; e) N. Gisch, J. Balzarini, C. Meier, J. Med.
Chem. 2009, 52, 3464–3473; f) C. Ducho, U. Gçrbig, S. Jessel, N.
Gisch, J. Balzarini, C. Meier, J. Med. Chem. 2007, 50, 1335–1346;
Product (RP)-4: General procedure D with (SP,4’RC,5’SC)-8,4’-dimethyl-2-
(5’-phenyl-2’-N-cyanimino-oxazolidin-3’-yl)(4H)-1,3,2-benzodioxaphos-
phorin-2-oxide ((SP)-27) (30 mg, 0.0783 mmol), BEN (18.5 mg,
0.0783 mmol), copper(II)triflate (28.3 mg, 0.0783 mmol) in dichlorome-
thane (1.5 mL) and acetonitrile (1.5 mL), d4T (2) (52.6 mg, 0.235 mmol),
and triethylamine (33 mL, 23.8 mg, 0.235 mmol) in dichloromethane
(1.5 mL) and acetonitrile (1.5 mL). The product (RP)-4 (5.43 mg, 17%,
94% de) was obtained as a colorless foam. 1H NMR (400 MHz, CDCl3):
d=7.96 (brs, 1H; N-H), 7.22 (q, 1H, 4JHÀH =1.2 Hz; H-6), 7.18 (d, 1H,
3JHÀH =7.6 Hz; H-12), 7.04 (dd, 1H, 3JHÀH =7.6, 3JHÀH =7.6 Hz; H-13),
7.01–6.97 (m, 1H; H-1’), 6.93 (dd, 1H, 4JHÀH =0.7, 3JHÀH =7.6 Hz; H-14),
2
6.37–6.32 (m, 1H; H-3’), 5.96–5.91 (m, 1H; H-2’), 5.36 (dd, 1H, JHÀH
=
13.9, 3JHÀP =15.8 Hz; H-8a), 5.30–5.21 (m, 1H; H-8b), 5.04–4.99 (m, 1H;
H-4’), 4.41–4.34 (m, 2H; H-5’), 2.26 (s, 3H; H-15), 1.66 ppm (d, 1H,
4JHÀH =1.2 Hz; H-7); 31P NMR: (162 MHz, CDCl3): d=À8.12 ppm.
Product (SP)-4: General procedure
D with (RP,4’SC)-8-methyl-2-(4’-
benzyl-2’-N-cyanimino-oxazolidin-3’-yl)(4H)-1,3,2-benzodioxaphosphor-
in-2-oxide ((RP)-28) (71.0 mg, 0.185 mmol), BEN (43.7 mg, 0.185 mmol),
copper(II)triflate (66.9 mg, 0.185 mmol) in dichloromethane (3.0 mL),
d4T (2) (0.124 mg, 0.555 mmol), and triethylamine (77 mL, 56.2 mg,
0.555 mmol) in dichloromethane (3 mL). The product (SP)-4 (22 mg,
28%, ꢀ95% de) was obtained as a colorless foam. 1H NMR (400 MHz,
CDCl3): d=7.91 (brs, 1H; N-H), 7.23–7.20 (m, 1H; H-6), 7.19 (d, 1H,
3JHÀH =7.6 Hz; H-12), 7.04 (dd, 1H, 3JHÀH =7.6, 3JHÀH =7.6 Hz; H-13),
3
7.01–6.97 (m, 1H; H-1’), 6.92 (d, 1H, JHÀH =7.6 Hz; H-14), 6.43–6.37 (m,
3
1H; H-3’), 5.96–5.91 (m, 1H; H-2’), 5.40 (dd, 1H, 2JHÀH =13.6, JHÀP
=
13.6 Hz; H-8a), 5.21 (dd, 1H, 2JHÀH =13.6, 3JHÀP =15.6 Hz; H-8b), 5.04–
4.99 (m, 1H; H-4’), 4.48–4.40 (m, 1H; H-5’a), 4.35–4.28 (m, 1H; H-5’b),
2.29 (s, 3H; H-15), 1.78 ppm (d, 3H, 4JHÀH =1.2 Hz; H-7); 31P NMR:
(162 MHz, CDCl3): d=À7.45 ppm.
Antiretroviral evaluation: Human immunodeficiency virus type 1 (HIV-
1) was originally obtained from a persistently HIV-infected H9 cell line,
as described previously, and was kindly provided by Dr. R.C. Gallo (then
at the National Institutes of Health, Bethesda, MD). Virus stocks were
prepared from the supernatants of HIV-infected MT-4 cells. HIV-2
(strain ROD) was kindly provided by Dr. L. Montagnier (then at the
Pasteur Institute, Paris, France), and virus stocks were prepared from the
supernatants of HIV-2-infected MT-4 cells. CEM cells were obtained
from the American Tissue Culture Collection (Rockville, MD). CEM
cells were infected with HIV as previously described. Briefly, 4ꢂ105
1658
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Synthesis of cycloSaligenyl-Nucleosyl-Phosphotriesters
FULL PAPER
g) N. Gisch, J. Balzarini, C. Meier, J. Med. Chem. 2007, 50, 1658–
1667.
[22] a) S. Jones, C. Smanmoo, Org. Lett. 2005, 7, 3271–3274; b) S. Jones,
D. Selitsianos, Org. Lett. 2002, 4, 3671–3673.
[15] H. J. Jessen, T. Schulz, J. Balzarini, C. Meier, Angew. Chem. 2008,
120, 8847–8850; Angew. Chem. Int. Ed. 2008, 47, 8719–8722.
[16] C. Meier, M. Lorey, E. De Clercq, J. Balzarini, J. Med. Chem. 1998,
41, 1417–1427.
[17] C. Meier, C. Ducho, U. Gçrbig, R. Esnouf, J. Balzarini, J. Med.
Chem. 2004, 47, 2839–2852.
[23] a) S.-Y. Wu, J. E. Casida, Phosphorus Sulfur Silicon Relat. Elem.
1994, 88, 129–137; b) Z. J. Lesnikowski, P. J. Wolkanin, W. Stec, Tet-
rahedron Lett. 1987, 28, 5535–5538; c) J. Michalski, M. Mikolajczyk,
Tetrahedron 1966, 22, 3055–3059; d) M. Mikolajczyk, Tetrahedron
1967, 23, 1543–1549; e) J. Michalski, M. Mikolajczyk, Chem.
Commun. (London) 1965, 35–36.
[18] a) C. Meier, T. Knispel, E. De Clercq, J. Balzarini, J. Med. Chem.
1999, 42, 1604–1614; b) C. Meier, T. Knispel, V. E. Marquez, M. A.
Siddiqui, E. De Clercq, J. Balzarini, J. Med. Chem. 1999, 42, 1615–
1624; c) N. Gisch, J. Balzarini, C. Meier, J. Med. Chem. 2008, 51,
6752–6760.
[19] a) K. K. Ogilvie, D. J. Iwacha, Tetrahedron Lett. 1973, 14, 317–319;
b) H. Weber, H. G. Khorana, J. Mol. Biol. 1972, 72, 219–249; c) E. J.
Corey, A. Venkateswarlu, J. Am. Chem. Soc. 1972, 94, 6190–6191.
[20] A. Meinzer, A. Breckel, B. A. Thaher, N. Manicone, H.-H. Otto,
Helv. Chim. Acta 2004, 87, 90–105.
[24] J. Emsley, D. Hall, The Chemistry of Phosphorus, Harger and Row,
London, 1976, Chapter 8, pp. 306–349.
[25] G. R. J. Thatcher, R. Kluger, Adv. Phys. Org. Chem. 1989, 25, 99–
265.
[26] J. Balzarini, L. Naesens, S. Aquaro, T. Knispel, C.-F. Perno, E. De
Clercq, C. Meier, Mol. Pharmacol. 1999, 56, 1354–1361.
[27] C. Arbelo Romꢄn, J. Balzarini, C. Meier, J. Med. Chem. 2010, 53,
7675–7681.
[21] a) R. S. Cahn, C. K. Ingold, J. Chem. Soc. 1951, 612–622; b) R. S.
Cahn, C. K. Ingold, V. Prelog, Angew. Chem. 1966, 78, 413–447;
Angew. Chem. Int. Ed. Engl. 1966, 5, 385–415.
Received: September 15, 2010
Published online: December 16, 2010
Chem. Eur. J. 2011, 17, 1649 – 1659
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1659