Diastereoselective synthesis of (aryloxy)phosphoramidate prodrugs

Article abstract of DOI:10.1002/ejoc.201100614

The first diastereoselective synthesis of aryloxyphosphoramidate prodrugs of 3′-deoxy-2′,3′-didehydrothymidinemonophosphate (d4TMP) was recently reported. The synthetic approach utilized the chiral auxiliary (S)-4-isopropylthiazolidine-2-thione (2). For this strategy, a stereochemically pure phosphorodiamidate intermediate was needed. The diastereoselective formation of this key compound was investigated by using different phenols and L-alanine methyl or benzyl ester. Generally, the reaction with 3- or 4-substituted phenols led to significantly better diastereoselectivities compared to their 2-substituted counterparts. Moreover, variation of the ester group in the amino acid residue resulted in no significant differences with regard to the obtained diastereoselectivity. From the reported results, a model for the transition state was elaborated. Finally, eight new (S _P)-arylphosphoramidates were synthesized with very high diastereoselectivities (up to ≥ 95 % de) and tested for their anti-HIV potency, showing a tendency for higher antiviral activity from the (S _P) diastereomers.

Full text of DOI:10.1002/ejoc.201100614

FULL PAPER
DOI: 10.1002/ejoc.201100614
Diastereoselective Synthesis of (Aryloxy)phosphoramidate Prodrugs
Cristina Arbelo Román,[a] Philip Wasserthal,[a] Jan Balzarini,[b] and Chris Meier*[a]
Keywords: Phosphoramidates / Asymmetric synthesis / Diastereoselectivity / Pronucleotides / Antiviral agents / Nucleosides
The first diastereoselective synthesis of aryloxyphosphor-
amidate prodrugs of 3Ј-deoxy-2Ј,3Ј-didehydrothymidine
monophosphate (d4TMP) was recently reported. The syn-
thetic approach utilized the chiral auxiliary (S)-4-isopropyl-
thiazolidine-2-thione (2). For this strategy, a stereochemically
pure phosphorodiamidate intermediate was needed. The
diastereoselective formation of this key compound was in-
vestigated by using different phenols and L-alanine methyl
or benzyl ester. Generally, the reaction with 3- or 4-substi-
tuted phenols led to significantly better diastereoselectivities
compared to their 2-substituted counterparts. Moreover, vari-
ation of the ester group in the amino acid residue resulted in
no significant differences with regard to the obtained dia-
stereoselectivity. From the reported results, a model for the
transition state was elaborated. Finally, eight new (SP)-aryl-
phosphoramidates were synthesized with very high dia-
stereoselectivities (up to Ն 95% de) and tested for their anti-
HIV potency, showing a tendency for higher antiviral activity
from the (SP) diastereomers.
tivity, toxicity, and pharmacokinetic profiles were found for
the individual diastereomers.
Introduction
Lipophilic nucleotide precursors (pronucleotides) are a
promising alternative to improve the biological activity of
nucleoside analogues in antiviral chemotherapy.[1] Pronu-
cleotides allow the intracellular delivery of 5Ј-nucleotides
that need subsequent conversion to the 5Ј-di- and 5Ј-tri-
phosphates. The latter are ultimately the biologically active
compounds. Several pronucleotide strategies have been
reported, for example, the phosphoramidates,[2,3] the
cycloSal-phosphate triesters,[4] the mixed-S-acyl-2-thioethyl
compounds,[5] the HepDirect technique,[6] and recently the
bis(acyloxybenzyl) approach for the intracellular delivery of
nucleoside diphosphates.[7] These pronucleotide approaches
use different means of activation, for example, by enzymes
or chemical cleavage. In the first four cases, the compounds
are phosphoric acid derivatives that contain four different
residues attached to the phosphorus center. As a conse-
quence of the stereogenic center at the phosphorus atom,
diastereomers of the pronucleotides result because of the
additional chiral centers in the nucleoside analogs. In these
syntheses, pronucleotides are formed as mixtures of two
diastereomers, and in most cases, their separation has been
a difficult or impossible task. Importantly, in cases where
the diastereomers were separable, different biological ac-
Sofia et al. recently reported the discovery of phos-
phoramidate prodrugs of 2Ј-deoxy-2Ј-α-fluoro-2Ј-β-C-
methyluridine-5Ј-monophosphate that show strong inhibi-
tion of hepatitis C virus (HCV) replication.[8] The prodrugs
were prepared as a 1:1 mixture of diastereomers that were
separated by chromatography and crystallization. The anti-
viral evaluation of the individual diastereomers showed that
the (SP) diastereomer was Ͼ 10-fold more active against
HCV than the (RP) diastereomer. Significant differences in
activity were also found for the phosphoramidates of 2Ј-C-
methylcytidine. Again, the compounds were synthesized as
mixtures, and then the individual diastereomers were sepa-
rated by reversed-phase HPLC. The antiviral evaluation of
the diastereomers proved that the more lipophilic dia-
stereomer was about 8-fold more active against HCV than
the second diastereomer.[9] These examples clearly demon-
strate the importance of the phosphorus configuration on
the biological activity.
Consequently, the development of strategies for isomer-
ically pure nucleotide prodrugs is important. Recently, we
published the first diastereoselective synthesis of cycloSal-[10]
and (aryloxy)phosphoramidate prodrugs 1.[11] In both
cases, the routes led to diastereomerically almost pure pro-
drugs (Ն 95% de), and both pathways were based on the
use of chiral auxiliaries. Interestingly, one chiral auxiliary
was not suitable for the cycloSal-pronucleotides; instead,
the auxiliary had to be adapted to the target molecule. For
the diastereoselective synthesis of phosphoramidates 1, (S)-
4-isopropylthiazolidine-2-thione (2) was used as the chiral
auxiliary.[12] Scheme 1 summarizes the reaction sequence for
the synthesis of the nucleoside phosphoramidates 1 starting
[a] Organic Chemistry, Department of Chemistry, Faculty of
Sciences, University of Hamburg,
Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
Fax: +49-40-42838-5592
E-mail: chris.meier@chemie.uni-hamburg.de
[b] Rega Institute for Medical Research, Katholieke Universiteit
Leuven,
Minderbroedersstraat 10, 3000 Leuven, Belgium
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100614.
Eur. J. Org. Chem. 2011, 4899–4909
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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C. Arbelo Román, P. Wasserthal, J. Balzarini, C. Meier
FULL PAPER
Scheme 1. Diastereoselective route to phosphoramidate prodrugs 1.
from auxiliary 2 and through achiral phosphorodichlorid- we reported that the conversion of 3 to the chiral phos-
ate 3, chiral phosphorochloridate 5, and phosphorodiamid- phorochloridates 5 was performed using the three phenol
ate 7.[11] The latter compound is the key intermediate of the derivatives 4b,d,g as well as 1-naphthol (4l). As mentioned
synthesis, because it is chiral and can be isolated.
above, the ratio of the two diastereomers obtained in this
The anti-HIV evaluation of the phosphoramidate pro- step, where the chirality transfer took place, was clearly de-
drugs of nucleoside analog 3Ј-deoxy-2Ј,3Ј-didehydro- pendent on the phenol derivatives and the reaction condi-
thymidine (d4T) confirmed the expected significant differ- tions.[11]
ences in the activities of the individually prepared dia-
stereomers (up to 65-fold).[11] In the recent report, only four
different phenols 4 and l-alanine methyl ester (6a) were
used in the reactions, and significantly different diastereo-
selectivities were obtained depending on the chosen phenol.
Here, a series of phenol derivatives (i.e., 4) were used to
gain more insight into this reaction. Moreover, in addition
to methyl ester 6a, the benzyl ester of l-alanine (6b) was
also used to expand the synthesis to other phenolic and
amino acid residues. Finally, the method was applied to the
syntheses of eight new phosphoramidate prodrugs starting
from diastereomerically pure phosphorodiamidate interme-
diates.
The proposed transition state shown in Figure 1 should
lead to the preferential formation of the (SP) diastereomer
because of the interaction of the bulky isopropyl group with
the incoming phenolate nucleophile. A trigonal-bipyrami-
dal intermediate should form from the subsequent displace-
ment of the pro-(RP)-chloride anion. This proposed transi-
tion state is supported by the X-ray crystal structure of
thiophosphorodichloridate 8, which was previously ob-
tained.[14] Here, a series of 2- and 4-donor- or acceptor-
substituted phenols along with 3-substituted derivatives
(i.e., 4a–m) were studied (Figure 2). The results for the reac-
tion between phosphorodichloridate 3 and 4a–m to yield
phosphorochloridates 5 are given in Table 1.
First, the synthesis of the phosphorochloridates 5 was
carried out by cooling phosphorodichloridate 3 at –91 °C
in the presence of 0.7–1.0 equiv. of the phenols 4 and the
Results and Discussion
(S)-4-Isopropylthiazolidine-2-thione (2), prepared ac- base DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) for 25–
cording to the procedure of Delaunay et al.,[13] was treated 75 min. The conversion of 3 ranged between a moderate
with an excess of phosphoryl chloride and NEt3 in CH2Cl2 59% to an excellent 93% depending on the phenol used
to give phosphorodichloridate 3 (Scheme 1). The crude ma- (Table 1). The phosphorochloridates (RP/SP)-5 were ob-
terial 3 displayed only one 31P NMR signal (δ = 3.70 ppm) tained in a ratio of up to 14:1. In all cases, the (SP)-config-
and thus was used directly in the next reaction. Previously, ured diastereomer was assumed to be preferentially formed
Figure 1. Possible transition state for the preferential formation of (SP)-5.
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Diastereoselective Synthesis of (Aryloxy)phosphoramidate Prodrugs
Figure 2. Synthesis of phosphorodiamidate derivatives (RP)- or (SP)-11 and (RP)- or (SP)-12 through phosphorochloridates (RP)/(SP)-5.
Table 1. Conversion in the reactions leading to 5, 11, and 12, respectively, and the diastereomeric excess values for 5, 11, and 12.
5
Conversion of 3 [%][a]
de [%][a]
11, 12[b]
Conversion of 5 [%][a]
de [%][a,c]
a
b
c
d
e
f
g
h
i
59
64
84
93
85
74
83
81
75
66
62
79
74
83
51
83
81
87
86
72
28
67
75
66
36
77
11a
11b
11c
11d
11e
11f
11g
11h
11i
39
54
66
78
64
68
60
55
46
58
36
62
59
95
93
74
30
81
81
85
78
72
15
25
52
44
28
72
48
81
j
k
l
11j
11k
11l
11m
12b
12d
m
[a] Conversion and de determined by 31P NMR spectroscopy of the crude mixture. [b] 11 (R6 = Me), 12 (R6 = Bn). [c] Starting materials
are the phosphorochloridate derivatives 5.
as a result of the addition/elimination mechanism. Always diastereoselectivities. The use of substoichiometric amounts
the resonance signal of the (SP) diastereomer was found to was particularly necessary in the cases of phenols 4c,f,h–k.
be low-field-shifted compared to that of the (RP) isomer If 1.0 equiv. of these phenols was used, considerable
[e.g.: (SP)-5e, δ = –2.02 ppm; (RP)-5e, δ = –2.53 ppm; see amounts of diarylphosphoramidates 13 were observed as
Exp. Sect.]. Due to their instability, phosphorochloridates 5 side products. For the other phenols 4, compounds 13 were
were purified only by one fast chromatography on a short formed in only very small amounts or not at all. The avoid-
silica gel column and could not be separated into the indi- ance of the formation of diarylphosphoramidates 13 was of
vidual diastereomers. The diastereomeric ratio was found to great importance, because compounds 13 and the phos-
be strongly dependent on the substitution of the aromatic phorochloridates 5 showed identical Rf values and conse-
moiety. Particularly, 2-methylphenol (4b) and 2-chloro- quently could not be separated by column chromatography.
phenol (4h) led to a significant reduction in diastereoselec- As a result, the diastereoselective synthesis of 5 worked best
tivity (51% de and 28% de, respectively). To our surprise, by using the 3- and 4-substituted phenol derivatives. With
2-methoxyphenol (4e) gave the best value (87% de) for all the exception of 2-methoxy, 2-substituted phenols led to
the reactions. This unexpected difference may be attributed poor diastereoselectivities and thus are not suitable for this
to the different electronic and/or steric properties of the diastereoselective synthesis. This loss of diastereoselectivity
chloro, methyl, and methoxy groups. Moreover, these ex- could be related to the proposed transition state, although
periments also showed pronounced differences between the a final explanation cannot be given (Figure 1).
diastereomeric ratios in the cases of 1- and 2-naphthol [4l
Next, the syntheses of phosphorodiamidates (RP)- and
and 4m yielding 5l (36% de) and 5m (77% de), respectively]. (SP)-11 and (RP)- and (SP)-12 (11, R6 = Me; 12, R6 = Bn)
Overall, the 2-substituted systems led to markedly lower were carried out by using the diastereomerically enriched
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C. Arbelo Román, P. Wasserthal, J. Balzarini, C. Meier
FULL PAPER
mixtures of phosphorochloridates 5a–m and l-alanine tween the chloride and the phenolate moieties in starting
methyl or benzyl ester hydrochloride (9 and 10, respec- material 5 can be achieved. Assuming that a small fraction
tively). l-Alanine was previously identified as the most ef- of the reaction of 5 with the amino acid esters 9 and 10
fective amino acid for use in this phosphoramidate ap- took place with displacement of the phenolate, one should
proach, and the different esters in the amino acid moiety expect intermediate 14 as a product (Figure 3, pathway c).
also play an important role for the antiviral potency. The This material should be formed with inversion of configura-
reaction began by the addition of NEt3 at 0 °C, and then tion at the P atom. In a subsequent step, the released phe-
the reaction mixture was stirred at room temperature for nolate can then react with compound 14 with displacement
16 h (Figure 2). The conversion of phosphorochloridates 5 of the chloride anion and again with inversion of configura-
and the diastereomeric excesses obtained for phosphorodi- tion. In total, this scenario would lead to the products 11
amidates 11 and 12 are also given in Table 1. In all cases, with the inverted configuration (Figure 3, pathway a). How-
the major diastereomer has the (RP) configuration, which ever, the released phenolate could react with the starting
was supported earlier by three X-ray crystal structure material 5 to lead to the diaryl derivative 13, again. There-
analyses.[11] In comparison to 5, the (RP) isomers of 11 or fore, both proposed reactions would lead to a reduction in
12 displayed the low-field 31P NMR signal compared to the stereochemical purity of the obtained phosphorodi-
their (SP) counterparts [e.g.: (SP)-11d, δ = 1.43 ppm; (RP)- amidates 11.
11d, δ = –0.83 ppm; see Exp. Sect.].[11] Interestingly in all
cases, except for 11d and 12d, the diastereomeric excess val-
ues were found to be lower as compared to those of the
starting mixture of diastereomers 5 (Table 1) which points
to some isomerization during the second substitution of the
amino acid ester. In contrast to compounds 5, the phos-
phorodiamidates 11 and 12 were sufficiently stable to be
purified and separated to give the stereochemically pure
diastereomers by silica gel column chromatography (Ն 95%
de for each diastereomer).
Again, the substitution pattern in the aromatic residue
played a role with regard to the observed diastereoselectivi-
ties. Particularly, the 2-methylphenol phosphorodiamidate
derivative of the l-alanine methyl ester 11b was obtained in
a drastically lower diastereoselectivity compared to phos-
phorochloridate 5b. A reason for the loss in stereospecificity
may be related to the presence of diarylphosphoramidate
13. In all reactions of phosphorochloridates 5 leading to the
phosphorodiamidates 11, some amounts of 13 were ad-
Figure 3. Proposed formation of side products 13 and 14 in the
synthesis of phosphorodiamidates 11.
1
ditionally formed. This was clearly proven by 31P and H
NMR spectroscopy and mass spectrometry. However, no
traces of the phenols were detected in the 1H NMR spectro-
To prove whether diarylphosphoramidates like 13 react
scopic data of 5. It was reported previously that phos- with the amino acid ester, a separate experiment was carried
phoramidates 13 can also undergo substitution reactions out (Figure 4). However, by using an identical experimental
(Figure 3, pathway b).[15] In contrast to compounds 5, di- setup, no formation of the expected phosphorodiamidates
aryl derivative 13 is an achiral compound with two identical (RP)-11d or (SP)-11d was detected. The 31P NMR spectrum
phenol groups. Thus, a reaction of 13 with the amino acid of the crude reaction mixture showed no conversion at all.
ester should lead to a diastereomeric mixture of the target Thus, this experiment excludes that the loss of stereoselecti-
compounds 11, which consequently lowers the overall dia- vity is related to the formation of compound 13. Intermedi-
stereospecificity of this reaction. In addition, it is still un- ate 14 still may play a role in the decrease of stereoselecti-
known to what extent the leaving group differentiation be- vity (Figure 3); however, the synthesis and isolation of inter-
Figure 4. Excluded reaction to the formation of phosphorodiamidates 11d.
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Diastereoselective Synthesis of (Aryloxy)phosphoramidate Prodrugs
Figure 5. Synthesis of d4T-phosphoramidates 16j,k and 17b,d.
mediate 14 was unsuccessful. Thus, it is impossible to give after column chromatography and were found to be at least
a final proof of the reaction mechanism explaining the for- 85% de. Except for the 85% de value for phosphoramidate
mation of the minor diastereomer (SP)-11.
prodrug (RP)-17b, the diastereomeric values almost corre-
Nevertheless, the formation of intermediate 14 can be sponded to the Ն 95% de in the starting materials.
proven indirectly by the preparation of diaryl derivative 13.
Table 2. Yields and diastereomeric excess values of phosphoramid-
If 14 is formed, 1 equiv. of phenol would be released, which
ate prodrugs 16j,k and 17b,d.
then could react in a subsequent reaction to give achiral
(SP) δ(31P) Yield[a] de[b] (RP) δ(31P) Yield[a] de[b]
compounds 13 as well as the diastereomer of 11. Interest-
[ppm]
[%]
[%]
[ppm]
[%]
[%]
ingly, the use of l-alanine benzyl ester hydrochloride 10,
which was prepared according to the procedure of Joullié
et al.,[16] did not lead to the formation of diaryl derivative
13. Its use led to very high conversions and almost to the
same diastereomeric excess values as those of 5b,d (12b,
48% de; 12d, 81% de).
16j
16k
17b
17d
3.13
3.13
2.98
3.27
20
15
11
14
95
93
16j
2.62
2.56
2.59
2.62
26
50
28
44
Ն 95
Ն 95
85
16k
Ն 95 17b
94
17d
Ն 95
[a] Isolated yields. [b] de determined by 31P NMR spectroscopy af-
ter purification.
For the following reaction, phosphorodiamidates 11j,k
and 12b,d were separately treated with 3Ј-deoxy-2Ј,3Ј-dide-
hydrothymidine (d4T, 15) to give phosphoramidate pro-
drugs 16j,k and 17b,d (Figure 5). The reactions were carried
out in a mixture of THF/CH3CN (1:1) with the addition
Antiviral Evaluation
Phosphoramidates 16j,k and 17b,d were evaluated for
of tert-butylmagnesium chloride. The Grignard reagent was their anti-HIV activity in vitro. All compounds showed ac-
used as a base analogous to Uchiyama’s method.[17]
tivity against HIV-1 and HIV-2 in wild-type CEM/0 cell
Table 2 shows the isolated yields and diastereomeric pu- cultures at a concentration range that was often superior to
rities of phosphoramidate prodrugs 16j,k and 17b,d. The that of the parental d4T (Table 3).
(SP) configuration at the phosphorus atom is supported by
Moreover, it was interesting to observe that both dia-
comparison with the X-ray crystal structure of phos- stereomeric prodrugs of d4T kept full antiviral activity
phoramidate prodrug (SP)-PSI-7977.[8] Furthermore, this against HIV-2 in TK-deficient CEM/TK– cells. In general,
X-ray analysis supports our previously proposed reaction the 4-substituted (SP) diastereomers 16j,k, and 17d were
mechanism for this base-induced substitution as being an found to be more active than the (RP) diastereomers (5-fold
addition/elimination reaction occurring at the phosphorus in the case of 16j,k and 3-fold for 17d against HIV-2 in
atom and proceeding with inversion of configuration, for CEM/TK-deficient cells). However, in the case of 2-methyl-
example, (RP)-11 to (SP)-16 and (RP)-12 to (SP)-17.[12] The substituted phosphoramidate prodrugs 17b, the dia-
diastereomeric excess values were determined by 31P NMR stereomers showed almost identical antiviral values.
Table 3. Antiviral activity of phosphoramidates 16j, k and 17b, d.
EC50 [μm][a]
CC50 [μm][b]
CEM/0
CEM/0[c]
CEM/TK–[d]
HIV-2(ROD)
HIV-1(IIIB)
HIV-2(ROD)
(SP)-16j
(RP)-16j
(SP)-16k
(RP)-16k
(SP)-17b
(RP)-17b
(SP)-17d
(RP)-17d
d4T (15)
0.021Ϯ0.0085
0.13Ϯ0.071
0.042Ϯ0.030
0.14Ϯ0.078
0.45Ϯ0.12
0.19Ϯ0.035
0.029Ϯ0.024
0.11Ϯ0.035
0.51Ϯ0.31
0.030Ϯ0.014
0.18Ϯ0.028
0.074Ϯ0.0035
0.17Ϯ0.064
0.58Ϯ0.0071
0.40Ϯ0.0
0.073Ϯ0.0078
0.11Ϯ0.035
0.89Ϯ0.11
0.035Ϯ0.0078
0.18Ϯ0.099
0.031Ϯ0.013
0.14Ϯ0.085
0.45Ϯ0.0
54Ϯ2.8
190Ϯ18
60Ϯ4.2
144Ϯ2.1
101Ϯ8.5
98Ϯ11
71Ϯ4.9
115Ϯ9.2
Ͼ 250
0.27Ϯ0.0
0.047Ϯ0.028
0.13Ϯ0.071
140Ϯ16
[a] Antiviral activity in T-lymphocytes, 50% effective concentration. [b] Cytostatic activity, 50% cytostatic concentration. [c] Wild-type
CEM/0 cells. [d] Thymidine kinase deficient CEM TK– cells.
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C. Arbelo Román, P. Wasserthal, J. Balzarini, C. Meier
FULL PAPER
of 0.5 mL/min, and UV detection at 265 nm. The purity of phos-
phoramidate prodrugs 16 and 17 was checked by using HPLC, and
in all cases was Ն 95%.
Conclusions
The diastereospecific synthesis of phosphoramidate pro-
drugs 16j,k and 17b,d was achieved by starting from stereo-
chemically pure phosphorodiamidates 11 and 12. These key
compounds were synthesized diastereoselectively in three
steps by using the chiral auxiliary (S)-4-isopropylthiazolid-
ine-2-thione (2). The formation of this key compound was
studied by investigating its dependence on different phenol
derivatives 4a–m and the l-alanine methyl or benzyl ester
hydrochloride (9 and 10, respectively) attached to the phos-
phorodiamidate moiety. The variation of the phenolic resi-
dues led to the proposed transition state shown in Figure 1,
explaining the preferential formation of (SP)-configured
phosphorochloridate derivatives 5. In addition, it was ob-
served that 3- and 4-substituted phenol derivatives led to
significantly better diastereoselectivities compared to 2-sub-
stituted phenols, which gave mostly poor stereoselectivities.
The variation of the amino acid ester residues did not lead
to significant differences with regard to the diastereoselec-
tivity. Finally, eight new (SP)-arylphosphoramidates were
synthesized as diastereomerically pure compounds and
tested for their antiviral activity. Interestingly, the (SP)-4-
substituted phosphoramidates were found to be antivirally
markedly more active than their (RP) counterparts, inde-
pendent of the substituent, demonstrating again the impor-
tance of diastereoselective access to these compounds. In
contrast, the 2-methyl derivatives were equipotent for un-
known reasons. Work to study the properties of the individ-
ual diastereomers is currently ongoing in our laboratories.
Preparation of [(4S)-4-Isopropyl-2-thioxo-1,3-thiazolidin-3-yl]phos-
phonic Dichloride (3): A solution of (4S)-4-isopropyl-1,3-thiazolid-
ine-2-thione (2, 0.80 g, 4.96 mmol) and phosphoryl chloride
(1.39 mL, 14.8 mmol) in CH2Cl2 (12 mL) was cooled to 0 °C. NEt3
(0.76 mL, 5.45 mmol) in CH2Cl2 (12 mL) was added dropwise. Fol-
lowing the addition, the reaction mixture was warmed to room
temperature and stirred for 16 h. The solvent was removed under
reduced pressure by using a high-vacuum pump, and the residue
was suspended in CH2Cl2 (1 mL) and Et2O (15 mL). The precipi-
tated triethylammonium chloride was filtered under nitrogen and
washed with Et2O (5 mL). The solvent of the filtrate was removed
under reduced pressure by using a high-vacuum pump to give the
crude product 3 as an oil. Further purification was not possible
due to high reactivity, and the 31P NMR spectrum showed only
one signal at δ = 3.70 ppm.
General Procedure A. Preparation of Aryl [(4S)-4-Isopropyl-2-thi-
oxo-1,3-thiazolidin-3-yl]phosphonochloridates 5: A solution of 3
(1.0 equiv.) and the phenol or 1-naphthol derivative 4 (0.7 or
1.0 equiv.) in acetone was cooled to –91 °C. DBU (1.0 equiv.) was
added dropwise to the vigorously stirred solution. After 25–75 min
(dependent on 4) at –91 °C, the reaction was quenched – without
allowing it to warm to room temperature – with saturated ammo-
nium chloride solution (approximately 10 mL) and extracted with
CH2Cl2 (3ϫ). The combined organic layers were dried with magne-
sium sulfate and concentrated under reduced pressure by using a
high-vacuum pump. The resulting residue was purified immediately
by very quick column chromatography (1.5 cm diameter, 54.5 cm
length) on silica gel (approximately 23 g) using petroleum ether
(boiling range 50–70 °C)/EtOAc (2:1). The solvent was removed un-
der reduced pressure by using a high-vacuum pump. Further purifi-
cation of 5 was not possible due to the decomposition of the chiral
auxiliary 2.
Experimental Section
General: All experiments were conducted under scrupulously dry
conditions and under nitrogen. The solvents CH2Cl2, CH3CN, and
NEt3 were distilled from CaH2 and stored over molecular sieves.
Et2O and THF (tetrahydrofuran) were distilled from sodium or
potassium benzophenone and stored over molecular sieves. Ace-
tone was distilled from phosphorus pentoxide and stored over mo-
lecular sieves. DBU was distilled under nitrogen and stored over
molecular sieves. The petroleum ether (boiling range 50–70 °C),
EtOAc, CH2Cl2, and CH3OH employed in chromatography were
distilled before use. For column chromatography, silica gel 60 (230–
400 mesh) was used. Thin layer chromatography was performed on
precoated aluminium plates 60 F254 with a 0.2 mm layer of silica
gel containing a fluorescence indicator. The NMR spectroscopic
data were recorded with 400 or 500 MHz spectrometers (AMX 400
General Procedure B. Preparation of Alanine Derivatives 11 and 12:
A suspension of 5 (1.0 equiv.) and l-alanine methyl ester hydro-
chloride (9, 1.0 equiv.) or l-alanine benzyl ester hydrochloride (10,
1.0 equiv.) in CH2Cl2 was cooled to 0 °C. NEt3 (3.0 equiv.) was
added dropwise. Following the addition, the reaction mixture was
warmed to room temperature and stirred for 16 h. The reaction
was quenched with a saturated ammonium chloride solution and
the mixture extracted with CH2Cl2 (3ϫ). The combined organic
layers were dried with magnesium sulfate and concentrated under
reduced pressure by using a rotary evaporator. The resulting resi-
due was purified by column chromatography on silica gel [petro-
leum ether (boiling range 50–70 °C)/EtOAc, 2:1].
General Procedure C. Preparation of Thymidine Derivatives 16 and
17: A solution of d4T (15, 1.5 equiv.) in THF/CH3CN (1:1) was
cooled to 0 °C. tert-Butylmagnesium chloride (1.7 m solution in
THF, 3.0 equiv.) was added dropwise. Following the addition, the
reaction mixture was warmed to room temperature and stirred for
30 min. A solution of 11 or 12 (1 equiv.) in THF/CH3CN (1:1) was
added to the nucleoside suspension at 0 °C. Following the addition,
the reaction mixture was warmed to room temperature and stirred
for 5 d. The reaction was quenched with saturated ammonium
chloride solution and the mixture extracted with CH2Cl2 (3ϫ). The
combined organic layers were dried with magnesium sulfate and
concentrated under reduced pressure by using a rotary evaporator.
The resulting residue was purified by column chromatography on
silica gel (CH2Cl2/CH3OH, 39:1). The product was freeze-dried.
1
or DRX 500). All H and 13C NMR chemical shifts are quoted in
ppm and were calibrated by solvent signals. 31P NMR chemical
shifts are quoted in ppm by using H3PO4 as an external reference.
High-resolution mass spectra were obtained with a VG Analytical
VG/70-250F spectrometer (FAB, m-nitrobenzyl alcohol matrix).
HR-ESI spectra were obtained with an Agilent Technologies ESI-
TOF 6224 spectrometer. Analytical HPLC was carried out with a
VWR-Hitachi LaChromElite HPLC system consisting of a VWR-
Hitachi 2130 Pump, autosampler, and VWR-Hitachi UV detector
2455. The column used was a Nucleodur C18 Isis, 5 μm (Mach-
erey–Nagel). Elution was performed by using a water/acetonitrile
(Sigma–Aldrich, HPLC grade) eluent: 0–80% CH3CN (0–60 min),
80–0% CH3CN (60–65 min), 0% CH3CN (65–70 min), a flow rate
4904
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 4899–4909

Diastereoselective Synthesis of (Aryloxy)phosphoramidate Prodrugs
5a: According to General Procedure A, compound 3 (1.38 g,
4.96 mmol) and phenol (4a, 0.47 g, 4.96 mmol) were dissolved in
NMR (400 MHz, CDCl3): δ = 7.34–7.19 (m, 4 H, Ar), 5.01–4.94
(m, 1 H, 4-H), 3.67 (dd, JH,H = 11.6 Hz, JH,H = 8.5 Hz, 1 H, 5-
2
3
acetone (9.2 mL). After the addition of DBU (0.75 mL, H), 3.21–3.14 (m, 1 H, 5Ј-H), 2.53–2.45 (m, 1 H, 6-H), 1.10 (d,
3
4.96 mmol), the reaction mixture was stirred at –91 °C for 40 min. 3JH,H = 6.9 Hz, 3 H, 7-H or 8-H), 1.07 (d, JH,H = 6.9 Hz, 3 H, 7-
1
Product 5a was obtained as a yellow oil (1.57 g, 94%). H NMR
(400 MHz, CDCl3): δ = 7.44–7.35 (m, 2 H, Ar), 7.34–7.27 (m, 3 H,
H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ = –1.85 ppm.
5j: According to General Procedure A, compound 3 (1.03 g,
3.72 mmol) and 4-chlorophenol (4j, 0.33 g, 2.60 mmol) were dis-
solved in acetone (6.9 mL). After the addition of DBU (0.39 mL,
2.60 mmol), the reaction mixture was stirred at –91 °C for 52 min.
Product 5j was obtained as a yellow oil (0.93 g, 65%). 1H NMR
(400 MHz, CDCl3): δ = 7.29–7.24 (m, 2 H, Ar), 7.21–7.16 (m, 2 H,
2
3
Ar), 5.03–4.93 (m, 1 H, 4-H), 3.66 (dd, JH,H = 11.6 Hz, JH,H
8.5 Hz, 1 H, 5-H), 3.18–3.11 (m, 1 H, 5Ј-H), 2.58–2.43 (m, 1 H, 6-
=
3
3
H), 1.13 (d, JH,H = 7.0 Hz, 3 H, 7-H or 8-H), 1.09 (d, JH,H
=
7.0 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ =
–1.73, –1.61 (dr = 1:9.6; 81% de) ppm.
2
3
5c: According to General Procedure A, compound 3 (1.03 g,
3.72 mmol) and 3-methylphenol (4c, 0.27 mL, 2.60 mmol) were dis-
solved in acetone (6.9 mL). After the addition of DBU (0.39 mL,
Ar), 4.93–4.85 (m, 1 H, 4-H), 3.57 (dd, JH,H = 11.5 Hz, JH,H
=
4.2 Hz, 1 H, 5-H), 3.14–3.04 (m, 1 H, 5Ј-H), 2.49–2.34 (m, 1 H, 6-
3
3
H), 1.04 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H), 1.00 (d, JH,H
=
2.60 mmol), the reaction mixture was stirred at –91 °C for 75 min. 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ =
1
Product 5c was obtained as a yellow oil (1.08 g, 83%). H NMR
(400 MHz, CDCl3): δ = 7.25–7.20 (m, 2 H, Ar), 7.11–7.02 (m, 2 H,
–1.53, –1.58 (dr = 5.9:1; 70% de) ppm.
5k: According to General Procedure A, compound 3 (1.73 g,
6.20 mmol) and 4-bromophenol (4k, 0.75 g, 4.34 mmol) were dis-
solved in acetone (11.5 mL). After the addition of DBU (0.65 mL,
4.34 mmol), the reaction mixture was stirred at –91 °C for 50 min.
2
3
Ar), 4.99–4.93 (m, 1 H, 4-H), 3.62 (dd, JH,H = 11.5 Hz, JH,H
8.5 Hz, 1 H, 5-H), 3.15–3.10 (m, 1 H, 5Ј-H), 2.54–2.43 (m, 1 H, 6-
=
3
H), 2.33 (s, 3 H, Ph-Me), 1.09 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-
H), 1.06 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
3
1
Product 5k was obtained as a yellow oil (0.93 g, 65%). H NMR
(162 MHz, CDCl3): δ = –1.71, –1.84 (dr = 12:1; 85% de) ppm.
(400 MHz, CDCl3): δ = 7.55–7.42 (m, 2 H, Ar), 7.23–7.13 (m, 2 H,
5e: According to General Procedure A, compound 3 (1.03 g,
3.72 mmol) and 2-methoxyphenol (4e, 0.41 mL, 3.72 mmol) were (m, 1 H, 5Ј-H), 2.53–2.39 (m, 1 H, 6-H), 0.99 (d, JH,H = 6.8 Hz,
Ar), 5.00–4.92 (m, 1 H, 4-H), 3.70–3.61 (m, 1 H, 5-H), 3.33–3.23
3
3
dissolved in acetone (6.9 mL). After the addition of DBU (0.56 mL,
3 H, 7-H or 8-H), 0.96 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H) ppm.
3.72 mmol), the reaction mixture was stirred at –91 °C for 45 min. 31P NMR (162 MHz, CDCl3): δ = –1.75, –1.81 (dr = 4.5:1; 64%
Product 5e was obtained as a yellow oil (1.21 g, 89%). 1H NMR de) ppm.
(400 MHz, CDCl3): δ = 7.36–7.30 (m, 1 H, Ar), 7.24–7.17 (m, 1 H,
5m: According to General Procedure A, compound 3 (1.03 g,
Ar), 7.02–6.90 (m, 2 H, Ar), 5.07–5.01 (m, 1 H, 4-H), 3.89 (s, 3 H,
3.72 mmol) and 2-naphthol (4m, 0.54 g, 3.72 mmol) were dissolved
2
3
Ph-OMe), 3.72 (dd, JH,H = 11.6 Hz, JH,H = 8.6 Hz, 1 H, 5-H),
in acetone (6.9 mL). After the addition of DBU (0.56 mL,
3.72 mmol), the reaction mixture was stirred at –91 °C for 45 min.
Product 5m was obtained as a colorless solid (0.93 g, 65%). 1H
NMR (400 MHz, CDCl3): δ = 7.90–7.77 (m, 4 H, Ar), 7.56–7.44
3
3.21–3.14 (m, 1 H, 5Ј-H), 2.60–2.47 (m, 1 H, 6-H), 1.13 (d, JH,H
3
= 6.9 Hz, 3 H, 7-H or 8-H), 1.08 (d, JH,H = 6.9 Hz, 3 H, 7-H or
8-H) ppm. 31P NMR (162 MHz, CDCl3): δ = –2.02, –2.53 (dr =
19.8:1; 90% de) ppm.
2
(m, 3 H, Ar), 5.05–5.00 (m, 1 H, 4-H), 3.65 (dd, JH,H = 11.6 Hz,
2
4
5f: According to General Procedure A, compound 3 (1.03 g,
3.72 mmol) and 3-methoxyphenol (4f, 0.29 mL, 2.60 mmol) were
dissolved in acetone (6.9 mL). After the addition of DBU (0.39 mL,
3JH,H = 8.4 Hz, 1 H, 5-H), 3.15 (dd, JH,H = 11.5 Hz, JH,H
=
=
3
2.5 Hz, 1 H, 5Ј-H), 2.60–2.50 (m, 1 H, 6-H), 1.14 (d, JH,H
6.8 Hz, 3 H, 7-H or 8-H), 1.11 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-
3
2.60 mmol), the reaction mixture was stirred at –91 °C for 75 min. H) ppm. 31P NMR (162 MHz, CDCl3): δ = –1.46, –1.65 (dr =
1
Product 5f was obtained as a yellow oil (0.96 g, quantitative). H
NMR (400 MHz, CDCl3): δ = 7.30–7.23 (m, 1 H, Ar), 6.94-6.80
(m, 3 H, Ar), 5.01–4.95 (m, 1 H, 4-H), 3.80 (s, 3 H, Ph-OMe), 3.66
26.8:1; 93% de) ppm.
(RP)-11a and (SP)-11a: General Procedure B was applied by using
compound 5a (0.55 g, 1.65 mmol), l-alanine methyl ester hydro-
chloride (9, 0.23 g, 1.65 mmol), and NEt3 (0.69 mL, 4.95 mmol) in
CH2Cl2 (2.4 mL). (RP)-11a: Product (RP)-11a was obtained as a
colorless oil (0.17 g, 25%). 1H NMR (400 MHz, CDCl3): δ = 7.37–
7.28 (m, 4 H, Ar), 7.22–7.16 (m, 1 H, Ar), 5.10 (dd, 2JH,P = 8.9 Hz,
3JH,H = 8.9 Hz, 1 H, NH-Ala), 4.99–4.92 (m, 1 H, 4-H), 4.26–4.13
(m, 1 H, CH-Ala), 3.69–3.62 (m, 1 H, 5-H), 3.65 (s, 3 H, MeO-
Ala), 3.17–3.09 (m, 1 H, 5Ј-H), 2.39–2.27 (m, 1 H, 6-H), 1.43 (d,
2
3
(dd, JH,H = 11.6 Hz, JH,H = 8.5 Hz, 1 H, 5-H), 3.19–3.11 (m, 1
3
H, 5Ј-H), 2.56–2.46 (m, 1 H, 6-H), 1.12 (d, JH,H = 6.8 Hz, 3 H, 7-
H or 8-H), 1.09 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P
3
NMR (162 MHz, CDCl3): δ = –1.66, –1.92 (dr = 14.1:1; 87% de)
ppm.
5h: According to General Procedure A, compound 3 (1.03 g,
3.72 mmol) and 2-chlorophenol (4h, 0.33 g, 2.60 mmol) were dis-
solved in acetone (6.9 mL). After the addition of DBU (0.39 mL,
3
3JH,H = 7.0 Hz, 3 H, Me-Ala), 0.98 (d, JH,H = 7.1 Hz, 3 H, 7-H
2.60 mmol), the reaction mixture was stirred at –91 °C for 52 min. or 8-H), 0.88 (d, 3JH,H = 7.1 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
1
Product 5h was obtained as a yellow oil (1.11 g, quantitative). H
NMR (400 MHz, CDCl3): δ = 7.51–7.44 (m, 2 H, Ar), 7.33–7.26
(m, 1 H, Ar), 7.24–7.18 (m, 1 H, Ar), 5.11–5.02 (m, 1 H, 4-H),
3.83–3.69 (m, 1 H, 5-H), 3.27–3.17 (m, 1 H, 5Ј-H), 2.59–2.43 (m,
(162 MHz, CDCl3): δ = –0.91 ppm. (SP)-11a: Product (SP)-11a was
obtained as a colorless oil (0.03 g, 5%). 1H NMR (400 MHz,
CDCl3): δ = 7.38–7.28 (m, 4 H, Ar), 7.24–7.17 (m, 1 H, Ar), 5.39
2
3
(dd, JH,P = 8.3 Hz, JH,H = 8.3 Hz, 1 H, NH-Ala), 4.64–4.56 (m,
1 H, 6-H), 1.14 (d, 3JH,H = 6.6 Hz, 3 H, 7-H or 8-H), 1.09 (d, 3JH,H 1 H, 4-H), 4.34–4.21 (m, 1 H, CH-Ala), 3.73 (s, 3 H, MeO-Ala),
= 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ 3.16 (dd, JH,H = 11.5 Hz, JH,H = 8.5 Hz, 1 H, 5-H), 2.98–2.92
2
3
3
= –1.94, –2.83 (dr = 2:1; 34% de) ppm.
(m, 1 H, 5Ј-H), 2.40–2.27 (m, 1 H, 6-H), 1.38 (d, JH,H = 7.0 Hz,
3
3 H, Me-Ala), 1.00 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H), 0.97 (d,
5i: According to General Procedure A, compound 3 (1.03 g,
3.72 mmol) and 3-chlorophenol (4i, 0.33 g, 2.60 mmol) were dis-
solved in acetone (6.9 mL). After the addition of DBU (0.39 mL,
3JH,H = 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz,
CDCl3): δ = 1.36 ppm.
2.60 mmol), the reaction mixture was stirred at –91 °C for 60 min. (RP)-11c and (SP)-11c: General Procedure B was applied by using
Product 5i was obtained as a yellow oil (0.80 g, quantitative). 1H
compound 5c (0.98 g, 2.80 mmol), l-alanine methyl ester hydro-
Eur. J. Org. Chem. 2011, 4899–4909
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4905

C. Arbelo Román, P. Wasserthal, J. Balzarini, C. Meier
FULL PAPER
chloride (9, 0.39 g, 2.80 mmol), and NEt3 (1.17 mL, 8.40 mmol) in
CH2Cl2 (4.0 mL). (RP)-11c: Product (RP)-11c was obtained as a
colorless oil (0.45 g, 38%). 1H NMR (400 MHz, CDCl3): δ = 7.23–
7.17 (m, 1 H, Ar), 7.13–7.08 (m, 2 H, Ar), 7.01–6.97 (m, 1 H, Ar),
or 8-H), 0.96 (d, 3JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
(162 MHz, CDCl3): δ = 1.31 ppm.
(RP)-11h and (SP)-11h: General Procedure B was applied by using
compound 5h (1.04 g, 2.80 mmol), l-alanine methyl ester hydro-
chloride (9, 0.39 g, 2.80 mmol), and NEt3 (1.17 mL, 8.40 mmol) in
CH2Cl2 (4.0 mL). (RP)-11h: Product (RP)-11h was obtained as a
colorless oil (0.16 g, 13%). 1H NMR (400 MHz, CDCl3): δ = 7.57–
7.53 (m, 1 H, Ar), 7.43–7.39 (m, 1 H, Ar), 7.26–7.21 (m, 1 H, Ar),
2
3
5.10 (dd, JH,P = 8.6 Hz, JH,H = 8.6 Hz, 1 H, NH-Ala), 4.98–4.92
(m, 1 H, 4-H), 4.24–4.14 (m, 1 H, CH-Ala), 3.68–3.61 (m, 1 H, 5-
H), 3.65 (s, 3 H, MeO-Ala), 3.16–3.10 (m, 1 H, 5Ј-H), 2.39–2.29
3
(m, 1 H, 6-H), 2.34 (s, 3 H, Ph-Me), 1.42 (d, JH,H = 7.1 Hz, 3 H,
3
3
Me-Ala), 0.98 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H), 0.90 (d, JH,H
= 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ
= –1.00 ppm. (SP)-11c: Product (SP)-11c was obtained as a color-
2
3
7.14–7.09 (m, 1 H, Ar), 5.36 (dd, JH,P = 8.3 Hz, JH,H = 8.3 Hz,
1 H, NH-Ala), 5.07–5.01 (m, 1 H, 4-H), 4.26–4.18 (m, 1 H, CH-
Ala), 3.68 (dd, 2JH,H = 11.6 Hz, 3JH,H = 9.3 Hz, 1 H, 5-H), 3.66 (s,
3 H, MeO-Ala), 3.23–3.17 (m, 1 H, 5Ј-H), 2.64–2.54 (m, 1 H, 6-
H), 1.44 (d, 3JH,H = 7.2 Hz, 3 H, Me-Ala), 1.12 (d, 3JH,H = 6.9 Hz,
1
less oil (0.05 g, 5%). H NMR (400 MHz, CDCl3): δ = 7.24–7.18
(m, 1 H, Ar), 7.13–7.07 (m, 2 H, Ar), 7.02–6.99 (m, 1 H, Ar), 5.37
2
3
(dd, JH,P = 8.8 Hz, JH,H = 8.8 Hz, 1 H, NH-Ala), 4.65–4.56 (m,
3
3 H, 7-H or 8-H), 1.05 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm.
1 H, 4-H), 4.33–4.21 (m, 1 H, CH-Ala), 3.72 (s, 3 H, MeO-Ala),
31P NMR (162 MHz, CDCl3): δ = –0.38 ppm. (SP)-11h: Product
(SP)-11h was obtained as a colorless oil (0.10 g, 8%). 1H NMR
(400 MHz, CDCl3): δ = 7.45–7.41 (m, 2 H, Ar), 7.25–7.21 (m, 1 H,
2
3
3.18 (dd, JH,H = 11.3 Hz, JH,H = 8.3 Hz, 1 H, 5-H), 3.01–2.92
(m, 1 H, 5Ј-H), 2.39–2.28 (m, 1 H, 6-H), 2.34 (s, 3 H, Ph-Me), 1.38
3
3
(d, JH,H = 7.0 Hz, 3 H, Me-Ala), 1.00 (d, JH,H = 6.8 Hz, 3 H, 7-
2
3
Ar), 7.16–7.10 (m, 1 H, Ar), 5.37 (dd, JH,P = 8.3 Hz, JH,H
=
H or 8-H), 0.97 (d, JH,H = 7.0 Hz, 3 H, 7-H or 8-H) ppm. 31P
3
8.3 Hz, 1 H, NH-Ala), 4.86–4.80 (m, 1 H, 4-H), 4.32–4.23 (m, 1
NMR (162 MHz, CDCl3): δ = 1.26 ppm.
2
H, CH-Ala), 3.72 (s, 3 H, MeO-Ala), 3.59 (dd, JH,H = 11.6 Hz,
3JH,H = 8.6 Hz, 1 H, 5-H), 3.13–3.08 (m, 1 H, 5Ј-H), 2.46–2.36 (m,
(RP)-11e and (SP)-11e: General Procedure B was applied by using
compound 5e (0.85 g, 2.31 mmol), l-alanine methyl ester hydro-
chloride (9, 0.32 g, 2.31 mmol), and NEt3 (0.96 mL, 6.95 mmol) in
CH2Cl2 (3.3 mL). (RP)-11e: Product (RP)-11e was obtained as a
colorless oil (0.28 g, 28%). 1H NMR (400 MHz, CDCl3): δ = 7.34–
7.30 (m, 1 H, Ar), 7.17–7.11 (m, 1 H, Ar), 6.96–6.86 (m, 2 H, Ar),
3
3
1 H, 6-H), 1.39 (d, JH,H = 7.0 Hz, 3 H, Me-Ala), 1.05 (d, JH,H
=
3
6.9 Hz, 3 H, 7-H or 8-H), 1.01 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-
H) ppm. 31P NMR (162 MHz, CDCl3): δ = 0.77 ppm.
(RP)-11i and (SP)-11i: General Procedure B was applied by using
compound 5i (0.61 g, 1.65 mmol), l-alanine methyl ester hydro-
chloride (9, 0.23 g, 1.65 mmol), and NEt3 (0.68 mL, 4.94 mmol)
in CH2Cl2 (2.3 mL). (RP)-11i: Product (RP)-11i was obtained as a
colorless oil (0.13 g, 18%). 1H NMR (400 MHz, CDCl3): δ = 7.36–
7.31 (m, 1 H, Ar), 7.29–7.15 (m, 3 H, Ar), 5.12 (dd, 2JH,P = 8.6 Hz,
3JH,H = 8.6 Hz, 1 H, NH-Ala), 4.98–4.91 (m, 1 H, 4-H), 4.24–4.11
(m, 1 H, CH-Ala), 3.70–3.62 (m, 1 H, 5-H), 3.66 (s, 3 H, MeO-
Ala), 3.17–3.11 (m, 1 H, 5Ј-H), 2.40–2.28 (m, 1 H, 6-H), 1.42 (d,
2
3
5.33 (dd, JH,P = 8.8 Hz, JH,H = 8.8 Hz, 1 H, NH-Ala), 5.06–4.99
(m, 1 H, 4-H), 4.22–4.08 (m, 1 H, CH-Ala), 3.87 (s, 3 H, Ph-OMe),
3.69–3.61 (m, 1 H, 5-H), 3.63 (s, 3 H, MeO-Ala), 3.20–3.14 (m, 1
3
H, 5Ј-H), 2.64–2.53 (m, 1 H, 6-H), 1.41 (d, JH,H = 7.1 Hz, 3 H,
3
3
Me-Ala), 1.09 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H), 1.06 (d, JH,H
= 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ
= 0.11 ppm. (SP)-11e: Product (SP)-11e was obtained as a colorless
1
oil (0.015 g, 2%). H NMR (400 MHz, CDCl3): δ = 7.35–7.31 (m,
3
3JH,H = 7.3 Hz, 3 H, Me-Ala), 0.99 (d, JH,H = 6.8 Hz, 3 H, 7-H
1 H, Ar), 7.18–7.09 (m, 1 H, Ar), 6.98–6.84 (m, 2 H, Ar), 5.32 (dd,
or 8-H), 0.91 (d, 3JH,H = 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
(162 MHz, CDCl3): δ = –0.64 ppm. (SP)-11i: Product (SP)-11i was
obtained as a colorless oil (0.05 g, 7%). 1H NMR (400 MHz,
CDCl3): δ = 7.35–7.31 (m, 1 H, Ar), 7.31–7.27 (m, 1 H, Ar), 7.22–
3
2JH,P = 8.8 Hz, JH,H = 8.8 Hz, 1 H, NH-Ala), 4.79–4.73 (m, 1 H,
4-H), 4.33–4.20 (m, 1 H, CH-Ala), 3.87 (s, 3 H, MeO-Ala), 3.72 (s,
2
3
3 H, Ph-OMe), 3.45 (dd, JH,H = 11.5 Hz, JH,H = 8.5 Hz, 1 H, 5-
H), 3.06–3.03 (m, 1 H, 5Ј-H), 2.46–2.36 (m, 1 H, 6-H), 1.34 (d,
2
3
7.17 (m, 2 H, Ar), 5.38 (dd, JH,P = 8.6 Hz, JH,H = 8.6 Hz, 1 H,
3
3JH,H = 7.1 Hz, 3 H, Me-Ala), 1.03 (d, JH,H = 6.9 Hz, 3 H, 7-H
NH-Ala), 4.69–4.61 (m, 1 H, 4-H), 4.33–4.19 (m, 1 H, CH-Ala),
or 8-H), 0.99 (d, 3JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
(162 MHz, CDCl3): δ = 1.01 ppm.
3
3.73 (s, 3 H, MeO-Ala), 3.29 (dd, 2JH,H = 11.7 Hz, JH,H = 8.6 Hz,
1 H, 5-H), 3.05–2.98 (m, 1 H, 5Ј-H), 2.40–2.27 (m, 1 H, 6-H), 1.37
3
3
(d, JH,H = 7.0 Hz, 3 H, Me-Ala), 1.01 (d, JH,H = 7.1 Hz, 3 H, 7-
(RP)-11f and (SP)-11f: General Procedure B was applied by using
compound 5f (0.80 g, 2.20 mmol), l-alanine methyl ester hydro-
chloride (9, 0.31 g, 2.20 mmol), and NEt3 (0.92 mL, 6.60 mmol)
in CH2Cl2 (3.1 mL). (RP)-11f: Product (RP)-11f was obtained as a
colorless oil (0.36 g, 38%). 1H NMR (400 MHz, CDCl3): δ = 7.23–
7.14 (m, 1 H, Ar), 6.91–6.83 (m, 2 H, Ar), 6.75–6.67 (m, 1 H, Ar),
H or 8-H), 0.98 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P
3
NMR (162 MHz, CDCl3): δ = 1.34 ppm.
(RP)-11j and (SP)-11j: General Procedure B was applied by using
compound 5j (0.78 g, 2.12 mmol), l-alanine methyl ester hydro-
chloride (9, 0.30 g, 2.12 mmol), and NEt3 (0.89 mL, 6.36 mmol)
in CH2Cl2 (3.0 mL). (RP)-11j: Product (RP)-11j was obtained as a
colorless oil (0.21 g, 23%). 1H NMR (400 MHz, CDCl3): δ = 7.30–
2
3
5.09 (dd, JH,P = 7.5 Hz, JH,H = 7.5 Hz, 1 H, NH-Ala), 4.97–4.89
(m, 1 H, 4-H), 4.24–4.12 (m, 1 H, CH-Ala), 3.76 (s, 3 H, Ph-OMe),
3.67–3.59 (m, 1 H, 5-H), 3.63 (s, 3 H, MeO-Ala), 3.15–3.07 (m, 1
2
3
7.16 (m, 4 H, Ar), 5.12 (dd, JH,P = 8.4 Hz, JH,H = 8.4 Hz, 1 H,
3
H, 5Ј-H), 2.39–2.27 (m, 1 H, 6-H), 1.39 (d, JH,H = 7.0 Hz, 3 H,
NH-Ala), 4.92–4.85 (m, 1 H, 4-H), 4.16–4.07 (m, 1 H, CH-Ala),
3
3
Me-Ala), 0.96 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H), 0.87 (d, JH,H 3.63–3.57 (m, 1 H, 5-H), 3.60 (s, 3 H, MeO-Ala), 3.17–3.09 (m, 1
= 6.7 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ H, 5Ј-H), 2.33–2.20 (m, 1 H, 6-H), 1.42 (d, JH,H = 7.3 Hz, 3 H,
3
3
3
= –0.99 ppm. (SP)-11f: Product (SP)-11f was obtained as a colorless
Me-Ala), 0.99 (d, JH,H = 7.1 Hz, 3 H, 7-H or 8-H), 0.89 (d, JH,H
oil (0.05 g, 5%). 1H NMR (400 MHz, CDCl3): δ = 7.25–7.20 (m, 1 = 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ
H, Ar), 6.93–6.85 (m, 2 H, Ar), 6.79–6.74 (m, 1 H, Ar), 5.40 (dd, = –0.58 ppm. (SP)-11j: Product (SP)-11j was obtained as a colorless
3
2JH,P = 8.8 Hz, JH,H = 8.8 Hz, 1 H, NH-Ala), 4.63–4.57 (m, 1 H,
4-H), 4.33–4.22 (m, 1 H, CH-Ala), 3.79 (s, 3 H, Ph-OMe), 3.72 (s,
3 H, MeO-Ala), 3.18 (dd, 2JH,H = 11.5 Hz, 3JH,H = 8.5 Hz, 1 H, 5-
oil (0.11 g, 6%). 1H NMR (400 MHz, CDCl3): δ = 7.35–7.20 (m, 4
H, Ar), 5.39 (dd, JH,P = 8.6 Hz, JH,H = 8.6 Hz, 1 H, NH-Ala),
2
3
4.67–4.56 (m, 1 H, 4-H), 4.32–4.18 (m, 1 H, CH-Ala), 3.73 (s, 3 H,
2
3
H), 2.99–2.93 (m, 1 H, 5Ј-H), 2.39–2.27 (m, 1 H, 6-H), 1.39 (d, MeO-Ala), 3.25 (dd, JH,H = 11.4 Hz, JH,H = 8.3 Hz, 1 H, 5-H),
3JH,H = 7.1 Hz, 3 H, Me-Ala), 0.99 (d, JH,H = 6.9 Hz, 3 H, 7-H
3.04–2.94 (m, 1 H, 5Ј-H), 2.39–2.26 (m, 1 H, 6-H), 1.38 (d, JH,H
3
3
4906
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 4899–4909

Diastereoselective Synthesis of (Aryloxy)phosphoramidate Prodrugs
3
= 7.3 Hz, 3 H, Me-Ala), 0.99 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-
3JH,H = 8.4 Hz, 1 H, 5-H), 3.06–3.00 (m, 1 H, 5Ј-H), 2.37–2.33 (m,
H), 0.97 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR 1 H, 6-H), 2.35 (s, 3 H, Ph-Me), 1.40 (d, 3JH,H = 7.3 Hz, 3 H, Me-
3
3
3
(162 MHz, CDCl3): δ = 1.43 ppm.
Ala), 0.96 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H), 0.95 (d, JH,H =
6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ =
(RP)-11k and (SP)-11k: General Procedure B was applied by using
compound 5k (1.47 g, 3.56 mmol), l-alanine methyl ester hydro-
chloride (9, 0.50 g, 3.56 mmol), and NEt3 (1.50 mL, 10.68 mmol)
in CH2Cl2 (5.1 mL). (RP)-11k: Product (RP)-11k was obtained as a
colorless oil (0.29 g, 17%). 1H NMR (400 MHz, CDCl3): δ = 7.46–
7.41 (m, 2 H, Ar), 7.21–7.17 (m, 2 H, Ar), 5.11 (dd, 2JH,P = 8.5 Hz,
3JH,H = 8.5 Hz, 1 H, NH-Ala), 4.96–4.91 (m, 1 H, 4-H), 4.22–4.12
(m, 1 H, CH-Ala), 3.68–3.63 (m, 1 H, 5-H), 3.66 (s, 3 H, MeO-
Ala), 3.15–3.12 (m, 1 H, 5Ј-H), 2.36–2.27 (m, 1 H, 6-H), 1.41 (d,
0.65 ppm.
(RP)-12d and (SP)-12d: General Procedure B was applied by using
compound 5d (0.72 g, 2.0 mmol), l-alanine benzyl ester hydrochlo-
ride (10, 0.44 g, 2.0 mmol), and NEt3 (0.85 mL, 6.1 mmol) in
CH2Cl2 (2.9 mL). (RP)-12d: Product (RP)-12d was obtained as a
colorless oil (0.70 g, 70%). 1H NMR (400 MHz, CDCl3): δ = 7.38–
7.31 (m, 3 H, Ar), 7.31–7.27 (m, 2 H, Ar), 7.20–7.14 (m, 2 H, Ar),
7.11–7.04 (m, 2 H, Ar), 5.17–5.07 (m, 3 H, NH-Ala, CH2-Bn),
4.98–4.89 (m, 1 H, 4-H), 4.31–4.15 (m, 1 H, CH-Ala), 3.63 (dd,
3
3JH,H = 7.3 Hz, 3 H, Me-Ala), 0.98 (d, JH,H = 7.0 Hz, 3 H, 7-H
or 8-H), 0.89 (d, 3JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
(162 MHz, CDCl3): δ = –0.66 ppm. (SP)-11k: Product (SP)-11k was
obtained as a colorless oil (0.07 g, 4%). 1H NMR (400 MHz,
CDCl3): δ = 7.49–7.43 (m, 2 H, Ar), 7.22–7.17 (m, 2 H, Ar), 5.39
2JH,H = 11.6 Hz, JH,H = 9.6 Hz, 1 H, 5-H), 3.14–3.08 (m, 1 H, 5Ј-
H), 2.39–2.32 (m, 1 H, 6-H), 2.30 (s, 3 H, Ph-Me), 1.44 (d, JH,H
3
3
3
= 7.4 Hz, 3 H, Me-Ala), 0.98 (d, JH,H = 7.0 Hz, 3 H, 7-H or 8-
H), 0.88 (d, JH,H = 6.8 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR
3
2
3
(dd, JH,P = 8.6 Hz, JH,H = 8.6 Hz, 1 H, NH-Ala), 4.63–4.58 (m,
(162 MHz, CDCl3): δ = –0.84 ppm. (SP)-12d: Product (SP)-12d was
obtained as a colorless oil (0.055 g, 5%). 1H NMR (400 MHz,
CDCl3): δ = 7.32–7.24 (m, 5 H, Ar), 7.14–7.09 (m, 2 H, Ar), 7.08–
7.02 (m, 2 H, Ar), 5.34 (dd, JH,P = 8.3 Hz, JH,H = 8.3 Hz, 1 H,
NH-Ala), 5.09 (s, 2 H, CH2-Bn), 4.54–4.46 (m, 1 H, 4-H), 4.31–
1 H, 4-H), 4.32–4.20 (m, 1 H, CH-Ala), 3.73 (s, 3 H, MeO-Ala),
2
3
3.24 (dd, JH,H = 11.4 Hz, JH,H = 8.4 Hz, 1 H, 5-H), 3.01–2.98
3
2
3
(m, 1 H, 5Ј-H), 2.38–2.27 (m, 1 H, 6-H), 1.38 (d, JH,H = 6.8 Hz,
3
3 H, Me-Ala), 0.99 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H), 0.97 (d,
3JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz,
CDCl3): δ = 1.33 ppm.
2
3
4.19 (m, 1 H, CH-Ala), 3.08 (dd, JH,H = 11.4 Hz, JH,H = 8.3 Hz,
1 H, 5-H), 2.89–2.83 (m, 1 H, 5Ј-H), 2.25 (s, 3 H, Ph-Me), 2.24–
3
2.15 (m, 1 H, 6-H), 1.32 (d, JH,H = 7.1 Hz, 3 H, Me-Ala), 0.85 (d,
(RP)-11m and (SP)-11m: General Procedure B was applied by using
compound 5m (0.77 g, 1.99 mmol), l-alanine methyl ester hydro-
chloride (9, 0.28 g, 1.99 mmol), and NEt3 (0.83 mL, 5.97 mmol) in
CH2Cl2 (2.8 mL). (RP)-11m: Product (RP)-11m was obtained as a
colorless oil (0.28 g, 30%). 1H NMR (400 MHz, CDCl3): δ = 7.84–
7.75 (m, 4 H, Ar), 7.51–7.42 (m, 3 H, Ar), 5.17 (dd, 2JH,P = 8.5 Hz,
3JH,H = 8.5 Hz, 1 H, NH-Ala), 5.02–4.96 (m, 1 H, 4-H), 4.26–4.15
3JH,H = 6.8 Hz, 3 H, 7-H or 8-H), 0.83 (d, JH,H = 7.0 Hz, 3 H, 7-
3
H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ = 1.44 ppm.
(SP)-16j: General Procedure C was applied by using compound
(RP)-11j (0.21 g, 0.47 mmol), d4T (15, 0.16 g, 0.70 mmol), tert-but-
ylmagnesium chloride (0.83 mL, 1.41 mmol), and THF/CH3CN
(6.2 mL). Product (SP)-16j was obtained as a colorless foam
(0.047 g, 20%). H NMR (400 MHz, CDCl3): δ = 8.19 (br. s, 1 H,
NH), 7.32–7.27 (m, 3 H, Ar), 7.15–7.09 (m, 2 H, Ar, 6-H), 7.04–
3
(m, 1 H, CH-Ala), 3.67 (dd, 2JH,H = 11.3 Hz, JH,H = 9.3 Hz, 1 H,
1
5-H), 3.52 (s, 3 H, MeO-Ala), 3.16–3.13 (m, 1 H, 5Ј-H), 2.44–2.34
(m, 1 H, 6-H), 1.43 (d, 3JH,H = 7.0 Hz, 3 H, Me-Ala), 0.98 (d, 3JH,H
6.99 (m, 1 H, 1Ј-H), 6.38–6.32 (m, 1 H, 2Ј-H), 5.93–5.87 (m, 1 H,
3Ј-H), 5.08–5.00 (m, 1 H, 4Ј-H), 4.41–4.27 (m, 2 H, 5Ј-H), 4.01–
3
= 7.0 Hz, 3 H, 7-H or 8-H), 0.85 (d, JH,H = 6.8 Hz, 3 H, 7-H or
8-H) ppm. 31P NMR (162 MHz, CDCl3): δ = –0.60 ppm. (SP)-11m:
Product (SP)-11m was obtained as a colorless solid (0.05 g, 6%).
1H NMR (400 MHz, CDCl3): δ = 7.86–7.74 (m, 4 H, Ar), 7.53–
2
3.88 (m, 1 H, CH-Ala), 3.71 (s, 3 H, MeO-Ala), 3.59 (dd, JH,P
=
3
10.5 Hz, JH,H = 10.5 Hz, 1 H, NH-Ala), 1.82 (s, 3 H, Me-Th),
3
1.32 (d, JH,H = 7.0 Hz, 3 H, Me-Ala) ppm. 31P NMR (162 MHz,
2
3
7.44 (m, 3 H, Ar), 5.46 (dd, JH,P = 8.8 Hz, JH,H = 8.8 Hz, 1 H,
CDCl3): δ = 3.13, 2.59 (dr = 37:1; 95% de) ppm.
NH-Ala), 4.65–4.60 (m, 1 H, 4-H), 4.37–4.25 (m, 1 H, CH-Ala),
3
3.73 (s, 3 H, MeO-Ala), 3.07 (dd, 2JH,H = 11.3 Hz, JH,H = 8.3 Hz,
(RP)-16j: General Procedure C was applied by using compound
(SP)-11j (0.05 g, 0.10 mmol), d4T (15, 0.04 g, 0.16 mmol), tert-but-
ylmagnesium chloride (0.18 mL, 0.31 mmol), and THF/CH3CN
(1.4 mL). Product (RP)-16j was obtained as a colorless foam
1 H, 5-H), 2.93–2.90 (m, 1 H, 5Ј-H), 2.40–2.30 (m, 1 H, 6-H), 1.38
3
3
(d, JH,H = 7.0 Hz, 3 H, Me-Ala), 0.99 (d, JH,H = 6.9 Hz, 3 H, 7-
H or 8-H), 0.97 (d, JH,H = 6.9 Hz, 3 H, 7-H or 8-H) ppm. 31P
3
1
(0.014 g, 26%). H NMR (400 MHz, CDCl3): δ = 8.49 (br. s, 1 H,
NMR (162 MHz, CDCl3): δ = 1.52 ppm.
NH), 7.32–7.27 (m, 2 H, Ar), 7.23–7.19 (m, 1 H, 6-H), 7.18–7.12
(m, 2 H, Ar), 7.04–6.98 (m, 1 H, 1Ј-H), 6.32–6.26 (m, 1 H, 2Ј-H),
5.96–5.87 (m, 1 H, 3Ј-H), 5.06–4.95 (m, 1 H, 4Ј-H), 4.34–4.20 (m,
2 H, 5Ј-H), 4.03–3.91 (m, 1 H, CH-Ala), 3.75–3.67 (m, 1 H, NH-
(RP)-12b and (SP)-12b: General Procedure B was applied by using
compound 5b (0.52 g, 1.49 mmol), l-alanine benzyl ester hydro-
chloride (10, 0.32 g, 1.49 mmol), and NEt3 (0.62 mL, 4.5 mmol) in
CH2Cl2 (2.1 mL). (RP)-12b: Product (RP)-12b was obtained as a
colorless oil (0.40 g, 55%). 1H NMR (400 MHz, CDCl3): δ = 7.37–
7.27 (m, 6 H, Ar), 7.19–7.02 (m, 3 H, Ar), 5.27 (dd, 2JH,P = 8.5 Hz,
3JH,H = 8.5 Hz, 1 H, NH-Ala), 5.14–4.99 (m, 3 H, 4-H, CH2-Bn),
4
Ala), 3.71 (s, 3 H, MeO-Ala), 1.87 (d, JH,H = 1.4 Hz, 3 H, Me-
3
Th), 1.36 (d, JH,H = 7.0 Hz, 3 H, Me-Ala) ppm. 31P NMR
(162 MHz, CDCl3): δ = 2.62 ppm.
2
3
4.31–4.16 (m, 1 H, CH-Ala), 3.66 (dd, JH,H = 11.3 Hz, JH,H
=
(SP)-16k: General Procedure C was applied by using compound
9.5 Hz, 1 H, 5-H), 3.21–3.14 (m, 1 H, 5Ј-H), 2.57–2.46 (m, 1 H, 6- (RP)-11k (0.15 g, 0.32 mmol), d4T (15, 0.11 g, 0.48 mmol), tert-but-
3
H), 2.34 (s, 3 H, Ph-Me), 1.44 (d, JH,H = 7.3 Hz, 3 H, Me-Ala),
ylmagnesium chloride (0.56 mL, 0.96 mmol), and THF/CH3CN
1.08 (d, 3JH,H = 7.0 Hz, 3 H, 7-H or 8-H), 1.04 (d, JH,H = 7.0 Hz,
(4.3 mL). Product (SP)-16k was obtained as a colorless foam
3
3 H, 7-H or 8-H) ppm. 31P NMR (162 MHz, CDCl3): δ =
(0.026 g, 15%). H NMR (400 MHz, CDCl3): δ = 8.52 (br. s, 1 H,
1
3
–0.95 ppm. (SP)-12b: Product (SP)-12b was obtained as a colorless
oil (0.12 g, 16%). H NMR (400 MHz, CDCl3): δ = 7.38–7.31 (m, 7.07 (d, JH,H = 8.5 Hz, 2 H, Ar), 6.37–6.32 (m, 1 H, 2Ј-H), 5.92–
5 H, Ar), 7.22–7.03 (m, 4 H, Ar), 5.45 (dd, JH,P = 8.6 Hz, JH,H 5.86 (m, 1 H, 3Ј-H), 5.07–5.00 (m, 1 H, 4Ј-H), 4.40–4.27 (m, 2 H,
= 8.6 Hz, 1 H, NH-Ala), 5.16 (s, 2 H, CH2-Bn), 4.79–4.72 (m, 1 5Ј-H), 4.03–3.90 (m, 1 H, CH-Ala), 3.77–3.64 (m, 1 H, NH-Ala),
H, 4-H), 4.39–4.28 (m, 1 H, CH-Ala), 3.46 (dd, JH,H = 11.6 Hz, 3.71 (s, 3 H, MeO-Ala), 1.82 (s, 3 H, Me-Th), 1.32 (d, JH,H
NH), 7.43 (d, JH,H = 8.8 Hz, 2 H, Ar), 7.29–7-27 (m, 1 H, 6-H),
1
3
2
3
2
3
=
Eur. J. Org. Chem. 2011, 4899–4909
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4907

C. Arbelo Román, P. Wasserthal, J. Balzarini, C. Meier
FULL PAPER
7.1 Hz, 3 H, Me-Ala) ppm. 31P NMR (162 MHz, CDCl3): δ = 3.13,
2.54 (dr = 27:1; 93% de) ppm.
4.29–4.15 (m, 2 H, 5Ј-H), 4.07–3.95 (m, 1 H, CH-Ala), 3.56 (dd,
3
2JH,P = 11.1 Hz, JH,H = 9.7 Hz, 1 H, NH-Ala), 2.30 (s, 3 H, Me-
Ph), 1.84 (s, 4JH,H = 1.0 Hz, 3 H, Me-Th), 1.36 (d, 3JH,H = 7.1 Hz,
3 H, Me-Ala) ppm. 31P NMR (162 MHz, CDCl3): δ = 2.62 ppm.
(RP)-16k: General Procedure C was applied by using compound
(SP)-11k (0.13 g, 0.26 mmol), d4T (15, 0.09 g, 0.39 mmol), tert-but-
ylmagnesium chloride (0.46 mL, 0.79 mmol), and THF/CH3CN
(3.5 mL). Product (RP)-16k was obtained as a colorless foam
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, Be-
thesda, MD). Virus stocks were prepared from the supernatants of
HIV-1-infected MT-4 cells. HIV-2 (strain ROD) was kindly pro-
vided 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 described previously.[18] Briefly,
4ϫ105 CEM cells/mL were infected with HIV-1(IIIB) or HIV-
2(ROD) at approximately 100 CCID50 (50% cell culture infective
dose) per mL of cell suspension. The thymidine kinase deficient
CEM cell cultures were also infected with HIV-2(ROD). Then, the
infected cell suspensions (100 μL) were transferred into 96-well
microtiter plate wells and mixed with the appropriate dilutions of
the test compounds (100 μL). After 4–5 d, giant cell formation was
recorded microscopically in the HIV-infected cell cultures. The 50%
effective concentration was defined as the compound concentration
required to inhibit virus-induced cytopathicity by 50%. The 50%
cytostatic concentration was defined as the compound concentra-
tion required to block CEM cell proliferation by 50%, as derived
by counting the cell numbers from CEM cell cultures exposed to
different compound concentrations by using a Coulter Particle
Counter ZI (Analysis, Gent, Belgium).
1
(0.074 g, 50%). H NMR (400 MHz, CDCl3): δ = 8.83 (br. s, 1 H,
4
NH), 7.46–7.40 (m, 2 H, Ar), 7.21 (d, JH,H = 1.0 Hz, 1 H, 6-H),
7.12–7.06 (m, 2 H, Ar), 7.02–6.98 (m, 1 H, 1Ј-H), 6.32–6.24 (m, 1
H, 2Ј-H), 5.94–5.87 (m, 1 H, 3Ј-H), 5.03–4.96 (m, 1 H, 4Ј-H), 4.33–
2
4.19 (m, 2 H, 5Ј-H), 4.03–3.91 (m, 1 H, CH-Ala), 3.80 (dd, JH,P
3
= 11.3 Hz, JH,H = 9.5 Hz, 1 H, NH-Ala), 3.71 (s, 3 H, MeO-Ala),
4
3
1.86 (s, JH,H = 1.0 Hz, 3 H, Me-Th), 1.36 (d, JH,H = 7.0 Hz, 3 H,
Me-Ala) ppm. 31P NMR (162 MHz, CDCl3): δ = 2.58 ppm.
(SP)-17b: General Procedure C was applied by using compound
(RP)-12b (0.22 g, 0.44 mmol), d4T (15, 0.15 g, 0.66 mmol), tert-but-
ylmagnesium chloride (0.78 mL, 1.32 mmol), and THF/CH3CN
(5.9 mL). Product (SP)-17b was obtained as a colorless foam
1
(0.027 g, 11%). H NMR (400 MHz, CDCl3): δ = 8.32 (br. s, 1 H,
NH), 7.39–7.28 (m, 6 H, Ar, 6-H), 7.24–6.98 (m, 5 H, Ar, 1Ј-H),
2
6.37–6.28 (m, 1 H, 2Ј-H), 5.93–5.83 (m, 1 H, 3Ј-H), 5.17 (d, JH,H
2
= 12.1 Hz, 1 H, CH2-Bn), 5.12 (d, JH,H = 12.1 Hz, 1 H, CH2-Bn),
5.03–4.94 (m, 1 H, 4Ј-H), 4.39–4.18 (m, 2 H, 5Ј-H), 4.13–3.99 (m,
2
3
1 H, CH-Ala), 3.58 (dd, JH,P = 10.1 Hz, JH,H = 10.1 Hz, 1 H,
NH-Ala), 2.24 (s, 3 H, Me-Ph), 1.75 (s, 3 H, Me-Th), 1.35 (d, 3JH,H
= 6.8 Hz, 3 H, Me-Ala) ppm. 31P NMR (162 MHz, CDCl3): δ =
2.95 ppm.
(RP)-17b: General Procedure C was applied by using compound
(SP)-12b (0.07 g, 0.14 mmol), d4T (15, 0.05 g, 0.22 mmol), tert-but-
ylmagnesium chloride (0.26 mL, 0.45 mmol), and THF/CH3CN
(1.9 mL). Product (RP)-17b was obtained as a colorless foam
Supporting Information (see footnote on the first page of this arti-
cle): 13C NMR spectroscopic data; mass spectrometric data; analyt-
ical HPLC data of phosphoramidate prodrugs 16j,k and 17b,d.
1
(0.018 g, 22%). H NMR (400 MHz, CDCl3): δ = 8.46 (br. s, 1 H,
NH), 7.39–7.27 (m, 6 H, Ar), 7.22–7.19 (m, 1 H, 6-H), 7.18–7.02
(m, 4 H, Ar), 6.99–6.95 (m, 1 H, 1Ј-H), 6.23–6.17 (m, 1 H, 2Ј-H),
2
5.88–5.81 (m, 1 H, 3Ј-H), 5.10 (d, JH,H = 12.3 Hz, 1 H, CH2-Bn),
5.05 (d, JH,H = 12.3 Hz, 1 H, CH2-Bn), 4.94–4.88 (m, 1 H, 4Ј-H),
Acknowledgments
2
4.24–4.18 (m, 2 H, 5Ј-H), 4.10–3.98 (m, 1 H, CH-Ala), 3.72 (dd,
We thank Leen Ingels and Lizette van Berckelaer for excellent tech-
nical assistance. C. M. is grateful for support obtained from the
Deutsche Forschungsgemeinschaft (DFG) (ME1161/9-1) and the
University of Hamburg. J. B. received a grant from the K. U.
Leuven (GOA 10/14).
3
2JH,P = 10.4 Hz, JH,H = 10.4 Hz, 1 H, NH-Ala), 2.26 (s, 3 H, Me-
3
Ph), 1.83 (s, 3 H, Me-Th), 1.39 (d, JH,H = 6.9 Hz, 3 H, Me-Ala)
ppm. 31P NMR (162 MHz, CDCl3): δ = 2.62 ppm.
(SP)-17d: General Procedure C was applied by using compound
(RP)-12d (0.16 g, 0.33 mmol), d4T (15, 0.11 g, 0.49 mmol), tert-but-
ylmagnesium chloride (0.57 mL, 0.98 mmol), and THF/CH3CN
(4.4 mL). Product (SP)-17d was obtained as a colorless foam
[1] C. McGuigan, C. Meier, C. Perigaud, C. R. Wagner, Mini-Rev.
Med. Chem. 2004, 4, 341–459.
[2] C. McGuigan, R. N. Pathirana, J. Balzarini, E. De Clercq, J.
Med. Chem. 1993, 36, 1048–1052.
[3] a) K. M. Fries, C. Joswig, R. F. Borch, J. Med. Chem. 1995,
38, 2672–2680; b) S. C. Tobias, R. F. Borch, J. Med. Chem.
2001, 44, 4475–4480.
[4] C. Meier, Eur. J. Org. Chem. 2006, 5, 1081–1102.
[5] a) J. L. Giradet, C. Périgaud, A. M. Aubertin, G. Gosselin, A.
Kim, J. L. Imbach, Bioorg. Med. Chem. Lett. 1995, 5, 2981–
2984; b) S. Peyrottes, D. Egron, I. Lefebvre, G. Gosselin, J. L.
Imbach, C. Perigaud, Mini-Rev. Med. Chem. 2004, 4, 395–408.
[6] M. D. Erion, K. R. Reddy, S. H. Boyer, M. C. Matelich, J. Go-
mez-Galeno, R. H. Lemus, B. G. Ugarkar, T. J. Colby, J.
Schanzer, P. D. van Poelje, J. Am. Chem. Soc. 2004, 126, 5154–
5163.
[7] H. J. Jessen, T. Schulz, J. Balzarini, C. Meier, Angew. Chem.
2008, 120, 8847–8850; Angew. Chem. Int. Ed. 2008, 47, 8719–
8722.
[8] M. J. Sofia, D. Bao, W. Chang, J. Du, D. Nagarathnam, S. Ra-
chakonda, P. G. Reddy, B. S. Ross, P. Wang, H.-R. Zhang, S.
Bansal, C. Espiritu, M. Keilman, A. M. Lam, H. M. Micoloch-
1
(0.025 g, 14%). H NMR (400 MHz, CDCl3): δ = 8.49 (br. s, 1 H,
NH), 7.38–7.28 (m, 6 H, Ar, 6-H), 7.10–6.98 (m, 5 H, Ar, 1Ј-H),
2
6.33–6.29 (m, 1 H, 2Ј-H), 5.87–5.82 (m, 1 H, 3Ј-H), 5.14 (d, JH,H
2
= 12.3 Hz, 1 H, CH2-Bn), 5.10 (d, JH,H = 12.5 Hz, 1 H, CH2-Bn),
4.99–4.94 (m, 1 H, 4Ј-H), 4.36–4.21 (m, 2 H, 5Ј-H), 4.08–3.96 (m,
2
3
1 H, CH-Ala), 3.60 (dd, JH,P = 10.8 Hz, JH,H = 10.8 Hz, 1 H,
NH-Ala), 2.29 (s, 3 H, Me-Ph), 1.79 (s, 3 H, Me-Th), 1.32 (d, 3JH,H
= 7.1 Hz, 3 H, Me-Ala) ppm. 31P NMR (162 MHz, CDCl3): δ =
3.18, 2.26 (dr = 33:1; 94% de) ppm.
(RP)-17d: General Procedure C was applied by using compound
(SP)-12d (0.11 g, 0.24 mmol), d4T (15, 0.08 g, 0.35 mmol), tert-but-
ylmagnesium chloride (0.41 mL, 0.70 mmol), and THF/CH3CN
(3.1 mL). Product (RP)-17d was obtained as a colorless foam
1
(0.058 g, 44%). H NMR (400 MHz, CDCl3): δ = 8.01 (br. s, 1 H,
NH), 7.40–7.29 (m, 5 H, Ar), 7.25–7.22 (m, 1 H, 6-H), 7.12–7.02
(m, 4 H, Ar), 7.00–6.95 (m, 1 H, 1Ј-H), 6.22–6.17 (m, 1 H, 2Ј-H),
2
5.88–5.82 (m, 1 H, 3Ј-H), 5.15 (d, JH,H = 12.3 Hz, 1 H, CH2-Bn),
2
5.13 (d, JH,H = 12.3 Hz, 1 H, CH2-Bn), 4.97–4.90 (m, 1 H, 4Ј-H),
4908
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 4899–4909

Diastereoselective Synthesis of (Aryloxy)phosphoramidate Prodrugs
ick Steuer, C. Niu, M. J. Otto, P. A. Furman, J. Med. Chem.
2010, 53, 7202–7218.
[9] C. Gardelli, B. Attenni, M. Donghi, M. Meppen, B. Pacini, S.
Harper, A. Di Marco, F. Fiore, C. Giuliano, V. Pucci, R.
Laufer, N. Gennari, I. Marcucci, J. F. Leone, D. B. Olsen, M.
MacCoss, M. Rowley, F. Narjes, J. Med. Chem. 2009, 52, 5394–
5407.
[13] D. Delaunay, L. Toupet, M. Le Corre, J. Org. Chem. 1995, 60,
6604–6607.
[14] J. O. Thomann, Dissertation, University of Hamburg, 2008.
[15] a) S. Jones, C. Smanmoo, Org. Lett. 2005, 7, 3271–3274; b) S.
Jones, D. Selitsianos, Org. Lett. 2002, 4, 3671–3673.
[16] J. Adrio, C. Cuevas, I. Manzanares, M. M. Joullié, J. Org.
Chem. 2007, 72, 5129–5138.
[10] E. H. Rios Morales, J. Balzarini, C. Meier, Chem. Eur. J. 2011,
[17] M. Uchiyama, Y. Aso, R. Noyori, Y. Hayakawa, J. Org. Chem.
1993, 58, 373–379.
17, 1649–1659.
[11] C. Arbelo Román, J. Balzarini, C. Meier, J. Med. Chem. 2010,
53, 7675–7681.
[12] E. H. Rios Morales, C. Arbelo Román, J. Thomann, C. Meier,
Eur. J. Org. Chem. 2011, 4397–4408.
[18] C. Meier, M. Lorey, E. De Clercq, J. Balzarini, J. Med. Chem.
1998, 41, 1417–1427.
Received: May 3, 2011
Published Online: July 13, 2011
Eur. J. Org. Chem. 2011, 4899–4909
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4909