A novel synthesis of antiviral nucleoside phosphoramidate and thiophosphoramidate prodrugs via nucleoside H -phosphonamidates

Article abstract of DOI:10.1080/15257770.2013.838262

GRAPHICAL ABSTRACT

Full text of DOI:10.1080/15257770.2013.838262

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A Novel Synthesis of Antiviral
Nucleoside Phosphoramidate and
Thiophosphoramidate Prodrugs via
Nucleoside H-Phosphonamidates
Qi Sun a , Xingjian Li a , Shanshan Gong a , Gang Liu a , Liang Shen a
& Liang Peng b
a Jiangxi Key Laboratory of Organic Chemistry , Jiangxi Science and
Technology Normal University , Nanchang , Jiangxi , PR China
b School of Pharmacy , Jiangxi Science and Technology Normal
University , Nanchang , Jiangxi , PR China
Published online: 18 Oct 2013.
To cite this article: Qi Sun , Xingjian Li , Shanshan Gong , Gang Liu , Liang Shen & Liang Peng (2013)
A Novel Synthesis of Antiviral Nucleoside Phosphoramidate and Thiophosphoramidate Prodrugs via
Nucleoside H-Phosphonamidates, Nucleosides, Nucleotides and Nucleic Acids, 32:11, 617-638, DOI:
10.1080/15257770.2013.838262
To link to this article: http://dx.doi.org/10.1080/15257770.2013.838262
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Nucleosides, Nucleotides and Nucleic Acids, 32:617–638, 2013
Copyright ꢀC Taylor and Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770.2013.838262
A NOVEL SYNTHESIS OF ANTIVIRAL NUCLEOSIDE
PHOSPHORAMIDATE AND THIOPHOSPHORAMIDATE
PRODRUGS VIA NUCLEOSIDE H-PHOSPHONAMIDATES
Qi Sun,1 Xingjian Li,1 Shanshan Gong,1 Gang Liu,1 Liang Shen,1
and Liang Peng2
1Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology Normal
University, Nanchang, Jiangxi, PR China
2School of Pharmacy, Jiangxi Science and Technology Normal University, Nanchang,
Jiangxi, PR China
GRAPHICAL ABSTRACT
A novel and efficient method for the preparation of antiviral nucleoside 5ꢁ-H-phosphonamidates
2
has been developed. The oxidization of the H-phosphonamidate intermediates with iodine and sulfur
afforded nucleoside 5ꢁ-phosphoramidates and 5ꢁ-thiophosphoramidates in high yields.
Keywords H-Phosphonamidate; phosphoramidate; thiophosphoramidate; antiviral nu-
cleoside; prodrug
Received 23 July 2013; accepted 22 August 2013.
We thank the National Natural Science Foundation of China (Nos. 21002041, 21262014), Natural
Science Foundation of Jiangxi Province (No. 20114BAB203008), Project of the Science Funds of Jiangxi
Education Office (No. GJJ12589), Key Project of Chinese Ministry of Education (No. 212092) for financial
support to Qi Sun
Address correspondence to Professor Qi Sun, Jiangxi Key Laboratory of Organic Chemistry,
Jiangxi Science and Technology Normal University, 605 Fenglin Avenue, Nanchang, China. E-mail:
sunqi96@tsinghua.org.cn
617

618
Q. Sun et al.
INTRODUCTION
Synthesis of proviral DNA by reverse transcriptase (RT) plays a pivotal
role in the replication of retroviruses. Currently, six nucleoside analog re-
verse transcriptase inhibitors (NRTIs), including zidovudine (AZT), didano-
sine (ddI), zalcitabine (ddC), stavudine (d4T), lamivudine (3TC), and aba-
cavir (ABC), have been licensed for HIV therapy.[1] To exert their antiviral
activity, all of these NRTIs must be consecutively phosphorylated to the
corresponding 5ꢁ-triphosphates in the host cells. AZT and ddC-induced de-
crease in nucleoside kinase activity has been ascribed as a major cause for
the reduced therapeutic efficacy and development of drug resistance in HIV
treatment. To overcome the clinical limitations of NTRIs, a variety of “pronu-
cleotide” strategies have been explored to improve their therapeutic activity
by promoting the intracellular uptake of monophosphorylated nucleoside
drugs.[2]
Among the numerous 5ꢁ-phosphorylated nucleoside prodrugs, amino
acid conjugated phosphoramidates of NTRIs have been proved effective
in enhancing the antiviral activity of the parent nucleoside analogs.[2] For
instance, McGuigan et al. reported that the amino acid methyl ester phos-
phoramidate diesters of AZT, d4T, and ddA exhibited significantly enhanced
potency against HIV via sequential metabolic activation.[3] In comparision,
aromatic amino acid methyl ester conjugated phosphoramidate monoesters
of AZT synthesized by Wagner et al. also showed enhanced antiviral activity
and low cytotoxicity via a direct P–N hydrolysis mechanism. While the phos-
phoramidate monoester prodrugs maintained the membrane permeability
of the parent AZT, their solubility in water, plasma half-life, and volume
of distribution were remarkably improved.[4] In 2007, Herdewijn et al. re-
ported that amino acid (l-Asp and l-His) phosphoramidate monoesters of
2ꢁ-deoxyadenosine could be recognized as 2ꢁ-deoxyadenosine triphosphate
(dATP) mimetics for viral DNA synthesis by HIV RT.[5] This result indicated
that amino acid phosphoramidate monoester prodrugs may circumvent all
three kinase activation steps and directly serve as substrates of RT.
Currently, several methods are available for the synthesis of amino acid
phosphoramidate monoesters and related compounds. While the DCC cou-
pling method condenses nucleoside 5ꢁ-monophosphate and amino acid
methyl esters under refluxing condition in 50–60% yields,[5a,6] amino acid
methyl esters could be coupled with nucleoside H-phosphonates by in situ
oxidation of nucleoside 5ꢁ-H-phosphonates with I2[7] or CCl4/Et3N in mod-
erate yields.[5b] Alternatively, aryl phosphoramidate diesters could be synthe-
sized by tandem substitution reactions on phenylphosphodichloridate with
l-alanine methyl ester and nucleosides,[8] or by phosphoramidite method-
ology followed by in situ oxidation.[4a,b] Removal of the phosphoester pro-
tecting groups under basic conditions afforded the desired nucleoside phos-
phoramidate monoesters in only low to moderate overall yields.

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 619
Nucleoside 5ꢁ-thiophosphoramidates have been synthesized in 63–80%
yields by treating the highly toxic and smelly thiophosphoryl chloride
with amino acid methyl esters, nucleosides, and aqueous ammonia se-
quentially in a one-pot manner.[9] The sequential N -phosphorylation
of amino acid methyl esters with a specific phosphitylating reagent,
1,3,2-oxathiaphospholane, oxidation with sulfur[10] or borane,[11] and
coupling with nucleosides provided another route to nucleoside thio-
phosphoramidates and boranophosphoramidates. For the synthesis of
nucleoside boranophosphoramidates, Shaw et al. also attempted the
H-phosphonamidate approach[11] based on the precedent report[12] of
dinucleoside P3ꢁ→N5ꢁ phosphoramidates. However, the low yields of
nucleoside 5ꢁ-H-phosphonamidates by aminolysis of aryl H-phosphonate
diesters[13] (produced in situ by condensing H-phosphonate monoesters
with trichlorophenol) and lack of an efficient purification method greatly
limited its application as versatile precursors for the synthesis of nucleoside
phosphoramidates and heteroatom-substituted phosphoramidates.
In this paper, we report a novel and efficient method for the syn-
thesis and isolation of amino acid H-phosphonamidates of AZT and d4T
based on the controlled tandem substitution reactions on PCl3. The sub-
sequent oxidation of H-phosphonamidates with I2 and S8 afforded the
phosphoramidates and thiophosphoramidates of AZT and d4T in excellent
yields.
RESULTS AND DISCUSSION
As shown in Scheme 1, monosubsituted nucleoside 5ꢁ-dichlorophos
phites (4−5) were prepared by treating AZT (1) and d4T (2) with 10-fold
excess of PCl3 (3). Concentration under reduced pressure afforded the de-
sired 4−5 in quantitative yields. To minimize the formation of the undesired
phosphorodiamidite byproduct, the solutions of amino acid methyl esters
in CH2Cl2 were added to those of 4−5 at −20◦C over 3 hours with 3-fold
excess of pyridine as base. Upon completion, hydrolysis of the chlorophos-
phoramidites gave the H-phosphonamidates of AZT and d4T (11−20) in-
stantly. Flash chromatography on silica gel with neat ethyl acetate containing
0.05% triethylamine (TEA) afforded 11−20 in good yields ranging from 65−
75%.
The nucleoside 5ꢁ-phosphoramidates (21−30) were obtained by oxidiz-
ing H-phosphonamidates 11−20 with I2/TEA in aqueous pyridine. Alter-
natively, 11−20 could be oxidized with elemental sulfur/TEA in pyridine
to afford the corresponding nucleoside 5ꢁ-thiophosphoramidates (31−40).
Column chromatography on silica gel afforded the phosphoramidates and
thiophosphoramidates of AZT and d4T in excellent yields (83−89%) and
high purity (Scheme 2).

620
Q. Sun et al.
SCHEME 1 Synthesis of amino acid H-phosphonamidates of AZT and d4T (11–20). Reagents and
conditions: (i) PCl3 (3, 10.0 equiv), CH2Cl2, −20◦C, 1 hour, RT, 2 hours; (ii) NH2-CHRꢁ-COOMe (6–10,
1.0 equiv), pyridine, CH2Cl2, −20◦C, 3 hours, RT, 30 minutes; (iii) H2O/THF, RT, 5 minutes.
Though nucleoside 5ꢁ-H-phosphonate diesters have long been recog-
nized and utilized as versatile precursors for the synthesis of nucleoside
5ꢁ-phosphates and heteroatom-substituted phosphates,[14] however, the
application of nucleoside 5ꢁ-H-phosphonamidates is still very limited due
SCHEME 2 Synthesis of 5ꢁ-phosphoramidates (21−30) and 5ꢁ-thiophosphoramidates (31−40) of AZT
and d4T. Reagents and conditions: (i) I2 (1.5 equiv), TEA (5.0 equiv), pyridine/H2O (98:2, v/v), RT,
1 hour; (ii) S8 (6.0 equiv), TEA (5.0 equiv), pyridine, RT, 4 hours.

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 621
TABLE 1 Effect of base on the yield of H-phosphonamidate 11
Entry
Base
Yield (%)a
1
2
3
4
5
Imidazole
TEA
DIEA
Pyridine
2,6-Lutidine
No product
18
No product
85
71
a 31P NMR yield.
to the lack of efficient synthetic methods for this type of compounds.
To solve this problem, we attempted to synthesize nucleoside 5ꢁ-H-
phosphonamidates directly from PCl3 based on the tandem substitution
method that has been applied for the synthesis of chlorophosphoramidite
reagents.[15] First, AZT and d4T were phosphitylated with large excess
of PCl3 according to the procedure reported by Zhao et al. avoided the
formation of multisubstituted byproducts.[16] After removal of excess PCl3,
nucleoside 5ꢁ-dichlorophosphites (4−5) could be obtained quantitatively.
To obtain the disubstituted nucleoside 5ꢁ-chlorophosphoramidites via
tandem substitution, phenylalanine methyl ester (6) was slowly added
to the solution of highly reactive 4 at –20◦C over 3 hours. Meanwhile,
a variety of organic bases with different pKas were tested as the deacid
reagents. After in situ hydrolysis, the crude yield of desired AZT 5ꢁ-H-
phosphonamidate of phenylalanine methyl ester (11) was determined by
31P NMR. The data in Table 1 showed that imidazole, which has been widely
used to react with PCl3 to form a less reactive phosphitylating reagent,
tri(imidazolyl)phosphite (PIm3),[14b,17] gave no 11. Similarly, TEA and
diisopropylethylamine (DIEA), which have been commonly used in the
preparation of chlorophosphoramidite reagents, afforded either low yield
(18%) of 11 or no 11 at all. In contrast, when weakly basic pyridine and
2,6-lutidine were used, 11 was obtained in 85% and 71%, respectively.
As shown in Figure 1, 31P NMR tracing experiment showed that when
pyridine was added to dichlorophosphite 4, it caused no change to the peak
of 4 at δP 181.1 ppm. Upon completion of the addition of phenylalanine
methyl ester, the major product (∼60%) was the desired chlorophospho-
ramidite (41, δP 163.3 ppm). Due to its highly hydroscopic nature, ∼35% of
41 had been hydrolyzed to the H-phosphonamidate (11, δP 12.5, 11.9 ppm)
during the sample transfer to the NMR tube. After H2O was added, 11

622
Q. Sun et al.
FIGURE 1 Analysis of sequential conversion of AZT-5ꢁ-dichlorophosphite (4) to AZT-5ꢁ-H-
phosphonamidate (11) by 31P NMR. (a) 4; (b) 5 minutes after addition of pyridine (3.0 equiv); (c)
30 minutes after addition of phenylalanine methyl ester (6, 1.0 equiv); (d) 5 minutes after addition of
H2O (20.0 equiv).
was obtained in over 85% yield with small amounts of nucleoside 5ꢁ-H-
phosphonate monoester and diester as the byproducts. Due to the insta-
bility of H-phosphonamidate on weakly acidic silica gel, trace amount of
TEA (0.05%, v/v) was added to the ethyl acetate eluent and flash chro-
matography was applied to the purification of compounds 11–20. The H-
phosphonamidate products were flushed out within 5 minutes and obtained
in 65–75% yields. Compounds 11–20 were fairly stable in solid form and
could be kept for at least 6 months without decomposition at –20◦C.
1
Compared to H-phosphonate diesters (δp = 8∼9 ppm, J P,H
=
∼700 Hz),[14c] H-phosphonamidates showed up at lower magnetic field rang-
ing from 10 to 14 ppm on 31P NMR spectra with significantly smaller J P,H
1
values around 660 Hz (Table 2).[12,13] The lowered electron density of the
P atom in H-phosphonamidates revealed by NMR data predicted that these
P–N compounds were less prone to be oxidized than their P–O counterparts.
When H-phosphonamidates 11–20 were treated with I2/TEA in
pyridine/H2O (98:2, v/v), the conversion to the corresponding phospho-
ramidates proceeded smoothly in high yields. Compared to the oxidation
reactions of H-phosphonate diesters, which typically finished within 5 min-
utes, complete consumption of 11–20 was much slower and required 1 hour.
The thiophosphoramidates could also be obtained in excellent yields
by conventional sulfur oxidation in the presence of TEA. Similar to
the oxidation with I2, the reactions of H-phosphonamidates with sulfur
(4 hours) were also significantly slower than those of H-phosphonate di-
esters (1–2 hours).[14c] It is worth noting that if a stronger base DBU was

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 623
TABLE 2 31P NMR data of amino acid H-phosphonamidates of AZT and d4T (11–20)
Compound
δ
(ppm)
1J P,H (Hz)
P
11
12
13
14
15
16
17
18
19
20
12.5, 11.9
12.6, 11.8
13.0, 12.3
12.8, 12.0
14.0, 11.5
11.2, 10.4
12.0, 10.8
11.8, 10.8
13.0, 12.2
13.1, 11.3
667
665
663
663
666
664
666
656
657
673
used instead of TEA, the reaction rate could be dramatically accelerated.
All reactions went to completion in only 5 minutes with only slightly low-
ered yields. This result suggested that deprotonation of the less acidic P–H
in phosphonamidate is crucial for the generation of the reactive phosphite
anion. All of the above observations about the oxidation of nucleoside 5ꢁ-
H-phosphonamidates of amino acid methyl esters were in good accordance
with the results reported for the dinucleoside P3ꢁ→N5ꢁ phosphoramidates
and thiophosphoramidates.[12]
CONCLUSIONS
In summary, a series of amino acid methyl ester H-phosphonamidates of
AZT and d4T were prepared in excellent yields from the controlled tandem
substitution reactions on PCl3 with pyridine as a suitable base. Due to the low-
ered electron density on the P atom of H-phosphonamidates, their oxidation
reactions with iodine and sulfur were slower than those of H-phosphonate
diesters, but afforded the desired amino acid phosphoramidates and thio-
phosphoramidates of AZT and d4T in high yields.
EXPERIMENTAL SECTION
General Methods
Chemical reagents and solvents were obtained from commercial suppli-
ers. All reactions were performed under an atmosphere of dry argon and
monitored by analytical thin-layer chromatography on plates coated with
0.25 mm silica gel 60 F254. TLC plates were visualized by UV irradiation
(254 nm). Flash column chromatography employed silica gel (particle size
32–63 μm). All NMR spectra were obtained with a 400 MHz instrument with
chemical shifts reported in parts per million (ppm, δ) and referenced to
CDCl3 or D2O. IR spectra were recorded on a FT-IR spectrometer. Low- and

624
Q. Sun et al.
high-resolution mass spectra were obtained with an ion trap and a TOFQ
mass spectrometer and reported as m/z.
Synthesis of Nucleoside-5ꢀ-H-phosphonamidates (11–20)
General Procedure
To a solution of PCl3 (0.87 mL, 10.0 mmol) in CH2Cl2 (10 mL) was added
nucleoside (1.0 mmol) and stirred at –20◦C for 1 hour. The reaction was
warmed up to ambient temperature and stirred for 2 hours. Concentration in
vacuo afforded nucleoside-5ꢁ-dichlorophosphite as white foam. To a solution
of dichlorophosphite and pyridine (0.24 mL, 3.0 mmol) in CH2Cl2 (10 mL)
was added a solution of amino acid methyl ester hydrochloride (1.0 mmol)
and TEA (0.14 mL, 1.0 mmol) in CH2Cl2 (10 mL) dropwise at –20◦C over
3 hours. The reaction was warmed up to ambient temperature and stirred
for 30 minutes. H2O (0.36 mL) was added to the solution. The reaction was
stirred for 5 minutes and diluted with CH2Cl2 (80 mL). The organic phase
was washed with saturated NaHCO3 aqueous solution (30 mL), HCl aqueous
solution (0.5 M, 30 mL), and saturated NaCl aqueous solution (30 mL).
The organic phase was dried with anhydrous Na2SO4, and concentrated in
vacuo to give the crude product. Flash column chromatography on silica gel
(Eluent: ethyl acetate with 0.05% TEA) afforded the diastereomeric mixture
of H-phosphonamidate as white foam.
3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl-L-phenylpropionyl-H-phosphonamidate
(11). Starting from AZT (267 mg, 1.0 mmol) and l-phenylalanine methyl
ester hydrochloride (216 mg, 1.0 mmol), the diastereomeric mixture of
compound 11 was synthesized according to the general procedure. Flash
1
column chromatography afforded 11 (335 mg, 68%) as white foam; H
NMR (400 MHz, CDCl3): δ 9.81, 9.77 (s, 1H, NH-3), 7.42–7.29 (m, 5H,
aromatic protons), 7.26, 7.24 (s, 1H, H-6), 6.88, 6.81 (d, J P,H = 667 Hz,
1H, PH), 6.21, 6.13 (t, J = 6.2 Hz, 1H, H-1ꢁ), 4.40–4.10 (m, 3H, H-3ꢁ,
H-5ꢁ), 4.01–3.87 (m, 3H, H-4ꢁ, NH, H-a), 3.84 (s, 3H, OCH3), 3.28–2.93
(m, 2H, CH2Ph), 2.50–2.30 (m, 2H, H-2ꢁ), 1.96 (s, 3H, CH3-5) ppm; 13C
NMR (100 MHz, CDCl3): δ 173.1, 163.9, 150.4, 136.1, 135.9, 135.6, 129.6,
129.5, 128.9, 127.4, 111.5, 111.4, 85.7, 85.1, 82.3, 62.2, 60.2, 60.0, 54.9, 54.7,
52.7, 40.4, 40.3, 37.3, 37.2, 12.6 ppm; 31P NMR (162 MHz, CDCl3): δ 12.49,
11.88 ppm; IR (KBr): νmax 3452, 3065, 2955, 2823, 2419, 2109, 1740, 1466,
1274, 1115, 967, 752, 558 cm−1; HRMS (ESI+): m/z Calcd. for C20H26N6O7P
[M+H]+ 493.1595; found 493.1604.
3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl-L-tryptophanyl-H-phosphonamidate
(12). Starting from AZT (267 mg, 1.0 mmol) and l-tryptophan methyl
ester hydrochloride (255 mg, 1.0 mmol), the diastereomeric mixture of
compound 12 was synthesized according to the general procedure. Flash
1
column chromatography afforded 12 (345 mg, 65%) as white foam; H

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 625
NMR (400 MHz, CDCl3): δ 9.37 (s, 1H, indole NH), 8.69, 8.65 (s, 1H, NH-3),
7.55, 7.53 (s, 1H, H-6), 7.34 (d, J = 8.1 Hz, 1H, indole H-4), 7.23–7.13 (m,
2H, indole H-7, indole H-2), 7.10 (m, 1H, indole H-6), 7.04 (s, 1H, indole
H-5), 6.87, 6.74 (d, J P,H = 665 Hz, 1H, PH), 6.01, 5.95 (t, J = 6.4 Hz, 1H,
H-1ꢁ), 4.39–4.21 (m, 1H, H-3ꢁ), 4.20–3.97 (m, 2H, H-5ꢁ), 3.96–3.70 (m, 6H,
H-4ꢁ, NH, H-α, OCH3), 3.35–3.11 (m, 2H, indole CH2), 2.36–2.12 (m, 2H,
H-2ꢁ), 1.83, 1.80 (s, 3H, CH3-5) ppm; 13C NMR (100 MHz, CDCl3): δ 173.5,
164.0, 150.3, 136.3, 136.1, 135.9, 127.4, 123.6, 122.4, 119.9, 119.8, 118.5,
111.7, 111.6, 111.4, 111.3, 109.8, 109.7, 86.2, 85.4, 82.3, 62.4, 60.1, 60.0,
54.2, 52.8, 37.2, 30.3, 30.1, 12.6, 12.5 ppm; 31P NMR (162 MHz, CDCl3):
δ 12.58, 11.81 ppm; IR (KBr): νmax 3446, 2374, 2109, 1657, 1274, 1108,
968, 738, 558 cm−1; HRMS (ESI+): m/z Calcd. for C22H27N7O7P [M+H]+
532.1704; found 532.1715.
3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl-L-leucyl-H-phosphonamidate (13). Start-
ing from AZT (267 mg, 1.0 mmol) and l-leucine methyl ester hydrochloride
(182 mg, 1.0 mmol), the diastereomeric mixture of compound 13 was syn-
thesized according to the general procedure. Flash column chromatography
1
afforded 13 (321 mg, 70%) as white foam; H NMR (400 MHz, CDCl3): δ
9.71 (s, 1H, NH-3), 7.35, 7.32 (s, 1H, H-6), 7.06, 7.04 (d, J P,H = 663 Hz, 1H,
PH), 6.16, 6.05 (t, J = 6.4 Hz, 1H, H-1ꢁ), 4.44–4.35 (m, 1H, H-3ꢁ), 4.34–4.10
(m, 2H, H-5ꢁ), 4.02–3.87 (m, 2H, H-4ꢁ, NH), 3.85–3.74 (m, 1H, H-α), 3.72
(s, 3H, OCH3), 2.47–2.31 (m, 2H, H-2ꢁ), 1.90 (s, 3H, CH3-5), 1.82–1.66
(m, 1H, CHCH2(CH3)2), 1.65–1.45 (m, 2H, CHCH2(CH3)2), 0.92 (d, J =
6.5 Hz, 6H, CHCH2(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 174.5,
163.9, 150.4, 136.1, 135.7, 111.6, 111.5, 86.0, 85.2, 82.4, 62.7, 62.5, 60.2,
60.1, 52.6, 51.9, 43.4, 37.3, 37.2, 24.7, 24.6, 22.9, 21.6, 12.5 ppm; 31P NMR
(162 MHz, CDCl3): δ 13.01, 12.32 ppm; IR (KBr): νmax 3434, 2107, 1639,
1405, 1206, 1111, 612 cm−1; HRMS (ESI+): m/z Calcd. for C17H28N6O7P
[M+H]+ 459.1752; found 459.1763.
3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl-L-valyl-H-phosphonamidate (14). Start-
ing from AZT (267 mg, 1.0 mmol) and l-valine methyl ester hydrochloride
(168 mg, 1.0 mmol), the diastereomeric mixture of compound 14 was syn-
thesized according to the general procedure. Flash column chromatography
1
afforded 14 (289 mg, 72%) as white foam; H NMR (400 MHz, CDCl3): δ
9.46 (s, 1H, NH-3), 7.35, 7.30 (s, 1H, H-6), 7.07, 7.03 (d, J P,H = 663 Hz, 1H,
PH), 6.16, 6.04 (t, J = 6.1 Hz, 1H, H-1ꢁ), 4.40 (m, 1H, H-3ꢁ), 4.37–4.10 (m,
2H, H-5ꢁ), 3.99 (s, 1H, H-4ꢁ), 3.92–3.78 (m, 1H, H-α), 3.74 (s, 3H, OCH3),
2.42 (m, 2H, H-2ꢁ), 2.15 (m, 1H, CH(CH3)2), 1.91 (s, 3H, CH3-5), 0.98
(d, J = 4.8 Hz, 3H, CH(CH3)2), 0.91–0.80 (m, 3H, CH(CH3)2) ppm; 13C
NMR (100 MHz, CDCl3): δ 173.5, 163.8, 150.4, 136.1, 135.7, 111.6, 111.5,
86.1, 85.3, 82.4, 62.6, 60.2, 60.1, 58.7, 52.6, 37.4, 37.3, 32.0, 31.8, 19.4, 19.3,
17.2, 17.0, 12.6 ppm; 31P NMR (162 MHz, CDCl3): δ 12.75, 11.97 ppm; IR
(KBr): νmax 3857, 3733, 3182, 2966, 2826, 2423, 2110, 1469, 1273, 1107, 773,

626
Q. Sun et al.
560 cm−1; HRMS (ESI+): m/z Calcd. for C16H26N6O7P [M+H]+ 445.1595;
found 445.1585.
3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl-L-aspartyl-H-phosphonamidate (15).
Starting from AZT (267 mg, 1.0 mmol) and l-aspartic acid dimethyl ester hy-
drochloride (198 mg, 1.0 mmol), the diastereomeric mixture of compound
15 was synthesized according to the general procedure. Flash column chro-
matography afforded 15 (313 mg, 66%) as white foam; 1H NMR (400 MHz,
CDCl3): δ 9.61, 9.57 (s, 1H, NH-3), 7.33, 7.28 (s, 1H, H-6), 7.17, 7.07 (d,
J P,H = 666 Hz, 1H, PH), 6.15, 5.98 (t, J = 6.4 Hz, 1H, H-1ꢁ), 4.52–4.13 (m,
5H, H-3ꢁ, H-5ꢁ, H-4ꢁ, NH), 4.04–3.90 (m, 1H, H-α), 3.73 (s, 3H, OCH3-α),
3.69 (s, 3H, OCH3-γ ), 3.07–2.75 (m, 2H, CH2-β), 2.52–2.34 (m, 2H, H-2ꢁ),
1.89, 1.88 (s, 3H, CH3-5) ppm; 13C NMR (100 MHz, CDCl3): δ 172.4, 172.3,
171.7, 171.4, 163.9, 150.4, 136.4, 135.8, 111.5, 86.5, 85.4, 82.4, 62.7, 62.4,
60.2, 59.9, 53.1, 52.3, 50.3, 49.9, 38.2, 37.3, 37.2, 12.6, 12.5 ppm; 31P NMR
(162 MHz, CDCl3): δ 14.07, 11.50 ppm; IR (KBr): νmax 3428, 2958, 2898,
2824, 2359, 1442, 1276, 1111, 997, 675, 556 cm−1; HRMS (ESI+): m/z Calcd.
for C16H24N6O9P [M+H]+ 475.1337; found 475.1329.
2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl-L-phenylpropionyl-H-
phosphonamidate (16). Starting from d4T (224 mg, 1.0 mmol) and
l-phenylalanine methyl ester hydrochloride (216 mg, 1.0 mmol), the
diastereomeric mixture of compound 16 was synthesized according to the
general procedure. Flash column chromatography afforded 16 (314 mg,
1
70%) as white foam; H NMR (400 MHz, CDCl3): δ 9.06 (s, 1H, NH-3),
7.33–7.09 (m, 6H, aromatic protons, H-6), 7.00, 6.97 (s, 1H, H-1ꢁ), 6.69
(d, J P,H = 664 Hz, 1H, PH), 6.28, 6.21 (d, J = 5.7 Hz, 1H, H-2ꢁ), 5.86 (m,
1H, H-3ꢁ), 4.90, 4.85 (s, 1H, H-4ꢁ), 4.27–3.98 (m, 2H, H-5ꢁ), 3.92–3.79 (m,
1H, NH), 3.75, 3.74 (s, 3H, OCH3), 3.59–3.40 (m, 1H, H-α), 3.18–2.80
(m, 2H, CH2Ph), 1.82, 1.81 (s, 3H, CH3-5) ppm; 13C NMR (100 MHz,
CDCl3): δ 173.0, 163.8, 150.9, 136.0, 135.6, 133.8, 133.1, 129.6, 129.5, 128.9,
127.7, 127.5 127.4, 127.2, 111.3, 111.0, 90.0, 89.8, 84.7, 84.6, 63.8, 62.8,
54.8, 54.7, 52.7, 40.6, 40.4, 12.6 ppm; 31P NMR (162 MHz, CDCl3): δ 11.19,
10.39 ppm; IR (KBr): νmax 3731, 3422, 3032, 2952, 2823, 2417, 2318, 1743,
1464, 1223, 1116, 965, 910, 779, 574 cm−1; HRMS (ESI+): m/z Calcd. for
C20H25N3O7P [M+H]+ 450.1425; found 450.1437.
2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl-L-tryptophanyl-H-
phosphonamidate (17). Starting from d4T (224 mg, 1.0 mmol) and
l-tryptophan methyl ester hydrochloride (255 mg, 1.0 mmol), the diastere-
omeric mixture of compound 17 was synthesized according to the general
procedure. Flash column chromatography afforded 17 (322 mg, 66%) as
1
white foam; H NMR (400 MHz, CDCl3): δ 9.41 (br, 1H, indole NH), 8.75
(s, 1H, NH-3), 7.52, 7.50 (s, 1H, H-6), 7.32 (d, J = 7.8 Hz, 1H, indole
H-4), 7.20–6.99 (m, 4H, indole H-7, indole H-6, indole H-2, indole H-5),
6.96–6.88 (m, 1H, H-1ꢁ), 6.76, 6.69 (d, J P,H = 666 Hz, 1H, PH), 6.21–6.04

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 627
(m, 1H, H-2ꢁ), 5.78 (d, J = 5.8 Hz, 1H, H-3ꢁ), 4.79 (s, 1H, H-4ꢁ), 4.33–4.15
(m, 1H, H-5ꢁ), 4.08–3.79 (m, 2H, H-5ꢁ, NH), 3.78–3.66 (m, 4H, OCH3, H-α),
3.32–3.11 (m, 2H, indole CH2), 1.77, 1.73 (s, 3H, CH3-5) ppm; 13C NMR
(100 MHz, CDCl3): δ 173.6, 173.4, 164.1, 151.1, 151.0, 136.4, 136.1, 135.8,
133.8, 133.1, 129.1, 128.3, 127.4, 127.0, 125.4, 123.7, 123.6, 122.4, 122.3,
119.7, 118.5, 118.4, 111.7, 111.6, 111.2, 111.0, 109.6, 90.0, 89.8, 84.7, 63.8,
63.1, 54.3, 54.1, 52.7, 30.3, 30.1, 12.5 ppm; 31P NMR (162 MHz, CDCl3): δ
12.05, 10.78 ppm; IR (KBr): νmax 3732, 3382, 3256, 2952, 2419, 1463, 1224,
1113, 1087, 983, 738, 576 cm−1; HRMS (ESI+): m/z Calcd. for C22H26N4O7P
[M+H]+ 489.1534; found 489.1547.
2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl-L-leucyl-H-phosphonamidate
(18). Starting from d4T (224 mg, 1.0 mmol) and l-leucine methyl ester hy-
drochloride (182 mg, 1.0 mmol), the diastereomeric mixture of compound
18 was synthesized according to the general procedure. Flash column
1
chromatography afforded 18 (299 mg, 72%) as white foam; H NMR
(400 MHz, CDCl3): δ 9.55 (s, 1H, NH-3), 7.25–7.17 (m, 1H, H-6), 7.03–6.96
(m, 1H, H-1ꢁ), 7.00, 6.95 (d, J P,H = 656 Hz, 1H, PH), 6.35, 6.31 (d, J =
6.0 Hz, 1H, H-2ꢁ), 5.87 (m, 1H, H-3ꢁ), 4.99 (s, 1H, H-4ꢁ), 4.33–4.08 (m, 2H,
H-5ꢁ), 3.97–3.81 (m, 1H, NH), 3.75–3.61 (m, 4H, OCH3, H-α), 1.87, 1.84
(s, 3H, CH3-5), 1.77–1.42 (m, 3H, CHCH2(CH3)2, CHCH2(CH3)2), 0.90 (t,
J = 5.7 Hz, 6H, CHCH2(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 174.4,
163.9, 151.0, 135.9, 135.6, 133.7, 133.2, 127.6, 127.3, 111.3, 111.1, 90.0,
84.8, 84.7, 64.1, 63.3, 52.5, 51.9, 43.5, 43.4, 24.8, 24.6, 22.8, 21.7, 12.5 ppm;
31P NMR (162 MHz, CDCl3): δ 11.79, 10.77 ppm; IR (KBr): νmax 3730,
3594, 3167, 2959, 2875, 2412, 1743, 1468, 1223, 1113, 988, 783, 576 cm−1;
HRMS (ESI+): m/z Calcd. for C17H27N3O7P [M+H]+ 416.1581; found 416.
1589.
2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl-L-valyl-H-phosphonamidate
(19). Starting from d4T (224 mg, 1.0 mmol) and l-valine methyl ester hy-
drochloride (168 mg, 1.0 mmol), the diastereomeric mixture of compound
19 was synthesized according to the general procedure. Flash column
1
chromatography afforded 19 (301 mg, 75%) as white foam; H NMR
(400 MHz, CDCl3): δ 9.68 (s, 1H, NH-3), 7.24–7.14 (m, 1H, H-6), 7.02–6.90
(m, 1H, H-1ꢁ), 6.97, 6.94 (d, J P,H = 657 Hz, 1H, PH), 6.34, 6.30 (d, J =
5.9 Hz, 1H, H-2ꢁ), 5.87 (m, 1H, H-3ꢁ), 4.98 (s, 1H, H-4ꢁ), 4.30–4.05 (m, 2H,
H-5ꢁ), 3.82–3.63 (m, 5H, NH, OCH3, H-α), 2.11 (m, 1H, CH(CH3)2), 1.86,
1.83 (s, 3H, CH3-5), 0.93 (t, J = 6.8 Hz, 3H, CH(CH3)2), 0.84, 0.80 (d, J =
6.8 Hz, 3H, CH(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 173.4, 164.0,
151.1, 151.0, 135.9, 135.6, 133.7, 133.2, 127.6, 127.3, 111.3, 111.0, 90.0, 89.7,
84.7, 64.1, 63.1, 58.6, 52.4, 31.9, 31.7, 19.3, 19.2, 17.2, 17.0, 12.5 ppm; 31P
NMR (162 MHz, CDCl3): δ 13.00, 12.24 ppm; IR (KBr): νmax 3731, 3450,
3222, 3065, 2965, 2881, 2414, 1468, 1223, 1086, 984, 781, 576 cm−1; HRMS
(ESI+): m/z Calcd. for C16H25N3O7P [M+H]+ 402.1425; found 402.1415.

628
Q. Sun et al.
2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl-L-aspartyl-H-
phosphonamidate (20). Starting from d4T (224 mg, 1.0 mmol) and
l-aspartic acid dimethyl ester hydrochloride (198 mg, 1.0 mmol), the
diastereomeric mixture of compound 20 was synthesized according to the
general procedure. Flash column chromatography afforded 20 (293 mg,
1
68%) as white foam; H NMR (400 MHz, CDCl3): δ 9.61 (s, 1H, NH-3),
7.23, 7.20 (s, 1H, H-6), 7.11, 6.96 (d, J P,H = 673 Hz, 1H, PH), 7.00, 6.97 (s,
1H, H-1ꢁ), 6.38–6.20 (m, 1H, H-2ꢁ), 5.86 (m, 1H, H-3ꢁ), 4.99 (s, 1H, H-4ꢁ),
4.39–4.06 (m, 4H, H-5ꢁ, NH, H-α), 3.75–3.56 (m, 6H, OCH3×2), 3.02–2.68
(m, 2H, CH2-β), 1.85, 1.82 (s, 3H, CH3-5) ppm; 13C NMR (100 MHz,
CDCl3): δ 172.3, 171.5, 171.3, 164.0, 151.1, 135.9, 135.7, 133.8, 133.2, 127.6,
127.2, 111.3, 111.0, 89.9, 89.7, 84.7, 64.0, 63.2, 53.1, 52.3, 50.2, 49.8, 38.2,
12.5 ppm; 31P NMR (162 MHz, CDCl3): δ 13.13, 11.25 ppm; IR (KBr): νmax
3731, 3447, 2958, 2892, 2429, 1696, 1443, 1223, 1086, 987, 782, 579 cm−1;
HRMS (ESI+): m/z Calcd. for C16H23N3O9P [M+H]+ 432.1166; found
432.1154.
Synthesis of Nucleoside-5ꢀ-Phosphoramidates (21–30)
General Procedure
To a solution of H-phosphonamidate (0.25 mmol) in pyridine (2.5 mL)
was added TEA (0.17 mL, 1.25 mmol), H2O (51 μL), and I2 (95 mg,
0.375 mmol). The reaction was stirred at ambient temperature for 1 hour
and concentrated in vacuo to give the crude product. Flash column chro-
matography on silica gel (CH2Cl2/MeOH 20:1 with 0.5% TEA) afforded
nucleoside-5ꢁ-phosphoramidate as light yellow oil.
2(S)-[3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl(hydroxy)phosphorylamino]-3-phe
nylproprionic acid methyl ester, triethylammonium salt (21). Starting
from 11 (123 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol), compound
21 was synthesized according to the general procedure. Flash column
1
chromatography afforded 21 (131 mg, 86%) as light yellow oil; H NMR
(400 MHz, CDCl3): δ 12.44 (br, 1H, Et3NH+), 9.93 (s, 1H, NH-3), 7.72
(s, 1H, H-6), 7.23–7.13 (m, 5H, aromatic protons), 6.23 (t, J = 6.5 Hz,
1H, H-1ꢁ), 4.33 (s, 1H, H-3ꢁ), 4.13–4.03 (m, 1H, H-4ꢁ), 3.91 (s, 1H, H-α),
3.87–3.68 (m, 2H, H-5ꢁ), 3.61 (s, 3H, OCH3), 3.11 (m, 1H, NH), 3.04–2.84
(m, 8H, N(CH2CH3)3, CH2Ph), 2.36–2.16 (m, 2H, H-2ꢁ), 1.93 (s, 3H,
CH3-5), 1.24 (t, 9H, N(CH2CH3)3) ppm; 13C NMR (100 MHz, CDCl3): δ
175.1, 164.3, 150.7, 137.4, 136.1, 129.5, 128.4, 126.7, 111.2, 84.5, 83.7, 64.0,
61.2, 56.6, 51.8, 45.4, 41.2, 37.6, 12.5, 8.6 ppm; 31P NMR (162 MHz, CDCl3):
δ 4.97 ppm; IR (KBr): νmax 3779, 3425, 2940, 2886, 2742, 2495, 2356,
2107, 1473, 1276, 1113, 1077, 701, 556 cm−1; LRMS (ESI−): m/z Calcd. for
C20H24N6O8P [M−H]– 507.1; found 507.3.

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 629
2(S)-[Hydroxy(3ꢁ-deoxy-3ꢁ-azidothymidin-5ꢁ-yl)phosphorylamino]-3-(3-
indolyl)proprionic acid methyl ester, triethylammonium salt (22). Starting
from 12 (133 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol), compound
22 was synthesized according to the general procedure. Flash column
1
chromatography afforded 22 (136 mg, 84%) as light yellow oil; H NMR
(400 MHz, CDCl3): δ 9.93 (br, 1H, indole NH), 9.42 (s, 1H, NH-3), 7.64 (s,
1H, H-6), 7.53 (d, J = 7.7 Hz, 1H, indole H-4), 7.33 (d, J = 8.1 Hz, 1H,
indole H-7), 7.12–6.96 (m, 3H, indole H-2, indole H-6, indole H-5), 6.15
(t, J = 6.7 Hz, 1H, H-1ꢁ), 4.26 (m, 1H, H-3ꢁ), 4.18 (m, 1H, H-4ꢁ), 3.94–3.82
(m, 3H, H-5ꢁ, H-α), 3.60 (s, 3H, OCH3), 3.24 (m, 1H, NH), 3.20–3.01 (m,
2H, indole CH2), 2.85 (q, 6H, N(CH2CH3)3), 2.20–2.07 (m, 2H, H-2ꢁ),
1.90 (s, 3H, CH3-5), 1.15 (t, 9H, N(CH2CH3)3) ppm; 13C NMR (100 MHz,
CDCl3): δ 175.6, 164.4, 150.7, 136.5, 136.3, 127.7, 123.6, 121.7, 119.1, 118.6,
111.5, 111.1, 110.6, 84.8, 83.7, 64.1, 61.3, 55.7, 51.9, 45.4, 37.3, 30.9, 12.6,
8.5 ppm; 31P NMR (162 MHz, CDCl3): δ 4.42 ppm; IR (KBr): νmax 3775,
3410, 2978, 2869, 1403, 1152, 683, 618, 540 cm−1; LRMS (ESI−): m/z Calcd.
for C22H25N7O8P [M−H]– 546.2; found 546.3.
2(S)-[3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl(hydroxy)phosphorylamino]-4-
methylvaleric acid methyl ester, triethylammonium salt (23). Starting
from 13 (115 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol), compound
23 was synthesized according to the general procedure. Flash column
1
chromatography afforded 23 (125 mg, 87%) as light yellow oil; H NMR
(400 MHz, CDCl3): δ 9.93 (s, 1H, NH-3), 7.76 (s, 1H, H-6), 6.26 (t, J =
6.5 Hz, 1H, H-1ꢁ), 4.45 (s, 1H, H-3ꢁ), 4.01 (m, 3H, H-5ꢁ, H-4ꢁ), 3.81 (m, 1H,
H-α), 3.63 (s, 3H, OCH3), 3.03 (q, 6H, N(CH2CH3)3), 2.29 (m, 2H, H-2ꢁ),
1.94 (s, 3H, CH3-5), 1.81–1.64 (m, 1H, CHCH2(CH3)2), 1.51–1.36 (m,
2H, CHCH2(CH3)2), 1.27 (t, 9H, N(CH2CH3)3), 0.87 (t, J = 5.5 Hz, 6H,
CHCH2(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 176.5, 164.3, 150.8,
136.1, 111.3, 84.5, 83.8, 64.1, 61.3, 53.6, 51.7, 45.4, 44.4, 37.6, 24.7, 22.9,
22.2, 12.6, 8.6 ppm; 31P NMR (162 MHz, CDCl3): δ 5.37 ppm; IR (KBr): νmax
3416, 2955, 2486, 2356, 2104, 1465, 1275, 1110, 1077, 927, 819, 555 cm−1;
LRMS (ESI−): m/z Calcd. for C17H26N6O8P [M−H]– 473.2; found 473.3.
2(S)-[3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl(hydroxy)phosphorylamino]-3-
methylbutyric acid methyl ester, triethylammonium salt (24). Starting
from 14 (111 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol), compound
24 was synthesized according to the general procedure. Flash column
1
chromatography afforded 24 (123 mg, 88%) as light yellow oil; H NMR
(400 MHz, CDCl3): δ 12.44 (br, 1H, Et3NH+), 10.16 (s, 1H, NH-3), 7.69 (s,
1H, H-6), 6.23 (m, 1H, H-1ꢁ), 4.42 (s, 1H, H-3ꢁ), 4.01 (m, 3H, H-5ꢁ, H-4ꢁ),
3.62 (m, 4H, H-α, OCH3), 3.03 (q, 6H, N(CH2CH3)3), 2.28 (s, 2H, H-2ꢁ),
2.00–1.84 (m, 4H, CH3-5, CH(CH3)2), 1.26 (t, 9H, N(CH2CH3)3), 0.90 (d,
J = 4.4 Hz, 3H, CH(CH3)2), 0.83 (d, J = 4.4 Hz, 3H, CH(CH3)2) ppm;
13C NMR (100 MHz, CDCl3): δ 175.2, 164.4, 150.8, 136.0, 111.2, 84.5, 83.6,

630
Q. Sun et al.
64.2, 61.2, 60.4, 51.6, 45.4, 37.5, 32.3, 19.2, 17.8, 12.5, 8.5 ppm; 31P NMR
(162 MHz, CDCl3): δ 4.82 ppm; IR (KBr): νmax 3383, 2938, 2743, 2678,
2110, 1472, 1368, 1275, 1072, 962, 768, 559 cm−1; LRMS (ESI−): m/z Calcd.
for C16H24N6O8P [M−H]– 459.1; found 459.3.
2(S)-[3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl(hydroxy)phosphorylamino]-
succinic acid dimethyl ester, triethylammonium salt (25). Starting from 15
(119 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol), compound 25 was
synthesized according to the general procedure. Flash column chromatog-
1
raphy afforded 25 (126 mg, 85%) as light yellow oil; H NMR (400 MHz,
CDCl3): δ 12.28 (br, 1H, Et3NH+), 9.53 (s, 1H, NH-3), 7.73 (s, 1H, H-6),
6.25 (t, J = 6.2 Hz, 1H, H-1ꢁ), 4.46 (s, 1H, H-3ꢁ), 4.18 (m, 1H, H-4ꢁ), 4.02 (s,
3H, H-5ꢁ, H-α), 3.69 (s, 3H, OCH3-α), 3.62 (s, 3H, OCH3-γ ), 3.54–3.35 (m,
1H, NH), 3.06 (q, 6H, N(CH2CH3)3), 2.90–2.74 (m, 2H, CH2-β), 2.33 (m,
2H, H-2ꢁ), 1.94 (s, 3H, CH3-5), 1.30 (t, 9H, N(CH2CH3)3) ppm; 13C NMR
(100 MHz, CDCl3): δ 173.8, 171.5, 164.1, 150.6, 136.1, 111.3, 84.7, 83.7,
64.1, 61.2, 52.4, 51.9, 45.6, 39.4, 37.6, 12.5, 8.6 ppm; 31P NMR (162 MHz,
CDCl3): δ 4.61 ppm; IR (KBr): νmax 3428, 2939, 2742, 2677, 2493, 2357,
2109, 1693, 1438, 1278, 1110, 853, 556 cm−1; LRMS (ESI−): m/z Calcd. for
C16H22N6O10P [M−H]– 489.1; found 489.2.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)(hydroxy)phosphoryl
amino]-3-phenylproprionic acid methyl ester, triethylammonium salt (26).
Starting from 16 (112 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol),
compound 26 was synthesized according to the general procedure. Flash
column chromatography afforded 26 (123 mg, 87%) as light yellow oil; 1H
NMR (400 MHz, CDCl3): δ 12.58 (br, 1H, Et3NH+), 9.81 (s, 1H, NH-3),
7.62 (s, 1H, H-6), 7.22–7.07 (m, 5H, aromatic protons), 6.97 (m, 1H, H-1ꢁ),
6.24 (d, J = 5.4 Hz, 1H, H-2ꢁ), 5.68 (d, J = 5.4 Hz, 1H, H-3ꢁ), 4.80 (s, 1H,
H-4ꢁ), 4.01 (m, 1H, H-5ꢁ), 3.93–3.84 (m, 1H, H-5ꢁ), 3.82–3.73 (m, 1H, H-α),
3.56 (s, 3H, OCH3), 2.96 (q, 6H, N(CH2CH3)3), 2.90 (d, J = 6.3 Hz, 2H,
CH2Ph), 1.92 (s, 3H, CH3-5), 1.22 (t, 9H, N(CH2CH3)3) ppm; 13C NMR
(100 MHz, CDCl3): δ 175.0, 164.4, 151.2, 137.3, 137.1, 134.8, 129.5, 128.3,
126.6, 126.0, 111.1, 89.5, 86.1, 65.1, 56.4, 51.6, 45.4, 41.2, 12.3, 8.5 ppm; 31
P
NMR (162 MHz, CDCl3): δ 4.87 ppm; IR (KBr): νmax 3730, 3417, 2936, 2743,
2677, 2493, 2350, 1470, 1207, 1071, 949, 775, 576 cm−1; LRMS (ESI−): m/z
Calcd. for C20H23N3O8P [M−H]– 464.1; found 464.3.
2(S)-[Hydroxy(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)phosphoryl
amino]-3-(3-indolyl) proprionic acid methyl ester, triethylammonium salt
(27). Starting from 17 (122 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol),
compound 27 was synthesized according to the general procedure. Flash
column chromatography afforded 27 (130 mg, 86%) as light yellow oil; 1H
NMR (400 MHz, CDCl3): δ 12.47 (br, 1H, Et3NH+), 9.69 (s, 1H, indole NH),
9.60 (s, 1H, NH-3), 7.60 (s, 1H, H-6), 7.49 (d, J = 7.8 Hz, 1H, indole H-4),
7.33 (d, J = 8.0 Hz, 1H, indole H-7), 7.11–6.94 (m, 4H, indole H-6, indole

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 631
H-2, indole H-5, H-1ꢁ), 6.20 (d, J = 5.8 Hz, 1H, H-2ꢁ), 5.66 (d, J = 5.8 Hz,
1H, H-3ꢁ), 4.81 (s, 1H, H-4ꢁ), 4.10 (m, 1H, H-5ꢁ), 4.01–3.83 (m, 2H, H-5ꢁ,
H-α), 3.54 (s, 3H, OCH3), 3.29–3.02 (m, 3H, NH, indole CH2), 2.81 (q, 6H,
N(CH2CH3)3), 1.91 (s, 3H, CH3-5), 1.12 (t, 9H, N(CH2CH3)3) ppm; 13C
NMR (100 MHz, CDCl3): δ 175.6, 164.4, 151.2, 137.1, 136.5, 134.9, 127.8,
126.0, 123.6, 121.6, 119.0, 118.6, 111.5, 111.1, 110.6, 89.6, 86.2, 65.3, 55.7,
51.8, 45.3, 30.9, 12.4, 8.5 ppm; 31P NMR (162 MHz, CDCl3): δ 4.86 ppm; IR
(KBr): νmax 3731, 3384, 2947, 2681, 2487, 2317, 1462, 1205, 1116, 1071, 912,
745, 520 cm−1; LRMS (ESI−): m/z Calcd. for C22H24N4O8P [M−H]– 503.1;
found 503.3.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)(hydroxy)phosphoryl
amino]-4-methylvaleric acid methyl ester, triethylammonium salt (28).
Starting from 18 (104 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol),
compound 28 was synthesized according to the general procedure. Flash
column chromatography afforded 28 (116 mg, 87%) as light yellow oil; 1H
NMR (400 MHz, CDCl3): δ 12.70 (br, 1H, Et3NH+), 9.83 (s, 1H, NH-3),
7.63 (s, 1H, H-6), 6.98 (m, 1H, H-1ꢁ), 6.33 (d, J = 5.6 Hz, 1H, H-2ꢁ), 5.69
(d, J = 5.6 Hz, 1H, H-3ꢁ), 4.90 (s, 1H, H-4ꢁ), 4.09–3.91 (m, 2H, H-5ꢁ),
3.76–3.67 (m, 1H, H-α), 3.61 (s, 3H, OCH3), 3.00 (q, 6H, N(CH2CH3)3),
1.92 (s, 3H, CH3-5), 1.75–1.60 (m, 1H, CHCH2(CH3)2), 1.45–1.33 (m,
2H, CHCH2(CH3)2), 1.24 (t, 9H, N(CH2CH3)3), 0.82 (d, J = 5.5 Hz, 6H,
CHCH2(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 176.3, 164.5, 151.2,
137.0, 134.8, 126.1, 111.1, 89.5, 86.1, 65.2, 53.4, 51.6, 45.3, 44.4, 24.6, 22.8,
22.2, 12.3, 8.5 ppm; 31P NMR (162 MHz, CDCl3): δ 4.87 ppm; IR (KBr): νmax
3730, 3383, 2939, 2743, 2677, 2492, 2350, 1471, 1257, 1209, 1073, 1042, 991,
737, 577 cm−1; LRMS (ESI−): m/z Calcd. for C17H25N3O8P [M−H]– 430.1;
found 430.3.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)(hydroxy)phosphoryl
amino]-3-methylbutyric acid methyl ester, triethylammonium salt (29).
Starting from 19 (100 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol),
compound 29 was synthesized according to the general procedure. Flash
column chromatography afforded 29 (115 mg, 89%) as light yellow oil; 1H
NMR (400 MHz, CDCl3): δ 12.70 (br, 1H, Et3NH+), 9.77 (s, 1H, NH-3),
7.65 (s, 1H, H-6), 6.98 (s, 1H, H-1ꢁ), 6.31 (d, J = 5.8 Hz, 1H, H-2ꢁ), 5.69 (d,
J = 5.8 Hz, 1H, H-3ꢁ), 4.89 (s, 1H, H-4ꢁ), 4.08–3.92 (m, 2H, H-5ꢁ), 3.61 (s,
3H, OCH3), 3.56 (m, 1H, H-α), 3.00 (q, 6H, N(CH2CH3)3), 1.93 (s, 3H,
CH3-5), 1.91–1.86 (m, 1H, CH(CH3)2), 1.24 (t, 9H, N(CH2CH3)3), 0.87 (d,
J = 6.8 Hz, 3H, CH(CH3)2), 0.81 (d, J = 6.8 Hz, 3H, CH(CH3)2) ppm; 13
C
NMR (100 MHz, CDCl3): δ 175.4, 164.5, 151.2, 137.1, 134.9, 126.0, 111.1,
89.5, 86.2, 65.2, 60.3, 51.4, 45.4, 32.4, 19.1, 17.9, 12.3, 8.5 ppm; 31P NMR
(162 MHz, CDCl3): δ 5.94 ppm; IR (KBr): νmax 3730, 3382, 2938, 2742,
2677, 2491, 1471, 1257, 1209, 1073, 913, 779, 581 cm−1; LRMS (ESI−): m/z
Calcd. for C16H23N3O8P [M−H]– 416.1; found 416.2.

632
Q. Sun et al.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)(hydroxy)phosphoryl
amino]-succinic acid dimethyl ester, triethylammonium salt (30). Starting
from 20 (108 mg, 0.25 mmol) and I2 (95 mg, 0.375 mmol), compound
30 was synthesized according to the general procedure. Flash column
1
chromatography afforded 30 (116 mg, 85%) as light yellow oil; H NMR
(400 MHz, CDCl3): δ 12.56 (br, 1H, Et3NH+), 9.55 (s, 1H, NH-3), 7.66 (s,
1H, H-6), 7.00 (s, 1H, H-1ꢁ), 6.32 (d, J = 5.4 Hz, 1H, H-2ꢁ), 5.72 (d, J =
5.4 Hz, 1H, H-3ꢁ), 4.92 (s, 1H, H-4ꢁ), 4.06 (m, 2H, H-5ꢁ), 4.00 (m, 1H, H-α),
3.66 (s, 3H, OCH3-α), 3.60 (s, 3H, OCH3-γ ), 3.54–3.32 (m, 1H, NH), 3.02
(q, 6H, N(CH2CH3)3), 2.88–2.70 (m, 2H, CH2-β), 1.93 (s, 3H, CH3-5), 1.26
(t, 9H, N(CH2CH3)3) ppm; 13C NMR (100 MHz, CDCl3): δ 173.7, 171.5,
164.4, 151.1, 137.1, 134.7, 126.2, 111.1, 89.5, 86.1, 65.2, 52.3, 51.8, 51.6, 45.4,
39.1, 12.3, 8.6 ppm; 31P NMR (162 MHz, CDCl3): δ 4.72 ppm; IR (KBr): νmax
3730, 3441, 2939, 2678, 1697, 1440, 1214, 1076, 993, 781, 584 cm−1; LRMS
(ESI−): m/z Calcd. for C16H21N3O10P [M−H]– 446.1; found 446.2.
Synthesis of Nucleoside-5ꢀ-thiophosphoramidates (31–40)
General Procedure
To a solution of H-phosphonamidate (0.25 mmol) in pyridine (2.5 mL)
was added elemental sulfur (48 mg, 1.5 mmol) and TEA (0.17 mL,
1.25 mmol). The reaction was stirred at ambient temperature for 4 hours and
concentrated in vacuo. The residue was dissolved in MeOH (2.5 mL). The
sulfur was removed by filtration, and the filtrate was concentrated to give the
crude product. Flash column chromatography on silica gel (CH2Cl2/MeOH
20:1 with 0.5% TEA) afforded the diastereomeric mixture of nucleoside-5ꢁ-
thiophosphoramidate as light yellow oil.
2(S)-[(3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl)thiophosphorylamino]-3-
phenylproprionic acid methyl ester, triethylammonium salt (31). Starting
from 11 (123 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the diastere-
omeric mixture of compound 31 was synthesized according to the general
procedure. Flash column chromatography afforded 31 (133 mg, 85%) as
light yellow oil; 1H NMR (400 MHz, CDCl3): δ 12.04 (br, 1H, Et3NH+), 9.38
(s, 1H, NH-3), 7.82, 7.68 (s, 1H, H-6), 7.24–7.11 (m, 5H, aromatic protons),
6.27, 6.23 (t, J = 6.6 Hz, 1H, H-1ꢁ), 4.34 (s, 1H, H-3ꢁ), 4.29–4.07 (m, 1H,
H-4ꢁ), 3.98–3.79 (m, 2H, H-5ꢁ), 3.62, 3.60 (s, 3H, OCH3), 3.57–3.48 (m,
1H, NH), 3.41–3.28 (m, 1H, H-α), 3.07 (q, 6H, N(CH2CH3)3), 3.00–2.80
(m, 2H, CH2Ph), 2.31–2.11 (m, 2H, H-2ꢁ), 1.98 (s, 3H, CH3-5), 1.26 (t, 9H,
N(CH2CH3)3) ppm; 13C NMR (100 MHz, CDCl3): δ 174.7, 164.2, 150.6,
137.3, 137.2, 136.3, 136.1, 129.5, 128.5, 128.4, 126.8, 126.7, 111.4, 84.7, 84.6,
83.5, 64.6, 64.5, 61.6, 61.5, 57.0, 56.5, 51.9, 51.7, 45.5, 40.9, 37.7, 37.6, 12.6,
12.4, 8.6 ppm; 31P NMR (162 MHz, CDCl3): δ 59.58, 58.87 ppm; IR (KBr):

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 633
νmax 3434, 2677, 2108, 1640, 1475, 1274, 1109, 562 cm−1; LRMS (ESI−): m/z
Calcd. for C20H24N6O7PS [M−H]– 523.1; found 523.3.
2(S)-[(3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl)thiophosphorylamino]-3-(3-
indolyl)proprionic acid methyl ester, triethylammonium salt (32). Starting
from 12 (133 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the diastere-
omeric mixture of compound 32 was synthesized according to the general
procedure. Flash column chromatography afforded 32 (138 mg, 83%) as
light yellow oil; 1H NMR (400 MHz, D2O): δ 7.52, 7.50 (s, 1H, H-6), 7.31 (m,
2H, indole H-4, indole H-7), 7.13 (m, 1H, indole H-2), 7.08 (t, J = 7.3 Hz,
1H, indole H-6), 6.97 (m, 1H, indole H-5), 5.94 (t, J = 6.7 Hz, 1H, H-1ꢁ),
4.21–4.10 (m, 1H, H-3ꢁ), 4.07–3.93 (m, 2H, H-5ꢁ), 3.84–3.73 (m, 2H, H-4ꢁ,
H-α), 3.68 (s, 3H, OCH3), 3.20–2.93 (m, 8H, N(CH2CH3)3, indole CH2),
2.13–2.02 (m, 1H, H-2ꢁ), 1.86–1.76 (m, 1H, H-2ꢁ), 1.73, 1.68 (s, 3H, CH3-5),
1.23 (t, 9H, N(CH2CH3)3) ppm; 13C NMR (100 MHz, D2O): δ 177.4, 177.0,
166.3, 151.4, 136.7, 136.2, 126.9, 126.8, 124.2, 124.1, 121.9, 119.1, 118.2,
111.6, 109.9, 109.7, 84.6, 83.1, 82.9, 64.3, 63.9, 60.7, 60.6, 56.9, 55.6, 52.6,
52.5, 46.8, 36.5, 36.3, 29.7, 29.6, 11.8, 11.7, 8.3 ppm; 31P NMR (162 MHz,
D2O): δ 58.80, 58.31 ppm; IR (KBr): νmax 3786, 3416, 2934, 2347, 2106,
1686, 1457, 1276, 1106, 845, 654, 556 cm−1; LRMS (ESI−): m/z Calcd. for
C22H25N7O7PS [M−H]– 562.1; found 562.3.
2(S)-[(3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl)thiophosphorylamino]-4-
methylvaleric acid methyl ester, triethylammonium salt (33). Starting
from 13 (115 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the diastere-
omeric mixture of compound 33 was synthesized according to the general
procedure. Flash column chromatography afforded 33 (124 mg, 84%) as
1
light yellow oil; H NMR (400 MHz, D2O): δ 7.73 (s, 1H, H-6), 6.20 (m,
1H, H-1ꢁ), 4.44 (s, 1H, H-3ꢁ), 4.14 (s, 1H, H-4ꢁ), 4.09–3.93 (m, 2H, H-5ꢁ),
3.86–3.70 (m, 1H, H-α), 3.66 (s, 3H, OCH3), 3.14 (q, 6H, N(CH2CH3)3),
2.51–2.34 (m, 2H, H-2ꢁ), 1.92 (s, 3H, CH3-5), 1.57 (m, 1H, CHCH2(CH3)2),
1.43 (m, 2H, CHCH2(CH3)2), 1.22 (t, 9H, N(CH2CH3)3), 0.84–0.74 (m,
6H, CHCH2(CH3)2) ppm; 13C NMR (100 MHz, D2O): δ 180.6, 180.4, 169.8,
154.7, 139.8, 114.2, 87.5, 85.8, 85.7, 67.0, 66.6, 63.3, 56.4, 56.0, 55.0, 54.9,
49.2, 45.5, 39.0, 26.7, 24.3, 24.0, 23.9, 14.4, 10.8 ppm; 31P NMR (162 MHz,
D2O): δ 57.43, 56.84 ppm; IR (KBr): νmax 3791, 3428, 2859, 2677, 2492,
2358, 1463, 1375, 1274, 1106, 665, 559 cm−1; LRMS (ESI−): m/z Calcd. for
C17H26N6O7PS [M−H]– 489.1; found 489.3.
2(S)-[(3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl)thiophosphorylamino]-3-
methylbutyric acid methyl ester, triethylammonium salt (34). Starting
from 14 (111 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the diastere-
omeric mixture of compound 34 was synthesized according to the general
procedure. Flash column chromatography afforded 34 (124 mg, 86%) as
1
light yellow oil; H NMR (400 MHz, CDCl3): δ 12.00 (br, 1H, Et3NH+),
9.67 (s, 1H, NH-3), 7.86, 7.69 (s, 1H, H-6), 6.28, 6.24 (t, J = 6.2 Hz, 1H,

634
Q. Sun et al.
H-1ꢁ), 4.46 (s, 1H, H-3ꢁ), 4.18–3.92 (m, 3H, H-5ꢁ, H-4ꢁ), 3.82–3.67 (m,
1H, H-α), 3.63, 3.61 (s, 3H, OCH3), 3.44–3.23 (m, 1H, NH), 3.09 (q, 6H,
N(CH2CH3)3), 2.35–2.18 (m, 2H, H-2ꢁ), 1.96 (m, 4H, CH3-5, CH(CH3)2),
1.28 (t, 9H, N(CH2CH3)3), 0.89 (m, 3H, CH(CH3)2), 0.83 (d, J = 6.4 Hz,
3H, CH(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 175.0, 174.9, 164.3,
164.2, 150.7, 150.6, 136.2, 135.9, 111.3, 84.5, 83.6, 64.8, 64.5, 61.6, 61.5,
60.7, 60.4, 51.6, 51.5, 45.5, 37.6, 37.5, 32.3, 32.2, 19.3, 19.2, 18.0, 12.5, 12.3,
8.6 ppm; 31P NMR (162 MHz, CDCl3): δ 60.67 ppm; IR (KBr): νmax 3447,
2964, 2814, 2677, 2491, 1472, 1273, 1105, 998, 886, 732, 560 cm−1; LRMS
(ESI−): m/z Calcd. for C16H24N6O7PS [M−H]– 475.1; found 475.3.
2(S)-[(3ꢁ-Deoxy-3ꢁ-azidothymidin-5ꢁ-yl)thiophosphorylamino]-succinic
acid dimethyl ester, triethylammonium salt (35). Starting from 15 (119 mg,
0.25 mmol) and sulfur (48 mg, 1.5 mmol), the diastereomeric mixture of
compound 35 was synthesized according to the general procedure. Flash
column chromatography afforded 35 (126 mg, 83%) as light yellow oil; 1H
NMR (400 MHz, CDCl3): δ 11.95 (br, 1H, Et3NH+), 9.08 (s, 1H, NH-3),
7.82, 7.71 (s, 1H, H-6), 6.29, 6.26 (t, J = 6.7 Hz, 1H, H-1ꢁ), 4.47 (s, 1H,
H-3ꢁ), 4.43–4.24 (m, 1H, H-4ꢁ), 4.20–3.98 (m, 3H, H-5ꢁ, H-α ), 3.70, 3.67
(s, 3H, OCH3-α), 3.62, 3.61 (s, 3H, OCH3-γ ), 3.10 (q, 6H, N(CH2CH3)3),
2.93–2.71 (m, 2H, CH2-β), 2.32 (m, 2H, H-2ꢁ), 1.97 (s, 3H, CH3-5), 1.31 (t,
9H, N(CH2CH3)3) ppm; 13C NMR (100 MHz, CDCl3): δ 173.5, 171.4, 164.1,
150.6, 136.2, 136.0, 111.3, 84.6, 83.6, 64.7, 64.5, 61.6, 61.5, 52.5, 52.3, 52.0,
51.8, 45.7, 39.1, 37.6, 12.5, 12.4, 8.6 ppm; 31P NMR (162 MHz, CDCl3): δ
60.10, 59.29 ppm; IR (KBr): νmax 3774, 3416, 2982, 2877, 2494, 2356, 1439,
1277, 1105, 673, 556 cm−1; LRMS (ESI−): m/z Calcd. for C16H22N6O9PS
[M−H]– 505.1; found 505.2.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)thiophosphoryl
amino]-3-phenylproprionic acid methyl ester, triethylammonium salt (36).
Starting from 16 (112 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the
diastereomeric mixture of compound 36 was synthesized according to the
general procedure. Flash column chromatography afforded 36 (124 mg,
85%) as light yellow oil; 1H NMR (400 MHz, CDCl3): δ 9.22 (s, 1H, NH-3),
7.66, 7.48 (s, 1H, H-6), 7.24–7.08 (m, 5H, aromatic protons), 6.99, 6.95 (s,
1H, H-1ꢁ), 6.30–6.21 (m, 1H, H-2ꢁ), 5.71 (d, J = 5.3 Hz, 1H, H-3ꢁ), 4.87,
4.83 (s, 1H, H-4ꢁ), 4.31–3.62 (m, 3H, H-5ꢁ, H-α), 3.59, 3.55 (s, 3H, OCH3),
3.33 (m, 1H, NH), 3.04 (q, 6H, N(CH2CH3)3), 2.96–2.86 (m, 2H, CH2Ph),
1.93 (s, 3H, CH3-5), 1.25 (t, 9H, N(CH2CH3)3) ppm; 13C NMR (100 MHz,
CDCl3): δ 174.7, 164.3, 151.1, 137.3, 137.2, 137.1, 136.8, 134.8, 134.7, 129.5,
128.4, 128.3, 126.7, 126.1, 126.0, 111.2, 89.8, 89.6, 85.9, 65.8, 56.9, 56.2, 51.8,
51.6, 45.6, 40.9, 12.5, 12.2, 8.6 ppm; 31P NMR (162 MHz, CDCl3): δ 59.51,
58.18 ppm; IR (KBr): νmax 3749, 3416, 2948, 2623, 2376, 1463, 1251, 1113,
1087, 906, 738, 619 cm−1; LRMS (ESI−): m/z Calcd. for C20H23N3O7PS
[M−H]– 480.1; found 480.3.

Synthesis of Antiviral Nucleoside Phosphoramidates and Thiophosphoramidates 635
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)thiophosphoryl
amino]-3-(3-indolyl)proprionic acid methyl ester, triethylammonium salt
(37). Starting from 17 (122 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol),
the diastereomeric mixture of compound 37 was synthesized according to
the general procedure. Flash column chromatography afforded 37 (130 mg,
1
84%) as light yellow oil; H NMR (400 MHz, CDCl3): δ 12.08 (br, 1H,
Et3NH+), 9.17, 9.13 (s, 1H, indole NH), 8.62 (s, 1H, NH-3), 7.67–7.44 (m,
2H, H-6, indole H-4), 7.31 (t, J = 7.5 Hz, 1H, indole H-7), 7.13–6.91 (m, 4H,
indole H-6, indole H-2, indole H-5, H-1ꢁ), 6.20 (m, 1H, H-2ꢁ), 5.66 (m, 1H,
H-3ꢁ), 4.87, 4.81 (s, 1H, H-4ꢁ), 4.35–3.75 (m, 3H, H-5ꢁ, H-α), 3.55, 3.50 (s,
3H, OCH3), 3.42 (m, 1H, NH), 3.16–3.05 (m, 2H, indole CH2), 2.98 (q, 6H,
N(CH2CH3)3), 1.93 (s, 3H, CH3-5), 1.21 (t, 9H, N(CH2CH3)3) ppm; 13C
NMR (100 MHz, CDCl3): δ 175.2, 175.0, 164.3, 164.2, 151.0, 137.1, 136.8,
136.3, 134.8, 134.7, 127.8, 127.7, 126.0, 125.9, 123.3, 123.1, 121.9, 119.3,
118.8, 118.7, 111.3, 111.2, 110.9, 89.8, 89.6, 85.9, 66.0, 55.9, 55.5, 51.9,
51.8, 45.5, 30.7, 12.5, 12.3, 8.6 ppm; 31P NMR (162 MHz, CDCl3): δ 58.08,
57.32 ppm; IR (KBr): νmax 3730, 3384, 2930, 2675, 2484, 1462, 1252, 1112,
1039, 908, 741, 616 cm−1; LRMS (ESI−): m/z Calcd. for C22H24N4O7PS
[M−H]– 519.1; found 519.3.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)thiophosphoryl
amino]-4-methylvaleric acid methyl ester, triethylammonium salt (38).
Starting from 18 (104 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the
diastereomeric mixture of compound 38 was synthesized according to the
general procedure. Flash column chromatography afforded 38 (118 mg,
1
86%) as light yellow oil; H NMR (400 MHz, CDCl3): δ 12.16 (br, 1H,
Et3NH+), 9.22 (s, 1H, NH-3), 7.73, 7.49 (s, 1H, H-6), 6.98 (d, J = 8.0 Hz, 1H,
H-1ꢁ), 6.33 (s, 1H, H-2ꢁ), 5.71 (s, 1H, H-3ꢁ), 4.94 (s, 1H, H-4ꢁ), 4.32–3.70 (m,
3H, H-5ꢁ, H-α), 3.63, 3.60 (s, 3H, OCH3), 3.30–2.94 (m, 7H, N(CH2CH3)3,
NH), 1.94 (s, 3H, CH3-5), 1.67 (m, 1H, CHCH2(CH3)2), 1.48–1.34 (m, 2H,
CHCH2(CH3)2), 1.28 (t, 9H, N(CH2CH3)3), 0.82 (m, 6H, CHCH2(CH3)2)
ppm; 13C NMR (100 MHz, CDCl3): δ 176.0, 164.3, 164.2, 151.0, 137.2, 136.8,
134.9, 134.8, 126.1, 125.9, 111.1, 89.7, 89.5, 86.0, 85.8, 65.8, 53.6, 53.2,
51.8, 51.6, 45.6, 44.2, 24.6, 24.5, 22.8, 22.7, 22.2, 12.5, 12.2, 8.6 ppm; 31P
NMR (162 MHz, CDCl3): δ 59.53, 58.87 ppm; IR (KBr): νmax 3729, 3384,
2951, 2875, 2677, 2493, 1470, 1253, 1089, 1039, 907, 736, 618 cm−1; LRMS
(ESI−): m/z Calcd. for C17H25N3O7PS [M−H]– 446.1; found 446.3.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)thiophosphoryl
amino]-3-methylbutyric acid methyl ester, triethylammonium salt (39).
Starting from 19 (100 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the
diastereomeric mixture of compound 39 was synthesized according to the
general procedure. Flash column chromatography afforded 39 (116 mg,
1
87%) as light yellow oil; H NMR (400 MHz, CDCl3): δ 12.12 (br, 1H,
Et3NH+), 9.14 (s, 1H, NH-3), 7.68, 7.51 (s, 1H, H-6), 6.98, 6.95 (s, 1H,

636
Q. Sun et al.
H-1ꢁ), 6.35 (m, 1H, H-2ꢁ), 5.74 (s, 1H, H-3ꢁ), 4.95 (s, 1H, H-4ꢁ), 4.31–3.94
(m, 2H, H-5ꢁ), 3.71 (m, 1H, H-α), 3.68–3.58 (m, 4H, OCH3, NH), 3.08
(q, 6H, N(CH2CH3)3), 1.98–1.84 (m, 4H, CH3-5, CH(CH3)2), 1.31 (t,
9H, N(CH2CH3)3), 0.87 (m, 3H, CH(CH3)2), 0.83 (d, J = 6.7 Hz, 3H,
CH(CH3)2) ppm; 13C NMR (100 MHz, CDCl3): δ 175.4, 175.1, 164.3, 151.1,
151.0, 137.3, 137.0, 134.8, 126.0, 111.3, 89.9, 89.7, 86.0, 65.9, 61.0, 60.2,
51.8, 51.5, 45.7, 32.3, 32.2, 19.2, 18.2, 18.1, 12.4, 12.2, 8.7 ppm; 31P NMR
(162 MHz, CDCl3): δ 60.10, 59.41 ppm; IR (KBr): νmax 3731, 3595, 2936,
2742, 2677, 2492, 1470, 1254, 1089, 909, 780, 621 cm−1; LRMS (ESI−): m/z
Calcd. for C16H23N3O7PS [M−H]– 432.1; found 432.3.
2(S)-[(2ꢁ,3ꢁ-Dideoxy-2ꢁ,3ꢁ-didehydrothymidin-5ꢁ-yl)thiophosphoryl
amino]succinic acid dimethyl ester, triethylammonium salt (40). Starting
from 20 (108 mg, 0.25 mmol) and sulfur (48 mg, 1.5 mmol), the diastere-
omeric mixture of compound 40 was synthesized according to the general
procedure. Flash column chromatography afforded 40 (119 mg, 84%) as
1
light yellow oil; H NMR (400 MHz, CDCl3): δ 9.54 (br, 1H, NH-3), 7.60,
7.48 (s, 1H, H-6), 7.05–6.89 (m, 1H, H-1ꢁ), 6.34 (m, 1H, H-2ꢁ), 5.77 (m, 1H,
H-3ꢁ), 4.98 (s, 1H, H-4ꢁ), 4.40–3.93 (m, 3H, H-5ꢁ, H-α), 3.84–3.73 (m, 1H,
NH), 3.68, 3.67 (s, 3H, OCH3-α), 3.61, 3.59 (s, 3H, OCH3-γ ), 3.10 (q, 6H,
N(CH2CH3)3), 2.91–2.68 (m, 2H, CH2-β), 1.93 (s, 3H, CH3-5), 1.28 (t, 9H,
N(CH2CH3)3) ppm; 13C NMR (100 MHz, CDCl3): δ 173.9, 173.7, 171.6,
164.5, 151.3, 137.2, 136.9, 134.7, 126.1, 111.4, 89.9, 89.8, 86.1, 86.0, 65.9,
52.6, 52.4, 51.9, 51.8, 45.6, 38.8, 12.5, 12.4, 8.7 ppm; 31P NMR (162 MHz,
CDCl3): δ 59.77, 58.42 ppm; IR (KBr): νmax 3730, 3424, 2954, 2680, 2487,
2377, 1738, 1470, 1225, 1088, 991, 839, 784, 617 cm−1; LRMS (ESI−): m/z
Calcd. for C16H21N3O9PS [M−H]– 462.1; found 462.2.
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