Synthesis of 9-[1-(substituted)-3-(phosphonomethoxy)propyl]adenine derivatives as possible antiviral agents

Article abstract of DOI:10.1080/15257770500268673

□ Acyclic N⁹ adenine nucleosides substituted at C-1′ position were prepared by the Mitsunobu reaction of 1-tert-butyldimethylsilyl-4- pivaloylbutan-1,2,4-triol (5) with adenine. Pivaloyl hydroxyl was modified to the phosphonomethoxy derivatives, and the tert-butyldimethylsilyl hydroxyl was converted to methoxy, azido, amino, fluoro, and α-hydroxyethyl and was eliminated to give vinyl. The resulting phosphonic acids were converted to prodrugs also. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15257770500268673

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Synthesis of 9-[1-(Substituted)-3-
(phosphonomethoxy)propyl]adenine Derivatives as
Possible Antiviral Agents
Minwan Wu a , Yahya El-Kattan a , Tsu-Hsing Lin a , Ajit Ghosh a , Satish Vadlakonda a , Pravin
L. Kotian a , Yarlagadda S. Babu a & Pooran Chand a
a BioCryst Pharmaceuticals, Inc. , Birmingham, Alabama, USA
Published online: 16 Aug 2006.
To cite this article: Minwan Wu , Yahya El-Kattan , Tsu-Hsing Lin , Ajit Ghosh , Satish Vadlakonda , Pravin L. Kotian ,
Yarlagadda S. Babu & Pooran Chand (2005) Synthesis of 9-[1-(Substituted)-3-(phosphonomethoxy)propyl]adenine Derivatives as
Possible Antiviral Agents, Nucleosides, Nucleotides and Nucleic Acids, 24:10-12, 1543-1568, DOI: 10.1080/15257770500268673
To link to this article: http://dx.doi.org/10.1080/15257770500268673
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Nucleosides, Nucleotides, and Nucleic Acids, 24:1543–1568, 2005
c
Copyright ꢀ Taylor & Francis Group, LLC
ISSN: 1525-7770 print/1532-2335 online
DOI: 10.1080/15257770500268673
SYNTHESIS OF
9-[1-(SUBSTITUTED)-3-(PHOSPHONOMETHOXY)PROPYL]ADENINE
DERIVATIVES AS POSSIBLE ANTIVIRAL AGENTS
Minwan Wu, Yahya El-Kattan, Tsu-Hsing Lin, Ajit Ghosh, Satish Vadlakonda,
ᮀ
Pravin L. Kotian, Yarlagadda S. Babu, and Pooran Chand
BioCryst Pharma-
ceuticals, Inc., Birmingham, Alabama, USA
Acyclic N9 adenine nucleosides substituted at C-1ꢀ position were prepared by the Mitsunobu
reaction of 1-tert-butyldimethylsilyl-4-pivaloylbutan-1,2,4-triol (5) with adenine. Pivaloyl hydroxyl
was modified to the phosphonomethoxy derivatives, and the tert-butyldimethylsilyl hydroxyl was
converted to methoxy, azido, amino, fluoro, and -hydroxyethyl and was eliminated to give vinyl.
The resulting phosphonic acids were converted to prodrugs also.
ᮀ
Keywords Acyclic nucleosides; Prodrugs; Antiviral
INTRODUCTION
Viral diseases are one of the major causes of deaths and economic
losses in the world. Out of various viral diseases, HIV, HBV, and HCV
infections are more important and responsible for a large number of
deaths. There are some drugs for HIV, only a few for HBV but no good
drug for HCV. Hepatitis C is a viral liver disease, caused by infection with
the hepatitis C virus (HCV). There are approximately 170 million people
worldwide with chronic HCV infection, of which about 2.7 million are in
the United States.[1] HCV is a leading cause of cirrhosis, a common cause of
hepatocellular carcinoma, and is the leading cause of liver transplantation in
the United States.[2] Currently, α-interferon monotherapy and α-interferon-
ribavirin combination therapy are the only approved treatments for HCV.[3]
Dedicated to the memory of John A. Montgomery.
Received 19 January 2005; accepted 16 May 2005.
The authors thank Drs. Charlie Bugg and Claude Bennett for their encouragement throughout
this work. The authors also express appreciation to Linda Kay First for preparation of this manuscript.
Address correspondence to Pooran Chand, BioCryst Pharmaceuticals, Inc., 2190 Parkway Lake
Drive, Birmingham, AL 35244. Fax: (205)444-4640; E-mail: pchand@biocryst.com
1543

1544
M. Wu et al.
Acyclovir (1a, Chart 1)[4] and ganciclovir (1b, Chart 1)[5–7] are well-
known antiviral drugs used for HIV and herpes virus. For most of the
nucleosides to be active against DNA or RNA viral polymerases, first the
formation of monophosphate occurs through specified kinases and then
triphosphate is formed by cellular kinases. This triphosphate in turn acts
as a viral polymerase inhibitor. A closely related drug, cidofovir, which is a
phosphonic acid derivative and has cytidine base instead of guanine also is
a drug used for herpes virus.[8]
The introduction of phosphonomethyl ether functionality in place of
phosphoric acid ester may be important because: (a) it is expected to be
chemically and metabolically more stable,[9] (b) the β-oxygen atom in phos-
phonomethyl ether functionality enhances the acidity of the phosphonate
and brings its second pKa closer to that of the phosphate ester,[10] and
(c) the oxygen atom in the immediate vicinity of phosphorus has been
demonstrated to play a critical role for the enzymatic phosphorylation and
thus for antiviral activity.[10]
Thus, a number of acyclic nucleoside analogs containing the phospho-
nomethyl ether functional group in place of the phosphoric acid ester
have been reported to have high activity against DNA viruses and retrovi-
ruses.[11,12] These compounds include (Chart 1), PMEA [9-(2-(phosphono-
methoxy)ethyl]adenine (2a), PMPA [9-(2-phosphonomethoxy)propyl]ade-
nine (2c), HPMPA [9-(3-hydroxy-(2-phosphonomethoxy)propyl)]adenine
(2e), FPMPA [9-(3-fluoro-(2-phosphonomethoxy)propyl)]adenine (2f) and
diaminopurine derivatives of PME (2g) and HPMP (2h). Some guanine
derivatives, such as PMEG (3a), PMPG (3b) and HPMPG (3c) are also re-
ported to have a very good profile of antiviral activities.[11–17] Out of these
compounds, two drugs, adefovir dipivoxil (2b) and tenofovir disoproxil
(2d), which are prodrugs of PMEA and PMPA, have been approved by FDA
for HBV and HIV infections, respectively.
There are a number of reports in the literature on modifications of the
base (purine and pyrimidine),[18,19] and substitutions on C-2ꢁ of PMEA. With
respect to the C-1ꢁ position of PMEA or PMPA, there are a limited number
of substitutions reported.[20–23] For example, methyl substitution from the
C-1ꢁ position with the guanine base as the phosphonic acid derivative has
been reported.[10] Other substitutions at the C-1ꢁ position are limited to only
nucleosides; attempts have not been made to prepare phosphonomethyl
ether derivatives and their prodrugs for the evaluation of antiviral activities.
In spite of strong similarity in structures of these compounds, different
modes of action and profiles of antiviral activity have been reported.
The important objective of this study was to examine the effect of the
side chain from the C-1ꢁ position of acyclic nucleosides, their phospho-
nomethyl ether derivatives and corresponding prodrugs on antiviral activity.
Based upon the structure of acyclovir, we have synthesized these compounds

Synthesis of Antiviral Agents
1545
CHART 1
keeping the spacer of 5 atoms between the adenine nitrogen and the phos-
phorus atom (as in acyclovir) and the β-oxygen to the phosphorus atom.
All the compounds synthesized here in this report are the substituted com-
pounds at C-1ꢁ of the acyclic chain.
RESULTS AND DISCUSSION
The synthesis of all the compounds reported here started from racemic
butan-1,2,4-triol, which could be easily made available in each enantiomeric
form from readily available (+) and ( ) malic acid, when needed. There
are some reports in the literature on the preparation of C-1ꢁ-substituted
PMEA and PMPA derivatives for racemic and nonracemic nucleosides.[20–23]
Racemic nucleosides were prepared from γ-butyrolactone[23] and diethyl-
maleate.[20] Nonracemic nucleosides were prepared from butan-1,2,4-triol
and amino acids.[21,22] Jeffery et al.[22] starting from threonine, attempted

1546
M. Wu et al.
the preparation of the C-1ꢁ hydroxymethyl PMPA derivative, but were not
successful because of the migration of the tert-butylsilyl group. However, they
successfully prepared the corresponding deoxygenated compound starting
from D-alanine. In our synthesis, we have chosen the monomethoxytrityl
group as the protecting group to avoid the problem of migration.
The synthesis of the appropriately protected desired phosphonomethyl
ether derivatives is described in Schemes 1–5. Compound 4 (Scheme 1), the
monopivaloyl ester of butan-1,2,4-triol, was prepared from literature proce-
dures from butan-1,2,4-triol.[24,25] The other primary hydroxyl group was
first protected with the trityl group and the resultant compound was sub-
jected to the Mitsunobu reaction, but the yield of the Mitsunobu reaction
SCHEME 1 Reagents: i) TBDMS-Cl, imidazole; ii) Adenine, Ph3P, DIAD; iii) Bu4NF, THF; iv) MMTrCl,
pyridine; v) NaOH; vi) NaH, TsO-CH2-P(O)(O-iPr)2; vii) HCl, CH3CN; viii) NaH, CH3I.

Synthesis of Antiviral Agents
1547
SCHEME 2 Reagents: i) MsCl; ii) NaN3; iii) Ph3P, H2O, THF; iv) MMTrCl, pyridine.
was very poor, probably because of the steric hindrance from the bulky trityl
group. In the later experiments, the primary hydroxyl of 4 was first protected
with the tert-butyldimethylsilyl (TBDMS) group in dichloromethane or DMF
using imidazole as base. The resultant compound 5, under Mitsunobu re-
action conditions with adenine, triphenylphosphine (TPP) and diethyla-
zodicarboxylate (DEAD) or diisopropylazodicarboxylate (DIAD) in dioxane
gave the desired compound 6 in good yield. The product obtained was iden-
tified as the N9 derivative based upon the literature reports[26] and UV spec-
trum at different pH,[27] which did not show any shift in the absorption. On
treatment with tetrabutylammonium fluoride (TBAF), compound 6 gave 7
in which both hydroxyl and amino functionalities were protected with the
monomethoxytrityl (MMTr) group by treating with MMTr-chloride in pyri-
dine to give 8. The pivaloyl group in compound 8 was removed under basic
conditions with sodium hydroxide to give 9, and the free hydroxyl was re-
acted with p-toluenesulfonyloxymethylphosphonate using sodium hydride
as base to give 10, a precursor for the targets 37a and 37i. Methoxy derivative
12 was prepared from 10 by deprotecting the primary hydroxyl selectively,
using 24 mM HCl in acetonitrile and alkylating the resultant 11 with methyl
iodide using sodium hydride as base to give 12, a precursor for the targets

1548
M. Wu et al.
SCHEME 3 Reagents: i) NaOMe; ii) MMTrCl, pyridine; iii) Bu4NF, THF; iv) Dess-Martin; v) MeMgBr;
vi) HCl; vii) TBDMS-Cl, imidazle; viii) NaH,TsO-CH2-P(O)(O-ip)2.
37b and 37j. Similarly the treatment of 11 (Scheme 2) with mesyl chloride
followed by azide displacement with sodium azide gave 14, a precursor for
target 37c. The reduction of azide in 14 with TPP and water in THF gave 15
and again, the resultant amino group was protected with MMTr to give 16,
a precursor for target 37d.
The introduction of the α-hydroxyethyl group in the side chain at the
C-1ꢁ position was achieved as per Scheme 3. The desired precursor 19,
to introduce the α-hydroxyethyl group, was prepared from 6 by removing
pivaloyl under basic conditions (NaOMe), protecting with MMTr and then
deprotecting the TBDMS group in resultant 18 with TBAF. Dess-Martin
oxidation of 19 gave aldehyde 20, which on reaction with methyl magnesium
bromide introduced hydroxyl and methyl as a diastereomeric mixture to
give 21. The mixture was not separable by chromatography, therefore was
taken as such for further modifications. Compound 21 was fully deprotected
under acidic conditions to give 22, the primary hydroxyl was protected
with TBDMS to give 23 and amino and the secondary hydroxyl groups

Synthesis of Antiviral Agents
1549
SCHEME 4 Reagents: i) Adenine, Ph3P, DIAD, 1,4-dioxane; ii) MMTr-Cl, pyridine; iii) Bu4NF, THF;
iv) NaH, TsO-CH2-P(O)(O-ip)2.
were protected with MMTr to give 24. The primary hydroxyl group was
now deprotected by reacting with TBAF and the resultant alcohol 25 was
subjected to phosphonomethylation reaction to give the desired precursor
1
26 for target 37e. Based upon H NMR, the ratio of the diastereomers was
1:2 in all of these compounds (22-25, 36e, and 37e).
The synthesis of precursors 31, 32, and 34 for targets 37f, 37g, and 37h,
respectively, is described in Schemes 4 and 5. Since deoxygenation of 11
failed, the synthesis of 31 was achieved from known 27[28] through the Mit-
sunobu reaction with adenine, protection of the amino group of resultant
28 with MMTr to give 29 and deprotection of TBDMS with TBAF to give 30.
SCHEME 5 Reagents: v) DAST, Et3N; vi) TsCl; vii) NaI, DBU.

1550
M. Wu et al.
The phosphonomethylation reaction of 30 with p-toluenesulfonyloxymethyl-
phosphonate and sodium hydride gave compound 31. The preparation of
32 was first attempted from 13 by the reaction with silver fluoride but this
reaction resulted in a mixture of 32 and the eliminated product 34 which
were not separable by chromatography. Later, 32 was prepared from 11 by
DAST reaction. Compound 34 was obtained through tosylate 33, prepared
from 11 followed by elimination of the tosyl group in 33 with sodium iodide
and DBU.
The precursors 10, 12, 14, 16, 26, 31, 32, and 34 on reaction with
trimethylsilyliodide in the presence of triethylamine gave the desired free
phosphonomethyl derivatives, 35a-35h (Scheme 6). The use of triethylamine
was essential to keep the MMTr protecting group intact, since the further
SCHEME 6 Reagents: i) TMSI, Et3N; ii) ClCH2OC(O)C(CH3)3 or ClCH2OC(O)OCH(CH3)2, Et3N;
iii) HCl.

Synthesis of Antiviral Agents
1551
reactions for the formation of prodrugs were not successful with the free
amino and hydroxyl groups in our hands. The reaction of 35a-35h with
an appropriate chloromethyl pivalate or chloromethyl-2-propylcarbonate
in the presence of triethylamine gave protected prodrugs 36a-36j and the
removal of the MMTr groups under mild acidic conditions yielded the
desired targets 37a-37j.
BIOLOGICAL ACTIVITY
These compounds showed poor activity against HCV virus in replicon
assay.[29]
EXPERIMENTAL
All reagents and solvents were purchased from Aldrich and used as
1
received. H NMR and 13C NMR were recorded on a Bruker 300 MHz
instrument. Chemical shifts (δ) are reported in parts per million (ppm)
referenced to TMS at 0.00 or respective deuterated solvent peak. Coupling
constants (J) are reported in hertz. IR spectra were obtained from films
on NaCl plates for oils or KBr pellets for solids with a scan range of
4000–500 cm−1 on a FT-IR spectrometer (BioRad FTS-3500GX). Mass
spectra data were acquired on a Waters ZMD mass spectrometer coupled
with a Waters System 2695 for loading of the samples in ES positive or
negative mode. HRMS data were recorded on Bruker Bioapex 4.7E. The
elemental analysis (C, H, and N) were performed by Atlantic Microlab in
Norcross, Georgia. The TLC solvent systems, CMA-80 and CMA-50, refer to
chloroform:methanol:conc. NH4OH (80:18:2) and chloroform:methanol:
conc. NH4OH (50:40:10), respectively. Tetraethyl ammonium bicarbonate
is abbreviated as TEAB. The non-UV active compounds were visualized by
charring the TLC plate sprayed with ammonium molybdate/cesium sulfate
spray prepared by dissolving conc. H2SO4 (22.4 mL), CeSO4 (45 mg),
(NH4)6Mo7O24 4 H2O (7 g) in 100 mL water. The olefin compounds were
visualized by using KMnO4 spray. The following conditions were used for
HPLC analysis. Column: Spherisorb ODS 4.6
250 mm. Mobile phase:
solvent A: water, solvent B: MeOH. Gradient: time: 0 min, A: 95%, B: 5%;
time: 20 min, A: 0%, B: 100%; then isocratic for 5 min. Time: 25.1 min,
A: 95, B: 5% then isocratic for 5 min. Flow rate 1.0 mL/min. Run time 30
min. Detection UV at 259 nm.
( )-4-Pivaloylbutan-1,2,4-triol (4). Butan-1,2,4-triol (139.0 g, 1.3 mol)
was stirred with acetone (5.0 L) and p-toluenesulphonic acid monohydrate
(7.0 g, 0.037 mol) at room temperature for 4 h. The mixture was neutralized
with triethylamine and concentrated under vacuum below 40◦C. It was

1552
M. Wu et al.
dissolved in 30% acetone in hexanes (0.5 L) and passed through a short plug
of silica gel and further eluted with 30% acetone in hexanes. The fractions
containing the product were pooled together and concentrated to give 186 g
(98%) of 1,2-isopropylidenebutan-1,2,4-triol which was dissolved in pyridine
(1.5 L) and pivaloyl chloride (161 g, 1.34 mol) added to it over a period of
1 h below 10◦C. The mixture was further stirred at room temperature for
16 h and filtered to remove insoluble material and the pyridine removed
under vacuum from the filtrate. The residue was partitioned between ethyl
acetate and water. The organic layer was separated, washed with water and
brine and dried over MgSO4. After filtration, the filtrate was concentrated
and the residue was taken in 80% acetic acid (2.5 L) and heated at 55◦C for
4 h. Acetic acid was removed under vacuum and the residue was purified
on a silica gel column using ethyl acetate:hexanes as eluent to give 182 g
1
(75%) of the desired target as an oil: H NMR (CDCl3): δ 4.25–4.42 (m,
1H), 4.08–4.22 (m, 1H), 3.60–3.81 (m, 3H), 3.42–3.52 (m, 1H), 2.02–2.12
(m, 1H), 1.65–1.80 (m, 2H), 1.17 (s, 9H).
( )-1-tert-Butyldimethylsilyl-4-pivaloylbutan-1,2,4-triol (5). To a solu-
tion of 4 (70 g, 0.368 mol) in CH2Cl2 (2.0 L) was added imidazole (31.3 g,
0.46 mol) and tert-butyldimethylsilyl chloride (58.2 g, 0.386 mol) and stirred
at room temperature for 3 h. The reaction mixture was diluted with water,
the organic layer separated and washed with water and brine and then dried
over MgSO4. After filtration, the filtrate was concentrated and the residue
was purified on a silica gel column using ethyl acetate:hexanes as eluent
1
to give 91.2 g (81%) of product as an oil: H NMR (DMSO-d6): δ 4.66 (d,
J = 5.2 Hz, 1H), 4.14–3.90 (m, 2H), 3.54–3.25 (m, 3H), 1.84–1.72 (m, 1H),
1.51–1.39 (m, 1H), 1.10 (s, 9H), 0.83 (s, 9H), 0.01 (s, 6H).
( )-9-[(1-tert -Butyldimethylsilyloxymethyl)(3-pivaloyloxy)propyl]ade-
nine (6). To a mixture of 5 (80 g, 0.263 mol), triphenylphosphine (138 g,
0.525 mol) and adenine (71 g, 0.525 mol) in anhydrous dioxane (3.2 L) was
added a solution of DIAD (104 mL, 0.525 mol) in dioxane (400 mL) over
a period of 3.5 h at room temperature and the mixture was stirred further
for 16 h. The reaction mixture was filtered through a short pad of Celite to
remove insoluble materials and the residue purified on a column of silica
gel eluting with chloroform:methanol (100:0 to 97:3) to provide the desired
compound, which was crystallized from ethyl acetate:hexanes (1:3) to afford
77 g (69%) of 6 as a white solid, mp 175–177◦C: 1H NMR (DMSO-d6): 8.14
(s, 1H), 8.08 (s, 1H), 7.15 (bs, 2H), 4.64 (m, 1H), 3.78–4.03 (m, 4H), 2.16–
2.48 (m, 2H), 1.02 (s, 9H), 0.70 (s, 9H), 0.12 (s, 3H) and 0.18 (s, 3H).
IR (KBr, cm−1) 3352, 3166, 2958, 2859, 1721, 1656, 1597, and 1477. MS
(ES+) 422.46 (M+H)+. Anal. calcd for C20H35N5O3Si 0.25 H2O: C, 56.37;
H, 8.39; N, 16.43. Found: C, 56.16; H, 8.13; N, 16.36.

Synthesis of Antiviral Agents
1553
( )-9-[(1-Hydroxymethyl)(3-tert-butylcarbonyloxy)propyl]adenine (7).
Partially purified 6 (91.5 g, obtained from 60.5 g of 5) was dissolved in THF
(1 L) and treated with tetrabutyl ammonium fluoride (1 M in THF, 130
mL) and the reaction mixture stirred at room temperature for 2 h followed
by concentration. The residue was purified on a silica gel column using
chloroform:CMA-80 (1:0 to 1:1) as eluent to give 21.1 g (35%, 2 steps) of
1
7 as a white solid, mp 188◦C: H NMR (DMSO-d6): δ 8.20 (s, 1H), 8.13 (s,
1H), 7.22 (bs, 2H), 5.16 (t, J = 5.4 Hz, 1H), 4.69–4.59 (m, 1H), 4.04–3.71
(m, 4H), 2.44–2.19 (m, 2H), 1.07 (s, 9H). IR (KBr, cm−1) 3334, 3172, 2968,
1727, 1676, 1607, and 1164. Anal. calcd for C14H21N5O3: C, 54.71; H, 6.89;
N, 22.79. Found: C, 54.41; H, 6.90; N, 22.48.
( )-9-[(1-Monomethoxytrityloxymethyl)(3-tert -butylcarbonyloxy)pro-
pyl]-N6-monomethoxytrityladenine (8). A solution of 7 (21 g, 0.068 mol)
in pyridine (370 mL) was treated with monomethoxytrityl chloride (86.2 g,
0.28 mol) and the reaction mixture heated at 70◦C with stirring for 20 h.
It was diluted with ethyl acetate (1.5 L) and washed with water (2 ) and
brine and the organic layer dried over MgSO4. After filtration, the filtrate
was concentrated and the residue purified on a silica gel column using ethyl
acetate:hexanes as eluent (0:1 to 1:1) to give 60.0 g (98%) of product as a
1
yellow solid: H NMR (DMSO-d6): δ 8.33 (s, 1H), 7.72 (s, 1H), 7.29–6.81
(m, 25H), 6.75 (d, J = 9.0 Hz, 2H), 6.67 (d, J = 9.1 Hz, 2H), 4.77–4.65
(m, 1H), 3.93–3.73 (m, 2H), 3.62 (s, 6H), 3.40–3.29 (m, 1H), 3.16–3.05 (m,
1H), 2.58–2.43 (m, 1H), 2.10–1.97 (m, 1H), 1.90 (s, 9H). IR (KBr, cm−1
)
3419, 2959, 1730, 1605, 1508, and 1250. MS (ES+) 874.27 (M+Na)+.
( )-9-[(1-Monomethoxytrityloxymethyl)(3-hydroxy)propyl]-N6 -mono-
methoxytrityladenine (9). A solution of 8 (59.5 g, 0.070 mol) in THF (375
mL) and methanol (150 mL) was treated with 2N NaOH (175 mL, 0.35
mol) at room temperature and stirred for 16 h. The reaction mixture was
neutralized with acetic acid to pH 8.0 and diluted with ethyl acetate (1.0 L)
and washed with water (2 ) and brine and the organic layer dried over
MgSO4. After filtration, the filtrate was concentrated and the residue was
purified on a silica gel column using ethyl acetate:hexanes:methanol (1:1:0
1
to 1:1:0.1) as eluent to give 49.8 g (92%) of product as a white solid: H
NMR (DMSO-d6): δ 8.31 (s, 1H), 7.70 (s, 1H), 7.28–6.83 (m, 25H), 6.74 (d,
J = 8.8 Hz, 2H), 6.66 (d, J = 9.1 Hz, 2H), 4.78–4.67 (m, 1H), 4.46 (t, J =
5.3 Hz, 1H ), 3.61 (s, 6H), 3.34–2.98 (m, 4H), 2.30–2.14 (m, 1H), 1.96–1.80
(m, 1H). IR (KBr, cm−1) 3412, 2932, 1734, 1608, and 1508. MS (ES+) 790.26
(M+Na)+.
( )-9-[(1-Monomethoxytrityloxymethyl)(3-(diisopropylphosphono)
methoxy)propyl]-N6-monomethoxytrityladenine (10). A solution of 9 (32 g,

1554
M. Wu et al.
41.7 mmol) in DMF (360 mL) was treated with sodium hydride (60%, 6.7 g,
167.5 mmol) at room temperature and the mixture was stirred for 1 h. To
this solution was then added a solution of p-toluenesulfonyloxymethylphos-
phonate (17.6 g, 50.2 mmol) in DMF (30 mL) and the mixture stirred at
room temperature for 24 h. The reaction mixture was diluted with ethyl
acetate (2 L), neutralized with acetic acid and washed with water (2 ) and
brine and the organic layer dried over MgSO4. After filtration, the filtrate
was concentrated and the residue purified on a silica gel column using ethyl
acetate:hexanes:methanol (1:1:0 to 1:1:0.05) as eluent to give 13.2 g (33%)
1
of product as a white solid: H NMR (DMSO-d6): δ 8.36 (s, 1H), 7.78 (s,
1H), 7.36–6.85 (m, 25H), 6.82 (d, J = 9.1 Hz, 2H), 6.74 (d, J = 8.8 Hz,
2H), 4.80–4.67 (m, 1H), 4.55–4.40 (m, 2H), 3.69 (s, 6H), 3.60 (d, J = 7.7
Hz, 2H), 3.45–3.25 (m, 3H), 3.20–3.10 (m, 1H), 2.47–2.37 (m, 1H), 2.18–
2.00 (m, 1H), 1.19–1.10 (m, 12H). IR (KBr, cm−1) 3418, 2978, 1606, 1508,
and 1250. Anal. calcd for C56H60N5O11P 0.5 H2O 0.25 EtOAc: C, 70.06; H,
6.50; N, 7.17. Found: C, 69.85; H, 6.49; N, 7.29.
( )-9-[(1-Hydroxymethyl)(3-(diisopropylphosphono)methoxy)propyl]-
N6-monomethoxytrityladenine (11). A solution of 10 (3.1 g, 3.3 mmol)
in acetonitrile (125 mL) was treated with conc. HCl (0.25 mL) at room
temperature and the mixture stirred for 1 h. The reaction was neutralized
by adding triethylamine (1 mL) and diluted with ethyl acetate (300 mL).
It was then washed with water (2 ) and brine and the organic layer dried
over MgSO4. After filtration, the filtrate was concentrated and the residue
purified on a silica gel column using ethyl acetate:hexanes:methanol (1:1:0
1
to 1:1:0.2) as eluent to give 1.21 g (55%) of 11 as a white solid: H NMR
(DMSO-d6): δ 8.13 (s, 1H), 7.82 (s, 1H), 7.28–7.10 (m, 13H), 6.78 (d, J =
8.9 Hz, 2H), 4.97 (t, J = 5.3 Hz, 1H), 4.53–4.40 (m, 3H), 3.81–3.54 (m,
4H), 3.65 (s, 3H), 3.41–3.22 (m, 2H), 2.22–2.00 (m, 2H), 1.18–1.06 (m,
12H). IR (KBr, cm−1) 3415, 2979, 1605, 1470, and 1250. Anal. calcd for
C36H44N5O6P 0.3 H2O 0.3 EtOAc: C, 63.32; H, 6.71; N, 9.93. Found: C,
63.42; H, 6.80; N, 9.92.
( )-9-[(1-Azidomethyl)(3-(diisopropylphosphono)methoxy)propyl]-N6-
monomethoxytrityladenine (14). A solution of 11 (0.5 g, 0.74 mmol) in
pyridine (10 mL) was treated with methanesulphonyl chloride (0.132 g,
1.15 mmol) at 0◦C and the mixture stirred for 20 h at room temperature.
The reaction mixture was diluted with ethyl acetate (100 mL), washed with
water (2 ) and brine and the organic layer dried over MgSO4 followed by
filtration and concentration. The residue (13) was dissolved in DMF (5 mL),
treated with sodium azide (0.138 g, 2.1 mmol) and the mixture stirred for
4 h at 100◦C. The reaction mixture was diluted with ethyl acetate (200 mL),
washed with water (2 ) and brine and the organic layer dried over MgSO4.

Synthesis of Antiviral Agents
1555
After filtration, the filtrate was concentrated to give 511 mg (99%, two steps)
of product as a light yellow oil: 1H NMR (CDCl3): δ 8.01 (s, 1H), 7.82 (s, 1H),
7.40–7.15 (m, 13H), 6.80 (d, J = 9.0 Hz, 2H), 4.81–4.67 (m, 3H), 4.21–4.10
(m, 1H), 3.82–3.55 (m, 4H), 3.78 (s, 3H), 3.35–3.25 (m, 1H), 2.49–2.19 (m,
2H), 1.39–1.29 (m, 12H). IR (KBr, cm−1) 3418, 2979, 2104, 1605, 1472, and
1250. Anal. calcd for C36H43N8O5P: C, 61.88; H, 6.20; N, 16.04. Found: C,
61.80; H, 6.25; N, 15.38. HRMS calcd for C36H43N8O5P (M+H)+ 699.3172.
Found 699.3149.
(
)-9-[(1-Aminomethyl)(3-(diisopropylphosphono)methoxy)propyl]-
N6-monomethoxytrityladenine (15). A mixture of 14 (0.95 g, 1.36 mmol)
in THF (9.5 mL) and water (1.9 mL) was treated with triphenylphosphine
(0.76 g, 2.9 mmol) and stirred at room temperature for 15 h. The reaction
mixture was concentrated and purified on a column using chloroform:CMA-
80 (1:0 to 1:1) as eluent to give 0.687 g (75%) as a light yellow oil: 1H NMR
(CDCl3): δ 8.01(s, 1H), 7.86 (s, 1H), 7.38–7.18 (m, 13H), 6.80 (d, J = 8.8
Hz, 2H), 4.80–4.66 (m, 2H), 4.65–4.55 (m, 1H), 3.78 (s, 3H), 3.64 (d, J =
8.5 Hz, 2H), 3.62–3.53 (m, 1H), 3.43 (dd, J = 13.5, 8.1 Hz, 1H), 3.43–
3.23 (m, 1H), 3.14 (dd, J = 13.5, 4.2 Hz, 1H), 2.41–2.17 (m, 2H), 2.10–
1.70 (2H), 1.35–1.29 (m, 12H). HRMS calcd for C36H45N6O5P (M+H)+
673.3267. Found 673.3292.
( )-9-[(1-N-Monomethoxytritylaminomethyl)(3-(diisopropylphospho-
no)methoxy)propyl]-N6-monomethoxytrityladenine (16). It was prepared
from 15 (652 mg) by following the same procedure as given for 8 except 2
equivalents of monomethoxytrityl chloride were used. The crude product
was purified on a silica gel column using ethyl acetate:hexanes:methanol
1
(1:1:0 to 1:1:0.1) as eluent to give 16 as a light yellow oil (yield: 69%): H
NMR (DMSO-d6): δ 8.21 (s, 1H), 7.79 (s, 1H), 7.37–6.85 (m, 25H), 6.81
(d, J = 9.0 Hz, 2H), 6.67 (d, J = 8.8 Hz, 2H), 4.62–4.39 (m, 3H), 3.66
(s, 3H), 3.65 (s, 3H), 3.55 (dd, J = 7.9, 3.6 Hz, 2H), 3.37–3.21 (m, 2H),
2.80–2.65 (m, 1H), 2.57–2.37 (m, 1H), 2.19–2.05 (m, 1H), 2.00–1.85 (m,
1H), 1.17–1.07 (m, 12H). IR (KBr, cm−1) 3419, 2978, 1605, 1508, and 1251.
Anal. calcd for C56H61N6O6P 1.0 H2O: C, 70.50; H, 6.55; N, 8.81. Found: C,
70.34; H, 6.53; N, 8.57. HRMS calcd for C56H61N6O6P (M+H)+ 945.4468.
Found 945.4474.
( )-9-[(1-tert-Butyldimethylsilyloxymethyl)(3-hydroxy)propyl]adenine
(17). To a solution of 6 (45 g, 0.107 mol) in MeOH (1.0 L) was added
NaOMe (5.4 M solution in MeOH, 39 mL, 0.213 mol) and the reaction mix-
ture was stirred at room temperature for 5 h. The solution was neutralized
with acetic acid and concentrated. The residue was purified on a silica gel
column using ethyl acetate:hexanes:methanol (1:19:0 to 1:1:0.1) as eluent to

1556
M. Wu et al.
provide 25 g (69%) of 17 as a white solid, mp 112–114◦C: 1H NMR (DMSO-
d6): 8.09 (s, 1 H), 8.08 (s, 1H), 7.15 (bs, 2H), 4.62–4.70 (m, 1H), 4.58 (t,
J = 4.9 Hz, 1H), 3.96–4.16 (m, 1H), 3.81–3.90 (m, 1H), 3.18–3.44 (m, 2H),
1.96–2.26 (m, 2 H). 0.70 (s, 9H), 0.14 (s, 3H), and 0.22 (s, 3H). IR (KBr,
cm−1) 3334, 3186, 2929, 2856, 1657, 1600, 1471, and 1414. MS (ES+) 338.49
(M+H). Anal. calcd for C15H27N5O2Si: C, 53.38; H, 8.06; N, 20.75. Found:
C, 53.43; H, 8.29; N, 20.65.
( )-9-[(1-tert -Butyldimethylsilyloxymethyl)(3-monomethoxytrityloxy)
propyl]-N6-monomethoxytrityladenine (18). It was prepared from 17 (25.0
g) by the same method used for 8 and obtained in 91% yield as a white solid,
mp 88–92◦C: 1H NMR (DMSO-d6): 8.16 (s, 1H), 7.88 (s, 1H), 7.02–7.36 (m,
25H), 6.83 (d, J = 8.8 Hz, 2H), 6.77 (d, J = 8.8 Hz, 2H), 4.84 (m, 1H),
3.70–3.94 (m, 2H), 3.71(s, 3H), 3.69 (s, 3H), 2.74–2.98 (m, 2H), 2.08–2.48
(m, 2H). 0.67 (s, 9H), 0.157 (s, 3H), and 0.24 (s, 3H). IR (KBr, cm−1
)
3416, 3030, 2951, 1604, 1508, 1467, and 1296. MS (ES+) 882.53 (M+H)+.
Anal. calcd for C55H59N5O4Si: C, 74.48; H, 6.78; N, 7.78. Found: C, 74.79;
H, 6.83; N, 7.43.
( )-9-[(1-Hydroxymethyl)(3-monomethoxytrityloxy)propyl]-N6-mono-
methoxytrityladenine (19). A solution of 18 (10.6 g, 12.02 mmol) in THF
(120 mL) was treated with tetrabutyl ammonium fluoride (1 M in THF, 12.1
mL) and the reaction mixture stirred at room temperature for 2 h followed
by concentration. The residue was purified on a silica gel column using ethyl
acetate:hexanes:methanol (1:1:0 to 1:1:0.1) to give 8.87 g (96%) of 19 as a
white solid: 1H NMR (DMSO-d6): δ 8.21 (s, 1H), 7.92 (s, 1H), 7.38–7.05 (m,
25H), 6.89 (d, J = 9.1 Hz, 2H), 6.82 (d, J = 9.0 Hz, 2H), 5.09 (t, J = 5.4 Hz,
1H), 4.88–4.77 (m, 1H), 3.77–3.70 (m, 2H), 3.76 (s, 3H), 3.73 (s, 3H), 2.96–
2.76 (m, 2H), 2.44–2.27 (m, 1H), 2.27–2.11 (m, 1H). IR (KBr, cm−1) 3412,
2932, 1734, 1606, 1509, 1251, and 1033. Anal. calcd for C49H45N5O4 0.25
H2O 0.4 EtOAc: C, 75.25; H, 6.08; N, 8.67. Found: C, 75.35; H, 6.04; N, 8.50.
( )-9-[(1-(2-Hydroxy)ethyl)(3-hydroxy)propyl]adenine (22). A solution
of 19 (4.16 g, 5.42 mmol) in methylene chloride (300 mL) was treated
with Dess-Martin reagent (4.74 g, 97%, 10.84 mmol) and stirred at room
temperature for 4 h. The reaction mixture was concentrated and purified
on a silica gel column using hexanes:ethyl acetate (1:0 to 1:2) as eluent
to provide 20 (white solid, 1.35 g) and its derivative with loss of one MMTr
group (white solid, 1.18 g). The combined products (2.5 g) were dissolved in
THF (150 mL), treated with 3 M methyl magnesium bromide (10.9 mL, 32.7
mmol) and the mixture stirred for 8 h at room temperature. The reaction
mixture was diluted with chloroform (400 mL) and water (100 mL). After
filtration through Celite and separation, the organic layer was dried over
MgSO4 followed by filtration and concentration. The residue (21 and its

Synthesis of Antiviral Agents
1557
derivative with loss of one MMTr) was dissolved in acetonitrile (300 mL) and
water (14 mL), treated with 2 M HCl (1.5 mL) at room temperature, and the
mixture stirred for 14 h. The reaction mixture was diluted with water (100
mL) and neutralized by adding 0.5 N NaOH followed by concentration to
remove most of the organic solvent. The aqueous phase was extracted with
ethyl acetate (2 100 mL) and concentrated to dryness. The residue was
treated with MeOH (100 mL) and filtered. The filtrate was concentrated
and purified on a silica gel column using chloroform:CMA-80 (1:0 to 0:1)
as eluent to give 472 mg (37%, three steps) of 22 as a colorless oil: 1H NMR
(a mixture of diastereomers, DMSO-d6): δ 8.17, 8.167, 8.11 (3s, 2H), 7.26,
7.25 (2s, 2H), 5.24, 5.17 (2d, J = 5.2 Hz each, 1H), 4.61–4.50 (m, 2H),
4.20–4.05 (m, 1H), 3.40–3.09 (m, 2H), 2.30–2.03 (m, 2H), 0.98, 0.96 (d,
J = 6.2 Hz each, 3H). HRMS calcd for C10H15N5O2 (M+H)+ 238.1304.
Found 238.1307.
( )-9-[(1-(α-Hydroxy)ethyl)(3-tert -butyldimethylsilyloxy)propyl]ade-
nine (23). The same method was used as for compound 5. The residue was
purified on a silica gel column using chloroform:CMA-80 (1:0 to 1:1) to give
415 mg (64%) of 23 as a white solid: 1H NMR (a mixture of diastereomers,
DMSO-d6): δ 8.24, 8.239, 8.18 (3s, 2H), 7.32, 7.30 (2s, 2H), 5.32, 5.24 (d,
J = 5.0 Hz each, 1H), 4.72–4.51 (m, 1H), 4.22–4.10 (m, 1H), 3.70–3.60 (m,
1H), 3.49–3.35 (m, 1H), 2.45–2.12 (m, 2H), 1.06, 1.04 (d, J = 6.2 Hz each,
3H), 0.93, 0.91 (s, 9H), 0.00, 0.02 (2s, 6H). HRMS calcd for C16H29N5O2Si
(M+H)+ 352.2168. Found 352.2176.
( )-9-[(1-(α-Monomethoxytrityloxy)ethyl)(3-tert-butyldimethylsilyloxy)
propyl]-N6-monomethoxytrityladenine (24). It was prepared from 23 (392
mg) by following the same procedure as given for 8. The crude product
was purified on a silica gel column using ethyl acetate:hexanes (1:0 to 2:1)
1
as eluent to give 66% of product as a colorless oil: H NMR (a mixture of
diastereomers, DMSO-d6): δ 8.39, 8.38, 7.99, 7.95 (4s, 2H), 7.57–7.23 (m,
25H), 7.08–6.89 (m, 4H), 4.91–4.76 (1H), 3.93, 3.92, 3.91, 3.88 (4s, 6H),
3.87–3.35 (m, 3H), 2.97–2.43 (m, 2H), 0.99, 0.92 (d, J = 6.0 Hz each, 3H),
0.93 (s, 9H), 0.03, 0.01, 0.00, 0.04 (4s, 6H). HRMS calcd for C56H61N5O4Si
(M+H)+ 1089.4891. Found 1089.4859.
( )-9-[(1-(α-Monomethoxytrityloxy)ethyl)(3-hydroxy)propyl]-N6-mono-
methoxytrityladenine (25). It was prepared from 24 (640 mg) by following
the same procedure as given for 19. The crude product was purified on a
silica gel column using a mixture of ethyl acetate:hexanes:methanol (1:1:0
1
to 1:1:0.1) as eluent to give 90% of product as a colorless film: H NMR (a
mixture of diastereomers, DMSO-d6): δ 8.26, 8.23 (2s, 1H), 7.79, 7.77 (2s,
1H), 7.45–6.71 (m, 29H), 4.73–4.50 (m, 2H), 3.76, 3.74, 3.72, 3.71 (4s, 6H),
3.54–3.40 (m, 1H), 3.27–3.12 (m, 1H), 3.09–2.93 (m, 1H), 2.59–2.12, 1.99–

1558
M. Wu et al.
1.83 (2m, 2H), 0.84, 0.80 (d, J = 6.1 Hz each, 3H). IR (KBr, cm−1) 3414,
1737, 1606, 1508, 1250, and 1033.
(
)-9-[(1-Methyl)(3-hydroxy)propyl]-N6 -monomethoxytrityladenine
(30). Compound 27 (1.93 g) was converted to 28 according to the proce-
dure used for 6. A small amount of the product was chromatographed two
times (eluting with CHCl3: MeOH, 100:0 to 95:5) to get the pure 28 for
characterization: 1H NMR (DMSO-d6): δ 8.28 (s, 1H), 8.20 (s, 1H), 7.26 (s,
2H), 4.89–4.76 (m, 1H), 3.67–3.56 (m, 1H), 3.54–3.44 (m, 1H), 2.41–2.27
(m, 1H), 2.20–2.04 (m, 1H), 1.61 (d, J = 7.1 Hz, 3H), 0.90 (s, 9H), 0.006 (s,
3H), 0.00 (s, 3H). HRMS calcd for C15H27N5OSi (M+H)+ 322.2063. Found
322.2066.
Impure compound 28 (chromatographed once) was converted to 29
with the method used for 8 (2 eq. of monomethoxytrityl chloride used)
and the TBDMS group of 29 was removed by the procedure used for 19.
The resultant crude product was purified on a silica gel column using ethyl
acetate:hexanes:methanol (1:1:0 to 1:1:0.2) as eluent to give 1.97 g (43%,
three steps) of 30 as a white solid: 1H NMR (DMSO-d6): δ 8.33 (s, 1H), 7.94
(s, 1H), 7.38–7.22 (m, 13H), 6.89 (d, J = 9.0 Hz, 2H), 4.82–4.73 (m, 1H),
4.59 (t, J = 5.1 Hz, 1H), 3.76 (s, 3H), 3.39–3.21 (m, 2H), 2.26–1.94 (m, 2H),
1.55 (d, J = 6.8 Hz, 3H). IR (KBr, cm−1) 3410, 2933, 1605, 1470, and 1250.
Anal. calcd for C29H29N6O2 0.2 H2O: C, 72.09; H, 6.13; N, 14.49. Found:
C, 71.99; H, 6.20; N, 14.33.
(
)-9-[(1-Fluoromethyl)(3-(diisopropylphosphono)methoxy)propyl]-
N6-monomethoxytrityladenine (32). A solution of 11 (1.0 g, 1.48 mmol) in
methylene chloride (20 mL) was treated with triethylamine (1.6 mL, 11.5
mmol) followed by DAST (0.6 mL, 4.54 mmol) and the reaction mixture
stirred for 18 h at room temperature. This was then treated with 1 M TBAF
(3.7 mL, 3.7 mmol) and stirred for 6 days and then concentrated. The
residue was purified on a silica gel column using ethyl acetate:hexanes:
methanol (1:1:0 to 1:1:0.3) as eluent to give 0.232 g (23%) of 32 as a colorless
oil and 0.567 g (57%) of the starting material recovered: 1H NMR (DMSO-
d6): δ 8.20 (s, 1H), 7.79 (s, 1H), 7.29–7.05 (m, 13H), 6.73 (d, J = 9.0
Hz, 2H), 4.92–4.51 (m, 3H), 4.48–4.37 (m, 2H), 3.60 (s, 3H), 3.55 (dd,
J = 7.9, 2.1 Hz, 2H), 3.40–3.20 (m, 2H), 2.20–2.00 (m, 2H), 1.12–1.00 (m,
12H). IR (KBr, cm−1) 3418, 2979, 1606, 1511, and 1472. Anal. calcd for
C36H43FN5O5P 1.0 H2O: C, 62.33; H, 6.54; N, 10.10. Found: C, 62.56; H,
6.38; N, 10.29.
( )-9-[(1-Tosyloxymethyl)(3-(diisopropylphosphono)methoxy)propyl]-
N6-monomethoxytrityladenine (33). A solution of 11 (1.18 g, 1.75 mmol)
in pyridine (25 mL) was treated with 4-toluenesulphonyl chloride (0.681 g,
3.5 mmol) at 5◦C and the mixture was stirred for 15 h at room temperature.

Synthesis of Antiviral Agents
1559
The reaction was not complete so more 4-toluenesulphonyl chloride (0.34 g,
1.8 mmol) was added and again stirred at room temperature for 8 h. The
reaction mixture was diluted with EtOAc (300 mL), washed with water (2 )
and brine, and dried over MgSO4. After filtration and concentration, the
residue was purified on a silica gel column using ethyl acetate:hexanes:
methanol (1:1:0 to 1:1:0.2) as eluent to give 1.11 g (76%) of product as a
white solid: 1H NMR (DMSO-d6): δ 8.03 (s, 1H), 7.55 (s, 1H), 7.26–6.97 (m,
17H), 6.72 (d, J = 9.0 Hz, 2H), 4.71–4.59 (m, 1H), 4.45–4.20 (m, 4H), 3.56
(s, 3H), 3.50–3.42 (m, 2H), 3.30–3.08 (m, 2H), 2.14 (s, 3H), 2.07–1.93 (m,
2H), 1.10–0.95 (m, 12H). IR (KBr, cm−1) 3419, 2980, 1606, 1472, and 1250.
Anal. calcd for C43H50N5O8SP 0.25 H2O 0.1 EtOAc: C, 61.96; H, 6.15; N,
8.33. Found: C, 61.87; H, 6.04; N, 8.17.
( )-9-[(1-Methylene)(3-(diisopropylphosphono)methoxy)propyl]-N6-
monomethoxytrityladenine (34). A solution of 33 (1.06 g, 1.28 mmol) in
DMF (3.0 mL) was treated with sodium iodide (0.485 g, 3.20 mmol) and
heated at 50◦C for 6 h. The solution was cooled to room temperature and
DBU (0.294 g, 1.93 mmol) in DMF (0.5 mL) added and heated at 80◦C
for 3 h. The solution on cooling was diluted with ethyl acetate (100 mL),
washed with water and brine, and dried over MgSO4. After filtration, the
filtrate was concentrated and the residue purified on a silica gel column
using ethyl acetate:methanol (19:0 to 19:1) as eluent to give 0.694 g (82%)
1
of product as a pale yellow oil: H NMR (CDCl3): δ 8.06 (s, 1H), 7.86 (s,
1H), 7.45–7.15 (m, 13H), 6.80 (d, J = 8.9 Hz, 2H), 5.47 (s, 1H), 5.27 (s,
1H), 4.80–4.66 (m, 2H), 3.78 (s, 3H), 3.80–3.64 (m, 4H), 3.07 (t, J = 5.84
Hz, 2H), 1.35–1.26 (m, 12H). IR (neat, cm−1) 3020, 1604, 1471, 1216, and
766. Anal. calcd for C36H42N5O5P 0.25 H2O 0.25 EtOAc: C, 65.14; H, 6.57;
N, 10.27. Found: C, 65.26; H, 6.52; N, 10.15.
( )-9-[(1-Monomethoxytrityloxymethyl)(3-phosphonomethoxy)propyl]-
N6-monomethoxytrityladenine (35a). A suspension of 10 (16.7 g, 17.7 mmol)
in DMF (170 mL) was treated with triethylamine (15 mL) followed by tri-
methylsilyliodide (25 mL, 174.9 mmol) and the reaction mixture flask cov-
ered with aluminum foil to protect from light and stirred for 14 h at room
temperature. It was then diluted with TEAB buffer (500 mL), water (750
mL), and chloroform (1.5 L) and stirred for 1 h. The organic phase was
collected and the aqueous phase extracted with chloroform (3 ). The com-
bined organic extracts were dried over MgSO4. After filtration, the filtrate
was concentrated and the residue purified on a silica gel column using
chloroform:methanol (1:0 to 85:15), then CMA-80:CMA-50 (1:0 to 0:1) as
1
eluent to give 7.0 g (46%) of 35a as a yellow solid: H NMR (DMSO-d6): δ
8.29 (s, 1H), 7.67 (s, 1H), 7.30–6.81 (m, 25H), 6.75 (d, J = 9.1 Hz, 2H),
6.65 (d, J = 9.1 Hz, 2H), 4.78–4.65 (m, 1H), 3.61 (s, 3H), 3.60 (s, 3H),
3.40–2.99 (m, 6H), 2.36–2.20 (m, 1H), 2.04–1.87 (m, 1H). HRMS calcd for
C50H48N5O7P (M+H)+ 862.3369. Found 862.3409.

1560
M. Wu et al.
(
)-9-[(1-Methoxymethyl)(3-phosphonomethoxy)propyl]-N6 -mono-
methoxytrityladenine (35b). A solution of 11 (0.5 g, 0.74 mmol) in DMF
(6.0 mL) was treated with sodium hydride (60%, 0.12 g, 3.0 mmol) at room
temperature and the mixture stirred for 0.5 h. To this mixture was then
added a solution of methyliodide (0.125 g, 0.88 mmol) in DMF (1 mL) and
the mixture stirred at room temperature for 12 h. The reaction mixture
was diluted with ethyl acetate (15 mL), neutralized with acetic acid and
chloroform (200 mL) added. The mixture was washed with water (2 )
and brine and the organic layer dried over MgSO4 followed by filtration
and concentration. The residue containing 12 was converted to 35b with
the same procedure used for 35a. The product was purified on a silica gel
column using chloroform:methanol (1:0 to 85:15), then CMA-80:CMA-50
(1:0 to 0:1) as eluent to give 222 mg (50%, two steps) of 35b as an off-white
film: 1H NMR (DMSO-d6): δ 8.31 (s, 1H), 7.87 (s, 1H), 7.38–7.16 (m, 13H),
6.84 (d, J = 8.9 Hz, 2H), 4.86–4.75 (m, 1H), 4.02–3.93 (m, 1H), 3.73–3.13
(m, 5H), 3.71 (s, 3H), 3.16 (s, 3H), 2.15–2.03 (m, 2H). HRMS calcd for
C31H34N5O6P (M+H)+ 604.2325. Found 604.2345.
( )-9-[(1-Azidomethyl)(3-phosphonomethoxy)propyl]-N6 -monometh-
oxytrityladenine (35c). It was prepared from 14 (345 mg) with the same
procedure as given for 35a. The product was purified on a silica gel column
using chloroform:methanol (1:0 to 85:15), then CMA-80:CMA-50 (1:0 to
0:1) as eluent to give 35c as a colorless film (yield, 63%): 1H NMR (DMSO-
d6): δ 8.39 (s, 1H), 7.89 (s, 1H), 7.37–7.11 (m, 13H), 6.84 (d, J = 9.0 Hz,
2H), 4.85–4.74 (m, 1H), 4.11 (dd, J = 11.7, 9.7 Hz, 1H), 3.87 (dd, J = 14.2,
4.1 Hz, 1H), 3.71 (s, 3H), 3.49–3.37 (m, 1H), 3.32–3.12 (m, 3H), 2.23–
2.06 (m, 2H). HRMS calcd for C30H31N8O5P (M+H)+ 615.2233. Found
615.2226.
( )-9-[(1-N-Monomethoxytritylaminomethyl)(3-phosphonomethoxy)
propyl]-N6-monomethoxytrityladenine (35d). It was prepared from 16 (540
mg) with the same procedure as given for 35a. The crude product was
purified on a silica gel column using chloroform:methanol (1:0 to 85:15),
then CMA-80:CMA-50 (1:0 to 0:1) as eluent to give 35d as a colorless film
1
(yield, 52%): H NMR (DMSO-d6): δ 8.33 (s, 1H), 7.80 (s, 1H), 7.41–6.92
(m, 25H), 6.84 (d, J = 9.0 Hz, 2H), 6.69 (d, J = 8.8 Hz, 2H), 4.74–4.61 (m,
1H), 3.69 (s, 3H), 3.67 (s, 3H), 3.34–2.32 (m, 7H), 2.16–2.04 (m, 1H), 1.96-
1.84 (m, 1H). HRMS calcd for C50H49N6O6P (M+H)+ 861.3529. Found
861.3568.
( )-9-[(1-Methyl)(3-phosphonomethoxy)propyl]-N6-monomethoxytrit-
yladenine (35f). Compound 30 (1.87 g) was converted to 31 with the same
method used for compound 10 and the resultant 31 was converted to 35f

Synthesis of Antiviral Agents
1561
following the same procedure used for 35a. The residue was purified on
a silica gel column using chloroform:methanol (1:0 to 85:15), then CMA-
80:CMA-50 (1:0 to 0:1) as eluent to give 760 mg (34%, two steps) of 35f
as a colorless film: 1H NMR (DMSO-d6): δ 8.33 (s, 1H), 7.88 (s, 1H), 7.35–
7.13 (m, 13H), 6.83 (d, J = 9.0 Hz, 2H), 4.79–4.66 (m, 1H), 3.70 (s, 3H),
3.45–3.31 (m, 1H), 3.31–3.12 (m, 3H), 2.23–2.10 (m, 1H), 2.10–1.97 (m,
1H), 1.51 (d, J = 6.8 Hz, 3H). HRMS calcd for C30H32N5O5P (M+H)+
574.2219. Found 574.2243.
( )-9-[(1-Methylene)(3-phosphonomethoxy)propyl]-N6-monomethoxy-
trityladenine (35h). It was prepared from 34 (597 mg) with the same
procedure as given for 35a. The crude product was purified on a silica gel
column using chloroform:methanol (1:0 to 85:15), then CMA-80:CMA-50
(1:0 to 0:1) as eluent to give 35h as an off-white solid (yield, 57%): 1H NMR
(DMSO-d6): δ 8.41 (s, 1H), 7.92 (s, 1H), 7.40–7.15 (m, 13H), 6.84 (d, J =
8.9 Hz, 2H), 5.61 (s, 1H), 5.25 (s, 1H), 3.70 (s, 3H), 3.57 (t, J = 6.3 Hz,
2H), 3.31 (d, J = 8.3 Hz, 2H), 2.96 (t, J = 6.3 Hz, 2H). HRMS calcd for
C30H30N5O5P (M+H)+ 572.2062. Found 572.2084.
(
)-9-[(1-Monomethoxytrityloxymethyl)(3-(di-tert -butylcarbonyloxy-
methylphosphono)methoxy)propyl]-N6 -monomethoxytrityladenine (36a).
A solution of 35a (500 mg, 0.58 mmol) in DMF (31 mL) was treated with
triethylamine (31 mL) followed by chloromethyl pivalate (11.2 mL, 76.93
mmol) and stirred for 3 days at room temperature. It was then diluted with
chloroform (300 mL) and washed with water (2 ). The organic layer was
dried over MgSO4. After filtration, the filtrate was concentrated and the
residue purified on a silica gel column using ethyl acetate:hexanes:methanol
(1:1:0 to 1:1:0.1) as eluent to give 174 mg (28%) of 36a as a colorless film:
1H NMR (DMSO-d6): δ 8.13 (s, 1H), 7.54 (s, 1H), 7.14–6.65 (m, 25H), 6.60
(d, J = 9.1 Hz, 2H), 6.51 (d, J = 9.1 Hz, 2H), 5.38–5.26 (m, 4H), 4.57–4.43
(m, 1H), 3.59–3.40 (m, 2H), 3.46 (s, 6H), 3.25–2.85 (m, 4H), 2.29–2.17
(m, 1H), 1.91–1.76 (m, 1H), 0.88 (s, 18H). HRMS calcd for C62H68N5O11P
(M+H)+ 1090.4731. Found 1090.4761.
( )-9-[(1-Methoxymethyl)(3-(di-tert-butylcarbonyloxymethylphospho-
no)methoxy)propyl]-N6-monomethoxytrityladenine (36b). It was prepared
from 35b (160 mg) with the same procedure as given for 36a. The crude
product was purified on a silica gel column using ethyl acetate:hexanes:
methanol (1:1:0 to 1:1:0.1) as eluent to give 36b as a colorless film (yield,
63%): 1H NMR (DMSO-d6): δ 8.16 (s, 1H), 7.82 (s, 1H), 7.30–7.10 (m, 13H),
6.78 (d, J = 8.8 Hz, 2H), 5.58–5.48 (m, 4H), 4.73–4.62 (m, 1H), 3.86–3.73
(m, 1H), 3.76 (d, J = 7.5 Hz, 2H), 3.65 (s, 3H), 3.60–3.53 (m, 1H), 3.43–
3.23 (m, 2H), 3.13 (s, 3H), 2.23–1.97 (m, 2H), 1.07 (s, 18H). HRMS calcd
for C43H54N5O10P (M+H)+ 832.3686. Found 832.3707.

1562
M. Wu et al.
( )-9-[(1-Azidomethyl)(3-(di-tert-butylcarbonyloxymethylphosphono)
methoxy)propyl]-N6-monomethoxytrityladenine (36c). It was prepared from
35c (174 mg) with the same procedure as given for 36a. The crude product
was purified on a silica gel column using ethyl acetate:hexanes:methanol
1
(1:1:0 to 1:1:0.1) as eluent to give 36c as a colorless film (yield, 56%): H
NMR (CDCl3): δ 8.00 (s, 1H), 7.87 (s, 1H), 7.38–7.20 (m, 13H), 6.79 (d,
J = 9.0 Hz, 2H), 5.75–5.62 (m, 4H), 4.78–4.65 (m, 1H), 4.13 (dd, J = 12.7,
8.2 Hz, 1H), 3.81–3.57 (m, 4H), 3.78 (s, 3H), 3.34–3.20 (m, 1H), 2.50–2.35
(m, 1H), 2.30–2.16 (m, 1H), 1.23 (s, 9H), 1.226 (s, 9H). HRMS calcd for
C42H51N8O9P (M+H)+ 843.3594. Found 843.3558.
( )-9-[(1-N-Monomethoxytritylaminomethyl)(3-(di-tert-butylcarbon-
yloxymethylphosphono)methoxy)propyl]-N6-monomethoxytrityladenine
(36d). It was prepared from 35d (150 mg) with the same procedure as
given for 36a. The crude product was purified on a silica gel column using
ethyl acetate:hexanes:methanol (1:1:0 to 1:1:0.1) as eluent to give 36d as
1
a colorless film (yield, 48%): H NMR (CDCl3): δ 7.964 (s, 1H), 7.958 (s,
1H), 7.47–6.95 (m, 25H), 6.78 (d, J = 8.9 Hz, 2H), 6.68 (d, J = 8.8 Hz,
2H), 5.76–5.60 (m, 4H), 4.66–4.52 (m, 1H), 4.20–4.02 (m, 1H), 3.79–3.65
(m, 2H), 3.72 (s, 6H), 3.58–3.44 (m, 1H), 3.31–3.16 (m, 1H), 2.88 (t, J =
10.8 Hz, 1H), 2.60–2.44 (m, 1H), 2.44–2.32 (m, 1H), 2.12–2.00 (m, 1H),
1.20 (m, 18H). HRMS calcd for C62H69N6O10P (M+H)+ 1089.4891. Found
1089.4859.
( )-9-[(1-(α-Monomethoxytrityloxy)ethyl)(3-(di-tert-butylcarbonyloxy-
methylphosphono)methoxy)propyl]-N6 -monomethoxytrityladenine (36e).
The conversions of 25 (427 mg) to 26, 26 to 35e, and 35e to 36e were
done by the methods used for 10, 35a, and 36a, respectively. The residue
was purified on a silica gel column using ethyl acetate:hexanes:methanol
(1:1:0 to 1:1:0.1) as eluent to give 21 mg (3.5%, three steps) of 36e as a
1
colorless film: H NMR (a mixture of diastereomers, CDCl3): δ 8.06, 7.89,
7.82 (3s, 2H), 7.43–7.05 (m, 25H), 6.92–6.66 (m, 4H), 5.73–5.60 (m, 4H),
5.00–4.02, 3.86–3.02 (2m, 6H), 3.78 (s, 3H), 3.72 (s, 3H), 2.69–2.24 (m, 2H),
1.22, 1.21 (2s, 18H), 0.99, 0.94 (2d, J = 6.6 Hz each, 3H). HRMS calcd for
C63H70N5O11P (M+H)+ 1104.4887. Found 1104.4925.
( )-9-[(1-Methyl)(3-(di-tert-butylcarbonyloxymethylphosphono)meth-
oxy)propyl]-N6-monomethoxytrityladenine (36f). It was prepared from 35f
(240 mg) with the same procedure as given for 36a. The crude product was
purified on a silica gel column using ethyl acetate:hexanes:methanol (1:1:0
1
to 1:1:0.1) as eluent to give 36f as a colorless oil (yield, 47%): H NMR
(DMSO-d6): δ 8.10 (s, 1H), 7.72 (s, 1H), 7.17–7.00 (m, 13H), 6.68 (d, J =
9.1 Hz, 2H), 5.46–5.38 (m, 4H), 4.54–4.45 (m, 1H), 3.65 (d, J = 7.7 Hz,

Synthesis of Antiviral Agents
1563
2H), 3.55 (s, 3H), 3.32–3.10 (m, 2H), 2.14–1.84 (m, 2H), 1.35 (d, J = 6.8
Hz, 3H), 0.97 (s, 18H). IR (KBr, cm−1) 3410, 2976, 1755, 1605, 1473, and
1252. Anal. calcd for C42H52N5O9P: C, 62.91; H, 6.54; N, 8.73. Found: C,
62.65; H, 6.76; N, 8.74.
( )-9-[(1-Fluoromethyl)(3-(di-isopropyloxycarbonyloxymethylphospho-
no)methoxy)propyl]-N6-monomethoxytrityladenine (36g). Compound 32
(210 mg) was converted to 35g and 35g to 36g with the methods used
for 35a and 36a, respectively. In this case (35g to 36g), chloromethyl-2-
propylcarbonate was used in place of chloromethyl pivalate. The time of
the reaction also increased to 7 days. The purification gave the desired 36g
in 29% yield: 1H NMR (CDCl3): δ 7.94 (s, 1H), 7.82 (s, 1H), 7.31–7.12 (m,
13H), 6.73 (d, J = 9.0 Hz, 2H), 5.69–5.55 (m 4H), 5.05–4.51 (m, 5H),
3.75 (d, J = 7.9 Hz, 2H), 3.71 (s, 3H), 3.64–3.54 (m, 1H), 3.35–3.24 (m,
1H), 2.41–2.26 (m, 1H), 2.26–2.11 (m, 1H), 1.24 (d, J = 6.2 Hz, 6H), 1.23
(d, J = 6.2 Hz, 6H). HRMS calcd for C40H47FN5O11P (M+H)+ 824.3072.
Found 824.3096.
( )-9-[(1-Methylene)(3-(di-tert-butylcarbonyloxymethylphosphono)
methoxy)propyl]-N6-monomethoxytrityladenine (36h). It was prepared from
35h (193 mg) with the same procedure as given for 36a. The crude product
was purified on a silica gel column using ethyl acetate:hexanes:methanol
1
(1:1:0 to 1:1:0.1) as eluent to give 36h as a colorless oil (yield, 55%): H
NMR (DMSO-d6): δ 8.58 (s, 1H), 8.16 (s, 1H), 7.62–7.41 (m, 13H), 7.08 (d,
J = 8.9 Hz, 2H), 5.86 (s, 1H), 5.84 (d, J = 1.5 Hz, 2H), 5.79 (d, J = 1.1
Hz, 2H), 5.46 (s, 1H), 4.12 (d, J = 7.8 Hz, 2H), 3.95 (s, 3H), 3.85 (t, J =
6.4 Hz, 2H), 3.26 (d, J = 6.4 Hz, 2H), 1.37 (s, 18H). IR (neat, cm−1) 3020,
1753, 1604, and 1216. Anal. calcd for C42H50N5O9P 0.25 H2O: C, 62.71; H,
6.33; N, 8.71. Found: C, 62.92; H, 6.70; N, 8.62.
( )-9-[(1-Monomethoxytrityloxymethyl)(3-(di-isopropyloxycarbon-
yloxymethylphosphono)methoxy)propyl]-N6-monomethoxytrityladenine
(36i). It was prepared from 35a (216 mg) with the same procedure as given
for 36a but using chloromethyl-2-propylcarbonate in place of chloromethyl
pivalate. The time of the reaction also increased to 7 days. The crude
product was purified on a silica gel column using ethyl acetate:hexanes:
methanol (1:1:0 to 1:1:0.1) as eluent to give 36i as a colorless film (yield,
1
50%): H NMR (CDCl3): δ 7.99 (s, 1H), 7.90 (s, 1H), 7.41–7.00 (m, 25H),
6.79 (d, J = 8.9 Hz, 2H), 6.70 (d, J = 8.7 Hz, 2H), 5.73–5.58 (m, 4H),
4.96–4.86 (m, 2H), 4.81–4.71 (m, 1H), 3.79–3.65 (m, 3H), 3.76 (s, 3H),
3.75 (s, 3H), 3.56–3.48 (m, 1H), 3.34–3.24 (m, 2H), 2.58–2.45 (m, 1H),
2.18–2.06 (m, 1H), 1.32–1.24 (m, 12H). HRMS calcd for C60H64N5O13P
(M+H)+ 1094.4316. Found 1094.4316.

1564
M. Wu et al.
( )-9-[(1-Methoxymethyl)(3-(di-isopropyloxycarbonyloxymethylphos-
phono)methoxy)-propyl]-N6-monomethoxytrityladenine (36j). It was pre-
pared from 35b (115 mg) with the same procedure as given for 36i. The
crude product was purified on a silica gel column using ethyl acetate:
hexanes:methanol (1:1:0 to 1:1:0.1) as eluent to give 36j as a colorless film
(yield, 42%): 1H NMR (CDCl3): δ 8.01 (s, 1H), 7.90 (s, 1H), 7.39–7.19 (m,
13H), 6.80 (d, J = 9.0 Hz, 2H), 5.75–5.64 (m, 4H), 4.99–4.87 (m, 2H), 4.87–
4.77 (m, 1H), 3.94 (dd, J = 10.3, 6.7 Hz, 1H), 3.81 (d, J = 7.9 Hz, 2H),
3.78 (s, 3H), 3.66 (dd, J = 9.8, 3.8 Hz, 1H), 3.63–3.56 (m, 1H), 3.41–3.32
(m, 1H), 3.32 (s, 3H), 2.43–2.12 (m, 2H), 1.31 (d, J = 6.3 Hz, 6H), 1.30 (d,
J = 6.2 Hz, 6H). HRMS calcd for C41H50N5O12P (M+H)+ 836.3271. Found
836.3235.
( )-9-[(1-Hydroxymethyl)(3-(di-tert-butylcarbonyloxymethylphospho-
no)methoxy)propyl]-adenine (37a). A solution of 36a (272 mg, 0.25 mmol)
in acetonitrile (54 mL) was treated with 0.2 M HCl (2.7 mL) and stirred for
14 h at room temperature. It was then carefully neutralized with 0.5 N NaOH
to pH 6.0 and diluted with water (20 mL) and concentrated to remove
acetonitrile. The residual material was again diluted with water (20 mL) and
extracted with chloroform:methanol (4:1, 2 ). The organic layer was dried
over MgSO4. After filtration, the filtrate was concentrated and the residue
purified on a silica gel column using chloroform:methanol (1:0 to 9:1) as
eluent to give 102 mg (75%) of 37a as a colorless oil. HPLC: tR = 22.240
min, 97.06%.
Procedure for the fumarate salt of 37a: A solution of 37a (50.0 mg, 0.092
mmol) in 2-propanol (0.25 mL) was treated with a solution of fumaric acid in
propanol (20.3 mg/mL, 1.62 mL, 0.092 mmol) followed by concentration.
The fumaric salt was obtained as a white solid: 1H NMR (DMSO-d6): δ 13.21
(bs, 2H), 8.16 (s, 1H), 8.15 (s, 1H), 7.25 (s, 2H), 6.69 (s, 2H), 5.70–5.60 (m,
4H), 5.11 (bs, 1H), 4.68–4.52 (m, 1H), 4.00–3.70 (m, 2H), 3.87 (d, J = 7.7
Hz, 2H), 3.53–3.30 (m, 2H), 2.35–2.13 (m, 2H), 1.20 (s, 18H). Anal. calcd
for C22H36N5O9P 1.0 C4H4O4: C, 47.18; H, 6.10; N, 10.59. Found: C, 47.30;
H, 6.11; N, 10.31.
( )-9-[(1-Methoxymethyl)(3-(di-tert-butylcarbonyloxymethylphospho-
no)methoxy)propyl]-adenine (37b). It was prepared from 36b (110 mg)
with the same procedure as given for 37a. The crude product was purified
on a silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to
give 37b as a colorless oil (yield, 49%): A portion was purified by HPLC
1
(tR = 21.260 min). H NMR (CDCl3): δ 8.30 (s, 1H), 7.96 (s, 1H), 5.84 (s,
2H), 5.75–5.63 (m, 4H), 4.92–4.80 (m, 1H), 3.93 (dd, J = 10.0, 6.2 Hz, 1H),
3.75 (dd, J = 7.9, 1.3 Hz, 1H), 3.67 (dd, J = 10.2, 3.8 Hz, 1H), 3.64–3.56
(m, 1H), 3.37–3.30 (m, 1H), 3.38–3.28 (m, 1H), 3.32 (s, 3H), 2.44–2.30 (m,

Synthesis of Antiviral Agents
1565
1H), 2.30–2.16 (m, 1H), 1.23 (s, 9H), 1.22 (s, 9H). IR (neat, cm−1) 3020,
2982, 1751, 1631, 1478, and 1216. HRMS calcd for C23H38N5O9P (M+H)+
560.2485. Found 560.2468.
( )-9-[(1-Azidomethyl)(3-(di-tert-butylcarbonyloxymethylphosphono)
methoxy)propyl]-adenine (37c). It was prepared from 36c (117 mg) with
the same procedure as given for 37a. The crude product was purified on a
silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to give
37c as a colorless oil (yield, 83%): 1H NMR (CDCl3): δ 8.30 (s, 1H), 7.91 (s,
1H), 5.80–5.62 (m, 6H), 4.84–4.70 (m, 1H), 4.23–4.12 (m, 1H), 3.83–3.69
(m, 3H), 3.67–3.56 (m, 1H), 3.34–3.21 (m, 1H), 2.56–2.40 (m, 1H), 2.32–
2.16 (m, 1H), 1.24 (s, 9H), 1.23 (s, 9H). IR (neat, cm−1) 3019, 2980, 2106,
1751, and 1633. HRMS calcd for C22H35N8O8P (M+H)+ 571.2393. Found
571.2386. HPLC: tR = 23.019 min, 95.64%.
( )-9-[(1-Aminomethyl)(3-(di-tert-butylcarbonyloxymethylphosphono)
methoxy)propyl]-adenine (37d). A solution of 36d (67 mg, 0.062 mmol) in
acetonitrile (10 mL) was treated with 0.2 M HCl (0.5 mL) and stirred for
16 h at room temperature. It was diluted with water (150 mL) and extracted
with ethyl acetate (2 ). The aqueous layer was concentrated to dryness to
give 37d as a gum. The product was dissolved in 3.5 mL of water and its
concentration measured to be 13.07 mM (74%) by UV at 259 nm: 1H NMR
(D2O): δ 8.32 (s, 1H), 8.31 (s, 1H), 5.57–5.43 (m, 4H), 5.03–4.91 (m, 1H),
3.78–3.45 (m, 5H), 3.30–3.20 (m, 1H), 2.43–2.29 (m, 1H), 2.25–2.12 (m,
1H), 1.08 (s, 9H), 1.07 (s, 9H). HRMS calcd for C22H37N6O8P (M+H)+
545.2488. Found 545.2476. HPLC: tR = 18.720 min, 95.61%.
( )-9-[(1-(α-Hydroxy)ethyl)(3-(di-tert-butylcarbonyloxymethylphospho-
no)methoxy)propyl]-adenine (37e). It was prepared from 36e (21 mg) with
the same procedure as given for 37a. The crude product was purified on a
silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to give
1
37e as a colorless oil (yield, 72%): H NMR (a mixture of diastereomers,
CDCl3): δ 8.29, 8.28, 7.96, 7.94 (4s, 2H), 6.06–5.65 (m, 7H), 4.64–4.14 (m,
2H), 3.89–3.50 (m, 3H), 3.14–3.00 (m, 1H), 2.37–2.17 (m, 2H), 1.33, 1.05
(d, J = 6.7 Hz each, 3H), 1.234, 1.231 (2s, 18H). IR (neat, cm−1) 3321, 3019,
1753, 1635, and 1216. HRMS calcd for C23H38N5O9P (M+H)+ 560.2485.
Found 560.2484. HPLC: tR = 21.865 min, 97.66%.
( )-9-[(1-Methyl)(3-(di-tert-butylcarbonyloxymethylphosphono)meth-
oxy)propyl]adenine (37f). It was prepared from 36f (127 mg) with the
same procedure as given for 37a. The crude product was purified on a silica
gel column using chloroform:methanol (1:0 to 9:1) as eluent to give 37f as
a colorless oil (yield, 97%): 1H NMR (CDCl3): δ 8.32 (s, 1H), 7.88 (s, 1H),

1566
M. Wu et al.
5.75–5.64 (m, 6H), 4.85–4.75 (m, 1H), 3.75 (d, J = 7.9 Hz, 2H), 3.60–
3.52 (m, 1H), 3.35–3.24 (m, 1H), 2.46–2.32 (m, 1H), 2.24–2.10 (m, 1H),
1.67 (d, J = 6.8 Hz, 3H), 1.23 (s, 9H), 1.22 (s, 9H). IR (neat, cm−1) 3020,
2981, 1751, 1630, 1478, and 1216. HRMS calcd for C22H36N5O8P (M+H)+
530.2379. Found 530.2356. HPLC: tR = 23.477 min, 99.03%.
( )-9-[(1-Fluoromethyl)(3-(di-isopropyloxycarbonyloxymethylphospho-
no)methoxy)propyl]-adenine (37g). It was prepared from 36g (40 mg) with
the same procedure as given for 37a. The crude product was purified on a
silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to give
1
37g as a light yellow oil (yield, 96%): H NMR (CDCl3): δ 8.32 (s, 1H),
7.96 (s, 1H), 5.79 (s, 2H), 5.76–5.64 (m, 4H), 5.13–4.60 (m, 5H), 3.81 (d,
J = 7.8 Hz, 2H), 3.72–3.63 (m, 1H), 3.38–3.30 (m, 1H), 2.50–2.36 (m, 1H),
2.35–2.20 (m, 1H), 1.32 (d, J = 6.3 Hz, 6H), 1.31 (d, J = 6.4 Hz, 6H).
IR (neat, cm−1) 3334, 2987, 1759, 1646, 1599, and 1268. HRMS calcd for
C20H31FN5O10P (M+H)+ 552.1870. Found 552.1847. HPLC: tR = 21.739
min, 98.59%.
( )-9-[(1-Methylene)(3-(di-tert-butylcarbonyloxymethylphosphono)
methoxy)propyl]-adenine (37h) It was prepared from 36h (135 mg) with
the same procedure as given for 37a. The crude product was purified on a
silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to give
1
37h as a colorless oil (yield, 95%): H NMR (CDCl3): δ 8.35 (s, 1H), 7.94
(s, 1H), 5.79 (s, 2H), 5.73–5.63 (m, 4H), 5.48 (s, 1H), 5.29 (s, 1H), 3.80 (d,
J = 7.9 Hz, 2H), 3.67 (t, J = 6.2 Hz, 2H), 3.11 (t, J = 6.2 Hz, 2H), 1.22
(s, 18H). IR (neat, cm−1) 3019, 2981, 1751, 1633, and 1216. HRMS calcd
for C22H34N5O8P (M+H)+ 528.2223. Found 528.2207. HPLC: tR = 23.029
min, 95.79%.
( )-9-[(1-Hydroxymethyl)(3-(di-isopropyloxycarbonyloxymethylphos-
phono)methoxy)-propyl]adenine (37i). It was prepared from 36i (122 mg)
with the same procedure as given for 37a. The crude product was purified on
a silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to give
37i as a colorless film (yield, 69%): 1H NMR (CDCl3): δ 8.22 (s, 1H), 7.90 (s,
1H), 5.73–5.58 (m, 6H), 4.87 (hept, J = 6.2 Hz, 2H), 4.72–4.62 (m, 1H),
4.03 (bs, 2H), 3.88–3.69 (m, 2H), 3.65–3.57 (m, 1H), 3.23–3.14 (m, 1H),
2.26–2.17 (m, 2H), 1.25, 1.24 (2d, J = 6.3 each, 12H). IR (neat, cm−1
)
3330, 2984, 1759, 1645, 1601, and 1472. HRMS calcd for C20H32N5O11P
(M+H)+ 550.1914. Found 550.1930. HPLC: tR = 20.352 min, 97.44%.
( )-9-[(1-Methoxymethyl)(3-(di-isopropyloxycarbonyloxymethylphos-
phono)methoxy)-propyl]adenine (37j). It was prepared from 36j (60 mg)
with the same procedure as given for 37a. The crude product was purified
on a silica gel column using chloroform:methanol (1:0 to 9:1) as eluent to

Synthesis of Antiviral Agents
1567
1
give 37j as a colorless oil (yield, 99%): H NMR (CDCl3): δ 8.30 (s, 1H),
7.96 (s, 1H), 6.09 (s, 2H), 5.81–5.62 (m, 4H), 5.03–4.81 (m, 3H), 3.95 (dd,
J = 10.0, 6.4 Hz, 1H), 3.80 (d, J = 7.7 Hz, 2H), 3.72–3.58 (m, 2H), 3.40–
3.30 (m, 1H), 3.32 (s, 3H), 2.46–2.32 (m, 1H), 2.32–2.20 (m, 1H), 1.32 (d,
J = 6.2 Hz, 12H). IR (neat, cm−1) 3020, 1761, 1631, and 1216. HRMS calcd
for C21H34N5O11P (M+H)+ 564.2070. Found 564.2060. HPLC: tR = 22.123
min, 96.91%.
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