Efficient electrophilic fluorination for the synthesis of novel 2'-fluoro-3'-methyl-5'-deoxyphosphonic acid apiosyl nucleoside analogues

Article abstract of DOI:10.1080/15257770.2013.832774

Novel 5'-deoxyapiosyl purine phosphonic acid analogues with a 2'-electropositive moiety, such as, a fluorine atom were designed and synthesized from commercially available hydroxylacetone. Condensation of a glycosyl donor 10 with purines under Vorbruggen conditions and cross-metathesis give the desired nucleoside phosphonic acid analogues 14, 17, 21, and 24. The synthesized nucleoside analogues were subjected to antiviral screening against HIV-1, and the adenine analogue 17 exhibited weak in vitro anti-HIV-1 activity (EC₅₀ = 26.6 μM)

Full text of DOI:10.1080/15257770.2013.832774

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Efficient Electrophilic Fluorination for
the Synthesis of Novel 2′-Fluoro-3′-
Methyl-5′-Deoxyphosphonic Acid Apiosyl
Nucleoside Analogues
Kyung Mi Kim a & Joon Hee Hong a
a BK-21 Project Team, College of Pharmacy, Chosun University ,
Kwangju , Republic of Korea
Published online: 14 Oct 2013.
To cite this article: Kyung Mi Kim & Joon Hee Hong (2013) Efficient Electrophilic Fluorination for
the Synthesis of Novel 2′-Fluoro-3′-Methyl-5′-Deoxyphosphonic Acid Apiosyl Nucleoside Analogues,
Nucleosides, Nucleotides and Nucleic Acids, 32:10, 555-570, DOI: 10.1080/15257770.2013.832774
To link to this article: http://dx.doi.org/10.1080/15257770.2013.832774
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Nucleosides, Nucleotides and Nucleic Acids, 32:555–570, 2013
Copyright ꢀC Taylor and Francis Group, LLC
ISSN: 1525-7770 print / 1532-2335 online
DOI: 10.1080/15257770.2013.832774
EFFICIENT ELECTROPHILIC FLUORINATION FOR THE SYNTHESIS
OF NOVEL 2ꢀ-FLUORO-3ꢀ-METHYL-5ꢀ-DEOXYPHOSPHONIC ACID
APIOSYL NUCLEOSIDE ANALOGUES
Kyung Mi Kim and Joon Hee Hong
BK-21 Project Team, College of Pharmacy, Chosun University, Kwangju, Republic of Korea
Novel 5ꢁ-deoxyapiosyl purine phosphonic acid analogues with a 2ꢁ-electropositive moiety, such
2
as, a fluorine atom were designed and synthesized from commercially available hydroxylacetone.
Condensation of a glycosyl donor 10 with purines under Vorbruggen conditions and cross-metathesis
give the desired nucleoside phosphonic acid analogues 14, 17, 21, and 24. The synthesized nucle-
oside analogues were subjected to antiviral screening against HIV-1, and the adenine analogue 17
exhibited weak in vitro anti-HIV-1 activity (EC50 = 26.6 μM)
Keywords HIV nucleoside; nucleoside phosphonate; synthetic methodology; the Vor-
bruggen reaction
INTRODUCTION
The antiviral activities of phosphonate nucleosides is largely explained by
their intracellular metabolisms following sequential activation by cellular ki-
nases to their diphosphate derivatives (nucleoside triphosphate analogues),
which act as potent inhibitors of viral DNA polymerases.[1] The selective
inhibitions of these enzymes, as opposed to host cell DNA polymerases, is
critical if such compounds are intended drug candidates. Various attempts
to improve the selectivity index have led to nucleoside analogues with a fu-
ranose ring system containing an electropositive moiety in the 2ꢁ-position.[2]
Recently, a nucleoside analogue with a fluorine atom in the 2ꢁ-position of the
furanose ring, GS-9148 (1), was reported to show excellent antiviral activity
(Figure 1).[3] By replacing OH with F, it is possible to create a ribo-like sugar
that has a substituent at the 2ꢁ-position sterically and electronically similar
to a hydroxyl group, but which cannot undergo oxidative catabolism. Thus,
the in vivo half-life of the compound may be improved.
Received 12 July 2013; accepted 5 August 2013.
This work was supported by the Chosun University research fund, 2013.
Address correspondence to Dr. Joon Hee Hong, BK-21 Project Team, College of Pharmacy, Chosun
University, Kwangju 501-759, Republic of Korea. E-mail: hongjh@chosun.ac.kr
555

556
K. M. Kim and J. H. Hong
FIGURE 1 Synthesis rationale of apiosyl 5ꢁ-deoxyphosphonic acid nucleosides as potent antiviral agents.
The 4ꢁ-modified ribonucleoside derivatives comprise a second distinct
structural class of HIV NIs. The methyl substituent at the 4ꢁ-position of the
sugar analogue (2) is accommodated by viral polymerase. Modeling stud-
ies have demonstrated the presence of a narrow, relatively hydrophobic
4ꢁ-pocket can accommodate these substitutions and contribute to their po-
tencies.[4]
Apiose nucleosides[5] and their phosphonate analogues,[6] such as,
PMDTA (3, phosphonomethoxydeoxythreosyladenine), have been synthe-
sized as potent antiviral agents because they can be assembled from natural
precursor molecules. It has been demonstrated that apiose nucleic acids
(TNA) form duplexes with DNAs and RNAs, reminiscent of natural nucleic
acid association.[7] The triphosphates of apiose nucleosides are accepted as
substrates by several polymerases, and can be enzymatically incorporated
into DNA.[8] In addition, these nucleosides are accepted as substitutes for
ribonucleosides in the catalytic site of hammerhead ribozyme, although
the catalytic efficiency of ribozyme is significantly reduced.[9] The phos-
phonoalkoxy group of apiosyl nucleoside phosphonates is bound at the
3ꢁ-position, which brings the phosphorus atom and the nucleobase closer to
each other than in furanose nucleoside phosphonates where the phospho-
nate group is bound to the primary hydroxyl group of the nucleoside.[10]
The presence of an anomeric center in apiosyl nucleoside phosphonates
confers on them stereoelectronic properties similar to those of natural nu-
cleosides. The phosphonate group is stable against enzymatic degradation
(hydrolysis), and the absence of a 4ꢁ-hydroxymethyl group avoids problems

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
557
FIGURE 2 NOE differences between the proximal hydrogen atoms of 8a and 8b.
of steric hindrance during phosphorylation reactions by kinases. To study
the influence of different substituents on anti-HIV activity further, we aimed
to synthesize of 3ꢁ-methylated and 2ꢁ-fluorinated analogues of PMDTA.
In the literature, several 5ꢁ-phosphate isosteres have been used to prepare
nucleoside phosphonates. As shown in Figure 1, compound 4[11] is a sim-
ple 5ꢁ-deoxynucleoside phosphonate, in which the 5ꢁ-oxygen of a nucleoside
phosphate is replaced by a methylene group. Furthermore, all of the resul-
tant phosphonates mimic the overall shape and geometry of a nucleoside
monophosphate.
Stimulated by the findings that 2ꢁ-electropositive nucleoside analogues
and 5ꢁ-deoxyphosphonic acid nucleosides have excellent antiviral activities,
we undertook to synthesize 3ꢁ-methyl-2ꢁ-fluoro-5ꢁ-deoxyapiosyl phosphonic
acid analogues in the hope of identifying more effective therapeutics against
HIV and to provide analogues for probing the conformational preferences
of enzymes associated with the nucleoside kinases of nucleosides and nu-
cleotides.
RESULTS AND DISCUSSION
Lactone was synthesized by the route described in Scheme 1 from hy-
droxyacetone 5.[12] For the fluorination, the order of addition of reagents
is important. Lactone and N -fluorodibenzenesulfonimide (NFSi) were dis-
solved together in THF and cooled to −78◦C. The slow addition of LiHMDS
(lithium hexamethyldisilazane) resulted in the formations of 8a and 8b at
yields of 35 and 17%, respectively.[13] Complete NOE studies allowed the un-
ambiguous determination of their relative stereochemistries. For compound
8a, strong NOE (0.9%) of H-2ꢁ ↔ 3ꢁ(vinyl-H), showed a cis relationship be-
tween 2ꢁ(H) and 3ꢁ(vinyl-H). On the other hand, for 8b compound, weak
NOE (0.6%) for H-2ꢁ ↔ 3ꢁ(vinyl-H), indicated a 1ꢁ,3ꢁ-trans relationship in
Figure 2. Fluorinated lactone 8a was transformed into lactol 9 by DIBALH
(diisobutylaluminum hydride) reduction and subsequent acetylation to pro-
vide the anomeric acetate 10. The synthesis of adenine nucleoside was car-
ried out by Vorbruggen condensation[14] of a compound 10 with silylated
6-chloropurine using TMSOTf (trimethylsilyl trifluoromethanesulfonate) as

558
K. M. Kim and J. H. Hong
FIGURE 3 NOE differences between the proximal hydrogen atoms of 11a and 11b.
a catalyst in DCE (1,2-dichloroethane) to give the protected 6-chloropurine
derivatives 11a and 11b, respectively. Relative stereochemistries were deter-
mined by NOE study, as shown in Figure 3.
Cross-metathesis[15] of 11b with vinyl diethylphosphonate using second-
generation Grubbs catalyst[16] gave the vinylidene phosphonate nucleoside
analogue 12 at a yield of 59%. The chlorine group of purine analogue 12
was then converted to amine with methanolic ammonia at 60◦C to give
a corresponding adenosine phosphonate derivative 13 at a yield of 50%.
Hydrolysis of the diethyl phosphonate functional groups of 13 by treatment
with bromotrimethylsilane in CH3CN in the presence of 2,6-lutidine gave the
adenosine phosphonic acid derivative 14 as the only N 9-isomer [UV (H2O)
λmax 261.5 nm].[17] The vinylidene phosphonate was then saturated under
transfer catalytic hydrogenation conditions[18] to give the ethyl phosphonate
nucleoside analogue 15 at a yield of 79%. The adenine phosphonic acid
analogue 16 was prepared using similar reaction conditions (ammonolysis
and hydrolysis) as those described for the preparation of 14.
For the synthesis of guanine analogues, 2-fluoro-6-chloropurine[19] was
condensed with glycosyl donor 10, under conditions similar to those used
for the preparation of 6-chloropurine, to give analogues 18a (29%) and
18b (30%), respectively (Scheme 2). A complete NOE study allowed the un-
ambiguous determination of the relative stereochemistries of as 18a and
18b, described above for 11a and 11b. Cross-metathesis of 18b with di-
ethylvinylphosphonate provided 19 in a 52% yield.
Bubbling ammonia into a solution of 19 gave the separable 2-fluoro-6-
aminopurine analogue[20] 20a (13%) and the 2-amino-6-chloropurine ana-
logue 20b (40%). The 2-amino-6-chloropurine derivative 20b was treated
with TMSBr (bromotrimethylsilane) to provide phosphonic acid and then
treated with sodium methoxide and 2-mercaptoethanol in methanol to give
the desired guanine phosphonic acid 21.[21] The guanine phosphonic acid
analogue 24 was synthesized from 19 via transfer catalytic hydrogenation, am-
monolysis, and hydrolysis using conditions similar to those described above
for the synthesis of corresponding adenine derivatives.

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
559
HO
H3C
O
i
ref.12
CO2Et
OP
6
O
1
O
73%
3
2
H3C
7
H3C
5
59% ii
Cl
N
O
N
N
O
iii
88%
O
X
1
v
R
3
2
N
Y
O
H3C
F
H3C
8a: X = H, Y = F (35%)
8b: X = F, Y = H (17%)
9: R = OH
10: R = OAc
iv
11a (30%)
(82%)
N
F
H3C
and
Cl
Cl
Cl
N
N
N
N
N
N
iX
79%
vi
N
N
O
O
EtO P
EtO
59%
N
N
N
O
P
O
O
EtO
EtO
15
H3C
53%
F
12
F
H3C
F
H3C
11b (32%)
vii
vii
50%
NH2
N
NH2
N
N
N
N
N
N
O
EtO P
EtO
N
O
EtO P
EtO
O
O
16
F
H3C
41%
13
F
H3C
39%
viii
viii
NH2
N
NH2
N
N
N
N
N
N
O
HO P
HO
O
N
O
O
HO P
HO
17
F
H3C
14
H3C
F
SCHEME 1 Synthesis of apiosyl 2ꢁ-fluoro-4ꢁ-methyl-5ꢁ-deoxyphosphonic acid adenine analogue.
Reagents: (i) TBAF, THF; (ii) NFSi, LiHMDS, THF; (iii) DIBALH, toluene; (iv) Ac2O, pyridine; (v)
silylated 6-chloropurine, TMSOTf, DCE; (vi) vinyldiethylphosphonate, Grubbs cat.(II) CH2CI2; (vii)
NH3, MeOH, 60◦C; (viii) (a) TMSBr, 2,6-lutidine, CH3CN and (b) NH4OH; and (ix) Pd/C, cyclohex-
ene, MeOH.
ANTIVIRAL ACTIVITIES
The antiviral activities of phosphonate nucleosides are largely due to
their intracellular metabolism to diphosphates, subsequent incorporation
into the viral genome, and chain termination.[22] MT-4 cells (1 × 105

560
K. M. Kim and J. H. Hong
Cl
N
Cl
N
N
N
N
N
O
i
OAc
N
F
N
F
O
O
and
F
H3C
10
F
F
H3C
H3C
18b (30%)
18a (29%)
52% ii
Cl
N
Cl
N
N
N
N
N
N
v
N
F
O
O
F
O
73%
O
EtO P
EtO
EtO P
EtO
19
F
H3C
22
F
H3C
iii
iii
X
X
N
N
N
N
N
N
N
Y
O
N
Y
O
O
EtO P
EtO
O
EtO P
EtO
F
H3C
F
H3C
20a: X = NH2, Y = F (13%)
20b: X = Cl, Y = NH2 (40%)
23a: X = NH2, Y = F (11%)
23b: X = Cl, Y = NH2 (39%)
iv
iv
44%
48%
O
O
N
N
NH
NH
N
N
N
NH2
O
HO P
HO
N
NH2
O
HO P
HO
O
O
24
21
F
F
H3C
H3C
SCHEME 2 Synthesis of apiosyl 2ꢁ-fluoro-4ꢁ-methyl-5ꢁ-deoxyphosphonic acid guanine analogues.
Reagents: (i) silylated 2-fluoro-6-chloropurine, TMSOTf, DCE; (ii) vinyldiethylphosphonate, Grubbs
cat.(II) CH2CI2; (iii) NH3, DME, rt; (iv) (a) TMSBr, 2,6-lutidine, CH3CN; (b) NaOMe, HSCH2CH2OH,
MeOH; and (c) NH4OH; and (v) Pd/C, cyclohexene, MeOH.
cell/mL) were infected with HIV-1 (HTLV-IIIB strain) at a multiplicity
of infection (MOI) of 0.02 and then cultured in the presence of various
concentrations of test compounds. After a 4-day incubation at 37◦C, num-
bers of viable cells were counted using the 3-(4,5-di-methylthiazole-2-yl)-
2,5-diphenyltetrazolium bromide method. Cytotoxicities were evaluated in

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
561
parallel with antiviral activities, based on the viabilities of mock-infected
cells.[23] The synthesized compounds 14, 17, 21, and 24 were tested against
HIV-1. The adenine phosphonic acid nucleoside analogue 17 showed weak
anti-HIV activity at concentrations up to 100 μM, but all other phosphonic
acid analogues were inactive (Table 1), indicating that HIV might not allow
the sugar moiety for diphosphorylation or weak affinity of its diphosphate
toward viral polymerases.
In summary, based on the potent anti-HIV activities of 2ꢁ-electropositive
nucleosides and 5ꢁ-deoxyphosphonic acid nucleoside analogues, we de-
signed and successfully synthesized novel 3ꢁ-methyl-2ꢁ-fluoro-5ꢁ-deoxyphos-
phonic acid nucleoside analogues starting from hydroxy acetone. However,
none of the synthesized nucleoside analogues exhibited significant antiviral
activity up to a concentration of 100 μM. Since the derivatives produced by
the 2ꢁ-fluorination of purine nucleoside phosphonic acids were not perfect
mimics of the ribofuranose moiety, mechanisms of virus inhibition, that is, via
phosphorylation or the inhibition of RNA synthesis, might be impaired for
these compounds. The syntheses of (bis)SATE-pro-drugs of 17 are progress
in our laboratory. As shown in the superimposition model of PMDTA (3)
and its corresponding analogue 17 (Figure 4), discrepancy of phosphonic
acid parts are more pronounced compared to the base moiety. Note the
furanose puckering of PMDTA (3) is positioned closer to that of adenine
analogue 17.[24]
EXPERIMENTAL SECTION
Melting points were determined on a Mel-temp II laboratory device
and are uncorrected. NMR spectra were recorded on a JEOL 300 Fourier
transform spectrometer (JEOL, Tokyo); chemical shifts are reported in
parts per million (δ) and signals are reported as s (singlet), d (doublet), t
TABLE 1 Median effective (EC50) and cytotoxic (CC50) concentrations of the synthesized nucleoside
analogues
Compound no.
Anti-HIV-1 EC50 (μM)c
Cytotoxicity CC50 (μM)d
14
17
21
24
42.5
26.6
77.8
52.4
0.003
0.26
98
90
98
98
100
100
AZTa
PMEAb
aAZT: azidothymidine.
bPMEA: 9-[2-(phosphonomethoxy)ethyl]adenine.
cEC50(μM): EC50 values are for the 50% inhibition of virus production as indicated by supernatant
RT levels.
dCC50(μM): CC50 values are for the 50% cytotoxic concentration of cell growth.

562
K. M. Kim and J. H. Hong
FIGURE 4 Superimpose of monophosphate of 3 and 17 (color figure available online).
(triplet), q (quartet), m (multiplet), or dd (doublet of doublets). UV spectra
were obtained using a Beckman DU-7 spectrophotometer (Beckman, South
Pasadena, CA). Mass spectra (HRMS) were obtained using a VARIAN MAT
311 at an ionizing potential of 70 eV. The elemental analyses were performed
using a Perkin-Elmer 2400 analyzer (Perkin-Elmer, Norwalk, CT, USA). TLC
was performed on Uniplates (silica gel) from Analtech Co. (7558, Newark,
DE, USA). All reactions were carried out under nitrogen unless otherwise
specified. Dry dichloromethane, benzene, and pyridine were obtained by
distillation from CaH2. Dry THF was obtained by distillation from Na and
benzophenone immediately prior to use.
( )-3-Methyl-3-vinyl-dihydrofuran-1-one (7): TBAF (5.03 mL, 1.0 M solu-
tion in THF) was added to a solution of 6 (1.2 g, 4.19 mmol) in THF (10 mL)
at 0◦C. The mixture was stirred overnight at rt and concentrated in vacuo.
The residue so obtained was purified by silica gel column chromatography
(Hexane/EtOAc, 10:1) to give 7 (375 mg, 71%): 1H NMR (CDCl3, 300 MHz)
δ 5.73–5.67 (m, 1H), 5.05–4.98 (m, 2H), 4.30 (d, J = 6.4 Hz, 1H), 4.21 (d,
J = 6.5 Hz, 1H), 2.31 (d, J = 7.0 Hz, 1H), 2.23 (d, J = 7.0 Hz, 1H), 1.25 (s,
3H); and 13C NMR (CDCl3, 75 MHz) δ 172.6, 148.8, 109.1, 84.2, 50.2, 31.7,
and 27.1.
(rel)-(2R,3S)-2-Fluoro-dihydro-3-methyl-3-vinylfuran-1-one(8a) and (rel)
-(2S,3S)-2-Fluoro-dihydro-3-methyl-3-vinylfuran-1-one(8b): N-Fluorodibenz
enesulfonimide (NFSi) (3.56 g, 11.28 mmol) in 50 mL of anhydrous THF
was added to a solution of the lactone derivative 7 (1.42 g, 11.28 mmol) and
cooled to −78◦C. LiHMDS in THF (13.6 mL, 1.0 M) was then added drop-
wise over 1 hour, and the solution was stirred at −78◦C for an additional
2.5 hours and then warmed to room temperature and stirred for 1 hour.
The reaction was then quenched with 2.0 mL of saturated NH4Cl, diluted

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
563
with diethyl ether (150 mL), and poured into an equal volume of saturated
NaHCO3. The organic layer was washed twice with saturated NaHCO3 and
once with brine, dried over MgSO4, filtered, and concentrated. The residue
was purified by silica gel column chromatography (Hexane/EtOAc, 30:1) to
give 8a (569 mg, 35%) and 8b (242 mg, 17%): data for 8a: 1H NMR (CDCl3,
300 MHz) δ 5.71 (dd, J = 7.2, 5.8 Hz, 1H), 5.05–4.96 (m, 2H), 4.40 (d, J =
8.2 Hz, 1H), 4.16 (d, J = 29.6 Hz, 1H), 4.14 (d, J = 8.1 Hz, 1H), 1.24 (s,
3H); 13C NMR (CDCl3, 75 MHz) δ 171.2 (d, J = 21.4 Hz), 154.8, 109.6, 91.2
1
(d, J = 181.2 Hz), 72.5, 35.4 (d, J = 21.6 Hz), 23.2; data for 8b: H NMR
(CDCl3, 300 MHz) δ 5.70 (dd, J = 7.4, 5.9 Hz, 1H), 5.03–4.95 (m, 2H), 4.38
(d, J = 8.1 Hz, 1H), 4.15 (d, J = 28.8 Hz, 1H), 4.12 (d, J = 8.1 Hz, 1H), 1.22
(s, 3H); 13C NMR (CDCl3, 75 MHz) δ 171.1 (d, J = 20.8 Hz), 155.2, 110.3,
93.2 (d, J = 180.6 Hz), 71.7, 36.2 (d, J = 21.0 Hz), 24.0.
(rel)-(2R,3S)-2-Fluoro-tetrahydro-3-methyl-3-vinylfuran-1-ol (9): A solu-
tion of DIBALH (37 mL, 1.0 M mL in hexane) was dropwise added to a
solution of lactone 8a (2.67 g, 18.52 mmol) in anhydrous THF (70 mL) over
30 min at −78◦C, and allowed to stir at −78◦C for 2 hours. The reaction was
then quenched by the slow addition of methanol (5.0 mL), and the reaction
mix was allowed to warm to room temperature with stirring for 1 hour and
then diluted with diethyl ether (140 mL). The precipitate was removed by
filtration through a pad of Celite, washed with ethyl acetate, filtrate, and
washings were concentrated in vacuo and the residue was purified by silica
gel column chromatography (EtOAc/hexane, 1:10) to give 9 (2.38 g, 88%)
as a colorless oil: 1H NMR (CDCl3, 300 MHz) δ 5.74–5.69 (m, 2H), 5.04–4.97
(m, 2H), 3.86–3.74 (m, 1.5H), 3.52 (d, J = 8.2 Hz, 1.5H), 2.1 (br s, 1H), 1.25
(s, 3H).
(rel)-(2R,3S)-2-Fluoro-tetrahydro-3-methyl-3-vinylfuran-1-yl acetate (10):
Ac2O (1.47 g, 14.4 mmol) was slowly added for 10 minutes to a solution
of compound 9 (421 mg, 2.88 mmol) and DMAP (35 mg, 0.288 mmol) in
anhydrous pyridine (30 mL). The mixture was then stirred overnight under
nitrogen, and pyridine was removed under reduced pressure and by co-
evaporation with added toluene. The residue so obtained was diluted with
H2O (100 mL), extracted with EtOAc (100 mL), dried over MgSO4, and fil-
tered. The filtrate was concentrated under reduced pressure, and the residue
obtained was purified by silica gel column chromatography (EtOAc/hexane,
1:20) to give compound 10 (444 mg, 82%) as a colorless oil: 1H NMR (CDCl3,
300 MHz) δ 6.32–6.25 (m, 1H), 5.73–5.68 (m, 1H), 5.05–4.98 (m, 2H),
4.14–3.93 (m, 1.5H), 3.56–3.50 (dd, J = 8.0, 6.8 Hz, 1.5H), 2.02 (s, 3H), 1.24
(s, 3H).
(rel)-(1ꢁS,2ꢁR,3ꢁS)-9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1ꢁ-yl) 6-c
hloropurine(11a) and (rel)-(1ꢁR,2ꢁR,3ꢁS)-9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetr
ahydrofuran-1ꢁ-yl) 6-chloropurine (11b): A mixture of 6-chloropurine
(345 mg, 2.232 mmol), anhydrous HMDS (20 mL), and a catalytic amount
of ammonium sulfate (16 mg) were refluxed for 3 hours to produce a clear

564
K. M. Kim and J. H. Hong
solution. Solvent was removed by distillation under anhydrous conditions,
and the residue obtained was dissolved in anhydrous 1,2-dichloroethane
(8 mL). A solution of 10 (210 mg, 1.116 mmol) in dry DCE (12 mL) and
TMSOTf (496 mg, 2.232 mmol) was then added, and the resulting mixture
was stirred for 6 hours at rt, poured into saturated NaHCO3 (80 mL), and
stirred for 1 hour. The resulting solid was filtered off using a Celite pad, and
the filtrate was extracted with CH2Cl2 (120 mL) 2 times. Combined organic
layers were dried over anhydrous MgSO4, filtered, and concentrated under
vacuum. The residue obtained was purified by silica gel column chromatog-
raphy (EtOAc/hexane/MeOH, 4:1:0.02) to give compounds 11a (94.6 mg,
1
30%) and 11b (101 mg, 32%): data for 11a: H NMR (CDCl3, 300 MHz) δ
8.75 (s, 1H), 8.33 (s, 1H), 6.23 (dd, J = 21.4, 6.0 Hz, 1H), 5.72 (dd, J =
8.0, 6.6 Hz, 1H), 5.02–4.95 (m, 2H), 3.85 (dd, J = 8.2, 6.2 Hz, 1.5H), 3.60
(dd, J = 8.2, 4.8 Hz, 1.5H), 1.25 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 154.3,
151.6, 151.2, 150.9, 144.6, 132.3, 108.2, 95.2 (d, J = 208.6 Hz), 87.2 (d, J =
21.6 Hz), 76.2, 38.4 (d, J = 21.8 Hz), 17.7; Anal. Calc. for C12H12ClFN4O:
C, 50.98; H, 4.28; N, 19.82. Found: C, 51.10; H, 4.33; N, 19.71. data for 11b:
1H NMR (CDCl3, 300 MHz) δ 8.72 (s, 1H), 8.31 (s, 1H), 6.19 (dd, J = 20.8,
6.2 Hz, 1H), 5.70 (dd, J = 8.0, 6.4 Hz, 1H), 5.04–4.98 (m, 2H), 3.86–3.79
(dd, J = 8.0, 6.8 Hz, 1.5H), 3.59 (dd, J = 8.1, 5.2 Hz, 1.5H), 1.23 (s, 3H); 13C
NMR (CDCl3, 75 MHz) δ 154.9, 151.5, 151.0, 149.7, 144.3, 132.1, 108.6, 93.8
(d, J = 212.2 Hz), 86.4 (d, J = 20.8 Hz), 74.4, 37.8 (d, J = 20.8 Hz), 16.9;
Anal. Calc. for C12H12ClFN4O (+0.5 MeOH): C, 50.36; H, 4.73; N, 18.79;
and Found: C, 50.45; H, 4.68; N, 18.70.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran
-1ꢁ-yl) 6-chloropurine} phosphonate (12): Second-generation Grubbs cata-
lyst (47.2 mg, 0.0556 mmol, 0.04 eq) was added to a solution of the 6-
chloropurine derivative 11b (215 mg, 1.391 mmol, 1.0 eq) in anhydrous
methylene chloride (15.0 mL) and diethyl vinylphosphonate (913 mg,
5.564 mmol, 4 eq). This reaction mixture was refluxed for 36 hours un-
der dry argon and concentrated under reduced pressure. The residue was
purified by silica gel column chromatography (EtOAc/n-Hexane/MeOH,
1
2:1:0.03) to give 12 (343 mg, 59%): H NMR (CDCl3, 300 MHz) δ 8.75 (s,
1H), 8.32 (s, 1H), 6.69 (dd, J = 18.2, 20.4 Hz, 1H), 6.21 (dd, J = 20.2, 5.6 Hz,
1H), 6.13 (dd, J = 17.4, 20.3. Hz, 1H), 4.15–4.09 (m, 4H), 3.85 (dd, J = 8.2,
6.0 Hz, 1.5H), 3.54 (dd, J = 8.2, 5.6 Hz, 1.5H), 1.32 (m, 3H), 1.18–1.14 (s,
6H); 13C NMR (CDCl3, 75 MHz) δ 151.7, 153.4, 151.1, 149.5, 143.6, 132.6,
118.1, 96.2 (d, J = 198.8 Hz), 85.8 (d, J = 19.2 Hz), 63.6, 62.4, 61.8, 39.6 (d,
J = 18.6 Hz), 17.2, 15.3; Anal. Calc. for C16H21ClFN4O4P (+1.0 MeOH): C,
45.36; H, 5.59; N, 12.44; and Found: C, 45.25; H, 5.65; N, 12.38.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-vinyl-3ꢁ-methyl -2ꢁ-fluoro-tetrahydrofura
n-1ꢁ-yl) adenine} phosphonate (13): A solution of 12 (168 mg, 0.40 mmol)
in saturated methanolic ammonia (8 mL) was stirred overnight at 68◦C in a

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
565
steel bomb. Volatiles were removed by evaporation, and the residue so ob-
tained was purified by silica gel column chromatography (MeOH/CH2Cl2,
1:10) to give 13 (80 mg, 50%) as a white solid: mp 162–164◦C; UV (MeOH)
λmax 262.5 nm; 1H NMR (DMSO-d6, 300 MHz) δ 8.38 (s, 1H), 8.18 (s, 1H),
6.68 (dd, J = 18.4, 20.2 Hz, 1H), 6.21 (dd, J = 20.0, 5.6 Hz, 1H), 6.12 (dd,
J = 17.8, 19.9. Hz, 1H), 5.98 (br s, 2H), 4.12–4.07 (m, 4H), 3.83–3.72 (dd,
J = 8.0, 5.4 Hz, 1.5H), 3.58 (d, J = 8.0 Hz, 1.5H), 1.31 (s, 6H), 1.12 (s,
3H); 13C NMR (DMSO-d6, 75 MHz) δ 155.2, 152.8, 151.3, 148.5, 143.2,
118.3, 112.7, 94.2 (d, J = 196.5 Hz), 87.6 (d, J = 18.6 Hz), 62.9, 62.4,
61.7, 41.1 (d, J = 18.8 Hz), 15.3, 14.2; Anal. Calc. for C16H23FN5O4P (+1.0
MeOH): C, 47.36; H, 6.31; N, 16.24; and Found: C, 47.43; H, 6.24; N,
16.32.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-9-(3ꢁ-Vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1ꢁ-yl) ad
enine} phosphonic acid (14): Trimethylsilyl bromide (0.743 mL, 5.63 mmol,
10 eq) was added to a solution of the phosphonate 13 (225 mg, 0.563 mmol)
in anhydrous CH3CN (15 mL) and 2,6-lutidine (1.31 mL, 11.26 mmol, 20
eq) and heated for 24 hours at 70◦C under nitrogen. The reaction mix-
ture was then concentrated in vacuum to give a brown residue, and then
co-evaporated from conc aqueous NH4OH (2 × 30 mL). The resultant pu-
rified by twice triturating the residue in acetone (10 mL) and removing
the acetone by evaporation. The residue so obtained was then purified by
preparative reverse-phase chromatography. Lyophilization of the appropri-
ate fraction provided the phosphonic acid salt 14 (79 mg, 39%) as a white
1
salt (ammonium salt): mp 168–170◦C; UV (H2O) λmax 261.5 nm; H NMR
(D2O, 300 MHz) δ 8.25 (s, 1H), 8.14 (s, 1H), 6.62 (dd, J = 18.6, 20.4 Hz,
1H), 6.18 (dd, J = 19.2, 5.4 Hz, 1H), 6.11 (dd, J = 17.4, 19.8. Hz, 1H), 3.85
(dd, J = 8.0, 5.2 Hz, 1.5H), 3.58 (dd, J = 8.1, 2.8 Hz, 1.5 H), 1.23 (m, 3H);
13C NMR (D2O, 75 MHz) δ 154.5, 153.6, 151.5, 141.6, 119.7, 113.5, 98.7 (d,
J = 202.4 Hz), 84.4 (d, J = 20.8 Hz), 40.4 (dd, J = 20.4 Hz), 17.2; HPLC
tR = 11.09; and HRMS [M–H]+ req. 342.0754, found 342.0755.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran
-1ꢁ-yl) 6-chloropurine} phosphonate (15): A solution of vinyl phosphonate
nucleoside analogue 12 (250 mg, 0.597 mmol) in methanol (10 mL) was
added to 10% Pd/C (10 mg) in cyclohexene (5 mL) under Ar and refluxed
for 24 hours. The reaction mixture was then filtered through a Celite pad,
solvents were removed by evaporation, and the residue was purified by silica
gel column chromatography using methanol and methylene chloride (10:1)
and eluent to give the ethyl phosphonate analogue 15 (198 mg, 79%) as
1
a white solid: mp 164–166◦C; H NMR (CDCl3, 300 MHz) δ 8.77 (s, 1H),
8.35 (s, 1H), 6.19 (dd, J = 19.8, 5.4 Hz, 1H), 4.12–4.08 (m, 4H), 3.82 (dd,
J = 8.0, 5.8 Hz, 1.5H), 3.52 (dd, J = 8.2, 4.8 Hz, 1.5H), 2.29 (m, 2H), 1.86
(m, 2H), 1.31–1.28 (m, 9H); 13C NMR (CDCl3, 75 MHz) δ 151.6, 151.2,
150.4, 143.5, 132.6, 96.2 (d, J = 201.2 Hz), 87.4 (d, J = 19.6 Hz), 62.8,

566
K. M. Kim and J. H. Hong
62.2, 37.6 (d, J = 19.7 Hz), 28.4, 18.6, 15.4; Anal. Calc. for C16H23ClFN4O4P
(+0.5 MeOH): C, 45.44; H, 5.78; N, 12.85; and Found: C, 45.54; H, 5.86; N,
12.92.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofura
n-1ꢁ-yl) adenine} phosphonate (16): The adenine derivative 16 was prepared
from the 6-chloropurine analogue 15 by ammonolysis, as described for 13:
yield 53%; mp 172–174◦C; UV (MeOH) λmax 260.5 nm; 1H NMR (DMSO-d6,
300 MHz) δ 8.36 (s, 1H), 8.15 (s, 1H), 6.20 (dd, J = 18.4, 5.4 Hz, 1H), 5.27
(br s, 2H), 4.15–4.08 (m, 4H), 3.85 (dd, J = 8.2, 5.6 Hz, 1.5H), 3.55 (d, J =
8.2 Hz, 1.5H), 2.21–1.98 (m, 4H), 1.31–1.25 (m, 9H); 13C NMR (DMSO-d6,
75 MHz) δ 154.8, 152.2, 149.5, 143.7, 119.5, 95.6 (d, J = 182.7 Hz), 86.6 (d,
J = 19.6 Hz), 62.3, 61.7, 36.8 (d, J = 19.7 Hz), 28.7, 18.2, 16.2, 15.1; Anal.
Calc. for C16H25FN5O4P (+1.0 MeOH): C, 47.13; H, 6.75; N, 16.16; and
Found: C, 47.22; H, 6.83; N, 16.23.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-{9-(3ꢁ-Ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1ꢁ-yl) a
denine} phosphonic acid (17): Phosphonic acid 17 was synthesized from
16 by hydrolysis, as described for 14: yield 41%, UV (H2O) λmax 262.5 nm;
1H NMR (D2O, 300 MHz) δ 8.34 (s, 1H), 8.13 (s, 1H), 6.17 (dd, J = 19.4,
5.6 Hz, 1H), 3.86 (dd, J = 8.0, 5.8 Hz, 1.5H), 3.57 (dd, J = 8.1, 4.0 Hz, 1.5H),
2.25–2.21 (m, 2H), 2.02–1.85 (m, 5H); 13C NMR (D2O, 75 MHz) δ 154.7,
152.6, 150.7, 142.2, 118.5, 94.3 (d, J = 194.6 Hz), 85.8 (d, J = 18.8 Hz), 61.4,
60.9, 38.2 (d, J = 19.2 Hz), 28.9, 19.1, 15.4; HPLC tR = 10.98; and HRMS
[M–H]+ req. 344.0687, found 344.0685.
(rel)-(1ꢁS,2ꢁR,3ꢁS)-9-(3ꢁ-Vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1ꢁ-yl) 6-
chloropurine(18a) and (rel)-(1ꢁR,2ꢁR,3ꢁS)-9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetra
hydrofuran-1ꢁ-yl) 2-fluoro-6-chloropurine (18b): Condensation of 10 with 2-
fluoro-6-chloropurine was performed under the Vorbruggen condensation
conditions described for 11a and 11b to give 18a and 18b, respectively: data
for 18a: yield 29%; UV (MeOH) λmax 267.0 nm; 1H NMR (CDCl3, 300 MHz)
δ 8.45 (s, 1H), 6.20 (dd, J = 19.6, 5.6 Hz, 1H), 5.69 (dd. J = 10.8, 8.4 Hz,
1H), 4.98–5.04 (m, 2H), 3.88 (dd, J = 8.2, 5.6 Hz, 1.5H), 3.57 (dd, J =
8.1, 4.2 Hz, 1.5H), 1.30 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ 157.2 (d, J =
220.2 Hz), 154.5, 153.4, 145.8, 137.0, 121.1, 109.7, 92.2 (d, J = 196.8 Hz),
85.6 (d, J = 19.8 Hz), 76.4, 38.9 (d, J = 19.2 Hz), 17.4; Anal. Calc. for
C12H11ClF2N4O (+1.0 MeOH): C, 47.01; H, 4.55; N, 16.87; Found: C, 46.92;
1
H, 4.61; N, 16.81. data for 18b: yield 30%; UV (MeOH) λmax 268.0 nm; H
NMR (CDCl3, 300 MHz) δ 8.46 (s, 1H), 6.22 (dd, J = 19.2, 5.5 Hz, 1H), 5.72
(dd. J = 10.6, 8.2 Hz, 1H), 4.97–5.03 (m, 2H), 3.86 (dd, J = 8.0, 5.5 Hz,
1.5H), 3.58 (d, J = 8.2 Hz, 1.5H), 1.28 (s, 3H); 13C NMR (CDCl3, 75 MHz)
δ 157.4 (d, J = 219.6 Hz), 155.1, 153.8, 146.2, 136.7, 120.4, 110.2, 93.4 (d,
J = 198.8 Hz), 84.8 (d, J = 19.6 Hz), 76.4, 39.5 (d, J = 20.0 Hz), 16.7; Anal.
Calc. for C12H11ClF2N4O: C, 47.93; H, 3.69; N, 18.63; and Found: C, 47.99;
H, 3.61; N, 18.71.

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
567
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofura
n-1ꢁ-yl) 2-fluoro-6-chloropurine} phosphonate (19): The phosphonate nucle-
oside analogue 19 was prepared from 18 using the cross metathesis pro-
1
cedure described for 12: yield 52%; mp 160–162◦C; H NMR (DMSO-d6,
300 MHz) δ 8.46 (s, 1H), 6.70 (dd, J = 20.6, 17.8 Hz, 1H), 6.23 (dd, J = 19.8,
5.4 Hz, 1H), 6.14 (dd, J = 20.4, 18.6 Hz, 1H), 4.14–4.09 (m, 4H), 3.88 (dd,
J = 8.0, 5.6 Hz, 1.5H), 3.60 (dd, J = 8.1, 2.4 Hz, 1.5H), 1.39 (m, 6H), 1.21 (s,
3H); 13C NMR (DMSO-d6, 75 MHz) δ 157.3 (d, J = 218.8 Hz), 154.7, 149.5,
143.1, 133.9, 124.3, 115.3, 95.7 (d, J = 166.6 Hz), 89.4 (d, J = 16.4 Hz), 62.2,
61.5, 60.9, 40.4 (d, J = 16.2 Hz), 15.7; Anal. Calc. for C16H20ClF2N4O4P
(+1.0 MeOH): C, 43.61; H, 5.17; N, 11.97; and Found: C, 43.73; H, 5.26; N,
11.89.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofura
n-1ꢁ-yl) 2-fluoro-6-aminopurine} phosphonate (20a) and (rel)-(1ꢁR,2ꢁR,3ꢁS)-
diethyl {9-(3ꢁ-vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1ꢁ-yl) 2-amino-6-chlor-
opurine} phosphonate (20b): Dry ammonia gas was bubbled into a stirred
solution of 19 (175 mg, 0.4 mmol) in DME (7.0 mL) at room temperature
overnight. Salts were removed by filtration and the filtrate was concentrated
under reduced pressure. The residue obtained was purified by silica gel col-
umn chromatography (MeOH/CH2Cl2, 1:8) to give 20a (24 mg, 13%) and
20b (80 mg, 40%), respectively: data for 20a; mp 167–169◦C; UV (MeOH)
1
λmax 262.0 nm; H NMR (DMSO-d6, 300 MHz) δ 8.24 (s, 1H), 7.71 (br s,
NH2, 2H), 6.63 (dd, J = 19.6, 18.4 Hz, 1H), 6.18 (dd, J = 18.8, 5.2 Hz,
1H), 6.09 (dd, J = 19.7, 18.2 Hz, 1H), 4.14–4.10 (m, 4H), 3.90 (dd, J = 8.2,
5.4 Hz, 1.5H), 3.64 (dd, J = 8.2, 2.6 Hz, 1.5H), 1.34 (s, 6H), 1.26 (s, 3H);
13C NMR (DMSO-d6, 75 MHz) δ 159.8 (d, J = 262.4 Hz), 154.8, 152.2, 147.8,
143.6, 118.6, 114.2, 93.6 (d, J = 178.8 Hz), 85.4 (d, J = 18.8 Hz), 63.2, 62.8,
61.5, 40.2 (d, J = 18.7 Hz), 17.4, 14.5; Anal. Calc. for C16H22F2N5O4P (+1.0
MeOH): C, 45.46; H, 5.83; N, 15.59; Found: C, 45.55; H, 5.78; N, 15.67. Data
1
for 20b; mp 164–166◦C; UV (MeOH) λmax 309.0 nm; H NMR (DMSO-d6,
300 MHz) δ 8.13 (s, 1H), 7.70 (br s, NH2, 2H), 6.61 (dd, J = 19.2, 18.2 Hz,
1H), 6.19 (dd, J = 18.6, 5.2 Hz, 1H), 5.98 (dd, J = 19.2, 17.4 Hz, 1H),
4.13–4.06 (m, 4H), 3.82 (dd, J = 8.0, 5.6 Hz, 1.5H), 3.59 (d, J = 8.1 Hz,
1.5H), 1.42 (s, 6H), 1.30 (s, 3H); 13C NMR (DMSO-d6, 75 MHz) δ 159.1,
155.2, 152.6, 148.5, 143.8, 124.7, 113.8, 93.6 (d, J = 186.4 Hz), 84.4 (d, J =
18.6 Hz), 62.4, 62.0, 61.3, 40.4 (d, J = 18.8 Hz), 17.3, 14.9; Anal. Calc. for
C16H22ClFN5O4P (+1.0MeOH): C, 43.89; H, 5.63; N, 15.05; and Found: C,
43.98; H, 5.56; N, 15.13.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-9-{(3ꢁ-Vinyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1ꢁ-yl) g
uanine} phosphonic acid(21): Trimethylsilyl bromide (0.0876 mL,
6.62 mmol) was added to a solution of 20b (164 mg, 0.379 mmol) in dry
CH3CN (12 mL) at room temperature. After stirring for 24 hours, the sol-
vent was removed, and the residue evaporated 3 times with methanol. The

568
K. M. Kim and J. H. Hong
residue was then dissolved in MeOH (15.0 mL) and 2-mercaptoethanol
(103.7 μL, 1.52 mmol) and NaOMe (80.64 mg, 1.52 mmol) was added. This
mixture was refluxed for 24 hours under N2, cooled, neutralized with glacial
AcOH, and evaporated to dryness under vacuum. The residue obtained
was co-evaporated from conc NH4OH (2 × 20 mL) and the resultant solid
was triturated with acetone (2 × 8 mL). After evaporating the acetone, the
residue was purified by preparative column chromatography using reverse-
phase C18 silica gel and elution with water. Lyophilization of the appropriate
fraction provided 21 (62.7 mg, 44%) as a yellowish salt (ammonium salt).
mp 169–171◦C; UV (H2O) λmax 252.0 nm; 1H NMR (D2O, 300 MHz) δ 7.76
(s, 1H), 6.54 (dd, J = 19.4, 17.8 Hz, 1H), 6.19 (dd, J = 19.2, 5.4 Hz, 1H),
6.02 (dd, J = 19.1, 17.4 Hz, 1H), 3.87 (dd, J = 8.4, 5.6 Hz, 1.5H), 3.62 (dd,
J = 7.9, 2.8 Hz, 1.5H), 1.31 (s, 3H); 13C NMR (D2O, 75 MHz) δ 157.4, 154.6,
151.7, 148.4, 137.5, 118.9, 114.6, 96.4 (dd, J = 189.6 Hz), 76.3, 74.3 (d,
J = 19.2 Hz), 40.3 (dd, J = 19.8, 18.4 Hz), 17.2; HPLC tR = 10.02 min; and
HRMS [M–H]+ req. 358.0687, found 358.0684.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofura
n-1-yl) 2-fluoro-6-chloropurine} phosphonate (22): Compound 22 was syn-
thesized from 19 using the transfer catalytic hydrogenation procedure de-
scribed for 15: yield 73%; 1H NMR (DMSO-d6, 300 MHz) δ 8.46 (s, 1H), 6.17
(dd, J = 18.6, 5.2 Hz, 1H), 4.11–4.07 (m, 4H), 3.90 (dd, J = 8.1, 5.2 Hz,
1.5H), 3.67 (dd, J = 7.6, 2.2 Hz, 1.5H), 2.15–2.06 (m, 4H), 1.53 (m, 6H), 1.19
(s, 3H); 13C NMR (DMSO-d6, 75 MHz) δ 157.3 (d, J = 220.2 Hz, 1H), 153.4,
145.4, 136.6, 121.5, 98.4 (d, J = 182.4 Hz), 87.4 (d, J = 19.2 Hz), 62.2, 61.7,
38.7 (d, J = 19.0 Hz), 28.6, 18.3, 14.5, 13.8; Anal. Calc. for C16H22ClF2N4O4P:
C, 48.80; H, 5.05; N, 12.77; and Found: C, 48.91; H, 5.12; N, 12.68.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-Diethyl {9-(3ꢁ-ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofura
n-1-yl) 2-fluoro-6-aminopurine} phosphonate (23a) and (rel)-(1ꢁR,2ꢁR,3ꢁS)-
diethyl {9-(3ꢁ-ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1-yl) 2-amino-6-chlo
ropurine} phosphonate (23b): Ammonolysis of 22 using the procedure de-
scribed for 14 gave 23a and 23b: Data for 23a; yield 11%; UV (MeOH) λmax
261.5 nm; 1H NMR (DMSO-d6, 300 MHz) δ 8.22 (s, 1H), 7.72 (br s, NH2, 2H),
6.16 (d, J = 18.4, 5.4 Hz, 1H), 4.15–4.09 (m, 4H), 3.89 (dd, J = 8.0, 5.2 Hz,
1.5H), 3.66 (dd, J = 7.6, 2.0 Hz, 1.5H), 2.14–1.98 (m, 4H), 1.54 (m, 6H), 1.23
(s, 3H); 13C NMR (DMSO-d6, 75 MHz) δ 161.3 (d, J = 232.2 Hz, 1H), 154.5,
151.8, 143.5, 124.6, 97.2 (d, J = 178.8 Hz), 84.9 (d, J = 18.8 Hz), 61.3, 60.8,
39.4 (d, J = 18.6 Hz), 29.2, 18.8, 15.4, 14.5; Anal. Calc. for C16H24F2N5O4P
(+1.0 MeOH): C, 45.25; H, 6.25; N, 15.52; Found: C, 45.34; H, 6.29; N, 15.62.
1
Data for 23b; yield 39%; UV (MeOH) λmax 308.0 nm; H NMR (DMSO-d6,
300 MHz) δ 8.19 (s, 1H), 7.71 (br s, NH2, 2H), 6.15 (d, J = 18.0, 5.0 Hz, 1H),
4.12–4.08 (m, 4H), 3.85 (dd, J = 8.1, 5.3 Hz, 1.5H), 3.62 (dd, J = 7.8, 2.2 Hz,
1.5H), 2.14–2.03 (m, 4H), 1.56 (m, 6H), 1.28 (s, 3H); 13C NMR (DMSO-d6,
75 MHz) δ 157.8, 154.3, 151.3, 144.6, 124.8, 96.2 (d, J = 178.8 Hz), 86.6 (d,

2ꢁ-fluoro-3ꢁ-methyl-5ꢁ-deoxyphosphonic Acid Nucleoside Analogues
569
J = 18.7 Hz), 62.3, 61.8, 39.5 (d, J = 18.6 Hz), 28.4, 18.5, 15.3, 14.8; Anal.
Calc. for C16H24ClFN5O4P (+1.0 MeOH): C, 43.71; H, 6.04; N, 14.99; and
Found: C, 43.60; H, 5.96; N, 15.11.
(rel)-(1ꢁR,2ꢁR,3ꢁS)-9-{(3ꢁ-Ethyl-3ꢁ-methyl-2ꢁ-fluoro-tetrahydrofuran-1-yl) g
uanine} phosphonic acid (24): The nucleoside phosphonic acid 24 was syn-
thesized by hydrolysis as described for 22. Yield 48%; mp 170–172◦C; UV
1
(H2O) λmax 252.5 nm; H NMR (D2O, 300 MHz) δ 7.70 (s, 1H), 6.20 (dd,
J = 18.4, 5.4 Hz, 1H), 3.88 (dd, J = 8.2, 5.3 Hz, 1.5H), 3.57 (dd, J = 7.8,
2.0 Hz, 1.5H), 2.15–1.97 (m, 4H), 1.31 (s, 3H); 13C NMR (D2O, 75 MHz) δ
157.7, 154.7, 151.5, 138.1, 117.2, 93.4 (dd, J = 184.8 Hz), 79.4, 76.4 (d, J =
19.4 Hz), 38.4 (dd, J = 19.8, 18.4 Hz), 29.2, 18.8, 16.2; HPLC tR = 9.98 min;
and HRMS [M–H]+ req. 360.0776, found 360.0775.
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