Synthesis of acyclic nucleoside and nucleotide analogues from amino acids: A convenient approach to a PMEA-PMPA hybrid

Article abstract of DOI:10.1016/S0040-4020(00)00422-1

Nonracemic amino alcohols derived from common amino acids have been used to assemble acyclic nucleoside and nucleotide analogues with control of absolute stereochemistry. Both (R)- and (S)-2-amino-1-propanol, readily available from D- or L-alanine, were used to prepare the nucleoside analogues (R)- and (S)-9-[1- methyl-2-hydroxyethyl]adenine, and then the nucleotide analogues (R)- and (S)-9-[1-methyl-2-phosphonomethoxyethyl]adenine. In a similar fashion, the CBz derivative of L-threonine was used to prepare first (1R,2R)-9-[1-hydroxymethyl-2-hydroxypropyl]adenine, and then the bis phosphonomethoxy derivative. The bis phosphonate derived from threonine represents a unique structural hybrid of PMEA and PMPA, both of which have well established antiviral activity. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00422-1

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 5077±5083
Synthesis of Acyclic Nucleoside and Nucleotide Analogues from
Amino Acids: A Convenient Approach to a PMEA±PMPA Hybrid
²
Arlen L. Jeffery, Jae-Hun Kim and David F. Wiemer
*
Department of Chemistry, University of Iowa, Iowa City, IA 52242-1294, USA
Received 14 April 2000; accepted 16 May 2000
AbstractÐNonracemic amino alcohols derived from common amino acids have been used to assemble acyclic nucleoside and nucleotide
analogues with control of absolute stereochemistry. Both (R)- and (S)-2-amino-1-propanol, readily available from d- or l-alanine, were used
to prepare the nucleoside analogues (R)- and (S)-9-[1-methyl-2-hydroxyethyl]adenine, and then the nucleotide analogues (R)- and (S)-9-[1-
methyl-2-phosphonomethoxyethyl]adenine. In a similar fashion, the CBz derivative of l-threonine was used to prepare ®rst (1R,2R)-9-[1-
hydroxymethyl-2-hydroxypropyl]adenine, and then the bis phosphonomethoxy derivative. The bis phosphonate derived from threonine
represents a unique structural hybrid of PMEA and PMPA, both of which have well established antiviral activity. q 2000 Elsevier Science
Ltd. All rights reserved.
Interest in nucleoside phosphonates has been stimulated by
a series of studies on the antiviral activity of acyclic
nucleotide analogues.1,2 One prototypical compound, 9-(2-
their in vitro antiviral potency.5 For example, a change in
absolute stereochemistry at the single asymmetric center of
PMPA has been reported to result in approximately a 45-
fold change in some EC50 values, which may be because the
enantiomers differ in their ability to serve as substrates for
AMP kinase.6 But whatever the reason for the different
biological activity of these enantiomers, these ®ndings
place a premium on synthetic methods that allow prepara-
tion of such compounds with control of their absolute
stereochemistry. In this paper we report the use of amino
alcohols readily available in nonracemic form through
reduction of common amino acids to assemble new non-
racemic nucleoside analogues, and the further elaboration
of some of these compounds into acyclic nucleotide
analogues of the phosphonomethoxy category.
phosphonylmethoxyethyl)adenine
(PMEA,
1),
has
impressive activity against retroviruses in vitro3 and potent
activity against HIV. These discoveries encouraged
preparation of a family of related compounds4 including,
most notably, the 9-(S)-(3-hydroxy-2-phosphonylmethoxy-
propyl) or HPMP series and the 9-(R)-(2-phosphonyl-
methoxypropyl) or PMP series, represented by the adenine
derivatives S-HPMPA (2) and R-PMPA (3), respectively
(Fig. 1). Extensive studies have revealed a broad spectrum
of potent antiviral activity for these compounds, and
different modes of action (and pro®les of antiviral activity)
despite the strong similarity of structures.4
It has been recognized for some time that the absolute
stereochemistry of HPMPA and PMPA signi®cantly affects
As a ®rst demonstration of this approach, the amino alcohol
obtained by reduction of d-alanine, (R)-2-amino-1-propanol
Figure 1.
Keywords: nucleosides; nucleotides; phosphonic acids and derivatives.
* Corresponding author. Tel.: 11-319-335-1365; fax: 11-319-335-1270; e-mail: david-wiemer@uiowa.edu
Present address: Department of Industrial Chemistry, Kangnung National University, Kangnung, Korea.
²
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00422-1

5078
A. L. Jeffery et al. / Tetrahedron 56 (2000) 5077±5083
Scheme 1.
(4), was converted into the corresponding nonracemic
adenine derivative 8 through minor variations on the classic
Montgomery sequence7 (Scheme 1). Condensation of
5-amino-4,6-dichloropyrimidine (5) with amine 4 in re¯ux-
ing 1-butanol provided the intermediate pyrimidine 6.8
Closure of the imidazo ring was brought about by reaction
with trimethyl orthoformate yielding purine 7 without
protection of the primary hydroxyl group, and a ®nal
reaction with methanolic ammonia gave the adenine
derivative 8 in an overall yield of 74% for the 3-step
sequence. The enantiomeric purity of the ®nal product
was established as .92% through condensation with (S)-
O-methylmandelic acid (MMA) and analysis of the 1H
NMR spectra of the resulting ester 9.
excess reagents or by reaction with the tri¯ate analogue
(10b) of phosphonate 10a10 went unrewarded. Hydrolysis
of the ethyl esters in phosphonate 11 was accomplished
under standard conditions11 to give the desired phosphonic
acid as its sodium salt (12) in nearly quantitative yield.
A parallel series of reactions (Scheme 2) was used to
prepare the enantiomeric acyclic nucleoside 14 from (S)-
2-amino-1-propanol (13). After an ee .92% was
established by preparation of the (S)-O-methylmandelate
derivative 15, the alcohol 14 was converted to the phos-
phonate ester 16 and then to the sodium salt 17 through
reactions parallel to those used to prepare compound 12.
In both enantiomeric series, the ee of the product follows
directly from that of the starting amino alcohol, and no
evidence of racemization was observed.
Addition of a phosphonomethoxy group to compound 8 was
best accomplished through reaction with tosylate 10a and
LiOtBu in DMF,9 which consistently gave phosphonate 11
in ,40% yield. Efforts to improve this yield through use of
In theory, the synthetic sequences described above could be
applied with an amino alcohol derived from any amino acid.
Scheme 2.
Figure 2.

A. L. Jeffery et al. / Tetrahedron 56 (2000) 5077±5083
5079
Scheme 3.
While there are a number of such targets that might be
interesting, one that we found particularly intriguing was
the acyclic nucleoside 18. This compound, which can be
viewed as a derivative of d-threonine, could be further
elaborated into nucleotide analogues that can be considered
members of either the PMPA or PMEA series (Fig. 2) and
might combine the varied aspects of their biological
activities. Thus, preparation of compound 18 became the
immediate goal.
protected amine 22 in HCO2H/CH3OH through a column
of palladium black.12 However, this procedure gave the
formate salt of the desired amine sometimes accompanied
by the formamide derivative. Use of triethylsilane as the
hydrogen donor13 with palladium black in ethanol resulted
in a product more readily isolated. After the silane reduc-
tion, the initial product was treated directly with compound
5 to obtain the substituted pyrimidine 23. Compound 23 was
converted to the desired purine 24 by reaction with trimethyl
orthoformate under standard conditions. Both preparation of
the pyrimidine 23 and the purine 24 could be accomplished
in good yield without protection of the hydroxyl groups. A
®nal reaction of compound 24 with ethanolic ammonia gave
the new adenine-derived diol 18 as a single diastereomer in
nonracemic form.
For preparation of compound 18, commercial threonine (19)
was ®rst protected as its Cbz derivative (20) and then
converted to the methyl ester (21) and reduced under
standard conditions to obtain the N-protected amino alcohol
22 (Scheme 3). The CBz group of compound 22 was
cleaved through hydrogenolysis upon treatment with 5%
formic acid in methanol in the presence of palladium
black, or more conveniently by passing a solution of the
Selective conversion of the diol 18 into a phosphono-
methoxy derivative apparently would bene®t from
Scheme 4.

5080
A. L. Jeffery et al. / Tetrahedron 56 (2000) 5077±5083
protection of one of the two hydroxyl groups. Selective
protection of the primary alcohol was readily achieved
upon treatment of diol 18 with TBSCl/DMAP/Et3N in
DMF. The site of silylation was easily established from
the 1H NMR spectrum of the product (25): when this spec-
trum was recorded in (CD3)2SO, a clean doublet observed at
d 5.18 re¯ected the presence of the free secondary hydroxyl
group. Unfortunately, treatment of compound 25 with
LiOtBu and phosphonate 10a gave a mixture of products
that proved dif®cult to separate rather than solely the desired
product 26. Based on the NMR spectra of the mixture it
appeared that rearrangement of the TBS group prior to
alkylation had resulted in formation of a mixture of two
regioisomeric phosphonomethoxy products.
trometry Facility. Elemental analyses were performed by
Atlantic Microlabs, Norcross, GA.
(R)-2-[(5-Amino-6-chloropyrimidin-4-yl)amino]-1-pro-
panol (6). A solution of (R)-2-amino-1-propanol (4, 0.96 g,
12.8 mmol) and 5-amino-4,6-dichloropyrimidine (5, 2.10 g,
12.8 mmol) in n-butanol (30 mL) was treated with sodium
bicarbonate (1.24 g, 14.8 mmol) and heated at re¯ux. After
48 h, the solution was concentrated in vacuo and the residue
was washed with chloroform (3£20 mL). The remaining
residue was dissolved in ethyl acetate and the solution
was ®ltered through silica gel. The ®ltrate was concentrated
in vacuo to afford an analytically pure sample of pyrimidine
6 (2.39 g, 92%): mp 778C; 1H NMR (DMSO) d 7.71 (s, 1H),
6.49 (br d, Jˆ7.4 Hz, 1H, exch. with D2O), 5.04 (br s, 2H,
exch. with D2O), 4.73 (dd, Jˆ4.9, 4.9 Hz, 1H, exch. with
D2O), 4.16 (m, 1H), 3.47 (m, upon D2O addition: dd,
Jˆ10.7, 5.3 Hz, 1H), 3.35 (m, upon D2O addition: dd,
Jˆ10.7, 5.8 Hz, 1H), 1.15 (d, Jˆ6.8 Hz, 3H); 13C NMR
(DMSO) d 151.6, 145.6, 136.8, 123.4, 64.1, 48.3, 17.2.
Anal. Calcd for C7H11ClN4O: C, 41.49; H, 5.47; N, 27.65;
Cl, 17.50. Found: C, 41.61; H, 5.46; N, 27.57; Cl, 17.44.
Instead of pursuing other routes to the mono phosphono-
alkylated products, compound 18 was treated with an excess
of base and phosphonate 10a in an effort to obtain the bis
phosphonate 27 (Scheme 4). However, this approach gave
only traces of the desired product by 31P NMR, which may
be consistent with literature reports on the dif®culty of this
type of reaction.9 Fortunately similar treatment of the
chloropurine derivative 24 with phosphonate 10b resulted
in formation of the bis phosphonate 28 in modest yield. This
chloropurine could be converted to the desired adenine
derivative 27 by treatment with ethanolic ammonia.
Hydrolysis of the phosphonate esters of compound 27 was
readily accomplished by treatment with TMSBr and
collidine, affording the target bis phosphonate 29.
(R)-9-(1-Methyl-2-hydroxyethyl)6-chloropurine (7). A
solution of compound 6 (2.05 g, 10 mmol) in trimethyl-
orthoformate (40 mL) was stirred under argon as conc.
HCl (0.7 mL, 23.0 mmol) was added. The resulting solution
was stirred for 6 h at room temperature and then concen-
trated in vacuo. The residue was crystallized from acetone,
providing an analytically pure sample of purine 7 (2.03 g,
1
In conclusion, these investigations have demonstrated that
nonracemic amino alcohols can be employed to construct
nucleoside analogues with control of the absolute stereo-
chemistry. Phosphonomethylation of the alcohol or diol
affords the corresponding nucleotide analogues. This
strategy has provided a convenient route to a novel hybrid
of the anti-viral agents PMPA and PMPA, the bis phospho-
nate 29. Expansion of this strategy to preparation of related
compounds and determination of the biological activity of
these new compounds will be pursued in due course.
94%): mp 203±2048C; H NMR (DMSO) d 8.76 (s, 1H),
8.74 (s, 1H), 5.04 (dd, Jˆ5.7, 5.7 Hz, 1H exch. with D2O),
4.76 (m, 1H), 3.85 (m, upon D2O addition: dd, Jˆ11.4,
7.4 Hz, 1H), 3.74 (m, upon D2O addition: dd, Jˆ11.4,
4.6 Hz, 1H), 1.54 (d, Jˆ7 Hz, 3H); 13C NMR (DMSO) d
154.2, 151.1, 148.8, 146.6, 131.0, 63.2, 53.9, 16.2. Anal.
Calcd for C8H9ClN4O: C, 45.19; H, 4.27; N, 26.35; Cl,
16.67. Found: C, 45.29; H, 4.24; N, 26.31; Cl, 16.58.
(R)-9-(1-Methyl-2-hydroxyethyl)adenine (8). A solution
of the chloropurine 7 (1.02 g, 4.8 mmol) in methanol
(40 mL) was saturated with ammonia at 08C in a pressure
¯ask. The pressure ¯ask was sealed, warmed to 65±708C in
an oil bath, and held at that temperature for 48 h. After the
¯ask had cooled to room temperature, the solvent was
removed in vacuo and the residue was washed with
chloroform to remove the side product, (R)-9-[1-methyl-2-
hydroxyethyl]6-methoxypurine (0.12 g, 12%). The remain-
ing residue was crystallized from methanol, providing the
desired product 8 (0.80 g, 86%): mp 2128C; 1H NMR
(DMSO) d 8.15 (s, 1H), 8.12 (s, 1H), 7.15 (br s, 2H, exch.
with D2O), 5.04 (dd, Jˆ5.5, 5.5 Hz, 1H, exch. with D2O),
4.60 (m, 1H), 3.80 (m, upon D2O addition: dd, Jˆ11.4,
7.0 Hz, 1H), 3.69 (m, upon D2O addition: dd, Jˆ11.4,
4.7 Hz, 1H), 1.48 (d, Jˆ6.8 Hz, 3H); 13C NMR (DMSO)
d 155.9, 152.0, 149.4, 139.7, 119.0, 63.4, 52.6, 16.7.
Anal. Calcd for C8H11N5O: C, 49.73; H, 5.74; N, 36.25.;
Found: C, 49.75; H, 5.75; N, 36.16.
Experimental
Immediately prior to use, tetrahydrofuran (THF) was
distilled from sodium/benzophenone, and both acetonitrile
and dichloromethane were distilled from calcium hydride.
Dimethylformamide (DMF) was distilled from calcium car-
bonate under reduced pressure and stored over magnesium
sulfate under argon. All reactions in nonaqueous media
were conducted under a positive pressure of argon. Flash
Ê
chromatography was performed with Merck grade 62 A
silica gel (40 mm) and preparative layer chromatography
was performed on plates of silica gel 60 F254. Preparative
reverse phase MPLC separations were conducted with a
C18 column. Melting points were obtained on a Thomas-
Hoover melting point apparatus and are uncorrected. NMR
spectra were recorded at 300 MHz for 1H (75 MHz for 13C)
with CDCl3 as solvent and (CH3)4Si (1H) or CDCl3 (13C,
77.0 ppm) as internal standards unless otherwise noted.
All 31P NMR chemical shifts are reported in ppm relative
to 85% H3PO4 (external standard). High-resolution mass
spectra were obtained at the University of Iowa Mass Spec-
(R)-9-[1-Methyl-2-(S)-(a-methoxy)phenylacetoxyethyl]-
adenine (9). A solution of the alcohol 8 (8.6 mg, 40 mmol),
EDC (43 mg, 200 mmol), DMAP (29 mg, 230 mmol), and
(S)-(a-methoxy)phenylacetic acid (9.6 mg, 60 mmol) in

A. L. Jeffery et al. / Tetrahedron 56 (2000) 5077±5083
5081
dichloromethane (1 mL) was stirred at room temperature.
After 48 h, water (1 mL) was added and the mixture was
stirred until both phases were clear. The product was
extracted into dichloromethane (4£20 mL), dried over
sodium sulfate, and concentrated in vacuo. The residue
was puri®ed by preparative layer chromatography (CHCl3)
to provide the desired product 9 (14 mg, 93%). Integration
of the resonances for the methoxy hydrogens at
d,3.35 ppm established a diastereomeric ratio of 92:8.
280 mmol), DMAP (33 mg, 270 mmol), and (S)-(a-methoxy)-
phenylacetic acid (13 mg, 80 mmol) in dichloromethane
(2 mL) was stirred at room temperature. After 48 h, water
(1 mL) was added and the mixture was stirred until both
phases were clear. The product was extracted into dichloro-
methane (4£20 mL), dried over sodium sulfate, and concen-
trated in vacuo. The residue was puri®ed by preparative
layer chromatography (CHCl3) providing the desired
product 15 (19 mg, 90%). Integration of the methoxy reso-
nances at d,3.33 ppm established a diastereomeric ratio of
96:4 (92% ee). For the major diastereomer: 1H NMR d 8.31
(s, 1H), 7.51 (s, 1H), 7.30 (m, 5H), 5.54 (br s, 2H, exch. with
D2O), 4.91 (m, 1H), 4.68 (dd, Jˆ11.6, 6.7 Hz, 1H), 4.67 (s,
1H), 4.32 (dd, Jˆ11.6, 3.7 Hz, 1H), 3.36 (s, 3H), 1.45 (d,
Jˆ7.1 Hz, 3H).
1
For the major diastereomer: H NMR d 8.32 (s, 1H), 7.44
(s, 1H), 7.33 (m, 5H), 5.61 (br s, 2H, exch. with D2O), 4.81
(m, 1H), 4.68 (s, 1H), 4.57 (dd, Jˆ11.6, 6.8 Hz, 1H), 4.49
(dd, Jˆ11.6, 4.2 Hz, 1H), 3.33 (s, 3H), 1.55 (d, Jˆ7.2 Hz,
3H).
(R)-9-[1-Methyl-2-((diethylphosphono)methoxy)ethyl]-
adenine (11). A slurry of nucleoside 8 (85 mg, 0.44 mmol)
in DMF (0.5 mL) was treated with lithium tert-butoxide
(0.65 mL, 1.0 M in THF) over 5 min. The thick slurry was
stirred an additional 5 min before the addition of phos-
phonate 10a (160 mg, 0.73 mmol) in THF (0.5 mL). The
resulting mixture was stirred at room temperature and
became homogeneous after 2 h, but stirring was continued
for an additional 48 h. The solution was quenched by addi-
tion of 50% acetic acid, the product was extracted into
dichloromethane (4£75 mL), and the extract was dried
over sodium sulfate. After concentration in vacuo, the
resulting oil was puri®ed by column chromatography
(10% MeOH/CHCl3) to afford a pure sample of compound
11 (63 mg, 41%): 1H NMR d 8.27 (s, 1H), 7.93 (s, 1H), 6.39
(br s, 2H, exch. with D2O), 4.85 (m, 1H), 4.00±3.70 (m,
8H), 1.59 (d, Jˆ7.0 Hz, 3H), 1.21 (t, Jˆ7.0 Hz, 6H); 13C
NMR d 155.6, 152.5, 149.6, 139.4, 119.4, 74.8 (d,
JCPˆ9.9 Hz), 65.2 (d, JCPˆ166 Hz), 62.3 (d, JCPˆ6.5 Hz),
50.5, 17.0, 16.3 (d, JCPˆ5.6 Hz); 31P NMR d 20.1. Anal.
Calcd for C13H22N5O4P: C, 45.48; H, 6.46; N, 20.39. Found:
C, 45.23; H, 6.40; N, 20.19.
N-Carbobenzyloxy-l-threonine (20).
A solution of
l-threonine (19, 2.77 g, 23.3 mmol) and sodium bicarbonate
(4.89 g, 58.2 mmol) in 50 mL water was cooled in an ice
bath as benzylchloroformate (4.0 mL, 28.0 mmol) was
added. The ice bath was removed and the solution was
stirred at room temperature while the evolution of carbon
dioxide was monitored. The aqueous solution was then
washed with ether and acidi®ed to pH 2 by addition of
HCl. The milky white solution was extracted with ethyl
acetate, dried over sodium sulfate, and concentrated in
vacuo to afford the desired product, identical to an authentic
1
sample (5.83 g, 99%): H NMR (DMSO) d 7.37 (s, 5H),
6.96 (d, Jˆ8.7 Hz, 1H, exch. with D2O), 5.06 (s, 2H), 4.08
(m, 1H), 3.95 (dd, Jˆ8.8, 3.5 Hz, 1H), 1.09 (d, Jˆ6.4 Hz,
3H).
N-Carbobenzyloxy-l-threonine methyl ester (21). A solu-
tion of acid 20 (5.83 g, 23.0 mmol) in methanol (100 mL)
was cooled in an ice bath and thionyl chloride (2.1 mL,
28.8 mmol) was added dropwise. After the addition was
complete, the ice bath was removed and the solution was
allowed to warm to room temperature and stirred for 24 h.
The methanol was removed in vacuo and the residue was
dissolved in chloroform. The resulting solution was washed
with saturated sodium bicarbonate, dried over sodium sul-
fate, and concentrated in vacuo to yield the desired product
21 identical to an authentic sample (5.97 g, 97%): 1H NMR
d 7.36 (s, 5H), 5.57 (br d, Jˆ8.3 Hz, 1H, exch. with D2O),
5.14 (s, 2H), 4.34 (m, 2H), 3.77 (s, 3H), 2.00 (br d,
Jˆ5.2 Hz, 1H, exch. with D2O), 1.25 (d, Jˆ6.3 Hz, 3H).
(2R,3R)-2-Carbobenzyloxyamino-1,3-butanediol (22).14
A solution of ester 21 (5.69 g, 21.3 mmol) in anhydrous
THF (50 mL) was cooled in an ice bath as lithium boro-
hydride (0.60 g, 27.7 mmol) was added. After hydrogen
evolution ceased, the ice bath was removed and the ¯ask
was heated at re¯ux for 12 h. After the reaction ¯ask had
cooled to room temperature, the THF was removed in
vacuo, methanol (30 mL) was added and the solution was
stirred for 24 h. The solution was neutralized by addition of
HCl and concentrated in vacuo. The residue was dissolved
in chloroform and that solution was washed with brine,
dried over sodium sulfate, and concentrated in vacuo to
(R)-9-(1-Methyl-2-phosphonomethoxyethyl)adenine sodium
salt (12). A solution of phosphonate 11 (74 mg, 0.2 mmol)
in acetonitrile (20 mL) was treated with TMSBr (0.3 mL,
2.2 mmol) and the reaction mixture was stirred at room
temperature for 48 h. The solution was concentrated in
vacuo and the resulting residue was dissolved in water
(20 mL) and stirred for 2 h. The aqueous solution was
washed with dichloromethane (2£20 mL) and concentrated
in vacuo. The glassy solid was dissolved in 5 mL water,
adjusted to pH 7 by addition of 2 M NaOH, and then
concentrated to a white solid. The solid was puri®ed by
reverse phase chromatography to afford the desired product
1
12 (69 mg, 97%): H NMR (D2O±DMSO) d 8.27 (s, 1H),
8.11 (s, 1H), 7.17 (br s, 2H, exch. with D2O), 4.76 (m, 1H),
3.95 (dd, Jˆ10.3, 7.1 Hz, 1H), 3.81 (dd, Jˆ10.3, 4.6 Hz,
1H), 3.35 (d, JPHˆ8.3 Hz, 2H), 1.46 (d, Jˆ6.8 Hz, 3H);
13C NMR (D2O) d 155.3, 152.0, 148.8, 141.2, 118.5, 74.2
(d, JCPˆ9.7 Hz), 68.7 (d, JCPˆ153 Hz), 51.1, 16.4; 31P NMR
(D2O±DMSO) d 13.5; ES LRMS calcd for C9H13N5O4PNa2
(M1H)1 332.1, found 332.1.
1
(S)-9-[1-Methyl-2-(S)-(a-methoxy)phenylacetoxyethyl]-
adenine (15). A solution of the alcohol 14 (12 mg,
60 mmol), prepared by a series of reactions parallel to
those described for the R enantiomer 8, EDC (54 mg,
afford the desired product 22 (5.04 g, 99%). H NMR d
7.35 (s, 5H), 5.59 (br d, 1H, exch. with D2O), 5.10 (s,
2H), 4.12 (m, 1H), 3.79 (s, 2H), 3.57 (m, 1H), 2.93 (br s,
2H, exch. with D2O), 1.19 (d, Jˆ6.5 Hz, 3H); 13C NMR d

5082
A. L. Jeffery et al. / Tetrahedron 56 (2000) 5077±5083
157.1, 136.2, 128.5 (2), 128.1, 128.0 (2), 68.2, 66.9 (±CH2±
from DEPT), 64.3 (±CH2± from DEPT), 56.2, 20.1.
in DMF (5 mL) was stirred at room temperature for 72 h.
The DMF solution was diluted by addition of water (30 mL)
and the product was extracted into dichloromethane
(5£30 mL), dried over sodium sulfate, and puri®ed by
column chromatography (10% MeOH/CHCl3) to afford
(2R,3R)-2-[(5-Amino-6-chloropyrimidin-4-yl)amino]-1,3-
butanediol (23). A solution of diol 22 (2.70 g, 11.3 mmol)
in ethanol (30 mL) was treated with 10% Pd±C (0.36 g,
0.34 mmol), triethylamine (0.56 g, 5.5 mmol), and triethyl-
silane (4.01 g, 34.5 mmol). The reaction mixture was heated
at re¯ux until the starting material could not be detected by
TLC (,3 h). After the solution cooled to room temperature,
the Pd±C was removed by ®ltration and the ®ltrate was
concentrated to afford a clear oil. This oil was treated with
pyrimidine 5 (1.82 g, 11.1 mmol) and sodium bicarbonate
(1.15 g, 13.7 mmol) in 1-butanol (20 mL) and heated at
re¯ux. After 48 h, the solution was allowed to cool to
room temperature and concentrated in vacuo. The residue
was dissolved in ethyl acetate and ®ltered through a short
plug of silica gel to provide the pure product 23 (1.82 g,
69%): 1H NMR (DMSO) d 7.69 (s, 1H), 6.29 (d, Jˆ8.2 Hz,
1H, exch.), 5.11 (s, 2H, exch. with D2O), 4.62 (m, 2H, exch.
with D2O), 4.12 (m, 1H), 3.98 (m, 1H), 3.56 (m, upon D2O
addition: dd, Jˆ10.9, 6.1 Hz, 1H), 3.45 (m, upon D2O addi-
tion: dd, Jˆ10.9, 6.3 Hz, 1H), 1.03 (d, Jˆ6.4 Hz, 3H); 13C
NMR (DMSO) d 152.5, 145.5, 137.0, 123.4, 64.5, 60.2,
57.4, 20.0; ESI HRMS calcd for C8H13N4O2Cl (M1H)1
233.0805, found 233.0800.
1
the desired product 25 (0.349 g, 76%). H NMR (DMSO)
d 8.10 (s, 1H), 8.06 (s, 1H), 7.15 (s, 2H, exch. with D2O),
5.18 (d, Jˆ5.4 Hz, 1H exch.), 4.43 (m, 1H), 4.21 (m, 1H),
4.00 (m, 2H) (s, 3H), 0.98 (d, Jˆ6.4 Hz, 3H), 0.69 (s, 9H),
20.09 (s, 3H), 20.18 (s, 3H).
(1R,2R)-9-[1-((Diethylphosphono)methoxy)methyl-2-
((diethylphosphono)methoxy)propyl]-6-chloropurine (28).
To a stirred suspension of NaH (49 mg, 1.23 mmol) in anhy-
drous THF (3 mL) was added the chloropurine 24 (60 mg,
0.25 mmol) at 2158C under argon. After 5 min, the solution
was treated with (diethoxyphosphono)methyl tri¯ate (10b
233 mg, 0.75 mmol) in anhydrous THF (2 mL). The solu-
tion was allowed to warm to 08C and stirred for 2 h. The
resulting solution was quenched by addition of water, the
product was extracted into dichloromethane, and this solu-
tion was dried over sodium sulfate. After concentration in
vacuo, the oil was puri®ed by column chromatography (5%
MeOH/CH2Cl2) to afford pure compound 28 (40 mg, 30%):
1
[a]2D7ˆ16.88 (cˆ0.9, CH3CH2OH); H NMR (DMSO) d
8.78 (s, 1H), 8.66 (s, 1H), 4.90 (m, 1H), 4.18 (m, 2H),
3.79 (m, 13H), 1.13 (d, Jˆ6.0 Hz, 3H), 1.06 (m, 12H);
13C NMR (DMSO) d 152.7, 151.5, 149.0, 146.6, 130.5,
75.4 (d, Jˆ12.4 Hz), 70.9 (d, Jˆ10.7 Hz), 64.0 (d,
Jˆ161.5 Hz), 61.7 (d, Jˆ163.7 Hz), 61.6 (d, Jˆ6.5 Hz,
3C), 61.5 (d, Jˆ6.0 Hz), 59.0, 16.14 (d, Jˆ5.1 Hz), 16.10
(d, Jˆ5.4 Hz, 3C), 15.8; 31P NMR (DMSO) d 23.7, 23.3;
ESI HRMS calcd for C19H33N4O8P2Cl (M1H)1 543.1540,
found 543.1537.
(1R,2R)-9-[1-Hydroxymethyl-2-hydroxypropyl]-6-chloro-
purine (24). A solution of pyrimidine 23 (0.81 g, 3.5 mmol)
in trimethylorthoformate (20 mL) was treated with HCl
(0.3 mL, 9.8 mmol). The resulting solution was stirred at
room temperature for 5 h and then concentrated in vacuo.
The residue was crystallized from acetone to afford the
analytically pure product 24 (0.74 g, 88%): 1H NMR
(DMSO) d 8.76 (s, 1H), 8.65 (s, 1H), 5.08 (d, Jˆ4.7 Hz,
1H, exch. with D2O), 4.98 (dd, Jˆ5.5 Hz, 1H, exch. with
D2O), 4.53 (m, 1H), 4.22 (m, 1H), 3.96 (m, 1H), 3.87 (m,
1H), 1.01 (d, Jˆ6.2 Hz, 3H); 13C NMR (DMSO) d 152.9,
151.2, 148.7, 147.1, 130.5, 64.4, 63.6, 60.4, 20.7. Anal.
Calcd for C9H11N4O2Cl: C, 44.55; H, 4.57; N, 23.09; Cl,
14.61. Found: C, 44.96; H, 4.64; N, 22.69; Cl, 14.28.
(1R,2R)-9-[1-((Diethylphosphono)methoxy)methyl-2-
((diethylphosphono)methoxy)propyl]adenine (27). A solu-
tion of compound 28 (41 mg, 0.07 mmol) in ethanol
(10 mL) in a pressure ¯ask was saturated with ammonia at
08C. The pressure ¯ask was sealed, warmed to 70±808C in
an oil bath, and maintained at that temperature for 2 days.
After the ¯ask had cooled to room temperature, the solvent
was removed in vacuo and the oil was puri®ed by column
chromatography (10% MeOH/CH2Cl2) to afford pure
compound 27 (19 mg, 53%) and recovered compound 28
(4 mg): [a]2D5ˆ17.48 (cˆ1.2, CH3CH2OH); 1H NMR d
8.33 (s, 1H), 8.10 (s, 1H), 5.76 (s, 2H), 4.86 (m, 1H), 4.08
(m, 10H), 3.78 (m, 5H), 1.31 (t, Jˆ7.0 Hz, 6H), 1.27 (t,
Jˆ7.0 Hz, 6H), 1.14 (d, Jˆ6.2 Hz, 3H); 13C NMR d
155.5, 153.0, 151.0, 140.9, 119.0, 76.1 (d, Jˆ11.7 Hz),
72.2 (d, Jˆ10.3 Hz), 65.5 (d, Jˆ166.3 Hz), 63.1 (d,
Jˆ169.0 Hz), 62.69 (d, Jˆ6.0 Hz), 62.67 (d, Jˆ6.0 Hz),
62.63 (d, Jˆ6.0 Hz), 62.58 (d, Jˆ6.0 Hz), 16.71 (d,
Jˆ6.6 Hz), 16.68 (d, Jˆ6.6 Hz), 16.62 (d, Jˆ5.6 Hz, 2C),
16.0; 31P NMR d 21.2, 20.7; ESI HRMS calcd for
C19H35N5O8P2 (M1H)1 524.2039, found 524.2036.
(1R,2R)-9-[1-Hydroxymethyl-2-hydroxypropyl]adenine
(18). A solution of the chloropurine 24 (0.81 g, 3.3 mmol) in
ethanol (50 mL) in a pressure ¯ask was saturated with
ammonia at 08C. The pressure ¯ask was sealed and warmed
to 65±708C in an oil bath, and maintained at that tempera-
ture for 48 h. After the ¯ask had cooled to room tempera-
ture, the solvent was removed in vacuo and the product was
crystallized from methanol to obtain the desired product 18
(0.63 g, 85%) as a white crystals: mp 2068C; [a]2D5ˆ117.68
(cˆ0.5, CH3OH); 1H NMR (DMSO) d 8.12 (s, 1H), 8.05 (s,
1H), 7.16 (s, 2H, exch. with D2O), 5.07 (d, Jˆ5.1 Hz, 1H,
exch. with D2O), 4.97 (dd, Jˆ5.3 Hz, 1H, exch. with D2O),
4.38 (m, 1H), 4.18 (m, 1H), 3.84 (m, 2H), 0.95 (d, Jˆ6.5 Hz,
3H); 13C NMR (DMSO) d 155.9, 152.0, 150.2, 140.5, 118.4,
64.5, 62.0, 60.7, 20.6. Anal. Calcd for C9H13N5O2: C, 51.92;
H, 5.81; N, 26.91. Found: C, 51.85; H, 5.86; N, 26.83.
(1R,2R)-9-[1-(Phosphonomethoxy)methyl-2-(phosphono-
methoxy)propyl]adenine (29). To a solution of compound
27 (19 mg, 0.036 mmol) in CH2Cl2 (2 mL) was added
TMSBr (0.2 mL, 0.15 mmol) at room temperature. After
being stirred for 18 h at room temperature, the solvent
was removed and the reaction mixture was diluted with
(2R,3R)-9-[1-t-Butyldimethylsilyloxymethyl-2-hydroxy-
propyl]adenine (25). A solution of the adenine derivative
18 (0.305 g, 1.4 mmol), TBSCl (0.21 g, 1.4 mmol), DMAP
(16 mg, 0.13 mmol), and triethylamine (0.7 mL, 5.0 mmol)

A. L. Jeffery et al. / Tetrahedron 56 (2000) 5077±5083
5083
J.; Rosenberg, I.; Holy, A.; De Clercq, E. Antimicrob. Agents
Chemother. 1988, 32, 1025±1030.
CH3OH and concentrated in vacuo. The residue was washed
with CH2Cl2 several times to give the desired phosphonic
acid 29 (14 mg, 94%): [a]2D5ˆ17.48 (cˆ0.12, CH3H2OH);
1H NMR (D2O) d 8.63 (s, 1H), 8.43 (s, 1H), 4.93 (m, 1H),
4.21 (m, 3H), 3.78 (m, 3H), 3.57 (m, 1H), 1.19 (d, Jˆ6.2 Hz,
3H); 13C NMR (D2O) d 152.9, 152.2, 147.0, 146.9, 120.3,
79.0 (d, Jˆ12.6 Hz), 74.1 (d, Jˆ11.7 Hz), 68.8 (d,
Jˆ168.2 Hz), 66.7 (d, Jˆ170.8 Hz), 62.1, 18.0; 31P NMR
(D2O) d 21.9, 21.1; ESI HRMS calcd for C11H19N5O8P2
(M2H)2 410.0631, found 410.0619.
4. (a) Holy, A. Collect. Czech. Chem. Commun. 1993, 58, 649±
674. (b) Holy, A.; Votruba, I.; Merta, A.; Cerny, J.; Vesely, J.;
Vlach, J.; Sediva, K.; Rosenberg, I.; Otmar, M.; Hrebabecky, H.;
Travnicek, M.; Vonka, V.; Snoeck, R.; De Clercq, E. Antiviral Res.
1990, 13, 295±312.
5. Balzarini, J.; Holy, A.; Jindrich, J.; Naesens, L.; Snoeck, R.;
Schols, D.; De Clercq, E. Antimicrob. Agents Chemother. 1993, 37,
332±338.
6. Merta, A.; Votruba, I.; Jindrich, J.; Holy, A.; Cihlar, T.;
Rosenberg, I.; Otmar, M.; Tchaou, H. Y. Biochem. Pharmacol.
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Acknowledgements
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We thank Prof. Kang-Yeoun Jung of Kangnung National
University, Kangnung, Korea for helpful discussions
through the conclusion of this project. Financial support
from the National Institutes of Health (GM 44986) is
gratefully acknowledged.
8. Lidak, M. Y.; Shluke, Y. Y.; Zarinya, B. V.; Poritere, S. E.
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