Synthesis of 2-deoxy-2-fluoro analogs of polyprenyl β-d-arabinofuranosyl phosphates

Article abstract of DOI:10.1016/j.carres.2006.08.020

Described is the synthesis of polyprenyl 2-deoxy-2-fluoro-β-d-arabinofuranosyl phosphate derivatives, including an analog of decaprenyl β-d-arabinofuranosyl phosphate, the donor species used by the arabinosyltransferases involved in mycobacterial cell-wal

Full text of DOI:10.1016/j.carres.2006.08.020

Carbohydrate Research 341 (2006) 2723–2730
Note
Synthesis of 2-deoxy-2-fluoro analogs of polyprenyl
b-D-arabinofuranosyl phosphates
Maju Joe and Todd L. Lowary*
Department of Chemistry and Alberta Ingenuity Centre for Carbohydrate Science, Gunning-Lemieux Chemistry Centre,
University of Alberta, Edmonton, Canada AB T6G 2G2
Received 4 August 2006; accepted 21 August 2006
Available online 14 September 2006
Abstract—Described is the synthesis of polyprenyl 2-deoxy-2-fluoro-b-D-arabinofuranosyl phosphate derivatives, including an ana-
log of decaprenyl b-D-arabinofuranosyl phosphate, the donor species used by the arabinosyltransferases involved in mycobacterial
cell-wall biosynthesis. The targets were synthesized via a route involving the synthesis of a protected b-D-arabinofuranosyl phos-
phate derivative, its coupling with a polyprenyl trichloroacetimidate, and then deprotection of the resulting product. The use of ara-
binofuranosyl phosphates with the monosaccharide hydroxyl groups protected as either silyl ethers or benzoate esters was explored.
Although the coupling yields between the phosphate and polyprenyl trichloroacetimidates were comparable with either type of pro-
tecting group, access to the benzoyl-protected derivative was more efficient and therefore gave the products in higher overall yield.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Glycosyl phosphate; Polyprenol; Mycobacteria; Arabinosyltransferase
The two major polysaccharide components of the
mycobacterial cell wall are an arabinogalactan (AG)
and a lipoarabinomannan (LAM), both of which contain
an arabinan domain composed entirely of arabinose res-
idues in the furanose ring form.1 This arabinan is assem-
bled by a family of arabinosyltransferases (AraT’s) that
use decaprenyl b-D-arabinofuranosyl phosphate, more
commonly known as decaprenol phosphoarabinose
(DPA, 1), as the donor species.2,3 The development of
AraT assays3,4 requires efficient access to 1, and two
methods have been reported to date. One method in-
volves the coupling of sugar and polyprenol via a phos-
phoramidite coupling followed by oxidation to the
phosphate.3,5 In the second approach, a b-D-arabinofur-
anosyl phosphate moiety is synthesized, which is then
coupled to decaprenyl trichloroacetimidate.6
a DPA analog in which the C-2 hydroxyl group had
been replaced with fluorine (2). In evaluating both of
the approaches described above, we selected the latter
method as the most suitable for our purposes and report
here its application to the synthesis of 2, as well as a
panel of shorter chain polyprenyl 2-deoxy-2-fluoro-
b-D-arabinofuranosyl phosphates that contain neryl
(3), geranyl (4), or farnesyl (5) moieties.
We envisioned an approach for the synthesis of 2–5 as
illustrated in Figure 1. A protected 2-deoxy-2-fluoro-
arabinofuranosyl bromide (6 or 7) could be converted
into the corresponding glycosyl phosphate (8 or 9),
which could in turn be coupled with the appropriate
polyprenyl trichloroacetimidate (10). The product ob-
tained, 11, could then be deprotected yielding 2–5. The
use of silyl ether protecting groups was in direct analogy
to earlier work on the synthesis of 1.3,5,6 We also chose
to explore the feasibility of an alternate approach,
involving protection of the carbohydrate hydroxyl
groups as benzoate esters, as the required glycosyl bro-
mide (7) could be obtained in fewer steps overall than
the corresponding silyl-protected bromide 6.
As part of a larger program on the synthesis of inhib-
itors of mycobacterial AraT’s,7 we needed to synthesize
*
Corresponding author. Tel.: +1 780 4921861; fax: +1 780 492
7705; e-mail: tlowary@ualberta.ca
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.08.020

2724
M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
O
P
O
P
O
O
O
O
F
HO
O
HO
HO
O
O
O
8
8
HO
HO
1
2
O
P
O
O
P
P
O
O
F
O
O
O
O
F
F
HO
HO
HO
O
O
O
O
O
O
HO
HO
HO
4
5
3
NH
O
P
O
P
Cl3C
O
R'
O
R'
O
O
O
F
F
F
RO
RO
RO
10
O
O
O
O
O
2–5
11
Br
RO
RO
RO
8, R = t-Bu(CH3)2Si
9, R = Bz
6, R = t-Bu(CH3)2Si
7, R = Bz
R' = polyprenyl chain
Figure 1. Retrosynthesis of 2–5.
The synthesis of the targets using silyl protection
began (Scheme 1) from the known8 glycosyl bromide
7, which was reacted with p-chlorothiophenol under
phase-transfer conditions9 to provide an 83% yield of
the corresponding thioglycoside 12. Subsequent treat-
ment with sodium methoxide in methanol afforded diol
13, which was then silylated under conventional condi-
tions (tert-butylchlorodimethylsilane, imidazole, N,N-
dimethylformamide) providing 14 in 81% yield over
the two steps. The reaction of 14 with bromine in carbon
tetrachloride yielded the corresponding glycosyl
bromide 6. This labile intermediate was not isolated
but instead immediately treated with dibenzyl phosphate
and triethylamine, affording a 67% yield of glycosyl
phosphate 15 as a 1:5 a:b mixture. The diastereomers
were separated by column chromatography along with
8% of unreacted 14 and 10% of its hydrolysis product.
In the 1H NMR spectrum of the major product, the ano-
meric proton signal appeared at 5.89 ppm as a doublet
of doublets with coupling constants of 4.3 and 5.5 Hz.
Selective 31P decoupling transformed this signal into a
doublet with a coupling constant of 4.3 Hz; clearly indi-
cating a 3JH1,P of 5.5 Hz. The 19F NMR spectrum of the
3
major isomer showed a JH1,F of 0 Hz. Therefore, the
O
P
OBn
O
F
F
F
S
Cl
F
t-Bu(CH3)2SiO
t-Bu(CH3)2SiO
RO
e
BzO
OBn
a
d
O
O
O
O
Br
Br
t-Bu(CH3)2SiO
t-Bu(CH3)2SiO
RO
BzO
15
6
7
12, R = Bz
13, R = H
14, R = t-Bu(CH3)2Si
b
c
f
8
Scheme 1. Reagents and conditions: (a) p-ClC6H4SH, KOH, H2O, CH2Cl2, n-Bu4NBr, rt, 83%; (b) NaOCH3, CH3OH, CH2Cl2, rt, 87%; (c) t-
Bu(CH3)2SiCl, imidazole, DMF, rt, 83%; (d) Br2, CCl4, rt; (e) dibenzyl phosphate, Et3N, CCl4, 67% from 14; (f) H2, Pd/C, EtOAc, Et3N, rt.

M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
2725
4.3 Hz coupling was assigned to 3JH1,H2, indicating the b
O
P
stereochemistry for the phosphate group at the anomeric
centre.10 Hydrogenation of 15 (H2, Pd/C) provided 8
together with 15–20% of partially desilylated byprod-
ucts. Attempts to find conditions under which cleavage
of the silyl ethers did not occur were unsuccessful, and
hence the mixture of compounds obtained after the
reaction was used directly in the next step.
F
OBn
O
F
BzO
BzO
a
b
O
OBn
O
9
Br
BzO
BzO
7
22
Scheme 3. Reagents and conditions: (a) dibenzyl phosphate, Et3N,
With glycosyl phosphate 8 in hand, we investigated its
coupling to activated derivatives of nerol, geraniol, and
trans,trans-farnesol (Scheme 2). Thus, each of the three
prenols was treated with DBU and trichloroacetonitrile
to afford the corresponding trichloroacetimidate deriva-
tives (16–18), which were of limited stability. Purifica-
tion could be achieved by rapid filtration through
silica gel using 12:1 hexanes–ethyl acetate as the eluant.
We also found that simple filtration of the reaction
mixture through cotton and sodium sulfate provided
trichloroacetimidates that could be used in the subse-
quent couplings in comparable yield to the reactions
with the compounds purified by chromatography. Upon
their formation, each prenyl trichloroacetimidate was
reacted with 8 in a solution of 5:1 toluene–DMF at
65 ꢁC, which provided each of the coupled products
(19–21) in modest (42–44%) yields. Subsequent treat-
ment with ammonium fluoride in methanol at 65 ꢁC
led to cleavage of the silyl ethers, affording the deprotec-
ted targets 3–5 in 54–58% yields.
ClCH2CH2Cl, CH2Cl2, 82%; (b) H2, Pd/C, EtOAc, Et3N, rt, 91%.
anosyl phosphate derivative, 9 (Fig. 1), could be synthe-
sized very efficiently as outlined in Scheme 3. The
reaction of glycosyl bromide 7 with dibenzyl phosphate
and triethylamine yielded the expected phosphate deriv-
ative 22 in 82% yield as a 1:6.4 a:b mixture, which could
be separated by chromatography. In the 1H NMR spec-
trum of the major product, the anomeric proton signal
appeared at 6.11 ppm as a doublet of doublets with cou-
pling constants 4.3 and 5.8 Hz. The same series of exper-
iments described above for 15 were used to establish that
3JH1,H2 in 22 is 4.3 Hz, thus supporting the b stereo-
chemistry of this arabinofuranosyl phosphate derivative.
1
Similar analysis of the 13C, H, and 19F spectra for the
minor isomer yielded couplings for the anomeric hydro-
gen resonance (doublet of doublets at 6.04 ppm) of 4.8,
3
3
3
8.1, and 0.0 Hz for the JH1,P, JH1,F, and JH1,H2 cou-
plings, respectively, thus indicating the a stereochemis-
try.10 Hydrogenation of the benzyl ethers gave 9 in
91% yield. Compared to the synthesis of the silyl
ether-protected phosphate 8, benzoyl-protected 9 can
be prepared not only in fewer steps but also in better
The modest overall yield and the number of steps
required to synthesize 8 prompted us to consider the
possibility of using benzoate ester protecting groups
in place of the silyl ethers. The required b-arabinofur-
NH
Cl3C
O
O
P
O
O
O
O
F
F
t
-Bu(CH3)2SiO
b
O
16
O
O
3
a
t-Bu(CH3)2SiO
19
NH
O
P
Cl3C
O
b
t-Bu(CH3)2SiO
17
4
O
8
a
t-Bu(CH3)2SiO
20
NH
O
Cl3C
P
O
O
O
b
F
t-Bu(CH3)2SiO
5
O
O
18
a
t-Bu(CH3)2SiO
21
Scheme 2. Reagents and conditions: (a) toluene, DMF, 65 ꢁC, 44% for 16, 43% for 17, 42 for 18; (b) NH4F, NH3, CH3OH, 65 ꢁC, 58% for 19, 54%
for 20, 54% for 21.

2726
M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
NH
O
Cl3C
O
P
O
O
b
F
BzO
BzO
17
4
O
O
a
BzO
24
NH
O
Cl3C
O
P
O
O
b
F
18
5
O
O
9
a
BzO
25
NH
O
Cl3C
O
P
O
O
b
F
BzO
23
8
O
2
O
8
a
26
BzO
Scheme 4. Reagents and conditions: (a) toluene, DMF, 65 ꢁC, 45% for 17, 46% for 18, 40% for 23; (b) CH3OH, H2O, Et3N, rt, 64% for 24, 60% for
25, 63% for 26.
yield and with higher stereoselectivity from the glycosyl
bromide precursor 7.
1. Experimental
1.1. General methods
The coupling of 9 to the polyprenyl imidate deriva-
tives was next explored by its reaction with 17 or 18
as was done for the silyl-protected intermediates
(Scheme 4). The yields of the coupled products, 24
and 25, were comparable with those obtained from 8,
and therefore changing the protecting groups from silyl
to benzoyl does not substantially improve the yield of
the coupling step. Cleavage of the benzoate esters in
24 and 25 could be achieved by stirring each compound
in a mixture of methanol, triethylamine, and water,
which provided 4 and 5 in 64% and 60% yield,
respectively.
Based on the results described above, we chose to
synthesize 2 from the benzoyl-protected phosphate
substrate 9 (Scheme 4). Thus, decaprenyl trichloroace-
timidate derivative 23 was prepared from decaprenol
and reacted with 9, affording a 40% yield of 26. Subse-
quent debenzoylation under the conditions described
previously gave 2 in 63% yield.
In summary, we describe here the synthesis of a 2-
deoxy-2-fluoro analog of DPA, the donor substrate used
by mycobacterial arabinosyltransferases. The key step in
this sequence was the coupling of a benzoyl-protected 2-
deoxy-2-fluoro-b-arabinofuranosyl phosphate derivative
with decaprenyl trichloroacetimidate. Product 2 was ob-
tained in 19% overall yield in four steps from the known
and readily prepared 2-deoxy-2-fluoro-arabinofuranosyl
bromide 7. Using the same route, a series of shorter
chain polyprenyl b-arabinofuranosyl phosphates were
also synthesized.
The reactions were carried out in an oven-dried glass-
ware. The reaction solvents were distilled from appro-
priate drying agents before use. Unless stated
otherwise, all reactions were carried out at room temper-
ature under a positive pressure of argon and were mon-
itored by TLC on Silica Gel 60 F254 (0.25 mm, E.
Merck). Spots were detected under UV light or by char-
ring with acidified p-anisaldehyde solution in EtOH.
Unless otherwise indicated, all column chromatography
was performed on silica gel (40–60 lM). The ratio
between silica gel and crude product ranged from 100
to 50:1 (w/w). Optical rotations were measured at
22 2 ꢁC. 1H NMR spectra were recorded at
500 MHz, and chemical shifts were referenced to either
1
TMS (0.0, CDCl3) or CD3OD (3.30, CD3OD). H data
are reported as though they were of first order. 13C
NMR spectra were recorded at 125 MHz, and 13C
chemical shifts were referenced to internal CDCl3
(77.23, CDCl3), or CD3OD (48.9, CD3OD). 19F spectra
were recorded at 376 or 468 MHz, and chemical shifts
were referenced to external CFCl3.11 31P spectra were re-
corded with proton decoupling at 162 MHz, and chem-
ical shifts were referenced using external 85% H3PO4.11
In the processing of the reaction mixtures, solutions of
organic solvents were washed with equal amounts of
aqueous solutions. The organic solutions were concen-
trated under vacuum at <40 ꢁC. Electrospray-ionization
mass spectra were recorded on samples suspended in

M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
2727
mixtures of THF with CH3OH and added NaCl. Deca-
prenol was purchased from Larodan Fine Chemicals,
Sweden, as a solution in hexane, and was used as such.
corresponding coupled products (24 or 25) in 45–46%
yield. The coupled product (0.05 g) was dissolved in a
solution of 5:2:1 CH3OH–H2O–Et3N (2 mL), and the
solution was stirred for 48–60 h. The reaction mixture
was directly concentrated and the syrupy residue was
purified by column chromatography (7:1:0.1 CH2Cl2–
CH3OH–33% NH4OH) to yield 2, 4, or 5 in 60–64%
yield.
1.2. General procedure for the preparation of polyprenyl
trichloroacetimidates
To a solution of the alcohol (1 mmol) in CH2Cl2
(2.5 mL) at 0 ꢁC was added DBU (15 lL, 0.1 mmol).
The mixture was stirred at 0 ꢁC for 30 min and then
warmed to rt over 30 min. The solvent was then
removed and dry hexane (3 mL) was added. After stir-
ring for 5 min, this solution was passed through a plug
of cotton and Na2SO4. The resulting solution was then
concentrated to yield the trichloroacetimidate deriva-
tive, which could be used without further purification.
Alternatively, the residue obtained after the initial sol-
vent evaporation following the reaction could be quickly
filtered through silica gel using 12:1 hexanes–EtOAc as
the eluant. The fractions containing the trichloroacet-
imidate derivative were concentrated and used
immediately.
1.5. Decaprenyl 2-deoxy-2-fluoro-b-D-arabinofuranosyl
phosphate (2)
To a solution of sugar 1-phosphate 9 (0.05 mg,
0.1 mmol) in dry toluene (1.5 mL) was added decaprenyl
trichloroacetimidate (0.1 mmol) followed by DMF
(0.3 mL). The reaction mixture was heated at 65 ꢁC for
16 h and then cooled to rt before being concentrated
to a syrupy residue that was purified by column chroma-
tography (7:1:0.1 CH2Cl2–CH3OH–33% NH4OH) to
yield the coupled product 26 (5 mg, 40%): ESIMS:
m/z calcd for [C69H97FO9P]ꢀ: 1119.6859. Found:
1119.6864. Compound 26 (4 mg) was dissolved in a solu-
tion of 5:2:1 CH3OH–H2O–Et3N (0.4 mL) and stirred
for 42 h before the mixture was concentrated to a syrupy
residue that was purified by column chromatography
(7:1:0.1 CH2Cl2–CH3OH–33% NH4OH) to yield 2
(2.3 mg, 63%): Rf 0.2 (7:1:0.1 CH2Cl2–CH3OH–33%
NH4OH); [a]D ꢀ8.6 (c 0.2, CH3OH); 1H NMR
(600 MHz, CD3OD, dH) 5.62 (dd, 1H, J 4.5, 4.5 Hz,
H-1), 5.40 (dd, 1H, J 7.2, 7.2 Hz, CH@), 5.05–5.16 (m,
9H, CH@), 4.80 (dddd, 1H, J 2.0, 4.5, 6.3, 53.0 Hz, H-
2), 4.44–4.36 (m, 3H, H-3, OCH2CH@), 3.80 (ddd,
1H, J 3.1, 5.6, 6.7 Hz, H-4), 3.73 (dddd, 1H, J 1.1, 3.1,
3.9, 12.8 Hz, H-5), 3.64 (dd, 1H, J 5.6, 12.8 Hz, H-50),
2.20–1.92 (m, 36H, 18 · CH2CH@), 1.72–1.50 (m,
21H, 7 · CH3), 1.36–1.25 (m, 6H, 2 · CH3), 0.92–0.86
(m, 6H, 2 · CH3); 31P NMR (162 MHz, CD3OD, dP)
3.85; 19F NMR (376 MHz, CD3OD/CD2Cl2, dF)
ꢀ208.19 (dd, J 17.2, 53.0 Hz); ESIMS: m/z calcd for
[C55H89FO7P]ꢀ: 911.6335. Found: 911.6333.
1.3. General procedure for coupling of 8 with polyprenyl
trichloroacetimidates and subsequent deprotection
To a solution of 8 (0.1 mmol) in dry toluene (1.5 mL)
was added the corresponding trichloroacetimidate
derivative (0.15 mmol) followed by DMF (0.3 mL).
The reaction mixture was heated at 65 ꢁC for 8 h and
then cooled to rt. The mixture was concentrated to a
syrupy residue that was purified by column chromato-
graphy (7:1:0.1 CH2Cl2–CH3OH–33% NH4OH) to yield
the corresponding product (19–21) in 42–44% yield.
The coupled products (0.05 g) were immediately dis-
solved in a mixture of methanolic aq NH3 (4 mL;
0.6 mL 33% NH4OH in 3.4 mL CH3OH), and solid
NH4F (0.15 g) was added. The reaction mixture was
heated at 65 ꢁC for 14 h and then cooled to rt and
diluted with CH2Cl2 (2 mL). The precipitated salts were
filtered, and the filtrate was concentrated to a syrupy
residue that was purified by column chromatography
(7:1:0.1 CH2Cl2–CH3OH–33% NH4OH) to yield 3–5
in 54–58% yield.
1.6. Neryl 2-deoxy-2-fluoro-b-D-arabinofuranosyl
phosphate (3)
Rf 0.13 (7:1:0.1 CH2Cl2–CH3OH–33% NH4OH); [a]D
1
1.4. General procedure for coupling of 9 with polyprenyl
trichloroacetimidates 17 and 18 and subsequent
deprotection
ꢀ39.8 (c 1.0, CH3OH); H NMR (500 MHz, CD3OD,
dH) 5.62 (dd, 1H, J 4.3, 9.1 Hz, H-1), 5.38 (ddd, 1H, J
0.6, 6.7, 6.7 Hz, CH@), 5.14–5.07 (m, 1H, CH@), 4.82
(dddd, 1H, J 1.8, 4.3, 6.1, 52.7 Hz, H-2), 4.45–4.34 (m,
3H, OCH2CH@, H-3), 3.81 (ddd, 1H, J 3.2, 5.6,
6.9 Hz, H-4), 3.74 (dd, 1H, J 3.2, 12.3 Hz, H-5), 3.64
(dd, 1H, J 5.6, 12.3 Hz, H-50), 2.14–2.04 (m, 4H,
2 · CH2CH@), 1.73 (s, 3H, CH3), 1.66 (s, 3H, CH3),
1.59 (s, 3H, CH3). 13C NMR (125 MHz, CD3OD, dC)
141.10 (@CCH3), 132.83 (@CCH3), 124.97 (CH@),
123.11 (d, J 8.7 Hz, CH@), 96.76 (dd, J 5.7, 18.1 Hz,
To a solution of 9 (0.1 mmol) in dry toluene (1.5 mL)
was added the corresponding trichloroacetimidate deriv-
ative (0.15 mmol) followed by DMF (0.3 mL). The reac-
tion mixture was heated at 65 ꢁC for 16 h and then
cooled to rt before being concentrated to a syrupy resi-
due that was purified by column chromatography
(7:1:0.1 CH2Cl2–CH3OH–33% NH4OH) to yield the

2728
M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
C-1), 96.50 (dd, J 7.2, 199.8 Hz, C-2), 84.27 (d, J 9.3 Hz,
C-4), 73.08 (d, J 21.2 Hz, C-3), 63.74 (OCH2CH@),
63.38 (d, J 5.2 Hz, C-5), 33.08 (CH2CH@), 27.76
(CH2CH@), 25.92 (CH3), 23.67 (CH3), 17.79 (CH3);
31P NMR (162 MHz, CD3OD, dP) 3.28; 19F NMR
(376 MHz, D2O, dF) ꢀ206.73 (dd, J 17.6, 52.7 Hz).
ESIMS: m/z calcd for [C15H25FO7P]ꢀ: 367.1316. Found:
367.1319.
J 17.0, 53.4 Hz); ESIMS: m/z calcd for [C20H33FO7P]ꢀ:
435.1942. Found: 435.1941.
1.9. 3,5-Di-O-tert-butyldimethylsilyl-2-deoxy-2-fluoro-b-
D-arabinofuranosyl phosphate (8)
Dibenzylphosphate 15 (50 mg, 0.08 mmol) was dissolved
in 10:1 EtOAc–Et3N (6 mL), and 10% Pd/C was added
(10 mg). The reaction mixture was hydrogenated at
1 atm pressure for 14 h, before the catalyst was filtered
and washed with EtOAc (2 mL). The combined filtrate
was concentrated and dried under vacuum to provide
debenzylated product 8, which was used immediately
in the next step. The product was contaminated with
15–20% of desilylated byproducts. Data for the major
1.7. Geranyl 2-deoxy-2-fluoro-b-D-arabinofuranosyl
phosphate (4)
Rf 0.12 (7:1:0.1 CH2Cl2–CH3OH–33% NH4OH); [a]D
1
ꢀ34.6 (c 1.0, CH3OH); H NMR (500 MHz, CD3OD,
dH) 5.63 (dd, 1H, J 4.2, 4.2 Hz, H-1), 5.39 (ddd, 1H, J
1.2, 6.9, 6.9 Hz, CH@), 5.13–5.07 (m, 1H, CH@), 4.82
(dddd, 1H, J 1.8, 4.2, 6.1, 53.4 Hz, H-2), 4.42–4.36 (m,
3H, OCH2CH@, H-3), 3.80 (ddd, 1H, J 3.2, 5.6,
6.9 Hz, H-4), 3.74 (dd, 1H, J 3.2, 12.3 Hz, H-5), 3.65
(dd, 1H, J 5.6, 12.3 Hz, H-50), 2.14–2.06 (m, 2H,
CH2CH@), 2.05–2.00 (m, 2H, CH2CH@), 1.67 (s, 3H,
CH3), 1.66 (s, 3H, CH3), 1.59 (s, 3H, CH3); 13C NMR
(125 MHz, CD3OD, dC) 140.97 (@CCH3), 132.49
(@CCH3), 125.07 (CH@), 122.24 (d, J 8.2 Hz, CH@),
96.71 (dd, J 5.7, 18.1 Hz, C-1), 96.53 (dd, J 7.7,
199.8 Hz, C-2), 84.25 (d, J 9.8 Hz, C-4), 73.03 (d, J
20.6 Hz, C-3), 63.70 (OCH2CH@), 63.56 (d, J 5.7 Hz,
C-5), 40.61 (CH2CH@), 27.47 (CH2CH@), 25.87
(CH3), 17.75 (CH3), 16.46 (CH3); 31P NMR
(162 MHz, CD3OD, dP) 3.50; 19F NMR (376 MHz,
CD3OD, dF) ꢀ208.50 (dd, J 17.3, 53.4 Hz); ESIMS:
m/z calcd for [C15H25FO7P]ꢀ: 367.1316. Found:
367.1317.
1
product: H NMR (400 MHz, CD3OD, dH) 5.72–5.64
(m, 1H, H-1), 4.88–4.82 (m, 1H, H-2), 4.38–4.32 (m,
H-3), 3.85–3.57 (m, 3H, H-4, 5, 50), 1.00–0.85 (m,
18H, C(CH3)3), 0.15–0.05 (m, 4 · SiCH3); 31P NMR
(162 MHz, CD3OD, dP) 3.40.
1.10. 3,5-Di-O-benzoyl-2-deoxy-2-fluoro-b-D-arabino-
furanosyl phosphate (9)
Compound 22 (0.2 g, 0.32 mmol) was dissolved in 10:1
EtOAc–Et3N (10 mL) and 10% Pd/C was added
(30 mg). The reaction mixture was stirred under hydro-
gen at 1 atm pressure for 14 h before the catalyst was fil-
tered and washed with 3:7 EtOAc–CH3OH (6 mL). The
combined filtrate was concentrated and dried under vac-
uum to provide 9 (as its triethylammonium salt, 0.16 g,
91%), sufficiently pure for use in the next step: 1H NMR
(500 MHz, CD3OD, dH) 8.05–7.95 (m, 4H, ArH), 7.65–
7.60 (m, 1H, ArH), 7.55–7.45 (m, 3H, ArH), 7.40–7.32
(m, 2H, ArH), 5.88 (ddd, 1H, J 1.6, 4.0, 5.6 Hz, H-1),
5.81 (ddd, 1H, J 5.4, 5.4, 16.6 Hz, H-3), 5.31 (dddd,
1H, J 1.2, 4.0, 5.4, 52.5 Hz, H-2), 4.68 (dd, 1H, J 6.0,
11.4 Hz, H-5), 4.62 (ddd, 1H, J 0.7, 6.1, 11.4 Hz, H-
50), 4.42 (ddd, 1H, J 5.4, 6.0, 6.1 Hz, H-4); 13C NMR
(125 MHz, CD3OD, dC) 167.62 (C@O), 167.07 (C@O),
134.80 (Ar), 134.27 (Ar), 131.02 (Ar), 130.80 (2C, Ar),
130.73 (2C, Ar), 130.41 (Ar), 129.72 (2C, Ar), 129.47
(2C, Ar), 97.41 (dd, J 4.6, 18.1 Hz, C-1), 94.08 (dd, J
6.7, 200.1 Hz, C-2), 79.45 (d, J 7.7 Hz, C-3), 77.86 (d,
J 24.3 Hz, C-4), 67.15 (C-5); 31P NMR (162 MHz,
CD3OD, dP) 3.52; 19F NMR (376 MHz, CD3OD, dF)
ꢀ207.08 (dd, J 16.6, 52.5 Hz); ESIMS: m/z calcd for
[C19H17FO9P]ꢀ: 439.0588. Found 439.0589.
1.8. trans,trans-Farnesyl 2-deoxy-2-fluoro-b-D-arabino-
furanosyl phosphate (5)
Rf 0.15 (7:1:0.1 CH2Cl2–CH3OH–33% NH4OH); [a]D
1
ꢀ44.0 (c 1.1, CH3OH); H NMR (500 MHz, CD3OD,
dH) 5.62 (dd, 1H, J 4.2, 4.2 Hz, H-1), 5.40 (ddd, 1H, J
1.2, 6.8, 8.0 Hz, CH@), 5.14–5.05 (m, 2H, CH@), 4.81
(dddd, 1H, J = 1.8, 4.2, 6.1, 53.4 Hz, H-2), 4.41–4.35
(m, 3H, OCH2CH@, H-3), 3.80 (ddd, 1H, J 3.2, 5.8,
6.9 Hz, H-4), 3.74 (dd, 1H, J 3.1, 12.3 Hz, H-5), 3.65
(dd, 1H, J 5.8, 12.3 Hz, H-50), 2.30–1.92 (m, 8H,
4 · CH2CH@), 1.67 (s, 3H, CH3), 1.65 (s, 3H, CH3),
1.59 (s, 6H, CH3); 13C NMR (125 MHz, CD3OD, dC)
140.90 (@CCH3), 136.23 (@CCH3), 132.10 (@CCH3),
125.43 (CH@), 125.17 (CH@), 122.28 (CH@), 96.69
(dd, J 5.2, 17.6 Hz, C–1), 96.48 (dd, J 7.2, 199.8 Hz,
C-2), 84.27 (d, J 9.8 Hz, C-4), 73.05 (d, J 21.2 Hz, C-
3), 63.81 (OCH2CH@), 63.54 (d, J 5.7 Hz, C-5), 40.85
(CH2CH@), 40.63 (CH2CH@), 27.81 (CH2CH@),
27.40 (CH2CH@), 25.89 (CH3), 17.76 (CH3), 16.48
(CH3), 16.07 (CH3); 31P NMR (162 MHz, CD3OD, dP)
3.87; 19F NMR (468 MHz, CD3OD, dF) ꢀ208.60 (dd,
1.11. p-Chlorophenyl 3,5-di-O-benzoyl-2-deoxy-2-fluoro-
1-thio-b-D-arabinofuranoside (12)
To a solution of 7 (0.5 g, 1.2 mmol) in CH2Cl2 (12 mL)
was added p-chlorothiocresol (0.26 g, 1.8 mmol) fol-
lowed by an aq solution of KOH (0.14 g in 1.8 mL
water) and n-Bu4NBr (0.08 g in 1.8 mL water). The reac-

M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
2729
tion mixture was stirred for 16 h and then diluted with
CH2Cl2 (20 mL). The CH2Cl2 layer was separated, dried
(Na2SO4) and concentrated to a syrup that was purified
by column chromatography (9:1 hexanes–EtOAc) to
yield 12 (0.48 g, 83%) as a syrup: Rf 0.4 (85:15 hex-
anes–EtOAc); [a]D ꢀ72.4 (c 0.8, CHCl3); 1H NMR
(500 MHz, CDCl3, dH) 8.13–8.08 (m, 2H, ArH), 8.04–
7.99 (m, 2H, ArH), 7.63–7.50 (m, 4H, ArH), 7.42–7.49
(m, 4H, ArH), 7.32–7.26 (m, 2H, ArH), 5.66 (ddd, 1H,
J 1.2, 2.7, 16.2 Hz, H-3), 5.55 (dd, 1H, J 3.4, 27.5 Hz,
H-1), 5.36 (ddd, 1H, J 1.2, 3.4, 50.0 Hz, H-2), 4.72
(dd, 1H, J 5.7, 11.8 Hz, H-5), 4.65 (dd, 1H, J 5.3,
11.8 Hz, H-50), 4.49 (ddd, 1H, J 2.7, 5.3, 5.7 Hz, H-4);
13C NMR (125 MHz, CDCl3, dC) 166.18 (C@O),
165.10 (C@O), 134.12 (Ar), 133.86 (Ar), 133.30 (2C,
Ar), 133.15 (Ar), 132.11 (Ar), 132.10 (Ar), 129.83 (4C,
Ar), 129.69 (Ar), 129.24 (2C, Ar), 128.60 (2C, Ar),
128.38 (2C, Ar), 95.78 (d, J 189.6 Hz, C-2), 89.29 (d, J
18.9 Hz, C-1), 82.14 (C-4), 77.71 (d, J 30.8 Hz, C-3),
63.71 (d, J 2.5 Hz, C-5); 19F NMR (376 MHz, CDCl3,
dF) ꢀ192.70 (ddd, J 16.2, 27.5, 50.0 Hz). ESIMS: m/z
calcd for [C25H20ClFO5S]Na+: 509.0596. Found:
509.0600.
organic layer was separated, dried (Na2SO4) and concen-
trated to a syrupy residue that was purified by column
chromatography (30:1 hexanes–EtOAc) to yield the title
compound 14 (0.34 g, 93%) as a syrup: Rf 0.46 (25:1 hex-
anes–EtOAc); [a]D ꢀ88.8 (c 1.2, CHCl3); 1H NMR
(500 MHz, CDCl3, dH) 7.46–7.42 (m, 2H, ArH), 7.25–
7.22 (m, 2H, ArH), 5.46 (dd, 1H, J 3.4, 27.7 Hz, H-1),
4.92 (ddd, 1H, J 1.8, 3.4, 51.6 Hz, H-2), 4.43 (ddd,
1H, J 1.8, 1.8, 17.3 Hz, H-3), 3.94 (ddd, 1H, J 1.8, 5.2,
7.8 Hz, H-4), 3.79 (ddd, 1H, J 2.0, 5.2, 10.2 Hz, H-5),
3.67 (ddd, 1H, J 1.8, 7.8, 10.2 Hz, H-50), 0.92 (s, 9H,
C(CH3)3), 0.89 (s, 9H, C(CH3)3), 0.13 (s, 3H, SiCH3),
0.12 (s, 3H, SiCH3), 0.08 (s, 3H, SiCH3), 0.09 (s, 3H,
SiCH3); 13C NMR (125 MHz, CDCl3, dC) 133.39 (Ar),
133.22 (Ar), 132.43 (2C, Ar), 129.08 (2C, Ar), 98.43
(d, J 188.4 Hz, C-2), 88.55 (d, J 18.1 Hz, C-1), 87.39
(C-4), 75.95 (d, J 25.8 Hz, C-3), 62.55 (d, J 3.6 Hz, C-
5), 25.92 (3C, C(CH3)3), 25.67 (3C, C(CH3)3), 18.37
(C(CH3)3), 17.93 (C(CH3)3), ꢀ4.86 (2C, SiCH3),
ꢀ5.36 (2C, SiCH3); 19F NMR (376 MHz, CDCl3,
dF) ꢀ190.71 (ddd, J 17.3, 27.7, 51.6 Hz); ESIMS: m/z
calcd for [C23H40ClFO3SSi2]Na+: 529.1801. Found
529.1801.
1.12. p-Chlorophenyl 2-deoxy-2-fluoro-1-thio-b-D-arabino-
furanoside (13)
1.14. Dibenzyl (3,5-di-O-tert-butyldimethylsilyl-2-deoxy-
2-fluoro-b-D-arabinofuranosyl) phosphate (15)
To a solution of 12 (0.4 g, 0.8 mmol) in 1:1 CH2Cl2–
CH3OH (12 mL) was added NaOCH3 (0.03 g,
0.5 mmol). After stirring for 3 h, the solution was neu-
tralized with a few drops of glacial HOAc and concen-
trated to a syrupy residue that was purified by column
chromatography (1:1 hexanes–EtOAc) to yield 13
(0.2 g, 87%) as a syrup: Rf 0.3 (1:1 hexanes–EtOAc);
[a]D ꢀ147.3 (c 1.0, CH3OH); 1H NMR (500 MHz,
CDCl3, dH) 7.37–7.44 (m, 2H, ArH), 7.26–7.21 (m,
2H, ArH), 5.42 (dd, 1H, J 3.6, 25.3 Hz, H-1), 4.99
(ddd, 1H, J 2.0, 3.0, 51.7 Hz, H-2), 4.28 (ddd, 1H, J
2.0, 3.4, 18.1 Hz, H-3), 3.90–3.85 (m, 1H, H-4), 3.76–
3.68 (m, 2H, H-5, 50); 13C NMR (125 MHz, CDCl3,
dC) 133.58 (Ar), 132.57 (Ar), 132.28 (2C, Ar), 129.17
(2C, Ar), 98.2 (d, J 188.4 Hz, C-2), 88.43 (d, J
18.6 Hz, C-1), 86.28 (d, J 2.1 Hz, C-4), 74.91 (d, J
26.3 Hz, C-3), 61.88 (d, J 1.6 Hz, C-5); 19F NMR
(376 MHz, CDCl3, dF) ꢀ192.31 (ddd, J 18.1, 25.3,
51.7 Hz); ESIMS: m/z calcd for [C11H12ClFO3S]Na+:
301.0071. Found 301.0068.
A solution of 14 (0.2 g, 0.4 mmol) in dry CCl4 (12 mL)
containing powdered 4 A molecular sieves (0.2 g) was
˚
stirred for 30 min before a solution of Br2 in dry CCl4
(44 mg in 0.7 mL CCl4) was added. This solution was
stirred for 1.5 h. Simultaneously, a solution of dibenzyl
phosphate (0.14 g, 0.52 mmol) in CH2Cl2 (8 mL) was
˚
stirred together with powdered 4 A molecular sieves
(ꢁ0.2 g) for 20 min before Et3N (94 lL, 0.67 mmol)
was added. After stirring for 3 min, this solution was
added to the mixture prepared from 14. The resulting
mixture was stirred for 16 h, neutralized with a few
drops of Et3N, and then filtered. The filtrate was con-
centrated to a syrupy residue that was purified by col-
umn chromatography (85:15 hexanes–EtOAc) to yield
15 (0.168 g, 67%) as a separable a:b mixture (a:b 1:5)
in addition to 8% of unreacted 14 and 10% of hydro-
lyzed 14. Data for the major isomer: Rf 0.22 (85:15 hex-
anes–EtOAc); [a]D ꢀ22.9 (c 0.6, CHCl3); 1H NMR
(500 MHz, CDCl3, dH) 7.40–7.25 (m, 10H, ArH), 5.89
(dd, 1H, J 4.3, 5.5 Hz, H-1), 5.16–5.02 (m, 4H, PhCH2),
4.85 (dddd, 1H, J 1.7, 4.3, 6.5, 52.6 Hz, H-2), 4.44 (ddd,
1H, J 6.5, 6.5, 16.5 Hz, H-3), 3.89 (ddd, 1H, J 4.3, 5.7,
6.5 Hz, H-4), 3.77 (dd, 1H, J 4.3, 11.3 Hz, H-5), 3.72
(dd, 1H, J 5.7, 11.3 Hz, H-50), 0.90 (s, 9H, C(CH3)3),
0.87 (s, 9H, C(CH3)3), 0.13 (s, 3H, SiCH3), 0.10 (s,
3H, SiCH3), 0.03 (s, 6H, 2 · SiCH3); 13C NMR
(125 MHz, CDCl3, dC) 135.80 (Ar), 135.73 (Ar),
128.47 (Ar), 128.41 (2C, Ar), 128.38 (3C, Ar), 127.92
(2C, Ar), 127.85 (2C, Ar), 97.50 (dd, J 4.6, 18.6 Hz,
1.13. p-Chlorophenyl 3,5-di-O-tert-butyldimethylsilyl-2-
deoxy-2-fluoro-1-thio-b-D-arabinofuranoside (14)
To a solution of 13 (0.2 g, 0.7 mmol) in dry DMF
(3 mL) was added imidazole (0.3 g, 4.4 mmol), followed
by t-Bu(CH3)2SiCl (0.27 g, 1.8 mmol). The reaction mix-
ture was stirred for 14 h and then poured into ice water
(50 mL) and extracted with toluene (2 · 15 mL). The

2730
M. Joe, T. L. Lowary / Carbohydrate Research 341 (2006) 2723–2730
C-1), 95.24 (dd, J 5.7, 201.3 Hz, C-2), 84.28 (d, J 9.3 Hz,
C-4), 73.21 (d, J 21.2 Hz, C–3), 69.28 (d, J 5.2 Hz,
PhCH2), 69.17 (d, J 5.2 Hz, PhCH2), 63.54 (C-5),
25.90 (3C, C(CH3)3), 25.59 (3C, C(CH3)3), 18.35
(C(CH3)3), 17.85 (C(CH3)3), ꢀ4.66 (SiCH3), ꢀ4.98
(SiCH3), ꢀ5.39 (SiCH3), ꢀ5.42 (SiCH3); 31P NMR
(162 MHz, CDCl3, dP) ꢀ1.78; 19F NMR (468 MHz,
CDCl3, dF) ꢀ204.49 (dd, J 16.5, 52.6 Hz); ESIMS:
m/z calcd for [C31H50FO7PSi2]Na+: 663.2709. Found,
663.2706.
ESIMS: m/z calcd for [C33H30FO9P]Na+: 643.1503.
Found, 643.1500.
Acknowledgements
This work was supported by the Alberta Ingenuity Cen-
tre for Carbohydrate Science, The University of Alberta,
and The Natural Sciences and Engineering Research
Council of Canada.
1.15. Dibenzyl (3,5-di-O-benzoyl-2-deoxy-2-fluoro-b-D-
arabinofuranosyl) phosphate (22)
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2006.08.020.
A solution of 7 (0.55 g, 1.3 mmol) in 1,2-dichloroethane
(6 mL) containing powdered 4 A molecular sieves (0.2 g)
˚
was stirred for 20 min. In a separate flask, a solution of
dibenzyl phosphate (0.47 g, 1.69 mmol) in CH2Cl2
(6 mL) was stirred together with powdered 4 A molecu-
References
˚
lar sieves (0.2 g) for 20 min and then Et3N (0.28 mL,
2.2 mmol) was added. After stirring for another 3 min,
this solution was added to the mixture containing 7.
The resulting reaction mixture was heated at 60 ꢁC for
2 h and then cooled to rt before being filtered. The fil-
trate was concentrated to a syrupy residue that was puri-
fied by column chromatography (7:3 hexanes–EtOAc)
to yield the title compound 22 (0.66 g, 82%) as a separa-
ble mixture (a:b 1:6.4). Data for the major isomer: Rf 0.1
(4:1 hexanes–EtOAc); [a]D ꢀ23.7 (c 1.0, CHCl3); 1H
NMR (500 MHz, CDCl3, dH) 8.08–7.98 (m, 4H, ArH),
7.64–7.60 (m, 1H, ArH), 7.53–7.44 (m, 3H, ArH),
7.40–7.22 (m, 12H, ArH), 6.11 (dd, 1H, J 4.3, 5.8 Hz,
H-1), 5.84 (ddd, 1H, J 6.1, 6.1, 16.6 Hz, H-3), 5.34
(dddd, 1H, J 1.7, 4.3, 6.1, 52.0 Hz, H-2), 5.14–5.00 (m,
4H, 2 · PhCH2), 4.72 (dd, 1H, J 4.0, 11.9 Hz, H-5),
4.57 (dd, 1H, J 6.4, 11.9 Hz, H-50), 4.49 (ddd, 1H, J
4.0, 6.1, 6.4 Hz, H-4); 13C NMR (125 MHz, CDCl3,
dC) 165.96 (C@O), 165.56 (C@O), 135.47 (Ar), 135.43
(Ar), 135.42 (Ar), 135.37 (Ar), 133.82 (Ar), 133.11
(Ar), 129.89 (2C, Ar), 129.77 (2C, Ar), 129.50 (Ar),
128.61 (Ar), 128.59 (2C, Ar), 128.56 (Ar), 128.49 (2C,
Ar), 128.45 (Ar), 128.32 (2C, Ar), 127.99 (2C, Ar),
127.78 (2C, Ar), 97.31 (dd, J 5.2, 18.6 Hz, C-1), 92.56
(dd, J 6.7, 204.4 Hz, C-2), 80.07 (d, J 7.7 Hz, C-4),
75.04 (d, J 24.3 Hz, C-3), 69.61 (d, J 5.2 Hz, OCH2),
69.41 (d, J 5.7 Hz, OCH2), 64.93 (C-5); 31P NMR
(162 MHz, CDCl3, dP) ꢀ1.66; 19F NMR (376
MHz, CDCl3, dF) ꢀ203.82 (dd, J 16.6, 52.0 Hz);
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