Synthesis of 2-deoxy-2-fluoro and 1,2-ene derivatives of the naturally occurring glycosidase inhibitor, salacinol, and their inhibitory activities against recombinant human maltase glucoamylase

Article abstract of DOI:10.1016/j.carres.2008.01.025

2-Deoxy-2-fluorosalacinol and a 1,2-ene derivative of the naturally occurring glycosidase inhibitor salacinol were synthesized for structure activity studies with human maltase glucoamylase (MGA). 2-Deoxy-2-fluorosalacinol was synthesized through the coup

Full text of DOI:10.1016/j.carres.2008.01.025

Available online at www.sciencedirect.com
Carbohydrate Research 343 (2008) 951–956
Note
Synthesis of 2-deoxy-2-fluoro and 1,2-ene derivatives of the naturally
occurring glycosidase inhibitor, salacinol, and their inhibitory
activities against recombinant human maltase glucoamylase
Niloufar Choubdar,a Lyann Sim,b David R. Roseb and B. Mario Pintoa,*
aDepartment of Chemistry, Simon Fraser University, Burnaby, B.C., Canada V5A 1S6
bDepartment of Medical Biophysics, University of Toronto and Division of Cancer Genomics and Proteomics,
Ontario Cancer Institute, Toronto, ON, Canada M5G 1L7
Received 2 January 2008; received in revised form 17 January 2008; accepted 20 January 2008
Available online 29 January 2008
Abstract—2-Deoxy-2-fluorosalacinol and a 1,2-ene derivative of the naturally occurring glycosidase inhibitor salacinol were synthe-
sized for structure activity studies with human maltase glucoamylase (MGA). 2-Deoxy-2-fluorosalacinol was synthesized through the
coupling reaction of 2-deoxy-2-fluoro-3,5-di-O-p-methoxybenzyl-1,4-anhydro-4-thio-D-arabinitol with 2,4-O-benzylidene-L-erythritol-
1,3-cyclic sulfate in hexafluoroisopropanol (HFIP) containing 0.3 equiv of K2CO3. Excess of K2CO3 resulted in the elimination of HF
from the coupled product, and the formation of an alkene derivative of salacinol. Nucleophilic attack of the 1,4-anhydro-4-thio-D-
arabinitol moiety on the cyclic sulfate did not proceed in the absence of K2CO3. No reaction was observed in acetonitrile containing
K2CO3. The target compounds were obtained by deprotection with TFA. The 2-deoxy-1-ene derivative of salacinol and 2-deoxy-2-
fluorosalacinol inhibited recombinant human maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of
glucose, with an IC50 value of 150 lM and a Ki value of 6 1 lM, respectively.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Glycosidase inhibitors; Salacinol derivatives; 2-Deoxy-2-fluorosalacinol; 2-Deoxy-1-ene-salacinol; Cyclic sulfates; Human maltase gluco-
amylase (MGA) inhibition
Glycosidase enzymes are fundamental in the biochemical
OH
processing of carbohydrates.1–5 For example, pancreatic
HO
HO
a-amylase converts starch to maltooligosaccharides,
and membrane-bound glucosidases convert these oligo-
saccharides to glucose in the small intestine. Inhibition
of these enzymes in patients suffering from type II diabetes
(noninsulin dependent diabetes) could be one strategy for
controlling blood glucose levels by delaying the break-
down of carbohydrates.6–8 One example of this class of
inhibitors is acarbose 1, a naturally occurring glycosidase
inhibitor, which has been used for the oral treatment of
type II diabetes.7,9–11 Deoxynojirimycin 2 is another
glucosidase inhibitor whose derivatives have been used
in the treatment of diabetes, Gaucher’s disease, and viral
infections.12–17
HO
HO
HO
NH
OH
HO
CH3
O
HN
HO
OH
HO
2
O
O
HO
OH
HO
O
O
OH
1
HO
OH
Salacinol 3 and kotalanol 4 are two naturally occur-
ring glycosidase inhibitors that have been isolated from
roots and stems of a Sri Lankan plant, Salacia reticu-
lata.18,19 We and others have synthesized salacinol and
compounds related to salacinol including heteroana-
logues, stereoanalogues, chain-extended homologues,
C-2 substituted analogues, and counterion variants.20
*
Corresponding author. Tel.: +1 778 782 4152; fax: +1 778 782
4860; e-mail: bpinto@sfu.ca
0008-6215/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2008.01.025

952
N. Choubdar et al. / Carbohydrate Research 343 (2008) 951–956
These inhibitors contain ammonium, selenonium, or sulf-
onium ion as putative mimics of the oxacarbenium-ion
like transition states in glycosidase-mediated hydrolysis
reactions.21–25
diol was protected with the acid labile protecting group,
p-methoxybenzyl (PMB), to afford compound 8 in 58%
yield (Scheme 2).
The alkylation reaction of 8 with 2,4-O-benzylidene-L-
erythritol-1,3-cyclic sulfate 930,31 in hexafluoroisopro-
panol (HFIP) as the solvent containing an excess of
K2CO3 in a sealed tube did not yield the desired com-
pound 7, but yielded the elimination product 11. Pre-
sumably elimination follows alkylation owing to the
increased acidity of the protons adjacent to the sulf-
onium-ion center. Compound 11 was deprotected
using trifluoroacetic acid (TFA, 90%) to afford com-
pound 6 for testing as a potential glycosidase inhibitor
(Scheme 3).
The alkylation reaction of 8 with the cyclic sulfate 9 in
HFIP did not proceed in the absence of K2CO3 at 50–
70 °C, and at higher temperatures, the starting materials
started to decompose. The alkylation reaction of 8 with
the cyclic sulfate 9 in acetonitrile containing K2CO3 was
attempted but the reaction did not proceed and starting
compounds were recovered. This result suggested that
HFIP might be the best choice of solvent for this type
of reaction.
OH
OH
OH
OH
4'
OH
3'
1'
2'
OH
-
-
5
OH
S + OSO3
1
S
+
OSO3
HO
HO
4
3
2
HO
HO
OH
OH
3
4
Theoretical and experimental studies on nucleotides
containing 1,2,4-trideoxy-2-fluoro-1,4-anhydro-4-thio-
D-arabinose sugar ring had indicated an unusual confor-
mational preference due to steric and stereoelectronic
effects.26 In addition, the substitution of a fluorine atom
for a hydroxyl group has proven advantageous in the
design of carbohydrate-based enzyme inhibitors. Thus,
a kinetic study with UDP-Galf and its C3- fluorinated
analogue, UDP-[3-F]Galf showed that the catalytic effi-
ciency (kcat/Km) of UDP-galactopyranose mutase for
UDP-[3-F]Galf decreased by approximately three orders
of magnitude in comparison to that of UDP-Galf.27
This difference has been attributed, by STD-NMR and
molecular dynamics, to the partial population of a bind-
ing mode of UDP-[3-F]Galf that is non-productive with
respect to reaction.28 Therefore, it was of interest to syn-
thesize a salacinol analogue with a fluorine atom at the
C-2 position (5) to probe its glycosidase inhibitory
activity.
Interestingly, the alkylation reaction of 8 with the
cyclic sulfate 9 in HFIP containing 0.3 M equiv of
K2CO3 in a sealed tube at 68 °C proceeded smoothly
to give the desired coupled product 7. The benzylidene
and p-methoxybenzyl protecting groups were then
removed using trifluoroacetic acid (90%) to afford the
desired product 5 (Scheme 3).
Finally, we comment on the inhibitory activities of
compounds 5 and 6 against recombinant human maltase
glucoamylase (MGA). Compound 6 inhibited MGA
with an IC50 = 150 lM, whereas compound 5 showed
greater inhibition with Ki = 6 1 lM. Because salacinol
itself shows a Ki = 0.2 0.02 lM,32 it would appear
that the OH group on C-2 of salacinol is critical as a
hydrogen-bond donor with functional groups in the
active site of MGA.
We report herein the synthesis of 5 and its elimination
product 6, together with their inhibitory activities
against human maltase glucoamylase (MGA), a key
intestinal enzyme involved in the breakdown of malto-
oligosaccharides into glucose.
OH
OH
4'
4'
1'
1'
S
3'
3'
2'
2'
OH
OH
5
5
-
-
+
+
OSO3
OSO3
S
HO
HO
1
1
4
4
2
F
2
3
3
HO
HO
1. Experimental
6
5
Retrosynthetic analysis indicated that the target com-
pound 5 could be synthesized by removal of the benzyl-
idene and p-methoxybenzyl (PMB) protecting groups
in compound 7, which could be synthesized, in turn,
by nucleophilic attack of compound 8 at the less hindered
carbon of 2,4-O-benzylidene-L-erythritol-1,3-cyclic sulf-
ate 9. Compound 8 could be synthesized from 1,4-an-
hydro-2-deoxy-2-fluoro-3,5-O-(1,1,3,3-tetraisopropyldi-
siloxane-1,3-diyl)-4-thio-D-arabinitol 10 (Scheme 1).26,29
Compound 10 was synthesized from 1,4-anhydro-4-
thio-D-arabinitol according to literature procedures.26,29
The silyl protecting group in 10 was removed using
tetrabutylammonium fluoride (TBAF), and the resulting
1.1. General methods
Optical rotations were measured at 21 °C. H and 13C
NMR were recorded with frequencies of 500 and
125 MHz, respectively. All assignments were confirmed
with the aid of two-dimensional H, H (gCOSY) and
1H, 13C (gHMQC) experiments using standard Varian
pulse programs. Processing of the data was performed
with MestRec software. Analytical thin-layer chromato-
graphy (TLC) was performed on aluminum plates pre-
coated with silica gel 60F-254 as the adsorbent. The
developed plates were air-dried, exposed to UV light
and/or sprayed with a solution containing 1% Ce(SO4)2
1
1
1

N. Choubdar et al. / Carbohydrate Research 343 (2008) 951–956
953
Ph
O
O
OH
OH
S
-
-
+
S
O
+
OSO3
OSO3
S
PMBO
PMBO
O
O
+
Ph
PMBO
PMB =
HO
O
O
S
O
F
PMBO
HO
F
F
9
8
p
-methoxybenzyl
5
7
S
O
Si
O
O
F
Si
10
Scheme 1.
(ESI) technique, using a ZabSpec OA TOF mass spectro-
meter at 10,000 RP.
S
O
S
1. TBAF
PMBO
PMBO
Si
2. a) NaH, DMF
b) PMBCl
O
O
F
F
Si
58%
8
1.2. Enzyme assays
10
Scheme 2.
Enzyme assays of MGA with compounds 5 and 6 were
determined using a pNP-glucoside assay to follow the
production of p-nitrophenol upon the addition of
enzyme (500 nM). Initially, IC50 values were deter-
mined; in the case of 6, a high value (150 lM) dictated
that further detailed kinetic analysis was not justified,
whereas in the case of 5, further kinetic analysis was
and 1.5% molybdic acid in 10% aqueous H2SO4, and
heated. Column chromatography was performed with
Silica Gel 60 (230–400 mesh). High resolution mass
spectra were obtained by the electrospray ionization
Ph
O
O
OH
OH
S
-
-
PMBO
PMBO
O
+
OSO3
S
+
OSO3
S
(b)
O
(a)
O
+
Ph
O
PMBO
PMBO
HO
O
S
F
O
HO
8
9
62%
74%
11
6
Ph
OH
O
F
O
OH
S
-
-
+
S
OSO3
+
PMBO
PMBO
OSO3
S
O
O
HO
+
O
(c)
PMBO
PMBO
Ph
(b)
O
O
S
F
O
HO
F
9
8
75%
70%
5
7
Scheme 3. Reagents and conditions: (a) K2CO3 (excess), HFIP, 55–70 °C; (b) TFA (90%); (c) K2CO3 (0.3 M equiv), HFIP, 68 °C.

954
N. Choubdar et al. / Carbohydrate Research 343 (2008) 951–956
pursued. The latter assay was carried out in 96-well
microtiter plates containing 100 mM MES buffer pH
6.5, inhibitor (at three different concentrations), and
p-nitrophenyl-a-D-glucopyranoside (pNP-glucoside) as
a substrate (2.5, 3.5, 5, 7.5, 15, and 30 mM) with a final
volume of 50 lL. Reactions were incubated at 37 °C for
35 min and terminated by the addition of 50 lL of 0.5 M
sodium carbonate. The absorbance of the reaction prod-
uct was measured at 405 nm in a microtiter plate reader.
All reactions were performed in triplicate, and absor-
bance measurements were averaged to give a final result.
Reactions were linear within this time frame. The
program GraFit 4.0.14 was used to fit the data to the
Michaelis–Menten equation and estimate the kinetic
parameters, Km, Kmobs (Km in the presence of inhibitor),
and Vmax of the enzyme. Ki value for the inhibitor was
determined by the equation Ki = [I]/((Kmobs/Km) ꢀ 1).
The Ki reported for the inhibitor was determined by
averaging the Ki values obtained from three different
inhibitor concentrations.
for C21H25O4SFNa [M+Na]+: 415.1349. Found:
415.1348.
1.4. 1,4-Dideoxy-1,2-ene-3,5-di-O-p-methoxybenzyl-1,4-
[[(2S,3S)-2,4-O-benzylidene-3-(sulfooxy)butyl]-episulfon-
iumylidene]-D-arabinitol inner salt (11)
Compound 8 (50 mg, 0.1 mmol), 2,4-benzylidene-L-
erythritol-1,3-cyclic sulfate (9) (46 mg, 1.3 equiv), and
K2CO3 (40 mg, 0.3 mmol) were dissolved in HFIP.
The mixture was stirred in a sealed tube in an oil bath
at 70 °C for 20 h. K2CO3 was removed by filtration
and the solvent was removed under reduced pressure.
Flash chromatography of the crude product (5:1
EtOAc–MeOH) afforded compound 11 as a syrup
(51 mg, 62%); [a]D +93 (c 0.3, MeOH); 1H NMR
(CD3OD): d 7.40–7.32 (5H, m, Ar), 7.20, 7.13, 6.90,
6.84 (8H, dd, Ar), 7.00 (1H, dd, J1,2 = 5.7,
J3,2 = 2.7 Hz, H-2), 6.57 (1H, d, H-1), 5.54 (1H, s,
CHPh), 4.88 (1H, dd, H-3), 4.59 (1H, d, JAB = 11.6 Hz,
CH2Ph), 4.50 (1H, d, CH2Ph), 4.44 (1H, dd,
J4 b;4 a ¼ 10:6, J3 ;4 a ¼ 5:3 Hz, H-40a), 4.43 (1H, m,
0
0
0
0
1.3. 1,4-Anhydro-2-deoxy-2-fluoro-3,5-di-O-(p-methoxy-
benzyl)-4-thio-D-arabinitol (8)
J2 ;3 ¼ 4:1 Hz, H-30), 4.32 (1H, m, H-20), 4.30, 4.28
0
0
(2H, d, JAB = 11.7 Hz, CH2Ph), 4.17 (1H, m, H-4),
4.11 (1H, d, J1 b;1 a ¼ 13:9, J2 ;1 a ¼ 4:1 Hz, H-10a), 3.88
0
0
0
0
To a solution of compound 10 (1.9 g, 4.9 mmol) in dis-
tilled THF (25 mL) was added tetrabutylammonium
fluoride (TBAF) in THF (9.8 mL, 1 M). The mixture
was stirred at room temperature for 2 h and then
quenched by the addition of ice. The organic phase
was separated and the solvent was removed under
reduced pressure. The crude product was dissolved in
DMF (20 mL) and the solution was added dropwise to
a suspension of sodium hydride (0.6 g, 26 mmol) in
DMF (50 mL) at 0 °C. After addition was complete,
the temperature was brought to room temperature and
the mixture was stirred at room temperature for 1 h.
PMBCl (2.3 g, 15 mmol) was added dropwise to the
mixture, the mixture was stirred at room temperature
overnight, and then the reaction was quenched by the
addition of ice. The mixture was extracted with ether
(150 mL), the organic phase was washed with brine,
and dried over Na2SO4. The solvent was removed under
reduced pressure, and the crude product was purified by
flash chromatography (5:1 hexane–EtOAc) to afford 8 as
a syrup (1.1 g, 58%); [a]D +21 (c 0.1, CH2Cl2); 1H NMR
(CDCl3): d 7.27–7.22, 6.90–6.85 (8H, m, Ar), 5.15 (1H,
m, JF,2 = 50.4, J3,2 = 3.2, J1a,2 = 7.4 Hz, H-2), 4.59–
4.50 (2H, d, JAB = 11.6 Hz, CH2Ph), 4.49–4.43 (2H, d,
CH2Ph), 4.21 (1H, m, JF,3 = 11.4 Hz, H-3), 3.82, 3.81
(6H, s, OMe), 3.61–3.56 (1H, m, H-4), 3.57 (1H, m,
H-5a), 3.47 (1H, m, H-5b), 3.39–2.83 (2H, m, H-1a,
H-1b); 13C NMR (CDCl3): d 159.6, 159.4, 130.3,
129.9, 129.7, 129.6, 114.1, 113.9 (8C, Ar), 97.7 (d,
JF,2 = 181.9 Hz, C-2), 84.2 (d, JF,3 = 24.2 Hz, C-3),
73.0 (CH2Ph), 71.8 (C-5), 71.7 (CH2), 55.5 (2 ꢁ OMe),
49.5 (C-4), 34.5 (d, JF,1 = 22.3 Hz, C-1). HRMS Calcd
(1H, dd, J2 ;1 b ¼ 3:4 Hz, H-10b), 3.80–3.73 (1H, m,
H-40b), 3.77, 3.76 (6H, s, 2 ꢁ OMe), 3.53 (1H, dd,
J5b,5a = 10.7, J4,5a = 3.9 Hz, H-5a), 3.36 (1H, dd,
J4,5b = 4.5 Hz, H-5b); 13C NMR (CD3OD): d 160.1,
160.0 (2C, Ar), 146.5 (C-2), 137.8, 136.9 (2C, Ar),
130.2, 129.7, 128.2, 127.9 (4C, Ar), 129.3, 129.0, 128.9,
128.7, 126.2, 126.1 (6C, Ph), 119.4 (C-1), 114.0, 113.9
(4C, Ar), 101.1 (CHPh), 85.9 (C-3), 75.3 (C-20), 72.8,
72.7 (2C, CH2Ph), 68.6 (C-40), 67.6 (C-30), 66.2 (C-4),
65.3 (C-5), 54.6 (OMe), 49.4 (C-10). HRMS Calcd for
C32H37O10S2 [M]+1: 645.1823. Found: 645.1828.
0
0
1.5. 1,4-Dideoxy-1,2-ene-1,4-[[(2S,3S)-2,4-dihydroxy-3-
(sulfooxy)butyl]episulfoniumylidene]-D-arabinitol inner
salt (6)
Compound 11 (50 mg, 0.1 mmol) was dissolved in tri-
fluoroacetic acid (2 mL, 90%) and the solution was
stirred at room temperature for 1 h. The solvent was
removed under reduced pressure and the crude product
was purified by flash chromatography (3:1 EtOAc–
MeOH) to afford compound 6 as a syrup (18.1 mg,
1
74%); [a]D +50 (c 0.02, MeOH); H NMR (CD3OD):
d 6.93 (1H, dd, J1,2 = 5.7, J3,2 = 2.6 Hz, H-2), 6.61
(1H, d, H-1), 5.18 (1H, m, J4,3 = 1.0 Hz, H-3), 4.39
(1H, m, J3 ;2 ¼ 8:4; J1 b;2 ¼ 4:1 Hz, H-20), 4.32 (1H,
0
0
0
0
m, J4 b;3 ¼ 3:2 Hz, H-30), 4.16 (1H, m, H-4), 4.15 (1H,
0
0
dd, J5b,5a = 12.7, J4,5a = 3.6 Hz, H-5a), 4.07 (1H, dd,
J1 b;1 a ¼ 13:4; J2 ;1 a ¼ 4:2 Hz, H-10a), 4.01 (1H, dd,
0
0
0
0
0
0
J4,5b = 5.2 Hz, H-5b), 3.95 (1H, dd, J4 b;4 a ¼ 12:2;
J3 ;4 a ¼ 3:4 Hz, H-40a), 3.86 (1H, dd, H-10b), 3.84 (1H,
0
0

N. Choubdar et al. / Carbohydrate Research 343 (2008) 951–956
955
dd, H-40b); 13C NMR (CD3OD): d 147.6 (C-2), 119.3
3.6 Hz, H-1a), 4.09 (1H, dd, J5a,5b = 14.0, J4,5b
4.0 Hz, H-5b), 4.01 (1H, dd, J2,1b = 6.0 Hz, H-1b),
=
(C-1), 79.3 (C-3), 78.6 (C-30), 70.9 (C-4), 65.7 (C-20),
60.4 (C-40), 58.7 (C-5), 53.6 (C-10). HRMS Calcd for
C9H17O8S2 [M]+1: 317.0359. Found: 317.0362.
3.97 (1H, dd, J4 b;4 a ¼ 11:9; J3 ;4 a ¼ 6:1 Hz, H-40a),
0
0
0
0
3.96 (1H, dd, J1 b;1 a ¼ 12:2; J2 ;1 a ¼ 3:5 Hz, H-10a),
0
0
0
0
3.85 (1H, dd, J2 ;1 b ¼ 1:9 Hz, H-10b), 3.83 (1H, dd,
H-40b); 13C NMR (CD3OD): d 97.7 (d, JF,2 = 184 Hz,
C-2), 79.1 (C-20), 76.5 (d, JF,3 = 25 Hz, C-3), 70.7
0
0
1.6. 1,2,4-Trideoxy-2-fluoro-3,5-di-O-p-methoxybenzyl-
1,4-[[(2S,3S)-2,4-O-benzylidene-3-(sulfooxy)butyl]-epi-
sulfoniumylidene]-D-arabinitol inner salt (7)
(C-4), 66.3 (C-30), 60.5 (C-40), 58.7 (d, JF,1 = 6.9 Hz,
C-10), 51.9 (C-1), 47.2 (C-5). HRMS Calcd for
C9H17O8S2FNa [M+Na]+: 359.0241. Found: 359.0247.
0
Compound 8 (53 mg, 0.1 mmol), 2,4-benzylidene-L-
erythritol-1,3-cyclic sulfate (9) (60 mg, 1.7 equiv), and
K2CO3 (5 mg, 0.04 mmol) were dissolved in HFIP.
The mixture was stirred in a sealed tube in an oil bath
at 68 °C overnight. K2CO3 was removed by filtration
and the solvent was removed under reduced pressure.
Flash chromatography of the crude product (5:1
EtOAc–MeOH) afforded compound 7 as a syrup
Acknowledgment
We are grateful to the Canadian Institutes for Health
Research for financial support.
1
(63 mg, 70%); [a]D +180 (c 0.008, CH2Cl2); H NMR
Supplementary data
(CDCl3): d 7.46–7.43, 7.38–7.35 (5H, m, Ar), 7.21, 7.07
(4H, dd, Ar), 6.88–6.83 (4H, dd, Ar), 5.57 (1H, d,
JF,2 = 48.1 Hz, H-2), 5.51 (1H, s, CHPh), 4.69 (1H, m,
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2008.01.025.
J2 ;3 ¼ 9:8; J4 a;3 ¼ 5:4 Hz, H-30), 4.62 (1H, d, JAB
=
0
0
0
0
11.9 Hz, CH2Ph), 4.60 (1H, dd, H-40a), 4.53 (1H, d,
CH2Ph), 4.46 (1H, dd, J5b,5a = 13.9, J4,5a = 3.0 Hz,
H-5a), 4.42 (1H, m, JF,3 = 8.3 Hz, H-3), 4.38 (1H,
ddd, J3,4 = 9.6 Hz, H-4), 4.28 (1H, dd, J4,5b = 2.9 Hz,
References
H-5b), 4.26–4.19 (1H, m, H-1a), 4.23, 4.17 (2H, JAB
=
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14. Butters, T. D.; Dwek, R. A.; Platt, F. M. Glycobiology
2005, 15, R43–R52.
15. Elstein, D.; Hollak, C.; Aerts, J.; van Weely, S.; Maas, M.;
Cox, T. M.; Lachmann, R. H.; Hrebicek, M.; Platt, F. M.;
Butters, T. D.; Dwek, R. A.; Zimran, A. J. Inherit. Metab.
Dis. 2004, 27, 757–766.
11.5 Hz, CH2Ph), 4.12 (1H, m, H-20), 4.10 (1H, m,
0
0
J1a,1b = 9.9 Hz, H-1b), 3.82 (1H, m, J3 ;4 b ¼ 6:1 Hz,
H-40b), 3.81, 3.78 (6H, s, OMe), 3.52 (1H, dd,
J1 b;1 a ¼ 10:1 Hz, H-10a), 3.48 (ddd, J2 ;1 ¼ 7:1; JF;1
¼
0
0
0
0
0
2:2 Hz, H-10b); 13C NMR (CDCl3): 160.1, 159.8, 136.8,
130.6, 130.2, 129.8 (6C, Ar), 129.6, 128.8, 128.6, 127.8,
126.4 (5C, Ph), 114.4, 114.2 (2C, Ar), 101.8 (CHPh),
95.6 (d, JF,2 = 185.2 Hz, C-2), 82.9 (d, JF,3 = 25.5 Hz,
C-3), 76.5 (C-4), 73.4, 72.5 (2C, CH2Ph), 69.3 (C-40),
66.8 (C-30), 65.8 (d, JF;1 ¼ 6:8 Hz, C-10), 65.2 (C-20),
0
55.5(2 ꢁ OMe), 49.7 (C-5), 47.9 (d, JF,1 = 23.8 Hz,
C-1). HRMS Calcd for C32H37O10S2FNa [M+Na]+:
687.1704. Found: 687.1709.
1.7. 1,2,4-Trideoxy-2-fluoro-1,4-[[(2S,3S)-2,4-dihydroxy-
3-(sulfooxy)butyl]episulfoniumylidene]-D-arabinitol inner
salt (5)
Compound 7 (50 mg, 0.1 mmol) was dissolved in triflu-
oroacetic acid (2 mL, 90%) and the solution was stirred
at room temperature for 1 h. The solvent was removed
under reduced pressure and the crude product was puri-
fied by flash chromatography (3:1 EtOAc–MeOH) to af-
ford compound 5 as a syrup (19 mg, 75%); [a]D +16 (c
0.24, MeOH); 1H NMR (CD3OD): d 5.51 (1H, d,
JF,2 = 48.4 Hz, H-2), 4.77 (1H, d, JF,3 = 4.8 Hz, H-3),
0
0
0
0
0
0
4.38 (1H, ddd, J2 ;3 ¼ 7:6; J4 a;3 ¼ 6:1; J4 b;3 ¼ 3:7 Hz,
H-30), 4.32 (1H, ddd, H-20), 4.19 (1H, dd, H-5a), 4.18
16. Karpas, A.; Fleet, G. W. J.; Dwek, R. A.; Petursson, S.;
Namgoong, S. K.; Ramsden, N. G.; Jacob, G. S.;
(1H, m, H-4), 4.12 (1H, dd, J1b,1a = 13.2, J2,1a
=

956
N. Choubdar et al. / Carbohydrate Research 343 (2008) 951–956
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