Synthesis and glycosidase inhibitory activities of chain-modified analogues of the glycosidase inhibitors salacinol and blintol

Article abstract of DOI:10.1016/j.carres.2007.02.020

The synthesis of chain-modified analogues of the naturally-occurring glycosidase inhibitor, salacinol, and its selenium analogue, blintol is described. The modification consists of a frame shift of the sulfate moiety by one carbon atom in the zwitterionic

Full text of DOI:10.1016/j.carres.2007.02.020

Carbohydrate Research 342 (2007) 1888–1894
Synthesis and glycosidase inhibitory activities
of chain-modified analogues of the glycosidase
inhibitors salacinol and blintol
Ravindranath Nasi,a Lyann Sim,b David R. Roseb and B. Mario Pintoa,*
aDepartment of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
bDepartment of Medical Biophysics, University of Toronto and Division of Molecular and Structural Biology,
Ontario Cancer Institute, Toronto, Ont., Canada M5G 2M9
Received 1 January 2007; received in revised form 14 February 2007; accepted 19 February 2007
Available online 23 February 2007
Abstract—The synthesis of chain-modified analogues of the naturally-occurring glycosidase inhibitor, salacinol, and its selenium
analogue, blintol is described. The modification consists of a frame shift of the sulfate moiety by one carbon atom in the zwitterionic
structures as well as an extension of the acyclic chain to five carbons. The target molecules were synthesized by alkylation of 1,4-
anhydro-2,3,5-tri-O-p-methoxybenzyl-4-thio (or seleno)-D-arabinitol at the ring heteroatom by 2,3,5-tri-O-p-methoxybenzyl D- or L-
xylitol-1,4-cyclic sulfate, followed by deprotection with trifluoroacetic acid. Two of the four compounds inhibit recombinant human
maltase glucoamylase, one of the key intestinal enzymes involved in the breakdown of glucose oligosaccharides in the small intestine,
with Ki values of 20 4 and 53 5 lM.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Glycosidase inhibitors; Salacinol analogues; Blintol analogues; Chain-modified analogues; 5-Carbon extended analogues; Sulfonium salt;
Selenonium salt; Cyclic sulfate; Human maltase glucoamylase (MGA)
1. Introduction
to create compounds that mimic the oxacarbenium-ion
transition state of the enzyme-catalyzed reaction.5 Many
of the natural and synthetic azasugars are believed to
mimic the transition state in either charge or shape.6
Recently, a new class of glycosidase inhibitors with an
intriguing inner salt, sulfonium-sulfate was isolated
from Salacia reticulata.7 Extracts of this plant have been
traditionally used in the Indian Ayurvedic system of
medicine for the treatment of diabetes.8 The active com-
ponents of these extracts are found to be the sulfonium
salts salacinol (1) and kotalanol (2) (Chart 1). It is
believed that the inhibition of glycosidases by 1 and 2
is in fact due to their ability to mimic the shape and/
or charge of the transition state involved in the enzy-
matic reactions. We and others previously reported the
synthesis of salacinol and its stereoisomers.9,10 We have
also reported the synthesis of blintol (3), the selenium
analogue of salacinol, as a potential glycosidase inhibi-
tor.11 Indeed both salacinol (1) and blintol (3) have been
Glycosidases are involved in several metabolic pathways
and specific reversible inhibitors of these enzymes can
have therapeutic utility in the treatment of diabetes,1
cancer,2 and viral infections.3 One important class of
these enzymes is responsible for the liberation of glucose
from its higher oligomers. Disruption in the function
and regulation of these enzymes can lead to disease
states such as diabetes. In the treatment of Type II non-
insulin dependent diabetes (NIDD) management of
blood glucose levels is critical.4 This can be achieved
by administering drugs which inhibit the activity of
glucosidases that mediate the hydrolysis of complex
starches to oligosaccharides in the small intestine. An
attractive approach to potent glucosidase inhibitors is
*
Corresponding author. Tel.: +1 604 291 4152; fax: +1 604 291
4860; e-mail: bpinto@sfu.ca
0008-6215/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2007.02.020

R. Nasi et al. / Carbohydrate Research 342 (2007) 1888–1894
1889
OH
OH
OH OH
-
OH
OH
OH
OH
-
-
OH
OSO3
OSO3
S
S
OSO3
Se
HO
HO
HO
HO
HO
OH
OH
HO
OH
1
3
2
Chart 1.
shown to be very effective in controlling blood glucose
levels in rats after a carbohydrate meal, thus providing
lead candidates for the treatment of Type 2 diabetes.12
As part of a program aimed at the synthesis of new
glycosidase inhibitors, we have focused recently on the
synthesis of chain-modified analogues of salacinol (1)
and blintol (3) that vary in the length of the polyhydr-
oxylated, sulfated chain. We have synthesized several
5-carbon and 6-carbon chain analogues in which the
sulfate moiety is located at C-30 as in salacinol and
blintol.13–15 These compounds were synthesized by a
strategy that involved cyclic sulfate derivatives of
different monosaccharides or alditols. We have also
reported the mapping of the active site of recombinant
human maltase glucoamylase using these synthetic
analogues15.
We now report on the effect of the positioning of the
sulfate group in the acyclic chain, in particular, the
synthesis of the chain-modified analogues 4–7 (Chart 2).
2. Results and discussion
Retrosynthetic analysis revealed that the desired ana-
logues could be synthesized by alkylation of a protected
anhydro-D-heteroarabinitol moiety at the ring hetero-
atom by either an open chain electrophile or a cyclic
sulfate derivative, whereby selective attack of the hetero-
atom at the least hindered primary centre would afford
the desired products (Scheme 1).
The seven-membered cyclic sulfates (12, 14), chosen as
the alkylating agents, were synthesized from the corre-
sponding diols. The diols were synthesized in turn from
D- or L-xylose in six steps according to the procedure
developed recently in our laboratory for the synthesis
of the PMB-protected anhydro-D-selenoarabinitol 11
(Scheme 2).16 Thus, diol 8 was used as a key intermedi-
ate to synthesize the thioether 10,17 the selenoether 11,
and the cyclic sulfate 12. Treatment of the diol 8 with
methanesulfonyl chloride in pyridine afforded the di-
mesylate 9, which on treatment with Na2SÆ9H2O pro-
duced the thioether 10; treatment of 9 with Se/NaBH4
produced the selenoether 11 (Scheme 2). Treatment of
the diol 8 with thionyl chloride and triethylamine gave
OH
OH
OSO3
OSO3
3'
OH
OH
5'
4'
3'
5'
4'
2'
2'
1'
1'
5
5
X
OH
X
OH
1
4
4
1
HO
HO
2
3
2
3
HO
HO
OH
OH
4. X = S
6. X = S
5. X = Se
7. X = Se
Chart 2.
OH
OSO3
OH
OP
OSO3
X
OP
PO
X
OH
HO
L
OP
PO
OP
HO
OH
O
O
O
OH
S
OH
O
PO
PO
PO
OP
PO
OP
L= Leaving group, P= Protecting group
Scheme 1.

1890
R. Nasi et al. / Carbohydrate Research 342 (2007) 1888–1894
S
OH
OMs
OH
OMs
PMBO
PMBO
PMBO
PMBO
PMBO
MsCl, Pyridine
CH2Cl2
NaS2.9H2O
DMF
PMBO
OPMB
OPMB
OPMB
10 (81%)
9 (84%)
8
1) SOCl2, Et3N, CH2Cl2
2) RuCl3, NaIO4
CCl4:CH3CN
Se, NaBH4
EtOH
O
O
S
O
O
Se
PMBO
PMBO
PMBO
PMBO
OPMB
OPMB
12 (62% two steps)
11 (80%)
O
O
OH
S
O
O
OH
1) SOCl2, Et3N, CH2Cl2
PMBO
PMBO
PMBO
PMBO
2) RuCl3, NaIO4
CCl4:CH3CN
OPMB
OPMB
13
14 (65% two steps)
Scheme 2.
the cyclic sulfite, which was subsequently oxidized with
sodium periodate and ruthenium(III) chloride as a cata-
lyst to afford the cyclic sulfate 12. The corresponding
isomer 14 was synthesized in an analogous manner from
the enantiomeric diol 13 (Scheme 2), which was obtained
in turn from D-xylose.
The alkylation of 10 and 11 with the cyclic sulfates 12
and 14 was examined next (Scheme 3). Thus, the reac-
tion of the thioarabinitol 10 with the cyclic sulfate 12
was found to proceed very slowly at 70 ꢁC in
1,1,1,3,3,3-hexafluoroisopropanol (HFIP) and was
terminated before complete consumption of starting
materials as we observed that longer reaction times led
to decomposition. The coupled product was obtained
as the sole product and immediate subsequent removal
of the PMB groups by treatment with trifluoroacetic
acid then afforded the target compound 4. The stereo-
chemistry at the stereogenic sulfonium center was
assigned by means of a NOESY experiment which
indicated the presence of the isomer with an anti
relationship between C-5 and C-10. The proton and car-
1
bon signals in the H and 13C NMR spectra of 4 were
OH
OSO3
OH
3'
5'
4'
2'
1'
5
X
X
OH
1
1) HFIP, K2CO3
4
PMBO
PMBO
HO
+
12
2
3
2) TFA
HO
OPMB
OH
10. X = S
11. X = Se
4. X = S (44% two steps)
5. X = Se (54% two steps)
OH
OSO3
OH
X
X
OH
1) HFIP, K2CO3
2) TFA
PMBO
PMBO
HO
+
14
OPMB
HO
OH
10. X = S
11. X = Se
6. X = S (44% two steps)
7. X = Se (51% two steps)
Scheme 3.

R. Nasi et al. / Carbohydrate Research 342 (2007) 1888–1894
1891
completely assigned with the help of 1H–1H COSY,
HMQC, and HMBC experiments.
fates were prepared from D- and L-xylose. Compounds 4
and 5 showed inhibition of recombinant human maltase
glucoamylase (MGA), a critical intestinal glucosidase,
with Ki values of 20 4 and 53 5 lM.
The results, when compared with previous data on
inhibitory activities of related compounds, add to our
knowledge of the requirements for an effective inhibitor
of MGA.
Analogously, the reaction of the selenoether 11 with
the cyclic sulfate 12 in HFIP gave a coupled product,
which was shown to be a 10:1 mixture of diastereomers
at the stereogenic selenium center; the major diastereo-
mer was isolated by flash chromatography. Removal
of the PMB groups afforded the desired selenonium salt
5. The stereochemistry at the stereogenic selenium center
was also assigned as being anti with respect to C5. In a
similar manner, reaction of the enantiomeric cyclic sul-
fate 14 with the thio-10 and seleno-11 ethers produced
the coupled products in 53% and 66% yield, respectively.
Subsequent removal of the PMB groups using TFA
yielded the desired products 6 and 7.
3. Experimental
3.1. General experimental
1
Optical rotations were measured at 23 ꢁC. H and 13C
It is of interest to comment on the inhibitory activities
of the compounds synthesized in this study and previous
studies against recombinant human maltase glucoamy-
lase (MGA),18 a critical intestinal glucosidase involved
in the processing of oligosaccharides of glucose into glu-
cose itself. Compounds 4 and 5, with the same configu-
ration at the stereogenic centers in the acyclic chain,
have Ki values of 20 4 and 53 5 lM, respectively.
These compounds are less active than salacinol and blin-
tol, with Ki values of 0.19 0.02 and 0.49 0.05 lM,
respectively.18 Interestingly, the analogue 15 (Chart 3),
in which the sulfate moiety is located at the C-30 and
not the C-40 position, is inactive.13 A second 5-carbon
chain-extended compound 16 (Chart 3), with the same
configuration at C-30 and C-40 as 6, but with the oppo-
site configuration at C-20 and in which the sulfate moiety
is located at the C-30 and not the C-40 position, has a Ki
value of 0.17 0.03 lM. In contrast, the analogues 6
and 7 are not active. We note that Tanabe et al. have
very recently reported the synthesis of de-O-sulfonated
analogues of salacinol with monomethyl sulfate and
chloride as external counter anions, and these analogues
had almost equal inhibitory activities to salacinol
against intestinal a-glucosidase in vitro.19 Further ratio-
nalization of these data will have to await knowledge of
the detailed contacts between the ligands and the active
site from X-ray crystal structures of MGA complexes
with candidate inhibitors.
NMR spectra were recorded at 500 and 125 MHz,
respectively. All assignments were confirmed with the
aid of two-dimensional experiments (1H–1H COSY,
HMQC, and HMBC). Column chromatography was
performed with Merck Silica Gel 60 (230–400 mesh).
MALDI-TOF mass spectra were recorded on a perSep-
tive Biosystems Voyager-DE spectrometer, using 2,5-
dihydroxybenzoic acid as a matrix.
3.2. Enzyme activity assay
Analysis of MGA inhibition was performed using
maltose as the substrate, and measuring the release of
glucose. Reactions were carried out in 100 mM MES
buffer pH 6.5 at 37 ꢁC for 15 min. The reaction was
stopped by boiling for 3 min. Aliquots (20 lL) were
taken and added to 100 lL of glucose oxidase assay
reagent (Sigma) in a 96-well plate. Reactions were
allowed to proceed for 1 h and absorbance was
measured at 450 nm to determine the amount of glucose
produced by MGA activity in the reaction. One unit of
activity is defined as the hydrolysis of one mole of
maltose per minute. All reactions were performed in
triplicate and absorbance measurements were averaged
to give a final result.
3.3. Enzyme kinetics
In conclusion, two chain-modified analogues of both
salacinol and blintol were synthesized using seven-mem-
bered cyclic sulfates as alkylating agents. The cyclic sul-
Kinetic parameters of recombinant MGA were deter-
mined using the glucose oxidase assay to follow the pro-
duction of glucose upon addition of enzyme (15 nM) at
increasing maltose concentrations (from 1 to 3.5 mM)
with a reaction time of 15 min. The program GRAFIT
4.0.14 was used to fit the data to the Michaelis–Menten
equation and estimate the kinetic parameters, Km and
Vmax, of the enzyme. Ki values for each inhibitor were
determined by measuring the rate of maltose hydrolysis
by MGA at varying inhibitor concentrations. Data were
plotted in Lineweaver–Burk plots (1/rate vs 1/[sub-
strate]) and Ki values were determined by the equation
Ki = Km[I]/(Vmax)m ꢀ Km, where ‘m’ is the slope of the
OH OH
OH OH
OH
OH
3'
5'
3'
5'
1'
1'
4'
4'
2'
2'
5
5
S
OSO3
S
OSO3
4
1
2
4
1
2
HO
HO
3
3
HO
HO
OH
OH
15
16
Chart 3.

1892
R. Nasi et al. / Carbohydrate Research 342 (2007) 1888–1894
line. The Ki reported for each inhibitor was estimated by
averaging the Ki values obtained from each of the differ-
ent inhibitor concentrations.
(10 mL) was then added and the reaction mixture was
stirred for 1 h at room temperature. The volatiles were
removed under high vacuum and the residue was puri-
fied by column chromatography (EtOAc/MeOH/H2O,
10:3:1) to give 4 as an amorphous solid (81 mg, 77%).
3.4. 2,3,5-Tri-O-p-methoxybenzyl-L-xylitol-1,4-cyclic
sulfate (12)
1
[a]D +40.0 (c 0.2, H2O); H NMR (D2O): d 4.57 (1H,
td, J2,1 = 4.0 Hz, J2,3 = 3.4 Hz, H-2), 4.29 (1H, ddd,
0
0
0
0
0
To a solution of 2,3,5-tri p-methoxybenzyl-L-xylitol (8)
(11.2 g, 0.021 mol) and triethylamine (11.7 mL,
0.084 mol) in CH2Cl2 (150 mL) at 0 ꢁC, was added thion-
yl chloride (2.4 mL, 0.031 mol) dropwise and the reac-
tion mixture was stirred for 30 min. The mixture was
poured into ice-cold water and extracted with additional
CH2Cl2 (300 mL). The combined organic layers were
washed with brine solution and dried over Na2SO4.
The solvent was removed and the residue was purified
by flash column chromatography to give an inseparable
mixture of two diastereomeric cyclic sulfites as a pale
brown oil (8.8 g, 72%). The mixture of the cyclic sulfites
was redissolved in a mixture of CH3CN/CCl4 (1:1,
100 mL). Sodium periodate (5.0 g, 0.02 mol) and RuCl3
(100 mg) were added followed by the addition of
50 mL of water. The mixture was stirred for 2 h and then
filtered through a bed of silica and washed with CH2Cl2.
The volatiles were removed and the residue was parti-
tioned between EtOAc (200 mL) and H2O (100 mL).
The organic layer was washed with brine solution and
dried over Na2SO4. The solvent was evaporated under
reduced pressure to give a pale yellow syrup that was
purified by flash chromatography to give 12 as a colorless
J4 ;3 ¼ 3:3; J4 ;5a0 ¼ 4:8; J4 ;5b ¼ 7:0 Hz; H-40), 4.25
0
0
(1H, dd, J3,4 = 3.2 Hz, H-3), 4.17 (1H, ddd, J2 ;3
¼
4:9; J2 ;1a0 ¼ 3:6; J2 ;1b ¼ 9:1 Hz, H-20), 3.98 (1H, dd,
J5a,4 = 4.4, J5a,5b = 11.3 Hz, H-5a), 3.95 (1H, ddd,
J4,5b = 7.8 Hz, H-4), 3.81–3.72 (6H, m, H-5b, H-1a, H-
0
0
0
0
1b, H-1a0, H-30, H-5a0), 3.70 (1H, dd, J5b ;5a0
¼
12:3 Hz, H-5b0), 3.67 (1H, dd, J1b ;1a0 ¼ 13:2 Hz,
0
13
H-1b0). C NMR (D2O): d 79.1 (C-40), 77.4 (C-3),
76.7 (C-2), 71.2 (C-30), 69.4 (C-4), 67.1 (C-20), 59.8
(C-50), 59.2 (C-5), 49.5 (C-10), 47.7 (C-1); MALDI-MS:
m/e 387.1 [M+Na]+, 365.0 [M+H]+, 285.2
[M+HꢀSO3]+. Anal. Calcd for C10H20O10S2: C, 32.96;
H, 5.53. Found: C, 32.79; H, 5.56.
3.6. 1,4-Dideoxy-1,4[[2S,3S,4S]-2,3,5-trihydroxy-4-
(sulfooxy)-pentyl]-epi-selenoniumylidene]-D-arabinitol
inner salt (5)
The selenoether 11 (246 mg, 0.44 mmol), the cyclic
sulfate 12 (305 mg, 0.53 mmol), and K2CO3 (35 mg) were
added to HFIP (4 mL) and the mixture was stirred in a
sealed tube for 48 h at 70 ꢁC. The solvent was removed
and the residue was purified by column chromatography.
The coupled product was obtained as colorless foam
(352 mg, 70%). The selenonium salts were deprotected
using TFA following the same procedure that was used
for compound 4. Purification by flash column chromato-
graphy (EtOAc/MeOH/H2O, 10:3:1) gave an amor-
phous solid 5 (98 mg, 76%). [a]D +27.0 (c 1.0, H2O);
1H NMR (D2O): d 4.63 (1H, dd, J2,3 = 4.0, J2,1 = 4.0,
H-2), 4.32 (1H, dd, J3,4 = 4.7 Hz, H-3), 4.29 (1H, m,
1
oil (7.8 g, 86%). [a]D ꢀ10.0 (c 0.4, CH2Cl2); H NMR
(CDCl3): d 7.23–6.80 (12H, 3 · PMB), 4.99 (1H,
dd, J4,5a = 7.1, J4,5b = 6.4 Hz, H-4), 4.53–4.32 (6H,
3 · CH2–Ph), 4.75 (1H, d, J1a,1b = 13.0 Hz, H-1a), 4.23
(1H, ddd, J1b,2 = 3.2 Hz, H-1b), 3.81 (6H, s, 2 ·
–OCH3), 3.83 (3H, s, –OCH3), 3.70 (1H, d,
J3,2 = 3.1 Hz, H-3), 3.63 (1H, dd, J5a,5b = 9.8 Hz, H-
5a), 3.48 (1H, dd, H-5b), 3.46 (1H, dd, H-2); 13C NMR
(CDCl3): d 159.9–114.0 (18C, 3 · PMB), 78.6 (C-4),
73.6 (C-3), 73.1, 73.0, 71.0 (3 · –CH2–Ph), 72.6 (C-2),
67.8 (C-1), 66.6 (C-5), 55.5 (3 · –OMe); MALDI-MS:
m/e 597.0 [M+Na]+. Anal. Calcd for C29H34O10S: C,
60.61; H, 5.96. Found: C, 60.32; H, 5.76.
H-40), 4.19 (1H, ddd, J2 ;1a0 ¼ 4:3; J2 ;1b ¼ 8:3; J2 ;3
¼
0
0
0
0
0
4:0 Hz, H-20), 4.02 (1H, ddd, H-4), 3.95 (1H, dd,
J5a,4 = 5.0, J5a,5b = 12.5 Hz, H-5a), 3.79 (1H, dd,
J5b,4 = 9.1 Hz, H-5b), 3.76 (3H, m, H-1a0, H-5a0, H-30),
3.69 (1H, dd, J5b ;5a0 ¼ 12:3; J4 ;5b ¼ 4:5 Hz, H-5b0),
0
0
0
3.68 (1H, dd, J1b ;1a0 ¼ 12:1 Hz, H-1b0), 3.64 (2H, d,
0
13
3.5. 1,4-Dideoxy-1,4[[2S,3S,4S]-2,3,5-trihydroxy-4-
(sulfooxy)pentyl]-epi-sulfoniumylidene]-D-arabinitol
inner salt (4)
H2-1); C NMR (D2O): d 79.5 (C-40), 78.1 (C-3), 77.4
(C-2), 71.7 (C-30), 68.8 (C-4), 66.9 (C-20), 59.9 (C-50),
59.3 (C-5), 47.4 (C-10), 45.0 (C-1); MALDI-MS: m/e
412.4 [M+H]+, 332.2 [M+HꢀSO3]+. Anal. Calcd for
C10H20O10SSe: C, 29.20; H, 4.90. Found: C, 28.80; H,
4.56.
The thioether 10 (257 mg, 0.50 mmol), the cyclic sulfate
12 (342 mg, 0.59 mmol), and K2CO3 (35 mg) were added
to HFIP (3 mL) and the reaction mixture was stirred in
a sealed tube for 72 h at 70 ꢁC. The solvent was removed
and the residue was purified by flash column chromato-
graphy (EtOAc/MeOH, 15:1) to afford the coupled
product as a colorless foam (312 mg, 57%). The coupled
product was redissolved in CH2Cl2 (2 mL), TFA
3.7. 2,3,5-Tri-O-p-methoxybenzyl-D-xylitol (13)
Compound 13 was synthesized from D-xylose in seven
steps with 15% overall yield following the procedure
reported for the synthesis of its L enantiomer.16 [a]D

R. Nasi et al. / Carbohydrate Research 342 (2007) 1888–1894
1893
1
ꢀ5.0 (c 1.0, CH2Cl2); H NMR (CDCl3): d 7.26–6.83
H2O, 10:3:1) gave 6 as an amorphous solid (67 mg,
83%). [a]D ꢀ21.2 (c 0.8, H2O); H NMR (D2O): d 4.59
1
(12H, 3 · PMB), 4.60–4.37 (6H, 3 · CH2–Ph), 4.01
(1H, ddd, J2,3 = 1.4, J2,1a = 6.5, J2,1b = 6.2 Hz, H-2),
3.80 (9H, s, 2 · –OCH3), 3.74 (1H, m, H-4), 3.68–3.63
(3H, m, H-3, H2-5), 3.47 (1H, dd, J1a,1b = 9.4 Hz,
H-1a), 3.38 (1H, dd, H-1b); 13C NMR (CDCl3): d
159.6–114.0 (18C, 3 · PMB), 78.3 (C-5), 76.9 (C-3),
73.9, 73.1, 72.5 (3 · –CH2–Ph), 71.7 (C-1), 68.8 (C-2),
60.8 (C-4), 55.5 (3 · –OMe); MALDI-MS: m/e 535.7
[M+Na]+. Anal. Calcd for C29H36O8: C, 67.95; H,
7.08. Found: C, 67.69; H, 6.88.
(1H, ddd, J2,3 = 3.8, J2,1a = 4.1, J2,1b = 4.0 Hz, H-2),
4.30 (1H, dd, J3,4 = 3.2 Hz, H-3), 4.28 (1H, m, H-40),
4.17 (1H, m, H-20), 3.95 (1H, ddd, J4,5a = 5.1,
J4,5b = 7.1 Hz, H-4), 3.92 (1H, dd, J5a,5b = 11.0 Hz, H-
5a), 3.79 (1H, dd, H-5b), 3.78–3.70 (6H, m, H-1a, H-
1a0, H-1b0, H-5a0, H-5b0, H-30), 3.36 (1H, dd,
J1a,1b = 11.8 Hz H-1b); 13C NMR (D2O): d 79.1 (C-
40), 77.7 (C-3), 76.8 (C-2), 71.2 (C-30), 69.8 (C-4), 67.3
(C-20), 59.9 (C-50), 59.2 (C-5), 49.1 (C-10), 49.3 (C-1);
MALDI-MS: m/e 387.1 [M+Na]+, 365.2 [M+H]+,
285.4 [M+HꢀSO3]+. Anal. Calcd for C10H20O10S2: C,
32.96; H, 5.53. Found: C, 32.58; H, 5.82.
3.8. 2,3,5-Tri-O-p-methoxybenzyl-D-xylitol-1,4-cyclic
sulfate (14)
To a solution of 2,3,5-tri-O-p-methoxybenzyl-D-xylitol
(13) (9.8 g, 0.019 mol) and triethylamine (10.6 mL,
0.076 mol) in CH2Cl2 (150 mL) at 0 ꢁC, was added thion-
yl chloride (2.2 mL, 0.028 mol) in CH2Cl2 (10 mL) drop-
wise. After stirring for 30 min, the mixture was poured
into ice-cold water and extracted with additional
CH2Cl2 (200 mL). The combined organic layers were
washed with brine solution and dried over Na2SO4.
The solvent was removed and the residue was purified
by flash column chromatography to give an inseparable
mixture of two diastereomeric cyclic sulfites as a pale
brown oil (8.1 g, 76%). The cyclic sulfites were oxidized
following the same procedure that was used for com-
pound 12. The residue was purified by flash column
chromatography to give 14 as a colorless oil (7.2 g,
3.10. 1,4-Dideoxy-1,4[[2R,3R,4R]-2,3,5-trihydroxy-4-
(sulfooxy)-pentyl]-epi-selenoniumylidene]-D-arabinitol
inner salt (7)
The selenoether 11 (253 mg, 0.45 mmol) was coupled to
the cyclic sulfate 14 (314 mg, 0.54) in HFIP (3 mL) fol-
lowing the same procedure that was used for the synthe-
sis of 5. Column chromatography (EtOAc/MeOH, 20:1)
of the crude product gave the selenonium salt as an
amorphous solid (341 mg, 66%). Removal of the protect-
ing groups and purification by column chromatography
(EtOAc/MeOH/H2O, 10:3:1) gave 7 as an amorphous
1
solid (97 mg, 78%). [a]D ꢀ95.0 (c 0.2, H2O); H NMR
(D2O):
d
4.59 (1H, ddd, J2,3 = 3.4, J2,1b = 4.0,
J2,1b = 4.1 Hz, H-2), 4.29 (1H, dd, J3,4 = 3.8 Hz, H-4),
1
86%). [a]D +11.4 (c 1.24, CH2Cl2); H NMR (CDCl3):
0
0
0
0
0
4.24 (1H, ddd, J4 ;5b ¼ 4:8; J4 ;5a0 ¼ 3:4; J4 ;3 ¼ 9:6 Hz,
H-40), 4.15 (1H, m, H-20), 4.07 (1H, ddd, J4,5a = 5.1,
J4,5b = 7.7 Hz, H-4), 3.94 (1H, dd, J5a,5b = 12.5 Hz
H-5a), 3.84 (1H, dd, H-5b), 3.80–3.73 (4H, m, H-1a0,
d 7.21–6.82 (12H, 3 · PMB), 4.99 (1H, dd, J4,5a = 7.1,
J4,5b = 6.4 Hz, H-4), 4.53–4.32 (6H, 3 · CH2–Ph), 4.75
(1H, d, J1a,1b = 13.0 Hz, H-1a), 4.23 (1H, ddd,
J1b,2 = 3.2 Hz, H-1b), 3.81 (6H, s, 2 · –OCH3), 3.83
(3H, s, –OCH3), 3.70 (1H, d, J3,2 = 3.1 Hz, H-3), 3.63
(1H, dd, J5a,5b = 9.8 Hz, H-5a), 3.48 (1H, dd, H-5b),
3.46 (1H, dd, H-2); 13C NMR (CDCl3): d 159.9–114.0
(18C, 3 · PMB), 78.6 (C-4), 73.6 (C-3), 73.1, 73.0, 71.0
(3 · –CH2–Ph), 72.6 (C-2), 67.8 (C-1), 66.6 (C-5), 55.5
(3 · –OMe); MALDI-MS: m/e 597.2 [M+Na]+. Anal.
Calcd for C29H34O10S: C, 60.61; H, 5.96. Found: C,
60.42; H, 5.86.
H-1b0, H-30, H-5a0), 3.69 (1H, dd, J5b ;5a0 ¼ 12:3 Hz,
0
H-5b0), 3.65 (1H, dd, J1a,1b = 12.3 Hz, H-1a), 3.61 (1H,
13
dd, H-1b); C NMR (MeOH-d4): d 79.2 (C-40), 78.8
(C-3), 78.2 (C-2), 71.8 (C-30), 70.8 (C-4), 67.5 (C-20),
60.0 (C-50), 59.6 (C-5), 47.3 (C-10), 45.0 (C-1); MAL-
DI-MS: m/e 412.8 [M+H]+, 332.6 [M+HꢀSO3]+. Anal.
Calcd for C10H20O10SSe: C, 29.20; H, 4.90. Found: C,
28.89; H, 4.82.
3.9. 1,4-Dideoxy-1,4[[2R,3R,4R]-2,3,5-trihydroxy-4-
(sulfooxy)-pentyl]-epi-sulfoniumylidene]-D-arabinitol
inner salt (6)
Acknowledgements
We are grateful to the Canadian Institutes of Health
Research for financial support and to B. D. Johnston
for helpful discussions.
The thioether 10 (212 mg, 0.41 mmol) was coupled to
the cyclic sulfate 14 (290 mg, 0.50 mmol) in HFIP
(3 mL) following the same procedure that was used for
the synthesis of 4. The residue was purified by flash col-
umn chromatography (EtOAc/MeOH, 15:1) to give the
sulfonium salt as an amorphous solid (240 mg, 53%).
Deprotection of the sulfonium salt using TFA and puri-
fication by column chromatography (EtOAc/MeOH/
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