Synthesis of thioswainsonine as a potential glycosidase inhibitor

Article abstract of DOI:10.1016/j.carres.2006.04.009

The synthesis of a bicyclic sulfonium-ion analogue of a naturally occurring glycosidase inhibitor, swainsonine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, has been achieved by a multi-step synthesis starting from 1,4-anhydro-2,3

Full text of DOI:10.1016/j.carres.2006.04.009

Carbohydrate Research 341 (2006) 1685–1691
Note
Synthesis of thioswainsonine as a potential glycosidase inhibitor
Nag S. Kumar and B. Mario Pinto*
Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
Received 18 March 2006; received in revised form 10 April 2006; accepted 13 April 2006
Available online 6 May 2006
Abstract—The synthesis of a bicyclic sulfonium-ion analogue of a naturally occurring glycosidase inhibitor, swainsonine, in which
the bridgehead nitrogen atom is replaced by a sulfonium ion, has been achieved by a multi-step synthesis starting from 1,4-anhydro-
2,3-di-O-benzyl-4-thio-D-lyxitol. The synthetic strategy relies on the intramolecular displacement of a leaving group on a pendant
acyclic chain by a cyclic thioether. This bicyclic sulfonium salt will serve as a candidate to test the hypothesis that a sulfonium salt
carrying a permanent positive charge would be an effective glycosidase inhibitor.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Glycosidase inhibitor; Swainsonine analogue; Bicyclic sulfonium salt; Indolizidine alkaloid analogue
Glycosidases play an important role in the metabolism of
carbohydrates and in the processing of specific oligosac-
charide structures on glycoproteins; the latter play impor-
tant roles in intercellular recognition processes, and their
modification has been implicated in disease states such as
cancer.1–7 Tumor cells displayvery complex carbohydrate
structures that are usually restricted to embryonic tissues
and it is believed that these structures provide signal stim-
uli for rapid proliferation and metastasis of tumor cells.
Because tumor and normal cells have different rates of cell
growth, a glycosidase inhibitor can be used to block the
assembly of complex oligosaccharide structures, which
might lead, in turn, to a therapeutic strategy for the
treatment of cancer. For example, swainsonine (1), a
plant-derived alkaloid, is an excellent inhibitor of
Golgi a-mannosidase II (GMII) and has been shown to
reduce tumor cell metastasis, enhance cellular immune
responses, and slow tumor growth in mice.8 Treatment
with swainsonine (1) has led to a significant reduction of
tumor mass in humans suffering from breast, liver, lung
cancer, and other malignancies.9,10 The most important
class of reversible glycosidase inhibitors is composed of
naturally occurring polyhydroxylated pyrrolidine, piper-
idine, pyrrolizidine, and indolizidine alkaloids11–17 which
are monocyclic and bicyclic amines such as 1-deoxynojiri-
mycin (2), castanospermine (3), and swainsonine (1). It is
postulated that these amines bind to glycosidase enzymes
by mimicry of the shape and charge of the oxacarbenium
ion transition state for the enzyme-catalyzed hydrolysis
reaction.18,19 The nitrogen atom is known to be proton-
ated in the enzyme active site, thus providing the stabiliz-
ing electrostatic interactions between the inhibitor and
the carboxylate residues in the enzyme active site. An
alternative means of achieving the required charged state
to provide such electrostatic interactions would be to syn-
thesize compounds that incorporate a permanent positive
charge at a suitable position.
H
N
HO
HO
N
OH
OH
OH
OH
OH
2
1
HO
HO
N
OH
OH
*
Corresponding author. Tel.: +1 604 291 4152; fax: +1 604 291
4860; e-mail: bpinto@sfu.ca
3
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.04.009

1686
N. S. Kumar, B. M. Pinto / Carbohydrate Research 341 (2006) 1685–1691
Recently, we described the synthesis of the sulfonium-
O
OH
OBn
3 steps
Ref. 29
ion analogue of 3-epi-swainsonine (4),20 the synthesis,
free and enzyme-bound conformations, and glycosidase
inhibitory activity (albeit weak) of a sulfonium-ion ana-
logue (5) of castanospermine (3),21,22 and the synthesis
of sulfonium ions (6, 7) of the pyrrolizidine alkaloid,
australine.23 Siriwardena and co-workers have also re-
ported the synthesis of bicyclic sulfonium salts to serve
as glycosidase inhibitors.24–26 Most recently they have
reported the synthesis of compound 8, which is not only
a potent inhibitor of several mannosidases, but shows
greater selectivity than swainsonine (1).26 The syntheses
of di-O-methylated sulfonium derivatives (9)27 of
swainsonine (1), as well as 5-O-methylthioswainsonine28
have also been reported in the literature. We now report
the first synthesis of the sulfonium-ion analogue (10) of
swainsonine (1) as a potential glycosidase inhibitor.
D-Lyxose
BnO
BnO
12
7 steps
Ref. 30
S
S
1) 1% H2SO4/Ac2O
BnO
HO
2) NaOMe/MeOH
65% (2 steps)
OBn
BnO
OBn
BnO
11
13
Scheme 2.
ate which was subsequently removed by methanolysis to
give compound 11.
ClO4
Cl
OTf
OH
OTf
HO
HO
S
S
S
S
OH
OH
OH
OH
HO
HO
OH
OH
OH
5
4
6
7
Cl
I
Cl
S
S
S
OH
OH
O
S
OH
O
OH
OH
10
OH
9
8
Retrosynthetic analysis indicates that the bicyclic sul-
fonium salt A could be synthesized by an intramolecular
displacement of a suitable side-chain leaving group by a
cyclic thioether (Scheme 1). The key intermediate B
could, in turn, be synthesized from C.
Compound 11, corresponding to C, was synthesized
from commercially available D-lyxose, as shown in
Scheme 2. 2,3,5-Tri-O-benzyl-D-lyxofuranoside (12) was
prepared in three steps starting from D-lyxose, as
described by Postema et al.,29 which was, in turn, trans-
formed using a multi-step procedure into 1,4-anhydro-
2,3,5-tri-O-benzyl-4-thio-D-lyxitol (13).30 The primary
benzyl ether was selectively removed using 1% sulfuric
acid in acetic anhydride to give the corresponding acet-
Swern oxidation of compound 11 using trifluoroacetic
anhydride furnished aldehyde 14, which was subse-
quently treated with a freshly prepared Grignard
reagent from the reaction of 2-(2-bromoethyl)-1,3-di-
oxane and magnesium to give inseparable diastereomers
15a and 15b as a 2:1 mixture, along with a trace amount
of diastereomer 15c (Scheme 3). Compound 15c was the
result of epimerization at C-4, facilitated by the alde-
hyde group in 14. After cyclization, it was found that
the major compound 15a had the required R configura-
tion at C-5. Most of the minor isomer 15b was recrystal-
lized out from the mixture using ethyl acetate and
hexane.
The secondary hydroxyl group at C-5 in each of com-
pounds 15a and 15c was protected as a benzyl ether to
give compounds 16a and 16c, respectively (Scheme 4),
which were separated by flash chromatography. The
1,3-dioxane protecting group in compound 16a was
hydrolyzed to give the corresponding aldehyde, which
was subsequently reduced using sodium borohydride
to furnish compound 17. Treatment of 17 with methane-
sulfonyl chloride furnished the corresponding sulfo-
nate ester, which was subsequently treated with LiBr
to give bromide 18. Compound 18 was treated with sil-
L
L
8
8 S
S
1
1
3
1
3
S
7
6
7
6
2
2
2
OP
OP
OP
4
4
4
3
5
5
5
OP
OP
OP
OP
OP
OH
A
B
C
P = protecting group
L = leaving group
Scheme 1.

N. S. Kumar, B. M. Pinto / Carbohydrate Research 341 (2006) 1685–1691
R1
1687
R2
S
O
O
O
MgBr
OBn
BnO
O
S
15a: R1 = OH, R2 = H (major)
15b: R1 = H, R2 = OH (minor)
O
DMSO / TFAA
H
11
DIPEA / CH2Cl2
THF
68% (2 steps)
dr. 2:1(15a:15b)
OBn
BnO
14
OH
S
O
O
OBn
BnO
15c (trace)
Scheme 3.
OBn
S
OBn
S
O
O
NaH / DMF
BnBr
15a / 15c
O
O
BnO
16c (7%)
BnO
OBn
OBn
16a (88%)
i) AcOH / H2SO4/
H2O / 1,4-dioxane
(78:0.5:20:1.5)
ii) NaBH4 / EtOH
71% (2 steps)
OBn
S
OBn
S
i) MsCl / Pyr.
ii) LiBr / THF / Reflux
90% 2 steps
OH
Br
BnO
BnO
OBn
OBn
AgOTf /
CH3CN
88%
18
17
i) BCl3 / CH2Cl2 /
-78oC
Cl
S
OTf
S
OH
OBn
ii) Ion Exchange
(Amberlyst A-26)
OH
OBn
OH
OBn
70%
19
10
Scheme 4.
ver triflate in acetonitrile to promote cyclization, giving
the desired sulfonium salt 19 as a stable, colorless oil.
The ring junction of this bicyclic compound 19 was cis
as expected.20,28,31 The configuration at C-5 of com-
pound 19 was assigned by means of a 1D-NOESY
experiment, which showed a correlation between H-3
and H-5; the stereochemistry of compound 15a was thus
assigned by inference. The benzyl protecting groups
were removed with boron trichloride at ꢀ78 ꢁC and
the product was subsequently treated with Amberlyst
A-26 (chloride form) to completely exchange the triflate
counterion with chloride ion to give compound 10,
because our previous work had shown that some of
the triflate counterion was exchanged to chloride ion
during the course of deprotection.20
1. Experimental
1.1. General methods
Optical rotations were measured at 23 ꢁC and reported in
1
deg dmꢀ1 gꢀ1 cm3. H and 13C NMR spectra were re-
corded with frequencies of 500 and 125 MHz, respec-
tively. All assignments were confirmed with the aid of
two-dimensional 1H,1H (gCOSY) and 1H,13C (gHMQC)
experiments using standard Varian pulse programs.
Processing of the spectra was performed with MestRec
software. 1D-NOESY experiments were recorded at
295 K on a 500 MHz spectrometer. For each 1D-NOESY
spectrum, 512 scans were acquired with a Q3 Gaussian
Cascade pulse. A mixing time of 500 ms was used in the

1688
N. S. Kumar, B. M. Pinto / Carbohydrate Research 341 (2006) 1685–1691
1D-NOESY experiments. Matrix-assisted laser desorp-
tion ionization time-of-flight (MALDI-TOF) mass
spectra were obtained using 2,5-dihydroxybenzoic acid
as a matrix. Analytical thin-layer chromatography
(TLC) was performed on aluminum plates precoated 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 and 1.5% molybdic acid
in 10% aqueous H2SO4, and heated. Column chromato-
graphy was performed with silica gel 60 (230–400 mesh).
added a solution of trifluoroacetic anhydride (0.87 mL,
11.6 mmol) in CH2Cl2 (5 mL) dropwise, and the mixture
was stirred at ꢀ78 ꢁC for 30 min. A solution of compound
11 (1.01 g, 3.06 mmol) in CH2Cl2 (15 mL) was added
dropwise while maintaining the temperature below
ꢀ78 ꢁC and the stirring was continued for 1.5 h. A solu-
tion of diisopropylethylamine (2.3 mL, 12.6 mmol) in
CH2Cl2 (15 mL) was added dropwise and the stirring
was continued at ꢀ78 ꢁC for an additional 2 h. The reac-
tion was quenched by the addition of aqueous HCl
(0.5 M, 5 mL) and the mixture was partitioned between
Et2O (200 mL) and H2O (50 mL). The Et2O layer was
washed withH2O (50 mL) and brine (50 mL). The organic
phase was dried over anhydrous Na2SO4, filtered, and
concentrated. The crude product was purified by flash
chromatography (6:1, hexanes/EtOAc) to give the alde-
hyde 14. Compound 14 was diluted with THF (15 mL)
and cooled to 0 ꢁC under N2. A Grignard reagent, freshly
prepared from 2-(2-bromoethyl)-1,3-dioxane (0.75 mL,
5.49 mmol) and Mg (272 mg, 10.90 mmol) in THF
(15 mL), was added dropwise. The reaction mixture was
stirred at ambient temperature for 14 h and then the reac-
tion was quenched by the addition of 0.5 M HCl (5 mL),
and concentrated. The residue was diluted with Et2O
(200 mL) and washed with H2O (2 · 50 mL) and brine
(50 mL). The organic phase was dried over anhydrous
Na2SO4, filtered, and concentrated. The crude product
was purified by flash chromatography (3:1, hexanes/
EtOAc) to give a 2:1 mixture of compounds 15a and
15b, respectively, along with a trace amount of compound
15c as a white solid (0.92 g, 68%).
1.2. 1,4-Anhydro-2,3-di-O-benzyl-4-thio-D-lyxitol (11)
A solution of 1,4-anhydro-2,3,5-tri-O-benzyl-4-thio-D-
lyxitol (13) (5.00 g, 11.9 mmol) in 1.0% H2SO4/Ac2O
(50.0 mL) was stirred at ambient temperature for 14 h
and then partitioned between EtOAc (200 mL) and
H2O (100 mL). The organic layer was washed with
H2O (100 mL), satd aq NaHCO3 (2 · 100 mL), followed
by brine (100 mL). The organic layer was dried over
anhydrous Na2SO4, filtered, and concentrated under re-
duced pressure. The crude product was dissolved in
CH3OH (200 mL) and 1 M NaOCH3/CH3OH solution
was added until the solution was basic. The reaction
mixture was stirred at room temperature for 1 h and
then neutralized with HOAc. The mixture was concen-
trated and then partitioned between EtOAc (300 mL)
and H2O (100 mL). The organic phase was washed with
H2O (100 mL) and brine (100 mL). The organic layer
was dried over anhydrous Na2SO4, filtered, and concen-
trated. The crude product was purified by flash chromato-
graphy (3:1, hexanes/EtOAc) to give compound 11 as
a colorless oil (2.55 g, 65%): [a]D ꢀ12.9 (c 1.1, CH2Cl2);
1H NMR (CDCl3): d 7.38–7.28 (m, 10H, Ar), 4.79 and
4.64 (2d, each 1H, Ja,b = 11.9 Hz, CH2Ph), 4.69 and
4.61 (2d, each 1H, Ja,b = 12.1 Hz, CH2Ph), 4.17–4.15
(m, 2H, H-2, H-3), 3.92 (dd, 1H, J4,5a = 7.1 Hz,
J5a,5b = 11.5 Hz, H-5a), 3.77 (dd, 1H, J4,5b = 4.9 Hz,
H-5b), 3.55 (ddd, 1H, J3,4 = 5.4 Hz, H-4), 3.04 (dd,
1H, J1a,2 = 4.2 Hz, J1a,1b = 10.5 Hz, H-1a), 2.92 (dd,
1H, J1b,2 = 4.6 Hz, H-1b); 13C NMR (CDCl3): d 138.1,
138.0 (2Cipso), 128.8–127.8 (10CAr), 81.7 (C-2), 81.2
(C-3), 73.4, 72.4 (2CH2Ph), 63.1 (C-5), 47.5 (C-4), 31.2
(C-1); MALDI-TOFMS: m/z 331.21 [M+H]+, 352.84
[M+Na]+, 368.97 [M+K]+. Anal. Calcd for C19H22O3S:
C, 69.06; H, 6.71. Found: C, 69.20; H, 6.85.
Data for the major diastereomer (15a): 1H NMR
(CDCl3): d 7.40–7.31 (m, 10H, Ar), 4.98 and 4.74 (2d, each
1H, Ja,b = 11.6 Hz, CH2Ph), 4.63 and 4.58 (2d, each 1H,
0
0
Ja,b = 12.1 Hz, CH2Ph), 4.54 (dd, 1H, J2 ,7a = J2 ,7b
=
4.8 Hz, H-20), 4.27 (dd, 1H, J2,3 = 3.0 Hz, J3,4 = 3.9 Hz,
H-3), 4.15– 4.08 (m, 2H, H-40eq, H-60eq), 4.02 (ddd, 1H,
J1b,2 = 6.2 Hz, J1a,2 = 9.0 Hz, H-2), 3.91 (ddd, 1H,
J5,6b = 2.0 Hz, J4,5 = J5,6a = 9.2 Hz, H-5), 3.72 (ddd,
0
0
0
0
0
0
1H, J4 ax,5 eq = 2.4 Hz, J4 ax,4 eq = J4 ax5 ax = 12.1 Hz,
H-40ax), 3.72 (ddd, 1H, J5 eq,6 ax = 2.4 Hz, J6 ax,6 eq
J5 ax,6 ax = 12.1 Hz, H-60ax), 3.19 (dd, 1H, H-4),
3.08 (dd, 1H, J1a,1b = 9.3 Hz, H-1a), 2.90 (dd, 1H,
=
0
0
0
0
0
0
0
0
0
0
H-1b), 2.07 (ddddd, 1H, J4 eq,5 ax = J5 ax,6 eq = 4.9 Hz,
J5 ax,5 eq = 12.7 Hz, H-50ax), 1.79–1.64 (m, 3H, H-6a, H-
7a, H-7b), 1.43–1.29 (m, 2H, H-50eq, H-6b); 13C NMR
(CDCl3): d 138.7, 138.2 (2Cipso), 128.7–127.7 (10CAr),
102.4 (C-20), 83.5 (C-2), 79.6 (C-3), 73.9, 72.4 (2CH2Ph),
71.5 (C-5), 67.13 (C-40), 67.11 (C-60), 51.6 (C-4), 31.4
(C-7), 31.0 (C-1), 29.7 (C-6), 25.9 (C-50).
0
0
1.3. 1,4-Anhydro-6,7-dideoxy-2,3-di-O-benzyl-4-thio-7-
(10,30-dioxan-20-yl)-D-manno-heptitol (15a); 1,4-anhydro-
6,7-dideoxy-2,3-di-O-benzyl-4-thio-7-(10,30-dioxan-20-yl)-
L-gluco-heptitol (15b) and 1,4-anhydro-6,7-dideoxy-2,3-
di-O-benzyl-4-thio-7-(10,30-dioxan-20-yl)-(D-talo/L-allo)-
heptitol (15c)
For the mixture of 15a,b and 15c: MALDI-TOF MS:
m/z 445.30 [M+H]+, 467.32 [M+Na]+, 483.30 [M+K]+.
Anal. Calcd for C25H32O5S: C, 67.54; H, 7.27. Found:
C, 67.20; H, 7.45.
To a stirred solution of DMSO (1.5 mL, 21.5 mmol) in
CH2Cl2 (15 mL) at ꢀ78 ꢁC under N2 atmosphere was
The minor isomer (15b) was obtained by crystallization
from hexanes/EtOAc as a white solid: mp 116–118 ꢁC;

N. S. Kumar, B. M. Pinto / Carbohydrate Research 341 (2006) 1685–1691
1689
[a]D +5.2 (c 0.6, CH2Cl2); 1H NMR (CDCl3): d 7.36–7.29
(m, 10H, Ar), 4.86 and 4.63 (2d, each 1H, Ja,b = 11.7 Hz,
CH2Ph), 4.70 and 4.59 (2d, each 1H, Ja,b = 12.1 Hz,
12.6 Hz, H-50ax), 1.93 (dddd, 1H, J6a,7a = 4.7 Hz,
J6a,7b = 11.2 Hz, J6a,6b = 14.8 Hz, H-6a), 1.78–1.63 (m,
2H, H-7a, H-7b), 1.51 (dddd, 1H, J6b,7b = 5.0 Hz,
J6b,7a = 10.7 Hz, H-6b), 1.31 (m, 1H, H-50eq); 13C
NMR (CDCl3): d 139.3, 138.9, 138.2 (3Cipso), 128.7–
127.5 (15CAr), 102.5 (C-20), 84.7 (C-2), 78.6 (C-3), 77.6
(C-5), 73.8, 72.4, 71.2 (3CH2Ph), 67.1 (2C, C-40, C-60),
49.4 (C-4), 30.7 (C-1), 29.4 (C-7), 26.0 (C-50), 25.1
(C-6); MALDI-TOFMS: m/z 535.08 [M+H]+, 556.96
[M+Na]+, 573.32 [M+K]+. Anal. Calcd for C32H38O5S:
C, 71.88; H, 7.16. Found: C, 71.59; H, 7.35.
CH2Ph), 4.50 (dd, 1H, J2 ,7a = J2 ,7b = 5.0 Hz, H-20),
4.16–4.03 (m, 4H, H-2, H-3, H-40eq, H-60eq), 4.01 (ddd,
1H, J4,5 = J5,6a = 4.2 Hz, J5,6b = 8.4 Hz, H-5), 3.74 (ddd,
0
0
0
0
0
0
0
0
1H, J4 ax,5 eq = 2.4 Hz, J4 ax,4 eq = J4 ax,5 ax = 12.0 Hz,
H-40ax), 3.71 (ddd, 1H, J5 eq,6 ax = 2.5 Hz, J6 ax,6 eq
=
0
0
0
0
J5 ax,6 ax = 11.8 Hz, H-60ax), 3.42 (dd, 1H, J3,4 = 4.1 Hz,
H-4), 3.05 (dd, 1H, J1a,2 = 7.0 Hz, J1a,1b = 10.5 Hz,
H-1a), 2.94 (dd, 1H, J1b,2 = 5.5 Hz, H-1b), 2.04 (ddddd,
0
0
0
0
0
0
0
0
1H, J4 eq,5 ax = J5 ax,6 eq = 5.0 Hz, J5 ax,5 eq = 12.6 Hz,
H-50ax), 1.77 (dddd, 1H, J6b,7a = 5.2 Hz, J6a,7a = 9.3 Hz,
J7a,7b = 14.0 Hz, H-7a), 1.65 (dddd, 1H, J6a,7b = 6.7 Hz,
J6b,7b = 8.6 Hz, H-7b), 1.53 (dddd, 1H, J6a,6b = 14.1 Hz,
Data for the minor diastereomer (16c): [a]D ꢀ17.1 (c
1
0.4, CH2Cl2); H NMR (CDCl3): d 7.37–7.22 (m, 15H,
Ar), 4.62 and 4.58 (2d, each 1H, Ja,b = 12.4 Hz, CH2Ph),
4.55 and 4.46 (2d, each 1H, Ja,b = 11.4 Hz, CH2Ph), 4.46
and 4.42 (2d, each 1H, Ja,b = 11.9 Hz, CH2Ph), 4.43 (dd,
0
0
H-6b) 1.46 (m, 1H, H-6a), 1.31 (ddddd, 1H, J4 eq,5 eq
=
J5 eq,6 eq = 1.2 Hz, J5 ax,5 eq = 13.4 Hz, H-50eq); 13C
NMR (CDCl3): d 138.1, 137.7 (2Cipso), 128.8–127.9
(10CAr), 102.3 (C-20), 82.1 (C-2), 81.6 (C-3), 73.5, 72.5
(2CH2Ph), 69.1 (C-5), 67.10 (C-40), 67.08 (C-60), 52.4
(C-4), 31.7 (C-7), 30.9 (C-1), 30.4 (C-6), 26.0 (C-50); MAL-
DI-TOFMS: m/z 445.26 [M+H]+, 467.30 [M+Na]+,
483.27 [M+K]+. Anal. Calcd for C25H32O5S: C, 67.54;
H, 7.27. Found: C, 67.80; H, 7.49.
1H, J7a,2, = J7b,2 = 3.6 Hz, H-20), 4.13–4.04 (m, 2H, H-
0
0
0
0
0
40eq, H-60eq), 4.00 (dd, 1H, J2,3 = J3,4 = 3.3 Hz, H-3),
3.96 (ddd, 1H, J1b,2 = 5.7 Hz, J1a,2 = 8.7 Hz, H-2),
0
0
0
0
0
0
3.69 (ddd, 1H, J4 ax,5 eq = 2.5 Hz, J4 ax,4 eq = J4 ax,5 ax
=
12.1 Hz, H-40ax), 3.68 (ddd, 1H, J5 eq,6 ax = 2.5 Hz,
0
0
J6 ax,6 eq = J5 ax,6 ax = 12.0 Hz, H-60ax), 3.60 (dd, 1H,
J4,5 = 7.0 Hz H-4), 3.35 (m, 1H, H-5), 3.03 (dd, 1H,
J1a,1b = 10.2 Hz, H-1a), 2.85 (dd, 1H, H-1b), 2.04
0
0
0
0
0
0
0
0
0
0
(ddddd, 1H, J4 eq,5 ax = J5 ax,6 eq = 4.9 Hz, J5 ax,5 eq
=
1.4. 1,4-Anhydro-6,7-dideoxy-2,3,5-tri-O-benzyl-4-thio-7-
(10,30-dioxan-20-yl)-D-manno-heptitol (16a) and 1,4-
anhydro-6,7-dideoxy-2,3,5-tri-O-benzyl-4-thio-7-(10,30-
dioxan-20-yl)-(D-talo/L-allo)-heptitol (16c)
12.6 Hz, H-50ax), 1.77–1.59 (m, 4H, H-6a, H-6b, H-7a,
H-7b), 1.31 (m, 1H, H-50eq); 13C NMR (CDCl3): d
138.32, 138.27, 138.11 (3Cipso), 128.8–127.6 (15CAr),
102.1 (C-20), 80.7 (C-2), 79.8 (C-3), 79.7 (C-5), 71.99,
71.96, 71.36 (3CH2Ph), 66.9 (2C, C-40, C-60), 51.3
(C-4), 30.9 (C-1), 30.4 (C-7), 25.8 (C-50), 25.5 (C-6);
MALDI-TOFMS: m/z 535.15 [M+H]+, 557.12
[M+Na]+, 572.95 [M+K]+. Anal. Calcd for
C32H38O5S: C, 71.88; H, 7.16. Found: C, 72.05; H, 7.27.
A mixture of compounds 15a/15c (145 mg, 0.33 mmol)
and 60% NaH (20 mg, 1.5 equiv) in DMF (8 mL) was
stirred in an ice bath for 15 min. Benzyl bromide
(66 lL, 1.3 equiv) was added and the solution was stir-
red at room temperature for 2 h. The reaction was
quenched by the addition of ice H2O (1 mL) and the
mixture was diluted with Et2O (50 mL). The organic
layer was washed with H2O (20 mL) and brine
(20 mL). The organic phase was dried over anhydrous
Na2SO4, filtered, and concentrated. The crude product
was purified by flash chromatography (5:1, hexanes/
EtOAc) to give 16a (153 mg, 88%) and 16c (12 mg, 7%).
Data for the major diastereomer (16a): [a]D ꢀ5.3 (c
1.5. 1,4-Anhydro-6,7-dideoxy-2,3,5-tri-O-benzyl-4-thio-
D-manno-octitol (17)
A solution of 16a (135 mg, 0.25 mmol) in 5 mL AcOH–
H2O–H2SO4–1,4-dioxane (78:20:0.5:1.5) was stirred at
room temperature for 20 h. The mixture was diluted
with Et2O (50 mL) and washed with H2O (20 mL), satd
aq NaHCO3 (2 · 20 mL), and brine (20 mL). The organ-
ic phase was dried over anhydrous Na2SO4, filtered, and
concentrated. The residue was diluted with 95% EtOH
(30 mL) and the solution was cooled to 0 ꢁC. NaBH4
(10 mg, 1 equiv) was added and the mixture was stirred
in an ice bath for 1 h. The reaction was quenched by the
addition of AcOH (0.2 mL) and the mixture was concen-
trated. The residue was diluted with Et2O (50 mL) and
washed with H2O (20 mL) and brine (20 mL). The
organic phase was dried over anhydrous Na2SO4, fil-
tered, and concentrated. The crude product was purified
by flash chromatography (3:1, hexanes/EtOAc) to give
compound 17 as a white solid (86 mg, 71%): mp 98–
1
1.1, CH2Cl2); H NMR (CDCl3): d 7.36–7.24 (m, 15H,
Ar), 5.07 and 4.59 (2d, each 1H, Ja,b = 11.4 Hz, CH2Ph),
4.56 (s, 2H, CH2Ph), 4.56 and 4.32 (2d, each 1H,
0
0
Ja,b = 11.0 Hz, CH2Ph), 4.50 (dd, 1H, J7a,2 = J7b,2
=
5.1 Hz, H-20), 4.34 (dd, 1H, J2,3 = J3,4 = 2.8 Hz, H-3),
4.09–4.05 (m, 2H, H-40eq, H-60eq), 4.02 (ddd, 1H,
J1b,2 = 6.5 Hz, J1a,2 = 10.5 Hz, H-2), 3.98 (ddd, 1H,
J5,6a = J5,6b = 4.3 Hz, J4,5 = 9.9 Hz H-5), 3.72 (ddd,
0
0
0
0
0
0
1H, J4 ax,5 eq = 2.4 Hz, J4 ax,4 eq = J4 ax,5 ax = 12.0 Hz,
H-40ax), 3.71 (ddd, 1H, J5 eq,6 ax = 2.4 Hz, J6 ax,6 eq
J5 ax,6 ax = 11.9 Hz, H-60ax), 3.44 (dd, 1H, H-4), 3.13
(dd, 1H, J1a,1b = 9.6 Hz, H-1a), 2.95 (dd, 1H, H-1b),
=
0
0
0
0
0
0
1
0
0
0
0
0
0
2.06 (ddddd, 1H, J4 eq,5 ax = J5 ax,6 eq = 5.0 Hz, J5 ax,5 eq
=
100 ꢁC; [a]D ꢀ6.0 (c 0.5, CH2Cl2); H NMR (CDCl3):

1690
N. S. Kumar, B. M. Pinto / Carbohydrate Research 341 (2006) 1685–1691
d 7.36–7.21 (m, 15H, Ar), 5.12 and 4.58 (2d, each 1H,
Ja,b = 11.3 Hz, CH2Ph), 4.59 and 4.56 (2d, each 1H,
Ja,b = 12.6 Hz, CH2Ph), 4.53 and 4.37 (2d, each
1.7. 2(S),3(R),4(R),5(R)-2,3,5-Tribenzyloxy-cis-1-thionia-
bicyclo[4.3.0]-nonane triflate (19)
1H, Ja,b = 11.1 Hz, CH2Ph), 4.34 (dd, 1H, J2,3 = J3,4
2.9 Hz, H-3), 4.05 (ddd, 1H, J1b,2 = 6.5 Hz,
J1a,2 = 10.4 Hz, H-2), 4.00 (ddd, 1H, J4,5 = J5,6b
3.9 Hz, J5,6a = 9.9 Hz, H-5), 3.62 (ddd, 1H, J7a,8a
=
A solution of compound 18 (55 mg, 0.10 mmol) in
CH3CN (3 mL) was treated with AgOTf (26 mg,
1 equiv) for 14 h at ambient temperature. Another
equivalent of AgOTf (26 mg) was added and the reac-
tion mixture was stirred for an additional 10 h. The sol-
vent was removed and the crude product was purified by
flash chromatography (20:1, CH2Cl2–CH3OH) to give
compound 19 as a colorless syrup (55 mg, 88%):
=
=
J7b,8a = 5.7 Hz, J8a,8b = 10.9 Hz, H-8a), 3.56 (ddd, 1H,
J7b,8b = 5.7 Hz, J7a,8a = 7.1 Hz, H-8b), 3.50 (br s, 1H,
H-4), 3.13 (dd, 1H, J1a,1b = 10.4 Hz, H-1a), 2.95 (dd,
1H, H-1b), 1.85–1.50 (m, 4H, H-6a, H-6b, H-7a,
H-7b); 13C NMR (CDCl3): d 139.2, 138.5, 138.1 (3Cipso),
128.7–127.6 (15CAr), 84.9 (C-2), 78.6 (C-3), 78.0 (C-5),
73.8, 72.5, 71.8 (3CH2Ph), 63.3 (C-8), 49.2 (C-4), 30.7
(C-1), 27.8 (C-6), 27.3 (C-7); MALDI-TOF MS: m/z
478.97 [M+H]+, 501.07 [M+Na]+, 516.91 [M+K]+.
Anal. Calcd for C29H34O4S: C, 72.77; H, 7.16. Found:
C, 73.01; H, 7.27.
1
[a]D ꢀ38.2 (c 0.5, CH2Cl2); H NMR (CDCl3): d 7.37–
7.20 (m, 15H, Ar), 4.98 and 4.59 (2d, each 1H,
Ja,b = 11.0 Hz, CH2Ph), 4.85 (ddd, 1H, J2,3 = 2.8 Hz,
J1b,2 = 7.2 Hz, J1a,2 = 10.0 Hz, H-2), 4.69 and 4.65 (2d,
each 1H, Ja,b = 11.5 Hz, CH2Ph), 4.66 and 4.46 (2d,
each 1H, Ja,b = 11.9 Hz, CH2Ph), 4.54 (dd, 1H,
J3,4 = 3.0 Hz, H-3), 4.39 (br s, 1H, H-4), 4.17 (dd, 1H,
J1a,1b = 12.2 Hz, H-1b), 3.93 (br s, 1H, H-5), 3.65 (m,
1.6. 1,4-Anhydro-8-bromo-6,7,8-trideoxy-2,3,5-tri-O-
benzyl-4-thio-D-manno-octitol (18)
1H, H-8eq), 3.34 (ddd, 1H, J7eq,8ax = 2.8 Hz, J7ax,8ax =
10.9 Hz, J8ax,8eq = 13.3 Hz, H-8ax), 3.19 (dd, 1H,
H-1a), 2.05–1.76 (m, 4H, H-6ax, H-6eq, H-7ax, H-7eq);
13C NMR (CDCl3): d 137.1, 137.1, 136.8 (3Cipso),
129.0–128.2 (15CAr), 120.9 (q, 1C, JC,F = 318.5 Hz,
OTf), 82.8 (C-2), 79.4 (C-3), 75.1, 74.1, 71.1 (3CH2Ph),
69.7 (C-5), 52.8 (C-4), 43.5 (C-1), 40.4 (C-8), 25.8
(C-6), 16.2 (C-7); MALDI-TOFMS: m/z 461.25
[MꢀOTf]+. Anal. Calcd for C30H33F3O6S2: C, 59.00;
H, 5.45. Found: C, 59.24; H, 5.52.
To a stirred solution of 17 (60 mg, 0.13 mmol) in pyridine
(4 mL) at 0 ꢁC under N2 was added methanesulfonyl chlo-
ride (12 lL, 1.2 equiv). The reaction mixture was stirred
at 0 ꢁC for 2 h and then quenched by the addition of ice
(0.5 mL). The mixture was concentrated under high vac-
uum and then diluted with Et2O (50 mL). The organic
phase was washed with H2O (20 mL), 1 M HCl (20 mL),
satd aq NaHCO3 (20 mL), and brine (20 mL). The organ-
ic layer was dried over anhydrous Na2SO4, filtered, and
concentrated. The residue in THF (4 mL) together with
LiBr (55 mg, 5 equiv) was heated at reflux under N2 for
2 h and then concentrated. The residue was diluted with
Et2O (50 mL) and washed with H2O (2 · 20 mL) and
brine (20 mL). The organic phase was dried over anhy-
drous Na2SO4, filtered, and concentrated. The crude
product was purified by flash chromatography (5:1, hex-
anes/EtOAc) to give compound 18 as a colorless oil
(61 mg, 90%): [a]D ꢀ6.2 (c 0.8, CH2Cl2); 1H NMR
(CDCl3): d 7.38–7.23 (m, 15H, Ar), 5.11 and 4.61 (2d, each
1H, Ja,b = 11.3 Hz, CH2Ph), 4.61 and 4.58 (2d, each 1H,
Ja,b = 12.2 Hz, CH2Ph), 4.51 and 4.37 (2d, each 1H,
1.8. 2(S),3(R),4(R),5(R)-2,3,5-Trihydroxy-cis-1-thionia-
bicyclo[4.3.0]-nonane chloride (10)
BCl3 gas was bubbled vigorously through a solution of
19 (50 mg, 82 lmol) in CH2Cl2 (5 mL) at ꢀ78 ꢁC under
N2 for 10 min. The mixture was stirred at ꢀ78 ꢁC for 2 h
and a stream of dry air was blown vigorously over the
solution to remove excess BCl3. The reaction was
quenched by the addition of CH3OH (2 mL) and the sol-
vent was removed. The residue was co-evaporated with
CH3OH (2 · 5 mL) and then washed with CH2Cl2
(2 · 2 mL) to give a white solid. The solid was dissolved
in CH3OH (5 mL) and a freshly washed ion exchange
resin (Amberlyst A-26 (chloride form), 60 mg) was
added. The mixture was stirred at room temperature
for 30 min and filtered. The filtrate was concentrated
and recrystallized from CH3OH–CH2Cl2 to give com-
pound 10 as white crystals (13 mg, 70%): mp > 219 ꢁC
(decomp.); [a]D ꢀ6.8 (c 0.3, CH3OH); 1H NMR
(CD3OD): d 4.52–4.42 (m, 3H, H-2, H-3, H-5), 3.80
(dd, 1H, J1b,2 = 7.7 Hz, J1a,1b = 12.2 Hz, H-1b), 3.79
(br s, 1H, H-4), 3.68 (m, 1H, H-8eq), 3.58, (ddd, 1H,
J7eq,8ax = 3.1 Hz, J7ax,8ax = 11.1 Hz, J8ax,8eq = 14.0 Hz,
H-8ax), 3.15 (dd, 1H, J1a,2 = 9.9 Hz, H-1a), 2.36 (dddd,
Ja,b = 11.4 Hz, CH2Ph), 4.35 (dd, 1H, J2,3 = J3,4
3.0 Hz, H-3), 4.06 (ddd, 1H, J1b,2 = 6.6 Hz, J1a,2
=
=
10.5 Hz, H-2), 3.98 (ddd, 1H, J5,6b = 3.3 Hz, J5,6b = 4.2
Hz, J4,5 = 10.0 Hz, H-5), 3.43 (dd, 1H, H-4), 3.41–3.36
(m, 2H, H-8a, H-8b), 3.15 (dd, 1H, J1a,1b = 9.4 Hz,
H-1a), 2.97 (dd, 1H, H-1b), 2.01–1.89 (m, 3H, H-6a,
H-7a, H-7b), 1.56 (m, 1H, H-6b); 13C NMR (CDCl3): d
139.2, 138.6, 138.1 (3Cipso), 128.7–127.6 (15CAr), 84.9
(C-2), 78.6 (C-3), 77.5 (C-5), 73.8, 72.5, 71.6 (3CH2Ph),
49.4 (C-4), 34.3 (C-8), 30.7 (C-1), 29.6 (C-6), 27.3 (C-7);
MALDI-TOFMS: m/z 461.29 [MꢀBr]+. Anal. Calcd
for C29H33BrO3S: C, 64.32; H, 6.14. Found: C, 64.08;
H, 6.32.
1H, J5,6ax = 2.6 Hz, J6ax,7eq = 3.7 Hz, J6ax,6eq = J6ax,7ax
14.0 Hz, H-6ax), 2.14 (ddddd, 1H, J7ax,8eq = J6eq,7ax
=
=

N. S. Kumar, B. M. Pinto / Carbohydrate Research 341 (2006) 1685–1691
1691
11. Asano, N.; Nash, R. J.; Molyneux, R. J.; Fleet, G. W. J.
Tetrahedron: Asymmetry 2000, 11, 1645–1680.
12. Watson, A. A.; Fleet, G. W. J.; Asano, N.; Molyneux, R.
J.; Nash, R. J. Phytochemistry 2001, 56, 265–295.
13. Lillelund, V. H.; Jensen, H. H.; Liang, X.; Bols, M. Chem.
Rev. 2002, 102, 515–553.
14. Elbein, A. D. Annu. Rev. Biochem. 1987, 56, 497–534.
15. Elbein, A. D. FASEB J. 1991, 5, 3055–3063.
16. Winchester, B.; Fleet, G. W. J. Glycobiology 1992, 2, 199–
210.
3.2 Hz, J7ax,7eq = 15.1 Hz, H-7ax), 1.97 (ddddd, 1H,
J7eq,8eq = J6eq,7eq = 3.6 Hz, H-7eq), 1.86 (dddd, 1H,
J5,6eq = 3.4 Hz, H-6eq); 13C NMR (CD3OD): d 74.5
(C-3), 74.3 (C-2), 63.3 (C-5), 57.5 (C-4), 43.8 (C-1),
40.6 (C-8), 27.5 (C-6), 15.3 (C-7); MALDI-TOF MS:
m/z 191.27 [MꢀCl]+. Anal. Calcd for C8H15ClO3S: C,
42.38; H, 6.67. Found: C, 42.29; H, 6.73.
17. Stutz, A. E. Iminosugars as Glycosidase Inhibitors: Noji-
rimycin and Beyond; Wiley-VCH: Weinheim, New York,
1999.
Acknowledgements
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20. Kumar, N. S.; Pinto, B. M. J. Org. Chem. 2006, 71, 1262–
1264.
We thank Dr. B. D. Johnston and Dr. X. Wen, for help-
ful discussions. We also thank the Natural Sciences and
Engineering Research Council of Canada, for financial
support and the Michael Smith Foundation for Health
Research, for a trainee fellowship (to N.S.K.).
21. Svansson, L.; Johnston, B. D.; Gu, J.-H.; Patrick, B.;
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