Synthesis of new analogues of salacinol containing a pendant hydroxymethyl group as potential glycosidase inhibitors

Article abstract of DOI:10.1016/j.carres.2006.06.022

The synthesis of new analogues of the naturally occurring glycosidase inhibitor, salacinol, and its ammonium analogue, ghavamiol is described. These analogues contain an additional hydroxymethyl group at C-1, which was intended to form additional polar co

Full text of DOI:10.1016/j.carres.2006.06.022

Carbohydrate Research 341 (2006) 2305–2311
Synthesis of new analogues of salacinol containing a
pendant hydroxymethyl group as potential glycosidase inhibitors
Ravindranath Nasi and B. Mario Pinto*
Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
Received 11 May 2006; received in revised form 20 June 2006; accepted 28 June 2006
Available online 18 July 2006
Abstract—The synthesis of new analogues of the naturally occurring glycosidase inhibitor, salacinol, and its ammonium analogue,
ghavamiol is described. These analogues contain an additional hydroxymethyl group at C-1, which was intended to form additional
polar contacts within the active site of glycosidase enzymes. The target zwitterionic compounds were synthesized by means of nucleo-
philic attack at the least hindered carbon atom of 2,4-O-benzylidene-L (or D)-erythritol 1,3-cyclic sulfate by 2,5-anhydro-1,3:4,6-di-
O-benzylidene-2,5-dideoxy-5-thio (or 1,5-imino)-L-iditol.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: Glycosidase inhibitors; Analogues of salacinol and ghavamiol; Ammonium salt; Sulfonium salt; Cyclic sulfate
1. Introduction
The glycosidase-mediated reaction can occur with one
of the two possible stereochemical outcomes—inversion
or retention of configuration at the anomeric center. The
currently accepted mechanisms of glycosidic bond cleav-
age involve general acid catalysis with protonation of
the exocyclic oxygen atom at the anomeric center by a
carboxylic acid group in the active site of the enzyme
that results in the formation of an oxacarbenium ion
transition state,4 which then reacts with a molecule of
water to form the products. An attractive approach to
potent inhibitors is to create compounds that mimic
the transition state of an enzyme-catalyzed reaction.5
Many natural and synthetic polyhydroxylated pyrrol-
idines and polyhydroxylated pyrrolizidines alkaloids,
such as nojirimycin 1, 1-deoxynojirimycin (DNJ) 2,
Glycosidases are responsible for the hydrolysis of poly-
and oligosaccharides into monomers or cleavage of
bonds between sugars and a noncarbohydrate aglycon.
These enzymes are involved in several metabolic path-
ways and an alteration of glycosidase activity by inhib-
itors in vivo has the potential for the control of certain
cellular functions. Thus, glycosidase inhibitors
have shown promising chemotherapeutic applications
against diabetes,1 cancer,2 and viral infections including
AIDS.3
H
N
H
N
R
and
2,5-dihydroxymethyl-3,4-dihydroxy-pyrrolidine
HO
HO
(DMDP) 3 are carbohydrate mimics, commonly re-
ferred to as azasugars, act as glycosidase inhibitors. It
has been postulated that their activity is due to their
resemblance to the oxacarbenium-ion-like transition
state that arises from the protonation of the ring nitro-
gen at physiological pH.5a DMDP (3), a common sec-
ondary metabolite, has been reported to be a good
glucosidase inhibitor, with mild inhibition of some other
glycosidases.
OH
HO
OH
HO
OH
OH
1. R = OH
2. R = H
3
*
Corresponding author. Tel.: +1 604 291 4152; fax: +1 604 291
4860; e-mail: bpinto@sfu.ca
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.06.022

2306
R. Nasi, B. M. Pinto / Carbohydrate Research 341 (2006) 2305–2311
OH
OH
OH
OH
OH
OH
OH
OH
_
_
_
+
+
+
S
S
OSO3
OSO3
NH
OH
OSO3
HO
HO
HO
HO
OH
HO
OH
HO
OH
4
6
5
Recently, a new class of naturally occurring glycosi-
dase inhibitor with an intriguing inner salt, sulfonium
sulfate was isolated from Salacia reticulata6 a plant from
India and Sri Lanka known for its anti-diabetic proper-
ties. The bioassay-guided separation using intestinal a-
glucosidase inhibitory activity resulted in the isolation
of two potent a-glucosidase inhibitors, namely, salacinol
(4) and kotalanol (5). The unique structure of salacinol
is a sulfonium ion (1,4-anhydro-4-thio-D-pentitol cat-
ion) stabilized by an internal sulfate counter ion (1-
deoxy-L-erythritol-3-sulfate anion). These glucosidase
inhibitors are also presumably mimics of the oxacarbe-
nium-ion transition state in glucosidase-mediated
hydrolysis reactions, but could function simply by pro-
viding stabilizing electrostatic interactions with active
site carboxylate residues.
In the search for new glycosidase inhibitors, we have
reported the synthesis and glucosidase inhibitory prop-
erties of the different stereoisomers and heteroatom
congeners of salacinol7 in which the ring sulfur atom
has been substituted by the cognate atoms nitrogen
and selenium. Enzyme inhibition assays with a panel
of glycosidase enzymes have indicated that the stereo-
chemistry at the different stereogenic centers, the nature
of the heteroatom, the size of the heterocyclic ring, and
the length and nature of the side chain play a significant
role in discrimination between different glycosidase en-
zymes.8 Our recent investigation by X-ray crystallogra-
phy9 of the interaction of salacinol and its analogues
with Golgi a-mannosidase II (GMII) indicated that, as
speculated, in all of these derivatives, the positively
charged sulfonium center was in close proximity to an
aspartate residue in the enzyme active site. In addition,
a comparison of the interactions with those of the natu-
rally occurring inhibitor, swainsonine demonstrated that
the coordination of salacinol 4 with the Zn atom in the
enzyme active site is pentacoordinate (T5) whereas that
of swainsonine is hexacoordinate (T6). We speculated
that octahedral coordination was important to generate
a good inhibitor. We report herein the synthesis of new
analogues 7–10 of salacinol (4) and the corresponding
ammonium analogue, ghavamiol 6 that incorporate an
additional hydroxymethyl group at C-1 that might
facilitate T6 coordination in the active site of GMII
but might also provide favorable polar contacts in the
active site of other glycosidase enzymes.
OH
OH
OH
_
_ OH
OSO3
+
+
OSO3
X
X
HO
HO
OH
OH
HO
OH
HO
OH
7. X = S
9. X = NH
8. X = S
10. X = NH
2. Results and discussion
The general synthetic strategy involved alkylation of the
anhydroalditol at the heteroatom by a cyclic sulfate
derivative, whereby selective attack of the heteroatom
at the least hindered primary center would afford the
desired target molecules.
H
N
S
O
O
O
O
O
O
O
O
Ph
Ph
Ph
Ph
11
12
Ph
O
Ph
O
O
O
O
O
O
O
O
O
S
S
O
O
13
14
Thioether (11) was synthesized according to a re-
ported method10 by the radical-mediated cyclization of
the corresponding 1,5-bis-dithiocarbonate derivative
using tributyltin hydride with a,a-diazoisobutyronitrile
(AIBN) as a radical initiator (Scheme 1). The corre-
sponding dithiocarbonate was synthesized, in turn, from
1,3:4,6-di-O-benzylidene-D-mannitol by the sequential
addition of sodium hydride, carbon disulfide, and
methyl iodide in THF (Scheme 1).

R. Nasi, B. M. Pinto / Carbohydrate Research 341 (2006) 2305–2311
2307
Ph
Ph
Ph
O
OH
Ph
O
O
OMs
O
O
c
N
d
O
O
O
O
OH
O
O
OMs
O
Ph
Ph
Ph
18
17
15
a
e
Ph
O
O
O
X
MeS(S)C
O
b
O
O
O
O
O
OC(S)SMe
Ph
Ph
Ph
11. X = S
12. X = NH
16
Scheme 1. Reagents and conditions: (a) NaH, CS2, THF and then MeI (82%); (b) Bu3SnH, AIBN, toluene, 80 ꢁC (77%); (c) MsCl/Py, CH2Cl2 (89%);
(d) BnNH2, 130 ꢁC (84%); (e) Pd(OH2)/C, H2, EtOAc–MeOH (90%).
The synthesis of the C2-symmetric iminoalditol (12)
was patterned after that of Masaki et al.11 The C-2
and C-5 hydroxyl groups in 15 were activated by mesyl-
ation, and pyrrolidine ring formation was effected by
heating the dimesylate in benzylamine for 12 h at
130 ꢁC. Cyclization proceeded with complete inversion
at both centers leading to 2,5-dideoxy-2,5-N-benzyl-
imino-1,3:4,6-di-O-benzylidene-L-iditol in 87% yield.
Unlike Masaki et al., we chose to use Pd(OH)2/C and
hydrogen for the removal of the N-benzyl group. The
origin of this selectivity is unknown at present. The
13C NMR spectrum of compound 12 exhibited only
three carbon resonances, thus confirming that the mole-
cule possessed a C2 axis of symmetry.
We chose to alkylate compounds 11 and 12 with the
protected D- and L-erythritol cyclic sulfates (13 and 14)
as the source of the sulfated alkyl side chain, both of
which were synthesized from D-glucose.5,12 Alkylation
of thioether 11 with the cyclic sulfate 13 in 1,1,1,3,3,3-
hexafluoroisopropanol (HFIP) proceeded smoothly in
24 h to give the sulfonium salt 19 as the sole product
in 81% yield (Scheme 2). Subsequent removal of all
the three benzylidene groups by treatment with trifluo-
1
roacetic acid afforded the target compound 7. The H
Ph
O
O
OH
_
+
OH
_
OSO3
X
X
+
OSO3
a
X
b
O
O
13
O
O
+
HO
OH
O
O
O
O
Ph
Ph
Ph
Ph
HO
OH
19. X = S
21. X = NH
7. X = S
9. X = NH
11. X = S
12. X = NH
Scheme 2. Reagents and conditions: (a) HFIP, K2CO3, 70 ꢁC for 19 (81%) and acetone, K2CO3, 60 ꢁC for 21 (88%); (b) TFA, for 7 (82%) and Pd/C,
aq acetic acid, H2 for 9 (86%).

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R. Nasi, B. M. Pinto / Carbohydrate Research 341 (2006) 2305–2311
Ph
O
O
OH
_
+
OH
_
OSO3
X
X
+
OSO3
a
X
b
O
O
14
O
O
+
HO
OH
O
O
O
O
Ph
Ph
Ph
Ph
HO
OH
20. X = S
22. X = NH
8. X = S
10. X = NH
11. X = S
12. X = NH
Scheme 3. Reagents and conditions: (a) HFIP, K2CO3, 70 ꢁC for 20 (78%) and acetone, K2CO3, 60 ꢁC for 22 (80%); (b) TFA, for 8 (79%) and Pd/C,
aq acetic acid, H2 for 10 (81%).
NMR and 13C NMR spectra of 7 were completely as-
signed with the help of 1H–1H COSY, HMQC, and
HMBC experiments. In a similar manner, the reaction
of 11 with the enantiomeric cyclic sulfate 14 yielded
the corresponding sulfonium sulfate 20 in 78% yield,
and deprotection with TFA produced the desired prod-
60F-254 as the absorbent. MALDI-TOF mass spectra
were recorded on a perSeptive Biosystems Voyager-DE
spectrometer, using 2,5-dihydroxybenzoic acid as a
matrix.
3.2. 2,5-Dideoxy-2,5-N-benzylimino-1,3:4,6-di-O-benzyl-
idene-L-iditol (18)
1
uct 8 (Scheme 3). The H NMR and 13C NMR spectra
for compound 8 were similar to those of 7. Each of
the sulfonium salts (7 and 8) were obtained as a single
isomer at the sulfur atom, correlated with the C2 axis
of the starting thioether (11).
Compound 17 (3.2 g, 5.89 mmol) in benzylamine
(10 mL) was stirred at 130 ꢁC for 12 h. The excess benz-
ylamine was removed under high vacuum, and the resi-
due was purified by flash column chromatography to
yield compound 18 (2.14 g, 84%) as a white solid; mp
118–120 ꢁC (lit. 120 ꢁC); [a]D +90 (c 1.6, CHCl3); lit.10
[a]D +90.6 (c 0.3, CHCl3). The spectral data were in
agreement with those reported.
Amine 12 reacted with L-cyclic sulfate 13 in dry ace-
tone containing K2CO3 to give the ammonium salt 21
in 88% yield. Deprotection was accomplished with Pd/
C/H2 in aqueous acetic acid to effect the hydrogenolytic
cleavage of the benzylidene groups, to give the target
1
compound 9. The H NMR resonances for compounds
were extremely broad in D2O, but sharpened when the
sample was made basic with K2CO3. Analogously, the
reaction of amine 12 with D-cyclic sulfate (14) produced
the corresponding ammonium salt 22 in 80% yield; sub-
sequent deprotection by hydrogenolysis, as before, gave
the desired product, 10.
3.3. 2,5-Dideoxy-2,5-imino-1,3:4,6-di-O-benzylidene-L-
iditol (12)
2,5-Dideoxy-2,5-N-benzylimino-1,3:4,6-di-O-benzylidene-
L-iditol (18, 1.98 g, 4.6 mmol) was dissolved in 100 mL
EtOAc–MeOH (1:1), and 20% Pd(OH)2/C (200 mg) was
added. The solution was stirred under an atmosphere of
H2 for 3 h. The catalyst was removed by filtration, the
solvents were removed under vacuum, and the residue
was purified by flash chromatography (20:1, EtOAc–
MeOH) to afford 12 (1.42 g, 90%) as a white solid; mp
130–131 ꢁC (lit. 130 ꢁC); [a]D +15.2 (c 1.0, CHCl3) (lit.10
[a]D +7.7 (c 0.5, CHCl3). The spectral data were in agree-
ment with those reported.
3. Experimental
3.1. General
1
Optical rotations were measured at 23 ꢁC. H and 13C
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) using standard Varian pulse pro-
grams. Processing of the spectra was performed using
Mestrac software. Column chromatography was per-
formed with Merck silica gel 60 (230–400 mesh), and
thin layer chromatography (TLC) was performed on
aluminum plates precoated with E. Merck Silica Gel
3.4. 1,3:4,6-Di-O-benzylidine-2,5-dideoxy-1,5-[[(2S,3S)-
2,4-O-benzylidene-2,4-dihydroxy-3-(sulfooxy)butyl]sulfo-
niumylidene]-L-iditol inner salt (19)
To 1,1,1,3,3,3-hexafluoro propanol (2 mL) were added
1,3:4,6-di-O-benzylidene-2,5-dideoxy-1,5-thio-L-iditol (11)
(282 mg, 0.79 mmol), 2,4-O-benzylidine-L-erythritol-

R. Nasi, B. M. Pinto / Carbohydrate Research 341 (2006) 2305–2311
2309
1,3-cyclic-sulfate (13) (260 mg, 0.94 mmol), and K2CO3
(45 mg) in a sealed tube and the reaction mixture was
stirred for 48 h at 75 ꢁC. The solvent was removed and
the crude product was purified by column chromatogra-
phy (15:1, EtOAc–MeOH) to afford the coupled product
19 as a colorless foam (405 mg, 81%); 1H NMR
(CDCl3): d 5.54, 5.52, 5.42 (3H, 3 · Ph-CH–), 4.94
(214 mg, 0.78 mmol) in HFIP (2 mL), following the
same procedure that was used for the synthesis of 19.
Column chromatography (15:1, EtOAc–MeOH) of the
crude product gave 20 as an amorphous solid (338 mg,
79%); H NMR (CD2Cl2): d 5.74 (1H, Ph–CH–), 5.62,
5.46 (2H, Ph–CH–), 5.20 (1H, d, J1a,1b = 14.8 Hz, H-
1
1a), 4.98 (1H, br s, H-3), 4.87 (1H, br s, H-4), 4.78
(2H, d, J1a,1b = 14.0, J1a0;1b ¼ 14:0 Hz, H-1a, H-1a0),
(1H, d, J1a0;1b ¼ 13:9 Hz, H-1a0), 4.72 (1H, ddd,
0
0
J3 ;2 ¼ 9:5, J3 ;4a0 ¼ 10:5 Hz, H-30), 4.62 (1H, dd,
0
0
0
4.80 (1H, br s, H-3), 4.79 (1H, br s, H-4), 4.66 (1H, d,
0
0
0
J6a;6b ¼ 14:0 Hz, H-6a), 4.56 (1H, dd, J4a;04b ¼ 10:3,
J1b,2 = 3.1 Hz, H-1b), 4.58 (1H, dd, J4a04b ¼ 10:5 Hz,
J3 ;4a0 ¼ 5:6 Hz, H-4a0), 4.48 (1H, ddd, J3 ;4a0 ¼ 5:6,
H-4a0), 4.56 (1H, br s, H-2), 4.45 (1H, dd,
0
0
J3 ;4b ¼ 10:7, J3 ;2 ¼ 9:7 Hz, H-30), 4.37 (1H, ddd,
J2 ;1b ¼ 3:0 Hz, H-20), 4.30 (1H, d, J6a,6b = 14.0 Hz, H-
6a), 4.06 (1H, br s, H-5), 3.89 (1H, dd, H-1b0), 3.83
(1H, d, H-4b0), 3.79 (1H, dd, H-6b); 13C NMR
(CD2Cl2): d 136.2–126.3 (18C), 101.5, 100.8, 100.4
(3H, Ph–CH–), 83.0 (C-3), 80.6 (C-4), 76.8 (C-20), 69.0
(C-40), 65.6 (C-30), 64.0 (C-5), 63.9 (C-6), 63.4 (C-1),
54.3 (C-2), 47.4 (C-10); MALDI-MS: m/z 651.20
[M+Na]+, 629.48 [M+1]+, 549.37 [MꢀSO3]+; HRMS
Calcd for C31H32O10S2Na [M+Na]+: 651.13291. Found:
651.13289.
0
0
0
0
0
0
J2 ;1a0 ¼ 3:0, J2 ;1b ¼ 6:1 Hz, H-20), 4.32 (1H, br s, H-5),
4.30 (1H, dd, J1b,2 = 3.2 Hz, H-1b), 4.21 (1H, br s, H-
2), 4.13 (1H, dd, H-1b0), 3.97 (1H, dd, J6b,5 = 1.8 Hz,
H-6b), 3.75 (1H, dd, H-4b0); 13C NMR (CD2Cl2): d
136.2–126.3 (18C), 101.5, 100.8, 100.4 (3H, Ph–CH–),
83.0 (C-3), 80.6 (C-4), 76.8 (C-20), 69.0 (C-40), 65.6 (C-
30), 64.0 (C-5), 63.9 (C-6), 63.4 (C-1), 54.3 (C-2), 47.4
(C-10); MALDI-MS: m/z 651.20 [M+Na]+, 629.48
[M+H]+, 549.37 [M+HꢀSO3]+. HRMS Calcd for
C31H32O10S2Na [M+Na]+: 651.1329. Found: 651.13263.
0
0
3.7. 2,5-Dideoxy-1,5-[[(2R,3R)-2,4-dihydroxy-3-(sulfo-
oxy)butyl]sulfoniumylidene]-L-iditol inner salt (8)
3.5. 2,5-Dideoxy-1,5-[[(2S,3S)-2,4-dihydroxy-3-(sulfo-
oxy)butyl]sulfoniumylidene]-L-iditol inner salt (7)
Compound 20 (190 mg, 0.30 mmol) was dissolved in
CH2Cl2 (1 mL) and 50% aqueous TFA (15 mL) was
added and stirred at room temperature for 2.5 h. The
solvents were removed by a high vacuum to give a
brown residue which was purified by column chroma-
tography (10:1, EtOAc–MeOH) to give 8 as an amor-
phous solid (83 mg, 76%); 1H NMR (D2O): d 4.60
(1H, dd, J3,2 = 2.4, J3,4 = 3.4 Hz, H-3), 4.50 (1H,
J4,5 = 2.1 Hz, H-4), 4.47 (1H, dd, J5,6a = 5.3,
Compound 19 (220 mg, 0.35 mmol) was dissolved in
CH2Cl2 (1 mL), and 50% aqueous TFA (15 mL) was
added and the mixture was stirred at room temperature
for 2 h. The solvents were removed by a high vacuum to
give a brown gummy product. Purification by column
chromatography (10:1, EtOAc–MeOH) gave 7 as an
amorphous solid (109 mg, 85%); 1H NMR (D2O): d
4.58 (1H, dd, J3,2 = 2.4, J3,4 = 2.2 Hz, H-3), 4.50 (1H,
dd, J4,5 = 2.3 Hz, H-4), 4.44 (1H, ddd, J5,6a = 5.0,
J5,6b = 9.8 Hz, H-5), 4.34 (1H, ddd, J2,1a
=
0
0
J5,6b = 9.0 Hz, H-5), 4.41 (1H, dd, J2,1a = 6.2, J2,1b
=
4.8,J2,1b = 9.6 Hz, H-2), 4.30 (1H, ddd, J2 ,1b = 10.5,
J2 ;1a0 ¼ 2:0, J2 ;3 ¼ 3:6 Hz, H-20), 4.18 (1H, ddd,
0
0
0
0
0
0
9.6 Hz, H-2), 4.27 (1H, ddd, J2 ;1b ¼ 7:6, J2 ;1a0 ¼ 10:5,
J2 ;3 ¼ 2:2 Hz, H-20), 4.16 (1H, dd, J6a,6b = 12.4 Hz,
J3 4a0 ¼ 3:4, J3 ;4b ¼ 3:3 Hz, H-30), 4.11 (1H, dd,
0
0
0
0
0
J1a0;1b ¼ 12:6 Hz, H-1a0), 4.04 (1H, d, J1a,1b = 12.5 Hz,
0
0
0
0
H-6a), 4.14 (1H, ddd, J3 ;4a0 ¼ 3:2, J3 ;4b ¼ 3:2 Hz, H-
30), 4.07 (1H, dd, J1a0;1b ¼ 14:0 Hz, H-1b0), 4.04 (1H,
12.5 Hz, H-1a), 3.98 (1H, dd, H-6b), 3.88 (1H, dd, H-
0
1b), 3.83 (1H, dd, J1a01b ¼ 13:0 Hz, H-1a0), 3.82 (1H,
13
0
dd, J1a,1b = 12.4 Hz, H-1a), 4.02 (1H, dd, H-1b), 4.00
(1H, dd, H-6b), 3.82 (1H, dd, J4a0;4b ¼ 12:8 Hz, H-4a0),
dd, J4a0;4b ¼ 12:8 Hz, H-4a0), 3.73 (1H, dd, H-4b0),
0
0
3.72 (1H, dd, H-4b0), 3.39 (1H, dd, H-1b0); 13C NMR
(D2O): d 80.9 (C-30), 78.4 (C-4), 76.9 (C-3), 70.0 (C-2),
66.6 (C-20), 63.1 (C-5), 59.7 (C-40), 57.7 (C-1), 55.5 (C-
6), 44.8 (C-10); MALDI-MS: m/z 387.15 [M+Na]+,
365.02 [M+H]+, 285.26 [M+HꢀSO3]+; HRMS Calcd
for C10H20O10S2Na [M+Na]+: 387.03901. Found:
387.03906.
3.38 (1H, dd, H-1b0); C NMR (D2O): d 80.6 (C-30),
78.1 (C-4), 77.1 (C-3), 70.2 (C-2), 64.5 (C-20), 62.5 (C-
5), 59.7 (C-40), 57.8 (C-6), 55.5 (C-1), 44.0 (C-10); MAL-
DI-MS: m/z 651.20 [M+Na]+, 629.48 [M+H]+, 549.37
[M+HꢀSO3]+; HRMS Calcd for C31H32O10S2Na
[M+Na]+: 387.03901. Found: 387.03904.
3.8. 1,3:4,6-Di-O-benzylidene-2,5-dideoxy-1,5-[[(2S,3S)-
2,4-O-benzylidene-2,4-dihydroxy-3-(sulfooxy)butyl]imi-
nonium]-L-iditol inner salt (21)
3.6. 1,3:4,6-Di-O-benzylidene-2,5-dideoxy-1,5-[[(2R,3R)-
2,4-O-benzylidene-2,4-dihydroxy-3-(sulfooxy)butyl]sulfo-
niumylidene]-L-iditol inner salt (20)
Imino alditol 12 (260 mg, 0.76 mmol) and cyclic sulfate
13 (228 mg, 0.83 mmol) were added to anhydrous ace-
tone (2 mL) containing K2CO3 (50 mg), and the mixture
Thio-L-iditol (11) (240 mg, 0.67 mmol) was coupled to
2,4-O-benzylidene-D-erythritol-1,3-cyclic-sulfate
(14)

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R. Nasi, B. M. Pinto / Carbohydrate Research 341 (2006) 2305–2311
0
0
was stirred in a sealed tube for 12 h at 65 ꢁC. The solvent
was removed and the mixture was purified by column
chromatography. The coupled product 21 was obtained
as a colorless foam (398 mg, 85%); H NMR (acetone-
d6, pH > 8): d 7.40–7.20 (15H), 5.57 (2H, 2 · Ph–
3.66 (1H, dd, J4b ;3 ¼ 10:4 Hz, H-4b0), 3.52 (2H, br s,
H-2, H-5), 3.46 (1H, br s, H-1b0); MALDI-MS: m/z
634.04 [M+Na]+, 612.15 [M+H]+, 532.19 [M+H
ꢀSO3]+.
1
CH–), 5.48 (1H, Ph–CH–), 4.69 (2H, d, J1a,1b(6a,6b)
=
3.11. 2,5-Dideoxy-1,5-[[(2R,3R)-2,4-dihydroxy-3-(sulfo-
oxy)butyl]iminonium]-L-iditol inner salt (10)
12.8 Hz, H-1a, H-6a), 4.60 (1H, m, H-4a0), 4.35 (2H,
br s, H-3, H-4), 4.20 (1H, m, H-30), 4.02 (2H, d, H-1b,
H-6b), 3.98 (1H, d, J1a0;1b ¼ 12:5 Hz, H-1a0), 3.91 (1H,
Compound 22 (216 mg, 0.35 mmol) was dissolved in a
4:1 mixture of CH3COOH–H2O (20 mL) and the solu-
tion was stirred with 10% Pd/C (160 mg) under 100 psi
of H2 for 44 h. The catalyst was removed by filtration
through a silica bed, and washed with water (30 mL).
The filtrate was evaporated, and the mixture was puri-
fied by column chromatography (10:3:1, EtOAc–
MeOH–H2O) to give an amorphous solid (10) (103
0
m, H-20), 3.68 (1H, m, H-4b0), 3.44 (2H, br s, H-2, H-
5), 2.98 (1H, m, H-1b0); MALDI-MS: m/z 634.08
[M+Na]+, 612.16 [M+H]+, 532.17 [M+HꢀSO3]+;
HRMS Calcd for C31H32NO10S [MꢀH]ꢀ: 610.1752.
Found: 610.1755.
3.9. 2,5-Dideoxy-1,5-[[(2S,3S)-2,4-dihydroxy-3-(sulfo-
oxy)butyl]iminonium]-L-iditol inner salt (9)
1
mg, 83%); H NMR (D2O, pH > 8): d 4.29 (1H, ddd,
J3 ;2 ¼ 2:1, J3 ;4a0 ¼ 3:4, J3 ;4b ¼ 5:1 Hz, H-30), 4.19
0
0
0
0
0
0
0
0
Compound 21 (230 mg, 0.37 mmol) was dissolved in a
4:1 mixture of CH3COOH–H2O (20 mL) and the solu-
tion was stirred with 10% Pd/C (180 mg) under 100 psi
of H2 for 30 h. The catalyst was removed by filtration
through a silica bed, and washed with water (25 mL).
The filtrate was evaporated, and the mixture was puri-
fied by column chromatography (10:3:1, EtOAc–
MeOH–H2O) to give an amorphous solid (9) (112 mg,
(2H, m, H-3, H-4),4.03 (1H, ddd, J2 ;1a0 ¼ 7:7, J2 ;1b
¼
5:6 Hz, H-20), 3.82 (1H, dd, J4a0;4b ¼ 12:7 Hz, H-4a0),
3.74 (1H, dd, H-4b0), 3.73 (2H, dd, J1a,1b(6a,6b) = 12.0,
J1a,2(6a,5) = 6.2 Hz, H-1a, H-6a), 3.61 (2H, dd, H-1b,
H-6b), 3.17 (2H, m, H-2, H-5), 2.94 (1H, dd,
0
J1a0;1b ¼ 3:9 Hz, H-1a0), 2.85 (1H, dd, H-1b0); 13C
0
NMR: d 81.5 (C-30), 76.2 (C-3, C-4), 69.9 (C-20), 63.8
(C-2, C-5), 59.8 (C-40), 58.4 (C-1, C-6), 51.0 (C-10);
MALDI-MS: m/z 370.03 [M+Na]+, 348.05 [M+H]+.
Anal. Calcd for C10H21NO10S: C, 34.58; H, 6.09; N,
4.03. Found: C, 34.27; H, 6.27; N, 3.81.
1
86%); H NMR (D2O, pH > 8): d 4.20 (3H, m, H-3,
H-4, H-30), 4.00 (1H, ddd, J2 ;3 ¼ 2:2, J2 ;1a0 ¼ 5:6,
0
0
0
J2 ;1b ¼ 10:2 Hz, H-20), 3.81 (1H, dd, J4a0;3 ¼ 3:5,
0
0
0
J4a0;4b ¼ 12:6 Hz, H-4a0), 3.75 (1H, dd, J4b ;3 ¼ 4:7 Hz,
0
0
0
H-4b0), 3.70 (2H, dd, J1a,1b(6a,6b) = 12.1, J1a,2
=
(6a,5)
4.3 Hz, H-1a, H-6a), 3.59 (2H, dd, J1b,2(6b,5) = 3.0 Hz,
Acknowledgements
H-1b, H-6b), 3.16 (3H, m, H-2, H-5, H-1a0), 2.59 (1H,
13
dd, J1b ;1a0 ¼ 13:9 Hz, H-1b0); C NMR: d 81.6 (C-30),
0
We are grateful to the Natural Sciences and Engineering
Research Council of Canada for financial support.
76.3 (C-3, C-4), 67.3 (C-20), 62.4 (C-2, C-5), 60.0 (C-
40), 58.1 (C-1, C-6), 50.9 (C-10); MALDI-MS: m/z
370.19
[M+Na]+,
347.99
[M+H]+,
268.32
[M+HꢀSO3]ꢀ. Anal. Calcd for C10H21NO10S: C,
34.58; H, 6.09; N, 4.03. Found: C, 34.82; H, 5.89; N,
3.94.
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