Synthesis of a biologically active isomer of kotalanol, a naturally occurring glucosidase inhibitor

Article abstract of DOI:10.1016/j.bmc.2010.03.027

The syntheses of an isomer of kotalanol, a naturally occurring glucosidase inhibitor, and of kotalanol itself are described. The target compounds were synthesized by nucleophilic attack of PMB-protected 1,4-anhydro-4-thio-d-arabinitol at the least hindered carbon atom of two 1,3-cyclic sulfates, which were synthesized from d-mannose. Methoxymethyl ether and isopropylidene were chosen as protecting groups. The latter group was critical to ensure the facile deprotection of the coupled products in a one-step sequence to yield kotalanol and its isomer. The stereoisomer of kotalanol, with the opposite stereochemistry at the C-6′ stereogenic centre, inhibited the N-terminal catalytic domain of intestinal human maltase glucoamylase (ntMGAM) with a K_i value of 0.20 ± 0.02 μM; this compares to a K_i value for kotalanol of 0.19 ± 0.03 μM. The results indicate that the configuration at C-6′ is inconsequential for inhibitory activity against this enzyme.

Full text of DOI:10.1016/j.bmc.2010.03.027

Bioorganic & Medicinal Chemistry 18 (2010) 2829–2835
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of a biologically active isomer of kotalanol, a naturally occurring
glucosidase inhibitor
Razieh Eskandari a, Kumarasamy Jayakanthan a, Douglas A. Kuntz b, David R. Rose b,c, B. Mario Pinto a,
*
a Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6
b Department of Medical Biophysics, University of Toronto and Division of Molecular and Structural Biology, Ontario Cancer Institute, Toronto, Ontario, Canada M5G 2M9
c Department of Biology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
a r t i c l e i n f o
a b s t r a c t
Article history:
The syntheses of an isomer of kotalanol, a naturally occurring glucosidase inhibitor, and of kotalanol itself
are described. The target compounds were synthesized by nucleophilic attack of PMB-protected 1,4-
Received 15 January 2010
Revised 10 March 2010
Accepted 11 March 2010
Available online 15 March 2010
anhydro-4-thio-
D-arabinitol at the least hindered carbon atom of two 1,3-cyclic sulfates, which were syn-
thesized from -mannose. Methoxymethyl ether and isopropylidene were chosen as protecting groups.
D
The latter group was critical to ensure the facile deprotection of the coupled products in a one-step
sequence to yield kotalanol and its isomer. The stereoisomer of kotalanol, with the opposite stereochem-
istry at the C-60 stereogenic centre, inhibited the N-terminal catalytic domain of intestinal human mal-
Keywords:
Kotalanol
Isomer of kotalanol
tase glucoamylase (ntMGAM) with a Ki value of 0.20 0.02
kotalanol of 0.19 0.03
M. The results indicate that the configuration at C-60 is inconsequential for
inhibitory activity against this enzyme.
lM; this compares to a Ki value for
l
D-Mannitol
Cyclic sulfate
Ó 2010 Elsevier Ltd. All rights reserved.
Glucosidase inhibitors
Human maltase glucoamylase
Type 2 diabetes
1. Introduction
fraction of this plant extract and also other plants that belong to
the Salacia genus such as Salacia chinensis, Salacia prinoides, and
Salacia oblonga which explain, at least in part, the antidiabetic
property of the aqueous extract of this plant.7–9 All these com-
pounds share a common structural motif that comprises a 1,4-
Glycosidases are enzymes that are involved in the catabolism of
glycoproteins and glycoconjugates and the biosynthesis of oligo-
saccharides. Disruption in regulation of glycosidases can lead to
diseases.1,2 Over the years, glycosidase inhibitors have received
considerable attention in the field of chemical and medicinal re-
search3 because of their effects on quality control, maturation,
transport, secretion of glycoproteins, and cell–cell or cell–virus rec-
ognition processes. This principle has potential for many therapeu-
tic applications, such as in the treatment of diabetes, cancer and
viral infections.1
anhydro-4-thio-D-arabinitol and a polyhydroxylated side chain.
So far, five components have been isolated, namely salaprinol
(1),9 salacinol (2),7 ponkoranol (3),9 kotalanol (4),8 and de-O-sulfo-
nated kotalanol (5)10 (Fig. 1). The absolute stereostructure for these
compounds, except salacinol, was not determined at the time of
isolation, but synthetic work has led to their stereochemical struc-
ture elucidation.11,12
Bioactive components isolated from medicinal plants that are
used in traditional medicine or folk medicine often provide the
lead structures for modern drug-discovery programs. For example,
the large woody climbing plant Salacia reticulata, known as Kothal-
ahimbutu in Singhalese, is used in traditional medicine in Sri Lanka
and Southern India for treatment of type 2 diabetes.4,5 A person
suffering from diabetes was advised to drink water stored over-
night in a mug carved from Kothalahimbutu wood.6 Several potent
glucosidase inhibitors have been isolated from the water soluble
The synthesis of kotalanol 4 and its stereoisomer 6 (Fig. 2) are of
interest here.
Our first attempt employed the reaction of the cyclic sulfates 8
in the coupling reaction (Scheme 1).12 However, attempts to re-
move the methylene acetal in the coupled products required forc-
ing conditions and resulted in de-O-sulfonation (Scheme 1).12 We
have also reported a successful synthesis of kotalanol using a cyclic
sulfate derived from a naturally occurring heptitol,
D-perseitol
(Scheme 2).12
However, it was of interest to develop a synthesis of the isomer
of kotalanol 6 in view of the fact that the C-60 stereoisomer of de-O-
sulfonated kotalanol was just as active an inhibitor as de-O-sulfo-
* Corresponding author. Tel.: +1 778 782 4152; fax: +1 778 782 4860.
E-mail address: bpinto@sfu.ca (B. Mario Pinto).
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.03.027

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R. Eskandari et al. / Bioorg. Med. Chem. 18 (2010) 2829–2835
OH
OH OH
OH
OH OH
S
S
OSO3
OSO3
S
OH
OSO3
HO
HO
HO
HO
HO
OH
OH
HO
OH
Salaprinol (1)
Ponkoranol (3)
Salacinol (2)
OH
OH OH
OH
OH OH
OH
OH
S
OH
S
OH
OSO3
OH
HO
HO
CH3OSO3
OH
HO
OH
HO
Kotalanol (4)
De-O-sulfonated kotalanol (5)
Figure 1. Components isolated from Salacia species.
required for removal of the benzylidene acetal. The cyclic sulfate
12 could be synthesized from -mannitol as shown in the retrosyn-
thetic analysis (Scheme 3).
Thus, the
-mannitol-derived diol 15,14 was protected as the
OH
OH OH
OH
D
S
OH
OSO3
D
HO
acetonide to give the C2-symmetric compound 14 in 73% yield.
Mild hydrolysis of this compound using catalytic PTSA in methanol
effected the removal of one benzylidene group to give the corre-
sponding diol in 70% yield based on recovered starting material.
Selective protection of the primary hydroxyl group as its TBDMS
ether followed by sequential protection of the secondary hydroxyl
group as its MOM ether and removal of the TBDMS group with tet-
rabutylammonium fluoride (TBAF) gave 17 in 73% yield over three
steps. Treatment of this alcohol with Dess–Martin periodinane pro-
vided the aldehyde which was reacted with methyltriphenylphos-
phonium bromide to yield the olefinic product 13 in 61% yield over
two steps (Scheme 4).
HO
OH
6
Figure 2. Kotalanol stereoisomer.
nated kotalanol 5 itself against a key intestinal enzyme, human
maltase glucoamylase.13 We report here a general synthetic route
to this isomer 6 and also an alternative synthesis of kotalanol 4.
2. Results and discussion
With compound 13 in hand, our next goal was to introduce the
two hydroxyl groups. OsO4-Catalyzed dihydroxylation of 13 affor-
ded compound 18 (Scheme 4) as the major product with a diaste-
reomeric ratio of 18:19 of 2.6:1. Kishi’s rule predicts that the
relative stereochemistry between the pre-existing hydroxyl group
and the adjacent newly-introduced hydroxyl group in the major
product should be erythro.15 This result is also analogous to that
We chose to replace the problematic methylene acetal group of
compounds 8 with an isopropylidene acetal (compound 12) to en-
sure not only its facile removal after the coupling reaction but also
to maintain some rigidity in the cyclic sulfate. We chose also to re-
place the benzyl ethers with methoxymethyl (MOM) ethers, be-
cause the latter can survive the hydrogenolysis conditions
OBn
OBn
O
O
OH
OH OH
OH
OH
OBn
OSO3
O
O
O
OBn
OBn
S
S
OH
S
PMBO
HO
1.0 M BCl3
then MeOH
HFIP, K 2CO3
PMBO
PMBO
CH3OSO3
OH
+
O
OBn
PMBO
OPMB
S
HO
OPMB
O
O
5
9
8
7
Scheme 1. First attempted synthesis of kotalanol.
PMBO
OPMB OPMB
PMBO
OPMB OPMB
80% TFA
7
D-perseitol
4
OSO3
O
O
S
HFIP, K 2CO3
O
S
O
O
O
O
O
PMBO
PMBO
Ph
Ph
OPMB
10
11
Scheme 2. Synthesis of kotalanol 4.

R. Eskandari et al. / Bioorg. Med. Chem. 18 (2010) 2829–2835
2831
O
O
O
O
O
O
O
O
O
O
OMOM
OMOM
D-Mannitol
O
O
O
O
OMOM
OMOM
S
Ph
Ph
Ph
O
O
14
13
12
Scheme 3. Retrosynthetic analysis.
Ph
O
O
O
O
O
O
O
O
OH
O
O
1. DMP, pTSA
(73%)
1. TBSCl, Imid.
1. pTSA, MeOH
(70%)
OH
OH
O
Ph
O
O
O
2. MOMCl, iPr2NEt
OMOM
O
OH
O
O
O
OH
3. TBAF, THF
(73%)
Ph
Ph
Ph
Ph
17
16
15
14
O
O
O
O
18
19
1.0
OH
O
OH
O
6
1
2
7
OsO4 2.6
5
6
5
4 3
2
3 4
2
6
1. Dess-Martin periodinane
O7
2. CH3PPh3Br, n-BuLi
dihydroxylation
1
3
+
4
OH
OH
O
O
7
1
3.3
3.5
1.0
1.0
AD-mix-α
AD-mix-β
O5 OMOM
O
OMOM
O
OMOM
(80%)
Ph
Ph
Ph
19
13
18
(61%)
Scheme 4. Synthesis of the diols 18 and 19.
obtained for dihydroxylation of
acetal.12
a
corresponding methylene
The target compounds were prepared by opening of the cyclic
sulfates 12 and 22 by nucleophilic attack of the sulfur atom in
Interestingly, AD-mix-
a
and AD-mix-b also afforded compound
2,3,5-tri-O-p-methoxybenzyl-1,4-anhydro-4-thio-D
-arabinitol 7.11
18 as a major product, with a diastereomeric ratio of 3.3:1 and
3.5:1 (determined by 600 MHz 1H NMR), respectively. The unsatis-
factory selectivity can be explained by the steric hindrance im-
Reactions were carried out at 72 °C in 1,1,1,3,3,3-hexafluoro-2-pro-
panol (HFIP) containing K2CO317 for six days to give the sulfonium
salts 23 and 24 in 65% and 57% yield, respectively. Finally, depro-
tection of the coupled products 24 and 23 using aqueous 30% triflu-
oroacetic acid (TFA) at 50 °C gave the desired compounds 4 and 6
in 91% and 93% yields, respectively (Scheme 6).
posed by the bicyclic structure, observed previously with
a
similar structure.16 The two isomers were separated by column
chromatography and each was converted into its cyclic sulfate 12
or 22 as follows. The hydroxyls in 18 were protected with MOM
groups and the product was subjected to hydrogenolysis to effect
removal of the benzylidene group and to yield the corresponding
diol 20 in 72% yield over two steps. The cyclic sulfate 12 was then
obtained by treatment of 20 with thionyl chloride in the presence
of triethylamine to give the mixture of diastereomeric sulfites, fol-
lowed by their oxidation with sodium periodate and ruthenium(III)
chloride as a catalyst. A similar sequence of reactions with the diol
19 yielded the cyclic sulfate 22 (Scheme 5).
Comparison of the 1H and 13C NMR spectra of kotalanol 4 with
those reported13 revealed identical data and served, therefore, to
confirm the stereochemistry at C-60, and, by inference, the stereo-
chemistry at C-2 in each of 18 and 19.
Finally, the inhibitory activities of compounds 4 and 6 were
examined against the N-terminal catalytic domain of recombinant
human maltase glucoamylase (ntMGAM), a critical intestinal glu-
cosidase for processing starch-derived oligosaccharides into glu-
cose. The stereoisomer of kotalanol 4 inhibited ntMGAM with a
O
O
O
O
O
O
OMOM
OMOM
O
O
OH
OH
1. SOCl2, Et3N, CH2Cl2
OMOM 2. NaIO4, RuCl3
OMOM
1. MOMCl, i-Pr2NEt
2. Pd(OH)2, MeOH
(72%)
O
O
HO
OMOM
OMOM
CCl4:CH3CN
S
HO
OMOM
O
O
Ph
(70%)
18
12
20
O
O
O
OMOM
OMOM
O
O
O
O
O
1. SOCl2, Et3N, CH2Cl2
OMOM
OH
OH
1. MOMCl, i-Pr2NEt
OMOM 2. NaIO4, RuCl3
2. Pd(OH)2, MeOH
(75%)
O
O
HO
OMOM
CCl4:CH3CN
S
OMOM
HO
OMOM
O
O
(76%)
Ph
22
19
21
Scheme 5. Synthesis of the cyclic sulfates 12 and 22.

2832
R. Eskandari et al. / Bioorg. Med. Chem. 18 (2010) 2829–2835
OH OH
5'
O
O
OH
2'
OMOM
3'
OH
1'
6'
4'
OMOM
OMOM
S
OH
S
OSO3
OSO3
OPMB
30% TFA
93%
12, HFIP,
K2CO3
65%
HO
PMBO
PMBO
HO
OH
23
6
7
OH
OH OH
O
O
OMOM
3'
5'
OH
1'
4'
2'
6'
OH
OMOM
OMOM
S
S
OSO3
OSO3
OPMB
30% TFA
91%
22, HFIP,
K2CO3
57%
PMBO
PMBO
HO
HO
OH
24
4
Scheme 6. Coupling reactions.
Ki value of 0.20 0.02
of 0.19 0.03
M,18 and Ki values of 0.10 0.02
0.13 0.02
l
M; this compares to a Ki value for kotalanol
(C-1, C-6), 61.7 (C-2, C-5), 24.4 (2Me). HRMS Calcd for C23H27O6
(M+H): 399.1802. Found: 399.1809.
l
lM
and
l
M for other stereoisomers of 4 with opposite configu-
rations at C-50 or both C-50 and C-60, respectively.16 It is clear,
therefore, that the configurations at C-50 and C-60 are not critical
for dictating enzyme inhibitory activity against ntMGA.
3.4. 1,3-O-Benzylidene-2,5-O-isopropylidene-D-mannitol (16)
To a solution of compound 14 (7.50 g, 18.84 mmol) in MeOH
(300 mL), was added PTSA (300 mg), and the reaction was stirred
at room temperature for 30 min. The reaction mixture was then
quenched by addition of Et3N to pH >9, and the solvent were re-
moved under vacuum to give a solid. The solid was dissolved in
CH2Cl2 (100 mL) and washed with water (50 mL). The organic solu-
tion was dried (Na2SO4), concentrated, and the crude product was
purified through a silica column with EtOAc/hexanes (1:1) as elu-
3. Experimental section
3.1. General
Optical rotations were measured at 23 °C. 1H and 13C NMR spec-
tra were recorded at 600 and 150 MHz, respectively. All assign-
ments were confirmed with the aid of two-dimensional 1H, 1H
(COSYDFTP) or 1H, 13C (INVBTP) experiments using standard pulse
programs. Column chromatography was performed with Silica 60
(230–400 mesh). High resolution mass spectra were obtained by
the electrospray ionization method, using an Agilent 6210 TOF
LC/MS high resolution magnetic sector mass spectrometer.
ent to yield 16 as a foam (4.1 g, 70%). ½a D23
ꢁ
= ꢂ15 (c 1, CH2Cl2). 1H
NMR (CDCl3) d 7.42–7.30 (5H, m, Ar), 5.40 (1H, s, CH–Ph), 4.12
(1H, dd, J1a,1b = 10.8, J1a,2 = 5.5 Hz, H-1a), 3.81 (1H, dd,
J6a,6b = 10.9, J6a,5 = 4.3 Hz, H-6a), 3.76–3.72 (2H, m, H-3, H-5), 3.66
(1H, m, H-6b), 3.60–3.53 (2H, m, H-4, H-1b), 3.43 (1H, t,
J1,2 = 8.9 Hz, H-2), 2.23 (2H, br, 2OH), 1.30 (6H, s, 2Me). 13C NMR
(CDCl3) d 137.3 (CMe2), 129.3- 101.7 (m, Ar), 101.1 (CH–Ph), 85.2
(C-2), 73.9 (C-4), 70.3 (C-5), 69.3 (C-1), 63.6 (C-6), 61.2 (C-3),
24.8, 24.6 (2Me). HRMS Calcd for C16H23O6 (M+H): 311.1489.
Found: 311.1487.
3.2. Enzyme inhibition assays
Compounds 4 and 6 were tested for inhibition of ntMGAM, as
previously described.16
3.5. 1,3-O-Benzylidene-2,5-O-isopropylidene-4-O-methoxyme-
thyl-D-mannitol (17)
3.3. 1,3,4,6-Di-O-benzylidene-2,5-O-isopropylidene-D-mannitol
(14)
To a solution of 16 (6.80 g, 21.93 mmol) in DMF (125 mL) was
added imidazole (4.47 g, 65.81 mmol). The reaction was cooled in
an ice bath, TBDMSCl (3.79 g, 24.13 mmol) was added portionwise,
and the mixture was stirred at 0 °C under N2 for 2 h. The reaction
was quenched by the addition of ice-water, and the reaction mix-
ture was extracted with Et2O (3 ꢀ 75 mL). The combined organic
solvents were dried (Na2SO4) and concentrated to give the crude
product which was used directly in the next step without further
purification. The crude product was dissolved in DMF (60 mL),
and i-Pr2NEt (26 mL, 150.75 mmol) and MOMCl (5.7 mL,
75.38 mmol) were added. The reaction mixture was heated at
60 °C overnight, then quenched with ice, and extracted with ether
(3 ꢀ 50 mL). The organic solution was dried (Na2SO4) and concen-
trated to give a crude product. The crude residue was dissolved in
THF (100 mL), TBAF (1.0 M solution in THF, 13.8 mL, 24.12 mmol)
was added, and the reaction mixture was stirred at room temper-
ature. After 4 h it was concentrated and the residue was purified by
flash chromatography (EtOAc/hexanes (1:3)) to yield 17 as a white
Compound 15 (9.30 g, 26.00 mmol) was dissolved in 2,2-di-
methoxypropane (150 mL), PTSA (1.50 g, 0.3 equiv) was added,
and the mixture was rotated on a rotary evaporator at room tem-
perature under reduced pressure for 1 h. The reaction mixture was
quenched by addition of Et3N to pH >9. The reaction mixture was
concentrated under vacuum to give a white solid which was dis-
solved in CHCl3 (200 mL) and washed with water (3 ꢀ 50 mL).
The separated organic layer was dried over Na2SO4, concentrated,
and the residue was purified by column chromatography with
EtOAc/hexanes (1:4) as eluent to afford 14 as a white solid
(7.55 g, 73%). Mp 160–162 °C; ½a D23
ꢁ
= ꢂ83 (c 1.1, CH2Cl2). 1H NMR
(CDCl3) d 7.54–7.37 (10H, m, Ar), 5.54 (2H, s, 2CH–Ph), 4.24 (2H,
dd, J1a,1b = 10.8, J2,1 = 5.3 Hz, H-1), 3.95–3.91 (2H, m, H-6a, H-5),
3.84–3.80 (2H, m, H-3, H-4), 3.74 (2H, t, J1,2 = J2,3 = J5,6b = J6a,6b
= 10.5, H-2, H-6b), 1.42 (6H, s, 2Me). 13C NMR (CDCl3) d 137.5
(CMe2), 129.9–126.2 (m, Ar), 100.7 (CH–Ph), 82.2 (C-3, C-4), 69.4

R. Eskandari et al. / Bioorg. Med. Chem. 18 (2010) 2829–2835
2833
solid (5.67 g, 73%). Mp 65–67 °C; ½a D23
ꢁ
= +22 (c 1, MeOH). 1H NMR
2), 69.2 (C-6), 69.1 (C-5), 69.0 (C-1), 62.3 (C-7), 61.1 (C-3), 55.3
(CDCl3) d 7.49–6.37 (5H, m, Ar), 5.50 (1H, s, CH–Ph), 4.93, 4.73
(2H, 2d, JA,B = 6.4 Hz, CH2OMe), 4.20 (1H, dd, J1a,1b = 10.9,
J1a,2 = 5.5 Hz, H-1a), 3.89–3.79 (4H, m, H-2, H-5, H-6a,b), 3.74
(1H, t, J3,4 = J5,4 = 8.1 Hz, H-4), 3.69–3.65 (2H, m, H-1b, H-3), 3.40
(3H, s, OMe), 2.69 (1H, t, J6,OH = 8.5 Hz, OH), 1.41, 1.38 (6H, 2s,
2Me). 13C NMR (CDCl3) d 137.5 (CMe2), 128.9–101.5 (m, Ar),
100.9 (CH–Ph), 98.6 (CH2–OMe) 85.3 (C-3), 78.2 (C-4), 70.4 (C-5),
69.5 (C-1), 63.1 (C-6), 61.3 (C-2), 56.4 (OMe), 24.7, 24.4 (2Me).
HRMS Calcd for C18H27O7 (M+H): 355.1751. Found: 355.1741.
(OMe), 23.5, 23.4 (2Me). HRMS Calcd for
385.1857. Found: 385.1875.
C19H29O8 (M+H):
3.8. 5,7-O-Benzylidene-3,6-O-isopropylidene-4-O-methoxyme-
thyl- -glycero- -galacto-heptitol (19)
D
D
½
a 2D3
ꢁ
= ꢂ20 (c 0.1, MeOH). 1H NMR (MeOD) d 7.48–7.34 (5H, m,
Ar), 5.51(1H, s, CH–Ph), 4.49, 4.47 (2H, 2d, JA,B = 6.2 Hz, CH2OMe),
4.13 (1H, dd, J7a,7b = 10.7, J6,7b = 5.4 Hz, H-7a), 4.08 (1H, m, H-2),
3.95 (1H, dd, J3,4 = 9.7, J5,4 = 2.8 Hz, H-4), 3.85 (1H, dd,
J1a,1b = 11.4, J2,1a = 3.6 Hz, H-1a), 3.78 (1H, dt, J6,7 = 9.9,
J5,6 = 5.4 Hz, H-6), 3.67–3.60 (4H, m, H-5, H-7b, H-1b, H-3), 3.35
(3H, s, OMe), 1.37, 1.36 (6H, 2s, 2Me). 13C NMR (MeOD) d 137.9
(CMe2), 128.5 -101.3 (m, Ar), 100.6 (CH–Ph), 97.7 (CH2OMe), 86.0
(C-5), 78.2 (C-3), 72.1 (C-4), 71.3 (C-2), 69.1 (C-7), 61.3 (C-1),
61.0 (C-6), 55.6 (OMe), 23.6, 23.4 (2Me). HRMS Calcd for
C19H29O8 (M+H): 385.1857. Found: 385.1865.
3.6. 5,7-O-Benzylidene-1,2-dideoxy-3,6-O-isopropylidene-4-O-
methoxymethyl-D-manno-hep-1-enitol (13)
Compound 17 (2.60 g, 7.34 mmol) was dissolved in CH2Cl2
(50 mL) and NaHCO3 (2.77 g, 33.03 mmol) and Dess–Martin peri-
odinane (3.73 g, 8.81 mmol) were added. The reaction mixture
was stirred for 2 h at room temprature, diluted with ether
(100 mL), and poured into saturated aqueous NaHCO3 (100 mL)
containing a seven fold excess of Na2S2O3. The mixture was stirred
to dissolve the solid, and the ether layer was separated and dried
over Na2SO4. The ether was removed to give the aldehyde that
was further dried under high vacuum for 1 h. Methyltriphenyl-
phosphonium bromide (2.99 g, 8.80 mmol) in dry THF (15 mL),
was cooled to ꢂ78 °C and n-BuLi (n-hexane solution, 14.67 mmol)
was added dropwise under N2. The reaction mixture was stirred at
the same temperature for 1 h, and a solution of the previously
made aldehyde in THF (10 mL) was added. The resulting mixture
was allowed to warm to rt and was stirred overnight. The reaction
was quenched by the addition of acetone (1.5 mL), and the mixture
was extracted with ether (3 ꢀ 100 mL). The combined organic lay-
ers were washed with brine, dried (Na2SO4), and concentrated in
vacuo. Chromatographic purification of the crude product
3.9. 2,5-O-Isopropylidene-4,6,7-tri-O-methoxymethyl-
-manno-heptitol (20)
D-glycero
-D
Compound 18 (580 mg, 1.51 mmol), was dissolved in DMF
(20 mL) and i-Pr2NEt (4.21 mL, 24.16 mmol) and MOMCl (0.9 mL,
12.08 mmol) were added. The reaction mixture was heated at
60 °C for 2 h, then quenched with ice, and extracted with ether
(3 ꢀ 30 mL). The organic solution was dried (Na2SO4) and concen-
trated to give a crude product that was further dried under high
vacuum for 1 h. The crude product was dissolved in MeOH
(50 mL) and the solution was stirred with Pd(OH)2 20 wt % on car-
bon (520 mg) under 100 Psi of H2 for 1 h. The catalyst was removed
by filtration through a bed of Celite, then washed with methanol.
The solvents were removed under reduced pressure and the resi-
due was purified by flash column chromatography (EtOAc/hexanes
(EtOAc/hexanes (1:10)) gave 13 as a foam (1.56 g, 61%). ½a D23
ꢁ
= +4
(c 0.5, CH2Cl2). 1H NMR (CDCl3) d 7.50–7.36 (5H, m, Ar), 6.05 (1H,
ddd, J5,6 = 6.1, J6,7b = 10.5, J6,7a = 16.6 Hz, H-6), 5.51 (1H, s, CH–Ph),
5.39 (1H, ddd, J7b,7a = 17.1, J6,7a = 3.3, J5,7a = 1.5 Hz, H-7a), 5.36
(1H, ddd, J7a,7b = 10.7, J6,7b = 3.1, J5,7b = 1.5 Hz, H-7b), 5.27, 5.26
(2H, 2d, JA,B = 6.25 Hz, CH2OMe), 4.25 (1H, m, H-5), 4.20 (1H, dd,
J1a,1b = 10.8, J1a,2 = 5.4 Hz, H-1a), 3.90 (1H, dt, J2,3 = 5.4,
J2,1 = 9.9 Hz, H-2), 3.68 (2H, m, H-3, H-1b), 3.56 (1H, dd, J3,4 = 8.1,
J4,5 = 9.7 Hz, H-4), 3.33 (3H, s, OMe), 1.40, 1.37 (6H, 2s, 2Me). 13C
NMR (CDCl3) d 137.6 (CMe2), 136.2 (C-6), 128.9–101.3 (m, Ar),
116.8 (C-7), 100.7 (CH–Ph), 97.9 (CH2OMe), 85.5 (C-3), 80.2 (C-4),
71.1 (C-5), 69.6 (C-1), 61.4 (C-2), 56.4 (OMe), 24.8,24.1 (2Me).
HRMS Calcd for C19H26NaO6 (M+Na): 373.1622. Found: 373.1606.
(1.5:1)) to give 20 as a colorless syrup (420 mg, 72%). ½a D23
ꢁ
= +48.0
(c 0.1, MeOH). 1H NMR (MeOD) d4.90–4.63 (6H, m, 3CH2OMe), 4.20
(1H, dd, br, H-6), 3.95 (1H, d, br, J4,5 = 8.6 Hz, H-5), 3.86–380 (2H,
m, H-1a, H-7a), 3.68–3.58 (3H, m, H-2, H-7b, H-1b), 3.45, 3.42,
3.36 (9H, 3s, 3OMe), 3.34 (2H, m, H-4, H-3), 1.35 (6H, s, 2Me).
13C NMR (CDCl3) d 100.7 (CMe2), 98.4, 96.3, 95.5 (3CH2OMe),
83.9 (C-4), 75.0 (C-6), 74.9 (C-3), 71.2 (C-2), 70.5 (C-5), 66.2 (C-
7), 62.5 (C-1), 55.3, 54.5, 54.1 (3OMe), 22.6, 22.4 (2Me). HRMS
Calcd for C16H33O10 (M+H): 385.2068. Found: 385.2083.
3.10. 3,6-O-Isopropylidene-1,2,4-tri-O-methoxymethyl-
cero- -galacto-heptitol (21)
D-gly-
D
3.7. 1,3-O-Benzylidene-2,5-O-isopropylidene-4-O-methoxyme-
thyl-D-glycero-D-manno-heptitol (18)
Compound 21 was obtained as a colorless syrup (285 mg, 75%)
from 19 (380 mg, 1 mmol) using the same procedure that was used
to obtain 20. ½a 2D3
ꢁ
= ꢂ30 (c 0.4, MeOH). 1H NMR (MeOD) d 4.84–4.61
To a solution of 13 (2.00 g, 5.71 mmol) in acetone/water (9:1,
6 mL) at rt were added NMO (N-methylmorpholine-N-oxide)
(735 mg, 6.28 mmol) and OsO4 (40 mg, 2.5 wt % solution in 2-
methyl-2-propanol). The reaction mixture was stirred at rt for
48 h before it was quenched with a saturated solution of NaHSO3.
After being stirred for an additional 15 min the reaction mixture
was extracted with ethyl acetate and the organic layer was washed
with water and brine, dried (Na2SO4), and concentrated in vacuo.
The crude material was purified by column chromatography on sil-
ica gel (MeOH/CH2Cl2 (1:100)) to give 18 (1.27 g, 58%) and 19
(6H, m, 3CH2OMe), 4.08 (1H, ddd, J3,2 = 1.3, J2,1a = 5.6, J2,1b = 7.2 Hz,
H-2), 3.86–3.84 (2H, m, H-7a, H-3), 3.74 (1H, dd, J1a,1b = 9.5,
J1a,2 = 5.6 Hz, H-1a), 3.69 (1H, ddd, J6,5 = 2.9, J6,7b = 6.8, J6,7a = 9.8 Hz,
H-6), 3.60–3.55 (2H, m, H-1b, H-7b), 3.45(1H, m, H-5), 3.44, 3.38,
3.35 (9H, 3s, 3OMe), 3.34 (1H, m, H-4), 1.36, 1.32 (6H, 2s, 2Me). 13C
NMR (CDCl3) d 100.1 (CMe2), 97.8, 96.8, 95.9 (3CH2OMe), 83.3 (C-
5), 75.1 (C-2), 73.8 (C-4), 70.3 (C-6), 67.8 (C-3), 65.9 (C-1), 61.8 (C-
7), 54.3, 54.1, 53.7 (3OMe), 22.9, 22.8 (2Me). HRMS Calcd for
C16H33O10 (M+H): 385.2068. Found: 385.2067.
(0.48 g, 22%) as foams. ½a D23
ꢁ
= +5.8 (c 4.6, MeOH). 1H NMR (MeOD)
3.11. 2,5-O-Isopropylidene-4,6,7-tri-O-methoxymethyl-
cero- -manno-heptitol-1,3-cyclic sulfate (12)
D-gly-
d 7.49–7.36 (5H, m, Ar), 5.54 (1H, s, CH–Ph), 4.82 (1H, s, CH2OMe),
4.13 (1H, dd, br, H-1a), 4.00 (1H, br, q, H-6), 3.87–3.77 (3H, m, H-4,
H-5, H-2), 3.68–3.55 (4H, H-1b, H-3, H-7a, H-7b), 3.32 (3H, s, OMe),
1.39, 1.34 (6H, 2s, 2Me). 13C NMR (MeOD) d 138.0 (CMe2), 128.4–
101.1 (m, Ar), 100.8 (CH–Ph), 97.7 (CH2OMe), 85.3 (C-4), 77.1 (C-
D
A mixture of 20 (400 mg, 1.04 mmol) and Et3N (0.57 mL,
4.16 mmol) in CH2Cl2 (10 mL) was stirred in an ice bath. Thionyl
chloride (0.12 mL, 1.56 mmol) in CH2Cl2 (2 mL) was then added

2834
R. Eskandari et al. / Bioorg. Med. Chem. 18 (2010) 2829–2835
dropwise over 15 min, and the mixture was stirred for an addi-
tional 30 min. The mixture was poured into ice-cold water and ex-
tracted with CH2Cl2 (3 ꢀ 30 mL). The combined organic layers were
washed with brine and dried over Na2SO4. The solvent was re-
moved under reduced pressure and the residue was dried under
high vacuum for 1 h. The diasteromeric mixture of cyclic sulfites
was dissolved in a mixture of CH3CN/CCl4 (1:1, 25 mL) and sodium
periodate (333 mg, 1.56 mmol) and RuCl3 (10 mg) were added, fol-
lowed by water (2 mL). The reaction mixture was stirred for 2 h at
rt, then filtered through a bed of Celite, and washed with ethyl ace-
tate. The volatile solvents were removed, and the aqueous solution
was extracted with EtOAc (2 ꢀ 30 mL). The combined organic lay-
ers were washed with brine, dried over Na2SO4, concentrated un-
der reduced pressure, and the residue purified by flash column
chromatography (EtOAc/hexanes (1:2)) to give 12 as a colorless
96.5, 95.2 (3CH2OMe), 83.5 (C-3), 81.2 (C-2), 79.7 (C-20), 78.6 (C-
40), 74.0 (C-60), 72.7, 71.6, 71.4 (3CH2Ph), 71.3 (C-50), 66.9 (C-70),
66.6 (C-30), 66.5 (C-5), 65.1 (C-4), 55.9–54.2 (6OMe), 51.5 (C-10),
47.4 (C-1), 24.4, 23.5 (2Me). HRMS Calcd for C45H65O18S2 (M+H):
957.3607. Found: 957.3604.
3.14. 1,4-Dideoxy-1,4-[[2S,3S,4R,5R,6R-2,4,5,6,7-pentahydroxy-
3-(sulfooxy)heptyl]-(R)-epi-sulfoniumylidine]-D-arabinitol
inner salt (6)
The protected sulfonium salt 23 (150 mg, 0.16 mmol) was dis-
solved in 30% aqueous solution of TFA (25 mL) and the mixture
was stirred at 50 °C for 5 h. The solvent was removed under re-
duced pressure and the residue was dissolved in water (5 mL)
and washed with CH2Cl2 (3 ꢀ 5 mL). The water layer was evapo-
rated to give the crude product that was purified on silica gel with
EtOAc/MeOH/H2O 6:3:1 (v/v) as eluent to give compound 6 as a
syrup (325 mg, 70%). ½a D23
ꢁ
= +1.2 (c 0.85, CH2Cl2). 1H NMR (CDCl3)
d 4.77–4.65 (6H, m, 3CH2OMe), 4.62 (1H, t, J2,3 = J4,3 = 9.1 Hz, H-
3), 4.54 (1H, t, J1a,1b = J2,1a = 11.1 Hz, H-1a), 4.37 (1H, dd,
J2,1a = 5.4, J1a,1b = 11.1 Hz, H-1b), 4.16 (2H, m, H-2, H-6), 3.98 (1H,
d, J4,5 = 9.8 Hz, H-5), 3.80 (1H, dd, J6,7a = 4.8, J7a,7b = 10.8 Hz, H-7a),
3.75 (1H, t, J3,4 = J4,5 = 8.6 Hz, H-4), 3.64 (1H, t, J7a,7b = J6,7b = 8.9 Hz,
H-7b), 3.44, 3.41, 3.39 (9H, 3s, 3OMe), 1.38, 1.36 (6H, 2s, 2Me). 13C
NMR (CDCl3) d 102.3 (CMe2), 97.9, 96.7, 96.1 (3CH2OMe), 89.2 (C-
3), 76.9 (C-4), 74.6 (C-6), 72.2 (C-1), 71.0 (C-5), 66.8 (C-5), 66.8
(C-7), 56.5 (C-2), 56.6, 55.7, 55.3 (3OMe), 24.4, 23.9 (2Me). HRMS
Calcd for C16H31O12S (M+H): 447.1531. Found: 447.1516.
colorless solid (61 mg, 93%). Mp 82–84 °C ½a D23
ꢁ
= +5.5 (c 0.55,
CH2Cl2). 1H NMR (D2O) d 4.67 (1H, dd, J1a,2 = 3.7, J1b,2 = 7.4 Hz, H-
2), 4.56 (1H, d, J2 ,3 = 8.2 Hz, H-30), 4.39 (1H, t, J2,3 = J3,4 = 3.1 Hz,
0
0
H-3), 4.35 (1H, dt, J2 ,3 = 3.3, J2 ,1 = 7.8 Hz, H-20), 4.02 (3H, m, H-
0
0
0
0
5a, H-10a, H-4), 3.91–3.83 (5H, m, H-60, H-50, H-5b, H-40, H-10b),
0
0
3.81 (2H, d, J1,2 = 3.9 Hz, H-1a,b), 3.71 (1H, dd, J7 a,7 b = 3.2,
J7 b,6 = 11.9 Hz, H-70b), 3.62 (1H, dd, J7 b,7 a = 7.8, J7 a,6 = 11.6 Hz,
0
0
0
0
0
0
13
H-70a). C NMR (D2O) d 78.3 (C-30), 77.7 (C-3), 76.7 (C-2), 72.9
(C-60), 70.7 (C-50), 70.0 (C-4), 69.1 (C-40), 66.0 (C-20), 61.6 (C-70),
59.2 (C-5), 50.7 (C-10), 47.7 (C-1). HRMS Calcd for C12H25O12S2
(M+H): 425.0782. Found: 425.0778.
3.12. 3,6-O-Isopropylidene-1,2,4-tri-O-methoxymethyl-
D-
glycero- -galacto-heptitol-5,7-cyclic sulfate (22)
D
3.15. 1,4-Dideoxy-1,4-[[2S,3S,4R,5R,6S-2,4,5,6,7-pentahydroxy-
Compound 22 was obtained as a colorless syrup (220 mg, 76%)
from 21 (250 mg, 0.65 mmol) using the same procedure that was
3-(sulfooxy)heptyl]-(R-)epi-sulfoniumylidine]-D-arabinitol
inner salt (4)
used to obtain 12. ½a D23
ꢁ
= ꢂ32 (c 0.46, CH2Cl2). 1H NMR (CDCl3) d
4.83–4.63 (6H, m, 3CH2OMe), 4.70 (1H, m, H-5), 4.55 (1H, t, J7a,7b = -
J6,7a = 11.1 Hz, H-7a), 4.39 (1H, dd, J6,7a = 4.9, J7a,7b = 10.7 Hz, H-7b),
4.24 (1H, td, J5,6 = 5.7, J6,7 = 10.5 Hz, H-6), 4.09 (1H, ddd, J1a,2 = 6.9,
J1b,2 = 5.3, J3,2 = 1.4 Hz, H-2), 3.97 (1H, dd, J4,3 = 10.0, J3,2 = 1.5 Hz,
H-3), 3.89 (1H, dd, J3,4 = 10.0, J5,4 = 7.7 Hz, H-4), 3.80 (1H, dd,
J2,1a = 5.4, J1a,1b = 9.8 Hz, H-1a), 3.58 (1H, t, J1a,1b = J2,1b = 9.2 Hz, H-
1b), 3.45, 3.41, 3.39 (9H, 3s, 3OMe), 1.43, 1.37 (6H, 2s, 2Me). 13C
NMR (CDCl3) d 102.32 (CMe2), 98.1, 98.0, 97.9 (3CH2OMe), 89.6 (C-
5), 76.6 (C-4), 75.1(C-2), 72.0 (C-7), 68.9 (C-3), 66.2 (C-1), 59.5 (C-
6), 56.4, 56.0, 55.7 (3OMe), 24.8, 23.8 (2Me). HRMS Calcd for
C16H30NaO12S (M+Na): 470.1383. Found: 470.1399.
A mixture of the thiosugar 7 (100 mg, 0.224 mmol) and the cyc-
lic sulfate 22 (137 mg, 0.269 mmol) in HFIP (1 mL) containing
K2CO3 (5 mg) was placed in a sealed reaction vessel and heated
at 72 °C with stirring for six days. The progress of the reaction
was followed by TLC analysis (developing solvent EtOAc/MeOH,
10:1). The mixture was cooled, then diluted with EtOAc and evap-
orated to give a syrupy residue. Purification by column chromatog-
raphy (EtOAc/MeOH 95:5) gave the protected sulfonium salt as a
foam (120 mg, 57%). The protected sulfonium salt 24 (100 mg,
0.11 mmol) was dissolved in 30% aqueous TFA (10 mL) and stirred
at 50 °C for 5 h. The solvents were removed under reduced pres-
sure and the residue was dissolved in water (5 mL) and washed
with CH2Cl2 (3 ꢀ 5 mL). The water layer was evaporated to give
the crude product that was purified on silica gel column with
EtOAc/MeOH/H2O 6:3:1 (v/v) as eluent to give compound 4 as a
colorless solid (40 mg, 91%).12
3.13. 2,3,5-Tri-O-p-methoxybenzyl-1,4-dideoxy-1,4-[[2S,3S,4R,
5R,6R]-2,5-isopropylidene-4,6,7-tri-O-methoxymethyl-3-(sul-
fooxy)heptyl]-(R)-epi-sulfoniumylidine-D-arabinitol inner salt
(23)
The cyclic sulfate 12 (260 mg, 0.58 mmol) and the thiosugar 7
(360 mg, 0.70 mmol) were dissolved in HFIP (1.5 mL), containing
anhydrous K2CO3 (10 mg). The mixture was stirred in a sealed reac-
tionvesselinanoil bathat 72 °Cforsixdays. Theprogressof thereac-
tion was followed by TLC analysis (developing solvent EtOAc/MeOH,
10:1). The mixture was cooled, then diluted with EtOAc and evapo-
rated to give a syrupy residue. Purification by column chromatogra-
phy (EtOAc/MeOH 99:1) gave the sulfonium salt 23 as a syrup
Acknowledgments
We are grateful to the Canadian Institutes for Health Research
(FRN79400) and the Heart and Stroke Foundation of Ontario (NA-
6305) for financial support.
Supplementary data
(360 mg, 65%). ½a D23
ꢁ
= +62 (c 0.85, CH2Cl2). 1H NMR (acetone-d6) d
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2010.03.027.
7.32–6.91(12H, m, Ar), 5.12–4.52 (12H, m, 3CH2OMe, 3CH2–Ph),
4.69 (1H, m, H-2), 4.55 (1H, m, H-3), 4.39–4.30 (4H, m, H-10a, H-20,
H-30, H-60), 4.08 (1-H, t, J3,4 = J5,4 = 7.4 Hz, H-4), 4.02–3.90 (4H, m,
H-1a, H-10b, H-50), 3.85–3.78 (3H, m, H-5a, H-70a, H-1b), 3.82 (9H,
References and notes
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13C NMR (acetone-d6) d 159.8–129 (m, Ar), 101.6 (CMe2), 98.7,
0
0
0
0
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