Action of acid on 6-thio-hexose derivatives. Synthesis of 1,6-epithio-hexofuranoses

Article abstract of DOI:10.1016/S0008-6215(00)00028-8

Reaction of 5,6-anhydro-1,2-O-isopropylidene-3-O-methanesulfonyl-β-L-idofuranose with thioacetic acid in pyridine gave 6-S-acetyl-1,2-O-isopropylidene-3-O-methanesulfonyl-6-thio-β-L-idofuranose, which was deacetylated and the resultant thiol was converted

Full text of DOI:10.1016/S0008-6215(00)00028-8

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Carbohydrate Research 326 (2000) 81–87
Action of acid on 6-thio-hexose derivatives. Synthesis of
1,6-epithio-hexofuranoses
Neil A. Hughes * , Nigel D. Todhunter
Department of Chemistry, Uni6ersity of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, UK
Received 14 October 1999; accepted 3 January 2000
Abstract
Reaction of 5,6-anhydro-1,2-O-isopropylidene-3-O-methanesulfonyl-b-
pyridine gave 6-S-acetyl-1,2-O-isopropylidene-3-O-methanesulfonyl-6-thio-b-
and the resultant thiol was converted into 1,2-O:5,6-O,S-diisopropylidene-3-O-methanesulfonyl-b-
Alkaline cleavage of the mesyl group gave 1,2-O: 5,6-O,S-diisopropylidene-b- -idofuranose, which on treatment with
hot dilute hydrochloric acid gave, after acetylation, 2,3,5-tri-O-acetyl-1,6-dideoxy-1,6-epithio-a- -idofuranose and
not the expected idopyranose isomer. 1,2:3,5-Di-O-isopropylidene-6-O-toluene-p-sulfonyl-a- -glucofuranose was
converted into 6-S-acetyl-1,2:3,5-di-O-isopropylidene-6-thio-a- -glucofuranose; conversion into the 6-thiol and
isomerisation in acidified acetone gave 1,2-O:5,6-O,S-diisopropylidene-6-thio-a- -glucofuranose. Acid treatment of
this diacetal, or the isomeric 1,2:3,5-di-O-isopropylidene-6-thio-a- -glucofuranose, followed by acetylation gave
2,3,5-tri-O-acetyl-1,6-dideoxy-1,6-epithio-b- -glucofuranose. Similar treatment of 1,2:3,4-di-O-isopropylidene-6-thio-
a- -galactopyranose gave 2,3,5-tri-O-acetyl-1,6-dideoxy-1,6-epithio-a- -galactofuranose. © 2000 Elsevier Science
Ltd. All rights reserved.
L
-idofuranose with thioacetic acid in
-idofuranose, which was deacetylated
-idofuranose.
L
L
L
L
D
D
D
D
D
D
D
Keywords: Anhydro sugars; Epithio sugars; Furanose–pyranose equilibria; 6-Thio-D-galactose derivatives; 6-Thio-D-glucose
derivatives; 6-Thio-L-idose derivatives; Thio sugars
1. Introduction
sugar and 1,6-anhydro-idose [2]. Owen and
co-workers had shown [3] earlier that the cor-
In an earlier paper [1] we reported that
aqueous acid hydrolysis of 1,2-O:5,6-S,O-di-
responding 1,6-dideoxy-1,6-epithio-5-thio-b-
idopyranose (6) was obtained by the action of
acid on 1,2-O-isopropylidene-5,6-dithio-b-
idofuranose. We therefore synthesised 1,2-
O:5,6-O,S-diisopropylidene-6-thio-b- -idofur-
L-
isopropylidene-5-thio-b-
1,6-anhydro-5-thio-b-
dition to 5-thio- -idose (3); both products
were isolated as their acetates 4 and 5, respec-
tively. The formation of the anhydro com-
pound 2 was not unexpected, for idose itself
exists in acid solution as a mixture of the free
L
-idofuranose (1) gave
L
-
L
-idopyranose (2) in ad-
L
L
anose (7) in the expectation that acid treat-
ment would yield the 1,6-epithio compound 8
in good yield. Models suggested that the
larger CꢀS bonds would facilitate the forma-
tion of the 1,6-linked system and such a sys-
tem is readily formed by cyclisation in a
hexopyranose bearing a thiol group at C-1 (or
C-6) and a leaving group at C-6 (or C-1) [4]
(Scheme 1).
* Corresponding author. Tel.: +44-191-2227074; fax: +
44-191-2226929.
E-mail address: n.a.hughes@ncl.ac.uk (N.A. Hughes)
0008-6215/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(00)00028-8

82
N.A. Hughes, N.D. Todhunter / Carbohydrate Research 326 (2000) 81–87
tion is talose, where approximately equal
amounts of furanose and pyranose forms are
present, albeit in a low overall yield [9]. For
idose the amount of 1,6-anhydro furanose is
very low (0.08%) compared with the pyranose
form (95%) [7].
The reasons for this unexpected behaviour
are not clear. Both 8 and 17 have similar
bicyclic systems, a five-membered ring cis-
fused to a six-membered ring. Models and the
ease of formation of 1,6-anhydro-5-thio-pyran-
oses referred to earlier suggest that 8 should
be preferred over 17. Energy calculations
(Chem 3D Pro Version 5.0) also indicate the
same preference: 8, 16.903 kcal/mol; 17,
21.547 kcal/mol.
The lack of formation of 8 is in further
contrast to the behaviour of 6-amino-6-deoxy-
L-idose, which undergoes almost quantitative
Scheme 1.
dehydration, albeit in alkaline solution, to
give the epimino pyranose 18 [10]. 1,6-Epithio
furanose derivatives have been described pre-
viously, but in these cases formation of a
pyranose compound was not possible because
C-5 was blocked either by a deoxy function as
in 19 [11] or by a methoxy group as in 20 [12].
Related experiments have been carried out
2. Results and discussion
Treatment of the epoxide 9 [5] with
thioacetic acid in pyridine gave the thioacetate
10. This was deacetylated to the thiol 11,
which was immediately converted into the di-
acetal 12 by the action of 2,2-dimethoxy-
propane in acidified acetone. The mesylate
ester of 12 was cleaved in refluxing methanolic
sodium methoxide to give the required diac-
etal 7. When 7 was heated in dilute hydrochlo-
ric acid and the products acetylated, a single
crystalline product was isolated in good yield,
the elemental analysis of which confirmed the
expected molecular formula for 13, the triac-
etate of 8. However, the coupling constants in
on 6-thio-
D
-glucose and 6-thio- -galactose
D
derivatives with similar results. Treatment of
the tosylate 21 [13] with potassium thioacetate
gave the thioacetate 22, which was deacetyl-
ated and the resultant thiol 23 was left in
1
the H NMR spectrum of the product bore
little resemblance to those of the anhydro
pyranoses 4 and 14 [6] (see Tables 1 and 2),
but did show close agreement with those of
the 1,6-anhydro-a-
(15) [7]. Thus, the product was 2,3,5-tri-O-
-idofuranose
L
-idofuranose triacetate
acetyl-1,6-dideoxy-1,6-epithio-a-
L
(16) and not the expected epithio pyranose 13
(Scheme 2).
The isolation of the triacetate 16 indicated
that the major product of the action of acid
on 7 was the triol 17. This was in sharp
contrast to the action of acids on hexoses,
which leads to varying amounts of 1,6-anhy-
dro compounds, but the furanose forms are
normally only minor products [8]. The excep-
Scheme 2.

N.A. Hughes, N.D. Todhunter / Carbohydrate Research 326 (2000) 81–87
83
Table 1
1H NMR data: chemical shifts (ppm)
Compound H-1 H-2 H-3 H-4 H-5 H-6a
H-6b
Other signals
10
5.99 4.91 5.11 4.22 4.03 3.26
5.88 4.71 4.99 4.37 4.45 3.07
5.84 4.26 4.01 4.10 4.28 3.08
5.47 4.94 5.33 5.20 3.77 4.77
5.45 4.74 5.16 4.95 4.71 4.05
5.12 5.42 5.15 4.90 5.15 4.10
4.94 5.65 5.27 4.70 5.24 3.46
5.99 4.65 4.21 4.25 3.63 3.37
5.97 4.55 4.35 4.17 4.50 3.35
5.37 4.64 4.90 4.55 4.69 3.13
4.97 4.33 4.23 4.34 3.71 4.11endo 3.69exo
5.01 5.62 5.36 4.65 4.81 3.60
5.57 5.25 5.32 4.22 5.05 2.93
5.20 4.12 4.14 4.08 3.92 3.92exo 3.44endo
5.44 4.82 5.11 5.15 4.75 3.34
2.96
2.72
2.84
3.91
3.70
3.92
2.85
3.00
3.15
3.02
3.25 (MeSO2); 2.62 (OH); 2.37 (SAc); 1.51; 1.33 (CMe2)
2.11 (MeSO2); 1.58, 1.50, 1.31, 1.02 (2×CMe2)
2.82 (OH); 1.57, 1.48, 1.39, 1.12 (2×CMe2)
2.07(2), 2.02 (3×Ac)
2.01(2), 1.97 (3×Ac)
2.12(2), 1.99 (3×Ac)
12 a
7 a
4 b
14 c
15 d
16
2.14, 2.12, 2.00 (3×Ac)
22
2.35 (SAc); 1.49, 1.35, 1.33, 1.32 (2×CMe2)
2.73 (OH); 1.68, 1.63, 1.51, 1.33 (2×CMe2)
2.10, 2.09, 1.95 (3×Ac)
24
25 e
26 f
27
2.80
2.82
2.14, 2.07. 1.99 (3×Ac)
2.16, 2.11, 2.10 (3×Ac)
30
31 f
32 e
3.04
2.10, 2.09, 2.03 (3×Ac)
a In C6D6.
b Ref. [1].
c Ref. [6].
d Ref. [7].
e Ref. [14].
f Ref. [15]; in D2O.
Table 2
1H NMR data: coupling constants (Hz)
Compound
J1,2
J2,3
J3,4
J4,5
J5,6a
J5,6b
J6a,6b
10
3.7
3.8
3.6
0.5
1.8
0
0
0
0
8.1
8.4
2.0
2.5
0
3.0
3.2
2.6
8.5
8.8
6.0
6.4
3.8
2.6
4.7
7.0
7.4
0
7.0
7.0
4.8
3.3
4.1
3.5
2.7
6.8
7.0
2.0
1.0
2.5
3.9
4.2
4.9
3.1
5.1
9.8
0
8.5
9.5
5.3
8.3
5.2
6.2
5.4
8.4
8.0
6.5
0
14.0
10.3
10.4
9.3
3.5 (J5,OH
)
)
12 a
7 a
4 b
1.5 (J1,5
)
14 c
15 d
16
0.7
10.0
11.2
4.3
5.4
1.0
3.0
3.3
11.1
6.6
0.8
8.4
11.0
12.8
13.7
10.9
10.0
13.5
14.9
13.0
11.3
10.0
1.0 (J4,6b
)
0
22
3.7
2.6
0.9
0
24
0
3.1 (J3,OH
25 e
26 f
27
3.5
2.0
2.3
2.4
2.4
1.5
0
2.0
6.0
11.1
7.2
0.5 (J1,6b); 0.5 (J4,6b
1.4 (J1,6b); 0.9 (J2,4); 1.5 (J4,6b
1.5 (J4,6a
1.4 (J1,3); 1.4 (J3,5
)
30
6.4
4.1
1.6
)
31 f
32 e
0
4.9
)
)
a In C6D6.
b Ref. [1].
c Ref. [6].
d Ref. [7].
e Ref. [14].
f Ref. [15]; in D2O.
of 1,2:5,6-di-O-isopropylidene-a- -glucofuran-
D
acidified acetone when it was isomerised into
1
ose. When 24 was heated in dilute hydrochlo-
ric acid followed by acetylation as for the
ido-isomer 7, it gave a single tri-acetate
the 1,2:5,6-diacetal 24. The H NMR spec-
trum of 24 showed the presence of a hydroxy
group and coupling constants similar to those

84
N.A. Hughes, N.D. Todhunter / Carbohydrate Research 326 (2000) 81–87
Scheme 3.
Scheme 4.
1
whose H NMR spectrum showed coupling
constants (see Table 2) that differed from
those of 2,3,4-tri-O-acetyl-1,6-dideoxy-1,6-epi-
spectrum with those of the anhydro furanose
31 [15] and the epithio pyranose 32 [14]. In
particular, the 1H NMR spectrum of 30
showed small W-couplings for all the equato-
rial hydrogens (H-1, H-4, H-6 exo) of the
1,3-oxathiane ring (Scheme 4).
thio-b-
D
-glucopyranose (25) [14], but closely
resembled those of 1,6-anhydro-b-
D-gluco-
furanose (26) [15], thus identifying the product
as the epithio furanose 27. The same product
27 was obtained when 23 was heated in acid
followed by acetylation (Scheme 3).
The similarity of the 13C NMR chemical
shifts (Table 3) for the three epithio furanose
triacetates 16, 27, and 30 provides further
evidence for their having the same bicyclic
ring system. In the foregoing experiments only
small quantities of the pentaacetates of the
6-thio-hexoses were detected. This was proba-
bly due to the vigour of the hydrolysis condi-
Deacetylation of the galactose thioacetate
28 [12] and treatment of the resultant thiol 29
as described for 23 also gave a single product,
which was similarly identified as the epithio
1
furanose 30 from comparisons of its H NMR

N.A. Hughes, N.D. Todhunter / Carbohydrate Research 326 (2000) 81–87
85
Table 3
Acetylation of 10 was carried out in the
usual way with Ac2O and pyridine and gave
5-O-acetyl-6-S-acetyl-1,2-O-isopropylidene-3-
13C NMR data: chemical shifts (ppm) a
Compound
C-1
C-2, C-3, C-4
C-5
C-6
O-methanesulfonyl-6-thio-b- -idofuranose,
L
mp 120–121 °C (from EtOH), [h]−51° (c
1.0). Anal. Calcd for C14H22O9S2: C, 42.20; H,
5.57. Found: C, 42.36; H, 5.59.
16
27
30
84.6
84.5
83.1
83.0, 78.8, 75.5
82.7, 77.5, 76.8
80.0, 79.9, 77.1
67.4
62.6
65.9
25.3
25.25
26.2
1,2 - O:5,6 - O,S - Diisopropylidene - 3 - O-
a In addition all spectra showed signals in regions: 169.5–
170.5 (COCH3) and 20.5–21.1 (COCH3).
methanesulfonyl - 6 - thio - i -
L
- idofuranose
(12). —The thioacetate 10 (1.50 g, 4.21 mmol)
was dissolved in methanolic NaOMe [from Na
(0.43 g) in MeOH (17 mL)] containing NaBH4
(0.13 g).
tions, which were chosen to maximise the
formation of anhydro/epithio compounds.
Use of milder conditions, namely hot
aqueous acetic acid [1], led only to free sugars
and no anhydro or epithio compounds were
detected.
After stirring at rt for 45 min, the mixture
was neutralised (CO2) and evaporated to dry-
ness. The residue was partitioned between
CH2Cl2 and H2O, the organic extract was
dried and concentrated and the resulting crude
thiol 11 was dissolved in Me2CO (10 mL) and
2,2-dimethoxypropane (2 mL) containing
toluene-p-sulfonic acid (0.12 g). After 1 h at rt
the mixture was neutralised (Na2CO3), filtered,
evaporated and partitioned between CH2Cl2
and H2O. The organic extract was dried,
filtered and evaporated to give the diacetal 12
(1.22 g, 3.45 mmol, 82%), mp 125–127 °C
(from EtOH), [h]D −72° (c 1.0). Anal. Calcd
for C13H22O7S2: C, 44.02; H, 6.26. Found: C,
44.12; H, 6.25.
3. Experimental
General methods.—Melting points are un-
corrected. Optical rotations were measured at
22 °C for solutions in CHCl3. NMR spectra
were recorded at 90 or 300 MHz (1H) or 75
MHz (13C) for solutions in CDCl3 unless oth-
erwise stated. The petroleum ether (PE) used
had the boiling range 60–80 °C. Kieselgel 60
was used for thin-layer chromatography
(TLC) (E. Merck, 5554) and column chro-
matography (E. Merck, 70–230 mesh ASTM).
Compounds were visualised on TLC plates
with 2% H2SO4 in EtOH and heating to
100 °C. Solutions in Et2O or CH2Cl2 were
dried with MgSO4.
1,2-O:5,6-O,S-Diisopropylidene-6-thio-i- -
L
idofuranose (7).—A solution of 12 (0.50 g,
1.41 mmol) in methanolic NaOMe [from Na
(0.17 g) in MeOH (6.5 mL)] was heated under
reflux for 5 h. The solution was neutralised
(CO2) and concentrated to half volume after
the addition of H2O (6.5 mL). The remaining
solution was extracted with CH2Cl2, which
after drying and evaporation gave the diacetal
7 (0.28 g, 1.02 mmol, 72%), mp 124–125°C
(from ether–PE), [h]D−67° (c 1.0). Anal.
Calcd for C12H20O5S: C, 52.16; H, 7.30.
Found: C, 52.22; H, 7.16.
6 - S - Acetyl - 1,2 - O - isopropylidene - 3 - O-
methanesulfonyl - 6 - thio - i -
L
- idofuranose
(10).—Thioacetic acid (0.30 mL, 0.32 g, 4.20
mmol) was added to a solution of 5,6-anhy-
dro-1,2-O-isopropylidene-3-O-methanesul-
fonyl-b- -idofuranose (9) [12] (0.73 g, 2.60
L
mmol) in pyridine (1.5 mL). After 1 h at room
temperature (rt), the mixture was partitioned
between water and CH2Cl2. The organic layer
was washed with 2 M H2SO4 (×2), 1 M
KHCO3, dried and concentrated. The residue
was chromatographed on a short silica
column and eluted with 1:1 EtOAc–PE to
give the thioacetate 10 (0.69g, 1.94 mmol,
75%), mp 88–89 °C (from EtOH), [h]D −45°
(c 1.0), Anal. Calcd for C12H20O8S2: C, 40.44;
H, 5.66. Found: C, 40.41; H, 5.61.
2,3,4-Tri-O-acetyl-1,6-dideoxy-1,6-epithio-
h- -idofuranose (16).—A mixture of the diac-
L
etal 7 (0.38 g, 1.38 mmol) and 1 M HCl (11
mL) was stirred and heated under reflux for
20 min. The solution was neutralised (PbCO3),
filtered and concentrated to dryness. The
residue was acetylated in the usual way with
Ac2O (2 mL) and pyridine (2 mL) to give a
product that was further purified by chro-

86
N.A. Hughes, N.D. Todhunter / Carbohydrate Research 326 (2000) 81–87
NaOMe [from sodium (40 mg)] at rt. After 5
min AcOH (1.5 mL) was added and the solu-
tion was evaporated to dryness. Acetic acid
(1.0 mL) and 1 M HCl (1.5 mL) were added
to the residual thiol 23 and the mixture was
heated with stirring under reflux for 5 min
when more 1 M HCl (4.5 mL) was added and
heating continued for 90 min. NaOAc (0.70g)
was added and the mixture was evaporated to
dryness. More NaOAc (0.30 g) and Ac2O (3.0
mL) were then added and the mixture was
stirred at 100 °C for 30 min. Water (10.0 mL)
was added and, after 30 min, the mixture was
extracted with CH2Cl2 (2×5 mL), the extract
was washed (dilute KHCO3), dried and evapo-
rated to yield a syrup which was purified by
chromatography on silica, eluting with 2:1
PE–EtOAc to give 27 (66 mg, 0.22 mmol,
36%).
matography on silica, eluting with 1:2 Et2O–
PE to give 16 (0.23 g, 0.76 mmol, 55%) mp
78–80 °C (from EtOH), [h]D −33° (c 0.8).
Anal. Calcd for C12H16O7S: C, 47.36; H, 5.30.
Found: C, 47.41; H, 5.20.
6-S-Acetyl-1,2:3,5-di-O-isopropylidene-6-
thio-h- -glucofuranose (22).—A mixture of
D
the tosylate 21 [11] (1.00 g, 2.42 mmol) and
KSAc (0.48 g, 4.21 mmol) in DMF (10 mL)
was heated at 90 °C for 30 min. The mixture
was partitioned between Et2O and H2O, the
Et2O layer was washed with 1 M KHCO3
(×2), dried and concentrated. The residue
was crystallised from EtOH to give the thioac-
etate 22 (0.58 g, 1.84 mmol, 76%), mp 73–
74 °C, [h]D +44° (c 1.0). Anal. Calcd for
C14H22O6S: C, 52.81; H, 6.97. Found: C,
53.00; H, 6.92.
1,2-O:5,6-O,S-Diisopropylidene-6-thio-h- -
D
2,3,5-Tri-O-acetyl-1,6-dideoxy-1,6-epithio-
glucofuranose (24).—A mixture of the thioac-
etate 22 (0.36 g, 1.13 mmol), NaBH4 (30 mg)
in methanolic NaOMe [from Na (0.12 g) in
MeOH (3.5 mL)] was stirred at rt for 45 min.
The mixture was neutralised (CO2), evapo-
rated to dryness and the residue was parti-
tioned between CH2Cl2 and H2O. The organic
layer was dried and evaporated to give the
crude thiol 23, which was dissolved in Me2CO
(2 mL) containing toluene-p-sulfonic acid (20
mg). After 1 h at rt, 1 M KHCO3 was added
and the mixture was extracted with CH2Cl2.
The extract was dried and concentrated to
h- -galactofuranose (30).—The thioacetate 28
D
(0.17 g, 0.53 mmol) was treated as described
for the gluco-thioacetate 22 in the previous
experiment to give the title compound 30 (50
mg, 0.165 mmol, 31%), mp 99–100 °C (from
PE), [h]D +234° (c 1.0). Anal. Calcd for
C12H16O7S: C, 47.36; H, 5.30. Found: C,
47.04; H, 5.04.
Acknowledgements
give
a
crude product that was chro-
We thank the SRC for financial support (to
N.D.T.), L. Cook and M.N.S. Hill for the
NMR data, D. Dunbar for the elemental
analyses, S. Addison for the MS data and S.
Jones for the energy calculations.
matographed on silica, eluting with 1:4 Et2O–
PE to give the pure diacetal 24 (0.15 g, 0.54
mmol, 48%), mp 66–67 °C (from PE), [h]D+
18° (c 1.0). Anal. Calcd for C12H20O5S: C,
52.16; H, 7.30. Found: C, 52.33; H, 7.20.
2,3,5-Tri-O-acetyl-1,6-dideoxy-1,6-epithio-
i- -glucofuranose (27).—(a) From 24. The
D
References
diacetal 24 (0.17 g, 0.62 mmol) was heated in
1 M HCl (4.5 mL) as described earlier for
diacetal 7. Work-up as before and acetylation
with Ac2O (1 mL) and pyridine (1 mL) gave,
as the major product after chromatography,
the furanose 27 (23 mg, 0.08 mmol, 12%),
[h]D−90° (c 1.0); m/z 304.0610 (C12H16O7S
Calcd: 304.0617).
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