Synthesis of thio- and selenoglycosides by cleavage of dichalconides in the presence of zinc/zinc chloride and reaction with glycosyl bromides

Article abstract of DOI:10.1016/j.tetlet.2005.11.074

A convenient odorless methodology has been devised for the preparation of 1,2-trans-thio- and selenoglycosides through zinc-mediated cleavage of disulfides and diselenides and reaction of the thiolate and selenides formed in situ with glycosyl bromides. T

Full text of DOI:10.1016/j.tetlet.2005.11.074

Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 441–445
Synthesis of thio- and selenoglycosides by cleavage of
dichalconides in the presence of zinc/zinc chloride and reaction
with glycosyl bromidesI
Chinmoy Mukherjee, Pallavi Tiwari and Anup Kumar Misra*
Medicinal and Process Chemistry Division, Central Drug Research Institute, Chattar Manzil Palace, Lucknow 226001, UP, India
Received 12 September 2005; revised 9 November 2005; accepted 16 November 2005
Available online 1 December 2005
Abstract—A convenient odorless methodology has been devised for the preparation of 1,2-trans-thio- and selenoglycosides through
zinc-mediated cleavage of disulfides and diselenides and reaction of the thiolate and selenides formed in situ with glycosyl bromides.
The yields were excellent in all cases.
Ó 2005 Elsevier Ltd. All rights reserved.
In the last decade, thiosugars have widely been used in
biochemical and structural investigations of glycosi-
dases due to their close structural similarity to the natu-
ral O-glycosides.1–5 Thioglycosides have found versatile
applications in the field of carbohydrate chemistry as
very effective and stable glycosyl donors.6–9 They are also
useful intermediates for the preparation of glycosyl fluo-
rides,10 sulfoxides and sulfones, which are used as glyco-
syl donors for O- and C-glycosylation.11–14 The ongoing
progress in the syntheses of complex oligosaccharides
has been greatly related to the development of newer gly-
cosylation methods exploiting thioglycosides as glycosyl
donors. Obviously, there are a number of reports in the
literature for the preparation of thioglycosides. The most
often employed protocol for thioglycoside preparation is
the treatment of glycosyl acetates with alkyl/aryl thiols
or alkyl/aryl thiotrimethylsilanes in the presence of a
Lewis acid.15–20 These methods suffer from a number
of drawbacks, such as, the necessity of working with malo-
dorous and toxic thiols and formation of anomerized
products. Another method for the preparation of 1,2-
trans-thioglycosides uses S-glycosyl isothiouronium salts
generated from glycosyl halides as the starting com-
pounds.21,22 Although this method gives a comparatively
odorless protocol, it requires pre-generation of S-glyco-
syl isothiouronium salts from relatively unstable glycosyl
halides and in general this method does not allow for the
preparation of aryl thioglycosides.
OAc
AcO
AcO
O
OAc
OAc
O
Zn-dust/ZnCl2 (cat)
CH3CN/70 oC
AcO
AcO
Br
SeR
SR
[(RSe)2Zn]
RSeSeR
RSSR
OAc
OAc
O
AcO
AcO
OAc
OAc
O
Zn-dust/ZnCl2 (cat)
CH3CN/70 oC
AcO
AcO
Br
[(RS)2Zn]
OAc
Scheme 1.
Keywords: Carbohydrate; Cleavage reactions; Thioglycosides; Selenoglycosides; Organometallics.
q CDRI Communication No. 6863.
*
Corresponding author. Tel.: +91 522 2612411 18; fax: +91 522 2623938; e-mail: akmisra69@rediffmail.com
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.11.074

442
C. Mukherjee et al. / Tetrahedron Letters 47 (2006) 441–445
Table 1. Zinc mediated cleavage of dichalconides and reaction with glycosyl bromides towards the formation of 1,2-trans-thio- and selenoglycosides
Entry Dichalconides
Glycosyl bromides 1 Products 2
Timea (min) Temperature (°C) Yieldb (%) Ref.
OAc
O
OAc
a
PhSSPh
O
25
30
20
70
70
70
92
90
88
35
36
37
AcO
AcO
AcO
AcO
SPh
OAc
OAc
Br
cO
A
OAc
O
OAc
OAc
O
b
c
PhSSPh
PhSSPh
AcO
SPh
AcO
OAc
OAc
Br
OAc
O
OAc
O
AcO
AcO
AcO
AcO
AcO
AcO
Br
SPh
OAc
O
OAc
O
AcO
AcO
AcO
AcO
d
e
PhSSPh
PhSSPh
45
25
70
70
92
85
38
39
Br
NPhth
SPh
NPhth
Br
SPh
H3C
AcO
H3C
AcO
O
O
AcO
AcO
OAc
OAc
OAc
OAc
O
O
AcO
AcO
AcO
AcO
f
(p-CH3C6H4)2S2
(p-CH3C6H4)2S2
(p-CH3C6H4)2S2
25
30
20
70
70
70
90
92
87
40
40
40
STol
OAc
OAc
Br
cO
A
OAc
O
OAc
OAc
O
g
h
AcO
STol
AcO
OAc
OAc
Br
OAc
O
OAc
O
AcO
AcO
AcO
AcO
AcO
AcO
Br
STol
Br
STol
H3C
AcO
H3C
AcO
O
O
i
(p-CH3C6H4)2S2
(C6H5CH2)2S2
(C6H5CH2)2S2
25
25
25
70
70
70
85
85
90
40
41
41
AcO
AcO
OAc
OAc
OAc
O
OAc
O
AcO
AcO
AcO
AcO
j
SBzl
OAc
OAc
Br
cO
A
OAc
O
OAc
OAc
O
k
AcO
SBzl
AcO
OAc
OAc
Br
OAc
O
OAc
O
AcO
AcO
AcO
AcO
l
(C6H5CH2)2S2
25
45
40
70
70
70
90
86
92
42
—
—
AcO
AcO
Br
SBzl
OAc
O
OAc
O
AcO
AcO
AcO
AcO
m
n
(C6H5CH2)2S2
Br
SBzl
NPhth
NPhth
OAc
O
OAc
O
AcO
AcO
AcO
AcO
(p-NO2C6H4CH2)2S2
SBzl(p-NO2)
OAc
OAc
Br
cO
OAc
O
A
OAc
OAc
O
o
p
(p-NO2C6H4CH2)2S2
40
45
70
70
95
92
43
26
AcO
SBzl(p-NO2)
AcO
OAc
OAc
Br
OAc
O
OAc
O
AcO
AcO
AcO
PhSeSePh
AcO
SePh
OAc
Br
OAc

C. Mukherjee et al. / Tetrahedron Letters 47 (2006) 441–445
443
Table 1 (continued)
Entry
q
Dichalconides
Glycosyl bromides 1
Products 2
Timea (min)
45
Temperature (°C)
Yieldb (%)
90
Ref.
cO
OAc
O
A
OAc
PhSeSePh
OAc
70
—
O
AcO
SePh
AcO
OAc
Br
OAc
OAc
O
OAc
O
AcO
AcO
AcO
AcO
r
s
PhSeSePh
PhSeSePh
40
45
70
70
90
88
23
26
AcO
AcO
Br
SePh
OAc
O
Br
NPhth
OAc
O
AcO
AcO
AcO
AcO
SePh
NPhth
Br
SePh
H3C
AcO
H3C
AcO
O
O
t
PhSeSePh
PhSSPh
40
60
60
70
70
70
85
26
46
47
AcO
AcO
OAc
O
OAc
OAc
OAc
AcO
AcO
AcO
COOMe
Cl
COOMe
u
v
56c
50c
AcO
AcHN
O
O
SPh
AcHN
AcO
OAc
AcO
OAc
AcO
AcO
COOMe
Cl
COOMe
SePh
PhSeSePh
AcO
AcHN
AcO
AcHN
O
AcO
AcO
a After formation of the thiolate or selenide anion.
b Isolated yield.
c With some of the b-isomer (ꢀ10%).
As in the case of thioglycosides, selenoglycosides have
also been used in carbohydrate chemistry for the prepa-
ration of oligosaccharides, C-glycosides, glycoconju-
gates, etc.23–25 Selenoglycosides can be selectively
activated in the presence of thioglycosides, which make
them attractive in oligosaccharide synthesis.26 In gen-
eral, selenoglycosides are prepared by treating halides
with selenium under sodium borohydride reduction con-
ditions27,28 or by treating glycosyl acetate with arylsele-
nol derived from the hypophosphorus acid reduction of
diphenyldiselenide in the presence of BF3ÆOEt2.26,29–31
In both the cases, there are similar drawbacks as in
the case of thioglycoside preparation including the use
of malodorous reagents and incompatibility of base
labile protecting groups under sodium borohydride
reaction conditions. Therefore, there is an urgent need
to develop an odorless, convenient and general reaction
protocol for the preparation of thio- and selenoglyco-
sides. Organometallic reactions have attracted consider-
able attention in synthetic organic chemistry.32,33
Recently, we noted a report on the preparation of dior-
ganyl selenides using zinc mediated cleavage of diaryl
diselenides followed by reaction of the selenide anions
formed in situ with alkyl halides.34 We envisioned that
a similar zinc mediated cleavage of disulfides and disel-
enides and reaction of the thiolate and selenide anions
formed in situ with glycosyl bromide could furnish thio-
and selenoglycosides under generalized one-pot reaction
conditions thereby avoiding the use of any malodorous
reagents. In this letter, we wish to report our findings
on the treatment of zinc with disulfides/diselenides fol-
lowed by reaction of the thiolate/selenide anions formed
in situ with glycosyl bromides to furnish thio- and sele-
noglycosides via an odorless, generalized reaction with
high stereoselectivity (Scheme 1).
In a first set of experiments, diphenyl disulfide was trea-
ted with an equimolar quantity of zinc-dust in CH3CN
at 70 °C for several hours to generate zinc thiolate but
no reaction occurred even after 24 h. In order to activate
the zinc, a catalytic amount of fused ZnCl2 was added to
the reaction mixture, which was placed in a preheated oil
bath at 70 °C. As expected the reaction started immedi-
ately and the reaction mixture became turbid in 45 min
indicating the formation of zinc thiolate. To the turbid
reaction mixture, a solution of acetobromo-D-glucose
(1.5 equiv) in CH3CN was added and the reaction was
allowed to stir at the same temperature. After 20 min,
TLC showed complete consumption of acetobromo-D-
glucose and formation of a new compound correspond-
ing to phenyl 2,3,4,6-tetra-O-acetyl-1-thio-b-D-gluco-
pyranoside. After further experimentation, by varying
the quantity of zinc-dust from 0.5 to 1.5 equiv with
respect to diphenyldisulfide, it was observed that initial
reaction of an equimolar mixture of diphenyldisulfide
and zinc-dust in the presence of a catalytic quantity of
fused ZnCl2 followed by addition of glycosyl bromide
(2.0 equiv) furnished 1,2-trans-thioglycosides in excel-
lent yields. Similar reaction conditions were applied
for the preparation of 1,2-trans-selenoglycosides using
diphenyl diselenides (Scheme 1). In the case of disele-
nide, it took slightly longer to form the selenide in com-
parison to disulfide cleavage. The findings on the
cleavage of disulfides and diselenides with zinc-dust

444
C. Mukherjee et al. / Tetrahedron Letters 47 (2006) 441–445
and concomitant reaction of the thiolates and selenide
anions formed, in situ with a variety of glycosyl bro-
mides towards the formation of thio- and selenoglyco-
sides are listed in Table 1. It is worth mentioning that
the procedure can be employed for the preparation of
sialic acid 2-thio- and 2-selenoglycosides. The use of
other common solvents; for example, CH2Cl2, CHCl3,
THF, DMF and nitromethane did not produce the same
results as with acetonitrile.
Science and Technology (DST), New Delhi (Project
No. SR/FTP/CSA-10/2002), India.
References and notes
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A typical experimental procedure is as follows: To a
solution of diaryl or diaralkyldisulfide or diaryl disele-
nide (1.0 mmol) in CH3CN (5.0 ml) was added zinc-dust
(66.0 mg, 1.0 mmol) followed by fused ZnCl2 (ꢀ25 mg).
The reaction mixture was placed in a pre-heated oil bath
at 70 °C for 45 min during which time the reaction mix-
ture became turbid indicating the formation of zinc-
thiolate or selenide. A solution of per-O-acetylated gly-
cosyl bromide (2.0 mmol) in CH3CN (5.0 ml) was added
to the turbid reaction mixture which was then stirred at
70 °C for the appropriate time as indicated in Table 1.
After completion of the reaction (TLC; hexane/EtOAc
1:1), the reaction mixture was concentrated under re-
duced pressure and the crude mass was dissolved in
CH2Cl2 (25.0 ml). The organic layer was washed with
aq NaHCO3 solution and water dried (Na2SO4) and
evaporated to dryness. The crude products were purified
over SiO2 using hexane–EtOAc as eluant to furnish pure
aryl and aralkyl thio- and selenoglycosides, the struc-
tures of which were confirmed from their NMR and
mass spectra. All the known compounds prepared gave
acceptable 1H NMR and 13C NMR spectra that
matched the reported data. It is noteworthy that only
1,2-trans-thio- and selenoglycosides were formed under
the reaction conditions without formation of any ano-
merized product.44 During the preparation of this man-
uscript, a report appeared in the literature using RuCl3
catalyzed cleavage of diselenides in the presence of
zinc.45 However, the present protocol should be consid-
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od for the preparation of thio- and selenoglycosides in
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In summary, an odorless general methodology has been
developed for the preparation of a series of 1,2-trans-
thio- and selenoglycosides through zinc mediated reduc-
tion of diaryl and diarylalkyl disulfides and diselenides
followed by reaction of glycosyl bromides with the thio-
lates and selenides generated in situ. The fast, stereoselec-
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Acknowledgements
Instrumentation facilities from SAIF, CDRI are grate-
fully acknowledged. C.M. and P.T. thank CSIR, New
Delhi, for providing Junior and Senior research fellow-
ships. This project was funded by the Department of

C. Mukherjee et al. / Tetrahedron Letters 47 (2006) 441–445
445
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p-Nitrobenzyl 2,3,4,6-tetra-O-acetyl-1-thio-b-D-glucopyr-
25
anoside (2n): Yield 92%; Yellow oil. ½aꢁ ꢂ37 (c 1.0,
CHCl3); 1H NMR (CDCl3, 300 MHz):D d = 8.18 (d,
J = 8.5 Hz, 2H), 7.51 (d, J = 8.5 Hz, 2H), 5.16 (t,
J = 9.0 Hz each, 1H), 5.10–5.0 (m, 2H), 4.38 (d,
J = 8.0 Hz, 1H), 4.27 (dd, J = 9.0 and 4.5 Hz, 1H), 4.14
(dd, J = 12.0 and 3.8 Hz, 1H), 4.0 (dd, J = 13.2 Hz each,
2H), 3.73–3.65 (m, 1H), 2.10, 2.05, 2.03, 2.01 (4s, 12H);
13C NMR (CDCl3, 50 Hz): d 170.7, 170.3, 169.7 (2C),
147.6, 145.3, 130.3 (2C), 124.1 (2C), 82.2, 76.4, 73.9, 70.1,
68.6, 62.5, 33.1, 21.0, 20.9, 20.8 (2C); IR (Neat): 1752,
1522, 1348, 1225, 1042 cmꢂ1; ESI-MS: m/z 522 [M+Na].
Anal. Calcd for C21H25NO11S (499): C, 50.50; H, 5.04%.
Found: C, 50.25; H, 5.30%.
Phenyl 2, 3,4,6-tetra-O-acetyl-1-seleno-b-D-galacto-pyran-
25
oside (2q): Yield 90%; Oil; ½aꢁD +7.2 (c 1.5, CHCl3); 1H
NMR (CDCl3, 300 MHz): d = 7.63 (d, J = 7.2 Hz, 2H,
aromatic protons), 7.33–7.26 (m, 3H, aromatic protons),
5.40 (d, J = 2.7 Hz, 1H, H-4), 5.26 (t, J = 9.6 and 9.9 Hz,
1H, H-2), 5.02 (dd, J = 9.6 and 3.3 Hz, 1H, H-3), 4.90 (d,
J = 9.9 Hz, 1H, H-1), 4.19–4.06 (m, 2H, H-6ab), 3.92–3.88
(m, 1H, H-5), 2.09, 2.07, 2.03, 1.96 (4s, 12H, 4COCH3);
13C NMR (CDCl3, 50 Hz): d = 170.7, 170.5 (2C), 169.9,
135.2–128.1 (aromatic carbons), 82.2, 75.8, 72.1, 68.4,
67.7, 62.0, 21.3, 21.1, 20.9 (2C); IR (Neat): 2926, 1748,
1654, 1370, 1225, 1052, 771 cmꢂ1; ESI-MS: m/z = 511
[M+Na]. Anal. Calcd for C20H24O9Se (488): C, 49.29; H,
4.96%. Found: 49.14; H, 5.15%.
44. Spectral data for compounds, which are not reported earlier:
Benzyl 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-1-thio-b-
D-glucopyranoside (2m): Yield 86%; White solid, mp
25
138.2 °C; ½aꢁ +6.6 (c 1.5, CHCl3); 1H NMR (CDCl3,
300 MHz): dD= 7.83–7.74 (m, 4H, aromatic protons), 7.28–
7.16 (m, 5H, aromatic protons), 5.79 (t, J = 9.9 Hz each,
1H, H-3), 5.30 (d, J = 10.5 Hz, 1H, H-1), 5.16 (t,
J = 9.6 Hz, 1H, H-4), 4.42 (t, J = 9.9 Hz, 1H, H-2), 4.30
(dd, J = 12.3 and 4.3 Hz, 1H, H-6a), 4.13 (d, J = 12.6 Hz,
1H, H-6b), 3.86 (Abq, J = 12.6 Hz each, 2H, SCH2), 3.6–
3.5 (m, 1H, H-5), 2.12, 2.04, 1.85 (3s, 9H, 3COCH3); 13C
NMR (CDCl3, 50 Hz): d = 171.0, 170.4, 169.8, 167.7 (2C),
137.1–124.1 (aromatic carbons), 80.7, 76.2, 71.8, 69.2,
62.6, 53.9, 34.6, 21.1, 21.0, 20.8; IR (KBr): 1757,
1713, 1379, 1252, 1222, 1092, 1038, 720 cmꢂ1; ESI-MS:
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L. J. Org. Chem. 2005, 70, 7338–7341.
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¨
42.
`
47. Carriere, D.; Meunier, S. J.; Tropper, F. D.; Cao, S.; Roy,
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