Chemistry Reference
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cyclic voltammetry of 21 thioglycosides, including 10 new compounds
prepared on purpose.
12
These included acetylated, benzoylated or
benzylated gluco, galacto, and fuco phenyl S-pyranosides, as well as
2-deoxy-2-phthalimido or 2-acetamido-2-deoxy derivatives, the anomeric
thiophenyl group being substituted by methyl or methoxy groups. It was
found, as expected, that the methyl or methoxy substituents in the para
or both the ortho and para positions lowered the oxidation potential
compared to the corresponding unsubstituted phenyl S-glycoside (de-
creasing potential: PhWp-MePhWp-MeOPhW(MeO)
3
-Ph). These glycosyl
donors were engaged in constant potential electrolysis in CH
3
CN in the
presence of simple alcohols or fluorides (NaF, CsF, LiF) to give the
corresponding glycosides stereoselectively in yields up to 97%. More re-
cently, the difference in the oxidation potential of the individual anomers
of thioglycopyranosides and thioglycofuranosides was analysed by cyclic
voltammetry.
13
In all cases, the b-
D
anomers were found to be oxidized at
more positive potentials than the corresponding a-
D
anomers.
The Lubineau team examined for the first time the behaviour of ami-
nosugars in electrochemical glycosylation. While the N-acetyl derivative
26 led exclusively to the oxazoline 28, the 2-phthalimido-1-thioglucoside
27 gave selectively the b-
D
-glucosides 29 (R
=
Me, CH
2
CH
2
CH
3
, CH(CH
3
)
2
,
C(CH
3
)
3
) in high yields (85-91%) by reaction with methanol, 1-propanol,
2-propanol and t-butanol.
14
This glycosyl donor was allowed to react with
the primary sugar alcohols 6 and 17 to prepare the b-
D
-disaccharides 30
and 31 in 70 and 64% yield, respectively, and also with the galactopyr-
anoside derivative 32 to afford the b-
D
-disaccharide 33 in 71% yield.
14
In the work described above, the electrolytes were used at a 0.1-0.2 M
concentration. Nokami and co-workers studied the possibility of
using very low (0.01 to 0.001 M) concentrations of sodium tri-
fluoromethanesulfonate as the supporting electrolyte for the glycosida-
tion of thioglycosides.
15
The electrolyte concentration did not affect the
yields of
the glycosylation, however, a higher applied voltage was
required.
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