Synthesis and characterisation of hexa- and tetrasaccharide mimics from acetobromomaltotriose and acetobromomaltose, and of C-disaccharide mimics from acetobromoglucose, obtained by electrochemical reduction on silver

Article abstract of DOI:10.1016/j.tetasy.2004.11.052

Glucose-based glycomimetics characterised by a direct C-interglycosidic bond were synthesised from acetobromomaltotriose (ABMT), acetobromomaltose (ABM) and acetobromoglucose (ABG). Electroreduction on silver cathode of acetobromomaltotriose afforded the diastereoisomeric hexasaccharide mimics 1-3, which were deacetylated to 4-6. The same procedure afforded biglucosyl derivatives 10-12 from acetobromoglucose and tetrasaccharide mimics 15 and 16 from acetobromomaltose. The C-Br bond was reduced affording an intermediate anomeric radical whose coupling formed the new C-C bond. The electrochemical induced coupling resulted in a one-pot reaction to double the parent sugar units. NMR and molecular modelling were used for the conformational analysis of the diastereoisomers.

Full text of DOI:10.1016/j.tetasy.2004.11.052

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 243–253
Synthesis and characterisation of hexa- and tetrasaccharide
mimics from acetobromomaltotriose and acetobromomaltose,
and of C-disaccharide mimics from acetobromoglucose, obtained
by electrochemical reduction on silver
Marco Guerrini,a Sara Guglieri,a Roberto Santarsieroa and Elena Vismarab,*
aIstituto di Ricerche Chimiche e Biochimiche ‘G. Ronzoni’, Via G. Colombo 81, I-20133 Milano, Italy
bDipartimento di Chimica, Ing. Chimica e Materiali ‘G.Natta’ Politecnico, Via Mancinelli 7, I-20131 Milano, Italy
Received 2 November 2004; accepted 19November 2004
Available online 5 January 2005
Abstract—Glucose-based glycomimetics characterised by a direct C-interglycosidic bond were synthesised from acetobromomalto-
triose (ABMT), acetobromomaltose (ABM) and acetobromoglucose (ABG). Electroreduction on silver cathode of acetobromom-
altotriose afforded the diastereoisomeric hexasaccharide mimics 1–3, which were deacetylated to 4–6. The same procedure afforded
biglucosyl derivatives 10–12 from acetobromoglucose and tetrasaccharide mimics 15 and 16 from acetobromomaltose. The C–Br
bond was reduced affording an intermediate anomeric radical whose coupling formed the new C–C bond. The electrochemical
induced coupling resulted in a one-pot reaction to double the parent sugar units. NMR and molecular modelling were used for
the conformational analysis of the diastereoisomers.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
graphy on silica gel. The b,b isomer was not found,
probably as it was dispersed in mixed fractions. In addi-
tion, 9 was the worst isomer to purify as it did not crys-
tallise and remained in the mother liquor.
C-Glycosides have gained interest as molecules of poten-
tial biological activity, also useful for enzymatic and
metabolic studies.1 Some examples of mixed O/C-glyco-
sides were also investigated.2 We described an electro-
chemical approach to C-disaccharide like mimics, that
is the reduction of glucosyl bromide3 in acetonitrile at
a silver electrode, a way already extensively applied to
glycoside syntheses (Fig. 1).4,5 Some evidence prompted
us to explain these syntheses via a radical pathway, that
is the dimerisation of carbon-centred radicals generated
by electroreduction of C–X.3–5 With this procedure,
both flexible and rigid C–C bonds can be build between
two sugar units (Fig. 1). Radical coupling is not stereo-
selective and generally afforded statistical mixtures of
the possible diastereoisomers. Electroreduction of aceto-
bromoglucose ABG afforded biglucosyl derivatives
7–9 (Scheme 1) that were separated by fractioned crys-
tallisation.3 Also tetrasaccharides 13 and 14 shown in
Scheme 1 were successfully obtained from acetobromo-
maltose ABM.4 They were isolated by flash chromato-
The present work was addressed to synthesise malto-
hexaose mimics from acetobromomaltotriose ABMT,
with the aim of testing if the electroreduction coupling
is still working to also double a trisaccharide moiety.
This attempt could be meaningful not only as an exten-
sion of the electrochemical approach, but also because
there have been many reports about the biological activ-
ity of oligosaccharides made by a very few numbers of
sugar units. It is well-known that sialyl Lewis is a tetra-
saccharide, ligand of selectins and obviously mimics of
few sugar units.6a Furthermore, possible oligomers
related to saccharide binding to animal lectins can be
made from four to six units.6b Finally, concerning the
characteristics of heparin binding, oligosaccharide size
starts from four monomers7a and sulfated oligosacchar-
ide-based inhibitors concerning angiogenesis and hepa-
ranase activity7b can be made by four to six saccharide
units.
*
The present work was also addressed to build up a
small library of di-, tetra- and hexaglucose-based
Corresponding author. Tel.: +39 02 23993088; fax: +39 02
23993080; e-mail: elena.vismara@polimi.it
0957-4166/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.11.052

244
M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
O
AcO
RIGID
O
O
Br
OAc
O
O
AcO
O
O
AcO
O
O
O
O
O
O
O
Br
O
I
+
O
O
O
O
O
O
O
O
O
AcO
FLEXIBLE
FLEXIBLE
O
Figure 1. Products available via an electrochemical approach to C-disaccharide-like mimics.
OAc
OAc
O
OR
O
AcO
OAc
RO
RO
AcO
AcO
OAc
OAc
O
Br
AcO
R = Ac (ABG)
7 (α,α) 8 (α,β) 9 (β,β)
13 (α,α ) 14 (α,β) not found (β,β)
⇒
⇒
R = tri-Ac-4-O-(α-D-glucopyranosyl) (ABM)
Scheme 1. Diastereoisomer compounds from electroreduction of ABG and ABM.
glycomimetics characterised by a direct C-interglycosi-
dic bond. This library presents different aspects of inter-
est. Some of them are common with the chemistry of
C-glycosides, as the proposed C-interglycosidic bond
introduces the same factors of stability largely discussed
in the literature. Indeed, as far as we know, direct C-
interglycosidic bond has remained practically unex-
plored, thus the library object of this paper can make
possible to study if and how a direct anomeric C–C link
might affect conformational properties, resulting in new
potential biological activities. In this context, molecular
modelling analysis of compounds of different configura-
tions at the new C–C bond and of different chain elon-
gation was taken into account to compare with data
obtained by NMR. Finally, the proposed library com-
ponents can be used as original chiral building blocks.
tration and generally does not occur in significant
amount due to the high reactivity of radicals that does
not allow a suitable concentration to dimerise to be re-
acted. We found that glycals always accomplished
dimers formation during the electroreduction of ABG,
ABM and ABMT on silver. In the single wave of the vol-
tammograms on silver there is probably an overlapping
of two peaks. The first one at a more positive potential is
responsible for the dimer formations due to the passage
of a single electron. The second one at more negative
potential is due to the passage of two electrons, responsi-
ble of glycal formation. Glycal formation process was
interpreted as a two electron C–Br bond cleavage coupled
to a very fast elimination of the acetate anion, see Scheme
2 that shows the mechanism for ABG. The concerted
elimination of the acetate anion can explain the absence
of glycitol that would be formed from an anomeric
intermediate carbanion. Experiments run on ABG under
different potentiostatic conditions on silver supported
the overlapping hypothesis as the ratios glucal/dimers
changed with the redox potential (Fig. 3). At more posi-
tive potentials, dimers prevailed while the amount of
glucal increased at more negative potentials. It seems
that the formation of glycals on silver cannot be avoided
and it is the more negative aspect of this approach as it
decreased the dimerisation yields. The electroreduction
of halosugars was studied also on glassy carbon, the
so-called innocent electrode widely used to avoid any
interactions between the electrode material and the sub-
strate to be reduced. Cyclic voltammetry was run and
once again showed a single irreversible peak, the redox
potentials being more negative than on silver, see Table
1 and Figure 2. This phenomenon is common for a large
number of halosugars and for simple alkyl halides, too.8
2. Results and discussion
2.1. Electrochemical parameters and preparative
electrolyses
Potentiostatic preparative electrolyses on silver were run
based on cyclic voltammetry experiments. Voltammo-
grams of ABG (Fig. 2), ABM and ABMT are quite sim-
ilar and showed one irreversible peak at the redox
potential Ep where C–X bond undergoes a single elec-
tron-transfer reduction (Table 1); the following elimina-
tion of the halogen anion leads to an intermediate
anomeric radical that dimerises; the mechanism being
illustrated with ABG in Scheme 2. The electrode process
on the silver cathode appears complex. It favours radical
dimerisation, a process that needs high radical concen-

M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
245
Figure 2. Cyclic voltammetry of ABG on silver and glassy carbon.
there is an interaction of silver with carbohydrate inter-
mediate radicals forming a sort of metal-free radical
complex of relatively longer life than simple radicals:
they survive enough time to couple. On carbohydrate
moiety, the high number of oxygen atoms with free dou-
blets of electrons could interact with the electrons of the
silver lattice. In 1961, Kochi and Rust observed a quite
similar phenomenon, that the interaction of radicals
Table 1. Reduction peak potentials of ABG, ABM and ABMT on
silver and on glassy carbon
Ep (Ag)/V (vs SCE)a
Ep (GC)/V (vs SCE)a
ABG
ABM
ABMT
ꢀ1.27
ꢀ1.29
ꢀ1.48
ꢀ2.39
ꢀ2.43
Not determined
a SCE = saturated calomel electrode.
3
Concerning the halosugars of interest in this paper,
ABG was the more investigated from a mechanistic
point of view and it was submitted to potentiostatic pre-
parative electrolysis also on graphite, giving dimerisa-
tion only as a side reaction, the main product being
the triacetylglucal (Scheme 2). The single peak on GC
is mainly due to a two-electron process consistent with
glucal formation. It is evident that silver and GC have
different behaviour towards halosugars. In the cyclic
voltammetry, silver electrode is electrocatalytic with re-
spect to glassy carbon, probably due to the well-known
affinity between silver and halogen atoms. As the prod-
uct distributions in preparative electrolyses also dramat-
ically changed, the differences between silver and GC are
huge. An important question is why dimers are typically
formed on silver. A possible explanation could be that
2.5
Ep -1.30
2
1.5
1
Ep -1.45
Ep -1.70
Ep -2.00
0.5
0
Figure 3. Reduction of ABG on silver at different Ep.
OAc
OAc
OAc
OAc
OAc
AcO
O
O
O
AcO
AcO
AcO
AcO
AcO
AcO
+ e-
on silver
.
O
OAc
OAc
OAc
AcO
Br
7,8,9
ABG
+ e-
OAc
OAc
O
O
on GC and on silver
AcO
AcO
AcO
AcO
-
OAc
Triacetylglucal
Scheme 2. Mechanism of electroreduction of ABG.

246
M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
OAc
OAc
O
O
O
OAc
OAc
OAc
AcO
OAc
OAc
O
OAc
Br
C
O
ABMT
A
OAc
OAc
B
OAc
O
O
O
O
OAc
OAc
OAc
OAc
AcO
AcO
C OAc
OAc
O
OAc
O
OAc
D
E
O
A
B
OAc
OAc
O
1, 2, 3
α,α
α,β
β,β
1 =
2 =
3 =
OH
O
O
OAc
OAc
AcO
OAc
F
OAc
Scheme 3. Products coming from electroreduction of ABMT.
with metal ion induced dimerisation.9 Glassy carbon
probably has no specific interaction either with halo-
sugars or with carbohydrate radicals that in fact mainly
undergo further reduction. At the moment we can con-
clude that silver is the only electrode surface useful for
our purposes. Apart from any speculations and syn-
thetic limitations, the simplicity, the possibility of
one-pot sugar unit doubling and the importance of
glycomimetics in different biological applications
prompted us to develop this electrochemical procedure.
tropy requirements and steric hindrance due to the chain
elongation are in part responsible for the more negative
potential. We were able also to separate the three diaste-
reoisomers 1–3 by flash silica gel chromatography. They
were further purified on a HPLC semi-preparative col-
umn (Fig. 4) and were successfully and fully character-
ised by NMR spectroscopy with a great accuracy.
NMR spectra of 2 reported in Figure 5, before and after
purification, demonstrate the usefulness of the
purification.
The first goal presented in this paper is that peracetyl-
ated hexasaccharides as a mixture of diastereoisomers
were successfully obtained by electroreduction of
ABMT on silver (Scheme 3), although the reduction is
more difficult passing from ABG and ABM to ABTM
as evinced by Ep reported in Table 1. Probably the en-
Deacetylation was carried out not only on 1–3, but also
on 7–9 and 13 and 14 to build up the library we had in
mind. A concise presentation of the library is shown in
Scheme 4, where n is the number of the glucose residue.
NMR characterisation was successfully performed for
all these new compounds with great accuracy, affording
20
15
10
5
(a)
*
0
min
0
5
10
15
20
-5
*
(b)
55
45
35
25
15
5
-5
min
0
5
10
15
20
Figure 4. Chromatograms related to HPLC purification of 3. (a) Crude fraction from silica gel flash chromatography enriched of the a,b
peracetylated maltotriose dimer 3 (peak marked with *); (b) a,b Peracetylated maltotriose 3 dimer after semi-preparative HPLC purification.

M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
247
3 isolated from flash
chromatography
*
*
*
* *
*
*
*
6.4
6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6
ppm
3 further purified by HPLC
6.4 6.2 6.0 5.8 5.6 5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6
ppm
Figure 5. NMR spectra of 3 isolated and further purified on semi-preparative HPLC column, * indicates the signals that disappeared due to the
purification.
OH
O
HO
O
OH
O
OH
HO
O
n
O
HO
O
n
OH
OH
HO
HO
HO
O
OH
OH
HO HO
HO
5, 11, 16
HO
4, 10, 15
O
OH
O
HO
O
OH
OH
HO
OH
HO
n
O
O
OH
OH
OH
OH
OH
HO
n
OH
O
HO
HO
OH
O
O
HO
n
OH
OH
HO
HO
O
HO
OH
O
O
n
OH
6,12
⇒
n = 0
n = 1
10 (α,α) 11 (α,β) 12 (β,β)
⇒
15 (α,α) 16 (α,β) not found (β,β)
4 (α,α) 5 (α,β) 6 (β,β)
⇒
n = 2
Scheme 4. Library of glucose-based glycomimetics from ABG, ABM and ABMT.
an important library of chemical shifts and coupling
constants for unprotected sugar-based molecules.
cations, molecular modelling conformation analysis was
carried out with the aim of investigating how the un-
usual C-interglycosidic bond influences the conforma-
tion and what roles the number of sugar units and the
consequent chain elongation play.
As these new glucose-based skeletons, especially the
hexasaccharide mimics, are suitable for biological appli-

248
M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
2.2. Molecular modelling conformational analysis
Ramachandran plot
MC1
MC2
Molecular modelling conformational analysis was per-
formed on a,b compounds because only for these asym-
metric products it is possible to measure the JH1–H1
(a)
0
18
14
10
NMR coupling constants, that have to be compared
with theoretical results. Conformations of 5, 11 and 16
were investigated by performing both 1D-Ramachan-
dran plots and Monte Carlo/energy minimisation
(MC/EM) conformational searches on models created
using MACROMODEL version 7.1. Particular attention
was put on C1–H1–C10–H10 torsional angles (h) describ-
ing C-glycosidic bond conformation.
6
In 1D-Ramachandran plots of all the analysed com-
pounds, three energy minima were found, corresponding
to h values of about 60ꢁ, 180ꢁ and 300ꢁ, respectively. In
this view, we can define three family of conformers, dif-
fering in C–C bond glycosidic moiety orientation:
gauche(+)- (h = 60ꢁ), anti- (h = 180ꢁ) and gauche(ꢀ)
(h = 300ꢁ).
(b)
18
14
10
In order to evaluate convergence of calculations, two
MC/EM simulations were carried out on each molecule,
starting from models having gauche(+)- (MC1) and
gauche(ꢀ)- (MC2) conformation. 30,000, 80,000 and
100,000 steps were run on 11, 16 and 5, respectively
(Fig. 6). Results of each pair of simulations are in very
good agreement (Table 2), indicating that all of them
were convergent. Conformers found in MC/EM calcula-
tions of 11 explore all the three energetic minima indi-
viduated by 1D-Ramachandran plot with the same
percentage distribution. On the contrary, more than
60% of conformers found out in MC/EM calculations
of both 16 and 5 explored the minimum corresponding
to gauche(ꢀ)-conformation. These different distribu-
tions prompted us to say that longer chains are accom-
plished by more rigid conformations.
6
(c)
26
22
18
14
In all the calculated structures, more than 90% of con-
0
formers of each minimum have JH1–H1 coupling con-
stant values included within ranges shown in Table 3.
0
90
180
270
360
θ(°)
0
Experimental JH1–H1 values measured on 16, 11 and 5
0
Figure 6. 1D-Ramachandran maps and MC scatter plots of h torsional
angle of compounds 11 (a), 16 (b) and 5 (c).
are in good agreement with theoretical values JH1–H1
of both gauche(+)- and gauche(ꢀ)-C–C bond conforma-
tions. gauche(ꢀ) Conformation gives the best fitting
with experimental data; for this reason it can be consid-
ered as the most probable C1–C1 bond conformation
for 16, 11 and 5 in water solution (Fig. 7).
Table 2. Percentage distribution of conformers found out by MC/EM
conformational searches on 16, 11 and 5
gauche(+) (%)
anti (%)
gauche(ꢀ) (%)
35
38
In the conformational analysis of 16 and 5, geometries
of glycosidic dihedral angles / and w were evaluated.
In most of the conformations individuated by MC/EM
simulations of both compounds, / and w range from
300ꢁ to 350ꢁ and from 270ꢁ to 360ꢁ, respectively.
NMR, optical rotation and computational analysis on
maltose in water solution10 indicated that maltose dis-
tributes between the states / = 29 0ꢁ, w = 320ꢁ and / =
330ꢁ, w = 345ꢁ. Therefore, we can observe that in both
1a-(b0-maltosyl)-1,5-anhydro-maltitol 11 and 1a-(b0-
maltotriosyl)-1,5-anhydro-maltotritol 5 the O-glucosidic
linkages seem to maintain the same conformation of O-
linked maltosides. Indeed, the presence of an unusual C–
11
16
5
MC 1
MC 2
34
31
31
31
MC 1
MC 2
14
13
20
1968
66
MC 1
MC 2
13
12
23
22
65
66
Percentage distribution of conformers found out by MC/EM confor-
mational searches on 11, 16 and 5 molecular models in the three
minima centered on h = 60ꢁ (gauche(+)), h = 180ꢁ (anti) and h = 300ꢁ
(gauche(ꢀ)), respectively. Two simulations were performed on each
compound, starting from gauche(+)- (MC 1) and gauche(ꢀ)- (MC 2)
conformers.

M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
249
Table 3. Comparison between experimental and theoretical H1–H10
coupling constants
cal pathway to double parent sugar units. The three
diastereoisomers built up between the new C-intergly-
cosidic bond show a prevalent gauche conformation
characterised by a drastic distorsion respect to the regu-
lar O-glucosidic bond.
Experimental Theoretical
0
Theoretical Theoretical
0
JH1–H1
0
0
JH1–H1
JH1–H1
JH1–H1
(Hz)
gauche(+) (Hz) anti (Hz)
gauche(ꢀ) (Hz)
11 1.4
16 2.5
2.2
2.4–4.9
9.6–9.8
0.7–2.9
5
4. Experimental
0
Experimental JH1–H1 values measured on compounds 11, 16 and 5 and
4.1. General procedures
0
theoretical JH1–H1 ranges including more than 90% of gauche(+), anti
and gauche(ꢀ) conformers individuated by MC/EM simulations per-
formed on the same compounds.
Peracetylated maltotriose was produced by known
methods. All other reagents and solvents were pur-
chased from Sigma–Aldrich. They were of reagent grade
and used without further purification. Reaction were
monitored by TLC visualising by charring with 10%
H2SO4 in water. Cyclic voltammetry experiment was
carried out with an Amel 2053 potentiostat coupled with
an Amel 7800 function generator. Cell temperature:
20 ꢁC, sample concn: 4 mM in ACN. Preparative elec-
trolyses were carried out with the Amel 553 potentiostat.
Analytical HPLC were performed with a 1100 series
Agilent HPLC instrument. Column: Hypersil BDS
C18 250 · 4.6 mm from Agilent Technologies. Rheodine
valve volume: 20 lL. Eluent: 55% acetonitrile/45%
water. Flow rate: 1.5 mL/min. Detection by UV at
210 nm. Samples were dissolved in ACN at the concen-
tration of 1 mg/mL; 20 lL were injected. Semi prepara-
tive HPLC was performed in the same conditions, using
an Hypersil BDS C18 250 · 10 mm column from Ther-
mo Hypersil, a Rheodine valve of 100 lL and a flow rate
of 5 mL/min. Samples were dissolved in ACN at the
concentration of 100 mg/mL; 70 lL were injected. 13C
NMR and 1H NMR spectra were recorded at
1
500 MHz for H and 125 MHz for 13C with a Bruker
1
AMX 500 spectrometer equipped with a 5 mm H/X in-
verse probe. Acetylated samples (10 mg) were dissolved
in benzene-d6 (0.6 mL, 99.96% D) and analysed at
303 K; chemical shift are expressed in ppm downfield
from TMS. Deprotected samples (10 mg) were dissolved
in D2O and lyophilised. The operation was repeated
three times, then samples were dissolved in D2O
(0.6 mL, 99.99% D) and analysed; chemical shift are ex-
pressed in ppm downfield from sodium 3-(trimethyl-
silyl)propionate. Assignments were made trough
HMQC, COSY and TOCSY experiments. MALDI-
TOF MS were acquired on a BIFLEX (Bruker) operat-
ing in the positive ion reflector mode. Ions, formed by a
pulsed UV laser beam (nitrogen laser, k = 337 nm) were
accelerated at 19keV. 2,5-DHB (10 mg/mL in ACN)
was used as matrix, 5 lL of the sample dissolved in
ACN (concn 20–40 pmol/lL) were added to 5 lL of
matrix solution and 1 lL was deposited on the target.
External calibration was performed with angiotensin II
peptide. Electron spray ionisation MS (ESI/MS) and
ESI-MS/MS experiments were performed in positive or
negative ion mode with a Esquire 3000 Plus ion trap
(Bruker) using the following instrumental parameters:
source voltage: 4.0 kV, nebuliser gas 12 psi, dry gas flow
rate 4 L/min at 280 ꢁC, capillary voltage 160 V. Samples
were sprayed by flow injection analysis at 4 lL/min at a
concentration of 20–50 pmol/lL in ACN for protected
analytes and in ACN/H2O (1:1, v/v) with 10 mM
Figure 7. gauche(ꢀ)-Conformers of 11 (a), 16 (b) and 5 (c).
C linkage of the parent reducing residues of these asym-
metrical diastereoisomers involves a drastic distorsion of
the chain conformation of 1–4 a-maltooligosaccharides,
as shown superimposing preferred conformation c (Fig.
8) of 5 with the most probable conformation of
maltohexaose.
3. Conclusion
An original library of potential glycomimetics including
glucose-based compounds of two, four and six units
characterised by one direct C-interglycosidic bond, was
built by a clean and simple approach, the electroreduc-
tion of the parent bromo sugars, that is a one-pot radi-

250
M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
Figure 8. Conformation (c) of 5 superimposed on maltohexaose.
ammonium acetate for deprotected samples. MS/MS
experiments were performed using an isolation width
of 4 Da and amplitude fragmentation of 1 V for 40 ms.
Melting points were measured with a 10· magnification
Reichert microscope equipped with an heating plate and
are not corrected. Optical rotations were measured on a
Dr. Kernichen Propol digital automatic polarimeter.
4.2. Preparative electroreduction of ABMT
The electrolysis was carried out under potentiostatic
condition at room temperature under nitrogen atmo-
sphere in a two-compartment cell, divided with an
anion-exchange membrane. Cathodic solution (50 mL)
made by anhydrous acetonitrile and containing 1.15 g
of tetraethylammonium perchlorate (TeaP) as support-
ing electrolyte were pre-electrolysed 10 min between
ꢀ1.0 V and ꢀ1.9V, using a silver plate as cathode and
a silver plate as anode in 50 mL of anhydrous acetoni-
trile saturated with tetraethylammonium bromide. A
Sybron membrane was used to separate anodic and
cathodic compartments. After the pre-electrolysis,
5.82 g (5.89mmol) of ABMT were added to the cathodic
solution and were exhaustively electrolysed at ꢀ1.600 V.
The solution at the cathodic compartment was concen-
trated and precipitated with AcOEt. The solid support-
ing electrolyte was filtered off. The filtrate was
evaporated at reduced pressure and the residue was
chromatographed on silica gel from 4:6 hexane/acetate
to acetate, obtaining a crude mixture of a,a, a,b and
b,b isomers (34% yields). After a second chromatogra-
phy in the same conditions, fractions enriched in single
isomer were obtained. These fractions were purified
through semi-preparative HPLC yielding pure isomers
of peracetylated 1a-(a0-maltotriosyl)-1,5-anhydro-mal-
totritol 1, 1a-(b0-maltotriosyl)-1,5-anhydro-maltotritol
2 and 1b-(b0-maltotriosyl)-1,5-anhydro-maltotritol 3.
4.1.1. 2,3,4,6-Tetra-O-acetyl-a-D-glucopyranosyl-(1!4)-
2,3,6-tri-O-acetyl-a-D-glucopyranosyl-(1!4)-2,3,6-tri-O-
acetyl-b-D-glucopyranosyl-bromide ABMT. HBr solu-
tion (18.5 mL, 39%) in CH3COOH were added at 0 ꢁC
to 6.16 g (6.38 mmol) of peracetylated maltotriose dis-
solved in 30 mL of anhydrous methylene chloride. After
stirring at 0 ꢁC for 1.5 h the mixture was diluted with
100 mL of CH2Cl2, washed subsequently with cold
water, NaHCO3 saturated water and again with water.
After solvent removal, the residue was flash chromato-
graphed on silica gel with 6:4 AcOEt/hexane obtaining
6.17 g of ABMT as a white solid in a 98% yield. Crystal-
lised from EtOH. Mp: 103 ꢁC. MALDI: m/z 1011.3
1
[M+Na+], 1025.2 [M+K+]. H NMR (C6D6, three rings
are termed for convenience: ABC–Br): 1.59–1.92 (m,
30H, CH3CO) 3.76 (dd, J6aC–5C = 3.4, J6aC–6bC = 12.8,
H-6aC); 3.93 (dd); 3.99 (dt, H-5B); 4.02 (dt, H-5C);
4.06 (dd); 4.17 (dd, J6bC–5C = 2.6, J6bC–6aC = 12.8, H-
6bC); 4.25 (dt, H-5A); 4.29 (dd, J6aB–5B = 3.1, J6aB–6bB
12.4, H-6aB); 4.38 (dd, J6aA–5A = 1.9, J6aA–6bB = 12.5,
H-6aA); 4.47 (H-6bA); 4.64 (dd, J2C–1C = 3.9, J2C–3C
=
=
9.7, H-2C); 4.66 (dd, J6bB–5B = 2.8, J6bB–6aB = 12.4, H-
6bB); 4.90 (dd, J2B–1B = 4.0, J2B–3B = 10.5, H-2B);
5.08 (dd, J2A–1A = 3.9, J2A–3A = 10.5, H-2A); 5.40 (d,
J1B–2B = 4.0, H-1B); 5.42 (t, J4A–3A = 9.0, J4A–5A = 9.0,
H-4A); 5.66 (d, J1A–2A = 3.9, H-1A); 5.85 (m, H-3A);
5.86 (m, H-3B, H-3C); 6.24 (d, J1C–2C = 3.9, H-1C).
13C NMR (C6D6): 20.6–21.0 (CH3CO) 62.6 (C-6aB, C-
6bB); 61.8 (C-6aA, C-6bA, C-6aC, C-6bC); 68.8 (C-
4A); 69.3 (C-5A); 69.7 (C-3A); 69.8 (C-5B); 70.7
(C-2A); 70.9(C-2B); 71.3 (C-2C); 72.1–73.1 (C-3B, C-
3C); 72.7–73.0 (C-4B, C-4C); 73.0 (C-5C); 87.0 (C-1C);
96.1 (C-1A); 96.4 (C-1B); 169.7–171.1 (CH3CO).
4.2.1. Compound 1 (a,a isomer). Tr (analytical column,
25
D
ID = 4.6 mm): 9.74 min. Mp = 120 ꢁC. ½aŠ ¼ þ101:4
(c 0.5, CHCl3). MALDI-MS: m/z = 1837.4 [M+Na+],
1
1853.4 [M+K+]. H NMR (C6D6, six rings are termed
for convenience: ABC–CBA): 1.62–2.11 (m, 60H,
CH3CO), 3.76 (dd, J4C–3C = 4.2, J4C–5C = 7.7, H-4C);
3.94 (dd, J4B–3B = 9.1, J4B–5B = 9.9, H-4B); 4.10 (m, H-
5C); 4.12 (m, C-6aC); 4.21 (dt, J5B–4B = 10.0, J5B–6aB
3.4, J5B–6bB = 3.4, H-5B); 4.27 (m, H-5A); 4.29(dd,
=
J6aB–5B = 4.0, J6aB–6bB = 12.3, H-6aB); 4.38 (dd, J6aA–5
2.4, J6aA–6bA = 12.3, H-6aA); 4.44 (m, H-6bC); 4.45
=

M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
251
(m, H-6bA); 4.57 (s, H-1C); 4.65 (dd, J6bB–5B = 2.8, J6bB–
6aB = 12.3, H-6bB); 4.97 (dd, J2B–1B = 3.9, J2B–3B = 10.4,
H-2B); 5.08 (dd, J2A–1A = 4.0, J2A–3A = 10.5, H-2A);
10.4, H-2A); 5.22 (d, J1B–2B = 3.9, H-1B); 5.31 (m, H-
2C); 5.37 (m, H-4A, H-3C); 5.59(d, J1A–2A = 3.9, H-
1A); 5.77 (dd, J3A–2A = 10.4, J3A–4A = 9.6, H-3A); 5.78
(dd, J3B–2B = 10.4, J3B–4B = 8.9, H-3B). 13C NMR
(C6D6): 61.6 (C-6aA, C-6bA); 62.6 (C-6aB, C-6bB);
63.2 (C-6aC, C6bC); 68.4 (C-2C); 68.5 (C-4A); 68.9
(C-5B); 69.3 (C-5A); 69.6 (C-3A); 70.6 (C-2A); 70.7
(C-2B); 71.8 (C-3B); 73.1 (C-4B); 73.9(C-1C); 74.2 (C-
4C); 76.5 (C-5C); 77.6 (C-3C); 95.8 (C-1A); 96.1 (C-1B).
1
5.30 (m, H-2C); 5.392 from monodimensional H spec-
trum (d, J1B–2B = 3.9, H-1B); 5.395 from monodimen-
sional 1H spectrum (t, J4A–5A = 9.7, J4A–5A = 9.7, H-
4A); 5.42 (dd, J3C–2C = 5.8, J3C–4C = 4.2, H-3C); 5.58 (d,
J1A–2A = 4.0, H-1A); 5.73 (dd, J3B–2B = 10.4, J3B–4B
=
9.1, H-3B); 5.78 (dd, J3A–2A = 10.5, J3A–4A = 9.4, H-
3A). 13C NMR (C6D6): 61.6 (C-6aA, C-6bA); 62.8 (C-
6aB, C-6bB); 63.3 (C-6aC, C-6bC); 68.5 (C-4A); 68.9
(C-1C); 69.0 (C-5A); 69.3 (C-5B); 69.4 (C-2C); 69.7 (C-
3A); 70.7 (C-2A, C-2B); 71.1 (C-3C); 72.0 (C-5C); 72.2
(C-3B); 73.4 (C-4B); 75.4 (C-4C); 96.1 (C-1A); 97.0 (C-1B).
4.3. Deacetylation of peracetylated compounds coming
from ABG, ABM and ABMT
4.3.1. 1a-(a0-Maltotriosyl)-1,5-anhydro-maltotritol 4.
Compound 1 (97 mg, 0.053 mmol) and 5.9 mL of
0.2 M MeONa in MeOH were stirred overnight at rt.
An equal volume of water was added and pH was ad-
justed to 7 with Amberlite IR-120 (H+ form). The resin
was filtered off and solvent was removed. After size
exclusion chromatography on Sephadex G25 resin com-
4.2.2. Compound 2 (a,b isomer). Tr (analytical column,
25
D
ID = 4.6 mm): 10.49min. Mp = 123 ꢁC; ½aŠ ¼ þ98:2
(c 1, CHCl3); ESI-MS: m/z = 1837.5 [M+Na+], 1853.4
1
[M+K+]. H NMR (C6D6, six rings are termed for con-
venience: ABC–DEF): 1.59–2.24 (m, 60H, CH3CO) 3.10
(ddd, J5D–4D = 9.6, J5D–6aD = 6.3, J5D–6bD = 2.6, H-5D);
3.62 (dd, J4D–3D = 8.2, J4D–5D = 9.6, H-4D); 3.71 (m, H-
4C); 3.74 (m, H-1D); 3.96 (m, H-4B, H-4E); 4.03 (dd,
J6aD–5D = 6.3, J6aD–6bD = 12.1, H-6aD); 4.15 (m, H-
1C); 4.23–4.23 (m, H-5B, H-5E); 4.25 (m, H-6bD);
4.26 (m, H-5C); 4.39(m, H-6aA, H-6aB); 4.46 (m, H-
6bA, H-6bB); 4.22–4.66 (m, H-6aB, H-6bB, H-6aE, H-
pound 4 was obtained as a white solid in quantitative
25
D
yield. ½aŠ ¼ þ147:3 (c 0.33, H2O); ESI-MS: m/z =
992.4 [M+NH4+], 997.3 [M+Na+], 1013.3 [M+ K+],
MS/MS (992.4): m/z = 975.3 [M+H]+, 813.2, 651.2,
489.1. H NMR (D2O, six rings are termed for conve-
1
nience: ABC–CBA): 3.42 (t, J4A–3A = 9.5, J4A–5A = 9.5,
H-4A); 3.59(dd, J2A–1A = 3.9, J2A–3A = 9.9, H-2A);
6bE, H-6aC, H-6bC), 4.93 (dd, J2B–1B = 3.9, J2B–3B
10.8, J2E–1E = 3.9, J2E–3E = 10.8, H-2B, H-2E); 5.09
(dd, J2A–1A = 3.9, J2A–3A = 9.2, J2F–1F = 3.9,
=
3.63 (dd, J2B–1B = 3.9 ,J2B–3B = 9.9, H-2B); 3.66 (t, J4B–3B
9.3, J4B–5B = 9.3, H-4B); 3.69 (t, J3A–2A = 9.4, J3A–4A
9.4, H-3A); 3.72 (m, H-5A); 3.75 (m, H-4C, H-6aC);
3.75–3.89(m, H-6aA, H-6bA, H-6aB, H-6bB); 3.83
(m, H-5B); 3.89(m, H-2C); 3.9(m, H-3B); 4.01 (m,
=
=
J2F–3F = 9.2, H-2A, H-2F); 5.20 (t, J2D–1D = 8.9,
J2D–3D = 8.9, H-2D); 5.28 (d, J1E–2E = 3.9, H-1E); 5.33
(m, H-2C); 5.36 (m, H-3D); 5.39(m, H-1B); 5.40 (m,
H-4A, H-4F); 5.58 (d, J1A–2A = 3.9, H-1A); 5.62 (m,
H-1F, H-3C); 5.82–5.75 (m, H-3B, H-3E); 5.79(m,
H-3A, H-3F). 13C NMR (C6D6): 61.6 (C-6aA, C-6bA,
C-6aF, C-6bF); 62.7 (C-6aB, C-6bB, C-6aC, C-6bC
C-6aE, C-6bE); 63.6 (C-6aD, C-6bD); 68.0 (C-2C);
68.5 (C-4A, C-4F); 68.9–69.4 (C-5A, C-5B,
C-5E, C-5F); 69.6 (C-3A, C-3F); 70.5 (C-1C, C-3C);
70.6 (C-2A, C-2F); 70.7 (C-2B, C-2E); 70.8 (C-2D);
71.9–72.0 (C-3B, C-3E); 72.8 (C-5C); 73.2 (C-4B, C-
4E); 74.6 (C-4D); 74.8 (C-4C); 76.0 (C-3D, C-5D);
76.4 (C-1D); 95.8 (C-1F); 96.0 (C-1A); 96.2 (C-1E);
96.8 (C-1B).
H-6bC); 4.08 (ddd, H-5C); 4.10 (t, J3C–2C = 5.3, J3C–4C
=
5.3, H-3C); 4.31 (s, H-1C); 5.25 (d, J1B–2B = 3.9, H-1B);
5.39(d, J1A–2A = 3.9, H-1A). 13C NMR (D2O): 62.2 (C-
6aC, C-6bC); 63.4 (C-6aA, C-6bA, C6aB, C6bB); 71.8
(C-2C); 71.9(C-1C); 72.0 (C-3C); 72.2 (C-4A); 74.0
(C-2B, C-5B); 74.6 (C-2A); 75.6 (C-5A); 75.8 (C-3A);
76.2 (C-3B); 76.8 (C-4C); 79.6 (C-5C); 79.8 (C-4B);
100.9(C-1B); 102.6 (C-1A).
4.3.2. 1a-(b0-Maltotriosyl)-1,5-anhydro-maltotritol 5.
Compound 2 (73 mg, 0.040 mmol) was deprotected to
compound 5 in quantitative yield, as above described
1
for 4. ESI-MS: m/z = 973.3 [MꢀH]ꢀ. H NMR (D2O,
six rings are termed for convenience: ABC–DEF): 3.42
(m, H-4A, H-4F); 3.53 (ddd, J5D–4D = 9.6, J5D–6aD =
4.2.3. Compound 3 (b,b isomer). Tr (analytical column,
ID = 4.6 mm): 12.84 min. ESI-MS: m/z = 1873.5
2.1, J5D–6bD = 5.0, H-5D); 3.58 (m, H-2A, H-2F); 3.61
(m, H-4C); 3.61–3.62 (m, H-2B,H-2E); 3.65 (m, H-4B,
H-4D, H-4E); 3.69(m, H-3A, H-3F); 3.73 (m, H-5A,
H-5F); 3.69(m, H-1D, H-2D); 3.72 (m, H-3D); 3.74–
3.88 (m, H-6aA, H6bA, H-6aB, H-6bB, H-6aE, H-
6bE, H-6aF, H-6bF); 3.79(m, H-6aD); 3.82 (m, H-
6aC); 3.84 (m, H5B, H-5E); 3.85 (m, H-6bC); 3.92 (m,
H-2C); 3.93 (m, H-6bD); 3.97 (m, H-3B, H-3E); 4.04
(m, H-5C); 4.28 (dd, J1C–1D = 2.2, J1C–2C = 5.1, H-1C);
4.31 (m, H-3C); 5.28 (d, J1B–2B = 3.9, H-1B); 5.38 (d,
1
[M+Na+], 1853.4 [M+K+]. H NMR (C6D6, six rings
are termed for convenience: ABC–CBA): 1.65–1.94 (m,
60H, CH3CO), 2.97 (ddd, J5C–4C = 9.8, J5C–6aC = 5.0,
J5C–6bC = 3.0, H5-C); 3.31 (d, J1C–2C = 8.8, H-1C);
3.55 (dd, J4C–3C = 8.2, J4C–5C = 9.8, H-4C); 3.95 (dd,
J6aC–5A = 5.0; J6aC–6bC = 12.1, H-6aC); 3.96 (t, J4B–3B
9.4, J4B–5B = 9.4, H-4B); 4.08 (dt, J5A–4A = 9.8,
J5A–6aA = 3.1, J5A–6bA = 3.1, H-5A); 4.12 (dd, J6bB–5B
3.0, J6bB–6aB = 12.1, H-6bC); 4.24 (dt, J5B–4B = 10.2,
J5B–6aB = 3.1, J5B–6bB = 3.1, H-5B); 4.27 (dd, J6aB–5B
=
=
=
J1A–2A = 3.9, J1F–2F = 3.9, H-1A, H-1F), 5.39 (J1F–2F =
3.6, J6aB–6bB = 12.4, H-6aB); 4.35 (dd, J6aA–5A = 2.6,
J6aA–6bA = 12.4, H-6aA); 4.44 (dd, J6bA–5A = 3.7,
J6bA–6aA = 12.4, H-6bA); 4.57 (dd, J6bB–5B = 2.9,
J6bB–6aB = 12.4, H-6bB); 4.87 (dd, J2B–1B = 3.9,
3.9, H-1F). 13C NMR (D2O): 63.1 (C-6aC, C-6bC)
63.4 (C-6aA, C-6bA, C-6aB, C-6bB, C-6aE, C-6bE, C-
6aF, C-6bF); 63.8 (C-6aD, C-6bD); 72.2 (C-4A, C-4F);
73.3 (C-2C); 74.0 (C-5B, C-1C, C-5E); 74.3 (C-2B, C-
2E); 74.6 (C-3C, C-2A, C-2F); 72.2–74.4 (C-2B, C-2E);
J2B–3B = 10.4, H-2B); 5.05 (dd, J2A–1A = 3.9, J2A–3A
=

252
M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
75.7 (C-3A, C-3F); 76.2 (C-3B, C3E); 78.4 (C-5C); 79.2
(C-4C); 79.7 (C-4B, C-4D, C-4E); 80.9 (C-3D); 81.1 (C-
5D); 83.8 (C-1D); 101.4 (C-1B); 102.4 (C-1E); 102.6 (C-
1A, C-1F).
J5–4 = 9.8, J5–6a = 5.9, J5–6b = 2.2, H-5); 3.52 (t, J3–2 =
8.9, J3–4 = 8.9, H-3); 3.59 (d, J1–2 = 9.4, H-1); 3.67 (t,
J2–1 = 9.3, J2–3 = 8.9, H-2); 3.70 (dd, J6a–5 = 5.9,
J6a–6b = 12.4, H-6a); 3.90 (dd, J6b–5 = 2.2, J6b–6a = 12.4,
H-6b). 13C NMR (D2O): 63.9(C-6a, C-6b); 71.3 (C-2);
72.7 (C4); 78.5 (C1); 80.4 (C3); 82.8 (C5).
4.3.3. 1b-(b0-Maltotriosyl)-1,5-anhydro-maltotritol 6.
Compound 3 (73 mg, 0.040 mmol) was deprotected to
compound 6 in quantitative yield, as above described
for 4. ESI-MS: m/z = 992.4 [M+NH4+], 997.3
[M+Na+], 1013.3 [M+K+], MS/MS (992.4): m/
z = 975.3 [M+H]+, 813.3, 651.2, 489.1; 1H NMR
(D2O, six rings are termed for convenience: ABC–
CBA): 3.42 (t, J4A–3A = 9.4, J4A–5A = 9.4, H-4A); 3.53
(ddd, J5C–4C = 9.8, J5C–6aC = 5.3, J5C–6bC = 2.0, H-5C);
3.58 (m, H-2A, H-4C); 3.59(m, H-1C); 3.63 (m, H-
2B); 3.64 (m, H-4B); 3.67 (m, H-3A); 3.70 (m, H-2C);
3.72 (m, H-5A); 3.74 (m, H-6aC); 3.74–3.88 (m, H-
6aA, H-6bA, H-6aB, H-6bB); 3.80 (m, H-3C); 3.84 (m,
H-5B); 3.93 (dd, J6bC–6aC = 12.5, J6bC–5C = 2.0, H-
4.3.7. 1a-(a0-Maltosyl)-1,5-anhydro-maltitol 15. Com-
pound 13 (329mg, 0.266 mmol) was deprotected as
described for compound 4 obtaining 15 in a quantita-
tive yield. MALDI-MS: m/z = 673 [M+Na+], 689
[M+K+]. 1H NMR (D2O, four rings are termed for con-
venience: AB–BA): 3.43 (t, J4A–3A = 9.6, J4A–5A = 9.6,
H-4A); 3.59(dd, J2A–1A = 3.9, J2A–3A = 9.8, H-2A);
3.72–3.75 (m, H-3A, H-5A, H-4B); 3.76 (dd, J6aB–6bB
=
12.4, J6aB–5B = 2.2, H-6aB); 3.77 (m, H-6aA); 3.87 (dd,
J6aA–5A = 2.3, J6aA–6bA = 12.2 H-6bA); 3.89(m, H-2B);
4.01 (dd, J6bB–6aB = 12.4, J6bB–5B = 7.5, H-6bB); 4.09
(m, H-5B); 4.11 (t, J3A–2A = 5.4, J3A–4A = 5.4 H-3B);
4.31 (s, H1-B); 5.25 (d, J1A–2A = 3.9, H-1A). 13C NMR
(D2O): 62.1 (C-6aB, C-6bB); 63.2 (C-6aA, C-6bA);
71.7 (C-2B); 71.8 (C1-B); 71.9(C3-B); 72.1 (C4-A);
74.0 (C-2A); 75.4–76.6 (C-3A, C-5A, C-4B), 79.4 (C-5A).
6bC); 3.96 (dd, H-3B); 5.38 (d, J1A–2A = 3.7, J1B–2B
=
3.7, H-1A, H-1B). 13C NMR (D2O): 63.4 (C-6aA, C-
6bA, C6aB, C6bB); 63.8 (C-6aC, C-6bC); 71.1 (C-2C);
72.2 (C-4A); 74.1 (C-5B); 74.4 (C-2B); 74.6 (C-2A);
75.6 (C-5A); 75.7 (C-3A); 76.2 (C-3B); 78.4 (C-1C);
79.9 (C-4B); 80.4 (C-4C); 80.7 (C-3C); 81.4 (C-5C);
102.6 (C-1A, C-1B).
4.3.8. 1a-(b0-Maltosyl)-1,5-anhydro-maltitol 16. Com-
pound 14 (570 mg, 0.226 mmol) was deprotected as
described for compound 4 obtaining 16 in quantita-
tive yield. MALDI-MS: m/z = 673 [M+Na+], 689
[M+K+]. 1H NMR (D2O, four rings are termed for con-
venience: AB–CD) 3.39(dd, H-4D); 3.41 (dd, H-4A);
3.52 (ddd, J5C–6aC = 5.0, J5C–6bC = 2.0, J5C–4C = 9.5, H-
5C); 3.54 (dd, J2A–1A = 3.9, J2A–3A = 6.5, H-2A); 3.56
4.3.4. 1a-(a0-Glucosyl)-1,5-anhydro-glucitol 10. Com-
pound 7 (15 mg, 0.023 mmol) was deprotected as de-
scribed for compound 4 obtaining 10 in quantitative
yield. ESI-MS: m/z = 325.0 [MꢀH]ꢀ, MS/MS (325.0):
1
m/z = 325.0, 306.9, 228.9, 205.0, 186.9, 139.0. H NMR
(D2O): 3.38 (m, H-4); 3.68 (m, H-6a, H-6b); 3.69(m,
H-3); 3.74 (m, H-2, H-5); 4.27 (d, J1–2 = 3.2, H-1). 13C
NMR (D2O): 63.2 (C-6); 71.9(t, J4–3 = 8.1, J4–5 = 8.1,
C-4); 73.0 (C-1); 73.7 (C-2); 75.9(C-3); 78.9(C-5).
(dd, J2D–1D = 3.9 ,J2D–3D = 6.5, H-2D); 3.59(t, J4B–3B
7.0, J4B–5B = 7.0, H-4B); 3.64 (t, J4C–3C = 8.5, J4C–5C
8.5, H-4C); 3.65–3.72 (m, H-3A, H-5A, H3D, H-5D);
3.66 (m, H-1C); 3.68 (m, H-2C); 3.70 (m, H-3C); 3.73–
3.78 (m, H-6aA, H-6aB, H-6aD); 3.77 (m, H-6aC);
3.81–3.74 (m, H-6bA, H-6bB, H-6bD); 3.90 (dd,
=
=
4.3.5. 1a-(b0-Glucosyl)-1,5-anhydro-glucitol 11. Com-
pound 8 (22 mg, 0.033 mmol) was deprotected as de-
scribed for compound 4 obtaining 11 in quantitative
yield. ESI-MS: m/z = 325.0 [MꢀH]ꢀ, MS/MS (325.0):
m/z = 325.0, 306.9, 228.9, 186.9, 139.0. 1H NMR
(D2O, two rings are termed for convenience: A–B):
3.37 (dd, J4A–3A = 8.4, J4A–5A = 9.4, H-4A); 3.41 (m,
J2B–1B = 5.3, J2B–3B = 7.3, H-2B); 3.91 (dd, J6bC–5C
=
2.3, J6bC–6aC = 13.2, H-6bC); 4.03 (ddd, J5B– = 3.4,
J5B– = 6.4, J5B– = 10.2, H-5B); 4.27 (dd, J1B–2B = 5.3,
J1B–1C = 2.5, H-1B); 4.31 (t, J3B–2B = 7.1, J3B–4B = 7.1,
H-3B); 5.28 (d, J1D–2D = 3.9, H-1D); 5.39 (d, J1A–2A
=
3.9, H-1A). 13C NMR (D2O): 63.0–63.2 (C-6aA,
C-6bA, C-6aB, C-6bB, C-6aD, C-6bD); 63.7 (C-6C);
72.1–72.2 (C-4A, C-4D); 73.2 (C-2B); 73.9(C-1B);
74.3–74.5 (C-2A, C-2D); 74.5 (C-2C); 74.6 (C-3B);
75.4–75.6 (C-3A, C-5A, C-3D, C-5D); 78.2 (C-5B);
78.8 (C-4B); 79.3 (C-4C); 80.8 (C-3C); 81.0 (C-5C);
83.9(C-1C); 101.3 (C-1D); 102.3 (C-1A).
H-5B); 3.43 (m, H-3B); 3.45 (t, J4B–5B = 8.5, J4B–5B
=
8.5, H-4B); 3.67 (dd, J6aA–5A = 6.4, J6aA–6bA = 12.3,
C-6aA); 3.69(m, H-2B); 3.70 (m, H-1B); 3.76 (dd,
J6aB–5B = 4.8, J6aB–6bB = 12.4, C-6aB); 3.83 (dd,
J6bA–5A = 2.4, J6bA–6aA = 12.3, C-6bA); 3.87 (m, H-
2A); 3.88 (m, H-5A); 3.91 (J6bB–5B = 2.1, J6bB–6aB
=
12.4, H-6bB); 4.13 (t, J3A–2A = 8.9, J3A–4A = 8.4, H-
3A); 4.35 (dd, J1A–2A = 6.5, J1A–1B = 1.4, H-1A). 13C
NMR (D2O): 63.8 (C-6aB, C-6bB); 64.0 (C-6aA, C-
6bA); 72.1 (C-4B); 73.2 (C-4A); 74.5 (C-2B); 74.8 (C-
2A); 75.0 (C-1A); 76.9(C-3A); 78.8 (C-5A); 80.8
(C-3B); 82.7 (C-5B); 86.1 (C-1B).
4.4. Conformation analysis methods
All the calculations were carried out using MACRO-
MODEL 7.1 version of BATCHMIN on a SGO2 work-
station. The force field used for energy minimization
was AMBER* which includes HomanÕs parameters for
pyranose.11 The GB/SA (generalized Born/surface area)
continuum water solvation model was used.12 1D-
Ramachandran plots were calculated increasing h angle
from 0ꢁ to 360ꢁ by 1ꢁ increments. MC/EM simulations
were performed on 16, 11 and 5 using 30,000, 80,000
and 100,000 steps, respectively.
4.3.6. 1-b-(b0-Glucosyl)-1,5-anhydro-glucitol 12. Com-
pound 9 (20 mg, 0.030 mmol) was deprotected as de-
scribed for compound 4 obtaining Compound 12 in
quantitative yield. ESI-MS: m/z = 325.0 [MꢀH]ꢀ, MS/
1
MS (325.0): m/z = 325.1, 306.9, 204.9, 139.0. H NMR
(D2O): 3.35 (dd, J4–3 = 8.8, J4–5 = 9.8, H-4); 3.40 (ddd,

M. Guerrini et al. / Tetrahedron: Asymmetry 16 (2005) 243–253
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Acknowledgements
Dott. A. Naggi and Dott. G. Torri, for discussion and
Dott. Elena Urso for Mass Spectra, Istituto ÔG. Ronz-
´
oniÕ. Prof. J.-M. Saveant, for discussion and Prof. M.
Robert for discussion and cyclic voltammetry, Labora-
toire dÕelectrochimie organique, CNRS, Paris 7, France.
This work was partially supported by EU (contract
number QLK3-CT-2002-02049) and by Italian Ministry
of research FIRB project (contract number
RBAU01LF3E).
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