Scope and limitation of the application of the (methoxydimethyl)methyl group in the synthesis of 2'-O-, 6'-O- and 2',6'-di-O-(α-L-arabinofuranosyl)-β-D-galactopyranosyl-(1→6)-D-galactoses

Article abstract of DOI:10.1016/S0008-6215(99)00094-4

For the characterisation of the anticipated epitope of an arabinogalactan, isolated from the extract of Echinacea purpurea, the trisaccharide α-L-Araf-(1→2)-β-D-Galp-(1→6)-D-Gal was synthesized. The easily available 3,4-O-isopropylidene-6-O-(methoxydimethyl)methyl-β-D-galactopyranosyl-(1→6)-1,2:3,4-di-O-isopropylidene-α-D-galactopyranose having the OH-2' free served as aglycone upon direct arabinosylation at the 2' position under Helferich conditions. The formed HgBr₂ cleaved the acid sensitive protecting group at position 6', but under basic conditions the desired, fully protected trisaccharide, or its symmetrical dimerization derivative linked 6'- to 6'-position via an isopropylidene bridge, could be obtained. An alternative route involved arabinosylation of a hepta-O-acetylated digalactose with free OH-2'. Two other oligosaccharides, namely, α-L-Araf-(1→6)-β-D-Galp-(1→6)-D-Gal and (α-L-Araf)₂-(1→2,6)-β-D-Galp-(1→6)-D-Gal were also synthesized and characterised. Copyright (C) 1999 Elsevier Science Ltd.

Full text of DOI:10.1016/S0008-6215(99)00094-4

www.elsevier.nl/locate/carres
Carbohydrate Research 318 (1999) 98–109
Scope and limitation of the application of the
(methoxydimethyl)methyl group in the synthesis of
2%-O-, 6%-O- and 2%,6%-di-O-(a-
L
-arabino-
furanosyl)-b- -galactopyranosyl-(1“6)-
D
D
-galactosesꢀ
Aniko´ Borba´s a, Lo´ra´nt Ja´nossy b, Andra´s Lipta´k a,b,
*
a Research Group for Carbohydrates of the Hungarian Academy of Sciences, Debrecen, PO Box 55,
H-4010 Hungary
b Institute of Biochemistry, L. Kossuth Uni6ersity, Debrecen, PO Box 55, H-4010 Hungary
Received 12 February 1999; accepted 9 April 1999
Abstract
For the characterisation of the anticipated epitope of an arabinogalactan, isolated from the extract of Echinacea
purpurea, the trisaccharide a- -Araf-(1“2)-b- -Galp-(1“6)- -Gal was synthesized. The easily available 3,4-O-iso-
propylidene-6-O-(methoxydimethyl)methyl-b- -galactopyranosyl-(1“6)-1,2:3,4-di-O-isopropylidene-a- -galactopy-
L
D
D
D
D
ranose having the OH-2% free served as aglycone upon direct arabinosylation at the 2% position under Helferich
conditions. The formed HgBr2 cleaved the acid sensitive protecting group at position 6%, but under basic conditions
the desired, fully protected trisaccharide, or its symmetrical dimerization derivative linked 6%- to 6%-position via an
isopropylidene bridge, could be obtained. An alternative route involved arabinosylation of a hepta-O-acetylated
digalactose with free OH-2%. Two other oligosaccharides, namely, a-
(a- -Araf)2-(1“2,6)-b- -Galp-(1“6)- -Gal were also synthesized and characterised. © 1999 Elsevier Science Ltd.
All rights reserved.
L
-Araf-(1“6)-b-
D
-Galp-(1“6)-D-Gal and
L
D
D
Keywords: Echinacea purpurea; Arabinogalactans; (Methoxydimethyl)methyl ethers; Oligosaccharides; Dimerization
1. Introduction
binoxylans [3] and arabinorhamnogalactans
[3]. Most recently an arabinogalactan fraction
possessing promising biological activity was
isolated [6] (Scheme 1). Structure elucidation
suggested that all third or fourth galactose
units of the b-(1“6)-linked galactan skele-
The medical use of the extracts of Echinacea
purpurea is long known and the polysaccha-
ride components of these extracts have been
systematically investigated by Wagner et al.
[1–3]. As a result of these studies, the polysac-
charides of Echinacea purpurea are produced
in industrial scale by cell cultures [4,5]. These
polysaccharides are 4-O-methylglucuronoara-
ton contain either an a-
L-arabinofuranosyl or
an a- -arabinofuranosyl-(1“5)-a-
L
L
-arabino-
furanosyl side chain. The presence of a rather
similar structural unit is supposed by Alber-
sheim et al. [7] in the polysaccharide isolated
from suspension-cultured sycamore maple
(Acer pseudoplatanus). Three different te-
trasaccharide derivatives were synthesized
most recently by van Boom et al. [8] for the
ꢀ This work was partly presented at the 9th European
Carbohydrate Symposium, 6–11 July 1997, Utrecht, The
Netherlands.
* Corresponding author. Fax: +36-52-512-913.
E-mail address: liptaka@tigris.klte.hu (A. Lipta´k)
0008-6215/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(99)00094-4

A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
99
well-defined parts of the next two structural
units and employ these oligosaccharides to
raise monoclonal antibodies. These antibodies
might be suitable tools for structure elucida-
tion of plant polysaccharides [9]. To the best
of our knowledge there are only four examples
in the literature [8,10–12] for the preparation
of non-symmetrically 2,6-di-O-glycosylated b-
D-galactopyranosyl derivatives. Now we re-
port our first results obtained with some
oligosaccharides having the desired minimal
structural unit.
We were the first to report [13] that the
reaction of alkyl b- -galactopyranosides with
D
Scheme 1. Suggested structure of the arabinogalactane frac-
tion isolated from Echinacea purpurea.
2,2-dimethoxypropane in the presence of a
catalytic amount of p-toluenesulfonic acid re-
sulted in alkyl 3,4-O-isopropylidene-6-O-
characterisation of several monoclonal anti-
bodies elucidated by the epitopes of polysac-
charides isolated from Acer pseudoplatanus.
(methoxydimethyl)methyl-b- -galactopyrano-
D
sides. Other authors [14–16] succesfully used
this procedure for the preparation of different
galactopyranoside derivatives having a free
OH-2 group, and abbreviated the (methoxy-
dimethyl)methyl group as MIP (2-methoxy-
isopropyl).
2. Results and discussion
The aim of the present synthetic work was
to establish a method for the preparation of
Scheme 2. Synthesis of the 6-O-(methoxydimethyl)methyl containing disaccharide building blocks.

100
A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
Scheme 3. Arabinosylation of the 6-O-(methoxydimethyl)methyl containing digalactose-type aglycon under Helferich conditions.
In the knowledge of this reaction, our strat-
egy was to galactosylate a galactopyranos(e)yl
unit having free OH-6, and after deprotection
of the second galactosyl unit and treatment
with 2,2-dimethoxypropane, a partially pro-
tected digalactose having the OH-2% free was
expected to be obtained. This should be
amenable to direct arabinosylation.
galactose under Helferich conditions (Schemes
2 and 3) and the known 6-O-(2,3,4,6-tetra-O-
acetyl-b-
propylidene-a-
obtained. Compound 2 was deacetylated to
give 6-O-(b- -galactopyranosyl)-1,2:3,4-di-O-
isopropylidene-a- -galactopyranose [19] (3),
D
-galactopyranosyl)-1,2:3,4-di-O-iso-
D
-galactopyranose [18] (2) was
D
D
and this disaccharide was treated with 50
equivalents of neat 2,2-dimethoxypropane in
the presence of p-toluenesulfonic acid. A
nearly quantitative reaction yielded 6-O-(3,4-
Based on the above considerations, 1,2:3,4-
di-O-isopropylidene-a- -galactopyranose [17]
D
(1) was glycosylated with a-acetobromo- -
D

A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
101
O-isopropropylidene-6-O-(methoxydimethyl)-
methyl - b - - galactopyranosyl) - 1,2:3,4-di-O-
assignable to J1%,2% and J2%,3%. The third (minor)
component was also a trisaccharide (11), in
which C-6% (62.38 ppm) was free, three acetal
rings were present (109.98, 109.46 and 108.74
ppm), and an arabinofuranosyl unit was an-
chored at C-2%. This compound was the
planned trisaccharide, although without the
terminal MIP substitutent: 6-O-[2-O-(2,3,-
D
isopropylidene-a- -galactopyranose (4). Com-
D
pound 5 with 6%-OH free was formed only as a
side product.
The direct treatment of b- -galactopyr-
D
anosyl-(1“6)- -galactose (6) with 2,2-dime-
D
thoxypropane also resulted in compound 4.
The MIP derivatives show very easily charac-
5-tri-O-benzoyl-a-
isopropylidene-b-
di-O-isopropylidene-a-
L
-arabinofuranosyl)-3,4-O-
-galactopyranosyl]-1,2:3,4-
-galactopyranose (11).
1
terisable H and 13C NMR signals: in com-
D
pound 4 there were eight C-methyl signals in
D
1
the H NMR spectrum between 1.50 and 1.30
In the knowledge of the extreme acid-sensi-
tive properties of the MIP derivatives, the
formation of the above oligosaccharides (8, 9
and 11) can be easily explained. In the initial
stage of the glycosylation reaction the OH-2%
is the only nucleophilic partner and the MIP-
containing 12 (vide infra) was produced. Dur-
ing this reaction mercury bromide was also
formed and this rather strong Lewis acid hy-
drolysed the acid-sensitive MIP blocking
group. Then, reaction of the more nucle-
ophilic OH-6% resulted in the trisaccharide
derivative 9, and the excess of the glycosyl
donor glycosylated it to the tetrasaccharide
main product 8. The small amount of com-
pound 11 formed from its 6-OMIP derivative
(12), which did not lose its MIP during the
coupling reaction, but was cleaved during the
work-up procedure. Similar reaction mixtures
were obtained by using Ag2O or Ag2CO3
promoters.
ppm; the OCH3 group resonated at 3.12 ppm.
In the 13C NMR spectrum the quaternary
acetal carbon of the (methoxydimethyl)methyl
group resonated at 100.1 ppm, the C-6
showed a rather strong upfield shift at 60.26
ppm, and the OCH3 signal appeared at 48.53
ppm. These signals also helped the structure
elucidation of other, more complex oligosac-
charide derivatives.
To synthesize the trisaccharide repeating
unit of structure I, compound 4 seemed to be
a good candidate as the aglycone. Arabinosy-
lation of 4 with 2,3,5-tri-O-benzoyl-a- -ara-
L
binofuranosyl bromide [20] (7) using Hg(CN)2
as promoter resulted in three chromatographi-
cally well-separable substances, but, unfortu-
nately, none of them contained the MIP
group. The fully protected compound proved
to be 6-O-[2,6-di-O-(2,3,5-tri-O-benzoyl-a-
arabinofuranosyl) - 3,4 - O-isopropylidene - b -
- galactopyranosyl-]-1,2:3,-4 - di - O - isopro-
pylidene -a- - galactopyranose (8). The pres-
L
-
D
To avoid the cleavage of the MIP group we
executed the glycosylation reaction promoted
by AgOTf in the presence of sym-collidine
(2,4,6-trimethylpyridine), hoping that this
strong base can prevent the hydrolysis of the
acid-sensitive mixed acetalic protecting group.
The reaction proceeded with an acceptable
rate and two products (12 and 13) were
formed. It was also observed that the chro-
matographically faster-moving component
(12) was transformed into the slower-moving
one (13). Although the two products showed
very similar chromatographic mobility, their
separation could be achieved rather easily.
D
ence of three quaternary acetalic signals
(110.24, 108.99 and 108.21 ppm), the four
anomeric carbon signals (105.67, 103.73,
101.19 and 95.94 ppm), the absence of the
MIP group and the glycosylation shift at the
carbon C-6% verified the structure of com-
pound 8. The second product in the reaction
mixture proved to be the trisaccharide 9. The
three anomeric carbon signals resonated at
105.60, 103.36 and 96.14 ppm, the C-6% was
glycosylated (C-6%: 65.72 ppm), and three
dioxolane-type isopropylidene groups were
present (109.89, 109.35 and 108.64 ppm).
Acetylation of 9 gave the monoacetyl deriva-
tive (10) and one proton triplet was shifted to
the lower field. The acetylated OH group was
assigned as OH-2%, having the triplet at 5.08
ppm, and 8.5 Hz coupling constants
1
The H and 13C NMR spectra of the faster-
moving component showed the presence of
the MIP group (l: 3.2 ppm, OCH3, 24 H was
integrated between l: 1.18–1.62 ppm), and
three benzoyl moieties were also present. The
13C NMR spectrum was more informative;

102
A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
Scheme 4. Arabinosylation of the 6-O-(methoxydimethyl)methyl containing digalactose-type aglycon under basic conditions.
three dioxolane-type acetalic carbon signals
couldbeassigned(l:110.15, 109.06and108.31),
the three anomeric carbon atoms resonated at
103.82, 101.28 and 96.04 ppm, and the quater-
nary acetalic carbon atom of the MIP appeared
at 100.10 ppm. The O-6% contained the -O-
C(CH3)2-OCH3 group, an upfield shift of ꢀ2
ppm could be detected (l: 60.08 ppm) and the
OCH3 group resonated at 48.49 ppm. Mild acid
hydrolysis of the MIP group in compound 12
resulted in 11 in a quantitative yield.
Barresi and Hindsgaul [21] in a publication
dealing with synthesis of b-mannopyranosides
by intramolecular aglycone delivery. The as-
sumed structure of 13 was verified by MALDI-
TOF MS measurement giving m/z: 1853.9. In
the spectrum of compound 13 two additional
fragments appeared with m/z: 906.5 and 946.5;
the first could be assigned to 11 and the second
to the 6-O-isopropenyl ether of 11. The symmet-
rical acetalic bond in compound 13 is more
stable than the bonds of the mixed acetals (MIP)
but more sensitive than the cyclic dioxolane-
type isopropylidene acetals. Mild acid hydroly-
sis of 13 resulted in 11 with a quantitative yield.
Compound 11 can be a choice as the aglycone
for additional glycosylation, or even an agly-
cone for dimerisation into the hexasaccharide I.
These results demonstrate that the easily
available MIP derivatives can serve as aglycones
in glycosylation reactions, but basic or neutral
conditions are required for the coupling reac-
tions and also for the work-up procedure.
It is known that the MIP derivatives can be
successfully etherified under basic conditions
[15] (Scheme 4). Benzylation of compound 4
gave the fully protected crystalline disaccharide
The 1H and 13C NMR spectra of the second,
slower-moving compound (13) showed a trisac-
charide character. The spectra did not contain
OCH3 signal(s), but there was a quaternary
carbon signal at 100.5 ppm which could be an
acetalic carbon resonance. The C-6% also ap-
peared at high field (l: 60.18 ppm), and there
were 21 hydrogens in the methyl-proton region.
These spectral data suggested a symmetrical
isopropylidene acetal structure in which the
alcoholic components were the two trisaccha-
ride molecules; its composition can be depicted
by structure 13. Formation of symmetrical
dimerization products of monosaccharides hav-
ing similar structure to 13 was reported by

Table 1
13C NMR data for protected oligosaccharides
2
3
4
5
8
9
10
11
12
13
14
15
C-1
C-2
C-3
C-4
C-5
C-6
96.60
71.06
71.23
70.84
67.48
70.03
96.14
70.99
71.07
70.31
67.57
68.92
96.27
70.73
71.17
70.39
67.73
68.72
96.23
70.62
70.99
70.33
67.55
68.72
95.94
70.64
71.54
69.73
67.13
69.41
96.14
70.57
71.03
70.26
67.79
69.09
96.08
70.49
71.17
70.40
67.86
69.34
96.13
70.72
71.42
70.19
67.02
68.94
96.04
70.77
71.69
69.84
67.18
69.19
96.02
70.64
71.18
70.40
67.18
69.22
96.33
70.69
71.92
70.39
67.24
69.12
96.28
70.34
70.23
69.30
67.06
68.79
/
Cquat
109.80
109.07
109.32
108.07
109.90
108.77
110.20
108.73
110.24
108.21
109.89
108.64
110.28
108.55
109.98
108.74
110.15
108.31
110.10
108.26
109.60
108.48
109.88
108.41
C-1%
C-2%
C-3%
C-4%
C-5%
C-6%
102.41
71.34
71.23
67.48
71.69
61.60
103.84
71.07
73.24
68.38
74.41
60.91
103.34
73.28
78.73
73.60
72.61
60.26
103.10
73.55
79.05
73.72
73.32
62.20
101.19
79.75
77.90
74.61
73.32
65.74
103.36
77.00
78.67
73.16
71.93
65.72
101.14
76.74
73.35
72.62
71.47
65.40
101.20
79.88
74.86
73.98
73.18
62.38
101.28
79.74
77.69
74.86
73.66
60.07
101.25
76.76
74.86
73.64
71.90
60.18
103.66
78.75
78.64
73.63
71.92
60.15
103.31
78.57
78.94
73.74
72.98
62.09
318
Cq% uat
109.48
100.10
48.53
109.44
108.99
109.35
109.22
109.46
109.06
100.10
48.49
109.03
109.26
100.02
48.48
109.22
9
COCH3
OCH3
100.50 a
9
C-1¦
105.67
103.73
105.60
105.55
103.90
103.82
103.82
109
C-2¦
C-3¦
C-4¦
C-5¦
80.97 80.34 80.89
77.68 77.60 77.91
82.78 82.50 82.08
63.62 64.13 63.57
80.96
77.92
82.11
63.60
80.65
77.68
82.15
64.08
80.44
77.69
83.30
64.18
80.45
77.66
82.26
64.16
a Signal of the bridge carbon atom of –OC(CH3)O–

104
A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
Scheme 5. Alternative route for the synthesis of the target trisaccharide.
14 (Scheme 2). Selective hydrolysis of the MIP
fgroup resulted in the crystalline 6-O-(2-O -
benzyl - 3,4 - O - isopropylidene - b - - galacto-
assignments. The 13C NMR data of the pro-
tected derivatives are collected in Table 1.
Similar measurements were done in the case of
the free oligosaccharides, too. These trisaccha-
rides, in aqueous solutions, occur as mixture of
two anomers, but in the case of the branched
D
pyranosyl) - 1,2:3,4 - di - O - isopropylidene-a- -
D
galactopyranose (15). Complete hydrolysis of
the isopropylidene acetals either of 14 or 15
gave 6-O-(2-O-benzyl-b-
-galactose (16). Acetylation of 16 afforded the
peracetylated derivative (17) from which, after
hydrogenolysis, 6-O-(3,4,6-tri-O-acetyl-
b- -galactopyranosyl)-1,2,3,4-tetra-O-acetyl-
a,b- -galactopyranose (18) was obtained.
D
-galactopyranosyl)-
tetrasaccharide 20, the reducing
D
-galactose
D
unit existed in four isomeric forms (a-, b-pyra-
nose and a-, and b-furanose forms) and in the
equilibrium mixture the quadruplication of
some individual carbon-13 signals could be
detected. Similar spectral behaviours have been
reported earlier from our laboratory [22,23]
(Scheme 6).
D
D
Compound 18 could be arabinosylated with 7
and the persubstituted trisaccharide 19 was
isolated.
For the removal of the isopropylidene groups
of the oligosaccharides 8, 9, 11 and 13 aqueous
90% trifluoroacetic acid was used. The acyl
groups were removed by Zemple´n transesterifi-
cation to furnish the tetrasaccharide 20 from
compound 8 and the trisaccharide 21 from the
protected 9. The target trisaccharide 22 was
obtained from three different protected inter-
mediates: 11, 13 and 19 (Scheme 5).
Detailed two-dimensional (2D) H and 13C
NMR studies resulted in the pertinent spectral
1
Scheme 6. Synthesis of the deprotected sugars.

A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
105
4.04 (dd, 1 H, H-6a, J5,6a 3.2 Hz, Jgem 11.5
Hz), 3.95–3.85 (m, 2 H, H-4, H-5), 3.69 (dd,
1 H, H-6b, J5,6b 7.6 Hz), 2.15–1.95 (4 s,
each 3 H, 4 CH3acetyl), 1.55–1.30 (4s, each 3
H, 4 CH3ip). Anal. Calcd for C26H38O15
(590.57): C, 52.87; H, 6.48. Found: C, 52.90;
H, 6.51.
3. Experimental
General methods.—Optical rotations were
measured at room temperature with
a
Perkin–Elmer 241 automatic polarimeter.
Melting points were determined on a Kofler
apparatus and are uncorrected. TLC was
performed on Kieselgel 60 F254 (E. Merck)
with detection by charring with 50% of
aqueous sulfuric acid. Column chromatogra-
phy was performed on Silica Gel 60 (E.
Merck 0.063–0.200 mm). The organic solu-
tion was dried over MgSO4, and concen-
i-
D
-Galactopyranosyl-(1“6)-1,2:3,4-di-O-
-galactopyranose (3).—To
isopropylidene-h-
D
a stirred solution of 2 (16.5 g, 0.028 mol) in
200 mL of dry MeOH NaOMe (100 mg)
was added (pH ꢀ8). After 2.5 h the TLC
(85:15 CH2Cl2–MeOH, Rf 0.5) showed com-
plete conversion. The solution was neutral-
1
trated in a vacuum. The H (200, 360 and
500 MHz) and 13C NMR (50.3, 90.54,
125.76 MHz) spectra were recorded with
Bruker WP-200 SY, Bruker AM-360 and
Bruker DRX-500 spectrometers in CDCl3 so-
lutions. Internal references: TMS (0.000 ppm
ized
with
Amberlite
IR-120
H+
ion-exchange resin, filtered and evaporated
to yield 3 as a white foam (11.7 g, 98.8%):
[h]2D2 −63.1° (c 1.0, CHCl3) lit. −49.7° (c 2,
1
aq 0.5 M TRIS) [19]; H NMR (360 MHz,
1
for H), CDCl3 (77.00 ppm for 13C).
CDCl3): l 5.50 (d, 1 H, H-1, J1,2 5 Hz), 4.62
(d, 1 H, H-1%, J1%,2% 8 Hz), 4.40–3.45 (m, 14
skeleton H), 1.45 (m, 12 H, 4 CH3ip). Anal.
Calcd for C18H30O11 (422.43): C, 51.17; H,
7.16. Found: C, 51.32; H, 7.13.
2,3,4,6-Tetra-O-acetyl-i-
syl-(1“6)-1,2:3,4-di-O-isopropylidene-h-
galactopyranose (2).—Powdered Hg(CN)2
(16.4 g, 0.065 mol) and 4 A molecular sieves
D
-galactopyrano-
D-
,
(10 g) were added to a solution of 1 (13.0 g,
0.050 mol) in 120 mL of dry CH3CN, and
the mixture was stirred overnight. To the
mixture was added 2,3,4,6-tetra-O-acetyl-a-
3,4-O-Isopropylidene-6-O-(methoxydimethyl)-
methyl-
O-isopropylidene-h-
3,4 - O - isopropylidene - i -
(1“6)-1,2:3,4-di-O-isopropylidene-h-
D
-galactopyranosyl-(1“6)-1,2:3,4-di-
-galactopyranose (4) and
- galactopyranosyl-
-gal-
D
D
D-galactopyranosyl bromide (24.6 g, 0.060
D
mol) in five portions. After 2 h the reaction
was complete (TLC, 23:2 CH2Cl2–acetone,
Rf 0.5). The mixture was diluted with 500
mL of CH2Cl2, the inorganic salts were
filtered off, and the filtrate was concentrated
in vacuo. The residue was dissolved in 1000
mL of CH2Cl2, the inorganic salts were
filtered off again, the filtrate was washed
with aq 5% KI solution (4×250 mL), and
water (2×250 mL). The organic layer was
dried and evaporated. The syrupy residue
was purified by column chromatography
(CH2Cl2 –acetone, 96:4“92:8) to yield 2
(19.0 g, 64.4%): [h]2D2 −44.2° (c 1.0, CHCl3)
actopyranose (5).—To a solution of 3 (11.5
g, 0.027 mol) in 2,2-dimethoxypropane (170
mL, 1.36 mol) was added 400 mg of p-tolu-
enesulfonic acid, and the mixture was stirred
overnight. By TLC (4:1 CH2Cl2–acetone; +
0.1% Et3N) the starting material disap-
peared, compounds 4 (Rf 0.54) and 5 (Rf
0.25) were formed in a ratio of 4:1. After
addition of Et3N (2 mL) the reaction mix-
ture was diluted with 1 L of CH2Cl2, washed
with water (3×400 mL), dried and evapo-
rated. The residue was chromatographed
with CH2Cl2–acetone, 9:1“8:2, containing
1% Et3N to give 4 (10.6 g, 72.5%) and 5 (2.5
g, 19.7%). The same products in similar ra-
tio were obtained from 6 by treatment of 50
equivalents of 2,2-dimethoxy-propane and
catalytic amount of p-toluenesulfonic acid.
Compound 4: [h]2D2 −35.6° (c 1.3, CHCl3);
1H NMR (500 MHz, CDCl3): l 5.54 (d, 1
H, H-1, J1,2 5.0 Hz), 4.60 (dd, 1 H, H-3, J2,3
1
lit. −44° [18]; H NMR (500 MHz, CDCl3):
l 5.51 (d, 1 H, H-1, J1,2 4.9 Hz), 5.39 (dd, 1
H, H-4%, J3%,4% 3.4 Hz, J4%,5% 1.0 Hz), 5.22 (dd,
1 H, H-2%, J1%,2% 7.9 Hz, J2%,3% 10.5 Hz), 5.03
(dd, 1 H, H-3%), 4.59 (2 d, 2 H, H-1%, H-3,
J3,4 8.0 Hz), 4.30 (dd, 1 H, H-2, J2,3 2.5 Hz),
4.16 (m, 3 H, H-5%, H-6%a,b, Jgem 11.1 Hz),

106
A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
stirred for 3 h and 1.0 g (1.9 mmol) of 7
[20] was added. After 2 h the TLC (49:1
CH2CL2–acetone) showed ꢀ50% conversion
of 4, 100 mg of Hg(CN)2 was added and the
mixture was kept at 50 °C for 6 h. The
work-up procedure was the same as that de-
scribed for compound 2. The crude product
was purified by coloumn chromatography to
give 8 (280 mg, 24.7%), 9 (190 mg, 24.8%)
and 11 (40 mg, 5.3%).
2.4 Hz, J3,4 7.9 Hz), 4.31 (dd, 1 H, H-2),
4.28 (dd, 1 H, H-1%, J1%,2% 8.4 Hz), 4.24 (dd, 1
H, H-4, J4,5 1.7 Hz), 4.16 (dd, 1 H, H-4%,
J3%,4% 5.4 Hz, J4%,5% 2.1 Hz), 4.06 (m, 2 H,
H-3%, H-6a, J2%,3% 7.8 Hz), 4.00 (m, 1 H, H-5),
3.85 (dt, 1 H, H-5%, J5%,6a%=J5%,6b% 6.2 Hz),
3.75–3.69 (m, 3 H, H-6a, H-6%a,b), 3.59 (dd,
1 H, H-2%), 3.25 (s, 3 H, OCH3), 1.50–1.27
(8 s, each 3 H, 8 CH3ip). Anal. Calcd for
C25H42O12 (534.58): C, 56.17; H, 7.91.
Found: C, 56.31; H, 8.00.
Compound 8: [h]2D2 +2.7° (c 1.0, CHCl3).
Anal. Calcd for C73H74O25 (1351.36): C,
64.88; H, 5.51. Found: C, 64.57; H, 5.53.
Compound 9: [h]2D2 −15.5° (c 1.0, CHCl3).
Anal. Calcd for C47H54O18 (906.94): C,
62.24; H, 6.00. Found: C, 62.44; H, 6.04.
Compound 11: [h]2D2 −3.17° (c 0.82,
CHCl3). Anal. Calcd for C47H54O18 (906.94):
C, 62.24; H, 6.00. Found: C, 62.11; H, 5.97.
Compound 5: [h]2D2 −29.6° (c 1.0, CHCl3);
1H NMR (500 MHz, CDCl3): l 5.48 (d, 1
H, H-1, J1,2 5.0 Hz), 4.55 (dd, 1 H, H-3, J2,3
2.4 Hz, J3,4 7.9 Hz), 4.26 (dd, 1 H, H-2),
4.22 (dd, 1 H, H-1%, J1%,2% 8.0 Hz), 4.20 (dd, 1
H, H-4, J4,5 1.7 Hz), 4.09–3.66 (m, 8 H),
3.49 (t, 1 H, H-2% J2%,3% 8.0 Hz), 1.50–1.27
(m, 18 H, 6 CH3ip). Anal. Calcd for
C21H34O11 (462.49): C, 54.53; H, 7.40,.
Found: C, 54.31; H, 7.37.
2,3,5-Tri-O-benzoyl-h-
(1“6)-2-O-acetyl-3,4-O-isopropylidene-i-
galactopyranosyl-(1“6)-1,2:3,4-di-O-isoprop-
ylidene-h- -galactopyranose (10).—To a so-
L
-arabinofuranosyl-
D-
i-
D
-Galactopyranosyl-(1“6)- -galactose
D
D
(6).—A solution of 4 (50 mg, 0.090 mmol)
in 1 mL of 90% trifluoroacetic acid was
stirred for 15 min, and concentrated at 20 °C
in vacuo. Ethyl acetate (6 mL) was added to
the residue, and the precipitate formed was
washed three times with ethyl acetate to
yield 6 (20 mg, 64%): [h]2D2 +17.3° (c 0.19,
H2O); Rf 0.4 (dichloromethane: methanol:
H2O, 80:50:13). Anal. Calcd for C12H22O11
(342.29): C, 41.10; H, 6.47. Found: C, 41.44;
H, 6.48.
lution of 9 (50 mg) in pyridine (1 mL) was
treated with acetic anhydride (1 mL). The
solution was evaporated with toluene to
yield 10, which was used for NMR measure-
ments only.
2,3,5-Tri-O-benzoyl-h-
(1“2)-3,4-O-isopropylidene-6-O-(methoxy-
dimethyl)methyl-i- -galactopyranosyl-(1“6)-
1,2:3,4 - di - O - isopropylidene-h- -galactopyra-
nose (12) and 2-propanone bis-[2,3,5-tri-O-
benzoyl-h- -arabinofuranosyl-(1“2)-3,4-O-
isopropylidene-i- -galactopyranosyl-(1“6)-
1,2:3,4-di-O-isopropylidene-h- -galactopyra-
nose]-6,6 acetale (13).—Powdered
L
-arabinofuranosyl-
D
D
L
2,3,5 -Tri-O-benzoyl-h-
(1“2)-[2,3,5-tri-O-benzoyl-h-
nosyl - (1“6)] - 3,4 - O - isopropylidene - i -
galactopyranosyl - (1“6) - 1,2:3,4 - di - O - iso-
L
-arabinofuranosyl-
D
L
-arabinofura-
D
D-
,
A
4
molecular sieves (1.2 g) were added to a so-
lution of 4 (534 mg, 1.0 mmol) and 7 [20]
(630 mg, 1.2 mmol) in dry CH2Cl2 (20 mL),
and the mixture was stirred in dark. After 2
h, the reaction mixture was cooled to −
25 °C, sym-collidine (0.29 mL, 2 equiv), and
silver triflate (514 mg, 2 equiv) in dry
toluene (4 mL) were added. After 2 h, the
TLC showed complete conversion and for-
mation of two products, Et3N (1 mL) was
added, the mixture was diluted with CH2Cl2
and filtered through a pad of Celite. The
propylidene-h-
O-benzoyl-h-
D
-galactopyranose (8), 2,3,5-tri-
-arabinofuranosyl-(1“6)-3,4-
L
O-isopropylidene-i-
1,2:3,4-di-O-isopropylidene-h-
nose (9) and 2,3,5-tri-O-benzoyl-h-
furanosyl-(1“2)-3,4-O-isopropylidene-i-
galactopyranosyl - (1“6) - 1,2:3,4 - di - O - iso-
propylidene-h-
D
-galactopyranosyl-(1“6)-
-galactopyra-
-arabino-
D
L
D-
D
-galactopyranose (11).—To a
solution of 4 (390 mg, 0.84 mmol) in 5 mL
of dry CH3CN were added powdered
Hg(CN)2 (512 mg, 2.4 equiv) and 4 A
molecular sieves (0.5 g), the mixture was
,

A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
107
was heated at reflux temperature for 3 h.
The mixture was diluted with CH2Cl2,
washed with aq NaHCO3 and water, dried
and evaporated. The solid residue (2.7 g)
was crystallized from c-hexane to yield 15
(2.4 g, 90.1%); mp 128–129 °C; Rf 0.45 (17:3
CH2Cl2–acetone); [h]2D2 −2.6° (c 1.3,
CHCl3). Anal. Calcd for C28H40O11 (552.62):
C, 60.85; H, 7.29. Found: C, 61.01; H, 7.27.
filtrate was washed with aq 10% Na2S2O3
and water, dried and evaporated. The prod-
ucts were separated by column chromatogra-
phy (23:2 CH2Cl2–acetone, +1% Et3N) to
give 12 (280 mg, 28.6%) and 13 (430
mg, 23.1%). Compound 12: [h]2D2 −13.4°
(c 0.48, CHCl3); Rf 0.45 (in the chromato-
graphic eluent). Anal. Calcd for C51H62O19
(979.0): C, 62.56; H, 6.38. Found: C, 62.81;
H 6.33.
3,4,6-Tri-O-acetyl-2-O-benzyl-i-
pyranosyl-(1“6)-1,2,3,4-tetra-O-acetyl-h,i-
-galactopyranose (17).—To a stirred solu-
D-galacto-
Compound 13: [h]2D2 −8.9° (c 0.76,
CHCl3); Rf 0.40; MALDI-TOF MS: m/z
D
[M+Na]+1876.9;
Anal.
Calcd
for
tion of 14 (300 mg, 0.48 mmol) in 30 mL of
CH2Cl2, 3 mL of trifluoroacetic acid and one
drop of water were added. After 16 h tri-
ethylamine was added, and the mixture was
evaporated to give 16 (Rf 0.53, 8:5:1 CH2-
Cl2–acetone–water) which was acetylated
without purification in a mixture of 5 mL of
pyridine and 5 mL of acetic anhydride to
give 17. The crude product was purified by
column chromatography (93:7 CH2Cl2–
acetone, Rf 0.40) to yield 17 (230 mg,
74.5% for two steps); [h]2D2 +25.2°
(c 1.0, CHCl3). Anal. Calcd for C26H42O18
(642.61): C, 48.59; H, 6.58. Found: C, 48.81;
H, 6.61.
C97H112O36 (1853.9): C, 62.84; H, 6.08.
Found: C, 63.11; H, 6.07.
2 - O - Benzyl - 3,4 - O - isopropylidene - 6 - O-
(methoxydimethyl)methyl - i -
osyl-(1“6)-1,2:3,4-di-O-isopropylidene-h-
D
- galactopyran-
D-
galactopyranose (14).—To a stirred solution
of 4 (10.0 g, 0.018 mol) in dry N,N-dimethyl
formamide (15 mL) 80% NaH (672 mg,
0.022 mol) was added at 0 °C. After 30 min
benzyl bromide (2.4 mL, 0.220 mol) was
added dropwise, and the mixture was stirred
for 3 h. The mixture was diluted with 400
mL of CH2Cl2, washed with water until neu-
tral, dried and evaporated. The crude
product was purified by column chromatog-
raphy (24:1 CH2Cl2–acetone) to yield 14 (8.2
3,4,6-Tri-O-acetyl-i-
(1“6)-1,2,3,4-tetra-O-acetyl-h,i-
D
-galactopyranosyl-
-galacto-
D
g, 70.1%); mp 116–117 °C (MeOH); [h]D22
−
pyranose (18).—Palladium on activated car-
bon (30 mg) was added to a solution of 17
(300 mg) in ethyl acetate (3 mL) and the
mixture was stirred under H2. After 4 h the
mixture was diluted with ethyl acetate,
filtered through a layer of Celite, and evapo-
rated to yield 18 (260 mg), which was used
for further conversion without purification.
1
7.09° (c 1.0, CHCl3); H NMR (360 MHz,
CDCl3): l 7.53–7.28 (m, 5 H, Ph), 5.63 (d, 1
H, H-1, J1,2 5 Hz), 4.93 (dd, 2 H, CH2-Ph,
Jgem 12 Hz), 4.67 (dd, 1 H, H-3, J2,3 8 Hz,
J3,4 2.1 Hz), 4.44 (d, 1 H, H-1%, J1%,2% 8 Hz),
4.38 (dd, 1 H, H-2), 4.32 (dd, 1 H, H-4,
J4,5 1.7 Hz), 4.21–4.10 (m, 4 H, H-3%, H-4%,
H-5, H-6), 3.86 (dt, 1 H, H-5%, J4%,5% 2 Hz,
J5%,6a%=J5%,6b% 6 Hz), 3.77 (m, 3 H, H-6,
H-6%ab), 3.43 (dd, 1 H, H-2%, J2%,3% 6 Hz),
3.28 (s, 3 H, OCH3), 1.61–1.32 (4 s, each 3
H, 4 CH3ip.). Anal. Calcd for C32H48O12
(624,73): C, 61.52; H, 7.74. Found: C, 61.37;
H, 7.72.
2,3,5-Tri-O-benzoyl-h-
(1“2)-3,4,6-tri-O-acetyl-i-
nosyl - (1“6) - 1,2,3,4 - tetra - O - acetyl - h,i -
L
-arabinofuranosyl-
D
-galactopyra-
D
-
galactopyranose (19).—A mixture of 18 (130
mg, 0.200 mmol), powdered Hg(CN)2 (110
,
mg, 2.2 equivalents), and 4 A molecular
sieves (500 mg) in dry CH3CN (3 mL) was
stirred for 30 min., compound 7 (200 mg,
0.380 mmol) in 1 mL of dry CH3CN was
added and the mixture was stirred overnight.
The work-up procedure was the same as
that described for compound 2. The residue
was purified by column chromatography
2-O-Benzyl-3,4-O-isopropylidene-i-
actopyranosyl-(1“6)-1,2:3,4-di-O-isopropyli-
dene-h- -galactopyranose (15).—To a solu-
D
-gal-
D
tion of 14 (3.0g, 4.8 mmol) in 50 mL of
CH2Cl2, 2 mL of 96% acetic acid and two
drops of water were added, and the solution

108
A. Borba´s et al. / Carbohydrate Research 318 (1999) 98–109
1a), 84.80 (C-4¦), 81.49 (C-2¦), 77.44 (C-3¦),
76.57 (C-2%), 75.66 (C-5%), 74.28 (C-5b), 73.50
(C-3b), 73.21 (C-2b), 72.37 (C-3%), 69.94 (C-
4a), 69.87 (C-6a), 69.86 (C-3a), 69.74 (C-5a),
69.59 (C-6b), 69.39 (C-4b, C-4%), 68.86 (C-
2a), 61.94 (C-5¦), 61.48 (C-6%). Anal. Calcd
for C17H30O15 (474.42): C, 43.03; H, 6.37.
Found: C, 43.37; H, 6.40.
(93:7 CH2Cl2–acetone, Rf 0.55) to yield 19
(152 mg, 70.1%), which was characterized af-
ter deprotection.
h-
furanosyl - (1“6)] - i -
(1“6)- -galactose (20).—To a solution of 8
L
-Arabinofuranosyl-(1“2)-[h-
L
-arabino-
D
- galactopyranosyl-
D
(370 mg, 0.270 mmol) in dry MeOH (10
mL) a catalytic amount of NaOMe was
added and was stirred overnight. The solu-
tion was neutralized with Amberlite IR-120
H+ ion-exchange resin, filtered and evapo-
rated. The residue was treated with aq 90%
trifluoroacetic acid for 15 min, the product
was precipitated by addition of diethyl ether,
filtered, and washed twice with diethyl ether
to yield 20 (120 mg, 73.3% for two steps);
[h]2D2 −26.38 (c 0.29, H2O); 13C NMR (90
MHz) l 108.79 (C-1¦1¦“2¦), 108.49 (C-1¦1¦“6¦),
103.75, 102.53 (C-1%), 97.32, 96.96 (C-1b),
93.13, 92.93 (C-1a), 70.06 (C-6a), 69.95 (C-
6b), 67.87 (C-6%), 61.95, 61.75 (2×C-5¦).
Anal. Calcd for C22H38O19 (606.52): C,
43.56; H, 6.31. Found: C, 43.81; H, 6.33.
Acknowledgements
This research was supported by the Hun-
garian Scientific Research Fund (OTKA
T025244).
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pyranosyl-(1“6)-
D
-galactose (21).—Com-
pound 21 was prepared from 9 by the same
method as described for 20. Compound 21:
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MHz) l 108.54 (C-1¦), 103.80 (C-1%), 97.05
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2), 77.03 (C-3¦), 74.45 (C-5b, C-5%), 73.17 (C-
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was also prepared starting from 11 and from
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.
.,