Chemical transformation of lactose into 4-O-beta-D-galactopyranosyl-D-glucuronic acid (pseudolactobiouronic acid) and some derivatives thereof.

Article abstract of DOI:10.1016/S0008-6215(02)00084-8

The selective oxidation of the primary alcoholic function of the reducing unit of lactose was achieved in good overall yield (67%) starting from 2',6'-di-O-benzyl-2,3:3',4'-di-O-isopropylidenelactose dimethyl acetal (1) through a simple multi-step procedure based on the selective acetylation of OH-5 of 1 (methoxyisopropylation, acetylation, de-methoxyisopropylation) followed by a two-step oxidation at C-6 (TPAP-NMO then TEMPO-NaOCl) and finally, complete removal of the protecting groups.

Full text of DOI:10.1016/S0008-6215(02)00084-8

Carbohydrate Research 337 (2002) 991–996
www.elsevier.com/locate/carres
Chemical transformation of lactose into
4-O-b-
D
-galactopyranosyl-
D
-glucuronic acid (pseudolactobiouronic
acid) and some derivatives thereofꢀ
Emanuele Attolino, Giorgio Catelani,* Felicia D’Andrea, Leonardo Puccioni
Dipartimento di Chimica Bioorganica e Biofarmacia, Uni6ersita` degli Studi di Pisa, 6ia Bonanno, 33, I-56126 Pisa, Italy
Received 11 January 2002; accepted 18 March 2002
Abstract
The selective oxidation of the primary alcoholic function of the reducing unit of lactose was achieved in good overall yield
(67%) starting from 2%,6%-di-O-benzyl-2,3:3%,4%-di-O-isopropylidenelactose dimethyl acetal (1) through a simple multi-step proce-
dure based on the selective acetylation of OH-5 of 1 (methoxyisopropylation, acetylation, de-methoxyisopropylation) followed by
a two-step oxidation at C-6 (TPAP-NMO then TEMPO-NaOCl) and finally, complete removal of the protecting groups. © 2002
Elsevier Science Ltd. All rights reserved.
Keywords: Lactose; Pseudoaldobiouronic acids; Pseudolactobiouronic acid; Oxidations
additive4 with equilibrating properties on the intestinal
microflora.5 We present here, a new and more efficient
preparation of 17 and some of its derivatives starting
from the diol 1, easily obtained from lactose through
a simple and short procedure recently described by
us.6
1. Introduction
Uronic acids are an important class of monosaccha-
ride constituents of various types of animal, bacterial,
and plant polysaccharides.2 Two different types of dis-
accharides could be formed from an uronic acid and a
neutral aldose. Those containing the neutral aldose unit
at the reducing end (aldobiouronic acids) are by far the
best known ones, because they are obtained as the main
products during the acid hydrolysis of natural polysac-
charides, owing to the higher stability of the uronic
glycosidic bond under these hydrolytic conditions.2 The
other type of disaccharides, having a reducing uronate
unit (pseudoaldobiouronic acids), is generally obtained
2. Results and discussion
The selective protection of the hydroxyl group at C-5
of 1, in order to realize a selective oxidation at C-6, was
performed using
a mixed 1-methoxy-1-methylethyl
(MIP) acetal as an easily removable temporary protect-
ing group of the primary alcoholic function. The
methoxyisopropylation reaction of 1 with pyridinium
tosylate (10% mol) as a catalyst and an excess (1.6
equiv) of 2-methoxypropene in dichloromethane at 0 °C
gave, in high yield ($90%), a 4:1 mixture of the two
isomeric mixed acetals 2 and 3. This reaction, however,
proved to be not completely reproducible, variable
amounts of the known6 5,6-O-isopropylidene acetal
(15) being obtained in some runs, evidently because of
a subsequent intramolecular transacetalation of either 2
or 3.
by synthetic procedures, as for instance, 4-O-b-
galactopyranosyl- -glucuronic acid (17, pseudolactobi-
ouronic acid), prepared in low yield from lactose by
Chiba et al.3 or its 3-O-b-
-galactopyranosyl isomer,
D-
D
D
obtained by enzymatic means, and proposed as a food
ꢀ Part 15 of the series ‘‘Rare and complex saccharides from
-galactose and other milk derived carbohydrates’’. For part
D
14, see Ref. 1.
* Corresponding author. Tel.: +39-050-44074; fax: +39-
050-43321.
E-mail address: giocate@farm.unipi.it (G. Catelani).
0008-6215/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(02)00084-8

992
E. Attolino et al. / Carbohydrate Research 337 (2002) 991–996
This side-reaction was completely avoided with the
Compound 16 is an interesting representative of the
very little explored class of glycosylated 1,5-dicarbonyl
hexoses that we recently used for the stereoselective
weaker acid-catalyst, triethylammonium chloride (50%
mol) and a small excess (1.2 equiv) of 2-methoxypropene
in dichloromethane at room temperature. Under these
conditions, we obtained with high yield (93%) and in a
completely reproducible manner the isomeric mixed
acetal mixture (2+3) in the same (4:1) ratio.
The routine acetylation with acetic anhydride in pyr-
idine of this mixture led, with about quantitative yield,
to a mixture of compounds 4 and 5 that were de-O-
methoxyisopropylated to the acetates 6 and 7, by treat-
ment with pyridinium tosylate in methanol. Whereas we
were not able to find satisfactory conditions for the
separation of compounds 4 and 5 over silica gel, the latter
two acetates have different Rf values. Their chromato-
graphic separation, however, caused an extensive isomer-
ization of 6 to 7, evidently arising from a silica gel
promoted migration of the acetyl group from a secondary
position to the primary one. For this reason, the crude
mixture containing 6+7 in 4:1 ratio was directly used
for the subsequent oxidation step. Initial attempts to
synthesis of 4-O-b-D-galactosylated 1-deoxynojirimycin
derivatives.9 The acetyl migration was, however, com-
pletely avoided using a two-step oxidation procedure
through the intermediate formation of the aldehyde 8.
The first step was achieved with tetrapropylammonium
perruthenate (TPAP) and 4-methylmorpholine-N-oxide
(NMO) giving a 4:1 mixture of 8 and 16, which was
directly transformed with TEMPO and NaOCl–
Bu4NBr into a mixture of 16 and the expected uronic
acid derivative 9. An easy chromatographic separation
of the above mixture gave pure 9 in high yield (70%)
from 1, through an overall procedure that, although
rather long (five steps), requires only one chromato-
graphic purification. The acid 9 was further quantita-
tively transformed into its methyl ester 12 by treatment
with an ethereal solution of CH2N2. Both 9 and 12 were
finally subjected to a standard sequence of deprotection
procedures. Their 5-O-deacetylation under Zemplen
conditions gave, in almost quantitative yield, crystalline
10 and 13, respectively, that in turn, were debenzylated
by catalytic hydrogenolysis with Pd(OH)2 on charcoal
to afford, in quantitative yields, the crystalline triols
11 and 14. Final treatment of 11 and 14 with 90%
aqueous trifluoroacetic acid allowed the removal of the
two isopropylidene protecting groups, the exposition of
the aldehyde function, and the concomitant formation
of the six-membered ring at the reducing uronate
moiety.
perform the direct oxidation of
6
to
9
were made through tetramethylpyrrolidine-N-oxide
(TEMPO) mediated reactions (TEMPO/NaOCl/
Bu4NBr7 or TEMPO/PhI(OAc)2 ), but in both cases, an
8
about quantitative formation of the 5-ulose derivative 16
was observed. Migration of the acetyl group to the
primary position is, evidently, faster than oxidation of
the primary alcoholic function, also under the mild
conditions employing hypervalent iodine as the co-
oxidant.

E. Attolino et al. / Carbohydrate Research 337 (2002) 991–996
993
carbon signals of the
D
-glucuronic moiety are different
3. Experimental
for the two anomers a- and b-17, with a general
deshielding for the b form, mainly for C-2 (Dl 4.2), C-1
(Dl 4.0), and C-3 and C-5 (Dl 2.3). We have not found
in literature any reference data for an anomeric couple
General methods.—Compound 1 was prepared ac-
cording to the published procedure.6 General methods
are those reported in a previous paper of this series.13
13C NMR assignments were made, whenever possible,
through DEPT experiments, by comparison with previ-
ously published data of analogous compounds,6,13 and
in the case of mixtures 2+3, 4+5, and 6+7, on the
basis of their relative signal intensities.
of 4-O-substituted
ever the 13C NMR data reported for the a and b
pyranose forms of
-glucuronic acid (20)11 and the a
D-glucopyranosyluronic acid; how-
D
and b pyranosides of methyl 4-O-methyl-D-glucuronate
(21)12† show a similar trend (Table 1), thus suggesting
the correctness of our assignments.
5-O-Acetyl-4-O-(2,6-di-O-benzyl-3,4-O-isopropyli-
The previously unreported methyl ester 18 was ob-
tained as a colorless syrup, consisting (13C NMR, D2O)
of an about 1:1 mixture of anomers, showing carbon
signal patterns very close to those of 17 (Table 1).
In conclusion, we have proposed here, a new efficient
synthetic access to pseudolactobiouronic acid (17). Al-
though this method requires a rather long sequence of
reactions, the simplicity of the methodologies, the high
yield of the overall sequence (67%), and the easy
availability of the starting material (1) appear very
attractive in view of the potential use of pseudolactobi-
ouronic acid (17) as a food additive.
dene-i-
D-galactopyranosyl)-2,3-O-isopropylidene-alde-
hydo- -glucuronic acid dimethyl acetal (9) and 6-O-ace-
D
tyl-4-O-(2,6-di-O-benzyl-3,4-O-isopropylidene-i-
galactopyranosyl) - 2,3 - O - isopropylidene - aldehydo -
xylo-aldohexos-5-ulose dimethyl acetal (16).
Methoxyisopropylation of 1:. A solution of 1 (4.20 g,
6.50 mmol) and triethylammonium chloride (464 mg,
3.5 mmol) in dry CH2Cl2 (90 mL) was stirred under an
Ar atmosphere for 10 min at rt. The solution was
cooled at 0 °C and a 1:10 (v/v) solution of freshly
distilled 2-methoxypropene in dry CH2Cl2 (9 mL, 8.10
mmol) was slowly added. After 1 h and 15 min stirring
D
-
-
D
Table 1
Selected 13C NMR signals in D2O (chemical shifts, l) of derivatives 17–21
C-1%
C-2%
C-3%
C-4%
C-5%
C-6%
C-1
C-2
C-3
C-4
C-5
C-6
COOMe
a
a-17
b-17
a-18
b-18
a-19
b-19
a-20
b-20
a,a-21
b,b-21
103.4
103.4
103.7
103.7
103.0
103.0
71.6
71.6
71.4
71.4
71.1
71.1
73.4
73.4
73.2
73.2
72.6
72.6
69.3
69.3
69.3
69.3
68.6
68.6
76.2
76.2
76.1
76.1
75.4
75.4
61.8
61.8
61.8
61.8
61.1
61.1
92.9
70.0
74.2
70.0
74.1
70.2
73.9
73.1
75.5
71.5
74.2
71.9
74.2
71.4
74.2
71.2
74.5
74.1
77.4
72.9
75.7
80.0
71.9
74.8
71.9
74.7
71.5
74.9
72.8
77.0
70.9
73.3
171.2
173.3
171.2
172.1
60.2
96.9
93.0
97.0
91.9
95.8
93.7
97.4
95.6
100.0
80.2 a
80.4 a
80.6 a
78.4
54.0
54.0
78.4
73.5
73.3
82.4
60.2
177.7
176.9
172.6
171.8
54.5
54.4
82.1
a Assignments may have to be interchanged.
† We thank a referee for having attracted our attention to
this helpful reference.

994
E. Attolino et al. / Carbohydrate Research 337 (2002) 991–996
at rt the mixture was neutralized with an excess of satd
NaHCO3 solution (20 mL), stirred for 10 min, extracted
with CH2Cl2 (4×50 mL), and the organic layer dried
over dry MgSO4. The solution was filtered and concen-
trated under diminished pressure to give a syrupy
residue (5.20 g) showing a single spot in TLC analysis
(Rf 0.54, 2:3 hexane–EtOAc). A flash chromatography
(3:2 hexane–EtOAc+0.1% Et3N) gave 4.35 g (93%
yield) of the mixed acetals 2 and 3 in a ratio of about
4:1 roughly estimated on the basis of the relative 13C
NMR signal intensities. Selected 1H NMR signals
(C6D6): l 3.08, 3.18, and 3.25 (2; 3 s, 3 H each, 3 OMe),
3.13, 3.14, and 3.22 (3; 3 s, 3 H each, 3 OMe). Selected
13C NMR signals (C6D6): l 24.7 and 24.8 (2; MIP
CMe2), 25.3 and 25.4 (3; MIP CMe2), 48.6 (2; MIP
OMe), 49.4 (3; MIP OMe), 62.3 (3; C-6), 62.7 (2; C-6),
69.6 (2; C-6%), 69.9 (3; C-6%), 72.6 (2; C-5 and C-5%), 73.0
(3; C-5, and C-5%), 74.3 (2; C-4%), 74.5 (3; C-4%), 75.7,
76.3, and 78.7 (3; C-2, C-3, and C-4), 76.5, 77.7, and
78.2 (2; C-2, C-3, and C-4), 79.8 (2 and 3; C-3%), 80.7 (2;
C-2%), 81.2 (3; C-2%), 100.3 (2; MIP CMe2), 101.6 (3;
MIP CMe2), 102.1 (3; C-1%), 102.9 (2; C-1%), 106.1 (2
and 3; C-1).
Acetylation of 2+ 3 mixtures: To a solution of the
2+3 mixture obtained as reported above (1.79 g, 2.48
mmol) in dry pyridine (10 mL), neat Ac2O (5.0 mL)
was added dropwise. The solution was stirred at rt and
left to react for 15 h, the mixture was concentrated
under diminished pressure, the residue coevaporated
with toluene (5×20 mL) to give a crude product
showing a single spot in TLC analysis (Rf 0.76, 2:3
hexane–EtOAc). The crude product was chro-
matographed on silica gel (2:3 hexane–EtOAc+0.1%
Et3N) to give 1.86 g (98% yield) of a mixture of
compounds 4 and 5, in an approximate ratio of 4:1.
Selected 13C NMR signals (C6D6): l 20.8 (4; MeCO),
21.4 (5; MeCO), 24.5 and 24.8 (4; MIP CMe2), 25.4 and
25.8 (5; MIP CMe2), 48.2 (4; MIP OMe), 49.5 (5; MIP
OMe), 53.5 and 55.3 (5; 2×OMe), 53.6 and 55.7 (4;
2×OMe), 59.3 (4; C-6), 65.4 (5; C-6), 69.5 (4; C-6%),
70.0 (5; C-6%), 73.0 (4; C-5, and C-5%), 73.2 (5; C-5, and
C-5%), 74.1 (4; C-4%), 74.4 (5; C-4%), 75.5, 76.6, and 78.2
(4; C-2, C-3, and C-4), 75.0, 75.0, and 76.2 (5; C-2, C-3,
and C-4), 78.9 and 79.8 (4 and 5; C-3%), 80.5 (4; C-2%),
80.7 (5; C-2%), 100.1 (4; MIP CMe2), 101.4 (5; MIP
CMe2), 101.7 (5; C-1%), 102.4 (4; C-1%), 105.9 (4 and 5;
C-1).
and extracted with CH2Cl2 (4×30 mL). The organic
phase was dried, filtered, and concentrated under re-
duce pressure to give a residue (1.60 g, 95% yield)
constituted exclusively by 6 and 7, showing two spots in
TLC analysis (Rf 0.40 and 0.33, 9:1 CH2Cl2–Me2CO) in
a 77:23 ratio roughly estimated from the relative inten-
sity of the peaks for the analogous carbons. Selected
13C NMR signals (CDCl3): l 21.4 (7; MeCO), 21.6 (6;
MeCO), 54.0 and 56.1 (7; 2×OMe), 54.1 and 56.2 (6;
2×OMe), 60.7 (6; C-6), 66.3 (7; C-6), 69.4 (6 and 7;
C-6%), 72.0 (7; C-5), 72.7 (6 and 7; C-5%), 74.2 and 75.2
(6; C-5, and C-4%), 74.2 (7; C-4%), 76.0, 76.5, and 78.3 (6;
C-2, C-3, and C-4), 77.0, 77.6, and 77.6 (7; C-2, C-3,
and C-4), 78.8 (7; C-3%), 79.6 (6; C-3%), 80.1 (6; C-2%),
80.3 (7; C-2%), 102.0 (6; C-1%), 103.2 (7; C-1%), 105.4 (7;
C-1), 105.6 (6; C-1). Anal. Calcd for C36H50O13: C,
62.54; H, 7.26. Found: C, 62.50; H, 7.43.
Two-step oxidation of 6+7 mixtures: To a solution
of a 6+7 mixture (1.20 g, 1.74 mmol) in dry CH2Cl2
,
(35 mL), activated crushed 4 A molecular sieves (1.20 g)
and NMO (380 mg, 2.85 mmol) were added. After 30
min stirring at rt under Ar, TPAP (73 mg, 0.21 mmol)
was added and the mixture was stirred for 2 h and then
filtered over two alternate paths of Celite and silica gel,
extensively washed first with CH2Cl2 and then with
EtOAc. The combined organic solutions were concen-
trated under diminished pressure to give a crude syrup
(1.20 g) containing of a mixture of 8 and 16, in an
$4:1 ratio, estimated on the basis of relative 13C NMR
signal intensities. Selected 1H NMR signals of 8
(CDCl3): l 1.30 (s, 6 H, CMe2), 1.42 and 1.43 (2 s, 3 H
each, CMe2), 2.10 (s, 3 H, MeCO), 3.37 (s, 6 H,
2×OMe), 5.46 (d, 1 H, J4,5 3.4 Hz, H-5), 9.83 (s, 1 H,
CHO). Selected 13C NMR signals of 8 (CDCl3): l 20.3
(MeCO), 25.9, 26.5, 27.1, and 27.3 (2×CMe2), 53.6
and 55.5 (2×OMe), 68.8 (C-6%), 71.9 (C-5%), 72.9 and
73.2 (2×benzylic CH2), 73.22, 75.3, and 75.5 (C-4, C-5,
and C-4%), 77.8, 78.3, 78.9, and 79.7 (C-2, C-3, C-2%, and
C-3%), 101.5 (C-1%), 104.7 (C-1), 195.8 (C-6).
The crude product (1.20 g) was dissolved in CH2Cl2
(10 mL), TEMPO (43 mg, 0.27 mmol) was added and
treated with satd aq NaHCO3 (2.0 mL) containing KBr
(14 mg) and Bu4NCl (32 mg). To the cooled (0 °C)
mixture, was slowly added, under vigorous stirring
during 45 min, a mixture of commercial aq NaClO
solution (3 M, 2.4 mL), satd aq NaCl (2.4 mL) and satd
aq NaHCO3 (1.2 mL). The mixture was warmed slowly
to rt and stirred until the starting material disappeared
(TLC analysis, 1:1 hexane–EtOAc). Dichloromethane
(50 mL) was added and the separated organic phase
washed with water (20 mL), dried (MgSO4), filtered and
concentrated under diminished pressure to give a
residue (1.10 g). Flash chromatography of the crude
product eluting first with 1:1 hexane–EtOAc, then with
10:1 EtOAc–MeOH, gave pure samples of 16 (218 mg,
18% yield) and 9 (998 mg, 80% yield).
Demethoxyisopropylation of 4+5 mixtures: A mix-
ture of 4+5 (1.86 g, 2.44 mmol), obtained as reported
above, was dissolved in MeOH (20 mL) and treated at
rt with pyridinium tosylate (16 mg, 0.06 mmol). The
mixture was stirred at rt for 30 min until the starting
material had disappeared (TLC analysis, 3:2 hexane–
EtOAc). The solution was concentrated under dimin-
ished pressure, diluted with CH2Cl2 (50 mL), and
neutralized by addition of satd aq NaHCO3 (20 mL),

E. Attolino et al. / Carbohydrate Research 337 (2002) 991–996
995
Compound 16: syrup, Rf 0.41 (1:1 hexane–EtOAc);
[h]D −37.2° (c 1.1, CHCl3); H NMR (CDCl3): l 1.32,
H-3, H-4, H-3%, and H-4%), 4.28 (d, 1 H, J1%,2% 7.8 Hz,
H-1%), 4.50 (d, 1 H, J1,2 7.0 Hz, H-1), 4.55 (s, 2 H,
benzylic CH2), 4.68 and 4.85 (AB system, 2 H, JA,B 12.0
Hz, benzylic CH2), 5.22 (d, 1 H, J4,5 7.8 Hz, H-5),
7.26–7.42 (m, 10 H, aromatic H). 13C NMR (CDCl3): l
20.5 (MeCO), 26.2, 26.7, 27.4, and 27.6 (2×CMe2),
52.6 (COOMe), 53.4 and 55.8 (2×OMe), 68.6 (C-6%),
71.9 (C-5%), 73.4 (2×benzylic CH2), 71.9, 74.4, 75.2,
76.6, and 76.6 (C-2, C-3, C-4, C-5, and C-4%), 78.7 and
79.3 (C-2% and C-3%), 102.0 (C-1%), 105.0 (C-1), 109.7 and
110.3 (2 CMe2), 127.4–128.3 (aromatic CH), 138.0 and
138.3 (aromatic C), 169.7 and 169.9 (MeCO and C-6).
Anal. Calcd for C37H50O14: C, 61.83; H, 7.01. Found:
C, 61.68; H, 7.16.
1
1.35, 1.38, and 1.42 (4 s, 3 H each, 2×CMe2), 2.10 (s,
3 H, MeCO), 3.31 and 3.35 (2 s, 3 H each, 2×OMe);
3.46 (m, 1 H, H-2%), 3.65–3.70 (m, 2 H, H-6%a, and
H-6%b), 3.85 (m, 1 H, H-5%), 4.13–4.39 (m, 7 H, H-3,
H-3%, H-4, H-4%, H-2, H-1, and H-1%), 4.49 and 4.58 (AB
system, 2 H, JA,B 12.1 Hz, benzylic CH2), 4.80 and 4.88
(AB system, 2 H, JA,B 11.9 Hz, benzylic CH2), 4.80 and
5.40 (AB system, 2 H, JA,B 18.3 Hz, H-6a, and H-6b),
7.24–7.41 (m, 10 H, aromatic H). 13C NMR (CDCl3): l
20.2 (MeCO), 26.0, 26.5, 27.0, and 27.5 (2×CMe2),
53.4 and 55.3 (2×OMe), 68.1 and 68.7 (C-6, and C-6%),
72.1 (C-5%), 72.8 and 73.2 (2×benzylic CH2), 73.4 and
74.9 (C-4, and C-4%), 78.4, 78.8, and 79.0 (C-3, C-2, and
C-3%), 80.8 (C-2%), 101.1 (C-1%), 104.8 (C-1), 109.7 and
110.5 (2×CMe2), 127.4–128.1 (aromatic CH), 137.6
and 137.8 (aromatic C), 169.9 (MeCO), 204.1 (C-5).
Anal. Calcd for C36H48O13: C, 62.78; H, 7.02. Found:
C, 62.60; H, 7.10.
4 - O - (2,6 - Di - O - benzyl - 3,4 - O - isopropylidene-i-
D-
galactopyranosyl)-2,3-O-isopropylidene-aldehydo- -glu-
D
curonic acid dimethyl acetal (10).—A solution of 9 (800
mg, 1.13 mmol) in MeOH (7 mL) was treated with 1 M
methanolic NaOMe (1.5 mL) and stirred at rt for 1 h.
The solution was neutralized with solid CO2 and con-
centrated under diminished pressure. The residue was
poured into water (5 mL) and extracted with CH2Cl2
(3×30 mL). The organic extracts were dried, filtered,
and concentrated to give pure (13C NMR) 10 (750 mg,
quantitative) as a white amorphous solid; Rf 0.21 (7:3
EtOAc–MeOH); mp 65–67 °C; [h]D −3.9° (c 1.0,
Compound 9: white solid foam, Rf 0.25 (7:3 EtOAc–
1
MeOH); mp 86–88 °C; [h]D +4.0° (c 1.0, CHCl3); H
NMR (CD3OD): l 1.34, 1.40, 1.49, and 1.54 (4 s, 3 H
each, 2×CMe2), 2.11 (s, 3 H, MeCO), 3.42 (s, 6 H,
2×OMe); 3.56–4.80 (m, 11 H, pyranose H), 4.86–5.02
(m, 4 H, 2×benzylic CH2), 5.35 (d, 1 H, J4,5 4.4 Hz,
H-5), 7.37–7.43 (m, 10 H, aromatic H). 13C NMR
(CD3OD): l 21.1 (MeCO), 26.6, 27.4, 27.7, and 28.1
(2×CMe2), 54.4 and 56.2 (2×OMe), 70.1 (C-6%), 73.0
(C-5%), 74.3 and 74.3 (2×benzylic CH2), 75.3 (C-4%),
76.0 and 76.0 (C-4, and C-5), 77.3, 78.3, and 79.9 (C-2,
C-3, and C-3%), 80.5 (C-2%), 102.1 (C-1%), 106.5 (C-1),
110.7 and 111.5 (2 CMe2), 128.4–129.3 (aromatic CH),
139.7 and 139.7 (aromatic C), 172.6 (MeCO), 176.2
(C-6). Anal. Calcd for C36H48O14: C, 61.35; H, 6.86.
Found: C, 61.05; H, 6.99.
1
CHCl3); H NMR (CD3OD): l 1.27 and 1.30 (2 s, 3 H
each, CMe2), 1.42 (s, 6 H, CMe2), 3.28 and 3.29 (2 s, 3
H each, 2×OMe); 3.16–3.90 (m, 18 H), 7.22–7.43 (m,
10 H, aromatic H). 13C NMR (CD3OD): l 26.5, 27.1,
27.8, and 28.2 (2×CMe2), 54.2 and 56.4 (2×OMe),
70.0 (C-6%), 73.0 and 74.0 (C-4% and C-5%), 74.3 (2×ben-
zylic CH2), 75.2, 77.1, 77.3, and 78.7 (C-2, C-3, C-4,
and C-5), 80.1 and 80.4 (C-2% and C-3%), 101.5 (C-1%),
106.2 (C-1), 110.8 and 111.8 (2×CMe2), 128.6–129.5
(aromatic CH), 139.2 and 139.5 (aromatic C), 177.9
(C-6). Anal. Calcd for C34H46O13: C, 61.62; H, 7.00.
Found: C, 61.87; H, 7.13.
Methyl 5-O-acetyl-4-O-(2,6-di-O-benzyl-3,4-O-iso-
propylidene - i -
dene-aldehydo-
D
- galactopyranosyl) - 2,3 - O - isopropyli-
D
-glucuronate dimethyl acetal (12).—A
Methyl 4-O-(2,6-di-O-benzyl-3,4-O-isopropylidene-i-
solution of 9 (800 mg, 1.13 mmol) in EtOAc (30 mL)
was treated with an ethereal solution of CH2N2, until
the yellow color persisted. Excess CH2N2 was destroyed
by dropwise addition of glacial AcOH, and then the
slightly acid solution was immediately washed with satd
aq NaHCO3, and extracted with EtOAc (3×30 mL).
The organic phase was dried (MgSO4), filtered, and
concentrated under diminished pressure to give 12 (826
mg) as a crude product. After a chromatography on
silica gel eluting with 1:1 hexane–EtOAc, a pure sample
of 12 (770 mg, 95% yield) was obtained as a syrup, Rf
0.43 (1:1 hexane–EtOAc); [h]D +9.6° (c 1.8, CHCl3);
1H NMR (CDCl3): l 1.28 and 1.32 (2 s, 3 H each,
CMe2), 1.42 (s, 6 H, CMe2), 2.11 (s, 3 H, MeCO), 3.34
(m, 1 H, H-2%), 3.34 and 3.35 (2 s, 3 H each, 2×OMe);
3.62 (s, 3 H, COOMe), 3.66–3.70 (m, 2 H, H-6%a, and
H-6%b), 4.11 (m, 1 H, H-5%), 4.19–4.36 (m, 5 H, H-2,
D-galactopyranosyl)-2,3-O-isopropylidene-aldehydo-D-
glucuronate dimethyl acetal (13).—A solution of 12 (800
mg, 1.11 mmol) was treated as described above for the
preparation of 10, giving in quantitative yield 13 (756
mg) as a crystalline white solid, Rf 0.33 (1:1 hexane–
EtOAc); mp 117 °C (from Et2O–hexane); [h]D +10.1°
1
(c 0.9, CHCl3); H NMR (CDCl3): l 1.32, 1.35, 1.40,
and 1.41 (4 s, 3 H each, 2×CMe2), 3.33 and 3.34 (2 s,
3 H each, 2×OMe), 3.40 (m, 2 H, H-2%, and H-5), 3.70
(s, 3 H, COOMe), 3.67–3.91 (m, 3 H, H-5%, H-6%a, and
H-6%b), 4.07–4.17 and 4.43–4.50 (2 m, 5 H, H-2, H-3,
H-4, H-3%, and H-4%), 4.31 (d, 1 H, J1,2 6.0 Hz, H-1),
4.46 (d, 1 H, J1%,2% 7.8 Hz, H-1%), 4.54 and 4.56 (AB
system, 2 H, JA,B 12.1 Hz, benzylic CH2), 4.75 and 4.90
(AB system, 2 H, JA,B 11.5 Hz, benzylic CH2), 7.23–
7.46 (m, 10 H, aromatic H). 13C NMR (CDCl3): l 26.3,
26.5, 27.3, and 27.8 (2×CMe2), 52.2 (COOMe), 53.4

996
E. Attolino et al. / Carbohydrate Research 337 (2002) 991–996
and 55.6 (2×OMe), 69.0 (C-6%), 72.1, 72.2, 73.5, and
75.3 (C-4, C-5, C-4%, and C-5%), 73.5 (2×benzylic CH2),
77.0 and 77.1 (C-2, and C-3), 79.0 and 79.5 (C-2%, and
C-3%), 102.2 (C-1%), 105.0 (C-1), 109.8 and 110.7 (2×
CMe2), 127.6–128.5 (aromatic CH), 137.9 and 138.0
(aromatic C), 172.7 (C-6). Anal. Calcd for C35H48O13:
C, 62.12; H, 7.15. Found: C, 62.38; H, 7.21.
pressure, coevaporated with toluene (3×25 mL), and
stored 24 h under diminished pressure over KOH pel-
lets, giving a white solid residue (350 mg, quantitative)
constituted (13C NMR, D2O) exclusively by a 45:55 a/b
anomeric mixture of 17, as established on the basis of
the integration of the anomeric carbon signals. An
analytical sample of 17 was obtained by crystallization
from a 1:5 mixture of 10% aq MeOH and EtOH, Rf
4-O-(3,4-O-Isopropylidene-i-
D -galactopyranosyl)-
2,3-O-isopropylidene-aldehydo- -glucuronic acid di-
D
0.16 (2:3 EtOAc–MeOH); mp 177–180 °C; [h]D +
methyl acetal (11).—A solution of 10 (740 mg, 1.12
mmol) in MeOH (10 mL) containing 5% Pd(OH)2 on
charcoal (40 mg) was stirred at rt under an H2 atmo-
sphere for 24 h. The solution was diluted with MeOH
(30 mL), filtered over Celite, concentrated under dimin-
ished pressure to give pure (13C NMR) 11 as a white
solid (526 mg, 97% yield), Rf 0.31 (2:3 EtOAc–MeOH);
mp 163–164 °C (from EtOAc); [h]D +3.3° (c 1.0,
28.9° (c 0.8, water); lit.3 mp 159–160 °C; [h]D +45.5°
(c 1.11, water); 13C NMR data see Table 1. Anal. Calcd
for C12H20O12: C, 40.45; H, 5.66. Found: C, 40.30; H,
5.80.
Methyl 4-O-i-D-galactopyranosyl-h,i-D-glucuronate
(18).—A solution of 14 (280 mg, 0.56 mmol) was
hydrolyzed as reported above for 11 giving pure 18 (208
mg, quantitative) as a syrup containing (13C NMR,
D2O) an about 1:1 a/b anomeric mixture, Rf 0.15 (7:3
EtOAc–MeOH); [h]D +38.0° (c 1.0, MeOH); 13C
NMR data see Table 1. Anal Calcd. for C13H22O12: C,
42.17; H, 5.99. Found: C, 42.06; H, 5.88.
1
CHCl3); H NMR (CD3OD): l 1.33 and 1.47 (2 s, 3 H
each, CMe2), 1.42 (s, 6 H, CMe2), 3.44 and 3.45 (2 s, 3
H each, 2×OMe), 3.20–4.93 (m, 16 H). 13C NMR
(CD3OD): l 26.6, 26.6, 27.6, and 28.5 (2×CMe2), 54.6
and 57.3 (2×OMe), 62.6 (C-6%), 74.5, 74.9, 74.9, and
75.2 (C-4, C-5, C-2%, and C-5%), 77.2, 77.6, 78.6, and
81.1 (C-2, C-3, C-3%, and C-4%), 102.0 (C-1%), 107.4
(C-1), 111.1 and 111.4 (2×CMe2), 177.8 (C-6). Anal.
Calcd for C20H34O13: C, 49.79; H, 7.10. Found: C,
49.98; H, 7.24.
References
1. Corsaro, A.; Catelani, G.; D’Andrea, F.; Fisichella, S.;
Mariani, M., Pistara`, V. En6iron. Sci. Poll. Res. Online
first: htpp//dx.dai.org/10.1065/espr2001.12.104.2
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New York, 1980; Vol. 1B, p 1013.
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hedron Lett. 2001, 42, 1139–1142.
Methyl 4-O-(3,4-O-isopropylidene-i-
osyl) - 2,3 - O - isopropylidene - aldehydo -
D
-galactopyran-
- glucuronate
D
dimethyl acetal (14).—A solution of 13 (450 mg, 0.66
mmol) was debenzylated in EtOAc (6 mL) as described
above for 11 to give 14 as a white solid (328 mg,
quantitative), Rf 0.16 (EtOAc); mp 118–120 °C (from
EtOAc–hexane); [h]D +29.7° (c 1.5, CHCl3); 1H NMR
(CDCl3): l 1.32 and 1.50 (2 s, 3 H each, CMe2), 1.42 (s,
6 H, CMe2), 3.50 (s, 6 H, 2×OMe); 3.53–3.75 (m, 3
H), 3.79 (s, 3 H, COOMe), 3.81–4.09 (m, 8 H), 4.25 (d,
1 H, J1%,2% 8.1 Hz, H-1%), 4.37 (d, 1 H, J1,2 6.6 Hz, H-1),
4.45 (m, 1 H), 4.56 (dd, 1 H, J2,3 7.7 Hz, H-2). 13C
NMR (CDCl3): l 26.1, 26.1, 27.0, and 28.0 (2×CMe2),
52.5 (COOMe), 54.4 and 57.5 (2×OMe), 62.2 (C-6%),
71.8 (C-5%), 73.4, 73.4, 74.6, and 75.3 (C-4, C-5, C-2%,
and C-4%), 76.4 and 76.9 (C-2, and C-3), 79.0 (C-3%),
102.1 (C-1%), 106.9 (C-1), 110.1 and 110.4 (2×CMe2),
173.0 (C-6). Anal. Calcd for C21H36O13: C, 50.80; H,
7.31. Found: C, 50.95; H, 7.36.
10. Bock K.; Pedersen C.; Pedersen H. Ad6. Carbohydr.
Chem. Biochem. 1984, 42, 193–225.
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13. Barili P. L.; Berti G.; Catelani G.; D’Andrea F.; Puccioni
L. J. Carbohydr. Chem. 2000, 19, 79–91.
4-O-i-
D
-Galactopyranosyl-h,i-
D
-glucuronic
acid
(pseudolactobiouronic acid) (17).—A solution of 11 (480
mg, 1.0 mmol) in 90% aq CF3COOH (5 mL) was
stirred at rt for 30 min, then concentrated at reduced