Efficient synthesis of building blocks for branched rhamnogalacturonan i fragments

Article abstract of DOI:10.1016/j.carres.2013.06.019

Starting from allyl 2-O-acetyl-3-O-benzyl-α-l-rhamnopyranoside (3), allyl (2,3,4,6-tetra-O-benzoyl-β-d-galactopyranosyl)-(1→4)-2-O-acetyl- 3-O-benzyl-α-l-rhamnopyranoside (5) was synthesized under Helferich conditions. Module 5 was converted to 2,3,4,6-te

Full text of DOI:10.1016/j.carres.2013.06.019

Carbohydrate Research 380 (2013) 9–15
Contents lists available at SciVerse ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Efficient synthesis of building blocks for branched
rhamnogalacturonan I fragments
Amayak Pogosyan a, Andreas Gottwald a, Dirk Michalik a,b, Hans-Ulrich Endress c, Christian Vogel a,
⇑
a University of Rostock, Institute of Chemistry, Albert-Einstein-Strasse 3a, D-18059 Rostock, Germany
b Leibniz Institute for Catalysis at the University of Rostock, Albert-Einstein-Str. 29a, D-18059 Rostock, Germany
c Herbstreith & Fox, Pectin-Factory Neuenbuerg, Turnstrasse 37, D-75305 Neuenbuerg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 May 2013
Received in revised form 15 June 2013
Accepted 20 June 2013
Available online 28 June 2013
Starting from allyl 2-O-acetyl-3-O-benzyl-
a
-
L
-rhamnopyranoside (3), allyl (2,3,4,6-tetra-O-
benzoyl-b-
under Helferich conditions. Module 5 was converted to 2,3,4,6-tetra-O-benzoyl-b-
(1?4)-2-O-acetyl-3-O-benzyl- -rhamnopyranosyl bromide (8) which was then coupled with methyl
(allyl 2,3-di-O-benzyl-b- -galactopyranosid)uronate (11) to provide methyl (2,3,4,6-tetra-O-benzoyl-
b- -galactopyranosyl)-(1?4)-(2-O-acetyl-3-O-benzyl- -rhamnopyranosyl)-(1?4)-(allyl 2,3-di-O-
benzyl-b- -galactopyranosid)uronate (14). Alternatively, module 5 was transformed into allyl
2,3,4,6-tetra-O-benzoyl-b- -galactopyranosyl-(1?4)-3-O-benzyl- -rhamnopyranoside (9) suitable as
an acceptor for the glycosylation with methyl 4-O-acetyl-2,3-di-O-benzyl- /b- -galactopyranosyluronate
N-phenyl trifluoroacetimidate (13) to yield allyl (methyl 4-O-acetyl-2,3-di-O-benzyl- -galactopyr-
anosyluronate)-(1?2)-[2,3,4,6-tetra-O-benzoyl-b- -galactopyranosyl]-(1?4)-3-O-benzyl- -rhamno-
D-galactopyranosyl)-(1?4)-2-O-acetyl-3-O-benzyl-
a-L-rhamnopyranoside (5) was synthesized
D-galactopyranosyl-
a
-L
D
D
a-L
Keywords:
D
D
-Galacturonate N-phenyl
trifluoroacetimidate
-Galactosyl- -rhamnose building block
D
a-L
a
D
D
L
a
-D
Pectin fragments
Glycosylation
D
a-L
Oligosaccharides
pyranoside (15). Both trisaccharides modules are suitable for the synthesis of branched pectin fragments.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
adopted for the synthesis of building blocks for
branched RG-I fragments involved the preparation of a b-
ose-(1?4)- -rhamnose intermediate (5) which allowed either as
donor the stereoselective formation of the required
glycosidic bond to a -galacturonate, or as acceptor the
linkage by a
methyl 4-O-acetyl-2,3-di-O-benzyl-
D
-galactose-
D-galact-
Highly branched pectins, which are comprised of a rhamnoga-
lacturonan (RG I) backbone carrying galactan and arabinan side-
chains, are generally referred to as hairy regions. Even though
the composition of the hairy regions has been well established in
many plants, their biological function is still unknown.1
L
a
a
-(1?4)-
-(1?2)-
D
D
-galacturonate. In the latter case the potential of
/b- -galactopyranosyluronate
a
D
While the isolation of such fragments of defined structure and
appreciable amounts remains cumbersome, to date, there also
has been no method available to prepare branched pectin frag-
ments with the aid of enzymes. Therefore, traditional synthetic
carbohydrate chemistry is applied to obtain these structures.2 Pur-
suing our programme directed towards the chemical synthesis of
well-defined pectin fragments for structure activity relationship
investigations3 we report herein an improved preparation of build-
N-phenyl trifluoroacetimidate (13) to function as glycosyl donor
has been proven for the first time. Both obtained trisaccharides
14 and 15 are suitable modules for branched pectin fragment
synthesis by modular design principle.
For the synthesis of a suitable galactosylrhamnose disaccharide,
allyl a-L
-rhamnopyranoside (1)4 was regioselectively mono-benzy-
lated (2)5 by stannylation methodology.6 Regioselective esterifica-
tion of benzyl derivative 2 was achieved by dropwise addition of
diluted acetyl chloride at low temperature7 to provide the rhamno-
syl acceptor 3 in 60% yield (Scheme 1). In 1H NMR, a significant
downfield shift of about 1.34 ppm of proton H-2 in compound 3
compared to compound 2 confirmed acetylation at the 2-position.
The benzoylated galactosyl donor 48 was derived from penta-O-
ing blocks for D-galactose-branched RG-I fragments.
2. Results and discussion
The backbone of the RG-I polymer is composed of repeating
benzoyl-
and co-workers.10 Details for experimental procedure as well as
analytical data for perbenzoylated -galactose and the correspond-
a-D
-galactopyranose8,9 using the procedure by Kochetkov
units of the disaccharide ?2)-
L-Rha-a-(1?4)-D-GalA-a-(1? In
these oligomers, the first -galactopyranose residue is b-glycosidi-
D
D
cally linked to the O-4 position of a rhamnose moiety. Our strategy
ing bromide 4 are provided in the experimental section, since the
available literature contains abridged information only.
Compound 3 was then glycosylated with bromide 4 in the pres-
⇑
Corresponding author. Tel.: +49 381 498 6430; fax: +49 381 498 6412.
E-mail address: christian.vogel@uni-rostock.de (C. Vogel).
ence of Helferich promotors11 to give disaccharide 5 in 82% yield.
0008-6215/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.carres.2013.06.019

10
A. Pogosyan et al. / Carbohydrate Research 380 (2013) 9–15
OR1
BzO
BzO
BzO
BzO
OBz
OBz
R2O
OAc
BnO
iii
O
O
R3O
+
O
O
O
BzO
BzO
Br
OAll
1 R1 = R2 = R3 = H
2 R1 = H R2 = Bn R3 = H
R1 = Ac R2 = Bn R3 = H
OAll
4
5
i
ii
3
iv
vii
BzO
BzO
BzO
BzO
OBz
OBz
OAc
OH
BnO
BnO
O
O
O
O
O
O
BzO
BzO
R
OAll
9
6 R = α/β OH
7 R = OAc
v
vi
8
R = Br
Scheme 1. Reagents and conditions: (i) Dibutyltin oxide, toluene, reflux, 3.5 h; then CsF, BnBr, DMF, 12 h, (2, 70%); (ii) AcCl in toluene, pyridine, 14 h, ꢀ40 ? ꢀ10 °C, Ar
atmosphere (3, 60%); (iii) 3+4 M ratio 1:1.3, Hg(CN)2, HgBr2, mol. sieves, acetonitrile, 24 h, 20 °C Ar atmosphere (5, 82%); (iv) PdCl2, AcOH, NaOAc, H2O, 2 h, 45 °C (6, 78%); (v)
Ac2O, pyridine, 20 °C, 24 h (7, 77%); (vi) Oxalylbromide, CH2Cl2, ꢀ40 °C, Ar atmosphere (8, 85%); (vii) 0.28 M methanolic HCl, 24 h, 20 °C (9, 63%).
The b-1,4 linkage was confirmed by 1D and 2D NMR experiments.
10 gave hemiacetal 12 , which appears in chloroform as an
ture in a ratio of 4:1 (Scheme 2). In the 1H NMR spectrum, the
assignment of the signals to and b anomers is based on the vic-
inal couplings of protons H-1 and H-2. The doublet at d 5.37 shows
a coupling constant of 3J1,2 3.6 Hz (H-1
) and the doublet at d 4.69
has a coupling constant of 3J1,2 7.5 Hz (H-1b). At this point, a novel
a,b mix-
1
In the H NMR spectrum of compound 5, proton H-10 appears as a
doublet at d 5.33 ppm with a coupling constant 3J1 ,2 7.9 Hz, while
HMBC shows a correlation between proton H-10 and carbon atom
C-4.
a
0
0
a
After deallylation of disaccharide 5 using palladium(II)chlo-
ride,12 resulting hemiacetal 6 was acetylated and then further con-
verted into bromide 8 applying the procedure of Wessel and
Bundle.13 In parallel, selective cleavage of the 2-O-acetyl group of
disaccharide 5 taking advantage of the differences in reactivity be-
tween the esters of acetic and benzoic acid14 furnished the glycosyl
acceptor 9 (Scheme 1).
leaving group for a
D-galacturonate glycosyl donor was intro-
duced.16 Treatment of 12 with N-phenyltrifluoro acetimidoyl
chloride17 in the presence of Cs2CO3 in acetone18 led to formation
of N-phenyl trifluoroacetimidate 13 which was isolated as an
a,b
mixture in a ratio of 1:5 in 88% yield. The anomeric proton signals
appear broadened at room temperature due to a dynamic process
in the N-phenyl trifluoroacetimidate moiety. Therefore, 1H NMR
spectra were recorded at lower temperature to allow the assign-
ment of the corresponding isomer signal. At ꢀ40°, both anomeric
Synthesis of either
D-galacturonate glycosyl acceptor 11 or
donor 13 starting from module 10 was performed following proce-
dures described previously by our group.15 Accordingly, deacetyla-
tion of 10 with 0.28 m methanolic HCl provided acceptor 5 with
only the O-4 position being unsubstituted, while deallylation of
signals appear as doublets, d 6.83 [3J1,2 3.3 Hz, H-1(
[3J1,2 8.3 Hz, H-1(b)], respectively.
a)] and d 5.78
HO
AcO
BnO
AcO
CO2Me
CO2Me
CO2Me
i
ii
O
O
O
OAll
OAll
BnO
BnO
BnO
BnO
BnO
R
11
10
12 R = α/β OH
iii
13 R = OC(=NPh)CF3
+ 8
iv
+ 9
v
AcO
BzO OBz
BzO
CO2Me
OAc
O
BnO
O
O
O
BnO
O
BnO
BnO
BzO
BzO
BzO
OBz
O
O
CO2Me
O
O
O
OAll
BzO
15
BnO
BnO
OAll
14
Scheme 2. Reagents and conditions: (i) 0.28 M methanolic HCl, 24 h, 20 °C(11, 90%); (ii) PdCl2, AcOH, NaOAc, H2O, 3 h, 45 °C (12, 75%) (iii) Cs2CO3, 2,2,2-trifluoro-N-phenyl-
acetimidoyl chloride, acetone, 3 h, 20 °C (13, 88%); (iv) 8:11 M ratio 1.3:1, Hg(CN)2, HgBr2, mol. sieves, acetonitrile, 24 h, 20 °C Ar atmosphere (14, 65%); (v) TMSOTf, mol.
sieves, dry CH2Cl2, 3 h, ꢀ30 ? 20 °C, Ar atmosphere (15, 66%).

A. Pogosyan et al. / Carbohydrate Research 380 (2013) 9–15
11
Earlier experiments using the
a- or b-steroisomers of the
3.2. Allyl a-L-rhamnopyranoside (1)
corresponding trichloroacetimidates have shown that the
a- or
b-configuration at the anomeric centre of the glycosyl donor had
no effect on the stereoselectivity of the subsequent glycosylation
a/b- mixture of 13 was used in the
glycosylation step with 9 as glycosyl acceptor. Using TMSOTf as
OH
2
reaction.12b Therefore, an
HO
4
3
HO
promoter, trisaccharide 15 was obtained in 66% yield (Scheme 2).
O
1
6
1
In the H NMR spectrum of 15 proton H-10 appears as a doublet
5
3
0
0
at d 4.97 with a coupling constant J1 ,2 3.8 Hz, proving an
a
-link-
O
7
age. This is also supported by the NOESY where no correlation
was found between H-10 and H-50 and the C,H coupling constant
9
8
1
0
0
JC-1 ,H-1 = 170 Hz, which is in the range of
a-manno configurated
O-glycosides.19
.
Hereby, according to our modular design principle,3,15 deacety-
lation of module 15 furnished the desired glycosyl acceptor, while
deallylation of module 15 followed by introduction of a suitable
leaving group provided a glycosyl donor. Here, the rhamnosyl
moiety carries the donor functionality whereas the hydroxyl group
of galacturonate residue serves as acceptor. Vice versa, galacturo-
nate acceptor 11 was coupled with rhamnosyl donor bromide 8
to provide trisaccharide 14 in 65% yield (Scheme 2). All reported
results are isolated yields. Due to the manno-configurated glycosyl
donor, the stereochemical outcome of a glycosylation reaction
cannot be proven on the basis of chemical shift and the coupling
Acetyl chloride (1.35 mL, 18.9 mmol) was added dropwise to al-
lyl alcohol (20 mL) at 0 °C. After stirring for 20 min -rhamnose
L
monohydrate (2.5 g, 13.7 mmol) was added and the solution was
heated under reflux. After 3 h (monitored by TLC) the equilibrium
among the glycosides is constant and the the reaction mixture was
neutralized with NaHCO3 (3 g). The salts were filtered off and then
washed with chloroform (3 ꢂ 10 mL). The combined organic solu-
tions were concentrated and the residue was purified by column
chromatography (1:1?0:1 PE–EtOAc) to remove unwanted iso-
mers. Compound 1 (2.27 g 81%) was obtained as a colourless syrup:
a 2D2
ꢃ
ꢀ 123:8 (c 1.0, CHCl3); Rf 0.25 (EtOAc); 1H NMR (300.13 MHz,
3
½
constant J1,2 alone, but again both the absence of a correlation
3
3
3
between protons H-10 and H-50 in a NOESY spectrum of 14 and
CDCl3): d 5.87 (dddd, 1H, J8,9(Z) 17.2 Hz, J7a,8 5.2 Hz, J7b,8 6.0 Hz,
3J8,9(E) 10.4 Hz, H-8), 5.27 (d0q0, 1H, J8,9(Z) 17.2 Hz, J7,9 = 2J 1.5 Hz,
3
4
the C,H coupling constant (1JC-1 ,H-1 = 174 Hz) suggest an
a
-linkage.
0
0
H-9(Z)), 5.18 (d0q0, 1H, J8,9(E) 10.4 Hz, J7,9 = 2J 1.5 Hz, H-9(E)), 4.79
3
4
In conclusion, the optimized conversion of
L-rhamnose into the
3
3
(d, 1H, J1,2 1.3 Hz, H-1), 4.66 (d, 1H, J3,OH 6.4 Hz, OH-3), 4.30 (d,
glycosyl acceptor 3, and its very successful coupling to disaccha-
ride module 5 which led either to glycosyl donor 8 or acceptor 9
are described. As counterparts, D-galacturonate acceptor 11 and
donor 13 were synthesized, and their glycosylation with 8 and
9, respectively, gave trisaccharides 14 and 15. The so obtained tri-
saccharides 14 and 15 are suitable as modules for the synthesis of
1H, 3J4,OH 4.7 Hz, OH-4), 4.22 (d, 1H, 3J2,OH 4.9 Hz, OH-2), 4.15 (dd0t0,
2
3
4
1H, J7a,7b 13.0 Hz, J7a,8 5.2 Hz, J7a,9 1.5 Hz, H-7a), 3.96 (dd0t0, 1H,
2J7a,7b 13.0 Hz, J7b,8 6.0 Hz, J7b,9 1.5 Hz, H-7b), 3.95–3.92 (m, 1H,
3
4
3
3
3
H-2), 3.77 (ddd, 1H, J3,4 9.5 Hz, J3,OH 6.4 Hz, J2,3 3.2 Hz, H-3),
3
3
3.64 (dq, 1H, J4,5 9.5 Hz, J5,6 6.2 Hz, H-5), 3.46 (ddd, 1H,
3J3,4 = 3J4,5 9.5 Hz, J4,OH 4.7 Hz, H-4), 1.29 (d, 3H, J5,6 6.2 Hz, H-
6); 13C NMR (75.5 MHz, CDCl3): d 133.6 (C-8), 117.6 (C-9), 98.9
(C-1), 72.8 (C-4), 71.7 (C-3), 71.0 (C-2), 68.2 (C-5), 68.0 (C-7),
17.5 (C-6). Anal. Calcd for C9H16O5 (204.22): C, 52.88; H, 7.83.
Found: C, 52.84; H, 7.81.
3
3
larger branched RG-1 fragments described in
article.
a consecutive
3. Experimental
3.1. General methods
3.3. Allyl 3-O-benzyl- -rhamnopyranoside (2)
a
-
L
Melting points were determined with a Boetius micro-heating
plate BHMK 05 (Rapido, Dresden) and were not uncorrected.
Optical rotation was measured for solutions in a 2-cm cell with
an automatic polarimeter GYROMAT (Dr. Kernchen Co.). 1H NMR
spectra (500.13 MHz and 300.13 MHz) and 13C NMR spectra
(125.8 and 75.5 MHz) were recorded using Bruker instruments
AVANCE 500 and AVANCE 300, with CDCl3 as solvents. NMR
spectra were calibrated using solvent signals (CDCl3: d 1H 7.25
and d 13C 77.0). The 1H and 13C NMR signals were assigned by DEPT
and two-dimensional 1H,1H COSY, 1H,1H NOESY and 1H,13C correla-
tion spectra (HMBC and HSQC). Elemental analysis was performed
on a CHNS-Flash-EA-1112 instrument (Thermoquest). All washing
solutions were cooled to ꢁ5 °C. The NaHCO3 solution was satu-
rated. Reactions were monitored by thin-layer chromatography
(TLC, Silica Gel 60, F254, 0.25 mm, Merck KGaA). The spots were
made visible by spraying with ethanolic 10% H2SO4 solution and
charring them for 10–30 s with a heat gun. Detection of benzyl
derivatives was effected by UV fluorescence. Preparative flash
chromatography was performed by elution from columns of
A mixture of allyl -L-rhamnopyranoside (1.43 g, 7.0 mmol) and
a
dibutyltin oxide (1.74 g, 7.0 mmol) in distiled toluene (35 mL) was
refluxed for 3.5 h in a Dean–Stark apparatus. Powdered CsF (2.11 g,
14.0 mmol) was added before the mixture was concentrated. The
residue was suspended in DMF (30 mL), benzyl bromide (1.2 mL,
14.0 mmol) was added and the resulting mixture was stirred over-
night at room temperature and then concentrated. The residue was
triturated with CH2Cl2 (30 mL), the mixture was filtered off and the
solids were repeatedly washed with CH2Cl2 (3 ꢂ 10 mL). The com-
bined filtrates were washed with brine (3 mL) and the organic
phase concentrated. The residue was purified by column chroma-
tography (2:1 PE/EtOAc) to provide compound 2 (1.45 g, 70%) as
a colourless syrup: ½a D22
ꢀ 42:5 (c 1.0, CHCl3); Rf 0.33 (1:1 PE/
ꢃ
EtOAc); 1H NMR (300.13 MHz, CDCl3): d 7.39–7.32 (m, 5H, Ph),
3
3
3
3
5.89 (dddd, 1H, J8,9(Z) 17.2 Hz, J8,9(E) 10.4 Hz, J7b,8 6.1 Hz, J7a,8
5.1 Hz, H-8), 5.28 (d0q0, 1H, J8,9(Z) 17.2 Hz, J7,9 = 2J 1.5 Hz, H-9(Z)),
3
4
5.20 (d0q0, 1H, J8,9(E) 10.4 Hz, J7,9 = 2J 1.5 Hz, H-9(E)), 4.86 (d, 1H,
3
4
3J1,2 1.6 Hz, H-1), 4.71 (d, 1H, 2J 11.5 Hz, CH2Ph), 4.57 (d, 1H, 2J
2
3
4
11.5 Hz, CH2Ph), 4.17 (dd0t0, 1H, J7a,7b 13.0 Hz, J7a,8 5.1 Hz, J7a,9
slurry-packed Silica gel 60 (Merck, 40–63 lm). All solvents and
2
1.5 Hz, H-7a), 4.04 (m, 1H, H-2), 3.98 (dd0t0, 1H, J7a,7b 13.0 Hz,
reagents were purified and dried according to standard proce-
dures.20 After classical work-up of the reaction mixtures, organic
layers were dried over MgSO4 and then concentrated under
reduced pressure (rotary evaporator).
3J7b,8 6.1 Hz, J7b,9 1.5 Hz, H-7b), 3.74–3.65 (m, 2H, H-3, H-5), 3.55
4
(ddd, 1H, J3,4 = 3J4,5 9.2 Hz, J4,OH 2.5 Hz, H-4), 2.43 (d, 1H, J2,OH
3
3
3
3
3
2.5 Hz, OH-2), 2.26 (d, 1H, J4,OH 2.5 Hz, OH-4), 1.30 (d, 3H, J5,6

12
A. Pogosyan et al. / Carbohydrate Research 380 (2013) 9–15
6.1 Hz, H-6); 13C NMR (75.5 MHz, CDCl3): d 137.7 (i-Ph), 133.7
(C-8), 128.7, 127.9 (o-Ph, m-Ph), 128.2 (p-Ph), 117.4 (C-9), 98.4
(C-1), 79.9 (C-3), 71.6 (C-4), 71.6 (CH2Ph), 67.9 (C-7), 67.8 (C-2),
67.7 (C-5), 17.6 (C-6). Anal. Calcd for C16H22O5 (294.34): C, 65.30;
H, 7.47. Found: C, 65.33; H, 7.46.
68.5 (C-3), 68.4 (C-4), 67.7 (C-2), 61.8 (C-6). Anal. Calcd for
C41H32O11 (700.69): C, 70.18; H, 4.56. Found: C, 70.27; H, 4.48.
Water (33 mL) was added dropwise to a mixture of acetyl bro-
mide (136 mL), glacial acetic acid (100 mL) and acetic anhydride
(4 mL) at ꢀ10 °C. The resulting, viscous solution, which contains
40% (w/w) of hydrogen bromide and 1% (w/w) of acetic anhydride,
can be safely kept in a refrigerator.10
3.4. Allyl 2-O-acetyl-3-O-benzyl-a-L-rhamnopyranoside (3)
The foregoing solution (10 mL) was added to a solution of ga-
lactose perbenzoate (2.1 g, 3.0 mmol) in dry chloroform (10 mL)
at 0 °C. The ice bath was removed and the reaction mixture was
stirred for 45 min at ambient temperature (monitored by TLC).
After cooling to 5 °C and dilution with cold chloroform (20 mL),
the mixture was poured into ice-water (30 mL). The organic layer
was separated and the aqueous layer was extracted with chloro-
form (3 ꢂ 3 mL), the combined organic layers were washed with
ice-water (2 ꢂ 10 mL), satd aq NaHCO3 (3 ꢂ 10 mL), ice-water
(10 mL), filtered through cotton and concentrated. The residue
was dried under high vacuum to give compound 5 (1.93 g, 97%)
as colourless foam. Bromide 4 was used for the next step directly
without further purification. An analytical sample gave the follow-
A solution of acetyl chloride (0.64 mL, 8.9 mmol) in toluene
(10 mL) was added dropwise to a solution of compound 2 (2.0 g,
6.8 mmol) in dry pyridine (50 mL) under an atmosphere of argon
at ꢀ40 °C. The mixture was stirred for 2 h at ꢀ40 °C, 2 h at –
20 °C and 12 h at –10 °C (monitored by TLC). After concentration
the residue was co-evaporated with toluene (4 ꢂ 10 mL). Purifica-
tion by column chromatography (4:1 PE/EtOAc) gave compound 3
(1.41 g, 60%) and allyl 2,4-di-O-acetyl-3-O-benzyl-
a
ꢃ
-
-rhamnopyr-
anoside (0.58 g, 14%) both as colourless syrup: ½a D22
L ꢀ 0:2 (c 1.0,
CHCl3); Rf 0.36 (2:1 PE/EtOAc); 1H NMR (300.13 MHz, CDCl3): d
3
3
7.38–7.27 (m, 5H, Ph), 5.89 (dddd, 1H, J8,9(Z) 17.2 Hz, J8,9(E)
3
3
3
10.4 Hz, J7b,8 6.1 Hz, J7a,8 5.1 Hz, H-8), 5.38 (dd, 1H, J2,3 3.2 Hz,
ing data: ½a 2D2
ꢃ
þ 237:3 (c 1.0, CHCl3); Rf 0.5 (2:1 PE/EtOAc); 1H NMR
3J1,2 1.8 Hz, H-2), 5.28 (d0q0, 1H, J8,9(Z) 17.2 Hz, J7,9 = 2J 1.5 Hz, H-
3
4
(300.13 MHz, CDCl3): d 8.10–7.20 (m, 20H, 4 ꢂ Ph), 6.00 (d, 1H, 3J1,2
3
4
9
(Z)), 5.21 (d0q0, 1H, J8,9(E) 10.4 Hz, J7,9 = 2J 1.5 Hz, H-9(E)), 4.79 (d,
3
3
4.0 Hz, H-1), 6.15 (dd, 1H, J3,4 3.2 Hz, J4,5 1.2 Hz, H-4), 6.07 (dd,
1H, J1,2 1.7 Hz, H-1), 4.72 (d, 1H, 2J 11.1 Hz, CH2Ph), 4.42 (d, 1H,
3
3
3
3
3
1H, J2,3 10.4 Hz, J3,4 3.2 Hz, H-3), 5.67 (dd, 1H, J2,3 10.4 Hz, J1,2
2J 11.1 Hz, CH2Ph), 4.17 (dd0t0, 1H, J7a,7b 13.0 Hz, J7a,8 5.1 Hz,
2
3
4.0 Hz, H-2), 4.95 (t, 1H, J5,6b 6.8 Hz,3J5,6a 6.4 Hz, H-5), 4.66 (dd,
3
4J7a,9 1.5 Hz, H-7a), 3.98 (dd0t0, 1H, J7a,7b 13.0 Hz, J7b,8 6.1 Hz,
4J7b,9 1.5 Hz, H-7b), 3.77–3.68 (m, 2H, H-3, H-5), 3.55 (0t0, 1H,
3J3,4 = 3J4,5 9.5 Hz, H-4), 2.35 (br s, 1H, OH), 2.12 (s, 3H, CH3CO),
1.32 (d, 3H, 3J 6.2 Hz, H-6); 13C NMR (75.5 MHz, CDCl3): d 170.3
(CH3CO), 137.6 (i-Ph), 133.5 (C-8), 128.5, 128.1(o-Ph, m-Ph),
128.0 (p-Ph), 117.6 (C-9), 97.0 (C-1), 77.7 (C-3), 71.6 (C-4), 71.4
(CH2Ph), 68.1 (C-5) 68.1 (C-2), 68.0 (C-7), 20.9 (CH3CO), 17.7 (C-
6). Anal. Calcd for C18H24O6 (336.38): C, 64.21; H, 7.14. Found: C,
64.27; H, 7.11. HRMS, ESI-TOF/MS positive (m/z): calcd for
2
3
1H, 2J 11.5 Hz, J5,6a 6.4 Hz, H-6a), 4.44 (dd, 1H, 2J 11.5 Hz, J5,6b
6.8 Hz, H-6b); 13C NMR (75.5 MHz, CDCl3): d 165.9, 165.5, 165.3,
164.3 (C@O), 133.8, 133.8, 133.3, 133.3 (p-Ph), 130.0, 129.9,
129.8, 129.7 (o-Ph), 129.2, 128.8, 128.7, 128.7, (i-Ph), 128.5,
128.5, 128.4, 128.3 (m-Ph), 88.3 (C-1), 71.8 (C-5), 68.9 (C-3), 68.6
(C-4), 68.1 (C-2), 61.6 (C-6).
3
3
3.6. Allyl (2,3,4,6-tetra-O-benzoyl-b-
D-galactopyranosyl)-(1?4)-
2-O-acetyl-3-O-benzyl- -rhamnopyranoside (5)
a-L
C
18H24O6 [M+Na]+: 359.2412, found: 359.2531.
Compound 4 (1.05 g, 1.6 mmol), compound 3 (0.4 g, 1.2 mmol)
and molecular sieves (4 Å, 0.4 g) were dried under high vacuum
for 2 h in darkness. The mixture was suspended in dry acetonitrile
(8 mL) and stirred under an atmosphere of argon at ambient tem-
perature. After 20 min Hg(CN)2 (0.3 g, 1.2 mmol), HgBr2 (0.2 g,
0.6 mmol) were added and stirring was continued at ambient tem-
perature. After 24 h (monitored by TLC) the mixture was diluted
with chloroform (40 mL) and filtrated over Celite. The filtrate
was extracted with ice-water (2 ꢂ 10 mL), aq 10% KI (3 ꢂ 10 mL),
ice-water (2 ꢂ 10mL), dried and concentrated. Purification of the
residue by column chromatography (4:1 PE/EtOAc) gave com-
3.5. 2,3,4,6-Tetra-O-benzoyl- -galactopyranosyl bromide (4)
a
-D
Molecular sieves (4 Å, 200 mg) were added to a solution of
-galactose (2 g, 11.1 mmol) in dry pyridine (25 mL) and the mix-
D
ture was stirred for 30 min under an atmosphere of argon. Benzoyl
chloride (8.5 mL, 66.6 mmol) was then added with intensive stir-
ring at ꢀ7 °C. After stirring for 18 h at room temperature (moni-
tored by TLC) the reaction mixture was cooled to 0 °C and excess
of benzoyl chloride was destroyed with methanol (3 mL). The
molecular sieves were filtrated off and washed with chloroform
(2 ꢂ 10 mL). The combined filtrate and washings were concen-
trated, and the residue was co-evaporated with toluene/ethylace-
tat/ethanol (5:3:1, 4 ꢂ 3 mL). The crude product was dissolved in
chloroform/heptane (1:2, 50 mL), washed with ice-water
(2 ꢂ 10 mL), satd aq NHCO3 (3 ꢂ 10 mL), ice-water (10 mL), filtered
through cotton and concentrated. The purification of the residue by
column chromatography (4:1 PE/EtOAc) gave 1,2,3,4,6-penta-O-
pound 5 (0.9 g, 82%) as colourless foam: ½a D22
þ 72:4 (c 1.0, CHCl3);
ꢃ
Rf 0.43 (2:1 PE/EtOAc); 1H NMR (500.13 MHz, CDCl3): d 8.09
(m, 2H), 8.02 (m, 2H), 7.88 (m, 2H), 7.76 (m, 2H, o-Bz), 7.65–7.21
3
3
0
0
0
0
(m, 17H, m-Bz, p-Bz, Ph), 5.98 (dd, 1H, J3 ,4 3.5 Hz, J4 ,5 0.9 Hz,
3
3
H-40), 5.86 (m, 1H, H-8), 5.80 (dd, 1H, J2 ,3 10.4 Hz, J1 ,2
0
0
0
0
3
3
7.9 Hz, H-20), 5.60 (dd, 1H, J2 ,3 10.4 Hz, J3 ,4 3.5 Hz, H-30), 5.33
0
0
0
0
3
(d, 1H, J1 ,2 7.9 Hz, H-10), 5.28–5.18 (m, 3H, H-2, H-9), 4.73 (d,
0
0
1H, J1,2 1.6 Hz, H-1), 4.68 (dd, 1H, 2J 11.1 Hz, J5 ,6a 6.5 Hz,
3
3
benzoyl-
a
-
D
-galactopyranose (7.7 g, quantitative) as colourless
0
0
crystals: mp 158–159 °C, lit.8a 158–159 °C; ½a D22
ꢃ
þ 187:1 (c 1.0,
0
0
H-6a0), 4.42 (dd, 1H, 2J 11.1 Hz, J5 ,6b 6.8 Hz, H-6b0), 4.41 (d, 1H,
3
CHCl3), lit.8a +187.1; Rf 0.35 (2:1 PE/EtOAc); 1H NMR
(300.13 MHz, CDCl3): d 8.15–7.81 (m, 10H, o-Ph), 7.68–7.24 (m,
0
0
0
0
0
0
2
3
3
3
J 11.0 Hz, CH2Ph), 4.32 (d0t0, 1H, J5 ,6b 6.8 Hz, J5 ,6a 6.5 Hz, J4 ,5
2
2
0.9 Hz, H-50), 4.20 (d, 1H, J 11.0 Hz, CH2Ph), 4.13 (dd0t0, 1H, J7a,7b
3
3
3
4
2
12.6 Hz, J7a,8 5.3 Hz, J7a,9 1.3 Hz, H-7a), 3.95 (dd0t0, 1H, J7a,7b
15H, m-Ph, p-Ph), 6.97 (d, 1H, J1,2 3.6 Hz, H-1), 6.21 (dd, 1H, J3,4
3
3
3
3
4
3.2 Hz, J4,5 1.2 Hz, H-4), 6.15 (dd, 1H, J2,3 10.6 Hz, J3,4 3.2 Hz,
12.6 Hz, J7b,8 6.3 Hz, J7b,9 1.3 Hz, H-7b), 3.82–3.75 (m, 3H, H-3,
3
3
H-4, H-5), 2.03 (s, 3H, CH3CO), 1.43 (d, 3H, J5,6 5.7 Hz, H-6); 13C
3
H-3), 6.05 (dd, 1H, J2,3 10.6 Hz, J1,2 3.6 Hz, H-2), 4.85 (d0t0, 1H,
3J5,6b 7.0 Hz, J5,6a 6.5 Hz, J4,5 1.2 Hz, H-5), 4.65 (dd, 1H, 2J
3
3
NMR (125.8 MHz, CDCl3): d 170.2 (CH3CO), 166.0, 165.6, 165.6,
165.4 (C@O), 137.8 (i-Ph), 133.4 (C-8), 133.5, 133.2, 133.2, 133.2
(p-Bz), 129.9, 129.7, 129.7, 129.6 (o-Bz), 129.4, 129.3, 129.2 128.8
(i-Bz), 128.7, 128.5, 128.5, 128.4, 128.3, 127.4 (m-Bz, o-Ph, m-Ph),
127.8 (p-Ph), 117.9 (C-9), 101.1 (C-10), 96.6 (C-1), 77.8, 77.1 (C-3,
C-4), 71.8 (C-30), 71.5 (CH2Ph), 70.8 (C-50), 70.3 (C-20), 68.5 (C-2),
11.3 Hz, J5,6a 6.5 Hz, H-6a), 4.44 (dd, 1H, 2J 11.3 Hz, J5,6b 7.0 Hz,
H-6b); 13C NMR (75.5 MHz, CDCl3): d 165.9, 165.7, 165.5, 165.4,
164.5 (C@O), 133.9, 133.7, 133.4, 133.4 133.2 (p-Ph), 129.9,
129.9, 129.7 (o-Ph), 129.5, 129.3, 129.0, 128.9, 128.8 (i-Ph),
128.7, 128.7, 128.4, 128.4, 128.3 (m-Ph), 90.6 (C-1), 69.4 (C-5),
3
3

A. Pogosyan et al. / Carbohydrate Research 380 (2013) 9–15
13
68.3 (C-40), 68.2 (C-7), 67.0 (C-5), 61.9 (C-60), 20.9 (CH3CO), 18.0 (C-
6). Anal. Calcd for C52H50O15 (914.94): C, 68.20; H, 5.46. Found: C,
68.23; H, 5.49.
concentration to half the volume toluene (8 mL) was added again
and concentrated. Obtained syrup of compound 8 (215 mg, 85%)
was unstable for storage and was used for the next step directly
without further purification: Rf 0.4 (2:1 PE/EtOAc).
3.7. 2,3,4,6-Tetra-O-benzoyl-b-
D-galactopyranosyl-(1?4)-2-O-
acetyl-3-O-benzyl- -rhamnopyranose (6)
L
3.10. Allyl 2,3,4,6-tetra-O-benzoyl-b-
D-galactopyranosyl-(1?4)-
3-O-benzyl- -rhamnopyranoside (9)
a
-L
Compound 6 (460 mg, 0.5 mmol) was added to a solution of
PdCl2 (180 mg, 1 mmol) and sodium acetate (136 mg, 1 mmol) in
aq 90% acetic acid (6 mL). After stirring for 2 h at 45 °C (monitored
by TLC) the reaction mixture was filtered through a layer of silica,
and the remaining salts were washed with methanol (2 ꢂ 3 mL).
The combined organic solutions were concentrated to a half of
the volume (ꢁ6 mL) and toluene (6 mL) was added. After concen-
tration to half the volume toluene (6 mL) was added again. The
procedure was repeated two times more. After concentration of
the mixture to dryness the residue was purified by column chro-
matography (5:1 Toluene/EtOAc) gave compound 7 (340 mg,
Compound 5 (3.4 g, 3.7 mmol) was added to a 0.28 M hydro-
chloric acid solution in methanol [prepared by adding of acetyl
chloride (2 mL) in ice-cold dry methanol (110 mL)] and the mix-
ture was stirred under argon atmosphere at ambient temperature.
After 24 h (monitored by TLC) PbCO3 ꢂ Pb(OH)2 (10 g) was added
to the reaction mixture and stirring was continued for an addi-
tional 2 h to neutralize hydrochloric acid. Salts were filtered off
by using a glass sintered filter funnel, with a layer of silica gel,
washed with methanol (3 ꢂ 30 mL) and the combined organic
solutions were concentrated. Purification of the residue by column
chromatography (3:1 PE/EtOAc) gave compound 9 (2.04 g, 63%) as
78%) as a colourless foam: Rf 0.3 (4:1 Toluene/EtOAc)
a and b; Anal.
Calcd for C49H46O15 (874.88): C, 67.27; H, 5.30. Found: C, 67.41; H,
5.42.
a colourless foam: ½a D23
þ 49:4 (c 1.0, CHCl3); Rf 0.3 (2:1 PE/EtOAc);
ꢃ
1H NMR (500.13 MHz, CDCl3): d 8.08 (m, 2H), 8.01 (m, 2H), 7.87 (m,
2H), 7.77 (m, 2H, o-Bz), 7.65–7.16 (m, 17H, m-Bz, p-Bz, Bn), 5.99
3
3
3
(dd, 1H, J3 ,4 3.5 Hz, J4 ,5 0.9 Hz, H-40), 5.87 (dddd, 1H, J8,9(Z)
0
0
0
0
3.8. 2,3,4,6-Tetra-O-benzoyl-b-
D-galactopyranosyl-(1?4)-1,2-di-
3
3
3
O-acetyl-3-O-benzyl- -rhamnopyranose (7)
a-L
17.2 Hz, J8,9(E) 10.4 Hz, J7b,8 6.0 Hz, J7a,8 5.2 Hz, H-8), 5.81 (dd,
3
3
3
1H, J2 ,3 10.4 Hz, J1 ,2 8.0 Hz, H-20), 5.63 (dd, 1H, J2 ,3 10.4 Hz,
0
0
0
0
0
0
3
3
J3 ,4 3.5 Hz, H-30), 5.30 (d, 1H, J1 ,2 8.0 Hz, H-10), 5.25 (d0q0, 1H,
0
0
0
0
Acetic anhydride (3 mL) was added to a solution of compound 6
(300 mg, 0.34 mmol) in dry pyridine (7 mL) at 0 °C and stirred for
24 h at room temperature (monitored by TLC). The reaction mix-
ture was poured into ice-water (10 mL), the aq layer was extracted
with chloroform (3 ꢂ 3 mL). The combined organic solutions were
washed with ice-water (2 mL), satd aq NHCO3 (3 ꢂ 2 mL), ice-
water (2 mL), dried and concentrated. Purification of the residue
by column chromatography (3:1 Toluene/EtOAc) gave compound
3J8,9(Z) 17.2 Hz, J7,9 = 2J 1.5 Hz, H-9(Z)), 5.19 (d0q0, 1H, J8,9(E)
4
3
10.4 Hz, J7,9 = 2J 1.5 Hz, H-9(E)), 4.81 (d, 1H, J1,2 1.6 Hz, H-1),
4
3
4.63 (dd, 1H, 2J 11.3 Hz, J5 ,6a 6.5 Hz, H-6a0), 4.43 (d, 1H, 2J
3
0
0
11.3 Hz, J5 ,6b 6.9 Hz, H-6b0), 4.35 (centre of AB spectrum, 2H, 2J
3
0
0
3
3
3
0
0
0
0
0
0
12.5 Hz, CH2Ph), 4.30 (ddd, 1H, J5 ,6b 6.9 Hz, J5 ,6a 6.5 Hz, J4 ,5
2
3
4
0.9 Hz, H-50), 4.14 (dd0t0, 1H, J7a,7b 12.9 Hz, J7a,8 5.4 Hz, J7a,9
2
3
4
1.5 Hz, H-7a), 3.96 (dd0t0, 1H, J7a,7b 12.9 Hz, J7b,8 6.3 Hz, J7b,9
7 (240 mg, 77%) as a colourless foam: ½a D22
ꢃ
þ 69:8 (c 1.0, CHCl3);
1.5 Hz, H-7b), 3.88 (m, 1H, H-2), 3.86–3.76 (m, 2H, H-4, H-5),
3
3
3
Rf 0.55 (2:1 Toluene/EtOAc); 1H NMR (500.13 MHz, CDCl3): d 8.08
(m, 2H), 8.02 (m, 2H), 7.90 (m, 2H), 7.76 (m, 2H), (o-Bz), 7.65–
3.67 (dd, 1H, J3,4 8.8 Hz, J2,3 3.5 Hz, H-3), 2.27 (d, 1H, J2,OH
2.2 Hz, OH), 1.42 (d, 3H, J5,6 6.0 Hz, H-6); 13C NMR (125.8 MHz,
3
3
3
0
0
0
0
0
0
7.17 (m, 17H, m-Bz, p-Bz, Bn), 5.98 (dd, 1H, J3 ,4 3.5 Hz, J4 ,5
CDCl3): d 166.0, 165.6, 165.5, 165.3 (C@O), 137.8 (i-Ph), 133.7 (C-
8), 133.5, 133.2, 133.2, 133.2 (p-Bz), 129.9, 129.7, 129.7, 129.6 (o-
Bz), 129.4, 129.3, 129.2, 128.8 (i-Bz), 128.6, 128.6, 128.4, 128.3,
128.2, 127.2 (m-Bz, o-Ph, m-Ph), 128.0 (p-Ph), 117.7 (C-9), 101.3
(C-10), 98.1 (C-1), 80.1 (C-3), 77.3 (C-4), 71.8 (CH2Ph), 71.8 (C-30),
71.0 (C-50), 70.3 (C-20), 68.3 (C-40), 68.0 (C-7), 68.0 (C-2), 66.6 (C-
5), 61.9 (C-60), 17.9 (C-6). Anal. Calcd for C50H48O14 (872.91): C,
68.80; H, 5.50. Found: C, 68.81; H, 5.48. HRMS, ESI-TOF/MS positive
(m/z): calcd for C50H48O14 [M+Na]+: 895.2936, found: 895.2937.
3
3
0.9 Hz, H-40), 5.96 (d, 1H, J1,2 1.9 Hz, H-1), 5.81 (dd, 1H, J2 ,3
0
3
3
3
10.4 Hz, J1 ,2 8.0 Hz, H-20), 5.61 (dd, 1H, J2 ,3 10.4 Hz, J3 ,4
0
0
0
0
0
3
3
3.5 Hz, H-30), 5.32 (d, 1H, J1 ,2 8.0 Hz, H-10), 5.18 (m, 1H , J2,3
0
0
3
3
3.5 Hz, J1,2 1.9 Hz, H-2), 4.68 (dd, 1H, 2J 11.3 Hz, J5 ,6a 6.6 Hz, H-
0
0
6a0), 4.44 (d, 1H, 2J 11.0 Hz, CH2Ph), 4.43 (dd, 1H, 2J 11.3 Hz,
3
3
3
J5 ,6b 6.6 Hz, H-6b0), 4.33 (dt, 1H, J5 ,6 6.6 Hz, J4 ,5 0.9 Hz, H-50),
0
0
0
0
0
0
4.25 (d, 1H, 2J 11.0 Hz, CH2Ph), 3.88–3.82 (m, 2H, H-4, H-5), 3.73
(m, 1H, H-3), 2.07 (s, 3H, CH3CO), 2.03 (s, 3H, CH3CO), 1.44 (d,
3
3H, J5,6 5.7 Hz, H-6); 13C NMR (125.8 MHz, CDCl3): d 169.9,
168.5 (CH3CO), 166.0, 165.5, 165.4, 165.4 (C@O), 137.4 (i-Ph),
133.6, 133.3, 133.3, 133.2 (p-Bz), 129.9, 129.7, 129.7, 129.6 (o-
Bz), 129.4, 129.2, 129.1, 128.7 (i-Bz), 128.6, 128.5, 128.5, 128.4,
128.2, 127.8 (m-Bz, o-Ph, m-Ph), 128.2 (p-Ph), 101.1 (C-10), 90.9
(C-1), 77.3 (C-3), 76.5 (C-4), 71.8 (C-30), 71.7 (CH2Ph), 70.9 (C-50),
70.3 (C-20), 69.3 (C-5), 68.2 (C-40), 67.4 (C-2), 61.8 (C-60), 20.9 (CH3-
CO), 20.8 (CH3CO), 18.0 (C-6). Anal. Calcd for C51H48O16 (916.92): C,
66.75; H, 5.23. Found: C, 66.78; H, 5.24. HRMS, ESI-TOF/MS positive
(m/z): calcd for C51H48O16 [M+Na]+: 939.2834, found: 939.2824.
3.11. Methyl (allyl 2,3-di-O-benzyl-b-D-galactopyranosid)
uronate (11)
Methyl (allyl 4-O-acetyl-2,3-di-O-benzyl-b-D-galactopyrano-
sid)uronate (10, 428 mg, 1.0 mmol) was added with stirring to
methanolic 0.28 M hydrochloric acid [prepared by adding of acetyl
chloride (2 mL) to ice-cold dry methanol (100 mL)], and the mix-
ture was stirred at ambient temperature for 24 h under an atmo-
sphere of argon (monitored by TLC). The solution was filtered
through a layer of alkaline alumina by elution with chloroform.
The combined eluates (ca. 400 mL) were dried, concentrated and
the crude product was purified by column chromatography (3:1
Pet/EtOAc) to provide acceptor 11 (430 mg, 90%): mp 111 °C
3.9. 2,3,4,6-Tetra-O-benzoyl-b-
D-galactopyranosyl-(1?4)-2-O-
acetyl-3-O-benzyl- -rhamnopyranosyl bromide (8)
a-L
Oxalyl bromide (0.38 mL, 2.7 mmol) was added to a solution of
compound 7 (250 mg, 0.27 mmol) in dry CH2Cl2 (7 mL) under an
atmosphere of argon at ꢀ40 °C. After stirring for 1 h the cooling
bath was removed and stirring was continued for 4 h at room tem-
perature (monitored by TLC). The reaction mixture diluted with
toluene (10 mL), the organic solution was concentrated to half
of the volume (ꢁ8 mL) and toluene (8 mL) was added. After
(EtOAc/Heptane); ½a D22
ꢀ 4:7 (c 1.0, CHCl3); Rf 0.45 (2:1 Heptane/
ꢃ
EtOAc); 1H NMR (300.13 MHz, CDCl3): d 7.38–7.27 (m, 10H, Ph),
3
4
5.96 (m, 1H, H-8), 5.35 (d0q0, 1H, J8,9(Z) 17.2 Hz, J7,9 = 2J 1.5 Hz,
H-9(Z)), 5.21 (d0q0, 1H, J8,9(E) 10.4 Hz, J7,9 = 2J 1.5 Hz, H-9(E)), 4.94
3
4
(d, 1H, 2J 11.0 Hz, CH2Ph), 4.74 (d, 1H, 2J 11.0 Hz, CH2Ph), 4.74 (br
s, 2H, CH2Ph), 4.50 (dd0t0, 1H, 2J 13.0 Hz, J7a,8 5.0 Hz, J7a,9 1.5 Hz,
3
4
H-7a), 4.43 (d, 1H, J1,2 7.7 Hz, H-l), 4.16 (dd0t0, 1H, 2J 13.0 Hz,
3

14
A. Pogosyan et al. / Carbohydrate Research 380 (2013) 9–15
3J7b,8 6.0 Hz, 4J7b,9 1.5 Hz, H-7b), 4.06 (0t0, 1H, 3J4,5 = 4J5,OH 1.5 Hz, H-
143.2 [i-NPh(b)], 137.8, 137.5 [i-Ph(
128.7 [m-NPh( )], 128.6 [m-NPh(b)], 128.5, 128.4, 128.2, 128.1
[o-Ph(b), m-Ph(b)], 128.4, 128.4, 127.8, 127.8 [o-Ph( ), m-Ph( )],
128.0, 128.0 [p-Ph(b)], 127.5, 127.5 [p-Ph( )], 124.3 [p-NPh(b)],
123.3 [i-NPh( )], 119.4 [o-NPh( )], 119.3 [o-NPh(b)], 96.4 [br,
C-1(b)], 93.5 [br, C-1( )], 78.7 [C-3(b)], 76.9 [C-2(b)], 75.7, 72.3
[PhCH2(b)], 73.7, 72.4 [PhCH2(
67.3 [C-4(b)], 52.7 [CH3O(b)], 20.7 [CH3CO(b)], 20.6 [CH3CO(
a)], 137.6, 137.2 [i-Ph(b)],
3
3
5), 3.83 (s, 3H, OCH3), 3.73 (dd, 1H, J2,3 9.3 Hz, J1,2 7.7 Hz, H-2),
a
3
3
3
3.57 (dd, 1H, J2,3 9.3 Hz, J3,4 3.5 Hz, H-3), 2.59 (dd, 1H, J4,OH
a
a
3.0 Hz, J5,OH 1.5 Hz, OH); 13C NMR (75.5 MHz, CDCl3): d 168.4
a
4
(COO), 138.3, 137.5 (i-Ph), 133.8 (C-8), 128.6, 128.4, 128.3, 127.8
(o-Ph, m-Ph), 127.9, 127.6 (p-Ph), 117.4 (C-9), 102.2 (C-l), 79.7,
78.2 (C-2, C-3), 75.2, 72.4 (CH2Ph), 73.6 (C-5), 70.2 (C-7), 68.0 (C-
4), 52.5 (OCH3). Anal. Calcd for C24H28O7 (428.47): C, 67.28; H,
6.59. Found: C, 67.29; H, 6.53.
a
a
a
a
)], 73.2 [C-5(b)], 68.2 [C-4(
a
)],
)].
a
HRMS, ESI-TOF/MS positive (m/z): calcd for
C31H30F3NO8
[M+Na]+: 624.1816, found: 624.1816.
3.12. Methyl 4-O-acetyl-2,3-di-O-benzyl-a/b-D-
galactopyranuronate (12)
3.14. Methyl 2,3,4,6-tetra-O-benzoyl-b-
(1?4)-2-O-acetyl-3-O-benzyl- -rhamnopyranosyl-(1?4)-
(allyl 2,3-di-O-benzyl-b- -galactopyranosid)uronate (14)
D-galactopyranosyl-
a
-L
Methyl (allyl 4-O-acetyl-2,3-di-O-benzyl-b-D-galactopyrano-
D
sid)uronate (10, 470 mg, 1.0 mmol), palladium(II) chloride
(180 mg, 1 mmol) and sodium acetate (656 mg, 8 mmol) were stir-
red in acetic acid (10 mL, 95%) for 3 h at 45 °C (monitored by TLC).
The mixture was diluted with chloroform (20 mL), filtrated over
Celite, co-evaporated with toluene (3 ꢂ 10 mL) and concentrated.
The residue was purified by column chromatography (1:1 PE/
EtOAc) to give compound 12 (323 mg, 75%) as a colourless syrup:
Compound
8 (250 mg, 0.25 mmol), compound 11 (94 mg,
0.22 mmol) and molecular sieves (4 Å, 300 mg) were dried for 2 h
under high vacuum in darkness. The mixture was suspended in
dry acetonitrile (4 mL) and stirred under an atmosphere of argon
at ambient temperature. After 20 min Hg(CN)2 (60 mg, 0.24 mmol)
and HgBr2 (50 mg, 0.14 mmol) were added and stirring was contin-
ued. After 24 h (monitored by TLC) the mixture was diluted with
chloroform (20 mL) and filtered through a layer of Celite. The fil-
trate was extracted with ice-water (2 ꢂ 5 mL), aq 10% KI
(3 ꢂ 5 mL), ice-water (2 ꢂ 5 mL), dried and concentrated. The resi-
due was purified by column chromatography (2:2 PE/EtOAc) to
Rf 0.2 (1:1 PE – EtOAc); 1H NMR (500.13 MHz, CDCl3,
d 7.36–7.26 (m, 10H, Ph), 5.86 [dd, 1H, J3,4 3.5 Hz, J4,5 1.5 Hz, H-
a
:b = 4:1):
3
3
3
3
4(
a
)], 5.78 [dd, 1H, J3,4 3.2 Hz, J4,5 1.5 Hz, H-4(b)], 5.37 [d, 1H,
3J1,2 3.6 Hz, H-1(
a
)], 4.89, 478 [2d, 2H, 2J 11.0 Hz, CH2Ph(b)], 4.83,
4.66 (2d, 2H, 2J 11.7 Hz, CH2Ph( )], 4.78, 4.57 [2d, 2H, 2J 11.4 Hz,
a
CH2Ph(
a
)], 4.77, 4.54 [2d, 2H, 2J 11.0 Hz, CH2Ph(b)], 4.76 [d, 1H,
give compound 14 (186 mg, 65%) as colourless foam: ½a D24
þ 71:4
ꢃ
3J4,5 1.5 Hz, H-5(
a
)], 4.69 [d, 1H, J1,2 7.5 Hz, H-1(b)], 4.17 [d, 1H,
3
(c 1.0, CHCl3); Rf 0.27 (2:1 PE/EtOAc); 1H NMR (500.13 MHz,
3J4,5 1.5 Hz, H-5(b)], 4.02 [dd, 1H, J2,3 9.8 Hz, J3,4 3.5 Hz, H-3(
a
)],
3.97 [br s, 1H, OH(bb)], 3.83 [dd, 1H, J2,3 9.8 Hz, J1,2 3.6 Hz, H-
2( )], 3.76 [s, 3H, CH3O(b)], 3.74 [s, 3H, CH3O( )], 3.64–3.57 [m,
2H, H-2(b), H-3(b)], 3.40 [br s, 1H, OH( )], 2.10 [s, 3H, CH3CO(b)],
2.08 [s, 3H, CH3CO(
)]; 13C NMR (125.8 MHz, CDCl3): d 169.9,
168.3 [COO( ), CH3CO( )], 169.9, 167.4 [COO(b), CH3CO(b)],
138.3, 137.4 [i-Ph(b)], 137.9, 137.7 [i-Ph( )], 128.4, 128.3, 128.0,
127.9 [o-Ph( ), m-Ph( )], 128.3, 128.3, 128.0, 128.0 [o-Ph(b), m-
Ph(b)], 127.9, 127.7 [p-Ph( )], 127.8, 127.7 [p-Ph(b)], 97.4 [C-
1(b)], 92.1 [C-1( )], 79.2, 78.6 [C-2(b), C-3(bbb)], 75.2 [C-3( )],
74.9 [C-2( )], 73.8, 72.0 [PhCH2( )], 72.5, 72.2 [PhCH2(b)], 68.5
[C-4( )], 68.4 [C-5( )], 67.6 [C-4(b)], 52.7 [CH3O(bb)], 52.5 [CH3-
O( )], 20.7 [CH3CO( )], 20.7 [CH3CO(b)]. Anal. Calcd for C23H26O8
(430.45): C, 64.18; H, 6.09. Found: C, 64.23; H, 6.04.
3
3
3
3
CDCl3): dd 8.07 (m, 2H), 8.01 (m, 2H), 7.87 (m, 2H), 7.77 (m, 2H,
3
00 00
o-Bz), 7.63–7.20 (m, 27H, m-Bz, p-Bz, Bn), 5.97 (dd, 1H, J3 ,4
a
a
3
3
00 00
00
00 00
3.5 Hz, J4 ,5 0.9 Hz, H-4 ), 5.94 (m, 1H, H-8), 5.77 (dd, 1H, J2 ,3
a
3
3
3
00 00
00
00 00
00 00
10.4 Hz, J1 ,2 8.0 Hz, H-2 ), 5.56 (dd, 1H, J2 ,3 10.4 Hz, J3 ,4
a
3
3
3.5 Hz, H-3 ), 5.42 (dd, 1H, J2 ,3 3.2 Hz, J1 ,2 1.9 Hz, H-20), 5.35
00
0
0
0
0
a
a
3
(m, 1H, H-10), 5.33 (m, 1H, H-9(Z)), 5.31 (d, 1H, J1 ,2 8.0 Hz, H-
00 00
a
100), 5.20 (m, 1H, H-9(E)), 4.89 (d, 1H, 2J 11.9 Hz, CH2Ph), 4.73 (d,
a
a
1H, 2J 11.9 Hz, CH2Ph), 4.73 (br s, 2H, CH2Ph), 4.66 (dd, 1H, 2J
a
3
11.2 Hz, J5 ,6a 6.5 Hz, H-6a00), 4.51–4.46 (m, 2H, H-4, H-7a), 4.50
00
00
a
a
(d, 1H, 2J 10.7 Hz, CH2Ph), 4.41 (dd, 1H, 2J 11.2 Hz, J5 ,6b 6.9 Hz,
3
00
00
a
a
3
3
H-6b00), 4.37 (d, 1H, J1,2 7.8 Hz, H-1), 4.29 (d0t0, 1H, J5 ,6b 6.9 Hz,
00
00
a
a
a
J5 ,6a 6.5 Hz, J4 ,5 0.9 Hz, H-500), 4.18 (d, 1H, 2J 10.7 Hz, CH2Ph),
3
3
00
00
00 00
a
3
4.13 (m, 1H, H-7b), 4.06 (d, 1H, J4,5 1.3 Hz, H-5), 3.79 (s, 3H,
3
OCH3), 3.78–3.72 (m, 3H, H-2, H-30, H-40), 3.59 (dq, 1H, J4 ,5
0
0
3
3
3
9.5 Hz, J5 ,6 6.2 Hz, H-50), 3.55 (dd, 1H, J2,3 9.8 Hz, J3,4 2.8 Hz,
3.13. Methyl 4-O-acetyl-2,3-di-O-benzyl- /b- -galactopyranosyl
uronate N-phenyl trifluoroacetimidate (13)
a
D
0
0
H-3), 1.95 (s, 3H, CH3CO), 1.42 (d, 3H, J5 ,6 6.2 Hz, H-60); 13C
NMR (125.8 MHz, CDCl3): d 169.6 (CH3CO), 168.3 (COO), 166.0,
165.5, 165.5, 165.3 (C@O), 138.3, 138.0, 137.8 (i-Ph), 133.7 (C-8),
133.5, 133.2, 133.2, 133.2 (p-Bz), 129.9, 129.8, 129.7, 129.7 (o-
Bz), 129.5, 129.3, 129.2, 128.8 (i-Bz), 128.7, 128.5, 128.4, 128.4,
128.3, 128.3, 128.2, 127.6, 127.6, 127.5 (m-Bz, o-Ph, m-Ph), 128.3.
127.7, 127.6 (p-Ph), 117.6 (C-9), 102.7 (C-1), 100.8 (C-100), 98.2
(C-10), 81.0 (C-3), 78.1 (C-2), 77.4, 76.3 (C-30, C-40), 75.2 (CH2Ph),
73.8 (C-5), 73.0 (CH2Ph), 71.8 (C-4), 71.8 (C-300), 71.5 (CH2Ph),
70.8 (C-500), 70.7 (C-7), 70.1 (C-200), 68.3 (C-400), 68.1 (C-20), 67.3
(C-50), 61.8 (C-600), 52.8 (OCH3), 20.9 (CH3CO), 17.9 (C-60). Anal.
Calcd for C73H72O21 (1285.34): C, 68.21; H, 5.65. Found: C, 68.29;
H, 5.58. HRMS, ESI-TOF/MS positive (m/z): calcd for C73H72O21
[M+Na]+: 1307.4458, found:1307.4477, calcd for C73H72O21
[M+K]+: 1323.4198, found:1323.4204.
3
0
0
Cs2CO3 (652 mg, 2.0 mmol) and 2,2,2-trifluoro-N-phenyl-acet-
imidoyl chloride (415 mg, 2.0 mmol) were consecutively added to
compound 12 (430 mg, 1.0 mmol) in acetone (20 mL) at 0 °C. The
cooling bath was removed, and reaction mixture was stirred at
ambient temperature. After 3 h (monitored by TLC) the reaction
mixture was diluted in CH2Cl2 (20 mL). Salts were filtered off and
washed with EtOAc (2 ꢂ 10 mL). The combined organic solutions
were concentrated and the residue was purified by column
chromatography (3:1 PE/EtOAc) to give compound 13 (529 mg,
88%) as a colourless gas: Rf: 0.59 (PE:EtOAc = 1:1); 1H NMR
(500.13 MHz, CDCl3,
m-NPh), 7.09 (m, 1H, p-NPh), 6.80 (d, 1H, J 7.9 Hz), 6.72 (d, 1H,
J 7.9 Hz), (o-NPh), 5.91 [br s, 1H, H-4( )], 5.79 [br s, 1H, H-4(bb)],
5.68 (br, 1H, H-1), 4.81 [qAB, 2H, 2J 11.7 Hz, CH2Ph(b)], 4.79
(d, 1H, 2J 12.0 Hz), 4.73 [d, 1H, 2J 12.0 Hz, CH2Ph(
)], 4.79 (d, 1H,
a:b = 1:5): d 7.36–7.24 (m, 12H, 2 Ph,
a
a
3.15. Allyl (methyl 4-O-acetyl-2,3-di-O-benzyl-
pyranosyluronate)-(1?2)- [2,3,4,6-tetra-O-benzoyl-b-
galactopyranosyl-(1?4)]-3-O-benzyl- -rhamnopyranoside (15)
a-D-galacto-
2J 11.3 Hz), 4.62 [d, 1H, 2J 11.3 Hz, CH2Ph(
a)], 4.79 (d, 1H,
D-
2J 11.3 Hz), 4.56 [d, 1H, 2J 11.3 Hz, CH2Ph(b)], 4.20 (br, 1H, H-5),
a-L
3
3.91 (0t0, 1H, J1,2 = 3J2,3 8.5 Hz, H-2), 3.70 (br m, 1H, H-3), 3.78
[s, 3H, CH3O(
2.09 [s, 3H, CH3CO(
[CH3CO(b)] , 169.7 [CH3CO(
a
)], 3.78 [s, 3H, CH3O(b)], 2.15 [s, 3H, CH3CO(b)],
)]; 13C NMR (125.8 MHz, CDCl3): d 169.8
)], 167.2 [COO( )], 166.4 [COO(b)],
Compound 9 (235 mg, 0.27 mmol), compound 13 (120 mg,
0.2 mmol) and molecular sieves (4Å, 2 g) were dried for 2 h under
high vacuum. The mixture was suspended in dry CH2Cl2 (20 mL).
a
a
a

A. Pogosyan et al. / Carbohydrate Research 380 (2013) 9–15
15
unravelling the biological significance of the individual components of pectin
hairy regions in plants. In Advances in Pectin and Pectinase Research; Voragen, F.,
Schols, H., Visser, R., Eds.; Kluwer Academic Publishers: Dordrecht, Boston,
London, 2003; pp 15–34.
Salts were filtered off and washed with EtOAc (2 ꢂ 10 mL). The
combined organic solution (10 mL) was stirred under an atmo-
sphere of argon at ambient temperature. After 20 min the mixture
2. (a) Maruyama, M.; Takeda, T.; Shimizu, N.; Hada, N.; Yamada, H. Carbohydr. Res.
2000, 325, 83–92; (b) Clausen, M. H.; Jorgensen, M. R.; Thorsen, J.; Madsen, R. J.
Chem. Soc., Perkin Trans. 1 2001, 543–551; (c) Clausen, M. H.; Madsen, R.
Carbohydr. Res. 2004, 339, 2159–2169; (d) Codée, J. D. C.; Litjens, R. E. J. N.;
Dinkelaar, J.; van der Overkleeft, H. S.; Marel, G. A. Eur. J. Org. Chem. 2007,
3963–3976; (e) Reiffarth, D.; Reimer, K. B. Carbohydr. Res. 2008, 343, 179–188;
(f) Rao, Y.; Boons, G.-J. Angew. Chem., Int. Ed. 2007, 46, 6148–6151.
3. a Nemati, N.; Karapetyan, G.; Nolting, B.; Endress, H.-U.; Vogel, C. Carbohydr.
Res. 2008, 343, 1730–1742; (b) Vogel, C.; Nolting, B.; Kramer, S.; Steffan, W.;
Ott, A.-J. Synthesis of Pectin Fragments by Modular Design Principle. In
Advances in Pectin and Pectinase Research; Vorhagen, F., Schols, H., Visser, R.,
Eds.; Khuwer Academic Publishers: Dordrecht/Boston/London, 2003; pp 209–
was cooled to ꢀ30 °C and TMSOTf (25
lL, 0.11 mmol) was added
dropwise. After stirring for 1 h the mixture was slowly warmed
up to room temperature, and stirring was continued for an addi-
tional 2 h in ambient temperature (monitored by TLC). The solu-
tion was neutralized by Et3N (0.25 mL, 1.8 mmol), molecular
sieves were filtered off and washed with chloroform (3 ꢂ 3 mL).
The combined organic solutions were concentrated. Purification
by column chromatography (6:1 Toluene/EtOAc) gave compound
15 (170 mg, 66%) as colourless foam: ½a D24
þ 111:9 (c 1.0, CHCl3);
ꢃ
Rf 0.45 (4:1 Toluene/EtOAc); 1H NMR (500.13 MHz, CDCl3): d 8.08
220 (ISBN 1-4020-1144-X). Part XIII of the series
Derivatives’.
‘D-Galacturonic Acid
(m, 2H), 8.01 (m, 2H), 7.73 (m, 2H), 7.61 (m, 2H, o-Bz), 7.50–7.03
4. Zhang, J.; Mao, J.; Chen, H.; Cai, M. Tetrahedron: Asymmetry 1994, 5, 2283–2290.
5. Fürstner, A.; Jeanjean, F.; Razon, P.; Wirtz, C.; Mynott, R. Chem. Eur. J. 2003, 9,
307–319.
6. David, S. Selective O-Substitution and Oxidation Using Stannylene Acetals and
Stannyl Ethers. In Preparative Carbohydrate Chemistry; Hanessian, S., Ed.;
Dekker: New York, 1997; pp 69–86 (ISBN-10: 0849384699).
3
(m, 27H, m-Bz, p-Bz, Bn), 6.02 (d, 1H, J3 ,4 3.5 Hz, H-400), 5.86
00 00
3
3
(m, 1H, H-8), 5.81 (dd, 1H, J2 ,3 10.4 Hz, J1 ,2 8.0 Hz, H-200), 5.80
00 00
00 00
3
3
3
00 00
(dd, 1H, J2,3 3.5 Hz, J1,2 1.5 Hz, H-2), 5.60 (dd, 1H, J2 ,3 10.4 Hz,
3
3
J3 ,4 3.5 Hz, H-300), 5.41 (d, 1H, J1 ,2 8.0 Hz, H-100), 5.23 (d0q0, 1H,
00 00
00 00
3J8,9(Z) 17.2 Hz, J7,9 = 2J 1.5 Hz, H-9(Z)), 5.18 (d0q0, 1H, J8,9(E)
4
3
7. Malysheva, N. N.; Kochetkov, N. K. Carbohydr. Res. 1982, 105, 173–179. There is
a misprint in that publication. The regioselective acetylation started at ꢀ40 °C
not at ꢁ20 °C (compound 4).
4
3
10.4 Hz, J7,9 = 2J 1.5 Hz, H-9(E)), 4.97 (d, 1H, J1 ,2 3.8 Hz, H-10),
4.83 (d, 1H, 2J 11.8 Hz), 4.61 (d, 1H, 2J 11.8 Hz), (CH2Ph), 4.71 (d,
1H, 2J 11.0 Hz), 4.44 (d, 1H, 2J 11.0 Hz), (CH2Ph), 4.54 (d, 1H, 2J
12.3 Hz), 4.18 (d, 1H, 2J 12.3 Hz), (CH2Ph), 4.80 (br s, 2H, H-1, H-
50), 4.65 (m, 1H, H-6a00), 4.47 (m, 1H, H-6b00), 4.45 (m, 1H, H-500),
0
0
8. (a) Lundt, I.; Pedersen, C. Acta Chem. Scand. 1976, B30, 680–684; (b) Mota, J. F.;
Mostowicz, D.; Ortiz, C.; Pradera, M. A.; Robina, I. Carbohydr. Res. 1994, 257,
305–316; (c) Wernerova, M.; Hudlicky, T. Synlett 2010, 2701–2707.
9. (a) Deferrari, J. O.; Deulofeu, V. J. Org. Chem. 1952, 17(1097–1101), 2299; (b) De
Lederkremer, R. M.; Deferarrari, J. O. J. Org. Chem. 1962, 27, 2561–2563.
10. Betaneli, V. I.; Ovchinnikov, M. V.; Backinowsky, L. V.; Kochetkov, N. K.
Carbohydr. Res. 1980, 84, 211–244.
3
3
3
0
0
4.04 (dd, 1H, J3,4 10.1 Hz, J2,3 3.5 Hz, H-3), 4.00 (dd, 1H, J3 ,4
3
3.5 Hz, J4 ,5 1.8 Hz, H-40), 4.13 (m, 1H, H-7a), 3.92 (m, 1H, H-7b),
0
0
3.85–3.75 (m, 3H, H-20, H-4, H-5), 3.29 (s, 3H, OCH3), 2.01 (s, 3H,
11. (a) Helferich, B.; Zirner, J. Chem. Ber. 1962, 95, 2604–2611; (b) Steffan, W.;
Vogel, C.; Kristen, H. Carbohydr. Res. 1990, 204, 109–120.
12. (a) Ogawa, T.; Nakabayashi, S. Carbohydr. Res. 1981, 93, C1–C5; (b) Nolting, B.;
Boye, H.; Vogel, C. J. Carbohydr. Chem. 2001, 20, 585–610.
13. Wessel, H.-P.; Bundle, D. R. J. J. Chem. Soc. Perkin Trans. 1 1985, 2251–2260.
14. (a) Petráková, E.; Schraml, J. Collect. Czech. Chem. Commun. 1983, 48, 877–888;
(b) Byramova, N. E.; Ovchinnikov, M. V.; Backinowsky, L. V.; Kochetkov, N. K.
Carbohydr. Res. 1983, 124, C8–C11.
15. (a) Nolting, B.; Boye, H.; Vogel, C. J. Carbohydr. Chem. 2000, 19, 923–938; (b)
Voss, A.; Nemati, N.; Poghosyan, H.; Endress, H.-U.; Krause, A.; Vogel, C.
CH3CO), 1.45 (d, 1H, J5,6 6.0 Hz, H-6); 13C NMR (125.8 MHz,
3
CDCl3): d 169.7 (CH3CO), 167.9 (COO), 166.1, 165.5, 165.5, 165.4
(C@O), 138.6, 137.9, 137.9 (i-Ph), 133.7 (C-8), 133.5, 133.3, 133.2,
132.9 (p-Bz), 129.9, 129.7, 129.7, 129.5 (o-Bz), 129.3, 129.2,
129.0, 128.7 (i-Bz), 128.7, 128.6, 128.4, 128.3, 128.2, 128.2, 127.9,
127.7, 127.6, 125.9 (m-Bz, o-Ph, m-Ph), 128.3. 127.6, 127.3 (p-Ph),
117.6 (C-9), 101.3 (C-100), 98.1 (C-10), 96.4 (C-1), 78.9 (C-30), 77.8
(C-4), 75.2 (C-3), 74.5 (C-20), 74.4 (C-40), 72.9 (CH2Ph), 71.9 (CH2Ph),
71.8 (C-300), 71.1 (CH2Ph), 70.8 (C-500), 70.1 (C-200), 69.4 (C-50), 68.7
(C-2), 68.2 (C-400), 67.9 (C-7), 67.2 (C-5), 61.8 (C-600), 52.1 (OCH3),
20.7 (CH3CO), 18.1 (C-6). Anal. Calcd for C73H72O21 (1285.34): C,
68.21; H, 5.65. Found: C, 68.24; H, 5.61. HRMS, ESI-TOF/MS positive
(m/z): calcd for C73H72O21 [M+Na]+: 1307.4458, found:1307.4436.
Efficient
galactopyranosid) uronates from
Kovac, P., Ed.; Taylor&Francis Group: Boca Raton, London, New York, 2011;
Synthesis
of
Methyl(allyl
4-O-acetyl-2,3-di-O-benzyl-b-D-
D-Galacturonic Acid In Proven Methods;
Chapter 36, pp 303–339 (ISBN: 978-1-4398-6689-4). Part XVI of the series ‘
Galacturonic Acid Derivatives’.
D-
16. a Presented at 26th International Carbohydrate Symposium, Madrid, Spain,
July 2012, as poster P335: Michalik, D. Pogosyan, A. Gottwald, A. Vogel, C.
Endress, H.-U. Synthesis and NMR Studies of Rhamnogalacturonan I Fragments
by Using a new Galacturonate Glycosyl Donor.
17. Tamura, K.; Mizukami, H.; Maeda, K.; Watanabe, H.; Uneyama, K. J. Org. Chem.
1993, 58, 32–35.
18. Pastore, A.; Adinolfi, M.; Iadonisi, A.; Valerio, S. Eur. J. Org. Chem. 2010, 711–
718.
19. Bock, K.; Pedersen, C. J. Chem. Soc., Perkin Trans. 2 1974(293–297), 21.
20. Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.;
Pergamon Press: Oxford, 1988.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.carres.2013.06.019.
References
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