Divergent strategy for the synthesis of α2-3-linked sialo-oligosaccharide libraries using a Neu5TFA-(α2-3)-gal building block

Article abstract of DOI:10.1055/s-0032-1317961

A novel Neu5TFA-(α2-3)-Gal building block with removable protecting group at N5′ was introduced and used in the divergent synthesis of a library of N-acetyl and N-glycolyl derivatives of oligosaccharides related to sialyl-(α2-3)-N-acetyl-lactosamine and sialyl-(α2-3)-N-acetyl- isolactosamine, with or without sulfate at O6 of glucosamine residue. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0032-1317961

226▌
LETTER
lDettiervergent Strategy for the Synthesis of α2-3-Linked Sialo-oligosaccharide
Libraries Using a Neu5TFA-(α2-3)-Gal Building Block
Synthesis of α2-3-Linked Sialo-oligosaccharide Libraries
Galina Pazynina,a Tatiana Tyrtysh,a Vitaly Nasonov,a Ivan Belyanchikov,a Alexander Paramonov,a Nelly Malysheva,b
Alexander Zinin,b Leonid Kononov,b Nicolai Bovin*a
a
M. M. Shemyakin and Yu. A. Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences, ul. Miklukho-Maklaya,
16/10, Moscow 117997, GSP-7, Russian Federation
Fax +7(495)3305592; E-mail: bovin@carb.ibch.ru
b
N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences, Leninsky prosp., 47, Moscow 119991, Russian Federation
Received: 09.10.2012; Accepted after revision: 08.12.2012
sized separately,9 the use of sialyl donor with a suitable
Abstract: A novel Neu5TFA-(α2-3)-Gal building block with re-
temporary protection at N5 is generally considered more
movable protecting group at N5′ was introduced and used in the di-
reasonable.2d,e One of the practical approaches to libraries
of sialo-oligosaccharides, which comprise α2-3 intersac-
vergent synthesis of a library of N-acetyl and N-glycolyl derivatives
of oligosaccharides related to sialyl-(α2-3)-N-acetyl-lactosamine
and sialyl-(α2-3)-N-acetyl-isolactosamine, with or without sulfate charidic linkage, with almost any N-substituent from the
at O6 of glucosamine residue.
single precursor involves the use of a sialyl-(α2-3)-galac-
tose [Neu-(α2-3)-Gal] building block with removable pro-
Key words: bioorganic chemistry, glycosides, glycosylation,
protecting groups, sialic acids
tecting group at the N5 of sialic acid residue.7
Herein we introduce a novel building block, Neu5TFA-
(α2-3)-Gal, and use it in the divergent synthesis of N-ace-
tyl and N-glycolyl derivatives of oligosaccharides related
to sialyl-(α2-3)-N-acetyl-lactosamine and sialyl-(α2-3)-
N-acetyl-isolactosamine, some of which carry sulfate at
O6 of glucosamine residue. All oligosaccharides were
synthesized as glycosides with the 3-aminopropyl spacer
aglycon that allows their use for the preparation of neo-
glycoconjugates and glycoarray printing.10
Glycoprotein and glycolipid carbohydrate chains termi-
nated by sialic acids are involved in a wide range of bio-
logical phenomena ranging from cell–cell adhesion and
mobility to oncogenesis and recognition by viruses and
bacteria.1 Therefore, the synthesis and the biomedical in-
vestigation of sialic acid containing glycoconjugates, oli-
gosaccharides, and their analogues is a very important
area of research aiming at understanding their biological
roles and determining their therapeutic relevance.
The Neu5TFA-(α2-3)-Gal building block was designed as
a per-O-acetylated glycosyl bromide 4 (Scheme 1) with
N-trifluoroacetyl (TFA) temporary protecting group at N5
of sialic acid residue that can be readily removed by alkali
treatment and then acylated with an appropriate reagent.
For this reason, the amino group in the aglycon was gen-
erated at the later stages of synthesis from orthogonal az-
ido group by catalytic hydrogenation.
Sialic acid residues are introduced into an oligosaccharide
by a glycosylation reaction called sialylation, which is by
no means a trivial one.2 Although a tremendous progress
has been achieved in chemical sialylation,2,3 the outcome
of a particular sialylation can rarely be predicted, which
makes optimization4d of almost every sialylation neces-
sary. Many variables2–4 may become important – the na-
ture of protecting groups both on glycosyl donor and
glycosyl acceptor,5 method of activation,6 concentration
of reagents,4b,d and the presence of other compounds in the
reaction mixture (including ‘nonreacting’ additives or im-
purities)4a–c to name a few. For this reason, it is not sur-
prising that synthetic strategies, which minimize the
number of sialylation steps by using common building
blocks, are becoming increasingly popular for the synthe-
sis of sialo-oligosaccharides.7,8 The preparation of sialo-
oligosaccharides becomes even more challenging when
both naturally occurring N-acetyl and N-glycolyl (Gc) de-
rivatives of the same oligosaccharide backbone and their
analogues with diverse substituents at N5 of sialic acid
residue are required. Although each form can be synthe-
The assembly of sialyl-(α2-3)-galactose building block by
sialylation of an appropriate glycosyl acceptor was opti-
mized earlier4d to give stereoselectively (α/β = 20:1) the
disaccharide 1 as a 4-methoxyphenyl (MP) glycoside in
71% yield. Straightforward de-O-benzylation, O-acetyla-
tion (→ 2, 93%) and oxidative removal of the MP agly-
cone followed by O-acetylation cleanly gave (Scheme 1)
glycosyl acetate 3 (95% from 2) as a mixture of anomers
(α/β = ca. 1:1).11 Glycosyl bromide 4 was readily obtained
by treatment of glycosyl acetate 3 with TiBr412 in CH2Cl2
and then directly used in glycosylations.13
In order to evaluate the glycosylation potential of the
building block 4, the latter was involved into glycosyl-
ation reaction with a primary alcohol, 3-chloropropanol
(5), in the presence of AgOTf and N,N,N′,N′-tetramethyl-
14
urea in CH2Cl2 analogously to the procedure described
earlier for Neu5Ac-(α2-3)-Gal building block8a (Scheme
3). The reaction of 4 with excess 5 (4 equiv) cleanly gave
the corresponding glycoside 14 in 80% yield.15–17 Substi-
SYNLETT 2013, 24, 0226–0230
Advanced online publication: 04.01.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1317961; Art ID: ST-2012-D0867-L
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of α2-3-Linked Sialo-oligosaccharide Libraries
227
CO2Me
AcO
OAc
CO2Me
BnO
OAc
OAc
O
OAc
O
OAc
O
OBn
O
a
AcO
AcO
TFA
TFA–N
O
OMP
N
O
OAc
OAc
H
AcO
OBn
H
X
2 X = β-OMP
3 X = OAc
4 X = α-Br
1
b
c
Scheme 1 Synthesis of Neu5TFA-(α2-3)-Gal glycosyl donor. Reagents and conditions: (a) (1) H2, Pd/C, MeOH; (2) Ac2O, pyridine (93%); (b)
(1) (NH4)2Ce(NO3)6, MeCN–H2O (5:1), 0 °C, 0.5 h; (2) Ac2O, pyridine (95%); (c) TiBr4, CH2Cl2, r.t., 3 h (quant.).
tution of chlorine with azide and deacylation under basic derivatives, either with or without sulfate group at O6 of
conditions18 gave the corresponding 3-azidopropyl glyco- the glucosamine residue, differing in the nature of the acyl
side as 5′-amino derivative 15 in 85% yield. Acylation of substituent at N5 of the sialic acid residue.
the free amino group in 15 with AcOCH2CO2C6H4NO2 in
The procedure for N-acylation of N5 of the sialic acid res-
idue in trisaccharides 18 and 26 essentially followed the
DMSO19 followed by reduction of the azide by catalytic
hydrogenation furnished N-glycolyl GM4 disaccharide as
one used for disaccharide 14. Thus, all O-protecting
the spacered glycoside 16 in 55% yield.20,21
groups were cleaved under basic conditions18 to give the
corresponding 5′′-amino derivatives 21 and 30, which
OH
O
OAc
O
were separately treated either with AcOCH2CO2C6H4NO2
in DMSO19 (N-glycolylation) or Ac2O in MeOH (N-acet-
ylation) followed by reduction of the azide by catalytic
hydrogenation to give the target spacered trisaccharides in
the following overall yields over three steps: 24 (50%),
258a (53%), 329b (73%), and 338a,22 (83%).20,21
a
b
HO
HO
AcO
AcO
OH
NHAc
AcNH
Cl
6
7
OR
O
e
RO
O
X
RO
Selective sulfation of the primary hydroxy group of trisac-
charide diol 18 with pyridine·SO3 in pyridine27 at low
temperature lead to preferential formation of 6-O-sulfated
(SO3Na = Su) derivative 19. Deprotection of 19 under ba-
sic conditions18 gave the corresponding 5′′-amino deriva-
tive 20, which was transformed as described above to the
target N-glycolyl- and N-acetyl-derivatives of spacered
trisaccharides 22 and 238a in 69% and 79% yields, respec-
tively.28
NHAc
8
9
X = Cl, R =Ac
X = N3, R = Ac
10 X = N3, R = H
c
d
Ph
O
O
RO
O
O
g
N3
NHAc
11 R =H
12 R = Ac
f
Hydroxy group at C6 of glucosamine residue to be sulfat-
ed was protected in trisaccharide 26 as O-benzyl ether that
is also cleavable under conditions of catalytic hydrogena-
tion used for reduction of azide in previous examples.
Therefore, in this case, the azido group in the aglycon of
26 was first reduced with Ph3P–H2O to give the corre-
sponding amine protected immediately as N-Boc deriva-
tive 27, from which the O-benzyl group was removed by
catalytic hydrogenolysis to furnish the N-Boc-protected
3-aminopropyl glycoside 28 in 75% yield. The released 6-
OH group of the glucosamine residue in 28 was then sul-
fated with pyridine·SO3 in pyridine27 to give 6-O-Su de-
rivative 29. All O-protecting groups in 29 were cleaved
under basic conditions18 to give the 5′′-amino derivative
31, which was treated either with AcOCH2CO2C6H4NO2
in DMSO19 or Ac2O in MeOH followed by removal of N-
Boc protecting group from the aglycon by treatment with
TFA29 to give spacered trisaccharides 34 and 358a in 80%
and 81% yields, respectively.28
OBn
O
HO
AcO
O
N3
NHAc
13
Scheme 2 Synthesis of GlcNHAc glycosyl acceptors. Reagents and
conditions: (a) AcCl; (b) Cl(CH2)3OH (5), Cl(CH2)2Cl; (c) NaN3,
DMSO, 80 °C; (d) 0.05 M MeONa, MeOH; (e) PhCH(OMe)2, TsOH,
MeCN (28% from 6); (f) Ac2O, pyridine; (g) NaBH3CN, MsOH, THF
(58% from 11).
Glycosylation of glycosyl acceptors 1122 and 13 (Scheme
2)23 with secondary hydroxy groups at C3 and C4, respec-
tively, was performed with a slight excess (1.3 equiv) of
glycosyl donor 4 analogously to the synthesis of glycoside
14 except for the different donor/acceptor ratio.16 Initially
formed trisaccharide 17 with O-benzylidene group with-
out purification was treated with AcOH to give the corre-
sponding diol 18. The trisaccharides 18 and 26 were
isolated in good yields (73% from 11 and 63% from 13,
respectively), which indicate efficiency of the proposed
approach for the assembly of sialo-oligosaccharides.15,25
Each oligosaccharide 18 and 26 obtained represents a
branching point for the straightforward access to a set of
The structures of all target compounds and key intermedi-
ates were confirmed by high-resolution NMR spectrosco-
py and mass spectrometry.30,31 Spectroscopic data of N-
acetyl-derivatives 23, 25, 33, and 35 coincided with those
described previously.8a 1H NMR spectra of N-glycolyl de-
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 226–230

228
G. Pazynina et al.
LETTER
4 + 5
a
CO2Me
OAc
CO2H
CO2H
OAc
OH
OH
OH
O
OH
O
OAc
O
OH
O
OH
O
AcO
HO
HO
b,c
d,f
AcO
HO
H2N
HO
NH
O
O
Cl
O
N3
O
NH2
TFA–N
O
O
O
O
AcO
HO
HO
AcO
HO
HO
H
14
15
16
OH
(Neu5Gcα2-3Galβ-Osp)
4 + 11
sp = (CH2)3NH2
a
OAc
OAc
CO2Me
CO2Me
OR2
O
OSO3Na
O
OAc
O
OAc
h
OAc
O
OAc
O
AcO
AcO
R1O
O
HO
O
AcO
O
N3
AcO
TFA–N
O
N3
O
TFA–N
O
O
NHAc
NHAc
AcO
AcO
AcO
AcO
H
H
17 R1,R2 = PhCH
18 R1 = R2 = H
19
j
c
c
OH
OH
CO2H
CO2H
OH
O
OH
O
OSO3Na
OH
O
OH
O
OH
HO
HO
O
HO
O
HO
O
HO
O
N3
HO
H2N
O
N3
O
H2N
O
O
NHAc
NHAc
HO
HO
HO
21
HO
20
d, f or e, f
d, f or e, f
OH
OH
CO2H
CO2H
OH
O
OH
O
OH
O
OSO3Na
OH
O
OH
O
HO
HO
O
HO
O
HO
O
HO
O
NH2
HO
O
NH2
R–N
R–N
O
O
NHAc
NHAc
HO
HO
HO
HO
H
H
24 R = HOCH2CO (Neu5Gcα2-3Galβ1-3GlcNAcβ-Osp)
22 R = HOCH2CO (Neu5Gcα2-3Galβ1-3(6-O-Su)GlcNAcβ-Osp)
25 R = Ac
(Neu5Acα2-3Galβ1-3GlcNAcβ-Osp)
23 R = Ac
(Neu5Acα2-3Galβ1-3(6-O-Su)GlcNAcβ-Osp)
4 + 13
a
OAc
OAc
CO2Me
CO2Me
OAc
O
OAc
O
OAc
O
OAc
O
AcO
AcO
27 R = Bn
OBn
O
OR
O
f
AcO
TFA–N
i
AcO
TFA–N
28 R = H
O
O
AcO
O
O
AcO
O
N3
O
NHBoc
h
AcO
AcO
AcO
AcO
c
29 R = SO3Na
H
H
NHAc
NHAc
26
c
OH
OH
CO2H
CO2H
OH
O
OH
O
OH
O
OH
O
HO
HO
OBn
O
OSO3Na
HO
HO
O
H2N
H2N
O
O
O
HO
O
HO
O
N3
O
NHBoc
HO
HO
HO
HO
NHAc
NHAc
30
31
d, f or e, f
d, g or e, g
OH
OH
CO2H
CO2H
OH
O
OH
O
OH
O
OH
O
HO
HO
OH
O
OSO3Na
O
O
HO
HO
R–N
R–N
O
O
HO
O
O
HO
O
NH2
NH2
HO
HO
HO
HO
H
H
NHAc
NHAc
32 R = HOCH2CO (Neu5Gcα2-3Galβ1-4GlcNAcβ-Osp)
33 R = Ac (Neu5Acα2-3Galβ1-4GlcNAcβ-Osp)
34 R = HOCH2CO (Neu5Gcα2-3Galβ1-4(6-O-Su)GlcNAcβ-Osp)
35 R = Ac (Neu5Acα2-3Galβ1-4(6-O-Su)GlcNAcβ-Osp)
Scheme 3 Synthesis of a library of sialo-oligosaccharides. Reagents and conditions: (a) AgOTf, Me2NCONMe2, MS 4 Å, CH2Cl2, r.t., 20 h
(80% of 14, 63% of 26); (b) NaN3, DMSO, 40 °C, 5 d; (c) (1) 0.1 M MeONa–MeOH, 1 h; (2) 0.1 M aq NaOH, 16 h (85% of 15); (d) (1)
AcOCH2CO2C6H4NO2, Et3N, DMSO, 16 h; (2) 0.1 M aq NaOH, 1 h; (e) Ac2O, MeOH, 0.5 h; (f) 10% Pd/C, H2, MeOH–H2O–NH3 (1:1:0.005),
16 h (for 27: MeOH, 2 h; 55% of 16 from 15, 69% of 22 from 18, 79% of 23 from 18, 50% of 24 from 18, 53% of 25 from 18, 75% of 28 from
26, 73% of 32 from 26, 83% of 33 from 26); (g) (1) TFA, 0.2 h; (2) 0.1 M aq NaOH, 0.5 h (80% of 34 from 28, 81% of 35 from 28); (h)
pyridine·SO3, py, 3 h (for 18: –15 °C to –20 °C; for 28: r.t.); (i) (1) Ph3P, THF–H2O (10:1), 16 h; (2) Boc2O, 1 h; (j) 80% aq AcOH, 70 °C, 2 h
(73% of 18 from 11).
Synlett 2013, 24, 226–230
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of α2-3-Linked Sialo-oligosaccharide Libraries
229
therein. (e) Wang, Y.; Xu, F.-F.; Ye, X.-S. Tetrahedron Lett.
2012, 53, 3658; and references cited therein.
rivatives were very close to those of the respective N-ace-
tyl derivatives. While the former exhibit a characteristic
signal for the CH2 group (s, 2 H, δ = ca. 4.1 ppm) of the
N-glycolyl moiety, the latter exhibit the NAc signal (s, 3
H, δ = ca. 2.0 ppm).
(4) (a) Kononov, L. O.; Malysheva, N. N.; Kononova, E. G.;
Garkusha, O. G. Russ. Chem. Bull. 2006, 55, 1311.
(b) Kononov, L. O.; Malysheva, N. N.; Kononova, E. G.;
Orlova, A. V. Eur. J. Org. Chem. 2008, 3251. (c) Kononov,
L. O.; Malysheva, N. N.; Orlova, A. V. Eur. J. Org. Chem.
2009, 611. (d) Kononov, L. O.; Malysheva, N. N.; Orlova,
A. V.; Zinin, A. I.; Laptinskaya, T. V.; Kononova, E. G.;
Kolotyrkina, N. G. Eur. J. Org. Chem. 2012, 1926; and
references cited therein.
(5) Hanashima, S.; Sato, K.; Ito, Y.; Yamaguchi, Y. Eur. J. Org.
Chem. 2009, 4215.
(6) Crich, D.; Li, W. Org. Lett. 2006, 8, 959.
(7) (a) Sherman, A. A.; Yudina, O. N.; Komarova, B. S.;
Tsvetkov, Y. E.; Iacobelli, S.; Nifantiev, N. E. Synthesis
2005, 1783. (b) Hanashima, S.; Castagner, B.; Esposito, D.;
Nokami, T.; Seeberger, P. H. Org. Lett. 2007, 9, 1777; and
references cited therein. (c) Hanashima, S.; Seeberger, P. H.
Chem. Asian J. 2007, 2, 1447.
In summary, we have introduced a novel sialyl-(α2-3)-ga-
lactose building block with removable protecting group at
N5′ and used it for the straightforward synthesis of a li-
brary of sialo-oligosaccharides. Although here we pre-
pared only natural N-acetyl and N-glycolyl derivatives,
other acyl groups can be introduced to N5 of the sialic acid
residue using this methodology. Due to its simplicity and
robustness (related to the rational choice of protecting and
leaving groups), the approach suggested may streamline
the preparation of complex sialo-oligosaccharide libraries
by researchers without specialized background in carbo-
hydrate chemistry.
(8) (a) Pazynina, G. V.; Sablina, M. A.; Tuzikov, A. B.;
Chinarev, A. A.; Bovin, N. V. Mendeleev Commun. 2003,
13, 245; and references cited therein. (b) Esposito, D.;
Hurevich, M.; Castagner, B.; Wang, C. C.; Seeberger, P. H.
Beilstein J. Org. Chem. 2012, 8, 1601; and references cited
therein.
(9) Examplesof synthesesofN-glycolyl-sialo-oligosaccharides:
(a) Simeoni, L. A.; Byramova, N. E.; Bovin, N. V. Russ. J.
Bioorg. Chem. 2000, 26, 183. (b) Sherman, A. A.; Yudina,
O. N.; Shashkov, A. S.; Menshov, V. M.; Nifantiev, N. E.
Carbohydr. Res. 2002, 337, 451; and references cited
therein. (c) Crich, D.; Wu, B. Org. Lett. 2008, 10, 403; and
references cited therein.
(10) Huflejt, M. E.; Vuskovic, M.; Vasiliu, D.; Xu, H.;
Obukhova, P.; Shilova, N.; Tuzikov, A.; Galanina, O.; Arun,
B.; Lu, K.; Bovin, N. Mol. Immunol. 2009, 46, 3037.
(11) Although the α- and β-anomers of 3 can easily be separated
by column chromatorgaphy on silica gel (10 → 60% EtOAc
in benzene) and crystallization (Me2CO–hexanes), their
mixture can be used in the preparation of glycosyl bromide
4.
(12) Paulsen, H.; Bünsch, A. Carbohydr. Res. 1982, 100, 143.
(13) In all further calculations quantitative transformation of 3 to
4 was assumed.
(14) Pazynina, G. V.; Severov, V. V.; Bovin, N. V. Russ. J.
Bioorg. Chem. 2008, 34, 625.
(15) The glycosylation yields achieved with N-trifluoroacetyl
glycosyl bromide 4 were comparable or slightly higher (5–
11%) than those achieved earlier (ref. 8a) with the
corresponding N-acetyl glycosyl bromide [Neu5Ac-(α2-3)-
Gal building block], which was prepared from the parent
glycosyl acetate by treatment with HBr in AcOH.
(16) Typical Glycosylation Procedure
Acknowledgment
The authors are grateful to Dr. A.O. Chizhov for recording high-re-
solution mass spectra. This work was financially supported by the
Russian Foundation for Basic Research (Projects No. 08-03-00839
and 11-03-00918), Russian Ministry of Education and Science, Sta-
te Contract No. 16.512.11.2039, code 2011-1.2-512-013-008, and
RAS Presidium Program Molecular and Cell Biology.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett. Included are
spectroscopic and analytical data for key building blocks and oligo-
saccharides synthesized. SnuIofigop
maotrinuSgIoiopmnfaitrr
r
t
References and Notes
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concentrated in vacuo, and the product was isolated by silica
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(17) In this particular case different amounts of glycosyl donor 4
(0.3 mmol) and glycosyl acceptor 5 (1.2 mmol) were used,
all other conditions were the same as described in the typical
procedure (ref. 16).
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© Georg Thieme Verlag Stuttgart · New York
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G. Pazynina et al.
LETTER
(18) Deprotection of compounds 14, 18, 19, 26, and 29 under
basic conditions involved treatment with MeONa in MeOH,
followed by aq NaOH, neutralization with AcOH, and
finally desalting by gel chromatography on Sephadex LH-20
(MeCN–H2O, 1:1) gave compounds 15, 20, 21, 30, and 31
with the NH2 group at C5 of the sialic acid residue and the
latent amino group in the spacer aglycon (N3 or NHBoc) in
virtually quantitative yields.
(19) In order to remove O-acyl substituent in glycolyl fragment,
the initially formed product was treated with aq NaOH,
neutralized with AcOH, and only then was the product
isolated by gel chromatography on Sephadex LH-20
(MeCN–H2O, 1:1). .
(20) Compounds 16, 24, 25, 32, and 33 (internal salts) were
isolated from the reaction mixtures by ion-exchange
chromatography on Dowex 50W × 4 resin (H+ form; elution
with 1 M aq pyridine).
(21) Oligosaccharides 16, 24, and 25 were additionally purified
by reversed-phase HPLC (Phenomenex Luna C18, 5 μm
particle size, 100 Å pore size) by elution with H2O.
(22) Choudhury (Mukherjee), I.; Minoura, N.; Uzawa, H.
Carbohydr. Res. 2003, 338, 1265.
form; elution with 1 M aq pyridine–AcOH, pH 6.5). After
freeze-drying and ion-exchange on Dowex 50W × 4 resin
(Na+ form, elution with H2O) the corresponding Na+ salts
were obtained.
(29) Treatment of the N-Boc derivatives of trisaccharides with
TFA was accompanied by concomitant formation of the
corresponding lactones, which were hydrolyzed with aq
NaOH (excess NaOH was neutralized with AcOH) prior to
isolation of the target spacered trisaccharides 34 and 35.
(30) Analytical Data of Sulfated Oligosaccharides
Compound 22: [α]D25 –0.2 (c 0.42, MeCN–H2O = 1:1). 1H
NMR (700 MHz, D2O): δ = 1.82 (dd ≈ t, J = 12.1 Hz, 1 H,
H-3ax′′), 1.99 (m, 2 H, CH2 sp), 2.07 (s, 3 H, NCOMe), 2.81
(dd, J3eq,3ax = 12.5 Hz, J3eq,4 = 4.6 Hz, 1 H, H-3eq′′), 3.142 (m
≈ t, J = 6.9 Hz, 2 H, NCH2 sp), 3.57 (dd, J1,2 = 7.9 Hz,
J2,3 = 9.8 Hz, 1 H, H-2′), 3.63 (m, 2 H, H-7′′, H-4), 3.67 (dd,
J9a,9b = 11.9 Hz, J8,9b = 6.1 Hz, 1 H, H-9b′′), 3.70 (ddd ≈ dd,
J5,6a = 3.9 Hz, J5,6b = 8.2 Hz, 1 H, H-5′), 3.73–3.93 (m, 10 H),
3.96 (dd ≈ t, J = 10.2 Hz, 1 H, H-5′′), 3.97 (dd ≈ d, J = 3.1
Hz, 1 H, H-4′), 4.03 (m, 1 H, OCH sp), 4.12 (dd, J2,3 = 9.8
Hz, J3,4 = 3.1 Hz, 1 H, H-3′), 4.15 (s, 2 H, CH2 Gc), 4.25 (dd,
J5,6b = 5.9 Hz, J6a,6b = 11.3 Hz, 1 H, H-6b), 4.41 (dd,
J5,6a = 1.9 Hz, J6a,6b = 11.3 Hz, 1 H, H-6a), 4.54 (d, J1,2 = 7.9
Hz, 1 H, H-1′), 4.60 (d, J1,2 = 8.5 Hz, 1 H, H-1). 13C NMR
(176 MHz, D2O): δ = 22.4, 26.7, 37.8, 39.9, 51.4, 54.4, 61.1
(2 C), 62.5, 67.3, 67.3, 68.1, 68.2, 68.3, 68.6, 69.2, 71.9,
72.6, 73.3, 75.2, 75.7, 82.2, 99.7, 101.1, 103.5, 173.9, 174.8,
175.8. ESI-HRMS: m/z calcd for C28H48N3O23S [M−]:
826.2405; found: 826.2402.
(23) Treatment of 6 with AcCl generated the corresponding
acetylated glycosyl chloride 7, which was further reacted
with alcohol 5 to give the mixture of anomeric 3-
chloropropyl glycosides 8. The β-glycoside was separated
by crystallization (EtOAc–Et2O–hexanes) and
chromatography of the mother liquor (silica gel, 5 → 30%
Me2CO in benzene), then chlorine in the aglycon was
substituted with azide (→ 9), and after de-O-acetylation (→
10) 4,6-O-benzylidene acetal was installed selectively to
give the target 3-OH alcohol 11 in 28% overall yield.
Acetylation of the single hydroxyl group in 11 followed by
regioselective reductive ring opening of the benzylidene
acetal in 12 with NaBH3CN–MsOH in THF24 gave the target
4-OH alcohol 13 in 58% overall yield.
Compound 34: [α]D25 –7 (c 0.46, MeCN–H2O = 1:1). 1H
NMR (700 MHz, D2O): δ = 1.80 (dd ≈ t, J = 12.1 Hz, 1 H,
H-3ax′′), 1.94 (m, 2 H, CH2 sp), 2.02 (s, 3 H, NCOMe), 2.75
(dd, J3eq,3ax = 12.4 Hz, J3eq,4 = 4.6 Hz, 1 H, H-3eq′′), 3.10 (m
≈ t, J = 6.8 Hz, 2 H, NCH2 sp), 3.54 (dd, J1,2 = 7.9 Hz,
J2,3 = 9.8 Hz, 1 H, H-2′), 3.58 (dd, J6,7 = 1.4 Hz, J7,8 = 9.2
Hz, 1 H, H-7′′), 3.63 (dd, J8,9b = 5.9 Hz, J9a,9b = 12.0 Hz, 1 H,
H-9b′′), 3.69–3.81 (m, 10 H), 3.87 (dd, J9a,9b = 12.1 Hz,
J8,9a = 2.2 Hz, 1 H, H-9a′′), 3.89–3.93 (m, 2 H, H-5′′, H-8′′),
3.95 (dd ≈ d, J = 2.9 Hz, 1 H, H-4′), 3.97 (m, 1 H, OCH sp),
4.10 (s, 3 H, CH2 Gc), 4.11 (dd, J2,3 = 9.9 Hz, J3,4 = 3.0 Hz,
1 H, H-3′), 4.31 (dd, J5,6a = 4.4 Hz, J6a.6b = 11.2 Hz, 1 H, H-
6a), 4.42 (dd ≈ d, J = 11.2 Hz, 1 H, H-6b), 4.53 (d, J1,2 = 8.4
Hz, 1 H, H-1), 4.58 (d, J1,2 = 7.8 Hz, 1 H, H-1′). 13C NMR
(176 MHz, D2O): δ = 22.2, 26.7, 37.9, 39.7, 51.5, 55.1, 61.1,
61.1, 62.6, 66.4, 67.5, 68.1, 68.2, 68.3, 69.5, 71.6, 72.2, 72.6,
72.7, 75.2, 75.4, 77.5, 99.8, 101.4, 102.3, 174.0, 174.8,
175.8. ESI-HRMS: m/z calcd for C28H48N3O23S [M–]:
826.2405; found: 826.2402.
(24) Zinin, A. I.; Malysheva, N. N.; Shpirt, A. M.; Torgov, V. I.;
Kononov, L. O. Carbohydr. Res. 2007, 342, 627.
(25) Glycosylation of secondary hydroxy groups at C3 and
especially at C4 of N-acetylglucosamine residue is
considered difficult (see ref. 26).
(26) (a) Paulsen, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 155.
(b) Debenham, J.; Rodebaugh, R.; Fraser-Reid, B. Liebigs
Ann./Recl. 1997, 791. (c) Crich, D.; Dudkin, V. J. Am.
Chem. Soc. 2001, 123, 6819.
(27) (a) Pazynina, G. V.; Severov, V. V.; Maisel, M. L.;
Belyanchikov, I. M.; Bovin, N. V. Mendeleev Commun.
2008, 18, 238. (b) Pazynina, G.; Sablina, M.; Mayzel, M.;
Nasonov, V.; Tuzikov, A.; Bovin, N. Glycobiology 2009, 19,
1078.
(31) For analytical data of other target oligosaccharides and key
intermediates, see Supporting Information.
(28) Sulfated derivatives 22, 23, 34, and 35 were isolated by ion-
exchange chromatography on DEAE Sephadex A-25 (OAc–
Synlett 2013, 24, 226–230
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