S-benzimidazolyl glycosides as a platform for oligosaccharide synthesis by an active-latent strategy

Article abstract of DOI:10.1002/anie.201007212

Doing the Biz: The S-benzimidazolyl (SBiz) anomeric moiety is a new leaving group that can be activated for glycosylation under a variety of conditions, including metal-assisted and alkylation pathways. Application of a substituted SBiz moiety (X=anisoyl, see picture) allows active-latent and armed-disarmed types of oligosaccharide assembly. Copyright

Full text of DOI:10.1002/anie.201007212

DOI: 10.1002/anie.201007212
Glycosylation
S-Benzimidazolyl Glycosides as a Platform for Oligosaccharide
Synthesis by an Active–Latent Strategy**
Scott J. Hasty, Matthew A. Kleine, and Alexei V. Demchenko*
The involvement of complex carbohydrates in a wide variety
of disease-related cellular processes has given this class of
natural compounds tremendous diagnostic and therapeutic
potential.[1] While scientists have been able to successfully
isolate certain classes of natural carbohydrates, the availabil-
ity of pure natural isolates is still inadequate to address the
challenges offered by modern glycosciences. As a conse-
quence, chemical glycosylation has become a viable means to
obtain both natural complex carbohydrates and nonnatural
analogues thereof.[2–4] Unfortunately, chemical synthesis of
oligosaccharides of even moderate complexity still remains a
considerable challenge, and many more complex structures
are not available at all. As such, the development of efficient
strategies for oligosaccharide and glycoconjugate synthesis
stands out as a demanding area of research.[5]
expeditious oligosaccharide synthesis based on S-benzimida-
zolyl (SBiz) glycosides. The SBiz moiety was previously
investigated as a leaving group for phosphorylation of
unprotected glycosyl donors.[32,33] We envisaged that the
SBiz moiety may also be compatible with a very attractive
active–latent concept pioneered by Roy,[34] Fraser-Reid,[16]
Boons,[35] and more recently further advanced by Kim[36,37]
and others.[38–40] According to this concept, an active (reac-
tive) leaving group (LGa) is selectively activated over its
latent (unreactive) counterpart (LGb, Scheme 1). Subse-
As a part of the ongoing research effort in our laboratory
to develop versatile methods for chemical glycosylation and
expeditious oligosaccharide synthesis, we became interested
in glycosyl thioimidates, glycosyl donors equipped with the
1
2
=
SCR NR leaving group. Among a variety of thioimidates
studied by us and others,[6,7] S-benzoxazolyl (SBox),[8] and
S-thiazolinyl (STaz)[9] moieties were found to be excellent
building blocks for oligosaccharide synthesis. We determined
that the SBox and STaz glycosides fit into existing progressive
strategies for oligosaccharide synthesis, such as selective
(including one-pot[10–12] and solid-phase synthesis),[13–15] che-
moselective (armed–disarmed),[16–18] and orthogonal[19–22]
strategies. In addition, the glycosyl thioimidates led us to
the development of conceptually new strategies for oligosac-
charide synthesis: the inverse armed–disarmed strategy,[23,24]
temporary deactivation concept,[25,26] O2/O5 cooperative
Scheme 1. Outline of the active–latent strategy and the SBiz leaving
group explored in this work.
quently, the latent LGb of the formed disaccharide is
converted into the active LGa. This modification does not
involve substitution at the anomeric center like in the two-
step activation strategy;[5] rather it is achieved by a modifi-
cation of the leaving group, usually at a remote position. We
assumed that in the case of the SBiz glycosides, deactivation
of the leaving group could be achieved by placing an easily
removable protecting group (PG) at the nitrogen atom of the
imidazolium ring. The active SBiz leaving group can then be
regenerated by simple deprotection as needed.
effect
(superarmed
and
superdisarmed
glycosyl
donors),[17,27–29] coordination-assisted glycosylation,[30] and
surface-tethered iterative carbohydrate synthesis (STICS).[31]
At the core of the study presented herein is the develop-
ment of a new method for chemical glycosylation and
To pursue this concept we obtained a range of differently
protected SBiz glucosides including perbenzylated 1a, per-
benzoylated 1b, and derivative 1c equipped with the super-
arming protecting-group pattern.[28] We also obtained the
SBiz donor of the d-galacto and d-glucosamino series 1d and
1e, respectively. With glycosyl donors 1a–e in hand, we began
evaluating their applicability to chemical glycosidation with
standard glycosyl acceptors 2–5.[41] Encouragingly, reaction of
glycosyl donor 1a with the primary glycosyl acceptor 2 in the
presence of silver(I) triflate completed in 15 min and
provided the corresponding disaccharide 6a in 98% yield
(Table 1, entry 1). Copper(II) triflate is a significantly milder
promoter for thioimidates, and although a significantly lower
reaction rate was observed (60 h) 6a was isolated in an
[*] S. J. Hasty, M. A. Kleine, Prof. Dr. A. V. Demchenko
Department of Chemistry and Biochemistry
University of Missouri—St. Louis
One University Boulevard, St. Louis, MO 63121 (USA)
Fax: (+1)314-516-5342
E-mail: demchenkoa@umsl.edu
Homepage: http://www.umsl.edu/chemistry/faculty/
demchenko.htm
[**] This work was supported by awards from the NIGMS (GM077170),
NIAID (AI067494), and AHA (0855743G). Lai-Ping (Pinky) Yan is
thanked for the experimental assistance. Dr. Winter and Mr. Kramer
(UM—St. Louis) are thanked for HRMS determinations.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201007212.
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Table 1: Glycosidation of SBiz glycosyl donors 1a–e with glycosyl
acceptors 2–5.
a stereoselectivity (up to 5.3:1 with AllBr) in comparison to
that of the metal-assisted glycosylations. Glycosylation of the
secondary glycosyl acceptors 3–5 was also proven feasible,
and the corresponding disaccharides 7a–9a were obtained in
the presence of AgOTf in 81–95% yield (Table 1, entries 4–
6).
Having investigated the reactivity of perbenzylated
(armed) glycosyl donor 1a, we turned our attention to testing
its perbenzoylated (disarmed) counterpart 1b. As anticipated,
the reactivity of 1b was significantly lower than that of 1a,
and only AgOTf-promoted glycosidations were proven to be
of preparative value. Thus, the desired disaccharides 6b–9b
were isolated in 84–94% yield (Table 1, entries 7, 10–12).
Copper(II) triflate-promoted glycosidation was very slow
(144 h; Table 1, entry 8) while alkyl halide-promoted reac-
tions did not proceed at all (Table 1, entry 9). These results
suggest that the SBiz glycosides can be applied in accordance
with the classic armed–disarmed strategy.[42] To develop a
more flexible route to the synthesis of 1,2-trans glycosides we
also investigated SBiz glycosyl donor 1c, which bears the
superarming protecting-group pattern.[28] As expected,
AgOTf-promoted glycosidation produced disaccharides 6c–
9c almost instantaneously in 84–98% yield (Table 1,
entries 13, 15–17). Also in the presence of Cu(OTf)2, the
reaction rate was significantly higher than that observed with
either the armed glycosyl donor 1a or its disarmed counter-
part 1b (2 h, 93%; Table 1, entry 14).
Entry
Donor +
acceptor
Promoter[a]
t
Product
(yield, a/b ratio)
1
2
3
1a+2
1a+2
1a+2
AgOTf
15 min
60 h
12 h
6a (98%, 1.1:1)
6a (93%, 1.3:1)
6a (84–90%,
Cu(OTf)2
AllBr, BnBr
MeI (558C)[b]
AgOTf
AgOTf
AgOTf
3.3–5.3:1)
4
5
6
1a+3
1a+4
1a+5
15 min
15 min
15 min
7a (81%, 1.8:1)
8a (91%, 1.3:1)
9a (95%, 1.6:1)
To broaden the scope of this glycosylation approach, we
tested its applicability to the synthesis of d-galactosides and 2-
amino-2-deoxyglucosides, highly important and abundant
sugar series.[43–45] Glycosidation of SBiz galactose donor 1d
with glycosyl acceptors 2–5 in the presence of AgOTf
proceeded smoothly and the corresponding disaccharides
6d–9d were obtained in 89–97% yield (Table 1, entries 18–
21). Also, glycosidation of N-(2,2,2-trichloroethoxy)carba-
moyl (N-Troc) glycosyl donor 1e with acceptors 2–5 in the
presence of AgOTf was successfully accomplished. The
resulting disaccharides 6e–9e were isolated in 86–94%
yields (Table 1, entries 22–25).
7
8
9
1b+2
1b+2
1b+2
AgOTf
2 h
144 h
120 h
6b (86%, b only)
6b (83%, b only)
no reaction
Cu(OTf)2
AllBr, BnBr
MeI (558C)
AgOTf
AgOTf
AgOTf
10
11
12
1b+3
1b+4
1b+5
45 min
2 h
2 h
7b (94%, b only)
8b (87%, b only)
9b (84%, b only)
13
14
15
16
17
1c+2
1c+2
1c+3
1c+4
1c+5
AgOTf
Cu(OTf)2
AgOTf
AgOTf
AgOTf
<5 min
2 h
<5 min
<5 min
<5 min
6c (98%, b only)
6c (93%, b only)
7c (84%, b only)
8c (90%, b only)
9c (88%, b only)
Having investigated the applicability of the SBiz glyco-
sides for chemical glycosylation, we next investigated the
effects that N-substitution may have on the reactivity of the
leaving group. For this purpose, we investigated a variety of
N-acyl substituents (acetyl, haloacetyls, benzoyl, substituted
benzoyls), and the most prominent results were achieved with
the N-anisoylated SBiz building block 10a obtained from 1a
by reaction with anisoyl chloride in the presence of pyridine
(Scheme 2). As projected, no product was formed in glyco-
sidations of 10a under alkylation conditions (up to 120 h at
558C). In addition, competitive glycosylation wherein two
glycosyl donors (1a and 10a) were allowed to compete for
glycosyl acceptor 2 allowed differentiation of the reactivities
of SBiz and anisoylated SBiz leaving groups. Thus, the
competition experiment in the presence of MeI allowed for
nearly complete recovery of the unreacted 10a (98%), while
only traces of 1a (2%) remained. Less expectedly, AgOTf-
promoted activation of the N-anisoylated glycosyl donor 10a
was as efficient as that of its SBiz counterpart 1a and
disaccharide 6a was rapidly produced (15 min) in 98% yield.
18
19
20
21
1d+2
1d+3
1d+4
1d+5
AgOTf
AgOTf
AgOTf
AgOTf
2 h
2 h
3 h
3.5 h
6d (97%, b only)
7d (94%, b only)
8d (89%, b only)
9d (89%, b only)
22
23
24
25
1e+2
1e+3
1e+4
1e+5
AgOTf
AgOTf
AgOTf
AgOTf
30 min
30 min
30 min
30 min
6e (94%, b only)
7e (92%, b only)
8e (86%, b only)
9e (92%, b only)
[a] Performed in the presence of 3 ꢀ molecular sieves at room temper-
ature, unless noted otherwise. [b] Reaction at room temperature was
much more sluggish. Bn=benzyl, Bz=benzoyl, Tf=triflate, All=allyl.
excellent yield of 93% (Table 1, entry 2). Subsequently, we
demonstrated that the SBiz moiety can be efficiently acti-
vated under alkylation conditions at elevated temperature,
similarly to STaz glycosides.[22] No significant difference
between AllBr-, BnBr-, or MeI-promoted glycosidations of
1a was detected, and 6a was obtained in 84–90% yield
(Table 1, entry 3). We noticed a significantly improved
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Angew. Chem. Int. Ed. 2011, 50, 4197 –4201

Scheme 4. Removal of the N-anisoyl group in the presence of the
O-benzoyl group. Conditions: a) 0.5m guanidine/MeOH (0.5 equiv) in
CH2Cl2/MeOH (9:1, v/v), RT, 5 min; b) 2 equiv 1m TBAF/THF in THF,
RT, 3 h; quantitative yield of 1b in both procedures.
benzoylated compound 10b can be effectively removed in the
presence of guanidine in MeOH or, alternatively, tetra-n-
butylammonium fluoride (TBAF) in THF. No competitive
O-benzoyl group removal was detected under these reaction
conditions and the desired SBiz donor 1b was obtained
quantitatively. In this context, we anticipate that other
acyl groups, for example, 2-(azidomethyl)benzoyl,[46]
3-(2’-benzyloxyphenyl)-3,3-dimethylpropanoate,[47] or
(2-nitrophenyl)acetyl,[48] which can be reductively cleaved in
the presence of conventional O-acyl substituents (benzoyl),
would also be suitable for the purpose of the temporary
N-acylation.
Since the N-protected latent SBiz moiety can be activated
with a stronger promoter (Scheme 2), we pursued this path-
way also. AgOTf-promoted activation of latent disaccharide
12 led to trisaccharide 14 in 84% yield (Scheme 3). By
exploring this two-way activation approach we showed that
the SBiz moiety serves as a suitable new platform for the
active–latent-like activations, but also allows for the direct
activation of the latent N-acylated leaving group using
stronger promoter.
Scheme 2. Synthesis and glycosidation of N-anisoylated glycosyl donor
10a; competition experiment with SBiz donor 1a. 1,2-DCE=
1,2-dichloroethane.
With these promising results, we next began investigating
whether SBiz donor 1a could be selectively activated in the
presence the N-anisoylated SBiz acceptor, which represents
the key step for executing the SBiz-based active–latent
concept. For this purpose we obtained glycosyl acceptor 11
(see the Supporting Information). Very encouragingly, MeI-
promoted glycosylation between building blocks 1a and 11
produced the expected latent disaccharide 12 in 75% yield
(a:b = 1:1.8, Scheme 3). After that, the N-anisoyl group was
removed by treatment with NaOMe in MeOH and the
resulting active disaccharide 13 was subsequently activated
with MeI to afford trisaccharide 14 in 71% yield. This two-
step SBiz activation sequence mimics the traditional active–
latent concept.[5]
What remained unknown is why alkylating reagents are
able to activate SBiz but not its N-anisoylated counterpart.
Based on the anticipation that the SBiz is activated by the
direct activation pathway A (Scheme 5) through the anome-
Scheme 5. Direct pathway A versus remote pathway B for SBiz
activation.
Scheme 3. Activation of SBiz donor 1a over N-anisoylated SBiz
acceptor 11 in the active–latent fashion.
It should be noted that although the removal of the
N-anisoyl moiety in 12 with NaOMe/MeOH is suitable for the
synthesis of benzylated building blocks, it would represent a
hurdle if the application of the active–latent methodology
were attempted with acylated compounds. To broaden the
scope of this transformation, we investigated other reaction
conditions that would not trigger concomitant O-deacylation.
As depicted in Scheme 4, we discovered that N-anisoyl in O-
ric sulfur, like in S-alkyl/aryl[49] or SBox glycosides,[22,50] one
possible explanation is the electronic effect. It is possible that
upon N-anisoylation the sulfur atom in compound 10a will
become too weak a nucleophile to displace the halogen atom
of the alkylating reagent. Alternatively, the activation of the
SBiz may also take place through the nitrogen atom of the
imidazole ring representing the remote activation pathway B,
Angew. Chem. Int. Ed. 2011, 50, 4197 –4201
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Communications
like in S-pyridyl[51,52] or STaz[22] derivatives. In this case, the
effect of the N-anisoyl group is steric as it will block the
N-activation site of the SBiz moiety.
3), 129.0, 137.4, 137.5, 137.7, 138.1, 146.5 ppm; HR-FAB MS: m/z
calcd for C41H41N2O5S: 673.2736 [M+H]+; found: 673.2732.
10: Anisoyl chloride (0.58 mL, 4.29 mmol) was added dropwise to
a stirred solution of 1a (0.962 g, 1.4 mmol) in pyridine (10 mL). The
resulting reaction mixture was stirred under argon for 15 min at room
temperature. After that, the volatiles were removed in vacuo and the
residue was co-evaporated with toluene (3 ꢁ 10 mL). The residue was
diluted with CH2Cl2 (200 mL), and washed with water (20 mL), 1n aq.
HCl (20 mL), water (20 mL), sat. aq. NaHCO3 (2 ꢁ 20 mL), and water
(3 ꢁ 10 mL). The organic phase was separated, dried over MgSO4, and
concentrated in vacuo. The residue was purified by column chroma-
tography on silica gel (ethyl acetate/toluene gradient elution) to
afford compound 10 (1.05 g, 91%) as an off-white foam. Rf = 0.50
To differentiate the two pathways we set up a model
experiment wherein SBiz donor 1a reacted with 2-propanol in
the presence of BnBr (Scheme 5). Upon completion of the
reaction, judged by the disappearance of 1a and formation of
16,[53] we separated and analyzed all components of the
reaction mixture. 2-Benzylsulfanyl-1H-benzimidazole 15[54,55]
was isolated and its identity was proven by spectral and X-ray
methods, whereas no trace of its N-benzylated counterpart
17[56,57] was detected. The result of this study indicates that
activation of SBiz under alkylation conditions takes place
through the sulfur atom, similarly to that found previously for
SBox glycosides.[22,50] Therefore, we conclude that the deac-
tivation effect of the N-anisoyl moiety in 10a is electronic.
However, whether this effect results from simple electron
withdrawal or distortion of the aromaticity of the imidazole
ring is yet to be determined. What makes this disarming effect
different from the well-documented disarming effect in
glycosylation[42] is that herein the disarming is achieved by
acylation of the leaving group, not by introducing the
neighboring acyl substituents in the sugar moiety.
In conclusion, we have investigated the S-benzimidazolyl
(SBiz) anomeric moiety as a new leaving group that can be
activated for chemical glycosylation under a variety of
conditions including metal-assisted and alkylation pathways.
Differentiation between the two possible reaction pathways
for activation of the SBiz moiety was achieved by an extended
mechanistic study. We also demonstrated that the application
of the substituted SBiz moiety allows execution of rapid
oligosaccharide assembly through active–latent- and armed–
disarmed-like concepts.
27
(ethyl acetate/toluene, 1:9, v/v); ½aꢀD ¼ + 119.58 (c = 1.0, CHCl3);
1H NMR: d = 3.66 (dd, 1H, J2,3 = 8.67 Hz; H-2), 3.70–3.87 (m, 5H; H-
3, 4, 5, 6a, 6b), 3.88 (s, 3H; OCH3), 4.54 (dd, 2H, J2 = 11.9 Hz;
CH2Ph), 4.71 (dd, 2H, J2 = 10.7 Hz; CH2Ph), 4.87 (dd, 2H, J2 =
10.7 Hz; CH2Ph), 4.88 (dd, 2H, J2 = 10.9 Hz; CH2Ph), 5.83 (d, 1H,
J
1,2 = 10.2 Hz; H-1), 6.89–7.71 ppm (m, 28H; aromatic); 13C NMR:
d = 55.8, 68.8, 73.5, 75.1, 75.5, 75.9, 77.9, 79.6, 81.2, 85.1, 86.9, 113.4,
114.4 (ꢁ 3), 119.3, 123.4, 124.2, 124.9, 127.7, 127.9 (ꢁ 3), 128.0 (ꢁ 7),
128.5 (ꢁ 3), 128.6 (ꢁ 4), 129.2, 132.8 (ꢁ 2), 134.7, 138.1, 138.3 (ꢁ 2),
138.6, 143.9, 151.8, 164.5, 167.3 ppm; HR-FAB MS: m/z calcd for
C49H47N2O7S: 807.3104 [M+H]+; found: 807.3081.
Typical AgOTf-promoted glycosylation procedure: A mixture of
glycosyl donor (0.045 mmol), glycosyl acceptor (0.030 mmol), and
freshly activated molecular sieves (3 ꢀ, 125 mg) in 1,2-dichloroethane
(1 mL) was stirred under argon for 1 h. AgOTf (0.090 mmol) was
added and the reaction mixture was monitored by TLC. Upon
completion (see Table 1), the solid was isolated by filtration and the
filtrate was diluted with CH2Cl2 (15 mL), and washed with 5% aq
NaOH (5 mL) and water (3 ꢁ 5 mL). The organic layer was separated,
dried with MgSO4, and concentrated in vacuo. The residue was
purified by silica gel column chromatography (ethyl acetate/toluene
gradient elution) to afford the corresponding oligosaccharide.
Typical alkyl halide-promoted glycosylation procedure: A mix-
ture of glycosyl donor (0.045 mmol), glycosyl acceptor (0.030 mmol),
and freshly activated molecular sieves (4 ꢀ, 125 mg) in 1,2-dichloro-
ethane (1 mL) was stirred under argon for 1 h. Alkyl halide
(0.027 mmol) was added and the reaction mixture was monitored
by TLC. Upon completion (see Table 1), the solid was isolated by
filtration and the filtrate was diluted with CH2Cl2 (15 mL), and
washed with 5% aq NaOH (5 mL) and water (3 ꢁ 5 mL). The organic
layer was separated, dried with MgSO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography (ethyl
acetate/toluene gradient elution) to afford the corresponding di-
saccharide.
Experimental Section
1a: A solution of ethyl 2,3,4,6-tetra-O-benzyl-1-thio-b-d-glucopyra-
noside[58] (2.19 g, 3.75 mmol) and activated molecular sieves (3 ꢀ,
1.88 g) in CH2Cl2 (56 mL) was stirred under argon for 1 h at room
temperature. A freshly prepared solution of Br2 in CH2Cl2 (36 mL,
1:165, v/v) was then added and the reaction mixture was stirred for
5 min at room temperature. After that, the solid was isolated by
filtration and the filtrate was concentrated in vacuo at room
temperature. The crude residue was dissolved in dry MeCN
(80 mL) and KSBiz (1.76 g, 9.36 mmol) and [18]crown-6 (0.20 g,
0.75 mmol) were added. The resulting reaction mixture was stirred
under argon for 16 h at room temperature. The solid was then isolated
by filtration and the filtrate was concentrated in vacuo. The residue
was diluted with CH2Cl2 (200 mL) and washed successively with 10%
aq. NaOH (20 mL) and water (3 ꢁ 20 mL). The organic layer was
separated, dried with MgSO4, and concentrated in vacuo. The residue
was purified by column chromatography on silica gel (ethyl acetate/
toluene gradient elution) to afford compound 1a (1.85 g, 73%) as an
Received: November 16, 2010
Revised: January 19, 2011
Published online: March 23, 2011
Keywords: carbohydrates · glycosides · glycosylation ·
.
oligosaccharides · synthetic methods
[1] A. Varki, R. D. Cummings, J. D. Esko, H. H. Freeze, C. R.
Bertozzi, P. Stanley, G. W. Hart, M. E. Etzler, Essentials of
Glycobiology, 2nd ed., CSH Laboratory Press, New York, 2009.
[2] A. V. Demchenko in Handbook of Chemical Glycosylation (Ed.:
A. V. Demchenko), Wiley-VCH, Weinheim, 2008, p. 1.
[3] X. Zhu, R. R. Schmidt, Angew. Chem. 2009, 121, 1932; Angew.
Chem. Int. Ed. 2009, 48, 1900.
[4] T. J. Boltje, T. Buskas, G. J. Boons, Nat. Chem. 2009, 1, 611.
[5] J. T. Smoot, A. V. Demchenko, Adv. Carbohydr. Chem. Bio-
chem. 2009, 62, 161.
off-white foam. Rf = 0.54 (ethyl acetate/toluene, 3:17, v/v);
28
½aꢀD ¼ꢁ28.78 (c = 1.0, CHCl3); 1H NMR: d = 3.45 (dd, 1H, J2,3
=
8.5 Hz; H-2), 3.58–3.82 (m, 5H; H-3, 4, 5, 6a, 6b), 4.57 (dd, 2H, J2 =
11.5 Hz; CH2Ph), 4.64 (dd, 2H, J2 = 11.1 Hz; CH2Ph), 4.76 (d, 1H,
J
1,2 = 9.6 Hz; H-1), 4.76 (dd, 2H, J2 = 10.0 Hz; CH2Ph), 4.82 (dd, 2H,
J2 = 10.9 Hz; CH2Ph), 6.38–7.38 ppm (m, 25H; aromatic, NH);
13C NMR: d = 68.8, 74.0, 75.3, 75.8, 76.0, 77.2, 78.3, 80.9, 84.1, 86.0,
122.5, 127.9 (ꢁ 3), 128.1 (ꢁ 4), 128.4, 128.5 (ꢁ 3), 128.6 (ꢁ 10), 128.9 (ꢁ
4200 www.angewandte.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2011, 50, 4197 –4201

[6] A. Ramakrishnan, P. Pornsuriyasak, A. V. Demchenko,
J. Carbohydr. Chem. 2005, 24, 649.
[7] W. Szeja, G. Grynkiewicz in Handbook of Chemical Glycosyla-
tion (Ed.: A. V. Demchenko), Wiley-VCH, Weinheim, 2008,
p. 329.
[31] P. Pornsuriyasak, S. C. Ranade, A. Li, M. C. Parlato, C. R. Sims,
O. V. Shulga, K. J. Stine, A. V. Demchenko, Chem. Commun.
2009, 1834.
[32] V. Ferriꢂres, S. Blanchard, D. Fischer, D. Plusquellec, Bioorg.
Med. Chem. Lett. 2002, 12, 3515.
[8] A. V. Demchenko, N. N. Malysheva, C. De Meo, Org. Lett. 2003,
5, 455.
[33] R. Euzen, V. Ferrieres, D. Plusquellec, J. Org. Chem. 2005, 70,
847.
[9] A. V. Demchenko, P. Pornsuriyasak, C. De Meo, N. N. Maly-
sheva, Angew. Chem. 2004, 116, 3131; Angew. Chem. Int. Ed.
2004, 43, 3069.
[10] Y. Wang, X. S. Ye, L. H. Zhang, Org. Biomol. Chem. 2007, 5,
2189.
[34] R. Roy, F. O. Andersson, M. Letellier, Tetrahedron Lett. 1992,
33, 6053.
[35] G. J. Boons, S. Isles, Tetrahedron Lett. 1994, 35, 3593.
[36] K. S. Kim, J. H. Kim, Y. J. Lee, Y. J. Lee, J. Park, J. Am. Chem.
Soc. 2001, 123, 8477.
[11] P. Pornsuriyasak, A. V. Demchenko, Tetrahedron: Asymmetry
2005, 16, 433.
[12] A. R. Parameswar, A. V. Demchenko in Progress in the Synthesis
of Complex Carbohydrate Chains of Plant and Microbial
Polysaccharides (Ed.: N. E. Nifantiev), Transworld Research
Network, Kerala, 2009, pp. 463.
[13] P. H. Seeberger, W. C. Haase, Chem. Rev. 2000, 100, 4349.
[14] R. R. Schmidt, S. Jonke, K. Liu in ACS Symp. Ser. (Frontiers in
Modern Carbohydrate Chemistry), Vol. 960 (Ed.: A. V. Dem-
chenko), Oxford University Press, 2007, p. 209.
[15] M. C. Parlato, M. N. Kamat, H. Wang, K. J. Stine, A. V.
Demchenko, J. Org. Chem. 2008, 73, 1716.
[37] K.-S. Kim, H.-B. Jeon in Handbook of Chemical Glycosylation
(Ed.: A. V. Demchenko), Wiley-VCH, Weinheim, 2008, p. 185.
[38] R. J. Hinklin, L. L. Kiessling, J. Am. Chem. Soc. 2001, 123, 3379.
[39] L. Huang, Z. Wang, X. Huang, Chem. Commun. 2004, 1960.
[40] P. Wang, P. Haldar, Y. Wang, H. Hu, J. Org. Chem. 2007, 72, 5870.
[41] S. C. Ranade, S. Kaeothip, A. V. Demchenko, Org. Lett. 2010, 12,
5628.
[42] B. Fraser-Reid, Z. Wu, U. E. Udodong, H. Ottosson, J. Org.
Chem. 1990, 55, 6068.
[43] A. Varki, Glycobiology 1993, 3, 97.
[44] A. F. G. Bongat, A. V. Demchenko, Carbohydr. Res. 2007, 342,
374.
[16] B. Fraser-Reid, U. E. Udodong, Z. F. Wu, H. Ottosson, J. R.
Merritt, C. S. Rao, C. Roberts, R. Madsen, Synlett 1992, 927.
[17] M. N. Kamat, A. V. Demchenko, Org. Lett. 2005, 7, 3215.
[18] A. F. G. Bongat, M. N. Kamat, A. V. Demchenko, J. Org. Chem.
2007, 72, 1480.
[19] O. Kanie, Y. Ito, T. Ogawa, J. Am. Chem. Soc. 1994, 116, 12073.
[20] P. Pornsuriyasak, A. V. Demchenko, Chem. Eur. J. 2006, 12,
6630.
[45] J. E. Robyt in Glycoscience: Chemistry and Chemical Biology,
Vol. 1 (Eds.: B. Fraser-Reid, K. Tatsuta, J. Thiem), Springer,
Berlin, 2001, p. 75.
[46] J. Xu, Z. Guo, Carbohydr. Res. 2002, 337, 87.
[47] D. Crich, F. Cai, Org. Lett. 2007, 9, 1613.
[48] K. Daragics, P. Fꢃgedi, Org. Lett. 2010, 12, 2076.
[49] W. Zhong, G.-J. Boons in Handbook of Chemical Glycosylation
(Ed.: A. V. Demchenko), Wiley-VCH, Weinheim, 2008, p. 261.
[50] M. N. Kamat, N. P. Rath, A. V. Demchenko, J. Org. Chem. 2007,
72, 6938.
[21] S. R. Vidadala, S. A. Thadke, S. Hotha, J. Org. Chem. 2009, 74,
9233.
[22] S. Kaeothip, P. Pornsuriyasak, N. P. Rath, A. V. Demchenko,
Org. Lett. 2009, 11, 799.
[51] S. Hanessian, C. Bacquet, N. Lehong, Carbohydr. Res. 1980, 80,
C17.
[23] J. T. Smoot, P. Pornsuriyasak, A. V. Demchenko, Angew. Chem.
2005, 117, 7285; Angew. Chem. Int. Ed. 2005, 44, 7123.
[24] J. T. Smoot, A. V. Demchenko, J. Org. Chem. 2008, 73, 8838.
[25] P. Pornsuriyasak, U. B. Gangadharmath, N. P. Rath, A. V.
Demchenko, Org. Lett. 2004, 6, 4515.
[26] P. Pornsuriyasak, N. P. Rath, A. V. Demchenko, Chem.
Commun. 2008, 5633.
[27] L. K. Mydock, A. V. Demchenko, Org. Lett. 2008, 10, 2107.
[28] L. K. Mydock, A. V. Demchenko, Org. Lett. 2008, 10, 2103.
[29] H. D. Premathilake, L. K. Mydock, A. V. Demchenko, J. Org.
Chem. 2010, 75, 1095.
[52] H. B. Mereyala, G. V. Reddy, Tetrahedron 1991, 47, 6435.
[53] K. Briner, A. Vasella, Helv. Chim. Acta 1989, 72, 1371.
[54] R. V. Kumar, K. R. Gopal, K. V. S. R. S. Kumar, J. Heterocycl.
Chem. 2005, 42, 1405.
[55] E. A. Yavo, R. Kakou-Yao, S. Coulibaly, A. Abou, A. J. Tenon,
Acta Crystallogr. Sect. E 2007, 63, o4551.
[56] T. R. Lee, K. Kim, J. Heterocycl. Chem. 1989, 26, 747.
[57] L. I. Kruse, C. Kaiser, W. E. DeWolf, J. A. Finkelstein, J. S.
Frazee, E. L. Hilbert, S. T. Ross, K. E. Flaim, J. L. Sawyer,
J. Med. Chem. 1990, 33, 781.
[58] F. Andersson, P. Fugedi, P. J. Garegg, M. Nashed, Tetrahedron
Lett. 1986, 27, 3919.
[30] P. Pornsuriyasak, C. Vetter, S. Kaeothip, M. Kovermann, J.
Balbach, D. Steinborn, A. V. Demchenko, Chem. Commun.
2009, 6379.
Angew. Chem. Int. Ed. 2011, 50, 4197 –4201
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