A Mild Glycosylation Protocol with Glycosyl 1-Methylimidazole-2-carboxylates as Donors

Article abstract of DOI:10.1002/ejoc.202100677

A mild glycosylation protocol is developed by using glycosyl 1-methylimidazole-2-carboxylates. Such a glycosylation can be promoted by a series of metal triflates and triflimides, especially Cu(OTf)₂. The reaction is initiated by activation of

Full text of DOI:10.1002/ejoc.202100677

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doi.org/10.1002/ejoc.202100677
A Mild Glycosylation Protocol with Glycosyl
1-Methylimidazole-2-carboxylates as Donors
Jianpeng Chen,[a] Yu Tang,*[b] and Biao Yu*[b]
A mild glycosylation protocol is developed by using glycosyl 1-
methylimidazole-2-carboxylates. Such a glycosylation can be
promoted by a series of metal triflates and triflimides, especially
Cu(OTf)2. The reaction is initiated by activation of the glycosyl
ester donor via coordination with the metal cation assisted by
the adjacent 1-methylimidazole chelating group.
Introduction
category are relatively limited so far.[11,12] In 1991, Kobayashi
et al. reported the first example of chelation assisted glycosyl
donor, i.e., glycosyl 2-pyridinecarboxylate (G) which can be
activated by Cu(OTf)2 or Sn(OTf)2.[13] In 2016, Salamone, Jensen,
and coworkers disclosed another chelation assisted donor, i.e.,
glycosyl ortho-methoxybenzoate (H) which can be catalytically
activated by a range of promoters including Bi(OTf)3, Fe(OTf)3,
TMSOTf, and triflic acid.[14] In 2017, Tang et al. further developed
glycosyl isoquinoline-1-carboxylate (I),[15] which can be effec-
tively activated by Cu(OTf)2 and can avoid a troublesome
transesterification side reaction observed in the glycosyl
pyridine-2-carboxylates glycosylation system.
In fact, the use of glycosylation donors bearing heterocyclic
anomeric leaving groups are pioneered by Mukaiyama et al.,
who employed 2-glycosyl 3-ethylbenzoxazolium salt for the
construction of N-glycosides,[16] and Hanessian et al., who
developed pyridine-2-yl 1-thioglycoside as donor for the
construction of O-glycosyl linkages.[17] Ever since, a series of
heterocycle-containing donors have been developed and
successfully applied in glycoside synthesis.[18,19] Most of these
donors contain N-heterocycles, particularly pyridine rings. The
nitrogen atom usually plays a critical role that act as a
coordinating site. It is noted that imidazole skeleton, an
important class of N-heterocycle, has rarely been applied in
glycosyl donor design.[20] The basicity of imidazole nitrogen is
about two orders of magnitude stronger than pyridine
nitrogen,[21] thus, the coordinating ability of the imidazole ring
acting as a N-donor is expected to be stronger than the pyridine
ring, and glycosyl donors bearing imidazole ring as the leaving
group are expected to exhibit better leaving abilities. With this
consideration in mind, a series of potential imidazole ring
containing leaving groups were carefully surveyed and glycosyl
1-methylimidazole-2-carboxylates (i.e., J) attracted our atten-
tion. This type of donors might be prepared from 1-methyl-2-
imidazolecarboxylic acid 1, a commercially available shelf-stable
reagent, and is expected to exhibit good glycosylation reactivity
under the promotion of metal promoters. In this article, we
report the preparation and evaluation of glycosyl 1-meth-
ylimidazole-2-carboxylates as a new type of glycosyl donors.
The design, synthesis, and glycosylation reactivity evaluation of
glycosyl donors bearing novel anomeric leaving groups con-
stitute an active area of research in glycoscience, and new
glycosylation donors are continuously being developed.[1,2] Of
the various glycosylation donors developed, glycosyl carbox-
ylates type donors have occupied an important position due to
their convenience of preparation, shelf stability, ease of
activation, and high glycosylation efficiency.[3–5] The activation
mode of these ester type donors can be classified into three
types (Figure 1). Type I involves direct activation of the carbonyl
group by a Lewis acid. Donors falling into this category include
glycosyl 1-O-acetates and formates, and the Lewis acid
promoters include BF3 ·Et2O, TMSOTf, ZnCl2, and Sc(OTf)3.[3] Type
II is activation of the carbonyl group via a transient carbocation
or vinyl cation generated through electrophilic activation of an
adjacent alkenyl or alkynyl group by an electrophilic reagent or
a transition metal catalyst. Donors belonging to this category
include glycosyl 1-O-4-hexynoate (Figure 1, A),[6] glycosyl o-
alkynylbenzoates (B),[7] alkynyl glycosyl carbonates (C),[8] phenyl-
propiolate glycosides (D),[5f] glycosyl ynolates (E),[5d] glycosyl
ortho-(1-phenylvinyl)benzoates (F),[5b] etc. The electrophilic
reagents or transition metal catalysts employed for the
activation of this type of donors include NIS/TMSOTf,[5b,h] HgX2
(X=OTf or NTf2),[6] R3PAuX (X=OTf, NTf2).[7–10] Type III is activation
of the carbonyl group via coordination with a metal cation
assisted by an adjacent chelating group, donors falling into this
[a] J. Chen
School of Physical Science and Technology,
ShanghaiTech University,
100 Haike Road, Shanghai 201210, China
[b] Dr. Y. Tang, Prof. B. Yu
State Key Laboratory of Bioorganic and Natural Products Chemistry,
Center for Excellence in Molecular Synthesis,
Shanghai Institute of Organic Chemistry
University of Chinese Academy of Sciences,
Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, China
E-mail: tangyu@sioc.ac.cn
byu@sioc.ac.cn
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202100677
Part of the joint “Carbohydrate Chemistry” Special Collection with Chem-
CatChem.
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Figure 1. Activation modes of ester type glycosyl donors, representative examples, and the present work.
Results and Discussion
Of the various possible preparation routes, the direct condensa-
tion of 1-methyl-2-imidazolecarboxylic acid with glycosyl hemi-
acetal derivatives is the most straightforward and convenient
route.[22] Thus, we selected the condensation of 2,3,4,6-tetra-O-
benzoyl-D-glucopyranose 2a and 1-methyl-2-imidazolecarbox-
To test the glycosylation reactivity of glycosyl 1-meth-
ylimidazole-2-carboxylates, the first problem to address is how
to prepare this type of compounds conveniently in high yields.
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1
ylic acid 1 as a model reaction and studied a series of
condensation conditions (Table 1). The condensation of 2a
(1 equiv.) and 1 (1.5 equiv.) in the presence of DCC (1.6 equiv.)
and a catalytic amount of DMAP (0.2 equiv.) in CH2Cl2 afforded
the desired 2,3,4,6-tetra-O-benzoyl-D-glucopyranosyl 1-meth-
ylimidazole-2-carboxylates 3a in 71% yield with the β anomer
as the major product (β/α=3/1, entry 1). Switching the
condensation agent from DCC to EDCI led to a diminished yield
(entry 2). These unsatisfactory results were attributable to the
poor solubility of 1-methyl-2-imidazolecarboxylic acid 1 in
CH2Cl2. A screening of solvents revealed that acid 1 dissolved
well in DMF. Indeed, the condensation of 2a (1 equiv.) and 1
(1.5 equiv.) in the presence of EDCI (1.6 equiv.) and DMAP
(1.6 equiv.) in DMF afforded the desired product 3a in 80%
yield with β/α ratio 3.5/1 (entry 4). Switching the condensation
agent from EDCI to DCC led to a diminished yield (entry 3).
Thus, the optimal conditions were established as either
β-D-xylopyranose, which also adopts a C4 chair conformation
slightly distorted toward the 5HO half-chair form.[23]
Apart from direct condensation, alternative methods for the
preparation of glycosyl 1-methylimidazole-2-carboxylate 3a
were also tested (Scheme 2). The reaction of glycosyl hemi-
acetal 2a with the corresponding 1-methyl-1-H-imidazole-2-
carboxylic acid chloride 4 in the presence of Et3N (2.0 equiv.)
and DMAP (0.1 equiv.) provided the desired product 3a in 72%
yield with the
α anomer predominantly (α/β=5.5/1). In
addition, pure β anomer of product 3a could be prepared in
66% yield from the corresponding glucosyl bromide 5 and acid
1 in the presence of Ag2CO3 (0.6 equiv.) in dry DMF (0.2 M).
Having established convenient methods for the preparation
of glycosyl 1-methylimidazole-2-carboxylates, the glycosylation
reactivity of this type of donors were next tested. The
glycosylation reaction between glycosyl donor 3a and glyco-
side acceptor 6a under the promotion of a metal salt bearing a
weakly coordinating counteranion (1.5 equiv.) in CH2Cl2 in the
presences of 4 Å molecular sieves were selected as a model
reaction system, and a series of commercially available metal
triflates and triflimides were evaluated. The results are depicted
in Table 2. To our delight, several of these tested metal
complexes, including Cu(OTf)2, Cu(NTf2)2, Zn(NTf2)2, In(OTf)3,
Bi(OTf)3, and Sn(OTf)2, were effective promoters, delivering the
desired 1!4-linked disaccharide 7a in 78–87% yields. Of these
promoters Cu(OTf)2 is the most cost-effective and the most
efficient one, the optimal conditions were thus established
employing Cu(OTf)2 as the glycosylation promoter.
The scope of the present glycosylation conditions was next
explored, and the results are illustrated in Scheme 3. With
respect to glycosyl donor scope, disarmed perbenzoylated
donors, including glucopyranosyl donor 3a, mannopyranosyl
donor 3c, rhamnopyranosyl donor 3d, xylopyranosyl donor 3e,
ribopyranosyl donor 3f, ribofuranosyl donor 3g, and armed
benzylated glucopyranosyl donor 3b all underwent glycosyla-
tion smoothly, affording the glycosylated products 7a–7z in
73–99% yields. With respect to glycosyl acceptor scope, primary
aliphatic alcohol (6g), secondary aliphatic alcohols (6e, 6h, and
6i), tertiary aliphatic alcohol (6c), primary sugar alcohols (6b,
6d) and secondary sugar alcohol (6a) were all suitable glycosyl
acceptors. It is noteworthy that the glycosylation of acceptors
bearing basic tertiary amine moieties, namely 2-(morpholin-4-yl)
performing the condensation of glycosyl hemiacetal
2
(1.0 equiv.) with acid 1 (1.5 equiv.) in DMF in the presence of
EDCI (1.6 equiv.) and DMAP (1.6 equiv.) (Conditions A) or in
CH2Cl2 in the presence of DCC (1.6 equiv.) and DMAP (0.2 equiv.)
(Conditions B).
Under the optimal condensation reaction conditions, a
series of glycosyl 1-methylimidazole-2-carboxylates were pre-
pared (Scheme 1). Benzoylated glycosyl hemiacetals, including
glucopyranosyl hemiacetal 2a, mannopyranosyl hemiacetal 2c,
rhamnopyranosyl hemiacetal 2d, xylopyranosyl hemiacetal 2e,
ribopyranosyl hemiacetal 2f, ribofuranosyl hemiacetal 2g, and
benzylated glucopyranosyl hemiacetal 2b all underwent
smoothly condensation with acid 1 in the optimal reaction
conditions, delivering the desired glycosyl 1-methylimidazole-2-
carboxylates 3a–3g in satisfactory 74–94% yields. All these
products are shelf-stable solids which can be stored under
ambient atmosphere for at least three months without
decomposition. The structures of xylopyranosyl carboxylates
3eβ (CCDC 2064548), ribopyranosyl 3fβ (CCDC 2064549), and
ribofuranosyl 3gβ (CCDC 2064547) were ambiguously con-
firmed by single crystal X-ray analysis. Interestingly, the
1
5
pyranosyl donors 3eβ and 3fβ crystallize in C4! HO forms. In
1
CDCl3 solutions, these two donors appeared to retain the C4
conformation, as evidenced by NMR analysis. Similar phenom-
enon was observed in the crystal structures of perbenzoylated
Table 1. Optimization of the condensation reaction of lactol 2a and acid 1.
Entry
Conditions
Yield[a]
β/α[b]
1
2
3
4
1 (1.5 eq.), DCC (1.6 eq.), DMAP (0.2 eq.), CH2Cl2, 12 h, RT
1 (1.5 eq.), EDCI (1.6 eq.), DIPEA (2.3 eq.), DMAP (1.5 eq.), CH2Cl2, 12 h, RT
1 (1.5 eq.), DCC (1.6 eq.), DMAP (1.6 eq.), DMF, 12 h, RT
1 (1.5 eq.), EDCI (1.6 eq.), DMAP (1.6 eq.), DMF, 12 h, RT
71%
57%
47%
80%
3:1
3:1
–
3.5:1
[a] Isolated yield. [b] The β/α ratio was determined by 1H NMR analysis.
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Scheme 1. [a] Conditions A. [b] Conditions B. The α/β ratio was determined by 1H NMR analysis.
ethanol 6g and pseudo tropine 6h, proceeded smoothly in high
yield with α anomer predominantly under mild conditions, in
sharp contrast to the previous reports for the glycosylation of
acceptors bearing tertiary amine moieties, which always
required harsh conditions (excess Lewis acid promoters) and
the yields were only moderate.[24,25]
The mechanism of the present glycosylation reaction was
briefly studied. The relationship between the equivalents of
Cu(OTf)2 and glycosylation yield was first investigated. The
glycosylation reaction between benzoylated ribopyranosyl 1-
methylimidazole-2-carboxylates donor 3fβ and L-menthol 6e
under the promotion of Cu(OTf)2 in CH2Cl2 in the presence of
4 Å molecular sieves was selected as a model reaction, and the
results are shown in Figure 2. In the presence of 1.0 equiv. of
Cu(OTf)2 the glycosylation yield reached 84%; a further increase
of Cu(OTf)2 to 1.4 equiv. led to a slightly increase of the yield to
97%. These results demonstrated that for this glycosylation
system, more than equal equivalent of Cu(II) promoter is
needed to promote the glycosylation reaction to get complete
conversion.
In order to compare the relative glycosylation reactivity of
the α and β anomers of the glycosyl 1-methylimidazole-2-
carboxylates donors,
a competition experiment was next
preformed (Scheme 4). Thus, a 1:1 mixture of the α and β
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Scheme 2. Alternative methods for the preparation of glycosyl 1-methylimidazole-2-carboxylate 3a.
Table 2. Screening of promoters for the glycosylation of sugar alcohol 6a with donor 3a.
Entry
MXn
Yielda
1
2
3
Cu(OTf)2
Cu(NTf2)2
AgOTf
87%
86%
N.R.
4
5
6
7
8
9
10
11
12
Zn(OTf)2
Zn(NTf2)2
In(OTf)3
Bi(OTf)3
Fe(OTf)2
Sn(OTf)2
Ni(OTf)2
Sc(OTf)3
La(OTf)3
25%b
79%
78%
85%
65%
81%
<10%
56%b
<10%
[a] Isolated yields. [b] Yield determined by 1H NMR analysis using 2-cyanopyrimidine as internal standard.
anomers of donor 3a (1.5 equiv. each relative to the acceptor)
was competitively reacted with 1.0 equiv. of acceptor 6e in
CH2Cl2 at room temperature for 14 h in the presence of
0.5 equiv. of Cu(OTf)2. After the reaction, the β anomer of donor
3a was recovered in 28% yield while the α anomer was
recovered in 86% yield, indicating that the β anomer is much
more reactive than the α anomer.
During the reaction process a blue precipitate gradually
formed, the composition of the precipitate was assumed to be
a Cu(II) complex with 1-methylimidazole-2-carboxylate anion
(LN) as ligand. Three possible structures of this complex were
assumed, namely, Cu(LN)2 (K), [Cu(LN)]+ ·TfOÀ (L), and [Cu-
(HLN)2]2+ ·2TfOÀ (M; Figure 3). The actual structure of this
complex was deduced via elemental analysis, in that the
measured elemental composition (including C, H, N, and Cu)
well matched that of structure K. This structure was also
supported by ESI-MS analysis, in that a peak at 336.76
corresponding to the [M+Na]+ ion was observed. The ligand
structure in this complex was further confirmed by NMR
analysis. Due to the paramagnetic character and rather low
solubility of Cu(II) complex, direct NMR analysis was not
successful. Thus, the free ligand was released through a
chemical transformation, namely, through reduction of this
complex by IÀ ion in acidic conditions, then, the aqueous
solution was filtered and directly analyzed by NMR. The 1H NMR
signals corresponding to free 1-methylimidazole-2-carboxylate
ligand were observed. Thus, the leaving species of this
glycosylation was confirmed to be the Cu(II) complex with two
1-methylimidazole-2-carboxylate as ligands,[26] providing
a
strong support for the proposed chelation assisted activation
mechanism of this type of donors.
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Scheme 3. Scope of the glycosylation using glycosyl 1-methylimidazole-2-carboxylates as donors under the promotion of Cu(OTf)2.
Scheme 4. Competition experiment between the α and β anomers of glucosyl 1-methylimidazole-2-carboxylate donor 3.
Conclusion
imidazolecarboxylic acid (1) via direct condensation. The
reaction initiates from activation of the glycosyl ester donor via
coordination with a metal cation assisted by the adjacent 1-
methylimidazole chelating group, followed by a classic glyco-
sylation mechanism via glycosyl oxocarbenium ion intermedi-
ate. The reaction enjoys a broad scope and especially suitable
for acceptors bearing tertiary amine moieties. With these salient
features, this glycosylation protocol is expected to find
applications in the construction of glycosidic linkages.
In conclusion, we have developed a mild glycosylation protocol
using glycosyl 1-methylimidazole-2-carboxylates as donors,
which can be promoted by a series of metal triflates and
triflimides, especially Cu(OTf)2. The glycosyl 1-methylimidazole-
2-carboxylates donors employed in this protocol can be
conveniently prepared in high yields from the corresponding
glycosyl hemiacetals and commercially available 1-methyl-2-
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Figure 2. The dependence of glycosylation yields on the equivalents of Cu(OTf)2.
Figure 3. Identification of the precipitate formed during the glycosylation process.
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128.72, 128.63, 128.62, 128.42, 128.38, 128.33, 128.32, 127.10, 92.58,
Experimental Section
73.31, 72.71, 70.87, 68.84, 62.69, 36.23; HRMS (ESI) calcd for
C39H32N2O11Na [M+Na]+ 727.1898, found 727.1901.
General Information. Commercial reagents were used without
further purification unless specialized. Crushed 4 Å molecular sieves
were activated through flame-drying under high vacuum immedi-
ately prior to use. Dry CH2Cl2 were obtained by refluxing with CaH2
(5%, w/v) under argon. Flash column chromatography was
performed on silica gel SiliaFlash P60 (40–63 μm, Silicycle). The TLC
plates were visualized with UV light and/or by staining with EtOH/
H2SO4 (8%, v/v). Flash column chromatography was performed on
Silica Gel 60 (40–64 μm, Fluka, Canada). NMR spectra were
2,3,4,6-Tetra-O-benzyl-D-glucopyranosyl-1-methylimidazole-2-carboxy-
late (3b) Esterification of hemiacetal 2b (5.0 g, 9.3 mmol) with acid
1 (1.8 g, 14 mmol) employing the General Procedure A afforded
donor 3b (5.1 g, 85%, α/β=1:1.3) as a colorless syrup: [α]25 D=
1
36.0 (c 1.0, CHCl3); H NMR (500 MHz, CDCl3) δ 7.36–7.26 (m, 23.1H),
7.25–7.21 (m, 3.3H), 7.21–7.17 (m, 3.70H), 7.06 (d, J=0.9 Hz, 1H),
7.04 (d, J=0.9 Hz, 0.67H), 6.57 (d, J=3.6 Hz, 0.7H), 5.85 (d, J=
7.9 Hz, 1H), 5.02 (d, J=6.0 Hz, 0.7H), 4.99 (d, J=5.9 Hz, 1H), 4.97 (d,
J=10.9 Hz, 1H), 4.89 (s, 0.74H), 4.88–4.84 (m, 3.55H), 4.80–4.71 (m,
1.52H), 4.64–4.60 (m, 1.75H), 4.59–4.54 (m, 1.61H), 4.51 (d, J=
12.1 Hz, 1H), 4.47 (d, J=12.1 Hz, 0.77H), 4.23 (t, J=9.4 Hz, 0.78H),
4.13 (dt, J=10.0, 2.6 Hz, 0.80H), 3.97 (d, J=1.0 Hz, 4.64H), 3.89–3.83
(m, 1.16H), 3.83–3.75 (m, 5.46H), 3.72–3.64 (m, 1.72H); 13C NMR
(126 MHz, CDCl3) δ 157.55, 138.68, 138.37, 138.23, 138.18, 138.05,
138.01, 137.78, 137.66, 135.94, 135.66, 129.88, 129.65, 128.39,
128.37, 128.33, 128.29, 128.18, 128.01, 128.00, 127.93, 127.90,
127.89, 127.87, 127.85, 127.76, 127.73, 127.68, 127.67, 127.58,
127.55, 127.53, 126.85, 126.61, 94.97, 91.20, 84.59, 81.61, 81.08,
78.76, 77.26, 76.96, 75.90, 75.72, 75.70, 75.09, 75.07, 75.04, 73.47,
73.43, 73.21, 73.09, 68.43, 68.02, 36.02, 35.91; HRMS (ESI) calcd for
C39H40N2O7Na [M+Na]+ 671.2728, found 671.2732.
measured on Bruker AM 400, Agilent 500 or 600 MHz NMR
1
spectrometer at 25 C. H and 13C NMR signals were calibrated to
°
the residual proton and carbon resonance of the solvent (CDCl3:
δH=7.26 ppm; δC=77.31 ppm). High-resolution mass spectra were
recorded with IonSpec 4.7 Tesla FTMS or APEXIII 7.0 Tesla FTMS.
Elemental analysis was obtained on a Vario EL III elemental
analyzer. Optical rotations were measured on an Anton Paar
MCP5500 polarimeter. Single crystal X-ray data were collected on a
Bruker Apex II CCD diffractometer operating at 50 kV and 30 mA
using Mo Kα radiation (λ=0.71073 Å) at 133 K.
General Procedure A for the Preparation of Glycosyl 1-Meth-
ylimidazole-2-carboxylates. To a solution of glycosyl hemiacetals 2
(1.0 eq.) in dry DMF (0.20 M) were added 1-methyl-2-imidazolecar-
boxylic acid 1 (1.5 eq.), EDCI (1.6 eq.), and DMAP (1.6 eq.). The
mixture was stirred at room temperature and monitored by TLC.
After stirring for 8 h, the mixture was diluted with CH2Cl2, and was
then washed with water and brine. The organic layer was dried
over Na2SO4, filtered, and concentrated in vacuo. The resulting
residue was purified by silica gel column chromatography to afford
the desired esterification product.
2,3,4,6-Tetra-O-benzoyl-D-mannopyranosyl-1-methylimidazole-2-car-
boxylate (3c) Esterification of mannopyranosyl hemiacetal 2c (1.0 g,
1.7 mmol) with acid 1a (0.32 g, 2.5 mmol) employing general
procedure B afforded donor 3c (1.1 g, 94%, α/β=1:3.3) as a white
solid. Alternatively, esterification of mannopyranosyl hemiacetal 2c
(100 mg, 0.17 mmol) with acid 1a (32 mg, 0.25 mmol) using the
General Procedure A afforded donor 3c (90 mg, 76%, α/β=1/1.5)
1
General Procedure B for the Preparation of Glycosyl 1-Meth-
ylimidazole-2-carboxylates. To a solution of glycosyl hemiacetals 2
(1.0 eq.) in dry CH2Cl2 (0.20 M) were added 1-methyl-2-imidazole-
carboxylic acid 1a (1.5 eq.), DCC (1.6 eq.), and DMAP (0.2 eq.). The
mixture was stirred at room temperature and monitored by TLC.
After stirring for 8 h, the reaction mixture was filtered through a
pad of Celite and concentrated in vacuo. The resulting residue was
purified by silica gel column chromatography to afford the
esterification product.
as a white solid: [α]25 D=À 21.8 (c 1.0, CHCl3); H NMR (500 MHz,
CDCl3) δ 8.15–8.05 (m, 5.81H), 8.01–7.97 (m, 2H), 7.97–7.93 (m,
1.25H), 7.90–7.87 (m, 1.21H), 7.87–7.82 (m, 2H), 7.62–7.54 (m, 3H),
7.52–7.46 (m, 1.65H), 7.46–7.33 (m, 10.65H), 7.31–7.21 (m, 4H), 7.14
(d, J=0.9 Hz, 1H), 7.11–7.08 (m, 0.65H), 6.94 (s, 0.63H), 6.64 (d, J=
2.0 Hz, 1H), 6.49 (d, J=1.3 Hz, 0.63H), 6.35 (t, J=10.2 Hz, 1H), 6.16
(td, J=6.3, 3.0 Hz, 2H), 5.96 (dd, J=3.3, 2.0 Hz, 1H), 5.83 (dd, J=9.6,
3.2 Hz, 0.72H), 4.83 (d, J=10.1 Hz, 1H), 4.79 (dd, J=12.2, 2.9 Hz,
0.67H), 4.75 (dd, J=12.5, 2.5 Hz, 1H), 4.61 (dd, J=12.3, 4.6 Hz,
0.70H), 4.52 (dd, J=12.5, 3.2 Hz, 1H), 4.40 (ddd, J=9.3, 4.5, 2.9 Hz,
0.70H), 4.03 (s, 3H), 3.79 (s, 1.85H); 13C NMR (126 MHz, CDCl3) δ
165.94, 165.39, 165.32, 165.28, 165.15, 165.05, 156.47, 156.32,
135.31, 135.01, 133.57, 133.52, 133.46, 133.42, 133.33, 133.16,
133.02, 132.98, 130.29, 129.91, 129.87, 129.84, 129.80, 129.71,
129.66, 129.12, 128.94, 128.87, 128.78, 128.67, 128.57, 128.52,
128.42, 128.38, 128.36, 128.28, 128.24, 127.36, 126.87, 91.69, 91.34,
73.38, 71.30, 71.27, 69.92, 69.35, 68.79, 66.35, 65.97, 62.59, 62.10,
36.06, 35.94; HRMS (ESI) calcd for C39H32N2O11Na [M+Na]+
727.1898, found 727.1902.
2,3,4,6-Tetra-O-benzoyl-D-glucopyranosyl-1-methylimidazole-2-car-
boxylate (3a) Esterification of hemiacetal 2a (100 mg, 0.17 mmol)
with acid 1 (32 mg, 0.25 mmol) employing General Procedure A
afforded 3a (94 mg, 80%, α/β=1:3.5) as a white solid. Alter-
natively, esterification of hemiacetal 2a (1.0 g, 1.8 mmol) with acid
1 (0.33 g, 2.6 mmol) with General Procedure B afforded 3a (0.90 g,
71%, α/β=1:3) as a white solid. 3aα: [α]25 D=113.1 (c 1.0, CHCl3);
1H NMR (500 MHz, CDCl3) δ 8.06 (dd, J=8.4, 1.3 Hz, 2H), 7.99–7.91
(m, 4H), 7.89–7.85 (m, 2H), 7.57–7.53 (m, 1H), 7.51–7.45 (m, 2H),
7.45–7.40 (m, 3H), 7.38–7.26 (m, 7H), 7.08 (d, J=1.0 Hz, 1H), 6.90 (d,
J=3.8 Hz, 1H), 6.39 (t, J=10.0 Hz, 1H), 5.90 (t, J=10.0 Hz, 1H), 5.64
(dd, J=10.2, 3.8 Hz, 1H), 4.85 (dt, J=10.3, 3.3 Hz, 1H), 4.66 (dd, J=
12.5, 2.8 Hz, 1H), 4.49 (dd, J=12.5, 3.7 Hz, 1H), 3.82 (s, 3H); 13C NMR
(126 MHz, CDCl3) δ 166.06, 165.57, 165.49, 165.15, 157.13, 135.26,
133.4, 133.44, 133.21, 133.09, 130.01, 129.92, 129.81, 129.72, 129.59,
128.94, 128.70, 128.69, 128.41, 128.38, 128.37, 128.30, 127.15, 90.27,
70.80, 70.67, 70.32, 68.52, 62.16, 35.94. 3aβ: [α]25 D=26.1 (c 1.0,
CHCl3); 1H NMR (500 MHz, CDCl3) δ 8.02 (dd, J=8.3, 1.4 Hz, 2H),
7.95–7.88 (m, 4H), 7.88–7.84 (m, 2H), 7.55–7.45 (m, 3H), 7.45–7.37
(m, 3H), 7.36–7.31 (m, 4H), 7.31–7.26 (m, 2H), 7.18 (s, 1H), 7.01 (s,
1H), 6.40 (d, J=7.8 Hz, 1H), 6.02 (t, J=9.3 Hz, 1H), 5.89–5.75 (m, 2H),
4.65 (dd, J=12.3, 3.1 Hz, 1H), 4.53 (dd, J=12.3, 5.0 Hz, 1H), 4.40
(ddd, J=9.6, 5.0, 3.1 Hz, 1H), 3.92 (s, 3H); 13C NMR (126 MHz, CDCl3)
δ 166.04, 165.65, 165.05, 164.85, 156.44, 135.02, 133.52, 133.45,
133.33, 133.11, 130.03, 129.89, 129.84, 129.83, 129.79, 129.45,
2,3,4-Tri-O-benzoyl-L-rhamnopyranosyl-1-methylimidazole-2-carboxy-
late (3d) Esterification of rhamnopyranosyl hemiacetal 2d (1.0 g,
2.1 mmol) with acid 1a (0.40 g, 3.2 mmol) employing General
Procedure A afforded donor 3d (0.99 g, 81%, α/β=1.5:1) as a
white solid: [α]25 D=97.2 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) δ
8.14–8.07 (m, 3.40H), 8.02 (dt, J=8.4, 1.3 Hz, 2.11H), 7.98–7.93 (m,
1.34H), 7.81 (m, 3.20H), 7.62 (m, 1.61H), 7.50 (qt, J=7.4, 6.5 Hz,
5.29H), 7.45–7.36 (m, 5.26H), 7.34–7.32 (m, 1.15H), 7.29–7.21 (m,
3.20H), 7.20–7.17 (m, 1.22H), 7.13 (t, J=1.2 Hz, 0.61H), 6.98 (d, J=
1.1 Hz, 0.59H), 6.56 (d, J=1.9 Hz, 1H), 6.37 (d, J=1.3 Hz, 0.65H), 6.10
(dt, J=2.9, 1.4 Hz, 1H), 6.08 (dd, J=3.6, 1.7 Hz, 0.63H), 5.89 (dd, J=
3.5, 1.9 Hz, 1H), 5.80 (t, J=10.0 Hz, 1H), 5.72–5.68 (m, 1.21H), 4.71–
4.56 (m, 1H), 4.08 (d, J=2.5 Hz, 3.70H), 3.83 (s, 1.88H), 1.47 (d, J=
6.1 Hz, 1.95H), 1.40 (d, J=6.2 Hz, 3H); 13C NMR (126 MHz, CDCl3) δ
165.81, 165.64, 165.57, 165.42, 165.36, 165.33, 156.23, 135.43,
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133.64, 133.53, 133.48, 133.38, 133.30, 133.14, 130.17, 130.00,
General Glycosylation Procedure. A solution of glycosyl donor 3
(1.3 eq.) and acceptor 6 (1.0 eq.) in dry CH2Cl2 (0.15 M) was stirred
at room temperature in the presence of activated 4 Å M.S. (3.0 g/
mmol) under argon atmosphere for 30 mins, to which Cu(OTf)2
(1.5 eq.) was added. The mixture was stirred at room temperature
and monitored by TLC. After completion (~3 h), the reaction
mixture was filtered through a pad of Celite and concentrated in
vacuo. The resulting residue was purified by silica gel column
chromatography to afford the glycosylated product.
129.98, 129.86, 129.77, 129.72, 129.69, 129.22, 129.10, 129.04,
129.03, 128.99, 128.74, 128.62, 128.59, 128.48, 128.44, 128.30,
128.26, 127.25, 126.83, 92.01, 91.51, 71.99, 71.41, 71.07, 69.81, 69.69,
69.20, 36.30, 36.12, 17.75, 17.64; HRMS (ESI) calcd for C32H28N2O9Na
[M+Na]+ 607.1687, found 607.1691.
2,3,4-Tri-O-benzoyl-D-xylopyranosyl-1-methylimidazole-2-carboxylate
(3e) Esterification of xylopyranosyl hemiacetal 2e (1.0 g, 2.2 mmol)
with acid 1a (0.42 g, 3.3 mmol) employing General Procedure A
afforded donor 3e (1.0 g, 83%, α/β=1:3.3) as a white solid: [α]25
Methyl 2,3,6-Tri-O-benzyl-4-O-(2,3,4,6-tetra-O-benzoyl-β-D-glucopyra-
nosyl)-α-D-glucopyranoside (7a). Glycosylation of acceptor 6a
(40 mg, 0.086 mmol) with donor 3aβ (79 mg, 0.11 mmol) using the
General Glycosylation Procedure afforded glycoside 7a (petroleum
ether/ethyl acetate=5/1; 78 mg, 87%) as a white solid. The 1H NMR
spectral data of 7a are identical with the literature data.[27]
1
D=À 22.4 (c 1.0, CHCl3); H NMR (500 MHz, CDCl3) δ 8.36–8.28 (m,
2H), 8.04 (ddt, J=14.0, 6.9, 1.4 Hz, 4H), 8.00–7.97 (m, 0.53H), 7.93
(dd, J=6.6, 5.1 Hz, 1.19H), 7.60–7.51 (m, 3.11H), 7.48–7.45 (m,
0.25H), 7.45–7.38 (m, 2.58H), 7.38–7.29 (m, 5.28H), 7.27 (dd, J=5.4,
1.0 Hz, 1.35H), 7.10 (d, J=0.9 Hz, 1H), 7.08 (d, J=1.0 Hz, 0.27H), 6.81
(d, J=3.8 Hz, 0.27H), 6.50 (d, J=2.8 Hz, 1H), 6.35 (t, J=9.9 Hz,
0.30H), 5.80 (tt, J=4.5, 1.1 Hz, 1H), 5.59 (dd, J=10.1, 3.8 Hz, 0.28H),
5.54 (td, J=9.4, 7.4 Hz, 0.26H), 5.51–5.49 (m, 1H), 5.29 (q, J=3.5 Hz,
1H), 4.71 (dd, J=13.1, 2.8 Hz, 1H), 4.30–4.23 (m, 0.56H), 4.07 (dd, J=
13.0, 3.5 Hz, 1H), 4.00 (s, 3H), 3.85 (s, 0.81H); 13C NMR (126 MHz,
CDCl3) δ 165.59, 165.52, 165.47, 164.97, 157.27, 157.21, 135.57,
135.27, 133.52, 133.48, 133.47, 133.43, 133.39, 133.23, 130.61,
130.06, 129.99, 129.92, 129.85, 129.72, 129.30, 129.09, 128.88,
128.87, 128.82, 128.72, 128.44, 128.40, 128.39, 128.34, 127.12,
127.09, 91.70, 90.53, 70.65, 69.84, 69.47, 67.84, 67.23, 67.02, 61.37,
61.09, 36.04, 36.01; HRMS (MALDI) calcd for C31H26N2O9K [M+K]+
609.1245, found 609.1270.
Methyl 2,3,6-Tri-O-benzyl-4-O-(2,3,4,6-tetra-O-benzyl-α/β-D-glucopyra-
nosyl)-α-D-glucopyranoside (7b). Glycosylation of acceptor 6a
(40 mg, 0.086 mmol) with donor 3b (77 mg, 0.12 mmol) using the
General Glycosylation Procedure afforded glycoside 7b (petroleum
ether/ethyl acetate=5/1; 80 mg, 94%, α/β=1/1.7) as a colorless
syrup. The 1H NMR spectral data of 7b are identical with the
literature data.[27]
Methyl 2,3,4-Tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzoyl-β-D-glucopyra-
nosyl)-α-D-glucopyranoside (7c). Glycosylation of acceptor 6b
(40 mg, 0.086 mmol) with donor 3aβ (79 mg, 0.11 mmol) using the
General Glycosylation Procedure afforded glycoside 7c (petroleum
ether/ethyl acetate=5/1; 86 mg, 96%) as a white solid. The 1H NMR
spectral data of 7c are identical with the literature data.[27]
2,3,4-Tri-O-benzoyl-D-ribopyranosyl-1-methylimidazole-2-carboxylate
(3f) Esterification of ribopyranosyl hemiacetal 2f (1.0 g, 2.2 mmol)
with acid 1a (0.42 g, 3.3 mmol) employing General Procedure A
afforded donor 3f (0.92 g, 75%, β only) as a white solid: [α]25 D=
Methyl 2,3,4-Tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzyl-αβ-D-glucopyra-
nosyl)-α-D-glucopyranoside (7d). Glycosylation of acceptor 6b
(42 mg, 0.090 mmol) with donor 3b (75 mg, 0.12 mmol) using the
General Glycosylation Procedure afforded glycoside 7d (petroleum
ether/ethyl acetate=5/1; 86 mg, 96%, α/β=1.4/1) as colorless
syrup. The 1H NMR spectral data of 7d are identical with the
literature data.[27]
1
À 98.5 (c 1.0, CHCl3). H NMR (500 MHz, CDCl3) δ 8.03 (dd, J=9.4,
8.1 Hz, 4H), 7.89–7.83 (m, 2H), 7.55 (t, J=7.4 Hz, 2H), 7.52–7.46 (m,
1H), 7.35–7.26 (m, 6H), 7.23 (s, 1H), 7.12 (s, 1H), 6.64 (d, J=2.6 Hz,
1H), 6.10 (t, J=3.9 Hz, 1H), 5.75 (dt, J=4.2, 2.3 Hz, 2H), 4.58 (dd, J=
13.3, 2.1 Hz, 1H), 4.27 (dd, J=13.1, 3.0 Hz, 1H), 4.03 (s, 3H); 13C NMR
(126 MHz, CDCl3) δ 166.03, 165.70, 165.00, 156.82, 135.18, 133.38,
133.25, 133.20, 130.04, 129.94, 129.88, 129.73, 129.69, 129.28,
129.25, 128.38, 128.36, 128.35, 127.34, 92.44, 67.64, 67.22, 66.07,
63.45, 36.08; HRMS (ESI) calcd for C31H26N2O9Na [M+Na]+ 593.1531,
found 593.1533.
1-Adamantanyl 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranoside (7e). Gly-
cosylation of acceptor 6c (14 mg, 0.092 mmol) with donor 3aβ
(85 mg, 0.12 mmol) using the General Glycosylation Procedure
afforded glycoside 7e (petroleum ether/ethyl acetate=6/1; 49 mg,
1
73%) as a white solid. The H NMR spectral data of 7e are identical
with the literature data.[27]
2,3,5-Tri-O-benzoyl-D-ribofuranosyl-1-methylimidazole-2-carboxylate
(3g) Esterification of ribofuranosyl hemiacetal 2g (0.32 g,
0.68 mmol) with acid 1a (0.13 g, 1.0 mmol) according to General
Procedure B afforded donor 3g (0.28 g, 74%, α/β=1/5) as a white
1-Adamantanyl 2,3,4,6-tetra-O-benzyl-α,β-D-glucopyranoside (7f).
Glycosylation of acceptor 6c (14 mg, 0.092 mmol) with donor 3b
(79 mg, 0.12 mmol) using the General Glycosylation Procedure
afforded glycoside 7f (petroleum ether/ethyl acetate=5/1; 60 mg,
1
solid. 3gα: [α]25 D=78.3 (c 1.0, CHCl3); H NMR (500 MHz, CDCl3) δ
8.35–8.23 (m, 2H), 8.17–8.08 (m, 2H), 7.83–7.79 (m, 2H), 7.62–7.57
(m, 1H), 7.57–7.53 (m, 1H), 7.49 (dd, J=8.3, 7.2 Hz, 2H), 7.44 (tt, J=
7.5, 1.3 Hz, 1H), 7.41–7.36 (m, 2H), 7.29–7.17 (m, 3H), 7.04 (d, J=
1.0 Hz, 1H), 6.94 (d, J=4.4 Hz, 1H), 5.94 (dd, J=6.5, 2.4 Hz, 1H), 5.78
(dd, J=6.6, 4.4 Hz, 1H), 5.02 (q, J=3.2 Hz, 1H), 4.75 (dd, J=12.2,
3.2 Hz, 1H), 4.64 (dd, J=12.2, 3.6 Hz, 1H), 3.81 (s, 3H); 13C NMR
(126 MHz, CDCl3) δ 166.07, 166.05, 164.97, 157.97, 135.89, 133.38,
133.36, 130.51, 129.78, 129.76, 129.72, 129.40, 129.20, 128.72,
128.61, 128.34, 128.28, 126.74, 95.51, 82.72, 71.25, 70.31, 63.97,
35.78. 3 gβ: [α]25 D=11.5 (c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) δ
8.02 (ddd, J=7.7, 6.3, 1.3 Hz, 4H), 7.91–7.85 (m, 2H), 7.63–7.55 (m,
1H), 7.52–7.39 (m, 4H), 7.30 (q, J=7.6 Hz, 4H), 7.21 (s, 1H), 7.07 (s,
1H), 6.61 (s, 1H), 6.09 (dd, J=7.1, 4.9 Hz, 1H), 6.04 (d, J=5.0 Hz, 1H),
4.84 (dt, J=7.1, 4.4 Hz, 1H), 4.74 (dd, J=12.2, 4.0 Hz, 1H), 4.63 (dd,
J=12.1, 4.9 Hz, 1H), 3.97 (s, 3H); 13C NMR (126 MHz, CDCl3) δ 166.14,
165.07, 164.96, 157.29, 135.27, 133.65, 133.46, 132.98, 129.85,
129.79, 129.76, 129.59, 129.40, 128.87, 128.71, 128.54, 128.37,
128.28, 127.09, 99.38, 80.51, 75.26, 71.36, 63.95, 36.02; HRMS (ESI)
calcd for C31H26N2O9Na [M+Na]+ 593.1531, found 593.1532.
1
97%, α/β=1.1:1) as a white solid. The H NMR spectral data of 7f
are identical with the literature data.[27]
6-O-(2,3,4,6-Tetra-O-benzoyl-β-D-glucopyranosyl)-1,2:3,4-di-O-isopro-
pylidene-α-D-galactopyranose (7g). Glycosylation of acceptor 6d
(28 mg, 0.11 mmol) with donor 3aβ (95 mg, 0.13 mmol) using the
General Glycosylation Procedure afforded glycoside 7g (petroleum
ether/ethyl acetate=3/1; 84 mg, 95%) as colorless syrup. The 1H
NMR spectral data of 7g are identical with the literature data.[27]
(1S,2R,5S)-(+)-1-Menthyl 2,3,4,6-Tetra-O-benzoyl-β-D-glucopyranoside
(7h). Glycosylation of acceptor 6e (10 mg, 0.064 mmol) with donor
3a (59 mg, 0.084 mmol) using the General Glycosylation Procedure
afforded glycoside 7h (petroleum ether/ethyl acetate=6/1; 40 mg,
85%) as colorless syrup. The 1H NMR spectral data of 7h are
identical with the literature data.[27]
Cholesteryl 2,3,4,6-Tetra-O-benzoyl-β-D-glucopyranoside (7i). Glycosy-
lation of acceptor 6f (36 mg, 0.093 mmol) with donor 3aβ (85 mg,
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0.12 mmol) using the General Glycosylation Procedure afforded
1-Adamantanyl 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranoside (7m).
Glycosylation of acceptor 6c (15 mg, 0.10 mmol) with donor 3c
(93 mg, 0.13 mmol) using the General Glycosylation Procedure
afforded glycoside 7m (petroleum ether/ethyl acetate=4/1; 73 mg,
99%) as a white solid. The 1H NMR spectral data of 7m are identical
with the literature data.[28]
glycoside 7i (petroleum ether/ethyl acetate=6/1; 67 mg, 75%) as
1
colorless syrup. The H NMR spectral data of 7i are identical with
the literature data.[27]
2-(N-morpholino)ethyl 2,3,4,6-Tetra-O-benzyl-αβ-D-glucopyranoside
(7j). Glycosylation of acceptor 6g (10 μL, 0.083 mmol) with donor
3b (74 mg, 0.11 mmol) using the General Glycosylation Procedure
afforded glycoside 7j (petroleum ether/ethyl acetate=10/1; 48 mg,
89%, α/β=5/1) as brown syrup: [α]25 D=28.8 (c 1.0, CHCl3); 1H
NMR (400 MHz, CDCl3) δ 7.38–7.21 (m, 17.43H), 7.17–7.09 (m,
2.56H), 4.97 (d, J=10.9 Hz, 1H), 4.94 (d, J=6.6 Hz, 0.21H), 4.91 (d,
J=6.2 Hz, 0.22H), 4.82 (m, 3.65H), 4.76 (s, 1H), 4.66 (d, J=12.0 Hz,
1H), 4.62–4.56 (m, 1.23H), 4.54 (d, J=4.1 Hz, 0.24H), 4.51 (d, J=
2.7 Hz, 0.17H), 4.50–4.44 (m, 2H), 4.42 (d, J=7.8 Hz, 0.22H), 4.08 (dt,
J=10.9, 5.6 Hz, 0.19H), 3.98 (t, J=9.3 Hz, 1H), 3.84–3.53 (m, 13.30H),
3.49–3.41 (m, 0.43H), 2.65 (dq, J=11.6, 5.8 Hz, 2.77H), 2.51 (q, J=
5.2 Hz, 5.37H); 13C NMR (101 MHz, CDCl3) δ 138.73, 138.49, 138.44,
138.13, 138.04, 138.00, 137.82, 128.42, 128.36, 128.34, 127.94,
127.91, 127.89, 127.87, 127.84, 127.81, 127.75, 127.70, 127.62,
127.57, 103.57, 97.06, 84.65, 82.06, 81.90, 79.91, 77.78, 77.63, 75.66,
75.06, 74.99, 74.80, 74.66, 73.48, 73.13, 70.28, 68.86, 68.49, 67.22,
66.70, 64.81, 58.14, 57.95, 53.97, 53.91; HRMS (ESI) calcd for
C40H48NO7 [M+H]+ 654.3425, found 654.3429.
6-O-(2,3,4,6-Tetra-O-benzoyl-α-D-mannopyranosyl)-1,2:3,4-di-O-iso-
propylidene-α-D-galactopyranose (7n). Glycosylation of acceptor 6d
(20 mg, 0.077 mmol) with donor 3c (75 mg, 0.11 mmol) using the
General Glycosylation Procedure afforded glycoside 7n (petroleum
ether/ethyl acetate=3/1; 60 mg, 93%) as colorless syrup. The 1H
NMR spectral data of 7n are identical with the literature data.[29]
Methyl 2,3,4-Tri-O-benzyl-6-O-(2,3,4,6-tetra-O-benzoyl-α-D-mannopyr-
anosyl)-α-D-glucopyranoside (7o). Glycosylation of acceptor 6b
(38 mg, 0.082 mmol) with donor 3c (77 mg, 0.11 mmol) using the
General Glycosylation Procedure afforded glycoside 7o (petroleum
ether/ethyl acetate=5/1; 86 mg, 99%) as colorless syrup. The 1H
NMR spectral data of 7o are identical with the literature data.[29]
6-O-(2,3,4-Tri-O-benzoyl-α-L-rhamnopyranosyl)-1,2:3,4-di-O-isopropy-
lidene-α-D-galactopyranose (7p). Glycosylation of acceptor 6d
(20 mg, 0.077 mmol) with donor 3d (59 mg, 0.10 mmol) using the
General Glycosylation Procedure afforded glycoside 7p (petroleum
ether/ethyl acetate=4/1; 47 mg, 85%) as colorless syrup. The 1H
NMR spectral data of 7p are identical with the literature data.[5d]
3-Exo-tropinyl 2,3,4,6-Tetra-O-benzyl-α/β-D-glucopyranoside (7k). Gly-
cosylation of acceptor 6h (13 mg, 0.092 mmol) with donor 3b
(83 mg, 0.13 mmol) using the General Glycosylation Procedure
afforded glycoside 7k (petroleum ether/ethyl acetate=10/1;
61 mg, 99%, α/β=3:1) as brown syrup: [α]25 D=32.9 (c 1.0,
Methyl 2,3,4-Tri-O-benzyl-6-O-(2,3,4-tri-O-benzoyl-α-L-rhamnopyrano-
syl)-α-D-glucopyranoside (7q). Glycosylation of acceptor 6b (41 mg,
0.088 mmol) with donor 3d (68 mg, 0.12 mmol) using the General
Glycosylation Procedure afforded glycoside 7q (petroleum ether/
ethyl acetate=5/1; 80 mg, 98%) as colorless syrup. The 1H NMR
spectral data of 7q are identical with the literature data.[27]
1
CHCl3); H NMR (400 MHz, CDCl3) δ 7.41–7.24 (m, 20.92H), 7.19 (dd,
J=7.3, 2.2 Hz, 0.79H), 7.15 (dd, J=7.3, 2.3 Hz, 2H), 5.00 (d, J=
10.9 Hz, 1H), 4.96 (d, J=8.5 Hz, 0.34H), 4.93 (d, J=8.4 Hz, 0.46H),
4.88 (d, J=3.7 Hz, 1H), 4.86–4.79 (m, 2.64H), 4.76 (d, J=12.2 Hz,
1.20H), 4.71 (d, J=11.0 Hz, 0.40H), 4.64 (d, J=4.2 Hz, 1.13H), 4.61 (d,
J=4.2 Hz, 1.27H), 4.59–4.53 (m, 0.78H), 4.50–4.44 (m, 2.37H), 4.04–
3.94 (m, 1.40H), 3.90–3.76 (m, 2.23H), 3.73 (dd, J=10.5, 4.0 Hz,
1.26H), 3.70–3.60 (m, 2.60H), 3.60–3.52 (m, 1.66H), 3.48 (dt, J=6.4,
3.2 Hz, 0.34H), 3.43 (dd, J=9.1, 7.8 Hz, 0.45H), 3.24 (dt, J=6.1,
2.7 Hz, 1.73H), 3.19 (m, 1H), 2.37 (s, 4.10H), 2.06–1.68 (m, 8.72H),
1.63–1.45 (m, 2.89H); 13C NMR (101 MHz, CDCl3) δ 138.86, 138.56,
138.36, 138.28, 138.20, 138.14, 138.02, 137.88, 128.37, 128.34,
128.32, 128.29, 128.17, 128.02, 127.97, 127.90, 127.88, 127.82,
127.78, 127.73, 127.68, 127.63, 127.61, 127.54, 127.49, 101.91, 95.18,
84.68, 82.09, 81.88, 80.06, 77.88, 77.79, 75.64, 75.58, 75.05, 74.96,
74.77, 74.73, 73.39, 73.34, 72.95, 71.63, 70.11, 69.68, 69.11, 68.60,
60.20, 60.11, 59.85, 59.80, 37.56, 37.45, 36.07, 35.74, 34.45, 26.99,
26.95, 26.70, 26.67; HRMS (ESI) calcd for C42H50NO6 [M+H]+
664.3633, found 664.3635.
Methyl 2,3,6-Tri-O-benzyl-4-O-(2,3,4-tri-O-benzoyl-α-L-rhamnopyrano-
syl)-α-D-glucopyranoside (7r). Glycosylation of acceptor 6a (42 mg,
0.090 mmol) with donor 3d (69 mg, 0.12 mmol) using the General
Glycosylation Procedure afforded glycoside 7r (petroleum ether/
ethyl acetate=5/1; 82 mg, 98%) as colorless syrup. The 1H NMR
spectral data of 7r are identical with the literature data.[27]
4-O-(2’’,3’’,4’’-Tri-O-benzoyl-α-L-rhamnopyranosyl)
podophyllotoxin
(7s). Glycosylation of acceptor 6i (37 mg, 0.089 mmol) with donor
3d (78 mg, 0.13 mmol) using the General Glycosylation Procedure
afforded glycoside 7s (petroleum ether/ethyl acetate=5/1; 56 mg,
1
72%) as a white solid. The H NMR spectral data of 7s are identical
with the literature data.[30]
6-O-(2,3,4-tri-O-benzoyl-β-D-xylopyranosyl)-1,2:3,4-di-O-isopropyli-
dene-α-D-galactopyranose (7t). Glycosylation of acceptor 6d
(20 mg, 0.077 mmol) with donor 3e (58 mg, 0.10 mmol) using the
General Glycosylation Procedure afforded glycoside 7t (petroleum
ether/ethyl acetate=3/1, 51 mg, 94%) as colorless syrup. The 1H
NMR spectral data of 7t are identical with the literature data.[27]
(1S,2R,5S)-(+)-1-Menthyl 2,3,4,6-Tetra-O-benzoyl-α-D-mannopyrano-
side (7l). Glycosylation of acceptor 6e (16 mg, 0.10 mmol) with
donor 3c (92 mg, 0.13 mmol) using the General Glycosylation
Procedure afforded glycoside 7l (petroleum ether/ethyl acetate=4/
1
Cholesteryl-2,3,4-tri-O-benzoyl-β-D-xylopyranose (7u). Glycosylation
of acceptor 6f (36 mg, 0.093 mmol) with donor 3e (69 mg,
0.12 mmol) using the General Glycosylation Procedure afforded
glycoside 7u (petroleum ether/ethyl acetate=6/1; 64 mg, 83%) as
1; 73 mg, 99%) as a white solid: [α]25 D=À 51.5 (c 1.0, CHCl3); H
NMR (500 MHz, CDCl3) δ 8.18–8.03 (m, 4H), 8.05–7.95 (m, 2H), 7.90–
7.81 (m, 2H), 7.62–7.54 (m, 2H), 7.54–7.49 (m, 1H), 7.46–7.34 (m, 7H),
7.30–7.24 (m, 2H), 6.07 (t, J=10.1 Hz, 1H), 5.94 (dd, J=10.1, 3.2 Hz,
1H), 5.63 (dd, J=3.3, 1.9 Hz, 1H), 5.20 (d, J=1.8 Hz, 1H), 4.67 (dd,
J=12.0, 2.4 Hz, 1H), 4.59 (ddd, J=10.1, 5.2, 2.3 Hz, 1H), 4.49 (dd, J=
12.0, 5.2 Hz, 1H), 3.50 (td, J=10.6, 4.4 Hz, 1H), 2.35–2.15 (m, 2H),
1.74–1.55 (m, 3H), 1.46–1.35 (m, 2H), 1.19 (q, J=11.8 Hz, 1H), 1.07–
0.94 (m, 4H), 0.84 (dd, J=15.9, 6.7 Hz, 6H); 13C NMR (126 MHz,
CDCl3) δ 165.22, 164.54, 164.50, 164.48, 132.39, 132.11, 132.03,
128.84, 128.81, 128.72, 128.70, 128.43, 128.13, 127.99, 127.55,
127.39, 127.37, 127.26, 98.25, 81.83, 70.00, 69.04, 68.00, 66.19, 62.28,
47.45, 41.78, 33.23, 30.66, 24.85, 22.22, 21.11, 20.05, 15.24; HRMS
(ESI) calcd for C44H46O10Na [M+Na]+ 757.2983, found 757.2986.
1
colorless syrup. The H NMR spectral data of 7u are identical with
the literature data.[27]
Methyl 2,3,4-Tri-O-benzyl-6-O-(2,3,4-tri-O-benzoyl-β-D-ribopyranosyl)-
α-D-glucopyranoside (7v). Glycosylation of acceptor 6b (52 mg,
0.11 mmol) with donor 3f (84 mg, 0.15 mmol) using the General
Glycosylation Procedure afforded glycoside 7v (petroleum ether/
ethyl acetate=3/1; 93 mg, 91%) as colorless syrup: [α]25 D=À 16.9
(c 1.0, CHCl3); 1H NMR (500 MHz, CDCl3) δ 8.01 (ddd, J=9.8, 8.2,
1.4 Hz, 4H), 7.95–7.87 (m, 2H), 7.60–7.48 (m, 3H), 7.42–7.19 (m, 21H),
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5.83 (t, J=3.8 Hz, 1H), 5.60 (d, J=3.3 Hz, 1H), 5.49 (t, J=3.3 Hz, 1H),
Acknowledgments
5.04 (d, J=2.9 Hz, 1H), 5.01 (d, J=10.9 Hz, 1H), 4.89 (d, J=11.2 Hz,
1H), 4.84 (d, J=9.0 Hz, 1H), 4.82 (d, J=10.3 Hz, 1H), 4.70 (d, J=
12.1 Hz, 1H), 4.65 (d, J=3.5 Hz, 1H), 4.61 (d, J=11.2 Hz, 1H), 4.27
(dd, J=12.9, 2.5 Hz, 1H), 4.06–3.98 (m, 3H), 3.82 (ddd, J=10.1, 4.6,
1.7 Hz, 1H), 3.71 (dd, J=10.8, 4.6 Hz, 1H), 3.61–3.54 (m, 2H), 3.41 (s,
3H); 13C NMR (126 MHz, CDCl3) δ 166.09, 165.72, 165.18, 138.75,
138.23, 138.16, 133.20, 133.17, 133.10, 129.97, 129.92, 129.80,
129.72, 129.63, 129.46, 128.48, 128.41, 128.37, 128.34, 128.30,
128.12, 127.91, 127.86, 127.72, 127.55, 98.65, 98.05, 82.12, 80.11,
77.50, 75.71, 75.05, 73.48, 69.78, 68.70, 67.65, 66.92, 66.50, 61.20,
55.29; HRMS (ESI) calcd for C54H52O13Na [M+Na]+ 931.3300, found
931.3294.
Financial support from the National Natural Science Foundation
of China (21871290, 22031011, and 21621002), Key Research
Program of Frontier Sciences of CAS (ZDBS-LY-SLH030), Shanghai
Municipal Science and Technology Major Project, and Youth
Innovation Promotion Association of CAS (2021251) is acknowl-
edged. We thank Dr. Xuebing Leng for X-ray crystallographic
analysis.
Conflict of Interest
(1S,2R,5S)-(+)-1-Menthyl 2,3,4-Tri-O-benzoyl-β-D-ribopyranoside (7w).
Glycosylation of acceptor 6e (15 mg, 0.096 mmol) with donor 3f
(72 mg, 0.13 mmol) using the General Glycosylation Procedure
afforded glycoside 7w (petroleum ether/ethyl acetate=6/1; 59 mg,
99%) as colorless syrup: [α]25 D=À 89.7 (c 1.0, CHCl3); 1H NMR
(500 MHz, CDCl3) δ 8.07–8.04 (m, 2H), 8.04–8.00 (m, 2H), 7.89 (dd,
J=8.4, 1.4 Hz, 2H), 7.58–7.50 (m, 2H), 7.49 (td, J=7.4, 1.3 Hz, 1H),
7.36–7.27 (m, 6H), 5.83 (t, J=3.8 Hz, 1H), 5.63 (q, J=3.0 Hz, 1H),
5.45–5.40 (m, 1H), 5.31 (d, J=2.5 Hz, 1H), 4.33 (dd, J=13.0, 2.3 Hz,
1H), 4.08 (dd, J=13.0, 3.0 Hz, 1H), 3.56 (td, J=10.6, 4.1 Hz, 1H), 2.33
(pd, J=6.9, 2.6 Hz, 1H), 2.20–2.11 (m, 1H), 1.74–1.65 (m, 2H), 1.45–
1.31 (m, 2H), 1.08–0.82 (m, 12H); 13C NMR (126 MHz, CDCl3) δ
166.24, 166.06, 165.27, 133.17, 133.14, 133.05, 130.00, 129.94,
129.78, 129.73, 129.48, 128.34, 128.31, 128.30, 95.02, 76.64, 69.73,
67.89, 66.46, 61.43, 47.83, 39.79, 34.33, 31.44, 25.47, 22.83, 22.26,
21.22, 15.47; HRMS (ESI) calcd for C36H40O8Na [M+Na]+ 623.2615,
found 623.2617.
The authors declare no conflict of interest.
Keywords: Glycoside · Glycosylation · Glycosyl ester donor ·
Glycosyl 1-methylimidazole-2-carboxylates · Metal triflate
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Manuscript received: June 5, 2021
Revised manuscript received: July 6, 2021
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J. Chen, Dr. Y. Tang*, Prof. B. Yu*
1 – 13
A Mild Glycosylation Protocol
with Glycosyl 1-Methylimidazole-
2-carboxylates as Donors
A mild glycosylation protocol is
developed by using glycosyl 1-meth-
ylimidazole-2-carboxylates as donors.
Such a glycosylation can be promoted
by a series of metal triflates and trifli-
mides, especially Cu(OTf)2.