Sequential Dy(OTf)3-Catalyzed Solvent-Free Per-O-Acetylation and Regioselective Anomeric De-O-Acetylation of Carbohydrates

Article abstract of DOI:10.1002/asia.201700867

Dysprosium(III) trifluoromethanesulfonate-catalyzed per-O-acetylation and regioselective anomeric de-O-acetylation of carbohydrates can be tuned by adjusting the reaction medium. In this study, the per-O-acetylation of unprotected sugars by using a near-stoichiometric amount of acetic anhydride under solvent-free conditions resulted in the exclusive formation of acetylated saccharides as anomeric mixtures, whereas anomeric de-O-acetylation in methanol resulted in a moderate-to-excellent yield. Reactions with various unprotected monosaccharides or disaccharides followed by a semi-one-pot sequential conversion into the corresponding acetylated glycosyl hemiacetal also resulted in high yields. Furthermore, the obtained hemiacetals could be successfully transformed into trichloroimidates after Dy(OTf)₃-catalyzed glycosylation.

Full text of DOI:10.1002/asia.201700867

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Sequential Dy(OTf)3-Catalyzed Solvent-Free Per-O-Acetylation
and Regioselective Anomeric De-O-Acetylation of Carbohydrates
Authors: Yi-Ling Yan, Jiun-Rung Guo, and Chien-Fu Liang
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To be cited as: Chem. Asian J. 10.1002/asia.201700867
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10.1002/asia.201700867
Chemistry - An Asian Journal
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al Dy(OTf)3-Catalyzed Solvent-Free Per-O-Acetylation and
ective Anomeric De-O-Acetylation of Carbohydrates
[a] Jiun-Rung Guo,[a] and Chien-Fu Liang*[a]
ional))
rosium(III) trifluoromethanesulfonate-catalyzed per-O-
gioselective anomeric de-O-acetylation of carbohydrates
adjusting the reaction medium. In this study, per-O-
rotected sugars by using a near stoichiometric amount of
under solvent-free conditions resulted in the exclusive
etylated saccharides as anomeric mixtures, whereas
etylation in methanol resulted in a moderate to excellent
with various unprotected monosaccharide or disaccharide
mi-one-pot sequential conversion into the corresponding
l hemiacetal also resulted in high yields. Furthermore, the
cetals could be successfully transformed into
ollowing Dy(OTf)3-catalyzed glycosylation.
acetic anhydride conditions.11a-b,14 Additionally, some previously
reported catalysts, such as Cu(OTf)22,11a-b Cu(ClO4)2·6H2O,18 p-toluene
sulfonic acid,22 and I2,28 have been employed in one-pot acetylation–
thioglycosylation in conjunction with boron trifluoride etherate and
thiol derivatives. Although numerous existing catalysts perform
acetylation efficiently, new catalysts that are more feasible and
environmentally friendly and use stoichiometric amounts of acetic
anhydride and solvent-free conditions are still in strong demand. In our
previous investigation into clean reactions performed using a Lewis
acid catalyst for acetylation, we found that the available lanthanide
triflates are very active environmentally friendly catalysts and can be
readily recycled.15 However, effective lanthanide triflate catalysts15
used in acetylation, such as cerium(Ш) and erbium(III) triflate, are
associated with a few limitations, such as the use of a large excess of
acetic anhydride15b-c and the use of organic solvents.15a,c In this study,
we used dysprosium(Ш) trilfate as a dual catalyst for the preparation of
peracetylated carbohydrates by using a stoichiometric amount of acetic
anhydride under solvent-free conditions, and we synthesized their
n
bohydrates and their derived hemiacetals are valuable
for the preparation of complex oligosaccharides and
derived hemiacetals through
sequential Dy(OTf)3-catalyzed
,2
Per-O-acetylation of carbohydrates is an important
regioselective anomeric deacetylation from free sugar. This practical
sequential catalysis reaction enabling the preparation of important
building blocks from unprotected reducing sugars would be useful. To
the best of our knowledge, this is the first study using Dy(OTf)3 for the
sequential peracetylation and anomeric deacetylation of carbohydrates,
considerably expanding the scope of lanthanide triflate catalysis in
carbohydrate chemistry.
used for the initial protection of free sugars and is a
r the structural elucidation and identification of target
dition, the acetylated carbohydrates may be valuable
he synthesis of inexpensive CO2-philes.3 Generally,
s performed using acetic anhydride as the reagent and
he solvent and the base. Occasionally, 4-
ridine is also added to accelerate the reactions.4 More
us reagents and catalysts, including PBu3 in CH2Cl2,5
DABCO,7 and imidazole8), Lewis acids (FeCl3,9
u(OTf)2,11a-b In(OTf)3,12 BF3-OEt2,13 Sc(OTf)3,11b,14
LiClO4,16 V(O)(OTf)2,17 Cu(ClO4)2·6H2O,18 and
Results and Discussion
The solvent-free conditions were optimized using
acetic anhydride with commercially available Dy(OTf)3, as shown in
Table 1. At 10 mol%, Dy(OTf)3 furnished -glycopyranosyl ester 2a
D-glucose 1a and
cluster trifluoroacetic acid adduct19), Bronsted acids
21
,
p-toluene sulfonic acid22), heterogeneous catalysts
D
K-10,23 H-β-zeolite,24 zirconyl sulfophenyl
with a 95% yield (entry 1). To determine the minimum amount of
catalyst required, the amount was reduced by 2-fold (entry 2), 10-fold
(entry 3), 20-fold (entry 4), and 100-fold (entry 5), and the results
revealed that the catalyst retained its activity without significant
variation in reaction yield, but a longer reaction time was required for
the full conversion of the starting material. Entry 5 was found to be the
minimum catalyst concentration for optimum activity, and the reaction
was not completed when a lower catalyst concentration (0.05 mol%)
was used (entry 6). This optimization study also demonstrated an
interesting phenomenon: the α/β ratios were affected by the catalyst
concentration.
To extend the scope of this study, the aforementioned optimized
conditions for the per-O-acetylation reaction were employed for a
series of unprotected sugars. The reaction was performed under
solvent-free conditions by using stoichiometric amounts of acetic
anhydride and 0.1 mol% Dy(OTf)3. The products of the per-O-
acetylation reaction with various substrates are shown in Table 2. Per-
ulfonic acid functionalized nano γ-Al2O3,26 and
27), I2,28 and ionic liquid,29 have been developed to
a large excess of the toxic and foul-smelling pyridine.
ung groups have developed metal-catalyzed per-O-
the solvent-free and use stoichiometric amounts of
-R. Guo, Prof. C.-F. Liang*
of Chemistry
ung Hsing University
Rd., South Dist., Taichung City 402 (Taiwan)
01@dragon.nchu.edu.tw
nformation for this article is given via a link at the end of
nt.
O-acetylation of fully unprotected reducing sugars such as
D-glucose,
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10.1002/asia.201700867
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synthesis of several important per-O-acetylated carbohydrates, such as
N-acetylglucosamine (1f), lactose monohydrate (1g), methyl α-glucose
(1h), sialic acid (1i), and 2,3-O-isopropylidene ribofuranose (1j). The
acetylation reaction was successful with disaccharides such as lactose
and led to the formation of the product 2g (90%). Reducing amino
sugars such as N-acetylglucosamine resulted in a high yield under the
on of Dy(OTf)3-catalyzed solvent-free per-O-acetylation of
a stoichiometric amount of acetic anhydride.
heating conditions (60 °C, 95%).
A representative complex
carbohydrate, N-acetylneuraminic acid methylester 1i, was acetylated
to the corresponding product 2i (91%), in which the hydroxyl group at
the C-2 position remained unaffected. The configuration of 2i was
characterized through 400 MHz 1H NMR spectral analysis and was
confirmed according to previous reports.16,19 Moreover, acid-labile
group such as isopropylidene ribofuranose was acetylated to the
corresponding product 2j with a good yield (73%). All products were
characterized through 1H and 133C spectrometry, and the data
corresponded substantially with the values described in the literature.
After the success of the solvent-free acetylation of the unprotected
sugars by using stoichiometric amounts of Ac2O and Dy(OTf)3, we
prepared peracetylated hemiacetals by using Dy(OTf)3 to catalyze a
sequential regioselective anomeric deacetylation reaction.
ere carried out with 50 mg of 1a in neat. [b] Isolated yields.
s not full completion checked by TLC analysis.
catalyzed solvent-free per-O-acetylation of carbohydrates.
Peracetylated hemiacetals of carbohydrates are important intermediates
for the preparation of anomeric trichloroacetimidate, a widely used
glycosyl donor.1,30 However, the preparation of such hemiacetals still
relies heavily on classical basic or acidic conditions, such as those
involving transamidation (benzyl amine, piperidine, and hydrazine
acetate),31 transesterification catalyzed by organic tin reagents,32
solvolysis by SnCl4,33 or hydrolysis using silver34 or mercuric35 salts
from anomeric halogenide. Recently, several species, including HClO4-
SiO2,36
FeCl3·6H2O,37
lanthanide
triflates,38
and
dimethylaminopropylamine,39 have been developed to facilitate
anomeric deacetylation. These reaction methods are useful; however,
these methods are associated with disadvantages such as low shelf
stability, toxicity,31-35 the production of a lipophilic amide byproduct,31a
the employment of high-temperature conditions,36,37 and the fact that
they are not metal catalytic reactions.37 Therefore, an effective and
environmentally friendly catalyst for regioselective anomeric
deacetylation under mild reaction conditions is highly desirable. For
the transesterification of anomeric acetate, lanthanide triflates have
been applied in anomeric deacetylation.38 To extend these findings, we
performed per-O-acetylation and anomeric deacetylation through a
sequential Dy(OTf)3-catalyzed one-pot reaction.
To investigate the potential of the Dy(OTf)3-catalyzed one-pot reaction,
an initial evaluation of the anomeric deacetylation of important
carbohydrates was performed (refer to the Supporting Information).40
The reaction was performed in the presence of 5 mol% Dy(OTf)3 at a
temperature ranging from 0 °C to room temperature and under a mild
heating condition (40 °C). The anomeric transesterification reaction
proceeded simply in commercial methanol under the mild heating
condition and cleanly provided a high reaction yield (72%–96%).40 All
1
products were characterized through H and 13C spectrometry, and the
ere carried out with gram scale of 1 in neat. [b] The isolated
ong with the α / β rations in parenthesis. [c] Reaction
C. [d] Sugar: lactose monohydrate.
data corresponded substantially with the values described in the
literature. After establishing optimal anomeric deacetylation conditions,
we performed the sequential Dy(OTf)3-catalyzed one-pot reaction. An
initial evaluation of the proposed catalytic reaction was conducted with
1c in the presence of 5 mol% Dy(OTf)3 and Ac2O (10 or 6 equiv); this
reaction yielded the corresponding per-O-acetate, as confirmed by thin-
layer chromatography (TLC). MeOH was added to the reaction mixture,
mannose,
D-xylose, and L-fucose resulted in the
fully acetylated products 2a (99%), 2b (99%), 2c
and 2e (97%), respectively. In the per-O-acetylation
e corresponding acetylated product was obtained in a
me (1 h). The procedure was also applied for the
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10.1002/asia.201700867
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at 40 °C (Table 3, entries 1 and 2). Monitoring of the
TLC revealed a slow conversion into the target
second step were considerably prolonged by 2 days. Hence, in the
second step, NaHCO3 combined with Dy(OTf)3 is likely to be less
reactive than only Dy(OTf)3 and likely results in the formation of fewer
side products.
ation of one-pot conversion of mannose 1c to per-O-
tal glycoside.
OH
O
OAc
O
HO
HO
HO
AcO
AcO
a, b
AcO
OH
OH
1c
3c
Scheme 1. Reagents and conditions: (aa) 0.1 mol% Dy(OTf)3, 10 eq. Ac2O, rt,
1h; (b) 5 mol% Dy2(CO3)3·4H2O, MeOH, 40 oC, 48h, 84%.
Consequently, we employed two methods (Method A and Method B)
for our reaction and performed the sequential Dy(OTf)3-catalyzed per-
O-acetylation–anomeric deacetylation reaction for a series of fully
unprotected sugars. The results are summarized in Table 4. The
developed protocol could be conducted easily and safely, as mentioned
earlier. The observations in Table 4 clearly suggest the necessity of
acetic acid removal in both methods, and that 5 mol% NaHCO3
addition improved the yield in several cases (Method B). For example,
from the fully unprotected reducing sugars (1a–1d, entries 1–4), higher
yields were obtained using Method B, with consistently high to
excellent yields of the acetylated glycosyl hemiacetals 3a (87%), 3b
(78%), 3c (90%), 3d (60%). The reaction with 1e–1g (entries 5–7)
could be performed using both methods without obvious differences in
the reaction yield. Importantly, acid-sensitive groups such as
isopropylidene ribofuranose (entry 8) were more tolerated under the
Method B condition. Moreover, we conducted a recycling protocol in
the sequential one-pot two-step strategy. After a work-up, the Dy(III)
catalyst was recovered from the aqueous phase as a white solid and
was reused after drying over P2O5. The recycling protocol for 1c was
repeated three times using the Method A condition, and the yield of the
peracetylated hemiacetal 3c was more than 70%, as shown in Figure 1.
LC grade. [b] Entry1-7 are 50 mg scale. [c] Isolated yields.
First step, the reaction was reacted in the presence of 0.1
er acetylation, acetic acid was removed in vacuo. Second
was reacted in the presence of 4.9 mol% Dy(OTf)3.
miacetal, and only 51% and 57% yields were obtained
. We assumed that the acetic acid formed as a
initial acetylation impeded the reaction. Hence, after
ion, we utilized different bases to neutralize the acetic
es including pyridine and triethylamine were utilized
ove the reaction yield (Table 3, entries 3 and 4). For
table inorganic base was utilized in the same reaction.
m bicarbonate condition provided a higher reaction
a faster reaction time (Table 3, entry 5). The amount
bonate was also reduced to 5 and 1 equiv, which
htly lower yield and a significantly prolonged reaction
ntries 6 and 7). However, regardless of the modified
action yield did not improve to our satisfaction when
was not removed after acetylation. To prove the
tic acid removal, we used a semi-one-pot reaction
after acetylation). In the first step, the acetylation
ormed under the optimized conditions (Table 2), and
as removed after complete acetylation. Subsequently,
immediately performed in the presence of 4.9 mol%
mmercial methanol (Table 3, entry 8). The results
hat acetic acid removal is necessary and provided the
with an 81% yield, but the side products of multi-
ormed in the reaction. However, when the reaction
the presence of 5 mol% NaHCO3 in the second step,
obtained in a 90% yield (Table 3, entry 9). It is
multi-hydration can be suppressed by adding sodium
ording to a similar previous report,41 we assumed that
s linked through a coordinated bicarbonate anion,
initial catalytic activity. To confirm this assumption,
Figure 1.
Finally, to verify the synthetic utility of our developed method in
comparison with that of other reported protocols, using the sequential
one-pot two-step strategy, both 1a and 1c were transformed into
glycosyl
hemiacetals,
which
were
then
converted
to
ted to
a one-pot two-step reaction by using
trichloroacetimidate derivatives by using trichloroacetonitrile and
K2CO3, as shown in Scheme 2. The glycosyl imidates 4a and 4c were
then used in a glycosylation reaction with Dy(OTf)3 as the
glycosylation activator, which is similar to the glycosidation reaction
arbonate tetrahydrate as a catalyst in the second step,
me 1. The results revealed that the desired product 3c
tained with an 84% yield by using dysprosium(Ш)
ydrate as a catalyst; however, the reactions in the
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pot conversion of free sugars to peracetylated hemiacetal glycosides.
O
O
1. 0.1 mil% Dy(OTf)3, 6~10 eq. Ac2O, t1
2. 4.9 mol% Dy(OTf)3, MeOH, 40 oC, t2
AcO
HO
OH
OH
3
1
Method Aa,b
Method Ba,c


ugar
Product
t1 (h)
t2 (h)
Yield (%)
t2 (h)
Yield (%)
AcO
AcO
O
7
9
71
1.9/1
2.3/1
440
224
87
2.8/1
1a
AcO
OH
OH
OAc
AcO
OAc
O
1b
5
12
48
78
2.0/1
AcO
OAc
OAc
AcO
AcO
AcO
O
1c
1d
1
3
9
81
54
5.4/1
1.9/1
111
12
90
60
6.3/1
1.9/1
OH
OH
O
AcO
AcO
20
OAc
OH
OAc
O
223
65
2.2/1
1e
2
10
71
1.4/1
OAc
AcO
AcO
O
AcO
1f
1/0
113
223
71
75
1/0
5
4
12
14
71
78
AcO
AcHN
OH
AcO
Ac4Gal
AcO
O
1g
1.6/1
1.7/1
OH
OAc
AcO
O
OH
messy
1k
2
23
0.2/1
448
53
O
O
Without NaHCO3 addition in second step. [c] 5 mol% NaHCO3 addition in second step.
nthanide triflates,42 to obtain the valuable per-O-
thoxyphenyl glycoside 5c and the disaccharide
respectively. Both products can be used as donors for
eparation of important oligosaccharides.
1c
1a
or
a, b, c
NH
CCl3
OAc
AcO
AcO
AcO
AcO
AcO
O
AcO
O
NH
CCl3
O
AcO
O
4a
4c
s
(3 steps 72%)
HO
d
d
O
MeO
that dysprosium(III) triflate is an effective and dual-
BzO
68%
STol
STol
4 steps 41%
OH
BzO
OBz
for the solvent-free per-O-acetylation and anomeric
of carbohydrates. Furthermore, we developed an
h-yield sequential one-pot two-step protocol for the
racetylated hemiacetals from free sugars. The reaction
mild, convenient, and nonhazardous. In addition, the
m(III) triflate as a catalyst minimized reagent use and
AcO
AcO
AcO
OAc
O
O
AcO
AcO
AcO
O
O
BzO
AcO
BzO
5a
5c
OPMB
OBz
Scheme 2. Reagents and conditions: (aa) 0.1 mol% Dy(OTf)3, 10eq. Ac2O, rt,
1h (for 1c) or 7h (for 1a); (b) 4.9 mol% DDy(OTf)3, 5 mol% NaHCO3, MeOH, 40
oC, 13h (for 1c) or 40h (for 1a); (c) CCl33CN, K2CO3, DCM, rt, 4h; (d) 5 mol%
Dy(OTf)3, DCM, rt to reflux, 5h.
e
believe that this method of protection and
protection for preparing commonly used building
d wide applications in oligosaccharide synthesis.
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under reduced pressure to remove MeOH. The residue was dissolved in
ethyl acetate, which was washed with brine. The combined organic layer
was dried over MgSO4, filtered, concentrated and purified by column
chromatography to afford the desired product (3a). After work-up, the
aqueous phase was evaporated under reduced pressure and the
Dy(OTf)3 was recovered and reused after drying over P2 O5 in vacuum for
overnight.
al Section
tion. The catalyst, Dy(OTf)3 (Strem Chemicals Inc.,
-4000) was obtained from commercial source and used
ut further precautions. 1H NMR, 13C NMR and COSY
orted on a Varian 400 MHz NMR spectrometer with
vent. Chemical shifts were reported in parts per million
residual solvent peak (7.26 ppm). The optical rotations
n a Roldulph Autopol Ⅳ Automatic Polarimeter at 589
C. IR spectra were measured on a Thermo Scientific
spectrophotometer. TLC was performed on pre-coated
lica Gel 60 F254 (0.25 mm, E. Merck); detection was
aying with a solution of 5% H2SO4 in MeOH. Flash
graphy was carried out on Silica Gel 60 (230–400 mesh,
mass spectra were analyzed on a Finnigan LTQ-
ment with an ESI† source. Incorporation
The Procedure for Dy2(CO3)3·4H2O Catalysed the Sequential One-Pot
Two Steps Per-O-Acetylation and Anomeric De-O-Acetylation. A
mixture of
D-mannose (1c) (0.5 g, 2.78 mmol), Dy(OTf)3 (1.8 mg, 0.1
mol%) and acetic anhydride (1.1–2 equivalents per –OH of
carbohydrates) was stirred at room temperature under nitrogen
atmosphere. Upon complete acetylation, the reaction mixture was
concentrated in vacuo to remove acetic anhydride. Without purification,
do the next step. To a solution of the residue in MeOH (69.4 mL) was
added Dy2(CO3)3·4H2O (78.5 mg, 4.9 mol%) and NaHCO3 (11.7 mg, 5
mol%) and stirred at 40 oC under nitrogen atmosphere. After the
completion of the reaction, the reaction mixture was concentrated under
reduced pressure to remove MeOH. The residue was dissolved in ethyl
acetate, which was washed with brine, dried over MgSO4, filtered and
concentrated. The crude product was purified by column chromatography
to afford the desired product 3c (two steps, 84% yield).
ure for Per-O-Acetylation of Carbohydrates.
A
ose (1a) (1g, 5.55 mmol), Dy(OTf)3 (3.4 mg, 0.1 mol%)
ide (1.1–2 equivalents per –OH of carbohydrates) was
temperature under nitrogen atmosphere. After the
reaction, the reaction mixture was diluted with ethyl
as washed with aqueous NaHCO3 followed by brine.
organic layer was dried over MgSO4, filtered and
he crude product was purified by flash column
o afford the desired product (2a).
1,2,3,4,6-Penta-O-acetyl-D
-glucopyranoside (2a).11 (2.15 g, 99%) [α]2D4
+57.64 (c 1.0, CHCl3); IR (cm-1): 2981, 1739, 1433, 1369, 1206, 1136; 1H
NMR (400 MHz, CDCl3) δ 6.32 (d, J = 3.7 Hz, 1H), 5.70 (d, J = 8.3 Hz,
0.48H), 5.49–5.43 (m, 1H), 5.24 (t, J = 9.4 Hz, 1H), 5.17–5.06 (m, 3H),
4.27 (ddd, J = 12.7, 8.6, 4.4 Hz, 1H), 4.15–4.05 (m, 2H), 3.83 (ddd, J =
10.0, 4.5, 2.2 Hz, 1H), 2.20–1.98 (m, 22H); 13C NMR (100 MHz, CDCl3) δ
170.5, 170.0, 169.5, 169.2, 168.6, 91.6, 88.9, 72.5, 72.6, 70.1, 69.6, 69.0,
67.7, 67.6, 61.3, 20.7, 20.5, 20.5, 20.4, 20.3.
dure for Anomeric De-O-Acetylation of Fully
ohydrates.40 A solution of 1,2,3,4,6-Penta-O-acetyl-
D-
2a) (1 g, 2.56 mmol) and Dy(OTf)3 (78.0 mg, 5 mol%)
was stirred at 0 oC or 40 oC under nitrogen atmosphere.
etion of the reaction, the reaction mixture was
er reduced pressure to remove MeOH. The residue was
l acetate, which was washed with brine, dried over
nd concentrated. The crude product was purified by
graphy to afford the desired product (3a).
1,2,3,4,6-Penta-O-acetyl-
D
-galactopyranoside (2b).18 (2.15 g, 99%) [α]
+62.78 (c 1.0, CHCl3); IR (cm-1): 2960, 1738, 1433, 1369, 1205, 1137;
24
D
1H NMR (400 MHz, CDCl3) δ 6.37 (d, J = 1.4 Hz, 1H), 5.69 (d, J = 8.3 Hz,
0.4H), 5.42 (d, J = 2.8 Hz, 1H), 5.38–5.28 (m, 3H), 5.10–5.05 (m, 1H),
4.38–4.29 (m, 1H), 4.24–4.02 (m, 3H), 2.19–1.96 (m, 26H); 13C NMR
(100 MHz, CDCl3) δ 170.2, 170.0, 170.0, 169.8, 168.8, 99.0, 92.0, 89.6,
71.6, 70.7, 69.1, 68.6, 67.7, 67.3, 67.2, 66.7, 66.3, 61.1, 20.8, 20.7, 20.5,
20.5, 20.4.
ure for Sequential One-Pot Two Steps Per-O-
Anomeric De-O-Acetylation (Method B). A mixture of
.5 g, 2.78 mmol), Dy(OTf)3 (1.80 mg, 0.1 mol%) and
(1.1–2 equivalents per –OH of carbohydrates) was
mperature under nitrogen atmosphere. Upon complete
eaction mixture was concentrated in vacuo to remove
Without purification, do the next step. To a solution of
OH (69.4 mL) was added Dy(OTf)3 (82.9 mg, 4.9 mol%)
.7 mg, 5 mol%) and stirred at 40 oC under nitrogen
r the completion of the reaction, the reaction mixture
under reduced pressure to remove MeOH. The residue
ethyl acetate, which was washed with brine, dried over
nd concentrated. The crude product was purified by
graphy to afford the desired product (3a).
1,2,3,4,6-Penta-O-acetyl-
D
-mannopyranoside (2c).11 (2.15 g, 99%) [α]
+27.93 (c 1.0, CHCl3); IR (cm-1): 2959, 1739, 1433, 1368, 1206, 1147;
24
D
1H NMR (400 MHz, CDCl3) δ 6.08 (d, J = 1.8 Hz, 1H), 5.86 (d, J = 0.9 Hz,
0.56H), 5.48 (d, J = 2.5 Hz, 1H), 5.38–5.24 (m, 4H), 5.13 (dd, J = 10.0,
3.3 Hz, 1H), 4.29 (ddd, J = 12.3, 10.2, 5.1 Hz, 2H), 4.17–4.00 (m, 3H),
3.80 (ddd, J = 9.8, 5.3, 2.3 Hz, 1H), 2.23–1.98 (m, 25H); 13C NMR (100
MHz, CDCl3) δ 170.5, 169.9, 169.6, 169.4, 167.9, 90.5, 90.3, 73.1, 70.5,
70.5, 68.6, 68.2, 68.1, 65.4, 65.3, 62.5, 62.0, 20.7, 20.6, 20.6, 20.5, 20.5.
1,2,3,4-Tetra-O-acetyl-D
-xylopyranoside (2d).43 (1.7 g, 96%) [α] 2D4
+39.98 (c 1.0, CHCl3); IR (cm-1): 2963, 1742, 1433, 1368, 1207, 1129; 1H
NMR (400 MHz, CDCl3) δ 6.24 (d, J = 3.5 Hz, 1H), 5.70 (d, J = 6.9 Hz,
0.68H), 5.45 (t, J = 9.8 Hz, 1H), 5.38–5.15 (m, 2H), 5.06–4.99 (m, 2H),
4.63 (dd, J = 12.2, 6.3 Hz, 0.52H), 4.27–4.08 (m, 2H), 3.92 (dd, J = 11.2,
5.9 Hz, 1H), 3.70 (t, J = 10.9 Hz, 1H), 3.51 (dd, J = 12.0, 8.5 Hz, 1H),
2.19–1.98 (m, 23H); 13C NMR (100 MHz, CDCl3) δ170.0, 169.7, 169.6,
169.6, 169.6, 169.2, 168.9, 168.8, 98.8, 92.7, 91.9, 89.1, 79.8, 79.3, 74.2, 69.2,
68.5, 62.7, 62.2, 61.5, 60.5, 20.9, 20.8, 20.7, 20.7, 20.6, 20.5, 20.4, 20.3.
re for Catalyst Recycle Used Strategy of Sequential
Steps Per-O-Acetylation and Anomeric De-O-
ixture of D-mannose (1c) (0.5 g, 2.78 mmol), Dy(OTf)3
%) and acetic anhydride (1.1–2 equivalents per –OH of
was stirred at room temperature under nitrogen
on complete acetylation, the reaction mixture was
vacuo to remove acetic anhydride and acetic acid.
on, do the next step. To a solution of the residue in
was added Dy(OTf)3 (82.9 mg, 4.9 mol%) and NaHCO3
) and stirred at 40 oC under nitrogen atmosphere. After
the reaction, the reaction mixture was concentrated
1,2,3,4-Tetra-O-acetyl-
(c 1.0, CHCl3); IR (cm-1): 2989, 1740, 1434, 1369, 1208, 1126; 1H NMR
L
-fucopyranose (2e).11 (1.78 g, 97%) [α]2D4 -55.81
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PER
) δ 6.33 (d, J = 2.8 Hz, 1H), 5.67 (d, J = 8.3 Hz, 1H),
J = 2.4 Hz, 1H), 5.41 (dd, J = 10.8, 3.3 Hz, 1H), 5.17 (dd, J = 10.8, 3.5 Hz,
1H), 5.07–5.00 (m, 1H), 4.47 (t, J = 6.5 Hz, 1H), 4.17–4.04 (m, 3H),
2.17–1.99 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 170.8, 170.6, 170.4,
170.3, 170.1, 170.1, 95.7, 90.4, 70.8, 70.7, 70.4, 68.3, 68.1, 67.2, 67.1,
65.9, 61.7, 61.4, 20.7, 20.6, 20.5, 20.5, 20.5, 20.4.
), 5.18–5.03 (m, 2H), 4.31–4.18 (m, 2H), 3.98–3.92 (m,
0.9 Hz, 1H), 3.51 (dd, J = 12.0, 8.5 Hz, 1H), 2.20–1.96
, J = 6.4 Hz, 3H), 1.15 (d, J = 6.5 Hz, 3H); 13C NMR
) δ 170.9, 170.6, 170.3, 90.9, 71.4, 68.6, 67.9, 64.7,
6.2.
2,3,4,6-Tetra-O-acetyl-D
-mannopyranose (3c).47 (870.7 mg, 90%) [α]2D4
cetyl-2-N-acetyl-
D
-glucosamine (2f).22 (2.04 g, 95%)
+26.71 (c 1.0, CHCl3); IR (cm-1): 3457, 2923, 2853, 1739, 1460, 1371,
213, 1126; 1H NMR (400 MHz, CDCl3) δ 5.39 (dd, J = 9.9, 3.2 Hz, 1H),
5.25 (ddd, J = 9.6, 9.1, 7.0 Hz, 3H), 4.26–4.18 (m, 2H), 4.17–4.07 (m,
2H), 2.15–1.95 (m, 12H); 13C NMR (100 MHz, CDCl3) δ 170.9, 170.3,
170.1, 169.8, 92.0, 70.0, 68.7, 68.3, 66.0, 62.5, 20.9, 20.7, 20.7, 20.7.
0, CHCl3); IR (cm-1): 3291, 2960, 1740, 1662, 1538,
1127; 1H NMR (400 MHz, CDCl3) δ 6.16 (d, J = 3.7 Hz,
8.8 Hz, 0.38H), 5.64 (d, J = 9.0 Hz, 1H), 5.27–5.16 (m,
, 1H), 4.52–4.44 (m, 1H), 4.29–4.20 (m, 2H), 4.14–3.95
H), 2.23–1.90 (m, 23H); 13C NMR (100 MHz, CDCl3) δ
2, 169.0, 168.6, 92.3, 90.5, 72.5, 72.5, 70.5, 69.5, 67.7,
2.6, 50.8, 22.8, 20.8, 20.6, 20.5, 20.4.
2,3,4-Tri-O-acetyl-D
-xylopyranose (3d).46 (461.3 mg, 60%) [α]2D4 +21.89
(c 1.0, CHCl3); IR (cm-1): 2955, 2923, 2854, 1462, 1377, 1260, 1097; 1H
NMR (400 MHz, CDCl3) δ 5.50 (t, J = 9.6, 1H), 5.38 (t, J = 3.3 Hz, 1H),
5.22 (t, J =9.2 Hz, 1H), 4.99–4.91 (m, 1H), 4.83 (dd, J = 9.9, 3.5 Hz, 1H),
4.67 (t, J = 7.7 Hz, 1H), 4.12 (dd, J = 11.7, 5.6 Hz, 1H), 3.88–3.77 (m,
2H), 3.43–3.42 (m, 1H), 2.08(s, 3H), 2.04(s, 3H), 2.03(s, 3H); 13C NMR
(100 MHz, CDCl3) δ 170.9, 170.2, 170.1, 170.1, 169.9, 95.9, 95.8, 90.3,
90.1, 71.2, 69.2, 69.1, 69.0, 62.7, 58.4, 58.2, 20.9, 20.8, 20.7, 20.7, 20.5.
O-acetate (2g).43 (3.39 g, 90%) [α]2D4 +29.72 (c 1.0,
2953, 1740, 1431, 1367, 1209; 1H NMR (400 MHz,
J = 3.7 Hz, 1H), 5.66 (d, J = 8.3 Hz, 0.71H), 5.50–5.40
J = 3.7, 2.6 Hz, 2H), 5.23 (t, J = 9.1 Hz, 1H), 5.15–4.91
0 (m, 3H), 4.20–3.95 (m, 6H), 3.91–3.71 (m, 4H), 2.19–
C NMR (100 MHz, CDCl3) δ 171.5, 170.6, 170.2, 169.0,
, 72.5, 72.5, 70.5, 69.5, 67.7, 67.4, 61.5, 61.4, 52.6,
0.7, 20.5, 20.4.
2,3,4-Tri-O-acetyl-L
-fucopyranose (3e).48 (525.3 mg, 65%) [α]2D4 +21.89
(c 1.0, CHCl3); IR (cm-1): 2955, 2923, 2854, 1462, 1377, 1260, 1097; 1H
NMR (400 MHz, CDCl3) δ 5.45 (t, J = 2.9, 1H), 5.39 (dd, J = 10.4, 2.8 Hz,
1H), 5.29 (d, J =3.8 Hz, 1H), 5.13 (dd, J = 10.8, 3.5, 1H), 4.68–4.61 (m,
1H), 4.40 (q, J = 6.4 Hz, 1H), 4.24 (t, J = 5.0 Hz, 1H), 3.84 (d, J = 7.8 Hz,
1H), 3.58 (d, J = 3.1 Hz, 1H), 3.45 (s, 1H), 2.18–1.96 (m, 17H), 1.21 (d, J
= 6.4 Hz, 1H), 1.13 (d, J = 6.5 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ
170.4, 170.1, 169.9, 169.8, 169.3, 169.0, 92.0, 89.0, 89.7, 70.5, 70.3,
70.2, 70.0, 67.8, 67.7, 67.2, , 67.1, 20.9, 20.8, 20.7, 20.6, 20.5, 20.4,
15.8, 15.7
6-tetra-O-acetyl-α-D
-glucopyranoside (2h).18 (1.93 g,
93 (c 1.0, CHCl3); IR (cm-1): 2939, 1739, 1460, 1372,
MR (400 MHz, CDCl3) δ 5.43 (t, J = 9.8 Hz, 1H), 5.03 (t,
.94–4.82 (m, 2H), 4.23 (dd, J = 12.3, 4.6 Hz, 1H), 4.07
Hz, 1H), 3.95 (ddd, J = 10.2, 4.5, 2.3 Hz, 1H), 3.38 (s,
m, 12H); 13C NMR (100 MHz, CDCl3) δ 170.5, 170.0,
, 70.6, 69.9, 68.3, 67.0, 61.8, 55.3, 20.6, 20.5, 20.5.
mido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-α-
D
-glycero-
D
2-Acetamido-2-deoxy-3,4,6-tri-O-acetyl-
D
-glucopyranose
(3f).46
opyranosonate (2i).44 (2.48 g, 91%) [α]2D4 -1.89 (c 1.0,
: 3253, 3071, 2924, 1734, 1720, 1649, 1570, 1434,
, 1211, 1159, 1130; 1H NMR (400 MHz, CDCl3) δ 5.85
H), 5.35 (dd, J = 5.2, 1.8 Hz, 1H), 5.26–5.16 (m, 2H),
(dd, J = 12.3, 2.3 Hz, 1H), 4.23–4.10 (m, 2H), 4.01 (dd,
H), 3.85 (s, 3H), 2.13 (s, 3H), 2.09 (s, 3H), 2.02 (s, 3H),
(s, 3H); 13C NMR (100 MHz, CDCl3) δ 171.5, 171.1,
2, 169.0, 94.8, 72.0, 71.2, 69.2, 68.3, 62.5, 53.2, 48.9,
0.8, 20.7, 20.7.
(684.2 mg, 71%) [α]2D4 +41.48 (c 1.0, CHCl3); IR (cm-1): 3366, 2960., 2360,
1744, 1661, 1542, 1371, 1244; 1H NMR (400 MHz, CDCl3) δ 6.00 (d, J =
9.3 Hz, 1H), 5.31–5.27 (m, 1H), 5.26–5.23 (m, 1H), 5.12 (t, J = 9.4 Hz,
1H), 4.23–4.09 (m, 4H), 2.10–1.94 (mm, 12H); 13C NMR (100 MHz, CDCl3)
δ 171.4, 171.1, 170.9, 169.5, 91.3, 70.9, 68.2, 67.2, 62.0, 52.2, 23.0,
20.7, 20.7, 20.6.
4’-O-(2,3,4,6-Tetra-O-acetyl-β-
D-galactopyranosyl)-2’,3’,6’-tri-O-
acetyl-
D
-glucopyranose (3g).47 (1.3 g, 75%) [α]D24 +33.99 (c 1.0, CHCl3);
IR (cm-1): 3433, 2923, 2853, 1740, 1432, 1367, 1214, 1171; 1H NMR
(400 MHz, CDCl3) δ 5.50 (t, J = 9.6 Hz, 1H), 5.33 (d, J = 3.5 Hz, 2H),
5.21 (t, J = 9.3 Hz, 1H), 5.14–5.04 (m, 1H), 4.98–4.90 (m, 1H), 4.84–4.75
(m, 1H), 4.73 (d, J = 6.3 Hz, 1H), 4.52–4.43 (m, 3H), 4.20–4.01 (m, 6H),
3.87 (t, J = 6.9 Hz, 2H), 3.76 (dd, J = 20.0, 10.4 Hz, 2H), 3.69–3.60 (m,
1H), 2.15–1.93 (m, 26H); 13C NMR (100 MHz, CDCl3) δ 171.1, 170.7,
170.6, 170.5, 170.1, 170.1, 100.4, 95.6, 90.5, 71.2, 71.1, 70.8, 70.2, 69.4,
68.4, 67.7, 64.3, 20.8, 20.6, 20.6, 20.6, 20.5, 16.0, 15.9.
,3-O-isopropylidene-D
-ribofuranose (2j).45 (1.11 g,
(c 1.0, CHCl3); IR (cm-1): 2990, 1739, 1436, 1373, 1209,
MR (400 MHz, CDCl3) δ 6.21 (s, 1H), 4.71 (s, 1H), 4.46
), 4.11 (dd, J = 6.7, 3.4 Hz, 2H), 2.08 (s, 3H), 2.05 (s,
, 1.33 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 170.7,
3, 85.5, 85.3, 81.7, 64.3, 26.6, 25.2, 21.4, 21.0.
cetyl-D
-glucopyranose (3a).46 (842.9 mg, 87%) [α]2D4
HCl3); IR (cm-1): 3468, 2922, 2853, 1740, 1456, 1367,
MR (400 MHz, CDCl3) δ 5.53 (t, J = 9.6 Hz, 1H), 5.46 (d,
25 (t, J = 9.6 Hz, 1H), 5.08 (t, J = 9.0 Hz, 1H), 4.90 (dd,
1H), 4.29–4.20 (m, 2H), 4.17–4.09 (m, 2H), 2.10–1.99
MR (100 MHz, CDCl3) δ 170.9, 170.8, 170.6, 170.2,
4, 90.0, 73.1, 72.3, 71.9, 71.1, 69.9, 69.6, 68.5, 68.4,
0.7, 20.6, 20.6, 20.5, 20.5.
5-O-Acetyl-2,3-O-isopropylidene-D
-ribofuranose (3j).49 (341.3 mg,
53%) [α]2D4 -17.39 (c 1.0, CHCl3); IR (cm-1): 3446, 2989, 2943, 1744, 1375,
1241, 1161; 1H NMR (400 MHz, CDCl3) δ 5.46 (s, 1H), 4.70 (d, J = 5.9
Hz, 1H), 4.65–4.62 (m, 2H), 4.40–4.35 (m, 1H), 4.34–4.28 (m, 2H), 4.16–
4.08 (m, 3H), 2.10 (s, 3H), 1.48 (s, 3H), 1.33 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 171.0, 112.4, 102.8, 85.6, 84.3, 81.8, 68.1, 65.2, 26.3, 24.7,
20.7.
cetyl-
D
-glactopyranose (3b).47 (755.2 mg, 78%) [α]2D4
4’-O-(2,3,4,6-Tetra-O-acetyl-α-D-gulcopyranosyl)-2’,3’,6’-tri-O-acetyl-
HCl3); IR (cm-1): 3467, 2925, 1738, 1433, 1369, 1212,
D-glucopyranose (3l).18 (1.53 g, 966%) [α]D24 +82.66 (c 1.0, CHCl3); IR
MR (400 MHz, CDCl3) δ 5.53 (t, J = 3.4 Hz, 1H), 5.48 (d,
(cm-1): 3503, 2923, 2853, 1739, 1429, 1366, 1224, 1148, 1127; 1H NMR
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PER
) δ 5.56 (t, J = 9.6 Hz, 1H), 5.41 (d, J = 3.9 Hz, 1H),
completion of the reaction, the reaction mixture was extracted with DCM,
dried over MgSO4 and concentrated. The residue was purified by column
chromatography to afford the product 5a (379 mg, 68% yield). [α]2D4 +4.70
(c 1.0, CHCl3); IR (cm-1): 2924, 1730, 1601, 1493, 1451,1366, 1278,
1215, 1177; 1H NMR (400 MHz, CDCl3) δ 7.96 (d, J = 7.2 Hz, 2H), 7.90
(d, J = 7.3 Hz, 2H), 7.77 (d, J = 7.2 Hz, 2H), 7.53 (td, J = 7.4, 3.9 Hz, 2H),
7.39 (p, J = 7.4 Hz, 7H), 7.26 (dd, J = 9.5, 6.9 Hz, 2H), 7.18 (d, J = 8.0
Hz, 2H), 5.85 (t, J = 9.5 Hz, 1H), 5.42 (t, J = 9.7 Hz, 1H), 5.33 (t, J = 9.8
Hz, 1H), 5.20 (t, J = 9.5 Hz, 1H), 5.09–4.98 (m, 2H), 4.95 (d, J = 10.0 Hz,
1H), 4.62 (d, J = 8.0 Hz, 1H), 4.20 (ddd, J = 12.3, 4.9 Hz, 1H), 4.08–3.97
(m, 3H), 3.81 (dd, J = 11.3, 7.7 Hz, 1H), 3.65 (ddd, J = 9.9, 4.7, 2.1 Hz,
1H), 2.38 (s, 3H), 2.03 (s, 3H), 2.03 (s, 3H), 2.02 (s, 3H), 2.00 (s, 3H);
13C NMR (100 MHz, CDCl3) δ 170.6, 170.2, 169.5, 169.4, 165.6, 165.3,
165.0, 138.6, 133.6, 133.3, 133.2, 129.9, 129.8, 129.8, 129.6, 129.1,
128.7, 128.5, 128.4, 128.3, 1282, 128.0, 100.8, 86.3, 77.9, 74.0, 72.8,
71.7, 71.1, 70.4, 69.4, 68.7, 68.2, 61.7, 21.2, 20.7, 20.6, 20.6; HRMS
), 5.35–5.31 (m, 2H), 5.30–5.23 (m, 1H), 5.09–4.99 (m,
= 10.5, 3.9, 2.0 Hz, 2H), 4.77–4.71 (m, 2H), 4.51–4.42
5 (m, 4H), 4.07–3.90 (m, 5H), 3.76–3.69 (m, 1H), 3.45
(m, 27H); 13C NMR (100 MHz, CDCl3) δ 170.7, 170.6,
0.6, 170.5, 170.5, 170.3, 170.1, 170.1, 169.9, 169.9,
4, 95.4, 94.7, 89.8, 74.8, 73.6, 72.5, 72.2, 71.5, 69.9,
8.3, 67.9, 67.5, 62.8, 62.7, 61.4, 61.3, 29.6, 20.9, 20.8,
0.5, 20.5.
enzyl-2,3,6-tri-O-acetyl-α-D-mannopyranoside (5c). A
nose (1c) (0.5 g, 2.78 mmol), Dy(OTf)3 (1.8 mg, 0.1
etic anhydride (1.1–2 equivalents per –OH of
was stirred at room temperature under nitrogen
on complete acetylation, the reaction mixture was
acuo to remove acetic anhydride. To a solution of the
(69.4 mL) was added Dy(OTf)3 (82.9 mg, 4.9 mol%)
.7 mg, 5 mol%) and stirred at 40 oC under nitrogen
r the completion of the reaction, the reaction mixture
under reduced pressure to remove MeOH. The residue
ethyl acetate, which was washed with brine, dried over
nd concentrated. The resulting residue was dissolved in
), followed by addition of CCl3CN (1.1mL, 11.1 mmol)
14.2 mmol) and stirred at room temperature. After the
reaction, the reaction mixture was filtered with a short
nsed with DCM and concentrated in vacuo. Without
e next step. Dy(OTf)3 (84.7 mg, 5 mol%) and p-methoxy
2 mL, 11.1 mmol) were added to a solution of residue in
nd stirred at reflux. After the completion of the reaction,
ure was extracted with DCM, dried over MgSO4 and
e residue was purified by column chromatography to
4 (515.7 mg, four steps 41% yield). [α]2D4 +57.18 (c 1.0,
: 2923, 2853, 1737, 1612, 1516, 1372, 1223, 1176,
00 MHz, CDCl3) δ 7.26–7.25 (m, 1H), 7.25–7.23 (m, 1H),
), 6.87–6.85 (m, 1H), 5.35 (dd, J = 10.0, 3.4 Hz, 1H),
, 5.24 (dd, J = 3.4, 1.8 Hz, 1H), 4.84 (d, J = 1.6 Hz, 1H),
Hz, 1H), 4.48 (d, J = 11.6 Hz, 1H), 4.27 (dd, J = 12.5,
(s, 3H), 2.12 (s, 3H), 2.10 (s, 3H), 2.02 (s, 3H), 1.96 (s,
00 MHz, CDCl3) δ 170.6, 170.0, 169.8, 169.7, 159.6,
1, 113.9, 96.3, 69.6, 69.3, 69.1, 68.5, 66.1, 62.4, 55.2,
20.7, 20.6; HRMS (ESI) [M + Na]+ Anal. Calcd for
.1512. Found: 491.1524.
(ESI) [M
951.2504.
+
Na]+ Anal. Calcd for C48H48O17NaS: 951.2488. Found:
Acknowledgements
This work is supported by grants from Ministry of Science and
Technology, Taiwan (Grant MOST 105-2113-M-005-006-MY2).
We also thank for the support from the National Chung Hsing
University
Keywords: Dysprosium(III) trifluoromethanesulfonate • Per-O-
acetylation • Anomeric deacetylation • Carbohydrates • One-pot
reaction
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P. Tiwari, R. Kumar, P. R. Maulik, A. K. Misra, Eur. J. Org. Chem. 2005,
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due in MeOH (69.4 mL) was added Dy(OTf)3 (82.9 mg,
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entrated under reduced pressure to remove MeOH. The
olved in ethyl acetate, which was washed with brine,
4, filtered and concentrated. The resulting residue was
(9.8 mL), followed by addition of CCl3CN (1.1 mL, 11.1
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the reaction, the reaction mixture was filtered with a
te, rinsed with DCM and concentrated in vacuo. The
ed by column chromatography to afford 2,3,4,6-tetra-O-
yranosyl trichloroacetimidate 4a (986.2 mg, three steps
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he Table of Contents (Please choose one layout)
PER
zed per-O-acetylation
Yi-Ling Yan, Jiun-Rung Guo, Chien-Fu
Liang*
elective
anomeric
ave been developed.
Page No. – Page No.
e
o
sugars can be
the peracetylated
Sequential Dy(OTf)3-Catalyzed
Solvent-Free Per-O-Acatylation and
Regioselective Anomeric De-O-
Acetylation of Carbohydrates
cetals by sequential
ep strategy. A further
e obtained hemiacetals
ssfully
sequential
to glycosyl imidates
Dy(OTf)3-catalyzed
PER
Author(s), Corresponding Author(s)*
TOC Graphic here; max. width: 11.5 cm; max. height: 2.5 cm))
Page No. – Page No.
Title
f Contents
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