Rapid glycosylations under extremely mild acidic conditions. Use of ammonium salts to activate glycosyl phosphites via P-protonation

Article abstract of DOI:10.1016/j.carres.2010.03.009

Trifluoromethanesulfonic acid salts of tertiary amines were employed as extremely mild acidic activators for rapid glycosylations. Glycosyl phosphite triesters bearing an acid-labile 4,4′-dimethoxytrityl (DMTr) group for transient protection worked as gly

Full text of DOI:10.1016/j.carres.2010.03.009

Carbohydrate Research 345 (2010) 1211–1215
Contents lists available at ScienceDirect
Carbohydrate Research
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Note
Rapid glycosylations under extremely mild acidic conditions. Use of
ammonium salts to activate glycosyl phosphites via P-protonation
*
Fumiko Matsumura, Shiro Tatsumi, Natsuhisa Oka, Takeshi Wada
Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Bioscience Building 702, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2009
Received in revised form 16 February 2010
Accepted 10 March 2010
Available online 3 April 2010
Trifluoromethanesulfonic acid salts of tertiary amines were employed as extremely mild acidic activators
for rapid glycosylations. Glycosyl phosphite triesters bearing an acid-labile 4,40-dimethoxytrityl (DMTr)
group for transient protection worked as glycosyl donors effectively in the presence of the activators
to afford the corresponding disaccharides in good yields without loss of the DMTr group.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Glycosylation
Glycosyl phosphites
Ammonium salts
P-Protonation
4,40-Dimethoxytrityl group
Oligosaccharides and their conjugates with other biomolecules
(glycoconjugates) play important roles in a wide variety of biolog-
ical processes and extensive studies are currently in progress to
clarify the whole picture.1–3 Oligosaccharides and glycoconjugates
with defined structures are indispensable for such studies.4–6
Chemical synthesis is a major approach to obtain these materials
and advantageous because it can provide pure materials in suffi-
cient quantities at relatively low costs. Oligosaccharides and glyco-
conjugates containing chemical modifications at defined sites are
also available by this approach and used as probes.7 In addition
to the applications to glycobiology, chemically synthesized frag-
ments of these carbohydrates and their modified analogues have
been applied to therapeutic studies.8,9
glycosyl donors. The results of this study are described in this
paper.
Glycosyl phosphite triesters are one of the most reactive glyco-
syl donors developed so far and have been applied to the synthesis
of a wide variety of oligosaccharides and glycoconjugates.10 Since
the early reports on their use as glycosyl donors,10a–c strong Lewis
acids, typically trimethylsilyl trifluoromethanesulfonate (TMSOTf),
10a,b have been used for their activation. On the other hand, some
research groups have reported that the glycosyl phosphites can be
activated under mild acidic conditions.10g–j For example, Hashim-
oto et al. have reported that glycosyl phosphites can be activated
by 2,6-tert-butylpyridinium iodide (DTBPI) to give the correspond-
ing O-glycosylation products in good yields.10g However, the rela-
tively long reaction time would be a bottleneck for the synthesis of
rather complex oligosaccharides and glycoconjugates. As they have
described, the activation of glycosyl phosphites by DTBPI generates
the corresponding glycosyl iodides as active intermediates. The
resultant glycosyl iodides have modest reactivity to alcohols and
react to afford the final glycosylation products typically within
24–48 h under standard reaction conditions.10g We anticipated
that the reactions of the glycosyl phosphites would be much faster
if they are activated only by P-protonation under mild acidic
conditions in the absence of any nucleophilic catalysts. It has been
reported that glycosyl phosphite triesters can be activated via
P-protonation by using strong Brønsted acids, such as TfOH and
Tf2NH,10d,k but it was not clear if the glycosyl phosphites would
work as glycosyl donors effectively with a much weaker Brønsted
acid, such as tertiary ammonium salts, without any nucleophilic
catalysts (Fig. 1).
Many of oligosaccharides and glycoconjugates have rather com-
plex structures. The complexity comes from the diversity of mono-
saccharides, which have multiple hydroxy groups and can be
connected to each other at different positions through a- or b-gly-
cosyl bonds. To synthesize these compounds, the development of
efficient glycosylation reactions that can be performed under mild
reaction conditions is strongly required so that a variety of orthog-
onal protecting groups can be used.4 With this background, we
sought to develop a glycosylation reaction that could be performed
under extremely mild acidic conditions and found that salts of ter-
tiary amines consisting of less-nucleophilic components were use-
ful for rapid glycosylations using glycosyl phosphite triesters as
* Corresponding author. Tel./fax: +81 4 7136 3612.
E-mail address: wada@k.u-tokyo.ac.jp (T. Wada).
0008-6215/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.03.009

1212
F. Matsumura et al. / Carbohydrate Research 345 (2010) 1211–1215
R+1
O
R2 N H
OR'
R3
O
O
R'OH
OR
OR
OR
H
OR
+
+
O P
O P
H
RO P OR
O
Figure 1. Glycosylation with tertiary ammonium salts via P-protonated glycosyl phosphites.
Glycosyl phosphites with an acid-labile 4,40-dimethoxytrityl
(DMTr) group at the O-6 position (5, 6) were synthesized as glyco-
syl donors for this study via regioselective tritylation of the O-6-
H TfO−
N+ CN
Et
N+ H TfO−
N+ H X−
Et
NC
position of reducing sugars (1,11 12) in the presence of silver ni-
2
trate and subsequent O-1 phosphitylation (Scheme 1). The DMTr
group is routinely used for transient protection of primary hydroxy
groups in nucleic acid synthesis13 for its advantages, such as the
regioselective protection of primary hydroxy groups, stability un-
der various reaction conditions, acid lability for facile deprotection
under mild acidic conditions, and the strong UV–vis absorption of
the resultant DMTr cation, which is used for quantitation.14 De-
spite these advantages, the DMTr group has been rarely used for
the synthesis of oligosaccharides,11,15 mainly because of its incom-
patibility with the common glycosylation conditions using strong
Brønsted or Lewis acids. The development of glycosylation reac-
tions which proceed rapidly under mild acidic conditions would al-
low the synthesis of oligosaccharides using more extensive
protecting groups than those currently used; the DMTr group
would be representative of acid-labile protecting groups. We also
expected that the bulky DMTr group at the 6-position might work
9: X− = TfO−
7
8
10: X− = I−
Figure 2. Tertiary ammonium salts containing less-nucleophilic triflate anion (7–9)
or highly-nucleophilic iodide anion (10).
disaccharides 13 and 14 were isolated in good to excellent yields
(entries 1–5 and 7). The reactions were slightly slower in polar sol-
vents (entries 3 and 4) than in less polar CH2Cl2 (entry 2). In sharp
contrast, the glycosylation proceeded very slowly when promoted
by N,N-diethylanilinium iodide 10 due to the formation of the gly-
cosyl iodide intermediate 19, though the
a-selectivity was excel-
lent as reported in the literature (entry 6).10g The formation of
the glycosyl iodide 19 from 5 and 10 was also confirmed by 1H
NMR.21 Removal of the O-6-DMTr group of the fully protected
disaccharides 13 and 14 was achieved by using 3 vol % dichloroace-
tic acid in CH2Cl2 within 2 min in the presence of Et3SiH as a scav-
enger of the liberated DMTr cation22 to afford the detritylated
disaccharides 1623 and 17,24 respectively, virtually quantitatively
(entries 5 and 7). In the cases of the sterically more-hindered gly-
cosyl acceptor 12, the reaction was completed within 5 min by
using the activator 8 (entry 8), whereas it was sluggish when the
activator 9 was used (entry 9). The resultant disaccharide 1511
was detritylated to afford 1825 in modest yields (entries 8 and 9).
as an a
-directing group in glycosylation reactions.11,16
Trifluoromethanesulfonic acid salts of tertiary amines (Fig. 2, 7–
9
17) were employed as activators for the following reasons: (1) the
activators must have a mild but sufficient acidity to protonate the
phosphorous atom of phosphite triesters and must be less-nucleo-
philic so that the formation of stable N-glycosides, such as pyridi-
nium glycosides,18 would be avoided. The suitable acidity and
extremely low nucleophilicity of 7 and 8 have already been dem-
onstrated by using them to activate P-stereogenic diastereopure
phosphoramidite derivatives via protonation to give the corre-
sponding phosphite derivatives in a stereospecific manner.17b,19
The N,N-diethylanilinium salt 9 was also employed because of its
modest acidity and low nucleophilicity. (2) The counter anion must
also be less nucleophilic. TfOꢀ would be a suitable counter anion
because the resultant glycosyl trifluoromethanesulfonates have
been reported to be extremely reactive even at ꢀ78 °C and act as
the corresponding oxocarbenium cations at ambient tempera-
tures.20 An N,N-diethylanilinium salt 10 containing a nucleophilic
iodide anion was used as a control.
Only the
a
-isomer of 18 was obtained in both of these reactions
most likely due to the
a
-directing effect of the O-6-DMTr group.
In summary, rapid glycosylations were achieved with glycosyl
phosphites as glycosyl donors and less-nucleophilic trifluorometh-
anesulfonic acid salts of tertiary amines as activators. The absence
of nucleophilic catalysts was essential for rapid reactions. Glycosyl
donors having an acid-labile DMTr group were compatible with the
present reaction conditions, indicating that a wide range of acid-la-
bile substrates and protecting groups can be used in this method.
1. Experimental
Glycosylation reactions of appropriately protected monosaccha-
rides 11 and 12 were then carried out by using the glycosyl donors
(5, 6) and the activators (7–10) (Table 1). The glycosylations of the
sterically less-hindered 11 were completed within 5–10 min when
the less-nucleophilic activators 7–9 were used and the desired
1.1. General methods
IR spectra were recorded on a JASCO FT/IR-480 Plus spectropho-
tometer. NMR spectra were recorded on a Varian Mercury 300. 1H
ODMTr
OH
ODMTr
R2
R2
O
R2
O
O
(a)
(b)
BnO
BnO
BnO
BnO
BnO
BnO
OEt
OEt
O P
OH
OH
R1
R1
R1
1: R1 = OBn, R2 = H
2: R1 = H, R2 = OBn
3: R1 = OBn, R2 = H, 81%
4: R1 = H, R2 = OBn, 88%
5: R1 = OBn, R2 = H, 77%
(α:β = 58:42)
6: R1 = H, R2 = OBn, 55%
(α:β = 93:8)
Scheme 1. Synthesis of glycosyl donors 5 and 6. Reagents and conditions: (a) DMTrCl, Et3N, AgNO3, THF–DMF (1:1, v/v); (b) (EtO)2PCl, Et3N, CH2Cl2.

F. Matsumura et al. / Carbohydrate Research 345 (2010) 1211–1215
1213
Table 1
Glycosylation reactions using glycosyl phosphites 5, 6, and acidic activators 7–10
OR5
OR5
OR3
R2
O
7−10
O
O
R4O
BnO
BnO
BnO
BnO
OEt
+
O
BnO
rt
O P
O
R1
BnO
BnO
(OBn)3
OEt
OMe
OMe
5: R1 = OBn, R2 = H, R5 = DMTr
6: R1 = H, R2 = OBn, R5 = DMTr
11: R3 = H, R4 = OBn
12: R3 = OBn, R4 = H
13−15: R5 = DMTr
16−18: R5 = H
DCA, Et3SiH
Entry
Substrate
Activator
Time
Solvent
Isolated yield of 13–15/% (
a
:b)a
Isolated yield of 16–18/% (a
:b)a
1b
2c
3c
4c
5b
6b
7b
8e
9e
5
5
5
5
5
5
6
5
5
11
11
11
11
11
11
11
12
12
7
8
8
8
9
10
9
8
5 min
5 min
10 min
10 min
5 min
120 h
5 min
5 min
1 h
CH2Cl2
CH2Cl2
CH3CN
1,4-Dioxane
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
13
13
73 (5:1)
16
16
16
16
16
16
17
18
18
—
—
—
—
83 (4:1)
81 (2:3)
82 (6:1)
91 (5:1)
13
13
13
13
14
15
15
86f (5:1)
—
25 (
71d
30 (
—
a
)
70f (2:1)
a
)
58g
43g
(
(
a
a
)
)
9
a
b
c
d
e
f
Anomeric ratios were determined by 1H NMR.
Glycosyl donor/acceptor/activator molar ratio = 2/1/2.
Glycosyl donor/acceptor/activator molar ratio = 1/0.8/2.
Anomeric ratio was not determined.
Glycosyl donor/acceptor/activator molar ratio = 2/1/4.
Yield from 11.
Yield from 12 without purification of 15.
g
OR5
R2
OR5
O
BnO
ODMTr
BnO
OBn
O
O
R1
BnO
BnO
BnO
O
O
BnO
BnO
O
O
BnO
BnO
BnO
BnO
BnO
BnO
I
OMe
OMe
15: R5 = DMTr
18: R5 = H
13: R1 = OBn, R2 = H, R5 = DMTr
14: R1 = H, R2 = OBn, R5 = DMTr
16: R1 = OBn, R2 = H, R5 = H
17: R1 = H, R2 = OBn, R5 = H
19
NMR spectra were obtained at 300 MHz with tetramethylsilane
(TMS) (d 0.0) as an internal standard in CDCl3. 13C NMR spectra
were obtained at 75.5 MHz with CDCl3 as an internal standard (d
77.0) in CDCl3. 31P NMR spectra were obtained at 121.5 MHz with
85% H3PO4 (d 0.0) as an external standard. ESI mass spectra were
recorded on an Applied Biosystems QSTAR. All the reactions were
conducted under an inert atmosphere. Silica gel column chroma-
concentrated under reduced pressure. The residue was purified
by column chromatography [hexane–AcOEt–Et3N (70:30:1, v/v/
v)] on silica gel to afford 311 (0.66 g, 81%).
1.3. 6-O-Dimethoxytrityl-2,3,4-tri-O-benzyl-D-mannopyranose
(4)
tography was carried out using Kanto Silica Gel 60 N (40–50
l
m).
Et3N (0.42 mL, 3.0 mmol) was added to a solution of 212 (0.46 g,
1.0 mmol), silver nitrate (0.18 g, 1.05 mmol), and DMTrCl (0.36 g,
1.05 mmol) in dry THF–DMF (1:1, v/v, 2 mL) at 0 °C. The reaction
mixture was stirred for 20 min at 0 °C, and the reaction was
quenched by the addition of MeOH (5 mL). The mixture was diluted
with CH2Cl2 (20 mL) and filtered. The filtrate was then washed with
satd aq NaHCO3 (3 ꢁ 10 mL), dried over Na2SO4, filtered, and con-
centrated under reduced pressure. The residue was purified by col-
umn chromatography [hexane–AcOEt–Et3N (30:10:0.4–20:10:0.3,
v/v/v)] on silica gel to afford 4 (0.67 g, 88%). Colorless form; IR
(KBr, cmꢀ1): 3434, 3061, 3031, 2931, 1607, 1583, 1509, 1454,
1363, 1301, 1251, 1177, 1155, 1098, 913, 829, 738, 698, 584; 1H
Analytical TLC was performed on Merck Kieselgel 60-F254 plates.
1.2. 6-O-Dimethoxytrityl-2,3,4-tri-O-benzyl-D-glucopyranose (3)
Et3N (0.70 mL, 5.0 mmol) was added to a solution of 111 (0.49 g,
1.1 mmol), silver nitrate (0.17 g, 1.0 mmol), and DMTrCl (0.34 g,
1.0 mmol) in dry THF–DMF (1:1, v/v, 2 mL) at 0 °C. The reaction
mixture was stirred at 0 °C for 50 min and warmed to rt. After stir-
ring for 20 min, silver nitrate (0.020 g, 0.12 mmol) and DMTrCl
(0.036 g, 0.11 mmol) were added, and the reaction mixture was
stirred for 100 min at rt. Then additional silver nitrate (0.035 g,
0.20 mmol) and DMTrCl (0.067 g, 0.20 mmol) were added, and
the reaction mixture was stirred for 40 min at rt. Then the reaction
was quenched by the addition of MeOH (5 mL). The mixture was
diluted with CHCl3 and filtered. The filtrate was then washed with
satd aq NaHCO3 (3 ꢁ 10 mL), dried over Na2SO4, filtered, and
NMR (CDCl3): d 7.58–6.68 (m, Ar), 5.30 (s,
bH-1, CH2Ph), 4.19–3.20 (m, H-2–6, bH-2–6, b-OH, OMe), 2.83
(d,
-OH); 13C NMR (CDCl3): d 158.3 (C), 158.2 (C), 145.0 (C),
aH-1), 5.22–4.25 (m,
a
a
138.7 (C), 138.5 (C), 138.4 (C), 138.2 (C), 138.1 (C), 138.0 (C),
136.4 (C), 136.3 (C), 136.0 (C), 130.1 (CH), 130.2 (CH), 130.3 (CH),

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F. Matsumura et al. / Carbohydrate Research 345 (2010) 1211–1215
128.5–127.4 (m, CH), 126.5 (CH), 113.0 (CH), 93.5 (CH,
a
C-1), 92.6
C11H16F3NO3S: C, 44.14; H, 5.39; N, 4.68. Found: C, 44.08; H,
(CH, bC-1), 85.7 (C), 85.6 (C), 83.0 (CH), 79.5 (CH), 75.8 (CH),
75.1–74.4 (m, CH, CH2), 72.9 (CH2), 72.7 (CH2), 72.4 (CH2), 72.1
(CH), 62.6 (CH2), 62.2 (CH2), 55.1 (CH3); ESIMS m/z: [M+Na]+ calcd
for C48H48NaO8þ: 775.3247; found: 775.3241.
5.48; N, 4.52.
1.7. N,N-Diethylanilinium iodide (10)
A 57% (w/w) aqueous solution of hydrogen iodide (1.4 mL,
10 mmol) was added dropwise to a stirred solution of N,N-diethyl-
aniline (1.6 mL, 10 mmol) in dry Et2O (5.0 mL) at 0 °C. The resul-
tant precipitate was collected by filtation, washed with dry Et2O
(20 mL), and dried under vacuum to afford 10 (1.9 g, 70%) as an
off-white solid; IR (KBr, cmꢀ1): 3500, 2973, 2906, 2867, 2738,
2705, 2650, 2456, 1596, 1495, 1479, 1418, 1269, 1155, 1017; 1H
NMR (CDCl3): d 11.5 (br, 1H, NH+), 7.84–7.82 (m, 2H, Ar), 7.62–
7.30 (m, 3H, Ar), 3.83–3.71 (m, 2H, CH2CH3), 3.53–3.39 (m, 2H,
CH2CH3), 1.31 (t, 6H, J = 72 Hz); 13C NMR (CDCl3): d 136.0 (C),
130.5 (CH), 122.6 (CH), 54.1 (CH2), 10.2 (CH3); Anal. Calcd for
C10H16NI: C, 43.34; H, 5.82; N, 5.05. Found: C, 43.15; H, 5.86; N,
4.80.
1.4. Diethyl 6-O-dimethoxytrityl-2,3,4-tri-O-benzyl-D-
glucopyranosyl phosphite (5)
Et3N (0.21 mL, 1.5 mmol) and diethyl chlorophosphite
(0.080 mL, 0.55 mmol) were added to a solution of 3 (0.37 g,
0.50 mmol) in dry CH2Cl2 (5.0 mL) at rt and the mixture was stirred
for 20 min at rt. The reaction was then quenched by the addition of
satd aq NaHCO3 (5 mL). The aqueous layer was separated and ex-
tracted with CH2Cl2 (20 mL). The organic layers were combined,
dried over Na2SO4, filtered, and concentrated under reduced pres-
sure. The residue was purified by column chromatography [hex-
ane–ethyl acetate–pyridine (70:10:0.4, v/v/v)] on silica gel to
give 5 (0.33 g, 77%,
a
:b = 58:42). Colorless foam: IR (KBr, cmꢀ1):
3061, 3011, 2929, 2835, 1607, 1582, 1508, 1454, 1388, 1356,
1.8. General protocol for glycosylation (13–15)
1300, 1250, 1176, 1149, 1071, 1028, 829, 698; 1H NMR (CDCl3): d
7.53–6.74 (m, Ar), 5.72 (dd, J1,2 = 2.7 Hz, JH–P = 8.7 Hz,
5.04–4.66 (m, bH-1, CH2Ph), 4.35–4.29 (m, CH2Ph), 4.06–3.22 (m,
H-2–H-6, bH-2–H-6, POCH2CH3, OMe), 1.30–1.16 (m, POCH2CH3);
31P NMR (CDCl3): d 140.8 (s, b), 139.7 (s, ); 13C NMR (CDCl3): d
97.2 (d, JC–P = 15 Hz, bC-1), 91.2 (d, JC–P = 15 Hz, C-1); ESIMS m/
z: [M+Na]+ calcd for C52H57NaO10þ: 895.3582; found: 895.3590.
a
H-1),
The acidic activator (7–9 or 10) was added to a solution (2.0 mL)
of glycosyl donor (5 or 6) (0.10 mmol) and glycosyl acceptor (11 or
12) (0.050 mmol) at rt. The reaction mixture was stirred until
either the glycosyl donor or the glycosyl acceptor was completely
consumed (TLC). The reaction was then quenched by the addition
of satd aq NaHCO3 (5.0 mL), and the mixture was extracted with
CH2Cl2 (25 mL). The organic layer was separated, washed with satd
aq NaHCO3 (25 mL ꢁ 3), dried over Na2SO4, filtered, and concen-
trated under reduced pressure. The residue was purified by column
chromatography [hexane–ethyl acetate (7:1 to 5:1, v/v)] on silica
gel.
a
a
a
1.5. Diethyl 6-O-dimethoxytrityl-2,3,4-tri-O-benzyl-D-
mannopyranosyl phosphite (6)
Synthesis of 6 from 4 (0.37 g, 0.50 mmol) was conducted follow-
ing a protocol similar to that used for the synthesis of 5. Purification
by column chromatography [hexane–ethyl acetate–pyridine
1.9. Methyl 6-O-(6-O-dimethoxytrityl-2,3,4-tri-O-benzyl-
D-
(70:10:0.4, v/v/v)] on silica gel to give 6 (0.24 g, 55%,
a:b = 92:8).
glucopyranosyl)- 2,3,4-tri-O-benzyl- -glucopyranoside (13)
a-D
Colorless oil; IR (KBr, cmꢀ1): 3061, 3030, 2976, 2931, 2835, 1607,
1582, 1509, 1454, 1387, 1361, 1300, 1250, 1176, 1154, 1096,
1028, 986, 830, 699; 1H NMR (CDCl3): d 7.55–6.70 (m, 28H, Ar),
5.64 (dd, 1H, J1,2 = 1.8 Hz, JH–P = 8.4 Hz, H-1), 4.90–4.63 (m, 5H,
CH2Ph), 4.28 (d, 1H, CH2Ph), 4.23 (t, 1H, J = 9.9 Hz, H-4), 3.97–3.70
(m, 15H, H-2–H-5, POCH2CH3, OMe), 3.51 (dd, 1H, J5,6 = 1.2 Hz,
J6,6 = 9.9 Hz, H-6), 3.28 (dd, 1H, J5,6 = 3.9 Hz, J6,6 = 9,9 Hz, H-6),
1.24–1.10 (q, 6H, POCH2CH3); 31P NMR (CDCl3): d 139.1 (s); 13C
NMR (CDCl3): d 158.2 (C), 145.1 (C), 138.5 (C), 138.2 (C), 136.4
(C), 136.0 (C), 130.3 (CH), 130.1 (CH), 128.3–126.5 (m, CH), 113.0
(CH), 112.9 (CH), 91.7 (d, JC–P = 11.8 Hz, CH, C-1), 85.5 (C), 79.2
(CH), 76.5 (d, JC–P = 3.2 Hz, CH), 75.1 (CH2), 74.7 (CH), 72.9 (CH),
72.6 (CH2), 72.5 (CH2), 62.1 (CH2), 58.4 (m, CH2), 55.1 (CH3), 16.8
(d, JC–P = 4.9 Hz, CH3); ESIMS m/z: [M+Na]+ calcd for
C52H57NaO10þ: 895.3582; found: 895.3586.
Colorless foam; IR (KBr, cmꢀ1): 3043, 2931, 1612, 1508, 1454,
1365, 1250, 1211, 1173, 1070, 1029, 830, 698; 1H NMR (CDCl3): d
7.55–6.70 (m, Ar), 5.10–4.20 (m, CH2Ph,
3.37 (m,
bH-2II– bH-6aII, bH-2I– bH-6I, OMe), 3.25 (dd,
J5,6 = 3.9 Hz, J6,6 = 10 Hz, bH-6bII), 3.14 (dd, J5,6 = 3.9 Hz, J6,6 = 10 Hz,
H-6bII); 13C NMR (CDCl3): d 103.8 (CH, bC-1II), 98.3 (CH, bC-1I),
a a
bH-1II, bH-1I), 4.06–
a
a
a
a
a
97.9 and 97.1 (CH,
a a
C-1I, C-1II); ESIMS m/z: [M+Na]+ calcd for
C76H78NaO13þ: 1221.5335; found: 1221.5329.
Anomeric ratios of 13 in Table 1 were determined by the inte-
gral ratios of the 1H signals at d 3.25 (bH-6II) and d 3.14 ( H-6II).
a
1.10. Methyl 6-O-(6-O-dimethoxytrityl-2,3,4-tri-O-benzyl-
a-D-
glucopyranosyl)-2,3,4-tri-O-benzyl- -glucopyranoside (13a)
a-
D
Colorless foam; IR (KBr, cmꢀ1): 3087, 3062, 3030, 3003, 2928,
2835, 1607, 1583, 1509, 1454, 1359, 1301, 1250, 1211, 1176,
1072, 1029, 829, 791, 698; 1H NMR (CDCl3): d 7.55–6.70 (m, 43H,
Ar), 5.08 (d, 1H, J = 3.3 Hz, H-1II), 4.98–4.54 (m, 12H, CH2Ph, H-
1I), 4.28 (d, 1H, J = 11 Hz, CH2Ph), 4.02–3.60 (m, 15H, H-2II–H-5II,
H-3I–H-6I, OMe), 3.46–3.36 (m, 5H, H-2I, H-6aII, OMe), 3.14 (dd,
1H, H-6bII, J5,6 = 3.9 Hz, J6,6 = 10 Hz); 13C NMR (CDCl3): d 158.3
(C), 145.0 (C), 138.8 (C), 138.7 (C), 138.6 (C), 138.3 (C), 138.1 (C),
136.3 (C), 135.9 (C), 130.2 (CH), 130.1 (CH), 128.4–126.6 (m, CH),
1.6. N,N-Diethylanilinium trifluromethanesulfonate (9)
Trifluoromethanesulfonic acid (1.8 mL, 20 mmol) was added
dropwise to
a stirred solution of N,N-diethylaniline (3.2 mL,
20 mmol) in dry Et2O (5.0 mL) at 0 °C. The reaction mixture was
kept under ꢀ30 °C until the formation of crystalline solid was ob-
served. The resultant crystals were collected by filtration, washed
with dry Et2O (20 mL), and dried under vacuum to afford 9
(5.3 g, 89%) as a colorless solid; mp 65.5–66.0 °C; IR (KBr, cmꢀ1):
3502, 3043, 2987, 2687, 1628, 1495, 1277, 1244, 1167, 1030; 1H
NMR (CDCl3): d 10.3 (br, 1H, NH+), 7.62–7.28 (m, 5H, Ar), 3.81–
3.71 (m, 2H, CH2CH3), 3.58–3.44 (m, 2H, CH2CH3), 1.19 (t, 6H,
J = 75 Hz); 13C NMR (CDCl3): d 136.2 (C), 130.6 (CH), 122.2 (CH),
120.3 (q, J = 319 Hz), 54.4 (CH2), 10.2 (CH3); Anal. Calcd for
113.0 (CH), 112.9 (CH), 97.91 (CH,
a a aC-
C-1I or C-1II), 97.1 (CH,
1I or C-1II), 85.5 (C), 82.1 (CH), 81.8 (CH), 80.3 (CH), 80.1 (CH),
a
78.0 (CH), 77.7 (CH), 75.8 (CH2), 75.7 (CH2), 75.0 (CH2), 74.8
(CH2), 73.4 (CH2), 72.3 (CH2), 70.5 (CH), 70.4 (CH), 65.8 (CH2),
62.1 (CH2), 55.1 (CH3), 55.0 (CH3); ESIMS m/z: [M+Na]+ calcd for
C76H78NaO13þ: 1221.5335; found: 1221.5336.

F. Matsumura et al. / Carbohydrate Research 345 (2010) 1211–1215
1215
1.11. Methyl 6-O-(6-O-dimethoxytrityl-2,3,4-tri-O-benzyl-
D
-
(m, CH), 101.5 (CH, C-1II), 97.8 (CH, C-1I), 82.2 (CH), 82.1 (CH),
79.7 (CH), 77.3 (CH), 75.7 (CH), 75.3 (CH2), 74.8 (CH), 74.7 (CH2),
73.8 (CH2), 73.6 (CH), 73.6 (CH2), 73.4 (CH2), 71.7 (CH2), 69.7
(CH), 68.4 (CH2), 62.5 (CH2), 55.1 (CH3); ESIMS m/z: [M+Na]+ calcd
for C55H60NaO11þ: 919.4028; found: 919.4022.
mannopyranosyl)-2,3,4-tri-O-benzyl- -glucopyranoside (14)
a-D
Colorless foam; IR (KBr, cmꢀ1): 3043, 3026, 2929, 1606, 1508,
1454, 1300, 1250, 1211, 1176, 1085, 1029, 829, 698; 1H NMR
(CDCl3): d 7.55–6.70 (m, 43H, Ar), 5.05–3.10 (m, 35H, CH2Ph,
a
bH-1II– bH-6aII, bH-1I– bH-6I, OMe); 13C NMR (CDCl3):
a a a d
Acknowledgments
101.5 (CH, bC-1II), 98.0, 97.7, 97.7 (CH,
a
C-1I and
a
C-1II); ESIMS
m/z: [M+Na]+ calcd for C76H78NaO13
:
1221.5335; found:
þ
We thank Professor Kazuhiko Saigo (University of Tokyo) for
helpful suggestions. We also thank the Futaba Electronics Memo-
rial Foundation for the scholarship to F.M. This work was finan-
cially supported by MEXT Japan.
1221.5336.
1.12. Methyl 4-O-(6-O-dimethoxytrityl-2,3,4-tri-O-benzyl-
D-
glucopyranosyl)-2,3,6-tri-O-benzyl- -glucopyranoside (15)
a-D
Supplementary data
Synthesis of 15 from 5 (0.088 g, 0.10 mmol) and 12 (0.023 g,
0.050 mmol) was conducted following the general protocol for gly-
cosylation. Purification by silica gel column chromatography [tolu-
ene–AcOEt–Et3N (18:1:0.19 v/v)] and preparative thin layer
chromatography [hexane–AcOEt–Et3N (5:1:0.06–3:1:0.04 v/v/v)]
afforded 1511 (0.018 g, 30%). The 1H NMR data were identical to
those reported in the literature.11 We synthesized the detritylated
disaccharide 18 without isolation of 15 as described above because
of its poor chromatographic separation from some byproducts.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2010.03.009.
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1.14. Methyl 6-O-(2,3,4-tri-O-benzyl-
2,3,4-tri-O-benzyl- -glucopyranoside (17
(2,3,4-tri-O-benzyl-b- -mannopyranosyl)-2,3,4-tri-O-benzyl-
-glucopyranoside (17b)
a
-
D
-mannopyranosyl)-
a-
D
a
), methyl 6-O-
D
a-
D
Spectral data for 17a
: 1H NMR spectrum was in good agreement
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1496, 1454, 1361, 1208, 1149, 1092, 1028, 698; 1H NMR (CDCl3):
d 7.45–7.15 (m, 30H, Ar), 5.01–4.47 (m, 14H, CH2Ph, H-1II, H-1I),
3.98–3.31 (m, 15H, H-2II–H-6II, H-2I–H-6I, OMe), 1.85 (br, 1H,
OH); 13C NMR (CDCl3): d 138.5 (C), 138.4 (C), 138.3 (C), 138.2 (C),
138.1 (C), 138.0 (C), 128.5–127.5 (m, CH), 98.4 (CH, C-1II), 97.8
(CH, C-1I), 82.1 (CH), 79.9 (CH), 79.5 (CH), 77.5 (CH), 75.8 (CH2),
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(CH2), 72.2 (CH), 72.1 (CH2), 69.6 (CH), 65.8 (CH2), 62.2 (CH2),
55.1 (CH3); ESIMS m/z: [M+Na]+ calcd for C55H60NaO11
:
þ
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13H, CH2Ph, H-1I), 4.09–3.68 (m, 8H, H-3I, H-5I, H-6aI, H-1II, H-
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OMe), 2.15 (t, 1H, J = 7.0 Hz, OH); 13C NMR (CDCl3): d 138.7 (C),
138.4 (C), 138.2 (C), 138.1 (C), 138.0 (C), 138.0 (C), 128.5–127.5
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