A convenient synthesis of the core trisaccharide of the N-glycans

Article abstract of DOI:10.1016/j.tetlet.2011.04.060

A convenient synthesis of the core trisaccharide of the N-glycans was described. Orthogonal one-pot glycosylation of three monosaccharide building blocks was performed to furnish β-glucosyl chitobiose, which was then transformed to β-mannosyl chitobiose b

Full text of DOI:10.1016/j.tetlet.2011.04.060

Tetrahedron Letters 52 (2011) 3320–3323
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
A convenient synthesis of the core trisaccharide of the N-glycans
Zhichao Lu a, Ning Ding b, Wei Zhang b, Peng Wang a, Yingxia Li b,
⇑
a School of Medicine and Pharmacy, Ocean University of China, Qingdao 266003, China
b School of Pharmacy, Fudan University, Shanghai 201203, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 15 February 2011
Revised 6 April 2011
Accepted 15 April 2011
Available online 23 April 2011
A convenient synthesis of the core trisaccharide of the N-glycans was described. Orthogonal one-pot gly-
cosylation of three monosaccharide building blocks was performed to furnish b-glucosyl chitobiose,
which was then transformed to b-mannosyl chitobiose by intramolecular epimerization of the C-2 posi-
tion of the b-glucoside. The key glucosyl donor 7c with differentiated 2,3-OH was prepared following the
4,6-O-benzylidene-protected 1,2-orthoester strategy.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
N-Glycan
One-pot glycosylation
Core trisaccharide
1,2-Orthoester
Glycoproteins with N-glycans found on cell surfaces and in the
blood serum play important roles in many biological events such
as cell–cell adhesion, immune system modulation, and signal
transduction. Subtle changes of the carbohydrate moieties may re-
sult in completely altered functionality of the glycoproteins. There-
fore, asparagine linked N-glycans have gained intensive
investigations.1 Actually, only a few of these oligosaccharides can
be isolated from natural sources due to their microheterogeneity.2
These circumstances have stimulated the chemical synthesis of N-
glycans as a method to provide sufficient quantities for further re-
search.3–9 All types of N-glycans comprise a common core struc-
ester strategy, we prepared the core trisaccharide 2 for the
synthesis of N-glycan octasaccharide of the bisecting type
(Scheme 1) in our previous work.14 The key intermediate orthoes-
ter B (Scheme 2) was designed for the construction of the trisac-
charide 2 and the following assembly of octasaccharide 1. The
1,2-orthoester unit allowed the differentiation of 2,3-OH in b-D-
glucopyranosyl moiety. While the cyclic 4,6-O-benzylidene per-
mitted the differentiation of OH-3 from OH-4 and OH-6, which
facilitated the introduction of three antennas. However, this ap-
proach still needs to be improved in two aspects. Firstly, step by
step glycosylation for the trisaccharide construction resulted in
multistep protecting manipulation and intermediate purification.
Secondly, since thioglycoside G and azide acceptor F were valuable
ture, the b-1,4-linked D-mannosyl chitobiose unit, suggesting that
a modular approach based on this scaffold could be particularly
useful.10 An efficient assembly of this appropriately protected core
structure will facilitate the development of practical synthesis of
N-linked glycoproteins. (Scheme 1) Thus, a great deal of effort
has been devoted to the synthesis of this core trisaccharide11–14
One part of the work for the synthesis of the core trisaccharide
is the daunting construction of b-mannosyl glycosidic bond. Sev-
eral methods have been developed for b-mannoside synthesis.
HO
O
HO
HO
HO
O
HO
O
NHAc
HO
HO
HO
O
O
HO
HO
O
O
HO
H2N
O
OH
O
OH
O
OH
NHAc
OH
O
HO
H
D
-mannoside coupling methods,15 the intra-
O
O
These include direct b-
N
O
HO
HO
HO
HO
HO
molecular aglycon delivery strategy,16 sequential oxidation/reduc-
O
NHAc
NHAc
O
O
1
tion routes17 as well as epimerization of b-
D-glucopyranosides
NHAc
methods,12,18 all of which have their respective advantages and
shortcomings. Owing to usually excellent yield and complete stere-
oselectivity, intramolecular epimerization of b-glucosides to b-
mannosides can be regarded as a reasonably safe way for the con-
struction of b-mannosides.13 Based on this method and 1,2-ortho-
OBn
OBn
OH
O
O
O
Ph
O
O
N3
NPhth
O
O
HO
BnO
BnO
NPhth
2
⇑
Corresponding author. Tel./fax: +86 21 51980127.
E-mail address: liyx417@fudan.edu.cn (Y. Li).
Scheme 1. Chemical structures of octasaccharide-asparagine 1 and core trisaccha-
ride 2.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.04.060

Z. Lu et al. / Tetrahedron Letters 52 (2011) 3320–3323
3321
2
O
O
Ph
O
O
O
O
LevO
a
O
Ph
b
SEt
Ph
SEt
O
O
OBn
O
O
O
OBn
O
HO
LevO
O
OH
OLev
Ph
O
O
O
N3
O
9
H3COCC2H4 OCH3
10
AcO
BnO
BnO
11
NPhth
OH
A
NPhth
O
O
O
Ph
O
O
O
Differentiation of
OH-2 from OH-3
O
Ph
O
e
O
d
Ph
O
HO
Ph
c
O
O
O
HO
RO
RO
OBn
OBn
O
O
HO
O
LevO
OH
OLev
O
O
H3COCC2H4
OCH3
NH
O
N3
NPhth
ClH2C
O
13 R = Bz
14
BnO
BnO
NPhth
12
R = Ac
B
O
O
Ph
O
f
OBn
O
OBn
O
RO
O
Ph
O
O
SEt
HO
LevO
O
N3
O
CCl3
ClAcO
BnO
BnO
OClAc
NPhth
NPhth
7b R = Bz
7c R = Ac
C
D
Step by step
glycosylation
OBn
O
OBn
O
OBn
O
Scheme 5. Reagents and conditions: (a): LevOH, EDCꢀHCl, DMAP, DCM, 2 h, 42 °C,
95%; (b): NBS, TMSOTf, DCM:CH3OH = 50:1, 4 Å MS, 0 °C, 0.5 h, (c) CH3ONa, CH3OH,
83% for two steps; (d): for compound 13: (1) BzCl, pyridine, DCM, DMAP; (2) 1 mol/
L hydrochloric acid, Silica, 81%; for compound 14: (1) Ac2O, Pyridine, DCM, DMAP;
(2) 1 mol/L hydrochloric acid, Silica, 87%; (e): Et3N/DCM = 1:4; 12 h. (f): DBU,
CCl3CN, DCM. Compound 7b (86%) or 7c (91%) for two steps.
HO
SEt
ClAcO
BnO
F
HO
BnO
N3
BnO
NPhth
NPhth
NPhth
G
E
F
Scheme 2. Previous synthesis of the core trisaccharide 2.
OBn
O
OBn
O
plied for differentiation of 2,3-OH of monoglucopyranose.19 Based
on this approach, the trichloroacetimidate 7a with the 2,3-OH
masked by two orthogonal groups was synthesized efficiently from
orthoester 5.19 On account of the difficult removal of the sterically
hindered 2-acetate,12 disaccharide 8 was first synthesized and then
applied for the subsequent selective removal of the acetyl group
(Scheme 4) before the one-pot glycosylation. However, the com-
patibility of protecting groups in compound 8 was not satisfactory,
since many reaction conditions for subsequent selective removal of
acetyl group were tested but failed. For instance, treating com-
pound 8 with acetyl chloride/methanol led to the deprotection of
4,6-O-benzylidene, while switched to typical basic conditions
(DBU, K2CO3, NH2NH2ꢀH2O, Mg(OEt)2), the cleavage of benzoyl
group was observed.
To circumvent this difficulty, new designed glucosyl donors 7b/
7c were prepared following a similar method to the preparation of
7a (Scheme 5).19 The difference is that these two donors were pre-
pared from a new type of orthoester 12. In addition, it was
equipped with an easier removable levulinyl group (Lev) in C-2 po-
sition. The synthesis started from compound 9,21 which was con-
verted to compound 10 with 2,3-diols protected by Lev in 95%
yield. When activated by N-bromosuccinimide (NBS)/TMSOTf in
the presence of CH3OH and subsequently cleaved Lev in one pot,
compound 10 was transformed to orthoester 1224 with two iso-
NH
O
O
Ph
O
HO
N3
HO
SEt
+
+
R1O
BnO
BnO
R2O
O
CCl3
NPhth
NPhth
F
7a R1 = Bz, R2 = Ac
7b R1 = Bz, R2 = Lev
G
7c
R1 = Ac, R2 = Lev
Scheme 3. Three building blocks for one-pot glycosylation.
building blocks, it’s not economical to differentiate 2,3-diols of the
glucosyl residue after the construction of the trisaccharide.
We herein describe an improved approach to the synthesis of
the core trisaccharide 2. The key glucosyl trichloroacetimidate
719 with well differentiated 2,3-diols, the thioglycoside G20, and
azide acceptor F12 were selected for orthogonal one-pot glycosyla-
tion. (Scheme 3) Then the b-mannosyl chitobiose was established
by intramolecular epimerization of the C-2 position of the b-gluco-
side. Compared with the former described differentiation of the
2,3-diols after the glycosylation, this prior differentiation in the
glucosyl donor stage diminished the loss of valuable building
blocks F and G. In addition, the one pot glycosylation simplified
the procedure for construction of the b-glucosyl chitobiose.
The 4,6-O-benzylidene-protected 1,2-orthoester, which has
been investigated by our group, can be prepared effectively and ap-
O
O
O
Ph
O
O
Ph
O
O
AcO
O
a
b
Ph
O
HO
SEt
O
O
AcO
O
O
O
OAc
4
5
3
OCH3
NH
OCH3
OBn
O
O
O
O
Ph
Ph
HO
BnO
SEt
d
c
O
O
BzO
BzO
NPhth
G
HO
AcO
O
CCl3
OAc
6
7a
e
OBn
O
O
O
Ph
SEt
O
O
BzO
BnO
NPhth
OAc
8
Scheme 4. Reagents and conditions: (a): NBS, TMSOTf, DCM:CH3OH = 50:1, 4 Å MS, 0 °C, 0.5 h, (b) CH3ONa, CH3OH, 89% for two steps; (c): (1) BzCl, pyridine, DCM, DMAP; (2)
2 mol/L hydrochloric acid, Silica, 81% for two steps; (d): (1) Et3N, DCM; 12 h; (2) DBU, CCl3CN, DCM, 88% for two steps; (e): TMSOTf, DCM, 4 Å molecular sieve (MS), ꢁ15 °C,
0.5 h, 65%.

3322
Z. Lu et al. / Tetrahedron Letters 52 (2011) 3320–3323
OBn
O
OBn
O
HO
SEt
HO
BnO
N3
OBn
O
OBn
O
BnO
O
NH
CCl3
Ph
O
O
G
NPhth
Ph
O
NPhth
F
O
N3
O
O
O
AcO
LevO
AcO
BnO
BnO
b
O
NPhth
OLev
NPhth
15
a
7c
OBn
O
OBn
O
OBn
O
OBn
O
OR2
O
d
O
O
c
Ph
Ph
Ph
O
N3
O
O
O
O
O
N3
O
R1O
BnO
BnO
AcO
BnO
BnO
NPhth
NPhth
NPhth
OH
NPhth
16 R1= Ac, R2= H
17 R1= H, R2= Ac
A
OBn
OBn
O
OH
O
O
O
O
N3
NPhth
O
O
HO
BnO
BnO
NPhth
2
Scheme 6. Reagents and conditions: (a): (1) G, TfOH, DCM, 4 Å MS, ꢁ15 °C, 0.5 h; (2) F, NIS, 4 Å MS, ꢁ15 °C, 0.5 h, 81%; (b): N2H4ꢀHOAc, DCM:CH3OH = 1:1, rt, 1 h, 89%; (c): (1)
Tf2O, pyridine, ꢁ15 °C, 3 h; 2) DMF:H2O = 20:1, 50 °C, 24 h; (d) CH3ONa, CH3OH, 87%.
mers (1:2) in 83% yield. After acetylation or benzoylation of OH-3
the hydrolysis of 1,2-orthoester intermediate with 1 M hydrochlo-
ric acid afforded compound 13 (81%) or 14 (87%). Notably, the
hydrolysis procedure could be accelerated by the addition of silica
gel. Then the anomeric center was liberated with the influence of
Et3N in CH2Cl2 and the resulting intermediate was converted to
the trichloroacetimidate donor 7b (86%) or 7c (91%) according to
the method developed by Schmidt.22
References and notes
1. Essentials of Glycobiology; Varki, A., Cummings, R. D., Esko, J. D., Freeze, H. H.,
Stanley, P., Bertozzi, C. R., Hart, G. W., Etzler, M. E., Eds., second ed.; Cold Spring
Harbor Laboratory Press: NY, 2009.
2. (a) Endo, T. J. Chromatogr. A. 1996, 720, 251–261; (b) Rice, K. G. Anal. Biochem.
2000, 283, 10–16.
3. (a) Ogawa, T.; Sugimoto, M.; Kitajima, T.; Sadozai, K. K.; Nukada, T. Tetrahedron
Lett. 1986, 27, 5739–5742; (b) Nukada, T.; Kitajima, T.; Nakahara, Y.; Ogawa, T.
Carbohydr. Res. 1992, 228, 157–170.
4. (a) Paulsen, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 155–173; (b) Paulsen, H.
Angew. Chem. Int. Ed. Engl. 1990, 29, 823–839.
5. (a) Unverzagt, C. Angew. Chem., Int. Ed. Engl. 1994, 33, 1102–1104; (b)
Unverzagt, C. Angew. Chem., Int. Ed. 1996, 35, 2350–2353; (c) Unverzagt, C.
Angew. Chem., Int. Ed. 1997, 36, 1989–1992; (d) Unverzagt, C. Carbohydr. Res.
1997, 305, 423–431; (e) Unverzagt, C.; Andre, S.; Seifert, J.; Kojima, S.; Fink, C.;
Srikrishna, G.; Freeze, H.; Kayser, K.; Gabius, H. J. J. Med. Chem. 2002, 45, 478–
491; (f) Eller, S.; Schuberth, R.; Gundel, G.; Seifert, J.; Unverzagt, C. Angew.
Chem., Int. Ed. 2007, 46, 4173–4175; (g) Eller, S.; Raps, C.; Niemietz, M.;
Unverzagt, C. Tetrahedron Lett. 2010, 51, 2648–2651.
6. Wu, X. Y.; Grathwohl, M.; Schmidt, R. R. Angew. Chem., Int. Ed. 2002, 41, 4489–
4493.
7. Ratner, D. M.; Swanson, E. R.; Seeberger, P. H. Org. Lett. 2003, 5, 4717–
4720.
With donor 7b and 7c in hand, the glycosylation with acceptor
G was conducted firstly. Under a similar condition for the glycosyl-
ation of 7a with G, donor 7b and 7c provided the corresponding
disaccharides in yields of 78% and 85%, respectively. Due to better
yield for donor 7c,25 it was selected for the following orthogonal
one-pot glycosylation.23 As shown in Scheme 6, trichloroacetimi-
date donor 7c (1.3 equiv) was activated by TfOH at ꢁ15 °C to be
coupled with acceptor G (1.0 equiv). When TLC showed the full
consumption of G (0.5 h), NIS and acceptor F (1.0 equiv) were
added. The mixture was stirred for another 0.5 h, giving the result-
ing trisaccharide 15 in 81% yield.26 Subsequent selective cleavage
of Lev by N2H4ꢀHOAc was conducted smoothly to afford intermedi-
ate A in high yield (89%). The transformation of b-glucoside to b-
mannoside was performed through the intramolecular inversion
of the C-2 hydroxyl of A by a three-step procedure with excellent
reproducibility and complete stereoselectivity.14 Firstly, the OH-2
position was activated with trifluoromethylsulfonic anhydride
and pyridine. The intermediate triflate was substituted by an intra-
molecular nucleophilic attack of the neighboring acetyl moiety to
afford a mixture of compound 16 and isomer 17. Subsequent
deprotection of the acetyl group by methanolysis gave the desired
core trisaccharide 2 in 87% yield over the reaction sequence. It
should be noted that no further purifications were needed after
simple workup for the intermediates during this three-step proce-
dure to convert A to compound 2.27
8. Li, B.; Zeng, Y.; Hauser, S.; Song, H. J.; Wang, L. X. J. Am. Chem. Soc. 2005, 127,
9692–9693.
9. (a) Geng, X.; Dudkin, V. Y.; Mandal, M.; Danishefsky, S. J. Angew. Chem., Int. Ed.
2004, 43, 2562–2565; (b) Mandal, M.; Dudkin, V. Y.; Geng, X.; Danishefsky, S. J.
Angew. Chem., Int. Ed. 2004, 43, 2557–2561; (c) Miller, J. S.; Dudkin, V. Y.; Lyon,
G. J.; Muir, T. W.; Danishefsky, S. J. Angew. Chem., Int. Ed. 2003, 42, 431–434; (d)
Dudkin, V. Y.; Miller, J. S.; Danishefsky, S. J. Tetrahedron Lett. 2003, 44, 1791–
1793.
10. (a) Davis, B. G. Chem. Rev. 2002, 102, 579–602; (b) Jonke, S.; Liu, K. G.; Schmidt,
R. R. Chem. Eur. J. 2006, 12, 1274–1290.
11. (a) Matsuo, I.; Isomura, M.; Waiton, R.; Ajisaka, K. Tetrahedron Lett. 1996, 37,
8795–8798; (b) Dudkin, V. Y.; Crich, D. Tetrahedron Lett. 2003, 44, 1787–1789;
(c) Attolino, E.; Rising, T. W. D. F.; Heidecke, C. D.; Fairbanks, A. J. Tetrahedron:
Asymmetry 2007, 18, 1721–1734; (d) Chang, S. S.; Shih, C. H.; Lai, K. C.; Mong, K.
K. T. Chem. Asian. J. 2010, 5, 1152–1162.
12. Unverzagt, C. Chem. Eur. J. 2003, 9, 1369–1376.
13. Serna, S.; Kardak, B.; Reichardt, N.; Martin-Lomas, M. Tetrahedron: Asymmetry
2009, 20, 851–856.
14. Wang, G. F.; Zhang, W.; Lu, Z. C.; Wang, P.; Zhang, X. L.; Li, Y. X. J. Org. Chem.
2009, 74, 2508–2515.
In conclusion, we have presented a convenient synthesis of the
core trisaccharidic scaffold for the assembly of N-glycans. Our
route improves the published procedure in simplicity and yield.
Notably, three monosaccharide building blocks for one-pot glyco-
sylation were easily prepared. Owing to its facility and mild reac-
tion conditions, the procedure can be applied to access a series of
N-glycans.
15. (a) Matsuo, I.; Nakahara, Y.; Ito, Y.; Nukada, T.; Nakahara, Y.; Ogawa, T. Bioorg.
Med. Chem. 1995, 3, 1455; (b) Jain, R. K.; Matta, K. L. Carbohydr. Res. 1996, 282,
101; (c) Grice, P.; Ley, S. V.; Pietruszka, J.; Osborn, H. M. I.; Priepke, H. W. M.;
Warriner, S. L. Chem. Eur. J. 1997, 3, 431; (d) Crich, D.; Sun, S. X. J. Org. Chem.
1996, 61, 4506; (e) Crich, D.; Sun, S. X. J. Am. Chem. Soc. 1997, 119, 11217; (f)
Crich, D.; Sun, S. X. J. Am. Chem. Soc. 1998, 120, 435.
16. (a) Barresi, F.; Hindsgaul, O. J. Am. Chem. Soc. 1991, 113, 9376; (b) Stork, G.; La
Clair, J. J. J. Am. Chem. Soc. 1996, 118, 247; (c) Ito, Y.; Ogawa, T. J. Am. Chem. Soc.
1997, 119, 5562; (d) Dan, A.; Lergenmuller, M.; Amano, M.; Nakahara, Y.;
Ogawa, T.; Ito, Y. Chem. Eur. J. 1998, 4, 2182.
17. (a) Kerekgyarto, J.; Vanderven, J. G. M.; Kamerling, J. P.; Liptak, A.; Vliegenthart,
J. F. G. Carbohydr. Res. 1993, 238, 135; (b) Liu, K. K. C.; Danishefsky, S. J. J. Org.
Chem. 1994, 59, 1892; (c) Danishefsky, S. J.; Hu, S.; Cirillo, P. F.; Eckhardt, M.;
Seeberger, P. H. Chem. Eur. J. 1997, 3, 1617; (d) Lichtenthaler, F. W.; Schneider-
Adams, T. J. Org. Chem. 1994, 59, 6728–6734; (e) Nitz, M.; Bundle, D. R. Org. Lett.
Acknowledgments
This work is supported by the National Nature Science Founda-
tion of China (NSFC21002014) and the Fundamental Research
Funds for the Central Universities of China.

Z. Lu et al. / Tetrahedron Letters 52 (2011) 3320–3323
3323
2000, 2, 2939–2942; (f) Wu, X. Y.; Lipinski, T.; Paszkiewicz, E.; Bundle, D. R.
Chem. Eur. J. 2008, 14, 6474–6482.
18. (a) Sato, K.; Yoshitomo, A. Chem. Lett. 1995, 1, 39; (b) Pratt, M. R.; Bertozzi, C. R.
J. Am. Chem. Soc. 2003, 125, 6149; (c) Dong, H.; Pei, Z.; Ramström, O. J. Org.
Chem. 2006, 71, 3306; (d) Dong, H.; Pei, Z.; Angelin, M.; Bystroem, S.;
Ramström, O. J. Org. Chem. 2007, 72, 3694.
1H, J = 9.8 Hz), 5.54 (s, 1H), 5.17 (dd, 1H, J = 10.0, 3.7 Hz), 4.35 (dd, 1H, J = 10.4,
4.9 Hz), 4.16–4.10 (m, 1H), 3.81–3.74 (m, 1H), 2.73–2.70 (m, 2H), 2.54–2.50 (m,
2H), 2.16 (s, 3H), 2.12 (s, 3H). 13C NMR: (100 MHz, CDCl3): d 205.9, 171.6, 169.9,
161.0, 136.6, 129.1, 128.3, 126.1, 101.6, 93.5, 90.8, 78.6, 70.5, 68.5, 68.5, 65.1,
37.5, 29.7, 27.7, 20.8.
26. General procedure for the one-pot synthesis of trisaccharide 15: after a mixture
19. General procedure for the preparation of compound 5. (The procedure for the
preparation of 12 is same as the compound 5): After a mixture of compound 3
(1.0 mmol), CH3OH (1 mL) and 4 Å molecular sieves in freshly distilled CH2Cl2
(50 mL) were stirred for 0.5 h at rt and then cooled to 0 °C, NBS (178 mg,
1.0 mmol) was added and the reaction mixture was stirred for 2 min. TMSOTf
of 7c (75 mg, 0.14 mmol), compound
activated 4Å molecular sieves in freshly distilled CH2Cl2 (10 mL) was
L, 0.03 mmol)
was added dropwise. The mixture was stirred for 0.5 h at ꢁ15 °C. Then
compound F (54 mg, 0.11 mmol) and NIS (31 mg, 0.14 mmol) was added.
The mixture was stirred for 30 min at ꢁ15 °C and then filtered through
Celite. The filtrate was diluted with CH2Cl2 and then washed with aqueous
NaHCO3, aqueous Na2S2O3, and brine. The organic layer was dried over
Na2SO4, filtered, and concentrated. The crude mixture was purified by
column chromatography on silica gel (EtOAc/petroleum ether = 1:3?1:2) to
G (56 mg, 0.11 mmol) and pre-
stirred at rt for 0.5 h and then cooled to ꢁ15 °C, TfOH (2.8
l
(18
15 min at 0 °C. Then NBS (178 mg, 1.0 mmol) and TMSOTf (18
were added for the second time. The reaction mixture was stirred for another
15 min at 0 °C, TLC (n-Hexane/EtOAc = 2:1) indicated that compound
l
L, 0.1 mmol) was added dropwise and the reaction mixture was stirred for
lL, 0.1 mmol)
3
completely converted to intermediate 1,2-orthoesters 4. Then a solution of
CH3ONa in MeOH (0.1 M, 40 mL) was added dropwise to the reaction mixture.
The solution was allowed to warm to rt and stirred for 30 min, then filtered
through Celite. Silica gel (activated by Et3N, 4 g) was added to the filtrate, and
then concentrated in vacuo. The crude mixture was purified by column
chromatography on Silica gel (Silica gel had been activated by Et3N) to afford
orthoester 5.
afford the trisaccharide 15 (117 mg, 81%) as a light yellow foam. ½a D23
ꢂ
+3.1 (c
0.1, CHCl3); 1H NMR: (400 MHz, CDCl3): d 7.85 (d, 1H, J = 7.4 Hz), 7.80–7.62
(m, 6H), 7.54 (s, 1H), 7.47–7.30 (m, 15H), 7.00 (d, 2H, J = 6.3 Hz), 6.96–6.88
(m, 5H), 6.77–6.76 (m, 3H), 5.37 (s, 1H), 5.29 (d, 1H, J = 8.2 Hz), 5.21 (t like,
1H, J = 9.4, 9.8 Hz), 5.15 (d, 1H, J = 9.4 Hz), 4.97 (t like, 1H, J = 7.8, 9.4 Hz),
4.89 (d, 1H, J = 12.5 Hz), 4.78 (d, 1H, J = 12.1 Hz), 4.72 (d, 1H, J = 7.8 Hz), 4.65
(d, 1H, J = 12.1 Hz), 4.58–4.37 (m, 5H), 4.31–4.11 (m, 8H), 4.04 (t, 1H,
J = 9.8 Hz), 3.75–3.68 (m, 2H), 3.56–3.49 (m, 2H), 3.44–3.38 (m, 3H), 3.25 (m,
1H), 2.79–2.64 (m, 2H), 2.55–2.35 (m, 2H), 2.17 (s, 3H), 2.07 (s, 3H). 13C
NMR: (100 MHz, CDCl3): d 205.6, 171.4, 170.2, 138.6, 138.5, 138.2, 137.8,
136.8, 133.8, 131.5, 129.1, 128.6, 128.2, 128.0, 127.9, 127.9, 127.8, 127.7,
127.6, 127.4, 127.1, 126.9, 123.3, 101.4, 100.5, 97.0, 85.5, 78.5, 78.0, 75.4,
74.7, 74.6, 73.3, 72.7, 71.6, 68.4, 67.6, 66.9, 66.1, 56.5, 55.2, 37.6, 29.7, 27.8,
20.8. HRMS (ESI): m/z calcd for C76H73N5O20Na: [M+Na]+ 1398.4741, found
1398.4798.
20. (a) Lönn, H. Carbohydr. Res. 1985, 139, 103–105; (b) Güther, W.; Kunz, H.
Carbohydr. Res. 1992, 228, 217–241.
21. Ennis, S. C.; Gridley, J. J.; Osborn, H. M. I.; Spackman, D. G. Synlett 2000, 1593–
1596.
22. Schmidt, R. R.; Kinzy, W. Adv. Carbohydr. Chem. Biochem. 1994, 50, 21–123.
23. For the first report of orthogonal glycosylation: (a) Kanie, O.; Ito, Y.; Ogawa, T. J.
Am. Chem. Soc. 1994, 116, 12073–12074; (b) Wang, Y. H.; Ye, X. S.; Zhang, L. H.
Org. Biomol. Chem. 2007, 5, 2189–2220; (c) Yamada, H.; Harada, T.; Takahashi,
T. J. Am. Chem. Soc. 1994, 116, 7919–7920; (d) Yamada, H.; Tetsuya, K.;
Takahashi, T. Tetrahedron Lett. 1999, 40, 4581–4584; (e) Yu, H.; Yu, B.; Wu, X.;
Hui, Y.; Han, X. J. Chem. Soc., Perkin Trans. 1 2000, 1445–1453.
27. Physical data for compound 2: ½a D23
ꢂ
+11.6 (c 0.1, CHCl3) 1H NMR: (400 MHz,
CDCl3): d 7.86(s, 1H), 7.71–7.67 (m, 6H), 7.56 (s, 1H), 7.46–7.44 (m, 2H), 7.38–
7.28 (m, 14H), 7.02 (d, 2H, J = 7.0 Hz), 6.97–6.90 (m, 5H), 6.81–6.75 (m, 3H),
5.45 (s, 1H), 5.30 (d, 1H, J = 8.6 Hz), 5.17 (d, 1H, J = 9.4 Hz), 4.84 (t like, 2H,
J = 12.1, 11.4 Hz), 4.75 (s, 1H), 4.59 (t like, 2H, J = 12.9, 12.1 Hz), 4.53–4.49 (m,
3H), 4.46–4.38 (m, 2H), 4.29 (t like, 1H, J = 9.4, 9.0 Hz), 4.23(dd, 1H, J = 10.6,
8.6 Hz), 4.17–4.12 (m, 3H), 4.06 (t like, 1H, J = 10.6, 9.4 Hz), 3.94 (d, 1H,
J = 3.1 Hz), 3.76 (t, 1H, J = 9.4 Hz), 3.67 (d, 1H, J = 11.7 Hz), 3.62–3.57 (m, 3H),
3.54 (t like, 1H, J = 10.6, 10.2 Hz), 3.44 (dd, 1H, J = 11.4, 3.5 Hz), 3.40–3.38 (m,
1H), 3.34–3.32 (m, 1H), 3.15–3.11 (m, 1H). 13C NMR: (100 MHz, CDCl3): d
138.3, 138.1, 137.5, 137.1, 133.8, 131.5, 129.2, 128.6, 128.3, 128.3, 128.0, 128.0,
127.9, 127.9, 127.5, 127.3, 127.2, 127.0, 126.2, 123.7, 123.4, 102.0, 100.4, 96.9,
85.6, 78.7, 78.4, 77.6, 76.7, 76.3, 75.0, 74.7, 74.5, 74.4, 73.5, 72.7, 70.7, 68.4,
67.7, 66.6, 56.5, 55.2. HRMS (ESI): m/z calcd for C69H65N5O17Na: [M+Na]+
1358.4273, found 1358.4268.
24. Physical data for compound 12: 1H NMR: (600 MHz, CDCl3): (mixture of isomers,
the ratio is 1:2) d 7.53–7.45 (m, 3H), 7.40–7.32 (m, 4.5H), 5.75 (d, J = 5.5 Hz,
1H), 5.59 (d, J = 5.8 Hz, 0.5H), 5.53 (d, 1.5H), 4.36 (ddd, J = 10.6, 5.3, 1.4 Hz,
1.5H), 4.31–4.23 (m, 1.5H), 4.14 (t, J = 5.7 Hz, 0.5H), 3.99 (dd, J = 9.5, 5.4 Hz,
1H), 3.89 (m, 0.5H), 3.78 (td, J = 9.8, 5.2 Hz, 1H), 3.68 (t, J = 10.3 Hz, 1.5H), 3.50
(td, J = 9.6, 7.8 Hz, 1.5H), 3.36 (s, 1.5H), 3.24 (s, 3H), 2.68–2.58 (m, 2H), 2.58–
2.53 (m, 1H), 2.20 (m, 2H), 2.15 (s, 3H), 2.14 (s, 1.5H), 2.14–2.10 (m, 1H). 13C
NMR: (150 MHz, CDCl3): d 207.9, 207.7, 177.5, 136.8, 136.8, 129.3, 128.3, 126.2,
126.1, 121.7, 121.0, 101.8, 101.6, 99.0, 98.4, 79.1, 78.9, 78.3, 73.3, 73.1, 68.5,
68.5, 63.1, 62.9, 60.4, 50.8, 49.7, 45.7, 38.0, 37.9, 30.5, 30.1, 29.5, 28.7, 14.1.
HRMS (ESI): m/z calcd for C19H24O8Na: [M+Na]+ 403.1369, found 403.1359.
25. Physical data for compound 7c: ½a D23
ꢂ
+49.6 (c 0.1, CHCl3); 1H NMR: (400 MHz,
CDCl3): d 8.67 (s, 1H), 7.44 (m, 2H), 7.35 (m, 3H), 6.52 (d, 1H, J = 3.5 Hz), 5.69 (t,