Synthesis of oligo-fructopyranoside with difructopyranosyl N-phenyltrifluoroacetimidate donor

Article abstract of DOI:10.1016/j.carres.2017.05.012

The hexa-fructopyranoside was synthesized with N-phenyltrifluoroacetimidate glycosylation. The synthesis was achieved by regioselective glycosylation on the 1-OH of fructopyranosyl acceptor. Fructosyl oligosaccharides were elongated with β-(2 → 1)-difructopyranosyl unit in every two steps, without any further protection/deprotection step. This work proved N-phenyltrifluoroacetimidate glycosylation a practical method for oligo-fructopyranoside synthesis.

Full text of DOI:10.1016/j.carres.2017.05.012

Accepted Manuscript
Synthesis of oligo-fructopyranoside with difructopyranosyl N-
phenyltrifluoroacetimidate donor
Hongliang Zhang, Hengtao Wang, Qiulong Xu, Rui Lu, Yunhua Cao, Zhefeng Wang,
Pingping Tang, Feng Lin, Yingxia Li
PII:
S0008-6215(17)30118-0
10.1016/j.carres.2017.05.012
CAR 7386
DOI:
Reference:
To appear in: Carbohydrate Research
Received Date: 15 February 2017
Revised Date: 9 May 2017
Accepted Date: 15 May 2017
Please cite this article as: H. Zhang, H. Wang, Q. Xu, R. Lu, Y. Cao, Z. Wang, P. Tang, F. Lin, Y.
Li, Synthesis of oligo-fructopyranoside with difructopyranosyl N-phenyltrifluoroacetimidate donor,
Carbohydrate Research (2017), doi: 10.1016/j.carres.2017.05.012.
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ACCEPTED MANUSCRIPT
Table of Contents Graphic
OH
O
PhN
F3C
LG
O
OAc
OBz
O
O
O
O
OBz
O
BzO
OAc
OBz
OBz
O
OBz
OBz
OBz
AcO
BzO
BzO
OBz
B
OBz
OBz
+
OBz
OBz
OBz
A
A
A
B
BzO
OBz
O
O
O
O
OBz
C
OBz
OBz
OH
O
OH
OH
HO
O
O
O
OBz
BzO
OAc
OBz
OBz
OBz
OBz
OBz
O
O
OBz
OBz
HO
O
OBz
OBz
n
OBz
OBz
OBz
OBz

ACCEPTED MANUSCRIPT
Synthesis of Oligo-Fructopyranoside with Difructopyranosyl
N-phenyltrifluoroacetimidate Donor
Hongliang Zhang, †‡ Hengtao Wang, # Qiulong Xu, ‡ Rui Lu, ‡ Yunhua Cao, ‡ Zhefeng
Wang, ‡ Pingping Tang,# Feng Lin, †‡$* Yingxia Li†*
†
Department of Medicinal Chemistry, School of Pharmacy, Fudan University,
Shanghai, 201203, China
‡ State Key Laboratory of New Drugs & Pharmaceutical Process, Shanghai Institute of
Pharmaceutical Industry, State Institute of Pharmaceutical Industry, 201203, China
#
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai
University, Tianjin 300071, China
$ Honghui Medical Group，No. 6 Beijingxi Road, Nanjing, 210008, China
* Corresponding author. Tel.: 86-25-85801888-1802; fax: 86-25-85803122; e-mail:
(FL) linfeng@ sioc.ac.cn; (YL) liyx417@fudan.edu.cn
Abstract
The hexa-fructopyranoside was synthesized with N-phenyltrifluoroacetimidate
glycosylation. The synthesis was achieved by regioselective glycosylation on the
1-OH of fructopyranosyl acceptor. Fructosyl oligosaccharides were elongated with
β-(2 → 1)-difructopyranosyl unit in every two steps, without any further
protection/deprotection step. This work proved N-phenyltrifluoroacetimidate
glycosylation a practical method for oligo-fructopyranoside synthesis.
Key Words
Glycosylation; fructopyranoside; N-phenyltrifluoroacetimidate; oligosaccharide
synthesis

ACCEPTED MANUSCRIPT
Inulins are naturally occurring polysaccharides produced by many types of plants as a
means of storing energy. Inulins also exhibit interesting bioactivities.1 Achyranthes
bidentata polysaccharides (ABPS), which is a kind of inulin isolated from traditional
Chinese herbal medicine Achyranthes bidentala, contain hexa- to octa-fructosyl unit
(around 1400 Da of MW) and exhibited antitumor and immunomodulating
activities.2,3,4
.
The synthesis of β-fructosides was difficult, especially for the
β-fructofuranosides.5,6 No
glycosylation method was applicable for
oligo-β-D-fructofuranosides’ preparation till now. The pyrano-type analogs of ABPS
could be an interesting alternative choice to study. There is no evidence that
oligo-β-D-fructopyranosides exist in nature,7,8 to the best of our knowledge. Although
fructopyranosides are simple and common, fructopyranosyl oligomer is the first
artificial designed oligosaccharide. Kaji and coworkers investigated the glycosylation
methods for β-D-fructopyranosides and reported a related work with poor yields for
trisaccharide preparation (<25%).9 There are some other works reported on the
preparation of β-D-fructopyranosides, but the glycosylation methods were not
applicable in oligomer synthesis.10 Recently we reported the β-selective synthesis of
fructopyranosides11 with N-phenyltrifluoroacetimidate donor.12,13 By these methods,
hexa-fructopyranoside was effectively synthesized with dimeric elongation strategy,
which we report herein.
Scheme 1. Retrosynthesis of fructopyranose oligomer.

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The retrosynthetic analysis is as Scheme 1. Diol 7 could be derived from diol 4.
According to our previous experiments, the anomeric OH of ketose is much more
inert than the primary 1-OH in glycosylation.11 The fructosyl diol could be directly
used for glycosylation, then the glycosylated product could be directly transformed to
the donor for subsequent reaction. Thus, the oligomer was elongated with difructosyl
unit in every second step. N-phenyltrifluoroacetimidate donor and acetyl donor were
both investigated. (Scheme 1).
Tribenzoate 3, obtained by reported procedures14, was deacetalized under 60%
TFA to obtain diol 4, which could be directly precipitated as white solid from reaction
mixture in 87% yield (Scheme 2). Deacetalization of 3 in Benito’s work leads to
di-fructose anhydride,14 which was not observed in our condition. Different from
Benito’s anhydrous reaction condition, our aqueous 60% TFA condition disfavored the
glycosylation pathway.
Scheme 2. Synthesis of acceptor 4. Condition: a) acetone, conc. H2SO4, 53%; b) HCl,
MeOH:H2O = 2:1, 80%; c) BzCl, py, 95%; d) 60% TFA, RT, 87%.
Acetyl donor 5 was prepared from 415. Glycosylation of donor 5 with the acceptor 4
with TMSOTf (0.1 equiv) proceeded with excellent regio- and stereo-selectivity, and
the β-(2→1)-fructopyranoside 6 was obtained in 91% yield. The β-glycosyl
13
configuration was determined by their C-2 anomeric C NMR data (in the range of
99~102 ppm).11 The primary O-Ac was deprotected with anhydrous 1N HCl/HOMe
solution in DCM to obtain diol 7 with all benzoyl groups intact. (Scheme 3)

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Scheme 3. Synthesis of acceptor 7. a) Ac2O, DMAP, NEt3, 0 ˚C, 92%; b) 4, TMSOTf,
20 ˚C, 91%; c) 1N HCl/HOMe, DCM, 0 ˚C, 95%.
Acetyl donor 8 and N-phenyltrifluoroacetimidate donor 9 (Scheme 4) were both
prepared. In various glycosylation conditions, acetyl donor 8 only resulted in
hydrolysis or decomposition, no tetramer was detected. Treatment of
N-phenyltrifluoroacetimidate donor 9 with diol 7 under standard glycosylation
condition in dichloromethane provided the tetra-saccharide 10 in 20% yields. Toluene
or THF as solvent did not improve the yield. Addition of DMSO in DCM or toluene did
not improve the yield but produced an unknown product of great polarity. Anhydrous
CH3CN as solvent dramatically improved the yield, and the amount of donor 9 was
increased to 1.5 equiv., the yield is 82%. (Table 1)16 Under these conditions,
β-(2→1)-fructopyranoside was obtained with high regio- and stereo-selectivity. The
solvent effect of N-phenyltrifluoroacetimidate glycosylation were also reported by
other groups.17
The stereochemistry of 10 was confirmed by X-ray analysis (Figure 1).18 The
crystal data were assigned to the CCDC (The Cambridge Crystallographic Data Centre)
numbers 1542763.
OAc
OBz
OAc
OBz
HO
O
O
O
AcO
O
O
O
various condition
a
OBz
OBz
no tetramer
OBz
6
OBz
OBz
8
OBz
OBz
OBz
OBz
OBz
OBz
OBz
PhN
OAc
OBz
HO
O
O
O
OAc
OBz
OAc
HO
O
O
O
O
O
O
O
OBz
OBz
OBz
F3C
b
c
OBz
OBz
OBz
OBz
OBz
O
O
OBz
OBz
OBz
OBz
OBz
OBz
10
OBz
OBz
OBz
2
9
6

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Scheme 4. Investigation of difructosyl donors. a) Ac2O, DMAP, NEt3, 0 ˚C, 76%; b)
N-phenyltrifluoroacetimidoyl chloride, K2CO3, acetone, 96%; c) diol 7, TMSOTf,
CH3CN, 82%.
Table 1. Study of glycosylation with Donor 9.a
PhN
OAc
OBz
HO
O
O
O
O
O
OAc
OBz
O
O
O
O
OBz
OBz
OBz
OBz
F3C
OBz
OBz
OBz
9
OBz
OBz
OBz
10
OBz
OBz
OBz
2
Entry
Solvent
Equiv.
of
Result
donor
1.2
1
2
DCM
20% yields
no 10
DCM:DMSO
(20:1)
1.2
obtained.
15%
3
4
Toluene
1.2
1.2
Tolene:DMSO
(20:1)
no 10
obtained.
no 10
5
THF
1.2
obtained.
62%
6
7
CH3CN
CH3CN
1.2
1.5
82%
a: The reaction was carry out with 0.1 equiv. of TMSOTf at -20 ˚C.16

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Figure 1 ORTEP drawing of compound 10
Diol
10
was
quantitatively
transformed
to
donor
11
under
N-phenyltrifluoroacetimidoyl chloride and K2CO3 in acetone. Donor 11 was
glycosylated with acceptor 7 in CH3CN, regio- and stereo-selectively provided the
β-(2→1)-fructopyranosyl hexa-saccharide in 51% yield. Because the protection and
deprotection of anomeric 2-OH suffered low yield,9 this straightforward method
benefited the synthesis efficiency. Hexa-saccharide was fully deprotected to obtain 13
in 86% yield. The overall yield was 27% in eight steps from diol 4. (Scheme 5)

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Scheme
5
Synthesis of β-D-fructopyranosyl oligomer. Condition: a)
N-phenyltrifluoroacetimidoyl chloride, K2CO3, acetone, 97%; b) diol 7, TMSOTf, -20
˚C, 51%; c) NaOMe, HOMe, 86%.
In conclusion, hexasaccharide 13 was synthesized with fructopyranosyl
N-phenyltrifluoroacetimidate glycosylation, which is the first practical synthesis of
β-D-fructopyranosyl oligomer. The solvent CH3CN plays a critical role. By
regioselective glycosylation on the 1-OH of acceptor 7, the β-fructopyranosyl
oligosaccharides were elongated with difructosyl unit in every second steps, without
any deprotection step. From these new oligomeric structures, functional materials and
drug candidates could be prepared, which will be an interesting field.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on ### website.
ACKNOWLEDGMENT
This work was supported by the Committee of Science and Technology of Shanghai
(10QB1403900), the National Natural Science Foundation of China (20902059) and
MOST (2011ZX09202-101-01). FL thanks Dr. Jason Wong for helpful discussion.
REFERENCES
(1) Roberfroid, M. B. Br. J. Nutr. 2003, 93, 13-26.

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(2) Zhu, X.; Pan, Y.; Zheng, L.; Cui, L.; Cao, Y. Malaria J. 2012, 11:49,1-7.
(3) Jin, L.; Zheng, Z.; Peng, Y.; Li, W.; Chen, X.; Lu, J. International
Immunopharmacology .2007, 7, 568-577.
(4) Xiang, D.; Li, X. Acta Pharm. Sinica .1993, 14, 556-561.
(5) Mueller, T.; Schneider, R.; Schmidt, R. R. Tetrahedron Lett. 1994，35(27)，
762-766
(6) Oscarson, S.; Sehgelmeble, F. W. J. Am. Chem. Soc. 2000, 122, 8869-8870
(7) Okada, H.; Fukushi, E.; Yamamori, A.; Kawazoe, N.; Onodera, S.; Kawabata, J.;
Shiomi, N. Carbohydr. Res. 2010, 345, 414-418 and the references therein. In the tri- or
di-saccharides, there is only one fructopyranosyl unit, and no fructopyranosyl oligomer
was reported.
(8) Chen, J.; Cheong, K.; Song, Z.; Shi, Y.; Huang, X. Carbohydrate Polymers, 2013,
92, 200-205. This is the only result indicating oligo-fructopyranosides by SciFinder®
and by Web of Science®. But the word “fructopyranose” in the abstract should be a
typo. The article clearly indicated that the oligomer was compose of
beta-D-Fructofuranose.
(9) Kaji, E.; Kurimoto, E.; Saiga, R.; Matsuura, A. ; Harada, K. ; Nishino, T.
Heterocycles. 2005, 66, 453-468.
(10) Ferrieres,V.; Benvegnu,T.; Lefeuvre,M.; Plusquellec,D.; Mackenzie,G.; Watson,
M. J.; Haley, J. A.; Goodby, J. W.; Pindak,R.;Durbin, M. K. J. Chem. Soc., Perkin
Trans. 2, 1999, 951–959.
(11) Lin, F.; Lian, G.; Xu, Q.; Zhu, X. Tetrahedron .2013, 69, 1128-1132.
(12) Huchel, U. Neue Methoden zur diastereoselektiven Glycosylierung.
Dissertation, Universitat Konstanz, 1998, Verlag Papierflieger, Clausthal-Zellerfeld,
ISBN 3-89720-221-2.
(13) Yu, B.; Tao, H. Tetrahedron Lett. 2001, 42, 2405-2407.
(14) Benito J. M.; Rubio E.; Gomez-Garcıa M.; Mellet C. O.; Garcıa Fernandez J. M.
Tetrahedron 2004, 60, 5899-5906.
(15) Lin, F.; Xu, Q.; Lu, R.; Yue. L. Tetrahedron Lett. 2014, 55, 98-100.

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(16) Key experiment procedures: A mixture of the acceptor 7, donor 9 (1.5 equiv.),
o
and 4Ǻ MS in anhydrous acetonitrile (7 ml) was stirred at 0 C for 0.5h under Ar.
TMSOTf in acetonitrile (0.1 equiv.) was added dropwise. The reaction was monitored
by TLC and quenched with Et3N. Then the resulting mixture was filtered through
Celite. The filtrate was concentrated and purified by column chromatography
(hexane:EtOAc = 2:1) to obtain 10 as white solid. m.p. 154 - 156 oC. [α]2D5 = –236.9 (c
= 1.00 in CHCl3). 1H NMR (400 MHz, CDCl3) δ 8.44 – 6.56 (m, 60 H), 6.31 (d, J = 10.4
Hz, 1 H), 6.17 (d, J = 9.9 Hz, 1 H), 6.03 (dd, J = 10.4, 3.5 Hz, 1 H), 5.93 – 5.70 (m, 5 H),
5.56 – 5.48 (m, 2 H), 4.49 – 4.32 (m, 3 H), 4.25 (d, J = 11.4 Hz, 1 H), 4.20 – 3.99 (m, 9
H), 3.94 – 3.71 (m, 5 H), 1.65 (s, 3 H). 13C NMR (101 MHz, CDCl3) δ 169.8-164.9(C,
C=O), 133.7-127.9 (C, Ar), 100.5, 100.3, 98.9, 97.1,70.4, 70.2, 70.1, 70.0, 69.7, 69.7,
69.6, 68.4, 68.4, 67.6, 67.3, 64.1, 63.0, 62.6, 62.5, 61.8, 61.6, 60.6, 60.4, 59.7,
20.0.ESI-MS (m/z) : [M+Na]+ : calcd for C110H92O34Na+ 1979.5362, found 1979.5368.
(17) Tanaka, H.; Iwata, Y.; Takahashi, D.; Adachi, M.; Takahashi, T. J. Am. Chem.
Soc. 2005, 127, 1630-1631.
(18) The product 10 was recrystallized from mixture of tetrahydrofuran and methanol
(1:5). Crystal data:C110H92O34; Mr =1957.84, monoclinic, P21,a=11.0760(2)Å,
b=15.3546(3)Å, c=28.8398(6)Å, Dcalcd =1.326g/cm3, T=173K, X-ray intensities were
measured on a graphite monochromatized CuKα radiation (λ=1.54178Å ).

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The first synthesis of β-D-fructopyranosyl hexamer
ꢀ
ꢀ
N-phenyltrifluoroacetimidate glycosylation was vital for oligomer synthesis.
ꢀ
ꢀ
Provided an interesting method for selective glycosylation of ketose.
Fructopyranosyl oligomer provide new backbone, with promising applications.