Synthesis of fructofuranosides: efficient glycosylation with N-phenyltrifluoroacetimidate as the leaving group

Article abstract of DOI:10.1016/j.carres.2008.09.001

Fructofuranosyl trifluoroacetimidate 3 was demonstrated to be an effective glycosyl donor that exhibited good α-selectivity and good yield in fructosylation reactions. The reaction proceeds via neighboring group participation, which was proved by the isolation of a stable allylic orthoester intermediate.

Full text of DOI:10.1016/j.carres.2008.09.001

Carbohydrate Research 343 (2008) 2992–2996
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Note
Synthesis of fructofuranosides: efficient glycosylation with
N-phenyltrifluoroacetimidate as the leaving group
Gaoyan Lian a, Qi Gao b, Feng Lin a,b,
*
a Department of Chemistry, Fudan University, 220 Handan Road, Shanghai 200433, PR China
b Shanghai Institute of Pharmaceutical Industry, No. 1111 Zhongshanbeiyi Road, Shanghai 200437, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2008
Received in revised form 27 August 2008
Accepted 1 September 2008
Available online 9 September 2008
Fructofuranosyl trifluoroacetimidate 3 was demonstrated to be an effective glycosyl donor that exhibited
good
a-selectivity and good yield in fructosylation reactions. The reaction proceeds via neighboring
group participation, which was proved by the isolation of a stable allylic orthoester intermediate.
Ó 2008 Elsevier Ltd. All rights reserved.
Dedicated to Professor Yongzheng Hui on
the occasion of his 70th birthday
Keywords:
Fructosylation
Trifluoroacetimidate
Glycosyl donor
Fructose is the second most abundant simple sugar (behind glu-
cose) in nature, and fructosides are found abundantly in both
plants and bacteria. Fructose-containing molecules are not only
storage materials, but are also involved in a wide range of biolog-
ical processes.1 However, the chemical synthesis of fructosides has
lagged far behind that of glucosides. The major impediment is that
fructosylation protocols with good stereoselectivity and good yield
base
BzO
O
OBz
NH
BzO
O
BzO
OBz
BzO
+
Cl3CCN
O
OH
OBz
OBz
1
CCl3
various conditions
Scheme 1.
2
are limited.2–4 Generally,
D-fructose occurs as b-furanosyl residues,
but fructosylation methods with b-selectivity are particularly lim-
ited.3 There are two major fructosylation protocols. One is the thi-
ofructoside glycosylation, developed by Oscarson et al.,2a which led
ultimately to the first stereospecific synthesis of sucrose, which
contains a b-fructofuranoside moiety, in 2000.3 This protocol is
b-stereoselective, but the donor required is costly to prepare,
which limits its synthetic application. The other method uses
fructosyl phosphite donors, with which good yields were obtained
but the stereochemical outcome was not predictable.4 We note
that the Schmidt glycosylation protocol using trichloroacetimidate
as leaving group is not suitable for fructosylation, because fructosyl
trichloroacetimidate 2 could not be prepared under various basic
conditions (Scheme 1).4,5 To reach the goal of efficient and stereo-
selective b-fructosylation, the development of new and effective
fructosylation methods are necessary.
Yu et al. recently developed an alternative donor to the trichlo-
roacetimidate, N-phenyl trifluoroacetimidate,6 which was success-
fully applied in direct sialylation,7 N-glycosylation of primary
amides,8 O-glycosylation of hydroxamic acid,9 and several total
synthesis.10 These results stimulated our interests to apply this
class of donors in fructosylation. Our preliminary work in this area
is reported here.
Initially, we investigated the preparation of trifluoroacetimidate
3 (Scheme 2 and Table 1). 1,3,4,6-Tetra-O-benzoylfructose 1, which
was readily prepared from
D
-fructose,11 was treated with
BzO
O
OBz
NPh
BzO
O
BzO
OBz
BzO
NPh
K2CO3
r.t.
Cl
+
O
OH
CF3
OBz
OBz
1
CF3
3
* Corresponding author. Tel.: +86 21 55514600x216; fax: +86 21 65169893.
E-mail address: linfeng@mail.sioc.ac.cn (F. Lin).
Scheme 2.
0008-6215/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2008.09.001

G. Lian et al. / Carbohydrate Research 343 (2008) 2992–2996
2993
Table 1
Optimization of the preparation of N-phenyl trifluoroacetimidate 3
Table 2
Glycosylation with tetrabenzoyl N-phenyl trifluoroacetimidate 3 as donor
Entry
N-phenyl trifluoroacetimidoyl
chloride (equiv)
Solvent
Reaction
time (h)
Yield
(%)
Entry
Acceptor
Conditions
Product
Yieldd (%)
a
:b
Only
Only
Only
Only
1
2
3
4
5
6
7
8
9
4a
4a
4b
4c
4d
4d
4d
4e
4f
Aa
Bb
A
A
A
5a
5a
5b
5c
—
—
5d
5e
97
92
97
96
a
a
a
a
1
2
3
7
7
3
Anhydrous CH2Cl2
‘Wet’ CH2Cl2
Acetone
20
4
2
10
70
Quant.
No product
No product
B
—
a
a
a
—
Cc
A
63
57e
70
63
63
—
Mainly
:b = 5:2f
N-phenyltrifluoroacetimidoyl chloride (7 equiv) in the presence of
K2CO3 (3 equiv) in anhydrous CH2Cl2 at room temperature over-
night to provide the donor 3, in only 10% yield.12 However, when
CH2Cl2 without drying pretreatment was used, the donor 3 was ob-
tained in 70% yield in 4 h. These results indicated that a little mois-
ture benefits the reaction. Further optimization showed a better
result: The donor 3 was obtained in quantitative yield in 2 h, with
acetone as solvent, and only 3 equiv of N-phenyltrifluoroacetimi-
doyl chloride was needed. Fructosyl imidate 3 was purified by sil-
ica gel column chromatography and was stable in storage at 4 °C
for at least five weeks. The facile preparation and stability of 3 bode
well for its possible advantages for applications in the synthesis of
fructofuranosides.
A
C
A
A
5f
Only
10
11
12
4g
4h
4i
5g or 5g0
5h
a
—
Only
No reaction
a
A: ꢀ20 °C, 0.06 equiv TMSOTf, CH2Cl2, then rt 1 h.
B: ꢀ20 °C, 0.06 equiv TMSOTf, CH3CN, then rt 1 h.
b
c
C: ꢀ20 °C, 0.06 equiv TMSOTf, CH2Cl2, then 0 °C, additional 0.06 equiv TMSOTf,
rt 1 h.
d
Isolated yield.
Isolated yield for the
The ratio was determined by HPLC.
e
f
a-anomer.
added slowly. After 2 h, the promotor was quenched with Et3N.
Usual workup provided admantanyl -fructofuranoside 5a stere-
oselectively in 97% yield (Table 2, entry 1). Replacement of CH2Cl2
The donor properties of 3 were first examined with admantanol
4a as the acceptor (Scheme 3). To a stirring mixture of 3, 4a and
4 Å MS in CH2Cl2 at ꢀ20 °C under argon, TMSOTf (0.06 equiv) was
a
with CH3CN as solvent also afforded 5a in 92% yield (entry 2).
BzO
O
OBz
NPh
BzO
BzO
O
OBz
OR
BzO
TMSOTf
+ HOR
O
OBz
OBz
CF3
3
4a-i
5a-h
OH
OH
O
MeO
O
O
BnO
O
OH
O
OH
O
O
OH
OAc
O
O
O
OAc
4e
AcO
O
O
4a
4b
4d
4c
O
OBn
HO
O
HO
O
HO
OPiv
BnO
O
BnO
HO
OMe
O
PivO
4f
4g
O
4i
4h
O
PivO
PivO OPiv
BzO
BzO
O
BzO
BzO
O
OBz
OBz
OBz
OBz
O
BzO
BzO
BzO
BzO
BzO
O
O
O
O
O
O
O
O
O
OMe
O
OBz
OBz
OBz
5c
OBz
O
O
O
5b
5d
5a
O
O
OBn
BzO
O
BzO
O
O
OBz
OBz
O
BzO
Ph
O
BzO
O
O
BzO
Ph
O
OAc
BzO
O
O
O
O
O
O
OBz
OBz
5f
AcO
AcO
OBz
OBz
5e
5g
OBz
5g'
BzO
O
OBz
OBn
BzO
O
O
BnO
OBz
5h
BnO
OMe
Scheme 3. Acceptor substrates (4) and products (5) in fructosylation reactions.

2994
G. Lian et al. / Carbohydrate Research 343 (2008) 2992–2996
BzO
O
BzO
BzO
OR
:OR
BzO
OBz
OBz
Ph
BzO
BzO
O
O
BzO
O
BzO
OBz
OR
O
BzO
O
OBz
β -fructoside
Ph
Ph
O
O
OBz
OBz
:OR
OBz
or
OBz
BzO
O
BzO
O
α -fructoside
O
5g'
OR
O
OBz
:OR
OBz
α -fructoside
5g
O
O
O
BzO
BzO
O
NaOMe
Ph
OH
O
HO
O
Ph
O
O
Suffered serious
loss during column
chromatography
OBz
OH
5g
6g
O
O
Ph
Ph
NaOMe
O
BzO
O
HO
O
O
O
O
OBz
OH
OBz
5g'
OH
6g'
Scheme 4.
Although acetonitrile was reported to improve the b-glycosylation
selectivity;13 here there was no solvent effect. The anomeric config-
uration of the fructofuranosides was assigned by the characteristic
C-2 signals in the 13C NMR spectra. C-2 resonances at higher field,
around 103–105 ppm, were assigned as b-fructofuranosides, and
C-2 signals at lower field, around 107–109 ppm, were assigned as
with sodium methoxide to determine the exact NGP pattern15
(Scheme 4). Unfortunately, due to the lability of deacylated orthoes-
ter to weak acidic conditions, the product 6g (or 6g0) suffered serious
loss during silica gel column chromatography with CH2Cl2–MeOH as
eluent. Although the exact NGP pattern was not resolved, the iso-
lated orthoester provided valuable mechanism information, helping
to explain the stereoselectivity of the glycosylation. Participation of
a
-linkages.2
Thus, the optimized glycosylation conditions were applied to
the acyl group on O-3 would result in exclusive a-selectivity, and
other acceptors (4bꢀi). For most of the acceptors, the
a
-fructofur-
participation by the acyl group on O-1 suggests a possible pathway
for b-fructosylation (Scheme 4).
anosides were obtained in fair to excellent yields (Table 2). This gly-
cosylation method worked well with several other kinds of
acceptors, including primary and secondary hydroxyl glycosyl
acceptors (entries 4, 7, and 11), phenolic or tertiary alcohols (entries
1, 3, and 9), and flavones(entry8). For acceptors4a–4c, 4f and4h, the
In conclusion, fructofuranosyl trifluoroacetimidate 3 exhibits
good glycosyl donor properties, with the
a-fructosylation of fla-
vone 4e and the highly hindered secondary hydroxyl acceptor 4d
being reported for the first time. The glycosylation, which shows
a-fructofuranosides were obtained stereoselectively, all in moder-
good a-selectivity, likely proceeds through an NGP pathway, which
ate to good yield. For the 4-hydroxy acceptor 4h, only the -anomer
a
was proven by the isolation of a stable allylic orthoester interme-
diate. Although the b-fructoside, which is of more biological inter-
est and more difficult to synthesize, could not be obtained in good
yields with the tetrabenzoyl donor 3, the successful application of
N-phenyl trifluoroacetimidate donors to this problem provides a
new protocol to the limited number of fructosylation methods.
Further application studies are ongoing in our laboratory.
was obtained in 63% yield (entry 11) while b-selectivity was re-
ported by Schmidt when phosphite donor was used.4 For 4d, when
0.06 equiv of TMSOTf was used, none of the desired product was ob-
tained; instead a compound, which was proposed to be the orthoes-
ter by-product (5g/5g0 entries 5 and 6) was obtained. With more
0.06 equiv TMSOTf, the a-fructoside was obtained as main product
in 63% yield (entry 7).14 It is noteworthy that for this kind of highly
hindered acceptor, no successful glycosylation of ketoses have been
reported previously, thus demonstrating the remarkable donor
properties of 3. However, for acceptor 4i, which has great steric hin-
drance, glycosylation did not occur (entry 12). For the fructosylation
1. Experimental
1.1. General methods
of flavone 4e, a mixture of fructofuranosides (
a:b = 5:2, by HPLC)
Solvents were purified in the usual way. Thin layer chroma-
tography (TLC) was performed on precoated plates of Silica Gel
was obtained, with the -anomer being isolated in 57% yield (entry
a
8). This reaction represents the first fructosylation of a flavone.
Interestingly, when allylic alcohol was used, an orthoester was
obtained in 63% yield (entry 10), which provided the evidence that
the glycosylation reaction proceeds through the neighboring group
participation (NGP) pathway. The formation of orthoester was con-
firmed by 1H and 13C NMR spectroscopy (123.03 ppm, quaternary
carbon of orthoester). The orthoester was further debenzoylated
The orthoester structure is stable under basic conditions. Treatment of 5g (5g0)
with NaOMe produced 6g or 6g0. For 6g, compared with 5g, the H-3 signal will be
shifted upfield and the two H-1 signals will remain unchanged; and for 6g0, compared
with 5g0, the two H-1 signals will shift upfield and the H-3 signal will remain
unchanged. By comparison of the 1H NMR data of the deacylated product and 5g (5g0),
the structure of the intermediate can be determined.

G. Lian et al. / Carbohydrate Research 343 (2008) 2992–2996
2995
HF254 (0.5 mm, Yantai, China). Flash column chromatography
was performed on Silica Gel H (10–40 m, Yantai, China). Optical
1.6. 1,3,4,6-Tetra-O-benzoyl-
a-fructofuranosyl-(2?6)-1,2:3,4-
l
di-O-isopropylidene- -galactopyranoside (5c)
a-D
rotations were determined with a Perkin–Elmer Model 241 MC
polarimeter. IR spectra were recorded on a NICOLET FTIR-360
spectrometer. NMR spectra were recorded on a Bruker AM 300
spectrometer with Me4Si as the internal standard. Mass spectra
were recorded on a HP5989A or a VG Quatro mass spectrometer.
Elemental analyses were recorded on a Perkin–Elmer Model
2400 instrument.
Yield: 96%.
½
a 2D5
ꢁ
ꢀ0.4 (c 1.1, CHCl3), 1H NMR (300 MHz,
CDCl3): d 8.20ꢀ7.23 (20H, Ar), 5.92 (d, 1H, J 1.2 Hz), 5.55 (dd,
1H, J 4.5 Hz), 5.51 (d, 1H, J 5.1 Hz), 4.97 and 4.40 (AB, 2H, J
12.0 Hz), 4.86 (dd, 1H, J 11.4 Hz), 4.74ꢀ4.67 (m, 2H), 4.54 (dd,
1H, J 8.1 Hz), 4.31ꢀ4.25 (m, 2H), 4.0 (td, 1H), 3.91ꢀ3.84 (m,
2H), 1.38, 1.37, 1.30, 1.13 (all s, 3H each, Me). 13C NMR
(75 MHz, CDCl3):
109.2, 108.4, 107.2, 96.3 (C-1), 81.4, 81.0, 78.9, 71.0, 70.6, 70.4,
d
166.1, 165.8, 165.5, 164.7, 133.4ꢀ128.2,
1.2. 1,3,4,6-Tetra-O-benzoyl-
a,b-
D
-fructofuranosyl-2-(N-
phenyl)-trifluoroacetimidate (3)
66.9, 63.6, 60.6, 59.5, 25.9, 25.8, 24.9, 24.2. ESIMS m/z calcd
for C46H46O15Na, 861.27. Found: 861.45. IR (cmꢀ1
) m 2983,
To fructoside 1 (594 mg, 1.0 mmol) and 2 (0.45 mL, 3 mmol)
in acetone (AR grade, 8 mL) was added K2CO3 (410 mg, 3 mmol),
and the mixture was stirred at rt for 2 h. The mixture was fil-
tered, concentrated, and the residue was purified by column
chromatography (hexane–EtOAc 7:1) to obtain 3 (691 mg, 90%).
1H NMR (300 MHz, CDCl3): d 8.04ꢀ7.07 (m, 22H, Ar), 7.07 (t,
1H, J 7.5 Hz, NPh–H), 6.73 (d, 2H, J 7.5 Hz, NPh–H), 6.29 (d,
1H, J 6.6 Hz), 6.12 (t, 1H, J 6.0 Hz), 5.27 (d, 1H, J 11.7 Hz), 4.97
(d, 1H, J 12.0 Hz), 4.83ꢀ4.73 (m, 3H). 13C NMR (75 MHz, CDCl3):
d 165.94, 165.59, 165.30, 164.99, 143.07, 141.28 (ddd, C@NPh),
131.90ꢀ128.23 (Ar), 119.25, 115.72 (ddd, CF3), 106.89, 80.58,
1720, 1270, 1067, 706. Anal. Calcd for C46H46O15: C, 65.86; H,
5.53. Found: C, 65.92; H, 5.71.
1.7. 1,3,4,6-Tetra-O-benzoyl-a-D-fructofuranosyl-(2?3)-1,2:5,6-
di-O-isopropylidene- -glucofuranoside (5d)
a-D
Yield: 63%. ½a 2D5
ꢁ
ꢀ4.1 (c 1.0, CHCl3), 1H NMR (300 MHz, CDCl3): d
8.12ꢀ7.21 (20H, Ar), 6.03 (d, 1H, J 1 Hz), 5.81 (d, 1H, J 3.6 Hz), 5.54
(br s, 1H), 4.82ꢀ4.67 (m, 5H), 4.57ꢀ4.50 (m, 2H), 4.35 (m, 1H),
4.14ꢀ4.01 (m, 2H), 3.87 (m, 1H), 1.47, 1.31, 1.14, 0.86 (all s, 3H
each, Me). 13C NMR (75 MHz, CDCl3): d 166.2, 165.5 (2C), 164.5,
133.9–128.3, 112.0, 109.2, 109.1, 105.0 (C-1), 84.0, 83.4, 80.9,
80.5, 78.6, 75.2, 71.8, 66.9, 63.9, 61.5, 27.0, 26.7, 26.1, 24.6. ESIMS
77.32, 76.61, 64.24, 63.95. Anal. Calcd for C42H52F3NO10
: C,
65.71; H, 4.20; N, 1.82. Found: C, 65.94; H, 4.35; N, 1.75. ESI-
MS (m/z): 790.5 (M+Na+).
m/z calcd for C46H46O15Na, 861.27. Found: 861.45. IR (cmꢀ1
) m
2988, 1728, 1273, 1071, 709. Anal. Calcd for C46H46O15: C, 65.86;
1.3. Typical procedure for the coupling of fructosyl N-
H, 5.53. Found: C, 65.89; H, 5.76.
phenyltrifluoroacetimidate with alcohols
1.8. 3,5,30-Triacetyl-7-benzylquercetin-40-yl-1,3,4,6-tetra-O-
A mixture of the fructosyl trifluoroacetimidate 3 (100 mg,
0.13 mmol), alcohol (0.2 mmol, 1.5 equiv), and 4 Å MS (150 mg)
in anhydrous CH2Cl2 (2 mL) was stirred at ꢀ20 °C for 30 min un-
der Ar. TMSOTf in CH2Cl2 (0.06 equiv, 0.09 mL, 0.09 M) was
added dropwise. After stirring for 1.5 h, the mixture was warmed
to rt and the reaction was monitored by TLC. When complete,
the solution was neutralized by Et3N (0.5 mL), and the resulting
mixture was filtered through Celite. The filtrates were concen-
trated and purified by column chromatography to obtain the
fructoside.
benzoyl-
a-D-fructofuranoside (5e)
a-Anomer was purified by preparative TLC (Rf = 0.28, toluene–
EtOAc 8:1) Yield: 57%. 1H NMR (300 MHz, CDCl3): d 8.14ꢀ7.78
(9 H, m, Ar), 7.70ꢀ7.26 (19H, m, Ar), 6.91 (d, 1H), 6.72 (m, 1H),
6.16 (d, 1H), 5.74 (d, 1H), 5.16 (s, 2H), 4.89ꢀ4.86 (m, 3H),
4.76ꢀ4.68 (m, 2H), 2.45 (s, 3H), 2.31 (s, 3H), 2.21 (s, 3H). 13C
NMR (75 MHz, CDCl3): d 167.0, 169.5, 168.3, 168.0, 166.0, 165.6,
165.2, 164.6, 162.7, 158.0, 153.4, 150.6, 147.5, 142.2, 135.1,
133.7–126.8 (m, Ar), 125.3, 123.5, 120.5, 111.1, 110.4, 109.2,
99.7, 81.9, 81.8, 70.7, 63.1, 60.3, 60.1, 21.1, 21.0, 20.5, 20.4. ESIMS
m/z calcd for C62H48O19Na: 1119.29. Found: 1119.60.
1.4. Adamantan-1-yl 1,3,4,6-tetra-O-benzoyl-a-D-
fructofuranoside (5a)
1.9. t-Butyl 1,3,4,6-tetra-O-benzoyl-
a
-
D
-fructofuranoside (5f)
Yield: 97%. ½a 2D5
ꢁ
+11.0 (c 1.0, CHCl3), 1H NMR (300 MHz, CDCl3):
d 8.13ꢀ7.22 (20H, Ar), 5.87 (d, 1H, J 1.6 Hz), 5.50 (dd, 1H, J 4.1 Hz),
4.82ꢀ4.63 (m, 5H), 2.11 (s, 3H), 2.0 (br s, 6H), 1.61 (br s, 6H). 13C
NMR (75 MHz, CDCl3): d 166.2, 165.8, 165.7, 164.7, 133.4ꢀ128.2,
108.0, 82.8, 81.3, 78.6, 77.2, 64.0, 63.5, 44.3, 36.1, 30.9. ESIMS m/
z calcd for C44H42O10Na: 753.27. Found: 753.35. Anal. Calcd for
Yield: 70%. ½a 2D6
ꢁ
+16.8 (c 1.1, CHCl3), 1H NMR (300 MHz, CDCl3):
d 8.15ꢀ7.22 (20H, Ar), 5.88 (d, 1H, J 0.9 Hz), 5.49 (d, 1H, J 2.7 Hz),
4.86ꢀ4.60 (m, 5H), 1.43 (s, 9H). 13C NMR (75 MHz, CDCl3): d
166.2, 165.8, 165.7, 164.7, 133.4ꢀ128.3, 108.1, 82.7, 81.5, 78.7,
64.1, 62.9, 60.3, 30.7. ESIMS m/z calcd for C38H36O10Na:
C44H42O10: C, 72.31; H, 5.79. Found: C, 72.20; H, 5.76. IR (cmꢀ1
max = 2910, 1725, 1273, 1112, 709.
)
675.2206. Found 675.2207. IR (cmꢀ1
1113, 710.
) mmax = 2979, 1725, 1273,
m
1.5. 40-Methoxyphenyl 1,3,4,6-tetra-O-benzoyl-
a-
D
-
1.10. Methyl 1,3,4,6-tetra-O-benzoyl-a-D-fructofuranosyl-
fructofuranoside (5b)
(2?4)-2,3,6-tri-O-benzyl- -glucofuranoside (5h)
a-D
Yield: 97%. ½a 2D5
ꢁ
ꢀ30.6 (c 0. 5, CHCl3), 1H NMR (300 MHz, CDCl3):
Yield: 63%. ½a 2D6
ꢁ
ꢀ11.8 (c 1.5, CHCl3), 1H NMR (300 MHz,
d 8.14ꢀ7.25 (m, 20H), 7.12 (d, 2H, MP-H), 6.80 (d, 2H, MP-H), 6.21
(t, 1H, J 1.5 Hz), 5.68 (dd, 1H, J 4.8, 1.8 Hz), 4.89ꢀ4.76 (m, 3H), 4.58
(s, 2H), 3.76 (s, 3H, OMe). 13C NMR (75 MHz, CDCl3): d 166.3, 165.9,
165.6, 164.8, 156.2, 146.5, 133.4–128.1, 123.1, 115.9, 114.4, 109.0,
81.4, 78.3, 63.5, 60.6, 55.5, 55.2. ESIMS m/z calcd for C41H34O11Na:
CDCl3): d 8.15ꢀ7.09 (35H, Ar), 6.01 (d, 1H, J 5.4 Hz), 5.70 (dd,
1H, J 5.4, 6.3 Hz), 4.94ꢀ3.56 (m, 18H), 3.45 (s, 3H). 13C NMR
(75 MHz, CDCl3):
d
165.9, 165.5, 165.4, 164.9, 138.2ꢀ125.3,
107.6, 97.6, 82.3, 80.3, 80.1, 78.5, 76.8, 75.8, 73.4, 73.1, 72.9,
70.2, 69.3, 64.1, 63.0, 55.1. ESIMS m/z calcd for C62H58O15Na:
725.1993. Found: 725.1998. IR (cmꢀ1
1236, 1029, 711.
)
m
max = 1728, 1511, 1273,
1065.3673. Found: 1065.3668. IR (cmꢀ1
1272, 1097, 710.
) mmax = 2918, 1729,

2996
G. Lian et al. / Carbohydrate Research 343 (2008) 2992–2996
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(N-phenyl)-trifluoroacetimidate (5g or 5g0)
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1H NMR (300 MHz, CDCl3): d 8.06ꢀ7.24 (m, 20H, Ar), 5.78 (m,
1H), 5.53 (d, 1H), 5.23–5.07 (m, 3H), 4.93ꢀ4.69 (m, 3H),
4.37ꢀ4.23 (m, 2H), 3.89 (m, 2H). 13C NMR (75 MHz, CDCl3): d
166.0, 165.9, 165.5, 135.2, 133.5ꢀ126.4, 123.0, 116.8, 114.3, 85.7,
84.9, 78.3, 65.0, 64.5, 63.9.
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This work was supported by the National Natural Science Foun-
dation of China (29925203) and the Committee of Science and
Technology of Shanghai (02QMA1401). F.L. thanks the Open Foun-
dation of State Key Lab of Biochemistry and Natural Products
Chemistry, SIOC.
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