A simple and convenient method for the synthesis of pyranoid glycals

Article abstract of DOI:10.1016/j.carres.2009.10.003

A simple, mild, and environmentally benign synthesis procedure of pyranoid glycals is described. In a novel fashion, protected glycopyranosyl bromides undergo the reductive elimination in the presence of zinc in phosphate buffer at room temperature. The pyranoid glycals were obtained in good-to-excellent yields (18 examples).

Full text of DOI:10.1016/j.carres.2009.10.003

Carbohydrate Research 345 (2010) 168–171
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Carbohydrate Research
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Note
A simple and convenient method for the synthesis of pyranoid glycals
Jinzhong Zhao a,b,c, Shanqiao Wei a,c, Xiaofeng Ma a,c, Huawu Shao a,
*
a Natural Products Research Center, Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu 610041, China
b Shanxi Agriculture University, Taigu Shanxi 030801, China
c Graduate School of Chinese Academy of Sciences, Shijingshan, Yuquan Road, 19(A), Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple, mild, and environmentally benign synthesis procedure of pyranoid glycals is described. In a
novel fashion, protected glycopyranosyl bromides undergo the reductive elimination in the presence of
zinc in phosphate buffer at room temperature. The pyranoid glycals were obtained in good-to-excellent
yields (18 examples).
Received 5 May 2009
Received in revised form 30 September
2009
Accepted 12 October 2009
Available online 15 October 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Glycals
Phosphate buffer
Glycopyranosyl bromides
Zinc
Reductive elimination
Glycals are used extensively in the synthesis of O-glycosides,1–3
C-glycosides,4–11 S-glycosides,12,13 N-glycosides,14–16 cyclopropa-
nated carbohydrates,17,18 and natural products.19–23 Many glyco-
conjugates can be synthesized via the glycal method, and glycals
have also been used in glycosylation reactions as glycosyl donors
or glycosyl acceptors.24–27 Most 2-C-branched sugars can be syn-
thesized through 1,2-cyclopropanation followed by selective ring
opening via solvolysis,28–32 and a majority of the 1,2-cyclopropane
derivatives have been prepared from glycals. Hence it is necessary
to develop a simple, convenient, and environmentally benign
method to produce a variety of glycals of different configurations.
The traditional synthesis of glycals involves treating a peracet-
ylated glycopyranosyl bromide with zinc in acetic acid.33 The
Fischer–Zach method has been one of the most popular methods
for synthesizing glycals, because the products of this method are
suitable for the synthesis of many other natural products. Over
the years, numerous synthetic methods for glycals have been
developed, including the reduction of protected glycosyl halides
by Na,34 lithium naphthalenide, Li–NH3,35 Zn–Ag, (Cp2TiCl)2,36–38
importance of glycals and their derivates in the synthesis of oligo-
saccharides and natural products, a strong impetus has been given
to develop a mild, simple, less toxic, economically convenient, and
user-friendly reaction protocol for the synthesis of glycals. How-
ever, there have been no reports on the use of phosphate buffer
for the synthesis of pyranoid glycals. As part of our continuing
interest in the development of new synthetic methodologies, we
disclose our results on the synthesis of pyranoid glycals from pro-
tected glycopyranosyl bromides in the presence of zinc in phos-
phate buffer at room temperature.
Initially, treatment of the tetra-O-acetyl-
bromide (1) with Zn–CuSO4 in acetic acid following the
Fischer–Zach method afforded the corresponding -glucal (2,
a-D-glucopyranosyl
a
D
Scheme 1), but the method requires a lower temperature and intri-
cate laboratory operations (Table 1, entry 1). When 1 was treated
with Zn–CuSO4 in phosphate buffer at room temperature, a good
result was obtained (Table 1, entry 2), and the yield was also the
same as that obtained by using Zn alone in phosphate buffer at
room temperature (Table 1, entry 3). But the reaction of 1 with
Fe in phosphate buffer gave only a modest yield of 2 (Table 1, entry
Cr(II),39,40 Al–Hg, K-graphite,41 Zn–AcOH–THF,42 Zn–N-base,43
44
Zn–MeOH–vitamin-B12
,
Zn–Ag, Na naphthalenide, and Al–Hg,45
or by using thiophenyl glycoside,46 glycosyl sulfones,47 glycosyl
sulfoxides,48 and an electrochemical approach.49 However, there
are several drawbacks in the above-mentioned methods, including,
for example, the use of very expensive and toxic reagents, low tem-
peratures, and intricate laboratory operations. In view of the
OAc
OAc
O
O
AcO
AcO
AcO
AcO
OAc
2
1
Br
* Corresponding author. Fax: +86 28 85222753.
E-mail address: shaohw@cib.ac.cn (H. Shao).
Scheme 1. Synthesis of glucal 2 from the protected tetra-O-acetyl-
anosyl bromide (1).
a-D-glucopyr-
0008-6215/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2009.10.003

J. Zhao et al. / Carbohydrate Research 345 (2010) 168–171
169
Table 1
Optimization for the synthesis of pyranoid glycal 2 from the protected tetra-O-acetyl-
-D-glucopyranosyl bromide (1)
Table 2
Synthesis of substituted pyranoid glycals from protected pyranosyl bromides
a
Entry
Starting material
Glycal
Yield (%)
Entry
Conditions
Yield (%)
OAc
OAc
1
2
3
4
5
6
7
8
9
Zn, CuSO4, NaOAc, HOAc, H2O, ꢀ15 to 0 °C, 6 h
Zn, CuSO4, phosphate buffer (pH 4.5), rt, 6 h
Zn, phosphate buffer (pH 4.5), rt, 6 h
Fe, saturated NaH2PO4 solution, rt, 4 h
Zn, phosphate buffer (pH 6.0), rt, 6 h
Zn, phosphate buffer (pH 7.0), rt, 6 h
Zn, phosphate buffer (pH 8.0), rt, 8 h
Zn, saturated NaH2PO4 solution, rt, 5 h
Zn, saturated NaH2PO4 solution, acetone, rt, 2 h
Zn, saturated NaH2PO4 solution, EtOAc, rt, 2 h
67
80
80
45
80
75
40
85
90
90
O
O
AcO
AcO
AcO
AcO
1
90
83
OAc
Br
1
2
OAc
OAc
OAc
O
O
AcO
AcO
AcO
AcO
2
3
10
2
Br
3
OAc
OAc
AcO
OAc OAc
O
O
4). Encouraged by the results obtained with the tetra-O-acetyl-a-D-
glucopyranosyl bromide 1 and Zn in phosphate buffer, we turned
our attention to Zn and a different phosphate buffer. Interestingly,
treating tetra-O-acetyl-
81
90
AcO
OAc
20
Br
O
4
a-D-glucopyranosyl bromide 1 with Zn in
AcO
O
different phosphate buffers (pH 6.0, 7.0, and 8.0), all afforded
D
-
AcO
glucal 2 (Table 1, entries 5–7). Saturated NaH2PO4 solution proved
to be a very efficient system, giving a good yield of 2 (Table 1, entry
8). When 1 was treated with Zn-saturated NaH2PO4 solution in the
presence of a little acetone or EtOAc, the yield of 2 was increased to
90%, and the reaction time was shortened to only 2 h (Table 1, en-
tries 9 and 10). Meanwhile, the glucal can also be synthesized un-
der neutral conditions (Table 1, entry 6). Hence, this method is
superior in comparison with the classical Fischer–Zach method.
To explore the synthetic potential of the method, reactions
involving 18 examples (Table 2, 1 and 3–19) were performed on
a preparative scale in Zn-saturated NaH2PO4 solution (Scheme 2).
To our delight, treatment of the acetylated glycopyranosyl bro-
mides 3–7 with Zn gave pyranoid glycals 2 and 20–23 in good-
to-excellent yields. Benzylated pyranoid glycals 29–31 and 6-O-
acetyl benzylated pyranoid glycals 32 could be afforded in modest
yield. In all cases the pyranoid glycals (2 and 20–23) were obtained
in 64–92% isolated yields (Table 2, entries 1–18). Importantly, 6-O-
mesyl, 6-O-tosyl, and 6-azido pyranoid glycals 24–28 were accessi-
ble in good yield using this method. A variety of protecting groups,
including acetyl, benzyl, methanesulfonyl, and p-tolylsulfonyl
groups, were stable under the reaction conditions. An advantage
of the new methodology is that the groups of the starting material
are typically either acid or base stable, and a wide variety of reac-
tions can be utilized in modifying the protecting groups on the gly-
cal products.
AcO
4
OAc
21
OAc
Br
5
O
O
AcO
AcO
AcO
AcO
5
6
76
87
OAc
Br
Br
6
22
O
Me
O
Me
AcO
AcO
OAc
23
OAc
OAc
7
OMs
OMs
O
O
AcO
AcO
AcO
7
8
89
75
65
71
AcO
OAc
Br
8
24
OTs
OTs
O
O
AcO
AcO
AcO
AcO
OAc
Br
9
OMs
25
OMs
OAc
O
O
AcO
AcO
AcO
AcO
9
In summary, we have developed a mild and efficient protocol
for the synthesis of variously protected pyranoid glycals using
Zn-saturated NaH2PO4 as an inexpensive and environmentally
friendly system. In the preparation of pyranoid glycals, various
methods have been used for enhancing the activity of zinc, but or-
dinary zinc dust has high activity and does not need to be activated
by using other reagents in phosphate buffer. The method offers sig-
nificant advantages, such as low toxicity, simple operation, mild
reaction conditions, high yields, and low cost, which makes it an
attractive process for the synthesis of pyranoid glycals.
Br
10
OTs
24
OTs
OAc
O
O
AcO
AcO
AcO
AcO
10
Br
11
OMs
25
OMs
OAc
AcO
OAc
AcO
O
O
11
92
OAc
26
Br
12
OTs
OTs
OAc
OAc
AcO
1. Experimental
O
O
12
13
80
85
AcO
The reactions were monitored by thin-layer chromatography
(TLC) using silica gel HSGF254 plates. Flash chromatography was
performed using silica gel HG/T2354-92. 1H NMR and 13C NMR
(600 and 150 MHz, respectively) spectra were recorded in CDCl3.
1H NMR chemical shifts are reported in ppm (d) relative to tetra-
methylsilane (TMS) with the solvent resonance employed as the
internal standard (CDCl3, d 7.26 ppm). Data are reported as follows:
chemical shift, multiplicity (s = singlet, d = doublet, t = triplet,
OAc
13
Br
27
N3
N3
OAc
O
O
AcO
AcO
AcO
AcO
28
(continued on next page)
Br
14

170
J. Zhao et al. / Carbohydrate Research 345 (2010) 168–171
1.1.2. 3,4,6-Tri-O-acetyl-D-galactal (20)
Table 2 (continued)
Colorless syrup: ½a D25
ꢁ
ꢀ9 (c 1.0, EtOAc); lit.50
½
a 2D3
ꢁ
ꢀ17 (c 1.1,
Entry
Starting material
Glycal
Yield (%)
67
CHCl3); Rf 0.38 (1:2 petroleum ether–EtOAc). 1H NMR (CDCl3): dH
2.03 (s, 3H), 2.09 (s, 3H), 2.13 (s, 3H), 4.22 (dd, 1H, J = 11.6, 5.2),
4.28 (dd, 1H, J = 11.6, 7.2), 4.33 (m, 1H), 4.73 (m, 1H), 5.43 (dd,
1H, J = 3.8, 1.1), 5.56 (d, 1H, J = 1.0), 6.46 (d, 1H, J = 5.2).
Br
O
Me
BnO
O
BnO
14
OBn
29
OBn
OAc
15
OBn
1.2. General procedure for the synthesis of pyranoid glycals 21
and 22
OBn
OAc
O
O
O
BnO
BnO
BnO
15
16
17
18
75
64
70
65
BnO
The glycopyranosyl bromide (1 mmol) was dissolved in acetone
(6.0 mL), and then sodium dihydrogen phosphate dihydrate (3.4 g,
21.7 mmol) and zinc dust (1.0 g, 15.3 mmol) were added. The mix-
ture was stirred for 10 min, then H2O (0.6 mL) was added. The
reaction mixture was stirred for 3 h at room temperature, and
TLC (1:1 petroleum ether–EtOAc) indicated that the reaction was
complete. The solution was extracted with EtOAc. The organic
phase was washed with water, satd NaHCO3, and brine, and then
dried over MgSO4 and concentrated. The residue was purified by
silica gel column chromatography (2:1 petroleum ether–EtOAc).
Br
30
16
OBn
OBn
O
BnO
BnO
BnO
BnO
OAc
17
Br
30
OBn
OBn
OBn
OBn
O
O
BnO
BnO
OAc
18
OAc
Br
31
1.2.1. 3,4-Di-O-acetyl-
D
-arabinal (21)
OAc
Colorless syrup: ½a D25
ꢁ
+200 (c 0.9, CH2Cl2), lit.40
½
a 2D5
+262 (c 0.9,
ꢁ
O
O
CHCl3); Rf 0.55 (2:1 petroleum ether–EtOAc). 1H NMR (CDCl3): dH
2.07 (s, 3H), 2.08 (s, 3H), 3.98 (dd, 1H, J = 10.6, 9.6), 4.03 (m, 1H),
4.85 (dd, 1H, J = 5.8, 5.2), 5.19 (m, 1H), 5.44 (dd, 1H, J = 4.8, 4.2),
6.50 (d, 1H, J = 6.0). HRESIMS: calcd for C9H12NaO5 [M+Na] m/z
223.0577; found m/z 223.0564.
BnO
BnO
BnO
BnO
OAc
19
Br
32
R"
R"
1.2.2. 3,4-Di-O-acetyl- -xylal (22)
Colorless syrup: ½a D25
ꢁ
D ꢀ301 (c 1.9, CHCl3), lit.40
½
a 2D5
ꢁ
ꢀ303 (c 2.3,
Zn-saturated NaH2PO4
rt
O
O
R'O
R'O
R'O
R'O
CHCl3); Rf 0.57 (2:1 petroleum ether–EtOAc). 1H NMR (CDCl3): dH
2.07 (s, 3H), 2.10 (s, 3H), 3.98 (dd, 1H, J = 12.3, 1.4), 4.19 (m, 1H),
4.95–4.97 (m, 2H), 5.00 (m, 1H), 6.60 (d, 1H, J = 6.3).
OAc
Br
Scheme 2. Synthesis of pyranoid glycals from protected pyranosyl bromides.
1.3. General procedure for the synthesis of pyranoid glycals
23–32
m = multiplet), integration, and coupling constants (Hz). 13C NMR
chemical shifts are reported in ppm from tetramethylsilane
(TMS) with the solvent resonance as the internal standard (CDCl3,
d 77.0 ppm). ESIHRMS spectra were recorded on a BioTOF Q instru-
ment. Optical rotations were acquired on a Perkin–Elmer 341 Dig-
ital Polarimeter.
The glycopyranosyl bromide (1 mmol) was dissolved in EtOAc
(2.0 mL), and then saturated sodium dihydrogen phosphate solu-
tion (4.0 mL) and zinc dust (0.82 g, 12.5 mmol) were added. The
reaction mixture was stirred for 3 h at room temperature, at the
end of which time TLC (2:1 petroleum ether–EtOAc) indicated that
the reaction was complete. The solution was extracted with EtOAc.
The organic phase was washed with water, satd NaHCO3, and
brine, then dried over MgSO4 and concentrated. The residue was
purified by silica gel column chromatography (4:1?2:1 petroleum
ether–EtOAc).
1.1. General procedure for the synthesis of pyranoid glycals
2 and 20
The glycopyranosyl bromide (1 mmol) was dissolved in acetone
(2.0 mL), and then satd sodium dihydrogen phosphate solution
(4.0 mL) and zinc dust (0.82 g, 12.5 mmol) were added. The reac-
tion mixture was stirred for 5 h at room temperature, at the end
of which time TLC (1:1 petroleum ether–EtOAc) indicated that
the reaction was complete. The solution was extracted with EtOAc.
The organic phase was washed with water, satd NaHCO3, and
brine, and then dried over MgSO4 and concentrated. The residue
was purified by silica gel column chromatography (2:1 petroleum
ether–EtOAc).
1.3.1. 3,4-Di-O-acetyl- -rhamnal (23)
Colorless syrup: ½aꢁ2DL5 +65 (c 1.1, CH2Cl2), lit.51
½
a 2D5
+55 (c 1.0,
ꢁ
CHCl3); Rf 0.63 (2:1 petroleum ether–EtOAc). 1H NMR (CDCl3): dH
1.31 (d, 3H, J = 6.6), 2.04 (s, 3H), 2.08 (s, 3H), 4.11 (m, 1H), 4.78
(dd, 1H, J = 6.2, 3.1), 5.03 (dd, 1H, J = 8.2, 6.2), 5.34 (m, 1H), 6.43
(d, 1H, J = 6.0).
1.3.2. 3,4-Di-O-acetyl-6-O-methanesulfonyl-D-glucal (24)
Colorless syrup: ½a D25
ꢁ
ꢀ4 (c 0.3, CHCl3), lit.52
½
a 1D7
+15 (c 1.6,
ꢁ
EtOH); Rf 0.43 (2:1 petroleum ether–EtOAc); 1H NMR (CDCl3) dH
2.06 (s, 3H), 2.10 (s, 3H), 3.07 (s, 3H), 4.35 (m, 2H), 4.47 (dd, 1H,
J = 11.6, 6.2), 4.89 (dd, 1H, J = 6.2, 3.5), 5.21 (dd, 1H, J = 7.4, 5.6),
5.35 (m, 1H), 6.48 (d, 1H, J = 6.2).
1.1.1. 3,4,6-Tri-O-acetyl-D-glucal (2)
White powder: mp 50–51 °C, lit.40 mp 50–52 °C; ½a D25
ꢀ22 (c
ꢁ
4.1, CHCl3), lit.40
½
a 2D0
ꢁ
ꢀ22 (c 2.1, CHCl3); Rf 0.38 (2:1 petroleum
ether–EtOAc); 1H NMR (CDCl3): dH 2.05 (s, 3H), 2.08 (s, 3H), 2.10
(s, 3H), 4.20 (dd, 1H, J = 12.4, 3.1), 4.26 (m, 1H), 4.40 (dd, 1H,
J = 12.2, 5.8), 4.85 (dd, 1H, J = 9.5, 3.3), 5.22 (dd, 1H, J = 7.5, 6.0),
5.35 (dd, 1H, J = 4.2, 3.7), 6.47 (d, 1H, J = 6.2).
1.3.3. 3,4-Di-O-acetyl-6-O-p-toluenesulfonyl-D-glucal (25)
White powder: mp 106–107 °C, lit.53 mp 106–107 °C; ½a 2D5
ꢁ
+16
(c 1.5, CHCl3), lit.53
½
a 2D2 +14 (c 1, CHCl3); 1H NMR (CDCl3): dH 2.03
ꢁ

J. Zhao et al. / Carbohydrate Research 345 (2010) 168–171
171
(s, 3H), 2.04 (s, 3H), 2.46 (s, 3H), 4.23 (m, 3H), 4.82 (dd, 1H, J = 6.2,
Supplementary data
3.5), 5.13 (dd, 1H, J = 3.7, 3.7), 5.27 (dd, 1H, J = 6.2, 5.5), 6.35 (d, 1H,
J = 6.0), 7.35 (d, 2H, J = 7.9), 7.80 (d, 2H, J = 8.4).
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.carres.2009.10.003.
1.3.4. 3,4-Di-O-acetyl-6-O-methanesulfonyl-D-galactal (26)
Colorless syrup: ½a D25
ꢀ5 (c 0.4, CH2Cl2); Rf 0.25 (2:1 petro-
ꢁ
References
leum ether–EtOAc). 1H NMR (CDCl3): dH 2.06 (s, 3H), 2.10 (s,
3H), 3.07 (s, 3H), 4.33–4.37 (m, 2H), 4.48 (dd, 1H, J = 6.0, 2.9),
4.89 (dd, 1H, J = 6.0, 3.3), 5.21 (dd, 1H, J = 7.2, 5.5), 5.35 (dd,
1H, J = 4.3, 3.5), 6.48 (d, 1H, J = 6.2). 13C NMR (CDCl3): dC 20.8,
20.9, 37.8, 65.6, 66.9, 67.0, 73.6, 99.4, 145.3, 169.8, 170.3. HRE-
SIMS: calcd for C11H16Na1O8S1 [M+Na] m/z 331.0464, found m/z
331.0474.
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1.3.5. 3,4-Di-O-acetyl-6-O-p-toluenesulfonyl-
D-galactal (27)
Colorless syrup: ½a D25
ꢁ
+3 (c 0.2, CH2Cl2); Rf 0.45 (2:1 petroleum
ether–EtOAc). 1H NMR (CDCl3): dH 2.01 (s, 3H), 2.05 (s, 3H), 2.46 (s,
3H), 4.14 (dd, 1H, J = 10.5, 4.4), 4.28 (dd, 1H, J = 10.6, 7.7), 4.32 (m,
1H), 4.72 (dd, 1H, J = 6.1, 3.1), 5.37 (s, 1H), 5.48 (s, 1H), 6.35 (d, 1H,
J = 6.1), 7.36 (d, 2H, J = 8.2), 7.79 (d, 2H, J = 8.2). 13C NMR (CDCl3):
dC 20.5, 20.7, 21.7, 63.5, 63.8, 66.7, 72.4, 98.9, 128.0, 129.9, 132.6,
145.2, 169.8, 170.1. HR-ESIMS: calcd for C17H20Na1O8S1 [M+Na] m/
z 407.0777, found m/z 407.0779.
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1.3.6. 3,4-Di-O-acetyl-6-azido-6-deoxy-D-glucal (28)
Colorless syrup: ½a D25
ꢁ
ꢀ46 (c 1.2, CH2Cl2), lit.54
[
a
] ꢀ6 (c 1.9,
CHCl3); Rf 0.61 (2:1 petroleum ether–EtOAc). 1H NMR (CDCl3) dH
2.06 (s, 3H), 2.10 (s, 3H), 3.56 (dd, 1H, J = 11.0, 6.5), 3.61 (dd, 1H,
J = 11.2, 5.0), 4.29 (dd, 1H, J = 11.8, 6.0), 4.87 (dd, 1H, J = 6.0, 3.5),
5.28–5.31 (m, 2H), 6.50 (d, 1H, J = 6.1).
24. Bussolo, V. D.; Romano, M. R.; Pineschi, M.; Crotti, P. Org. Lett. 2005, 7, 1299–
1302.
1.3.7. 3,4-Di-O-benzyl-
L
-rhamnal (29)
Colorless syrup: ½a D25
ꢁ
+37 (c 0.9, CH2Cl2), lit.55
½
a 2D2
+64 (c 1.0,
ꢁ
25. Kim, J. Y.; Bussolo, V. D.; Gin, D. Y. Org. Lett. 2001, 3, 303–306.
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4726–4734.
CHCl3); Rf 0.72 (5:1 petroleum ether–EtOAc). 1H NMR (CDCl3): dH
1.40 (d, 3H, J = 6.5), 3.51 (dd, 1H, J = 9.0, 7.3), 3.97 (m, 1H), 4.24
(m, 1H), 4.59 (d, 1H, J = 11.7), 4.68 (d, 1H, J = 11.8), 4.73 (d, 1H,
J = 11.3), 4.87–4.91 (m, 2H), 6.38 (d, 1H, J = 6.1), 7.29–7.38 (m,
10H).
29. Shao, H.; Ekthawatchai, S.; Wu, S.-H.; Zou, W. Org. Lett. 2004, 6, 3497–3499.
30. Lebel,H.;Marcoux,J.-F.;Molinaro,C.;Charette,A.B.Chem. Rev. 2003,103, 977–1050.
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1.3.8. 3,4,6-Tri-O-benzyl-D-glucal (30)
White powder: mp 56–57 °C, lit.56 mp 55 °C; ½a D25
ꢀ6 (c 1.9,
ꢁ
CH2Cl2), lit.56
½
a 2D2
ꢁ
ꢀ3 (c 16.5, CHCl3); Rf 0.53 (4:1 petroleum
ether–EtOAc). 1H NMR (CDCl3): dH 3.77–3.85 (m, 2H), 3.88 (m,
1H), 4.08 (m, 1H), 4.23 (s, 1H), 4.56–4.62 (m, 3H), 4.64–4.68 (m,
2H), 4.85 (dd, 1H, J = 11.3, 4.1), 4.88 (m, 1H), 6.44 (m, 1H), 7.26–
7.34 (m, 15H).
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1.3.9. 6-O-Acetyl-3,4-di-O-benzyl-D-glucal (32)
Colorless syrup, ½a D25
ꢁ
ꢀ7 (c 1.2, CH2Cl2), lit.57
½
a 2D5
+2 (c 1.1,
ꢁ
CHCl3); Rf 0.44 (4:1 petroleum ether–EtOAc). 1H NMR (CDCl3): dH
2.06 (s, 3H), 3.79 (dd, 1H, J = 13.6, 7.0), 4.11 (m, 1H), 4.24 (m,
1H), 4.37 (dd, 1H, J = 12, 5.4), 4.42 (d, 1H, J = 12.1), 4.57 (d, 1H,
J = 11.6), 4.67 (d, 1H, J = 12.1), 4.68 (d, 1H, J = 11.4), 4.87 (d, 1H,
J = 11.2), 4.92 (dd, 1H, J = 3.8, 2.2), 6.41 (d, 1H, J = 6.0), 7.28–7.37
(m, 10H).
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Acknowledgments
We are grateful for the financial support from the Chinese Acad-
emy of Sciences (Hundreds of Talents Program). We also thank the
Analytical and Testing Center of Chengdu Institute of Biology for
NMR and MS analyses.
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