The synthesis and biological activity of novel spiro-isoxazoline C-disaccharides based on 1,3-dipolar cycloaddition of exo-glycals and sugar nitrile oxides

Article abstract of DOI:10.1016/j.tetlet.2007.09.007

A series of novel spiro-isoxazoline C-disaccharides were synthesized by the key step of 1,3-dipolar cycloaddition reactions of exo-glycals and sugar nitrile oxides, and followed by catalytic debenzylation in the presence of Pd(OH)₂/C. The cyclo

Full text of DOI:10.1016/j.tetlet.2007.09.007

Tetrahedron Letters 48 (2007) 7813–7816
The synthesis and biological activity of novel spiro-isoxazoline
C-disaccharides based on 1,3-dipolar cycloaddition
of exo-glycals and sugar nitrile oxides
Ping-Zhu Zhang, Xiao-Liu Li,* Hua Chen, Ya-Nan Li and Rui Wang
Department of Chemistry, Laboratory of Chemical Biology, Hebei University, Baoding, Hebei 071002, China
Received 19 June 2007; revised 3 September 2007; accepted 4 September 2007
Available online 6 September 2007
Abstract—A series of novel spiro-isoxazoline C-disaccharides were synthesized by the key step of 1,3-dipolar cycloaddition reactions
of exo-glycals and sugar nitrile oxides, and followed by catalytic debenzylation in the presence of Pd(OH)2/C. The cycloaddition
reactions were carried out stereoselectively and afforded a-isomers exclusively except in the case of galactose. The biological activ-
ities of the novel disaccharides against the glycosidases (a-amylase, a-glucosidase, and b-glucosidase) and HIV and BVDV were
evaluated.
Ó 2007 Elsevier Ltd. All rights reserved.
Spiro-glycosides, such as spiro-nucleosides, spiro-ortho-
esters, and spiro-ketals are very important substructures
found in many biologically active natural products.1–3
For instance, the first isolated natural spironucleoside
(+)-hydantocidin (A) exhibited non-toxically herbicidal
and regulatory plant growth activities,1 glucopyranosyl
spirooxathiazole (B)4 and spiro-(thio)hydantoins (C)5
showed a good glycogen phosphorylase inhibition (see
Fig. 1). These results indicated that the spiro-glycosides
may often have potential bioactivities and have trig-
gered great interest in synthesizing such spiro-furanoid
and pyranoid derivatives and analogues for bioactive
study.6 However, the study on spiro-isoxazoline glyco-
side derivatives is very scarce.7 Considering the strong
biological activities of isoxazoline and spiro-isoxazoline
derivatives including anticancer, antibiotic, or antiviral
and anti-HIV activities,8 we turned our interest to the
synthesis of spiro-isoxazoline saccharides as the contin-
uation of the synthesis of functionalized C-glycosides
using exo-glycal as the precursor,7e,9 and would like to
report herein the synthesis of novel spiro-isoxazoline
C-disaccharides by the key step of the stereoselective
1,3-dipolar cycloaddition of exo-glycals to sugar nitrile
oxides and the studies on the glycosidase inhibitory
and antiviral activities of the C-disaccharides.
exo-Glycals (3–5) were prepared by the methylenation10
from their corresponding sugar lactones with Petasis’s
reagent.11 The sugar nitrile oxides (2a–c) would be
synthesized by the dehydrochlorination of oximinoyl
halides (Huisgen procedure) generated in situ by the
chlorination reaction7b,c of oximes (1a–c), which were
prepared from the corresponding sugar aldehyde deriv-
atives12 as shown in Scheme 1. However, the pure nitrile
oxides (2) were not isolated due to their easily dimeriza-
tion13–15 during separation, and they were directly used
to the next step reaction of 1,3-dipolar cycloaddition
without further purification. It should be mentioned
that the other method for preparing the nitrile oxides
were also examined with 1a, for instance, by a direct oxi-
dation of oxime with hypochlorite14 and by oxime halo-
genation and then dehydrohalogenation using NBS15
O
HO
HO
O
HO
HO
HO
O
O
O
NH
O
NH
N
N
H
OH
O
O
N
H
Ar
S
HO
OH
OH
HO
HO
Keywords: Spiro-isoxazoline; C-Disaccharide; 1,3-Dipolar cycloaddi-
a
b
c
tion; Nitrile oxide; Glycosidase inhibition.
*
Corresponding author. Tel./fax: +86 312 5971116; e-mail: lixl@
hbu.cn
Figure 1.
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.09.007

7814
P.-Z. Zhang et al. / Tetrahedron Letters 48 (2007) 7813–7816
H
C
O
O
O
OBn
HO N
O
OBn
OBn
N
N
C
C
O
OBn
i
ii
O
O
O
O
O
O
O
O
HO
HO
HO
D-Mannose
O
ref.12a
1a
2a
O
OH
H
O
OH
O
OBn
O
HO N
C
O
OBn
i
ii
O
O
O
O
2b
1b
H
C
O N
BnO
C
HO N
BnO
HO
HO
O
O
O
O
O
ref.12b
ii
i
BnO
BnO
OMe
OMe
OMe
OMe
OBn
OBn
OH
BnO
OBn
HO
BnO
2c
1c
Scheme 1. Synthesis of sugar nitrile oxides (2). Reagents and conditions: (i) HONH2HCl (1.2 equiv), THF, Na2CO3, rt, 1 h; (ii) (a) NCS, DCE,
reflux, 20 min; (b) Et3N, rt.
11
BnO
6
BnO
BnO
BnO
BnO
1
7 O
9
R
O
2
N3
O
O
O
O
5'
BnO
i
N
5
4
N
8
N
C
R
O
10
+
O
+
N
6'
O
+
OBn
4'
BnO
OBn
R
R
BnO
3a
BnO
2a-c
OBn
8a2
OBn
6a
6a-c
O
9a-c
O
3: D-Glucoside
4: D-Mannoside
7a-c
12
8a1-c
5: D-Galactoside
5'
O
O
OBn
OBn
O
O
1'
4'
BnO
BnO
OMe
a
R =
c
3'
b
2'
OBn
O
O
O
Scheme 2. The 1,3-dipolar cycloaddition of exo-glycals and sugar nitrile oxides. Reagents and conditions: (i) DCE, reflux 24 h.
and chloramines-T16 as the halogenation reagent,
respectively.
Similarly, the 1,3-dipolar cycloadditions of exo-glycals
(3–5) with the other sugar nitrile oxides 2b, and 2c were
investigated and afforded the corresponding cyclo-
adducts 6b, 6c, 7b, 7c and 8b, 8c, and the dimers (9b
and 9c) of the nitrile oxides 2b and 2c, respectively.
The results are shown in Scheme 2 and Table 1.
The 1,3-dipolar cycloaddition reactions were firstly car-
ried out with exo-glycal (3) and the in situ generated
nitrile oxide (2a).17 Thus, a solution of the L-ribose
oxime (1a) and NCS in 1,2-dichloroethane (DCE) was
refluxed for 20 min, and after cooling to room tempera-
ture the solution of the benzylated exo-glycal 3 and
Et3N in DCE was added dropwise. The reaction mixture
was refluxed for 24 h to afford spiro-isoxazoline disac-
charide 6a as a single diastereoisomer in good yield
and a small amount of dimer (9a) of nitrile oxide (2a)
as the by-product (Scheme 2). It should be mentioned
that although the 1,3-dipolar cycloadditions of the
exo-glycals with the nitrile oxide should be supposed
to afford two diastereomers, that is, the a- and b-ano-
meric isomers, the 1,3-dipolar cycloaddition of 3 with
2a underwent stereospecifically and gave anomeric iso-
mer (6a) exclusively, which was consistent with the
RajanBabu’s report7a and our previous observation.7e
Under the same conditions the cycloaddition of the
mannose derivative 4 to nitrile oxide 2a was carried
out and afforded the corresponding cycloadduct 7a
and the nitrile oxide dimer (9a). However, the cycloaddi-
tion of exo-galactal (5) and 2a provided an inseparable
mixture of two anomeric isomers (diastereoisomers)
8a1 and 8a2 in the ratio of 3:2 which was determined
Subsequently, the debenzylation of cycloadducts (6–8)
was carried out by catalytic hydrogenation with
Table 1. The 1,3-dipolar cycloaddition of exo-glycals (3–5) with nitrile
oxides (2) and the chemical shifts of the spiro carbons of adducts (6–8)
Entry exo-Glycal
Nitrone Products Yields dC-spiro
(%)
(ppm)
BnO
1
2
3
2a
2b
2c
6a
6b
6c
50
71
65
109.23
109.08
108.79
O
BnO
BnO
OBn
3
4
BnO
BnO
4
5
6
2a
2b
2c
7a
7b
7c
50
83
81
109.61
109.77
108.79
O
BnO
OBn
BnO
BnO
7
8a1
8a2
8b
109.82
116.45
109.78
109.47
O
2a
52
8
9
2b
2c
53
55
BnO
OBn
1
8c
by H NMR spectra, and dimer (9a) of the nitrile oxide
5
(2a) (Scheme 2).

P.-Z. Zhang et al. / Tetrahedron Letters 48 (2007) 7813–7816
7815
HO
HO
HO
BnO
BnO
O
O
R'
OH
OH
O
R
O
a
c
b
i
R' =
N
O
N
O
O
O
O
O
OH
BnO
OBn
O
10a-c
6a-c
HO
HO
OMe
11a-c
12a-c
7a-c
8a-c
OH
Scheme 3. Debenzylation of adducts (6–8) by catalytic hydrogenation. Reagents and conditions: (i) MeOH, Pd(OH)2/C, H2, 2 h.
Table 3. Inhibitory activities of the compounds against glycosidases
Pd(OH)2/C in MeOH solution at room temperature and
produced the corresponding debenzylated spiro-isoxaz-
oline C-disaccharides (10–12), respectively (Scheme
3).17 Although the mixture of cycloadducts 8a1 and
8a2 was difficult to separation, the corresponding deben-
zylated products 12a1 and 12a2 could be readily isolated
by flash column chromatography.
Compounds
Inhibition % (in vitro at 2.6 mmol/mL)
a-Amylase
b-Glucosidase
a-Glucosidase
Glucoside
10a
10b
a
23.07
—
16.85
7.35
18.20
8.71
—
—
a
10c
1.87
Mannoside
11a
11b
The structures of cycloadducts (6–8) and the debenzyl-
ated products (10–12) were determined by the analyses
of their spectral data of 1H NMR, 13C NMR, 2D-COSY
and NOESY, and mass spectra. It has been reported
10.60
17.51
39.97
10.45
8.07
12.33
—
1.43
1.76
11c
13
that in the C NMR spectra of C-glycosides9a and
Galactoside
12a1
12b
spiro-C,O-ketosides9b the signals of the anomeric car-
bon in the a-isomers appeared in higher field than those
in the b-isomers. From this point of view, we have pre-
viously assigned the anomeric configurations of spiro-
isoxazolindine C-glycosides by the comparison of the
anomeric signals of the 13C NMR spectra between each
two anomeric isomers.7e,9c Accordingly, with the iso-
lated two anomeric isomers of 12a1 and 12a2 in hand
and considering the structural similarity of the cycload-
ducts, the configuration of cycloadducts 6–8 and their
debenzylated products 10–12 could be confirmed to be
a-form, and 8a2 and 12a2 to be b-isomers by compari-
son of the anomeric signals of their 13C NMR spectra
(see Tables 1 and 2). The stereochemistry of the cycload-
dition was identical to the reports.7a,e,f
24.95
24.01
26.56
5.58
6.90
12.28
—
6.93
—
12c
Acarbose
54.57b
a No inhibition.
b In the concentration of 22.46 lmol/mL.
the spiro-isoxazoline disaccharides on HIV-1 (replica-
tion in MT-4 cells) and BVDV (nose strain, replication
in MDBK cells, a model system of HCV) were also eval-
uated.17 It was found that the compounds had little
inhibitory effects on both the viruses. Further synthesis
and biological study of new C-disaccharides are under
way in this lab.
The glycosidase inhibitory activities of the compounds
were examined on hydrolytic reactions of a-amylase,
a-glucosidase, and b-glucosidase by comparison with
acarbose, respectively.17 As shown in Table 3, although
the compounds gave low inhibitory effects on the glyco-
sidases contrasted to the positive control, a certain
inhibitory selectivity to the three glycosidases was ob-
served, and the inhibitory activities of the compounds
against the enzymes are in the order of a-amylase > b-
glucosidase > a-glucosidase. The antiviral activities of
In summary, we have synthesized a series of novel spiro-
isoxazoline C-disaccharides via the key step of 1,3-di-
polar cycloaddition of exo-glycals and carbohydrate
nitrile oxides, which were in situ generated from the
corresponding oximes. The cycloaddition was carried
out stereospecifically and provided the a-anomeric
isomer exclusively in the cases of D-glucose and D-man-
nose. Hydrogenation of the cycloadducts under the
catalysis of Pd(OH)2/C gave the debenzylated products
with the spiro-isoxazoline ring remaining. The spiro-
isoxazoline C-disaccharides exhibited certain selective
inhibitions against a-amylase, b-glucosidase, and
a-glucosidase, but no anti-HIV and anti-BVDV
activities, providing useful information on the structure
design for the future study.
Table 2. Debenzylation of cycloadducts (6–8) and the chemical shifts
of the spiro carbons of products (10–12)
Entry
Adducts
Products
Yields (%)
dC-spiro (ppm)
1
2
3
4
5
6
6a
6b
6c
7a
7b
7c
10a
10b
10c
63
54
72
60
53
85
45
30
55
73
109.56
108.64
109.54
109.78
109.48
109.75
109.92
116.91
109.71
109.45
Acknowledgments
11a
11b
11c
We are grateful to Professor Mineo Saneyoshi in the
Biotechnology Research Center, Teikyo University of
Science and Technology, Japan, for antiviral evaluations
on HIV and BVDV, and for useful discussion. The
financial supports from the National Natural Science
12a1
12a2
12b
12c
7
8a1 + 8a2
8
9
8b
8c

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P.-Z. Zhang et al. / Tetrahedron Letters 48 (2007) 7813–7816
Vidal, S.; Gueyard, D.; Goekjian, P. G.; Msaddek, M.;
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Foundations of China (NSFC) (20472015, 20672027),
the Program of Science and Technology (S&T) of Hebei
(3276414), the Natural Science Foundation of Hebei
(2005000106), and the Natural Science Foundation of
the Education Department of Hebei Province
(2004306) are gratefully acknowledged.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.
2007.09.007.
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