Synthesis of interglycosidically S-linked 1-thio-oligosaccharides under microwave irradiation

Article abstract of DOI:10.1080/07328300500282540

Microwave irradiation (MWI) has accelerated the synthesis of S-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)thiouronium bromide (2a), whose reaction with 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (1a) in the presence of Et₃N afforded stereoselectively the acetylated β,β-1-thiotrehalose 4a. Similarly, the respective D-galactopyranosyl 4b and 2-acetylamino-2-deoxy-D-glucopyranosyl 4c analog as well as 4,4′-di-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl) 4d and 4,4′-di-O-(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl) 4e derivatives of 2,2′,3,3′,6,6′-hexa-O-acetyl β,β-1-thiotrehalose were prepared. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1080/07328300500282540

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Synthesis of Interglycosidically
S‐Linked 1‐Thio‐Oligosaccharides Under
Microwave Irradiation
El Sayed H. El Ashry a , Laila F. Awad a , H. M. Abdel Hamid a & Atta
I. Atta a
a Chemistry Department, Faculty of Science, Alexandria University,
Alexandria, Egypt
Version of record first published: 20 Aug 2006.
To cite this article: El Sayed H. El Ashry , Laila F. Awad , H. M. Abdel Hamid & Atta I. Atta (2005):
Synthesis of Interglycosidically S‐Linked 1‐Thio‐Oligosaccharides Under Microwave Irradiation , Journal
of Carbohydrate Chemistry, 24:7, 745-753
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Journal of Carbohydrate Chemistry, 24:745–753, 2005
Copyright # Taylor & Francis, Inc.
ISSN: 0732-8303 print 1532-2327 online
DOI: 10.1080/07328300500282540
Synthesis of
Interglycosidically S -Linked
1-Thio-Oligosaccharides
Under Microwave
Irradiation
El Sayed H. El Ashry, Laila F. Awad, H. M. Abdel Hamid, and
Atta I. Atta
Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt
Microwave irradiation (MWI) has accelerated the synthesis of S-(2,3,4,6-tetra-O-acetyl-
b-D-glucopyranosyl)thiouronium bromide (2a), whose reaction with 2,3,4,6-tetra-O-
acetyl-a-D-glucopyranosyl bromide (1a) in the presence of Et3N afforded stereoselectively
the acetylated b,b-1-thiotrehalose 4a. Similarly, the respective D-galactopyranosyl 4b
and 2-acetylamino-2-deoxy-D-glucopyranosyl 4c analog as well as 4,40-di-O-(2,3,4,6-
tetra-O-acetyl-b-D-galactopyranosyl) 4d and 4,40-di-O-(2,3,4,6-tetra-O-acetyl-a-D-gluco-
pyranosyl) 4e derivatives of 2,20,3,30,6,60-hexa-O-acetyl b,b-1-thiotrehalose were
prepared.
Keywords Microwave, Thio-oligosaccharides, Thiotrehaloses, Glycosyl isothiouro-
nium salt, Glycosyl halide
INTRODUCTION
Thioglycosides are considered an important class of carbohydrate deriva-
tives.[1–4] There is increasing interest in using them as glycosyl donors,[5]
and they are promising candidates for carbohydrate mimics, potential thera-
Address correspondence to El Sayed H. El Ashry, Chemistry Department, Faculty of
Science, Alexandria University, Alexandria, Egypt. E-mail: eelashry60@hotmail.com;
eelashry60@link.net
Atta I. Atta is on leave from Faculty of Medical Sciences, Al-Hodiedah University,
Yemen.
745

E. S. H. El Ashry et al.
746
peutics, and enzyme inhibitors.[6] The interest in their enzyme inhibition[1,2] is
due to their stability to the action of glycosidases, which is more promising than
that of the corresponding O-glycosides. Thus, they can inhibit enzymatic
hydrolysis, which may be a versatile approach to map the active site of
glycosyl hydrolases. The thioanalog of oligosaccharides have gained a recent
continuous development not only devoted to their synthesis but also for bio-
chemical and x-ray studies.[1,2,7–9] 1,1-Thio-a,a-trehalose and a-D-glucopyra-
nosyl-1-thio-a-D-mannopyranoside have been found to be inhibitors for
cockchafer trehalase.[10] Moreover, thiosucrose inhibits levansucrase from
Bacillus subtilis and yeast invertase.[11] Although the b,b-thiotrehalose was
synthesized[12] in 1917, the a,a-thiotrehalose was synthesized[13] 60 years
later, in 1978. Since then a number of their analog have been prepared and
various conditions utilized.[14–23]
RESULTS AND DISCUSSION
Recently there has been a growing interest in employing microwave irradiation
(MWI) for the synthesis of organic compounds.[24–27] This technique is based on
the empirical observation that some organic reactions proceed much faster and
with higher yields under MWI compared to conventional heating. Continuing
our work[27] on accelerating organic reactions under MWI, we have developed
a convenient, efficient, and practical one-pot method for the synthesis of b,b-
thio-oligosaccharides.
The b,b-thiotrehaloses have been conventionally prepared from the
reaction of 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide with either potas-
sium sulfide or 2,3,4,6-tetra-O-acetyl-1-thio-b-D-glucopyranose.[12,16] The
former can be catalyzed by the presence of quaternary alkylammonium[14] or
phosphonium[15] salts.
In the present work, the readily available S-(2,3,4,6-tetra-O-acetyl-b-D-
glucopyranosyl)-thiouronium bromide[4] (2a) has been used under MWI as a
source for generating the respective thiol at the anomeric center to act as a
nucleophile that upon reaction with the anomeric electrophile, generated
from 1a, would give the respective thiotrehalose. Thus, the precursor 2a was
prepared by MWI of a solution of 1a and thiourea in acetone for 3 min. Then
the electrophilic thiol was generated, in situ, by MWI of 2a in a mixture with
1a in the presence of triethylamine as a catalyst to give 2,3,4,6-tetra-O-
acetyl-b-D-glucopyranosyl 2,3,4,6-tetra-O-acetyl-1-thio-b-D-glucopyranoside
(acetyl derivative of b,b-1-thiotrehalose) (4a) within 3 min in a higher yield
than that resulting from the conventional method.[15] The galacto and 2-acetyl-
amino-2-deoxy analog 4b and 4c were also obtained from the reaction of 1b
with 2b and 1c with 2c, respectively, under similar conditions (Fig. 1).
Similarly, the reaction was extended to the disaccharides, whereby the
isothiouronium derivatives 2d and 2e were prepared from the respective

Microwave Irradiation Synthesis
747
bromides 1d and 1e by reaction with thiourea under MWI. Further reaction of
1d with 2d and 1e with 2e in the presence of Et3N under MWI gave 4,40-di-O-
(2,3,4,6-tetra-O-acetyl-b-D-galactopyranosyl) 2,20,3,30,6,60-hexa-O-acetyl-b,b-
1-thiotrehalose (4d) and 4,40-di-O-(2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl)
2,20,3,30,6,60-hexa-O-acetyl-b,b-1-thiotrehalose (4e), respectively. The struc-
tures of the products were confirmed by their spectral data. The b-anomeric
configuration in the products was readily deduced from their 1H NMR
spectra; H-1 appeared as a doublet with J1,2 value 10.2 Hz, and 13C-1
appeared at dC 80.7 in compound 4a. Moreover, the DEPT, HMQC, and DQF
COSY correlations assisted in assigning the spectra; the symmetrical nature
of such oligosaccharides are apparent in their spectra. Similarly, the spectra
of 4b–e showed high coupling constant values between H-1 or H-1a and
H-2 or H-2a, respectively, indicating b-orientation at such anomeric positions.
Moreover, the orientation of the glycosidic linkage within the lactosyl and
maltosyl moieties was confirmed by the coupling of H-1b with H-2b with
values 9.0 and 3.8 Hz, respectively for the b-and a-orientations. Their
carbons appeared at dC 101.1 and 95.6, respectively .
In conclusion, a practical one-pot stereoselective synthesis of the nonredu-
cing thio-oligosaccharides has been achieved by using MWI technology in
higher yields than by conventional methods in addition to the quick termi-
nation of the reaction. The reactions were clean, and pure products have been
readily obtained without chromatography. Moreover, the S-glycosyl isothio-
uronium salts have been also readily prepared under MWI.
EXPERIMENTAL
General Methods
Melting points were determined on a Mel-temp apparatus and are uncor-
rected. 1H NMR and 13C NMR spectra were recorded on a Bruker DRX
600 MHz, Jeol spectrometer (500 MHz) and a Bruker Advance 300 MHz spec-
trometer. The chemical shifts are expressed on the d-scale using Me4Si as a
standard, and coupling-constant values are given in Hz. The assignments of
1H NMR spectra were based on chemical-shift correlation DQFCOSY
spectra, while the assignment of 13C NMR spectra were based on heteronuclear
multiple quantum coherence (HMQC) experiments. TLC was preformed on
Merck Silica Gel 60F254 with detection by charring in sulfuric acid and by
UV light. Irradiation was achieved using a domestic microwave oven EM-230
M (800-watt output power). Microanalyses were performed in the Microanaly-
sis Unit at the Faculty of Science, Cairo University.
Glycosyl isothiouronium salts (2a–e): General Procedure. A mixture
of the glycosyl halide 1a–e (1.0 mmol) and thiourea (1.0 mmol) in dry acetone

E. S. H. El Ashry et al.
748
Figure 1: Synthesis of thiotrehaloses.

Microwave Irradiation Synthesis
749
(5 mL) was irradiated for 3 min in a domestic microwave oven EM-230 M (800-
watt output power). The reaction mixture was left to cool at rt to afford
products of 2a–e.
2,3,4,6-Tetra-O-acetyl-b-D-glucopyranosyl isothiouronium bromide
(2a). mp 203–2058C, lit[4] mp 2058C; yield 90%.
2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl isothiouronium bromide
(2b). mp 168–1708C, lit[28] mp 169.58C; yield 88%
2-Acetamido-3,4,6-tri-O-acetyl-2-deoxy-b-D-glucopyranosyl isothiouro-
nium chloride (2c). 180–1828C, lit[29] mp 179–1818C, yield 89%.
2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl-(1 ! 4)-2,3,6-tri-O-
acetyl-b-D-glucopyranosyl isothiouronium bromide (2d). Syrup,[31] yield
83%; 1H NMR (500 MHz, DMSO-d6): 1.92, 1.95, 1.98, 2.04 (5s, 21H,
7 ꢀ CH3CO), 3.94–3.99 (m, 2H, H-5a, H-4a), 4.09–4.13 (m, 4H, H-5b, H-60a,
H-6b, H-60b), 4.41 (dd, 1H, J6a,6 a ¼ 11.5 Hz, H-6a), 4.87 (dd, 1H,
0
J3b,4b ¼ 3.8 Hz, J3b,2b ¼ 9.9 Hz, H-3b), 4.95 (d, 1H, H-1b), 4.98 (dd, 1H, H-2a),
5.19 (t, 1H, J2b,3b ¼ J2b,1b ¼ 9.9 Hz, H-2b), 5.23 (d, 1H, J4b,5b ¼ 3.8 Hz, H-4b),
5.31 (dd, 1H, J3a,4a ¼ 9.2 Hz, J3a,2a ¼ 9.9 Hz, H-3a), 5.63 (d, 1H,
J1a,2a ¼ 10.0 Hz, H-1a), 9.25, 9.00 (2s, 2 ꢀ 2H, 2 ꢀ NH2).
2,3,4,6-Tetra-O-acetyl-a-D-glucopyranosyl-(1 ! 4)-2,3,6-tri-O-acetyl-
b-D-glucopyranosyl isothiouronium bromide (2e). mp 199–2018C; yield
86%; 1H NMR (500 MHz, DMSO-d6): d ¼ 1.91, 1.94, 1.95, 1.98, 2.01, 2.03,
2.05 (7s, 21H, 7 ꢀ CH3CO), 3.94–3.99 (m, 2H, H-5b, H-4a), 4.17–4.06
(m, 4H, H-5a, H-6b, H-60a, H-60b), 4.41 (dd, 1H, J6 a,6a ¼ 11.4 Hz, H-60a), 4.87
0
(dd, 1H, J2a,1a ¼ 10.7 Hz, J2a,3a ¼ 8.4 Hz, H-2a), 4.94 (dd, 1H, J2b,3b
¼
10.0 Hz, J2b,1b ¼ 3.1 Hz, H-2b), 4.95 (dd, 1H, J4b,3b ¼ 10.0 Hz, J4b,5b ¼ 6.1 Hz,
H-4b), 5.17 (t, 1H, J3b,2b ¼ J3b,4b ¼ 10.0 Hz, H-3b), 5.23 (d, 1H, J1b,2b
¼
3.1 Hz, H-1b), 5.30 (dd, 1H, J3a,4a ¼ 9.2 Hz, J3a,2a ¼ 8.4 Hz, H-3a), 5.68
(d, 1H, J1a,2a ¼ 10.7 Hz, H-1a), 9.24, 9.06 (2s, 2 ꢀ 2H, 2 ꢀ NH2).
Anal. Calcd for C27H39BrN2O17S (775.57): C, 41.81, H, 5.07, N, 3.61. Found:
C, 40.12, H, 5.39, N, 3.48.
Acetylated b,b-1-thiotrehaloses (4a–e): General Procedure. A sus-
pension of the glycosyl isothiouronium salts 2a–e (1.1 mmol) and the respec-
tive glycosyl halide (1.0 mmol) in acetonitrile (5 mL) and triethylamine
(5 mmol) were placed in a domestic microwave oven and irradiated for 3 min.
Methylene chloride (30 mL) was added to the reaction mixture and the
solution was washed with water (3 ꢀ 10 mL), dried (Na2SO4), and evaporated
under reduced pressure. The residue was crystallized from methanol to
afford pure products of 4a–e.
2,3,4,6-Tetra-O-acetyl-b-D-glucopyranosyl 2,3,4,6-tetra-O-acetyl-1-
thio-b-D-glucopyranoside (4a). mp 173–1758C, lit[15] mp 174–1758C; yield
63%; 1H NMR (600 MHz, CDCl3): d ¼ 2.00, 2.01, 2.02, 2.03 (4s, 24H,
0
8 ꢀ CH3CO), 3.60 (ddd, 2H, J5,4 ¼ 9.6 Hz, J5, 6 ¼ 4.9 Hz, J5,6 ¼ 2.3 Hz, 2 ꢀ H-
0
5), 4.12 (dd, 2H, J6,5 ¼ 2.3 Hz, J6,6 ¼ 12.4 Hz, 2 ꢀ H-6), 4.23 (dd, 2H,

E. S. H. El Ashry et al.
750
J6 ,5 ¼ 4.9 Hz, J6 ,6 ¼ 12.4 Hz, 2 ꢀ H-60), 4.81 (d, 2H, J1,2 ¼ 10.2 Hz, 2 ꢀ H-1),
5.03 (dd, 2H, J2,1 ¼ 10.2 Hz, J2,3 ¼ 9.6 Hz, 2 ꢀ H-2), 5.06 (dd, 2H,
J4,3 ¼ 9.6 Hz, J4,5 ¼ 9.6 Hz, 2 ꢀ H-4), 5.19 (t, 2H, J3,2 ¼ 9.6 Hz, J3,4 ¼ 9.6 Hz,
2 ꢀ H-3); 13C NMR (150.9 MHz, CDCl3): d ¼ 20.4, 20.5, 20.6, 20.7
(8 ꢀ CH3CO), 62.1 (2 ꢀ C-6), 68.1 (2 ꢀ C-4), 70.1 (2 ꢀ C-2), 73.8 (2 ꢀ C-3),
76.2 (2 ꢀ C-5), 80.7 (2 ꢀ C-1), 169.2, 169.3, 170.1, 170.5 (8 ꢀ CO).
0
0
2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl 2,3,4,6-tetra-O-acetyl-1-
thio-b-D-galactopyranoside (4b). mp 201–2038C; lit[14] mp 199–2028C;
yield 65%; 1H NMR (600 MHz, CDCl3): d ¼ 2.0, 2.01, 2.09, 2.18 (4s, 24H,
8 ꢀ CH3CO), 3.89–3.93 (m, 2H, 2 ꢀ H-5), 4.12 (dd, 2H, J6,5 ¼ 6.5 Hz,
0
0
0
J6,6 ¼ 11.3 Hz, 2 ꢀ H-6), 4.18 (dd, 2H, J6 ,5 ¼ 6.7 Hz, J6 ,6 ¼ 11.3 Hz,
2 ꢀ H-60), 4.80 (d, 2H, J1,2 ¼ 10.0 Hz, 2 ꢀ H-1), 5.05 (dd, 2H, J3,4 ¼ 3.3 Hz,
J3,2 ¼ 10.0 Hz, 2 ꢀ H-3), 5.23 (t, 2H, J2,1 ¼ 10.0 Hz, J2,3 ¼ 10.0 Hz, 2 ꢀ H-2),
5.45 (dd, 2H, J4,3 ¼ 3.3 Hz, J4,5 ¼ 2.8 Hz, 2 ꢀ H-4), 13C NMR (150.9 MHz,
CDCl3): d ¼ 19.8, 19.88, 19.9, 20.0 (8 ꢀ CH3CO), 60.6 (2 ꢀ C-6), 66.4
(2 ꢀ C-4), 66.5 (2 ꢀ C-2), 71.0 (2 ꢀ C-3), 73.9 (2 ꢀ C-5), 80.6 (2 ꢀ C-1), 168.7,
169.2, 169.4, 169.6 (8 ꢀ CO).
2-Acetamido-2-deoxy-3,4,6-tri-O-acetyl-b-D-glucopyranosyl 2-acet-
amido-2-deoxy-3,4,6-tri-O-acetyl-1-thio-b-D-glucopyranoside (4c). mp
312–3148C; lit[30] mp 314–3168C; yield 62%; 1H NMR (600 MHz, CDCl3):
d ¼ 1.76 (s, 6H, 2 ꢀ NCOCH3), 1.90, 1.96, 2.02 (3s, 18H, 6 ꢀ CH3CO), 3.78
0
(ddd, 2H, J5,4 ¼ 9.6 Hz, J5,6 ¼ 5.1, J5,6 ¼ 2.1 Hz, 2 ꢀ H-5), 3.92 (dd, 2H,
J2,1 ¼ 10.2 Hz, J2,3 ¼ 9.6 Hz, 2 ꢀ H-2), 4.05 (dd, 2H, J6,5 ¼ 2.1 Hz,
0
0
0
J6,6 ¼ 12.1 Hz, 2 ꢀ H-6), 4.16 (dd, 2H, J6 ,5 ¼ 5.1 Hz, J6 ,6 ¼ 12.1 Hz,
2 ꢀ H-60), 4.85 (t, 2H, J4,5 ¼ 9.6 Hz, J4,3 ¼ 9.6 Hz, 2 ꢀ H-4), 4.92 (d, 2H,
J1,2 ¼ 10.2 Hz, 2 ꢀ H-1), 5.08 (t, 2H, J3,2 ¼ 9.6 Hz, J3,4 ¼ 9.6 Hz, 2 ꢀ H-3); 13C
NMR (150.9 MHz, CDCl3): d ¼ 20.3, 20.4, 20.5 (6 ꢀ CH3CO), 22.6
(2 ꢀ NCOCH3), 52.0 (2 ꢀ C-2), 62.1 (2 ꢀ C-6), 68.6 (2 ꢀ C-4), 73.7 (2 ꢀ C-3),
75.0 (2 ꢀ C-5), 80.0 (2 ꢀ C-1), 169.3, 169.3, 169.6, 170.1 (8 ꢀ CO).
4,40-Di-O-(2,3,4,6-tetra-O-acetyl-b-D-galactopyranosyl) 2,20,3,30,6,60-
hexa-O-acetyl-b,b-1-thiotrehalose (4d). mp 143–1458C; yield 58%; 1H
NMR (600 MHz, CDCl3) d ¼ 1.96–2.18 (14s, 42H, 14 ꢀ CH3CO), 3.58 (ddd,
0
2H, J5a,
¼ 9.2 Hz, J5a,
¼ 5.3 Hz, J5a,
¼ 3.8 Hz, 2 ꢀ H-5a), 3.78 (dd,
4a
6 a
6a
2H, J4a,3a ¼ 9.9 Hz, J4a,5a ¼ 9.2 Hz, 2 ꢀ H-4a), 3.89 (ddd, 2H, J5b,4b ¼ 7.7 Hz,
0
J5b,
¼ 3.1 Hz, J5b,6b ¼ 4.6 Hz, 2 ꢀ H-5b), 4.07 (dd, 2H, J6b,5b ¼ 4.6 Hz,
0 0
6 b
0
J6b, 6 b ¼ 11.5 Hz, 2 ꢀ H-6b), 4.13 (dd, 2H, J6 b,5b ¼ 3.1 Hz, J6 b,6b ¼ 11.5 Hz,
2 ꢀ H-60b), 4.17 (dd, 2H, J6a,5a ¼ 3.8 Hz, J6a,
¼ 12.2 Hz, 2 ꢀ H-6a), 4.46
0
6 a
0
(d, 2H, J1b,2b ¼ 9.0 Hz, 2 ꢀ H-1b), 4.57 (dd, 2H, J6 a,5a ¼ 5.3 Hz,
J6 a,6a ¼ 12.2 Hz, 2 ꢀ H-60a), 4.76 (d, 2H, J1a,2a ¼ 10.0 Hz, 2 ꢀ H-1a), 4.93 (dd,
0
2H, J2a,1a ¼ 10.0 Hz, J2a,3a ¼ 9.9 Hz, 2 ꢀ H-2a), 4.98 (dd, 2H, J3b,4b ¼ 3.8 Hz,
J3b,2b ¼ 9.9 Hz, 2 ꢀ H-3b), 5.11 (dd, 2H, J2b,3b ¼ 9.9 Hz, J2b,1b ¼ 9 Hz,
2 ꢀ H-2b), 5.23 (dd, 2H, J3a,2a ¼ 9.9 Hz, J3a,4a ¼ 9.2 Hz, 2 ꢀ H-3a), 5.34
(dd, 2H, J4b,5b ¼ 7.7 Hz, J4b,3b ¼ 3.8 Hz, 2 ꢀ H-4b). 13C NMR (150.9 MHz,

Microwave Irradiation Synthesis
751
CDCl3): d ¼ 20.4–20.8 (14 ꢀ CH3CO), 60.7 (2 ꢀ C-6b), 62.1 (2 ꢀ C-6a), 66.5
(2 ꢀ C-4b), 69.0 (2 ꢀ C-2b), 70.4 (2 ꢀ C-2a), 70.5 (2 ꢀ C-5b), 70.9 (2 ꢀ C-3b),
73.8 (2 ꢀ C-3a), 75.7 (2 ꢀ C-4a), 76.1 (2 ꢀ C-5a), 80.4 (2 ꢀ C-1a), 101.1
(2 ꢀ C-1b), 169.0, 169.5, 169.6, 170.0, 170.1, 170.2, 170.3 (14 ꢀ CO).
Anal. Calcd for C52H70O34S (1271.16): C, 49.13, H, 5.55. Found: C, 49.14,
H, 5.79.
4,40-Di-O-(2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl)
2,20,3,30,6,60-
hexa-O-acetyl-b,b-1-thiotrehalose (4e). mp 110–1128C; yield 57%; 1H
NMR (600 MHz, CDCl3) d ¼ 1.99–2.18 (14s, 42H, 14 ꢀ CH3CO), 3.68–3.73
(m, 2H, 2 ꢀ H-5a), 3.93 (m, 2H, 2 ꢀ H-5b), 400 (t, 2H, J4a,5a ¼ J4a,3a ¼ 9.2 Hz,
2 ꢀ H-4a), 4.03 (dd, 2H, J6 a,6a ¼ 12.0 Hz, 2 ꢀ H-60a), 4.21 (dd, 2H,
0
0
0
J6a,6 a ¼ 12.0 Hz, 2 ꢀ H-6a), 4.23 (dd, 2H, J6b,6 b ¼ 12.2 Hz, J6b,5b ¼ 3.8 Hz,
2 ꢀ H-6b), 4.78 (dd, 2H, J2b,1b ¼ 3.8 Hz, J2b,3b ¼ 9.9 Hz, 2 ꢀ H-2b), 4.82 (dd,
2H, J2a,1a ¼ 10.7 Hz, J2a,3a ¼ 9.2 Hz, 2 ꢀ H-2a), 4.83 (d, 2H, J1a,2a ¼ 10.7 Hz,
2 ꢀ H-1a), 5.06 (dd, 2H, J4b,3b ¼ 9.9 Hz, J4b,5b ¼ 9.9 Hz, 2 ꢀ H-4b), 5.28
(t, 2H, J3a,2a ¼ J3a,4a ¼ 9.2 Hz, 2 ꢀ H-3a), 5.34 (t, 2H, J3b,2b ¼ J3b,4b ¼ 9.9 Hz,
2 ꢀ H-3b), 5.4 (d, 2H, J1b,2b ¼ 3.8 Hz, 2 ꢀ H-1b). 13C NMR (CDCl3,
150.9 MHz): d ¼ 20.5–20.8 (14 ꢀ CH3CO), 61.5 (2 ꢀ C-6b), 62.9 (2 ꢀ C-6a),
68.0 (2 ꢀ C-4b), 72.2 (2 ꢀ C-4a), 68.5 (2 ꢀ C-3b), 74.9 (2 ꢀ C-3a), 70.1
(2 ꢀ C-2b), 69.4 (2 ꢀ C-5b), 72.4 (2 ꢀ C-5a), 73.8 (2 ꢀ C-2a), 90.0 (2 ꢀ C-1a),
95.6 (2 ꢀ C-1b), 169.3, 169.5, 169.8, 170.0, 170.1, 170.3, 170.4 (14 ꢀ CO).
Anal. Calcd for C52H70O34S (1271.16): C, 49.13, H, 5.55. Found: C, 48.89,
H, 5.80.
ACKNOWLEDGMENTS
The continued supports from the AvH and DFG are highly appreciated.
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