Successful combination of (methoxydimethyl)methyl (MIP) and (2-naphthyl)methyl (NAP) ethers for the synthesis of arabinogalactan-type oligosaccharides

Article abstract of DOI:10.1055/s-2002-31893

In order to characterise the presumed epitopes of arabinogalactans, isolated from the extract of the cell-cultured Echinacea purpurea, two oligosaccharides were synthesized. The whole synthetic route was based on the successful combination of the (methoxydimethyl)methyl (MIP) and the (2-naphthyl)methyl ether (NAP) protecting groups. A β-(1→6)-linked trigalactoside was prepared, which contained a NAP ether at position 2′.This protecting group was selectively removed using either DDQ or Pd-C/H₂ and the acceptor was ready for further glycosylation. We have used two arabinofuranosyl donor compounds: 2,3,5-tri-O-acetyl arabinofuranosyl trichloroacetimidate and a peracetylated α-(1→5)-linked diarabinofuranosyl trichloroacetimidate. For the deprotection of the tetra- and pentasaccharides a common procedure was used. All of the synthesized compounds were characterized by ¹H and ¹³C NMR spectroscopy, as well as by MALDI-TOF mass-spectrometry.

Full text of DOI:10.1055/s-2002-31893

LETTER
887
Successful Combination of (Methoxydimethyl)methyl (MIP) and
(2-Naphthyl)methyl (NAP) Ethers for the Synthesis of Arabinogalactan-
Type Oligosaccharides
C
ombination of (Meth
a
g
l)methyl and
d
(2-Naphthy
o
l)methyl Eth
l
er
s
na Csávás,a Anikó Borbás,a László Szilágyi,b András Lipták*a
a
Research Group for Carbohydrates of the Hungarian Academy of Sciences, 4010 Debrecen, P.O. Box 55, Hungary
b
Department of Organic Chemistry, University of Debrecen, 4010 Debrecen, P.O. Box 20, Hungary
Fax +36(52)512913; E-mail: liptaka@tigris.klte.hu
Received 9 April 2002
complex oligosaccharides is a rather laborious task and
very often the combination of the available and the suit-
able protecting groups is the bottleneck of the whole
synthesis. Here, we report on the successful combination
Abstract: In order to characterise the presumed epitopes of ara-
binogalactans, isolated from the extract of the cell-cultured Echina-
cea purpurea, two oligosaccharides were synthesized. The whole
synthetic route was based on the successful combination of the
(methoxydimethyl)methyl (MIP) and the (2-naphthyl)methyl ether of two relatively new protecting groups; (methoxydime-
thyl)methyl (MIP)13 and (2-naphthyl)methyl (NAP)
(NAP) protecting groups. A -(1 6)-linked trigalactoside was pre-
ethers.14–16
pared, which contained a NAP ether at position 2 .This protecting
group was selectively removed using either DDQ or Pd-C/H2 and
It was shown that treating either the -D-galactopyrano-
syl-(1 6)-D-galactose, or the -D-galactopyranosyl-
(1 6)-1,2:3,4-di-O-isopropylidene- -D-galactopyran-
ose with 2,2-dimethoxy propane in the presence of protic
or Lewis acid resulted in 3,4-O-isopropylidene-6-O-
(methoxydimethyl)methyl- -D-galactopyranosyl-(1 6)-
1,2:3,4-di-O-isopropylidene- -D-galactopyranose3 (3).
Compound 3 has a free OH-2 group, but its glycosylation
is hampered because during the glycosylation reaction the
MIP group can either hydrolyze or can form, by conden-
sation, a stable isopropylidene acetal. On the other hand,
compound 3, bearing the acetal-type MIP group, can be
readily (2-naphthyl)methylated to give 4 in excellent
yield. The MIP group can be cleaved by very mild acid
hydrolysis to give compound 5 with a free 6 -OH group. 5
was subsequently glycosylated with -acetobromo-D-ga-
lactose to furnish the fully protected trisaccharide 6. From
compound 6 the NAP group was removed either by oxida-
tion using DDQ or by catalytic hydrogenolysis with Pd-C
as catalyst, yielding the trisaccharide type aglycon (7)
(Scheme 2).
the acceptor was ready for further glycosylation.We have used two
arabinofuranosyl donor compounds: 2,3,5-tri-O-acetyl arabinofura-
nosyl trichloroacetimidate and a peracetylated -(1 5)-linked diar-
abinofuranosyl trichloroacetimidate. For the deprotection of the
tetra- and pentasaccharides a common procedure was used. All of
the synthesized compounds were characterized by 1H and 13C NMR
spectroscopy, as well as by MALDI-TOF mass-spectrometry.
Key words: arabinogalactan, oligosaccharides, protecting groups,
(methoxydimethyl)methyl ether (MIP), (2-naphthyl)methyl ether
(NAP)
Monoclonal antibodies play a very important role in the
structure determination of plant polysaccharides.1 Their
production or the evaluation of their specificity require
well-defined oligosaccharides which are the epitopes of
the antigens. Among the plant cell-wall polysaccharides
or the plant cell exudates the arabinogalactans are very
common representatives. Unfortunately, the number of
the L-arabinose and D-galactose containing synthetic oli-
gosaccharides is rather limited.2–9 Study of the structure of
arabinogalactans isolated from cell-cultured Echinacea
purpurea required10–12 the following two oligosaccharides
(Figure).
It is worth to mention that the NAP group, like the benzyl
group, can be removed by catalytic hydrogenation but the
NAP is more sensitive and can be selectively deprotected
in the presence of latter one.17 The NAP group is very sim-
ilar to the p-methoxybenzyl, but the NAP is more resistant
The methoxycarbonyl undecyl glycoside2 of compound 1
has been prepared recently, but its preparation needed
many synthetic steps. Generally, the chemical synthesis of
β-D-Galp-(1→6)-β-D-Galp-(1→6)-D-Gal (1)
β-D-Galp-(1→6)-β-D-Galp-(1→6)-D-Gal (2)
2
2
1
α-L-Araf-
α-L-Araf-(1→5)-α-L-Araf-
1
Figure
Synlett 2002, No. 6, 04 06 2002. Article Identifier:
1437-2096,E;2002,0,06,0887,0890,ftx,en;D03902ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214

888
M. Csávás et al.
LETTER
CH3
C
OR
O
OH
ONAP
O
O
O
i
O
O
O
O
O
O
O
MIP= CH3O
OAc
AcO
AcO
O
O
O
iii
O
O
CH3
O
O
O
OMIP
O
OR
O
O
O
O
O
O
NAP=
OAc
iv
O
O
O
4
5
R=MIP
R=H
6
R=NAP
ii
3
7 R=H
Scheme 1 i) NaH, NAPBr, DMF, 0 °C r.t., 78%; ii) CH3COOH, H2O, reflux, 3 h, 73%; iii) 2,3,4,6-tetra-O-acetyl- -D-galactopyranosyl
bromide, anhyd CH3CN, Hg(CN)2, r.t., 55% iv) CH2Cl2–CH3OH, 4:1, DDQ (1.5 equiv), r.t., 89%
OAc
OAc
D
AcO
O
NH
O
O
CCl3
B
O
O
O
i
ii
OAc
O
OAc
AcO
AcO
O
O
O
1
iii
O
O
7 +
AcO
A
O
C
OAc
O
OAc
O
8
9
Scheme 2 i) anhyd CH2Cl2, TMSOTf, –45 °C r.t., 1 h, 69%; ii) NaOMe, MeOH, r.t., 4 h, quant.; iii) 90% aq. CF3COOH, r.t., 15 min.
to acids and can survive the removing of the isopropy- Glycosylation of compound 7 with imidate 16 in the pres-
lidene groups.14 The p-methoxybenzyl derivatives are not ence of trimethylsilyltriflate gave the fully substituted
compatible with the MIP technology.
pentasaccharide 17 (Scheme 4).
Compound 7 was treated with 2,3,5-tri-O-acetyl- , -L- For the deprotection of compounds 9 and 17 common pro-
arabinofuranosyl trichloroacetimidate 8 in the presence of cedures were followed; Zemplén’s deacylation and con-
trimethylsilyltriflate in dichloromethane to give the fully secutive mild hydrolysis of the isopropylidene groups by
protected tetrasaccharide 9. Its structure was confirmed by trifluoroacetic acid resulted in the free tetra- (1) and pen-
1H- and 13C NMR spectra, as well as by MALDI-TOF MS tasaccharide (2).
measurement (Scheme 2).
The identity and stereochemical integrity of all com-
The synthetic plan for the pentasaccharide followed the pounds described here were verified by HPLC and by 1H-
route used for compound 9, but employing a (1 5)-di- and 13C NMR spectra. MALDI-TOF MS measurements
arabinoside derivative as glycosyl donor. 1,2,3,5-Tetra-O- provided further support for these structures. The charac-
acetyl- -L-arabinofuranose was treated with p-methoxy- teristic NMR, MALDI-TOF MS and physical data are
phenol in dichloromethane using BF3 Et2O as catalyst. given in refs.18–22
The glycoside acetate (11) was deacetylated and the crys-
talline p-methoxyphenyl -L-arabinofuranoside (12) was
In summary, we have demonstrated the useful combina-
tion of MIP [(methoxydimethyl)methyl] and NAP [(2-
used as aglycon in an ‘open glycosylation’ reaction using
naphthyl)methyl ether] groups for the preparation of
2,3,5-tri-O-acetyl- , -L-arabinofuranosyl trichloroace-
branched arabinogalactan-type oligosaccharides. Presum-
timidate as donor and trimethylsilyltriflate as catalyst.
ably these oligosaccharides are epitopes of arabinogalac-
Similar procedure was applied for the synthesis of -L-
tan polysaccharides isolated from cell-cultured exudates
Araf-(1 5)- -L-Ara by Kong et al.4 using methyl -L-
of Echinacea purpurea.
arabinofuranoside as aglycon and 2,3,5-tri-O-benzoyl- -
L-arabinofuranosyl trichloroacetimidate as donor. The
Acknowledgement
coupling product (13) was isolated, acetylated and the dis-
accharide derivative 14 was fully characterized by spec-
troscopic methods. The aglycon of compound 14 was
This work was supported by grants from the Ministry of Education
(FKFP T035128), the Hungarian Academy of Sciences (AKP 2000-
easily removed by oxidative methods (CAN or DDQ) to 162 2,4) and the Hungarian Scientific Research Fund (OTKA
T025244 and T034515).
obtain a free anomeric OH group (15), which was then
transformed into trichloroacetamidate derivative (16)
(Scheme 3).
Synlett 2002, No. 6, 887–890 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Combination of (Methoxydimethyl)methyl and (2-Naphthyl)methyl Ethers
889
OAc
O
OCH3
O
OAc
O
OR
i
AcO
RO
OAc
OR
11 R=Ac
ii
10
12 R=H
O
OCH3
NH
O
O
OR
v
iii
CCl3
O
OAc
+ 12
O
O
OAc
AcO
OR
13 R=H
14 R=Ac
OAc
AcO
iv
OAc
O
OAc
OR
15 R=H
16 R=(NH)CCl3
O
vi
O
OAc
OAc
AcO
OAc
Scheme 3 i) 4-Methoxyphenol, BF3 Et2O, 0 °C, 12 h, 77%; ii) NaOCH3, MeOH, r.t., 12 h, 73%; iii) anhyd CH2Cl2, TMSOTf (0.15 equiv),
–42 °C, 1 h, 32% iv) Ac2O, pyridine, r.t., 2 h, 83%; v) CAN (5 equiv), toluene–CH3CN–H2O = 1:2:1, r.t., 1 h, 83%; vi) K2CO3, CCl3CN,
r.t., 12 h.
OAc
(11) Wagner, H.; Proksch, A.; Riess-Maurer, I.; Vollmar, A.;
OAc
Odenthal, S.; Stuppner, H.; Jurcic, K.; Le Turdu, M.; Heur,
Y. H. Arzneim.- Forsch. 1984, 34, 659.
(12) Proksch, A.; Wagner, H. Phytochemistry 1987, 26, 1989.
(13) Lipták, A.; Fügedi, P.; Kerékgyártó, J.; Nánási, P.
Carbohydr. Res. 1983, 113, 225.
E
OAc
AcO
O
O
D
AcO
O
O
(14) Xia, J.; Abbas, S. A.; Locke, R. D.; Piskorz, C. F.; Alderfer,
J. L.; Matta, K. L. Tetrahedron Lett. 2000, 41, 169.
(15) Liao, W.; Locke, R. D.; Matta, K. L. Chem. Commun. 2000,
369.
(16) Lipták, A.; Borbás, A.; Jánossy, L.; Szilágyi, L. Tetrahedron
Lett. 2000, 41, 4949.
O
B
O
ii
O
i
OAc
AcO
AcO
2
O
7 + 16
O
O
iii
O
O
O
A
O
C
OAc
O
(17) Gaunt, M. J.; Yu, J.; Spencer, J. B. J. Org. Chem. 1998, 63,
4172.
17
(18) Spectroscopic data of compound 9: 1H NMR (500 MHz,
CDCl3): 5.44 (d, 1 H, J1,2 = 5.6 Hz, A-1), 4.26–4.28 (m, 1
H, A-2), 4.59 (dd, 1 H, J2,3 = 7.9 Hz, J3,4 = 2.3 Hz, A-3), 4.19
(dd, 1 H, J4,5 = 1.9 Hz, A-4), 3.98–4.1 (m, 1 H, A-5), 4.15 (d,
1 H, J5,6 = 8.6 Hz, A-6a), 3.58 (dd, 1 H, J6a,6b = 10.3 Hz, A-
6b), 4.26 (d, 1 H, J1,2 = 5.2 Hz, B-1), 3.82 (dd, 1 H, J2,3 = 8.3
Hz, B-2), 4.25 (s, 1 H, B-3), 4.07 (dd, 1 H, J4,5 = 1.9 Hz, B-
4), 3.94–3.96 (m, 1 H, B-5), 4.05 (dd, 1 H, J5,6 = 2.3 Hz, J6a,6a
= 7.7 Hz, B-6a), 3.94–3.98 (m, 1 H, B-6b), 4.72 (d, 1 H, J1,2
= 8.1 Hz, C-1), 5.23 (dd, 1 H, J2,3 = 10.5 Hz, C-2), 5.01 (d, 1
H, J3,4 = 3.4 Hz, C-3), 5.38 (dd, 1 H, J4,5 = 0.9 Hz, C-4),
3.92–3.95 (m, 1 H, C-5), 4.15 (d, 2 H, J6a,6b = 6.7 Hz, C-6a,
C-6b), 5.45 (s, 1 H, d-1), 5.13 (s, 1 H, D-2), 4.99 (d, 1 H, J3,4
= 3.7 Hz, D-3), 4.68 (dd, 1 H, J4,5 = 7.1 Hz, D-4), 4.48 (dd,
1 H, J5,6a = 3.4 Hz, J6a,6b = 12.5 Hz, D-5a), 4.32 (dd, 1 H, J5,6b
= 2.5 Hz, D-5b), 1.25, 1.28, 1.38, 1.49, 1.52 (s, 24 H, 6
CH3ip), 1.95, 2.02, 2.08, 2.01, 2.13, 2.15 (s, 21 H, 7 CH3acetyl).
13C NMR (500 MHz, CDCl3): 95.71 (A-1), 69.59 (A-2),
70.47 (A-3), 71.16 (A-4), 66.80 (A-5), 69.40 (A-6), 100.78
(B-1), 73.94 (B-2), 79.55 (B-3), 73.46 (B-4), 70.36 (B-5),
68.38 (B-6), 101.02 (C-1), 68.46 (C-2), 70.44 (C-3), 66.74
(C-4), 72.85 (C-5), 60.88 (C-6), 103.07 (D-1), 80.52 (D-2),
76.62 (D-3), 80.49 (D-4), 63.58 (D-5), 20.28, 20.36, 20.51,
20.54, 20.68 (CH3acetyl), 23.75, 24.51, 25.60, 25.69, 26.02,
27.71 (CH3ip), 108.03, 108.55, 110.34 (Cquat).
Scheme 4 i) anhyd CH2Cl2, TMSOTf, -45 °C r.t., 1 h, 65%;
ii) NaOMe, MeOH, r.t., 4 h, quant.; iii) 90% aq CF3COOH, r.t.,
15 min.
References
(1) Hoson, T. Int. Rev. Cytol. 1991, 130, 233.
(2) Timmers, C. M.; Wigchert, S. C. M.; Leeuwenburgh, M. A.;
van der Marel, G. A.; van Boom, J. H. Eur. J. Org. Chem.
1998, 91.
(3) Borbás, A.; Jánossy, L.; Lipták, A. Carbohydr. Res. 1999,
318, 98.
(4) Du, Y.; Pan, Q.; Kong, F. Synlett 1999, 1648.
(5) Du, Y.; Pan, Q.; Kong, F. Carbohydr. Res. 2000, 323, 28.
(6) Pan, Q.; Du, Y.; Kong, F.; Pan, J.; Lu, M. J. Carbohydr.
Chem. 2001, 20, 297.
(7) Li, B.; Yu, B.; Hui, Y.; Li, M.; Han, X.; Fung, K. P.
Carbohydr. Res. 2001, 331, 1.
(8) Gu, G.; Yang, F.; Du, Y.; Kong, F. Carbohydr. Res. 2001,
336, 99.
(9) Csávás, M.; Borbás, A.; Jánossy, L.; Batta, G.; Lipták, A.
Carbohydr. Res. 2001, 336, 107.
(10) Wagner, H.; Proksch, A. Angew. Phytother. 1981, 2, 166.
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M. Csávás et al.
LETTER
[ ]D: –45.32 (c 0.26, CHCl3). MALDI-TOF measurements:
1073.25 [M + Na]+
70.74 (A-3), 71.40 (A-4), 67.04 (A-5), 69.55 (A-6), 101.07
(B-1), 74.08 (B-2), 79.84 (B-3), 73.75 (B-4), 70.74 (B-5),
68.62 (B-6), 101.30 (C-1), 68.75 (C-2), 70.74 (C-3), 67.04
(C-4), 70.74 (C-5), 61.13 (C-6), 104.91 (D-1), 80.84 (D-2),
77.63 (D-3), 80.98 (D-4), 63.35 (D-5), 104.91 (E-1), 81.34
(E-2), 76.13 (E-3), 81.84 (E-4), 64.87 (E-5), 20.58, 20.75
(CH3acetyl), 24.08, 24.73, 25.87, 26.00, 26.29, 27.94, 29.19,
30.83 (CH3ip), 108.12, 108.85, 110.57 (Cquat), 169.27,
169.35, 169.80, 169.88, 170.15, 170.27, 170.36, 170.48
(CH3CO).
(19) Spectroscopic data of compound 14: 1H NMR (500 MHz,
CDCl3): 5.59 (s, 1 H, H-1), 5.32 (d, 1 H, J2,3 = 2.16 Hz, H-
2), 5.28 (dd, 1 H, J3,4 = 6.5 Hz, H-3), 4.32–4.35 (m, 1 H, H-
4), 3.95 (dd, 1 H, J4,5a = 4.3 Hz, J5a,5b = 12.9 Hz, H-5a), 3.75
(dd, 1 H, J4,5b = 3.8 Hz, H-5b), 5.14 (s, 1 H, H-1 ), 5.16 (s, 1
H, H-2 ), 4.94 (d, 1 H, J3,4 = 4.3 Hz, H-3 ), 4.26–4.30 (m, 1
H, H-4 ), 4.45 (dd, 1 H, J4,5a = 3.9 Hz, J5a,5b = 12.9 Hz, H-
5 a), 4.23 (dd, 1 H, J4,5b = 4.7 Hz, H-5 b), 3.76 (s, 3 H, -
OCH3), 2.09–2.18 (s, 15 H, CH3acetyl), 6.78–7.02 (m, 4 H, -
Ph). 13C NMR (500 MHz, CDCl3): 104.49 (C-1), 81.74 (C-
2), 76.04 (C-3), 81.38 (C-4), 64.87 (C-5), 105.18 (C-1 ),
80.68 (C-2 ), 76.96 (C-3 ), 80.49 (C-4 ), 62.96 (C-5 ), 55.31
(-OCH3), 20.30, 20. 43, 20.48 (CH3acetyl), 169.11, 169.50,
169.85, 169.93, 170,26 (CH3CO-), 114.25, 117.97 (-Ph),
149.72, 154.89 (-Phquat).
[ ]D: -66.18 (c 0.3173, CHCl3). MALDI-TOF
measurements: 1289.87 [M + Na]+
(21) Spectroscopic data of compound 1: 1H NMR (500 MHz,
D2O): 5.21 (A-1 , J1,2 = 3.8 Hz), 4.53 (A-1 , J1,2 = 7.9 Hz),
3.41 (A-2 ), 3.60 (A-3 ), 4.49 (B-1, J1,2 = 7.8 Hz), 3.58 (B-
2), 3.72 (B-3), 4.40 (C-1, J1,2 = 7.8 Hz), 3.44 (C-2), 3.60 (C-
3), 5.24 (D-1, J1,2 = 3.7 Hz), 4.12 (D-2), 3.90 (D-3), 4.17 (D-
4), 3.67 and 3.75 (D-5a and d-5b).
[ ]D: –30.35 (c 0.32, CHCl3). MALDI-TOF measurements:
621.51 [M + Na]+
(20) Spectroscopic data of compound 17: H NMR (500 MHz,
13C NMR (500 MHz, H2O): 92.07 (A-1 ), 96.09 (A-1 ),
71.52 (A-2 ), 72.39 (A-3 ), 69.16 (A-6 ), 101.61 (B-1),
75.66 (B-2), 72.49 (B-3), 68.73 (B-6), 103.07 (C-1), 70.43
(C-2), 72.41 (C-3), 60.69 (C-6), 107.93 (D-1), 80.64 (D-2),
76.57 (D-3), 83.95 (D-4), 61.07 (D-5).
1
CDCl3): 5.42 (d, 1 H, J1,2 = 5.2 Hz, A-1), 4.24–4.27 (m, 2
H, A-2, B-3), 4.56 (d, 1 H, J3,4 = 2.3 Hz, A-3), 4.18 (dd, 1 H,
J4,5 = 8 Hz, A-4), 3.94–3.98 (m, 1 H, A-5), 3.58 (d, 1 H, A-
6a), 4.13 (dd, 1 H, J5,6b = 2.3 Hz, J6a,6b = 10.3 Hz, A-6b), 4.26
(d, 1 H, J1,2 = 8.5 Hz, B-1), 3.81 (dd, 1 H, J2,3 = 6 Hz, B-2),
4.03 (dd, 1 H, J3,4 = 1.8 Hz, B-4), 3.92–3.95 (m, 1 H, B-5),
3.92–3.96 (m, 1 H, B-6a), 4.03–4.06 (m, 1 H, B-6b), 4.69 (d,
1 H, J1,2 = 8 Hz, C-1), 5.22 (dd, 1 H, J2,3 = 10 Hz, C-2), 4.98
(dd, 1 H, J3,4 = 3.5 Hz, C-3), 5.36 (dd, 1 H, J4,5 = 1.1 Hz, C-
4), 3.89–3.93 (m, 1 H, C-5), 4.13–4.16 (m, 2 H, C-6a, C-6b),
4.17 (s, 1 H, D-1), 5.08 (s, 1 H, D-2), 5.15 (d, 1 H, J3,4 = 1.6
Hz, D-3), 4.56–4.5 (m, 1 H, D-4), 4.14 (d, 1 H, J4,5a = 1.1 Hz,
D-5a), 3.58 (dd, 1 H, J4,5ab = 1.6 Hz, J5a,5b = 9.8 Hz, d-5b),
5.46 (s, 1 H, E-1), 5.18 (s, 1 H, E-2), 4.91 (dd, 1 H, J = 4.9
Hz, J = 0.8 Hz, E-3), 4.29–4.34 (m, 1 H, E-4), 4.44 (dd, 1 H,
[ ]D: –1.55 (c 0.1931, H2O).MALDI-TOF measurements:
657.14 [M + Na]+
(22) Spectroscopic data of compound 2: 1H NMR (500 MHz,
D2O): 5.20 (A-1 , J1,2 = 3.98 Hz,), 4.52 (A-1 , J1,2 = 8.16
Hz), 3.72 (A-2 ), 3.44 (A-2 ), 3.59 (A-3), 3.91 (A-4), 4.48
(B-1, J1,2 = 8.16 Hz), 3.59 (B-2), 3.71 (B-3), 3.91 (B-4), 4.40
(C-1, J1,2 = 8.16 Hz), 3.48 (C-2), 3.59 (C-3), 3.87 (C-4), 5.03
(D-1, J1,2 = 2.39 Hz,), 4.08 (D-2), 5.23 (E-1), 4.12 (E-2).
13C NMR (500 MHz, H2O): 92.08 (A-1 ), 96.10 (A-1 ),
71.55 (A-2), 72.41 (A-3), 60.69 (A-6), 101.69 (B-1), 75.60
(B-2), 74.85 (B-3), 102.84 (C-1), 70.43 (C-2), 72.35 (C-3),
69.17 and 68.73 (B-6 and C-6), 107.10 (D-1), 80.60 (D-2),
76.24 (D-3), 82.25 (D-4), 66.55 (D-5), 107.98 (E-1), 80.60
(E-2), 76.90 (E-3), 83.63 (E-4), 60.89 (E-5).
J4,5a = 3.1 Hz, J5a,5b = 11.8 Hz, E-5a), 4.21–4.24 (m, 1 H, E-
5b), 1.26, 1.30, 1.31, 1.36, 1.49, 1.53 (s, 24 H, CH3ip), 1.95,
2.04, 2.06, 2.07, 2.08, 2.09, 2.10, 2.12, 2.15 (CH3acetyl).
13C NMR (200 MHz, CDCl3): 96.00 (A-1), 69.91 (A-2),
MALDI-TOF measurements:791.13 [M + Na]+.
Synlett 2002, No. 6, 887–890 ISSN 0936-5214 © Thieme Stuttgart · New York