A facile approach to diosgenin and furostan type saponins bearing a 3β-chacotriose moiety

Article abstract of DOI:10.1016/S0008-6215(02)00275-6

Combination of a one-pot coupling technique and the use of benzyl ethers as permanent protecting groups offered a short and simple route to dioscin-type saponins. This strategy in combination with a mild reductive opening procedure of the spiroketal function in diosgenin also offered a convenient approach to bidesmosidic furostan type saponins. Me₃N·BH₃/AlCl₃ promoted acetal opening of 3-O-TBDMS-protected diosgenin gave the 26-OH acceptor 9 into which a benzylated β-glucose moiety was introduced by a S_N2-type imidate coupling. After cleavage of the silyl ether, the 3β-O-glucose and the 4-O-linked rhamnose of the chacotriose unit were introduced by a NIS/AgOTf-promoted one-pot coupling sequence utilising thioglycoside donors and their different reactivity in different solvents. After removal of a benzoyl group, the same coupling conditions were also used for the coupling of the second 2-O-linked rhamnose unit. The target substance was obtained after cleavage of the protecting benzyl ethers under Birch-type conditions, which did not affect the double bond in the steroid skeleton.

Full text of DOI:10.1016/S0008-6215(02)00275-6

Carbohydrate Research 337 (2002) 2153–2159
www.elsevier.com/locate/carres
A facile approach to diosgenin and furostan type saponins bearing
a 3b-chacotriose moiety
Martina Lahmann,a Helena Gyba¨ck,a Per J. Garegg,a Stefan Oscarson,a,* Rene´ Suhr,b
Joachim Thiemb
aDepartment of Organic Chemistry, Stockholm Uni6ersity, S-10691 Stockholm, Sweden
bDepartment of Organic Chemistry, Uni6ersity of Hamburg, D-20146 Hamburg, Germany
Received 16 April 2002; accepted 30 April 2002
Dedicated to Professor Derek Horton on the occasion of his 70th birthday
Abstract
Combination of a one-pot coupling technique and the use of benzyl ethers as permanent protecting groups offered a short and
simple route to dioscin-type saponins. This strategy in combination with a mild reductive opening procedure of the spiroketal
function in diosgenin also offered a convenient approach to bidesmosidic furostan type saponins. Me3N·BH3/AlCl3 promoted
acetal opening of 3-O-TBDMS-protected diosgenin gave the 26-OH acceptor 9 into which a benzylated b-glucose moiety was
introduced by a SN2-type imidate coupling. After cleavage of the silyl ether, the 3b-O-glucose and the 4-O-linked rhamnose of
the chacotriose unit were introduced by a NIS/AgOTf-promoted one-pot coupling sequence utilising thioglycoside donors and
their different reactivity in different solvents. After removal of a benzoyl group, the same coupling conditions were also used for
the coupling of the second 2-O-linked rhamnose unit. The target substance was obtained after cleavage of the protecting benzyl
ethers under Birch-type conditions, which did not affect the double bond in the steroid skeleton. © 2002 Elsevier Science Ltd. All
rights reserved.
Keywords: Saponins; One-pot glycosylation; Reductive acetal opening; Birch-type reduction; Chacotriose; Diosgenin
1. Introduction
for biologically active substances, new furostan sa-
ponins have been found.4 Recently the isolation of a
glycosylated furostan 1 and its cytotoxity against the
HL-60 tumour cell line (IC50=29 mM) has been re-
ported.5 Therefore, dihydrodiosgenin 2, a dioscin-re-
lated substance should be of interest as a mimetic of
this labile compound.
Compelled by the heterogeneity of saponins in plants
and the difficulties of isolation of homogeneous mate-
rial, several synthetic routes of spirostan saponins have
recently been presented, but only one synthesis of a
furostan saponin has been reported.6 The use of one-
pot glycosylation techniques has reduced the number of
synthetic steps; however, the protection group strategies
are still often a problem (mainly orthogonal ester func-
tions have been used).7–10 Another drawback has been
the rather harsh conditions used when opening the
spiroketal function to produce the essential steroid
acceptor.11–14
The large family of saponins has received consider-
able attention because of the variety of their promising
pharmaceutical properties.1,2 Since ancient times plant
extracts containing saponins have been used in tradi-
tional Chinese medicine. Cholestan and spirostan sa-
ponins, 3-OH glycosylated steroids (Fig. 1), have been
the best-studied representatives of this class of com-
pounds. The discovery of the bidesmosidic furostan
saponins (e.g., 1, Fig. 1), which have an additional
b-D-glucopyranosyl substituent at 26-OH, was delayed
due to formation of the ring F under acidic isolation
conditions, yielding spirostan saponins (e.g., dioscin 3)
as artefacts.3 However, by screening saponin-rich plants
* Corresponding author. Tel.: +46-8-162480; fax: +46-8-
154908
E-mail address: s.oscarson@organ.su.se (S. Oscarson).
0008-6215/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(02)00275-6

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M. Lahmann et al. / Carbohydrate Research 337 (2002) 2153–2159
Figure 1. Target saponins 1–3.
In a continuation of previous studies,15–17 we present
rates between various solvents.20 The thioethyl
rhamnopyranosyl donor 421 reacted in almost quantita-
tive yield with the thiophenyl glucopyranosyl acceptor
(5) promoted by NIS/AgOTf in Et2O. The addition of
diosgenin alone to the mixture, as well as together with
an additional portion of promoter, did not lead to any
further coupling. However, as soon as enough CH2Cl2
was present in the mixture, the next glycosylation oc-
curred. The use of mainly benzyl ethers as protecting
groups guaranteed an activated glycosyl donor, and,
thus, a high yield in the coupling step with the steroid
was obtained (“6, 85% overall yield). The 2-O-benzoyl
group, which is essential for selective b-linkage forma-
tion, has been known to be difficult to remove if the
3-substituent was an 3-O-TBDMS group.9 However,
the use of NaOMe in CH2Cl2/MeOH at elevated tem-
perature removed the benzoate in a satisfying yield
(“7, 71%). The introduction of the second rhamnosyl
residue with NIS/AgOTf in Et2O proceeded smoothly
and gave 8 in excellent yield (93%). As planned, the
application of Birch-type conditions removed the ben-
zyl protecting groups almost quantitatively (95%), but
preserved the double bond in the steroid skeleton,
which often is saturated under hydrogenolysis condi-
tions. Thus, dioscin 3 was prepared starting from two,
easily prepared monosaccharide units and commercially
available diosgenin in a 55% overall yield over four
steps.
here a short and simple approach to dioscin 3 (Fig. 1),
a diosgenyl glycoside presenting the main constituents
of the saponin family with marked cytotoxic activity
(GI50=1.12–0.40 mg/mL)18 and the furostan saponin 2.
Furthermore, we describe a mild reductive opening of
the spiroketal function allowing a wide range of pro-
tecting groups in the steroid moiety, giving easy access
to the steroid acceptor 9 with differentiation of the 3b
and the 26 position.
2. Results and discussion
A common strategy preparing spirostan saponins has
been to construct the glycosidic bond between the
steroid and a monosaccharide moiety first, before ex-
tending the sugar part by standard carbohydrate chem-
istry.7–10,19 Still, the yields of the first coupling step
have been low to moderate, probably due to the low
reactivity of the (most often) used glycosyl donor, ethyl
2,3-di-O-benzoyl-4,6-O-benzylidene-1-thio-b-D-gluco-
pyranoside.7–10
We decided to introduce the 4-O-substituent and the
b-linkage to the steroid in a one-pot coupling sequence
(Scheme 1). The main attraction of this approach was
to perform subsequent couplings just by changing of
the solvent system, using the difference in glycosylation
The combination of this one-pot coupling technique,
benzyl protecting groups and a mild reductive opening
procedure of the spiroketal function in diosgenin re-
sulted in a short and simple route also to the corre-
sponding furostan saponins. Diosgenin was silylated
under standard conditions and transformed into the
acceptor 9 in high yield (91%) using the BH3·Me3N
complex together with AlCl3 (Scheme 2). This reaction
proceeded without any loss of the silyl protecting
group, which has been a known side reaction when
conducting the reductive opening with either LiAlH4/
AlCl3 or NaCNBH3 in HOAc.
During the synthesis of dioscin we had already
shown that the selection of the benzyl ether was an
appropriate choice as a permanent protecting group
despite the presence of the double bond in the steroid.
Because no modification has to be done at the 26-O-
glucoside, a perbenzylated donor was preferable to
,
Scheme 1. (a) NIS–AgOTf–Et2O, rt, 4 A MS then diosgenin,
CH2Cl2–Et2O, 85%; (b) NaOMe, MeOH, CH2Cl2, 50 °C,
,
71%; (c) NIS–AgOTf–CH2Cl2, rt, 4 A MS, 93%; (d) Na/NH3
(l), 95%.

M. Lahmann et al. / Carbohydrate Research 337 (2002) 2153–2159
2155
Scheme 2. (a) TBDMSOTf, sym-collidine, 0 °C, 92%; (b) BH3·NMe3, AlCl3, −70 °C“ −10 °C, 91%; (c) BF3·Et2O, CH2Cl2,
−30 °C, 91%; (d) TBAF, THF, rt, 96%.
,
Scheme 3. (a) NIS–AgOTf–Et2O, rt, 4 A MS, then 11, DMTST, CH2Cl2–Et2O, 65%; (b) NaOMe, MeOH, CH2Cl2, 50 °C, 90%;
,
(c) NIS–AgOTf–CH2Cl2, rt, 4 A MS, 93%; (d) Na/NH3 (l), 97%.
simplify deprotection. The coupling was accomplished
3. Experimental
with the perbenzylated a-D
-glucopyranosyl imidate22
and aglycon 9 using a catalytic amount of BF3·Et2O,
which formed the desired b-linkage in high yield (“10,
91%) without neighbouring group assistance. Removal
of the TBDMS protecting group afforded acceptor 11
(96%), which was subjected to a procedure similar to
that described for the preparation of dioscin (Scheme
3). The one-pot glycosylations furnished the saponin
derivative 12 in 65% yield. Cleavage of the 2-O-benzoyl
group (“13, 90%), followed by NIS/AgOTf-promoted
coupling with 4 as donor (“14, 72%), and finally a
one-step deprotection applying Birch-type conditions,
gave the target compound 2 in 38% overall yield over
eight steps.
In conclusion, using a combination of a one-pot
coupling technique, a mild reductive opening procedure
of the spiroketal function in diosgenin and benzyl
groups as permanent protecting groups, an effective
and high-yielding approach towards diosgenin and
furostan type saponins has been developed.
General methods.—All organic solvents were distilled
before use, except Et2O, which was stored over Na.
Organic solutions were dried over MgSO4 before con-
centration, which was performed under reduced pres-
sure at B40 °C (bath temperature). NMR spectra were
recorded at 300 or 400 MHz (Varian) (1H) or at 75 or
100 MHz (13C), respectively, in CDCl3 or CD3OD.
Me4Si was used as the internal standard (l=0) for
1H-spectra. 13C-spectra were referenced to the chloro-
form signal (l=77.17). Silica Gel 60 (E. Merck)
(0.040–0.063) was used for flash chromatography. TLC
was performed on Silica Gel 60 F254 (E. Merck) plates
with detection by UV-light and/or charring with 8%
sulfuric acid. Column chromatography was performed
on silica gel (Matrix Silica Si 60A, 35–70m, Amicon).
MALDI TOF mass spectra were recorded on a Bruker
Biflex III using PEG 600, PEG 1000 and PEG 1500 as
calibration reference and 2%,4%,6%-trihydroxyacetophe-
none monohydrate (THAP) as matrix.

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M. Lahmann et al. / Carbohydrate Research 337 (2002) 2153–2159
Diosgenyl 3,6-di-O-benzyl-2,4-di-O-(2,3,4-tri-O-ben-
zyl-h- -rhamnopyranosyl)-i- -glucopyranoside (8).—
Phenyl 2-O-benzoyl-3,6-di-O-benzyl-1-thio-b- -gluco-
pyranoside (5) was prepared from phenyl 3-O-benzyl-
4,6-O-benzylidene-1-thio-b-
-glucopyranoside,23 which
was benzoylated under standard conditions with ben-
zoyl chloride in pyridine, followed by reductive opening
of the 4,6-O-benzylidene acetal using NaCNBH3 and
HCl in Et2O. 13C NMR (CDCl3): l 70.46, 71.91, 72.24,
73.88, 74.86, 78.52, 83.78, 86.55, 127.79–130.23, 132.41,
133.03, 133.30, 133.66, 137.80, 165.19 (PhCO). A solu-
18.0, 19.5, 21.0, 28.9, 29.8, 30.4, 31.5, 32.0, 32.2, 37.0,
L
D
37.4, 39.0, 39.9, 40.4, 41.7, 50.2, 56.6, 62.2, 67.0, 68.8,
72.2, 72.6, 73.6, 74.8, 75.0, 75.1, 75.4, 75.5, 79.2, 79.8,
80.8, 80.9, 83.0, 98.5, 100.4 (C1, C1%), 109.4 (Cdio22),
121.9 (Cdio6), 125.4, 127.6–129.2, 138.3, 138.5, 138.7,
138.8, 138.9 (Ar C), and 140.5 (Cdio5).
D
D
A solution of 7 (80 mg, 68 mmol) and 4 (40 mg, 84
mmol) in dry Et2O (2 mL) was stirred with powdered
,
molecular sieves (4 A) under argon for 1 h when NIS
(20 mg, 89 mmol) and a catalytic amount AgOTf (dis-
solved in toluene) were added. After 24 h stirring at
room temperature, an additional amount of donor (7,
10 mg) and AgOTf solution were added. The reaction
was quenched after a further 24 h by addition of Et3N
(50 mL), and the mixture was diluted with CH2Cl2 (20
mL), filtered through Celite and concentrated. The
residue was applied onto a silica gel column and eluted
(toluene (Et3N)“18:1 toluene–EtOAc) to give 8 (100
mg, 63 mmol, 93%); [h]D −31° (c 4.3, CH2Cl2): 1H
NMR (CDCl3): l 0.78–2.40 (m, 42H), 3.30–3.85,
4.20–5.00 (m, 36H), 5.26 (m, 2H), and 7.10–7.42 (m,
40H). 13C NMR, l 14.8, 16.6, 17.4, 18.1, 18.2, 19.5,
21.1, 29.0, 29.9, 30.0, 30.6, 31.7, 32.1, 32.4, 37.1, 37.5,
38.6, 40.0, 40.5, 41.8, 50.3, 56.7, 62.3, 67.0, 68.2, 68.9,
69.1, 72.0, 72.2, 72.7, 73.6, 74.0, 75.0, 75.1, 75.4, 75.7,
76.8, 77.5, 78.8, 79.7, 80.1, 80.6, 80.7, 81.0, 84.1, 98.1
98.6, 100.0 (C1, C1%, C1%%), 109.4 (Cdio22), 121.5 (Cdio6),
126.3, 127.2–129.0, 138.0, 138.1, 138.3, 138.4, 138.6,
138.7, 138.8, 139.1 (Ar C), and 140.6 (Cdio5). MALDI
TOFMS: Calcd for C101H120O16 1588.86 [M]. Found
1590.04 [M+H]+, 1611.93 [M+Na]+, 1627.94 [M+
K]+.
tion of ethyl 2,3,4-tri-O-benzyl-1-thio-a-
ranoside (4,21 77 mg, 138 mmol) and phenyl
2-O-benzoyl-3,6-di-O-benzyl-1-thio-b- -glucopyran-
L-rhamnopy-
D
oside (5, 66 mg, 138 mmol) in dry Et2O (2 mL) was
,
stirred with powdered molecular sieves (4 A) under
argon for 1 h when NIS (40 mg, 0.18 mmol) and a
catalytic amount AgOTf were added. TLC (18:1 tolu-
ene–EtOAc) showed complete conversion into the dis-
accharide after 45 min. Subsequently, diosgenin (57 mg,
137 mmol), NIS (40 mg, 0.18 mmol) and a catalytic
amount of AgOTf or DMTST (dimethyl(methyl-
thio)sulfonium triflate) (117 mg, 0.45 mmol) dissolved
in CH2Cl2 (8 mL) containing molecular sieves were
added. After 30 min the reaction was quenched by
addition of Et3N (50 mL) and the mixture was diluted
with CH2Cl2 (20 mL), filtered through Celite and con-
centrated. The residue was applied onto a silica gel
column and eluted (toluene (Et3N)“20:1 toluene–
EtOAc) to give diosgenyl 2-O-benzoyl-3,6-di-O-benzyl-
4-O-(2,3,4-tri-O-benzyl-a-
L
-rhamnopyranosyl)-b-D-
1
glucopyranoside (6, 150 mg, 117 mmol, 85%): H NMR
(CDCl3): l 0.78–2.20 (m, 39H), 3.30–3.95, 4.38–4.73
(m, 23H), 4.94 (d, 1 H, J 11 Hz, 5.09 (s, 1 H), 5.22 (sb,
1H), 5.28 (t, 1H, J 8 Hz), 7.00–7.60 (m, 28H), and 8.05
(d, 2H, J 9 Hz). 13C NMR: l 14.8, 16.5, 17.4, 18.1,
19.6, 21.0, 29.0, 29.8, 30.5, 31.6, 32.0, 32.3, 37.0, 37.4,
39.1, 40.0, 41.8, 50.3, 56.7, 62.3, 67.0, 69.0, 72.2, 72.6,
73.7, 74.3, 74.6, 74.9, 75.5, 75.6, 79.6, 79.8, 80.7, 80.9,
81.7, 98.7, 100.1 (C1, C1%), 109.3 (Cdio22), 121.5 (Cdio6),
125.3, 127.5–130.1, 133.0, 137.6, 138.2, 138.3, 138.6,
138.8 (Ar C), 140.7 (Cdio5), and 165.1 (PhCO).
Diosgenyl
2,4-di-O-(h-L-rhamnopyranosyl)-i-D-
glucopyranoside (dioscin) (3).—Compound 8 (10 mg, 6
mmol) dissolved in dry THF (1 mL) was dropped into
liquid ammonia (10 mL). A catalytic amount of sodium
was added to the white emulsion, which rapidly turned
into a deep blue solution. After 15 min, NH4Cl (s) was
carefully added until the solution turned white again.
The liquid ammonia was allowed to evaporate. The dry
residue was treated with Et2O and MeOH and concen-
trated. The residue was then dissolved in water (5 mL)
and freeze-dried. After filtration through a short RP
C18 column (Sep-Pak), 3 (5 mg, 95%) was obtained,
[h]D −111° (c 0.2, MeOH); lit.9 −113.6°; MALDI
TOFMS: Calcd for C45H72O16 868.48 [M]. Found
869.51 [M+H]+, 891.51 [M+Na]+.
NaOMe (1 M, 0.2 mL) was added to a solution of 6
(125 mg, 98 mmol) in 4:1 MeOH–CH2Cl2 (5 mL). The
mixture was stirred at 50 °C overnight, at the end of
which time the reaction was quenched by addition of
CO2, and the mixture was concentrated and purified by
flash chromatography (toluene“6:1 toluene–EtOAc)
to yield diosgenyl 3,6-di-O-benzyl-4-O-(2,3,4-tri-O-ben-
26-Hydroxy-25(R)-furost-5-en-3i-ol
3-tertbutyl-
dimethylsilyl ether (9).—A solution of TBDMSOTf
(freshly prepared from TBDMSCl (135 mg, 0.9 mmol)
and AgOTf (230 mg, 0.9 mmol) in CH2Cl2 (1.5 mL)
was dropped to a cooled (0 °C) mixture of diosgenin
(250 mg, 0.60 mmol) and sym-collidine (158 mL,
1.8 mmol) under argon. The mixture was left to attain
room temperature, and TBDMSCl (90 mg, 0.6 mmol)
was added after 18 h to obtain complete conversion.
zyl-a-
L
-rhamnopyranosyl)-b- -glucopyranoside (7, 82
D
1
mg, 70 mmol, 71%): H NMR (CDCl3): l 0.78–2.20 (m,
39H), 3.30–3.60 (m, 9H), 3.72 (m, 2H), 3.82 (dd, 2H, J
9 Hz, J 3 Hz), 3.98 (m, 1H), 4.38 (d, 1H, J 8 Hz), 4.42
(m, 1H), 4.56 (s, 2H), 4.62 (m, 5H), 4.76 (d, 1H, J 11
Hz), 4.93 (t, 2H, J 8 Hz), 5.05 (s, 1H), 5.38 (m, 1H),
and 7.10–7.42 (m, 25H). 13C NMR: l 14.7, 16.4, 17.3,

M. Lahmann et al. / Carbohydrate Research 337 (2002) 2153–2159
2157
After concentration, the crude product was purified by
flash chromatography (pentane“6:1 pentane–EtOAc)
to produce diosgenyl 3-O-tertbutyldimethylsilyl ether
and 141.6 (Cdio5). MALDI TOFMS: Calcd for
C67H92O8Si 1052.66 [M]. Found 1075.66 [M+Na]+,
1091.66 [M+K]+.
1
(290 mg, 0.55 mmol, 92%): H NMR (CDCl3): l 0.02
26-O-(2,3,4,6-Tetra-O-benzyl-i-D-glucopyranosyl)-
(s, 6H, Me2Si), 0.78–2.38 (m, 47H), 3.41 (m, 3H), 4.40
(m, 1H), and 5.26 (d, 1H). 13C NMR: l −4.9 (Me2Si),
14.7, 16.4, 17.3, 18.4, 19.6, 21.0, 26.1 (tBuSi), 29.0, 30.5,
31.5, 31.6, 32.0, 32.2, 32.3, 36.9, 37.5, 40.0, 40.4, 41.8,
43.0, 50.3, 56.7, 62.3, 67.0, 72.7, 81.0, 109.4 (Cdio22),
121.0 (Cdio6), and 141.8 (Cdio5). MALDI TOFMS:
Calcd for C33H56O3Si 528.40 [M]. Found 529.59 [M+
H]+; mp 132–134 °C; lit.13 mp 134–136 °C.
3i-hydroxy-25(R)-furost-5-en (11).—TBAF (tetra-
butyl ammonium tetrafluoroborate) (0.4 mL, 1 M in
THF) was added to a solution of 10 (260 mg, 0.25
mmol) in freshly distilled THF (5 mL). After 18 h the
mixture was concentrated. The crude material was
purified by flash chromatography (6:1 pentane–
EtOAc“6:1 toluene–EtOAc) to give 11 (227 mg, 0.24
mmol, 96%): [h]D −8.5° (c 2.0, CH2Cl2): 1H NMR
(CDCl3): l 0.80–2.38 (m, 36H), 3.30 (m, 1H), 3.38–
3.82 (m, 9H), 4.30 (m, 1H), 4.40 (d, 1H, J 8 Hz),
4.44–5.02 (m, 8H), 5.36 (m, 1H), and 7.10–7.40 (m,
20H). 13C NMR: l 16.6, 17.2, 19.1, 19.6, 20.8, 30.7,
31.1, 31.7, 32.1, 32.4, 33.9, 36.7, 37.4, 38.0, 39.6, 40.8,
42.4, 50.2, 57.1, 65.3, 69.1, 71.8, 73.6, 74.9, 75.0, 75.1,
75.3, 75.8, 78.1, 82.4, 83.3, 84.8, 90.4, 103.9 (C1), 121.6
(Cdio6), 127.7–128.5, 138.3, 138.4, 138.7, 138.8 (Ar C),
and 140.9 (Cdio5). MALDI TOFMS: Calcd for
C61H78O8 938.57 [M]. Found 961.62 [M+Na]+, 977.63
[M+K]+.
Diosgenyl 3-O-tertbutyldimethylsilyl ether (285 mg,
0.54 mmol) and BH3·Me3N complex (1.6 g, 22 mmol)
were dissolved in dry 6:1 CH2Cl2–Et2O (70 mL). Pow-
,
dered molecular sieves (4 A) were added, and the
mixture was stirred for 1 h and then cooled (−70 °C).
AlCl3 (275 mg) was slowly added into another flask
containing Et2O (10 mL, 0 °C). This mixture was then
added dropwise to the above mixture. During 2 h the
reaction mixture was allowed to warm up to −10 °C,
and it was then poured onto a slurry of ice (ca. 100 mL)
and CH2Cl2 (100 mL). The organic phase was sepa-
rated, washed with NaHCO3 and brine and concen-
trated The residue was applied onto a silica gel column
and eluted (toluene (Et3N)“6:1 toluene–EtOAc) to
give 9 (260 mg, 0.49 mmol, 91%): [h]D −30° (c 0.4,
CH2Cl2): 1H NMR (CDCl3): l 0.04 (s, 6H, Me2Si),
0.80–2.38 (m, 45H), 3.32 (m, 2H), 3.37 (t, 1 H, J 11
Hz), 3.46 (m, 2H), 4.30 (m, 1H), and 5.28 (m, 1H). 13C
NMR: l −4.4 (Me2Si), 16.6, 16.8, 18.4, 19.6, 20.8, 26.1
(tBuSi), 30.2, 30.6, 31.7, 32.1, 32.2, 32.4, 35.9, 36.8,
37.5, 38.0, 39.6, 40.8, 42.9, 50.3, 57.2, 65.2, 68.1, 72.7,
83.4, 90.5, 121.0 (Cdio6), 141.7 (Cdio5) ppm. MALDI
TOFMS: Calcd for C33H58O3Si 530.41 [M]. Found
553.36 [M+Na]+, 569.30 [M+K]+.
26-O-(2,3,4,6-Tetra-O-benzyl-i-
3i-O-[4-O-(2,3,4-tri-O-benzyl-h- -rhamnopyranosyl)-
3,6-di-O-benzyl-i- -glucopyranosyl]-25(R)-furost-5-en
D-glucopyranosyl)-
L
D
(13).—A solution of 4 (77 mg, 138 mmol) and 5 (66 mg,
138 mmol) in dry Et2O (2 mL) was stirred with pow-
,
dered molecular sieves (4 A) under argon for 1 h at the
end of which time NIS (40 mg, 0.18 mmol) and a
catalytic amount AgOTf were added. TLC (18:1 tolu-
ene–EtOAc) showed complete conversion into the dis-
accharide after 45 min. Subsequently 11 (130 mg, 138
mmol) and DMTST (117 mg, 0.45 mmol) dissolved in
,
CH2Cl2 (8 mL) containing molecular sieves (4 A) were
added. After 30 min the reaction was quenched by
addition of Et3N (50 mL), diluted with CH2Cl2 (20 mL),
filtered through Celite, and concentrated. The residue
was applied onto a silica gel column and eluted (toluene
(Et3N)“12:1 toluene–EtOAc) to give 26-O-(2,3,4,6-
26-O-(2,3,4,6-Tetra-O-benzyl-i-D-glucopyranosyl)-
3i-O-tertbutyldimethylsilyl-25(R)-furost-5-en (10).—A
solution of 9 (35 mg, 66 mmol) and 2,3,4-tri-O-benzyl-
a-D-glucopyranosyl trichloracetimidate (100 mg, 145
mmol) in dry CH2Cl2 (5 mL) was cooled (−40 °C) and
BF3·Et2O (10 mL of 50 mL BF3·Et2O in 1 mL of
CH2Cl2) was added. After 2 h at −30 °C the reaction
mixture was concentrated, and the residue was applied
onto a silica gel column and eluted (19:1 pentane
(Et3N)–EtOAc“9:1 pentane–EtOAc) to give 10 (63
mg, 60 mmol, 91%); [h]D −2.6 (c 1.0, CH2Cl2): 1H
NMR (CDCl3): l 0.10 (s, 6H, Me2Si), 0.80–2.38 (m,
45H), 3.33 (m, 1H), 3.42–3.86 (m, 9H), 4.33 (m, 1H),
4.42 (d, 1H, J 8 Hz), 4.48–5.06 (m, 8H), 5.37 (m, 1H),
and 7.10–7.40 (m, 20H); 13C NMR: l −4.4 (Me2Si),
16.6, 17.1, 18.3, 19.1, 19.6, 20.8, 26.1 (tBuSi), 30.7, 31.0,
31.7, 32.1, 32.2, 32.3, 33.9, 36.8, 37.5, 38.0, 39.6, 40.8,
42.9, 50.3, 57.1, 65.3, 69.1, 72.7, 73.6, 74.9, 75.0, 75.1,
75.2, 75.8, 78.1, 82.4, 83.2, 84.8, 90.3, 103.8 (C1), 121.0
(Cdio6), 127.6–128.6, 138.2, 138.3, 138.6, 138.8 (Ar C),
tetra-O-benzyl-b-
tri-O-benzyl-a- -rhamnopyranosyl)-2-O-benzoyl-3,6-di-
O-benzyl-b- -glucopyranosyl]-25(R)-furost-5-en (12,
D
-glucopyranosyl)-3b-O-[4-O-(2,3,4-
L
D
160 mg, 89 mmol, 64%): 1H NMR (CDCl3): l 0.78–2.20
(m, 36H), 3.30 (m, 1H), 3.40–3.82 (m, 18H), 4.30 (m,
1H), 4.40 (d, 1H, J 8 Hz), 4.44–5.02 (m, 19H), 5.10 (d,
1H, J 2 Hz), 5.21 (m, 1H), 5.27 (dd, 2H, J 8 Hz, J 9
Hz), 7.05–7.60 (m, 48H), and 8.04 (d, 2H). 13C NMR:
l 16.6, 17.2, 18.0, 19.1, 19.5, 20.8, 29.7, 30.7, 31.1, 31.7,
32.1, 32.3, 33.9, 36.9, 37.4, 38.1, 39.0, 39.6, 40.8, 50.3,
57.1, 65.3, 69.0, 69.1, 72.2, 72.6, 73.6, 73.7, 74.3, 74.6,
74.9, 75.0, 75.1, 75.3, 75.4, 75.5, 75.6, 75.8, 78.1, 79.5,
79.9, 80.7, 81.7, 82.4, 83.3, 84.9, 90.4, 98.7, 100.1, 103.9
(C1, C1%, C1%%, C1%%%), 121.6, 127.6–129.8, 130.2, 133.2,
137.7, 138.3, 138.4, 138.6, 138.7, 138.8, 138.9 (Ar C),
140.8, and 165.3 (PhCO).

2158
M. Lahmann et al. / Carbohydrate Research 337 (2002) 2153–2159
Compound 12 (70 mg, 39 mmol) was dissolved in 3:1
residue was dissolved in water (5 mL) and freeze dried.
MeOH–CH2Cl2 (4 mL), and NaOMe was added. The
mixture was stirred at 50 °C overnight, at the end of
which time the reaction was quenched by addition of
CO2, and the mixture was concentrated and purified by
flash chromatography (toluene (Et3N)“12:1 toluene–
EtOAc) to yield 13 (62 mg, 35 mmol, 90%): [h]D −21°
After filtration through a short RP C18 column (Sep-
1
Pak) 2 (31 mg, 97%) was obtained. H NMR (MeOD,
35 °C): l 0.80–2.06 (m, 41H), 2.29 (m, 1H), 2.44 (m,
1H), 3.18 (dd, 1H, J 8 Hz, J 9 Hz), 3.21–3.42, 3.43–
3.88 (m, 21H), 4.11 (m, 1H), 4.22 (d, 1H, J 8 Hz), 4.31
(m, 1H), 4.49 (d, 1H, J 8 Hz), 4.83 (d, 1H, J 2 Hz), 5.20
(d, 1H, J 2 Hz) 5.37 (m, 1H). 13C NMR (25 °C), l 17.1,
17.4, 18.0, 18.1, 19.4, 20.0, 22.0, 30.9, 31.5, 31.9, 33.1,
33.3, 34.8, 38.2, 38.7, 39.2, 39.6, 40.7, 42.0, 51.8, 58.3,
62.1, 62.9, 66.6, 69.9, 70.8, 71.8, 72.3, 72.6, 73.8, 74.0,
75.3, 76.2, 76.7, 78.0, 78.1, 78.2, 79.3, 79.5, 80.0, 84.8,
91.8, 100.5, 102.5, 103.1, 104.8, 122.8, and 142.0 [h]D
−62° (c 1.2, MeOH); MALDI TOFMS: Calcd for
C51H84O21 1032.55 [M]; 1055.46 [M+Na]+.
1
(c 0.3, CH2Cl2): H NMR (CDCl3): l 0.80–2.40 (m,
40H), 3.30–3.82 (m, 20H), 4.00 (m, 1H), 4.30 (m, 1H),
4.34 (d, 1H, J 8 Hz), 4.40 (d, 1H, J 8 Hz), 4.52–5.06
(m, 18H), 5.21 (m, 1H), and 7.18–7.46 (m, 45H). 13C
NMR: l 16.6, 17.2, 18.0, 19.1, 19.5, 20.8, 29.8, 30.7,
31.1, 31.7, 32.2, 32.3, 33.9, 37.0, 37.4, 38.1, 39.0, 39.6,
40.8, 50.3, 57.1, 65.3, 68.8, 69.1, 72.2, 72.6, 73.5, 73.6,
74.8, 74.9, 75.0, 75.1, 75.3, 75.4, 75.5, 75.8, 78.1, 79.2,
79.8, 80.8, 82.4, 83.0, 83.3, 84.9, 90.4, 98.5, 100.4, 103.9
(C1, C1%, C1%%, C1%%%), 122.0, 127.6–129.2, 138.2, 138.3,
138.4, 138.5, 138.6, 138.7, 138.8, 138.9 (Ar C), and
140.5. MALDI TOFMS: Calcd for C108H128O17 1696.92
[M]; 1720.05 [M+Na]+.
Acknowledgements
Financial support from EU (Program Carenet-2,
Contract Number ERB FMRX CT96 0025) and from
the Swedish Natural Science Research Council and the
Fonds der Chemischen Industrie, Frankfurt, is grate-
fully acknowledged.
26-O-(2,3,4,6-Tetra-O-benzyl-i-
3i-O-[2,4-di-O-(2,3,4-tri-O-benzyl-h-
osyl) - 3,6 - di - O - benzyl - i - - glucopyranosyl] - 25(R)-
D
-glucopyranosyl)-
L
-rhamnopyran-
D
furost-5-en (14).—A solution of 13 (120 mg, 71 mmol)
and 4 (40 mg, 84 mmol) in dry Et2O (2 mL) was stirred
,
with powdered molecular sieves (4 A) under argon for
1 h at the end of which time NIS (20 mg, 89 mmol) and
a catalytic amount AgOTf were added. After 1 h stir-
ring at room temperature, the reaction mixture was
quenched by addition of Et3N (50 mL), diluted with
Et2O (20 mL), filtered through Celite and concentrated.
The residue was applied onto a silica gel column and
eluted (toluene (Et3N)“18:1 toluene–EtOAc) to give
14 (108 mg, 51 mmol, 72%): [h]D −14° (c 3.5, CH2Cl2):
1H NMR (CDCl3): l 0.80–2.45 (m, 43H), 3.30–3.82,
4.20–5.05 (m, 51H), 5.30 (s, 1H), 5.33 (m, 1H), and
7.18–7.40 (m, 60H); 13C NMR: l 16.6, 17.2, 18.0, 18.1,
19.1, 19.3, 20.8, 29.8, 30.8, 31.1, 31.7, 32.2, 32.4, 33.9,
37.0, 37.4, 38.1, 38.5, 39.6, 40.8, 50.3, 57.1, 65.3, 68.2,
68.9, 69.1, 72.0, 72.2, 72.6, 73.6, 73.7, 74.9, 75.0, 75.1,
75.3, 75.5, 75.7, 75.8, 76.8, 78.1, 78.8, 79.6, 80.1, 80.6,
80.7, 82.4, 84.2, 84.9, 90.4, 98.2 (JC1,H1 175 Hz), 98.7
(JC1,H1 174 Hz), 100.0 (JC1,H1 155 Hz), 103.9 (JC1,H1 162
Hz), 121.7, 127.3–128.5, 138.2, 138.3, 138.4, 138.5,
138.6, 138.7, 138.8, 138.9, 139.0, 139.2 (Ar C), and
140.8. MALDI TOFMS: Calcd for C135H156O21 2113.11
[M]. Found 2136.34 [M+Na]+.
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