Synthesis of a D,D- and L,D-heptose-containing hexasaccharide corresponding to a structure from Haemophilus ducreyi lipopolysaccharides

Article abstract of DOI:10.1016/S0957-4166(99)00554-6

The synthesis of a linear hexasaccharide, 2-(4-trifluoroacetamidophenyl)ethyl (β-D-galactopyranosyl)-(1→4)-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(1→3)-(β-D-galactopyranosyl)-(1→4)-(D-glycero-α-D-manno-heptopyranosyl)-(1→6)-(β-D-glucopyranosyl)-(1→4)-L-

Full text of DOI:10.1016/S0957-4166(99)00554-6

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 481–492
Synthesis of a D,D- and L,D-heptose-containing hexasaccharide
corresponding to a structure from Haemophilus ducreyi
lipopolysaccharides
Christian Bernlind, Simon Bennett and Stefan Oscarson ∗
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, S-106 91 Stockholm, Sweden
Received 1 November 1999; accepted 2 December 1999
Abstract
The synthesis of a linear hexasaccharide, 2-(4-trifluoroacetamidophenyl)ethyl (β-D-galactopyranosyl)-(1→4)-
(2-acetamido-2-deoxy-β-D-glucopyranosyl)-(1→3)-(β-D-galactopyranosyl)-(1→4)-(D-glycero-α-D-manno-hepto-
pyranosyl)-(1→6)-(β-D-glucopyranosyl)-(1→4)-L-glycero-α-D-manno-heptopyranoside, corresponding to
a
structure found in Haemophilus ducreyi LPS, is described. A Barbier reaction between benzyloxymethyl chloride
and a properly protected 6-aldo-1-thio-mannopyranoside yielded both the D,D- and the L,D-heptopyranoside
(2 and 3, ratio 2:3), which were separated and both used in the synthesis. p-Methoxybenzyl and chloroacetyl
groups were employed as temporary protecting groups, selectively removed in the presence of the persistent
benzyl, acetyl, benzoyl and isopropylidene groups by treatment with DDQ/H2O and hydrazine dithiocarbonate,
respectively. Thioglycosides were utilised as donors throughout using either NIS/TfOH or DMTST as promoters.
The introduction of the spacer into thioglycoside 5 was high-yielding (95%) but with low stereoselectivity (α:β
5:3). All other glycosylations are completely stereoselective. The target hexasaccharide is obtained via a 3+3
block approach with the yield in the final NIS/TfOH-promoted coupling between an N,N-diacetyl-trisaccharide
thioglycosyl donor 20 and a 400-OH trisaccharide acceptor 13 being 75%. © 2000 Elsevier Science Ltd. All rights
reserved.
1. Introduction
Haemophilus ducreyi is a gram-negative bacterium causing genital chancroids. Outer membrane
lipopolysaccharide (LPS) structures from H. ducreyi have been shown to cause substantial tissue damage
if injected into animals,1 but the exact role of these structures in the infection and the development of the
disease is not known. Recently, H. ducreyi LPS structures from various strains have been elucidated.2,3
As for Haemophilus influenzae the structures lack the polymeric O-antigen and a substantial structural
∗
Corresponding author.
0957-4166/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00554-6
tetasy 3189

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heterogeneity is found. Both H. influenzae and ducreyi LPSs seem to contain a common core structure,
a branched pentasaccharide built up of one β-D-glucose, three L-glycero-α-D-manno-heptose and one
α-Kdo residues (Fig. 1). They differ, however, in the substitution pattern of the common core, both
considering phosphate and glycan groups. The H. ducreyi structures found are generally substituted
at the 6-position of the glucose moiety with various oligosaccharides; a number of these are also
found in human glycoconjugate structures. We have earlier synthesised a lactose-containing linear
trisaccharide found in H. ducreyi LPS and also branched parts of the common core structure.4,5 We
now describe the synthesis of a linear hexasaccharide, (β-D-galactopyranosyl)-(1→4)-(2-acetamido-2-
deoxy-β-D-glucopyranosyl)-(1→3)-(β-D-galactopyranosyl)-(1→4)-(D-glycero-α-D-manno-heptopyran-
osyl)-(1→6)-(β-D-glucopyranosyl)-(1→4)-L-glycero-α-D-manno-heptopyranoside, corresponding to
a structure found in H. ducreyi LPS, containing both D- and L-glycero-α-D-manno-heptopyranose
as synthetic challenges. The hexasaccharide is synthesised as its 2-(4-trifluoroacetamidophenyl)ethyl
glycoside to facilitate the formation of immunogenic glycoconjugates by the coupling of the spacer
amino group to a protein, to allow various biological experiments.
Fig. 1. Generalised structure of the dephosphorylated LPS of H. ducreyi without the lipid A moiety
2. Results and discussion
Reactions of organomagnesium reagents of various silyl- and alkoxymethyl chlorides with 1,6-dialdo-
mannopyranosides generally give good yields of heptopyranosides with a strong preponderance for the
L-glycero-D-manno-heptose isomer, due to complexation of the magnesium reagent to the ring oxygen.6
Initially the D,D-heptose moiety was therefore planned to be obtained through an inversion at C-6 of an
L,D-heptose derivative. A precursor 1, containing a free 6-OH group to allow oxidation to the aldehyde
and subsequent carbon elongation, and an orthogonal p-methoxybenzyl group to allow later coupling in
the 4-position, was therefore synthesised according to methods described by Grzeszczyk and Zamojski
in the preparation of the corresponding benzyl glycoside.7 When the carbon elongation was performed,
using bensyloxymethyl chloride and Barbier reaction conditions,5 a good yield of the heptopyranoside
was obtained, but surprisingly almost equal amounts of the 6-D and the 6-L form, 2 and 3 (ratio 2:3, 52%),
were obtained (Scheme 1). The stereochemistry was determined by transformation into the perbenzylated
thioglycosides and comparison with a derivative with known L,D-configuration. Grignard conditions
gave almost identical results. The ratio between the two stereoisomers is known to be dependent on
the protecting group pattern of the aldehyde precursor,6 but the identically protected benzyl glycoside
gave a 2:7 ratio in a reaction with the allyloxymethyl Grignard reagent,7 showing that probably also the
nature of the aglycon affects the stereochemical outcome of the reaction. Since both a 4-linked D,D- and
L,D-heptose was part of the target structure, this however meant that suitable precursors for both of these
residues were obtained directly in the carbon elongation reaction.
The hexasaccharide was designed to be synthesised through a 3+3 block synthesis. To construct the
acceptor trisaccharide block containing both heptose residues, both 2 and 3 were benzylated at the
6-position to give 4 (86%) and the previously known8 compound 5 (82%), respectively (Scheme 1).

C. Bernlind et al. / Tetrahedron: Asymmetry 11 (2000) 481–492
483
Scheme 1. (i) (a) DMSO, (COCl)2, Et3N, CH2Cl2, (b) BnOCH2Cl, Mg, THF (52%, 2:3 2:3); (ii) BnBr, NaH, DMF [86% (4),
82% (5)]; (iii) p-CF3CONHPhCH2CH2OH, NIS/AgOTf, CH2Cl2/MeCN (95%, α:β 5:3); (iv) DDQ, H2O, CH2Cl2 (80%); (v)
ClAcCl, CH2Cl2/pyridine (79%); (vi) NIS/AgOTf, CH2Cl2 (95%); (vii) HDTC, THF/DMF (89%); (viii) DMTST, Et2O (71%);
(ix) DDQ, H2O, CH2Cl2 (69%)
Thioglycoside 5 was transformed into a spacer glycoside through an NIS/AgOTf-promoted9 coupling
with 2-(4-trifluoroacetamidophenyl)ethanol to give an excellent yield of glycoside (95%), but with low
stereoselectivity (α:β 1.7:1) as found earlier in similar couplings.10 This time, in contrast to our earlier
experiences, it was not possible to anomerise the β-glycoside to the α-anomer by BF3–etherate treatment.
Removal of the p-methoxybenzyl group using DDQ from the α-glycoside 6 yielded the 4-OH acceptor
7 (80%). Reductive benzylidene opening (borane–trimethylamine complex/AlCl3 in CH2Cl2/diethyl
ether)11 of the known ethyl 2,3-di-O-benzoyl-4,6-O-benzylidene-1-thio-β-D-glucopyranoside12 gave 8
(84%), chloroacetylation of which afforded 9 (79%). NIS/AgOTf-promoted coupling between 9 and
7 yielded the (1→4)-β-linked disaccharide 10 (95%), from which the chloroacetate was removed
selectively by hydrazine dithiocarbonate13 (HDTC) to give the new acceptor 11 (89%). Coupling between
11 and the D,D-heptosyl donor 4, this time with dimethyl(methylthio) sulfonium triflate (DMTST) as
promoter,14 rendered the exclusively α-(1→6)-linked trisaccharide block 12, which was turned into the
400-OH acceptor 13 by orthogonal deprotection of the p-methoxybenzyl group with DDQ (69%).
The other trisaccharide block, containing, inter alia, lactosamine, was designed to be a thioglycoside
donor, because of our successful experiences with the use and couplings of thioglycoside building
blocks, and synthesised by a consecutive synthesis starting from monosaccharides. Initially, ethyl 4-
O-acetyl-2,6-di-O-benzoyl-1-thio-β-D-galactopyranoside15 was chosen as a precursor acceptor, but, in
spite of the deactivating benzoyl groups, severe problems with transglycosylations and hydrolysis
in both the couplings to give the target trisaccharide made a change to a more resistant anomeric
protecting group necessary. Hence, the corresponding (trimethylsilyl)ethyl (TMSE) glycoside 1516 was
synthesised following the same protecting group protocol. Acceptor 15 was glycosylated with the
known15 disaccharide thioglycoside donor 14 using NIS/AgOTf as promoter to give the trisaccharide 16,
which was subsequently converted into the thioglycoside donor 19 in three steps (Scheme 2). Finally,
the trisaccharide donor 19 was coupled to the trisaccharide acceptor 13 promoted by NIS/AgOTf,
to give the target hexasaccharide 21 in a rather sluggish reaction where 38% of unreacted acceptor

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could be recovered (45% yield of 21, 72% calculated on consumed acceptor). Observations have
been published where couplings involving acetamido-containing donors were found to be more high-
yielding if diacetylamino donors were used.17 When this approach was tried in the coupling to give
the hexasaccharide using the diacetylamino donor 20 and the same acceptor 13, a more effective
glycosylation took place and the hexasaccharide could be isolated in a 75% yield.
Scheme 2. (i) AgOTf, toluene/CH2Cl2 (93%); (ii) NIS/TfOH Et2O/CH2Cl2 (70%); (iii) (a) NaOMe, MeOH, (b) H2NNH2,
EtOH/dioxane, (c) Ac2O, pyridine, DMAP (81%); (iv) BF3–Et2O, Ac2O, toluene (42%); (v) EtSH, BF3–Et2O CH2Cl2 (73%);
(vi) NIS/TfOH, CH2Cl2 [45% (21), 75% (22)]
3. Experimental
3.1. General methods
These were as described earlier.5

C. Bernlind et al. / Tetrahedron: Asymmetry 11 (2000) 481–492
485
3.2. Ethyl 2,3-O-isopropylidene-4-O-p-methoxybenzyl-1-thio-α-D-mannopyranoside 1
Ethyl 2,3,4,6-tetra-O-acetyl-1-thio-α-D-mannopyranoside18 (44.3 g, 113 mmol) was dissolved in
MeOH (500 mL). The pH was adjusted to 10 by addition of a 1 M solution of sodium methoxide in
MeOH. After stirring for 4 h the mixture was neutralised by Dowex H+, filtered and concentrated.
The residue was co-evaporated twice from dry pyridine and dissolved in the same solvent (500 mL),
whereafter triphenylmethyl chloride (34.6 g, 124 mmol) and 4-dimethylaminopyridine (1 g) were added.
The solution was stirred overnight and then concentrated. The residue was dissolved in CHCl3 (400 mL)
and washed with H2O (7×150 mL). The organic phase was dried (Na2SO4), filtered, and concentrated
in vacuo. The residue was dissolved in DMF (200 mL), 2,2-dimethoxypropane (100 mL) and p-
toluenesulfonic acid (5 g) were added, and the solution was stirred at room temperature for 2 h, and
then diluted with toluene (500 mL). The organic phase was stirred with NaHCO3 (aq., satd, 300 mL) for
1 h, separated, washed once with H2O, dried (Na2SO4), filtered, and concentrated. The crude residue was
purified on a silica gel column, which was packed in CH2Cl2, whereafter the crude substance was applied
and washed into the gel. The top of the column was equipped with a reflux condenser which was in turn
connected to a 500 mL round-bottomed flask containing CH2Cl2 (250 mL). The outlet of the column was
connected to the flask via a teflon tube, and the flask content was brought to boiling and the outflow from
the column was carefully adjusted to maintain the solvent level above the gel. As soon as the desired
substance was eluting (as monitored by TLC of the outcoming flow) the flask was exchanged for an
identical one containing Et2O (250 mL). The apparatus was refluxed and eluted until no more substance
was detected. The ethereal solution was then concentrated to yield ethyl 2,3-O-isopropylidene-1-thio-
6-O-triphenylmethyl-α-D-mannopyranoside (45.6 g, 90 mmol, 80%). To a flask containing washed
(hexane) sodium hydride (10.9 g, 0.27 mol, 60% dispersion in oil) was added dry DMF (200 mL).
The solution was cooled (0°C) and a solution of the above residue (45.6 g, 90 mmol) in DMF (150
mL) was slowly added dropwise during 30 min. After an additional 1 h, a solution of p-methoxybenzyl
bromide (29.8 g, 148 mmol) in DMF (50 mL) was added dropwise, and the mixture was stirred for
2 h at 0°C. The reaction was carefully quenched by the addition of MeOH (20 mL), and the mixture
diluted with toluene (500 mL), washed with H2O (3×200 mL), dried (Na2SO4), filtered, concentrated,
and purified by the same silica gel column procedure as above, to give ethyl 2,3-O-isopropylidene-4-O-
p-methoxybenzyl-1-thio-6-O-triphenylmethyl-α-D-mannopyranoside (45.0 g, 80%). 13C NMR (CDCl3):
δ 14.2, 23.9 (CH3CH2S), 26.5, 28.0 [(CH3)2C], 55.2 (ArCH2O), 63.1, 69.2, 72.7, 76.1, 76.5, 78.7,
78.9, 86.4 (C-1–6, ArCH2O, Ph3CO), 109.3 [(CH3)2C], 113.5–159.0 (aromatic C). To a solution of
this derivative (18.0 g, 28.7 mmol) in EtOAc (140 mL) was added formic acid (85% aq., 70 mL). The
mixture was stirred for 2.5 h and neutralized by addition of K2CO3 (aq., satd, 200 mL). The organic
phase was separated, dried (MgSO4) and evaporated. Purification of the crude product on a silica gel
column (toluene:EtOAc, 4:1) gave 6.83 g (17.8 mmol, 62%) of 1. [α]D +160 (c 1.0, CHCl3); 13C NMR
(CDCl3): δ 14.5, 24.3 (CH3CH2S), 26.5, 28.0 [(Me)2C], 55.3 (ArCH2O), 62.5, 69.0, 72.7, 76.1, 76.7,
78.5, 79.6 (C-1–6, ArCH2O), 109.4 [(Me)2C], 113.8, 129.7, 130.2, 159.3 (aromatic C). Anal. calcd for
C19H28O6S: C, 59.35; H, 7.34. Found: C, 59.34; H, 7.35.
3.3. Ethyl 7-O-benzyl-2,3-O-isopropylidene-4-O-p-methoxybenzyl-D-thio-1-glycero-α-D-manno-hepto-
pyranoside 2 and 7-O-benzyl-2,3-O-isopropylidene-4-O-p-methoxybenzyl-1-thio-L-glycero-α-D-manno-
hepto-pyranoside 3
Swern-oxidation of 1 was performed under standard conditions: A solution of oxalyl chloride (1.42
mL, 16.5 mmol) in dry CH2Cl2 (mL) was cooled to −60°C. DMSO (2.4 mL, 31.1 mmol) in CH2Cl2

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was added dropwise during 10 min. Stirring was continued for 5 min when 1 (5.45 g, 14.2 mmol) in
CH2Cl2 was added during 10 min. After an additional 30 min at −60°C, Et3N (10 mL, 72 mmol) was
added dropwise and the solution was slowly brought to room temperature (1 h). The solution was diluted
(CH2Cl2) and washed twice with water. Drying (MgSO4), concentration and co-evaporation three times
from sodium-dried toluene yielded crude ethyl 1,6-dialdo-2,3-O-isopropylidene-4-O-p-methoxybenzyl-
1-thio-α-D-mannopyranoside which was used directly in the next step. Freshly acid-washed and dried
magnesium turnings (1.03 g, 42.4 mmol) were added to a 100 mL round-bottomed flask equipped with
a dropping funnel, a magnetic stirrer and an internal thermometer. To the dropping funnel was added
the above aldehyde (from 14.2 mmol of 1) and benzyloxymethyl chloride (3.9 mL, 28 mmol) in dry
THF (30 mL). HgBr2 (70 mg, 0.19 mmol) was added to the Mg turnings and after 10 min the solid
material was covered with dry THF. The formation of the organomagnesium compound was initiated
by the addition of a few drops of neat benzyloxymethyl chloride. When the exothermic reaction had
started, the flask was partially immersed into an ice-water bath (0°C). The aldehyde/alkyl halide solution
was added dropwise at such a rate (approx. 2 mL/min) that the internal reaction temperature was kept
between 10 and 12°C. The mixture was then left stirring overnight, slowly attaining room temperature.
The mixture was diluted (Et2O) and transferred to an Ehrlenmeyer flask containing a freshly made (0°C)
saturated NH4Cl solution (100 mL). After 2 h of stirring the organic phase was separated, dried (MgSO4)
and concentrated. Silica gel purification of the residue (toluene:EtOAc 6:1) gave first 2 (1.52 g, 3.01
mmol, 21%) followed by 3 (2.20 g, 4.36 mmol, 31%). Compound 2: [α]D +113 (c 1.0, CHCl3); 13C
NMR (CDCl3): δ 14.2, 24.1 (CH3CH2S), 26.4, 28.1 [(Me)2C], 55.3 (MeO), 68.4, 70.9, 72.4, 72.5, 73.5,
76.5, 77.8, 78.7, 79.6 (C-1–7, ArCH2O), 109.5 [(Me)2C], 113.8, 127.6, 127.7, 128.3, 129.8, 129.9, 138.2,
159.4 (aromatic C); compound 3: [α]D +71 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 14.3, 24.2 (CH3CH2S),
26.5, 28.0 [(Me)2C], 55.3 (MeO), 69.7, 68.6, 71.7, 73.0, 73.4, 75.3, 76.5, 78.8, 79.9 (C-1–7, ArCH2O),
109.4 [(Me)2C], 113.8–159.2 (aromatic C).
3.4. Ethyl 6,7-di-O-benzyl-2,3-O-isopropylidene-4-O-p-methoxybenzyl-1-thio-D-glycero-α-D-manno-
heptopyranoside 4
Sodium hydride (310 mg, 60% dispersion in oil) was washed once with dry light petroleum (bp
40–65°C). DMF (4 mL) was added and a solution of 2 (961 mg, 1.90 mmol) in DMF (8 mL) was added
dropwise at 0°C. After 2 h, benzyl bromide (905 µL, 7.61 mmol) in DMF (2 mL) was added, and the
solution was allowed to attain room temperature. After 2 h, MeOH (0.4 mL) was carefully added and
the mixture was diluted with toluene, washed three times with H2O, dried (Na2SO4) and concentrated in
vacuo. Purification on a silica gel column (toluene:EtOAc 12:1) gave 4 (970 mg, 1.63 mmol, 86%). [α]D
+109 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 14.4, 23.8 (CH3CH2S), 26.5, 28.0 [(Me)2C], 55.2 (MeO),
69.3, 70.6, 72.4, 73.2, 76.0, 76.4, 76.6, 79.0, 79.4 (C-1–7, ArCH2O), 109.3 [(Me)2C], 113.6–159.1
(aromatic C). Anal. calcd for C34H42O7S: C, 68.66; H, 7.12. Found: C, 68.34; H, 7.13.
3.5. Ethyl 6,7-di-O-benzyl-2,3-O-isopropylidene-4-O-p-methoxybenzyl-1-thio-L-glycero-α-D-manno-
heptopyranoside 5
Following the procedure described above for 4, 3 (1.27 g, 2.52 mmol) was benzylated to give 5 (1.23
g, 2.07 mmol, 82%). [α]D +109 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 14.4, 24.2 (CH3CH2S), 26.5, 28.0
[(Me)2C], 55.2 (MeO), 69.4, 70.8, 71.9, 73.4, 73.6, 75.1, 75.5, 76.5, 79.0, 80.0 (C-1–7, ArCH2O), 109.4
[(Me)2C], 113.7–159.1 (aromatic C).

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487
3.6. 2-(4-Trifluoroacetamidophenyl)ethyl 6,7-di-O-benzyl-2,3-O-isopropylidene-4-O-p-methoxybenzyl-
L-glycero-α-D-manno-hepto-pyranoside 6 and 2-(4-trifluoroacetamidophenyl)ethyl 6,7-di-O-benzyl-2,
3-O-isopropylidene-4-O-p-methoxybenzyl-L-glycero-β-D-manno-heptopyranoside 7
To a solution of 5 (804 mg, 1.35 mmol) and 2-(4-trifluoroacetamidophenyl)ethanol (426 mg, 1.83
mmol) in CH2Cl2:MeCN (5:1, 30 mL) under argon was added powdered molecular sieves (4 Å). The
solution was stirred for 1 h at room temperature when N-iodosuccinimide (NIS, 410 mg, 1.82 mmol)
followed by a catalytic amount of silver trifluoromethanesulfonate (AgOTf) were added. After stirring
for 1.5 h the mixture was filtered through Celite and diluted with CH2Cl2. The organic phase was
washed with a mixture of NaHCO3 (aq., satd, 10 mL) and Na2S2O3 (10% aq., 10 mL), dried (Na2SO4),
concentrated and purified by silica gel chromatography (toluene/EtOAc 14→20%). Concentration of
appropriate fractions gave 624 mg of the α-isomer 6 (0.814 mmol, 60%) followed by 363 mg of β-isomer
(0.474 mmol, 35%). Compound 6: [α]D +32 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 26.4, 27.9 [(Me)2C],
35.2 (ArCH2CH2), 55.2 (MeO), 67.9, 68.2, 70.2, 71.8, 73.3, 73.5, 74.6, 75.1, 75.6, 79.2 (C-2–7, ArCH2O,
ArCH2CH2O), 97.3 (C-1, JC,H 171 Hz), 109.4 [(Me)2C], 113.7–159.1 (aromatic C); β-isomer: [α]D +7
(c 1.0, CHCl3); 13C NMR (CDCl3): δ 26.3, 27.4 [(Me)2C], 35.5 (ArCH2CH2), 55.2 (MeO), 69.9, 70.1,
71.6, 73.3, 73.4, 73.8, 74.3, 74.6, 75.5, 80.3 (C-2–7, ArCH2O, ArCH2CH2), 98.7 (C-1, JC,H 159 Hz),
110.8 [(Me)2C], 113.7–159.2 (aromatic C).
3.7. 2-(4-Trifluoroacetamidophenyl)ethyl 6,7-di-O-benzyl-2,3-O-isopropylidene-L-glycero-α-D-manno-
heptopyranoside 7
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ, 251 mg, 1.11 mmol) and H2O (2 mL) were added
to a solution of 6 (578 mg, 0.755 mmol) in CH2Cl2 (40 mL) and the mixture was left stirring for
2 h. Separation of the organic phase followed by washing (Na2S2O3, 5% aq.), drying (Na2SO4) and
concentration gave a residue, which was purified on a silica gel column (toluene/EtOAc 0→33%) to give
7 (392 mg, 607 µmol, 80%). [α]D +30 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 26.3, 28.1 [(Me)2C], 35.3
(ArCH2CH2), 67.9, 68.7, 69.0, 69.6, 73.1, 73.3, 74.4, 75.6, 78.4 (C-2–7, ArCH2O, ArCH2CH2O), 97.3
(C-1), 109.4 [(Me)2C], 120.5–138.2 (aromatic C). Anal. calcd for C34H38F3NO8: C, 63.25; H, 5.93; N,
2.17. Found: C, 63.28; H, 5.87; N, 2.15.
3.8. Ethyl 2,3-di-O-benzoyl-4-O-benzyl-1-thio-β-D-glucopyranoside 8
Ethyl 2,3-di-O-benzoyl-4,6-O-benzylidene-1-thio-β-D-glucopyranoside11 (6.0 g, 11.5 mmol) and
borane–trimethylamine complex (33.6 g, 461 mmol) were dissolved in dry CH2Cl2:Et2O (5:2, 280 mL).
Powdered molecular sieves (4 Å) were added and the mixture was stirred for 1 h and then cooled to
0°C. To another cooled flask (0°C) with 50 mL of dry Et2O was slowly and carefully added AlCl3 (6.3
g, 47 mmol). This solution was then added dropwise to the above mixture at 0°C. The mixture was
stirred for an additional 30 min, when it was filtered (Celite) and stirred with aqueous sulfuric acid (1
M, 100 mL). The organic phase was separated and washed with H2O followed by NaHCO3 (aq., satd),
dried (MgSO4), filtered and concentrated. The residue was dissolved in boiling Et2O (600 mL) and
left overnight. Filtration gave 21 g of unreacted borane–trimethylamine complex (as was determined by
NMR). The filtrate was concentrated and purified on a silica gel column (toluene/EtOAc 0→33%) to yield
8 (5.02 g, 9.61 mmol, 84%). [α]D +53 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 14.9, 24.5 (CH3CH2S), 61.7,
70.9, 74.8, 75.4, 76.2, 79.7, 83.8 (C-1–6, PhCH2O), 127.0–137.1 (aromatic C), 165.4, 165.7 (PhCO).
Anal. calcd for C29H30O7S: C, 66.65; H, 5.79. Found: C, 66.58; H, 5.76.

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3.9. Ethyl 2,3-di-O-benzoyl-4-O-benzyl-6-O-chloroacetyl-1-thio-β-D-glucopyranoside 9
Monochloroacetyl chloride (318 µL, 4.00 mmol) was added to a cooled (10°C) solution of 8 (1.023
g, 1.96 mmol) in CH2Cl2:pyridine (15:1, 25 mL). After 1 h the solution was washed with H2O, dried
(MgSO4), filtered and concentrated. After silica gel column chromatography (toluene/EtOAc 0→10%),
9 (930 mg, 1.55 mmol, 79%) was obtained. [α]D +70 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 14.9, 24.4
(CH3CH2S), 40.7 (ClCH2CO), 64.3, 70.6, 74.7, 75.2, 76.4, 76.8, 83.7 (C-1–6, PhCH2O), 128.2–136.7
(aromatic C), 165.4, 165.6, 166.9 (PhCO, ClCH2CO).
3.10. 2-(4-Trifluoroacetamidophenyl)ethyl (2,3-di-O-benzoyl-4-O-benzyl-6-O-chloroacetyl-β-D-gluco-
pyranosyl)-(1→4)-6,7-di-O-benzyl-2,3-O-isopropylidene-L-glycero-α-D-manno-heptopyranoside 10
A solution of 9 (208 mg, 347 µmol) and 7 (159 mg, 246 µmol) in dry CH2Cl2 (20 mL) was stirred with
powdered molecular sieves (4 Å) under argon for 40 min. The mixture was cooled to 0°C and NIS (86 mg,
382 µmol) and a catalytic amount of AgOTf were added. After 10 min the cooling bath was removed and
stirring was continued for 1 h. The reaction was quenched by the addition of Et3N (50 µl) and the mixture
filtered through Celite, washed (Na2S2O3, aq., satd) and dried (MgSO4). Filtration and concentration
yielded a residue, which was subjected to silica gel column chromatography (toluene/EtOAc 0→20%) to
give 10 (277 mg, 234 µmol, 95%). [α]D +54 (c 1.0, CHCl3); mp 144–146°C (corr.); 13C NMR (CDCl3):
δ 26.4, 27.9 [(Me)2C], 35.1 (ArCH2CH2), 40.7 (ClCH2CO), 63.9, 67.2, 67.8, 69.9, 72.2, 72.6, 72.8, 73.0,
73.3, 75.0, 75.3, 76.8 (C-2–7, C-20–60, PhCH2O, ArCH2CH2O), 96.5 (JC,H 169 Hz, C-1), 100.5 (JC,H 161
Hz, C-10), 109.2 [(Me)2C], 121.0–138.7 (aromatic C), 165.6, 165.7, 167.0 (PhCO, ClCH2CO).
3.11. 2-(4-Trifluoroacetamidophenyl)ethyl (2,3-di-O-benzoyl-4-O-benzyl-β-D-glucopyranosyl)-(1→4)-
6,7-di-O-benzyl-2,3-O-isopropylidene-L-glycero-α-D-manno-heptopyranoside 11
To a solution of 10 (275 mg, 233 µmol) in THF:DMF (4:1, 15 mL) was added hydrazine dithiocar-
bonate (2.0 mL of a stock solution, approx 350 mM). After stirring for 1 h at room temperature the
solution was diluted with CH2Cl2 and washed with H2O. Drying (Na2SO4), filtration, concentration and
purification by silica gel column chromatography (toluene:EtOAc 4:1) then gave 11 (229 mg, 207 µmol,
89%). [α]D+38 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 26.0, 27.7 [(Me)2C], 35.1 (ArCH2CH2), 62.9,
66.9, 67.0, 70.0, 72.7, 72.9, 73.0, 74.3, 74.5, 74.6, 74.9, 75.8, 77.8, 78.5 (C-2–7, C-20–60, PhCH2O,
ArCH2CH2O), 95.8, 101.2 (C-1,10), 109.2 [(Me)2C], 121.3–138.7 (aromatic C), 165.7, 166.0 (PhCO).
Anal. calcd for C61H62F3NO15: C, 66.24; H, 5.65; N, 1.27. Found: C, 66.13; H, 5.77; N, 1.25.
3.12. 2-(4-Trifluoroacetamidophenyl)ethyl (6,7-di-O-benzyl-2,3-O-isopropylidene-4-O-p-methoxy-
benzyl-D-glycero-α-D-manno-heptopyranosyl)-(1→6)-(2,3-di-O-benzoyl-4-O-benzyl-β-D-glucopyran-
osyl)-(1→4)-6,7-di-O-benzyl-2,3-O-isopropylidene-L-glycero-α-D-manno-heptopyranoside 12
Compounds 11 (129 mg, 117 µmol) and 4 (90 mg, 151 µmol) were dissolved in dry benzene (2 mL),
and the solution concentrated and dried under vacuum. The residue was dissolved in dry Et2O (10 mL)
and powdered molecular sieves (4 Å) were added. The mixture was stirred for 40 min under argon,
whereafter dimethyl(methylthio)sulfonium triflate (DMTST, 125 mg, 484 µmol) was added. Continued
stirring for 3 h followed by filtration and concentration gave a crude product which was purified by silica
gel column chromatography (toluene:EtOAc 6:1) to yield 12 (136 mg, 83.0 µmol, 71%). [α]D +37 (c 1.0,
CHCl3); 13C NMR (CDCl3): δ 26.3, 26.5, 27.9, 28.0 [(Me)2C], 35.2 (ArCH2CH2), 55.2 (MeO), 64.3,

C. Bernlind et al. / Tetrahedron: Asymmetry 11 (2000) 481–492
489
67.3, 67.9, 69.1, 70.0, 70.7, 72.3, 72.6, 72.8, 72.9, 73.2, 74.4, 74.5, 75.0, 75.2, 75.3, 75.5, 76.9, 78.4, 79.3
(C-2–7, C-20–60, C-200–700, PhCH2O, ArCH2CH2O), 96.7 (JC,H 169 Hz), 97.5 (JC,H 172 Hz) (C-1,100),
100.7 (JC,H 165 Hz, C-10), 109.1, 109.5 [(Me)2C], 113.6–159.1 (aromatic C), 165.6, 165.8 (PhCO).
3.13. 2-(4-Trifluoroacetamidophenyl)ethyl (6,7-di-O-benzyl-2,3-O-isopropylidene-D-glycero-α-D-
manno-heptopyranosyl)-(1→6)-(2,3-di-O-benzoyl-4-O-benzyl-β-D-glucopyranosyl)-(1→4)-6,7-di-O-
benzyl-2,3-O-isopropylidene-L-glycero-α-D-manno-heptopyranoside 13
A solution of 12 (165 mg, 101 µmol) and DDQ (34 mg, 150 µmol) in CH2Cl2 (10 mL) and H2O (0.5
mL) was stirred at room temperature overnight. The mixture was washed with H2O and Na2S2O3 (aq.,
satd), dried (MgSO4) and concentrated. The crude product was purified (silica gel column, toluene:EtOAc
3:1) to give 13 (105 mg, 69.1 µmol, 69%). [α]D +30 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 26.3,
27.9, 28.1 [(Me)2C], 35.2 (ArCH2CH2), 64.7, 67.3, 67.8, 68.3, 69.5, 70.0, 71.2, 72.5, 72.6, 72.8, 72.9,
73.5, 74.4, 74.5, 74.9, 74.97, 75.02, 75.2, 75.3, 77.2, 78.0, 80.2 (C-2–7, C-20–60, C-200–700, PhCH2O,
ArCH2CH2O), 96.7, 97.8, 100.8 (C-1,10,100), 109.0, 109.6 [(CH3)2C], 121.0–138.7 (aromatic C), 165.6,
165.8 (PhCO). Anal. calcd for C85H90F3NO21: C, 67.23; H, 5.97; N, 0.92. Found: C, 67.63; H, 5.68; N,
1.07.
3.14. Ethyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl-(1→4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-
1-thio-β-D-glucopyranoside 14
2,3,4,6-Tetra-O-acetyl-β-D-galactosyl bromide19 (1.645 g, 4.00 mmol) and 3,6-di-O-benzyl-2-deoxy-
2-phthalimido-1-thio-β-D-glucopyranoside15 (1.063 g. 1.99 mmol) were dissolved in a mixture of dry
toluene and CH2Cl2 (1:1, 18 mL). Powdered molecular sieves (4 Å) were added and the mixture was
stirred under argon for 1 h. The flask was wrapped in aluminium foil and cooled to −45°C by means of
a CO2/MeCN bath. AgOTf (1.15 g, 4.48 mmol) dissolved in dry toluene (12 mL) was added during 1 h
under the exclusion of light. After additional stirring for 30 min at −45°C solid Na2S2O3·5 H2O (2 g,
8 mmol) was added at the same temperature. The mixture was stirred for 5 min, whereafter the cooling
bath was removed and toluene (30 mL) and H2O (20 mL) were added. The mixture was stirred for 10
min and then transferred to a separatory funnel via a Celite-packed glass filter funnel. The organic phase
was separated, dried (Na2SO4), filtered, and concentrated. Purification of the residue by silica gel column
chromatography (toluene containing/EtOAc 10→40%) gave 1.595 g (1.85 mmol, 93%) of 14. NMR was
in agreement with published data.15
3.15. 2-(Trimethylsilyl)ethyl 4-O-acetyl-2,6-di-O-benzoyl-β-D-galactopyranoside 15
2-(Trimethylsilyl)ethyl β-D-galactopyranoside16 (1.07 g, 3.82 mmol) was dissolved in acetone (10
mL). The pH was adjusted to 1 by means of the addition of p-toluenesulfonic acid. After stirring for 2 h
the solution was neutralised by pyridine. The mixture was concentrated and co-evaporated once from dry
pyridine. The residue was then dissolved in pyridine (4 mL) and benzoyl chloride (2.0 mL, 17.2 mmol)
was added. The solution was immediately cooled in a water bath and CH2Cl2 (3 mL) was added. Stirring
for another 45 min followed by dilution (toluene), washing (twice with H2O), filtration through a glass
filter funnel containing MgSO4 and concentration gave a crude residue, which was purified on a silica gel
column (toluene/EtOAc 0→10%) to give, in the order of elution, the tetrabenzoyl derivative, followed by
the benzoylated 3,4-isopropylidene isomer [1.45 g, 2.74 mmol, 72%; 13C NMR (CDCl3): δ −1.6 (MeSi),
17.8 (CH2Si), 26.3, 27.6 [(Me)2C], 63.7, 67.0, 70.9, 73.6, 73.7, 77.3 (C-2–6, OCH2CH2Si), 99.9 (C-

490
C. Bernlind et al. / Tetrahedron: Asymmetry 11 (2000) 481–492
1), 110.8 [(Me)2C], 128.2–133.6 (aromatic C), 165.3, 166.3 (PhCO)], and lastly the 4,6-isopropylidene
derivative. A solution of the 3,4-O-isopropylidene derivative (890 mg, 1.68 mmol) in HOAc (80% aq., 10
mL) was stirred for 40 min at 90°C, whereafter the solution was cooled and concentrated. Co-evaporation
from toluene gave crude crystals of 2-(trimethylsilyl)ethyl 2,6-di-O-benzoyl-β-D-galactopyranoside,
which were re-crystallised from diethyl ether–light petroleum (40–65°C). Yield 783 mg (1.60 mmol,
95%). To a solution of this derivative (2.00 g, 4.09 mmol) in dry MeCN (14 mL) was added trimethyl
orthoacetate (1.13 mL) and then p-toluenesulfonic acid until acidic reaction (pH 1). The solution was
stirred for 30 min and then concentrated. The residue was co-concentrated once from toluene, dried
on a vacuum pump, and dissolved in dry MeCN (14 mL). 500 µL of trifluoroacetic acid (90% aq.)
was added and the solution was stirred for 30 min. Neutralisation (1.3 mL of pyridine) followed by
concentration yielded a crude residue which was dissolved in toluene, washed once with water, dried
(Na2SO4), filtered, concentrated, and finally purified on a silica gel column (toluene:EtOAc 4:1) to give
15 (1.72 g, 3.25 mmol, 79%). [α]D −24 (c 1.0, CHCl3); 13C NMR (CDCl3): δ −1.6 (CH3Si), 17.9
(CH2Si), 20.8 (CH3CO), 62.2, 67.5, 69.9, 71.0, 71.6, 73.5 (C-2–6, CH2CH2Si), 100.5 (C-1), 128.3–133.3
(aromatic C), 166.0, 166.8 (PhCO), 171.0 (CH3CO).
3.16. 2-(Trimethylsilyl)ethyl (2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-(2-phthalimido-3,6-
di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-4-O-acetyl-2,6-di-O-benzoyl-β-D-galactopyranoside
16
A solution of 14 (1.59 g, 1.84 mmol) and 15 (1.07 g, 2.02 mmol) in dry CH2Cl2 (10 mL) and Et2O (13
mL) was stirred with powdered molecular sieves under argon for 30 min. The mixture was then cooled
(0°C) and NIS (502 mg, 2.23 mmol) and TfOH (25 µL, 0.28 mmol) were added, and the reddish brown
mixture was stirred at 0°C for 20 min and then filtered through Celite. The solids were washed with
additional CH2Cl2 and the combined organic phases were washed with Na2S2O3 (aq., satd). Drying
(Na2SO4), filtration, concentration and gradient silica gel column chromatography (toluene/EtOAc
10→40%) gave 16 (1.92 g, 1.44 mmol, 70%). [α]D +32 (c 1.0, CHCl3); 13C NMR (CDCl3): δ −1.7
(CH3Si), 17.7 (CH2Si), 20.5, 20.6, 20.7, 20.8 (CH3CO), 55.5, 60.7, 62.9, 66.9, 67.3, 67.7, 69.5, 70.5,
70.97, 71.05, 71.2, 71.4, 73.5, 74.2, 74.9, 76.2, 77.6 (C-2–6, C-20–60, C-200–600, PhCH2O, CH2CH2Si),
99.0 (JC,H 169 Hz), 100.3 (JC,H 163 Hz), 100.7 (JC,H 159 Hz) (C-1–100), 122.9–138.4 (aromatic C),
164.4, 166.1 (PhCO), 169.1, 170.0, 170.1, 170.3, 170.4 (CH3CO). HRMS: calcd for C69H77NO24SiNa:
1354.4503. Found: 1354.4521.
3.17. Ethyl (2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-(2-acetamido-3,6-di-O-benzyl-
2-deoxy-β-D-glucopyranosyl)-(1→3)-2,4,6-tri-O-acetyl-1-thio-β-D-galactopyranoside 19
Compound 16 (1.55 g, 1.16 mmol) was dissolved in dry MeOH. The pH was adjusted to 11 by
the addition of a methanolic 1 M NaOMe solution. After stirring for 2 h when TLC (CHCl3:MeOH
5:1) showed one major product, the mixture was neutralised by adding Dowex H+ ion exchange resin,
then filtrated and concentrated to give a residue, which was dissolved in EtOH:1,4-dioxane (1:1, 40
mL). Hydrazine monohydrate (4 mL) was added and the solution was stirred at reflux temperature
for 3 h until TLC (CHCl3:MeOH 5:1, ninhydrin evolution) indicated a free amine. The solution
was cooled, carefully concentrated, and co-evaporated twice from EtOH, once from toluene:EtOH
1:1, and finally once from pyridine. The residue was dissolved in pyridine:Ac2O (1:1, 40 mL) at
0°C. Complete acetylation was eventually effected after addition of an unexpectedly large amount of
4-dimethylaminopyridine (approximately 2 g). After stirring for 30 min the solution was concentrated,

C. Bernlind et al. / Tetrahedron: Asymmetry 11 (2000) 481–492
491
redissolved in toluene (100 mL), washed with H2O, dried (Na2SO4), filtered, and concentrated.
Purification by silica gel column chromatography (toluene:EtOAc 1:1) gave 2-(trimethylsilyl)ethyl
(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-
glucopyranosyl)-(1→3)-2,4,6-tri-O-acetyl-β-D-galactopyranoside (17, 1.05 g, 0.937 mmol, 81%); 13C
NMR (CDCl3): δ −1.4 (CH3Si), 17.9 (CH2Si), 20.6, 20.8, 21.1 (CH3CO), 23.4 (CH3CON), 57.2,
60.8, 62.4, 66.9, 67.3, 68.1, 69.5, 70.6, 70.8, 70.9, 71.3, 73.5, 74.3, 74.6, 76.6, 77.0 (C-2–6, C-20–60,
C-200–600, PhCH2O, CH2CH2Si), 99.6, 100.0, 100.7 (C-1–100), 123.2–138.7 (aromatic C), 169.3,
169.7, 170.0, 170.1, 170.2, 170.5, 170.6 (CH3CO). Compound 17 (403 mg, 360 µmol) was dissolved
in dry toluene (4 mL). Ac2O (0.4 mmol) and BF3–Et2O (36 µL, 0.29 mmol) were added at room
temperature, and the solution was heated to 40°C. After 1 h more BF3–Et2O (36 µL, 0.29 mmol) was
added. The heating bath was removed, and the solution was stirred at rt for an additional 2 h, then
diluted (CH2Cl2), washed with NaHCO3 (aq., satd), dried (Na2SO4), filtered and concentrated in vacuo.
The residue was purified by gradient silica gel column chromatography (toluene/EtOAc 33→100%) to
yield (2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-
D-glucopyranosyl)-(1→3)-1,2,4,6-tetra-O-acetyl-β-D-galactopyranose (18, 159 mg, 150 µmol, 42%);
13C NMR (CDCl3): δ 20.6, 20.8 (CH3CO), 23.3 (CH3CON), 56.7, 60.8, 62.1, 66.9, 68.1, 69.1, 69.4,
69.7, 70.6, 70.8, 72.4, 73.5, 74.2, 74.7, 76.1, 76.3, 76.9 (C-2–6, C-20–60, C-200–600, PhCH2O), 92.2 (JC,H
161 Hz), 99.7 (JC,H 169 Hz), 100.0 (JC,H 163 Hz) (C-1–100), 127.6–138.6 (aromatic C), 169.1, 169.3,
169.5, 169.9, 170.0, 170.1, 170.2, 170.4 (CH3CO). A solution of 18 (159 mg, 150 µmol) in dry CH2Cl2
(3 mL) was stirred with powdered molecular sieves for 30 min. The mixture was cooled (−10°C) and
EtSH (30 µL), followed by BF3–Et2O (50 µL), were added. After 30 min stirring, more EtSH (40 µL)
and BF3–Et2O (50 µL) were added and stirring was continued for another 1.5 h (temp. +10°C). Then the
mixture was filtered through Celite, the filtrate diluted with CH2Cl2, washed (NaHCO3, aq., satd), dried
(Na2SO4), concentrated and purified by silica gel column chromatography (toluene/EtOAc 10→75%) to
yield 19 (116 mg, 109 µmol, 73%); [α]D +8 (c 1.0, CHCl3); 13C NMR (CDCl3): δ 14.8 (CH3CH2S),
20.5, 20.6, 20.9 (CH3CO), 23.3, 24.0 (CH3CH2S, CH3CON), 56.9, 60.6, 62.4, 66.7, 68.0, 68.9, 69.3,
69.5, 70.5, 70.7, 73.3, 74.1, 74.6, 75.1, 76.4, 76.7 (C-2–6, C-20–60, C-200–600, PhCH2O), 83.8 (JC,H 154
Hz), 99.5 (JC,H 167 Hz), 99.9 (JC,H 163 Hz) (C-1–100), 127.4–138.6 (aromatic C), 169.2, 169.7, 169.8,
170.0, 170.3 (CH3CO). HRMS: calcd for C50H66NO22S: 1064.3797. Found: 1064.3822.
3.18. 2-(4-Trifluoroacetamidophenyl)ethyl (2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-
(2-acetamido-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-(2,4,6-tri-O-acetyl-β-D-galacto-
pyranosyl)-(1→4)-(6,7-di-O-benzyl-2,3-O-isopropylidene-D-glycero-α-D-manno-heptopyranosyl)-
(1→6)-(2,3-di-O-benzoyl-4-O-benzyl-β-D-glucopyranosyl)-(1→4)-6,7-di-O-benzyl-2,3-O-isopropyl-
idene-L-glycero-α-D-manno-heptopyranoside 21
Compounds 13 (77 mg, 51 µmol) and 19 (85 mg, 80 µmol) were co-evaporated and dried from dry
toluene and then dissolved in freshly distilled CH2Cl2 (4 mL) under argon. Powdered molecular sieves (4
Å) were added and the mixture was stirred at rt for 1 h. After cooling (−13°C) the mixture, NIS (24 mg,
0.11 mmol) and TfOH (2 µL, 23 µmol) were added. Stirring was continued for 20 min at −10°C and then
at rt for additional 20 min. The reaction mixture was then filtered through Celite down into a separatory
funnel containing Na2S2O3 (10% aq.) and the solids were washed with additional CH2Cl2. The organic
phase was separated, dried (Na2SO4), filtered and concentrated. Purification of the residue by silica gel
chromatography (toluene/EtOAc 10→50%) gave 29 mg (19 µmol, 38%) of unreacted 13 followed by
58 mg (23 µmol, 45%) of target hexasaccharide 21 (72% based on consumed aglycon); [α]D +29 (c
1.0, CHCl3); 13C NMR (CDCl3): δ 20.6, 20.8, 20.9 (CH3CO), 23.4 (CH3CON), 26.3, 26.6, 27.9, 28.2

492
C. Bernlind et al. / Tetrahedron: Asymmetry 11 (2000) 481–492
(Me2C), 35.1 (OCH2CH2Ar), 57.2, 60.8, 62.1, 63.9, 66.9, 67.3, 67.8, 68.2, 68.4, 69.5, 69.6, 69.9, 70.5,
70.6, 70.9, 71.5, 72.5, 72.7, 72.9, 73.1, 73.3, 73.5, 74.3, 74.4, 74.7, 74.9, 75.1, 76.8, 78.3, 78.8 (C-2–7,
C-20–60, C-200–700, C-2000–6000, C-20000–60000, C-200000–600000, PhCH2O, ArCH2CH2O), 96.7, 97.5, 99.7,
100.0, 100.7, 100.9 (C-1–100000), 109.0 ((Me)2C), 121.0–138.7 (aromatic C), 165.6, 165.8 (PhCO), 169.3,
169.9, 170.0, 170.18, 170.23, 170.5 (CH3CO).
3.19. 2-(4-Trifluoroacetamidophenyl)ethyl (2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-(2-di-
acetylamino-3,6-di-O-benzyl-2-deoxy-β-D-glucopyranosyl)-(1→3)-(2,4,6-tri-O-acetyl-β-D-galacto-
pyranosyl)-(1→4)-(6,7-di-O-benzyl-2,3-O-isopropylidene-D-glycero-α-D-manno-heptopyranosyl)-
(1→6)-(2,3-di-O-benzoyl-4-O-benzyl-β-D-glucopyranosyl)-(1→4)-6,7-di-O-benzyl-2,3-O-isopropyl-
idene-L-glycero-α-D-manno-heptopyranoside 22
Ethyl
(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-(1→4)-(2-diacetylamino-3,6-di-O-benzyl-2-
deoxy-β-D-glucopyranosyl)-(1→3)-2,4,6-tri-O-acetyl-1-thio-β-D-galactopyranoside (20, 32 mg, 28.9
µmol) and 13 (30 mg, 19.8 µmol) were dissolved in 4 mL of dry CH2Cl2 under argon, and stirred with
powdered molecular sieves (4 Å) at rt for 1 h. The mixture was then cooled to 0°C and NIS (10 mg,
44 µmol) and TfOH (1.0 µL, 11 µmol) were added consecutively. Stirring of the increasingly violet
solution was continued at 0°C for 30 min and at rt for 10 min, whereafter the mixture was filtered
through Celite, washed (Na2S2O3, 10% aq.), dried (Na2SO4), filtered and concentrated. The residue was
purified by silica gel chromatography (toluene/EtOAc 10→50%) to give 22 (38 mg, 15 µmol, 75%).
HRMS: calcd for C135H151N2O44F3: 2560.9592. Found: 2560.9768.
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