A new strategy in oligosaccharide synthesis using lipophilic protecting groups: synthesis of a tetracosasaccharide

Article abstract of DOI:10.1016/S0957-4166(99)00553-4

The use of lipophilic, acyl-type protecting groups in the synthesis of higher-membered oligosaccharides is described by the example of oligosaccharides corresponding to the O-specific polysaccharide (O-SP) of Shigella dysenteriae type 1. Thus, O-stearoyla

Full text of DOI:10.1016/S0957-4166(99)00553-4

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 11 (2000) 151–172
A new strategy in oligosaccharide synthesis using lipophilic
protecting groups: synthesis of a tetracosasaccharide
Vince Pozsgay ∗
National Institute of Child Health and Human Development, National Institutes of Health, 6 Center Dr., MSC 2720, Bethesda,
MD 20892-2720, USA
Received 1 November 1999; accepted 1 December 1999
Abstract
The use of lipophilic, acyl-type protecting groups in the synthesis of higher-membered oligosaccharides
is described by the example of oligosaccharides corresponding to the O-specific polysaccharide (O-SP) of
Shigella dysenteriae type 1. Thus, O-stearoylated and O-lauroylated L-rhamnose and D-galactose precursors,
respectively, were synthesized and were combined together with a 2-azido-2-deoxy-D-glucopyranosyl donor to
form a fully protected lipidated repeating unit of the O-SP. This module was condensed with another tetrasaccharide
containing conventional blocking groups. The resulting lipidated octasaccharide was isolated in a pure form
by adsorption to a reverse phase adsorbent from which it could be selectively desorbed by alcoholic solvents.
Subsequent chain elongation using the conventionally protected tetrasaccharide module as glycosyl donor afforded
oligosaccharides up to and including a tetracosasaccharide. The proposed approach can substantially alleviate the
difficulties associated with the conventional silica gel chromatographic purification of protected oligosaccharide
intermediates and utilizes environmentally friendly solvents that are less expensive than the solvents used for silica
gel chromatography. A new, highly efficient method is also proposed for the synthesis of carbohydrate acetals and
cyclic orthoesters employing scandium trifluoromethanesulfonate as the catalyst. © 2000 Elsevier Science Ltd. All
rights reserved.
1. Introduction
Complex oligosaccharides are essential reagents in glycomedicine, for example, in antibacterial
vaccine research,1–3 in purification of medically important proteins using saccharide-based affinity
materials,4 in mapping the carbohydrate binding specificity of anti-carbohydrate antibodies,5,6 and in
numerous other areas. Advances in oligosaccharide synthesis, including the development of versatile
glycosidation methods and powerful protecting group schemes, have made chemical synthesis of many
highly complex oligosaccharides possible.7 Contrary to this evolution, little progress has occurred in the
∗
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tetasy 3188

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separation and purification phase of the synthetic operations. Practitioners are well aware of the fact that
product isolation requires as much attention in chemical synthesis of oligosaccharides as do protecting
group manipulations and glycosyl-bond formations. Therefore, the possible methods for product isolation
should already be taken into account in the planning phase of the synthetic approaches. In recent years,
explorations of solid-phase techniques for oligosaccharide synthesis have received much attention.8
While this technique has been very successful in the peptide and the oligonucleotide fields, its general
advantage in oligosaccharide synthesis over liquid-phase methods has yet to be demonstrated by way
of direct comparison. Additionally, chemical synthesis of oligosaccharides on solid support has so far
been limited to small- to medium-sized structures.8 As a variation on this theme, the use of soluble
macromolecular carriers that can be precipitated under suitable conditions has also been proposed.9 In
another approach towards efficient product isolation a glycolipid was employed as glycosyl-acceptor
in an enzymatic glycosylation.10 After the glycosylation step, the lipid-containing product could be
extracted selectively on a dimethyloctadecylsilyl-coated silica particle. This technique was adopted for
glycosyltransferase assays using synthetic substrates containing the lipophilic 8-methoxycarbonyloctyl
group as the aglycon.11,12 The hydrophobic 8-p-methoxyphenoxyoctyl aglycon was also exploited for
partial separation of glycosylation mixtures using the C-18 adsorbent technique.13 As an interesting
recent development towards efficient product isolation in oligosaccharide synthesis, Curran proposed the
use of a fluoroalkyl-substituted benzyl protecting group that renders the sector to which it is attached
insoluble in water and common organic solvents, and soluble in a perfluorinated solvent, thus permitting
the isolation of the oligosaccharide product in a three-phase liquid–liquid extraction procedure.14,15
Because of the large number of fluorines in the proposed protecting group, the molecular weight of the
fluorine-tagged intermediates is high, that makes characterization of the fluorous derivatives a challenge
even at the disaccharide level. As a new entry to facilitate product isolation in oligosaccharide synthesis,
I have reported the preparation and use of a lipophilic benzyl-type O-protecting group that allowed the
isolation of a protected disaccharide using a reverse phase adsorbent in a simple adsorption–elution
process without the need of silica gel chromatography.16
In this paper some initial results are reported towards a new strategy to higher-membered oligo-
saccharides that relies on lipophilic, O-acyl protecting groups. The proposed approach combines the
advantages of solution phase glycosylations and the solid–liquid extraction methods and sidesteps many
of the difficulties associated with the exclusive reliance on conventional silica gel chromatography.
As will be demonstrated, purification of the lipid-tagged products is also possible by using silica gel
chromatography, if necessary. The objective of the experiments described herein is to demonstrate the
feasibility of the proposed approach for the synthesis of large oligosaccharides and to evaluate the
optimum number of lipophilic tags that are necessary for efficient product isolation. This new method is
presented by the example of synthesis of oligosaccharides corresponding to the O-specific polysaccharide
of Shigella dysenteriae type 1 that consists of the tetrasaccharide repeating unit 1.
3)-α-L-Rhap-(1→2)-α-D-Galp-(1→3)-α-D-GlcNAcp-(1→2)-α-L-Rhap-(1→
1
2. Results and discussion
A blockwise approach to higher-membered oligosaccharides corresponding to this polysaccharide
which were used as saccharide components of experimental vaccines3 has previously been reported.2,17
In these endeavors, a tetrasaccharide donor/acceptor module (2) that was first attached to a spacer moiety
was assembled. Subsequent, iterative addition of unit 2 to the first module produced the targeted octa-,
dodeca-, and hexadecasaccharides. Because of the identical protecting groups in the starting materials,

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
153
product, and side-products, isolation of the product was difficult at and above the dodecasaccharide level,
necessitating repeated silica gel chromatographic procedures.2 These difficulties prompted a re-design of
the modular approach with the important issue of product isolation in mind. Here it is reported that
tagging the initial module of the oligosaccharide chain with lipophilic protecting groups substantially
alleviates the separation problem through the use of a reverse-phase adsorbent that preferentially adsorbs
the lipid-tagged compounds while having no or only weak adsorption toward the untagged molecules.
First, I describe the synthesis of the key lipid-tagged monosaccharide intermediates followed by their
assembly to provide the lipid-labeled tetrasaccharide unit. Then the utility of this module in the synthesis
of a tetracosasaccharide corresponding to six contiguous repeating units of 1 is shown.
2.1. Synthesis of the lipid-tagged monosaccharides
2.1.1. The rhamnose moiety
Rhamnosyl trichloroacetimidate 9 (Scheme 1) was selected as the key intermediate for the rhamnose
residues featuring a participating benzoyl group at O-2, a selectively removable monochloroacetyl group
at O-3, and the stearoyl lipid label at O-4. This compound was synthesized from the thiorhamnoside 3
that was first converted to the acetal 4.18 In this study, the use of scandium trifluoromethanesulfonate
[Sc(OTf)3] as the catalyst has been investigated and it was found that Sc(OTf)3 is a powerful activator
in the synthesis of carbohydrate acetals and orthoesters (vide infra).19 Thus, treatment of 3 and DMP
in acetone in the presence of less than 0.1% molar equivalents of Sc(OTf)3 afforded 4 in a nearly
quantitative yield. It is noted that conventional approaches often require much larger amounts of the
promoters, e.g. CSA or p-toluenesulfonic acid.20 Treatment of 4 with stearoyl chloride in the presence
of pyridine, followed by acid-catalyzed removal of the isopropylidene group, afforded the diol 5.
Conversion to the benzoylated derivative 6 was achieved in a two-step procedure. First, the diol 5 was
treated with trimethyl orthobenzoate in the presence of Sc(OTf)3 to give a cyclic orthoester. Next, this
intermediate was treated with aqueous acetic acid to afford compound 6 in 84% overall yield. Acylation
with monochloroacetic anhydride (→7, 94%) followed by (CF3CO2)2Hg-assisted hydrolysis21 gave the
hemiacetal 8 in 76% yield. Subsequent reaction of 8 with trichloroacetonitrile in the presence of DBU
afforded the trichloroacetimidate donor 9 that was condensed with 5-(methoxycarbonyl)pentanol22 to
yield the spacer-linked rhamnoside 10 (89%). The HO-3 group in 10 was unmasked by treatment with
thiourea to provide the rhamnose acceptor 11 in 86% yield.
2.1.2. The galactose moiety
The galactosyl donor 14 was prepared (Scheme 2) from the known thiogalactoside23 12 which was
first treated with DMP in the presence of Sc(OTf)3 to afford the mixed isopropylidene acetal20 13 in 86%

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V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
Scheme 1. Reagents and conditions: (a) CH3COCH3, (CH3)2C(OCH3)2, Sc(OTf)3 (cat.), 23°C, 2 h, 96%; (b) 1.2 equiv. of
C17H37COCl, C5H5N, CH2Cl2, 0°C, 15 min; (c) AcOH–H2O, 50°C, 2 h, 79% for two steps; (d) 1.5 equiv. of PhC(OCH3)3,
CH2Cl2, Sc(OTf)3 (cat.), 23°C, 1 h; (e) MeOH–AcOH, 23°C, 8 h, 84% for two steps; (f) 1.3 equiv. of (ClCH2CO)2O,
C5H5N, CH2Cl2, 0°C, 1 h, 94%; (g) 1.6 equiv. of Hg(OCOCF3), CH2Cl2, H2O, 23°C, 76%; (h) 2.9 equiv. of CCl3CN,
1,8-diazabicyclo[5.4.0]undec-7-ene (cat.), CH2Cl2, −10°C, 76%; (i) 1.5 equiv. of 5-(methoxycarbonyl)pentanol, CH2Cl2,
CF3SO3Si(CH3)3 (cat.), 0°C, 89%; (j) 7.5 equiv. of CS(NH2)2, C5H5N, DMF, 23°C, 3 h, 86%
yield. Next, 13 was benzylated with benzyl bromide in the presence of sodium hydride (→14) followed by
removal of the acetal groups in aqueous acetic acid to provide the triol 15 in 68% overall yield. Reaction
of 15 with lauroyl chloride in the presence of pyridine gave the lipid-tagged galactosyl donor 16 as a
crystalline material in 98% yield. It was noted that 16 separated from the reaction mixture and could
be isolated in an analytically pure form by filtration followed by washing with EtOH. Unexpectedly,
attempted synthesis of the corresponding O-stearoylated derivative failed because of solubility problems.
2.2. Assembly of the lipid-tagged tetrasaccharide module
The lipidated tetrasaccharide module 26 was assembled by stepwise condensation of the four mono-
saccharide components. Thus, glycosyl bromide 18 obtained from thioglucoside24 17 by treatment with
bromine was condensed with rhamnosyl acceptor 11 in the presence of silver trifluoromethanesulfonate to
afford the protected disaccharide 19 in 57% yield (Scheme 3). Treatment of this compound with thiourea
afforded the disaccharide acceptor 20 in 85% yield. The galactosyl donor 21 was obtained from the thio-
galactoside 16 by treatment with chlorine (Scheme 4) and was condensed without purification with the
disaccharide 20 in the presence of silver trifluoromethanesulfonate and 2,6-di-tbutyl-4-methylpyridine

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
155
Scheme 2. Reagents and conditions: (a) CH3COCH3, (CH3)2C(OCH3)2, Sc(OTf)3 (cat.), 23°C, 2 h, 86%; (b) approximately 2
equiv. of NaH, 1.2 equiv. of benzyl bromide, DMF, 0°C, 30 min; (c) MeOH–AcOH, 70°C, 24 h, 68% for two steps; (d) 1.3
equiv. of lauroyl chloride, CH2Cl2, C5H5N, 0°C, 3 h, 98%
(DBMP) to give the trisaccharide 22. At this stage, use was made of the lipophilic nature of 22 to
remove impurities from 22 before further transformations. Thus, the crude reaction mixture was applied
to a C-18 column containing dimethyloctadecylsilyl groups on silica particles, made in MeOH. The
column was washed with MeOH that completely removed DBMP and the phenylthio moiety obtained
in the chlorinolysis of 16. Subsequent washing with MeOH–EtOH and EtOH eluted 22 together with
decomposition products from 21. Crude 22 was then subjected to a Staudinger reaction by treatment
with PPh3 followed by hydrolysis to afford the amine 23 in 78% overall yield (from 20). Subsequent
N-acetylation with Ac2O in EtOH followed by hydrogenolytic removal of the benzyl group afforded
the trisaccharide 24 in 93% yield. As the final step in the tetrasaccharide assembly, condensation of
the rhamnosyl trichloroacetimidate 9 with the acceptor 24 (Scheme 5) in the presence of trimethylsilyl
trifluoromethanesulfonate afforded tetrasaccharide 25, which was subjected to treatment by thiourea
to afford the lipidated tetrasaccharide module 26 in 85% overall yield. The assigned interglycosidic
1
stereochemistry for 26 and the intermediates were verified by H and 13C NMR spectroscopic data
described in the Experimental section.
Scheme 3. Reagents and conditions: (a) 4.4 equiv. of Br2, CH2Cl2, 0°C, 10 min, then hex-1-ene (excess); (b) 0.5 equiv. of 11,
2.0 equiv. of 2,6-di-tbutyl-4-methylpyridine, 3 equiv. of CF3SO3Ag, 0°C, 20 min, 57%; (c) 6.5 equiv. of CS(NH2)2, C5H5N,
DMF, 23°C, 8 h, 85%
2.3. Construction of the target oligosaccharides
Having prepared the lipid-tagged tetrasaccharide sector 26, it was possible to examine the hypothesis
that lipid protecting groups may, indeed, facilitate the isolation of protected oligosaccharides without

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V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
Scheme 4. Reagents and conditions: (a) Cl2 (excess), CH2Cl2–CCl4, 0°C, 10 min; (b) 0.3 equiv. of 20, 3 equiv. of
2,6-di-tbutyl-4-methylpyridine, 5 equiv. of CF3SO3Ag, 0°C, 20 min; (c) approximately 10 equiv. of PPh3, CH2Cl2, 23°C, 24 h,
then H2O, 23°C, 24 h, 78%; (d) Ac2O, CH2Cl2, 0°C, 2 h; (e) H2 Pd–C, EtOH–AcOH, 200 psi, 23°C, 24 h, 93% for two steps
Scheme 5. Reagents and conditions: (a) 2.3 equiv. of 9, CH2Cl2, CF3SO3Si(CH3)3 (cat.), 0→23°C, 30 min; (b) approximately
13 equiv. of CS(NH2)2, DMF, 23°C, 8 h, 85% for two steps
the need of silica gel chromatography. As the first step toward higher-membered oligosaccharides, 26
was condensed with the tetrasaccharide donor 2 available from an earlier study2 under promotion by
a catalytic amount of trimethylsilyl trifluoromethanesulfonate (Scheme 6). The product mixture was
applied to a C-18 column made in MeOH. Elution by a MeOH–EtOH gradient up to 40% EtOH
concentration removed all the impurities and side products arising from 2. A 1:1 mixture of MeOH–EtOH
i
eluted unreacted acceptor 26. Further elution with EtOH and PrOH eluted the octasaccharide 27 in a
pure form in 84% yield based on recovered 26. The all-α-glycosidic linkages were verified by the one-
bond heteronuclear coupling constants for all the anomeric proton–carbon pairs that are in the range
of 167–172 Hz.25 Next, 27 was treated with thiourea to afford the acceptor 28 in 97% yield using
i
the C-18 column and EtOH and PrOH for isolation. Two more cycles (Schemes 6 and 7) involving
glycosylation with approximately 4 equivalents of the tetrasaccharide donor 2 under trimethylsilyl
trifluoromethanesulfonate activation and deprotection by thiourea afforded the dodeca- (29 and 30)
and hexadecasaccharides (31 and 32). Crucial for the structural proof of these intermediates were the
NMR and mass spectroscopic data that provided evidence for the proposed structures as described in
the Experimental section. All these intermediates were isolated in pure form by application of the crude
reaction mixtures to a C-18 column followed by elution with MeOH, EtOH, and iPrOH. In one instance
(compound 32) MeCN and benzene were also tested as possible eluants. These had no advantages over
the alcohols used in the other cases. The excellent yields in these reactions combined with the ease of

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
157
purification prompted the exploration of the limits of this new approach. Therefore, donor 2 was reacted
with the hexadecasaccharide 33 in the presence of trimethylsilyl trifluoromethanesulfonate. The resulting
product mixture containing eicosasaccharide 34 could be isolated by using the C-18 technique with
i
MeOH, EtOH, and PrOH as the eluants. However, the purity of the product was only approximately
80% as judged by HPLC, necessitating the use of silica gel chromatography to obtain 33 in pure
form. Thus, it appears that the five lipid protecting groups, including two stearoyl and three lauroyl
groups, can render the hexadecasaccharide 31 sufficiently lipophilic for product isolation by using solely
the C-18 technique, whereas this combination of lipophilic protecting groups is not sufficient for the
purification of higher-membered oligosaccharides. Dechloroacetylation of 33 with thiourea afforded
the eicosasaccharide acceptor 34 in 84% yield after purification through the C-18 column. As the
final glycosylation experiment in this work, alcohol 34 and tetrasaccharide 2 were condensed under
trimethylsilyl trifluoromethanesulfonate activation to afford the tetracosasaccharide 35. Again, much of
the side products could be removed by using the C-18 technique and silica gel chromatography was
used for the final purification. Conventional deprotection of 35 involving NaOMe-assisted methanolysis
(→36) and hydrogenolysis afforded the spacer-linked tetracosasaccharide 37 after purification by Biogel
P-6 chromatography (Fig. 1). The structure of 37 is supported by spectroscopic evidence reported in the
Experimental section.
3. Conclusions
In summary, a new approach has been proposed for chemical synthesis of higher-membered oligo-
saccharides that involves the use of strategically positioned lipid-type protecting groups. It has been
demonstrated that intermediates containing such groups may be isolated and purified by the use of a
commercially available reverse-phase adsorbent that can be re-used many times. It has been shown that
five lipid groups can provide sufficient hydrophobicity to an oligosaccharide up to a hexadecasaccharide
to allow product isolation solely by the C-18 technique. This number may show some variance with
other protecting group combinations. The proposed approach can substantially alleviate the difficulties
associated with the conventional silica gel chromatographic purification of protected oligosaccharide
intermediates and utilizes environmentally friendly solvents that are less expensive than the solvents
conventionally used for silica gel chromatography. The technique preserves the efficiency of the solution-
phase reactions. Importantly, the lipidated intermediates may also be purified by the conventional me-
thods, that may be necessary when anomeric mixtures are present. Additionally, a new, highly efficient
method has been proposed for the synthesis of carbohydrate acetals and cyclic orthoesters employing
scandium trifluoromethanesulfonate as the catalyst.
4. Experimental
4.1. General methods
All chemicals were commercial grade and used without purification. Solvents for chromatography
were distilled prior to use. Anhydrous solvents were obtained from Aldrich. Column chromatography
was performed on either dimethyloctadecylsilyl-bonded amorphous silica (C-18 adsorbent, 125 Å)
obtained from Waters Corp., Milford, MA, or on silica gel 60 (0.040–0.063 mm). HPTLC plates were
obtained from Merck. Melting points were taken on a Meltemp capillary melting point apparatus and

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V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
Scheme 6. Reagents and conditions: (a) approximately 3.6 equiv. of 2, CF3SO3Si(CH3)3 (cat.), 0°C, 4 h, 84%; (b) 5 equiv.
of CS(NH2)2, C5H5N, DMF, 23°C, 24 h, 97%; (c) 4.5 equiv. of 2, CF3SO3Si(CH3)3 (cat.), 0°C, 3 h, 89%; (d) 12 equiv. of
CS(NH2)2, 2,6-di-tbutyl-4-methylpyridine, DMF, 23°C, 24 h, 97%

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
159
Scheme 7. Reagents and conditions: (a) 4 equiv. of 2, CF3SO3Si(CH3)3 (cat.), 0°C, 3 h, 77%; (b) 6.5 equiv. of CS(NH2)2,
2,6-di-tbutyl-4-methylpyridine, DMF, 23°C, 24 h, 92%; (c) 4 equiv. of 2, CF3SO3Si(CH3)3 (cat.), 0°C, 2 h, 53%; (d) 10 equiv.
of CS(NH2)2, 2,6-di-tbutyl-4-methylpyridine, DMF, 23°C, 24 h, 84%

160
V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
Fig. 1.

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
161
are uncorrected. Optical rotations were measured at 23°C with a Perkin–Elmer Type 341 polarimeter.
The 1H and 13C NMR spectra were recorded at 300 and 75.5 MHz, respectively, in CDCl3, unless stated
otherwise. Internal references: TMS (0.000 ppm for 1H for solutions in CDCl3), acetone (2.225 ppm for
1
1H and 31.00 ppm for 13C for solutions in D2O), methanol (3.358 ppm for H and 49.68 ppm for 13C
for solutions in D2O), and CDCl3 (77.00 ppm for 13C for solutions in CDCl3). Coupling constants are
given in hertz. The mass spectra were recorded at the Laboratory of Analytical Chemistry, NIDDK, NIH,
Bethesda, MD. Ammonia was used as the ionizing gas for the chemical ionization (CI) mass spectra. The
fast atom bombardment (FAB) mass spectra were obtained using 6 keV Xe atoms to ionize samples from
dithiothreitol/dithioerythritol, 3-nitrobenzyl alcohol or glycerol as the matrix. Elemental analyses were
performed by Atlantic Microlab, Inc., Norcross, GA.
Abbreviations:
Ac=acetyl,
AgOTf=silver
trifluoromethanesulfonate,
Bz=benzoyl,
Bn=benzyl, CA=chloroacetyl, CI=chemical ionization, DBMP=2,6-di-tbutyl-4-methylpyridine,
DBU=diazabicyclo[5.4.0]undec-7-ene, DMF=N,N-dimethylformamide, FAB=fast atom bombardment,
Galp=galactopyranosyl, Glcp=glucopyranosyl, GlcpNAc=2-acetamido-2-deoxy-D-glucopyranosyl,
HPTLC=high performance thin layer chromatography, Ph=phenyl, Rhap=rhramnopyranosyl,
TMSOTf=trimethylsilyl trifluoromethanesulfonate.
4.2. Phenyl 2,3-O-isopropylidene-1-thio-α-L-rhamnopyranoside 4
Scandium trifluoromethanesulfonate (50 mg, 0.1 mmol) was added to a solution of 318 (45 g, 330
mmol) in a 1:1 mixture of acetone and 2,2-dimethoxypropane (200 mL) at room temperature. After
2 h, the solution was treated with Et3N (2 mL) and was concentrated. Trituration of the residue in
hexane afforded 4 (50.0 g, 96%) whose physical and spectral properties matched those of the authentic
preparation.18
4.3. Phenyl 4-O-stearoyl-1-thio-α-L-rhamnopyranoside 5
To a stirred solution of 4 (10.0 g, 33.8 mmol) in CH2Cl2 (40 mL) and C5H5N (10 mL) was added
stearoyl chloride (13.7 mL, 40.6 mmol) at 0°C. After 15 min, the reaction mixture was treated with
MeOH (excess). The volatiles were removed by distillation to afford a solid {[α]D −110 (c 0.7, CHCl3);
1H NMR: δ 7.25–7.50 (m, 5H), 5.77 (br s, 1H), 4.95 (dd, 1H, J=7.9, J=9.8), 4.36 (dd, 1H, J=1.0, J=5.3),
4.24 (dd, 1H, J=5.3, J=7.7), 4.21 (dq, 1H), 2.28–2.44 (m, 2H), 1.60–1.70 (m, 2H), 1.57 (s, 3H), 1.36 (s,
3H), 1.19–1.33 (m), 1.12 (d, 1H, J=6.3), 0.88 (m, 3H); 13C NMR: δ 172.9, 131.8, 129.1, 127.7, 110.0,
83.7, 76.5, 75.6, 74.3, 65.7, 34.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.2, 29.1, 27.7, 26.6, 24.9, 22.7, 16.9, 14.1.
CI-MS: m/z 580 (C33H54O5S+NH4). Anal. calcd for C33H54O5S: C, 70.42; H, 9.67. Found: C, 70.59; H,
9.80.} Toluene was added to and removed from the residue several times. A solution of the residue in
AcOH (100 mL) and H2O (20 mL) was stirred at 50°C for 2 h. Cooling to 0°C afforded a precipitate
which was isolated by filtration followed by washing with H2O to afford 5 (14.2 g, 79%): mp 79–81°C;
[α]D –160 (c 0.6, CHCl3); 1H NMR: δ 7.22–7.49 (m, 5H), 5.54 (d, 1H, J=1.6), 4.86 (t, 1H, J=9.5), 4.30
(dq, 1H), 4.21 (dd, 1H, J=1.6, J=3.5), 3.90 (dd, 1H, J=3.5, J=9.5), 2.40 (dd, 1H, J=6.9, J=8.0), 1.60–1.70
(m, 1H), 1.25–1.35 (m), 1.23 (d, 1H, J=6.3), 0.88 (m, 3H); 13C NMR: δ 175.0, 131.3, 129.1, 127.5, 87.2,
75.6, 72.3, 70.9, 66.9, 34.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.2, 29.1, 24.7, 22.7, 17.4, 14.1). CI-MS: m/z
540 (C30H50O5S+NH4). Anal. calcd for C30H50O5S: C, 68.93; H, 9.64. Found: C, 69.07; H, 9.70.

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4.4. Phenyl 2-O-benzoyl-4-O-stearoyl-1-thio-α-L-rhamnopyranoside 6
A stirred mixture of 5 (21.0 g, 40.2 mmol), trimethyl orthobenzoate (10.3 mL, 60.3 mmol), and CH2Cl2
(100 mL) was treated at room temperature with scandium trifluoromethanesulfonate (50 mg). After 1 h,
to the solution was added Et3N (1 mL) followed by removal of the volatiles by distillation. To a solution
of the residue in MeOH (80 mL) was added 90% acetic acid (150 mL). After 8 h, the solution was
concentrated to afford a residue that was purified by column chromatography (10:1 hexane:EtOAc) to
1
give 6 as a syrup (21.1g, 84%): [α]D −61 (c 0.7, CHCl3); H NMR: δ 7.05–7.87 (m, 5H), 5.41 (d,
1H, J=1.5), 5.39 (dd, 1H, J=1.5, J=3.3), 4.88 (t, 1H, J=9.5), 4.19 (dq, 1H), 3.92 (ddd, 1H), 2.21 (t,
2H, J=7.9), 1.46 (m, 2H), 0.97–1.15 (m), 0.67 (m, 3H); 13C NMR: δ 174.5, 165.7, 122.7–133.4, 85.8,
74.8, 69.6, 67.4, 34.4, 31.9, 29.7, 29.6, 29.4, 29.3, 29.2, 29.1, 24.9, 22.7, 17.4, 14.1. CI-MS: m/z 644
(C37H54O6S+NH4). Anal. calcd for C37H54O6S: C, 70.89; H, 8.68. Found: C, 70.71; H, 8.52.
4.5. Phenyl 2-O-benzoyl-3-O-chloroacetyl-4-O-stearoyl-1-thio-α-L-rhamnopyranoside 7
To a solution of 6 (8.5 g, 13.6 mmol) in CH2Cl2 (50 mL) were added at 0°C C5H5N (10 mL) and
chloroacetic anhydride (3.0 g, 17.6 mmol). After 1 h, the solution was treated with MeOH (excess) and
was concentrated. Column chromatographic purification of the residue (10:1 hexane:EtOAc) gave 7 as a
syrup (8.9 g, 94%): [α]D −33 (c 2.5, CHCl3); 1H NMR: δ 728–8.08 (m, 10H), 5.76 (dd, 1H), 5.57 (d,
1H), 5.47 (dd, 1H, J=3.1, J=9.9), 5.30 (t, 1H, J=3.9, J=9.9), 4.45 (dq, 1H), 3.98 (d, 1H, J=∼15), 3.92
(d, 1H, J=∼15), 2.33 (br t, 2H, J=7.4), 1.54–1.66 (m, 2H), 1.29 (d, 1H, J=6.3), 1.23–1.27 (m), 0.88 (m,
3H); 13C NMR: δ 174.2, 166.1, 165.7, 121.9–133.0, 85.7, 71.6, 71.5, 70.7, 67.9, 40.5, 34.2, 29.7, 29.4,
29.1, 24.9, 17.5. CI-MS: m/z 720 (C39H55ClO7S+NH4). Anal. calcd for C39H55ClO7S: C, 66.60; H, 7.88.
Found: C, 66.92; H, 8.01.
4.6. 2-O-Benzoyl-3-O-chloroacetyl-4-O-stearoyl-L-rhamnopyranose 8
To a stirred mixture of 7 (10.0 g, 14.2 mmol), CH2Cl2 (90 mL), and H2O (8.7 mL) was added
Hg(OCOCF3)2 (9.1 g, 21.3 mmol) at 0°C. After 3 h, the mixture was treated with an aqueous solution
of KI. The solids so obtained were removed by filtration through a layer of Celite. The organic layer
was concentrated and the residue was treated with isopropyl ether. Removal of the solids followed
by concentration of the solution afforded a residue that was purified by column chromatography (6:1
hexane:EtOAc) to give crystalline 8 (6.6 g, 76%): [α]D +53 (c 0.5, CHCl3); 1H NMR: δ 7.46–8.09 (m,
5H), 5.58–5.53 (m, 2H), 5.35 (dd, 1H), 5.25 (t, 1H, J=9.8 Hz), 4.20 (dq, 1H, J=6.3), 3.97 and 3.91 (1 d,
2H, J=∼15), 2.83 (d, 1H, J=3.9), 2.31 (t, 2H, J=7.4), 1.52–1.64 (m, 2H), 1.36–1.62 (m), 0.88 (m, 3H);
13C NMR: δ 172.9, 166.6, 165.7, 133.6, 130.0, 128.7, 128.6, 92.2, 70.9, 70.6, 70.4, 66.5, 40.5, 34.2,
31.9, 29.7, 29.6, 29.4, 29.3, 29.2, 29.1, 24.9, 22.7, 17.6, 14.1. Anal. calcd for C31H51ClO8: C, 63.41; H,
8.75. Found: C, 65.05; H, 8.45.
4.7. 2-O-Benzoyl-3-O-chloroacetyl-4-O-stearoyl-L-rhamnopyranosyl trichloroacetimidate 9
To a stirred solution of 8 (8.15 g, 13.3 mmol) in CH2Cl2 (50 mL) were added at −10°C CCl3CN (3.1
mL, 38.8 mmol) and DBU (0.2 mL). The reaction mixture was allowed to reach room temperature then
was concentrated. Filtration through a column of silica gel (10:1 hexane:EtOAc) afforded 9 (7.7 g, 76%)
as a syrup: (major isomer) 1H NMR: δ 7.40–8.77 (m, 5H), 6.36 (d, 1H, J=1.5), 5.71 (dd, 1H), 5.53 (dd,

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
163
1H, J=3.4, J=10.0), 5.33 (t, 1H, J=10.0), 2.32 (t, 2H, J=7.6), 1.53–1.65 (m, 2H), 1.33 (d, 3H, J=6.3),
1.2–1.3 (m), 0.88 (m, 3H).
4.8. 5-(Methoxycarbonyl)pentyl 2-O-benzoyl-3-O-chloroacetyl-4-O-stearoyl-α-L-rhamnopyranoside 10
To a solution of 9 (1.5 g, 1.98 mmol) and 5-(methoxycarbonyl)pentanol (430 µL, 3 mmol) in CH2Cl2
(10 mL) was added TMSOTf (5 µL) at 0°C. After 10 min, the solution was treated with Et3N (excess) and
was concentrated. Column chromatographic purification of the residue (10:1 hexane:EtOAc) afforded 10
(1.3 g, 89%) as a syrup: [α]D +20 (c 0.5, CHCl3); 1H NMR: δ 7.45–8.09 (m, 5H), 5.43–5.49 (m, 2H),
5.22 (t, 1H, J=9.6), 4.87 (br s, 1H), 3.96 (dq, 1H), 3.89 and 3.96 (2 d, 2H, J=∼15), 3.72 (m, 1H), 3.68
(s, 3H), 3.46 (m, 1H), 2.35 and 2.30 (2 t, 4H), 1.60–1.73 (m, 4H), 1.47–1.38 (m, 2H), 1.22–1.33 (m),
0.87 (m, 3H); 13C NMR: δ 173.0, 166.8, 165.7, 139.9, 133.5, 128.6, 97.4, 71.3, 70.7, 70.3, 68.0, 66.4,
51.5, 40.6, 34.2, 33.9, 31.9, 29.7, 29.5, 29.4, 29.3, 29.2, 29.1, 29.0, 25.6, 24.9, 24.7, 22.7, 17.5, 14.1.
CI-MS: m/z 756 (C40H63ClO10+NH4). Anal. calcd for C40H63ClO10: C, 64.98; H, 8.59. Found: C, 64.84;
H, 8.44.
4.9. 5-(Methoxycarbonyl)pentyl 2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 11
A solution of 10 (3.9 g, 5.27 mmol), thiourea (3 g, 39.5 mmol), C5H5N (2 mL), and DMF (20 mL) was
kept at 23°C for 3 h followed by removal of the volatiles under vacuum. The residue was treated with
CHCl3 and the solids so obtained were removed by filtration. Extractive work-up (CHCl3/H2O) followed
by column chromatographic purification of the residue (10:1 hexane:EtOAc) afforded 11 (3.0 g, 86%)
as a syrup: [α]D +14 (c 0.7, CHCl3); 1H NMR: δ 7.45–8.09 (m, 5H), 5.30 (dd, 1H, J=1.4, J=3.4), 5.00
(t, 1H, J=10.0), 4.90 (d, 1H), 4.14 (ddd, 1H, J=3.4, J=8.3, J=10.0), 3.87 (dq, 1H), 3.70 (m, 1H), 3.68 (s,
3H), 3.45 (m, 1H), 2.40 (br t, 1H), 2.33 (br t, 1H), 2.20 (d, 1H, J=8.2), 1.59–1.73 (m, 6H), 1.35–1.46 (m,
2H), 1.18–1.33 (m), 0.88 (m, 3H); 13C NMR: δ 174.6, 165.9, 133.5, 129.9, 128.5, 97.2, 74.7, 73.4, 69.0,
67.9, 66.0, 51.5, 34.4, 33.9, 31.9, 29.7, 29.6, 29.5, 29.4, 29.3, 29.1, 25.7, 25.0, 24.7, 22.7, 17.6, 14.1.
CI-MS: m/z 680 (C38H62O9+NH4). Anal. calcd for C38H62O9: C, 68.85; H, 9.43. Found: C, 68.70; H,
9.39.
4.10. Phenyl 3,4-O-isopropylidene-6-O-(2-methoxy-2-methyl-ethyl)-1-thio-β-D-galactopyranoside 13
To a solution of phenyl 1-thio-β-D-galactopyranoside23 (12, 15.0 g, 55.4 mmol) in acetone (200 mL)
were added 2,2-dimethoxypropane (100 mL) and scandium trifluoromethanesulfonate (50 mg) at 23°C.
After 30 min, the solution was treated with Et3N (1 mL) and was concentrated. Column chromatographic
purification of the residue (3:1 hexane:EtOAc containing 0.01% of Et3N) afforded 13 (18.2 g, 86%) as
1
a syrup: [α]D –11 (c 0.7, CHCl3); H NMR: δ 4.48 (d, 1H, J=10.1), 4.20 (dd, 1H, J=2.0, J=5.4), 4.04
(br t, 1H), 3.90 (ddd, 1H), 3.76 (dd, 1H, J=6.9, J=9.9), 3.67 (dd, 1H, J=5.2, J=9.9), 3.58 (dd, 1H, J=6.9,
J=10.1), 3.23 (s, 3H), 1.42 (s, 3H), 1.38 (s, 3H), 1.37 (s, 3H), 1.33 (s, 3H); 13C NMR: δ 132.3, 128.9,
127.8, 110.2, 100.1, 87.8, 79.1, 76.0, 73.8, 71.5, 60.5, 48.6, 28.1, 26.3, 24.4. Anal. calcd for C19H28O6S:
C, 59.35; H, 8.34. Found: C, 59.47; H, 7.50.
4.11. Phenyl 2-O-benzyl-1-thio-β-D-galactopyranoside 15
To a stirred solution of 13 (21.3 g, 55.4 mmol) in DMF (100 mL) was added at 0°C NaH (4.0 g of
a 60% suspension in mineral oil, approximately 100 mmol) in small portions over 15 min. The mixture

164
V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
was stirred for another 20 min, then was treated with benzyl bromide (7.9 mL, 66.4 mmol). After 30 min,
the mixture was treated with MeOH (excess). Extractive work-up (CHCl3/H2O) followed by column
chromatographic purification of the residue (4:1 hexane:EtOAc) afforded phenyl 2-O-benzyl-3,4-O-
isopropylidene-6-O-(2-methoxy-2-methyl-ethyl)-1-thio-β-D-galactopyranoside 14 as a syrup {[α]D –17
(c 0.7, CHCl3); 1H NMR: δ 7.20–7.58 (m, 5H), 4.82 (d, 1H, J=12.2), 4.68 (d, 1H, J=12.2), 4.66 (d, 1H,
J=9.6), 4.26 (dd, 1H), 4.21 (dd, 1H, J=1.7, J=5.7), 3.85 (ddd, 1H), 3.74 (dd, 1H, J=7.1, J=9.9), 3.64 (dd,
1H, J=5.0, J=9.9), 3.53 (dd, 1H, J=6.2, J=9.6), 3.13 (s, 3H), 1.41 (s, 3H), 1.35 (s, 6H), 1.34 (s, 3H); 13
C
NMR: δ 137.8, 137.1, 131.5, 128.7, 128.3, 128.2, 128.1, 127.7, 127.1, 110.0, 100.0, 86.1, 79.8, 78.2,
75.8, 73.9, 73.4, 60.5, 48.6, 27.8, 26.3, 24.4. Anal. calcd for C26H34O6S: C, 65.80; H, 7.22. Found: C,
65.55; H, 7.14.} To a solution of 14 in MeOH (100 mL) was added 80% aqueous acetic acid (200 mL).
After 24 h at 70°C the volatiles were removed by distillation under vacuum. Trituration of the residue
1
with ether afforded crystalline 15 (13.5 g, 68%): mp 125–126°C; [α]D –18 (c 0.5, DMF); H NMR
(CD3OD): δ 7.17–7.56 (m, 5H), 4.82 (d, 1H, J=10.9), 4.77 (d, 1H, J=10.9), 4.66 (d, 1H, J=8.8), 3.90
(br d, 1H, J=2.7), 3.78 (dd, 1H, J=6.7, J=11.4), 3.71 (dd, 1H, J=5.5, J=11.4), 3.65 (m, 1H), 3.62 (t, 1H,
J=9.2), 3.54 (br t, 1H), 3.31 (m, 1H); 13C NMR: δ 140.4, 136.7, 132.6, 130.5, 129.9, 129.8, 129.3, 128.6,
89.8, 81.0, 80.2, 77.0, 71.3, 63.2. CI-MS: m/z 380 (C19H22O5S+NH4). Anal. calcd for C19H22O5S: C,
62.96; H, 6.12. Found: C, 62.83; H, 6.12.
4.12. Phenyl 2-O-benzyl-3,4,6-tri-O-lauroyl-1-thio-β-D-galactopyranoside 16
To a stirred solution of 15 (5.8 g, 16.0 mmol) in CH2Cl2 (25 mL) were added, in succession at 0°C,
C5H5N (12 mL) and lauroyl chloride (14.0 mL, 60.5 mmol). After 3 h, the mixture was treated with
cold EtOH (150 mL). Filtration afforded crystalline 16 (14.5 g, 98%): mp 83–85°C; [α]D +12 (c 0.6,
1
CHCl3); H NMR: δ 7.30–7.60 (m, 5H), 5.43 (br d, 1H, J=3.0), 5.05 (dd, 1H, J=3.2, J=9.6), 4.83 (d,
1H, J=10.7), 4.73 (d, 1H, J=9.6), 4.57 (d, 1H, J=10.7), 4.18 (dd, 1H), 4.08 (d, 1H), 3.92 (br t, 1H), 3.72
(t, 1H, J=9.6), 2.36 (t, 1H, J=7.3), 2.28 (t, 1H, J=7.5), 2.34 (m 1H), 1.45–1.68 (m), 0.98–1.40 (m), 0.88
(m, 9H); 13C NMR: δ 173.2, 172.7, 172.6, 132.5, 129.0, 128.8, 128.0, 87.8, 75.4, 75.2, 74.3, 74.0, 67.4,
61.6, 34.1, 34.0, 31.9, 29.6, 29.5, 29.4, 29.35, 29.26, 29.14, 25.1, 24.8, 24.6, 22.7, 14.1. CI-MS: m/z 926
(C55H88O8S+NH4). Anal. calcd for C55H88O8S: C, 72.64; H, 9.75. Found: C, 72.86; H, 9.42.
4.13. 5-(Methoxycarbonyl)pentyl (4,6-di-O-acetyl-2-azido-3-O-chloroacetyl-2-deoxy-α-D-Glcp)-
(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 19
A solution of compound 1724 (2.2 g, 5.30 mmol) in CH2Cl2 (10 mL) was treated at 0°C with Br2
(1.2 mL, 23.3 mmol). After 10 min, the solution containing 18 was treated with hex-1-ene (excess), then
was transferred to a stirred mixture of 11 (1.6 g, 2.41 mmol), 2,6-di-tbutyl-4-methylpyridine (2.0 g), and
4 Å molecular sieves (∼2 g) at 23°C. After 15 min, the mixture was cooled to 0°C, then was treated
with AgOTf (4.0 g, 14.7 mmol). After 20 min, the mixture was treated with aqueous NaHCO3. The
usual processing, followed by column chromatographic purification of the residue (3:1 hexane:EtOAc),
1
afforded 19 (1.4 g, 57%) as a syrup: [α]D +80 (c 0.6, CHCl3); H NMR (selected): δ 5.52 (dd, 1H),
5.13–5.24 (m, 3H), 4.97 (t, 1H, J=9.7), 4.82 (d, 1H, J=1.7), 3.78 (dq, 1H), 3.63 (m, 1H), 3.61 (s, 3H),
3.39 (m, 1H), 3.27 (dd, 1H, J=3.2, J=9.7), 2.25–2.32 (m, 2H), 2.03 (s, 3H), 1.92 (s, 3H), 1.51–1.68
(m, 2H), 1.13–1.39 (m), 0.81 (m, 3H); 13C NMR: δ 173.9, 172.2, 170.4, 169.5, 169.1, 166.1, 165.9,
133.4, 129.9, 129.0, 128.4, 97.5, 93.5, 72.1, 71.5, 71.3, 68.0, 67.6, 67.5, 66.5, 61.4, 60.3, 51.5, 40.3,
34.1, 33.8, 31.8, 29.6, 29.5, 29.3, 29.0, 25.6, 24.7, 24.6, 22.6, 20.6, 20.5, 17.6, 14.1. CI-MS: m/z 1027
(C50H76ClN3O16+ NH4). Anal. calcd for C50H76ClN3O16: C, 59.42; H, 7.58. Found: C, 59.17; H, 7.46.

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
165
4.14. 5-(Methoxycarbonyl)pentyl (4,6-di-O-acetyl-2-azido-2-deoxy-α-D-Glcp)-(1→3)-2-O-benzoyl-
4-O-stearoyl-α-L-rhamnopyranoside 20
A solution of 19 (2.0 g, 1.98 mmol), thiourea (1.0 g, 13.1 mmol), C5H5N (0.5 mL), and DMF (10 mL)
was kept at 23°C for 8 h followed by removal of the volatiles under vacuum. The residue was treated
with CHCl3 then the solids so obtained were removed by filtration. Extractive work-up (CHCl3/H2O)
followed by column chromatographic purification of the residue (4:1 hexane:EtOAc) afforded 20 (1.55
g, 85%) as a syrup: [α]D +56 (c 0.6, CHCl3); 1H NMR (selected): δ 5.58 (dd, 1H), 5.38 (t, 1H, J=9.8),
5.15 (d, 1H, J=3.4), 4.44 (d, 1H, J=1.7), 4.44 (t, 1H, J=∼9.6), 4.21 (ddd, 1H), 3.69 (m, 1H), 3.67 (s,
3H), 3.45 (m, 1H), 3.22 (dd, 1H, J=3.4, J=9.7); 2.05 (s, 3H), 1.96 (s, 3H), 1.50–1.68 (m, 2H), 1.12–1.42
(m), 0.81 (m, 3H); 13C NMR: δ 174.0, 172.4, 170.5, 165.9, 163.2, 162.9, 133.4, 129.9, 129.3, 128.4,
97.6, 93.8, 71.8, 71.4, 70.6, 69.8, 68.0, 67.9, 67.7, 66.4, 63.0, 61.8, 51.5, 34.2, 33.9, 31.9, 29.7, 29.5,
29.3, 29.0, 25.6, 24.8, 24.6, 22.7, 20.7, 17.6, 14.1. CI-MS: m/z 951 (C48H75N3O15+NH4). Anal. calcd
for C48H75N3O15: C, 61.72; H, 8.09. Found: C, 61.88; H, 8.11.
4.15. 5-(Methoxycarbonyl)pentyl (3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-
GlcpNAc)-(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 24
To a solution of 16 (860 mg, 0.945 mmol) in CH2Cl2 (5 mL) was added at 0°C a solution of chlorine in
CCl4 (excess). After 10 min, 1H NMR indicated complete disappearance of 16. The solution containing
21 was treated with hex-1-ene (excess), then was transferred via syringe to a stirred mixture of 20
(290 mg, 0.315 mmol), 2,6-di-tbutyl-4-methylpyridine (600 mg, 2.92 mmol), 4 Å molecular sieves
(approximately 1 g), and CH2Cl2 (4 mL). The mixture was stirred at 23°C for 20 min, then was cooled
to 0°C followed by treatment with AgOTf (1.3 g, 5.0 mmol). The mixture was allowed to reach room
temperature then was treated with aqueous sodium hydrogen carbonate. Filtration followed by extractive
work-up afforded a syrup that was purified through a C-18 column made in MeOH. Elution with
MeOH–EtOH mixtures up to 25% EtOH eluted impurities. Subsequently, the column was eluted with
1:1 MeOH:EtOH, then with EtOH. The fractions containing the product were pooled and concentrated
to afford impure 22 as a syrup. A stirred solution of the residue in CH2Cl2 (5 mL) was treated with
PPh3 (1.0 g, 3.71 mmol) for 24 h followed by addition of H2O (0.5 mL). After an additional 24 h, the
volatiles were removed by distillation to afford a residue that was purified by column chromatography
(3:1 hexane:EtOAc) to give 23 (420 mg, 78%) as a homogeneous syrup. A solution of this material
in CH2Cl2 (5 mL) was treated with Ac2O (0.5 mL) at 0°C for 2 h, then the volatiles were removed.
Intermediate so obtained was dissolved in a mixture of EtOH (5 mL) and AcOH (0.5 mL) and the
solution stirred under H2 in the presence of Pd–C (10%, ∼0.2 g) at 200 psi for 24 h. The mixture was
filtered and the filtrate concentrated. Filtration of the residue through a short column of silica gel (1:1
hexane:EtOAc) afforded 24 (370 mg, 93%): [α]D +42 (c 0.5, CHCl3); 1H NMR: δ 7.49–8.14 (m, 5H),
6.54 (d, 1H, J=9.6), 5.47 (dd, 1H, J=1.8, J=3.7), 5.38 (dd, 1H, J=1.0, J=3.3), 5.10 (t, 1H, J=9.8), 5.08 (t,
1H, J=9.6), 5.01 (dd, 1H, J=3.4, J=10.7), 4.99 (d, 1H, J=3.7), 4.88 (d, 1H, J=3.9), 4.85 (d, 1H, J=1.8),
3.69 and 3.44 (2 m, 2H), 3.67 (s, 3H), 3.57 (t, 1H, J=9.9), 2.30–2.38 (m, 6H), 2.27–2.22 (m, 4H), 2.08,
1.95, 1.82 (3 s, 3×3H), 1.18–1.72 (m), 0.89 (m, 12H); 13C NMR: δ 178.0, 173.1, 173.0, 172.5, 170.7,
170.2, 170.0, 166.5; 134.0, 131.0, 129.0, 128.8, 100.8 (J=167), 98.5 (J=170), 97.6 (J=170), 77.7, 77.2,
76.7, 76.3, 72.5, 70.0, 69.9, 69.6, 68.7, 68.0, 67.2, 66.9, 66.2, 61.0, 60.0, 52.1, 51.5, 34.5, 34.0, 33.8,
31.9, 29.7, 29.6, 29.5, 29.4, 29.3, 29.11, 29.08, 29.0, 25.6, 25.0, 24.8, 22.7, 22.6, 20.8, 20.7, 17.6, 14.1.
Anal. calcd for C92H155NO24: C, 66.60; H, 9.42. Found: C, 66.72; H, 9.37.

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V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
4.16. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-stearoyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-
α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamno-
pyranoside 26
To a stirred solution of 24 (3.4 g, 2.09 mmol) and 9 (3.6 g, 4.76 mmol) in CH2Cl2 (30 mL) was added
TMSOTf (40 µL, 0.22 mmol) at 0°C, then the solution was allowed to reach ambient temperature. After
30 min, the solution was treated with Et3N (excess) followed by concentration. Column chromatographic
purification of the residue (3:1 hexane:EtOAc) afforded 25 (4.60 g): [α]D +43 (c 0.8, CHCl3); 1H NMR
(selected): δ 7.39–8.11 (m, 10H), 6.47 (d, 1H, J=9.5), 5.46 (dd, 1H, J=1.9, J=3.4), 5.33–5.41 (m, 3H),
5.25 (dd, 1H, J=8.9, J=9.9), 5.20 (dd, 1H, J=3.3, J=10.0), 5.11 (t, 1H, J=9.9), 5.07 (d, 1H, J=3.2),
5.04 (d, 1H, J=1.8), 4.97 (d, 1H, J=3.8), 4.84 (d, 1H, J=1.9), 4.45 (ddd, 1H, J=3.4, J=9.8), 4.35 (dd,
1H, J=6.1, J=9.2), 3.92 (d, 1H, J=∼15), 3.85 (d, 1H, J=∼15), 3.68 (s, 3H), 3.44 (m, 1H), 2.11, 2.03,
1.77 (3 s, 3×3H), 1.15–1.33 (m), 1.06 (d, 3H, J=5.9), 0.83–0.91 (m, 15H); 13C NMR: δ 173.2, 172.9,
172.8, 172.5, 172.3, 170.8, 170.3, 168.9, 166.3, 166.0, 165.3, 133.8, 133.6, 130.1, 129.9, 129.1, 129.0,
128.6, 98.5 (170), 97.7 (168), 97.6 (170), 97.5 (172), 75.0, 74.4, 74.1, 72.1, 70.5, 70.1, 69.9, 69.7, 68.7,
68.1, 67.4, 67.1, 66.5, 66.4, 61.4, 60.0, 51.8, 51.5, 40.4, 34.5, 34.1, 34.0, 33.9, 33.8, 31.9, 29.7, 29.6,
29.5, 29.4, 29.3, 29.1, 29.0, 25.6, 25.0, 24.9, 24.8, 24.7, 24.6, 24.4, 22.6, 20.8, 20.7, 17.6, 17.5, 14.1.
To a stirred solution of 25 (4.60 g) in DMF (20 mL) was added thiourea (2 g). After 8 h, the solution
was concentrated under vacuum and the residue was treated with CHCl3. The solids were removed by
filtration. Concentration of the filtrate followed by column chromatographic purification of the residue
1
(3:1 hexane:EtOAc) afforded amorphous 26 (3.80 g, 85% for two steps): [α]D +36 (c 1.1, CHCl3); H
NMR (selected): δ 7.42–8.12 (m, 10H), 6.32 (d, 1H, J=9.6), 5.48 (dd, 1H, J=2.0, J=3.6), 5.38 (dd, 1H,
J=1.6, J=3.2), 5.22–5.10 (m, 3H), 5.07 (d, 1H, J=1.6), 5.03 (d, 1H, J =3.4), 4.99 (d, 1H, J=3.5), 4.98
(t, 1H, J=∼10.0), 4.85 (d, 1H, J=2.0), 4.43 (ddd, 1H, J=3.5, J=9.5), 4.35 (dd, 1H), 4.22 (dd, 1H, J=6.3,
J=11.0), 4.15 (dd, 1H, J=3.2, J=10.0), 3.68 (s, 3H), 3.45 (m, 1H), 2.25–2.47 (m), 2.13–2.23 (m), 2.11,
2.02, 1.73 (3 s, 3×3H), 1.15–1.33 (m), 1.13 (d, 3H, J=5.9), 0.83–0.92 (m); 13C NMR: δ 174.4, 173.3,
172.5, 170.7, 170.3, 168.8, 166.1, 165.5, 133.8, 133.4, 130.0, 129.8, 129.3, 129.1, 128.7, 128.5, 98.2,
97.6, 97.4, 96.6, 74.2, 74.0, 73.6, 72.9, 72.1, 72.0, 70.1, 69.5, 69.0, 68.6, 68.1, 67.9, 67.3, 67.0, 66.4,
61.5, 60.2, 51.6, 51.5, 34.5, 34.3, 34.0, 33.9, 33.8, 31.9, 29.7, 29.6, 29.5, 29.4, 29.3, 29.2, 29.1, 29.0,
28.9, 25.6, 25.0, 24.9, 24.8, 24.7, 24.6, 24.5, 22.7, 20.9, 20.7, 17.6, 14.1. Anal. calcd for C123H203NO30:
C, 67.89; H, 9.40. Found: C, 67.14; H, 9.31.
4.17. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-3-O-chloroacetyl-α-L-Rhap)-(1→2)-(3,4,6-
tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-
Rhap)-(1→3)-(2-O-benzoyl-4-O-stearoyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,
6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 27
To a stirred solution of the imidate2 2 (1.12 g, 0.68 mmol) and the alcohol 26 (618 mg, 0.27 mmol) in
CH2Cl2 (5 mL) was added at 0°C TMSOTf (10 µL). After 3 h, more 2 (approximately 0.5 g) was added
to the reaction mixture. After an additional 1 h, the mixture was treated with Et3N then was concentrated.
The reaction mixture was applied to a C-18 column made in MeOH that was subsequently eluted with
6:4 MeOH:EtOH to remove impurities. Elution with 1:1 MeOH:EtOH removed unreacted 26 (170 mg).
Subsequent elution with EtOH followed by iPrOH eluted 27 (625 mg, 84% based on recovery) obtained
1
as amorphous substance after removal of the volatiles: [α]D +62 (c 0.5, CHCl3); H NMR (selected):
δ 7.29–8.16 (m), 6.37 (d, 1H, J=9.7), 5.66 (d, 1H, J=∼10), 5.60 (dd, 1H, J=1.7, J=3.5), 5.47 (dd, 1H,
J=1.8, J=3.5), 5.37–5.41 (m, 2H), 5.26 (dd, 1H, J=1.7, J =3.4), 5.05 (d, 1H, J=3.6), 5.02 (d, 1H, J=1.8),

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
167
4.97 (d, 1H, J=3.8), 4.82 (d, 1H, J=1.6), 4.80 (d, 1H, J=3.5), 4.75 (d, 1H, J=3.6), 3.81 (d, 1H, J=∼15),
3.73 (d, 1H, J=∼15), 3.67 (s, 3H), 3.22 (t, 1H, J=9.6), 2.29–2.42 (m), 2.01, 2.00, 1.98, 1.92, 1.72, 1.61 (6
s, 6×3H), 1.18–1.40 (m), 1.13, 1.10, 0.85 (3 d, 3×3H, J=∼6), 0.84–0.91 (m); 13C NMR: δ 173.3, 172.8,
172.7, 172.5, 172.4, 170.8, 170.5, 170.1, 170.0, 169.3, 168.6, 166.0, 165.8, 165.5, 165.2, 138.3, 137.8,
137.7, 137.5, 133.7, 133.6, 133.5, 133.3, 130.0–126.7, 99.2 (171), 98.9 (168), 98.8 (172), 98.3 (171),
97.5 (167), 96.8 (172), 96.2 (171), 95.4 (168), 78.8, 78.7, 78.5, 76.6, 75.1, 74.7, 74.6, 74.4, 74.2, 73.8,
73.7, 73.6, 73.5, 73.3, 72.8, 72.2, 72.1, 72.0, 71.8, 71.7, 70.5, 70.1, 69.5, 69.4, 69.2, 69.1, 69.0, 68.5,
68.1, 68.0, 67.8, 67.5, 67.1, 66.8, 66.3, 65.9, 61.4, 60.9, 60.1, 51.6, 51.4, 51.2, 40.4, 34.3, 34.1, 34.0,
33.9, 33.8, 33.7, 33.6, 31.8, 28.9–30.0, 24.3–25.5, 22.8, 22.6, 22.4, 20.9, 20.8, 20.7, 20.5, 17.9, 17.6,
17.5, 17.4, 14.1. FAB-MS: m/z 3785.0 [(C204H289ClN2O53+Cs)+]. Anal. calcd for C204H289ClN2O53: C,
67.08; H, 7.97. Found: C, 67.09; H, 8.03.
4.18. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-
Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-(2-
O-benzoyl-4-O-stearoyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-
D-GlcpNAc)-(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 28
To a solution of 27 (900 mg, 0.241 mmol) in DMF (5 mL) and C5H5N (0.5 mL) was added thiourea (92
mg, 1.20 mmol) at 23°C. After 24, the mixture was processed as described for compound 11 followed
i
by C-18 chromatographic purification using EOH to elute impurities followed by elution with PrOH.
Concentration of the iPrOH fractions afforded 28 (860 mg, 97%) as an amorphous substance: [α]D +59
(c 0.4, CHCl3); 1H NMR (selected): δ 7.00–8.11 (m), 6.31 and 5.57 (2 d, 2H, J=∼10), 5.48, 5.42, 5.38 (3
dd, 3H, J=∼1.7, ∼3.5), 5.30 (d, 1H, J=1.8), 5.05 (d, 1H, J=∼1.7), 5.04 (d, 1H, J=3.4), 5.01 (d, 1H, J=1.8),
4.97 (d, 1H, J=3.5), 4.84 (d, 1H, J=1.8), 4.78 (d, 1H, J=∼10), 4.76 and 4.97 (2 d, 2H, J=11), 4.57 (d, 1H,
J=2.0), 4.36 and 4.28 (2 d, 2H, J=∼12), 3.65 (s, 3H), 3.23 (t, 1H, J=9.6), 2.29–2.42 (m), 2.11–2.22 (m),
2.01, 2.00, 1.98, 1.85, 1.72, 1.54 (6 s, 6×3H), 1.08–1.40 (m), 0.83–0.93 (m); 13C NMR: δ 173.9, 173.3,
172.8, 172.7, 172.5, 172.4, 170.7, 170.6, 170.0, 169.9, 169.0, 168.6, 166.1, 166.0, 165.5, 165.2, 138.4,
138.3, 137.9, 137.8, 137.7, 133.8, 133.7, 133.5, 133.2, 133.3–126.8, 99.2, 98.9, 98.4, 98.2, 97.6, 96.9,
96.5, 94.8, 81.6, 79.2, 78.9, 76.4, 75.3, 75.1, 74.7, 74.6, 74.3, 74.0, 73.4, 73.1, 73.0, 72.9, 72.3, 72.2,
72.1, 71.9, 71.8, 70.6, 70.3, 69.7, 69.4, 69.3, 69.2, 69.1, 69.0, 68.6, 68.3, 68.1, 68.0, 67.5, 67.2, 66.9,
66.4, 66.0, 61.4, 61.0, 60.2, 51.6, 51.5, 51.3, 34.4, 34.2, 34.0, 33.9, 33.8, 33.7, 31.9, 29.0–29.8, 25.6,
25.0, 24.9, 24.8, 24.7, 24.6, 24.4, 22.8, 22.7, 22.5, 20.9, 20.7, 20.6, 17.9, 17.8, 17.7, 17.6, 14.1. FAB-
MS: m/z 3709.5 [(C202H288N2O52+Cs)+]. Anal. calcd for C202H288N2O52: C, 67.84; H, 8.12. Found: C,
67.71; H, 8.13.
4.19. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-3-O-chloroacetyl-α-L-Rhap)-(1→2)-(3,4,
6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-
L-Rhap)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,
6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-(2-O-benzoyl-4-O-
stearoyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-
(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 29
To a solution of 28 (500 mg, 0.137 mmol) and 2 (1.0 g, 0.61 mmol) in CH2Cl2 (5 mL) was added
TMSOTf (8 µL) at 0°C. After 3 h, the mixture was processed as described for 27. The syrupy residue

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V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
was applied to a C-18 column that was eluted, in succession, with MeOH, 3:1 MeOH:EtOH, 3:2
EtOH:MeOH, and EtOH. Concentration of the EtOH fraction afforded amorphous 29 (620 mg, 89%):
[α]D+69 (c 0.5, CHCl3); 1H NMR (selected): δ 7.32–8.14 (m), 6.32 (d, 1H, J=10), 5.80 (d, 1H, J=∼10),
5.68 (d, 1H, J=9.6), 5.60 (dd, 1H, J=1.7, J=3.4), 5.54 (dd, 1H, J=1.3, J=3.3), 5.51 (d, 1H, J=1.4), 5.47
(dd, 1H, J=1.8, J=3.2), 5.38 (d, 2H, J=∼3.6), 5.35 (d, 1H, J=3.6), 4.86 and 4.82 (2 d, 2H, J=∼15),
3.62 (s, 3H), 2.05, 1.95, 1.94, 1.92, 1.79, 1.73, 1.72, 1.71 1.46 (9 s, 9×3H), 1.1–1.3 (m), 0.83–0.96
(m); 13C NMR: δ 173.8, 173.3, 172.8, 172.7, 172.5, 172.4, 170.7, 170.53, 170.48, 170.45, 170.0, 169.5,
169.4, 168.8, 168.5, 166.1, 165.8, 165.6, 165.4, 165.2, 165.1, 164.9, 138.4, 138.2, 138.05, 138.0, 137.9,
137.6, 137.57, 137.5, 133.7, 133.5, 133.3, 133.2, 126.5–130.8, 99.5, 99.3, 99.2, 98.9, 98.4, 97.9, 97.8,
97.6, 96.8, 96.5, 96.2, 93.9, 80.1, 79.4, 79.0, 78.9, 78.6, 78.2, 75.4, 75.3, 75.2, 75.0, 74.8, 74.6, 74.5,
74.3, 74.1, 73.9, 73.5, 73.3, 72.7, 72.2, 72.0, 71.9, 71.8, 71.7, 70.5, 70.1, 69.8, 69.6, 69.5, 69.4, 69.2,
68.8, 68.5, 68.4, 68.1, 68.0, 67.9, 67.8, 67.7, 67.6, 67.4, 67.1, 66.9, 66.3, 66.0, 61.4, 60.8, 60.6, 60.2,
51.6, 51.4, 51.3, 51.2, 40.8, 38.7, 34.5, 34.3, 33.9, 33.7, 32.0, 28.2–30.3, 25.5, 25.0, 24.8, 24.7, 24.5,
24.3, 23.7, 23.1, 22.9, 22.6, 22.5, 20.9, 20.7, 20.5, 20.4, 18.1, 17.8, 17.6, 17.5, 17.2, 17.1. FAB-MS:
m/z 5186.1 [(C283H374ClN3O75+Cs)+]. Anal. calcd for C283H374ClN3O75: C, 67.26; H, 7.46. Found: C,
67.12; H, 7.48.
4.20. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-
Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-(2-
O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-
GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-(2-O-benzoyl-4-O-stearoyl-α-L-Rhap)-
(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-2-O-benzoyl-
4-O-stearoyl-α-L-rhamnopyranoside 30
A solution of 29 (570 mg, 0.113 mmol), 2,6-di-tbutyl-4-methylpyridine (300 mg), and thiourea (100
mg) in DMF (5 mL) was stirred at 23°C for 24 h. The usual processing as described for 11 afforded
a syrup that was dissolved in MeOH. The resulting solution was applied to a C-18 column made in
MeOH that was then sequentially eluted with MeOH, 9:1 MeOH:EtOH, 1:1 MeOH:EtOH, and i-PrOH.
Concentration of the i-PrOH fraction afforded 30 (545 mg, 97%) as an amorphous substance: [α]D +68 (c
0.6, CHCl3); 1H NMR (selected): δ 7.32–8.14 (m), 6.32, 5.74, 5.68 (3 d, 3H, J=∼10), 5.53, 5.47, 5.41 (3
dd, 3H, J=∼1.7, J=3.3), 5.49 (d, 1H, J=1.7), 5.38 (dd, 1H, J=1.2, J=3.4), 3.67 (s, 3H), 1.99 (s, 6H), 1.97,
1.84, 1.74, 1.73, 1.72, 1.71, 1.46 (7 s, 7×3H), 0.83–0.92 (m); 13C NMR: δ 173.2, 172.7, 172.6, 172.4,
172.3, 170.6, 170.5, 170.3, 170.0, 169.4, 168.9, 168.8, 168.5, 166.0, 165.5, 165.4, 165.1, 164.9, 138.3,
138.2, 138.1, 138.0, 137.9, 137.8, 137.7, 137.5 137.4, 133.1–134.0, 130.0, 129.8, 139.7, 126.5–129.2,
99.25, 99.20, 98.8, 98.33, 98.28, 97.9, 97.5, 96.8, 96.4, 95.4, 93.8, 81.5, 80.1, 79.3, 79.0, 78.9, 78.8,
78.0, 76.4, 75.34, 75.29, 75.2, 75.0, 74.7, 74.6, 74.3, 74.1, 73.9, 73.8, 73.4, 73.3, 73.2, 73.1, 72.8, 72.6,
72.5, 72.1, 72.0, 71.9, 71.8, 71.7, 70.5, 70.3, 69.8, 69.6, 69.5, 69.4, 69.3, 69.1, 68.8, 68.5, 68.4, 68.1,
68.0, 67.9, 67.8, 67.5, 67.4, 67.3, 67.1, 66.9, 66.3, 65.9, 61.3, 60.9, 60.6, 60.1, 51.5, 51.4, 51.2, 51.1,
34.2, 34.1, 33.9, 33.7, 31.8, 28.9–29.6, 25.5, 25.0, 24.7, 24.6, 24.5, 24.3, 23.0, 22.6, 22.5, 20.8, 20.7,
20.5, 20.3, 17.9, 17.8, 17.6, 17.5, 14.0. FAB-MS: m/z 5109.5 [(C281H373N3O74+Cs)+]. Anal. calcd for
C281H373N3O74: C, 67.81; H, 7.55. Found: C, 67.16; H, 7.45.

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
169
4.21. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-3-O-chloroacetyl-α-L-Rhap)-(1→2)-(3,4,
6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-
L-Rhap)-(1→3)-[(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,
6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-]22-O-benzoyl-4-O-
stearoyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-
(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 31
To a solution of 30 (480 mg, 0.096 mmol) and 2 (667 mg, 0.407 mmol) in CH2Cl2 (4 mL) was added
TMSOTf (8 µL) at 0°C. After 3 h, the mixture was processed as described for 27. The syrupy residue was
applied to a C-18 column that was eluted, in succession, with 1:1 MeOH:EtOH, EtOH, 1:1 EtOH:i-PrOH,
and iPrOH. Fractions containing iPrOH were pooled and concentrated. Repeated purification through a
C-18 column, using a gradient of EtOH and iPrOH, afforded amorphous 31 (480 mg, 77%): [α]D +75
(c 0.6, CHCl3); 13C NMR: δ 173.2, 172.7, 172.6, 172.44, 172.40, 172.3, 170.7, 170.5, 170.42, 170.38,
170.0, 169.8, 169.5, 169.4, 168.9, 168.8, 168.5, 166.0, 165.8, 165.5, 165.4, 165.3, 165.2, 165.1, 165.0,
164.8, 138.4, 138.2, 138.0, 133.7, 133.4, 133.3, 133.2, 126.4–130.1, 99.5, 99.3, 98.9, 98.4, 98.0, 97.6,
96.9, 96.6, 96.1, 94.3, 94.0, 80.1, 79.4, 79.3, 79.0, 78.6, 78.3, 77.9, 75.4, 75.2, 75.0, 74.8, 74.6, 74.4,
74.2, 74.0, 73.9, 73.5, 73.4, 73.3, 72.9, 72.7, 72.5, 72.4, 72.2, 72.0, 71.9, 71.5, 70.5, 70.1, 69.8, 69.5,
69.3, 69.0, 68.8, 68.5, 67.9, 67.7, 67.6, 67.4, 67.2, 66.9, 66.3, 66.0, 61.37, 61.32, 60.81, 60.85, 60.68,
60.63, 51.6, 51.4, 51.3, 51.2, 51.1, 40.4, 33.7–34.3, 31.8, 28.9–30.0, 24.3–25.5, 22.5–23.1, 17.5–18.0,
17.2, 14.1. FAB-MS: m/z 6586.9 [(C362H459ClN4O97+Cs)+]. Anal. calcd for C362H459ClN4O97: C, 67.37;
H, 7.17. Found: C, 67.14; H, 7.22.
4.22. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-
Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-[(2-
O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-
GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-]22-O-benzoyl-4-O-stearoyl-α-L-Rhap)-
(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-2-O-benzoyl-
4-O-stearoyl-α-L-rhamnopyranoside 32
A solution of 31 (450 mg, 0.069 mmol), 2,6-di-tbutyl-4-methylpyridine (200 mg), and thiourea (0.5 g)
in DMF (5 mL) was stirred at 23°C for 24 h. The usual processing as described for 11 afforded a syrup
that was dissolved in MeOH. The resulting solution was applied to a C-18 column made in MeOH that
was then sequentially eluted with MeOH, MeCN, and benzene. Concentration of the benzene fraction
afforded a syrup that was equilibrated between CHCl3 and H2O. The organic layer was dried (Na2SO4)
and concentrated to afford 32 (410 mg, 92%) as an amorphous substance: [α]D +71 (c 1.1, CHCl3);
1H NMR: δ 7.9–8.10 (m), 6.84–7.65 (m), 6.30, 5.74, 5.73, 5.66 (4 d, 4H, J=∼9.5–10.1), 3.62 (s, 3H),
2.26–2.46 (m), 2.10–2.22 (m), 1.98, 1.97, 1.84, 1.73, 1.72, 1.71, 1.70, 1.64, 1.60, 1.47 (10 s), 1.05–1.37
(m), 0.82–0.92 (m); 13C NMR: δ 173.9, 173.3, 172.7, 172.6, 172.4, 170.6, 170.5, 170.4, 170.3, 170.0,
169.8, 169.5, 168.9, 168.8, 168.7, 168.5, 166.1, 165.4, 165.1, 165.0, 164.8, 137.5–138.4, 133.1–133.7,
126.4–131.0, 99.2, 98.9, 98.4, 98.0, 97.6, 96.9, 96.6, 95.4, 94.3, 94.0, 81.6, 80.1, 79.4, 79.3, 79.1, 79.0,
78.9, 78.2, 77.8, 77.7, 75.4, 75.2, 75.0, 74.7, 74.6, 74.4, 74.2, 74.1, 74.0, 73.9, 73.5, 73.2, 73.0, 72.8, 72.6,
72.4, 72.2, 72.0, 71.9, 71.8, 71.5, 70.4, 69.8, 69.7, 69.6, 69.3, 69.0, 68.8, 68.5, 68.1, 68.0, 67.8, 67.5, 67.4,
67.2, 66.9, 66.3, 66.0, 61.4, 60.9, 60.7, 60.2, 51.5, 51.46, 51.3, 51.2, 51.1, 33.8–34.3, 31.9, 28.9–29.6,
24.3–25.5, 22.5–23.0, 20.4–20.9, 17.6–17.9, 14.1. FAB-MS: m/z 6510.4 [(C360H458N4O96+Cs)+]. Anal.
calcd for C360H458N4O96: C, 67.80; H, 7.24. Found: C, 67.36; H, 7.31.

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4.23. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-3-O-chloroacetyl-α-L-Rhap)-(1→2)-(3,4,
6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-
L-Rhap)-(1→3)-[(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,
6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-]3(2-O-benzoyl-4-O-
stearoyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-
(1→3)-2-O-benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 33
To a stirred mixture of 32 (360 mg, 0.056 mmol), 2 (390 mg, 0.238 mmol), and CaSO4 (3 g) in
CH2Cl2 (5 mL) was added TMSOTf (6 µL) at 0°C. After 2 h, the mixture was processed as described
for 27. The syrupy residue was applied to a C-18 column that was eluted, in succession, with MeOH, 1:1
MeOH:EtOH, EtOH, and iPrOH. The latter two fractions were pooled and and concentrated. Silica gel
column chromatography of the residue (3:2 hexane:EtOAc) afforded amorphous 33 (235 mg, 53%): [α]D
+65 (c 0.5, CHCl3); 1H NMR (selected): δ 6.90–8.1 (m), 6.33 (d, 1H, J=10.1), 5.81 (d, 1H, J=10.5), 5.77
(d, 2H, J=∼10.3), 5.69 (d, 1H, J=10.1), 3.66 (s, 3H), 2.28–2.40 (m), 2.05, 1.95, 1.94, 1.79, 1.74, 1.73,
1.70, 1.68, 1.63, 1.62 (10 s), 1.08–1.48 (m), 0.84–0.95 (m); 13C NMR: δ 173.3, 172.8, 172.7, 172.45,
172.41, 170.7, 170.5, 170.44, 170.1, 170.0, 169.9, 169.6, 169.4, 168.9, 168.8, 168.7, 168.5, 167.7, 167.6,
166.0, 165.8, 165.5, 165.4, 165.3, 165.2, 165.1, 165.0, 164.9, 164.8, 137.5–138.4, 133.1–133.8, 132.4,
130.8, 126.5–131.0, 99.5, 99.3 (3C), 99.2, 98.9, 98.4, 98.2, 98.0 (5C), 97.6, 96.8, 96.4, 96.1, 94.4, 94.3,
94.0, 80.1, 79.3, 78.9, 78.6, 78.3, 77.9, 75.4, 75.3, 75.2, 75.1, 75.0, 74.8, 74.6, 74.3, 74.2, 73.9, 73.4,
73.3, 72.9, 72.7, 72.5, 72.3, 72.2, 72.0, 71.8, 71.4, 70.5, 70.1, 69.8, 69.5, 69.4, 69.2, 68.8, 68.5, 68.0,
67.8, 67.6, 67.4, 67.1, 66.9, 66.3, 65.9, 62.0, 61.4, 60.8, 60.6 (2C), 60.1, 51.6, 51.4, 51.3, 51.1 (2C), 40.4,
38.6, 36.6, 34.3, 34.1, 33.94, 33.90, 33.8, 31.8, 30.3, 28.8–29.6, 25.5, 25.0, 24.8, 24.7, 24.6, 24.5, 24.3,
23.7, 23.3, 23.1, 22.9, 22.6, 22.5, 20.9, 20.7, 20.5, 18.0, 17.9, 17.8, 17.1, 17.6, 17.5, 17.2, 14.05, 13.98.
FAB-MS: m/z 7856.2 [(C441H544ClN5O119+H)+]. Anal. calcd for C441H544ClN5O119: C, 67.44; H, 6.98.
Found: C, 67.71; H, 6.78.
4.24. 5-(Methoxycarbonyl)pentyl (2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-
Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-[(2-
O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→2)-(3,4,6-tri-O-benzyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-
D-GlcpNAc)-(1→3)-(2-O-benzoyl-4-O-benzyl-α-L-Rhap)-(1→3)-]3(2-O-benzoyl-4-O-stearoyl-α-L-
Rhap)-(1→2)-(3,4,6-tri-O-lauroyl-α-D-Galp)-(1→3)-(4,6-di-O-acetyl-α-D-GlcpNAc)-(1→3)-2-O-
benzoyl-4-O-stearoyl-α-L-rhamnopyranoside 34
A solution of 33 (210 mg, 0.027 mmol), 2,6-di-tbutyl-4-methylpyridine (100 mg), and thiourea (0.2 g)
in DMF (5 mL) was stirred at 23°C for 24 h. The usual processing as described for 11 afforded a syrup
that was dissolved in MeOH. The resulting solution was applied to a C-18 column made in MeOH that
was then sequentially eluted with MeOH, EtOH, and 1:1 EtOH:i-PrOH. Concentration of the EtOH:i-
1
PrOH fraction afforded 34 (175 mg, 84%) as an amorphous substance: [α]D +76 (c 0.4, CHCl3); H
NMR (selected): δ 6.90–8.12 (m), 6.28 (d, 1H, J=10.0), 5.74 (d, 3H, J=∼9.5), 5.66 (d, 1H, J=9.0), 3.67
(s, 3H), 2.27–2.42 (m), 2.12–2.20 (m), 2.00, 1.98, 1.97, 1.84, 1.74, 1.73, 1.72, 1.64, 1.62, 1.47 (10 s),
1.04–1.42 (m), 0.84–0.90 (m); 13C NMR (selected): δ 173.3, 172.8, 172.7, 172.4, 170.7, 170.1, 170.0,
169.9, 169.6, 169.5, 168.9, 168.8, 168.5, 167.8, 166.1, 165.8, 165.5, 165.4, 165.2, 165.1, 165.0, 164.8,
99.2, 98.9, 98.3, 98.2, 98.0, 97.6, 96.8, 96.5, 95.4, 94.5, 94.3, 94.0, 81.5, 80.1, 79.3, 79.0, 78.0, 77.7,
75.4, 75.0, 74.7, 74.6, 74.4, 74.0, 73.9, 73.4, 73.2, 72.8, 72.5, 72.2, 72.0, 71.9, 71.5, 70.5, 70.4, 69.6,
69.3, 68.5, 68.1, 68.0, 67.8, 67.5, 67.4, 67.2, 66.9, 66.4, 61.4, 60.9, 60.6, 60.2, 51.5, 51.45, 51.3, 51.15,

V. Pozsgay / Tetrahedron: Asymmetry 11 (2000) 151–172
171
51.1, 31.9–34.3, 31.9, 28.9–29.6, 24.3–25.5, 22.5–23.1, 20.4–20.9, 17.6–17.9, 14.1. FAB-MS: m/z 7778
[(C439H542N5O118+H)+]. Calcd for C439H542N5O118: C, 67.80; H, 7.02. Found: C, 68.11; H, 6.95.
4.25. 5-(Methoxycarbonyl)pentyl
α-L-Rhap-(1→2)-α-D-Galp-(1→3)-α-D-GlcpNAc-(1→3)-α-L-
Rhap-(1→3)-[α-L-Rhap-(1→2)-α-D-Galp-(1→3)-α-D-GlcpNAc-(1→3)-α-L-Rhap-(1→3)-]4α-L-Rhap-
(1→2)-α-D-Galp-(1→3)-α-D-GlcpNAc-(1→3)-α-L-rhamnopyranoside 37
To a stirred mixture of 34 (150 mg, 19.3 µM), compound 2 (260 mg, 159 µM), CaSO4 (2 g), and
CH2Cl2 was added TMSOTf (7 µL) at 0°C. After 2 h, the mixture was treated with Et3N then filtered.
The residue obtained upon concentration of the filtrate was applied to a C-18 column made in MeOH. The
column was eluted successively with MeOH, EtOH, and 1:1 EtOH:i-PrOH. The latter two fractions were
combined and concentrated. The residue so obtained was further purified by silica gel chromatography
(3:2 hexane:EtOAc) to afford the intermediate 35 (45 mg) in pure form (HPTLC). An additional amount
(26 mg) was also obtained that contained <10% impurities. Yield: approximately 35%. To a solution of
compound 35 (35 mg) in CH2Cl2 (1 mL) was added MeOH followed by NaOMe in MeOH. After 4 days
at 23°C, the crystalline precipitate formed was removed by filtration. The clear solution was treated with
Dowex 50×8 (H+), filtered, and concentrated. The residue was purified by silica gel chromatography
(10:1 MeOH:EtOAc) to afford 36 as an amorphous material {[α]D +90 (c 0.2, CHCl3); FAB-MS m/z
5345.6 (C338H422N6O111+H)+} which was dissolved in EtOH (4 mL) and AcOH (0.5 mL). The solution
was stirred under H2 at 200 psi in the presence of Pd–C (10%, approximately 100 mg) for 48 h. The
mixture was filtered and the filtrate concentrated. The residue was purified by gel filtration through Biogel
P-6 using H2O as eluant to give, after freeze-drying, 37 (10 mg, 67%): [α]D +62 (c 0.4, H2O); 1H NMR
(selected): δ 5.60 (br s, 6H), 5.10 (br s, 5H), 5.07 (br s, 1H), 5.04 (br s, 10H), 4.99 (d, 1H, J=3.3), 3.57
(br t, J=∼10), 3.37 (s, 3H), 2.17 (br t, 2H, J=7.5), 2.05 (br s, 18H), 1.51–1.66 (m, 4H), 1.35–1.44 (m,
2H), 1.27–1.35 (m); 13C NMR: δ 175.0, 102.7 (5C), 102.3, 102.2 (5C), 100.2, 98.4 (6C), 94.8 (6C),
78.9, 75.7, 75.6, 75.4, 75.0, 74.5, 74.4, 72.6, 72.4, 72.0, 71.9, 71.6, 71.1, 70.8, 70.6, 70.3, 70.2, 70.1,
70.0, 69.7, 69.3, 68.6, 67.4, 61.4, 61.2, 60.8, 60.7, 52.7, 38.3, 29.1, 26.4, 26.1, 22.8, 17.6, 17.4, 17.3.
FAB-MS: m/z 4091.8 (C163H272N6O111+H)+, 4113.7 (C163H272N6O111+Na)+.
Acknowledgements
The author thanks Dr. Lewis Pannell and Mr. Noel Whittaker for the mass spectra.
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