Rapid, iterative assembly of octyl α-1,6-oligomannosides and their 6-deoxy equivalents

Article abstract of DOI:10.1039/b503919c

Mycobacterium tuberculosis is the cause of the deadly human disease tuberculosis. In studies over the last 40 years it has been revealed that this organism possesses a complex cell wall including glycophospholipids such as the phosphatidylinositiol mannos

Full text of DOI:10.1039/b503919c

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A R T I C L E
Rapid, iterative assembly of octyl a-1,6-oligomannosides and their
6-deoxy equivalents†
Jacinta A. Watt and Spencer J. Williams*
School of Chemistry, Bio21 Molecular Science and Biotechnology Institute, University of
Melbourne, Parkville, Australia 3010. E-mail: sjwill@unimelb.edu.au; Fax: +61 3 9347 5180;
Tel: +61 3 8344 2422
Received 17th March 2005, Accepted 8th April 2005
First published as an Advance Article on the web 20th April 2005
Mycobacterium tuberculosis is the cause of the deadly human disease tuberculosis. In studies over the last 40 years it
has been revealed that this organism possesses a complex cell wall including glycophospholipids such as the
phosphatidylinositiol mannosides (PIMs), lipomannan (LM) and lipoarabinomannan (LAM). These glycolipids all
contain a common a-1,6-linked mannoside core, and the higher PIMs and LAM possess a-1,2-linked mannosyl
residues. It has been shown that simple a-1,6-linked oligomannosides can act as substrates for
a-1,6-mannosyltransferases in mycobacteria. Here we report a simple iterative synthesis of a series of hydrophobic
octyl a-1,6-linked oligomannosides from mono- through to tetrasaccharides. We have utilized a single thioglycoside
donor and alcohol acceptor. Further, we have developed conditions for the conversion of each of these compounds to
the 6-deoxy congeners. Deoxygenation of the 6-position of the terminal mannosyl residue should prevent these
compounds acting as substrates for the abundant a-1,6-mannosyltransferases in mycobacteria and should permit
detection of the elusive a-1,2-mannosyltransferase activity responsible for elaboration of LM to mature LAM and
the biosynthesis of the higher PIMs.
aspects of cell wall biosynthesis.3,4 The cell wall is critical for the
Introduction
integrity of the bacterium, allowing it to survive and propagate
An estimated one third of the global population (almost 2 billion
within the human host. Mycobacteria possess a unique set
people) carries Mycobacterium tuberculosis, the causative agent
of cell wall glycolipids, the phosphatidylinositol mannosides
of tuberculosis (TB). Each year approximately 9 million of those
(PIMs), lipomannan (LM), and lipoarabinomannan (LAM)
infected will develop active disease, resulting in up to 2 million
(Fig. 1).5 Biochemical studies have revealed that PIMs, LM
deaths. TB is the leading killer of women of child bearing age
and LAM are biosynthetically related6,7 and recent genetic
and is the major cause of death of HIV positive individuals.1
studies have validated this set of molecules as a promising target
The advent of the HIV/AIDS pandemic is the principal cause
for therapeutic intervention in the treatment of mycobacterial
of the dramatic resurgence of TB, particularly in sub-Saharan
diseases including tuberculosis.8,9 Studies on an early step of
Africa. In tandem recent outbreaks of drug resistant TB in many
PIM, LM, and LAM biosynthesis, that catalyzed by the a-
industrialized nations have resulted in a resurgence of interest
mannosyltransferase PimA, have provided clear, unambiguous
in the disease, and basic research and drug development have
again become priorities.
evidence for the essentiality of these molecules. In particular
a study of a conditional mutant of pimA in Mycobacterium
smegmatis have shown this to be an essential gene in this
An ideal TB drug target is the biosynthesis of the mycobac-
terial cell wall, which is unusually thick and lipid rich.2 Drugs
organism and provides strong evidence that PIM, LM and LAM
such as isoniazid, ethambutol and ethionamide already target
biosynthesis are essential for the survival of mycobacteria.9
† Dedicated to Associate Professor Bob Stick on the occasion of his 60th
birthday.
Fig. 1 Typical structures of phosphatidylinositol mannosides (PIMs), lipomannan (LM) and lipoarabinomannan (LAM). Common accepted ranges
for the number of mannose residues are given. “R” stands for various fatty acyl groups such as palmitic, stearic and tuberculostearic acids.
1 9 8 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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Fig. 2 Abbreviated biosynthesis of PIMs, LM and LAM highlighting the action of a-1,6- and a-1,2-mannosyltransferases. The hexagon indicates
inositol, an open circle indicates phosphate and a-mannosyl residues are shown with a closed circle.
PIM, LM and LAM share a common phosphatidylinositol
core. This core is elaborated with a-mannosyl residues, with
the first being added to the 6-position (to afford PIM1) and a
chain of a-1,6-linked mannosyl residues being built up on the
2-position, leading sequentially to the higher PIMs, LM, and
then LAM (Fig. 2).6 Mature LAM possesses single a-1,2-linked
mannosyl residues off the main a-1,6-linked mannan chain.
Efforts to study PIM and LAM biosynthesis have been restricted
by the limited availability of substrates for these enzymes.
While total syntheses of some PIMs have been reported,10–13
these challenging routes are not readily accessible for the wider
community, and systematic modifications of these molecules
is by no means simple. Simplified structures that can act as
substrates for enzymes in PIM, LM and LAM biosynthesis offer
an alternative method for their study.
In pioneering studies Yokoyama and Ballou showed that
mannose, methyl a-mannopyranoside and a-1,6-linked mannose
oligomers could act as substrates for a-1,6-mannosyltransferases
from M. smegmatis.14 More recently, Brown and co-workers
have reported the synthesis of a series of alkyl and alkenyl
di- and trimannosides for the study of mycobacterial gly-
colipid biosynthesis.15 These compounds were demonstrated
to act as substrates for polyprenolmannose-dependent a-1,6-
mannosyltranferases within a mycobacterial cell free system.
Brown et al. showed that each of the dimannosides was extended
by M. smegmatis extracts to the respective tri- and tetraman-
nosides, whilst the trimannoside underwent extension to both
the tetra- and pentamannoside; subsequent characterization of
these products showed them all to be a-1,6-linked. Together these
studies have shown that much simpler analogues of the PIMs can
function as substrates for mycobacterial mannosyltransferases.
However, the syntheses of these substrates were rather inefficient,
with the mannose oligomers in the work of Yokoyama and
Ballou being obtained through laborious degradation of yeast
mannan and in the case of Brown et al. each compound
was synthesized individually through synthetic routes that
utilized different donors to prepare the di- and trisaccharides.
Zhu and Kong have reported a simple iterative approach to
di- through to dodecamannosides using largely unprotected
glycosides as acceptors.16 While quite efficient this route, along
with those of Brown and co-workers, does not allow simple
modification of the carbohydrate rings, which could be of great
value to learn more about the active site architecture of these
mannosyltransferases. Additionally, modified substrates may
also show inhibitory effects towards these mannosyltransferases
and may act as substrates of other mannosyltransferases. Besra
and co-workers have recently reported studies of modified a-1,6-
dimannosides and have identified moderate inhibitors obtained
through modifications of the 2ꢀ,6ꢀ-positions.17 Notably, while
the di- and trimannosides of Brown and co-workers were
excellent substrates for a-1,6-mannosyltransferases, none of
these compounds could act as substrates for the much rarer a-
1,2-mannosyltransferase(s) involved in the biosynthesis of PIM5
and PIM6 and in installing a-1,2-linked mannosyl groups on
mature LAM.
Here we report an efficient iterative synthesis of a series of
a-1,6-linked hydrophobic mono-, di-, tri-, and tetramannosides.
The choice of a hydrophobic octyl glycoside capping group was
made as such derivatives allow simple solvent partitioning of
products from radiolabelled GDP-mannose in enzymic assays.18
We have utilized a single glycosyl acceptor 1 and donor 2,
each prepared from mannose pentaacetate. Further, we have
developed conditions for the conversion of each of these com-
pounds to the corresponding 6-deoxy congeners. Deoxygenation
of the 6-position of the terminal mannosyl residue should
prevent these compounds acting as substrates for the abundant
a-1,6-mannosyltransferases in mycobacteria and should per-
mit detection of the elusive a-1,2-mannosyltransferase activity
responsible for elaboration of LM to mature LAM and the
biosynthesis of PIM5 and PIM6.
Results and discussion
Previous approaches to the synthesis of a-1,6-oligomanno-
sides have largely relied on glycosyl halides or trichloro-
acetimidates.15,16,19 While these agents are effective glycosyl
donors the lability of the anomeric leaving group does not
permit facile modification of the carbohydrate ring prior to
glycosylation as is sought here for the preparation of the 6-deoxy
congeners. Thioglycosides present themselves as a possible
alternative glycosyl donor, with the robustness of the anomeric
thio substituent allowing protecting group manipulations prior
to glycosylation. Thioglycosides as donors have recently been
reported for the synthesis of several modified a-1,6-linked
dimannosides.17,20,21 Here, owing to the repeating nature of the
target oligomers, an iterative approach was thought appropriate,
using a single glycosyl donor 1 and an alcohol 2 (Scheme 1).
The alcohol 2, derived in turn from the TPS ether 3, can
immediately give rise to the 6-deoxy monomannoside 4 through
sequential deoxygenation and deprotection. Alternatively, fol-
lowing condensation of donor 1 and alcohol 2 to give the
disaccharide 5, the silyl ether can be removed, affording the
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2
1 9 8 3

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Scheme 1 Iterative synthesis of octyl oligomannosides and 6-deoxy congeners using a single glycosyl donor 1 and acceptor 2.
disaccharide alcohol 6. This alcohol can then provide access to
the dimannoside 7, or the 6-deoxy dimannoside 8 through an
intermediate deoxygenation step. Iteration of these steps gives
access to the higher homologues: glycosylation of the alcohol 6
with donor 1 will furnish the trimannoside 9, which again can
be converted to either of the trimannosides 10 or 11 or in turn
become a glycosyl acceptor 12 for extension to a tetramannoside
13. The tetramannoside 13 can be treated in an identical manner
to give the tetramannosides 14 and 15, via the intermediate
alcohol 16.
The donor 1 was prepared from mannose pentaacetate 17 in a
simple four-step sequence (Scheme 2). Tin(IV) chloride-catalyzed
condensation of pentaacetate 17 and thiocresol afforded the
thioglycoside 18, which was deacetylated with catalytic sodium
in methanol to afford the tetraol 19. Thiocresol was chosen as
it is a crystalline thiol and significantly less malodorous than
thiophenol. Additionally, the 4-methyl group is an excellent
spectroscopic reporter of the presence of this substituent in
1H NMR spectra, particularly when other aromatic protecting
groups obscure the remaining aromatic protons. The tetraol 19
Scheme 2 Reagents and conditions: (i) thiocresol, cat. SnCl4, CH2Cl2;
(ii) cat. NaOMe, MeOH, 27% from mannose; (iii) a) TPSCl, imidazole,
DMF, b) BzCl, pyridine, 49%.
was selectively protected at the primary position with a bulky
TPS ether by treatment with TPSCl according to the procedure
1 9 8 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2

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of Corey and Venkateswarlu.22 The TPS ether was chosen over
the more readily cleaved TBS alternative as it has been reported
that TBS ethers are unstable to halonium ion sources (e.g. NIS),
conditions that were planned for the eventual glycosylation.23
Finally, treatment of the intermediate triol with benzoyl chloride
and pyridine afforded the target donor 1. Surprisingly, residual
benzoic acid at this step proved challenging to remove, perhaps
due to the presence of silanol by-products, with the sugar after
chromatography requiring a wash with potassium carbonate
solution in order to give pure donor 1.
was selectively removed using HCl, MeOH and diethyl ether
(prepared in situ from AcCl) to afford the alcohol 2 in a good
yield (58%).
While a 6-deoxy monomannoside 4 was unlikely to act as
a particularly efficacious substrate for mycobacterial a-1,2-
mannosyltransferases, its synthesis provided a simple model for
deoxygenation that could be applied to the higher homologues.
The 6-deoxy monomannoside 4 was synthesized from the
alcohol 2 over three steps. Initially, the primary alcohol 2 was
treated with Ph3P, imidazole and iodine, to afford the iodide 22
in a good yield (86%). The successful introduction of iodine
was revealed in the 13C NMR spectrum, which reported a
characteristic chemical shift (d 5.1 ppm) for C6 attached to I. The
iodide 22 underwent reduction upon treatment with Bu3SnH
and catalytic AIBN in toluene, to give the protected 6-deoxy
mannoside 23 in a good yield (76%). Here, partitioning between
petroleum spirit and acetonitrile was used to separate the bulk
of tributyltin species; however, the surprisingly good solubility
of the 6-deoxy mannoside 23 in the non-polar phase required
repeated back extraction with acetonitrile to ensure good mass
recovery. The protected 6-deoxy mannoside 23 underwent global
deprotection using catalytic NaOMe in MeOH to give the
fully deprotected 6-deoxy mannoside 4. Purification of 6-deoxy
mannoside 4 by flash chromatography was not complete, so
4 was further purified on a C18 reverse phase silica column
using a water–methanol gradient. This worked in removing trace
impurities that had been otherwise inseparable.
Efforts then moved to the coupling of the glycosyl donor
1 and the glycosyl acceptor 2. The monosaccharides 1 and 2
were treated with N-iodosuccinimide and catalytic triflic acid
to afford the fully protected disaccharide 5. The stereoselective
formation of the a-anomer in this case can be explained
by invoking neighbouring group participation by the benzoyl
group at the 2-position of the glycosyl donor 1.‡ Despite
our best efforts the disaccharide 5 could not be purified by
flash chromatography, so the crude product was selectively
deprotected using HCl, MeOH and Et2O, yielding alcohol 6,
Scheme 3 Reagents and conditions: (i) octanol, cat. SnCl4, CH2Cl2; (ii)
cat. NaOMe, MeOH, 33% from mannose; (iii) a) TPSCl, imidazole,
DMF, b) BzCl, pyridine, 55%; (iv) HCl, MeOH, Et2O, 58%.
Acquisition of the glycosyl acceptor 2 was the next objective
(Scheme 3). Mannose pentaacetate 17 was treated with 1-octanol
and stannic chloride to afford the intermediate tetraacetate 20.
The tetraacetate 20 was deacetylated using catalytic sodium
methoxide in methanol to afford the octyl mannoside 21.24 As
for the glycosyl donor, the octyl mannoside 21 was selectively
protected at the primary alcohol using TPSCl, with the remain-
ing hydroxyls protected as benzoate esters through treatment
with BzCl, pyridine and DMAP, affording the silyl ether 3
in good yield (55%). Again, residual benzoic acid could not
be completely removed during work-up or by chromatography
but was readily separated afterwards. The silyl ether of 3
‡ Evidence for the exclusive formation of the a-anomer in this and
subsequent glycosylations was obtained through examination of the
1JC,H coupling constants for the anomeric carbons of the tetramannoside
16. Each coupling constant was > 170 Hz, thereby showing that all O-
glycosidic linkages formed in this manuscript were a.28
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2
1 9 8 5

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which was readily purified (71% over two steps). The primary
alcohol 6 underwent global deprotection using catalytic NaOMe
in MeOH to afford the dimannoside 7. Again, C18 silica gel
chromatography was necessary to effect adequate purification
of 7.
The corresponding 6-deoxy dimannoside 8 was synthesized
in an identical fashion as for the 6-deoxy monomannoside 4,
by way of conversion of the primary alcohol to the iodide and
then its reduction. Thus, the primary alcohol 6 was treated with
Ph3P, imidazole and iodine in toluene to afford the iodide 24
in high yield (94%). The iodide 24 was reduced using Bu3SnH–
cat. AIBN in toluene, affording the 6-deoxy dimannoside 25
(79%). Here, and for the higher homologues, no difficulties were
encountered in the acetonitrile–petroleum spirit partitioning
step used to remove tributyltin species. Debenzoylation of the
protected dimannoside 25 using NaOMe in MeOH yielded the
6-deoxy dimannoside 8 (77%).
The next targets were the trimannosides 10 and 11. Illustrating
the iterative nature of this synthetic route, the primary alcohol 6
was coupled with the glycosyl donor 1 under identical conditions
as for the disaccharides, using NIS and TfOH, affording the silyl
trimannoside 9 (90%). The silyl trimannoside 9 was selectively
deprotected as for 3 and 5, providing the primary alcohol 12.
As for the corresponding dimannoside, the partially protected
trimannoside 12 was treated with catalytic NaOMe in methanol,
affording the trimannoside 10 (70%). The 6-deoxy trimannoside
11 was synthesized in the same manner as for the mono-
and dimannosides 4 and 8. The trisaccharide alcohol 12 was
treated with Ph3P, imidazole and iodine in toluene affording the
iodide 26 (87%). Treatment of 26 with Bu3SnH–cat. AIBN in
toluene afforded the protected 6-deoxy trimannoside 27 (88%).
Deacylation of the protected trimannoside 27 using NaOMe
and methanol yielded the 6-deoxy trimannoside 11.
the transferase activity being detected is polyprenolmannose-
dependent. Thus, the disaccharide 7 can be used as a reagent to
detect polyprenol-mannose dependent mannosyltransferase(s).
Density centrifugation of a cell free extract of M. smegmatis
resulted in separation of polyprenolmannose synthase and
polyprenolmannose-dependent mannosyltransferases, suggest-
ing functional compartmentalization of enzymes involved in
mycobacterial glycolipid biosynthesis.26 Additionally, the 6-
deoxy di- and trisaccharides 8 and 11 also appear to act as
weak mannosyltransferase substrates. Ongoing studies aim to
elucidate the structures of the new products.
Conclusion
We have defined a rapid, stepwise route to a series of a-
1,6-linked hydrophobic oligomannosides. The donor 1 and
acceptor 2 are prepared from mannose pentaacetate 17 in 3
and 4 steps, respectively. Couplings are performed using highly
efficient NIS–TfOH thioglycosylations. The choice of benzoate
esters as protecting groups will allow future modification of the
synthetic route to install sensitive aglycons for bioconjugations.
Deoxygenation of the primary alcohols of the products is
achieved through iodination and reductive deoxygenation to give
the corresponding 6-deoxy analogues and in future introduction
of alternative substituents at this position will be possible.
The inclusion of a hydrophobic aglycon allowed for simple
purification of the deprotected compounds on reverse phase
silica and will assist in solvent partitioning of radiolabelled
products in biochemical assays, or the capture of radiolabelled
products on hydrophobic membranes. We shall report on the use
of these oligomannosides as tools for the study of mycobacterial
glycolipid biosynthesis in due course.
The robust capabilities of this synthetic approach were
demonstrated through the synthesis of the 6-hydroxy and 6-
deoxy tetramannosides 14 and 15. The primary alcohol 12 was
coupled with the glycosyl donor 2, again using NIS–TfOH, to
give the fully protected trimannoside 13 isolated in good yield
(91%). The silyl ether was removed from 13 using HCl, MeOH
and diethyl ether to yield the primary alcohol 16 (78%). The
alcohol 16 was globally deprotected in the usual fashion to
yield the tetramannoside 14 in a low but acceptable yield (30%).
Again, a three step procedure was used to give rise to the 6-
deoxy tetramannoside 15. The alcohol 16 was treated with Ph3P,
imidazole and iodine in toluene to afford the primary iodide 28
(92%). The iodide 28 was reduced using Bu3SnH–cat. AIBN in
toluene, to yield the 6-deoxy protected tetramannoside 29 (93%).
Finally, deacetylation using NaOMe and methanol afforded the
last of the targets, the 6-deoxy tetramannoside 15 (44%).
Several features of this efficient route merit comment. The
method used for selective deprotection of the TPS group,
HCl in MeOH–Et2O, is extremely robust and gave consistent
results throughout this sequence.25 It appears to be independent
of the chain length of the oligomers and in no cases were
appreciable amounts of methanolysis of any glycosidic linkage
observed. Glycosylation of the carbohydrate alcohols was also
efficient and, while this route was enacted only to the point of
tetrasaccharides as the octyl moiety loses efficiency in solvent
partitioning for longer oligomers, higher homologues should
be accessible without appreciable reductions in yield. It is
noteworthy that the inclusion of an octyl glycoside, originally
made with consideration of the ability of this group to assist in
solvent partitioning during biochemical assays, provides a useful
hydrophobic handle for C18 reverse phase silica chromatography
of the deprotected compounds.
Experimental
Thin layer chromatography (TLC) was performed with Merck
Silica Gel 60 F254, using mixtures of petroleum spirits–ethyl
acetate unless otherwise stated. Detection was effected by either
charring in a mixture of 5% sulfuric acid–MeOH and/or by
visualization in UV light. NMR spectra were obtained on a
Unity 400 machine (Melbourne, Australia). J values are given
in Hz. Superscript
A, B, C, D
refer to carbohydrate rings labelled
from the reducing end for di-, tri- and tetrasaccharides. Flash
chromatography was performed according to the method of
Still et al. with Merck Silica Gel 60, using adjusted mixtures
of ethyl acetate–petroleum spirits unless otherwise stated.27
Fully deprotected compounds were purified by reverse phase
chromatography using C18 silica cartridges (900 mg, C18, Alltech
Associates). (CH2Cl)2 was dried over P2O5. Toluene was dried
over sodium metal. Solvents were evaporated under reduced
pressure using a rotary evaporator. Optical rotations were
obtained using a JASCO DIP-1000 polarimeter. [a]D values are
given in 10−1 cm2 g−1. The melting point was obtained using
an Electrothermal melting point apparatus and is uncorrected.
Elemental analyses were performed by C.M.A.S. (Belmont,
Victoria). High resolution mass spectra were performed by Sally
Duck at the Chemistry Department, Monash University.
1,2,3,4,6-Penta-O-acetyl-a-D-mannose 17
Sulfuric acid (2 drops) was added at 0 ◦C to a stirred mixture of
acetic anhydride (27 mL) and D-mannose (4.98 g, 27.8 mmol).
The mixture was stirred for 10 min at 0 ◦C and then allowed
to warm to room temperature and stirred for a further 30 min.
The mixture was then diluted with ice–water (100 mL), and the
organic phase extracted with EtOAc (100 mL). The extract was
washed with water (3 × 100 mL) and then sat. aq. NaHCO3. The
extract was dried (MgSO4) and the solvent evaporated under
reduced pressure to afford the pentaacetate 17 (9.64 g) as a pale
yellow oil, dH(399.7 MHz; CDCl3; Me4Si) 1.99, 2.04, 2.08, 2.15,
2.16 (15 H, s, Me), 4.02–4.06 (1 H, m, H5), 4.08 (1H, dd, J5,6
Preliminary studies have revealed that the di-, tri- and
tetrasaccharides 7, 10 and 14 all appear to act as substrates
for mannosyltransferases in a cell free M. smegmatis system
using radiolabelled GDP-mannose as substrate. The mannosyl-
transferase activity is amphomycin sensitive demonstrating that
1 9 8 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2

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2.4, J6,6 12.4, H6), 4.26 (1 H, dd, J5,6 5.2, J6,6 12.4, H6), 5.23–
5.34 (3 H, m, H2,3,4), 6.06 (1 H, d, J1,2 2.0, H1); dC(100.1 MHz;
d4-MeOH; MeOH) 20.59, 20.66, 20.72, 20.81 (5 C, CH3), 61.99,
65.40, 68.23, 68.65, 70.51 (5 C, C2,3,4,5,6), 90.51 (1 C, C1),
Octyl a-D-mannopyranoside 21
SnCl4 (2.92 mL, 24.9 mmol) was added to a mixture of
pentaacetate 17 (9.77 g, 25.1 mmol), CH2Cl2 (120 mL) and 1-
octanol (4.9 mL, 30.8 mmol) containing 4 A molecular sieves
˚
=
168.03, 169.48, 169.69, 169.95, 170.61 (5C, C O).
stirring at 0 ◦C. After 30 min the reaction was allowed to
warm to room temperature and left to stir for 19 h. The
mixture was filtered, washed with HCl (3 × 100 mL), aq.
NaHCO3 (100 mL) and brine solution (30 mL). The organic
extract was dried (MgSO4), and the solvent evaporated under
reduced pressure. The residue was dissolved in MeOH (30 mL)
and treated with a small piece of sodium metal. The solution
was stirred for 1 h at which stage TLC (17 : 2 : 1 EtOAc–
MeOH–H2O) indicated conversion to a more polar compound.
Dowex-50 resin (H+ form) was added to neutralize the reaction
and, following filtration, the solvent was evaporated from the
filtrate to give a pale yellow oil. This oil was purified by flash
chromatography (17 : 2 : 1 EtOAc–MeOH–H2O), to give the
tetraol 21 (2.43 g, 33% from mannose) as a yellow oil, [a]2D4 +57
(c 0.82 in MeOH); dH(399.7 MHz; d4-MeOH, MeOH) 0.89–
1.61 (15H, m, OCH2(CH2)6CH3), 3.41 (1 H, m, OCH2CH2),
3.50–3.84 (6 H, m, H2,3,5,6,6,OCH2CH2), 3.62 (1 H, dd, J3,4
9.6, J4,5 9.2, H4), 4.74 (1 H, dd, J1,2 2.0, H1); dC(100.5 MHz;
d4-MeOH) 14.59, 23.85, 27.49, 30.53, 30.67, 30.74, 33.14 (7
C, OCH2(CH2)6CH3), 63.00, 68.70, 72.38, 72.79, 74.64 (6 C,
C2,3,4,5,6,OCH2CH2), 101.64 (1 C, C1).
4-Methylphenyl 1-thio-a-D-mannopyranoside 19
SnCl4 (0.75 mL) was added to a stirred mixture of thiocresol
(2.85 g, 22.9 mmol) and the crude pentaacetate 17 (8.54 g,
21.9 mmol) dissolved in CH2Cl2 (35 mL). The mixture was
stirred for 24 h, then was quenched with HCl (1 M, 100 mL),
and stirred for 10 min. The mixture was washed with HCl
(1 M, 2 × 100 mL), followed by aq. NaHCO3 (100 mL). The
organic extract was dried (MgSO4) and the solvent evaporated
under reduced pressure. Flash chromatography (35:65 EtOAc–
pet. spirits) afforded the tetraacetate 18 (6.64 g, 14.6 mmol) as a
yellow oil. This oil was dissolved in MeOH (30 mL) and treated
with a small piece of sodium metal. The solution was stirred
for 1 h until TLC (17 : 2 : 1 EtOAc–MeOH–H2O) indicated the
reaction was complete. Dowex-50 resin (H+ form) was added to
neutralize the solution (litmus paper) and, following filtration,
the solvent was evaporated from the filtrate to give a pale brown
residue. This residue was recrystallized to give the tetraol 19
(2.19 g, 27% from mannose) as white cubic crystals, mp 138.5–
◦
140 C (from MeOH–EtOAc–petroleum spirits); [a]1D9 +279 (c
Octyl 2,3,4-tri-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-
a-D-mannoside 3
0.7 in MeOH); dH(399.7 MHz; d4-MeOH, MeOH) 2.29 (3H, s,
CH3), 3.68–4.09 (4 H, m, H3,4,6,6), 4.04 (1 H, dd, J1,2 1.6, J2,3
2.8, H2), 4.85 (1 H, br s, H5), 5.35 (1 H, d, H1), 7.09–7.39 (4
H, m Ar); dC(100.1 MHz; d4-MeOH, MeOH) 21.09 (1 C, CH3),
62.53, 68.63, 73.08, 73.57, 75.44 (5 C, C2,3,4,5,6), 90.68 (1 C,
C1), 130.71, 132.00, 133.44, 138.84 (4 C, Ar); m/z (ESI) 309.0767
([M + Na]+ C13H18O5S requires 309.0773).
tert-Butylchlorodiphenylsilane (2.60 mL, 9.98 mmol) was added
to a mixture of the tetraol 21 (2.43 g, 8.32 mmol), and imidazole
(1.50 g, 20.8 mmol) in DMF (5 mL). The mixture was stirred
at 35 ◦C for 3 h, then was quenched with water (2 mL) and
stirred for 10 min. EtOAc (30 mL) was added and the mixture
washed with water (3 × 30 mL), 1 M HCl (40 mL), and aq.
NaHCO3 (40 mL). The organic extract was dried (MgSO4) and
the solvent evaporated under reduced pressure. To the residue
BzCl (4.35 mL, 37.4 mmol), pyridine (6.05 mL, 74.9 mmol)
and catalytic DMAP (40 mg) were added with stirring at
room temperature. The mixture was stirred for 18 h and then
was quenched with water (2 mL) and stirred for a further
10 min. The organic phase was extracted with EtOAc (30 mL)
and washed with water (3 × 30 mL) and K2CO3. solution
(0.5 M). The organic phase was dried (MgSO4) and the solvent
evaporated under reduced pressure. Flash chromatography (8 :
92 EtOAc–pet. spirits) yielded a residue, which was washed with
aq. K2CO3 solution (0.5 M) until TLC indicated no benzoic
acid was present. The solvent was evaporated to afford the
silyl ether 3 (3.80 g, 55%) as a yellow oil, [a]2D0 −60 (c 0.8 in
CHCl3); dH(399.7 MHz; CDCl3; Me4Si) 0.87–1.72 (15 H, m,
OCH2(CH2)6CH3), 1.04 (9 H, s, t-butyl), 3.53 (1 H, ddd, J
6.4, 9.2, 13.2, OCH2CH2), 3.81 (1 H, ddd, J 6.8, 9.2, 14.0,
OCH2CH2), 3.84 (1 H, dd, J5,6 1.6, J6,6 11.2, H6), 3.91 (1 H, dd,
4-Methylphenyl 2,3,4-tri-O-benzoyl-6-O-(tert-butyldiphenyl-
silyl)-1-thio-a-D-mannoside 1
tert-Butylchlorodiphenylsilane (1.19 mL, 4.51 mmol) was added
to a mixture of the tetraol 19 (0.994 g, 3.47 mmol) and imidazole
(0.63 g, 8.69 mmol) in DMF (2.0 mL). The mixture was stirred
at 35 ◦C for 3 h then was quenched with water (5 mL) and stirred
for 10 min. The mixture was diluted with EtOAc (30 mL) and
washed sequentially with water (3 × 30 mL), HCl (1 M, 40 mL),
and sat. aq. NaHCO3 (40 mL). The organic extract was dried
(MgSO4) and the solvent evaporated under reduced pressure.
To the syrupy residue benzoyl chloride (1.81 mL, 15.6 mmol),
pyridine (2.52 mL, 31.2 mmol) and catalytic DMAP (20 mg)
were added. The mixture was stirred for 18 h and then quenched
with water (2 mL) and stirred for a further 10 min. The mixture
was diluted with EtOAc (30 mL) and washed with water (3 ×
30 mL) and aq. K2CO3 solution (0.5 M). The organic phase
was dried (MgSO4) and the solvent evaporated under reduced
pressure. Flash chromatography (8 : 92 EtOAc–pet. spirits)
yielded a residue, which was washed with aq. K2CO3 solution
(0.5 M) until TLC indicated no benzoic acid was present. The
solvent was evaporated to afford the silyl ether 1 (1.36 g, 49%)
as a yellow oil, [a]1D9 −39 (c 0.6 in CHCl3) (Found: C, 71.75; H,
5.70. C50H48O8SSi requires C, 71.74; H, 5.78%); dH (300 MHz;
CDCl3; Me4Si) 1.04 (9 H, s, t-butyl), 2.33 (3 H, s, ArCH3), 3.85
(1 H dd, J5,6 1.6, J6,6 11.6, H6), 3.94 (1 H, dd, J5,6 4.0, H6), 4.69
(1 H, br d, H5), 5.73 (1 H, d, J1,2 0.8, H1), 5.80 (1 H, dd, J2,3
3.2, J3,4 10.4, H3), 5.97 (1 H, dd, H2), 6.26 (1 H, dd, J4,5 10.0,
H4), 7.08–8.17 (29 H, Ar, Ph); dC(100.5 MHz; CDCl3; Me4Si)
9.15 (1 C, (CH3)3C), 21.12 (1 C, ArCH3), 26.54 (3 C, (CH3)3C),
60.36, 62.31, 66.59, 70.96, 72.55 (5 C, C2,3,4,5,6), 86.43 (1 C,
J
5,6 4.4, J6,6 11.2, H6), 4.15 (1 H, br d, H5), 5.09 (1 H, d, J1,2 1.7,
H1), 5.69 (1 H, dd, J2,3 3.2, H2), 5.85 (1 H, dd, J3,4 10.4, H3), 6.10
(1 H, dd, J4,5 10.0, H4), 7.14–8.17 (25 H, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 14.09, 19.17, 22.65, 26.14, 26.52, 26.60, 29.24,
29.40, 31.81 (9 C, OCH2(CH2)6CH3, (CH3)3C), 62.69, 66.78,
68.32, 70.72, 70.88, 71.37 (6 C, C2,3,4,5,6,OCH2CH2), 97.45
(1 C, C1), 127.51–135.65 (25 C, Ph), 165.28, 165.59, 165.62 (3
+
=
C, C O); m/z (ESI) 865.3745 (C51H58O9Si [M + Na] requires
865.3748).
Octyl 2,3,4-tri-O-benzoyl-a-D-mannopyranoside 2
Acetyl chloride (6.13 mL) was added dropwise to MeOH
(150 mL) with stirring and the solution cooled to 20 ◦C. The
silyl ether 3 (3.81 g, 4.61 mmol) was dissolved in diethyl ether
(150 mL) and this was then added to the methanol solution. The
mixture was stirred for 4 days. The solvent was evaporated and
C1), 127.53–138.00 (24 C, Ar, Ph), 165.21, 165.45, 165.54 (3 C,
+
=
C O); m/z (ESI) 859.2733 ([M + Na] C50H48O8SSi requires
859.2737).
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2
1 9 8 7

View Article Online
the residue co-evaporated with toluene under reduced pressure.
The crude product was purified using flash chromatography (15 :
85 then 20 : 80 then 25 : 75 EtOAc–pet. spirits) yielding the
alcohol 2 (1.62 g, 58%) as a pale yellow oil, [a]2D0 −115 (c 0.8
in CHCl3) (Found: C, 69.53; H, 6.70. C35H40O9: C, 69.52; H,
6.67%); dH(399.7 MHz; CDCl3; Me4Si) 0.85–1.80 (15 H, m,
OCH2(CH2)6CH3), 2.69 (1 H, t, JOH,6 6.8, OH), 3.55 (1 H, ddd, J
6.8, 9.6, 13.2, OCH2CH2), 3.77–3.86 (3 H, m, H6,6, OCH2CH2),
4.07 (1 H, br d, H5), 5.10 (1 H, d, J1,2 1.2, H1), 5.68 (1 H, dd, J2,3
3.2, H2), 5.84 (1 H, dd, J3,4 10.0, J4,5 10.0, H4), 6.00 (1 H, dd, H3),
7.23–8.12 (15 H, m, Ph); dC(100.5 MHz; CDCl3; Me4Si) 14.06,
22.61, 26.07, 29.18, 29.33, 31.78 (7 C, OCH2(CH2)6CH3), 61.34,
67.33, 68.61, 69.69, 70.72, 70.81 (6 C, C2,3,4,5,6,OCH2CH2),
5.61. C132H124O33Si requires C, 69.95; H, 5.51%); dH(399.7 MHz;
CDCl3; Me4Si) 0.83–1.71 (15 H, m, OCH2(CH2)6CH3), 0.99 (9
H, s, t-butyl), 3.76, 4.19, 4.33, 4.53 (4 H, 4 br d, H5A,5B,5C,5D),
3.39–4.20 (10 H, m, H(6,6)A,(6,6)B,(6,6)C,(6,6)D,OCH2CH2),
4.86 (1 H, d, J1,2 1.6), 4.95 (1 H, d, J1,2 1.6), 5.15 (1 H, d, J1,2
1.6), 5.24 (1 H, d, J1,2 1.2, H1A,1B,1C,1D), 5.65 (1 H, dd, J1,2
1.6, J2,3 3.2), 5.76 (1 H, dd, J1,2 2.0, J2,3 3.2), 5.79 (1 H, dd, J1,2
1.6, J2,3 3.6), 5.94 (1 H, dd, J1,2 1.2, J2,3 2.4, H2A,2B,2C,2D), 5.89
(1 H, dd, J2,3 3.2, J3,4 10.4), 5.92 (1 H dd, J2,3 4.0, J3,4 12.0),
5.97 (1 H, dd, J2,3 3.2, J3,4 10.0), 6.07 (1 H, dd, J2,3 3.6, J3,4
10.4, H3A,3B,3C,3D), 6.11 (1 H, dd, J3,4 9.6, J4,5 10.0), 6.11 (1
H, dd, J3,4 10.8, J4,5 10.0), 6.21 (1 H, dd, J3,4 10.0, J4,5 10.0),
6.25 (1 H, dd, J3,4 10.0, J4,5 10.4, H4A,4B,4C,4D), 7.05–8.21
(70 H, m, Ph); dC(100.5 MHz; CDCl3; Me4Si) 14.32, 19.30,
22.86, 26.36, 29.45, 29.68, 32.04 (7 C, OCH2(CH2)6CH3),
26.73 (4 C, t-butyl), 61.97, 65.75, 66.01, 66.20, 66.57, 66.92,
68.84, 69.53, 69.60, 70.38, 70.56, 70.88, 71.08, 71.30 (21 C,
C(2,3,4,5,6)A,(2,3,4,5,6)B,(2,3,4,5,6)C,(2,3,4,5,6)D,OCH2CH2 ),
97.79, 97.97, 98.10, 98.20 (4 C, C1A,1B,1C,1D), 127.64–135.86
(84 C, Ph), 154.41, 165.46, 165.60, 165.69, 165.92, 166.00 (12 C,
97.63 (1 C, C1), 128.22–133.58 (18 C, Ph), 165.43, 165.51, 166.46
+
=
(3 C, C O); m/z (ESI) 627.2559 (C35H40O9 [M + Na] requires
627.2570).
General procedure for glycosylation reactions using donor 1 and
alcohols 6 and 12
TfOH was added to a mixture of the donor 1, the alcohol accep-
=
C O).
◦
˚
tor, NIS and 4 A molecular sieves in dry dichloroethane at 0 C
under N2. The solution was stirred for 5 min during which time
the mixture went dark purple and TLC showed consumption of
starting materials. The reaction was quenched with aq. NaHCO3
and 0.5 M sodium thiosulfate. The solution was filtered and
the organic phase extracted with dichloromethane and dried
(MgSO4). The solvent was evaporated under reduced pressure,
and the residue purified by flash chromatography to afford the
protected oligomannosides.
General procedure for removal of the tert-butyldiphenylsilyl
group from 5, 9 and 13
Acetyl chloride (1.3 mL mmol−1) was added dropwise to MeOH
(33 mL mmol−1) with stirring and the solution cooled to
20 ◦C. The silyl ether was dissolved in diethyl ether (33 mL
mmol−1) and this solution was added to the methanol solution
and the mixture was stirred for 4 days. The solvent was
evaporated and the residue co-evaporated with toluene. The
residue was purified by flash chromatography.
Octyl (2,3,4-tri-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-a-D-
mannopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyra-
nosyl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranoside)
9.
Octyl (2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,
4-tri-O-benzoyl-a-D-mannopyranoside) 6. TfOH (5 ll) was
added to a mixture of the donor 1 (2.65 g, 3.86 mmol), the
acceptor 2 (2.80 g, 4.63 mmol), NIS (1.22 g, 5.41 mmol) and
TfOH (8 lL) was added to a mixture of the donor 1 (294 mg,
369 lmol), the alcohol 6 (330 mg, 306 lmol), NIS (94 mg,
˚
418 lmol) with 4 A molecular sieves in dry dichloroethane
(10 mL), with the solution treated as for the general procedure
above. The product was purified by flash chromatography (25 :
75 then 30 : 70 then 35 : 65 EtOAc–pet. spirits) affording the
protected trimannoside 9 (486 mg, 90%) as a clear oil, [a]D19
−71 (c 0.8 in CHCl3) (Found: C, 70.29; H, 5.81. C105H102O25Si
requires C, 70.38; H, 5.74%); dH(399.7 MHz; CDCl3; Me4Si)
0.79–1.74 (15 H, m, OCH2(CH2)6CH3), 1.01 (9 H, s, t-butyl),
4.05, 4.25, 4.54 (3 H, 3 br d, H5A,5B,5C), 3.32–4.33 (8 H, m,
H(6,6)A,(6,6)B,(6,6)C,OCH2CH2), 4.84, 5.15, 5.21 (3 H, 3 br s,
H1A,1B,1C), 5.54, 5.80, 5.93 (3 H, 3 m, H2A,2B,2C), 5.86 (1 H,
dd, J2,3 3.0, J3,4 10.5), 5.98 (1 H, dd, J2,3 3.6, J3,4 9.9), 6.07 (1
H, dd, J2,3 3.0, J3,4 10.2, H3A,3B,3C), 5.98 (1 H, dd, J3,4 9.9, J4,5
9.9), 6.14 (1 H, dd, J3,4 9.9, J4,5 9.9), 6.30 (1 H, dd, J3,4 10.2, J4,5
10.2, H4A,4B,4C), 7.06–8.24 (55 H, Ph); dC(100.5 MHz; CDCl3;
Me4Si) 14.06, 19.06, 22.60, 26.09, 26.52, 29.17, 29.40, 31.77
(9 C, OCH2(CH2)6CH3, (CH3)3C), 60.33, 62.06, 65.55, 66.19,
66.63, 66.82, 68.58, 69.33, 69.42, 70.35, 70.41, 70.59, 70.65,
71.16 (16 C, C(2,3,4,5,6)A,(2,3,4,5,6)B,(2,3,4,5,6)C,OCH2CH2),
97.20, 97.76, 97.84 (3 C, C1A,1B,1C), 127.43–135.61 (66 C, Ph),
165.11, 165.13, 165.21, 165.26, 165.43, 165.48, 165.57, 165.76 (9
4 A molecular sieves in dry dichloroethane at 0 ◦C under
˚
N2. The solution was stirred for 5 min, during which time
the mixture went deep purple, and TLC showed consumption
of the starting material. The reaction was quenched with aq.
NaHCO3 and 0.5 M sodium thiosulfate. The mixture was filtered
and the organic phase extracted with dichloromethane and
dried (MgSO4). The solvent was evaporated under reduced
pressure to give a residue that could not be resolved by flash
chromatography so the crude disaccharide was desilylated as
for the general procedure above. This yielded the alcohol 6
(2.95 g, 71%) as a colourless oil, [a]2D0 −99 (c 0.8 in CHCl3)
(Found: C, 69.06; H, 5.84. C62H62O17 requires C, 69.00; H,
5.79%); dH(399.7 MHz; CDCl3; Me4Si) 0.81–1.82 (15 H, m,
OCH2(CH2)6CH3), 2.61 (1 H, t, JOH,6 7.2 OH), 3.51–3.66 (3
H, m, H6A,6A,OCH2CH2), 3.79 (1 H, dd, J5,6 2.0, J6,6 11.2, H6B),
3.92 (1 H, ddd, J 6.8, 9.6, 13.6, OCH2CH2), 4.02–4.10 (2 H,
m, H5A,6B), 4.39 (1 H, dd, H5B), 5.12 (1 H, d, J1,2 1.2), 5.17
(1 H, J1,2 1.6, H1A,1B), 5.75–5.77 (2 H, m, H2A,2B), 5.83 (1
H, dd, J3,4 10.0, J4,5 10.0), 6.05 (1 H, dd, J3,4 10.4, J4,5 10.0,
H4A,4B), 5.94 (1 H, dd, J2,3 3.60, J3,4 10.0), 6.07 (1 H, dd, J2,3
3.2, J3,4 10.0, H3A,3B), 7.25–8.20 (30 H, m, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 14.06, 22.63, 26.16, 29.24, 29.43, 29.64, 31.80 (7
C, OCH2(CH2)6CH3), 60.95, 66.64, 67.07, 68.71, 69.32, 70.30,
70.34, 70.66, 70.92 (11 C, C(2,3,4,5,6)A,(2,3,4,5,6)B,OCH2CH2),
97.63, 97.74 (2 C, C1A,1B), 128.23–133.61 (36 H, Ph), 165.08,
C, C O); m/z (ESI) 1813.6374 (C105H102O25 [M + Na]+ requires
=
1813.6377).
Octyl (2,3,4-tri-O-benzoyl-6-O-(tert-butyldiphenylsilyl)-a-D-
mannopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyra-
nosyl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-
(2,3,4-tri-O-benzoyl-a-D-mannopyranoside) 13. TfOH (10 lL)
was added to a mixture of the donor 1 (229 mg, 0.29 mmol),
the alcohol 12 (373 mg, 0.24 mmol), NIS (76 mg, 0.34 mmol)
=
165.28, 165.48, 165.64, 166.55 (6 C, C O).
Octyl (2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,
4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,4-tri-O-ben-
zoyl-a-D-mannopyranoside) 12. The protected trimannoside 9
(293 mg, 0.163 mmol) was treated as for the general procedure
above. Flash chromatography (30 : 70 then 35 : 65 then 40
: 60 EtOAc–pet. spirits) afforded the trimannoside alcohol
12 (251 mg, 70%) as an oil, [a]1D8 −75 (c 0.8 in CHCl3)
˚
and 4 A molecular sieves in dry dichloroethane (20 mL). The
solution was treated as for the general procedure above. Flash
chromatography (35 : 65 then 40 : 60 EtOAc–pet. spirits)
afforded the protected tetramannoside 13 (499 mg, 91%) as
a yellow oil, [a]1D4 −62 (c 1.3 in CHCl3) (Found: C, 69.95; H,
1 9 8 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2

View Article Online
(Found, C, 68.95; H, 5.49. C89H84O25 requires C, 68.80; H,
68.95%); dH(399.7 MHz; CDCl3; Me4Si) 0.83–1.77 (15 H, m,
OCH2(CH2)6CH3), 2.26 (1 H, br s, OH), 3.43–3.66 (4 H, m,
OCH2CH2,H(6,6)C), 3.82–3.95 (4 H, m, H5A,6A,(6,6)B), 4.24
(1 H, dd, J5,6 4.4, J6,6 10.8, H6A), 4.28 (1 H, dd, J5,6 4.8), 4.52
(1 H, dd, J4,5 10.0, J5,6 2.8, H5B,5C), 4.88 (1 H, d, J1,2 2.0),
5.16 (1 H, d, J1,2 1.6), 5.20 (1 H, d, J1,2 1.6. H1A,1B,1C), 5.57
(1 H, br d), 5.80 (1 H, br s), 5.91 (1 H br s, H2A,2B,2C), 5.77
(1 H, dd, J3,4 10.0, J4,5 10.0), 6.24 (1 H, dd, J3,4 10.0, J4,5 10.0,
H4A,4B), 5.98 (1 H, dd, J2,3 2.4, J3,4 10.4, H3A), 6.02–6.07 (3
H, m, H3B,3C,4C), 7.22–8.23 (45 H, m, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 14.06, 22.62, 26.16, 29.23, 29.44, 29.65, 31.80
(7 C, OCH2(CH2)CH3), 60.90, 65.91, 66.37, 66.72, 66.77,
67.01, 68.67, 69.30, 69.33, 69.49, 70.28, 70.54, 70.67, 70.86 (16
C, C(2,3,4,5,6)A, (2,3,4,5,6)B, (2,3,4,5,6)C, OCH2CH2), 97.53,
97.77, 97.88 (3 C, C1A,1B,1C), 128.25–133.61 (54 C, Ph), 165.13,
165.15, 165.17, 165.41, 165.46, 165.48, 165.56, 165.74, 166.55 (9
3.95 (1 H, ddd, OCH2CH2), 4.07 (1 H, dd, H5), 5.10 (1 H, d,
J1,2 1.6, H1), 5.68 (1 H, dd, J2,3 3.2, H2), 5.76 (1 H, dd, J3,4 9.6,
J
4,5 10.0, H4), 5.90 (1 H, dd, H3); dC(100.5 MHz; CDCl3; Me4Si)
5.10 (1 C, C6), 14.32, 22.86, 26.33, 29.43, 29.51, 29.58, 32.02
(7 C, OCH2(CH2)6CH3), 68.94, 69.81, 70.25, 70.80, 70.98 (5 C,
C2,3,4,5,OCH2CH2), 97.74 (1 C, C1), 128.45–133.76 (18 C, Ph),
=
165.56, 165.66, 165.75 (3 C, C O).
Octyl (2,3,4-tri-O-benzoyl-6-deoxy-6-iodo-a-D-mannopyrano-
syl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranoside) 24.
A
mixture of the alcohol 6 (304 mg, 316 lmol), imidazole (62 mg,
859 lmol) and Ph3P (135 mg, 514 lmol) in toluene (5 mL)
was treated with iodine (130 mg, 512 lmol) as for the general
procedure above. Flash chromatography (15 : 85 then 20 : 80
then 25 : 75 EtOAc–pet. spirits) afforded the iodide 24 (0.352 g,
94%) as a yellow oil, [a]2D0 −80 (c 0.8 in CHCl3) (Found: C, 62.64;
H, 5.09. C62H61IO16 requires C, 62.63; H, 5.17%); dH(399.7 MHz;
CDCl3; Me4Si) 0.85–1.70 (15 H, m, OCH2(CH2)6CH3), 3.24 (2
H, m, H(6,6)B), 3.63 (1 H, ddd, J 6.4, 13.2), 3.93 (1 H, ddd,
J 6.8, 9.2, OCH2CH2), 3.81 (1 H, br d,), 4.08 (1 H, dd, J5,6
6.0, J6,6 10.0, H(6,6)A), 4.24 (1 H, dd, J4,5 10.8 J5,6 5.6), 4.41
(1 H, dd, J4,5 10.0, J5,6 5.2, H5A,5B), 5.13, 5.17 (2 H, 2 br s,
H1A,1B), 5.74 (1 H, dd, J3,4 10.0, J4,5 10.0), 6.07 (1 H, dd, J3,4
10.0, J4,5 10.0, H4A,4B), 5.75–5.77 (2 H, m, H2A,2B), 5.94–5.99
(2 H, m, H3A,3B), 7.25–8.19 (30 H, m, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 4.55 (1 C, C6B), 14.08, 22.66, 26.19, 29.28, 29.45,
31.83 (7 C, OCH2(CH2)6CH3), 66.55, 67.05, 68.74, 69.11, 69.94,
70.27, 70.57, 70.63 (10 C, C(2,3,4,5,6)A,(2,3,4,5)B, OCH2CH2),
97.42, 97.61 (2 C, C1A,1B), 128.25–133.54 (36 C, Ph), 165.01,
C, C O); m/z (ESI) 1575.5171 (C89H84O25 [M + Na]+ requires
=
1575.51990.
Octyl (2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,
4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,4-tri-O-ben-
zoyl-a-D-mannopyranosyl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-man-
nopyranoside) 16. The protected tetramannoside 13 (389 mg,
17 lmol) was treated as for the general procedure above.
Flash chromatography (40 : 60 then 45 : 65 then 50 : 50
EtOAc–pet. spirits) afforded the tetramannoside alcohol
16 (270 mg, 78%) as an oil, [a]1D5 −67 (c 0.9 in CHCl3)
(Found: C, 68.79; H, 5.33. C116H106O33 requires C, 68.70; H,
5.27%); dH(399.7 MHz; CDCl3; Me4Si) 0.82–1.82 (15 H, m,
OCH2(CH2)6CH3), 2.62 (1 H, br s, OH), 3.37–3.98 (10 H,
m, H(6,6)A,(6,6)B,(6,6)C,(6,6)D,OCH2CH2), 4.23 (1 H br dd),
4.28–4.36 (2 H, m), 4.54 (1 H, dd,J4,5 10.4,J5,6 2.8, H5A,5B,5C,5D),
4.88, 4.99, 5.17, 5.25 (4 H, 4 br d, H1A,1B,1C,1D), 5.65 (1 H, br
dd, H2A), 5.71–5.76 (2 H, m, H2B,3A), 5.68 (1 H, dd,J1,2 1.6,J2,3
3.2, H2C), 5.91–5.94 (2 H, m, H2D,3B), 5.97 (1 H, dd,J2,3 3.2,J3,4
10.0), 6.04 (1 H, dd,J2,3 3.2, J3,4 10.0 H3C,3D), 6.07–6.11 (2 H,
m), 6.14 (1 H, dd,J3,4 10.0,J4,5 10.0), 6.24 (1 H, dd,J3.4 10.0,J4,5
10.0, H4A,4B,4C,4D), 7.22–8.21 (60 H, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 14.29, 16.82, 22.83, 26.35, 29.42, 29.67, 32.01
(7 C, OCH2(CH2)6CH3), 60.97, 66.11, 66.54, 66.93, 67.23,
68.85, 69.47, 69.59, 69.79, 70.38, 70.50, 70.55, 70.81, 70.87,
71.04 (21 C, C(2,3,4,5,6)A, (2,3,4,5,6)B, (2,3,4,5,6)C, (2,3,4,5,6)D,
OCH2CH2), 97.84, 97.97, 98.16, 98.21 (4 C, C1A,1B,1C,1D),
128.47–133.88 (72 C, Ph), 165.29, 165.39, 165.47, 165.54,
=
165.24, 165.53, 165.74, 165.65 (6 C, C O); m/z (ESI) 1211.2912
(C62H61IO16 [M + Na]+ requires 1211.2902).
Octyl (2,3,4-tri-O-benzoyl-6-deoxy-6-iodo-a-D-mannopyrano-
syl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-
(2,3,4-tri-O-benzoyl-a-D-mannopyranoside) 26. A mixture of
the alcohol 12 (159 mg, 100 lmol), imidazole (18.4 mg, 255 lmol)
and Ph3P (39.3 mg, 150 lmol) in toluene (5 mL) was treated
with iodine (38.1 mg, 150 lmol) as for the general procedure
above. Flash chromatography (15 : 85 then 20 : 80 then 25 : 75
EtOAc–pet. spirits) furnished the iodide 26 (144 mg, 87%) as a
yellow oil, [a]2D3 −63 (c 0.54 in CHCl3) (Found C, 64.29; H, 5.02.
C89H83IO24 requires C, 64.26; H, 5.03%); dH(399.7 MHz; CDCl3;
Me4Si) 0.81–1.79 (15 H, m, OCH2(CH2)6CH3), 3.20 (1 H, m,
OCH2CH2), 3.48 (1 H, br dd, H6A), 3.64 (1 H, m, OCH2CH2),
3.90 (1 H, br dd, H6A), 3.90–4.08 (4 H, H(6,6)B,(6,6)C), 4.26 (1
H, dd, J4,5 11.2, J5,6 4.8), 4.32 (1 H m), 4.52 (1 H, dd, J4,5 10.0,
J5,6 2.4, H5A,5B,5C), 4.90 (1 H, d, J1,2 1.2), 5.16 (1 H, d, J1,2 1.6),
5.22 (1 H, d, J1,2 1.2, H1A,1B,1C), 5.57 (1 H, dd, J1,2 1.6, J2,3
3.2), 5.80 (1 H, dd, J1,2 1.6, J2,3 3.2, H2A,2B), 5.92–5.95 (2 H, m,
H3A,2C), 5.99 (1 H, dd, J2,3 3.6, J3,4 10.4, H3B), 6.08–6.09 (2 H,
m, H4A,3C), 5.69 (1 H, dd, J3,4 9.6, J4,5 10.0), 6.27 (1 H, dd, J3,4
10.4, J4,5 10.0, H4B,4C), 7.22–8.24 (45 H, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 4.55 (1 C, C6C), 14.03, 22.60, 26.13, 29.19, 29.41,
29.44, 31.77 (7 C, OCH2(CH2)6CH3), 52.01, 65.84, 66.35, 66.69,
68.64, 69.08, 69.32, 69.42, 69.84, 70.17, 70.21, 70.48, 70.54,
70.62 (15 C, C(2,3,4,5,6)A,(2,3,4,5,6)B,(2,3,4,5)C,OCH2CH2),
97.14, 97.77, 97.88 (3 C, C1A,1B,1C), 128.22–133.50 (54 C, Ph),
165.02, 165.08, 165.15, 165.36, 165.43, 165.50, 165.52, 165.55,
=
165.66, 165.70, 165.79, 165.97, 166.9 (12 C, C O).
General procedure for the iodination of the primary alcohols 2, 6,
12 and 16
A mixture of the primary alcohol, imidazole and Ph3P in toluene
was distilled for 10 minutes to azeotropically remove excess
◦
water. The temperature was then reduced to 90 C and iodine
was added and the mixture stirred under nitrogen overnight.
MeOH (1 mL) was added and the mixture stirred for 30 min.
The organic solution was washed with water (3 × 20 mL),
0.25 M sodium thiosulfate (20 mL) and dried over MgSO4 and
the solvent removed under reduced pressure. The product was
purified by flash chromatography to give the iodide.
=
165.73 (9 C, C O).
Octyl 2,3,4-tri-O-benzoyl-6-deoxy-6-iodo-a-D-mannopyrano-
side 22. A mixture of the alcohol 2 (193 mg, 399 lmol),
imidazole (72 mg, 998 lmol) and Ph3P (157 mg, 599 lmol)
in toluene (10 mL) was treated with iodine (152 mg, 0.599 lmol)
as for the general procedure above. Flash chromatography (10 :
90 then 15 : 85 then 20 : 80 EtOAc–pet. spirits) gave the iodide
22 (196 mg, 86%) as a yellow gum, [a]1D5 −65 (c 0.7 in CHCl3)
(Found: C, 58.68; H, 5.47. C35H39IO8 requires C, 58.83; H,
5.50%); dH(399.7 MHz; CDCl3; Me4Si) 0.89–1.74 (15 H, m,
OCH2(CH2)6CH3), 3.37 (1 H, dd, J5,6 5.4, J6,6 10.8, H6), 3.47
(1 H, dd, J5,6 5.4, J6,6 10.8, H6), 3.58 (1 H, ddd, OCH2CH2),
Octyl (2,3,4-tri-O-benzoyl-6-deoxy-6-iodo-a-D-mannopyrano-
syl)-(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranosy)-(1→6)-(2,
3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,4-tri-O-ben-
zoyl-a-D-mannopyranoside) 28. A mixture of the alcohol 16
(279 mg, 138 lmol), imidazole (25.0 mg, 344 lmol) and Ph3P
(54.0 mg, 207 lmol) in toluene (10 mL) was treated with iodine
(53 mg, 207 lmol) as for the general procedure above. Flash
chromatography (40 : 60 then 45 : 55 then 50 : 50 EtOAc–pet.
spirits) afforded the iodide 28 (273 mg, 92%) as a clear gum, [a]D15
−55 (c 1.35 in CHCl3) (Found: C, 66.09; H, 5.03. C116H105IO32
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2
1 9 8 9

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requires C, 66.17; H, 4.95%); dH(399.7 MHz; CDCl3; Me4Si)
0.83–1.78 (15 H, m, OCH2(CH2)6CH3), 3.11–3.70 (2 H, m, H6A,
OCH2CH2), 3.48 (2 H, m, H6A,6B), 3.62 (1 H, m, OCH2CH2),
3.87–4.03 (5 H, m, H6B,(6,6)C,(6,6)D), 4.23–4.35 (3 H, m,
H5A,5B,5C), 4.53 (1 H, br dd, H5D), 4.88, 5.00, 5.16, 5.25 (4
H, s, H1A,1B,1C,1D), 5.66–5.71 (1 H, m, H2A), 5.69 (1 H, dd,
J3,4 9.6, J4,5 10.0, H4A), 5.74 (1 H, dd, J1,2 1.2, J2,3 3.2), 5.80
(1 H, dd, J1,2 1.6, J2,3 3.2), 5.94 (1 H, dd, J1,2 1.2, J2,3 3.2,
H2B,2C,2D), 5.95–5.99 (3 H, m), 6.08 (1 H, dd, J2,3 3.2, J3,4
10.0, H3A,3B,3C,3D), 6.13 (1 H, dd, J3,4 9.6, J4,5 10.0), 6.17 (1
H, dd, J3,4 10.0, J4,5 10.0), 6.25 (1 H, dd, J3,4 10.0, J4,5 10.4,
H4B,4C,4D), 7.23–8.24 (60 H, m, Ph); dC(100.5 MHz; CDCl3;
Me4Si) 4.79 (1 C, C6-I), 13.66, 14.32, 22.85, 26.38, 29.45, 29.68,
29.89, 32.03 (7 C, OCH2(CH2)6CH3), 66.08, 66.47, 66.88, 68.85,
69.34, 69.59, 69.81, 70.09, 70.32, 70.45, 70.57, 70.64, 70.80 (20
C, C(2,3,4,5,6)A,(2,3,4,5,6)B,(2,3,4,5,6)C,(2,3,4,5)D,OCH2CH2),
97.89, 97.97, 98.17 (4 C, C1A,1B,1C,1D), 128.47–133.78 (72 C,
Ph), 165.19, 165.64, 165.41, 165.48, 165.56, 165.69, 165.85,
29.47, 29.68, 31.85 (8 C, OCH2(CH2)6CH3,C6B), 66.56, 66.73,
67.15, 68.71, 69.40, 69.90, 70.37, 70.66, 70.75, 71.67 (10 C,
C(2,3,4,5,6)A,(2,3,4,5)B,OCH2CH2), 97.52, 97.66 (2 H, C1A,1B),
128.22–133.39 (36 C, Ph), 165.13, 165.39, 165.51, 165.54,
=
165.71, 165.80 (6 C, C O); m/z (ESI) 1085.3939 (C62H62O16
[M + Na]+ requires 1085.3936).
Octyl (2,3,4-tri-O-benzoyl-6-deoxy-a-D-mannopyranosyl)-
(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,
4-tri-O-benzoyl-a-D-mannopyranoside) 27. A solution of the
iodo trimannoside 26 (133 mg, 80 lmol) and Bu3SnH (32 lL,
118 lmol) and catalytic AIBN in toluene was treated as for the
general procedure above. Flash chromatography (20 : 80 then
25 : 75 then 30 : 70 EtOAc–pet. spirits) afforded the protected
deoxy dimannoside 27 (108 mg, 88%) as yellow oil, [a]1D8 −76
(c 0.8 in CHCl3) (Found: C, 69.37; H, 5.64. C89H84O24 requires
C, 69.52; H, 5.57%); dH(399.7 MHz; CDCl3; Me4Si) 0.83–1.78
(15 H, m, OCH2(CH2)6CH3), 1.13 (3 H, d, J5,6 6.4, H6C), 3.40
(1 H, br dd, J5,6 1.6, J6,6 10.8, H6A), 3.62 (1 H, m, OCH2CH2),
3.84–4.09 (4 H, m, H6A,(6,6)B,OCH2CH2), 4.26 (1 H, dd, J4,5
11.2, J5,6 6.4), 4.27–4.31 (1 H, m), 4.52 (1 H, dd, J4,5 10.0, J5,6
2.4, H5A,5B,5C), 4.77 (1H, br s), 5.16 (1 H, d, J1,2 1.6), 5.21 (1
H, d, J1,2 1.2, H1A,1B,1C), 5.55 (1 H, dd, J1,2 2.0, J2,3 3.2), 5.79
(1 H, dd, J1,2 2.0, J2,3 3.2), 5.92 (1 H, br d, H2A,2B,2C), 5.85
(1 H, dd, J2,3 3.2, J3,4 10.0), 5.98 (1 H, dd, J2,3 3.2, J3,4 10.0,
H3A,3B), 6.05–6.06 (2 H, m, H4A,3C), 5.59 (1 H, dd, J3,4 10.0,
J4,5 10.0), 6.25 (1 H, dd, J3,4 10.4, J4,5 10.0, H4B,4C), 7.22–8.23
(45 H, Ph); dC(100.5 MHz; CDCl3; Me4Si) 14.05, 17.37, 22.62,
26.15, 29.21, 29.43, 29.65, 31.79 (8 C, OCH2(CH2)6CH3,C6C),
60.35, 65.68, 66.30, 66.63, 66.75, 68.65, 69.34, 69.85, 70.32,
70.50, 70.58, 70.69, 71.57 (15 C, C(2,3,4,5,6)A, (2,3,4,5,6)B,
(2,3,4,5)C,OCH2CH2), 97.24, 97.76, 97.85 (1 C, C1A,1B,1C),
128.23–133.34 (54 C, Ph) 165.13, 165.17, 165.20, 165.42, 165.46,
=
165.99 (12 C, C O).
General procedure for tributyltin hydride reduction of iodides 22,
24, 26 and 28
A solution of the iodide and Bu3SnH in toluene with catalytic
AIBN (2–5 mg) was stirred under reflux overnight. The solvent
was removed under reduced pressure and the residue was
partitioned between MeCN and pet. spirits. The MeCN layer
was separated and washed with pet. spirits (5 × 20 mL). The
solvent was removed under reduced pressure and the product
was purified by flash chromatography to afford the protected
6-deoxy compounds.
Octyl 2,3,4-tri-O-benzoyl-6-deoxy-a-D-mannopyranoside 23.
The monomannoside iodide 22 (299 mg, 0.42 mmol) and
Bu3SnH (182 mg, 0.63 mmol) and catalytic AIBN in toluene
(15 mL) was treated as for the general procedure above.
Following partitioning between MeCN and pet. spirit, the pet.
spirit phase was extracted with additional MeCN (8 × 10 mL).
The solvent was evaporated from the MeCN phase under
reduced pressure. Flash chromatography (10 : 90 then 15 : 85
then 20 : 80 EtOAc–pet. spirits) afforded the protected deoxy
monomannoside 23 (186 mg, 76%) as a clear oil, [a]1D5 −115 (c
0.8 in CHCl3) (Found C, 71.46; H, 6.91. C35H40O8 requires C,
71.41; H, 6.85%); dH(399.7 MHz; CDCl3; Me4Si) 0.85–1.73 (15
H, m, OCH2(CH2)6CH3), 1.37 (3 H, d, J5,6 6.0, H6), 3.53 (1 H,
m, J 6.8, 9.59, 13.2, OCH2CH2), 3.69 (1 H, m, J 6.8, 9.6, 14.0,
OCH2CH2), 4.19 (1 H, ddd, J4,5 12.8, J5,6 6.4, H5), 5.00 (H 1, d,
H1), 5.66 (1 H, dd, J1,2 1.6, J2,3 3.2, H2), 5.67 (1 H, dd, J3,4 10.0,
J4,5 9.6, H4), 5.85 (1 H, dd, J2,3 3.6, J3,4 10.0, H3), 7.24–8.12 (15
H, m, Ph); dC(100.5 M, CDCl3) 14.35, 17.91, 22.90, 26.35, 29.48,
29.61, 29.44, 32.07 (8 C, OCH2(CH2)CH3, C6), 66.75, 68.68,
70.28, 71.20, 72.13 (5 C, C2,3,4,5,OCH2CH2), 97.71 (1 C, C1),
=
165.56, 165.75 (9 C, C O).
Octyl
(2,3,4-tri-O-benzoyl-6-deoxy-a-D-mannopyranosyl)-
(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,
4-tri-O-benzoyl-a-D-mannopyranosyl)-(1→6)-(2,3,4-tri-O-benzo-
yl-a-D-mannopyranoside) 29.
A
solution of the iodo
tetramannoside 28 (187 mg, 87 lmol) and Bu3SnH (38.0 mg,
13 lmol) and catalytic AIBN in toluene (10 mL) was treated
as for the general procedure above. Flash chromatography (30 :
70 then 35 : 65 then 40 : 60 EtOAc–pet. spirits) to afford
the protected deoxy tetramannoside 29 (162 mg, 93%) as a
clear gum, [a]1D7 −48 (c 0.49 in CHCl3) (Found: 69.30; H,
5.40. C116H106O32 requires C, 69.24; H, 5.31%); dH(399.7 MHz;
CDCl3; Me4Si) 0.83–1.76 (15 H, m, OCH2(CH2)6CH3), 1.03 (3
H, d, J5,6 6.4, C6D), 3.41–3.47 (2 H, m, H(6,6)A), 3.60 (1 H, m,
OCH2CH2), 3.79 (1 H, dd, J5,5 3.6, J6,6 11.2, H6B), 3.86–3.07
(m, 4 H, H6B,(6,6)C,OCH2CH2), 4.23 (1 H, br dd), 4.27–4.32 (2
H, m), 4.52–4.55 (dd, J4,5 10.0, J5,6 2.4, H5A,5B,5C,5D), 4.87 (1
H, br d), 4.88 (1 H, d, J1,2 0.8), 5.16 (1 H, d, J1,2 1.6), 5.24 (1
H, br d, H1A,1B,1C,1D), 5.59 (1 H, dd, J3,4 10.0, J4,5 9.6, H4A),
5.65 (1 H, dd, J1,2 1.6, J2,3 2.8), 5.72 (1 H, dd, J1,2 1.6, J2,3 3.2),
5.79 (dd, J1,2 2.0, J2,3 3.2, H2A,2B,2C), 5.88 (1 H, dd, J2,3 3.2, J3,4
10.0, H3A), 5.92–5.99 (3 H, m, H2D,3B,3C), 6.09–6.12 (2 H, m,
H3D,4B), 6.15 (1 H, dd, J3,4 10.0, J4,5 10.4), 6.26 (1 H, dd, J3,4
10.4, J4,5 10.0. H4C,4D), 7.22–8.22 (60 H, m, Ph); dC(100.5 MHz;
CDCl3; Me4Si) 14.32, 17.44, 22.86, 26.38, 29.46, 29.69, 29.91,
32.05 (8 C, OCH2(CH2)6CH3, C6D), 66.55, 66.82, 66.91, 68.85,
69.29, 69.63, 70.18, 70.38, 70.54, 70.65, 70.83, 71.69 (20 C,
C(2,3,4,5,6)A, (2,3,4,5,6)B, (2,3,4,5,6)C, (2,3,4,5)D, OCH2CH2),
97.81, 97.97, 98.16 (4 C, C1A,1B,1C,1D), 128.48–133.56 (72 C,
Ph), 165.29, 165.41, 165.45, 165.50, 165.59, 165.71, 165.82,
=
128.46–133.64 (18 C, Ph), 165.72, 165.85, 166.01 (3 C, C O).
Octyl
(2,3,4-tri-O-benzoyl-6-deoxy-a-D-mannopyranosyl)-
25. The
(1→6)-(2,3,4-tri-O-benzoyl-a-D-mannopyranoside)
iodide 24 (250 mg, 211 lmol) and Bu3SnH (85 lL, 316 lmol)
and catalytic AIBN in toluene was treated as for the general
procedure above. Flash chromatography (20 : 80 then 25 : 75
then 30 : 70 EtOAc–pet. spirits) afforded the protected deoxy
dimannoside 25 (0.176 g, 79%) as yellow oil, [a]2D0 −93 (c 0.7 in
CHCl3) (Found: C, 70.31; H, 6.04. C62H62O16 requires C, 70.04;
H, 5.88%); dH(399.7 MHz; CDCl3; Me4Si) 0.84–1.79 (15 H, m,
OCH2(CH2)6CH3), 1.18 (3 H, d, J5,6 6.4, H6B), 3.63 (1 H, ddd,
OCH2CH2), 3.75 (1 H. br d), 4.07 (1 H, dd, J5,6 5.6, J6,6 10.8,
H(6,6)A), 3.93 (1 H, ddd, OCH2CH2), 4.15 (1 H, dd, J4,5 9.6, J5,6
6.0), 4.39 (1 H, m, H5A,5B), 5.06, 5.12 (2 H, 2 br s, H1A,1B), 5.64
(1 H, dd, J3,4 10.0, J4,5 10.0), 6.03 (1 H, dd, J3,4 9.6, J4,5 10.4,
H4A,4B), 5.74 (2 H, m, H2A,2B), 5.89 (1 H, dd, J2,3 3.2, J3,4 10.0),
5.94 (1 H, dd, J2,3 3.2, J3,4 10.0, H3A,3B), 7.26–8.19 (30 H, Ph);
dC(100.5 MHz; CDCl3; Me4Si) 14.08, 17.43, 22.67, 26.21, 29.30,
=
166.00, 166.06 (9 C, C O).
General method for global deprotection of 6, 12, 16, 23, 25, 27
and 29
The protected oligomannoside was dissolved in MeOH and
treated with a small piece of sodium metal. The solution
1 9 9 0
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 9 8 2 – 1 9 9 2

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was stirred for 1–4 h until TLC (7 : 2 : 1 EtOAc–MeOH–
H2O) indicated the reaction was complete. Dowex-50 resin
(H+ form) was added to neutralize the reaction. Following
filtration, the filtrate was treated with Amberlite IRA 400 (OH−
form), the solvent evaporated and the residue purified by flash
chromatography. Following this a small portion was purified by
C18 reverse phase chromatography (100% H2O to 100% MeOH).
Octyl
(6-deoxy-a-D-mannopyranosyl)-(1→6)-(a-D-manno-
pyranoside) 8. The protected deoxy dimannoside 25 (170 mg,
160 lmol) was treated as for the general procedure above. Flash
chromatography (9 : 1 MeOH–EtOAc then 17 : 2 : 1 then 7 :
2 : 1 EtOAc–MeOH–H2O) yielded the deoxy dimannoside 8
(53.9 mg, 77%) as a yellow gum, [a]1D5 +62 (c 1.1 in MeOH);
dH(399.7 MHz; d4-MeOH, MeOH) d 0.89–1.59 (15 H, m,
OCH2(CH2)6CH3), 1.25 (3 H, d, J5,6 6.4, H6B), 3.31 (2 H, m,
OCH2CH2), 3.35–3.86 (10 H, H(2,3,4,5,6,6)A,(2,3,4,5)B), 4.71
(1 H, d, J1,2 1.2), 4.74 (1 H, d, J1,2 1.2, H1A,1B); dC(100.5 MHz,
d4-MeOH) 14.59, 18.16, 22.87, 27.57, 30.55, 30.66, 30.76, 33.14
(8 C, OCH2(CH2)6CH3,C6B), 67.52, 68.70, 69.74, 72.32, 72.57,
73.01, 73.22, 74.18 (10 C, C(2,3,4,5,6)A,(2,3,4,5,6)B,OCH2CH2),
101.53, 101.73 (2 C, C1A,1B); m/z (ESI) 461.2360 (C20H38O10
[M + Na]+ requires 461.2363).
Octyl (a-D-mannopyranosyl)-(1→6)-(a-D-mannopyranoside)
7. The dimannoside alcohol 6 (0.153 g, 153 lmol) was treated
as for the general procedure above. Flash chromatography (9 : 1
MeOH–EtOAc then 17 : 2 : 1 then 7 : 2 : 1 EtOAc–MeOH–
H2O) afforded the dimannoside 7 (41.7 mg, 60%) as a pale
yellow oil, [a]D18 +50 (c 1.2 in MeOH) (lit.,17,24 +27.3, +55.6
(H2O)); dH(399.7 MHz; d4-MeOH; MeOH) 0.90–1.60 (15 H,
m, OCH2(CH2)6CH3), 3.31–3.44 (2 H, m, OCH2CH2), 3.64–
3.93 (12 H, m, H(2,3,4,5,6,6)A, (2,3,4,5,6,6)B), 4.72, 4.83 (2
H, 2 br s, H1A,1B); dC(100.5 MHz, d4-MeOH) 14.59, 23.88,
27.58, 30.56, 30.68, 30.77, 33.16 (7 C, OCH2(CH2)6CH3),
67.53, 68.73, 72.26, 72.34, 72.79, 72.99, 73.23, 74.46 (11
C, C(2,3,4,5,6)A,(2,3,4,5,6)B,OCH2CH2), 101.51, 101.75 (2 C,
C1A,1B); m/z (ESI) 477.4 (C20H38IO11 [M + Na]+ requires 477.2).
Octyl
(6-deoxy-a-D-mannopyranosyl)-(1→6)-(a-D-manno-
pyranosyl)-(1→6)-(a-D-mannopyranoside) 11. The protected
deoxy trimannoside 27 (108 mg, 70 lmol) was treated as for the
general procedure above. Flash chromatography (9 : 1 then 17 :
2 : 1 then 7 : 2 : 1 EtOAc–MeOH–H2O) afforded the deoxy
trimannoside 11 (27.8 mg, 66%) as an opaque yellow gum, [a]D20
+66 (c 0.7 in MeOH) (Found: C, 52.03; H, 7.96. C26H48O15
requires C, 51.99; H, 8.05%); dH(399.7 MHz; d4-MeOH,
MeOH) 0.91–1.62 (15 H, OCH2(CH2)6CH3), 1.28 (3 H, d, J5,6
6.4, H6C); 3.13–3.89 (17 H, m, H(2,3,4,5,6,6)A, (2,3,4,5,6,6)B,
(2,3,4,5,6,6)C, OCH2CH2), 4.75, 4.80 (2 H, br s, H1A,1B),
solvent peak obscured H1C; dC(100.5 MHz, d4-MeOH, MeOH)
14.59, 18.18, 23.85, 27.56, 30.52, 30.65, 30.74, 33.13 (8 C,
OCH2(CH2)6CH3,C6C), 67.18, 67.44, 68.73, 68.78, 69.79, 72.13,
72.23, 72.41, 72.98, 73.04, 73.10, 74.24 (15 C, C(2,3,4,5,6)A,
(2,3,4,5,6)B, (2,3,4,5,)C, OCH2CH2) 100.96, 101.20, 101.55 (3 C,
C1A,1B,1C).
Octyl (a-D-mannopyranosyl)-(1→6)-(a-D-mannopyranosyl)-
(1→6)-(a-D-mannopyranoside) 10. The trimannoside alcohol
12 (0.153 g, 98.4 lmol) was treated as for the general procedure
above. Flash chromatography (9 : 1 EtOAc–MeOH then 17 : 2 :
1 then 7 : 2 : 1 EtOAc–MeOH–H2O) afforded the trimannoside
10 (42.6 mg, 70%) as clear glass, [a]2D0 +78 (c 1.1 in MeOH)
(Found: C, 50.79; H, 7.79. C26H48O16 requires C, 50.64; H,
7.85%); dH(399.7 MHz; d4-MeOH, MeOH) 0.89–1.59 (15 H,
m, OCH2(CH2)6CH3), 3.41 (1 H, m, OCH2CH2), 3.60–3.87 (19
H, m, H(2,3,4,5,6,6)A,(2,3,4,5,6,6)B,(2,3,4,5,6,6)C,OCH2CH2),
4.73, 4.78 (2 H, 2 br s, H1A,1B), solvent peak obscured
H1C; dC(100.5 MHz, d4-MeOH) 14.59, 23.88, 27.59, 30.56,
30.68, 30.77, 33.16 (7 C, m, OCH2(CH2)6CH3), 62.99, 67.27,
67.49, 68.78, 72.14, 72.44, 72.63, 73.00, 73.15, 74.55 (16 C,
m, C(2,3,4,5,6)A, (2,3,4,5,6)B, (2,3,4,5,6)C, OCH2CH2), 100.98,
101.22, 101.58 (3 C, C1A,1B,1C); m/z (ESI) 615.4 [C89H84O25 (M −
H)+ requires 615.3].
Octyl (6-deoxy-a-D-mannopyranosyl)-(1→6)-(a-D-mannopy-
ranosyl)-(1→6)-(a-D-mannopyranosyl)-(1→6)-(a-D-mannopy-
ranoside) 15. The protected deoxy tetramannoside 29 (144 mg,
0.072 mmol) was treated as for the general procedure above.
Flash chromatography (17 : 2 : 1 then 7 : 2 : 1 then 5 : 2 :
1 EtOAc–MeOH–H2O) afforded the deoxy tetramannoside
15 (23.9 mg, 44%) as a glass, [a]1D2 +80◦ (c 0.8 in MeOH)
(Found: C, 52.11; H 7.99. C33H60O19 requires C, 51.10; H,
7.95%); dH(399.7 MHz; d4-MeOH, MeOH) 0.76–1.48 (15 H, m,
OCH2(CH2)6CH3), 1.13 (3 H, d,J5,6 6.0, H6D), 3.13–3.76 (24
H, m, H(2,3,4,5,6,6)A, (2,3,4,5,6,6)B, (2,3,4,5,6,6)C, (2,3,4,5)D,
OCH2CH2), 4.60 (1H, d,J1,2 1.2), 4.64 (1 H, d,J1,2 1.6), 4.67
(1 H, d,J1,2 2.0), 4.69 (1 H, d,J1,2 1.6, 4H, H1A,1B,1C,1D);
dC(100.5 MHz, d4-MeOH) 14.62, 18.21, 23.89, 27.60, 30.58,
30.69, 30.78, 33.17 (8C, OCH2(CH2)6CH3, C6D), 67.09, 67.24,
67.45, 68.70, 69.78, 72.10, 72.21, 72.27, 72.38, 72.67, 72.88,
72.96, 73.05, 73.13, 74.26 (20 C, C(2,3,4,5,6)A, (2,3,4,5,6)B,
(2,3,4,5,6)C, (2,3,4,5)D, OCH2CH2), 100.76, 101.09, 101.58 (4 C,
C1A,1B,1C,1D).
Octyl (a-D-mannopyranosyl)-(1→6)-(a-D-mannopyranosyl)-
(1→6)-(a-D-mannopyranosyl)-(1→6)-(a-D-mannopyranoside)
14. The tetramannoside alcohol 16 (223 mg, 0.11 mmol) was
treated as for the general procedure above. Flash chromato-
graphy (7 : 2 : 1 then 5 : 2 : 1 EtOAc–MeOH–H2O) afforded
the tetramannoside 14 (25.3 mg, 30%) as a clear glass, [a]D11
+91 (c 0.54 in MeOH); dH(399.7 MHz; d4-MeOH, MeOH)
0.84–1.54 (15 H, m, OCH2(CH2)6CH3), 3.25–3.84 (26 H,
H(2,3,4,5,6,6)A,(2,3,4,5,6,6)B,(2,3,4,5,6,6)C,(2,3,4,5,6,6)D,OCH2-
CH2), 4.68, 4.74, 4.77, 4.80 (4 H, 4 br s, H1A,1B,1C,1D);
dC(100.5 MHz, d4-MeOH) 14.62, 23.89, 27.59, 30.57,
30.69, 30.77, 33.16 (7 C, OCH2(CH2)6CH3), 63.00, 67.08,
67.29, 67.47, 68.75, 72.06, 72.18, 72.36, 72.45, 72.63, 72.83,
72.97, 73.05, 73.10, 75.52 (21 C, C(2,3,4,5,6)A, (2,3,4,5,6)B,
(2,3,4,5,6)C, (2,3,4,5,6)D, OCH2CH2), 100.74, 101.07, 101.57 (4
C, C1A,1B,1C,1D).
Acknowledgements
This work was supported by Australian Research Council Dis-
covery Grant (DP0449626) and a University of Melbourne Early
Career Researcher Grant. JAW was supported by a University of
Melbourne Science Faculty Scholarship. Carlie Gannon, Helena
Qin and Naomi Kirkpatrick are warmly thanked for exploratory
efforts in the early stages of this work.
Octyl 6-deoxy-a-D-mannopyranoside 4. The protected deoxy
monomannoside 23 (161 mg, 0.27 mmol) was treated as for
the general procedure above. Flash chromatography (17 : 2 : 1
EtOAc–MeOH–H2O) afforded the deoxy monomannoside 4
(33 mg, 44%) as a clear gum, [a]1D5 +52 (c 0.5 in MeOH)
(Found: C, 60.71; H, 10.14. C19H28O5 requires C, 60.84; H,
10.21%); dH(399.7 MHz; d4-MeOH, MeOH) 0.86–1.60 (15 H, m,
OCH2(CH2)3CH3), 1.25 (3 H, d,J5,6 6.0, H6), 3.26–3.78 (6 H, m,
H2,3,4,5,OCH2CH2), 4.64 (1 H, d,J1,2 6.0, H1); dC(100.5 MHz,
d4-MeOH) 47.41, 47.59, 47.88, 48.06, 48.22, 48.22, 48.23, 48.35
(8 C, OCH2(CH2)3CH3, C6), 50.13, 50.19. 50.32, 50.41 (5 C,
C2,3,4,5,OCH2CH2), 51.79 (1 C, C1).
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