Synthesis of a core arabinomannan oligosaccharide of Mycobacterium tuberculosis

Article abstract of DOI:10.1021/jo061233x

The synthesis of a core arabinomannan (AM) oligosaccharide from Mycobacterium tuberculosis has been achieved using a convergent [6 + 6] glycosylation strategy and a defined set of building blocks. Dodecasaccharide 1, containing the key AM structural featu

Full text of DOI:10.1021/jo061233x

Synthesis of a Core Arabinomannan Oligosaccharide of
Mycobacterium tuberculosis
Alexandra Ho¨lemann,† Bridget L. Stocker,† and Peter H. Seeberger*
Laboratory for Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zu¨rich,
Wolfgang-Pauli-Strasse 10, HCI F 315, CH-8093 Zu¨rich, Switzerland
seeberger@org.chem.ethz.ch
ReceiVed June 15, 2006
The synthesis of a core arabinomannan (AM) oligosaccharide from Mycobacterium tuberculosis has been
achieved using a convergent [6 + 6] glycosylation strategy and a defined set of building blocks.
Dodecasaccharide 1, containing the key AM structural features of lipoarabinomannan (LAM), was obtained
in excellent yield and selectivity from hexamannan 3 and hexaarabinan 5. This flexible synthetic strategy
involves late-stage couplings and modifications, thus providing ready access to several different LAM
fragments. The incorporation of a thiol linker at the reducing end of the oligosaccharide allows for the
attachment of these compounds to microarrays and protein carriers.
Introduction
cause two million deaths annuallysa mortality rate that makes
TB one of the three most serious infectious diseases alongside
HIV and malaria.1 Indeed, it is this co-infection with HIV,2
Tuberculosis (TB) is one of the most devastating infectious
diseases in the world. The result of infection by Mycobacterium
tuberculosis, TB is estimated to infect eight million people and
(1) The World Health Organization. http://www.who.int/tb/en/.
(2) Dolin, P. J.; Raviglione, M. C.; Kochi, A. Bull. World Health Org.
1994, 72, 213-220.
† These authors contributed equally.
10.1021/jo061233x CCC: $33.50 © 2006 American Chemical Society
Published on Web 09/19/2006
J. Org. Chem. 2006, 71, 8071-8088
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Ho¨lemann et al.
togetherwith the emergence of multiple-drug resistant strains
of M. tuberculosis,3 limited treatment regimes,4 and the increase
in global travel that has led to a rapid increase in the number
of reported TB cases. In 1993, the World Health Organization
(WHO) declared TB a “global health emergency”.
Much of the pathogenicity of M. tuberculosis results from
its unique and complex cell envelope. The major components
of this mycobacterial envelope are the mycolyl arabinogalactan-
peptidoglycan complexes (mAGPs) and the lipoarabinomannan
(LAM)-associated lipoglycans.5 Combined, both form a thick
cellular envelope that aids in the bacteria’s ability to survive
within the host and to resist antibiotic treatment.6 It is generally
believed that LAMs are also implicated in the immunogenicity
of M. tuberculosis. LAMs have been shown to inhibit T-cell
activation,7 protein kinase C activity,8 and various INF-γ
induced functions including macrophage microbicidal and
tumoricidal activity.9 They also induce a large array of cytokines
associated with macrophages such as TNF-R,5b,10 granulocyte-
macrophage-CSF, IL-1a, IL-1b, IL-6, and IL-10.5b,10c Further-
more, oligosaccharides, derived from LAM purified from M.
tuberculosis H37 Rv and covalently conjugated to tetanus toxoid
and cross-reactive mutant (CRM197) diphtheria toxoid, have
proven to be highly immunogenic, inducing an IgG response
in rabbit and guinea pig models.11
Although the gross structural features of LAM have been
elucidated5,6,12 (Figure 1), the degree of branching of the mannan
and arabinan backbone and the attachment site for the arabinan
chain remain elusive. The LAM is believed to contain a lipo-
mannan (LM) core, comprised of R-(1f6) linked D-manno-
pyranose residues bound, via an R-glycosidic linkage, to the
O-6 position of an inositol. Approximately half of these mannose
residues contain an R-(1f2) D-mannopyranosyl branch. An
R-(1f5) linked D-arabinofuranosyl chain, with periodic R-(1f3)
branch points, is attached to the mannan core. These arabinan
branch points frequently contain further R-(1f3) and R-(1f5)
FIGURE 1. Key structural features of lipoarabinomannan (LAM) from
M. tuberculosis.
branching. The arabinan core is usually terminated with a
hexaarabinan motif containing two â-(1f2) linkages that, in
the case of LAMs isolated from M. tuberculosis, are often
capped with R-(1f5)-linked mono-, di-, or trimannosides. Such
mannosylated LAMs are referred to as ManLAMs.
(3) Collins, F. M. CRC Crit. ReV. Microbiol. 1993, 19, 1-16.
(4) Jarlier, V.; Nikaido, H. FEMS Microbiol. Lett. 1994, 123, 11-18.
(5) (a) Brennan, P. J. Annu. ReV. Biochem. 1995, 64, 29-63. (b)
Vercellone, A.; Nigou, J.; Puzo, G. Front. Biosci. 1998, 3, 149-163.
(6) Chatterjee, D. Curr. Opin. Chem. Biol. 1997, 1, 579-588.
(7) Kaplan, G.; Gandhi, R. R.; Weinstein, D. E.; Levis, W. R.; Patarroyo,
M. E.; Brennan, P. J.; Cohn, Z. A. J. Immunol. 1987, 138, 3028-3034.
(8) Chan, J.; Fan, X.; Hunter, S. W.; Brennan, P. J.; Bloom, B. R. Infect.
Immun. 1991, 59, 1755-1761.
Due to their biological importance, significant effort has
been made toward the synthesis of M. tuberculosis capsular
oligosaccharides. Much of this work has concerned the syn-
thesis of the nonreducing portion of the LAM.12,13 In this
context, Lowary focused on the development of p-cresol
thioglycoside methodology for the installation of the â-arabino
linkage12 and the synthesis of a protected core arabinan frag-
ment of the LAM was accomplished using n-pentenylortho
esters.14 The synthesis of a LM has been reported,15 although
the strategy employed does not readily allow for the coupling
of further arabinan motifs. The first total synthesis of phos-
phatidylinositol mannosides (PIM2 and PIM6) was reported
recently.16 Despite considerable efforts in the assembly of TB
oligosaccharides, the synthesis of TB arabinomannans (AMs)
has not been reported.
(9) Sibley, L. D.; Hunter, S. W.; Brennan, P. J.; Krahenbuhl, J. L. Infect.
Immun. 1988, 56, 1232-1236.
(10) (a) Moreno, C.; Mehlert, A.; Lamb, J. Clin. Exp. Immunol. 1988,
74, 206-210. (b) Moreno, C.; Taverne, J.; Mehlert, A.; Bate, C. A. W.;
Brealey, R. J.; Meager, A.; Rook, G. A. W.; Playfair, J. H. L. Clin. Exp.
Immunol. 1989, 76, 240-245. (c) Barnes, P. F.; Chatterjee, D.; Brennan,
P. J.; Rea, T. H.; Modlin, R. L. Infect. Immun. 1992, 60, 1441-1446. (d)
Chatterjee, D.; Roberts, A. D.; Lowell, K.; Brennan, P. J.; Orme, I. M.
Infect. Immun. 1992, 60, 1249-1253. (e) Adams, L. B.; Fukutomi, Y.;
Krahenbuhl, J. L. Infect. Immun. 1993, 61, 4173-4181.
(11) (a) Beston, H.; Kallenius, G.; Svenson, S. B. Vaccine 1999, 17,
2853-2861. (b) Hamasur, B.; Haile, M.; Pawlowski, A.; Schroder, U.;
Williams, A.; Hatch, G.; Hall, G.; Marsh, P.; Kallenius, G.; Svenson, S. B.
Vaccine 2003, 21, 4081-4093.
(12) (a) Lowary, T. L. J. Carbohydr. Chem. 2002, 21, 691-722. (b)
Gadikota, R. R.; Callam, C. S.; Appelmelk, B. J.; Lowary, T. L. J.
Carbohydr. Chem. 2003, 22, 459-480. (c) Ayers, J. D.; Lowary, T. L.;
Morehouse, C. B.; Besra, G. S. Bioorg. Med. Chem. Lett. 1998, 8, 437-
442. (d) D’Souza, F. W.; Ayers, J. D.; McCarren, P. R.; Lowary, T. L. J.
Am. Chem. Soc. 2000, 122, 1251-1260. (e) Han, J.; Gadikota, R. R.;
McCarren, P. R.; Lowary, T. L. Carbohydr. Res. 2003, 338, 581-588. (f)
Yin, H.; D’Souza, F. W.; Lowary, T. L. J. Org. Chem. 2002, 67, 892-
903. (g) D’Souza, F. W.; Lowary, T. L. Org. Lett. 2000, 2, 1493-1495.
(h) Gadikota, R. R.; Callam, C. S.; Appelmelk, B. J.; Lowary, T. L. J.
Carbohydr. Chem. 2003, 22, 149-170.
(13) (a) Mereyala, H. B.; Hotha, S.; Gurjar, M. K. Chem. Commun. 1998,
685-686. (b) Bamhaoud, T.; Sanchez, S.; Prandi, J. Chem. Commun. 2000,
659-660. (c) Marotte, K.; Sanchez, S.; Bamhaoud, T.; Prandi, J. Eur. J.
Org. Chem. 2003, 3587-3598.
(14) (a) Lu, J.; Fraser-Reid, B. Org. Lett. 2004, 6, 3051-3054. (b) Lu,
J.; Fraser-Reid, B. Chem. Commun. 2005, 862-864.
(15) Jayaprakash, K. N.; Lu, J.; Fraser-Reid, B. Angew. Chem., Int. Ed.
2005, 44, 5894-5898.
(16) Liu, X.; Stocker, B. L.; Seeberger, P. H. J. Am. Chem. Soc. 2006,
128, 3638-3648 and references cited herein.
8072 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
SCHEME 1. Retrosynthesis for the Target Arabinomannan Portion of LAM
LAM exhibits a wide variety of immunomodulatory functions,
yet the biological implication of the in vitro immunological data
is not always clear.17 The synthesis of key AM and analogues
thereof, and their attachment to microarrays and protein carriers
for biological testing, will provide insight into the structure-
activity relationship (SAR) of these compounds.
ingly, hexamannoside 3 was synthesized from imidate 2, rather
than commencing with a thiol linker at the reducing end (R2)
of the mannoside. Construction of the mannan core in turn
required the use of three building blockssmannose 7 for the
terminating monosaccharide caps, 8 for the R-(1f2) and
R-(1f6) branching, and 9a for the R-(1f6) mannan backbone.
All three monomers could be obtained from one common ortho
ester precursor. An allyl substituent was used as a temporary
protecting group for the mannan reducing end and required the
incorporation of building block 9b (R5 ) allyl). The arabinan
core 4 could again be synthesized from three building blockss
monomer 10 for the terminal arabinan caps, 11 for the R-(1f3)
and R-(1f5) branching, and 12a for the linear R-(1f5) arabinan
backbone. The incorporation of a temporary pent-4-enyl sub-
stituent at the reducing end (R6 ) pent-4-enyl) was to be achieved
by incorporating 12b. To test the possibility of elongating the
arabinan core at a later date, building block 12a was also to be
incorporated at the nonreducing end of the arabinan core.
Results and Discussion
Synthetic Strategies and Target Structures. Synthesis of
the AM core 1 of the LAM was envisioned to proceed via a
[6 + 6] glycosylation between hexamannoside 3 and arabinan
imidate 5 (Scheme 1).18 A subsequent synthesis of a more
elaborate LAM would require the coupling of the mannan hexa-
saccharide core to an inositol pseudotrisaccharide.15 Accord-
(17) Chatterjee, D.; Khoo, K.-Y. Glycobiology 1998, 8, 113-120.
(18) Although the linkage of the arabinan core to the mannan core has
not been conclusively characterized, consensus favors an R-linkage at the
2 position of the arabinan. See ref 5a.
J. Org. Chem, Vol. 71, No. 21, 2006 8073

Ho¨lemann et al.
SCHEME 2. Synthesis of Mannose Building Blocks 7 and
9aa
a Reagents and conditions: (a) (i) 2,6-lutidine, MeOH, CH2Cl2, rt; (ii)
NaOMe, MeOH/CH2Cl2, rt, 67% (2 steps); (b) BnBr, NaH, DMF, imidazole,
rt, 94%; (c) (i) AcOH, H2O, rt; (ii) Cl3CCN, DBU, CH2Cl2, 0 °C, 78%
(two steps); (d) TIPSCl, imidazole, DMF, rt, 66%; (e) BnBr, NaH, DMF,
imidazole, rt, 95%; (f) (i) AcOH, H2O, rt; (ii) Cl3CCN, DBU, CH2Cl2, 0
°C, 80% (2 steps).
FIGURE 2. Arabinan and mannan oligosaccharides for SAR studies.
SCHEME 3. Synthesis of Mannose Building Block 8a
In addition to the synthesis of target AM 1, we report herein
the synthesis of a series of arabinan and mannan precursors
13-15 (Figure 2), portions of the larger AM motif. These
oligosaccharides will be prepared following protocols similar
to those used for the preparation of the AM. As with AM 1, all
oligosaccharides were prepared using a defined set of building
blocks, thus allowing for the synthesis of further AM analogues,
and the complete LAM motif, at a later date.
Synthesis of the Mannose Building Blocks. Ortho ester 17,
prepared from known glycosyl bromide 16,19 was the common
intermediate for the synthesis of all three mannosyl trichloro-
acetimidates. Conversion of 17 to imidate 7 proceeded smoothly
following benzylation to yield ortho ester 18, acid-catalyzed
hydrolysis of the ortho ester, and installation of the anomeric
trichloroacetimidate20 (Scheme 2). Similarly, synthesis of imi-
date 9a was readily achieved by regioselective silylation of 17,
subsequent benzylation to yield crystalline ortho ester 19b,
hydrolysis of the ortho ester, and installation of the anomeric
leaving group. Starting from D-mannose, both building blocks
were prepared on multigram scale in six or seven steps requiring
minimal purification by column chromatography.
a Reagents and conditions: (a) R5 ) allyl: allyl alcohol, TMSOTf (cat.),
CH2Cl2, 0 °C, R/â ) 11:1, 88%; (b) R5 ) pent-4-enyl: pent-4-en-1-ol,
TMSOTf (cat.), CH2Cl2, 0 °C, 88%; (c) (i) NaOMe, MeOH/CH2Cl2, rt,
99% (R5 ) allyl), 88% (R5 ) pent-4-enyl); (ii) LevOH, DMAP, DIPC,
CH2Cl2, 0 °C to rt, 94% (R5 ) allyl), 96% (R5 ) pent-4-enyl); (d) R5 )
allyl: Pd(OAc)2, PPh3, HNEt2, MeOH, rt 78%; (e) R5 ) pent-4-enyl: NBS,
THF (aq), rt 65%; (f) Cl3CCN, DBU, CH2Cl2, 0 °C, 76%.
To maximize the convergence of our strategy, synthesis of
building block 8 commenced with the glycosylation of 9a with
allyl alcohol (Scheme 3). Despite the participation of the benzoyl
substituent at C-2, this glycosylation furnished 9b as a mixture
of anomers (R/â ) 11:1), presumably due to the increased
nucleophilicity of allyl alcohol. This anomeric mixture was used
directly for the synthesis of imidate 8, though if required, the
mixture of anomers can be readily separated using standard flash
column chromatography. Allyl glycoside 9b was then deben-
zoylated using Zemple´n conditions and the levulinoyl substituent
installed to give 20b in 87% yield over two steps. Removal of
the allyl moiety to allow for the installation of the imidate,
however, proved more problematic. Deallylation with catalytic
(10%) Pd(PPh3)4 and p-toluenesulfinic acid21 proceeded slowly,
(19) Ness, R. K.; Fletcher, H. G.; Hudson, C. S. J. Am. Chem. Soc. 1950,
72, 2200-2240.
(20) (a) Schmidt, R. R. Angew. Chem., Int. Ed. Engl. 1986, 25, 212-
235. (b) Schmidt, R. R.; Kinzy, W. AdV. Carbohydr. Chem. Biochem. 1994,
50, 21-123. (c) Schmidt, R. R. Front. Nat. Prod. Res. 1996, 1, 20-54. (d)
Schmidt, R. R. Pure Appl. Chem. 1989, 61, 1257-1270.
(21) Opatz, T.; Kunz, H. Tetrahedron Lett. 2000, 41, 10185-10188.
8074 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
SCHEME 4. Synthesis of Mannan Hexasaccharide 13a
a Reagents and conditions: (a) TBAF, THF, rt, 82%; (b) 9a, TMSOTf (cat.), CH2Cl2, 0 °C, 92%; (c) AcCl in MeOH/CH2Cl2, rt, 96%; (d) 8, TMSOTf
.
(cat.), CH2Cl2, 0 °C, 80%; (e) H2NNH2 H2O, pyridine, AcOH, CH2Cl2, rt, 92%; (f) 7, TMSOTf (cat.), CH2Cl2, 0 °C, 90%; (g) AcCl in MeOH/CH2Cl2, rt,
90%; (h) 8, TMSOTf (cat.), CH2Cl2, 0 °C, 85%; (i) (i) AcCl in MeOH/CH2Cl2, rt, 84%; (ii) 7, TMSOTf (cat.), CH2Cl2, 0 °C, 92%; (j) (i)
{Ir(COD)[PCH3(C6H5)2]2}PF6 (cat.), THF, rt; (ii) I2, THF/H2O, rt; (iii) Cl3CCN, DBU, CH2Cl2, 0 °C, 81% (3 steps); (k) (i) HO(CH2)6SBn, TMSOTf (cat.),
.
CH2Cl2, 0 °C; (ii) pyridine, Ac2O, rt, 89% (2 steps); (l) H2NNH2 H2O, pyridine, AcOH, rt, 96%; (m) Na, NH3 (l), THF, -78 °C, 92%.
with competing decomposition of the allyl glycoside. The use
of PdCl2 under buffered conditions (AcOH, NaOAc)22 was
unreliable as it furnished lactol 21 in yields from 40 to 70%
along with varying amounts of the corresponding Wacker
oxidation product. To prevent formation of the oxidation
byproduct, anhydrous conditions, requiring the use of catalytic
PdCl2 in MeOH,23 were explored. Unfortunately, due to the in
situ generation of HCl, desilylation was observed even under
dilute (15 µM) conditions. We then turned our attention to the
synthesis of the pentenyl derivative 9c24 in anticipation of NBS-
mediated cleavage of the pentenyl moiety.25 Though successful,
the halohydrin byproduct was also observed resulting in a
suboptimal (65%) yield of lactol 21. Returning to the allyl
glycoside 9b, attempts were then made at cleaving the allyl
moiety via a two-step protocol involving the isomerization of
the allyl moiety to the enol ether followed by oxidative cleavage
to the lactol. Wilkinson’s catalyst26 (Ph3P)3RhCl gave poor
(approximately 30%) yield for the isomerization of the allyl
moiety; however, the iridium catalyst27 {Ir(COD)[PCH3-
(C6H5)2]2}PF6 proved more viable. Allyl isomerization followed
by oxidative cleavage with either I2 in THF/H2O,28 or NIS in
1% aqueous THF,29 produced lactol 21 in 70-75% yield. This
was an encouraging result. Nevertheless, the strictly anhydrous
(26) Dufour, M.; Gramain, J.-C.; Husson, H.-P.; Sinibaldi, M.-E.; Troin,
Y. Tetrahedron Lett. 1989, 30, 3429-3432.
(22) Smith, A. B.; Rivero, R. A.; Hale, K. J.; Vaccare, H. A. J. Am.
Chem. Soc. 1991, 113, 2092-2112.
(27) Oltyoort, J. J.; Van Boeckel, C. A. A.; De Koning, J. H.; Van Boom,
J. H. Synthesis 1981, 305-308.
(23) Ogawa, T.; Kaburagi, T. Carbohydr. Res. 1982, 110, 12-15.
(24) 9c was prepared from 9a using a protocol similar to that for the
synthesis of 9b (see Scheme 3).
(28) Timmer, M. S. M.; Code´e, J. D. C.; Overkleeft, H. S.; Van Boom,
J. H.; Van der Marel, G. A. Synlett 2004, 2155-2158.
(29) Halkes, K. M. Slaghek, T. M.; Vermeer, H. J.; Kamerling, J. P.;
Vliegenthart, J. F. G. Tetrahedron Lett. 1995, 36, 6137-6140.
(25) Wilson, B. G.; Fraser-Reid, B. J. Org. Chem. 1995, 60, 317-
320.
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Ho¨lemann et al.
SCHEME 5. Synthesis of Mannan Tetrasaccharide 14a
a Reagents and conditions: (a) 32, TMSOTf (cat.), CH2Cl2, 0 °C, 98%; (b) AcCl in MeOH/CH2Cl2, rt, 93%; (c) 32, TMSOTf (cat.), CH2Cl2, 0 °C, 83%;
(d) (i) {Ir(COD)[PCH3(C6H5)2]2}PF6 (cat.), THF, rt; (ii) I2, THF/H2O, rt; (iii) Cl3CCN, DBU, CH2Cl2, 0 °C, 81% (3 steps); (e) (i) HO(CH2)6SBn, TMSOTf
(cat.), CH2Cl2, 0 °C; (ii) pyridine, AcOH, rt, 93% (2 steps); (f) Na, NH3 (l), THF, -78 °C, 93%.
and inert conditions required during the isomerization30 prompted
us to identify a less demanding protocol. Fortunately, an in situ
generated Pd(PPh3)4-catalyzed deallylation under basic condi-
tions31 was amenable to our substrate and gave lactol 21 in 78%
yield. With a suitable deallylation protocol established, lactol
21 was transformed to imidate 8 to complete the synthesis of
the mannose building block.
with I2 in THF/H2O, produced the corresponding lactol in
excellent (92%) yield. The lactol was then converted to imidate
2 using DBU and Cl3CCN. Glycosylation of 6-(benzylthio)-
hexan-1-ol with imidate 2 followed. Although this glycosylation
occurred readily, problems were encountered with separating
the excess linker from hexasaccharide 31. Though differing in
Rf values, hexasaccharide 31 and the linker had a propensity to
coelute during silica gel column chromatography. This separa-
tion problem could not be solved even when the excess of linker
was reduced to 1.5 equiv and several solvent conditions for
purification by column chromatography were tried. To circum-
vent this problem, acetylation of the linker in the crude reaction
mixture was performed, which in turn allowed for the purifica-
tion of hexasaccharide 31 by flash chromatography. The
levulinoyl substituent of hexasaccharide 31 was then removed,
using hydrazine monohydrate in neat pyridine/AcOH, to give
alcohol 3, ready for coupling to the arabinan core 5, in a
respectable 84% yield over three steps. In accordance with our
objective to prepare intermediate arabinan and mannan motifs
for SAR studies, mannan hexasaccharide 3 was also deprotected
using Birch conditions to afford 13, exclusively as the disulfide
dimer, in 92% yield.
Synthesis of the mannan tetrasaccharide intermediate 14
(Scheme 5) commenced with the glycosylation of disaccharide
24 using building block 3232 to give trisaccharide 33 in excellent
yield. Though this strategy required the incorporation of an
additional building block, the readily synthesized acetylated
building block 32 was considered to be the most appropriate
choice.33 Trisaccharide 33 was then selectively deprotected to
give alcohol 34 in 93% yield and the final monosaccharide 32
incorporated to furnish tetrasaccharide core 35. The allyl moiety
was then cleaved, using {Ir(COD)[PCH3(C6H5)2]2}PF6-catalyzed
isomerization followed by I2-mediated cleavage, and the trichlo-
Assembly of the Mannan Hexasaccharide Core 13 and
the Tetrasaccharide Intermediate 14. Synthesis of the core
mannan hexasaccharide (Scheme 4) commenced with glycoside
9b that was desilylated with TBAF to give alcohol 22. Union
of 22 and imidate 9a using standard TMSOTf-catalyzed
glycosylation methodology furnished disaccharide 23 in 75%
over two steps. Desilylation under mildly acidic conditions,
using acetyl chloride in MeOH/CH2Cl2 rather than TBAF,
proved optimal for the formation of disaccharide 24. Disaccha-
ride 24 was then coupled, with complete R-selectivity, to
monomer 8 to install the branching point in the trisaccharide
mannan chain 2. Delevulinoylation of 25, using hydrazine
monohydrate in buffered conditions, also occurred smoothly and
in excellent yield to give trisaccharide 26. Installation of the
R-(1f2) linked mannose cap was achieved by glycosylation
with 7 to give tetrasaccharide 27 in 90% yield. Tetrasaccharide
27 was desilylated under mildly acidic conditions to give alcohol
28, which was subsequently coupled to levulinoyl imidate 8
for installation of the second branch point in the mannan core.
Again, elongation of the R-(1f6) linked mannan backbone by
desilylation of pentasaccharide 29 followed by glycosylation
with imidate 9a proceeded smoothly with complete R-selectivity
to give mannan hexasaccharide 30 in 77% yield over two steps.
To allow for the attachment of target AM 1 (or hexasaccharide
mannan precursor 3) to a microarray or protein carrier, the allyl
moiety of 30 had to be cleaved. In the case of allyl glycoside
30, it was found that isomerization of the allyl moiety using
{Ir(COD)[PCH3(C6H5)2]2}PF6, followed by oxidative cleavage
(32) (a) Fischer, E.; Oetker, R. Ber. Dtsch. Chem. Ges. 1913, 46, 4029-
4040. (b) Kaur, K. J.; Hindsgaul, O. Carbohydr. Res. 1992, 226, 219-231.
(c) Bore´n, H. B.; Ekborg, G.; Ekland, K. Acta Chim. Scand. 1973, 27, 2639-
2644. (d) Mayer, T. G.; Schmidt, R. R. Eur. J. Org. Chem. 1999, 1153-
1166.
(30) For optimal yields, requiring a lower catalytic loading, the reaction
should be performed in THF freshly distilled from sodium and benzophe-
none that is subsequently degassed for 30 min.
(31) Harvey, J. E.; Raw, S. A.; Taylor, R. J. Org. Lett. 2004, 6, 2611-
2614.
(33) Imidate 32 is easier to prepare than imidate 8 and has the protecting
group pattern to allow for the installation of the second R-(1f2) linkage.
8076 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
SCHEME 6. Synthesis of Arabinose Building Blocks
of 11 was readily achieved by installation of the levulinoyl
substituent to yield ortho ester 42 prior to hydrolysis of the ortho
ester and installation of the anomeric imidate. Similarly, 12a
was obtained by benzylation of 41 to give ortho ester 43,
hydrolysis of the ortho ester and conversion of the lactol to the
anomeric imidate.
10-12a
During the construction of the oligoarabinans, a temporary
protecting group for the reducing end of the arabinan chain was
required. Literature precedence14 prompted us to select a pen-
tenyl moiety for this purpose, in turn necessitating the synthesis
of building block 12b. Pentenyl glycoside 12b was readily
prepared following TMSOTf-catalyzed glycosylation of 12a
with pent-4-en-1-ol at -40 to -30 °C.
Assembly of the Arabinan Hexasaccharides. The assembly
of the arabinan hexasaccharide core commenced with the
desilylation of pentenyl glycoside 12b, again under mildly acidic
conditions, followed by coupling to imidate 12a under standard
TMSOTf activation (Scheme 7). Subsequent desilylation af-
forded known disaccharide 4514a in 79% yield over three steps.
Disaccharide 45 was then coupled to imidate 11 in the presence
of TMSOTf to install the branching point. Although this
glycosylation proceeded smoothly with complete R-selectivity,
problems were encountered in the separation of trisaccharide
46 from the byproduct trichloroacetamide. Several solvent
conditions for purification by flash column chromatography, as
well as purification by size-exclusion chromatography, were
screened with limited success. Consequently, the mixture was
treated directly with hydrazine monohydrate under buffered
conditions to remove the levulinoyl group. This process allowed
for successful purification and afforded the desired trisaccharide
47 in 82% yield over two steps. Installation of the R-(1f3)
branch was then achieved by glycosylation of 47 with imidate
12a under TMSOTf activation to give tetrasaccharide 48 with
complete R-selectivity. Removal of both silyl ethers under
mildly acidic conditions provided key tetrasaccharide 49 in 87%
yield. Subsequent capping with two equivalents of 10 in the
presence of TMSOTf occurred readily, with complete R-selec-
tivity, to give the desired arabinan hexasaccharide 4 in 92%
yield. To test the possibility of elongating the arabinan core at
a later date, hexasaccharide 6, containing two unprotected
primary hydroxyl groups, was also synthesized. Thus, bis-
glycosylation of tetrasaccharide 49 with imidate 12a under
TMSOTf activation, followed by removal of both silyl ethers,
gave the desired hexasaccharide 6 in 89% yield over two steps.
Pentenyl glycoside 4 needed to be transformed to the
anomeric imidate 5 to allow for the attachment of the arabinan
core to the mannan hexasaccharide precursor 3 or to the thiol
linker. Cleavage of the pentenyl moiety by treatment with NBS
in aqueous acetonitrile25,35 produced the desired lactol, though
varying amounts of the halohydrin byproduct were also observed
resulting in an acceptable, though variable, yield of the lactol.
The mixture was directly treated with trichloroacetonitrile and
DBU to furnish imidate 5 in 55-72% yield over two steps.
Surprisingly, the subsequent installation of the 6-(benzylthio)-
hexan-1-ol linker to give intermediate 50 was somewhat
problematic. Glycosylations with imidates 10, 11, and 12a
typically proceeded smoothly at -40 to -30 °C with complete
R-selectivity, yet in the case of imidate 5, elevated temperatures
a Reagents and conditions: (a) (i) Cl2CHOMe, SnCl4, CH2Cl2, rt; (ii)
allyl alcohol, 2,6-lutidine, CH2Cl2, rt; (iii) NaOMe, MeOH, CH2Cl2, rt, 79%
(3 steps); (b) BnBr, NaH, DMF, 0 °C to rt, 95%; (c) (i) p-TsOH.H2O, 1,2-
dimethoxyethane, H2O, 0 °C to rt; (ii) DBU, Cl3CCN, CH2Cl2, 0 °C, 70%
(2 steps); (d) TIPSCl, imidazole, DMF, 0 °C to rt, 76%; (e) LevOH, DMAP,
DIPC, CH2Cl2, rt, quant; (f) (i) p-TsOH.H2O, 1,2-dimethoxyethane, H2O,
0 °C to rt, 99%; (ii) DBU, Cl3CCN, CH2Cl2, 0 °C, 88%; (g) NaH, BnBr,
DMF, rt, 12 h; (h) (i) p-TsOH.H2O, 1,2-dimethoxyethane, H2O, 0 °C to rt,
86% (2 steps); (ii) DBU, Cl3CCN, CH2Cl2, 0 °C, 98%; (i) pent-4-en-1-ol,
TMSOTf (cat.), CH2Cl2, -40 to -30 °C, 97%.
roacetimidate moiety installed to give imidate 36 in 81% over
three steps. Again, attempts to remove the excess thiol linker,
following glycosylation with 6-(benzylthio)hexan-1-ol, were
problematic, and purification of 37 was only possible after the
excess linker was acetylated. Finally, global deprotection under
Birch conditions gave 14, again as the disulfide dimer, in
excellent (93%) yield.
Synthesis of the Arabinose Building Blocks. All required
arabinofuranoside imidates were synthesized on large scale from
D-arabinose in eight or nine steps (Scheme 6). Ortho ester 39,
prepared in three steps from crystalline methyl 2,3,5-tri-O-
benzoyl-R-D-arabinofuranoside (38),34 was used as the key
intermediate for the synthesis of all three building blocks.
Conversion of 39 to imidate 10 proceeded smoothly via bis-
benzylation to furnish ortho ester 40, acid-induced hydrolysis
of the ortho ester, and installation of the anomeric imidate.
Alternatively, regioselective silylation of the primary hydroxyl
group of 39 gave ortho ester 41 that was used as the common
intermediate for the synthesis of imidates 11 and 12a. Synthesis
(35) The use of NBS for the pentenyl removal is preferred to the use of
NIS. Traces of iodine were always present in the lactol if the reaction is
performed with NIS, leading to incomplete formation of the imidate or
decomposition of the starting material.
(34) Callam, C. S.; Lowary, T. L. J. Chem. Educ. 2001, 78, 73-74.
J. Org. Chem, Vol. 71, No. 21, 2006 8077

Ho¨lemann et al.
SCHEME 7. Synthesis of the Arabinan Hexasaccharidesa
a Reagents and conditions: (a) (i) AcCl in MeOH/CH2Cl2, 0 °C, 96%; (ii) 12a, TMSOTf (cat.), CH2Cl2, -40 to -30 °C, 94%; (b) AcCl in MeOH/
.
CH2Cl2, 0 °C, 92%; (c) 11, TMSOTf (cat.), CH2Cl2, -40 to -30 °C; (d) H2NNH2 H2O, pyridine, AcOH, CH2Cl2, rt, 82% (2 steps); (e) 12a, TMSOTf (cat.),
CH2Cl2, -40 to -30 °C, 87%; (f) AcCl in MeOH/CH2Cl2, 0 °C to rt, 87%; (g) 10, TMSOTf (cat.), CH2Cl2, -40 to -30 °C, 92%; (h) (i) NBS, MeCN, H2O,
rt; (ii) DBU, Cl3CCN, CH2Cl2, 0 °C, 72% (2 steps); (i) (i) HO(CH2)6SBn, TMSOTf (cat.), CH2Cl2, 0 °C; (ii) Ac2O, pyridine, rt, 78% (2 steps, R/â ≈ 12:1);
(j) Na, NH3 (l), THF, -78 °C, 37%; (k) (i) 12a, TMSOTf (cat.), CH2Cl2, -40 to -30 °C, 96%; (ii) AcCl in MeOH/CH2Cl2, 0 °C to rt, 93%.
(-20 to 0 °C) were necessary to achieve complete conversion.
Coupling of 5 to the thiol linker proceeded in 78% yield under
TMSOTf activation at -20 to -10 °C, albeit with lower
R-selectivity (R/â ≈ 12:1). Attempts were made to improve this
selectivity, though all solvent and temperature combinations
resulted in similar ratios.36 After acetylation of the reaction
mixture, to allow for the removal of excess linker, it was possible
to separate the anomers, and R-50 was isolated in 66% yield.
Finally, global deprotection of the hexasaccharide under Birch
conditions provided 15 exclusively as the disulfide linked dimer
in 37% yield.
Synthesis of the Arabinomannan Dodecasaccharide. Syn-
thesis of arabinomannan 1 was envisioned to occur via a [6 +
6] glycosylation strategy using glycosylating agent 5 and
acceptor 3 (Scheme 8). First attempts to couple both fragments
under TMSOTf activation at -40 to -30 °C failed owing to
the poor reactivity of 5 at lower temperatures. Under these
conditions acceptor 3 and the hydrolyzed imidate were recovered
after workup. A change in the reaction conditions to TBSOTf
activation at 0 °C in diethyl ether,37 however, allowed for the
successful coupling of 5 with 3 to afford dodecasaccharide 51
in 70% yield exclusively as the R-anomer. The structure of 51
was analyzed by 1H NMR and 13C NMR spectroscopy, as well
as high-resolution MALDI mass spectrometry. Though the
anomeric proton of the newly formed glycosidic linkage was
difficult to assign, in the 1H NMR spectrum all anomeric signals
showed coupling constants of less than 2 Hz. In the 13C NMR
spectrum, all anomeric arabinose signals were between 105.3
and 106.7 ppm. These data are indicative of the presence of
R-linkages only12f,38sas was anticipated due to the presence of
a C-2 benzoyl participating group on imidate 5.
In an attempt to improve our modest yield during the global
deprotection of arabinan 50, global deprotection of 51 was
achieved using a two-step protocol. Dodecasaccharide 51 was
first debenzoylated under basic conditions (NaOMe), and the
resulting polyol was subjected to Birch conditions to give target
1 as the disulfide-linked dimer in 52% yield.
Further Elongation of the AM Core. LAM oligosaccharides
are often capped with R-(1f2)-linked mono-, di- or trimanno-
sides at the arabinan termini, with M. tuberculosis frequently
capped with a dimannoside.5b,39 Thus, we explored the further
elongation of the arabinan chains with dimannan caps.40 Initial
attempts were made at bis-glycosylating hexasaccharide 6 with
2 equiv of 32 by TMSOTf activation at 0 °C. This transforma-
tion resulted in a mixture of the corresponding hepta- (minor)
and octasaccharide (major product) along with varying amounts
of different di- and trisaccharides.41 These byproducts were the
result of an acid-induced fragmentation of the hexaarabinan core
that presumably occurs at elevated temperatures due to the Lewis
(38) Mizutani, K.; Kasai, R.; Nakamura, M.; Tanaka, O.; Matsuura, H.
Carbohydr. Res. 1989, 185, 27-38.
(39) Chatterjee, D.; Lowell, K.; Rivoire, B.; McNeil, M. R.; Brennan,
P. J. J. Biol. Chem. 1992, 267, 6234-6249.
(40) Though most arabinan caps contain a challenging â-(1f2) arabinan
linkage in the hexaarabinan cap, we first wanted to test the overall
plausibility of attaching a mannose cap. Many of the elegant strategies,
most notably those developed by Lowary and co-workers, could be used at
a later date to install the appropriate â-linkage; see ref 12. The terminal
regions of the linear AM chain however, have been shown to contain
R-linkages only (for example, see ref 5a).
(36) Similar R/â-ratios ranging from 93:7 to 97:3 were obtained in the
glycosylation of imidate 12a with the linker [HO(CH2)6SBn].
(37) These conditions have been successfully applied to the coupling of
larger oligoarabinan fragments ([4 + 4 + 4] coupling). See ref 14b.
8078 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
SCHEME 8. Synthesis of Dodecasaccharide 1a
a Reagents and conditions: (a) TBSOTf (cat.), Et2O, 0 °C, 70%; (b) (i) NaOMe, MeOH, CH2Cl2, rt; (ii) Na, NH3 (l), THF, -78 °C, 52% (2 steps).
SCHEME 9. Synthesis of Mannoarabinansa
acidity of TMSOTf. To circumvent this problem, less acidic
TBSOTf was used as the activator and the desired octasaccharide
was obtained in greater than 85% yield, though minor impurities
were observed. For the attachment of the subsequent mannose
units, the acetates had to be selectively removed. In addition, it
was hoped that deacetylation would facilitate the subsequent
removal of any impurities. Unfortunately, deprotection under
mildly acidic and highly dilute conditions proceeded very
slowly,42 and further addition of acetyl chloride gave only a
complex mixture of products.
Consequently, this strategy was abandoned and the incorpora-
tion of a temporary levulinoyl protecting group was pursued.
Imidate 52 (Scheme 9), synthesized from 32,43 was coupled to
hexasaccharide 6 to provide the desired octasaccharide as the
major product (approximately 70-75% yield) along with the
corresponding heptasaccharide. The separation of the octa- and
heptasaccharides proved difficult.44 Silylation of the mixture
(41) The following compounds have been isolated as byproducts or
detected by MS analysis:
a Reagents and conditions: (a) (i) TBSOTf (cat.), Et2O, 0 °C; (ii) TIPSCl,
.
imidazole, DMF, rt, 30% (2 steps); (b) H2NNH2 H2O, pyridine, AcOH,
CH2Cl2, rt, 80%.
with TIPSCl and imidazole facilitated the separation of both
compounds by flash column chromatography, but also led to
degradation, as observed by TLC analysis. Consequently
(42) Even after 3 days at room temperature starting material was still
present in the reaction mixture.
(43) Similar to the synthesis of imidate 8, imidate 52 was prepared via
glycosylation of 32 with allyl alcohol (90%, R/â ) 94:6), removal of the
acetate (99%) and protection with levulinic acid (92%, R/â ) 94:6), removal
of the allyl group using catalytic PdCl2 in MeOH (84%), and installation
of the imidate (85%).
octasaccharide 53 was isolated in only 30% yield over two steps.
(44) No complete separation was achieved using flash column chroma-
tography or size-exclusion chromatography.
J. Org. Chem, Vol. 71, No. 21, 2006 8079

Ho¨lemann et al.
1H), 4.90 (d, J ) 11.4 Hz, 1H), 4.84 (d, J ) 11.1 Hz, 1H), 4.77
(d, J ) 11.4 Hz, 1H), 4.66 (d, J ) 10.8 Hz, 1H), 4.57 (d, J ) 11.1
Hz, 1H), 4.52 (d, J ) 10.8 Hz, 1H), 4.48 (d, J ) 10.8 Hz, 1H),
4.21-3.70 (m, 12H), 1.11-1.06 (m, 21H). 13C NMR (CDCl3, 75
MHz): δ 165.7, 165.6, 138.7, 138.3, 137.9, 137.8, 133.3, 133.2,
133.0, 129.9, 129.8, 128.5, 128.2, 128.1, 128.0, 127.8, 127.6, 127.5,
127.4, 118.0, 97.9, 96.8, 78.5, 78.1, 75.1, 74.2, 73.9, 72.9, 71.5,
71.3, 70.8, 68.9, 68.8, 68.1, 65.9, 62.4, 18.0, 17.9, 11.9. IR
(CHCl3): νmax 3067, 2945, 2862, 1718, 1453, 1269, 1113, 1026
cm-1. MALDI-HRMS calcd for C66H78O13SiNa (m/z): [MNa+]
1129.5109, found 1129.5090.
Allyl 6-O-(2-O-Benzoyl-3,4-di-O-benzyl-R-D-mannopyrano-
syl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranoside (24). AcCl
(200 µL) was slowly added dropwise to a solution of 23 (0.620 g,
0.56 mmol) in CH2Cl2 (4.05 mL) and MeOH (20 mL). The solution
was stirred at room temperature for 2.5 h before being quenched
by dropwise addition of Et3N (350 µL). The solvent was removed
under reduced pressure and the residue purified by gradient flash
silica gel column chromatography (hexanes/EtOAc, 5:1 to 2:1) to
give 24 (0.515 g, 96%) as a colorless oil. Spectral data matched
that previously reported.45
Removal of the levulinoyl groups proceeded smoothly upon
exposure to hydrazine monohydrate in buffered conditions to
give octasaccharide 54 in 80% yield. Further mannosylation of
54 proved even more strenuous, leading to a complex mixture
of products in which only trace amounts of the desired
decasaccharide were observed, as indicated by mass spectrom-
etry analysis.
Conclusion
Here we report the first total synthesis of an arabinomannan
oligosaccharide from M. tuberculosis as well as a series of
related arabinan and mannan oligosaccharides. Our flexible
synthetic strategy involves late-stage couplings and modifica-
tions, to enable ready access to several different LAM fragments
for SAR studies. Synthesis of target oligosaccharide 1 involved
the preparation of hexamannan 3 and hexaarabinan 5. Both
intermediates were prepared in excellent yield and stereoselec-
tivity using three different mannose and arabinose building
blocks. Union of arabinan 5 to mannan 3, the first reported
example of the coupling of an arabinan imidate to an oligo-
mannan core, proceeded smoothly via a [6 + 6] glycosylation
to afford dodecasaccharide 51 in excellent yield. Incorporation
of a thiol linker at the reducing end of the oligosaccharide allows
for the easy conjugation of the compounds to carrier proteins
or microarrays. In our laboratory, microarrays containing the
synthetic oligomers are currently used to screen TB antibodies.
Future work will investigate the elongation of the arabinan
core and the synthesis of mannan-capped arabinomannans.
Later, the â-arabinoside linkage will be included. These mol-
ecules will serve as molecular tools for biological studies and
will eventually help to find a carbohydrate antigen for vaccina-
tions against TB.
Allyl 6-O-(6-O-(3,4-Di-O-benzyl-2-O-levulinoyl-6-O-triisopro-
pylsilyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-
mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyr-
anoside (25). Imidate 8 (0.550 g, 0.73 mmol) and disaccharide 24
(0.600 g, 0.63 mmol) were combined and coevaporated three times
with toluene before being placed under nitrogen and dissolved in
CH2Cl2 (10 mL). The solution was cooled to 0 °C, TMSOTf (11.4
µL, 63 µmol) added dropwise, and the solution stirred for 30 min
before being quenched by NEt3 (20 µL). The solvent was removed
under reduced pressure and the resulting oil purified by gradient
flash silica gel column chromatography (hexanes/EtOAc, 5:1 to 3:1)
to give 25 (0.780 g, 80%) as a colorless oil. Rf ) 0.30 (hexanes/
1
EtOAc, 3:1). [R]D ) +34.6 (c 0.61, CHCl3). H NMR (CDCl3,
300 MHz): δ 8.18-8.14 (m, 4H), 7.54-7.47 (m, 6H), 7.37-7.14
(m, 30H), 5.98-5.85 (m, 1H), 5.82 (dd, J ) 1.9, 2.8 Hz, 1H), 5.72
(dd, J ) 1.5, 3.1 Hz, 1H), 5.52 (ddt, J ) 17.1, 10.3, 5.2 Hz, 1H),
5.32 (dq, J ) 17.1, 1.2 Hz, 1H), 5.22 (dq, J ) 10.3, 1.5 Hz, 1H),
5.12 (d, J ) 1.5 Hz, 1H), 5.01 (d, J ) 1.5 Hz, 1H), 4.94-4.80 (m,
5H), 4.68-4.40 (m, 7H), 4.23-3.56 (m, 18H), 2.76-2.65, (m, 4H),
2.18 (s, 3H), 1.10-1.06 (m, 21H). 13C NMR (CDCl3, 75 MHz): δ
205.9, 171.6, 165.5, 165.3, 138.6, 138.3, 138.1, 137.7, 137.6, 137.4,
133.1, 133.0, 129.8, 129.7, 128.4, 128.1, 128.0, 127.9, 127.6, 127.4,
127.2, 127.1, 117.9, 97.9, 97.8, 96.8, 78.5, 78.1, 77.8, 75.1, 75.0,
74.9, 74.1, 73.8, 73.7, 72.8, 71.5, 71.3, 71.2, 70.9, 70.8, 68.9, 68.5,
68.4, 68.1, 66.0, 65.7, 62.3, 38.0, 29.8, 28.1, 18.0, 12.0. IR
Experimental Section
Allyl 2-O-Benzoyl-3,4-di-O-benzyl-R-D-mannopyranoside (22).
To a solution of allyl glycoside 9b (6.60 g, 9.90 mmol) in THF
(150 mL) at 0 °C was added TBAF (20.1 mL of a 1 M solution in
THF, 20.1 mmol) and the solution stirred overnight with gradual
warming to room temperature. The solution was then extracted with
EtOAc (2 × 150 mL), the combined organic extracts were washed
once with water and once with brine and dried over MgSO4, and
the solvents were removed under reduced pressure. The resulting
oil was purified by gradient flash silica gel column chromatography
(hexanes/EtOAc, 3:1 to 2:1) to give 22 (4.06 g, 82%) as a colorless
oil. Spectral data matched that previously reported.45
(CHCl3): νmax 3008, 2942, 2867, 1719, 1270, 1116, 1097 cm-1
.
MALDI-HRMS calcd for C91H106O20SiNa (m/z): [MNa+] 1569.6944,
found 1569.6913.
Allyl 6-O-(6-O-(3,4-Di-O-benzyl-6-O-triisopropylsilyl-R-D-
mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyra-
nosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranoside (26).
To a solution of 25 (0.765 g, 0.49 mmol) in CH2Cl2 (4.8 mL) was
added a premixed solution of pyridine (577 µL) and AcOH (343
µL). Hydrazine monohydrate (48 µL, 0.36 mmol) was then added
dropwise and the solution stirred for 90 min before being quenched
by the addition of acetone (200 µL). After an additional 10 min,
the solvent was removed under reduced pressure and the residue
purified by gradient flash silica gel column chromatography
(hexanes/EtOAc, 5:1 to 3:1) to give 26 (0.657 g, 92%) as a colorless
oil. Rf ) 0.26 (hexanes/EtOAc, 3:1). [R]D ) +33.3 (c 1.20, CHCl3).
1H NMR (CDCl3, 300 MHz): δ 8.16-8.10 (m, 4H), 7.53-7.42
(m, 6H), 7.36-7.14 (m, 30H), 5.89 (ddt, J ) 15.6, 10.5, 4.1 Hz,
1H), 5.78 (dd, J ) 1.9, 3.0 Hz, 1H), 5.70 (dd, J ) 1.9, 3.3 Hz,
1H), 5.30 (dq, J ) 15.6, 1.5 Hz, 1H), 5.20 (dq, J ) 10.5, 1.5 Hz,
1H), 5.09 (d, J ) 1.6 Hz, 1H), 5.06 (d, J ) 1.5 Hz, 1H), 4.99 (d,
J ) 1.9 Hz, 1H), 4.91 (d, J ) 11.1 Hz, 1H), 4.89 (d, J ) 11.7 Hz,
1H), 4.87 (d, J ) 11.4 Hz, 2H), 4.85 (d, J ) 11.4 Hz, 1H), 4.66
(d, J ) 10.6 Hz, 1H), 4.65 (d, J ) 11.4 Hz, 1H), 4.60 (d, J ) 11.4
Allyl 6-O-(2-O-Benzoyl-3,4-di-O-benzyl-6-O-triisopropylsilyl-
R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-man-
nopyranoside (23). Alcohol 22 (2.67 g, 5.30 mmol) and imidate
9a (4.46 g, 5.83 mmol) were combined and coevaporated three times
with toluene before being placed under nitrogen and dissolved in
CH2Cl2 (65 mL). The solution was then cooled to 0 °C, TMSOTf
(96 µL, 0.53 mmol) added dropwise, and the solution stirred for
30 min before being quenched by the addition of NEt3 (200 µL).
The solvent was removed under reduced pressure and the residue
purified by flash silica gel column chromatography (hexanes/EtOAc,
10:1) to give 23 (5.75 g, 98%) as a colorless oil. Rf ) 0.20 (hexanes/
1
EtOAc, 10:1). [R]D ) +8.0 (c 0.15, CHCl3). H NMR (CDCl3,
300 MHz): δ 8.15-8.11 (m, 4H), 7.61-7.59 (m, 1H), 7.59-7.42
(m, 5H), 7.34-7.16 (m, 20H), 5.90 (ddt, J ) 17.1, 10.5, 5.3 Hz,
1H), 5.96-5.83 (m, 1H), 5.68 (dd, J ) 1.8, 3.0 Hz, 1H), 5.30 (dq,
J ) 17.1, 1.5 Hz, 1H), 5.20 (dq, J ) 10.5, 1.5 Hz, 1H), 5.06 (d,
J ) 1.5 Hz, 1H), 4.98 (d, J ) 1.8 Hz, 1H), 4.90 (d, J ) 10.8 Hz,
(45) Heng, L.; Ning, J.; Kong, F. Carbohydr. Res. 2001, 331, 431-437.
8080 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
Hz, 1H), 4.58 (d, J ) 11.4 Hz, 1H), 4.50 (d, J ) 11.4 Hz, 1H),
4.48 (d, J ) 11.4 Hz, 1H), 4.47 (d, J ) 10.8 Hz, 1H), 4.22-3.59
(m, 18H), 2.29 (d, J ) 3.6 Hz, 1H), 1.07-1.04 (m, 21H). 13C NMR
(CDCl3, 75 MHz): δ 165.5, 165.2, 138.4, 138.2, 138.1, 137.6,
137.4, 133.1, 133.0, 129.8, 129.7, 129.6, 128.4, 128.3, 128.1, 128.0,
127.6, 127.4, 127.3, 127.2, 117.9, 99.3, 97.8, 96.8, 79.8, 78.5, 77.9,
75.1, 74.9, 74.0, 73.9, 72.9, 72.5, 71.7, 71.5, 71.4, 71.2, 70.7, 68.9,
68.5, 68.3, 68.1, 66.0, 65.2, 62.5, 18.0, 12.0. IR (CHCl3): νmax 3569,
3008, 2941, 2867, 1719, 1269, 1118, 1075, 1028 cm-1. MALDI-
HRMS calcd for C86H100O18SiNa (m/z): [MNa+] 1471.6577, found
1471.6592.
4.39 (m, 14H), 4.22-3.50 (m, 28H), 2.66-2.61 (m, 4H), 2.11 (s,
3H), 1.12-1.08 (m, 21H). 13C NMR (CDCl3, 75 MHz): δ 206.2,
171.7, 165.7, 165.5, 165.3, 138.8, 138.6, 138.4, 138.2, 138.0, 137.9,
137.8, 137.6, 133.2, 132.9, 129.9, 129.8, 129.7, 128.5, 128.4, 128.3,
128.1, 128.0, 127.8, 127.6, 127.5, 127.3, 127.3, 127.2, 117.9, 99.7,
99.2, 97.9, 97.7, 97.0, 79.5, 78.5, 78.3, 78.0, 77.8, 75.1, 75.0, 74.9,
74.8, 74.4, 74.1, 73.7, 73.1, 72.5, 72.2, 71.8, 71.6, 71.3, 70.9, 69.0,
68.9, 68.6, 68.1, 66.1, 65.8, 65.6, 62.2, 38.0, 29.7, 28.0, 17.9, 12.0.
IR (CHCl3): νmax 3008, 2940, 2866, 1720, 1453, 1362, 1269, 1115,
1028 cm-1. MALDI-HRMS calcd for C145H160O31SiNa (m/z):
[MNa+] 2448.0611, found 2448.0560.
Allyl 6-O-(6-O-(2-O-(2-O-Benzoyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-
3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-
benzyl-R-D-mannopyranoside (28). Imidate 7 (0.627 g, 0.90 mmol)
and trisaccharide 26 (1.00 g, 0.69 mmol) were combined and
coevaporated three times with toluene before being placed under
nitrogen and dissolved in CH2Cl2 (10 mL). The solution was then
cooled to 0 °C, TMSOTf (19 µL, 0.10 mmol) added dropwise, and
the solution stirred for 30 min before being quenched by the addition
of NEt3 (50 µL). The solvent was removed under reduced pressure
and the resulting oil purified by gradient flash silica gel column
chromatography (hexanes/EtOAc, 5:1 to 3:1) to give 27 (1.23 g,
90%) as a colorless oil. To a solution of 27 (1.23 g, 0.62 mmol) in
CH2Cl2 (10.5 mL) was then added MeOH (12.6 mL) before AcCl
(200 µL) was added dropwise. The solution was stirred at room
temperature for 3 h before being quenched by the addition of Et3N
(400 µL). The solvent was removed under reduced pressure and
the residue purified by gradient flash silica gel column chroma-
tography (hexanes/EtOAc, 5:1 to 3:1) to give 28 (1.02 g, 90%) as
a white foam. Rf ) 0.28 (hexanes/EtOAc, 3:1). [R]D ) +18.3 (c
0.99, CHCl3). 1H NMR (CDCl3, 300 MHz): δ 8.15-8.06 (m, 6H),
7.57-7.05 (m, 54H), 5.94-5.81 (m, 1H), 5.76-5.74 (m, 2H), 5.68
(dd, J ) 2.1, 3.3 Hz, 1H), 5.28 (dq, J ) 17.1, 1.5 Hz, 1H), 5.19
(dq, J ) 10.2, 1.5 Hz, 1H), 5.10 (d, J ) 1.5 Hz, 1H), 5.08 (d, J )
1.5 Hz, 1H), 4.97-4.96 (m, 2H), 4.90 (d, J ) 10.5 Hz, 2H), 4.88
(d, J ) 11.7 Hz, 1H), 4.87 (d, J ) 10.5 Hz, 1H), 4.84 (d, J ) 12.0
Hz, 1H), 4.83 (d, J ) 12.0 Hz, 1H), 4.77 (d, J ) 11.4 Hz, 1H),
4.63 (d, J ) 12.0 Hz, 2H), 4.60s4.43 (m, 7H), 4.59 (s, 2H), 4.42
(d, J ) 11.4 Hz, 2H), 4.18-3.47 (m, 22H). 13C NMR (CDCl3, 75
MHz): δ 165.7, 165.5, 165.3, 138.4, 138.3, 137.9, 137.5, 133.2,
133.1, 133.0, 129.8, 129.7, 128.4, 128.3, 128.2, 128.1, 128.0, 127.6,
127.5, 127.4, 127.3, 118.1, 99.5, 99.0, 98.0, 96.9, 79.2, 78.6, 78.0,
77.6, 75.3, 75.0, 74.8, 74.0, 73.7, 73.2, 72.2, 72.1, 71.8, 71.5, 71.4,
71.2, 71.0, 70.7, 68.9, 68.9, 68.8, 68.7, 68.5, 68.1, 66.0, 65.6, 61.8.
IR (CHCl3): νmax 3066, 3008, 2929, 2873, 1720, 1453, 1362, 1269,
1117 cm-1. MALDI-HRMS calcd for C111H112O24Na (m/z):
[MNa+] 1851.7441, found 1851.7403.
Allyl 6-O-(6-O-(2-O-(2-O-Benzoyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-6-O-(6-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-3,4-di-O-benzyl-2-O-levulinoyl-R-D-mannopyra-
nosyl)-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-
di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-
R-D-mannopyranoside (30). To a solution of 29 (2.00 g, 0.82
mmol) in CH2Cl2 (13 mL) and MeOH (15 mL) was added AcCl
(255 µL) dropwise. The solution was then stirred at room
temperature for 6 h before being quenched by the addition of Et3N
(500 µL). The solvent was removed under reduced pressure and
the residue purified by gradient flash silica gel column chroma-
tography (hexanes/EtOAc, 5:1 to 2:1) to give the corresponding
alcohol (1.56 g, 84%) as a colorless oil, Rf ) 0.29 (hexanes/EtOAc,
2:1). Imidate 7 (0.532 g, 0.76 mmol) and the alcohol (1.50 g, 0.66
mmol) were combined and coevaporated three times with toluene
before being placed under nitrogen and dissolved in CH2Cl2 (10
mL). The solution was cooled to 0 °C, TMSOTf (12 µL, 66 µmol)
was added dropwise, and the solution was stirred for 30 min before
being quenched by the addition of NEt3 (30 µL). The solvent was
removed under reduced pressure and the resulting oil purified by
gradient flash silica gel column chromatography (hexanes/EtOAc,
5:1 to 2:1) to give 30 (0.170 g, 92%) as a colorless oil. Rf ) 0.22
1
(hexanes/EtOAc, 3:1). [R]D ) +55.7 (c 0.95, CHCl3). H NMR
(CDCl3, 300 MHz): δ 8.16-8.03 (m, 8H), 7.56-7.48 (m, 6H),
7.37-7.07 (m, 76H), 5.88-5.86 (m, 1H), 5.82-5.80 (m, 1H), 5.76
(dd, J ) 2.1, 3.3 Hz, 1H), 5.75 (dd, J ) 2.1, 3.0 Hz 1H), 5.69 (dd,
J ) 1.8, 3.0 Hz, 1H), 5.40 (t, J ) 1.5 Hz, 1H), 5.28 (dq, J ) 17.1,
1.5 Hz, 1H), 5.21-5.20 (m, 1H), 5.18 (d, J ) 1.5 Hz, 1H), 5.13
(d, J ) 1.2 Hz, 1H), 5.11 (d, J ) 1.8 Hz, 1H), 5.03 (d, J ) 1.0 Hz,
1H), 4.95 (d, J ) 1.5 Hz, 1H), 4.93-4.53 (m, 23 H), 4.50 (d, J )
11.1 Hz, 1H), 4.47 (d, J ) 10.2 Hz, 1H), 4.45 (d, J ) 10.2 Hz,
1H), 4.45 (d, J ) 12.0 Hz, 1H), 4.43 (d, J ) 12.0 Hz, 1H), 4.35
(d, J ) 10.2 Hz, 1H), 4.16-3.46 (m, 33H), 2.74-2.70 (m, 2H),
2.62-2.58 (m, 2H), 2.02 (s, 3H). 13C NMR (CDCl3, 75 MHz): δ
205.8, 171.9, 165.6, 165.4, 165.2, 138.5, 138.4, 138.3, 138.2, 138.0,
137.9, 137.7, 137.6, 133.2, 133.0, 129.9, 129.8, 129.7, 128.5, 128.4,
128.3, 128.2, 128.0, 127.8, 127.6, 127.5, 127.4, 127.3, 127.2, 118.0,
99.8, 99.2, 98.1, 97.7, 97.1, 79.6, 78.6, 78.3, 78.1, 77.9, 77.7, 75.2,
75.0, 74.9, 74.5, 74.1, 73.8, 73.6, 73.4, 73.2, 72.3, 71.9, 71.8, 71.7,
71.4, 71.3, 71.2, 71.1, 70.8, 69.1, 69.0, 68.8, 68.6, 68.5, 68.2, 66.6,
65.9, 65.7, 65.1, 37.8, 29.7, 28.3. IR (CHCl3): νmax 3008, 2928,
2859, 1723, 1453, 1266, 1116, 1093, 975, 909 cm-1. MALDI-
HRMS calcd for C170H172O37Na (m/z): [MNa+] 2828.1475, found
2828.1419.
1-O-(6-O-(6-O-(2-O-(2-O-Benzoyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-6-O-(6-O-(2-O-benzoyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-3,4-di-O-benzyl-2-O-levulinoyl-R-D-mannopyra-
nosyl)-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-
di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-
R-D-mannopyranosyl) Trichloroacetimidate (2). Hexasaccharide
30 (0.630 g, 0.22 mmol) was dissolved in THF (15 mL) and
degassed with argon for 30 min. {Ir(COD)[PCH3(C6H5)2]2}PF6
(0.010 g, 11 µmol) was added and the solution degassed for another
5 min before being purged with hydrogen for 5 min and argon for
further 5 min. The solution was stirred at room temperature for
2.5 h before the solvent was removed under reduced pressure. The
residue was dissolved in THF/H2O (4:1, 25 mL), and iodine (0.168
g, 0.66 mmol) was added. The resulting brown solution was stirred
Allyl 6-O-(6-O-(2-O-(2-O-Benzoyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-6-O-(3,4-di-O-benzyl-2-O-levulinoyl-6-O-triisopro-
pylsilyl-R-D-mannopyranosyl)-3,4-di-O-benzyl-R-D-mannopyr-
anosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-
benzoyl-3,4-di-O-benzyl-R-D-mannopyranoside (29). Imidate 8
(0.920 g, 1.21 mmol) and tetrasaccharide 28 (1.85 g, 1.01 mmol)
were combined and coevaporated three times with toluene before
being placed under nitrogen and dissolved in CH2Cl2 (18 mL). The
solution was then cooled to 0 °C, TMSOTf (18.3 µL, 0.10 mmol)
was added dropwise, and the solution was stirred for 30 min before
being quenched by the addition of NEt3 (50 µL). The solvent was
removed under reduced pressure and the resulting oil purified by
gradient flash silica gel column chromatography (hexanes/EtOAc,
5:1 to 3:1) to give 29 (2.06 g, 85%) as a colorless oil. Rf ) 0.25
1
(hexanes/EtOAc, 3:1). [R]D ) +26.1 (c 0.64, CHCl3). H NMR
(CDCl3, 300 MHz): δ 8.19-8.06 (m, 6H), 7.56-7.51 (m, 4H),
7.38-7.09 (m, 60H), 5.97-5.84 (m, 1H), 5.84-5.83 (m, 1H), 5.78
(t, J ) 2.1 Hz, 1H), 5.72 (dd, J ) 1.8, 3.0 Hz, 1H), 5.42-5.40 (m,
1H), 5.31 (dq, J ) 17.4, 1.5 Hz, 1H), 5.22 (dq, J ) 10.5, 1.5 Hz,
1H), 5.15 (d, J ) 1.5 Hz, 1H), 5.14 (d, J ) 1.8 Hz, 1H), 5.06-
5.05 (m, 1H), 4.98 (d, J ) 1.5 Hz, 1H), 4.95-4.80 (m, 9H), 4.68-
J. Org. Chem, Vol. 71, No. 21, 2006 8081

Ho¨lemann et al.
at room temperature for 1.5 h, quenched by the addition of saturated
aqueous Na2SO4 solution, and diluted with EtOAc (60 mL). The
organic phase was separated and washed twice with water and dried
over MgSO4, and the solvent was removed under reduced pressure.
The pale yellow residue was purified by gradient flash silica gel
column chromatography (hexanes/EtOAc, 3:1 to 1:1) to give the
corresponding lactol (0.566 g, 93%) as a colorless oil. The lactol
was dissolved in CH2Cl2 (5 mL), trichloroacetonitrile (205 µL, 2.1
mmol) added, and the solution cooled to 0 °C before DBU (3.1
µL, 2.0 µmol) was added. The reaction was stirred at 0 °C for 30
min before being passed through a small silica gel plug, and the
plug was washed with EtOAc (80 mL). The solvent was removed
under reduced pressure to afford a pale yellow residue that was
purified by gradient flash silica gel column chromatography
(hexanes/EtOAc, 3:1 to 2:1) to give 2 (0.500 g, 86%) as a color-
less oil. Rf ) 0.53 (hexanes/EtOAc, 2:1). [R]D ) +18.8 (c 1.50,
(CDCl3, 300 MHz): δ 8.15-8.03 (m, 8H), 7.56-7.46 (m, 6H),
7.37-7.10 (m, 81H), 5.79-5.75 (m, 2H), 5.74 (dd, J ) 1.8, 3.0
Hz, 1H), 5.64 (dd, J ) 1.5, 3.0 Hz, 1H), 5.11 (d, J ) 1.8 Hz, 1H),
5.10-5.09 (m, 2H), 5.06 (d, J ) 1.8 Hz, 1H), 5.04 (d, J ) 1.2 Hz,
1H), 4.92-4.35 (m, 30H), 4.16-3.33 (m, 33H), 3.69 (s, 2H), 2.73
(d, J ) 3.3 Hz, 1H), 2.40 (t, J ) 6.9 Hz, 2H), 1.57-1.51 (m, 4H),
1.35-1.27 (m, 4H). 13C NMR (CDCl3, 75 MHz): δ 165.8, 165.5,
165.4, 165.4, 138.6, 138.5, 138.3, 138.0, 137.9, 137.8, 137.7, 137.6,
133.2, 133.0, 132.9, 130.0, 129.9, 129.8, 129.7, 128.8, 128.5, 128.4,
128.3, 128.2, 128.1, 127.9, 127.8, 127.7, 127.6, 127.5, 127.4, 127.3,
127.2, 126.8, 99.9, 98.9, 98.3, 98.0, 97.8, 79.6, 79.2, 78.6, 78.1,
77.2, 76.0, 75.4, 75.1, 75.0, 74.7, 74.1, 73.8, 73.6, 73.3, 73.2, 72.0,
71.7, 71.1, 70.8, 69.0, 68.7, 67.8, 67.6, 66.2, 65.9, 65.7, 65.0, 36.2,
31.3, 29.2, 29.0, 28.6, 25.8. IR (CHCl3): νmax 3036, 3007, 2928,
1721, 1496, 1453, 1362, 1269, 1117, 1077, 1028, 980, 909 cm-1
.
MALDI-HRMS calcd for C175H180O35SNa (m/z): [MNa+] 2896.1924,
found 2896.1823.
1
CHCl3). H NMR (CDCl3, 300 MHz): δ 8.70 (s, 1H), 8.13-8.08
(m, 8H), 7.61-7.54 (m, 6H), 7.40-7.16 (m, 76H), 6.41 (d,
J ) 1.8 Hz, 1H), 5.85-5.84 (m, 2H), 5.81-5.80 (m, 1H), 5.76 (t,
J ) 1.2 Hz, 1H), 5.70 (t, J ) 1.8 Hz, 1H), 5.38 (t, J ) 1.8 Hz,
1H), 5.15 (d, J ) 1.8 Hz, 1H), 5.11 (d, J ) 1.8 Hz, 1H), 5.06 (d,
J ) 1.5 Hz, 1H), 5.01 (d, J ) 1.2 Hz, 1H), 4.90-4.31 (m, 29H),
4.14-3.42 (m, 30H), 2.78-2.68 (m, 2H), 2.62-2.05 (m, 2H), 2.01
(s, 3H). 13C NMR (CDCl3, 75 MHz): δ 205.7, 171.7, 165.3, 165.2,
165.1, 159.3, 138.4, 138.3, 138.3, 138.2, 138.1, 137.8, 137.7, 137.6,
137.4, 137.2, 133.3, 133.0, 132.8, 129.8, 129.6, 129.3, 128.5, 128.2,
128.1, 128.1, 128.0, 128.0, 127.9, 127.8, 127.6, 127.4, 127.2, 127.2,
127.1, 127.1, 99.6, 99.1, 97.9, 97.8, 97.6, 95.1, 90.6, 79.5, 78.1,
78.0, 77.7, 77.5, 77.4, 77.0, 76.5, 75.3, 75.1, 74.9, 74.8, 74.3, 74.0,
73.7, 73.6, 73.5, 73.4, 73.3, 73.1, 72.1, 71.8, 71.7, 71.6, 71.6, 71.3,
71.1, 71.1, 71.0, 70.7, 69.0, 68.8, 68.7, 68.6, 68.4, 68.3, 67.5, 66.4,
65.7, 65.4, 65.0, 38.0, 29.6, 28.1. IR (CHCl3): νmax 3011, 2929,
6-Thiohexyl 6-O-(6-O-(2-O-(R-D-Mannopyranosyl)-6-O-(6-O-
(R-D-mannopyranosyl)-R-D-mannopyranosyl)-R-D-mannopyra-
nosyl)-R-D-mannopyranosyl)-R-D-mannopyranoside (13). Liquid
ammonia (15 mL) was condensed in a three-necked receiver flask
cooled to -78 °C in a cooling bath. Small pieces of sodium were
then added until a bright blue solution was obtained. To this solution
was added dropwise a solution of hexasaccharide 3 (0.065 g, 0.023
mmol) in THF (10 mL). The bright blue solution was stirred at
-78 °C for 2 h before being quenched by the dropwise addition of
MeOH. The cooling bath was then removed, and the ammonia was
removed by bubbling nitrogen through the solution. After neutral-
ization with Amberlite IR 120 resin, the solution was filtered
through a glass frit, washing with 100 mL of MeOH, and the solvent
removed under reduced pressure to give crude 13 as a very pale
yellow oil. The residue was purified by gradient reversed-phase
C18 column chromatography (H2O/MeOH, 1:0 to 0:1) and freeze-
dried to give 13 (0.0233 mg, 92%) isolated as the sulfur-linked
dimer as a white amorphous solid. [R]D ) +70.6 (c 0.57, H2O).
1H NMR (D2O, 300 MHz): δ 5.12 (d, J ) 1.4 Hz, 2H), 5.03 (d,
J ) 1.7 Hz, 2H), 4.89 (m, 4H), 4.88 (d, J ) 1.4 Hz, 2H), 4.84 (d,
J ) 1.6 Hz, 2H), 4.07 (dd, J ) 1.8, 3.3 Hz, 2H), 4.02-3.63 (m,
70H), 3.62-3.52 (m, 2H), 2.77 (t, J ) 7.1 Hz, 4H), 1.74-1.61
(m, 8H), 1.46-1.40 (m, 8H). 13C NMR (D2O, 75 MHz): δ 105.0,
102.7, 102.3, 102.1, 100.8, 81.6, 75.9, 75.4, 73.7, 73.6, 73.3, 73.1,
72.8, 72.7, 70.6, 69.4, 69.3, 69.2, 69.1, 68.6, 68.4, 68.3, 67.8, 63.7,
63.6, 40.9, 31.0, 30.9, 29.8, 27.7. ESI-HRMS calcd for C84H146O62S2-
Na2(m/z): [M2Na2+] 1128.3749, found 1128.3745.
Allyl 6-O-(6-O-(2-O-Acetyl-3,4,6-tri-O-benzyl-R-D-mannopy-
ranosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-
O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranoside (33). Glycosyl
trichloroacetimidate 32 (0.600 g, 0.94 mmol) and disaccharide 24
(0.727 g, 0.66 mmol) were combined and coevaporated three times
with toluene before being placed under nitrogen and dissolved in
CH2Cl2 (20 mL). The solution was cooled to 0 °C, TMSOTf (12
µL, 0.10 mmol) added dropwise, and the solution stirred for 30
min before being quenched by the addition of NEt3 (20 µL). The
solvent was removed under reduced pressure and the resulting oil
purified by gradient flash silica gel column chromatography
(hexanes/EtOAc, 5:1 to 3:1) to give 33 (0.918 g, 98%) as a colorless
oil. Spectral data matched that previously reported.45
2862, 1721, 1453, 1362, 1269, 1117, 1092, 1028, 980 cm-1
.
MALDI-HRMS calcd for C169H168Cl3NO37Na (m/z): [MNa+]
2931.0258, found 2931.0316.
6-(Benzylthio)hexyl 6-O-(6-O-(2-O-(2-O-Benzoyl-3,4,6-tri-O-
benzyl-R-D-mannopyranosyl)-6-O-(6-O-(2-O-benzoyl-3,4,6-tri-O-
benzyl-R-D-mannopyranosyl)-3,4-di-O-benzyl-R-D-mannopyra-
nosyl)-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-
di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-benzyl-
R-D-mannopyranoside (3). Imidate 2 (0.286 g, 0.098 mmol) and
6-(benzylthio)hexan-1-ol (0.033 g, 0.15 mmol) were combined and
coevaporated three times with toluene before being placed under
nitrogen and dissolved in CH2Cl2 (2 mL). The solution was then
cooled to 0 °C, TMSOTf (50 µL of a 0.036 M solution in CH2Cl2,
9.8 µmol) was added dropwise, and the solution was stirred for 30
min before being quenched by the addition of NEt3 (10 µL). The
solvent was removed under reduced pressure, and the resulting oil
was passed through a small silica gel plug, washing with hexanes/
EtOAc (3:1, 50 mL). The solution was dissolved in pyridine (3.66
mL), acetic anhydride (2.18 mL) added, and the solution stirred at
room temperature for 16 h. The reaction was quenched by the slow
addition of water and extracted with EtOAc, and the organic extracts
were dried over MgSO4. The solvent was removed under reduced
pressure by coevaporation with toluene and the residue purified
by gradient flash silica gel column chromatography (hexanes/
EtOAc, 20:1 to 5:1) to give 31 (0.260 g, 89%), Rf ) 0.33 (hexanes/
EtOAc, 2:1), and the acetylated linker 6-(benzylthio)hexyl acetate,
Rf ) 0.25 (hexanes/EtOAc, 2:1), that was discarded. A premixed
solution of pyridine (1.32 mL) and AcOH (785 µL) was then added
to 31 (0.250 g, 84 µmol) and hydrazine monohydrate (50 µL of a
0.16 M solution in CH2Cl2, 0.17 mmol) was added dropwise. The
reaction was stirred at room temperature for 90 min before being
quenched by the addition of acetone (50 µL). The solution was
stirred for another 15 min at room temperature before the solvent
was removed under reduced pressure and the residue purified by
gradient flash silica gel column chromatography (hexanes/EtOAc,
5:1 to 2:1) to give 3 (0.231 g, 96%) as a white foam. Rf ) 0.56
Allyl 6-O-(6-O-(3,4,6-Tri-O-benzyl-R-D-mannopyranosyl)-2-
O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-
3,4-di-O-benzyl-R-D-mannopyranoside (34). AcCl (130 µL) was
added dropwise to a solution of trisaccharide 32 (0.520 g, 0.36
mmol) in CH2Cl2 (2.6 mL) and MeOH (13 mL). The solution was
stirred for 48 h at room temperature before additional AcCl (130
µL) was added, and the solution stirred for further 24 h. The solution
was quenched by the dropwise addition of NEt3 (350 µL) and the
solvent removed under reduced pressure. The residue was purified
by gradient flash silica gel column chromatography (hexanes/
EtOAc, 3:1 to 2:1) to give 34 (0.469 g, 93%) as a colorless oil.
Rf ) 0.34 (hexanes/EtOAc, 2:1). [R]D ) +37.7 (c 0.35, CHCl3).
1
(hexanes/EtOAc, 2:1). [R]D ) +28.9 (c 1.00, CHCl3). H NMR
8082 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
1H NMR (CDCl3, 300 MHz): δ 8.14-8.08 (m, 4H), 7.51-7.12
(m, 41H), 5.95-5.82 (m, 1H), 5.76 (dd, J ) 2.2, 3.0 Hz, 1H), 5.68
(dd, J ) 1.9, 3.1 Hz, 1H), 5.29 (dq, J ) 17.1, 1.5 Hz, 1H), 5.19
(dq, J ) 10.2, 1.5 Hz, 1H), 5.14 (d, J ) 1.6 Hz, 1H), 5.07 (d, J )
1.6 Hz, 1H), 4.98 (d, J ) 1.6 Hz, 1H), 4.90 (d, J ) 11.1 Hz, 1H),
4.88 (d, J ) 12.3 Hz, 1H), 4.48 (d, J ) 11.1 Hz, 1H), 4.80 (d, J )
10.5 Hz, 1H), 4.79 (d, J ) 11.1 Hz, 1H), 4.64-4.42 (m, 9H), 4.20-
3.54 (m, 18H), 2.37 (d, J ) 3.0 Hz, 1H). 13C NMR (CDCl3, 75
MHz): δ 165.7, 165.4, 138.4, 138.3, 138.2, 138.1, 137.8, 137.6,
133.2, 133.1, 129.8, 128.5, 128.4, 128.3, 128.2, 128.1, 127.8, 127.7,
127.6, 127.5, 127.4, 118.1, 99.4, 97.9, 96.9, 79.9, 78.6, 78.1, 75.2,
75.1, 75.1, 74.2, 74.2, 74.0, 73.4, 71.8, 71.7, 71.5, 71.4, 71.2, 70.9,
69.0, 68.7, 68.6, 68.3, 68.3, 66.2, 65.5. IR (CHCl3): νmax 3559,
of a 0.011 M solution in CH2Cl2, 7.4 µmol) were added. The
solution was stirred at 0 °C for 30 min before being filtered through
a small silica gel plug, washing with EtOAc (50 mL), and the
solvent removed under reduced pressure. The resulting oil was
purified by gradient flash silica gel chromatography (hexanes/
EtOAc, 5:1 to 3:1) to give 36 (0.117 g, 81%, 3 steps) as a colorless
oil. Rf ) 0.38 (hexanes/EtOAc, 3:1). [R]D ) +24.3 (c 0.91, CHCl3).
1H NMR (CDCl3, 300 MHz): δ 8.73 (s, 1H), 8.19-8.10 (m, 4H),
7.55-7.13 (m, 56H), 6.39 (d, J ) 1.8 Hz, 1H), 5.82 (dd, J ) 1.2,
2.7 Hz, 1H), 5.73 (dd, J ) 1.2, 2.6 Hz, 1H), 5.56 (dd, J ) 1.5, 2.7
Hz, 1H), 5.11 (d, J ) 1.5 Hz, 1H), 5.04 (d, J ) 1.3 Hz, 1H), 5.01
(d, J ) 1.2 Hz, 1H), 4.91 (d, J ) 10.8 Hz, 1H), 4.88 (d, J ) 10.8
Hz, 1H), 4.85 (d, J ) 10.8 Hz, 1H), 4.84 (d, J ) 11.4 Hz, 1H),
4.78 (d, J ) 11.1 Hz, 1H), 4.67-4.36 (m, 15H), 4.20-3.49 (m,
21H), 2.14 (s, 3H). 13C NMR (CDCl3, 75 MHz): δ 170.1, 165.5,
165.4, 160.0, 138.5, 138.4, 138.2, 138.0, 137.9, 137.6, 137.4, 133.5,
133.2, 129.9, 129.8, 129.5, 128.6, 128.4, 128.3, 128.2, 128.1, 127.9,
127.8, 127.7, 127.6, 127.4, 127.3, 99.5, 99.1, 97.8, 96.0, 90.7, 79.4,
78.2, 78.1, 77.8, 75.3, 75.0, 74.9, 74.6, 74.4, 74.1, 73.7, 73.5, 73.3,
73.1, 72.0, 71.9, 71.7, 71.3, 70.9, 68.8, 68.7, 68.5, 67.6, 65.9, 65.7,
21.1. IR (CHCl3): νmax 3067, 3026, 2923, 2862, 1723, 1267, 1113,
1092, 974 cm-1. MALDI-HRMS calcd for C112H112Cl3NO24Na
(m/z): [MNa+] 1982.6538, found 1982.6532.
3067, 3035, 3005, 2933, 2872, 1712, 1451, 1359, 1267, 1118 cm-1
.
MALDI-HRMS calcd for C84H86O18Na (m/z): [MNa+] 1405.5712,
found 1405.5681.
Allyl 6-O-(6-O-(2-O-(2-O-Acetyl-3,4,6-tri-O-benzyl-R-D-man-
nopyranosyl)-3,4,6-tri-O-benzyl-R-D-mannopyranosyl)-2-O-ben-
zoyl-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-
O-benzyl-R-D-mannopyranoside (35). Imidate 32 (0.543 g, 0.85
mmol) and trisaccharide 34 (0.993 g, 0.71 mmol) were combined
and coevaporated three times with toluene before being placed under
nitrogen and dissolved in CH2Cl2 (12 mL). The solution was cooled
to 0 °C, TMSOTf (6 µL, 0.032 mmol) was added dropwise, and
the solution stirred for 30 min before being quenched by the addition
of NEt3 (12 µL). The solvent was removed under reduced pressure
and the resulting oil purified by gradient flash silica gel column
chromatography (toluene/EtOAc, 50:1 to 20:1) to give 35 (1.08 g,
6-(Benzylthio)hexyl 6-O-(6-O-(2-O-(2-O-Acetyl-3,4,6-tri-O-
benzyl-R-D-mannopyranosyl)-3,4,6-tri-O-benzyl-R-D-mannopy-
ranosyl)-2-O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranosyl)-2-
O-benzoyl-3,4-di-O-benzyl-R-D-mannopyranoside (37). Imidate
36 (0.110 g, 0.056 mmol) and 6-(benzylthio)hexan-1-ol (0.019 g,
84 µmol) were combined and coevaporated three times with toluene
before being placed under nitrogen and dissolved in CH2Cl2 (1 mL).
The solution was then cooled to 0 °C, and TMSOTf (50 µL of a
0.022 M solution in CH2Cl2, 60 µmol) was added dropwise. The
solution was stirred for 30 min before being quenched by the
addition of NEt3 (20 µL). The solvent was removed under reduced
pressure, and the resulting oil was dissolved in pyridine (1 mL)
before acetic anhydride (500 µL) was added dropwise. The solution
was stirred at room temperature for 16 h before being quenched
by the slow addition of water, extracted with EtOAc, and the organic
extracts dried over MgSO4. The solvent was removed under reduced
pressure by coevaporation with toluene and the residue purified
by gradient flash silica gel column chromatography (hexanes/
EtOAc, 5:1 to 3:1) to give 37 (0.105 g, 93%) as a colorless oil.
Rf ) 0.38 (hexanes/EtOAc, 3:1). [R]D ) +21.6 (c 0.90, CHCl3).
1H NMR (CDCl3, 300 MHz): δ 8.16-8.08 (m, 4H), 7.51-7.12
(m, 61H), 5.77 (dd, J ) 1.8, 3.1 Hz, 1H), 5.66 (dd, J ) 1.8, 3.3
Hz, 1H), 5.55 (dd, J ) 1.9, 3.0 Hz, 1H), 5.10 (d, J ) 1.8 Hz, 1H),
5.09 (d, J ) 1.7 Hz, 1H), 5.00 (d, J ) 1.6 Hz, 1H), 4.91 (d, J )
1.6 Hz, 1H), 4.90-4.76 (m, 5H), 4.64 (d, J ) 10.9 Hz, 1H), 4.61
(d, J ) 11.9 Hz, 1H), 4.60 (d, J ) 11.7 Hz, 1H), 4.57 (d, J ) 10.9
Hz, 2H), 4.55 (d, J ) 11.7 Hz, 1H), 4.53 (d, J ) 11.1 Hz, 1H),
4.49-4.35 (m, 8H), 4.15-3.37 (m, 23H), 3.70 (s, 2H), 2.41 (t,
J ) 7.1 Hz, 2H), 2.13 (s, 3H), 1.61-1.51 (m, 4H), 1.44-1.22 (m,
4H). 13C NMR (CDCl3, 75 MHz): δ 170.1, 165.9, 165.5, 138.7,
138.6, 138.5, 138.4, 138.3, 138.1, 138.0, 137.6, 133.3, 130.0, 129.9,
128.9, 128.6, 128.5, 128.4, 128.3, 128.2, 127.9, 127.8, 127.7, 127.5,
127.4, 127.3, 126.9, 99.6, 99.1, 98.1, 97.9, 79.5, 78.7, 78.3, 78.2,
77.3, 75.2, 75.1, 74.9, 74.8, 74.5, 74.3, 73.9, 73.4, 73.2, 72.1, 72.0,
71.9, 71.8, 71.7, 71.4, 71.1, 70.8, 69.1, 68.8, 68.6, 67.9, 66.2, 36.3,
31.4, 29.3, 29.1, 28.7, 25.9, 21.2. IR (CHCl3): νmax 3067, 3008,
83%) as a colorless oil. Rf ) 0.50 (toluene/EtOAc, 10:1). [R]D
)
1
+25.8 (c 1.88, CHCl3). H NMR (CDCl3, 300 MHz): δ 8.16-
8.09 (m, 4H), 7.51-7.11 (m, 56H), 5.95-5.82 (m, 1H), 5.76 (dd,
J ) 1.5, 2.8 Hz, 1H), 5.69 (dd, J ) 1.5, 3.0 Hz, 1H), 5.54 (dd,
J ) 1.5, 2.7 Hz, 1H), 5.34-5.26 (m, 1H), 5.21-5.18 (m, 1H), 5.10
(d, J ) 1.5 Hz, 1H), 5.07 (d, J ) 1.5 Hz, 1H), 5.00 (d, J ) 1.5 Hz,
1H), 4.97 (d, J ) 1.5 Hz, 1H), 4.91-4.76 (m, 5H), 4.66-4.34 (m,
15H), 4.19-3.47 (m, 23H), 2.12 (s, 3H). 13C NMR (CDCl3, 75
MHz): δ 170.1, 165.8, 165.5, 138.6, 138.5, 138.4, 138.3, 138.2,
138.1, 137.9, 137.6, 133.3, 130.0, 129.8, 128.6, 128.5, 128.3, 128.2,
127.9, 127.7, 127.6, 127.5, 127.4, 127.3, 118.1, 99.6, 99.1, 98.0,
97.0, 79.5, 78.6, 78.1, 75.2, 75.0, 74.9, 74.7, 74.4, 74.2, 73.8, 73.3,
73.2, 72.0, 71.9, 71.7, 71.6, 71.3, 71.0, 70.9, 69.0, 68.9, 68.8, 68.6,
68.2, 66.1, 66.0, 21.2. IR (CHCl3): νmax 3056, 3005, 2923, 2866,
1723, 1496, 1364, 1262, 1113, 1097, 1028, 980 cm-1. MALDI-
HRMS calcd for C113H116O24Na (m/z): [MNa+] 1879.7754, found
1879.7714.
6-O-(6-O-(2-O-(2-O-Acetyl-3,4,6-tri-O-benzyl-R-D-mannopy-
ranosyl)-3,4,6-tri-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-
3,4-di-O-benzyl-R-D-mannopyranosyl)-2-O-benzoyl-3,4-di-O-
benzyl-R-D-mannopyranosyl) Trichloroacetimidate (36). To
tetrasaccharide 35 (0.146 g, 0.09 mmol), coevaporated three times
with toluene under argon, was added THF (10 mL) and the solution
degassed for 30 min with argon. {Ir(COD)[PCH3(C6H5)2]2}PF6 (4.0
mg, 4.0 µmol) was added and the solution degassed for a further 5
min before being flushed with hydrogen for 5 min. The solution
was then purged with argon for 10 min and stirred at room
temperature for 2 h before the solvent was removed under reduced
pressure. The resulting oil was passed through a small silica gel
plug (hexanes/EtOAc, 1:1). The solvent was removed under reduced
pressure, the residue dissolved in THF/H2O (4:1, 11.3 mL), and
iodine (0.069 g, 0.27 mmol) added. The solution was stirred at room
temperature for 90 min before being quenched by the addition of
saturated aqueous Na2S2O3 solution (20 mL) and extracted with
EtOAc. The organic extract was washed twice with water and once
with brine and dried over MgSO4 and the solvent removed under
reduced pressure. The resulting oil was purified by gradient flash
silica gel column chromatography (hexanes/EtOAc, 5:1 to 3:1) to
give the corresponding lactol (0.136 g, 82%). The lactol was then
dissolved in CH2Cl2 (1 mL) and the solution cooled to 0 °C before
trichloroacetonitrile (74 µL, 0.74 mmol) and then DBU (100 µL
2932, 2862, 1721, 1496, 1453, 1363, 1266, 1098, 1028, 974 cm-1
.
MALDI-HRMS calcd for C123H130O24SNa (m/z): [MNa+] 2045.8570,
found 2045.8573.
6-Thiohexyl 6-O-(6-O-(2-O-(R-D-Mannopyranosyl)-R-D-man-
nopyranosyl)-R-D-mannopyranosyl)-R-D-mannopyranoside (14).
Liquid ammonia (15 mL) was condensed in a three-necked re-
ceiver flask cooled to -78 °C in a cooling bath. Small pieces of
sodium were added until a bright blue solution was obtained. A
solution of tetrasaccharide 38 (0.040 g, 19.8 µmol) in THF (10
mL) was added dropwise. The bright blue solution was stirred at
J. Org. Chem, Vol. 71, No. 21, 2006 8083

Ho¨lemann et al.
-78 °C for 2 h before being quenched by the dropwise addition
of MeOH. The cooling bath was removed and the ammonia
removed by bubbling nitrogen through the solution. After neutral-
ization with Amberlite IR 120 resin, the solution was filtered
through a glass frit, washing with 100 mL of MeOH, and the sol-
vent removed under reduced pressure to give crude 14 as a very
pale yellow oil. The residue was then purified by gradient re-
versed-phase C18 column chromatography (H2O/MeOH, 1:0 to 0:1)
and freeze-dried to give pure 14 (0.018 g, 93%) isolated as the
sulfur linked dimer as a white amorphous solid. [R]D ) +60.2 (c
Pent-4-enyl 5-O-(2-O-Benzoyl-3-O-benzyl-R-D-arabinofura-
nosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofuranoside (45). A
solution of 44 (7.15 g, 7.99 mmol) in anhydrous MeOH/CH2Cl2
(4:1, 160 mL) was cooled to 0 °C, and AcCl (5.70 mL, 79.9 mmol)
was added. After 4 h at 0 °C, the reaction was quenched by addition
of saturated aqueous NaHCO3 solution (200 mL). The aqueous layer
was extracted with CH2Cl2 (4 × 300 mL). The combined organic
extracts were washed with brine (400 mL), dried over Na2SO4,
filtered, and evaporated. Purification by gradient flash silica gel
column chromatography (hexanes/EtOAc, 4:1 to 3:1) yielded 45
(5.44 g, 92%) as a colorless oil. Rf ) 0.20 (hexanes/EtOAc, 3:1).
1
0.47, H2O). H NMR (D2O, 300 MHz): δ 5.13 (d, J ) 1.2 Hz,
1
2H), 5.02 (d, J ) 1.8 Hz, 2H), 4.87 (d, J ) 1.2 Hz, 2H), 4.83 (d,
J ) 1.5 Hz, 2H), 4.06 (dd, J ) 1.8, 3.3 Hz, 2H), 4.00-3.51 (m,
50H), 2.76 (t, J ) 7.2 Hz, 4H), 1.74-1.58 (m, 8H), 1.44-1.37
(m, 8H). 13C NMR (D2O, 75 MHz): δ 105.0, 102.7, 102.3, 100.8,
81.4, 75.9, 75.4, 73.8, 73.6, 73.0, 72.9, 72.8, 72.7, 70.6, 69.6, 69.3,
69.2, 68.6, 68.4, 63.8, 63.6, 40.9, 31.1, 30.9, 29.9, 27.7. ESI-HRMS
calcd for C60H106O42S2Na2 (m/z): [M2Na2+] 804.2692, found
804.2693.
[R]D ) +106.9 (c 0.29, CHCl3). H NMR (CDCl3, 300 MHz): δ
8.05 (d, J ) 7.6 Hz, 2H), 8.00 (d, J ) 7.6 Hz, 2H), 7.61-7.53 (m,
2H), 7.47-7.40 (m, 4H), 7.36-7.20 (m, 10H), 5.89-5.76 (m, 1H),
5.41 (s, 2H), 5.28 (s, 1H), 5.16 (s, 1H), 5.06-4.95 (m, 2H), 4.82
(d, J ) 12.1 Hz, 1H), 4.66 (d, J ) 11.4 Hz, 1H), 4.63 (d, J ) 11.5
Hz, 1H), 4.48 (d, J ) 12.1 Hz, 1H), 4.37-4.33 (m, 1H), 4.17 (d,
J ) 5.6 Hz, 1H), 4.11-4.07 (m, 1H), 3.99-3.90 (m, 2H), 3.83-
3.73 (m, 3H), 3.61-3.46 (m, 2H), 2.20-2.12 (m, 2H), 1.80-1.69
(m, 3H). 13C NMR (CDCl3, 75 MHz): δ 165.5, 165.2, 138.2, 137.8,
137.6, 133.4, 133.3, 129.8, 129.7, 129.5, 129.4, 128.5, 128.3, 127.8,
127.7, 127.6, 114.8, 106.2, 106.0, 83.3, 82.8, 82.1, 81.8, 81.4, 72.3,
72.2, 66.8, 65.7, 61.9, 30.2, 28.6. IR (CHCl3): νmax 3590, 2933,
1718, 1451, 1267, 1113, 1072, 1026 cm-1. MALDI-HRMS calcd
for C43H46O11Na (m/z): [MNa+] 761.2938, found 761.2945.
Pent-4-enyl 5-O-(5-O-(2-O-Benzoyl-5-O-triisopropylsilyl-R-D-
arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofurano-
syl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofuranoside (47). Dis-
accharide 45 (4.60 g, 6.23 mmol) and imidate 11 (4.86 g, 7.47
mmol) were coevaporated with anhydrous toluene (4 × 25 mL)
and dried in vacuo overnight. The mixture was dissolved in
anhydrous CH2Cl2 (100 mL) and cooled to -40 °C, and TMSOTf
(0.14 mL, 0.72 mmol) was added. After 45 min at -40 to -30 °C,
the suspension was treated with Et3N, the solution was stirred for
15 min at room temperature, and the solvents were evaporated.
Purification by flash silica gel column chromatography (hexanes/
EtOAc, 4:1) gave trisaccharide 46 (3.35 g, 44%) as a colorless oil
and a mixture of 46 and trichloroacetamide. 46: Rf ) 0.30 (hexanes/
Pent-4-enyl 5-O-(2-O-Benzoyl-3-O-benzyl-5-O-triisopropyl-R-
D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofura-
noside (44). A solution of 12b (1.29 g, 2.27 mmol) in anhydrous
MeOH/CH2Cl2 (4:1, 30 mL) was cooled to 0 °C, and AcCl (1.60
mL, 22.4 mmol) was added. After 3 h at 0 °C, the reaction was
quenched by addition of saturated aqueous NaHCO3 solution (50
mL). The aqueous layer was extracted with CH2Cl2 (4 × 100 mL).
The combined organic extracts were washed with brine (200 mL),
dried over Na2SO4, filtered, and evaporated. Purification by flash
silica gel column chromatography (hexanes/EtOAc, 5:1) yielded
pent-4-enyl 2-O-benzoyl-3-O-benzyl-R-D-arabinofuranoside (0.894
g, 96%) as a colorless oil. Rf ) 0.20 (hexanes/EtOAc, 3:1). [R]D )
1
+80.7 (c 0.55, CHCl3). H NMR (CDCl3, 300 MHz): δ 8.02-
7.98 (m, 2H), 7.60-7.54 (m, 1H), 7.46-7.41 (m, 2H), 7.34-7.21
(m, 5H), 5.88-5.74 (m, 1H), 5.36 (d, J ) 1.5 Hz, 1H), 5.12 (s,
1H), 5.06-4.92 (m, 2H), 4.81 (d, J ) 12.2 Hz, 1H), 4.59 (d, J )
12.2 Hz, 1H), 4.24-4.20 (m, 1H), 4.07-4.04 (m, 1H), 3.90-3.83
(m, 1H), 3.74 (td, J ) 6.7, 9.5 Hz, 1H), 3.69-3.60 (m, 1H), 3.48
(td, J ) 6.4, 9.5 Hz, 1H), 2.19-2.11 (m, 2H), 1.80-1.67 (m, 3H).
13C NMR (CDCl3, 75 MHz): δ 165.4, 138.1, 137.6, 133.4, 129.7,
129.4, 128.5, 128.4, 127.8, 114.9, 106.2, 82.9, 82.1, 72.4, 66.9,
62.0, 30.2, 28.6. IR (CHCl3): νmax 3590, 3005, 1718, 1451, 1318,
1267, 1108, 1036 cm-1. MALDI-HRMS calcd for C24H28O6Na
(m/z): [MNa+] 435.1784, found 435.1767.
1
EtOAc, 3:1). [R]D ) +79.6 (c 0.24, CHCl3). H NMR (CDCl3,
300 MHz): δ 8.06-7.98 (m, 6H), 7.59-7.52 (m, 3H), 7.47-
7.38 (m, 6H), 7.36-7.18 (m, 10H), 5.88-5.74 (m, 1H), 5.44 (s,
1H), 5.39 (d, J ) 1.5 Hz, 1H), 5.29 (s, 2H), 5.24 (d, J ) 5.2 Hz,
1H), 5.21 (s, 1H), 5.14 (s, 1H), 5.05-4.92 (m, 2H), 4.80 (d, J )
12.3 Hz, 1H), 4.67 (d, J ) 12.3 Hz, 1H), 4.62 (d, J ) 12.3 Hz,
1H), 4.52 (d, J ) 12.3 Hz, 1H), 4.36-4.31 (m, 1H), 4.21-4.15
(m, 2H), 4.04 (d, J ) 5.2 Hz, 1H), 3.99-3.72 (m, 7H), 3.65 (dd,
J ) 3.7, 11.1 Hz, 1H), 3.48 (td, J ) 6.4, 9.6 Hz, 1H), 2.66-2.34
(m, 3H), 2.27-2.11 (m, 3H), 2.08 (s, 3H), 1.76-1.67 (m,
2H), 1.06-1.02 (m, 21H). 13C NMR (CDCl3, 75 MHz): δ 205.9,
171.7, 165.5, 165.2, 138.2, 137.8, 137.8, 133.4, 133.3, 129.8, 129.5,
129.3, 128.5, 128.3, 127.8, 127.6, 127.6, 114.8, 106.1, 106.0, 105.7,
83.3, 82.1, 82.0, 81.6, 81.5, 72.3, 71.9, 66.8, 65.7, 65.6, 62.8, 37.6,
30.2, 29.7, 28.6, 27.5, 17.9, 11.9. IR (CHCl3): νmax 2933, 2862,
1718, 1446, 1318, 1297, 1267, 1113, 1072, 1026 cm-1. MALDI-
HRMS calcd for C69H84O18SiNa (m/z): [MNa+] 1251.5325, found
1251.5296.
Imidate 12a (6.57 g, 10.2 mmol) and pent-4-enyl 2-O-benzoyl-
3-O-benzyl-R-D-arabinofuranoside (3.50 g, 8.49 mmol) were
combined, coevaporated with anhydrous toluene (5 × 25 mL), and
dried in vacuo overnight. The mixture was dissolved in anhydrous
CH2Cl2 (140 mL) and cooled to -40 °C, and TMSOTf (0.20 mL,
1.03 mmol) was added. After 1 h at -40 to -30 °C, the suspension
was treated with Et3N, the solution was stirred for 10 min at room
temperature, and the solvents were removed in vacuo. Purification
by flash silica gel column chromatography (hexanes/EtOAc, 10:1)
gave disaccharide 44 (7.15 g, 94%) as a colorless oil. Rf ) 0.37
1
(hexanes/EtOAc, 7:1). [R]D ) +66.7 (c 0.39, CHCl3). H NMR
(CDCl3, 300 MHz): δ 8.02-7.94 (m, 4H), 7.56-7.47 (m, 2H),
7.41-7.34 (m, 4H), 7.30-7.12 (m, 10H), 5.84-5.70 (m, 1H), 5.39
(d, J ) 1.1 Hz, 1H), 5.35 (d, J ) 1.5 Hz, 1H), 5.22 (s, 1H), 5.09
(s, 1H), 5.01-4.88 (m, 2H), 4.73 (d, J ) 11.9 Hz, 1H), 4.62 (d, J
) 12.1 Hz, 1H), 4.55 (d, J ) 11.9 Hz, 1H), 4.47 (d, J ) 12.1 Hz,
1H), 4.32-4.28 (m, 1H), 4.14-4.12 (m, 1H), 4.10-4.03 (m, 2H),
3.89 (dd, J ) 4.1, 11.4 Hz, 1H), 3.75-3.67 (m, 4H), 3.44 (td, J )
6.4, 9.6 Hz, 1H), 2.14-2.07 (m, 2H), 1.72-1.63 (m, 2H), 1.04-
0.89 (m, 21H). 13C NMR (CDCl3, 75 MHz): δ 165.5, 165.3, 138.2,
137.9, 137.8, 133.3, 133.2, 129.8, 129.7, 129.6, 129.5, 128.4, 128.3,
128.2, 127.8, 127.7, 127.6, 127.5, 114.8, 106.1, 106.0, 84.0, 83.4,
82.9, 82.1, 82.0, 81.5, 72.3, 72.0, 66.7, 65.5, 62.6, 30.2, 28.6, 17.9,
11.8. IR (CHCl3): νmax 2944, 2862, 1718, 1451, 1267, 1113, 1067
cm-1. MALDI-HRMS calcd for C52H66O11SiNa (m/z): [MNa+]
917.4272, found 917.4282.
The combined fractions of trisaccharide 46 containing some
trichloroacetamide were dissolved in anhydrous CH2Cl2 (62 mL)
and premixed pyridine (5.90 mL) and AcOH (3.60 mL), followed
by hydrazine monohydrate (0.60 mL, 10.4 mmol), were added. The
mixture was stirred at room temperature for 45 min and then
quenched by the addition of acetone (3 mL) and stirred for 10 min.
The solvents were evaporated, and the residue was purified by flash
silica gel column chromatography (hexanes/EtOAc, 5:1) to give
47 (5.76 g, 82%, 2 steps) as a colorless oil. Rf ) 0.25 (hexanes/
1
EtOAc, 4:1). [R]D ) +82.6 (c 0.93, CHCl3). H NMR (CDCl3,
300 MHz): δ 8.04-7.96 (m, 6H), 7.60-7.51 (m, 3H), 7.44-7.39
(m, 6H), 7.34-7.18 (m, 10H), 5.88-5.74 (m, 1H), 5.39 (s, 1H),
5.38 (s, 1H), 5.27 (s, 1H), 5.25 (s, 1H), 5.13 (s, 1H), 5.04-4.92
8084 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
(m, 2H), 5.02 (d, J ) 2.5 Hz, 1H), 4.79 (d, J ) 11.9 Hz, 1H), 4.65
(d, J ) 11.9 Hz, 1H), 4.61 (d, J ) 11.9 Hz, 1H), 4.48 (d, J ) 11.9
Hz, 1H), 4.35-4.30 (m, 1H), 4.19-4.13 (m, 3H), 4.02-3.71 (m,
8H), 3.64 (dd, J ) 3.4, 11.0 Hz, 1H), 3.47 (td, J ) 6.3, 9.6 Hz,
1H), 2.96 (d, J ) 5.3 Hz, 1H), 2.18-2.10 (m, 2H), 1.76-1.67 (m,
2H), 1.12-0.98 (m, 21H). 13C NMR (CDCl3, 75 MHz): δ 166.4,
165.3, 165.1, 138.1, 137.7, 137.5, 133.4, 133.3, 133.2, 129.6, 129.4,
129.3, 129.0, 128.4, 128.2, 127.7, 127.6, 114.7, 106.1, 105.9, 105.1,
85.7, 84.7, 83.3, 83.2, 82.1, 81.8, 81.6, 81.4, 72.3, 72.1, 66.8, 65.7,
62.9, 30.3, 28.7, 18.0, 12.0. IR (CHCl3): νmax 2942, 2868, 1721,
1452, 1316, 1300, 1269, 1114, 1070, 1028 cm-1. MALDI-HRMS
calcd for C64H78O16SiNa (m/z): [MNa+] 1153.4957, found 1153.4932.
Pent-4-enyl 5-O-(5-O-(2-O-Benzoyl-3-O-(2-O-benzoyl-3-O-
benzyl-5-O-triisopropylsilyl-R-D-arabinofuranosyl)-5-O-triiso-
propysilyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-
arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arainofurano-
side (48). Trisaccharide 47 (5.76 g, 5.09 mmol) and imidate 12a
(4.31 g, 6.68 mmol) were coevaporated with anhydrous toluene (5
× 25 mL) and dried under vacuum overnight. The mixture was
dissolved in anhydrous CH2Cl2 (100 mL) and cooled to -40 °C,
and TMSOTf (0.13 mL, 0.675 mmol) was added. After 20 min at
-40 to -30 °C, the suspension was treated with Et3N, the solution
was stirred for 15 min at room temperature, and the solvents were
evaporated. Purification by flash silica gel column chromatography
(hexanes/EtOAc, 7:1) gave tetrasaccharide 48 (7.14 g, 87%) as a
colorless oil. Rf ) 0.40 (hexanes/EtOAc, 5:1). [R]D ) +74.5 (c
0.99, CHCl3). 1H NMR (CDCl3, 300 MHz): δ 8.12-8.02 (m, 8H),
7.62-7.54 (m, 4H), 7.47-7.18 (m, 23H), 5.92-7.79 (m, 1H),
5.53-5.52 (m, 2H), 5.45 (s, 2H), 5.43 (s, 1H), 5.32 (s, 1H), 5.31
(s, 1H), 5.19 (s, 1H), 5.10-4.97 (m, 2H), 4.84 (d, J ) 12.1 Hz,
1H), 4.78 (d, J ) 12.1 Hz, 1H), 4.70 (d, J ) 11.9 Hz, 1H), 4.67
(d, J ) 12.1 Hz, 1H), 4.61-4.56 (m, 3H), 4.42-4.17 (m, 7H),
4.03-3.72 (m, 9H), 3.52 (dt, J ) 6.4, 9.4 Hz, 1H), 2.23-2.16 (m,
2H), 1.81-1.72 (m, 2H), 1.15-0.95 (m, 42H). 13C NMR (CDCl3,
75 MHz): δ 165.5, 165.3, 165.1, 138.2, 137.9, 133.1, 129.8, 129.7,
129.5, 128.4, 128.2, 127.8, 127.6, 127.5, 114.7, 106.2, 106.0, 105.0,
84.1, 83.4, 83.1, 82.8, 82.2, 82.1, 81.9, 81.5, 78.7, 72.3, 72.1, 66.8,
65.8, 65.5, 62.5, 62.3, 30.2, 28.7, 17.9, 12.0, 11.9. IR (CHCl3):
72.3, 72.2, 66.7, 65.7, 65.6, 61.9, 61.4, 30.1, 28.5. IR (CHCl3):
ν
max 3015, 1723, 1452, 1316, 1298, 1268, 1114, 1070, 1028 cm-1
.
MALDI-HRMS calcd for C74H76O21Na (m/z): [MNa+] 1323.4777,
found 1323.4745.
Pent-4-enyl 5-O-(5-O-(5-O-(2-O-Benzoyl-3,5-di-O-benzyl-R-
D-arabinofuranosyl)-2-O-benzoyl-3-O-(5-O-(2-O-benzoyl-3,5-di-
O-benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-
arabinofuranosyl)-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-
R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabino-
furanoside (4). Tetrasaccharide 49 (0.800 g, 0.615 mmol) and
imidate 10 (1.12 g, 1.93 mmol) were coevaporated with anhydrous
toluene (3 × 15 mL) and dried in vacuo overnight. The mixture
was dissolved in anhydrous CH2Cl2 (13 mL) and cooled to -40
°C, and TMSOTf (0.16 mL, 0.083 mmol) was added. After 35 min
at -40 to -30 °C, the suspension was treated with Et3N and the
solution stirred for 15 min at room temperature before the solvents
were evaporated. Purification by gradient flash silica gel column
chromatography (hexanes/EtOAc, 5:1 to 3:1) gave hexasaccharide
4 (1.20 g, 92%) as a colorless foam. Rf ) 0.15 (hexanes/EtOAc,
3:1). [R]D ) +96.3 (c 0.90, CHCl3). 1H NMR (CDCl3, 300 MHz):
δ 8.05-7.89 (m, 12H), 7.57-7.09 (m, 53H), 5.87-5.74 (m, 1H),
5.48 (s, 1H), 5.44 (d, J ) 1.5 Hz, 1H), 5.39 (d, J ) 1.3 Hz, 1H),
5.38-5.37 (m, 3H), 5.30 (s, 1H), 5.29 (d, J ) 1.2 Hz, 1H), 5.26
(s, 1H), 5.24 (s, 1H), 5.16 (s, 1H), 5.11 (s, 1H), 5.05-4.97 (m,
1H), 4.96-4.91 (m, 1H), 4.76 (d, J ) 12.0 Hz, 1H), 4.71 (d, J )
11.9 Hz, 1H), 4.63 (d, J ) 11.9 Hz, 1H), 4.60 (d, J ) 12.0 Hz,
1H), 4.58 (d, J ) 12.5 Hz, 1H), 4.53-4.14 (m, 18H), 4.09-4.04
(m, 1H), 4.00-3.39 (m, 16H), 2.17-2.10 (m, 2H), 1.75-1.66
(m, 2H). 13C NMR (CDCl3, 75 MHz): δ 165.5, 165.3, 165.2,
165.1, 138.2, 138.0, 137.9, 137.8, 137.7, 133.2, 133.1, 129.8, 129.7,
129.6, 129.5, 128.4, 128.3, 128.2, 127.8, 127.7, 127.6, 127.5,
127.4, 114.7, 106.1, 106.0, 105.3, 83.3, 83.3, 83.2, 82.6, 82.4,
82.2, 81.9, 81.8, 81.7, 81.5, 79.9, 73.3, 72.3, 72.2, 71.8, 69.2, 66.8,
65.7, 65.5, 65.3, 65.0, 30.2, 28.6. IR (CHCl3): νmax 3003, 2923,
1722, 1452, 1316, 1299, 1268, 1115, 1071, 1027 cm-1. MALDI-
HRMS calcd for C126H124O31Na (m/z): [MNa+] 2156.8058, found
2156.8005.
1-O-(5-O-(5-O-(5-O-(2-O-Benzoyl-3,5-di-O-benzyl-R-D-ara-
binofuranosyl)-2-O-benzoyl-3-O-(5-O-(2-O-benzoyl-3,5-di-O-
benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-ar-
abinofuranosyl)-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-
R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabino-
furanosyl) Trichloroacetimidate (5). To a solution of hexasaccharide
4 (0.250 g, 0.117 mmol) in acetonitrile (8.0 mL) and water (0.5
mL) was added NBS (0.063 g, 0.35 mmol), and the solution was
stirred at room temperature for 1.5 h. After MS analysis showed
complete conversion (ca. 1-1.5 h), the reaction was quenched by
addition of aqueous Na2S2O3 solution (5 mL), water (5 mL), and
brine (5 mL). The aqueous phase was extracted with EtOAc (4 ×
20 mL). The combined organic extracts were dried over MgSO4,
filtered, and concentrated. Purification by gradient flash silica gel
column chromatography (hexanes/EtOAc, 2:1 to 1:1) gave the
corresponding lactol as a mixture with the halohydrin byproduct,
Rf ) 0.25 (hexanes/EtOAc, 3:2). The mixture was dissolved in
anhydrous CH2Cl2 (1.5 mL) and cooled to 0 °C. Trichloroaceto-
nitrile (0.11 mL, 1.11 mmol) followed by DBU (0.0025 mL, 0.016
mmol) were added. After 30 min at 0 °C, the mixture was filtered
over a plug of silica gel and washed with CH2Cl2, and the solvents
were evaporated. Purification by gradient flash silica gel column
chromatography (hexanes/EtOAc, 3:1 to 2:1) gave 5 (0.177 g, 72%,
2 steps) as a colorless foam. Rf ) 0.30 (hexanes/EtOAc, 2:1). [R]D
) +66.7 (c 1.07, CHCl3). 1H NMR (CDCl3, 300 MHz): δ 8.65 (s,
1H), 8.16-7.98 (m, 12H), 7.65-7.18 (m, 53H), 6.55 (s, 1H), 5.75
(d, J ) 1.3 Hz, 1H), 5.57 (s, 1H), 5.49-5.45 (m, 4H), 5.39 (s,
1H), 5.38 (d, J ) 1.2 Hz, 1H), 5.34 (s, 1H), 5.30 (s, 1H), 5.25 (s,
1H), 4.91 (d, J ) 11.9 Hz, 1H), 4.79 (d, J ) 11.9 Hz, 1H), 4.72
(d, J ) 11.9 Hz, 1H), 4.68-3.48 (m, 35H). 13C NMR (CDCl3, 75
MHz): δ 165.3, 165.1, 160.8, 138.0, 137.9, 137.7, 133.5, 133.2,
133.1, 129.9, 129.8, 129.7, 129.6, 129.5, 129.4, 129.1, 128.6, 128.4,
ν
max 2943, 2867, 1722, 1452, 1316, 1299, 1268, 1115, 1070, 1028
cm-1. MALDI-HRMS calcd for C92H116O21Si2Na (m/z): [MNa+]
1635.7445, found 1635.7479.
Pent-4-enyl 5-O-(5-O-(2-O-Benzoyl-3-O-(2-O-benzoyl-3-O-
benzyl-R-D-arabinofuranosyl)-R-D-arabinofuranosyl)-2-O-ben-
zoyl-3-O-benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-
R-D-arabinofuranoside (49). Tetrasaccharide 48 (5.20 g, 3.22
mmol) was dissolved in anhydrous MeOH/CH2Cl2 (4:1, 50 mL)
and cooled to 0 °C, and AcCl (2.30 mL, 32.2 mmol) was added.
The solution was stirred for 4 h, while slowly warming to room
temperature. The reaction was quenched by addition of saturated
aqueous NaHCO3 solution (100 mL), and the aqueous layer was
extracted with CH2Cl2 (4 × 100 mL). The combined organic
extracts were dried over Na2SO4, filtered, and evaporated. Purifica-
tion by gradient flash silica gel column chromatography (hexanes/
EtOAc, 3:1 to 1:2) gave 49 (3.65 g, 87%) as a colorless solid.
Rf ) 0.10 (hexanes/EtOAc, 1:1). [R]D ) +99.8 (c 0.91, CHCl3).
1H NMR (CDCl3, 300 MHz): δ 8.07-7.97 (m, 8H), 7.61-7.52
(m, 3H), 7.47-7.15 (m, 24H), 5.89-5.76 (m, 1H), 5.50 (s, 1H),
5.46 (s, 1H), 5.40 (s, 1H), 5.35 (s, 2H), 5.29 (s, 1H), 5.27 (s, 1H),
5.14 (s, 1H), 5.03 (d, J ) 17.1 Hz, 1H), 4.96 (d, J ) 10.7 Hz, 1H),
4.80 (d, J ) 12.1 Hz, 1H), 4.74 (d, J ) 12.1 Hz, 1H), 4.68 (d, J )
12.1 Hz, 1H), 4.63 (d, J ) 12.1 Hz, 1H), 4.53 (d, J ) 11.9 Hz,
1H), 4.52 (d, J ) 11.9 Hz, 1H), 4.39-4.33 (m, 2H), 4.27-4.23
(m, 1H), 4.18-4.09 (m, 4H), 3.98-3.67 (m, 9H), 3.62-3.54 (m,
1H), 3.48 (td, J ) 6.5, 9.6 Hz, 1H), 2.21-2.12 (m, 2H), 2.03 (dd,
J ) 4.4, 8.5 Hz, 1H), 1.98 (dd, J ) 4.9, 7.6 Hz, 1H), 1.77-1.68
(m, 2H). 13C NMR (CDCl3, 75 MHz): δ 165.5, 165.3, 165.2, 165.0,
138.2, 137.8, 137.7, 137.4, 133.3, 133.2, 129.7, 129.4, 129.3, 128.4,
128.3, 128.2, 127.8, 127.7, 127.6, 127.5, 114.8, 106.1, 106.0, 105.9,
105.2, 83.6, 83.3, 83.2, 82.9, 82.6, 82.5, 82.1, 81.8, 81.7, 81.4, 79.5,
J. Org. Chem, Vol. 71, No. 21, 2006 8085

Ho¨lemann et al.
128.3, 128.2, 127.8, 127.7, 127.6, 127.5, 127.4, 106.3, 106.1, 105.3,
103.9, 91.1, 84.6, 83.3, 83.2, 83.1, 82.8, 82.6, 82.4, 82.3, 82.2, 82.0,
81.9, 81.7, 81.5, 80.8, 79.8, 73.3, 72.2, 71.8, 69.2, 65.5, 65.3, 65.0.
IR (CHCl3): νmax 1723, 1452, 1316, 1298, 1268, 1115, 1071, 1027
cm-1. MALDI-HRMS calcd for C123H116Cl3NO31Na (m/z): [MNa+]
2230.6495, found 2230.6432.
Pent-4-enyl 5-O-(5-O-(5-O-(2-O-Benzoyl-3-O-benzyl-R-D-ara-
binofuranosyl)-2-O-benzoyl-3-O-(5-O-(2-O-benzoyl-3-O-benzyl-
R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabino-
furanosyl)-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-
arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofurano-
side (6). Tetrasaccharide 49 (0.500 g, 0.384 mmol) and imidate
12a (0.743 g, 1.15 mmol) were coevaporated with anhydrous
toluene (4 × 15 mL) and dried in vacuo overnight. The mixture
was dissolved in CH2Cl2 (10 mL) and cooled to -40 °C, and
TMSOTf (0.010 mL, 0.054 mmol) was added. After 15 min at -40
to -30 °C, the suspension was treated with Et3N, the solution was
stirred for 10 min at room temperature, and the solvents were
evaporated. Purification by flash silica gel column chromatography
(hexanes/EtOAc, 5:1) gave the corresponding hexasaccharide (0.836
g, 96%) as a colorless foam. Rf ) 0.25 (hexanes/EtOAc, 4:1). [R]D
) +89.4 (c 0.95, CHCl3). 1H NMR (CDCl3, 300 MHz): δ 8.07-
7.97 (m, 12H), 7.59-7.12 (m, 43H), 5.89-5.76 (m, 1H), 5.49 (s,
1H), 5.47 (s, 1H), 5.44 (s, 1H), 5.40 (s, 3H), 5.33 (s, 1H), 5.30 (s,
1H), 5.29 (s, 1H), 5.26 (s, 1H), 5.14 (s, 2H), 5.03 (d, J ) 17.1 Hz,
1H), 4.96 (d, J ) 10.1 Hz, 1H), 4.79 (d, J ) 12.0 Hz, 1H), 4.71
(d, J ) 12.1 Hz, 1H), 4.65 (d, J ) 12.1 Hz, 1H), 4.63 (s, 1H), 4.63
(d, J ) 12.0 Hz, 1H), 4.55-4.49 (m, 5H), 4.40 (d, J ) 12.1 Hz,
1H), 4.37-4.10 (m, 9H), 4.04-3.65 (m, 15H), 3.48 (td, J ) 6.4,
9.7 Hz, 1H), 2.19-2.12 (m, 2H), 1.78-1.68 (m, 2H), 1.05-0.78
(m, 42H). 13C NMR (CDCl3, 75 MHz): δ 165.5, 165.3, 165.1,
138.2, 137.9, 137.8, 133.2, 133.1, 133.0, 129.8, 129.7, 129.6, 129.5,
129.4, 128.4, 128.3, 128.2, 128.1, 128.0, 127.8, 127.7, 127.6, 127.5,
127.4, 127.3, 114.7, 106.2, 106.1, 105.9, 105.2, 83.9, 83.3, 83.2,
82.7, 82.5, 82.2, 82.0, 81.9, 81.7, 81.5, 79.9, 72.3, 72.1, 71.8, 66.7,
65.7, 65.5, 65.2, 65.0, 62.6, 62.5, 30.2, 28.6, 17.9, 17.8, 11.9, 11.8.
IR (CHCl3): νmax 2942, 2867, 1722, 1452, 1316, 1299, 1268, 1116,
1070, 1027 cm-1. MALDI-HRMS calcd for C130H152O31Si2Na
(m/z): [MNa+] 2288.9787, found 2288.9788.
6-(Benzylthio)hexyl 5-O-(5-O-(5-O-(2-O-Benzoyl-3,5-di-O-
benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-(5-O-(2-O-ben-
zoyl-3,5-di-O-benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-
benzyl-R-D-arabinofuranosyl)-R-D-arabinofuranosyl)-2-O-benzoyl-
3-O-benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-
arabinofuranoside (50). Imidate 5 (0.030 g, 0.0136 mmol) and
6-(benzylthio)hexan-1-ol (0.0061 g, 0.0271 mmol) were coevapo-
rated with anhydrous toluene (4 × 5 mL) and dried in vacuo
overnight. The mixture was dissolved in anhydrous CH2Cl2 (0.3
mL) and cooled to -20 °C, and TMSOTf (0.39 mL of a 0.052 M
solution in CH2Cl2, 0.002 mmol) was added. After 30 min, the
reaction was quenched with Et3N, the solution was stirred for 15
min at room temperature, and the solvents were evaporated. Pyridine
(4 mL) and acetic anhydride (2 mL) were added, and the mixture
was stirred at room-temperature overnight. The solvents were
evaporated, and the residue was purified by flash silica gel column
chromatography (toluene/EtOAc, 9:1) to afford R-50 (0.203 g, 66%)
and R/â-50 (0.0038 g, 12%, R/â ) 1:1) as colorless oils. R-50:
Rf ) 0.35 (toluene/EtOAc, 9:1). [R]D ) +84.5 (c 0.44, CHCl3).
1H NMR (CDCl3, 500 MHz): δ 8.04-7.89 (m, 12H), 7.54-7.09
(m, 58H), 5.47 (s, 1H), 5.44 (d, J ) 1.6 Hz, 1H), 5.39 (d, J ) 1.2
Hz, 1H), 5.37-5.36 (m, 3H), 5.29 (s, 1H), 5.28 (d, J ) 1.1 Hz,
1H), 5.25 (s, 1H), 5.22 (s, 1H), 5.15 (s, 1H), 5.10 (s, 1H), 4.75 (d,
J ) 12.0 Hz, 1H), 4.70 (d, J ) 11.9 Hz, 1H), 4.62 (d, J ) 12.0
Hz, 1H), 4.59 (d, J ) 12.1 Hz, 1H), 4.57 (d, J ) 12.5 Hz, 1H),
4.54-4.26 (m, 13H), 4.22-4.19 (m, 2H), 4.15-4.14 (m, 2H),
4.08-4.05 (m, 1H), 3.98-3.82 (m, 6H), 3.77 (dd, J ) 2.5, 11.6
Hz, 1H), 3.72-3.65 (m, 5H), 3.67 (s, 2H), 3.58 (dd, J ) 3.7, 10.7
Hz, 1H), 3.53-3.47 (m, 2H), 3.44-3.40 (m, 2H), 2.38 (t, J ) 7.5
Hz, 2H), 1.60-1.50 (m, 4H), 1.35-1.31 (m, 4H). 13C NMR (CDCl3,
125 MHz): δ 165.5, 165.3, 165.2, 165.1, 138.7, 138.0, 137.9, 137.8,
137.7, 133.2, 133.1, 133.1, 129.9, 129.8, 129.7, 129.6, 129.5, 128.8,
128.5, 128.4, 128.3, 128.2, 127.9, 127.8, 127.7, 127.6, 127.5, 127.4,
126.8, 106.2, 106.1, 106.0, 105.4, 83.3, 83.2, 82.6, 82.4, 82.3, 82.2,
81.9, 81.7, 81.6, 81.5, 79.9, 73.3, 72.4, 72.3, 72.2, 71.8, 69.3, 69.2,
67.4, 65.7, 65.5, 65.3, 65.1, 36.3, 31.3, 29.3, 29.2, 28.6, 25.7. IR
(CHCl3): νmax 3008, 2928, 1722, 1452, 1316, 1299, 1268, 1115,
1071, 1027 cm-1. MALDI-HRMS calcd for C134H134O31SNa (m/
z): [MNa+] 2295.8595, found 2295.8578. â-50: Rf ) 0.20 (toluene/
EtOAc, 9:1). 1H NMR (CDCl3, 500 MHz) only characteristic signals
for the â-anomer are given: δ 5.49 (s, 1H), 5.45 (d, J ) 1.7 Hz,
1H), 5.40 (d, J ) 1.7 Hz, 1H), 5.39 (s, 1H), 5.38 (s, 1H), 5.29-
5.28 (m, 4H), 5.19 (s, 1H), 5.15 (s, 1H), 5.13 (dd, J ) 4.6 (â), 6.4
Hz, 1H), 2.18 (t, J ) 7.5 Hz, 2H). MALDI-HRMS calcd for
The hexasaccharide (0.195 g, 0.086 mmol) was dissolved in
anhydrous MeOH/CH2Cl2 (4:1, 2 mL) and cooled to 0 °C, and AcCl
(0.061 mL, 0.85 mmol) was added. The solution was stirred for 7
h while slowly warming to room temperature. The reaction was
quenched by addition of saturated aqueous NaHCO3 solution (5
mL), and the aqueous layer was extracted with CH2Cl2 (5 × 5 mL).
The combined organic extracts were washed with brine (20 mL),
dried over Na2SO4, filtered, and evaporated. Purification by gradient
flash silica gel column chromatography (hexanes/EtOAc, 2:1 to 1:1)
gave 6 (0.157 g, 93%) as a colorless foam. Rf ) 0.10 (hexanes/
1
EtOAc, 1:1). [R]D ) +113.4 (c 0.92, CHCl3). H NMR (CDCl3,
300 MHz): δ 8.15-8.02 (m, 12H), 7.67-7.21 (m, 43H), 5.97-
5.83 (m, 1H), 5.56 (s, 1H), 5.54 (d, J ) 1.5 Hz, 1H), 5.50 (d, J )
1.5 Hz, 1H), 5.48 (d, J ) 1.6 Hz, 1H), 5.46 (d, J ) 1.6 Hz, 2H),
5.41 (d, J ) 1.5 Hz, 1H), 5.38 (s, 1H), 5.35 (s, 1H), 5.34 (s, 1H),
5.27 (s, 1H), 5.21 (s, 1H), 5.14-5.00 (m, 2H), 4.86 (d, J ) 11.8
Hz, 1H), 4.82 (d, J ) 10.9 Hz, 1H), 4.73 (d, J ) 12.0 Hz, 1H),
4.71 (d, J ) 12.2 Hz, 1H), 4.70 (d, J ) 11.8 Hz, 1H), 4.65 (d, J )
12.5 Hz, 1H), 4.63 (d, J ) 12.0 Hz, 1H), 4.60 (d, J ) 12.5 Hz,
1H), 4.56-4.54 (m, 1H), 4.53 (d, J ) 12.0 Hz, 1H), 4.50 (d, J )
12.2 Hz, 1H), 4.44-4.28 (m, 5H), 4.26-4.22 (m 2H), 4.20-4.13
(m, 2H), 4.08-3.76 (m, 13H), 3.67-3.61 (m, 2H), 3.56 (td, J )
6.5, 9.8 Hz, 1H), 2.64 (br s, 1H), 2.27-2.19 (m, 2H), 1.88 (br s,
1H), 1.85-1.75 (m, 2H). 13C NMR (CDCl3, 75 MHz): δ 165.5,
165.3, 165.2, 165.1, 165.0, 138.2, 138.0, 137.7, 137.5, 137.4, 133.3,
133.2, 133.1, 129.7, 129.6, 129.5, 129.4, 129.3, 128.4, 128.3, 128.2,
127.8, 127.7, 127.6, 127.5, 114.7, 106.2, 106.1, 106.0, 105.9, 105.5,
83.6, 83.5, 83.3, 83.2, 82.9, 82.8, 82.7, 82.2, 82.0, 81.9, 81.8, 81.7,
81.5, 80.1, 72.3, 72.2, 71.9, 66.7, 65.9, 65.7, 65.6, 65.0, 62.1, 61.9,
30.1, 28.6. IR (CHCl3): νmax 3008, 2932, 1723, 1452, 1316, 1298,
1268, 1114, 1071, 1027 cm-1. MALDI-HRMS calcd for C112H112O31-
Na (m/z): [MNa+] 1976.7119, found 1976.7150.
C
134H134O31SNa (m/z): [MNa+] 2295.8595, found 2295.8593.
6-Thiohexyl 5-O-(5-O-(5-O-(R-D-arabinofuranosyl)-3-O-(5-O-
(R-D-arabinofuranosyl)-R-D-arabinofuranosyl)-R-D-arabinofura-
nosyl)-R-D-arabinofuranosyl)-R-D-arabinofuranoside (15). A so-
lution of hexasaccharide 50 (0.030 g, 0.013 mmol) in anhydrous
THF (10 mL) was added dropwise to a dark blue solution of sodium
in liquid ammonia at -78 °C over 10 min. The dark blue solution
was stirred for 1 h and then quenched with MeOH. The ammonia
was removed with a stream of nitrogen and the solution was then
neutralized with Amberlite IR 120 resin. The resin was filtered,
washed with MeOH and the filtrate was concentrated. The residue
was purified by gradient reversed-phase C18 column chromatogra-
phy (MeOH/H2O, 0:1 to 1:0) and freeze-dried to give 15 exclusively
as the sulfur-linked dimer (0.0044 g, 37%) as a colorless amorphous
1
solid. H NMR (D2O, 500 MHz): δ 5.11 (s, 2H), 5.01 (s, 2H),
4.97-4.96 (m, 6H), 4.90 (s, 2H), 4.21-3.58 (m, 62H), 3.47 (td,
J ) 6.3, 9.7 Hz, 2H), 2.67 (t, J ) 7.0 Hz, 4H), 1.63-1.57 (m,
4H), 1.54-1.49 (m, 4H), 1.34-1.28 (m, 8H). ESI-HRMS calcd
for C72H122O50S2Na2 (m/z): [M2Na2+] 948.3115, found 948.3127.
Dodecamer 51. Hexamannoside 3 (0.020 g, 6.96 µmol) and
imidate 5 (0.038 g, 17.2 µmol) were coevaporated with anhydrous
toluene (4 × 2 mL) and dried in vacuo overnight. The mixture
was dissolved in Et2O (0.15 mL) and cooled to 0 °C, and TBSOTf
8086 J. Org. Chem., Vol. 71, No. 21, 2006

Synthesis of an Arabinomannan Oligosaccharide of M. tuberculosis
(0.032 mL of a 0.044 M solution in Et2O, 1.4 µmol) was added.
After 30 min, the reaction was quenched with Et3N, the mixture
was stirred at room temperature for 15 min, and the solvents were
evaporated. Purification by gradient flash silica gel column chro-
matography (hexanes/EtOAc, 2.1 to 1:1) gave dodecasaccharide
51 (0.024 g, 70%) as a colorless foam. Rf ) 0.17 (hexanes/EtOAc,
3:2). [R]D ) +57.9 (c 0.56, CHCl3). 1H NMR (CDCl3, 500 MHz):
δ 8.11-6.92 (m, 160H), 5.83-5.82 (m, 1H), 5.74-5.73 (m, 1H),
5.70-5.69 (m, 2H), 5.61-5.60 (m, 1H), 5.53 (s, 1H), 5.45 (s, 1H),
5.42 (d, J ) 1.3 Hz, 1H), 5.37 (d, J ) 1.3 Hz, 1H), 5.33 (d, J )
1.5 Hz, 1H), 5.32 (d, J ) 1.3 Hz, 1H), 5.28 (s, 1H), 5.27 (d, J )
1.2 Hz, 1H), 5.22 (s, 1H), 5.17 (s, 1H), 5.13 (s, 1H), 5.09 (d, J )
1.6 Hz, 1H), 5.07 (d, J ) 1.8 Hz, 1H), 5.03 (d, J ) 1.6 Hz, 1H),
5.00 (d, J ) 1.2 Hz, 1H), 4.89 (s, 1H), 4.86-3.30 (m, 103H), 2.36
(t, J ) 7.4 Hz, 2H), 1.52-1.46 (m, 4H), 1.34-1.23 (m, 4H). 13C
NMR (CDCl3, 125 MHz): δ 165.8, 165.5, 165.3, 165.2, 165.1,
139.1, 139.0, 138.7, 138.4, 138.3, 138.2, 138.0, 137.9, 137.8, 137.7,
133.2, 133.1, 133.0, 132.8, 132.6, 130.3, 130.1, 130.0, 129.9, 129.8,
129.7, 129.6, 129.5, 128.8, 128.6, 128.5, 128.4, 128.3, 128.2, 128.1,
128.0, 127.8, 127.7, 127.6 127.5, 127.4, 127.3, 127.2, 126.9, 126.8,
106.7, 106.2, 106.1, 106.0, 105.3, 99.8, 99.3, 98.2, 98.1, 97.9, 83.3,
83.2, 82.9, 82.6, 82.5, 82.4, 82.3, 82.1, 81.9, 81.7, 81.6, 80.9, 80.4,
79.8, 79.6, 78.6, 78.1, 75.5, 75.3, 75.2, 75.0, 74.8, 74.7, 74.5, 74.2,
73.8, 73.3, 73.2, 72.3, 72.2, 72.1, 71.8, 71.7, 71.6, 71.5, 71.4, 71.3,
71.1, 71.0, 70.9, 69.3, 69.2, 69.1, 69.0, 68.9, 68.8, 68.7, 67.8, 67.0,
65.8, 65.7, 65.4, 65.3, 65.0, 64.7, 36.3, 31.3, 29.3, 29.1, 28.7, 25.8.
1H NMR (CDCl3, 300 MHz): δ 7.40-7.17 (m, 15H), 5.95-5.82
(m, 1H), 5.41 (dd, J ) 1.8, 3.3 Hz, 1H), 5.31-5.18 (m, 2H), 4.90
(s, 1H), 4.88 (d, J ) 12.3 Hz, 1H), 4.71 (d, J ) 11.2 Hz, 1H), 4.79
(d, J ) 12.3 Hz, 1H), 4.56-4.49 (m, 3H), 4.21-4.14 (m, 1H),
4.04-3.68 (m, 6H), 2.79-2.68 (m, 4H), 2.14 (s, 3H). 13C NMR
(CDCl3, 75 MHz): δ 206.2, 172.0, 138.3, 138.2, 138.0, 133.4,
128.3, 128.0, 127.9, 127.7, 127.6, 127.5, 117.6, 96.8, 78.1, 75.1,
74.3, 73.3, 71.6, 71.3, 68.8, 68.1, 37.9, 29.7, 28.1. IR (CHCl3):
νmax 3008, 1737, 1720, 1454, 1363, 1137, 1087, 1028 cm-1
.
MALDI-HRMS calcd for C35H40O8Na (m/z): [MNa+] 611.2621,
found 611.2604. 3,4,6-Tri-O-benzyl-2-O-levulinoyl-R/â-D-man-
nopyranoside (1.22 g, 2.09 mmol) was dissolved in anhydrous
MeOH (35 mL), and PdCl2 (0.111 g, 0.626 mmol) was added. After
8 h at room temperature the suspension was filtered over Celite
and washed with CH2Cl2, and the solvents were evaporated. The
residue was dissolved in hexanes/EtOAc (1:1), filtered over a plug
of silica gel, eluted with hexanes/EtOAc (1:1), and concentrated
in vacuo. Purification by gradient flash silica gel column chroma-
tography (hexanes/EtOAc, 2:1 to 1:1) gave the corresponding lactol
(0.958 g, 84%) as a colorless oil. Rf ) 0.28 (hexanes/EtOAc, 1:1).
The lactol (0.800 g, 1.46 mmol) was dissolved in anhydrous CH2-
Cl2 (24 mL) and cooled to 0 °C, and trichloroacetonitrile (2.90 mL,
28.9 mmol) followed by DBU (0.033 mL, 0.22 mmol) were added.
After 30 min at 0 °C, the mixture was filtered over a plug of silica
gel and eluted with EtOAc and CH2Cl2, and the solvents were
removed under reduced pressure. Purification by flash silica gel
column chromatography (hexanes/EtOAc, 2:1) gave 52 (0.857 g,
85%, R/â ) 95:5) as a colorless oil. Rf ) 0.30 (hexanes/EtOAc,
2:1). [R]D ) +36.9 (c 0.84, CHCl3). 1H NMR (CDCl3, 300 MHz):
δ 8.72 (s, 1H), 7.39-7.21 (m, 15H), 6.32 (d, J ) 2.1 Hz, 1H),
5.52 (t, J ) 2.1 Hz, 1H), 4.91 (d, J ) 10.7 Hz, 1H), 4.76 (d, J )
11.3 Hz, 1H), 4.70 (d, J ) 12.0 Hz, 1H), 4.60 (d, J ) 11.3 Hz,
1H), 4.58 (d, J ) 10.7 Hz, 1H), 4.54 (d, J ) 12.0 Hz, 1H), 4.07-
4.03 (m, 3H), 3.88 (dd, J ) 3.2, 11.1 Hz, 1H), 3.75 (dd, J ) 1.4,
11.1 Hz, 1H), 2.76 (br s, 4H), 2.16 (s, 3H). 13C NMR (CDCl3, 75
MHz): δ 206.0, 171.7, 159.8, 138.1, 138.0, 137.5, 128.3, 128.2,
128.0, 127.8, 127.7, 127.5, 95.2, 90.7, 77.1, 75.3, 74.2, 73.5, 73.3,
71.8, 68.3, 67.4, 37.8, 29.7, 28.0. IR (CHCl3): νmax 3008, 1743,
1720, 1675, 1363, 1155, 1102, 1028 cm-1. MALDI-HRMS calcd
for C34H36Cl3NO8Na (m/z): [MNa+] 714.1399, found 714.1401.
IR (CHCl3): νmax 3008, 2928, 1722, 1452, 1268, 1115, 1028 cm-1
.
MALDI-HRMS for C296H294O65SNa (m/z): [MNa+] 4944.9368,
found 4944.9151.
Dodecamer 1. Dodecasaccharide 51 (0.030 g, 0.0061 mmol) was
dissolved in anhydrous MeOH/CH2Cl2 (1:1, 0.8 mL), and NaOMe
(0.003 g, 0.056 mmol) was added. After 5 d at room temperature,
the solvents were evaporated and the residue was passed through
a short plug of silica gel (hexanes/EtOAc, 1:1 to 0:1) to remove
the methyl benzoate. The residue was dissolved in anhydrous THF
(10 mL), and this solution was added dropwise over 10 min to a
dark blue solution of sodium in liquid ammonia at -78 °C. The
dark blue solution was stirred for 1 h and then quenched with
MeOH, and small pieces of sodium were added to the mixture until
the blue color of the solution persisted. After 1 h, the reaction was
quenched with MeOH and the ammonia was removed with a stream
of nitrogen. The solution was neutralized with Amberlite IR 120
resin. The resin was filtered and washed with MeOH, and the filtrate
was concentrated. The residue was purified by gradient reversed-
phase C18 column chromatography (MeOH/H2O, 0:1 to 1:0) and
freeze-dried to give 1 exclusively as the sulfur-linked dimer (0.006
g, 52% over 2 steps) as a colorless amorphous solid. 1H NMR (D2O,
500 MHz): δ 5.07 (s, 2H), 5.05 (s, 2H), 5.02 (s, 2H), 5.01 (s, 2H),
4.97 (s, 6H), 4.93 (s, 2H), 4.91 (s, 2H), 4.80 (s, 2H), 4.78 (s, 2H),
4.74 (s, 2H), 4.21-4.18 (m, 4H), 4.12-3.53 (m, 130H), 3.49-
3.44 (m, 2H), 2.67 (t, J ) 7.1 Hz, 4H), 1.64-1.58 (m, 4H), 1.57-
Pent-4-enyl 5-O-(5-O-(5-O-(2-O-Benzoyl-3-O-benzyl-5-O-(3,4,6-
tri-O-benzyl-2-O-levulinoyl-R-D-mannopyranosyl)-R-D-arabino-
furanosyl)-2-O-benzoyl-3-O-(5-O-(2-O-benzoyl-3-O-benzyl-5-O-
(3,4,6-tri-O-benzyl-2-O-levulinoyl-R-D-mannopyranosyl)-R-D-
arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofuranosyl)-
R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabino-
furanosyl)-2-O-benzoyl-3-O-benzyl-R-D-arabinofuranoside (53).
Hexasaccharide 6 (0.400 g, 0.205 mmol) and imidate 52 (0.710 g,
1.02 mmol) were coevaporated with anhydrous toluene (3 × 20
mL) and dried in vacuo overnight. The mixture was dissolved in
Et2O (6.5 mL) and cooled to 0 °C, and TBSOTf (0.0094 mL, 0.042
mmol) was added. After 30 min at 0 °C, the reaction was quenched
with Et3N and stirred at room temperature for 10 min, and the
solvents were evaporated. Purification by recycling preparative
HPLC (Japan Analytical Industry, JAIGEL-2H and 2.5H, CHCl3)
gave a mixture (0.426 g, >68%) of the desired octasaccharide 53
together with small amounts of the heptasaccharide. The mixture
was dissolved in anhydrous DMF (2 mL), and imidazole (0.050 g)
followed by TIPSCl (0.063 mL) were added. The solution was
stirred at room temperature overnight. Water was added, and the
aqueous phase was extracted with EtOAc. The combined organic
extracts were washed with water and brine, dried over MgSO4,
filtered, and evaporated. Purification by gradient flash silica gel
column chromatography (hexanes/EtOAc, 2:1 to 3:2) gave octasac-
charide 53 (0.183 g, 30%, 2 steps) as a colorless oil. Rf ) 0.15
1.50 (m, 4H), 1.37-1.27 (m, 8H). ESI-HRMS calcd for C144H242
-
O110S2Na3 (m/z): [M3Na3+] 1288.4170, found 1288.4159.
1-O-(3,4,6-Tri-O-Benzyl-2-O-levulinoyl-R/â-D-mannopyrano-
syl) Trichloroacetimidate (52). To a solution of allyl 3,4,6-tri-O-
benzyl-R/â-D-mannopyranoside46 (2.07 g, 4.22 mmol) in anhydrous
CH2Cl2 (26 mL) were added DMAP (0.774 g, 6.34 mmol) and
DIPC (0.99 mL, 6.3 mmol) at 0 °C. After 5 min at 0 °C, levulinic
acid (0.71 mL, 6.7 mmol) was added, and the mixture was stirred
at room temperature for 2 h. The suspension was diluted with
hexanes/EtOAc (1:1), filtered over a plug of silica gel, and washed
with hexanes/EtOAc (1:1), and the solvents were evaporated.
Purification by flash silica gel column chromatography (hexanes/
EtOAc, 1:1) gave allyl 3,4,6-tri-O-benzyl-2-O-levulinoyl-R/â-D-
mannopyranoside (2.28 g, 92%, R/â ) 94:6) as a colorless oil.
Rf ) 0.30 (hexanes/EtOAc, 2:1). [R]D ) +21.9 (c 1.23, CHCl3).
1
(hexanes/EtOAc, 3:2). [R]D ) +84.6 (c 0.24, CHCl3). H NMR
(CDCl3, 300 MHz): δ 8.04-7.95 (m, 12H), 7.53-7.03 (m, 73H),
5.84-5.76 (m, 1H), 5.49 (s, 1H), 5.44 (d, J ) 1.6 Hz, 1H), 5.38-
5.37 (m, 3H), 5.37 (d, J ) 1.5 Hz, 1H), 5.34 (dd, J ) 1.8, 3.2 Hz,
(46) Goddat, J.; Grey, A. A.; Hricov´ıni, M.; Grushcow, J.; Carver, J. P.;
Shah, R. N. Carbohydr. Res 1994, 252, 159-170.
J. Org. Chem, Vol. 71, No. 21, 2006 8087

Ho¨lemann et al.
1H), 5.29 (s, 1H), 5.29 (dd, J ) 2.0, 3.6 Hz, 1H), 5.27 (d, J ) 1.2
Hz, 1H), 5.25 (s, 1H), 5.23 (s, 1H), 5.08 (s, 1H), 5.06 (s, 1H),
4.98-4.94 (m, 1H), 4.90-4.87 (m, 1H), 4.80 (d, J ) 1.6 Hz, 1H),
4.75 (d, J ) 1.7 Hz, 1H), 4.77 (d, J ) 10.9 Hz, 1H), 4.76 (d, J )
10.8 Hz, 1H), 4.76 (d, J ) 12.7 Hz, 1H), 4.69 (d, J ) 12.2 Hz,
1H), 4.65 (d, J ) 12.2 Hz, 1H), 4.63 (d, J ) 11.1 Hz, 1H), 4.61
(d, J ) 11.7 Hz, 1H), 4.61 (d, J ) 12.2 Hz, 1H), 4.60 (d, J ) 12.1
Hz, 1H), 4.52 (d, J ) 12.0 Hz, 1H), 4.52 (d, J ) 11.9 Hz, 1H),
4.48-4.42 (m, 7H), 4.34-4.13 (m, 11H), 4.10 (d, J ) 10.9 Hz,
1H), 4.05 (d, J ) 10.9 Hz, 1H), 3.95-3.89 (m, 4H), 3.86-3.52
(m, 21H), 3.48-3.43 (m, 2H), 2.68-2.61 (m, 8H), 2.15-2.11 (m,
2H), 2.08 (s, 3H), 2.08 (s, 3H), 1.73-1.67 (m, 2H). 13C NMR
(CDCl3, 75 MHz): δ 206.2, 171.7, 165.5, 165.3, 165.1, 138.5,
138.3, 138.2, 138.0, 137.9, 137.6, 133.3, 133.2, 133.1, 129.9, 129.8,
129.7, 129.6, 129.5, 129.4, 128.5, 128.4, 128.3, 128.2, 128.0, 127.9,
127.8, 127.7, 127.1, 127.6, 127.5, 114.7, 106.4, 106.2, 106.1, 106.0,
105.2, 98.2, 83.4, 83.2, 83.0, 82.9, 82.4, 82.3, 81.9, 81.8, 81.7, 81.5,
80.0, 78.3, 75.1, 74.0, 73.4, 72.3, 72.2, 72.0, 71.8, 71.5, 71.4, 68.7,
68.5, 66.8, 66.2, 66.1, 65.8, 65.5, 65.1, 38.0, 30.2, 29.7, 28.6, 28.2.
IR (CHCl3): νmax 3066, 3008, 2932, 2872, 1721, 1452, 1363, 1299,
1114, 1028 cm-1. MALDI-HRMS calcd for C176H180O45Na (m/z):
[MNa+] 3036.1694, found 3036.1615.
(d, J ) 1.5 Hz, 1H), 5.37 (d, J ) 1.5 Hz, 1H), 5.36 (s, 3H), 5.28
(s, 1H), 5.26 (s, 1H), 5.25 (d, J ) 1.1 Hz, 1H), 5.22 (s, 1H), 5.14
(s, 1H), 5.10 (s, 1H), 5.02-4.91 (m, 4H), 4.75 (d, J ) 12.0 Hz,
1H), 4.73 (d, J ) 10.9 Hz, 1H), 4.72 (d, J ) 11.1 Hz, 1H), 4.70
(d, J ) 13.0 Hz, 1H), 4.63 (d, J ) 12.0 Hz, 1H), 4.62 (d, J ) 10.5
Hz, 1H), 4.59 (d, J ) 10.0 Hz, 1H), 4.58 (d, J ) 12.3 Hz, 1H),
4.57 (d, J ) 12.0 Hz, 1H), 4.52 (d, J ) 12.0 Hz, 1H), 4.51 (d, J )
12.1 Hz, 1H), 4.50 (d, J ) 12.1 Hz, 1H), 4.46-4.41 (m, 6H), 4.37-
4.12 (m, 13H), 3.98-3.53 (m, 28H), 3.45 (td, J ) 6.6, 9.8 Hz,
1H), 2.50 (d, J ) 2.0 Hz, 1H), 2.42 (d, J ) 2.3 Hz, 1H), 2.15-
2.10 (m, 2H), 1.72-1.67 (m, 2H). 13C NMR (CDCl3, 75 MHz): δ
165.5, 165.3, 165.1, 138.4, 138.3, 138.2, 137.9, 137.8, 137.7, 137.6,
133.4, 133.2, 133.1, 129.9, 129.8, 129.7, 129.6, 129.5, 129.4, 128.5,
128.4, 128.3, 128.2, 127.8, 127.7, 127.6, 127.5, 114.8, 106.2, 106.1,
106.0, 105.3, 99.6, 99.5, 83.4, 83.2, 83.0, 82.8, 82.6, 82.3, 82.1,
81.9, 81.7, 81.5, 80.2, 80.1, 79.9, 75.0, 74.1, 74.0, 73.4, 72.4, 72.3,
72.2, 72.0, 71.9, 71.6, 71.5, 71.3, 68.8, 68.0, 67.9, 66.8, 65.8, 65.6,
65.5, 65.4, 65.3, 30.2, 28.7. IR (CHCl3): νmax 3562, 3066, 3008,
2927, 1723, 1452, 1299, 1114, 1071, 1028 cm-1. MALDI-HRMS
calcd for C166H168O41Na (m/z): [MNa+] 2840.0959, found 2840.1035.
Acknowledgment. This research was supported by the ETH
Zu¨rich (ETH Grant No. TH-37/05-1), the Deutsche Forschungs-
gemeinschaft (Emmy Noether postdoctoral fellowship for A.H.),
and the Foundation for Research, Science and Technology, New
Zealand (postdoctoral fellowship for B.L.S). We thank Simone
Bufali, Christian Noti, and Mattie Timmer for their help with
the acquisition of high-field NMR spectra, as well as Marian
Kehl and Kyrill Stanek for their help in the preparation of
intermediates.
Pent-4-enyl 5-O-(5-O-(5-O-(2-O-Benzoyl-3-O-benzyl-5-O-(3,4,6-
tri-O-benzyl-R-D-mannopyranosyl)-R-D-arabinofuranosyl)-2-O-
benzoyl-3-O-(5-O-(2-O-benzoyl-3-O-benzyl-5-O-(3,4,6-tri-O-benzyl-
R-D-mannopyranosyl)-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-
benzyl-R-D-arabinofuranosyl)-R-D-arabinofuranosyl)-2-O-benzoyl-
3-O-benzyl-R-D-arabinofuranosyl)-2-O-benzoyl-3-O-benzyl-R-D-
arabinofuranoside (54). Octasaccharide 53 (0.090 g, 0.0298 mmol)
was dissolved in CH2Cl2 (1.3 mL), and premixed AcOH/pyridine
(0.037 mL/0.063 mL) followed by hydrazine monohydrate (0.0064
mL, 0.132 mmol) were added. After 2 h at room temperature the
reaction was quenched with acetone and the solvents were
evaporated. Purification by gradient flash silica gel column chro-
matography (hexanes/EtOAc, 2:1 to 1:1) gave 54 (0.067 g, 80%)
as a colorless oil. Rf ) 0.25 (hexanes/EtOAc, 1:1). [R]D ) +85.1
Supporting Information Available: Full experimental data for
all new mannose and arabinose building blocks and spectral data
(1H and 13C NMR) of all new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
1
(c 0.75, CHCl3). H NMR (CDCl3, 300 MHz): δ 8.04-7.94 (m,
12H), 7.53-7.03 (m, 73H), 5.84-5.76 (m, 1H), 5.48 (s, 1H), 5.43
JO061233X
8088 J. Org. Chem., Vol. 71, No. 21, 2006