Synthesis of glycoconjugate fragments of mycobacterial phosphatidylinositol mannosides and lipomannan

Article abstract of DOI:10.3762/bjoc.7.47

Mycobacterium tuberculosis, the causitive agent of tuberculosis (TB), possesses a complex cell wall containing mannose-rich glycophospholids termed phosphatidylinositol mannosides (PIMs), lipomannan (LM), and lipoarabinomannan (LAM). These glycophospholipids play important roles in cell wall function and host-pathogen interactions. Synthetic PIM/LM/LAM substructures are useful biochemical tools to delineate and dissect the fine details of mannose glycophospholipid biosynthesis and their interactions with host cells. We report the efficient synthesis of a series of azidooctyl di- and trimannosides possessing the following glycan structures: α-Man-1,6-α-Man, α-Man-1,6-α-Man-1,6-α-Man, α-Man-1,2-α-Man-1,6- α-Man and 2,6-di-(α-Man)-α-Man. The synthesis includes the use of non-benzyl protecting groups compatible with the azido group and preparation of the branched trisaccharide structure 2,6-di-(α-Man)-α-Man through a double glycosylation of a 3,4-butanediacetal-protected manno-side. The azidooctyl groups of these synthetic mannans were elaborated to fluorescent glycoconjugates and squaric ester derivatives useful for further conjugation studies.

Full text of DOI:10.3762/bjoc.7.47

Synthesis of glycoconjugate fragments of
mycobacterial phosphatidylinositol mannosides
and lipomannan
Benjamin Cao, Jonathan M. White and Spencer J. Williams*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 369–377.
School of Chemistry and Bio21 Molecular Science and Biotechnology
Institute, University of Melbourne, Parkville, Victoria, Australia, Fax:
+61 3 9347 8124; Tel: +61 3 8344 2422
doi:10.3762/bjoc.7.47
Received: 18 January 2011
Accepted: 11 March 2011
Published: 28 March 2011
Email:
Spencer J. Williams* - sjwill@unimelb.edu.au
Associate Editor: S. Flitsch
* Corresponding author
© 2011 Cao et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
fluorescently-labelled sugars; glycoconjugates; lipomannan;
mycobacteria; tuberculosis
Abstract
Mycobacterium tuberculosis, the causitive agent of tuberculosis (TB), possesses a complex cell wall containing mannose-rich
glycophospholids termed phosphatidylinositol mannosides (PIMs), lipomannan (LM), and lipoarabinomannan (LAM). These
glycophospholipids play important roles in cell wall function and host–pathogen interactions. Synthetic PIM/LM/LAM substruc-
tures are useful biochemical tools to delineate and dissect the fine details of mannose glycophospholipid biosynthesis and their
interactions with host cells. We report the efficient synthesis of a series of azidooctyl di- and trimannosides possessing the
following glycan structures: α-Man-1,6-α-Man, α-Man-1,6-α-Man-1,6-α-Man, α-Man-1,2-α-Man-1,6-α-Man and 2,6-di-(α-Man)-α-
Man. The synthesis includes the use of non-benzyl protecting groups compatible with the azido group and preparation of the
branched trisaccharide structure 2,6-di-(α-Man)-α-Man through a double glycosylation of a 3,4-butanediacetal-protected manno-
side. The azidooctyl groups of these synthetic mannans were elaborated to fluorescent glycoconjugates and squaric ester deriva-
tives useful for further conjugation studies.
Introduction
The incidence of TB is now at an all-time historical high with development of new therapies to bolster the physician's arma-
over 2 billion people infected globally [1]. TB is the leading mentarium for TB control [3]. Many existing TB drugs target
infectious killer of people with HIV/AIDS and is second only to aspects of mycobacterial cell wall biosynthesis (e.g., thiaceta-
HIV/AIDS as an infectious cause of death for adults [2]. It is zone, isoniazid, ethambutol, pyrazinamide, and ethionamide)
sobering that it has been more than 40 years since the last front- with the cell wall of the tubercule bacillus being widely agreed
line TB drug (rifampicin) was deployed [3]. Drug resistance is as a promising target for new drugs [4,5]. The cell wall of all
now widespread and growing, underscoring the need for the mycobacteria is especially rich in lipids and polysaccharides,
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Beilstein J. Org. Chem. 2011, 7, 369–377.
with the major component being a macromolecule composed of linear backbone is then elaborated with single α-1,2-linked
mycolic acids, arabinogalactan, and peptidoglycan, termed the mannose residues to give mature LM [20]. LAM is formed by
mycolyl–arabinogalactan–peptidoglycan complex [6,7]. One addition of arabinan to the penultimate mannose residue of LM,
intriguing class of cell wall associated molecules are those and is subsequently capped with a variety of groups including
based on a phosphatidylinositol (PI) core, which include the inositol phosphate, 5-methylthioxylose and its sulfoxide, and
PIMs, LM, and LAM [8].
short 1,2-mannose oligomers [7].
Through studies with gene deletion mutants of mycobacterial Studies into the biosynthesis of the PIMs, LM and LAM have
strains, several steps in the biosynthesis of the PIMs, LM and been greatly facilitated by the development of glycomimetic
LAM have been shown to be essential for bacterial survival and compounds. Homogeneous synthetic substructures have been
it is now well appreciated that they are crucial cell-surface used to deconvolute aspects of substrate recognition by biosyn-
molecules that mediate host–pathogen interactions [8,9]. thetic enzymes and the structural determinants of host–pathogen
Biochemical studies support the general biosynthetic relation- interactions including antibody recognition and immune
ship PIMs → LM → LAM, although it is also clear that pattern-recognition systems such as the dendritic cell specific
Ac2PIM2 and Ac2PIM6 represent important metabolic end intercellular adhesion molecule-grabbing non-integrin (DC-
products in their own right [10]. Scheme 1 summarizes the SIGN) [8]. Thus, while total syntheses of many PIM structures
biosynthesis of the mannan core of the PIMs, LM and LAM. have now been reported, the synthesis of substructures remains
PIM biosynthesis commences with the stepwise transfer of two a worthwhile endeavor as these are useful to clarify fine details
mannosyl residues onto inositol, catalyzed by the GDP- of enzymatic substrate recognition and are substantially easier
mannose dependent α-mannosyltransferases PimA [11] and to prepare [4,8]. As a shining example, synthetic octyl α-1,6-
PimB' [12,13], followed by acylation by the acyltransferase linked oligomannoside analogues of the 1,6-mannan core are
(Rv2611c) to give AcPIM2 [14,15]. Additional α-1,6-mannosyl- effective substrates for mycobacterial cell free systems [21-23],
ations of AcPIM2 give rise to AcPIM3 and AcPIM4, the last of and were used to confirm the activity of the polymerizing α-1,6-
which is hypothesized to be a key biosynthetic precursor for the mannosyltransferases MptB and MptA [18,19], and to demon-
synthesis of the so-called polar PIMs, AcPIM5 and Ac2PIM6, strate functional compartmentalization of PPM synthase activity
and LM and LAM [16].
and MptB/MptA [24]. They have also been used as glycolipid
substrates supporting the development of inhibitors of PIM/LM/
The biosynthesis of LM and LAM (Scheme 1) commences from LAM biosynthesis [25-28]. Various 1,2-linked aminooctyl
AcPIM4 with the installation of a linear α-1,6-linked mannan oligomannosides corresponding to the capping groups of
backbone on the terminal mannose [17]. Two α-1,6-mannosyl- ManLAM were prepared and conjugated to carrier proteins and
transferases, MptB and MptA, have been identified to be used to study antibody reactivity in a serological TB assay
involved in the elongation of the LM backbone [18,19]. The [29,30]. A complete set of the phosphoglycan head groups of
Scheme 1: Indicative topology model for the biosynthesis of the glycophospholipids PIMs, LM and LAM in mycobacteria. The timing for translocation
of PIM intermediates across the membrane is unclear. Hexagon = myo-inositol; closed circle = mannose; P = phosphate.
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Beilstein J. Org. Chem. 2011, 7, 369–377.
PIM1–PIM6 with a thiol linker in place of the diacylglycerol allows easy product isolation by either reversed-phase chroma-
were prepared and, following immobilization on glass slides, tography or simple solvent partitioning. Incorporation of an
their binding to the lectin DC-SIGN was assessed [31].
azidooctyl group confers many of the same benefits as an octyl
aglycon, with the additional advantage that the azido group may
Significant questions remain in the area of PIM/LM/LAM be elaborated into glycoconjugates. However, the synthesis of
biosynthesis that could be assisted by suitable well-defined azidooctyl glycosides can be challenging as the use of reduc-
mannan substructures. For example, the identity of the α-1,2- tively-removed protecting groups such as benzyl ethers must be
mannosyltransferase(s) involved in the conversion of AcPIM4 avoided owing to their incompatibility with the azido group
→ AcPIM5 → Ac2PIM6 remain incompletely characterized when using H2/Pd or Na/NH3. We therefore sought to develop a
[17]. Similarly, the timing of the introduction of the single synthesis based on the use of esters, silyl ethers and acetals
α-1,2-mannose residues onto the α-1,6-linked mannan core only.
versus the elongation of this core is unclear [32]. For these
reasons, we have undertaken the synthesis of a suite of frag- Synthesis of monosaccharide building blocks
ments of the PIMs and LM, 1–4, and report their elaboration Glycosidation of 8-azidooctan-1-ol (Supporting Information
into glycoconjugates 5–10 for use as biological reagents to File 2) using glycosyl bromide 11 [36] in the presence of
study PIM/LM/LAM biosynthesis and immunogenicity AgOTf, and debenzoylation of the crude product gave 12 in
(Figure 1 and Figure 2). The azidooctyl aglycon has particular 81% yield over 2 steps (Scheme 2). Regioselective silylation of
utility in this regard because of its (i) lipophilicity allowing the primary alcohol of 12 with TPSCl followed by benzoyl-
biphasic partitioning between butanol/water or purification by ation of the remaining hydroxyl groups afforded the glycoside
reversed-phase extraction, (ii) ability to be reduced to an 13, which was desilylated with HF·pyridine complex to yield
aminooctyl chain for use in squarate conjugation chemistry, and 14. This chemoselective transformation uses conditions that are
(iii) capacity to be conjugated with fluorescent terminal alkynes similar to those reported by Tam et al. [23], and result in
using the Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) desilylation in a significantly shorter period than that previ-
reaction [33,34].
ously reported using HCl in MeOH/Et2O [22]. The diol 15 was
prepared by treatment of 12 with 2,3-butanedione and trimethyl
orthoformate in the presence of catalytic acid in refluxing
Results and Discussion
Since their introduction by Palcic and co-workers [35], MeOH (Scheme 2) [37]. Trace amounts of the corresponding
hydrophobic alkyl glycosides have proven to be valuable methyl glycoside were also obtained, arising from limited
derivatives for enzymatic assays, as their lipophilic nature methanolysis of the glycosidic linkage.
Figure 1: Chemical structures of (A) a representative PIM, AcPIM5 and (B) a mannan fragment of LM from mycobacteria. Boxes denote the relation-
ship of PIMs and LM to trisaccharide fragments synthesized in this study.
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Figure 2: Target di- and trisaccharide glycoconjugate fragments of PIMs and LM.
Scheme 2: Synthesis of azidooctyl alcohol 14 and diol 15.
For α-mannosylation of primary and secondary alcohols, the vation of a nuclear Overhauser effect transfer between the
mannosyl donors 16 [38] and 17 were used. Treatment of methine proton of the benzylidene acetal and H2 [40]. Unam-
glycosyl bromide 11 with NaBH4/KI in MeCN [39] afforded biguous stereochemical assignment of (7S)-18 was achieved by
the crystalline 1,2-O-benzylidene acetal 18 as a single dia- single crystal X-ray analysis as shown in Figure 3, and is
stereoisomer in quantitative yield (Scheme 3). The stereochem- consistent with stereoselective delivery of hydride to the exo-
istry of the benzylidene acetal 18 formed by this method has face of the intermediate dioxolenium ion. Acetolysis of the
been studied by Suzuki et al. who assigned the product as the benzylidene acetal 18 using 2% H2SO4/Ac2O provided diac-
(7S)-stereoisomer (but reported it as the (7R)-isomer) by obser- etate 19 in 60% yield. Compound 19 was converted into the
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Beilstein J. Org. Chem. 2011, 7, 369–377.
Scheme 3: Synthesis of mannosyl donors 16 and 17.
trichloroacetimidate 16 following the approach of Kong and ment of the 1JC,H coupling constants for the anomeric carbons
coworkers [38] or to the thioglycoside 17 by treatment with of the newly formed products. Each coupling constant was
p-thiocresol and BF3·Et2O in toluene.
>170 Hz, thereby showing that all new O-glycosidic linkages
were α-configured (Supporting Information File 2) [42]. Global
debenzoylation of disaccharide 20 and trisaccharide 25 with
catalytic NaOMe in MeOH/CH2Cl2 provided 1 and 2 in yields
of 99% and 94%, respectively.
Our strategy towards the synthesis of the trisaccharide 3 sought
to utilize a glycosyl donor possessing a 2-O-acetyl group with
benzoyl groups at the remaining positions, anticipating that
selective deacetylation post-glycosylation could be achieved to
allow the subsequent synthesis of the α-Man-1,2-Man linkage
(Scheme 5). Activation of a mixture of alcohol 14 and
trichloroacetimidate 16 at 0 °C with 0.1 equiv of BF3·Et2O
provided disaccharide 26 in only 21% yield, with a 1,2-glycosyl
orthoester as the major product (40%). Orthoesters are common
by-products of glycosylation reactions and typically rearrange
under acidic conditions to give trans-linked glycosides [43].
Thus, 14 and 16 were treated with 0.25 equiv of an alternative
Lewis acid, TMSOTf, and allowed to react for a longer time to
allow the intermediate orthoester to isomerize. Under these
conditions the disaccharide 26 was isolated in an improved
Figure 3: ORTEP plot of single crystal X-ray determination of (7S)-18.
Thermal ellipsoids denote 20% electron probability.
Assembly of mannosides 1–4
Synthesis of the protected disaccharide 20 was achieved by yield of 63%. Also isolated was a 6-O-trimethylsilyl ether (6%),
glycosylation of 14 with the thioglycoside donor 21 [41] using resulting from the reaction of alcohol 14 with TMSOTf. Better
NIS/TfOH in 84% yield (Scheme 4). The protected tri- still, treatment of 14 and 16 with 0.25 equiv of BF3·Et2O
saccharide 25 was prepared by an approach similar to that afforded 26 in 76% yield. A similar outcome was obtained
reported for the corresponding octyl trisaccharide [22,23]. Thus using NIS/TfOH activation of thioglycoside donor 17 to furnish
glycosylation of 14 with the silylated donor 22 using NIS/TfOH disaccharide 26 in 72% yield. Selective deacetylation of 26 was
afforded the silylated disaccharide 23 (99%). Compound 23 was achieved by acidic transesterification using 3% AcCl in MeOH/
desilylated using HF·pyridine and the primary alcohol 24 was CH2Cl2 to give the secondary alcohol 27 in 73% yield. Manno-
glycosylated using thioglycoside 21 to give the trimannoside sylation of 27 using donor 21 under NIS/TfOH activation gave
25. Evidence for the exclusive formation of the α-anomer in all trisaccharide 28 in 61% yield, and global debenzoylation
mannosylations in this work was obtained through measure- proceeded smoothly to give 3.
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Beilstein J. Org. Chem. 2011, 7, 369–377.
Scheme 4: Synthesis of disaccharide 1 and trisaccharide 2.
Scheme 5: Synthesis of trisaccharide 3.
The trisaccharide 4 was prepared by simultaneous glycosyl- Synthesis of glycoconjugates 5–10
ation of the 2 and 6 positions of acceptor 15 (Scheme 6). Treat- Nitrobenzodiazole (NBD) dyes are useful fluorescent labels
ment of the diol 15 with 4 equiv of donor 21, and NIS/TfOH owing to their small size, low cost, superior water solubility
afforded the protected trisaccharide 29 in 68% yield. Deprotec- relative to other common alternatives, and ability to be excited
tion was achieved by sequential treatment with TFA/H2O and using visible, rather than ultraviolet light [44]. Hindsgaul and
NaOMe/MeOH to afford the trisaccharide 4.
coworkers have reported the use of glycoconjugates with NBD
Scheme 6: Synthesis of trisaccharide 4.
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Beilstein J. Org. Chem. 2011, 7, 369–377.
dyes to streamline the detection of carbohydrate-lectin interac-
tions and report that the NBD group displayed substantially less
nonspecific interaction with proteins over other fluorescent dyes
[45]. Using alkynyl-NBD 30 (prepared in one step from NBD
chloride and propargylamine) [34], the disaccharide 1 and
trisaccharides 2 and 3 were coupled upon treatment with
CuSO4, sodium ascorbate and the Cu(I)-stabilizing ligand
tris(benzyltriazolylmethyl)amine (TBTA) (Scheme 7) [46,47].
The resulting dye-labelled glycoconjugates 5–7 were isolated in
90–95% yields and possessed excellent fluorescent properties
with λex = 400 nm and λem = 530 nm.
Supporting Information
Supporting Information File 1
Experimental part.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-7-47-S1.pdf]
Supporting Information File 2
1H and 13C NMR spectra for new compounds and
fluorescence spectra for 5–7.
The crystallographic data file for the structure reported in
this paper has been deposited with the Cambridge
Crystallographic Data Centre as file CCDC 804936 and is
available on request from http://www.ccdc.cam.ac.uk/.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-7-47-S2.pdf]
Acknowledgements
This work was supported by grants from the Australian
Research Council and the National Health and Medical
Research Council of Australia. Bradley Coleman and Marcus
Angelin are thanked for technical assistance.
References
1. Dye, C.; Williams, B. G. Science 2010, 328, 856–861.
Scheme 7: Synthesis of glycoconjugates 5–7 and 8–10.
doi:10.1126/science.1185449
2. WHO: "Tuberculosis" Fact sheet No. 104, November 2010,
http://www.who.int/mediacentre/factsheets/fs104/en/index.html
(accessed Jan 18, 2011).
The squarate diester methodology introduced by Tietze and
coworkers [48] and recently refined by the Kováč group [49]
for the attachment of amine-derivatized carbohydrates to carrier
proteins has particular advantages over other linker methodolo-
gies as diethyl squarate is commerically available and exhibits
good selectivity in each coupling step, with the intermediate
squaramate ester being sufficiently stable to allow its purifica-
tion and storage. It should be noted that a key limitation of the
methodology is the potential immunogenicity of the squarate
group [50]. The three trisaccharides 2–4 were reduced to the
aminooctyl derivatives by treatment with Ph3P in THF/water,
and treated with diethyl squarate according to the procedure of
Kováč (Scheme 7) [49]. Purification by reversed-phase chroma-
tography afforded the ethyl squaramyl derivatives 8–10 in
84–94% yields.
3. Ma, Z.; Lienhardt, C.; McIlleron, H.; Nunn, A. J.; Wang, X. Lancet 2010,
375, 2100–2109. doi:10.1016/S0140-6736(10)60359-9
4. Umesiri, F. E.; Sanki, A. K.; Boucau, J.; Ronning, D. R.; Sucheck, S. J.
Med. Res. Rev. 2010, 30, 290–326. doi:10.1002/med.20190
5. Janin, Y. L. Bioorg. Med. Chem. 2007, 15, 2479–2513.
doi:10.1016/j.bmc.2007.01.030
6. Brennan, P. J.; Nikaido, H. Annu. Rev. Biochem. 1995, 64, 29–63.
doi:10.1146/annurev.bi.64.070195.000333
7. Kaur, D.; Guerin, M. E.; Škovierová, H.; Brennan, P. J.; Jackson, M.
Adv. Appl. Microbiol. 2009, 69, 23–78.
doi:10.1016/S0065-2164(09)69002-X
8. Cao, B.; Williams, S. J. Nat. Prod. Rep. 2010, 27, 919–947.
doi:10.1039/c000604a
9. Fischer, K.; Scotet, E.; Niemeyer, M.; Koebernick, H.; Zerrahn, J.;
Maillet, S.; Hurwitz, R.; Kursar, M.; Bonneville, M.; Kaufmann, S. H. E.;
Schaible, U. E. Proc. Natl. Acad. Sci. U. S. A. 2004, 101,
10685–10690. doi:10.1073/pnas.0403787101
Conclusion
10.Guerin, M. E.; Kordulakova, J.; Alzari, P. M.; Brennan, P. J.;
Jackson, M. J. Biol. Chem. 2010, 285, 33577–33583.
doi:10.1074/jbc.R110.168328
We report the synthesis of four di/trisaccharide fragments of
mycobacterial PIMs/LM/LAM and their elaboration to fluores-
cently-labelled glycoconjugates and haptens for the preparation
of antigens. A readily prepared and crystalline 1,2-O-benzyli-
dene acetal 18 has been used as a central precursor for the
preparation of 2-O-acetyl mannosyl donors 16 and 17. The syn-
thetic routes are compatible with the azido group.
11.Korduláková, J.; Gilleron, M.; Mikuśová, K.; Puzo, G.; Brennan, P. J.;
Gicquel, B.; Jackson, M. J. Biol. Chem. 2002, 277, 31335–31344.
doi:10.1074/jbc.M204060200
375

Beilstein J. Org. Chem. 2011, 7, 369–377.
12.Lea-Smith, D. J.; Martin, K. L.; Pyke, J. S.; Tull, D.; McConville, M. J.;
Coppel, R. L.; Crellin, P. K. J. Biol. Chem. 2008, 283, 6773–6782.
doi:10.1074/jbc.M707139200
32.Sena, C. B.; Fukuda, T.; Miyanagi, K.; Matsumoto, S.; Kobayashi, K.;
Murakami, Y.; Maeda, Y.; Kinoshita, T.; Morita, Y. S. J. Biol. Chem.
2010, 285, 13326–13336. doi:10.1074/jbc.M109.077297
33.Cheng, L.; Chen, Q.; Liu, J.; Du, Y. Carbohydr. Res. 2007, 342, 975.
doi:10.1016/j.carres.2007.01.015
13.Batt, S. M.; Jabeen, T.; Mishra, A. K.; Veerapen, N.; Krumbach, K.;
Eggeling, L.; Besra, G. S.; Futterer, K. J. Biol. Chem. 2010,
37741–37752. doi:10.1074/jbc.M110.165407
34.McGill, N. W.; Williams, S. J. J. Org. Chem. 2009, 74, 9388–9398.
doi:10.1021/jo902100q
14.Korduláková, J.; Gilleron, M.; Puzo, G.; Brennan, P. J.; Gicquel, B.;
Mikuśová, K.; Jackson, M. J. Biol. Chem. 2003, 278, 36285–36295.
doi:10.1074/jbc.M303639200
35.Palcic, M. M.; Heerze, L. D.; Pierce, M.; Hindsgaul, O.
Glycoconjugate J. 1988, 5, 49–63. doi:10.1007/BF01048331
36.Ness, R. K.; Fletcher, H. G., Jr.; Hudson, C. S. J. Am. Chem. Soc.
1950, 71, 2200–2205. doi:10.1021/ja01161a091
37.Hense, A.; Ley, S. V.; Osborn, H. M. I.; Owen, D. R.; Poisson, J.-F.;
Warriner, S. L.; Wesson, K. E. J. Chem. Soc., Perkin Trans. 1 1997,
2023–2031. doi:10.1039/A702497E
15.Guerin, M. E.; Kaur, D.; Somashekar, B. S.; Gibbs, S.; Gest, P.;
Chatterjee, D.; Brennan, P. J.; Jackson, M. J. Biol. Chem. 2009, 284,
25687–25696. doi:10.1074/jbc.M109.030593
16.Morita, Y. S.; Patterson, J. H.; Billman-Jacobe, H.; McConville, M. J.
Biochem. J. 2004, 378, 589–597. doi:10.1042/BJ20031372
17.Morita, Y. S.; Sena, C. B. C.; Waller, R. F.; Kurokawa, K.;
Sernee, M. F.; Nakatani, F.; Haites, R. E.; Billman-Jacobe, H.;
McConville, M. J.; Maeda, Y.; Kinoshita, T. J. Biol. Chem. 2006, 281,
25143–25155. doi:10.1074/jbc.M604214200
38.Heng, L.; Ning, J.; Kong, F. J. Carbohydr. Chem. 2001, 20, 285–296.
doi:10.1081/CAR-100104864
39.Betaneli, V. I.; Ovchinnikov, M. V.; Backinowsky, L. V.;
Kochetkov, N. K. Carbohydr. Res. 1982, 107, 285–291.
doi:10.1016/S0008-6215(00)80547-9
18.Mishra, A. K.; Alderwick, L. J.; Rittmann, D.; Tatituri, R. V. V.; Nigou, J.;
Gilleron, M.; Eggeling, L.; Besra, G. S. Mol. Microbiol. 2007, 65,
1502–1517. doi:10.1111/j.1365-2958.2007.05884.x
19.Mishra, A. K.; Alderwick, L. J.; Rittman, D.; Wang, C.; Bhatt, A.;
Jacobs, W. R., Jr.; Takayama, K.; Eggeling, L.; Besra, G. S.
Mol. Microbiol. 2008, 68, 1595–1613.
40.Suzuki, K.; Mizuta, T.; Yamaura, M. J. Carbohydr. Chem. 2003, 22,
143–147. doi:10.1081/CAR-120020483
41.Tam, P.; Lowary, T. L. Carbohydr. Res. 2007, 342, 1741–1772.
doi:10.1016/j.carres.2007.05.001
42.Bock, K.; Pedersen, C. J. Chem. Soc., Perkin Trans. 2 1974, 293–299.
doi:10.1039/p29740000293
doi:10.1111/j.1365-2958.2008.06265.x
20.Kaur, D.; Obregon-Henao, A.; Pham, H.; Chatterjee, D.; Brennan, P. J.;
Jackson, M. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 17973–17977.
doi:10.1073/pnas.0807761105
43.Kong, F. Carbohydr. Res. 2007, 342, 345–373.
doi:10.1016/j.carres.2006.09.025
44.Ghosh, P. B.; Whitehouse, M. W. Biochem. J. 1968, 108, 155.
45.Dowlut, M.; Hall, D. G.; Hindsgaul, O. J. Org. Chem. 2005, 70,
9809–9813. doi:10.1021/jo051503w
21.Brown, J. R.; Field, R. A.; Barker, A.; Guy, M.; Grewal, R.; Khoo, K. H.;
Brennan, P. J.; Besra, G. S.; Chatterjee, D. Bioorg. Med. Chem. 2001,
9, 815–824. doi:10.1016/S0968-0896(00)00300-X
46.Donnelly, P. S.; Zanatta, S. D.; Zammit, S. C.; White, J. M.;
Williams, S. J. Chem. Commun. 2008, 7, 2459–2461.
doi:10.1039/b719724a
22.Watt, J. A.; Williams, S. J. Org. Biomol. Chem. 2005, 3, 1982–1992.
doi:10.1039/b503919c
23.Tam, P. H.; Besra, G. S.; Lowary, T. L. ChemBioChem 2008, 9,
267–278. doi:10.1002/cbic.200700391
47.Chan, T. R.; Hilgraf, R.; Sharpless, K. B.; Fokin, V. V. Org. Lett. 2004,
6, 2853–2855. doi:10.1021/ol0493094
24.Morita, Y. S.; Velasquez, R.; Taig, E.; Waller, R. F.; Patterson, J. H.;
Tull, D.; Williams, S. J.; Billman-Jacobe, H.; McConville, M. J.
J. Biol. Chem. 2005, 280, 21645–21652. doi:10.1074/jbc.M414181200
25.Subramaniam, V.; Gurcha, S. S.; Besra, G. S.; Lowary, T. L.
Tetrahedron: Asymmetry 2005, 16, 553–567.
48.Tietze, L. F.; Schröter, C.; Gabius, S.; Brinck, U.; Goerlach-Graw, A.;
Gabius, H.-J. Bioconjugate Chem. 1991, 2, 148–152.
doi:10.1021/bc00009a003
49.Hou, S.; Saksena, R.; Kováč, P. Carbohydr. Res. 2008, 343, 196–210.
doi:10.1016/j.carres.2007.10.015
doi:10.1016/j.tetasy.2004.11.063
50.Wu, X.; Ling, C. C.; Bundle, D. R. Org. Lett. 2004, 6, 4407–4410.
doi:10.1021/ol048614m
26.Subramaniam, V.; Gurcha, S. S.; Besra, G. S.; Lowary, T. L.
Bioorg. Med. Chem. 2005, 13, 1083–1094.
doi:10.1016/j.bmc.2004.11.027
27.Lo Conte, M.; Marra, A.; Chambery, A.; Gurcha, S. S.; Besra, G. S.;
Dondoni, A. J. Org. Chem. 2010, 75, 6326–6336.
doi:10.1021/jo100928g
28.Tam, P. H.; Lowary, T. L. Org. Biomol. Chem. 2010, 8, 181–192.
doi:10.1039/b916580k
29.Gadikota, R. R.; Callam, C. S.; Appelmelk, B. J.; Lowary, T. L.
J. Carbohydr. Chem. 2003, 22, 459–480. doi:10.1081/CAR-120025322
30.Tong, M.; Jacobi, C. E.; van de Rijke, F. M.; Kujiper, S.;
van de Werken, S.; Lowary, T. L.; Hokke, C. H.; Appelmelk, B. J.;
Nagelkerke, N. J. D.; Tanke, H. J.; van Gijlswijk, R. P. M.;
Veuskens, J.; Kolk, A. H. J.; Raap, A. K. J. Immunol. Methods 2005,
301, 154–163. doi:10.1016/j.jim.2005.04.004
31.Boonyarattanakalin, S.; Liu, X.; Michieletti, M.; Lepenies, B.;
Seeberger, P. H. J. Am. Chem. Soc. 2008, 130, 16791–16799.
doi:10.1021/ja806283e
376

Beilstein J. Org. Chem. 2011, 7, 369–377.
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