301
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Rising TWDF, Claridge TDW, Davies N, Gamblin DP, Moir JWB, Fairbanks AJ. Synthesis of N-glycan oxazolines: donors for endohexosaminidase catalysed glycosylation. Carbohydr Res 2006; 341:1574-96. [PMID: 16584712 DOI: 10.1016/j.carres.2006.03.007] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Revised: 02/24/2006] [Accepted: 03/07/2006] [Indexed: 11/20/2022]
Abstract
Oxazoline mono-, di-, tri- and hexasaccharides, corresponding to the core components of N-linked glycoprotein high mannose glycans, are synthesised as potential glycosyl donors for endohexosaminidase catalysed glycosylation of glycopeptides and glycoprotein remodelling. The crucial beta-D-Manp-(1-->4)-D-GlcpNAc linkage is synthesised via epimerisation of gluco disaccharide substrates by sequential triflation and nucleophilic substitution. Oxazolines are formed directly from the anomeric OPMP protected N-acetyl glucosamine derivatives. Efficient endohexosaminidase catalysed glycosylation of a synthetic beta-D-GlcpNAcAsn glycosyl amino acid is demonstrated with the trisaccharide oxazoline donor.
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Affiliation(s)
- Thomas W D F Rising
- Chemistry Research Laboratory, Oxford University, Mansfield Road, Oxford OX1 3TA, UK
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302
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Müllegger J, Chen HM, Warren RAJ, Withers SG. Glycosylation of a Neoglycoprotein by Using Glycosynthase and Thioglycoligase Approaches: The Generation of a Thioglycoprotein. Angew Chem Int Ed Engl 2006. [DOI: 10.1002/ange.200503900] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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303
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Müllegger J, Chen HM, Warren RAJ, Withers SG. Glycosylation of a Neoglycoprotein by Using Glycosynthase and Thioglycoligase Approaches: The Generation of a Thioglycoprotein. Angew Chem Int Ed Engl 2006; 45:2585-8. [PMID: 16528765 DOI: 10.1002/anie.200503900] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Johannes Müllegger
- Protein Engineering Network of Centres of Excellence, Department of Chemistry, University of British Columbia, Vancouver, B. C. V6T 1Z1, Canada
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304
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305
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306
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Ichikawa Y, Matsukawa Y, Isobe M. Synthesis of Urea-Tethered Neoglycoconjugates and Pseudooligosaccharides in Water. J Am Chem Soc 2006; 128:3934-8. [PMID: 16551100 DOI: 10.1021/ja056253f] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A novel approach to the synthesis of urea glycosides in aqueous media has been explored. Steyermark's glucopyranosyl oxazolidinone was found to be a good synthon for anchoring glucosyl moieties onto amines and thiols. The present method was successfully applied to establish a new route for the synthesis of urea-tethered neoglycoconjugates and pseudooligosaccharides in water.
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Affiliation(s)
- Yoshiyasu Ichikawa
- Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan.
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307
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Chen J, Warren JD, Wu B, Chen G, Wan Q, Danishefsky SJ. A route to cyclic peptides and glycopeptides by native chemical ligation using in situ derived thioesters. Tetrahedron Lett 2006. [DOI: 10.1016/j.tetlet.2006.01.077] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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308
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Hovinen J. Synthesis of Aminooxy-Functionalized Lanthanide(III) Chelates for Carbonyl-Group Conjugation. Chem Biodivers 2006; 3:296-303. [PMID: 17193266 DOI: 10.1002/cbdv.200690032] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The syntheses of three new aminooxy-tethered lanthanide(III) chelates, compounds 1-3, incorporating DOTA (= 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), DTPA (= diethylenetriaminepentaacetic acid), or a substituted terpyridine (2,2',2'',2'''-[2,2': 6',2''-terpyridine-6,6''-diylbis(methylenenitrilo)]tetraacetic acid), respectively, are described. Reagents 1-3 can be used for carbonyl 'labeling', as shown by the formation of the corresponding oxime-ether bioconjugates of naltrexone (16) and 2-deoxy-beta-D-glucose (17) (Scheme 4).
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Affiliation(s)
- Jari Hovinen
- PerkinElmer Life and Analytical Sciences, Turku Site, P. O. Box 10, FIN-20101 Turku, Finland.
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309
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Crich D, Krishnamurthy V, Hutton TK. Allylic selenosulfide rearrangement: a method for chemical ligation to cysteine and other thiols. J Am Chem Soc 2006; 128:2544-5. [PMID: 16492032 PMCID: PMC4658652 DOI: 10.1021/ja057521c] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Alkylation of potassium selenosulfate with allylic halides gives Se-allyl seleno Bunte salts. On reaction with thiols at room temperature, these afford mixed dialkyl selenosulfides, which undergo 2,3-sigmatropic rearrangement with loss of selenium, either spontaneously or with assistance by triphenylphosphine, thereby providing mixed dialkyl sulfides and a new permanent chemical ligation method. The process is illustrated through the lipidation of cysteine-containing tripeptides and by the allylation of 1-thioglucose tetraacetate.
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Affiliation(s)
- David Crich
- Department of Chemistry, University of Illinois at Chicago, 60607-7061, USA.
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310
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Highly efficient synthesis of sialylglycopeptides overcoming unexpected aspartimide formation during activation of Fmoc-Asn(undecadisialyloligosaccharide)-OH. Tetrahedron Lett 2006. [DOI: 10.1016/j.tetlet.2005.12.064] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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311
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Tiwari P, Misra AK. Acylation of carbohydrates over Al2O3: preparation of partially and fully acylated carbohydrate derivatives and acetylated glycosyl chlorides. Carbohydr Res 2006; 341:339-50. [PMID: 16364271 DOI: 10.1016/j.carres.2005.11.035] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2005] [Revised: 11/11/2005] [Accepted: 11/18/2005] [Indexed: 11/21/2022]
Abstract
Selective and per-O-acylation of carbohydrate derivatives using acyl chlorides and Al2O3, a solid support reagent, is reported. This protocol does not require the addition of any base or activator. This methodology has been further extended to the selective acylation of carbohydrate diols and the one-pot preparation of acetylated glycosyl chlorides direct from free reducing sugars. The yields obtained in most of the cases are excellent.
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Affiliation(s)
- Pallavi Tiwari
- Medicinal and Process Chemistry Division, Central Drug Research Institute, Chattar Manzil Palace, Lucknow 226 001, UP, India
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312
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Liu L, Hong ZY, Wong CH. Convergent Glycopeptide Synthesis by Traceless Staudinger Ligation and Enzymatic Coupling. Chembiochem 2006; 7:429-32. [PMID: 16444769 DOI: 10.1002/cbic.200500437] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Lei Liu
- Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
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313
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Carçabal P, Hünig I, Gamblin DP, Liu B, Jockusch RA, Kroemer RT, Snoek LC, Fairbanks AJ, Davis BG, Simons JP. Building Up Key Segments of N-Glycans in the Gas Phase: Intrinsic Structural Preferences of the α(1,3) and α(1,6) Dimannosides. J Am Chem Soc 2006; 128:1976-81. [PMID: 16464099 DOI: 10.1021/ja055891v] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The intrinsic conformer specific vibrational spectra of two important subunits of the core pentasaccharide of N-linked glycans, the alpha(1,3) and alpha(1,6) dimannosides, have been recorded in the gas phase. Coupling these measurements with a computational exploration of their conformational landscapes has enabled their conformational assignment and has identified characteristic vibrational signatures associated with particular conformational families-including those that do or do not display inter-ring hydrogen bonding across the glycosidic linkage. In addition, the IR spectra of the monosaccharide moieties provide benchmarks, through which the conformational assignments can be refined. This introduces a general concept of modularity and secondary structure in oligosaccharides--essential for the success of similar studies on larger oligosaccharides in the future.
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Affiliation(s)
- Pierre Carçabal
- Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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314
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Seibel J, Hellmuth H, Hofer B, Kicinska AM, Schmalbruch B. Identification of New Acceptor Specificities of Glycosyltransferase R with the Aid of Substrate Microarrays. Chembiochem 2006; 7:310-20. [PMID: 16416490 DOI: 10.1002/cbic.200500350] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Finding opportunities to construct sugar motifs and to transfer them to targets of biological relevance and rapid identification of glycosylation events are important goals for glycobiology and a field of increasing interest. Here we have applied an enzyme microarray screening system for the identification of new acceptor specificities of the glycosyltransferase R (GTFR) from Streptococcus oralis (E.C. 2.4.1.5), which was able to effect the synthesis of sugar motifs in short times and with low amounts of substrate. These observations resulted in the development of a convenient alpha-glycosylation by the non-Leloir glycosyltransferase GTFR, with sucrose as substrate and with different alcohols and amino acid derivatives as acceptors, for the synthesis of glycoethers and glycosylated amino acids not observed with the use of familiar GTFs with high sequence homology.
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Affiliation(s)
- Jürgen Seibel
- Technical Chemistry, Department for Carbohydrate Technology, Technical University Braunschweig, Langer Kamp 5, 38106 Braunschweig, Germany.
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315
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Doores KJ, Gamblin DP, Davis BG. Exploring and Exploiting the Therapeutic Potential of Glycoconjugates. Chemistry 2006; 12:656-65. [PMID: 16187378 DOI: 10.1002/chem.200500557] [Citation(s) in RCA: 142] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Carbohydrates, either bound to proteins or in lipids, play essential roles as communication molecules in many intercellular and intracellular processes. In particular, carbohydrates are important mediators of cell-cell recognition events and have been implicated in related processes such as cell signaling regulation, cellular differentiation and immune response. This diverse utility has long suggested the power of carbohydrates in therapeutic approaches. This Concepts article highlights the recent potential uses of glycoconjugates as therapeutics, with particular reference to glycopeptides, glycoproteins, glycodendrimers, and glycoarrays.
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Affiliation(s)
- Katie J Doores
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, UK
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316
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Williams Z, Litscher ES, Jovine L, Wassarman PM. Polypeptide encoded by mouseZP3 exon-7 Is Necessary and Sufficient for binding of mouse sperm in vitro. J Cell Physiol 2006; 207:30-9. [PMID: 16245311 DOI: 10.1002/jcp.20532] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Fertilization in mice is initiated by species-specific binding of sperm to mZP3, one of three mouse zona pellucida (ZP) glycoproteins. At nanomolar concentrations, purified egg mZP3 binds to acrosome-intact sperm heads and inhibits binding of sperm to eggs in vitro. Although several reports suggest that sperm recognize and bind to a region of mZP3 encoded by mZP3 exon-7 (so-called, sperm combining-site), this issue remains controversial. Here, exon-swapping and an IgG(Fc) fusion construct were used to further evaluate whether mZP3 exon-7 is essential for binding of sperm to mZP3. In one set of experiments, hamster ZP3 (hZP3) exon-6, -7, and -8 were individually replaced with the corresponding exon of mZP3. Stably transfected embryonal carcinoma (EC) cell lines carrying the recombinant genes were produced and secreted recombinant glycoprotein was purified and assayed for the ability to inhibit binding of sperm to eggs. While EC-hZP3, a recombinant form of hZP3 made by EC cells, is unable to inhibit binding of mouse sperm to eggs in vitro, the results suggest that substitution of mZP3 exon-7 for hZP3 exon-7, but not mZP3 exon-6 or -8, can impart inhibitory activity to EC-hZP3. In this context, a fusion construct consisting of human IgG(Fc) and mZP3 exon-7 and -8 was prepared, an EC cell line carrying the recombinant gene was produced, and secreted chimeric glycoprotein, called EC-huIgG(Fc)/mZP3(7), was purified and assayed. It was found that the chimeric glycoprotein binds specifically to plasma membrane overlying sperm heads to a similar extent as egg mZP3 and, at nanomolar concentrations, inhibits binding of mouse sperm to eggs in vitro. Collectively, these observations provide new evidence that sperm recognize and bind to a region of mZP3 polypeptide immediately downstream of its ZP domain that is encoded by mZP3 exon-7. The implications of these findings are discussed.
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Affiliation(s)
- Zev Williams
- Brookdale Department of Molecular, Cell and Developmental Biology, Mount Sinai School of Medicine, New York, New York, USA
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317
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Doores KJ, Mimura Y, Dwek RA, Rudd PM, Elliott T, Davis BG. Direct deprotected glycosyl–asparagine ligation. Chem Commun (Camb) 2006:1401-3. [PMID: 16550280 DOI: 10.1039/b515472c] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A simple and efficient synthesis of N-linked glycoamino acids and glycopeptides from deprotected sugars using the Staudinger reaction.
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Affiliation(s)
- Katie J Doores
- Department of Chemistry, Oxford University, Chemistry Research Laboratory, Mansfield Road, Oxford, UKOX1 3TA
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318
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Abstract
The development of chemical and enzymatic methods for the synthesis of homogeneous glycoproteins is a fascinating challenge at the interface between chemistry and biology. Discussed here are the currently available methods for preparation of homogeneous glycoproteins. These methods include (1) glycopeptide ligation; (2) glycoprotein remodeling; and (3) in vivo suppressor tRNA technology.
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Affiliation(s)
- Lei Liu
- Department of Chemistry and Skaggs Institute for Chemical Biology, Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
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319
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Renaudet O, Dumy P. On-bead synthesis and binding assay of chemoselectively template-assembled multivalent neoglycopeptides. Org Biomol Chem 2006; 4:2628-36. [PMID: 16791327 DOI: 10.1039/b604391g] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The investigation of recognition events between carbohydrates and proteins, especially the control of how spatial factors and binding avidity are correlated in, remains a great interest for glycomics. Therefore, the development of efficient methods for the rapid evaluation of new ligands such as multivalent glycoconjugates is essential for diverse diagnostic or therapeutic applications. In this paper we describe the synthesis of chemoselectively-assembled multivalent neoglycopeptides and the subsequent recognition assay on a solid support. Aminooxylated carbohydrates (betaLac-ONH(2) 4, alphaGalNAc-ONH(2) 9 and alphaMan-ONH(2) 13) have been prepared as carbohydrate-based recognition elements and assembled as clusters onto a cyclopeptidic scaffold by an oxime-based strategy in solid phase. Further binding tests between lectins and beads of resin derivatized with neoglycopeptides displaying clustered lactoses, N-acetylgalactoses and mannoses (18-20) have shown specific recognition and enhanced affinity through multivalent interactions, suggesting that the local density of carbohydrate-based ligands at the bead surface is crucial to improve the interaction of proteins of weak binding affinity. This solid phase strategy involving both molecular assembly and biological screening provides a rapid and efficient tool for various applications in glycomics.
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Affiliation(s)
- Olivier Renaudet
- LEDSS, UMR-CNRS 5616 & ICMG FR 2607, Université Joseph Fourier, Grenoble, France
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320
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Röhrig CH, Retz OA, Hareng L, Hartung T, Schmidt RR. A new strategy for the synthesis of dinucleotides loaded with glycosylated amino acids--investigations on in vitro non-natural amino acid mutagenesis for glycoprotein synthesis. Chembiochem 2005; 6:1805-16. [PMID: 16142818 DOI: 10.1002/cbic.200500079] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The in vitro non-natural amino acid mutagenesis method provides the opportunity to introduce non-natural amino acids site-specifically into proteins. To this end, a chemically synthesised aminoacylated dinucleotide is enzymatically ligated to a truncated suppressor transfer RNA. The loaded suppressor tRNA is then used in translation reactions to read an internal stop codon. Here we report an advanced and general strategy for the synthesis of the aminoacyl dinucleotide. The protecting group pattern developed for the dinucleotide facilitates highly efficient aminoacylation, followed by one-step global deprotection. The strategy was applied to the synthesis of dinucleotides loaded with 2-acetamido-2-deoxy-glycosylated amino acids, including N- and O-beta-glycosides and O- and C-alpha-glycosides of amino acids, thus enabling the extension of in vitro non-natural amino acid mutagenesis towards the synthesis of natural glycoproteins of high biological interest. We demonstrate the incorporation of the glycosylamino acids--although with low suppression efficiency--into the human interleukin granulocyte-colony stimulating factor (hG-CSF), as verified by the ELISA technique.
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Affiliation(s)
- Christoph H Röhrig
- Department of Chemistry, University of Konstanz, Fach M 725, 78457 Konstanz, Germany
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321
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322
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Mukhopadhyay B, Maurer SV, Rudolph N, van Well RM, Russell DA, Field RA. From Solution Phase to “On-Column” Chemistry: Trichloroacetimidate-Based Glycosylation Promoted by Perchloric Acid−Silica. J Org Chem 2005; 70:9059-62. [PMID: 16238354 DOI: 10.1021/jo051390g] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[reaction: see text] Activation of ester-protected glycosyl trichloroacetimidate donors by perchloric acid immobilized on silica afforded 1,2-trans disaccharides in 60-90% yields. Applying this approach to one-pot sequential glycosylation resulted in efficient syntheses of the N-linked glycan trimannoside and Le(X) and Le(A) trisaccharides in very good yield (76%, 62%, and 59% yields, respectively). Solution phase reactions were also translated to a solid phase format; priming the top of a standard silica chromatography column with perchloric acid immobilized on silica facilitated "on-column" glycosylation with subsequent "in situ" purification of products. Coupling yields from this approach were comparable to those obtained from the corresponding solution-phase disaccharide couplings. A series of glycosylated amino acids were also synthesized in high yield with use of the on-column approach.
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Affiliation(s)
- Balaram Mukhopadhyay
- Centre for Carbohydrate Chemistry, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, UK
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323
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Ito Y, Hagihara S, Matsuo I, Totani K. Structural approaches to the study of oligosaccharides in glycoprotein quality control. Curr Opin Struct Biol 2005; 15:481-9. [PMID: 16154739 DOI: 10.1016/j.sbi.2005.08.012] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2005] [Revised: 06/08/2005] [Accepted: 08/31/2005] [Indexed: 11/23/2022]
Abstract
High-mannose-type oligosaccharides have been shown to play important roles in protein quality control. Several intracellular proteins, such as lectins, chaperones and glycan-processing enzymes, are involved in this process. These include calnexin/calreticulin, UDP-glucose:glycoprotein glucosyltransferase (UGGT), cargo receptors (such as VIP36 and ERGIC-53), mannosidase-like proteins (e.g. EDEM and Htm1p) and ubiquitin ligase (Fbs). They are thought to recognize high-mannose-type glycans with subtly different structures, although the precise specificities are yet to be clarified. In order to gain a clear understanding of these protein-carbohydrate interactions, comprehensive synthesis of high-mannose-type glycans was conducted. In addition, two approaches to the synthesis of artificial glycoproteins with homogeneous oligosaccharides were investigated. Furthermore, a novel substrate of UGGT was discovered.
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Affiliation(s)
- Yukishige Ito
- RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
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324
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Esteves AP, Rodrigues LM, Silva ME, Gupta S, Oliveira-Campos AM, Machalicky O, Mendonça AJ. Synthesis and characterization of novel fluorescent N-glycoconjugates. Tetrahedron 2005. [DOI: 10.1016/j.tet.2005.07.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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325
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Grigalevicius S, Chierici S, Renaudet O, Lo-Man R, Dériaud E, Leclerc C, Dumy P. Chemoselective Assembly and Immunological Evaluation of Multiepitopic Glycoconjugates Bearing Clustered Tn Antigen as Synthetic Anticancer Vaccines. Bioconjug Chem 2005; 16:1149-59. [PMID: 16173792 DOI: 10.1021/bc050010v] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this paper we investigated the use of regioselectively addressable functionalized templates (RAFTs) as new scaffolds for the design of anticancer vaccine candidates. We report the synthesis of well-defined multiepitopic RAFT scaffolds and their immunological evaluation. These conjugates exhibit clustered Tn analogue as tumor-associated carbohydrate antigen (TACA, B-cell epitope) and the CD4+ helper T-cell peptide from the type 1 poliovirus. The saccharidic and peptidic epitopes were both synthesized separately and combined regioselectively to the RAFT core using a sequential oxime bond formation strategy. B- and T-antigenicity and immunogenicity of the vaccine candidates were investigated in vitro and in vivo. These studies clearly demonstrate that the saccharidic part of the conjugates is recognized by Tn-specific monoclonal antibodies. Moreover, the antibodies elicited by immunization of mice with our vaccine candidates recognize the native form of Tn epitope expressed on human tumor cells. Together with oxime ligation technique, these results suggest that the RAFT scaffold provides a promising and suitable tool for engineering potent synthetic anticancer vaccine.
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Affiliation(s)
- Saulius Grigalevicius
- LEDSS UMR 5616 and ICMG-FR2607, Université Joseph Fourier, BP 53, 38041 Grenoble Cedex 9, France
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326
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Iñigo S, Porro MT, Montserrat JM, Iglesias LE, Iribarren AM. Deprotection of peracetylated methyl d-ribosides through enzymatic alcoholysis: Different recognition of the anomers. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/j.molcatb.2005.05.010] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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327
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van Well R, Ravindranathan Kartha K, Field R. Iodine Promoted Glycosylation with Glycosyl Iodides: α‐Glycoside Synthesis. J Carbohydr Chem 2005. [DOI: 10.1081/car-200067028] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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328
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Renaudet O, Dumy P. Synthesis of multitopic neoglycopeptides displaying recognition and detection motifs. Bioorg Med Chem Lett 2005; 15:3619-22. [PMID: 15982871 DOI: 10.1016/j.bmcl.2005.05.072] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2005] [Revised: 05/03/2005] [Accepted: 05/11/2005] [Indexed: 11/26/2022]
Abstract
We describe herein the synthesis of cyclic decapeptide template displaying clustered carbohydrate recognition motifs and detection agent on spatially separated domains. Such multitopic labeled neoglycopeptides represent attractive tools for binding assays with carbohydrate binding proteins in glycomic research.
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Affiliation(s)
- Olivier Renaudet
- LEDSS, UMR-CNRS 5616 & ICMG FR 2607, Université Joseph Fourier, BP 53 38041 Grenoble Cedéx 9, France
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329
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Thayer DA, Yu HN, Galan MC, Wong CH. A General Strategy toward S-Linked Glycopeptides. Angew Chem Int Ed Engl 2005. [DOI: 10.1002/ange.200500090] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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330
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Abstract
Enzymatic macrolactamization of linear glycosidated peptides provides access to an important class of drug-like molecules. The work presented in this issue [1] shows that it may be possible to make complex libraries of glycosidated cyclic peptides by incorporating glycosidated amino acids into linear peptides via solid-phase peptide synthesis followed by thioesterase-mediated peptide cyclization.
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331
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Shao N, Guo Z. Solution-Phase Synthesis with Solid-State Workup of an O-Glycopeptide with a Cluster of Cancer-Related T Antigens. Org Lett 2005; 7:3589-92. [PMID: 16048349 DOI: 10.1021/ol0514193] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An N-terminal glycopeptide of asialoglycophorin AM with three O-linked T antigens was prepared by "solution-phase synthesis with solid-state workup" using unprotected glycosyl amino acids as building blocks. For the glycopeptide assembly, all reactions were conducted in homogeneous NMP solutions, while the product of each reaction was readily isolated as solid precipitates upon addition of diethyl ether. In the preparation of building blocks, a robust approach was established to selectively alpha-glycosylate Ser and Thr derivatives. [reaction: see text]
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Affiliation(s)
- Ning Shao
- Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7078, USA
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332
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Swanwick RS, Daines AM, Tey LH, Flitsch SL, Allemann RK. Increased Thermal Stability of Site-Selectively Glycosylated Dihydrofolate Reductase. Chembiochem 2005; 6:1338-40. [PMID: 16003807 DOI: 10.1002/cbic.200500103] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Richard S Swanwick
- School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, UK
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333
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Li B, Zeng Y, Hauser S, Song H, Wang LX. Highly Efficient Endoglycosidase-Catalyzed Synthesis of Glycopeptides Using Oligosaccharide Oxazolines as Donor Substrates. J Am Chem Soc 2005; 127:9692-3. [PMID: 15998066 DOI: 10.1021/ja051715a] [Citation(s) in RCA: 140] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A highly efficient chemoenzymatic synthesis of N-glycopeptides was achieved. It was found that using synthetic oligosaccharide oxazolines, the mimics of the presumed oxazolinium ion intermediate formed in a retaining mechanism of substrate-assisted catalysis, as the donor substrates and GlcNAc-peptides as the acceptors, the endo-beta-N-acetylglucosaminidase (ENGase)-catalyzed transglycosylation gave a high yield (73-82%) of the corresponding glycopeptides in a regio- and stereospecific manner, regardless of the size of the peptide portions. The use of the oligosaccharide oxazolines as donor substrates not only expanded the substrate availability but also led to a substantial enhancement of the synthetic efficiency, compared to the use of natural N-glycans.
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Affiliation(s)
- Bing Li
- Institute of Human Virology, University of Maryland Biotechnology Institute, University of Maryland, Baltimore, Maryland 21201, USA
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334
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Synthesis of Higher Aluminum Content Hexagonal and Cubic Mesoporous Aluminosilicates toward Catalysts. Top Catal 2005. [DOI: 10.1007/s11244-005-3810-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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335
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Dong CM, Chaikof EL. Self-assembled nanostructures of a biomimetic glycopolymer–polypeptide triblock copolymer. Colloid Polym Sci 2005. [DOI: 10.1007/s00396-005-1323-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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336
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Galonić DP, Ide ND, van der Donk WA, Gin DY. Aziridine-2-carboxylic Acid-Containing Peptides: Application to Solution- and Solid-Phase Convergent Site-Selective Peptide Modification. J Am Chem Soc 2005; 127:7359-69. [PMID: 15898784 DOI: 10.1021/ja050304r] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The development of a method for site- and stereoselective peptide modification using aziridine-2-carboxylic acid-containing peptides is described. A solid-phase peptide synthesis methodology that allows for the rapid generation of peptides incorporating the aziridine residue has been developed. The unique electrophilic nature of this nonproteinogenic amino acid allows for site-selective conjugation with various thiol nucleophiles, such as anomeric carbohydrate thiols, farnesyl thiol, and biochemical tags, both in solution and on solid support. This strategy, combined with native chemical ligation, provides convergent and rapid access to complex thioglycoconjugates.
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Affiliation(s)
- Danica P Galonić
- Department of Chemistry, University of Illinois, Urbana, 61801, USA
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337
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Wei P, Kerns RJ. Factors Affecting Stereocontrol during Glycosidation of 2,3-Oxazolidinone-Protected 1-Tolylthio-N-acetyl-d-glucosamine. J Org Chem 2005; 70:4195-8. [PMID: 15876119 DOI: 10.1021/jo047812o] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] It is demonstrated that a ring-fused 2,3-oxazolidinone-protected derivative of 1-tolylthio-N-acetyl-D-glucosamine undergoes high-yield glycosidation under mild donor activation conditions. Stereoselective formation of alpha-linked or beta-linked glycosides is dependent on reactivity of acceptor alcohols, where rate of glycosidation correlates to stereochemical outcome. Evidence for the role of glycosyl triflate intermediates and the N-acetyl substituent of the 2N,3O-oxazolidinone ring in stereochemical control is presented.
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Affiliation(s)
- Peng Wei
- Division of Medicinal & Natural Product Chemistry, University of Iowa, Iowa City, Iowa 52242-1112, USA
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338
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Hölemann A, Seeberger PH. Carbohydrate diversity: synthesis of glycoconjugates and complex carbohydrates. Curr Opin Biotechnol 2005; 15:615-22. [PMID: 15560990 DOI: 10.1016/j.copbio.2004.10.001] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The fundamental role of glycoconjugates in many biological processes is now well appreciated and has intensified the development of innovative and improved synthetic strategies. All areas of synthetic methodology have seen major advances and many complex, highly branched carbohydrates and glycoproteins have been prepared using solution- and/or solid-phase approaches. The development of an automated oligosaccharide synthesizer provides rapid access to biologically relevant compounds. These chemical approaches help to produce sufficient quantities of defined oligosaccharides for biological studies. Synthetic chemistry also supports an improved understanding of glycobiology and will eventually result in the discovery of new therapeutics.
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Affiliation(s)
- Alexandra Hölemann
- Eidgenössische Technische Hochschule Zürich, Laboratory for Organic Chemistry, ETH Hönggerberg, HCI F315, Wolfgang-Pauli-Strasse 10, CH-8093 Zürich, Switzerland
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339
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Ambrosi M, Cameron NR, Davis BG. Lectins: tools for the molecular understanding of the glycocode. Org Biomol Chem 2005; 3:1593-608. [PMID: 15858635 DOI: 10.1039/b414350g] [Citation(s) in RCA: 364] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Recent progress in glycobiology has revealed that cell surface oligosaccharides play an essential role in recognition events. More precisely, these saccharides may be complexed by lectins, carbohydrate-binding proteins other than enzymes and antibodies, able to recognise sugars in a highly specific manner. The ubiquity of lectin-carbohydrate interactions opens enormous potential for their exploitation in medicine. Therefore, extraordinary effort is made into the identification of new lectins as well as into the achievement of a deep understanding of their functions and of the precise mechanism of their association with specific ligands. In this review, a summary of the main features of lectins, particularly those found in legumes, will be presented with a focus on the mechanism of carbohydrate-binding. An overview of lectin-carbohydrate interactions will also be given, together with an insight into their energetics. In addition, therapeutic applications of lectins will be discussed.
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Affiliation(s)
- Moira Ambrosi
- Department of Chemistry, University of Durham, South Road, Durham, UKDH1 3LE
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340
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Mezzato S, Schaffrath M, Unverzagt C. Ein orthogonales Linkerpaar zur effizienten Festphasensynthese von Glycopeptidthioestern mit N-Glycanen des komplexen Typs und Einsatz in der nativen chemischen Ligation. Angew Chem Int Ed Engl 2005. [DOI: 10.1002/ange.200461125] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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341
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342
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Misra AK, Tiwari P, Madhusudan SK. HClO4–SiO2 catalyzed per-O-acetylation of carbohydrates. Carbohydr Res 2005; 340:325-9. [PMID: 15639254 DOI: 10.1016/j.carres.2004.11.021] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Accepted: 11/21/2004] [Indexed: 10/26/2022]
Abstract
An efficient per-O-acetylation of carbohydrates catalyzed by HClO4-SiO2 is reported using a stoichiometric quantity of acetic anhydride avoiding the use of pyridine and excess acetic anhydride under solvent-free conditions.
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Affiliation(s)
- Anup Kumar Misra
- Division of Medicinal and Process Chemistry, Central Drug Research Institute, Chattar Manzil Palace, Lucknow 226 001, India.
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343
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Seibel J, Hillringhaus L, Moraru R. Microwave-assisted glycosylation for the synthesis of glycopeptides. Carbohydr Res 2005; 340:507-11. [PMID: 15680608 DOI: 10.1016/j.carres.2004.12.014] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2004] [Revised: 11/30/2004] [Accepted: 12/15/2004] [Indexed: 10/25/2022]
Abstract
An efficient one-step synthesis of O-linked glycosylamino acids is described. This methodology converts commercially available peracetylated mono- and disaccharides activated by cheap and environmentally safe FeCl(3) under microwave irradiation with Fmoc-Ser-OBn to the corresponding beta-glycosides in short reaction times and moderate yields.
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Affiliation(s)
- Jürgen Seibel
- Technical University of Braunschweig, Department for Carbohydrate Technology, Langer Kamp 5, D-38106 Braunschweig, Germany.
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344
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Tanaka H, Adachi M, Takahashi T. One-Pot Synthesis of Sialo-Containing Glycosyl Amino Acids by Use of anN-Trichloroethoxycarbonyl-?-thiophenyl Sialoside. Chemistry 2005; 11:849-62. [PMID: 15580651 DOI: 10.1002/chem.200400840] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We describe an efficient synthesis of 2,6- and 2,3-sialyl T antigens linked to serine in a one-pot glycosylation. We first investigated the glycosidation of thiosialosides by varying the N-protecting group. Modification of the C-5 amino group of beta-thiosialosides into the N-9-fluorenylmethoxycarbonyl, N-2,2,2-trichloroethoxycarbonyl (N-Troc), and N-trichloroacetyl derivatives enhanced the reactivity of these compounds towards glycosidation. Addition of a minimum amount of 3 A molecular sieves was also effective in improving the yield of alpha-linked sialosides. Next, we conducted one-pot syntheses of the glycosyl amino acids by using the N-Troc sialyl donor. The N-Troc derivative can be converted into the N-acetyl derivative without racemization of the amino acids. Branched-type one-pot glycosylation, initiated by regioselective glycosylation of the 3,6-dihydroxy galactoside with the N-Troc-beta-thiophenyl sialoside, provided the protected 2,6-sialyl T antigen in good yield. Linear-type one-pot glycosylation, initiated by chemoselective glycosylation of galactosyl fluoride with the N-Troc-beta-thiophenyl sialoside, afforded the protected 2,3-sialyl T antigen in excellent yield. Both protected glycosyl amino acids were converted into the fully deprotected 2,6- and 2,3-sialyl T antigens linked to serine in good yields.
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Affiliation(s)
- Hiroshi Tanaka
- Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8552, Japan
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345
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346
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Guo Z, Shao N. Glycopeptide and glycoprotein synthesis involving unprotected carbohydrate building blocks. Med Res Rev 2005; 25:655-78. [PMID: 15895471 DOI: 10.1002/med.20033] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This review summarizes the chemical and chemoenzymatic synthesis of glycopeptides and glycoproteins using unprotected carbohydrates as key intermediates. The synthetic methods covered herein include the convergent synthesis of glycopeptides by chemoselective ligation of peptides and free glycans, solution- and solid-phase synthesis of glycopeptides by sequential peptide elongation with unprotected glycosyl amino acids or short glycopeptides as building blocks, and the synthesis of glycopeptides by enzymatic and/or chemical elongation of the free glycans. The use of unprotected carbohydrates in these syntheses can circumvent the final-stage carbohydrate deprotection, lead to highly convergent synthetic designs, and more significantly, take advantage of the commercially available free glycans isolated from nature, which could considerably facilitate the synthesis of complex glycopeptides and glycoproteins.
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Affiliation(s)
- Zhongwu Guo
- Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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347
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Abstract
Although chemists can synthesize virtually any small organic molecule, our ability to rationally manipulate the structures of proteins is quite limited, despite their involvement in virtually every life process. For most proteins, modifications are largely restricted to substitutions among the common 20 amino acids. Herein we describe recent advances that make it possible to add new building blocks to the genetic codes of both prokaryotic and eukaryotic organisms. Over 30 novel amino acids have been genetically encoded in response to unique triplet and quadruplet codons including fluorescent, photoreactive, and redox-active amino acids, glycosylated amino acids, and amino acids with keto, azido, acetylenic, and heavy-atom-containing side chains. By removing the limitations imposed by the existing 20 amino acid code, it should be possible to generate proteins and perhaps entire organisms with new or enhanced properties.
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Affiliation(s)
- Lei Wang
- Department of Pharmacology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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348
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Ambrosi M, Cameron NR, Davis BG, Stolnik S. Investigation of the interaction between peanut agglutinin and synthetic glycopolymeric multivalent ligands. Org Biomol Chem 2005; 3:1476-80. [PMID: 15827644 DOI: 10.1039/b411555b] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The interaction between synthetic glycoplymers bearing beta-D-galactose side groups and the lectin peanut agglutinin (PNA) was investigated by UV-difference spectroscopy and isothermal titration calorimetry (ITC). UV-difference spectroscopy indicated that the polymer-lectin interaction was stronger than that between PNA and either the corresponding monomer, D-galactose or D-lactose. The thermodynamics of binding (K, DeltaG, DeltaH, DeltaS and n) were determined from ITC data by fitting with a two-site, non-cooperative binding model. It was found that the glycopolymer displayed around a 50 times greater affinity for the lectin than the parent carbohydrate, and around 10 times greater than the monomer, on a valency-corrected basis. Binding was found to be entropically driven, and was accompanied by aggregation and precipitation of protein molecules. Furthermore, interesting differences between polymers prepared either from deacetylated monomers, or by deacetylation of pre-formed polymers, were found.
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Affiliation(s)
- Moira Ambrosi
- Department of Chemistry and Interdisciplinary Research Centre in Polymer Science and Technology, University of Durham, UK
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349
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Abstract
The strategy of combined site directed mutagenesis and chemical modification with polar prosthetic groups was used to broaden substrate specificity of proteases resulting in the first successful formation of glycopeptides through the use of glucoamino acid acyl donors in yields of up to 90%.
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Affiliation(s)
- Katie J Doores
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford, UK OX1 3TA
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350
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Dong CM, Sun XL, Faucher KM, Apkarian RP, Chaikof EL. Synthesis and characterization of glycopolymer-polypeptide triblock copolymers. Biomacromolecules 2004; 5:224-31. [PMID: 14715030 DOI: 10.1021/bm0343500] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Glycopolymer-polypeptide triblock copolymers of the structure, poly(l-alanine)-b-poly(2-acryloyloxyethyl-lactoside)-b-poly(l-alanine) (AGA), have been synthesized by sequential atom transfer radical polymerization (ATRP) and ring-opening polymerization (ROP). Controlled free radical polymerization of 2-O-acryloyl-oxyethoxyl-(2,3,4,6-tetra-O-acetyl-beta-d-galactopyranosyl)-(1-4)-2,3,6-tri-O-acetyl-beta-d-glucopyranoside (AEL) by ATRP with a dibromoxylene (DBX)/CuBr/bipy complex system was used to generate a central glycopolymer block. Telechelic glycopolymers with diamino end groups were obtained by end group transformation and subsequently used as macroinitiators for ROP of l-alanine N-carboxyanhydride monomers (Ala-NCA). Gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy analysis demonstrated that copolymer molecular weight and composition were controlled by both the molar ratios of the Ala-NCA monomer to macroinitiator and monomer conversion and exhibited a narrow distribution (Mw/Mn = 1.06-1.26). FT-IR spectroscopy of triblock copolymers revealed that the ratio of alpha-helix/beta-sheet increased with poly(l-alanine) block length. Of note, transmission electron microscopy (TEM) demonstrated that selected amphiphilic glycopolymer-polypeptide triblock copolymers self-assemble in aqueous solution to form nearly spherical aggregates of several hundreds nanometer in diameter. Significantly, the sequential application of ATRP and ROP techniques provides an effective method for producing triblock copolymers with a central glycopolymer block and flanking polypeptide blocks of defined architecture, controlled molecular weight, and low polydispersity.
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Affiliation(s)
- Chang-Ming Dong
- Laboratory for Biomolecular Materials Research, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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