Concise assembly of linear α(1→6)-linked octamannan fluorescent probe

Abstract

Synthesis of a fluorescently labelled (dansylated) linear α(1→6)-linked octamannan, using glycosyl fluoride donors and thioglycosyl acceptors is described. A selective and convergent two-stage activation progression was executed to construct di-, tetra and octa-mannosyl thioglycosides in three glycosylation steps with excellent yield. Further a 5-N,N-Dimethylaminonaphthalene-1-sulfonamidoethyl (dansyl) group was coupled to 1-azidoethyl octamannosyl thioglycoside. Global deprotection of the coupled product afforded the desired dansylated homo-linear α(1→6)-linked octamannan.Mannans are constituents of many bacterial and fungal cell walls. 1 They are functional components of proteins and play important roles in defining the structures of proteins, their stabilization under physiological conditions, tuning of enzymatic activities, cell-cell recognition and in the adhesion of the microorganism to host cells. 2 The α(1→6)-linked oligomannans are found in the cell wall polysaccharides of yeast. 3 Polysaccharides, especially oligomannan, can be used to deliver drugs, genes and antigens through polysaccharide receptors present in cells and macrophages. 4 Macrophages are known to express high levels of specific polysaccharide receptors, e.g. mannan, glucan, and galactin receptors, on their membranes that generally bind neutral or charged polysaccharides and internalize these ligands. 5 Receptor mediated delivery of drug-polysaccharide conjugates is an approach that can deliver small and effective amounts of drugs specifically to target organisms, minimizing patient exposure and potential toxic side effects. We have recently demonstrated the selective, receptor-mediated delivery of an antibacterial drug to macrophages infected with Mycobacterium tuberculosis via conjugation of moxifloxacin with 1,3-β-glucan. 6 Drug loading on commercially available high molecular weight polysaccharides is very low and it is attributed to their poor solubility in solvents during the drug conjugation reactions. Therefore, we describe here a simple and efficient method for the synthesis of a low molecular weight homo-linear α(1→6)-linked octamannan fluorescent probe 1 (figure 1) that may be utilized to study uptake by macrophages through the mannan receptor present on the plasma membrane. Further, in the future, such conjugation can be exploited for selective receptormediated delivery of drugs. We have previously synthesized and reported dansylated disaccharide fluorescent probes to study glycosyltransferases in the biosynthesis of M. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.Supplementar...

Lipoarabinomannan biosynthesis in Corynebacterineae: the interplay of two α(1→2)‐mannopyranosyltransferases MptC and MptD in mannan branching

“…5A,B ). The synthesis of the target nonamannopyranoside 1 was planned starting from the previously synthesized 2 ( Aqueel et al ., 2008 ) via synthesis of oligosaccharide 3 ( Fig. 5A ).…”

Chemical approaches for the study of the mycobacterial glycolipids phosphatidylinositol mannosides, lipomannan and lipoarabinomannan

“…A related fluorescently-labelled a-1,6-linked octamannoside 23 has been reported. 108 7 Analogues and inhibitors of the lipid-linked donors polyprenolphosphomannose and polyprenolphosphoarabinose…”

Imidazolium Cation Supported Solution-Phase Assembly of Homolinear α(1→6)−Linked Octamannoside: An Efficient Alternate Approach for Oligosaccharide Synthesis

“…The IL–tagged mannosyl synthons 2 and 3 were synthesized from a common known p -thiotolyl mannoside 4 9,17. The thioglycoside 4 was chosen as the starting precursor because it can be prepared in a multigram scale in just two steps from D-mannose through a known precursor 1,6-di- O -acetyl-2,3,5-tri- O -benzoyl-α-D-mannose 20.…”

“…The IL-tagged mannosyl synthons 2 and 3 were synthesized from a common known p-thiotolyl mannoside 4. 9,17 The thioglycoside 4 was chosen as the starting precursor because it can be prepared on a multigram scale in just two steps from D-mannose through a known precursor 1,6-di-O-acetyl-2,3,5-tri-O-benzoyl-R-D-mannose. 20 The thioglycoside 4 was converted to IL-tagged glycosyl fluoride 3 using DAST and NBS at -20 °C followed by installation of the imidazolium tag as reported in excellent yield.…”

“…Branched oligomannan syntheses are reported in the literature using several different methodologies including solution- and solid-phase polymer supports and fluorous-tag assisted solution phase. Specifically, the homolinear α(1→6) oligomannans were previously synthesized in the solution phase , and by an automated solid-phase approach. In a tedious conventional solution-phase process, we recently synthesized a linear α(1→6)-octamannosyl fluorescent probe via the two-stage activation procedure for the synthesis of oligosaccharides, combining the chemistry of thioglycosides with that of glycosyl fluorides.…”