There has been growing interest in aminopolysaccharide synthesis due to their critical natural functions and potential for biomedical applications. Regioselective introduction of amino groups into polysaccharide backbones is a challenging endeavor. Natural curdlan is a linear β-(1→3)-glucan that is of interest both for its physical properties and its biomedical applications. Aminocurdlans are intriguing target molecules for study of, for example, their interactions with the proteins that form tight junctions between enterocytes. A series of aminated curdlan derivatives were synthesized starting from 6-bromo-6-deoxycurdlan. Curdlan was first regioselectively brominated at the C-6 position in DMAc/LiBr. The bromide was then displaced by nucleophilic substitution with sodium azide in DMSO to produce the crucial precursor 6-azido-6-deoxycurdlan. On one hand, O-acylated 6-amido-6-deoxycurdlan was produced by a one-pot method of Staudinger reduction, followed by reaction in situ with excess carboxylic anhydride, without isolation of the 6-amino intermediate. On the other hand, the O-2, 4 groups were acylated with hydrophilic oligo(ethylene oxide) esters, so as to enhance aqueous solubility. The azide groups of the resultant 6-azido-2,4-di-O-trioxadecanoylcurdlans were then reduced with sodium borohydride to produce water-soluble 6-trioxadecanoamido-6-deoxycurdlan. Alternatively, direct borohydride reduction of the parent azido precursor afforded 6-amino-6-deoxycurdlan which, unexpectedly, was also water-soluble. Additionally, 6-azido curdlan was treated with triphenylphosphine in the presence of benzaldehyde and sodium cyanoborohydride to produce 6-monoalkylamine via one-/two-step procedures. Regioselectivity and degree of substitution of those derivatives were characterized by means of 1H-, 13C- NMR and FTIR- spectroscopy, elemental analysis, and titration.

Regioselective preparation of curdlan derivatives aminated at the C-6 position for biomedical applications

249th National Meeting (2015)

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