tert-Butyldimethylsilyl O-protected chitosan and chitooligosaccharides: useful precursors for N-modifications in common organic solvents |
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Authors: | Rúnarsson Ogmundur Vidar Malainer Clemens Holappa Jukka Sigurdsson Snorri Th Másson Már |
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Institution: | Faculty of Pharmacy, University of Iceland, Hofsvallagata 53, IS-107 Reykjavik, Iceland. |
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Abstract: | An efficient and chemoselective procedure for preparing highly organosoluble 3,6-di-O-tert-butyldimethylsilyl (TBDMS)-chitosan and chitooligosaccharides is reported. The selective modification of the chitooligosaccharides with 0.50 degree of N-acetylation was achieved by using TBDMSCl as the reagent in combination with DMF/imidazole. These protocols yielded partly TBDMS-substituted chitooligosaccharides that were subsequently reacted with TBDMSOTf in dichloromethane in order to silylate the remaining, more sterically hindered hydroxyl groups. In the case of the chitosan polymer, a mesylate salt of chitosan was silylated using TBDMSCl in DMSO, yielding full silylation of the hydroxyl groups without using N-protection groups. The silyl-protected polymers displayed excellent solubility in a number of common organic solvents. The 3,6-di-O-TBDMS-chitosan and chitooligosaccharides were reacted with acetic anhydride, and deprotected to obtain the corresponding N-acetyl derivatives (chitin and chitinoligosaccharide). Our results show that the readily prepared 3,6-di-O-TBDMS-chitosan and chitooligosaccharides are useful precursors for selective N-modifications in common organic solvents. |
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Keywords: | Chitosan Chitin Protection groups tert-Butyldimethylsilyl chloride 3 6-Di-O-TBDMS-chitosan Silylation |
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