title: tert-Butyldimethylsilyl O-protected chitosan and chitooligosaccharides: useful precursors for N-modifications in common organic solvents.
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.
authors.affiliation: Faculty of Pharmacy, University of Iceland, Hofsvallagata 53, IS-107 Reykjavik, Iceland.
authors.forename: Ogmundur Vidar
authors.initials: OV
authors.lastname: Rúnarsson
authors.forename: Clemens
authors.initials: C
authors.lastname: Malainer
authors.forename: Jukka
authors.initials: J
authors.lastname: Holappa
authors.forename: Snorri Th
authors.initials: ST
authors.lastname: Sigurdsson
authors.forename: Már
authors.initials: M
authors.lastname: Másson