A. Koschella, D. Fenn, Th. Heinze
Center of Excellence for Polysaccharide Research, Friedrich Schiller University of Jena, Humboldtstraße 10, D-07743 Jena, Germany
Email: Thomas.Heinze@uni-jena.de
Tel. +493641948270 Fax +493641948272
The regioselective functionalization is an important objective in polysaccharide chemistry. It provides access to derivatives with regular distribution of substituents mostly by using protective group techniques. A typical group for 6-O-protection is the triphenylmethyl group, capable of the synthesis of 2,3-O-functionalized ethers. In addition, silyl ethers with at least one bulky alkyl substituent may be efficient to control the regioselectivity. Mostly studied in our work is the thexyldimethylsilyl (TDMS) group that opens a route to 2,3-O-functionalized ethers with higher selectivity compared with the triphenylmethyl group, on the one hand, and to 3-O-functionalized ethers on the other. Thus, the silylation can be carried out either with dissolved cellulose (N,N-dimethylacetamide (DMA)/lithiumchloride) or hetero-geneously in N-methyl-pyrrolidone (NMP)/ammonia mixtures:
Subsequently the unmodified hydroxyl groups can be derivatized, e.g., etherified applying alkyl halides and sodium hydride followed by deprotection with tetrabutylammonium fluoride (TBAF). These highly regioselective cellulose ethers are valuable products in the investigation of structure-property relationships and for the understanding of intra- and intermolecular interactions in cellulose derivatives, e.g. state of solution or hydrogen bond systems.
Literature:
1 Koschella, A. Klemm D., Silylation of cellulose regiocontrolled by bulky reagents and dispersity in the reaction media, Macromol.Symp., 120 (1997) 115
2 Koschella, A., Th. Heinze, Klemm D., First synthesis of 3-O-functionalized cellulose ethers via 2,6-di-O-protected silyl cellulose, Macromol.Biosci., 1 (2001) 49
3 Petzold,K.; Klemm,D.; Heublein,B.; Burchard,W.; Savin,G., Investigations on structure of regioselectively functionalized celluloses in solution exemplified by using 3-O-alkyl ethers and light scattering, Cellulose, 11 (2004) 177