Exclusive and complete introduction of amino groups and their N-sulfo and N-carboxymethyl groups into the 6-position of cellulose without the use of protecting groups.
A new regioselective synthesis of 6-amino-6-deoxycellulose with a DS 1.0 (degree of substitution) at C-6, and its 6-N-sulfonated and its 6-N-carboxymethylated derivatives, without using protecting groups is described in this paper. The reaction conditions were optimized for preparing cellulose tosylate with full tosylation at C-6 and partial tosylation at C-2 and C-3. The nucleophilic substitution (S(N)) reaction of the tosyl group by NaN(3) at low temperature of 50 degrees C in Me(2)SO was achieved completely at C-6, whereas the tosyl groups at C-2 and C-3 were not displaced. In contrast to this, at 100 degrees C the tosyl groups at C-6, and also those at C-2 and C-3, were replaced by azido groups. This regioselective reaction that depends on temperature makes it possible to reach a selective and quantitative S(N) reaction at C-6 at low temperatures. In the subsequent reduction step with LiAlH(4), the azido group at C-6 was reduced to the amino group, and the tosyl groups at C-2 and C-3 were simultaneously completely removed. Also reported is a temperature-dependent, regioselective and complete iodination by nucleophilic substitution of the tosyl group at C-6 at 60 degrees C. At higher temperatures from 75 to 130 degrees C, substitution is also observed to occur at C-2. The selective iodination at 60 degrees C was employed to confirm the complete tosylation at C-6 of cellulose. The reaction products were identified by four different independent quantitative methods, namely 13C NMR, elemental analysis, ESCA, and fluorescence spectroscopy. 6-N-Sulfonated and 6-N-carboxymethylated cellulose derivatives were also synthesized. The new derivatives are potent candidates for structure-function studies, e.g., studies in relation to regioselectively 2-N-sulfonated and 2-N-carboxymethylated chitosan derivatives.
Liu
Chun
C
ITMC, Macromolecular Chemistry and Textile Chemistry, Hemocompatible and Biocompatible Biomaterials, University of Technology Aachen, Worringer Weg 1, D-52074 Aachen, Germany.
Baumann
Hanno
H
D000588:Amines / Q000737:chemistry*; D002236:Carbohydrate Conformation; D002266:Carboxymethylcellulose Sodium / Q000138:chemical synthesis*; D002482:Cellulose / Q000031:analogs & derivatives* / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D012997:Solvents; D013431:Sulfates / Q000378:metabolism*; D013816:Thermodynamics
D000588:Amines; D007202:Indicators and Reagents; D012997:Solvents; D013431:Sulfates; D002482:Cellulose; D002266:Carboxymethylcellulose Sodium