Regioselectivity and stereochemistry of the synthesized sulfated polysaccharides

[出版社版]A novel sulfated β-1,3-xylan product was synthesized from algal cell wall microfibril homoxylan by the N,N-dimethylformamide (DMF)-SO3 complex sulfation method. Antithrombin activity appeared in this product was 6.5 times higher than that of standard heparin. From the results of 1H- and 13C-NMR spectroscopic analysis by DQF-COSY and HMQC, it was revealed that the ordered structure of β-1,3-xylan as a triple helix decayed and the resulting conformational change had been caused by the sulfation reaction. The sulfated positions on the C-4 hydroxyl groups of the xylose residues were determined from 13C-NMR chemical shifts, and it was found that regioselective sulfation had occurred predominantly with the C-4 secondary hydroxyl groups to produce mono-substituents. Another type of sulfation of β-1,4-xylan that showed no regioselectivity is considered to have been due to the different conformation of both xylan chains such as triple helix in β-1,3-xylan and the double straight chain like cellulose in β-1,4-xylan. Therefore, the different type of regioselective sulfation of β-1,3- and β-1,4-xylan was caused by the difference in steric hindrance due to these conformations. These different types of regioselective sulfation with different linkage positions are also discussed for the secondary hydoxyl groups in β-1,3- and β-1,4-glucan after chempselective sulfation of the C-6 primary hydroxyl groups