NMR SPECTROSCOPIC ANALYSIS OF SULFATED BETA-1,3-XYLAN AND SULFATION STEREOCHEMISTRY

A novel sulfated beta-1,3-xylan product was synthesized from algal cel l wall microfibril homoxylan by the N,N-dimethylformamide (DMF)SO3 com plex sulfation method, Antithrombin activity appeared in this product, vas 6.5 times higher than that of standard heparin, From the results o f H-1- and C-13-NMR spectroscopic analyses by DQF-COSY and HMQC and an infrared spectroscopic analysis, it was revealed that the ordered str ucture of beta-1,3-xylan as a triple helix had decayed and the resulti ng conformational changes had been caused by the sulfation reaction, T he sulfated positions on the C-4 hydroxyl groups of the xylose residue s were determined from C-13-NMR chemical shifts, and it was found that regioselective sulfation had occurred predominantly with the C-4 seco ndary hydroxyl groups to produce a mono-substituent. Another type of s ulfation of beta-1,4-xylan that showed no regioselectivity is consider ed to have been due to the different conformation of both xylans chain s such as the triple helix in beta-1,3-xylan and the double straight c hain like cellulose in beta-1,4-xylan. Therefore, the different type o f regioselective sulfation of beta-1,3- and beta-1,4-xylan was caused by the difference in steric hindrance due to these conformations, Thes e different types of regioselective sulfation with different linkage p ositions are also discussed for the secondary hydroxyl groups in beta- 1,3- and beta-1,4-glucan after chemoselective sulfation of the C-6 pri mary hydroxyl groups.