T. Yamagaki et al., NMR SPECTROSCOPIC ANALYSIS OF SULFATED BETA-1,3-XYLAN AND SULFATION STEREOCHEMISTRY, Bioscience, biotechnology, and biochemistry, 61(8), 1997, pp. 1281-1285
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.