Physicochemical properties and antitumor activities for sulfated derivatives of lentinan

Abstract

Five fractions of lentinan, a β-(1→3)- d-glucan bearing β-(1→6)- d-glucopyranosyl branches, were treated with chlorosulfonic acid for 90 min at 60 °C in pyridine medium to synthesize water-soluble sulfated derivatives having the substitution degree of 1.44–1.76. The 13C NMR spectra of the sulfated β-glucans indicated that the C-6 position was preferentially substituted by the sulfate groups. The values of the weight-average molecular weight ( M w), radius of gyration ( 〈 s 2 〉 z 1 / 2 ), and intrinsic viscosity ([ η]) of the sulfated lentinan fractions were determined by size-exclusion chromatography with multi-angle laser light scattering (SEC–MALLS) and viscometry in 0.15 M aq NaCl at 25 °C, respectively. The dependence of [ η] on M w for the sulfated lentinan was found to be [ η] = 8.93 × 10 −3 M w 0.73 ± 0.02 (mL/g) in 0.15 M aq NaCl (for M w ranging from 14.6 × 10 4 to 50.4 × 10 4). On the basis of the Yamakawa–Fujii–Yoshizaki (YFY) theory, the conformational parameters of the sulfated lentinan were calculated as 950 nm −1 for the molar mass per unit contour length ( M L), 4.8 nm for the persistence length ( q), and 13.9 for the characteristic ratio ( C ∞), indicating relatively extended single flexible chains in solution. The sulfated glucan fractions exhibited in vitro antiproliferative activities against sarcoma 180 (S-180) cells, and their inhibition ratios were lower than that of the triple-helix lentinan, but higher than that for the one with single random-coil lentinan chains.