Conformational changes of the two different conformers of grifolan in sodium hydroxide, urea or dimethylsulfoxide solution.

Grifolan is an antitumor (1→3) -β-D-glucan with a β-glucosyl substitution at C-6 of every three main chain units, and is produced by Grifola frondosa. Grifolan possesses two different solid-state conformations, N (native) and H (helix) (N. Ohno et al., Chem. Pharm. Bull., 34, 2555 (1986)), and both form a gel in an aqueous neutral media. In this study, the gel-to-sol or sol-to-gel transition of these forms in sodium hydroxide, urea and dimethylsulfoxide solutions were examined by carbon-13 nuclear magnetic resonance (13C-N MR) spectroscopy. The N gel showed 13C-signals in sodium hydroxide of more than 0.15 N, and the H gel showed them at more than 0.05 N. Gel-to-sol transitions of the N and H gels in urea were induced at 8 and 2 M, respectively. Sol-to-gel transitions of the glucans in dimethylsulfoxide were induced by the addition of more than 20% of water. These results suggested firstly that the architecture of the two gels is different because the gel-to-sol transition occurred more easily in the case of the H gel than the N gel, and secondly that the structure of the two glucans in the sol state is essentially the same.