Immunologically active O6-branched (1»3)-β-glucan from the lichen Thamnolia vermicularis var. subuliformis

Summary A lentinan-type gel-forming β-glucan, Ths-2, has been isolated in about 1.5% yield from the alkali extract of the lichen Thamnolia vermicularis var. subuliformis , using ethanol fractionation, dialysis and gel filtration. The mean M r of Ths-2 was determined by GP-HPLC to be 67 kD, and the optical rotation was measured to be –14°. The structure of Ths-2 was further elucidated by methylation analysis by GC-MS, 1 H- and 13 C-NMR spectroscopy and selective enzymatic hydrolysis with exo-(1→3)-β-D-glucanase followed by analysis of oligosaccharides by HPAEC-PAD. Ths-2 was found to be consisting of a (1→3)-β-D-glucopyranosyl main chain with branches of a (1→6) linked glucopyranosyl unit on every third unit of the main chain. Similar polysaccharide structures have been described from fungi, but this is the first report of a lentinan-type (1→3)-β-D-glucan from a lichen species. The immunomodulating activity of Ths-2 was tested in an in vitro anti-complementary assay, and proved to be strongly active.