CHEMICAL-STRUCTURE AND BIOLOGICAL-ACTIVITY OF POLYSACCHARIDES FROM HIBISCUS-SABDARIFFA

Three water-soluble polysaccharides have been isolated from flower bud s of Hibiscus sabdariffa L. (HIB 1, 2, 3). The neutral polysaccharides (HIB 1 and 2) are composed of arabinans and arabinogalactans of low r elative molecular mass. The major fraction was investigated by methyla tion analysis, pectinase-treatment, mild acid hydrolysis, and NMR stud ies, and it was shown to be a pectin-like molecule (M(r) = 10(5) d). T he main chain is composed of alpha-1,4-linked GalA (24% methyl-esterif ied) and alpha-1,2-linked Rha. Side chains are built of Gal and Ara an d are connected to the main chain via C-4 of every third Rha. Its stru cture seems to be different from polysaccharide structures described i n other species of the Hibiscus genus and the Malvaceae family. All fr actions were assayed for possible immune-modulating effects. All fract ions showed some activity, but the main acidic fraction was contaminat ed with lipopolysaccharide, and therefore its shown activity has to be discussed carefully.