Etude d'oligosaccharides bioactifs issus d'exopolysaccharides bactériens : obtention, caractérisation et relation structure/fonction

Unusual exopolysaccharides (EPS) produced by heterotrophic aerobic and mesophilic bacteria originating from hydrothermal vent, were reviewed as a new source of polysaccharidic structures endowed with innovative biological properties. The first step of this study was the structure determination of the EPS GY785, synthesized by Alteromonas infernus. A highly branched nonasaccharidic repetitive unit was identified using chemical modifications and nuclear magnetic resonance spectroscopy. This 106 g/mol polysaccharide is composed of glucose, galactose, glucuronic acid, galacturonic acid, and contains a single branched ramification and one sulphate group. The second step was the preparation of low molecular weight bioactive polysaccharides presenting interest in the treatment of diseases. Three chemically modified EPS (GY785, HE800, and HYD721) were prepared using free radical depolymerization, sulphation and phosphation. Physicochemical studies of those homogeneous derivatives showed that sulphate contents modulate the anticoagulant activity. Preliminary studies of a highly sulphated fraction of low molecular weight EPS GY785 showed a high affinity for antithrombin with a less in vitro anticoagulant activity than heparin. Marine exopolysaccharides are a great source of molecules endowed with biotechnological interest but a perfect knowledge of structureactivity relationships is essential before the conception of drugs.