Chemical synthesis of charbohydrates and glycopeptides for biological application

This thesis describes chemical synthesis of carbohydrates and glycopeptides useful in studies of biologically interesting systems. The following topics are addressed: [Papers I-IV and supporting information]: [I] The non-reducing end di- and trisaccharide structures of an erythrocyte glycolipid responsible for the rare NOR polyagglutination were chemically synthesized. The syntheses were based on a α-D-Galp-(1→4)-β-D-GalpNAc-(1→) structural element found only recently in Nature, and derivatives thereof have not been synthesized before. Both the synthesized oligosaccharides specifically inhibited human anti-NOR antibodies, with the trisaccharide being 300 times more active than the disaccharide. [II] Derivatives of lactose with the galactose ring substituents replaced by 2´, 3´, 4´ and 6´ deoxy and 3´ acylamino functions were prepared. The lactosyl derivatives were tested as acceptors for the Neisseria menigitidis N-acetylglucosaminyltransferase catalyzed β-(1→3) glycosylation reaction, using UDP-GlcNAc as donor. The 6´-deoxy compound showed nearly a threefold increase in activity compared with the reference substance phenyl β-lactoside, whereas the 2´ and 4´-deoxy derivatives were less active. The 3´-deoxy and 3´-acylamino derivatives will be used in studies of the inhibitory capacity. [III] In order to develop the non-viral Bioplex vector system for non-viral gene delivery to hepatocytes, biotinylated ligands were synthesised to study the structure-function relationship of specific binding and uptake to the asialoglycoprotein receptor ASGPr. Cluster glycosides containing two, three and six β-D-GalpNAc residues were synthesized and tested for binding and uptake to liver cells. The derivative displaying six GalNAc units showed the highest uptake efficacy. However, the number of GalNAc units above three seems only to have a minor contribution to the overall affinity, while using longer spacer between the GalNAc ligands markedly influenced the uptake efficacy. [IV] An analgetically active glycopeptide from the cone snail Conus geographus, contulakin G, has recently been analyzed and synthesized. Contulakin-G has been found to be a neurotensin agonist and have entered pre-clinical trials for short-term management of post-operative pain. The glycan part of contulakin-G has been found to be important for the biological in vivo activity. In order to further investigate the importance of the glycan part, three analogues of contulakin-G have been synthesized, were the α/β conformation of the anomeric centers as well as the glycosidic bond pattern of the disaccharide have been altered. In addition to the contulakin G analogues, a heavily posttranslational modified glycopeptide from Conus textile, tx5a, has been synthesized