Structural characterization and semi-synthetic modification of bacterial glycolipids

The present PhD thesis aims to discover new natural lipid A structures and to obtain semi-synthetic derivatives thereof to be tested as candidates for the pharmacological use as vaccine adjuvants. Recently, many researchers focused on the development of effective innate immunity ligands as vaccine adjuvants. However, most of innate immunity ligands including LPS, one of the bacterial cell surface component that is a main topic in this thesis, involve undesired effects typified by a strong inflammatory induction in addition to useful adjuvant effects. Therefore, the development of novel non-toxic safer LPS is deeply desired. In the first topic of this thesis, we focused on two psychrophilic bacteria to reveal novel non-toxic LPS. As for Colwellia psychrerythraea strain 34H, was accomplished the complete characterization and immunological function analysis of its lipid A having very unique 3-hydroxy unsaturated tetradecenoic acid and acylated phosphoglycerol moiety. As for Psychrobacter arcticus strain 273-4 grown at 4°C, we worked on the lipid A structure investigation and immunological function analysis. In the second topic, a semisynthetic strategy for novel lipid A derivatives from E. coli LPS was reported. The advantages of a fermentative access to complex natural products was combined with the development of site-selective chemical reactions modifying lipid A structures. The selective oxidation method of the primary hydroxyl group at position C-6 of GlcN II enables the introduction of various functional group to lipid A and various lipid A derivatives including clickable lipid As. Semi-synthesized lipid A derivatives showed moderate immunostimulating activity but no-toxicity. In addition, the modification method of the lipid pattern of lipid A was also investigated. These novel strategies will promote structure activity relationship study to reveal non-toxic lipid A. It was also shown by the synthesis of Tn or TF antigen conjugated lipid A derivatives that this strategy is very useful in developing a prospective self-adjuvanting vaccine strategy. Furthermore, this strategy is also useful in the construction of a labeled lipid A that is applicable to elucidation of immune activation mechanism.