Hydrogenolytic cleavage of naphthylmethyl ethers in the presence of sulfides

Structure-Based Design and Synthesis of Lipid A Derivatives to Modulate Cytokine Responses

Agonists of Toll like receptors (TLRs) have attracted interest as adjuvants and immune modulators. A crystal structure of TLR4/MD2 with E. coli LPS indicates that the fatty acid at C-2 of the lipid A component of LPS induces dimerization of two TLR4-MD2 complexes, which in turn initiates cell signaling leading to the production of (pro)inflammatory cytokines. To probe the importance of the (R)-3-hydroxymyristate at C-2 of lipid A, a range of bis- and mono-phosphoryl lipid A derivatives with different modifications at C-2 were prepared by a strategy in which 2-methylnaphthyl ethers were employed as permanent protecting group that could be readily removed by catalytic hydrogenation. The C-2 amine was protected as 9-fluorenylmethyloxycarbamate, which at a later stage could be removed to give a free amine that was modified by different fatty acids. LPS and the synthetic lipid As induced the same cytokines, however, large differences in activity were observed. A compound having a hexanoyl moiety at C-2 still showed agonistic properties, but further shortening to a butanoyl abolished activity. The modifications had a larger influence on monophosphoryl lipid As. The lipid As having a butanoyl moiety at C-2 could selectively antagonize TRIF associated cytokines induced by LPS or lipid A.

Advances in glycoside and oligosaccharide synthesis

The structural complexity of glycans poses a serious challenge in the chemical synthesis of glycosides, oligosaccharides and glycoconjugates. Glycan complexity, determined by composition, connectivity, and configuration far exceeds what nature achieves with nucleic acids and proteins. Consequently, glycoside synthesis ranks among the most complex tasks in organic synthesis, despite involving only a simple type of bond-forming reaction. Here, we introduce the fundamental principles of glycoside bond formation and summarize recent advances in glycoside bond formation and oligosaccharide synthesis.

Reagent controlled stereoselective synthesis of teichoic acid α-(1,2)-glucans

The stereoselective construction of 1,2-cis-glycosidic linkages is key in the assembly of biologically relevant glycans, but remains a synthetic challenge. Reagent-controlled glycosylation methodologies, in which external nucleophiles are employed to modulate the reactivity of the glycosylation system, have become powerful means for the construction of 1,2-cis-glycosidic linkages. Here we establish that nucleophilic additives can support the construction of α-1,2-glucans, and apply our findings in the construction of a d-alanine kojibiose functionalized glycerol phosphate teichoic acid fragment. This latter molecule can be found in the cell wall of the opportunistic Gram-positive bacterium, Enterococcus faecalis and represents a structural element that can possibly be used in the development of therapeutic vaccines and diagnostic tools.

Microwave-assisted cleavage of cysteine perfluoroaryl thioethers

The cysteine- perfluoroarene S_NAr reaction allows for the sequence-specific attachment of dyes and affinity tags to peptides and proteins. However, while many methods exist for the desulfuration of native and functionalized cysteine residues, there are no reports of their application to perfluoroarylated cysteines. Herein we report both the hydrogenolysis of a perfluoroarylated cysteine to alanine and elimination to dehydroalanine, reactions that are both accelerated by microwave irradiation.

Synthetic preparation and immunological evaluation of β-mannosylceramide and related N-acyl analogues

The synthesis of the invariant natural killer (iNK) T cell agonist β-mannosylceramide along with a series of fatty amide analogues is reported. Of the six β-glycosylation protocols investigated, the sulfoxide methodology developed by Crich and co-workers proved to be the most effective where the reaction of a mannosyl sulfoxide and phytosphingosine derivative gave a key glycolipid intermediate as a 95 : 5 mixture of β- to α-anomers in high yield. A series of mannosyl ceramides were evaluated for their ability to activate D32.D3 NKT cells and induce antitumour activity.