ABSTRACT
A novel Pt-catalyzed rearrangement of oxaspirohexanes to 3-methylenetetrahydrofurans is reported. Mechanistic studies by (13)C-labeling experiments confirm oxidative addition of Pt(II) regioselectively to the least substituted carbon-carbon bond of the cyclopropane to form a platinacyclobutane intermediate. To our knowledge, this is the first alkoxy-substituted platinacyclobutane that has been observed spectroscopically. The scope and a proposed mechanism of this new Pt-catalyzed transformation are described.
Subject(s)
Carbon Radioisotopes/chemistry , Cyclopropanes/chemistry , Furans/chemical synthesis , Platinum Compounds/chemistry , Platinum Compounds/chemical synthesis , Spiro Compounds/chemistry , Catalysis , Furans/chemistry , Oxidation-ReductionABSTRACT
Structural studies of ternary complexes of CD1d/glycosyl ceramides/iNKT cells and CD1d/sulfatide/sulfatide reactive Type II NKT cells have shown how the polar moieties on the glycolipids interact with both the antigen presenting protein (CD1d) and the T cell receptors. However, these structures alone do not reveal the relative importance of these interactions. This study focuses on the synthesis of the previously unknown 2"-deoxy-ß-galactosyl ceramide 2. This glycolipid is also evaluated for its ability to stimulate iNKT cells and sulfatide-reactive Type II NKT cells.
Subject(s)
Galactosylceramides/chemical synthesis , Animals , Antigens, CD1d/metabolism , Galactosylceramides/chemistry , Galactosylceramides/pharmacology , Interleukin-2/biosynthesis , Mice , Natural Killer T-Cells/drug effects , Natural Killer T-Cells/metabolismABSTRACT
Natural killer T (NKT) cells respond to a variety of CD1d-restricted antigens (Ags), although the basis for Ag discrimination by the NKT cell receptor (TCR) is unclear. Here we have described NKT TCR fine specificity against several closely related Ags, termed altered glycolipid ligands (AGLs), which differentially stimulate NKT cells. The structures of five ternary complexes all revealed similar docking. Acyl chain modifications did not affect the interaction, but reduced NKT cell proliferation, indicating an affect on Ag processing or presentation. Conversely, truncation of the phytosphingosine chain caused an induced fit mode of TCR binding that affected TCR affinity. Modifications in the glycosyl head group had a direct impact on the TCR interaction and associated cellular response, with ligand potency reflecting the t(1/2) life of the interaction. Accordingly, we have provided a molecular basis for understanding how modifications in AGLs can result in striking alterations in the cellular response of NKT cells.
