Natural Sphingomonas glycolipids vary greatly in their ability to activate natural killer T cells.

Mouse natural killer T (NKT) cells expressing an invariant T cell antigen receptor (TCR) recognize glycosphingolipids (GSLs) from Sphingomonas bacteria. The synthetic antigens previously tested, however, were designed to closely resemble the potent synthetic agonist alpha-galactosyl ceramide (alphaGalCer), which contains a monosaccharide and a C18:0 sphingosine lipid. Some Sphingomonas bacteria, however, also have oligosaccharide-containing GSLs, and they normally synthesize several GSLs with different sphingosine chains including one with a cyclopropyl ring-containing C21:0 (C21cycl) sphingosine. Here we studied the stimulation of NKT cells with synthetic GSL antigens containing natural tetrasaccharide sugars, or the C21cycl sphingosine. Our results indicate that there is a great degree of variability in the antigenic potency of different natural Sphingomonas glycolipids, with the C21cycl sphingosine having intermediate potency and the oligosaccharide-containing antigens exhibiting limited or no stimulatory capacity.

Synthesis and evaluation of an acyl-chain unsaturated analog of the Th2 biasing, immunostimulatory glycolipid, OCH.

An alpha-galactosyl ceramide (alpha-GalCer) 2 was synthesized and evaluated for its ability to stimulate iNKT-cell proliferation and elicit T-helper cytokines, IL-4 and IFNgamma. Compound 2 combines the acyl chain of the potent, Th2 biasing alpha-GalCer 1 with a sphingoid base of the same length as that found in OCH, which also exhibits Th2 skewing, Such complementation may enhance cytokine bias, which is thought to be important for therapeutic applications of iNKT cell stimulation. Two related alpha-GalCers, 3 and 4, with saturated acyl chains were prepared for comparison.

Synthesis and evaluation of 3''- and 4''-deoxy and -fluoro analogs of the immunostimulatory glycolipid, KRN7000.

Four 3''- and 4''-deoxy and -fluorogalactosyl ceramides were synthesized, and their ability to stimulate iNKT cells, based on levels of IL-2 production, was assessed in three NKT cell receptor hybridomas. In two of the hybridomas, 1.2 and 2H4, all of the analogs were immunostimulatory, while in the 1.4 hybridoma only the 4''-fluoro analog led to the production of significant levels of IL-2.

Cross metathesis of alpha-methylene lactones II: gamma- and delta-lactones.

[reaction: see text] The cross metathesis reactivities of alpha-methylene-gamma-butyrolactone and an alpha-methylene-delta-lactone have been investigated. alpha-Methylene-gamma-butyrolactone undergoes rapid and efficient olefin isomerization in the presence of second-generation metathesis catalysts. However, cross metathesis can be achieved with the additive 2,6-dichlorobenzoquinone. In contrast, the alpha-methylene-delta-lactone neither isomerizes nor couples under similar conditions.

Cross metathesis with strained exocyclic enones: synthesis of 3-alkylideneoxetan-2-ones from 3-methyleneoxetan-2-ones.

[reaction: see text] 3-Alkylideneoxetan-2-ones have been prepared in good to excellent yields with high Z-selectivity by olefin cross metathesis with 3-methyleneoxetan-2-ones in the presence of second generation metathesis catalysts 1 or 2.

Mouse and human iNKT cell agonist ß-mannosylceramide reveals a distinct mechanism of tumor immunity.

Type 1 or invariant NKT (iNKT) cell agonists, epitomized by α-galactosylceramide, protect against cancer largely by IFN-γ-dependent mechanisms. Here we describe what we believe to be a novel IFN-γ-independent mechanism induced by ß-mannosylceramide, which also defines a potentially new class of iNKT cell agonist, with an unusual ß-linked sugar. Like α-galactosylceramide, ß-mannosylceramide directly activates iNKT cells from both mice and humans. In contrast to α-galactosylceramide, protection by ß-mannosylceramide was completely dependent on NOS and TNF-α, neither of which was required to achieve protection with α-galactosylceramide. Moreover, at doses too low for either alone to protect, ß-mannosylceramide synergized with α-galactosylceramide to protect mice against tumors. These results suggest that treatment with ß-mannosylceramide provides a distinct mechanism of tumor protection that may allow efficacy where other agonists have failed. Furthermore, the ability of ß-mannosylceramide to synergize with α-galactosylceramide suggests treatment with this class of iNKT agonist may provide protection against tumors in humans.

Imidazolylsulfonates: electrophilic partners in cross-coupling reactions.

Aryl imidazolylsulfonates participate as electrophilic coupling partners in palladium-mediated cross-coupling reactions. The aryl imidazolylsulfonates display good stability while maintaining good reactivity in a variety of palladium-catalyzed coupling reactions. Imidazolylsulfonates are a practical and economic alternative to triflates.

Reduction of tertiary phosphine oxides with DIBAL-H.

The reduction of tertiary phosphine oxides (TPOs) and sulfides with diisobutylaluminum hydride (DIBAL-H) has been studied in detail. An extensive solvent screen has revealed that hindered aliphatic ethers, such as MTBE, are optimum for this reaction at ambient temperature. Many TPOs undergo considerable reduction at ambient temperature and then stall due to inhibition. 31P and 13C NMR studies using isotopically labeled substrates as well as competition studies have revealed that the source of this inhibition is tetraisobutyldialuminoxane (TIBAO), which builds up as the reaction proceeds. TIBAO selectively coordinates the TPO starting material, preventing further reduction. Several strategies have been found to circumvent this inhibition and obtain full conversion with this extremely inexpensive reducing agent for the first time. Practical reduction protocols for these critical targets have been developed.