Use of the NEO strategy (Nucleophilic addition/Epoxide Opening) for the synthesis of a new C-galactoside ester analogue of KRN 7000

Intercepted dehomologation of aldoses by N-heterocyclic carbene catalysis – a novel transformation in carbohydrate chemistry

Examples of strong substrate governance and tuning of selectivity between two borderline scenarios by successful catalyst design are reported.

Indium- and Zinc-Mediated Acyloxyallylation of Protected and Unprotected Aldotetroses-Revealing a Pronounced Diastereodivergence and a Fundamental Difference in the Performance of the Mediating Metal

The acyloxyallylation of unprotected aldoses was first demonstrated more than a decade ago as a potentially elegant two-carbon homologation of reducing sugars (upon ozonolysis); however, its application in real case syntheses remained scarce. Following up on such a successful showcase and to answer several pending questions about this attractive transformation, we engaged in an in depth methodological reinvestigation. The epimeric tetroses l-erythrose and d-threose in unprotected and protected form were successfully applied to the indium and also zinc-mediated acyloxyallylation, with the latter being a first for an unprotected sugar. The investigation largely benefited from the choice of these more exotic starting materials as it allowed unambiguous identification/quantification of the hexose-products which are available as authentic reference materials. The observed diastereoselectivities indicate a strong substrate control (stereochemistry at O2), and the influence of the reagent’s structure on the selectivity was investigated in great detail. A strong facial diastereodivergence between related protected and unprotected structures was demonstrated and an unexpected, pronounced principle difference in performance between indium and zinc was revealed.

Synthesis and biological activities of C-glycosides of KRN 7000 with novel ceramide residues

The identification of immunoactive agents for clinical and mechanistic applications is a very active area of research. In this vein, analogues of the potent immunostimulant KRN 7000 with diverse cytokine profiles have attracted considerable attention. These compounds have been shown to activate iNKT cells via presentation by CD1d. Herein, we report on the synthesis and activity for four new C-glycosides of KRN 7000, 11-phenylundecanoyl and 11-p-fluorophenylundecanoyl derivatives of C-KRN 7000, 2,3-bis-epi-C-KRN 7000 and the reverse amide of C-KRN 7000. In mice, compared to C-KRN 7000, 2,3-bis-epi-C-KRN 7000 stimulated higher release of the anti-inflammatory cytokine IL-4 and lower release of the inflammatory cytokines IFN-γ and IL-12. The phenyl terminated alkanoyl and reverse amide analogues were inactive. These data suggest that structure activity effects for KRN 7000 are not necessarily additive and their use in the design of new analogues will require an improved understanding of how subtle structural changes impact on cytokine activity.

The Crotylation Way to Glycosphingolipids: Synthesis of Analogues of KRN7000

A synthesis of glycosphingolipids that centers on the reaction of O- and C-glycosyl crotylstannanes and relatively simple lipid aldehydes is described. The modularity of this strategy and versatility of the crotylation products make this an attractive approach to diverse, highly substituted libraries. The methodology is applied to analogues of the potent imunostimulatory glycolipid KRN7000, including O-, methylene-, and fluoromethine-linked isosteres with diastereomeric ceramide segments and 2-amido substitutes.