4-Deoxy-alpha-GalCer analogues are considered weaker agonists than KRN7000 for the stimulation of human iNKT cells, but this remains strongly debated. In this work, we described a strategy toward 4-deoxy-alpha-GalCers with, as a key step, a metathesis reaction allowing sphingosine modifications from a single ethylenic alpha-galactoside precursor. The 4-deoxy-KRN7000 derivative 2, described here, induced potent cytokinic responses, comparable to those of KRN7000, both from human iNKT cells in vitro and from their murine counterpart in vivo.
We propose here the synthesis and biological evaluation of 3,4-dideoxy-GalCer derivatives. The absence of the 3- and 4-hydroxyls on the sphingoid base is combined with the introduction of mono or difluoro substituent at C3 (analogues 8 and 9, respectively) to evaluate their effect on the stability of the ternary CD1d/GalCer/TCR complex which strongly modulate the immune responses. Biological evaluations were performed in vitro on human cells and in vivo in mice and results discussed with support of modeling studies. The fluoro 3,4-dideoxy-GalCer analogues appears as partial agonists compared to KRN7000 for iNKT cell activation, inducing T(H)1 or T(H)2 biases that strongly depend of the mode of antigen presentation, including human vs mouse differences. We evidenced that if a sole fluorine atom is not able to balance the loss of the 3-OH, the presence of a difluorine group at C3 of the sphingosine can significantly restore human iNKT activation.
A set of pyrimidine nucleosides fused with a 4′‐C,3′‐O‐propylene bridge was successfully synthesised in 12 steps from 1,2:5,6‐di‐O‐isopropylidene‐α‐D‐glucofuranose, an inexpensive starting material, based on a ring‐closing metathesis (RCM) reaction followed by Vorbrüggen‐type nucleobase coupling. Antiviral and cytotoxicity activities of the targeted modified nucleosides, as well as their phosphoramidate prodrugs, are described.
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