Chemoselective Staudinger-phosphite reaction of symmetrical glycosyl-phosphites with azido-peptides and polygycerols.

In this paper we present the synthesis of glyco-phosphoramidate conjugates as easily accessible analogs of glyco-phosphorous esters via the Staudinger-phosphite reaction. This protocol takes advantage of synthetically accessible symmetrical carbohydrate phosphites in good overall yields, in which ethylene or propylene linkers can be introduced between phosphorous and galactose or lactose moieties. The phosphites were finally applied for the chemoselective reaction with azido-peptides and polyazido(poly)glycerols.

4,5,6-Trisubstituted piperidinones as conformationally restricted ceramide analogues: synthesis and evaluation as inhibitors of sphingosine and ceramide kinases and as NKT cell-stimulatory antigens.

The conformationally based piperidinone sphingosine analogues 7, 8, 15, and 16 were synthesized from allylic alcohol 34 via lactams 31 and 32. The L-arabino diol 7 and the L-ribo diol 8 were transformed into the amino alcohols 17-24. The L-gluco ceramide analogues 43, 46a, and 47, and the L-altro ceramide analogues 51a and 52 were synthesized from either 31 or 32. The L-ribo diols 8 and 16, and the amino alcohols 19 and 20 inhibit sphingosine kinase 1 (SPHK1), while the L-arabino analogues 7, 15, 17, and 18 are inactive. The L-arabino and the L-ribo dimethylamines 21-24, the L-gluco ceramide analogues 43, 46a, and 47, and the L-altro ceramide analogues 51a and 52 did not block SPHK1. Neither the L-arabino diol 7 nor the L-ribo diol 8 inhibited SPHK2 or ceramide kinase. The L-arabino diols 7 and 15 stimulate invariant natural killer T (iNKT) cells when presented by living antigen-presenting cells (APC) and also by plate-bound human CD1d, whereas the L-ribo diols 8 and 16, the L-arabino amino alcohols 17-18, and the dimethylamines 21-22 did not activate iNKT cells. The L-gluco ceramide analogues 43, 46a, and 47 had strongly stimulatory effects on iNKT cells when presented by living APC and also by plate-bound human CD1d, whereas the L-altro ceramide analogue 52 activated only weakly. All activatory compounds induced preferentially the release of pro-inflammatory cytokines, indicating the formation of a stable CD1d--lipid--T-cell receptor complex.

Synthesis of 7-aza- and 7-thiasphingosines, and evaluation of their interaction with sphingosine kinases and with T-cells.

The synthesis of 7-oxasphingosine (3) and 7-oxaceramide (4) was improved by starting from the 4-methoxybenzyl-protected d-galactal 9. The sphingosine analogues 5-7 and 24 were synthesized via the azido alcohol 13. The 7-thiasphingosine 5 is a poorer substrate for both isoforms of sphingosine kinase (SPHK) than sphingosine, but showed a slight preference for SPHK2. The sulfone 6 and the 7-aza compounds 7 and 24 were not phosphorylated by either SPHK1 or SPHK2, and none of 5-7 and 24 activated invariant natural killer T (iNKT) cell clones when presented by human CD1d-transfected antigen-presenting cells (APC) or by plate-bound human CD1d. Only 7 and 24 associated with plate-bound recombinant CD1d prevented stimulation of iNKT cells by alpha-galactosylceramide (alpha-GalCer).

Synthesis and evaluation of sphingolipid analogues: modification of the hydroxy group at C(1) of 7-oxasphingosine, and of the hydroxy group at C(1) and the amide group of 7-oxaceramides.

The analogues 7-9 of 7-oxaceramide and 7-oxasphingosine were synthesized from the known azidosphingosine 21. The 1,4-disubstituted 1,2,3-triazole analogues 10-16 of ceramides were synthesized by the click reaction of the known azide 24. None of the analogues 7-15 was active as inhibitor of SPHK type 1 and of acid sphingomyelinase, whereas 16 is a weak inhibitor of SPHK1. Triazoles 10, 11, and 15 did not inhibit ceramide phosphorylation by CerK, and none of 7, 8, and 10-15 activated invariant natural killer T (iNKT) cell clones when presented by human CD1d-transfected antigen-presenting cells (APC) or by plate-bound human CD1d [55]. Triazoles 14 and 15 prevent binding of alpha-galactosylceramide (alpha-GalCer) to plate-bound human CD1d and subsequent T-cell response to alpha-GalCer. Only 15 reduced activation by alpha-GalCer significantly and independently of the cytokine measured.