Synthesis of C-5″ and C-6″-modified α-GalCer analogues as iNKT-cell agonists

Abstract

Alpha-Galactosyl Ceramide (α-GalCer) is a prototypical synthetic ligand of invariant natural killer T (iNKT) cells. Upon presentation by the MHC class I-like molecule CD1d, this glycolipid stimulates iNKT cells to secrete a vast amount of both pro-inflammatory Th1 and anti-inflammatory Th2 cytokines. Recently, we discovered that selected 6″-modified α-GalCer analogues may produce markedly Th1-biased responses due to the formation of either an additional anchor with CD1d or by establishing extra interactions with the T-cell receptor of iNKT cells. Here, we report a practical synthesis towards 6″-O-carbamate and galacturonamide analogues of α-GalCer and their evaluation as iNKT cell agonists in mice.

4“‐O‐Alkylated α‐Galactosylceramide Analogues as iNKT‐Cell Antigens: Synthetic, Biological, and Structural Studies

“…[17] Because the 6"-OH group is solvente xposed, forming no direct contacts with either CD1d or the TCR,s tructuralv ariations at this positionh ave been extensively explored. [18][19][20][21][22][23][24][25] This has led to the discovery of selected analoguesw ith ad istinctly improved Th1-polarized antigenic profile (Figure 2), including the 1-naphthylurea (NU-a-GalCer, 3), [26,27] the O-methylated (RCAI-61, 4), [28] the 4-pyridinylcarbamate (PyrC-a-GalCer, 5) [29] and other carbamate derivatives. [30] The 4"-OH is aH -bond donor to the carboxamide side chain of Asn30a (mTCR-CDR1a-loop) and the backbone carbonyl group of Phe29a (hTCR-CDR1a-loop).I ts importance for iNKTcell activation has been less profoundly studied, but severe disturbance of the hydrogen bond through either its removal (4"deoxy-a-GalCer) [31] or inversion of its configuration( a-glucosylceramide or a-GlcCer), [4] resultsi np oorly immunostimulating compounds.…”

“…Because the 6“‐OH group is solvent exposed, forming no direct contacts with either CD1d or the TCR, structural variations at this position have been extensively explored . This has led to the discovery of selected analogues with a distinctly improved Th1‐polarized antigenic profile (Figure ), including the 1‐naphthylurea (NU‐α‐GalCer, 3 ), the O ‐methylated (RCAI‐61, 4 ), the 4‐pyridinylcarbamate (PyrC‐α‐GalCer, 5 ) and other carbamate derivatives…”

Synthesis and structure-activity relationships of cerebroside analogues as substrates of cerebroside sulphotransferase and discovery of a competitive inhibitor

“…b-KRN7000 21 and a-glycosides 11, 13-16 and 18-21 were prepared as previously described. [22][23][24][25][26][27] The synthetic route to obtain a-galactosylceramides 12, 17 and 22 is depicted in Scheme 1.…”

Efficient Divergent Synthesis of New Immunostimulant 4″-Modified α-Galactosylceramide Analogues

“…Indeed, our laboratory has already explored the mild yet powerful regioselective benzylidene ring-opening route to access the 6"-position for the synthesis of fucosyl, galacturonic acid, triazole, carbamate and urea analogues. [13][14][15] Second, and more importantly, this hydroxyl group does allow for modifications due to the absence of any major interactions with either CD1d or the TCR, 16 and this has given rise to an array of new immunoactive analogues. [17][18][19][20][21][22] In contrast to this, only few 4"-analogues of -GalCer are known ( Figure 1) and, as a consequence, the SAR of this position has been poorly investigated.…”

“…First, the 6″-OH is the only primary hydroxyl group of the sugar part, which from a chemoselective point of view implies that straightforward modification of this position is possible. Indeed, our laboratory has already explored the mild yet powerful regioselective benzylidene ring-opening route to access the 6″-position for the synthesis of fucosyl, galacturonic acid, triazole, carbamate, and urea analogues. − Second, and more importantly, this hydroxyl group does allow for modifications due to the absence of any major interactions with either CD1d or the TCR, and this has given rise to an array of new immunoactive analogues. − …”