Stereospecific Synthesis and Biological Evaluation of KRN7000 Analogues with Thio-modifications at the Acyl Moiety

Abstract

α-Galactosylceramide (KRN7000 or α-GalCer) analogues terminated with phenyl (Ph) groups at the acyl moiety possess more potency than KRN7000 to activate invariant natural killer T (iNKT) cells for inducing a T helper 1 (Th1)-biased immune response. However, biological activities of phenyl glycolipids with thio-modifications at the acyl moiety remain unknown, and facile approaches for highly stereoselective synthesis of KRN7000 and its analogues are rather scarce. Herein, we exploited 4,6-di-O-tert-butylsilylene (DTBS)-directed stereospecific galactosylation to efficiently synthesize various α-GalCer analogues bearing thioamide, terminal thiophenyl and dual modifications at the acyl moiety. Biological evaluations suggest that a new analogue S34 featuring a terminal Ph-S-Ph-F group exhibits a more superior Th1-biased immune response in mice. Molecular docking analysis revealed that the introduction of a sulfur atom influences vital hydrogen bonding interactions between glycolipids and the cluster of differentiation 1d (CDld), thus adjusting the stability of the glycolipid-CDld complex.

Rationally Designed Highly Potent NKT Cell Agonists with Different Cytokine Selectivity through Hydrogen-Bond Interaction

“…As the prototype NKT cell-activating ligand, α-galactosylceramide (αGalCer) has been extensively studied for applications in immunotherapy , and vaccine as adjuvant, − among which conjugating αGalCer to antigens has shown effective enhancement in vaccine efficacy as other conjugate vaccines. − On the other hand, scientists are still making efforts to pursue new αGalCer analogues, as structural alterations to αGalCer have been found to profoundly shape the balance between Th1 and Th2 responses. , However, the fundamental principles governing the preferential generation of either Th1 or Th2 cytokines still remain uncovered. Nonetheless, an intensified interaction between glycolipids and CD1d has been reported to promote Th1-skewed polarization. , In line with this premise, several representative Th1-biasing ligands have been designed regarding the structure–activity relationship (SAR) of glycolipid binding to CD1d, such as αGalCer analogues with aromatic groups introduced in the fatty acyl chain, − sphingosine chain, , or hydroxyl groups on the pyranose ring. − In addition, altering the stability of the CD1d/glycolipid binary or the association between the binary and T cell receptor (TCR) was also reported to favor the production of IFN-γ. − A collection of representative αGalCer analogues with Th1-biased modifications is shown in Table S1, most of which are designed to regulate the interaction between ligands and CD1d.…”