Synthesis and biological evaluation of α-galactosylceramide (KRN7000) and isoglobotrihexosylceramide (iGb3)

Glycoceramides can activate NKT cells by binding with CD1d to produce IFN-γ, IL-4, and other cytokines. An efficient synthetic pathway for α-galactosylceramide (KRN7000) was established by coupling a protected galactose donor to a properly protected ceramide. During the investigation, it was discovered that when the ceramide was protected with benzyl groups, only β-galactosylceramide was produced from the glycosylation reaction. In contrast, the ceramide with benzoyl protecting groups produced α-galactosylceramide. Isoglobotrihexosylceramide (iGb3) was prepared by glycosylation of Galα1-3Galβ1-4Glc donor with 2-azido-sphingosine in high yield. Biological assays on the synthetic KRN7000 and iGb3 were performed using human and murine iNKT cell clones or hybridomas.