Synthesis of 6-hydroxyceramide using ruthenium-catalyzed hydrosilylation–protodesilylation. Unexpected formation of a long periodicity lamellar phase in skin lipid membranes
The synthesis of a ceramide with a 6-hydroxysphingosine base, a unique component of the human epidermal barrier, is reported. The key step involves a mild and selective trans-reduction of a triple bond using [Cp*Ru(CH3CN)3]PF6-catalyzed hydrosilylation followed by protodesilylation. The oxidation of sphingosine-based ceramide to 6-hydroxyceramide is also described. X-Ray powder diffraction on the model skin lipid membranes showed that 6-hydroxyceramide promotes the formation of a lamellar phase with 10.6 nm periodicity, which might explain why keratinocytes hydroxylate some ceramides at carbon 6.