First asymmetric synthesis of 6-hydroxy-4-sphingenine-containing ceramides. Use of chiral propargylic alcohols to prepare a lipid found in human skin.

6-Hydroxy-(4E)-sphingenine-containing ceramides were found recently in human skin. We present here the first synthesis of the 6S and 6R diastereoisomers 2 and 3, which represent analogues of (2S,3R)-ceramide (1) having two allylic hydroxyl groups. Chiral propargylic alcohols 8 and 11, which were prepared by asymmetric dihydroxylation of alpha,beta-unsaturated ester 13 and allylic chloride 22, respectively, were employed as precursors of 2 and 3. Nucleophilic addition of lithiated TBS-protected propargylic ethers 25 and 32 to l-serine-derived aldehyde 26, respectively, afforded oxazolidine intermediates 27 and 33. Acid-mediated deprotection of the oxazolidine, followed by N-acylation and Birch reduction, completed the syntheses of 2 and 3.