Synthesis of <scp>D</scp>‐<i>Erythro</i>‐ and <scp>D</scp>‐<i>Threo</i>‐Sphingosine Derivatives From <scp>L</scp>‐Serine

Abstract

Abstract The protected serine aldehyde 10 was converted to the crystalline N ‐Boc‐protected sphingosines 6 – 9 by a three‐step reaction sequence. Compound 10 was transformed with high diastereoselectivity (95%) either to the erythro ‐ or threo ‐alkynols, 17 and 18 , respectively. The erythro ‐isomer 17 is formed by the addition to 10 of lithium pentadecyne 16 in THF/HMPT at −78°, whereas the corresponding threo ‐isomer 18 is produced in the presence of ZnBr 2 in Et 2 O. Deprotection of the acetal moiety afforded 1,3‐diols 19 and 20 . These diols were selectively reduced with Red‐Al to the (E) ‐sphingosines 6 and 8 , or the (Z) ‐isomers 7 and 9 by partial hydrogenation over Lindlar's catalyst. Cleavage of the N ‐Boc group and further transformation to ceramides were readily achieved as demonstarted by the conversion of 6 to N ‐octadecanoyl‐ D ‐ erythro ‐sphingosine 5 .