| 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 ZnBr2 in Et2O. 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 . |
