SYNTHESES OF ALL 4 STEREOISOMERS WHICH ARE CONFORMATIONALLY CONSTRAINED 1,4-DIOXANYL ANALOGS OF THE ANTINEOPLASTIC ETHER LIPID ET-18-OCH3

The syntheses of each of the four nearly optically pure stereoisomers of [[(5-heptadecyl-1,4-dioxan-2-yl)-methyl]oxy]phosphocholine (2,3,2',3') were performed by two parallel divergent sequences. Phosphocholines 2 and 3 were prepared via the corresponding 5-heptadecyl-2-(hydroxymethyl)-1,4-dioxanes 21 and 23, respectively, from the completely regiospecific mixed-hydride reductions of (1R,4S,5S)-4-heptadecyl-3,6,8-trioxabicyclo[3.2.1]octane (19) and (1R,4R,5S)-4-heptadecyl-3,6,8-trioxabicyclo[3.2.1]octane (20), respectively. The two 4-heptadecyl-3,6,8-trioxabicyclo[3.2.1]octanes 19 and 20 were the two separable products from an intramolecular cyclization reaction. By a parallel divergent sequence from the enantiomeric starting material, 3-O-benzyl-sn-glycerol (16'), the other two diastereomeric [[(5-heptadecyl-1,4-dioxan-2-yl)methyl]oxy]phosphocholines 2' and 3' were prepared. These four monocyclic [[(5-heptadecyl-1,4-dioxan-2-yl)methyl]oxy]phosphocholines (2,3,2',3') are conformationally constrained analogs of the antineoplastic and immunomodulatory ether lipid rac-2-O-methyl-1-O-octadecylglycero-3-phosphocholine (rac-1) (rac-ET-18-OCH3, rac-Edelfosine).