NEW OPTICALLY PURE DIMETHYLACETALS OF GLYCERALDEHYDES AND THEIR APPLICATION FOR LIPID AND PHOSPHOLIPID-SYNTHESIS

A convenient synthesis of new and enantiomerically pure 2-O-protected D-glyceraldehyde dimethylacetals as chiral C-3 building blocks for the synthesis of lipids and phospholipids is described. Benzyl- or allyle thers are used as protecting groups in position 2 and 5 of D-mannitol. These intermediates are converted to 2-O-benzyl- or 2-O-allyl-D-glyce raldehyde dimethylacetals by cleavage with periodic acid in methanol. The two dimethylacetals are useful for the synthesis of mixed chain ph ospholipids with natural configuration of ester-ester, ester-ether or ether-ether composition. Also, triglycerides with three different alky l chains, ester or ether, can be prepared. As an example of the versat ility of the new intermediates, we describe the synthesis of -hexahecy l-2-O-acetyl-sn-glycero-3-phosphocholine, the so-called 'platelet acti vating factor' (PAF), via 1-O-hexadecyl-2-O-benzyl-sn-glycerol.