Synthesis of 1,2-di-O-hexadecanoyl-3-O-(β-D-galactopyranosyl)-L-glycerol (a ‘galactosyl diglyceride’) and 1,2-di-O-octadecanoyl-3-O-(6-O-octadecanoyl-β-D-galactopyranosyl)-L-glycerol
1,2-Di-O-benzyl-L-glycerol (prepared by a new method via 3-O-allyl-1,2-di-O-benzyl-L-glycerol) was glycosylated to give 1,2-di-O-benzyl-3-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosly)-L-glycerol. This compound was converted into the crystalline 3-O-(2,3,4-tri-O-benzyl-β-D-galactopyranosyl)-L-glycerol, which was used as an intermediate for the synthesis of the title compounds. 3-O-(2,3,4-Tri-O-benzyl-β-D-galactopyranosyl)-L-glycerol is also a potential intermediate for the syntheses of ‘polygalactosyl diglycerides’ which are the serologically active components of the glycolipids of Mycoplasma pneumoniae. 1,2-Bis-O-(2-methylallyl)-L-glycerol was prepared and attempts were made to condense this, in β-linkage, with 2,3,4-tri-O-benzyl-6-O-(but-2-enyl)-α-D-galactopyranosyl chloride [prepared by a new route from allyl 6-O-(but-2-enyl)-α-D-galactopyranoside] in order to provide a more direct route to 3-O-(2,3,4-tri-O-benzyl-β-D-galactopyranosyl)-L-glycerol. 3-O-(α-D-Galactopyranosyl)-L-glycerol was also prepared by a new route via 1,2-O-isopropylidene-3-O-[2,3,4-tri-O-benzyl-6-O-(but-2-enyl)-α-D-galactopyranosyl]-L-glycerol. The migration of an isopropylidene group under the conditions of our α-glycoside synthesis is suspected.