ALLYL ETHER AS A PROTECTING GROUP IN CARBOHYDRATE-CHEMISTRY .10. SYNTHESIS OF 3-0-(BETA-D-GALACTOPYRANOSYL 3-SULPHATE)-2-0-HEXADECANOYL-1-0-HEXADECYL-L-GLYCEROL, SEMINOLIPID

3-O-Allyl-L-glycerol was converted, by way of the 1-O-trityl derivative, into 3-O-allyl-2-O-(but-2-enyl)-L-glycerol, which was alkylated with hexadecyl bromide and sodium hydride in NN-dimethylformamide. The product was converted, by the action of potassium t-butoxide in dimethyl sulphoxide, into 1-O-hexadecyl-3-O-(prop-1-enyl)-L-glycerol which was alkylated with 'crotyl bromide' and the product was hydrolysed to give 2-O-(but-2-enyl)-1-O-hexadecyl- L-glycerol. This was condensed with acetobromogalactose to give the β-galactoside which was converted into crystalline 2-O-(but-2-enyl)-1-O- hexadecyl-3-O-(3,4-O-isopropylidene-β-D-galactopyranosyl)-L-glycerol. This, on benzylation followed by acidic hydrolysis, gave 3-O-(2,6-di-O-benzyl-β- D-galactopyranosyl)-2-O-(but-2-enyl)-1-O-hexadecyl-L-glycerol which was converted, by way of the O-dibutylstannylidene derivative, into 3-0-(3-O-allyl-2,6-di-O-benzyl-β-D-galactopyranosyl)-2-O-(but-2-enyl) -1-O-hexadecyl-L-glycerol. Benzylation of this compound and subsequent treatment with potassium t-butoxide in dimethyl sulphoxide gave 3-O-[2,4,6-tri-O-benzyl- 3-O-(prop-1-enyl)-β-D-galactopyranosyl]-1 -O-hexadecyl-L-glycerol which was acylated with hexadecanoyl chloride in pyridine. The prop-1-enyl group was cleaved by the action of mercury(II) chloride to give crystalline 3-O-(2,4,6-tri-O-benzyl-β-D-galactopyranosyl)-2-O-hexadecanoyl-1-O- hexadecyl-L-glycerol. This compound was sulpnated with the pyridine-sulphur trioxide complex and the benzyl groups were removed by catalytic hydrogenolysis in glacial acetic acid to give 'seminolipid' with properties similar to those reported for the natural material. 'Desulphato-seminolipid' [3-O-(β-D- galactopyranosyl)-2-O-hexadecanoyl-1-O-hexadecyl-L-glycerol] was also prepared by catalytic hydrogenolysis of 3-O-(2,4,6-tri-O-benzyl-β-D- galactopyranosyl)-2-O-hexadecanoyl-1-O-hexadecyl-L-glycerol.