Lipids based on dihydric alcohols are widespread minor constituents of many fats and oils1-4). However, none has been isolated as such with the exception of coixenolide -a diol lipid from the seeds of the Far Eastern plant Coix lachryma 5, 6). Coixenolide is a mixed ester of trans-vaccenic and palmitoleic acids with meso-butane-2,3-diol. Its isolation was apparently facilitated by its high content in Coix lachryma seeds and its easy adsorption chromatographic separability from triglycerides in contrast to fatty acid esters of the other C2-C4-diols.
The present communication deals with the isolation of still another diol lipid -an ethyleneglycol derivative -from the triglyceride fraction of regenerating rat liver. Although unsaturated diol lipids can as a rule be separated from triglycerides by partition chromatography 7) it is impossible to isolate saturated ethyleneglycol diesters from triglyceride mixtures by adsorption or partition silica gel chromatography in commonly used systems. Such separation of the diol lipid from the triglycerides of regenerating rat liver has been achieved by preparative gas-liquid chromatography. The isolated lipid was identified as ethyleneglycol dipalmitate by its melting point, chromatographic behavior and mass-spectrum.
All experiments were made on adult female rats of 180-200 g weight. They were housed in wire bottom cages and allowed free access to food and water. The rats were divided into two groups of 12 to 15 animals each. At 6, 12, 24 and 48 hr periods after partial hepatectomy 8) 3 to 4 animals from each group were killed by decapitation, their livers homogenized in a 2:1 chloroform-methanol mixture and the lipid extracts washed with water (20% v/v) 9). The chloroform layers were evaporated to dryness in vacuo and the residues were taken up in chloroform stabilized by 1 2% of methanol.
Aliquots of the lipid extracts (150-200 mg of total lipids) were separated by chromatography on a 2 Γ 10 cm column packed with 6 g KSK silica gel