Wheat flour lipids: III. structure of the mono- and digalactosylglycerol lipids

Determination of the structures of the mono- and digalactosylglycerol lipids of wheat flour is reported. Methylation of these lipids, followed by alkaline saponification, yielded partially methylated derivatives. Periodate oxidation of these substances in each case gave 1 mole uptake with the formation of formaldehyde. These data establish the presence of two vicinal hydroxyls in the glycerol residue: and strongly indicate that in the original lipid the two acyl groups are attached to these hydroxyl groups. This assignment was confirmed by acidic hydrolysis studies. The monogalactosylglycerol derivative gave 2,3,4,6-tetra-O-methy1-d-galactose plus glycerol; the digalactosylglycerol derivative yielded, in addition, 2,3,4-tri-O-methyl-d-galactose. In a control experiment, free digalactosylglycerol was methylated and hydrolyzed, giving only on papergrams 2,3,4tri-O-methyl- and 2,3,4,6-tetra-O-methyl-d-galactose. These results clearly define the structure of the galactosylglycerol lipids as a 2,3-diglyceride with a carbohydrate moiety attached in the 1-position. Infrared data suggest the d-configuration for the glycerol residue.