Preparation and characterization of acid hydrolysis products of the tomato glycoalkaloid α-tomatine

As part of an effort to define the biological roles of carbohydrate groups of the tomato glycoalkaloid alpha-tomatine in plants and animals, experiments were carried out to optimize the acid hydrolysis of the tetrasaccharide side chain of alpha-tomatine to products with three, two, one, and zero sugar groups. This was accomplished by following the time course for hydrolysis in 1 N HCl at 100 degrees C, isolating the hydrolysis products by chromatography on an aluminum oxide column, and determining the number and nature of hydrolysis products, including free sugars, with the aid of thin-layer chromatography and gas chromatography/mass spectrometry of alditol acetate sugar derivatives. The results show that a 20-min hydrolysis time appears useful for the formation of a mixture of the monosaccharide delta-tomatine, the disaccharide gamma-tomatine, and the trisaccharide beta(1)-tomatine. Efforts to isolate the other possible trisaccharide, beta(2)-tomatine, were unsuccessful, apparently because xylose is degraded during the hydrolysis. A 70-min exposure achieved complete hydrolysis of alpha-tomatine to the aglycon tomatidine. alpha-Tomatine was stable to hydrolysis at 37 degrees C, suggesting that it may also be stable to comparable acid conditions of the gut of insects, animals, and humans. The approach used should be generally useful for preparing hydrolysis products of glycoalkaloids and other glycosides such as saponins to facilitate assessing the role of the carbohydrate groups of these compounds in host-plant resistance, nutrition, and microbiology.