KINETICS OF ACID-CATALYZED HYDROLYSIS OF CARBOHYDRATE GROUPS OF POTATO GLYCOALKALOIDS ALPHA-CHACONINE AND ALPHA-SOLANINE

As part of a broader plan designed to characterize Solanum glycoalkaloids and their hydrolysis products and biosynthetic intermediates, to identify plant enzymes in the biosynthetic pathways, and to develop a relative toxicity scale for glycoalkaloids, we examined conditions that favor the hydrolysis of carbohydrate portions of alpha-chaconine and alpha-solanine. These two triglycosides can each form two diglycosides, one monoglycoside, the so- called beta1-, beta2-, and gamma-chaconines and -solanines, and a common aglycon, solanidine. An incomplete hydrolysis mixture should therefore contain nine compounds. Hydrolyses were carried out in 0.1, 0.2, and 0.5 N HCl-methanol at 38, 55, and 65-degrees-C for various time periods. The individual carbohydrate residues in tri-, di-, and monosaccharides differed significantly in their susceptibilities to acid hydrolysis. Hydrolysis rates increased with HCl concentration and temperature. Hydrolytic stabilities of the carbohydrate groups attached to alpha-chaconine and alpha-solanine situated in a potato matrix appear to be similar to those of the pure compounds. By varying the hydrolysis conditions, it was possible to optimize the formation of specific compounds. Eight compounds were isolated and characterized with the aid of preparative chromatography on aluminum oxide columns, thin-layer chromatography, high-performance liquid chromatography, and mass spectrometry. Efforts to isolate beta1-solanine were unsuccessful. Our findings should facilitate characterization of biosynthetic intermediates in plants and of metabolites in animal tissues, as well as assessment of relative safety. Mechanistic aspects of the acid hydrolysis and the significance of the findings to food safety and plant molecular biology are discussed.