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 glycoalkalo ids and their hydrolysis products and biosynthetic intermediates, to i dentify plant enzymes in the biosynthetic pathways, and to develop a r elative 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-chaconin es and -solanines, and a common aglycon, solanidine. An incomplete hyd rolysis mixture should therefore contain nine compounds. Hydrolyses we re carried out in 0.1, 0.2, and 0.5 N HCl-methanol at 38, 55, and 65-d egrees-C for various time periods. The individual carbohydrate residue s in tri-, di-, and monosaccharides differed significantly in their su sceptibilities to acid hydrolysis. Hydrolysis rates increased with HCl concentration and temperature. Hydrolytic stabilities of the carbohyd rate 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 cha racterized with the aid of preparative chromatography on aluminum oxid e columns, thin-layer chromatography, high-performance liquid chromato graphy, and mass spectrometry. Efforts to isolate beta1-solanine were unsuccessful. Our findings should facilitate characterization of biosy nthetic intermediates in plants and of metabolites in animal tissues, as well as assessment of relative safety. Mechanistic aspects of the a cid hydrolysis and the significance of the findings to food safety and plant molecular biology are discussed.