ACID-CATALYZED PARTIAL HYDROLYSIS OF CARBOHYDRATE GROUPS OF THE POTATO GLYCOALKALOID ALPHA-CHACONINE IN ALCOHOLIC SOLUTIONS

As part of an effort to improve the safety of plant-derived foods, the role of the carbohydrate side chain has been explored in biological effects of potato glycoalkaloids such as alpha-chaconine. This steroid glycoalkaloid has a trisaccharide attached to the 3-hydroxy position of the steroidal aglycon solanidine. This study attempts to define the effect of structurally different alcohols on the partial hydrolysis of alpha-chaconine to beta(1)-chaconine, beta(2)-chaconine, gamma-chaconine, and solanidine. Partial hydrolyses were carried out in 97.5% alcohol-0.25 N HCl at 60 degrees C. HPLC was used to measure the distribution of hydrolysis products as a function of time. The rate of hydrolysis of alpha-chaconine in the straight-chain alcohol solutions was as follows: methanol > ethanol = l-butanol > propanol > pentanol much greater than water. The longer the chain, the slower the rate of hydrolysis except for the anomalous result that the extent of hydrolysis in l-butanol was equal to that in ethanol. However hydrolysis in 2-butanol was slower than in l-butanol. Surprisingly, hydrolysis in tert-butyl alcohol was slowest, proceeding more slowly than even in l-pentanol. The formation of gamma-chaconine was also greatly reduced in tert-butyl alcohol. Mechanistic rationalizations are offered to explain the observed trends in terms of the hydrophobic-hydrophilic nature of the glycoalkaloids and the solvation properties of the alcohols. The results should be generally useful for optimizing or minimizing the formation of specific hydrolysis products.