NOVEL MECHANISM FOR OXIDATIVE CLEAVAGE OF GLYCOSIDIC BONDS - EVIDENCE FOR AN OXYGEN-DEPENDENT REACTION

In a previous work from our laboratory, an optimized procedure was worked out for cleavage of the glucosidic bonds in ginsenosides (Cui, J. F.; Garle, M.; Lund, E.; Bjorkhem, I.; Eneroth, P. Anal. Biochem. 1993, 210, 411-417). When the reaction was performed in n-butanol, alkaline conditions were found to give a considerably better and almost quantitative yield of intact aglyconic-specific products than did acidic conditions. This is surprising in view of the current concept that glucosidic bonds are more stable under alkaline than acidic conditions. It is shown here that the alkaline cleavage is oxygen dependent and that there is little or no conversion when oxygen or air is replaced with nitrogen. Addition of an anti-oxidant, glucose or water also reduces the degree of cleavage under the conditions employed. Replacement of n-butanol for sec-, iso- or 2-methyl-2-propanol, decreased the yield of products to about 75% and when n- or isopropanol was used as solvent the yield decreased to about 40%. It was shown that the glucose moiety was completely degraded under the conditions employed and that formate and carbonate, in a ratio of 5/1, were the major products. A mechanistic rationale for the oxygen dependent cleavage of the glucosidic bonds is suggested. The possibility that this mechanism may be of protective importance in biological systems under some specific conditions is also discussed.