Effects of digitoxigenin, digoxigenin, and various cardiac glycosides on cardenolide accumulation in shoot cultures of Digitalis lanata

Various cardenolide genins and cardenolide glycosides were administered to light-grown and dark-grown Digitalis lanata shoot cultures to investigate c onversion reactions related to the formation and rearrangement of the sugar side chain of Digitalis glycosides. Digitoxigenin was converted to digitox igen-3-one, 3-epidigitoxigenin, and digoxigenin. In addition, various cardi ac glycosides were formed, including monoglycosides with glucose, glucometh ylose, fucose, and digitalose, as well as the corresponding diglycosides, a ll containing a terminal glucose. Digitoxosylated cardenolides were not for med, although the light-grown shoot cultures were capable of producing thes e compounds. Exogenous cardenolide fucosides were not converted into carden olide digitoxosides. Administration of evatromonoside (digitoxigenin monodi gitoxoside) did not force the formation of cardenolide di- or tridiqitoxosi des. Our results support the hypothesis that cardenolide fucosides and digi toxosides are formed via different biosynthetic routes and that cardenolide genins can be fucosylated but not digitoxosylated, indicating that digitox osylation may only occur at an earlier stage in the cardenolide pathway.