Abstract
Various cardenolide genins and cardenolide glycosides were administered to light-grown
and dark-grown Digitalis lanata shoot cultures to investigate conversion reactions related to the formation and rearrangement
of the sugar side chain of Digitalis glycosides. Digitoxigenin was converted to digitoxigen-3-one, 3-epidigitoxigenin,
and digoxigenin. In addition, various cardiac glycosides were formed, including mono-glycosides
with glucose, glucomethylose, fucose, and digitalose, as well as the corresponding
diglycosides, all containing a terminal glucose. Digitoxosylated cardenolides were
not formed, although the light-grown shoot cultures were capable of producing these
compounds. Exogenous cardenolide fuco-sides were not converted into cardenolide digitoxosides.
Administration of evatromonoside (digitoxigenin monodigitoxoside) did not force the
formation of cardenolide di- or tridigitoxosides. Our results support the hypothesis
that cardenolide fucosides and digitoxosides are formed via different biosynthetic
routes and that cardenolide genins can be fucosylated but not digitoxosylated, indicating
that digitoxosylation may only occur at an earlier stage in the cardenolide pathway.
Key words
Biosynthesis - biotransformation - cardenolides - cardiac glycosides -
Digitalis lanata
- Scrophulariaceae - digitalose - fucose - fucosylation - glycosylation - shoot culture
