Natural products chemistry of Lilium longiflorum: Structural elucidation, quantification, biological activity and fungal metabolism of steroidal glycosides

The Easter lily (Lilium longiflorum Thunb., Liliaceae) has beautiful white flowers and a delicate aroma and is appreciated worldwide as an attractive ornamental plant. In addition to its economic importance and popularity in horticulture, lily bulbs are regularly consumed in Asia, as both food and medicine. The Easter lily is a rich source of steroidal glycosides, a group of compounds that may be responsible for some of the traditional medicinal uses of lilies and may play a role in the pant-pathogen interaction. This research project was designed to: 1) Isolate and characterize new steroidal glycosides from the bulbs of L. longiflorum, 2) quantify their contents in all of the organs of L. longiflorum, and 3) perform studies on the antifungal activity and fungal metabolism of the compounds.;A phytochemical investigation conducted on the bulbs resulted in the discovery of several novel steroidal glycosides. A novel acetylated steroidal glycoalkaloid and two novel steroidal furostanol saponins, along with three other steroidal glycosides were isolated from the bulbs of L. longiflorum for the first time. A LC-MS/MS method performed in multiple reaction monitoring (MRM) mode was developed for the simultaneous quantitative analysis of the five steroidal glycosides in the different organs of L. longiflorum . The highest concentrations of total steroidal glycosides were detected in flower buds, lower stems, and leaves. The steroidal glycoalkaloids were detected in higher concentrations as compared to the furostanol saponins in all of the plant organs except for the fibrous and fleshy roots. The proportions of steroidal glycoalkaloids to furostanol saponins were higher in the plant organs exposed to light and decreased in proportion from the aboveground organs to the underground organs. The highest concentrations of the steroidal glycoalkaloids were detected in flower buds, leaves, and bulbs.;Purified steroidal glycosides were evaluated for fungal growth inhibition activity against the plant pathogenic fungus, Botrytis cinerea. All of the compounds showed weak fungal growth inhibition activity; however, the natural acetylation of C-6''' of the terminal glucose in the acetylated steroidal glycoalkaloid, increased the antifungal activity by inhibiting the rate of metabolism of the compound by the fungus. A model system was developed to generate fungal metabolites of the steroidal glycoalkaloids and this system led to the discovery of several new fungal metabolites. The fungal metabolites characterized from the model system were subsequently identified by LC-MS and found to naturally occur in Easter lily tissues infected with the fungus.