Amatoxins and phallotoxins constitute two classes of fungal toxins that are predominantly produced by their host organism Amanita phalloides and account for a significant proportion of its extreme toxicity. Amanita phalloides is responsible for the majority of mushroom poisoning within Europe, owing to its wide geographical distribution and the remarkable thermal stability of its toxins, which are neither degraded nor significantly inactivated by cooking. Both amatoxins and phallotoxins belong to a class of bicyclic peptides characterized by conventional amide linkages as well as a distinctive thioether bridge that forms the secondary macrocyclic structure. This work focuses on the generation of a comprehensive library of amanitin derivatives with the aim of reprogramming their binding selectivity from eukaryotic RNA polymerase II (RNAP-II) towards prokaryotic RNAP-II. For the synthesis of these derivatives, a solid-phase strategy was employed that enabled formation of the thioether linkage on the resin. Systematic sequence modifications of the amanitin scaffold resulted in significant increases in activity toward prokaryotic RNAP-II. Consequently, the targeted inversion of binding selectivity towards bacterial RNAP-II was successfully achieved. These findings may serve as a foundation for the development of novel antibiotics based on fungal toxin scaffolds. In addition, this work addresses the synthesis and evaluation of novel phalloidin derivatives with potential applications in human medicine. In this context, the suitability of phallotoxins as carrier molecules (payloads) for antibody-drug conjugates was investigated. Particular emphasis was placed on enhancing the polymerization rate towards filamentous actin (F-actin) in order to generate highly efficient payloads. Therefore, an extensive collection of potentially viable phalloidin derivatives was synthesized using the same linear on-resin strategy applied for the amanitin derivatives. Sequence variations were designed based on two distinct hypotheses aimed at improving biological activity. The resulting compounds were evaluated using a fluorescence spectroscopy-based assay to determine their actin polymerization rates, which served as a qualitative metric for assessing relative activity within the collection. Notably, several phalloidin derivatives exhibited polymerization rates that significantly exceeded those of the native phalloidin.
Tino Damaszek (Thu,) studied this question.