Alpha-amanitin is a natural product toxin that was first isolated from the notorious death-cap mushroom, A. phalloides. Alpha-amanitin is a highly selective allosteric inhibitor of RNA polymerase II (Pol II), that has been depicted in every modern biochemistry textbook and has been featured in thousands of publications (&gt;1500 by Web of Science). Moreover, it has everything that a peptide drug should have - high potency, metabolic stability and oral bioavailability. Recently, it has been featured as a promising toxic payload for antibody-drug conjugates (ADCs). ADCs loaded with amanitin are now entering clinical trials. Its bicyclic octapeptide structure contains two key oxidized amino acids: trans-4-hydroxy-proline (Hyp) and notably (2S,3R,4R)-4,5-dihydroxy-isoleucine (DHIle) with an all-anti configuration. In addition, an intra-annular staple comprising 6-hydroxy-tryptathionine-(R)-sulfoxide is unique among natural products. Our quest to re-investigate and update the chemical biology/pharmacology of this toxin was impeded by inaccessibility of toxic analogs and highlighted the need to ultimately address a total synthesis. By establishing a delicate three-fold oxidation of tryptophan to deliver the key 6-hydroxy-tryptathionine-(R)-sulfoxide along with the first enantioselective DHIle, we sealed the first total synthesis of amanitin in the synthetic record. This work now provides access to derivatives to probe critical structure-activity relationships as well as a means of accessing scalable quantities of the toxin. We have applied aspects of this methodology to the synthesis of a prototypical phalloidin library as well as other monocyclic peptides of clinical interest. Finally, we have developed a new peptide stapling method that enables user-friendly one-step stapling that creates a fluorescent isoindole with brilliance that is on par with fluorescent blue proteins. This method in turn provides for high bioactivity in the context of stapled macrocycles whose linear precursors have no measurable affinity for known targets.

From tryptathionine-based natural product peptide toxins to fluorescent iso-indole stapled peptide macrocycles

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.