Scalable Total Syntheses of Nonthmicin and Ecteinamycin Reveal a Dual Antibacterial and Antitoxin Profile against Clostridioides difficile

Clostridioides difficile infection (CDI) is a severe diarrheal disease with substantial mortality, frequent recurrence, and limited treatment options. Here, we describe a scalable total synthesis of ecteinamycin, a polyether ionophore with anti-C. difficile activity, and its congener nonthmicin. Key steps include two electrochemical decarboxylative alkenylations, an enzyme-catalyzed anti-Baldwin cyclization, and a redox-economic asymmetric C–C bond formation. This synthesis enabled systematic biological evaluation. Nonthmicin showed potent and selective suppression of C. difficile, protected mammalian cells from toxin B (TcdB)-induced cytopathology, and displayed therapeutic efficacy in a mouse model of CDI. Preliminary structure–function studies suggest that the exo-methylene group of the tetronic acid motif is an important contributor to the observed exceptional potency. These findings challenge the prevailing view of polyether ionophores as broad-spectrum membrane-active agents and suggest new therapeutic possibilities for CDI.