Discovery and Structure-Activity Relationship of Cadazolid: A First-In-Class Quinoxolidinone Antibiotic for the Treatment of Clostridioides difficile Infection.

Clostridioides difficile (C. difficile) is one of the leading causes of healthcare-associated infections worldwide. The increasing incidence of strains resistant to currently available therapies highlights the need for alternative treatment options with a novel mode of action. Oxazolidinones that are connected to a quinolone moiety with a pyrrolidine linker, such as compound 1, are reported to exhibit potent broadspectrum antibacterial activity. In an effort to optimize this class of compounds for the treatment of C. difficile infection (CDI), we have identified cadazolid (9), a first-in-class quinoxolidinone antibiotic, which is a potent inhibitor of C. difficile protein synthesis. In order to achieve narrow-spectrum coverage of clinically most relevant strains without affecting the gut microbiota, an emphasis was placed on abolishing activity against commensals of the intestinal microbiome while retaining good coverage of pathogenic C. difficile, including hypervirulent and epidemic strains.

Discovery and Characterization of ACT-451840: an Antimalarial Drug with a Novel Mechanism of Action.

More than 40 % of the world's population is at risk of being infected with malaria. Most malaria cases occur in the countries of sub-Saharan Africa, Central and South America, and Asia. Resistance to standard therapy, including artemisinin combinations, is increasing. There is an urgent need for novel antimalarials with new mechanisms of action. In a phenotypic screen, we identified a series of phenylalanine-based compounds that exhibit antimalarial activity via a new and yet unknown mechanism of action. Our optimization efforts culminated in the selection of ACT-451840 [(S,E)-N-(4-(4-acetylpiperazin-1-yl)benzyl)-3-(4-(tert-butyl)phenyl)-N-(1-(4-(4-cyanobenzyl)piperazin-1-yl)-1-oxo-3-phenylpropan-2-yl)acrylamide] for clinical development. Herein we describe our optimization efforts from the screening hit to the potential drug candidate with respect to antiparasitic activity, drug metabolism and pharmacokinetics (DMPK) properties, and in vivo pharmacological efficacy.