Formal Single Atom Editing of the Glycosylated Natural Product Fidaxomicin Improves Acid Stability and Retains Antibiotic Activity.

Fidaxomicin (Fdx) constitutes a glycosylated natural product with excellent antibacterial activity against various Gram-positive bacteria but is approved only for Clostridioides difficile infections. Poor water solubility and acid lability preclude its use for other infections. Herein, we describe our strategy to overcome the acid lability by introducing acid-stable S-linked glycosides. We describe the direct, diastereoselective modification of unprotected Fdx without the need to avoid air or moisture. Using our newly established approach, Fdx was converted to the single atom exchanged analogue S-Fdx, in which the acid labile O-glycosidic bond to the noviose sugar was replaced by the acid stable S-glycosidic bond. Studies of the antibacterial activity of a structurally diverse set of thioglycoside derivatives revealed high potency of acyl derivatives of S-Fdx against Clostridioides difficile (MIC range: 0.12-4 μg/mL) and excellent potency against Clostridium perfringens (MIC range: 0.06-0.5 μg/mL).