Biotransformation of <i>Allium</i> Sulfur Metabolites by <i>Proteus mirabilis</i> Yields Cepathiosoxide, a Trithiabicyclic Sulfoxide

Exposing onion-derived sulfur metabolites to <i>Proteus mirabilis</i> yielded cepathiosoxide, a structurally distinct trithiabicyclic sulfoxide formed through microbial biotransformation. LC-MS revealed the loss of native <i>Allium</i> tetrasulfides and the emergence of a unique cepathiosoxide. NMR spectroscopy and ECD established the existence of a rigid [4.2.1] framework with an embedded sulfoxide. Cepathiosoxide affected colorectal cancer cell viability without impacting normal human colon epithelial cells. These findings indicate that microbial sulfur metabolism provides structurally distinct and potentially relevant metabolites.