Enfumafungin (1) is a hemiacetal, triterpene glycoside that was isolated from a fermentation of Hormonema sp. as a mixture of two interconverting forms. The primary structure of the major component of the mixture was determined as part of the mixture, mainly via NMR and comparison with hyalodendroside A (2), a related hemiacetal, triterpene glycoside that exists in a single form. The primary structure was confirmed, and the relative stereochemistry determined, based on a pair of methylacetal derivatives (3 and 4). Enfumafungin is an antifungal agent that acts as a specific inhibitor of glucan synthesis in cells and in vitro, and leads to morphological changes in yeasts and molds.