Isomallotusinin is mallotusinin: a structural misassignment caused by conformational flexibility

A reexamination of the reported structure of isomallotusinin, previously described as an anomer of the ellagitannin mallotusinin, demonstrates that the compound is identical to mallotusinin, thereby correcting a structural misassignment. This conclusion is supported by a detailed conformational analysis of mallotusinin, which bears a distinctive tetrahydroxydibenzofuranoyl (THDBF) group. Using a DFT-assisted analysis of 1H–1H coupling constants, we demonstrate that mallotusinin exists as a solvent-dependent equilibrium of 3S1 and 1C4 conformers. Our findings resolve a structural ambiguity in the literature and highlight the importance of considering conformational dynamics in the structural elucidation of conformationally flexible ellagitannins.