Structure Revision of Isomallotusinin to Mallotusinin by NMR-Based Conformational Analysis

A reexamination of the reported structure of isomallotusinin, previously proposed as an anomer of the ellagitannin mallotusinin, demonstrates that isomallotusinin is identical to mallotusinin, thus correcting a structural misassignment. This conclusion is supported by a detailed conformational analysis of mallotusinin, which bears a distinctive tetrahydroxydibenzofuranoyl (THDBF) group. Through 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.