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.