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.