An Unprecedented Neolignan Skeleton from Chimarrhis turbinata

A lignan with a new skeleton named chimarrhinin (1) was isolated from an extract of the leaves of Chimarrhis turbinata, a Rubiaceae plant species. ¹³C NMR spectrometric techniques including 1D and 2D experiments and HRESIMS provided unequivocal structural confirmation of this new C₆.C₃ skeleton type. The relative configuration of 1 was established by 2D ¹H−H analysis and J couplings, while its conformation was evaluated through molecular modeling using the RM1 semiempirical method, with the aid of coupling constants obtained by NMR analysis. The antioxidant activity of the new derivative 1 and two known and previously isolated phenolic derivatives (2 and 3) was investigated. An IC₅₀ value of 7.50 ± 0.5 μmol L⁻¹ was obtained for the new derivative 1, while 2 and 3 showed IC₅₀ values of 18.60 ± 0.4 and 18.50 ± 0.6 μmol, respectively.