Structure Revision of Anti-Inflammatory Indole Alkaloids with a 1,2-Benzisoxazole Ring.

( R )- and ( S )-2-(benzo[ d ]isoxazol-3-yl)-2-ethylindolin-3-one [(±)- 1 ] were previously isolated from NIRAM, a natural blue dye from Polygonum tinctorium , and their structures were initially proposed to possess a 1,2-benzisoxazole ring. In this study, the structures of (±)- 1 were revised to have an indole-anthranilic acid fused tetracyclic ring rather than the 1,2-benzisoxazole ring by reanalysis of one-dimensional (1D) and two-dimensional (2D) NMR followed by density functional theory (DFT) chemical shift calculation, DP4+ technique, and ECD simulation.