Spirotrichilins A and B: Two Rearranged Spirocyclic Limonoids from Trichilia connaroides

Spirotrichilins A (1) and B (2), two novel limonoids with an unprecedented spiro[cyclopenta[b]furan2,1'-cyclopentan] ring system in A/B/C rings, were isolated from the fruits of trichilia connaroides. Their planar structures and absolute configurations were established based on 1D-, 2D-NMR data, electronic circular dichroism (ECD) exciton chirality method and time-dependent density functional theory (TDDFT)/ECD calculation. A benzilic acid-like rearrangement in ring A was proposed as the key step in the plausible biogenetic pathway of 1 and 2.