Elodeoidins A–H, acylphloroglucinol meroterpenoids possessing diverse rearranged skeletons from Hypericum elodeoides

Abstract

Inspired by a geranyl-originated undecanoate acid ethyl ester (biosynthetic fragment, 9), elodeoidins A–H (1–8), representing four unprecedented rearranged acylphloroglucinol meroterpenoids, were discovered from the herb of Hypericum elodeoides. Their structures were elucidated by HRESIMS, NMR, Mosher, ECD, quantum chemical calculations, and biosynthetic pathways. Structurally, the six-membered acylphloroglucinol core rearranged to a five-membered β-diketone unit possessing an exocyclic carbonyl group (C-1 or C-3) through an α-ketol rearrangement. Subsequently, key cyclizations with C-1 or C-3 established a 2-cyclopentyltetrahydrofuran moiety in 1 and 2, a [5,5]-spiroketal-fused 5–5–5–5 skeleton in 3 and 4, a 1,2-dioxonane-bridged 5–9–5 framework in 5 and 6, and a 2,5-dioxabicyclo[2.2.2]octane caged structure in 7 and 8. (±)-5 and 6 showed significant anti-inflammatory activity (IC₅₀: 6.06 ± 0.41–10.46 ± 0.14 μM). These diversiform skeletons indicated that the biosynthetic fragment inspired discovery and elucidation strategy is valuable for the discovery of novel and unprecedented natural products.