Boereguasins A–D, Cytochalasins from Boeremia exigua with Differential MAPK/NF-κB Inhibition

Abstract Four unprecedented cytochalasins, boereguasins A–D (1–4, respectively), were purified from the endophytic fungus Boeremia exigua. Structurally, compound 1 contains an adenosine moiety and features a novel bridged 5/6/13/5/6/5 ring system. Compound 2 represents the first cytochalasin with an odd-numbered carbon chain (19 carbons), which is presumably assembled via the fungal polyketide synthase pathway from an unusual propionyl-CoA starter unit. Compound 3 incorporates an unusual 15-membered carbocyclic ring, while compound 4 possesses a novel 5/6/14/6 tetracyclic scaffold. The structures were established by comprehensive spectroscopic analysis, ECD calculations, and DP4+ analysis. Compound 2 exhibited potent anti-inflammatory activity in LPS-induced RAW264.7 macrophages, significantly reducing NO, TNF-α, IL-6, and PGE2 levels. It suppressed the MAPK/NF-κB signaling pathway by inhibiting the phosphorylation of ERK, JNK, IκBα, and p65 and downregulating iNOS and COX-2 expression. Transcriptomic and docking studies confirmed that 2 targets key regulators and stably binds to the active pockets of TPL2 and NF-κB p65. In vivo, 1 and 2 reduced foot edema and inflammatory cytokines, with no acute toxicity observed.