Epicochalasines A and B: Two Bioactive Merocytochalasans Bearing Caged Epicoccine Dimer Units from Aspergillus flavipes

Two bioactive merocytochalasans, epicochalasines A (1) and B (2), a new class of cytochalasans bearing unexpected scaffolds consisting of fused aspochalasin and epicoccine dimer moieties, were isolated from the liquid culture broth of Aspergillus flavipes. Both 1 and 2 possess a hendecacyclic 5/6/11/5/6/5/6/5/6/6/5 ring system containing an adamantyl cage and as many as 19 stereogenic centers; however, the fusion patterns of 1 and 2 differ greatly, thus resulting in different carbon skeletons. The absolute configurations of 1 and 2 were determined by X‐ray diffraction and calculated ECD, respectively. The biogenetic pathways of 1 and 2 are proposed to involve Diels–Alder and nucleophilic addition reactions. Both 1 and 2 induced significant G2/M‐phase cell‐cycle arrest. Furthermore, we found that merocytochalasans induce apoptosis in leukemia cells through the activation of caspase‐3 and the degradation of PARP. Adamantly original: Two bioactive merocytochalasans isolated from the liquid culture broth of Aspergillus flavipes represent a new class of cytochalasans with unexpected scaffolds consisting of fused aspochalasin and epicoccine dimer moieties. Epicochalasines A (1) and B both possess a hendecacyclic 5/6/11/5/6/5/6/5/6/6/5 ring system with an adamantyl cage but have different carbon skeletons.