Aspochalasine A

Cytochalasans are a group of structurally diverse fungal polyketide-amino acid hybrid metabolites that exhibit diverse biological functions. Asperchalasine A was identified and isolated from an extract of the marine-derived fungus, Aspergillus. Asperchalasine A is a cytochalasan dimer which consists of two cytochalasan molecules connected by an epicoccine. This study investigated the potential antiangiogenic effects of Aspergillus extract and asperchalasine A, which significantly inhibited cell adhesion and tube formation in human umbilical vein endothelial cells (HUVECs). Aspergillus extract and asperchalasine A decreased the vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor (VEGFR)-2 mRNA expression in a concentration-dependent manner. In addition, Aspergillus extract and asperchalasine A inhibited angiogenesis via downregulation of VEGF, p-p38, p-extracellular signal-regulated protein kinase (ERK), p-VEGFR-2, and p-Akt signaling pathways. Moreover, Aspergillus extract and asperchalasine A significantly inhibited the amount of blood vessel formation in fertilized chicken eggs using a chorioallantoic membrane assay. Our results provide experimental evidence of this novel biological activity of the potential antiangiogenic substances, Aspergillus extract, and asperchalasine A. This study also suggests that Aspergillus extract and its active component asperchalasine A are excellent candidates as adjuvant therapeutic substances for cancer prevention and treatment.

The first total syntheses of the cytochalasan dimers asperchalasines A, D, E, and H have been accomplished. The key steps of the synthesis include a highly stereoselective intermolecular Diels-Alder reaction and a Horner-Wadsworth-Emmons macrocyclization to establish the key monomer aspochalasin B, and an intermolecular Diels-Alder reaction followed by a biomimetic oxidative heterodimerization by 5+2 cycloaddition to furnish asperchalasine A. The synthetic efforts provide insight into the biosynthetic pathway of cytochalasan dimers and enables the further study of their biological properties.

The first total syntheses of asperchalasines A-E, a collection of unprecedented merocytochalasans, are reported. Aspochalasin B, a key tricyclic cytochalasan monomer, was first synthesized through a unified approach that hinges on a Diels-Alder reaction and a ring-closing metathesis reaction. The bioinspired Diels-Alder reactions of aspochalasin B with different epicoccine precursors were then explored, which enabled the divergent access of the heterodimers asperchalasines B-E as well as related congeners. Furthermore, the heterotrimer asperchalasine A was obtained from one epicoccine unit and two aspochalasin B units through a biomimetic Diels-Alder reaction followed by an oxidative [5+2]-cycloaddition.