Asperchalasine A, a Cytochalasan Dimer with an Unprecedented Decacyclic Ring System, from <i>Aspergillus flavipes</i>

Asperchalasine A (1), the first cytochalasan dimer featuring a unique decacyclic 5/6/11/5/5/6/5/11/6/5 ring system consisting of 20 chiral centers, was isolated from the culture broth of Aspergillus flavipes. Three biogenetically related intermediates, asperchalasines B-D (2-4), were also isolated. Their structures, including their absolute configurations, were elucidated using a combination of HRESIMS, NMR, ECD, molecular modeling, and single-crystal X-ray diffraction techniques. Compound 1, which possesses an unprecedented 13-oxatetracyclo[7.2.1.1(2,5).0(1,6)]tridec-8,12-dione core structure, is the first example of a dimeric cytochalasan alkaloid. The biogenetic pathways of 1-4 were described starting from the co-isolated compounds 5 and 6. More importantly, 1 induced significant G1-phase cell cycle arrest by selectively inhibiting cyclin A, CDK2 and CDK6 in cancerous, but not normal, cells, highlighting it as a potentially selective cell cycle regulator against cancer cells.