Aspergilasines A–D: Four Merocytochalasans with New Carbon Skeletons from Aspergillus flavipes QCS12

Aspergilasines A–D (1–4), four merocytochalasans with new skeletons, were isolated from the liquid culture broth of Aspergillus flavipes QCS12. Aspergilasine A (1) possesses a uniquely caged pentacyclo[7.2.0.14,11.02,7.05,10]dodecane skeleton with an unexpected cyclobutane ring that formed by the fusion of two epicoccine moieties via two [3 + 2] cycloadditions. Aspergilasines B–D (2–4) are key biosynthetic intermediates of epicochalasine B that fit well with our previous biosynthetic proposal.