Ustilobisorbicillinol A, a Cytotoxic Sorbyl-Containing Aromatic Polyketide from Ustilaginoidea virens

Ustilobisorbicillinol A (1), which is a novel bisorbicillinoid featuring a unique cage structure that incorporates one sorbicillinol and one sorbyl-containing phenanthrenone unit, was isolated from the culture of Ustilaginoidea virens. Three biogenetically related new metabolites (2-4) were also isolated. Their structures were elucidated by extensive spectroscopic analyses, including the C-13 NMR and electronic circular dichroism (ECD) calculations for the configurational assignment. The biosynthetic pathway for these sorbyl-containing polyketides was proposed. Compound 1 showed pronounced cytotoxicity, and it induced significant cell cycle arrest and apoptosis.