Neocucurins A and B, two novel rearranged diterpenes from marine-derived fungus Neocucurbitaria unguis-hominis

Abstract

Neocucurins A and B were isolated from Neocucurbitaria unguis-hominis FS685, which is a marine derivative fungus collected from the South China Sea. Neocucurin A is a diterpene with a unique 5/6/6/9 tetracyclic system, while neocucurin B features the characteristic of bicyclo[8.3.1]tetradeca core skeleton, which is rearranged from the phomactin diterpene. The structures of them were fully characterized on the basis of extensive spectroscopic analysis, and their absolute configurations were determined by X-ray diffraction. A plausible biogenetic pathway involving an intriguing Diels–Alder cycloaddition and pinacol rearrangement as the key chemical transformation is proposed to account for probable biosynthesis. Moreover, neocucurins A and B were evaluated for in vitro cytotoxicity and antimicrobial activity.