Novel sesquiterpenoids from cultures of the basidiomycete Irpex lacteus

Irlactins A–D (1–4), four novel sesquiterpenoids with a rearranged 6/6 bicyclic system, together with their presumed biosynthetic precursor irlactin E (5), were isolated from cultures of the Irpex lacteus. Their structures were elucidated by means of spectroscopic methods, and the absolute configurations of 1–4 were established by single crystal X-ray diffraction analysis. A hypothetical biogenetic pathway for irlactins A–D (1–4) was proposed.