Chermesins A–D: Meroterpenoids with a Drimane-Type Spirosesquiterpene Skeleton from the Marine Algal-Derived Endophytic Fungus <i>Penicillium chermesinum</i> EN-480

Chermesins A–D (1–4), four
new spiromeroterpenoids containing a drimane-type sesquiterpene skeleton,
were isolated and identified from the culture extract of Penicillium
chermesinum EN-480, an endophytic fungus obtained from the
inner tissue of the marine red alga Pterocladiella tenuis. The structures of these new spiromeroterpenoids were elucidated
based on detailed spectroscopic analyses, and their absolute configurations
were confirmed by single-crystal X-ray diffraction experiments and
by ECD data. This is the first report of the crystal structures of
spiromeroterpenoids that contain a drimane-type sesquiterpene skeleton
with a rare cyclohexa-2,5-dienone unit, which resulted in the unambiguous
assignment of their relative and absolute configurations. Compounds 1 and 2 exhibited antibacterial activity against
the opportunistic pathogen Micrococcus luteus, with
an MIC value of 8 μg/mL.