| Summary: | A chemical study of the ethyl acetate (EtOAc) extract from the deep-sea-derived fungus <i>Penicillium</i> <i>thomii</i> YPGA3 led to the isolation of a new austalide meroterpenoid (<b>1</b>) and seven known analogues (<b>2</b>−<b>8</b>), two new labdane-type diterpenoids (<b>9</b> and <b>10</b>) and a known derivative (<b>11</b>). The structures of new compounds <b>1</b>, <b>9</b>, and <b>10</b> were determined by comprehensive analyses via nuclear magnetic resonance (NMR) and mass spectroscopy (MS) data. The absolute configurations of <b>1</b>, <b>9</b>, and <b>10</b> were determined by comparisons of experimental electronic circular dichroism (ECD) with the calculated ECD spectra. Compound <b>1</b> represented the third example of austalides bearing a hydroxyl group at C-5 instead of the conserved methoxy in other known analogues. To our knowledge, diterpenoids belonging to the labdane-type were discovered from species of <i>Penicillium</i> for the first time. Compound <b>1</b> showed cytotoxicity toward MDA-MB-468 cells with an IC<sub>50</sub> value of 38.9 μM. Compounds <b>2</b> and <b>11</b> exhibited inhibition against α-glucosidase with IC<sub>50</sub> values of 910 and 525 μM, respectively, being more active than the positive control acarbose (1.33 mM).
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