Penibruguieramine A, a Novel Pyrrolizidine Alkaloid from the Endophytic Fungus <i>Penicillium</i> sp. GD6 Associated with Chinese Mangrove <i>Bruguiera gymnorrhiza</i>

A novel pyrrolizidine alkaloid, penibruguieramine A (1), characterized by an unprecedented 1-alkenyl-2-methyl-8-hydroxymethylpyrrolizidin-3-one skeleton, was isolated from the endophytic fungus Penicillium sp. GD6, associated with the Chinese mangrove Bruguiera gymnorrhiza. The absolute configuration of penibruguieramine A (1) was established by TDDFT ECD calculations of the vacuum and solution conformers, exploiting the transitions of the lactam chromophore. A plausible pathway for its biosynthesis has been proposed.