Differential metabolism of diastereoisomeric diterpenes by Preussia minima, found as endophytic fungus in Cupressus lusitanica

The plant diastereoisomeric diterpenes ent-pimara-8(14)-15-dien-19-oic acid, obtained from Viguiera arenaria, and isopimara-8(14)-15-dien-18-oic acid, isolated from Cupressus lusitanica, were distinctly functionalized by the enzymes produced in whole cell cultures of the fungus Preussia minima, isolated from surface sterilized stems of C. lusitanica. The ent-pimaradienoic acid was transformed into the known 7 beta-hydroxy-ent-pimara-8(14)-15-dien-19-oic acid, and into the novel diterpenes 7-oxo-8 beta-hydroxy-ent-pimara-8(14)-15-dien-19-oic and 7-oxo-9 beta-hydroxy-ent-pimara-8(14)-15-dien-19-oic acids. Isopimara-8(14)-15-dien-18-oic acid was converted into novel diterpenes 11 alpha-hydroxyisopimara-8(14)-15-dien-18-oic acid, 7 beta, 11 alpha-dihydroxyisopimara-8(14)-15-dien-18-oic acid, and 1 beta, 11 alpha-dihydroxyisopimara-8(14)-15-dien-18-oic acid, along with the known 7 beta-hydroxyisopimara-8(14)-15-dien-18-oic acid. All compounds were isolated and fully characterized by 1D and 2D NMR, especially C-13 NMR. The diterpene bioproduct-7-oxo-9 beta-hydroxy-ent-pimara-8(14)-15-dien-19-oicacid is an isomer of sphaeropsidin C, a phytotoxin that affects cypress trees produced by Shaeropsis sapinea, one of the main phytopathogen of Cupressus. The differential metabolism of the diterpene isomers used as substrates for biotransformation was interpreted with the help of computational molecular docking calculations, considering as target enzymes those of cytochrome P450 group.