Antibacterial 3,6-Disubstituted 4-Hydroxy-5,6-dihydro-2H-pyran-2-ones from Serratia plymuthica MF371-2.

Bioassay-guided fractionation of culture extracts of Serratia plymuthica strain MF371-2 resulted in the isolation of two new antibacterial compounds with potent activity against Gram-positive bacteria, including Staphylococcus aureus LMG 15975 (MRSA). A spectroscopic investigation, in combination with synthesis, enabled the characterization of the compounds as 3-butyryl-4-hydroxy-6-heptyl-5,6-dihydro-2H-pyran-2-one (plymuthipyranone A, 1) and 3-butyryl-4-hydroxy-6-nonyl-5,6-dihydro-2H-pyran-2-one (plymuthipyranone B, 2). The MIC values for 1 and 2 against S.

The furan-osteroid viridiol.

The asymmetric unit of the title compound, C20H18O6 (systematic name: 1β,3β-dihy-droxy-2β-meth-oxyfuro[4',3',2':4,5,6]-18-norandrosta-8,11,13-triene-7,17-dione), a dihydro derivative of the fungal steroid viridin, contains two mol-ecules with similar conformations. The rings bearing the hy-droxy groups adopt boat conformations. The absolute structure was assigned based on the known chirality of a precursor compound.

Viridin-like steroids from Hymenoscyphus pseudoalbidus.

Three furanosteroids were isolated from the ash dieback causing fungus Hymenoscyphus pseudoalbidus along with the known compounds viridiol and demethoxyviridiol. The compounds were characterized by 1D and 2D NMR spectroscopy, LC-HRMS and polarimetry.

B-norsteroids from Hymenoscyphus pseudoalbidus.

Two viridin-related B-norsteroids, B-norviridiol lactone (1) and B-norviridin enol (2), both possessing distinct unprecedented carbon skeletons, were isolated from a liquid culture of the ash dieback-causing fungus Hymenoscyphus pseudoalbidus. Compound 2 was found to degrade to a third B-norsteroidal compound, 1β-hydroxy-2α-hydro-asterogynin A (3), which was later detected in the original culture. The proposed structure of 1 is, regarding connectivity, identical to the original erroneous structure for TAEMC161, which was later reassigned as viridiol.