Eremophilane Sesquiterpenoids with Antibacterial and Anti-inflammatory Activities from the Endophytic Fungus Septoria rudbeckiae

Fourteen
eremophilane sesquiterpenoids (1–14), including nine new congeners, septoreremophilanes A–I
(1–9), together with three known
sesquiterpenes (15–17), two known
tetralone derivatives (18, 19), and two
known cholesterol analogues (20, 21), were
isolated from the endophytic fungus Septoria rudbeckiae. Compounds 1–6 and 7a belong to the family of the highly oxygenated eremophilane sesquiterpenoids
with a 6/6/5 tricyclic system and bearing a hemiacetal moiety. The
inhibitions of all metabolites against eight bacteria were estimated in vitro, and nine new metabolites (1–9) were tested for antineuroinflammatory activity. Notably,
the effects of 4 against Pseudomonas syringae pv. actinidae and 20 against Bacillus cereus displayed potent inhibitory, with
the MIC values of 6.25 and 6.25 μM, respectively.
Further, scanning electron microscopy analyses indicated that 4 and 20 were to change the outer configuration
of bacterial cells, respectively, and the investigations demonstrated
that 4 and 20 may act as potential structure
templates for the development of the agrochemical bactericides. Additionally,
compound 6 displayed potent inhibition of NO generation
in lipopolysaccharide-induced BV-2 microglial cells (IC50 = 12.0 ± 0.32 μM), and the conceivable
anti-inflammatory mechanisms implicated were also investigated by
molecular docking. Thus, the bioactive metabolites of the strain S. rudbeckiae may serve as a novel resource to be
developed.