Novel Antifungal Pyridine Alkaloids from Endophytic Fungus Penicillium citrinum VDL118

Three novel alkaloids, penicitrioids A–C (1–3), and two known compounds (4–5) were isolated from the ethyl acetate (EtOAc) extract of the solid fermentation ofPenicillium citrinumVDL118, an endophytic fungus harbored in the leaves ofVaccinium dunalianumWight (Ericaceae), a perennial evergreen shrub native to the southwestern regions of China, Myanmar, and Vietnam. Compounds1and2are novel pyridine alkaloids characterized by an unprecedented dihydrofuro[3,4-c]pyridine core, while3features a distinct pyrrolo[3,4-c]pyridine framework. Their structures were unambiguously established by comprehensive spectroscopic analysis and electronic circular dichroism (ECD) calculations. In vitro antifungal assays revealed that compounds1–5exhibited moderate to potent inhibitory effects against five tested phytopathogenic fungi, with minimum inhibitory concentrations (MICs) ranging from 3.1 to 100 μg/mL. Notably, four of them (1–4) displayed broad-spectrum and potent activity againstGloeophyllum trabeum,Coriolus versicolor,Fusarium solani, andBotrytis cinerea, with MIC values as low as 3.1–12.5 μg/mL. Furthermore, a plausible biosynthetic pathway for compounds1–3was proposed.