Unprecedented spirodioxynaphthalenes from the endophytic fungus Phyllosticta ligustricola HDF-L-2 derived from the endangered conifer Pseudotsuga gaussenii

Abstract

Four undescribed palmarumycin-type spirodioxynaphthalenes (phyligustricins A–D) and a known biogenetic precursor (palmarumycin BG1) were isolated from a solid fermentation of Phyllosticta ligustricola HDF-L-2, an endophyte associated with the endangered Chinese conifer Pseudotsuga gaussenii. The structures were elucidated by spectroscopic methods, single-crystal X-ray diffraction analyses, and electronic circular dichroism calculations. Both phyligustricins A and B have an unprecedented spirodioxynaphthalene-derived skeleton containing an extra 4H-furo [3,2-c]pyran-4-one moiety, while phyligustricins C and D are p-hydroxy-phenethyl substituted spirodioxynaphthalenes. The plausible biosynthetic relationships of the isolates were briefly proposed. Phyligustricins C and D and palmarumycin BG1 showed considerable antibacterial activity against Staphylococcus aureus, each with an MIC value of 16 μg/mL. Palmarumycin BG1 displayed significant inhibitory effects against ACL and ACC1, with IC50 values of 1.60 and 8.00 μM, respectively.