Crepidamycins A–E, pyranonaphthoquinones from endophytic Streptomyces sp. MG-F-1 of Dendrobium crepidatum by the co-culture strategy

On the basis of the co-culture strategy, five previously undescribed S-bridged pyranonaphthoquinones, crepidamycins A–E (1–5) and five known analogues (6–10) were isolated from a medicinal plant endophytic Streptomyces sp. MG-F-1 in Dendrobium crepidatum with Bacillus cereus MG-1. The structures and absolute configurations of 1–5 were elucidated by the interpretation of data from detailed spectroscopic analysis and electronic circular dichroism spectra, together with consideration of the biogenetic origins. Interestingly, these previously undescribed compounds were only found in the co-cultures and absent from the pure culture controls. Compounds 1–10 were assayed for their anti-inflammatory potential using LPS-stimulated RAW264.7 cells, of which compound 4 showed strong nitric oxide inhibitory effect with an IC₅₀ of 0.22 ± 0.16 μM. The results of extracellular acidification rate and molecular docking suggest that it may play a role by regulating PKM2-mediated glycolysis.