Discovery of structurally diverse sesquiterpenoids from Streptomyces fulvorobeus isolated from Elephas maximus feces and their antifungal activities

Thirty-six structurally diverse sesquiterpenoids, including caryolanes (1-12), germacranes (13-16), isodaucane (17), cadinanes (18-22), epicubenols (23, 24), oplopanane (25), pallenanes (26, 27), and eudesmanes (28-36), were isolated from the fermentation broth of Streptomyces fulvorobeus derived from Elephas maximus feces. Pallenane is a kind of rarely reported sesquiterpene with a distinctive C5/C3 bicyclic skeleton and was firstly found from microbial source. The structures of fifteen new compounds (1-4, 13-15, 17, 18, 22, 23, 25-28) were established through detailed spectroscopic data analysis, which included data from experimental and calculated ECD spectra as well as Mosher's reagent derivative method. Compound 34 exhibited moderate antifungal activity against Cryptococcus neoformans and Cryptococcus gattii with MIC values of 50 μg/mL. It effectively inhibited biofilm formation and destroyed the preformed biofilm, as well as hindered the adhesion of Cryptococcus species. The current work would enrich the chemical diversity of sesquiterpenoid family.