Steroids from Toona sureni-derived Endophytic Fungi Stemphylium sp. MAFF 241962 and Their Heme Polymerization Inhibition Activity

Abstract Antimalarial drug resistance is a major cause of the increasing incidence of malaria worldwide, necessitating an urgent demand for the development of new antimalarial drugs. However, the availability of bioactive natural compounds derived from plants is often limited. To address this issue, continuous exploration of bioactive secondary metabolites from endophytic fungi derived from medicinal plants has been recognized as a viable alternative. Therefore, this research aimed to isolate and characterize three ergosteroids, namely isocyathisterol (1), ergosterol-5,8-peroxide (3), cerevisterol (4), and a phytosterol, β-sitosterol (2), from the rice cultures of endophytic fungus Stemphylium sp. MAFF 241962, derived from Toona sureni. Endophytic fungi species were determined using molecular analysis of the internal transcribed region (ITS) of the ribosomal DNA. After comparing the sequence data to the NCBI database using BLAST, endophytic fungi were identified as Stemphylium sp. 241962 with 100% similarity. The chemical structures were elucidated using spectroscopic methods, including 1D and 2D NMR. Antimalarial activities of compounds 1-4 were evaluated using heme polymerization inhibition activity (HPIA) method. The results showed moderate inhibition activities with IC50 values of 7.70 ± 0.11, 9.48 ± 0.09, 7.88 ± 0.10, and 8.36 ± 0.56 mg/mL, respectively, compared to positive control chloroquine diphosphate with IC50 values of 1.59 ± 0.03 mg/mL. Keywords: Steroid, Stemphylium sp., Toona sureni, Antimalarial activity, Heme polymerization inhibition