Evaluation of the DPPH ⋅ free radical scavenging activity of 236 marine microbial metabolites

A total of 236 marine microbial metabolites were evaluated for their DPPH⋅ (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity. Initial assay showed that 27 compounds at 100 µM had radical scavenging activity in different degrees with RSA% values of 53.93–99.00%. Further testing revealed that 13 compounds had potent activity with IC50 values of 4.94–18.64 µM, including peniciphenalenin F (53), asperindopiperazine A (82), asperindopiperazine C (83), 2-deisoprenyl-neoechinulin A (84), dipodazine (85), 20 R,25S-preshamixanthone (100), phthalimidinic acid A (104), 2-hydroxyemodic acid (105), asperthecin (106), talamin A (120), 2-aminobenzamide (146), isodihydroauroglaucin (231), and flavoglaucin (232). Asperindopiperazine C (83), dipodazine (85), 2-hydroxyemodic acid (105), talamin A (120), isodihydroauroglaucin (231), and flavoglaucin (232) were six most active compounds with IC50 values of 4.94–9.86 µM, which were stronger than or equivalent to that of the control ascorbic acid (IC50: 9.56 µM). These identified compounds show promising in vitro radical-scavenging activity and warrant further investigation using complementary antioxidant assays and appropriate cellular or biological models.