Screening, Discovery, and Optimization of the Natural Antitubercular Chlorflavonin from a Marine-Derived Fungal Library

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis (Mtb), is still a leading cause of mortality worldwide. Fifty-fungi from a marine-derived fungal library were screened for anti-Mtb activity, and an Aspergillus candidus strain with strong anti-Mtb activity was found. Three known flavones, chlorflavonin (1), dechlorflavonin (2), and bromoflavone (3), were isolated from this fungus. Chlorflavonin and bromoflavone showed inhibitory activity with MIC90 values of 2.6 and 1.2 μM, respectively. In combination with molecular docking, a series of new chlorflavonin derivatives (4–41) were rationally designed and semisynthesized. Three new derivatives substituted with (2)-chlorocinnamate (14), (3)-chlorocinnamate (15), and benzoate (18) at position 2′ showed MIC90 values ranging from 0.7 to 1.0 μM, having the potential to be further explored as antitubercular agents.