Efficient Mutasynthesis of "Non-Natural" Antitubercular Ilamycins with Low Cytotoxicity

Ilamycins are a type of cyclopeptide exhibiting potent antitubercular and cytotoxic activities, which make them promising leads for antitubercular and antitumor drugs with unique mechanisms. Mutasynthesis, a strategy utilized to generate natural product analogues by intercepting the biosynthesis of natural products with analogues of biosynthetic precursors, offers a distinct advantage in the eco-friendly and powerful synthesis of "non-natural" natural products. This study developed the mutasynthesis of "non-natural" ilamycins by constructing three genetically engineered strains. Feeding four types of tyrosine-derived mutasynthons to two biosynthetically simplified mutants resulted in the production of 18 new ilamycin analogues (7-24), including 16 halogenated and dinitro-containing ilamycin variants (7-22), along with two previously unreported ilamycin congeners (23 and 24). Most of the generated compounds, particularly the halogenated ilamycins (13, 16-18), exhibited potent antitubercular activity (MICs ca. 0.30 mu M) while showing minimal or no cytotoxicity (IC50 > 50 mu M). Furthermore, the bromine-containing ilamycin derivatives (16-18) demonstrated enhanced antitubercular activity and lower cytotoxicity compared to those with chlorine, fluorine, or nitro groups, making them promising candidates for further investigation in antitubercular drug development.