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 μM) while showing minimal or no cytotoxicity (IC50 > 50 μM). 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.