Investigation of (S)-(-)-Acidomycin: A Selective Antimycobacterial Natural Product That Inhibits Biotin Synthase

The synthesis, absolute stereochemical configuration, complete biological characterization, mechanism of action and resistance, and pharmacokinetic properties of (S)-(-)-acidomycin are described. Acidomycin possesses promising antitubercular activity against a series of contemporary drug susceptible and drug-resistant M. tuberculosis strains (minimum inhibitory concentrations (MICs) = 0.096-6.2 mu M) but is inactive against nontuberculosis mycobacteria and Gram-positive and Gram-negative pathogens (MICs > 1000 mu M). Complementation studies with biotin biosynthetic pathway intermediates and subsequent biochemical studies confirmed acidomycin inhibits biotin synthesis with a K-i of approximately 1 mu M through the competitive inhibition of biotin synthase (BioB) and also stimulates unproductive cleavage of S-adenosyl-L-methionine (SAM) to generate the toxic metabolite 5'-deoxyadenosine. Cell studies demonstrate acidomycin selectively accumulates in M. tuberculosis providing a mechanistic basis for the observed antibacterial activity. The development of spontaneous resistance by M. tuberculosis to acidomycin was difficult, and only low-level resistance to acidomycin was observed by overexpression of BioB. Collectively, the results provide a foundation to advance acidomycin and highlight BioB as a promising target.