Thiolactomycin

β-Ketoacyl-ACP synthases (KAS) are key enzymes involved in the type II bacterial fatty acid biosynthesis (FASII) pathway and are putative targets for antibacterial discovery. Several natural product KAS inhibitors have previously been reported, including thiolactomycin (TLM), which is produced by Nocardia spp. Here we describe the synthesis and characterization of optically pure 5R-thiolactomycin (TLM) analogues that show improved whole cell activity against bacterial strains including methicillin-resistant Staphylococcus aureus (MRSA) and priority pathogens such as Francisella tularensis and Burkholderia pseudomallei. In addition, we identify TLM analogues with in vivo efficacy against MRSA and Klebsiella pneumoniae in animal models of infection.

Tuberculosis (TB) is a leading infectious disease which kills a huge number of people every year over a decade, caused by Mycobacterium tuberculosis. The conventional drugs in the market are no longer effective due to the increasing mycobacterial resistance to antibiotics. Hence, the need of finding efficient drugs to solve this multiple drug resistant factor is becoming an immediate issue. The first-line drugs in current practice for the treatment of TB emphasize on mycolic acid, which protects the bacteria from an immune response generated by the host. A key enzyme involved in this mycolic acid biosynthesis, M. tuberculosis beta-ketoacyl-ACP synthase A (MTB-KasA) is a prime candidate in this study. Thiolactomycin is a natural product inhibitor has shown good inhibitory activity against MTB-KasA. Hence, several thiolactomycin derivatives collected from the literature were taken for absorption, distribution, metabolism, excretion and toxicity prediction, molecular docking and molecular dynamics simulation studies with MTB-KasA. The in silico drug designing methods used in this study suggests that the thiolactomycin derivatives are having a better binding activity against MTB-KasA and among them the ligand C14 is identified as a promising lead molecule to inhibit multidrug resistance of tuberculosis by showing a long time binding activity.

Following the in vivo investigation of thiotetronate assembly in Lentzea sp. and in S. thiolactonus NRRL 15439 (Havemann et al., Chem. Commun., 2017, DOI: 10.1039/c6cc09933e), the minimal set of genes required for thiolactomycin production was determined through heterologous expression and the mechanism for polyketide assembly was established in vitro through incubation of recombinant TlmB with its substrates in the presence of either nonhydrolysable or hydrolysable chemical probes. The results presented here constitute unequivocal evidence of enzymatic processing by an unusual iterative polyketide synthase.