Analogues of the antibiotic thiolactomycin, with biphenyl-based 5-substituents, were found to have excellent in vitro inhibitory activity against the recombinant Mycobacterium tuberculosis β-ketoacyl-ACP synthase mtFabH condensing enzyme. In particular, 5-(4′-benzyloxy-biphen-4-ylmethyl)-4-hydroxy-3,5-dimethyl-5H-thiophen-2-one exhibited approximately a 4-fold increased potency against this key condensing enzyme involved in M. tuberculosis mycolic acid biosynthesis, compared to thiolactomycin. [Copyright &y& Elsevier]