*2.2. Rifampicin Analogs*

Rifampicin was obtained through the chemical modification of the natural product rifamycin [17]. Derivatives of rifampicin, like rifabutin, were synthesized and found to have favorable properties in terms of compatibility with anti-HIV drugs but could not overcome the cross-resistance with rifampicin [18].

## *2.3. Ethambutol Derivatives*

Increased throughput in chemistry also contributed to finding new leads. A combinatorial library created around ethambutol led to the discovery of a clinical candidate SQ-109 [19,20]. SQ-109 was found to be active even on ethambutol-resistant strains of MTB. SQ109 has been shown to target the Mycobacterial Membrane Protein Large 3 (Mmpl3) [21]. It is interesting to note that ethambutol does not inhibit Mmpl3.
