Mtb-Selective 5-Aminomethyl Oxazolidinone Prodrugs: Robust Potency and Potential Liabilities

Linezolid is a drug with proven human antitubercular activity whose use is limited to highly drug-resistant patients because of its toxicity. This toxicity is related to its mechanism of action─linezolid inhibits protein synthesis in both bacteria and eukaryotic mitochondria. A highly selective and potent series of oxazolidinones, bearing a 5-aminomethyl moiety (in place of the typical 5-acetamidomethyl moiety of linezolid), was identified. Linezolid-resistant mutants were cross-resistant to these molecules but not vice versa. Resistance to the 5-aminomethyl molecules mapped to an N-acetyl transferase (Rv0133) and these mutants remained fully linezolid susceptible. Purified Rv0133 was shown to catalyze the transformation of the 5-aminomethyl oxazolidinones to their corresponding N-acetylated metabolites, and this transformation was also observed in live cells of Mycobacterium tuberculosis. Mammalian mitochondria, which lack an appropriate N-acetyltransferase to activate these prodrugs, were not susceptible to inhibition with the 5-aminomethyl analogues. Several compounds that were more potent than linezolid were taken into C3HeB/FeJ mice and were shown to be highly efficacious, and one of these (9) was additionally taken into marmosets and found to be highly active. Penetration of these 5-aminomethyl oxazolidinone prodrugs into caseum was excellent. Unfortunately, these compounds were rapidly converted into the corresponding 5-alcohols by mammalian metabolism which retained antimycobacterial activity but resulted in substantial mitotoxicity.

Synthesis and Assessment of Fused β-Carboline Derivatives as Kappa Opioid Receptor Agonists

The synthesis of 5-formyl-6-aryl-6H-indolo[3,2,1-de][1,5] naphthyridine-2-carboxylates by reaction between 1-formyl-9H-β-carbolines and cinnamaldehydes in the presence of pyrrolidine in water with microwave irradiation is described. Pharmacophoric modification of the formyl group offered several new fused β-carboline derivatives, which were investigated for their κ-opioid receptor (KOR) agonistic activity. Two compounds 4 a and 4 c produced appreciable agonist activity on KOR with EC₅₀ values of 46±19 and 134±9 nM, respectively. Moreover, compound-induced KOR signaling studies suggested both compounds to be extremely G-protein-biased agonists. The analgesic effect of 4 a was validated by the increase in tail flick latency in mice in a time-dependent manner, which was completely blocked by the KOR-selective antagonist norBNI. Moreover, unlike U50488, an unbiased full KOR agonist, 4 a did not induce sedation. The docking of 4 a with the human KOR was studied to rationalize the result.

Tuberculosis Drug Discovery: A Decade of Hit Assessment for Defined Targets

More than two decades have elapsed since the publication of the first genome sequence of Mycobacterium tuberculosis (Mtb) which, shortly thereafter, enabled methods to determine gene essentiality in the pathogen. Despite this, target-based approaches have not yielded drugs that have progressed to clinical testing. Whole-cell screening followed by elucidation of mechanism of action has to date been the most fruitful approach to progressing inhibitors into the tuberculosis drug discovery pipeline although target-based approaches are gaining momentum. This review discusses scaffolds that have been identified over the last decade from screens of small molecule libraries against Mtb or defined targets where mechanism of action investigation has defined target-hit couples and structure-activity relationship studies have described the pharmacophore.

Synthesis of N-alkyl pyrroles via decarboxylation/dehydration in neutral ionic liquid under catalyst-free conditions

A catalyst-free benign route toN-alkyl pyrroles by reacting aromatic, heteroaromatic or aliphatic aldehydes with 4-hydroxyproline in neutral ionic liquid under microwave irradiation is presented.