Novel Solution- and Solid-Phase Strategies for the Parallel and Combinatorial Synthesis of Small-Molecular-Weight Compound Libraries

In this account dedicated to '100 years Roche' in CHIMIA, we present some of our strategies towards the synthesis of interesting novel amino-acid-derived building blocks; multigeneration synthesis of thiazole libraries in solution; a novel solid-phase approach towards highly substituted pyrimidines using a novel safety-catch linker principle and a multidirectional cleavage procedure; a versatile solid-phase synthesis of quinazolones taking advantage of the Staudinger phosphorylimine chemistry combined with a novel cyclization and cleavage strategy, and finally a novel solid-phase diketopiperazine synthesis combining the Ugi four-component reaction with a final ring-forming cleavage step

Identification of Morpholino Thiophenes as Novel Mycobacterium tuberculosis Inhibitors, Targeting QcrB

With the emergence of multidrug-resistant strains of <i>Mycobacterium tuberculosis</i> there is a pressing need for new oral drugs with novel mechanisms of action. Herein, we describe the identification of a novel morpholino–thiophenes (MOT) series following phenotypic screening of the Eli Lilly corporate library against <i>M. tuberculosis</i> strain H37Rv. The design, synthesis, and structure–activity relationships of a range of analogues around the confirmed actives are described. Optimized leads with potent whole cell activity against H37Rv, no cytotoxicity flags, and in vivo efficacy in an acute murine model of infection are described. Mode-of-action studies suggest that the novel scaffold targets QcrB, a subunit of the menaquinol cytochrome <i>c</i> oxidoreductase, part of the bc1-aa3-type cytochrome <i>c</i> oxidase complex that is responsible for driving oxygen-dependent respiration

A high-throughput screen against pantothenate synthetase (PanC) identifies 3-biphenyl-4-cyanopyrrole-2-carboxylic acids as a new class of inhibitor with activity against Mycobacterium tuberculosis

The enzyme pantothenate synthetase, PanC, is an attractive drug target in Mycobacterium tuberculosis . It is essential for the in vitro growth of M. tuberculosis and for survival of the bacteria in the mouse model of infection. PanC is absent from mammals. We developed an enzyme-based assay to identify inhibitors of PanC, optimized it for high-throughput screening, and tested a large and diverse library of compounds for activity. Two compounds belonging to the same chemical class of 3-biphenyl-4- cyanopyrrole-2-carboxylic acids had activity against the purified recombinant protein, and also inhibited growth of live M. tuberculosis in manner consistent with PanC inhibition. Thus we have identified a new class of PanC inhibitors with whole cell activity that can be further developed

Novel Solution- and Solid-Phase Syntheses of Heterocyclic Systems

Heterocyclic compounds are an attractive source of screening library structures because they possess varied structural diversity and can exhibit potent biological activity. In this context, we present some of our new and versatile approaches to rapid and efficient syntheses of pharmacologically relevant core structures. These include: combination of both solution- and solid-phase processes in the synthesis of pyrazolo[1,5-a]-[1,3,5]-triazin-4-ones and pyrazolo[1,5-a]-[1,3,5]-triazines; parallel, multi-generation synthesis of highly functionalized heterocyclic compounds in solution; a multi-step synthesis of 2,5-diketopiperazine on solid support taking advantage of a bicyclic ?-lactam scaffold, and a combined solid- and solution-phase synthesis of a new class of 2,4-diaminothiazoles

Novel Solution- and Solid-Phase Syntheses of Heterocyclic Systems

Heterocyclic compounds are an attractive source of screening library structures because they possess varied structural diversity and can exhibit potent biological activity. In this context, we present some of our new and versatile approaches to rapid and efficient syntheses of pharmacologically relevant core structures. These include: combination of both solution- and solid-phase processes in the synthesis of pyrazolo[1,5-a]-[1,3,5]-triazin-4-ones and pyrazolo[1,5-a]-[1,3,5]-triazines; parallel, multi-generation synthesis of highly functionalized heterocyclic compounds in solution; a multi-step synthesis of 2,5-diketopiperazine on solid support taking advantage of a bicyclic ?-lactam scaffold, and a combined solid- and solution-phase synthesis of a new class of 2,4-diaminothiazoles

Prediction of drug penetration in tuberculosis lesions

The penetration of antibiotics in necrotic tuberculosis lesions is heterogeneous and drug-specific, but the factors underlying such differential partitioning are unknown. We hypothesized that drug binding to macromolecules in necrotic foci (or caseum) prevents passive drug diffusion through avascular caseum, a critical site of infection. Using a caseum binding assay and MALDI mass spectrometry imaging of tuberculosis drugs, we showed that binding to caseum inversely correlates with passive diffusion into the necrotic core. We developed a high-throughput assay relying on rapid equilibrium dialysis and a caseum surrogate designed to mimic the composition of native caseum. A set of 279 compounds was profiled in this assay to generate a large data set and explore the physicochemical drivers of free diffusion into caseum. Principle component analysis and modeling of the data set delivered an in silico signature predictive of caseum binding, combining 69 molecular descriptors. Among the major positive drivers of binding were high lipophilicity and poor solubility. Determinants of molecular shape such as the number of rings, particularly aromatic rings, number of sp² carbon counts, and volume-to-surface ratio negatively correlated with the free fraction, indicating that low-molecular-weight nonflat compounds are more likely to exhibit low caseum binding properties and diffuse effectively through caseum. To provide simple guidance in the property-based design of new compounds, a rule of thumb was derived whereby the sum of the hydrophobicity (clogP) and aromatic ring count is proportional to caseum binding. These tools can be used to ensure desirable lesion partitioning and guide the selection of optimal regimens against tuberculosis

Synthesis and Evaluation of the 2-Aminothiazoles as Anti-Tubercular Agents.

The 2-aminothiazole series has anti-bacterial activity against the important global pathogen Mycobacterium tuberculosis. We explored the nature of the activity by designing and synthesizing a large number of analogs and testing these for activity against M. tuberculosis, as well as eukaryotic cells. We determined that the C-2 position of the thiazole can accommodate a range of lipophilic substitutions, while both the C-4 position and the thiazole core are sensitive to change. The series has good activity against M. tuberculosis growth with sub-micromolar minimum inhibitory concentrations being achieved. A representative analog was selective for mycobacterial species over other bacteria and was rapidly bactericidal against replicating M. tuberculosis. The mode of action does not appear to involve iron chelation. We conclude that this series has potential for further development as novel anti-tubercular agents