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.

A well reproducible and inexpensive preparation of the cyclopropylideneacetates 2 ± 4 has been developed. The key intermediate 2-(1'-mesyloxycyclopropyl)acetic acid (8), produced either from methyl phenylacetate (1) or 3,3-dimethoxypropionate (5-Me) and 3,3-diethoxypropionate (5-Et) in a sequence of Kulinkovich reductive cyclopropanation, mesylation and oxidative cleavage or cleavage and oxidation, respectively, was either converted to the benzyl ester 11b, or chlorinated (brominated) via the in situ formed acid chloride. The a-chloro-12a and a-bromo ester 12b were dehydromesylated by treatment with triethylamine to furnish methyl 2-chloro-2-cyclopropylideneacetate (3-Me) and the 2-bromo analogue 4-Me with an overall yield of 68% (65%, 68%) and 52% (49%, 51%) respectively, starting from 1 (5-Me, 5-Et). The parent benzyl cyclopropylideneacetate 2-Bn was obtained by dehydromesylation of 11b with potassium t-butoxide in t-butyl methyl ether with an overall yield of 60% (57%, 9%) from 1 (5-Me, 5-Et).

Nitazoxanide has antiparasitic and antibiotic activities including activity against Mycobacterium tuberculosis. We prepared and evaluated a set of its analogues to determine the structure–activity relationship, and identified several amide- and urea-based analogues with low micromolar activity against M. tuberculosis in vitro. Pharmacokinetics in the rat suggested a path forward to obtain bioavailable compounds. The series had a good microbiological profile with bactericidal activity in vitro against replicating and nonreplicating M. tuberculosis. Analogues had limited activity against other Gram-positive bacteria but no activity against Gram-negative bacteria. Our studies identified the key liability in this series as cytotoxicity. Future work concentrating on identifying the target(s) could assist in removing activity against eukaryotic cells.

The 2,4-diaminoquinazoline class of compounds has previously been identified as an effective inhibitor of Mycobacterium tuberculosis growth. We conducted an extensive evaluation of the series for its potential as a lead candidate for tuberculosis drug discovery. Three segments of the representative molecule N-(4-fluorobenzyl)-2-(piperidin-1-yl)quinazolin-4-amine were examined systematically to explore structure-activity relationships influencing potency. We determined that the benzylic amine at the 4-position, the piperidine at 2-position and the N-1 (but not N-3) are key activity determinants. The 3-deaza analog retained similar activity to the parent molecule. Biological activity was not dependent on iron or carbon source availability. We demonstrated through pharmacokinetic studies in rats that good in vivo compound exposure is achievable. A representative compound demonstrated bactericidal activity against both replicating and non-replicating M. tuberculosis. We isolated and sequenced M. tuberculosis mutants resistant to this compound and observed mutations in Rv3161c, a gene predicted to encode a dioxygenase, suggesting that the compound may act as a pro-drug.

Keywords:Nitrogen heterocycles / Michael addition / Cycloaddition / 5,6,7,8-Tetrahydro-3H-quinazolin-4-ones Under basic conditions (Et 3 N, dioxane), the aromatic amidines 4 and also S-methylisothiourea 4g cleanly undergo Michael addition to methyl 2-chloro-2-cyclopropylideneacetate (5), followed by intramolecular nucleophilic substitution, cyclopropyl to cyclobutyl ring enlargement, deprotonation and cyclization with elimination of methanol to afford the cyclobutene-annelated pyrimidinones 6 in 43-83 % yield (7 examples). Thermal cyclobutene-ring opening of the latter at 175°C followed by regioselective Diels-Alder cycloaddition with phenyl vinyl sulfone gives the 2-aryl-6-(phenylsulfonyl)-5,6,7,8-tetrahydroquinazolinone derivatives 12 in 39-83 % yield (7 examples). Base-induced elimination of ben-