3'-bromo analogues of pyrimidine nucleosides as a new class of potent inhibitors of Mycobacterium tuberculosis

Tuberculosis (TB) is a major health problem worldwide. We herein report a new class of pyrimidine nucleosides as potent inhibitors of Mycobacterium tuberculosis (M. tuberculosis). Various 2'- or 3'-halogeno derivatives of pyrimidine nucleosides containing uracil, 5-fluorouracil, and thymine Bases were synthesized and evaluated for antimycobacterial activities. Among the compounds tested, 3'-bromo-3'-deoxy-arabinofuranosylthymine (33) was the most effective antituberculosis agent in the in vitro assays against wild-type M. tuberculosis strain (H37Ra) (MIC(50) = 1 microg/mL) as well as drug-resistant (H37Rv) (rifampicin-resistant and isoniazid-resistant) strains of M. tuberculosis (MIC(50) = 1-2 microg/mL). Compound 33 also inhibited intracellular M. tuberculosis in a human monocytic cell line infected with H37Ra, demonstrating higher activity against intramacrophagic mycobacteria (80% reduction at 10 microg/mL concentration) than extracellular mycobacteria (75% reduction at 10 microg/mL concentration). In contrast, pyrimidine nucleosides possessing 5-fluorouracil base were weak inhibitors of M. tuberculosis. No cytotoxicity was found up to the highest concentration of compounds tested (CC(50) > 100-200 microg/mL) against a human cell line. Overall, these encouraging results substantiate the potential of this new class of compounds as promising antituberculosis agents.