We herein report a new category of 5-substituted pyrimidine nucleosides as potent inhibitors of mycobacteria. A series of 5-alkynyl derivatives of 2'-deoxyuridine (1-8), 2'-deoxycytidine (9-14), uridine (15-17), and 2'-O-methyluridine (18, 19) were synthesized and evaluated for their antimycobacterial activity in vitro. 5-Decynyl, 5-dodecynyl, and 5-tetradecynyl derivatives showed the highest antimycobacterial potency against M. bovis and M. avium, with the 2'-deoxyribose derivatives being more effective than the ribose analogues. Nucleosides bearing short alkynyl side chains 5-ethynyl, 5-propynyl, 5-pentynyl, and 5-heptynyl were mostly not inhibitory. Incorporation of a phenylethynyl function at the 5-position diminished the antimicrobial effect. Furthermore, related bicyclic analogues (20-24) were devoid of antimycobacterial activity, indicating that an acyclic side chain at the C-5 position of the pyrimidine ring is essential for potent activity. Compounds 1-17 were synthesized by the Pd-catalyzed coupling reactions of respective alkynes with 5-iodo derivatives of 2'-deoxyuridine, 2'-deoxycytidine, and uridine. Intramolecular cyclization of 1 and 3-6 in the presence of Cu afforded the corresponding bicyclic compounds 20-24. The investigated nucleosides are recognized here for the first time to be potent inhibitors of mycobacteria. This class of compounds could be of interest for lead optimization as antimycobacterial agents.

The prevalence of tuberculosis (TB) and mutidrug-resistant tuberculosis (MDR-TB) has been increasing, leading to serious infections, high mortality, and a global health threat. Here, we report the identification of a novel class of dideoxy nucleosides as potent and selective inhibitors of Mycobacterium bovis, Mycobacterium tuberculosis, and drug-resistant Mycobacterium tuberculosis. A series of 5-acetylenic derivatives of 2',3'-dideoxyuridine (3-8) and 3'-fluoro-2',3'-dideoxyuridine (22-27) were synthesized and tested for their antimycobacterial activity against M. bovis, M. tuberculosis, and M. avium. 2',3'-Dideoxyuridine possessing 5-decynyl, 5-dodecynyl, 5-tridecynyl, and 5-tetradecynyl substituents (4-7) exhibited the highest antimycobacterial activity against all three mycobacteria. In contrast, in the 3'-fluoro-2',3'-dideoxyuridine series, a 5-tetradecynyl analogue (26) displayed the most potent activity against these mycobacteria. Among other derivatives, 5-bromo-2',3'-dideoxycytidine (11), 5-methyl-2',3'-dideoxycytidine (12), and 5-chloro-4-thio-2',3'-dideoxyuridine (19) exhibited modest inhibition of M. bovis and M. tuberculosis. In the series of dideoxy derivatives of adenosine, guanosine, and purines, 2-amino-6-mercaptoethyl-9-(2,3-dideoxy-beta-d-glyceropentofuranosyl)purine (32) and 2-amino-4-fluoro-7-(2,3-dideoxy-beta-d-glyceropentofuranosyl)pyrrolo[2,3-d]pyrimidine (35) were the most efficacious against M. bovis and M. tuberculosis, and M. avium, respectively.

A new class of 5-(1-cyanamido-2-haloethyl)-2′-deoxyuridines (4-6) and arabinouridines (7, 8) were synthesized by the regiospecific addition of halogenocyanamides (X-NHCN) to the 5-vinyl substituent of the respective 5-vinyl-2′-deoxyuridine (2) and 2′-arabinouridine (3). Reaction of 2 with sodium azide, ceric ammonium nitrate, and acetonitrile-methanol or water afforded the 5-(1-hydroxy-2-azidoethyl)-( 10) and 5-(1-methoxy-2-azidoethyl)-2′-deoxyuridines (11). In vitro antiviral activities against HSV-1-TK + (KOS and E-377), HSV-1-TK -, HSV-2, VZV, HCMV, and DHBV were determined. Of the newly synthesized compounds, 5-(1-cyanamido-2-iodoethyl)-2′-deoxyuridine (6) exhibited the most potent anti-HSV-1 activity, which was equipotent to acyclovir and superior to 5-ethyl-2′-deoxyuridine (EDU). In addition, it was significantly inhibitory for thymidine kinase deficient strain of HSV-1 (EC 50 ) 2.3-15.3 µM). The 5-(1cyanamido-2-haloethyl)-2′-deoxyuridines (4-6) all were approximately equipotent against HSV-2 and were ∼1.5and 15-fold less inhibitory for HSV-2 than EDU and acyclovir, respectively. Compounds 4-6 were all inactive against HCMV but exhibited appreciable antiviral activity against VZV. Their anti-VZV activity was similar or higher to that of EDU and approximately 5-12-fold lower than that of acyclovir. The 5-(1-cyanamido-2-haloethyl)-(7,8) analogues of arabinouridine were moderately inhibitory for VZV and HSV-1 (strain KOS), whereas compounds 10 and 11 were inactive against herpes viruses. Compounds 5 and 6 also demonstrated modest anti-hepatitis B virus activity against DHBV (EC 50 ) 19.9-23.6 µM). Interestingly, the related 5-(1-azido-2-bromoethyl)-2′-deoxyuridine (1n) analogue proved to be markedly inhibitory to DHBV replication (EC 50 ) 2.6-6.6 µM). All compounds investigated exhibited low host cell toxicity to several stationary and proliferating host cell lines as well as mitogen-stimulated proliferating human T lymphocytes.

Tuberculosis (TB) has become an increasing problem since the emergence of human immunodeficiency virus and increasing appearance of drug-resistant strains. There is an urgent need to advance our knowledge and discover a new class of agents that are distinct than current therapies. Antimycobacterial activities of several 5-alkyl, 5-alkynyl, furanopyrimidines and related 2'-deoxynucleosides were investigated against Mycobacterium tuberculosis. Compounds with 5-arylalkynyl substituents (23-26, 33, 35) displayed potent in vitro antitubercular activity against Mycobacterium bovis and Mycobacterium tuberculosis. The in vivo activity of 5-(2-pyridylethynyl)-uracil (26) and its 2'-deoxycytidine analogue, 5-(2-pyridylethynyl)-2'-deoxycytidine (35), was assessed in BALB/c mice infected with M. tuberculosis (H37Ra). Both compounds 26 and 35 given at a dose of 50 mg/kg for 5 weeks showed promising in vivo efficacy in a mouse model, with the 2'-deoxycytidine derivative being more effective than the uracil analogue and a reference drug d-cycloserine. These data indicated that there is a significant potential in this class of compounds.

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