Tuberculosis: annual update

Synthesis, characterization and in vitro biological evaluation of some novel 1,3,5-triazine-Schiff base conjugates as potential antimycobacterial agents

A series of some novel 1,3,5-triazine-Schiff base conjugates (1-32) have been synthesized and evaluated for their in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv using Alamar Blue assay and the activity expressed as the minimum inhibitory concentration (MIC) in μg/mL. Compounds 4 (4-Methoxy-6-methyl-N-(3,4,5-trimethoxybenzylidene)-1,3,5-triazin-2-amine), 11 (4-Methoxy-6-methyl-N-(2-hydroxy-3-bromo-5-chloro-benzylidene)-1,3,5-triazin-2-amine) and 24 (4-Methoxy-6-methyl-N-(1-(2,5-dihydroxyphenyl)ethylidene)-1,3,5-triazin-2-amine) exhibited a significant activity at 3.125, 6.25 and 6.25μg/mL, respectively, when compared with the antitubercular drugs such as ethambutol (3.125μg/mL), pyrazinamide (6.25μg/mL) and streptomycin (6.25μg/mL) and it could be a potential starting point to develop new lead compounds in the fight against Mycobacterium tuberculosis H37Rv.

Synthesis and anti-tubercular evaluation of 4-quinolylhydrazones

A series of 4-quinolylhydrazones were synthesized and tested against Mycobacterium tuberculosis H37Rv. Preparation of the title compounds was achieved by reaction of 4-quinolylhydrazine and aryl- or heteroaryl-carboxaldehyde. For the most of derivatives interesting antitubercular properties were showed; two compounds (3(2) and 3(25)), identified as the most active, were tested also against Mycobacterium avium.

Synthesis and antitubercular activity of imidazo[2,1-b]thiazoles

A number of selected imidazo[2,1-b]thiazoles entered the screening at the Tuberculosis Antimicrobial Acquisition and Coordinating Facility (TAACF) and one of these compounds, 2-chloro-6-phenylimidazo[2,1-b]thiazole, showed antitubercular activity. On this basis we planned the synthesis of new analogues bearing a substituted ring at the 6 position. For one compound only (2-chloro-6-p-chlorophenylimidazo[2,1-b]thiazole) the 5-nitroso derivative was also prepared. The antitubercular activity of these compounds was compared with the known analogues lacking the chlorine at the 2 position. 5-Nitroso-6-p-chlorophenylimidazo[2,1-b]thiazole showed potent antitubercular activity.

9-Benzylpurines with inhibitory activity against Mycobacterium tuberculosis

9-Benzylpurines with a variety of substituents in the 2-, 6- and/or 8-position have been prepared and screened for antimycobacterial effects. High inhibitory activity against Mycobacterium tuberculosis was found for 9-benzylpurines carrying a phenylethynyl-, trans-styryl or aryl substituents in the 6-position and generally chlorine in the 2-position tends to increase activity.

Antimycobacterial pyrroles: synthesis, anti-Mycobacterium tuberculosis activity and QSAR studies

A number of known antifungal pyrrole derivatives and some newly synthesized compounds (5-33) were tested in vitro against Mycobacterium tuberculosis CIP 103471. The majority of tested compounds were efficient antimycobacterial agents showing MIC values ranging from 0.5 to 32 microg/mL. A 3-D-QSAR study has been performed on these pyrrole derivatives to correlate their chemical structures with their observed inhibiting activity against M. tuberculosis. Due to the absence of information on a putative receptor responsible for this activity, classical quantitative structure-activity relationships (QSAR) and comparative molecular field analysis (CoMFA) have been applied. A model able to well correlate the antimycobacterial activity with the chemical structures of pyrrole derivatives 5-33 has been developed which is potentially helpful in the design of novel and more potent antituberculosis agents. The combination of CoMFA with classical QSAR descriptors led to a better hybrid 3-D-QSAR model, that successfully explains the structure-activity relationships (r2 = 0.86) of the training set. A comparison between the QSAR, CoMFA and mixed QSAR-CoMFA models is also presented. The hybrid model is to be preferred, however, because of its lowest values of the average absolute error of prediction toward a limited external test set.

Accumulation of rifampicin by Mycobacterium aurum, Mycobacterium smegmatis and Mycobacterium tuberculosis

The characteristics of the accumulation of 2 mg/L [(14)C]rifampicin by wild-type strains of Mycobacterium aurum (A(+)), Mycobacterium smegmatis (mc(2)155) and Mycobacterium tuberculosis (H37Rv) were determined. After 10 min exposure M. aurum had accumulated 220 ng rifampicin/mg cells, M. smegmatis had accumulated 120 ng rifampicin/mg cells and M. tuberculosis had accumulated 154 ng rifampicin/mg cells. A steady-state concentration (SSC) of rifampicin was accumulated rapidly by M. aurum and M. tuberculosis within minutes of drug exposure, unlike M. smegmatis, which accumulated rifampicin more slowly. With an increase in the concentration of rifampicin from 0.12 mg/L to 2 mg/L there was an increase in the concentration of rifampicin accumulated by M. tuberculosis, with no detectable loss of viability over the 20 min of the accumulation experiment. With an increase in temperature there was also an increase in the concentration of rifampicin accumulated by M. tuberculosis; between 15 and 30 degrees C the increase was linear. For all three species sub-inhibitory concentrations of ethambutol increased the concentration of rifampicin accumulated. However, both growth and accumulation of rifampicin were lower in the presence of 0.05% Tween 80. Accumulation of rifampicin by M. smegmatis was unaffected by the presence of the proton motive force inhibitor, 2,4-dinitrophenol (1 mM), whether added before or after the addition of rifampicin to the mycobacterial culture. For all three species, the Gram-positive bacterial efflux inhibitor reserpine (20 mg/L) slightly increased the SSC of rifampicin, but the increase was not statistically significant. Addition of glucose to energize a putative efflux pump had little effect on the accumulation of rifampicin in the presence or absence of reserpine for M. tuberculosis; however, for M. aurum and M. smegmatis the reserpine effect was abolished by the addition of glucose. These data suggest that rifampicin may be removed from wild-type mycobacteria by efflux, but that the pump(s) is expressed at low level.

Pyrrolnitrin and related pyrroles endowed with antibacterial activities against Mycobacterium tuberculosis

During development of nitroheterocycles with potential antimycobacterial activities we have tested against Mycobacterium tuberculosis a number of pyrroles strictly related to pyrrolnitrin, an antifungal antibiotic isolated from Streptomyces pyrrocinia. Some of the tested arylpyrrole derivatives and pyrrolnitrin have shown appreciable inhibiting activity against M. tuberculosis and M. avium. SAR studies well correlate antimycobacterial potency with the presence of halogens in the phenyl ring and a nitro group at position 3 of pyrrole.