Effect of substitution on the antimycobacterial activity of 2-(substituted benzyl)sulfanyl benzimidazoles, benzoxazoles, and benzothiazoles--a quantitative structure-activity relationship study.

A set of 1160 minimum inhibitory concentration (MIC) values evaluating effect of substitution on the antimycobacterial activity of the previously published 2-(substituted benzyl)sulfanyl benzimidazoles, benzoxazoles, and benzothiazoles has been analyzed by the methods of multidimensional analysis (exploratory analysis, 2D-nonlinear mapping (NLM), principal component analysis (PCA), factor analysis (FA), multiple linear regression (MLR)). The antimycobacterial activity of 2-(subst. benzyl)sulfanyl derivatives of benzimidazole (BIM), 5-methylbenzimidazole (5-Me-BIM), benzoxazole (BOZ), and benzothiazole (BTZ) increased in the order of BTZ<BOZ~BIM<5-Me-BIM. The sensitivity of particular strains towards these compounds decreased in the order of Mycobacterium kansasii 6509/96, M. avium My 330/88, M. kansasii My 235/80, and M. tuberculosis My 331/88. In general, derivatives with 3-CSNH(2), 2,4-(NO(2))(2), 4-CSNH(2), 3,5-(NO(2)), and partially 4-NO(2) substituents possess the highest antimycobacterial activity. The effect of substitution was also described quantitatively with good correlation factor R of 0.79-0.88. The log MIC values depended with a negative slope on the Hammett substituent constants σ or molar refractions MR and, for the given set of substituents, were dominantly raised with increasing log P value and partially lowered with (log P)(2) or σ×Δ log P. The derivatives featuring high polarizability, low lipophilicity and electron-withdrawing substituents showed the highest antimycobacterial activity. The dependence on the steric substituent constant v was not statistically significant and, therefore, the ortho effect was most probably not important.