Factors Affecting the Antimicrobial Activity of Phenols

Design and Synthesis of Highly Active Antimycobacterial Mutual Esters of 2-(2-Isonicotinoylhydrazineylidene)propanoic Acid

The combination of two active scaffolds into one molecule represents a proven approach in drug design to overcome microbial drug resistance. We designed and synthesized more lipophilic esters of 2-(2-isonicotinoylhydrazineylidene)propanoic acid, obtained from antitubercular drug isoniazid, with various alcohols, phenols and thiols, including several drugs, using carbodiimide-mediated coupling. Nineteen new esters were evaluated as potential antimycobacterial agents against drug-sensitive Mycobacterium tuberculosis (Mtb.) H₃₇Rv, Mycobacterium avium and Mycobacterium kansasii. Selected derivatives were also tested for inhibition of multidrug-resistant (MDR) Mtb., and their mechanism of action was investigated. The esters exhibited high activity against Mtb. (minimum inhibitory concentrations, MIC, from ≤0.125 μM), M. kansasii, M. avium as well as MDR strains (MIC from 0.25, 32 and 8 µM, respectively). The most active mutual derivatives were derived from 4-chloro/phenoxy-phenols, triclosan, quinolin-8-ol, naphthols and terpene alcohols. The experiments identified enoyl-acyl carrier protein reductase (InhA), and thus mycobacterial cell wall biosynthesis, as the main target of the molecules that are activated by KatG, but for some compounds can also be expected adjunctive mechanism(s). Generally, the mutual esters have also avoided cytotoxicity and are promising hits for the discovery of antimycobacterial drugs with improved properties compared to parent isoniazid.

Antimicrobial properties of natural phenols and related compounds: obtusastyrene and dihydro-obtusastyrene

Factors influencing the antimicrobial properties of obtusastyrene and dihydro-obtusastyrene were studied. Both of these compounds were soluble in acetone, alcohol, and olive oil. In water, they were soluble at concentrations of 34 and 53 mug/ml, respectively. The minimal inhibitory concentrations against gram-positive bacteria and yeast were below 100 mug/ml. The compounds were not effective against gram-negative bacteria at 200 mug/ml or lower concentrations. With initial populations of cells greater than 10(6)/ml, the concentrations of these compounds required to prevent growth were greater than with lower cell populations. Changing the pH of the growth medium did not decrease the effectiveness of these two compounds in the pH range of 3 through 8. Both obtusastyrene and dihydro-obtusastyrene were rapidly bactericidal to Staphylococcus aureus and Bacillus cereus at 25 mug/ml.

A basic model for the evaluation and prediction of preservative action

basic integrated model for the quantification of preservative action must consider the availability or thermodynamic activity of the biologically effective concentration, μ, of the preservative in the aqueous phase. A derived expression for the total concentration, PT, of preservative (of dissociation constant Ka) degrading by an apparent first order rate constant, k', in an oil/water emulsion (of q volume ratio and k intrinsic partition coefficient of undissociated preservative) needed to maintain a minimum inhibitory concentration μ of free undissociated acid in the aqueous phase at any hydrogen ion concentration [H+] and for any known binding or complexing phenomena (where there are n sites on binding macromolecule Mi and the intrinsic dissociation constant is ki) is PT = μ (f1 × f2 × f3). The binding enhancement factor of μ is

and in many practical instances when μ < Ki it reduces to

The oil/water partition and ionization enhancement factor is f2 = 1 + Ka/[H+] + kq where kq vanishes in the absence of oil. The instability enhancement factor is f3 = ek't. The ultracentrifuge can be used to define operationally the parameters in macromolecular binding and the apparent partition in dispersions, emulsions and solutions. The premises for the use of preservative combinations are critically evaluated and kinetic methods to determine proper choices of response to characterise combined preservative action are recommended.