Synthesis, antimycobacterial, antifungal and photosynthesis-inhibiting activity of chlorinated N-phenylpyrazine-2-carboxamides

A series of sixteen pyrazinamide analogues with the -CONH- linker connecting the pyrazine and benzene rings was synthesized by the condensation of chlorides of substituted pyrazinecarboxylic acids with ring-substituted (chlorine) anilines. The prepared compounds were characterized and evaluated for their antimycobacterial and antifungal activity, and for their ability to inhibit photosynthetic electron transport (PET). 6-Chloro-N-(4-chlorophenyl)pyrazine-2-carboxamide manifested the highest activity against Mycobacterium tuberculosis strain H37Rv (65% inhibition at 6.25 μg/mL). The highest antifungal effect against Trichophyton mentagrophytes, the most susceptible fungal strain tested, was found for 6-chloro-5-tert-butyl-N-(3,4-dichlorophenyl)pyrazine-2-carboxamide (MIC=62.5 μmol/L). 6-chloro-5-tert-butyl-N-(4-chlorophenyl)pyrazine-2-carboxamide showed the highest PET inhibition in spinach chloroplasts (Spinacia oleracea L.) chloroplasts (IC50=43.0 μmol/L). For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds as well as their structure-activity relationships are discussed.     

Enzymatic biosensor for the electrochemical detection of 2,4-dinitrotoluene biodegradation derivatives

In this work, we demonstrate for the first time that 4-methyl-5-nitrocatechol (4M5NC) and 2,4,5-trihydroxytoluene (2,4,5-THT), two compounds obtained from the 2,4-DNT biodegradation are recognized by polyphenol oxidase as substrates. An amperometric biosensor is described for detecting these compounds and for evaluating the efficiency of the 2,4-DNT conversion into 4M5NC in the presence of bacteria able to produce the 2,4-DNT-biotransformation. The biosensor format involves the immobilization of polyphenol oxidase into a composite matrix made of glassy carbon microspheres and mineral oil. The biosensor demonstrated to be highly sensitive for the quantification of 4M5NC and 2,4,5-THT. The analytical parameters for 4M5NC are the following: sensitivity of (7.5 ± 0.1) × 10⁵ nAM⁻¹, linear range between 1.0 × 10⁻⁵ and 8.4 × 10⁻⁵ M, and detection limit of 4.7 × 10⁻⁶ M. The sensitivity for the determination of 2,4,5-THT is (6.2 ± 0.6) × 10⁶ nAM⁻¹, with a linear range between 1.0 × 10⁻⁶ and 5.8 × 10⁻⁶ M, and a detection limit of 2.0 × 10⁻⁷. Under the experimental conditions, it was possible to selectively quantify 4M5NC even in the presence of a large excess of 2,4-DNT. The suitability of the biosensor for detecting the efficiency of 2,4-DNT biotransformation into 4M5NC is demonstrated and compared with HPLC-spectrophotometric detection, with very good correlation. This biosensor holds great promise for decentralized environmental testing of 2,4-DNT.     

Cu2+ and Cu+ bathocuproine disulfonate complexes promote the oxidation of the ROS-detecting compound dichlorofluorescin (DCFH)

The water-soluble Cu⁺chelator bathocuproine disulfonate (BCS) is widely used to quantify Cu⁺ or detect Cu⁺ formation in Cu²⁺-initiated oxidation reactions. The dichlorofluorescin (DCFH) assay is commonly used to monitor free radical reactions, reactive oxygen species (ROS), or reactive nitrogen species (RNS). Upon oxidation the non-fluorescent DCFH is converted into the fluorescent compound dichlorofluorescein (DCF). In the present communication we show that the Cu⁺ reagent BCS strongly facilitated the oxidation of DCFH in the presence of Cu²⁺ or Cu⁺. In contrast, 2,2′-dipyridyl (DP), which is also a Cu⁺-complexing reagent, but not as well known and therefore not as commonly used as BCS, did not cause any oxidative modification of DCFH in the presence of Cu²⁺ or Cu⁺. We therefore recommend that DP should be used instead of BCS to complex Cu⁺ in reactions which are initiated by Cu²⁺ and when ROS/RNS are analyzed by the DCFH oxidation assay.     

S,N‐Chelated organotin(IV) compounds containing 6‐phenylpyridazine‐3‐thiolate ligand—structural,antibacterial and antifungal study

A series of tri‐ and diorganotin(IV) compounds containing potentially chelating S,N‐ligand(s) (L^SN, where L^SN is 6‐phenylpyridazine‐3‐thiolate) were prepared and structurally characterized by multinuclear NMR spectroscopy. X‐ray diffraction techniques were used for determination of the structure of compounds containing one [(L^SN)Ph₂SnCl], two [(n‐Bu)₂Sn(L^SN)₂] and the combination of two L^SN and one L^CN [(L^CN)(n‐Bu)Sn(L^SN)₂] (where L^CN is {2‐[(CH₃)₂NCH₂]C₆H₄}‐) ligands. The coordination number of the tin atom varies from five to seven and is dependent on the number of chelating ligands present. The formation of the five‐membered azastanna heterocycle is favored over the formation of four‐membered azastannathia heterocycle in compounds containing both types of ligands. The di‐n‐butyl‐substituted compounds are the most efficient ones in inhibition of growth of yeasts, molds and G⁺ bacteria strains. Copyright © 2011 John Wiley & Sons, Ltd.     

Facile synthesis of two oxocan derivatives using some chemical strategies

There are several studies for the synthesis of oxacycle derivatives using some reagents which require special conditions have been reported. The aim of this study was to synthesize two oxocan derivatives from either imidazole or 2-methylimidazole. The chemical structure was evaluated through both ¹H NMR and ¹³C NMR spectroscopic analysis. The results showed a moderate yielding from oxocan derivatives. It should be mentioned that reagents used in this investigation are not expensive and do not require special conditions for handling.