Ana N. Santiago

New Synthesis and Biological Evaluation of Benzothiazole Derivates as Antifungal Agents

In search of new antifungal agrochemicals that could replace commercially available, aryl-2-mercaptobenzothiazoles were synthesized. They were prepared by two methodologies, using both photostimulated reaction and microwave assisted reaction. These reactions took place without the use of metallic catalyst by a one-pot procedure with excellent yields (70-98%). Synthesized compounds were evaluated for fungal growth inhibition against Botrytis cinerea. Most of the compounds have an excellent antifungal activity, and three of these showed a superior inhibitory effect to commercial fungicide Triadimefon. IC50 values observed for 2-(phenylthio)benzothiazole, 2-(2-chlorophenylthio)benzothiazole, and 2-(3-chlorophenyl thio)benzothiazole were 0.75, 0.69, and 0.65 μg mL(-1), respectively.

Strain energy effect on the reactivity of bridgehead halides in electron transfer reactions

Abstract We here report MNDO and AM1 calculations for halobridgehead compounds which indicate that an increase in their angular strain is aoocmpanied by more negative reduction potentials as measured through their LUMO energies. The theoretically predicted reactivity agrees with that determined experimentally. The dissociative or non-dissociative nature of the electron capture reaction for the compounds is estimated through the localization of the corresponding radical anion intermediates as minimum of the potential surfaces. Our calculations indicate that for bridgehead chlorides, which lead to pyramidal radicals, the electron transfer is a non-dissociative step, while for t-butyl chloride, the process is dissociative leading to a planar t-butyl radical. The presence of a substituent that lowers the LUMO of the halobridgehead compounds increases their reactivity in ET reactions. This effect is explained through an orbital mixing of the molecular orbitals involved in the ET process.

Selective and eco-friendly procedures for the synthesis of benzimidazole derivatives. The role of the Er(OTf)3 catalyst in the reaction selectivity

An improved and greener protocol for the synthesis of benzimidazole derivatives, starting from o-phenylenediamine, with different aldehydes is reported. Double-condensation products were selectively obtained when Er(OTf)3 was used as the catalyst in the presence of electron-rich aldehydes. Conversely, the formation of mono-condensation products was the preferred path in absence of this catalyst. One of the major advantages of these reactions was the formation of a single product, avoiding extensive isolation and purification of products, which is frequently associated with these reactions. Theoretical calculations helped to understand the different reactivity established for these reactions. Thus, we found that the charge density on the oxygen of the carbonyl group has a significant impact on the reaction pathway. For instance, electron-rich aldehydes better coordinate to the catalyst, which favours the addition of the amine group to the carbonyl group, therefore facilitating the formation of double-condensation products. Reactions with aliphatic or aromatic aldehydes were possible, without using organic solvents and in a one-pot procedure with short reaction time (2–5 min), affording single products in excellent yields (75–99%). This convenient and eco-friendly methodology offers numerous benefits with respect to other protocols reported for similar compounds.

Synthesis and Evaluation of Phytotoxicity of Disugran Analogues

Fil: Basso, Silvana M.. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones en Fisico-quimica de Cordoba. Universidad Nacional de Cordoba. Facultad de Ciencias Quimicas. Instituto de Investigaciones en Fisico-quimica de Cordoba; Argentina

Determination of Volatile Organic Compounds in Andean Tomato Landraces by Headspace Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry

Fil: Cortina, Pablo Ramiro. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones en Fisico-quimica de Cordoba. Universidad Nacional de Cordoba. Facultad de Ciencias Quimicas. Instituto de Investigaciones en Fisico-quimica de Cordoba; Argentina

Study of the distribution of dichlorobenzenes in sediment and water of Suquia River basin (Cordoba-Argentina) by an optimised SPME-GC-MS procedure

Three dichlorobenzene isomers (DCBs) were monitored in water and sediment from the Suquia River basin by Solid Phase Microextraction (HS-SPME), coupled to Gas Chromatography?Mass Spectrometry (GC?MS). DCBs were not detected in water or sediments corresponding to the upper basin. Pollution with DCBs became evident when the river flows through small cities. As expected, Cordoba city causes the most severe pollution, presenting up to 764.7 µg kg−1 DW DCBs in the sediment of urban areas. Results show that DCBs mainly originate in domestic activities, reaching the river by non-point sources such as urban run-off or sewage discharge, resulting in a widespread distribution in the basin. The high level of DCBs found in sediments involves absorption of these xenobiotics in the natural organic matter of sediments. This organic layer could be responsible for transporting DCBs downstream from their discharge, thus spreading the pollution throughout the basin.

Regioselectivity of methyl chlorobenzoate analogues with trimethylstannyl anions by radical nucleophilic substitution: theoretical and experimental study

Reactions of methyl 2,5-dichlorobenzoate, methyl 4-chlorobenzoate, methyl 2-chlorobenzoate and methyl 3-chlorobenzoate with Me3Sn− ions gave the corresponding substitution products by an SRN1 mechanism. Competition experiments showed that the relative reactivity of chlorine as the leaving group with respect to the ester group in methyl chlorobenzoate is para ≥ ortho ≫ meta toward Me3Sn− ions. Theoretical studies were able to explain the observed reactivity on the basis of the energetic properties of the transition states of the radical anions formed in these reactions.

Reactions of halonorbornane and oxo-substituted derivatives with different anions by the electron transfer mechanism; redox catalysis in stabilized radicals

Reactions of 2-bromo-, 2-chloronorbornane, 3-chloronorbornan-2-one and 3-bromocamphor with Me3Sn−, Ph2P− or PhS− ions were studied by an SRN1 mechanism in liquid ammonia or DMSO. The results show that substrates having a carbonyl group facilitate electron transfer reactions, which are impeded in the absence of such a group. However, when the free radical formed is stabilized by conjugation, the coupling reaction decreases, causing a concomitant increase in the reduction product. Theoretical studies explain the observed reactivity on the basis of a mechanism involving reductive cleavage as a function of the π–σ interactions.

Reactivity of endo-3-bromocamphor with sulfur-centered nucleophiles by an electron transfer mechanism. Electrophilic behaviour of the 3-camphoryl radical

The photostimulated reaction of arylthiolate ions with endo-3-bromocamphor produced both reduction and substitution products. The pK(a) and proton affinities of the conjugated acids were found to be good indicators of the reactivity.

Reactions of 1-haloadamantanes and ethylmercury chloride with nitronate anions by the SRN1 mechanism

Secondary or tertiary nitro compounds can be easily obtained by photostimulated reaction of the anions corresponding to primary or secondary nitroalkanes with either 1-iodoadamantane (1-AdI) or ethylmercury chloride (EtHgCl) by the SRN1 mechanism. Only 1-AdI requires the presence of the enolate anion of acetone as an entrainment reagent. The procedure works well with the nitroanions derived from 1-nitropentane, nitroethane or 6-nitrohex-1-ene, but with 2-nitropropane ion the outcome depends on the substrate and solvent.