An efficient protocol for the synthesis of quinoxaline derivatives at room temperature using recyclable alumina-supported heteropolyoxometalates.

We report a suitable quinoxaline synthesis using molybdophosphovanadates supported on commercial alumina cylinders as catalysts. These catalysts were prepared by incipient wetness impregnation. The catalytic test was performed under different reaction conditions in order to know the performance of the synthesized catalysts. The method shows high yields of quinoxaline derivatives under heterogeneous conditions. Quinoxaline formation was obtained using benzyl, o-phenylenediamine, and toluene as reaction solvent at room temperature. The CuH(2)PMo(11)VO(40) supported on alumina showed higher activity in the tested reaction. Finally, various quinoxalines were prepared under mild conditions and with excellent yields.

Quantitative structure-activity relationships of mosquito larvicidal chalcone derivatives.

The mosquito larvicidal activities of a series of chalcones and some derivatives were subjected to a quantitative structure-activity relationship (QSAR) study, using more than a thousand constitutional, topological, geometrical, and electronic molecular descriptors calculated with Dragon software. The larvicidal activity values for 28 active compounds of the series were predicted, showing in general a good approximation to the experimental values found in the literature. Chalcones having one or both electron-rich rings showed high toxicity. However, the activity of chalcones was reduced by electron-withdrawing groups, and this was roughly diminished by derivatization of the carbonyl group. A set of six chalcones being structurally similar to some of the active ones, with a still unknown larvicidal activity, were prepared. Their activity values were predicted by applying the developed QSAR models, showing that two chalcones of such set, both 32 and 34, were expected to be highly active.

Sustainable synthesis of flavonoid derivatives, QSAR study and insecticidal activity against the fall armyworm, Spodoptera frugiperda (Lep.: Noctuidae).

A simple, clean, solvent-free preparation of flavones by the use of a silica-supported Preyssler heteropolyacid as reusable catalyst is described. High selectivity and very good yields (87-94%) were obtained in short reaction times (7-13 min). Bioassays for insecticidal activity against Spodoptera frugiperda were carried out with a set of flavones. Bioassays showed that some of the flavones had moderate insecticidal activity. Quantitative structure-activity relationships were established on the available data with the purpose of predicting the insecticidal activity of a number of structurally related flavones. A relationship between the molecular structure and biological activity is proposed.

A suitable preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines and their ring homologs with a reusable Preyssler heteropolyacid as catalyst.

The preparation of N-sulfonyl-1,2,3,4-tetrahydroisoquinolines, N-sulfonyl-2,3,4,5-tetrahydro-1H-2-benzazepines and N-sulfonyl-1,2,3,4,5,6-hexahydrobenzazocine was catalyzed by a Preyssler heteropolyacid, H(14)[NaP(5)W(30)O(110)], (PA), supported on silica (PASiO(2)40) with excellent yields by means of the Pictet-Spengler reaction of N-aralkylsulfonamides with s-trioxane. The reactions proceed with 0.5 mol% of silica-supported catalyst in toluene at 70°C. The catalyst can be recycled without appreciable loss of the catalytic activity.

QSAR analysis on Spodoptera litura antifeedant activities for flavone derivatives.

We establish useful models that relate experimentally measured biological activities of compounds to their molecular structure. The pED(50) feeding inhibition on Spodoptera litura species exhibited by aurones, chromones, 3-coumarones and flavones is analyzed in this work through the hypothesis encompassed in the Quantitative Structure-Activity Relationships (QSAR) Theory. This constitutes a first necessary computationally based step during the design of more bio-friendly repellents that could lead to insights for improving the insecticidal activities of the investigated compounds. After optimizing the molecular structure of each furane and pyrane benzoderivative with the semiempirical molecular orbitals method PM3, more than a thousand of constitutional, topological, geometrical and electronic descriptors are calculated and multiparametric linear regression models are established on the antifeedant potencies. The feature selection method employed in this study is the Replacement Method, which has proven to be successful in previous analyzes. We establish the QSAR both for the complete molecular set of compounds and also for each chemical class, so that acceptably describing the variation of the inhibitory activities from the knowledge of their structure and thus achieving useful predictive results. The main interest of developing trustful QSAR models is that these enable the prediction of compounds having no experimentally measured activities for any reason. Therefore, the structure-activity relationships are further employed for investigating the antifeedant activity on previously synthesized 2-,7-substituted benzopyranes, which do not pose any measured values on the biological expression. One of them, 2-(alpha-naphtyl)-4H-1-benzopyran-4-one, results in a promising structure to be experimentally analyzed as it has predicted pED(50)=1.162.

Spectroscopic and theoretical study of 2-acetylphenyl-2-naphthoate.

Mid-, far-infrared and Raman vibrational spectra of 2-acetylphenyl-2-naphthoate have been measured at room and low temperatures. The molecule was also analyzed by means of ab initio calculations. The conformational space has been scanned using molecular dynamics and complemented with functional density calculations that optimize the geometry of the lowest energy conformers 2-acetylphenyl-2-naphthoate as obtained in the simulations. The vibrational frequencies and the (1)H and (13)C NMR chemical shifts were assigned using functional density calculations. The theoretical chemical shift values were compared with the experimental ones. The molecular electrostatic potential maps were obtained and analyzed.

QSAR prediction of inhibition of aldose reductase for flavonoids.

We performed a predictive analysis based on quantitative structure-activity relationships (QSAR) of an important property of flavonoids, which is the inhibition (IC(50)) of aldose reductase (AR). The importance of AR inhibition is that it prevents cataract formation in diabetic patients. The best linear model constructed from 55 molecular structures incorporated six molecular descriptors, selected from more than a thousand geometrical, topological, quantum-mechanical, and electronic types of descriptors. As a practical application, we used the obtained QSAR model to predict the AR inhibitory effect of newly synthesized flavonoids that present 2-, 7-substitutions in the benzopyrane backbone.

QSAR modeling of the interaction of flavonoids with GABA(A) receptor.

Experimentally assigned values to binding affinity constants of flavonoid ligands towards the benzodiazepine site of the GABA(A) receptor complex were compiled from several publications, and enabled to perform a predictive analysis based on Quantitative Structure-Activity Relationships (QSAR). The best linear model established on 78 molecular structures incorporated four molecular descriptors, selected from more than a thousand of geometrical, topological, quantum-mechanical and electronic types of descriptors and calculated by Dragon software. An application of this QSAR equation was performed by estimating the binding affinities for some newly synthesized flavonoids displaying 2-,7-substitutions in the benzopyrane backbone which still do not have experimentally measured potencies.