198,896 research outputs found
Carcinogenicity prediction of noncongeneric chemicals by augmented top priority fragment classification
No full textCarcinogenicity prediction is an important process that can be performed to cut down experimental costs and save animal lives. The current reliability of the results is however disputed. Here, a blind exercise in carcinogenicity category assessment is performed using augmented top priority fragment classification. The procedure analyses the applicability domain of the dataset, allocates in clusters the compounds using a leading molecular fragment, and a similarity measure. The exercise is applied to three compound datasets derived from the Lois Gold Carcinogenic Database. The results, showing good agreement with experimental data, are compared with published ones. A final discussion on our viewpoint on the possibilities that the carcinogenicity modelling of chemical compounds offers is presented
Studies toward a model for the prediction of the regioselectivity in the Fischer indole synthesis. Part 2. Derivatives of cyclic ketones
No full textA previously reported model for the prediction of the regioselectivity in the Fischer indole synthesis has been applied to the study of three compounds derived from cyclic ketones. The new features added in order to obtain reasonable results in these cases are reported. The results are discussed and show good agreement with the available experimental data. The use of transition state structures and of various possible alternative intermediates is commented on. The unexpected experimental products obtained in one case are qualitatively examined and discussed
Studies toward a model for the prediction of the regioselectivity in the Fischer indole synthesis
No full textA preliminary model for the prediction of the regioselectivity in the Fischer indole synthesis has been deveLoped. It is based on the use of the energy differences between the starting compound and the energy maximum compound along an a priori chosen reaction coordinate calculated with the AM1 program. The modeL has been applied to three examples and its results are in agreement with the available experimental data. All the possible alternative intermediates have been considered in order to accurately verify the proposed multistep mechanism
Determination of Toxicant Mode of Action by Augmented Top Priority Fragment Class
No full textTheor. models can be an efficient tool to assess compd. toxicity as an alternative to exptl. detns. Their application must follow some requirements that include the possibility of understanding the rationale that supports the prediction; here, the detn. of the mode of action (MOA) is important. A combination of similarity and reactivity anal. has been applied to group chem. compds. with the aim at selecting groups that share structure and electronic state. The model is not based on exptl. data but only on structural features. The result is a no. of groups that contains similar compds. with similar reactivity and, possibly, similar MOA. The comparison of these groups to the exptl. detd. MOAs available for the EPAFHAM database permits the discussion of the validity of both the model and the exptl. data
Model studies for predicting the diastereoselectivity in the condensation of aldehydes with zinc and copper complexes of amino acid derivatives. Part 2. Application of the models and analysis of results
No full textThe asymmetric synthesis of beta-hydroxy-alpha-amino acids with good stereochemical selectivity represents a highly interesting synthetic goal. The possibility of predicting the stereochemical outcome of such preparation gives rise to the opportunity to direct synthetic efforts toward a well-defined objective. A model study on the role played, in this respect, by transition metal containing complexes is described. Four different models are considered and their construction is thoroughly examined
Classification of organic reactions using similarity
No full textOrganic reaction classification allows for better understanding of organic reactivity, better data sharing, and better reaction storage and retrieval. The power of similarity has been often used to strengthen search methodology and to help reaction prediction systems, but seldom to optimise reaction classification. A hierarchical classification by similarity measures is proposed. It is based on electronic energy and chemical potential descriptors and on a general description of reactions. Using a main division into three reaction sets, additions, eliminations, and substitutions, followed by two successive subdivisions by number and types of reactive atoms it is possible to arrive at a hierarchy of groups containing homogeneous reaction classes. In addition, inside each set the reactions can be ordered. Some simple examples are used to demonstrate the efficiency of the classification and its overall consistency. The application of the final system to more complex examples is further proof of its efficiency. The reported classification can also be used in synthesis planning
Quantitative aquatic toxicity prediction: using group contribution and classification methods on polar and non-polar narcotics
No full textA model based on a Group Contribution Method (GCM) approach developed to correlate aquatic toxicity to fathead minnow (Pimephales promelas) has been applied to an external set containing 190 organic chemicals. This set was also previously partitioned into polar and non-polar toxicants using a different classification model. The application of the GCM approach to develop specific models both of the entire set and of its partitions permits to discuss the importance of the subclassification in order to improve the result
Organic synthesis planning: Some hints from similarity
No full textDespite of the present popularity of the new usages of similarity in chemistry, and of its counterpart dissimilarity, few approaches have used it in the design of organic synthesis. In addition mast of the known applications refer to the mere comparison between structures of the synthetic tree. We would like to discuss the power of the use of similarity in organic synthesis planning and to give some examples. The possibilities of analysis of a synthesis at different levels, from the single step to the entire tree, are presented and criticised. Special attention is dedicated to the role of similarity, whilst the identification of good descriptors is postponed to future developments
Analysis of the transferability of similarity calculations from substructures to complex compounds
No full text- …
