QSAR parameters

An effective QSAR parameter should correlate only to its specific property, be it electronics, lipophilicity, sterics, or something else, a- Values for R-groups in the meta and para positions have been found to account for only electronic effects. Substitution at the ortho position, however, is another story. Because ortho substituents are physically so close to the carboxylic acid, ortho R-groups affect the acid-base equilibrium through both electronic and steric effects. Therefore, the ortho tr-value (electronic parameter for QSAR studies. Despite their limitations, Hammett constants are by far the most commonly encountered electronic parameter in Hansch analysis. 

A fundamental difference between 3D- and a 2D-QSAR equation is the non-existence of conformational dependent secondary sites in the latter. Hence, a direct transposition of 3D- and 2D-models is not always possible but the global properties of the chemical structures, if relevant to the activity, may show their presence in both of them. Moreover, in a broader perspective, all 2D-QSAR parameters—physicochemical as well as structural—can be considered as one or the other form of global descriptors. In light of this, to bridge the 2D- and 3D-features the following 2D-QSAR equations have been derived for the antifungal activity of 2,3,4-substituted thiazolidines (Table 21). 

Makes chemical structure drawings from ChemDraw and ISIS/Draw understandable to Microsoft Excel spreadsheets. Library of QSAR parameters for 250 substituents. Protecting Groups and Methods in Organic Synthesis (MOS) reaction databases. PCs. 

Approach was used in deriving mechanistic information about odor intensity as well as insight into how this biological activity may be predicted. This paper will first briefly describe the history of QSAR, the QSAR parameters used, and how substituents for QSAR studies are selected. Several examples of the Hansch Approach used in taste and odor quality studies will next be presented. The balance of the paper will deal with the development of quantitative structure odor intensity relationships which will further expand upon the earlier study reported by this author (11). For example, the use of relatively new QSAR steric parameters in correlations with odor intensity data, and correlations of log P with literature odor intensity data determined on animal panels will be presented. This will be followed by conclusions derived from those studies, and areas of future work. 

Franke, R. (1985) QSAR parameters, in QSAR and Strategies in the Design of Bioactive Compounds (ed. J. K. Seydel), VCH, Weinheim. 

Besides correlating QSAR parameters with measured toxicity, we also qualitatively compared measured toxicity with the presence of functional groups on the molecules. Although we tested only two to 13 chemicals in each class, certain relationships were suggested. The presence and position of methyl groups on PAHs were related to toxicity (e.g., the 48-hr EC50 for naphthalene was 4.66 + 0.14 (SE, n = 4) mg L, compared with 0.193 + 0.116 (n - 3) for 2,6-dimethylnaphthalene and 0.506 + 0.158 (n = 3) for 1,3-... 

The intent of OECD QSAR Principle 5 (Section 3.1.5) is not to reject models that have no apparent mechanistic basis but to ensure that some consideration is given to the possibility of a mechanistic association between the descriptors used in a model and the endpoint being predicted and to ensure that this association is documented. Since the physicochemical QSAR parameters were chosen in this study, a mechanistic interpretation of the models is possible. This nevertheless follows specific steps, some of them integrated in the previously discussed OECD-QSAR principles (Putz et al., 2011c) ... 

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