Qualitative structure-activity

Qualitative structure-activity relationship (QSAR) methods (see Sect. 5.2). 

The toxicology of a solvent is determined by many factors, such as bioavailabihty, metabolism, and the presence of structural features that may attenuate or enhance the reactivity of the parent molecule. Despite the structure-activity data available for many classes of commercial chemical substances, chemists have not recognized the use of structure-activity relations as a rational approach for choosing or designing new, less toxic commercial chemical substances. With qualitative structure-activity relationships, comparing the structures of the substances in the series with corresponding effects on the toxicity makes the correlation between toxic effect and structure. Through these, it may then be possible to predict a relationship between structure and toxicity... 

With qualitative structure-activity relationships (SARs), the correlation of toxic effect with structure is made by visual comparison of the structures of the chemicals in a series of congeneric substances and the corresponding effects their structural differences have on toxic potency, for example, as represented by their LD50 values. From qualitative examination of structure-activity data the chemist may be able to see a relationship between structure and toxicity, and identify the least toxic members of the class as possible commercial alternatives to the more toxic members. 

Roberts, D.W. 1989. Aquatic toxicity of linear alkyl benzene sulphonates (LAS) - a QSAR analysis. Communicaciones Presentadas a las Jomadas del Comite Espanol de la Detergencia, 20 (1989) 35-43. Also in J.E. Turner, M.W. England, T.W. Schultz and N.J. Kwaak (eds.) QSAR 88. Proc. Third International Workshop on Qualitative Structure-Activity Relationships in Environmental Toxicology, 22-26 May 1988, Knoxville, Tennessee, pp. 91-98. Available from the National Technical Information Service, US Dept, of Commerce, Springfield, VA... 

V j Activity significantly decreased by subsitunents Figure 5.9. Qualitative structure activity relationships of benzodiazepin-2-ones. 

C Hanseh Qualitative, Structure-Activity Relationship in Drug Design,Vol. I,... 

Early attempts to map the properties of an unknown receptor (or any other ligand binding site) started from qualitative structure-activity relationships [878], from MO calculations of preferred conformations of ligands [879] and from the interpretation of multiparameter Hansch equations (e.g. Figure 48) [28]. 

In recent years, structural evolution, detailed quantitative and qualitative structure-activity studies have been performed with a range of chemically different PDS inhibitors. Reference [27] reviews the early literature until about 1990. Subsequent years, to the late 1990s, is the topic of another review [34]. 

As previously mentioned, the acronym QSAR stands for the quantitative structure-activity relationship. However, there may be some ambiguity associated with the attribute quantitative. It does not necessarily follows that results expressed or having numerical representation are necessarily quantitative. Qualitative results can equally be numerically represented. Strictly speaking, we define and view QSAR models as quantitative only when the numerically expressed models allow meaningful interpretation of the numerical results obtained for the structure-activity relationship within the basic concepts of the particular model. This means that the physicochemical models should allow quantitative interpretation of the numerical physicochemical descriptors used and that the structure-mathematical models should allow quantitative interpretation of the numerical structure-mathematical descriptors used. We will use the symbol qsar and QSAR as the abbreviation for qualitative structure-activity relationship. Such are the relationships that are non-numerical and the relationships that may be numerical but the variables used are interrelated and thus do not allow unique interpretation of the MRA equations. Because all molecular descriptors hitherto used in QSAR, whether they are based on physicochemical properties, quantum mechanical calculations, or molecular graphs, are all interrelated, it follows that all such hitherto reported results, without further elaboration, remain essentially qualitative, being qsar rather than QSAR. 

In this chapter, we have provided a critical view of the 3D-QSAR arena, some practical steps for modeling with CoMFA, and a set of criteria for assessing model validity. The need for quantitative models stems from the difficulty in discerning simple, intuitive (qualitative) structure-activity relationships. Although QSAR provides a rational framework for testing hypotheses, the QSAR models remain oversimplifications of the modeled process, and as such, are incomplete. The ultimate utility of any model rests with the scientist Is the model better than having no model at all ... 

SAR work can be classified into two categories QSAR (quantitative structure-activity relationships) and qSAR (qualitative structure-activity relationships). In QSAR analysis, biological activity is quantitatively expressed as a function of physico-chemical properties of molecules. QSAR involves modeling a continuous activity for quantitative prediction of the activity of new compounds. qSAR aims to separate the compounds into a number of discrete types, such as active and inactive or good and bad. It involves modeling a discrete activity for qualitative prediction of the activity of new compounds. 

An attempt has been made to quantitate what appear to be qualitative structure-activity relationships for chloroquine analogs. ... 

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