Molecular field analysis, comparative

The simplicity of Hansch analysis also means that experienced medicinal chemists may be able to identify trends in activity without the assistance of a QSAR equation. Making individual new lead analogues is generally a slow process, and a medicinal chemist has ample time to examine SAR data. While a chemist will not be able to quantify a structure-activity relationship, just knowing the approximate trend of the relationship is usually adequate for lead optimization. Hansch analysis is valuable only if it can reveal something that is not already known about the compounds being tested. 

A second problem for Hansch analysis and any other predictive method is combinatorial chemistry. As methods in combinatorial chemistry continue to be refined and advanced, directed combinatorial libraries constructed around the scaffold of a lead have become a more standard practice. The availability of hundreds of lead analogues greatly diminishes the potential contribution from a Hansch equation. Why predict a structure s activity when one can make a library of essentially all interesting analogues, screen the library, and know the activity for certain  

The criticisms in the previous paragraphs lead to a question If Hansch analysis is of such questionable value, then why has an entire chapter of this textbook been devoted to the subject Despite the fading utility of classical QSAR methods such as Hansch analysis, the logic behind Hansch analysis is invaluable to medicinal chemistry. Synthetic chemists in the pharmaceutical industry intuitively consider the ideas used to construct Hansch equations. Ideas such as electronics, sterics, and lipophilicity underlie traditional SAR approaches in the laboratory. Critical analysis of activity data and emphasis on seeking holes in R-group selection are also fundamental to successful SAR on a lead. Through the study of Hansch analysis, all these crucial ideas are presented in a rational framework that helps demonstrate their relevance. Just as importantly, Hansch analysis provides the foundation for the next generation of QSAR comparative molecular field analysis. 

Comparative molecular field analysis (CoMFA) is a modern, powerful extension of the classical QSAR methods that were developed in the 1960s.14 While Hansch analysis is simple to understand and fairly easy for any medicinal chemist to perform, CoMFA requires specialized software and an understanding of statistics. Since CoMFA is outside the experience of most synthetic chemists, pharmaceutical companies have dedicated computational chemistry groups to handle advanced QSAR tasks. 

CoMFA begins with the consistent alignment of each molecule into a separate three-dimensional grid. Alignment of the molecules must be representative of the binding conformation and orientation of the compound with the target. Three-dimensional coordinates within the grid are then probed for both steric and electrostatic interactions with the 

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Before the comparative molecular field analysis (CoMFA), BCUT descriptors, 4D-QSAR, and HYBOT descriptors arc discussed in more detail, some further descriptors are listed briefly. 

After an alignment of a set of molecules known to bind to the same receptor a comparative molecular field analysis CoMFA) makes it possible to determine and visuahze molecular interaction regions involved in hgand-receptor binding [51]. Further on, statistical methods such as partial least squares regression PLS) are applied to search for a correlation between CoMFA descriptors and biological activity. The CoMFA descriptors have been one of the most widely used set of descriptors. However, their apex has been reached. 

Cramer R D III, D E Patterson and J D Bunce 1988, Comparative Molecular Field Analysis (CoMFA). Effect of Shape on Binding of Steroids to Carrier Proteins. Journal of the American Chemical Societ 110 5959-5967. 

Poso A, R Juvonen and J Gynther 1995. Comparative Molecular Field Analysis of Compounds wii CYP2A5 Binding Affinity. Quantitative Structure-Activity Relationships 14 507-511. 

RD Cramer III, DE Patterson, JD Bunce. Comparative molecular field analysis (CoMFA). 1. Effect of shape on binding of steroids to carrier proteins. J Am Chem Soc 110 5959-5967, 1988. 

Bis(oxazohnes) figands have been so widely used for the Diels-Alder reaction between N-2-alkenoyl-l,3-oxazolidine-2-one and cyclopentadiene that Lipkowitz and Pradhan developed a QSAR (quantitative structure-activity relationship) using Comparative Molecular Field Analysis (CoMFA) for a set of 23 copper-catalysts containing mainly bis(oxazoline) figands. The generated... 

Cho SJ, Tropsha A. Cross-validated R2-Guided region selection for comparative molecular field analysis a simple method to achieve consistent results. I Med Chem 1995 38(7) 1060-6. 

Asikainen A, Tarhanen J, Poso A, Pasanen M, Alhava E, Jnvonen RO. Predictive valne of comparative molecular field analysis modelling of naphthalene inhibition of human CYP2A6 and mouse CYP2A5 enzymes. Toxicol In Vitro 2003 17 449-55. 

A widely used 3-D QSAR method that makes use of PLS is comparative molecular field analysis (CoMFA), in which a probe atom is used to calculate the steric and electronic fields at numerous points in a 3D lattice within which the molecules have been aligned. Poso et al. [56] used the technique to model the binding of coumarins to cytochrome P450 2A5, with similar results to those obtained by Bravi and Wikel [55]. Shi et al. [57] used it to model the estrogen receptor binding of a large diverse set of compounds, and Cavalli et al. [58] used it to develop a pharmacophore for hERG potassium... 

Poso A, luvonen R, Gynther I. Comparative molecular field analysis of compounds with CYP2A5 binding affinity. Quant Struct-Act Relat 1995 14 507-11. 

Swaan PW, Szoka FC, Jr. and Oie S. Molecular modeling of the intestinal bile acid carrier a comparative molecular field analysis study. J Comput Aided Mol Des 1997 11 581-8. 

Kim, K. H. Calculation of hydrophobic parameters directly from three-dimensional structures using comparative molecular field analysis. J. Comput.-Aided Mol. Des. 1995, 9,... 

Partial Least Squares (PLS) regression (Section 35.7) is one of the more recent advances in QSAR which has led to the now widely accepted method of Comparative Molecular Field Analysis (CoMFA). This method makes use of local physicochemical properties such as charge, potential and steric fields that can be determined on a three-dimensional grid that is laid over the chemical stmctures. The determination of steric conformation, by means of X-ray crystallography or NMR spectroscopy, and the quantum mechanical calculation of charge and potential fields are now performed routinely on medium-sized molecules [10]. Modem optimization and prediction techniques such as neural networks (Chapter 44) also have found their way into QSAR. 

J. W. McFarland, Comparative Molecular Field Analysis (CoMFA) of anticoccidial triazines. J. Med. Chem., 35 (1992) 2543-2550. 

To refine this model qualitatively, the binding of several of these compounds was subjected to a CoMFA (Comparative Molecular Field Analysis) [39], This program examines electrostatic and steric parameters... 

E. E., Tukker, J. J., Mapping the binding site of the small intestinal peptide carrier (PepTl) using comparative molecular field analysis, Receptors Channels 1998, 6, 189-200. 

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