Structure-activity relationships specific substituent groups

Several studies on structure-activity relationships of succinate dehydrogenase inhibitors have been published [22-28]. Each of the analyses has focused on specific carboxylic acid moieties of the molecule. The influence of substituents of the carboxylic acid and of the aniline has then been studied based on enzyme inhibition and biological data. Some empirical relationships have been established within each structural subclass. The importance of electron-withdrawing groups on the carboxylic acid and of lipophilic effects on the aniline has been observed. The orientation of the amide bond has also been discussed, suggesting that the cis configuration of the amide bond may be important in molecules with bulky ortho substituents [28]. 

One problem was that three different groups had to be connected regioselec-tively to the 1,2- and 3-positions of the benzene ring in the phthaloyl moiety. An iodine atom was introduced selectively into the 3-position of the phthaloyl moiety by a palladium-catalyzed reaction in the presence of a specific substituent in the 2-position. On the basis of the structure-activity relationship, the introduction of lipophilic alkyl substituents, including fluorine atoms, seemed to increase the activity though a practical method of introduction was not available. The overcoming of such difficulties led to dramatic advances in terms of a more detailed study on the structure-activity relationship as well as the establishment of a facile synthetic method that provided various new derivatives. 

Existing structure-activity relationships for reaction of OH with organics (e.g., Kwok and Atkinson, 1995 Bethel et al., 2001b) already include substituent factors for alcohol and ether functional groups, and thus what is given below represents an update to these previous studies. The procedure used is as follows. The group rate coefficients and substituent factors of Kwok and Atkinson (1995) that are specific to the alkanes are... 

Researchers have used 3D quantitative structural activity relationship (QSAR) of deet and related analogs to construct pharmacophores to better understand the structural basis that leads to repellency by these amide compounds."- Their model was constructed primarily from the protection time data of Suryanarayana and others. Ma and others" showed that one could predict repellent duration based on compound structure and specifically that the amide group and attached substituents played a significant role in the experimentally determined repellent efficacy. Using the same data set, Katritzky and others applied Codessa Pro software to develop a QSAR model for the prediction of complete protection time (CPT) from descriptors related to the structural and electronic properties of deet analogs. This work is the foundation for current projects that involve the examination of repellency and toxicity data for subsets of compounds within the U.S. Department of Agriculture (USDA) archive. 

The specific structural requirements for lysozyme substrates are clearly explained by the precise relationships of the amino acid residues lining the active site to the substituents on the hexopyranosyl units of the bound substrate. By inspection of the three-dimensional enzyme-substrate structure it can be seen that N-acetyl groups are required for binding so that chitin is a substrate (177) but chitosan and cellulose are not (227). 

The tertiary structure describes the complete three-dimensional stmcture of the whole polypeptide chain. It includes the relationship of different domains formed by the protein s secondary structure and the interactions of the amino acid substituent -R groups. An example of a protein chain with a-helices and /3-folding, the enzyme ribonuclease, is shown in Fig. 1.17. The specific folding of a protein is only thermodynamically stable within a restricted range of environmental parameters, i.e. the right temperature, pH and ionic strength. Outside of this range, the protein could unfold and lose its activity. 

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