SAR relationships

Pinacidil (6) itself exhibits no selectivity for a particular smooth muscle type and at high concentrations has a mechanism of action that is independent of channel opening [3]. Thus, caution must be exercised when studying SAR relationships as this KCA-independent mechanism can be enhanced. 

This is the domain of establishing Structure-Property or Structure-Activity Relationships (SPR or SAR), or even of finding such relationships in a quantitative manner (QSPR or QSAR). 

The fundamental assumption of SAR and QSAR (Structure-Activity Relationships and Quantitative Structure-Activity Relationships) is that the activity of a compound is related to its structural and/or physicochemical properties. In a classic article Corwin Hansch formulated Eq. (15) as a linear frcc-cncrgy related model for the biological activity (e.g.. toxicity) of a group of congeneric chemicals [37, in which the inverse of C, the concentration effect of the toxicant, is related to a hy-drophobidty term, FI, an electronic term, a (the Hammett substituent constant). Stcric terms can be added to this equation (typically Taft s steric parameter, E,). 

M. G. J. Beets, SAR Structure—Activity Relationships in Human Chemoreception, AppHed Science Pubhshers, London, 1978. 

Elucidation of the stmctural requirements for dmg interaction at the recognition site is by the study of stmcture—activity relationships (SAR), in which, according to a specific biologic response, the effects of systematic molecular modification of a parent dmg stmcture are determined. Such studies have permitted the classification of discrete classes of pharmacological receptors. For example, the neurotransmitter acetylcholine acts at both peripheral and central receptors which are of at least three distinct types. The effects of acetylcholine are mimicked in smooth and cardiac muscles and secretory... 

Relatively unambiguous monotonic SARs also occur where activity depends on the ionization of a particular functional group. A classic example (Fig. 5) is that of the antibacterial sulfonamides where activity is exerted by competitive inhibition of the incorporation of j -amin ohenzoic acid into foHc acid (27). The beU-shaped relationship is consistent with the sulfonamide acting as the anion but permeating into the cell as the neutral species. 

Methylpyrazole has been investigated as a possible treatment for alcoholism. The stmcture—activity relationship (SAR) associated with a series of pyrazoles has been examined ia a 1992 study (51). These compounds were designed as nonprostanoid prostacyclin mimetics to inhibit human platelet aggregation. In this study, 3,4,5-triphenylpyrazole was linked to a number of alkanoic acids, esters, and amides. From the many compounds synthesized, triphenyl-IJT-pyrazole-l-nonanoic acid (80) was found to be the most efficacious candidate (IC g = 0.4 //M). 

The structure activity relationships ( SAR) of newly synthesized analogues of nucleosides, xanthine heterocycles, and nonxanthine heterocycles have been explored at the ARs. Potent and selective AR antagonists have been prepared for all four subtypes [3, 4], and selective agonists are known for three subtypes [1]. Thus, numerous pharmacological tools are available for in vitro and in vivo use (Table 2). Potent and selective A2b AR agonists are yet to be repotted, although several research groups have identified lead compounds. 

Traditionally, in pursuit of their structure-activity relationships, medicinal chemists had focused almost exclusively on finding compounds with greater and greater potency. However, these SARs often ended up with compounds that were unsuitable for development as pharmaceutical products. These compounds would be too insoluble in water, or were not orally bioavailable, or were eliminated too quickly or too slowly from mammalian bodies. Pharmacologists and pharmaceutical development scientists for years had tried to preach the need for medicinal chemists to also think about other factors that determined whether a compound could be a medicine. Table 1.1 lists a number of factors that determine whether a potent compound has what it takes to become a drug. Experimentally, it was difficult to quantitate these other factors. Often, the necessary manpower resources would not be allocated to a compound until it had already been selected for project team status. 

Attaching some short peptidic sequences to adamantane makes it possible to design novel antagonists. The bradykinin antagonist, which is used as an anticancer agent, is an example. The adamantane-based peptidic bradykinin analog was utilized in strucmre-activity relationship (SAR) studies on the bradykinin receptors and showed a potent activity in inhibition of bradykinin-induced cytokine release and stimulation of histamine release [142]. 

Most relevant for the affinity for A9-THC and analogs to CB-receptors are the phenolic hydroxyl group at C-1, the kind of substitution at C-9, and the properties of the side chain at C-3. Relating to the structure-activity relationships (SAR) between cannabinoids and the CB-receptors, many different modified strucfures of fhis subsfance group were developed and fesfed. The most important variations include variations of the side chain at the olivetolic moiety of the molecules and different substitutions at positions C-11 and C-9. One of the most popular analogous compounds of A9-THC is HU-210 or (-)-trans-ll-OH-A8-THC-DMH, a cannabinoid with a F,l-dimethylheptyl side... 

To establish the structure-activity relationships (SARs) of a set of molecules, a knowledge of the 3D structure is of great importance [2]. Thevand et al. recently (2004) reported the 3D structural analysis of tetrandrine using NMR and molecular modeling (the structure is shown in Fig. 1) [2]. They employed... 

Croni MT et al. (2000) Structure-toxicity relationships for aliphatic compounds encompassing a variety of mechanisms of toxic action to Vibrio fischeri. SAR QSAR Environ Res 11(3-4) 301-312... 

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