Sigma biological activities

Although sulfation of dextran is an easy synthetic step, most of the studies directed towards biological activity of dextran sulfate are carried out with commercially available products. The DS of these derivatives is usually rather high. The DS of the most widely applied dextran sulfate from Sigma is 2.3. A typical 13C NMR spectrum of a commercial dextran sulfate is shown in Fig. 12. The spectrum confirms the high degree of sulfation and reveals com-... 

Substituent Parameters. A significant advance was made, in the structure-activity studies with the Hill reaction, when Hansch and Deutsch (12) evaluated some of the published Hill inhibition data with a multiple regression analysis, an extra-thermodynamic approach, or the so-called sigma, pi (a, T ) regression analysis. The principle of the approach rests on the assumption that changes in biological activity can be correlated with measurable molecular or substituent parameters. This analysis involved equations of the following type ... 

The Hansch equation mathematically describes two events controlling the biological activity of a compound. The first involves cell or membrane penetration (influenced by the partition coefficient), and the second involves interaction of the active molecule at a receptor site (modified by variations in the Hammett sigma constant). 

The matrix of molecular descriptors and biological activity data was scaled and variables with unchanging values were removed using feature selection with the StripMiner/Analyze software previously described [140,141], From the descriptors with more that 95% correlation between each other (i.e., cousin descriptors ), only the descriptor most correlated with the response was retained. In addition 4 sigma outliers were brought within 2.5 sigma. 

The diverse biological activities which add to the "sigma enigma" include ... 

Interestingly, sigma (and therefore activity) was also closely correlated with the calculated LUMO values (21) these compounds (r - 0.82). The strong dependence of biological activity on electronic parameters fits in well with the assiunption that these compounds elicit their toxic effects by photochemical generation of singlet oxygen. 

Disulfide bonds form after a protein has folded into its biologically active conformation. Once disulfide bonds have formed, the protein conformation is much less flexible. We recall that conformations around sigma bonds can be either s-cis or s-trans and that the s-tram conformation is usually more stable because it minimizes steric repulsion. When disulfide bonds exist in proteins, they nearly all have an s-trans conformation (Figure 27.13). 

Collection of pharmacological compounds 500-5,000 Commercially available, low toxicity, known pharmacology, high biological activity, known targets Not novel, biased Tocris, Sigma, Prestwick, NIH, Microsource... 

Flood, Thomas C., Stereochemistry of Reactions of Transition Metal-Carbon Sigma Bonds, 12, 37. Floss, Heinz G., Stereochemistry of Biological Reactions at Proprochiral Centers, 15, 253. Freedman, T. B., Stereochemical Aspects of Vibrational Optical Activity, 17, 113. 

Molecular biology phorbol esters/Sigma 2000 diterp./carcinogens, NO promoters activators of protein kinase C pantrop. and tranpa te Euphorbiaceae, Ang. (also a standard for phorbol-class receptor in cancer studies)... 

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