Stereospecificity Biology

In many cases only the racemic mixtures of a-amino acids can be obtained through chemical synthesis. Therefore, optical resolution (42) is indispensable to get the optically active L- or D-forms in the production of expensive or uncommon amino acids. The optical resolution of amino acids can be done in two general ways physical or chemical methods which apply the stereospecific properties of amino acids, and biological or enzymatic methods which are based on the characteristic behavior of amino acids in living cells in the presence of enzymes. 

The stereospecificity of the biological oxidation reactions has been exploited in the preparation of optically active sulphoxides. One enantiomer of the sulphoxide is oxidized to the sulphone faster than the other and so there is an excess of one enantiomeric sulphoxide after partial reaction has occurred164. 

Cycloaddition reactions with the Si(lOO) surface have been investigated for the purpose of designing microelectronics, nonlinear optical materials, sensors, and biologically active surfaces. The features of the [2+2] cycloadditions characteristic of the reactions in the pseudoexcitation band [133] predicts that [2+2] cycloadditions of electron-donating alkenes with Si(100)-2 x 1 surface could proceed with retention of configurations, in agreement with the observation [134]. Such stereospecific functionalizations of surfaces are of potential use for specific applications. 

Entry 4 involves nitrogen participation and formation of an iminium ion that is reduced by NaBH4. The reaction in Entry 5 creates an 11-methylenebicyclo[4.3.1]undecen-3-one structure found in a biologically active natural product. Note that this fragmentation creates a bridgehead double bond. Entry 6 involves construction of a portion of the taxol structure. The reaction in Entry 7 is stereospecific, leading to the E-double bond. 

Presumably, 7-tetadecene was also formed, but its presence was not reported. This reaction could be important as a means for the preparation of insect pheromones. This in itself presents a challenge namely, discovering stereospecific catalysts which are capable of yielding the biologically active cis isomers. 

Racemase deficiency. The biological role of 2-methyl-acyl-CoA racemase has only recently been clarified. This peroxisomal enzyme is essential for certain steps of the oxidation of phytol and bile acid derivatives, which are stereospecific. Biochemically there is accumulation of pristanic acid and C27 bile acid intermediates. Clinical symptoms may include adult-onset peripheral neuropathy, pigmentary degeneration of the retina and liver disease [ 13]. 

Biological activities such as enzyme reactions and metabolic changes are highly stereospecific, hence enantiomers and diastereomers may have entirely different... 

Ariens, E. J. Stereospecificity of bioactive agents General aspects of exemplified by pesticides and drugs. In Stereoselectivity of Pesticides, Biological and Chemical Problems Chemicals in Agriculture, Vol. 1, Ariens, E. J., van Rensoen, J. J. S. W. W., Eds., Elsevier Science, New York, 1988. 

Virtually all biological reactions are stereospecific. This generalization applies not only to the enzyme-catalyzed reactions of intermediary metabolism, but also to the processes of nucleic acid synthesis and to the process of translation, in which the amino acids are linked in specific sequence to form the peptide chains of the enzymes. This review will be restricted mainly to some of the more elementary aspects of the stereospecificity of enzyme reactions, particularly to those features of chirality which have been worked out with the help of isotopes. 

The true biological function of liver mevaldic reductase is not clear. It is not thought to be involved in cholesterol synthesis, and because of the difference in its stereospecificity for the substrate, it is thought to be only a distant relative of the hydroxymethylglutaryl CoA reductases. But all of these enzymes have the same A stereospecifidty for the pyridine nucleotide. 

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