Diastereomeric relationships specification

A number of examples have been mentioned which illustrate that the receptor site can differentiate between enantiomeric forms of a pheromone. It is common knowledge that many enzymes are specific for only one of a pair of enantiomers. Also, many differentiate between enantiotopic groups of a single substrate molecule 347). If binding of a pheromone to a receptor takes place, it is probably analogous to the formation of an enzyme-substrate complex. The combination of each member of an enantiomeric pair with receptors of a given chirality results in the formation of two complexes that are physically and chemically distinct diastereomeric combinations. Therefore the differentiation between enantiomers may be dependent upon the creation of diastereomeric relationships. Should two enantiomers have equal activity, then the pheromone-receptor interaction may not involve the chiral centers of the enantiomers. 

When dealing with reactions leading to stereoisomeric products we have the additional complication that descriptors such as enantiomeric (diastereomeric) excess and enantiomeric (diastereomeric) ratio are used to describe product purities. The evaluation of RME for a specific stereoisomer, say the R enantiomer, is exactly as above using the connecting relationships for the fraction of each product shown below. 

Method development for chiral separation is a multidisciplinary task. It requires knowledge of stereochemistry, organic chemistry, and separation techniques. Separation of enantiomers is not linked to a certain technique (i.e., GC, HPLC, etc.) but rather to an understanding of the specific interactions between the enantiomeric analytes and a certain chiral stationary phase. Knowing these types of relationships will enable one to easily understand the formation of transient diastereomeric complexes between enantiomers and a chiral stationary phase during a chromatographic separation as well as their stereochemical relationship within the complex. Once such dependencies are established, development of a method for the separation of enantiomers becomes an easy process. Based on such a relationship, chiral stationary phases can be divided in five categories [161] ... 

As we might expect, a-D-glucopyranose and P-D-glucopyranose have different physical properties because their relationship is diastereomeric. For example, compare the specific rotation for these two compounds ... 

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