Diastereomers classification

Steinreiber J, Faber K, Griengl H. De-racemization of enantiomers versus de-epimerization of diastereomers-classification... 

From 1 Steinreiber, K. Faber, H. Griengl, De-racemization of enantiomers versus de-epimerization of diastereomers-classification of dynamic kinetic asymmetric transformations (DYKAT), Chemistry 14 (2008) 8060. Copyright 2008 Wiley). 

The classification of stereo-differentiation (63) (see Section VII) is as follows enantiomer-differentiation includes enantioface-difTerentiation, enantiotopos-dilferentiation, and enantiomer-differentiation diastereo-differentiation includes diastereoface-differentiation, diaster-eotopos-differentiation, and diastereomer-differentiation. 

As noted previously, the classification of stereoisomers preferred by contemporary organic chemists is the enantiomer-diastereomer dichotomy17 and this may be quite conveniently applied to coordination compounds. Thus, complexes (9a) and (9b) are enantiomers, but (9a) and (9c), and (9b) and (9c), are diastereomers. Older terminology might have led to the description of A and B as optical antipodes and to (A+B) and C as geometrical isomers. 

An immediate consequence of Pasteur s law is that the relationship between enantiomers is established by symmetry alone and does not require any knowledge of molecular bonding connectedness (constitution). This is in contrast to diastereomers, the other class of stereoisomers Diastereomers are not related by symmetry, and their relationship can be defined only by first specifying that their constitutions are the same—otherwise, there would be nothing to distinguish them from constitutional isomers. Thus enantiomers, which have identical scalar properties and differ only in pseudoscalar properties, have more in common with homomers than with diastereomers, while diastereomers, which differ in all scalar properties, have more in common with constitutional isomers than with enantiomers.51, 52 It therefore makes more sense, in an isomer classification scheme, to give priority to isometry rather than to constitution.52 In such a scheme there is no need for the concept stereoisomer the concept retains its usefulness only because it normally proves convenient, in chemical reaction schemes, to combine enantiomers and stereoisomers in a common class. 

The olefinic substrates that are cis-trans isomers are by modern stereochemical nomenclature more generally termed diastereomers. That is, they are stereoisomers that are not enantiomers. The fact that they contain no asymmetric carbons is irrelevant to this classification. 

Classification of Carbohydrates 1102 23-3 Monosaccharides 1103 23-4 Erythro andThreo Diastereomers 1106 23-5 Epimers 1107... 

A pair of geometric isomers are, then, diastereomers. Where do they fit into the other classification scheme, the one based on how the stereoisomers are interconverted... 

The affinity differences for the diastereomers of PIA are often used as criteria for adenosine receptor subtype classification. The results summarized in Table III demonstrate that the diastereomeric selectivity for R- and S-PIA at Aj adenosine receptors is remarkably stable in a variety of radioligand binding and physiological assays. The largest difference in affinity was observed in the solubilized porcine atrial Aj adenosine receptor where R-PIA was approximately 43 fold more potent than S-PIA as an inhibitor of [1 I]HPIA binding. 

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