Enantiotopicity, definition

The general subject of asymmetric synthesis has been reviewed extensively (1-5). The term asymmetric synthesis has been defined in more than one way (1,4) however, a useful definition is the one given by Morrison and Mosher (1) a process which converts a prochiral unit [refs. 6 and 7] into a chiral unit so that unequal amounts of stereoisomeric products result. The stereoisomeric products may be enantiomeric or they may be diastereomeric. The substrate molecule must contain either enantiotopic or diastereotopic groups or faces (8,9), since the attack of a reagent at equivalent groups or faces cannot lead to isomeric products. 

In retrospect, it seems unfortunate that in 1971 Morrison and Mosher8 generalized the definition, while keeping the term, an asymmetric synthesis is a reaction in which an achiral unit in an ensemble of substrate molecules is converted by a reactant into a chiral unit in such a manner that the stereoisomeric products arc produced in unequal amounts ( Footnote The substrate molecule must have either enantiotopic or diastereotopic groups or faces) . Obviously the phrase "an achiral unit in an ensemble of substrate molecules is too inexact and requires a great deal of additional explanation, which was partially given by the footnote (note that molecule, i.e., singular, was used ). Currently, the Morrison-Mosher term appears to be equivalent to stereoselective reaction. Unfortunately, this term was only defined in the modem sense by Izumi in 1971, i.e., in the same year the Morrison-Mosher definition was published. 

Enantiotopic atoms or groups 479 Endergonic reactions 286 Endo ring conformation 212 Endocytosis 13,425-427 Endoderm 23 Endoglucanases 602 Endoglycanases 593, 602 Endonexin SeeAnnexin Endoplasmic reticulum (ER) 10,13,14, 521 cisternae of 14 definition of 14 in micrograph 13 rough 14 smooth 14 Endosomes 13, 426 Endosperm 30... 

By this definition, ethanol is a prochiral molecule. The two methylene hydrogens are enantiotopic (Section 9-10C) and substituting each separately (with, say, one deuterium) leads to a pair of enantiomers ... 

Now, does this ring any bells It should remind you very much of the definitions in Chapter 32 of H enantiotopic and diastereotopic in connection with NMR spectra. Replacing one of two enantiotopic Enantiotopic and diastereotopic groups with another group leads to one of two enantiomers replacing one of two diastereotopic chapter 32 pr<837 dl9CU9sed in... 

Enantiotopic ligands definition, 359 Enantio-zeroplane definition, 359 endo/exo-Selective reactions ... 

For definitions of homotopicity, enantiotopicity and diastereotopicity see Mislow and Raban (1967) and Jennings (1975). 

The two protons at C(l) are topologically nonequivalent, since substitution of one produces a product that is stereoisomerically distinct from that produced by substitution of the other. Ligands of this type are termed heterotopic, and, because the products of substitution are enantiomers, the definition can be made more precise.Ligands that on substitution produce enantiomers are enantiotopic. If a chiral assembly is generated when a point ligand is replaced by a new point ligand, the original assembly is prochiral Both C(l) and C(3) of 1,3-propanediol are prochiral centers. 

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