Proproprochiral center

In a system Xaaaa the a groups are, of course, also homotopic and thus indistinguishable. By the same formalism used above such a center can be called proproprochiral, because it is three substitution steps removed from a chiral center. Hence, three isotopic and/or heteroatomic replacements are required in order to study the steric course of reactions at such a center. The only chiral version of a proproprochiral center synthesized to date is an inorganic phosphate molecule carrying one heteroatomic and two isotopic replacements, (R)- and (S)-[I60,170,180]phosphorothioate. The presence of the sulfur heteroatom, of course, gives this chirally labeled species the properties of a proprochiral center with the concomitant simplification in the analytical methodology required to distinguish an R from an S isomer. 

In the following sections we discuss the methods that have been developed to study the steric course of reactions at proprochiral and proproprochiral centers on carbon and phosphorus, and some of the biochemical applications of these methods. Specifically, we consider chiral methyl groups, chiral malonic acid, chiral phosphate monoesters, and chiral inorganic phosphate. 

The enzymes in this category inlcude phosphatases, nucleotidases, ATPases, and so on. Except for the phosphatases, which also catalyse the transfer reaction in addition to the hydrolysis reaction (112, 166), the stereochemistry has to be studied by use of a chiral inorganic phosphate (Pj, a proproprochiral center). To make a Pj chiral, it is necessary to use 160,170,180 and sulfur. The synthesis and configurational analysis of chiral [160,170,180]thiophosphate (Psj) have been described in previous sections the first application of chiral [160,170,180]Psj in the reaction type c is the elucidation of the stereochemistry... 

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