Stereochemically cryptic reactions

The stereospecificity is not limited to reactions for which the steric course is evident from the chemical configuration of substrate and product. Even at centers that are not chiral, the reactions are in many cases stereospecific (stereochemically cryptic reactions). The steric course of these reactions may be deduced by stereospecific isotope labeling of the substrates, transforming the reaction center into a chiral center of discernible stereochemical behavior. 

Of course, in the enzymatic oxidation of unlabeled ethanol one cannot operationally discern that the hydrogen abstracted is pro-R. Reactions of this type which are prostereoselective have been called stereochemically cryptic m>. 

Aside from selected PLP-dependent enzymes, a range of different enzymes catalyze either syn-eliminations, in which the leaving groups are eclipsed (Table X) (281-290), or anti-eliminations, in which the leaving groups are antiperi-planar (Table XI) (291-310). In the vast majority of cases these two options are stereochemically cryptic (giving the same product), since one of the carbons involved in the elimination reaction is a prochiral methylene carbon [e.g., Eq. (59)] ... 

---