2′,3′-OS-Silylierung von Tubercidin mittert-Butyl(chlor)-dimethylsilan

Oxygen chiral phosphate esters

During the past four years, methods have been reported for the syntheses and configurational analyses of virtually any phosphate mono- and diester chiral by virtue of oxygen isotope substitution, and these techniques have already been applied to an impressive number of enzymic and chemical reactions. At present, no experimental information is available that contradicts the simplest interpretations that have been applied to the results obtained for enzymic reactions: inversion of configuration indicating a direct displacement of the leaving group by the attacking group, and retention of configuration implying the formation of a phosphorylated or nucleotidylated enzyme intermediate. However, it does seem necessary to further investigate the mechanisms of at least some of the reactions discussed in this review to ensure that the simplest interpretation is correct. For example, the caveat we have raised about the interpretation of inversions of configurations in phosphohydrolase reactions is chemically reasonable, and these reactions should be reexamined to evaluate the importance of covalent catalysis by carboxylate groups. However, for the vast majority of the enzymic reactions that have been investigated, the stereochemical approach to ascertaining whether catalysis involves the formation of covalent intermediates remains the simplest and most direct method.