[14] Stereochemistry of selected phosphotransferases and nucleotidyltransferases

In recognition of the experimental imperatives for carrying out stereochemical analyses of chemical reactions, this chapter deals with the methodologies of such research. It describes methods for synthesizing chirally substituted phosphorothioate analogs of biological phosphates. The methods used for assigning configurations to these molecules and the strategies employed in the applications of the foregoing methods to the stereochemical analysis of enzymic substitution at phosphorus are also discussed. The chapter presents the methods by which sulfur may be displaced from chiral phosphorothioates by H2O (or H218O or H217O) to produce chiral phosphates. The availability of chirally substituted phosphorothioates makes them logical precursor molecules for syntheses of chirally substituted phosphates; if stereochemically defined, methods can be devised for displacing sulfur from the chiral centers with 18O or 17O. It is possible to synthesize ATP or ADP with 18O or/and 17O enrichment coupling highly stereoselective or stereospecific enzymatic phosphorylations of ADPβS,β18O or AMPS,18O with the methods discussed in the chapter.