Chiral phosphate esters

Methods based on the effects of the quadrupolar O nucleus (/ = f) and the 0 nucleus (7 = 0) on the P NMR spectral properties of the isotopically labeled P nucleus are now the only methods used to ascertain the configurations of tetrahedral phosphorus atoms in oxygen chiral phosphate esters. The chemical... 

The first application of this 0 effect for determining the configuration of an oxygen chiral phosphate ester was the author s determination of the configuration of diastereomeric samples of cyclic [, 0]dAMP, the chiral substrate for studying the stereochemical consequences of the reverse reaction catalyzed by adenylate cyclase (formation of cyclic AMP from ATP), and of the hydrolysis reaction catalyzed by 3, 5 -cyclic nucleotide phosphodiesterase (25) (see Fig. 

These comparative studies constituted the first example of an enzyme-catalyzed hydrolysis reaction whose stereochemical course was unaffected by sulfur substitution. At the time these experiments were performed, the stereochemical courses of the reactions catalyzed by glycerol kinase (83, 84) and by the bacterial adenylate cyclase (85, 86) had already been compared in the laboratories of Knowles and Gerlt, respectively, and these were also found to be unaffected by the sulfur substitution. A number of other comparisons of this type have been made, and in no case were the stereochemical consequences of the reactions studied with chiral phosphate esters and the chiral thiophosphate analogs found to differ. This agreement suggests that the necessary use of oxygen chiral thiophosphate monoesters to study the stereochemical course of phospho-monoesterases will provide pertinent results for ascertaining whether phosphory-lated intermediates are involved in the reaction mechanism. 

Conformational isomers can be distinguished by their NMR spectra, as can chiral phosphate esters based on isotopic substitution. 

III. Configurational Analyses of Oxygen Chiral Phosphate Esters... 

Stereochemical Studies Using Oxygen Chiral Phosphate Esters and P-NMR Methods of... 

Methods have been developed for the synthesis of essentially any oxygen chiral phosphate ester of biological importance, and the P-NMR methods described and illustrated in this chapter provide a convenient method for determining their configurations and elucidating the stereochemical consequences of enzyme-catalyzed phosphoryl and nucleotidyl transfer reactions. 

Much effort has been placed in the synthesis of compounds possessing a chiral center at the phosphoms atom, particularly three- and four-coordinate compounds such as tertiary phosphines, phosphine oxides, phosphonates, phosphinates, and phosphate esters (11). Some enantiomers are known to exhibit a variety of biological activities and are therefore of interest Oas agricultural chemicals, pharmaceuticals (qv), etc. Homochiral bisphosphines are commonly used in catalytic asymmetric syntheses providing good enantioselectivities (see also Nucleic acids). Excellent reviews of low coordinate (coordination numbers 1 and 2) phosphoms compounds are available (12). 

These ether lipids are all chiral molecules with an R configuration but are derivatives of the nonchiral glycerol. The carbon atoms of glycerol are numbered using the stereochemical system which is described on p. 470. The ether linkage is to the sn-1 carbon atom. Most phospholipids are derivatives of the sn-3 phosphate ester of glycerol. 

Considerable ingenuity was required in both the synthesis of these chiral compounds695 697 and the stereochemical analysis of the products formed from them by enzymes.698 700 In one experiment the phospho group was transferred from chiral phenyl phosphate to a diol acceptor using E. coli alkaline phosphatase as a catalyst (Eq. 12-36). In this reaction transfer of the phospho group occurred without inversion. The chirality of the product was determined as follows. It was cyclized by a nonenzymatic in-line displacement to give equimolar ratios of three isomeric cyclic diesters. These were methylated with diazomethane to a mixture of three pairs of diastereoisomers triesters. These dia-stereoisomers were separated and the chirality was determined by a sophisticated mass spectrometric analysis.692 A simpler analysis employs 31P NMR spectroscopy and is illustrated in Fig. 12-22. Since alkaline phosphatase is relatively nonspecific, most phosphate esters produced by the action of phosphotransferases can have their phospho groups transferred without inversion to 1,2-propanediol and the chirality can be determined by this method. 

Phosphate esters, particularly AMP, ADP and ATP, have vital biological functions and this fact has generated intense interest in their reaction mechanisms. Subtle stereochemical experiments, such as the use of isotopically chiral compounds, have been important and, since all biological phosphorylation reactions appear to involve metal ion catalysis, the stereochemistry of phosphate ion coordination has also been subject to much attention.229,230 Apart from its biological significance, this work has revealed some interesting contrasts with the stereochemistry of ligand systems in which saturated carbon units link the donor atoms. 

J.R. Knowles and coworkers used chiral [l60, l70, lsO]phosphate esters to show that the transphosphorylation catalyzed by E. coli alkaline phosphatase proceeds with overall retention of configuration [52]. They synthesized phenyl-[160, l70, lsO]phosphate by the procedure in Fig. 19 and used it as the phosphoryl-donor substrate with 1,2-propanediol as acceptor according to Equation 12. They determined the configuration of the 1,2-propanediol-1-[16O, l70, lsO]phosphate by the procedure described in Figs. 21 and 22 and found it to be the same as that of the phenyl-[l60, l70, lsO]phosphate they used as the phosphate donor. 

A -oxides) In sulfones, the sulfur bonds with a tetrahedral array, but since two of the groups are always oxygen, no chirality normally results. However, the preparation of an optically active sulfone (2) in which one oxygen is and the other illustrates the point that slight differences in groups are all that is necessary. This has been taken even further with the preparation of the ester 3, both enantiomers of which have been prepared. Optically active chiral phosphates 4 have similarly been made. ... 

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