Spirophosphoranes hydrolysis

In the hydrolysis of neutral tricyclic hexacoordinate spirophosphorane 143 with internal N—>P dative bonds, the six-membered phosphorinane ring is retained during the first stage of hydrolysis. Five-, seven-, and eight-membered rings were preferentially hydrolysed (Equation 4) <1998POL3643>. 

Ester exchange of the oxyphosphorane 25 with ribonucleosides 26a-d gave a series of interesting, but labile, spirophosphoranes (27 a-d) which were characterised by MS and H/ P nmr in solution. Hydrolysis of 27a, followed by acetylation gave 28 with a high degree of regioselectivity. ... 

The five coordinate spirophosphoranes have played an important role with respect to understanding the stereochemistry of four coordinate phosphorus reactions which proceed via phos-phorane intermediates. Variable temperature NMR studies have established the apicophilicities of a wide range of groups (i.e. relative preferences of a series of groups to occupy an apical position rather than an equatorial position of a trigonal bipyramidal (t.b.p.) conformation of a phosphorane). The spiro ring system has been used to stabilize transient reaction intermediates of acyclic compounds, for example hydrolysis intermediates such as hydroxyphosphoranes. 

A series of bis cyclotriphosphazenyl spermines such as (161) have been prepared and shown to have anticancer activity in six murine tumour systems. These compounds had a higher potency and lower toxicity than related aziran derivatives <87PS(29)147). Spirophosphorane derivatives of thymidine such as (162 R = CF3) have been used as models for the study of the stereochemistry of cyclic AMP interactions with enzymes <90JA6092>. The base catalyzed proton transfer observed for the equilibrium shown in Scheme 23, mimics the role of the bases histidine 12 and histidine 119 in the active site of Rnase A during the hydrolysis of ribonucleic acids <84PS(19)173>. 

Enzymatic phosphoryl transfer reactions are ubiquitous in nature and play significant roles in ATP hydrolysis and protein phosphorylation processess. As previously described, pentacoordinate phosphorus species have been assumed as transient intermediates or transition states in these pathways and their structural and electronic properties are undoubtedly related to the outcome of the process. Therefore, to aid understanding of the phosphorus-catalyzed biological routes, many model pentacoordinated phosphoranes have been synthesized. While most studies have focused on aspects of apicophilicity, anti-apicophilicity or Berry pseudorotation, there have been limited investigations on the stereochemistry of pentacoordinated spirophosphoranes with a chiral phosphorus atom. In the past year, much attention has been paid to the synthesis and determination of absolute configuration of several chiral pentacoordinate spirophosphoranes derived from D- and L-aminoacids. Some significant achievements in this area will be discussed in this section. 

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