Uncatalyzed reactions phosphotriesters

The mechanism of phosphate ester hydrolysis by hydroxide is shown in Figure 1 for a phosphodiester substrate. A SN2 mechanism with a trigonal-bipyramidal transition state is generally accepted for the uncatalyzed cleavage of phosphodiesters and phosphotriesters by nucleophilic attack at phosphorus. In uncatalyzed phosphate monoester hydrolysis, a SN1 mechanism with formation of a (POj) intermediate competes with the SN2 mechanism. For alkyl phosphates, nucleophilic attack at the carbon atom is also relevant. In contrast, all enzymatic cleavage reactions of mono-, di-, and triesters seem to follow an SN2... 

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