Phosphoryl transfer between amines

The possibility that phosphoryl transfer between amines occurs... 

Hydrolysis of Phosphates. The conclusion that phosphoryl transfer between amines is concerted does not exclude the formation of a metaphosphate intermediate in reactions with weaker nucleophiles, including water. Pyridine is a much stronger nucleophile than water and it is possible that phosphoryl transfer between pyridines is concerted because the metaphosphate ion does not have a significant lifetime in the presence of pyridine the metaphosphate ion might exist for a short time in water. However, it is much more difficult to determine whether or not the mechanism is concerted for a reaction with water than for a reaction with pyridine. 

The role of zinc ions as catalysts for phosphoryl transfer between phosphorimidazole and pyridine-2-carboxaldoxime is attributed to a lowering of the electrostatic barrier for attack of the anion of (26) on phosphorus it may also act as a template for the proper alignment of the entering and leaving groups. With amine nucleophiles it was found that zinc, in common with several bivalent cations, inhibited attack on phosphorimidazole. 

A very clever three-phase test for the detection of metaphosphate intermediates in phosphoryl transfer reactions has been described by Rebek and coworkers (44). The basis of this test is the use of two polymers suspended in solution. The donor polymer contains a potential precursor to metaphosphate anion, e.g., an acyl phosphate or a phosphoramidate, and the recipient polymer contains an acceptor nucleophile, e.g., an amine. After reaction and physical separation of the polymers, the recipient polymer is analyzed for covalently bound phosphate. Since very few of the phosphoryl groups to be transferred will be on the surface of the donor polymer, detection of significant transfer to the recipient polymer provides evidence for a diffusible intermediate, i.e., free metaphosphate anion. Significant transfer did occur in dioxane or acetonitrile suspensions of the polymers, thereby providing evidence for an intermediate. However, this test for diffusible and, therefore, relatively stable metaphosphate anion is compromised by the choice of solvent. Both dioxane and acetonitrile can provide unshared electron pairs for the highly electrophilic metaphosphate anion such that the actual species that migrates from the donor polymer to the recipient polymer may be a complex between metaphosphate anion and the solvent. Such a role for solvent has been investigated stereochemically, the results of which will be described later in this section. 

Group-transfer reactions (transfer of an electrophile [acyl RCOX, phosphoryl (OPOsX -), and glycosyl groups] between nucleophiles [alcohols, amines, thiols, etc.])... 

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