The use of phosphorimidazolidate intermediates for the conversion of ribonucleoside 5′-monophosphates to diphosphates and 5′-diphosphates to triphosphates is described and several examples are cited. The specific phosphorylation of ribonucleoside 5′-diphosphates to afford the linear rather than branched triphosphates is demonstrated. Also reported is the successful synthesis of the branched isomer of adenosine 5′-triphosphate, ψATP, the attempted preparation of which was first reported in 1949. Certain chemical and enzymatic properties of ψATP are described, as is the conversion of ψATP to ATP via a presumed cyclic meta-phosphate intermediate.
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