Synthesis of deoxyadenosine‐5′‐( 35 S)‐thiomonophosphate [dAMP( 35 S)] of high specific activity – a key intermediate for the synthesis of Sp‐deoxyadenosine‐5′‐( alpha; ‐ 35 S)‐thiotriphosphate [Sp‐dATP ( α ‐ 35 S)]

Unprotected deoxyadenosine 1 was treated with an excess of phosphorus acid and stoichiometric proportions of N , N ′‐di‐ p ‐tolylcarbodiimide in anhydrous pyridine to give deoxyadenosine‐5′‐monophosphite 2 . The latter was activated with trimethylsilyl chloride followed by sulphurisation with elemental 35 S (specific activity>1000 Ci/mmol) in toluene solution to give deoxyadenosine‐5′‐( 35 S)‐thiomonophosphate [dAMP( 35 S)] 3 . Enzymatic conversion of deoxyadenosine‐5′‐( 35 S)‐thiomonophosphate to Sp‐deoxyadenosine‐5′‐( α ‐ 35 S)‐thiotriphosphate [Sp‐dATP ( α ‐ 35 S)] 5 was carried out following a standard reaction protocol. Copyright © 2001 John Wiley & Sons, Ltd.