Synthesis of phosphopeptides via global phosphorylation on the solid phase: Resolution of H-phosphonate formation

Summary The formation of the H-phosphonate by-products from the ‘global’ phosphorylation of a Thr-containing peptide resin using both di-t-butyl and dibenzylN,N-diethylphosphoramidite was identified to result from 1H-tetrazolemediated cleavage of thet-butyl or benzyl from the intermediate dialkyl phosphite triester and re-arrangement of the resultant hydroxy phosphite diester to the H-phosphonate form. This side reaction was rectified by the use of aqueous iodine for the oxidation step in which the H-phosphonate is oxidised to the benzyl phosphorodiester which, on acidolytic treatment, gives the desired dihydrogen phosphate.