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Activation of phosphoramidites as phosphitylating reagents in the synthesis of biophosphates and their structural analogues is of great importance. Tetrazole a customary activator can be conveniently replaced by trimethylchlorosilane (TMCS) or 2,4-dinitrophenol. Advantages of use of these reagents in the synthesis of biophosphates and their mechanism of action are discussed. Phosphites containing 4-nitrophenoxy leaving group are activated by DBU which role is revealed. Readily accessible P(III)-F structures, can be "activated" by their facile transformation into the corresponding bromides using trimethylbromosilane (TMBS). Application of phosphoramidites in synthesis of phosphates of biological interest and their activation by azolides and acids salts, including and stereochemical aspects was described in 'Topics in Current Chemistry.