Phosphoric acid esters 2-cyanoethyl phosphate

Protective group for nucleosides. Stepwise synthesis of oligonucleotides utilizing 2-cyanoethyl phosphate (1, 172-173) requires protection of the 3 -hydroxyl group which can be cleaved under essentially neutral conditions, since a methoxy-trityl ether is sensitive to acid and a /3-cyanoethyl phosphoric ester is sensitive to alkali. The /3-benzoylpropionyl group meets these requirements, since it is quantitatively cleaved by dilute solutions of hydrazine hydrate in pyridine-acetic acid. The esters are prepared by condensation with DCC (dicyclohexylcarbodiimide). Definitive paper R. L. Letsinger and P. S. Miller, Am. Soc., 91, 3356 (1969)... 

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