Acetic acid, cyanoethyl ester

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)... 

These compounds are prepared starting from chloroace-tic acid or its ethyl ester. For chains longer than acetic, cyanoethylation and hydrolysis of the nitrile obtained leads to the propionic chain, alkylation with ethyl 4-bromobuty-rate and saponification leads to the butyric chain. The propanesulfonic chains are particularly accessible by means of ring opening of propane-sultone. 

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