A NEW APPROACH FOR CHEMICAL PHOSPHORYLATION OF OLIGONUCLEOTIDES AT THE 5'-TERMINUS

A new efficient method for chemical 5'-phosphorylation of synthetic oligonucleotides is described. Accordingly, 2-cyanoethyl 3-(4,4'-dimethoxytrityloxy)-2,2-di(ethoxycarbonyl)propyl-1 N,N-diisopropyl phosphoramidite (1) was introduced as the 5'-terminal building block during the normal chain assembly. Conventional ammonolysis gave rise to an oligomer protected at 5'-phosphate with a dimethoxytritylated tether. At this step, the oligonucleotide may be easily separated from truncated impurities by RP HPLC. Successive detritylation and brief treatment with aqueous ammonia gave the oligonucleotide 5'-monophosphate. Alternatively, the yield of the last coupling may be quantified by detritylation of the oligonucleotide still anchored to the solid support. Usual deprotection then leads directly to the 5'-phosphorylated oligomer.