Synthesis of polynucleotides which contain 3,N4-ethanocytidine, a nucleoside modification resulting from the action of bis(chloroethyl)-nitrosourea.

BCNU,N,N1-bis(2-chloroethyl)-N-nitrosourea is known to produce 3-hydroxyethylcytidine and 3,N4-ethanocytidine when it reacts with polycytidylic acid. The nucleoside, 3,N4-ethanocytidine, presumably results from cyclization of 3-chloroethylcytidine formed initially by transfer of chloroethyl carboniumions from BCNU to cytidine. In order to study the significance of this unusual derivative, we have synthesized 3,N4-ethanocytidine and converted it to the corresponding 5'-mono- and diphosphates. 3,N4-Ethanocytidine diphosphate has been successfully converted to a high molecular weight polymer.