Specific modification of nucleic acids inside the cell with alkylating derivatives of oligonucleotides ethylated at internucleotide phosphates

The alkylating derivatives of (C6H5NH)2P[dTp(Et)]4U and [dTp(Et)]9 U with completely esterified internucleotide phosphates bearing reactive 2,3 -O-4(N-2-chloroethyl N-methylamino)-benazylidene moiety attached to 3 -end cis-diol group were prepared. These alkylating derivatives of non-ionisable oligonucleotide analogs were demonstrated to penetrate efficiently into Krebs ascites tumor cells and to alkylate nucleic acids inside the cells with a strong preference towards complementary poly(A)-fragments of mRNA.