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[Study of the structural-energy aspects of complementary-addressed modifications of nucleic acids by reactive oligonucleotide derivatives having a 4-[N-methyl-N-(2-chloroethyl)amino[benzylidene group at the 3'end by a molecular mechanics method].

Calculations of probabilities of the complementary addressed modification of a target nucleic acid by derivatives of oligonucleotides carrying a 4-[N-(2-chloroethyl)-N-methyl]aminobenzylidene group attached to the 3'-end (3'-BDO) have been made. The results show that the complementary complex of a target NA with 3'-BDO having R-configuration of carbon atom of the dioxalane ring is more stable than the complex including the S-stereoisomer. The S- and R-epimeres of 3'-BDO have essentially different positional abilities for alkylation of the target. The R-epimer alkylates best of all the third base of the target NA from terminal complementary pair of the complex. The S-epimer has another site the most sensitive to alkylation, which is a terminal complementary base of the target NA or the adjacent nonpaired base. Formation of the alkylation complexes are accompanied with a loss or a breakdown of hydrogen bonds in the terminal complementary base pair, thus decreasing the efficiency of alkylation. The modelling results are considered along with experimental data on modification which therefore can be interpreted on the fundamental structural level.