[Reactive derivatives of phosphorothioate oligonucleotide analogues. II. Properties of phosphorothioate oligodeoxyribonucleotide derivatives containing an aromatic residue of nitrogen mustard gas]

The alkylating properties of the derivatives of phosphorothioate oligonucleotide analogues containing the alkylating 3'-[N-methyl-4-(N'-methyl-N'-2-chloroethylamino)benzyl]phosphamide group were studied using the alkylating 3'-phosphamide derivative of trithymidine phosphorothioate TpsTpsTpN(CH3)CH2RCl. It was shown by ion-exchange chromatography and 31P NMR spectroscopy that reagents of this type are able to alkylate, depending on the conditions, both their own internucleotide phosphorothioate residues and nucleophiles in the medium. In the absence of external nucleophiles in aqueous media, TpsTpsTpN(CH3)CH2RCl forms predominantly the products of intramolecular alkylation of ps-groups rather than the products of hydrolysis of the RCl-group. In the presence of a nucleophile (1 M aqueous ethylenediamine), the reagent alkylates mainly the aliphatic amino groups of the nucleophile. If the ethylenediamine concentration is reduced to 0.1 M, both processes take place, whereby the rate of reaction with EDA is twice as high as that of intramolecular alkylation. The rate constant of the limiting stage of alkylation (ionization of the C-Cl bond), k0, does not depend on the presence of the competitive nucleophile (ethylenediamine) and is 3.95 x 10(-4) s-1 at 37 degrees C.