REACTIVE DERIVATIVES OF PHOSPHOROTHIOATE OLIGONUCLEOTIDE ANALOGS .2. PROPERTIES OF PHOSPHOROTHIOATE OLIGODEOXYRIBONUCLEOTIDE DERIVATIVES CONTAINING AN AROMATIC ANALOG OF NITROGEN LOST

The alkylating properties of the derivatives of phosphorothioate oligo nucleotide analogues containing the alkylating N'-methyl-N'-2-chloroet hylamino)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 P-31 NMR spec troscopy that reagents of this type are able to alkylate, depending on the conditions, both their own internucleotide phosphorothioate resid ues and nucleophiles in the medium. In the absence of external nucleop hiles in aqueous media, TpsTpsTpN(CH3)CH2RCl forms predominantly the p roducts of intramolecular alkylation of ps-groups rather than the prod ucts of hydrolysis of the RCl-group. In the presence of a nucleophile (1 M aqueous ethylenediamine), the reagent alkylates mainly the alipha tic amino groups of the nucleophile. If the ethylenediamine concentrat ion is reduced to 0.1 M, both processes take place, whereby the rate o f reaction with EDA is twice as high as that of intramolecular alkylat ion. The rate constant of the limiting stage of alkylation (ionization of the C-Cl bond), k(0), does not depend on the presence of the compe titive nucleophile (ethylenediamine) and is 3.95 x 10(-4) s(-1) at 37 degrees C.