ALKYLATION OF DNA BY MELPHALAN WITH SPECIAL REFERENCE TO ADENINE-DERIVATIVES AND ADENINE-GUANINE CROSS-LINKING

Alkylation of DNA by melphalan gave four principal products, derived b y mono-alkylation of adenine at N-3 and guanine at N-7, and by cross-l inking of adenine N-3 to guanine N-7, or of guanine N-7 to guanine N-7 . Adenine-guanine cross-linking was unexpected because the two princip al nucleophilic centres, N-7 of guanine and N-3 of adenine, are situat ed in the 'wide' and 'narrow' grooves of the DNA double helix, respect ively. These products could be isolated by their hydrolysis from DNA a t neutral pH, followed by chromatography of the hydrolysate in an ion- pair ODS system using a solvent containing tetrabutylammonium hydroxid e as ion-pairing reagent; this gave better separation than the previou sly described method using SP-Sephadex.