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 by mono-alkylation of adenine at N-3 and guanine at N-7, and by cross-linking 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 principal nucleophilic centres, N-7 of guanine and N-3 of adenine, are situated in the 'wide' and 'narrow' grooves of the DNA double helix, respectively. These products could be isolated by their hydrolysis from DNA at neutral pH, followed by chromatography of the hydrolysate in an ion-pair ODS system using a solvent containing tetrabutylammonium hydroxide as ion-pairing reagent; this gave better separation than the previously described method using SP-Sephadex.