The synthesis of several new 4-amino substituted and 4-unsubstituted 1,10-phenanthroline-3-carboxylic acid derivatives are reported. The 4-amino derivatives (5,6,7) were prepared from 1,4-dihyro-4-oxo-1,10-phenanthroline-3-carboxylic acid (2) via aromatization and 4-chlorination, followed by nucleophilic substitution at C4 by the appropiate alkyl amine. The 4-unsubstituted derivatives (10,11,12) were prepared by aromatization and 4-chlorination of ethyl 1,4-dihydro-1-oxo-1,10-phenanthroline-3-carboxylate. The substituent at C4 was removed by conversion to the 4-tosyl hydrazide, followed by base-catalysed elimination of the hydrazide group. These phenanthroline derivatives were designed as metal-ion-complex mediated DNA cleavage reagents. In both series the 3-carboxylic acid side chain was coupled to beta-alanine to facilitate its conjugation with DNA binding molecules.