Nitro analogues of chlorambucil as potential hypoxia-selective anti-tumour drugs.

The chlorambucil isomer 4-[3-[N,N-bis(2-chloroethyl)amino]phenyl] butanoic acid (m-chlorambucil) has been synthesized for the first time, and the two isometric nitro derivatives of both m-chlorambucil and chlorambucil itself have been prepared as potential hypoxia-selective cytotoxins. Reduction potentials (E1/2) of the two nitro compounds were determined by cyclic voltammetry, and one-electron reduction potentials (E(1] were estimated. Both the chlorambucil isomers and the derived nitro compounds crosslink DNA, as determined by their cytotoxicity ratios in DNA repair-proficient and -deficient cell lines, but neither of the nitro derivatives showed selective toxicity under hypoxic conditions, probably due to their rather low reduction potentials.