STRUCTURE OF TRANSIENT RADICALS FROM CYTOSTATIC-ACTIVE P-ALKOXYPHENOLS BY CONTINUOUS-FLOW EPR

Para-alkoxyphenols are of medical significance as futural cytostatic d rugs in antimelanoma chemotherapy. They take part in a radical redox-r eaction in which the catalytically essential protein-linked tyrosyl ra dical in the functional subunit R2 of the growth-regulating enzyme rib onucleotide reductase (RR) is quenched. EPR spectroscopy has been empl oyed in conjunction with a continuous-flow system to study the structu re of transient radicals from p-alkoxyphenols with different alkyl cha in lengths, Radicals of p-alkoxyphenols were generated by oxidation in a Fenton system (Ti3+/H2O2, pH1) after rapid mixing in a novel contin uous-flow EPR cavity designed especially for low consumption of substa nce. Hyperfine structures identified by spectral simulation show that the structure of transient radicals from oxidized para-alkoxyphenols ( methyl-, ethyl-, allyl-, propyl-,iso-propyl-, butyl-, iso-butyl-) belo ng to the type of phenoxyl radicals formed after abstraction of the OH proton. Hyperfine coupling constants are similar and vary only slight ly with alkyl substituents.