Lawsone dimerization in cobalt(III) complexes toward the design of New prototypes of bioreductive prodrugs

摘要

Dimerization of lawsone occurs upon reaction with Co(BF_4) _2·6H_2O and N,N′-bis(pyridin-2-ylmethyl) ethylenediamine (py_2en) to produce the mononuclear complex [Co ~(III)(bhnq)(py_2en)]BF_4·H_2O (1). This complex has been investigated as a prototype of a bioreductive prodrug, where the bhnq~(2-) ligand acts as a model for cytotoxic naphthoquinones. Cyclic voltammetry data in aqueous solution have shown a quasi-reversible Co~(III)/Co~(II) process at E_(1/2) = -0.26 V vs Fc/Fc~+. Reactivity studies revealed the dissociation of bhnq~(2-) from the complex upon reduction of 1 with ascorbic acid, and a dependence of the reaction rate on the oxygen concentration suggests the occurrence of redox cycling.