Organometallic Antitumor Compounds: Ferrocifens as Precursors to Quinone Methides

The synthesis and chemical oxidation profile of a new generation of ferrocifen derivatives with strong anti-proliferative behavior in vitro is reported. In particular, the hydroxypropyl derivative HO(CH2)(3)C(Fc)= C(C6H4OH)(2) (3b) exhibited exceptional antiproliferative activity against the cancer cell lines HepG2 and MDA-MB-231 TNBC, with IC50 values of 0.07 and 0.11 mu m, respectively. Chemical oxidation of 3b yielded an unprecedented tetrahydrofuran-substituted quinone methide (QM) via internal cyclization of the hydroxyalkyl chain, whereas the corresponding alkyl analogue CH3CH2-C(Fc)= C(C6H4OH)(2) merely formed a vinyl QM. The ferrocenyl group in 3b plays a key role, not only as an intramolecular reversible redox "antenna", but also as a stabilized carbenium ion "modulator". The presence of the oxygen heterocycle in 3b-QM enhances its stability and leads to a unique chemical oxidation profile, thus revealing crucial clues for deciphering its mechanism of action in vivo.