Synthesis, characterisation, reactivity and in vitro antiamoebic activity of hydrazone based oxovanadium(IV), oxovanadium(V) and μ-bis(oxo)bis{oxovanadium(v)} complexes

Binuclear, mu-bis(oxo)bis{oxovanadium(v)} complexes [(VOL)(2)(mu-O)(2)] (2 and 7) (where HL are the hydrazones Hacpy-nah I or Hacpy-fah II; acpy = 2-acetylpyridine, nah = nicotinic acid hydrazide and fah = 2-furoic acid hydrazide) were prepared by the reaction of [VO(acac)(2)] and the ligands in methanol followed by aerial oxidation. The paramagnetic intermediate complexes [VO(acac)(acpy-nah)] (1) and [VO(acac)(acpy-fah)] (6) have also been isolated. Treatment of [VO(acac)(aepy-nah)] and [VO(acac)(acpy-fah)] with aqueous H2O2 yields the oxoperoxovanadium(v) complexes [VO(O-2)(acpy-nah)] (3) and [VO(O-2)(acpy-fah)] (8). In the presence of catechol (H,cat) or benzohydroxamic acid (H,bha), 1 and 6 give the mixed chelate complexes [VO(cat)L] (HL = 1: 4, HL = 11: 9) or [VO(bha)L] (HL = 1: 5, HL = II:10). Complexes 4, 5, 9 and 10 slowly convert to the corresponding oxo-mu-oxo species 2 and 7 in DMF solution. Ascorbic acid enhances this conversion under aerobic conditions, possibly through reduction of these complexes with concomitant removal of coordinated catecholate or benzohydroxamate. Acidification of 7 with HCl dissolved in methanol afforded a hydroxo(oxo) complex. The crystal and molecular structure of 2(.)1.5H(2)O has been determined, and the structure of 7 re-determined, by single crystal X-ray diffraction. Both of these binuclear complexes contain the uncommon asymmetrical {VO(mu-O)}(2) diamond core. The in vitro tests of the antiamoebic activity of ligands I and 11 and their binuclear complexes 2 and 7 against the protozoan parasite Entarnoeba histolytica show that the ligands have no amoebicidal activity while their vanadium complexes 2 and 7 display more effective amoebicidal activity than the most commonly used drug metronidazole (IC50 values are 1.68 and 0.45 mu M, respectively vs 1.81 mu M for rnetronidazole). Complexes 2 and 7 catalyse the oxidation of styrene and ethyl benzene effectively. Oxidation of styrene. using H2O2 as an oxidant, gives styrene epoxide, 2-phenylacetaldehyde, benzaldehyde, benzoic acid and 1-phenyl-ethane-1,2-diol, while ethyl benzene yields benzyl alcohol, benzaldehyde and I -phenyl-ethane- 1,2-diol.