title: Synthesis, characterisation, reactivity and in vitro antiamoebic activity of hydrazone based oxovanadium(IV), oxovanadium(V) and mu-bis(oxo)bis{oxovanadium(V)} complexes.
abstract: 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)(acpy-nah)] and [VO(acac)(acpy-fah)] with aqueous H2O2 yields the oxoperoxovanadium(V) complexes [VO(O2)(acpy-nah)](3) and [VO(O2)(acpy-fah)](8). In the presence of catechol (H2cat) or benzohydroxamic acid (H2bha), 1 and 6 give the mixed chelate complexes [VO(cat)L](HL =I: 4, HL =II: 9) or [VO(bha)L](HL =I: 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 2.1.5H2O 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 II and their binuclear complexes 2 and 7 against the protozoan parasite Entamoeba 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 microM, respectively vs 1.81 microM for metronidazole). 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 1-phenyl-ethane-1,2-diol.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee, 247 667, India. rkmanfcy@iitr.ernet.in
authors.forename: Mannar R
authors.initials: MR
authors.lastname: Maurya
authors.forename: Shalu
authors.initials: S
authors.lastname: Agarwal
authors.forename: Mohammad
authors.initials: M
authors.lastname: Abid
authors.forename: Amir
authors.initials: A
authors.lastname: Azam
authors.forename: Cerstin
authors.initials: C
authors.lastname: Bader
authors.forename: Martin
authors.initials: M
authors.lastname: Ebel
authors.forename: Dieter
authors.initials: D
authors.lastname: Rehder
mesh_terms: D000818:Animals; D000981:Antiprotozoal Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D004748:Entamoeba histolytica / Q000187:drug effects*; D006835:Hydrazones / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D014638:Vanadates / Q000737:chemistry*
chemical_list: D000981:Antiprotozoal Agents; D006835:Hydrazones; C075743:oxovanadium IV; D014638:Vanadates