A potentiometric and spectrofluorimetric approach to unravel inhibitory effects of semi- and thiosemicarbazones on mushroom tyrosinase activity.

The inhibitory effects on mushrooms tyrosinase activity of some semi- and thiosemicarbazones were investigated. While the semicarbazones are inactive, the thiosemicarbazones are, in general, more active than the reference (kojic acid, IC50 = 70 µM), with maximum activity obtained with benzaldehyde thiosemicarbazone (IC50 = 7 µM). These inhibitors probably act by coordination of the copper(II) metal ions in the active site of tyrosinase: effectively, potentiometric studies conducted in water solutions confirm that the most active thiosemicarbazone is a good ligand for copper(II) ions. The tyrosinase CD spectra do not show any significant difference by addition of an inhibitor or an inactive compound. On the contrary, interesting results were obtained by spectrofluorimetric titrations of mushrooms tyrosinase aqueous solutions with some of the investigated compounds, giving helpful information about possible mechanism of action. The thiosemicarbazones here reported are not cytotoxic on human fibroblasts and do not activate cells in a pro-inflammatory way.

Hydroxyphenyl thiosemicarbazones as inhibitors of mushroom tyrosinase and antibrowning agents.

Tyrosinase is a metalloenzyme involved in o-hydroxylation of monophenols and oxidation of o-diphenols to o-quinones, with formation of brown or black pigments (melanines). Tyrosinase inhibitors are of great interest in medicine and cosmetics (skin whitening compounds), but also in food and beverage industry (antibrowning agents). Here we report on the activity as mushroom tyrosinase inhibitors of a series of hydroxyphenyl thiosemicarbazones (1-5): one of them revealed an inhibitory activity stronger than kojic acid, used as reference. Enzymatic inhibition activity was confirmed by colorimetric measurements on small wheels of Fuji apples treated with the hydroxyphenyl thiosemicarbazones. The mechanism of action of compounds 1-5 was investigated by molecular modelling and by studying in solution their speciation with Cu(II) ions, the ions in the active site of the enzyme. Finally, compounds 1-5 were tested on human fibroblasts: they are not cytotoxic and they do not activate cells in a pro-inflammatory way.

Antiviral activity and metal ion-binding properties of some 2-hydroxy-3-methoxyphenyl acylhydrazones.

Here we report on the results obtained from an antiviral screening, including herpes simplex virus, vaccinia virus, vesicular stomatitis virus, Coxsackie B4 virus or respiratory syncytial virus, parainfluenza-3 virus, reovirus-1 and Punta Toro virus, of three 2-hydroxy-3-methoxyphenyl acylhydrazone compounds in three cell lines (i.e. human embryonic lung fibroblast cells, human cervix carcinoma cells, and African Green monkey kidney cells). Interesting antiviral EC50 values are obtained against herpes simplex virus-1 and vaccinia virus. The biological activity of acylhydrazones is often attributed to their metal coordinating abilities, so potentiometric and microcalorimetric studies are here discussed to unravel the behavior of the three 2-hydroxy-3-methoxyphenyl compounds in solution. It is worth of note that the acylhydrazone with the higher affinity for Cu(II) ions shows the best antiviral activity against herpes simplex and vaccinia virus (EC50 ~ 1.5 µM, minimal cytotoxic concentration = 60 µM, selectivity index = 40).

A versatile salicyl hydrazonic ligand and its metal complexes as antiviral agents.

Acylhydrazones are very versatile ligands and their coordination properties can be easily tuned, giving rise to metal complexes with different nuclearities. In the last few years, we have been looking for new pharmacophores able to coordinate simultaneously two metal ions, because many enzymes have two metal ions in the active site and their coordination can be a successful strategy to inhibit the activity of the metalloenzyme. As a part of this ongoing research, we synthesized the acylhydrazone H2L and its complexes with Mg(II), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II). Their characterization, both in solution--also by means of potentiometric studies--and in the solid state, evidenced the ability of the o-vanillin hydrazone scaffold to give rise to different types of metal complexes, depending on the metal and the reaction conditions. Furthermore, we evaluated both the free ligand and its metal complexes in in vitro studies against a panel of diverse DNA- and RNA-viruses. In particular, the Mg(II), Mn(II), Ni(II) and Zn(II) complexes had EC50 values in the low micromolar range, with a pronounced activity against vaccinia virus.

Antimicrobial and mutagenic properties of organotin(IV) complexes with isatin and N-alkylisatin bisthiocarbonohydrazones.

A new series of ligands is synthesised starting from thiocarbonohydrazide and isatin (H(2)itc) or N-alkylisatin (methyl, H(2)mtc; butyl, H(2)btc; pentyl, H(2)ptc); the X-ray structure of H(2)mtc is discussed. The bis imine ligands are reacted with diorganotin(IV) compounds, obtaining monometallic complexes. In order to establish unequivocally their coordination geometry, the X-ray structures of (C(2)H(5))(2)Sn(Hmtc)Cl.THF (THF, tetrahydrofuran) and (C(6)H(5))Sn(Hptc)Cl(2) are determined. In (C(2)H(5))(2)Sn(Hmtc)Cl.THF, the ligand results monodeprotonated and, essentially, monodentate through the sulphur atom, while in (C(6)H(5))Sn(Hptc)Cl(2) the ligand is still monodeprotonated but SNO tridentate. The organotin(IV) complexes of isatin and N-methylisatin exhibit good antibacterial activity, better than that of the corresponding N-butyl and N-pentylisatin derivatives. Gram positive bacteria are the most sensitive microorganisms. No growth inhibition of fungi is detected up to the concentration of 100 microg/ml. H(2)mtc shows mutagenic activity with and without metabolic activation, whereas no mutagenicity is found for its organotin complexes and for the other compounds.

Antimicrobial and mutagenic activity of some carbono- and thiocarbonohydrazone ligands and their copper(II), iron(II) and zinc(II) complexes.

Several mono- and bis- carbono- and thiocarbonohydrazone ligands have been synthesised and characterised; the X-ray diffraction analysis of bis(phenyl 2-pyridyl ketone) thiocarbonohydrazone is reported. The coordinating properties of the ligands have been studied towards Cu(II), Fe(II), and Zn(II) salts. The ligands and the metal complexes were tested in vitro against Gram positive and Gram negative bacteria, yeasts and moulds. In general, the bisthiocarbonohydrazones possess the best antimicrobial properties and Gram positive bacteria are the most sensitive microorganisms. Bis(ethyl 2-pyridyl ketone) thiocarbonohydrazone, bis(butyl 2-pyridyl ketone)thiocarbonohydrazone and Cu(H2nft)Cl2 (H2nft, bis(5-nitrofuraldehyde)thiocarbonohydrazone) reveal a strong activity with minimum inhibitory concentrations of 0.7 microgram ml-1 against Bacillus subtilis and of 3 micrograms ml-1 against Staphylococcus aureus. Cu(II) complexes are more effective than Fe(II) and Zn(II) ones. All bisthiocarbono- and carbonohydrazones are devoid of mutagenic properties, with the exception of the compounds derived from 5-nitrofuraldehyde. On the contrary a weak mutagenicity, that disappears in the copper complexes, is exhibited by monosubstituted thiocarbonohydrazones.

Organotin complexes with pyrrole-2,5-dicarboxaldehyde bis(acylhydrazones). Synthesis, structure, antimicrobial activity and genotoxicity.

Mono- and bimetallic organotin complexes with pyrrole-2,5-dicarboxaldehyde bis(2-hydroxybenzoylhydrazone) (H5dfps) and pyrrole-2,5-dicarboxaldehyde bis(2-picolinoylhydrazone) (H3dfpp) were synthesized and characterized by IR, 1H and 119Sn NMR spectroscopy. X-ray analysis of the complex [Sn(H3dfps)(C6H5)2].(CH3)2SO revealed a pentacoordination around tin through a N,N,O terdentate ligand behaviour of the hydrazone. This complex is the most active compound, exhibiting MIC values of 3 and 12 micrograms/ml against Gram positive and Gram negative bacteria, respectively. None of the ligands or complexes produced DNA-damage in the Bacillus subtilis rec-assay or showed mutagenic activity in the Salmonella-microsome test.

Antimicrobial and genotoxic activity of 2,6-diacetylpyridine bis(acylhydrazones) and their complexes with some first transition series metal ions. X-ray crystal structure of a dinuclear copper(II) complex.

The antibacterial and antifungal properties of five 2,6-diacetylpyridine bis(acylhydrazones) (acyl:benzoyl, H2dapb; 2-aminobenzoyl, H2dapab; salicyloyl, H2daps; picolinoyl, H2dappc; 2-thenoyl, H2dapt) and of a series of metal complexes were investigated. The x-ray crystal structure of the [Cu(dapt)]2 complex was also determined. It consists of dimeric units in which both copper atoms have sixfold coordination. The evaluation of in vitro antimicrobial properties showed some compounds to exhibit good activity against Gram positive bacteria. In most cases, complexes showed a similar or reduced activity as compared to the ligand itself. Only the iron complexes were found to be more active than the chelating agent involved. None of the compounds showed any significant antifungal activity. The genotoxicity of the compounds described was studied in vitro with Bacillus subtilis rec-assay and Salmonella-microsome reversion assay. No DNA-damaging activity was detected in the Bacillus subtilis rec-assay. H2dapb, H2dapb, and H2dappc were active in the Salmonella test. In several cases, the genotoxic properties of the ligands disappeared in the complexes.