Lorenzo Biancalana

Arene Ruthenium(II) Complexes with Phosphorous Ligands as Possible Anticancer Agents

Ruthenium(II) complexes of formula [Ru(η6-arene)Cl2 (PTA)] (RAPTA) are potential anticancer drugs with notable antimetastatic and antiangiogenic activity, which are now pointing to clinical trials. Following the great interest aroused by these compounds, a variety of RAPTA derivatives, obtained by chloride substitution and/or containing functionalized arene ligands, and complexes resembling the RAPTA structure but bearing different phosphorous ligands have been synthesized and evaluated for their anticancer activity. An overview of all of these biologically relevant complexes will be given, with particular reference to the anticancer behaviour exhibited by the compounds and the possible relationship with structural aspects.

Structural characterization of α-amino acid complexes of molybdates: a spectroscopic and DFT study

The reactions of L-enantiopure α-amino acids (aaH) with Na2MoO4 led to the high-yield isolation of Mo(VI) complexes of general formula Mo2O4(OH)4(aaH). A similar outcome was achieved by using (NH4)6Mo7O24 in the place of Na2MoO4. Solid-state IR and NMR spectroscopy indicated the presence of cis-MoO2 units linked by a zwitterionic amino acid ligand, via a bidentate bridging coordination through the carboxylate group. Thus possible dinuclear and polynuclear structures are proposed on the basis of DFT calculations.

α-Diimines as Versatile, Derivatizable Ligands in Ruthenium(II) p-Cymene Anticancer Complexes

α-Diimines are among the most robust and versatile ligands available in synthetic coordination chemistry, possessing finely tunable steric and electronic properties. A series of novel cationic ruthenium(II) p-cymene complexes bearing simple α-diimine ligands, [(η6- p-cymene)RuCl{κ2 N-(HCNR)2}]NO3 (R = Cy, [1]NO3; R = 4-C6H10OH, [2]NO3; R = 4-C6H4OH, [3]NO3), were prepared in near-quantitative yields as their nitrate salts. [2]NO3 displays high water solubility. The potential of the α-diimine ligand in [3]NO3 as a carrier of bioactive molecules was investigated via esterification reactions with the hydroxyl groups. Thus, the double-functionalized derivatives [(η6- p-cymene)RuCl{κ2 N-(HCN(4-C6H4OCO-R))2}]NO3 (R = aspirinate, [5]NO3; valproate, [6]NO3) and also [4]Cl (R = Me) were obtained in good-to-high yields. UV-vis and multinuclear NMR spectroscopy and cyclic voltammetric studies in aqueous solution revealed only minor ruthenium chloride hydrolytic cleavage, biologically accessible reduction potentials, and pH-dependent behavior of [3]NO3. Density functional theory analysis was performed in order to compare the Ru-Cl bond strength in [1]+ with the analogous ethylenediamine complex, showing that the higher stability observed in the former is related to the electron-withdrawing properties of the α-diimine ligand. In vitro cytotoxicity studies were performed against tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK-293) cell lines, with the complexes bearing simple α-diimine ligands ranging from inactive to IC50 values in the low micromolar range. The complexes functionalized with bioactive components, i.e., [5]NO3 and [6]NO3, exhibited a marked increase in the cytotoxicity with respect to the precursor [3]NO3.

Ruthenium arene complexes with triphenylphosphane ligands: cytotoxicity towards pancreatic cancer cells, interaction with model proteins, and effect of ethacrynic acid substitution

The ruthenium-arene complexes [(η6-p-cymene)RuCl2(κP-PPh2(4-C6H4CO2H))], 1, [(η6-p-cymene)RuCl(κ2P,O-PPh2(2-C6H4CO2))], 2, [(η6-p-cymene)RuCl2(κP-PPh2(2-C6H4OCO-EA))], 3, and [(η6-p-cymene)RuCl2(κP-PPh2(4-C6H4CO2CH2CH2OCO-EA))], 4 (EA-CO2H = ethacrynic acid), were synthesized in good to high yields and characterized by analytical techniques, IR, UV-Vis and multinuclear NMR spectroscopy, and single crystal X-ray diffraction in the cases of 1 and 2. The unstable compounds [(η6-arene)RuCl2(κP-PPh2(2-C6H4CO2CH2CH2OCO-EA))] (arene = p-cymene, 5a; arene = C6H6, 5b) were obtained and identified in solution by NMR. Electrochemical and spectro-electrochemical experiments were performed in order to assess the redox behaviour of 1–4 in CH2Cl2. The in vitro cytotoxicity of 1–4 was determined on the human pancreatic cancer cell line BxPC3 and the mouse embryo fibroblast Balb/3T3 Clone A31 cell line, the latter acting as a model for normal cells. Furthermore, the interaction of 1, 3 and 4 with two model proteins was investigated by high resolution ESI-MS.

Ruthenium p-cymene complexes with α-diimine ligands as catalytic precursors for the transfer hydrogenation of ethyl levulinate to γ-valerolactone

The ruthenium compounds [(η6-p-cymene)RuCl{κ2N-(HCNR)2}]NO3 (R = 4-C6H4Me, [1]NO3; 4-C6H4OH, [2]NO3; C6H11Cy, [3]NO3; 4-C6H10OH, [4]NO3; tBu, [5]NO3) were prepared in high yields from [(p-cymene)RuCl2]2, AgNO3 and the appropriate α-diimine. Compounds [2]PF6 and [4]PF6 were obtained by a straightforward reaction of [(η6-p-cymene)RuCl(MeCN)0.66]PF6, [6]PF6, with α-diimine, whereas [4]BPh4 was obtained by metathesis between [4]NO3 and NaBPh4. All the ruthenium products were characterized by analytical methods, IR, NMR and UV-Vis spectroscopy; in addition, the structure of [1]NO3 was ascertained by an X-ray diffraction study. Compounds [1–4]NO3, [4]PF6 and [4]BPh4 were investigated as catalytic precursors in the transfer hydrogenation reaction of ethyl levulinate to γ-valerolactone in isopropanol solution under microwave irradiation. [4]BPh4 was revealed to be the best catalytic precursor, affording γ-valerolactone in 62% yield under optimized experimental conditions.

The reactions of α-amino acids and α-amino acid esters with high valent transition metal halides: synthesis of coordination complexes, activation processes and stabilization of α-ammonium acylchloride cations

Titanium tetrachloride smoothly reacted with a selection of α-amino acids (aaH) in CH2Cl2 affording yellow to orange solid coordination compounds, 1a–d, in 70–78% yields. The salts [NHEt3][TiCl4(aa)], 2a–b, were obtained from TiCl4/aaH/NEt3 (aa = L-phenylalanine, N,N-dimethylphenylalanine), in 60–65% yields. The complex , 3, was isolated from the reaction of L-proline with NbCl5/NHiPr2, performed in CH2Cl2 at room temperature. The X-ray structure of 3 features a bridging (E)-1,2-bis(3,4-dihydro-2H-pyrrol-5-yl)ethene-1,2-diolate ligand, resulting from the unprecedented C–C coupling between two proline units. Unusually stable α-ammonium acyl chlorides were prepared by the reactions of PCl5/MCln (MCln = NbCl5, WCl6) with L-proline, N,N-dimethylphenylalanine, sarcosine and L-methionine. MX5 (M = Nb, Ta; X = F, Cl) reacted with L-leucine methylester and L-proline ethylester to give ionic coordination compounds, [MX4L2][MX6] (M = Nb, L = Me2CHCH2CH(NH2)CO2Me, X = F, 9; Cl, 11a; M = Nb, X = Cl, , 11c; Ta, 11d), in moderate to good yields. [NbCl5(Me2CHCH2CHNH3CO2Me)][NbCl6], 12, was isolated as a co-product of the reaction of NbCl5 with L-leucine isopropylester, and crystallographically characterized. The reaction of NbCl5 with L-serine isopropylester afforded NbCl3(OCH2CHNHCO2iPr), 13, in 66% yield. The activation of the ester O–R bond was observed in the reactions of L-leucine methyl ester with NbF5 and L-proline ethyl ester with MBr5 (M = Nb, Ta), these reactions proceeding with the release of EtF and EtBr, respectively. All the metal products were characterized by analytical and spectroscopic methods, while DFT calculations were carried out in order to provide insight into the structural and mechanistic aspects.

Synthesis and study of the stability of amidinium/guanidinium carbamates of amines and α-amino acids

Thermally stable amidinium/guanidinium N,N-dialkylcarbamates, including vacuum stable compounds, have been prepared, and then isolated in the solid state, by reaction of tetramethylguanidine (TMG) or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with secondary amines under atmospheric pressure of CO2. The same method has been successfully applied to α-amino acids, thus the corresponding carbamates of sarcosine, L-proline and L-phenylalanine have been obtained. All the products are highly moisture sensitive, and have been characterized by analytical and spectroscopic (IR, multinuclear NMR) techniques.

Vanadium(V) oxoanions in basic water solution: a simple oxidative system for the one pot selective conversion of L-proline to pyrroline-2-carboxylate

The unprecedented, direct chemical oxidation of l-proline to pyrroline-2-carboxylate was achieved in water (pH 9-10) by means of NH4VO3/NH3 or V2O5/MOH (K = Na, K), and the anion was fully characterized as ammonium or alkaline metal salts. Quantitative yield and higher atom economy performance were achieved with the latter system, the alkaline salts being more stable than the ammonium one. Different mixed valence V(iv)/V(v) compounds precipitated from the reaction mixtures depending on the nature of the employed base. A possible reaction mechanism is proposed according to DFT calculations. The analogous reaction of trans-4-hydroxy-l-proline with NH4VO3/NH3 afforded pyrrole-2-carboxylic acid in 81% yield, while sarcosine underwent prevalent decomposition under similar experimental conditions. Instead, no reaction was observed with primary (glycine, l-alanine, l-phenylalanine) and tertiary α-amino acids (N,N-dimethyl-l-phenylalanine, N,N-dimethylglycine).

Ovalbumin labeling with p-hydroxymercurybenzoate: The effect of different denaturing agents and the kinetics of reaction.

The aim of our study was to investigate how denaturing agents commonly used in protein analysis influence the labeling between a reactive molecule and proteins. For this reason, we investigated the labeling of ovalbumin (OVA) as a globular model protein with p-hydroxymercurybenzoate (pHMB) in its native state (phosphate buffer solution) and in different denaturing conditions (8 molL(-1) urea, 3 molL(-1) guanidinium thiocyanate, 6 molL(-1) guanidinium chloride, 0.2% sodium dodecyl sulfate, and 20% methanol). In addition to chemical denaturation, thermal denaturation was also tested. The protein was pre-column simultaneously denatured and derivatized, and the pHMB-labeled denatured OVA complexes were analyzed by size exclusion chromatography (SEC) coupled online with chemical vapor generation-atomic fluorescence spectrometry (CVG-AFS). The number of -SH groups titrated greatly depends on the protein structure in solution. Indeed, we found that, depending on the adopted denaturing conditions, OVA gave different aggregate species that influence the complexation process. The results were compared with those obtained by a common alternative procedure for the titration of -SH groups that employs monobromobimane (mBBr) as tagging molecule and molecular fluorescence spectroscopy as detection technique. We also investigated the labeling kinetics for denatured OVA and pHMB, finding that the 4 thiolic groups of OVA have a very different reactivity toward mercury labeling, in agreement with previous studies.

CCDC 1843860: Experimental Crystal Structure Determination

Related Article: Niccolo Bartalucci, Lorenzo Biancalana, Marco Bortoluzzi, Guido Pampaloni, Luca Giordano, Stefano Zacchini, Fabio Marchetti|2018|Chem. Sel.|3|8844|doi:10.1002/slct.201801865