A Palladium(II) Center Activates Nitrile Ligands toward 1,3-Dipolar Cycloaddition of Nitrones Substantially More than the Corresponding Platinum(II) Center

Novel Non-Toxic Highly Antibacterial Chitosan/Fe(III)-Based Nanoparticles That Contain a Deferoxamine—Trojan Horse Ligands: Combined Synthetic and Biological Studies

In this study, we prepared chitosan/Fe(III)/deferoxamine nanoparticles with unimodal size distribution (hydrodynamic diameter ca. 250 nm, zeta potential ca. 32 mV). The elaborated nanoparticles are characterized by outstanding in vitro and in vivo antibacterial activity, which exceeds even that of commercial antibiotics ampicillin and gentamicin. Moreover, the nanoparticles are non-toxic. We found that the introduction of iron ions into the chitosan matrix increases the ability of the resulting nanoparticles to disrupt the integrity of the membranes of microorganisms in comparison with pure chitosan. The introduction of deferoxamine into the obtained nanoparticles sharply expands their effect of destruction the bacterial membrane. The obtained antibacterial nanoparticles are promising for further preclinical studies.

Towards Anion Recognition and Precipitation with Water-Soluble 1,2,4-Selenodiazolium Salts: Combined Structural and Theoretical Study

The synthesis and structural characterization of a series of supramolecular complexes of bicyclic cationic pyridine-fused 1,2,4-selenodiazoles with various anions is reported. The binding of trifluoroacetate, tetrachloroaurate, tetraphenylborate, perrhenate, and pertechnetate anions in the solid state is regarded. All the anions interact with selenodiazolium cations exclusively via a pair of “chelating” Se⋯O and H⋯O non-covalent interactions, which make them an attractive, novel, non-classical supramolecular recognition unit or a synthon. Trifluoroacetate salts were conveniently generated via novel oxidation reaction of 2,2′-dipyridyl diselenide with bis(trifluoroacetoxy)iodo)benzene in the presence of corresponding nitriles. Isolation and structural characterization of transient 2-pyridylselenyl trifluoroacetate was achieved. X-ray analysis has demonstrated that the latter forms dimers in the solid state featuring very short and strong Se⋯O and Se⋯N ChB contacts. 1,2,4-Selenodiazolium trifluoroacetates or halides show good solubility in water. In contrast, (AuCl₄)⁻, (ReO₄)⁻, or (TcO₄)⁻ derivatives immediately precipitate from aqueous solutions. Structural features of these supramolecular complexes in the solid state are discussed. The nature and energies of the non-covalent interactions in novel assembles were studied by the theoretical methods. To the best of our knowledge, this is the first study that regards perrhenate and pertechnetate as acceptors in ChB interactions. The results presented here will be useful for further developments in anion recognition and precipitation involving cationic 1,2,4-selenodiazoles.

The first selenium containing chitin and chitosan derivatives: Combined synthetic, catalytic and biological studies

Ultrasonic approach to the synthesis of the first selenium-containing derivatives of chitin and chitosan has been developed. The synthetic procedure is simple, provides high yields, does not require harsh conditions, and uses water as the reaction medium. The elaborated chitin and chitosan derivatives and their based nanoparticles are non-toxic and possess high antibacterial and antifungal activity. Their antimicrobial activity exceeds the effect of the classic antibiotics (Ampicillin and Gentamicin) and the antifungal drug Amphotericin B. The obtained selenium-containing cationic chitin and chitosan derivatives exhibit a high transfection activity and are promising gene delivery vectors. Nanoparticles of the synthesized polymers are highly efficient catalysts for the oxidation of 1-phenylethyl alcohol to acetophenone by bromine at room temperature.

Ultrasound and click chemistry lead to a new chitin chelator. Its Pd(II) complex is a recyclable catalyst for the Sonogashira reaction in water

For the first time the possibility of chitin use as an accessible and easily-modifiable support for an efficient Pd(II) catalyst has been demonstrated. The modification of chitin avoiding a noticeable chain scission or deacetylation, is achieved by sonochemical alkylation with 1-azido-3-chloropropan-2-ol followed by a convenient azido-alkyne click reaction. The obtained polymer represents an extremely rare case of the chitin derivative soluble both in water and organic solvents. The treatment of that derivative with imino-isonitrile Pd(II) complex solution yielded a chitin-supported Pd(II) complex. The latter could be obtained as a powder or as uniform nanoparticles in different size ranges. The nanoparticles with a hydrodynamic diameter of 30 nm were shown to be the most efficient form of catalyst for the copper- and phosphine-free Sonogashira cross-coupling in water.

Copper(I)-Catalyzed 1,3-Dipolar Cycloaddition of Ketonitrones to Dialkylcyanamides: A Step toward Sustainable Generation of 2,3-Dihydro-1,2,4-oxadiazoles

Cu^I-catalyzed cycloaddition (CA) of the ketonitrones, Ph₂C=N⁺(R')O^- (R' = Me, CH₂Ph), to the disubstituted cyanamides, NCNR₂ (R = Me₂, Et₂, (CH₂)₄, (CH₂)₅, (CH₂)₄O, C₉H₁₀, (CH₂Ph)₂, Ph(Me)), gives the corresponding 5-amino-substituted 2,3-dihydro-1,2,4-oxadiazoles (15 examples) in good to moderate yields. The reaction proceeds under mild conditions (CH₂Cl₂, RT or 45 °C) and requires 10 mol % of [Cu(NCMe)₄](BF₄) as the catalyst. The somewhat reduced yields are due to the individual properties of 2,3-dihydro-1,2,4-oxadiazoles, which easily undergo ring opening via N-O bond splitting. Results of density functional theory calculations reveal that the CA of ketonitrones to Cu^I-bound cyanamides is a concerted process, and the copper-catalyzed reaction is controlled by the predominant contribution of the HOMO_dipole-LUMO_{dipolarophile} interaction (group I by Sustmann's classification). The metal-involving process is much more asynchronous and profitable from both kinetic and thermodynamic viewpoints than the hypothetical metal-free reaction.

PdII-mediated integration of isocyanides and azide ions might proceed via formal 1,3-dipolar cycloaddition between RNC ligands and uncomplexed azide

The generation of (tetrazolate)Pd^II complexes via the integration of (isocyanide)Pd^II precursors with uncomplexed azides and the verification of plausible reaction mechanisms.

Regio- and Stereoselective 1,3-Dipolar Cycloaddition of Cyclic Azomethine Imines to Platinum(IV)-Bound Nitriles Giving Δ(2)-1,2,4-Triazoline Species

The complex trans-[PtCl4(EtCN)2] (14) reacts smoothly at 25 °C with the stable cyclic azomethine imines R(1)CH═N(a)NC(O)CH(NHC(O)C6H4R(3))C(b)H(C6H4R(2))((a-b)) [R(1)/R(2)/R(3) = p-Me/H/H (8); p-Me/p-Me/H (9); p-Me/p-MeO/H (10); p-Me/p-Cl/p-Cl (11); p-MeO/p-Me/H (12); p-MeO/p-Cl/m-Me (13)], and the reaction proceeds as stereoselective 1,3-dipolar cycloaddition to one of the EtCN ligands accomplishing the monocycloadducts trans-[PtCl4(EtCN){N(a)═C(Et)N(b)C(O)CH(NHC(O)C6H4R(3))CH(C6H4R(2))N(c)C(d)HR(1)}])((a-d;b-c)) [R(1)/R(2)/R(3) = p-Me/H/H (15); p-Me/p-Me/H (16); p-Me/p-MeO/H (17); p-Me/p-Cl/p-Cl (18); p-MeO/p-Me/H (19); p-MeO/p-Cl/m-Me (20)]. Inspection of the obtained and literature data indicate that the cycloaddition of the azomethine imines to the C≡N bonds of HCN and of Pt(IV)-bound EtCN has different regioselectivity leading to Δ(2)-1,2,3-triazolines and Δ(2)-1,2,4-triazolines, respectively. Platinum(II) species trans-[PtCl2(EtCN){N(a)═C(Et)N(b)C(O)CH(NHC(O)C6H4R(3))CH(C6H4R(2))N(c)C(d)HR(1)}]((a-d;b-c)) [R(1)/R(2)/R(3) = p-Me/H/H (21); p-Me/p-Me/H (22); p-Me/p-MeO/H (23); p-Me/p-Cl/p-Cl (24); p-MeO/p-Me/H (25); p-MeO/p-Cl/m-Me (26)] were obtained by a one-pot procedure from 14 and 8-13 followed by addition of the phosphorus ylide Ph3P═CHCO2Me. Δ(2)-1,2,4-Triazolines N(a)═C(Et)N(b)C(O)CH(NHC(O)C6H4R(3))CH(C6H4R(2))N(c)C(d)HR(1(a-d;b-c)) [R(1)/R(2)/R(3) = p-Me/H/H (27); p-Me/p-Me/H (28); p-Me/p-MeO/H (29); p-Me/p-Cl/p-Cl (30); p-MeO/p-Me/H (31); p-MeO/p-Cl/m-Me (32)] were liberated from 21-26 by the treatment with bis(diphenylphosphyno)ethane (dppe). Platinum(II) complexes 21-26 were characterized by elemental analyses (C, H, N), high-resolution electrospray ionization mass spectrometry (ESI-MS), and IR and (1)H and (13)C{(1)H} NMR spectroscopies and single crystal X-ray diffraction in the solid state for 25·CH3OH, 26·(CHCl3)0.84. The structure of 26 was also determined by COSY-90 and NOESY NMR methods in solution. Quantitative evaluation of several pairs of interproton distances obtained by NMR and X-ray diffraction agrees well with each other and with those obtained by the MM+ calculation method. Platinum(IV) complexes 15-20 were characterized by (1)H NMR spectroscopy. Metal-free 6,7-dihydropyrazolo[1,2-a][1,2,4]triazoles (27-32) were characterized by high-resolution ESI-MS and IR and (1)H and (13)C{(1)H} NMR spectroscopies and single crystal X-ray diffraction for 29·CDCl3. Theoretical density functional theory calculations were carried out for the investigation of the reaction mechanism, interpretation of the reactivity of Pt-bound and free nitriles toward azomethine imines and analysis of the regio- and stereoselectivity origin.

Zinc(ii)-mediated generation of 5-amino substituted 2,3-dihydro-1,2,4-oxadiazoles and their further ZnII-catalyzed and O2-involving transformations

Zn^II-activated cyanamides NCNR₂ react with the acyclic N-alkyl ketonitrones Ph₂CN⁺(O⁻)R′ achieving uncomplexed 2,3-dihydro-1,2,4-oxadiazoles.

Aerobic oxidation at benzylic positions catalyzed by a simple Pd(OAc)2/bis-triazole system

An extremely active palladium catalyst system for the aerobic oxidation of benzyl alcohols and benzylic C–H oxidation is described.

Novel (cyanamide)ZnIIcomplexes and zinc(ii)-mediated hydration of the cyanamide ligands

The Zn^II-mediated hydration of cyanamides does not require any co-catalyst.