Synthesis and characterization of novel silica gel supported N-pyrazole ligand for selective elimination of Hg(II)

The polar organic molecule N-(2-hydroxyethyl)-3,5-dimethylpyrazole reacted with a 3-glycidoxypropyltrimethoxysilane silylant agent, previously anchored on a silica surface in a heterogeneous way to yield the product SiPz. The epoxide group was opened yielding chelating pendant group bonded to the inorganic surface. The product was characterized through elemental analysis, infrared spectroscopy, ¹³C NMR, surface area and thermogravimetry. The binding and adsorption abilities of SiPz was investigated for Hg²⁺, Cd²⁺, Pb²⁺, Cu²⁺, Zn²⁺, K⁺, Na⁺ and Li⁺ cations and compared to results of classical liquid-liquid extraction with the unbound N-pyrazole compound. The grafting at the surface of silica does not affect complexing properties of the ligand and the SiPz exhibits a high selectivity toward Hg²⁺ ion with no complexation being observed towards Zinc and alkali metals. The extracted and the complexing cation percentage were determined by atomic absorption measurements.     

Spectral modulation of charge transfer fluorescence probe encapsulated inside aqueous and non-aqueous β-cyclodextrin nanocavities

In this work, we report the spectral modulations of a intramolecular charge transfer (ICT) molecule ethyl ester of N,N-dimethylaminonaphthyl-(acrylic)-acid (EDMANA) when encapsulated in the water and N,N-dimethylformamide (DMF) solution of β-CD nanocavities. From the nature of the Benesi-Hildebrand (B-H) plots, the stoichiometry of the host guest inclusion complexes are found to be 1:1 in water β-CD solution and both 1:1 and 1:2 in DMF β-CD solution. The preferential location and difference in orientation of EDMANA molecule inside the β-CD cavity has been accessed by analysis of the effect of acid and metal cation Ni²⁺ on the spectral characteristics in both the media. In case of 1:1 complex, the polar donor group prefers to expose to bulk aqueous phase capable of binding with H⁺ and Ni²⁺ ions and the acceptor to the hydrophobic interior. On the other hand, the acceptor group remains exposed to the non-polar bulk phase and the donor group is orientated preferentially inside the non-polar core in 1:2 inclusion complexes.     

Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

gem-Difluoromethylation of α- and γ-ketoesters: preparation of gem-difluorinated α-hydroxyesters and γ-butyrolactones

PhSCF₂SiMe₃ has been demonstrated as difluoromethyl carbanion synthon (⁻CF₂H). It reacts chemoselectively with α- and γ-ketoesters at the keto group in the presence of a catalytic amount of TBAF in THF to give the corresponding α-hydroxy ester adducts as well as γ-gem-difluorophenylsulfanylmethylated-γ-butyrolactones in good yields. Reductive cleavage of the phenylsulfanyl group of these products employing Bu₃SnH/AIBN gives the corresponding gem-difluoromethylated α-hydroxyesters and γ-butyrolactones in good yields.     

Introducing difluoromethylene sulfonamide group via nucleophilic addition of difluoromethylene anion with aromatic aldehydes

A new fluorine-containing synthon, R¹COCF₂SO₂R² (2, R¹, R²=morpholino, piperidino, etc.), was developed for the introduction of difluoromethylene sulfonamide or difluoromethylene group. Under different conditions, 2 reacted readily with aromatic aldehydes to give the corresponding difluoromethylene-containing alcohols or diols in moderate to good yields in the presence of potassium tert-butoxide. Difluoromethylene sulfonamide group was introduced into organic compounds directly for the first time by this method.     

Ferro- and antiferromagnetic interactions in polymeric and molecular complexes of Cu(hfac)2 with 1-oxoazin-2-yl-substituted nitronyl nitroxides

Solid heterospin compounds based on Cu(hfac)₂ complexes with a new group of nitronyl nitroxides bearing different azine-N-oxide substituents at position 2 of the 2-imidazoline ring (Lⁿ) were studied. The major factor responsible for the change in the magnetic characteristics of the [Cu(hfac)₂L¹] complex with triazine nitronyl nitroxide with temperature was shown to be the specific pairwise packing of heterospin molecules with the dominant antiferromagnetic exchange between the radical fragments of adjacent molecules. For complexes of Cu(hfac)₂ with 1-oxoazin-2-yl-substituted nitronyl nitroxides L² and L⁴, 7-membered metallocycles were obtained, although they form rarely. It was shown that polymer chains formed in the solid complex with spin-labeled pyrazine-N-oxide [(Cu(hfac)₂)₃(L³)₂] due to the cross-linking of {(Cu(hfac)₂)₂(L³)₂} binuclear fragments via the bridging [Cu(hfac)₂].     

Synthesis of N-functionalized 2,2′-dipyridylamine ligands, complexation to ruthenium (II) and anchoring of complexes to papain from papaya latex

2,2′-Dipyridylamine (dpa) derivatives carrying a thiol-targeted maleimide group located at the end of an alkyl substituent on the central amine were synthesized. Reaction with the organometallic precursors [(η⁶-arene)RuCl₂]₂ (arene = benzene or p-cymene) yielded the half-sandwich cationic complexes [(η⁶-arene)Ru(dpa)Cl]⁺ where the dipyridylamine derivatives were coordinated as bidentate N,N donor ligands. Enzymatic studies showed that these derivatives were able to inactivate the cysteine endoproteinase papain by S-alkylation of the cysteine active site.     

Copper(I) tert-butoxide-promoted coupling of o-(1-hydroxyalkyl)arylsilanes with organic halides

Copper(I) tert-butoxide-promoted coupling of arylsilanes possessing a 1-hydroxyalkyl group at the o-position with organic halides proceeded to give disubstituted arenes. The results indicate that an intermediary arylcopper species is formed by aromatic C^sp2-to-O silyl migration.     

New approach to preparation of N-acylphosphoramido(thio)(seleno)ates

N-[2-(X)-1,3,2-Oxathiaphospholane] derivatives (X = S, Se, O) of carboxamides were prepared and their DBU-assisted reaction with alcohols led to the corresponding O-alkyl-N-acylphosphoramido(thio)(seleno)ates. Their structures were confirmed by MS analysis and ¹H and ³¹P NMR spectroscopy. Independently N-acylphosphoramidoselenoates were converted to N-acylphosphoramidates by treatment with tert-butylperoxytrimethylsilane. The oxathiaphospholane approach was also applied to the synthesis of derivatives having N-prolylphosphoramido(thio)(seleno)ate linkages on the 5′-OH group of AMP.     

Electrostatic forces that determine O,O-trans versus O,S-cis conformers in the aminated porphyrin complexes of Cd(N-NHCO-2-C4H3O-tpp)(OAc) and Cd(N-NHCO-2-C4H3S-tpp)(OAc)

Two new diamagnetic, mononuclear and aminated porphyrin complexes of O,O-trans-Cd (3-trans) and O,S-cis-Cd (4-cis) have been synthesized and characterized by ¹H, ¹³C NMR spectroscopy. The crystal structures of (acetato)(N-2-furancarboxamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C₄H₃O-tpp)(OAc); 3-trans] and (acetato)(N-2-thiophenecarboxamido-meso-tetraphenylporphyrinato)cadmium(II) [Cd(N-NHCO-2-C₄H₃S-tpp)(OAc); 4-cis] were determined. The coordination sphere around Cd²⁺ is a distorted square-based pyramid in which the apical site is occupied by a bidentate chelating OAc⁻ group for 3-trans and 4-cis. The plane of three pyrrole nitrogen atoms [i.e., N(1), N(2), N(4) for 3-trans and N(1), N(2), N(3) for 4-cis] strongly bonded to Cd²⁺ is adopted as a reference plane 3N. The N(3) and N(4) pyrrole rings bearing the 2-furancarboxamido (Fr) and 2-thiophenecarboxamido groups in 3-trans and 4-cis, respectively, deviate mostly from the 3N plane, thus orienting separately with a dihedral angle of 33.4° and of 31.0°. In 3-trans, Cd²⁺ and N(5) are located on different sides at 1.06 and −1.49 Å from its 3N plane, while in 4-cis, Cd²⁺ and N(5) are also located on different sides at 1.04 and −1.53 Å from its 3N plane. An attractive electrostatic interaction between the Cd²⁺ and O(4)⁻ atoms in furan stabilizes the O,O-trans conformer of 3. A repulsive electrostatic interaction between Cd²⁺ and S(1)⁺ destabilizes the O,S-trans conformer of 4. Both of these repulsive and the mutually attractive interactions between S(1)⁺ and O(3)⁻ atoms favor the O,S-cis rotamer of 4 both in the vapor phase and in low polarity solvents. NOE difference spectroscopy, HMQC and HMBC were employed for the unambiguous assignment of the ¹H and ¹³C NMR resonances of 3-trans and 4-cis in CDCl₃ at 20 and −50 °C.     

Synthesis of imidazolidin-4-one and 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-dione derivatives of primaquine: scope and limitations

The synthesis of imidazolidin-4-one derivatives of primaquine as potential antimalarial agents is described. The target compounds were synthesized in three steps: (i) condensation of (±)-primaquine with N^α-protected amino acids, (ii) removal of the N^α-protecting group, and (iii) reaction of the N-acylprimaquine with a carbonyl compound: acetone, three cyclic ketones and veratraldehyde. Using 2-formylbenzoic acid in the third step afforded 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-diones. All products were isolated in good to excellent yields. Whereas imidazolidin-4-ones were formed as mixtures of all possible diastereomers in equal amounts, 1H-imidazo[2,1-a]isoindole-2,5(3H,9bH)-diones were produced in a stereoselective fashion. The compounds hydrolyse very slowly (t_1/2 5-30 d) in pH 7.4 buffer to release primaquine. These primaquine derivatives are being submitted to biological assays, and preliminary results of their antimalarial activity are quite encouraging.     

Total synthesis of cucurbitoside A using a novel fluorous protecting group

The first total synthesis of cucurbitoside A was achieved using a new fluorous N-phenylcarbamoyl (^FCar) protecting group. The ^FCar group was introduced into carbohydrates in high yield and was selectively removed with Bu₄NNO₂ without damaging other acyl protecting groups. The synthetic intermediates were easily isolated by fluorous solid-phase extraction.     

Thyonosides A and B, two new saponins isolated from the holothurian Thyone aurea

The structures of two saponins, thyonosides A and B, isolated from the holothurian Thyone aurea collected in Namibia, were elucidated by 1D and 2D NMR (¹H, ¹³C, ¹H-¹H COSY, ¹H-¹H J-resolved, TOCSY, HMQC, HMBC and NOESY). The two compounds have the same aglycon but different oligosaccharidic chains. Thyonoside A has a 3-O-methyl-β-d-xylopyranosyl-(1→3)-6-O-sodium sulphate-β-d-glucopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain, and thyonoside B a 3-O-methyl-β-d-xylopyranosyl-(1→4)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl-(1→2)-4-O-sodium sulphate-β-d-xylopyranosyl chain. The holostane-type aglycon features an endocyclic double bond at position 7-8, a double bond at position 25-26 and a β-acetoxy group at C16.     

Three new monoterpene indole alkaloids from Psychotria umbellata Thonn.

Three new psychollatine-derived monoterpene indole alkaloids were obtained from Psychotria umbellata Thonn.: 3,4-Dehydro-18,19-β-epoxy-psychollatine (2), N⁴-[1-((R)-2-hydroxypropyl)]-psychollatine (3), and N⁴-[1-((S)-2-hydroxypropyl)]-psychollatine (4). Their structures were determined by ¹H and ¹³C NMR spectra, 2D correlations (COSY, HMQC, and HMBC), and mass and UV spectra. Compounds 3 and 4 were synthesized for structural confirmation and for the determination of the stereochemistry of the hydroxyl group.     

Synthesis of dinucleoside phosphates and their analogs by the boranophosphotriester method using azido-based protecting groups

Oligodeoxyribonucleotides and their backbone-modified analogs were synthesized in good yields by the boranophosphotriester method in solution. The oligodeoxyriobonucleoside boranophosphates, fully protected with 2-(azidomethyl)benzoyl groups, were converted to the various backbone-modified DNA analogs via the corresponding H-phosphonate intermediates. A new efficient protecting group for the O⁶-position of 2′-deoxyguanosine, 4-[(2-azidomethyl)benzoyloxy]benzyl (AZBn) group, was also developed. The AZBn group was found to be quickly removed by treatment with MePPh₂ in dioxane-2-mercaptoethanol-H₂O.     

Versatility of an intramolecularly hydrogen-bonded 4-(N,N-dimethylamino)benzoate group as a signaling subunit for anion recognition

The versatility of the 4-(N,N-dimethylamino)benzoate (DMAB) group embedded in host 1 as a signaling subunit for anion recognition was elucidated in terms of ¹H NMR, CD, and fluorescence studies. Host 1 showed 1:1 complexation with monovalent anions and stepwise 1:1 and 2:1 (host 1: anion) complexation with divalent phosphate anions. The binding constants between host 1 and anions were determined by means of ¹H NMR titrations in CD₃CN (HPO₄²⁻: log K_1:1=6.2, log K_2:1=4.9; H₂P₂O₇²⁻: log K_1:1=4.4, log K_2:1=1.8; AMP²⁻: log K_1:1>7, log K_2:1>5) and the affinity of host 1 toward divalent anions, HPO₄²⁻, H₂P₂O₇²⁻, and AMP²⁻, is stronger than that toward monovalent anions, NO₃⁻, BF₄⁻, ClO₄⁻, HSO₄⁻, and PF₆⁻. The CD exciton chirality studies of host 1 with divalent anions, HPO₄²⁻ and AMP²⁻, revealed that the two DMAB groups in the 2:1 complexes were arranged with negative chirality (counterclockwise). The dual fluorescence behavior of the DMAB group demonstrated not only the complexation stoichiometry but also the role(s) of the lipophilic countercation such as tetrabutylammonium and/or the hydrophilic residue in AMP during anion recognition.     

Synthesis,spectral characterization of the zinc(II) mixed-ligand complexes of N(4)-allyl thiosemicarbazones and N,N,N′,N′-tetramethylethylenediamine,and crystal structure of the novel [ZnL2(tmen)] compound

Mixed-ligand zinc complexes with N,N,N′,N′-tetramethylethylenediamine (tmen) and R-salicylaldehyde N(4)-allyl thiosemicarbazones (R: 3-OCH₃ (L₁), 5-Br(L₂)), [ZnL_1,2(tmen)], were synthesized and the complexes were characterized by elemental analysis, atomic absorption spectrometer, magnetic susceptibility, molar conductivity, electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) mass spectra and IR, UV–Vis, ¹H NMR and ¹⁵N spectroscopies. Crystal of [ZnL₂(tmen)] have a slightly distorted square pyramid involving O, N, S atoms of thiosemicarbazone and one N atom of tmen in basal plane and the other N atom of tmen in apex of the pyramid. The non-coordinated allyl group is disordered.     

Crystal Structure of Pseudorhombohedral InFe1−xTixO3+x/2 (x=2/3)

The structure of pseudorhombohedral-type InFe_1−xTi_xO_3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO₃-In₂Ti₂O₇ including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P2₁/a is the alternate stacking of an edge-shared InO₆ octahedral layer and an Fe/Ti-O plane along c^*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10⁻⁴ S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.     

Synthesis, structure, and bridge-terminal alkyl exchange kinetics of pyrazolate-bridged dialuminum complexes containing bridging n-alkyl groups

Treatment of triethylaluminum with 3,5-diphenylpyrazole in a 2:1 stoichiometry afforded the ethyl-bridged complex Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ (79%) as a colorless crystalline solid. Treatment of tri-n-propylaluminum with 3,5-di-tert-butylpyrazole in a 2:1 stoichiometry afforded the n-propyl-bridged complex (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂ (63%) and the dimeric complex [(nPr)₂Al(μ-tBu₂pz)]₂ (3%), respectively, as colorless crystalline solids. Treatment of tri-n-propylaluminum (1 equiv.) or triisobutylaluminum (1 or 2 equiv.) with 3,5-di-tert-butylpyrazole afforded exclusively the dimeric complexes [(nPr)₂Al(μ-tBu₂pz)]₂ (68%) or [(iBu)₂Al(μ-tBu₂pz)]₂ (96%), respectively, as colorless crystalline solids. The solid state structures of Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ and (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂ consist of 3,5-disubstituted pyrazolato ligands with a di-n-alkylalumino group bonded to each nitrogen atom. An ethyl or n-propyl group acts as a bridge between the two aluminum atoms. The kinetics of the bridge-terminal exchange was determined for the bridging n-alkyl complexes by ¹³C NMR spectroscopy, and afforded ΔH^‡ = 1.5 ± 0.1 kcal/mol, ΔS^‡ = −46.8 ± 39.0 cal/K mol, and for Et₂Al(μ-Ph₂pz)(μ-Et)AlEt₂ and ΔH^‡ = 1.7 ± 0.1 kcal/mol, ΔS^‡ = −46.6 ± 43.4 cal/K mol, and for (nPr)₂Al(μ-tBu₂pz)(μ-nPr)Al(nPr)₂. The negative values of ΔS^‡ imply ordered transition states relative to the ground states, and rotation along the N-AlR₃ vector without aluminum-nitrogen bond cleavage is proposed.     

Tricarbonyl-6,6′-dimethylfulvene chromium(0) - Structural properties

The crystal structure of tricarbonyl-6,6′-dimethylfulvene chromium(0) was determined using X-ray diffraction at room temperature and at 120 K. The title compound crystallizes in the centrosymmetric, monoclinic space group P2₁/n (no. 14) with one complete molecule in the asymmetric unit. The deviation of the chromium(0) complex from C_s(m) symmetry is negligible in agreement with results derived from density functional calculations using three different methods as well as ab initio calculations (MP2). The 6,6′-dimethylfulvene ligand is bent by 30.9° as a result of the π-η²:π-η²:π-η² coordination to the Cr(0) metal. In addition, the chromium(0) complex was studied by IR and Raman spectroscopy and selected vibrational data are compared to values derived from DFT calculations.