Oxo Function Research Articles

Reduction of Pentavalent Uranyl to U(IV) Facilitated by Oxo Functionalization

Addition of 2 equiv of B(C(6)F(5))(3) to [Cp*(2)Co][U(V)O(2)((Ar)acnac)(2)] (1) [(Ar)acnac = ArNC(Ph)CHC(Ph)O; Ar = 3,5-(t)Bu(2)C(6)H(3)] results in the formation of [Cp*(2)Co][U(V){OB(C(6)F(5))(3)}(2)((Ar)acnac)(2)] (2) in good yield. Reduction of 2 with 1 equiv of Cp*(2)Co generates [Cp*(2)Co](2)[U(IV){OB(C(6)F(5))(3)}(2)((Ar)acnac)(2)] (3), also in good yield. This reaction is chemically reversible, as shown by the reaction of 3 with AgOTf, which regenerates 2. Interestingly, addition of only 1 equiv of B(C(6)F(5))(3) to 1 does not produce the monofunctionalized U(V) complex. Instead, the products of disproportionation, namely, 3 and U(VI)O(2)((Ar)acnac)(2), are observed in a 1:1 ratio.

Synthesis of New Chiral Ketones from D‐Glucose Derivatives and Their Use in the Enantioselective Epoxidation of Arylalkenes

AbstractA new backbone model for a chiral carbohydrate‐derived ketone for asymmetric epoxidation is presented. The oxo function is sited in a seven‐membered ring fused to the sugar moety. The synthesized compound is an effective chirality‐transfer agent in dioxirane‐mediated epoxidation, giving ees of up to 74 %. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

New daunomycin–oligoarginine conjugates: Synthesis, characterization, and effect on human leukemia and human hepatoma cells

In this article, the synthesis, a novel chromatographic procedure and characteristics of a new class of daunomycin (Dau)-oligoarginine conjugates are described. In these compounds oligoarginine with 6 or 8 residues (Arg(n), n = 6, 8) is attached to Dau by different covalent bond: squaric amide (Dau- square-Arg(n)), oxime (Dau=N-O-CH2-CO-Arg(n)), or hydrazone (H-Glu(Arg(n))-NH-N=Dau). Conjugates were characterized by RP-HPLC and mass spectrometry. We report also on our findings concerning chemical and biological properties of Dau-conjugates as a function of covalent linkage, site of conjugation and length of the oligoarginine moiety. Stability, fluorescent properties as well as cytostatic effect and cellular uptake of these compounds were studied. Dau-conjugates with squaric amide or oxime linkage were stable, but continuous release of free Dau was observed from the hydrazone conjugate in solution. We found that some spectral characteristics (e.g., the amplitude of the emission spectrum) of conjugates could be sensitive for the site of coupling (amino vs. oxo function). Cytostasis and cellular uptake of conjugates were investigated both on human leukemia (HL-60) and human hepatoma (HepG2) cell lines by MTT assay and flow cytometry We found that cytostatic effect and uptake properties of Dau-conjugates were dependent on the acid stability of the linkage (hydrazone vs. oxime/amide) applied and more markedly on the cell line studied.

In Situ Spectroscopic Investigation of the Molecular and Electronic Structures of SiO2 Supported Surface Metal Oxides

Groups 5−7 transition metal oxides (V2O5, Nb2O5, Ta2O5, CrO3, MoO3, WO3, Re2O7) were anchored on a SiO2 support via incipient wetness impregnation and calcination. The molecular and electronic structures of the dehydrated supported metal oxides and the SiO2 support were determined by combined in situ Raman, IR, and UV−vis spectroscopy under dehydrated conditions. In situ Raman characterization reveals that the supported metal oxides are only present as surface species below the maximum dispersion limit (where crystalline metal oxide nanoparticles are absent). In situ IR analysis shows that the surface metal oxides anchor to the SiO2 support at Si−OH and adjacent Si−O−Si sites. The corresponding in situ UV−vis diffuse reflectance spectroscopy indicates that the dehydrated surface metal oxide species are present as isolated structures. Isotopic D2O−H2O exchange demonstrates that the dehydrated surface MOx species possess the MO oxo functionality but no MOH bonds. The number of MO oxo bonds was found to be r...

Facile Synthesis of Thiazoles via an Intramolecular Thia‐Michael Strategy.

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Characterization of a reduced molybdenum-oxo compound derived from an oxo-transfer process under stoichiometric conditions

The stoichiometric oxidation of phosphanes or alcohols by a Mo(VI)-dioxo complex ( 1) followed both by UV spectroscopy results in the formation of a Mo(V) dimer with two μ-oxo bridges and two terminal oxo functions ( 3). Its structure is determined by an X-ray analysis depicting a Mo–Mo bond well in accord with the diamagnetic character of the complex. The spectroscopic follow up of the oxygen atom transfer process shows clearly that complex 3 is the end product of a series of intermediates among which one ( 2) is postulated as being a geometrical isomer of 3.

Selective Oxo Functionalization of the Uranyl Ion with 3d Metal Cations

The linear uranyl dication [UO2]2+ can be bound in one of two coordination sites in the ditopic Pacman-shaped pyrrolic macrocyle H4L. Incorporation of Mn2+, Fe2+, or Co2+ cations in the second donor compartment affords the first uranyl complexes with a transition-metal-functionalized oxo group.

Analysis of fungal cyclopentenone derivatives from Hygrophorus spp. by liquid chromatography/electrospray‐tandem mass spectrometry

Fruitbodies of the genus Hygrophorus (Basidiomycetes) contain a series of anti-biologically active compounds. These substances named hygrophorones possess a cyclopentenone skeleton. LC/ESI-MS/MS presents a valuable tool for the identification of such compounds. The mass spectral behaviour of typical selected members of this group under positive and negative ion electrospray conditions is discussed. Using the ESI collision-induced dissociation (CID) mass spectra of the [M + H]+ and [M - H]- ions, respectively, the compounds can be classified with respect to the substitution pattern at the cyclopentenone ring and the type of oxygenation at C-6 (hydroxy/acetoxy or oxo function) of the side chain. The elemental composition of the fragment ions was determined by ESI-QqTOF measurements. Thus, in case of the negative ion CID mass spectra an unusual loss of CO2 from the deprotonated molecular ions could be observed.

Synthesis, structure and NMR of cis-dioxotungsten (VI) complexes with 2-methoxypyridine and 2,3-dihydroxynaphthalene bidentate ligands

Two novel cis-dioxotungsten (VI) complexes, [WO 2(L a) 2](1) and [WO 2(L b) 2R 2Pr](2) [L a=2-methoxypyridine, L b=2,3-dihydroxynaphthalene, R=the six-member ring ion (C 5H 11N 2), Pr=1,3-propanediamine] have been synthesized and characterized by X-ray crystallography, 1H, 13C NMR and IR spectra. It is found that the tungsten atom is coordinated in a pseudo-octahedral fashion by two cis–oxo functions. The complex 1 is a neutral molecule, which is packed in crystal lattice via O⋯H–C hydrogen bonds and π–π interactions while there are two six-member ring cations (C 5H 11N 2) to compensate the negative charge of [W(VI)(OC 10H 6O) 2] 2− anion in complex 2. The new molecules of C 5H 11N 2 are the by-products produced by the protonated 1,3-propanediamine and ethanenitrile.

Synthesis and Structure-Activity Relationships of Vasicine Analogues as Bronchodilatory Agents

The series of vasicine (1) analogues, an alkaloid from Adhatoda vasica Nees., were synthesized with changes in A, B or C rings. Compounds 13-19 were evaluated for in vitro bronchodilatory activity using isolated guinea pig tracheal chain. Compounds 3-8 were also synthesized in good yields using microwave-mediated synthesis under solvent free conditions. Compounds 5 and 8 with seven-member C ring were more active than etofylline and caused 100% relaxation of both the histamine and acetycholine pre-contracted guinea pig tracheal chain. The structure-activity relationship studies showed that the quinazoline and oxo functionalities were essential for activity. The compounds without C ring and instead having aliphatic and phenyl substitutions in B ring showed relaxation against histamine pre-contracted tracheal chain only, 2-methyl substituted analogues, 12 and 13, being most active with 100% relaxation effect.

Small organoselenium molecules. 1. Dimethyl selenoxide: structure, complexation, and gas-phase transformation.

For the first time the structural characterization of dimethyl selenoxide coordinated to metal complexes has been performed confirming the Me(2)SeO arrangement assigned by spectroscopic techniques for the molecule in solution and solid state. The structure of Me(2)SeO is trigonal pyramidal with Se-O and Se-C bond lengths of 1.70 and 1.92 A, respectively, and sigma(X-Se-Y) = 301 degrees. As a ligand, dimethyl selenoxide was found to bind to the rhodium centers of various Lewis acidity strengths by using only its oxo functionality in both terminal and bridging fashions. This O-directed coordination preference contrasts with an ambidentate (-S and -O) binding character revealed by dimethyl sulfoxide upon formation of analogous donor-acceptor complexes. The study of dimethyl selenoxide in the gas phase at 135-140 degrees C resulted in a thermal degradation of this molecule. The major decomposition product has been entrapped by a metal complex and identified as dimethyl selenide. The isolation of the coordinated Me(2)Se fragment clearly demonstrates that the Me(2)SeO molecule is less thermally stable than Me(2)SO, which under similar reaction conditions shows no sign of decomposition at temperatures up to 160 degrees C.

Reactions of oxo- and peroxo-molybdenum complexes with B(C6F5)3: crystal structures of cis-[MoO{OB(C6F5)3}(η2-ONEt2)2] and cis-[MoO{OB(C6F5)3}{η2-PhN(O)C(O)Ph}2

The oxometal complexes [MoO2(η2-O-NR2)2], R = Et or CH2Ph, reacted with the strong Lewis acid B(C6F5)3 at their oxo functionality to give cis-[MoO{OB(C6F5)3}(η2-ONR2)2], (R = Et 1 or CH2Ph 2). Reaction of the peroxo complex [MoO(O2){η2-PhN(O)C(O)Ph}2] with the same Lewis acid led initially to the formation of [MoO(O2){B(C6F5)3}{η2-PhN(O)C(O)Ph}2] 3, which decomposes to form [MoO{OB(C6F5)3}{η2-PhN(O)C(O)Ph}2] 4. Compounds 1 and 4 have been characterised by X-ray crystallography.

New synthetic routes to α-amino acids and γ-oxygenated α-amino acids. Reductive denitration and oxidative transformations of γ-nitro-α-amino acids

Transformation of γ-nitro-α-amino acid derivatives into α-amino acids by reductive denitration, into the γ-oxo-α-amino acids by ozonolysis of the corresponding amino acid ester nitronate derivatives, and into γ-hydroxy-α-amino acid derivatives by subsequent reduction of the oxo functionality, can be achieved in good yields. As the γ-nitro-α-amino acid derivatives are prepared from N,O-protected dehydroalanines derivable from the corresponding alanine, serine and cysteine derivatives by specific routes, the overall procedures provide a means for selective conversion of these simple α-amino acids into more complex ones.

Reactions of organometallic oxometal complexes with B(C6F5)3: synthesis, structure, bonding and reactivity of [Mo(η5-C5H4Me)2{OB(C6F5)3}

Organometallic oxo complexes [M(C5H4R)2O] reacted with the strong Lewis acid B(C6F5)3 at their oxo functionality to yield [M(C5H4R)2{OB(C6F5)3}] (M = Mo, R = Me 1; M = W, R = H 2). The structure of 1 has been determined by X-ray crystallography. Density functional theory (DFT) calculations on [Mo(C5H5)2O] and [Mo(C5H5)2(OBF3)] have been used to model the changes in geometry to the [Mo(C5H5)2O] fragment on co-ordination by B(C6F5)3 and indicate that this process is charge rather than orbitally controlled. Compound 1 reacted with PhNCO to yield [Mo(C5H4Me)2{OC(O)NPh}{B(C6F5)3}]; spectroscopic evidence and DFT calculations suggest that the Lewis acid is bound to the molybdenum oxygen atom.

Beryllium Chelation by Dicarboxylic Acids in Aqueous Solution

Maleic and phthalic acids are found to react with Be(OH)(2), generated in situ from BeSO(4)(aq) and Ba(OH)(2)(aq), in aqueous solution at pH 3.0 or 4.4, respectively (25 degrees C), to give solutions containing the complexes (H(2)O)(2)Be[(OOCCH)(2)] (1) and (H(2)O)(2)Be[(OOC)(2)C(6)H(4)] (3). The products can be isolated in high yield and identified by microanalytical data. With 2 equiv of the dicarboxylic acids and the pH adjusted to 5.5 and 5.9, respectively, by addition of ammonia, the bis-chelate complexes [(NH(4))(+)](2){[Be[(OOCCH)(2)](2)}(2)(-) (2) and [(NH(4))(+)](2){Be[(OOC)(2)C(6)H(4)](2)}(2)(-) (4) are obtained, which can also be isolated. The compounds show distinct (9)Be, (1)H, and (13)C resonances in their NMR spectra in aqueous solutions. Layering of an aqueous solution of compound 4 with acetone at ambient temperature leads to the precipitation of single crystals suitable for an X-ray structure determination. This salt (5) was found to contain the bis-chelated dianion {Be[(OOC)(2)C(6)H(4)](2)}(2)(-) with the beryllium atom in the spiro center of two seven-membered rings and an overall geometry approaching closely C(2) symmetry. These anions are associated with two crystallographically independent but structurally similar counterions [MeC(O)CH(2)CMe(2)NH(3)](+), which are the product of a condensation reaction of the ammonium cation with the acetone solvent. In the crystal the ammonium hydrogen atoms of the cations form N-H.O hydrogen bonds with the oxo functions of the dianion.

Derivatives of the triazoloquinazoline adenosine antagonist (CGS15943) are selective for the human A3 receptor subtype.

The adenosine antagonist 9-chloro-2-(2-furanyl)[1,2,4]triazolo[1,5-c]quinazolin-5-amine (CGS15943) binds to human A3 receptors with high affinity (Ki = 14 nM), while it lacks affinity at rat A3 receptors. Acylated derivatives of the 5-amino group and other modifications were prepared in an effort to provide A3 subtype selectivity. Affinity was determined in radioligand binding assays at rat brain A1 and A2A receptors using [3H]-(R)-PIA ([3H]-(R)-N6-(phenylisopropyl)-adenosine) and [3H]CGS 21680 ([3H]-2-[[4-(2-carboxy ethyl)phenyl]ethylaminol]-5'-(N- ethyl- carbamoyl)adenosine), respectively. Affinity was determined at cloned human A3 receptors using [125I]AB-MECA (N6-(4-amino-3-iodobenzyl)-5'-(N-methylcarbamoyl)adenosine). A series of straight chain alkyl amides demonstrated that the optimal chain length occurs with the 5-N-propionyl derivative, 3, which had a Ki value of 7.7 nM at human A3 receptors, and was 40- and 14-fold selective vs rat A1 and A2A receptors, respectively. The 5-N-benzoyl derivative, 10, displayed Ki values of 680 and 273 nM at rat A1 and A2A receptors, respectively, and 3.0 nM at human A3 receptors. A 5-N-phenylacetyl derivative, 12, was 470-fold selective for human A3 vs rat A1 receptors with a Ki value of 0.65 nM. A conjugate of Boc-gamma-aminobutyric acid was also prepared but was nonselective. Conversion of the 5-amino group of CGS15943 to an oxo function resulted in lower affinity but 15-fold selectivity for human A3 receptors.

The mineralocorticoid activity of progesterone derivatives depends on the nature of the C18 substituent.

To investigate the role of the C18 substituents in the agonist/antagonist properties of mineralocorticoids, the activities of certain C18-substituted progesterone (P) derivatives were examined. These compounds were characterized by an unsaturated side-chain in the case of 18-vinylprogesterone (18VP) and 18-ethynylprogesterone (18EP) and by an enone group in the case of 18-oxo-18-vinylprogesterone (18OVP). P and its 18-substituted derivatives bind to the recombinant human MR (hMR) overexpressed in Sf9 cells with the following hierarchy of affinity: P > aldosterone > 18VP > 18EP >> 18OVP. Functional cotransfection assays in CV-1 cells, using mouse mammary tumor virus promoter as a steroid receptor-inducible DNA target sequence, indicated that the mineralocorticoid activity depends on the nature of the C18 substituent. 18VP and 18EP retained the antimineralocorticoid feature of P, with the following order of activity: P = 18VP > 18EP. The antagonist potency of 18VP was higher (IC50, approximately 10(-8) M) than that of spironolactone (IC50, approximately 7 x 10(-8) M), the most widely used aldosterone antagonist. Interestingly, introducing an oxo function at C18 conferred agonist mineralocorticoid properties; 18OVP behaves as a full agonist (ED50, approximately 10(-7) M) with no antagonist activity. In contrast to what was observed when the three 18-substituted P derivatives acted through hMR, they retained the agonist feature of P through the human P receptor, with the following order of potency: P > 18VP = 18OVP > 18EP. The activity of the 18-substituted P derivatives through the human glucocorticoid receptor was only detected at concentrations higher than 10(-6) M; P and 18VP displayed a partial antagonist activity, whereas 18OVP had a full agonist activity (ED50, approximately 2 x 10(-6) M). Thus, the presence of an oxo group at C18(18OVP) does not change the agonist feature of P through human P receptor, but confers to the ligand an agonist activity through hMR, suggesting that the C18 carbonyl group of aldosterone plays a crucial role in its agonist activity.

The mineralocorticoid activity of progesterone derivatives depends on the nature of the C18 substituent

To investigate the role of the C18 substituents in the agonist/antagonist properties of mineralocorticoids, the activities of certain C18-substituted progesterone (P) derivatives were examined. These compounds were characterized by an unsaturated side-chain in the case of 18-vinylprogesterone (18VP) and 18-ethynylprogesterone (18EP) and by an enone group in the case of 18-oxo-18-vinylprogesterone (18OVP). P and its 18-substituted derivatives bind to the recombinant human MR (hMR) overexpressed in Sf9 cells with the following hierarchy of affinity: P > aldosterone > 18VP > 18EP >> 18OVP. Functional cotransfection assays in CV-1 cells, using mouse mammary tumor virus promoter as a steroid receptor-inducible DNA target sequence, indicated that the mineralocorticoid activity depends on the nature of the C18 substituent. 18VP and 18EP retained the antimineralocorticoid feature of P, with the following order of activity: P = 18VP > 18EP. The antagonist potency of 18VP was higher (IC50, approximately 10(-8) M) than that of spironolactone (IC50, approximately 7 x 10(-8) M), the most widely used aldosterone antagonist. Interestingly, introducing an oxo function at C18 conferred agonist mineralocorticoid properties; 18OVP behaves as a full agonist (ED50, approximately 10(-7) M) with no antagonist activity. In contrast to what was observed when the three 18-substituted P derivatives acted through hMR, they retained the agonist feature of P through the human P receptor, with the following order of potency: P > 18VP = 18OVP > 18EP. The activity of the 18-substituted P derivatives through the human glucocorticoid receptor was only detected at concentrations higher than 10(-6) M; P and 18VP displayed a partial antagonist activity, whereas 18OVP had a full agonist activity (ED50, approximately 2 x 10(-6) M). Thus, the presence of an oxo group at C18(18OVP) does not change the agonist feature of P through human P receptor, but confers to the ligand an agonist activity through hMR, suggesting that the C18 carbonyl group of aldosterone plays a crucial role in its agonist activity.

Oxo Complexes of Tungstenocene via Oxidation of [W(.eta.5-C5H5)2(OCH3)(CH3)] and Related Reactions: Synthesis, Structural Characterization, and Photodisproportionation of the Spin-Paired d1-d1 Oxo-Bridged Dimer [{W(.eta.5-C5H5)2(CH3)}2(.mu.-O)]2+ and Synthesis and Characterization of the d0 Terminal Oxo Complex [W(.eta.5-C5H5)2(O)(CH3)

Abstract : There has been remarkable growth throughout the 1980s in the chemistry of transition metal oxo complexes. Interest in what had been regarded as a mature area was rekindled in part by the recognition of the role of the oxo functionality as a 'spectator' ligand in catalytic alkene metathesis, and has been fueled by developments in the chemistry of transition metal porphyrin oxo complexes (including their roles in hydrocarbon oxidations and in alkene epoxidation and hydroxylation reactions), by continuing rapid evolution of our understanding of biologically relevent oxo transfer reactions, by extraordinary advances in the use of oxo complexes as catalysts for alkene hydroxylation and epoxidation, and most recently, by the remarkable catalystic activity demonstrated by high valent rehenium oxo alkyls. These development have been paralleled by significant advances in the syntheses of oxo complexes, including the preparations of 'low valent' oxo complexes and of high valent oxo alkyl complexes, and marked extentions of the rational synthesis of organometallic oxo complexes.

Derivate des Hydrazins als Liganden in Vanadium(IV)- und -(V)-Komplexen. Darstellung und Struktur dreier dimerer Verbindungen mit Hydrazido- und Hydrazonato-Liganden / D erivatives of H ydrazine as Ligands in V anadium (IV ) and -(V) Complexes. Synthesis and Crystal Structures of Three D im eric C om plexes with H ydrazido and H ydrazonato Ligands

Abstract The complexes [(μ-PhCONNCOPh){VOCl(NHNHCOPh)}2 ·5CH3CN, (1), [(μ-PhCONNCOPh){V(dbh)}2]-2CH3CN, (2) and [{VO}2(tbh)], (3) have been prepared by reaction of VCl2(acac)2, acac = acetylaceto n a to (l-), and VCl2(acpn), acpn = propylendiim ino-bis(acetylacetonato(2-)), with benzoylhydrazine. The structures of the centrosymmetric dimeric molecules 1 -3 have been determined by single crystal X-ray diffraction. 1 and 2 contain both doubly deprotonated N,N′-dibenzoylhydrazine as bridging, doubly N,O chelating ligand. In 1 the two remaining coordination sites at the VOCl group are occupied by the hydrazid o(1-) ligand [NHNHCOPh]- . 2 is a non-oxo vanadium(IV) complex. The coordination geometry is approximately trigonal prismatic. The π-back donating effect of the oxo function is substituted by back donation from three negatively charged enolic oxygen atoms. The V - O bond lengths range from 192.0(2) to 193.7(2) pm. 3 contains a unique highly symmetrical octadentate ligand, formed during the synthesis. It is coordinated to two oxovanadin(IV) centers by N,O chelation. The coordination geometry is square pyramidal.