Oxo Function Research Articles

Mehrfachbindungen zwischenübergangsmetallen und hauptgruppenelementen CXXIV. 17O-NMR-spektroskopie an organorhenium(VII)-oxiden

A series of organorhenium(VII) oxides of general composition RReO3 (e.g. R alkyl, alkenyl, σ-arly, π-aryl) as well as five- and six-coordinate adducts of formula RReO3 ·Ln ( n = 1, 2) were subjected to 17O-NMR spectroscopy. The chemical shift of the oxo function depends mainly on the donor properties of the ligand R and correlates well with the electron density at the rhenium. The chemical shift also depends on the solvent, especially if the ligand R: (1) is not a strong donor, and (ii) causes no steric hindrance.

Proton nuclear magnetic resonance studies of nucleosides: hindered internal rotation in N-dimethylaminomethylene derivatives of adenosine, guanosine, and cytidine

Studies of the internal rotation about the C—N bond of the dimethylaminomethylene (DMAM) group of DMAM-adenosine, 1, DMAM-guanosine, 2, and DMAM-cytidine, 3, was determined by high-resolution 1H NMR spectroscopy. Arrhenius plots (ln k = ln A − Ea/RT) were used to determine the barriers to internal rotation, Ea, of the compounds. They were found to be 58.0 ± 2.4 kJ mol−1, 71.2 ± 1.4 kJ mol−1, and 62.8 ± 2.4 kJ mol−1 for 1, 2, and 3, respectively. At the same time the coalescence temperatures, tc, for the compounds were determined and found to be 93.5 °C for 1, 124.7 °C for 2, and 119.6 °C for 3 in DMSO. In D2O, compound 1 was found to have a tc of 104.5 °C. The compound decomposed so rapidly at this temperature that the barrier to internal rotation could not be determined. The results indicate that the oxo function in the nucleobase has a considerable effect on the barrier to internal rotation and coalescence temperature.

Metal Ion Binding by Dipeptides: Structure of the Product Generated in “Aspartame” Hydrolysis, Sodium cyclo(L‐α‐Aspartyl‐L‐phenylalanine) Tetrahydrate, Na[c(L‐Asp‐L‐Phe)] 4H2O

Ester cleavage of aspartame (L‐α‐aspartyl‐L‐phenylalanine methyl ester, 1) by equimolar quantities of NaOH is accompanied by intramolecular cyclisation to sodium 3‐benzyl‐6‐(carboxylatomethyl)‐2,5‐dioxopiperazine (2). The solid‐state structure of the crystalline tetrahydrate has been determined by single‐crystal X‐ray diffraction analysis. The cations are arranged in strings, and each sodium atom is in a distorted octahedral environment of six oxygen atoms, including a β‐carboxylato (O1) and an oxo function (O4) of two different dioxopiperazines and four water molecules. No nitrogen coordination is observed. Through the ligand bridging (O1, O4) of the metals and a set of hydrogen bonds involving the amide and carboxylate groups and all water molecules a three‐dimensional network is established.

Nitroazines. 15. Contraction of the pyrimidine ring in 6-nitroazolo[1,5-a]pyrimidines

It is shown that contraction of the pyrimidine ring occurs when 6-nitro-7-oxo-4,7-dihydroazolo[1,5-a]pyrimidines are heated with hydrazine hydrate. Complexes of 4-nitropyrazole with 5-aminoazoles, the structures of which were proved by x-ray diffraction analysis, are formed in a similar reaction of nitrosubstituted azolopyrimidines that do not contain an oxo function.

Oxygen Activation. Various Aspects of the Metal Oxo and Peroxo Function

Oxygen Activation. Various Aspects of the Metal Oxo and Peroxo Function

New low-valent titanium reagents for dicarbonyl coupling and their use in a general method of annulation

Ketones carrying a chain that incorporates a suitably placed oxo function (aldehyde or ketone) undergo intramolecular dicarbonyl coupling when treated with a reagent prepared either from titanium trichloride and C8K (relative molar ratio 1 : 2) or from titanium tetrachloride and sodium–naphthalene (relative molar ratio ca. 1 : 2.75); the reagent is used in excess (16 to 17 mol titanium halide per mol of dicarbonyl compound) and the process is the key step in a general method of anpulation.

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: LXII. Alkin-Komplexe der Organorheniumoxide: Redox-Chemie und Nucleophilie der Oxo-Funktion von (η 5-Pentamethylcyclopentadienyl)(η 2-diphenylethin) oxorhenium(III)

The novel Re III oxo alkyne complexes (η 5-C 5Me 5)Re(=O)(η 2-RCCR) ( 3a–c; R = C 6H 5, CH 3, C 2H 5) are obtained almost quantitiatively by alkaline hydrolysis of the dichloro precursor compounds (η 5C 5Me 5)ReCl 2(η 2-RCCR) ( 4a-c). An X-ray diffraction study has revealed that in the phenyl derivative 3a the alkyne group is best described as a two-electron ligand. 17O NMR spectroscopy shows the remarkable electron deficiency of the terminal oxo group. This oxo function however is sufficiently nucleophilic to be converted into the hydroxo psecies [η 2-diphenylalkyne)hydroxo(η 5-pentamethylcyclopentadienyl)rhenium(III)] tetrafluoroborate ( 5a) and [(η 2-butyne(2))hydroxo(η 5-pentamethylcyclopentadienyl)rhenium(III)] tetrafluoroborate ( 5b) by O-protonation with HBF 4. One-electron oxidation of 3a leads to the dinuclear Re IV species [(μ-O)(η 5-C 5Me 5)Re(η 2-C 6H 5CCC 6H 5) 2] 2+ without loss of the alkyne ligand. The Re V systems (η 5-C 5Me 5)Re(=O) 2(η 2-RCCR) ( 2, generated oxidatively, are not stable as they decompose rapidly by eliminating the alkyne ligand.

Studies on the interaction between human serum protein fractions and 18O-labeled oxosteroids.

The nature of the interaction between progesterone or testosterone and human albumin as well as the interaction between progesterone and partially purified human transcortin has been studied. Modification of lysine residues of albumin with maleic anhydride resulted in a decreased binding of the steroid as judged from equilibrium dialysis experiments. This suggested that lysine residues in albumin interact with the oxosteroids. In order to check this hypothesis, steroids labeled with 18O in their oxo function (testosterone and progesterone) were synthesized for use as probes of the interactions. However, no loss of label was noted when testosterone or progesterone specifically 18O-labeled in their oxo functions were incubated with albumin. This suggested that no covalent interaction between the steroidal oxo group and albumin took place. This was in contrast to the results obtained with 3,20-18O-labeled progesterone and partially purified transcortin, where a complete loss of 18O label in the protein-bound steroid was found. The nonbound steroid showed an almost complete retention of label. These results indicate a participation of steroid oxo groups in the binding of progesterone to transcortin. Of the possible mechanisms discussed, imine bonds between the steroid and transcortin seem most likely although other types of interactions cannot be ruled out.

Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen: LII. 17O-NMR-untersuchungen an organoherniumoxiden

A series of compounds of general composition (η 5C 5Me 5)Re(O)X 2 (X  halogen, alkyl, alkoxy) was synthesized with ca. 10% 17O enrichment and subjected to 17O NMR spectroscopy. The chemical shift of the terminal oxo function depends on the σ-donor ability of the ligand X and, to a rough approximation correlates to the electron density at rhenium. These results should serve as a useful means to predict and understand reactivities of this class of compounds.

The Relationship Between Octahedral and Trigonal-Prismatic Coordination in Bis Tridentate Complexes of TiIV and VIV

The crystal structures of two vanadium complexes V( aabh )2 (1) and V( aasalh )2 (2) and of two titanium complexes Ti( aabh )2 (3) and Ti( babh )2 (4), where aabh is the dinegative, tridentate ligand pentane-2,4-dione benzoylhydrazonato (2-), aasalh is pentane-2,4-dione salicyloylhydrazonato (2-) and babh is 4-phenylbutane-2,4-dione benzoylhydrazonato (2-), were determined by X-ray diffraction methods. Crystals of (1) are monoclinic, space group P21/c, a 8.906(3), b 11.840(2), c 22.450(6)Ǻ, β 97.72(3)°, V 2345.8 and Z 4; those of (2) are triclinic, space group Pī , a 9.802(4), b 10.205(3), c 13.688(6)Ǻ, α 100.56(3),β 94.07(4),γ 112.89(3)°, V 1224.6 Ǻ3 and Z 2; those of (3) are monoclinic, space group C2/c, a 18.543(4), b 10.269(4), c 12.589(4)Ǻ, β 106.80(2)°, V 2294.9 Ǻ3 and Z 4; and those of (4) are monoclinic, space group P21/n, a 10.923(4), b 19.139(3), c 14.610(5)Ǻ, β 94.54(3)°, V 3044.7 Ǻ3 and Z 4. The structures were refined by a full-matrix least-squares procedure in each case to final values of R 0.102, 0.044, 0.049 and 0.058 for the structures (1), (2), (3) and (4), respectively, and values of Rw 0.099, 0.049, 0.053 and 0.065 for 1735, 3405, 1185 and 2911 statistically significant reflections, respectively. In the vanadium complexes the coordination geometry is approximately trigonal prismatic, whereas in each of the titanium complexes the two tridentate ligands are in a meridional arrangement with an approximately octahedral coordination. The stabilization of vanadium(IV) in the absence of the oxo function and the role of the metals in producing different coordination geometries are discussed.

ChemInform Abstract: NUCLEOSIDES AND NUCLEOTIDES. LIV. SYNTHESIS OF 6,6′‐CYCLO‐5′,6′‐DIDEOXYHEXOFURANOSYLURACILS VIA RADICAL CYCLIZATION OF A 6‐CYANOURIDINE

AbstractDie radikalische Cyclisierung des aus (I) dargestellten Uridins (IIIb) führt zu dem Cyclonucleosid (IV), das, wie im Formelschema angegeben, in die im Titel genannte Verbindung (VIIIb) übergeführt wird.

Nucleosides and nucleotides. LIV. Synthesis of 6,6'-cyclo-5',6'-dideoxyhexofuranosyluracils via radical cyclization of a 6-cyanouridine.

Synthesis of hexofuranosyluracil cyclonucleosides carbon-bridged between C-6 and C-6'is described. Treatment of 6-cyano-5'-iodo-2', 3'-O-isopropylidene-5'-deoxyuridine with tri-n-butyltin hydride and 2, 2'-azobisisobutyronitrile gave the 6'-imino-6, 6'-cyclo-5', 6'-dideoxyallofuranosyluracil, which was converted to the 6'-oxo derivative. The 6'-oxo function was reduced with sodium borohydride and the 6'-hydroxyl group was eliminated to give the 5', 6'-unsaturated cyclodideoxyallofuranosyluracil, which was hydrogenated to furnish 6, 6'-cyclo-5', 6'-dideoxyallofuranosyluracil, a uridine derivative fixed in the anti form.

The dispersion of cholesterol with phospholipids and glycolipids

Of the polar lipids studied (phospholipids and glycolipids), only phosphatidylcholine and sphingomyelin can disperse in water with up to 2 mol cholesterol/mol polar lipid. However, mixtures of phosphatidylethanolamine with small amounts of phosphatidylcholine and mixed lipids from mitochondria and myelin will also form sterol-rich dispersions. Steroids in which the 3β-OH group is replaced by an oxo function do not form such steroid-rich dispersions. Electron microscopy and optical rotatory dispersion (ORD) show that sterols disperse with cerebrosides and gangliosides to form cylindrical structures with the regions around C atoms 3 and 7 of the sterol in less polar environments than those they occupy in phospholipid liposomes.It is proposed that choline-containing phospholipids facilitate entry of sterol molecules into the outer leaflet of cell surface membranes but that the phospholipid composition itself will not give rise to an asymmetric distribution of sterol in membranes with a high cholesterol content.

ChemInform Abstract: STEREOCHEMISTRY OF THE REDUCTION OF SOME 2,2,4,5‐TETRASUBSTITUTED 1,3‐CYCLOPENTANEDIONES

AbstractDie Reduktion des Dioxodiesters (I) unter verschiedenen Bedingungen liefert die isomeren Hydroxypentanone (II) und die isomeren Diole (III), (IV) und /oder (V); mit Li‐tris‐tert‐butoxyalanat werden nur die Hydroxyketone (VIa) und (VIb) erhalten (die angegebenen Prozentzahlen bezeichnen den jeweiligen Anteil im Produktgemisch).

Stereochemistry of the reduction of some 2,2,4,5‐tetrasubstituted 1,3‐cyclopentanediones

AbstractThe reduction of the oxo functions in ethyl 5‐(6‐ethoxycarbonylhexyl)‐3,3‐dimethyl‐2,4‐dioxocyclopentanecarboxylate (1) with NaBH4, with LiAlH(O‐t‐Bu)3 and by catalytic hydrogenation is described. Four isomeric hydroxycyclopentanones and four isomeric cyclopentanediols were isolated and their stereochemistry was determined, providing 1H‐NMR and 13C‐NMR data which should be useful in structural assignment of isomeric prostaglandin analogues.

Removal of the C 4 methyl groups from triterpenoids. Conversion of lanosterol into 14α-Methylcholesta-4,8-dien-3-one and the modification of ring A of methyl glycyrrhetinate

14α-Methylcholesta-4,8-dien-3-one (9a) has been synthesized from lanosterol by a route involving the ?abnormal? Beckmann rearrangement of the oxime of 5α-lanost-8-en-3-one to the 3,4-seco nitrile (1a), from which the steroidal ring A was formed via the 3,5-dioxo 4,5-seco intermediate (8a). The formation of (8a) from the seco nitrile (1a) was readily achieved in a high-yielding sequence, which entailed stepwise degradation of the isopropenyl group, protection of the introduced 5- oxo function, and reaction of the cyano group with a Grignard reagent. The application of the above route to the modification of ring A of methyl glycyrrhetinate has also been investigated. Although the required triketone (8b) could be obtained, the method was rather low- yielding due to attack by the Grignard reagent on (11b) occurring at both C3 and C 11.

Products of a linoleic hydroperoxide-decomposing enzyme of alfalfa seed

Alfalfa seeds and seedlings contain an enzyme that catalyzes a reaction with the 13- and 9-hydroperoxides of linole- ic acid to form 13-hydroxy-10-oxo-truns-octadecenoic acid and 9-hydroxy-12-oxo-trans-lO-octadecenoic acid, respectively. When commercial lipoxygenase is used to generate the hydro- peroxides, the above acids appear in about 2:l proportions, re- spectively. The products of the action of the enzyme on the hy- droperoxides were stabilized for analysis by reduction with Hz and LiAIHr. Trimethylsilyl derivatives of reduced products were analyzed by combined gas-liquid chromatography-mass spec- trometry. Specific deuterium labeling permitted definite location of the oxo functions. 180z labeling experiments showed that the oxygens of both the oxo and the hydroxyl functions were derived from the hydroperoxide. Retention of both oxygens suggests that the reaction proceeds through a cyclic epiperoxide followed by a ketohydroxy-forming rearrangement. No products of hydro- peroxide isomerase- were found in reactions catalyzed by the crude enzyme from alfalfa seeds.