Conversion of aliphatic and alicyclic polyalcohols to the corresponding primary polyamines

Transition-metal(ii) complexes with a tripodal hexadentate ligand, 1,1,1-tris[2-aza-3-(imidazol-4-yl)prop-2-enyl]ethane, exhibiting incomplete total or absolute spontaneous resolution

Crystal structures and solid-state CD spectra of the compounds, [M(H₃L)]Cl(ClO₄) (M = Mn, Fe, Co, Ni and Zn) were examined.

Design, synthesis and photophysical properties of 8-hydroxyquinoline-functionalized tripodal molecular switch as a highly selective sequential pH sensor in aqueous solution

TAME5OX can act as a good candidate with potential applications in chemical and biological fields. Fluorescence reduction due to ESIPT between protonated NH⁺ ∼ –OH and deprotonated N ∼ –O⁻ forms was proven by DFT calculation.

Triamidetriamine bearing macrobicyclic and macrotricyclic ligands: potential applications in the development of copper-64 radiopharmaceuticals

A versatile and straightforward synthetic approach is described for the preparation of triamide bearing analogues of sarcophagine hexaazamacrobicyclic cage ligands without the need for a templating metal ion. Reaction of 1,1,1-tris(aminoethyl)ethane (tame) with 3 equiv of 2-chloroacetyl chloride, yields the tris(α-chloroamide) synthetic intermediate 6, which when treated with either 1,1,1-tris(aminoethyl)ethane or 1,4,7-triazacyclononane furnished two novel triamidetriamine cryptand ligands (7 and 8 respectively). The Co(III) and Cu(II) complexes of cryptand 7 were prepared; however, cryptand 8 could not be metalated. The cryptands and the Co(III) complex 9 have been characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and X-ray crystallography. These studies confirm that the Co(III) complex 9 adopts an octahedral geometry with three facial deprotonated amido-donors and three facial amine donor groups. The Cu(II) complex 10 was characterized by elemental analysis, single crystal X-ray crystallography, cyclic voltammetry, and UV-visible absorption spectroscopy. In contrast to the Co(III) complex (9), the Cu(II) center adopts a square planar coordination geometry, with two amine and two deprotonated amido donor groups. Compound 10 exhibited a quasi-reversible, one-electron oxidation, which is assigned to the Cu(2+/3+) redox couple. These cryptands represent interesting ligands for radiopharmaceutical applications, and 7 has been labeled with (64)Cu to give (64)Cu-10. This complex showed good stability when subjected to L-cysteine challenge whereas low levels of decomplexation were evident in the presence of L-histidine.

Electronic design criteria for O-O bond formation via metal-oxo complexes

Metal-oxos are critical intermediates for the management of oxygen and its activation. The reactivity of the metal-oxo is central to the formation of O-O bonds, which is the essential step for oxygen generation. Two basic strategies for the formation of O-O bonds at metal-oxo active sites are presented. The acid-base (AB) strategy involves the attack of a nucleophilic oxygen species (e.g., hydroxide) on an electrophilic metal-oxo. Here, active-site designs must incorporate the assembly of a hydroxide (or water) proximate to a high-valent metal-oxo of even d electron count. For the radical coupling (RC) strategy, two high-valent metal-oxos of an odd d electron count are needed to drive O-O coupling. This Forum Article focuses on the different electronic structures of terminal metal-oxos that support AB and RC strategies and the design of ligand scaffolds that engender these electronic structures.

The Sila-Explosives Si(CH2N3)4 and Si(CH2ONO2)4: Silicon Analogues of the Common Explosives Pentaerythrityl Tetraazide, C(CH2N3)4, and Pentaerythritol Tetranitrate, C(CH2ONO2)4

The reaction of tetrakis(chloromethyl)silane, Si(CH2Cl)4, with sodium azide afforded tetrakis(azidomethyl)silane (sila-pentaerythrityl tetraazide, Si(CH2N3)4 (1b)). Nitration of tetrakis(hydroxymethyl)silane, Si(CH2OH)4, with nitric acid resulted in the formation of tetrakis(nitratomethyl)silane (sila-pentaerythritol tetranitrate, Si(CH2ONO2)4 (2b)). Compounds 1b and 2b are extremely shock-sensitive materials and very difficult to handle. Spectroscopic data were obtained as good as sensitivity and safety allowed for umambiguous identification. Quantum chemical calculations (DFT) of the C/Si pairs C(CH2OH)4/Si(CH2OH)4, 1a/1b, and 2a/2b regarding the structures and electronic populations were performed.

Modular syntheses of multidentate ligands with variable N-donors: applications to tri- and tetracopper(i) complexes

A general method for the preparation of multidentate ligands comprised of a multi-imine platform derived from 1,1,1-tris(aminomethyl)ethane or tris(aminoethyl)amine connected to bi- and tridentate N-donor chelates has been developed. The feasibility of the method has been demonstrated through the synthesis and characterization of a large set of these ligand types. Complexation to Cu(I) was accomplished for several cases, yielding tri- and tetracopper(I) complexes that have been characterized in solution by NMR spectroscopy and conductivity, and in the solid state by elemental analysis, mass spectrometry, and/or X-ray crystallography. These complexes are potentially useful for modeling multicopper protein active sites.

Tuning tetranuclear manganese-oxo core electronic properties: adamantane-shaped complexes synthesized by ligand exchange

A series of adamantane-shaped [Mn4O6]4+ aggregates has been prepared. Ligand substitution reactions of [Mn4O6(bpea)4](ClO4)4 (1) with tridentate amine and iminodicarboxylate ligands in acetonitrile affords derivative clusters [Mn4O6(tacn)4](ClO4)4 (4), [Mn4O6(bpea)2(dien)2](ClO4)4)(5), [Mn4O6(Medien)4](ClO4)4 (6), [Mn4O6(tach)4](ClO4)4 (7), [Mn4O6(bpea)2(me-ida)2] (8), [Mn4O6(bpea)2(bz-ida)2] (9), [Mn4O6(bpea)2((t)bu-ida)2] (10), and [Mn4O6(bpea)2((c)pent-ida)2] (11) generally on the order of 10 min with retention of core nuclearity and oxidation state. Of these complexes, only 4 had been synthesized previously. Characterization of two members of this series by X-ray crystallography reveals that compound 7 crystallizes as [Mn4O6(tach)4](ClO4)4 x 3CH3CN x 4.5H2O in the cubic space group Fmm and compound 11 crystallizes as [Mn4O6(bpea)2((c)pent-ida)2].7MeOH in the monoclinic space group C2/c. The unique substitution chemistry of 1 with iminodicarboxylate ligands afforded asymmetrically ligated complexes 8-11, the mixed ligand nature of which is most likely unachievable using self-assembly synthetic methods. A special feature of the iminodicarboxylate ligand complexes 8-11 is the substantial site differentiation of the oxo bridges of the [Mn4O6]4+ cores. While there are four site-differentiated oxo bridges in 8, the solution structural symmetry of 8H+ reveals essentially a single protonation isomer, in contrast to the observation of two protonation isomers for 1H+, one for each of the site-differentiated oxo bridges in 1. Magnetic susceptibility measurements on 4, 7, 8, and 9 indicate that each complex is overall ferromagnetically coupled, and variable-field magnetization data for 7 and 9 are consistent with an S = 6 ground state. Electrochemical analysis demonstrates that ligand substitution of bpea affords accessibility to the Mn(V)(Mn(IV))3 oxidation state.

Application of a New Bicyclic Triaminophosphine Ligand in Pd-Catalyzed Buchwald−Hartwig Amination Reactions of Aryl Chlorides, Bromides, and Iodides

The new bicyclic triaminophosphine ligand P(i-BuNCH2)3CMe (3) has been synthesized in three steps from commercially available materials and its efficacy in palladium-catalyzed reactions of aryl halides with an array of amines has been demonstrated. Electron-poor, electron-neutral, and electron-rich aryl bromides, chlorides, and iodides participated in the process. The reactions encompassed aromatic amines (primary or secondary) and secondary amines (cyclic or acyclic). It has also been shown that the weak base Cs2CO3 can be employed with ligand 3, allowing a variety of functionalized substrates (e.g., those containing esters and nitro groups) to be utilized in our amination protocols. This ligand provides a remarkably general, efficient, and mild palladium catalyst for aryl iodide amination. Although 3 is slightly air and moisture sensitive, easy procedures can be adopted that avoid the need of a glovebox. Comparisons of the efficacy of 3 in these reactions with that of the proazaphosphatrane P(i-BuNCH2CH2)3N (2) reveal that in addition to the opportunity for transannulation in 2 (but not in 3), other significant stereoelectronic contrasts exist between these two ligands which help account for differences in the activities of the Pd/2 and Pd/3 catalytic systems.

A new synthesis of 2-azabicyclo[2.1.1]hexanes

An efficient synthesis of the 2-azabicyclo[2.1.1]hexane ring system has been accomplished starting from cis-cyclobut-3-ene-1,2-dicarboxylic anhydride 7, which was prepared using a photochemical method. The key step of this new strategy involved a stereoselective electrophilic addition of phenylselenyl bromide to the double bond of cyclobutene dicarbamate 16 derived from 7. The subsequent ring closure of 17a in the presence of sodium hydride afforded the 2-azabicyclohexane compound 18 with a satisfying overall yield. Reductive removal of the phenylselenyl group and subsequent deprotection led rapidly to the amino derivative 4a functionalized on the carbon ring. Syntheses of the hydroxy and carboxylic derivatives 4b,c were then achieved from the intermediary disulfonamide 23. Displacement of the activated amino group by potassium acetate yielded hydroxy derivative 4b after three additional steps. Finally, oxidation of the alcohol function of 4b under Jones conditions followed by hydrogenolysis afforded the carboxylic derivative 4c, which is the first reported beta-isomer of 2,4-methanoproline 1.

Synthesis and electrochemical study of a new chiral tris-catecholamide analogue of enterobactin

The comparison of siderophore complex redox potentials with those of physiological reductants may aid in the clarification of the mechanism of iron metabolism. In this paper, a new chiral tris-catecholamide compound N,N',N''-tris-(2,3-dihydroxybenzoyl)-1,1,1-tris-(L-methioninemethyl++ +)-ethane or H6L (11) has been synthesised in nine steps, and may mimic the release of iron from enterobactin to the agents which are directly involved in cell metabolism. The choice of methionine as a constituent of the siderophore incorporates divalent sulphur which leads to the increase of the reduction potential of the siderophore, and consequently facilitates the iron release [Fe(III)/Fe(II) redox potential E(1/2)=-0.749 V vs (SCE)].

Structural characteristics of low-molecular-mass displacers for cation-exchange chromatography. II. Role of the stationary phase

The relative efficacy of a variety of low-molecular-mass displacers was examined on three different stationary phase materials. Several homologous series of displacer molecules were evaluated on these ion-exchange resins using a displacer ranking plot based on the steric mass action model. The results demonstrate that while aromaticity and hydrophobicity can play a significant role in the affinity of displacer molecules on polymethacrylate based and hydrophilized polystyrene-divinylbenzene based materials, this effect is much less pronounced on an agarose based resin. The work presented in this paper demonstrates that different structural features of low-molecular-mass displacers can dominate their affinity on various stationary phase materials employed and provides rules of thumb for the design of high affinity, low-molecular-mass displacers for a variety of commercial cation-exchange materials.

Tripodal trisamides based on nicotinic and picolinic acid derivatives

A number of polydentate arylamide ligands have been prepared by coupling various acyclic tripodal or linear polyamines with derivatives of nicotinic and picolinic acids. Two synthetic procedures were utilized; tris{[(2-hydroxynicotinyl)carbonyl]-2-aminoethyl}amine (H3NICTREN) was prepared by Method A, the HOSu/DCC method, and the other arylamides in this study were prepared by Method B, the CDI method. Method A involved the reaction of N-hydroxysuccinimide with 2-hydroxynicotinic acid (in the presence of dicyclohexylcarbodiimide (DCC) as a dehydrative coupling reagent) to form the succinimide ester, followed by reaction with TREN to yield H3NICTREN. Method B involved reaction of a carboxylic acid (2-hydroxynicotinic, 3-hydroxypicolinic, nicotinic, or picolinic acids) with carbonyldiimidazole (CDI) to form the N-acylimidazolide, followed by reaction with the amine (TREN, TAME, spermidine, or TRPN) to yield the desired arylamide. The X-ray structure of 1,1,1-tris{[(3-hydroxypicolinyl)carbonyl]-2-aminomethyl}ethane (H3PICTAME) was determined; crystals of H3PICTAME are monoclinic, a = 10.257(2), b = 15.572(3), c = 15.208(2) Å, β = 96.124(15)°, Z = 4, space group P21/a. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R = 0.041 and Rw = 0.038 for 2506 reflections with I >= 3 sigma (I). In the solid state, H3PICTAME contains an extensive hydrogen-bonding network, with eight intra- and one intermolecular H-bonds per molecule; the ligand is partially preorganized for metal ion chelation. The acid dissociation constants of H3NICTREN and those of 1,1,1-tris{[(2-hydroxynicotinyl)carbonyl]-2-

aminomethyl}ethane (H3NICTAME) have been determined; pKa1 = 11.2 (10.68), pKa2 = 10.7 (10.58), pKa3 = 10.0 (9.71), and pKa4 = 6.25 for H3NICTREN (H3NICTAME); the high phenolic pKa's are consistent with the hydrogen bonding observed in the solid state.Key words: arylamide, hydrogen bonding, preorganization.

Synthesis of chemically and functionally diverse scaffolds from pentaerythritol

Pentaerythritol (2,2-bis-hydroxymethyl-propane-1,3-diol) was converted into a series of mono-, di-, and trisubstituted derivatives, comprising allyl ethers and amino-alkyl ethers, by systematic chemical manipulation of the hydroxy groups. The remaining hydroxymethyl group in the case of the trisubstituted analog was functionalized with ether groups bearing terminal ω-carboxyl or ω-alkene groups. These derivatives are versatile templates and scaffolds for single, double, or triple substitution with appropriate ligands forming amides and esters, and allowing the attachment of the ω-alkene or ω-carboxyl group to solid support for combinatorial chemistry. Key words: molecular diversity, scaffolds, templates and tris(2-aminoethyl)-pentaerythritol.

Synthesis and characterization of novel N3O3-Schiff base complexes of 99gTc, and in vivo imaging studies with analogous 99mTc complexes

Sixteen novel derivatives of 1,1,1-tris (salicylaldiminomethyl)ethane have been synthesized for the purpose of encapsulating 99mTc(IV) ions and generating new 99mTc radiopharmaceuticals. Two methods for the preparation of the 99gTc(IV) analog complexes are presented; one utilizes SnCl2 reduction on 99gTcO4- and the other a direct substitution route starting with [99gTcCl6]2-. Free ligands (H3L) are characterized by melting points, 1H NMR, 13C NMR, mass spectroscopy, TLC, and/or elemental analyses. [99gTcL]+ complexes are characterized by FAB-ms, UV-VIS, IR and/or CV. An X-ray structural analysis was performed on a crystal of [M(6,6'-[[2-[[((4-Methoxy-2-hydroxyphenyl) methylene)-amino]methyl]-2-methyl- 1,3-propanediyl]bis(nitrilomethylidyne)]-bis-3-methoxyphenol )] tetraphenylborate, where M represents a 1/3 isomorphous mixture of 99gTc/Sn as determined by SEM. The metal coordination site is 6-coordinate, composed of N3O3 donor atoms, and intermediate between octahedral and trigonal prismatic geometry. The [99mTcL]+ complexes were prepared in a stannous environment; equivalence of the 99mTc and 99gTc complexes is demonstrated by HPLC techniques. The [SnL]+ complex was prepared for comparison purposes. An unusual ligand oxidation occurs for one series of ligands in which in situ amine-->imine conversion is observed during the complexation reaction in reducing media. Guinea pig, rat, dog, and human metabolism studies are reported for selected [99mTcL]+ complexes, the myocardial uptake of which approaches 2% of the injected dose.