Publications by authors named "Jonathan A Iggo"

Amino acid ester prodrugs of the thiazolides, introduced to improve the pharmacokinetic parameters of the parent drugs, proved to be stable as their salts but were unstable at pH > 5. Although some of the instability was due to simple hydrolysis, we have found that the main end products of the degradation were peptides formed by rearrangement. These peptides were stable solids: they maintained significant antiviral activity, and in general, they showed improved pharmacokinetics (better solubility and reduced clearance) compared to the parent thiazolides.

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Bridged amides and anilines display interesting properties owing to perturbation of conjugation of the nitrogen lone-pair with the adjacent π-system. A convergent approach to diazabicyclic scaffolds which contain either twisted amides or anilines is described, based on the photocatalysed hydroamination of cyclic enecarbamates and subsequent cyclisation. The modular nature of the synthesis allows for variation of the degree of 'twist' and hence the properties of the amides and anilines.

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p is an important property of a molecule which impacts many fields, such as drug design, catalysis, reactivity, and environmental toxicity. It is often necessary to measure p in nonaqueous media due to the poor solubility of an analyte in water, for example, many compounds of pharmaceutical interest. Although NMR methods to measure p in water are well established, determining p in organic solvents is laborious and problematic.

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Trimethylaluminum finds widespread applications in chemical and materials synthesis, most prominently in its partially hydrolyzed form of methylalumoxane (MAO), which is used as a cocatalyst in the polymerization of olefins. This work investigates the sequential reactions of trimethylaluminum with hexaprotic phosphazenes (RNH)PN (=XH) equipped with substituents R of varied steric bulk including tert-butyl (1H), cyclohexyl (2H), isopropyl (3H), isobutyl (4H), ethyl (5H), propyl (6H), methyl (7H), and benzyl (8H). Similar to MAO, the resulting complexes of polyanionic phosphazenates [XH ] accommodate multinuclear arrays of [AlMe] and [AlMe].

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A cyclometalated rhodium complex has been shown to perform highly selective and efficient reduction of aldehydes, deriving the hydrogen from methanol. With methanol as both the solvent and hydrogen donor under mild conditions and an open atmosphere, a wide range of aromatic aldehydes were reduced to the corresponding alcohols, without affecting other functional groups.

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It can be very informative to acquire NMR spectra of a sample as a function of the solution pH. Examples can be found in the design of host-guest complexes or in the determination of the p K values of organic molecules. In the conventional procedure, a series of spectra must be recorded and the pH of the sample adjusted manually between successive NMR measurements.

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The surface chemistry of self-assembled hydrogel fibres - their charge, hydrophobicity and ion-binding dynamics - is recognised to play an important role in determining how the gels develop as well as their suitability for different applications. However, to date there are no established methodologies for the study of this surface chemistry. Here, we demonstrate how solution-state NMR spectroscopy can be employed to measure the surface chemical properties of the fibres in a range of hydrogels formed from N-functionalised dipeptides, an effective and versatile class of gelator that has attracted much attention.

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Supramolecular hydrogels are formed via the self-assembly of gelator molecules upon application of a suitable trigger. The exact nature of this self-assembly process has been widely investigated as a practical understanding is vital for the informed design of these materials. Solution-state NMR spectroscopy is an excellent non-invasive tool to follow the self-assembly of supramolecular hydrogels.

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The magnetic-field-induced alignment of the fibrillar structures present in an aqueous solution of a dipeptide gelator, and the subsequent retention of this alignment upon transformation to a hydrogel upon the addition of CaCl2 or upon a reduction in solution pH is reported. Utilising the switchable nature of the magnetic field coupled with the slow diffusion of CaCl2 , it is possible to precisely control the extent of anisotropy across a hydrogel, something that is generally very difficult to do using alternative methods. The approach is readily extended to other compounds that form viscous solutions at high pH.

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Asymmetric hydrogenation of imines leads directly to chiral amines, one of the most important structural units in chemical products, from pharmaceuticals to materials. However, highly effective catalysts are rare. This article reveals that combining an achiral pentamethylcyclopentadienyl (Cp*)-iridium complex with a chiral phosphoric acid affords a catalyst that allows for highly enantioselective hydrogenation of imines derived from aryl ketones, as well as those derived from aliphatic ones, with ee values varying from 81 to 98 %.

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A wide range of multisubstituted 1-indanones of potential pharmaceutical use were synthesized in a one-pot fashion in moderate to excellent yields via palladium catalysis in ethylene glycol. The Heck reaction first installs an enol functionality on the aromatic ring; this is followed by an ethylene glycol promoted aldol-type annulation with a neighboring carbonyl group, resulting in the formation of various 1-indanones.

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The first, general, and highly efficient catalytic system that allows a wide range of activated and unactivated aryl chlorides to couple regioselectively with olefins has been developed. The Heck arylation reaction is likely to be controlled by the oxidative addition of ArCl to Pd(0). Hence, an electron-rich diphosphine, 4-MeO-dppp, was introduced to facilitate the catalysis.

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Pd(II) complexes in which 2-pyridyldiphenylphosphine (Ph(2)Ppy) chelates the Pd(II) centre have been prepared and characterized by multinuclear NMR spectroscopy and by X-ray crystallographic analysis. trans-[Pd(kappa(1)-Ph(2)Ppy)(2)Cl(2)] is transformed into [Pd(kappa(2)-Ph(2)Ppy)(kappa(1)-Ph(2)Ppy)Cl]Cl by the addition of a few drops of methanol to dichloromethane solutions, and into [Pd(kappa(2)-Ph(2)Ppy)(kappa(1)-Ph(2)Ppy)Cl]X by addition of AgX or TlX, (X = BF(4)(-), CF(3)SO(3)(-) or MeSO(3)(-)). [Pd(kappa(1)-Ph(2)Ppy)(2)(p-benzoquinone)] can be transformed into [Pd(kappa(2)-Ph(2)Ppy)(kappa(1)-Ph(2)Ppy)(MeSO(3))][MeSO(3)] by the addition of two equivalents of MeSO(3)H.

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Novel cis-1,2-bis(di-tert-butyl-phosphinomethyl) carbocyclic ligands 6-9 have been prepared and the corresponding palladium complexes [Pd(O(3)SCH(3))(L-L)][O(3)SCH(3)] (L-L=diphosphine) 32-35 synthesised and characterised by NMR spectroscopy and X-ray diffraction. These diphosphine ligands give very active catalysts for the palladium-catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9, containing four- and six-membered ring backbones giving more active systems.

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We present a study of the acyl nitroso Diels-Alder (ANDA) reaction of sorbate esters and sorbic alcohol derivatives, using alkoxycarbonyl nitroso dienophiles. An optimisation of the reaction conditions for ethyl sorbate is first presented, and the product is used in an efficient synthesis of 5-methylornithine. Structure-reactivity trends in sorbic alcohol (E,E-2,4-hexadien-1-ol) and its acylated analogues are then discussed.

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The fragmentation and redistribution reactions of [Rh4(CO)12-x{P(OPh)3}x] (x = 1-4) with carbon monoxide have been studied using high-resolution, high-pressure NMR spectroscopy. Under the conditions of efficient gas mixing in a high-pressure NMR bubble column, [Rh4(CO)9{P(OPh)3}3] fragments to give mainly [Rh2(CO)6{P(OPh)3}2]; [Rh4(CO)11{P(OPh)3}] is also observed,implying redistribution of the phosphite ligand and/or recombination of the dimers to tetrameric clusters. Fragmentation of[Rh4(CO)10{P(OPh)3}2] is found to be pressure-dependent giving predominantly [Rh2(CO)6{P(OPh)3}2] at low CO pressure (1-40 bar), and increasing amounts of [Rh2(CO)7{P(OPh)3}] at higher (40-80 bar) pressure.

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A new protocol for the direct acylation of aryl bromides with aldehydes is established. It appears to involve palladium-amine cooperative catalysis, affording synthetically important alkyl aryl ketones in moderate to excellent yields in a straightforward manner, and broadening the scope of metal-catalyzed coupling reactions.

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The mechanism of aqueous-phase asymmetric transfer hydrogenation (ATH) of acetophenone (acp) with HCOONa catalyzed by Ru-TsDPEN has been investigated by stoichiometric reactions, NMR probing, kinetic and isotope effect measurements, DFT modeling, and X-ray structure analysis. The chloride [RuCl(TsDPEN)(p-cymene)] (1), hydride [RuH(TsDPEN)(p-cymene)] (3), and the 16-electorn species [Ru(TsDPEN-H)(p-cymene)] (4) were shown to be involved in the aqueous ATH, with 1 being the precatalyst, and 3 as the active catalyst detectable by NMR in both stoichiometric and catalytic reactions. The formato complex [Ru(OCOH)(TsDPEN)(p-cymene)] (2) was not observed; its existence, however, was demonstrated by its reversible decarboxylation to form 3.

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The progressive addition of anhydrous pyridine, (py), to a solution of [Rh(4)(CO)(12)] in CH(2)Cl(2) under CO, even at low temperature, results in immediate disproportionation to give cis-[Rh(CO)(2)py(2)][Rh(5)(CO)(15)]; further addition of pyridine results in the progressive replacement of CO's by py on the same apical rhodium in [Rh(5)(CO)(15)](-) to give cis-[Rh(CO)(2)py(2)][Rh(5)(CO)(15-x)py(x)] (x = 1, 2). The analogous reactions with 2,2'-bipyridine (bipy) give only [Rh(CO)(2)bipy][Rh(5)(CO)(13)bipy]. IR and low temperature, multinuclear NMR measurements have been used to establish the structures of all the above anions and the structures of [Rh(5)(CO)(13)(bipy)](-) and [Rh(5)(CO)(13)py(2)](-) are subtly different.

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The reaction of [Rh7(CO)16]3- with SnCl(2).2H2O in a 1 : 1 molar ratio under N2 results in the formation of the new heterometallic cluster, [Rh12Sn(CO)27]4-, in very high yield (ca. 86%).

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All the intermediates in the "carboalkoxy" pathway, and their interconversions giving complete catalytic cycles, for palladium-diphosphine-catalyzed hydroalkoxycarbonylation of alkenes, and for alkene-CO copolymerization, have been demonstrated using (31)P{(1)H} and (13)C{(1)H} NMR spectroscopy. The propagation and termination steps of the "hydride" cycles and the crossover between the hydride and carboalkoxy cycles have also been demonstrated, providing the first examples of both cycles, and of chain crossover, being delineated for the same catalyst. Comparison of the propagation and termination steps in the pathways affords new insight into the selectivity-determining steps.

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Two novel heterometallic octahedral clusters [Rh(4)Pt(2)(CO)(11)(dppm)(2)](1) and [Ru(2)Rh(2)Pt(2)(CO)(12)(dppm)(2)](2) were synthesized by the reaction of [Rh(2)Pt(2)(CO)(6)(dppm)(2)] with [Rh(6)(CO)(14)(NCMe)(2)] and Ru(3)(CO)(12), respectively. Solid state structures of 1 and 2 have been established by a single crystal X-ray diffraction study. Two dppm ligands in 1 are bonded to one platinum and three rhodium atoms, which form an equatorial plane of the Rh(4)Pt(2) octahedron.

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