Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1994"

Hydrogen bonding. Part 34. The factors that influence the solubility of gases and vapours in water at 298 K, and a new method for its determination

Abstract: The solubility of 408 gaseous compounds in water at 298 K has been correlated through eqn. (i), where the solubility is expressed as the Ostwald solubility coefficient, Lw, and the solute explanatory variables are R2 an excess molar refraction, π2H the dipolarity/polarizability, Σα2H and Σβ2H the effective hydrogen-bond acidity and basicity, and Vx the McGowan characteristic volume. A similar equation using the log L16 parameter instead of Vx can also be used; L16 is the Ostwald solubility coefficient on hexadecane at 298 K. log Lw=–0.994 + 0.577R2+ 2.549 π2H+ 3.813Σα2H+ 4.841Σβ2H– 0.869 Vx(i), n= 408 ρ= 0.9976 sd = 0.151 F= 16810 The main factors leading to increased solubility are solute π2H, Σα2H and Σβ2H values; conversely, the corresponding properties of water are dipolarity/polarizability, hydrogen-bond basicity and hydrogen-bond acidity. Solute size plays a minor role, and slightly decreases solubility, contrary to observations on all non-aqueous solvents. It is shown that this peculiar behaviour of water is due to (a) a greater increase in the unfavourable cavity effect with increase in solute size, for solvent water, and (b) a smaller increase in the favourable general dispersion interaction with size, for solvent water.A new method for the determination of log Lw values is put forward, using the relationship Lw=L16/P where L16 is as above, and P is either the water–hexadecane partition coefficient or the water–alkane partition coefficient. For 14 solutes using the former P-value, agreement with values calculated through eqn. (i) is 0.08 log units on average and for 45 solutes using the latter P-value, the corresponding agreement is 0.15 log units, with log Lw values ranging up to 8 log units.

Identification and synthesis of new ferulic acid dehydrodimers present in grass cell walls

Abstract: Seven isomeric dehydrodimers of ferulic acid (4-hydroxy-3-methoxycinnamic acid) have been synthesized and identified in extracts of saponified cell walls of cocksfoot, switchgrass, and suspension-cultured corn. Dehydrodimers (E,E)-4,4′-dihydroxy-5,5′-dimethoxy-3,3′-bicinnamic acid, trans-5-[(E)-2-carboxyvinyl]-2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-2,3-dihydrobenzofuran-3-carboxylic acid, (Z)-β-{4-[(E)-2-carboxyvinyl]-2-methoxyphenoxy}-4-hydroxy-3-methoxycinnamic acid, (E)-3-{4-[(E)-2-carboxyvinyl]-2-methoxyphenoxy}-4-hydroxy-5-methoxycinnamic acid, (E,E)-4,4′-dihydroxy-3,5′-dimethoxy-β,3′-bicinnamic acid, 4,4′-dihydroxy-3,3′-dimethoxy-β,β′-bicinnamic acid, and trans-7-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-6-methoxy-1,2-dihydronaphthalene-2,3-dicarboxylic acid, all arise from oxidative coupling of ferulate esters in cell walls and represent products of 8–5, 8–8, 8–O–4, 4–O–5, and 5–5 radical coupling. Prior literature has acknowledged only the presence of the 5–5-coupled dehydrodimer (E,E)-4,4′-dihydroxy-5,5′-dimethoxy-3,3′-bicinnamic acid. Consequently, by measuring only a single dehydrodimer and assuming inappropriate response factors, ferulate dehydrodimers have been underestimated by factors of up to 20. Synthetic routes to all seven isomers have been developed to provide structural authentication and determination of GC response factors.

The nature of halogen ⋯ halogen interactions and the crystal structure of 1,3,5,7-tetraiodoadamantane

Abstract: An analysis of halogen ⋯ halogen (X ⋯ X) intermolecular interactions in crystals, using the Cambridge Structural Database (CSD). is presented. A total of 794 crystal structures yielded 1051 contacts corresponding to symmetrical and unsymmetrical X ⋯ X interactions of the type Cl ⋯ Cl, Br ⋯ Br, I ⋯ I, Cl ⋯ F, Br ⋯ F, I ⋯ F, Br ⋯ Cl, I ⋯ Cl and I ⋯ Br. These 1051 contacts are divided mainly into two categories, type I and type II depending upon the values of the two C–X ⋯ X angles θ1and θ2around the X atoms in a fragment of the type C–X ⋯ X–C. Type I contacts are defined as those in which θ1=θ2 while type II are defined as those in which θ1≅ 90° and θ2≅ 180°. Our results indicate that as the polarisability of the X atom increases, type II contacts become more significant than type I contacts and the X ⋯ X interaction may be more nearly considered to arise from specific attractive forces between the X atoms. A number of these concepts are succinctly illustrated in the crystal structure of 1,3,5,7-tetraiodoadamantane, 1. This structure has been reported to a very limited accuracy previously and the present work reveals an unusual twinned structure for this compound wherein the geometry of the stabilising I ⋯ I interactions is retained across the twin boundary. Compound 1 is tetragonal, space group I41/a, a= b = 7.1984(7) and c= 28.582(4)A, and Z = 4. The packing of the molecules in the crystal is controlled by I ⋯ I interactions. The supramolecular network of I ⋯ I connected molecules in crystalline 1 is closely related to that in adamantane-1,3,5,7-tetracarboxylic acid. Indeed, the stabilising nature of the I ⋯ I interactions is crucial for the crystallisation of 1 in this particular structure because otherwise, it should also have formed plastic crystals as do the analogous tetrachloro and tetrabromo derivatives.

Solvent effects on chemical processes. Part 7. Quantitative description of the composition dependence of the solvent polarity measure ET(30) in binary aqueous–organic solvent mixtures

Abstract: The solvation effect component of the phenomenological model of solvent effects is applied to ET(30), the molar transition energy of the Dimroth–Reichardt betaine, in binary aqueous–organic solvents. The dependence of ET(30) on x2, the mole fraction of organic cosolvent, can be quantitatively described for all 17 systems studied. New data are given for 9 of these systems. It is found that a 1-parameter model suffices to describe the composition dependence of the highly polar cosolvents, whereas a 2-parameter model is needed to account for other cosolvents, which yield a nonhyperbolic composition dependence. The solvation parameters, which are exchange equilibrium constants, yield correlations suggesting their positive dependence on cosolvent hydrophobicity and electron-pair donor ability.

The use of chemical probes for the characterization of solvent mixtures. Part 2. Aqueous mixtures

Abstract: The question of whether chemical properties, such as polarity or hydrogen bond donation or acceptance, can be measured in aqueous solvent mixtures by means of indicator probes, or whether their use is obviated because of preferential solvation, is examined. In some cases, such as the Kamlet–Taft π* or β parameters, the use of several probes yielding convergent results provides acceptable values of the properties. In another case—i.e. the Kamlet–Taft α parameter—this question must remain open because of the relatively large spread of values obtained with different probes, which is not necessarily related to preferential solvation. A single probe such as the betaine used for the ET(30) polarity parameter, cannot provide an answer.

Chemical evidence for the de-astringency (insolubilization of tannins) of persimmon fruit

Abstract: After artificial removal of the astringency from persimmon fruit by treatment with ethanol, thiol-promoted degradation of the insolubilized proanthocyanidin polymers with 2-sulfanylethanol yielded 4β-(2-hydroxyethylsulfanyl)-6- and -8-[1-(2-hydroxyethylsulfanyl)ethyl]-flavan-3-ols 9–14. Furthermore, when deuteriated ethanol was used for de-astringency, the deuterium atoms were incorporated into the C2 unit attached to the A-ring of these compounds. These findings evidently show that acetaldehyde formed in situ from ethanol plays an important role in polymerization (insolubilization) of water-soluble proanthocyanidins, causing the loss of astringency.

Molecular recognition among alcohols and amines: super-tetrahedral crystal architectures of linear diphenol–diamine complexes and aminophenols

Abstract: Hydroxy and amino groups are complementary as regards hydrogen-bond donors and acceptors. This is expected to lead to molecular recognition among alcohols and primary amines, i.e., to a propensity towards formation of 1 : 1 alcohol–amine complexes, driven by a 50% increase of the number of hydrogen bonds as compared with the uncomplexed constituents. Possible hydrogen-bonded architectures of such complexes are suggested, and the concept is successfully exploited for crystal engineering purposes by drawing upon linear diphenols, aromatic diamines, and aminophenols as supramolecular partners. Specifically, the crystal-structural chemistry is reported of the 1 : 1 molecular complexes between hydroquinone and p-phenylenediamine, hydroquinone and benzidine, 4,4′-dihydroxybiphenyl and p-phenylenediamine, 4,4′-dihydroxybiphenyl and benzidine, as well as of p-aminophenol, and of 4,4′-hydroxyaminobiphenyl. The diphenol–diamine complexes form hyderogen-bonded super-diamond lattices with 1.5 O(H) N bonds per oxygen and nitrogen atoms, respectively. Again exclusively via O(H)N bonds, the aminophenol structures are also supertetrahedral but after the manner of the polar wurtzite variant. Some similar reported structures are analysed in the light of the present concepts and results, and implications are discussed of the finding that molecular recognition is possible among molecules as standard as simple alcohols and amines.

Keynote article. Environmentally friendly chemistry using supported reagent catalysts: structure–property relationships for clayzic

Abstract: Supported reagents have been widely used in organic synthesis for some 25 years and their importance is likely to increase as a result of new environmental legislation and the drive towards clean technology. While many supported reagents are stoichiometric in reactions the successful development of genuinely catalytic materials greatly enhances their value especially in liquid phase, typically fine chemical syntheses. Achieving an understanding of the nature of these fascinating materials is also an important aspect of their development and is essential if their true potential is to be realised. Solid acids are the most widely studied of supported reagents and their use as more environmentally acceptable replacements for conventional Bronsted and Lewis acids is likely to become increasingly important. Clayzic is a good example of an environmentally friendly catalyst with particular value as an alternative to the hazardous reagent aluminium chloride in Friedel–Crafts reactions. The structure and properties of this catalyst are, however, poorly understood. X-Ray diffraction studies show that thermal treatment of either clayzic or its base material K10 results in the loss of any montmorillonite crystallinity that remained after the acid treatment of tonsil 13 used to form K10. Thermal treatment of clayzic also results in a steady increase in the surface area of the material. While this is also consistent with structural changes the increase is also likely to be partly due to the dehydration allowing the non-polar adsorbate to enter more of the polar regions of the material. These polar regions can be identified as mesopores created by the acid treatment of the clay and in which the zinc ions largely reside. Spectroscopic titration of the acid sites in clayzic show these to be largely Lewis acid in character. Thus clayzic owes its remarkable Friedel–Crafts activity to the presence of high local concentrations of zinc ions in structural mesopores. Relative reaction rates for the clayzic catalysed benzylation of alkylbenzenes also reveal the importance of these highly polar mesopores. Considerable rate enhancements can be achieved by thermally activating the catalyst and this can be largely attributed to the dehydration of the catalyst enabling better partitioning of the alkylbenzenes into the mesopores. Clayzic can be considered as being a large pore molecular sieve but where the sieving of molecules is controlled more by molecular polarities/polarisibilities than by molecular shape.

Leptosins, antitumour metabolites of a fungus isolated from a marine alga

Abstract: Leptosins A B, C, D, E and F, chaetocin derivatives, have been isolated from the mycelium of a strain of Leptosphaeria sp. attached to the marine alga Sargassum tortile. Their stereostructures, with a different configuration from that of related compounds, have been elucidated by spectroscopic analyses using various 1D and 2D NMR techniques and some chemical transformations. All the compounds showed potent cytotoxicity against cultured P388 cells, and leptosins A and C exhibited significant antitumour activity against Sarcoma 180 ascites.

Molecular recognition directed self-assembly of tubular liquid crystalline and crystalline supramolecular architectures from taper shaped (15-crown-5)methyl 3,4,5-tris(p-alkyloxybenzyloxy)benzoates and (15-crown-5)methyl 3,4,5-tris(p-dodecyloxy)benzoate

Abstract: The syntheses and characterization of a series of (15-crown-5)methyl 3,4,5-tris(p-alkyloxybenzyloxy)benzoatest with alkyl tails of four 25, six 26, and twelve 27 carbon atoms and of (15-crown-5)methyl 3,4,5-tris(p-dodecyloxybenzoate)28 are described. Complexation of the crown ether endo-receptor with NaCF3SO3 destabilizes the crystalline phase of 25, 26, 27 and 28 and induces for the case of 27 and 28 the self-assembly of a supramolecular cylindrical channel-like architecture which displays a thermotropic hexagonal columnar (Φh) mesophase. Most remarkably, in the crystalline phase of the complexes of 27 with NaCF3SO3 the cylindrical structure of the Φn mesophase is maintained. Characterization of these supramolecular architectures was performed by a combination of differential scanning calorimetry (DSC), thermal optical polarized microscopy, X-ray scattering and molecular modelling. A model is proposed in which a stratum of the column is formed by six molecules of 27 and 28 with the crown ether receptors residing in the column centre and the alkyl tails radiating toward the column periphery. endo-Recognition generated via the (15-crown-5)methyl receptor upon complexation, and exo-recognition provided by the tapered 3, 4, 5tris(p-dodecyloxybenzyloxy)benzoate and 3, 4, 5-tris(p-dodecyloxy)benzoate fragments of 27 and 28 provide the driving force for the self-assembly of this cylindrical supramolecule.

Synthesis, surface active properties and antimicrobial activity of new bis quaternary ammonium compounds

Abstract: New dimeric surfactants 1 and 2 containing two saturated hydrocarbon chains and two quaternary ammonium salts linked through an alkene spacer chain with amide and disulfide bonds have been prepared from a betaine type amphoteric surfactant. They show a high effectiveness of adsorption in comparison with their single chain homologues. Surfactants 1 and 2 are very water soluble compounds with extraordinary micelle-forming properties. Both are very active against a wide range of microorganisms including gram negative bacteria.

Ytterbium Triflate and High Pressure-Mediated Ring Opening of Epoxides with Amines.

Abstract: Ring opening of epoxides with amines in THF takes place very readily in the presence of catalytic amounts of ytterbium triflate to give the corresponding β-amino alcohols in good to high yields. With tri- and tetra-substituted epoxides, the use of an excess (2–3 equiv.) of the amine is needed. The Yb(OTf)3-catalysed reaction of epoxides with amines in CH2Cl2 is quite complex; the yield of amino alcohols is generally lower and depends upon the addition order of the catalyst, amine and epoxide. The ring opening is accomplished also under high pressures in the absence of Yb(OTf)3. Ring opening with a combination of Yb(OTf)3 in CH2Cl2 and high pressure is more effective than the use, independently, of either Yb(OTf)3 or the high-pressure method. Oxetanes and β-lactones undergo ring opening in the presence of Yb(OTf)3.

An efficient and selective palladium-catalysed oxidative dicarbonylation of alkynes to alkyl- or aryl-maleic esters

Abstract: Terminal alkyne dicarbonylation can be readily effected under mild conditions by treating alkynes with carbon monoxide and alcohols or water at 25–80 °C in the presence of Pdl2, KI and air, with unprecedented catalytic efficiency. Dicarbonylated products are mainly maleic esters or acids and their ring-chain tautomers. The latter are formed to a large extent at room temperature. Reaction pathways are discussed.

Thiol-reactive fluorescent probes for protein labelling

Abstract: Cyclisation of N-alkylmaleamic acids mediated by acetic anhydride in dimethylacetamide in the presence of traces of cobalt naphthenate has been used for efficient assembly of a range of fluorescent maleimide reagents. The fluorescence responses of these reagents to addition of thiol across the maleimide double bond, and to hydrolysis of the maleimide ring, are described.

Asymmetric synthesis of anti-α-alkyl-β-amino acids

Abstract: An investigation into the asymmetric induction accompanying alkylations of enolates derived from the highly diastereoselective conjugate addition of lithium (R)-N-benzyl-N-α-methylbenzylamide (R)-1 to crotonate and cinnamate esters has been performed. The access to different enolate geometries afforded by the conjugate addition process and subsequent enolate regeneration by deprotonation of the β-amino ester conjugate adducts enabled two disparate sets of selectivity data to be compiled. Although both approaches furnished predominantly anti-α-alkyl-β-amino esters, the two-step procedure proved to be considerably more selective. Several factors which play a major role in determining the alkylation selectivity are identified, including the cooperative influence of the α-methylbenzylamino stereocentre. Since debenzylation and hydrolysis of the alkylated products was straightforward, this methodology provides a direct route to anti-α-alkyl-β-amino acids in homochiral form.

Palladium-catalysed asymmetric allylic substitution: a ligand design incorporating steric and electronic effects

Abstract: Enantiomerically pure ligands containing a 4,5-dihydrooxazole moiety tethered to an auxiliary sulfur or phosphorus donor have been prepared. These ligands have been exploited for palladium-catalysed asymmetric allylic substitution, providing enantioselectivities of 40–96% ee. The origin of the enantioselectivity in the catalytic reaction is discussed in terms of the steric and electronic influences provided by the ligand.

Alkene epoxidation catalysed by iron(III) and manganese(III) tetraarylporphyrins coordinatively bound to polymer and silica supports

Abstract: Four tetraaryl metalloporphyrin catalysts [FeIII, Ar = phenyl and pentafluorophenyl; FeIII and MnIII, Ar = 2,6-dichlorophenyl (FeIIITDCPP and MnIIITDCPP)] have been coordinatively bonded to poly(4-vinylpyridine), and imidazole modified polystyrene (PS-Im) and silica (Si-Im). Evidence is presented that suggests that the iron(III) porphyrins are predominantly bis-ligated to the polymer supports whereas with MnIIITDCPP mono-ligation is preferred. On Si-Im all the complexes are mono-ligated. A fifth metalloporphyrin, the ionic manganese(III) 5,10,15,20-tetra(N-methyl-4-pyridyl)porphyrin (MnIIIT4MPyP); which binds strongly to unmodified silica, does not ligate to Si-lm.Leaching experiments show that FeIIITDCPP is most strongly anchored to the supports. The resulting materials have been used as catalysts for the oxidation of cyclohexene and cyclooctene by iodosylbenzene. The oxidant accountabilities are good and product distributions from reactions under nitrogen are very comparable to those from analogous homogeneous oxidations. However, the rates of the former are markedly lower. Oxidations of cyclohexene, but not of cyclooctene, in air are biphasic. The first phase, where epoxidation predominates, is attributable to an FeIIITDCPP-catalysed oxidation by PhIO and the second, which leads to allylic oxidation, to radical autoxidation.The best catalysts for large turnover epoxidations are FeIIITDCPP and MnIIITDCPP on Si–lm. The causes of the lower yields with catalysts on the more flexible polymer supports are discussed.A limited study with H2O2 as the oxidant reveals that MnIIITDCPP on Si–Im, in contrast to the ionic MnIIIT4MPyP on silica, catalyses the epoxidation of cyclooctene.

One- and two-electron reduction potentials of peroxyl radicals and related species

Abstract: Utilising gaseous and aqueous thermodynamic quantities, estimates (in water versus NHE) have been made of the one-electron reduction potentials of alkyl peroxyl radicals including CCl3OO˙, percarboxyl and carboxyl radicals, and alkoxyl radicals, including CCl3O˙ and two-electron reduction potentials of alkyl hydroperoxides including CCl3OOH, alkyl peroxyl radicals including CCl3OO˙ and of percarboxyl radicals.

On the proton affinity of some α-amino acids and the theory of the kinetic method

Abstract: A rationalization of the kinetic method for determination of proton affinities (Epa) has been formulated. When a proton-bound amine dimer with the general structure amine1–amine2–H + decomposes to either amine1–H+ or amine2–H+ the critical energies for the competing fragmentations can be calculated from a simplified version of the Marcus equation, which is supported by published values of molecular pair proton affinities. Consequently reaction rates of the metastable ions can be calculated from the expression k(E)=ν[(E–E0)/E]s– 1 and ion abundances from the expression ∫EP(E)F(E)dE, where P(E) is the probability of reaction and F(E) is the energy distribution function of the metastable ions. It is argued that for metastable ions generated by ionization methods such as Cl or FAB, the energy distribution functions will be smooth and that consequently the relative ion abundances from two competing decompositions will not depend on F(E). Model calculations of fragment ion abundances from metastable decomposition of ions with the general structure pentylamine–aminex–H+ show a linear relationship between the logarithm to the ratio: I(aminex–H+)/(pentylamine–H+) and the Epa of aminex. This provides a rationalization of the kinetic method that avoids any introduction of a thermodynamic temperature. Determination of the fragment ion abundances from decomposition of metastable protonated clusters with the general structure α-amino acid–aminex–H for 17 different α-amino acids gave the following Epa/kcal mol–1 values: Ser, 217.2; Val, 218.1; Asp, 218.1; Leu, 218.7; Ile, 219.2; Thr, 219.2; Phe, 219.9; Tyr, 220.7; Met, 221.0; Asn, 222.1; Glu, 222.3; Pro, 222.4; Trp. 223.5; Gln, 226.9; Lys, 228.7; His, 230.5; Arg, > 242.8.

An extended form of the Evans–Polanyi equation: a simple empirical relationship for the prediction of activation energies for hydrogen-atom transfer reactions

Abstract: An empirical approach has been used to devise a simple relationship [eqn. (B)] between the activation energy for an elementary hydrogen-atom transfer reaction (A) and ground state properties A˙+ H–B → A–H + B˙(A), Ea=Eof+αΔH°(1–d)+βΔχAB2+γ(sA+sB)(B) of the reactants and products. The role of polar effects, which operate in the transition state, is emphasised and described quantitatively in terms of the difference in Mulliken electronegativities (ΔχAB) of the radicals A˙ and B˙. Eqn. (B) reproduces the activation energies for 65 reactions, taken from the literature, within a standard error of ±2.0 kJ mol –1 and with a correlation coefficient of 0.988. Reactions of widely differing types are included and no distinction is made between gas-phase reactions and those which take place in non-polar solvents. Examples of hydrogen-atom transfer reactions which are not treated satisfactorily by eqn. (B) are discussed.

Use of chemical probes for the characterization of solvent mixtures. Part 1. Completely non-aqueous mixtures

Abstract: The use of chemical probes for the characterization of chemical properties (polarity, hydrogen bonding ability) is explored for solvent mixtures not involving water as a component. Preferential solvation is more important in such mixtures than in those that contain water. This implies that contrary to common practice, polarity indices etc. obtained in the mixtures with a given probe may not be generally valid for the solvation of other solutes. Still, approximate values of these properties can be obtained by judicious use of such probes.

NMR spectroscopic and X-ray crystallographic studies of calix[4]arene·Ag+complexes. Influence of bound Ag+ on C2v–C2v interconversion in cone-calix[4]arenes

Abstract: The Ag+ complexes of conformationally immobilized tetra-O-propylcalix[4]arene with a cone or a partial-cone conformation (cone-2Prn or partial-cone-2Prn, respectively) have been successfully analysed by X-ray crystallography. In both complexes Ag+ was bound to the upper rim cavity, sandwiched by the two para carbons in the distal phenyl units. The findings provide clear evidence for π-base participation. In particular, the basic calix[4]arene skeleton in partial-cone-2Prn·Ag+ is almost the same as that in partial-cone-2Prnitself. This establishes that partial-cone-2R possesses two distal benzene rings ideally preorganized for Ag+-binding. 1H NMR spectroscopic studies for the Ag+ complexes in solution indicated that Ag+ is bound to the same site as that in the solid state. In conformationally mobile 2Me, which exists in solution in equilibrium between cone and partial-cone, Ag+ induced a shift of the equilibrium to partial-cone to form the partial-cone-2Me·Ag+complex. This is ascribed to the ideal preorganization in partial-cone-2R for the Ag+-binding. These results are of great significance for an understanding of π-base participation in the metal-binding events and have important implications on the cation–π interaction in biological systems.

What did W. H. Perkin actually make when he oxidised aniline to obtain mauveine

Abstract: The literature structure for mauveine has been shown to be wrong. Analysis of samples of mauveine made by Perkin in his factory show them to be primarily a mixture of two phenazinium dyes, 3-amino-2methyl-5-phenyl-7-(p-tolyl)phenazinium acetate and 3-amino-2,9-dimethyl-5-phenyl-7-(p-tolyl) phenazinium acetate

Asymmetric synthesis of syn-α-alkyl-β-amino acids

Abstract: An investigation into the reactivity of the highly stereoselective conjugate nucleophile lithium N-benzyl-N-α-methylbenzylamide 1 with α-alkyl-α,β-unsaturated esters has led to the development of a versatile asymmetric synthesis of syn-α-alkyl-β-amino acids. By performing the conjugate additions in toluene and diluting the reaction mixtures with THF prior to quenching of the reactions with the hindered acid, 2,6-di-tert-butylphenol 13, the product syn-α-alkyl-β-amino esters may be generated in good yield and with excellent stereocontrol. Several examples illustrate the ease with which these products may be debenzylated and hydrolysed to afford homochiral syn-α-alkyl-β-amino acids.

Transnitrosation between nitrosothiols and thiols

Abstract: Transfer of the nitroso group from nitrosothiols to thiols occurs very readily in aqueous solution particularly at pH > ≈8. The results are consistent with attack by the thiolate anion at the nitroso nitrogen atom of the nitrosothiol. Results have been obtained for the reaction of S-nitroso-N-acetylpenicillamine (SNAP) with thioglycolic acid and also for the reaction of S-nitrosocysteine (SNCys) with thiomalic acid. Both reactions showed the same kinetic characteristics. The results are discussed in terms of transnitrosation reactions of nitroso compounds generally, and also in the case of nitrosothiols, in terms of possible in vivo transnitrosation and subsequent decomposition of a possibly more unstable nitrosothiol to yield nitric oxide; this may have implications for the mechanism of action of nitric oxide in a range of physiological processes.

Asymmetric synthesis of (−)-(1R,2S)-cispentacin and related cis- and trans-2-amino cyclopentane- and cyclohexane-1-carboxylic acids

Abstract: The antifungal antibiotic (–)-(1R,2S)-2-aminocyclopentane-1-carboxylic acid (cispentacin)8 and its cyclohexane homologue 14 have been prepared utilizing the highly stereoselective conjugate addition of homochiral lithium N-benzyl-N-α-methylbenzylamide 5. The corresponding trans-β-amino acids 10 and 16 were also prepared via the selective epimerization of the cis-β-amino ester conjugate addition products.

Synthesis and properties of a potential extracellular fluorescent probe for potassium

Abstract: Development of a new, selective, high affinity, fluorescent probe CD222, 2, for potassium is described. Coincidentally two related probes, CDF18, 3, and CTF18, 4, were prepared and showed selectivity for the cations sodium and calcium, respectively, and possible reasons for these differences are discussed. The bicyclic probe CD222, 2, with observed KD values for K+ ranging from 1 to 10 mmol dm–3, has potential applications as an extracellular probe for potassium.

Selective mono-methylation of arylacetonitriles and methyl arylacetates by dimethyl carbonate

Abstract: Both arylacetonitriles and methyl arylacetates react with dimethyl carbonate (DMC)(20 molar excess) at 180–200 °C in the presence of K2CO3 to produce monomethylated 2-arylpropionitriles and methyl 2-arylpropionates, respectively, with a selectivity >99.5%. The reaction, with wide application, proceeds by DMC acting as a methoxycarbonylating agent towards the ArCH–X anion (X = CN, CO2Me) and as a methylating agent to ArC–(CO2Me)X. DMC also proved to be the best solvent for such reactions.

Formation of hydrides of fullerene-C60 and fullerene-C70

Abstract: Fullerene-C60 and fullerene-C70 have been reduced by various methods to di- and tetra-hydro derivatives. Reduction by diimide is the most satisfactory method with regard to both yield and ease of carrying out of the reaction. The 1H NMR chemical shifts are highly solvent dependent, and are ca. 1 ppm further downfield in carbon disulfide than in benzene; the shifts for C60Hn compounds are downfield compared with those for C70Hn compounds, due possibly to differences in strain between the cages and/or a field effect operating across the cage void. 1,2,3,4-Tetrahydrofullerene-C60 is the main product from reduction of fullerene-C60 with diimide, and all other tetrahydro derivatives that can be produced by addition across the high order bonds appear to be present, together with more highly hydrogenated derivatives. Eight products are obtained on diimide reduction of fullerene-C70; two have been characterised as 1,5,6,9-tetrahydrofullerene-C70 and 1,7,8,9-tetrahydrofullerene-C70, and two others are the 1,9- and 7,8-dihydrofullerenes obtained by reduction with diborane. The other four derivatives may be the other tetrahydro isomers which can be obtained by addition across the 1,9-bond and its other equivalents. The hydrogenated fullerenes are more soluble in carbon disulfide than in either benzene or toluene, thus facilitating observation of the 13C satellites of 1,2-dihydrofullerene-60 in the 1H NMR spectrum. The C–H and H–H coupling constants are 141.2 and 15.7 Hz respectively; a 13C–12C isotope shift of –17 ppb is also observed. Coupling constants for interhexagon (6:5) bonds range from 9.3–9.8 Hz, whilst those for interpentagon (6:6) bonds range from 13.9–16.3 Hz. The latter are exceptionally large, and the differentiation between the two types should prove a valuable aid in structure determination of hydrogenated fullerenes and derivatives thereof.