Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1991"

Chemically modified calix[4]arenes. Regioselective synthesis of 1,3-(distal) derivatives and related compounds. X-Ray crystal structure of a diphenol-dinitrile

Abstract: p-tert-Butylcalix[4]arene has been chemically modified in a regioselective manner at the 1,3-(distal) phenolic groups of the lower rim using electrophiles such as ethyl bromoacetate, chloroacetone, bromopinacolone, chloroacetonitrile, and prop-2-ynyl bromide. X-Ray diffraction analysis of one of these 1,3-derivatives reveals that it exists in a highly distorted cone conformation. Crystals of the dinitrile 7 are triclinic, space group P, with two molecules in a cell of dimensions a= 13.191 (3), b= 16.755(3), c= 10.424(1)A; α= 100.32(1), β= 93.23(1), γ= 84.89(2)°. The structure was solved by direct methods and refined by full-matrix least squares calculations; R= 0.066 for 4155 observed reflections. The two phenolic rings (A and C) are tilted (interplanar angle 102.3°) so as to place the hydroxy groups inside the cavity, whereas rings B and D bearing OCH2CN moieties are almost parallel to each other (interplanar angle 13.3°). This arrangement allows for relatively facile intramolecular hydrogen bond formation between proximal hydroxy and ether functional groups [O(H)⋯ O 2.941(3) and 2.903(3)A]. These products are useful precursors of other 1,3-disubstituted derivatives including double calixarenes and of a variety of tetrasubstituted calix[4]arenes with dual functionality on the lower rim.

Structure and solution stability of indium and gallium complexes of 1,4,7-triazacyclononanetriacetate and of yttrium complexes of 1,4,7,10-tetraazacyclododecanetetraacetate and related ligands: kinetically stable complexes for use in imaging and radioimmunotherapy. X-Ray molecular structure of the indium and gallium complexes of 1,4,7-triazacyclononane-1,4,7-triacetic acid

Abstract: Of the four triazacycloalkanetriacetic acids screened for their ability to bind 111ln, triazacyclononanetriacetate bound indium most quickly and formed a complex whose dissociation as a function of pD was monitored by 13C NMR spectrometry using a labelled ligand (k296 1.8 × 10–1 dm3 mol–1 s–1) in the pD range 0 to –0.6. The corresponding gallium complex is even more stable with respect to acid dissociation and may be observed by 71Ga NMR spectrometry both in vitro(δGa+ 171 ppm) and in vivo. Crystal structures of the neutral gallium and of the protonated indium complexes are reported. The syntheses of a series of octadentate ligands are described and their relative efficiency to bind 90Y reported. Ligands based on tetraazacyclododecane bind 90Y most rapidly, and tetraazacyclododecanetetraacetate forms a strong complex with yttrium (log Ks 24.9, 298 K) which dissociates at low pH (< 2) as measured by HPLC and 13C NMR spectrometry.

Novel perfluoroalkylation of alkenes with perfluoroalkanesulphonyl chlorides catalysed by a ruthenium(II) complex

Abstract: The perfluoroalkylation of acyclic and cyclic alkenes by perfluoroalkanesulphonyl chlorides 1 has been investigated in the presence of a ruthenium(II) catalyst. The addition reactions proceeded smoothly, with extrusion of sulphur dioxide, in alkenes possessing either an electron-donating or an electron-withdrawing group, at 120 °C to give the corresponding chloroperfluoroalkylated compounds in high yield.

Expedient synthesis of polyhydroxyisoflavones

Abstract: A general and direct synthesis of polyhydroxy isoflavones (3-phenyl-4H-1-benzopyran-4-ones) starting from the corresponding unprotected phenols and arylacetic acids is described. The aryl rings may carry additional alkyl, methoxy and/or halogeno groups. Intermediate polyhydroxy deoxybenzoins (1,2-diphenylethanones) can also be isolated in good yield.

Polymers with controlled molecular architecture: control of surface functionality in the synthesis of dendritic hyperbranched macromolecules using the convergent approach

Abstract: The synthesis of unsymmetrically or non-uniformly surface-functionalized dendritic macromolecules using a stepwise convergent-growth approach is described By stepwise alkylation of the monomer unit, 3,5-dihydroxybenzyl alcohol, with unsubstituted and substituted benzylic bromides, followed by activation of the group located at the focal point, dendritic ‘wedges’ can be obtained in which there is only a single substituent such as a cyano group at the periphery Use of only substituted benzylic bromides in the first step of growth allows fully functionalized dendritic wedges to be obtained Coupling to a polyfunctional core such as 1,1,1-tris-(4′-hydroxyphenyl)ethane can also be done in a stepwise manner with both mono or fully substituted and unsubstituted ‘wedges’ to give dendritic macromolecules containing one, two, or three cyano groups or sixteen or thirty-two bromine atoms at the periphery of the macromolecule These hyperbranched dendritic polymers were purified by normal flash chromatography and fully characterized by a combination of spectroscopic and chromatographic techniques By using variations of this general scheme both the number and placement of the functional groups at the periphery of the dendritic macromolecule can be accurately controlled to afford a large variety of functionalized hyperbranched moieties

Penaresidin A and B, two novel azetidine alkaloids with potent actomyosin ATPase-activating activity from the Okinawan marine sponge Penares sp.

Abstract: Two novel sphingosine-derived azetidine alkaloids, penaresidin A, 1a, and B, 1b, were isolated as potent actomyosin ATPase activators from the Okinawan marine sponge Penares sp. and the structures elucidated on the basis of spectral data, especially two-dimensional NMR spectra of their acetates.

pH and solvent effects on the copigmentation reaction of malvin with polyphenols, purine and pyrimidine derivatives

Abstract: The influence of pH on the copigmentation reaction of malvin has been investigated from an experimental and theoretical viewpoint The general equation for the copigment effect, when monitored by visible absorption spectrometry, is derived and it is shown to be in good agreement with results obtained in the case of three different copigments, namely chlorogenic acid, caffeine and adenosine In particular, we demonstrate that association of malvin with the copigment occurs for all coloured malvin species and the corresponding stability constants are given A few tannins and a few purine or pyrimidine derivatives have also been tested for their ability to act as copigments; some were shown to associate quite strongly with malvin On the effect of the solvent on the extent of the copigmentation phenomenon, we reached an interesting conclusion: no solvent is better than water Such a result seems to indicate that the strength of the copigment effect parallels the cohesion of the hydrogen-bonded tetrahedral network of water molecules

Synthesis of isotopically labelled 3-amino-2-phenylpropionic acid and its role as a precursor in the biosynthesis of tenellin and tropic acid

Abstract: A synthesis of [3-13C]- and [3-14C]-3-amino-2-phenylpropionic acids 7a and 7b is described. The incorporation of this amino acid into tenellin 1 from Beauveria bassiana(Bals.) Vuill. and into tropic acid 10 moiety of the tropane alkaloids hyscoyamine 8 and scopolamine 9 from Datura innoxia was studied but proved unsuccessful in each case.

Total synthesis of the anthelmintic macrolide avermectin B1a

Abstract: A highly convergent total synthesis of the anthelmintic macrolide avermectin B1a 1 is described. The key features of this synthesis include the introduction of the C(11)–C(15) portion by selective ring opening of a symmetrical 1,4-bis-epoxide 4 followed by reaction with the anion derived from the 3-methyl-2-(1-methylpropyl)-6-phenylsulphonylpyran 3 to afford the ‘northern’ C(11)–C(25) fragment 39. Coupling of the derived C(11)–C(25) aldehyde unit 42 with a C(1)–C(10)‘southern’ fragment 2 was achieved via a novel deconjugative vinyl sulphone anion sequence. Macrolactonisation and subsequent introduction of the 3,4-double bond gave the aglycone portion 51. The oleandrosyloleandrose disaccharide was introduced by a novel silver-mediated coupling between the 5-acetylated aglycone 70 and the thiocarbonylimidazolide 69. Final deacetylation was accomplished using Super-Hydride to give the natural product 1.

Novel neurotrophic isocuparane-type sesquiterpene dimers, mastigophorenes A, B, C and D, isolated from the Liverwort Mastigophora diclados

Abstract: Four dimeric isocuparane-type sesquiterpenes, mastigophorenes A, B, C and D, isolated together with a new 3,4-dihydroxylated isocuparene from the liverwort Mastigophora diclados, have been assigned structures on the basis of detailed spectroscopic analyses. Among them, mastigophorenes A, B and D have been found to accelerate neuritic sprouting at 10–5–10–7 mol dm–3 in a neuritic cell culture of foetal rat cerebral hemisphere; their biosynthesis, initiated by phenolic oxidation of (–)-herbertenediol, is proposed.

Polyphenol interactions. Part 5. Anthocyanin co-pigmentation

Abstract: In aqueous media, anthocyanins undergo several structural transformations and exist in a series of equilibria between carbinol-base 6a, 6b, flavylium cation 3, quinonoidal anhydro-base 4a, 4b and chalcone 7a, 7b forms. A detailed interpretation of the proton NMR (400 MHz) spectra of malvin 3 in D2O is given for the first time in the context of these equilibria. The phenomenon of co-pigmentation is reviewed and the efficacy of various phenolic flavonoids, galloyl and hexahydroxycinnamyl esters as natural co-pigments is determined quantitatively. Association constants at 22 °C in H2O/CF3CO2H (0.02% v/v) of 1686 (±58) and 987 (±37) dm3 mol–1 were measured by UV-visible spectroscopy for the complexation of 3 with quercetin-3-β-D-galactoside 11 and β-1,2,3,4,6-penta-O-galloyl-D-glucose 10, respectively. In D2O/CF3CO2D (1.1% v/v) at 45 °C an association constant of 508 (±8) dm3 mol–1 was determined by proton NMR for the interaction of 3 with 10. DNA, RNA and ATP also act as effective co-pigments for the flavylium ion 3 but both caffeine 16 and theophylline 17 preferentially stabilise the quinonoidal-base forms 4a, 4b of the anthocyanin. In media (pH 3.5 to 7.0), they give rise to stable violet through to blue and finally green colours of the anthocyanin 3. Proton NMR studies of all these intermolecular co-pigmentation reactions are reported and the phenomenon is provisionally interpreted in terms of hydrophobically reinforced ‘π-π’ stacking of anthocyanin and co-pigment molecules in the aqueous environment.

Biocatalysis as the strategy of choice in the exhaustive enantiomerically controlled synthesis of conduritols

Abstract: An approach to several conduritols, both naturally occurring and unnatural derivatives, is described. The key strategy of this potentially exhaustive approach relies on the bio-oxidation of chloro- or bromobenzene to their corresponding cis-diols. Subsequent synthetic manipulations enjoy extensive use of symmetry considerations in the introduction of functionalities. Complete stereo- and enantio-control is achieved in the preparation of conduritols E 5 and F 6, aminoconduritols A-1 7 and F-4 9, fluorodeoxyconduritol F 13, chlorodeoxyconduritol F 14, and deoxyconduritol E 15. A detailed discussion of the stereoelectronic parameters that control opening of epoxy alkenes of type 33 or 37 is advanced. Full experimental details are provided for all compounds.

Highly conjugated π-electron donors for organic metals: synthesis and redox chemistry of new 1,3-dithiole and 1,3-selenathiole derivatives

Abstract: The bis(1,3-dithiolium) dication salts 8a–c have been synthesised in three steps (31–51% overall yields) starting from 1,4-bis(bromomethyl)naphthalene, 9,10-bis(chloromethyl)anthracene and 4,4′-bis(chloromethyl)biphenyl, respectively. The bis(halogenomethyl) compounds 5 were converted into the dipiperidiniumbis(dithiocarboxylate) salts 6, which on alkylation with 3-chlorobutane-2-one yielded bis(dithioesters)7; cyclisation of 7 occurred on treatment with concentrated sulphuric acid to give dication salts 8. Dimethyl 1,3-dithiol-2-ylphosphonate 20, dimethyl 4,5-dimethyl-1,3-dithiol-2-ylphosphonate 21 and dimethyl 1,3-selenathiol-2-ylphosphonate 22 were treated with butyllithium in the presence of a range of carbonyl compounds and quinones, e.g., cyclopentanone, cyclohexanone, benzophenone, acetophenone, benzaldehyde, thioxanthen-9-one, anthraquinone, bianthrone and naphthacene-5,12-quinone to yield Wittig–Horner products, e.g., alkenes 26–34 and the anthracenediylidene derivatives 35, 36, 40–43 and 53. Unsymmetrical derivatives 37–39 were prepared in two steps as follows: anthrone reacted with 2-methylthio-1,3-dithiolium iodides 45 and 46 in pyridine-acetic acid to yield ketones 48 and 49 which were then treated with the Wittig–Horner reagents 23–25. Cyclic voltammetric data for the new tetrathiafulvalene, selenatrithiafulvalene and diselenadithiafulvalene derivatives 35–43and 53, show that these systems undergo two-electron redox behaviour which is observed as a single wave. Complexes of these donors with electron acceptors, e.g. 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), have been obtained, some of which are organic semiconductors.

Free-radical reactions of benzenethiol and diphenyl disulphide with alkynes. Chemical reactivity of intermediate 2-(phenylthio)vinyl radicals

Abstract: Reaction of benzenethiol at 100 °C with neat alkyl- and dialkyl-acetylenes leads to virtually quantitative formation of isomeric mixtures of (E)- and (Z)-vinyl sulphide adducts in ratios which depend largely upon both the extent and the nature of alkyl substitution. Results are explained in terms of rapidly interconverting sp2-hybridized (E)- and (Z)-1-alkyl-2-(phenylthio)vinyl radical intermediates which can undergo hydrogen transfer from benzenethiol to an extent which is essentially dependent upon the steric hindrance of their cis-2-substituent. Consistent results are provided by related radical reactions of diphenyl disulphide with alkyl-substituted alkynes to afford varying amounts of 1,2-bis(phenylthio)ethylene adducts ascribable to SH2 reaction of the resulting 1-alkyl-2-(phenylthio)vinyl radicals with the disulphide present. Under analogous conditions benzenethiol and diphenyl disulphide react with phenylacetylenes to give vinyl sulphide or bissulphide adducts in a trans-stereoselective fashion. The findings are interpreted by suggesting, for the intermediate sp-hybridized 1-phenyl-2-(phenylthio)vinyl radicals, the occurrence of significant bonding interaction between the unpaired electron and the adjacent sulphur, which would essentially prevent attack of radical scavenger on the side cis to PhS. Evidence is also presented that 1-phenyl-2-(phenylthio)vinyl radicals can exhibit homolytic intramolecular cyclization reactions, leading to benzothiophene products to a comparatively much greater extent than the 1-alkyl-2-substituted analogues; however, 1-tert-butyl-2-(phenylthio)vinyl radical would represent a special case.

Intercalation and photochromism of spiropyrans on clay interlayers

Abstract: 1′,3′,3′-Trimethylspiro[2H-1-benzopyran-2,2′-indoline](abbreviated to H–SP) and its derivatives, 6-nitro (NO2–SP) and 6-nitro-8-(pyridinium)methyl spiropyrans (Py+–SP), have been intercalated in the interlayers of Montmorillonite. The intercalation was highly dependent on the substituent groups on the SPs. Charged Py+–SP was quantitatively adsorbed on the clay as an equilibrium mixture with the corresponding merocyanine (Py+–MC) in aqueous colloidal solution, the ratio Py+–SP:Py+–MC being 35:65 and exhibiting reversed photochromism. In contrast, a preferential adsorption as Py+–SP was observed for the hydrophobic clay layers coadsorbing cetyltrimethylammonium bromide (CTAB), which displays normal photochromism. The thermal isomerization of Py+–SP intercalated in aqueous colloidal clay exhibited a linear combination of two components of the first-order reactions, while that of the Py+–SP–CTAB coadsorbed system satisfied a single first-order kinetics. The two-component kinetics are explicable in terms of the intervention of at least two different kinds of microscopic environment, e.g. non-polar and polar phases, in the clay interlayers. We also show that the photochemical decoloration of Py+–MC was significantly retarded by the intercalation. All of these results are discussed on the basis of the polarity of the intercalation.

Radical chain reduction of alkyl halides, dialkyl sulphides and O-alkyl S-methyl dithiocarbonates to alkanes by trialkylsilanes

Abstract: Saturated primary, secondary and tertiary alkyl halides RX (X = Cl, Br or I) are reduced to the corresponding alkanes RH in essentially quantitative yield by triethylsilane in refluxing hexane or cyclohexane in the presence of a suitable initiator and an alkanethiol catalyst. Reduction proceeds by a radical chain mechanism and the thiol acts as a polarity reversal catalyst which mediates hydrogen-atom transfer from the Si–H group of the silane to the alkyl radical R˙. Triphenylsilanethiol and perfluorohexanesulphenyl chloride are also effective catalysts; the latter is probably reduced in situ to the corresponding fluorinated thiol. Other silanes R3SiH (R = Prn, Pri or Ph) also bring about reduction. The silane–thiol couple therefore serves as a useful replacement for tributylstannane as a homolytic reducing agent for alkyl halides. Reduction of 6-bromohex-1-ene, to give a mixture of hex-1-ene and methylcyclopentane, is more sluggush than reduction of saturated halides and this is attributed to removal of the thiol catalyst by addition across the CC bond. Ethyl 4-bromobutanoate is smoothly reduced to ethyl butanoate without interference from the ester function. Dialkyl sulphides are reduced to alkanes by triethylsilane in a radical chain reaction, but the effect of added thiol depends on the nature of the S-alkyl groups in the sulphide. The trialkylsilanethiol couple can also successfully replace trialkylstannane as the reducing agent in the Barton–McCombie deoxygenation of primary and secondary alcohols via their S-methyl dithiocarbonate (xanthate) esters. Good yields of deoxy compounds are obtained from octan-1-ol, octan-2-ol, octadecan-1-ol, 5α-cholestan-3β-ol, cholesterol and 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose.

Structural elucidation of new dimeric ellagitannins from Quercus robur L. roburins A–E

Abstract: Eight ellagitannins from Quercus robur L. wood have been studied by high-resolution 1H and 13C NMR and FAB-MS spectroscopy. Three of these polyphenols are known compounds, namely, castalagin, vescalagin, and grandinin. Five of the ellagitannins are new oligomeric compounds containing vescalagin or castalagin moieties bonded to a pentose, lyxose or xylose. The inter-unit linkages are carbon–carbon bonds between C-1 of the glucosyl residue of one unit and either the C-2′ of the hexahydroxydiphenoyl (HHDP) group of a second unit or the C-1 of a pentosyl sugar.

Structural elucidation and solution conformation of the novel herbicide hydantocidin

Abstract: The structure of a novel herbicide, hydantocidin isolated from the fermentation broth of Streptomyces hygroscopics SANK 63584, was determined by the combined analysis of MS and 1H NMR spectra. Hydantocidin is a novel spiro compound containing a subofuranoid ring, at the anomeric position of which a hydantoin ring is used such that the C(1)–N(1) linkage is β. The relative configuration and the conformation in solution was determined by quantitative analysis of the NOE spectra and T1 values. In CD3OD and [2H6]DMSO (dimethyl sulphoxide) solutions, the ribofuranose moiety of hydantocidin was found to be fixed in a C2-endo conformation, probably due to the rigidity of the spiro structure and hydrogen bonding between 3-OH and the carbonyl group at C-4′.

Enol formates: ruthenium catalysed formation and formylating reagents

Abstract: The one-step synthesis of the enol formates, isopropenyl, hex-1-en-2-yl, and α-methylenebenzyl formates, directly from terminal alkynes and formic acid with arene–ruthenium(II) catalysts is reported. They have been shown to be effective formylating reagents, under mild and neutral conditions, to produce formamides from primary and secondary amines, formylamino esters, and in the presence of a catalytic amount of imidazole, formates from alcohols or phenols.

Preparation of Ca2+ selective sorbents by molecular imprinting using polymerisable ionophores

Abstract: Molecular imprints against calcium and magnesium ions, respectively, were prepared in divinylbenzene-based polymers. A vinylic, Ca2+-selective, neutral ionophore N,N′-dimethyl-N,N′-bis-(4-vinylphenyl)-3-oxapentanediamide was synthesized and used as the ion-complexing monomer. In order to investigate the ion-complexing abilities of this neutral ionophore, this compound was tested as a neutral carrier in the plasticised PVC membrane of an ion-selective electrode. Electrode response and selectivity coefficients recorded for the ionophore proved to be equivalent to the values recorded for similar parent diglycolic acid amides. In analogy with other 3-oxapentanediamide derivatives, the ionophore is expected to form complexes with calcium and magnesium ions with a molar ratio, ligand to metal ion, of 3 : 1 and 2 : 1, respectively. Therefore the metal ion, added to the polymerisation mixture, was expected to act as a template for the ionophore during the polymerisation. The resulting polymers were analysed for their ability to extract calcium ions from methanolic water. The polymers prepared against calcium and magnesium ions were found to bind calcium ions with 6- and 1.7-times lower Kdiss-values, respectively, when compared with reference polymers prepared in the absence of metal ions. The increased binding strength is attributed to the spatial arrangement of ionophore units in the resulting polymers by the template ions during the polymerisation. In addition, the number of binding sites for calcium ions, determined for the respective polymer preparation, fitted well with theoretical values calculated from the stoichiometry of complexation of the ionophore by calcium and magnesium ions, respectively.

Functional carbonates: cyclic α-methylene and β-oxopropyl carbonates from prop-2-ynyl alcohol derivatives and CO2

Abstract: The phosphine-catalysed synthesis of cyclic α-methylene carbonates 2 directly from prop-2-ynyl alcohol derivatives and CO2 is described. These cyclic carbonates 2 are key intermediates for the selective access to β-oxopropyl carbonates 3 by reaction with alcohols under mild conditions, but in the presence of Et2N or KCN as catalyst.

Oxoiron(IV) porphyrins derived from charged iron(III) tetraarylporphyrins and chemical oxidants in aqueous and methanolic solutions

Abstract: The oxidation of six charged iron(III) tetraarylporphyrins with chemical oxidants has been investigated. In aqueous solution each can be converted by tert-butyl hydroperoxide or monqpersulphate into its corresponding oxoiron(IV) porphyrin, whereas in methanol only the iron(III) tetra(N-methylpyridyl)porphyrins form detectable ferryl porphyrins at ambient temperatures. On standing, the iron species revert to the parent porphyrin with a small loss due to non-reversible oxidative destruction. That the oxidised porphyrin intermediates are oxoiron(IV) species has been determined using UV–VIS, resonance Raman, 1H NMR and EPR spectroscopy.The mechanism of formation of the ferryl porphyrins and the factors that influence their stability are examined and discussed. In particular steric effects and to a lesser extent electron-withdrawing substituents are shown to be important in stabilising the iron(IV) species. These effects are explained in terms of their influence on the disproportionation of two ferryl species into an iron (III) porphyrin and an iron(IV) porphyrin π radical cation.

Reactivity of nitro- and nitroso-arenes with vinyl grignard reagents: synthesis of 2-(trimethylsilyl)indoles

Abstract: The reaction of nitrosoarenes and 1 -(trimethylsilyl)vinylmagnesium bromide in dibutyl ether represents a useful tool for the synthesis of 2-(trimethylsilyl)indoles by cyclisation of benzene derivatives. The use of more common ethers as the solvent leads to large amounts of azo and azoxy derivatives. Conversely, the reaction of nitroarenes and 1-(trimethylsilyl)vinylmagnesium bromide gives conjugate addition products. The reasons for this behaviour are discussed.

Stereoselective synthesis of sperabillins and related compounds

Abstract: Baker's yeast reduction of methyl (4S)-4-(tert-butoxycarbonylamino)-3-oxopentanoate 6 stereoselectively afforded methyl (3R,4S)-erythro-4-Boc-amino-3-hydroxypentanoate 7, which was converted into the erythro keto δ-lactone 3a in three steps. The threo keto δ-lactones 3b–c were diastereoselectively prepared by cyclocondensation of N-Boc D- and L-alaninal 4 with 1 -methoxy-1, 3-bis(trimethylsiloxy)buta-1,3-diene 9 in the presence of a catalytic amount of tin(II) chloride. Recluctive amination of the keto lactones 3 using 5% platinum on carbon as catalyst in an acidic medium stereoselectively afforded the N-protected 3,6-diamino-5-hydroxyheptanoic acid lactones 1 with 3,5-anti stereochemistry. These were transformed into the enantiomerically pure sperabillin 17 and negamycin 20 derivatives in good yields. The configuration of sperabillin B and D was determined to be (3R,5R,6R) by comparison of the synthetic amino lactone 1e with a degradation product of sperabillin B and by the successful transformation of the synthetic amino lactone 1b into sperabillin D.

Studies on pyruvate decarboxylase: acyloin formation from aliphatic, aromatic and heterocyclic aldehydes

Abstract: Evidence is described that supports the view that the enzyme responsible for acyloin formation from aldehydes in the yeast Saccharomyces cerevisiae is pyruvate decarboxylase.

Arsenic-containing ribosides from the brown alga Sargassum lacerifolium: X-ray molecular structure of 2-amino-3-[5′-deoxy-5′-(dimethylarsinoyl)ribosyloxy]propane-1-sulphonic acid

Abstract: Three novel arsenic-containing ribosides, methyl 5-deoxy-5-(dimethylarsinoyl)-β-D-riboside, 1-O[5′-deoxy-5′-(dimethylarsinoyl)-β-D-ribosyl]mannitol, and a dimethylarsonio-β-D-riboside have been isolated from extracts of the brown alga Sargassum lacerifolium. In addition, five previously reported arsenic-containing ribosides, and some arsenate, were isolated from Sargassum, and dimethylarsinic acid was also shown to be present. The compounds were identified chiefly by NMR spectroscopy, and an X-ray molecular structure is reported for one of them, 2-amino-3-[5′-deoxy-5′-(dimethyl-. arsinoyl)ribosyloxy]propane-1-sulphonic acid. The stereochemistry of the aglycones in these arseniccontaining ribosides is discussed and the configuration of 3-[5′-deoxy-5′-(dimethylarsinoyl)-β-D-ribosyloxy]-2-hydroxypropane-1-sulphonic acid 4 was assigned as 2S on the basis of a comparison of NMR spectra with those of synthetic model compounds.

Model systems for cytochrome P450 dependent monooxygenases. Part 8. A study of the epoxidation of (Z)-cyclooctene by iodosylbenzene catalysed by cationic iron(III) tetra(N-methylpyridyl)porphyrins adsorbed on Dowex MSC1

Abstract: Tetra(N-methyl-4-pyridyl)porphyrinatoiron(III) pentachloride and its N-methyl-2-pyridyl isomer have been adsorbed onto the highly crosslinked cation ion-exchange resin Dowex MSC1 and have been used to catalyse the reaction of Z-cyclooctene with iodosylbenzene in methanol. Two oxidation products have been detected, epoxycyclooctane and formaldehyde. The dependence of the initial rate of epoxidation and the yields of the oxidation products on the concentrations of oxidant, alkene and catalyst and on the solvent composition and catalyst loading have been investigated. The results are interpreted in terms of the following competitive reactions of the active oxidant; alkene epoxidation, solvent oxidation and oxidative degradation of catalyst and support. Adsorption of the metalloporphyrins on the polymeric resin surprisingly leads to a decrease in the catalyst efficiency when compared with the same metalloporphyrin in free solution. The cause of this effect is discussed and it is proposed that it arises through the aggregation of the metalloporphyrins on the resin favouring the intermolecular self-oxidation of the catalyst.

Carboxylic and phosphate ester hydrolysis catalysed by bivalent zinc and copper metallosurfactants

Abstract: The syntheses of three new lipophilic ligands are reported: Nα-(1,10-phenanthrolin-2-ylmethyl)-Nτ-dodecylhistamine (1), N-dodecyl-2-aminomethyl-1,10-phenanthroline (2), and Nα-(2-pyridylmethyl)-Nτ-dodecylhistamine (3). Mixed micellar systems made of complexes of these ligands with ZnII and CuII in the presence of an inert cosurfactant (CTABr or Brij 35) are efficient catalysts in the hydrolysis of p-nitrophenyl picolinate (PNPP) and diphenyl-p-nitrophenyl phosphate (DPPNPP). Kinetic studies strongly indicate the formation of a reactive ternary complex composed of metal ion, ligand, and substrate. These synzymes operate via a metal–hydroxide-ion catalysed mechanism and exhibit turn-over behaviour while retaining their full catalytic activity.

Biotransformation of endo-bicyclo[2.2.1 ]heptan-2-ols and endo-bicyclo[3.2.0]hept-2-en-6-ol into the corresponding lactones

Abstract: The secondary alcohols 3, 4 and 10 have been converted into the corresponding lactones using Acinetobacter calcoaceticus NCIMB 9871: the transformations (endo-4)⇒6+11 and 10⇒8+9 can be conducted in vitro using a coupled enzyme system (Thermoanaerobium brockii dehydrogenase and Acinetobacter calcoaceticus monooxygenase) with in situ recycling of NADPH/NADP+.

General and convenient route to alkenylidenecyclopropanes: generation of alkenylidenecarbenes from 1,1-dibromocyclopropanes under phase-transfer conditions

Abstract: Alkenylidenecyclopropanes have been prepared in a stereospecific manner by the reaction of 1,1-disubstituted 2,2-dibromocyclopropanes with sodium hydroxide under phase-transfer conditions in the presence of alkenes.