Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1973"

Organocobalt complexes. Part II. Reaction of acetylenehexacarbonyldicobalt complexes, (R1C2R2)Co2(CO)6, with norbornene and its derivatives

Abstract: Tetra- and hexa-hydro-4,7-methanoinden-1-ones and the analogous indacenediones (VIII)–(X) are formed stoicheiometrically by the title reaction or catalytically from acetylenes, norbornene derivatives, and carbon monoxide in the presence of octacarbonyldicobalt. The process leads stereoselectively to ketones of theexo-series and methyl or phenyl groups derived from the appropriate monosubstituted acetylenes are always found adjacent to the carbonyl group. The 1H n.m.r. spectra of the products are discussed and the use of an europium shift reagent together with spin decoupling is shown to allow clear distinction of the isomeric methanoindacenediones (VIII) and (IX).

Experiments in the biosynthesis of curcumin

Abstract: The biogenesis of natural diarylheptanoids is discussed, with particular reference to curcumin [1,7-bis-(4-hydroxy-3-methoxyphenyl)hepta-1,6-diene-3,5-dione], the pigment of Curcuma Ionga rhizome. Methods for the isolation, characterisation, and degradation of curcumin, suitable for biosynthetic work, are reported. In administration of labelled precursors to C. Ionga,[1- and 3-14C]phenylalanine were incorporated into curcumin without scrambling of the label. [1- and 2-14C]-Acetate and -malonate were also incorporated, and the fractional distribution of label along the heptane chain was determined; the results do not provide satisfactory support for the expected biosynthetic scheme, in which two cinnamate units condense with one malonate unit. Other interpretations are discussed. [3H]-4-Hydroxy-3-methoxy-, -4-hydroxy-, and -3,4-dihydroxy-cinnamic acids were prepared, and supplied to C. Ionga with [14C]phenylalanine. The first two cinnamic acids are incorporated into curcumin significantly better than the last, although none was utilised quite as efficiently as phenylalanine.

13 C nuclear magnetic resonance spectra of glucobioses, glucotrioses, and glucans

Abstract: Natural-abundance carbon-13 n.m.r. spectra of all the glucobioses and of four selected glucotrioses in aqueous solution have been measured and are discussed. Peak assignments were made on the basis of comparison with the spectra of methyl glucopyranosides, four mono-O-methylglucoses and five methyl glucobiosides. Carbon-13 n.m.r. spectroscopy proved to be a useful tool for stereochemical characterisation of these oligosaccharides. In addition, carbon-13 n.m.r. spectra of the β-limit dextrins from glycogen and amylopectin have been measured and the differences between them are discussed.

Syntheses of flufenamic acid metabolites I and II and other N-aryl-anthranilic acids

Abstract: The syntheses of two metabolites of flufenamic acid, 5-hydroxy-N-(ααα-trifluoro-m-tolyl)anthranilic acid and N-(4-hydroxy-ααα-trifluoro-m-tolyl)anthranilic acid, are described. Syntheses of a number of other N-aryl-anthranilic acids, mono-, di-, tri-, and tetra-substituted in the aryl ring lacking a carboxy-group, and with substituents in both aryl rings, are reported.

Thermodynamics of binding of guest molecules to α- and β-cyclodextrins

Abstract: Values of ΔG, ΔH, and ΔS are reported for the interaction of eighteen molecules and ions with α-cyclodextrin and of four molecules with β-cyclodextrin. The conclusions of this study are (1) the cyclodextrin–ClO4– complex has been shown to bind a cation, (2)α- and β-cyclodextrin have equilibrium constants for binding the same guest that are similar but the enthalpy and entropy changes are quite different in some cases, and (3) changes in ΔH are largely compensated for by changes in ΔS and it is suggested that this effect is due principally to the nature of the solvent, i.e. water.

The interaction of N-bromo-N-sodiobenzenesulphonamide (bromamine B) with p-nitrophenoxide ion

Abstract: By using the interaction with p-nitrophenol as a mechanistic probe it has been established that solutions of N-bromo-N-sodiobenzenesulphonamide (bromamine B) in dilute alkali contain two reactive brominating species, the conjugate acid (PhSO2NHBr) and hypobromous acid; formation of the latter can be suppressed by the addition of the parent sulphonamide. These solutions are fully described by a system of four equilibria: three are proton transfer reactions, for which pKa values have been obtained, and the fourth is the alkaline hydrolysis of the conjugate acid, for which an equilibrium constant has been estimated from model experiments with sodium 3-(N-bromophenylsulphonamido)propanesulphonate. These data have been used to establish a species distribution diagram and the predictive value of this has been tested.

N-alkylation of indole and pyrroles in dimethyl sulphoxide

Abstract: The potassium salts of indole, pyrrole, and 2,5-dimethylpyrrole were converted into N-alkyl derivatives in high yield in dimethyl sulphoxide by use of iodomethane, iodoethane, 1-iodopropane, and benzyl bromide. Dehydrohalogenation occurred when 2-iodo- and 2-bromo-2-methylpropane were used; when 2-iodopropane was employed alkylation and dehydrohalogenation were observed.

Organocobalt complexes. Part I. Arene complexes derived from dodecacarbonyltetracobalt

Abstract: A series of tetranuclear arenecobalt carbonyls, ArHCo4(CO)9, are formed by treating hexacarbonylacetylenedicobalt complexes, (R1C2R2)Co2(CO)6, with arenes in the presence of norbornene derivatives, or from the cobalt carbonyls Co4(CO)12 and Co2(CO)8 by direct reaction with arenes. Stable complexes are obtained from alkyl- and alkoxy-benzenes, but not from halogeno- or acyl derivatives. The spectroscopic properties of the new complexes are reported.

The meso-reactivity of porphyrins and related compounds. Part VI. Oxidative cleavage of the haem system. The four isomeric biliverdins of the IX series

Abstract: The oxidative cleavage of haemin in aqueous pyridine under various conditions (ascorbic acid–oxygen; hydrazine–oxygen; and ascorbic acid–hydrogen peroxide) gives four isomeric biliverdins of the IX series which have been isolated (from a much improved ascorbic acid–oxygen reaction) as their crystalline dimethyl esters. The properties of the four isomers are described. On the basis of mass and n.m.r. spectra, structures are assigned to all four isomers for the first time. A key observation in the n.m.r. spectra of these compounds is the chemical shift of the heteroaryl methyl group. The implications of these results are discussed.

The structure and absolute configuration of the antibiotic aphidicolin: a tetracyclic diterpenoid containing a new ring system

Abstract: The structure and absolute configuration of the novel tetracyclic diterpenoid aphidicolin, an antimitotic and antiviral metabolite of Cephalosporium aphidicola Petch, have been determined, and a systematic nomenclature is proposed. Possible biosynthetic routes to aphidicolin are discussed. Derivatives of aphidicolin, including possible biogenetic precursors and the C(3)- and C(16)-epimers of the antibiotic have been prepared. The high resolution i.r. hydroxyfrequencies are reported for a number of ring-A 1,3-diols derived from aphidicolin.

Carrageenans. Part VII. Polysaccharides from Eucheuma spinosum and Eucheuma cottonii. The covalent structure of ι-carrageenan

Abstract: ι-Carrageenan has been characterized by chemical methods to provide a firm basis for interpretation of data from X-ray diffraction and optical rotation, and so to confirm the carrageenan double helix. This polysaccharide was isolated from the red seaweed Eucheuma spinosum and shown by methylation analysis and partial fragmentation, and by other evidence, to have a masked repeating structure in which D-galactose 4-sulphate and 3,6-anhydro-D-galactose 2-sulphate residues are arranged alternately in linear chains, with formal replacement of approximately one in every ten anhydride residues by D-galactose 2,6-disulphate. Treatment with alkaline borohydride converts this structure to a genuinely alternating copolymer.A polysaccharide from E. cottonii has similarly alternating 1,4- and 1,3-linked residues but is distinctive in that it has not detectable 2-sulphate. It therefore corresponds more closely than any other known natural polysaccharide to an idealized κ-carrageenan.

Pyrroles and related compounds. XXIV. Separation and oxidative degradation of chlorophyll derivatives.

Abstract: A convenient, large-scale method for separation of the aand b series metal-free chlorophyll derivatives is described, utilising the Girard ‘T’ reagent with subsequent chromatography. Efficient procedures for conversion of phaeophytin-a(3) into rhodoporphyrin-XV dimethyl ester (1) and the corresponding 2-vinyl compound (2), involving the classical oxidation to purpurin derivatives, followed by further degradation, are described: n.m.r. data for several important chlorophyll degradation products are reported. Novel oxidative reactions of the isocyclic ring in methyl mesopyrophaeophorbide-a(19) are also described.

Kinetics of the reaction of hydrogen peroxide with cysteine and cysteamine

Abstract: The rate of the reaction between hydrogen peroxide and cysteine or cysteamine is proportional to [H2O2] and [NH3+CHXCH2S–](X = H or CO2–) consistent with nucleophilic attack by the thiolate ions on peroxide oxygen. The rate decreases at higher pH where loss of the NH3+ proton occurs, and it is suggested that hydrogen bonding between this group and hydrogen peroxide facilitates the reaction.

Studies in the xanthone series. Part XII. A general synthesis of polyoxygenated xanthones from benzophenone precursors

Abstract: Various 2-mono-, 2,3- and 1,7-di-, 1,3,7-, 1,5,6-, 1,6,7- and 2,3,4-tri-, 1,3,4,7-, 1,3,5,6-, 1,3,6,7-, 1,5,6,7- and 2,3,4,5-tetra-, and 1,3,5,6,7-penta-oxygenated xanthones have been synthesised by preparation of 2-hydroxy-2′-methoxybenzophenones under Friedel–Crafts conditions, and subsequent base catalysed cyclisation to eliminate methanol. Acid or base catalysed selective demethylations of polymethoxyxanthones, and of benzophenones lead to efficient synthesis of natural hydroxymethoxyxanthones, and of hydroxymethoxybenzophenones. Selective methylation procedures are also given.

Spin trapping by use of nitroso-compounds. Part VI. Nitrosodurene and other nitrosobenzene derivatives

Abstract: The utility of nitrosodurene (4), 2,4,6-trimethoxycarbonylnitrosobenzene (6), 2,4,6-trichloronitrosobenzene (7), and pentafluoronitrosobenzene (8) as spin traps has been examined, and nitrosodurene has proved to be particularly useful. Various kinds of free radicals can be successfully scavenged by nitrosodurene to produce relatively stable nitroxides whose e.s.r. spectra are as simple as those obtained from 2-methyl-2-nitrosopropane, although line widths are slightly broader. Nitrosodurene is as stable towards photolysis as 2,4,6-tri-t-butylnitrosobenzene. Some characterisation of spin adducts of nitrosodurene from spectral data is discussed. A few examples of spin adducts to other nitroso-compounds are shown. The results of preliminary experiments with 2,3,5,6-tetrakis(trideuteriomethyl)nitrosobenzene are also briefly described.

Spin trapping by use of nitroso-compounds. Part V. 2,4,6-Tri-t-butylnitrosobenzene: a new type of spin-trapping reagent

Abstract: The utility of 2,4,6-tri-t-butylnitrosobenzene as a spin-trapping reagent has been examined, and two main advantages of its use have been clarified. 2,4,6-Tri-t-butylnitrosobenzene has two sites for spin trapping. Primary alkyl radicals normally attack the nitrogen atom of the nitroso-group to generate nitroxides. Tertiary alkyl radicals, however, attack the oxygen atom of the nitroso-group to form N-alkoxyanilino-radicals which are sufficiently stable for e.s.r. spectra to be recorded. Secondary alkyl radicals usually add both on the nitrogen and oxygen atoms to produce both the corresponding spin adducts, whose ratio varies with the structure of the radical trapped. Solutions of the nitroso-compound produce no detectable paramagnetic species during u.v. irradiation. The relation between the structure of a spin adduct and the spectral datum is discussed.

Electron spin resonance studies. Part XXXVIII. Evidence for the formation of dimeric radical-cations, R2S˙S2+˙, in the one-electron oxidation of sulphides

Abstract: Evidence is adduced by e.s.r. spectroscopy for the mediation of radical-cations R2S˙S2+˙ during oxidation of a sulphide R2S by the titanium(III)–hydrogen peroxide or –persulphate couple. It is suggested that they arise from a first-formed transient, R2S+˙, which is subject to competing reactions of which one is with a further molecule of sulphide. Other reactions, and the variation of their relative importance with structure, are briefly discussed.

Precision neutron diffraction structure determination of protein and nucleic acid components. Part V. Crystal and molecular structure of the amino-acid L-arginine dihydrate

Abstract: L-Arginine dihydrate, C6H14N4O2,2H2O, crystallizes in the orthorhombic space group P212121 with a= 5·638(6), b= 11·85(1), c= 15·68(1)A, and Z= 4. The structure has been refined to R 0·034 (1364 reflections) by neutron diffraction techniques, and all hydrogen atoms located precisely. The arginine molecule is a zwitterion, with the positive charge residing in the guanidinium group. The neutral α-amino-group is not involved in the network of nine distinct N–H ⋯ O, N–H ⋯ N, and O–H ⋯ O hydrogen bonds present in the crystal structure. The barrier for internal rotation of the α-NH2 group is estimated to be significantly less than the corresponding barrier for the hydrogen-bonded NH3+ group in L-asparagine monohydrate. The N–H lengths in the guanidinium group are ca. 0·02 A less than those found for comparably hydrogen-bonded ammonium groups in other aminoacids.

Carrageenans. Part IX. Methylation analysis of galactan sulphates from Furcellaria fastigiata, Gigartina canaliculate, Gigartina chamissoi, Gigartina atropurpurea, Ahnfeltia durvillaei, Gymnogongrus furcellatus, Eucheuma isiforme, Eucheuma uncinatum, Aghardhiella tenera, Pachymenia hymantophora, and Gloiopeltis cervicornis. Structure of ξ-carrageenan

Abstract: In continuation of the search for polysaccharide structures with which to develop conformational analysis, the sixteen polysaccharides for which a preliminary characterization was described in the preceding paper have been investigated by the methylation method. The earlier conclusions are confirmed and extended, with few qualifications. Amongst the structural variations in the χ and ιcarrageenans are undersulphation on C(4) of the 3-linked residue and on C(6) of the 4-linked residue. A new polysaccharide type is discovered in certain Gigartina species and the (as yet hypothetical) idealized form of it is named ξ-carrageenan. It is the polymer of D-galactose 2-sulphate in which the glycosidic linkages are 1,4 and 1,3, probably arranged alternately with β- and α-configurations respectvelyTwo polysaccharides emerge with exceptional promise for conformational analysis, namely an agarose sulphate from Gloiopeltis furcata and a possible ξ-carrageenan from Gigartina atropurpurea.

Simmondsin, an unusual 2-cyanomethylenecyclohexyl glucoside from Simmondsia californica

Abstract: Simmondsin, a monoglucoside extracted from seeds of the jojoba plant (Simmondsia californica), has been shown to be 2-(cyanomethylene)-3-hydroxy-4,5-dimethoxycyclohexyl β-D-glucoside (1). Analysis of the n.m.r. spectra of this compound and its penta-acetate permits assignment of the stereochemistry as well as establishing the point of attachment of the glucose.

Studies on the metabolites of Verticillium sp. Structures of verticillins A, B, and C

Abstract: Three new antibiotics, verticillins A (Ia), B (XVIII), and C have been isolated from Verticillium sp. Stereo-structures of verticillins A and B, which are derivatives of bi-(3,11 a-epidithio-1.4-dioxopyrazino[1′,2′ : 1,5]pyrrolo-[2,3-b]indol-10b-yl), have been elucidated by chemical and physicochemical methods. Verticillin C is thought to be an epitrithio-analogue of verticillin B.

An assessment of the fractionation of carbohydrates on concanavalin A-sepharose 4B by affinity chromatography.

Abstract: Assessment of a water-insoluble but active form of the lectin Concanavalin A has established that a number of monosaccharides may be separated by elution from a column of Concanavalin A immobilised on Sepharose 4B with aqueous phosphate buffer at near neutral pH values as eluant. Branched-chain polysaccharides may also be fractionated on the column. Weakly interacting polysaccharide fractions are eluted in the phosphate buffer; more tightly bound fractions may be eluted with borate buffer. The use of borate buffer for this purpose overcomes the problems arising in the use of carbohydrates for the elution of bound polysaccharide. The work demonstrates that mixtures of carbohydrates which are not separable by complex formation with Concanavalin A in solution may be separated by use of an immobilised form of the lectin.

Minor diterpenoid constituents of Andrographis paniculata Nees

Abstract: Three diterpenoids closely related to andrographolide have been isolated from Andrographis paniculata Nees. These have been identified as 14-deoxy-11-oxoandrographolide (6), 14-deoxy-11,12-didehydroandrographolide (23), and 14-deoxyandrographolide (26).

Allenes. Part XXIV. Preparation of α-allenic alcohols from the mono-O-tetrahydropyran-2-yl derivatives of butyne-1,4-diols

Abstract: α-Allenic alcohols are obtained in high yield by the ready reductive elimination of the tetrahydropyranyloxy-group from the mono-O-tetrahydropyran-2-yl derivatives of butyne-1,4-diols with lithium aluminium hydride. Attempted reduction of the mono-O-tetrahydropyranyl derivative of an enynediol gave an isomeric mixture of an allenic and an acetylenic alcohol. O-Tetrahydropyranyl groups on secondary or tertiary alcohol functions have been shown to migrate to primary systems.

Elimination–addition mechanism for the hydrolysis of carbamates. Trapping of an isocyanate intermediate by an o-amino-group

Abstract: The hydrolytic conversion of aryl carbamates to amines is base catalysed and evidence is presented that the process involves an E1cB elimination with the formation of isocyanate intermediates. Substituents in the leaving group (O-aryl ring) have a larger effect (ρ=+3·17) on the observed rate of hydrolysis than those in the N-aryl ring (ρ=+0·64) where the effects of a substituent are compensatory. Using N-(p-nitrophenyl)carbamates, it was possible to measure both the acidity of the carbamate (Ka1) and the rate of reaction of the carbamate anion (k2); k2 was sensitive to substituent effects (ρ=+2·90) for aryl carbamates indicating a high degree of acyl–oxygen bond cleavage in the transition state. A change in mechanism from E1cB to BAC2 attack by hydroxide ion was noted for poorer leaving groups. The pH profile for the conversion of p-nitrophenyl N-(o-aminophenyl)carbamates to o-phenyleneurea was interpreted to show that the o-amino-group traps an isocyanate intermediate after the rate determining E1cB elimination. Substituent effects for NN-disubstituted carbamates which hydrolyse via a BAC2 mechanism are also discussed.

New corynanthé alkaloids from Strychnos angustiflora

Abstract: Three alkaloids isolated from Strychnos angustiflora, angustoline, angustine, and angustidine, have, respectively, the corynanthe structures (1) and (2), and the 21-norcorynanthe structure (5). They differ in the nature and position of side-chains on a fused pyridine ring. 1H N.m.r. long-range coupling data have been used in arriving at the structures. The biogenetic relationship between the alkaloids is discussed.

Anodic oxidation of phenolic compounds. Part III. Anodic hydroxylation of phenols. A simple general synthesis of 4-alkyl-4-hydroxycyclo-hexa-2,5-dienones from 4-alkylphenols

Abstract: The oxidation of simple, monohydric phenols at a lead dioxide anode in aqueous sulphuric acid has been studied. The effects of current density, electrolysis time, pH, concentration of phenol, and method of anode preparation on conversion and product distribution have been investigated, and optimal conditions for anodic hydroxylation of simple phenols have been deduced. In all cases studied the hydroxy-group entered the 4-position: thus 4-substituted phenols gave 4-substituted 4-hydroxycyclohexa-2,5-dienones, and phenols without substituents at C-4 gave p-benzoquinones. The former reaction provides a simple and efficient synthesis of these cyclohexa-2,5-dienone derivatives. A mechanism involving hydrolysis of an anodically generated phenoxonium ion is suggested. Evidence is presented which indicates that the phenoxonium ion is formed by ‘chemical’ oxidation with anodically generated lead dioxide. The lead dioxide anode is superior to carbon, nickel, and platinum anodes for hydroxylation.

Organometallic complexes in synthesis. Part IV. Abstraction of hydride from some tricarbonylcyclohexa-1,3-dieneiron complexes and reactions of the complexed cations with some nucleophiles

Abstract: Isomeric 1- and 2-methoxy-derivatives of tricarbonylcyclohexa-1,3-dieneiron can frequently be separated by chromatography. The positions of removal of hydride from such complexes, relative to OMe and/or Me sub-stituents, have been examined. Some of the resulting mesomeric cations have been treated with the nucleophiles borohydride, hydroxide, and morpholine to define positions of reaction relative to substitution. Among other nucleophiles which react are enamines and ketones. Conditions for removal of the tricarbonyliron group from the resulting complexes have been examined.

Purines, pyrimidines, and imidazoles. Part XL. A new synthesis of a D-ribofuranosylamine derivative and its use in the synthesis of pyrimidine and imidazole nucleosides

Abstract: 2,3-O-Isopropylidene-D-ribofuranosylamine has been prepared in high yield as the stable crystalline toluene-p-sulphonate by reaction of D-ribopyranosylamine with acetone, 2,2-dimethoxypropane, and toluene-p-sulphonic acid. The anomeric configuration of the furanosylamine in various solvents has been investigated by n.m.r. spectroscopy and optical rotation measurements. In chloroform the β-form predominates whereas in dimethyl sulphoxide a high proportion of the α-form is present. A bis(isopropylideneribofuranosyl)amine of unknown anomeric configuration has also been prepared from the furanosylamine toluene-p-sulphonate; this has also been obtained as a by-product in some reactions.Reaction of the furanosylamine with several, α-cyano, -acetyl, or -ethoxycarbonyl-β-ethoxy-N-ethoxycarbonyl-acrylamides occurs in both aqueous and non-aqueous solutions to give corresponding 5-substituted uracil α- and β-ribofuranosides. Assignments of anomeric configurations were confirmed by n.m.r. spectroscopy, by comparison with known compounds, and, in the case of 5-ethoxycarbonyluridine, by hydrolysis to the uridine-5-carboxylic acid and smooth decarboxylation of this to uridine by a new method which has also been used to decarboxylate uracil-5-carboxylic acid and its 1-methyl and 1-phenyl derivatives.The furanosylamine with β-methoxy-α-methylacryloyl isothiocyanate also gave, via an intermediate acyclic thiourea riboside, 2-thiothymine 1-(isopropylidene-β-D-ribofuranoside).Treatment of the furanosylamine either with ethyl N-[alkoxycarbonyl or carbamoyl(cyano)methyl]formimidates, or with ethylformimidate hydrochloride [to give a mixture of ethyl N-(2,3-O-isopropylidene-α- and β-ribofuranosyl)-formimidates], followed by ethyl α-amino(cyano)acetate, gave 5-amino-4-(alkoxycarbonyl or carbamoyl)imidazole isopropylidene-α- and β-ribofuranosides, from which the isopropylidene groups may be removed by aqueous acetic acid. Phosphorylation of the two anomeric esters gave corresponding 5-aminoimidazole-4-carboxylic acid α- and β-ribotides.Structures of the aminoimidazole nucleosides and nucleotides were confirmed by comparisons with known compounds and by use of spectral (especially c.d.) techniques. Rates of reaction of several formimidates and acetimidates with cyclohexylamine have been examined.

Isoxazoline derivatives. Part VI. Regioselectivity in the 1,3-dipolar cycloaddition of nitrile oxides to αβ-unsaturated ketones

Abstract: 1,3-Cycloadditions of nitrile oxides to αβ-unsaturated ketones have been studied. In most cases a mixture of the two regioisomeric 3-substituted 4- and 5-acyl-Δ2-isoxazolines was obtained. The individual compounds were characterised by chemical and/or spectroscopic methods. Effects of steric and electronic factors on the cycloadditions are discussed.