Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1976"
TL;DR: The structure of compactin, a metabolite isolated from cultures of Penicillium brevicompactum, has been determined by a combination of spectroscopic, chemical, and X-ray crystallographic methods.
Abstract: The structure of compactin (I){7-[1,2,6,7,8,8a-hexahydro-2-methyl-8-(2-methylbutyryloxy)naphthyl]-3-hydroxyheptan-5-olide}, a metabolite isolated from cultures of Penicillium brevicompactum, has been determined by a combination of spectroscopic, chemical, and X-ray crystallographic methods.
325 citations
TL;DR: In this article, the stabilization energies of conjugated cyclic cyclic hydrocarbons are derived by minimizing extraneous energy contributions to the reaction heat arising from changes in hybridization and C-H binding.
Abstract: New homodesmotic reactions are designed that provide and alternative basis for evaluating stabilization energies of benzenoid and other conjugated cyclic hydrocarbons. As in previous cases, carbon–carbon bonds are matched in the sense of having equal numbers of Csp2–Csp2, Csp2Csp2, Csp2–Csp3, etc. bonds in reactants and products, while simultaneously the various carbon–hydrogen bonds are matched as closely as possible. By minimizing extraneous energy contributions to the reaction heat arising from changes in hybridization and C–H binding, such reactions single out those structural features resulting in stabilization. These new reactions have the advantage that experimental ΔHf° data is currently available for the necessary reactant molecules, thus allowing an explict evaluation of the homodesmotic stablization energy to be made, which is compared to quantum theoretical calculations wherever possible.
212 citations
TL;DR: It is suggested that similar structures are present in the cross-linked products formed by the action of glutaraldehyde on proteins, such as 1,3,4,5-tetrasubstituted pyridinium salts, analogous to desmosine.
Abstract: The products of interaction of glutaraldehyde with 6-aminohexanoic acid and with α-N-acetyl-lysine have been separated and partially purified; studies of the most highly purified fraction are indicative of the formation of 1,3,4,5-tetrasubstituted pyridinium salts, such as (II), analogous to desmosine. It is suggested that similar structures are present in the cross-linked products formed by the action of glutaraldehyde on proteins.
107 citations
TL;DR: It is shown that the acetylation of phenolic Hydroxy-group can be used to identify the positions of the hydroxy-groups on an aromatic ring, a technique which is particularly useful when both hydroxy and methoxy-groups are present.
Abstract: The 13C n.m.r. spectra of a wide variety of flavonoids and related compounds and vanillin isomers are reported. Particular attention is directed towards features of the spectra which are most useful for structure elucidation, and the principle of additivity of substituent effects in such systems is critically examined. It is shown that the acetylation of phenolic hydroxy-group can be used to identify the positions of the hydroxy-groups on an aromatic ring, a technique which is particularly useful when both hydroxy- and methoxy-groups are present.
95 citations
TL;DR: A variety of alkoxyl radicals have been generated in aqueous solution by the one-electron reduction of alkyl hydroperoxides by titanium(III) ion, and their behavior has been studied by e.g. spectroscopy in conjunction with a rapid-flow system as discussed by the authors.
Abstract: A variety of alkoxyl radicals has been generated in aqueous solution by the one-electron reduction of alkyl hydroperoxides by titanium(III) ion, and their behaviour has been studied by e.s.r. spectroscopy in conjunction with a rapid-flow system. Although the alkoxyl radicals themselves are not directly detectable by e.s.r., both the adducts which they form with the spin-trap CH2:NO2– and the carbon-centred radicals into which they are transformed can be monitored; in this way, a novel 1,2-shift [e.g. PrO·→·CH(OH)Et], as well as intramolecular 1,5-hydrogen transfer, intramolecular addition to an olefinic bond, and fragmentation, have been demonstrated. Estimates have been obtained for the rate constants for some of these processes (e.g. that for the 1,2-shift mentioned is ca. 107 s–1). and the behaviour of alkoxyl radicals in aqueous and non-aqueous media has been compared.
87 citations
TL;DR: In this article, the reaction of gold(III) compounds with alkynes, arenes, and cyclopropanes has been studied, and the results show that the products can be accounted for in terms of electrophilic attack by the metal on the unsaturated centre.
Abstract: The reaction of gold(III) compounds with alkynes, arenes, and cyclopropanes have been studied. With the first two, the products can be accounted for in terms of electrophilic attack by the metal on the unsaturated centre. The reaction with alkynes bears a close resemblance to the mercury(II)-catalysed hydration but leads to higher conversions. Aromatic compounds react to give chloroarenes, the isomer distribution being consistent with initial metallation of the ring followed by replacement of the dichlorogold group by a chlorine atom. However, isolation of the intermediate arygold compounds did not prove possible. Cyclopropanes were not oxidised to the expected 1,3-adducts; instead 1,2-adducts resulting from initial gold(III)-catalysed isomerisation to an alkene were obtained.
81 citations
TL;DR: In this paper, the lower homologues of the series of 4-n-alkoxy- and 4nalkyl-4′-cyanobiphenyls have been prepared and their liquid crystal transition temperatures determined.
Abstract: The lower homologues of the series of 4-n-alkoxy- and 4-n-alkyl-4′-cyanobiphenyls have been prepared and their liquid crystal transition temperatures determined. The trends in the nematic–isotropic liquid (N–I) transition temperatures along the series are compared with observed trends for other homologous series. These results reveal deficiencies in the theoretical treatments that have been proposed to explain trends in N–I transition temperatures in such series. However, the results may be explained by the existence, in the case of the higher homologues, of certain alkyl chain conformations which are especially favourable to the stability of the nematic phase
76 citations
TL;DR: In this paper, the structure of the title compound was determined from 2 807 observed X-ray intensities, measured by diffractometer, and the phase problem was solved by Patterson rotation and translation methods.
Abstract: Crystals of the title compound are monoclinic, space group A2, with lattice parameters a= 10.260(8), b= 7.596(8), c= 101.43(9)A, β= 94.41(5), and Z= 8 [2 independent molecules (A) and (B)]. The structure was determined from 2 807 observed X-ray intensities, measured by diffractometer. The phase problem was solved by Patterson rotation and translation methods. Refinement by block-diagonal least-squares gave R 0.079. Molecules (A) and (B) have almost fully extended conformations, but differ significantly in the rotation about the ester bond and in the C(17) chains. The crystal structure consists of stacked bilayers 50·7 A thick. The C(17) chain ends, which lie at the bilayer surfaces, are virtually liquid. Within a bilayer cholesterols pack with cholesterols, and myristate chains pack with myristate chains. The chain packing has an orthorhombic (Oa) subcell. The inner diffraction ring at sin θ/λ 0.015 A–1, 0.016 A–1 which has been observed for the smectic A and cholesteric mesophases respectively, may be a result of multiple almost parallel 33 A vectors which exist between atoms of cholesterols on opposite sides of a bilayer. Thus, we infer that the mesophases retain some characteristics of the crystal structure.
76 citations
TL;DR: In this article, a tetra-t-butylethylene was obtained from di-tbutyl ketone and 1,3,3-trimethylnorbornan-2-one through heating their triphenylphosphoranylidenehydrazones with selenium.
Abstract: Monomeric selenoketones (selones) have been prepared from di-t-butyl ketone and (–)-1,3,3-trimethylnorbornan-2-one through heating their triphenylphosphoranylidenehydrazones with selenium. Although selones show greater reactivity towards diazo-compounds than thiones it was still not possible to prepare the elusive tetra-t-butylethylene. However, (–)-1,1′,3,3,3′,3′-hexamethyl-2,2′-binorbornylidene, which is a ‘tied back’ tetra-t-butylethylene, was obtained without difficulty and is stable to oxygen.The chemistry of selones has been briefly explored and compared with that of thiones. An improved preparation of di-t-butylketen is reported.
73 citations
TL;DR: Tautomeric equilibria of the hydroxypyridine-pyridone type are investigated for five compounds in this paper, and the proportion of pyridine form, dominant for H2O solutions, falls roughly linearly with the solvent polarity as measured by Z.
Abstract: Tautomeric equilibria of the hydroxypyridine–pyridone type are investigated for five compounds: the proportion of pyridone form, dominant for H2O solutions, falls roughly linearly with the solvent polarity as measured by Z. In cyclohexane solution, comparable amounts of both forms are present.
72 citations
TL;DR: Avarol is the first naturally occurring sesquiter-penoid of the 9,4-friedodrimane type to be isolated as discussed by the authors, obtained from the marine sponge Disidea avara.
Abstract: With the aid of circular dichroism, n.m.r. shift reagents, and 13C n.m.r. spectroscopy the absolute stereochemistry has been assigned to avarol {2-[(1R)-1,2,3,4,4a,7,8,8aα-octahydro-1β,2β,4aβ,5-tetramethyl-1-naphthylmethyl]-hydroquinone}, obtained from the marine sponge Disidea avara. Avarol is the first naturally occurring sesquiter-penoid of the 9,4-friedodrimane type to be isolated.
TL;DR: In this paper, the biliverdin chromophore (II) was solved by direct methods and refined to R 0.090 for 2 357 diffractometer-measured unique reflections.
Abstract: Crystals of the title compound (II) are triclinic, space group P, with a= 12.467(6), b= 14.567(5), c= 9.788(4)Aα= 111.56(3), β= 90.64(4), γ= 97.91(3)°, Z= 2. The biliverdin chromophore, which is in the lactam form with three ‘pyrrole’ N–H protons, takes up a near-planar helical conformation. Two such molecules, related by a crystallographic centre of symmetry are linked into dimers with an extended helical conformation, through two N–H ⋯ O hydrogen bonds (N–H ⋯ O 2.80, N–H 1.12, H ⋯ O 1.74 A) between symmetry-equivalent pyrrolone rings. A considerable degree of bond fixation is observed within the tetrapyrrole skeleton. The vinyl and one of the methyl ester groups are disordered. The structure was solved by direct methods and refined to R 0.090 for 2 357 diffractometer-measured unique reflections.
TL;DR: The reaction between nitrones and copper acetylides in pyridine yields cis-and trans-azetidinones as discussed by the authors, and the trans-compound is produced from the initially formed cis-isomer and the amount of cis-product may be increased by using non-basic solvents.
Abstract: The reaction between nitrones and copper acetylides in pyridine yields cis- and trans-azetidinones Deuteriation and isomerisation studies indicate that the trans-compound is produced from the initially formed cis-isomer and that the amount of cis-product may be increased by using non-basic solvents Lactams with aromatic, aliphatic, and ethoxycarbonyl substituents may be obtained from appropriately substituted acetylenes, and the use of cyclic nitrones leads to bicyclic compounds
TL;DR: In oxygen-free propan-2-ol solution electronically excited chlorpromazine [2-chloro-N-(3-dimethylaminopropyl)phenothiazine] undergoes a carbon-chlorine bond fission to form free radicals which react with the solvent to produce promazine, isopropoxypromazine, hydrogen chloride, and acetone as mentioned in this paper.
Abstract: In oxygen-free propan-2-ol solution electronically excited chlorpromazine [2-chloro-N-(3-dimethylaminopropyl)phenothiazine] undergoes a carbon–chlorine bond fission to form free radicals which react with the solvent to produce promazine, isopropoxypromazine, hydrogen chloride, and acetone. In oxygen-saturated solution energy transfer occurs from excited chlorpromazine to molecular oxygen to produce excited singlet oxygen. Under these conditions chlorpromazine does not undergo any permanent photochemical change.
TL;DR: In this paper, the anodic oxidation of a selection of tertiary alkyl- and aralkyl-amines has been studied by iinear sweep voltammetry and controlled potential electrolysis at a glassy-carbon electrode in aqueous alkaline solution.
Abstract: The anodic oxidation of a selection of tertiary alkyl- and aralkyl-amines has been studied by iinear sweep voltammetry and controlled potential electrolysis at a glassy-carbon electrode in aqueous alkaline solution. Each amine shows only one oxidation wave. The oxidation peak potentials of a number of substituted NN-dimethylbenzylamines have been correlated with the Hammett σ values of the substituents (ρ–0.94) and the pKa values of the amines (α 0.82). The size and magnitude of these values agree well with those from oxidations by one-electron chemical oxidants and are consistent with a potential-determining loss of one electron from the nitrogen of the amine. As expected α-deuteriation has little effect on the oxidation peak potential. Structural features in the amines that influence the ease of rehybridisation of the nitrogen (sp3→sp2) in the potential-determining step have been studied using a selection of cyclic and bicyclic amines. These show that the transition state in the potential-determining step resembles the aminium radical. The distribution of products is close to that predicted statistically showing that the product-determining α-C–H cleavage is very unselective. When coupled with a love primary isotope effect for the deprotonation this suggests that in the transition state the α-C–H bond is almost intact and that the transition state resembles the aminium radical more than the α-amino-radical.
TL;DR: The rate constants for nucleophilic reaction of nine substituted pyridines with methyl chloroformate give a sharply curved Bronsted plot, the slope changing from β 0.93 to 0.15 with increasing reactivity.
Abstract: The rate constants for nucleophilic reaction of nine substituted pyridines with methyl chloroformate gives a sharply curved Bronsted plot, the slope changing from β 0.93 to 0.15 with increasing reactivity. This contrasts with the straight line (β 0.93) observed with p-nitrophenyl acetate, and is shown to be quantitatively consistent with a change in rate-determining step. It is argued that this is from breakdown to formation of a zwitterionic tetrahedral intermediate which is only just stable enough to exist. The hydrolytic stabilities of some of the methoxycarbonylpyridinium ions produced by this reaction, and the nucleophilic reactivities towards methyl cloroformate of imidazole, of phenolate, p-nitrophenolate, and acetate anions, and of phosphate dianion are reported and discussed.
TL;DR: In this article, Vilsmeier reagents, [Me2NCHX]-X-(X = Cl or Br), interact with alcohols to give good yields of the corresponding alkyl halides.
Abstract: Vilsmeier reagents, [Me2NCHX]+X–(X = Cl or Br), interact with alcohols to give good yields of the corresponding alkyl halides. Isolation of the product is facilitated by the use of water-soluble solvents. Little or no rearrangement of the alkyl group occurs, except in the case of a branched-chain secondary alcohol, e.g. 3-methylbutan-2-ol. In dioxan or acetonitrile, (+)-octan-2-ol yields the optically pure chloride with inversion of configuration, although some racemisation occurs in dimethylformamide. 2-Bromo-octane is obtained with no detectable rearrangement and with an optical purity of ca. 75% by reaction in dioxan.
TL;DR: Two synthetic routes to the octahydroindeno[1,2-b]furanone derivative strigol (1), a germination stimulant of witchweed seeds, and its stereoisomers are described in this paper.
Abstract: Two synthetic routes to the octahydroindeno[1,2-b]furanone derivative strigol (1), a germination stimulant of witchweed seeds, and its stereoisomers are described.
TL;DR: These results and other published data on 13C-labelled sterigmatocystin agree with a biosynthetic scheme based on a C20 polyketide precursor and the distribution pattern of acetate units has been determined.
Abstract: The 13C n.m.r. spectra of two secondary fungal metabolites of related structure, aflatoxin B1 and sterigmatocystin, have been completely assigned. The distribution pattern of acetate units has been determined from 13C n.m.r. spectra of aflatoxin B1 derived from singly and doubly labelled [13C]acetate. These results and other published data on 13C-labelled sterigmatocystin agree with a biosynthetic scheme based on a C20 polyketide precursor.
TL;DR: In this article, the reaction of carbonyl compounds with sodium borohydride in a two-phase system, in the presence of chiral ammonium salts containing a secondary hydroxy-group affords the corresponding carbinols with 0.32% enantiomeric excess.
Abstract: Reaction of carbonyl compounds with sodium borohydride in a two-phase system, in the presence of chiral ammonium salts containing a secondary hydroxy-group affords the corresponding carbinols with 0–32% enantiomeric excess. The optical yields are higher when the hydroxy group is β to the ‘onium’ function and the catalyst is conformationally more rigid.
TL;DR: Some dibenz[b,f][1,4]oxazepines and dibenzine-like substances, variously substituted in the aromatic rings but not substituted at the azomethine group, are described.
Abstract: Some dibenz[b,f][1,4]oxazepines and dibenz[b,e]azepines, variously substituted in the aromatic rings but not substituted at the azomethine group, are described.
TL;DR: In this paper, it was shown that the rate of acid catalysis is related to the activity of water in accordance with Bunnett's hypothesis and the energy and entropy of activation and frequency factor have been calculated and a mechanism in agreement with the observations is suggested.
Abstract: The rate of oxidation of glycine, DL-alanine, DL-valine, and DL-leucine by potassium permanganate in aqueous sulphuric and perchloric acid solution is proportional to the concentration of the amino-acid. For each amino-acid, the total order of the reaction is two at a given concentration of sulphuric and perchloric acid. The rate of oxidation of the amino-acids is greater in sulphuric than in perchloric acid for the same concentration. Various hypotheses for the mechanism of acid catalysis have been tested and it has been found that the rate is related to the activity of water in accord with Bunnett's hypothesis. There is no primary salt effect, but at higher concentrations of added neutral salts, the logarithm of the rate constant is linearly related to ionic strength. Specific ionic effects have also been found. The energy and entropy of activation and frequency factor have been calculated and a mechanism in agreement with the observations is suggested.
TL;DR: Protection of the ring B diene system of ergosterol by (i) a two-step addition of the elements of water across the 5,6-double bond and (ii) formation of the 4-phenyl-1,2,4-triazoline-3,5-dione adduct gave a high yield of 22,23-dihydroergosterol.
Abstract: Protection of the ring B diene system of ergosterol by (i) a two-step addition of the elements of water across the 5,6-double bond, (ii) formation of the 4-phenyl-1,2,4-triazoline-3,5-dione adduct, or (iii) formation of the iron tricarbonyl adduct by treatment with p-methoxybenzylideneacetonetricarbonyliron, allowed selective reduction of the 22,23-double bond by catalytic or, as appropriate, ionic hydrogenation. Regeneration of the 5,7-diene system in each case gave a high yield of 22,23-dihydroergosterol.
TL;DR: Carbon-13 and carbon-14 labelling experiments have shown that the fungal xanthone ravenelin is acetatederived and enrichment studies with [1,2–13C]acetate have demonstrated that an oxygenated benzophenone derivative is an intermediate in the biosynthesis pathway.
Abstract: Carbon-13 and carbon-14 labelling experiments have shown that the fungal xanthone ravenelin (1) is acetatederived. Enrichment studies with [1,2–13C]acetate have demonstrated that an oxygenated benzophenone derivative is an intermediate in the biosynthetic pathway.
TL;DR: The title compound of as mentioned in this paper is orthorhombic with a= 11.116(11), b= 12.043(9), c= 7.646(5)A, space group Pbca, Z= 8.029 for 1029 observed reflections.
Abstract: Crystals of the title compound are orthorhombic with a= 11.116(11), b= 12.043(9), c= 7.646(5)A, space group Pbca, Z= 8. The structure was solved from three-dimensional diffractometer data by Patterson and Fourier methods and refined by block-diagonal least-squares to R 0.029 for 1029 observed reflections. The structure consists of protonated cations in the cis-conformation, i.e. with the –NH–NH2 group bent towards the CS bond, and of chloride anions. Packing is determined by hydrogen-bonds formed by the –NH2+, –NH2, and NH groups with Cl- and S.
TL;DR: The fungal metabolite dihydrodeoxy-8-epi-austdiol, elaborated by Aspergillus ustus, has been identified as (7R,8R)-7,8-dihydro-7, 8- dihydroxy-3,5,7-trimethyl-2-benzopyran-6-one.
Abstract: The fungal metabolite dihydrodeoxy-8-epi-austdiol, elaborated by Aspergillus ustus, has been identified as (7R,8R)-7,8-dihydro-7,8-dihydroxy-3,5,7-trimethyl-2-benzopyran-6-one. The absolute configuration of the azaphilones has been deduced.
TL;DR: In this paper, a number of 3-substituted quaternised pyridines and 4-subtituted oxazoles have been prepared and studied, with a view to discovering substituents appropriate for reactions involving opening of the pyridine or oxazole ring with closure onto the substituent to form a new ring at the 2-(pyridine) or 5-(oxazole) position.
Abstract: Various 3-substituted quaternised pyridines and 4-substituted oxazoles have been prepared and studied, with a view to discovering substituents appropriate for reactions involving opening of the pyridine or oxazole ring with closure onto the substituent to form a new ring at the 2-(pyridine) or 5-(oxazole) position. None of these potential rearrangements succeeded; the reasons for this are discussed together with the evidence that this provides for the mechanism of previously reported rearrangements.
TL;DR: In this article, seven new hydroquinones have been isolated from the green alga Cymopolia barbata and the structure and absolute stereochemistry of cyclocymopol monomethyl ether acetate were established by X-ray crystallography.
Abstract: Seven new hydroquinones have been isolated from the green alga Cymopolia barbata. These are cymopol [2-bromo-5-(3,7-dimethylocta-2,6-dienyl)hydroquinone] and its monomethyl ether, cyclocymopol [1-bromo-3-(4-bromo-2,5-dihydroxybenzyl)-2,2-dimethyl-4-methylenecyclohexane] and its monomethyl ether, cymopolone [(4-bromo-2,5-dihydroxyphenyl)trans-(2,6-dimethylhepta-1,5-dienyl) ketone], and its cis-isomer, and cymopochromenol [7-bromo-6-hydroxy-2-methyl-2-(4-methylpent-3-enyl)-2H-1-benzopyran]. The structure and absolute stereochemistry of cyclocymopol monomethyl ether acetate were established by X-ray crystallography.
TL;DR: Treatment of 6-(N-alkylanilino)uracils with Vilsmeier-type reagents gave 5-deazaflavines, which cyclized to 6-chloro-5-formyl-3-methyluracil and 2,4,6-trichloro- 5- formylpyrimidine, respectively.
Abstract: Treatment of 6-(N-alkylanilino)uracils with Vilsmeier-type reagents (dimethylformamide–phosphoryl chloride or dimethylformamide–ethyl chloroformate) gave 5-deazaflavines {10-alkylpyrimido[4,5-b]quinoline-2,4(3H,10H)-diones}; this cyclization was also achieved with triethyl orthoformate. Treatment of 3-methylbarbituric and barbituric acids with dimethylformamide–phosphoryl chloride gave 6-chloro-5-formyl-3-methyluracil and 2,4,6-trichloro-5-formylpyrimidine, respectively. Reactions of these 6-chloro-5-formylpyrimidines with N-substituted anilines gave directly the corresponding 5-deazaflavines.
TL;DR: A convenient general synthesis of hydroquinone diacetates from polycyclic aromatic quinones through reduction with sodium borohydride in dimethylformamide is described and the use of this technique is proposed for the characterization of carcinogen metabolites.
Abstract: A convenient general synthesis of hydroquinone diacetates from polycyclic aromatic quinones through reduction with sodium borohydride in dimethylformamide is described. Improved methods for the synthesis and chromatographic separation of the 1,6-, 3,6-, and 6,12-diones of benzo[a]pyrene are also described. 270 MHz N.m.r. spectroscopy is employed to confirm the structural assignments of the latter and the use of this technique is proposed for the characterization of carcinogen metabolites.