Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1984"

1-Aminoalkylphosphonous acids. Part 1. Isosteres of the protein amino acids

Abstract: The synthesis of 1-aminoalkylphosphonous acids, isosteres of the protein amino acids, by addition of hypophosphorous acid to diphenylmethylimines is described. These analogues of glycine, alanine, valine, leucine, isoleucine, phenylalanine, tyrqsine, tryptophan, serine, threonine, methionine, cysteine, cystine, glutamic acid, lysine, ornithine, arginine, and proline have been prepared and the analogues of alanine, valine, leucine, phenylalanine, and methionine resolved. Tha alanine, valine and methionine analogues have interesting antimicrobial activity and the alanine analogue has plant growth inhibiting properties. Oxidation of the appropriate 1-aminoalkylphosphonous acids gave the 1-aminoalkyl-phosphonic acid analogues of (±)-alanine, (–)-alanine, (±)-valine, (–)-valine, (±)-serine, (±)-threonine, (±)-lysine, (–)-leucine, and (±)-ornithine.

The structure of cyanoginosin-LA, a cyclic heptapeptide toxin from the cyanobacterium Microcystis aeruginosa

Abstract: The structure of cyanoginosin-LA (previously referred to by us as toxin BE-4) is cyclo(-D-Ala-L-Leu-erythro-β-methyl-D-isoAsp-L-Ala-Adda-D-Glu-N-methyldehydroAla)(17a), where Adda refers to the novel β-amino acid residue of 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (11). The connectivity of Adda is deduced from 1H- and 13C-n.m.r. data, but the stereochemistry at carbons 2,3,8, and 9 remains unknown. The residue sequence is derived from the mass spectra of cyclic and linear derivatives of the toxin. A new nomenclature for the related toxins of Microcystis aeruginosa is discussed.

Regioselective reductive ring-opening of 4-methoxybenzylidene acetals of hexopyranosides. Access to a novel protecting-group strategy. Part 1

Abstract: Reduction of fully protected 4,6-O-(4-methoxybenzylidene) hexopyranosides with sodium cyanoboro-hydride–trifluoroacetic acid in NN′-dimethylformamide, or trimethylsilyl chloride in acetonitrile, gives the 6- and 4-O-(4-methoxybenzyl) ethers, respectively, in good yield and good regioselectivity. The 4-methoxybenzyl ether linkage in products containing benzyl ethers or other protective groups is selectively cleaved upon treatment with cerium(IV) ammonium nitrate in aqueous acetonitrile.

The synthesis and metal binding characteristics of novel, isopolar phosphonate analogues of nucleotides

Abstract: Dichloromethylene-, difluoromethylene-, and fluoromethylene-bisphosphonic acids condense with the 5′-phosphoromorpholidates of adenosine and guanosine to give nucleotide analogues of ATP and GTP which are isopolar and isosteric. An isopolar but non-isosteric analogue of ATP results from the condensation of acetylene-1,2-bisphosphonic acid with AMP-morpholidate. 31 P N.m.r. and pKa, data show that the physical analogy improves in the series CH2 < CCl2⩽ CFH < CF2 < CC < O with respect to the β,γ-bridging function. N.m.r. and ion-selective electrode measurements on the binding of the divalent metals Mg, Ca, Zn, and Ba suggest that the pattern of metal cation binding to the nucleotide tetra-anion responds both to steric and to electronic features of the phosphonates, with the β,γ-difluoromethylene analogue most closely resembling ATP.

Photocatalysis of the Pschorr reaction by tris-(2,2′-bipyridyl)ruthenium(II) in the phenanthrene series

Abstract: The photocatalytic conversion of the tetrafluoroborate salt of the stilbenediazonium ion (1) into the corresponding phenanthrene (2)(Pschorr reaction) by Ru(bpy)32+(bpy = 2,2′-bipyridyl) has been investigated. We have shown that this particular Pschorr reaction takes place quantitatively with a high quantum yield (φ > 0.4) upon selective photoexcitation of a catalytic amount of Ru(bpy)32+. Quenching and conventional flash photolysis experiments have revealed that quenching of the excited state of Ru(bpy)32+ probably occurs by an electron-transfer process. In contrast it has been shown that direct photolysis of (1) leads to the Pschorr reaction with a poorer yield (10–20%).

Luminescent metal complexes. Part 1. Tris-chelates of substituted 2,2′-bipyridyls with ruthenium (II) as dyes for luminescent solar collectors

Abstract: Ruthenium(II) and osmium(II) complexes of 2,2′-bipyridyls (bipy) and 1,10-phenanthrolines (phen) are identified as feasible dyes for use in luminescent solar collectors. Twenty-seven RuII(bipy)32+ complexes are prepared and the absorption and emission spectra of their solutions in EtOH–MeOH at room temperature are reported. Quantum efficiencies, Which are sensitive to oxygen quenching, vary between 0.002 and 0.306 depending upon substituents. The effect of the medium on the spectral properties of selected compounds has also been investigated. Measured quantum yields of non-aqueous solutions are higher than those for aqueous solutions but lower than for doped plastic films.

Observation on the synthesis of allenes by homologation of alk-1-ynes

Abstract: An investigation is reported on the homologation of alk-1-ynes to allenes by the cuprous bromide-catalyzed reaction with formaldehyde and di-isopropylamine, including extension to an aromatic acetylene and a diacetylene. Optimization of yields was studied. A mechanism is proposed involving an intermediate hydrido-cuprate species derived from a 1:1 Mannich base–cuprous bromide π-complex. The mechanism is supported by labelling experiments and observed substituent effects.

Reductive aminations of ketones and aldehydes using borane–pyridine

Abstract: Borane–pyridine is introduced as a cheap and readily available alternative to sodium cyanotrihydroborate for the purpose of the reductive amination of a wide variety of carbonyl compounds. It does not suffer from the severe toxicity associated with sodium cyanotrihydroborate.

Effects of ionizing radiation on deoxyribonucleic acid and related systems. Part 1. The rôle of oxygen

Abstract: Exposure of aqueous solutions of calf-thymus DNA to 60Co γ-rays at 77 K results in the formation of equal yields of G+ and T– centres, detected by e.s.r. spectroscopy. In the presence of oxygen, O2– ions are also formed at the expense of T–, the primary yield of G+ centres being unaffected. On annealing above 77 K the e.s.r. features for O2– ions were initially modified as a result of changes in solvation, and then, at ca. 193 K, they were lost irreversibly. A large growth in signals due to RO2· radicals was observed simultaneously. These radicals are formed from T– anions or the protonated form, TH, and probably also indirectly from G+ radicals. In parallel experiments, under comparable conditions, we have analysed for single and double stand breaks using plasmid DNA (pBR 322). Both single and double strand breaks persist under conditions in which G+ and T– are the only detectable primary radical products. The presence of oxygen causes only a slight increase in damage to DNA.

Molecular inclusion in functionalized macrocycles. Part 8. The crystal and molecular structure of calix[4]arene from phenol and its (1 : 1) and (3 : 1) acetone clathrates

Abstract: The cyclic tetramer (2c), formally derived from the condensation of phenol and formaldehyde but actually obtained by dealkylating p-t-butyl- and p-octylcalix[4]arenes, crystallizes from acetone in two crystal forms. The first one, obtained in the presence of 1,2,4,5-tetramethylbenzene, is the (2c)–acetone (1 : 1) clathrate, orthorhombic, space group Pnma, a= 17.010(8), b= 14.127(6), c= 10.667(3)A, Z= 4, final R value 0.090. The second, obtained from pure acetone or in the presence of thymol, is the (2c)–acetone (3 : 1) clathrate, space group P63/m, a=b= 14.543(5), c= 18.228(7)A, γ= 120°, final R value 0.070. The geometry of macrocycle (2c) in the two forms, in the ‘cone’ conformation in both cases, is slightly different. The orthorhombic crystals show a molecular arrangement of an intercalatoclathrate type and the hexagonal one a tubulato-clathrate type.

Oxo complexes of ruthenium(VI) and (VII) as organic oxidants

Abstract: Oxidation of a variety of saturated and unsaturated primary and secondary alcohols by tetraoxoruthen-ate(VI), [RuO4]2–, tetraoxoruthenate(VII), [RuO4]–, barium trans-trioxodihydroxoruthenium(VI), trans-Ba[Ru(OH)2O3], dioxotrichlororuthenate(VI), [RuO2Cl3]–, and dioxodichlorobipyridylruthenate(VI), [RuO2(bipy)Cl2], has been studied; [RuO4]2–may be used catalytically in conjunction with [S2O8]2– under basic aqueous conditions. For some of these systems, the oxidation of several aldehydes and amines were also examined. Both [RuO4]2–and [RuO4]– oxidise primary alcohols to carboxylic acids and secondary alcohols to ketones; the reactivity of these reagents towards unsaturated alcohols was studied in particular. The new species [PPh4][RuO2Cl3] and also [RuO2(bipy)Cl2] cleanly oxidise a wide range of alcohols to aldehydes and ketones without attack of double bonds. Ba[Ru(OH)2O3] functions as a heterogeneous oxidant in dichloromethane, oxidising only the most reactive alcohols to aldehydes.

Tris(bipyridyl)ruthenium(II)-photosensitized reaction of 1-benzyl-1,4-dihydronicotinamide with benzyl bromide

Abstract: An NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), reduces benzyl bromide to yield toluene as the main product under irradiation of the absorption band of BNAH in the presence of pyridine in acetonitrile, while the addition of a sensitizer tris(bipyridyl)ruthenium(II){[Ru(bpy)3]2+} to the BNAH-benzyl bromide system results in a drastic change in the photoreduced products, yielding 1,2-diphenylethane as the main product. Photosensitization by [Ru(bpy)3]2+ has been shown to change the mechanism of the photochemical reaction of BNAH with benzyl bromide; reaction in the absence of [Ru(bpy)3]2+ proceeds by a radical chain mechanism involving benzyl bromide. However, the [Ru(bpy)3]2+-mediated photoreduction of benzyl bromide with BNAH occurs in the presence of [Ru(bpy)3]2+, where benzyl bromide is subject to two-electron reduction by [Ru(bpy)3]+ which is formed by an electron transfer from BNAH to the excited state of [Ru(bpy)3]2+.

Synthesis, properties, and multinuclear (1H, 13C, 77Se) nuclear magnetic resonance studies of selenoethers containing two or more selenium atoms

Abstract: A convenient synthesis of MeSeLi from MeLi and Se8 in tetrahydrofuran (THF) has been used to prepare the bis-selenoethers MeSe[CH2]nSeMe (n= 1,2,3,6, or 12) and cis-MeSeCHCHSeMe. PhSe[CH2]nSePh (n= 1–3) and cis-PhSeCHCHSePh have been prepared from PhSe–, itself produced from Ph2Se2 and LiAIH4–THF or sodium hydroxymethanesulphinate. The bis-selenoethers o-C6H4(SeR)2(R = Me or Ph) were obtained from R2Se2 and benzyne. The syntheses of (RSeCH2)3CMe (R = Me or Ph), (MeSeCH2)4C, and (MeSeCH2CH2CH2)2Se are also described. The 1H, 13C, and 77Se n.m.r. spectra of these selenoethers have been recorded, and the chemical shifts and coupling constants (nJSe–H, nJSe–C) are discussed in terms of structures. Mass spectra of the selenoethers have been recorded and the principle fragmentation modes identified.

The protection of thymine and guanine residues in oligodeoxyribonucleotide synthesis

Abstract: Thymidine is converted in four steps into its crystalline 4-O-phenyl derivative (14b) in 72% overall yield. 2′-Deoxyguanosine is converted in five steps into its 6-O-(2-nitrophenyl)-2-N-phenylacetyl and crystalline 6-O-(3,5-dichlorophenyl)-2-N-phenylacetyl derivatives [(19a) and (19b), respectively] in ca. 39 and 42% overall yields, respectively. Compounds (14b), (19a), and (19b) are converted into the corresponding crystalline 5′-O-(9-phenyl-9H-xanthen-9-yl) derivatives (15), (20a), and (20b), respectively. The actions of N1,N1,N3,N3-tetramethylguanidinium 2-nitrobenzaldehyde oximate, 80% acetic acid, potassium carbonate in aqueous dioxane, pyridine, and triethylammonium toluene-p-thiolate on (14b), (19a), and (19b) have been investigated.

Observations on various silyl-cuprate reagents

Abstract: The mixed silyl-cuprate reagent (6), made from 1 equiv. of methyl-lithium, 1 equiv. of phenyldimethylsilyl-lithium, and 1 equiv. of copper(I) cyanide, reacts with 3-methylcyclohexenone (7), with methyl cinnamate (9), with 1-vinylcyclohexyl acetate (11), and with hex-1-yne (13) to transfer, in each case, the silyl group, and to give the β-silylcarbonyl compounds (8) and (10), the allylsilane (12), and the vinylsilane (14), without the concomitant formation of involatile silicon-containing by-products. The silyl-cuprate reagent (15), prepared from trimethylsilyl-lithium and copper(I) cyanide, reacts with similar substrates, in the same way, even though hexamethylphosphoric triamide (HMPA) is present in the reaction medium.

Solid-state fluorescent photophysics of some 2-substituted benzothiazoles

Abstract: The solid-state fluorescence properties of a series of benzothiazoles with phenyl, naphthalene, and coumarin moieties substituted at the 2-position have been investigated. The necessity for a 2′-OH substituent for fluorescence has been confirmed and the effects of further substitution in the 2-phenyl ring are reported.

Saponins from roots of Platycodon grandiflorum. Part 2. Isolation and structure of new triterpene glycosides

Abstract: Seventeen new saponins (2)–(18) have been isolated from the roots of Platycodon grandiflorum A. DC. and their structures determined by comparison of their 13C n.m.r. signals with those of known prosapogenins (19)–(26) and of the sugar chain at C-28 in platycodin-D (1). Eight of these saponins were found to have an O-acetyl group which migrated both readily and reversibly between the 2-O- and 3-O-positions of the rhamnose moiety in their sugar chain.

Palladium- and rhodium-catalysed cyclisation of 1,6-, 1,7- and 1,8-dienes to cyclopentenes and methylenecyclopentenes. Crystal structure of dichloro(4,4-diacetylhepta-1,6-diene)platinum(II)

Abstract: Hepta-1,6-dienes disubstituted at C-4 with certain carbonyl-containing groups cyclise, in good yield, to the corresponding 4,4-disubstituted 1,2-dimethylcyclopent-2-enes when treated with a catalytic amount of palladium acetate in chloroform containing hydrogen chloride. Changing the catalyst precursor to chlorotris(triphenylphosphine)rhodium(I) led to the formation of the corresponding 1-methyl-2-methylenecyclopentanes which, in turn, isomerised to 1,2-dimethylcyclopent-1-enes in ethanolic hydrogen chloride containing the rhodium complex. The effect of terminal substitution of the dienes with methyl groups was examined. 1,7- and 1,8-Dienes give rise to mixtures of five-membered ring products. Possible mechanisms for the catalytic processes are discussed. The X-ray crystal structure analysis of dichloro(4,4-diacetylhepta-1,6-diene)platinum(II) is reported.

2,5-Dilithiation of N-protected imidazoles. Syntheses of 2,5-disubstituted derivatives of 1-methoxymethyl-, 1-triphenylmethyl-, and 1-(N,N-dimethylsulphonamido)-imidazole

Abstract: The conditions previously established for the dilithiation of 1-methylimidazole are shown to be applicable to 1-methoxymethyl- and 1-triphenylmethyl-imidazole allowing good-yielding syntheses of 1,2,5-trisubstituted imidazole derivatives. The suitability of the 1 -substituents (and of other groups) for the N-protection of imidazoles in dilithiation experiments is discussed and the use of the N,N-dimethyl-sulphamoyl protecting group is proposed. 1-Sulphamoylimidazole undergoes mono- and 2,5-di-lithiation quantitatively at low temperatures and in short reaction times. The results of work-up of the 2,5-dilithio intermediate with 1 mol equiv. of iodomethane or dimethyl sulphate indicate selectivity in favour of reaction at the 5-position.

Formation of indoles, isoquinolines, and other fused pyridines from azidoacrylates

Abstract: Mild thermal decomposition in boiling toluene or xylene of the azidocinnamates (1)–(6), readily prepared from the corresponding aldehyde and ethyl azidoacetate, gives indoles in good yield when there is an unsubstituted ortho position, and dihydroisoquinolines, and hence isoquinolines, when there is an o-methyl or methylene group. In the presence of iodine, which seems to favour a radical type process, the yield of isoquinoline is increased, and isoquinoline formation can compete with the indole-forming cyclisation to a free ortho-position. Iodine also catalyses primary enamine formation by a hydrogen abstraction process. The thiophene (7) and pyrazole (8) are formed and decomposed similarly to give the corresponding c-fused pyridines (28) and (29). The 2,6-dichloro compound (9) thermolyses to the stable 2H-azirine (32) which isomerises to the nitrile (33) on stronger heating. Yields in these azide decompositions are sometimes high, though they can be variable and the reactions, though easily carried out, can be complex.

XY–ZH systems as potential 1,3-dipoles. Part 1. Background and scope

Abstract: XY–ZH Systems are considered in general terms and divided into four classes according to the number of constituent atoms that possess lone-pair electrons. Those systems in which the central Y atom possesses a lone pair are shown to be capable of participating in formal 1,2-H shifts generating 1,3-dipolar species. The scope of the reaction, including its possible relevance to the biochemistry of pyridoxal enzymes is discussed and the influence of structure on reactivity is demonstrated with rate data for the cycloaddition of a series of aryl imines of phenylglycine and alanine methyl esters to N-phenylmaleimide.

Asymmetric synthesis using chirally modified borohydrides. Part 2. Enantioselective reduction of ketones with polymeric (S)-prolinol–borane reagent

Abstract: Chiral polymeric reagents have been prepared from polymeric (S)-prplinols and borane and used in the enantioselective reduction of a series of prochiral ketones under various conditions. Reductions with these polymeric reagents are shown to give alcohols of reasonably good optical purity (up to 80%). The results are compared to those obtained with (S)-N-benzylprolinol–borane complex which is a soluble model reagent.

Enhanced selectivity by an ‘open-well effect’ in a metalloporphyrin-catalysed oxygenation reaction

Abstract: A selection of aliphatic alkenes, substituted styrenes, and cis-stilbene has been epoxidised with aqueous NaOCl, employing two different porphyrins, Mn(TPP)OAc and Mn(TMP)Cl, as catalysts. Large increases in reaction rate, product selectivity, and stereoselectivity are found with the bulkier TMP ligand. The results are interpreted in terms of an ‘open-well effect’ around the manganese–oxygen active site.

Quantification of effective polarisability. Applications to studies of X-ray photoelectron spectroscopy and alkylamine protonation

Abstract: Two new empirical methods lead to a quantification of polarisability-derived stabilisation of charge in molecules. These take account of the all-important attentuation of substituent influence as it is further from the charged center. The first is derived from a formula for calculating mean molecular polarisabilities and also takes account of heteroatom substitution. A simple bond-counting procedure is an alternative for unsubstituted alkyl groups. The value of these two models is shown with studies on Cl and Ge ESCA/Auger spectral data, nitrogen 1s binding energy shifts, and with data on the gas phase proton affinities of alkyl substituted amines.

A versatile new synthesis of quinolines and related fused pyridines. Part 12. A general synthesis of 2-chloropyridines and 2-pyridones

Abstract: The Vilsmeier formylation of tertiary and secondary enamides leads to 2-pyridones and 2-chloropyridines, respectively. The reaction appears to be quite general allowing substitution in the 1-, 3-, 5-, or 6-position or combinations of these. The major limitation arises with enamides which are unsymmetrically substituted on the double bond with alkyl groups, when mixtures can result. Attempts to introduce a 4-substitutent by a variation of the Vilsmeier reagent had limited success.

N-alkoxy-N-acylnitrenium ions as possible intermediates in intramolecular aromatic substitution: novel formation of N-acyl-3,4-dihydro-1H-2,1-benzoxazines and N-acyl-4,5-dihydro-1H,3H-2.1-benzoxazepine

Abstract: N-Halogeno-N-alkoxyamides undergo intramolecular aromatic substitution by thermal- or Lewis acid-catalysed heterolysis of the nitrogen–halogen bond. N-Acyl-N-alkoxynitrenium ions are likely intermediates. N-Chloro-N-methoxybiphenyl-2-carboxamide (4) yields N-methoxyphenanthridone (11) quantitatively with AgBF4, while O-2-phenylethyl-N-chlorobenzohydroxamate (19) is converted in good yield into N-benzoyl-3,4-dihydro-1H-2,1-benzoxazine (21) with AgBF4, AgClO4, HgO, and Hg(OAc)2. N-Acetyl-3,4-dihydro-1H-2,1-benzoxazine (22) is formed similarly. O-3-Phenylpropyl-N-chlorobenzohydroxamate (23) cyclises to N-benzoyl-4,5-dihydro-1H,3H-2,1-benzoxazepine (24) with AgBF4.

Reductive cleavage of the nitrogen–nitrogen bond in hydrazine derivatives

Abstract: The reductions of the 1,2-disubstituted hydrazines (4)–(7) having the activating groups toluene-p-sulphonyl, acetyl, ethoxycarbonyl, and trifluoroacetyl respectively have been studied with zinc in acetic acid, aluminium amalgam, sodium in liquid ammonia, sodium in ethanol, and Raney nickel. Satisfactory conditions have been defined for the reductive cleavage of each of these substituted hydrazines (4)–(7). The Diels–Alder adduct (12) of cyclopentadiene and diethyl azodicarboxylate has been oxidised, by m-chloroperoxybenzoic acid to give the epoxide (20), by osmium tetraoxide to give the diol (21), and via hydroboration to give the alcohol (22). Using sodium in liquid ammonia these hydrazine derivatives (20)–(22) and others have been reduced by cleavage of the nitrogen–nitrogen bond to give derivatives of oxygenated cyclic diamines.

Stereochemistry of olefin and fatty acid oxidation. Part 3. The allylic hydroperoxides from the autoxidation of methyl oleate

Abstract: Methods have been developed, using 13C n.m.r. spectroscopy and mass spectrometry, for the analysis of all eight cis and trans allylic 8-, 9-, 10-, and 11-hydroperoxides formed on autoxidation of methyl oleate.

Clavulanic acid and its derivatives. Structure elucidation of clavulanic acid and the preparation of dihydroclavulanic acid, isoclavulanic acid, esters and related oxidation products

Abstract: Clavulanic acid, a novel β-lactamase inhibitor from Streptomyces clavuligerus, has been shown to be Z-(2R,5R)-3-(β-hydroxyethylidene)-7-oxo-4-oxa-1 -azabicyclo[3.2.0]heptane-2-carboxylic acid (1). The structure and absolute stereochemistry was confirmed by X-ray analysis of the p-nitrobenzyl and p-bromobenzyl esters, (14) and (15). The conversion of clavulanic acid into a variety of esters and acyl derivatives is described. An account of its isomerisation to the E isomer (30) and the formation of an oxetane (45) as a by-product of the photolysis of the phenacyl ester (18) is given. The reduction and oxidation of acid (1) under a variety of conditions has also been examined in detail.

Structure elucidation of the janthitrems, novel tremorgenic mycotoxins from Penicillium janthinellum

Abstract: The assignment of the structures (1)–(3) to janthitrems E-G, tremorgenic mycotoxins isolated from cultures of Penicillium janthinellum is based on a detailed study of their highfield 1H and 13C n.m.r. spectra. In the structure elucidation extensive use was made of heteronuclear 13C-{1H} selective population inversion (SPI) and homonuclear 1H-{1H} n.O.e. experiments.