Showing papers in "Journal of The Chemical Society-perkin Transactions 1 in 1985"

Polyphenol interactions. Part 1. Introduction; some observations on the reversible complexation of polyphenols with proteins and polysaccharides

Abstract: Early studies of the interactions between polyphenols and proteins are reviewed. The complexation of some simple phenols and a group of biosynthetically inter-related esters of gallic acid with bovine serum albumin (BSA) is examined by equilibrium dialysis and microcalorimetry. The phenomenon is pH dependent. The results indicate that molecular size and conformational flexibility of the polyphenol substrate lead to enhanced interactions with the protein. Preliminary studies with polysaccharides indicate that the binding here is pH independent. These studies suggest that whilst the binding of polyphenols to these macromolecules is influenced by similar structural features the ability of the polysaccharide to form structures which encapsulate the polyphenol is, in this instance, a further critical feature of the complexation.

Structural studies on cyanoginosins-LR, -YR, -YA, and -YM, peptide toxins from Microcystis aeruginosa

Abstract: The structures of the hepatotoxins of general name cyanoginosins-XY are proposed to be cyclo-D-Ala-L-X-erythro-β-methyl-D-isoAsp-L-Y-Adda-D-isoGlu-N-methyldehydroAla (1) where X and Y represent variable amino acids and Adda is 3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (2). The structural studies on four variant toxins utilised n.m.r. and mass spectral methods analogous to those recently used to determine the structure of cyanoginosin-LA. [graphic omitted] (1)

Acid-catalysed benzylation and allylation by alkyl trichloroacetimidates

Abstract: Benzyl and allyl trichloroacetimidate (1) and (2) are convenient reagents for the O-alkylation of hydroxy groups under mildly acidic conditions, which are compatible with imide, ester, and acetal protecting groups. The base-catalyzed addition of benzyl alcohol or allyl alcohol to trichloroacetonitrile provides a simple synthesis of these imidates, but published methods for the recovery of related molecules by distillation leads to variable amounts of a rearranged product, N-alkyl trichloroacetamide. A modified procedure, suitable for the large scale synthesis of (1) and (2) without the need for a distillation step, is reported. The introduction of benzyl and allyl ethers to a variety of carbohydrate derivatives illustrates the potential of these reagents.

Asymmetric synthesis using chirally modified borohydrides. Part 3. Enantioselective reduction of ketones and oxime ethers with reagents prepared from borane and chiral amino alcohols

Abstract: The asymmetric reduction of aromatic and aliphatic ketones, halogeno ketones, hydroxy ketones, keto esters, and ketone oxime ethers with reagents prepared from borane and chiral amino alcohols has been investigated When α,α-diphenyl β-amino alcohols, such as (2S,3R)-(–)-2-amino-3-methyl-1,1 -diphenylpentanol (2d), were used as a chiral auxiliary, very high enantioselectivities (ca 90 % ee) were obtained in the reduction of various ketones and oxime ethers

Molecular inclusion in functionalized macrocycles. Part 9. The crystal and molecular structure of p-t-butylcalix[4]arena–anisole (2 : 1) complex: a new type of cage inclusion compound

Abstract: p-t-Butylcalix[4]arene (1a), the cyclic tetramer obtained by the condensation of p-t-butylphenol and formaldehyde, crystallizes from anisole forming a new type of cage inclusion compound with the solvent. Crystals having a 2 : 1 host–guest stoicheiometry are tetragonal, space group P4/n, a=b= 12.823(6); c= 25.618(8)A, Z= 2, final R values 0.073. Two molecules of the macrocycle, in the cone conformation, face the methyl groups of the para-substituents creating a closed cavity which encapsulates one molecule of anisole. The guest is disordered in the cavity in at least eight equivalent orientations.

Luminescent metal complexes. Part 5. Luminescence properties of ring-substituted 1,10-phenanthroline tris-complexes of ruthenium(II)

Abstract: The absorption characteristics, emission spectra, luminescent quantum yields, and lifetimes are reported for 24 ruthenium(II) tris-1,10-phenanthroline complexes in EtOH–MeOH solution. Quantum yields fall between 0.019 and 0.403, the highest values being recorded for complexes substituted at the 4,7-sites with aryl groups. Incorporation of these derivatives into poly(vinyl chloride) film raises the quantum yields leading to values ranging from 0.40 to 0.75.

Polyphenol interactions. Part 2. Covalent binding of procyanidins to proteins during acid-catalysed decomposition; observations on some polymeric proanthocyanidins

Abstract: The kinetics of the acid-catalysed decomposition of some procyanidins are determined The reactions are specific acid-catalysed The rate-determining step is that of the initial protonation of the procyanidin The relevance of this degradation to haze formation in certain beverages is discussed The structure of some polymeric proanthocyanidins is briefly commented upon in the light of this work

Synthesis of (E)- and (Z)-pulvinones

Abstract: Two new routes to pulvinones have been developed, one of which involves a novel Wittig reaction. For the first time, members of the E-series, including the parent (E)-pulvinone, are reported and the structural elucidation of the geometric isomers is described. A method for quantitatively converting (E)-pulvinones into (Z)-pulvinones is presented, together with a technique for differentiating between the isomers.

Structures of the cephalosporolides B–F, a group of C10 lactones from Cephalosporium aphidicola

Abstract: The structures of the pentaketides lactones, the cephalosporolides B–F, were elucidated by a combination of spectroscopic, chemical, and X-ray analyses.

S∴N and S∴O three-electron-bonded radicals and radical cations in aqueous solutions

Abstract: Intramolecularly formed S∴N three-electron-bonded radical cations have been identified as transient intermediates in the ′OH radical-induced oxidation of 3-(methylthio)propylamine, methionine, and methionine ethyl ester A similarly bonded radical is also indicated in the reduction of dehydromethionine by hydrated electrons Intramolecular S∴O-bonded intermediates are suggested to be formed in the ˙OH-induced oxidation of 4-(methylthio)butyric acid and S-methylcysteine All these three-electron-bonded species exhibit optical absorptions with maxima in the 380–400 nm range The observable S∴O-bonded transient from S-methylcysteine is presumed to be protonated at oxygen Favourable steric structures, particularly five-membered rings, significantly increase the probability of formation and the overall stability of a particular three-electron bond Under comparable conditions, ie structure, substituents, consecutive chemistry, etc, the S∴O bond appears to be considerably weaker than corresponding S∴N and S∴S bonds

Enthalpy–entropy compensation in complexation of cations with crown ethers and related ligands

Abstract: Thermodynamic parameters indicate that the enthalpy–entropy compensation effect holds in general for complexation of cations with glymes/podands, crown ethers, cryptands, and macrocyclic antibiotics in various solvents. Thus the ΔH–TΔS plots give fairly good linear relationships for each type of ligand, with different slopes (α) and intercepts (TΔS0) characteristic of the type. The nature of the cation–ligand interaction is discussed in terms of α and TΔS0 values.

A new method for the oxidation of alkenes to enones. An efficient synthesis of Δ5-7-oxo steroids

Abstract: A variety of cycloalkenes were converted into α,β-unsaturated ketones using t-butyl hydroperoxide in the presence of chromium hexacarbonyl catalyst. The scope of the reaction has been partly investigated, and it was found that the allylic oxidation proceeds selectively in the presence of some secondary alcohols. High-yield conversions of steroidal 5,6-enes into the corresponding 5,6-en-7-ones are reported.

Metal-carbonyl-induced reaction of isoxazoles. Ring cleavage and reduction by hexacarbonylmolybdenum, pentacarbonyliron, or nonacarbonyldi-iron

Abstract: In the presence of [Mo(CO)6] and water the isoxazoles (1a–f) undergo thermally induced reductive cleavage of the N–O bond to give β-amino enones in good yield. Similar results were obtained by the use of [Fe(CO)5] and water with photoirradiation, or of [Fe2(CO)9] and water with heating. A mechanism involving an N-complexed isoxazolepentacarbonylmolybdenum or isoxazoletetracarbonyliron, and a [Mo(CO)5]- or [Fe(CO)4]-complexed (β-oxo vinyl)nitrene intermediate is proposed for the reactions. The complexed nitrene moiety could be reduced by the central metal in the presence of water to give amine. Furthermore, treatment of 2-benzoyl-3-phenyl-2H-azirine (8a), which is an isomer of 3,5-diphenylisoxazole, with the metal carbonyls and water also resulted in the formation of a β-amino enone possibly via the corresponding complexed (β-oxo vinyl)nitrene. An N-complexed isoxazolepentacarbonylmolybdenum intermediate was prepared by the photoreaction of [Mo(CO)6] with 3,5-dimethylisoxazoie. Its characterization, and chemical transformations, have been carried out to investigate the proposed mechanism.

Amine basicities in benzene and in water

Abstract: The constants for ion-pair formation with 2,4-dinitrophenol in benzene (KB), and the pKa, values in water, of thirty-three amines have been measured. According to the class of amine, two different situations can be observed: for primary amines and secondary cyclic amines, the effects of structural variations on basicity are higher in water than in benzene; on the other hand, for tertiary amines these effects are similar in the two solvents. KB, Values of primary amines give a good correlation with σ*. The Taft and Hancock equation allows a unifying treatment of KB, values of the various classes of amines.

The stereocontrolled Horner-Wittig reaction: synthesis of disubstituted alkenes

Abstract: Addition of the lithium derivatives of phosphine oxides Ph2P(O)CH2R1 to aldehydes gives erythro adducts (11) with good stereoselectivity. Reduction of α-diphenylphosphinoyl ketones (12) gives threo adducts (11) with even better stereoselectivity. Purification by flash chromatography and/or crystallisation followed by elimination of Ph2PO2) gives pure Z- or E-alkenes with high material conversion. Explanations are offered for the stereoselectivities, conditions defined for full stereochemical control, and guidelines suggested for approaches to a given alkene.

Pentavalent organobismuth reagents. Part 3. Phenylation of enols and of enolate and other anions

Abstract: The phenylation of enols and of enolate anions of ketones, β-diketones and keto esters has been studied using a range of Bi reagents. Under basic conditions C-phenylation is observed and, even hindered, perphenylated compounds are easily synthesized. Under neutral and acidic conditions ordinary ketones do not react and enolic systems give O-phenylation. A number of other anions have been phenylated under basic conditions, including the key compound indole which mainly gave 3-C-phenylation. All these reactions can be supposed to have one of two alternative mechanisms, which parallel the two mechanisms proposed for the phenylation of phenols.

Asymmetric synthesis of 3-methyl-2-phenyl-1,4-benzodioxanes. Absolute configuration of the neolignans eusiderin and eusiderin C and D

Abstract: The asymmetric synthesis of 2S,3S- and 2R,3S-3-methyl-2-phenyl-1,4-benzodioxane from (–)-ephedrine is reported. Comparison of the c.d. curves of these compounds with those of the natural neolignans eusiderin and eusiderin C allows the assignment of 2R,3R configuration to eusiderin and of 2R,3S configuration to eusiderin C and eusiderin D.

Photoredox properties of tetra-2,3-pyridinoporphyrazines (29H,31H-tetrapyrido[2,3-b: 2′, 3′-g : 2″,3″-l:2‴,3‴-q]porphyrazine)

Abstract: Tetra-2,3-pyridinoporphyrazines (29H,31H-tetrapyrido[2,3-b : 2′,3′-g : 2″,3″-l : 2‴,3‴-q]porphyrazine)(1) and the corresponding water-soluble NN′N″N‴-tetramethylated quaternized tetracationic forms (2) with different central metal atoms were prepared and their photoredox activities investigated. The synthesis of (2; M = Zn, Cu) leads to mixtures of different constitutional isomers, which were isolated and characterized. The photoredox activities of (1) upon irradiation with visible light in the presence of EDTA and methylviologen (MV2+) are comparable with those of phthalocyanines. The photochemical reaction of (2) with different donors works clearly through a reductive quenching mechanism. Reaction with EDTA proceeds by a two-step sensitization to the dicationic species of (2).

The complexation of the diquat dication by dibenzo-3n-crown-n ethers

Abstract: Spectrophotometric investigations of equimolar mixtures of diquat bis(hexafluorophosphate)(2) and a range of dibenzo-3n-crown-n ethers [n=6–12; (10)–(16)] in acetonitrile reveal the existence of charge-transfer absorption bands at ca.λmax. 400 nm. These absorptions are attributable to intermolecular π–π charge transfer between the electron-rich catechol units of the dibenzo-crown ethers and the electron-deficient bipyridinium ring system of the diquat dication. The qualitative conclusion from these experiments, that the most stable 1 : 1 complex is formed between dibenzo-30-crown-10 (14) and diquat bis(hexafluorophosphate)(2). led to the isolation from dichloromethane methanol–n-heptane of red crystals of [diquat.dibenzo-30-crown-10][PF6]2 suitable for X-ray crystallography. Although the crystal structure analysis revealed that there are two independent sets of 1 : 1 complexes (I and II) in the unit cell, the gross structural features of the two complexes are very similar. In addition to the parallel alignment of their three aromatic rings to accommodate the stabilising intermolecular π-π charge-transfer interaction, there is probably some further host–guest stabilisation to be gained on account of favourable electrostatic interactions between the phenolic oxygen atoms in the host and the nitrogen atoms in the pyridinium rings of the guest. Moreover, there is some evidence for weak C–H ⋯ O hydrogen bonding involving principally H-6 and H-6′ on the bipyridinium ring system of the guest and certain –CH2OCH2– oxygen atoms in the host. As evidenced by 1H n.m.r. spectroscopy in CD3COCD3, these non-covalent bonding interactions are probably responsible for the formation of stable and ordered 1 : 1 complexes with similar gross structural features in solution, at least in the cases where dibenzo-30- crown-10 (14). dibenzo-33-crown-11 (15), and dibenzo-36-crown-12 (16) are the hosts. Further evidence for the 1 : 1 stoicheiometry of these solution complexes, as well as for the complex involving dibenzo-27-crown-9 (13), has come from equilibrium constant measurements for the association between the dibenzo-3n-crown-n(n=9–12) hosts (13)–(16) and diquat bis(hexafluorophosphate)(2) in acetone. A quantitative treatment of the charge-transfer absorption bands at 400 nm, which affords Kavalues of 410, 17 500, 10 800, and 2 000 M–1 for n=9, 10, 11, and 12, respectively, provides convincing quantitative evidence for (a) 1 : 1 stoicheiometry and (b) the relative stabilities of the 1 : 1 complexes in solution. In the case of dibenzo-24-crown-8 (12), a complex of 2:l (guest:host) stoicheiometry is believed to be formed in acetone with a Kavalue of 385 000 M–2, as shown by a successful quantitative treatment of the charge-transfer absorption data by an independent method.

Mechanism of the oxidation of sulphides with sodium periodate

Abstract: The kinetics of the oxidation of RSAr, R2S, and (CH2)nS sulphides with NaIO4yielding sulphoxides were investigated in ethanol–water solutions, and the rate equation v=k2[sulphide][IO4–] was found to be valid. The observed substituent (ρ– 1.40 for YC6H4SMe; ρ*–1.06 and –0.60 for RSPh and R2S, respectively) and solvent effects (m 0.722 for MeSPh) are explained by an electrophilic attack of periodate oxygen on sulphide, leading to a polar transition state. The slight steric requirements of the reaction (δ 0.27 and 0.105 for RSPh and R2S, respectively) and the lack of solvent isotope effect exclude the participation of water in an SN2-type nucleophilic displacement on a sulphonium centre, which might be considered to have been formed from sulphide and periodate in a fast pre-equilibrium. A moderate anchimeric assistance was observed for the conversion of XC6H4SMe sulphides with o-X =CO2Me, CO2H, and CO2–(k2°/k2pca. 1). From the results it is concluded that oxidation proceeds by a one-step electrophilic oxygen transfer from IO4– to sulphide through a polar product-like transition state that is stabilized by a polar neighbouring group or by the increasing polarity of the medium.

Peptide synthesis. Part 7. Solid-phase synthesis of conotoxin G1

Abstract: The neurotoxin conotoxin G1 from Conus geographus has been synthesised by a solid-phase method using fluorenylmethoxycarbonylamino acids and a polar, poly(dimethylacrylamide)-based support. The two disulphide bridges were formed selectively by differential protection of cysteine residues using S-acetamidomethyl and S-t-butylsulphenyl groups.

Free radical one-electron versus hydroxyl radical-induced oxidation. Reaction of trichloromethylperoxyl radicals with simple and substituted aliphatic sulphides in aqueous solution

Abstract: One-electron oxidation of organic sulphides leading to sulphur-centred radical cations, R2S+˙, can conveniently be initiated by CCl3O2˙ radicals. Absolute rate constants have been measured for the reaction of CCl3O2˙ with dimethyl sulphide, 2-(ethylthio)ethanol, and methionine to be 1.8 × 108, 4 × 107, and 2.9 × 107 mol–1 dm3 s–1, respectively. Oxidation of dimethyl sulphide and methionine by the halothane-derived CF3CHClO2˙ radical occurs with absolute rate constants of k 6 × 106 and 1.4 × 106 mol–1 dm3s–1, respectively. The R2S+˙ generally equilibrates according to R2S+˙+ R2S ⇌(R2S ∴ SR2)+ to yield sulphur-centred three-electron-bonded radical cations. Amino-substituted sulphides such as 3-(methylthio)propylamine, methionine, and methionine ethyl ester also stabilize as intramolecularly formed S ∴ N three-electron-bonded radical cations. This competing reaction route requires a free electron pair at nitrogen, i.e. an unprotonated amino group, and steric assistance by five- or six-membered ring structures. The pH profiles of S ∴ S and S ∴ N bond formation are significantly different in the oxidation of the amino-substituted sulphides by one-electron oxidants from those for the ˙OH radical-induced process. The underlying mechanisms are compared and discussed.

Effects of magnesium(II) ion on hydride-transfer reactions from an NADH model compound to p-benzoquinone derivatives. The quantitative evaluation based on the reaction mechanism

Abstract: The effects of Mg2+ ion on hydride-transfer reactions from an NADH model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), to a series of p-benzoquinone derivatives (Q) as well as on the redox potentials of BNAH and Q in acetonitrile have been examined. The Mg2+ ion shows both accelerating and retarding effects on the hydride-transfer reactions depending on the p-benzoquinone derivative and the Mg2+ concentration. Such dual effects of the Mg2+ ion have been well correlated with the change of the redox potentials of BNAH and Q in the presence of Mg2+ ion since it has been found that there is a simple correlation between the logarithm of the rate constant and the difference of the redox potentials between BNAH and Q in the absence and presence of Mg2+ ion. It is shown that a proposed reaction mechanism involving electron transfer from BNAH to Q followed by proton transfer from BNAH+˙ to Q–˙ in the rate-determining step of the hydride-equivalent transfer provides a quantitative evaluation of the single and unified correlation between the logarithm of the rate constant and the difference between the redox potentials of BNAH and Q in the absence and presence of Mg2+ ion. The effect of Mg2+ ion on the primary kinetic isotope effects on hydride transfer from BNAH to Q is also shown to be consistent with the proposed reaction mechanism. Moreover, a ternary complex involving BNAH, Mg2+ ion, and Q as a reaction intermediate prior to electron transfer from BNAH to Q has been detected for the first time.

Pentavalent organobismuth reagents. Part 2. The phenylation of phenols

Abstract: The phenylation of a variety of phenols by pentavalent bismuth reagents under neutral, acid and basic conditions has been investigated. Under basic conditions well defined pentavalent intermediates have been isolated and fully characterised. Their decomposition gives only ortho-C-phenylation (except in the case of a p-nitrophenol derivative). O-Phenylation is seen under neutral or acidic conditions. Another mechanism is proposed to explain this reaction with no pentavalent bismuth intermediate.

Experimental and theoretical study of electronic substituent effects in 4-aminoaryl (4-substituted aryl) sulphones

Abstract: Substituent effects on the electronic structure of 23 biologically active 4-aminoaryl (4-substituted aryl) sulphones were investigated by means of 1H nmr, 13C nmr, and ir spectroscopy, as well as by semiempirical all-valence CNDO/2 calculations, with and without sulphur d orbital participation Good linear intercorrelations were found among the spectral data and between these and the computed electronic charges and the Hammett σp values On this basis the substituent effects are interpreted in terms of electronic charge perturbation, which is linearly transmitted from the substituent to the whole molecule, bridging SO2 group included The agreement between experimental and theoretical data is good and the trends do not depend on the inclusion or exclusion, in the calculations, of the sulphur d orbitals Strong and linearly related σ–π electron interactions operate between C-1 and C-1′ in the C(1)SO2C(1′) moiety; thus Koch and Moffitt's qualitative π-electron conjugation model for Case 2 type sulphones seems inadequate

Metabolic products of Phomopsis oblonga. Part 2. Phomopsolide A and B, tiglic esters of two 6-substituted 5,6-dihydro-5-hydroxypyran-2-ones

Abstract: Phomopsolide A and B, two boring/feeding deterrents for elm bark beetles, produced in vitro by the fungus Phomopsis oblonga, are shown to be (5S,6S)-5,6-dihydro-6-(4-hydroxy-3-oxopent-1Z-enyl)-5-(2-methylbut-2E-enoyloxy)-2H-pyran-2-one and (5S,6S)-5,6-dihydro-6-[(3S,4S)-3,5-dihydroxypent-1E-enyl)-5-(2-methylbut-2E-enoyloxy)-2H-pyran-2-one, respectively Another active compound, (–)-6-(4-hydroxy-3-oxopent-1E-enyl)-2H-pyran-2-one, was also isolated but is considered to be an artefact

Formation and reactions of C-nitrosoformate esters, a new class of transient dienophiles

Abstract: Oxidation of N-hydroxycarbamic esters, ROCONHOH, with tetraethylammonium or sodium periodate in the presence of conjugated dienes gave N-alkoxycarbonyl-3,6-dihydro-2H-1,2-oxazines, formed apparently by cycloaddition of transient C-nitrosoformate esters, ROCONO, with the dienes. Cleavage of various N-alkoxycarbonyl derivatives under mild conditions is exemplified. The cycloadduct (10a) of benzyl nitrosoformate and 9,10-dimethylanthracene decomposed in benzene at 80 °C in the presence of thebaine (3) to give the corresponding adduct (4a) of thebaine, together with 9,10-dimethylanthracene. Similarly, the adduct (6b) of 2,2,2-trichloroethyl nitrosoformate and cyclopentadiene, when heated with ergosteryl acetate, gave the corresponding adduct (8b) of the steroid. Benzyl and t-butyl azidoformates decomposed in dimethyl sulphoxide at 115–130 °C in the presence of thebaine to give the adducts (4a) and (4c) of benzyl and t-butyl nitrosoformate and the alkaloid. The other, major products were the sulphoximides (20a) and (20c). Alkoxycarbonylnitrenes, therefore, attack dimethyl sulphoxide either on sulphur, to give sulphoximides, or on oxygen, to give nitrosoformates. Benzyl nitrosoformate, generated thermally from either the adduct (10a) or (6a), reacted with triphenylphosphine to give, apparently, benzyloxycarbonylnitrene which attacked the solvent, benzene, to form N-benzyloxycarbonylazepine (24a). The adduct (6c) of t-butyl nitrosoformate and cyclopentadiene behaved likewise to give the azepine (24c). The reaction of (6c) with triphenylphosphine in benzene or dichloromethane gave a small quantity of 5,5-dimethyloxazolidin-2-one (26), a known cyclisation product of t-butyloxy-carbonylnitrene.

Asymmetric synthesis using chirally modified borohydrides. Part 4. Enantio-selective reduction of ketones and oxime ethers with the reagent prepared from borane and polymer-supported (S)-(–)-2-amino-3-(p-hydroxyphenyl)-1,1-diphenylpropan-1-ol

Abstract: The polymer-supported chiral amino alcohol (3) has been prepared by the reaction of chloromethylated polystyrene resin and (S)-(–)-2-amino-3-(p-hydroxy)phenyl-1,1-diphenylpropan-1-ol (2); the chiral polymeric reagent has been prepared from (3) and borane. The asymmetric reductions of ketones and oxime ethers with the polymeric reagent have been shown to give optically active alcohols (up to 97% optical purity) and amines (up to 67% optical purity), respectively. The results are compared with those obtained with (S)-(–)-2-amino-1,1,3-triphenylpropan-1-ol (4) or (S)-(–)-2-amino-3-(p-benzyl-oxyphenyl)-1,1 -diphenylpropan-1-ol (5) which are soluble model reagents.

Photoresponsive crown ethers. Part 14. Photoregulated crown–metal complexation by competitive intramolecular tail(ammonium)-biting

Abstract: New photoresponsive crown ethers (1H+) having a crown ether ring and an ammoniumalkyl [H3N+-(CH2)n, n= 4,6,10] group attached to the two sides of an azobenzene have been synthesized. These photoresponsive ‘tail-biting’ crown ethers have been designed so that intramolecular ‘biting’ of the ammonium group to the crown can only occur upon photoisomerisation to the cis-forms. In the thermal cis–trans isomerisation, the first-order rate constants for cis-(1H+) were smaller by 1.6–2.2-fold than those for (1)(the analogous free amines). Moreover, this rate increased with increasing added K+ concentration. This suggests that the ammonium tail is intramolecularly bound to the crown ether ring in cis-(1H+). This intramolecular ‘biting’ is further reflected in the relative affinities of (1H+) for alkali-metal cations. The affinities were markedly reduced by u.v,-light irradiation and in particular, cis-(1H+)(n= 6) and cis-(1H+)(n= 10) showed almost no metal-binding ability. This marked difference in the metal-binding ability was used to generate the light-controlled systems for the passive or active ion-transport of ions across a liquid membrane.

Chain-elongated analogues of a pheromone component of the turnip moth, Agrotis segetum. A structure–activity study using molecular mechanics

Abstract: Chain-elongated analogues of (Z)-dec-5-enyl acetate, a pheromone component of the turnip moth, Agrotis segetum, have been studied. The conformational energies required for the analogues to mimic spatial relationships in the parent molecule, assumed to be crucial for the receptor interaction, were calculated by molecular mechanics (MM2). The calculated energies show a striking correlation with measured single-cell electrophysiological activities. The results indicate that an elongated alkyl chain is conformationally rearranged when the analogue is bound to the receptor, and that the biological activity is determined by the corresponding conformational energy.