Robert A. W. Johnstone

A rapid simple and mild procedure for alkylation of phenols alcohols amides and acids

Abstract A general, rapid method is described for alkylation of phenols and alcohols to give ethers, for amides to give N-substituted amides, and for acids to give esters. Differences in optimum reaction times suggest that where two or more such groups as phenol, alcohol, amide, and acid occur in the same molecule, differential alkylation could be effected with suitable substrates. Alkylation with primary alkyl halides was very effective but secondary halides showed evidence for competitive dehydrohalogenation before alkylation was complete and tertiary halides were rapidly dehydrohalogenated with no formation of alkylated derivatives. The method has been applied successfully to N,O-alkylation of peptides for mass spectrometric sequence determination. C-Methylation of peptidic amino-acid residues was observed only on carbon α to a carboxylic ester.

Rapid catalytic transfer reduction of aromatic nitro compounds to hydroxylamines

Abstract A general method has been developed for the rapid, metal-catalysed transfer reduction of nitro compounds to N-substituted hydroxylamines.

Keggin-type polyoxotungstates as catalysts in the oxidation of cyclohexane by dilute aqueous hydrogen peroxide

Abstract Oxidation of cyclohexane by hydrogen peroxide in the presence of catalytic amounts of the Keggin-type heteropolytungstates [PW 11 O 39 ] 7− and [PW 11 M(L)O 39 ] (7− m )− , M m + =first row transition metal cation, L=H 2 O or CH 3 CN, was found to produce cyclohexanol, cyclohexanone and, in certain cases, cyclohexyl hydroperoxide. The presence of the latter was demonstrated by negative chemical ionization GC-MS. The reactions were carried out in acetonitrile, using tetra n -butylammonium salts of the catalysts and aqueous 30% hydrogen peroxide as oxidant. The polyanions [PW 11 O 39 ] 7− and [PW 11 Fe(H 2 O)O 39 ] 4− showed higher catalytic activity and different selectivity for the oxidation of cyclohexane than did the corresponding Cu-, Co-, Mn- and Ni-substituted complexes.

Fast atom bombardment of crown ether/cation complexes in solution: Inferences on mechanisms of energy transfer

Abstract Mechanisms of energy transfer leading to the mass spectrometric detection of ionized species during fast atom bombardment are discussed. These mechanisms may be of an equilibrium or non-equilibrium nature but consideration of either mechanism suggests that the observed mass spectral peak heights for desorbed ionic species should be proportional to the concentrations of these species in solution. Solutions of crown-ethers with added metallic salts provide a means for testing this deduction. Under fast atom bombardment, a wide range of metal ions has been found to desorb as crown ether/cations and the technique affords a sensitive means of detecting metal ions in solution. The variation in concentration of a crown ether/cation complex in solution at normal temperatures with different molar ratios of crown ether to added metal salt is reflected accurately by the accompanying changes in mass spectral peak heights of the crown ether/cations. From the mass spectral data, it seems possible that quantitative determination of crown ether/metal salt stability constants can be effected simply. Methods for extracting such information are discussed.

A kinetic investigation of the thermal rearrangement of allyloxytetrazoles to N-allyltetrazolones

The mechanism of the thermal rearrangement of 1-aryl-5-allyloxytetrazoles 1 to give 1-aryl-4-allyltetrazolones 2 in very high yield has been investigated through kinetic studies in one polar and one less polar solvent. The results suggest mainly a concerted [3,3] sigmatropic process, in which a partially positively charged allyl group migrates from oxygen to nitrogen, similar to the polar transition state found in the Claisen rearrangement.

Structural effects on sigmatropic shifts in heteroaromatic allyl ethersElectronic supplementary information (ESI) available: selected crystal data for compound 7. See http://www.rsc.org/suppdata/p1/b1/b102674g/

In contrast to the known thermal, exclusively [3,3], O- to N- rearrangement of allyl groups in phenyltetrazoles (1, Scheme 1), the comparable migration of the allyl group in pseudosaccharyl ethers (3; Scheme 2) has been shown to proceed through both [1,3]- and [3,3]-mechanisms, 4, 5; for the pseudosaccharyl derivative of the natural product myrtenol (6; Scheme 3) only the product 7 of a [1,3]-shift has been observed; crystallographic data and theoretical calculations provide an explanation of this ease of [1,3]-isomerization and the observed selectivity as being due to conformational constraints and electronic factors.

Determination of Fluorescence Yields, Singlet Lifetimes and Singlet Oxygen Yields of Water-Insoluble Porphyrins and Metalloporphyrins in Organic Solvents and in Aqueous Media

Abstract— Fluorescence quantum yields and singlet lifetimes for a wide range of hydrophilic to hydrophobic porphyrins and metalloporphyrins have been determined in toluene, methanol or acetone. Photosensitized singlet oxygen yields have been determined in the same solvents. For some porphyrins, the same quantities were determined in an aqueous medium, through use of an amphiphilic polymer to solubilize the porphyrin sensitizer and target molecule, 1, 3‐diphenylisobenzofuran. Because rate constants for the deactivation of singlet oxygen (kd) and for its reaction with a target molecule (ka) are unknown in such aqueous polymer systems, a new method was developed for evaluating yields of singlet oxygen formation that also provides a value for the ratio kd/ka. A variation observed in quantum yield of singlet oxygen production for the aqueous polymer system with variation in initial concentration of the target molecule is discussed.

Metal-assisted reactions. Part 22. Synthesis of perhalogenated prophyrins and their use as oxidation catalysts

Abstract Meso-tetrakisarylporphyrins have been perchlorinated and perbrominated at peripheral (β)-positions of the pyrrole rings by high-yielding procedures. These halogenated porphyrins show enhanced catalytic activity towards oxidation of alkanes and alkenes but are not stable when hydrogen peroxide is used as the oxygen donor. The reason for this instability appears to lie in excessive homolytic dissociation of H 2 O 2 with consequent rapid attack at the porphyrin β-position.

Catalysed ipso replacement of phenolic ethers by Grignard reagents

Nickel catalysed ipso displacement of phenolic ethers, ArOR, by Grignard reagents, R′MgX, to give arenes, ArR′, has been achieved.

Isolation of a pure toxic polypeptide from the venom of the spider Phoneutria nigriventer and its neurophysiological activity on an insect femur preparation.

The venom of the South American spider Phoneutria nigriventer has been separated into eleven fractions by gel filtration. The neurophysiological activity of each fraction was tested by perfusion of a locust femur preparation. Fractions which gave a neurophysiological response on this perfusion were fractionated further by ion-exchange chromatography. The purity of each sub-fraction was monitored by isoelectrofocusing on polyacrylamide gels and isoelectric points determined. From one of the polypeptide-containing fractions, a pure, almost neutral polypeptide was isolated and shown to have a molecular weight between 5500 and 5900. The amino acid composition of the pure polypeptide was: Ala6,7 Arg2,3 Asx3 Cys8 Glx3 Gly4 Ile4 Leu1 Lys5,6 Phe2 Ser5 Thr3 Trp1 Tyr2 Val2. This polypeptide elicited the greatest neurophysiological activity of all fractions tested. When the polypeptide (2 X 10(-7) M) was perfused through the locust femur preparation, action potentials were generated along the length of the axons in the crural nerve, resulting in very rapid and uncontrolled twitching of the skeletal muscles. At higher concentrations, the crural nerve discharged repetitively, both spontaneously and in response to a single electrical stimulus. The other polypeptide fractions, although less pure, had neurophysiological responses similar to those observed with the pure polypeptide; the effects of some fractions could be reversed. Further fractions of low molecular weight were purified by thin-layer or paper chromatography to give two pure components that are probably nucleosides or nucleotides. After the initial gel filtration of the total venom had separated the high molecular weight proteinases from the polypeptides, all of the polypeptides retained their neurophysiological activity in solution for several days. In the presence of the proteinases, the polypeptides were inactivated in solution in a few hours at room temperature.