De la chimie des ptérines. 15e communication. Hydroxylation non-enzymatique de la phénylalanine en tyrosine à l'aide de ptérines tétrahydrogénées

The non-enzymatic hydroxylation of phenylalanine to tyrosine has been effected by atmospheric oxygen in aqueous solution in the presence of 5,6,7,8-tetrahydropterines, Fe^II or Fe^III, and EDTA, in a phosphate buffer at pH 6,9. A possible reaction mechanism is discussed.     

Analyse Conformationnelle de Pseudoprotoberbérines Naturelles. II. Etude Structurale par RMN de 13C des Tétrahydropseudoprotoberbérines provenant de I'Isopyrum thalictroïdes

The four pseudoprotoberberins extracted from Isopyrum thalictroides L. were reduced with sodium borohydride to the corresponding tetrahydropseudoprotoberberins. Comparison between the ¹³C NMR spectra of these and of synthetic protoberberins allowed us to assign a trans-1 configuration to the four reduced alkaloids and also to provide for this particular configuration an unequivocal criterion for the differentiation (based on the chemical shift of C-8) between tetrahydroprotoberberins (9, 10 substituted) and tetrahydropseudoprotoberberins (10, 11 substituted).     

De la chimie des ptérines. 78e Communication.. Synthèse de l'ester tripolyphosphorique de la tétrahydro-5, 6, 7, 8-D-néoptérine. Essai d'interprétation de la biosynthèse de la L-sépiaptérine

Synthesis of 5, 6, 7, 8-Tetrahydro-D -neopterine tripolyphosphate. Attempt to Interpret the Biosynthesis of L -Sepiapterine The synthesis was achieved by phosphorylation of tetrahydro-5, 6, 7, 8-D -neopterine with polyphosphoric acid. The product is sensitive to light, moisture and oxidation like the other tetrahydropetrines. After oxidation in aqueous solution, D , L -sepiapterine was isolated in 5% yield. The oxidation of non-phosphorylated tetrahydro-5, 6, 7, 8-D -neopterine under the same conditions led to D -sepiapterine without inversion of the configuration. These findings were used to give a tentative explanation for the biosynthesis of natural L -sepiapterine from the D -neopterine.     

Application de la réduction polarographique des sulfones aromatiques et des p-toluènesulfonates d'alkyle à des problèmes de structure

The polarographic reduction potentials of a series of aromatic sulfones and homologous alkyl tosylates in anhydrous NN-dimethylformamide have been measured. The relation between reduction potential and structure is discussed on the basis of HMO. calculations, under the assumption that compounds PhSO₂X (X = NR¹R², OR, halogens) are sulfone derivatives A critical approach is made of the use of the Taft-Hammett relation for correlating half-wave potentials. The different reduction mechanisms at the electrode observed in aprotic and protic media for the above compounds are satisfactorily accounted for by simple MO. calculations.     

Etude expérimentale et théorique de la substitution de N-méthyl-halogéno-triazoles-1,2,4 par les réactifs nucléophiles

Kinetic studies of the substitution of isomeric N-methyl-halogeno-1,2,4-triazoles with piperidine or the methoxide ion have been carried out. The experimental results show that the 1-mcthyl-5-halogcno isomer is more reactive than the 4-methvl-3-halogeno isomer. Various theoretical treatments of the reaction have been applied. The calculations show that the “frontier charge” and “delocalised bond” models give (he best results.     

Effets stériques des groupes alkyle sur le déplacement chimique des hydrogènes d'un méthyle: Correlation avec les termes Es de Taft

The effect of alkyl groups (Me, Et, i-Pr, t-Bu) on the ortho methyl proton chemical shifts is shown to be linearly correlated with the Taft (E_s) scale in model compounds 1 . Experimental results can be expressed by Δδ = δ_R – δ_Me = λ′E_s in which λ′ is solvent and model dependent. The calculations of the chemical shifts according to ApSimon and Buckingham are used to show the predominant influence of steric effects on the observed substituent effect.     

Notiz über die Photoelektronen-Spektren des Nortricyclens und des Triasterans

The photocelectron spectra of nortricyclene (=tricyclo[2.2.1.0^2,6]heptane) and of triasterane (=tetracyclo[3.3.1.0^2,8.0^4,6]nonane) have been recorded and a tentative assignment of the bands has been put forward on the basis of MINDO/2 SCF calculations.     

Réactions d'élimination présentées par des acides polyhydroxyadipiques

The tetrahydroxyadipic acids and one trihydroxyadipic acid have been methylated, using methyl iodide and silver oxide in the presence of dimethylformamide. In addition to Δ²-di- or tri-methoxyadipic esters and the products expected for a double E2 elimination, cis-trans α, α'-dimethoxymuconic ester was frequently the principal product. The proposed theoretical interpretations involve as intermediates either a silver complex or a lactonic compound. A few preferential conformations, based on NMR. data, are proposed.     

Théorie quantique des phénomènes de biréfringence electrique et magnétique des molécules

A general formalism is set up to apply the variation-perturbation method to the quantum theory of non-linear optical effects, in particular to the electric and magnetic birefringence (Kerr and Cotton-Mouton effects). The quantities describing these effects are obtained from the wave function Ψ of the ground state of the unperturbed molecule and the different vectors and tensors which are determined by a variation method. With this method an approximate computation of the Kerr and Cotton-Mouton constants of some simple molecules has been made.     

Recherches dans la série des cyclitols XLIII. Sur des éthylène-cétals de cétoses dérivés du cyclopentane

The synthesis of a series of keto derivatives of cyclopentane is described. The configurations of these derivatives have been determined by chemical methods and verified by IR. and NMR. spectroscopy. The preferred conformation of the cyclopentane part of the molecule has been established by the study of intramolecular hydrogen bonds and the values of the coupling constants J_{H? C? OH} and J_{H, H}.     

Polymétallorotaxanes conjugués contenant des unités pentacoordinantes

Conjugated polymetallorotaxanes containing pentacoordinating units. The present paper reports the synthesis and cyclic voltammetry study of new conjugated polyrotaxanes containing penta-coordinating units around copper or zinc centres. The gathering and threading effect of these metal centres has been used to prepare the desired prerotaxanes, whose macrocyclic and linear components incorporate a tridentate chelate of the terpy type (terpy = 2,2′,6′,2″-terpyridine) and a phen (phen = 1,10-phenantroline) derivative, respectively. Electrochemical oxidative coupling of the end groups (thiophene or pyrrole) leads to the corresponding polymers. Ion-exchange processes, induced by demetalation/remetalation, have been investigated as well as the conductivity of the polymer films prepared.     

Polymérisation et copolymérisation cationiques des methylindenes

A study of cationic polymerization and copolymerization of methylindenes has been carried out by experimental methods and by means of quantic chemistry. The study showed a great variation among initiators in efficiency for the various monomers. The study of the effect of temperature on polymerization was carried out for dimethyl-5,7-indene. Polymerization enthalpies and reactivity ratios were determined; the values that were obtained allowed a classification of methylindenes with regard to their reactivity toward a single cation. Total electron densities, free valences, and mobile bond orders, frontier electron densities, and superdelocalizabilities on position 1 and 2 were calculated for all methylindenes. In determining location energies of the electronic double bond in position 2 and the stabilization energies at the time of the attack by a cation, a theoretical classification of the monomers with respect to their reactivity in cationic polymerization was obtained. The agreement between calculation and experimental results is shown to be satisfactory.     

Spectres RMN des Polysaccharides et de leurs Dérivés: Influence des Substituants sur le Déplacement Chimique 13C

Methyl and acetyl substituent effects on ¹³C chemical shift have been determined on (α 1→3), (α 1→4), (β 1→3) and (β 1→4) linked polysaccharides such as pseudo-nigerane, β-cyclodextrine, amylose, laminarane and cellulose. Methyl α- and β-D -glucopyranoside have been used as monomer model compounds. Shift determination of hydroxylated and substituted polysaccharides requires unambiguous assignment of their ¹³C spectra. Selective heteronuclear spin decoupling and the isotope effect of deuterated hydroxyl have been used as assignment techniques.     

Etude des mécanismes de réarrangement dans la fragmentation des benzoyloxy-cyclopentànes par impact électronique

The fragmentation modes of 3-benzoyloxy-cyclopentene and of 4-benzoyloxy-cyclopentene have been studied on deuterium-labelled analogues. A mathematical model is proposed for the study of the rearrangement reactions which occur during the expulsion of H₂O and of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CO}_2 {\rm H}^. $\end{document} from the molecular ion of 3-benzoyloxy-cyclopentene.     

Etude dans la série des radicaux hétérocycliques. Partie XV. Décomposition aprotique de l'amino-6-éthyl-2-benzothiazole dans des substrats aromatiques et hétéroaromatiques: préparation des mésityl-6- et furyl-6-éthyl-2-benzothiazoles,des sels quaternaires et des spiropyrannes correspondants

Study of heteroaromatic radicals. Part XV .

1 Partie XIV: cf. [1].

Aprotic decomposition of 6-amino-2-ethylbenzothiazole in aromatic and heteroaromatic substrates: preparation of 6-mesityl- and 6-furyl-2-ethylbenzothiazoles and of the corresponding quaternary salts and spyropyrans In the presence of excess isopentyl nitrite in aprotic solvent, the 6-amino-2-ethyl-benzothiazole leads to 6-aryl- and 6-heteroaryl-2-ethylbenzothiazoles 1 to 14 in ca. 20–50% yield (Scheme 1, Table 1). The 2-ethyl-6-benzothiazolyl radicals generated during these reactions exhibit a weak electrophilic character (Table 2). Preparatively this method has been applied to the synthesis of 6-mesityl- and 6-furyl-2-ethylbenzothiazoles 6 and 7 , which were used to prepare the corresponding quaternary salts 15 , 16 and the spiropyrans 19, 20 (Scheme 4).