Methode generale de preparation de N-alkyl N-trimethylsilyl alkoxymethylamines,agents efficaces de monoalkylaminomethylation d'organometalliques

The easy preparation of N-alkyl N-trimethylsilyl alkoxymethylamines is described; these new reagents are very convenient to lead to unsymmetrical secondary amines from organometallic compounds.     

Etude de la fragmentation de semi-carbazones terpeniques

Terpene semicarbazones have been investigated using high resolution mass spectrometry. We have studied correlations between rings and functional semicarbazone degradations. The mass spectra are more complicated than the mass spectra of oximes, methyloximes and hydrazones. Cleavages are explained by known mechanisms. An interpretation of almost all the peaks is offered. The fragmentation of the semicarbazone skeleton is less marked than in the oximes. Fragmentation processes induced by the functional group are numerous. Ions obtained are concerned in secondary cleavages. Thus it is not surprising that the predominant feature is localisation of charge upon the imino nitrogen atom. Other centres may, however, be responsible for the appearance of several peaks.     

Etude par analyse thermique differentielle de melanges diphasiques de polyethylene basse densite et de polystyrene atactique

Differential thermal analysis of two-phase polymer blends (low density polyethylene/polystyrene) shows that the way of marking the blend has an effect on the crystallization behavior. A secondary crystallization peak (that may be important) appears around 71° for high PE content. The general shape of the thermograms depends on the way of blending and on the thermomechanical history. The influence of interface agents is also pointed out.     

Étude d'une méthode de résolution matricielle en vue de la détermination du pourcentage de fixation de modèles chimiques sur le polychloroformiate de vinyle

Poly(vinyl chloroformate) obtained by free radical polymerization has been used as a polymer support for biological active compounds. Some preliminary experiments with model molecules (phenol and amine) have permitted to determine the percentage of fixation by mathematical resolution. This paper describes the study of a method by matrix resolution in using the results of analysis of modified polymers. This work can be used in all cases of modified polymers when there are identified secondary reactions.     

Addition de l'hydrure de diethylaluminium sur des copolymeres porteurs de groupements nitrile

Addition of diethylaluminiumhydride (DEAH) to nitrile functions was studied by nitrogen determination and i.r. spectroscopy in the case of styrene-methacrylonitrile (S-MAN) and styrene-acrylonitrile (S-AN) random copolymers. The various reaction parameters have been studied. The yield of ketimin derivatives is maximum for equimolecular quantities of DEAH and nitrile. Deficiency of hydride leads to secondary reactions of insertion and cyclization in the case of S-MAN copolymers as well as with S-AN copolymers. With the SAN copolymers however, elimination reactions also take place, leading to covalent crosslinking.     

Utilisation de techniques d'amination réductrice pour la synthèse d'amino-sucres de différents types. Communication préliminaire

Synthesis of amino-sugars using reductive amination reactions. Preliminary communication Treatment of aldehydo- or keto-sugars with primary or secondary amines and hydrogen in the presence of a catalyst (Pd/C) gave with good to excellent yields (67–96%) the expected secondary or tertiary amines. Primary amines can be obtained by using benzylamine, a hydrogenolysis taking place during the reaction.     

Etude de la chimioselectivite de la reaction des dichloroboranes avec les azides fonctionnels : une synthese efficace d'amines secondaires fonctionnalisees.

The reaction of cyclohexyldichloroborane, used as a model, with a wide variety of functionalized azides has been studied. It has been shown to be an efficient synthesis of secondary amines in terms of chemioselectivity, yields and wide applicability.     

Action des homocuprates sur les cetones α,α′-dibromees. Une nouvelle methode de synthese de cetones encombrees

The reaction between alkyllithium homocuprates and α,α′-dibromoketones permits the monoalkylation of ketones after hydrolysis of the reaction intermediate; the latter reacts with an excess of alkyl halide and gives the dialkylated product. Four alkylation reactions (methylation, ethylation, isopropylation and t-butylation) of α,α′-dibromoketones have been studied. While monoalkylation leads to secondary/primary and tertiary/secondary ketones from bis-primary and bis-secondary structures, dialkylation permits the synthesis of bis-secondary and bis-tertiary ketones. The introduction of two tertiary groups in the same structure is nevertheless impossible.     

Alkylation de la dimethyl-5 5′ isoxazolidinone-3 en catalyse par transfert de phase

Alkylation by phase transfert catalysis of ambidents anions of the N-C-0 type, leads to a mixture of N and O substitution. Isomers per cent are 20% for O alkylation and 80% for N alkylation when primary halides are used. With secondary halides, these figures are 35% and 65%. In both cases the overall yield ranges around 60%.     

Synthese de polymeres a proprietes pharmacologiques. Introduction de sequences peptidiques au sein de la chaine macromoleculaire

The introduction of peptidic sequences into polymers with pharmacological properties may increase the biocompatibility of the macromolecular prodrug. The synthesis of polypeptides from N-carboxyanhydrides bearing the active principles defines this objective. The l-lysine blocked as copper complex reacts with steroidic chloroformates (cholesterol-testosterone). After deblocking of the complex and treatment by phosgene, the corresponding N-carboxyanhydrides are obtained. Polymerization and copolymerization (with glycine N-carboxyanhydride) give oligopeptides bearing steroidic backbone as side-group. The low molecular weight of the synthesized compounds, the limited water solubility and the presence of secondary products limit the development of the method. Pharmacological tests are being undertaken to study delayed effects due to slow release of the steroid, to compare the biocompatibility of such prodrugs.     

Spectres de masse des composés organiques. 4e communication. Fragmentation de l'hexane

With the help of metastable peaks and high resolution, and by making extensive use of deuterated species we determined the main paths of fragmentation of hexane. Beside the simple splitting of a C? C-bond there are a series of internal rearrangement reactions. The loss of neutral fragments from alkyl ions is often, but not always, statistical. A small primary (0.96) and an even smaller (0.99) secondary isotope effect for a hydrogen transfer can be observed.     

Les phenomenes de relaxation non isotherme dans les copolymeres ethylene-acetate de vinyle—I. Courants de depolarisation thermique

Depolarization thermocurrent curves for ethylene-vinyl acetate copolymers, previously polarized by the thermoelectret effect at a temperature higher than the glass transition temperature, have been compared with dielectric loss curves described in the literature, in order to establish a possible relation between thermocurrents and the intrinsic relaxation phenomena. The two main peaks observed correspond to loss peaks described in dielectric measurements and result from primary and secondary dipolar relaxation, i.e. α and β type relaxation, respectively. We systematically used a partial polarization method consisting of polarizations in restricted temperature zones during a slow linear cooling of the sample, to describe the specific properties of these peaks. In this manner, we showed that the β relaxation, poorly resolved by dielectric measurements, consists of three discrete components having comparable activation energies, each of them presenting a distribution of the characteristic relaxation time. On the other hand, the amplitude of the α relaxation was found to be one order of magnitude higher than that of the β relaxation. It was characterized by a dipole concentration dependence of the activation energy and also presented an important distribution of characteristic relaxation times.     

Essai de stabilisation du polychlorure de vinyle par un système totalement organique

Owing to its Lewis acid character, dichloromaleic anhydride (DCAM) has been tried as a thermal stabilizer of polyvinylchloride (PVC), in association with nucleophilic oxiranes; comparative experiments have been carried out using maleic anhydride and maleic acid. Chlorohexene was used as model compound for labile allylic chloride in dichlorobutane solution at 80°. Experiments with plasticized PVC were carried out at 180°. DCAM in an efficient catalyst for the production of the intermediate carbocation, although it is less efficient than organostannic chlorides; it causes oxirane polymerization and other secondary reactions more than nucleophilic substiution on the carbocation. Moreover it is not an efficient dienophilic agent for conjugated polyene, although it gives with them a strongly coloured complex. For these reasons, it cannot be used as a major component of a stabilizer recipe for PVC.     

Effet α. influence de la substitution sur l'exaltation de reactivite d'oximes vis-a-vis de l'acetate de p-nitrophenyle

Kinetic measurements show the relation between the magnitude of the “α effect” exhibited by trifluoromethyloximate anions RR'C=N-O^? and the electron attracting properties of the substituents. Indeed, the reactivity enhancement which is observed for α-trifluoromethyloximes is similar to that found in earlier studies of α-hydroxyiminoketones. This characteristic behaviour is no longer observed for oximes bearing an electron releasing substituent at the α-position of the hydroxyimino group. On the basis of sodium oximate molecular orbital energies the “α effect” induced by electron attracting substituents appears to depend on both the interactions of nitrogen and oxygen lone pairs of electrons and the lowering of the π^* vacant orbital thus favouring a secondary interaction between the π^* anion orbital and the π orbital of p-nitrophenylacetate carbonyl group.     

Synthese et isomerisations thermique ou ionique de vinylcyclopropylcarbinols

Stereoselective reduction of cis-vinylcyclopropylcarbonyl compounds is achieved with aluminium hydrides and organometallic reagents. Tertiary vinylcyclopropylcarbinols are transformed by homoallylic rearrangements into trans-dienols in acidic media. Thermal treatment of secondary alcohols quantitatively gives cis enones by a [1,5] sigmatropic rearrangement, while tertiary alcohols are thermostable.     

Action de O- et N-nucléophiles sur les sels de phényl-3 benzopyrylium-1

3-Phenyl-1-benzopyrylium percholorates 1a, 1i react exculusively at C-2 with ethanol and isopropyl alcohol, affording mixed acetals 2a, 3a, 3i . Aqueous ammonia gives symmetrical secondary amines 4a, 4b or bis(3-phenyl-2H-1-benzopyran-2-yl)amines, while with aqueous aliphatic amines (40%) bis-acetals 5a, 5b or 2,2′-oxy-bis(3-phenyl-2H-1-benzopyrans) are characterized. In some other acidic conditions, 5a and 5b are also obtained.     

Structure des peroxydates obtenus par action de lóxygene moleculaire sur des organometalliques derives du bromure de crotyle

Butenylmagnesium, butenylzinc and butenylaluminium bromides are oxidized at low temperature (?80 and ?100°C). The qualitative and quantitative studies of the reaction products after reduction by PPh₃, LiAlH₄ and n-BuMgBr show that the secondary structure is dominant in the peroxides formed.     

Mise en evidence du mecanisme “s2 (intermediaire)” dans des solvolyses de tosylates secondaires encombres. absence de correspondance vitesses-produits

k_s/k_c, ratios, representative of nucleophilic solvent assistance wore obtained for solvolyses of hindered secondary substrates. Reactions products were also investigated. Failure to observe a rate-product correlation underlines the nonidentity of the rate-determining and product-determining steps. These results which support the occurrence of solvent assistance and of a cationic intermediate, afford evidence for the “S_N2 (intermediate)” mechanism.     

Preparation of de novo globular proteins based on proline dendrimers

A synthetic method for the preparation of protein-like globular dendrimers derived from a combination of proline, glycine and imidazolidin ring as branching unit is described. The methodology allows the synthesis of novel peptide dendrimers up to fourth generation. Dendrimers were synthesized by a convergent solid-phase peptide synthesis approach. The conformational properties of branched polyproline peptides and proline dendrimers were studied by CD experiments. CD data suggest conformational plasticity of branched peptides for PPI and PPII, and a stable well-defined secondary structure of proline dendrimers for PPII.     

β-发夹多肽的全新设计和构象研究

引入跨股氨基酸队的方法进行β-发夹结构的设计,序列[R1G2T3F4W5V6d-P7S8V9N10Y11F12, β2] 中包含二个氨基酸对V6V9和F4Y11,并以d-P7S8作转角来稳定结构.多肽合成采用Fmoc/But固相合成方法.圆二色谱研究显示,β2在202 nm呈现正峰,在217.5 nm处呈负峰,为β转角和β折叠共同贡献的叠加,是典型的β-发夹结构圆二色谱特征.红外光谱研究进一步验证了圆二色谱的结果,表明β2在溶液中主要以β-发夹结构存在.