Giuseppe Casnati

Solubilization and spectroscopic properties of α-chymotrypsin in cyclohexane

Abstract Using methyl-tryoctyl-ammonium chloride (which is soluble in cyclohexane and insoluble in water) it is possible to transport α-chymotrypsin in 20% yield from a water solution to a supernatant cyclohexane solution. The spectroscopic properties of the protein in the aprotic phase are investigated. On the basis of these spectroscopic data, it is argued that under certain conditions no extensive denaturation of the protein takes place in cyclohexane in the presence of the ammonium salt. The possible reason for this unexpected finding and its implications, are discussed.

Occurrence of D-amino acids in food : Detection by capillary gas chromatography and by reversed-phase high-performance liquid chromatography with L-phenylalaninamides as chiral selectors

Abstract The presence of D -amino acids was investigated in dairy products, in raw ham and in roasted coffee. The analysis was carried on by capillary gas chromatography, using a very stable tetraamidic selector derived from L -phenylalanine, which allowed the detection of D -alanine, D -aspartic acid, D -glutamic acid and other D -amino acids. Moreover, D -glutamic acid and D -alanine were detected also by reversed-phase high-performance liquid chromatography, using L -phenylalaninamide and copper(II) acetate as chiral additives to the eluent. The presence of D -amino acids may be ascribed to thermal racemization or to microbial activity.

Oxidative coupling of dichloroaluminium phenolates: Highly selective synthesis of hydroxylated Bi- and tetraaryls

Abstract Dichloroaluminium phenolates 4 undergo highly selective FeCl3-promoted oxidative coupling. Variously substituted symmetric 2,2′-dihydroxy biaryls 2 are obtained in good yields and excellent selectivities. The chelation control in the final reaction products 7 promotes the chemoselectivity of the process.

Template catalysis via non-transition metal complexes. New highly selective syntheses on phenol systems

A methodological approach to conventional phenol chemistry based on the concepts and achievements of modern coordination chemistry allowed to find specific conditions for improving classical reactions and discovering new selective processes. Substrates, reagents, and ligands could be organized around non transition metal cations in suitable complexes, which were able to control the reactions and to determine highly selective ortho—attack on phenol systems. Template reactions of phenol substrates with carbonyl compounds in the presence of suitable ligands led to new general processes of ortho—formylation, ortho—acylation, ortho—alkylation and allylation. A rational route to all—ortho regular novolac resins was also disclosed. By using the basic strategy of Ziegler—Natta catalysis, the first synthesis of isotactic and syndiotactic all—ortho ethylidene—linked polyphenols was performed. Other synthetically useful Friedel—Crafts processes were performed according to an intramolecular template mechanism leading to new syntheses of important classes of oxygen heterocycles such as flavenes, chromanes, benzofuran derivatives, benzodioxins, and benzopyrylium salts. STRATEGY Activation of phenols, enols and indoles, which are typical ambident nucleophilic systems, is traditionally achieved by using strong bases which convert the substrates into the corresponding anions (phenolate, enolate, etc.), along with the use of dipolar aprotic solvents of high donicity (1) or phase transfer catalysis (2). In these conditions, the negative influence of the cation on reactivity is strongly reduced and, as a consequence, high activation of the substrate is usually observed. Moreover, predominant or exclusive functionalization at the more negative center (0, N) of the ambident system occurs (3). Reversing this general synthetic strategy, some years ago we focused our attention on the possible positive role of the cation and looked at these reactions in terms of coordinated processes in self—organized systems rather than of anion activation only (4). As far as phenol chemistry is concerned, we studied the possibility to exploit the complex structures of phenol salts as self—catalyzing systems, thereby systematically changing their organization in order to control and diversify their reactivity. In this systems the cation can play a fundamental role in coordinating both the phenolic substrate and the reagent, inducing intramolecular irreversible reactions within the phenolate—reagent complex. In order to achieve this goal the following rules are strictly required: i) the structure of the salt has to be designed according to the reagent or, viceversa, the reagent has to be selected in order to chelate the cation; ii) solvent and any species present in the reaction medium must not exclude the reagent from complexation in the reactive structure of the salt. On these bases a systematic research on phenol salts of highly coordinating non—transition metals was undertaken, utilizing mainly salts of lithium, magnesium, zinc, titanium, etc., in aprotic non polar media. Initially we selected as reagents carbonyl compounds and their oxygen derivatives according to their known complexing ability towards the aforementioned hard cations.

Chiral aminoacid containing acyclic ligands-I. Syntheses and conformations

Abstract Synthesis and spectral properties of optically active acyclic ligands, containing two (S)-phenylalanine residues ( 3a–f ) are described. The synthesis is achieved by two different routes. Conformational studies in different solvents are performed by dilution and temperature-dependent experiments of 1H and 13C NMR spectroscopy.

Metal template ortho-acylation of phenols; a new general approach to anthracyclinones

Abstract Direct and mild synthesis of dihydroxyanthraquinones including 4-demethoxy-7-deoxydaunomycinone 8 from ortho-phthaloyl dichloride and hydroquinone derivatives is described.

Regiochemical control in the oxidative coupling of metal phenolates: Highly selective synthesis of symmetric, hydroxylated biaryls

Abstract Oxidative coupling of highly coordinating metal phenolates promoted by FeCl 3 afforded variously substituted symmetric 2,2′-dihydroxy biaryls in good yield and high regiochemical control.

Reaction of aldehydes and ketones with t-butyl bromide-dimethyl sulphoxide

Abstract Reacting aldehydes and ketones with the “ButBr-Me2SO” system produces the corresponding α-bromoderivatives 2 . In the case of ketones, is possible, bromination is obtained exclusively at the more highly substituted α-position. With slight modifications of the reaction conditions (add to obtain “in situ” formation of either dimethyl(2-oxo-2-phenylalkyl)sulphonium salts 3 or of α-methylthioderivatives 4 . Dimethyl(l-m bromide ( 3h ) during crystallization undergoes spontaneous resolution of the two enantiomers, as demonstrated by single crystal X-ray analysis a

Chiral aminoacid containing acyclic ligands - II. Complexation of alkaline earth cations

Abstract The abilities of the title ligands for alkali and alkaline earth cations are estimated by 1H and 13C NMR and by picrate extraction from water to methylene chloride. These ligands are shown to be excellent complexing agents for alkaline earth cations. Complexation occurs preferably at the ether and amide carbonyl groups. The stoichiometry of complexation is evaluated by 1H NMR.

Unusual Friedel–Crafts reactions. Part 7. Synthesis of α-(2-hydroxyphenyl)ethyl lactates and their reductive cyclization to 3-methyl-2,3-dihydrobenzofuran-2-ols

A mild procedure has been developed where α-(2-hydroxyphenyl)ethyl lactates (3), obtained via aluminium trichloride-promoted ortho-specific alkylation of lithium phenolates (1) with ethyl pyruvate (2), are reductively cyclized to racemic 3-methyl-2,3-dihydrobenzofuran-3-ols (4) in high yields and purity.