In the previous papers of this series we have described the preparation and properties of some polymers of glycine2" and d,Z alanine.2b As an extension of this work the study of the polymerization of poly-functional a-amino acids was undertaken. In the present paper the formation of poly-lysine by the polymerization of a 1-lysine derivative is described.The following considerations had to be taken into account in the choice of a suitable monomer for polymerization: (a) the e-amino group of the lysine had to be masked in order to prevent its participation in the polymerization and thus to insure that all the -CONH-bonds in the polymer are derived from the a-amino groups of the monomer. The e-amino group was masked by Bergmann's method of introducing the carbobenzoxy group.; (b) the monomer must consist of a lysine derivative having a pronounced tendency to polymerize. e-Carbobenzoxylysine itself is comparatively stable owing to its zwitterionic structure, while its methyl ester yields mainly the corresponding diketopiperazine on heating;a both these lysine derivatives did not appear therefore to be the proper starting material. A more suitable monomer was eventually found in e-carbobenzoxy-a-carboxyl-lysine anhydride.' It was found that this substance polymerizes on heating with the evolution of carbon dioxide in a manner similar to the polymerization of N-carboxyl anhydrides of other amino acids.The steps of preparation of poly-lysine from the chosen monomer are summarized in the first part of the scheme: c-carbobenzoxy-a-carboxyl-1-lysine anhydride (I), yields on heating, under the catalytic action of water, poly-carbobenzoxylysine (11), carbon dioxide being evolved. The carbobenzoxy groups of (11) were removed by phosphonium iodide, and poly-lysine hydriodide (111) obtained.For each polymerization experiment, the starting material, e-carbobenzoxy-a-carboxyl-1-lysine anhydride, had to be freshly prepared from a,€carbobenzoxy-1-lysine kept in stock. This was prepared substance undergoes rapid polymerization a t its melting point (loo'), the same substance after having been allowed to stand for several weeks did not polymerize even a t higher temperatures (160-170 ), but decomposed slowly under such conditions. In this connection the observation of Bergmann, Zervas and ROSS,' may be recalled that the melting point of freshly prepared e-carbobenzoxy-a-carboxyl-1-lysine anhydride rises on standing several months to above 250'. Our attempts to recover the e-carbobenzoxy-a-carboxyl-1-lysine anhydride with a melting point of 100' from the preparation having a high melting point by recrystallization were unsuccessful as no solvent for the latter was found.During search for other precautions to be taken in the polymerization of e-carbobenzoxy-a-carboxyl-1-lysine anhydride, the following findings were useful: (a) pure a,€-di-carbobenzoxy-1-lysine, as well as pure carbobenzoxy-glycine, give no amino N values on using Van Slyke's6 manometric method for amino N determination.(b) e-Carbobenzoxy-1-lysine yields practically the...
Various S-alkylcysteine derivatives have been prepared and polymerisedProperties of the by various methods through their N-carboxy-anhydrides. amino-acids and their polymers are reported. SOME S-alkylcysteine derivatives have been found to occur in Nature. isolated S-allyl-L-cysteine S-oxide ( a h ) from garlic. S-Methylcysteine S-oxide has been found in various plants; the deoxo-compound was enzymically synthesised from serine and methanethiol and has been suggested as an intermediate in the microbial biosynthesis of c y~t e i n e .~ S-Ethylcysteine has antituberculosis a~t i v i t y .~ S-Dichlorovinylcysteine produces fatal aplastic anzmia in young calve^.^ In an investigation of the biological mode of action of alkyl alkanesulphonates as alkylating agents,6 S-alkyl derivatives of cysteine were isolated. Finally poly-S-benzyl-7 and -S-allyl-cysteine have been synthesised.It seemed interesting. to synthesise a series of S-alkylcysteines and their polypeptide polymers. General methods for the preparation of S-alkylcysteines, summarised by Armstrong and Lewis,g comprise Schotten-Baumann reaction of an alkyl halide with cysteine in liquid ammonia or in sodium hydroxide solution. In the latter procedure the reactants are dissolved in alcohol-water, and sufficient sodium hydroxide is added to neutralise the hydrogen halide formed and to enable salt formation with the carboxyl group of cysteine. We have found that on use of a smaller quantity of alkali, sufficient to remove only the hydrogen halide acid formed, the reaction proceeds relatively fast and the S-alkylcysteine is precipitated, as it is formed, provided it is insoluble in the alcohol-water mixture used; thus the equilibrium shifts in favour of the formation of additional alkylcysteine. In this way it was possible to prepare pure crystalline S-ethyl-or S-benzyl-cysteine in high yield in a comparatively short time. The use of a smaller amount of alkali is especially advisable in the preparation of S-alkylcysteine derivatives which are soluble in water and insoluble in ethanol, and thus are difficult to free from sodium halides. For the same reason triethylamine instead of sodium hydroxide is recommended.The following S-alkyl-L-cysteines were prepared and polymerised : the known methyl, ethyl, propyl, isopropyl, butyl, and pentyl derivatives as well as the new hexyl-, dodecyl-, and l-naphthylmethyl-L-cysteine.Reaction of the reactive a-chloromethylnaphthalene and of benzyl chloride with cysteine was complete within a few to 30 min., while the reaction with dodecyl bromide required several days.Generally, the lower S-alkylcysteines, such as methyl, ethyl, and allyl, are soluble in water and insoluble in ethanol. The higher homologues are less soluble in water and more soluble in ethanol. Recrystallisation of the former is effected from aqueous ethanol, and of the latter from a large volume of water, ethanol, or dilute acetic acid. Ascending paper chromatography with (A) 80% aqueous phenol, (B) butanol-acetic acid-water (40 : 10 : 10) (C) 65% aqueous pyridine, o...
The reaction of amino-acid N-carboxyanhydrides with hydrochlorides of aminobenzoic acids and of aminooxy-acids gave amino-acid amides in a one-step synthesis. The coupling of L-alanine N-carboxyanhydride with anthranilic and with p-aminobenzoic acid hydrochloride gave peptide-like compounds of high optical activity. indicating the presence of little or no racemate. Glycyl and DL-phenylalanyl amides with aminobenzoic acid were obtained in this way, and trimers were formed by reaction of the N-carboxyanhydrides with p-aminobenzoyl-L-glutamic acid hydrochloride.Parallel procedures led to the u-, p-, and r-amido-oxy-peptides of amino-oxy-acetic, -propionic, and -butyric acid, respectively.
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