Leuchs’ substances

In 1906 Leuchs observed, first on glycine, that iV-carboethoxyamino acid chlorides at temperatures as low as 70 °C are transformed, with the loss of alkyl chloride, to the so called Leuchs schen Korper (Leuchs substances), N carbamoic acid amino acid inner anhydrides. As he noted in the case of the glycine derivative these AT-carboxyanhydrides (NCA-s) readily polymerize. For instance in the presence of a small amount of water they form poly-a-amino acids consisting, as shown by later studies, of several hundred residues. 

The Leuchs substances, NCA-s, oxazolidine-2,4-diones, can also be synthesized by the method of Fuchs (1910) from amino acids and phosgene, a method further developed by Farthing (1950). According to Curtius, NCA s can be generated from malonic acid half azides as well, through a-isocyanatocarbonic acids (Curtius degradation. Fig. 4). 

Leuchs, Hermann (1879-1945, p. 35, Plate 29) born in 1879 in Nuremberg, studied chemistry in Munich and graduated in 1902, Ph.D. with a thesis guided by E. Fischer in Berlin. He then became associate professor there and, in 1926 Associate Director of the Institute of Chemistry of the University. After his discovery of the Leuchs substances (p. 35) in 1906 and some of their reactions he turned to strychnine chemistry on which he worked until his death in the destroyed Berlin in 1945. 

These substances can be regarded as derived from strychnine (or brucine) by tbe loss of carbon atoms of tbe benzene ring, and Leuchs and Wegener have suggested they should be named as derivatives of hypothetical bases nucine and micidine, arising from strychnine and strychnidine in the following way —... 

The constitution of these acids was confirmed in 1908 by Leuchs and Felser, who converted them, by reduction with hydriodic acid, into proline. Their attempt to determine whether natural oxyproline was the active form of one of the synthetical compounds by converting the natural substance into its racemic form by heating with baryta to 200° C. was unsuccessful, since complete racemisation did not occur. As, however, all compounds containing one asymmetric carbon atom to which a carboxyl group is attached are easily racemised, the result led to the conclusion that oxyproline contains two asymmetric carbon atoms. Of the four possible formulae,... 

The N-carboxy-a-amino-acid anhydrides, referred to as Leuchs anhydrides, or briefly as NCA s, are well-defined, colourless, crystalline substances having sharp melting points when pure. The synthesis of the simplest member of this class of compounds, viz. oxazolidine-2,5-dione,... 

It is of interest to observe that Leuchs found that the anhydride, when treated with a small quantity of water, gave an anhydride of glycine which was not identical with diketopiperazine, but possibly the same substance which Balbiano and Trasciatti (p. 7) obtained by heating glycine with glycerol, or as that obtained by Curtius from the biuret base (p. 7). 

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