Methionine, a naturally occurring amino acid containing sulphur: an investigation into the structure and a synthesis

Abstract

(1) Isolation of amino acid.Mueller obtained the amino acid by precipitation with mercuric sulphate after hydrolysis of casein. The precipitate was decomposed with baryta, the barium and mercury removed with sulphuric acid and hydrogen sulphide respectively and the solution evaporated to small volume. A second precipitation, this time with mercuric chloride, was brought about, and the precipitate was decomposed by passing hydrogen sulphide into an aqueous suspension. The silver oxide method was used to obtain the free amino acid which was finally crystallised from 75 per cent. alcohol. This method did not give a pure product, the chief contamination being apparently phenyl alanine. By repeating the mercuric chloride precipitation, the substance was obtained pure, but only at the expense of a large loss. The yield of crude product varied from 1 -2 grams per lb. of casein. The same method used with gelatin gave smaller yields.(2) Investigation of structure of amino acid.The first experimental work carried out with the amino acid was a repetition of Mueller's comparison with ethyl cysteine. The results obtained confirmed his statement regarding their relative stabilities to alkali.(3) Synthesis of amino acid.The methods of synthesis of amino acids used by Erlenmeyer and by Strecker were considered.(4) Derivatives of amino acid.The α-naphthyl isocyanate described by Mueller was prepared and the synthetic and natural products were again identical. Further confirmation was obtained by the preparation of the thio hydantoin and the picrolonpate. In each case the products from the synthetic and natural amino acid were identical.