96 SCIENCE PROGRESS 



with ammonia gave two oxypyrrolidine carboxylic acids. One 

 of these is probably the inactive form of the optically active 

 oxyproline isolated by Fischer from the products of hydrolysis 

 of gelatine. 



Tryptophane was first isolated by Hopkins and Cole and 

 supposed to be either scatoleaminoacetic acid or indoleamino- 

 propionic acid. The work of Ellinger during the last few years 

 points to its having the latter constitution. 



The last amino acid which we have to consider is cystine. 

 Our knowledge of this compound rests chiefly upon the work of 

 Morner and of Friedmann, who showed that on oxidation and 

 loss of carbon dioxide it yielded taurine. Together with Suzuki, 

 Fischer has prepared several of its derivatives and has compared 

 the cystine as obtained from proteins on hydrolysis with that 

 from cystine calculi. Contrary to the statement of Neuberg and 

 Mayer, the two products were found to be identical, and 

 Rothera's work in Cambridge was thus confirmed. At present, 

 therefore, only the one cystine is a decomposition product of 

 proteins, though the isomeric, isocystine, has been synthesised. 



Finally, diaminotrioxydodecanic acid, which has only recently 

 been isolated by Fischer and Abderhalden from the products 

 of the hydrolysis of proteins, has not yet been synthesised, and 

 its exact constitution is unknown. 



Not only has Fischer synthesised the amino acids, but he has 

 also prepared a large number of derivatives, in addition to the 

 benzoyl and formyl compounds, whereby their isolation, purifi- 

 cation, and recognition can be determined. The benzenesulpho 

 derivatives, and especially the /S-naphthalene sulpho derivatives, 

 which are obtained by shaking an alkaline solution of the amino 

 acid with the sulphochloride, are very useful for separating 

 amino acids from very dilute or impure solutions. The latter 

 derivative forms compounds with all the amino acids and with 

 many of the polypeptides. It has been used by many workers 

 to isolate amino acids from urine and other secretions (Samuely, 

 Abderhalden and Schittenhelm, Lipstein, Emden and Reese). 



The combination of the amino acids with phenylisocyanate 

 in alkaline solution to form phenylureido acids, and the action 

 of hydrochloric acid on these compounds to form their anhy- 

 drides, i.e. derivatives of hydantoine, first observed by Mouney- 

 rat, has been much used to characterise the amino acids on 

 account of the ease of crystallisation and sharp melting points 



