110 SCIENCE PROGRESS 
this method, e.g. leucylalanine, alanylleucine, alanylleucyl- 
glycine, leucylalanylglycine, glycylalanylleucine, etc. 
Fischer has ultimately been able to prepare the acid chloride 
of the amino acid so that it can be used directly for synthesis. 
Whereas the acid chlorides of the halogenacyl derivatives were 
easily prepared by the action of phosphorus chloride, this 
did not take place with hippuric acid. After many attempts 
to prepare hippuryl chloride, success at length was attained 
when hippuric acid was heated with acetylchloride and phos- 
phorus pentachloride together. By simply extending this method 
of preparation to the amino acids themselves, z.e. by shaking 
them in a finely powdered condition with acetylchloride and 
phosphorus pentachloride, Fischer obtained the acid chlorides 
of the amino acids, whereby a step in the synthetical processes 
can be saved. 
During the course of the last year several higher poly- 
peptides have been synthesised by these methods; these are 
two hexapeptides, a heptapeptide, an octapeptide, and even a 
dodekapeptide. They all consist principally of glycine residues, 
the dodekapeptide having one leucine and eleven glycine 
radicles. Such long glycine chains probably do not exist in 
the protein molecule, except possibly in gelatine, which contains 
about 20 per cent. glycine. Their study, however, is of great 
importance in that they cannot exist in stereoisomeric forms, 
and the knowledge of their properties may lead to the isolation 
of a higher polypeptide from the proteins themselves. Further, 
the material is of easy access, glycine being readily prepared 
synthetically, which is not the case with the other amino acids, 
many of which are more easily obtained by the hydrolysis of 
proteins than by synthesis. 
Ina quite recent paper Fischer gives an account of the prepara- 
tion of an octadecapeptide, built up of fifteen glycine and three 
]-leucine residues, ¢.c.a polypeptide containing six more members 
in its molecule than the above-mentioned dodekapeptide. Its 
preparation is of great interest, as it shows very clearly how the 
synthetical method has been employed in these researches. 
Pentaglycylglycine and _  d-a-bromisocapronyldiglycylglycine, 
BrCH(C,H,)CO.[NHCH,CO}],. NHCH,COOH are. used.. The 
acid chloride of the latter compound is first prepared and 
combined with the hexapeptide. The bromo compound so 
obtained on treatment with liquid ammonia gives 1-leucyl- 
—— 
OO a—_ 
