POLYPEPTIDES 33 



and the anhydride is the lactone : 



./CH, CH, 

 (CHJ, . CH . CH, . CH CO N< 



\CH -CH. 



1 io 



This reaction is apparently due to the tertiary nitrogen atom, for it 

 occurs also with bromisocapronyl-N-phenyl-glycine ; the amide, 

 (CH,), . CH . CH, . CH CO N . C,H, 



OH CH, . CO . NH, 



was formed. 



A different reaction took place with chloracetyl-N-phenyl-glycine : 

 the anhydride of imino-diacetyl-N-phenyl-glycine (cf. p. 58) resulted: 



CH,. CO . N(C 6 H B )CH, CO 



\CH,. CO . N(C 8 H,)CH,. COOH 



Not only can these radicles be combined with amino acids but also 

 with di, tripeptides, etc., as can be seen from the appended list of 

 polypeptides synthesised by this method. This method only allows 

 of the chain of amino acids being lengthened on one side, namely at 

 the amino group end. 



The majority of the polypeptides synthesised by this method are 

 optically inactive, but the optically active compounds can also be pre- 

 pared by employing the optically active halogen acyl chloride. As 

 previously described under the optically active amino acids, these com- 

 pounds undergo the Walden inversion ; the method therefore allows of 

 the whole of an inactive amino acid being employed for the synthesis 

 of an optically active polypeptide ; thus dl-leucine after separation into 

 d-leucine and 1-leucine can be converted into 1-leucyl-l-leucine by pre- 

 paring the d-bromisocapronyl chloride from the d-leucine and combining 

 it with 1-leucine ; treatment with ammonia gives 1-leucyl-l-leucine as 

 the compound undergoes the Walden inversion. The four isomers 



d-leucyl-l-leucine "I d-leucyl-d-leucine "4 



1-leucyl-d-leucine j 1-leucyl-l-leucine J 



can be thus prepared. The A compound is the former inactive leucyl- 

 leucine. Also 1-phenylalanyl-glycine was obtained from d-phenyl-a- 

 bromopropionyl chloride and glycine, and glycyl-1-phenylalanine from 

 chloracetyl chloride and 1-phenylalanine, the dl-phenylalanine used 

 having been separated into its optical isomers by means of its formyl 

 compound. 



Methylated polypeptides are obtained by treating the halogen 



PT. II. 3 



