192 ABIOGENIC ORGANIC-CHEMICAL EVOLUTION 



ric, the alkaloid brucine. Marckwald combined the brucine 

 with methylethylmalonic acid, which is not dissymmetric 

 as two of the valencies of its a carbon atom are occupied by 

 carboxyl groups. When the resulting compound was de- 

 carboxylated only the free carboxyl group (that which was 

 not combined with brucine) was split off. When the brucine 

 was later removed leaving methylethylacetic acid, this was 

 dissymmetric with a definite preponderance of the laevo 

 isomer. 



COOH COOH H 



\_ \_ _\_ 



/ / . / 



COOH COOH — brucine gooh 



A. McKenzie^^* later used the same method for carrying 

 out a whole series of dissymmetric syntheses. Thus, if we 

 have dissymmetric substances at our disposal, we can use 

 them to obtain other dissymmetric substances. From this 

 point of view special interest attaches to the work of the 

 school of G. Bredig^" on dissymmetric syntheses with the 

 help of catalysts, among them dissymmetric substances. 



For example, G. Bredig and M. Minaeff^^*^ showed that if 

 the chemical combination of hydrocyanic acid with aldehydes 

 is brought about by the catalytic activity of quinine or quini- 

 dine, then, in the one case the dextro and in the other the 

 laevo form of cyanhydrin is obtained. The catalysts of living 

 cells, the enzymes, are dissymmetric. Synthesis brought about 

 by them must, therefore, also lead to the formation of dis- 

 symmetric compounds. Such syntheses have, indeed, been 

 carried out by many workers, especially C. Neuberg^" in his 

 work on the dehydrases, carboligase, aldehyde mutase and 

 other enzymes of yeast. 



In living cells the differential adsorption of the different 

 antipodes on structures composed of dissymmetric materials 

 may play an important part. Under laboratory conditions 

 separations of this kind can be carried out on paper or 

 silica gel containing an optically active substance (camphor- 

 sulphonic acid, mandelic acid, etc.y'^^ or in other ways. 



Thus it is now to some extent clear in principle in what 



